GB2304838A

GB2304838A - Electrically operated parking brake

Info

Publication number: GB2304838A
Application number: GB9518613A
Authority: GB
Inventors: Jacques Loche; Nouredine Benkaza; Philippe Landry
Original assignee: Delphi Automotive Systems France
Current assignee: Delphi Automotive Systems France
Priority date: 1995-09-12
Filing date: 1995-09-12
Publication date: 1997-03-26
Anticipated expiration: 2015-09-12
Also published as: GB9518613D0; GB2304838B

Abstract

An actuator 12 for an electrically operable parking brake comprises a screw 20 drivable by an electric motor 18, a first nut 34 threadably engaged with the screw and connectible, via a yoke (36, figure 2) and cable(s) 16 with brake(s) 14, and a second nut 46 threadably engaged with the screw and having teeth 50 thereon. The first and second nuts can be locked in a brake applied position by teeth 58 on a lever 54 engaging the teeth 50 on the second nut. A solenoid device 62 on actuation disengages the teeth so that the nuts are returned to the brake release position by a spring 52. Different locking arrangements are disclosed (figures 5B and 6), and in one embodiment a cable (126, figure 7) is also connected to a hand brake or a pedal.

Description

ELECTRICALLY OPERATED PARKING BRAKE The present invention relates to an electrically operated parking brake for a motor vehicle, and to an actuator therefor.

In general, motor vehicles are provided with a parking brake which is operated by a hand brake lever or foot pedal positioned inside the vehicle. One or more cables connect the lever or pedal to brakes at the front or rear wheels of the vehicle. The application of tension to the cable(s) by operation of the lever or pedal actuates the parking brake. There have been numerous proposals to replace or supplement the manually operated parking brake by an electrically operated system. In general, these proposals make use of an electric motor which is driven to apply tension to the cable(s). Examples can be found in US-A-5180038, DE-A-4129919 and FR-A-2691934. These known arrangements are complicated and expensive to produce. Further, none of them provide a locking arrangement which adequately locks the parking brake in the park mode.

It is an object of the present invention to provide an improved arrangement.

An actuator in accordance with the present invention for an electrically operated parking brake comprises an electric motor; a screw rotatably drivable about its longitudinal axis by the electric motor; a first nut threadably engaged with the screw and connectable with a cable for operating a brake; a second nut threadably engaged with the screw and having teeth thereon extending in the axial direction, the first and second nuts being movable along the screw between a brake applied position and a brake released position; a lever pivotable about a pivot pin and having teeth thereon engageable with the teeth on the second nut when the second nut is in the brake applied position; and a solenoid device which on actuation allows the disengagement of the teeth when the second nut is in the brake applied position.

The present invention also includes an electrically operated parking brake for a motor vehicle comprising a wheel brake; a cable connected to the wheel brake for operating the wheel brake; an actuator including an electric motor, a screw rotatably drivable about its longitudinal axis by the electric motor, a first nut threadably engaged with the screw and connected with the cable, a second nut threadably engaged with the screw and having teeth thereon extending in the axial direction, the first and second nuts being movable along the screw between a brake applied position and a brake released position, a lever pivotable about a pivot pin and having teeth thereon engageable with the teeth on the second nut when the second nut is in the brake applied position, and a solenoid device which on actuation allows the disengagement of the teeth when the second nut is in the brake applied position; and a control circuit for controlling the actuation of the electric motor and the solenoid device.

The present invention provides a parking brake which is simple and cheap. Further, the latching of the teeth provides a mechanical locking arrangement for the parking brake when the parking brake is in the park mode.

