14.9. Antiblocking system (ABS)
The principle of action of antiblocking system ABS is not considered in the present management, however it is necessary to stop on following moments:
- If the car is equipped ABS usually on the back bridge disk brakes are established. At cars of mark Polo the given system is established at presence on the back bridge of drum-type brakes;
- Safety determinative at work ABS is ability to interfere with blocking of wheels at sharp braking of the car that improves controllability. Even at emergency braking the chance to go round an obstacle without danger of drift of back wheels always remains. It is not necessary to forget that ABS cannot work wonders. At too high speed can bring the car and with ABS;
Fig. 311. Installation of a gear wreath and the electronic gauge of frequency of rotation of a wheel on back drum-type brakes: 1 — a gear wreath; 2 — the electronic gauge
Fig. 312. Installation of a gear wreath and the electronic gauge of frequency of rotation of a wheel on forward disk brakes: 1 — a gear wreath; 2 — the electronic gauge
- Established in rotary fists and naves of a back wheel four electronic gauges constantly, independently from each other supervise frequency of rotation of the gear wreaths established on wheels. On fig. 311
it is shown, where gauges and gear wreaths are established. Signals from gauges arrive in the electronic block of management which registers them and analyzes deviations from norm in comparison with the braking program. As a result the brake effort rendered on the corresponding wheel in a combination to work of hydraulic system of the given brake, decreases or increases with frequency from four to ten times a second, that is much faster, than it can achieve periodic pressing of a pedal of a brake, but also, the brake effort is regulated on each wheel separately, instead of on all wheels simultaneously by pressing a brake pedal cars without ABS;
- Two hydraulic valves precisely distribute necessary brake effort between forward brakes depending on a road condition. Two more regulating valves operate back brakes. In this case the electronic block of management weakens brake effort to a wheel which is blocked by the first. At optimum factor of braking the car remains operated, its stability and the control over a situation remain.
Fig. 313. The scheme of antiblocking system (ABS): 1 — the electronic gauge of frequency of rotation of a forward wheel; 2 — a forward wheel; 3 — the two-planimetric pump with the electric motor; 4 — the gauge of a course of a pedal of a brake; 5 — the main brake cylinder; 6 — a broad tank; 7 — the vacuum amplifier; 8 — a back wheel; 9 — the electronic gauge of number of turns of a wheel; 10 — a pressure regulator; 11 — hydraulic valves; 12 — the electronic block of management
On fig. 313
scheme ABS is resulted.
As system ABS should provide additional safety, it is not recommended to spend on it any works, despite the fact that what some of them are simple for executing. Nevertheless at performance of some works on brake system with ABS it is necessary to observe following requirements:
- Before dismantling carefully to clear all connections and elements of the equipment directly adjoining to them;
- The surface where the removed details take places, should be pure. The detail should cover with a film or a white paper. Not to use for this purpose fleecy rags;
- Carefully to close open parts of system or to close them if repair cannot be begun immediately. It concerns especially those cases when the car should be put on open parking;
- To establish only absolutely pure details. Not to establish at all again the details which were long time in storage;
- In the presence of air compressors always there is a temptation to use compressed air for cleaning of details. In no event it is impossible to do it if system connections are opened.
After ignition inclusion the hydraulic pump during 60 with creates working pressure in system. Alarm lamp ABS lights up for a while from 2 to 20 with depending on pressure in system. The electronic block of management begins check of work of all components of system. At detection of any malfunctions the brake system works, as usual system without ABS. If it occurs (alarm lamp ABS continues to burn) it is necessary to address in car-care centre where by means of special devices will define malfunction in system which can be connected with failures in an electric equipment or in a hydraulic contour of system.