Abstract:
A damper assembly includes a piston assembly which has a piston body which is designed to be manufactured from a powdered metal process. In one embodiment, the compression and extension passages are generally S-shaped with their inlets being disposed radially outward from their outlets. In this manner, compression and extension check valves can be designed to only extend radially to cover the outlets and not affect the inlets. In another embodiment, the compression and extension passages are straight and the compression and extension sealing lands wind around between the inlets and the outlets so only the outlets are sealed and the inlets are not affected.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to hydraulic dampers or shock absorbers adapted for use in a suspension system such as the suspension systems used for automotive vehicles. More particularly, the present invention relates to a single piece piston having a sealing land design and a fluid passage design which allow manufacture of the single piece piston by powdered metal processes. 
     BACKGROUND OF THE INVENTION 
     Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb the unwanted vibrations, shock absorbers are generally connected between the sprung portion (body) and the unsprung portion (suspension) of the automobile. A piston is located within a pressure tube of the shock absorber and the pressure tube is connected to the unsprung portion of tile vehicle. The piston is connected to the sprung portion of the automobile through a piston rod which extends through the pressure tube. The piston divides the pressure tube into an upper working chamber and a lower working chamber both of which are filled with hydraulic fluid. Because the piston is able, through valving, to limit the flow of the hydraulic fluid between the upper and the lower working chambers when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which counteracts the vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the vehicle of the vehicle. In a dual tube shock absorber, a fluid reservoir or reserve chamber is defined between the pressure tube and a reserve tube. A base valve is located between the lower working chamber and the reserve chamber to also produce a damping force which counteracts the vibrations which would otherwise be transmitted from the unsprung portion of the vehicle to the sprung portion of the automobile. 
     As stated above, the valving on the piston limits the flow of damping fluid between the upper and lower working chambers when the shock absorber is compressed or extended. During driving, the suspension system moves in jounce (compression) and rebound (extension). During jounce movements, the shock absorber is compressed causing damping fluid to move through the piston from the lower working chamber to the upper working chamber. A one-way check valve is normally located on the upper side of the piston to control the flow of damping fluid and thus the damping force created. During rebound movements, the shock absorber is extended causing damping fluid to move through the piston from the upper working chamber to the lower working chamber. A one-way check valve is normally located on the lower side of the piston to control the flow of damping fluid and thus the damping force created. 
     The piston normally includes a plurality of compression passages and a plurality of extension passages extending through the body of the piston. The compression check valve on the upper side of the piston opens the compression passages during jounce or compression movements of the shock absorber and closes the compression passages during rebound or extension movements of the shock absorber. Similarly, the extension check valve on the lower side of the piston opens the extension passages during rebound or extension movements of the shock absorber and closes the extension passages during jounce or compression movements of the shock absorber. Thus, the compression check valve must not interfere with the inlet to the extension passages and the extension check valve must not interfere with the inlet to the compression passages. 
     In order to avoid interference between the check valves and their opposing fluid passages, various non-interference methods have been designed into the piston. One method is to incorporate a radial offset between the compression passages and the extension passages. In this manner, one inlet is located radially outward of its opposing check valve and the opposite inlet is located radially inward of its opposing check valve. Another method is to angle the compression passages in one direction while angling the extension passages in the opposite direction. In this manner, both sets of inlets are located radially inward and both sets of outlets are located radially outward. 
     While the various methods for avoiding interference between the check valves and their opposing fluid passages have met with commercial success, continued development of shock absorber pistons includes development of lower cost systems enabling lower cost manufacturing for the piston itself, the valving system and thus the cost for the shock absorber. 
     SUMMARY OF THE INVENTION 
     The present invention provides the art with a single piece piston design which has an upper side which is identical to its lower side but rotated 45° from each other. The sealing lands on each side of the piston have a unique shape which eliminates interference between the check valves and their opposing passages. In one embodiment, the passages are formed in an S shape and in a second embodiment, the passages are formed straight. Both embodiments enable the single piece piston to be manufactured by powered metal processes. 
