Patent Description:
The present invention relates to disc brakes for vehicles, and in particular to brake pads in disc brakes, such as air-operated disc brakes utilized on commercial vehicles. Commercial vehicles in this context include vehicles having disc brakes substantially larger than typical automotive (i.e., passenger car) brakes, such as busses, trucks in class <NUM> and above, off-road utility vehicles such as construction equipment, a railroad vehicle, and aircraft.

An example of a commercial vehicle air-operated disc brake is shown in <FIG> of <CIT>. In the <FIG> embodiment the disc brake <NUM> includes a brake disk <NUM> which rotates in direction A about its rotation axis B. A brake caliper <NUM> straddling the brake disk <NUM> is affixed to a carrier mount <NUM> which in turn is fixed to a vehicle axle, typically via a torque plate or a brake spider (not illustrated). In this embodiment the carrier mount <NUM> receives and supports both the caliper <NUM> and the brake pads <NUM>. The caliper <NUM> is actuated in this embodiment by a pneumatic actuator (not illustrated) mounted at the actuator mounting face <NUM> of the caliper. The actuator acts upon a brake pad application mechanism contained within caliper <NUM> to press the brake pads <NUM> against the brake disk <NUM> to slow the vehicle. The present invention is not restricted to a particular type of brake actuator, for example, a pneumatic actuator or an electrically-driven actuator may be used. Nor is the invention limited to a particular type of brake caliper mount arrangement. For example, the brake caliper may be mounted in a fixed manner on a carrier or may be a sliding caliper.

In disc brake applications such as commercial vehicle disc brakes the brake pads typically have had a generally rectangular shape, in part due to the limitations on the size and configuration of the disc brake components (the disc brake having to exist within a highly-space constrained envelope provided by wheel rims), and in part due to cost and structural limitations discussed further below. An example of such a previous brake pad is shown in <FIG>.

A common feature of a previous brake pad <NUM> is their having essentially parallel lateral sides <NUM>, <NUM>, i.e., the brake pad sides facing in the circumferential direction of the brake disc toward adjacent brake pad abutment surfaces are parallel to one another. The generally rectangular shape may include radially inner and radially outer sides of the brake pad <NUM>, <NUM> that are slightly curved to generally follow the curvature of the brake disc as shown in <FIG>, or in the case of the radially outer side, follow the shape of an adjacent outer region of the brake caliper. (not illustrated). The use of parallel lateral sides of the brake pad has in part been the de facto standard in commercial vehicle disc brakes in part due to practical manufacturing considerations (for example, less costly machining of brake pad abutment surfaces and parallel-sided brake pad backing plates) and in part due to structural reasons to ensure adequate brake pad abutment strength, wear, and braking force absorption performance.

With their generally rectangular shape, the previous commercial vehicle disc brake pads have presented to the brake disc essentially constant width and height profiles from one lateral side of the brake pad to the other. Such brake pad shapes have several disadvantages during brake operation. Among these is the fact that the specific braking energy transfer from the brake disc to the brake pad is not constant across the radial height of the brake pad. Instead, the energy transfer varies as a function of radial height relative to the rotation axis of the brake disc (i.e., braking torque varying as a function of the distance from the brake disc rotation axis, where force x distance = torque), and as a function of the length of the friction surface of the brake pad friction material at different radial heights. As a result, the energy transfer to the brake pad, and the resulting localized wear of the brake pad, is inconsistent across the face of the brake pad friction material. This can lead to premature wear of the friction material in some areas of the brake pad and thereby shorten the time before the brake pad must be replaced. A further generic disk brake is known from <CIT>.

The present invention addresses this and other problems by providing a disk brake having brake pads with more efficient and even braking energy transfer distribution across the face of the brake pad lining material. The approach of the present invention provides for more even pad lining material wear, thereby extending service life of the brake pad. The improved brake pad performance also enables reduction in overall brake size by allowing the use of smaller brake pads while still providing satisfactory braking performance.

