Abstract:
One preferred embodiment of the present invention provides a method for centering the reactive force of a coil spring to an applied load. The method provides a coil spring which defines a spring natural centerline. The spring has opposing ends and at least one end coil with an end coil tip. Opposing loads with parallel load axes and at least one fixed load surface are applied to the opposing ends of the spring. The spring natural centerline is maintained parallel to the applied load axes. The end coil is initially engaged to at least one of the applied loads at a point substantially opposite the end coil tip. In an alternate embodiment of the present invention, a coil spring and an applied load are combined. A plurality of helically wound coils define a spring with a natural centerline and at least one end coil. The end coil defines an end coil tip. A load with at least one fixed load surface is applied parallel to the natural centerline, wherein the applied load initially engages the end coil at a point substantially opposite the end coil tip.

Description:
[0001]     This application claims priority to and incorporates by reference U.S. Provisional Application Ser. No. 60/630,316 filed Nov. 23, 2004. 
     
    
     FIELD OF THE INVENTION  
       [0002]     Certain preferred embodiments of the present invention relate generally to centering reactive forces in 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 typically follows a single helix angle to the end of the wire. An unground, closed end spring has an end with a reduced angle so the wire end touches the last coil of the spring. In a ground, closed end spring, the face of the final coil is shaped and ground flat such that when the face touches the last coil of the spring, a flat spring surface is produced that is substantially square to the central axis of the main helix. Most standard automotive suspension 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]     Typically, as a load is applied to compress a coil spring, the reactive 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 reactive force is concentrated between the end of the spring and the point at which the load leaves 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 reactive force is concentrated primarily at or near 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]     One of the most highly used coil springs types is the “closed and ground” style spring, shown illustrated in  FIGS. 1A and 1B  between fixed parallel load surfaces  40  and  44 . In spring  8  the last coil  11  is wound at a helical angle shallower than that of the main body of the spring  8  in order to allow the cut end  12  of the wire to touch the end of the previous coil. The last coil  11 —the “end coil”—is then ground to produce a surface that is substantially flat and preferably square; (i.e. perpendicular) to the spring central axis C. Often the opposing end is ground in the same manner. It has always been presumed that producing such a precision surface would centralize the spring reactive loads, and minimize the potential for the production of undesirable lateral loads.  
         [0006]     However, in springs of this type, as illustrated by vector arrows in  FIG. 1A , the reactive force produced within the wire of the spring in the compressed (stressed) state is actually concentrated near the cut wire end, in the area of the overlap between the last active coil and the end coil  14 , and does not spread over the full face of the end coil in an equal manner. As a result, the virtual spring load axis V L  ( FIG. 1A ) in these springs is resolved at an angle, or an offset, to the spring central axis C, with that angle or offset dependent on many factors in the design of the spring, the bearing surfaces against which it is loaded, and the load level. The offset load axis produces highly undesirable side loads (lateral loads) upon those load bearing surfaces, which decrease the spring efficiency, for example by increasing frictional losses in most devices upon which that spring is loaded.  
       SUMMARY OF THE INVENTION  
       [0007]     One preferred embodiment of the present invention, provides a method for centering the reactive force of a coil spring to an applied load. The method provides a coil spring which defines a spring natural centerline. The spring has opposing ends and at least one end coil with an end coil tip. Opposing loads with parallel load axes and at least one fixed load surface are applied to the opposing ends of the spring. The spring natural centerline is maintained parallel to the applied load axes. The end coil is initially engaged to at least one of the applied loads at a point substantially opposite the end coil tip.  
         [0008]     In an alternate embodiment of the present invention, a coil spring and an applied load are combined. A plurality of helically wound coils define a spring with a natural centerline and at least one end coil. The end coil defines an end coil tip. A load is applied parallel to the natural centerline with at least one fixed load surface, wherein the applied load initially engages the end coil at a point substantially opposite the end coil tip.  
         [0009]     Further objects, features and advantages of the present invention shall become apparent from the detailed drawings and descriptions provided herein. Each embodiment described herein is not intended to address every object described herein, and each embodiment does not include each feature described. Some or all of these features may be present in the corresponding independent or dependent claims, but should not be construed to be a limitation unless expressly recited in a particular claim.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIGS. 1A and 1B  illustrate a prior art closed end ground spring between fixed load surfaces.  
         [0011]      FIG. 2A  illustrates a prior art closed end ground spring between a fixed load surface and a non-fixed load surface.  
