Abstract:
A drive assembly for a closed loop cable system in which a flexible driver member drives a door or the like back and forth has the flexible drive member wrapped around and driven by a drive pulley. The drive assembly includes a motor unit having a motor shaft that rotates about a drive axis for rotating the drive pulley about a pulley axis, and a tensioning mechanism for adjusting the position of the pulley axis with respect to the drive axis responsive to tension in the flexible drive member.

Description:
TECHNICAL FIELD 
   This invention relates generally to a closed loop system, such as a sliding door closure system for opening and closing a sliding door on a vehicle, and more particularly to a drive assembly for driving a flexible drive member, such as a cable, in any closed loop system. 
   BACKGROUND OF THE INVENTION 
   Van type vehicles for passengers and for cargo are frequently equipped with sliding side doors. Many vans include a single sliding door on the passenger side of the van. However, the van may be equipped with sliding doors on both sides. Drivers and passengers can open or close sliding doors of this type manually from inside or outside of the vehicle. However, the sliding door is usually heavy and often inconvenient and/or difficult to move manually, particularly from inside the vehicle. 
   For convenience, power operated sliding door closure systems have been developed to allow drivers and passengers to open and close a sliding door virtually effortlessly. Moreover the sliding door usually can be opened or closed from the driver&#39;s seat and/or one or more other locations remote from the sliding door. 
   One type of power operated sliding door closure system, known as a “closed loop” system, is disclosed in U.S. Pat. No. 6,390,535 which issued May 21, 2002 to David Joseph Chapman. The Chapman &#39;535 patent discloses a power operated sliding door closure system in which a sliding door is mounted on a van by travelers that are slidably supported in upper, center and lower tracks. An opening and closing module is mounted inside the van adjacent the center track. A front cable is attached to one end of a cable drive spool and extends from the spool to the traveler via a fixed idler roll. A rear cable is attached to an opposite end of the cable drive spool and extends from the spool to the traveler via another fixed idler roll. A motor drive unit rotates the cable drive spool in one direction to open the sliding door and in an opposite direction to close the sliding door. The closed loop cable closure system disclosed in the Chapman &#39;535 patent also includes two spring biased rollers that are mounted on the vehicle frame between the cable drive spool and the two idler rolls. The spring biased rollers engage the front and rear cables to provide a generally constant tension in the cables. 
   While the “closed loop” type of system disclosed in the Chapman &#39;535 patent is satisfactory for its intended purpose, the system requires considerable space for the idler rolls and the spring biased rollers. Moreover, one or more of the spring biased rollers may produce reverse bending in the cable which increases fatigue and reduces durability. 
   Another type of closed loop system is disclosed in the U.S. Pat. No. 6,464,287 granted to Lloyd Walker Rogers, et al. Oct. 15, 2002. The Rogers &#39;287 system includes a guide pulley at one end of a loop of beaded cable and a drive pulley at the opposite end of the loop that drives the beaded cable. The specification of the Rogers &#39;287 patent states that additional guide pulleys can be used. However, a spring biased guide pulley to take up slack in the beaded cable is not shown or describe specifically. 
   SUMMARY OF THE INVENTION 
   According to the invention, a drive assembly for a closed loop system which not only drives the cable but also takes up the slack in the cable or cables to maintain cable tension thus eliminating, or at least reducing the number of spring biased idler pulleys or rollers in the closed loop system. 
   The drive assembly includes an electric motor that can be mounted on a fixed support, a drive pulley driven by the electric motor and an intervening tensioning mechanism that moves the drive pulley automatically with respect to the fixed motor to take up slack and provide tension in the cable or cables of a closed loop system. 
   The drive assembly may be adapted to any closed loop system that uses any type of flexible drive member, including a drive belt, a chain, a plain cable or a beaded cable. 
   The drive assembly preferably provides a tension in the cable that is equally balanced so that the drive assembly can be used in a closed loop system that also has spring biased idler roller to take up slack in the cable or cables. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the invention will become apparent to those skilled in the art in connection with the following detailed description and drawings, in which: 
       FIG. 1  is a schematic perspective view of a sliding door closure apparatus having a drive assembly in accordance with the invention; 
       FIG. 2  is an exploded perspective view of the drive assembly that is shown in  FIG. 1 ; 
       FIG. 3  is a perspective view of the drive assembly that is shown in  FIGS. 1 and 2 ; 
       FIG. 4  is a perspective view of an alternate drive assembly in accordance with the invention; and 
       FIG. 5  is a perspective view of another alternate drive assembly in accordance with the invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   A power operated, sliding door closure system for opening and closing a sliding door on a vehicle is generally shown at  10  in schematic  FIG. 1 . In  FIG. 1  the system  10  is shown configured to be installed with a door closure apparatus in a van that includes a sliding door (not shown) supported on a plurality of sliding door tracks mounted on a vehicle frame. System  10  includes a traveler, shown at  12  in  FIG. 1 , that connects the closure system  10  to the sliding door. The door closure system moves the sliding door and traveler  12  along one of the sliding door tracks  18  between a closed position and an open position by means of a closed loop cable  14 . Cable  14  which is illustrated as a beaded cable is attached to traveler  12  and loops around an idler pulley  16  and a drive pulley  22  of a drive assembly of the invention that is shown schematically at  20  in  FIG. 1 . 
