S-class W202 Mercedes
1993-2000 of release
Repair and car operation
+ 1.2. General information
+ 2. Maintenance
+ 3. Engines
+ 4. Greasing system
+ 5. Cooling system
+ 6. Heating, ventilation
+ 7. Ignition system
+ 8. Fuel system
+ 9. Transmission
+ 10. Running gear
+ 11. Steering
- 12. Brake system
12.2. Anti-blocking system – ABS
12.3. The additional equipment – ASR system
12.4. Specifications of brake system
12.5. Overlays of forward brake shoes
+ 12.6. Overlays of back disk brakes
12.8. Forward brake disk
12.9. Back brake disk
12.10. Brake liquid
12.11. Air removal from brake system
12.12. Brake pipelines / hoses
12.13. Replacement of brake highways
12.14. Brake shoes of the parking brake
12.15. Adjustment of the parking brake
12.16. Stoplight switch
12.17. Diagnostics of malfunctions of brakes
+ 12.18. Wheels and tires
+ 13. Body
+ 14. Electric equipment
+ 14.2. Electroschemes
12.2. Anti-blocking system – ABS
The serial system ABS prevents blocking of brakes at sharp braking. Thanks to it the car remains operated. The ABS system works at speed more than 5 km/h and at the included ignition. It completely regulates braking process if speed of the car at least once exceeded 8 km/h.
The system measures speed of rotation of wheels by means of two sensors on forward wheels and one sensor – on back. On signals of separate sensors the electronic device calculates rough average speed of the car. The operating device defines extent of pro-slipping of a separate wheel by comparison of speed of the car and establishes, brakes are how close to blocking.
As soon as the wheel showed tendency to blocking, the ABS system blocks pressure upon a brake, keeping its this condition. It means that pressure in the brake mechanism does not raise even in that case when pressing a pedal of a brake increases. If there is a tendency to blocking further, pressure in this brake decreases ABS system at the expense of opening of the final valve. This process goes until the wheel again will not start to be accelerated.
If the wheel again starts to be accelerated, ABS increases pressure in its brake system, but it does not reach value of pressure in the general brake system. This process repeats at sharp braking for each wheel so long, the brake pedal, respectively, to a full stop of the car (speed of 3 km/h) will not be released yet.
The safety system in an electronic monitor watches that ABS was disconnected at a faulty food or too low voltage (tension on the accumulator less than 11 In); in this case on the dashboard during a trip the control radiator of ABS lights up. The brake system thus functions as usual. The car when braking behaves as if the ABS system is absent.
The hydraulic device consists of the pump of return giving, and also from three electromagnetic valves – on one for forward wheels, and one – for back brakes.
Pressure increase: the inlet valve in the device of the electromagnetic valve is open, pressure of liquid in the brake mechanism can raise to value which is provided with the main brake cylinder.
Pressure is constant: inlet and final valves in the device of the electromagnetic valve are closed. Pressure of liquid in the brake mechanism does not change, even if pressure between the main brake cylinder and the electromagnetic valve raises.
Pressure decline: the inlet valve in the electromagnetic valve is open. Brake liquid follows via the store from which it is downloaded back in system of the main brake cylinder by the pump of return giving.
It is required, that liquid from the main brake cylinder was not lost. Operation of this pump is felt on appreciable pulsations of a brake pedal. Noise of the pump are weakened by means of a damper of a brake contour.
If during a trip the ABS indicator lights up, it specifies that the ABS system is disconnected.
Further checks of ABS should be carried out in a workshop. The operating device tests ABS system before each trip and remembers the appeared malfunctions which codes remain in his memory even at accumulator shutdown. In firm workshops these mistakes will be decoded by means of the special device, and then purposefully eliminated.