         [0012]      FIG. 2B  illustrates a prior art closed end ground spring between two non-fixed load surfaces.  
         [0013]      FIGS. 3-5  illustrate a sequence of load distribution of a spring according to a preferred embodiment of the present invention.  
         [0014]      FIGS. 6A-6C  illustrate a sequence of load distribution of a spring according to a second preferred embodiment of the present invention.  
         [0015]      FIGS. 7A-7C  illustrate a sequence of load distribution of a spring according to a third less preferred embodiment of the present invention.  
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0016]     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.  
         [0017]     Coil springs are used in a variety of applications. For example, in the vehicle industry, they are used in suspension systems with struts, or in a different application with valves and valve lifter assemblies. Such uses prefer to maximize efficient spring performance, for example, balancing spring weight and size for a desired load and reaction. In order to reduce or eliminate the lateral loads which result when using prior art springs, the end coil or engagement method can be pre-arranged and allowed to flex relative to the spring natural centerline to reach a perpendicular or “square” orientation as the spring accepts loads upon its full face. The allowance for flexing, or the ability to “tilt” to square relative to the spring central axis upon loading, allows the force developed within the stressed spring wire to distribute itself evenly around the face of the end coil. Once the loading is evenly distributed, the spring load, by definition, is centered on the spring central axis, and lateral load production is eliminated.  
         [0018]     In some cases, the surface upon which the spring acts can be designed to allow this desired end coil flexing or tilting ability apart from the spring. Examples of spring perch devices which allow tilting apart from the spring through a mechanical movement can be seen in U.S. patent application Ser. No. 10/205,163, filed Jul. 25, 2002. At present, these tilting spring “perches” are in use in the automobile and motorcycle racing industry to decrease frictional losses in spring-over-damper assemblies (“coilovers”), with the result being increased tire grip, and faster lap times. There are, however, many applications within which separate spring perches cannot be physically fit due to space restrictions, or where operating conditions are too severe for long-term operation reliability.  
         [0019]     Preferably, embodiments of the present invention automatically center the load on a coil spring from at least one, or alternately two, fixed load surfaces through modification of the physical construction of the spring, or modification of the engagement between the spring and the surfaces through which the external load is applied. Equal distribution of an applied load can be produced by “pre-tilting” or “reverse tilting” the end coils or the load surfaces in such a manner that the end coils flex as desired during the initial application of the designed load. In certain preferred embodiments of the present invention, it is possible to significantly reduce the development of undesirable lateral loads by pre-tilting or reverse tilting the end coil of the spring or the load surface in a manner that will produce concentric and equal loading about the face of that end coil at a specified load level, and near-concentric loading at load levels somewhat lesser and greater than that specified load. Alternately, the engagement with the load surface can be configured to create a tilted effect.  
         [0020]     In contrast to two opposing fixed load surfaces,  FIGS. 2A and 2B  illustrate arrangements of a square ground spring between at least one fixed surface and a free-to-tilt surface, such as a spring perch, or between two free-to-tilt surfaces respectively. In an arrangement between a fixed surface and a tiltable spring perch, the tilting action of the spring perch distributes the load on the spring face at one end of the spring, reducing the offset of the virtual load axis, and causing the virtual load axis to be in greater, although not complete, alignment with the spring natural centerline. In an arrangement between two tiltable spring perches, the offset of the virtual load axis at each end is substantially eliminated by the tilting movement of the perches which distribute the opposing loads on the spring face, and causes the virtual load axis to be substantially aligned with the spring natural centerline. This distribution does not occur between a spring end and a fixed load surface. Certain preferred embodiments of the present invention are used with at least one, and alternately two, fixed load surfaces.  
         [0021]     In greater detail,  FIG. 2A  illustrates one embodiment of the present invention, with a square ground spring  8  between a fixed lower surface  44  and a non-fixed upper load applying surface  40 ′. In the illustration, the spring upper load application surface  40 ′ is free to tilt with the end coil during application of the upper external load  42 ′ in response to the spring reactive forces. For the purpose of clarity, the external load  42 ′ is shown to be a point applied at the plane across a surface on the upper end coil  11  of the spring. A spring ID or “inner diameter” flange  13  is illustrated with each load surface as an example means to retain the spring perch in position.  
