Mercedes W124

since 1985-1995 of release

Repair and car operation



W124 Mercedes
+ Governing bodies and control devices
+ MAINTENANCE
+ 2. Maintenance (diesel engines)
+ ENGINE
+ 4. Repair of 6-cylinder petrol SOHC engines
+ 5. Repair of 6-cylinder petrol DOHC engines
+ 6. Repair of the diesel engine established in the car
+ 7. Major maintenance of engines
+ COOLING SYSTEM
+ FUEL SYSTEM
+ 10. System of injection of BOSCH CIS-E fuel (KE-JETRONIC)
+ 11. System of injection of BOSCH HFM fuel
+ 12. Fuel system of diesel engines
+ 13. Fuel system of diesel engines
+ SYSTEMS OF START, IGNITION
+ 15. System of ignition of 4-cylinder petrol engines
+ 16. System of ignition of four-cylinder petrol engines
+ PRESTARTING HEATING
+ TRANSMISSION
+ 19. Mechanical transmission
+ 20. Automatic transmission
+ POWER SHAFTS
- BRAKE SYSTEM
   22.2. General information
   22.3. Pumping of hydraulic brake system
   22.4. Brake pipelines and hoses
   + 22.5. Replacement of forward brake shoes
   22.6. Replacement of back brake shoes
   22.7. Forward brake disk
   22.8. Back brake disk
   22.9. Forward brake support
   + 22.10. Support repair
   22.11. Back brake support
   22.12. Main brake cylinder
   22.13. Vacuum amplifier of brakes
   22.14. Unilateral valve of the vacuum amplifier of brakes
   22.15. Adjustment of the parking brake
   22.16. Brake shoes of the parking brake
   22.17. Pedal of the parking brake
   22.18. Cables of the parking brake
   22.19. Stoplight switch
   22.20. Anti-blocking system (ABS)
   + 22.21. Elements of anti-blocking system
   22.22. The vacuum pump on models with diesel engines
+ SUSPENSION BRACKET
+ BODY
+ ELECTRIC EQUIPMENT
+ CHECK OF MALFUNCTIONS






22.20. Anti-blocking system (ABS)

GENERAL INFORMATION

Prevention

On models with a control system of speed of movement the ABS block carries out functions of anti-blocking brake system (ABS) and a control system of speed of movement of the car (ASR).


Models without a control system of speed of movement of the car

The anti-blocking system is established by the producer on the majority of cars, and on the remained cars it is possible to establish as the additional equipment. The system consists of the hydrodevice with three hydraulic electromagnetic valves on one on each forward brake and one valve on back brakes, the pump with the electric drive, three sensors of a wheel and the electronic control device (ECU). The anti-blocking system prevents blocking of wheels at sharp braking. Thanks to it the car at complete braking remains operated. On the basis of signals from wheel sensors the ECU block can define speed of the car. At the expense of comparison of speed of separately taken wheel with average speed of the car the control unit defines a condition of blocking of a wheel. When the wheel comes nearer to blocking, pressure of brake liquid is too high, therefore pressure in a support decreases on a signal to the control unit at the expense of turning on of the corresponding electromagnetic valve which isolates a support of the corresponding brake from the main brake cylinder.

If speed of rotation of a wheel continues to decrease, on a signal of the ECU block the returnable pump turns on and pumps out liquid from the corresponding support in the main brake cylinder. After the wheel starts to rotate with normal speed, the pump is switched off and the electromagnetic valve therefore brake liquid moves to a support in a normal mode opens and wheel braking is made. Work of anti-blocking system at sharp braking repeats on each wheel until the effort or the car is made a pedal will not stop. The cycle of work of anti-blocking system repeats to 10 times a second. At work of anti-blocking system the pulsation on a brake pedal is felt.

At any malfunction in anti-blocks to rovochny system there is its shutdown. The control lamp of ABS on the dashboard in this case lights up and the brake system works in a usual mode. Elimination of malfunctions of anti-blocking system is necessary for making at service station.

Models with a control system of speed of movement of the car (ASR)

On models with a control system of speed of movement of the car the hydraulic system consists of four electromagnetic valves, the returnable pump with an electric drive, the valve which switches the hydraulic device from anti-blocking system to performance of functions of a control system by speed of movement of the car and the pressurizing valve of a control system in the speed of movement. On the car two electronic control devices (ECU) one of which operates the hydraulic block, and the second – executive mechanisms of provision of a butterfly valve are established. Additional pump and the pressure accumulator are also established. To create and support pressure in the system, necessary for performance of functions of braking at work of a control system as speed of movement of the car.

The control system of speed of movement of the car excludes loss of coupling of wheels with a paving. The system corrects speed of rotation of back wheels at the expense of braking of a wheel or butterfly valve closing depending on speed of movement of the car. In certain cases it can be made both wheel braking, and butterfly valve closing.

Braking of a wheel is carried out as follows. At loss of coupling of a wheel with a paving the wheel starts to rotate with the increased speed, and the hydrodevice from the accumulator of pressure submits under pressure brake liquid to a support of the corresponding wheel and затормаживает a wheel. After wheel return to normal speed of rotation the hydrodevice returns liquid in the pressure accumulator.

Management of a butterfly valve occurs as follows. After loss of coupling of a wheel with a paving the second electronic control device puts in action the executive mechanism of a butterfly valve which, closing a butterfly valve, reduces engine turns. As soon as the wheel starts to rotate with normal speed, the executive mechanism of a butterfly valve returns it in a starting position.

At detection of malfunctions in a control system of speed of movement of the car it is necessary to address on service station.