Patent Application
20080041670
This application claims priority to United Kingdom Patent Application No. GB 0609258.9 filed on May 10, 2006.
This invention relates generally to wheel brakes of vehicles, and particularly to an actuator for a disc brake.
Conventionally, a disc brake includes a rotor which forms part of a wheel hub and a caliper which straddles the rotor and is grounded on a vehicle axle. Brake pads of the caliper can be urged on demand against opposite annular faces of the rotor to slow a wheel, and brake reaction torque is transmitted to the axle, and via suspension arrangements, to the vehicle body. In cars, the caliper is usually hydraulically actuated, whereas in commercial vehicles the caliper is operated by a relatively large air actuator.
Calipers which straddle the disc conventionally require mountings on a vehicle axle housing. Typically, these are provided by fixed lugs to which the caliper is attached by screws. The lugs may, for example, be integrally formed as part of a cast stub axle housing or provided by any suitable way at an end of a rigid axle. Once designed and manufactured, the relative position of the caliper is fixed with respect to the wheel and the suspension components. However, space within a wheel arch is tightly constrained, and in certain circumstances it may be desirable to locate the caliper at a different angular orientation, for example to permit fitting of different components in the wheel arch space. These methods of caliper mounting do not permit relocation without design and manufacture of a different axle housing, with the disadvantage of additional cost and plurality of components.
It has also been proposed to use an adaptor plate to vary a circumferential position of the caliper, by for example providing a ring of bolt holes around the axle. However, this adds to cost and weight, and is generally undesirable.
What is required is an alternative caliper mounting which permits variability of angular position with minimum adaptation of standard components.
According to a first aspect of the invention, there is provided an arcuate support of a disc brake caliper of a vehicle. The support is adapted to receive an axle casing and has an abutment for non-rotational engagement with respect to the axle casing.
The axle casing may include a tubular half shaft housing of a rigid axle, or a stub axle housing of a vehicle with an independent suspension. Non-rotational is defined as restrained against any relative arcuate movement, such as by a woodruff key or a spline.
Such an arrangement avoids the usual cast or welded mounting flange on the axle casing and is suitable to locate the caliper at different arcuate positions. In one embodiment, a discontinuity, such as a key, is provided between the support and the axle casing. Non-rotational engagement ensures that braking torque generated at the caliper is grounded via the axle casing. Several key or spline positions may be provided, or alternatively one of the support and the casing can have a fixed key position, whereas the other can be machined to suit the intended arcuate location.
A conventional brake caliper typically consists of a fixed member anchored to the axle and a relatively movable member slidable thereon via, for example, slide pins. In this form of construction, the fixed member transmits braking torque to the axle, whereas the sliding member applies a clamping force to the brake pads.
In one embodiment of the invention, the support may be adapted for sliding movement along a drive axis, for example, via a keyway. This arrangement avoids the requirement for separate sliding members of the caliper assembly. Typically, the caliper includes a single member incorporating a bridge which straddles the brake rotor. The outboard pad is fixed relative to the bridge, whereas the inboard pad transmits brake torque to the bridge but is slidable in the direction of the drive axis under the action of an actuator mounted on the single member. Wear of the outboard pad is accommodated by sliding of the single member relative to the vehicle axle. Wear of the inboard pad is by adjustment of the actuator output shaft, typically via an automatic wear adjuster.
A particular advantage of the invention is that stress raisers of welded joints are avoided, and accordingly fatigue failures of the axle casing are less likely. Distortion of the casing under welding is also avoided. Furthermore, a discontinuity which transfers braking torque from the support to the axle casing can be accurately machined, and thus designed to resist fatigue failure, in contrast to a welded join, which is somewhat unpredictable. Yet another advantage over welded construction is that the materials of the support and axle casing can be optimized without regard to mutual weldability. Cast axle casings have integral flanges, but are not suitable for modification after manufacture.
In one embodiment, the support includes an annulus assembled axially over an axle end in advance of the brake rotor and the hub. A single woodruff key may be provided to restrain the support against relative rotation. The keyway can be provided at any circumferential location, for example, on the neutral bending axis and of a length and a thickness to suit the intended duty. An axle with a fixed keyway design can have different supports fitted thereon to give different angular caliper positions. Thus, a single axle design may be adapted to a variety of vehicles having different wheel arch envelopes, and thus a variety of possible caliper locations. The support and/or axle may have plural keyways to permit components to be assembled in one of a number of angular positions.
