Vehicle steering control device

1. A device for controlling a steering characteristic of a vehicle, the vehicle having a vehicle body, at least one pair of left and right wheels including at least one pair of left and right steered wheels, a steering wheel and a steering apparatus operated based upon a motion of the steering wheel and a control of the device, so as to enhance an effect of suppressing a change in a behavior of the vehicle body due to a difference between driving and braking forces on the left and right wheels, wherein:

the device makes an amount of controlling the steering characteristic smaller as an index indicating an amount of a shift of vertical loads between the left and right wheels is increased; and

in the vehicle, a traction control is executed in which a braking force of a driven wheel of the wheels is controlled when either of acceleration slips on the driven wheels is excessive; the steering characteristic is controlled so as to enhance an effect of suppressing a change in a behavior of the vehicle due to a difference between driving forces on the left and right wheels; and the difference between the driving forces on the left and right wheels are estimated based upon a difference between the braking forces on the left and right driven wheels under the traction control for either of the driven wheels.

2. A device according to claim 1 , wherein the amount of controlling the steering characteristic is controlled by controlling a steering assist torque.

3. A device according to claim 2 , wherein the steering assist torque is controlled in a direction of reducing an effect of a yaw moment imparted on the vehicle body induced by the difference between the driving and braking forces of the left and right wheels.

4. A device according to claim 3 , wherein the steering assist torque is controlled based upon a sum of a basic steering assist torque based upon steering torque and an auxiliary steering assist torque produced in a direction of reducing the effect of the yaw moment imparted on the vehicle body induced by the difference between the driving and braking forces of the left and right wheels; and the magnitude of the auxiliary steering assist torque is reduced as the index indicating an amount of a shift of vertical loads between the left and right wheels increases.

5. A device according to claim 1 , wherein the amount of controlling the steering characteristic is controlled by controlling a steering angle of a steered wheel.

6. A device according to claim 5 , wherein the vehicle has an active steering apparatus steering the steered wheels irrespective of a steering operation of a driver; and, under control of the steering control device, the active steering means steers the steered wheels in a direction of reducing an effect of a yaw moment imparted on the vehicle body induced by the difference between the driving and braking forces of the left and right wheels.

7. A device according to claim 6 , wherein the steering control device reduces the magnitude of a control amount of steering of the steered wheel of the active steering apparatus as the index indicating an amount of a shift of vertical loads between the left and right wheels increases.

8. A device according to claim 1 , wherein the index indicating an amount of a shift of vertical loads between the left and right wheels is selected from a group of a yaw rate of the vehicle body, a lateral acceleration of the vehicle body, a steering angle, a difference between the vertical loads on the left and right wheels and a combination thereof.

9. A device according to claim 1 , wherein, in the vehicle, an anti-skid control is executed in which a braking pressure of a wheel is controlled when either of braking slips of the wheels is excessive; the steering characteristic is controlled so as to enhance an effect of suppressing a change in a behavior of the vehicle due to a difference between braking forces on the left and right wheels; and the difference between the braking forces on the left and right wheels are estimated based upon a difference between the braking pressures on the left and right wheels under the anti-skid control for either of the wheels.

10. A device according to claim 1 , wherein the vehicle has a driving apparatus and at least a front wheel driven by the driving apparatus.

11. A device for controlling a steering characteristic of a vehicle, the vehicle having a vehicle body, at least one pair of left and right wheels including at least one pair of left and right steered wheels, a steering wheel and a steering apparatus operated based upon a motion of the steering wheel and a control of the device, so as to enhance an effect of suppressing a change in a behavior of the vehicle body due to a difference between driving and braking forces on the left and right wheels, wherein:

the device makes an amount of controlling the steering characteristic smaller as an index indicating an amount of a degree of turning of the vehicle is increase; and

in the vehicle, a traction control is executed in which a braking force of a driven wheel of the wheels is controlled when either of acceleration slips on the driven wheels is excessive: the steering characteristic is controlled so as to enhance an effect of suppressing a change in a behavior of the vehicle due to a difference between driving forces on the left and right wheels; and the difference between the driving forces on the left and right wheels are estimated based upon a difference between the braking forces on the left and right driven wheels under the traction control for either of the driven wheels.