Abstract:
A track system ( 18 ) of the type used to adjust the position a supported element such as vehicular seat ( 12 ) includes a pair of base rails ( 20 ) that slidably interact with a respective pair of driven rails ( 22 ). A transverse rail ( 24 ) is attached to each of the driven rails ( 22 ) so that the driven rails ( 22 ) slide together as a unit. A motor ( 34 ) is supported on the transverse rail ( 24 ) and includes a pair of drive shafts ( 36 ) emanating from either end. The drive shafts ( 36 ) carry on their distal ends&#39; respective worm gears ( 38 ) which are contained within a transmission assembly ( 26 ). The worm gears ( 38 ) mesh with external teeth on respective drive nuts ( 54 ) which interact with a lead screw ( 28 ) that can be oriented to either remain stationary relative to the base rails ( 20 ) or can be rotatably fixed within the driven rails ( 22 ). The drive nut ( 54 ) is prevented from causing objectionable noise and premature wear in operation by the inclusion of one or two compressible washers ( 66 ).

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This Application claims priority to U.S. Provisional Application No. 60/878,712 filed Jan. 4, 2007. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates generally to a motorized track system, and more particularly toward a transmission for a motorized track system of the type used in position adjustors for vehicular seats, windows and the like. 
   2. Related Art 
   Vehicle seat assemblies are often provided with a motorized track system that enable the position of the seat assembly within a motor vehicle to be adjusted in the forward and rearward directions. Similarly, vehicular window assemblies may include a motorized track system of similar construction to enable the position of the window to be adjusted in up and down directions. In each case, the supported element is guided by the motorized track system for back and forth movement to change its position, as desired. 
   In the case of vehicular seat assemblies, for example, such adjustment capability is desired to enable vehicle operators of various body dimensions to be seated comfortably within the motor vehicle. In these systems, an electric motor may be coupled to a lead screw positioned within a sliding track assembly. In such an arrangement, the lead screw may be fixed or may rotate but a drive nut interacts with the lead screw through motor-driven rotation to move the vehicle seat assembly forward or rearward. A motorized window regulator assembly may work in much the same manner. 
   A transmission is generally provided in these types of motorized track systems for transferring power from the motor to the drive nut. In configurations where a pair of sliding tracks are employed, the electric motor may be mounted on a transverse beam bridging each of the tracks, for example in the center of the tracks or at one end of the tracks. Because certain components within the transmission rotate while others are held generally stationary, vibrations may be produced within the transmission when the transmission is operational, thereby causing noise. Another cause of noise is lateral movement of the components within the transmission housing. 
   Various proposals have been advanced for addressing the noise issues in a transmission for a motorized track system. For example, U.S. Pat. No. 7,051,986 to Taubmann et. al., granted May 30, 2006, discloses a system wherein a shim disk, identified as item number  96 ′, is used to compensate for axial play. Shim disks are subject to manufacturing variances, however and may not consistently address the noise issues. Accordingly, there is a need for a motorized track system for use in vehicular applications that meets or exceeds the established strength, speed and noise requirements. There is also a need to provide a reliable transmission that includes shock absorbing components to reduce the vibration between those components in the transmission, and to reduce noise and to eliminate lateral movement of certain components. There is a further need to provide a reliable, acceptable motorized track system for providing translational adjustment, which avoids one or more of the above-noted problems. 
   SUMMARY OF THE INVENTION 
   The invention overcomes the disadvantages and shortcomings of the prior art by providing a transmission assembly for a motorized track system of the type used to adjust the position of a support element such as a vehicular seat, window or the like. The assembly comprises an externally threaded lead screw establishing a longitudinal direction along which a supported element is moved back and forth to change its longitudinal position. A drive nut is operatively engaged with the lead screw. Motor-driven rotation of the drive nut causes the supported element to be longitudinally displaceable along the lead screw. A housing generally surrounds the drive nut. The housing includes a mounting bracket for attaching to the supported element so as to translate the supported element together with the drive nut longitudinally along the lead screw. A compressible washer is disposed between the drive nut and the housing. The compressible washer exerts a bias between the drive nut and the housing so as to eliminate lateral movement of the drive nut within the housing and to dampen or otherwise eliminate noise producing vibrations from the transmission. 
