CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent

Application Serial No. 61/463889, filed February 24, 201 1 , the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to shock absorbers, and more particularly to an improved, low-cost modular piston face to alter the performance characteristics of shock absorbers.

BACKGROUND OF THE INVENTION

[0003] Shock absorbers and the functioning of shock absorbers in the suspension system of a vehicle are well known. A shock absorber (or simply, "shock") can be considered a type of hydraulic piston pump that is connected to the vehicle chassis at one end and the vehicle suspension at the other end. Suspension travel causes the shock piston to move inside the shock body, which is a tube typically filled with fluid, such as hydraulic oil. When the piston moves in the shock body, the oil moves through openings in the piston. The manner in which the oil flows through the piston greatly determines the performance characteristics of the shock.

[0004] While the overall concept of a shock absorber and how it performs is generally understood, the design of shocks varies greatly. Therefore, great importance is placed upon the many individual components of a shock and how they work together in the overall performance of the shock. While safety and other factors are important considerations for most shock designs and use, racing applications require an even sharper focus on the shock design and performance.

[0005] Shocks play an important role in affecting how the vehicle tires, suspension, and chassis respond under various loads, such as under braking or impacting a bump or other object. By dampening or controlling the movements of the suspension, the tires of the vehicle remain in contact with the road or other driving surface. A tire that loses contact with the driving surface significantly reduces the overall traction, steering, handling, and braking capabilities of the vehicle. Therefore, the shock's primary function is to control how fast and how much the suspension compresses and rebounds under such loads.

[0006] In a typical shock, the primary dampening is controlled by one or more ports or channels through the piston along with one or more valving shims that cover exit ports in the piston. Each side of the piston (compression and rebound) has valving shims that set the high speed dampening as described herein. Shims are well known devices in shock technology, whereby stiffer shims provide more deflection resistance and are used for greater shaft (piston) speeds, and softer shims for slower shaft speeds. Shims are typically made of metal, and the shim size and thickness affect how likely the shim will flex or deflect to let the fluid to pass by or through the shim, and then return to its original state. Shims can be direction dependent, so they only flex when the piston is travelling in a particular direction (i.e., compression or rebound). Typically this is achieved because the shims are in direct contact with the flat piston face, which provides a solid backstop and preventing shim flex in the direction of the piston. Multiple shims can be assembled together to create a "shim stack" for the desired flow characteristics. The shaft speed and other factors determine the optimum shim stack.

[0007] Dampening can also be affected by dish and preload adjustments to the shim stack. By adding dish and/or preload to the shim stack, more force is required to open or deflect the shims. Typically, adding dish/preload is performed for high velocity or high degree changes in dampening and is most valuable in high speed shaft or piston movements, which may occur when the racing vehicle encounters jumps, large bumps, or other changes in the racing surface. A large amount of dish/preload adds stability and control under violent shaft movements. Drawbacks when preload is too high include a stiff and violent chassis feel.

[0008] By decreasing dish and/or preload to the shim stack, less force is required to open or deflect the shims. Decreasing the dish reduces high speed dampening, which results in a plusher or smoother driving feeling over bumps and jumps. Drawbacks when not enough preload is used include bottoming out the suspension under high shaft speed movements.

[0009] Piston design and structure can also vary greatly depending on the performance needs. There are two main piston designs: linear and digressive. A piston is said to be linear when the face has a flat surface, but defines one or more channels that pass through the piston face and body and exit on the other side. The cumulative surface area of these channels is less than the total surface area of the piston face, and as the cumulative surface area of the channels increases, more fluid flow is possible through the piston. The shims deflect to reveal these openings when the fluid passes through the piston until the openings are fully exposed. At this maximum flow position, the piston velocity curve is essentially linear, so as the piston velocity increase, the dampening force increases in a direct relationship.

[0010] In a digressive type piston, the face of the piston is recessed except for a circumferential lip at the outer edge of the piston face. The shim or shim stack maintains contact with the circumferential lip until a certain pressure is reached, at which point the shim stack deflects evenly and away from the entire lip all at once, allowing for rapid fluid flow through the piston. This is sometimes known as "blow off and is particularly advantageous for reducing the possibility of building excessive dampening forces that are usually associated with high shaft accelerations, such as when hitting a bump or hole.

