Hill descent system for vehicle and control method thereof

1. A hill descent system for a vehicle, comprising:

a plurality of wheels;

a plurality of wheel speed sensors, corresponding to the plurality of wheels and used for detecting the speeds of the plurality of wheels;

a plurality of motors, corresponding to the plurality of wheels and used for selectively driving or braking the plurality of wheels;

a plurality of motor controllers, respectively connected to the plurality of motors and used for controlling the working states of the plurality of motors;

a plurality of resolver sensors, corresponding to the plurality of motors and used for detecting the rotational speeds of the plurality of motors; and

a vehicle control unit, respectively connected to the plurality of wheel speed sensors, the plurality of motor controllers and the plurality of resolver sensors, and used for determining the actual downhill speed of the vehicle based on the speeds of the plurality of wheels and the rotational speeds of the plurality of motors, and controlling the plurality of motor controllers according to the actual downhill speed of the vehicle to adjust the working states of the plurality of motors.

2. The hill descent system according to claim 1 , wherein the predetermined speed of the vehicle is V0, and the actual downhill speed of the vehicle is V1,

when V1<V0, the plurality of motors are used for driving the plurality of wheels to rotate until V1=V0;

when V1>V0, the plurality of motors are used for braking the plurality of wheels until V1=V0.

3. The hill descent system according to claim 2 , further comprising: a power battery, wherein the power battery is connected to the plurality of motor controllers, a state of charge of the power battery is SOC, and the plurality of motors are respectively motor generators,

when V1>V0 and SOC<95%, the plurality of motors are used for braking the plurality of wheels.

4. The hill descent system according to claim 3 , also comprising a hydraulic brake system,

when V1>V0 and SOC≥95%, the hydraulic brake system is used for braking the plurality of wheels.

5. The hill descent system according to claim 3 , also comprising a hydraulic brake system, wherein the hydraulic brake system is connected to the vehicle control unit and adapted to, in a process when the plurality of motors brake the plurality of wheels, brake the plurality of wheels when a total braking moment required for the vehicle to maintain the predetermined speed is greater than a maximum braking moment of the plurality of motors.

6. The hill descent system according to claim 2 , also comprising a hydraulic brake system, wherein the hydraulic brake system is connected to the vehicle control unit and adapted to, in a process when the plurality of motors brake the plurality of wheels, brake the plurality of wheels when a total braking moment required for the vehicle to maintain the predetermined speed is greater than a maximum braking moment of the plurality of motors.

7. The hill descent system according to claim 1 , wherein the plurality of motors are respectively in-wheel motors.

8. The hill descent system according to claim 1 , wherein transmissions are connected to the motor shafts of the plurality of motors.

9. The hill descent system according to claim 1 , further comprising: a steering wheel angle sensor and a yaw rate sensor, wherein the steering wheel angle sensor and the yaw rate sensor are respectively connected to the vehicle control unit, and the vehicle control unit selectively controls torque distribution of the plurality of motor controllers to the plurality of motors according to detection results of the steering wheel angle sensor and the yaw rate sensor, thereby performing control of the correction yaw moment.

10. The hill descent system according to claim 9 , wherein the speed difference between a yaw rate calculated by the vehicle control unit and a yaw rate measured by the yaw rate sensor is Δψ, the sideslip angle of the vehicle estimated by a whole vehicle model is Δβ, a predetermined yaw rate difference threshold value ψ and a sideslip angle threshold value β are set for the hill descent system, and

the steering wheel angle sensor detects that when a driver does not operate the steering wheel, and Δψ>ψ or Δβ>β, the torques of the plurality of motors are distributed by the plurality of motor controllers to perform control of the correction yaw moment.

11. The hill descent system according to claim 10 , also comprising a hydraulic brake system, wherein the hydraulic brake system is connected to the vehicle control unit, and the vehicle control unit is adapted to control the hydraulic brake system to brake the plurality of wheels when a yaw moment generated by the plurality of motors is smaller than a correction yaw moment required by the vehicle.

12. The hill descent system according to claim 1 , wherein a hill descent control button is arranged in the driving cabin of the vehicle, and the hill descent control button is connected to the vehicle control unit.

13. A control method for the hill descent system according to claim 1 , comprising:

detecting the speeds of a plurality of wheels by a plurality of wheel speed sensors, and detecting the rotational speeds of the plurality of motors by a plurality of resolver sensors;

acquiring the actual downhill speed of the vehicle by the vehicle control unit according to the speeds of the plurality of wheels and the rotational speeds of the plurality of motors;

comparing the actual downhill speed of the vehicle with the predetermined speed, wherein the actual downhill speed of the vehicle is V1, and the predetermined speed of the vehicle is V0;

when V1<V0, driving the plurality of wheels to rotate by a plurality of motors until V1=V0; and

when V1>V0, braking the plurality of wheels by the plurality of motors until V1=V0.

14. The control method according to claim 13 , wherein the hill descent system further comprises a power battery, the power battery is connected to the plurality of motor controllers, the state of charge of the power battery is SOC, and the plurality of motors are motor generators; and the control method further comprises: when V1>V0 and SOC<95%, braking the plurality of wheels by the plurality of motors.

15. The control method according to claim 14 , wherein the hill descent system further comprises: a hydraulic brake system; and the control method further comprises: when V1>V0 and SOC≥95%, braking the plurality of wheels by the hydraulic brake system.

16. The control method according to claim 14 , wherein the hill descent system further comprises: a hydraulic brake system, the total braking moment required for the vehicle to maintain the predetermined speed during hill descent is ΔMb, and the maximum braking moment provided by the plurality of motors is ΔMm_max,

the control method further comprises: in a process when the plurality of motors brake the plurality of wheels, when V1>V0 and ΔMb>ΔMm_max, braking the plurality of wheels by the plurality of motors and the hydraulic brake system together.

17. The control method according to claim 13 , wherein the hill descent system further comprises: a hydraulic brake system, the total braking moment required for the vehicle to maintain the predetermined speed during hill descent is ΔMb, and the maximum braking moment provided by the plurality of motors is ΔMm_max,

the control method further comprises: in a process when the plurality of motors brake the plurality of wheels, when V1>V0 and ΔMb>ΔMm_max, braking the plurality of wheels by the plurality of motors and the hydraulic brake system together.

18. The control method according to claim 13 , wherein the hill descent system further comprises: a steering wheel angle sensor and a yaw rate sensor, and the steering wheel angle sensor and the yaw rate sensor are respectively connected to the vehicle control unit,

the speed difference between the yaw rate calculated by the vehicle control unit and the yaw rate measured by the yaw rate sensor is Δψ, the sideslip angle of the vehicle estimated by a whole vehicle model is Δβ, and a predetermined yaw rate difference threshold value ψ and a sideslip angle threshold value β are set for the hill descent system,

the control method further comprises: detecting, when the steering wheel angle sensor, that a driver does not operate the steering wheel, and Δψ>ψ or Δβ>β, distributing the torques of the plurality of motors by the plurality of motor controllers to perform control of the correction yaw moment.