Abstract:
A motor vehicle shock absorber ( 12 ) that has an additional or further spring biased fluid control valve ( 96 ) that disposed between the blow-off valve ( 46 ) and the compression chamber ( 34 ) of the shock absorber ( 12 ) and that provides enhanced damping performance characteristics during relatively low velocity movements of the piston assembly ( 24 ) in the recoil stroke direction, that is, at velocities lower than those which cause the blow-off valve ( 46 ) of the shock absorber ( 12 ) to open. The further spring biased fluid control valve ( 96 ) affords the shock absorber ( 12 ) a firmness vis-a-vis roll stability to the vehicle steering yet provides the consumer a desired “boulevard”or soft cushioned ride.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the priority of U.S. provisional application Serial No. 60/180, 968, filed Feb. 8, 2000. The specification and drawings of that provisional application are hereby incorporated herein by reference thereto. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to hydraulic shock absorbers. More particularly, the present invention relates to an improved hydraulic shock absorber that is adapted for use with motor vehicle suspension systems and that includes additional valving that enhances the dampening characteristics of the shock absorber during low velocity movement of the piston assembly in the recoil or rebound stroke or motion direction.  
           [0003]    Hydraulic shock absorbers have long been commonly used in motor vehicle suspension systems to absorb unwanted road caused vibrations that normally occur while the vehicle is being driven. Specifically, shock absorbers are generally connected between the body (the sprung mass) and the suspension (the unsprung mass) of the motor vehicle to dampen vibrations transmitted from the suspension to the body.  
           [0004]    Hydraulic shock absorbers usually include a cylindrical tube (frequently known as the inner tube), that defines a cylindrical inner cavity. A piston assembly is slidably disposed in and is reciprocally movable within the inner cavity and serves to divide the inner cavity into two working chambers: a compression chamber; and a rebound chamber, both of which are filled with hydraulic fluid. A fluid reservoir communicates, through valving, with the working chambers, and is usually annularly defined between the inner tube and an outer tube which is concentrically mounted about the inner tube.  
           [0005]    One end of the outer or reservoir tube, normally the end adjacent to the compression chamber, is closed by an end cap assembly that is usually connected to the vehicle suspension by a suitable connector. A piston rod extends through a seal assembly and end cap mounted in the other end of the inner tube. The inner end of the piston rod is connected to the piston assembly, and the outer end of the piston rod is connected to the vehicle body by a suitable connector.  
           [0006]    The piston assembly typically includes valving that permits fluid to flow across the piston assembly between the working chambers as the piston assembly moves relatively within the internal cavity, that is, relatively with respect to the inner tube. More specifically, the valving limits the flow of fluid across the piston assembly and between the compression and rebound chambers during movement of the piston assembly in a compression stroke direction or in a recoil stroke (sometimes also called the rebound or extension stroke) direction. This provides a damping force that “smoothes” or “dampens” vibrations transmitted from the suspension to the body. This damping force is, in part, determined by the velocity or speed at which the piston assembly is moved in the inner tube in response to the external forces applied to the shock absorber.  
           [0007]    Various different types of valves or valving components have been used with piston assemblies to affect the damping force characteristics of shock absorbers. When a shock absorber piston assembly moves in the recoil stroke direction, these generally include restrictors or restrictor openings, a blow-off valve and orifices or orifice slots. The restrictors are usually holes drilled in the neck of the piston assembly although they may also be drilled in the piston rod. The blow-off valve is usually spring biased closed against a valve seat. The orifices are usually a plurality of rectangular slots coined in the valve seat of the blow-off valve.  
           [0008]    During the recoil stroke of a shock absorber, the restrictors are the primary means by which fluid enters the piston assembly from the rebound chamber. Fluid then flows either through the orifice slots, or through the blow-off valve—when that valve&#39;s spring biasing force has been overcome—to the compression chamber. At low velocities of the suspension (that is, at low recoil stroke velocities of the piston assembly) the orifice slots are the primary contributors by way of the damping characteristics. At intermediate recoil stroke velocities of the suspension, it is the blow-off spring&#39;s biasing force that primarily determines the damping characteristics. At relatively high velocities, it is the restrictor openings that determine the damping characteristics. The restrictor openings do, of course, function at all velocities, but the contribution of the restrictors is significantly higher at higher velocities. The contribution of each of these valves or valving components is also dependent on the size of the orifice slots, the diameter of the restrictor openings, and the biasing force on the spring that biases the blow-off valve to a closed position.  
