How to diagnose the brake system - general recommendations. Diagnostics of the brake system of the car at the stand Diagnostics of malfunctions of the brake system

19.10.2019

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

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INTRODUCTION ....................................................................................................

1.1. The principle of operation of the brake system………………………………
1.2. Types of brake systems……………………………………………….
1.3. The main elements of the braking system of a car……………….
2.METHODS AND EQUIPMENT FOR DIAGNOSTICS OF BRAKING SYSTEMS
2.1. The main malfunctions of the brake system……………………….
2.2. Requirements for braking systems…………………………………...
2.3. Methods and equipment for diagnosing brake systems……

3.1. Selection of diagnostic equipment……………………………...
3.2. Technical characteristics of the selected equipment…………...
CONCLUSION …………………………………………………………….
…………………...

INTRODUCTION

The number of cars is getting bigger and bigger, their number is increasing all over the world, every year. And with the number of cars, the number of accidents also increases, due to which more people die and even more remain disabled and crippled. Improper technical condition and operation of vehicles is one of the main causes of many accidents. Accidents that occur due to the failure of various vehicle systems have the most serious consequences.

Relevance of the topiccourse work is that the most important system responsible for the safety of the car is the brake system. The design of cars is constantly being improved, but the presence of a braking system remains unchanged, which helps to stop the car if necessary, which saves the lives of pedestrians, drivers and passengers, as well as other road users. Repair of the brake system is necessary on all cars, however, it is necessary to diagnose the technical condition of the brake system every few thousand kilometers, this is necessary to reduce the likelihood of a car brake failure.

The purpose of the course workImproving the efficiency of diagnosing the brake system of a car, by developing recommendations for choosing diagnostic equipment for brake systems, etc.

To do this, you need to solve the following tasks :

perform an analysis of the structure of the brake system of cars;
to study the methods of diagnosing the brake system;
to study the equipment used in the diagnosis of brake systems.

Object of studyis a technology for diagnosing the brake system e we cars.

Subject of studyis a means and methods of diagnosing O repairing the braking system of the car.

Research methodsused in this work are the methods of generalization, comparison, analysis and analogy.

The structure of the course workconsists of an introduction, three chapters, A keys and a list of 10 sources used.

1. DEVICE OF THE BRAKING SYSTEM

1.1. The principle of operation of the braking system of a car

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

This assembly converts the force applied to the brake pedal into hydraulic brake pressure to slow and stop the vehicle.

Rice. 1.1. Master cylinder device

Today, to improve the reliability of the brake system, two-section master cylinders are installed on all cars, which divide the brake system into two circuits. The brake two-section cylinder can ensure the performance of the brake system, even if one of the circuits depressurizes.

If there is a vacuum booster in the car, then the main brake cylinder is mounted above the cylinder itself or it happens in another place where the brake fluid reservoir is located, which is connected to the brake master cylinder sections through flexible tubes. The reservoir is necessary to control and replenish the brake fluid in the system, if necessary. On the walls of the tank are available to view the liquid level. And also, a sensor is mounted in the tank that monitors the level of brake fluid.

Rice. 1.2. Scheme of the main brake cylinder:

1 vacuum brake booster rod; 2 retaining ring; 3 bypass opening of the primary circuit; 4 compensation hole of the primary circuit; 5 the first section of the tank; 6 the second section of the tank; 7 bypass hole of the second circuit; 8 compensation hole of the second circuit; 9 return spring of the second piston; 10 main cylinder body; 11 cuff; 12 second piston; 13 cuff; 14 return spring of the first piston; 15 cuff; 16 outer cuff; 17 anther; 18 the first piston.

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

Some vehicles are equipped with a sensor on the brake master cylinder that monitors the differential pressure in the circuits. If a leak occurs, it warns the driver in a timely manner.

About the operation of the brake master cylinder:

1. When you press the brake pedal, the vacuum booster rod drives the 1st piston (Fig. 1.3.)

Rice. 1.3. Operation of the brake master cylinder

2. The compensation hole is closed by a piston moving along the cylinder and pressure is created that acts on the 1st circuit 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 created in the circuits ensures the operation of the working brake cylinders. And the void that was formed during the movement of the pistons is immediately filled with brake fluid through special bypass holes, thereby preventing unnecessary air from entering the system.

4. At the end of braking, the pistons return to their original position due to the action of the return springs. In this case, the compensation holes receive communications with the tank and due to this, the pressure equalizes with atmospheric pressure. And at this time, the wheels of the car are braked.

The piston in the master brake cylinder, in turn, which starts to move and thereby increases the pressure in the system of hydraulic pipes leading to all the wheels of the car. Brake fluid under high pressure, on all wheels of the car, affecting the wheel brake piston.

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

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

There is also a vacuum brake booster used in the brake systems of cars. Its use greatly facilitates the entire work of the braking system of the car.

1.2. Types of car brake systems

The braking system is necessary to slow down the vehicle and bring the vehicle to a complete stop, as well as to hold it in place.

To do this, some brake systems are used on a car, such as a parking, working, auxiliary system and a spare one.

Service brake systemused continuously, at any speed, to slow down and stop the vehicle. The service brake system is activated by pressing the brake pedal. It is the most efficient system of all.

Spare brake systemused in the event of a main failure. It can be in the form of an autonomous system or its function is performed by a part of a serviceable service brake system.

Parking brake systemneeded to keep the car in one place. I use the parking system to prevent spontaneous movement of the car.

Auxiliary brake systemused on cars with increased weight. The auxiliary system is used for braking on slopes and descents. It often happens that on cars the role of an auxiliary system is played by the engine, where the exhaust pipe is blocked by a damper.

The brake system is the most important integral part of the car, serving to ensure the active safety of drivers and pedestrians. Many vehicles use various devices and systems that increase the efficiency of the system during braking - this is an anti-lock braking system ( ABS ), emergency brake booster ( BAS ), brake booster.

1.3. The main elements of the braking system of a car

The brake system of a car consists of a brake actuator and a brake mechanism.