In an embodiment of the present invention, the brake pad lining material, and preferably the brake pad backing plate carrying the lining material, has a generally arc-shaped profile, with the radially outer portion of the lining material having a width in the circumferential direction that is longer than the width of the lining material at the radially inner portion of the brake pad. Preferably, the width of the brake pad lining material as a function of radial distance from the brake disc rotation axis is established by generally aligning the lateral sides of the lining material along radial lines that intersect at or near the rotation axis of the brake disc. The lateral sides of the brake pad need not be exactly aligned with the radial lines from the rotation axis; rather the present invention contemplates the greatest lining material width at the radially outer region of the brake pad, while the width is smaller at the radially inner region of the lining material. The closer the intersection is to the center of the brake disc rotor, the more efficient the energy distribution at the pad-disc interface.

The present invention also includes variations in which the brake pad friction material still has a generally arc-shaped profile, but due to the requirements of a particular installation (for example, the dimensions of the particular brake caliper and/or caliper mount, or the thermal and wear performance needs of the application) the angle of lateral sides of the arc-shaped friction material and the backing plate are adjusted to suit. This may resulting result in the sides of the backing plate and friction material being arranged at an angle between the prior art's parallel lateral sides and the radii from the brake disc rotation axis. Thus, while a typical brake pad friction material included angle of a brake pad in accordance with the present invention may be approximately <NUM>°, variations with angles on the order of <NUM>° or <NUM>° are envisioned, with corresponding adjustments to the arc lengths at the upper and lower regions of the brake pad.

Another further advantage of the present invention is that the reduced width in the radially inner region of the brake pad permits the abutment faces of the brake pad carrier and the lateral sides of the brake pad to meet along a line that is more nearly perpendicular to a radius from the rotation axis. This arrangement allows the transfer braking forces between the lateral side of the brake pad and pad abutment surface of the pad carrier at or nearly normal to the abutment line. This provides for more uniform distribution of the abutment forces over the abutment surface, i.e., more even (and thus lower) contact pressures, helping minimize brake pad vibrations and associated brake noise, improved fatigue life performance and reduce component wear.

In addition, the arrangements can help in reducing the effects of "pad kick," an in-place rotation of the brake pad that can generate undesired brake application noise due to pad vibrations, increase fatigue damage to typical brake pad retaining hardware (e.g., over-pad leaf springs) and increase wear and damage to the brake pad and/or brake caliper mounting structure. An illustration of pad kick is provided in <FIG>. When a brake pad <NUM> is applied against a friction surface of a brake disk (not illustrated) which is rotating in direction DR, the brake disk's rotation induces motion and reaction forces between the brake pad <NUM> and its adjacent mount abutment surfaces (not illustrated). At the leading edge <NUM> of the brake pad the brake pad attempts to move upward in direction LU in response to the friction forces along the face of the brake pad (illustrated here by force arrows across the face of brake pad <NUM>). At the trailing edge <NUM> of the brake pad, the brake pad attempts to move downward in direction TD. However, because the brake pad <NUM> is constrained by adjacent mount abutment surfaces, the overall motion of the brake pad is generally a rotation about an axis parallel to the brake disk rotation axis. This motion may be unilateral during the brake application, or may manifesting itself as a moderate-to-severe oscillation of the brake pad in its mount, significantly increasing wear of the abutting brake pad and mount surfaces.

One of ordinary skill in the art will recognize that the brake pad support function may be provided by a brake caliper mount designed to support the brake pads, or by a brake pad carrier which is separate from the caliper mounting structure. For convenience in this description, the terms caliper carrier, caliper mount and brake pad carrier may be interchanged without intending to limit the brake par supporting structure to any specific brake pad and brake caliper carrying structure.

A further advantage of the present invention is that the reduced width in the radially inner region of the brake pad permits brake pad retention features, such as those disclosed in co-pending application Ser. No. <CIT>, to be moved closer together to enable further reduction in the size of the disc brake components while maintaining a desired level of braking performance and/or or increasing braking performance by increasing brake pad lining surface area while still keeping overall brake size within the space-constrained envelope of the wheel rim and other nearby components.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

<FIG> is an oblique view of a brake pad <NUM> including a backing plate <NUM> with brake pad friction material <NUM> affixed thereon. The lateral sides <NUM>, <NUM> of the brake pad <NUM> are generally aligned, as shown in <FIG>, along radii extending from the rotation axis of the brake disc <NUM> (not illustrated). The radially inner side <NUM> and the radially outer side <NUM> of the brake pad <NUM> are slightly curved, generally following the curvature of the brake disc.

