Abstract:
A hydraulic piston assembly includes a cylinder assembly having an inner bore that defines an internal space. A piston is disposed in the space and divides the space into first and second fluid chambers. The piston comprises a side annular surface, a first surface adjacent the first fluid chamber and a second surface adjacent the second fluid chamber. The side annular surface comprising a first portion, a second portion and an annular groove between the first and second portions. The first portion has a maximum diameter that is less than the maximum diameter of the second portion. A sealing member is positioned within the annular groove. In some embodiments, the cylinder assembly forms part of a dampening system that interrelates at least two suspension assemblies. Methods for assembling the hydraulic piston assembly are also disclosed.

Description:
RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the priority of Japanese Patent Application No. 2001-128488, filed on Apr. 25, 2001, which is hereby incorporated by reference in its entirety.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention relates to a vehicle suspension system and more particularly to a sealing arrangement for a hydraulic piston of the vehicle suspension system.  
           [0004]    2. Description of the Related Art  
           [0005]    Conventional vehicle suspension systems include at least one hydraulic shock absorber. Each shock absorber typically includes a piston that reciprocates within a hollow cylinder. The piston is fixed to one end of a piston rod and the piston is disposed within the internal space of the cylinder to divide the cylinder into first and second chambers. The chambers are typically filled with a fluid such as oil to resist the motion of the piston within the cylinder. The reciprocating movement of the piston is resisted because the fluid must flow through a resistance mechanism when flowing from one chamber to the other chamber. Typically, the resistance mechanism comprises throttle plates or check valves that control the damping of the shock absorber. The movement of the fluid through the resistance mechanism dissipates the input energy to the shock absorber by displacing the fluid through the resistance mechanism. The velocity of the reciprocating piston, which determines the amount of energy dissipated, is controlled by the amount of resistance to the fluid flow.  
           [0006]    U.S. Pat. No. 6,250,658 describes a vehicle suspension system wherein each wheel is associated with an individual shock absorber to provide individual wheel dampening. As best seen in FIG. 2 of the &#39;658 patent, the shock absorbers for at least two wheels are coupled together by a dampening system, which includes a hydraulic cylinder to control the roll and pitch of the vehicle. More specifically, the hydraulic cylinder includes a cylinder body, which defines a cylinder bore and is supported on the body of the vehicle. A piston is positioned within the cylinder bore and divides the cylinder bore into a first and second chamber. The piston includes an annular groove and an elastic sealing ring that is positioned in the annular groove. The sealing ring presses against the bottom surface of the annular groove and the cylinder bore to form a tight seal between the piston and the bore and between the first and second chambers. Hydraulic pipes are provided for coupling the hydraulic cylinder to the internal spaces of the associated shock absorbers.  
           [0007]    As each of the shock absorber moves up and down with the upward and downward movement of the wheels, the piston of the hydraulic cylinder slides back and forth to dampen the upward and downward movement of both shock absorbers as fluid in the first and second chambers pass through a valve in the piton. In this manner, the dampening system reduces rolling and pitching of the vehicle.  
         SUMMARY OF THE INVENTION  
         [0008]    Assembling the hydraulic cylinder involves fitting the sealing ring into the annular groove. Typically, this involves radially expanding the sealing ring such that it deforms elastically and fits over one end of the piston. The sealing ring is then slid along the piston until the ring reaches the annual groove and contracts to its original shape within the groove.  
           [0009]    There are several problems associated with the above-described method for assembling the hydraulic cylinder. For example, the sealing ring may undergo plastic deformation as it is expanded to fit over the end of the piston body. This may prevent the sealing ring from returning to its original shape, which will reduce the contact force between the sealing ring and the piston and reduce the effectiveness of the seal. Another problem associated with the above-described method is that, after the seal ring is positioned in the annular groove, its outside diameter is significantly larger than the outside diameter of the piston. This makes inserting the piston into the cylinder bore difficult as the outside edge of the sealing ring can become caught on the opening edge of the bore.  
