Abstract:
A spring perch assembly for automatically centering a load applied to a spring is provided. The assembly includes a body portion and a base portion which form a hollow cavity when engaged and may tilt relative to one another. When disposed between a spring and an applied load, the assembly automatically centers the load along the spring&#39;s centerline.

Description:
[0001]    This application claims priority to and incorporates by reference U.S. Provisional Application Serial No. 60/307,767 filed Jul. 25, 2001. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to an improved device and method for centering a load on a spring.  
         BACKGROUND OF THE INVENTION  
         [0003]    Three basic types of coil compression springs are known in the industry. An open end spring consists of a wire coil which follows a single helix angle to the end of the wire. An unground, closed end spring has an end which touches the last coil of the spring. In a ground, closed end spring, the tip of the final coil is shaped such that when the tip touches the last coil of the spring, a flat upper surface is produced. Most standard automotive springs are open end springs as they are relatively inexpensive to produce. In contrast, most high-performance springs used in racecars are ground, closed end springs.  
           [0004]    As a load is applied to compress a coil spring, the force is not distributed evenly across the face of the spring. Where this load concentration occurs on the spring varies with the type of spring used. For example, in an open end spring the load is concentrated between the end of the spring and the point at which the load ceases contact with the spring. As the load is increased, this point moves away from the end tip of the spring. In closed end springs, the load is concentrated primarily at the end tip. The consequences of this uneven loading are illustrated in lateral or offset loads such as in vehicle suspension systems. In general, a vehicle suspension system is provided with a helical compression spring designed to provide a coil axis that coincides with the direction of reaction force of the spring. In a strut-type suspension system, a shock absorber is employed as a strut for positioning the vehicle&#39;s wheels. If there is a displacement between the load axis and the strut axis, a bending moment is exerted on the strut. This lateral force may prevent the piston from sliding smoothly in the guide to act as a shock absorber.  
           [0005]    This problem is illustrated in FIGS.  1 - 2 . A traditional closed-end coil spring  200  having a load-bearing platform  210  at one end is shown in an unloaded state in FIG. 1 disposed against a base  212 . In the unloaded state, the first side of the spring  202  is substantially equal in height to the second side of the spring  204 . In this example, the point of first contact  206  between the spring  200  and the platform  210  is on the second side of the spring  204 .  
           [0006]    When a load  220  is applied to the spring  200 , the spring is compressed as shown in FIG. 2. As the load is applied, the spring initially compresses to a greater degree at the first point of contact  206  than compared to the first side of the spring  202 . As a result, the second side of the spring  204  is compressed to a greater degree than the first side of the spring  202 . This offset loading of the spring results in a bending moment applied to the spring. This bending moment is usually undesirable and may result in unanticipated or degraded performance or premature wear of the final spring assembly. Typically this problem has been addressed by using larger and heavier springs in the context of vehicle suspension systems.  
           [0007]    Accordingly, there is a need for a device which assists in centering the load applied to a coil spring, allowing the load to be concentrated at the centerline of the spring. In the context of vehicle suspension systems, preferably such a device is lighter and more efficient than current devices. Prior attempts to solve these problems have been unsuccessful. The present invention addresses these concerns.  
         SUMMARY OF THE INVENTION  
         [0008]    The invention is set forth in the claims below, and the following is not in any way to limit, define or otherwise establish the scope of legal protection. In general terms, the present invention relates to an assembly for automatically centering the load applied to a spring.  
           [0009]    One object of the present invention is to provide an assembly having two pivotably coupled members and a cavity disposed therebetween. When disposed between a spring and an applied load, the members of the assembly pivot relative to one another to center the load on the spring.  
           [0010]    Another object of the present invention is to provide a method for automatically centering a load applied to a spring using a load-centering assembly disposed between the spring and the load.  
           [0011]    Yet another object of one embodiment of the present invention is to provide an assembly for centering the load applied to a spring which utilizes hydraulic pressure to automatically center the load.  
