Patent Publication Number: US-9428085-B2

Title: Harmonic drive disc recliner for automotive vehicle seat

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 14/123,309, which in turn claims priority to and all the benefits of U.S. Provisional Application No. 61/491,963 filed on Jun. 1, 2011 and entitled “Harmonic Drive Disc Recliner For Automotive Vehicle Seat” and U.S. Provisional Application No. 61/522,898 filed on Aug. 12, 2011 and entitled “Seat Recliner With Harmonic Drive and Bearing Cage.” 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicle seat assembly. More particularly, the present invention relates to a harmonic drive disc recliner operatively coupling a seat back and seat cushion. 
     2. Description of Related Art 
     Automotive vehicles typically include one or more seat assemblies having a seat cushion and a seat back for supporting passengers above a vehicle floor. The seat assembly is commonly mounted directly to the vehicle floor or, more commonly, the seat assembly is operatively coupled to the floor by a seat track assembly for providing fore and aft sliding adjustment of the seat assembly for passenger comfort. The seat back is typically operatively coupled to the seat cushion by a recliner assembly for providing pivotal movement relative to the seat cushion. 
     For some vehicles, particularly those for the luxury market, the recliner assembly is electrically powered. A typical power seat recliner assembly includes an electric drive motor that meshes with a series of reduction gears. Rotation of the drive motor adjusts the recline angle of the seat back relative to the seat cushion. Forward and rearward reclining movement of the seat back is provided through reversing the direction of rotation of the drive motor. 
     It is desirable that an improved recliner assembly be compact, lightweight and low-cost. It is also desirable that an improved recliner assembly reduce any gear backlash or “chuck.” “Chuck” refers to any imperfection or play within the recliner assembly that allows movement of the seat back while the recliner assembly is in a locked condition. Further, it is desirable that an improved recliner assembly allows for a high gear ratio which allows for a smaller drive motor and less drive motor gear reduction. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a seat assembly for an automotive vehicle includes a harmonic drive disc recliner operatively coupling a seat back to a seat cushion to allow pivotal movement of the seat hack relative to the seat cushion. The disc recliner includes a fixed plate secured to the seat cushion and a rotatable plate secured to the seat back and rotatably coupled to the fixed plate. The fixed and rotatable plates each have a plurality of teeth disposed therearound that extend radially inward. The number of teeth on the fixed plate does not equal the number of teeth on the rotatable plate. A flex spline is disposed between the fixed and rotatable plates and includes a plurality of teeth that extend radially outward. The flex spline has the same number of teeth as the fixed plate. A wave generator is disposed within the flex spline and has an outer profile with lobes that cause the teeth on the flex spline to meshingly engage with the teeth on the fixed and rotatable plates in distinct regions corresponding with the lobes. As the wave generator rotates, the regions where the teeth on the flex spline meshingly engage with the teeth on the fixed and rotatable plates change and simultaneously the teeth on the flex spline urge the teeth on the rotatable plate to align with the teeth on the fixed plate in those regions, thereby causing rotation of the rotatable plate relative to the fixed plate, which in turn causes the seat back to pivot relative to the seat cushion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a side view of a vehicle seat assembly including a seat back operatively coupled to a seat cushion with a recliner assembly having a harmonic drive disc recliner; 
         FIG. 2  is an exploded perspective view of a harmonic drive disc recliner according to a first embodiment of the invention; 
         FIG. 3  is a side view of the disc recliner shown in  FIG. 2  illustrating a wave generator causing meshing engagement between a flex spline, fixed plate, and rotatable plate; 
         FIG. 4  is a close-up side view of the disc recliner shown in  FIG. 3 ; 
         FIG. 5  is an exploded perspective view of a harmonic drive disc recliner according to a second embodiment of the invention; 
         FIG. 6  is a side view of the disc recliner shown in  FIG. 5  illustrating a wave generator causing meshing engagement between a flex spline, fixed plate, and rotatable plate; 
         FIG. 7  is a close-up side view of the disc recliner shown in  FIG. 6 ; 
         FIG. 8  is an exploded perspective view of a harmonic drive disc recliner according to a third embodiment of the invention; 
         FIG. 9  is a perspective view of a wave generator from the disc recliner shown in  FIG. 8 ; 
         FIG. 10  is a side view of the wave generator shown in  FIG. 9  in rolling contact with a flex spline; 
         FIG. 11  is a side view of the disc recliner shown in  FIG. 8  illustrating the wave generator causing meshing engagement between the flex spline, fixed plate, and rotatable plate; 
         FIG. 12  is a fragmentary perspective view of a harmonic drive disc recliner according to a fourth embodiment of the invention; 
         FIG. 13  is a side view of the disc recliner shown in  FIG. 12  illustrating the wave generator causing meshing engagement between the flex spline, fixed plate, and rotatable plate; 
         FIG. 14  is perspective view of a wave generator from the disc recliner shown in  FIG. 12 ; and 
         FIG. 15  is a perspective view of a roller of the wave generator from the disc recliner shown in  FIG. 12 . 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a seat assembly for use in an automotive vehicle is generally shown at  10 . Referring to  FIG. 1 , the seat assembly  10  includes a generally horizontal seat cushion  12  and a generally upright seat back  14  operatively coupled by a recliner assembly  16  to the seat cushion  12 . The recliner assembly  16  includes a pair of spaced apart and synchronized disc recliners  18 , only one of which is shown. 