           [0010]    Accordingly, in one aspect of the present invention is a hydraulic suspension system comprising a cylinder assembly having an inner bore that defines an internal space. A first piston is disposed within the internal space to separate the internal space into a first fluid chamber and a second fluid chamber. The piston comprising a side annular surface located adjacent the internal bore, a first surface adjacent the first fluid chamber, and a second surface located adjacent the second fluid chamber. The side annular surface comprises a first annular surface located adjacent the first surface, a second annular surface located adjacent the second surface, and an annular groove that lies between the first annular surface and the second annular surface. The first annular surface has a maximum diameter that is less than the maximum diameter of the second annular surface. A first sealing member is positioned within the groove.  
           [0011]    Another aspect of the present invention is a hydraulic suspension system that comprises a cylinder assembly having a smaller diameter portion with a first inner bore that defines small diameter internal space and larger diameter portion with a second inner bore that defines a large diameter internal space that is in communication with the small diameter internal space. A piston rod extends within the small and larger diameter internal spaces. A first piston is coupled to the piston rod and is disposed within the large diameter space to separate the large diameter space into a first fluid chamber and a second fluid chamber. A second piston is coupled to the piston rod and is disposed with the small diameter internal space to separate the small diameter space into a third fluid chamber and a fourth fluid chamber. The third fluid chamber being in communication with the first fluid chamber. The first piston comprising a side annular surface located adjacent the internal bore, a first surface adjacent the first fluid chamber, and a second surface located adjacent the second fluid chamber. The side annular surface comprises a first annular surface located adjacent the first surface, a second annular surface located adjacent the second surface, and an annular groove that lies between the first annular surface and the second annular surface. The first annular surface having a maximum diameter that is less than the maximum diameter of the second annular surface. A first sealing member is positioned within the annular groove.  
           [0012]    Yet another embodiment of the present invention is a method for assembling a hydraulic cylinder of a hydraulic suspension system. The method comprises providing a piston with a side annular surface, a first surface, and a second surface. The side annular surface includes a first annular surface located adjacent the first surface, a second annular surface located adjacent the second surface, and an annular groove that lies between the first annular surface and the second annular surface. The first annular surface has a maximum diameter that is less than the maximum diameter of the second annular surface. The method further comprises providing a cone shaped jig having a first end with a smaller diameter than a second end of the jig, providing an annular press, placing the second end of the jig adjacent the first surface of the piston, placing a sealing ring adjacent the first end of the jig, and using the annular press to move a sealing ring over the jig and onto the annular surface of the piston and into the annular groove.  
           [0013]    All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a partially schematic cross-sectional view of a suspension system that comprises a hydraulic cylinder having certain features and advantages according a preferred embodiment of the present invention.  
         [0015]    [0015]FIG. 2 is an enlarged cross-sectional view of a portion of FIG. 1.  
         [0016]    [0016]FIG. 3 is an enlarged cross-sectional view of a portion of FIG. 2 showing a modified embodiment.  
         [0017]    [0017]FIG. 4 is an enlarged cross-sectional view of a portion of the hydraulic cylinder showing how a sealing ring is inserted onto a piston of the hydraulic cylinder. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]    [0018]FIG. 1 illustrates a suspension system  10  that includes a left suspension assembly  12 L, a right suspension assembly  12 R, and a dampening system  14  having certain features and advantages according a preferred embodiment of the present invention. As will be explained below, the illustrated dampening system  14  interrelates the left and right suspension assemblies  12 L,  12 R (i.e., suspension assemblies associated with the wheels located on the left and right sides of a vehicle). Such an arrangement is particularly useful in dampening and controlling vehicle roll, which can occur when the vehicle is cornering. However, it should be appreciated that the dampening system  14  can also be used to interrelate front and rear suspension assemblies (i.e., suspension assemblies associated with the wheels located on the front and rear sides of a vehicle). Such an arrangement is particularly useful in dampening and controlling vehicle pitch, which can occur during acceleration or deceleration. The dampening system  14  may also be used interrelate more than two suspension assemblies from the left, right, front or rear sides of the vehicle.  