           [0012]    Further objects, embodiments, forms, benefits, aspects, features and advantages of the present invention may be obtained from the present disclosure.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a side view of a coil spring according to the prior art in an unloaded state.  
         [0014]    [0014]FIG. 2 is a side view of a coil spring according to the prior art in a loaded state.  
         [0015]    [0015]FIG. 3 is a partial cross-sectional view of a spring perch assembly according to one embodiment of the present invention.  
         [0016]    [0016]FIG. 4 is a partial cross-sectional view of a spring perch assembly according to another embodiment of the present invention.  
         [0017]    [0017]FIG. 4A is a partial cross-sectional view of another embodiment of a spring perch assembly according to the present invention  
         [0018]    [0018]FIG. 5 is a partial cross-sectional view of a spring perch assembly according to another embodiment of the present invention.  
         [0019]    [0019]FIG. 6 is a partial cross-sectional view of a spring perch assembly according to yet another embodiment of the present invention.  
         [0020]    [0020]FIG. 7 is a perspective view of a spring according to one embodiment of the present invention.  
         [0021]    [0021]FIG. 8 is a perspective view of a spring according to another embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0022]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and alterations and modifications in the illustrated device and method and further applications of the principles of the invention as illustrated therein, are herein contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0023]    [0023]FIG. 3 shows a partial cross-sectional view of a spring perch assembly  10  according to one preferred embodiment of the present invention. The perch assembly comprises a body portion  15  and a base portion  20 . The body portion  15  includes an outer flange  45  having a straight inner wall  75  and an inner flange  60  having a curved outer wall  55 . Optionally the body portion may also include one or more wrench sockets  40  and a central, threaded socket  25  for attachment to a load. For example, in a vehicle suspension system a shock absorber may be attached to the socket. The base  20  portion of the perch assembly includes an annular wall  70 , a lateral flange  30  and a spring locating guide  35 . The annular wall portion  70  of the base has a curved outer wall  50  and a straight inner wall  65 . A less preferred alternative includes straight outer and inner walls for the body portion and base portions.  
         [0024]    The body portion of the assembly is sized to receive the base portion such that outer surface  55  of the inner flange  70  of the body member has a slightly smaller diameter than the inner surface  65  of the annular wall  70  of the base member and such that the outer surface  50  of the annular wall  70  of the base member has a slightly smaller diameter than the inner wall  75  of the outer flange  45  of the body member. This allows the body member to freely pivot relative to the base member without disengaging the base member. In one embodiment of the present invention, the body member may pivot up to approximately 4° relative to the base member. The present invention also contemplates assemblies which allow a greater or lesser range of pivot between the body member and the base member.  
         [0025]    Preferably, the inner and outer wall of the body member and the inner and outer wall of the base member are machined to a smooth finish to reduce friction. Optionally, these surfaces may be coated with a low-friction material to further reduce friction. This material may be applied in any suitable manner such as spraying, spray and bake, or as a dry film. Examples of suitable materials include Krytox® and Teflon® manufactured by DuPont, although other suitable materials may also be used.  
         [0026]    When the base member  20  is engaged with the body member  15 , the inner surface  65  of the annular base wall  70  engages the outer surface  55  of the inner body flange  60  and the inner surface  75  of the outer body flange  45  engages the outer surface  50  of the annular base wall  70 . This forms a circular cavity  90  between the body portion and the base portion of the assembly. To ensure the cavity is tightly sealed, suitable seals, such as O-rings  80  and  85 , may be disposed between the inner surface of the annular base wall and the outer surface of the inner body flange and between the inner surface of the outer body flange and the outer surface of the annular base wall. Optionally, these O-rings  80  and  85  may be impregnated or coated with a low-friction material such as Krytox®. As the outer wall  55  of the inner flange  60  of the body member and the outer wall  50  of the annular wall  70  of the base member are curved, they exert an even pressure across the face of the O-rings  80  and  85  as the body member is pivoted relative to the base member.  
