Abstract:
The retractable wheel system of the present invention may be installed on a snowmobile ski without affecting its structural integrity by installing the system on the reinforced portion of the snowmobile ski. When a user circulates in a path with little or no snow, the retractable wheel system is positioned in the extended configuration by the user and the system will automatically return to the retracted configuration when the user returns in a snowy zone. This is realized by using a pre-tensioned spring that will reposition the wheel in the retracted configuration. The spring transmits a rotational movement to the member on which the wheel is fixed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application claims the benefits of priority of commonly assigned Canadian Patent Application no. 2,647,375, entitled “Roue rétractable pour ski de motoneige” and filed at the Canadian Patent Office on Dec. 8, 2008. 
     FIELD OF THE INVENTION 
     The present invention generally relates to vehicles partially supported by one or more skis. More specifically, this invention is related to a snowmobile having a retractable wheel to circulate in a zone with little or no snow. 
     BACKGROUND OF THE INVENTION 
     Snowmobiles are vehicles adapted to circulate on snowy or icy surfaces. However, users often have to circulate on surface having little or no snow. These non-snow surfaces are often made from asphalt, concrete, stony ground, for example, which are highly abrasive for the undersurface of the snowmobile ski. Prior art shows some systems in which the user has to install wheels on the skis to circulate on abrasive surface to prevent the undersurface of the ski to contact the abrasive surface. 
     Disadvantage of such system is that the manipulation to install the wheel is complex and difficult. Indeed, in many of systems provided in prior art, the user has to stop the snowmobile, get down from it and install manually the wheels, pass through the zone with little or no snow, stop again the snowmobile and remove the wheels. These manipulations have for consequence that the users will not install the wheel and pass through the zone with little or no snow on the ski, causing a premature wear of the ski. 
     Also, in snowy condition, the wheel systems may be jam with snow or ice, increasing the difficulty of the manipulation. 
     Finally, it is important to consider where the systems are installed on skis. Since the weight of the snowmobile is directly transmitted to the ski, the latter are under high mechanical stresses. In some systems of prior art, fixation holes are practiced in the ski, weakening the ski and causing eventually the breaking of the ski. Since the skis are reinforced where they are attached to the snowmobile, it would be advantageous to install the wheel in this section. Indeed, if the wheels are installed in a non-reinforced zone, the ski will bend, diminishing the contact surface between the snow and the ski. This configuration diminishes the performance of the ski on snow. It also causes an inadequate distribution of the weight of the snowmobile on the ski and a premature wear. 
     A deformation of the skis may occur if the wheel system is installed on a part of the ski that is not reinforced, causing the ski to bend under the weight of the snowmobile. Furthermore, the wear bar usually install on the undersurface of a ski will be highly affected by such a stress and curvature. It is known that the wear bar is made from carbide having high hardness and thus being highly fragile. As a consequence, the wear bar will become cracked and chipped. 
     SUMMARY OF THE INVENTION 
     The aforesaid and other objectives of the present invention are realized by generally providing a retractable wheel system for snowmobile ski, the snowmobile ski being connected to the snowmobile with a kingpin, the kingpin being connected to the snowmobile ski through a first opening and a second opening in the ski, the system having a retracted configuration and an extended configuration, the extended configuration being actuated by a user of the snowmobile and wherein the system is configured to return automatically in the retracted configuration, the system comprising a spring having a first extremity and a second extremity, s the aid spring being pre-tensioned at a predetermined amount, a pivoting member connected to the ski and to the spring, the pivoting member being actuated by the spring, a shaft having a first and a second extremity, the shaft comprising a slot at the second extremity, the pivoting member being pivotally mounted along the shaft, and the wherein the first extremity of the spring is inserted in the slot, a connector, the connector being mounted on the second extremity of the shaft, the connector comprising a plurality of holes configured to receive second extremity of the spring, a wheel rotatably connected to the pivoting member; and a stopper. 
     In a preferred embodiment, the spring is a helical torsion spring. In another embodiment, the spring is of the mainspring type. 
     In a preferred embodiment, slot in the shaft is perpendicular to the second extremity of the shaft. In another embodiment, the top portion and the bottom portion of the slot of the shaft are at an angle π, the angle π preferably comprised between 10° and 14°. 
     In another embodiment, the present invention provides a shaft to be used with a spring, the spring having a first and a second extremity, the shaft comprising a slot, wherein the slot has a top portion and a bottom portion, and wherein there is an angle π between the bottom portion of the slot and the top portion of the slot, wherein the first extremity of the spring is inserted in said slot, wherein the slot forces the first extremity of the spring towards the bottom portion of the slot when the spring is twisted to be tighter. The angle π is comprised between 10° and 14°. 