         [0019]    The left and right suspension assemblies  12 L,  12 R include a hydraulic damper  16 L,  16 R. Each hydraulic damper  16 L,  16 R comprises a cylinder assembly  18  that has a trunnion portion  20  for attachment to either the vehicle body  22  or a wheel suspension  24  for the wheel (not shown). In the illustrated embodiment, the trunnion portion  20  is attached to the wheel suspension  24 .  
         [0020]    The cylinder assembly  18  defines a cylinder bore  26 , which defines an internal chamber  27 . A piston  28  is positioned in the internal chamber  27  and divides the internal chamber  27  into a lower or working chamber  30  and an upper or reservoir chamber  32 . These chambers  30 ,  32  are sealed from each other by sealing members carried by the piston  28 . A control valve or control passage (not shown) is preferably provided in the piston  48  for permitting a controlled amount of flow between the working chamber  30  and the reservoir chamber  32 . In a modified embodiment, the control valve or passage can be provided in a bypass passage.  
         [0021]    A piston rod  34  extends through the reservoir chamber  32  and is connected to the vehicle body  22 . As noted above, the arrangement of the suspension assembly  12 L,  12 R can be reversed. That is, the piston rod  34  can be connected to the wheel suspension  24  while the tunnion portion is connected to the vehicle body  22 .  
         [0022]    The working chambers  30  of the left and right suspension assemblies  12 L,  12 R are connected to the dampening system  14  by a pair of pressure lines  36 L,  36 R such that the left and right suspension assemblies  12 L,  12 R are in hydraulic communication with the dampening system  14 . It should be appreciated that the functions and positions of the working chamber  30  and the reservoir chamber  32  can be reversed.  
         [0023]    With continued reference to FIG. 1, the dampening system  14  will now be described. The dampening system  14  comprises a cylinder assembly  38 , which, in the illustrated embodiment, comprises a first smaller diameter portion  42  and a second larger diameter portion  44 . The smaller diameter portion  42  has an internal bore  46  that defines a smaller diameter chamber  48  in which a first piston  50  is positioned. The first piston  50  divides the smaller diameter chamber  48  in to a first sub-chamber  52  and a second sub-chamber  54 . In the illustrated embodiment, the working chamber  30  of the left suspension assembly  12 L is connected to the first sub-chamber  52  by the pressure line  36 L. In a similar manner, the working chamber  30  of the right suspension assembly  12 R is connected to the second sub-chamber  54  by the pressure line  36 R. A small passage or pressure valve  56  is provided in the first piston  50 . The passage  56  permits controlled flow of fluid between the first and second sub-chambers  52 ,  54  to provide dampening as will be explained in more detail below. It should be appreciated that in modified embodiments the valve  56  can be placed outside or within the cylinder assembly  38  in a bypass passage.  
         [0024]    The larger diameter portion  44  also has an internal bore  58 , which defines a larger diameter chamber  60  in which a second piston  62  is positioned. The first and second pistons  50 ,  62  are coupled together by a piston rod  63  such that they move in unison along a longitudinal axis  63  of the cylinder assembly  38 . The second piston  62  divides the larger diameter chamber  60  into a third and fourth sub-chambers  64 ,  66 . In the illustrated arrangement, the first and third sub-chambers  52 ,  64  of the smaller and larger diameter chambers  48 ,  60  lie adjacent to each other (i.e., the first and third sub-chambers  52 ,  64  are in communication with each other). In the illustrated embodiment, a spring  70  is provided in the fourth sub-chamber  66  for biasing the pistons  50 ,  62  toward the second sub-chamber  54 .  
         [0025]    Preferably, the internal chambers  27  of the suspension assemblies  12 L,  12 R and the smaller diameter chamber  48  of the dampening system  12  are filled with a fluid or oil. In contrast, the fourth sub chamber  66  is preferably filled with a fluid or gas (e.g., nitrogen).  
