Patent ID: 7668635

Claim:
A front wheel steering control device for improving vehicle handling and stability, comprising, input means for obtaining a steering wheel angle δ SW and a vehicle velocity V; first computing means for computing a yaw-rate γd for a vehicle which maintains a vehicle gravity center point sideslip angle at zero based on the steering wheel angle δ SW and the vehicle velocity V obtained by the input means based on a following equation (1) ; γ d ⁡ ( s ) δ sw ⁡ ( s ) = k γ ⁢ ⁢ d τ γ ⁢ ⁢ d ⁢ s + 1 ( 1 ) wherein kγd and tγd are a steady-state gain and a time constant of the target yaw-rate respectively and are given by equations (2) and (3), and s is an operand of Laplace Transformation, k γ ⁢ ⁢ d = V l f ⁡ ( 1 + ml r ⁢ V 2 2 ⁢ ll f ⁢ C f ) · 1 N ( 2 ) τ γ ⁢ ⁢ d = I z ⁢ V ml r ⁢ V 2 + 2 ⁢ ll f ⁢ C f ( 3 ) wherein lf represents a distance between a front wheel axis and a gravity center point, l represents a wheelbase, N represents a gear ratio of a rack and a pinion, m represents a vehicle weight, lr represents a distance between a rear wheel axis and the gravity center point, Cr represents a cornering power of front wheel tires, and Iz represents a yaw inertial moment, second computing means for computing a target front wheel actual steering angle for realizing the yaw-rate that was calculated by the first computing means, based on a following equation (4); δ f ⁡ ( s ) = G ff ⁡ ( s ) ⁢ δ sw ⁡ ( s ) ( 4 ) wherein a feed-forward controller transform function Gff(s) is given by equation (5), G ff ⁡ ( s ) = k γ ⁢ ⁢ d k γ + k γ ⁢ ⁢ d k γ · ( τ γ - τ γ ⁢ ⁢ d ) ⁢ s τ γ ⁢ ⁢ d ⁢ s + 1 , and ( 5 ) control means for performing a steering control of the vehicle based on the target front wheel actual steering angle calculated by the second computing means, wherein the target front wheel actual steering angle is calculated by adding a feed forward actual steering angle in proportion to the steering wheel angle of the vehicle to a feed forward actual steering angle that is a differential value of the steering wheel angle with a linear delay element, and when said vehicle velocity is below a predetermined value, a steering angle ratio of the steering wheel angle and the front wheel actual steering angle is controlled to be smaller than the gear ratio of the rack and the pinion, and when said vehicle velocity is above the predetermined value, the steering angle ratio is controlled to be greater than the gear ratio of the rack and the pinion.