Fig.1.3. Scheme of the hydraulic drive of the brakes:
1 pipeline circuit "left front-right rear brake"; 2-signal device; 3 pipeline of the circuit "right front left rear brake"; 4 master cylinder reservoir; 5 the main cylinder of the hydraulic drive of the brakes; 6 vacuum booster; 7 brake pedal; 8 rear brake pressure regulator; 9 parking brake cable; 10 rear wheel brake; 11 adjusting tip of the parking brake; 12 parking brake lever; 13 front wheel brake.

brake mechanismthe rotation of the wheels of the car is blocked and as a result, a braking force appears, which causes the car to stop. The brake mechanisms are located on the front and rear wheels of the car.

Simply put, all brake mechanisms can be called shoe. And already, in turn, they can be divided by friction - drum and disk. The brake mechanism of the main system is mounted in the wheel, and behind the transfer case or gearbox is the mechanism of the parking system.

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

Drum brakes(Fig. 1.4.) most often stand on the rear wheels of the car. During operation, due to wear, the gap between the block and the drum increases and mechanical regulators are used to eliminate it.

Rice. 1.4. Rear wheel drum brake:
1 cup; 2 pressure spring; 3 drive lever; 4 brake shoe; 5 top return spring; 6 spacer bar; 7 adjusting wedge; 8 wheel brake cylinder; 9 brake shield; 10 bolt; 11 rod; 12 eccentric; 13 pressure spring; 14 lower return spring; 15 spacer bar pressure spring.

Various combinations of brake mechanisms can be used on cars:

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

In disc brake(Fig. 1.5.) - the disk rotates, and two fixed pads are installed inside the caliper. Working cylinders are installed in the caliper, during braking they press the brake pads against the disc, and the caliper itself is securely fixed to the bracket. Ventilated discs are often used to increase heat dissipation from the work area.

Rice. 1.5. Diagram of the disc brake mechanism:
1 wheel stud; 2 guide pin; 3 viewing hole; 4 caliper; 5 valve; 6 working cylinder; 7 brake hose; 8 brake shoe; 9 air vent; 10 brake disc; 11 wheel hub; 12 dirt cap.

2. METHODS AND EQUIPMENT FOR DIAGNOSTICS OF BRAKING SYSTEMS

2.1. The main malfunctions of the brake system

The brake system requires the closest attention to itself, 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 how to eliminate them.

Larger, longer brake pedal travel. It occurs due to a lack or leakage of brake fluid from the working cylinders. In this case, it is necessary to replace the failed working cylinders, wash the pads, discs, drums and add brake fluid if necessary. And this is also facilitated by the ingress of air into the brake system, in this case, you just need to remove it by pumping the system.

Insufficient braking performance. Insufficient brake efficiency occurs when the brake pads are oiled or worn, it is also possible for the pistons to jam in the working cylinders, overheating of the brake mechanisms, depressurization of one of the circuits, the use of poor-quality pads, and malfunction ABS, etc.

Incomplete release of the wheels of the car.This problem occurs when the brake pedal has no free play, you just need to adjust the position of the pedal. Also, the problem may be in the master cylinder itself, due to jamming of the pistons. The protrusion of the vacuum booster rod may be increased, or the rubber seals are simply swollen due to the ingress of gasoline or oil, then in this case it is necessary to replace all rubber parts, as well as flush and bleed the entire hydraulic drive system.

Braking one of the wheels, with the pedal released.Most likely, the return spring of the rear wheel pads has weakened, or due to corrosion, or simply contamination - the piston in the wheel cylinder is stuck, then it is necessary to replace the working cylinder. It is also possible to violate the position of the caliper relative to the brake disc of the front wheel, when the mounting bolts are loosened. There may also be a malfunction ABS , swelling of the O-rings of the wheel cylinder, improper adjustment of the parking system, etc.

Skidding, or deviation from the rectilinear movement during braking.If the car, moving on a flat and dry road, begins to deviate in any direction during braking, then jamming of the piston of the main cylinder, clogging of pipes due to clogging, contamination or oiling of the brake mechanisms, different pressure in the wheels, and also possibly not one of the brake circuits is working.

Increased effort on the brake pedal when braking. If it is necessary to apply a lot of force to the brake pedal to stop the car, then most likely the vacuum booster is simply faulty, but the hose that connects the engine intake pipe to the vacuum booster can also be damaged. And it is also possible that the piston of the main cylinder seizes, wear of the pads, and new pads that simply have not yet run in can still be installed.

Increased noise when braking. When the brake pads are worn, there is a squealing sound when braking due to the friction of the wear indicator rubbing against the disc. Also, the pads or disc may be greasy or dirty.

2.2. Requirements for vehicle braking systems

The brake system of the car, in addition to the general requirements for the design, has increased special requirements, because. it ensures the safety of vehicles on the road. Therefore, the braking system, in accordance with these requirements, must provide:

minimum braking distance;
vehicle stability during braking;
stability of braking parameters during frequent braking;
quick response of the brake system;
proportionality of effort on the brake pedal and on the wheels of the car;
ease of management.

There are requirements for the braking systems of a car that are regulated by UNECE Rules No. 13, which are also applied in Russia:

Minimum stopping distance. The braking system on cars must be highly efficient. The number of accidents and accidents will be less if the maximum deceleration value is high and approximately equal for vehicles of various weights and types moving in heavy traffic.

Also, the braking distances of cars should be simultaneously close to each other, with a difference of about 15%. If the minimum braking distance is reduced, then not only high traffic safety will be ensured, but also an increase in the average speed of the car.

The necessary conditions for obtaining the minimum braking distance is the shortest time required for the vehicle's brake drive to actuate, as well as braking all wheels simultaneously and the possibility of bringing the braking forces to the maximum traction value and ensuring the desired distribution of braking forces between the vehicle's wheels in accordance with the load.

Braking stability. This requirement increases the braking efficiency of the vehicle on roads with low friction coefficients (icy, slippery, etc.) and thus increases the level of safety for all road users.

