GB2563080A

GB2563080A - A brake pad

Info

Publication number: GB2563080A
Application number: GB1708864.2A
Authority: GB
Inventors: Knoop Dietmar; Hubbard Dave; Cleary Sean
Original assignee: Meritor Heavy Vehicle Braking Systems UK Ltd
Current assignee: Meritor Heavy Vehicle Braking Systems UK Ltd
Priority date: 2017-06-02
Filing date: 2017-06-02
Publication date: 2018-12-05
Also published as: GB2563099A; GB201708864D0; GB201714674D0

Abstract

A brake pad 211a for a heavy vehicle disc brake (10, fig 1), the brake pad 211a defining a first circumferential surface 277a and a second opposing circumferential surface 277b for contact with corresponding pad abutment surfaces, 274a and 274b. The brake pad 211a having first and second resilient arms, 282a and 282b projecting in a generally circumferential direction to contact the corresponding pad abutment structures, so as to urge the brake pad 211a in a direction away from the rotor (10, fig 1) when the brake pad 211a is urged towards the rotor during application of the brake, thus preventing brake dragging. The resilient arms may be wire (fig 8-9) or sheet material (figs 10-13) and may be integral with or attached to a brake backplate.

Description

FIELD OF THE INVENTION

The present invention relates to a brake pad. More particularly, the present invention relates to a brake pad for a heavy vehicle.

BACKGROUND OF THE INVENTION

Commonly, air actuated heavy vehicles disc brakes do not have mechanisms that actively retract the brake pads once a braking operation is complete. Instead such brakes typically rely on the brake rotor to be slightly uneven or have a degree of runout and therefore to push the pads back to a rest position. However in many situations a residual amount of drag between the pads and the rotor may remain especially with a sliding caliper design. This may increase wear of the pad friction material and have a negative effect on the fuel economy and emissions of the vehicle upon which the disc brake is fitted.

For light vehicles it is known to provide resilient elements to actively retract brake pads once a braking operation is complete. Examples of these include US2014/0367208 (Nissin Kogyo) and US2973837 (Wilson). However these arrangements are relatively complex and are not practically applicable to heavy vehicle brakes which utilise different pad mounting arrangements and require a greater degree of relative movement to account for wear of friction material over the life of the pads.

The present invention seeks to overcome, or at least mitigate the problems of the prior art.

SUMMARY OF INVENTION

One aspect of the present invention provides a brake pad for a heavy vehicle disc brake, the brake pad comprising a layer of friction material having a friction face for contacting and retarding rotation of a rotor, the brake pad defining a first circumferential surface and a second opposing circumferential surface for contact with first and second corresponding circumferential pad abutment surfaces of first and second pad abutment structures of a disc brake in use;the brake pad further comprising first and second resilient arms projecting in a generally circumferential direction from the friction material and being arranged to contact the first and second corresponding pad abutment structures so as to urge the brake pad in a direction away from the rotor when the brake pad is urged towards the rotor during application of the brake.

Advantageously this arrangement enables the brake pad to be retracted after a brake application force has been removed. This reduces residual drag between the pad and the rotor and may reduce pad wear, improve the fuel economy and reduce emissions of the vehicle to which it is fitted

The brake pad may further comprise a backplate secured to a face of the friction material opposing the friction face so as to increase the flexural strength of the brake pad, and wherein the first and second resilient arms are mounted to the backplate.

The mounting of the resilient arms to the backplate provides a strong and secure connection to the brake pad.

The brake pad may have a rear face opposing the friction face and the rear face comprises a recess therein, the recess at least partially accommodating at least part of at least one of the resilient arms.

By having a recess in the backplate, the overall thickness of the clamp mechanism is minimised, thereby maximising the available thickness of friction material to prolong pad life.

The recess and the arm may be dimensioned such that the portion of the arm accommodated by the recess does not project beyond the rear face of the brake pad.

This further minimises the thickness of the brake actuation/clamp mechanism overall.

The recess may comprise a stiffening rib of the backplate.

By accommodating the resilient arm and acting as a stiffening rib, the pad is strengthened without adding to the thickness of the clamp mechanism.

The backplate may comprise a plurality of stiffening ribs and the arm can be formed so as to be at least partially accommodated in recesses defining the stiffening ribs.

This provides a convenient arrangement for mounting the arm to the backplate.]

The stiffening rib may extend generally circumferentially across the full width of the backplate and the first and second arms are formed from a single piece of material at least part of which is accommodated in the recess.

