Abstract:
A gas spring suspension system that adjusts the spring rate as the travel is adjusted. The suspension system includes a frame, a pressure chamber, a compression piston assembly, an adjustment assembly, a piston tube, and a shaft. The piston tube is operatively connected to the adjustment assembly and the compression piston assembly, and the compression piston assembly is configured to slidably displace along the piston tube to change the pressure in the pressure chamber. The adjustment assembly is associated with the frame and is operable to axially position the piston tube and, in turn the compression piston assembly, relative to the frame to adjust the travel of the suspension system. The shaft is configured to be variably positionable within the pressure chamber in response to axial displacement of the piston tube and the compression piston assembly by the adjustment assembly, the variable positioning of the shaft within the pressure chamber changing the pressure therein.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to gas spring suspension systems and more particularly to a gas spring suspension system that adjusts the spring rate as the travel is adjusted.  
         [0002]     Bicycles include suspension systems to cushion the rider from irregularities in the terrain. Bicycle suspension systems are typically located at the front and rear forks, the seat tube, or at other bicycle frame locations. A typical front suspension fork includes two legs, each leg having inner and outer telescoping tubes. At least one leg includes a resilient member for biasing the inner and outer tubes apart from each other and for absorbing compressive forces applied to the fork. The resilient member may be a coil spring, an elastomer spring, a gas spring or the like. The maximum amount the tubes may compress relative to each other is commonly referred to as the travel of the fork. Early suspension forks were capable of about 50 mm of travel. However, as riders began to traverse rougher terrain at higher speeds, a greater amount of travel was needed to absorb the higher riding forces. Thus, newer suspension forks were designed with travel settings of 125 mm or more. However, forks with longer travel may be cumbersome to ride, especially when riding uphill, due to the raised front end geometry and the resulting softer spring rate. A rider may choose a fork according to the type of terrain he is going to be traversing. For example, a long travel fork is used for rough downhill terrain, a medium travel fork for flat terrain and a short travel fork for uphill terrain.  
         [0003]     Another problem with existing bicycle suspension forks is that they are unnecessarily heavy. Besides increasing the overall weight of the bicycle, the weight of the fork affects the handling of the bicycle. Accordingly, reduced weight is important to riders, particularly to those involved in racing where reduced weight offers an important competitive advantage.  
         [0004]     Bicycle suspension systems with adjustable travel have been designed, however, most use a helical compression spring that adds unnecessary weight. To solve this problem, gas spring suspension systems are sometimes used. One problem with existing gas spring forks is that the rider must perform a two-step process to adjust the travel. First, a knob is turned to select the desired travel, and then the fork is manually compressed to the desired travel setting. Therefore, there is a need for a lightweight bicycle suspension system that provides easily adjustable travel that can be optimized for downhill, flat and uphill terrain.  
       SUMMARY OF THE INVENTION  
       [0005]     The present invention relates to gas spring suspension systems and more particularly to a gas spring suspension system that adjusts the spring rate as the travel is adjusted. The suspension system includes a frame, a pressure chamber, a compression piston assembly, an adjustment assembly, a piston tube, and a shaft. The piston tube is operatively connected to the adjustment assembly and the compression piston assembly, and the compression piston assembly is configured to slidably displace along the piston tube to change the pressure in the pressure chamber. The adjustment assembly is associated with the frame and is operable to axially position the piston tube and, in turn the compression piston assembly relative to the frame to adjust the travel of the suspension system. The shaft is configured to be variably positionable within the pressure chamber in response to axial displacement of the piston tube and the compression piston assembly by the adjustment assembly, the variable positioning of the shaft within the pressure chamber changing the pressure therein.  
         [0006]     The adjustment assembly, by adjusting the position of the shaft within the pressure chamber and the position of the piston assembly along the piston tube, also adjusts the spring rate for a new travel setting. Typically, for a shorter travel setting, a stiffer or higher spring rate is desired, while for a longer travel setting, a softer spring rate is desired. When the adjustment assembly is adjusted to decrease the travel, the shaft further enters the pressure chamber and the piston assembly is displaced or positioned along the piston tube, both displacements decreasing the volume of the pressure chamber to increase the spring rate. Likewise, when the adjustment assembly is adjusted to increase the travel, the shaft is further withdrawn from the pressure chamber and the piston assembly is displaced or positioned in an opposite direction, both displacements increasing the volume of the pressure chamber to decrease the spring rate. Thus, the present invention provides a desirable spring rate at any travel setting without having to separately adjust the gas pressure, allowing riders to change the travel of their forks while riding—on the fly—without having to externally add or remove gas from the pressure chamber. Nonetheless, a valve, attached to the frame and in communication with the pressure chamber, may be included to adjust pressure settings in the pressure chamber as needed.  
