Patent Publication Number: US-2020300330-A1

Title: Methods and apparatus for position sensitive suspension damping

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and is a Continuation of the co-pending patent application Ser. No. 14/506,420, Attorney Docket Number FOX-0055USD1 entitled “METHODS AND APPARATUS FOR POSITION SENSITIVE SUSPENSION DAMPING,” with filing date Oct. 3, 2014, by Everet Owen Ericksen et al., which is incorporated herein, in its entirety, by reference. 
     The application with Ser. No. 14/506,420 claims priority to and is a Divisional of the patent application Ser. No. 13/485,401, now Abandoned, Attorney Docket Number FOXF/0055US, entitled “METHODS AND APPARATUS FOR POSITION SENSITIVE SUSPENSION DAMPING”, with filing date May 31, 2012, by Everet Owen Ericksen et al., which is incorporated herein, in its entirety, by reference. 
     The application with Ser. No. 13/485,401 claims priority to the patent application, Ser. No. 61/491,858, Attorney Docket Number FOXF/0055USL entitled “METHODS AND APPARATUS FOR POSITION SENSITIVE SUSPENSION DAMPING”, with filing date May 31, 2011, by Everet Owen Ericksen et al., which is incorporated herein, in its entirety, by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates generally to vehicle suspensions and, more specifically, to variable damping rates in vehicle shock absorbers and forks. 
     Description of the Related Art 
     Vehicle suspension systems typically include a spring component or components and a damping component or components. Often, mechanical springs, like helical springs, are used with some type of viscous fluid-based damping mechanism, the spring and damper being mounted functionally in parallel. In some instances a spring may comprise pressurized gas and features of the damper or spring are user-adjustable, such as by adjusting the air pressure in a gas spring. A damper may be constructed by placing a damping piston in a fluid-filled cylinder (e.g., liquid such as oil). As the damping piston is moved in the cylinder, fluid is compressed and passes from one side of the piston to the other side. Often, the piston includes vents there-through which may be covered by shim stacks to provide for different operational characteristics in compression or extension. 
     Conventional damping components provide a constant damping rate during compression or extension through the entire length of the stroke. As the suspension component nears full compression or full extension, the damping piston can “bottom out” against the end of the damping cylinder. Allowing the damping components to “bottom out” may cause the components to deform or break inside the damping cylinder. 
     As the foregoing illustrates, what is needed in the art are improved techniques for varying the damping rate including to lessen the risk of the suspension “bottoming out.” 
     SUMMARY OF THE INVENTION 
     One embodiment of the present disclosure sets forth a vehicle suspension damper that includes a cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, where an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and where the piston borders each of the compression chamber and the rebound chamber. The vehicle suspension damper further includes a damping liquid within the cylinder and a bypass fluid flow path connecting the compression chamber and the rebound chamber, which forms a fluid path extending between an inner diameter of the piston and a side surface of the piston directly bordering one of the compression or rebound chambers. 
     Another embodiment of the present disclosure sets forth a vehicle suspension damper that includes a cylinder and a damping liquid within the cylinder, the cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, where an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and where the piston borders each of the compression chamber and the rebound chamber. The piston includes multiple flow paths that enable the damping liquid to flow from the compression chamber to the rebound chamber. The multiple flow paths include a damping flow path that comprises a first fluid path extending between a first side surface of the piston directly bordering the compression chamber and a second side surface of the piston directly bordering the rebound chamber and a bypass flow path that comprises a fluid path extending between an inner diameter of the piston and one of the first side surface of the piston or the second side surface of the piston. 
     Yet another embodiment of the present disclosure sets forth a vehicle suspension system that includes a first damper unit. The first damper unit includes a cylinder having a compression chamber and a rebound chamber and containing at least a portion of a piston rod having a piston attached thereto, wherein an outer diameter of the piston engages an inner diameter of the cylinder and is relatively movable therein, and wherein the piston borders each of the compression chamber and the rebound chamber. The first damper unit further includes a damping liquid within the cylinder and a bypass fluid flow path connecting the compression chamber and the rebound chamber, which forms a fluid path extending between an inner diameter of the piston and a side surface of the piston directly bordering one of the compression or rebound chambers. 