   The drive assembly  20  constructed according to the invention and configured for use in a closed loop cable closure system  10  briefly described above is shown in more detail in  FIGS. 2 and 3 . 
   Referring now to  FIGS. 2 and 3 , drive assembly  20  comprises a drive pulley  22  that rotates about a pulley axis  24  to drive cable  14 , a motor sub-assembly  26  having an motor shaft  28  that rotates about a drive axis  30  to rotate drive pulley  22 , and an intervening, tensioning mechanism  32  that automatically adjusts the position of the pulley axis  24  with respect to the drive axis  30  to take up slack in cable  14 . 
   Motor sub-assembly  26 , which generally includes an electric motor  34  and a speed reducing gear set  36 , and tensioning mechanism  32  are both fixedly mounted to a bracket  38  for attachment to vehicle structure (not shown). 
   Tensioning mechanism  32  comprises a housing  39  for a ring gear  40 , a planet gear  42  that meshes with the ring gear  40  and a planet carrier  44  that supports the planet gear  42  rotationally. Preferably, ring gear  40  is an internal ring gear and planet gear  42  is inside ring gear  40  to conserve space. 
   Ring gear  40  is rotated about drive axis  30  by motor shaft  28  via an optional torsional damper  50 . Torsional damper  50  comprises an input member  52  that is driven by motor shaft  28  and that in turn drives an output member  54  via a plurality of coil springs  56 . Ring gear  40  is fixed to output member  54  in any suitable manner so that the ring gear is driven by the output member of the torsional damper  50 . Torsional damper  50  is conventional and operates in a well known manner to smooth out any variation in torque applied to ring gear  40 . 
   Planet carrier  44  is mounted in housing  39  for rotation about drive axis  30 . Planet gear  42  is rotationally supported by planet carrier  44  off center so that planet gear  42  has an axis that travels in a circular orbit about drive axis  30  when planet carrier  44  is rotated. 
   Planet gear  42  is connected to drive pulley  22  by planet shaft  46  and thus moveable pulley axis  24  also travels in the same circular orbit about drive axis  30  as the axis of the planet gear  42  when planet carrier  44  is rotated. Tensioning mechanism  32  also includes a tension spring  48  that rotates planet carrier  44  about drive axis  30  incrementally to locate pulley axis  24  in the circular orbit and thus adjust the location of the pulley axis  24  with respect to drive axis  30  so as to take up slack in cable  14 . More particularly, tension spring  48  is connected to a radial arm  49  of planet carrier  44  at one end and to a fixed anchor  47  on bracket  38  at the opposite end. Tension spring  48  produces a clockwise moment force on carrier  44  that tends to move pulley axis  24  toward the right as viewed in  FIG. 1 . This movement is resisted by cable  14  that is wrapped around the right side of pulley  22 . Hence, the location of the pulley axis  24  is automatically adjusted when the tension in cable  14  produces a counterclockwise moment force on carrier  44  that cancels the clockwise moment force produced by tension spring  48 . 
   Planet gear  42  preferably has a similar pitch diameter as the drive pulley  22 . This allows a balancing of forces. The gearing is aligned such that the tangential tooth load is opposite in direction to the load imposed by the cable. Thus the cable force is balanced. As the planet gear  42  and drive pulley  22  are rigidly connected, torque is transferred from planet gear  42  to drive pulley  22 . Thus the torque in the planet gear  42  and drive pulley  22  are equal. The force in the cable  14  is equal to the torque divided by the radius of the pulley  22 . Likewise the tangential tooth load is equal to the torque divided by the pitch radius of the planet gear  42 . Therefore the radii are of similar size and the forces are balanced. 
   Referring now to  FIG. 4 , a drive assembly of the invention having an alternate tensioning mechanism  132  is disclosed. Tensioning mechanism  132  comprises a housing  139  for a sun gear  140 , a planet gear  142  that meshes with the sun gear  140  and a planet carrier  144  that supports the planet gear  142  rotationally. 
   Sun  140  is rotated about drive axis  30  by drive shaft  28  via an optional torsional damper (not shown) if necessary. Planet carrier  144  is mounted in housing  139  for rotation about drive axis  30 . Planet gear  142  is rotationally supported by planet carrier  144  off center so that planet gear  142  has an axis that travels in a circular orbit about drive axis  30  when planet carrier  144  is rotated. 