The brake pad backing plate in this embodiment includes lateral projections <NUM> which are formed to engage corresponding brake pad retention features in the carrier mount <NUM> in the manner disclosed in co-pending application Ser. No. <CIT>, 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 <NUM> in this embodiment also includes radially outer features, including hook portions <NUM> suitable for receiving the ends of brake pad vibration suppression and/or reaction devices such as leaf springs (not illustrated), and a notch <NUM> 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.

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> and the following equations.

<FIG> is a schematic annotated elevation view of the <FIG> embodiment of the brake pad. As shown in this figure, the angle spanned by the arc of the pad material <NUM>, centered on the rotation axis O is of the brake disc ϕB. The inner and outer radii of the pad material are r<NUM> and r<NUM>, respectively. The incremental area used in the integration calculations below over which pressure P<NUM> (P<NUM>) is applied is dAB<NUM> (dAB<NUM>).

Using this nomenclature, the energy transfer into brake pad from the brake disc in each incremental area dA is related as: <MAT> where dE<NUM> = µp<NUM>dAB<NUM>r<NUM>ϕ̇t and dE<NUM> = µp<NUM>dAB<NUM>r<NUM>ϕ̇t.

The specific energy at any radius r is <MAT>.

The incremental area is: <MAT> and therefore the specific energy transfer is <MAT> where K is a constant.

It is known that the brake pad material wear rate and pressure applied between the brake disc and the pad material have a <NUM>:<NUM> relationship: <MAT> 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.

The pressure distribution function (and therefore the pad material wear) may be obtained from the specific energy transfer equation: <MAT>.

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: <MAT>.

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.

For example, in one comparison of an existing generally rectangular brake pad to the inventive brake pad shape, the inventive brake pad had a <NUM> greater arc length in the radially outer region of the brake disc (the arc angle ϕB 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 <NUM>% 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 <NUM>: <NUM>. In other words, despite the decrease in brake pad material area, with the inventive brake pad arrangements the wear rate was <NUM>% lower than the existing generally rectangular brake pad. Depending on the needs of a particular disk brake application, the included angle and the upper and lower arc lengths may be adjusted to obtain higher or lower pressure ratios. For example, in a particularly space-constrained brake environment, the arc angle may be restricted such that the decrease in the pressure ratio and resulting improvement in friction material wear performance is limited, however, preferably the increase in wear performance exceeds <NUM>%. Another variation may be the result of a difference in how the brake pressure is applied to the caliper piston-side of the backing plate, e.g., a compared to a caliper design having two adjacent pressure pistons, in an application in which the brake caliper has a single pressure piston and a friction material area <NUM>% less than an equivalent parallel-sided brake pad, the increase in brake pad wear performance may be somewhat lower, for example <NUM>% or less, due to the concentration of the brake application force to the center of the pad backing plate. The effect of the concentration of the brake application force to the center of the brake pad may be at least partially mitigated by providing a thicker backing plate.

<FIG> is an elevation view of a preferred carrier mount <NUM> configured to complement the brake pad of <FIG>, having carrier mount brake pad abutment surfaces <NUM> configured to support the brake pad <NUM> 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 <NUM>, <NUM> of the brake pad <NUM> (and hence the pad abutments surfaces <NUM>) 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 <NUM> and the carrier mount <NUM> 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 <NUM>. <FIG> also shows this carrier mount embodiment's brake pad lateral projection receiving features <NUM>, complementarily shaped to receive brake pad <NUM>'s lateral projections <NUM> to positively retain the brake pad within the disc brake.

