BACKGROUND OF THE INVENTION 
     The present invention relates generally to a belt drive having a speed selection shift mechanism. In particular, the present invention relates to a shift collar that is moveable and engageable between a pair of drive pulleys. 
     To shift between speeds on conventional belt drive mechanisms, such as those used on agricultural combines, involves stopping the rotation of the belt drive, removing tension on the belt and moving the belt from one set of pulleys to another. Typically, to accomplish this, a tensioning mechanism for the pulley belt or belts must be disengaged or released. The belt or belts must then be moved from one set of pulleys to a second set of pulleys. Then, the belt tension mechanism must be re-engaged. Belt tension on such belt drive mechanisms is relatively high and thus a mechanical advantage device, such as a relatively long lever arm, is utilized to engage and disengage the tensioning mechanism. Moreover, moving the belt or belts can be difficult due to the length of the belts and/or the location of the belts within the framework of e.g., an agricultural combine. 
     Thus, what is sought is a belt drive shift mechanism for rotatable items on agricultural machines, such as combines and the like, which eliminates the need for engaging and disengaging the belt tensioning mechanism, and physically moving the belt or belts from one set of pulleys to another. However, conventional belt drive shift mechanisms have a number of drawbacks. For example, due to the arrangement, complexity and shape of conventional shifter mechanisms, such devices are very expensive, difficult to manufacture and easily susceptible to mechanical malfunction as a result of harvesting debris interfering with the mechanical operation of the shifter mechanism. 
     Thus, there is still a need for a shifter mechanism capable of shifting between a pair of pulleys that addresses the aforementioned drawbacks of conventional shifter mechanisms. Such a need is satisfied by the shift mechanism for a belt drive having a shift mechanism of the present invention. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with a preferred embodiment, the present invention provides a speed select shift mechanism for a belt drive assembly that includes a shaft rotatable about an axis, a first pulley, a second pulley, and a shift collar. The first pulley is mounted on and rotatable about the shaft and includes a first aperture. The second pulley is mounted on and rotatable about the shaft and positioned adjacent the first pulley, and includes a second aperture. The shift collar is mounted on the shaft for rotation therewith and for axial movement relative to the shaft and positioned between the first and second pulleys. The shift collar is moveable between first and second positions. The shift collar includes an annular body, a first dowel and a second dowel. The first dowel extends from a first surface of the annular body and is engageable with the first aperture of the first pulley. The second dowel extends from a second surface of the annular body and is engageable with the second aperture of the second pulley. In the first position, the first dowel is engaged with the first aperture and in the second position the second dowel is engaged with the second aperture. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The foregoing summary, as well as the following detailed description of the preferred embodiments of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
       In the drawings: 
         FIG. 1  is a simplified side view of an agricultural combine including a belt drive assembly according to the present invention; 
         FIG. 2  is an enlarged side view of the belt drive assembly of  FIG. 1 ; 
         FIG. 3  is a cross-sectional perspective view of a shift mechanism of the belt drive assembly of  FIG. 2  in accordance with a first preferred embodiment of the present invention; 
         FIG. 4  is a perspective view of the shift mechanism of  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of the shift mechanism of  FIG. 3 ; 
         FIG. 6  is a side elevation view of a shaft of the shift mechanism of  FIG. 3 ; 
         FIG. 7  is a perspective view of a first pulley of the shift mechanism of  FIG. 3 ; 
         FIG. 7A  is an enlarged partial perspective view of apertures of the first pulley of the shift mechanism of  FIG. 3 ; 
         FIG. 7B  is an enlarged partial perspective view of an alternative configuration of the apertures of the first pulley of the shift mechanism of  FIG. 3 ; 
         FIG. 8  is a perspective view of a second pulley of the shift mechanism of  FIG. 3 ; 
         FIG. 8A  is an enlarged partial perspective view of apertures of the second pulley of the shift mechanism of  FIG. 3 ; 
         FIG. 8B  is an enlarged partial perspective view of an alternative configuration of the apertures of the second pulley of the shift mechanism of  FIG. 3 ; 
