Abstract:
A drive assembly for a toothed rack and channel track type of power liftgate attaches the liftgate lift rod to the toothed rack indirectly, through a shoe-yoke assembly that transfers axial loads, but isolates the rack from non axial reactive loads transferred through the lift rod. A rigid yoke fits closely within axially spaced ends of a notch in the rack, but has a clearance elsewhere from the outside of the rack. The outside of the yoke is closely surrounded by a shoe, which provides a close fitting, slidable bearing layer with the inside of the channel track, maintaining the yoke to rack clearance. The maintenance of the yoke-rack clearance prevents the transmission of undesired reactive loads back to the rack through the yoke.

Description:
RELATED APPLICATION 
     This application claims priority from prior provisional patent application Serial No. 60/207,072 filed May 25, 2000. 
    
    
     TECHNICAL FIELD 
     This invention relates to power actuators for vehicle closure panels generally, and specifically to a non binding toothed rack and channel track type of drive assembly for a power actuator. 
     BACKGROUND OF THE INVENTION 
     More and more vehicles are incorporating power actuated closure panels, such as doors, hoods, trunk lids and rear liftgates. One such device particularly useful for a rear liftgate of the type found on minivans and SUVs is a stationary electric motor that turns a toothed wheel to slide an elongated toothed rack up and down inside a channel track. A link between the toothed rack and the liftgate pushes it up and open or swings in down and closed. Two such devices, one on each side, may be needed for large and heavy rear liftgates. Typically, the link between the power actuator and the rear liftgate is a rod that is attached at an upper end to the liftgate by a ball joint, and attached directly to the toothed rack by another ball joint at the lower end. The rod is subjected to shifting, twisting reactive loads as it moves up and down, and these are translated directly to the moving toothed rack sliding within the channel track. The non axial reactive loads tend to cause the rack to twist and bind within the channel track. 
     SUMMARY OF THE INVENTION 
     The subject invention provides an improved connection between the toothed rack and the lift rod that allows the toothed rack to slide within the channel track as it moves the lift rod up and down, but which prevents the lift rod from reacting on the toothed rack to bind it within the track. 
     In the embodiment disclosed, the toothed rack is thin enough and narrow enough to slide within the interior of the channel track with a significant clearance all the way around. A rigid yoke has a pair of side walls that straddle a notch in the upper surface of the rack, fitting closely into the axially spaced ends of the notch but spaced apart sufficiently to significantly clear the sides of the rack other than at the ends of the notch. A ball stud on the top of the yoke is pivotally joined to the lower end of the lift rod. An outer shoe of suitable bearing material, solid, but not as rigid as the yoke, surrounds the yoke, and fits closely to both the outer surface of the yoke and to the inner surface of the channel track. When the rack-yoke-shoe subassembly is installed in the channel track, the close fit of the shoe to both the inside of the track and the outside of the yoke maintains the yoke&#39;s clearance from the rack. 
     In operation, the yoke-shoe assembly slides closely back and forth within the track as the toothed wheel shifts the rack, with axial loads being efficiently transferred between the rack and yoke by the close fit to the ends of the rack notch. The all round clearance maintained by the shoe at all other points between the rack and yoke prevents non axial twisting loads from being transferred back from the yoke to the rack, however, so that the rack does not bind within the channel track. Twisting loads are instead transferred from the yoke, through the surrounding shoe, to the close fitting channel track. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will appear from the following written description, and from the drawings, in which: 
     FIG. 1 is a perspective view of a part of a vehicle with a liftgate swung open; 
     FIG. 2 is a perspective view of a power actuator&#39;s motor, lift rod and channel track removed from a vehicle; 
     FIG. 3 is a perspective view of the various components of the drive assembly of the invention before assembly; 
     FIG. 4 is a cross sectional view of the various components of the assembly taken along the lines  4 — 4  in FIG. 3; 
     FIG. 5 is a cross sectional view of the yoke taken along the line  5 — 5  of FIG. 3; 
     FIG. 6 is a cross sectional view of the show taken along the line  6 — 6  of FIG. 3; 
     FIG. 7 shows the yoke fitted to the rack; 
     FIG. 8 shows the shoe being fitted over the yoke; 
     FIG. 9 shows the rack, shoe and yoke being installed into the channel track; 
     FIG. 10 shows a cross section through the completed assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, the body of a vehicle such as a van or SUV  10  has a rear opening  12  closed by a closure panel such as a liftgate, indicated generally at  14 . The top of liftgate  14  is pivoted freely to the vehicle to swing open and closed about a pair of hinges  16 . Liftgate  14  is opened by one or more power actuators, indicated generally at  18 . A pair of such is shown, one on each side, although smaller, lighter closures could make do with only one. Most of the mechanism of the power actuators  18  would be enclosed and concealed within the body trim, and is not visible in FIG. 1. A conventional hold open means, such as a gas spring, would typically be pivoted between liftgate  14  and the vehicle body  10 , as well, but is not illustrated separately. 