<FIG> shows an elevation view of an alternative embodiment of the brake pad of the present invention, in which the brake pad friction material <NUM> has a generally arc-shaped profile, but the relatively long arc length <NUM> of the upper region of the pad friction material relative to the radial height of the brake pad results in the friction material lower region arc length <NUM> at radius r<NUM> extending laterally notably farther beyond the radii r<NUM> from the rotation axis O to the lateral ends of upper arc length <NUM>. In this embodiment the brake pad friction material's upper region arc length is <NUM>, corresponding to an included angle from the rotation axis O of the brake disc ϕB of <NUM>°, while the lower region arc length, at <NUM>, extends laterally beyond the radii of the included angle. In this case, where the friction material's lower region arc length <NUM> extends beyond the radii r<NUM> from the ends of the upper region arc length <NUM> to the rotation axis O, lines <NUM> extending from the non-parallel lateral sides of the brake pad friction material do not intersect at the rotation axis O, but instead intersect at a location I on the far side of the rotation axis O. Thus, in the present invention the lower region arc length need not exactly correspond to the radii from the rotation axis O to the ends of the upper region arc length, as long as a majority of the friction material is located in the radially upper region of the brake pad in order to provide the benefits of increased torque generation in the upper region and lower overall brake pad wear.

<FIG> similarly shows an elevation view of a further embodiment in which the generally arc-shaped profile has a relatively short long upper region arc length <NUM> relative to the radial height of the brake pad of <NUM>, with the included angle ϕB between radii r<NUM> being <NUM>°. The lower region arc length <NUM> of this embodiment is <NUM>, resulting in the lateral sides of the friction material being located with the lateral ends of the lower region arc length <NUM> being closer to the radial lines than in the <FIG> embodiment.

While substantial portions of the lateral side of the brake pad are parallel to the adjacent faces of the brake pad carrier, relatively small portions of the arc length of the friction material may vary as desired for a specific application. For example, in the radially outer region the friction material may follow the brake pad backing plate laterally beyond the substantially linear side of the brake pad, for example, along a laterally-extending pad guidance tab (thereby providing an even larger amount of friction material at the outermost region of the brake pad). Alternatively, the radially-outer region of the backing plate and friction material may be "cropped," i.e., turning inward from the substantially linear sides of the brake pad, to ensure the overall width of the brake pad is not too wide to be inserted into the pad carrier in a particular brake application.

In all of the embodiments, the present invention's approach remains of "shifting material" from the radially inner region of the brake pad to its radially outer region in order to more effectively and evenly use the friction material where it will be more effective during braking. For example, an embodiment may have an upper region arc length, included angle and lower region arc length between those of the <FIG> examples, such as a <NUM>° pad with upper and lower arc lengths of <NUM> and <NUM>, respectively. Preferably the included angle is <NUM>° to <NUM>°, and especially preferably is <NUM>° to <NUM>°.

Claim 1:
A commercial vehicle disc brake, comprising:
a brake caliper;
a brake pad (<NUM>) including a brake pad backing plate (<NUM>) and a brake pad friction material (<NUM>) affixed to the backing plate (<NUM>), and
a carrier mount (<NUM>) having brake pad abutment surfaces (<NUM>) configured to receive the brake pad (<NUM>),
a brake disk (<NUM>),
wherein the brake pad friction material (<NUM>) of the brake pad (<NUM>) has a radial height, non-parallel lateral sides (<NUM>, <NUM>) and arc lengths in a circumferential direction of the brake disc (<NUM>) that are larger at a radially outer side (<NUM>) of the brake pad (<NUM>) than at a radially inner side (<NUM>) of the brake pad (<NUM>), wherein the arc length (<NUM>) at the radially outer side of the brake pad (<NUM>) has a radius of curvature,
wherein the brake pad friction material (<NUM>) has non-parallel lateral sides along their entire length and
lines extending from each of the non-parallel friction material lateral sides (<NUM>, <NUM>) intersect one another at an included angle which is smaller than an included angle between lines extending from circumferential ends of the radially outer side of the brake pad (<NUM>) to a point of origin of a rotation axis of the brake disk (<NUM>),
characterized in that
the brake pad backing plate non-parallel lateral sides include brake pad retention features (<NUM>) projecting laterally from the brake pad lateral sides,
the carrier mount brake pad abutment surfaces (<NUM>) are configured with a shape that complements a shape of the brake pad backing plate lateral sides and include brake pad retention feature receiving features,
the brake pad retention features (<NUM>) project laterally from the lateral sides of the brake pad backing plate no further than a maximum lateral extent of the brake pad backing plate in a radially outer region, the maximum lateral extent not including a laterally-projecting portion of the brake pad retaining features.