     One advantage of some disclosed embodiments is that multiple bypass flow paths enable the vehicle suspension damper to be setup such that the damping rate changes (i.e., is increased) as the damper nears full compression. The increased damping rate, caused by fluid being forced through fewer flow paths formed by the multiple bypass flow paths causes the force opposing further compression of the damper to increase, thereby decreasing the chance that the damper “bottoms out.” 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features can be understood in detail, a more particular description, briefly summarized above, may be had by reference to certain example embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments and are therefore not to be considered limiting the scope of the claims, which may admit to other equally effective embodiments. 
         FIG. 1  shows an asymmetric bicycle fork having a damping leg and a spring leg, according to one example embodiment; 
         FIGS. 2A-2C  show sectional side elevation views of a needle-type monotube damping unit in different stages of compression, according to one example embodiment; 
         FIG. 3  shows a detailed view of the needle and bore at the intermediate position proximate to the “bottom-out” zone, according to one example embodiment; 
         FIGS. 4A and 4B  illustrate the castellated or slotted valve, according to one example embodiment; 
         FIGS. 5A and 5B  illustrate a damping unit having a “piggy back” reservoir, according to one example embodiment; 
         FIG. 6  illustrates a half section, orthographic view of a damping unit, according to another example embodiment; 
         FIGS. 7A through 7E  illustrate the piston of  FIG. 6 , according to one example embodiment; and 
         FIGS. 8A and 8B  illustrate the shaft of  FIG. 6 , according to one example embodiment. 
     
    
    
     For clarity, identical reference numbers have been used, where applicable, to designate identical elements that are common between figures. It is contemplated that features of one example embodiment may be incorporated in other example embodiments without further recitation. 
     DETAILED DESCRIPTION 
     Integrated damper/spring vehicle shock absorbers often include a damper body surrounded by or used in conjunction with a mechanical spring or constructed in conjunction with an air spring or both. The damper often consists of a piston and shaft telescopically mounted in a fluid filled cylinder. The damping fluid (i.e., damping liquid) or damping liquid may be, for example, hydraulic oil. A mechanical spring may be a helically wound spring that surrounds or is mounted in parallel with the damper body. Vehicle suspension systems typically include one or more dampers as well as one or more springs mounted to one or more vehicle axles. As used herein, the terms “down”, “up”, “downward”, “upward”, “lower”, “upper”, and other directional references are relative and are used for reference only. 
       FIG. 1  shows an asymmetric bicycle fork  100  having a damping leg and a spring leg, according to one example embodiment. The damping leg includes an upper tube  105  mounted in telescopic engagement with a lower tube  110  and having fluid damping components therein. The spring leg includes an upper tube  106  mounted in telescopic engagement with a lower tube  111  and having spring components therein. The upper legs  105 ,  106  may be held centralized within the lower legs  110 ,  111  by an annular bushing  108 . The fork  100  may be included as a component of a bicycle such as a mountain bicycle or an off-road vehicle such as an off-road motorcycle. In some embodiments, the fork  100  may be an “upside down” or Motocross-style motorcycle fork. 
     In one embodiment, the damping components inside the damping leg include an internal piston  166  disposed at an upper end of a damper shaft  136  and fixed relative thereto. The internal piston  166  is mounted in telescopic engagement with a cartridge tube  128  connected to a top cap  180  fixed at one end of the upper tube  105 . The interior volume of the damping leg may be filled with a damping liquid such as hydraulic oil. The piston  166  may include shim stacks (i.e., valve members) that allow a damping liquid to flow through vented paths in the piston  166  when the upper tube  105  is moved relative to the lower tube  110 . A compression chamber is formed on one side of the piston  166  and a rebound chamber is formed on the other side of the piston  166 . The pressure built up in either the compression chamber or the rebound chamber during a compression stroke or a rebound stroke provides a damping force that opposes the motion of the fork  100 . 
