Method and system for collision avoidance

1. A method for collision avoidance for a host vehicle, the method comprising:

detecting a target in the vicinity of the host vehicle;

determining a threat in that the host vehicle is travelling on a collision course with the target;

detecting a user initiated steering action for steering the host vehicle towards one side of the target;

determining a degree of understeering of the host vehicle resulting from the user initiated steering action and a time duration of the understeering, wherein the degree of understeering is caused by overreactive user initiated steering action;

determining a stability parameter value indicative of a driving stability of the host vehicle prior to application of a steering torque overlay by a steering control system of the host vehicle to thereby reduce the degree of understeering;

when the degree of understeering exceeds a first understeering threshold, controlling the steering control system to counteract the user initiated steering action by applying the steering torque overlay to thereby reduce the degree of understeering and dampen the overreactive user initiated steering action only when:

the threat is determined,

when the time duration of the understeering exceeds a first threshold time duration and as long as the time duration of the understeering is within a second threshold time duration that exceeds the first threshold time duration, and

when the stability parameter value indicates that the host vehicle is stable; and

deactivating the steering control system to stop providing the steering torque overlay when the threat is not determined, or the degree of understeering is below a second understeering threshold lower than the first understeering threshold, or the time duration of the understeering exceeds the second threshold time duration, or the stability parameter value indicates that the host vehicle is unstable.

2. The method according to claim 1 , wherein the degree of understeering is a deviation between a calculated reference steering angle determined from a vehicle model, and a measured actual steering angle of the host vehicle.

3. The method according to claim 2 , comprising:

determining vehicle specific parameters and vehicle driving parameters, and

calculating the reference steering angle based on the vehicle specific parameters, the vehicle driving parameters, and the vehicle model.

4. The method according to claim 2 , wherein a steering torque for the counteracting steering action is determined based on the deviation between the calculated reference steering angle and the measured actual steering angle.

5. The method according to claim 4 , wherein the steering torque for the counteracting steering action is proportional to the deviation between the calculated reference steering angle and the measured actual steering angle.

6. The method according to claim 1 , wherein the degree of understeering is based on the understeering gradient.

7. The method according to claim 1 , wherein when the degree of understeer is subsequently determined to be below a second understeering threshold which is lower than the first understeer threshold, controlling the steering control system to stop providing the counteracting steering action.

8. An evasive steering system configured to provide an intervening action for a host vehicle for avoiding a collision with a target, the evasive steering system comprising:

a driving environment detection unit comprising a processor executing instructions stored in a memory configured to detect a target in the vicinity of the host vehicle;

a collision determining unit comprising a processor executing instructions stored in a memory configured to determine a threat in that the host vehicle is on collision course with the target;

a steering control system configured to control a steering torque of the host vehicle;

a vehicle stability measuring unit comprising a processor executing instructions stored in a memory configured to determine a stability parameter value indicative of a driving stability of the host vehicle prior to application of a steering torque overlay by the steering control system to thereby reduce a degree of understeering of the host vehicle resulting from a user initiated steering action; and

a vehicle control unit configured to:

detect the user initiated steering action for steering the host vehicle towards one side of the target;

determine the degree of understeering of the host vehicle resulting from the user initiated steering action and a time duration of the understeering, wherein the degree of understeering is caused by overreactive user initiated steering action;

when the degree of understeering exceeds a first understeering threshold, control the steering control system to counteract the user initiated steering action by applying the steering torque overlay to thereby reduce the degree of understeering and dampen the overreactive user initiated steering action only when:

the threat is determined,

when the time duration of the understeering exceeds a first threshold time duration and as long as the time duration of the understeering is within a second threshold time duration that exceeds the first threshold time duration, and

when the stability parameter value indicates that the host vehicle is stable; and

deactivate the steering control system to stop providing the steering torque overlay when the threat is not determined, or the degree of understeering is below a second understeering threshold lower than the first understeering threshold, or the time duration of the understeering exceeds the second threshold time duration, or the stability parameter value indicates that the host vehicle is unstable.

9. The evasive steering system according to claim 8 , comprising a steering angle sensor for measuring an actual steering angle of the host vehicle, wherein the vehicle control unit is configured to:

calculate the degree of understeer based on a deviation between a calculated reference steering angle determined from a model, and the measured actual steering angle.

10. The evasive steering system according to claim 8 , wherein the vehicle control unit is configured to:

determine a steering torque for the counteracting steering action based on the deviation between the calculated reference steering angle and the measured actual steering angle.

11. A vehicle comprising the evasive steering system according to claim 8 .