         [0022]     As the load is applied, the load application surface  40 ′ tilts in response to the spring reactive forces until those forces become equally distributed about the face of the end coil, at which time the applied load V L ′ and the spring reactive forces are in equilibrium at the spring upper surface, and the spring reactive force at the spring upper surface is centered at the point of external load application and is coincides with the spring natural centerline C at that upper surface. In contrast, the lower load surface  44  is fixed and does not tilt with the lower end coil. This results in the spring reactive virtual load axis V L ′ being offset from the spring centerline C when the spring is loaded. The offset of the virtual load axis V L ′ has been substantially reduced compared to  FIG. 1 , and is now in substantially greater agreement with the spring natural centerline C.  
         [0023]      FIG. 2B  illustrates a square ground spring  8  between two non-fixed load application surfaces such as spring perches  40 ′ and  44 ′. In the illustration, both perches are free to tilt with the end coils during compression. For the purpose of clarity, the external loads  42 ′ and  46 ′ are shown to be points applied to the spring perches at the planes describing the coil surfaces. As the external load is applied, the load application surfaces tilt in response to the spring reactive forces until those forces become equally distributed about the faces of the end coils, at which time the virtual load axis V L ′ is in agreement with the natural spring centerline C. This distribution does not occur if the load application surfaces are fixed.  
         [0024]     A spring according to one preferred embodiment of the present invention is illustrated in a side view in  FIG. 3  in combination with parallel fixed load surfaces  40  and  44 . Spring  10  is formed of a helical wire or metal coil wound with substantially equal turning angles except for the end coils. Upper end coil  20  is wound in a shallower or a horizontally “reverse” angle to the coil angles of the remainder of spring  10 , so that upper wire tip  22  contacts the adjacent or prior coil. The reverse angle can be characterized as offset in a direction across an axis perpendicular to the spring natural centerline, the direction being opposite the turning angle direction of the other coils. Similarly, lower end coil  30  is wound with a reverse angle so that lower wire tip  32  contacts the adjacent or prior coil. For the sake of clarity, the illustration shows the upper and lower tip ends wound to end in symmetric positions 180 degrees apart. In actual practice, the ends may be clocked at positions other than symmetrical.  
         [0025]     In spring  10 , the upper end coil  20  is arranged so it is “reverse-tilted” at an angle θ 1  extending from upper wire tip  22  to the diametrically opposed point  24  of end coil  20 . Preferably this angle is slightly offset from perpendicular to the spring central axis A 1 . As illustrated in  FIG. 3 , when the spring is oriented vertically, the perceived tilt of spring  10  results in the highest point or point of initial contact  50  with upper load surface  40  being a point  24  substantially diametrically opposite the tip  22 . For upper end coil  20 , the reverse angle θ 1  places end coil tip  22  below a line which intersects a point  24  substantially opposite coil tip  22  and which is perpendicular to the spring centerline A 1 .  
         [0026]     In one preferred embodiment, upper coil  20  is ground so that opposed point  24  is higher, i.e., has less grinding, than does wire tip  22 . The angle θ 1  that can be ground will be limited by the thickness of the wire and the end coil winding angle.  
         [0027]      FIG. 3  schematically illustrates spring  10  between parallel, fixed orientation load surfaces  40  and  44 . Although not shown for clarity, spring  10  is maintained “vertical” or with axis A 1  perpendicular to the load surfaces, and in inhibited from tilting as an entire structure. In certain embodiments, contact points  50  and  60  are retained from lateral movement. The retention can occur through friction, or for example with an ID guide  13  such as shown in  FIG. 2B , an outer diameter guide, a fastener, a bracket, a seat, a flange or a similar physical restraint.  
         [0028]     As further illustrated in  FIG. 3 , when the spring is oriented vertically, the perceived resulting lowest point or point of initial contact  60  with lower load surface  44  is opposing point  34 . Preferably, the lower end coil  30  is ground at a parallel angle θ 1  to the upper end coil  20 . For example, lower end coil  30  is ground at an angle extending from lower wire tip  32  to the diametrically substantially opposed point  34  of end coil  30 . In the illustrated embodiment, lower coil  30  is ground so that opposed point  34  is lower than wire tip  32 .  
         [0029]     Preferably, the size, material, and tilt angles of spring  10  are selected and designed to distribute a specified applied load applied through load surfaces  40  and  44  to centralized distribution along natural spring center axis A, and to substantially eliminate lateral loading in a desired or preferred load range for the spring.  