This arrangement provides a convenient mounting arrangement of the arms and also enables the arms to deflect sufficiently to enable retraction even when the brake pad is nearly fully worn.

Two stiffening ribs may extend the full width of the backplate and the arms may be formed from a single piece of material at least part of which is accommodated in the two stiffening ribs.

This arrangement allows the arm to be looped around thereby stabilising the pad retraction operation.

The arms may comprise wire material e.g. having a circular cross-section.

This cross-section may be easily manufactured from the wire and accommodated in a recess.

The arms may alternatively comprise sheet material.

This arrangement may enable the arms to be manufactured easily and have a minimal thickness.

The arms can be mounted to the brake pad by at least one of welding, gluing, riveting, press fitting, clip-fitting, snap fitting, plastic deformation of one or both of the arms or brake pad to cause physical engagement therebetween or brazing.

At least one arm may be integral and monolithic with the same piece of material as the backplate

By manufacturing and providing the or each arm as an integral and monolithic part of the same piece of material as the backplate, further cost and/or weight savings may be achieved.

The backplate may formed from sheet metal material.

A backplate of this type may be easily formed with stiffening ribs and other features.

The backplate may comprise a rear plate supporting the friction material and a peripheral flange extending around the perimeter of the rear plate and arranged substantially normal thereto.

A further aspect of the present invention provides a heavy vehicle disc brake incorporating a brake pad according to a first aspect of the present invention.

A still further aspect of the present invention may comprise a heavy vehicle disc brake incorporating a first and second brake pads according to the first aspect of the present invention and disposed on opposing sides of a brake rotor.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which:

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is an isometric view of a disc brake, according to an embodiment of the present invention;

Figures 2 and 3 are side views of a brake pad and carrier of the disc brake of Figure 1 in a part-fitted and fitted position respectively;

Figures 4 and 5 are isometric views of a brake pad of the disc brake of Figure 1 from opposing directions;

Figure 6 is a cross-sectional view through the brake pad of Figures 4 and 5 on a plane 6-6;

Figure 7 is an isometric view of a backplate of the brake pad of Figures 4 to 6; and

Figure 8 is an isometric view of a brake pad of the present invention mounted to a carrier of disc brake.

Figure 9 is a cross section through the brake pad of Figure 8 on the plane 9-9.

Figures 10 and 12 are isometric views of a brake pad according to second and third embodiments of the present invention; and

Figures 11 and 13 are cross sections through the brake pads of Figures 10 and 12 on the planes 11-11 and 13-13 respectively.

DETAILED DESCRIPTION

Figure 1 illustrates a disc brake 2 of an embodiment of the present invention into which brake pads 211a and 211b of an embodiment of the present invention may be fitted. The disc brake 2 incorporates an actuation mechanism (not visible) comprising a single piston and which is suitable for a commercial vehicle. This type of brake is particularly suitable for lighter duty heavy vehicles, for example smaller trucks, or a trailer of a tractor-trailer combination. In other embodiments the disc brake may be a twin piston brake - for example a variant of the applicant's existing ELSA 2 family of disc brakes.

Various orientations of the disc brake are described. In particular the directions inboard and outboard refer to the typical orientation of the disc brake when fitted to a vehicle and with reference to the longitudinal centre line of the vehicle. In this orientation the brake pad closest to the centre of the vehicle is the pad directly actuated by an actuation mechanism and being the inboard pad, and the outboard pad being one mounted to a bridge portion of the caliper. Thus inboard can be equated with an actuating side of the disc brake, and outboard with a reaction side. The terms radial (denoted by arrow R) describes an orientation with reference to the centre of the wheel (rotor). Circumferential (denoted by arrow C), or also called tangential, describe orientations with respect to the brake rotor. Radial refers to a direction towards or away from the centre of rotation of the brake rotor, whereas circumferential (C) describes a direction of rotation of the rotor about its centre of rotation (denoted CR).

The disc brake 2 comprises a caliper 3 having a housing 6 to accommodate the actuation mechanism and which is slideably mounted on a carrier 4 for movement in an inboard-outboard direction.

The caliper 3 can slide on the carrier 4 in an inboard-outboard direction, by way of first and second guide pins (not shown) as is well known.

An inboard brake pad 11a comprises a layer of friction material 13 and is arranged so that the friction material 13 faces a brake rotor 10 (also known as a brake disc). The inboard brake pad 11a is mounted on the carrier via an inboard brake pad support structure 69. In this embodiment, the inboard brake pad support structure 69 is a window or recess in brake carrier, described in more detail below. The inboard brake pad 11a is moveable in the direction of arrow 14 against the brake rotor 10.

