Abstract:
A transfer case comprising a rotational input member, a rotational output member, a rotational planetary gear portion operatingly engaged between the input member and the output member, a moveable cam member selectively engagable with the planetary gear portion, whereby the rotation of the planetary gear portion is stopped when the cam member is engaged with the planetary gear portion, the rotational direction of the output member is in the same direction as the input member when the cam member is not engaged with the planetary gear portion, and the rotational direction of the output member is opposite the rotational direction of the input member when the cam member is engaged with the planetary gear portion.

Description:
FIELD OF THE INVENTION 
     The invention relates to a reverse sprocket transfer case having a moveable cam member selectively engagable with a planetary gear portion, whereby the rotation of the planetary gear portion is stopped when the cam member is engaged with the planetary gear portion, thereby reversing the rotational direction of an output member. 
     BACKGROUND OF THE INVENTION 
     All terrain vehicles (ATV&#39;s) have been known for many years. They comprise an engine and transmission used to propel the vehicle over rough terrain. The engine generally comprises a two stroke or four stroke arrangement with a transmission attached. The transmission is generally similar those used on motorcycles, particularly since the engines are also usually derived from motorcycles. 
     One drawback for ATV&#39;s is the ability to back the vehicle should the need arise. Transmissions are available for this function, however, they can be costly, bulky and complex. Complexity can adversely affect performance and reliability since component failure is often related to the number of moving parts. The size of the reversing transmission can be a limiting factor in vehicle design as well. A large, heavy transmission is not desirable when total vehicle weight is in the range of only 400-500 pounds. 
     U.S. Pat. No. 6,742,618 (2004) which discloses a reduction drive system including planetary gears. In an alternate embodiment, a reversing unit is provided. 
     What is needed is a reverse sprocket transfer case having a moveable cam member selectively engagable with a planetary gear portion, whereby the rotation of the planetary gear portion is stopped when the cam member is engaged with the planetary gear portion. The present invention meets this need. 
     SUMMARY OF THE INVENTION 
     The primary aspect of the invention is to provide a reverse sprocket transfer case having a moveable cam member selectively engagable with a planetary gear portion, whereby the rotation of the planetary gear portion is stopped when the cam member is engaged with the planetary gear portion. 
     Other aspects of the invention will be pointed out or made obvious by the following description of the invention and the accompanying drawings. 
     The invention comprises a transfer case comprising a rotational input member, a rotational output member, a rotational planetary gear portion operatingly engaged between the input member and the output member, a moveable cam member selectively engagable with the planetary gear portion, whereby the rotation of the planetary gear portion is stopped when the cam member is engaged with the planetary gear portion, the rotational direction of the output member is in the same direction as the input member when the cam member is not engaged with the planetary gear portion, and the rotational direction of the output member is opposite the rotational direction of the input member when the cam member is engaged with the planetary gear portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate preferred embodiments of the present invention, and together with a description, serve to explain the principles of the invention. 
         FIG. 1  is a rear perspective exploded view. 
         FIG. 2  is a front perspective exploded view. 
         FIG. 3  is a side view. 
         FIG. 4  is a front view. 
         FIG. 5  is section A-A in  FIG. 4 . 
         FIG. 6  is section B-B in  FIG. 3 . 
         FIG. 7  is section C-C in  FIG. 3 . 
         FIG. 8  is a rear view. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  is a rear perspective exploded view. The inventive transfer case  100  comprises sprocket  1 . A hub  4  is rotationally engaged with sprocket  1  through needle bearing  5 . Hub  4  is rotationally engaged with planetary cage  2  through a ball bearing  16 , see  FIG. 2 . Sprocket surface  10  has a toothed profile for engaging a toothed belt (not shown). Toothed belts are known in the art. Sprocket  1  is typically the input member, although it can function as the output member as well. Hub  4  is typically the output member, although it can function as the input member as well. 
     Planetary gears  8  are rotatingly engaged with and are disposed in an annular fashion about planetary cage  2 . Each planetary gear  8  comprises a gear having a relatively larger first diameter  81  and a relatively smaller second diameter  82 . Five planetary gears are used in this embodiment. Gears  82  engage gear  41  on hub  4 . Gears  81  engage ring gear  110  on an inner surface of sprocket  1 . 
     Planetary cage  2  and gears  8  comprise the planetary gear portion. Planetary cage  2  is rotationally engaged with sprocket  1  through bearing  11 . 
     Shifter spring  21  is disposed between hub  4  and shift ring  13 . Spring  21  urges shift ring  13  into contact with movable cam  20 . Shifter spring  21  is a coil spring. 
     Outer disc  12  is fixedly connected to sprocket  1  using bolts  10 . Shift ring gear  130  cooperatively engages gear  120  on outer disc  12 . 
     Cam  20  comprises a ratchet portion  201 . Cam  20  also comprises lever  200  which engages an actuator cable (not shown) such as a Bowden cable. 
     Cam  20  slidingly and rotationally engages bearing plate  19 . Camming member  202  cooperatively engages camming body  190 . 