         [0007]     The gas spring suspension system of the present invention may further include a reserve chamber separated from the pressure chamber by a choke piston. The choke piston is configured to permit restricted gas flow from the pressure chamber to the reserve chamber, and less restricted gas flow from the reserve chamber back to the pressure chamber.  
         [0008]     These and other features and advantages of the invention will be more fully understood from the following description of certain embodiments of the invention, taken together with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     In the drawings:  
         [0010]      FIG. 1  is a front view of a front gas suspension fork in accordance with one embodiment of the present invention;  
         [0011]      FIG. 2  is a cross-sectional view of one of the legs of the gas suspension fork in  FIG. 1 ;  
         [0012]      FIG. 3  is a partial cross-sectional view of the leg shown in  FIG. 2 , showing in particular, an adjustment assembly;  
         [0013]      FIG. 4  is a cross-sectional view of the leg shown in  FIG. 2 , showing in particular, a shaft connected to an actuator or knob;  
         [0014]      FIG. 5  is a cross-sectional view of the leg shown in  FIG. 2 , showing in particular, a shaft slidably connected to a follower element;  
         [0015]      FIG. 6  is a partial cross-sectional view of the leg shown in  FIG. 2 , showing in particular, a choke piston;  
         [0016]      FIGS. 7-9  are cross-sectional views of the leg of the gas suspension system shown in  FIG. 2 , showing in particular, different travel settings of the fork;  
         [0017]      FIG. 10  is a cross-sectional view of another embodiment of the present invention;  
         [0018]      FIG. 11  is a partial cross-sectional view of an adjustment assembly shown in  FIG. 10 ;  
         [0019]      FIG. 12  is a cross-sectional view of yet another embodiment of the present invention; and  
         [0020]      FIG. 13  is a partial cross-sectional view of an adjustment assembly shown in  FIG. 12 . 
     
    
     DETAILED DESCRIPTION  
       [0021]      FIGS. 1-9  illustrate a bicycle front suspension fork  10  that includes a gas spring suspension system  11  in accordance with one embodiment of the present invention. However, a gas spring suspension system according to the present invention may be used in a rear shock, a seat post, or at other locations on a bicycle frame. Likewise, the gas spring suspension of the present invention may be used on motorcycles as well as other handlebar-steered vehicles. Looking to  FIG. 1 , the bicycle front suspension fork  10  includes a crown  12  that is connected to a steerer tube  14 , a first leg  16  and a second leg  18 . Each of the legs  16 ,  18  include an upper tube  20  and a lower tube  22 . Although the upper tubes  20  are shown as inner tubes slidable within the lower outer tubes  22 , it will be appreciated that the lower tubes may alternatively be reconfigured as inner tubes slidable within the reconfigured outer tubes. Additionally, although the tubes  20 ,  22  are shown to have substantially circular cross sections, it is understood that they may be configured to any cross-sectional shape. The inner and outer tubes  20 ,  22  are connected at their remote ends  24  to the crown  12 , and at remote ends  26  to a wheel axle (not shown) through dropouts  28 .  
         [0022]     Looking to  FIG. 2 , the gas spring suspension system generally includes a piston tube  30 , a compression piston assembly  32 , a pressure chamber  34  or gas spring for biasing the inner and outer tubes  20 ,  22  apart from each other, an adjustment assembly  36  for adjusting the travel of the suspension system  11 , and a shaft  64  variably positionable in the pressure chamber  34 , all configured about a frame member, in this embodiment, the inner tube  20 . It is to be understood that although the present invention is described with respect to a front suspension fork, typically including both inner and outer tubes  20 ,  22 , it may also be embodied in a rear suspension fork, typically including a piston assembly sliding within a single piston tube. The piston tube  30  is slidably mounted in the frame or inner tube  20 . The piston assembly  32  typically includes a compression piston  38  secured to an end  39  of a piston rod  40  by a retaining ring  42  such that piston  38  is permitted to rotate about the piston rod  40 . The piston rod  40  extends through a bottom portion of the inner tube  20  and is secured to the outer tube  22  by a nut  44 . The piston  38  has internal and external O-rings  46 ,  48  that form a gas-tight seal with the piston rod  40  and the piston tube  30 , respectively. A bushing  50  is secured proximate the bottom of the inner tube  20  by a retaining ring  52  and serves as a guide for the piston rod  40 .  