     Referring to  FIGS. 1 through 4 , the disc recliners  18  allow for pivotal or angular adjustment of the seat back  14  relative to the seat cushion  12  about a pivot axis  20  that extends laterally or in an axial direction. The seat back  14  is adjustable between an upright seating position, shown at A, and a plurality of reclined positions disposed rearwardly of the upright seating position A, one of which is shown at B. Only one of the disc recliners  18  will be described in detail, however, it is contemplated that both of the disc recliners  18  may have generally the same construction. The disc recliner  18  generally includes a fixed plate  22 , an input shaft  24 , a flex spline  26 , a wave generator  28 , and a rotatable plate  30 . In the current embodiment, the fixed plate  22  is adapted to be mounted to the seat cushion  12  and the rotatable plate  30  is adapted to be mounted to the seat back  14 . The fixed plate  22  and the rotatable plate  30  are held together by a retaining ring  32  in a manner well known in the art such that the rotatable plate  30  can rotate about the pivot axis  20  relative to the fixed plate  22 . It is understood that rotation of the rotatable plate  30  relative to the fixed plate  22  results in pivotal movement of the seat back  14  relative to the seat cushion  12 . 
     The fixed plate  22  is circular, generally cup-shaped, and includes an end wall  34  having a first central bore  36  extending therethrough in the axial direction. When the disc recliner  18  is assembled, the first central bore  36  is coaxial with the pivot axis  20 . An outer side of the end wall  34  is adapted to be fixedly secured to the seat cushion  12  by any suitable means. A side wall  38  protrudes from the end wall  34  in the axial direction and extends circumferentially around the fixed plate  22  to define an inner surface. A first plurality of teeth  40  is disposed around the inner surface of the side wall  38 . The teeth  40  extend radially inward toward the pivot axis  20 . 
     The rotatable plate  30  is also circular, generally cup-shaped, and includes an end wall  42  having a second central bore  44  extending therethrough in the axial direction. When the disc recliner  18  is assembled, the second central bore  44  is coaxial with the pivot axis  20 . An outer side  45  of the end wall  42  is adapted to be fixedly secured to the seat back  14  by any suitable means. A side wall  46  protrudes from the end wall  42  in the axial direction and extends circumferentially around the rotatable plate  30  to define an inner surface. A second plurality of teeth  48  is disposed around the inner surface of the side wall  46 . The teeth  48  extend radially inward toward the pivot axis  20 . 
     The flex spline  26  is ring-shaped and has a thin flexible wall  50 . A third plurality of teeth  52  is disposed around an outside surface of the flexible wall  50 . The teeth  52  extend radially outward away from the pivot axis  20 . The flex spline  26  is disposed in the axial direction between the fixed plate  22  and the rotatable plate  30  such that the teeth  52  on the flex spline  26  meshingly engage with the teeth  40  on the fixed plate  22  and the teeth  48  on the rotatable plate  30 , as will be described in further detail below. 
     The wave generator  28  is disposed circumferentially within the flex spline  26  and includes an outer profile that is adapted for engaging an inner surface  54  of the flex spline  26  thereby deforming the flex spline  26  and causing the teeth  52  on the flex spline  26  to meshingly engage with the teeth  40  on the fixed plate  22  and the teeth  48  on the rotatable plate  30  in three distinct regions. Each region where the teeth  52  on the flex spline  26  meshingly engage with the teeth  40  on the fixed plate  22  and the teeth  48  on the rotatable plate  30  corresponds with a lobe or high point on the outer profile of the wave generator  28 . 
     In the current embodiment, the wave generator  28  is a disc-shaped cam and the outer profile includes three lobes  56  generally equally spaced apart in the circumferential direction. Thus, each lobe  56  is spaced approximately one hundred and twenty (120) degrees apart from each adjacent lobe  56 . Each lobe  56  contacts the inner surface  54  of the flex spline  26  and applies a normal force F thereto, thereby deforming the shape of the flex spline  26 . Rotation of the wave generator  28  causes the flex spline  26  to deform to the shape of the rotating wave generator  28 . The flex spline  26  does not rotate with the wave generator  28 , the reason for which is described below. The wave generator  28  also includes a third central bore  58  extending therethrough in the axial direction and which is adapted for receiving the input shaft  24 . When the disc recliner  18  is assembled, the third central bore  58  is coaxial with the pivot axis  20 . It is contemplated that the wave generator  28  could have more than three lobes  56  causing the teeth  52  on the flex spline  26  to meshingly engage with the teeth  40  on the fixed plate  22  and the teeth  48  on the rotatable plate  30  in more than three regions. 
