GB2539717A

GB2539717A - A disc brake

Info

Publication number: GB2539717A
Application number: GB1511289.9A
Authority: GB
Inventors: Mazumdar Abhisher; Tirovic Marko; V Spurr Nigel; J Mcginn Matthew; Taylor Martin
Original assignee: Meritor Heavy Vehicle Braking Systems UK Ltd
Current assignee: Meritor Heavy Vehicle Braking Systems UK Ltd
Priority date: 2015-06-26
Filing date: 2015-06-26
Publication date: 2016-12-28
Also published as: GB201511289D0

Abstract

A brake having a rotor 250; a pilot friction element 252 for applying a braking force to the rotor, an actuator 274 for actuating movement of the pilot friction element to apply a braking force to the rotor; a main friction element 254 for applying a further braking force to the rotor; and a transmission arrangement, comprising a link arm 268 and lever 258, for transmitting a friction force to the main friction element so as to move the main friction element towards the rotor. The friction force resulting between the pilot friction element and the rotor during braking to the pilot friction element (or brake pad) as the pilot friction element is moved in a tangential direction to the rotation direction of the rotor or disc. This arrangement may be used to decrease the size of the brake components, such as the actuator, or lessen the force required to be transmitted by the brake.

Description

A Disc Brake

FIELD OF THE INVENTION

The present invention relates to a disc brake for applying a braking drag force to a rotor of a disc brake. In particular, the present invention relates to a disc brake for use on a heavy vehicle, such as a truck or a bus.

BACKGROUND OF THE INVENTION

An example (of many) of a known disc brake for use on a heavy vehicle is shown generally at 110 in Figure 1. This disc brake 110 is an air actuated disc brake. The disc brake 110 has a brake carrier 112 that carries an outboard brake pad 114, an inboard brake pad 116, and a caliper 124. A brake disc or rotor 118 is positioned between the two brake pads 114 and 116. Two pistons 120 and 122 are positioned in the caliper 124 and are operable by an air actuator (not shown) via an operating shaft 121 to push the inboard brake pad 116 towards the brake disc 118. The brake disc 118 is fixed in an inboard-outboard direction, such that movement along an axis 126 perpendicular to a principal plane of the brake disc is prevented. This arrangement is such that when the inboard brake pad 116 is pushed towards and contacts the brake disc 118, further pushing of the inboard brake pad towards the brake disc causes the caliper to move inboard. As the caliper 124 moves inboard it moves the outboard brake pad 114 towards the brake disc 118 clamping the brake disc 118 between the outboard and the inboard pads. As the brake pads are restrained from tangential motion by the carrier braking is thereby effected by frictionally inhibiting rotation of the brake disc 118. The torque that is induced is reacted through the carrier to the axle or steering knuckle on which it is mounted.

In brakes of this type, all the force required to induce the friction to inhibit rotation of the brake disc is provided by compressed air being introduced into the air actuator.

Various arrangements have been proposed to enable disc brakes to self servo", but hitherto no such self servo disc brake has been offered commercially to the knowledge of the applicant

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved disc brake.

A first aspect of the invention provides a brake having: a rotor; a pilot friction element for applying a braking force to the rotor; an actuator for actuating movement of the pilot friction element to initiate contact between the pilot friction element and the rotor; a main friction element for applying a braking force to the rotor; and a transmission arrangement for transmitting a pilot friction force, generated between the pilot friction element and the rotor during application of the pilot friction element, to the main friction element so as to move the main friction element into contact with the rotor.

During braking, the pilot friction element is actuated into engagement with the rotor. As the pilot friction element contacts the rotor a friction force is established between the rotor and the pilot friction element. Contrary to conventional friction elements in prior art brakes, the pilot friction element is not restrained in a circumferential IS direction. Therefore, the friction force causes the pilot friction element to move at a tangent to the rotation of the rotor. The transmission arrangement transmits the friction force to the main friction element. The transmission arrangement then utilises the friction force to move the main friction element.

Accordingly, the brake requires a reduced external force input, for example a reduced force input from an air, hydraulic or electro-mechanical actuator, than a brake of the prior art. This beneficial reduction in the external force input required can advantageously result in a decreased size of the actuation mechanism used with the brake.