     Referring next to FIGS. 2 and 3, power actuator  18  has an electric drive motor  19  which, through a suitable gear reduction mechanism, turns a toothed wheel  20  to drive a toothed rack  22  back and forth within a channel track  24 , the end to end extent of which provides a defined axis along with the actuator  18  operates. End bearing blocks  23  of semi rigid plastic or other suitable material on rack  22  slide closely within channel track  24  to keep rack  22  aligned within channel track  24 , as described in more detail below, and to keep the teeth of wheel  20  engaged with the teeth of rack  22 . Channel track  24  has a smooth inner surface with a consistent, generally rectangular cross section all along its length, folded from steel sheet to leave a full length slot  25  at the top. A lift rod  26  is attached by a socket joint  28  to one side of liftgate  14 . A socket joint  30  at the lower end of lift rod  26  is drivingly interconnected to rack  22  and channel track  24  by an assembly of rack  22 , track  24 , and other components, described next. 
     Referring next to FIGS. 3 and 4, a drive assembly indicated generally at  32  comprises, rack  22 , channel track  24 , as well as an included assemlby of a yoke, indicated generally at  34 , and a bearing shoe, indicated generally at  36 . Rack  22  is substantially narrower and thinner than the inside dimensions of channel track  24 , and would be too narrow, barring other provisions, to be attached directly to lift rod  26 . Still, it is sufficiently strong to withstand the axial driving loads from wheel  20 . Rack  22  also has a notch  38  cut into its top edge, an edge that would normally be uninterrupted, with axially opposed ends defining a length of L 1  for notch  38 . Yoke  34  is formed from a suitable rigid metal, such as cast aluminum or steel, and is generally U shaped in cross section, with a top wall  40 , depending side walls  42 , and a ball stud  44  at the top that is sufficiently tall and narrow to extend out of channel track slot  25 . The end to end length of top wall  40  L 2  is substantially identical to the length L 1  of rack notch  38 . A pair of central notches  46  are cut into the bottom edges of yoke side walls  42 . Shoe  36  is molded from a durable plastic material which provides good sliding wear resistance, but is still substantially lubricious, especially in sliding contact with steel, but also elastic enough to give slightly under twisting and compressive loading. Shoe  36  is also generally U shaped in cross section, with a top wall  48 , depending side walls  50 , and a window in top wall  48  through which ball stud  44  can extend. The end to end length L 3  of shoe top wall  48  is substantially equal to the length L 2  of yoke top wall  40 . The lower edges of shoe side walls  50  are inturned slightly, with central, thickened tabs  54  sized to fit closely within the yoke side wall notches  46 . 