   According to another aspect of the subject invention, a motorized track system is provided of the type used to adjust the position of a supported element such as vehicular seat, window or the like. The track system comprises a base track, and an externally threaded lead screw. The lead screw establishes a longitudinal direction along which a supported element is moved back and forth to change its longitudinal position. A driven track is interactive with the base track for longitudinal sliding movement there between. A drive nut is operatively engaged with the lead screw. A housing is fixedly connected to the driven track and generally surrounds the drive nut. The housing includes a mounting bracket for attaching to the supported element to translate the supported element together with the drive nut and the driven track longitudinally along the lead screw. A compressible washer is disposed between the drive nut and the housing. 
   According to a further embodiment of the invention, a method is provided for eliminating play between a drive nut mounted in a transmission for use in a motorized track system having a lead screw, the transmission including a housing and a worm gear. The method comprises the steps of locating first and second bushings on opposite sides of the drive nut, placing a wave washer between at least one of the first and second bushings and the drive nut, and capturing the drive nut, worm gear, first and second bushings, and wave washer in a housing so that the wave washer is partially compressed. The wave washer provides an axial biasing force that reduces the tendency for the drive nut to vibrate longitudinally relative to the first and second bushings which might otherwise produce noise. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein: 
       FIG. 1  is a simplified perspective view of an exemplary automobile; 
       FIG. 2  is a perspective view of vehicular seat including a motorized track system according to the subject invention; 
       FIG. 3  is a prospective view of a motorized track system according to one embodiment of the subject invention; 
       FIG. 4  is an end elevation view of the motorized track system of  FIG. 3 ; 
       FIG. 5  is an exploded view of a portion of the motorized track system depicting the base and driven tracks, together with the lead screw and transmission assembly according to the subject invention; 
       FIG. 6  is an enlarged view of the transmission assembly as circumscribed by broken lines in  FIG. 5 ; 
       FIG. 7  is an exploded view of an alternative embodiment of the transmission assembly; 
       FIG. 8  is a partially sectioned view as taken longitudinally through the transmission assembly; and 
       FIG. 9  is a view as in  FIG. 8  but showing the compression washers deflected in response to reaction forces between drive nut and housing. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, an exemplary motor vehicle is generally shown at  10  in  FIG. 1 . The vehicle  10  in  FIG. 1  is merely exemplary, and may instead take the form of a light duty truck, SUV, minivan, bus, train, airplane, boat, or any other such vehicle or stationary application in which a motorized track assembly may be employed. In this specific example, however, the vehicle  10  is depicted including a passenger seat  12  having the customary back rest  14  and seat cushion  16 , as illustrated in  FIG. 2 . The seat  12  is supported above a motorized track system, generally indicated at  18 , that is configured to allow an occupant to adjust the position of the seat  12  in longitudinally forward and rearward directions relative to the vehicle  10 . Although the following description of the subject invention is carried out by reference to vehicular seating application, it will be understood by those of skill in the art that the subject track system  18  is adaptable for other uses, including window regulator systems, and other applications which include a supporting element which is moved back and forth under the influence of a motor to change its longitudinal position. 
   Referring to  FIGS. 2-5 , the track system  18  is shown in greater detail including two track sets that are generally parallel to one another. Each track set includes a base rail  20  that is coupled to a structure such as the floor of the vehicular passenger compartment. An upper, driven rail  22  is coupled to the seat  12  and is slidably interconnected to the base rail  20  so that the two can slide relative to one and other in a fore and aft direction, in the case of the vehicular seating application. In the case of a window regulator application, the driven rail  22  would be oriented so as to slide up and down relative to the base rail  20 . Those of skill in the art will envision other applications and orientations for the track system  18 . A bridge-like transverse rail  24  interconnects the driven rails  22  from each track set so that they are coupled together and move in unison when the seat  12  is adjusted forward or rearward. 
   A transmission assembly, generally indicated at  26 , is operatively disposed between the base  20  and driven  22  rails so as to forcibly displace one rail relative to the other during position adjustment of the supported element—be that a vehicular seat  12 , a window, or other component. 