Further, the brake arrangement of the first aspect means that less force may be required to be transmitted by one or more components of the brake, which means that in some cases it may be possible to modify components of the brake for reduced weight e.g. the components may be manufactured from an alternative material or have an alternative configuration The transmission arrangement may comprise a mechanism for transmitting the friction force in a direction substantially perpendicular to the rotor instead of a direction substantially tangential to the direction of rotation of the rotor as applied to the pilot friction element The transmission arrangement may comprise a mechanism configured for converting movement of the main friction element in a direction substantially tangential to the direction of rotation of the rotor to a direction towards the rotor. Such a mechanism advantageously permits the brake to self-servo (self-apply a braking effect) The transmission arrangement may further control a control system and actuation mechanism for moving the main friction element in a direction away from the rotor.

The transmission arrangement may comprise a mechanism for using mechanical gain to amplify the friction force Amplification of the friction force further reduces the external force input required to operate the brake. The mechanism may, for example, comprise a lever, an offset cam, a chain, a belt and/or gear(s) The transmission arrangement may comprise adjustable connections such that the mechanical gain can be adjusted For example, the effective lever length of a lever or offset rotary connection may be adjustable.

The transmission arrangement may comprise a lever. A lever provides a simple method of achieving mechanical gain. The transmission arrangement may comprise a plurality of levers and/or effective levers.

The brake may comprise a single pivot point or multiple pivot points, for example, two, three or four pivot points.

The transmission arrangement may comprise a member positioned between the main friction element and a support The support and/or the connection between the member and the support may be configured to permit movement of the member relative to the support so as to move the main friction element towards and away from the rotor as desired.

The member may be configured to be moveable to move the main friction element towards the rotor due to a friction force applied to the main friction element, resulting in an increased frictional force between the main friction element and the rotor.

In exemplary embodiments, the member is a lever pivotally connected to the main friction element. The lever may be pivotally connected to the support. The lever may be arranged such that rotation of the lever in a predetermined direction moves the main friction element towards the rotor.

The support may be configured to move in an arcuate path. The arcuate path may be arranged to have an arcuate portion on each side of a point spaced to be a maximum distance from the rotor, so as to permit the transmission arrangement to be utilised in both forward and rearward drive.

The brake may comprise an arcuate slot. The support may be positioned in the arcuate slot and be moveable therein.

The transmission arrangement may comprise a linkage between the pilot friction element and the lever so as to transmit the pilot friction force to the lever. The linkage may be a link arm. The link arm may be pivotally connected to the pilot friction element and to the lever.

Alternatively or additionally, the transmission arrangement may comprise any suitable, or any suitable combination of, a crank system, a piston, a chain, a gear arrangement, and/or a rack and pinion arrangement.

The member may comprise a roller. The support may comprise a ramp. The roller may be positioned between a backing plate of the main friction element and the ramp.

The roller may be cylindrical or spherical in shape.

The ramp may be a generally V-shaped block. Use of a V-shaped block permits the transmission arrangement to be utilised in both forward and rearward drive.

The ramp may have a varying incline for optimising braking performance.

The ramp may be fixed in a direction tangential to rotation of the rotor. The main friction element may be connected to the pilot friction element for transmitting the pilot friction force to the main friction element. For example, the main friction element and the pilot friction element may share a backplate. Alternatively, a

S

connection member may connect the pilot and the main friction element. The connection member may be rigid.

The brake may comprise a drive for moving the support in a direction towards and away from the rotor so as to control braking of the rotor. Movement of the support in such a manner permits the mechanical advantage achieved by the transmission arrangement to be adjusted. Further, when the brake is arranged to take advantage of a self servo effect, movement of the support in such a manner enables the brake to be released, and also in some embodiments is used to prevent locking up of the brake.

The drive may be operated by a control system.

The brake may comprise a wear adjustment mechanism for moving the pilot and/or main friction element relative to the rotor so as to account for wear of the pilot and/or friction element The wear adjustment mechanism may be integrated with the drive, and optionally with the control system.

The ramp may be moveable in a direction tangential to a direction of rotation of the rotor. The ramp may be fixed in an inboard-outboard direction.

The transmission arrangement may comprise a cam, e.g. an eccentrically rotatable disc. A link arm may be pivotally connected between the pilot friction element and the cam. The cam may be mounted within or connected to a block that connects to the main friction element. The cam may be connected to the pilot friction element and the main friction element via an arrangement that moves the main friction element in an inboard-outboard direction when a force in a direction tangential to the direction of rotation of the rotor is applied to the pilot friction element.