           [0009]    Also in the past, some “premium” shock absorbers had piston assemblies in which additional valving was utilized to provide a more “plush” feel at lower operating velocities of the suspension. In these premium shock absorbers, the blow-off valves included valve members, which were spring biased against a valve seat, and in this respect, these valve members were like the valve members used in non-premium shock absorbers. The valve members of the premium-brand shock absorbers were, however, different in that they had an internal thin, flexible disk. This disk normally assumed a flat position and, while in this position, a relatively small flow of fluid was permitted to pass through the blow-off valve member when the blow-off valve was otherwise spring biased closed. This flow through the blow-off valve disk was in addition to the flow through the orifices. Increased fluid flow, resulting from a higher piston assembly velocity, caused the flexible valve disk to assume a flexed, bent or curved position. When in its flexed position, the disk prevented this further fluid flow through the blow-off valve member. The disk assumed its flexed or closed position before the piston assembly velocity caused the blow-off valve to open against the force of its spring bias.  
         SUMMARY OF THE INVENTION  
         [0010]    In principal aspects, the improved shock absorber of the present invention includes a further valve that enhances the damping performance of the shock absorber during low velocity movement of the piston assembly in the recoil stroke direction. This novel valve includes a second spring-loaded valve member that normally blocks the flow of fluid past or across the piston assembly downstream, so to speak, from the blow-off valve, that is, after the fluid has flowed through the orifices, and/or through the valve disk that has been used in some premium shock absorbers. This further valve provides an initial firmness to the suspension movement before the blow-off valve opens, and more specifically, offers a firmness vis-a-vis roll stability to the vehicle steering yet provides the desired “boulevard” or soft ride that is particularly desired by consumers.  
           [0011]    An object of the present invention is to provide an improved shock absorber, as described, where the shock absorber is adapted for connection between the body of a motor vehicle and the suspension of the motor vehicle and serves to dampen vibrations transmitted from the suspension to the body while the vehicle is being driven.  
           [0012]    Another object of the present invention is to provide an improved shock absorber, as described, that includes further valving, as described, and that affords advantageous firmness regarding vehicle steering roll stability, together with a boulevard or soft ride, during relatively low velocity movement of the piston assembly in the recoil stroke direction. A related object of the present invention is to provide an improved shock absorber, as described, where the shock absorber includes: an inner tube having a first fluid filled cylindrical internal or inner cavity, that has compression and extension ends and that has a longitudinal central axis extending between the compression and extension ends; a piston assembly that has a longitudinal central axis co-axial with the longitudinal central axis of the inner tube, that has a second internal chamber and a third chamber, that is disposed in and reciprocally moveable, within the internal first cavity, selectively in a recoil stroke direction and in a compression stroke direction, and that serves to divide the internal cavity into a compression and rebound chambers; a restrictor opening for permitting restrictive flow of fluid between the rebound chamber and the second chamber of the piston assembly during movement of the piston assembly in the recoil stroke direction; an orifice for permitting a first predetermined volume of fluid to flow between the second chamber and the third chamber during relatively low velocity movement of the piston assembly in the recoil stroke direction; a blow-off valve that is in the piston assembly between the second chamber and the third chamber, that when opened, permits a relatively large volume of fluid, as compared to the first predetermined volume of fluid flow, to flow from the second chamber to the third chamber, and that is normally biased closed with a first predetermined biasing force; piston rod that has a longitudinal central axis, co-axial with the longitudinal central axis of the inner tube, that has an inner end connected with the piston assembly, and that has an outer end extending out of the extension end of the inner tube; and a further or second valve that is in the piston assembly between the blow-off valve and the compression chamber, that when open, permits a relatively large volume of fluid, as compared to the first predetermined volume of fluid, to flow from the third chamber to the compression chamber, and that is normally biased to a closed position with a second predetermined biasing force, which is less than the first predetermined biasing force, so that the second valve provides an initial firmness to the shock absorber damping before the blow-off valve opens and affords the shock absorber a firmness in regard to the roll stability to the vehicle steering yet providing a relatively soft cushioned or boulevard ride for the vehicle.  
           [0013]    A still further object of the present invention is to provide an improved shock absorber, as described, where a first valve seat is defined adjacent to the end of the piston assembly adjacent to the compression chamber, where the second valve includes a second valve member, and where a first coil compression spring biases the valve member against the first valve seat to close the second valve, where the first valve seat is annular, where the first coil compression spring is disposed without the third chamber, where the longitudinal central axes of the first coil compression spring and the inner tube are coaxial, and where the first valve seat is annularly disposed about the longitudinal axis of the piston assembly.  
