Abstract:
A piston valve assembly for a damper comprises a piston having a central hole and a fluid passageway spaced from the hole. A deflection disc having a central aperture is aligned with the hole. The deflection disc is arranged adjacent to the piston and at least partially blocks the fluid passageway for regulating the flow of hydraulic fluid between the fluid chambers when installed in the damper. A hub, common across different dampers, includes a neck that is arranged in the hole and the aperture of the deflection disc. A retainer abuts an unthreaded outer surface of the hub. During assembly, the retainer is received on the cylindrical outer surface in a slip fit relation. The deflection disc and pistons are loaded to a predetermined clamp load. The retainer can be positioned axially to account for variability due to tolerance stack-ups. The retainer is secured to the outer surface by a securing material such as a weld bead.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates to dampers such as vehicle suspension shock absorbers, struts and the like. More particularly, the invention relates to a common hub design for piston and base valve arrangements enabling a more modular damper.  
         [0002]     Dampers such as shock absorbers and struts are used in vehicles to absorb inputs from the roadway to provide a desirable vehicle ride. Typically, vehicle dampers employ a piston that moves through a cylinder having hydraulic fluid. The fluid flows through fluid passageways and valves in the piston, which absorbs the roadway inputs in the form of heat. One common type of piston valve assembly uses deflection discs on either side of the piston. The deflection discs at least partially block the fluid passages in the piston to regulate the fluid flow rate through the passages during the compression and rebound strokes of the damper.  
         [0003]     The piston and deflection discs are secured in abutment with one another by the piston rod and nut. The rod includes a shoulder with a neck extending from the shoulder to support the piston and deflection discs. An end of the neck is threaded to receive the nut. The nut is tightened onto the rod to a predetermined torque so that the deflection discs are held securely against the piston. The damping characteristics of the damper are adversely affected if the deflection discs are not properly loaded against the piston. Springs and plates may be used to bias the deflection discs to the closed position. Tolerance stack-ups in the valve assembly components can cause variability in the performance characteristics of the valves within a manufactured lot of valve assemblies, which can increase scrap. Variability within manufactured lots is also undesirable because customers are increasingly requiring valve assemblies to be manufactured to tight performance tolerances. Therefore what is needed is a damper design that provides more consistent loading of the damper valve bodies by reducing variations due to tolerance stack ups.  
       SUMMARY OF THE INVENTION AND ADVANTAGES  
       [0004]     One example of the present invention provides a piston valve assembly for a damper comprising a piston having a central hole and a fluid passageway spaced from the hole. A deflection disc having a central aperture is aligned with the hole. The deflection disc is arranged adjacent to the piston and at least partially blocks the fluid passageway for regulating the flow of hydraulic fluid between the fluid chambers when installed in the damper. A hub arranged between the rod and piston includes a neck that is arranged in the hole and the aperture of the deflection disc. However, the inventive clamping arrangement may also use a rod directly supporting the piston. A retainer abuts an unthreaded outer surface of the hub. Said another way, a line parallel to a hub axis extends along the outer surface and lies in a plane tangential to the outer surface. In one example embodiment, the outer surface is cylindrical in shape having a smooth surface. During assembly, the retainer is received on the cylindrical outer surface in a slip fit relation. The retainer is secured to the outer surface by a securing material such as a weld bead.  
         [0005]     The inventive piston valve assembly is manufactured using an inventive method of manufacturing. In one example, the method of manufacturing comprises the steps of providing a hub and installing a deflection disc and piston on the hub. Of course, multiple deflection discs using various configurations may be arranged on either side of the piston. Furthermore, valve components other than deflection discs, such as wire spring biased valves, may be used. The deflection disc and pistons are loaded to a predetermined clamp load. The retainer is positioned axially to the predetermined clamp load, for example, to achieve a desired load on the spring without having to rely on mating locating features, which due to tolerance stack-ups can adversely affect the spring load. A retainer is placed on the hub in a slip fit relationship thereto and secured to the hub while the deflection disc and pistons are maintained under the predetermined clamp load.  