         [0027]    The cavity  90  may be filled with a volume of oil, hydraulic fluid or other suitable fluid through a fluid passage  94  in the base portion which is sealed using a screw  95 . Air may be removed from the cavity during the filling process through an air bleed passage  99  which is sealed with a screw  100 . Preferably, the cavity  90  is filled with a suitable fluid until the body member floats on the fluid without disengaging from the base member.  
         [0028]    [0028]FIG. 4 shows an alternate preferred embodiment of the present invention. In this embodiment, the body portion  115  of the assembly  110  includes an outer flange  145  having a straight inner wall  175 . The base portion  120  of the assembly includes an annular wall  170  having a curved outer surface  150 , a lateral flange  130  and a spring locating guide  135 . The base and body portions of the assembly are sized such that the outer surface  150  of the annular wall  170  has a slightly smaller diameter than the inner surface  175  of the outer flange  145  of the body member. This allows body member  115  to freely pivot relative to the base member  120  without disengaging the base member.  
         [0029]    When the base member is engaged with the body member, the inner surface of the body flange  175  engages the outer surface of the annular base wall  150 . This forms a cavity  190  between the body member and the base member. An O-ring  180  such as described in FIG. 3 may be positioned between the inner surface  175  of the body flange and the outer surface  150  of the annular base wall to ensure the cavity  190  is tightly sealed. Optionally, the inner surface  175  of the body flange, the outer surface  150  of the annular base wall and the O-ring  180  may be coated with a low-friction material. This cavity  190  may be filled with a hydraulic fluid such as oil through a fluid passage  94  in the base portion which is sealed using a screw  195 . Air may be removed from the cavity during the filling process through an air bleed passage  199  which is sealed with a screw  198 . Operation of the embodiments described by FIGS.  3 - 4  will be described in greater detail with reference to FIGS.  7 - 8 .  
         [0030]    An alternate preferred embodiment of the present invention is shown in FIG. 4A. The perch assembly  510  comprises a body portion  515  and a base portion  520 . The body portion  515  includes an outer flange  545  having a straight inner wall  575  and an inner flange  560  having a curved outer wall  555 . The body portion  515  also includes a spring locating guide  535 . Optionally the body portion may also include a central socket  525  for attachment to a load. The base  520  portion of the perch assembly includes an annular wall  570  and a lateral flange  530 . The annular wall portion  570  of the base has a curved outer wall  550  and a straight inner wall  565 . The body portion  515  of the assembly is sized to receive the base portion  520  such that outer surface  555  of the inner flange  570  of the body member has a slightly smaller diameter than the inner surface  565  of the annular wall  570  of the base member and such that the outer surface  550  of the annular wall  570  of the base member has a slightly smaller diameter than the inner wall  575  of the outer flange  545  of the body member. This allows the body member to freely pivot relative to the base member without disengaging the base member. In one embodiment of the present invention, the body member may pivot up to approximately 4° relative to the base member. The present invention also contemplates assemblies which allow a greater or lesser range of pivot between the body member and the base member.  
         [0031]    Preferably, the inner and outer wall of the body member and the inner and outer wall of the base member are machined to a smooth finish to reduce friction. Optionally, these surfaces may be coated with a low-friction material to further reduce friction. This material may be applied in any suitable manner such as spraying, spray and bake, or as a dry film. Examples of suitable materials include Krytox® and Teflon® manufactured by DuPont, although other suitable materials may also be used.  
         [0032]    When the base member  520  is engaged with the body member  515 , the inner surface  565  of the annular base wall  570  engages the outer surface  555  of the inner body flange  560  and the inner surface  575  of the outer body flange  545  engages the outer surface  550  of the annular base wall  570 . This forms a circular cavity  590  between the body portion and the base portion of the assembly. To ensure the cavity is tightly sealed, O-rings  580  and  585  may be disposed between the inner surface of the annular base wall and the outer surface of the inner body flange and between the inner surface of the outer body flange and the outer surface of the annular base wall. Optionally, these O-rings  580  and  585  may be impregnated or coated with a low-friction material such as Krytox®. This cavity  590  may be filled with a volume of oil, hydraulic fluid or other suitable fluid, preferably until the body member floats on the fluid without disengaging from the base member.  
