A.I. Podgorny Diagnosis and adjustment of vehicle steering
Introduction
1 Requirements for the technical condition of active safety systems
1.1 Requirements for the technical condition of brake control systems
1.2 Conditions for checking the technical condition of the brake control
1.3 Methods for checking brake control
1.3.1 Checking the service brake system
1.3.2 Checking the parking and emergency brake systems
1.3.3 Checking the auxiliary brake system
1.4 Requirements for the technical condition of the steering
1.5 Steering test methods
2 Characteristics of MUP “VPATP-7”
2.1 Rolling stock
2.2 Technological process TO-1 and TO-2, equipment used
2.3 Zone TO-2. Location and available equipment
3 Equipment used for diagnosing active safety systems
3.1 Equipment for diagnosing brake systems
3.2 Steering diagnostic equipment
3.2.1 Equipment for measuring steering play
3.2.2 Equipment for measuring wheel alignment angles
3.3 Diagnostic equipment offered on the market
3.3.1 Brake testers
3.3.2 Wheel alignment stands
Conclusion
List of used literature
Introduction
It is unthinkable to imagine a modern city without a developed urban transport system. Road transport is the most unsafe in this system. In the first four months, more than 700 accidents occurred in the Volgograd region, almost half of them with serious consequences. In 40 cases out of 100, the cause of an accident is the unsatisfactory technical condition of cars; more than half of all accidents and road accidents caused by technical reasons are due to faulty brake and steering controls. In PATP conditions, when the health of a large number of passengers depends on the health of a large number of passengers, special attention should be paid to the technical condition of the brake and steering systems.
In this regard, the purpose of this work is to analyze the equipment of the Municipal Unitary Enterprise "VPATP-7" with appropriate diagnostic equipment, the compliance of this equipment with modern requirements and, in the absence of the necessary equipment, to make proposals for equipping the maintenance zone of the Municipal Unitary Enterprise "VPATP-7" with equipment of a specific brand and model.
1 Requirements for the technical condition of active safety systems
1.1 Requirements for the technical condition of brake control systems
The braking system of cars, consisting of brake mechanisms and their drive, is designed to reduce the speed of movement until a complete stop with a minimum braking distance. It allows you to maintain a given speed when driving downhill, as well as ensure the vehicle remains stationary in parking lots. Thus, the braking system characterizes the braking properties of the vehicle or the braking dynamics.
In accordance with modern requirements, a car must have brake systems that perform various functions. The main one is the service braking system, designed to reduce the speed of movement until the vehicle comes to a complete stop. The parking brake system is designed to hold the vehicle in place. These two systems should be structurally independent of each other. In addition, cars are equipped with an auxiliary and spare brake system, which serves as a working one in the event of a failure of the latter.
The braking performance of cars is one of the main indicators of their technical condition and suitability for use. Good braking qualities of cars guarantee timely stopping of the car without skidding, reliably holding it in the parking lot, and also create confidence in the driver when driving on roads with heavy traffic.
In accordance with GOST R 51709-2001, the service brake system is checked according to indicators of braking efficiency and stability of the vehicle during braking, and the spare, parking and auxiliary brake systems - according to indicators of braking efficiency according to tables 1.1a and 1.1b.
Table 1a - Use of indicators of braking efficiency and vehicle stability during braking during tests on roller stands.
Table 1b - Use of indicators of braking efficiency and vehicle stability when braking during checks in road conditions
Note to tables 1.1a, 1.1b - The “+” sign means that the corresponding indicator should be used when assessing the braking efficiency or stability of the vehicle during braking; the “-” sign should not be used.
In road conditions, when braking with the service braking system with an initial braking speed of 40 km/h, the vehicle should not leave any part of the vehicle outside the standard traffic corridor of 3 m wide. Standards for the braking efficiency of vehicles using the service brake system are given in Tables 1.2 – 1.4.
The movement corridor is a part of the supporting surface, the right and left boundaries of which are marked so that during the movement the horizontal projection of the vehicle onto the plane of the supporting surface does not intersect them with any point.
When testing on stands, the relative difference in the braking forces of the wheels of an axle (as a percentage of the highest value) for vehicle axles with disc wheel brakes is allowed to be no more than 20% and for axles with drum wheel brakes no more than 25%.
Table 1.2 - Standards for the braking efficiency of vehicles using the service brake system when tested on roller stands.
Table 1.3 - Standards for the braking efficiency of vehicles using the service brake system in road conditions using a device for checking brake systems.
Table 1.4 - Standards for the braking efficiency of vehicles using the service braking system in road conditions with registration of braking parameters.
The parking brake system is considered operational if, when activated, the following is achieved:
for vehicles with a technically permissible maximum weight:
Or the specific braking force value is not less than 0.16;
Or the stationary state of the vehicle on a supporting surface with a slope of (16±1)%;
for vehicles in running order:
Or the calculated specific braking force, which is equal to the lesser of two values:
0.15 ratio of the technically permissible maximum weight to the weight of the vehicle during testing or 0.6 ratio of the curb weight per axle(s) affected by the parking brake system to the curb weight;
Or a stationary vehicle on a surface with a slope of 23±1% for vehicles of categories M1 - M3 and (31±1)% for categories N1 - N3.
The force applied to the parking brake system control to activate it must not exceed:
In case of manual control:
589 N - for vehicles of other categories.
In case of foot control:
688 N - for vehicles of other categories.
Parking brake system with a drive using spring chambers, separate from the drive of the spare brake system, when braking on road conditions with an initial speed of 40 km/h for vehicles of categories M2 and M3, in which at least 0.37 of the weight of the vehicle in running order falls on the axle (s), equipped with a parking brake system, must provide a steady deceleration of at least 2.2 m/s2.
The auxiliary braking system, with the exception of the engine retarder, when tested on road conditions in the speed range of 25 - 35 km/h must provide a steady deceleration of at least 0.5 m/s2 for vehicles with a permissible maximum weight and 0.8 m/s2 for vehicles in running order, taking into account the driver's weight.
The spare brake system, equipped with a control element independent from other braking systems, must ensure compliance with the standards for vehicle braking performance indicators on a stand in accordance with Table 1.5, or in road conditions in accordance with Table 1.6 or 1.7. The initial braking speed during tests in road conditions is 40 km/h.
Table 1.5 - Standards for braking efficiency of vehicles using a spare brake system during testing on benches.
Table 1.6 - Standards for braking efficiency of vehicles using a spare brake system in road conditions using a device for checking brake systems.
Table 1.7 - Standards for the braking efficiency of vehicles using a spare brake system during tests in road conditions with registration of braking parameters.
It is allowed to drop the air pressure in the pneumatic or pneumohydraulic brake drive by no more than 0.05 MPa when the engine is not running during:
30 min - with the brake system control in the off position;
15 minutes - after the brake system control is fully activated.
The operation of the working and spare brake systems must ensure a smooth, adequate decrease or increase in braking forces (slowing down the vehicle) with a decrease or increase, respectively, in the force exerted on the brake system control.
Vehicles equipped with anti-lock braking systems (ABS), when braking in running order at an initial speed of at least 40 km/h, must move within the traffic corridor in a straight line without skidding, and their wheels must not leave traces of skidding on the road surface until the ABS is turned off when reaching a driving speed corresponding to the ABS deactivation threshold (no more than 15 km/h). The functioning of ABS warning lights must correspond to its good condition.
1.2 Conditions for checking the technical condition of the brake control
Vehicles are checked with “cold” brakes. “Cold” brake mechanism is a brake mechanism whose temperature, measured on the friction surface of the brake drum or brake disc, is less than 100 °C.
The tires of the vehicle being tested at the stand must be clean, dry, and the pressure in them must correspond to the standard pressure established by the vehicle manufacturer in the operational documentation.
Checks on stands and in road conditions (except for checking the auxiliary brake system) are carried out with the engine running and disconnected from the transmission, as well as the drives of additional drive axles and unlocked transmission differentials (if the specified units are present in the vehicle design).
Checks in road conditions are carried out on a straight, flat, horizontal, dry, clean road with a cement or asphalt concrete surface. Slope checks are performed on a hard, non-slip supporting surface cleared of ice and snow. Braking by the service brake system is carried out in the emergency full braking mode by applying a single action to the control. The time for complete actuation of the brake system control should not exceed 0.2 s. Emergency braking is braking in order to reduce the speed of the vehicle as quickly as possible.
Control actions on the steering of the vehicle during braking when checking the service brake system in road conditions are not allowed. If such an impact was made, then the test results are not taken into account.
The total weight of technical diagnostic equipment installed on vehicles for carrying out checks in road conditions should not exceed 25 kg.
1.3 Methods for checking brake control
1.3.1 Checking the service brake system
When checking the braking efficiency of vehicles under road conditions without measuring the braking distance, it is allowed to directly measure the steady-state deceleration indicators and the braking system response time or calculate the braking distance indicator according to the method specified below, based on the results of measuring the steady-state deceleration, the delay time of the brake system and the rise time of the deceleration at given initial braking speed.
Calculation of the braking distance St (in meters) for the initial braking speed based on the results of checking the deceleration indicators of the vehicle during braking is carried out using the formula:
, (1)
where is the delay time of the braking system, s;
Deceleration rise time, s;
Steady deceleration, .
When checking on benches, the relative difference in the braking forces of the wheels of the axle is calculated using formula (2) and the resulting value is compared with the maximum permissible values according to GOST R 51709-2001. Measurements and calculations are repeated for the wheels of each axle of the vehicle.
, (2)
where are the braking forces on the right and left wheels of the vehicle axle being tested, measured simultaneously at the moment the first of these wheels reaches the maximum value of the braking force, N;
The greatest of the specified braking forces.
The stability of the vehicle when braking in road conditions is checked by performing braking within the standard traffic corridor. The axis, right and left boundaries of the traffic corridor are preliminarily designated by parallel markings on the road surface. Before braking, the vehicle must move in a straight line with a set initial speed along the corridor axis. The exit of the vehicle by any part of it beyond the normative traffic corridor is determined visually by the position of the projection of the vehicle onto the supporting surface or by a device for checking brake systems in road conditions when the measured displacement of the vehicle in the transverse direction exceeds half the difference between the width of the standard traffic corridor and the maximum width of the vehicle .
When checking in road conditions the braking efficiency of the working brake system and the stability of the vehicle during braking, deviations of the initial braking speed from the set value of 40 km/h are allowed no more than ±4 km/h. In this case, the braking distance standards must be recalculated using formula (3):
, (3)
where A is a coefficient characterizing the response time of the brake system.
Based on the results of testing in road conditions or on stands, the braking distance (1) or the specific braking force (4) and the relative difference in the braking forces of the axle wheels (2) are calculated, respectively. Vehicles are considered to have passed the test of braking efficiency and stability when braking with the service braking system if the calculated values of these indicators correspond to the standards given in Tables 1-3, or, regardless of the achieved specific braking force, all wheels of the vehicle are blocked on the rollers of a stand not equipped with the system automatic shutdown of the stand, or automatic shutdown of a stand equipped with an automatic shutdown system, due to slipping of any of the wheels of the axle along the rollers, with a force on the control of 686 N, in accordance with tables 1-3, and for vehicle axles, in the brake drive of which a regulator is installed braking forces, with a force on the control no more than 980 N.
where is the sum of braking forces on the wheels of a tractor or trailer (semi-trailer), N;
M – mass of the tractor or trailer (semi-trailer) when performing the test;
g – free fall acceleration, .
1.3.2 Checking the parking and emergency brake systems
Checking the parking brake system on a slope is carried out by placing the vehicle on a supporting surface with a slope equal to 23±1% for vehicles of categories M1 - M3, or another value for vehicles of other categories in accordance with the requirements of GOST R 51709-2001, braking the vehicle with the service brake system , and then - the parking brake system with simultaneous measurement of the dynamometer force applied to the parking brake system control, and the subsequent shutdown of the service brake system. When checking, the possibility of ensuring a stationary state of the vehicle under the influence of the parking brake system is determined for at least 1 minute.
The test on the stand is carried out by alternately causing the wheel to rotate with the rollers of the stand in one direction or in opposite directions and performing braking of the wheels of the vehicle axle, which is affected by the parking brake system. Wheels that do not rest on the stand's rollers when performing the test must be secured with at least two wheel chocks to prevent the vehicle from rolling out of the stand. A force not exceeding 589 N in the case of a hand control and 688 N in the case of a foot control is applied to the parking brake system control. Based on the test results, the specific braking force is calculated using formula (4) and the obtained value is compared with the calculated standard. For vehicles of categories M2 and M3, in which at least 0.37 of the weight of the vehicle in running order falls on the axle(s) equipped with a parking brake system, it must provide a steady deceleration of at least 2.2 m/s2. The vehicle is considered to have passed the test of the braking efficiency of the parking brake system if the wheels of the tested axle are blocked on the rollers of a stand that is not equipped with an automatic shutdown system, or the stand equipped with an automatic shutdown system is automatically switched off due to slipping of any of the wheels of the axle along the rollers under force on the control, not exceeding the standard value, or if the specific braking force is not less than the calculated standard value.
