Abstract:
An adjustable shock absorber includes a shock rod having a longitudinal axis. A shock body is disposed around a portion of the shock rod, the shock body defining a first fluid chamber therein and being slidable along the longitudinal axis. A piston is disposed on the shock rod in sealing engagement with the shock body. The piston has at least one channel therethrough in communication with the first fluid chamber. At least one valve is in fluid communication with the channel to control fluid movement through the channel. A support is movable longitudinally along the shock rod and is disposed adjacent to the valve. An adjustment mechanism is provided for altering a longitudinal position of the movable support to adjust the valve&#39;s operation by altering the fluid movement through the channel.

Description:
[0001]    This application claims priority to U.S. application Ser. No. 60/270,878, filed Feb. 26, 2001, which is incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The field of the present invention relates to shock absorbers of the type that are adjustable. More particularly, the present invention relates to shock absorbers that are adjustable in the compression stage only.  
         BACKGROUND OF THE INVENTION  
         [0003]    Shock absorbers are widely use to dampen shocks experienced, for example, when a recreational vehicle such as a snowmobile travels over rough terrain. In the case of the snowmobile, the shock absorbers are positioned between the chassis and the slide frame around which an endless track rotates to propel the vehicle or in the front suspension between the skis and the chassis. The shock absorbers allow the slide frame or the skis to compress towards the chassis at a controlled rate.  
           [0004]    Shock absorbers typically have a cylindrical wall sealed between two end caps creating a cavity in which a fluid is contained to provide hydraulic damping. The interior of the cylinder is separated into two sections by a piston, which contains passages therethrough to increase or decrease the fluid flow between each section of the cylinder. A shock rod, which passes through the rod eye end cap, is attached to the piston at one end and to the vehicle at its other end. Normally the shock rod is attached to the vehicle through a rod eye, hence the name “rod eye end cap”. The other end cap is secured to the slide frame, in the case of a snowmobile. The shock rod and the shock body, which includes the cylindrical wall and both of the end caps, move in relation to one another to dampen any forces applied thereto.  
           [0005]    Passages are formed through the longitudinal axis of the piston and connect one section of the cylinder, the shock body, to the other. Portions of these passages are covered with leaf valves while the remainder of the openings serve as a bypass with no restriction other than the diameter of the passages. These bypass portions function primarily when the speed of the piston is low, i.e.: 0 to 0.3 m/s. The “speed” of a piston is the rate at which the piston and the shock body move with respect to one another when an external force is applied thereto. In certain shock absorbers, once the speed of the piston increases above 0.3 mls, the fluid pressure increases enough to open the leaf valves. This may vary depending on the intended use of the shock absorber.  
           [0006]    A typical “Piston Speed vs. Compression Force” graph, such as the one depicted in FIG. 8, may be divided into three sections: low, medium and high. The low speed curve corresponds to speeds from about 0 m/s to approximately 0.3 m/s. The medium speed range corresponds to speeds from about 0.3 m/s to 1 m/s, and the high-speed range corresponds to speeds higher than about 1 m/s.  
           [0007]    Because the lower speeds do not have an adverse effect on the driver or the driving performance of the snowmobile, the medium and high-speed ranges tend to be where attention is focused when designing a shock absorber. Since the fluid inside the shock body travels across the piston through the bypass portions during the low speed range, any adjustments to the valves have little or no effect on the low speed functioning of the shock.  
           [0008]    Conventional adjustable hydraulic shock absorbers, such as the one shown in U.S. Pat. No. 5,542,509, are adjustable in both the compression and in the rebound stages. The compression stage occurs when the vehicle encounters uneven terrain and the force generated by the encounter is transferred to the piston of the shock absorber. The rebound stage is the traveling of the piston back to its steady state position, normally by the aid of a coil spring. The coil spring, which compresses when the vehicle encounters uneven terrain, will force the vehicle away from the ground and generate the force required to return the shock absorber to its steady state position during the rebound stage. The force exerted by the spring is usually quite low, because the force of the spring only needs to be high enough to overcome the force of gravity and not the forces associated with uneven terrain.  
           [0009]    U.S. Pat. No. 5,542,509 describes a twin-tube shock absorber with an adjustment mechanism. The adjustment mechanism is a screw cam, which is screwed into a bore in the endcap of the shock absorber. The screw cam abuts the spring seat for the compression or blow off valve spring. Tightening or loosening the screw cam, relative to the endcap, increases or decreases the pre-load of the compression valve spring, thereby adjusting the manner in which the shock absorber responds to compression forces applied thereto.  
