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 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. The load on the deflection discs may decrease even after the predetermined torque has successfully been achieved and the damper has passed the final test. Base valves in dampers may experience the same problem. Therefore what is needed is a damper design that provides more consistent loading of the damper valve bodies.  
       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. The same configuration maybe used for a base valve.  
         [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. 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. The retainer is secured to the hub, for example, by welding.  
         [0006]     Accordingly, the above mentioned provides a damper design that provides consistent loading of the damper valve bodies. 
     
    
     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;  
         [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;  
         [0012]      FIG. 5  is a cross-sectional view of a base valve for a twin tube shock absorber using the inventive clamping arrangement;  
         [0013]      FIG. 6  is a cross-sectional view of a base valve using the inventive clamping arrangement.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0014]     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  and base valve  8  incorporate an inventive hub  12 , which is shown in  FIGS. 2-6 .  
         [0015]     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 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 .  
         [0016]     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.  
         [0017]     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.  
         [0018]     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.  
         [0019]     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.  
         [0020]     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.  
         [0021]     As will be appreciated from the description of  FIGS. 3-6 , the inventive common hub  12  may be used in any number of configurations of piston valve assemblies  10  or base valves  8 . 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 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. 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. The inventive clamping arrangement is first used for the assembly shown in  FIG. 3  to provide a predetermined of 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 . 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 load. 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 . 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  66  and retainer  70 . 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 .  
         [0023]      FIG. 4  depicts a piston valve assembly similar to that shown in  FIG. 3 , except the compression side includes a fixed disc configuration. The hub  12  includes a shoulder having the same diameter as the shoulder  16  shown in  FIGS. 2 and 3 . However, the piston valve assembly  10  additionally includes a stop  76  arranged between the shoulder  16  and piston  22 . A spacer  78  is arranged between the stop  76  and compression discs  34  so that the compression discs  34  pivot about the spacer  78  until they engage the stop  76 . The stop  76  need not be affixed or welded to the hub  12  loading the shoulder  16  and guide  72  to a predetermined clamp load applies a desired load to both the discs  34 ,  36 . The guide  72  and retainer  70  are secured in a manner similar to that described relative to  FIG. 3 .  
         [0024]      FIGS. 5 and 6  show the inventive hub  84  for use with base valves  8 . Referring to  FIG. 5 , the hub  84  includes a base valve head  86  received by a neck  90  of the hub  84 . The head  86  abuts a hub shoulder  88 . A guide  94  extends radially from the hub  84  and is spaced axially from the shoulder  88  away from the head  86 . A spring  100  is arranged between the spring retainer  94  and rebound deflection disc  98  biasing the deflection disc  98  with the head  86 . On the compression side, a retainer  106  are loaded to a desired clamp load and secured to the hub  84  in the manner described relative to  FIG. 2 . Compression disc  102  engages the head  86 , and a spacer  104  is arranged between the compression deflection disc  102  and the retainer  106 .  
         [0025]     The base valve  8  shown in  FIG. 6  uses a fixed rebound disc arrangement so that the hub  84  does not need the spring retainer shown in  FIG. 7 . A spacer  108  is arranged between the shoulder  88  and rebound discs  98 .  
         [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.