         [0030]     In one less preferred embodiment, a closed-end, unground spring with pre-tilted end coils is used. In an alternate, less preferred embodiment, an open end spring with pre-tilted end coils is used. In these embodiments, the upper and lower faces of the spring are pre-tilted by angling the upper and lower end coils from a base point in the coil adjacent the wire tip so that the end coil is tilted at an angle so that a point opposite the wire tip is higher or lower, respectively, than the corresponding upper or lower wire tip.  
         [0031]     A load distribution progression as a designed load X is applied between two fixed parallel load surfaces  40  and  44  to spring  10  is illustrated in  FIGS. 3-5 .  FIG. 3  shows spring  10  at the instant of initial contact with the load surfaces  40  and  44 . The initial contact points  50  and  60  are approximately 180 degrees circumferentially away from the upper and lower wire ends  22  and  32  respectively. In this position, no load is yet applied to the spring and a gap exists between the coil end tips  22  and  32  and the load surfaces.  
         [0032]      FIG. 4  shows the upper and lower end coils  20  and  30  in full contact with the load surfaces  40  and  44  at the instant that a pre-calculated portion (illustrated as “X-x”), for example with x=½, of the designed load X is applied. At this instant, a pre-calculated portion of the design load X has been absorbed by the flexing of the upper coil  20  and lower coil  30  from an angled upper and lower arrangement to a substantially flat or parallel engagement to load surfaces  40  and  44 . At this point, there is zero or near zero load applied at tip contact points  52  and  62  between load surfaces  40  and  44  and the wire ends  22  and  32 . The effective load axis L 1  is angled between initial contact points  50  and  60  under this applied load.  
         [0033]      FIG. 5  shows the spring  10  partially compressed to accept the fully applied design load X. At this instant, in the example of x=½, substantially one-half of the applied load X is spread over one-half of the end coil face symmetrically around the circumference to either side of the respective initial contact points  50  and  60 , and one-half of the applied load X is spread over the end coil face symmetrically around the circumference to either side of the tip contact points  52  and  62 . Preferably at this instant and load, the applied load is evenly distributed over substantially the full face of the end coils, the load axis L 1  is centralized with the spring central axis A 1  and preferably there are no lateral loads produced.  
         [0034]     A second preferred embodiment with tilted or offset from perpendicular fixed load application surfaces is illustrated in  FIGS. 6A-6C .  FIG. 6A  illustrates a side view of a standard closed-and-ground spring  110  with the ground end coil surfaces substantially perpendicular to the spring central axis A 2 . In this example, the load axis is parallel with the spring axis A 2 ; however, the fixed load-applying surfaces  140  and  144  are tilted or offset at a reverse angle θ 2  measured from a line perpendicular to spring axis A 2 . Angle θ 2  is calculated for a particular spring and the designed load level. In this example, points  124  and  134  are substantially opposite the coil end tips  122  and  132  and are arranged to contact the load applying surfaces first.  
         [0035]     A load distribution progression as a designed load X is applied between two tilted load surfaces  140  and  144  to spring  110  is illustrated in  FIGS. 6A-6C . For the sake of clarity, guides to keep the spring central axis A 2  in alignment with the load direction are omitted.  FIG. 6A  shows spring  110  at the instant of initial contact with the load surfaces  140  and  144 . For illustration the initial contact points  150  and  160  are approximately  180  degrees circumferentially away from the upper and lower wire ends  122  and  132  respectively. In this position, no load is yet applied to the spring.  
         [0036]      FIG. 6B  shows the upper and lower end coils  120  and  130  in full contact with the load surfaces  140  and  144  at the instant pre-calculated portion X-x of the design load X has been absorbed by the flexing of the upper coil  120  and lower coil  130  from substantially flat upper and lower surface to a tilted or parallel engagement to load surfaces  140  and  144 . At this point, there is zero or near zero load applied at tip contact points  152  and  162  between load surfaces  140  and  144  and the wire ends  122  and  132 . The effective load axis L 2  is angled between initial contact points  150  and  160  under this pre-calculated load.  
         [0037]      FIG. 6C  shows the spring  110  partially compressed to accept the fully applied design load X. At this instant, with an example of x=½, substantially one-half of the applied load X is spread over one-half of the end coil face around the face circumference symmetrically to either side of the respective initial contact points  150  and  160 , and one-half of the applied load X is spread over the end coil face for one-forth of the face circumference to either side of the tip contact points  152  and  162  at the points of closure. Preferably at this instant and load, the applied load X is evenly distributed over substantially the full face of the end coils, with the load axis L 2  centralized with the spring central axis A 2 , and preferably there are no lateral loads produced.  