           [0010]    In the case where a shock absorber is used in a recreational vehicle, such as a snowmobile, the compression stage of the shock absorber has a greater effect on the vehicle than the rebound stage. As mentioned, this is due to the fact that the weight of the vehicle is relatively small and, therefor, the rebound force required is equally small. This stands in dramatic contrast to the very high compressive forces that the shock absorber may experience as the recreational vehicle traverses uneven terrain.  
           [0011]    Additionally, different riders prefer different response characteristics of the shock absorbers on their vehicles. For example, those engaged in snowmobile racing prefer a “stiffer” shock than those enjoying a leisurely excursion on the outdoor snowmobile trail or through an ungroomed rural setting.  
         SUMMARY OF THE INVENTION  
         [0012]    A need has developed for a simple, effective mechanism that permits adjustment of the compression response of a shock absorber such that the recreational vehicle including the shock absorber may satisfy several different riding preferences. The prior art does not address this deficiency.  
           [0013]    It is, therefore, an object of the present invention to provide a simple, cost-effective, reliable, adjustable shock absorber with improved characteristics.  
           [0014]    It is another object of the present invention to provide a shock absorber that is adjustable in compression in medium and high piston speed ranges.  
           [0015]    It is still an object of the present invention to provide an adjustable shock absorber that is adjustable electrically using a solenoid.  
           [0016]    It is yet another object of the present invention to provide an adjustable shock absorber, which is adjustable hydraulically.  
           [0017]    It is still another object of the present invention to provide an adjustable shock absorber, which is adjustable mechanically.  
           [0018]    In furtherance of these objects, one aspect of the present invention is to provide an adjustable shock absorber having a shock rod with a longitudinal axis. A shock body is disposed around the shock rod and is slidable along the longitudinal axis of the shock rod. The interior of the shock body defines a first fluid chamber. A piston is disposed on the shock rod in such a manner that the piston sealingly engages with the interior of the shock body. The piston includes channels passing therethrough in communication with the first fluid chamber. At least one valve is positioned to be in communication with the channel to control fluid movement through the channel. A support, movable longitudinally on the shock rod, is disposed adjacent to the valve. An adjustment mechanism is provided for altering the position of the movable support to adjust the fluid movement through the channel.  
           [0019]    Yet another aspect of the of the present invention is to provide an adjustable shock absorber including a solenoid, which alters the fluid movement through the channel in the piston.  
           [0020]    According to yet another aspect of the present invention, a snowmobile is provided that includes a chassis. An engine is disposed on the chassis. A steering column is attached to at least one ski for steering the snowmobile over the snow. An endless track is disposed under the chassis and is operatively connected to the engine for propelling the snowmobile. The snowmobile includes an adjustable shock absorber. The adjustable shock absorber has a shock rod with a longitudinal axis. A shock body is disposed around the shock rod and is slidable along the longitudinal axis of the shock rod. The shock body defines a first fluid chamber. A piston is disposed on the shock rod in such a manner that the piston sealingly engages with interior of the shock body. The piston includes channels passing therethrough in communication with the first fluid chamber. At least one valve is in communication with the channel to control fluid movement through the channel. A support, movable longitudinally on the shock rod, is disposed adjacent the valve. An adjustment mechanism is provided for altering the position of the movable support to adjust the fluid movement through the channel.  
           [0021]    Yet another aspect of the present invention is to provide a snowmobile with an adjustable shock absorber that includes a solenoid which alters the fluid movement through the channel in the piston.  