[0011] Small amounts of fluid flow through the piston can be achieved through a bleed system, which is typically a channel or bypass through the piston and other components of the shock, such as by one or openings defined in a particular shim known as a bleed shim. A bleed system typically has a fixed flow rate and act as a fluid bypass that allows the shock piston to move with less restriction at low piston velocity, such as 1 -5 inches of travel per second. Once the piston velocity and pressure are great enough to override the bleed system, such as 5 to 10 inches of travel per second or more, the shim stack opens so that the fluid passes through the piston and out the exhaust or exit ports to further dampen the piston velocity.

[0012] Decreasing the bleed flow rate, which may be achieved by, for example, incorporating smaller bleed openings in the piston or bleed shim(s) for the fluid to pass through, adds to the low speed (i.e., slow piston movements) dampening, which may result in less dynamic chassis movement and a more stable feel for the driver. Typically, this is desirable and beneficial for racing in high traction or high grip conditions. Incorporating less bleed is less desirable in low traction or low grip conditions, such as when a racing surface is coated in dust, snow, ice, or other material that may detrimentally affect tire grip.

[0013] Increasing bleed flow rate, which may be achieved by, for example, incorporating larger bleed openings in the piston or bleed shim(s) for the fluid to pass through, decreases the low speed dampening and thus more dynamic chassis movement and less stable feel for the driver. A driver may desire to have this less stable feel, however, depending on the driver's preferences. Incorporating more bleed is typically desirable in low traction or low grip conditions, such as racing on dirt or other low grip racing surfaces. More bleed is less desirable in high grip conditions because the vehicle suspension will have a lot of movement and be very hard to control.

[0014] Regardless of a driver's preferences, bleed is generally a fixed amount for both compression and rebound that is calculated in part by using the sum of the bleed shim openings on the compression and rebound sides of the piston. For tuning purposes, however, there is a need to provide independent bleed rates for the compression and rebound cycles of a shock absorber.

[0015] Another problem with current shock absorbers is that the bleed shims and the valving shims are the only adjustments that can be made once a particular piston is chosen. If additional changes are required to fluid flow rate, port size, port shape, or piston dish, the entire piston must be replaced. This is very expensive for racing applications, because multiple pistons must be purchased, stored, maintained, and replaced depending on what performance characteristics are desired for optimal handling. [0016] Typically, a race team purchases dozens of pistons and must replace pistons throughout a race weekend as the suspension is modified and adjusted for optimal performance. Accordingly, a shock specialist is often at the race track and remains busy tearing apart and rebuilding shocks, creating further expense and using valuable manpower. This has been a necessary use of resources, however, because by changing pistons, bleed shims, and valving shims, different flow patterns can be created to achieve a softer or stiffer feel at any point of the piston velocity curve. A similar use of time and resources is encountered when conducting shock absorber testing in a race shop or laboratory. Testing flow patterns, shim manipulation, and frequency .response through port size and shape are typically expensive and time consuming affairs because of the piston limitations. Thus, there is a need for a piston design that reduces the complexities and inventory needs in the marketplace.

SUMMARY OF THE INVENTION

[0017] A modular piston face is provided for a shock absorber. The modular piston face includes a body having a top side and a bottom side and configured or adapted for fluid communication with the piston of the shock absorber. The body defines at least one opening therethrough, and in one embodiment defines multiple openings spaced around the modular piston face. The shape of the opening(s) may include one or more shapes, including geometric shapes.

[0018] The modular piston face is configured or adapted for use with a digressive piston face that defines a recessed area and a circumferential lip. The modular piston face is in communication with or releasably attached to the circumferential lip of the digressive piston face, and provides a linear flow rate or linear dampening through the digressive piston face.

[0019] The modular piston face is configured or adapted for use with at least one shim, which deflects under load, such as when a fluid flows through the piston and the modular piston face. The fluid flow cannot deflect the shim around the circumference thereof due to the modular piston face.

[0020] In one embodiment, the modular piston face is used in combination with a bleed check valve, which restricts fluid flow in one direction through the piston. The bleed check valve is configured to be positioned between the piston and the bottom side of the modular piston face.

[0021] A method of tuning a shock absorber is also provided. The method includes providing a digressive or double digressive piston body and selecting a modular piston face that defines at least one opening therethrough, and positioning the modular piston face in communication with the digressive face of the piston body, such as the circumferential lip of the piston body. The method also includes positioning a bleed check valve between the modular piston face and the piston body for independently controlling a compression bleed and a rebound bleed. The modular piston face can be replaced with a different modular piston face to tune the shock absorber.

