VW Passat repair


+ 1. Ekspluatatsiiya of the car
+ 2. Maintenance
+ 3. Engines
+ 4. Cooling system
+ 5. Power supply system
+ 6. Ignition system
+ 7. Coupling
+ 8. Transmission
+ 9. Drive of forward wheels
+ 10. Suspension brackets
+ 11. Steering
- 12. Brake system
   12.1. Technical characteristics
   12.2. General information
   + 12.3. Maintenance
   + 12.4. Replacement of forward brake shoes
   12.5. Replacement of a forward support
   12.6. Replacement of a forward brake disk
   12.7. Replacement of a brake drum and back brake shoes on brakes of drum-type type
   12.8. Wheel cylinder of the back brake mechanism
   12.9. Replacement of brake shoes on back disk brakes
   12.10. Replacement of a support of the back brake mechanism
   12.11. Pressure regulator
   12.12. Main brake cylinder
   12.13. Tubes and hoses of brake system
   12.14. Air removal from a hydraulic actuator of brake system
   - 12.15. Anti-blocking system of brakes (ABS)
      12.15.1. Action principle
      12.15.2. Anti-blocking system of brakes with an electronic differential blokirator (EDS)
   12.16. Brake pedal
   12.17. Lever of the parking brake
   12.18. Cables of the parking brake
   12.19. Adjustment of the parking brake
   12.20. Vacuum amplifier of brakes
   12.21. Stoplight switch
   12.22. Elimination of noise of brakes
+ 13. Wheels and tires
+ 14. Systems of heating, ventilation and conditioning
+ 15. Electric equipment
+ 16. Body
+ 17. Electric circuits


Repair B3-B4/Passat B3-B4 Volkswagen Passat>> Brake system>> Anti-blocking system of brakes (ABS)>> Action principle
The greatest efficiency of braking is reached at the maximum coupling of the tire with a road surface. When sliding tire on a surface in the course of braking linear speed of a wheel becomes less speed of the car. The minimum sliding (0 %) is reached at freely sliding wheel, and maximum (100 %) — if the wheel is blocked. Optimum efficiency of braking is reached at the sliding equal of 15 %. At such size of sliding stability and controllability of the car fully remains.
The anti-blocking system is intended to limit the pressure created in hydraulic system of brakes the size of sliding was close to the optimum. The action principle is put in a basis of work of anti-blocking system separate for each wheel. The system is urged to react immediately to each change of factor of coupling of a wheel with a surface and loads of the car.
The anti-blocking system interferes with blocking of wheels at sharp braking. Thanks to it the brake way decreases, especially at low coupling with a paving at a rain and snow. Force of adhesion between wheels and the road is more, if when braking a wheel continue rotation. Besides, even at complete braking the car remains operated. Sensors of turns — on one on each wheel — measure speed of rotation of wheels. On signals, postupayemy from sensors, the electronic control unit calculates the average speed approximately corresponding to speed of movement of the car. Comparing speed of rotation of each separate wheel with the average calculated speed, the electronic block defines factor of a proskalzyvaniye of each separate wheel and by that defines, what wheel is in a preblocking condition.
When one of four sensors of speed of rotation of a wheel will transmit a signal about blocking of the corresponding wheel, the electronic actuation device will give out a signal of closing to the corresponding inlet electromagnetic valve which will immediately block supply of brake liquid via the brake pipeline to a brake of this wheel and force of braking remains to a constant. If sliding after all proceeds, the final valve will open and pressure in hydraulic system of this brake mechanism will decrease. As soon as the wheel again will start to rotate, will open inlet and the final valve will be closed. Pressure will increase in a contour, and the wheel will begin again braking.
The cycle of braking and free rotation of a wheel is carried out for very short period (several times in a second) and repeats to a full stop of the car or to an otpuskaniye of a pedal of a brake. Action of this process extends on each separate wheel.
The system of an emergency shutdown provides ABS system shutdown at any malfunction or at low (below 10 In) tension in an onboard network of the car.
The electronic actuation device carries out also diagnostic function, warning the driver fire of a control lamp about registration of malfunction of electric chains or elements of anti-blocking system. At faulty system ABS of a brake continue to work in a usual mode (without anti-blocking).
Fire of a control lamp of ABS during movement signals about malfunction and system shutdown. In this case it is necessary to arrive as follows:
stop the car, switch off and again start the engine;
check tension of the storage battery. In case tension is lower 10,5 In, the storage battery is required to be charged;

       PREVENTION
If the control lamp of ABS burns at the beginning of a trip, and then dies away, it means that tension was below an admissible limit for ABS work, but then raised as a result of operation of the generator.

check, whether conclusions of the storage battery were oxidized;
will hang out the car, remove wheels and check serviceability of electroconducting of sensors of speed of rotation of wheels;
if malfunction is not revealed, further check of anti-blocking system of brakes is necessary for carrying out at specialized service station.

       NOTE
Since June, 1988 the ABS control unit has the module defining and remembering defects, arising in use. At service station information is read out from the block of memory and defect is eliminated.