Maintenance of brake systems. Road and bench methods and parameters of car diagnostics Diagnosing brake system Equipment

19.10.2019

Repairs brake system It is necessary on all cars, however, it is necessary to diagnose the technical condition of the brake system every several thousand kilometers, it is necessary to reduce the likelihood of a car brake failure.

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Introduction ....................................................................................................

1.1. Principle of operation of the brake system ....................................
1.2. Types of brake systems ......................................................
1.3. The main elements of the brake system of the car ...................
2. Methods and equipment for diagnosing brake systems
2.1. The main malfunctions of the brake system ..............................
2.2. Requirements for brake systems ....................................... ...
2.3. Methods and equipment for diagnosing brake systems ......

3.1. Choice diagnostic equipment……………………………...
3.2. Technical characteristics of the selected equipment ............ ...
Conclusion …………………………………………………………….
…………………...

Introduction

The number of cars is becoming more and more, their number increases worldwide, every year. And with the number of cars, the number of accidents increases, due to which a larger number of people die and still remain disabled and cripples. Inappropriate technical condition And the operation of cars is one of the main causes of many accidents. Accidents arising from the failure of the various car systems carry the most serious consequences.

Relevance of the topic term paper It is that the most important system responsible for the safety of the car is the brake system. The designs of cars are constantly improving, but the presence of a brake system remains unchanged, which contributes to, if necessary, stop the car, which retains the lives of pedestrians, drivers and passengers, as well as other participants road. The repair of the brake system is necessary on all vehicles, however, it is necessary to diagnose the technical condition of the brake system every several thousand kilometers, this is necessary to reduce the likelihood of a car brake failure.

The goal of the course work - Improving the efficiency of diagnosing the car braking system, by developing recommendations on the selection of diagnostic equipment of brake systems and.

To do this, it is necessary to solve the followingtasks :

perform an analysis of the brake system of cars;
explore the methods of diagnosing the brake system;
examine the equipment used in the diagnosis of brake systems.

Object research is the technology of diagnosing a braking systeme We are cars.

Subject of study represents the means and methods of diagnosisabout streaming the brake system of the car.

Research methodsUsed in this work are methods of generalization, comparisons, analysis and analogies.

Structure of coursework consists of introduction, three chapters, sbut kesty and list of 10 sources used.

1. Brake system device

1.1. Principle of car brake system

It is easy to understand the example of the hydraulic system. When pressed on the brake pedal, the pressure force on the brake pedal is transmitted to the main brake cylinder (Fig. 1.1).

This node converts an effort that is applied to the brake pedal, into the pressure in the hydraulic brake system, to slow down and stop the car.

Fig. 1.1. The main cylinder device

Today, to increase the reliability of the brake system, two-section main cylinders are installed on all cars, which share the brake system into two contours. The two-section cylinder braking can ensure the performance of the brake system, even if one of the contours is deployed.

If there is a vacuum amplifier in the car, then the main brake cylinder is attached over the cylinder itself or is there in another place where the brake fluid is locatedwhich connects to the sections of the main brake cylinder through flexible tubes. The tank is necessary to control and replenish the brake fluid in the system, if necessary. On the walls of the tank is available to view the level of fluid. And also, a sensor is mounted in the tank, which follows the level of the brake fluid.

Fig. 1.2. Scheme of the main brake cylinder:

1 - rod of vacuum brake amplifier; 2 - retaining ring; 3 - byproof opening of the first circuit; 4 - compensatory opening of the first circuit; 5 - the first tank section; 6 - the second tank; 7 - bypasic opening of the second contour; 8 - compensation opening of the second circuit; 9 - Return spring of the second piston; 10 - the main cylinder case; 11 - cuff; 12 - second piston; 13 - cuff; 14 - Return spring of the first piston; 15 - cuff; 16 - external cuff; 17 - boot; 18 - first piston.

In the housing of the main brake cylinder there are 2 pistons with two return springs and with sealing rubber cuffs. Piston, with the help of brake fluid, create pressure in the working circuits of the system. Then, return springs return the piston to its original position.

Some cars are equipped with a sensor, on the main brake cylinder, which controls the pressure drop in the contours. If not a tightness occurs, it warns the driver in a timely manner.

About the work of the main brake cylinder:

1. When pressing the brake pedal, the rod of the vacuum amplifier leads to movement 1st piston (Fig. 1.3.)

Fig. 1.3. The work of the main brake cylinder

2. The compensation opening is closed, moving through the cylinder by the piston and the pressure is created, which acts on the 1st outline and moves the 2nd piston of the next circuit. Also moving forward the 2nd piston in its circuit closes the compensation hole and also creates pressure in the 2nd circuit system.

3. The pressure generated in the contours provides the operation of working brake cylinders. And the emptiness that was formed when the pistons movement is immediately filled with a brake fluid through special bypass holes, thereby preventing entering the system, unnecessary air.

4. At the end of braking, pistons due to the action of return springs, returned to its original position. At the same time, compensation holes receive messages with a tank and due to this pressure levels with atmospheric. And at this time, the wheels of the car are stamped.

The piston in the main brake cylinder, in turn, which begins to move and thereby increases the pressure in the system of hydraulic tubes leading to all the wheels of the car. Brake fluid under high pressure, on all wheels of the car, having an impact on the piston of the wheel brake mechanism.

And which, already in turn, moves the brake pads and those pressed against the brake disc or brake drum of the car. The rotation of the wheels is slow down and the car stops due to the friction force.

After we release the brake pedal, the return spring returns the brake pedal to its original position. The effort that acts on the piston in the main drum also weakens, then its piston, also returns to his place, forcing the brake pads with friction linings on them, thereby freeing the drum wheels or discs.

There is also a vacuum brake amplifier used in brake systems of cars. Its use, significantly facilitates all the operation of the brake system of the car.

1.2. Types of brake systems

The brake system is necessary for slowing the vehicle and the complete stop of the car, as well as its retention on the spot.

To do this, the car uses some brake system, as is the parking, working, auxiliary system and spare.

Working brake system Used constantly, at any speed, to slow down and stop the car. The working brake system is activated by pressing the brake pedal. It is the most effective system of all others.

Spare brake system Used when the main fault. It happens in the form of an autonomous system or its function performs part of a working working brake system.

Parking brake system Need to hold the car in one place. The parking system I use to avoid spontaneous movement of the car.

Auxiliary brake system Applied on a car with an increased mass. The auxiliary system is used to brake on the slopes and descents. It does not rarely, it happens that on cars the role of the auxiliary system is played by the engine, where the exhaust pipe overlaps the flap.

The brake system is the most important integral part of the car, serving to ensure active security Drivers and pedestrians. Many cars use various devices and systems that increase the efficiency of the system when braking is an anti-lock system (ABS ), emergency braking amplifier (Bas. ), brake amplifier.

1.3. The main elements of the car brake system

The brake system of the car consists of a brake drive and brake mechanism.

Fig.1.3. Brake hydraulic diagram:
1 - Contour Pipeline "Left Front-Right Rear Brake"; 2-signal device; 3 - Contour Pipeline "Right Front - Left Rear Brake"; 4 - the main cylinder tank; 5 is the main cylinder of hydraulic brakes; 6 - vacuum amplifier; 7 - brake pedal; 8 - pressure regulator rear brakes; 9 - cable parking brake; 10 - brake mechanism rear wheel; 11 - the adjusting tip of the parking brake; 12 - parking brake drive lever; 13 - Brake mechanism of the front wheel.

Brake mechanism The rotations of the vehicle wheels are blocked and, as a result, the brake force appears, which causes the car stop. Brake mechanisms are on the front and rear wheels car.

Simply put, all brake mechanisms can be called well. And already in turn, they can be separated by friction - drum and disc. The braking mechanism of the main system is mounted in the wheel, and the mechanism of the parking system is located behind a handout or transmission.

Brake mechanisms usually consist of two parts, from fixed and rotating. The fixed part is the brake pads, and the rotating part of the drum mechanism is the brake drum.

Drum brake mechanisms(Fig. 1.4.) Most often stand on the rear wheels of the car. During operation due to wear, the gap between the shoe and the drum increases and mechanical regulators use to eliminate it.

Fig. 1.4. Drum Brake Rear Wheel Mechanism:
1 - cup; 2 - clamping spring; 3 - drive lever; 4 - brake shoe; 5 - upper blast spring; 6 - spacer plank; 7 - adjusting wedge; 8 - wheel brake cylinder; 9 - brake shield; 10 - bolt; 11 - rod; 12 - eccentric; 13 - Purpose Spring; 14 - lower chamber spring; 15 - clamping spring space plank.

On cars can use various combinations of brake mechanisms:

two drum rear, two disk front;
four drums;
four disk.

In the brake disk mechanism(Fig. 1.5.) - The disk rotates, and inside the caliper is installed, two fixed blocks. In the caliper, workers cylinders are installed, when braking, they press brake pads to the disk, and the caliper itself is securely fixed on the bracket. To increase the heat removal from the working area, ventilated discs are often used.

Fig. 1.5. Disc brake diagram:
1 - wheel heap; 2 - guide finger; 3 - viewing hole; 4 - caliper; 5 - valve; 6 - work cylinder; 7 - brake hose; 8 - brake shoe; 9 - ventilation hole; 10 - brake disc; 11 - wheel hub; 12 - Miscoring cap.

2. Methods and equipment for the diagnosis of brake systems

2.1. Basic brake system malfunctions

The brake system requires itself close attention, because It is forbidden to operate a car, with a faulty brake system. This chapter discusses the main malfunctions of the brake system, their causes and ways to eliminate them.

Enlarged brake pedal work. It occurs due to lack, or leakage of brake fluid from working cylinders. It should be replaced by working cylinders, rinse the pads, discs, drums and add brake fluid if necessary. And also this contributes to the hit in the brake system, in this case, it is simply necessary to remove it by pumping the system.

Insufficient braking efficiency. Insufficient brake efficiency occurs during grinding or wear of the brake pads, it is also possible to join the pistons in working cylinders, overheating brake mechanisms, depressurization of one of the contours, the use of low-quality pads, violation in operationABS, etc.

