Some VW Passat cars in addition to the ABS system can be equipped with system of the electronic mechanism of blocking of differential (EDS). Being additional in relation to the ABS system, the EDS system reduces torque transmission of the engine under adverse traffic conditions, especially, on rises and at accelerations of the car by method of elimination of pro-slipping of one of driving wheels, and also start-off from the place and dispersal. Thanks to the electronic mechanism of blocking of differential improvement of torque transmission as at the same time the party with great value of coefficient of friction can transfer bigger torque is reached. Electronic blocking of differential begins to work at start-off from the place and is automatically turned off at a speed of 40 km/h. The fact that in the start-off mode from the place it does not exert negative impact on the mode of the movement of the car and comfort of management belongs to one of advantages of such way of improvement of traction effort.

Principle of action of EDS

Fig. 12.22. The brake system of the car equipped with ABS: 1 – ABS sensor; 2 – forward brake disk; 3 – ABS sensor rotor; 4 – ABS electronic control unit; 5 – back brake disk; 6 – electric conducting; 7 – hydraulic modulator; 8 – block of valves; 9 – brake tubes

The electronic control unit obtains constant information from ABS sensors on the speed of rotation of driving wheels and in the presence of a speed difference over about 110 min.-1 EDS joins automatically and reduces torque transmission by the revolving wheel until its speed is approximately equal speed of the slipping wheels. Thanks to such management the increased torque is transferred to a wheel with the best conditions of coupling with the road. The EDS system as it was already mentioned, is automatically disconnected at a speed of the movement of the car over 40 km/h, and also during the passing of turns and an overheat of brakes. The EDS system is reliably protected from failures of management of brakes. In the EDS system a number of elements of the ABS system are used. In case the car is equipped with the EDS system, the hydraulic ABS unit is equipped with the additional block of EDS valves, and ABS 4 electronic control unit ( fig. 12.22 ) has the "sewed" program memory of EDS.

Hydraulic block

Fig. 12.23. ABS block: 1 – pusher; 2 – pressure accumulator; 3 – hydraulic pump; 4 – block of valves; 5 – main brake cylinder; 6 – tank; 7 – stopper

The hydraulic block and its components are presented in fig. 12.23 and 12.24 .

Fig. 12.24. ABS block elements: 1 – stopper; 2 – tank; 3 – clip of brake tubes; 4 – arm; 5 – nut; 6 – bolt; 7 – laying; 8 – pressure sensor; 9 – connecting hose; 10 – pressure accumulator; 11 – sealing ring; 12 – hydraulic pump; 13 – brake tube; 14 – block of valves; 15 – block of the hydraulic amplifier and main brake cylinder; 16 – sealing plug; 17 – plug; 18 – sealing ring

NOTE After carrying out any kind of repair work in anti-blocking system it is necessary to carry out diagnostics of serviceability of system at VW service station with use of the special equipment.

You make removal of the hydraulic block in the following order:

before work disconnect a "minus" wire from the plug of the rechargeable battery;

— to get access to the ABS control unit, remove an air inlet branch pipe between the air filter and the case of throttles;

— press a brake pedal about twenty times (at the same time the effort made for a brake pedal has to increase) to remove pressure in pressure accumulator;

— disconnect electric sockets and the tire of grounding from the ABS block;

— uncover a tank and pump out brake fluid from a tank;

— having turned off connecting nuts, disconnect brake tubes from the block. Muffle the ends of tubes the corresponding traffic jams;

— in interior of the car from the driver remove the lower finishing of the dashboard;

— remove a lock ring and take a pin from a brake pedal pusher;

— turn off nuts of fastening of the hydraulic block and remove the block.

You make installation in the sequence, the return to removal.

Before installation of an air branch pipe remove air from the brake system.

Electronic control unit

The electronic control unit is located under the left pillow of back sitting.

You make removal of the block in the following order:

— before work disconnect a "minus" wire from the plug of the rechargeable battery;

— remove a pillow of a back seat;

— release a clip and disconnect the contact electric socket from the block;

Fig. 12.25. Arrangement of screws of fastening of the electronic block управленияРис. 12:22. The brake system of the car equipped with ABS: 1 – ABS sensor; 2 – forward brake disk; 3 – ABS sensor rotor; 4 – ABS electronic control unit; 5 – back brake disk; 6 – electric conducting; 7 – hydraulic modulator; 8 – block of valves; 9 – brake tubes

— having unscrewed two screws of fastening ( fig. 12.25 ), remove an electronic control unit.

You carry out installation to the sequences, the return to removal.

Make sure that the clip accurately fixed the contact electric socket on the block.

Relay and safety locks

The anti-blocking system has two relays: one general relay of system and relay of the hydraulic pump. Both relays are placed over the main block of safety locks and the relay under the dashboard, from the driver.

Wheel speed sensors

Fig. 12.26. Principle operation of the sensor of speed of a wheel: 1 – wheel speed sensor; 2 – magnetic field; 3 – gear rotor; 4 – electric signal

The gear rotor 2 ( fig. 12.26 ) the sensor, rigidly fixed in a wheel nave, rotates together with a wheel. Teeths of the rotor passing through magnetic field And the sensor 1 induce an electric signal In, proportional to the speed of rotation of a wheel which is transferred to an electronic control unit.

You make removal in the following order:

— before work disconnect a "minus" wire from the plug of the rechargeable battery;

— you will hang out a forward or back part of the car and record on basic racks;

— remove the corresponding wheel;

Fig. 12.27. Wheel speed sensor

— having turned off a fastening bolt, remove the sensor ( fig. 12.27 ) from a rotary fist or a pin.

You carry out installation of the sensor to the sequences, the return to removal.

Before installation of the sensor, apply on it paste for the brake cylinder.

Gear rotors of sensors

Forward gear rotors are located on internal surfaces of naves of a forward wheel.

For removal of a forward rotor remove a nave of a wheel and separate a rotor from a nave.

Back rotors are located in back naves of a brake disk.

You make removal of a back rotor in the following order:

— before work disconnect a "minus" wire from the plug of the rechargeable battery;

— for removal of a rotor remove a brake disk;

— pass a core through an opening under a bolt of fastening of a wheel and take a rotor from a nave.

You make installation of rotors in the sequence, the return to removal.

At installation of a gear rotor it is necessary use a tubular mandrel of the corresponding diameter.

Pressure sensor

On early models of cars the sensor of pressure is installed in the case of the main brake cylinder, and on the cars released since January, 1989, the sensor is installed on the case of the hydraulic pump.