Wear Optimized Pad Design

Abstract

A brake pad for a disc brake with decreased wear characteristics is provided. The brake pad is configured with the distribution of brake pad friction material weighted toward the radially outer region of the brake pad, with the lateral sides of the pad material being generally aligned with radial lines originating at the rotation axis of the brake disc of the disc brake. The brake pad friction material distribution results in decreased brake application pressure between the brake pad and the brake disc while obtaining the same braking force provided by a comparable generally rectangular brake pad, resulting in lower brake pad wear at the same braking force levels.

Claims

1. A disc brake, comprising: a brake caliper; a brake pad including a brake pad backing plate and a brake pad friction material affixed to the backing plate, and a carrier mount having brake pad abutment surfaces configured to receive the brake pad, wherein the brake pad includes non-parallel lateral sides generally aligned along radii extending from a rotation axis of the brake disc, the carrier mount brake pad abutment surfaces are configured with a shape that complements a shape of the brake pad lateral sides, the brake pad friction material has a radial height and arc lengths in a circumferential direction of the brake disc that are larger at a radially outer side of the friction material than at a radially inner side of the friction material, the brake pad friction material has a friction surface area less than or equal to a friction surface area of a friction material of a brake pad having parallel lateral sides, the same radial height, and a circumferential arc length that is between the arc lengths at the radially outer and radially inner sides of the non-parallel side brake pad friction material, and at a same rate of energy absorption during a braking event, a brake application pressure applied to the non-parallel side brake pad friction material is lower than a brake application pressure of the parallel side brake pad friction material.

2. The disc brake according to claim 1, wherein lateral sides of the brake pad backing plate and lateral sides of the brake pad friction material have matching shapes.

3. The disc brake according to claim 2, wherein each of the brake pad backing plate lateral sides is parallel to an adjacent one of the brake pad friction material lateral sides.

4. A brake pad, comprising: a brake pad backing plate; and a brake pad friction material affixed to the backing plate, wherein the brake pad friction material includes lateral sides generally aligned along radii having a common origin, the brake pad friction material has a radial height and arc lengths in a circumferential direction of the brake disc that are larger at a radially outer side of the friction material than at a radially inner side of the friction material, the brake pad friction material has a friction surface area less than or equal to a friction surface area of a friction material of a brake pad having parallel lateral sides, the same radial height, and a circumferential arc length that is between the arc lengths at the radially outer and radially inner sides of the non-parallel side brake pad friction material, and at a same rate of energy absorption during a braking event, a brake application pressure applied to the non-parallel side brake pad friction material is lower than a brake application pressure of the parallel side brake pad friction material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is an oblique view of a disc brake.

[0015] FIG. 2 is an oblique view of a brake pad in accordance with an embodiment of the present invention.

[0016] FIG. 3 is an elevation view of the brake pad in FIG. 2.

[0017] FIG. 4 is an elevation view of a known generally rectangular brake pad, annotated to illustrate pad motion in response to brake application.

[0018] FIG. 5 is an elevation view of an embodiment of a carrier mount configured to complement the brake pad of FIG. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

[0019] FIG. 2 is an oblique view of an embodiment of the present invention in which a brake pad 10 includes a backing plate 11 with brake pad friction material 19 affixed thereon. The lateral sides 12, 13 of the brake pad 10 are generally aligned, as shown in FIG. 3, along radii extending from the rotation axis of the brake disc 2 (not illustrated). The radially inner side 14 and the radially outer side 15 of the brake pad 10 are slightly curved, generally following the curvature of the brake disc.

[0020] The brake pad backing plate in this embodiment includes lateral projections 16 which are formed to engage corresponding brake pad retention features in the carrier mount 4 in the manner disclosed in co-pending application Ser. No. 14/640,152, such that even in the absence of any additional brake pad retention devices, once engaged in the carrier mount's receiving features the brake pad is positively retained within the disc brake. The backing plate 20 in this embodiment also includes radially outer features, including hook portions 17 suitable for receiving the ends of brake pad vibration suppression and/or reaction devices such as leaf springs (not illustrated), and a notch 18 configured to receive a brake wear sensor (not illustrated). The brake pad backing plate lateral projections, hook portions and wear sensor notch are features of this embodiment, but are not required by the present invention.

[0021] The advantages of the present invention's performance in terms of braking energy, brake application pressure and reduced brake pad material wear is illustrated with the aid of FIG. 3 and the following equations.

[0022] FIG. 3 is a schematic annotated elevation view of the FIG. 2 embodiment of the inventive brake pad. As shown in this figure, the angle spanned by the arc of the pad material 30, centered on the rotation axis O is of the brake disc .sub.B. The inner and outer radii of the pad material are r.sub.1 and r.sub.2, respectively. The incremental area used in the integration calculations below over which pressure P.sub.1 (P.sub.2) is applied is dA.sub.B1 (dA.sub.B2).

