Control method of an active suspension of a car

1. A control method for an active suspension of a vehicle, the control method comprises the steps of:

cyclically determining an optimal camber angle of the active suspension; and

driving the active suspension in order to confer the optimal camber angle to the active suspension;

wherein the step of determining the optimal camber angle comprises the further steps of:

determining a slip angle (α) of a wheel of the active suspension;

determining a vertical force (Fz) weighing on the wheel of the active suspension;

determining a transverse force (Fy) which is transferred to the ground by the wheel of the active suspension; and

determining the optimal camber angle as a function of the transverse force (Fy) which is transferred to the ground by the wheel of the active suspension,

wherein the transverse force (Fy), which is transferred to the ground by the wheel of the active suspension, is estimated as a function of the slip angle (α) of the wheel of the active suspension and as a function of the vertical force (Fz) which weighs on the wheel of the active suspension.

2. A control method according to claim 1 and comprising the further steps of:

cyclically determining an optimal toe angle for the active suspension as a function of the transverse force (Fy) which is transferred to the ground by the wheel of the active suspension; and

driving the active suspension in order to confer an optimal toe angle to the active suspension.

3. A control method according to claim 1 , wherein the optimal camber angle increases with the increase of the transverse force (Fy) which is transferred to the ground by the wheel of the active suspension.

4. A control method according to claim 1 , wherein the optimal camber angle is determined using an empirical control function (F C ) which provides the optimal camber angle as a function of the transverse force (Fy) which is transferred to the ground by the wheel of the active suspension.

5. A control method according to claim 4 , wherein the empirical control function (F C ) varies depending on the type of maneuvers.

6. A control method according to claim 4 , wherein the control function (F C ) varies, during cornering, for an inner wheel of the corner and for an outer wheel of the corner.

7. A control method according to claim 1 , wherein the step of estimating the slip angle (α) of the wheel of the active suspension further comprises the further steps of:

determining a sideslip angle (β) of the vehicle, the sideslip angle (β) being between a longitudinal axis of the vehicle and a direction of the velocity (V) of the vehicle in its center of gravity (B);

determining a yaw angle of the vehicle; and

determining the slip angle (α) of the wheel of the active suspension as a function of the sideslip angle (β) of the vehicle and of the yaw angle of the vehicle under the assumption that the vehicle is a rigid body.

8. A control method according to claim 7 , wherein the step of estimating the slip angle (α) of the wheel of the active suspension comprises the further steps of:

determining a level of compression/extension of the active suspension as a function of the vertical force (Fz) weighing on the wheel of the active suspension;

estimating a bump-steer effect on the slip angle (α) as a function of the level of one of compression and extension of the active suspension; and

correcting the slip angle (α) of the wheel of the active suspension to compensate for the bump-steer effect.

9. A control method according to claim 7 , wherein the step of estimating the slip angle (α) of the wheel of the active suspension comprises the further steps of:

estimating effect of the transverse force (Fy) on the slip angle (α), transverse force (Fy) being transferred to the ground by the wheel of the active suspension; and

correcting the slip angle (α) of the wheel of the active suspension as a function of the effect of the transverse force (Fy) which is transferred to the ground by the wheel of the active suspension.

10. A control method according to claim 7 , wherein the step of estimating the slip angle (α) of the wheel of the active suspension comprises the further steps of:

estimating a longitudinal force (Fx) which is transferred to the ground by the wheel of the active suspension;

estimating effect of the longitudinal force (Fx) on the slip angle (α), longitudinal force (Fx) being transferred to the ground by the wheel of the active suspension; and

correcting the slip angle (α) of the wheel of the active suspension as a function of the effect of the longitudinal force (Fx) which is applied to the ground by the wheel of the active suspension.

11. A control method according to claim 1 , wherein the step of estimating the vertical force (Fz) which weighs on the wheel of the active suspension comprises the further steps of:

measuring a side acceleration (ay) of the vehicle;

calculating a total transverse force (Fy TOT ) on the vehicle by multiplying the mass (M) of the vehicle by the side acceleration (ay) of the vehicle; and

estimating the vertical force (Fz) which weighs on the wheel of the active suspension as a function of the total transverse force (Fy TOT ) on the vehicle.

12. A control method according to claim 1 , wherein the transverse force (Fy) is determined by using an empiric estimation function (F αy ) which provides the transverse force (Fy) as a function of the slip angle (α) of the wheel of the active suspension and as a function of the vertical force (Fz) which weighs on the wheel of the active suspension.

13. A control method according to claim 1 and comprising the further step of:

measuring a steering angle of the front wheels of the vehicle; and

subtracting beforehand the steering angle from the slip angle (α) of one of the front wheels before estimating the transverse force (Fy) which is transferred to ground by the front wheel.

14. A control method according to claim 1 and comprising the further steps of:

measuring a side acceleration (ay) of the vehicle;

calculating a total transverse force (Fy TOT ) on the vehicle by multiplying the mass (M) of the vehicle by the side acceleration (ay) of the vehicle;

estimating a transverse force (Fy R ) on the rear axle and/or the transverse force on the front axle (Fy F ) as a function of the total transverse force on the vehicle;

comparing the transverse force (Fy R , Fy F ) on a single axle with the sum of the transverse forces (Fy) on the two wheels of the same axle to check the correctness of the estimate of the transverse forces on the two wheels; and

repeating, in case of significant deviations in the comparison, one or more iterations of the estimate of the transverse force (Fy) on each wheel by making corrections to at least one parameter.