Checking the parking brake system driven by spring chambers in road conditions is carried out similarly to checking the service brake system, in compliance with the requirements for the road surface. Deviations of the initial braking speed from the set value of 40 km/h are allowed within ±4 km/h, subject to the recalculation of braking distance standards using formula (3).
The compliance of the parameters of the spare brake system, equipped with a control element independent of other brake systems, with the parameters set out in Table 4, is checked on stands using the methods established for checking the service brake system.
1.3.3 Checking the auxiliary brake system
The auxiliary braking system is tested under road conditions by actuating it and measuring the deceleration of the vehicle when braking in the speed range of 25 - 35 km/h. In this case, the transmission of the vehicle must be in a gear that prevents the maximum permissible rotation speed of the engine crankshaft from being exceeded.
An indicator of the braking efficiency of the auxiliary braking system in road conditions is the value of steady-state deceleration. A vehicle is considered to have passed the braking efficiency test of the auxiliary braking system if the steady-state deceleration is at least 0.5 m/s2 for a vehicle with a permissible maximum weight and 0.8 m/s2 for a vehicle in running order, taking into account the driver’s weight.
During road tests, it is difficult to objectively assess the operation of the brake of each wheel and the simultaneity of operation, and therefore, determine the nature and location of a possible malfunction. Also, the organization of checking brake control in road conditions within the framework of the ATP is complicated by the lack of sufficient territory. Therefore, for diagnosing brake systems, preference is given to brake stands using inertial, force or inertial-force operating principles.
1.4 Requirements for the technical condition of the steering
In accordance with the requirements of GOST R 51709-2001, the parameters of the technical condition of the steering must meet the requirements set out below.
The change in force when turning the steering wheel should be smooth throughout its entire range of rotation. Inoperability of the vehicle's power steering (if equipped on the vehicle) is not permitted.
Spontaneous rotation of the steering wheel with power steering from the neutral position when the vehicle is stationary and the engine is running is not allowed.
The total play in the steering must not exceed the limit values established by the manufacturer in the operational documentation, or in the absence of data established by the manufacturer, the limit values specified in Table 1.8.
Table 1.8 – total values of play in the steering
The maximum rotation of the steering wheel should be limited only by the devices provided for in the design of the vehicle.
Damage and absence of fastening parts of the steering column and steering gear housing, as well as increased mobility of steering gear parts relative to each other or the body (frame), not provided for by the vehicle manufacturer (in the operational documentation), are not allowed. Threaded connections must be tightened and secured in the manner specified by the vehicle manufacturer. Play in the connections of the steering axle arms and steering rod joints is not allowed. The steering column locking device with the adjustable steering wheel must be operational.
The use of parts with traces of residual deformation, cracks and other defects in the steering mechanism and steering drive is not allowed.
The level of working fluid in the power steering reservoir must meet the requirements established by the vehicle manufacturer in the operational documentation. Leakage of working fluid in the booster hydraulic system is not allowed.
1.5 Steering test methods
The requirement for the performance of the power steering is checked on a stationary vehicle by comparing the forces required to rotate the steering wheel with the engine running and off. The requirements for the smoothness of the change in force when turning the steering wheel and for the limiters of the angle of rotation of the steering wheel are checked on a stationary vehicle with the engine running by alternately turning the steering wheel to the maximum angle in each direction.
The requirement that the steering wheel with power steering not spontaneously rotate from the neutral position when the vehicle is stationary and the engine is running is checked by observing the position of the steering wheel of a stationary vehicle with power steering after installing the steering wheel in a position approximately corresponding to straight-line motion and starting the engine.
The value of the total play in the steering is checked on a stationary vehicle without hanging the wheels using instruments for determining the total play in the steering, recording the angle of rotation of the steering wheel and the beginning of rotation of the steered wheels.
The fastening parts of the steering column and steering gear housing, as well as threaded connections, are checked for damage organoleptically on a stationary vehicle with the engine not running by applying loads to the steering components and tapping the threaded connections.
The mutual movements of the steering gear parts, the fastening of the steering gear housing and the steering axle levers are checked by rotating the steering wheel relative to the neutral position by 40 - 60° in each direction and applying an alternating force directly to the steering gear parts. To visually assess the condition of the articulated joints, steering gear test stands are used.
The performance of the device for fixing the position of the steering column is checked by putting it into action and then swinging the steering column when it is in a fixed position by applying alternating forces to the steering wheel in the plane of the steering wheel perpendicular to the column in mutually perpendicular planes passing through the axis of the steering column.
The stability of the car when driving, ease of control, normal rolling resistance of the front wheel tires and their wear, as well as fuel consumption per unit of travel largely depend on the installation of the steered (front) wheels of the car.
The stability of a car is its ability to move without the danger of tipping over and sliding sideways under the influence of lateral forces. Depending on the direction of overturning and sliding, longitudinal and lateral stability are distinguished. More likely and more dangerous is the loss of lateral stability, which occurs under the influence of centrifugal force, the transverse component of the vehicle's gravity, lateral force, and also as a result of wheel impacts on uneven roads.
Indicators of lateral stability of a car are the maximum possible speed along a curve and the angle of the transverse slope of the road (slope). Each indicator can be determined from the conditions of lateral wheel slip (skidding) and vehicle rollover. This results in four lateral stability factors:
Maximum (critical) speed of a car moving along a curve, corresponding to the beginning of its skidding, m/s;
Maximum (critical) speed of a vehicle moving along a curve, corresponding to the beginning of its rollover, m/s;
Maximum (critical) slope angle corresponding to the beginning of transverse wheel slip (skidding), degrees;
The maximum (critical) slope angle corresponding to the beginning of the vehicle rollover, degrees.
The front wheels, taking into account the loads experienced by the car, are installed with some deviations from the plane of movement of the car. The initial alignment of the front wheels is disrupted during operation, and a systematic check and adjustment of the wheel alignment angles is required: toe angle, camber angle, longitudinal and lateral inclination angles of the king pins.
For trucks and buses, only the toe angle parameter of the front wheels is adjustable. Toe angles are needed to ensure that the wheels take a straight position when moving. An increased toe angle leads to wear on the front tires on the outside tracks. Reduced - along external tracks. The ideal operating position for the wheel is vertical and straight, in which case the tire has the best grip and the least wear. In theory, toe-in parameters should be selected optimally for each car.
In accordance with the technical documentation, control and adjustment of toe angles must be carried out at each TO-2. In practice, due to unsatisfactory road conditions, adjustment of the steering wheel alignment angles needs to be carried out more often than with each TO-2.
In this regard, in order to diagnose the steering and adjust the alignment angles of the steered wheels under ATP conditions, it is necessary to equip the posts in the maintenance area with appropriate diagnostic stands.
2 Characteristics of MUP "VPATP-7"
2.1 Rolling stock
The municipal unitary enterprise "Volgograd Passenger Motor Transport Enterprise No. 7" is located in the Kirovsky district of the city of Volgograd at the address: st. General Shumilov, 7a. MUP "VPATP-7" transports passengers on city and country routes.
The company has 124 buses in its fleet. The average age of buses is 8.6 years, which indicates a rather worn-out condition of the rolling stock. The qualitative composition of the park is shown in Table 2.1. Part of the rolling stock is stored in a closed heated room designed for 15 buses. The remaining buses are stored in open areas. Open storage areas are equipped with steam heating lines for 74 buses to facilitate cold engine starting in winter.
Table 2.1 - Qualitative composition of the fleet of the municipal unitary enterprise "VPATP-7"
As a result of the implementation of measures to update the rolling stock of municipal unitary enterprises of passenger transport in Volgograd using leasing for the period 2007 - 2010. approved by the decision of the Volgograd City Duma dated July 18, 2007 No. 48/1164 “On measures to update the rolling stock of municipal passenger transport enterprises in Volgograd using leasing for the period 2007 - 2010” in 2008, the municipal formation - the Volgograd urban district received 92 buses with for use on citywide routes.
In 2008, as a result of the implementation of measures to update the rolling stock on public passenger transport routes using leasing, approved by the decision of the Volgograd City Duma dated July 18, 2007 No. 48/1164, MUP “VPATP No. 7”:
8 country routes were accepted for service with the additional involvement of 27 buses;
Service on five bus routes has been restored: No. 2 from June 20, 2008 (6 buses); No. 21e from July 18, 2008 (4 buses); No. 23 from 09/01/2008 (2 buses); No. 55 from October 13, 2008 (2 buses); No. 59 from 12/01/2008 (4 buses);
The number of buses on previously served routes has been increased by 14 buses;
From 07/01/2008, bus route No. 88 (train station - Maxim Gorky village) was put into service with 10 buses.
Figure 2.1 shows the dynamics of changes in the rolling stock fleet for the period from 2000 to 2009.
Rice. 2.1 – Change in the composition of the MUP VPATP-7 fleet
2.2 Technological process TO-1 and TO-2, equipment used
The main purpose of TO-1 and TO-2 is to reduce the wear rate of parts, identify and prevent failures and malfunctions through timely performance of inspection, diagnostic, lubrication, fastening, adjustment and other work.
TO-1 consists of an external inspection of the vehicle and performance of inspection, fastening, electrical and refueling work to the extent established by the technical documentation. TO-2 includes a more in-depth check of the condition of all mechanisms and instruments. During TO-2, individual units are removed from the vehicle for testing on stands.
The frequency of maintenance is established by standards, technical documentation for rolling stock, and is also adjusted depending on the mileage of the vehicle. So for the LiAZ-525625 TO-1 bus it is mandatory every 5000 km. mileage If the average monthly mileage of a car is less than the frequency of maintenance-1, then it is carried out at least once a month.
Maintenance 2 must be carried out every 20,000 km. If the average monthly mileage is less than the frequency of TO-1, then TO-2 is carried out at least twice a year.
Table 2.2 shows a list of operations and equipment used during maintenance-2 of the LiAZ-525625 bus.
