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Anti-lock brakes (ABS)
Principle of operation Anti-lock brakes (ABS) is used to regulate the pressure in the brake mechanism of the wheels under braking in difficult road conditions to prevent the wheels from locking. The system provides: - Avoiding obstacles with a higher degree of safety, including during emergency braking; - Reduction of braking distance during emergency braking with the preservation of stability and controllability of the car, including cornering. In case of malfunction of antiblocking system provides the function of diagnosis and emergency operation of the system. Gidroelektronny control unit (GEBU) anti-lock system receives in-formation about the speed and direction of travel, and traffic conditions from the wheel speed sensors. On the basis of this data the control unit determines the best mode of braking wheels.
| Fig. 6.48. Elements of the anti-lock braking system: 1 - gidroelektronny control unit ABS (GEBU); 2 - speed sensor of the front wheel; 3 - speed sensor of the rear wheel; 4 - control lamp ABS and electronic brake force distribution; 5 - Diagnostic connector
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| Fig. 6.49. Hydraulic ABS: 1 - brake pipe right front wheel; 2 - the brake pipe of the left front wheel; 3 - the brake pipe of the right rear wheel; 4 - brake pipe left rear wheel; 5 - a brake hose right front wheel; 6 - the brake hose of the left front wheel; 7 - the brake hose of the right rear wheel; 8 - the brake hose of the left rear wheel; 9 - gidroelektronny control unit ABS (GEBU); 10 - the vacuum brake booster and master cylinder
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Elements of the anti-lock braking system is shown in Fig. 6.48. The hydraulic anti-lock braking system is shown in Fig. 6.49.
ABS control Normal braking. Under normal braking the solenoid valve is de-energized, the inlet valve is open, the outlet valve is closed. When you press the brake pedal brake fluid pressure is supplied to the wheel cylinder via a solenoid valve and causes brake operation. When the brake pedal is released, the brake fluid is returned to the master cylinder through the inlet valve and check valve. Operating mode. If emergency braking begins locking wheel GEBU gives command to the solenoid valve to reduce the flow of brake fluid, then the voltage is applied to each solenoid valve. The input valve is closed and the supply of brake fluid in the master cylinder is covered; The outlet valve is opened and the brake fluid flows through the wheel cylinder to the reservoir, which causes a reduction in pressure. Pressure maintenance mode. When the maximum pressure decrease in the wheel cylinder GEBU outputs a command to the solenoid valve to maintain the brake fluid pressure, the input voltage is applied to the valve and not supplied to the outlet valve. At the same inlet and outlet valves are closed, and the brake fluid from the wheel cylinder-tion does not go away. Mode pressure rise. If GEBU determines that the wheel is not blocked, it de-energizes the solenoid valve. The voltage on the solenoid valve is not applied, the brake fluid through the inlet valve into the wheel cylinder, giving-tion which increases.
Electronic brake force distribution (EBD) Electronic brake distribution (EBD) - ABS is a subsystem, which serves to provide efficient coupling of the rear wheels with the road surface. In addition, the EBD system prevents lock and skid the rear wheels in the partial braking mode. If you have a brake force distribution braking force is maintained close to the optimum value and is regulated by an electronic system that allows you to do without the usual pressure regulator. Since the pressure regulator - a mechanical device, its scope is limited in terms of achieving the ideal brake force distribution between the front and rear wheels as well as the flexible brake force distribution depending on the vehicle load. Furthermore, mechanical failure of the pressure regulator driver usually is not detected. Electronic brake force distribution (EBD) is controlled by management ABS. When driving brake force distribution is constantly determines the degree of slip of each wheel of a vehicle and controls the fluid pressure in the rear wheel brake mechanism so that it is higher than the pressure in the front wheel brake mechanism. In case of failure (Table 6.1.) Brake force distribution (EBD) in the instrument cluster warning lamp EBD (and parking brake).