     The input shaft  24  is coaxial with the pivot axis  20  and extends in the axial direction through the first central bore  36  of the fixed plate  22 , the third central bore  58  of the wave generator  28 , and the second central bore  44  of the rotatable plate  30 . The input shaft  24  is rotatably driven by a motor (not shown) in a first or second direction depending on the desired direction of movement of the seat back  14 . Alternatively, it is appreciated that the input shaft  24  may be manually rotated in the first or second direction without varying from the scope of the invention. The wave generator  28  is coupled to the input shaft  24  for rotation therewith. As the wave generator  28  rotates, the lobes  56  are in sliding contact with the inner surface  54  of the flex spline  26  such that rotation of the wave generator  28  creates friction between the lobes  56  and the inner surface  54 . The friction, along with the normal force F, determines the amount of torque required to rotate the input shaft  24 . As the wave generator  28  rotates, the teeth  52  on the flex spline  26  which meshingly engage with the teeth  40 ,  48  on the fixed and rotatable plates  22 ,  30  change. In other words, the regions where the teeth  52  on the flex spline  26  meshingly engage with the teeth  40 ,  48  on the fixed and rotatable plates  22 ,  30  change and revolve around the pivot axis  20  at the same rate as rotation of the wave generator  28 . 
     In the current embodiment, the number of teeth  52  or tooth count on the flex spline  26  is equal to the number of teeth  40  or tooth count on the fixed plate  22 . For example, the number of teeth  52  on the flex spline  26  and the number of teeth  40  on the fixed plate  22  is one hundred and eighty (180). Since the flex spline  26  and the fixed plate  22  have the same number of teeth there is no relative rotation between the flex spline  26  and the fixed plate  22  during rotation of the wave generator  28 . Rather, the teeth  52  on the flex spline  26  simply engage and disengage with the teeth  40  on the fixed plate  22  as the wave generator  28  rotates, thereby causing the flex spline  26  to flex inwardly and outwardly. In contrast, the rotatable plate  30  has more teeth than the flex spline  26 . In one embodiment, for example, the number of teeth  48  or tooth count on the rotatable plate  30  is one hundred and eighty-three (183). Since the rotatable plate  30  has more teeth than the flex spline  26 , the rotatable plate  30  will rotate relative to the flex spline  26  during rotation of the wave generator  28 . More specifically, the different number of teeth results in a misalignment between a profile of the teeth  48  on the rotatable plate  30  and a profile of the teeth  40  on the fixed plate  22 . Thus, as the wave generator  28  causes the flex spline  26  to flex outwardly, the teeth  52  on the flex spline  26  push against the teeth  48  on the rotatable plate  30  to align the profile of the teeth  48  on the rotatable plate  30  with the profile of the teeth  40  on the fixed plate  22  in the regions where the teeth  52  on the flex spline  26  meshingly engage with the teeth  40 ,  48  on the fixed and rotatable plates  22 ,  30 , thereby causing the rotatable plate  30  to rotate relative to the flex spline  26  and the fixed plate  22 . 
     For every full rotation of the wave generator  28 , the rotatable plate  30  will rotate a slight amount (three teeth, for example) backward relative to the flex spline  26 . The reduction ratio from the input shaft  24  to the rotatable plate  30  can be calculated as: 
               reduction   ⁢           ⁢   ratio     =               number   ⁢           ⁢   of   ⁢           ⁢   teeth   ⁢           ⁢   on   ⁢           ⁢   flex   ⁢           ⁢   spline     -               number   ⁢           ⁢   of   ⁢           ⁢   teeth   ⁢           ⁢   on   ⁢           ⁢   rotatable   ⁢           ⁢   plate             number   ⁢           ⁢   of   ⁢           ⁢   teeth   ⁢           ⁢   on   ⁢           ⁢   flex   ⁢           ⁢   spline             
For example, if the number of teeth  48  on the rotatable plate  30  is one hundred and eighty-three (183) and the number of teeth  52  on the flex spline  26  is one hundred and eighty (180), the reduction ratio is −0.0167. Thus, the rotatable plate  30  will rotate at 1/60 th  the speed of the input shaft  24  and in the opposite direction. It is appreciated that the difference between the number of teeth  48  on the rotatable plate  30  and the number of teeth  52  on the flex spline  26  will depend on the number of regions in which the teeth  52  on the flex spline  26  meshingly engage with the teeth  48  on the rotatable plate  30 .