     Other advantages and objects of the present invention will become apparent to those skilled in the art from the subsequent detailed description, appended claims and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings which illustrate the best mode presently contemplated for carrying out the present invention: 
     FIG. 1 is an illustration of an automobile having shock absorbers which incorporate the unique piston design in accordance with the present invention; 
     FIG. 2 is a side view, partially in cross section, of a shock absorber incorporating the unique piston design in accordance with the present invention; 
     FIG. 3 is an enlarged side view, partially in cross section, of the piston from the shock absorber shown in FIG. 2; 
     FIG. 4 is a top plan view of the piston shown in FIG. 3; 
     FIG. 5 is a top plan view of a piston in accordance with another embodiment of the present invention; 
     FIG. 6 is a top plan view of a piston in accordance with another embodiment of the present invention; and 
     FIG. 7 is a cross-sectional side view of the piston shown in FIG. 6 taken in the direction of arrows  7 — 7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings in which like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a vehicle incorporating a suspension system having shock absorbers each of which includes a piston in accordance with the present invention which is designated generally by the reference numeral  10 . Vehicle  10  includes a rear suspension  12 , a front suspension  14  and a body  16 . Rear suspension  12  has a transversely extending rear axle assembly (not shown) adapted to operatively support a pair of rear wheels  18 . The rear axle is attached to body  16  by means of a pair of shock absorbers  20  and a first pair of helical coil springs  22 . Similarly, front suspension  14  includes a transversely extending front axle assembly (not shown) to operatively support a pair of front wheels  24 . The front axle assembly is attached to body  16  by means of a second pair of shock absorbers  26  and by a pair of helical coil springs  28 . Shock absorbers  20  and  26  serve to dampen the relative motion of the unsprung portion (i.e., front and rear suspension  12  and  14 , respectively) with respect to the sprung portion (i.e., body  16 ) of vehicle  10 . While vehicle  10  has been depicted as a passenger car having front and rear axle assemblies, shock absorbers  20  and  26  may be used with other types of vehicles or in other types of applications including, but not limited to, vehicles incorporating independent front and/or independent rear suspension systems. Further, the term “shock absorber” as used herein is meant to refer to dampers in general and thus will include MacPherson struts. 
     Referring now to FIG. 2, shock absorber  20  is shown in greater detail. While FIG. 2 shows only shock absorber  20 , it is to be understood that shock absorber  26  also includes the unique piston in accordance with the present invention. Shock absorber  26  only differs from shock absorber  20  in the way it is adapted to be connected to the sprung and unsprung portions of vehicle  10 . Shock absorber  20  comprises a pressure tube  30 , a piston assembly  32  and a piston rod  34 . 
     Pressure tube  30  defines a working chamber  42 . Piston assembly  32  is slidably disposed within pressure tube  30  and divides working chamber  42  into an upper working chamber  44  and a lower working chamber  46 . A seal  48  is disposed between piston assembly  32  and pressure tube  30  to permit sliding movement of piston assembly  32  with respect to pressure tube  30  without generating undue frictional forces as well as sealing upper working chamber  44  from lower working chamber  46 . Piston rod  34  is attached to piston assembly  32  and extends through upper working chamber  44  and through an upper end cap or rod guide  50  which closes the upper end of both pressure tube  30 . A sealing system  52  seals the interface between rod guide  50 , pressure tube  30  and piston rod  34 . The end of piston rod  34  opposite to piston assembly  32  is adapted to be secured to the sprung portion of vehicle  10 . The end of pressure tube  30  opposite to rod guide  50  is adapted to be connected to the unsprung portion of vehicle  10 . Extension valving within piston assembly  32  controls the movement of fluid between upper working chamber  44  and lower working chamber  46  during an extension movement of piston assembly  32  within pressure tube  30 . Compression valving within piston  32  controls the movement of fluid between lower working chamber  46  and upper working chamber  44  during a compression movement of piston assembly  32  within pressure tube  30 . 
     Referring now to FIGS. 3 and 4, the present invention is directed towards a unique construction for piston assembly  32 . Piston assembly  32  comprises a compression valve assembly  60 , a piston body  62  and an extension valve assembly  64 . Piston rod  34  defines a reduced diameter section  66  onto which compression valve assembly  60 , piston body  62  and extension valve assembly  64  are located. A nut  68  secures piston assembly  32  onto section  66  of piston rod  34  with compression valve assembly  60  abutting a shoulder  70  located on piston rod  34 , piston body  62  abutting compression valve assembly  60 , extension valve assembly  64  abutting piston body  62  and nut  68  abutting extension valve assembly  64 . 
     Compression valve assembly  60  comprises a stop  72 , a pair of spacers  74  and a plurality of valve plates  76 . In a similar manner, extension valve assembly includes stop  72 , the pair of spacers  74  and the plurality of valve plates  76 . Thus, compression valve assembly  60  is the same as extension valve assembly  64  which is one advantage provided by the unique design of piston body  62 . The commonization of components between compression valve assembly  60  and extension valve assembly  64  reduces the number of different part numbers required for piston assembly  32  which reduces costs by reducing components and complexities for the assembly. 
