Patent Application
20060011430
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.
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.
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.
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 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.
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.
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:
A twin tube shock absorber 2 is shown in
A piston valve assembly 10 of the present invention is shown in
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.
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.
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.
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.
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.
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.
As will be appreciated from the description of
The inventive clamping arrangement is first used for the assembly shown in
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
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
Referring to
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.
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.