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view, partially in crosssect ion, of an actuator in accordance with the present invention for an electrically operated parking brake in accordance with the present invention; Figure 2 is a cross-sectional view on the line II-II of Figure 1; Figure 3 is a perspective view, partially in cross-section, of a second embodiment of actuator in accordance with the present invention for an electrically operated parking brake in accordance with the present invention; Figure 4 is a perspective view of some of the components of the actuator of Figure 3; Figures 5A to 5C are side views of three working positions of some of the components of the actuator of Figure 3;; Figure 6 is a perspective view similar to that of Figure 4 of a modification the second embodiment of actuator; Figure 7 is a cross-sectional view similar to that of Figure 2 of a modification of the first embodiment of actuator; Figure 8 is a diagram of a control circuit for use with the actuator of Figures 1 and 2, Figure 6 or Figure 7; Figure 9 is a diagram of a modified form of the control circuit of Figure 8; Figure 10 is a diagram of a control circuit for use with the actuator of Figures 1 and 2, Figures 3 to 5, Figure 6, or Figure 7; and Figure 11 is a diagram of a control circuit for use with the actuator of Figures 1 and 2, Figures 3 to 5, Figure 6, or Figure 7.

Referring to Figures 1 and 2, an electrically operated parking brake 10 for a motor vehicle comprises an actuator 12, right and left brakes 14 for the front or the rear of the motor vehicle, and a control circuit (described below). The brakes 14 may be drum brakes or disc brakes or any other known type of brakes and will not be described in detail. Each brake 14 is connected to the actuator 12 by a Bowden cable 16. The actuator 12 comprises an electric motor 18 which rotatably drives a ball screw 20 by way of a gear train 22. The ball screw 20 is rotatably mounted by way of a pair of bearings 24,26 and is rotatable about a longitudinal axis A. The bearings 24,26 and the motor 18 are mounted in a housing 28.The outer sheath 30 of each Bowden cable 16 is secured to the housing 28, and the inner cable 32 of each Bowden cable extends in a longitudinal direction substantially parallel to axis A. The inner cables 32 are positioned on opposed sides of the ball screw 20.

A first nut 34 is threadably mounted on the ball screw 20. A yoke 36 is attached to the first nut 34, with the arms of the yoke extending outwardly substantially perpendicular to the axis A. The free end 38 of one of the inner cables 32 is secured to the free end 40 of one of the arms of the yoke 36.

Similarly, the free end 42 of the other inner cable 32 is secured to the free end 44 of the other arm of the yoke 36.

A second nut 46 is threadably mounted on the ball screw 20 and positioned adjacent the first nut 34.

A plate member 48 having a number of teeth 50 in an edge extending substantially parallel with axis A is secured to the second nut 46. A helical spring 52 positioned around the ball screw 20 and coaxial therewith acts on and biases the first and second nuts 34,46 in an axial direction towards the outer sheaths 30 of the Bowden cables 16.

A lever 54 is pivotally mounted on the housing 28 by way of a pivot pin 56 such that a pair of teeth 58 on the lever are positioned adjacent the teeth 50 on the plate member 48. A spring 60 acts on and biases the lever 54 such that the teeth 50,58 are normally in engagement. The teeth 50,58 are either shaped to allow relative axial movement in a brake apply direction, but prevent it in a brake release direction (in a form of ratchet and pawl arrangement), or are shaped to prevent relative axial movement in either direction. As can be seen from Figure 1, the teeth 58 on the lever 54 are positioned between the pivot pin 56 and the spring 60. A solenoid device 62 is positioned inside the spring 60 and is linked with the lever 54. The lever 54 has a free end 64, remote from the pivot pin 56, which extends outside of the housing 28.The relative positions of the first and second nuts 34,46 may be reversed with suitable repositioning of the lever 54. The solenoid device 62 may be positioned elsewhere, but still be connected to, and act on, the lever 54.

Examples of control circuits for operating the electric motor 18 and the solenoid device 62 are detailed below with reference to Figures 8 to 11. When application of the parking brake is required, power is applied to the electric motor 18. If the teeth 50,58 are shaped to allow relative axial movement in a brake apply direction, but prevent it in a brake release direction, no power is applied to the solenoid device 62. However, if the teeth 50,58 are shaped to prevent relative axial movement in either direction, power is simultaneously applied to the solenoid device 62 which pulls the lever 54 to pivot the lever about the pivot pin 56 to disengage the teeth 58 on the lever from the teeth 50 on the plate member 48. The application of power to the electric motor 18 cause the ball screw 20 to rotate about axis A. Rotation of the ball screw 20 causes the first and second nuts 34,46 to move in an axial direction X away from the outer sheathes 30 of the Bowden cables 16 against the bias of the spring 52.