The pilot and main friction element may both be positioned on the same side of the rotor in an inboard-outboard direction. One or more further friction elements may be positioned on an opposing side of the rotor, such that during a braking operation the rotor can be clamped between the pilot, main and further friction elements.

The pilot and main friction elements may be manufactured from different friction material. For example, one of the friction elements may be designed for regular use under normal braking conditions, and the other friction element may be optimised for power and performance, e.g. emergency stops.

The brake may comprise one, two, three, four or more main friction elements.

The brake may comprise a resilient element such as a return spring. Such a return spring can be positioned and configured to return the pilot and/or main friction element to a non-braking position.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 shows a partial cross section of an example of an air actuated disc brake of the prior art, Figure 2 shows a schematic plan view of a rotor, friction elements and transmission arrangement of a brake according to an embodiment of theinvention; Figure 3 shows a schematic plan view of a rotor, friction elements and transmission arrangement of a brake according to another embodiment of the invention; Figure 4 shows a schematic plan view of a rotor, friction elements and transmission arrangement of a brake according to a further embodiment of the invention; and Figure 5 shows a schematic plan view of a rotor, friction elements and transmission arrangement of a brake according to yet a further embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENT(S)

Several embodiments of the invention will now be described with reference to Figures 2 to 5, which schematically show a rotor, friction elements, an actuator and transmission, the arrangement of which can be applied to new disc brakes or by adapting a disc brake of the prior art, including the brake shown in Figure 1 The embodiments will be described with reference to an inboard I and outboard 0 direction. When the disc brake is mounted to a vehicle, the inboard direction is innermost a vehicle chassis and the outboard direction is outermost the vehicle chassis Referring to Figure 2, a pilot friction element 252 and a main friction element 254 are positioned on an inboard planar face of a rotor 250. One or more further friction elements are positioned on the outboard planar face of the rotor 250, in the present embodiment one further friction element 251 is provided. The friction element 251 on the outboard side is supported in an outboard direction at least by the caliper 224. The caliper 224 is shown in cut away view and sectioned so that the rotor 250 and components of the braking mechanism are visible.

On the inboard side of the main friction element 254 a mount 256 is provided, to IS which a lever 258 is connected. In this embodiment the lever 258 is pivotally connected to the friction element mount 256 at pivot point 262 An arcuate slot 266 is positioned inboard and spaced from the main friction element 254. The arcuate slot 266 is fixed with respect to the caliper. The arcuate slot is shaped and positioned to have two portions that arc towards the rotor, as viewed in Figure 2, one portion is positioned nearest the pilot friction element and the other portion is positioned furthest the pilot friction element.

A runner, in this embodiment a die block 260 is positioned in the slot 266 and is able to slide along the slot under the influence of a suitable drive 296 and control system 298.

The lever 258 is connected to the die block 260 In this embodiment, the lever 258 is pivotally connected to the die block 260 at pivot point 261.

A link arm 268 couples the pilot friction element 252 to the lever 258. In this embodiment, a pilot friction element mount 253 is positioned inboard of the pilot friction element. The link arm 268 is pivotally connected to the mount 253 at pivot point 267. The link arm is also pivotally connected to the lever 258 at a pivot point 272.

An actuator 274 is provided to apply a force F to the pilot friction element 252 so as to move the pilot friction element into contact with the rotor 252 when braking is required. The actuator 274 may be an air, hydraulic or electro-mechanical actuator.

In the present embodiment, the rotor is fixed in an inboard-outboard direction and the friction element 251 on the outboard side of the rotor is fixed relative to the caliper. The caliper, pilot friction element 252 and main friction element 254 are moveable in an inboard-outboard direction, e.g. by being supported on guide pins mounted on the carrier (not shown) fixed to an axle or steering knuckle. The pilot friction element and main friction element are non-fixidly mounted in a circumferential direction and so they are capable of moving in a direction tangential to the inboard-outboard direction in the plane of Figure 2. In alternative embodiments, the rotor may be a sliding rotor and the caliper may be fixed, or both the rotor and caliper fixed, with an actuation mechanism for the outboard friction element.

Although not shown in Figure 2, a wear adjustment mechanism may be provided to adjust the position of the friction elements 251, 252 and 254 relative to the rotor 250 so as to account for wear of the friction elements. In some embodiments, the drive and control system may be configured to move the block in the arcuate slot to adjust for wear of the main friction element.