     Referring next to FIG. 4, rack  22  is shown aligned within channel track  24 , centered side to side, and in an up-down orientation that is designed to maintain its engagement with the toothed wheel  20 . As noted above, it is the end bearing blocks  23  that maintain this nominal, ideal alignment, and the invention prevents any significant misalignment in operation. In general, a close fit of the outside of shoe  36  to the inside of channel track  24 , combined with a close fit of the inside of shoe  36  to the outside of yoke  34  and a maintained clearance of the inside of yoke  34  from the outside of rack  22 , all cooperate to allow the rack  22  to efficiently move rod  26 , but so as to prevent rod  26  from undesirably re acting on rack  22 . Specifically, this inter relationship is created by a complex interaction of various dimensions of rack  22 , track channel track  24 , yoke  34  and shoe  36 , which allow the four components to cooperate as a single assembly  32 , as described further below. 
     Referring next to FIGS. 4 through 6, the various cooperating dimensions of the components are illustrated. The interior width X 1  of channel track  24  is substantially identical to the exterior width X 2  of shoe  36 . The interior height of channel track  24  is substantially identical to the exterior height X 4  or shoe  36 . In short, the exterior surface of shoe  36  fits closely, but still slidably, with the interior surface of channel track  24 . The interior width X 5  of shoe  36  is substantially identical to the exterior width X 6  of yoke  34 . The interior height X 7  of shoe  36 , shown in FIG. 6, is substantially identical to the exterior height X 8  of yoke  4 . In short, the exterior surface of yoke  34  fits closely within the interior surface of shoe  36 . There is no relative axial sliding between yoke  34  and shoe  36 , however, because of the close fit of ball stud  44  through window  52 , and the close fit of tabs  54  within notches  46 . While channel track  24  and shoe  36 , and yoke  34  and shoe  36 , make a close fit, yoke  34  and rack  22  deliberately do not. The interior width X 9  of yoke  34  is significantly larger than the exterior width X 1 O of rack  22 , approximately 5 to 8 mm larger on each side. In addition to the side to side clearance of yoke  34  and rack  22 , there is up down clearance. The thickness X 11  of the inturned bottom edges of the shoe side walls  50  plus the interior height X 12  of the yoke side walls  42  is greater, by a differential of approximately 2 to 3 mm, than the ideal height X 13  of the bottom of rack notch  38  above the bottom of the interior of channel track  24 . The ideal height X 13  is maintained by the end bearing blocks  23 , which keep toothed rack  22  aligned within channel track  24 . This inter relationship of dimensions allows the components to be fitted together and cooperate as described next. 
     Referring next to FIGS. 7 through 9, a subassembly of rack  22 , yoke  34 , and shoe  36  is first built up as follows. Yoke  34  is sent into rack notch  38  as shown in FIG.  7 . The matching of lengths L 1  and L 2  noted above prevents back and forth rattle between rack  22  and yoke  34 , and notch  38  is deep enough that the ends of notch  38  overlap the ends of yoke top wall  40  sufficiently to establish an adequate, load transferring connection between the two. Next, as seen in FIG. 8, shoe  36  is snapped down over yoke  34 , which the shoe side walls  50  are flexible enough to permit. The yoke side walls  42  are captured inside the shoe side walls  50 , the shoe side wall tabs  54  are captured in the yoke side wall notches  46 , and the yoke ball stud  44  is captured through the shoe window  52 . Yoke  34  and shoe  36  are thereby held together as their own subassembly, though neither is yet held to the rack  22 . Consequently, the shoe  36  could have been snapped over the yoke  34  before the yoke  34  was set down into the rack notch  38 . Either way, the three make up another loosely held subassembly, as shown in FIG.  9 . Next, this subassembly, with the bearing blocks  23  added to then ends of rack  22 , is axially inserted within channel track  24 , as shown by the arrow in FIG. 9, to complete the assembly  32 . The end blocks  23 , of course, could be attached to rack  22  at any point. 
     Referring back to FIGS. 1 and 2, with the assembly  32  described above completed, the motor  19  and toothed wheel  20  can be engaged with rack  22 , and the lift rod lower socket joint  30  pivotally attached to the yoke ball stud  44 . Finally, the completed actuator  18  would be installed to vehicle  10 , and the upper socket joint  28  attached to the side of liftgate  14 . As noted above, essentially all the components would most likely be installed inside suitable interior trim covers, so that only the channel track slot  25  and the ball stud  44 -socket  30  joint would be visible. 
