Patent ID: 7853378

Claim:
A steering system for a vehicle comprising: a variable gear transmission system for changing ratio (θ o /θ s ) for a steered angle of a vehicle wheel with respect to a steering angle (θ s ) of a steering wheel, in accordance with a rotation angle (θ g ) 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 (T sn ) 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 (v 1 ) 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 (T snref ) to be generated at the electrical power steering system, and for calculating a second command value (v 2 ) 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 (T snref ); 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 (θ g ) of the first electric motor is reduced when the second electric motor is driven by the second command value (v 2 ) calculated by the second calculating portion, the first output portion calculating a first compensation command signal (i gref ) by adding the first compensation amount to the first command value (v 1 ), so that the first compensation command signal (i gref ) 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 (T sn ) of the steering shaft device is reduced when the first electric motor is driven by the first command value (v 1 ) calculated by the first calculating portion, the second output portion calculating a second compensation command signal (i pref ) by adding the second compensation amount to the second command value (v 2 ), so that the second compensation command signal is applied to the second electric motor; wherein the first and second output portions calculate corrected amounts by substituting the first and second command values (v 1 , v 2 ) calculated by the first and second calculating portions into a second mathematical model, and the first and second output portions calculate the first and second compensation command signal (i gref , i pref ) by respectively adding the first and second compensation amounts to the above corrected amounts.