A core component of driving safety for motor vehicles has celebrated its twenty-fifth anniversary: the ABS anti-lock braking system. It took a large number of engineers many years to develop and test this brake control system. Before ABS was introduced, control of steering under emergency braking was not possible, and tires suffered enormously.
The anti-lock system, first produced by Bosch in 1978, prevents the wheels from locking, leaving the vehicle under control and allowing the driver to steer around obstacles. Braking distance is also reduced in most cases. The increasing use of ABS in motor vehicles is a major contribution to safety on the roads. People had been wondering how to prevent wheels from locking since the beginning of the twentieth century – not only on cars but also on railway vehicles and even on airplanes.
During the succeeding years, developers concentrated on simplifying the system. In 1989 Bosch’s engineers succeeded in attaching a hybrid control unit directly to the hydraulic modulator. This allowed them to dispense with both the wiring harness (linking the control unit and the hydraulic modulator) and the vulnerable plug-in connectors, thus significantly reducing the overall weight of this ABS 2E generation. Using new solenoid valves Bosch engineers created generation 5.0 in 1993, and in subsequent year’s versions.
The main features were once again a significantly reduced weight and additional functions such as electronically distributed brake pressure, which replaced the mechanical brake pressure reduction mechanism on the rear axle.
Diagnosing chassis electrical system faults
able 15.1 lists some common symptoms of chassis electrical system malfunctions together with suggestions for the possible fault. The faults are generic but will serve as a good reminder. It is assumed an appropriate pressure gauge set has been connected.
Testing procedure – black box technique
Chassis electrical systems’ covers a large area of the vehicle. The generic fault-finding lists presented in other chapters may be relevant but the technique that will be covered here is known as ‘black box fault-finding’. This is an excellent technique and
The same technique will often work with ‘outputs’. If the resistance of all the operating windings in, say, a hydraulic modulator were the same, then it would be reasonable to assume the figure was correct. Somatic
Advanced chassis systems technology
The friction between the type and the road surface is a key issue when considering anti-lock brakes. Frictional forces must be transferred between the tire contact patch and the road surface when the vehicle is accelerating or braking. The normal rules for friction between solid bodies have to be adapted because of the springy nature of rubber tyros. To get around this complicated problem, which involves molecular theory, the term ‘slip’ is used to describe the action of tire and road.
Serves to highlight that a fixed slip threshold as a reference point, for when ABS should operate, would not make the best use of the available adhesion coefficient.
where Total propulsion force; FH force transmitted to H part of road; FL force transmitted to L part of road; FB braking force; H high braking force coefficient; L low braking force coefficient.