           [0014]    These and other objects, advantages and benefits of the present invention will become more apparent from the following description of the preferred embodiment of the invention taken in conjunction with the following drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    In the drawings:  
         [0016]    [0016]FIG. 1 is a partial, vertical cross-sectional view of an improved shock absorber of the present invention, taken along its central longitudinal axis;  
         [0017]    [0017]FIG. 2 is a vertical cross-sectional view of the piston assembly of the present invention, taken along its central longitudinal axis, where the blow-off valve and second valve are shown in their closed positions; and  
         [0018]    [0018]FIG. 3 is vertical cross-sectional view, similar to that shown in FIG. 2, of the piston assembly of the present invention where the blow-off valve and second valve are shown in their open positions. 
     
    
       [0019]    In the following description of the preferred embodiment of the present invention, the terms “upper” and “lower” and “inner” and “outer” are used, for convenient reference, to describe parts of the shock absorber as those parts appear in the FIGURES, their usage is not intended to otherwise limit the scope of the invention or how the shock absorber might be oriented when in actual use.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    A shock absorber  12 , which includes the present invention, is generally shown in FIG. 1. The shock absorber  12  is of conventional design and construction except as noted below with respect to the additional or second valving. More specifically, the shock absorber includes a cylindrical inner tube  14  that defines a cylindrical internal or inner cavity  16 . An outer tube  18  is positioned concentrically about and radially outwardly from the inner tube  14  so that their central longitudinal axes are coaxial. The annular space between the tubes  14  and  16  defines a reservoir  22  for the hydraulic fluid or oil used with the shock absorber  12 .  
         [0021]    A piston assembly  24 , which will be described in more detail below, is disposed for reciprocal movement within the inner cavity  16 . A piston rod  26  is connected at its lower or inner end  28  with the piston assembly  24  in a conventional manner. The outer or upper end  30  of the piston rod  26  extends without the inner cavity  14  in a conventional manner. The upper end  30  of the piston rod has a connector, not shown, which enables the shock absorber  12  to be connected with a vehicle body, not shown, in a conventional manner. The central longitudinal axes of the internal cavity  16 , the tubes  14  and  18 , piston assembly  24 , and piston rod  26  are coaxial.  
         [0022]    The piston assembly  24  divides the internal cavity  16  into: an extension, or sometime called rebound chamber  32 , which is adjacent the upper end of the internal cavity, as shown in FIG. 1; and a compression chamber  34 , which is adjacent the lower end of the inner cavity  16 , as shown in FIG. 1.  
         [0023]    The upper end, as shown in FIG. 1, of the shock absorber  12  is closed in a conventional manner. More specifically, the upper ends, again as shown in FIG. 1, of the tubes  14  and  16  are closed by an end cap  36 . As is conventional, the end cap  36  may include valving, not shown, and passages, including the passage  38 , for permitting fluid communication between the reservoir  22  and the extension chamber  32  in a conventional manner. A piston rod seal assembly  42  forms a seal about the outer peripheral surface of the piston rod  26  as it, and the piston assembly  24 , reciprocally move within the inner cavity  16 . As is also conventional, a cover member  44  encloses and protects the seal assembly  42  and end cap  36 .  
         [0024]    The lower end  46  of the compression chamber  34  and reservoir  22  are similarly closed in a conventional manner. More specifically, a compression head  46  is mounted within and closes the lower end of the inner tube  14 . Conventional valving, including a replenishing valve, not shown, and a compression valve, shown at  48 , are mounted in the compression head  46  so as to permit the fluid to flow between the reservoir  22  and the compression chamber  34 .  
         [0025]    An end cap  52  is mounted on the lower end, as shown in FIG. 1, of the outer tube  18 , and with the head  46 , closes both the lower end of the compression chamber  34 , and the lower end of the reservoir  22  in a conventional manner. Additionally, a connector, not shown, may be mounted on the outer surface of the end cap  52  for connecting the lower end of the shock absorber with the vehicle suspension, also not shown.  
         [0026]    Referring now to FIGS. 2 and 3, the piston assembly  24  includes a generally cylindrical piston body  54  that has an upper portion  56  and a lower portion  58 . The lower end  28  of the piston rod  26  is connected with the upper portion  56  of the piston body in a conventional manner.  