Subject to proportionality between the braking forces and the loads on the rear and front wheels, the vehicle is braked with maximum deceleration under all road conditions.

Stable braking. This requirement is related to the heating of the brake mechanism during braking and possible violations of their actions during heating. So, when heated between the brake drum (disk) and the friction linings of the pads, the coefficient of friction decreases. In addition, when the brake linings are heated, their wear increases significantly.

The stability of the braking parameters during frequent braking of the car is achieved with a coefficient of friction of the brake linings, equal to about 0.3-0.35, practically independent of the sliding speed, heating and water ingress.

The braking distance will depend on the response time of the brake system of the car, which significantly affects traffic safety. The response time of the brake system mainly depends on the type of brake actuator. Hydraulic driven vehicles will have 0.2-0.5, pneumatic driven vehicles 0.6-0.8 and pneumatic driven road trains 1-2. When these requirements are met, a significant increase in the safety of vehicles in various road conditions is provided.

The force on the brake pedal during the braking of the car should be 500 - 700 N (minimum value for cars) with a pedal stroke of 80 - 180 mm.

2.3. Methods for diagnosing brake systems

For diagnosing the brake systems of cars, two main methods of diagnosing are used - road and bench.

the road diagnostic method is designed to determine the length of the braking distance; steady-state deceleration; vehicle stability during braking; brake system response time; the slope of the road on which the car must stand still;
bench test method is necessary to calculate the total specific braking force; the coefficient of non-uniformity (relative non-uniformity) of the braking forces of the wheels of the axle.

To date, there are many different stands and instruments for measuring braking performance by various methods and methods:

inertial platform;
static power;
power roller stands;
inertial roller;
instruments that measure the deceleration of a vehicle during a road test.

Inertial platform stand. The principle of operation of this stand is based on the measurement of inertia forces (from rotationally and translationally moving masses) that occur during vehicle braking and are applied at the interface between vehicle wheels and dynamometer platforms.

Static Power Stands. These stands are roller and platform devices that are designed to rotate the “break” of a braked wheel and measure the force applied in this case. Statistical power stands have pneumatic, hydraulic or mechanical drives. Braking force is measured with the wheel suspended or resting on smooth running drums. This method has a disadvantage of diagnosing brakes - this is the inaccuracy of the results, as a result of which the conditions of a real dynamic braking process are not repeated.

Inertial roller stands. They have rollers driven by an electric motor or a car engine. In the second example, due to the rear (driving) wheels of the car, the rollers of the stand rotate, and from them with the help of a mechanical transmission and the front (driven) wheels.

After the car is installed on the inertial stand, the linear speed of the wheels is brought to 50-70 km / h and braked sharply, while disengaging all the carriages of the stand by turning off the electromagnetic clutches. At the same time, at the points of contact of the wheels with the rollers (tapes) of the stand, inertia forces arise that counteract the braking forces. After some time, the rotation of the drums of the stand and the wheels of the car is stopped. The paths traveled by each wheel of the car during this time (or the angular deceleration of the drum) will be equivalent to the braking distances and braking forces.

Power roller standsusing the adhesion forces of the wheel with the roller, it is possible to measure the braking force during its rotation at a speed of 2.10 km / h. The rotation of the wheels is carried out by the rollers of the stand from the electric motor. The braking forces are determined by the reactive torque that occurs on the stator of the stand's gear motor when the wheels are braked.

Roller brake testers allow you to get fairly 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) that are absolutely the same as the previous ones, which is ensured by the exact setting of the initial braking speed by an external drive. In addition, when testing on power roller brake stands, the measurement of the so-called “out-of-roundness” is provided assessment of the unevenness of the braking forces per one revolution of the wheel, i.e. the entire braking surface is examined.

When tested on roller brake stands, when the force is transmitted from the outside (from the brake stand), the physical picture of braking is not disturbed. The braking system must absorb energy from outside, even though the car has no kinetic energy.

There is another important condition test safety. The safest tests are on power roller brake stands, since the kinetic energy of the test vehicle on the stand is zero. In the event of a failure of the brake system during road tests or on site brake testers, the probability of an emergency is very high.

It should be noted that, in terms of the totality of their properties, it is power roller stands that are the most optimal solution both for diagnostic lines of service stations and for diagnostic stations conducting state inspections.

Modern power roller stands for testing brake systems can determine the following parameters:

According to the general parameters of the vehicle and the state of the brake system resistance to rotation of unbraked wheels; uneven braking force per wheel revolution; mass per wheel; weight per axle.
For working and parking brake systems the greatest braking force; brake system response time; coefficient of non-uniformity (relative non-uniformity) of braking forces of axle wheels; specific braking force; effort on the control.

Control data (Fig. 2.3.) are displayed in the form of digital or graphical information. The diagnostic results can be printed out and stored in the computer memory in the database of vehicles being diagnosed.

Rice. 2.3. Vehicle brake monitoring data:

1 indication of the axis being checked; Software front axle service brake; CT parking brake system; ZO rear axle service brake

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

The dynamics of the braking process (Fig. 2.5.) can be observed in graphical interpretation. The graph shows the brake forces (vertically) versus the force on the brake pedal (horizontal). It reflects the dependence of the braking forces on the force of pressing the brake pedal for both the left wheel (upper curve) and the right wheel (lower curve).

Rice. 2.4. Instrument rack brake tester

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

With the help of graphical information, you can also observe the difference in the braking forces of the left and right wheels (Fig. 2.6.). The graph shows the ratio of the braking forces of the left and right wheels. The deceleration curve should not go beyond the limits of the regulatory corridor, which depend on specific regulatory requirements. Observing the nature of the change in the schedule, the operator-diagnostician can draw a conclusion about the state of the brake system.

Rice. 2.6. Values of brake forces of the left and right wheels

RECOMMENDATIONS FOR THE SELECTION OF EQUIPMENT FOR DIAGNOSTICS OF THE BRAKING SYSTEM

3.1. Selection of diagnostic equipment

SPACE brake testers have a quality management system certificate according to UNI EN ISO 90012000, which confirms the use of advanced technologies, the use of modern coatings, high-quality materials and components, which makes it possible to export equipment to more than forty countries around the world.