In use, when the above described arrangement is provided on a brake and braking is required, the actuator 274 applies a force F to the pilot friction element 252. The application of force F moves the pilot friction element 252 into contact with the rotor 250.

The rotary motion of the rotor 250 means that the rotor applies a friction force to the pilot friction element 252 in a direction tangential to the rotary motion of the rotor 250. As the pilot friction element is not directly restrained in a circumferential direction, the friction force causes the pilot friction element to move at a tangent to the rotation of the rotor. The movement of the pilot friction element and therefore the friction force is transmitted through the mount 253 to the link arm 268. The link arm 268 transmits the friction force to the lever 258 which causes the lever 258 to pivot at the pivotal connection 261 with the die block 260.

Considering the arrangement shown in Figure 2, upon application of the friction force to the lever 258, the lever 258 rotates in an anti-clockwise direction about pivot point 261. Such anti-clockwise motion of the lever 258 moves the main brake friction element 254 into contact with the rotor 250 by virtue of the geometry of the arrangement with the die block 260 positioned as shown in Figure 2. As can be seen in Figure 2, when the lever 258 rotates an arcuate path is formed. The end of the lever mounted to the main friction element 254 moves closer to the rotor as it follows the arcuate path in an anti-clockwise direction. The main friction element thereby moves closer to the rotor and contacts it.

A reaction force due to contact of the main friction element 254 with the rotor 250 causes the caliper 224 to move inboard which in turn moves the outboard friction element 251 into contact with the rotor 250 to cause a clamping braking effect.

IS When the main friction element 254 contacts the rotor 250 the rotor applies a friction force in a direction tangential to the rotary motion of the rotor 250 to the main friction element 254. This friction force causes the main friction element 254 to move in a direction of the friction force. Said tangential movement of the main friction element 254 further rotates the lever 258 in an anti-clockwise direction about the pivotal connection 261. As discussed above, rotation of the lever 258 in said direction (towards the pilot friction element as viewed in Figure 2) means that an end of the lever 258 connected to the main friction element is moved further closer to the rotor 250.

Accordingly, said further rotation of the lever 258 increases the force applied by the main friction element 254 to the rotor 250. The increasing force acts as a braking drag force which restrains the tangential motion of the main friction element and restricts the rotation of the rotor.

As the main friction element 254 is moved further towards and in further contact with the rotor 250, the caliper 224, and thereby the outboard friction element 251 (which is retrained tangentially by the carrier) are also further urged towards the rotor 250 to further increase the clamping braking force applied to the rotor and the rotation of the rotor is further retarded.

Additionally, the braking drag force of the main friction element and restraining of the tangential motion of the main friction element causes the pilot friction element to be restrained tangentially so this now applies a braking drag force proportional to force F to additionally retard rotation of the rotor 250 Without intervention from the control system, the braking drag force applied by the main and outboard friction element 254 arid 251 continues to increase until the rotor is substantially static (i.e. in a fully braked position). More typically, the control system adjusts the position of the die block 260 to remove the self-servo effect once it senses that driver brake demand has reduced.

The use of the friction force to apply the main friction element 254 to the rotor and provide a braking drag force provides a self-servo effect. The self-servo effect reduces the overall energy input required to effect braking of the system.

The force applied by the main friction element 254 can be altered by changing the force F applied to the pilot friction element 252. Alternatively or additionally, the mechanical advantage (also referred to as mechanical gain) can be adjusted by changing the position of the die block 260 in the arcuate slot 266 using the suitable drive and control system mentioned previously.

The provision of an arcuate slot that arcs towards the rotor in both a direction towards the pilot friction element and away from the pilot friction element (as shown in Figure 2), and of the link arm 268 to transmit forces in compression and tension, permits the advantages of the force transmission to be utilised in both forward and rearward drive of the rotor. That is, to operate the force transmission in rearward (or reverse) drive, the die block 260 is moved to a portion of the arc opposite the portion used for forward drive, i.e. taking the orientation as shown in Figure 2. To operate in rearward drive the die block is moved upwards past the point where the lever 258 is substantially horizontal.