This movement of the first nut 34 pulls the inner cables 32 of the Bowden cables 16 relative to their outer sheathes 30 to apply the brakes 14. The movement of the second nut 46 moves the teeth 50 on the plate member 48 relative to the teeth 58 on the lever 54.

The power to the electric motor 18 (and to the solenoid device 62, if actuated) is then removed. The teeth 50,58 engage to mechanically lock the brakes 14 in the applied position.

In order to release the parking brake, power is applied to the solenoid device 62. The solenoid device 62 pulls the lever 54 to pivot the lever about pivot pin 56 to disengage the teeth 50,58. The bias force of spring 52 pushes the first and second nuts 34,46 towards the outer sheathes 30 of the Bowden cables 16 in the reverse direction to X, and hence pushes the inner cables 32 relative to their outer sheathes to release the brakes 14. Also, the ball screw 20 rotates to reverse drive the gear train 22 and the motor 16. The power to the solenoid device 62 is then removed. If, for any reason, the power supply to the solenoid device 62 should fail, the parking brake may be released by manually operating the lever 54 (by gripping its free end 64) to pivot the lever about pivot pin 56 to disengage the teeth 50,58.

The second embodiment of actuator 72 shown in Figures 3 to 5 is similar to the actuator 12 shown in Figures 1 and 2, and like parts have been given the same reference number. In this embodiment of actuator 72, the single lever has been replaced by a pair of levers 74,76. The first lever 74 is pivotally mounted on a pivot pin 78 at one end 80 and at the other end is shaped into the form of a hook 82. Intermediate the ends 78,80, the first lever 74 has a pair of teeth 84 which are directed towards the plate member 48 and engageable with the teeth 50 on the plate member. A leaf spring 86 acts on and biases the teeth 84 on the first lever 74 towards the plate member 48.The teeth 50,84 (when not locked together, as explained below) are shaped to allow relative axial movement in either the brake apply direction or in the brake release direction - that is, the teeth 84 will click or ratchet over the teeth 50 as the plate member 48 moves in an axial direction. The second lever 76 is connected at one end 88 to the solenoid device 62 and is pivotally mounted on a pivot pin 90 at the other end 92.

Intermediate the ends 88,92 of the second lever 76 is a pin 94 which is latchable with the hook 82 on the first lever 74. The solenoid device 62 may be positioned elsewhere, but still be connected to, and act on, the second lever 76.

Examples of control circuits for operating the electric motor 18 and the solenoid device 62 of the actuator 72 are detailed below with reference to Figures 10 and 11. In the parking brake released position (Figure 5A), no power is applied to the motor 18 or to the solenoid device 62. The hook 82 on the first lever 74 is engaged with the pin 94 on the second lever 76 to lock the first lever. When application of the parking brake is required, power is applied to the electric motor 18 and to the solenoid device 62. The solenoid device 62 pulls the second lever 76 to pivot the second lever about its pivot pin 90. This action disengages the pin 94 on the second lever 76 from the hook 82 on the first lever 74 - see Figure 5B. The application of power to the electric motor 18 causes the ball screw 20 to rotate about axis A.Rotation of the ball screw 20 causes the first and second nuts 34,46 to move in an axial direction X away from the outer sheathes 30 of the Bowden cables 16 against the bias of the spring 52. This movement of the first nut 34 pulls the inner cables 32 of the Bowden cables 16 relative to their outer sheathes 30 to apply the brakes. The movement of the second nut 46 moves the teeth 50 on the plate member 48 relative to the teeth 84 on the first lever 74. The power to the electric motor 18 and to the solenoid device 62 is then removed.

The solenoid device 62 pushes the second lever 76 to move the second lever back so that the hook 82 on the first lever 74 becomes latched with the pin 94 on the second lever and the teeth 50,84 become locked in engagement to mechanically lock the brakes in the applied position - see Figure SC.