Incomplete disbuilt wheels of the car.This problem occurs when the brake pedal does not have a free move, you just need to adjust the position of the pedal. The problem may also be in the most important cylinder, due to the encounter of the pistons. There may be increased protrusion of a vacuum amplifier rod, or rubber seals, just swelling, due to gasoline or oil, then in this case it is necessary to replace all rubber parts, as well as rinse and pump the entire hydraulic system.

Turning one of the wheels when the pedal is released.Most likely weakened the brass spring of the rear wheel pads, or due to corrosion, or simply contaminants - the piston in the wheel cylinder, then it is necessary to replace the working cylinder. It is also possible to disturb the position of the caliper relative to the front wheel brake disc, when weakening the fastening bolts. There may still be a violation in the workABS , swelling of the sealing rings of the wheel cylinder, incorrect adjustment of the parking system, etc.

Driva, or deviation from straight movement when braking.If the car, moving along a flat and dry road, during braking began to be rejected in any direction, then this can be promoting the piston of the main cylinder, clogging the tubes due to clogging, pollution or combustion of brake mechanisms, different pressure in wheels, and may not be It works one of the brake system circuits.

Increased effort on brake pedals when braking. If it is necessary to attach a lot of effort to stop the car, then the vacuum amplifier is most likely faulty, but also the hose is also damaged, which connects the engine inlet tube with a vacuum amplifier. And it is also possible to host the piston of the main cylinder, wear the pads and new blocks can still be installed, which simply have not worked.

Increased noise when braking. When the brake pads are worn, a squeaking sound occurs when braking, due to the friction of the wear indicator, sliding the disk. Also, the pads or the disk can be salted or contaminated.

2.2. Requirements for car brake systems

The brake system of the car, except for the general requirements for the design, has increased special requirements, because It ensures the safety of car traffic on the road. Therefore, the brake system in accordance with these requirements should provide:

minimum braking distances;
car stability during braking;
stability brake parameters with frequent braking;
quick triggering of the brake system;
proportionality of effort on the brake pedal and on the wheel wheels;
ease of control.

The brake systems of the car, there are requirements that are regulated by the UNECE Rules No. 13 applied in Russia:

Minimum brake path. Brake system on cars should be highly efficient. The number of accidents and accidents will be less if the maximum value of the deceleration is high and approximately equal to various cars and the type of car moving in the intensive stream.

And also brake routes of cars must be simultaneously close to each other, with a difference of about 15%. If the minimum brake path is reduced, not only high traffic safety will be ensured, but also an increase in the average velocity of the car.

The necessary conditions To obtain a minimum braking path, it is the smallest time required to trigger the vehicle braking car, as well as the braking of all wheels at the same time and the ability to bring brake forces to the maximum clutch value and ensure the desired distribution of the brake forces between the vehicle wheels in accordance with the load.

Brake stability. This requirement increases the efficiency of car braking on the road with small clutch coefficients (icy, slippery, etc.) and thereby increases the level of security of all participants in the roads.

In compliance with the proportionality between the brake forces and the loads on the rear and front wheels, the car braking with the maximum slowdown is ensured at any road conditions.

Stable braking. This requirement is associated with the heating of the braking mechanism during braking and possible impairment of their actions when heated. So, when heating between the brake drum (disk) and friction pads of the pads, the friction coefficient decreases. In addition, when heating brake linings, their wear is significantly increased.

The stability of the brake parameters at frequent braking of the vehicle is achieved with the coefficient of friction of the brake linings, equal to about 0.3-0.35, practically independent of the speed of sliding, heating and water from entering the water.

From the time of operation of the brake system of the car, the braking path will depend on that significantly affects the safety of motion. Mainly, the type of brake drive depends on the triggering system. Car S. hydraulic drive There will be 0.2-0.5, in vehicles with a pneumatic drive of 0.6-0.8 and in road trails with a pneumatic drive 1-2. When performing these requirements, a significant increase in car safety is ensured in various road conditions.

The brake pedal effort during car braking should be 500 - 700 H (minimum value for passenger cars) During the course of the pedal 80 - 180 mm.

2.3. Methods for diagnosing brake systems

To diagnose brake systems of cars, two main diagnostic methods are used - road and stand.

Road diagnostic method is designed to determine the length of the braking pass; steady slowdown; car stability in time of braking; brake system operation time; The slope of the road on which the car must still stand;
The stand test method is necessary for calculating the overall specific brake force; The coefficient of non-uniformity (relative unevenness) of the brake forces of the axis wheels.

To date, there are many different stands and appliances for measuring brake qualities by various methods and methods:

inertial platforms;
static power;
power roller stands;
inertial rolleries;
devices measuring the deceleration of the car during road testing.

Inertial platform stand. The principle of operation of this stand is based on the measurement of inertia forces (from rotationally and progressively moving masses) arising during the car braking and applied in the pairing places of the vehicle with dynamometer platforms.

Static power stands. These stands are roller and platform devices that are designed to turn the "breakdown" of the inverted wheel and the measurement of force applied at the same time. Statistical power stands have, pneumatic, hydraulic or mechanical drives. The brake force is measured when hanging the wheel or when it is supported on smooth running drums. This method has a lack of diagnosing brakes - is the inaccuracy of the results, as a result of which the conditions of the present dynamic braking process are not repeated.

Inertial roller stands. They have rollers that have a drive from the electric motor or from the car engine. In the second example, due to the rear (leading) wheels of the car, the rollers of the stand rotate, and from them with mechanical transmission - And the front (slave) wheels.

After the car is installed on an inertial stand, the linear velocity of the wheels is adjusted to 50-70 km / h and sharply slow down, at the same time separating all the bench carriages by turning off the electromagnetic couplings. At the same time, in the places of contact of the wheels with rollers (ribbons) of the stand arise inertia forces, opposing the brake forces. After some time, the rotation of the bench drums and wheels of the car stop. The ways passed by each car wheel during this time (or the angular slowdown of the drum) will be equivalent to brake paths and brake forces.

The braking path is determined by the frequency of rotation of the rollers of the stand, fixed by the meter, or by the duration of their rotation, measured by the stopwatch, and the slowdown is an angular desperometer.

Power roller stands Using the clutch forces of the wheel with a roller make it possible to measure braking force in the process of its rotation at a speed of 2.10 km / h. Rotation of wheels is carried out by the rollers of the stand from the electric motor. Brake forces are determined by the reactive moment that occurs on the stator motor gearbox of the stand when braking wheels.

Roller brake stands allow to obtain quite accurate results of checking brake systems. With each repetition of the test, they are able to create conditions (first of all the speed of rotation of the wheels), are absolutely identical with the previous ones, which is provided with an accurate job of the initial braking speed by external drive. In addition, when testing on power roller brake stands, a measurement of the so-called "ovality" is provided - an assessment of the non-uniformity of the brake forces in one turnover of the wheel, i.e. The entire braking surface is investigated.

When testing on roller brake stands, when the force is transmitted from the outside (from the brake bench), the physical pattern of braking is not violated. The brake system should absorb the incoming energy even though the car does not have kinetic energy.

There is another important condition - safety tests. The safest tests are on power roller brake stands, since the kinetic energy of the test car on the stand is zero. In case of failure of the brake system during road testing or on the platform brake stands, the probability of an emergency is very high.

It should be noted that by the totality of its properties, it is the power roller stands that are the most optimal solution for both diagnostic lines of maintenance stations and for diagnostic stations conducted by GOSTHAS.

Modern power roller stands for checking brake systems can define the following parameters:

According to the general parameters of the vehicle and the state of the brake system - the resistance to the rotation of the non-rotated wheels; non-uniformity of the brake force in one turnover of the wheel; Mass coming on the wheel; Mass coming on the axis.
On working and parking brake systems - the greatest brake force; brake system operation time; non-uniformity coefficient (relative unevenness) brake forces of axis wheels; Specific brake force; Effort on the control body.

Control data (Fig. 2.3.) Displays the display in the form of digital or graphic information. The diagnostic results can print and stored in the computer's memory in the database of diagnosed cars.

Fig. 2.3. Brake system monitoring data:

1 - indication of the inspected axis; Software front axle brake; ST - parking brake system; ZO - the rear axle brake

The results of checking the brake systems can also be displayed on the dashboard (Fig. 2.4.)

The dynamics of the braking process (Fig. 2.5.) Can be observed in graphical interpretation. The schedule shows the brake forces (vertically) relative to the effort on the brake pedal (horizontally). It reflects the dependence of the brake forces from the injection force on the brake pedal for both the left wheel (the upper curve) and the right (lower curve).

Fig. 2.4. Brake Stand Dashboard

Fig. 2.5. Graphic display of the dynamics of the braking process

With the help of graphic information, you can also observe the difference in the brake forces of the left and right wheels (Fig. 2.6.). The graph shows the ratio of the brake forces of the left and right wheels. The braking curve should not go beyond the boundaries of the regulatory corridor, which depend on the specific regulatory requirements. Observing the character of changing the schedule, the diagnostic operator can make a conclusion about the state of the brake system.

Fig. 2.6. The values \u200b\u200bof the brake forces of the left and right wheels

Recommendations for the choice of brake diagnostics equipment

3.1. Selection of diagnostic equipment

SPACE brake stands have a certificate of quality management system according to UNI EN ISO 9001-2000 confirms the use advanced technology, the use of modern coatings, high-quality materials and components, which makes it possible to export equipment in more than forty countries of the world.

Diagnosing the car braking system is carried out by rollers, which are divided into 3 types. Brake stands have a different design and engine power, but the main main feature is the maximum value of the brake force (Table 3.1).

Table 3.1

Roller aggregates for brake stands

Model	Max. Brake force
PFB 035.	5000 kg
PFB 040.	6000 kg
PFB 050.	7500 kg
PFB 715.	7500 kg (dual speed)

As well as one more important characteristic - This is a coefficient of friction between the wheel of the car and the rollers of the stand. In our case, we take a value equal to 0.7. To select the brake stand, we define the braking force.