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

Table 3.1

Roller units for brake testers

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

And also another important characteristic is the coefficient of friction between the car wheel and the rollers of the stand. In our case, we take the value equal to 0.7. To select a brake stand, we determine the braking force.

Braking force is the force of interaction of the car wheel with the outside of the roller (imitation of car movement on the road). It is expressed in Dan.

1 Newton = 0.101972 kg.

1 Dan = 10 Newton = 1.01 kg.

For the convenience of calculations, we accept 1 Dan = 1 kg with a 1% minor error.

µ = F/M

Friction coefficient µ - force ratio F to mass M .

This expression means the ratio between the mass of the car and the force required to move on the road.

If we have mass M , interacting with the surface and 0.5 kg of force F to move it, then the coefficient of friction µ will be equal to 0.5.

Based on this average value, a roller brake tester is selected, for example, PFB 035 = 500 Dan.

The power of the motor (and roller drive) allows accurate measurements of the force F over 510.2 kg. to the tangent surface of the roller. After this value is measured, the motor slows down and no further measurements are made. To determine the maximum mass, use the previous formula:

W = F/µ

We get 500 kg / 0.7 = 714 kg (mass acting on one roller). It follows that the maximum weight per axle is 1428 kg.

For the obtained maximum theoretical weight per axle, we can choose model PFB 035. This choice is not accurate because the coefficient of friction is highly dependent on tire characteristics (bad tires have lower friction) and other conditions. For example, maximum brake force does not measure the braking time of a previously damaged tire to avoid further wear. It also allows you to slightly increase the maximum weight of the axle. Note that the weight of an axle is not just half of the total weight of the vehicle, since an unloaded vehicle has more weight per axle, but if the vehicle is loaded, the axle load increases accordingly.

3.2. Technical characteristics of the selected equipment

The principle of operation of the SPACE line (Italy) consists in the sequential collection and software processing of the results of measurements and visual control of the technical condition of the automatic telephone exchange using equipment measuring instruments that are included in the instrumental control line. The vehicle testing procedure is controlled from the remote control or from the keyboard, processed and stored by the processor, testing visualization using a monitor, all images are 3D graphics, printing results on a printer, interface for connection:

withdrawal stand ;
suspension tester ;
gas analyzer;
dymometer;
tachometer .

List of measured parameters:

rolling resistance;

Oval discs or misalignment of the brake drum;

Maximum braking force per wheel;

The difference in braking force between the right and left wheels of the same axle;

Braking efficiency of service and parking brakes;

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

Vehicles with 4WD all-wheel drive can also be tested on the brake stand. The test procedure for 4WD vehicles is divided into two separate phases for each axle. In the first phase, the left roller assembly begins to rotate in the direction of travel, and the right one in the opposite direction. In this case, the transmission to the second axle is disengaged in the transfer case, and, consequently, the torque is not transmitted to the wheels that are not on rollers. The results will be shown after both axles have been tested. After completing the brake force measurements on each axle, you can view the brake force progress graph.

Rice. 3.2. Test procedure for all-wheel drive vehicles.

After all the data has been entered into the computer memory and the car has left the roller assembly, a page appears on the monitor screen with the final test results of the entire brake system (Fig. 3.2.).

Technical characteristics of stands PFB 035, PFB 040 and PFB 050 are shown in table 3.2

Table 3.2

Specifications

Specifications	PFB 035	PFB 040	PFB 050
Axle load during testing / during transit, kg	2500/4000	2500/4000	2500/4000
Maximum braking force, N	5000	6000	7500
Accuracy, %
Test speed
Engine power, kW		2x4.7	2x5.5
Drum diameter, mm
Adhesion coefficient	Over 0.7	Over 0.7	Over 0.7
Power, V	380 / 3f	380 / 3f	380 / 3f

Comparison of cost-benefit, repair costs and uptime is shown in Figure 3.3

Rice. 3.3. Bench comparison chart (percentage).

CONCLUSION

A modern car operates in a wide variety of road and climatic conditions. Long-term operation inevitably leads to deterioration of its technical condition. The performance of the vehicle or its units is determined by their ability to perform the specified functions without violating the established parameters. The performance of a car depends primarily on its reliability, which is understood as the ability of a car to safely transport goods or passengers, subject to certain operational parameters.

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

In the course of writing a term paper, the device of the brake system was studied. Methods and methods for restoring the performance of the brakes were considered. And in conclusion, based on the studied material, recommendations were developed for choosing SPASE diagnostic equipment from three roller stands PFB 035, PFB 040 and PFB 050. During the study of technical characteristics, price category, repair costs and service life, it was accepted the decision to choose the first PFB 035 unit, since it is the best option in terms of price category, and the technical characteristics are not much inferior to other stands, as well as in terms of repair costs and service life, which is shown in Figure 3.3, is more cost-effective.

LIST OF USED SOURCES

1. GOST R 51709-2001. Vehicles. Safety requirements for technical condition and methods of verification. M.: Standartinform, 2010. 42 p.

2. Derevianko V.A. Brake systems of cars M.: Petit, 2001. 248 p.

3. Car diagnostics. Workshop: textbook. allowance // ed. A.N. Kartashevich. Minsk: New knowledge; M.: INFRA-M, 2011. 208 p.

4. Roller brake testers for cars: SPACE [electronic resource]. URL : http :// www . alpoca. ru / catalog / str 1__13__ itemid __73. html.

5. Means of diagnostics and control of vehicles [electronic resource]. URL: http://ktc256.ts6.ru/index.html.

6. Maintenance and repair of automobiles: 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 students. // V. M. Vlasov, S. V. Zhankaziev, S. M. Kruglov et al. M.: Publishing Center Academy, 2003. 480 p.