In alternative embodiments to that described above, the friction elements may have an alternative arrangement. For example, a further pilot friction element may be provided on the outboard side of the rotor 250 in addition to the pilot friction element 251 provided on the inboard side of the rotor 250. Further alternatively, the pilot friction element may be provided on the outboard side of the rotor instead of the inboard side and an alternative lever and link arm arrangement may be used to apply the main friction element 254.Referring now to Figure 3 another embodiment is shown. Similar to the previously described embodiment, a pilot friction element 352 and a main friction element 354 are positioned on one planar side of a rotor 350. One or more further friction elements 394 are positioned on the opposite planar side of the rotor 350. The one or more further friction elements are fixed relative to a caliper in an inboard-outboard direction, as shown in the embodiment of Figure 2, but for clarity the caliper is not shown in Figure 3.

A disc 376 is positioned on an inboard side of the main friction element 354. The disc 376 is circular in shape and has a centre of rotation 377 that is offset from the Geometric centre of the disc in order to act as a cam.

A link arm 368 is pivotally connected to the pilot friction element 352 and extends for connection with the disc 376. The link arm 368 is pivotally connected to the disc 376 at a point 372 which is offset 373a, 373b from the centre of rotation 377 of the disc.

In use, an actuator 374 applies a force F to move the pilot friction element 352 into contact with the rotor 350. Similarly to the previously described embodiment, when the pilot friction element 352 contacts the rotor 350, the rotor applies a friction force to the pilot friction element 352. The friction force is transmitted from the pilot friction element 352 through the link arm 368 to the disc 376. Said transmission of the friction force to the disc 376 causes the disc to rotate. The offset nature of the centre of rotation 377 means that rotation of the disc (in the anti-clockwise direction as shown in Figure 3 upon application of a friction force in a downwards direction as shown in Figure 3) moves the main friction element 354 towards the rotor 350.

When the main friction element 354 contacts the rotor 350 a friction force in a direction tangential to the rotary motion of the rotor 350 is applied to the main friction element 354. The friction force causes the main friction element 354 to move in a direction of the friction force. Said tangential movement of the main friction element 354 further rotates cam 376 about the centre of rotation 377. As discussed above, rotation of the cam 376 in said direction (anti-clockwise as viewed in Figure 3) means that the main friction element 354 moves further towards the rotor 350 creating a braking drag force As the main friction element moves towards the rotor, the caliper, and thereby the outboard friction element 251 are also urged towards the rotor to provide a clamping braking effect.

Similar to the previously described embodiment, a control system (not shown) is used to rotate the cam 376 (e.g. via movement of the centre of rotation 377) to control the braking force and/or adjust for wear of the main friction element.

Similarly to the embodiment of Figure 2, a wear adjustment mechanism may be provided to adjust the position of the friction elements 351, 352 and 354 relative to the rotor 350 so as to account for wear of the friction elements The force applied by the main friction element 354 may be altered by changing the force F applied to the pilot friction element 352.

The use of the friction force to apply the main friction element 354 reduces the overall force input required to the system.

Referring now to Figure 4, a further embodiment is shown. Similar to the previously described embodiments a pilot friction element 452 and a main friction element 454 are positioned on the inboard side of a rotor 450, and one or more further friction elements 495 are positioned on the outboard side of the rotor 450. Similar to the embodiment of Figure 2 the further friction element 495 is fixed relative to a caliper that is moveable in aninboard-outboard direction, but for clarity the caliper is not drawn in Figure 4.

In this embodiment, the pilot friction element and the main friction element are mounted on a shared backplate 478, such that the backplate 478 connects the pilot friction element 452 and the main friction element 454. However, in alternative embodiments, the pilot and main friction elements may be connected by some other connection member, for example the pilot and main friction elements may be mounted on separate backplates (as in the previously described embodiments) and connected using a connection member. The pilot friction element 452 and main friction element 454 can move in an inboard-outboard direction, and as viewed in Figure 4 in a direction that is tangential to the inboard-outboard direction and in a plane of Figure 4.

A generally V-shaped ramp 480 is positioned on an inboard side of the main friction element 454. A roller 482 is seated in the ramp. The roller 482 may be cylindrical or spherical in shape. In exemplary embodiments, the V-shaped ramp 480 may have a varying incline over its profile so as to optimise braking performance. In alternative embodiments, the ramp may not be generally V-shaped and instead be any suitable shape including a ramped profile which the roller can climb. The V-shaped ramp is fixed in a direction that, in use, is tangential to the rotation of the rotor.