     The spring components inside the spring leg include a helically wound spring  115  contained within the upper tube  106  and axially restrained between top cap  181  and a flange  165 . The flange  165  is disposed at an upper end of the riser tube  135  and fixed thereto. The lower end of the riser tube  135  is connected to the lower tube  111  in the spring leg and fixed relative thereto. A valve plate  155  is positioned within the upper leg tube  106  and axially fixed thereto such that the plate  155  moves with the upper tube  106 . The valve plate  155  is annular in configuration, surrounds an exterior surface of the riser tube  135 , and is axially moveable in relation thereto. The valve plate  155  is sealed against an interior surface of the upper tube  106  and an exterior surface of the riser tube  135 . A substantially incompressible lubricant (e.g., oil) may be contained within a portion of the lower tube  111  filling a portion of the volume within the lower tube  111  below the valve plate  155 . The remainder of the volume in the lower tube  111  may be filled with gas at atmospheric pressure. 
     During compression of fork  100 , the gas in the interior volume of the lower tube  111  is compressed between the valve plate  155  and the upper surface of the lubricant as the upper tube  106  telescopically extends into the lower tube  111 . The helically wound spring  115  is compressed between the top cap  181  and the flange  165 , fixed relative to the lower tube  111 . The volume of the gas in the lower tube  111  decreases in a nonlinear fashion as the valve plate  155 , fixed relative to the upper tube  106 , moves into the lower tube  111 . As the volume of the gas gets small, a rapid build-up in pressure occurs that opposes further travel of the fork  100 . The high pressure gas greatly augments the spring force of spring  115  proximate to the “bottom-out” position where the fork  100  is fully compressed. The level of the incompressible lubricant may be set to a point in the lower tube  111  such that the distance between the valve plate  155  and the level of the oil is substantially equal to a maximum desired travel of the fork  100 . 
       FIGS. 2A-2C  show sectional side elevation views of a needle-type monotube damping unit  200  in different stages of compression, according to one example embodiment. In one embodiment, the components included in damping unit  200  may be implemented as one half of fork  100 . In another embodiment, damping unit  200  may be implemented as a portion of a shock absorber that includes a helically-wound, mechanical spring mounted substantially coaxially with the damping unit  200 . In yet other embodiments, damping unit  200  may be implemented as a component of a vehicle suspension system where a spring component is mounted substantially in parallel with the damping unit  200 . 
     As shown in  FIG. 2A , the damping unit  200  is positioned in a substantially fully extended position. The damping unit  200  includes a cylinder  202 , a shaft  205 , and a piston  266  fixed on one end of the shaft  205  and mounted telescopically within the cylinder  202 . The outer diameter of piston  266  engages the inner diameter of cylinder  202 . In one embodiment, the damping liquid (e.g., hydraulic oil or other viscous damping fluid) meters from one side to the other side of the piston  266  by passing through vented paths formed in the piston  266 . Piston  266  may include shims (or shim stacks) to partially obstruct the vented paths in each direction (i.e., compression or rebound). By selecting shims having certain desired stiffness characteristics, the damping effects can be increased or decreased and damping rates can be different between the compression and rebound strokes of the piston  266 . The damping unit  200  includes an annular floating piston  275  mounted substantially co-axially around a needle  201  and axially movable relative thereto. The needle  201  is fixed on one end of the cylinder  202  opposite the shaft  205 . A volume of gas is formed between the floating piston  275  and the end of cylinder  202 . The gas is compressed to compensate for motion of shaft  205  into the cylinder  202 , which displaces a volume of damping liquid equal to the additional volume of the shaft  205  entering the cylinder  202 . 
