Electronic control unit for passenger car antiskid

By introducing modern technologies for the electronics, Bosch succeeded in developing a high-quality antiskid system for passenger cars. Two well-known German automakers are introducing the system just now, others will follow in the near future. Two wheel speed sensors measure the angular velocity of the front wheels. In order to minimize brake force differences of the rear axle on roadways with split coefficients, a common control for the rear wheels has been chosen. The hydraulic unit comprises three (for front-rear brake system) or four (for diagonal brake system) novel solenoid valves and a return pump driven by an electric motor. Brake pressure can be raised in a steady or stepwise way, held at a constant level or decreased. The electronic unit is mainly of digital design and consists of a few integrated circuits. The antiskid system comprises many sophisticated functions which result in a high complexity of the circuit. The digital design was chosen because it allows for a greater integration than the analog design. To ensure optimal system safety the main components of the system are checked for their proper functioning prior to driving the vehicle. En route the main system components are Continuously monitored. The overall antiskid system is switched off once a critical defect has been detected. In that case the normal brake system is available and a warning lamp indicates to the driver that the antiskid system is not functioning.