As in the previously described embodiments, in use, an actuator 474 applies a force F to the pilot friction element 452 to move the pilot friction element into contact with the rotor 450. The rotary motion of the rotor 450 means that a friction force is applied to the pilot friction element 452. The friction force pulls the pilot friction element 452 in the direction of rotation of the rotor 450 and displaces the pilot friction element 452. Since the pilot friction element 452 is mounted on the same backplate 478 as the main friction element 454, displacement of the pilot friction element 452 also results in displacement of the backplate 478 and the main friction element 454.

The displacement of the main friction element 454 causes the roller 482 to roll up an incline of the V-shaped ramp 480. The motion of the roller 482 up the ramp 480 causes the main friction element 454 to move towards and contact the rotor 450 causing increased braking of the rotor 450.

A reaction force due to contact of the main friction element 454 with the rotor 450 causes the outboard friction element 495 to move into contact with the rotor 450, such that clamping braking is effected.

Once the main friction element 454 contacts the rotor 450, the rotor applies a friction force to the main friction element 454, in a direction tangential to the rotational direction of the rotor. The applied friction force causes the main friction element 454 to move in a direction opposite the direction of the applied friction force Said movement of the main friction element causes the roller 482 to further roll up the incline of the V-shaped ramp, causing the main friction element to move closer to the rotor. The force applied by the main friction element to the rotor 450 is thereby increased and the tangential motion of the main friction element is retrained. In turn, the further application of the main friction element on the rotor further urges the outboard friction element 495 towards the rotor 450 such that a clamping braking effect acts to inhibit rotation of the rotor 450.

Again, without intervention from the control system, the braking force applied to the rotor continues to increase in the described manner until the rotor is substantially stationary (i.e. full braking is effected). More commonly, the control system intervenes to move the position of the V-shaped ramp in an inboard direction by utilising a suitable actuation mechanism (not shown in Figure 4), thereby moving the roller down the ramp and away from the rotor. Once the roller is at the "starting point", i.e. a location on the ramp furthest from the rotor in the present embodiment, the V-shaped ramp is moved towards the rotor 250 to reset the position of the V-shaped ramp.

Due to the common backplate, the tangential restraint of the main friction element 454 also restrains tangential movement of the pilot friction element 452, so this also generates a drag force proportional to force F applied thereto.

Similarly to the embodiment of Figures 2 and 3, a wear adjustment mechanism may be provided to adjust the position of the friction elements 451, 452 and 454 relative to the rotor 450 so as to account for wear of the friction elements. In the present embodiment the wear adjustment mechanism is separate from the control and actuation mechanism used to move the V-shaped ramp in an inboard-outboard direction, but in alternative embodiments the wear adjustment mechanism may be integrated with the control and actuation mechanism The degree of self servo effect can be adjusted by changing the angle of the incline of the V-shaped ramp, or retracting the ramp inboard with respect to the caliper under the influence of the control and actuation mechanism (not shown) The use of the friction force to apply the main friction element 454 reduces the overall energy input required to the system The energy input required is further reduced because of the self servo effect of the main friction element.

The provision of a V-shaped ramp, e.g. instead of a block having a ramp on only one side, means that the mechanical advantage of the arrangement can be utilised in both forward and rearward drive of the rotor Yet a further embodiment is shown in Figure 5. This embodiment is similar to the embodiment shown in Figure 4, and similar features are given similar reference numerals In the embodiment shown in Figure 5, the pilot and main friction elements are mounted to separate backing plates 578a and 578b. The main friction element 578a is free to move in a direction tangential to, in use, the rotational direction of the rotor.

A further friction element 594 is provided on an outboard side of the rotor 550. As in the previously described embodiments the rotor is fixed in an inboard-outboard direction. The further friction element is fixed relative to a caliper (not shown in Figure 5). The caliper being moveable in an inboard-outboard direction.

A link arm 588 is pivotally connected to the pilot friction element 552 and is pivotally connected at a link mechanism 5100. The link mechanism 5100 is pivotally connected at pivot point 592 to a V-shaped ramp 580. The V-shaped ramp 580 is positioned on an inboard side of rotor. As in the previously described embodiment a roller 582 is provided between the V-shaped ramp 580 and the main friction element 554, and is configured to move up an inclined surface of the V-shaped ramp 580.

The link mechanism 5100 includes two opposing racks 5102, 5104 and a pinion 5106 interconnecting the two racks. The racks are fixed in an inboard-outboard direction but are free to move in a direction tangential to the direction of rotation of the rotor. One of the racks 5102 is connected to the link arm 588 and the other one of the racks 5104 is connected to the V-shaped ramp 580.

