Steering ratio control system of vehicle

A steering ratio control system of a vehicle comprising:

• a variable steering ratio mechanism for variably adjusting a steering ratio of a steer angle at left and right steered road wheels to a rotation angle of a steering wheel;
• braking/driving force control means for individually controlling braking force and/or driving force of the left and right steered road wheels, the braking/driving force control means comprising a left-and-right braking/driving force difference arithmetic calculation means for calculating a difference in braking force and/or driving force between the left and right steered road wheels;
• and
• steering ratio control means comprising:
• (a) steering ratio decision means for determining a reference steering ratio based on a driving state of the vehicle;
• (b) variable steering ratio mechanism driving means for driving the variable steering ratio mechanism depending on the reference steering ratio based on the vehicle's driving state;
• and
• (c) steering-ratio correction value arithmetic-calculation means for calculating a steering-ratio correction value based on the difference calculated by the left-and-right braking/driving force difference arithmetic calculation means, for canceling torque steer resulting from a difference in braking force and/or driving force between the left and right steered road wheels;
• wherein
• the variable steering ratio mechanism driving means determines a final steering ratio based on both of the reference steering ratio and the steering-ratio correction value to drive the variable steering ratio mechanism responsively to the final steering ratio.

A method of controlling a steering ratio of a vehicle employing a variable steering ratio mechanism capable of variably adjusting the steering ratio of a steer angle at left and right steered road wheels to a rotation angle of a steering wheel, and a braking/driving force control unit capable of individually controlling braking force and/or driving force of the left and right steered road wheels, the method comprising:

• calculating a difference in braking force and/or driving force between the left and right steered road wheels;
• determining a reference steering ratio based on a driving state of the vehicle;
• calculating a steering-ratio correction value based on the calculated difference for canceling torque steer resulting from a difference in braking force and/or driving force between the left and right steered road wheels;
• determining a final steering ratio based on both of the reference steering ratio and the steering-ratio correction value;
• and
• driving the variable steering ratio mechanism responsively to the final steering ratio.