Brake effort is the power of the car's wheel interaction with the outside of the roller (imitation of the movement of the car along the road). It is expressed in Dan.

1 Newton \u003d 0,101972 kg.

1 Dan \u003d 10 Newton \u003d 1.01 kg.

For the convenience of calculations, we take 1 dan \u003d 1 kg with 1% minor error.

μ \u003d f / m

Friction coefficient μ - Power ratioF to mass m.

This expression means the relationship between the mass of the car and the power required to move along the road.

If we have a lotM. interacting with the surface and 0.5 kg of powerF. For its movement, then the friction coefficient μ will be 0.5.

Upon this averaged value, the roller brake stand is chosen, for example, PFB 035 \u003d 500 DEN.

Motor power (and roller actuator) allows accurate measurements of force F Over 510.2 kg. To the tangent surface of the roller. After measuring this magnitude, the motor reduces the speed, and further measurements are not performed. For determining maximum massWe use the previous formula:

W \u003d f / μ

We get 500 kg / 0.7 \u003d 714 kg (a mass acting on one roller). It follows that the maximum weight on the axis is 1428 kg.

For the maximum theoretical mass value on the axis, we can choose the PFB 035 model. This choice is not accurate, because the friction coefficient is highly dependent on the characteristics of the tire (the poor tire has lower friction) and other conditions. For example, the maximum braking force does not measure the braking time of the previously damaged tire, in order to avoid its further wear. It also allows you to slightly increase the maximum axis weight. It should be noted that the weight of the axis is not just half the total weight of the car, since the unloaded car has a greater weight on the axis, but if you load the car, respectively, the axis load increases.

3.2. Specifications of selected equipment

The operating principle of SPACE line (Italy) is the consistent collection and software processing the results of measurements and visual inspection of the technical condition of the PBX using the instrumentation of equipment included in the packaging line of instrumental control. The testing procedure of the car is controlled by remote control or a keyboard, is processed and stored processor rendering test using the monitor, all the images 3D graphics, print the results to a printer interface for connecting:

stand of the station;
suspension tester;
gas analyzer;
chymometer;
tachometer.

List of measured parameters:

Rolling resistance;

Disks ovality or brake drum relative;

Maximum brake force on the wheel;

The difference between the brake efforts between the right and left wheels of one bridge;

The efficiency of braking working and parking brakes;

Effort on the foot brake pedal and on the hand brake lever

On the brake stand you can experience both cars with a drive for all 4WD wheels. The test procedure for full 4WD drive cars is divided into two separate phases for each bridge. In the first phase, the left roller aggregate begins to rotate along the movement, and the right - in the opposite direction. At the same time B. dispensing box The transfer to the second axis is discharged, and, therefore, the moment of rotation is not transmitted to the wheels that are not standing on the rollers. The results will be shown after testing both axes. At the end of the measurements of the brake efforts on each bridge, you can see the brake effort schedule.

Fig. 3.2. Testing procedure is full of drive cars.

Once entered into the computer memory all data and car off the roller unit and the monitor displays a page with the final results of the tests of the entire brake system (Fig. 3.2.).

Technical characteristics of standsPFB 035, PFB 040 and PFB 050 are shown in Table 3.2

Table 3.2.

Specifications

Specifications	PFB 035.	PFB 040.	PFB 050.
Load on the axis when testing / during transit, kg	2500/4000	2500/4000	2500/4000
Maximum brake forceN.	5000	6000	7500
Accuracy,%
Speed \u200b\u200bwhen testing
Power engines, kW		2x4.7	2x5.5.
Diameter of drums, mm
Clutch coefficient	More than 0.7.	More than 0.7.	More than 0.7.
Nutrition, V.	380 / 3F.	380 / 3F.	380 / 3F.

Comparison of price profitability, repair and duration of performance are shown in Figure 3.3

Fig. 3.3. Comparative stand chart (in percentage ratio).

Conclusion

The modern car works in a wide variety of road and climatic conditions. Long operation inevitably leads to the deterioration of its technical condition. The performance of the car or its aggregates is determined by their ability to perform the specified functions without violating the established parameters. The performance of the car depends primarily on its reliability, which is understood by the ability of the car to safely transport goods or passengers when complying with certain operational parameters.

When writing work, special literature was studied, including articles and textbooks, theoretical aspects are described and the key concepts of research are disclosed.

During the writing course, the brake system was studied. Methods and methods for restoring the performance of the brakes were considered. And in conclusion on the basis of the studied material, recommendations were developed to select the SPASE diagnostic equipment, from three roller stands PFB 035, PFB 040 and PFB 050. During the study of technical specifications, price category, costs for repair and service life, it was decided to select the first PFB 035 unit, as it is a more optimal option for the price category, and technical characteristics Not much inferior to the rest of the stands, as well as on the cost of repair and service life, which is given in Figure 3.3, is more profitable.

List of sources used

1. GOST R 51709-2001. Motor vehicles. Safety requirements for technical condition and verification methods. - M.: Starotinform, 2010. - 42 p.

2. Derevko V.A. Brake systems of passenger cars - M.: Petit, 2001. - 248 p.

3. Diagnosing cars. Workshop: studies. Manual // Ed. A.N. Kartashevich. - Minsk: new knowledge; M.: Infra-M, 2011. - 208 p.

4. Roller brake stands for passenger cars:Space. [electronic resource].URL: http: // www. Alpoka. RU / CATALOGUE / STR 1__13__ ITEMID __73. HTML.

5. Diagnostic and control tools vehicle [electronic resource]. URL: http://ktc256.ts6.ru/index.html.

6. Maintenance and repair of cars: Mechanization and environmental safety of production processes // V.I. Sarbaev, S.S. Selivanov, V.N. Konoplev - Rostov: Phoenix, 2004. - 448 p.

7. Maintenance and repair of cars: a textbook for the stud. // V. M. Vlasov, S. V. Zhankaziev, S. M. Kruglov et al. - M.: Publishing Center Academy, 2003. - 480 p.

8. Technological processes of diagnosing, maintenance and repair of cars: studies. Manual // V.P. Ovchinnikov, R.V. Needin, M.Yu. Bazhenov - Vladimir: Publishing House Vladim. State University, 2007. - 284 p.

9. Technological processes of maintenance, repair and diagnostics of cars: studies. Manual for studies Higher. studies. institutions // V.G. PERSIONS, V.V. Mishoustin. - Novocherkassk: Yurgu (NPI), 2013. - 226 p.

10. Harazov A.M. Diagnostic Support for Maintenance and Car Repair: Ref. Manual - M.: Higher. Shk., 1990. - 208 p.

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1. Brake system malfunctions

2. General diagnosis of brake systems

3. Types of stands and methods of testing brake systems

4. Principal device for power roller stands for diagnosing brake systems

5. Principle of operation of power roller stands

6. Metters of efficiency of brake systems of cars by the road method

7. Enemy diagnostics and adjustment work on the brake system

8. Replacement of brake fluid

9. Features of maintenance of the brake system with a pneumatic receipt

Bibliography

1. Brake system malfunctions

According to the statistics of traffic accidents caused by malfunctions in the brake system of cars, up 40 ... 45% of the total number of accidents that occur due to technical reasons. We present the main malfunctions of the brake system that appear during the operation of the car under the action of wear, aging and other factors.

Insufficient braking efficiency may be caused by a decrease in the friction coefficient between brake pads and drums due to wear or grinding of friction linings, increase the gap between them.

Non-chronic braking of all wheels can lead to a car drift, the reasons for this: unequal gaps between friction linings and brake drums, lubrication of lining, wear of wheel brake cylinders or pistons (hydraulic drive), stretching the brake diaphragms (pneumatic actuator), uneven wear of brake or friction linings.

The peeing the brake mechanisms occurs when the brake pads of the brake pads are cut, strongly contaminated the brake drums or brake drive rollers, breaking the brake linings rivets and jamming them between the shoe and the drum (disk). In vehicles with hydraulic galling occurs when jamming of the pistons in the wheel brake cylinders or blockage compensating opening of the main brake cylinder.

The driving of the brake pedal when braking in vehicles with hydraulic equipment occurs due to air in the brake system.

Vehicles with braking pedal is released is due to a loose fit of the intake valve of the brake valve control, lack of clearance between the pusher and the piston (hydraulic drive).

Weak pressure in the system and air leakage (pneumatic) are due to slippage of the belt of the compressor, air leaks in compounds and pipelines of the highway, laundrances of the adjustment of the valves to the clips of the compressor.

2. General diagnosis of brake systems

General diagnosis of brake systems in ATO, auto-service organizations (OA) or control when passing a state technical inspection includes:

Measuring control vehicle braking performance (TC) of the working and parking brake, and vehicle stability during braking braking system;

Sensory and, if necessary, the measuring tightness control pneumatic or pneumatic portion of fluid and the brake actuator elements wheel brake mechanisms.

The braking efficiency of the vehicle is measured using a roller brake stand to test the brake systems or the road method, if due to its dimensional or structural characteristics of the vehicle can not undergo control of these indicators on the stand.

3. Types of stands and metreatment Testing Brake Systems

There are several types of stands, using a variety of techniques and methods for measuring the inhibitory qualities: static power, the inertial platform and 12 roller, power roller, as well as instruments to measure the deceleration of the vehicle during a road test.

Static power stands They are roller or platform devices designed to turn the "breakdown" of the inverted wheel and the measurement of force applied at the same time. Such stands may have a hydraulic, pneumatic or mechanical drive. The measurement of the brake force is possible when the wheel is elected or when it is supported on smooth running drums. The disadvantage of the static method of diagnosing the brakes is the inaccuracy of the results, as a result of which the conditions for the real dynamic braking process are not reproduced.

Principle of operation of an inertial platform stand It is based on measuring inertia forces (from progressively and rotationally moving masses) arising when braking the car and attached in the contact places of wheels with dynamometer platforms. Such stands are sometimes used on ATP for input control of brake systems or express diagnostics of vehicles.

