The present invention relates to a brake pad. More particularly, the present invention relates to a brake pad for a heavy vehicle.
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 U.S. Pat. No. 2,973,837 (Wilson). However, these arrangements are relatively complex and are not practically applicable to heavy vehicle brakes which utilize 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.
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.
At least one of the first and second resilient arms may comprise a generally radially extending torsion portion arranged to provide torsional resilience to urge the brake pad away from the rotor.
Advantageously, the use of torsional resilience in arm may result in a more constant spring rate across the full range of deflection of the arm as the brake pad advances towards a brake rotor. In addition, it may reduce stresses in the arm and allow for a more compact way of achieving the required deflection of the arm.
Whilst certain springs with helically wound wire may be referred to as torsion springs, it should be noted that in this case as the torsion portion is not linear, extending in a radial direction, the wire does not act in a truly torsional (i.e., twisting) action.
The radially extending torsion portion may overlie the brake pad.
Optionally, the radially extending torsion portion is located beyond the extent of the brake pad.
Optionally, at least one of the first and second resilient arms comprises first and second circumferentially extending portions mounted to the brake pad for pivoting about first and second axes offset in a generally circumferential direction and wherein the torsion portion connects the circumferentially extending portions at a location remote from both axes.
Advantageously, this arrangement provides an effective way for torsion to be generated without necessarily requiring additional material to restrain the resilient arms and generate the torsion.
Optionally, the torsion portion is located at an opposite end of the circumferentially extending portions from the first and second axes.
Advantageously, this arrangement enables the torsion portion to also act as the contact portion with the abutment surfaces of the carrier, and thereby reducing the risk of excess wear of the resilient arms and/or carrier.
Optionally, the at least one resilient arm further comprises a mounting portion arranged to mount the resilient arm to the brake pad.
Optionally, the mounting portion defines an axle extending in the same direction as the axis of rotation of the circumferentially extending portion.
The brake pad may further comprise a reaction portion arranged to ground a first end of the torsion portion on the brake pad.
Providing such a portion allows the torsional forces to be reacted conveniently within the brake pad.
Two torsion portions may be provided.
The use of two torsion portions may further reduce stresses and/or enable thinner arms to be used.
The reaction portion optionally connects the two torsion portions.
This arrangement enables a single component to provide the arms at one circumferential side of the brake pad.
The two torsion portions are optionally substantially coaxially aligned.
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. The first and second resilient arms are optionally 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 minimized, thereby maximizing the available thickness of friction material to prolong pad life.
The recess may be dimensioned such that at least one of the resilient arms is held to the recess a form fitting relationship, e.g., an interference fit.
This arrangement may allow the assembly of the arm to the brake pad without the use of additional components such as fasteners, thereby reducing manufacturing complexity and cost.
The recess may be plastically deformed so as to hold the at least one arm therein.
This arrangement may also allow the assembly of the arm to the brake pad without the use of additional components such as fasteners, thereby reducing manufacturing complexity and cost.
The at least one resilient arm may be shaped for resiliently mounting to the recess.
This arrangement may also allow the assembly of the arm to the brake pad without the use of additional components such as fasteners, thereby reducing manufacturing complexity and cost.
The backplate may comprise an aperture and the at least one arm is held within the aperture.
This arrangement may also allow the assembly of the arm to the brake pad without the use of additional components such as fasteners, thereby reducing manufacturing complexity and cost.
The aperture may be a through aperture in the backplate from a non-friction side to a friction side of the backplate.
The aperture may be defined by an additional component, e.g., a plate, mounted to the backplate.
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 minimizes 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 is 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 may be 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 optionally 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 stabilizing the pad retraction operation.
Optionally, the backplate is formed from a plate having a thickness across a majority of its surface in a range of 5 mm to 12 mm, preferably 7 mm to 11 mm wherein the recess is at least 3 mm thinner than a remainder of the plate.
The arms may comprise wire material e.g., having a circular cross-section, at least in part.
This cross-section may be easily manufactured from the wire and accommodated in a recess.
The arms may comprise sheet material, at least in part.