         [0033]    An alternate preferred spring perch assembly is shown in FIG. 5. A means for connecting objects to this particular embodiment and the embodiment illustrated in FIG. 6 such as the threaded socket  25  described in FIG. 3 has been omitted for clarity. It is understood that suitable means for attaching objects such as shock absorbers to this particular embodiment is used. In this embodiment of the present invention, the assembly  300  includes a body portion  310  and a base portion  320 . The base portion includes a lateral flange  360 , a spring locating guide  330  and a curved outer wall  340 . The body portion includes a flange  325  having a curved inner surface  350 . The curve of the inner surface  350  of the body flange complements the curve of the outer wall  340  of the base portion. Preferably, this curve is approximately spherical. The center of this curve is preferably located a distance above or below the face of the engaged spring. The components of the assembly are sized such that the outer wall  340  of the base portion has a slightly smaller diameter than the inner surface  350  of the body flange. This allows the body portion of the assembly to pivot relative to the base portion without disengaging the base portion. In one embodiment of the invention, the outer wall of the base portion has a diameter of 1.374 inches and the inner wall of the body portion has a diameter of 1.375 inches. In another embodiment, the body portion  310  of the assembly may pivot up to approximately 4° relative to the base portion  320 . The present invention also contemplates assemblies which allow a greater or lesser range of pivot between the body member and the base member.  
         [0034]    Optionally, the outer wall  340  of the base portion and the inner surface  350  of the body flange may be coated or impregnated with a low-friction material. In this embodiment, when the body portion and the base portion are engaged, the inner surface of the body portion directly engages the outer wall of the base portion. This forms a cavity  315  between the base portion and the body portion of the assembly. Preferably the outer wall  340  of the base portion and the inner wall  350  of the body portion are machined smooth to minimize friction between the two surfaces. Also, it is preferred that these surfaces be coated with a low-friction material to further minimize friction. This material may be applied in any desired fashion. Examples of suitable materials include Krytox® and Teflon® manufactured by DuPont, although other suitable materials may also be used. An alternate embodiment of this assembly having a larger cavity  316  is shown in FIG. 6.  
         [0035]    [0035]FIG. 7 shows a spring perch assembly  410  according to one embodiment of the present invention engaged with a coil spring  450 . The assembly is engaged with the spring  450  by inserting the spring locating guide (not shown) through the center of the spring coil until the upper surface of the coil  452  contacts the lateral flange  430  of the base portion of the assembly. The spring locating guide prevents lateral movement of the assembly relative to the spring. In this particular example, the end of the spring distal from the assembly is in contact with a fixed base  412 . Although FIG. 7 shows a perch assembly engaged with the top of a spring, it is also contemplated by the present invention to use a single perch assembly engaged with the bottom of a spring. As seen in FIG. 8, a coil spring  450  may be engaged with one perch assembly  410 ,  411  at each end of the spring to further improve the load-centering performance of the present invention.  
         [0036]    First, the operation of the embodiments of the present invention discussed previously in FIGS.  3 - 4  will be described with reference to FIG. 7. When a load is applied to the spring perch assembly body member, the load is initially concentrated at the point of first contact  460  between the spring and the perch assembly. The perch will tilt to accommodate the shape and twisting strength of the end coil. This load concentration depresses this area of the body portion of the assembly causing the hydraulic fluid in the cavity at that location to be compressed. This compression of the fluid forces a redistribution of the fluid throughout the cavity. Preferably, the cavity has sufficient clearance such that complete compression of the fluid is achieved before the load begins to be supported around the entire body portion of the assembly. Compression of the fluid continues until equal hydrostatic pressure is achieved throughout the fluid. Although tilting assists in redistribution, it will not redistribute the load with complete efficiency. Hydrostatic equilibrium within the fluid cavity completes the redistribution of the load evenly across the entire body portion of the assembly thereby maintaining the center of the applied load along the natural centerline  455  of the spring, thereby minimizing and/or eliminating any lateral components of the load. Although ideally minimized, residual friction between the body portion and the base portion prevents completely efficient redistribution.  
