Control system and method for an articulated vehicle comprising an autonomous emergency braking system

1. A control system for an articulated vehicle comprising a towing vehicle, a trailer and an autonomous emergency braking system, characterized in that the control system comprises:

brake control means adapted to apply a friction-estimating braking;

brake force capacity estimation means adapted to estimate the brake force capacity of the vehicle as a function of longitudinal wheel slip based on the applied friction-estimating braking,

axle load estimation means adapted to estimate the normal force on each wheel axle of the vehicle;

friction estimation means adapted to estimate a friction coefficient based on the estimated brake force capacity and at least one of the estimated normal forces; and

brake strategy adaptation means configured to adapt the brake strategy of the autonomous emergency braking system by adjusting the brake force for at least one wheel axle of the vehicle based on the estimated friction coefficient and the at least one wheel axle's estimated normal force,

wherein longitudinal tire force (Fx) of the estimated brake force is determined based on:

Fx =(BrakePressure×ToWheelTorque−(dwheelspeed/ dt )×InertiaWheel)/WheelRadius,

wherein BrakePressure comes from the friction-estimating braking, ToWheelTorque is brake factor, (dwheelspeed/dt) is wheel acceleration, InertiaWheel is the rotational inertia of a studied wheel, and WheelRadius is the radius of the studied wheel.

2. A control system according to claim 1 , wherein for preventing swing-out of the trailer, the brake strategy adaptation means is configured to adapt the brake strategy such that over usage of the trailer's brakes is avoided.

3. A control system according to claim 2 , wherein the brake strategy adaptation means is configured to adapt the brake strategy by reducing the brake force for each wheel axle of the trailer.

4. A control system according to claim 1 , wherein for preventing jack-knifing of the articulated vehicle, the brake strategy adaptation means is configured to adapt the brake strategy such that under usage of the trailer's brakes is avoided.

5. A control system according to claim 4 , wherein the brake strategy adaptation means is configured to adapt the brake strategy by increasing the brake force for each wheel axle of the trailer, such that coupling forces between the towing vehicle and the trailer are reduced or eliminated.

6. A control system according to claim 1 , wherein the trailer comprises at least two wheel axles, the axle load estimation means is adapted to summarize the normal forces on the trailer's wheel axles, and the brake strategy adaptation means is configured to adapt the brake strategy of the autonomous emergency braking system by adjusting the brake force for the trailer's wheel axles collectively based on the summarized normal forces.

7. A control system according to claim 1 , wherein a value of the normal force on each wheel axle of the vehicle is provided by an air bellow suspension system of the vehicle.

8. A control system according to claim 1 , wherein the brake control means is adapted to apply the friction-estimating braking directly when, or a predetermined time after, the autonomous emergency braking system has initiated a possible intervention.

9. A control system according to claim 1 , wherein the brake control means is adapted to apply the friction-estimating braking only to one wheel axle of the vehicle.

10. A control system according to claim 1 , wherein the one wheel axle is a pusher axle or a tag axle of the vehicle.

11. A control system according to claim 9 , wherein the one wheel axle is lifted when the friction-estimating braking is applied.

12. A control system according to claim 1 , wherein the brake force capacity estimation means is further adapted to:

find the optimal longitudinal braking point based on the estimated brake force capacity; and

apply a slip margin to the optimal longitudinal braking point, which slip margin reduces the longitudinal braking force used by the autonomous emergency braking system.

13. A control system according to claim 12 , wherein the slip margin is set such that an anti-lock braking system of the vehicle is not activated when the autonomous emergency braking system brakes the vehicle.

14. A control system according to claim 13 , the longitudinal braking force used by the autonomous emergency braking system is constant.

15. A control system according to claim 12 , wherein the slip margin is increased if it is determined that the vehicle is under-steering, whereby the longitudinal braking force on the front wheel axle of the vehicle is further reduced.

16. A control system according to claim 1 , further comprising an articulation angle measurement means adapted to measure the articulation angle between the towing vehicle and the trailer to detect swing-out or jack-knifing, wherein the brake strategy adaptation means is configured to release the braking of the trailer if swing-out is detected and to increase the braking of the trailer if jack-knifing is detected.

17. An articulated vehicle comprising a control system according to claim 1 .

18. A control method for an articulated vehicle comprising a towing vehicle, a trailer and an autonomous emergency braking system, which method is characterized by the steps of:

applying a friction-estimating braking;

estimating brake force capacity of the vehicle as a function of longitudinal wheel slip based on the applied friction-estimating braking;

estimating the normal force on each wheel axle of the vehicle;

estimating a friction coefficient based on the estimated brake force capacity and at least one of the estimated normal forces; and

adapting the brake strategy of the autonomous emergency braking system by adjusting the brake force for at least one wheel axle of the vehicle based on the estimated friction coefficient and the at least one wheel axle's estimated normal force

wherein longitudinal tire force (Fx) of the estimated brake force is determined based on:

Fx =(BrakePressure×ToWheelTorque−(dwheelspeed/ dt )×InertiaWheel)/WheelRadius,

wherein BrakePressure comes from the friction-estimating braking, ToWheelTorque is brake factor, (dwheelspeed/dt) is wheel acceleration, InertiaWheel is the rotational inertia of a studied wheel, and WheelRadius is the radius of the studied wheel.

19. A computer comprising a computer program for performing the steps of claim 18 when the program is run on the computer.

20. A non-transitory computer readable medium comprising a computer program for performing the steps of claim 18 when the program product is run on a computer.