         [0026]    The operation of the suspension system  10  will now be described with continued reference to FIG. 1. When both the left and right wheels encounter the same obstacle, the wheels may be raised as indicated by the solid arrows in FIG. 1. Such movement will compress the fluid in the working chambers  30  of the left and right suspension assemblies  12 L,  12 R. The compressed fluid is forced through the control valves in the piston  28  into the reservoir chambers  32 . Some of the compressed fluid may also be forced through the pressure lines  36 L,  36 R into the dampening system  14 . Because the left and right suspension assemblies  12 L,  12 R are displaced the same amount, an equal amount of fluid is displaced in each suspension assembly  12 L,  12 R and no fluid will be displaced between the assemblies  12 L,  12 R. More specifically, the pressure in the first and second sub-chambers  52 ,  54  are equal and no fluid passes through the valve  56 . Because the cross-sectional area of the second piston  62  is greater than the first piston  50 , the two pistons  62 ,  50  move downwardly and their motion is dampened by the gas in the fourth sub-chamber  66  and/or the spring  70 . In this situation, the suspension assemblies  12 L,  12 R essentially operate as conventional shock absorbers.  
         [0027]    In a similar manner, when both the left and right wheels encounter the same obstacle, the wheels may be depressed in a direction opposite the direction indicated by the solid arrows in FIG. 1. In such a situation, the fluid in the reservoir chambers  32  is compressed and forced through the control valves in the piston  28  into the working chamber  30 . Some fluid from the dampening system  14  may also flow into the working chamber  30 . Because the left and right suspension assemblies  12 L,  12 R are displaced the same amount, an equal amount of fluid is displaced in each suspension assembly  12 L,  12 R and no fluid will be displaced between the assemblies  12 L,  12 R. The two pistons  50 ,  62  move upwardly and their motion is dampened by the gas in the fourth sub-chamber  66  and/or the spring  70 .  
         [0028]    When, for example, the vehicle is cornering, the left and right suspension assemblies will be moved in opposite directions as indicated by the dashed arrows of FIG. 1. This causes the fluid in the working chamber  30  of the right assembly  12 R to be rapidly compressed while the working chamber  30  of the left assembly  12 L is rapidly expanded. Thus, fluid is withdrawn from the first sub-chamber  52  of the dampening system  14  and fluid is delivered to the second sub-chamber  54 . This creates a pressure differential between the first and second sub-chambers  52 ,  54 . The valve  56  permits controlled flow between the first and second sub-chambers  52 ,  54  to reduce and control the body roll caused by the cornering.  
         [0029]    The physical structure of the dampening system will now be described in more detail with initial reference to FIG. 2. The second piston  62  includes a piston body  70 . The piston body  70  has top end surface  71 , a side annular surface  72 , and a bottom end surface  73 . The side annular surface  72  includes an annular groove  74  that includes an top surface  74   a , a side surface  74   b  and a bottom surface  75   c . A first sealing ring  76  is fitted into the annular groove  74  such that it engages the upper, side and lower surfaces  74   a - c . In one embodiment, the first sealing ring  76  is preferably made of an elastic material, such as, for example, polytetrafluoroethylene (e.g., Teflon™).  
         [0030]    With continued reference to FIG. 2, the outer annular surface  72  comprise a first or upper portion  78 , which is generally located above the annular groove  74  in an axial direction, and a second or lower portion  80 , which is generally located below the annular groove  74 . The second portion  80  preferably also includes another annular groove  82 . A second sealing ring  84  is positioned within the annular groove  82 . In one embodiment, the elastic sealing ring is made of an elastic material, such as, for example, rubber.  