     The retractable wheel system of the present invention is easily installed on an existing snowmobile ski. To do so, the transmission arm and the kingpin of the ski are dismounted and the retractable wheel system is fixed to the ski using the kingpin. The retractable wheel system comprises a wheel, a pivoting member, a fixation member and a spring. The fixation member is fixed to the snowmobile ski using the kingpin and is secured with bolt and nut. An important feature of the present invention is the installation of the retractable wheel system using the kingpin to prevent deformation and damage of the ski. 
     It is to be noted that the fixation member could be omitted if the ski was already equipped with fixation means for the pivoting member. 
     An advantage of the present invention is that it has little or no effect on the structural integrity of the ski compared to prior art. Indeed, the retractable wheel system of the present invention is installed on the reinforced portion of the ski. Also, the system is secured with the kingpin thus the force distribution is almost the same as the normal use, i.e. with the skis. 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the invention will become more readily apparent from the following description, reference being made to the accompanying drawings in which: 
         FIG. 1   a  is an exploded view showing a first embodiment of the retractable wheel system according to the present invention, for the left ski of a snowmobile. 
         FIG. 1   b  is an exploded view showing a first embodiment of the retractable wheel system according to the present invention, for the right ski of a snowmobile. 
         FIG. 2   a  is an exploded view of the fixation system of the embodiment shown in  FIG. 1   a.    
         FIG. 2   b  is an exploded view of the fixation system of the embodiment shown in  FIG. 1   b.    
         FIG. 3   a  is an exploded view of the retraction system of the embodiment shown in  FIG. 1   a.    
         FIG. 3   a  is an exploded view of the retraction system of the embodiment shown in  FIG. 1   b.    
         FIG. 4   a  is a partially exploded view of the retractable wheel system of the embodiment shown in  FIG. 1   a.    
         FIG. 4   b  is a partially exploded view of the retractable wheel system of the embodiment shown in  FIG. 1   b.    
         FIG. 5   a  is an isometric view of the retractable wheel system of the embodiment shown in  FIG. 1   a.    
         FIG. 5   b  is an isometric view of the retractable wheel system of the embodiment shown in  FIG. 1   b.    
         FIG. 6  is an isometric view showing one of the steps to mount the retractable wheel system on a snowmobile ski. 
         FIG. 7  is an isometric view showing one of the steps to mount the retractable wheel system on a snowmobile ski. 
         FIG. 8  is an isometric view showing the retractable wheel system of  FIG. 1  as mounted on a snowmobile ski. 
         FIG. 9  is an isometric exploded view showing a second embodiment of the retractable wheel system for snowmobile ski. 
         FIG. 10  is an isometric view showing the retractable wheel system of  FIG. 9 , in a retracted configuration. 
         FIG. 11  is an isometric exploded view of the embodiment shown in  FIG. 9 . 
         FIG. 12  is an isometric view of the embodiment of  FIG. 9  in an extended configuration. 
         FIG. 13  is an isometric view of the embodiment of  FIG. 9  in a retracted configuration. 
         FIG. 14  shows one of the steps to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 15  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 16  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 17  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 18  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 19  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 20  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 21  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 22  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 23  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 24  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 25  shows another step to mount the second embodiment of the retractable wheel system on a snowmobile ski. 
         FIG. 26   a  is a side view showing a second embodiment of a shaft, to be used with the left ski of a snowmobile. 
         FIG. 26   b  is a side view showing a second embodiment of a shaft, to be used with the right ski of a snowmobile. 
         FIG. 26.1   a  is a close-up view of detail b of  FIG. 26   a.    
         FIG. 26.1   b  is a close-up view of detail b of  FIG. 26   b.    
         FIG. 26.2   a  is a top view of the shaft shown in FIG.  26 . a    
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A novel retractable wheel system for snowmobile ski will be described hereinafter. Although the invention is described in terms of specific illustrative embodiment(s), it is to be understood that the embodiment(s) described herein are by way of example only and that the scope of the invention is not intended to be limited thereby. 
     In  FIGS. 1 to 6 , the figures             a           are referring to the retractable wheel system of the left snowmobile ski and the figures &lt;&lt;b&gt;&gt; are referring to the retractable wheel system of the right snowmobile ski. Since the part on left and right sides are symmetric, the same numbers are attributed to identical part of the left and right sides.