Inertial roller stands Consist of rollers that have a drive from the electric motor or from the engine of the car, when the driving wheels of the vehicle drive the rollers of the stand, and from them using a mechanical transmission - and front (slave) wheels.

After installing the vehicle on the stand, the circumferential speed of the wheels is adjusted to 50 ... 70 km / h and sharply slow down, at the same time separating all carriages of the stand by turning off the electromagnetic couplings. At the same time, in the places of contact of the wheels with rollers (ribbons) of the stand arise inertia forces, opposing the brake forces. After a while, the rotation of the bench drums and wheels of the car stops. The ways passed by each car wheel during this time (or the angular slowdown of the drum) will be equivalent to brake paths and brake forces.

The braking path is determined by the frequency of rotation of the rollers of the stand, fixed by the counter, or by the duration of their rotation, measured by the stopwatch, and slow down - the angular desperometer.

The method implemented by an inertial roller bench creates the conditions of car braking, as close as possible to real. However, due to the high cost of the stand, the lack of security, the complexity and high cost of time required for diagnosis, stands this type of irrational use in conducting diagnosis on ATP.

Power roller stands In which the clutch forces are used with a roller, allow measurement of brake forces during its rotation at a speed of 2 ... 10 km / h. Such speed is selected because at a speed of 13 tests, more than 10 km / h significantly increases the amount of information about the performance of the brake system. The brake force of each wheel is measured by braking it. Rotation of wheels is carried out by the rollers of the stand from the electric motor. Brake powers are determined by the reactive moment that occurs on the stator of the motor gearbox when braking the wheels.

Power roller stands allow to obtain quite accurate results of checking brake systems. With each re-test, they are able to create conditions (first of all the speed of rotation of the wheels), are absolutely identical with the previous ones, which is provided with an accurate job of the initial braking rate by external drive. Additionally, when tested on the power roller stands is measured so called roundness - evaluation of uneven brake force per wheel revolution, i.e., The entire braking surface is investigated.

When testing on power roller stands, when the force is transmitted from the outside, i.e. From the brake stand, the physical pattern of braking is not broken. The brake system should absorb the incoming energy, even though the car does not move (its kinetic energy is zero).

There is another important test condition - safety. The most secure - tests on strength roller stands, since the kinetic energy of the test car on the stand is zero. It should be noted that by the aggregate of its properties, it is the power roller stands that are the most optimal solution for both ATP and diagnostic stations conducted by GOSTHAS.

Modern power roller stands To check brake systems, a number of parameters can be determined:

General parameters of the vehicle and the state of the brake system: resistance to the rotation of non-optical wheels; non-uniformity of the brake force in one turnover of the wheel; Mass coming on the wheel; Mass coming on the axis; the power of resistance to the rotation of the non-rotated wheels;

The parameters of the working brake system: the greatest brake force; brake system operation time; non-uniformity coefficient (relative unevenness) brake forces of axis wheels; Specific brake force; effort on the management body;

Parking brake parameters: the greatest brake force; Specific brake force; Effort on the control body.

Information on the results of the control is displayed on the display in digital or graphic form or on the instrument rack (in the case of the application of the arrow output of the information). The diagnostic results may also be displayed on the print and stored in the computer's memory as a database of diagnosed cars.

4. Principal device of power roller stands for dibrake Systems Agnostation

The main components of such stands are usually: two interconnected set of rollers placed in a supporting and perceiving device, respectively, for the left and right sides of the car; power cabinet; rack; remote control; Silic meter pressure on the brake pedal. The vehicle is installed on the test bench so that the wheels of the inspected axis are located on the rollers.

(Persistently perceiving device (Figure 1) is intended for placing the support rollers and the forced rotation of the wheels of the diagnosed axis of the car, as well as for the formation (using the brake force sensors and the mass) of the electrical signals, proportional to the braking force and part of the mass of the vehicle coming to each Wheel diagnosed axis.

Figure 1. The scheme of the reference device: 1, 5, 7, 10 - rollers; 2.9 - gear motors; 3.8 - strain gauges; 4, 11 - tracking rollers; 6 - frame; 12 - Mass sensors.

The reference-perceive device consists of a box 6 of a box cross section, in which two pairs of support rollers (5, 7 and 1, 10) are located on spherical self-aligning bearings (5, 7 and 1, 10) interconnected by a drive chain.

Rollers 1 and 5 are connected via deaf clutches with coaxial gearboxes 2 and 9. Each pair of rollers has an autonomous drive from an electric motor connected to it 4 ... 13 kW. Electrical engine The gearbox leads rollers in motion and maintains a constant speed of rotation. Drive engines for rollers sets can be activated using remote control, thanks to which the measurement commands can be supplied from the car, or using an integrated automatic two-position switch.

As a rule, there are planetary gearboxes in the brake stands having high gear ratios (32 ... 34), which makes it possible to obtain a small speed of rotation of the rollers. The AC motor leads in motion the leading roller by means of a toothed transmission. The rear ends of the gearboxes are installed in spherical bearings, while the motor gearboxes are balanced suspended. Corps motor gearboxes Tensometric sensors 3 and 8 are associated.

Between the supporting rollers are installed freely rotating spring-loaded tracks 4 and 11, having two sensors: a sensor for the presence of a car on the support rollers, which, when lowering the tracking roller, gives the corresponding signal; Wheel rotation tracking sensor, outstanding the corresponding signals when the wheels are rotated for the diagnosed TC

Currently, some manufacturers, such as Cartec, are not installed in their stands of the tracking rollers. Such benches are equipped with sensors that provide contactless determination of the presence of the car on the rollers of the stand. Sensors determine the presence of a car on the stand and with the correct position of the vehicle on the rollers of the stand (in the longitudinal and transverse directions) give a signal to start drive engines.

On the frame 6 at the bottom under the supporting rollers there are four mass sensors 12, having the stops at the ends to set and fix the support device in the foundation pit (or on the frame).

The frame of the support-perceive device is placed on rubber lining to pay off vibration. The surfaces of the rollers of power stands are made by corrugated with steel welcox, providing a constant 16 clutch coefficient as the rollers wear - or are covered with basalt, concrete and other materials providing good grip tires For a better clutch of rollers with wheels, both rollers are made by lead, and the distance between them is to make it impossible to make a car from the braking stand. Carry out a car from the stand after checking the brakes of the drive axis is provided by the reactive torque of gearboxes or lifts located between the rollers. Sometimes for this purpose, one of the rollers (from the departure side) provide a device that allows you to rotate only one way.

Brake stands are equipped with special devices that prevent start of roller aggregates in the case when one or both wheels are blocked. Thus, the car and tires are protected from damage by the rollers. Run is also blocked in the case of pressing the brake pedal ahead of time, too high resistance to the rotation of the rollers of one or both wheels, clamping the brake pads, etc.

5. Principle of operation of power roller stands

At the entrance of the car on the brake stand, the mass of the axis is measured if there is a weighing device; With its absence, the mass of the axis can be administered from another stand, for example, a stand for checking the shock absorbers. When the car is installed on the test bench, then the tracking rollers 4 pressed and transmit a stand signal on bringing the stand into action; Both tracking rollers should be pressed to turn on the stand. In the future, the tracking rollers are used to determine the tire slipping relative to running rollers and give a signal to disable drive motor gearboxes when slipping.

The principle of the stands of the stands is based on the transformation of strain-spector sensors of the reactive moments of the brake forces arising from the braking of the vehicle wheels, as well as the gravity of the axis of the car acting on the roller aggregates into the analog electrical signals. The braked wheel is driven by rollers. During braking, depending on the magnitude of the brake force on a balancingly suspended motor gearbox, a jet occurs. The motor of the gearbox is rotated at an angle proportional to the braking force. The reactive moment that occurs during the rotation of the gear motor is perceived by the strain gauge sensors 3 and 8 (see Figure 1), one end of which is fixed on the paws of motor gearboxes 2 and 9, and the second on the frame 6.

The speed of rotation of the brake bend rollers is compared at the speed of rotation of the tracking rollers. The difference of speeds of rotation of the tracking rollers and the brake stand rollers determines the magnitude of the slippage. With such a slippage of the stands automatically turn off the drive of the braking rollers 17 stand, which protects the tires from damage. Usually, when checking, it is hampered until at least one of the tracking rollers will notice the exceeding the normative values \u200b\u200bof the slippage and will not turn off the drive engines. When one wheel is reached by one wheel of the installed slipping boundary, both support rollers are disconnected. The maximum measured value is written as the maximum brake force.

Checking the brake pedal effort allows you to determine not only normalized values, but also the performance of the vacuum amplifier of the brake system, and compare the operating modes of wheel braking mechanisms.

Signals from strain resistor sensors come to the computer, where they are automatically processed by a special program. According to the results of measurements of the brake forces and the mass of the car, the axial and total specific brake forces and non-uniformity of the brake forces are calculated. Measurement results and calculated values \u200b\u200bare presented in graphic and digital form on the monitor, then the print device prints the measurement protocol.

Consider the technological sequence of measurement of parameters on the power roller brake stands on the example of a passenger car. 1. The car is installed on the stand to diagnose brake systems (Figure 2).

Figure 2. Car position on the brake stand: 1 - diagnosed car; 2 - dashboard; 3 - booth rollers; 4 - Measurement sensor Pressing brake pedal.

Before checking the technical condition of the TC brake systems on the brake stand, it is necessary:

Check the air pressure in TC tires and, if necessary, bring it to normal;

Check the TC bus in the absence of damage and degradation of the tread, which can lead to the destruction of the tire when braking on the stand;

Inspect the wheels of the vehicle and make sure the reliability of their attachment, as well as the absence of foreign objects between the dual wheels;

Assess the degree of heating the elements of the brake mechanisms of the test axis by the organoleptic method (the temperature of the elements of the brake mechanisms should not be higher than 100 ° C). The optimal for the inspection can be considered conditions under which the heating of brake drums (disks) allows you to keep a person's unprotected hand in direct contact with this item for a long time (it follows such an assessment, observing precautions to avoid burns);

Install on the brake pedal, the device (Pressing force sensor) to control the parameters of the brake systems when the specified force actuate is reached;

Carrying out wet wheels to remove moisture from brake mechanisms, it is carried out by repeatedly pressing the brake pedal.