         [0031]    Both the first and second sealing rings  76 ,  84  are configured such that their outer circumferential surfaces contact and press against the inside circumferential surface of the large diameter chamber  60 . The first and second sealing rings  76 ,  84  therefore seal the third sub-chamber  64  from the fourth sub-chamber  66 . Preferably, the first sealing ring  76  is made from a material that is harder (i.e., has a higher modulus of elasticity) than the material of the second sealing ring  84 . In one embodiment, the first sealing ring  76  is made of polytetrafluoroethylene (e.g., Teflon™) and the second sealing ring  84  is made of rubber.  
         [0032]    To aid assembling, the first or upper portion  78  of the illustrated embodiment has a maximum outer diameter D 1  that is smaller than the maximum diameter D 2  of the lower portion  80 . In a modified embodiment, which is illustrated in FIG. 3, the diameter D 1  of the upper portion. 78  gradually decreases from the annular groove  74  to the top end  71  of the second piston  62 . Preferably, in both embodiments, the upper or smaller diameter portion  78  of the annular surface  72  is located adjacent the third sub-chamber chamber  64 , which generally is configured to have a larger maximum hydraulic pressure as compared to the fourth sub-chamber  66  as will be explained below. In a similar manner, the lower portion  80  is preferably located adjacent the fourth sub-chamber  66 .  
         [0033]    In a modified embodiment, which is indicated by the dashed lines in FIG. 2, a third sealing ring  88  is placed between the side surface  74   b  of the annular groove  74  and the first sealing ring  76 . The third sealing ring  88  urges the first sealing ring  76  radially outward. The third sealing ring  88  is preferably made of a material that is more elastic (i.e., has a lower modulus of elasticity) than the material of the first sealing ring  76 . For example, in one embodiment, the first sealing ring  76  is made of polytetrafluoroethylene (e.g., Teflon™) while the third sealing ring  88  is made of rubber. This arrangement is advantageous because the third sealing ring  88 , which has a smaller diameter than the first sealing ring  76 , must undergo more deformation than the first sealing ring  76  as it is inserted over the first end  71  of the second piston  62 . As such, forming the third sealing ring  88  out a more elastic material allows it to be more easily inserted over the first end  71  of the second piston  62 . This arrangement also allows the first sealing ring  76  to have a larger relaxed diameter because it is fitted over the third sealing ring  88 . Thus, the first sealing ring  76  can be made of a more resilient material because it undergoes less deformation when it is fitted over the first end  71  of the second piston  62 .  
         [0034]    A method for positioning the sealing ring  76  on the second piston  62  will now be described with reference to FIG. 4. A cone shaped jig  90  is placed over the first end  71  of the second piston  62 . The cone shaped jig  90  has an outer surface  92  that has a larger diameter on the side  94  that faces the first end  71  of the second piston  62 . The first sealing ring  76  is fitted over a smaller diameter side  96  of the jig  90 . An annular press  98  is used to move the first sealing ring  76  from the smaller diameter side  96  of the jig  90  towards the larger diameter side  94  of the jig  90 . In this manner, the first sealing ring  76  is gradually expanded until it reaches the first portion  78  of the second piston  62 . The annular press  98  continues to move the first sealing ring  76  along the first portion  78  of the second piston  62  until the first sealing ring  76  falls into the annular groove  74  as indicated by the phantom lines in FIG. 4.  
         [0035]    The embodiments described above have several advantages. For example, as described above, the maximum outside diameter D 1  of the first portion  78  is smaller than the maximum diameter D 2  of the second portion  80 . Therefore, less work is required to pass the first sealing ring  76  over the second piston  62  and into the annular groove  74 . This also reduces the amount that the first sealing ring  76  has to expand; so the sealing ring  76  is less likely to become damaged or deformed. This preserves the elasticity of the first sealing ring  76  and promotes a tighter seal between the second piston  62  and the larger diameter chamber  60 .  