In order to release the parking brake, power is again applied to the solenoid device 62. The solenoid device 62 pulls the second lever 76 to pivot the second lever about its pivot pin 90. This action disengages the pin 94 on the second lever 76 from the hook 82 on the first lever 74 - see Figure SB. The bias force of spring 52 pushes the first and second nuts 34,46 towards the outer sheathes 30 of the Bowden cables 16 in the reverse direction to X, and hence pushes the inner cables 32 relative to their outer sheathes to release the brakes. The power to the solenoid device 62 is then removed. The solenoid device 62 pushes the second lever 76 to move the second lever back so that the hook 82 on the first lever 74 becomes latched with the pin 94 on the second lever see Figure 5A.

The actuator 100 partially shown in Figure 6 is a modification of the second embodiment shown in Figures 3 to 5, and like parts have been given the same reference number. In this embodiment, the first lever 102 and the second lever 104 are secured together at one end 106,108 respectively and pivot about a pivot pin 110 at that one end. The first lever 102 has a pair of teeth 112 at its other end 114 which are directed towards the plate member 48 and engageable with the teeth 50 on the plate member. The second lever 104 is attached to the solenoid device at its other end 116 in a similar manner to the second lever 76 of the actuator 72 of Figures 3 to 5. The teeth 50,112 are shaped to allow relative axial movement in a brake apply direction, but prevent it in a brake release direction (in a form of ratchet and pawl arrangement).

Examples of control circuits for operating the electric motor and the solenoid device of the actuator 100 are detailed below with reference to Figures 8 to 11. In the parking brake released position as shown in Figure 6, no power is applied to the motor or the solenoid device. When application of the parking brake is required, power is applied to the electric motor. The application of power to the electric motor causes the ball screw 20 to rotate about axis A. Rotation of the ball screw 20 causes the first and second nuts 34,46 to move in an axial direction X away from the outer sheathes 30 of the Bowden cables 16 against the bias of the spring 52. This movement of the first nut 34 pulls the inner cables 32 of the Bowden cables 16 relative to their outer sheathes 30 to apply the brakes. The movement of the second nut 46 moves the teeth 50 on the plate member 48 in an axial direction relative to the teeth 112 on the first lever 102, with the teeth 112 ratcheting or clicking over the teeth 50. The power to the electric motor is then removed. The teeth 50,112 become engaged to mechanically lock the brakes in the applied position.

Movement of the first lever 102 to disengage the teeth 50,112 is prevented by the tension in the inner cable 32 and the shape of the teeth 50,112.

In order to release the parking brake, power is applied to the solenoid device. The solenoid device pulls the second lever 104 to pivot the second lever and the first lever 102 about pivot pin 110. This action disengages the teeth 50,112. The bias force of spring 52 pushes the first and second nuts 34,46 towards the outer sheathes 30 of the Bowden cables 16 in the reverse direction to X, and hence pushes the inner cables 32 relative to their outer sheathes to release the brakes. The power to the solenoid device is then removed. The solenoid device pushes the second lever 104 to pivot the second lever and the first lever 102 back to the position shown in Figure 6. During this release step, power may also be applied for a limited time to the electric motor to slightly rotate the ball screw 20 and axially move the second nut 46 to encourage the disengagement of the teeth 50,112.This action means that a smaller solenoid device may be used.

The actuator 120 partially shown in Figure 7 is a modification of the first embodiment shown in Figures 1 and 2, and like parts have been given the same reference number. In this embodiment, the actuator 120 has been adapted to operate the parking brake of a motor vehicle by way of a single Bowden cable 16. In this case, one end 40 of the yoke 36 is connected to the free end 38 of the inner cable 32 of the Bowden cable 16. The other end 44 of the yoke 36 has a roller 122 mounted thereon. The roller 122 engages and is capable of rolling along in an axial direction, an internal surface 124 in the housing 28.