         [0037]    Next, the operation of the embodiments of the present invention discussed previously in FIGS.  5 - 6  will be described with reference to FIG. 7. When a load is applied to the spring perch assembly body member, the load is initially concentrated at the point of first contact  160  between the spring and the perch assembly. This load concentration depresses this area of the body portion of the assembly initially causing an uneven loading of the spring. As an uneven load is applied, the centerline of the applied load deviates from the centerline of the spring, causing the body member of the assembly to pivot relative to the base member. This pivoting of the body member centers the load evenly across the body member, substantially returning the centerline of the applied load to the natural centerline of the spring. The minimization of friction enhances the equalization.  
         [0038]    Additionally, the system can be made “self energizing” by changing the radius of curvature of the walls to move the center of rotation away from the spring face. While this introduces a slight buckling effect, it has been found that moving the center of rotation upward, away from the spring can increase the tilting effect and thus enhances the load equalization. This benefit is limited by the effect of the lateral movement of the spring end off of a centered position, which results in the final load being placed slightly off center.  
         [0039]    As seen in FIG. 8, a spring  450  may be engaged with two assemblies  410 ,  411  according to the present invention. In this example, a first assembly  410  is engaged to a first end  452  of the spring  450  and a second assembly  411  is engaged to a second end  442  of the spring  450 . The first assembly  410  is engaged with the spring  450  by inserting the spring locating guide (not shown) through the center of the spring coil until the upper surface of the coil  452  contacts the lateral flange  430  of the base portion of the assembly  410 . The spring locating guide prevents lateral movement of the assembly relative to the spring. Similarly, the second assembly  411  is engaged with the spring  450  by inserting the spring locating guide through the center of the spring coil until the lower surface of the spring  453  contacts the lateral flange  431  of the base portion of the assembly  411 .  
         [0040]    A series of tests were performed to measure the reduction of lateral forces provided by spring perch assemblies according to several embodiments of the present invention. During the tests, various loads were applied to a test spring and the resulting lateral force measured. The test spring measured 4 inches long and 2.25 inches wide with a spring constant of 500 pounds per inch. Subsequently, spring perch assemblies according to the embodiment of the present invention depicted in FIG. 3 (Type 3) and in FIG. 4A (Type 4A) were employed in combination with the test spring during the testing procedure. The results of these tests are summarized in the following chart:  
                                                                                               Lateral Force (lbs.)                Load   Load   Load   Load           (lbs.)   (lbs.)   (lbs.)   (lbs.)           222   376   532   695                            Spring only   116   233   402   571           Type 3 on top   59   91   166   313           Type 3 on bottom   61   98   151   240           Type 3 on top and bottom   7   10   21   50           Type 4A on top   68   174   337   514           Type 4A on bottom   62   148   306   466           Type 4A on top and bottom   40   140   303   482           Type 4A on top, Type 3 on   26   55   100   191           bottom           Type 3 on top, Type 4A on   43   70   156   295           bottom                      
 
         [0041]    As can been seen in the chart, the greatest reduction in lateral force over that experienced by the spring alone was achieved by employing perch assemblies of the type shown in FIG. 3 at the top and bottom of the spring. This resulted in a 98% reduction in lateral force in the spring at an applied load of 376 pounds and a 96% reduction at an applied load of 532 pounds. While employing two perch assemblies clearly leads to the greatest reduction in lateral force, significant reductions were also achieved using a single perch assembly. For example, the use of a single Type 3 assembly on top of the test spring resulted in a 61% reduction in lateral force with an applied load of 376 pounds while a single Type 4 assembly on top of the test spring produced a 25% reduction using the same applied load.  
         [0042]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. The articles “a”, “an”, “said” and “the” are not limited to a singular element, and include one or more such element.