Table 6.1 Work systems ABS and EVD detection of faults
The advantages of the electronic brake force distribution are as follows. 1. Improving the primary braking system. 2. Compensation difference in the coefficients of friction (for each wheel of the car). 3. No need for a conventional pressure regulator. 4. Failure Alarm via a control lamp on the instrument panel.
Lamp control
| Fig. 6.50. Indicator lamps ABS and EBD
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Location of control lamps ABS and EBD in the instrument cluster is shown in Fig. 6.50. The module control lamp ABS. ABS warning lamp indicates the degree of performance ABS. The warning lamp lights up in the following cases: - In the initialization phase after switching on the ignition (3); - In the case of the ban on the action of ABS at fault; - If the computer does not turn on when the ignition; - In diagnostic mode. Lamp Module EBD. The indicator lamp shows the degree of efficiency EBD EBD. The warning lamp lights up in the following cases: - During the initialization phase after switching on the ignition (3); - In the case of the ban on the action of EBD at fault; - If the computer does not turn on when the ignition; - The parking brake or the brake fluid level is too low.
NOTE The following phenomena do not indicate a defect in ABS or EBD. |
Features of the ABS system Sound checking system ABS. When starting the engine from the engine compartment is sometimes heard a thud. It is linked to the System Health Validator. The sound during the term ABS. The sound of the motor hydraulic unit ABS (howling sound). Scraping sound followed by a vibration of the brake pedal. While ABS acts on the vehicle chassis are sounds that are caused by repetitive cycles of braking and brake release wheels (thumping coming from the suspension, the creak of the tire). Big stopping distance. Some road surfaces, including snow-covered roads or gravel, the braking distance of vehicles equipped with ABS, can be more than usual. Therefore, when driving on such roads should be the owner of the vehicle to be cautious and move at a reduced speed. The vibration of the brake pedal is normal. ABS fault codes are listed in Table. 6.2.
Table 6.2 Fault codes ABS Brakes
| Fig. 6.51. Cable connector gidroelektronnogo ABS control unit
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Cable connector gidroelektronnogo ABS control unit shown in Fig. 6.51. Addressing the connector cable gidroelektronnogo ABS control unit is shown in Table. 6.3.
Table 6.3 Addressing connector pins gidroelektronnogo control unit (GEBU) ABS system room contact | Address (assignment) | Maximum amperage | Minimum amperage | Note | 1 | - | - | - |
| 2 | - | - | - |
| 3 | - | - | - |
| 4 | The indicator lamp EBD | 30 mA | 5 mA |
| 5 | Interface diagnostics | 6 mA | 3mA |
| 6 | Right front wheel sensor | 16 mA | 6 mA |
| 7 | Right front wheel sensor | 16 mA | 6 mA |
| 8 | Right rear wheel sensor | 16 mA | 6 mA |
| 9 | - | - | - |
| 10 | The left rear wheel sensor | 16 mA | 6 mA |
| eleven | Left front wheel sensor | 16 mA | 6 mA |
| 12 | "Mass" | A 5-15 | 2.5 A | ABS control | 13 | Voltage A / B 1 (power lapane) | A 5-15 | 2A | ABS control | 14 | Voltage A / B 2 (motor power) | A 20-39 | 10A | ABS control | 15 | "Mass" | A 20-39 | 10A | ABS control | 16 | - | - | - |
| 17 | - | - | - |
| 18 | - | - | - |
| 19 | - | - | - |
| 20 | ABS warning lamp | 30 mA | 5 mA |
| 21 | - |
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| 22 | Brake Light Switch | 10 mA | 5 mA |
| 23 | Right rear wheel sensor | 16 mA | 6 mA |
| 24 | Ignition | 1A | 500 mA |
| 25 | The left rear wheel sensor | 16 mA | 6 mA |
| 26 | Left front wheel sensor | 16 mA | 6 mA |
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Removal and installation of elements of the anti-lock brake system Gidroelektronny control unit (GEBU) ABS Withdrawal Remove the air filter and air intake tube.