         FIG. 9  is a perspective view of a shift collar of the shift mechanism of  FIG. 3 ; 
         FIG. 10  is a cross-sectional perspective view of a shift mechanism in accordance with a second preferred embodiment of the present invention; 
         FIG. 11  is an enlarged partial, cross-sectional, elevation view of the shift mechanism of  FIG. 10 ; 
         FIG. 12  is a side elevation view of a shaft of the shift mechanism of  FIG. 10 ; 
         FIG. 13  is a partial perspective view of the shaft, the shift collar and the shift collar spacer of the shift mechanism of  FIG. 10 ; 
         FIG. 14  is a perspective view of the shift collar of the shift mechanism of  FIG. 10 ; 
         FIG. 15  is a perspective view of a first pulley of the shift mechanism of  FIG. 10 ; 
         FIG. 16  is a perspective view of a second pulley of the shift mechanism of  FIG. 10 ; 
         FIG. 17  is a perspective view of the shift collar spacer of the shift mechanism of  FIG. 10 ; 
         FIG. 18  is a perspective view of a shifter of the shift mechanism of  FIG. 10 ; 
         FIG. 19  is a perspective view of an alternative configuration of the shifter of the shift mechanism of  FIG. 18 ; and 
         FIG. 20  is a schematic block diagram of a control system in accordance with a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the invention illustrated in the accompanying drawings. Wherever possible, the same or like reference numbers will be used throughout the drawings to refer to the same or like features. It should be noted that the drawings are in simplified form and are not drawn to precise scale. In reference to the disclosure herein, for purposes of convenience and clarity only, directional terms such as top, bottom, above, below and diagonal, are used with respect to the accompanying drawings. Such directional terms used in conjunction with the following description of the drawings should not be construed to limit the scope of the invention in any manner not explicitly set forth. Additionally, the term “a,” as used in the specification, means “at least one.” The terminology includes the words above specifically mentioned, derivatives thereof, and words of similar import. 
     Referring now to the drawings, wherein preferred embodiments of the present invention are shown,  FIG. 1  illustrates a belt drive assembly  8  having a speed selection shift mechanism of the present invention as applied to an agricultural combine  1 . In particular, the belt drive assembly  8  is shown to be operatively connected to a rotary straw chopper  2  (having a driven shaft) and a rotatable power source  3 , such as an internal combustion engine or the like, for rotatably driving the straw chopper  2  for receiving straw and other crop residue from a threshing mechanism  4  and cutting, chopping and propelling the residue rearwardly and outwardly from the agricultural combine  1 . 
     Referring to  FIGS. 2-9 , in a first preferred embodiment, the present invention provides a shift mechanism  100  of the belt drive assembly  8  for shifting between a first pulley e.g., a low speed pulley  124  and a second pulley e.g., a high speed pulley  136 . The shift mechanism  100  includes a shaft  102  rotatable about an axis A, the first pulley  124 , the second pulley  136 , a shifter  178  mounted to the shaft  102  and a shift collar  156 . 
     Referring to  FIG. 6 , the shaft  102  is preferably configured as shown and is rotatable about axis A concentric with a longitudinal axis of the shaft  102 . The shaft  102  can be connected to the straw chopper  2 . Alternatively, the shaft  102  can be connected to any device that has use for a rotationally driven shaft. 
     The shaft  102  has a proximal end that can be connected to a rotatably driven device and a distal end  120  opposite the proximal end. Progressing from the proximal end towards the distal end  120 , the shaft  102  includes a first diameter section  104 , a second diameter section  108  adjacent to the first diameter section  104 , a third diameter section  110  adjacent to the second diameter section  108 , and a fourth diameter section  112  adjacent to the third diameter section  110 , each progressively smaller in diameter than the preceding section. 
     The third diameter section  110  includes splines  116  for engaging corresponding splines  160  on the shift collar  156  ( FIG. 9 ). The third diameter section  110  further includes a through hole opening  118 . The through hole opening  118  is preferably configured as an elongated slot  118  that extends completely through the shaft  102  in a direction transverse to axis A. 
     The second diameter section  108  is sized to receive a bearing assembly  194  situated between the second diameter section  108  and the first pulley  124 . Similarly, the fourth diameter section  112  is sized to receive a bearing assembly  196  situated between the fourth diameter section  112  and the second pulley  136 . 