         [0023]     The pressure chamber  34  may be pressurized with gas through a Schrader valve  54  preferably located at one end  56  of the frame or inner tube  20 . In the embodiment of  FIGS. 1-9 , the gas enters the Schrader valve  54  and then flows through a passage  58  before entering the pressure chamber  34 . The pressure within the pressure chamber  34  may be adjusted according to the desired stiffness of the suspension fork  10 . The pressure within the pressure chamber  34  biases the compression piston  38  against a negative spring  60  located between the piston  38  and a bushing  61  secured to the spring tube  20  by a retaining ring  63 .  
         [0024]     When the bicycle encounters an impact, the compression piston  38  is displaced upward toward the end  56  of the inner tube  20 , against the increasing pressure in the pressure chamber  34 , to absorb the impact. After the impact, the compression piston  38  rebounds back toward its initial position against the negative spring  60 . The negative spring  60  is shown as a coil spring, but may include other types of springs such as gas springs or elastomer springs.  
         [0025]     In the embodiment of  FIGS. 1-9 , the axial bottom-out distance separating the inner tube  20  from the outer tube  22  is called the travel of the fork, and may be adjusted by operating the adjustment assembly  36  located at the end  56  of the inner tube  20 , as shown in  FIG. 3 . The adjustment assembly  36  may include an actuator, in this embodiment, a knob  62  rotatable in a first direction to position the inner and outer tubes  20 ,  22  closer together, to reduce the travel of the fork  10 , and rotatable in a second direction, to position the inner and outer tubes further apart, to increase the travel of the fork  10 . In the embodiment shown, the knob  62  is rotationally fixed to a shaft  64  by cooperating octagonal surfaces formed on the knob  62  and the shaft  64  (see  FIG. 4 ). The adjustment shaft  64  is substantially cylindrical and may be made of aluminum. The Schrader valve  54  is preferably located at an end  66  of the shaft  64  and a choke piston  74  is preferably mounted at another end  70  of the shaft  64  by retaining ring  76 . The Schrader valve  54  and choke piston  74  may be alternatively disposed in the suspension fork, so long as they remain in communication with the pressure chamber  34 .  
         [0026]     The adjustment assembly  36  may further include a driver element  78  rotatable with the actuator  62 , in this embodiment, the driver element threaded into the end  51  of the frame or inner tube  20 . The driver element  78  further includes threads  80  matingly engaging threads  82  of a follower element  84 . The follower element  84  is slidably guided along the shaft  64  with keys  72  formed on the shaft  64  received by slots  73  on the follower element  84  (see  FIG. 5 ). So configured, when the knob  62  is rotated, the follower element  84  is axially displaced by the rotating driver element  78 . A lower portion of the follower element  84  may include a cylindrical portion  86  sealing attached to the piston tube  30 , with an O-ring  88  providing a seal between the piston tube  30  and the cylindrical portion  86 , and an O-ring  92  providing a seal between the shaft  64  and the cylindrical portion  86 . The cylindrical portion  86  is secured in the piston tube  30  by an internal retaining ring  94 . The follower element  84  may be made of a lubricious plastic such as injection molded Delrin. The shaft  64  is configured to extend through a bore  96  of the follower element  84 .  
         [0027]     The suspension fork  10  may further include a reserve chamber  90  separated from the pressure chamber  34  by the choke piston  74 , also known as a leaky piston. The choke piston is configured to permit restricted gas flow from the pressure chamber  34  to the reserve chamber  90 , and less restricted gas flow from the reserve chamber back to the pressure chamber. In the embodiment shown, the gas flow path is between the choke piston  74  and the shaft  64 . Referring to  FIG. 6 , when pressure in the pressure chamber  34  is greater than the pressure in the reserve chamber  90 , the choke piston  74  is displaced such that an upper surface  98  of the choke piston  74  contacts a lower surface  100  of the adjustment shaft  64 , resulting in restricted gas flow from the pressure chamber  34  to the reserve chamber  90 . The surfaces  98 ,  100  of the choke piston  74  and the adjustment shaft  64  may be textured or otherwise deformed to allow gas to slowly pass from the pressure chamber  34  to the reserve chamber  90 . Alternatively, a textured washer or a washer made of permeable material, such as felt, may be located between the upper surface  98  of the choke piston  74  and the lower surface of the shaft  64 . Conversely, when the pressure in the reserve chamber  90  is greater than the pressure chamber  34 , the choke piston  74  is displaced downward against the retaining ring  76  whereby the upper surface  98  of the choke piston  74  and the lower surface  100  of the shaft  64  are separated, resulting in less restricted gas flow from the reserve chamber  90  back into the pressure chamber  48 , as the retaining ring  76  is not circularly uniform. When the knob  62  is adjusted to change the travel, the pressures in the pressure chamber  34  and the reserve chamber  90  remain substantially equal as the amount of gas flow—even restricted gas flow from the pressure chamber to the reserve chamber—is sufficient to permit the pressures to equalize. However, under external impact loading, the flow path across the choke piston  74  from the pressure chamber to the reserve chamber—in this embodiment, between the surfaces  98 ,  100  of the choke piston and the shaft  64 —becomes too restricted to equalize the pressures between the chambers in the short time frame of an external load. Accordingly, as the additional volume of the reserve chamber becomes unavailable during the short time frame of a sudden sharp external load, there is a resulting spike or increase in the spring rate that is desirable.  
