By introducing modern digital electronics, BOSCH succeeded in developing a high-performance antiskid system for passenger cars. A digital design approach was chosen since it allows for a greater degree of integration than an analog design.
This results in increased reliability. The hydraulic unit comprises three of four solenoid valves and a return pump driven by an electric motor. The system prevents vehicle swerving and maintains steerability while attaining remarkable gains in stopping distance at the same time.
As passenger cars developed, brake systems also improved steadily. Today almost optimal brake force generation has been achieved which assures stable braking on uniform roadways without any yaw movements as long as there is no excessive braking.
Excessive braking will result in wheel lock-up. In this case the vehicle is no longer steerable, may even swerve and in general the stopping distance will be longer than with optimal brake action.
Therefore, the objective of the antiskid system (ABS) is to reduce the brake pressure in the individual wheel should excessive braking occur so that the wheels generate maximum brake force without locking. Thus vehicle steerability is maintained and vehicle swerving prevented.
Although the first patents concerning antiskid systems date back to 1905, actual development did not begin until 1957. By 1966 the control problems experienced had been essentially solved. However, the introduction of high-performance antiskid systems, which also maintain steerability, failed in the following period due to their complexity and reliability problems with the electronic control unit which comprised numerous discrete electronic components. Simplified mechanical components and introduction of new technologies for the electronic control unit characterize the BOSCH high-performance ABS system for passenger cars.