         [0027]    The upper portion  56  also includes a bore or internal chamber  62 . The lower portion  58  of the piston body  54  likewise includes a lower counterbore or chamber  64 . The upper chamber  62  has a relatively smaller diameter, as compared with the average diameter of the stepped diameter portions of the lower chamber  64 . The largest diameter portion of the chamber  64  is adjacent the lower end of the piston body  54  as shown in FIGS. 2 and 3.  
         [0028]    A neck passage  68  interconnects the upper and lower chambers  62  and  64 . The central longitudinal axes of the chambers  62  and  64  and the neck passage  68  are coaxial with the longitudinal axes of the piston body  54  and the piston assembly  24 . The chambers  62  and  64 , and the neck passage  68  are symmetrical about their longitudinal axes.  
         [0029]    A valve assembly  72  is mounted about the upper portion  56  of the piston body  54 . The assembly  72  is of conventional design and construction and is used to control the flow of fluid from the compression chamber  34  to the extension chamber  32  when the piston assembly  24  moves in its compression stroke direction. More specifically, the assembly  72  includes an O-ring  74 , an annular ring  76  and a support ring member  78 . The lower end of a coil compression spring  82  abuts against and biases the support member  78 , together with the O-ring  74  and ring  76 , against an external shoulder  84 , which is defined between the upper and lower portions  56  and  58  of the piston body  54 . The upper end of the coil compression spring  82  abuts an annular member  86 , which is disposed about the piston rod  26  adjacent the upper end of the body portion  56 .  
         [0030]    A plurality of restrictor openings  88 , one of which is shown in FIG. 1, permits fluid to flow from the extension chamber  32  into the upper chamber  62 , and more particularly, the portion of the upper chamber  62  below the lower end  28  of the piston rod  26 . As noted above, the upper chamber  62  is in fluid communication with the lower chamber  64  through the neck passage  68 , which is defined by a central wall portion  92  of the piston body  54 . The lower facing surface of this central wall portion  92  defines a valve seat  94 . A spring biased blow-off valve assembly  96  abuts the valve seat  94 .  
         [0031]    As is conventional, however, a plurality of orifices  98  (two of which are shown in FIGS. 2 and 3) are coined in the valve seat  94 . The orifices permit a relatively small, predetermined volume of fluid to flow from the upper chamber  62  to the lower chamber  64 , particularly when the piston assembly is moved in its recoil stroke direction, even though the blow-off valve assembly  96  is otherwise closed.  
         [0032]    The blow-off valve assembly  96  may be of any conventional construction design and includes a valve member  102 . The assembly  96 , as shown in FIGS. 2 and 3, is like the blow-off valve assembly that has been described above as having been used in “premium” shock absorbers. The blow-off valve assembly  96  could, however, be like those assemblies, which were used in the non-premium shock absorbers, where the valve member  102  is a solid and does not permit any fluid to flow through the valve member.  
         [0033]    More particularly, a compression spring  104  biases the valve member  102  against the valve seat  94 . The lower end of the spring  104  abuts against a closure member  106  that is mounted in the lower end of the lower portion  58  of the piston body  54  and that defines and closes the lower end of the lower chamber  64 . A spring clip member  108  is mounted in the upper surface of the closure member  106  within the coils of the spring  104 . The upper end of the spring  104 , as shown in FIGS. 2 and 3, is abutted against the lower facing surface of the valve member  102 .  
         [0034]    The valve member  102  includes an upper part  112 , which has a central circular opening  114  in its upper facing surface. A lower part  116  of the member  102  is disposed and mounted within the side edges of the upper part  112  and has a central circular opening  118  in its lower facing surface. A gap or space  122  is defined between the central portions of the parts  112  and  116 . A relatively thin, flexible disk  124  is secured within the space  122  by having its peripheral edge clamped between the parts  112  and  116 . The disk has a plurality of apertures  126  adjacent its peripheral edge. The unclamped central portion of the disk  124  will deflect under predetermined fluid pressure from its normal, flat disposition. When it is in its normal flat position, as shown in FIG. 2, the disk  124  permits a predetermined volume of fluid to flow through the opening  114  into the space  122 , through the apertures  126  and out of the space  122  through the opening  118 . When the volume of flow exceeds a predetermined amount—due to increased piston assembly velocity—the disk  124  will flex or bend and will be deflected downwardly so as to block the fluid flow by reason of the central portion of the disk abutting the upper facing surface of the part  116  as shown in FIG. 3.  
