Brakes – Wheel – Transversely movable
Reexamination Certificate
1999-06-17
2001-07-03
Oberleitner, Robert J. (Department: 3613)
Brakes
Wheel
Transversely movable
Reexamination Certificate
active
06253890
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Related Invention
This invention is an improvement on U.S. Pat. No. 5,865,277, patented Feb. 2, 1999, by Marc Hunter, the entire contents of which are incorporated herein by reference.
(ii) Field of the Invention
This invention relates to a brake system and brake actuator system for trucks. In one embodiment, it is particularly concerned with pneumatic air braking systems which are used on large trucks which are used in the forestry trucking industry.
(iii) Description of the Prior Art
Drum brakes are known to have certain advantages over disc brakes. Those advantages include superior braking force in some situations, and, the continued application of braking force where temperature variations occur while the brake is on.
A problem, however, with prior art drum brake assemblies was that they were of complex construction and assembly, and they were generally comprised of a large number of components and parts. Such a large number of parts resulted in the brake assembly being expensive, and time-consuming to both assemble and to fix to a vehicle.
A further problem with drum-type parking brake assemblies was that the drum shoe friction linings did not become properly-bedded by wearing against the inner surface of the drum. Unless there was a near-perfect match between the diameters of the lining when the brake was applied and the drum, the drum shoe would not properly-contact the drum over its entire surface and thus, an inferior braking force would result.
Drum brakes which included a plurality of brake shoes which were expanded within a brake drum attached to a wheel, required an actuating system to expand the brake shoes. In one type of actuating mechanism, the shoes were expanded by a cam, which was mounted on a shaft which was supported by bearings carried by a backing plate and by a spaced support which was fixed to an un-sprung part of the vehicle. The cam shaft generally extended between the backing plate and the spaced support in a direction which was substantially-parallel to the axle or to the axle housing to which the backing plate was fixed.
In mechanisms of the above-described type, the spaced support was welded or bolted to the axle or to the housing itself. In either case, however, the cam shaft bearings in the backing plate and in the support had to be in exact alignment to prevent binding of the cam shaft therein when completely assembled. It was known that, after the bracket was welded or bolted into place, unless extreme care was taken, the bearing in the bracket did not exactly align with the bearing in the backing plate. This caused the shaft to bind in its bearings. When the parts were welded into place, for maximum strength, the difficulties of securing proper bearing alignment were increased. During the manufacture of the backing plate and the support, they were stamped or otherwise formed, and usually had the necessary holes, etc., bored into them before they were welded to the axle or to the housing. While the customary jigs or other devices could be used to hold them in position during welding, it was extremely-difficult to hold them in the exact desired position so that when welded into place they would be properly-aligned for the attachment of other parts. It was also necessary accurately to machine the parts. Such proper alignment was particularly-necessary in the case of the spaced-bearings for the cam shaft.
Conventional brake mechanisms for automobile and truck wheels usually included a cylindrical brake drum which was mounted for rotation with each wheel. Pairs of semi-cylindrical brake shoes were mounted on the opposite sides of an axle housing for pivotal movement inwardly and outwardly between expanded and contracted positions. Brake linings were positioned between the brake shoes and the brake drums and were compressed therebetween incident to brake shoe expansion. Cams were positioned between free ends of the brake shoes for urging them into expanded positions and releasing them for spring contraction. The cams were controlled by linkages which were connected to a foot pedal or hand lever of the vehicle. When the brake lining wore out there was brake failure and the cam was normally ineffective to apply the brakes in such a manner as to stop the vehicle. This could also result from excessive heating and expansion of the brake drums so that proper shoe engagement could not be attained.
One current drum brake system has shoes that make contact with the drum. The wheel cylinder activates the shoes at the top, while there is separate linkage that is operated by a cable which throws out the shoes to come into contact with the drum. It also needs to be adjusted, but often it becomes rusty and therefore is not possible to adjust.
In most drum brakes, whether actuated manually, hydraulically or pneumatically, the arcuate brake shoes were interconnected by retraction springs. When the brakes were not applied, the brake shoes were held away from the rotating drum by the retraction springs. When the brakes were applied, e.g., in a hydraulic or pneumatic system, pressurization of the hydraulic or pneumatic cylinder forced the piston links outwardly from the cylinder against the brake shoes and caused the brake shoes to engage the rotating brake drum.
However, it was found in practice that the retraction springs occasionally became inoperative. The need, therefore, arose to provide brakes whose retraction was not provided by spring means, but which would be positively-actuated.
Heretofore, it was also a conventional practice in brake constructions to utilize relatively-inflexible brake shoes which had generally been reinforced against flexing by stiffening webs. Such brake shoes were pressed against a rotating drum by applying a force to an end of one shoe by means, e.g., of a pneumatic cylinder, or of a hydraulic cylinder, and provided an anchor at an opposite end of the shoe for anchoring the shoe against the circumferential-movement with the drum. It was also a conventional practice in such constructions to link together a pair of torque shoes at adjacent ends, whereby a single cylinder could be utilized for applying an actuating force at a free end or at an opposite end of a first shoe in the pair and whereby a single anchor could be located at the adjacent free end of a second shoe in the pair to receive friction forces which were developed along the surfaces of both of the shoes of the pair. In the latter arrangement, the frictional force which developed along the surface of the first shoe was transmitted to an end of the second shoe as an actuating force.
In conventional air brake systems, pressurized air was supplied by way of a service brake (control) line and an emergency brake (supply) line. The control line is connected through a relay valve to operate service brakes which are associated with each wheel pneumatically. In order to assure that the service system had adequate volume to provide for repeated service brake applications, the braking system further included a service reservoir or tank which was connected through the relay valve so that pressure may be supplied to the service brakes from a relatively large storage volume. The reservoir was pressurized through the supply (emergency) pressurization system which also provided pressure to the emergency or parking brakes of the vehicle. The emergency or parking brakes were generally spring-operated with the force of the springs being offset to release the brakes by the use of pressure within the emergency supply system.
In the pneumatic system of prior art air brake systems, the emergency brake was either an air pot with an auxiliary air tank separate from air lines, or a separate system which was reliant on the S-cam system. In such pneumatic system, when the air lines lost air pressure, a valve sensed the loss of air pressure and let all the air from the auxiliary tank. The air would eventually seep out and leave no pressure in the air pots. Thus, it was necessary to use blocks of wood as a back-up.
The S-cam system worked differently. It was not reliant
Oberleitner Robert J.
Pezzlo Benjamin A.
Wood Phillips VanSanten Clark & Mortimer
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