ELECTRIC PARKING BRAKE SYSTEM AND METHOD FOR CONTROLLING THE ELECTRIC PARKING BRAKE SYSTEM

• US 20080071457A1
• Filed: 09/14/2007
• Published: 03/20/2008
• Est. Priority Date: 09/15/2006
• Status: Active Grant

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: SHIRAKI, Takahiro
• Granted Patent: US 7,881,849 B2
• Time in Patent Office: Days
• US Class Current: 701/70
• CPC Class Codes: B60T 13/746 and mechanical transmission of the braking action
• CPC Class Codes: B60T 2201/06 Hill holder; Start aid systems on inclined road
• CPC Class Codes: B60T 7/122 for locking of reverse movement
• CPC Class Codes: H02P 3/04 Means for stopping or slowing by a separate brake, e.g. friction brake, eddy-current brake brakes F16D, H02K49/00

Abstract

In an electric parking brake system, the moving force-based target tension is set based on the inclination angle of a vehicle and the shift position, and the slack compensation amount is determined based on the inclination angle of the vehicle and the shift position. The control target tension is set to a smaller value from among the slack-based target tension, which is the sum of the moving force-based target tension and the slack compensation amount, and the maximum value of the output power that can be produced by an electric motor. The electric motor is controlled such that the tension of the cable matches the control target tension (the slack-based target tension, in most cases).

Claims

1. An electric parking brake system, comprising:

a drum brake that includes;

a drum which rotates together with a wheel of a vehicle and of which an inner peripheral face is used as a friction face;

a shoe which is fitted to a backing plate that is a non-rotating body so as to be movable relative to the backing plate, and which has a friction member on an outer peripheral face; and

a pushing mechanism that pushes the shoe against the friction face to suppress a rotation of the drum;

an electric motor;

a motion conversion mechanism that converts a rotation of a rotating shaft of the electric motor into a linear motion of an output member of the motion conversion mechanism;

a cable that is connected at one end to the output member of the motion conversion mechanism, and that is connected at the other end to the pushing mechanism;

a maintaining mechanism that maintains a friction member pushing force that is a force with which the friction member is pushed against the friction face in the drum brake, when electric current is not supplied to the electric motor; and

a tension control unit that controls a tension of the cable by controlling the electric motor such that the friction member pushing force in the drum brake is controlled, wherein

the tension control unit includes a slack-based tension control unit that controls the tension of the cable to a slack-based target tension that is a sum of a moving force-based target tension, which is a target value determined based on a moving force applied to the vehicle, and a slack compensation amount, which is used to compensate for a decrease in the friction member pushing force due to a slack in the cable, the slack being caused in accordance with an amount of change in a torque applied to the wheel when the drum brake is on.

2. The electric parking brake system according to claim 1, wherein the slack-based tension control unit includes a first slack compensation amount determination unit that determines the slack compensation amount based on at least one of the amount of change in the torque and a moving force-based friction member pushing force that corresponds to the moving force-based target tension.

3. The electric parking brake system according to claim 2, wherein the first slack compensation amount determination unit includes at least one of a torque amount-based slack compensation amount determination unit that sets the slack compensation amount to a larger value when the amount of change in the torque is large than when the amount of change in the torque is small, and a torque direction-based slack compensation amount determination unit that sets the slack compensation amount to a larger value when the torque is applied in a direction in which the wheel is rotated to move the vehicle forward than when the torque is applied in a direction in which the wheel is rotated to back up the vehicle.

4. The electric parking brake system according to claim 2, wherein the first slack compensation amount determination unit includes a moving force-based slack compensation amount determination unit that sets the slack compensation amount to a larger value when the moving force-based friction member pushing force is large than when the moving force-based friction member pushing force is small.

5. The electric parking brake system according to claim 1, wherein the slack-based tension control unit includes a second slack compensation amount determination unit that determines the slack compensation amount based on at least one of an inclination angle of a road on which the vehicle is at a standstill and a shift position of a transmission of the vehicle.