Table 2.2 – Technological map TO-2 of the LiAZ-525625 bus
| the name of the operation | Location of execution | Number of service locations | Labor intensity person-min | Equipment, devices, tools | ||||||||||
| 1. Wash the bus | Top, bottom, interior, rear engine compartment | - | 220 | Bus washing machine, brush jet, jet wash, washing machine, washing brush | ||||||||||
| 2. check the tightness of the intake air tract |
motor compartment, in the cabin through the hatch |
- | 25 | Special device, open-end wrenches 10, 13, 14, 17, 22 and 24 mm, screwdriver 8 mm | ||||||||||
| 3. Check the condition of the fan clutch |
motor |
1 | 8,4 | Open wrenches 12, 13, 14, 19, 22 and 24 mm. | ||||||||||
| 4. Check the condition of the power unit supports |
motor compartment, in the cabin through the hatch |
5 | 12 | Open spanners 17, 19, 22, 24, 27 mm | ||||||||||
| 5. check the condition of the pipelines and manifolds of the exhaust gas system | Below and behind the engine compartment | - | 15,6 | Open wrenches 10, 12, 13, 14 and 17 mm, box wrench 17 mm. | ||||||||||
| 6. Attach the clutch housing to the engine | Below and in the cabin through the hatch | 1 | 12 | Open wrench 19 mm | ||||||||||
| 7. Check the play in the joints and splines of the cardan transmission | From below | 2 | 0,8 | |||||||||||
| 8. Secure the propeller shaft flanges | From below | 2 | 8,6 | Open spanners 14, 17 mm | ||||||||||
| 9. Adjust the play in the rear wheel hub bearings | Right and left | 2 | 104 | Oil drain container, hex key 12 mm, socket wrench 14 mm, bit, hammer, special wrench for bearing nuts, chisel, wrench, funnel, filling syringe | ||||||||||
| 10. Check the tightness of the rear axle | Bottom, right and left | - | 1,2 | Hex wrench 12 mm, box wrench 14 and 19 mm, open wrench 12, 14 and 17 mm, mandrel, tray, bit, oil drain container, special wrench for bearing nuts with support, wrench, filling syringe, funnel | ||||||||||
| 11. check the condition of the reaction rods of the rear and front suspensions | From below | 5 | 28,6 | Open wrenches 19, 32, 41, 46, 50 and 55 mm, box spanner 19 mm, hammer, bit, screwdriver 8 mm, pliers, tape measure | ||||||||||
| 12. Check the correct location of the rear axle | Right and bottom, left | - | 19,4 | Open spanners 19 and 50 mm, box spanner 19 mm, screwdriver 8 mm, tape measure, pliers | ||||||||||
| 13. Check the condition of the front A-frame joint | From below | 1 | 4,8 | Open wrenches 24, 65 mm, hammer, bit, pliers, screwdriver 8 mm. | ||||||||||
| 14. Check the condition of the A-frame | From below | 1 | 14,6 | Welding unit TS-500, hammer | ||||||||||
| 15. Check the condition of the wheels | - | 6 | 31 | Open-end wrenches 12 and 15 mm, screwdriver 8 mm, pliers, air distribution box, pressure gauge, device for inflating tires, tire mounting stand, mounting blades | ||||||||||
| 16. Rearrange the wheels (if necessary) | Top, right and left | 6 | 6 | Wheel nut wrench 32 mm, open wrench 12 mm, sliding trolley | ||||||||||
| 17. check the condition of the shock absorbers and their fastening parts | Below and in the cabin through the floor hatches | 6 | 18,6 | Open wrenches 12, 22, 24 and 80 mm, ring wrench 22 mm, hammer, screwdriver 8 mm, fixture | ||||||||||
| 18. Adjust the height of the body level | From below | 3 | 28 | Open spanners 10, 14, 17, 19 and 24 mm | ||||||||||
| 19. Check the condition of the pivot joints | Right and left | 2 | 37,6 | Open wrenches 12, 19, 24, 32 mm, replaceable head 27 mm, wrench with connecting squares, socket wrench 19 mm, wrench for front wheel hub bearing nuts 75 mm, hammer, bit, screwdriver 8mm, pliers, mounting, container for washing, hydraulic jack, lift, device for pressing out pins | ||||||||||
| 20. Check the condition of the front wheel hub bearings | Right and left | 4 | 82,8 | Lifter, open wrench 12 mm, hammer, bit, screwdriver 8 mm, pliers, socket wrench 19 mm, replaceable head 19 mm, wrench for front wheel hub bearing nuts 75 mm, mounting blade, bearing puller, head wrench, brush | ||||||||||
| 21. Check the condition of the front wheel hub seals | Right and left | 2 | 1,6 | Hammer, bit, mandrel | ||||||||||
| 22. Adjust the toe-in of the front wheels | From below | 1 | 34,4 | Ruler for checking wheel alignment, open-end wrenches 17 and 19 mm, pipe wrench |
||||||||||
| 23. check the play in the splines and joints of the propeller shaft | 1 | 0,6 | Open wrenches 12 and 13 mm, pliers, play meter | |||||||||||
| 24. Secure the steering gear housing and the coupling bolts of the adapter connecting the steering gear shaft to the extension shaft | 1 | 7,6 | Open spanner 22 mm, box spanner 24 mm | |||||||||||
| 25. Check the condition of the brake drums | Right and left with brake drums removed | 4 | 102 | Open wrench 12 mm, wheel nut wrench 32 mm, bolt pullers, screwdriver 10 mm, hammer, device for fastening wheel nuts, mounting blades, bits | ||||||||||
| 26. Check the condition of the pads and friction linings | Right and left | 8 | 36,6 | Special mounting, 8 mm screwdriver, washing container | ||||||||||
| 27. check the fastening of the expansion mechanism housings to the caliper | 8 | 30,4 | Special wrench 10 mm, bit, hammer, open wrenches 22 and 24 mm | |||||||||||
| 28. Check the condition of the wedge, rollers, pushers and covers of the release mechanisms | Right and left | 8 | 31,6 | Screwdriver 8 mm, spanner 19 mm, hammer | ||||||||||
| 29. Check the condition of the tensioning and fixing springs of the pads | Right and left | 8 | 3 | Special mounting, open wrench 14 mm, screwdriver 8 mm | ||||||||||
| 30. Check the condition of the ABS gear rings on the wheel hubs | Right and left | 4 | 2,4 | Screwdriver 8 mm | ||||||||||
| 31. Adjust the clearances of the ABS wheel speed sensor | Right and left | 4 | 4,1 | Open wrench 13 mm | ||||||||||
| 32. Check the proper functioning of the ABS after maintenance. | In the cockpit | - | 8,3 | - | ||||||||||
| 33. Check the condition of the electrical wiring | - | - | 14,8 | Knife, 6.5 mm screwdriver, square key, control lamp | ||||||||||
| 34. Bring the electrolyte density in batteries to normal | 2 | 3,8 | Hydrometer, probe, open wrenches 12,13,14 and 19 mm | |||||||||||
| 35. Clean the glow plug spiral from carbon deposits | On the left in the heater compartment | 1 | 3,2 | Open spanners 27 and 41 mm, brush | ||||||||||
| 36. Check the condition of the door seals | Outside and inside | 3 | 11,8 | Screwdriver 8 mm, Phillips screwdriver | ||||||||||
| 37. Check the condition and operation of emergency ventilation hatches | In the cabin | 3 | 4,2 | Screwdriver 8 mm, pliers | ||||||||||
| 38. Check the condition of the rubber hinges of the lids | Right and left | 8 | 12,8 | Open wrench 10 mm, screwdriver 8 mm | ||||||||||
| 39. Check the condition of the floor and manhole covers | Inside and below | - | 26,6 | 8 mm screwdriver, hammer, drill, drill set, Phillips screwdriver | ||||||||||
| 40. Check the height of the door leaves | Inside and below | 6 | 4,2 | Open-end wrenches 12, 13 and 19 mm, hex key 12 mm, pliers, screwdriver 8 mm, hammer, chisel | ||||||||||
| 41. Check the condition of the axle stops of the lower door leaf clamps | Inside and below | 6 | 4,2 | Open wrenches 10, 19 mm. Screwdriver 8 mm | ||||||||||
| 42. Secure the door guide roller brackets | In the saloon and cockpit | 6 | 8,6 | Special key 12 mm | ||||||||||
| 43. Secure the door roller chute guides | In the salon and cabin above | 6 | 5,4 | Open wrench 10 mm, socket wrench 10 mm | ||||||||||
| 44. Secure the axes of the door guide rollers | In the saloon and cockpit | 6 | 3,6 | Open wrenches 10 and 19 mm, box wrench 19 mm, socket wrench 10 mm | ||||||||||
| 45. Check the condition of the seat upholstery and safety cushions | In the saloon and cockpit | - | 9,2 | Screwdriver 8 mm | ||||||||||
| 46. Secure the seat frames and backrests | In the cabin | - | 8,6 | Open wrenches 12 and 17 mm, screwdriver 8 mm | ||||||||||
| 47. check the condition of the movable base of the batteries | On the right in the battery compartment | 1 | 4,4 | Open wrench 19 mm, lever-plunger syringe, screwdriver 6.5 mm | ||||||||||
| 48. Secure pillars, handrails and door partitions | In the cabin | - | 4,2 | Open wrench 12 mm, hex key 6 mm, screwdriver 10 mm, drill, drill set, Phillips screwdriver | ||||||||||
| 49. Attach the glass guard brackets to the door leaves | In the cabin | 10 | 2,8 | Special key 17 mm | ||||||||||
| 50. Change the oil in the GMT crankcase (when the mileage reaches 60 thousand km, but at least once a year) | In the cabin through the hatch and below | - | 29,4 | Hex key 12 mm, oil drain container, oil dispenser, funnel | ||||||||||
| 51. Replace the replacement filter element of the GMP oil filter (when replacing GMP oil) | Inside or below | 1 | 6,1 | Open wrenches 14, 36 mm, head 36 mm, wrench, container for used filter elements | ||||||||||
| 52. Rinse the fuel coarse filter | From below | 1 | 27,4 | Wrenches 13 and 22 mm, box spanner 14 mm, water container | ||||||||||
| 53. Lubricate the contact surfaces of the brake pad ribs and pushers | Right and left | 16 | 2,4 | Grease container, spatula | ||||||||||
| 54. Lubricate the working surfaces of the release mechanism parts | Right and left | 8 | 12 | Container for lubricant, bath for washing parts, air dispenser | ||||||||||
| 55. Lubricate the front axle hub bearings | Right and left | 2 | 12 | Container for lubricant, bath for washing parts, wooden spatula | ||||||||||
The total labor intensity is 23.5 person-hours. TO-2 operations are quite labor-intensive, but do not provide full information about the efficiency of the brake and steering systems, in contrast to checking these systems on diagnostic stands. Bench tests require much less time, and at the same time provide detailed information about the state of the system being diagnosed.
2.3 Zone TO-2. location and available equipment
Zone TO-2 "MUP VPATP-7" is located in a separate building, has two entrances and two exits for through traffic. The dimensions of the TO-2 zone allow it to accommodate four buses at the same time. The diagram of the TO-2 zone and the location of the equipment is shown in Fig. 1
Rice. 1 – Scheme of the TO-2 zone
1 – pneumatic rivet machine; 2 – vertical drilling machine; 3 – metal workbench; 4 – machine for turning brake pads and drums; 5 – mobile lift; 6 – stationary lift.
Having analyzed the diagram of the TO-2 zone, you can see that this production room has sufficient space to accommodate equipment for diagnosing brake and steering systems.
Table 2.3 shows a list of equipment available in the TO-2 zone and its modern analogues.
Table 2.3 – Equipment of the TO-2 zone of the municipal unitary enterprise “VPATP-7”
| Name of equipment | year-on-year | Compliance with modern requirements | Modern analogues |
Mobile lift PP-24. load capacity 24 t. 4 racks with gear drive, pick-up by wheels. |
2008 | corresponds | Mobile lift PP-20. load capacity 20 t. 4 racks with gear drive, wheel pick-up |
Stationary lift PS-16. load capacity 16 t. 4 racks with gear drive, lifting by jacking platforms |
2006 | corresponds | Stationary lift PS-15. load capacity 15 t. 4 racks, picked up by jacking platforms |
| Universal vertical drilling machine ZIL 2A135 | 1987 | outdated | Geared vertical drilling machine JETGHD-27 |
| Pneumatic rivet machine | 1985 | outdated | Hydro-pneumatic rivet machine Comec CC-30 |
| Machine for turning brake pads and drums produced by the Gomel Machine Tool Plant named after. CM. Kirov | 1983 | outdated | Machine for turning brake discs, drums and flywheels ComecTR 1500. ComecTCE 560 brake pad turning machine |
From the analysis of the equipment available in the TO-2 zone of the municipal unitary enterprise "VPATP-7" we can conclude that most of the equipment used is very outdated and does not meet modern requirements for the quality and accuracy of processing parts. For example, modern machines for turning brake drums and shoes provide greater processing accuracy and better alignment of the working surfaces than the existing one. In addition, in the TO-2 zone there is no equipment for diagnosing brake and steering systems responsible for the active safety of the car. Due to the importance of ensuring reliable and trouble-free operation of the steering and brake control systems, it is advisable to equip the TO-2 area with appropriate diagnostic equipment
3 Equipment used for diagnosing active safety systems
Currently, two directions have been identified in diagnosing car brake systems:
Comprehensive diagnostics, which allows you to assess the technical condition of the vehicle’s brakes as a whole based on the value of the estimated (output) parameters (braking distance, deceleration, braking force, response time);
Causal diagnosis, during which a decrease in brake efficiency is determined by determining the technical condition of individual units and elements of the brake system.
Comprehensive diagnostics is the primary stage; it is performed on special stands in a planned manner with a certain frequency. In this case they measure:
Braking distance of a car (the distance covered by a car from the moment you press the brake pedal until it comes to a complete stop);
Slowing down a car when braking;
Braking force on each wheel.
Related parameters may be the brake response time of each wheel (axle), the difference in the values of the main parameters for individual wheels.
In addition to the above-mentioned parameters of the technical condition of the brakes, on the stands it is possible to determine the force of free rotation of the wheels, the braking force developed by each wheel, the presence of blocking, i.e., wheel gripping, the pressure force on the brake pedal, uneven wear (ellipseness) of the brake drums.
The force of free rotation of the wheels characterizes the adjustment of the brake pads and the state of the vehicle's mechanical transmission (transmission). With optimal adjustment of the pads and the absence of defects in the mechanical transmission, the force of free rotation of truck wheels is in the range of 300-400 N (30-40 kgf).
Braking force is the reaction of the supporting surface on the wheels of the car, causing braking. Braking is the process of creating and changing artificial resistance to vehicle movement.