This arrangement may enable the arms to be manufactured easily and have a minimal thickness.
At least one of the arms may comprise a region of increased surface area for contact with the corresponding abutment structure.
Advantageously this may reduce stress in the arm in this region.
At least one of the arms may 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 be formed from sheet metal material.
A backplate of this type may be easily formed with stiffening ribs and other features.
The backplate optionally 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.
A second aspect of the present invention provides a heavy vehicle disc brake incorporating a brake pad according to the first aspect of the present invention.
A third aspect of the present invention provides a heavy vehicle disc brake incorporating a first and second brake pad according to the first aspect of the present invention disposed on opposing sides of a brake rotor.
The heavy vehicle disc brake may comprise a caliper having a support portion arranged to support a rear face of the brake pad during a braking operation, the portion having a recess in a region of at least one of the first and second arms arranged so as to receive the arm as the brake pad advances towards the friction material and the arm is caused to deflect.
The caliper may comprise a bridge portion arranged to extend over a brake rotor and support an outboard brake pad, and wherein the support portion is a surface of a bridge portion arranged to face the rotor.
A further aspect of the present invention provides brake carrier for a heavy vehicle disc brake, the brake carrier comprising first and second brake pad abutment structures, each defining a circumferential pad abutment surface to take the load from a brake pad during a braking operation, wherein the brake pad abutment structures further comprise a resilient arm arranged to engage a corresponding brake pad 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
Mounting the arms to the carrier may provide a suitable alternative way to provide pad retraction functionality with many of the associated benefits as described in relation to the first aspect of the present invention.
The resilient arms may be mounted to the carrier abutments in one of the ways described in respect of the first aspect of the present invention for mounting the arms to a brake pad.
The resilient arms may be manufactured using similar materials and shaped similarly to the arms of the first aspect, but with the orientations reversed.
The carrier may additionally comprise a brake pad mounted therein, and the arms may be arranged to extend over and engage a formation in the brake pad that enables the arms to engage and resiliently retract or “pull” the pad away from a rotor of the associated disc brake in operation.
The formations may be hook shapes formed into a backplate of the brake pad.
The arms may be as described in relation to the first aspect of the present invention and may be resilient in torsion and/or bending to urge the pad to retract.
Embodiments of the present invention will now be described, by way of example only, with reference to the drawings in which:
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.
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 center line of the vehicle. In this orientation the brake pad closest to the center 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 center 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 center of rotation of the brake rotor, whereas circumferential (C) describes a direction of rotation of the rotor about its center 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 also comprises a bridge that extends over the rotor 10 support the outboard brake pad 11b. The bridge 5 in combination with the sliding of the caliper enables the force from the operating shaft to be transmitted to the outboard brake pad 11b so as to clamp the rotor 10 between the inboard and outboard brake pads 11a, 11b so as to retard its rotation.
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 11b, also with a layer of friction material 13, is also provided. The outboard brake pad 11b is mounted to an outboard brake pad support structure 70 as described in further detail below. Suitable components are provided to urge an outboard brake pad 11b 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 11b. 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 center of the pad (where the piston is applied) can be reduced, to provide a more even distribution of wear.
With reference to
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 center 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
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 r1 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 r2. 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 part-circular 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 center of the second radius r2 substantially coincides with the center a of the first radius r1.
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
However, since vehicles typically also maneuver 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
In the disc brake 2 of
Thus, a fitting operation of the outboard brake pad 11b 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 11b is mounted to the bridge 5 of the caliper 3 by the outboard brake pad support structure 70. As such, the outboard brake pad 11b 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 11b 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 11b.
So as to maintain the benefit of the outboard brake pad 11b 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, 11b 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
This arrangement means that the pad retaining plate 92 for the outboard brake pad 11b 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 11b 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 4 mm. This arrangement optimizes 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 maximize the swept pad area.
Fitting of either brake pad 11a, 11b 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 center 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, 11b 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
As shown in
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
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
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 minimized.
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, flat-bottomed 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
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 behavior.
