12.23. Antiblocking system (ABS)

THE GENERAL DATA

Antiblocking system of brakes (Bendix ABS)

1 – the electronic operating module, 2 – hydraulic knot, 3 – knot of the pump with an electric drive,

4 – gauges of forward wheels, 5 – gauges of back wheels

Function chart Bendix ABS

1 – knot of the pump with an electric drive, 2 – the gauge 16,0 МПа, 3 – the gauge 18,0 МПа, 4 – the gauge 9,0 МПа, 5 – the electronic operating module, 6 – the accumulator of pressure, 7 – transmitters of pressure, 8 – gauges,

9 – hydraulic knot, 10 – cogwheels, 11 – an alarm bulb, 12 – a control socket (М897), А/Е – электрически operated inlet-final valves, F – brakes, R – a tank of a brake liquid

Work principle

During intensive braking the wheel can slide on a surface. District speed of a wheel in this case is less than speed of the car.

Sliding minimum (0 %) when the wheel slides freely, and maximum (100 %) when the wheel is blocked. Efficiency of braking the greatest when the sliding factor makes 15 % that allows to keep good stability and controllability of the car.

Role ABS consists in pressure restriction in brake system so that value of factor of sliding was approximately equally recommended.

Action of this system should be immediate and independent for each wheel. The system should react immediately to each change of a road covering and loading on the car.

Design

ABS consists of electronic and hydraulic elements. Its structure includes following parts.

Placed on a place of the classical main brake cylinder hydraulic knot which has two transmitters of pressure feeding two independent contours of system of type "Х" and six электронно of operated valves of modulation of pressure. Four of them receive the electric signals sent by operating module, and modulate pressure in a brake contour. Other two valves protect from sudden changes of pressure in forward brakes so that not to worsen car characteristics.

Four gauges (on one on each wheel) which send to the operating module the data about instant speed of each wheel.

The electronic operating module (placed on a wall of a forward left wing) which on the basis of the data from gauges operates electric valves of hydraulic knot. This module is equipped also by the autodiagnostic adaptation which informs the driver on malfunction occurrence.

Knot of the pump with an electric drive which creates necessary pressure in brake system.

Three various types ABS can be applied depending on car model.

SYSTEM BENDIX WITH COMPOUND ABS

This system was established on some models till 1993 as the standard equipment. The system is adapted instead of usual system, action of a brake pedal is transferred to the block of hydraulic management which is replaced with the main brake cylinder and the vacuum amplifier in usual brake system.

The system works at very high pressure, usually from 158 to 183 bar which is created by the electric pump established on the modulator.

The system will continue to work, even if the gauge established on a wheel of the car, has failed. In case of the general breakage the management block will return system to usual braking.

SYSTEM BENDIX WITH ADDITIONAL ABS

System Bendix with additional ABS is established on some models, ABS is adapted in addition to usual elements of brake system.

The system uses the pressure created by the usual main brake cylinder and the vacuum amplifier.

The system will continue to work in a mode of usual braking in case of breakage ABS.

SYSTEM BOSCH 2E WITH ADDITIONAL ABS

System Bosch 2E with additional ABS is established on some models since 1993 and is similar Bendix with additional ABS.

Functioning

If one of gauges registers the beginning of blocking of a wheel the operating module influences the corresponding electric valve which is closed and thanks to it keeps necessary pressure of braking (for this wheel).

If all the same there comes full blocking of a wheel the electric valve connects a corresponding brake to a compensatory tank and pressure sharply falls. The wheel again starts to rotate. It causes change of a condition of the electric valve thanks to what again there is a pressure growth. This cycle is carried out very quickly (some times in a second), and all process lasts or to a car stop, or before easing of pressing a pedal.

The control

ABS it is supplied by the device of autodiagnostics connected to operating module which in case of occurrence of malfunction of an electronic part of system causes fire of a control bulb on a combination of devices. This bulb does not specify in a malfunction source. It is necessary to apply the following method to exact definition of a cause of defect.

PERFORMANCE ORDER

1. Between a tip designated by symbol М897, and weight to connect the switch. 2. To include ignition and to close the switch for 3 seconds. The control bulb on an instrument guard will light up. 3. To open the switch. The control bulb will light up once that corresponds to figure 1 among tens. Then the bulb dies away for 1,5 seconds and twice lights up that corresponds to figure 2 among units. 4. This signal should be interpreted, as figure 12 which is a code designation of the beginning of the test.

Search of causes of defect

Code designation of malfunction is number 51.

PERFORMANCE ORDER

1. To close the switch for 3 seconds, the control bulb should light up. 2. At the opened switch the control bulb lights up, for example, 5 times that corresponds to figure 5 among tens. The bulb again dies away for 1,5 seconds and lights up once (figure 1 among units).

Malfunction code	Faulty element	Check subject
14	The hydraulic device	Level of a brake liquid
		Hydraulic pressure
		Management of the hydraulic device
23	Contour of alarm bulb ABS	The diode
		Site of an electric chain between alarm bulb ABS and a safety lock
24–33	The gauge of a back left wheel	The signal going from the gauge Resistance of the gauge Site of an electric chain between the gauge and the electronic module
25–34	The gauge of a forward right wheel
31–35	The gauge of a back right wheel
32–41	The gauge of a forward left wheel
42	Электрически the operated valve the forward right	Functioning электрически the operated valve Resistance электрически the operated valve Site of an electric chain between электрически the operated valve and электроннным the module
43	Электрически the operated valve (restriction) the forward right
44	Электрически the operated valve the forward left
45	Электрически the operated valve (restriction) the forward left
51	Электрически the operated valve the back right
52	Электрически the operated valve the back left