An outboard brake pad lib, also with a layer of friction material 13, is also provided. The outboard brake pad lib is mounted to an outboard brake pad support structure 70 as described in further detail below. Suitable means are provided to urge an outboard brake pad lib against the opposite side of the rotor 10. In this embodiment, the caliper comprises a bridge 5 arranged so as to straddle the rotor 10 and to transmit the reaction force from an inboard operating shaft (not shown) of the actuating mechanism to the outboard pad lib. In this embodiment the housing 6 and bridge 5 are manufactured as a single monolithic casting, but in other embodiments, the bridge may be bolted or otherwise secured to the housing.

In this embodiment, a spreader plate (not visible) is provided in the form of an enlarged outboard head of the piston. The main function of the spreader plate is to spread the load applied by the single piston across a greater proportion of the circumferential width of the inboard pad 11a, which is particularly useful for high pressure applications (e.g. an emergency stop), to more evenly distribute the load applied to the pads. There is also an effect on wear; i.e. wear closer to the centre of the pad (where the piston is applied) can be reduced, to provide a more even distribution of wear.

With reference to Figure 2, the carrier 4 has radial pad abutment surfaces 74a, 74b to support the inboard pad 11a in a radial direction. The radial abutment surfaces 74a, 74b are located either side of an arched 'link' portion 4a of the carrier, the link portion 4a connecting the left and right sides of the carrier 4.

The carrier 4 further comprises a first and second circumferential pad abutment surfaces 75a and 75b. The radial pad abutment surfaces 74a, 74b and circumferential pad abutment surfaces 75a and 75b are machined in this embodiment, but they could be forged, or just left as cast as desired.

The circumferential and radial pad abutment surfaces 74, 74b, 75a and 75b define the inboard pad support structure 69 that is arranged to support the inboard pad 11a in a radially inward and circumferential (i.e. rotational) direction. As the brake is actuated, the abutment surfaces 74a, 74b, 75a and 75b react the torque that is created as the inboard pad 11a clamps the rotor 10. The abutment surfaces also act to locate the inboard brake pad 11a.

The inboard brake pad 11a and the corresponding inboard pad support structure 69 comprise complementary profiles on circumferential faces thereof arranged so as to permit the brake pad to be inserted into the mounting structure in a transverse direction T of the brake pad 11a and at an angle to the circumferential direction C of the structure until the pad abuts the first circumferential abutment surface 75a, and then for the brake pad to be pivoted in a direction P about a fixed centre of rotation X when the first circumferential surface 77a of the brake pad is in contact with the first circumferential abutment surface 75a of the structure to be brought into a fitted position in the structure. The fitted position is shown in Figure 3.

In this embodiment, the first circumferential surface 77a of the inboard brake pad 11a has a profile that defines a part circular segment of a first fixed radius ri for contact with the complementary first circumferential abutment surface 75a. It will also be appreciated that in this embodiment a first radial surface 78a of the brake pad is partially contiguous with the first circumferential abutment surface 77a. In other words, because the surface is curved it transmits force with both a circumferential and radial component in some locations.

In addition, the first circumferential abutment surface 75a extends around the first circumferential surface of the inboard brake pad 11a such that a gap distance from the radially outermost tip 76a of the first circumferential abutment surface 75a to the corresponding tip 76b of the second circumferential abutment surface 75b is less than the greatest distance between corresponding points on the two circumferential abutment surfaces 75a, 75b radially inward of the tips. In other words a portion of the first circumferential abutment surface 75a radially outward of the brake pad extends above a portion of the brake pad 11a at the first end thereof.

This means that in effect the brake pad is accommodated within a curved undercut defined by the first circumferential abutment surface 75a. This prevents the brake pad 11a being lifted from the inboard pad support structure 69 by it pivoting about the second end of the brake pad , rather than about the first end of the brake pad i.e. only fitting and removal in the way described below is possible when the disc brake 2 is assembled.

The second circumferential surface of the brake pad 77b has a profile that also defines a part circular segment of a second fixed radius Γ2. The second fixed radius is greater than the first fixed radius and is arranged to contact the complementary second circumferential abutment surface 75b, which is also partcircular with a similar radius.

In order that the brake pad 11a, when fitted, has a large bearing area in contact with the second circumferential abutment surface 75b for transmitting the brake force under braking, the centre of the second radius Γ2 substantially coincides with the centre a of the first radius ri.

