- 1 - ASR switch;
- 2 - stoplight switch;
- 3 - rear left wheel speed sensor;
- 4 - rear right wheel speed sensor;
- 5 - right front wheel rotation speed sensor;
- 6 - left front wheel rotation speed sensor;
- 7 - control unit ABS / EBV / EDS / ASR / MSR;
- 8 - control lamp ABS / EDS;
- 9 - control lamp ASR / ESP;
- 10 - brake fluid level control lamp;
- 11 - master brake cylinder, vacuum brake booster and brake pedal;
- 12 - hydraulic block
ABS. Anti-Lock Braking System
Braking efficiency is greatest when the grip of the tire with the road surface is maximum. During braking, the tire slides over the surface and the circumferential speed of the wheel becomes less than the speed of the car.
Slip minimum (0%), when the wheel rolls freely, and the maximum (100%), when the wheel is locked. Maximum braking performance is achieved when the slip is 15%. This value also allows you to maintain the stability and controllability of the car.
The role of the anti-lock braking system is to limit the pressure generated in the hydraulic brake system so that the amount of slip is kept near the optimum amount (15%). The action of this system must be immediate and separate for each wheel. The system must immediately respond to every surface change (adhesion coefficient) and vehicle loads.
The anti-lock braking system performs the functions of power supply, brake drive and vacuum booster, as well as anti-lock wheel control. The hydraulic block is installed instead of the standard installed vacuum booster with an integrated brake master cylinder. The installation of ABS is only possible at the factory during the manufacture of the vehicle and cannot be installed additionally. The anti-lock braking system prevents the wheels from locking during heavy braking. This reduces the braking distance, especially when grip is low in rain and snow. The grip force between the wheels and the road in this case is greater when the wheels continue to rotate during braking. In addition, even with full braking, the car remains steerable. RPM sensors, one for each wheel, measure wheel speed. Based on the signals from the wheel speed sensors in the electronic control unit, the average speed is calculated, approximately corresponding to the speed of the vehicle. By comparing the rotation speed of each individual wheel with the average calculated speed, the electronic unit determines the slip state of the individual wheel and thereby determines which wheel is in the pre-lock state.
When one of the four speed sensors transmits a lock signal to the corresponding wheel, immediately the electronic control device issues a close signal to the corresponding inlet solenoid valve, which immediately shuts off the flow of brake fluid through the brake pipeline to the brake of that wheel - the braking force remains constant. If the sliding still continues, then the release valve opens and the pressure in the hydraulic system of this brake decreases - the wheel does not brake (excess brake fluid returns to the reservoir). As soon as the wheel begins to rotate again, the intake valve immediately opens and the exhaust valve closes. The pressure in the circuit increases and the wheel is braked again.
This cycle of braking and free spinning of the wheel is very fast (several times per second) and continues until the car stops or until the brake pedal is released.
This process is repeated during hard braking separately for each wheel until the brake pedal is released or when the vehicle speed decreases to 2-3 km / h. The driver determines the operation of the ABS by the pulsation of the brake pedal.
The emergency shutdown system ensures that the ABS system is turned off in case of any malfunction or low voltage in the vehicle's electrical network (below 10V).
The electronic control device also performs an auto-diagnostic function, warning the driver by illuminating a control lamp about the registration of a malfunction of electrical circuits or elements of the anti-lock braking system. If the ABS system is faulty, the brakes are still intact and function as if the system were not in the car.
EBV. Electronic brake force distribution on the rear wheels
The electronic brake force distributor performs the functions of a mechanical pressure regulator, but works more accurately and has a wider adjustment range. When driving in a straight line, the brake fluid supply to the rear wheel brakes is fully open. To ensure stable cornering with braking, the supply of brake fluid to the rear brakes is limited. Based on the signals from the ABS wheel rotation sensors, the EBV control unit determines when the vehicle is moving in a corner. When the vehicle is cornering, the braking force transmitted to the rear wheels is reduced, resulting in less chance of the vehicle skidding.
EDS. Electronic differential lock
As an addition to the ABS elements, EDS reduces the transmission of engine torque under adverse driving conditions, especially on hills and during vehicle acceleration, eliminating slippage of one of the drive wheels. Thanks to the mechanical differential lock, better torque transmission is achieved, since the side with a higher friction coefficient can transmit more torque.
The electronic control unit receives information from the ABS sensors about the speed of rotation of the drive wheels and constantly compares them. If there is a difference in speed of more than about 110 rpm, the EDS will automatically turn on and reduce the transmission of torque to the spinning wheel until it has approximately the same speed as the non-spinning wheels. This control achieves that an increased torque is transmitted to the wheel with the best traction conditions. EDS is automatically deactivated at vehicle speeds above 40 km/h, as well as when cornering and when the brakes overheat.
ASR. Reducing the torque transmitted to the drive wheels
Reducing the torque when slipping both drive wheels is carried out by reducing engine power. In this case, the engine power is limited in such a way that only the torque necessary to move the car is transmitted.
The ASR system must always be on. Only in certain exceptional cases, when wheel spin is desired, is it preferable to switch the system off.
MSR. Anti-blocking system for drive wheels
The MSR system is installed on vehicles with TDI diesel engines and prevents the drive wheels from locking up on slippery roads if the driver abruptly releases the accelerator pedal. In this case, the ABS sensor sends a signal to the engine control unit and it briefly increases the engine speed, as a result of which the wheels begin to rotate without blocking and the car remains normally controlled.
In the event of a malfunction, the electronic control system is automatically switched off, and the indicator lamps in the instrument cluster light up. In this case, the braking system operates normally.
If the ABS and EBV warning lights come on while driving, be aware that the rear wheels may lock up during heavy braking.
When one or more warning lights come on while driving, the system is deactivated. In this case, you must perform the following steps.
Order of execution
1. Stop the car, turn off and start the engine.
2. Check battery voltage. If it is below 10.5V, charge the battery.
Warning: If the ABS warning light comes on at the beginning of a trip and then goes out, this indicates that the voltage was within the acceptable limit for ABS operation, but then increased as a result of the alternator.
3. Check the condition of the battery terminals.
4. Raise the vehicle, remove the wheels and check the wiring of the wheel speed sensors.
5. If the fault persists, further checks must be made at a service station.
Visitor comments