To improve the force distribution across the backplate the elongate stiffening ribs 16d extend across the full width of the rear wall 16a. To optimize 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 optimize the stiffening effect and help minimize 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 localized 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
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 4 mm or less. The trough may preferably have a depth of between approximately 5 mm to approximately 7 mm. Backplates 16 can be formed from a sheet metal, e.g., sheet steel, having a thickness of between approximately 1 mm to approximately 4 mm, preferably approximately 3 mm.
By using relatively thin sheet metal material the overall mass of the backplate is minimized, 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
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.
Brake Pad Retraction
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
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 is 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
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 20 mm 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 maximized in this embodiment by mounting the wire 282 to the backplate 216 proximate to the center 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 center of the pad.
In other circumstances, for example if the disc brake is a twin-piston brake or a spreader plate is interposed between the piston and backplate, or 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
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
The sheet 482 is in this embodiment approximately 1 mm 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
In addition, the first resilient arm 582a differs from that of the first embodiment in that it comprises two generally radially extending torsion portions 584. The torsion portions are arranged to provide a torsional resilience to urge the brake pad away from the rotor. This torsional resilience may be in addition to or as an alternative to flexural or bending resilience that may be provided in circumferentially extending portions of the arm 586 (depending upon the material used for these and its thickness.) In this embodiment the two torsion portions 584 are substantially coaxially aligned and of a similar length, but in other embodiments may be laterally offset and/or of differing length. By altering one or both of these parameters the retraction force applied by the circumferential portions may be individually adjusted to allow for an even retraction of the brake pad 11a in use.
The arm of this embodiment is formed from wire having a circular cross-section, however the circumferentially extending portions 586 of this embodiment terminate in pads 590 of enlarged surface area to reduce stresses at the end of the arm. In other embodiments the arm is a closed loop.
The use of torsional resilience in the arm may result in a more constant spring rate across the full range of deflection of the arm. In addition, it may reduce stresses in the arm and allow for a more compact way of achieving the required deflection of the arm.
It can be seen that the torsion portions 584 are straight sections of wire in this embodiment, rather than helically coiled wire arranged to flex in a torsional manner. The arrangement of this embodiment of the present invention is chosen so that the torsion portion is compact and can be restrained by the backplate as described below.
A reaction portion 588 of the arm 582a is integral with and is additionally arranged to ground a first end of each torsion portion 584 on the brake pad. In this embodiment the reaction portion 588 extends circumferentially towards a midpoint of the brake pad 511a and is formed from a length of wire that is looped back on itself so that it interconnects the torsion portions 584. Thus, it can be seen that torsion portion is arranged approximately at right angles to both the reaction portion 588 and circumferentially extending portion 586.
The reaction portion 588 is mounted to the backplate 516 and length of the reaction portion enables it to better counteract the forces imposed on it as the arm 582a deflects. The circumferentially extending portions 586 may be angled with respect to the reaction portion 588 in the plane of the backplate in order to preload the resilient arm and enhance the retraction force provided by the arms 582a once a braking operation has ceased.
The torsion portions 584 overlie the brake pad. In this embodiment the backplate is of the type shown in
The transverse recesses 529 are dimensioned so the torsion portions 584 are held along at least part of their length in a form fitting relationship with the recesses. As illustrated in the cross-sectional view of
To further secure the arm 582a to the brake pad 511a the reaction formation may also or alternatively be mounted to the backplate in a form fitting engagement as above, or by welding, use of adhesive or suitable fasteners such as rivets.
In the sixth embodiment of
In the seventh embodiment of
Each arm 882a′ and 882a″ extends through a respective aperture 834′ and 834″ with a recess 828 between the torsion portions 884′ and 884″ and reaction portions 888′ and 888″ such that the reaction portions are located on the friction side of the backplate. The friction material may be molded on to the backplate after the arms 882a′ and 882a″, and in which case the friction material may hold the arms in place.
The eighth embodiment of
The frame 505 has a substantially planar surface, commonly referred to as a cushion 520, that contacts the rear face of the outboard brake pad 511b and pushes the outboard brake pad in an inboard direction so as to clamp it against the rotor during a braking operation.
