Brake actuator apparatus and method for actuating a brake

A brake actuating apparatus includes a force transmission element operable to transmit a brake actuating force and an abutment member moveable to abut the force transmission element. A piezo-electric device operable on expansion applies a force between the abutment member and the force transmission element to move the force transmission element in a direction of brake actuation. A support member moveable independently of the abutment member supports the force transmission element in the new position following expansion of the piezo-electric device.

This application claims priority to PCT application PCT/GB02/01463 filed on Mar. 27, 2002, which claims priority to Great Britain patent application GB0110438.9 filed Apr. 27, 2001.

TECHNICAL FIELD

The present invention relates to a brake actuator apparatus and method for actuating a brake.

BACKGROUND OF THE INVENTION

A known vehicle braking system includes a disc fixed for rotation with a wheel and a brake clamping mechanism including a tappet mechanically actuated to bring brake pads into contact with the disc and to apply a force between the pads and the disc to provide frictional braking.

Piezo-electric devices, which expand when energized by an electric voltage, are known for applying a mechanical actuating force over a short distance.

SUMMARY OF THE INVENTION

The brake actuating apparatus of the present invention includes a force transmission element operable to transmit a brake actuating force and an abutment member moveable to abut the force transmission element. A piezo-electric device operable on expansion applies a force between the abutment member and the force transmission element to move the force transmission element in a direction of brake actuation. A support member is moveable independently of the abutment member to support the force transmission element in its new position following expansion of the piezo-electric device.

Preferably, the piezo-electric device is fixed for movement with the first abutment member. Alternately, the piezo-electric device may be fixed for movement with the force transmission element.

Preferably, the apparatus further includes a body member. The abutment member has a threaded portion in threaded engagement with the body member to be moveable by relative rotation between the abutment member and the body member.

Preferably, the support member includes a threaded portion in threaded engagement with a second body member of the apparatus and is axially moveable by relative rotation between the support member and the second body member.

The abutment member and support member are rotatable by respective rotation devices. Alternately, the body member and the second body member are rotatable by respective rotation devices. Preferably, the rotation devices are electric motors.

For releasing the brake, the support device is arranged to support the force transmission element for movement of the abutment member, with the piezo-electric device contracted, to a position wherein expansion of the piezo-electric device causes the abutment member to abut the force transmission element. The support member is moveable to a position wherein contraction of the piezo-electric device allows the force transmission element to move into abutment with the support member.

A method for actuating a brake includes moving an abutment member into abutment with a force transmission element operable for transmitting a brake actuating force. A piezo-electric device expands to apply a force between the abutment member and the force transmission member to move the force transmission element in a direction of brake actuation. A support member is moved into abutment with the force transmission element to support the force transmission element in its new position, and the piezo-electric device is contracted. These steps are repeated as many times as required to actuate the brake. When the brake is to be released, the force transmission element is supported by the support member and the piezo-electric device contracts, moving the abutment member out of abutment with the force transmission element. The piezo-electric device is expanded, and causing the abutment member to abut the force transmission element. The support member is moved away from the force transmission element, contracting the piezo-electric device, causing the support member to support the force transmission element. These steps are repeated as many times as required to release the brake.

Although the distance the piezo-electric device moves is small, by repeatedly expanding and contracting the device and moving the abutment member and support member to abut the force transmission element, the piezo-electric device may be used to provide a substantially larger movement to the force transmission element.

A braking mechanism has a degree of elasticity in its structure, and a degree of elastic deformation has to be taken up by the structure before the force applied by the actuating device is transmitted to the brake pads. The piezo-electric device may be used to move the force transmission element beyond the elastic deformation of the structure and to apply the braking force.

A further advantage is that the same apparatus may also be used to release the brake.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1ashows an actuator5for actuating a brake24including an abutment member in the form of a pin10arranged on an axis of the actuator5. The pin10has a threaded portion11in threaded engagement with an associated first body member12of a vehicle brake mechanism. The first body member12is axially fixed with respect to the brake mechanism. A piezo-electric device14including at least one piezo-electric element is fixed to the pin10and is expandable by application of an electric voltage. The pin10abuts a force transmission element in the form of a tappet16for transmitting an applied actuating force in an axial direction. The tappet16forms part of a clamping mechanism for exerting a clamping force on a pair of brake pads in response to application of the brake24.

A support member in the form of a sleeve18has a threaded portion19in threaded engagement with an associated second body member20of the brake mechanism. The second body member20is axially fixed with respect to the brake mechanism. The sleeve18is substantially coaxial with and surrounds the pin10. The sleeve18abuts the tappet16to support it.

The engagement of the threaded portions11and19of the pin10and the sleeve18, respectively, provide axial movement by relative rotation between the pin10and the sleeve18and their respective associated body members12and20. Rotational motion is provided to the pin10or the sleeve18by associated electric motors22. Alternately, rotational motion may be provided to the first and second body members12and20, respectively.

The piezo-electric device14does not have to directly abut the tappet16(as shown inFIGS. 1ato1eand2ato2e), but may be situated at any position along the length of the pin10so that expansion of the piezo-electric device14causes the pin10to abut the tappet16and to apply a force in the axial direction. Alternately, the piezo-electric device14can be attached to the tappet16.

Referring toFIG. 1b, in the first stage of actuation of the brake24, the piezo-electric device14is expanded by application of the electric voltage to apply a force to the tappet16and move the tappet16in the axial direction out of contact with the sleeve18.

In the second stage, as shown inFIG. 1c, the sleeve18is rotated to move axially to abut the tappet16.

In the third stage, as shown inFIG. 1d, the piezo-electric device14is contracted by removal of the electric voltage, moving the pin10out of contact with the tappet16.

In the fourth stage, as shown inFIG. 1e, the pin10is rotated to move axially to abut the tappet16. The actuator5is in the same configuration as inFIG. 1a, although the tappet16, the pin10, and the sleeve18have been moved in the axial direction.

The stages shown inFIGS. 1ato1eare repeated as many times as required to take up the elastic deformation of the brake mechanism and to apply the required braking force to the brake24.

Although only a small movement of the tappet16can be affected by a single expansion of the piezo-electric device14, the brake24can be actuated by repeated expansion and contraction of the piezo-electric device14.

Referring toFIG. 2a, in the first stage of releasing the brake24, the pin10is rotated to move a first predetermined distance axially away from the tappet16.

The first predetermined distance is set such that in the second stage, as shown inFIG. 2b, the piezo-electric device14is expanded to abut the tappet16and move the tappet16just clear of the sleeve18.

In the third stage, shown inFIG. 2c, the sleeve18is rotated to move a second predetermined distance axially away from the tappet16.

The second predetermined distance is set such that in the fourth stage, as shown inFIG. 2d, the sleeve18is in a position such that, when the piezo-electric device14is contracted, the tappet16moves axially to just abut the sleeve18before the piezo-electric device14has fully contracted.

The stages shown inFIGS. 2aand2dare repeated to further release the brake24.