In this embodiment, the second radial surface of the brake pad 78b has a generally planar profile and is arranged to contact the complementary second radial abutment surface 74b, which is also generally planar.

The second radial abutment surface 74b, in contrast to the first, is arranged with a defined angle at its intersection to the second circumferential abutment surface 75b, in order to support the brake pad in a radially inward direction at its second end. In some variants of the carrier (not shown) a stress-relief feature may separate the second radial and circumferential abutment surfaces 74b, 75b, however.

The first circumferential abutment surface 75a is arranged on a leading side (denoted LE) of the disc brake with respect the usual direction of rotation of the rotor 10 (clockwise in Figure 2). The second circumferential abutment surface 75b is arranged on the trailing side (denoted TR). Thus, in the forward direction of movement of a vehicle to which the disc brake 2 is fitted, the forces acting on the brake pad 11a tend to hold the brake pad within the pad support structure without additional retention structures coming into use.

However, since vehicles typically also manoeuvre in a reverse direction (at low speed and for a small proportion of their operating time), the geometry set out above may require a structure to counteract the forces acting on the brake pad 11a when rotation of the rotor 10 is reversed. Thus, as is shown in Figure 3, a pad retainer in the form of a plate 92 is provided, which extends from the second circumferential abutment 75b over part of the radially outer face of the brake pad 11a. A bolt 94 (or other appropriate fastening component) passes through the plate 92 and into a threaded bore in the carrier 4, to releasably secure the plate 92 in place.

In the disc brake 2 of Figure 1 the outboard pad support structure 70 is arranged so as to have a similar geometry of radial and circumferential abutment surfaces 74a, 74b, 75a, 75b in order to receive and support an outboard brake pad lib with similar or identical shape to the inboard brake pad 11a. In other embodiments, the outboard pad may have a different geometry and this may be advantageous in some circumstances, dependent upon functional requirements of the brake and/or whether some form of poka-yoke feature (foolproofing of fitting of pads in inboard and outboard locations) is to be provided.

Thus a fitting operation of the outboard brake pad lib is similar to that of the inboard brake pad 11a. However, whilst the inboard brake pad 11a is mounted on the carrier 4 of disc brake 2 via the inboard brake pad support structure 69 the outboard brake pad lib is mounted to the bridge 5 of the caliper 3 by the outboard brake pad support structure 70. As such, the outboard brake pad lib is supported radially and circumferentially by the caliper 3 when fitted in the outboard brake pad support structure 70. The equivalent radial and circumferential abutment surfaces of the outboard brake pad support structure 70 are provided in a face of the bridge 5 that is adjacent the rotor 10. However, as the position of the outboard pad lib is fixed inboard-outboard with respect to the bridge 5, the abutment surfaces do not need to be as deep inboard-outboard as in the carrier 4, e.g. they may only be as deep as the corresponding circumferential and radial surfaces on the outboard brake pad lib

So as to maintain the benefit of the outboard brake pad lib being inherently retained in the outboard pad support structure 70 in the normal rotational direction, in this embodiment, the inboard and outboard brake pads 11a, lib are shaped such that when facing each other in a parallel relationship with friction material facing friction material, the brake pads have mirror symmetry about a plane parallel to friction faces of the brake pads and rotor 10. Thus, when fitted within the disc brake 2 as illustrated in Figure 1, the pads have mirror symmetry about a plane normal to the centre of rotation CR of the rotor 10 at the axial midpoint of the rotor.

This arrangement means that the pad retaining plate 92 for the outboard brake pad lib is at the same trailing side of the pad as for the inboard brake pad, but is instead secured in a threaded bore on the bridge 5. A benefit of this pad shape is that it inherently provides a poka-yoke feature that prevents an individual pad being fitted in a reversed orientation within its corresponding support structure (i.e. with the backplate rather than friction material facing the rotor.

The friction material 13 of the brake pads 11a and lib is mounted to a strengthening backplate 16 e.g. of metallic material. The friction material 13 at the circumferential surfaces of the backplate follows substantially the same profile as the backplate 16. However for manufacturing reasons the friction material is stepped in from the entire perimeter surface by up to 4mm. This arrangement optimises the weight to friction material volume ratio of the brake pads, which is made possible by the simple pad retention arrangement in particular. The profile of the friction material and the backplate on the radially outermost and radially innermost edges (intermediate radial surfaces 78a, b) follows as closely as possible the contact area of the rotor so as to maximise the swept pad area.