2. Includes booth electric motors and measure brake force (without pressing the brake pedal) caused by the resistance to the rolling of the wheels. This magnitude is proportional to the vertical load on the wheel and for passenger cars is usually 49 ... 196 N.

If the resistance force of the wheel is greater than 294 ... 392 N, this means that the wheel is inhibited, so it should be found out the possible reason for this (the small gap between the brake pads and the drum (disk), jamming the pistons in the working cylinders, the abnormal tightening of the wheel hub bearings etc.).

3. Smoothly press on the brake pedal with an effort no more than 392 N and remove the testimony (the permissible difference of brake forces for the wheels of one axis should not exceed 50%).

4. Smoothly press the brake pedal so as to create 490 ... 784 N on each wheel, and maintain it constant for 30 ... 40 s. Brake Diagnostics Malfunction Roller

If the difference in the testimony of the brake forces is very big, it means that moisture got into the brake mechanisms. This can usually be observed when checking cars entered on the stand after washing. In the event that the difference between the two testimony is preserved and after heating the brakes, this is explained by one of the following reasons: the surface of the brake pads underwent crystallization and severe grinding and has a low coefficient of friction, which can be confirmed when performing the entire test cycle, if the brake force is small increases despite the presence of significant efforts on the brake pedal; The pistons of work cylinders are fully bred in the initial position, this is confirmed by the fact that 19 Increasing the efforts on brake pedals do not cause the brake force on the wheel.

To clarify the possible malfunction, it is necessary to inspect the brake mechanism of the wheel. If in the process of testing the brake forces of one or two wheels rhythmically fluctuate (the amplitude of oscillations of 196 ... 392 H) with a constant force of pressing the brake pedal (147 ... 196 H), this indicates the issues of ellipseality or intimacy of the drums and Wheels, deformation of disks, incorrect tire profile. It is conventionally assumed that ellipsence or inconception is approximately 0.1 mm for every 98 H oscillations of the brake force.

5. When the brake pedal is released, the measuring arrows (numbers) are returned to minimal values \u200b\u200bcreated by rolling resistance. The speed and uniformity of the return arrows (digits) estimate simultaneousness and quality of wheels.

6. Increase the force of pressing the brake pedal to 49 H, the brake force is recorded until the wheel blocking is reached. During these tests, the uniformity of the brakes is evaluated.

If there is a minor increase in the brake forces of both wheels (for example, with an effort on the pedal 98 H, the brake force on wheels is 833 N, and with an increase in force to 196 H, it increases to 1176 N instead of 1568 ... 1666 N), then it means that the type of friction linings applied on the car or is unsuitable due to excessively high hardness or their surface crystallized or grilled during operation.

If there is a rapid increase in the brake forces (for example, with an effort on the pedal 98 H, the brake force on wheels is 833 N, and with an increase in force to 196 H, it increases to almost 1960 N), then the brakes have a tendency to self-blocking. This is especially dangerous when braking on a wet road. Increased tendency to self-blocking can be caused by the use of friction linings from too soft materials.

In drum brakes, a similar phenomenon may occur if the pads are incorrectly adjusted. In addition, cars having a brake amplifier, the tendency to block the wheels can be caused by incorrect operation of the amplifier.

Brake forces that are created on wheels at the time of their blocking are crucial to evaluate the performance of brakes. However, it should be borne in mind that the magnitude of the brake force at which the wheels are blocked is determined by factors, many of which do not depend on the technical condition of the vehicle braking system, for example, 20 weighing per wheel, tires, wear and tread pattern .

7. Similar to checking the brakes of the front wheels, checking the brakes of the rear wheels.

8. Summing up the brake forces on each wheel, determine the specific brake force, which should be at least 50% of the total vehicle. In this case, the specific brake force is checked separately for the front and rear axles.

To check the manual (parking) brakes, it is necessary to gradually move the parking brake lever before blocking the wheels. This operation should be carried out especially carefully, since at the time of blocking the wheels, the car that is not retained by the non-optical front wheels can move from the bench to the jerk back, so during tests at a distance of 2 m from the car there should be no people.

By moving the manual brake lever, count the number of snore mechanism clicks in order to check the correctness of the drive adjustment. Simultaneously check the efficiency of braking and the uniformity of the drive. Technically, a serviceable manual brake should provide brake forces on both wheels, the sum of which should not be less than 16% of the total mass of the car.

In the same sequence, measurements of the parameters of the brake systems with a pneumatic receipt are made. In the pneumatic system, the pressure sensor is installed. To do this, it is necessary to remove the plug from the valve of the control output of the supply circuit of the pneumatic brake system and screw the pressure sensor in its place.

The dynamics of the braking process can be observed in graphical interpretation. In Figure 3, and the dependence of the brake force changes (vertically) from the thread of the brake pedal (horizontally) for the left (upper curve) and for the right wheel (lower curve) are shown.

Figure 3, B shows a change in the difference in the brake forces (vertically) when braking the left and right wheels. It can be seen that the braking curve goes beyond the boundaries of the stability corridor, and this is unacceptable and testifies to unstable braking.

Watching a change in the schedule, the diagnostic operator can make a conclusion about a particular brake system malfunction, for example, by the difference in braking forces, or by the character of the change of the waveform.

Figure 3. Graphic display of the dynamics of the braking process: a - change of brake forces depending on the effort of pressing the brake pedal; b - the difference in the difference of the brake forces of the left and right wheels; 1 - width of the stability corridor.

6. Brake System Efficiency Measuresvehicle road method

The effectiveness of the brake system of the car can be checked with the help of special meters - desperometers or desktop. Such meters are used in the absence of brake stands and in field conditions or if it is impossible to check the vehicle (for example, motorcycles) on the stand.

When using a TC deslerometer in a circular state, they accelerate and dramatically slow down to a one-time foot brake pedal. The principle of the desserometer is to fix the path of moving the moving inertial mass of the device relative to its body, fixed by car. This movement occurs under the action of inertia strength during the braking of the car proportional to its slowdown. Translationally moving load, pendulum, liquid, or acceleration sensor, and a meter - a switch, a scale, a signal lamp, a self-inspector, a composter, etc. To ensure stability, the dessemerometer is equipped with a damper (liquid, air, spring), and for Ease of measurements - a mechanism that locks the maximum slowdown.

The most widely distributed meter of the efficiency of the braking systems of the "Effect" (Figure 4).

Figure 4. General view of the efficiency meter of the effect of brake systems "Effect" (Russia): 1 - socket for connecting the printer (computer); 2 - power cable connector; 3 - Effort sensor cable connector; 4 - dashboard; 5 - suction cup; 6 - "Cancel" button; 7 - "Select" button; 8 - clamp; 9 - indicator; 10 - clamp pen; 11 - Power button "On"; 12 - "Enter" button; 13 - Effort sensor; 14 - printer cable connector; 15 - connector for connecting to the cigarette lighter socket; 16 - printer power button; 17 - printer.

The device determines the installed slowdown, the peak value of the force of pressing the pedal, the length of the braking path, the response time of the brake system, the initial braking speed and the linear deviation of the vehicle, and also produces recalculation of the brake path rate to the real initial braking rate.

To check the braking system efficiency, the device is attached on the glass of the right or left door of the car. The arrow of the arrow of the device must coincide with the direction of movement of the car being checked. A force sensor is installed on the brake pedal. The sensor cable is connected to the instrument block depending on the source used (car on-board network or rechargeable batteryincluded in the instrument). The device has the ability to print information using a special cable.

7. Elementary diagnostics and adjustmentbrake system work

Organoleptic control. Organoleptic control includes controlling the technical condition of the brake drive elements and the brake mechanisms of the wheels.

When monitoring the technical condition of the brake elements, the following checks are carried out:

Inspection for damage;

Estimate of the performance of a pneumatic brake drive;

Inspection of the correct functioning.

The elements of the TC brake drive are considered faulty in the case of:

The presence of a pipeline contact not provided for by the vehicle with elements of TCs and other defects;

The inability to hold the lever locking device (handle) of the parking brake system;

Non-working state of a pneumatic or pneumatic-hydraulic brake driving pressure gauge;

Disorders of the tightness of the hydraulic brake actuator (the presence of leakage of the brake fluid);

Unreliable fastening;

Response system of signaling and controlling the operation of brake systems in less than four cycles of complete actuation of the working brake system;

Swelling of the brake drive hoses under pressure, damage to the outer layer of hoses, reaching the layer of their reinforcement;

Non-working state of the system of signaling and controlling the operation of brake systems;

The presence of hotels or lateral displacement of the brake pedal;

An inoperable state of the function of automatic emergency braking of the trailer;

Lack of vestment provided by the construction or installation without coordination with the manufacturer or another authorized organization additional elements Brake drive.

When monitoring the technical condition of the elements of the brake mechanisms of the wheels, the following checks :

Inspection for damage (cracks, residual deformation and other defects);

Assessment of fastening reliability;

Inspection of ease of movement.

The elements of the brake mechanisms of the TC wheels are considered faulty in the case of:

The presence of contaminants impede checks;

The presence of residual deformation, cracks and other defects;

Jamming elements of the brake mechanism; - unreliable attachment;

The lack of a vesicle-provided vehicle or installation without coordination with the manufacturer or another authorized organization of additional elements of brake mechanisms.

With the elementary diagnosis of the car brake system, it is determined by: the free course of the brake pedal; gaps between friction linings and brake drums of wheels; pressure in the brake system; time of operation of the brake mechanisms; The size of the outlet of the rods from the brake chambers; The distance from the end of the pressure regulator lever to the body spar; The performance of the vacuum amplifier.

Free move of the pedal of the brake hydraulic wheels are determined using a special or conventional line. The end of the line is rest in the floor, and the middle part is installed opposite the pedal. Press your hand to the pedal to a noticeable increase in resistance from the pedal when it moves. On the scale of the line records the free move of the pedal.