[0022] A shock absorber is also provided that includes a piston having a compression side and a rebound side, and associated compression and rebound bleed rates. According to one embodiment, the shock absorber provides linear dampening on the compression and rebound sides, and the compression bleed rate and the rebound bleed rate are different. [0023] Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will become more fully understood from the detailed description and the accompanying drawings, which are not necessarily to scale, wherein:

[0025] FIG. 1 is a cross sectional view of a shock absorber in accordance with the present invention;

[0026] FIG. 2 is an exploded view of the shock absorber of FIG. 1 ;

[0027] FIGS. 3A-3D are views of a modular piston face for a shock absorber in accordance with the present invention;

[0028] FIGS. 4A-4F are perspective views of different configurations of a modular piston face for a shock absorber in accordance with the present invention; and

[0029] FIGS. 5A-5C are perspective views of a bleed system in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION [0030] The following detailed description of the embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.

[0031] Referring now to the drawings and the following written description of the present invention, it will be readily understood by those persons skilled in the art that present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications, and equivalent arrangements will be apparent from or reasonably suggested by the present invention and the detailed description thereof, without departing from the substance or scope of the present invention. This disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended nor is it to be construed to limit the present invention or otherwise to exclude any such other embodiments; adaptations or variations, modifications and equivalent arrangements, the present invention being limited only by claims that pended hereto and the equivalents thereof.

[0032] Referring to the figures, a shock absorber 10, such as a shock absorber for use with a vehicle, is shown in Figure l . The shock absorber 10 comprises a cylindrical shock body 12 that surrounds a movable piston 20 and main shaft 14. The shock absorber 10 is positioned between and operably connected to the vehicle wheel system and chassis (not shown) and serves to dampen the forces applied to the vehicle through the driving surface, steering input, and other factors. In particular, the piston 20 defines a central opening 22 that receives the main shaft 14 and is secured in place by a top plate 30 and a nut 34 that is threaded to the main shaft 14. A piston wear band 21 is disposed between the piston 20 and the shock body 12 to allow sliding but sealed movement of the piston 20 within the shock body 12. The piston 20 could be mounted or secured in the shock body 12 any number of ways that are contemplated by those of skill in the art. A fluid (not shown), such as oil, is sealed within the shock body 12 and as the piston 20 oscillates within the shock body 12, the fluid passes through the piston as described herein. Such movement, which can be quite violent at times, generates heat, and therefore the materials used in the shock absorber 10 are robust, including without limitation metals such as steel, titanium, aluminum, other metals and alloys thereof, as well as polymeric, natural, and composites and combinations thereof.

[0033] In addition to defining the central opening 22, the piston 20 has a compression side 24 and a rebound side 26. In order for the fluid to pass through the piston 20, the compression side 24 and rebound side 26 each define one or more ports 50 that pass through the piston 20 and include an intake port 54 and an exhaust port 56. A modular piston face 60, as presented below, is in communication with the exhaust ports 56. The intake ports 54 are arranged or positioned on the piston 20 so that fluid flows in the intake ports 54 and, if unobstructed, would flow through the piston 20 and out the exhaust ports 56.

[0034] In order to dampen the travel of the piston 20 as it oscillates through the fluid inside the shock body 12, one or more shims 40 may be positioned at the compression side 24 and/or rebound side 26 of the piston 20 to help restrict flow therethrough. Specifically, the shims 40 cover the exhaust ports 56 and "open" or deflect away from the exhaust ports 56 as fluid flows through the ports from the port intakes 54. The shape, size, location, and quantity of ports 50, as well as the thickness, quantity, and combination of shims 40 determine how much fluid will flow through the piston 20 and the exhaust ports 56. The shims 40 come in a variety of diameters and thicknesses, such as from 0.002 inches to 0.020 inches, and the combination of shims allows for independent tuning of rebound and compression dampening rates. For example, as the shim "stack" increases, the amount of force required to bend or flex the shims, and thus the dampening rate increases. Once the shims 40 begin to deflect, fluid begins to pass through the piston and past the shims. As the velocity of the piston 20 increases, the shims 40 continue to deflect until all the exhaust ports 56 are exposed. From this point, as piston velocity increases, the dampening force increases in a generally direct or linear relationship. Thus, a piston having this type of design is known as a linear piston. A graph of this relationship is shown below as Figure A.