     During compression, shaft  205  moves into the cylinder  202 , causing the damping liquid to flow from one side of the piston  266  to the other side of the piston  266  within cylinder  202 .  FIG. 2B  shows the needle  201  and shaft  205  at an intermediate position as the damping unit  200  has just reached the “bottom-out” zone. In order to prevent the damping components from “bottoming out”, potentially damaging said components, the damping force resisting further compression of the damping unit  200  is substantially increased within the “bottom-out” zone. The needle  201  (i.e., a valve member) compresses fluid in a bore  235 , described in more detail below in conjunction with  FIG. 3 , thereby drastically increasing the damping force opposing further compression of the damping unit  200 . Fluid passes out of the bore around the needle through a valve that is restricted significantly more than the vented paths through piston  266 . As shown in  FIG. 2C , the damping rate is increased substantially within the “bottom-out” zone until the damping unit  200  reaches a position where the damping unit  200  is substantially fully compressed. 
       FIG. 3  shows a detailed view of the needle  201  and bore  235  at the intermediate position proximate to the “bottom-out” zone, according to one example embodiment. As shown in  FIG. 3 , the needle  201  is surrounded by a check valve  220  contained within a nut  210  fixed on the end of shaft  205 . During compression within the “bottom out” zone, the valve  220  is moved, by fluid pressure within the bore  235  and flow of fluid out of bore  235 , upward against seat  225  of nut  210  and the bulk of escaping fluid must flow through the annular clearance  240  that dictates a rate at which the needle  201  may further progress into bore  235 , thereby substantially increasing the damping rate of the damping unit  200  proximate to the “bottom-out” zone. The amount of annular clearance  240  between the exterior surface of the needle  201  and the interior surface of the valve  220  determines the additional damping rate within the “bottom-out” zone caused by the needle  201  entering the bore  235 . In one embodiment, the needle  201  is tapered to allow easier entrance of the needle  201  into the bore  235  through valve  220 . 
     During rebound within the “bottom out” zone, fluid pressure in the bore  235  drops as the needle  201  is retracted and fluid flows into the bore  235 , causing the valve  220  to move toward a valve retainer clip  215  that secures the valve  220  within the nut  210 . In one embodiment, the valve is castellated or slotted on the face of the valve  220  adjacent to the retainer clip  215  to prevent sealing the valve against the retainer clip  215 , thereby forcing all fluid to flow back into the bore  235  via the annular clearance  240 . Instead, the castellation or slot allows ample fluid flow into the bore  235  during the rebound stroke to avoid increasing the damping rate during rebound within the “bottom out” zone. The valve  220  is radially retained within the nut  210 , which has a recess having a radial clearance between the interior surface of the recess and the exterior surface of the valve  220  that allows for eccentricity of the needle  201  relative to the shaft  205  without causing interference that could deform the components of damping unit  200 . 
       FIGS. 4A and 4B  illustrate the castellated or slotted valve  220 , according to one example embodiment. As shown in  FIGS. 4A and 4B , the valve  220  is a washer or bushing having an interior diameter sized to have an annular clearance  240  between the interior surface of the valve  220  and the exterior surface of the needle  201  when the needle  201  passes through the valve  220 . Different clearances  240  may be achieved by adjusting the interior diameter of the valve  220  in comparison to the diameter of the needle  201 , which causes a corresponding change in the damping rate proximate to the “bottom-out” zone. A spiral face groove is machined into one side of the valve  220  to create the castellation or slot  230 . It will be appreciated that the geometry of the slot  230  may be different in alternative embodiments and is not limited to the spiral design illustrated in  FIGS. 4A and 4B . For example, the slot  230  may be straight (i.e., rectangular) instead of spiral, or the edges of the slot  230  may not be perpendicular to the face of the valve  220 . In other words, the geometry of the slot  230  creates empty space between the surface of the retainer clip  215  and the surface of the valve  220  such that fluid may flow between the two surfaces. 