     The distal end  120  of the shaft  102  includes an aperture  103  ( FIG. 5 ) extending through the center of the shaft  102  concentric with the longitudinal axis A of the shaft  102 . The aperture  103  is sized and configured to receive the shifter  178 . The shifter  178  slides into the aperture  103  to operatively connect the shifter  178  to the shift collar  156 , as further discussed below. The distal end  120  of the shaft  102  can optionally include through hole  122  extending transverse of the longitudinal axis of the shaft  102  for receiving a retaining pin that engages the shifter  178  to hold the shifter  178  in a fixed position. 
     Referring to  FIGS. 3, 5 and 7 , the first pulley  124  is configured as best shown in  FIG. 7 . The first pulley  124  includes an annular body  128  having a central through hole  126  sized to mount onto the shaft&#39;s second diameter section  108  in conjunction with the bearing assembly  194 . The first pulley  124  also includes a first cylindrical flange  130  (i.e. a first wall segment) having a first diameter extending from the annular body  128  or (sheave  128 ) towards the distal end  120  of the shaft  102  in a direction substantially parallel to the longitudinal axis A of the shaft  102  when mounted thereon. However, the first cylindrical flange  130  can alternately be configured frustoconical or frustospherical in shape or any other shape suitable for purposes of forming an enclosure. 
     The annular body  128  further includes at least one aperture  132  having an abutment  132   a  for cooperatively engaging corresponding elements  168  ( FIG. 9 ) on the shift collar  156 , as further described below. Preferably the first pulley  124  includes three apertures and more preferably nine apertures that are circumferentially and equidistantly spaced apart. The apertures  132  are positioned between the central through hole  126  and the first cylindrical flange  130 . More preferably the apertures  132  are configured as counterbore apertures, as opposed to through hole apertures. 
     The apertures  132  are positioned with an annular recess  131 . The annular recess  131  is also configured to have a sloped entry  133  leading into each aperture  132  (as best shown in  FIGS. 7 and 7A ). While  FIGS. 7 and 7A  illustrate the sloped entry  133  sloping inwardly into the body of the first pulley  124  going in the counterclockwise direction, the sloped entry  133  can also be configured to slope inwardly into the body of the first pulley  124  going in the clockwise direction. Whether or not the sloped entry  133  is in the clockwise or counterclockwise direction will depend on the direction the shaft  102  is configured to rotate. Alternatively, the apertures  132  can be configured as elongated curved slots  132 ′ ( FIG. 7B ), which preferably do not extend completely through the annular body  128  and which can optionally include sloped entries. 
     Referring back to  FIG. 3 , the annular body  128  of the first pulley  124  is also configured to have a conical shape so as to resemble a belleville washer, with the first cylindrical flange  130  preferably extending from an inner side of the conical shaped annular body  128 . 
     As best shown in  FIG. 3 , the first pulley  124  is attached to the shaft  102  via bearing assembly  194 . The first pulley  124  is configured to be in pressing engagement with the bearing assembly  194  which is also configured to be in pressing engagement with the shaft  102 . The bearing assembly  194  is positioned about the second diameter section  108  of the shaft  102 . The bearing assembly  194  is also retained on the shaft  102  via a snap ring  195  about a lateral end of the bearing assembly  194 , a flange extension  135  of the first pulley  124  and a spacer  109  about an opposite end i.e., a medial end of the bearing assembly  194 . 
     An endless belt  10 , as shown in  FIGS. 2 and 3 , is wrapped around the circumference of the first pulley  124  and engages with grooves  134  formed on the outer circumference of the first pulley  124 . The endless belt  10  is also wrapped around and engaged with a corresponding pulley  5  attached to a drive shaft  7  of the belt drive assembly  8  to transfer power from the drive shaft  7  to the driven shaft i.e., shaft  102 . 
     Referring to  FIGS. 3, 5 and 8 , the second pulley  136  is configured as best shown in  FIG. 8 . The second pulley  136  includes an annular body  140  having a central through hole  138  sized to mount onto the shaft&#39;s fourth diameter section  112  in conjunction with bearing assembly  196 . The second pulley  136  also includes a second cylindrical flange  142  (i.e. a second wall segment) having a second diameter extending from the annular body  140  (or sheave  140 ) towards the proximal end of the shaft  102  in a direction substantially parallel to the longitudinal axis A of the shaft  102  when mounted thereon. However, the second cylindrical flange  142  can alternatively be configured as frustoconical or frustospherical in shape (or any other shape suitable for purposes of forming an enclosure) that correspondingly engages with the frustoconical or frustospherical extensions of the first pulley  124 . 
