Brake by wire type brake system

Abstract

A BBW type brake system which operates fluid pressure generators having electric motors as drive sources based on an electrical signal to brake a wheel, field weakening control of the electric motors is performed in the initial stage of operation of the fluid pressure generators to increase the rotational speed of the electric motors. Therefore, it is possible to reduce a time lag before the braking force actually generates after the electrical signal for operating the fluid pressure generators is outputted, thereby improving operational responsiveness. After the braking force actually generates, the field weakening control is cancelled to secure a required braking force with a sufficient torque.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fluid pressure system diagram during normal operation of a BBW type brake system according to an embodiment of the present invention.

FIG. 2 is a fluid pressure system diagram during abnormal operation corresponding to FIG.

FIG. 3 is a view showing the structure of a disc brake device.

FIG. 4 is a block diagram of the control system of an electric motor.

FIG. 5 is a graph showing the relationship between the piston reaction force and the piston stroke of a wheel cylinder.

FIG. 6 is a diagram showing the map for retrieving a d-axis current command value from the piston stroke of a fluid pressure generator.

Claims

1. A BBW type brake system which outputs an electrical signal corresponding to an operational amount of a brake operating element operated by a driver, and operates an actuator having an electric motor as a drive source based on the electrical signal to brake a wheel, wherein field weakening control of the electric motor is performed in an initial stage of operation of the actuator.

2. The BBW type brake system according to claim 1, wherein the initial stage of the operation is a time period from start of operation of the electric motor until contact of brake pads of a disc brake device with a brake disc.

3. The BBW type brake system according to claim 1, wherein the field weakening control is cancelled when braking force is actually generated by the brake system after the initial stage of operation of the actuator.

4. The BBW type brake system according to claim 1, further comprising a first fluid pressure sensor which detects brake fluid pressure between a master cylinder which is operated by the brake operating element and a fluid pressure generator which is operated by the actuator, and a second fluid pressure sensor which detects brake fluid pressure between the fluid pressure generator and a wheel cylinder; wherein during normal operation, the fluid pressure generator is controlled so that the brake fluid pressure detected by the second fluid pressure sensor changes in accordance with the brake fluid pressure detected by the first fluid pressure sensor.

5. The BBW type brake system according to claim 3, wherein the master cylinder communicates with a stroke simulator via a reaction force permission valve which opens during normal operation and closes during abnormal operation.

6. The BBW type brake system according to claim 3, further comprising a stepping force shutoff valve, which closes during normal operation and opens during abnormal operation, between the master cylinder and the fluid pressure generator; wherein a fluid passage between the stepping force shutoff valve and the fluid pressure generator communicates with a reservoir via an atmosphere valve which opens during normal operation and closes during abnormal operation.

7. The BBW type brake system according to claim 2, further comprising a first fluid pressure sensor which detects brake fluid pressure between a master cylinder which is operated by the brake operating element and a fluid pressure generator which is operated by the actuator, and a second fluid pressure sensor which detects brake fluid pressure between the fluid pressure generator and a wheel cylinder; wherein during normal operation, the fluid pressure generator is controlled so that the brake fluid pressure detected by the second fluid pressure sensor changes in accordance with the brake fluid pressure detected by the first fluid pressure sensor.

8. The BBW type brake system according to claim 7, wherein the master cylinder communicates with a stroke simulator via a reaction force permission valve which opens during normal operation and closes during abnormal operation.

9. The BBW type brake system according to claim 7, further comprising a stepping force shutoff valve, which closes during normal operation and opens during abnormal operation, between the master cylinder and the fluid pressure generator; wherein a fluid passage between the stepping force shutoff valve and the fluid pressure generator communicates with a reservoir via a atmosphere valve which opens during normal operation and closes during abnormal operation.

10. A BBW type brake system for a vehicle comprising: a brake operating element to be operated by a driver;a sensor which senses an operational amount of the brake operating element and outputs an electrical signal based thereon;a actuator which brakes a wheel of the vehicle, the actuator including an electric motor; anda controller which controls operation of the actuator based on the electrical signal output by the sensor;wherein the controller performs field weakening control of the electric motor in an initial stage of operation of the actuator.

11. The BBW type brake system according to claim 10, further comprising a disc brake device including brake pads and a brake disc, and the initial stage of the operation is a time period from start of operation of the electric motor until contact of the brake pads with the brake disc.

12. The BBW type brake system according to claim 10, wherein the controller cancels the field weakening control when braking force is actually generated by the brake system after the initial stage of operation of the actuator.

13. The BBW type brake system according to claim 10, further comprising a master cylinder which is operated by the brake operating element, a fluid pressure generator which is operated by the actuator, a wheel cylinder, a first fluid pressure sensor which detects brake fluid pressure between the master cylinder and the fluid pressure generator, and a second fluid pressure sensor which detects brake fluid pressure between the fluid pressure generator and the wheel cylinder; wherein during normal operation, the fluid pressure generator is controlled so that the brake fluid pressure detected by the second fluid pressure sensor changes in accordance with the brake fluid pressure detected by the first fluid pressure sensor.

14. The BBW type brake system according to claim 13, further comprising a stroke simulator and a reaction force permission valve which opens during normal operation and closes during abnormal operation, and the master cylinder communicates with the stroke simulator via the reaction force permission valve.

15. The BBW type brake system according to claim 13, further comprising a stepping force shutoff valve which closes during normal operation and opens during abnormal operation, a fluid reservoir, and an atmosphere valve which opens during normal operation and closes during abnormal operation, the stepping force shutoff valve is disposed between the master cylinder and the fluid pressure generator; and a fluid passage between the stepping force shutoff valve and the fluid pressure generator communicates with the reservoir via the atmosphere valve.

16. A method of controlling a BBW type brake system for a vehicle which outputs an electrical signal corresponding to an operational amount of a brake operating element operated by a driver, and operates an actuator having an electric motor as a drive source based on the electrical signal to brake a wheel of the vehicle, the method comprising the steps of: performing field weakening control of the electric motor in an initial stage of operation of the actuator; andcanceling the field weakening control when braking force is actually generated by the brake system after the initial stage of operation of the actuator.

17. The method according to claim 16, wherein the initial stage of the operation is a time period from start of operation of the electric motor until contact of brake pads of a disc brake device with a brake disc.

18. The method according to claim 16, wherein in the brake system a first fluid pressure sensor detects brake fluid pressure between a master cylinder which is operated by the brake operating element and a fluid pressure generator which is operated by the actuator, and a second fluid pressure sensor detects brake fluid pressure between the fluid pressure generator and a wheel cylinder, and the method further comprises the step of controlling the fluid pressure generator during normal operation so that the brake fluid pressure detected by the second fluid pressure sensor changes in accordance with the brake fluid pressure detected by the first fluid pressure sensor.

19. The method according to claim 18, wherein in the brake system the master cylinder communicates with a stroke simulator via a reaction force permission valve, and the method further comprises the steps of opening the reaction force permission valve during normal operation and closing the reaction force permission valve during abnormal operation.

20. The method according to claim 18, wherein in the brake system a stepping force shutoff valve is disposed between the master cylinder and the fluid pressure generator, and a fluid passage extends between the stepping force shutoff valve and the fluid pressure generator and communicates with a fluid reservoir via an atmosphere valve, and the method further comprising the steps of: controlling the stepping force shutoff valve to close during normal operation and open during abnormal operation; andcontrolling the atmosphere valve to open during normal operation and close during abnormal operation.