     When assembled, the valve  200  is oriented such that the side with the slot  230  is proximate to the upper face of the valve retainer clip  215 , thereby preventing the surface of the valve  220  from creating a seal against the retainer clip  215 . The slot  230  is configured to allow fluid to flow from cylinder  202  to bore  235  around the exterior surface of the valve  220 , which has a larger clearance than the annular clearance  240  between the valve  220  and the needle  201 . In one embodiment, two or more slots  230  may be machined in the face of the valve  220 . In some embodiments, the valve  220  is constructed from high-strength yellow brass (i.e., a manganese bronze alloy) that has good characteristics enabling low friction between the valve  220  and the needle  201 . In alternate embodiments, the valve  220  may be constructed from other materials having suitable characteristics of strength or coefficients of friction. 
       FIGS. 5A and 5B  illustrate a damping unit  300  having a “piggy back” reservoir  350 , according to another example embodiment. As shown in  FIG. 5A , damping unit  300 , shown fully extended, includes a cylinder  302  with a shaft  305  and a piston  366  fixed on one end of the shaft  305  and mounted telescopically within the cylinder  302 . Damping unit  300  also includes a needle  301  configured to enter a bore  335  in shaft  305 . However, unlike damping unit  200 , damping unit  300  does not include an annular floating piston mounted substantially co-axially around the needle  301  and axially movable relative thereto. Instead, the piggy back reservoir  350  includes a floating piston  375  configured to perform a similar function to that of floating piston  275 . A volume of gas is formed between the floating piston  375  and one end of the piggy back reservoir  350 . The gas is compressed to compensate for motion of shaft  305  into the cylinder  302 . Excess damping liquid may enter or exit cylinder  302  from the piggy back reservoir  350  as the volume of fluid changes due to ingress or egress of shaft  305  from the cylinder  302 . In  FIG. 5B , the damping unit  300  is shown proximate to the “bottom out” zone where needle  301  has entered bore  335 . 
       FIG. 6  illustrates a half section, orthographic view of a damping unit  400 , according to another example embodiment. As shown in  FIG. 6 , damping unit  400  includes a piston  466  fixed on one end of a shaft  405  and mounted telescopically within a cylinder  402 . The shaft  405  includes a bore  435  that enables ingress of a needle (e.g.,  201 ,  301 ) to change the damping characteristics of the damping unit  400  proximate to the “bottom out” zone. The piston assembly includes a top shim stack  481  and a bottom shim stack  482  attached to the top face and bottom face of the piston  466 , respectively, which enable different damping resistances to be set during the compression stroke and the rebound stroke. During operation, where a needle has not entered bore  435 , the damping liquid flows from one side of the piston  466  to the other side through multiple flow paths  451 ,  452 , and  453 . In compression, a first flow path  451  (i.e., a damping flow path) allows the damping liquid to flow from an upper portion of the cylinder  402  through vented paths in the piston  466  and into a lower portion of the cylinder  402 , forcing the bottom shim stack  482  away from the bottom face of the piston  466 . A second flow path  452  (i.e., a bypass flow path) allows the damping liquid to flow from an upper portion of the cylinder  402  through the bore  435  and shaft ports  440  in shaft  405  and into additional vented paths in the piston  466  through the bottom shim stack  482  and into the lower portion of the cylinder  402 . In rebound, a third flow path  453  (i.e., a rebound flow path, not shown in  FIG. 6 ) allows the damping liquid to flow from a lower portion of the cylinder  402 , through different vented paths in the piston  466 , through the top shim stack  481 , and into an upper portion of the cylinder  402 . In some embodiments, the first flow path  451  and the second flow path  452  may be associated with separate and distinct shim stacks. For example, the bottom shim stack  482  may be replaced by two shim stacks configured in a clover pattern and arranged such that a first shim stack covers the vented paths in the piston  466  corresponding to the first flow path  451  and a second shim stack covers the additional vented paths in the piston  466  corresponding to the second flow path  452 . 