       FIG. 1  shows the retractable wheel system comprising a wheel  2 , a pivoting member  4 , a fixation member  6 , and a spring  8 . In this preferred embodiment, the fixation member  6  is fixed on the snowmobile ski with the kingpin  18  and the position is secured with bolts  14  and nuts  16 , or other appropriate means such as bolt and nut, welding, rivets, etc. The fixation member  6  comprises an opening  5  configured to receive the kingpin  18 . The snowmobile ski  50  is connected to the snowmobile with an arm  78  and the kingpin  18 . The fixation member  6  provides attachment means for the retractable wheel system so that the system may be retrofit to an existing snowmobile ski. 
     The spring  8 , or helical torsion spring  8 , is a spring that works by torsion or twisting, it stores mechanical energy when twisted. The amount of force or torque it exerts is proportional to the amount it is twisted or rotated on itself. To create the pretension in the spring, the latter is subjected to twisting about its longitudinal axis by sideways forces (bending moments) applied to its ends, twisting the spring tighter. 
     The pivoting member  4  comprises an opening  82  to receive the shaft  20 , an opening  84  on which the stopper  44  is installed and an opening  86  on which the wheel  2  is connected. The pivoting member  4  is rotatively connected to the fixation member  6  with the shaft  20 . The pivoting member  4  rotates along the longitudinal axis of the shaft  20 , under the force applied by the spring  8  (to retract the system) or under a force applied by a user (to extend the system). 
     The shaft  20  comprises a first extremity  133  and a second extremity  233 . The shaft  20  comprises a slot  33  at its second extremity  233 . If a first embodiment, the slot is substantially perpendicular to the second extremity  233 , as shown in  FIGS. 1 to 3 . 
     The connector  24  is a piece configured to be connected to the first extremity  133  of the shaft  20 . The connector  24  comprises a plurality of holes  34 , these holes being configured to receive the second extremity  30  of the spring  8 . In a preferred embodiment, the connector  24  comprises eleven holes  34 . In a preferred embodiment, the connector  24  is screwed to the shaft  20  so that the connector  24  may be changed for reparation or to change the number of holes  34  to provide a plurality of tension levels in the spring. The connector  24  is preferably connected to the pivoting member  4 . In the preferred embodiment, the connector  24  is screwed to the pivoting member  4 . The connector  24  transmits the rotation induced by the spring  8  to the pivoting member  4 . 
     The adaptator  12  is a hollow cylindrical part configured to receive the shaft  20 . The adaptator  12  comprises a groove  32  configured to receive the first extremity  28  of the spring  8 . 
     The retraction system  22 , composed by the spring  8  and the shaft  20 , is comprised in the case  10 . The case  10  is preferably threaded at its open extremity and may be connected to the connector  24  which is also threaded. The connection between the case  10  and the connector  24  is preferably leakproof. 
     The first extremity  28  of the spring  8  is folded so it can be inserted into the slot  33  of the shaft  20 . The second extremity  30  of the spring  8  is folded to interact with the one of the holes  34  of the connector  24 . 
     To install the spring  8 , the first extremity  28  is firstly inserted in the groove  32  of the adaptator  12  and the adaptator  12  is installed on the shaft  20 . It is to be noted that after installation, the first extremity  28  of the spring  8  passes into the slot  33  and into the groove  32 . The second extremity  30  is then inserted in one the holes  34 . To create the pretension in the spring  8 , the spring  8  is rotated or twisted on itself until the desired tension is reached, and the second extremity is then inserted in one of the holes  34  to maintain this pretension in the spring  8 . 
     Retaining rings  36  and  37  are preferably inserted on the shaft  20 , on each sides of the spring  8 . 
     The retractable wheel system comprises a stopper  44  which is fixed, in the present embodiment, to the pivoting member  4 . An o-ring  46  is installed to the side of the stopper  44 . In a retracted configuration, the stopper  44  is in contact with the fixation member  6 . 
     The wheel  2  is rotatably connected to the pivoting member  4  with the wheel shaft  38 . The wheel  2  is mounted on a sleeve  40  and two washers  42  are installed on both sides of the wheel  2 , on the wheel shaft  38 . As shown in  FIG. 4   a , in the retracted configuration, the stopper  44  contacts the fixation member. The role of the stopper  44  is to stop the rotation of the pivoting member induced by the spring  8 . The stopper  44  also dictates the position of the wheel  2  and of the pivoting member  4  in the retracted position. The tension in the spring  8  causes the pivoting member  4  to rotate counterclockwise (for the right ski) until the stopper  44  contacts the fixation member  6 . 
       FIGS. 6 to 8  show how the retractable wheel system is mounted on a snowmobile ski  50 . The ski  50  usually comprises a first opening  52  and a second opening  54  to receive the kingpin. Bushings  56  and  58  are preferably inserted in the first opening  52  and second opening  54 . The kingpin  18  is then inserted in the bushing  56  and  58 . The kingpin  18  is then fixed to the ski  50 , using a bolt  60  for example. A washer  62  is preferably installed between the bushing  54  and the bolt  60 . 
