Application of an optical torque sensor to a vehicle power steering system

The author describes the application of an optical torque sensor in a concept electric power assisted steering (EPAS) system for small cars which has been developed at Lucas Advanced Engineering Centre. A novel design of sensor enables the required performance to be obtained while still having the potential of low-cost manufacture compatible with the automotive market. An EPAS system uses an electric motor to provide the steering assistance, with control from an electronic torque sensor. Power is only consumed when assistance is actually required, thus improving fuel consumption, and the installation complexity and size are reduced. It is also possible to provide additional functions such as road-speed dependence and to interface with other vehicle systems such as active suspension at little extra cost. The system comprises a motor and epicyclic gearbox assembly mounted concentrically on the steering column. The torque sensor is incorporated within this assembly. An electronic control unit (ECU) processes the signals from the torque sensor and drives the motor