Control of the free stroke of the brake drive pedal It is recommended to hold on a new car through 2 ... 3 thousand km, and in the future every 20 thousand km. In most brands of passenger cars, with a good braking system, the magnitude of the free move the drive pedal is within 3 ... 6 mm. If free running does not match the norm, the adjustment is made by changing the length of the pusher.

For trucks and buses, the full and free move of the brake pedal can be checked and regulated.

The performance of the vacuum amplifier The brake system is checked in the following sequence. Press the wheel brake pedal to approximately until the middle of its full move when the engine is not working, the engine is started and if the brake drive pedal moves downwards, then the vacuum amplifier is good.

When diagnosing the pressure regulator, the car is installed on a lift or inspection ditch. Carefully clean the knit controller and remove the protective case. Sharply click on the brake drive pedal. With a working pressure regulator, the protruding part of the piston will move relative to the housing.

To maintain the brake system in a working condition, periodically before departure, it is necessary to control the level of brake fluid in the tanks, perform adjustment operations.

At that every 10 thousand km, the mileage controls the level of the brake fluid in the tank (tanks), which, when the lid is installed, should reach the lower edge of the filling neck. Value should be liquid only the brand that was used before; Mixing liquids of different brands is unacceptable. If the tank is equipped with a fluid control sensor, then it is necessary to check the sensor operation: by pressing the pusher on the tank cover, observe the turning on the control lamp on the instrument panel. At the time of verification, the engine ignition system must be enabled.

Reducing the level of brake fluid in the tank indicates its possible leakage. Having found a leak, you should carefully examine the entire system and, if necessary, make a suspender of connections or replacing cylinder cylinder cylinders.

An increase in the free stroke of the pedal, its failure and the appearance from the second or third pitching of the feeling of elasticity from the sidden pedal indicate the presence of air in the brake system.

To remove air produce pumping the brake system as well as for the clutch drive. The order of pumping the brake system for each car is individual, but in the absence of specific recommendations, it may be as follows. For automobiles with front and rear contours, first pump the contour of the front wheels, and then the rear, starting in each contour from the wheel, the most remote from the main brake cylinder. For vehicles with diagonal contours, consistently pump out: left rear, right front, right rear and left front wheels.

8. Replacing the brake fluid

After 2 years of operation or every 45 thousand km, the mileage replaces the brake fluid. If the brake system is used with heavy load, for example, when driving through a hilly area or with high humidity, the brake fluid must be changed once a year. Gigroscopic brake fluid, i.e. It is capable of absorbing water molecules from the air. Absorption occurs through the brake hoses and the tank surface made according to rubber and plastics, which are permeable to air molecules. Increased water content in the brake fluid leads to a significant decrease in its boiling temperature, as well as corrosion of the elements of the brake system. As a result, damage to the brake system occurs, and its functioning is significantly worsening and in the hot season of year can lead to the formation of air traffic jams due to water evaporation.

In order to replace the brake fluid into the hydraulic drive system, the air does not fall, the following rules must be followed:

Adhere to the same procedure of action as when pumping the clutch, but use a hose with a glass tube at the end, which is lowered into a vessel with brake fluid;

Pressing the brake pedal, pump up the old brake fluid until the new brake fluid does not appear in the tube; After that, there are two full stroke of the brake pedal and holding it down, the fitting is cleaned; When pumping, they monitor the level of fluid in the tank and the liquid is rapped in a timely manner to the maximum level; repeat this operation on each working cylinder in the same order as when pumping;

Fill the tank to the maximum level and check the operation of the brakes when the car is moving.

For pumping hydraulic brake systems, special installations can be used.

The principle of operation of the installation (Figure 5) lies in the fact that with the help of an elastic inner membrane, it first separates the brake fluid from the air, thereby preventing their mixing and formation of a hazardous emulsion, and then under pressure in 20 MPa, it removes the old brake fluid, replacing it with a new one And removing the air from the system.

Figure 5. Appearance Installations for replacing the brake fluid.

Installation with a large set of adapters included in the basic bundle can replace the brake fluid both in passenger cars and in light trucks.

9. Maintenance features Tor.motor System with Pneumatic Driver

For the pneumatic acting brake systems of the construction of past years (ZIL, MAZ, KRAZ, KAMAZ), adjustment of the gap is produced by changing the position of the 28 expansion fist, which is achieved by rotating the worm of the adjustment lever. The need to adjust the gap is determined by the length of the brake chamber rod, which should not exceed 35 mm for the front and 40 mm for the rear brakes. The difference during brake chamber rods on one axis should not exceed 5 mm.

To check the rod run, you must click on the brake pedal until it stops, feeding compressed air into the brake chamber, and measure the stroke. If the stroke of the brake chamber is exceeding the normative values, then you need to adjust, turning the hexagon head of the adjusting lever shaper counterclockwise (Figure 6) counterclockwise (Figure 6).

Figure 6. Adjustment lever scheme: 1 - housing; 2 - pusher; 3 - movable half-guns; 4 - spring; 5 - plug; 6 - Worm worm; 7 - Sealing ring.

In modern cars and buses to maintain a constant gap between the friction pads of the pad and the disc brake mechanism, equipped with a device for automatically compensating for brake pads. However, the degree of wear of the brake linings and the brake disc should be periodically checked. The frequency of inspections depends on the intensity of the operation of the vehicle, but it should be carried out at least once every three months (if limiting wear sensors are not provided).

The total thickness of the new brake pad C (Figure 7) should be 30 mm, and its thickness of the base D is 9 mm. If the thickness of the friction overlay is at least in one place less than 2 mm, then the brake block is subject to replacement. An insignificant painting of friction material on the edges of the lining is allowed.

Figure 7. Permissible dimensions Disc and blocks of vehicles with a pneumatic drive of the brake system: A - the thickness of the brake disc; C - the total thickness of the new brake pad; D - the thickness of the base of the brake pad; E - the thickness of the brake lining; E is the minimum thickness of the brake pad, including the thickness of the base.

The thickness of the brake disk A is measured in the thinner; For a new disk it is 45 mm. The minimum thickness of the brake disc, at which it is subject to replacement is 37 mm. The minimum thickness of the brake pad, including the thickness of the base F, 11 mm; Upon reaching this magnitude, the brake block is replaced.

The brake disk flow seems appropriate only in exceptional cases - to increase the working surface of the friction lining in the process of work, for example, if there are numerous scratches on the working surface of the brake disc. The minimum disk thickness after the duct should be at least 39 mm.

When replacing the brake pads and, if necessary, a check of the mechanism of automatic clearance adjustment can be checked (Figure 8, a).

To do this, remove the wheel, shifted the movable bracket by its guides in the direction of the inside of the TC, press the inner brake block 5 from the stops.

Figure 8. Check (A) and adjustment (b) mechanism of automatic adjustment of disc brake mechanisms of vehicles with a pneumatic drive of the brake system: 1 - movable bracket; 2 - tongue-plug; 3 - adapter; 4 - regulator; 5 - brake shoe; 6 - probe; 7 - key.

The clearance is measured between the base of the brake pad and the stops (it must be within 0.6 ... 1.1 mm). The gap is greater or less specified may indicate a malfunction of the mechanism of automatic clearance adjustment, and its performance should be checked. To do this, from the regulator, a special tongue-plug is removed from the regulator 2. The key is put on the adapter 3 and, rotating the adapter counterclockwise, turn the regulator 4 for two or three clicks (towards zazon increases). Press the TC brake pedal 5-10 times (at a pressure of about 0.2 MPa). In this case, if the automatic adjustment mechanism is running, the wrench must turn slightly clockwise. With each next click on the pedal, the angle to which the key rotates will decrease.

If the key does not rotate at all, it turns only when the brake pedal is first pressed or rotated at each press on the pedal, but then returns back, the mechanism of automatic clearance adjustment is faulty and the mobile brake brake brake is replaced.

The pressure regulator in the compressor is adjusted to the beginning of the air supply by the compressor by rotating the cap of the pressure regulator, and the disconnection of the compressor from the system is made using gaskets (with an increase in the thickness of the gasket, the shutdown pressure decreases, and with a decrease - increases). Regulator's response pressure value: 0.6 MPa - switching on; 0.70 ... 0.74 MPa - shutdown.

The safety valve is adjusted with a screw fixed screw, pressure 0.90 ... 0.95 MPa

When servicing a pneumatic drive of the car brakes, first of all, it is necessary to monitor the tightness of the system as a whole and its individual elements. Special attention is paid to the tightness of the connections of pipelines and flexible hoses and at the places of hose attachment, since it is here that compressed air leaks occur. The places of severe air leakage can be determined by ear, and the places of weak leakage - with a soap emulsion.

Air leakage from pipelines connections are eliminated by a suspender with a certain point or replacement of individual connections. If the leakage is not eliminated after tightening, then you need to replace rubber sealing rings.

The tightness check should be carried out at rated pressure in the pneumatic reception of 60 MPa, the compressed air consumers included and the non-working compressor. The drop in the pressure from the nominal in air balloons should not exceed 0.03 MPa for 30 minutes with the free position of the drive controls and for 15 minutes with the included.

Care and maintenance of cameras with spring energy accumulators is a periodic inspection, cleaning from dirt, checking the tightness and operation of brake chambers, tightening fastening nuts to the bracket.

Checking spring-pneumatic brake chambers for tightness is carried out in the presence of compressed air in the drive circuit of the emergency or parking brake and in the rear trolley brake drive circuit.

The pneumatic brake actuator has a pressure regulator, combined with a compressed air adsorption dryer. For drying air used adsorbents (special granulated substances). The normal functioning of the desiccant is ensured when 50% of the time it works in air injection mode, and the remaining 50% of the time is regeneration, the process of purging the adsorbent with dry air from the regeneration receiver. Therefore, for the effective operation of the desiccant, it is necessary to monitor the tightness of the pneumatic actuator, not allowing leaks exceeding the established limits. The replacement of the filter element (cartridge) of the compressed air dryer is made as needed when the presence of condensate is found in the pneumatic system receivers. Depending on the operating conditions and the technical condition of the air acceptor devices, the replacement frequency can be from one to two years.

