Four wheel steering system for vehicle

Claim 1

A steering system for a vehicle, comprising; actuator means for varying a rear wheel steer angle in response to a control signal representing said rear wheel steer angle, sensor means for determining a front wheel steer angle and a speed of said vehicle, and controller means, connected with said sensor means, for producing said control signal in accordance with a transfer function expressed as; ##EQU8## where δ f (s) is a Laplace transform of said front wheel steer angle, δ r (s) is a Laplace transform of said rear wheel steer angle, s is an operator used in Laplace transformation, and a 0 , a 1 , a 2 , a 3 , a 4 and a 5 are first, second, third, fourth, fifth, and sixth parameters which are determined in accordance with said vehicle speed, vehicle constants determined by said vehicle, and a desired characteristic, said first, second, third, fourth, fifth and sixth parameters a 0 , a 1 , a 2 , a 3 , a 4 and a 5 being determined in accordance with first, second, third, fourth, fifth and sixth equations expressed as; ##EQU9## where V is said vehicle speed, M is a constant representing a mass of said vehicle, I is a constant representing a yawing moment of inertia of said vehicle, C 1 is a constant representing a front wheel cornering power of said vehicle, C 2 is a constant representing a rear wheel cornering power, a is a constant representing a distance from a center of gravity of said vehicle to a front axle, b is constant representing a distance from said center of gravity to a rear axle of said vehicle, l is a wheelbase and equal to a+b, and K and τ are constants specifying a predetermined desired yaw rate response characteristic.