The surface 124 extends in a direction substantially parallel to the axis A. The operation of this actuator 120 is as described above with respect to the actuator 12 of Figures 1 and 2. This modification may also be made to the actuators 72 and 100 of Figures 3 to 5 and Figure 6 respectively. Optionally, a cable 126 may be secured to the one end 40 of the yoke 36 to allow the brakes to be operated manually by a hand brake or parking brake pedal.

Figure 8 shows a control circuit 130 which can be used in conjunction with the actuator 12 of Figures 1 and 2, the actuator 100 of Figure 6, or the actuator 120 of Figure 7, where the engageable teeth are shaped to allow relative axial movement in a brake apply direction, but prevent it in a brake release direction (in a form of ratchet and pawl arrangement), to define an electrically operable parking brake in accordance with the present invention. The control circuit 130 comprises a manually operable two-way toggle switch 132 which can be switched to provide power from a power source V (such as, the vehicle battery - not shown) to a brake apply circuit 134 or to a brake release circuit 136.The brake apply circuit 134 comprises a timer relay 138 which switches power to the electric motor 18 for a predetermined time to apply the parking brake when the toggle switch 132 is moved to the brake apply position. The brake release circuit 136 provides power to the solenoid device 62 to pull the lever 54,104 about its pivot pin 56,110 when the toggle switch 132 is moved to the brake release position to release the parking brake.

Figure 9 shows a modification to the control circuit of Figure 8, and like parts have been given the same reference number. The control circuit 140 of Figure 9 includes a pair of manually operable pushbutton switches 142,144 for brake apply and brake release respectively. Further still, a diode 146 is connected across the outputs of the push-button switches 142,144 and a switch 148 in the power supply line to the timer relay 138 is mechanically connected with the solenoid device 62. The brake apply circuit 134 operates as mentioned above on depression of the push-button switch 142. The brake release circuit 136, on depression of the push-button switch 144, provides power to the timer relay 138 to actuate the motor 18 until the solenoid device 62 pulls the lever 54,104 about its pivot pin 56,110 and simultaneously moves the switch 148 to an open circuit.This burst of power to the motor 18 helps to disengage the engaged teeth, allowing a smaller solenoid device to be used when compared to the control circuit 130 of Figure 8.

The control circuit 150 of Figure 10 is usable in conjunction with any of the above described embodiments of actuator 12,72,110,120 to define an electrically operable parking brake in accordance with the present invention. The control circuit 150 includes a pair of manually operable push-button switches 152,154 which can be switched to provide power from a power source V (such as, the vehicle battery not shown) to a brake apply circuit 156 or to a brake release circuit 158 respectively. The brake apply circuit 156 comprises a timer relay 160 which switches power to the electric motor 18 for a predetermined time to apply the parking brake when the push-button switch 152 is pressed.Further still, a diode 162 is connected across the outputs of the push-button switches 152,154 and a switch 164 in the power supply line to the timer relay 160 is mechanically connected with the solenoid device 62. Depression of the push-button switch 152 therefore also applies power to the solenoid device 62 to pull the lever 54,76,104 about its pivot pin 56,90,110 and to close the switch 164. This arrangement ensures that the engaged teeth either become disengaged, or are unlocked, before the motor 18 drives the ball screw 20 to apply the parking brake. The brake release circuit 158 provides power to the solenoid device 62 to pull the lever 54,76,104 about its pivot pin 56,90,110 when the push-button switch 154 is depressed to release the parking brake.

In the control circuits 130,140,150 described above, the timer relay 138,160 may be omitted and power may be applied directly to the motor 18 on actuation of the brake apply switch. In this case, the solenoid controlled switches 148,164 would be in the power supply line to the motor 18. This arrangement would rely on the vehicle operator actuating the brake apply switch for enough time to apply the parking brake.

The control circuits 130,140,150 described above may include a door lock switch which automatically applies the parking brake on locking of the vehicle doors and/or an automatic park switch which automatically applies the parking brake when a vehicle with an automatic transmission is placed in park mode and/or an anti-theft switch which would prevent release of the parking brake unless authorised by the vehicle operator.

