Vehicle braking system and vehicle braking method

1. A vehicle braking system comprising:

a regenerative braking device that generates a regenerative braking force to a wheel according to an amount of power generated by a motor;

a friction braking device that generates a friction braking force to the wheel according to a frictional force;

a detection unit that directly detects a longitudinal force and a brake torque that act on the wheel;

a computation unit that computes a current value of the friction braking force based on the brake torque and a current value of the regenerative braking force by subtracting a longitudinal force generated by a friction braking from said longitudinal force;

a brake sensor;

a calculation unit that calculates a required braking force based on a result of a detection by the brake sensor;

a setting unit that sets a target value of the regenerative braking force and a target value of the friction braking force based on the required braking force; and

a control unit that controls the regenerative braking device based on the current value of the regenerative braking force so as to approach to the target value for the regenerative braking force, and controls the friction braking device based on the current value of the friction braking force so as to approach to the target value for the friction braking force.

2. The vehicle braking system according to claim 1 , wherein the vehicle includes a plurality of wheels and a plurality of motors respectively provided to the plurality of wheels, and

the control unit adjusts the regenerative braking force for each of the wheels by controlling each of the motors.

3. The vehicle braking system according to claim 1 , wherein the vehicle includes a plurality of wheels and a plurality of motors, and the vehicle braking system further comprises:

a power distribution device that variably sets a distribution ratio of the regenerative braking force generated to each of the wheels by the plurality of motors, and

wherein the control unit adjusts the regenerative braking force for the respective wheels as a group by controlling the power distribution device and the plurality of motors.

4. The system of claim 1 , wherein the detection unit is on an axle of a vehicle.

5. The system of claim 1 , wherein the detection unit is on an output shaft of the motor.

6. The system of claim 1 , wherein the detection unit detects a net longitudinal force, a net lateral force, a net vertical force and a net brake torque on the wheel.

7. The system of claim 1 , wherein the detection unit comprises a strain gauge.

8. The system of claim 1 , wherein the brake sensor comprises a sensor for detecting a pedaling force applied onto a brake pedal.

9. The system of claim 8 , wherein the sensor comprises a pressure sensor for detecting a cylinder pressure of a brake master cylinder.

10. A vehicle braking method for braking by controlling a regenerative braking device for generating a regenerative braking force to a wheel according to an amount of power generated by a motor and a friction braking device for generating a friction braking force to the wheel according to a frictional force, the vehicle braking method comprising:

directly detecting a longitudinal force and a brake torque that act on the wheel;

computing a current value of the friction braking force based on the brake torque, and a current value of the regenerative braking force by subtracting a longitudinal force generated by a friction braking from said longitudinal force;

detecting an output of a brake sensor;

calculating a required braking force based on the output of the brake sensor;

setting a target value for the regenerative braking force and a target value for the friction braking force based on a required braking force; and

controlling the regenerative braking device based on the current value of the regenerative braking force so that the regenerative braking force approaches to the target value for the regenerative braking force and controlling the friction braking device based on the current value of the friction braking force so that the friction braking force approaches to the target value for the friction braking force.

11. The method of claim 10 , wherein said directly detecting comprises detecting a net operating force on an axle of a vehicle.

12. The method of claim 10 , wherein said directly detecting comprises detecting a net force on an output shaft of the motor.

13. The method of claim 10 , wherein said directly detecting comprises detecting a net longitudinal force, a net lateral force, a net vertical force and a net brake torque on the wheel.

14. The method of claim 10 , wherein said directly detecting comprises detecting a deformation using a strain gauge.

15. The method of claim 10 , wherein said detecting the output of the brake sensor comprises detecting a pedaling force applied onto a brake pedal.

16. The method of claim 15 , wherein said detecting the pedaling force comprises detecting a cylinder pressure of a brake master cylinder.

17. A vehicle braking system comprising:

a regenerative braking device that generates a regenerative braking force to a wheel according to an amount of power generated by a motor;

a friction braking device that generates a friction braking force to the wheel according to a frictional force;

a detection unit that directly detects a longitudinal force and a brake torque that act on the wheel;

a brake sensor;

a calculation unit that calculates a required braking force that is required braking force to the wheel based on a result of a detection by the brake sensor;

a computation unit that computes a current value of the friction braking force based on the brake torque and a current value of the regenerative braking force by subtracting a longitudinal force generated by a friction braking from said longitudinal force;

a setting unit that sets a target value of the regenerative braking force and a target value of the friction braking force based on the required braking force; and

a control unit that controls the regenerative braking device based on the current value of the regenerative braking force so as to approach to the target value for the regenerative braking force, and controls the friction braking device based on the current value of the friction braking force so as to approach to the target value for the friction braking force.

18. The system of claim 17 , wherein the detection unit is on an axle of a vehicle.

19. The system of claim 17 , wherein the detection unit is on an output shaft of the motor.

20. The system of claim 17 , wherein the detection unit detects a net longitudinal force, a net lateral force, a net vertical force and a net brake torque on the wheel.

21. The system of claim 17 , wherein the detection unit comprises a strain gauge.

22. The system of claim 17 , wherein the brake sensor comprises a sensor for detecting a pedaling force applied onto a brake pedal.

23. The system of claim 22 , wherein the sensor comprises a pressure sensor for detecting a cylinder pressure of a brake master cylinder.