Fitting of either brake pad 11a, lib into the caliper is a simple matter of inserting the brake pad into the mounting structure in a transverse direction T of the pad and at an angle to the circumferential direction of the structure and then pivoting the brake pad about a fixed centre of rotation when a circumferential surface of the brake pad is in contact with a complementary circumferential surface of the structure until the brake pad is brought into the fitted position in the structure in which the second radial surface 78b of the brake pad rests on the second radial pad abutment surface 74b. The pad retainer plate 92 may then be secured over the pad 11a, lib by tightening down the bolt 94. Removal is achieved by the reverse procedure.

The construction of the backplate is now discussed in more detail in relation to Figures 2 to 7. The strengthening backplate 16 of the brake pads 11a, lib must have sufficient strength and integrity to withstand the forces acting on brake pads during braking, and as the vehicle to which the disc brake is fitted travels, e.g. over uneven surfaces.

As shown in Figure 6 and 7, the strengthening backplate 16 comprises a rear wall 16a with an inner surface facing towards and for supporting the friction material 13 and an outer, opposing surface facing away from the friction material. When mounted for use, the inner surface faces the brake rotor 10 of the disc brake and the outer surface faces away from the rotor.

The strengthening backplate may comprise at least one stiffening flange extending from the inner surface side of the rear wall. The at least one stiffening flange may surround at least a perimeter portion of the rear wall. The stiffening effect of the flange helps to strengthen the backplate as well as increasing the area in contact with corresponding abutment surfaces of the disc brake 2.

In the embodiment depicted in Figures 3 to 7, the strengthening backplate comprises a stiffening peripheral flange 16b fully encircling the perimeter of the rear wall. The rear wall 16a defines a plane and the stiffening peripheral flange 16b extends substantially perpendicular from the inner surface side of the rear wall. First and second circumferential portions 167a, 167b of peripheral flange define the first and second circumferential surfaces 77a, 77b of the brake pad. First and second radial portions 168a, 168b of the peripheral flange define the first and second radial surfaces 78a, 78b of the brake pad.

The rear wall and at least one stiffening flange form a trough on the friction material side of the brake pad. In the embodiment depicted, the rear wall 16a and peripheral flange 16b define a trough 16c having a tub shape.

The trough is configured to accommodate at least one functional component of the brake pad. The functional component may be selected from a bonding to bond the friction material to the backplate, a thermal insulator to inhibit the transfer heat from the friction material into the backplate of the brake pad, and a noise dampener to absorb noise generated by the brake pad and/or to alter the resonant frequency of the brake pad. The bonding may comprise a steel mesh around which the friction material may be formed.

The trough may additionally accommodate a rear portion of friction material.

In the embodiment depicted in Figures 3 to 7, the friction material is attached to the inner surface of the rear wall 16a using a friction material bonding 17. As shown, a rear portion 13a of the friction material and layer of friction material bonding 17 is located in the trough 16c of the backplate, whilst a front portion 13b of the friction material protrudes from the backplate. The rear portion may be a wear limit portion of the friction material and the outer edge of the flange 16' may define a wear limit of the friction material.

The trough is substantially filled by the at least one functional component (e.g. a bonding, thermal insulator and/or noise dampener), and optionally the rear portion of the friction material. Substantially filling the trough enhances the stiffening of the at least one flange and reduces the risk of plastic deformation during operation. By substantially filling the trough, the friction material at the circumferential surfaces of the backplate follows substantially the same profile as the backplate 16. The friction material is stepped back from the outer perimeter of the backplate by the thickness of the at least one flange. The at least one flange provides additional mechanical contact between the friction material and the backplate, aids bonding and reduces the risk of the friction material becoming separated from the backplate during braking. Further, by filling the trough, the risk of water and other foreign matter entering a gap between the at least one flange and the friction material etc. and causing corrosion is minimised.

By recessing the at least one functional component (e.g. a bonding, thermal insulator and/or noise dampener), and optionally a rear portion of the friction material in the backplate, the thickness of sacrificial friction material in the brake pad that may be worn away in operation can be increased and the lifespan of the brake pad improved.

The backplate 16 may alternatively or additionally comprise at least one stiffening rib to help strengthen the backplate. The at least one stiffening rib is configured to help strengthen the backplate with respect to the forces acting on the brake pad during use. The forces may include, for example, a retaining force from a retainer, an applied load of the piston, an applied clamping force, a drag braking force induced between the friction material and rotor, and/or abutment forces from the abutment surfaces. The at least one stiffening rib may also be configured to change the eigen frequency of the backplate and thereby help to reduce the generation of squeal noise during operation.