Preferably, the support fits closely to the exterior of the axle casing, for example against a cylindrical external surface. In the case of an annular support, a close sliding fit is desirable.
The support may include a portion of an annulus having sufficient circumferential extent for opposite discontinuities to prevent rotation relative to the axle casing. Thus, the support may, for example, be ‘C’ shaped. Fixed inward or outward discontinuities, in the form of fingers, may be provided and for direct location in corresponding recesses. Separate keys and the like are thereby avoided. A spline connection may be provided to give a very large number of potential support locations.
In the alternative, the abutment may include a torque reaction arm grounded directly or indirectly on the axle casing. The arm may, for example, be grounded indirectly on a suspension component, such as a trailing radius arm, or on the vehicle body/chassis. In this embodiment, a keyway may permit sliding movement of a caliper to accommodate pad wear, but is relieved of substantially all braking torque.
In one embodiment, the trailing arm may include end connections which permit arcuate movement to accommodate slight change of orientation during working of the vehicle suspension. Such connections, which may, for example, pivot parallel to the drive axis, are required only if such orientation changes are features of the selected grounding point.
A feature of many disc brake installations is the use of a single-sided caliper in which the actuating element (piston or tappet) is at the inboard side and acts directly on the inboard brake pad. The outboard brake pad is applied by a bridge which straddles the rotor and receives the reaction force of the actuating element. The bridge (or bridge assembly) is slidably mounted on a fixed member of the vehicle axle or the stub axle.
According to a second aspect of the invention, a bridge member of a disc brake caliper includes an arcuate support adapted to receive an axle casing in the arcuate support for sliding, non-rotational engagement.
Such sliding non-rotational engagement may, for example, be provided by a keyway or spline and permits the bridge member to adopt an appropriate position with respect to the rotor having regard to the brake pad wear.
Several forms of arcuate support are possible, as mentioned in connection with the first embodiment of the invention. In one embodiment, the bridge member includes an annular support adapted for close fitting assembly on a tubular end of an axle or stub axle and restrained against rotation by a suitable keyway or spline. Thus, a sliding connection can be provided at the axle rather than by a caliper mounting attached to the axle. In the case of a splined connection, a plurality of angular mounting positions are readily available.
Such a non-rotational connection may also be used to ground brake torque to the axle or grounding may be via a separate feature, such as a torque reaction arm.
Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying drawings in which:
With reference to
In the embodiment of
An axle to which the arcuate flange 18 has been welded, or which has a fixed bolting position, may be unsuitable for fitting to a different kind of vehicle or a variant vehicle solely because the flange is in the wrong position with respect to the desired caliper mounting. Furthermore, a welded joint, which is most commonly used, tends to distort the relatively thin axle casing and may lead to stress raisers and fatigue cracking, neither of which is acceptable. Other difficulties of welding are that the welded join may be at an undesirable circumferential location on the axle casing 10, such as a location subject to maximum bending stresses, and that the support and casing must be of compatible weldable materials.
An annular support 31 is an integral part of the brake caliper 25 and surrounds the axle casing 20. The annular support 31 may be cast in unit, or be bolted or attached in any other suitable manner. The brake caliper 25 may be a single component or may be assembled from parts, e.g., with a bridge permanently attached by screws.
Keyways 32 and 33 are formed respectively in the axle casing 20 and the annular support 31 so that insertion of a woodruff key 34 retains the axle casing 20 and the annular support 31 against relative rotation. Thus, braking torque is grounded to the axle casing 20 via the woodruff key 34 and welded connections are avoided. Dust boots 35 and 36 prevent ingress of dirt and moisture.
The invention permits selection of appropriate materials for the axle casing 20 and the annular support 31. For example, the axle casing 20 may be of thin steel tube, whereas the annular support 31 may be a cast or forged component. A brake caliper 25 is generally insensitive to angular location, and accordingly the invention provides an improved chance that a large component, such as the air actuator 27, can be accommodated in a convenient and protected location.
The foregoing description is only exemplary of the principles of the invention. Many modifications and variations are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than using the example embodiments which have been specifically described. For that reason the following claims should be studied to determine the true scope and content of this invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0609258.9 | May 2006 | GB | national |