So as to accommodate the angular displacement of the circumferentially extending portions 588, the cushion 520 has circumferentially extending recesses 522 therein arranged at the correct radial height to receive them. In the inboard side, similar recesses or slots may be provided on a spreader plate or piston.
The ninth embodiment of
The resilient arms 1082a and 1082b of this embodiment differ from those of the previous embodiments in two important ways. Firstly, the torsion portion 1084 no longer overlies the backplate 1016, but instead is at the free end of the circumferentially extending portions 1086 and therefore is located outside of the footprint of the backplate. Secondly, the two circumferentially extending portions 1086 are mounted to the backplate 1016 about mounting portions 1092. The mounting portions 1092 are offset from each other in a circumferential or lateral direction. In other words, one of the mounting points is closer to a circumferential midpoint of the pad than the other. The mounting portions 1092 act to allow the circumferentially extending portions to rotate in a plane that is generally defined by the circumferential and axial directions, i.e., the plane is generally horizontal.
The consequence of the offset arrangement is that as the resilient arms 1082a and 1082b are pivoted during the advance of the brake pad towards the rotor, the angle at which the individual circumferentially extending portions pivot differs, as can be seen most clearly in
By virtue of this differential pivoting, a torsional load is generated in the torsion portion 1084 by virtue of its role in connecting the first and second circumferentially extending portions at a distance from the mounting portions, and in this embodiment with its distance being at the circumferentially outermost ends of the circumferentially extending portions.
In this embodiment, the mounting portions 1092 are supported by a pair of apertures (not visible) that extend generally radially through the walls of adjacent stiffening ribs 1016d and therefore provide pivotable mounts for each of the mounting portions 1092. In order to retain the mounting portions within the support, the ends thereof may be flattened as depicted in
Further, the circumferentially extending portions 1086 are bent or angled part way along the length thereof, as can most readily be seen in
In this embodiment, specific recesses 1128 are cast into the backplate 1116 in order to accommodate the desired shape of resilient arms 1182a. In this embodiment, the circumferentially extending portions 1186 are arranged adjacent each other and therefore the torsion portion 1184 is short. Further, the mounting portions 1192, of course remain offset in order to generate torsion in the torsion portion 1184. In this embodiment the mounting portions 1092 extend in a generally radial direction away from each other in contrast to the arrangement of
To hold the mounting portions 1192 within the recess 1128, in this embodiment pips or projections 1194 from the surface are cast into the backplate adjacent to the recess 1128. When the resilient arms 1182a are fitted, these pips 1194 are then peened or coined over the mounting portions 1192. This results in material extending over the mounting portions in order to hold the resilient arms in place. Once deformed over the mounting portions 1192, it will be appreciated that the resilient arms 1182 and the pips 1194 do not project beyond the rear face of the backplate when in the rest position.
Further, although it can be seen that the backplate 1116 has two raised circular portions on the rear face thereof intended to the contacted by corresponding pistons of the disc brake actuation mechanism (not shown), even when the arm is deflected at maximum wear of the friction material (see
Referring to
The embodiment of
In
Depending on the location of the bridge 1599 and the amount of play or clearance between the bridge and the loop, the resilient arm 1582a may exhibit a combination of torsional resilience up to a predetermined deflection, before the loop 1598 grounds on the bridge 1599, and thereafter the arm may exhibit a resilience in bending of the loop.
In
In
In
In a further embodiment (not shown) the resilient arms may be mounted to the carrier abutments in one of the ways described above for pad mounting, and the arms are arranged to extend over an engage a formation in the pad backplate that enables the arms to engage and resiliently retract or “pull” the pad away from the rotor. The formation may be in the form of one or more hooks provided in the backplate within which the resilient arms may readily engage during fitting of the brake pads.
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 or stamped type. The brake pad backplate may not have a flange around its entire perimeter.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.
Number | Date | Country | Kind |
---|---|---|---|
1708864.2 | Jun 2017 | GB | national |
1714674.7 | Sep 2017 | GB | national |
1719874.8 | Nov 2017 | GB | national |