     The second diameter of the second cylindrical flange  142  is configured to be slightly smaller than or larger than the first diameter of the first cylindrical flange  130  of the first pulley  124 . More preferably, the first and second diameters of the first and second cylindrical flanges  130 ,  142  are sized to slidingly engage each other or sized such that the second cylindrical flange  142  is received within the first cylindrical flange  130  or vice versa. 
     The second pulley  136  also includes at least one aperture  144  having an abutment  144   a  for cooperatively engaging with corresponding elements  168  on the shift collar  156 , as further described below. Preferably the second pulley  136  includes three apertures and more preferably nine apertures that are circumferentially and equidistantly spaced apart. The apertures  144  are positioned between the central through hole  138  of the annular body  140  and the second cylindrical flange  142 . More preferably the apertures  144  are configured as counterbore apertures, as opposed to through hole apertures. 
     The apertures  144  are positioned with an annular recess  141 . The annular recess  141  is also configured to have a sloped entry  143  leading into each aperture  144  (as best shown in  FIG. 8A ). While  FIG. 8  illustrates the sloped entry  143  sloping inwardly into the body of the second pulley  136  going in the clockwise direction, the sloped entry  143  can also be configured to slope inwardly into the body of the pulley going in the counterclockwise direction. Whether or not the sloped entry  143  is in the clockwise or counterclockwise direction will depend on the direction the shaft  102  is configured to rotate. Alternatively, the apertures  144  can be configured as elongated curved slots  144 ′ ( FIG. 8B ), which preferably do not extend completely through the annular body  140  and which can optionally include sloped entries. 
     As best shown in  FIG. 3 , the second pulley  136  is attached to the shaft  102  via bearing assembly  196 . The second pulley  136  is configured to be in pressing engagement with the bearing assembly  196  which is also configured to be in pressing engagement with the shaft  102 . The bearing assembly  196  is positioned about the fourth diameter segment  112  of the shaft  102 . The bearing assembly  196  is also retained on the shaft  102  via a snap ring  197  about a lateral end of the bearing assembly  196  and a flange extension or detent  199  of the second pulley  136  about an opposite end of the bearing assembly  196 . 
     A second endless belt  12  ( FIGS. 2 and 3 ) is wrapped around the circumference of the second pulley  136  and engaged with grooves  146  formed on the outer circumference of the second pulley  136 . The endless belt  12  is wrapped around and engaged with a corresponding pulley  6  attached to the drive shaft  7  of the belt drive assembly  8  to transfer power from the drive shaft  7  to the shaft  102 . 
     Referring to  FIG. 9 , the shift collar  156  includes an annular body  162  having a central axial hole  158  sized for operatively receiving and engaging the shaft  102 . The shift collar  156  also includes internal splines  160  about the inner surface of the axial hole  158  for engaging corresponding splines  116  on the shaft  102 . The shift collar  156  also includes at least one dowel  168  extending from planar side surfaces  164  (a first surface) and  166  (a second surface) (i.e. a first dowel extending from a first surface and a second dowel extending from a second surface) of the annular body  162 . Preferably, the shift collar  156  includes a plurality of dowels  168  extending from surfaces  164 ,  166  of the annular body and more preferably three dowels  168  that are circumferentially and equidistantly spaced apart extending from each surface  164 ,  166 . The dowels  168  are positioned radially from central axis B so as to match up in position with apertures  132 ,  144  on the first and second pulleys  124 ,  136 . 
     The dowel  168  can be formed as a unitary structure with the annular body  162 . Alternatively, the annular body  162  can be formed to have a through hole  169  sized and shaped to receive a unitary dowel  168  that is press-fitted into the through hole  169  and fixed in position. The unitary dowel  168  extends from the annular body  162  of the shift collar  156  in a direction substantially parallel to a central axis B of the shift collar  156 . Thus, each end of the unitary dowel  168  forms a first dowel or dowel portion while the opposite end of the unitary dowel  168  forms a second dowel or dowel portion. 
