Land vehicles – Wheeled – Running gear
Reexamination Certificate
2001-03-20
2002-08-27
Culbreth, Eric (Department: 3616)
Land vehicles
Wheeled
Running gear
C267S064150, C280S124100, C280S124116, C280S124128, C280S124157
Reexamination Certificate
active
06439587
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to heavy-duty axle/suspension systems and specifically to rebound stops for such axle/suspension systems. More particularly, the invention is directed to a rebound stop for heavy-duty axle/suspension systems which is easily adjustable, thus making it simple to install and useful on a variety of axle/suspension systems without customization, and further which generally eliminates the need for replacement of the rebound stop and minimizes damage to shock absorbers of the axle/suspension system due to changes in the rebound distance after installation of the rebound stop.
2. Background Art
A heavy-duty vehicle such as a semi-trailer typically is equipped with at least one and usually more than one axle/suspension system. The axle/suspension systems are suspended from the frame of the vehicle. More specifically, each axle/suspension system conventionally is comprised of a pair of transversely spaced-apart trailing or leading arms or beams which capture an axle extending between the beams. One end of each of the beams is pivotally attached to a respective one of a pair of depending frame hangers using a pivot bolt or the like which passes through the hanger and a bushing assembly of the beam. The other end of each of the beams is attached to the frame via a respective one of a pair of air springs, each of which extends between and is attached to its respective beam and the bottom of the frame. A shock absorber typically also is attached to and extends between the beam and the frame.
During, normal operation of the vehicle, the beams of each axle/suspension system pivot about their bushing ends in upward and downward arcs of travel as the wheels attached to the axle encounter bumps and depressions, respectively, in the road over which the vehicle is traveling. Various components of the axle/suspension system, and in particular the beam bushing assemblies, the air springs and the shock absorbers, all cooperate in reacting the loads encountered by the vehicle wheels which are transferred to the two suspension assemblies of the axle/suspension system through the axle. The suspension assemblies, each of which generally comprises one of the beams and its associated air spring and shock absorber, serve to cushion the vehicle frame and ultimately minimizes undue wear and damage to the frame and any cargo being transported, and also makes the ride comfortable for passengers.
During maximum downward travel or full rebound of the suspension assemblies and axle, it is a function of the shock absorbers to act as a positive stop. Without such a stop, damage likely would occur at least to the air springs, and in severe cases to the beams and/or the vehicle frame. However, relying solely on the shock absorber as a positive rebound stop for its respective suspension assembly can significantly shorten the life of the shock absorber.
Therefore, it has been a common practice to install a rebound stop suspension assembly accessory to extend the life of the shock absorbers of the axle/suspension system by limiting the impact loads imparted on the shock absorbers. Such a rebound stop for limiting the downward travel of the axle/suspension system conventionally has taken the form of a woven nylon strap, or for heavy-duty applications, a chain. The strap or chain is attached at one of its ends to the beam or axle, usually adjacent to the air spring, and at the other of its ends to the vehicle frame.
Although such rebound stops operate satisfactorily, at least initially, when properly installed, a number of problems exist with prior art rebound stops due to the fact that they are non-adjustable. First, various axle/suspension systems have different distances between the beam and the vehicle frame as well as different rebound distances. Thus, each non-adjustable rebound stop must be customized for installation on a specific axle/suspension system application. Typically, such customization involves determining the proper rebound stop chain or strap length and locations of attachment for that chain or strap. Such customization often involves hit or miss experimentation if the non-adjustable rebound stop has not already been designed into a specific axle/suspension system and vehicle frame, which is time consuming and costly.
Moreover, the non-adjustability of such prior art rebound stops also presents problems after installation. More particularly, it is understood that maintaining the proper length of the rebound stop chain or strap after installation is very important. This is because the rebound distance of the axle/suspension system can change after installation. Proper functioning of a prior art rebound stop after installation is dependent upon a measurement called “rebound margin” remaining generally unchanged. Rebound margin is defined as the difference in length between the full extension position of the shock absorber without a rebound stop, which is the longer length, and the full extension position of the shock absorber with a rebound stop installed, which is the shorter length. The rebound margin preferably is very small because rebound stops optimally should positively stop the rebound or downward travel of the axle/suspension system just before the shock absorbers are fully extended and experience the impact of rebound, while sacrificing as little as possible of the travel of the shock absorbers so that the cushioning function of the shock absorbers also can be maximized.
If, however, the vehicle alignment, or fore-aft position of the axle/suspension system, is adjusted, either by the manufacturer, or after the vehicle has been in use and is being serviced, the preferred small rebound margin can be significantly reduced or even eliminated, depending on the initial amount of the rebound margin. Other factors that also can adversely effect rebound margin include normal variations in manufacturing tolerances of shock absorber mounting bracket locations, and wear and elongation of the rebound stop components. If the rebound margin is eliminated as a result of such factors, then the shock absorbers are subjected to the full impact of rebound, and consequently, the purpose of the rebound stop is defeated and the life of the shock absorbers could be significantly reduced or damage and failure of the shock absorbers could occur. Failure of the shock absorbers in turn could result in damage to and/or failure of other components of the axle/suspension system.
The present invention solves the above-described problems associated with prior art non-adjustable rebound stops, through the use of an adjustable rebound stop, which is easy to install, economical and simple to use.
SUMMARY OF THE INVENTION
Objectives of the invention include providing a rebound stop which can be utilized on a variety of axle/suspension systems without customization.
Another objective of the present invention includes providing a rebound stop which is adjustable after installation to minimize the possibility of elimination of the rebound margin after the vehicle has been in use.
Still another objective of the invention is to provide a rebound stop which is easy to install, economical and simple to adjust.
These objectives and advantages are obtained by the rebound stop assembly for limiting the downward rebound travel distance of a vehicle axle/suspension system of the present invention, the general nature of which may be stated as including the axle/suspension system including a pair of transversely spaced suspension assemblies, each one of the pair of suspension assemblies including a longitudinally extending beam, the beams each being pivotally mounted on and depending from a frame of the vehicle, the beams further capturing a transversely extending axle having at least one wheel mounted on each end of the axle, one of the rebound stop assemblies being incorporated into each one of the pair of suspension assemblies, each one of the rebound stop assemblies including elongated vertically extending stop means, a first end of the stop means being immovably attached
Buckingham Doolittle & Burroughs LLP
Culbreth Eric
Dureska David P.
The Boler Company
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