         [0028]     When the knob  62  is rotated in a first direction, the shaft  64  rotates the driver element  78 , which in turn axially displaces the follower element  84  upward. The upward movement of the follower element  84  also displaces the connected piston tube  30 , the bushing  61 , the negative spring  60 , and the compression piston assembly  33  upward. The upward movement of these parts reduces the relative distance between the inner tube bushing  50  and a compression bumper  104  located at the bottom of the outer tube  22 , resulting in the travel of the fork  10  being reduced. The upward movement of the follower element  84  relative to the choke piston  74  also increases the volume of the reserve chamber  90  and decreases the volume of the pressure chamber  34 . The combined volume of the reserve chamber  90  and pressure chamber  34  is also reduced by positioning the shaft  64  further into the pressure chamber  34 , resulting in an increased spring rate.  
         [0029]     When the knob  62  is rotated in a second direction, the shaft  64  rotates the driver element  78 , which in turn axially displaces the follower element  84  downward. The downward movement of the follower element  84  also displaces the connected piston tube  30 , the bushing  61 , the negative spring  60 , and the compression piston assembly  33  downward. The downward movement of these parts increases the relative distance between the inner tube bushing  50  and the compression bumper  104  located at the bottom of the outer tube  22 , resulting in the travel of the fork  10  being increased. The downward movement of the follower element  84  relative to the choke piston  74  also decreases the volume of the reserve chamber  90  and increases the volume of the pressure chamber  34 . The combined volume of the reserve chamber  90  and pressure chamber  34  is also increased by the further positioning of the shaft  64  out of the pressure chamber  34 , resulting in a decreased spring rate.  
         [0030]     As the travel of the fork  10  is being adjusted in either direction, gas flow—whether restricted or less restricted—is permitted between the pressure chamber  34  and the reserve chamber  90 , such that the pressure in the pressure chamber  34  and the reserve chamber  90  remains substantially the same.  
         [0031]      FIGS. 7-9  illustrate the suspension fork  10  adjusted to long, medium and short travel settings, respectively. It is desirable to have different spring rates for different travel settings. For example, for a shorter travel setting, a stiffer spring rate is desirable to prevent bottoming out of the fork. When the travel of the suspension fork is adjusted, the spring rate is simultaneously adjusted for the new travel setting. For example, when the travel of the fork  10  is reduced, the overall volume of the pressure chamber  34  is reduced, resulting in increased pressure in the pressure chamber  34  is reduced, resulting in increased pressure in the pressure chamber  34  and a corresponding increase in the spring rate. Likewise, when the travel of the fork  10  is increased, the overall volume of the pressure chamber  34  is increased, resulting in decreased pressure in the pressure chamber  34  and a corresponding decrease in the spring rate. Advantageously, a desirable spring rate may be achieved at any travel setting without having to externally adjust the gas pressure.  
         [0032]     Looking to  FIGS. 10-11 , another embodiment of the present invention is depicted, similar to the embodiment of  FIGS. 1-9 , except that a gas suspension system  200  includes an extended adjustment shaft  202 , and excludes a choke piston and a reserve chamber. In this embodiment, the larger adjustment shaft  202  displaces a larger volume of gas in the pressure chamber  34  resulting in a correspondingly larger change in the spring rate as the actuator  62  is adjusted.  
         [0033]     Looking to  FIGS. 12-13 , a further embodiment of the present invention is depicted, similar to the embodiment of  FIGS. 1-9 , except that it includes a follower element  302  with internal threads  304  matingly engaging an adjustment shaft  306  with external threads  308 . This configuration may be easily adapted to include a choke piston and a reserve chamber as described in the previous embodiments of the present invention shown in  FIGS. 1-11 .  
         [0034]     While this invention has been described by reference to several embodiments, it will be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it include the full scope permitted by the language of the following claims.