In the present embodiment, the ramp 580 is free to move in a direction that in use is tangential to the rotation of the rotor 550 and is in the plane of Figure 5. Under application of a suitable control and actuation mechanism the ramp 580 is selectively fixed in the inboard-outboard direction. To control the braking force applied to the rotor, the ramp is selectively moveable in an inboard-outboard direction. The pilot friction element 552 is free to move in the inboard-outboard direction and also in a direction tangential to the direction of rotation of the rotor.

Similarly to the previously described embodiments, a wear adjustment mechanism may be provided to adjust the position of the friction elements 551, 552 and 554 relative to the rotor 550 so as to account for wear of the friction elements.

In use, a force F is applied to the pilot friction element 552 to move the pilot friction element into initial contact with the rotor 550. The rotating rotor applies a friction force to the pilot friction element. The friction force experienced by the pilot friction element 552 is transmitted through the link arm 588, which displaces the rack 5102 (in a downwards direction as orientated in Figure 5). Displacement of the rack 5102 displaces the rack 5104 in the opposite direction (in an upwards direction as orientated in Figure 5) via the pinion 5106, which in turn displaces the V-shaped ramp 580. Displacement of the V-shaped ramp 580 causes the roller 582 to roll up an incline of the V-shaped ramp 580. The motion of the roller 582 up the ramp 580 causes the main friction element 554 to move towards and contact the rotor 550 causing increased braking of the rotor.

The further friction element 594 will be applied as a result of a reaction force to the application of the pilot 552 and main 554 friction elements, so as to effect braking of the rotor.

Once the main friction element 554 contacts the rotor 550, a friction force is applied to the main friction element 554, in a direction tangential to the rotational direction of the rotor. The applied friction force causes the main friction element 554 to move in a direction opposite the direction of the applied friction force. Said movement of the main friction element causes the roller 582 to further roll along the incline of the V-shaped ramp, causing the force applied by the main friction element to the rotor 550 to increase, which in turn further urges the outboard friction element 595 towards the rotor 550 to further inhibit rotation of the rotor 550 Reaction forces due to the contact of the main friction element 554 with the rotor 550 cause the outboard friction element 595 to move into contact with the rotor 550, creating a clamping braking effect.

The embodiments described all utilise the friction force as a result of contact of the pilot friction element with the rotor so as to apply the main friction element. This reduces the overall external force input required to the brake which means a reduced energy requirement. In certain embodiments this arrangement will also permit a smaller actuation mechanism to be used which may improve the packaging of the brake and actuator. In certain embodiments, the reduced force input to the system may also permit components of the brake or associated components to be reduced in weight, for example through alternative materials or a more compact design.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

In the present application the two friction elements on the inboard side of the rotor are referred to as the main and pilot friction elements. However, this language is not limiting and in some embodiments the pilot friction element may apply more force in normal use than the main friction element.

A return spring or other resilient element may be provided to return the pilot and/or main friction element to a non-braking position when required.

The pilot and main friction elements may be of dissimilar materials. For example, the material may be optimised for differing duty cycles of the friction elements. E.g. a one friction element may be designed for regular use under normal braking conditions, i.e. low wear, low temperature and low wear. The other friction element may be optimised for power and performance, e.g. for emergency stops, etc. In this case the other friction element may be less sensitive to infrequent use (i.e. the low and medium torque stops done by the friction element designed for regular use, and the relatively high torque stops done by the other friction element).

In alternative embodiments more than one main friction element may be provided. The above described arrangement can be particularly advantageous because it may be desirable to have the main friction elements manufactured from dissimilar materials to meet one of the above described functions.

The brake may utilise a control system to guard against spragging (the binding of the friction couple in an uncontrolled manner) The brake has been described using various levers, ramps and disc, but other suitable arrangements may be used, for example, including any one of or any suitable combination of, a crank system, a piston, a chain, a gear arrangement, a cam and follower, and/or a rack and pinion arrangement Further, in embodiments where levers and link arms are used, straight levers and link arms have been described, but in alternative embodiments the lever and link arms, may for example be cranked. Instead of a single roller and ramp arrangement, multiple balls or roller and ramps may be utilised in unison Further any additional number of levers or link arms may be used as required