     While the dowel  168  is illustrated as being a cylindrical dowel, the dowel  168  can alternatively be configured with any other shape, such as parallel piped, of oval cross-section, of triangular cross-section and the like, which are suitable for the stated purpose of engaging corresponding apertures  132 ,  144  within one of the first and second pulleys  124 ,  136 . The dowel  168  can alternatively be configured to extend outwardly at an angle relative to axis B so long as the corresponding aperture on the first and second pulleys  124 ,  136  are correspondingly configured or angled to receive the angled dowel  168 . 
     The shift collar  156  further includes a thru hole  170  that completely extends through the shift collar  156  in a direction perpendicular to axis B. The thru hole  170  is positioned about the shift collar  156  so as to align with the axial slot  118  on the third diameter section  110  of the shaft  102  when the shift collar  156  is mounted thereon. This alignment is aided by the addition of a flat section  171  along the curved inner surface of the shift collar  156 . 
     Referring back to  FIG. 3 , the shifter  178  includes a handle  182  and an elongated shift rod  180  extending from the handle  182 . The elongated shift rod  180  is sized to be slidingly received within the aperture  103  of the shaft  102 . The shift rod  180  has a through hole  184  about an end opposite the end of the shift rod  180  connected to the handle  182 . The through hole  184  is positioned along the shift rod  180  so as to align with the axial slot  118  of the shaft  102  and thru hole  170  of the shift collar  156  when mounted on the shaft  102 . When the shift rod  180  is fully seated within the aperture  103  and its through hole  184  is aligned with the axial slot  118 , a locking pin  192  (i.e., cross pin) is inserted therethrough i.e., through the thru hole  170 , axial slot  118  and the through hole  184  to operatively connect the shifter  178  to the shift collar  156 . Retaining pins  190  (i.e., a retaining element) can then be inserted within opposite ends of the thru hole  170  to secure the locking pin  192  in position. The retaining pins  190  can be fixed in position by threads engaging corresponding threads within thru hole  170  or be press-fitted in place. 
     As shown in  FIG. 3 , at the distal end of the shaft  102  and extending from the shaft is the handle  182  of the shifter  178 . The handle  182  is used by applying pressure to the handle  182  in a pushing or pulling direction parallel to axis A of the shaft  102 . The handle  182  can axially move the shifter  178  and thus move the shift collar  156  to one of three desired positions e.g. a high speed position, a low speed position or a neutral speed position. 
     When the first and second pulleys  124 ,  136  are properly mounted on the shaft  102 , the first flange  130  and the second flange  142  extend towards each other a sufficient length so as to form an overlapping edge. The overlapping edges of the first and second flanges  130 ,  142  can be configured to receive a seal  188  that sealingly engages the first and second flanges  130 ,  142 . The seal  188  can be an elastomeric o-ring seal, a radial seal, a chevron seal, a felt seal or the like suitable for the invention&#39;s intended use. 
     As shown in  FIG. 3 , a cavity or enclosure  101  is formed by the walls of the first pulley  124 , the second pulley  136 , the first and second flanges  130 ,  142 , and first and second bearing assemblies  194 ,  196 . The cavity  101  is an enclosure that is completely sealed from the outside environment and which encases the shift collar  156  therein. As such, the shift collar  156  advantageously operates within an environment that is completely closed off to contamination by debris, such as debris generated from harvesting operations which can adversely effect mechanical function of conventional shifter mechanisms. 
     Referring to  FIGS. 10-20 , there is illustrated a shift mechanism  200  of the belt drive assembly  8  in accordance with a second preferred embodiment of the present invention. As shown in  FIG. 10 , the shift mechanism  200  includes a shaft  202 , a shifter  278 , a shift collar  256 , a first bearing assembly  294 , a second bearing assembly  296 , a first pulley  224  and a second pulley  236 . The shaft  202 , shifter  278 , shift collar  256 , first pulley  224  and second pulley  236  operate substantially the same as described above for the corresponding components discussed in the first preferred embodiment, except as further described below. 
     Referring to  FIG. 12 , the shaft  202  has a proximal end that can be connected to a rotatably driven device and a distal end  220  opposite the proximal end. Progressing from the proximal end towards the distal end  220 , the shaft  202  includes a first diameter section  204 , a second diameter section  206  adjacent to the first diameter section  204 , a third diameter section  208  adjacent to the second diameter section  206 , a fourth diameter section  210  adjacent to the third diameter section  208 , a fifth diameter section  212  adjacent to the fourth diameter section  210  and a sixth diameter section  214  adjacent to the fifth diameter section  212 , each progressively smaller in diameter than the preceding section. 