As an alternative to the above described control circuits, the control circuit 170 of Figure 11 may be used in conjunction with any of the above described embodiments of actuator 12,72,110,120 to define an electrically operable parking brake in accordance with the present invention. The control circuit 170 comprises a control module 172 (which is computer based) which receives input signals from a wheel speed sensor, brake apply and release switch, the vehicle battery, electrical ground, and optionally an anti-theft switch, a door lock switch, the vehicle ignition switch, and the acceleration pedal. Based on these input signals, the control module can control the operation of the motor and solenoid device, and optionally operate a park brake light, or the brake lights, or send information to other control modules within the vehicle. This arrangement can prevent the application of the parking brake if the control module senses that the vehicle wheels are still rotating.

The present invention can be used as a sole means for operating the parking brake of a motor vehicle, or may be used in conjunction with a known hand brake lever or parking brake pedal.

Claims

Claims:

1. An actuator for an electrically operable parking brake comprising an electric motor; a screw rotatably drivable about its longitudinal axis by the electric motor; a first nut threadably engaged with the screw and connectable with a cable for operating a brake; a second nut threadably engaged with the screw and having teeth thereon extending in the axial direction, the first and second nuts being movable along the screw between a brake applied position and a brake released position; a lever pivotable about a pivot pin and having teeth thereon engageable with the teeth on the second nut when the second nut is in the brake applied position; and a solenoid device which on actuation allows the disengagement of the teeth when the second nut is in the brake applied position.

2. An actuator as claimed in Claim 1, wherein a yoke is secured to the first nut, the yoke extending in a direction substantially normal to the longitudinal axis and having means at one end for connecting with the cable.

3. An actuator as claimed in Claim 2, wherein the yoke has means at its other end for connecting with a second cable.

4. An actuator as claimed in Claim 2, wherein the yoke has means at its other end for mounting a roller.

5. An actuator as claimed in any one of Claims 1 to 4, wherein the solenoid device is connected with the lever and pivots the lever about the pivot pin on actuation of the solenoid device to disengage the teeth.

6. An actuator as claimed in any one of Claims 1 to 4, wherein the solenoid device is connected to a second lever which is pivotable about a pivot pin and which has means thereon for latching with corresponding means on the lever with the teeth thereon, the second lever being pivoted about its pivot pin on actuation of the solenoid device to release the latching means.

7. An actuator as claimed in Claim 6, wherein the latching means comprises a pin on the second lever which is engageable with a hook on the lever with the teeth thereon.

8. An actuator as claimed in any one of Claims 1 to 7, wherein a spring acts on the first and second nuts to bias them towards the brake released position.

9. An actuator as claimed in any one of Claims 1 to 8, wherein a spring acts on the lever to bias the teeth thereon towards the teeth on the second nut.

10. An electrically operable parking brake for a motor vehicle comprising a wheel brake; a cable connected to the wheel brake for operating the wheel brake; an actuator including an electric motor, a screw rotatably drivable about its longitudinal axis by the electric motor, a first nut threadably engaged with the screw and connected with the cable, a second nut threadably engaged with the screw and having teeth thereon extending in the axial direction, the first and second nuts being movable along the screw between a brake applied position and a brake released position, a lever pivotable about a pivot pin and having teeth thereon engage able with the teeth on the second nut when the second nut is in the brake applied position, and a solenoid device which on actuation allows the disengagement of the teeth when the second nut is in the brake applied position; and a control circuit for controlling the actuation of the electric motor and the solenoid device.

11. An electrically operable parking brake as claimed in Claim 10, wherein the control circuit comprises a manually operable switch for switching electrical power to the electric motor which, when actuated, rotates the screw to move the first and second nuts to the brake applied position; and a manually operable switch for switching electrical power to the solenoid device which, when actuated, allows the disengagement of the teeth.

12. An electrically operable parking brake as claimed in Claim 10 or Claim 11, wherein the control circuit includes a timer relay associated with the electric motor for actuating the electric motor for a predetermined time.

13. An electrically operable parking brake substantially as herein described with reference to, and as shown in, the accompanying drawings.

14. An actuator substantially as herein described with reference to, and as shown in, Figures 1 to 7 of the accompanying drawings.