   The transmission assembly  26  interacts with an externally threaded lead screw  28  to produce the desired longitudinal displacement. The particular method by which the transmission assembly  26  interacts with the lead screw  28  can be varied among different mechanically equivalent arrangements, two of which are depicted in the figures. More specifically, as shown in  FIGS. 5 and 6 , the transmission assembly  26  is longitudinally fixed relative to the lead screw  28  and translates, as a unit, therewith. However, in an alternative embodiment of the invention which will be described subsequently in connection with  FIGS. 7-9 , the transmission assembly  26 ′ interacts with the lead screw  28 ′ by traveling the length of the lead screw  28 ′. I.e., in this latter example, the transmission assembly  26 ′ translates longitudinally relative to a stationary lead screw  28 ′. 
   Referring specifically now the embodiment depicted in  FIGS. 5 and 6 , the lead screw  28  is rotatably supported at one end by a bearing block  30  which in turn is affixed to the driven rail  22  by a fastener  32 . The other end of the lead screw  28  is coupled to the transmission assembly  26 , which in turn is attached to the opposite end of the driven rail  22 . The transmission assembly  26  receives a rotary input from an electric motor  34  as shown in  FIGS. 2-4 . The motor  34  is provided with flexible drive shafts  36  extending from opposite ends. Each drive shaft  36  couples to a worm gear  38  which is a component of the transmission assembly  26 . Thus, as each drive shaft  36  is turned by the armature of the motor  34 , the worm gear  38  is caused to spin. The transmission assembly  26  includes a housing, generally indicated at  40 , that rotatably supports the worm gear  38  via a pair of left and right cover halves  42 ,  44  as depicted in  FIG. 6 . The cover halves  42 ,  44  may be made from a lubris polymeric material of the type known to possess inherent dry bearing qualities. Alternatively, bushings  46  may be interposed between the worm gear  38  and cover halves  42 ,  44  to provide a bearing function. Fasteners (not shown), heat staking, self-locking clips, or other methods may be used to securely join the cover halves  42 ,  44  together as an integral unit. 
   The left  42  and right  44  cover halves are surrounded at their longitudinally spaced ends by a pair of isolators  48  which serve primarily to dampen vibrations between the left  42  and right  44  cover halves and a rigid, preferably metallic, outer bracket  50 . The isolators  48  may be manufactured from a rubber or highly resilient material. The bracket  50  has, in this embodiment, a generally U-shaped configuration with outwardly bent flanges containing mounting holes  52 . According to the embodiment of this invention illustrated in  FIGS. 5 and 6 , the transmission assembly  26  is affixed to the driven rail  22  via fasteners (not shown) passing through the mounting holes  52  in the bracket  50 . 
   The transmission assembly  26  further includes a drive nut  54  having external gear teeth in meshing contact with the threads of the worm gear  38 . The drive nut  54  has a rotational axis which is generally transverse to the rotational axis of the worm gear  38 . Like the worm gear  38 , the drive nut  54  is also rotationally captured between the left  42  and right  44  cover halves of the housing  40 . In this embodiment of the invention, the lead screw  28  is fixedly joined to the drive nut  54  such that they rotate in unison about a common axis. As a result, when the drive nut  54  is forcibly rotated through the interaction of the worm gear  38 , the lead screw  28  turns within its bearing block  30 . 
   Located along the length of the lead screw  28 , between the transmission assembly  26  and the bearing block  30 , a fixed nut  56  is threadably disposed on the lead screw  28 . The fixed nut  56  is affixed relative to the base rail  20  by a mounting bracket  58  secured through fasteners  60 . In this manner, the fixed nut  56  is stationary relative to the base rail  20 . As the lead screw  28  is turned through operation of the transmission assembly  26 , its screw threads interact with internal threads in the fixed nut  56 , propelling the attached driven rail  22 , transmission  26  and transverse rail  24  in a longitudinal direction relative to the length of the lead screw  28 . By this means, the supported element, be it a seat  12 , window or other, is advanced or retracted in a longitudinal direction, as powered by the motor  34 . 
