Control device for electrical power steering system

A steering system for a vehicle comprising:

• a variable gear transmission system for changing a gear ratio (θo/θs) for a steered angle of a vehicle wheel with respect to a steering angle (θs) of a steering wheel, in accordance with a rotation angle (θg) of a first electric motor;
• an electrical power steering system for generating an auxiliary steering torque by a second electric motor in accordance with a torque (Tsn) applied to a steering shaft device connected with the steering wheel;
• and
• a control device for controlling the variable gear transmission system and the electrical power steering system, wherein the control device comprises;
• a first calculating portion for setting a target gear ratio (z) for the variable gear transmission system, and for calculating a first command value (v1) for the rotation angle of the first electric motor, such that an actual gear ratio coincides with the target gear ratio (z);
• a second calculating portion for setting a target torque (Tsnref) to be generated at the electrical power steering system, and for calculating a second command value (v2) for the torque generated by the second electric motor, such that the auxiliary steering torque generated by the second electric motor coincides with the target torque (Tsnref);
• a first output portion for generating a first compensation amount based on a first mathematical model, so that an influence of the interference to be applied to the rotation angle (θg) of the first electric motor is reduced when the second electric motor is driven by the second command value (v2) calculated by the second calculating portion, the first output portion calculating a first compensation command signal (igref) by adding the first compensation amount to the first command value (v1), so that the first compensation command signal (igref) is applied to the first electric motor;
• and
• a second output portion for generating a second compensation amount based on the first mathematical model, so that an influence of the interference to be applied to the torque (Tsn) of the steering shaft device is reduced when the first electric motor is driven by the first command value (v1) calculated by the first calculating portion, the second output portion calculating a second compensation command signal (ipref) by adding the second compensation amount to the second command value (v2), so that the second compensation command signal is applied to the second electric motor.