[0023] Using this nomenclature, the energy transfer into brake pad from the brake disc in each incremental area dA is related as:

[00001]$\begin{array}{cc}\frac{E_1}{A_{B.Math..Math.1}}=\frac{E_2}{A_{B.Math..Math.2}}& \left[1\right]\end{array}$

[0024] where dE.sub.1=p.sub.1dA.sub.B1r.sub.1{dot over ()}t and dE.sub.2=p.sub.2dA.sub.B2r.sub.2{dot over ()}t

[0025] The specific energy at any radius r is

[00002]$\begin{array}{cc}E\left(r\right)=.Math..Math.r.Math..Math.\stackrel{.}{}.Math..Math.t.Math.\frac{1}{{}_B}.Math.{}_{-{}_B/2}^{{}_B/2}.Math.p\left(r,\right).Math.r.Math..Math.r& \left[2\right]\end{array}$

[0026] The incremental area is:

dA.sub.s(r)=2rdr [3]

[0027] and therefore the specific energy transfer is

[00003]$\begin{array}{cc}\frac{E\left(r\right)}{A_S\left(r\right)}=\frac{2.Math.}{.Math.\stackrel{.}{}.Math..Math.t}.Math.\frac{r}{{}_B}.Math.{}_{-{}_B/2}^{{}_B/2}.Math.p\left(r,\right).Math.r.Math.=K& \left[4\right]\end{array}$

[0028] where K is a constant.

[0029] It is known that the brake pad material wear rate and pressure applied between the brake disc and the pad material have a 1:1 relationship:

h=KPvt [5]

[0030] where h is the pad wear, P is the applied pressure, k is the wear coefficient (material dependent) and v is velocity. Pressure and wear therefore have a direct relationship.

[0031] The pressure distribution function (and therefore the pad material wear) may be obtained from the specific energy transfer equation:

[00004]$\begin{array}{cc}\hat{p}=\frac{2.Math.}{.Math.\stackrel{.}{}.Math..Math.t}.Math.\frac{E\left(r\right)}{A_S\left(r\right)}=\frac{1}{{}_B}.Math.{}_{-{}_B/2}^{{}_B/2}.Math.p\left(r,\right).Math.r.Math.=K& \left[6\right]\end{array}$

[0032] This relationship permits assessment of the relative change in wear performance between two brake pad shapes. Holding other variables constant, the pressure (and wear) ratio between two pad shapes is:

[00005]$\begin{array}{cc}\frac{P_1}{P_2}=\frac{{}_{B.Math..Math.2}}{{}_{B.Math..Math.1}}.Math.\frac{{}_{-{}_B/2}^{{}_B/2}.Math.p\left(r_1,\right).Math.r.Math.}{{}_{-{}_B/2}^{{}_B/2}.Math.p\left(r_2,\right).Math.r.Math.}& \left[7\right]\end{array}$

[0033] In the case of a brake pad in accordance with the present invention, as compared to a generally rectangular brake pad with the same inner radial height and outer radial height, when both brake pads are being applied to generate the same amount of braking force, the inventive brake pad's greater arc length at the radially outer region of the brake pad results in generation of greater braking force at a lower local pressure as compared to a generally rectangular brake pad, while simultaneously decreasing the amount of braking force needed from the pad material at the radially inner region of the brake pad.

[0034] For example, in one comparison of an existing generally rectangular brake pad to the inventive brake pad shape, the inventive brake pad had a 20 cm greater arc length in the radially outer region of the brake disc (the arc angle .sub.B was approximately five degrees, as determined by the radius of the brake disc and the original arc length of the existing rectangular brake pad. Despite a 4% reduction in the overall brake pad surface area for the inventive wedge shaped brake pad, the re-distribution of brake application pressure and braking force resulting from the alteration of the distribution of the pad material along the radial height of the brake pad resulted in a reduction of the P1/P2 brake application pressure ratio reduction, while still obtaining the same braking force, of 1.31:1. In other words, despite the decrease in brake pad material area, with the inventive brake pad arrangements the wear rate was 31% lower than the existing generally rectangular brake pad.

[0035] FIG. 5 is an elevation view of a preferred carrier mount 26 configured to complement the brake pad of FIG. 2, having carrier mount brake pad abutment surfaces 27 configured to support the brake pad 10 in the circumferential direction in response to braking reaction forces generated between the brake disc and the brake pads. This is a preferred embodiment, however it is not necessary to change the carrier to obtain many of the benefits of the present invention. As a result of the lateral sides 12, 13 of the brake pad 10 (and hence the pad abutments surfaces 27) being generally aligned along radii extending from the brake disc rotation axis, the transfer of braking forces between the trailing edge of the brake pad 10 and the carrier mount 26 occurs substantially parallel to the tangential direction of the brake disc rotation (i.e., across a surface that is perpendicular to the rotation direction), thereby minimizing forces tending to shift the trailing edge of brake pad radially outward relative to its adjacent carrier mount abutment surface 27. FIG. 5 also shows this carrier mount embodiment's brake pad lateral projection receiving features 28, complementarily shaped to receive brake pad 10's lateral projections 16 to positively retain the brake pad within the disc brake.

[0036] The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Because such modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

LISTING OF REFERENCE LABELS:

[0037] 1 disc brake

[0038] 2 brake disc

[0039] 3 brake caliper

[0040] 4 carrier mount

[0041] 5 caliper actuator mounting face

[0042] 6 brake pads

[0043] 10 brake pad

[0044] 11 brake pad backing plate

[0045] 12, 13 brake pad lateral sides

[0046] 14 brake pad radially inner side

[0047] 15 brake pad radially outer side

[0048] 16 backing plate lateral projections

[0049] 17 radially outer retaining hooks

[0050] 18 radially outer pad wear sensor notch

[0051] 19 brake pad friction material

[0052] 20 brake pad

[0053] 22, 23 brake pad lateral sides

[0054] 24 brake pad radially inner side

[0055] 25 brake pad radially outer side

[0056] 26 carrier mount

[0057] 27 carrier mount brake pad abutment surfaces

[0058] 28 carrier mount brake pad lateral projection receiving features

[0059] 101 brake pad

[0060] 102 brake pad leading edge

[0061] 103 brake pad trailing edge