   Turning now to  FIGS. 7-9 , an alternative yet mechanically equivalent construction of this transmission assembly  26 ′ is depicted, wherein prime designations are used for convenience to distinguish between the two embodiments of this invention. In this example, the lead screw  28 ′ is fixedly attached to the base rail (not shown) so that it does not rotate. In furthering this example, the drive nut  54 ′ is provided with internal screw threads  62 ′ that threadably interact with the outer turns of the lead screw  28 ′. The bracket  50 ′ is provided with through holes  64 ′ that allow the lead screw  28 ′ to pass completely through the transmission assembly  26 ′. 
   When the drive nut  54 ′ is turned by the worm gear  38 ′, its internal threads  62 ′ advance along the lead screw  28 ′, in either longitudinal direction depending upon which way the drive nut  54 ′ is rotated, and thereby propel the entire transmission assembly  26 ′ in either longitudinal direction. 
   A particular issue arising from prior art designs of transmission assemblies used for such motorized track systems results from premature component wear particularly in the area of the drive nut  54 ,  54 ′ between the cover halves  42 ,  44 ,  42 ′,  44 ′. Similarly, noise of an objectionable level is created whenever the transmission assembly  26 ,  26 ′ is activated from a rest condition. This is caused by the interaction between the threads of the worm gear  38  and the external teeth on the drive nut  54 , which causes a reaction force in the drive nut  54  to move in either longitudinal direction, depending upon the turning direction of the worm gear  38 ,  38 ′. This reaction force is home internally in the housing  40 ,  40 ′, and in particular on the interior components of the left  42 ,  42 ′ and right  44 ,  44 ′ cover halves. The subject invention overcomes this objectionable wear and noise phenomenon by inserting at least one, and preferably two compressible washers  66 ′ as shown in  FIGS. 7-9 . It will be understood, however, that the embodiment of the invention depicted in  FIGS. 5-6  includes corresponding features, although they are not visible from the illustrations. The one, or two, compressible washers  66 ′ are disposed between either one or both ends of the drive nut  54 ′ and first and second bushings  68 ′ which are disposed on opposite, longitudinally spaced sides of the drive nut  54 ′ for bearing axial loads between the drive nut  54 ′ and the housing  40 ′. The first and second bushings  68 ′ may include an anti-rotation feature which interacts with the left  42  and right  44  cover halves. In this example, the anti-rotation feature is depicted as hex flats which engage complimentary hex pockets  70  in the left  42  and right  44  cover halves. Other anti-rotation techniques may be used instead of a hex. 
     FIG. 8  illustrates a simplified cross-sectional view through the transmission assembly  26 ′, and depicting the compressible washers  66 ′ in a balanced, static condition. This is typical of the transmission assembly  26 ′ at rest. By comparison to  FIG. 9 , however, when the worm gear  38 ′ begins to turn, as suggested by the clockwise directional arrow, reaction forces between the meshing threads and gear teeth urge the drive nut  54 ′ to press against the left side of the cover halves  42 ′,  44 ′, as viewed from  FIG. 9 . The compressible washers  66 ′ react by harmoniously compressing and/or expanding to accommodate the shift. The result is a dampening effect which produces very little noise and prevents the drive nut  54 ′ from bearing harshly against either of the bushings  68 ′. Although two compressible washers  66 ′ are illustrated in  FIGS. 8 and 9 , those of skill in the art will appreciate that similar functionality can be accomplished with but a single compressible washer  66 ′ disposed on either side of the drive nut  54 ′. 
   Preferably, the compressible washer  66 ′ is of the so-called wave washer type manufactured from a spring steel material. While preferred, however, this is not the only construction for the compressible washer  66 ′ which will produce acceptable results. Other compressible washer designs may be substituted with similar effectiveness, including compressible foam designs, coil spring designs, and the like. 
   Accordingly, a transmission assembly  26 ,  26 ′ manufactured according to the disclosed construction, wherein a compressible washer  66 ,  66 ′ or washers is shown to improve functionality, extend service life and reduce objectionable noises in the operation of a track system  18 . 
   The foregoing invention has been described in accordance with the relevant legal standards, thus the description is exemplary rather than limiting in nature. Variations and modifications to the disclosed embodiment may become apparent to those skilled in the art and fall within the scope of the invention. Accordingly the scope of legal protection afforded this invention can only be determined by studying the following claims.