Torque regulation with the General Motors ABS VI electric brake system

The primary goal of an automotive brakes system is to achieve a complete and safe stop as fast as possible. Anti-lock braking systems (ABS) seek to avoid wheel lock-up and skidding to minimize stopping distances and maximize lateral stability during braking (i.e., to make it possible for the driver to steer out of a problem during an emergency braking scenario). This brief paper focuses on the "base braking problem" where the authors seek to construct a controller that makes the actual braking torque track a reference braking torque (i.e., the driver's input to the brake pedal). Effective base braking algorithms can improve brake system performance for adverse (i) road conditions and environmental influences, and (ii) for operating conditions. High performance base braking can also improve the performance of ABS systems since they ensure that the torque profile generated by an active ABS is achieved at the wheel. The paper describes the General Motors ABS VI unit, an electromechanical-hydraulic system consisting of electric drives, gearing, pistons, and hydraulic lines for disk brake operation. A key component of the overall system is the innovative torque sensor. The motivation for wheel torque regulation lies in the fact that wide swings in specific torque can occur at the wheel during normal operation, depending on various factors such as line pressure, brake pad temperatures, and other conditions. The ABS VI anti-lock system has a computer controlled solenoid system which, when closed, forces the driver out of the braking process temporarily when the wheels approach the locked condition. The computer takes over when it senses a certain value of wheel slip at a wheel, and then controls the brake line pressure via an actuator.