The braking force developed by each wheel, with the same pressure on the pedal, is an important parameter that determines the car's skidding during sudden braking. The normal distribution of braking force between the front and rear wheels is determined by the vehicle manufacturers. The difference between the braking forces developed by the right and left wheels is allowed no more than 15-20%.
An assessment parameter for the effectiveness of brakes in general is the ratio of braking force to vehicle weight. The braking force must be at least 65% of the vehicle's weight.
The force of pressure on the pedal characterizes the state of the hydraulic brake drive; it should not exceed 500 N (50 kgf) when the wheels are locked.
Uneven wear of brake drums around the circumference is characterized by instability of braking force readings, manifested in oscillations of the instrument needle synchronously with the wheel speed (measurement is best carried out at low speeds). The permissible ellipse of the brake drum causes the instrument needle to oscillate within the limits determined by the design of the stand.
For example, on the KI-4998 stand for a truck, the permissible oscillation of the instrument needle is 10 divisions, i.e. 700 N (70 kgf).
Currently, several types of stands have been developed for diagnosing brakes of cars and trucks:
Stands for static tests, where braking forces are measured with a stationary vehicle and wheel speeds close to zero;
Stands for kinematic tests, where the car is stationary, the wheels rotate using stand rollers (moving belt);
Stands for dynamic tests, where a car drives at a certain speed onto dynamometer pads and brakes (the car and the stand influence each other in the same way as the car and the road during braking).
Diagnostic equipment is designed to check the technical condition of both the vehicle as a whole and its main components and systems. The technical condition as a whole is assessed by the level of traffic safety, environmental impact, traction and economic characteristics.
3.1 Equipment for diagnosing brake systems
According to GOST 25478 - 82, brake efficiency is checked using road and bench testing methods. The method of road testing is that the equipped car is accelerated on a flat area with a dry asphalt concrete surface (adhesion coefficient not lower than 0.6) to a speed of 40 km/h and the driver applies emergency braking. In this case, the vehicle's braking distance and deceleration are assessed, the normative values of which are established by the standard depending on the type of vehicle. The parking brake system is assessed to ensure a stationary state when a vehicle (road train) drives onto an inclined overpass with different slope values: for a vehicle with a gross weight of 16%, for cars and buses in running order 23%, and for trucks and road trains in running condition 31%. .
During road testing of brakes, decelerometers (devices for determining acceleration) can be used, but mainly visual observation methods are used, which makes the assessment of the technical condition of the brakes subjective and, as a result, not reliable enough. In this regard, recently an increasing emphasis in organizing brake diagnostics has been transferred to bench methods that provide an objective assessment of the braking properties of a car. Brake stands are divided into platform and roller, and the latter into inertial and power type stands. The diagram of the platform brake tester is shown in Fig. 3.1.
Rice. 3.1 - Scheme of an area brake test stand.
1 – platform; 2 – sensor; 3 – roller; 4 – wheel; 5 – spring;
The method for diagnosing brakes with its use consists in accelerating the car to a speed of 6 - 12 km/h and sharp braking when wheels 4 collide with areas 1 of the stand. If the brakes are ineffective, then the car's wheels roll over the stand areas and the latter do not move. If the brakes are effective, the wheels are braked and blocked, and under the influence of inertial forces and frictional forces between the wheels and the surface of the platforms, the car moves forward and takes the platforms with it. The value of the movement of each platform on rollers 3, not limited by springs 5, is sensed by sensors 2 and recorded by measuring instruments located on the console. The main advantages of on-site stands are their speed, low metal and energy consumption. The most convenient stands are for carrying out inspection control with the issuance of a “pass or fail” conclusion. The disadvantages of these stands include, first of all, the low stability of readings due to changes in the coefficient of adhesion of the car’s wheels to the platforms (the wheels are wet, dirty, etc.) and the car’s entry with a misalignment. It is for these reasons that serial production of these stands has not yet been implemented.
These disadvantages are absent in stands with running rollers (drums), which have become widespread throughout the world. In Fig. 3.2 shows a schematic diagram of an inertial type brake stand.
Structurally, it is made of two pairs of drums connected to avoid wheel slipping by chain drives. The drive is carried out from an electric motor with a power of 55 - 90 kW through a gearbox and electromagnetic couplings, when disconnected, the drum blocks become independent dynamic systems. The running drums are connected to the flywheel masses.
The physical meaning of checking the effectiveness of brakes on an inertial stand is as follows. If in real conditions on the road the kinetic energy of a forward moving car is extinguished with the help of brake mechanisms, then on a stand where the car is stationary, due to the action of the brakes, the rotational energy of the drums and flywheel masses with which “the moving road rolls under the car” is extinguished. To ensure the simulation of real conditions, the flywheel masses are selected in such a way that the moment of inertia of them and the running drums at a given rotation speed provides kinetic energy corresponding to the kinetic energy of the translationally moving mass of the car per one axis.
Rice. 3.2 - Scheme of an inertial type brake tester with running drums:
1 - flywheel; 2 - stand drums: .3 - chain drive; 4 - electromagnetic clutch, 5 - gearbox; 6 - electric motor
The advantages of inertia-type brake testers are a high degree of accuracy and reliability in determining indicators (by ensuring high stability of the coefficient of adhesion between the wheels of the car and the drums of the stand), the ability to test brakes in conditions approaching real ones, which ensures high information content of the test. However, inertial-type stands are metal-intensive (with inertial masses up to 5 tons) and energy-intensive. It is most advisable to use stands of this type when carrying out acceptance inspection of cars for the purpose of a comprehensive assessment of their braking properties.
The most widespread at present are power-type brake stands, the schematic diagram of which is shown in Fig. 3.3.
Rice. 3.3 - Scheme of a power type roller brake tester:
1 – frame; 2 - roller; 3 - chain drive; 4 - shaft; 5 - gear motor; 6 - locking roller; 7 - car wheel; 8 - pressure sensor.
Just like inertial ones, they are made in the form of two pairs of rollers connected by chain drives. Each pair of rollers has an autonomous drive from an electric motor with a power of 4 - 13 kW connected to it by a rigid shaft with a built-in gearbox (geared motor). Due to the use of planetary type gearboxes with high gear ratios (32 - 34), a low rotation speed of the rollers during brake testing is ensured, corresponding to 2 - 4 km/h vehicle speed. The rollers of the stand have a notch or a special asphalt concrete coating, which ensures stable adhesion of the wheels to the rollers. To ensure a compact design and ease of installation, the roller blocks are installed in a common frame. The stand must be equipped with a force sensor on the brake pedal and provide the ability to determine the maximum braking force and the response time of the brake drive. The advantages of power-type brake stands are their fairly high accuracy, and the low rotation speed of the rollers when testing brakes determines their high manufacturability. The disadvantages of stands include their metal and energy consumption. These stands are most convenient when carrying out operational control, when they are used to determine the effectiveness of the brakes, carry out adjustment work if necessary, and re-check the quality of the adjustments made. For power-type stands, there are developments for the use of automation of the diagnostic process, which significantly increases the information content and reliability of diagnostic results.
3.2 Steering diagnostic equipment
3.2.1 Equipment for measuring steering play
The steering as a whole is checked with a model K-187 device. The K-187 device is portable, includes a dynamometer with a scale and a play meter, which is mounted on the steering wheel; The arrow of the play meter is mounted on the steering column. It allows you to determine the total play (by the angle of rotation of the steering wheel), as well as the total friction force, for which the front wheels are suspended to eliminate friction of the tires in the contact patch, and the force of rotation of the steering wheel is measured with a special dynamometer.
When servicing steering systems equipped with a hydraulic booster, the K465M model is additionally used, which allows you to determine oil leakage, hydraulic pump pressure, and pump performance. The wear of the kingpin assembly of the front axle of a truck is checked using a model T-1 device.
There are also more accurate and easy-to-use instruments for measuring total play in the steering, developed by domestic scientists. For example, a dynamometer with a hydraulic playmeter on a disk for diagnosing steering.
The measuring element of this device is a sealed transparent ampoule containing liquid and an air bubble left in it. The prototype is shown in Fig. 3.4.
The device is made of three structural parts connected into one block: a dynamometer, a backlash meter and a connecting device.
The double-acting dynamometer is equipped with two torque handles 1 with scales 2 and locking rings 7. Its springs are housed in a cylindrical body closed with covers 12.
The play meter is arranged on disk 6 and is a sealed transparent ampoule 5 filled with a low-freezing liquid (alcohol) with an air bubble 4 left. This ampoule is graduated and combined with the play meter scale 3, consisting of two parts - respectively, with the starting point from left to right and from right to left. Disk 6 is installed in sleeve 8 with the ability to rotate both left and right. The axial movement of disk 6 is limited by two setscrews 11.
Rice. 3.4 - Device for checking steering control DL-G (hydromechanical dynamometer-play meter):
1 – torque handle; 2 – dynamometer scale; 3 – backlash meter scale; 4 – air bubble; 5 – ampoule; 6 – backlash meter disk; 7 – locking ring; 8 – disk bushing; 9 – bracket; 10 – pressure screw; 11 – setscrew; 12 – dynamometer cover.
The connecting device consists of an L-shaped bracket 9 with a nut pressed into it, into which a pressure screw 10 is screwed. To assemble the device into one unit, sleeve 8 is rigidly attached to the dynamometer cylinder from above, and bracket 9 is also connected to this body, but from below.
The operating principle of a dynamometer-backlash meter. The device is secured with screw 10 to the lower or upper point of the steering wheel rim. In this case, it is desirable that the plane of the disk 6 be parallel to the plane of rotation of the specified rim. The locking rings 7 are pressed against the covers 12. The device is ready for use.
The force on the steering wheel rim (friction force) is checked by turning the rim by the torque handles 1 from one extreme position to another. The springs are deformed and, as a result, the handles move, as well as the locking rings shift along the specified handles. When the handles are released, they return to their original position, and the rings are held on them by friction. Based on the position of the hairline on ring 7 relative to the strokes of scale 2 on handle 1, the measurement result is found - the maximum force on the steering wheel rim.
To measure the total play, turn the steering wheel first, for example, clockwise, applying a given (normalized) force to the handle 1 and in this position set zero on the play meter by rotating disk 6. In this case, the left edge of the air bubble 4 is aligned with the zero mark of the play meter scale – extreme mark on ampoule 5. Then turn the steering wheel in the opposite direction, applying the same force to the other handle. When the steering wheel rotates, the ampoule makes a portable movement, and the air bubble moves in its cavity under the action of a lifting force. Therefore, the measurement results do not depend on both the angle of inclination of the steering wheel rim to the horizontal plane and the diameter of the specified rim. By the movement of bubble 4 relative to the corresponding scale of the play meter - the mark on ampoule 5, the play of the steering wheel is determined.
If necessary, repeat the measurement by starting to turn the steering wheel rim in the opposite direction. Diagnosis is complete. Loosen screw 10 and remove the device from the rim.
3.2.2 Equipment for measuring wheel alignment angles
Drive-through platform or rack stands for checking wheel alignment angles, the diagram of which is shown in Figure 3.5, are designed for express diagnostics of the geometric position of a car wheel by the presence or absence of lateral force in the contact patch.
Rice. 3.5 - Means for monitoring wheel alignment angles in dynamic mode: a - drive-through platform stand; b - diagram of the drive-through rack stand;
c - diagram of a stand with running drums; 1 - platform for transverse movement; 2 - transverse movement rack; 3 - driving drum; 4 - driven drum of axial movement.
When the wheel alignment angles do not meet the requirements, a lateral force arises in the contact patch, which acts on the platform (rack) and displaces it in the transverse direction. The displacement is recorded on the measuring device. These stands do not indicate which wheel alignment angle needs to be adjusted. If necessary, further vehicle maintenance is performed on stands operating in static mode.
Platform stands are installed under one vehicle track, rack stands - under two. A car passes through the stand at a speed of approximately 5 km/h.
Stands with running drums are designed to measure lateral forces at the points of contact of the driven wheels of a car with the supporting surface of the drum. To measure lateral forces, the car is placed on a stand and the electric motors of the drums are turned on. Using the steering wheel, observing the instruments, they achieve equality of lateral forces on both wheels. If the readings do not correspond to the norm, adjust the toe-in. If the required result could not be achieved, further vehicle maintenance is carried out on stands operating in static mode.
Stands with running drums are mainly intended for cars that only have toe adjustment. These stands are metal-intensive and expensive, so it is advisable to use them only at large ATPs.
Stands (devices) for monitoring wheel alignment angles in static mode allow you to measure the angles of: longitudinal and transverse inclination of the king pin axis, camber, rotation angle ratio, toe. These stands are most widespread due to their simplicity of design and low cost. The functionality of the stands is approximately the same, the main differences are in the measurement principle.