         [0035]    As explained above, the disk  124  will deflect—and block fluid flow through the valve member  102 —as a result of the velocity of the piston assembly  24  in the recoil direction exceeding a predetermined speed. Thereafter, a further increase in the velocity will overcome the biasing force of the spring  104  so that the valve member  102  will move away from its abutment against the valve seat  94 . This opening of the blow-off valve assembly  96  permits a much larger volume of fluid flow from the chamber  62  to the chamber  64  than the predetermined volumes of fluid flow permitted to flow through the orifices  98  and/or by the disk  124 .  
         [0036]    As also noted above, the foregoing description of the valving and fluid flow through the piston assembly  24 , when the assembly  24  is moved relatively with respect to the inner tube  14  in a recoil stroke direction, is conventional. In this regard, any of a variety of other constructions and designs of the piston assembly and/or of its component parts—other than those shown in FIGS. 2 and 3—may be used as will be well recognized by those working in this art.  
         [0037]    A principal novel feature of the piston assembly  24  of the present invention is the inclusion of a second valve  132  downstream from the blow-off valve assembly  96 , that is, downstream considering the fluid flow during recoil stroke motion of the piston assembly. The valve  132  includes an annular, relatively stiff (non-flexible) disk  134 , which serves as a valve member. The annular disk  134  has an outer diameter sufficient to overlay and thus block fluid flow through the plurality of the openings  136  in the closure member  106 . The openings  136  define valve seats about their peripheries, are spaced radially outwardly from the central longitudinal axis of the piston body  54  from the spring  104  and are of a size such that all of the fluid flowing into the lower chamber  64  may readily flow from the lower chamber  64  into the compression chamber  34  when the valve  132  is open.  
         [0038]    A coil compression spring  138  biases the annular disk  134  against the lower facing surface (as shown in FIGS. 2 and 3) of the closure member  106  with a force that is selected to be less than the force the spring  104  exerts on the valve member  102 . The longitudinal central axes of the springs  104  and  138  are coaxial with the central longitudinal axis of the piston body  54 . The lower end of the spring  138  abuts a spring retention  142  member mounted at the lower end of a cylindrical guide  144 . The central opening of the annular disk  134  fits about the guide  144 , which serves to guide the movement of the disk  134 , up and down, toward and away from its abutment against the member  106 .  
         [0039]    As noted above, fluid flow through the piston body  54  from the extension chamber  32  to the compression chamber  34 , as the piston assembly  24  moves relatively in the recoil stroke direction, occurs in a conventional manner, except for the fluid flow control exerted by the valve  132 . Specifically, fluid flows into the upper chamber  62  through the restrictor openings  88  and through the orifices  94  into the lower chamber  64  as long as the velocity of the piston assembly  24 , in the recoil stroke direction, remains relatively low, as for example, below 0.20 FPS. Also if desired, the valve member  102  may include the disk  124  which permits additional flow to pass through the valve member  102  providing a softer ride. The disk  124  will close when the velocity of the piston assembly increases (for example, 0.50 FPS or above) such that the pressure resulting on the disk, from the flow of fluid, causes the disk to deflect and block further flow. Thereafter, if the velocity of the piston assembly  24  increases further (as, for example, above 0.50 FPS), an increased volume of flow through the piston assembly is permitted by reason of the opening of the blow-off valve assembly  96  against the bias of the spring  104 .  
         [0040]    The addition of the valve  132  to the piston assembly  24  adds an initial firmness to the suspension movement before the blow-off valve  102  opens. More specifically, this valve  132  affords a firmness vis-a-vis roll stability and eliminates “float” to the vehicle steering while also providing the desired boulevard or soft ride that is particularly desired by some of the consumers.  
         [0041]    The force exerted by the spring  138  is less than the force exerted by the spring  104  so that the valve  132  opens fully before the blow-off valve assembly  96  opens. In other words, the valve  132  will permit fluid to flow from the chamber  64  to the compression chamber  34  during movement of the piston assembly in the recoil stroke direction (at a velocity of, for example, above 0.20 FPS) before the blow-off valve assembly  96  opens.  
         [0042]    In conclusion, the present invention, and the manner and process of making and using it, has been described in its preferred and best form in such full, clear, concise and exact terms so as to enable any person skilled in the shock absorber art to make and use the same. It is, however, to be understood that the present disclosure of the preferred embodiment has been made only by way of example and numerous changes in the details of construction and design, and in the combination and arrangement of the parts may be utilized without departing from the spirit or the scope of the invention.