           [0022]    The foregoing objects are not meant to limit the scope of the present invention. To the contrary, still other objects of the present invention will become apparent from the description that follows. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]    Reference will be made hereinafter to the accompanying drawings, which illustrate embodiments of the present invention discussed herein below, wherein:  
         [0024]    [0024]FIG. 1 is a cross sectional side view of a first embodiment constructed in accordance with the present invention;  
         [0025]    [0025]FIG. 2 is a cross sectional side view of a second embodiment of the present invention;  
         [0026]    [0026]FIG. 3 is a cross sectional side view of a third embodiment of the present invention;  
         [0027]    [0027]FIG. 4 is a cross sectional side view of a fourth embodiment of the present invention;  
         [0028]    [0028]FIG. 5 is a cross sectional side view of a fifth embodiment of the present invention;  
         [0029]    [0029]FIG. 6 is a top view of the fifth embodiment illustrated in FIG. 5;  
         [0030]    [0030]FIG. 7 is a cross sectional side view of a sixth embodiment of the present invention;  
         [0031]    [0031]FIG. 8 is a “Piston Speed vs. Force” graph;  
         [0032]    [0032]FIG. 9 is a side view of a snowmobile with an adjustable shock absorber;  
         [0033]    [0033]FIG. 10 is a partial cross sectional view showing the piston and movable support of the second, fifth and sixth embodiments in greater detail; and  
         [0034]    [0034]FIG. 11 is a partial cross sectional view showing the piston and movable support of the first, third and fourth embodiments in greater detail. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0035]    An adjustable shock absorber  10  according to the present invention is shown in FIGS.  1 - 11 . The shock absorber  10  is preferably made from steel or aluminum and is circular in shape. However, the shock absorber  10  could be made in any shape and from any suitable material(s) capable of withstanding shocks experienced in the environment in which the shock absorber is designed to operate.  
         [0036]    In the embodiment illustrated in FIG. 1, the shock rod  12  of the adjustable shock absorber  10  is cylindrical in shape with a shoulder  14  separating the lower portion  16  from the upper portion  18 . The upper portion  18  of the shock rod  12  includes a first set of threads  20  to which the rod eye  22  is attached. The upper portion  18  of shock rod  12  also includes a passage  24  through the center. The passage  24  has a first opening  26  near the threads  20  and a second opening  28  near the shoulder  14  of the shock rod  12 . The lower portion  16  of the shock rod  12  has a second set of threads  30 . The second set of threads  30  engages a nut  50  to secure a piston  40  to the shock rod  12 . The shock rod  12  is preferably made from steel, but other materials may be suitable therefor.  
         [0037]    A shock body  32  is preferably made of aluminum with a circular cross-section. The shock body  32  is connected between a first end cap  34  and a second end cap  36 . The end caps  34  and  36  are preferably threaded into the shock body  32 , but other methods of attachment are available. The first end cap  34  includes a hole  38  through which the shock rod  12  passes. The hole  38  is sealed such that no fluid will exit between the shock rod  12  and end cap  34 .  
         [0038]    Piston  40  is preferably circular in cross-section to facilitate a sealing engagement with the interior of the shock body  32 . The piston  40  is preferably situated on the lower portion  16  of shock rod  12 . The piston  40  has a round central hole  41  through which the shock rod  12  passes. The piston  40  moves longitudinally inside the shock body  32  to separate the first fluid chamber  42  into two communicating sections  44  and  45 . The piston  40  includes a plurality of channels  46  through which the two communicating sections  44  and  45  communicate with one another. Preferably, the piston  40  is held stationary on the shock rod  12  between the shoulder  14  and the nut  50 , but other methods of attachment are available.  
         [0039]    A valve  48  is preferably shaped like a circular disk made of a flexible metal material, but other valves are available. The valve  48 , preferably situated so that it extends around the perimeter of the piston  40 , alters the opening of the channels  46  between the two communicating sections  44  and  45  of the first fluid chamber  42 . The valve  48  also has a round central hole  47  through which the shock rod  12  passes. In the preferred embodiment, the valve  48  is constructed to flex when pressure is applied thereto.  
         [0040]    In the embodiment illustrated in FIG. 1, a movable support  52  is preferably shaped like a truncated cylinder. The movable support  52  is situated on the upper portion  18  of the shock rod  12 . The movable support  52  has a round central hole  54  through which the shock rod  12  passes. The round central hole  54  sealingly engages the shock rod  12 . The movable support  52  is slidable along the shock rod  12  such that it makes contact with the valve  48  when the valve  48  opens. Preferably, the movable support  52  is made of aluminum, but other materials are available. In the embodiment depicted, the movable support  52  is sealingly engaged with a support housing  56  to form a second fluid chamber  58 . The support housing  56  is attached to the shock rod  12  in such a manner that no fluid will leak between the support housing  56  and the shock rod  12 . The second fluid chamber  58  is in fluid communication with the passage  24  within the shock rod  12 .  
         [0041]    A screw  60  is placed into a hole  62  in the rod eye  22 , which is attached to the shock rod  12  by first set of threads  20 . The passage  24  through the shock rod  12  is also in fluid communication with the threaded hole  62  of the rod eye  22 . When screw  60  is rotated in threaded hole  62  and moves toward the passage  24 , the volume of liquid, preferably hydraulic, is displaced through the passage  24  in the shock rod  12  into the second fluid chamber  58 . The increase in volume of fluid within the second fluid chamber  58  causes the movable support  52  to travel along the longitudinal axis of the shock rod  12  and, thus, narrows the gap between the movable support  52  and the valve  48  to reduce the allowable movement of the valve  48 .  
