Method and device for determining a force exercised by the ground on a wheel

1. A method for determining a longitudinal force (Fx) exerted on a wheel of a motor vehicle by a ground surface supporting the wheel, the vehicle comprising connection means which connect the wheel to a body of the vehicle, the method comprising:

measuring an actual force (FAX) at a level of at least one measurement point in the connection means,

calculating a force (FDx, Fx) resulting from a transmission via the connection means from the at least one measurement point to the wheel, of a body-associated force (FADX, FAX), which depends at least on the actual force,

calculating the longitudinal force (Fx) exerted on the wheel by the ground surface as a function at least of the force (FDx; Fx) resulting from the transmission of the body-associated force.

2. The method according to claim 1 , wherein the force (FDx; Fx) resulting from the transmission of the body-associated force is calculated as a function of at least one parameter chosen from among: a steering angle (α) of the wheel, a vertical distance (z) of the wheel relative to the body, an activity condition of a braking system coupled to the wheel, and a drive torque (Γ) applied to the wheel by an engine of the vehicle.

3. The method according to claim 2 , further comprising:

measuring the steering angle (α) of the wheel, and

calculating the force (FDx; Fx) resulting from transmission of the body-associated force as a function of the steering angle.

4. The method according claim 2 , further comprising:

measuring the vertical distance (z) of the wheel relative to the body is measured, and

calculating the force (FDx; Fx) resulting from transmission of the body-associated force as a function of the vertical distance.

5. The method according to claim 2 , further comprising:

detecting the activity condition (L) of the braking system coupled to the wheel, and

calculating the force (FDx; Fx) resulting from transmission of the body-associated force as a function of the detected activity condition.

6. The method according to any of claims 1 to 5 , wherein the force (FDx; Fx) resulting from the transmission of the body-associated force is calculated by applying to the body-associated force (FADX; FAX) a transfer function representative of the connection means.

7. The method according to claim 6 , wherein the transfer function is applied by means of at least one neuronal network.

8. The method according to claim 2 , wherein the wheel is a driving wheel and the method further comprises:

measuring the drive torque (Γ) applied to the wheel by the engine of the vehicle, and

calculating the force (FDx; Fx) resulting from transmission of the body-associated force as a function of the drive torque (Γ).

9. The method according to any of claims 1 to 5 , wherein the body-associated force consists of the actual force (FAX).

10. The method according to claim 8 , further comprising calculating a virtual, wheel-associated driving force (FMx), which represents a reaction of the ground surface to the drive torque, wherein:

the body-associated force (FADX) depends on the virtual wheel-associated driving force (FMx),

the force resulting from transmission of the body-associated force is calculated as a virtual, wheel-associated resistance force (FDx), and

the longitudinal force (Fx) exerted on the wheel by the ground surface is calculated as a function of the virtual, wheel-associated driving force (FMx) and of the virtual, wheel-associated resistance force (FDx).

11. The method according to claim 10 , wherein the calculation of the body-associated force (FADX) comprises:

calculating a virtual, body-associated driving force (FAMX), which would result from a transmission of the virtual, wheel-associated driving force (FMx) from the wheel to the at least one measurement point via the connection means, and

calculating the body-associated force as a virtual, body-associated resistance force (FADX), as a function of the actual force (FAX) and of the virtual, body-associated driving force (FAMX), the virtual, body-associated resistance force being applied at the level of the at least one measuring point.

12. The method according to any of claims 1 to 5 , wherein the at least one measuring point comprises a connection point between the connection means and the body, and the actual force (FAX) measured is a force exerted on the body at the level of the connection point.

13. The method according to claim 12 , wherein the connection means comprises a hub support on which the wheel is mounted, a suspension wishbone or arm connected to the hub support, and at least one elastic joint comprising two mountings connected by an elastic body, a first of the mountings being fixed to the suspension wishbone, and a second of the mountings being fixed to the body and constituting the at least one connection point to the body.

14. The method according to claim 13 , wherein the actual force (FAX) is measured by determining a deformation of the elastic body.

15. The method according to any of claims 1 to 5 , wherein the actual force (FAX) is measured parallel to a longitudinal direction of the vehicle.

16. A device for determining a longitudinal force (Fx) exerted on a wheel of a motor vehicle by a ground surface supporting the wheel, the vehicle comprising connection means that connect the wheel to a body of the vehicle, the device comprising:

means for measuring an actual force (FAX) at a level of at least one measurement point in the connection means,

means for calculating a force (FDx; Fx) that results from a transmission via the connection means, from the at least one measurement point to the wheel, of a body-associated force (FADX; FAX) that depends at least on the actual force (FAX), and

means for calculating the longitudinal force (Fx) exerted on the wheel by the ground surface as a function at least of the force (FDx; Fx) resulting from the transmission of the body-associated force.

17. The device according to claim 16 , further comprising means for measuring a steering angle (α) of the wheel, wherein the force (FDx; Fx) resulting from the transmission of the body-associated force is calculated as a function of the steering angle.

18. The device according to claim 16 , further comprising means for measuring a vertical distance (z) of the wheel relative to the body, wherein the force (FDx; Fx) resulting from the transmission of the body-associated force is calculated as a function of the vertical distance.

19. The device according to claim 16 , further comprising means for detecting an activity condition (L) of a braking system coupled to the wheel, wherein the force (FDx; Fx) resulting from the transmission of the body-associated force is calculated as a function of the activity condition.

20. The device according to claim 16 , further comprising means for measuring a drive torque (Γ) applied to the wheel by an engine of the vehicle, wherein the force (FDx; Fx) resulting from transmission is calculated as a function of the drive torque (Γ).

21. The device according to claim 20 , further comprising:

means for calculating a virtual, wheel-associated driving force (FMx) that represents a reaction of the ground surface to the driving torque (Γ),

means for calculating a virtual, body-associated driving force (FAMX) that would result from transmission of the virtual wheel-associated driving force (FMx) from the wheel to the at least one measurement point via the connection means,

means for calculating the body-associated force as a virtual, body-associated resistance force (FADX), as a function of the actual force (FAX) and of the virtual, body-associated driving force (FAMX), the virtual, body-associated resistance force (FADX) being applied at the level of the at least one measurement point,

wherein the force resulting from transmission of the body-associated force is calculated as a virtual, wheel-associated resistance force (FDx), and the longitudinal force (Fx) exerted on the wheel by the ground surface is calculated as a function of the virtual, wheel-associated driving force (FMx) and of the virtual, wheel-associated resistance force (FDx).