         [0006]     Accordingly, the above mentioned provides a damper design that provides consistent loading of the damper valve bodies by reducing variations due to tolerance stack-ups. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
         [0008]      FIG. 1  is a side elevational view of a fully assembled damper manufactured according an inventive manufacturing process for the inventive piston valve assembly;  
         [0009]      FIG. 2  is a cross-sectional view of an inventive piston valve assembly including a common inventive hub;  
         [0010]      FIG. 3  is a cross-sectional view of the inventive piston valve assembly having a floating compression deflection disc and a fixed rebound deflection disc; and  
         [0011]      FIG. 4  is a cross-sectional view of the inventive piston valve assembly having fixed compression and rebound deflection discs with a fixed stop on the compression side and a spring loaded biasing member on the rebound side.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     A twin tube shock absorber  2  is shown in  FIG. 1 . The shock absorber  2  schematically depicts a cylinder head  3  at one end slidingly receiving a rod  4 , as is well known in the art. An end of the rod  4  is secured to the inventive piston valve assembly  10 , which is arranged in a fluid chamber  6 . During a compression stroke, the piston valve assembly  10  moves towards a base valve  8 , which regulates the flow of fluid from the fluid chamber  6  to an outer chamber  7 . As will be appreciated from the description below, the piston assembly  10  incorporates an inventive hub  12 , which is shown in  FIGS. 2-4 .  
         [0013]     A piston valve assembly  10  of the present invention is shown in  FIG. 2 . The assembly  10  may be used in a monotube or a twin tube shock absorber. The assembly  10  includes a hub  12  that is designed to be used with different sized pistons and deflection discs to facilitate a more modular damper assembly. However, it should be understood that the inventive clamping arrangement may also be used directly with a rod. The inventive clamping arrangement enables variations in valve performance due to tolerance stack-ups to be greatly reduced or eliminated.  
         [0014]     The hub  12  includes a first end  14  that is adapted to receive a piston rod. The first end  14  includes a shoulder  16  and a neck  18  extending from the shoulder  16  to a second end  20 . A piston  22  having a hole  24  is installed onto a longitudinal member such as the hub  12 , in the example showing or the rod  4 , with the neck  18  received in the hole  24 . The neck  18  has a generally uniform cylindrical circumference along its length. The piston  22  includes an outer circumference  26  that engages the inner wall of the damper cylinder, as is well known in the art, when the damper is assembled.  
         [0015]     The piston  22  includes one or more fluid passages  28  extending between compression  30  and rebound  32  sides of the piston  22 . One or more compression deflection discs  34  are arranged on the rebound side  32  of the piston, and one or more rebound deflection disc  36  are arranged on the compression side  30  of the piston  22 . The discs  34  and  36  include a central aperture that receives the neck  18 . The discs  34  and  36  regulate the fluid flow through the fluid passages  28  to provide a desired damping characteristic as the piston valve assembly  10  moves through the fluid chambers and the damper. The discs  34  and  36  deflect upward and away from the sides  32  and  30  as the fluid within the fluid passage  28  exerts pressure on the discs  34  and  36 , as is well known in the art. If the discs  34  and  36  are not firmly retained against the piston  22 , the discs  34  and  36  will open under lower pressures resulting in undesired damping characteristics.  
         [0016]     The neck  18  includes an outer surface  40  at the end  20 . The surface  40  is preferably smooth, cylindrical, and unthreaded. The end  20  may have a shape different than the rest of the neck  18 , if desired. The surface  40  may also have a non-circular cross-sectional shape. The surface  40  has a line extending along a length parallel to a hub axis A. The line lies in a plane tangential to the outer surface. A retainer  38  includes a portion having a generally cylindrical inner surface  42  that is received in a slip fit relationship on the outer surface  40  of the neck  18 . The slip fit relationship enables the retainer  38  to be moved axially along the surface  40  during loading, as described below. To achieve the slip fit relationship, for example, in the case of a cylinder the smallest diameter along the inner surface  42  is greater than the largest diameter along the outer surface  40  so that the retainer  38  can slide along the neck  18 . However, this should not be construed to exclude a configuration in which there is a slight interference fit.  
         [0017]     The piston  22  and retainer  38  are loaded to a predetermined clamp load L to force the discs  34  and  36  firmly into abutment with the piston  22 , shoulder  16  and retainer  38 , in the example shown. As one of ordinary skill will appreciate, it is preferred to have a slip fit relationship between the retainer  38  and neck  18  so that the predetermined clamp load L may be more easily determined. A slight interference fit, while permissible is not as preferred, because the predetermined clamp load L is more difficult to determine since some of the applied load is used to overcome the interference fit, which may vary from one assembly to the next. While the assembly  10  is maintained under a predetermined clamp load L, a securing material  44  is used to secure the retainer  38  to the neck  18 . The securing material  44  is a material separate from that of hub  12  or retainer  38 , such as a weld bead, in the example shown. At this point in the piston valve assembly manufacturing process, a completed sub-assembly is provided.  
         [0018]     Some prior art arrangements use a rod that has a shoulder at its end. The end is threaded to receive a nut. Tolerance stack-ups in the shoulder, piston and deflection discs could position the shoulder such that the nut bottoms out on the shoulder prior to achieving the desired torque necessary to sufficiently clamp the deflection discs. The inventive clamping arrangement avoids this by enabling the retainer  38  to be positioned axially anywhere along the end  20  so that the predetermined clamp load is achieved regardless of tolerances in the piston, deflection discs or other valve assembly components.  