6. The electric parking brake system according to claim 5, wherein the second slack compensation amount determination unit includes at least one of an inclination direction-based slack compensation amount setting unit that sets the slack compensation amount to a larger value when the vehicle is at a standstill on a downhill slope than when the vehicle is at a standstill on an uphill slope, and an inclination amount-based slack compensation amount setting unit that sets the slack compensation amount to a larger value when an absolute value of an inclination angle of the road on which the vehicle is at a standstill is large than when an absolute value of an inclination angle of the road on which the vehicle is at a standstill is small.

7. The electric parking brake system according to claim 1, wherein:

the slack-based tension control unit includes an application start-time control unit that executes a control such that the tension of the cable approaches the slack-based target tension when the drum brake is applied; and

the tension control unit includes a standstill state maintenance control unit that actuates the electric motor to increase the tension when the tension of the cable is smaller than the moving force-based target tension in a state in which the friction member pushing force in the drum brake is maintained by the maintaining mechanism.

8. The electric parking brake system according to claim 7, wherein the standstill state maintenance control unit actuates the electric motor such that the tension is equal to or larger than the moving force-based target tension.

9. A method for controlling an electric parking brake system including:

a drum brake that includes;

a drum which rotates together with a wheel of a vehicle and of which an inner peripheral face is used as a friction face;

a shoe which is fitted to a backing plate that is a non-rotating body so as to be movable relative to the backing plate, and which has a friction member on an outer peripheral face; and

a pushing mechanism that pushes the shoe against the friction face to suppress a rotation of the drum;

an electric motor;

a motion conversion mechanism that converts a rotation of a rotating shaft of the electric motor into a linear motion of an output member of the motion conversion mechanism;

a cable that is connected at one end to the output member of the motion conversion mechanism, and that is connected at the other end to the pushing mechanism;

a maintaining mechanism that maintains a friction member pushing force that is a force with which the friction member is pushed against the friction face in the drum brake, when electric current is not supplied to the electric motor; and

a tension control unit that controls a tension of the cable by controlling the electric motor such that the friction member pushing force in the drum brake is controlled, the method comprising;

controlling the tension of the cable to a slack-based target tension that is a sum of a moving force-based target tension, which is a target value determined based on a moving force applied to the vehicle, and a slack compensation amount, which is used to compensate for a decrease in the friction member pushing force due to a slack in the cable, the slack being caused in accordance with an amount of change in a torque applied to the wheel when the drum brake is on.

10. The method according to claim 9, wherein the slack compensation amount is determined based on at least one of the amount of change in the torque and a moving force-based friction member pushing force that corresponds to the moving force-based target tension.

11. The method according to claim 10, wherein there is executed at least one of a control for setting the slack compensation amount to a larger value when the amount of change in the torque is large than when the amount of change in the torque is small, and a control for setting the slack compensation amount to a larger value when the torque is applied in a direction in which the wheel is rotated to move the vehicle forward than when the torque is applied in a direction in which the wheel is rotated to back up the vehicle.

12. The method according to claim 10, wherein the slack compensation amount is set to a larger value when the moving force-based friction member pushing force is large than when the moving force-based friction member pushing force is small.

13. The method according to claim 9, wherein the slack compensation amount is determined based on at least one of an inclination angle of a road on which the vehicle is at a standstill and a shift position of a transmission of the vehicle.

14. The method according to claim 13, wherein there is executed at least one of a control for setting the slack compensation amount to a larger value when the vehicle is at a standstill on a downhill slope than when the vehicle is at a standstill on an uphill slope, and a control for setting the slack compensation amount to a larger value when an absolute value of an inclination angle of the road on which the vehicle is at a standstill is large than when an absolute value of an inclination angle of the road on which the vehicle is at a standstill is small.

15. The method according to claim 9, further comprising:

executing a control such that the tension of the cable approaches the slack-based target tension when the drum brake is applied; and

actuating the electric motor to increase the tension when the tension of the cable is smaller than the moving force-based target tension in a state in which the friction member pushing force in the drum brake is maintained by the maintaining mechanism.

16. The method according to claim 15, wherein the electric motor is actuated such that the tension is equal to or larger than the moving force-based target tension.