VELOCITY

[0035] Before the shims 40 open, however, a certain amount of fluid may be permitted to flow through the piston 20. This flow, known as bleed, allows for slow movement of the piston 20 without drastic movement of the piston 20 within the shock body 12. Bleed can be determined by defining small openings or notches in one of the shims 40, which is known accordingly as a bleed shim, such as by machining, cutting, punching, stamping, or other methods, on the compression side 24 and/or the rebound 26 of the piston 20. Alternatively, it is also possible to define a bleed hole or opening in the modular piston face 60. In a conventional linear piston, the cumulative amount of openings in the bleed shims creates an overall bleed amount that is the same for both compression and rebound. Until the present invention, a linear shock could not be independently tuned for compression and rebound bleed because the bleed shims in conjunction with the piston create a fixed passage for the fluid to flow through regardless of direction. However, as described herein, the shock absorber 10 of the present invention provides a shock having linear dampening, but wherein the compression bleed and rebound bleed can be independently determined and selected.

[0036] Figure A also shows the relationship between dampening force and velocity for a full digressive piston, which does not define a series of openings but instead defines one opening around the circumference thereof, so that when the shims deflect, the shims deflect around the full (360 degree) circumference of the piston face. This is known as a full digressive piston design, and is particularly suited for very high piston velocities where a linear piston could possibly break due to excessive dampening forces that result from the piston movement.

[0037] Another type of piston is known as a progressive piston, which provides more dampening as the piston velocity increases. This is due to the flow pattern that is determined by the piston and ports defined thereby, in conjunction with the piston velocity and shims 40. As the number of openings for the fluid to pass through decreases, the more progressive the piston behaves. In some cases, if the piston velocity is too great, little to no fluid flows through the piston and the dampening greatly increases.

[0038] Figure 2 illustrates an exploded view of the piston 20 and other portions of the shock absorber 10 of the present invention. In particular, the piston 20 defines a recessed area 28 and a circumferential lip 29 in a conventional full digressive piston design. Figure 2 shows the recessed area 28 and circumferential lip 29 of the compression side 24 of the piston 20. The present invention also contemplates a piston having the same design on the rebound side 26, wherein the piston would be called a "double digressive" piston.

[0039] In order to provide a linear or other type of dampening to the full digressive (or double digressive) piston 20, a modular piston face 60 is releasably attached or secured to the piston 20. In one embodiment, the modular piston face 60 is urged directly against the circumferential lip 29 of the piston 20 by the nut 34, although it is possible that a washer, shim, or other spacer could be inserted between the modular piston face 60 and circumferential lip 29. Alternatively, the modular piston face 60 may be attached to the piston 20 in various other ways, such as by way of threads or other locking techniques or devices. Shims 40, including a bleed shim defining one or more bleed openings 42, are positioned between the modular piston face 60 and the nut 34 as discussed above. As described herein, only one shim 40 is shown in the figures for simplicity, and it is known in the art to provide more than one shim to tune the characteristics of the shock 10. It is also possible to have no shims against the modular piston face 60. If used, the shims 40 may also be urged against the modular piston face 60 and deflect into a concave or dished shape. This additional load, known as preload, on the shims 40 increases the force required to deflect the shims 40 away from the modular piston face 60, and thus providing further tuning options for the shock absorber 10.

[0040] In accordance with the present invention, the modular piston face 60 provides, in effect, progressive, digressive, and/or linear dampening for the shock absorber, but utilizes a standard full digressive piston 20. As such, the dampening provided by the modular piston face 60 is greater than the dampening provided by a full digressive piston, which is allows the fluid to "blow off around the entire circumference of the piston face. The modular piston face 60 is configured to work with a full digressive piston to provide unlimited dampening combinations by simply changing the modular piston face, while retaining the full digressive piston. Accordingly, the properties of the shock absorber 10 can be influenced by replacing one modular piston face 60 with another modular piston face having a different design and defining different openings, where in the past this was achieved by replacing the entire piston with another piston. Accordingly, the modular piston face of the present invention greatly reduces the piston inventory and costs associated with tuning a shock absorber, which as discussed herein has been extraordinarily difficult to manage in certain applications, such as auto racing and testing.

[0041] Figure 2 also shows a check valve 80 that is disposed within the recessed area 28 of the piston 20. The check valve 80 includes a check valve plate 82 and an urging mechanism, such as a coil spring 84, positioned on the compression side 24 of the piston 20, such that the check valve plate 82 is urged by the spring 84 against the exhaust ports 56 and thus cutting off any bleed that may have otherwise traveled through bleed openings 42 in the shim 40 and the exhaust ports 56 back through the piston 20 to the rebound side 26. The urging mechanism may a conical spring, finger shim, Belleville disk, or wave spring. Note that bleed may still enter the intake ports 54 on the compression side 24, travel through the piston 20 and out the exhaust ports 56 on the rebound side 26, with the bleed openings on the shim (not shown) on the rebound side 26 determining the bleed rate.