         [0036]    Another advantage of the illustrated embodiments is that, because the first sealing ring  76  can be made of a more resilient material, its outside diameter can be configured to more closely match the inside diameter of the larger diameter chamber  60 . If the first sealing ring  76  is made of a less resilient material (e.g., rubber), the sealing ring  76  would generally have an outside diameter that is significantly larger than the inside diameter of the larger diameter chamber  60  to ensure a tight seal. By forming the first sealing ring  76  out of a more resilient material, the diameter of the first sealing ring  76  can be only slightly larger than the inside diameter of the larger diameter chamber  60  while still maintaining a tight seal. This arrangement prevents the first sealing ring  76  from being caught on the opening edge of the cylinder assembly  38  when the second piston  62  is inserted into the larger diameter chamber  60 .  
         [0037]    Another advantage of the illustrated embodiments is that the length of the first portion  78  of the second piston  62  is less than the length of the second portion  80  of the second piston  62 . As such, the first sealing ring  76  travels a smaller distance along the second piston  62 .  
         [0038]    In the embodiment illustrated in FIG. 3, the outside diameter of the first portion  78  tapers outwardly toward the annular groove  74 . In this arrangement, the first sealing ring  76  is gradually expanded before it is fitted over the first portion  78 . This reduces the amount of work required to fit the sealing ring  76  onto the piston  62 .  
         [0039]    Another advantage of the illustrated embodiment is that the smaller diameter first portion  78  is located adjacent the first and third sub-chambers  52 ,  64 . As explained above, in the illustrated embodiment, the second piston  62  is biased by a spring  70 . As such, the dampening system  14  is configured such the maximum hydraulic pressure in the first and third sub-chambers  52 ,  64  is higher than maximum hydraulic pressure in the fourth sub-chamber  66 . As such, the hydraulic pressure of the first and third sub-chambers  52 ,  64  presses the first sealing ring  76  against the bottom surface  74   c  of the annular seal  74 . Because the diameter of the bottom portion  80  is larger than the diameter of the upper portion  78 , the lower surface  74   c  of the annular groove  74  has a greater surface area than the upper surface  74   a  of the annular groove  74 . Thus, the larger hydraulic force of the first and third sub-chambers  52 ,  64  is spread out over the larger cross-sectional area of the lower surface  74   c . This reduces the stress on the first sealing ring  76  and increases the its service life.  
         [0040]    In the embodiment illustrated in dashed lines in FIGS. 2 and 4, the second piston  62  includes a third sealing member  88  that is placed between the side surface  74   b  of the annular groove  74  and the first sealing member  76 . The third sealing ring  88  urges the first sealing ring  76  outwardly. As mentioned above, the third sealing ring  88  is preferably made of a material that has a lower modulus of elasticity than the material of the first sealing ring  76 . This arrangement, permits the more elastic sealing ring (i.e., the third sealing ring  88 ) to have a smaller diameter and still be fitted easily into the annular groove  74 . This also allows the first sealing ring  76  to have a larger inside diameter such that it is deformed less when inserted over the first end  71  of the second piston  62  without causing plastic deformation of the first sealing ring  76 .  
         [0041]    The illustrated embodiments show certain features and aspects of the present invention as applied to the damping system  14  of the suspension system  10 . However, it should be appreciated that certain features and advantages of the illustrated embodiments may also find utility in other parts of the suspension system  10 . For example, certain aspects of the arrangement of the second piston ring  62  and the first sealing ring  76  may also be applied to the piston  28  of the left and right suspension assemblies  12 L,  12 R.  
         [0042]    Although this invention has been disclosed in the context of certain preferred embodiments and examples, it will be understood by those skilled in the art that the present invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses of the invention and obvious modifications and equivalents thereof. In addition, while a number of variations of the invention have been shown and described in detail, other modifications, which are within the scope of this invention, will be readily apparent to those of skill in the art based upon this disclosure. For example, it is contemplated that various combination or sub-combinations of the specific features and aspects of the embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments can be combined with or substituted for one another in order to form varying modes of the disclosed invention. Thus, it is intended that the scope of the present invention herein disclosed should not be limited by the particular disclosed embodiments described above, but should be determined only by a fair reading of the claims that follow.