The at least one stiffening rib may comprise a recess and/or ridge arranged on the rear wall. The rib may comprise a recess formed in the rear wall 16a of the backplate, preferably on the outer surface of the rear wall. The recess may have any suitable cross-sectional profile including for example, a curved profile, flatbottomed profile or saw-tooth profile. Preferably, a rib recess shaped on one surface of the rear wall forms a corresponding rib ridge on the opposing surface of the rear wall. For example, a rib recess formed on the outer surface of the rear wall forms a corresponding rib ridge on the inner surface of the rear wall. The ridge may aid the attachment of the insulator, noise dampener and/or friction material in the trough.

In the embodiment depicted in Figures 3 to 7, the backplate 16 comprises a plurality of elongate stiffening ribs 16d formed in the rear wall 16a to help strengthen the backplate. As shown in the Figures 4, 6 and 7, the ribs are elongate ridges 26 arranged on the inner face of the rear wall facing the friction material 13 and corresponding recesses 28 arranged on the outer face of the rear wall. The ridges 26/recesses 28 have a cross-sectional curved profile.

In this particular embodiment, the elongate stiffening ribs 16d are configured to help strengthen the backplate with respect to an applied load of the piston, an applied clamping force, a drag braking force induced between the friction material and rotor, and/or abutment forces from the abutment surfaces. The elongate stiffening ribs are also configured to tune the backplate and improve its noise behaviour.

To improve the force distribution across the backplate the elongate stiffening ribs 16d extend across the full width of the rear wall 16a. To optimise the reaction of the brake pad to the drag brake force, the elongate stiffening ribs 16d are configured to follow the vector pathway of the tangential drag force acting across the rear wall. To counter abutting forces of the abutment surfaces acting on the brake pad, the elongate stiffening ribs 16d are configured to extend across the rear wall 16a between the first and second circumferential surface portions 167a, 167b of the peripheral flange and between the first and second radial surface portions 168a, 168b of the peripheral flange. To optimise the stiffening effect and help minimise plastic deformation of the backplate at the abutment interface, each stiffening rib is substantially perpendicular to the intersection between the rear wall and peripheral flange.

The backplate may further or alternatively comprise at least one stiffening rib formed in the rear wall that is configured to strengthen the backplate with respect to retaining forces applied by a brake pad retainer. The retaining forces generally act on a localised region of the backplate and so the at least one local stiffening rib is preferably arranged in the region of the rear wall adjacent to the brake pad retainer. To further strengthen the embodiment of the brake pad depicted in Figures 3 to 7 with respect to the retaining forces applied by the pad retainer plate 92, local stiffening ribs 16e are formed in a region of the rear wall adjacent the pad retainer. To optimise the stiffening effect and help minimise plastic deformation of the backplate by the pad retainer each stiffening rib is orientated to extend in a substantially perpendicular direction to the interface between the pad retainer plate 92 and rear wall.

The provision of the at least one flange and/or at least one stiffening rib allows for the thickness of the backplate material to be reduced whilst maintaining a backplate with sufficient strength and integrity to withstand the braking forces and travel forces acting on the vehicle in which the disc brake is fitted.

The enhanced stiffening effect of the at least one flange (e.g. peripheral flange 16b) and/or the at least one stiffening rib (e.g. stiffening ribs 16d, 16e) allows the backplate 16 to be formed from relatively thin sheet metal material.

The sheet metal material preferably has a thickness of approximately 4mm or less. The trough may preferably have a depth of between approximately 5mm to approximately 7mm. Backplates 16 can be formed from a sheet metal, e.g. sheet steel, having a thickness of between approximately 1mm to approximately 4mm, preferably approximately 3mm.

By using relatively thin sheet metal material the overall mass of the backplate is minimised, which in turn leads to environmental and costs benefits. Also, the backplate may be press-formed from the sheet metal material and cheap to manufacture.

In the embodiment depicted in Figures 3 to 7, the backplate 16 is press-formed from a sheet steel plate having a thickness of approximately 3mm, whereby the rear wall and peripheral flange are integrally formed from the same sheet of material as a starting point and the trough has a depth of approximately 7mm.

The backplate is preferably manufactured from a blank of sheet metal plate (normally coils of sheet metal plate) and press-formed between appropriate contoured dies in a press to form the at least one stiffening rib and/or at least one flange. The method of making the backplate comprises the initial step of cutting a blank from sheet metal. The method may further comprise the step(s) of pressing the blank to form ridges/recesses so as to define at least one stiffening ribs and/or drawing the blank in a press to turn the outer edges of the sheet metal to an angle approaching 90° so as to form the rear wall and at least one flange.