[0042] If fluid bleeds through the piston 20 from the rebound side 26 to the compression side 24, the check valve plate 82 is urged away from the exhaust ports 56 by the fluid, thus allowing the fluid to bleed through the modular piston face 60 and bleed openings 42 of the shim 40 on the compression side 24. As such, the bleed for compression and rebound can be independently determined and selected, including without limitation compression bleed only or rebound bleed only, by way of incorporating the modular piston face 60 and check valve 80 of the present invention.

[0043] Figures 3A-3D show various sides and perspectives of an exemplary modular piston face 60 according to the present invention. The modular piston face 60 is sized according to the piston 20 and has a top surface 62 and a bottom surface 64. The modular piston face 60 from metallic, polymeric, natural and/or composite materials, and may be manufactured by one or more methods, including without limitation CNC machining, forge casting, sintered metal powder processes, and composite molding. A main opening 68 is defined along the central axis of the modular piston face 60, and at least one opening 66 is defined through the top side or surface 62 and bottom side or surface 64. The top surface 62 includes a unique patterning that defines one or more stiction cavities 70 that help prevent the modular piston face 60 from adhering to the shims 40. The stiction cavities 70 may have many shapes, sizes, and locations, as shown in but not limited by Figures 3A-3D and Figures 4A-4F. In one embodiment, a step 72 extends away from the bottom surface 64 of the modular piston face 60, and in another embodiment the bottom surface 64 is flat, and various shims can be used in place of the step 72. The modular piston face 60 may also have a concave or dish 74 (shown in broken lines) as an alternative design for preload adjustment.

[0044] The opening 66 can be multiple openings having various sizes, shapes, dimensions and locations, including geometric shapes, such as circles, squares, rounded squares, triangles, polygons, or custom shapes and designs, such as text, pictures, and the like. See Figures 4A-4F for exemplary variations of the openings 66 as contemplated by the present invention. As such, the cumulative surface area in the modular piston face 60 taken by the openings 66 is less than the total surface available on the modular piston face 60. Accordingly, when the shims 40 deflect away from the modular piston face, the flow through the modular piston face 60 is less than the 360 degree "blow off flow of a full digressive piston. In particular, the shims 40 do not deflect around the entire circumference of the modular piston face 60, as would be seen with a full digressive piston. As discussed above, the flow through the modular piston face 60 may be linear, progressive, or digressive, but in any event the flow is more restricted than that of a full digressive piston.

[0045] Figures 5A-5C show an alternative arrangement for a bleed system in accordance with the present invention. As shown in Figures 5A-5C, an alternative piston 90 defines a recessed area 93 and a circumferential lip 95. The circumferential lip 95 defines one or more openings 98. An alternative modular piston face 92 defines one or more openings 94 that correspond and communicate with the openings 98 of the circumferential lip 95 when the alternative modular piston face 92 is place upon the alternative piston 90. The amount of bleed is determined by the positioning of the alternative modular piston face 92, and in particular how the openings 94 and openings 98 align. The desired amount of bleed through openings 94 and openings 98 can be obtained by rotating or placing the alternative modular piston face 92 to the desired location relative to the alternative piston 90, which therefore allows for very fine tuning of the bleed through the openings 94 and openings 98. One advantage of the bleed system shown in Figures 5A-5C is the ability to change a particular bleed rate without taking the shims and other shock components apart, or in the case where no shims are used and bleed is controlled through an opening in the piston, the ability to adjust bleed without changing the piston or piston face.

[0046] It will therefore be readily understood by those persons skilled in the art that the present invention is susceptible of broad utility and application. Many embodiments and adaptations of the present invention other than those herein described, as well as many variations, modifications and equivalent arrangements, will be apparent from or reasonably suggested by the present invention and the foregoing description thereof, without departing from the substance or scope of the present invention. Accordingly, while the present invention has been described herein in detail in relation to its preferred embodiment, it is to be understood that this disclosure is only illustrative and exemplary of the present invention and is made merely for purposes of providing a full and enabling disclosure of the invention. The foregoing disclosure is not intended or to be construed to limit the present invention or otherwise to exclude any such other embodiments, adaptations, variations, modifications and equivalent arrangements.