8. Technological processes for diagnosing, servicing and repairing cars: textbook. allowance // V.P. Ovchinnikov, R.V. Nuzhdin, M.Yu. Bazhenov Vladimir: Publishing house Vladim. state un-ta, 2007. 284 p.

9. Technological processes of maintenance, repair and diagnostics of cars: textbook. allowance for students. higher textbook institutions // V.G. Perederiy, V.V. Mishustin. Novocherkassk: YuRGTU (NPI), 2013. 226 p.

10. Kharazov A.M. Diagnostic support for the maintenance and repair of vehicles: Ref. allowance M.: Higher. school, 1990. 208 p.

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Methods and tools for diagnosing brake systems are developed in relation to the diagnostic parameters and requirements of technological processes for the maintenance and repair of a car. Accordingly, there are means for general diagnostics of brakes on the road, for general stationary diagnostics before maintenance or repair, for element-by-element diagnostics during maintenance and repair or after their completion.

The existing means of technical diagnostics of brakes (STDT) can be classified according to five criteria:

1. on the use of forces of adhesion of the wheel to the supporting surface;

2. at the place of installation;

3. according to the method of loading;

4. according to the mode of movement of the wheel;

5. according to the design of the supporting device.

Rice. 2.1. Means of technical diagnostics of brakes.

2.1. Stands for technical diagnostics of car brakes.

All stands for technical diagnostics of brakes (STDT) are divided into two large groups. The first, which includes the bulk of the stands, is more numerous. This group of STDT works using the forces of adhesion of the wheel to the supporting surface. In these stands, the realized braking torque is limited by the force of adhesion of the wheel to the supporting surface of the stand, therefore, in most of them it is impossible to realize the full braking torque of the car. The second group of stands, operating without the use of forces of adhesion of the wheel to the supporting surface, is structurally different in that the braking torque is transmitted directly through the wheel or through the hub. This group of stands has not found wide application due to the complexity of the design and low technology of testing.

Stands, in turn, according to the method of loading, are power and inertial. Power stands of the first group according to the wheel movement mode on the stand can be: with partial wheel rotation and with full wheel rotation. The first mode, as a rule, is typical for platform stands, and the second - for all other stands.

According to the design of the supporting devices, the stands are divided into: platform, roller and tape (the first group); with hanging wheel axles and without hanging wheel axles (second group).

In power platform stands, the wheels of the car are motionless, therefore, when you press the brake pedal, only the force of shifting (breaking) of the locked wheels from their place changes, i.e. the force of friction between the brake linings and the drum (disk). There are stands with one common platform for all wheels and with platforms for each wheel of the car.

Power platform stands have a number of significant drawbacks that preclude their widespread use. For example, the test does not take into account the influence of driving speed on the coefficient of sliding friction and dynamic effects in the braking system. The results of measurements largely depend on the position of the wheels on the platform of the stand, on the state of the supporting surface and wheel treads. Only the pull-off force of the braked wheels is measured.

Platform inertial stands, having movable (one common for each side or for each wheel) platform, in comparison with power platform stands are more perfect, because they more fully take into account the dynamics of the action of braking forces in real conditions. However, these stands have a number of significant drawbacks: the need for a territory for accelerating a car, a decrease in the level of safety of work during diagnosis, and insufficient accuracy and reliability of diagnostic information.

Inertial load belt stands reproduce the road conditions of the interaction of the tire with the supporting surfaces. However, they have significant dimensions and do not provide sufficient vehicle stability during diagnosis, but such design flaws as tape slippage and large mechanical losses in friction pairs.

Roller brake testers. Of these, the overwhelming majority use stands based on the power method of diagnosis. The power method makes it possible to determine the braking forces of each wheel with a given pedal pressing force, the response time of the brake drive, to assess the condition of the working surfaces of the brake linings and drum, the ellipse of the drums, etc. In the vast majority of these stands, with forced scrolling of the braked wheels of the car, a speed of 2-5 km / h is simulated, rarely up to 10 km / h,

The most reliable is inertial method diagnostics on roller inertial stands. They measure the braking distance for each individual wheel, the response time of the brake drive and deceleration (maximum and for each wheel separately), but due to the complexity, high cost and lower manufacturability in operation, these stands are used extremely limitedly.

For diagnosing brakes in cramped conditions, as well as for the purpose of localizing faults and in-depth diagnosing, portable STDTs are most effective. The essence of the method of operation of these devices is that the wheel of the car is forcibly spun, and when the rotation speed reaches a predetermined value, the device for pressing the brake pedal is activated; the wheel is braked, during which the brake drive response time, the deceleration rise time in a given range of wheel speeds and the braking distance at a steady value of the braking force are recorded.

Due to the small inertial mass of the suspended wheels, the braking process differs significantly from the real one. Bringing the results of diagnosing brakes to real conditions is carried out through conversion factors for the braking distance and deceleration.

General diagnostics of a car on the road is carried out by the following methods; visually by the braking distance and the synchronism of the start of braking by all wheels; using portable devices; by the maximum deceleration of the car; using built-in devices; by automatic signaling when the diagnostic parameter reaches the limit value.

Diagnosis by braking distance on a dyno road consists in observing the car with a sharp single press on the pedal (clutch disengaged) and measuring the braking distance. At the same time, the synchronism of braking is monitored by the traces of tires left on the road. The test area must be level, dry and level. The standard braking distance (at a speed before braking equal to 30 km / h) is at least 7.2 m for cars, and for trucks and buses, depending on the load capacity, 9.5-11 m. This method does not give reliable results, and its use is difficult due to the need to have a sufficiently large section of a horizontal road with a hard, dry and even surface.

Diagnostics of brakes by slowing down vehicles using portable decelerometers is also carried out on a flat horizontal section of the road. The car is accelerated to a speed of 10-20 km / h and braked sharply by pressing the pedal once with the clutch disengaged. At the same time, J max is measured. Standard deceleration (it does not depend on the vehicle speed) for cars is at least 5.8 m/s 2 , and for trucks, depending on the carrying capacity, from 5.0 to 4.2 m/s 2 . For hand brakes, the deceleration should be within 1.5-2.5 m/s 2 .