Level measurement. The device is attached to the car wheel and its “horizon” is set according to the liquid levels (Fig. 3.6, a). By turning the wheels to the right and left, you determine what slope the levels have received. The magnitude of these tilts depends on the actual wheel alignment angles. The domestic device of this type is M2142. The principle of a level (or plumb line) is incorporated into the measuring systems of most modern designs. The deviation of the wheel from these basic positions is read visually, and in some designs automatically and displayed on a punched card or display.
Rice. 3.6 - Means for monitoring wheel alignment angles in static mode:
1 - device with levels; 2 - measuring head with guides; 3 - measuring rods; 4 - contact disk for mounting on a wheel; .5 - projector; 6 - source of light beam with measuring scale; 7 - mirror reflector.
Contact measurement. A metal disk is attached to a car wheel strictly parallel to its plane of rotation. A device with movable measuring rods is brought to it along guides. The value of the wheel alignment angles is determined by the amount of recessing of the rods (Fig. 3.6, b). The currently produced stand of this type, K622, is intended for passenger cars, but can easily be upgraded for trucks and is technologically convenient for measuring toe-in and camber angles on maintenance production lines.
Measurement along the projected beam. A projector is attached to a car wheel, sending a narrow light or laser beam onto the screen (Fig. 3.6, c). By changing the position of the wheel on the appropriate scales, the wheel alignment angles are measured one by one, as well as the geometry of the vehicle base. A representative of stands of this type is the K111 model for passenger cars and K62I for trucks.
Reflected beam measurement. A triangular mirror reflector is attached to a car wheel, the central mirror of which should be parallel to the rolling plane of the wheel. A beam with a sighting symbol is sent to the mirror (Fig. 3.6, d). By changing the position of the wheel, the angles of the wheel are determined in turn from the position of the sight on the corresponding scales. Stands of this type are most widely used at ATP (model 1119M), as they are reliable, have high measurement accuracy, and are easy to operate and maintain. To measure only the toe angle, use a special ruler (model 2182), which is universal and suitable for all cars. The use of a ruler is justified only in the absence of other equipment, since the accuracy it provides is approximately 2–4 times lower than that of stationary stands, which is not enough for modern cars.
3.3 Diagnostic equipment offered on the market
3.3.1 Brake testers
Currently, the market offers a fairly wide range of brake diagnostic stands. Power-type stands are the most widespread. There are both stationary and movable stand models. In the conditions of the municipal unitary enterprise “VPATP-7”, with a fairly large production maintenance program, as well as for the convenience of diagnosing the brake control before going to the line, a stationary brake tester should be installed.
Stand STS-10U-SP-11
Stand STS-10U-SP-11 is a stationary universal test stand for monitoring brake systems of cars and trucks, buses and road trains with an axle load of up to 10 tons. The measurement results are processed on a personal computer and displayed on the screen. Measures the load on the axle, the braking force on each wheel, the force on the controls, displays brake diagrams. Determines the design parameters in accordance with GOST R 51709-2001: specific braking force, the relative difference in the braking forces of the wheels of the axle, asynchronous response time of the brake drive of the links of the road train. Additionally can measure the response time of the braking system. Table 3.1 shows the main technical parameters of the stand.
Table 3.1 – Technical parameters of the stand Stand STS-10U-SP-11
| Diameter of car wheels, mm | 520 - 1300 |
| Roller track width, mm | 880 - 2300 |
| Initial braking speed simulated on the stand, km/h, not less | 4,4 / 2,2 |
| 1 – 6 / 3 - 30 | |
| 100 - 1000 | |
| Limit of permissible reduced error, % | 10000 |
| 0 – 1,5 | |
| 15 | |
| 8 | |
| Equipment area | 6,5*15 |
Rice. 1 – Placement of equipment in working position
1 - right support device; 2 - left support device; 3 - power cabinet; 4 - instrument cabinet; 5 – photodetector; 6 - control stand; 7 - socket for connecting the control stand
Stand STM-8000
The stand is designed to monitor the effectiveness of brake systems of cars, trucks, buses, as well as multi-axle all-wheel drive vehicles with an axle load of up to 8000 kg, a track width of 960-2800 mm.
The stand can be used at vehicle service stations, automobile enterprises, state technical inspection stations to monitor brake systems in operation, during production on the line, as well as during annual technical inspection using diagnostic tools. The main technical parameters of the stand are given in Table 3.2.
The stand provides determination of the following parameters:
Axle weight;
Specific braking force;
Ovality of the wheels of the diagnosed axle.
Table 3.2 – technical characteristics of the STM-8000 stand
| Diameter of car wheels, mm | 520 - 1300 |
| Roller track width, mm | 800 - 2300 |
| 3,0 / 2,3 | |
| Braking force measurement range on each wheel of the tested axle, kN | 0 - 25 |
| Limit of permissible reduced error, % | |
| Range of force measurement on the control, N | 0 - 1000 |
| Limit of permissible reduced error, % | 8000 |
| Brake system response time measurement range, s | 0 – 1,5 |
| Time to establish operating mode, min, no more | 15 |
| Continuous operation time, h, not less | 8 |
| Equipment area | 6*15 |
Cartec BDE 3504-10t stand (spec CeSi)
The CartecBDE 3504-10t (specCeSi) stand is a computerized roller brake tester for trucks, buses and road trains with an axle load of up to 10 tons. The rollers of the stand have a ceramic-silicon coating that imitates the road surface. The stand has two tracking rollers. The brake tester only turns on when both follower rollers are down (ie the vehicle is on the brake tester), this prevents accidental starting and provides additional safety. The stand is supplied with a fundamental frame, which greatly facilitates the preparation of the foundation of the diagnostic line and reduces the likelihood of errors when installing equipment.
To recreate test conditions on the bench that are closest to real road conditions, cars must be diagnosed in a loaded condition. For these purposes, the stand equipment includes a device for simulating the load on a car. It consists of two hydraulic cylinders installed in an inspection ditch and attached via chains to the frame or axle of the vehicle. The force created by the hydraulic cylinders presses the car wheels against the rollers and thus simulates loading the car. Table 3.3 shows the technical characteristics of the stand.
The stand measures the following parameters:
Axle weight;
Control force;
Relative difference in braking forces on one axle;
Specific braking force;
Brake system response time;
Ovality of the wheels of the diagnosed axle;
The force of free rotation of the wheels.
Table 3.3 – Technical characteristics of the CartecBDE 3504-10t stand
| Diameter of car wheels, mm | 520 - 1300 |
| Roller track width, mm | 850 - 2300 |
| Braking speed simulated on the stand, km/h | 2,8 / 2,2 |
| Braking force measurement range on each wheel of the tested axle, kN | 0 – 6 / 0 - 30 |
| Limit of permissible reduced error, % | |
| Range of force measurement on the control, N | 0 - 1000 |
| Limit of permissible reduced error, % | 10000 |
| Brake system response time measurement range, s | 0 – 1,5 |
| Time to establish operating mode, min, no more | 15 |
| Continuous operation time, h, not less | 10 |
| Equipment area | 5*15 |
The results of the comparative analysis of the considered stands are shown in Table 3.4.
Table 3.4 – Comparative characteristics of brake testers
Having compared the three selected brake stands, we can conclude that the Cartec stand, unlike the others considered, in addition to the brake system parameters required by GOST R 51709-2001, additionally determines the ovality of the brake drums of the diagnosed axle and the force of free rotation of the wheels. Also important is the ability to simulate the loading of a vehicle, which allows you to evaluate the operation of the bus’s braking system when driving with passengers. Therefore, this stand is the most preferable for installation in the municipal unitary enterprise "VPATP-7".
3.3.2 Wheel alignment stands
Let's consider diagnostic stands for adjusting wheel alignment angles, which are in greatest demand on the diagnostic equipment market.
Stand KDS-5K T
The KDS-5K T computer diagnostic stand is designed to adjust the angles of steering wheels of trucks and buses. The parameters measured by the stand, the limits and errors of measurements are given in Table 3.5.
Table 3.5 – Characteristics of the KDS-5K T stand
The price of the KDS-5K T stand is 270 thousand rubles.
Stand Techno Vector 4108
Computerized wheel alignment stand designed for any car with a rim diameter from 12 to 24 inches. The characteristics of the parameters measured by the stand are given in Table 3.6.
Table 3.6 - Characteristics of the Techno Vector 4108 stand
The measurement results before and after adjustment are displayed on the display and printing device.
The price of the stand is 250 thousand rubles.
The HunterPA100 stand is a computer stand with infrared sensors for adjusting wheel alignment angles. The stand comes with self-centering wheel grips designed for rim diameters from 10 to 24 inches. Infrared sensors allow you to measure toe angles with an accuracy of 1’. A special feature of this stand is the absence of a hard drive. The software is built on the Linux operating system platform; a flash card is used as a storage medium, as a result of which the stand is almost impossible to disable by software. The name and accuracy of the parameters measured by the stand are given in Table 3.7.
Table 3.7 – HunterPA100 stand characteristics
The price of the stand is 295 thousand rubles.
Of the three diagnostic stands considered, the most preferable option is the Hunter stand, since it provides a sufficiently high accuracy of measurement of all necessary parameters in combination with higher reliability, which is ensured by infrared communication of sensors installed on wheels, in contrast to laser or cord, as well as the presence of a failure-resistant operating system.
Conclusion
The relevance of the topic of this work is due to the current unfavorable situation on the city’s roads, a large number of accidents. In forty percent of cases, one of the causes of an accident is the unsatisfactory technical condition of the vehicle systems responsible for active safety. In accidents involving buses, the health of many more people is at risk than in accidents involving cars. Therefore, in the conditions of road transport it is especially important to pay increased attention to the technical condition of active safety systems of rolling stock.
In the first section of the work, the requirements of GOST R 51709-2001 for the technical condition of brake and steering systems and methods for checking them were considered. Methods for checking brake systems on diagnostic stands are preferable to checks on the road, since road tests are difficult to organize in a limited area of the highway, and their results do not provide complete information about the state of the system as a whole and its individual components.
In the second section, an analysis of the equipment of the municipal unitary enterprise “VPATP-7” with equipment for diagnosing brake and steering control is carried out. The necessary diagnostic equipment is missing, and what is available is very outdated. The free production areas of the TO-2 zone make it possible to place stands for diagnosing brake and steering systems.
In the third section, an analysis of the diagnostic equipment market is carried out, and some of the suitable diagnostic stands are selected. A comparative analysis of the stands was carried out, and the optimal models for installation in the PATP-7 municipal unitary enterprise were selected.
The use of these stands both for maintenance and for diagnostics before going on line will increase the productivity of maintenance work and reduce the risk of accidents due to malfunction of the brake and steering systems.
This topic is voluminous and cannot be fully covered within the framework of a bachelor’s thesis. The study of this topic can be continued further for a more complete coverage of the issues raised.
List of used literature
1. GOST R 51709 – 2001. Motor vehicles: safety requirements for technical condition and inspection methods. – M.: Publishing house of standards, 2001. – 73 p.
2. Chamber of Control and Accounts of Volgograd [Electronic resource], 2009.
3. Osipov, A.G. New devices that increase the reliability of diagnosing brake systems of vehicles / A.G. Osipov // Automotive industry - M., 2009. - No. 9. - P. 27 - 30.
4. Pat. 2161787 Russian Federation. Dynamometer with a hydraulic playmeter on a disk for diagnosing steering control / V.N. Khabardin, S.V. Khabardin, A.V. Khabardin; publ. 06/17/01, Bulletin. No. 1. – 6 p.: ill.
5. Spichkin, G.V. Workshop on car diagnostics [Electronic resource] / G.V. Spichkin, A.M. Tretyakov. – M.: Higher. school, 1986.
6. Auto theory: everything about the structure of a car [Electronic resource], 2010. –
7. Technical operation of automobiles: lecture notes [Electronic resource], 2009.
8. Technology for maintenance of LiAZ-525625 buses with a Caterpillar-3116 engine. – Likinsky Bus LLC, 2004. – 276 p.
9. Car structure [Electronic resource], 2007
Steering
Steering Diagnostics
Steering mechanisms are checked by visual inspection of the systems; for this, the car is installed on an overpass or an inspection hole is used. To check the steering, the front wheels of the car are set in straight-line mode.
Having prepared the car for technical inspection, the first thing to do is check the free play of the steering wheel, for which they begin to turn it first in one direction and then in the other. Normally, the free play of the wheel before the front wheels begin to turn should not exceed 5°, while the wheel rim moves no more than 20 mm.
