Wheel ground-contact state judging device and method

1. A wheel ground-contact state judging device comprising:

a detector for directly detecting, as a lateral force, a force acting on a wheel in a direction perpendicular to a wheel center plane of the wheel;

an acceleration sensor for detecting an acceleration in the lateral direction of a vehicle;

a calculator for calculating a cornering force acting on the wheel on the basis of the acceleration in the lateral direction detected by the acceleration sensor; and

a judging unit for judging the ground-contact state of the wheel on the basis of comparison between the detected lateral force and the calculated cornering force, wherein said judging unit determines an existence of a bad ground-contact state of the wheel upon a criteria being established that the calculated cornering force is smaller than the detected lateral force by a predetermined amount.

2. The wheel ground-contact state judging device according to claim 1 , wherein the detector detects the lateral force with respect to each of plural wheels provided to the vehicle as a detection target, the calculator calculates a total of the cornering forces acting on the respective wheels, and the judging unit judges the ground-contact state with the whole of the plural wheels set as a judging unit on the basis of a comparison between a total of the lateral forces (Ftot_y) and the total of the cornering forces (Ytot), and wherein the judging unit determines the existence of said criteria when Ytot<K·Ftot_y) with K satisfying (0<K<1).

3. The wheel ground-contact state judging device according to claim 1 , further comprising

a yaw rate sensor for detecting a yaw rate of the vehicle is further provided,

wherein the detector detects the lateral force with respect to each of plural wheels provided at the front and rear sides of the vehicle as a detection target, the calculator calculates a total of the cornering forces acting on the front wheels and a total of the cornering forces acting on the rear wheels on the basis of the detected yaw rate and the detected acceleration, and the judging unit judges the ground-contact state of the front wheels on the basis of comparison between the total of the lateral forces detected for the front wheels and the total of the cornering forces acting on the front wheels and also judges the ground-contact state of the rear wheels on the basis of comparison between the total of the lateral forces detected for the rear wheels and the total of the cornering forces acting on the rear wheels.

4. The wheel ground-contact state judging device according to claim 1 , further comprising:

a controller for controlling the roll rigidity of the vehicle on the basis of a judgment result of said judging device.

5. A wheel ground-contact state judging method comprising:

a first step of directly detecting, as a lateral force, a force acting on a wheel in a direction perpendicular to a wheel center plane of the wheel;

a second step of detecting an acceleration in the lateral direction of a vehicle;

a third step of calculating a cornering force acting on the wheel on the basis of the acceleration in the lateral direction thus detected; and

a fourth step of judging the ground-contact state of the wheel on the basis of a comparison between the detected lateral force and the calculated cornering force, wherein a judging unit determines an existence of a bad ground-contact state of the wheel upon a criteria being established that the calculated cornering force is smaller than the detected lateral force by a predetermined amount.

6. The wheel ground-contact state judging method according to claim 5 , wherein the second step of detecting the acceleration in the lateral direction includes detecting the lateral forces with respect to each of a plurality of wheels provided to the vehicle, the third step of calculating the cornering force includes calculating a total of the cornering forces acting on the respective plurality of wheels on the basis of the acceleration in the lateral direction, and the fourth step of judging the ground-contact state includes judging the ground-contact state with respect to the whole of plurality of wheels set as a judging unit on the basis of comparison between a total of the detected lateral forces (Ftot_y) and the total of the cornering forces (Ytot), and wherein the judging unit determines the existence of said criteria when Ytot<K·Ftot_y with K satisfying (0<K<1).

7. The wheel ground-contact state judging method according to claim 5 , further comprising:

a fifth step of detecting the yaw rate of the vehicle, and

wherein the second step of detecting the acceleration in the lateral direction includes detecting the lateral force with respect to each of a plurality of wheels provided at the front and rear sides of the vehicle as a detection target, the third step of calculating the cornering force includes calculating a total of the cornering forces acting on the front wheels and the total of the cornering forces acting on the rear wheels on the basis of the detected yaw rate and the detected acceleration, and the fourth step of judging the ground-contact state includes judging the ground contact state of the front wheels on the basis of a comparison between the total of the lateral forces detected for the front wheels and the total of the cornering forces acting on the front wheels and also judging the ground-contact state of the rear wheels on the basis of a comparison between the total of the lateral forces detected for the rear wheels and the total of the cornering forces acting on the rear wheels.

8. The wheel ground-contact state judging method according to claim 5 , further comprising:

a sixth step of controlling roll rigidity of the vehicle on the basis of a result in the fourth step.

9. The wheel ground-contact state judging method according to claim 5 wherein the first step of directly detecting the force on the wheel is based on a detector that is provided to the wheel or a wheel axle for the wheel.

10. The wheel ground-contact state judging device according to claim 1 , wherein the detector is provided to the wheel or a wheel axle for that wheel.