Disconnect the connector GEBU (Fig. 6.52) with a double lock by pulling it up. Disconnect the brake pipes GEBU.
| Fig. 6.53. GEBU bracket bolts (arrows)
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Tightening torque bracket GEBU - 8-10 Nm.
WARNINGS Dismantling GEBU not allowed. It allowed the transport and storage GEBU upright with plugged holes. Do not drain fluid from GEBU. |
Setting Installation GEBU spend in the reverse order of removal. Tighten GEBU torque 8-10 Nm, the union mount brake Trou-laying torque 13-17 Nm. Checking the voltage signal speed sensors Install the vehicle on a lift, turn off the parking brake. Disconnect the connector GEBU and perform checks on the contacts of the cable connector.
NOTE When checking remove the double lock connector and attach the wires to the control panel on the side opposite to the pin terminals. Connecting the device to the measuring probes by the contacts does not provide a reliable connection |
Use a tester or an oscilloscope, check the voltage of the signal speed sensors, wheel rotating at a speed corresponding to 0.5-1 s -1. Connecting the control unit to check the speed sensor signal voltage Wheel sensor Pin Numbers Left Front .............. 11 26 Right front ............ 6 7 Left Rear .................. 10 25 Right back ................ 8 23 Voltage signal as measured by an oscilloscope, In: lower level ..... 0,535 (at a current of 7 mA) top level ..... 1,050 (at a current of 14 mA)
Wheel speed sensor
| Fig. 6.54. The gauge of speed of rotation of the front wheel: 1 - pin speed sensor front wheel; 2 - speed sensor of the front wheel
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| Fig. 6.55. Speed Sensor Rear wheels: 1 - the gauge speed of the rear wheel
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Removing the front wheel sensor
| Fig. 6.56. Bolt front wheel sensor
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In the engine compartment, disconnect the connector of the front wheel sensor. Remove the fastening elements of the wheel sensor wiring (see. Fig. 6.54). Remove the wheel sensor. Removing the rear wheel sensor Disconnect the connector on the rear wheel sensor wheel hub (see. Fig. 6.55). Remove the brake drum by removing the screw securing it to the wheel hub. Remove the four screws on the hub of the rear wheel to the rear axle.
| Fig. 6.57. Removing the rear wheel hub
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Remove the hub of the rear wheel through a braking mechanism (Fig. 6.57).
A WARNING Do not remove the wheel hub with a sensor with a hammer, as this may cause damage to the sensor failure. |
Removal of air from hydraulic brakes The operation is performed to effectively remove the air from the hydraulic brakes and brake fluid filling the hydraulic unit Anti-lock braking systems, brake lines and the brake master cylinder. To remove air from the hydraulic brakes of vehicles equipped with anti-lock braking system, use the diagnostic tool HI-SCAN. During this operation, the device connected to the diagnostic connector under the dashboard, controls the solenoid valves and electric pump anti-lock system. Remove the brake fluid reservoir cap and fill the brake fluid reservoir. For topping up, use only brake fluid DOT-3 or DOT-4.
A WARNING If you get brake fluid in the body paintwork, wash immediately with plenty of water. |
NOTE When using a special installation for the removal of air, do not press the brake pedal. |
Attach a clear plastic hose to the bleeder valve on the wheel Qi-cylinder and lower the other end of the hose into a transparent container half-filled with brake fluid. Connect the device to the HI-SCAN diagnostic connector located under the dashboard. The instrument HI-SCAN switch electric solenoid valves and the anti-lock system. Proceed according to the instructions on the screen of the device HI-SCAN.
A WARNING To prevent burnout of the windings of the motor pump anti-lock system does not exceed the maximum working time specified on the instrument HI-SCAN. |
Repeatedly press the brake pedal, opening the bleeder valve as long as the effluent air bubbles stop appearing, then tighten the bleeder valve. Perform the operation on the remaining wheels of a vehicle in the following order: rear right wheel (in direction of travel), the front left wheel, the rear left wheel, the front right wheel. Tightening torque pumping fittings 7-13 Nm.
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