If it is difficult to determine the free play of the steering wheel by eye, you can make appropriate measurements and calculations. To take measurements, you will need a ruler, which must be placed with its narrow side against the instrument panel, while the plane of the ruler should fit snugly against the outer surface of the steering wheel. Then they turn the steering wheel until the wheels begin to turn and make a mark on the steering wheel; thin wire, a felt-tip pen or chalk are suitable for this. Then the steering wheel is turned in the other direction before the wheels begin to turn and a second mark is made.
If, after setting the wheels to move in a straight line, the steering wheel spokes do not occupy a strictly horizontal position, but are shifted, it is necessary to adjust the wheel alignment angles and check the steering and suspension systems.
After this, use a ruler to measure the distance between the two marks (Fig. 70) and compare it with the calculated one made using the formula: L = (5°/360°) pD, where L is the steering wheel play (unit of measurement – mm), p = 3.14, D is the outer diameter of the steering wheel (unit of measurement - mm).
Steering wheel rotation that is too tight or too free requires further inspection and troubleshooting.
To check for a knock in the steering mechanism, press the brake pedal and, holding it down, rock the steering wheel. If knocking noises are heard, you need to additionally inspect the system elements, first checking the threaded connections and ball joints of the steering rods - perhaps they are damaged or worn out.
Figure 70. Checking the free play of the steering wheel
After this, they proceed to inspect the steering mechanisms from below the car.
Technical inspection of steering components
Before inspection, the protective covers of the steering rod joints and other elements of the steering system should be thoroughly cleaned of dirt. During the inspection, you should check the attachment points of the bracket and gearbox to the car body. If the bolts and nuts are loose, they should be tightened.
Then the axes of the pendulum lever are inspected: using a slight swing of the hands, the absence of radial or axial play in the mechanisms is determined. If play is noticed, the pendulum arm must be replaced with a new mechanism assembly.
When diagnosing steering mechanisms, you need to pay attention to the condition of the protective covers of the steering rod joints. The appearance of cracks, peeling, ruptures, and signs of wear on these parts that protect the hinges from dirt is unacceptable; otherwise, they are replaced with new ones.
During the inspection, the steering tips and pin axes are inspected, and the amount of displacement of the steering tips along the pin axis is determined. First, the tip is measured in a free state, then - after pressing the rod near the tip and moving it along the axis of the fingers. The difference between these measurements will be the axial displacement. Normally, it should not exceed 1.5 mm (Fig. 71).
Figure 71. Checking the axial movement of the tie rod ends
During the inspection, you need to make sure that there is no play in the ball joints. To check, you need to sharply shake the steering rods with your hands (Fig. 72 a). If damage or wear is detected, they must be replaced with new ones. When checking the caps, squeeze them a little with your fingers: if grease appears when pressed, the caps need to be replaced (Fig. 72 b).
Figure 72. Checking the steering rod ball joints
Typical faults
Problem: Steering wheel moves too freely
1. Check the fasteners of the steering rod ball pins. Loosening the nuts can cause the steering mechanism to increase free movement. In this case, the threaded connections should be tightened.
2. Check the ball joints of the steering rods. Increasing the gap often causes this problem. If the cause is worn parts, the tie rod ends should be replaced or new rods installed.
3. Check the rubber-metal joints of the steering rods. If they are worn out or damaged, depending on the condition of the steering rods, only the silent blocks or the entire rods are replaced.
4. Check the front wheel hub bearings. If the gap is increased, adjust. If the bearings show signs of wear, replace the parts.
5. Check the rivet connection. If the rivets are loose and play appears, they need to be replaced with new ones.
6. Inspect the steering mechanism, check the steering rack. If, as a result of wear of parts, the gap between the steering rack stop and the nut has increased, the rack must be replaced.
7. Check the axis of the pendulum arm and bushings for wear and damage; if the bushings are heavily worn, replace them with new ones. If there is other damage to the system elements, the bracket is completely replaced.
Problem: Steering wheel is hard to turn
1. Check the bearing of the upper support of the front suspension strut; if it is damaged or shows signs of wear, the bearing should be replaced. Additionally, inspect the rack support; if damage or deformation is detected, it is worth replacing the entire thing.
2. Check the support sleeve. If it is damaged, replace it with a new one. Lubricate the bushing with grease.
3. Check the steering rack for damage and presence of lubrication. If necessary, add lubricant or completely replace the part.
4. Check tire pressure. Too low pressure can cause the steering wheel to move stiffly. Restore normal pressure.
5. Inspect the elements of the ball joints of the steering rods and the telescopic suspension strut. Replace damaged parts with new ones.
Excessively tight rotation of the steering wheel makes driving a car a difficult and unpleasant experience. Since a heavy ride only indicates a problem in the steering system, it is necessary to establish the cause and eliminate the malfunction.
6. Check the steering drive elements for deformation and damage, replace worn or damaged parts with new ones.
7. Check the alignment of the front wheel angles and, if necessary, adjust them at a service station.
8. Check the axis of the pendulum arm. When overtightening the adjusting nut, a problem with the steering movement may occur; in this case, the nut should be slightly loosened.
9. Check the presence of oil in the steering gear housing. If necessary, top up and check
oil seal; if wear and signs of oil leakage are detected, replace the crankcase with a new one.
10. Check the upper shaft bearings. If the bearings are damaged or worn, they are replaced with new ones.
The problem is knocking and noise in the steering
1. Check the fasteners of the steering rod ball joints. If they become loose, tighten the threaded connections.
2. Noise in the steering wheel can result from an increase in the gap between the steering rack stop and the nut beyond the permissible limits. You should inspect the parts, replace worn ones and adjust the gap.
3. Check the steering gear fastening elements. If the nuts are loosened, they should be tightened.
4. Check the clearance between the front wheel hub bearings. If necessary, replace the bearings and adjust the distance between them.
5. Inspect the fasteners of the steering rod ball pins. Loosening the nuts can cause a knocking noise. After tightening the threaded connections, the knocking noise disappears.
6. Check the fastenings of the intermediate shaft, the steering gear housing rotary arms and the pendulum arm bracket. Tighten the nuts if the fastenings are loose.
7. Check the swing arm axle and bushing for wear and damage. If the bushings are severely worn, replace them with new ones. If there is other damage to the system elements, the bracket is completely replaced.
8. Check the ball joints of the steering rods. Increasing the gap often leads to knocking. If the reason is wear of parts, the tie rod ends should be replaced or new rods should be installed completely.
The problem is self-generated angular oscillation of the front wheels
1. Check the tire pressure and adjust to normal.
2. Check the angle of the front wheels; if a violation is detected, adjust the angle at a service station.
3. Inspect the front wheel hub bearings and adjust if the gap is increased.
If the bearings show signs of wear, replace the parts.
4. Check wheel balancing. If it is broken, balance it on a special stand at a service station.
5. Check the fasteners of the steering rod ball pins.
Loose nuts can cause angular wobble of the front wheels. After tightening the threaded connections, the problem should disappear.
Front wheel wobble can occur for a number of reasons, but is usually the result of wheel imbalance or improper front wheel angle setting.
6. Check the fastenings of the steering gear housing and the pendulum arm bracket, tighten the nuts if the fastenings are loose.
The problem is loss of vehicle stability
1. Check the alignment angles of the front wheels; if a violation is detected, adjust the angle at a service station.
2. Inspect the front wheel bearings. If an increased gap between the bearings is detected, it must be adjusted. After this, the car should gain stability.
3. Check the fasteners of the steering rod ball pins. When loosening the nuts, it is necessary to tighten the threaded connections.
4. Check the ball joints of the steering rods. Increasing the gap may cause instability. Inspect parts for wear and damage, if necessary, replace tie rod ends or install new tie rods entirely.
5. Check the fastenings of the steering gear housing and the pendulum arm bracket. Tighten the nuts if the fastenings are loose.
6. Inspect the steering knuckles of the suspension, the deformation of which may cause instability. Replace damaged and deformed parts.
The problem is oil leakage from the crankcase
1. Check the seals and replace if worn.
2. Check the fastening of the steering gear housing cover; if it is loose, tighten the bolts.
3. Check the integrity and tightness of the sealing gaskets, if worn, replace them with new ones.
Brake system
Brake system diagnostics
To maintain a car's brake system in working condition, it is necessary to regularly and timely diagnose and replace parts.
When diagnosing the brake system, you should check:
Mobility of brake caliper pistons;
Brake fluid level;
Hydraulic drive tightness.
If necessary, carry out the following activities:
Replacing brake fluid;
Checking and adjusting the parking brake;
Testing the operation of the vacuum booster and pressure regulator;
Adjusting the brake pedal.
To prevent the car from pulling to the side when braking, you should regularly check the mobility of the brake caliper pistons. To inspect them, remove the pads from the car, then quietly press the brake several times so that the pistons almost completely come out of the caliper, after which they are carefully pushed back in so as not to damage the guide pins. The procedure is repeated 2 times on each side. This helps restore mobility to the brake pistons. If the pistons fit very tightly into the caliper and require a lot of force to push them in, the entire caliper kit must be replaced.
When diagnosing the brake system, it is necessary to inspect all rubber boots. If they are damaged, torn, worn out, they are replaced with new ones. During the inspection, the guide pin anthers are lubricated. To check the condition of the brake discs, their thickness is measured. If it is less than 10.8 mm, the part is worn out and must be replaced.
Attention! When the brake drums are removed, do not press the brake pedal, this may cause the pistons to come out of the wheel cylinders and cause depressurization of the drive!
Checking the brake fluid level (general recommendations)
When checking the brake fluid level and replenishing it, you must remember that it is toxic and quite aggressive towards paint and plastic, so if the fluid gets on wires, painted or plastic parts, you need to quickly wipe off the drops.
Normally, the brake fluid level is between the “MAX” mark on the neck and its lower edge (Fig. 73 a).
If the level drops, you need to add brake fluid. To do this, you need to disconnect the wires of the brake fluid level sensor, remove the cap from the reservoir and remove it together with the float from the fluid level sensor (Fig. 73 b).
Only the liquid that is already there should be added to the tank; reusing the liquid is not allowed. When choosing a brand, you need to purchase those fluids that are recommended by the car manufacturer.
The lid is carefully placed on a previously prepared clean rag, liquid is added to the tank so that its level is equal to the “MAX” mark (Fig. 73 c), after which the lid is wrapped, the wires are connected and the operation of the level sensor on the tank lid is checked (Fig. 73 d ). To do this, turn on the ignition and press the pusher on the tank lid with your finger; The red indicator light on the instrument panel turns on and should not go out while the pusher is pressed.
After checking the operation, the ignition is turned off.
Figure 73. Checking the brake fluid level
Checking the tightness of the hydraulic drive
To check the tightness of the hydraulic drive, the car is placed on an overpass or raised on supports, the front wheels are removed. A visual inspection is carried out from above, opening the hood, from below and from the sides of the car.
During the inspection, check the tightness of the nuts, the tightness of the clamps and plugs; If necessary, fasteners are tightened, all damaged hoses are replaced with new ones.
If during the inspection damage and depressurization of the wheel cylinders are revealed, they must be replaced at a service station.
Figure 74. Main components for checking the hydraulic drive
During the inspection, you should check the place where the hoses are connected to the tank, the hoses themselves along their entire length (Fig. 74 a), the master cylinder plug, the places where pipelines and hoses are connected (Fig. 74 b), the air release fitting and the protective caps of the wheel cylinder.
When inspecting the pipeline, the hydraulic drive must be under pressure, for which, at the beginning of the diagnosis, press the brake pedal several times and keep it pressed during the entire inspection.
You can check the hydraulic drive without creating pressure, but then the inspection will not be as effective.
Checking the wheel cylinder protective caps
To check the protective caps, you need to remove the brake drums and clean the parts; Large dirt is removed with a special hard brush, after which the wheel cylinders are wiped with a soft cloth to completely remove any remaining dirt.
In order to inspect the internal cavities of the cap, they need to be carefully picked up with a screwdriver and moved from the groove located on the cylinder body, and then check the groove for the absence of brake fluid accumulation in it.
After inspection, return all parts to their place and continue checking on the opposite side of the car.
Replacing brake fluid
To replace the brake fluid in the hydraulic drive, the car is first placed on a lift or the front part is hung and placed on special supports.
Before replacing the brake fluid, a complete inspection of the hydraulic drive system is carried out, all worn parts are replaced and identified faults are eliminated, the brake drums are installed, but the wheels are not put on.
If the brake fluid is replaced without first checking the hydraulic drive system, the rear wheels can be left in place.