Rice. 2.2. Schematic diagram of a decelerometer with a translationally moving mass.

1 - inertial mass;
2 - signal lamp;
3 - leaf spring;
4- adjusting screw;
5 - battery.

The principle of operation of the decelerometer is to fix the path of movement of the moving inertial mass of the device relative to its body, which is fixedly fixed on the car. This movement occurs under the action of the force of inertia that occurs when the car brakes and is proportional to its deceleration. The inertial mass of the decelerometer can be a translationally moving load, a pendulum, a liquid or an acceleration sensor, and a gauge can be a pointer device, a scale, a signal lamp, a recorder, a composter, etc. To ensure the stability of the readings, the decelerometer is equipped with a damper (liquid, air, spring), and for the convenience of measurements - a mechanism that fixes the maximum deceleration.

To diagnose car brakes with the help of structurally built-in devices, systems are used that provide information about the wear of brake pads, the level of brake fluid, the pressure in the pneumatic or hydraulic drive, the operation of the handbrake, the malfunction of the anti-lock device, etc.

The system consists of built-in sensors and panel indicators or alarms. Built-in diagnostics provide the ability to continuously monitor the state of the brakes. From this point of view, it is ideal. The limited use of built-in diagnostics is due to its significant cost. The development of modern instrumentation and electronics allows us to expect a rapid development of built-in diagnostic tools for modern cars.

General stationary express diagnostics is performed at specialized posts and lines, using high-speed platform stands of inertial or power type. For general diagnostics with adjustment work, roller-type brake stands are also used.

The principle of operation of the inertial platform stand is based on the measurement of inertia forces (from the translationally and rotationally moving masses of the vehicle) arising during its braking and applied at the points of contact of the wheels with the dynamometer platforms.

The platform inertial stand consists of four movable platforms with a corrugated surface, on which the car runs with wheels at a speed of 6-12 km / h and stops when braking hard. The resulting vehicle inertia forces correspond to the braking forces. They act on the platforms of the stand, are perceived by liquid, mechanical or electronic sensors and are recorded by measuring instruments located on the console.

The disadvantages of stands of the platform inertial type include: a large production area occupied by them (taking into account the need for preliminary acceleration of the car); instability of the coefficient of adhesion of tires, depending on their pollution, humidity and temperature.

According to the principle of operation, a power-type platform brake stand differs from the inertial one in that the braking forces arising during braking at the points of contact of the wheels with the dynamometric platforms are obtained not due to the inertia of the car, but as a result of its forced movement through the platforms using a traction conveyor.

For element-by-element diagnostics at posts and lines of maintenance and repair of vehicles, inertial stands with running drums and power stands with rollers are used. They are divided into two classes: with the use of traction forces for scrolling the braked wheels and without the use of these forces.

In the first case, the braked wheel is turned with the help of adhesion forces that arise at the points of contact between the wheel and the drum (roller), to which the inertial torque or the moment of the electric motor is applied directly to the car wheel. In the practice of diagnosing cars, stands of the first type are mainly used, since they are cheaper and more technologically advanced.

Inertial stands with a running or belt support-drive device using adhesion forces can be driven by the wheels of a running car or driven by electric motors. The stand driven by the wheels of the car consists of two support-drive units, kinematically connected to each other and providing simultaneous checking of the brakes of both axles of the car. Each support-drive unit of the drum stand consists of a frame and two pairs of running drums on which the vehicle wheels rest. Running drums are connected with the flywheel masses.

The stand with an electric drive consists of one unit and, as a rule, is intended for alternately checking the brakes of vehicles with two driving axles. The support-drive unit is equipped with additional support drums.

The principle of operation of all inertial stands using adhesion forces is the same. If the stand has an electric drive, then the wheels of the car are driven by the rollers of the stand, and if not, then from the car engine. In the latter case, the driving wheels of the car rotate the rollers of the stand, and from them, with the help of a mechanical transmission, the front, driven, wheels.

After installing the car on the inertial stand, the circumferential speed of the wheels is brought to 50-70 km / h and braked sharply, while disengaging all the carriages of the stand by turning off the electromagnetic clutches (the specified force of pressing the brake pedal is provided by an automatic machine or a gauge with a pointer installed on the brake pedal). In this case, in the places of contact of the wheels with the rollers of the stand, inertia forces arise that counteract the braking forces. After some time, the rotation of the drums of the stand and the wheels of the car stops. The paths traveled by each wheel of the car during this time, or the angular deceleration of the drum, will be equivalent to their braking distances and braking forces.

The braking distance 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 a stopwatch, and the deceleration is determined by the angular decelerometer. On the inertial stand, it is also possible to directly measure the braking torque by the value of the reactive torque that occurs on the stand shaft between the flywheel and the drum. For the reliability of the obtained results, it is necessary that the braking conditions of the car wheels on the stand correspond to the actual conditions of the car braking on the road. This means that the kinetic energy absorbed by the brakes of the car when they are tested on the stand should be the same as on the road.

Power stands using wheel adhesion forces allow measuring braking forces during its rotation at a certain speed V=2…10 km/h. At the same time, the braking force of each of the wheels of the car installed on the stand is measured by braking them during rotation. The rotation of the wheels is carried out by the rollers of the stand from the electric motor. Braking forces are determined by the amount of torque that occurs on the rollers when the wheels are braked.

When diagnosing brakes with a hydraulic drive, this method determines the dependence of the measurement of the braking force Pt on each of the wheels of the car on the pressure force on the brake pedal Pn. This dependence, called the brake diagram, gives a fairly complete description of the performance of the brake system. With the force method of diagnosing brakes, the general parameter of efficiency is the specific braking force ∑P t /G a ·100%. For most cars, this force is 45-80%, the last figure is an indicator of the excellent condition of the brakes. The difference in braking forces on the wheels of one axle of the car, ensuring the absence of skidding, should not be more than 10-15%.