In other embodiments, the backplate can be cast, or formed using other suitable processes.

Figure 8 illustrates a brake pad according to the present invention mounted to a brake carrier. In this embodiment, like components are denoted by the same reference numerals as in the examples above, but with the prefix 2. Only differences with respect to the examples are discussed in detail.

In this embodiment, the carrier 204 supports both the inboard brake pad 211a and outboard brake pad 211b in complementary inboard and outboard pad support structures 269 and 270. The plate and bolt of the pad retainers are omitted for clarity.

As can be seen from Figure 8, the backplate 216 of the brake pad 211a has generally circumferentially extending stiffening ribs 216d described above that define recesses 228 in the rear face of the backplate opposing the friction material

213. Certain recesses 228 extend the full width of the backplate from the first circumferential surface 277a to the second circumferential surface 277b.

The brake pad 211a further comprises first and second resilient arms 282a and 282b. These arms 282a, 282b project in a generally circumferential direction from the backplate 216 and are arranged to rest inboard of corresponding abutment structures 272a, 272b that define the circumferential pad abutment surfaces 274a, 274b of the carrier 204. In this way, when the brake pad 211a is moved outboard by the actuation mechanism the arms flex and generate an opposite (lower) restoring force that urges the brake pad back in an inboard direction. Thus, when the actuation mechanism is released, the pad is actively retracted away from the rotor 10 by the arms 282a, 282b.

In order for this to be effective, it is necessary for the arms to be mounted (or be integral) to the backplate 216. The mounting at least ensures that when the arms 282a, 282b move inboard, the brake pad 211a is also caused to move inboard. In this embodiment the mounting as achieved by spot-welding the arms to the backplate. In other embodiments, the mounting may be via other forms of welding, gluing, riveting, press fitting, snap fitting, brazing, screws, bolts or other fasteners. In addition mounting may be achieved by plastically deforming one or both of the backplate and arms to cause physical engagement therebetween.

In this embodiment, the first and second resilient arms 282a and 282b are part of a single piece of wire 282 formed into a closed loop that is accommodated in two recesses 228 defined by two stiffening ribs extending the full width of the backplate between the first circumferential surface 277a and the second circumferential surface 277b.

With particular reference to Figure 9, which is a vertical cross-section through the brake pad 211a of Figure 8, it can be seen that the wire 282 has substantially circular cross-section and is dimensioned such that it does not project beyond the rear face of the backplate 216. As such, a head 218 of a piston 220 that is arranged to actuate the brake pad 211a and bring it into contact with the rotor during a braking operation, contacts the rear face and therefore spreads the brake force over a maximal area thereof.

Whilst the wire 282 in this embodiment has a circular cross-section and the recesses 228 are substantially semi-circular, it will be appreciated that suitable alternative shapes may be employed and that the profile of either or both may be different at different locations.

In heavy vehicles brake pads, the friction material 213 may be 20mm or more thick. Therefore, as the friction wears away, the backplate 216 is required to move by a similar distance, which in turn requires the resilient arms to flex by a significant amount. The amount of elastic deflection may be maximised in this embodiment by mounting the wire 282 to the backplate 216 proximate to the centre of the backplate only. This is particularly achievable when the pad is being actuated by a single piston disc brake, as contact between the piston and pad may only be proximate the centre of the pad.

In other circumstances, for example if the disc brake is a twin-piston brake, a spreader plate is interposed between the piston and backplate, the pad is mounted outboard rather than inboard, or indeed with single piston brakes the wire may flex beyond its elastic limit and deform plastically. In this instance there would be a residual amount of elastic force generated by the wire 282 to pull the brake pad 211a back clear of the rotor.

Whilst the description above has been in relation to the inboard brake pad 211a, it will be appreciated that a similar arrangement may be provided on the outboard brake pad 211b provided it is mounted to a carrier as in Figure 8, rather than directly to a caliper.

Figures 10 and 11 show a brake pad 311a of another embodiment of the present invention. In this embodiment, like parts are denoted by like numerals, but with the prefix 3 and only differences are discussed below.

In this embodiment, the backplate 316 of the brake pad 311a is formed as a sheet metal pressing with a rear wall 316a and peripheral flange 316b encircling the perimeter of the rear wall and extending substantially perpendicular to the rear wall. The brake pad 311a of this embodiment is of a more conventional shape to the brake pad 211a, having parallel circumferential surfaces and radial surfaces at right angles thereto.

