Patent Application
20070012529
Slack adjusters are often used in vehicle brake systems to make adjustments to compensate for brake wear. For example, heavy duty vehicles, such as trucks, often employ brake systems that include an air brake cylinder attached to an automatic slack adjuster. The automatic slack adjuster mounts to one end of a brake shaft such that force applied by the air brake cylinder pivots the slack adjuster and rotates the brake shaft. An S-cam attaches to the other end of the brake shaft and couples to brake shoes such that rotation of the shaft applies the brakes against brake drums. As the brakes wear, however, the clearance between the pads or liners and drums increases and the brake system must be adjusted in order to take up this slack to ensure proper braking.
The automatic slack adjuster serves this purpose by automatically adjusting the brake system to compensate for the slack. Typically, however, components of the slack adjuster can wear over time and adversely affect the slack adjusting function. For example, it is common to employ a one-way conical clutch-type mechanism as part of the automatic slack adjuster. This mechanism typically contains numerous small, fine teeth. When these teeth wear beyond a certain point, the brake adjustment can no longer be made and the slack adjuster has reached the end of its useful life.
The present invention relates to an automatic slack adjuster for vehicle brakes. More specifically, the present invention relates to an automatic slack adjuster for vehicle brakes having at least one component with a toothed portion that includes a ceramic material. It will be appreciated, however, that the invention is also amenable to other applications.
The present invention also relates to a method of adjusting the slack of a vehicle brake system that includes the step of using an automatic slack adjuster that has at least one wear part that includes a ceramic material.
In the accompanying drawings which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which together with a general description of the invention given above, and the detailed description given below, serve to exemplify the embodiments of this invention, wherein:
The present invention relates to an automatic slack adjuster for vehicle brakes. In particular, the present invention relates to an automatic slack adjuster for vehicle brakes having at least one wear part that includes a ceramic material to increase the life of the slack adjuster.
Since the exemplary automatic slack adjuster 10 of
A rack follower ring 28 rotatably mounts to the body 12, coaxial to the worm gear 26. The rack follower ring 28 includes a rack engaging portion 30, such as for example a notch, and is rigidly joined to a control arm 32. The control arm 32 mounts to a fixed point 34 such that the body 12 may rotate relative to the rack follower ring 28 in response to force applied by the force transmitting device 18.
A rack 36 having a toothed portion 38 on a first end 40 and a ring engaging portion 42 at a second end 44. The rack 36 is movable along its longitudinal axis, perpendicular to the second axis 24. The toothed portion 38 engages a rack gear 46 that is positioned within the second bore 22 centered on the second axis 24 such that axial movement of the rack 36 rotates the rack gear. The rack gear 46 is positioned onto a worm shaft 48, which is coaxial with the rack gear within the second bore 22. The rack gear 46 can both rotate about the worm shaft 48 and move axially along the worm shaft.
A clutch gear 50 also resides in the second bore 22 coaxial with the worm shaft 48 and rack gear 46. The clutch gear 50 connects to the rack gear 46 by a clutch spring 52. The connection between the clutch gear 50, the clutch spring 52, and the rack gear 46 allows the rack gear to rotate independent of the clutch gear in one direction (during brake application). In the opposite direction (during brake release), however, the rack gear 46 and the clutch gear 50 rotate together. A load spring 54 also resides in the second bore 22. The load spring 54 acts between the body 12 and the wormshaft 48, and may also interact with a spring retainer 55, to bias the wormshaft into engagement with the clutch gear 50.
The clutch gear 50 and the worm shaft 48 form a toothed clutch of the exemplary automatic slack adjuster 12.
Since the exemplary automatic slack adjuster 10 of
During release of the brakes, the body 12 pivots in the opposite direction of brake application. As the body 12 pivots back and the brakes begin to disengage, the torque on the worm gear 26 lessens, allowing the load spring 54 to bias the wormshaft 48 back into engagement with the clutch gear 50. As the body 12 continues to pivot back, the rack follower ring 28 causes the rack 36 to move to its lowest position in the body. As a result, the rack 36 rotates the rack gear 46, which rotates the clutch gear 50. Because the clutch gear 50 and wormshaft 48 are engaged, rotation of the clutch gear, rotates the wormshaft, which rotates the worm gear 26 and the brake shaft 27. By rotating the worm gear 26 (and brake shaft 27) relative to the automatic slack adjuster 10, the angular relationship between the brake shaft and automatic slack adjuster is modified; effectively taking up the slack in the brake assembly.
As illustrated above, the automatic slack adjuster 10 includes a number of components that engage to transmit motion between the components. Often these engaging components, such as the worm gear 26, the rack 36, the rack gear 46, the wormshaft 48, and the clutch gear 50, have toothed portions that mesh with each other. This is typical of most automatic slack adjuster designs. These engaging components are susceptible to wear, deformation, etc., which can adversely affect the operation of the slack adjuster. For example, every time the brakes are engaged and released, the toothed portions 66, 76 of the clutch gear 50 and wormshaft 48 engage and disengage. Overtime, the toothed portions 66, 76 wear to the point where the teeth cannot properly engage and slack adjustment can no longer be made. The present invention addresses wear concerns such as this by including a ceramic material in select wear parts of the adjuster 10. For example, in the exemplary embodiment of
Ceramic material can be introduced to the wear parts, such as for example the toothed portions 66, 76, in a variety of ways. For example, the toothed portion 76 of the worm shaft 48 can be a part of a separate, ceramic piece adapted to slide over the second end 72 of the worm shaft and be secured or attached in position. Attachment of the ceramic toothed portion 76 can be done in a variety of ways, such as for example, a press fit between the ceramic toothed portion and the wormshaft can be provided. Alternatively, a type of mechanical interlock, such as for example threads, a slot-tab arrangement, a tooth-notch arrangement, or some other interlocking arrangement, can be provided. Further, the separate ceramic toothed portion can be bonded to the wormshaft by known methods. In a similar manner, the toothed portion 66 of the clutch gear 50 can be a part of a separate piece that attaches to the clutch gear via bonding, a press fit, mechanical interlock, or other manner.
Ceramic material can be introduced to the wear parts in the automatic slack adjuster 10 by forming the parts from a ceramic material or a material that includes a ceramic material. For example, the entire clutch gear 50 can be formed from a ceramic material. In addition, ceramic material can also be introduced by coating the toothed-portion with a material containing ceramics. Ceramic coatings are widely used in a variety of industries and they can be deposited by a range of deposition technologies including thermal spraying, plasma spraying, vapour deposition (both chemical and physical), sol gel processing or others.
A variety of wear-resistant ceramic materials have been identified as suitable for the present invention. Suitable ceramic materials may include alumina, silicon nitride, chromium nitride, titanium nitride, zirconium nitride, chromium oxide, aluminum oxide, zirconium oxide, titanium chromate, aluminum chromate, silicon carbide, titanium aluminum nitride, titanium carbo nitride, and titanium carbide, although other ceramic materials may be suitable.
While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerate detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modification will readily appear to those skilled in the art. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant's general inventive concept.