     Referring next to FIG. 10, the inter relationship of the four components of rack  22 , channel track  24 , yoke  34  and shoe  36  within the completed assembly  32  is illustrated. In general, the outer surface of rack  22  has a clearance from the inner surface of yoke  34  maintained all the way around. Specifically, by virtue of the complex dimensional inter relationships described above, a side to side clearance C 1  of approximately 5 to 8 mm and an up down clearance C 2  of approximately 2 to 3 mm are maintained between the inner surface of yoke  34  and the outer surface of rack  22 . This clearance is maintained all round, that is, everywhere in the area of notch  38  where yoke  34  straddles rack  22 , but for the axial contact between the yoke  34  and the spaced ends of the rack notch  38 . That axial contact is maintained by the alignment of rack  22  within track  24 , as held by the end bearing blocks  23 , and by the alignment of yoke  34  within track  24 , as maintained by shoe  36 . The net result is that the yoke top wall  40  is maintained seated down in the notch  38 , solidly captured between the axially spaced ends of notch  38 , as shown by the dotted line. This assures that as toothed rack  22  is run back and forth within channel track  24 , the ends of the rack notch  38  push and pull back and forth on the rigid yoke  34  to adequately transfer axial force thereto and slide the ball stud  44  up and down in the slot  25 , thereby moving lift rod  26  up and down. The reaction force of lift rod  26  back onto yoke ball stud  44  acts in widely varying directions, however, as shown by the arrows, not just axially along the channel track  24 . This is why the pivotal connection between the lower end of rod  26  and rack  22  is needed. The varying reactive force on the ball stud  44  creates twisting and tilting loads on yoke  34 . In the case where the ball stud  44  is fixed directly to the top edge of rack  22 , as is conventional, these non axial reactive loads are transferred directly to the rack  22 , as noted above. With the subject invention, the outside of yoke  34  is instead twisted into the inside of shoe  36 , which is ultimately twisted against the inner surface of channel track  24 . Shoe  36 , being an outer bearing layer of a suitable material different from yoke  34 , does not bind, but continues to slide squarely and freely along the inside of channel track  24 . The yoke  34  is sufficiently guided by the shoe  36 , and the shoe  36  by the track  24 , so that the inside of the yoke  34  does not twist or tilt enough to overcome either clearance C 1  or C 2  from the rack  22 . In short, the desired axial, up and down loads are transferred between yoke  34  and rack  22 , but the rack  22  is isolated from the undesired twisting and tilting reactive loads. 
     Variations in the disclosed embodiment could be made. A drive member other than toothed rack  22  could be moved by other means back and forth along the defined axis of the channel track  24 . Regardless, the drive member will have to be joined to the lift rod  26  or other like end in such a way as to transfer axial loads. Yoke  34  could fit between two axially spaced stops on the rack  22  other than the ends of the notch  38 . The notch  38  is easily manufactured, however. Yoke  34  and shoe  36  could be held together as an assembly by some other means than the snap fit of the tabs  54  into the notches  46 . Fundamentally, a suitably sized bearing layer could even be molded in place over the outside of yoke  34 , before or after the yoke  34  was installed between the stop members on rack  22 . Yoke  34 , fundamentally, has to serve as in inner, rigid, force transferring portion of the assembly, trapped between the stops on rack  22  and pivotally attached to the lower end of rod  26 , so that it can efficiently transfer axial loads from actuator  19  into rod  26 , but still kept clear of the rack  22  at points other than where it is captured between the axially spaced stops, so that it will not transfer non axial, reactive loads from rod  26  back into the rack  22 . The particular shoe  36  and yoke  34  assembly disclosed is relatively easy to manufacture and install, however, especially the snap fit of the shoe  36  down over the yoke  34 . A provision could also be made for some part of the shoe  36  to also retain to the rack  22 , so long as the path of toothed wheel  20  along the bottom of rack  22  was not blocked. Therefore, it will be understood that it is not intended to limit the invention to just the embodiment disclosed.