     When a needle just enters bore  435 , the needle impedes the damping liquid in the upper portion of the cylinder  402  from flowing through the second flow path  452  due to the “plugging” effect of the needle blocking the entrance to the bore  435 . However, the damping liquid may continue to pass through the piston  466  through the first flow path  451 . In addition, some damping liquid may continue to flow out of ports  440  from bore  435  as the needle continues ingress into bore  435  and decreases the fluid volume inside the bore  435 . It will be appreciated that the damping rate will increase as the needle blocks the second flow path  452 , thereby forcing substantially all damping liquid in the upper portion of the cylinder  402  to move through piston  466  via the first flow path  451 . At some point during ingress of the needle, the full diameter of the needle is adjacent to the shaft ports  440 , substantially blocking additional damping liquid from leaving bore  435  through the shaft ports  440 . Again, the damping rate will increase as the needle blocks the shaft ports  440  and fluid pressure rapidly builds up within bore  435  and acts on the needle to oppose any further compression of the damping unit  400 . 
       FIGS. 7A through 7E  illustrate the piston  466  of  FIG. 6 , according to one example embodiment. As shown in  FIGS. 7A and 7B , the piston  466  includes two vented paths (i.e.,  421 ,  422 ) that allow damping liquid to flow from the upper portion of the cylinder  402  to the lower portion of the cylinder  402  via the first flow path  451  (i.e., bypassing the top shim stack and entering the piston  466  proximate to the inner surface of cylinder  402 ). The piston  466  also includes two additional vented paths (i.e.,  423 ,  424 ) that allow damping liquid to flow from the upper portion of the cylinder  402  to the lower portion of the cylinder  402  via the second flow path  452  (i.e., through the bore  435  and shaft ports  440 ). The additional vented paths are connected to the bore  435  via channels  425  that fluidly couple the additional vented paths to the shaft ports  440  in shaft  405  through a surface on the inner diameter of the piston  466 . The four vented paths described above (i.e.,  421 - 424 ) allow damping liquid to flow from an upper portion of the cylinder  402  to a lower portion of the cylinder  402  during a compression stroke. In rebound, yet another set of four vented paths (i.e.,  426 ,  427 ,  428 ,  429 ) allow damping liquid to flow from the lower portion of the cylinder  402  to the upper portion of the cylinder  402  via the third flow path  453  (i.e., bypassing the bottom shim stack  482  and passing into the upper portion of the cylinder  402  through the top shim stack  481 ).  FIG. 7C  shows a side view of the piston  466  of  FIGS. 7A and 7B .  FIG. 7D  shows a cross section of the piston  466  showing the inner diameter that is fit over shaft  405  as well as one channel  425  connected to one of the additional vented paths in the piston corresponding to the first second flow path  452 .  FIG. 7E  shows a cross section of the piston  466  showing vented paths  423  and  424 . 
       FIGS. 8A and 8B  illustrate the shaft  405  of  FIG. 6 , according to one example embodiment. As shown in  FIGS. 8A and 8B , the shaft  405  includes a bore  435  formed (e.g., drilled, milled, etc.) into a top portion of the shaft. In one embodiment, the top portion of the shaft may have a smaller diameter than the body of the shaft  405 , forming a seat a particular distance from one end of the shaft  405 . The piston assembly including the piston  466  and the shim stacks may be mounted over the top portion of the shaft  405  and secured with a nut threaded onto the end of the shaft  405 . In alternative embodiments, the nut may be press fit onto the shaft  405  or secured in any other technically feasible manner. 
     Shaft ports  440  may be formed through an outer face of the top portion of the shaft  405  proximate a surface on the inner diameter of the piston  466  when mounted on the shaft  405 . The shaft ports  440  fluidly couple the bore  435  in the shaft  405  with the additional vented paths (i.e.,  423 ,  424 ) in the piston  466  such that fluid may flow through the bore  435  via the second flow path  452 . In other words, the second flow path  452  enables additional fluid to flow through the bottom shim stacks  482  when a needle is not blocking the bore  435 . 
     It should be noted that any of the features disclosed herein may be used alone or in combination. While the foregoing is directed to embodiments of the present disclosure, other and further embodiments may be implemented without departing from the scope of the disclosure, the scope thereof being determined by the claims that follow.