     Referring to  FIGS. 10 and 15 , the first pulley  224  is configured as best shown in  FIG. 15 . The first pulley  224  includes an annular body  228  having a central through hole  226  sized to mount on the shafts third diameter section  208  in conjunction with the bearing assembly  294 . The first pulley  224  also includes a first cylindrical flange  230  (i.e. a first wall segment) having a first diameter extending from the annular body  228  or (sheave  228 ) towards the distal end  220  of the shaft  202  in a direction substantially parallel to a longitudinal axis A of the shaft  202  when mounted thereon. However, the first cylindrical flange  230  can alternately be configured e.g., frustroconical or frustospherical in shape. The annular body  228  further includes at least one aperture  232  substantially similar to aperture  132  of the first embodiment described above. 
     Referring to  FIGS. 10 and 16 , the second pulley  236  is configured as best shown in  FIG. 16 . The second pulley  236  includes an annular body  240  having a central through hole  238  sized to mount on the shaft&#39;s fifth diameter section  212  in conjunction with bearing assembly  296 . The second pulley  236  also includes a second cylindrical flange  242  (i.e. a second wall segment) having a second diameter extending from the annular body  240  (or sheave  240 ) towards the proximal end of the shaft  202  in a direction substantially parallel to the longitudinal axis A of the shaft  202  when mounted thereon. However, the second cylindrical flange  242  can alternatively be configured as e.g., frustoconical or frustospherical in shape for correspondingly engaging applicable frustoconical or frustospherical extensions of the first pulley  224 . The annular body  240  further includes at least one aperture  244  substantially similar to aperture  144  of the first embodiment described above. 
     The outside diameter of the second cylindrical flange  242  is configured to be slightly smaller than the inside diameter of the first cylindrical flange  230  of the first pulley  224 . However, the outside diameter of the first cylindrical flange  230  can alternatively be configured to be smaller than the inside diameter of the second cylindrical flange  242 . More preferably, the diameters of the first and second cylindrical flanges  230 ,  242  are sized to slidingly engage each other or sized such that the second cylindrical flange  242  is received within the first cylindrical flange  230  or vice versa. Further, the first and second cylindrical flanges  230 ,  242  are sized and configured to receive a seal therebetween, such as seal  288 . 
     The shift mechanism  200  includes a shift collar spacer  248  about which the shift collar  256  mounts thereon. The shift collar  256  is located along the shaft  202  between the first pulley  224  and the second pulley  236 . Located between the shift collar  256  and shaft  202  is the shift collar spacer  248 . The shift collar  256  and shift collar spacer  248  are completely enclosed within a cavity  201  formed by the first and second pulleys  224 ,  236 . A seal  288  is located between first and second flanges  230 ,  242  of the first and second pulleys  224 ,  236 . The seal  288  can be configured as an elastomeric o-ring seal, a radial seal, a chevron seal, a felt seal or the like suitable for the invention&#39;s intended use. 
     The shift collar spacer  248  is configured as best shown in  FIG. 17 . The shift collar spacer  248  has a substantially tubular body  251  with internal splines  252  and external splines  250  formed thereon. The internal splines  252  are configured to operatively engage corresponding splines  216  on the shaft  202 . The external splines  250  are configured to operatively engage corresponding splines  260  on the shift collar  256 . The shift collar spacer  248  also includes an axial slot  254  that extends through the cylindrical body  251  in a direction transverse to a central longitudinal axis of the shift collar spacer  248 . The shift collar spacer  248  is also configured and positioned between the first and second bearing assemblies  294 ,  296 , as shown in  FIG. 10   
     Referring to  FIG. 10 , the shift mechanism  200  further includes a locking nut  298  located about the distal end  220  of the shaft  202  for locking the assembly of the shift mechanism  200  in a fixed position on the shaft  202 . The shift collar spacer  248  in conjunction with the locking nut  298  clamps the bearing assemblies  294 ,  296  to the distal end of the shaft  202 . A spacer  209  is also placed on the shaft  202  and situated about the third diameter section  208  of the shift  202  to facilitate locking of the overall assembly on the shaft  202 . 