Diagnosing brakes with the help of power stands is the most common. This is due to the great suitability of power stands for element-by-element diagnostics when combining diagnostic work with adjustment work, their relatively low cost, small occupied or production area and economical power consumption.

The undoubted advantage of inertial brake stands is the ability to diagnose brakes at high speeds. It is this factor that is fundamental for testing brake systems with ABS, because. this system starts its work from a speed of about 20…30 km/h.

The braking system is one of the main elements in the vehicle control system, which can prevent most accidents. For this reason, the diagnosis of the brake system must be carried out in a timely manner and with high quality. Even the most minor malfunction of the brakes must be immediately eliminated. Otherwise, it may result in a serious accident.

Car brake system diagnostics

Due to the great responsibility of the brake system for people's lives and road safety, its adjustment should be carried out exclusively by qualified specialists with extensive experience. In our car service, the diagnostics of the brake system is carried out by professional craftsmen using specialized equipment. The high quality of work performed is confirmed by numerous positive reviews from our customers. Efficiency of diagnostics and troubleshooting provide the opportunity to pick up your car on the day of delivery for service. Each diagnostic of the brake system includes a large number of control operations recommended by car manufacturers. You can find our workshop near the metro stations "Altufievo", "Medvedkovo", "Bibirevo" (Moscow, SVAO region).

Brake system diagnostics: what indicates a malfunction?

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

extraneous noise;
sticking brakes;
brake fluid leaks (of any intensity);
easy pedal travel;
brake failure;
increase in stopping distance.

These problems can be caused by leakage, lack of brake fluid, wear of brake pads, untimely replacement of brake fluid, pads.

If even one of these signs of deviation from normal operation is detected, competent diagnostics of the brake system will be required, including checking the tightness of all elements of the system, the vacuum booster, the operation of indicator devices, and the tightness of the pneumatic actuator. For cars with an on-board computer, the best option is to diagnose using a computer or a car diagnostic scanner that can read errors from the controller unit.

Diagnostics of malfunctions of the brake system

Today, the diagnostics of the operating parameters of the brake system can be checked using two main methods: bench and road. Diagnostics of malfunctions of the brake system by each of them includes the following tests and measurements:

stopping distance;
steady deceleration of the vehicle;
deviation is linear;
the slope of the road at which the vehicle is held by the vehicle;
specific braking force;
operating time of the brake system;
coefficient of uneven braking forces on one axle.

Today, the road diagnostic method is practically not used due to the lack of objectivity and the influence of external factors. Diagnostics of malfunctions of the brake system on a specialized stand provides the most accurate measurements. Based on the data obtained, it will be possible to judge the state of the elements of the braking system and the safety of driving the test vehicle. The quantity and quality of measurements are strictly regulated at the legislative level, so the test bench is periodically verified for compliance with the accuracy of measurements.

Brake system diagnostics: illustrative examples

Diagnostics of the brake system of the car begins with fixing the car in one position. If the efficiency of stopping in one place does not meet the required parameters, then one can judge the leakage of brake fluid from the system.

If the brake pedal fails all the time, then diagnostics of the brake system will most likely indicate air in the system. After removing air from the braking system, it will be necessary to restore the level of brake fluid in the reservoir to the original mark.

Often a possible cause of deviations in the normal operation of the brake system is the presence of oil on the brake pads. At the same time, during the braking of the car, a characteristic creak is heard. Diagnostics of the brake system will show the physical wear of the brake pads, after replacing them, extraneous noise will disappear. If you do not perform this procedure in a timely manner, you can damage the brake disc.

Too tight travel of the brake pedal indicates a breakdown of the vacuum booster or a leak. Timely diagnostics of the brake system of the car will help to quickly determine the location of the malfunction.

Spontaneous braking can be triggered by a violation of the position of the brake caliper or its breakdown. In this case, the diagnostics of the brake system is reduced to examining the operation of the calipers and making a diagnosis of their serviceability. Very often, the main cause of failure is a violation of the tightness of the connecting hoses of the system due to mechanical influences.

Pulling the car to the side when braking may indicate a problem with the brake caliper or brake pads. Diagnostics of the brake system will consist in conducting a survey of the steering and brake system elements on the wheels of the car. In addition, there is a possibility of uneven wear of the brake pads.

Loud braking noise can be caused by worn brake pads or severely corroded brake discs. Sometimes the diagnosis of the car's brake system with these symptoms indicates the presence of foreign objects between the brake pad and the disc.

The presence of a large stroke of the brake pedal is most often the result of a malfunction of the vacuum booster. In some cases, these symptoms are characteristic of the presence of air in the hydraulic brake system. Diagnostics of the brake system will help to accurately determine the cause of the breakdown and prevent further development of the accident.

Too "soft" stroke of the brake pedal is most likely caused by a depressurization of the hydraulic system or a malfunction of the master brake cylinder. Diagnostics of the brake system can also show the unsatisfactory condition of the brake fluid.

Large resistance when pressing the brake pedal is usually caused by a malfunction of the vacuum booster or damage to the hydraulic circuit. In addition, new brake pads that have not had time to run in can cause a similar phenomenon. 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 pedal indicate severe wear of the brake discs, loosening of the brake calipers, wear of the brake linings. High-quality diagnostics of the brake system of the car will provide accurate detection and localization of the place of failure.

Constant braking can be caused by improper adjustment of the parking brake, vacuum booster or brake master cylinder. To say exactly what is the cause of this phenomenon, professional diagnostics of the car's brake system is necessary.

External factors of influence

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

Tires with different grip coefficients have completely different braking characteristics. At the same time, the following factors affect grip: tire pressure, tread depth and pattern, wheel width.

The degree of loading of the car greatly affects its braking distance. The heavier the vehicle is loaded, the longer its braking distance will be.

The natural wear of the rubber brake hoses results in a damping effect that smooths out the harshness of the brakes and thus the degree of their effectiveness.

Violation of the angles of collapse and convergence leads to the withdrawal of the car from the rectilinear direction of motion during braking.

