ELECTRIC POWER STEERING DEVICE

摘要

PROBLEM TO BE SOLVED: To add an auxiliary torque to a steering system by forming an electric power steering device so that it can be switched over between a normal control mode in which the device is free from any defect and a failure mode in which an assist ratio is changed for the normal control mode when the device is under a specific failure. SOLUTION: An electronic control means 15 of an electric power steering device 1 in which a variable gear ratio mechanism is installed in a steering gear box 5 drives an electric motor 10 through an electric motor drive means with a torque signal detected by a steering torque sensor 12 and a control signal for electric motor control to provide a steering assist force according to a running condition. Also the electronic control means 15 is provided with a failure detector means and, when a failure is detected, the control mode is switched over between a normal control mode and a failure control mode according to the content of the failure. When the mode is switched over to the failure control mode, the assist ratio of a signal from the electric motor driving means to the electric motor 10 relative to a normal control mode is varied to inform an operator of a failure by giving a feeling as a steering feeling.