       FIG. 2  is a front perspective exploded view. Ratchet portion  201  cooperatively engages ratchet portion  42  on planetary cage  2 . Hub  4  engages planetary cage  2  through bearing  16 . 
     Ring gear  210  is fixedly disposed on an inward surface of planetary cage  2 . 
       FIG. 3  is a side view. Camming body  190  slidingly engages camming member  202 . Cam  20  rotates through a range of approximately 25° with respect to bearing plate  19  by application of a force to lever  200 .  FIG. 3  shows cam  20  in the fully retracted position. In operation cam  20  rotationally moves in direction D about the axis of rotation A-A of the transfer case as shown in  FIG. 1 . 
       FIG. 4  is a front view. Toothed surface  10  engages a toothed belt (not shown). 
       FIG. 5  is section A-A in  FIG. 4 . Rivets or bolts  14  may be used to connect the bearing plate  19  to a mounting surface such as a vehicle engine (not shown). Bolts  10  connect the outer disc  12  to sprocket  1 . Hub  4  connects to an output drive shaft (not shown). The drive shaft may be connected to a vehicle axle. 
       FIG. 6  is section B-B in  FIG. 3 . Gears  82  engage hub gear  41 . 
       FIG. 7  is section C-C in  FIG. 3 . Gears  81  engage sprocket ring gear  110 . 
       FIG. 8  is a rear view. Actuator engaging portion  204  is connected to an actuator by a cable (not shown). Lever  200  moves through an arc of approximately 25° between each position of operation, namely, forward and reverse. 
     Normal Mode—Forward (Non-reverse). 
     In normal mode operation a drive shaft (not shown) is connected to hub  4 . A belt (not shown) is connected to input member sprocket  1  which transmits a torque to sprocket  1  causing it to rotate. 
     In this mode cam  20  is retracted meaning that camming member  202  and camming body  190  are in the relative positions shown in  FIG. 3 . The retracted position of cam  20  allows spring  21  to urge shift ring  13  toward cam  20 , causing gear  130  to engage gear  120  of outer disc  12 . Gear  130  of shift ring  13  is also simultaneously engaged with ring gear  210 . This engagement causes planetary cage  2  to rotate in locked relation with outer disc  12  and sprocket  1 . In other words, in this mode sprocket  1 , outer disc  12 , shift ring  13  and planetary cage  2  comprise and are driven as a single unit because there is no relative rotation between planetary cage  2  and sprocket  1 . Since planetary cage  2  rotates in unison with sprocket  1 , gears  8  do not rotate relative to ring gear  110 . Therefore, gears  8  drive gear  41  and thereby hub  4  at the same rotational speed and direction as sprocket  1 . Hence, in the normal mode the planetary cage  2  rotates in unison with the sprocket  1 , thereby, the output member hub  4  rotates at the same speed and direction as the input member sprocket  1 . 
     In this Normal mode the drive ratio is 1:1. 
     Reverse Mode. 
     In reverse mode cam  20  is actuated, causing it to partially rotate with respect to bearing plate  19 . Partial rotation causes camming body  190  and camming member  202  to move relative to each other. Such movement causes cam  20  to move axially away from bearing plate  19 , which in turn causes gear  130  to disengage from gear  120 . This “breaks” the mechanical driving connection between the planetary cage  2  (gear  210 ) and the sprocket  1  (gear  120 ). This also causes ratchet teeth  201  to come into contact with ratchet teeth  42 . Since cam  20  only rotates partially through approximately 25° during actuation, this has the overall effect of stopping rotation of planetary cage  2 . However, sprocket  1  still rotates because gear  130  and gear  120  are disengaged. The rotation of the planetary gear portion planetary case  2  is stopped when the cam  20  is engaged with the planetary cage  2 . 
     Once planetary cage  2  is stopped from rotating, the engagement of gears  81  and gear  110  cause gears  8  to rotate. Rotation of gears  8  causes gears  82  to rotate, in turn driving hub gear  41 . However, hub  4  rotates in the direction opposite the direction of rotation of sprocket  1  due to the fixed position of gears  8 . Rotation of hub  4  within stationary planetary cage  2  is made possible by bearing  5  and bearing  16 . 
     In the reverse mode the drive ratio between the input member (sprocket  1 ) and the output member (hub  4 ) is approximately 1.28:1. This is because if, for example, gear  8  comprised only one gear then hub  4  would speed up when in reverse. The increase of speed would equal the ratio between the number of teeth of the sprocket gear  110 , and the hub gear  41 , which in this case, for example, is 75:35 (2.14:1). A single-gear planetary gear ( 8 ) would only be a torque transmitting/reversing medium, consequently its number of teeth would play no role in this ratio. However, since gear  8  has a larger diameter gear  81  and a smaller diameter gear  82 , and each is engaged with gear  110  and gear  41  respectively, this reduces the transmitted speed by the gear ratio of: 
     (# of teeth in gear  81 ):(# of teeth in gear  82 ) 
     which in this case by way of example is:
 
15:25=0.6.
 
     Consequently the total speed change/increase in reverse mode between input sprocket  1  and output hub  4  is:
 
2.14×0.6=1.28
 
     This means the overall drive ratio in reverse mode is 1.28:1. The inventive device achieves reverse operation without significant change to the output speed in reverse as compared to the output speed in forward. This minimizes speed surges that might otherwise be caused by small throttle inputs using other transmissions with larger ratios. 
     The drive ratio may be adjusted depending upon the relative diameters of gears  81  and  82 . 
     The input member and output members may also be reversed so that the input member is now hub  4  and the output member is now sprocket  1  with equal operating success. 
     Although forms of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of parts and method without departing from the spirit and scope of the invention described herein.