Competent diagnostics of the brake system of the car necessarily takes into account all these factors of external influence.

One of the most important safety systems is the braking system. The ability to stop in time in the presence of some obstacles on the way depends on its quality. It is important to keep your brakes in good and predictable condition. To do this, they must be checked regularly.

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

Under the concept of a stand, it is customary to mean devices located in specialized rooms, the main purpose of which is a multi-level check of the technical condition of the car. When bench diagnostics, the following parameters are most often controlled:

data on the total specific braking force;
the value of the coefficient of relative non-uniformity;
asynchronous operation options.

Several different types of instruments are used in industry. Most of them operate on the principle of simulating asphalt pavement, where during the braking process, the instruments record the required data.

Stand for diagnostics of the brake system

Such stands can be in the form of stand-alone equipment or be part of a large diagnostic complex.

The Need for Diagnostics

Diagnostics and repair of the brake system of the car is carried out both according to the established maintenance interval for each car model, and after the detection of alleged malfunctions. The most common signs that the machine needs to be examined are the following situations:

a clear increase in braking distance on dry and hard surfaces;
problems with the stroke of the brake pedal, in which either deep sinking or sticking of the stroke occurs;
visible departure from rectilinear movement when pressing the brake pedal;
vibrations, hum, creaking in the area of the brake system;
constant decrease in the liquid level, visible streaks.

Vehicle braking system

Indirect symptoms include uneven wear of the surface of the brake pads, visible mechanical damage to the hoses or brake pipes. Such information is difficult to obtain without removing the wheels. Means the driver must independently inspect the problem areas behind the wheel every 30-40 thousand km.

Carrying out the procedure

During testing, it is necessary to monitor the state of the system as a whole and individual nodes for performance. Before the brake system is diagnosed at the stand, the following sections are checked:

container with brake fluid;
condition of discs and drums;
brake pads;
stable operation of the wheel bearing;
caliper;
functioning of working cylinders;
the operation of the booster and the main brake cylinder;
the condition of the brake lines.

During diagnostics at the stand, the car must drive onto special rollers with a pair of wheels. The rotation of the rollers, simulating the road surface, is connected with the help of electronics and various sensors with a computer. The installed program displays on the monitor data on force-measuring information, wheel speed, brake torque readings. The analysis is carried out by a specialized specialist of the enterprise.

At service stations, you can also find stands that store information about the optimal braking distance data depending on the vehicle. When they work, the monitor displays not only absolute values, but also the error.

The sensors work on the hydraulic principle. They are filled with oil or brake fluid with minimum viscosity readings so that the data have a reduced error at low temperatures.

After testing one axis, you need to check the performance of the second axis. To do this, the car simply moves to the rollers with other wheels. For all-wheel drive cars, separate stands are used.

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

Repair based on diagnostic results

After identifying problems with the brakes, the car must be sent for repair. Most of the procedures related to the operation of the brake system in mid-range cars are not among the most expensive in a car. Most of them the motorist is able to perform independently even in garage conditions. For example, the replacement of brake pads is included in the list of mandatory maintenance work.

More laborious are the replacement of the hose or main channels. Here you need experience or the help of professionals. Air bubbles must be evacuated from the system, which can adversely affect its performance. To pump fluid from air, you will need the help of a partner.

Probably, none of the car systems needs such serviceability as the brake system, otherwise, we think, it makes no sense to talk about the consequences.

Brake Fluid Diagnosis

Periodic diagnostics of the brake system is proof that the brakes will not let you down in any, even in the most critical situation. Well, and most importantly, every car owner can carry out diagnostics on their own, moreover, such a procedure does not require any special tools or certain skills. All you need is a clean cloth, a standard tool kit, a tape measure or ruler, and a small can of brake fluid.

Start diagnosing the brake system should be with the control of the brake fluid level. It is worth noting that such a procedure must be carried out periodically, at least once a month, it is also required after the hydraulic line has been pumped, and of course, when the system itself signals a lack of fluid. Brake fluid control is a fairly simple task that can be done visually, since there are two divisions on the brake fluid reservoir - minimum and maximum, it is considered normal when the brake fluid level is between them.

If you have established a lack of fluid, then you must immediately add it - by disconnecting the tip of the wire harness, unscrew the reservoir cap and pour in pre-prepared (required new) brake fluid to the maximum mark. After that, tightly tighten the cover, connect all the harnesses in reverse order. You can make sure that you did everything correctly, with the engine running, by the control light on the dashboard, which should light up when you press on the tank cap.

Diagnostics of the entire brake system

After the above operation, attention should be paid to the vacuum brake booster. It is worth noting that this procedure must be carried out with the ignition off, so if the engine was running before, it must be turned off. Now you need to do it - press the brake at intervals, you need to continue until the hiss in the amplifier completely disappears. Then, pressing the pedal, you need to start the engine. Serviceability can be judged by the pedal, which has gone down a little.

Pay attention to the travel of the parking brake lever. The fact that it is in order will be reported by a stroke of about three clicks, in addition, the handbrake should hold the car without tension, standing on a descent of about 23 degrees. If the parking brake does not cope with at least one of the tasks, it is necessary to replace the failed parts, we recommend not to delay this, because you can guess the consequences, we think, yourself.

Well, the final stage in diagnosing the brake system is, we have already written about a similar procedure, so we will not duplicate the topics. If the need was established during the check, then it must be carried out immediately, because with brakes, as we have said more than once, the jokes are very bad.

This is how the diagnostics of the brake system is presented on their own. Agree, with enough free time, patience and desire, it is quite easy to implement. And once again, we urge you to immediately eliminate them if any malfunctions are discovered, since the consequences will be extremely sad.

Finally, no matter what system in the car needs to be diagnosed or repaired, the satisfaction of this need should not be postponed. Remember: the iron horse does not forgive negligence and indifference to itself, because it is, first of all, your comrade-in-arms, with whom you are in fire, and in water and through copper pipes, you must be 100% sure of its devotion and reliability % at any time, otherwise, even the most insignificant problem will turn into a global problem.