12:23. Anti-blocking system (ABS)
Anti-blocking system of brakes (Bendix ABS)|
1 – the electronic operating module,
2 – hydraulic knot, 3 – pump knot with the electric drive, |
4 – sensors of forward wheels, 5 – sensors of back wheels |
Function chart of Bendix ABS
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1 – pump knot with the electric drive,
2 – sensor of 16,0 MPas, 3 – sensor of 18,0 MPas, 4 – sensor of 9,0 MPas, 5 – the electronic operating module, 6 – pressure accumulator, 7 – pressure transmitters, 8 – sensors, |
9 – hydraulic knot, 10 – cogwheels, 11 – alarm bulb, 12 – control socket (M897), А/Е – electrically the operated inlet-final valves, F – brakes, R – tank of brake fluid |
Principle of work
During intensive braking the wheel can slide on a surface. District speed of a wheel in this case is less than the 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 coefficient of sliding makes 15% that allows to keep good stability and controllability of the car.
The role of ABS consists in restriction of pressure in the brake system so that value of coefficient of sliding was approximately equally recommended.
Action of this system has to be immediate and independent for each wheel. The system has to react to each change of a paving and load of the car immediately.
Design
ABS consists of electronic and hydraulic elements. The following parts are its part.
The hydraulic knot placed on the place of the classical main brake cylinder which has two transmitters of pressure feeding two independent contours of "X" system and six electronically the operated valves of modulation of pressure. Four of them receive the electric signals sent by the operating module and modulate pressure in a brake contour. Two other valves protect from sudden changes of pressure in forward brakes so that not to worsen characteristics of the car.
Four sensors (on one on each wheel) which send data on the instantaneous velocity of each wheel to the operating module.
The electronic operating module (placed on a wall of a forward left wing) which on the basis of data from sensors operates electric valves of hydraulic knot. This module is equipped with also autodiagnostic adaptation which informs the driver on malfunction emergence.
Pump knot with the electric drive which creates necessary pressure in the brake system.
Three various ABS types can be applied depending on car model.
THE BENDIX SYSTEM WITH COMPOUND ABS
This system was installed 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 by the main brake cylinder and the vacuum amplifier in the ordinary brake system.
The system works with very high pressure, usually from 158 to 183 bars which is created by the electric pump installed on the modulator.
The system will continue to work even if the sensor installed on a car wheel failed. In case of the general breakage the control unit will return system to usual braking.
THE BENDIX SYSTEM FROM ADDITIONAL ABS
The Bendix system from additional ABS is installed on some models, ABS is adapted in addition to usual elements of the brake system.
The system uses pressure created by the ordinary main brake cylinder and the vacuum amplifier.
The system will continue to work in the mode of usual braking in case of ABS breakage.
THE BOSCH 2E SYSTEM FROM ADDITIONAL ABS
The Bosch 2E system from additional ABS is installed on some models since 1993 and Bendix from additional ABS is similar.
Functioning
If one of sensors registers the beginning of blocking of a wheel, then the operating module influences the corresponding electric valve which is closed and thanks to it keeps the necessary pressure of braking (for this wheel).
If after all there comes full blocking of a wheel, then the electric valve connects the corresponding brake to a compensation tank and pressure sharply falls. The wheel starts over again rotating. It causes change of a condition of the electric valve thanks to what there is a growth of pressure again. This cycle is expedited very much (several times in a second), and all process lasts or to a car stop, or before weakening of pressing a pedal.
Control
ABS is supplied connected with autodiagnostics device operating the module which in case of malfunction of an electronic part of system causes fire of a control bulb on a combination of devices. This bulb does not indicate a malfunction source. It is necessary to apply the following method to exact definition of a cause of defect.
| PERFORMANCE ORDER | ||||
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Search of causes of defect
Code designation of malfunction is number 51.| PERFORMANCE ORDER | ||
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Malfunction code
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Faulty element
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Check subject
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14
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Hydraulic device
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Level of brake fluid
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Hydraulic pressure
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Control of the hydraulic device
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23
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Contour of an alarm bulb of ABS
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Diode
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The site of an electric chain between an alarm bulb of ABS and a safety lock
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24–33
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Sensor of a back left wheel
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The signal going from the sensor
Sensor resistance The site of an electric chain between the sensor and the electronic module |
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25–34
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Sensor of a forward right wheel
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31–35
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Sensor of a back right wheel
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32–41
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Sensor of a forward left wheel
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42
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Electrically the operated valve forward right
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Functioning electrically the operated valve
Resistance electrically the operated valve The site of an electric chain between electrically the operated valve and the electronic module |
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43
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Electrically the operated valve (restriction) forward right
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44
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Electrically the operated valve forward left
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45
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Electrically the operated valve (restriction) forward left
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51
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Electrically the operated valve back right
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52
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Electrically the operated valve back left
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