Spring devices – Coil
Reexamination Certificate
2002-03-05
2004-07-06
Schwartz, Chris (Department: 3683)
Spring devices
Coil
C267S162000
Reexamination Certificate
active
06758465
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to compression springs, and, more particularly, to a compact compression spring made from an elongate flat strip which is circularly coiled and formed with a circular flat shim portion at one end of the compression spring.
Crest-to-crest compression springs are coiled springs which are typically made from a flat metal strip and formed in a generally sinusoidal wave pattern. These springs are described as “crest-to-crest” because of the particular orientation of the individual spring turns in which the crest portions of the waves of one turn abut the trough portions of the waves in the turns immediately adjacent it.
In an ordinary crest-to-crest compression spring, an imbalance of the spring occurs due to the difficulty of arranging a completely symmetrical orientation of the crests (or troughs) of successive waves of the final spring turns at the opposite ends of the spring. The compression spring naturally tilts toward the point on its ends where the spring is lacking a wave crest portion to supply the required balance to the spring as a result of the helical format. Also, a continuous coiled spring naturally possesses a helical pitch at its spring ends which results in the lack of a support surface that is perpendicular to the spring longitudinal axis.
The lack in support surface can cause an imbalance which becomes apparent when the spring is loaded, where the loading member rests on the wave crest portions of the last turn of the compression spring ends. Due to this imbalance, such compression springs can undergo uneven axial pressures when loaded. These uneven axial loads can cause the spring to exert opposite forces in both its radial and axial directions which detract from the designed load carrying ability of the spring, which is to exert a force only along the axial direction.
To minimize this imbalance problem, the compression spring designer must either increase the number of waves per spring turn to provide additional load support wave crest portions or decrease the amplitude of each wave of the entire spring to decrease the imbalance at the spring ends.
Other attempts to solve this imbalance problem have included using round wire for the compression spring in which the round wire at the opposite end portions of the compression spring are ground to form flat disc-like load support surfaces. However, this method is relatively expensive and time consuming because it requires a thick wire cross-section to provide a strong load support surface at the spring ends.
U.S. Pat. No. 4,901,987, which is assigned to the assignee of the present invention, presents a solution to the imbalance problem by illustrating a compression spring having a flat shim at each end of the spring. The compression spring is formed from a flat, elongate wire strip into a continuous circular and substantially sinusoidal wave path comprising three wave regions. The first wave region is in the center of the spring and all of the waves of the first wave region have the same amplitude. The second wave region includes a second wave portion adjacent to each side of the first wave region. The waves in the second wave portion have a diminishing amplitude which incrementally diminishes down to zero. The third wave region includes a third wave portion adjacent to each end of the second wave portions such that each third wave portion forms a flat circular shim end. The flat circular shim ends form a plane generally perpendicular to the longitudinal axis of the spring.
However, the compression spring with the two circular shim ends has disadvantages. The compression spring is cumbersome. It has a large height and weight because it requires a substantial amount of material to form the complete compression spring with two shim ends. Additionally, when the spring is under a light load, the spring tends to shift positions. Often, the edge or end of each shim end scratches and damages the surface on which it sits.
Accordingly it is an object of the present invention to provide an improved wave spring that balances the axial and radial load on the spring.
It is another object of the invention to provide a wave spring that is lighter and less expensive to manufacture.
It is another object of the invention to provide a wave spring that is compact and includes a single shim end.
It is another object of the invention to provide a wave spring assembly that includes a support surface for the non-shimmed end of the spring.
These and other objects of the present invention, as well as the advantages thereof over existing prior art forms, which will become apparent from the description to follow, are accomplished by the improvements herein after described and claimed.
SUMMARY OF THE INVENTION
The present invention is directed to a wave spring and a wave spring assembly. The wave spring includes a crest-to-crest helical spring formed from a continuous elongate wire strip with three separate wave regions. The first wave region begins at one end of the spring with a terminal wave and includes one or more spring turns. The amplitude of the waves in the first wave region is constant. The second wave region is adjacent to the first wave region. The amplitude of the waves in the second wave region vary uniformly from the amplitude of the first wave region down to a zero wave amplitude. The third wave region begins where the second wave amplitude reaches zero. The amplitude of the wave in the third wave region is a constant zero, thereby forming a flat circular shim end.
The wave spring assembly includes a base and the wave spring with a non-shimmed end and a shimmed end. The base includes an arc shaped recess with edges that align with the radius of the spring. The arc shaped recess receives the terminal wave at the non-shimmed end of the first wave region of the wave spring. The recess supports the terminal wave and prevents rotation of the wave spring around its axis.
REFERENCES:
patent: 4752178 (1988-06-01), Greenhill
patent: 4807859 (1989-02-01), Bolthouse
patent: 4901987 (1990-02-01), Greenhill et al.
patent: 5470049 (1995-11-01), Wohler et al.
patent: 5558393 (1996-09-01), Hawkins et al.
patent: 5622358 (1997-04-01), Komura et al.
patent: 5639074 (1997-06-01), Greenhill et al.
patent: 6050557 (2000-04-01), Shimoseki
patent: 6068250 (2000-05-01), Hawkins et al.
Greenhill Mark
Greenhill Michael
Piper Rudnick LLP
Schwartz Chris
Smalley Steel Ring Company
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