Regenerative braking system and method

1. A regenerative braking system comprising a controller configured to:

determine whether or not a vehicle satisfies an entry condition for regenerative braking based on information collected by the vehicle;

calculate a hydraulic braking torque according to a pressure of a master cylinder and a target amount of a regenerative braking torque varied according to the pressure of the master cylinder, if the vehicle satisfies the entry condition; and

perform braking of the vehicle based on the target amount of the regenerative braking torque and the hydraulic braking torque,

wherein the target amount of the regenerative braking torque is calculated using an upper limit of the regenerative braking torque calculated by the controller, a coast regenerative torque when an accelerator pedal of the vehicle is released, and the pressure of the master cylinder.

2. The regenerative braking system of claim 1 , wherein the braking of the vehicle is performed based on a coast regenerative torque generated from a motor at a moment when tip-out caused by release of an accelerator pedal of the vehicle occurs.

3. The regenerative braking system of claim 2 , wherein:

a deceleration of the vehicle is generated by a sum of a total braking force and the coast regenerative torque; and

the total braking force is defined by a sum of the target amount of the regenerative braking torque and the hydraulic braking torque.

4. The regenerative braking system of claim 1 , wherein the information collected by the vehicle comprises at least one of an anti-lock braking system (ABS) state signal, a traction control system (TCS) state signal, a vehicle dynamic control (VDC) state signal, a vehicle speed, a wheel speed, a gear state, or the pressure of the master cylinder.

5. The regenerative braking system of claim 4 , wherein:

the entry condition includes a case in which the pressure of the master cylinder is sensed; and

the controller determines that the vehicle does not satisfy the entry condition, if slip of the vehicle occurs, a gear is in neutral, a defect of a motor of the vehicle is sensed, or a defect of an ABS of the vehicle is sensed.

6. The regenerative braking system of claim 1 , wherein the controller monitors the coast regenerative torque in real time so as to calculate the target amount of the regenerative braking torque.

7. The regenerative braking system of claim 1 , wherein the controller:

sets a difference between the upper limit of the regenerative braking torque and the coast regenerative torque as an allowable regenerative braking torque; and

compares a target amount of a pre-regenerative braking torque, calculated according to the pressure of the master cylinder, with the allowable regenerative braking torque, and sets the allowable regenerative braking torque as the target amount of the regenerative braking torque when the target amount of the pre-regenerative braking torque is greater than the allowable regenerative braking torque.

8. The regenerative braking system of claim 1 , wherein the controller sets a plurality of pressure sections of the master cylinder and sets the target amount of the regenerative braking torque based on whether the pressure of the master cylinder is within any one of the pressure sections.

9. The regenerative braking system of claim 8 , wherein:

the controller sets the target amount of the pre-regenerative braking torque as a value acquired by multiplying the pressure of the master cylinder by a conversion rate, if the pressure of the master cylinder is less than a first reference pressure; and

the controller sets the target amount of the pre-regenerative braking torque as a value acquired by multiplying the first reference pressure by the conversion rate, if the pressure of the master cylinder is the first reference pressure or more and less than a second reference pressure.

10. The regenerative braking system of claim 1 , wherein, when the vehicle enters a low speed region:

the controller calculates a change in the target amount of the regenerative braking torque so that the target amount of the regenerative braking torque becomes 0 when a speed of the vehicle reaches a lower threshold from an upper threshold of the low speed region; and

the controller performs regenerative braking of the vehicle according to the change in the target amount of the regenerative braking torque calculated by the controller.

11. The regenerative braking system of claim 7 , wherein the controller sets the target amount of the regenerative braking torque as 0, if the pressure of the master cylinder is a second reference pressure or more.

12. The regenerative braking system of claim 1 , wherein the controller maintains a hydraulic pressure caused by the pressure of the master cylinder, even if braking of the vehicle according to the target amount of the regenerative braking torque is performed.

13. A regenerative braking method comprising:

decelerating, by a controller, a vehicle based on a coast regenerative torque generated from a motor at a moment when tip-out caused by release of an accelerator pedal of the vehicle occurs;

determining, by the controller, whether or not the vehicle satisfies an entry condition for regenerative braking based on information collected by the vehicle;

calculating, by the controller, a hydraulic braking torque according to a pressure of a master cylinder and a target amount of a regenerative braking torque varied according to the pressure of the master cylinder, if the vehicle satisfies the entry condition; and

performing, by the controller, braking of the vehicle based on the target amount of the regenerative braking torque and the hydraulic braking torque,

wherein the target amount of the regenerative braking torque is calculated using an upper limit of the regenerative braking torque calculated by the controller, a coast regenerative torque when an accelerator pedal of the vehicle is released, and the pressure of the master cylinder.

14. The regenerative braking method according to claim 13 , wherein the determination as to whether or not the vehicle satisfies the entry condition comprises:

determining that the vehicle does not satisfy the entry condition, if slip of the vehicle occurs, a gear is in neutral, or a defect of the motor of the vehicle is sensed.

15. The regenerative braking method according to claim 13 , wherein the calculation of the target amount of the regenerative braking torque comprises:

determining an upper limit of the regenerative braking torque based on a torque output from the motor;

setting a difference between the upper limit of the regenerative braking torque and the coast regenerative torque as an allowable regenerative braking torque;

comparing a target amount of a pre-regenerative braking torque, calculated according to the pressure of the master cylinder, with the allowable regenerative braking torque; and

setting the allowable regenerative braking torque as the target amount of the regenerative braking torque when the target amount of the pre-regenerative braking torque is greater than the allowable regenerative braking torque.

16. The regenerative braking method according to claim 15 , wherein the calculation of the target amount of the pre-regenerative braking torque further comprises:

setting the target amount of the pre-regenerative braking torque as a value acquired by multiplying the pressure of the master cylinder by a conversion rate, if the pressure of the master cylinder is less than a first reference pressure.

17. The regenerative braking method according to claim 13 , wherein the calculation of the target amount of the regenerative braking torque comprises:

when the vehicle enters a low speed region during regenerative braking of the vehicle, calculating a change in the target amount of the regenerative braking torque so that the target amount of the regenerative braking torque becomes 0 until a speed of the vehicle reaches a lower threshold from an upper threshold of the low speed region.

18. The regenerative braking method according to claim 15 , wherein the calculation of the target amount of the pre-regenerative braking torque further comprises:

setting the target amount of the pre-regenerative braking torque to a value acquired by multiplying a first reference pressure by a conversion rate, if the pressure of the master cylinder is the first reference pressure or more and less than a second reference pressure.

19. The regenerative braking method according to claim 13 , wherein the calculation of the target amount of the regenerative braking torque further comprises:

setting, by the controller, the target amount of the regenerative braking torque as 0, if the pressure of the master cylinder is a second reference pressure or more.