Patent Application
20080135352
The present invention relates to disk brakes, and in particular to a mounting system for a brake caliper mounting frame assembly of a disk brake.
Pneumatically-operated disc brakes have been undergoing development and deployment, particularly on commercial vehicles, since at least the 1970's. These disk brakes are beginning to replace drum-style brakes due to advantages in areas such as cooling, fade resistance and serviceability. German patent publication DE 40 32 886 A1, and in particular
The adaptation of disc brake technology to commercial vehicle applications has not been without engineering challenges. Commercial vehicle wheel rims are sized, both in diameter and axial offset, to provide adequate clearance for the drum-type brakes historically employed on such vehicles. The resulting space envelope between the wheel and its axle is limited, leaving little space available for a pneumatic disc brake. This lack of available space in turn results in the need to design the brake components, such as mounting flanges (for example, “torque plates” which are bolted to an axle housing, or flanges permanently fixed to the axle housing), to conform to the constrained space envelope and avoid interference with nearby vehicle components, such as an immediately adjacent axle flange.
Previous pneumatic disk brake designs typically use a brake caliper which straddles a friction portion of brake disk located on an axle hub. The brake caliper in such brakes is mounted to an intermediate mounting frame (also known as a “carrier”), which in turn is affixed to a mounting plate (known as a “torque plate”) which transfers the braking torque generated by the caliper to the vehicle axle. An example of such prior art brake arrangements is shown in
There are several disadvantages to the previous caliper mounting frame arrangements, many of which stem from the configuration of the frame mounting bolts, which are generally parallel to longitudinal axis of the axle. The previous designs require installation tool clearance behind the torque plate to permit insertion and/or removal of the frame mounting bolts and insertion of an installation tool to tighten and/or loosen the bolts. Achieving sufficient clearance for frame mounting bolt installation and/or removal is problematic due to the close proximity of other vehicle components, such as the axle housing, axle flanges, vehicle suspension (e.g., leaf springs and brackets, shock absorbers and mounts), and steering components (e.g., tie rod ends, and arms, steering arm). These space constraining components frequently require the disk brake caliper and its mounting frame to be “clocked” (rotated about the longitudinal axis of the axle) away from an optimum brake performance position, in order to avoid interference with other vehicle components during brake operation or service. Even with clocking of the brake to a sub-optimum position about the axle, access to at least one of the mounting frame bolts usually remains limited, preventing the use of time- and labor-saving power tools (e.g., a pneumatic wrench) during bolt installation and removal.
Further disadvantages of the previous mounting bolt arrangements result from the need to include excess additional material to certain portions of the caliper mounting frame and torque plate, which can lead to compromising the strength of these components in order to fit the disk brake into the available space envelope. For example, because the frame mounting bolts are parallel to the longitudinal axis of the axle, and must be threaded into the mounting frame (in order to minimize bolt projection from the torque plate toward the longitudinal center of the axle), a significant amount of extra frame material must be provided around the mounting bolt holes to support the bolt threads. Given its location at the extreme ends of the caliper mounting frame, this extra frame material does not improve the structural strength of the mounting frame, and thus only adds to the weight of the frame. Further, in order to provide sufficient material about the mounting bolt holes to ensure sufficient bolt thread engagement in the mounting frame, the mounting frame ends typically are so thick that the portion of the torque plate containing the mounting frame mounting bolt holes must be offset away from the brake disk so that there is enough room between the disk and the torque plate to accommodate the enlarged mounting frame ends. As a result of the offset, thin-walled sections are created in the torque plate in the transition regions between the offset mounting bolt holes and the center portion of the plate that is bolted to the axle flange. These thin-walled sections are highly stressed, and past practice has been to added additional material in adjoining areas of the torque plate to reduce the stress concentration in the thin-walled sections. This additional material, resulting from the longitudinal mounting frame mounting bolt orientation, is an additional inefficient use of structural material, further increasing brake weight and cost.
Many of the problems of the prior art caliper mounting designs are addressed by the new disk brake caliper mounting arrangement set forth in of U.S. patent application Ser. No. 11/110,774, the disclosure of which is incorporated herein by reference in its entirety. This Application is directed to an improved disk brake mounting arrangement, as shown for example in
While the vertical caliper mounting arrangements of the Ser. No. 11/110,774 approach offers numerous advantages over prior art longitudinally-oriented mounting bolt designs, new brake designs utilizing the concepts of the Ser. No. 11/110,774 application require careful design of the caliper mounting bracket, torque plate, and the joints between these components to ensure design limits for allowable stresses, fatigue life, etc., will be met. Prior art mounting bracket-to-axle mounts (e.g., torque plates) typically had pairs of parallel machined mating surfaces perpendicular to the longitudinal axis of the axle, with one or more fastener clamping the components together. Due to their orientation, a primary loading direction when the brake is applied is in shear along the components' mating surfaces. These joints rely on friction between the faces (a function of the clamping load of the fasteners) to maintain the orientation of the parts relative to one another, and thereby avoid flexing or other displacements which can lead to distortion of the caliper, binding of the caliper on its sliding pins and highly-localized stress in brake components.
The arrangements taught by the Ser. No. 11/110,774 application place the mounting frame/torque plate mating surfaces perpendicular to the prior art location of these surfaces. These surfaces and their mounting bolts therefore are loaded in an entirely different manner when the brake is applied than with a prior art mounting arrangement. Nonetheless, it remains important to maintain a postionally-fixed relationship between the caliper bracket and its mount to prevent flexing or shifting of the brake components relative to one another, which can lead to very high stresses in localized areas of the brake, including in the portion of the mounting bracket straddling the brake disk rotor. These high stresses raise concerns with not only immediate component failure, but also a greatly decreased fatigue life and potential fatigue failure well short of the typical 50,000 cycle life of a commerical vehicle brake.