The resilient arms 382a, 382b in this embodiment are integrally formed from the same sheet of metal as the backplate 316. This is achieved by providing an extra tongue of material in a blank to form the backplate that is folded back 180° on the peripheral flange 316b and is folded at approximately 90° to be in substantial alignment with the rear face of the backplate and form each of the arms 382a and 382b that may engage behind the abutment structures in a similar way to that depicted in Figure 8.

Figures 12 and 13 illustrate a further embodiment of brake pad 411a of similar shape and pressed structure to the pad 311a. In this embodiment a separate metal sheet 482 e.g. of spring steel is mounted to the backplate 416 by spot welds 496. The sheet 482 extends beyond the circumferential surfaces 477a and 477b of the brake pads to define the resilient arms 482a and 482b. The spot welds 496 are located close to the circumferential mid-point of the brake pad 411a, thereby permitting the sheet 482 to flex significantly before reaching its elastic limit.

The sheet 482 is in this embodiment approximately 1mm thick, so does not increase the thickness of the pad significantly.

In other embodiments, a sheet or sheets may however be shaped so as to be mounted within recesses only in the backplate similar to the wire of Figure 8. Alternatively, two separate sheets may be mounted to the backplate 416 proximate the circumferential surfaces only.

It will be understood that numerous changes may be made within the scope of the present invention. For example the backplate may be of a conventional cast or stamped type. The brake pad backplate may not have a flange around its entire perimeter.

Claims

1. A brake pad for a heavy vehicle disc brake, the brake pad comprising a layer of friction material having a friction face for contacting and retarding rotation of a rotor, the brake pad defining a first circumferential surface and a second opposing circumferential surface for contact with first and second corresponding circumferential pad abutment surfaces of first and second pad abutment structures of a disc brake in use;

the brake pad further comprising first and second resilient arms projecting in a generally circumferential direction from the friction material and being arranged to contact the first and second corresponding pad abutment structures so as to urge the brake pad in a direction away from the rotor when the brake pad is urged towards the rotor during application of the brake.

2. A brake pad according to claim 1 and further comprising a backplate secured to a face of the friction material opposing the friction face so as to increase the flexural strength of the brake pad, and wherein the first and second resilient arms are mounted to the backplate.

3. A brake pad according to claim 1 or claim 2 wherein the brake pad has a rear face opposing the friction face and the rear face comprises a recess therein, the recess at least partially accommodating at least part of at least one of the resilient arms.

4. A brake pad according to claim 3 wherein the recess and the arm are dimensioned such that the portion of the arm accommodated by the recess does not project beyond the rear face of the brake pad.

5. A brake pad according to claim 3 or claim 4 when dependent upon claim 2 wherein the recess comprises a stiffening rib of the backplate.

6. A brake pad according to claim 5 wherein the backplate comprises a plurality of stiffening ribs and the arm is formed so as to be at least partially accommodated in recesses defining the stiffening ribs.

7. A brake pad according to claim 5 or 6 wherein the stiffening rib extends generally circumferentially across the full width of the backplate and the first and second arms are formed from a single piece of material at least part of which is accommodated in the recess.

8. A brake pad according to claim 7 when dependent upon claim 6 wherein two stiffening ribs extend the full width of the backplate and the arms are formed from a single piece of material at least part of which is accommodated in the two stiffening ribs.

9. A brake pad according to any preceding claim wherein the arms comprise wire material e.g. having a circular cross-section.

10. A brake pad according to claims 1 to 8 wherein the arms comprise sheet material.

11. A brake pad according to any preceding claim wherein the arms are mounted to the brake pad by at least one of welding, gluing, riveting, press fitting, clipfitting, snap fitting, plastic deformation of one or both of the arms or brake pad to cause physical engagement therebetween or brazing.

12. A brake pad according to any one of claims 2 to 12 wherein at least one arm is integral and monolithic with the same piece of material as the backplate

13. A brake pad according to any one of claims 2 to 12 wherein the backplate is formed from sheet metal material.

14. A brake pad according to claim 13 wherein the backplate comprises a rear plate supporting the friction material and a peripheral flange extending around the perimeter of the rear plate and arranged substantially normal thereto.

15. A heavy vehicle disc brake incorporating a brake pad according to any preceding claim.

16. A heavy vehicle disc brake incorporating a first and second brake pads according to any one of claims 1 to 14 disposed on opposing sides of a brake rotor.