Bibliography

Lecture №5 "Diagnostation and that brake system" is presented in the 2nd part of the lectures on the discipline "Technical operation of cars" and developed for students of specialties 1-37 01 06 Technical operation of cars (in directions) and 1-37 01 07 Full-time car service and correspondence forms of training.

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Diagnostics of the brake system of the car

Due to the large responsibility of the brake system for the life of people and road safety, its adjustment should be carried out exclusively qualified specialists with extensive experience. In our car service, the diagnosis of the brake system is carried out by professional craftsmen using specialized equipment. High quality performance is confirmed by numerous positive reviews our clients. The efficiency of diagnosing and troubleshooting provides the ability to pick up your car on the day of service delivery. Each diagnostics of the brake system includes a large number of control operations recommended by car manufacturers. Find our workshop can not far from Altufyevo metro stations, Medvedkovo, Bibirevo (Moscow, Svao district).

Diagnostics of the brake system: What does the malfunction indicate?

Most often, the diagnosis of the car brake system is performed when:

outsided noises;
brakes are hot;
leaks of brake fluid (any intensity);
mild pedals;
failure of the brakes;
increase brake path.

These malfunctions can be caused by disruption of tightness, brake fluid deficiency, brake pad wear, undime replacement Brake fluid, pads.

If one of these signs is detected, the deviation from normal operation will require competent diagnostics of the braking system, including checking the tightness of all elements of the system, vacuum amplifier, the operation of the indicator devices, the tightness of the pneumatic actuator. For cars S. on-board computer The optimal option is to diagnose using a computer or car diagnostic scanner that can read errors from the controller block.

Brake System Fault Diagnostics

Today, the diagnosis of the operating parameters of the brake system can be verified using two main methods: bench and road. Diagnostics of brake system malfunctions Each of them includes the following tests and measurements:

the length of the brake path;
established vehicle slowing;
linear deviation;
the road slope at which the machine is held by PBX;
specific braking force;
the operation time of the brake system;
the coefficient of non-uniformity of the brake forces on the same axis.

At present, the road diagnostic method is practically not applied due to the lack of objectivity and influence external factors Impact. Diagnostics of brake system malfunctions on a specialized stand provides the most accurate measurements. Based on the data obtained, it will be possible to judge the status of the brake system and safety control of the test vehicle. The amount and quality of measurements is strictly regulated at the legislative level, therefore the test stand passes a periodic verification for compliance with the accuracy of measurements.

Brake System Diagnostics: Visual Examples

The diagnosis of the car braking system begins with the fixation of the car in the same position. If the stopping efficiency in one place does not match the required parameters, then you can judge the leakage of the brake fluid from the system.

If the brake pedal fails all the time, then the diagnosis of the brake system is likely to indicate the enforcement of the system. Removing air from the braking system, it will be necessary to restore until the initial level of the brake fluid level in the tank.

Often possible cause Deviations in normal operation of the brake system is the presence of oil on brake pads. At the same time, a characteristic creak is heard during braking machine. The diagnosis of the brake system will show the physical wear of the brake pads, after their replacement, the outsiders will disappear. If you do not execute this procedure in a timely manner, you can spoil the brake disc.

Too tight, the brake pedal move speaks of a breakdown of a vacuum amplifier or a violation of hermetic. Timely diagnostics of the brake system of the car will help to quickly determine the place of fault.

Spontaneous braking can be provoked by a violation of the position of the brake caliper or its breakdown. The diagnosis of the brake system is reduced to the survey of the work of the calipers and formulate the diagnosis of their health. Very often, the main cause of breakage is the disruption of the tightness of the connecting hoses of the system due to mechanical impacts.

Having a car in the direction when braking can talk about the presence of problems with brake caliper or brake pads. The diagnosis of the brake system will be to conduct a steering survey and the elements of the brake system on the wheels of the machine. In addition, there is a chance of uneven wear of the brake pads.

A strong noise in braking can be caused by the wear of the brake lining or strong corrosion of the brake disc. Sometimes the diagnosis of the brake system of the car with these symptoms indicates the presence of foreign objects between the brake shoe and the disk.

The presence of a large stroke of the brake pedal is most often due to the malfunction of the vacuum amplifier. In some cases, such signs are characteristic of the presence of air in the hydraulic brake system. The diagnosis of the brake system will help accurately establish the cause of the breakdown and prevent the further development of the accident.

Too "soft" braking pedal stroke is most likely caused by the depressurization of the hydraulic system or the main brake cylinder fault. The diagnosis of the brake system can also show the unsatisfactory state of the brake fluid.

A large resistance when you press the brake pedal is usually caused by a malfunction of a vacuum amplifier or damage to the hydraulic system contour. In addition, new brake pads can cause a similar phenomenon that did not have time to take. Diagnostics of the brake system of the car in this case will help determine the true cause of the malfunction.

Strong vibrations on the steering wheel and brake pedals indicate a strong wear of brake discs, weakening fastening brake calipers, wear brake linings. The high-quality diagnosis of the car braking system will ensure accurate detection and localization of the breakdown location.

Permanent slow motion can be caused by improper adjustment of the parking brake, vacuum amplifier or the main brake cylinder. To say exactly what the reason for this phenomenon is necessary, a professional diagnosis of the car braking system is necessary.

External influence factors

The operation of the brake system of the machine may vary depending on the impact of certain environmental factors:

Tires with different clutch coefficient with road web have absolutely different braking characteristics. At the same time, the following factors affect the clutch with the road: the pressure in the tires, the depth and ornament of the tread, the wheel width.

The degree of loading of the car greatly affects its braking path. The stronger the vehicle is loaded, the longer it will be its braking path.

Natural wear of rubber brake hoses leads to the effect of damping, which smooths the sharpness of the brakes and, accordingly, the degree of their effectiveness.

The violation of the corners of the collapse and convergence leads to the insulation of the car from the rectilinear direction of movement during braking.

Competent diagnosis of the car braking system necessarily takes into account all these factors of external influence.

One of the main security systems is the brake system. From its quality, it depends on the possibility of stopping in time if there are some obstacles to the way. It is important to contain brakes in a good and predictable state. To do this, they must be checked regularly.

The brake system is diagnosed on the stand or on road conditions. More accurate readings can be obtained on modern diagnostic stands. Works are carried out with any type of machines.

Under the concept of the stand, it is customary to mean fixtures placed in specialized premises, the main purpose of which is a multi-level check of the technical condition of the car. With stand diagnostics, such parameters are most often controlled:

data on the overall strength of braking;
the value of the relative unevenness coefficient;
the parameters of asynchronous work.

In industry, several different types of devices are used. Most of them operate on the principle of imitation of asphalt coating, where during the braking process the instruments record the required data.

Stand for the diagnosis of the brake system

Such stands may be in the form of detached equipment or be part of a large diagnostic complex.

Diagnostic need

Diagnostics and repair of the vehicle braking system is carried out both at the set interval, then for each model of the car and after identifying the proposed faults. The most frequent signs that the machine needs to be examined, these situations are:

an explicit increase in the brake path on dry and solid coating;
problems with the pedal of the brakes, in which either deep evinges, or the stroke;
visible departure from straight movement when pressed on the brake pedal;
vibration, hum, creaking in the brake area;
a constant decrease in fluid level, visible drums.

Brake system car

The indirect symptoms include uneven wear of the surface of the brake pads, visible mechanical damage to the hoses or brake tubes. Such information is seriously obtained without removing the wheels. So the driver must once at 30-40 thousand km independently examine the problem areas behind the wheel.

Procedure

During testing it is necessary to control the state of the system as a whole and separate nodes For performance. Before diagnosing the brake system on the stand, such sites are checked:

capacity with brake fluid;
condition of disks and drums;
brake pads;
stable operation of the hub bearing;
caliper;
operation of worker cylinders;
operation of the amplifier and the main brake cylinder;
the state of brake hoses.

During diagnostics on the stand, the car should call on the special collar of a pair of wheels. Rotation of rollers imitating the road surface is associated with electronics and various sensors with a computer. The installed program displays data on the silymeter information, wheel speed, brake point indications. The analysis is carried out by a specialist enterprise.

At maintenance stations, it is also possible to detect stands stored in memory information about the optimal data of the brake path depending on the car. When you work, the monitor displays not only absolute values, but also the error.

Sensors operate on the hydraulic principle. They poured oil or brake fluid with minimal viscosity readings so that the data has a reduced error at negative temperatures.

After testing one axis, you need to check the operability of the second axis. For this, the car simply moves to the rollers by other wheels. For all-wheel drive cars are used individual stands.

There is an equipment that determines the effort that is formed when the brake pedal is pressed. As a result, the information is displayed as a graph on the computer display. The cost of various stands, depending on the complexity, is usually in the range of 500 ... 900 thousand rubles.

Repair based on diagnostics

After identifying problems with brakes, the car must be sent for repairs. Most procedures associated with the operation of the brake system in the middle-class cars are not the most expensive in the car. Most of them motorist are capable of performing independently even in garage conditions. For example, the brake pad replacement is included in the list of mandatory work on regular maintenance.

More time-consuming are the replacement of the hose or main channels. Here you need experience or help professionals. From the system, it is necessary to roll out air bubbles that can negatively affect its performance. For pumping fluid from the air, you will need a partner help.

Diagnostic parameters, properties of car brake systems and factors affecting braking are described in operation.

To determine the technical status of the brakes, three methods are used:

In road conditions, running tests;
during operation due to the built-in diagnostic tools;
Inpatient conditions using brake stands.

The list of diagnosing and localization of faults in

the brakes establishes GOST 26048-83. These parameters are divided into two groups. The first group includes integral parameters of general diagnostics, and the second - additional (private) parameters of element diagnostics to find faults in individual systems and devices.

The diagnostic parameters of the first group: the brake path of the car and the wheel, the deviation from the corridor of the movement, slowing down (installed brake force) of the car and the wheel, the specific brake force, the slope of the road (on which the car is held in the inhibited state), the coefficient of non-uniform brake forces of the axis wheels, axial The brake force distribution coefficient, the response time (or discharging) of the brake drive, pressure and the rate of change in it in the contours of the brake drive, etc.