         [0019]     Different size piston rods may be installed onto the assembly  10 . The hub  12  includes a collar  46  extending from the shoulder  16 . The collar  46  includes an inside surface  48  and an outside surface  50 . A solid rod  52 , for example 12 mm in diameter, may be received in the collar  46  in close fitting relationship to the inside surface  48 . The rod  52  may be impulse welded to the inside surface  48  forming a weld bead  54 . The rod  52  may also be laser welded forming a weld bead  56  about the circumference of the rod  52  where it meets the collar  46  to form a seal past which fluid will not leak. Alternatively, the hub  12  may be eliminated and the rod  52  may be used to directly support the piston  22  and deflection discs  34 ,  36 . For this type of configuration, the rod  52  provides the shoulder and the end having the surface to which the retainer  38  is attached.  
         [0020]     As will be appreciated from the description of  FIGS. 3 and 4 , the inventive common hub  12  may be used in any number of configurations of piston valve assemblies  10 . Referring to  FIG. 3 , a floating-fixed disc arrangement is shown in which the compression side discs  34  are permitted in their entirety to move axially along the axis provided by the hub  12  or float. A spring retainer  60  supporting an end of a spring  62  is received on the neck  18  and is in abutting engagement with the shoulder  16 . The spring  62  biases the compression deflection disc  34  into engagement with the piston  22 . The spring retainer  60  also acts as a guide upon which the deflection discs  34  may move axially relative thereto. The rebound side has a fixed disc configuration. Specifically, the rebound discs  36  are captured between a guide  72  such that the deflection discs  36  are axially fixed at the inner periphery.  
         [0021]     The inventive clamping arrangement is first used for the assembly shown in  FIG. 3  to provide a predetermined clamp load to the deflection disc  36  by applying the load to the shoulder  16  and guide  72 . The guide  72  is secured to the hub  12  in the same manner described relative to the retainer  38  in  FIG. 2 .  
         [0022]     A plate  70  is slidingly received on the guide  70 , and the spring  68  is captured between the retainer  70  and plate  74 . Springs can introduce a high degree of variability by having variations in spring loads and lengths. As a result, when the spring  68  is installed using conventional arrangements, the spring  68  will not be at its target installed spring load. The inventive clamping arrangement is also used to apply a desired preload to the outer periphery of the discs  36  by compressing the spring  68  to a desired spring load. In this manner, the variability due to the spring is greatly reduced or eliminated. The spring  68  is loaded to a desired spring load and the retainer  70  secured to the hub  12 , as described above relative to the retainer  38  in  FIG. 2 . The inventive arrangement is also unaffected by variations in thickness of the plate  74 . A retainer  70  is secured to an end  20  of the neck  18 , in the same manner described above relative to  FIG. 2 , to capture a spring  68  between the plate  74  and retainer  70 .  
         [0023]     The inventive hub  12  and retainer  70  arrangement provides the unique advantage of enabling a preload to be used to load the spring  68  to a desired spring load prior to securing the retainer  70  to the end  20 . Similar to the clamp load applied in  FIG. 2 , the end of the hub  12  is retained and the retainer  70  is loaded to achieve the desired spring load  68 , which enables variation in spring loads due to tolerance stack-ups experienced in manufacturing the piston valve assembly to be eliminated. Once the desired spring load on the spring  68  is achieved, the retainer  70  is welded to the hub  12 .  
         [0024]     Referring to  FIG. 4 , a floating-floating disc arrangement is shown in which the discs in their entirety are permitted to move axially along the axis provided by the hub  12 . Similar to  FIG. 3 , a spring retainer  60  supporting an end of a spring  62  is received on the neck  18  and is in an abutting engagement with the shoulder  16 . The spring  62  biases the compression deflection disc  34  into engagement with the piston  22 . The spring retainer  60  also acts as a guide upon which the deflection discs  34  may move axially relative thereto. Another guide  64  is arranged on the neck  18  opposite the guide  60  retaining the piston  22  between the guide  60  and  64 . The guide  64  is secured to the neck  18 , for example, by welding. A plate  66  is arranged adjacent to the rebound disc  36  and is slidable relative to the guide  64 . A flange extending outwardly from an end of the guide  64  acts as a rearward stop for the plate  66  as the rebound deflection discs  36  move away from the piston  22 .  
         [0025]     In addition to minimizing or eliminating the effects of tolerance stack-ups amongst the components, the inventive clamping arrangement also permits looser tolerances of some of the machining dimensions of the components, which reduces the cost of manufacture.  
         [0026]     The invention has been described in an illustrative manner, and it is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.