One approach to preventing relative motion (e.g., slippage) between the brake mounting components is to apply greater clamping loads between the mounting frame and the torque plate to increase the friction force between these two components. This can be accomplished by increasing the size of the mounting bolts, which in turn requires increasing the size of the mounting frame and torque plate to accommodate the larger bolts. However, this approach may be viable in applications such as Euorpean commerical vehicles which have considerably larger wheel rims, it is not practical in more demanding vehicle applications, such as U.S. commerical vehicles which typically operate with smaller wheels with extremely limited space between the brake and the inner wheel rim surface.
The present invention addresses the problems of brake component relative motion arising from the re-location of mounting and fastening surfaces in the vertical mounting system by use of locator features between the caliper mounting frame and the corresponding torque plate mating surfaces to minimize bolted joint tolerances and to resist rotating and/or sliding movements, thereby minimizing slippage-induced distortion of the caliper and maintaining a precise alignment of the caliper mounting frame relative to the brake disk rotor.
One embodiment of a locator feature to prevent relative motion between the mounting frame and the torque plate is a shear sleeve engaging both frame and plate mating surfaces. This so-called “4-way locator” limits two degrees of freedom, preventing slippage in both the transverse and axial directions relative to the axle.
This locator feature may be combined in other embodiments with other locator features, such as a “clocking” feature which limits a third degree of freedom (i.e., rotation about an axis perpendicular to the axle). Such a clocking feature may include, for example, a ridge on the opposite torque plate mating surface. The ridge could be located at the edge of either the torque plate or the mounting frame mating surface, thereby requiring only simple machining of a corresponding receiving groove on a side surface of the receiving plate or frame component. Alternatively, the ridge may be located more toward the center of the mating surface, and a corresponding groove provided in the face of the opposite mating surface.
It will be readily understood by one of ordinary skill that the clocking feature is not limited to a ridge, but could be any suitable engagement feature, such as a pin or dowel inserted into corresponding holes or slots in the opposing mating surfaces or in an abutting engagment similar to the ridge described above. Moreover, several locating features may be provided on one mating surfaces, including ridges, pins and other such elements. Further, a second shear sleeve (or alternatively, a pin or dowel, etc.) may also be used with the first locating feature, for example, in the opposing mating surface. However, in all these alternative embodiments of the present invention, care must be taken to avoid over-constraint of the degrees of freedom of the joint, lest the mating halves become prone to binding during brake assembly and servicing.
In another embodiment, a ridge, such as a shoulder located at an inboard or outboard edge of the frame or plate mating surfaces, may be provided on both mating surfaces, preferably in parallel with one another. This arrangement would provide resistance against movement either inboard or outboard in the axial direction relative to the axle, as well as provide resitance to rotating (“clocking”) about an axis perpendicular to the axle. A third ridge could be provided on one of the adjacent perpedicular mating surfaces to prevent movement in the transverse direction. The combination of these three ridges would thus desirably contrain three degrees of freedom in a simple and cost-effective manner.
Additional embodiments may include other motion-resisting locator features which engage corresponding receiving holes in the flange and/or plate mating surfaces, such as pins, separate ridges (rather than ridges formed from the component base material) or other insertable objects which present lateral surfaces to both the mounting frame and torque plate, shoulder bolts with close tolerance fit into corresponding counter-bores, etc.
One advantage of the present invention is that the locator features may be designed to provide the desired resistance to movement, yet need not over-constrain the joint, such that there is unnecessary binding which might cause difficulty in assembly or service operations. Other advantages include improved brake pad wear as a result of the more precise and accurate alignment of the brake caliper relative to the brake disk rotor, and the ability to “error proof” assembly processes by arranging the locator features on the mounting frame and/or torque plate in a manner which precludes improper assembly of a left-side brake component in a right-side installation, and vice-versa.
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.
An embodiment of the present invention is illustrated in
The caliper mounting frame 20 is located in this embodiment on torque plate 30, and secured by frame mounting bolts 32 which pass through the torque plate and thread into corresponding threads in mounting frame bosses 36, 38. The mounting bolts 32 apply clamping forces to secure the mating surfaces 40, 42 of the torque plate 30 against the mating surfaces 41, 43 or the mounting frame. There are a plurality of mounting bolts 32 at each end of the mounting frame 20, the bolts being aligned in one or more planes approximately perpendicular to the longitudinal axis of the axle 33. The torque plate 30 is configured to be located concentrically about a hub end of a vehicle axle (not illustrated) having, and secured to an axle flange (not illustrated) by bolts passing through holes 34. As will be evident to those of ordinary skill in the art, the mounting bolts 32 securing the caliper mounting frame 20 to the torque plate 30 are located sufficiently far away from the longitudinal axis of the axle 33 that when disk brake caliper assembly 10 is located on an axle and the associated wheel has been removed, a technician will have essentially unfettered access to the mounting bolts 32 to permit their rapid removal and installation, preferably with pneumatic tools to minimize the effort and time required for the service operation.
As shown in
The ridge 46 provided on torque plate mating surface 46 in this embodiment is integrally formed with the torque plate and machined to its final dimensions, as is its corresponding receiving slot in mating surface 41 of mounting frame 20. As with the counter-bore in mounting frame mating surface 43 which receives shear sleeve 45, the slot is machined to provide a close-tolerance fit to the ridge 46 to minimize component motion as the ridge resists rotation of the mounting frame relative to the torque plate.
A further embodiment of the present invention is shown in
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. For example, one of ordinary skill will recognize that wide variety of mechanical devices may be used to provide the desired constraints on the degrees of freedom of motion between the mounting frame and its mount onto the vehicle axle. Because other 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.