     Piston body  62  defines a plurality of compression passages  80 , a plurality of extension passages  82 , a compression sealing land  84  and an extension sealing land  86 . Compression passages  80  are generally S-shaped passages having an inlet  88  at the lower end of piston body  62  positioned radially outward from an outlet  90  at the upper end of piston body  62 . This S-shape of compression passages  80  enables valve plates  76  of compression valve assembly  60  to close passages  80  at outlet  90  but also allows inlet  88  to be unaffected by valve plates  76  of extension valve assembly  64 . Extension passages  82  are also generally S-shaped passages having an inlet  92  at the upper end of piston body  62  positioned radially outward from an outlet  94  at the lower end of piston body  62 . This S-shaped configuration of extension passages  82  enables valve plates  76  of extension valve assembly  64  to close passages  82  at outlet  94  but also allows inlet  92  to be unaffected by valve plates  76  of compression valve assembly  60 . Thus, during a compression stroke, fluid in lower working chamber  46  is compressed and fluid flows into inlet  88 , through passages  80  to outlet  90  where the fluid pressure flexes valve plates  76  of compression valve assembly  60  to open outlet  90  and allow fluid flow through passages  80 . Fluid flow through passages  82  is prohibited by valve plates  76  of extension valve assembly  64  sealing against extension sealing land  86 . During an extension stroke, fluid in upper working chamber  44  is compressed and flows into inlet  92 , through passages  82  to outlet  94  where the fluid pressure flexes valve plates  76  of extension valve assembly  64  to open outlet  94  and allow fluid flow through passages  82 . Fluid flow through passages  80  is prohibited by valve plates  76  of compression valve assembly  60  sealing against compression sealing land  84 . 
     Compression sealing land  84  is a generally octagonally shaped passage which allows for the sealing of outlets  90  of compression passages  80  without affecting inlets  92  of extension passages  82 . Extension sealing land  86  has the identical shape to that of compression sealing land  84  but it is rotated or shifted 45° with respect to land  84 . This enables the sealing of outlets  94  of extension passages  82  without affecting inlets  88  of compression passages  80 . 
     The S-shaped configuration of passages  80  and  82 , the shape of sealing lands  84  and  86  and the overall configuration of piston body  62  enables piston body  62  to be manufactured as a single piece component using powdered metal processes and technology. The powdered metal process produces a blank for manufacturing piston body  62  which requires a minimum amount of machining while eliminating the need to drill or bore fluid passages within piston body  62 . This significantly reduces the manufacturing costs associated with piston body  62 , 
     Referring now to FIG. 5, a piston body  162  in accordance with another embodiment of the present invention is disclosed. Piston body  162  is the same as piston body  62  except that compression sealing land  84  is replaced by compression sealing land  184  and extension sealing land  86  is replaced by extension sealing land  186 . Sealing lands  184  and  186  are generally rectangular in shape rather than being octagonal. Sealing land  186  is the same as sealing land  184  but it is rotated or shifted  45 ° with respect to sealing land  184 . The function and operation of piston body  162  is the same as that desired above for piston body  62 . 
     Referring now to FIGS. 6 and 7, a piston body  262  in accordance with another embodiment of the present invention is disclosed. Piston body  262  is the same as piston body  62  except that the plurality of compression passages  80  are replaced by a plurality of compression passages  280 ; the plurality of extension passages  82  are replaced by a plurality of extension passages  282 ; the compression sealing land  84  is replaced by a compression sealing land  284 ; and the extension sealing land  86  is replaced by an extension sealing land  286 . Passages  280  and  282  extend linearly or straight through piston body  262  and are all located the same radial distances from the center. Passages  280  and  282  are circumferentially spaced around the circumference with passages  280  and  282  alternating around the circumference. Sealing lands  284  and  286  are formed to wind around passages  280  and  282  in a clover leaf shape in order to seal the outlets of the passages while not affecting the inlets of the passages. Again, sealing land  286  is rotated or shifted 45° with respect to sealing land  284 . The function and operation of piston body  262  is the same as that described above for piston body  62 . 
     While the above detailed description describes the preferred embodiment of the present invention, it should be understood that the present invention is susceptible to modification, variation and alteration without deviating from the scope and fair meaning of the subjoined claims.