When replacing brake fluid, it is necessary to constantly replenish its supply in the reservoir, ensuring that its level constantly exceeds 10 mm; in this case, the old brake fluid will be gradually replaced with a new one without draining the hydraulic drive.
The operation is carried out in several stages.
First you need to open the brake fluid reservoir, remove the cap with the sensor float and add fluid to the bottom edge of the neck.
After this, remove the front wheels and clean the fittings of the front wheel cylinders from dirt with a soft cloth. Now you need to unlock the pressure regulator in the rear brake drive, for which you need to disconnect the rod and torsion bar.
After removing the nut from the bolt securing the part, the torsion bar is removed from the rack and a spacer about 150 mm high is installed between the lever and the rear axle housing. After this, remove the protective cap from the fitting, bleed air from the rear cylinder, and put a prepared rubber hose on the fitting for bleeding.
To drain the liquid, you will need outside help, since at this stage you need to sharply and quickly, at intervals of up to 3 seconds, press the brake pedal 5 times, and then hold it pressed until the liquid is drained. At this moment, the second person lowers the opposite end of the hose into a container specially prepared for draining, unscrews the fitting and drains the liquid (Fig. 75).
Figure 75. Replacing brake fluid
The brake fluid is replaced on a lift with the rear wheels hanging up; the regulator is unlocked in advance.
The pedal is pressed all the way while draining; after all the liquid has drained, the fitting is screwed back on.
This procedure is repeated several times with constant addition of new brake fluid to the reservoir.
When clean liquid begins to flow from the hose, the fitting is finally tightened (the brake pedal must be pressed), the hose is removed and the protective cap is returned to its place. The operation is repeated with the remaining three wheels.
After replacing the fluid, you should check the operation of the hydraulic drive by pressing the brake pedal several times. If the pedal stroke and the forces applied to press it are proportionate, the hydraulic drive is ready for operation.
If, with each subsequent press on the brake, the pedal travel decreases and its rigidity increases, air has entered the hydraulic drive and bleeding is required to remove it from the system.
Bleeding the hydraulic drive
Bleeding is carried out if, as already mentioned, air gets into the latter when filling the system with new brake fluid or replacing individual elements of the hydraulic drive.
Before bleeding, you need to determine the cause of the hydraulic drive depressurization and eliminate it.
If air has entered only one of the circuits, and the second is fully operational, you can pump only the depressurized hydraulic circuit. Bleeding is performed in the same way as replacing brake fluid.
After air bubbles completely disappear from the liquid coming out of the hose, the hydraulic drive is again checked for leaks.
Checking the brake mechanism and replacing the front brake pads
If during a test run, when the car is braking, a characteristic metallic sound is heard from the front wheels, you need to inspect the brake pads and measure the thickness of the linings and brake discs.
If the linings become oily, damaged or become thinner than 1.5 mm, and the discs become thinner to 9 mm, the parts should be replaced with new ones, and all elements should be replaced in pairs. Along with changing the discs, the hub is also changed.
Before replacing parts of the brake mechanism, the front wheels of the car are hung up and removed, the brake mechanism is thoroughly cleaned
from dirt.
After removing the two cotter pins, the fingers are knocked out of the cylinder, the pressure springs are released, then the free inside of the cylinders is thoroughly wiped with a rag.
After inspecting the cylinder dust caps, remove the clamping springs, inspect and measure the brake discs, replace them with new ones if necessary, then install the pistons back into the cylinders, change the brake pads and replace the wheel.
Typical faults
Problem - the car pulls to the side
1. Check tire pressure. Often the reason for the slip is different pressures in the tires of the car. It needs to be leveled, and then regularly check the tire pressure level.
2. Check the alignment angles of the front wheels; if any irregularities are detected, adjust the angles at a service station.
3. Check the front suspension springs. If one of the springs settles, the entire pair must be replaced.
4. Inspect the steering knuckles of the suspension. If, after inspection, damaged or deformed parts are found, they must be replaced.
5. Check the brake system. The reason for the vehicle to pull away from straight-line motion may be incomplete release of the wheel brake. The fault must be corrected.
Problem: Brakes squeak or vibrate
1. Check the tension spring of the rear brake pads. Perhaps she is weakened. If necessary, it must be replaced.
2. Check the brake disc. If it wears unevenly or excessively, the brake pedal vibrates noticeably.
The disc should be ground or replaced if its thickness is less than 17.8 mm.
3. Check the friction linings. If they are oily, dilute the detergent in warm water and clean the linings with a wire brush. Determine the cause of grease or liquid getting on the brake pads and eliminate it.
4. Check the brake drums. If ovality is detected, the drum should be bored.
5. Check the linings for foreign bodies and wear. If necessary, replace the pads.
The problem is incomplete release of the brakes on all wheels.
1. Check the rubber seals of the master cylinder. Perhaps they are swollen.
To troubleshoot problems, the entire hydraulic drive system must be thoroughly flushed with brake fluid and pumped. Replace rubber parts with new ones.
Rubber seals
they swell and fail when mineral oils, gasoline and other foreign substances get into the brake fluid.
2. The reason for incomplete release of the wheels may be the lack of free play in the brake pedal - it needs to be adjusted.
3. Check the master cylinder piston. It is quite possible that it is jammed. If a malfunction is detected, the cylinder must be replaced and the system must be pumped.
4. Check the adjusting bolt of the vacuum booster rod. If a violation of its protrusion relative to the mounting plane of the master cylinder is detected, the bolt must be adjusted.
The protrusion of the adjusting bolt of the vacuum booster rod relative to the mounting plane of the master cylinder should be 1.25–0.2 mm.
Problem – the brake pedal stroke is increased
1. Check the brake system for the presence of air. If it is detected, the hydraulic drive must be pumped.
2. Check the brake disc. If its runout exceeds 0.15 mm, the disc should be ground. The brake disc is replaced when its thickness is less than 17.8 mm.
3. Check the rubber O-rings. If they are damaged in the master brake cylinder, they must be replaced and the system must be bled.
4. Check the wheel cylinders for brake fluid leaks. If it is detected, the failed parts are replaced with new ones, the pads, drums and discs are thoroughly washed and dried. The hydraulic drive system should be bled.
5. Check the O-rings of the pressure regulator pusher. If brake fluid leaks through them, the O-rings should be replaced.
6. Check the rubber hoses of the hydraulic brakes. If damage is found, they should be replaced with new ones and the system should be bled.
Problem: when the pedal is released, one wheel slows down
1. Check the parking brake system for correct adjustment and adjust if necessary.
2. Check the rear brake pads. If their tension spring is weakened or broken, replace it with a new one.
3. Check the wheel cylinder O-rings. If they swell due to mineral oils, gasoline, etc. getting into the brake fluid, it is necessary to replace the rings with new ones, flush the hydraulic drive system with brake fluid and pump it.
4. Check the position of the caliper relative to the brake disc. There may have been a violation of the caliper position due to loosening of the bolts securing the pad guide to the steering knuckle. In this case, the fastening bolts should be tightened and damaged parts replaced if necessary.
5. Check the piston in the wheel cylinder. Corrosion or contamination of the cylinder body could cause the piston to seize. To fix the problem, the cylinder must be disassembled, the parts must be cleaned and washed thoroughly, and damaged ones must be replaced. Finally, the hydraulic drive system should be bled.
Problem – braking is not effective enough
1. Check that the linings match the pads. It is necessary to use only those pads recommended by the manufacturer.
2. Check the pistons in the wheel cylinders. If they jam, eliminate the cause of its occurrence. If necessary, replace damaged parts and bleed the system.
3. Check the brakes for overheating. If it is detected, stop immediately and let the mechanisms cool down.
4. Check the circuits for leaks.
Partial failure of the brake pedal is the first signal indicating that one of the circuits has lost its tightness. If one of them has lost its tightness, the part must be replaced and the system must be pumped.
5. Check the brake pad linings. If oiling of the linings is detected, the pads should be thoroughly washed and dried. If they are severely worn, the brake pads must be replaced.
6. Check the pressure regulator. If it is found to be incorrectly adjusted, the pressure regulator drive should be adjusted.
Basic malfunctions. Steering malfunctions pose a threat to traffic safety and make driving difficult. The main signs of steering malfunctions are increased free play of the steering wheel, tight rotation or jamming in the steering mechanism, knocking and leakage, insufficient or uneven reinforcement, etc.
Increased free play of the steering wheel appears when the steering rod joints are worn out, the adjustment of the worm and roller is not correct, the worm bearings are worn out, the steering gear housing is loosened, and the clearances in the bearings of the front wheel hubs and king pins increase. These malfunctions are eliminated by performing adjustment work, replacing or repairing worn parts.
Stiff rotation or jamming in the steering mechanism is caused by improper adjustment of the steering gear gearbox, bent rods, or insufficient lubrication in the gearbox housing. These malfunctions are eliminated by adjusting, repairing rods, and replenishing oil in the steering gearbox to the required level. Leaks in the steering mechanism are eliminated by replacing gaskets and tightening fasteners and connections.
Insufficient or uneven gain in the power steering mechanism may be due to low tension in the pump drive belt, a decrease in the oil level in the tank, air entering the system, or a stuck spool or bypass valve due to contamination. After identifying the causes of malfunctions, they are eliminated by adjusting the tension of the drive belt, adding oil to a given level, flushing the system and changing the oil, repairing the pump, hydraulic booster or control valve. All work to determine the causes of steering malfunctions is carried out during diagnostics and maintenance, and troubleshooting is carried out during technical repair.
Steering diagnostics. It allows you to assess the condition of the steering mechanism and steering gear without disassembling its components; includes work to determine the free play of the steering wheel, the total friction force, and play in the steering rod joints.
The free play of the steering wheel and the friction force are determined using a universal device, model NIIAT K-402 (Fig. 29.1). The device consists of a playmeter and a two-scale dynamometer. The play meter consists of a scale 3 attached to the dynamometer and an indicator arrow 2, which is rigidly fixed to the steering column with clamps 7. The dynamometer is secured with clamps to the rim of the steering wheel. The dynamometer scales are located on the handles 5 and provide a reading of the force applied to the steering wheel in the ranges of up to 20 N and from 20 to 120 N.
Rice. 29.1.
When measuring the steering wheel play, a force of 10 N is applied through handle 5, first acting to the right and then to the left. Moving arrow 2 from the zero position to the left and right extreme positions will indicate the total wheel play. For vehicles with a transverse continuous rod, the left front wheel must be suspended at the time of measurement. For vehicles with hydraulic booster, the backlash is determined with the engine running (at low speeds).
The total friction force in the steering is checked with the front wheels fully suspended by applying force to the handles 5 of the dynamometer. Measurements are taken with the wheels in a straight position and in the positions of maximum rotation to the right and left. In a correctly adjusted steering mechanism, the steering wheel should turn freely from the middle position to move in a straight line with a force of 8-16 N. The condition of the steering rod joints is assessed visually or by touch at the moment of sudden application of force to the steering wheel. In this case, the play in the hinges will manifest itself as mutual relative movement of the connected parts.
Checking the power steering comes down to measuring (Fig. 29.2) the pressure in the power steering system. To do this, install Pressure Gauge 2 with valve 3 in the discharge line. Add oil to tank 1 to the required Level, start the engine at low speeds and, opening Valve 3 completely, turn the wheels to their extreme positions. In this case, the pressure developed by the pump must be at least 6 MPa. If the pressure is less than the specified value, slowly close the valve, observing the increase in pressure on the pressure gauge, which should rise to 6.5 MPa. If the pressure does not increase, this indicates a pump malfunction. The faulty pump is removed from the car and repaired.
Rice. 29.2.
Adjustment work on steering.
Steering mechanisms such as worm-roller, screw-nut, rack-gear sector have two adjustments: axial clearance in the bearings of the propeller shaft and in engagement. The condition of the steering mechanism is considered normal if the steering wheel play when driving in a straight line does not exceed 10°. If the play deviates in the direction of increase, it is necessary first of all to check the clearance in the bearings of the worm (screw shaft). To do this, turn the steering wheel sharply in both directions and use your finger to feel the axial movement of the wheel relative to the steering column. If there is a large gap in the bearings, the axial play will be easily felt.
To adjust and eliminate axial play in the shaft bearings, unscrew the bolts and remove the bottom cover 1 crankcase 2 steering gear (Fig. 29.3, A). One adjusting shim is removed from under the cover 3, after which the mechanism is assembled and the axial play is checked again. If the adjustment turns out to be insufficient, then all operations are repeated again until the desired result is obtained. After adjusting the tension in the bearings, check the force on the steering wheel rim by disconnecting the bipod from the steering linkage. The steering force should be 3 - 6 N.