     The first pulley  224  is positioned on the shaft  202  about the third diameter section  208 . Additionally, the first bearing assembly  294  is positioned on the third diameter section  208  and in pressing engagement with the shaft  202 . Spacer  209  and snap ring  296  facilitate locking the first bearing assembly  294  in position. 
     The second pulley  236  is positioned on the shaft  202  about the fifth diameter section  212 . Additionally, the second bearing assembly  296  is positioned on the fifth diameter section  212  and in pressing engagement with the shaft  202 . Shift collar spacer  248  and snap ring  297  facilitate locking the second bearing assembly  296  in position. 
     As shown in  FIG. 17 , the shift collar spacer  248  is a substantially tubular member having an axial through hole for receiving the shaft  202  and internal splines  252  for mating with corresponding splines  216  on the shaft  202 . The mating splines  216 ,  252  transfer power (i.e., rotational forces) from the shift collar spacer  248  to the shaft  202 . External splines  250  of the shift collar spacer  248  are configured to engage with corresponding splines  260  on the shift collar  256  which thereby transfer power from the shift collar  256  to the shift collar spacer  248 . 
     Further, the shift collar spacer  248  includes a planar chord-like segment  255  that extends the length of the shift collar spacer  248  and about which the axial slot  254  extends through. As shown in  FIGS. 11 and 13 , the axial slot  218  of the shaft  202  and the axial slots  254  of the shift collar spacer  248  are aligned so as to be concentric with or overlapping with each other. 
     Operatively, the shift collar spacer  248  is positioned along the fourth diameter section  210  of the shaft  202 . The shift collar spacer  248  is held in position between the first pulley bearing assembly  294  and the second pulley bearing assembly  296 . The shift collar  256  slidingly engages the shift collar spacer  248  to move in an axial direction along the length of the shift collar spacer  248 . 
     Referring to  FIG. 18 , the shifter  278  can be locked into place along a length of the shaft  202  (i.e., at a first, second or third position) with a cotter pin  299  ( FIG. 11 ) placed through one of a plurality of holes  286  on the distal end of the shifter rod  280  and a mating locking hole  222  on the distal end of the shaft  202  to maintain the shifter  278  in a fixed position during use of the device. As the cotter pin  299  has an opposite end that is fixed to the shaft  202 , its use eliminates unwanted movement by the shift collar  256  during use and the need for any detents to releasably hold the shift collar  256  in place, such as detents  117 , as discussed in the first preferred embodiment. Alternatively, the cotter pin  299  can be replaced with a shifter detent or any other locking mechanism suitable for the invention&#39;s intended use. 
     Referring back to  FIGS. 11 and 14 , the shift collar  256  is configured the same as shift collar  156  except for locking holes  274  and the size of the hole  258 , which is configured to receive and mate with the shift collar spacer  248 . The shift collar  256  includes locking holes  274 , (i.e., thru holes) and corresponding pins  276  that slidingly engage the locking holes  274 . The locking holes  274  run perpendicular to thru holes  270 . Similar to locking pin  192  as discussed in the first embodiment, a locking pin  292  connects the shift collar  256  to the shifter  278 . That is, the locking pin  292  engages the shift collar  256 , the shift collar spacer  248  and the shifter  278 , as shown in  FIG. 11 . The locking pin  292  is held in place by pins  276  that prohibit the ends of the locking pin  292  from exiting through the thru holes  270 . 
     Alternatively, the shifter  278  can be a shift fork or operatively connected to an actuator  207  ( FIG. 19 ), such as a hydraulic or electric actuator for moving the shifter rod  280  between first and second positions. Thus, for example, as shown in  FIG. 20  the actuator/shifter assembly allows for control of the shifter via a controller  205  from a remote location, such as the cab of the combine or a wireless handheld device operated by a user outside of the combine to allow the user to make simple and efficient changes in belt speed between high speed, low speed and neutral positions depending on the requirements of the rotatably driven device. 
     The operation of the shift mechanism  100  is now described with reference to the first preferred embodiment. However, the foregoing operational description of the shift mechanism  100  is equally applicable to the shift mechanism  200 . 
     In operation, the shift mechanism  100  is used to transfer power from a driver shaft  7  to the shaft  102 . The driver shaft  7  has two pulleys  5 ,  6 , each of which is in connection with corresponding pulleys  124 ,  136  on the shaft  102  via endless belts  10 ,  12 . The endless belts  10 ,  12  are in tension while wrapped around and engaged with the pulleys. 