   Planet gear  142  is connected to drive pulley  22  by planet shaft  146  and thus moveable pulley axis  24  travels in the same circular orbit about drive axis  30  as the axis of planet gear  142  when planet carrier  144  is rotated. Tensioning mechanism  132  also includes a tension spring, shown schematically at  148  that rotates planet carrier  144  counterclockwise about drive axis  30  as shown in  FIG. 4 . Planet carrier  144  is rotated incrementally to the locate pulley axis  24  in the circular orbit and thus adjust the location of the pulley axis  24  with respect to drive axis  30  so as to take up slack in cable  14 . More particularly, tension spring  148  is connected to an tubular arm  149  of planet carrier  144  at one end and to a fixed anchor of housing  139  at the opposite end. Tension spring  148  produces a counterclockwise moment force on planet carrier  144  that tends to move pulley axis  24  toward the right as viewed in  FIG. 4 . This movement is resisted by cable  14  that is wrapped around the right side of pulley  22 . Hence, the location of the pulley axis  24  is automatically adjusted when the tension in cable  24  produces a clockwise moment force on planet carrier  144  that cancels the counterclockwise moment force produced by tension spring  148 . 
   Tensioning mechanism  132  further includes means to limit the travel of pulley axis  24  in the circular orbit about the drive axis  30  comprising an arcuate slot  152  in a side wall  150  of housing  139  and a roller that is journalled on planet shaft  146  and disposed in the arcuate slot  152 . 
   Planet gear  142  preferably has a similar pitch diameter as the drive pulley  22 . This allows a balancing of forces as explained above. 
   Tensioning mechanisms  32  and  132  adjust the position of the pulley axis  24  in a circular or arcuate path using a planetary gear, such as planet gear  42  or  142 . 
   Referring now to  FIG. 5 , a drive assembly of the invention having another alternate tensioning mechanism  232  that adjusts the position of the pulley axis  24  in a linear path. Tensioning mechanism  232  comprises a housing  239  for a worm gear  240  of extended length, a helical gear  242  that meshes with the worm gear  240  and a carrier  244  that supports the helical gear  242  rotationally. 
   Worm gear  240  is rotated about drive axis  30  by motor shaft  28  directly thus eliminating the need for a speed reducing gear between the electric motor  34  and the tensioning mechanism  232 . Carrier  244 , which comprises slide blocks  245  disposed in parallel slides  247  equidistantly spaced on either side of helical gear  242 , is mounted in housing  239  for translation parallel to drive axis  30 . Helical gear  242  is rotationally supported by carrier  244  so that helical gear  242  has an axis that is transverse to drive axis  30  and travels in its transverse orientation in an imagary plane or path that is parallel to drive axis  30  when carrier  244  is translated. 
   Helical gear  242  is connected to drive pulley  22  by gear shaft  246  that is journalled in slide blocks  245 . Thus moveable pulley axis  24  is also transverse to drive axis  30  and travels in the imaginary plane or path that is parallel to drive axis  30  when carrier  244  is translated. Tensioning mechanism  232  also includes tension springs  248  (one shown) that translate slide blocks  245 , gear shaft  246 , helical gear  242  and drive pulley  22  toward the right as view in  FIG. 5  to locate pulley axis  24  along the path that is parallel to drive axis  30 . Pulley axis  24  is translated incrementally to locate pulley axis  24  in the path and thus adjust the location of the pulley axis  24  with respect to drive axis  30  so as to take up slack in cable  14 . More particularly, tension springs  248  are connected to respective slide blocks  245  at one end and to fixed anchors of housing  239  at their respective opposite ends. Tension springs  248  are preferably aligned with axis  24  to produce a linear force on drive pulley  22  that tends to move pulley axis  24  toward the right as viewed in  FIG. 5 . This movement is resisted by cable  14  that is wrapped around the right side of pulley  22 . Hence, the location of the pulley axis  24  is automatically adjusted when the tension in cable  14  produces a countert force on drive pulley  22  that cancels the linear force produced by tension springs  248 . 
   Worm gear is preferably aligned so that drive axis  30  is approximately parallel to the main length of cable  14  while helical gear  242  preferably has a similar pitch diameter as the drive pulley  22 . This allows a balancing of forces between the load on the helical gear  242  and the cable  14  as explained above. 
   While the preferred embodiment has been described in connection with a particular flexible drive member, beaded cable  14 , and a particular rotary drive member, drive pulley  22 , it should be understood that the drive assembly of the invention can be adapted for any flexible drive member in conjunction with any rotary drive member that can drive the flexible drive member in a closed loop. In other words, the above description is intended to illustrate a preferred embodiment of the invention rather than to limit the invention. Therefore, descriptive rather than limiting words are used. Obviously, it is possible to modify this invention from what the description teaches. Within the scope of the claims, one may practice the invention other than as described.