This article describes the Wabco anti-skid braking system, that uses a microprocessor to calculate the correct pressure to apply. The term 'slip ratio' is used to define the percentage by which the wheel speed is less than the vehicle speed during braking. Optimal braking performance seems to occur when the slip ratio is between 15% and 30%. The relationship between the slip ratio and the grip betweenthe tyre and the road can be plotted on a graph; a virtual reproduction of that graph is stored in the microprocessor program, which uses it as a reference, from which it compares the information about the wheel speed and vehicle speed provided by the system's sensors. The system can respond quickly to varying friction levels between tyre and road, and to excessive differences between the grips of the front tyres. In the event of any component or circuit failure, the microprocessor will automatically step down through different levels ofcontrol by switching off one or more wheel circuits. The system hassensors, actuators, an electronic control unit (microprocessor) andinterconnecting cables. There is one sensor at each wheel. The mainactuators are the electropneumatic valves controlling brake pressure build-up, brake air pressure hold and brake air pressure reduction.
Samenvatting