     Before using the retractable wheel system, an appropriate quantity of protective material and/or lubricant  91  such as synthetic oil is preferably applied in the case  10  to lubricate the mechanism while protecting it from environment such as water, salt, etc. 
       FIG. 8  shows the retractable wheel system in a retracted configuration, the wheel  2  being located at a horizontal level higher that the undersurface of the ski  50 . The pivoting member  4  rotates along the rotation axis  64 . 
     It is to be noted that the shaft or kingpin that is initially used to fix the ski to the snowmobile may be used to fix the retractable wheel system of the present invention. It is also possible to use another shaft conceived for the retractable wheel system. 
     To move the wheel  2  in an extended configuration the user pushes with his foot on the actuator  27  in the direction indicated by the arrow  66 . The user applies the adequate force to overcome the tension in the spring  8 . The actuator  27  is a piece used to push downwardly the wheel  2  in an extended configuration and which is easily actuated with a foot. This manipulation moves the wheel so that the bottom of the wheel  2  is at a horizontal level lower than the undersurface of the ski  50 . The wheel  2  is then in contact with the ground and is maintained in this configuration because of the weight of the snowmobile, this weight creating a force greater than the tension in the spring  8 . It is possible to adjust the distance between the bottom of the wheel  2  and the undersurface of the ski  50 , by modifying the dimensions of the parts of the system, for example. This distance may be of 1 inch or 2 inches, for example. 
     While the user goes back in a snowy zone, the non-snowy surface is gradually or suddenly replaced by a snowy surface. When there is enough snow under the ski  50 , i.e. more than the distance between the ski  50  and the bottom of the wheel  2 , the tension in the spring  8  will cause the wheel to go back in a retracted configuration. The tension in the spring  8  has to be adjusted to bring back the wheel in a retracted configuration. It is possible to adjust the tension according to the show condition. For example, if the snow is dense or hard, it is possible to adjust the spring  8  to obtain a higher retraction force to insure that the wheel will go back in a retracted configuration. 
       FIGS. 9 to 25  show a second embodiment of the retractable wheel system according to the present invention. The retractable wheel system comprises a fixation member  106 , a pivoting member  104 , a wheel  102  and a retraction system  122 . The fixation member  106  is fixed to the snowmobile ski  150  with attachment means, such as bolt  114  and nut  116 . The bushing  156  is inserted in the opening  152  of the ski and in the opening  151  of the fixation member  106 . As shown in  FIG. 9 , the bushing  156  is preferably fixed to the fixation member  106 . This configuration allows the distribution of the forces in the reinforced portion of the ski and preserves the structural integrity of the ski  150 . It has been found in experimentation that the kingpin is more subject to deformation without the use of the bushing  156 . 
     In this second embodiment, the spring  108  is of mainspring type. A mainspring is typically a spiral spring of metal ribbon. Winding, or twisting the spiral tighter, stores energy in the mainspring. 
     The pivoting member  104  is rotatably connected to the fixation member  106  with the shaft  118 . In this embodiment, the shaft  118  is screwed to the fixation member  106  and allows the pivoting member  106  to rotate along the shaft  118 . The wheel  102  is rotatably fixed to the pivoting member  104  with the wheel shaft  188 . A washer  142  is installed between the wheel  102  and the bolt head of the wheel shaft  188 . 
     The case  180  comprises the spring  108 . The spring  108  is an elongated strip made from a resilient material having rigidity, such as steel for example, that is rolled on itself. The case  180  comprises an opening  181  configured to received the cylindrical part  186 . The spring  108  comprises a first hook  194  and a second hook  196 . The first hook  194  is retained by the slot  197  of the cylindrical part  186 . The second hook is retained by the extension  198  extending from the fixation member. The tension in the spring is adjusted by modifying the number of loops of the strip. To obtain a higher tension in the spring, the spring is rotate to create more loops. 
     The hooks  194  and  196  are a folded portion of the strip allowing the spring  108  to be retained by the slot  197  and the extension  198 . It is to be noted that the strip could be retained otherwise, with a supplementary part for example or by using other appropriate means. 
     A stopper  144  is connected, screwed in this preferred embodiment, to the extremity of the bushing  156  extending on the other side of the fixation member  106 . An o-ring  146  is preferably installed on the stopper  144 . As shown more specifically in  FIG. 10 , the pivoting member  104  comprises an extension  192  forming an arcuate portion  190 . The arcuate portion is configured to mates the stopper  144  and the o-ring  146 . The stopper  144  could be installed elsewhere on the system, for example on the fixation member, without departing from the scope of the present invention. 