         [0038]     A third, less preferred embodiment illustrating a combination using tapered shims to create the effect of a tilted load engagement between fixed load application surfaces and a spring is illustrated in  FIGS. 7A through 7C .  FIG. 7A  illustrates a side view of a standard closed-and-ground spring  210  with the ground end coil surfaces substantially square to the spring central axis A 3 . For simplicity of illustration, the fixed load-applying surfaces  240  and  244  are substantially parallel or square to the spring and perpendicular to central axis A 3 . Tapered shims  270  and  280  each have a load engaging surface and a spring engaging surface. The load engaging surface and the spring engaging surface are non-parallel, and are tapered at an angle θ 3 . Angle θ 3  is calculated for the desired spring and the desired load level. Angle θ 3  is a reverse angle slightly offset from perpendicular to spring axis A 3  In this example, points  224  and  234  are substantially opposite coil end tips  222  and  232 , and arranged to contact the applied loads, via the shims, first.  
         [0039]     As illustrated, shims  270  and  280  are shown with perpendicular surfaces abutting load surfaces  240  and  244  and a gap between end coil tips  222  and  232  and the load surfaces. Alternately, the shims can be reversed so that the perpendicular surfaces abut end coils  220  and  230 , yet still define a reverse angle and a gap between the end coil tips  222  and  232  and the load surfaces. In a preferred embodiment, two shims are used between two fixed, parallel load surfaces; alternately one shim can be used for a partial effect or alternately a combination may have one shim at one end of a spring and a reverse tilted end coil or reverse tilted load surface engaged at the opposing end.  
         [0040]     Preferably, the shim engaging sides are configured to matingly engage with the load surface and the spring end coil surface respectively. In this context, the shim surface is configured when engaged to have a substantially continuous contact with the respective surface. For example, in a closed-end spring, the engagement may be substantially planar. In an open end spring, the shim may have a helically matched surface to mate with an end coil. Although not shown for clarity, the shims optionally include flanges, such as the ID guides  13  shown in  FIG. 2B , engaging the inside or outside of the spring coil to maintain the position of the shims to the spring.  
         [0041]     A load distribution progression as a designed load X is applied between two fixed and shimmed load surfaces  240  and  244  to spring  210  is illustrated in  FIGS. 7A-7C .  FIG. 7A  shows spring  210  at the instant of initial contact with shims  270  and  280  between the spring and load surfaces  240  and  244 . The initial contact points  250  and  260  are approximately 180 degrees circumferentially away from the upper and lower wire tip ends  222  and  232  respectively. In this position, no load is yet applied to the spring.  
         [0042]     The load surfaces are illustrated as parallel to each other and perpendicular to the load axis for ease of reference in the present example. Alternately, the load surfaces may be tilted with respect to a line perpendicular to the axis. Alternately the spring and the load surfaces may be tilted with respect to each other and/or with respect to the perpendicular to the spring centerline. In these arrangements, the angle θ 3  of each shim may be configured to compensate.  
         [0043]      FIG. 7B  shows the upper and lower end coils  220  and  230  in full contact with the parallel shimmed load surfaces  240  and  244  at the instant pre-calculated portion X-x of the design load X (for example with x=½) has been absorbed by the flexing of the upper coil  220  and lower coil  230  from a substantially flat upper and lower surface orientation to a tilted or parallel engagement to engage the spring engagement surfaces  272  and  282  of the shims. At this point, there is zero or near zero load applied at tip contact points  252  and  262  between shim engagement surfaces  272  and  282  and the wire ends  222  and  232 . The effective load axis is substantially angled between initial contact points  250  and  260  under this pre-calculated load.  
         [0044]      FIG. 7C  shows the spring  210  partially compressed to accept the fully applied design load X. At this instant, in the example of x=½, substantially one-half of the applied load X is spread over one-half of the end coil face for one-forth of the face circumference to either side of the respective initial contact points  250  and  260 , and one-half of the applied load X is spread over the end coil face for one-forth of the face circumference to either side of the tip contact points  252  and  262  at the points of closure. Preferably at this instant and load, the applied load X is evenly distributed over substantially the full face of the end coils, the load axis L 3  is centralized at the spring central axis A 3 , and preferably there are no lateral loads produced.  
         [0045]     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.