     As the pulleys on the driver shaft  7  rotate, the endless belts  10 ,  12  rotate in corresponding fashion. The rotating endless belts  10 ,  12  cause the corresponding first and second pulleys  124 ,  136  on the shaft  102  to rotate without any power being transferred to the shaft  102  as the pulleys  124 ,  136  rotate freely about the shaft on the bearing assemblies  194 ,  196 . Power is transferred from either of the first and second pulleys  124 ,  136  to the shaft  102  only when the shift collar  156  operatively engages one of the first and second pulleys  124 ,  136 . 
     The shift collar  156  is configured to move between first, second and third positions along the axial length of the shift collar&#39;s third diameter section  110 . The shift collar  156  is moved between positions by the shifter  178 , which is connected to the shift collar  156  via locking pin  192  that extends through the shifter&#39;s through hole  184 . Thus, the shift collar  156  is moved between first, second and third positions by moving the shifter  178  in an axial direction, either towards the right or left, as shown in  FIG. 3  to engage or disengage from the first or second pulleys  124 ,  136 . 
     In the first position (e.g., a low speed position, as illustrated in  FIG. 3 ), the shift collar  156  is adjacent to and engaged with the first pulley  124 . That is, when the shift collar  156  engages the first pulley  124 , the plurality of dowels  168  are received within the apertures  132  of the first pulley  124  to operatively transfer rotational forces from the first pulley  124  to the shift collar  156 , which then transfers rotational forces to the shaft  102  owing to the engaging splines  160  and  116  on the shift collar  156  and shaft  102 , respectively. 
     In the second position (e.g., a high speed position), the shift collar  156  is engaged with the second pulley  136  and disengaged from the first pulley  124 . That is, when the shift collar  156  engages the second pulley  136 , the plurality of dowels  168  are received within the apertures  144  of the second pulley  136  to operatively transfer rotational forces from the second pulley  136  to the shift collar  156 , which then transfers rotational forces to the shaft  102  owing to the engaging splines  160  and  116  on the shift collar  156  and shaft  102 , respectively. 
     In the third position (i.e., a neutral position), the shift collar  156  is neither engaged with the first pulley  124  nor the second pulley  136 . That is, the dowels  168  of the shift collar  156  are not operatively engaged with either of the first or second pulleys  124 ,  136 . As such, the shift collar  156  is free from rotational forces acting upon it and the first and second pulleys  124 ,  136  are free to rotate about the shaft  102  without the shaft  102  rotating. The shift collar  156  is maintained in the respective first, second and third positions by appropriate detents  117  or friction features. As shown in  FIG. 6 , two sets of detents  117  are located within the elongated slot  118  of the shaft  102  for releasably holding the shift collar  156  in one of three positions. In an alternative configuration, three sets of detents  117  can be configured and positioned within the elongated slot  118  of the shaft  102  for releasably holding the shift collar  156  in one of three positions. While such detent mechanisms are preferred, alternative detent mechanisms suitable for the present invention can be used, such as the detent mechanism disclosed in U.S. Pat. No. 6,773,367, the entire disclosure of which is hereby incorporated by reference herein in its entirety. 
     The instant invention advantageously provides a number of benefits over the prior art. For example, the shift collar  156  includes dowels  168  which allow for simplicity in design (i.e., easier to machine with less tolerance issues) and easier mechanical operations for engaging and disengaging from first and second pulleys  124 ,  136 . Further, the instant invention provides for a shift collar  156  that operatively moves within a sealed environment (i.e., a sealed enclosure) which drastically reduces the adverse impact of debris on the mechanical operations of the shift mechanism. 
     It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. For example, alternative components and methods of cooperatively engaging the pulleys to the shift collar can be used. It is to be understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.
A speed select shift mechanism for a belt drive assembly to be installed on a shaft capable of shifting between high, low and neutral speeds is disclosed. The shift mechanism includes a shift collar that is enclosed within an enclosure to prevent debris from contacting the inner operations of the shift mechanism and thereby reduce wear and tear of the shift mechanism along with down time for maintenance of the device. The shift mechanism includes a shaft, a first pulley, a shift collar, a second pulley and a shifter. The shift collar further includes dowels that cooperatively engage corresponding apertures on the pulleys.