Rice. 29.3. Adjusting the axial clearance (A) and engagement of the worm with the roller (b) in the steering mechanism.
Engaging the worm with the roller (Fig. 29.3, b) adjust without removing the steering gear from the vehicle. To adjust, unscrew the nut 3 and, removing the washer 2 from the pin, turn the adjusting screw with a special key 1 several notches in the lock washer. This changes the lateral clearance in the engagement of the roller ridges and the worm cutting, which changes the free play of the steering wheel. After adjustment, the nut is put in place.
Rice. 29.4. Examination (A) and adjustment (b) of play in the steering drive joints.
Play in the joints of the steering drive is determined by sharply shaking the steering wheel bipod when turning the steering wheel, wrapping your hands around the joint being tested (Fig. 29.4, a). In this case, the increased play is easily felt and, in order to eliminate it, tighten the threaded plug (Fig. 29.4, b) in the following order: first unscrew the plug, then use a special key to tighten the plug until it stops and, loosening it one slot until it coincides with the hole in the rod head , pinned.
When adjusting the axial play, add lubricant to the joints. In case of significant wear, if it is not possible to eliminate the play in this way, replace the ball pin of the joint or the entire rod assembly. Non-separable steering joints on passenger cars cannot be adjusted, so when they wear out and there is play, they are replaced.
Before checking the technical condition of the steering elements, you should prepare the diagnostic object:
- Place the vehicle on a horizontal, level area with an asphalt or cement concrete surface.
- Set the steered wheels to a position corresponding to straight-line movement.
- Move the gear lever (automatic transmission selector) to the neutral position. Place wheel chocks under the non-steerable wheels of the vehicle.
- Determine the presence or absence of power steering on the vehicle; if available, determine the pump drive method and the location of its main elements.
- Assess the compliance of all steering elements with the vehicle structure.
- Inspect the steering wheel for damage. If a steering wheel braid is used, the reliability of its fastening should be assessed.
- Assess the reliability of fastening the steering wheel to the steering column shaft by applying alternating non-standardized forces to its rim in the direction along the axis of the steering column.
- Inspect the steering column elements located in the vehicle cabin. Check the functionality of the column position adjustment device (if equipped) and the reliability of its fixation in the specified positions.
- Assess the reliability of the steering column fastening by applying alternating non-standardized forces to the steering wheel rim in the radial direction in two mutually perpendicular planes.
- Check the functionality of the device that prevents unauthorized use of the vehicle and affects the steering by removing the ignition key from the lock and locking the steering column.
- Assess the ease of rotation of the steering wheel over the entire range of rotation angles of the steered wheels, for which turn the steering wheel in the direction of travel and counterclockwise until it stops. When turning, pay attention to the ease of rotation without jerking or jamming, as well as the absence of extraneous noise and knocking. On vehicles with power steering, check with the engine running. After completing the check, return the steering wheel to the position corresponding to straight-line movement.
- On vehicles with hydraulic booster, determine the absence of spontaneous rotation of the steering wheel from the neutral position when the engine is running.
- Inspect the universal joints or elastic couplings of the steering column, assess the reliability of their fastening and make sure that there are no backlashes or wobbles in these connections not provided for by the design.
- Inspect the steering gear for damage and leakage of lubricating oil and working fluid (if the steering gear is an element of the power steering system). If possible, make sure that there is no play in the input and output shafts or their runout when turning the steering wheel. Assess the reliability of fastening the steering gear housing to the frame (body) by the presence of all fasteners and the absence of its mobility when the steering wheel is rotated in both directions.
- Inspect the steering gear parts for damage and deformation. Assess the reliability of fastening the parts to each other and to supporting surfaces. Check the presence of elements for fixing threaded connections. Fixation of threaded connections is carried out, as a rule, in three ways: using self-locking nuts, a cotter pin and safety wire.
A self-locking nut may have either a plastic insert or a deformed thread section to provide a tight fit around the screw threads.Rice. Methods for fixing steering threaded connections:
a - self-locking nut; b - cotter pin; c - wireIn the case of cotter pins, the nut has a series of slots in the radial direction, and the screw has a diametrical hole in the end of the thread. After tightening such a connection, the cotter pin is inserted into the hole and works to shear, preventing the nut from unscrewing.
The safety wire is usually used to secure screws that are screwed into blind holes. In this case, the screw head has diametrical drillings into which the wire is inserted. To fix it, it is twisted into a closed loop encircling some fixed element of the base and slightly stretched. The tension of the wire when turning the screw head prevents it from unscrewing spontaneously. - If you have a hydraulic booster system, check the level of working fluid in the pump reservoir with the engine running. This level is monitored using appropriate marks and must be within the limits specified by the manufacturer. Assess the condition of the working fluid by visual indicators of homogeneity, the absence of foreign impurities and foaming.
- If there is a belt drive for the power steering pump, inspect the drive belt for damage. Determine the belt tension by its deflection from the pressing force of the thumb in the place farthest from the points of contact of the belt with the pulleys. If necessary, measure the belt tension using a suitable device.
- Check for any movements of steering parts and assemblies not provided for by the design of the vehicle relative to each other or the supporting surface. In this case, the alternating movement of drive parts is set by rotating the steering wheel relative to the neutral position by 40.60° in each direction. The play in the hinges is determined by applying the back of the hand to the mating surfaces of the hinge. With significant play, in addition to the mutual movement of the hinge parts, the palm perceives a distinct knock that occurs when the mating parts reach their final position. Such knocking is not allowed. In the hinge, slight mutual movement of the mating parts may be observed, caused by the damping effect of the elastic elements. Such movement may be provided for by the design of the vehicle and is not a malfunction. In some cases, the elements of the steering rod joint act as a control element for the spool valve of the power steering system. Mutual movement in such a hinge is determined by the stroke of the spool valve in both directions. The specified stroke can be up to 3 mm.
- Inspect the devices that limit the maximum rotation of the steered wheels. These devices must be provided for by the design of the vehicle and be in working condition. Turn the steered wheels to maximum angles in both directions and make sure that the tires and wheel rims do not touch the body elements, chassis, pipelines and electrical harnesses in these positions.
- Inspect the elements of the power steering system for the absence of leakage of working fluid, which is not provided for by the design of the contact of the pipelines with the elements of the frame and chassis of the vehicle, and the reliability of fastening of the pipelines. Make sure that the flexible hoses of the power steering system do not have cracks or damage reaching their reinforcement layer.
Measure the total play in the steering using a play meter and compare the obtained values with the standard ones. Check a vehicle equipped with a hydraulic booster with the engine running. Before starting the check, make sure that the steered wheels are in a position corresponding to the straight direction of the vehicle's movement. The steering angle of the steering wheels is measured at a distance of at least 150 mm from the center of the wheel rim circumference. The extreme positions of the steering wheel when measuring the total play are considered to be the positions at which the steering wheels begin to turn. The steering wheel is turned to a position corresponding to the beginning of turning of the vehicle's steered wheels in one direction, and then to the other to a position corresponding to the beginning of turning of the steered wheels in the direction opposite to the position corresponding to straight-line motion. The beginning of rotation of the steered wheels should be recorded for each separately or only for one of them, the one farthest in relation to the steering column. In this case, the angle between the indicated extreme positions of the steering wheel is measured, which is the total play in the steering.
Checking the steering play
To check the angular free play of the steering wheel, it is necessary to rock the steering wheel while the engine is idling before the steering wheels begin to turn.
The test can be carried out using a spring dynamometer model K-402.
Free play should be checked by first setting the front wheels straight. The amount of free play of the steering wheel when the engine is running should not exceed 25°.
If the free play of the steering wheel is more than permissible, you need to check the air pressure in the tires, the presence of lubrication in the steering units and wheel hubs, the adjustment of the wheel bearings, steering rods and the correctness of their position, the normal adjustment of the steering mechanism, the clearances in the joints and splines of the propeller shaft, tightening the driveshaft mounting wedges, tightening the thrust bearing nuts in the steering mechanism, as all this affects the operation of the steering.
In addition, you should check the oil level in the power steering pump reservoir, the lack of air in the system, and oil leaks in the pipeline connections.
If the steering mechanism or rods are not adjusted correctly, the unit must be repaired.
If there are increased gaps of more than 2 ° in the cardan joints, the cardan shaft must be replaced. After making sure that the listed components are in satisfactory condition, you should check the tightness of the steering gear thrust bearing nuts.
Axial movement of the steering wheel is not permitted. If there is axial movement of the steering wheel, it is necessary to tighten the nut at the lower end of the shaft, having first straightened the antennae of the lock washer. After adjustment, bend one of the antennae into the groove of the nut. The rotation moment of the steering shaft, disconnected from the propeller shaft, should be 0.3-0.8 N*m.
Excessive tightening of the nut and then unscrewing it to obtain the specified shaft rotation torque is unacceptable, as it may cause damage to the bearing.
The operation of the steering mechanism can be checked without removing it from the vehicle with the steering linkage disconnected, by measuring the force in the following three positions using a spring dynamometer attached to the steering wheel rim.
First, the steering wheel is turned more than 2 turns from the middle position, the force on the steering wheel rim should be 5.5-13.5 N.
Second, the steering wheel is turned 3/4 -1 turn from the middle position, the force should not exceed 23 N.
The third steering wheel has passed the middle position, the force on the steering wheel rim should be 8.0-12.5 N greater than the force obtained when measured in the second position, but should not exceed 28 N.
If the force does not correspond to the specified values, then the steering mechanism must be adjusted.
When checking the torque of the steering wheel, it is recommended to simultaneously check the torque of the bipod shaft (with the longitudinal steering rod disconnected), which should not exceed 120 N*m.
When checking the torque of the bipod shaft on a car, you must perform the following operations:
- -start the engine and warm up the oil to approximately 50°C, stop the engine and set the steering wheel to the middle position;
- - hook the dynamometer in the center of the bipod ball pin hole and pull in any direction, maintaining the angle between the dynamometer and the bipod at approximately 90 °. The dynamometer should show no more than 510N, corresponding to a torque of 120 N*m.
If these indicators exceed the specified values, then you should adjust the force on the steering wheel rim in the third position by rotating the adjusting screw of the bipod shaft, since this does not require disassembling the steering mechanism. When you rotate the adjusting screw clockwise, the force will increase, and when you rotate it counterclockwise, it will decrease.
The discrepancy between the force on the wheel rim in the second position and the value indicated above can be caused by damage to the parts of the ball nut assembly, and in the first position, by the same reason and incorrect adjustment of the preload of the thrust ball bearings.
To adjust the thrust bearings (without removing the steering gear from the vehicle), you must do the following;
- - drain the oil from the power steering system;
- - disconnect the driveshaft;
- -unscrew the bolts securing the top cover and remove it. To avoid damaging the cuff and o-ring, use a safety mandrel placed on the end of the screw;
- - using a special wrench, unscrew the tail screw together with the control valve body by 10-15 mm so that the valve body rotates freely on thrust bearings without touching the intermediate cover;
- -check the axial movement of the tail rotor in the ball nut while holding the bipod.
If it exceeds 0.2 mm, disassemble the steering mechanism and replace the screw pair (the factory supplies a screw-nut kit as spare parts); if it does not exceed 0.2 mm, it is necessary to unlock the thrust bearing nut and tighten it so that the moment of rotation of the valve body relative to the tail rotor is 0.6-0.85 N*m.
You can measure the turning torque with a spring dynamometer, which is hooked onto one of the bolt holes of the control valve housing. In this case, a torque of 0.6-0.85 N*m corresponds to dynamometer readings of 11-15 N.
Checking the hydraulic booster pump on a car
On a car, checking the pressure developed by the pump and the serviceability of the steering mechanism is carried out by installing a device between the pump and the high-pressure hose, which includes a pressure gauge with a scale of up to 1500 mPa and a valve that shuts off the oil supply to the steering mechanism. To check you need to do the following:
- - open the valve in the device;
- - start the engine and at a crankshaft rotation speed of 1000 rpm, slowly close the valve (if the pump is working, the pressure should be at least 9.0 MPa);
- - open the valve;
- - turn the wheels to the right all the way and record the pressure on the pressure gauge, then turn the wheels to the left all the way and also record the pressure.
If the mechanism is working properly, in each of these checks the pressure should not decrease by more than 0.5 mPa compared to the pressure measured during the operation specified in paragraph 2.
The check must be carried out at an oil temperature in the pump reservoir of 65-75°C. If necessary, the oil can be heated by turning the wheels from lock to lock and holding them in their extreme positions for no more than 3 s.
When checking the pump, in order to avoid damage due to overheating, do not leave the valve in the closed position or the wheels turned all the way for more than 3 seconds.