     The spring  108  is maintained in a compressed state by retaining its extremities in the slot and the extension, creating a rotational force on the pivoting member  104 . This rotational force allows the wheel to stay in a retracted configuration as shown in  FIG. 13 , and allows the wheel to return automatically from the extended configuration to the retracted configuration when the snowmobile returns on a snowy zone. 
     To move the wheel  102  in an extended configuration prior to circulate in an non-snowy zone or lightly snowy zone, the use pushes on the pivoting member to move the wheel  102  in an extended configuration as shown in  FIG. 12 . The user applies a force sufficient to overcome the tension of the spring. This will position bottom part the wheel  102  at a horizontal level lower than the undersurface of the ski  150 . The wheel is then in contact with the ground and is maintained in this configuration under the weight of the snowmobile. It is possible to adjust the distance between the bottom of the wheel  2  and the undersurface of the ski  50 , by using pieces having different dimension, for example. This distance may be of 1 inch or 2 inches, for example. 
     While the user goes back in a snowy zone, the non-snowy surface is gradually or suddenly replaced by a snowy surface. When there is enough snow under the ski  150 , i.e. more than the distance between the ski  150  and the bottom of the wheel  102 , the tension in the spring  108  will cause the wheel to go back in a retracted configuration. The tension in the spring  108  has to be adjusted to bring back the wheel in a retracted configuration. It is possible to adjust the tension according to the show condition. For example, if the snow is dense or hard, it is possible to adjust the tension in the spring  108  to obtain a higher retraction force to insure that the wheel will go back in a retracted configuration. 
     Referring now to  FIGS. 14 to 25 , to install the retractable wheel system, the kingpin  182  of the snowmobile ski and the arm  178  are dismounted from the ski and the piece  184  is removed. The bushing  156  is installed where the piece  184  has been removed. The retractable wheel system  100  is fixed to the ski using the fixation member. The spring  108  is wind up by rotating the pivoting member  106  counterclockwise in the embodiment shown, as shown in  FIG. 23 . The pivoting member  106  is turned a predetermined number of times corresponding to the desired tension to be transferred to the spring. The stopper  144  is then installed to prevent the spring to unwind. 
       FIGS. 26   a ,  26   b ,  26 . 1   a ,  26 . 1   b  and  26 . 2   a  show another embodiment of a shaft  220  used with the first embodiment of the retractable wheel system illustrated in  FIG. 1 . To pass from the retracted configuration to the extended configuration, the spring  8  rotates on its longitudinal axis, causing a small longitudinal elongation of the spring  8 . Even if the elongation is small, the stress induced on the retaining ring  37  may be enough to dislodge it from the groove  245 . The second embodiment of the shaft  220  provides a solution to this problem. The slot  233  is configured to receive the first extremity  28  of the spring  8 . As shown in  FIG. 26.2   a , there is an angle π between the bottom  235  of the slot and the top  237  of the slot. The walls  239  and  241  are not at a perpendicular angle relatively to the surface  243  of the shaft. This configuration forces the first extremity  28  of the spring  8  to stay in the bottom portion of the slot  233 . It is to be noted that this shaft could be use in other application such as with a transmission arm on which a spring is connected. 
     The angle π may vary between 8° and 15°, more preferably between 10° and 14°. It has been found during experimentation that an angle of 12° provides better results. 
     The material of the parts of the retractable wheel system are resistant to impacts, winter conditions, principally. For example, the structure of the system may be made from composite, aluminium, steel, or other alloys. The spring is typically made from steel. The case may be made from a variety of materials, for example composites, metal or metal alloy or from plastics. The case is preferably made from polyethylene (UHMW). The wheel is preferably made from a resilient material that is resistant to cold temperatures, as known in the art. 
     It is to be noted that the tension in the spring is not the same in the retracted configuration and in the extended configuration. Indeed, when the wheel is in an extended configuration, it induces a supplementary tension in the spring. In the retracted configuration, the tension is at least sufficient to maintain the wheel in the retracted configuration. In the retracted configuration, the tension may be of 5 to 15 lbs for example. In the extended position, the tension may go up to 15 to 20 lbs. 
     It is to be noted that the different parts of the retractable wheel system may be unitary, or they may be assembled by using known means in the art, such as welding, screws, rivets, etc. 
     While illustrative and presently preferred embodiment(s) of the invention have been described in detail hereinabove, it is to be understood that the inventive concepts may be otherwise variously embodied and employed and that the appended claims are intended to be construed to include such variations except insofar as limited by the prior art.