The diagnostic parameters of the second group: the full and free course of the pedal, the level of brake fluid in the tank, the resistance force to the rotation of the non-optical wheel, the path and slowing down the wheel of the wheel, ovality and thickness of the brake drum wall, the brake drum wall deformation, the thickness of the brake lining, the stroke of the brake cylinder The clearance in the friction pair, the pressure in the drive, in which the pads relate to the drum, etc.

From among these parameters, in accordance with GOST 254780-82, the brake forces on separate wheels, the total specific braking force, the axial non-uniformity of the brake forces, the brake forces, are necessarily determined during the brakes. At the same time, the indicators of the overall specific brake force and the axial non-uniformity coefficient are calculated.

Road tests are used, as a rule, for the "coarse" assessment of the brake quality of the car. At the same time, the test results can be determined visually on the braking path and synchronization of the start of braking wheels with a sharp one-time pressing on the brake pedal (clutch is turned off), as well as using portable instruments - desperometers (or teene eerographs).

The road tests often impose hope of answering the traction, economic, brake qualities of the car. At the same time for traction, economic, brake properties Car, on the controllability and stability of its movement, behavior at different speeds, with different loads, in the established and unspecified modes, in various road and climatic conditions, etc. However, road tests have a number of shortcomings. The diagnosis on the braking path should be carried out on an even, dry, horizontal section of the road with a solid coating free from the moving transport.

This test method is still quite widespread, although it has the following fairly significant disadvantages:

1. When braking it is impossible to provide stable pressure on the brake pedal with the same effort, as a result of which the measurement results differ significantly at each of the braking.
2. The braking path largely depends on the experience of the driver's driver, the state of the road coating and the conditions of movement.
3. Only the total deceleration of the car is determined. It is impossible to differentiate the deviation of the brake force on the individual wheels, which determines the stability of the movement of the car during braking.
4. When testing, the danger of accidents occurred is likely.
5. Significant time spent on testing with large tire wear and suspension due to wheel lock.
6. With bad climatic conditions (rain, snow, ice), it is impossible to carry out measurements.

For the reasons listed, the control of brakes on the road along the brake path does not fully satisfy modern requirements.

Diagnosing car brakes on the road to slower cars is performed using descererometers (desperographs) Also on a flat, dry, horizontal section of the road. At a speed of 10 ... 20 km / h, the driver dramatically slows down once pressing the brake pedal when the clutch is turned off. At the same time, the slowdown of the car is measured, independent of the test speed.

For passenger cars, the slowdown should be at least 5.8 m / s 2, and for freight (depending on the carrying capacity) - from 5.0 to 4.2 m / s 2. For manual brakes The slowdown must be within 1.5 ... 2 m / s 2. The principle of the desserometer (desperograph) is to move the moving inertial mass of the device with respect to its housing, fixed by car. This movement is caused by the action of the inertia strength arising from the braking of the car and proportional to its slowing down.

The inertial mass of the disolerometer (deslegorograph) can be a progressively moving load, the pendulum (Table 9.1), a liquid or an acceleration sensor, and the limit deceleration meter - the gear device, scale, alarm lamp, a recorder, etc.

The dessellometer is descended to assess the effectiveness of automotive brakes by measuring the magnitude of the maximum slowing down the movement of the car during braking.

Type of device - manual, inertial action, pendulum.

Table 9.1.

Technical characteristics of the descererometer mod. 1155m

The basis of the device is the pendulum, which is influenced by the inertial forces arising from braking, deviates from the zero position to a certain angle, depending on the value of the slowdown. The deviation of the pendulum is registered with an arrow that is self-defined on the division of the scale corresponding to the maximum deceleration achieved. The instrument readings compare with the data of the reference table (placed on the back cover of the device enclosure) and judge the quality of the brake system.

Slow measurement is made when braking a car, overclocked to a speed of 30 km / h, on a dry level horizontal section of roads with asphalt or cement concrete coating.

The device using rubber suits is fixed on the inside of the windshield of the car.

Using multi-mounted brake systems, equipping them with additional devices (anti-locking devices, hydraulic amplifiers, automatic adjustment devices in the friction pair, etc.) and the tightening of the vehicle braking requirements make ineffective road tests.

In Ukraine, from 01/01/1999, the standard DSTU 3,649-97 "TRANSPORT ROOM INDUSTRY was put into force. Safety operational requirements for technical condition and control methods "Instead of the previously operating interstate standard of GOST 25478-91. This document provides two types of control of the working brake system (RTS): road tests and bench tests. Below are the calculated control methods of brake systems, borrowed from work and NJ and 686 N for DTS of the remaining categories. During the braking process, the driver of the DTS motion trajectory is not allowed if it is not required to ensure traffic safety. In the case when the trajectory is adjusted, the test result is not counted.

The RTS state is estimated at the actual brake path value, which should not exceed the standard specified in Table. 9.1.

According to the DSTU, it is allowed to evaluate the performance of the RTS on the criterion for the value of the established deceleration of DTS (j yct.), which must be at least 5.8 m / s 2 for the DTS category MJ and 5.0 m / s 2 for all others (taking into account road trays based on DTS Categories of MD. At the same time it is necessary to control the response time of the brake system, which for DTS with hydraulic drive must be no more than 0.5 s and for DTS with another drive - no more than 0.8 s.

The response time of the brake system (T C) is determined by the standard of Ukraine DSTU 2886-94 as a period of time from the start of braking until the time in which the slowdown (DTS braking force) takes the setting value.

The greatest effectiveness of diagnosing brake systems provide specialized stands that guarantee accuracy and accuracy of diagnosis.

In the process of developing stands, a wide variety of designs were tested. The main element determining all the differences was the supporting surfaces for the wheels checked.

The main type of stand is a uniaxial stand with running drums.

Bench testsbased on the principle of reversibility of movement: the car being checked is immobile, and its rotating wheels are based on a moving support surface. The most common stands are the cylindrical surfaces of the paired rollers. All wheels are rotating on full-headed stands, on uniaxial stands - only the wheels of one axis.

The car's work on the bench simulates his real work on the road. As with any modeling, not all factors are reproduced here. real Movement, but only the most significant (from the point of view of the developer of the stand and technology test). Thus, the incoming air flow is not modeled, which is why there is no aerodynamic resistance during traction tests, and the thermal mode of the operating engine is changing. Further, in operation, use mostly uniaxial stands, which significantly affects modeling operating modes.

Nevertheless, bench tests have a number of very important advantages.

Table 9.2.

The normative values \u200b\u200bof the brake path for road vehicles in operation (byDasta 3649-97)

Note: V 0 - Initial braking speed in km / h.

By destinationstands can be divided into traction to control traction and economic properties (that is power aggregate), brakes and other systems.

By the method of creating the current forcesdistinguish power, inertial and combined inertial-power stands. The most common principle of stand control is that the vehicle wheels interact with the support elements of the stand, and the forces of two groups act on the wheels: driving and braking. Create them either by power devices - engines and brakes or inertial elements - masses and flywheels. Accordingly, called power and inertial test methods.

In case of a power method, as a rule, installed modes are used, that is, control at constant speed. In the inertial method, the modes only unidentified (dynamic), speeds change, due to accelerations, inertial forces are created (Table 9.3).

With bench teststhe criteria for the technical condition of the RTS are the total specific brake force and the time of operation of the vehicle on the stand, as well as the axial uniformity coefficient of the brake forces for each axis. Total specific brake force (y,) There must be at least 0.59 for single DTS category MJ and 0.51 for all others. At the same time, the maximum value of the non-uniformity coefficient of any axis (a "h) should not exceed 20% in the range of brake forces from 30 to 100% of the maximum values. These criteria are calculated according to the following formulas:

where R T. Max i - The maximum value of the brake force on / c wheel, n; p - the total number of wheels equipped with brake mechanisms; M A - Mass of the car, kg; g - Acceleration of free fall, 9,80665 m / s 2;

where R TL, R TP - the values \u200b\u200bof the brake force on the left and right wheels of the same axis, respectively, n; R T. TAX - more of the two mentioned brake force values.

Table 9.3.

Purpose of stands and test methods

According to GOST 25478, the non-uniformity coefficient is calculated otherwise:

The time of operation of the brake system on the stand (T SP) is a period of time from the start of braking until the time in which the brake force of the DTS wheel, which is in the worst conditions, reaches the steady value, is determined by DSTU 2886-94.

At the PTS stand should be tested in a state of full mass. It is allowed to test DTS with a pneumatic actuator in a circular state. In this case, the maximum brake forces of the wheels and the response time must be recalculated. The total specific braking force and response time on the bench should be determined as an arithmetic value according to the results of three tests, rounded to tenths. If the difference between any of these values \u200b\u200band averages more than 5%, the tests must be repeated. As with the road method, tests should be carried out at the "cold" brake mechanisms.

The requirement to perform the stand control of the brakes of the DTS in the state of full mass proceeds from limited opportunities most power stands on the implementation of the brake forces (0.7 ... 0.9 from the load of the load on the wheel; in inertial stands, this ratio is somewhat higher - q. \u003d 1.0 ... 1,2). The requirement is unrealistic; It is not by chance that the standard admits for DTS with a pneumatic reception (that is, most trucks and buses) tests in a curb state. It is possible that it will be observed with state vehicles of passenger cars, where you can put in the driver's salon, inspector and two or three people from the queue. But already for minibuses, not to mention trucks And buses with hydraulic drive brakes, it is impracticable. With regular operational control, carried out in motor transport enterprises (ATP) and at maintenance stations (service station). This requirement will never be observed. The output can serve as an artificial feeding of the checked wheels, but the stands with the mass propagation stoppers did not receive.

In all current standards for calculating standards, a simplified representation of the braking process was used. The actual brake diagram of the car has a rather complicated configuration. One of the examples of recording a deceleration of the time function is shown in Fig. 9.1 (Thin gear line))

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