 
     Referring to  FIGS. 5 through 7 , in a second embodiment of the invention, the disc recliner  18  includes a wave generator  60  that is a disc-shaped cam having an outer profile with three lobes  62  generally equally spaced apart in the circumferential direction. Thus, each lobe  62  is spaced approximately one hundred and twenty (120) degrees apart from each adjacent lobe  62 . Each lobe  62  is formed by a series of cylindrical rollers  64  set in a series of corresponding recesses  66  formed in an outer edge  68  of the wave generator  60 . The rollers  64  are arranged to rotate about individual axes of rotation that extend in the axial direction and are generally parallel with the pivot axis  20 . The rollers  64  contact the inner surface  54  of the flex spline  26 . As the wave generator  60  rotates, the rollers  64  are in rolling contact with the inner surface  54  of the flex spline  26 , thereby reducing the friction between the wave generator  60  and the flex spline  26  as compared with the first embodiment. The reduced friction lowers the torque required to rotate the input shaft  24 . In the current embodiment, each lobe  62  includes seven (7) rollers  64  and seven (7) corresponding recesses  66 . It is appreciated, however, that any number of rollers  64  and corresponding recesses  66  may be used without varying from the scope of the invention. It is contemplated that the rollers  64  could be spherical bearings without varying from the scope of the invention. It is also contemplated that each lobe  62  could include a single recess elongated in the circumferential direction with multiple rollers disposed in the recess, wherein each roller is mounted for rotation about a center axle extending in the axial direction that is generally parallel with the pivot axis  20 . 
     Referring to  FIGS. 8 through 11 , in a third embodiment of the invention, the disc recliner  18  includes a wave generator  70  that is a disc-shaped cam having an outer profile with three lobes  72  generally equally spaced apart in the circumferential direction. Thus, each lobe  72  is spaced approximately one hundred and twenty (120) degrees apart from each adjacent lobe  72 . Each lobe  72  is formed by a series of three cylindrical rollers  74  held between a first cage part  76  and a second cage part  78 . Each roller  74  is rotatably mounted on a shaft  80  that extends in the axial direction and which is supported at each end by openings  82  in the first and second cage parts  76 ,  78 . In other words, the first and second cage parts  76 ,  78  form a bearing cage for supporting the rollers  74  therebetween. The axis of each shaft  80  is generally parallel with the pivot axis  20 . The first cage part  76  is circular and is disposed adjacent to the fixed plate  22 . The second cage part  78  is also circular and includes a third central bore  84  extending therethrough in the axial direction. The input shaft  24  is fixedly secured to the first cage part  76  for rotation therewith. When the disc recliner  18  is assembled, the input shaft  24  is coaxial with the pivot axis  20  and extends from the first cage part  76  in the axial direction through the first central bore  36  in the fixed plate  22 . The input shaft  24  also extends from the first cage part  76  in the axial direction through the third central bore  84  in the second cage part  78  and the second central bore  44  in the rotatable plate  30 . The rollers  74  contact the inner surface  54  of the flex spline  26 . As the wave generator  70  rotates, the rollers  74  are in rolling contact with the inner surface  54  of the flex spline  26 , thereby reducing the friction between the wave generator  70  and the flex spline  26  as compared with the first embodiment. The reduced friction lowers the torque required to rotate the input shaft  24 . 
     Referring to  FIGS. 12 through 15 , in a fourth embodiment of the invention, the disc recliner  18  includes a wave generator  90  that is a disc-shaped cam having an outer profile with three lobes  92  generally equally spaced apart in the circumferential direction. Thus, each lobe  92  is spaced approximately one hundred and twenty (120) degrees apart from each adjacent lobe  92 . The wave generator  90  includes a pair of rollers  94  flanking each lobe  92  in the circumferential direction such that there is a total of six (6) rollers  94  in the current embodiment. Each roller  94  is disposed in a recess  96  formed in the outer profile of the wave generator  90 . More specifically, each roller  94  includes spaced apart first and second wheels  98 ,  100  mounted on opposite ends of a spacer or shaft  102  that extends in the axial direction. The first and second wheels  98 ,  100  are disposed within reliefs  104  formed on each side of the wave generator  90  and the shaft  102  is rotatably supported in the recess  96  by the wave generator  90 . The axis of each shaft  102  is generally parallel with the pivot axis  20 . The lobes  92  and the rollers  94  contact the inner surface  54  of the flex spline  26 . As the wave generator  90  rotates, the lobes  92  are in sliding contact with the inner surface  54  of the flex spline  26  and the rollers  94  are in rolling contact with the inner surface  54  of the flex spline  26 , thereby reducing the friction between the wave generator  90  and the flex spline  26  while also ensuring the teeth  52  on the flex spline  26  remain meshingly engaged with the teeth  40 ,  48  on the fixed and rotatable plates  22 ,  30 . 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described.