         [0042]    Another embodiment of the present invention involves connecting passage  24  to an external source providing preferably hydraulic fluid to the passage  24 . A control for controlling the amount of fluid entering and exiting the passage  24  is preferably situated on the dashboard of the vehicle or near the operator while driving the vehicle.  
         [0043]    In still another embodiment of the present invention shown in FIG. 2, a first rod  66  extends through the passage  24  in the shock rod  12 . A second rod  68  passing through the hole  62  in the rod eye  22  is attached to the first rod  66  preferably through a worm gear  70 . Rotation or translation of the second rod  68 , causes the first rod  66  to extend further into the shock rod  12  towards the piston  40 . The movable support  52  is attached to the first rod  66 . Movement of the first rod  66  in the longitudinal direction translates into movement of the movable support  52  also in the longitudinal direction of the shock rod  12  and, thus, narrows the gap between the movable support  52  and the valve  48  to reduce the allowable movement of the valve  48 .  
         [0044]    In yet another embodiment of the present invention shown in FIG. 3, a solenoid  72  may be attached to the screw  60  by a mechanical linkage or plunger  74 . Actuation of the solenoid  72  rotates the screw  60  through the mechanical linkage  74 . Rotation of the screw  60  causes the volume of fluid within the second fluid chamber  58  to increase which causes the movable support  52  to travel along the longitudinal axis of the shock rod  12  and, thus, narrows the gap between the movable support  52  and the valve  48  to reduce the allowable movement of the valve  48 . Although shown as a linear solenoid, a rotational solenoid could be used as well.  
         [0045]    In still another embodiment of the present invention shown in FIG. 4, a solenoid  72  is placed within the passage  24 . Attached to the solenoid  72  is a second piston  76  sealingly engaged with the passage  24 . Actuation of the solenoid  72  alters the fluid pressure with in the passage  24  causing the movable support  52  to travel along the longitudinal axis of the shock rod  12  and, thus, narrowing the gap between the movable support  52  and the valve  
         [0046]    reduce the allowable movement of the valve  48 .  
         [0047]    In yet another embodiment of the present invention, which is illustrated in FIGS. 5 and 6, a mechanical linkage  74  attaches a solenoid  72  to the second rod  68 . Actuation of the solenoid  72  rotates the second rod  68  through the mechanical linkage  74 . The second rod  68 , passing through the hole  62  in the rod eye  22 , is preferably attached to the first rod  66  through a worm gear  70 . Rotation of the second rod  68 , causes the first rod  66  to extend further into the shock rod  12  toward the piston  40 . The movable support  52  is attached to the first rod  66 . Movement of the first rod  66  in the longitudinal direction translates into movement of the movable support  52  also in the longitudinal direction of the shock rod  12  and, thus, narrows the gap between the movable support  52  and the valve  48  to reduce the allowable movement of the valve  48 .  
         [0048]    In yet another embodiment of the present invention illustrated in FIG. 7, the solenoid  72  is directly attached to the movable support  52 . Actuation of the solenoid  72  in the longitudinal direction translates into movement of the movable support  52  also in the longitudinal direction of the shock rod  12  and, thus, narrows the gap between the movable support  52  and the valve  48  to reduce the allowable movement of the valve  48 . Movement of the movable support  52  away from the valve  48  is also permitted to increase the allowable movement of the valve  48 .  
         [0049]    The adjustable shock absorber  10  of the present invention may be used on any suitable vehicle including a snowmobile  78 , which is shown in FIG. 9. Snowmobile  78  has a chassis  80  on which the engine  82  is disposed. A pair of skis  84  (only one of which is depicted in FIG. 9) are attached to the front portion of the chassis  80  and are connected to a steering device  86  to steer the snowmobile  78  across a snow-covered surface. An endless track  88 , connected to the engine  82 , is placed under the chassis  80  to propel the snowmobile  78 . The snowmobile  78  includes an adjustable shock absorber  10  as described above.  
         [0050]    While the above mentioned embodiments have placed the second rod  68  and the screw  60  in the rod eye  22 , it will be recognized that these components could be placed in the shock rod  12  or any part which does not move with respect to the shock rod  12 .  
         [0051]    While the invention has been described with reference to several preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention.