Abstract:
A conveyance seat includes: a pair of lower rails; a pair of upper rails, each of which is slidably assembled to the corresponding lower rail; an electric drive mechanism; a pair of brackets, each of which is assembled to an upper surface of the corresponding upper rail; and a pair of buffer members, each of which is arranged between the upper surface of the upper rail and the bracket. The electric drive mechanism includes a drive source fastened to one of the brackets; a shaft; a pair of screws assembled one to each rail of the lower rails or the upper rails; a pair of nuts; and a pair of gear subassemblies. The electric drive mechanism electrically slides each upper rail with respect the corresponding lower rail by the screw moving relative to the nut or by the nut moving relative to the screw, by rotation of the shaft when the drive source is driven.

Description:
INCORPORATION BY REFERENCE 
     The disclosure of Japanese Patent Application No. 2013-204160 filed on Sep. 30, 2013 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a conveyance seat. 
     2. Description of Related Art 
     Technology of such a conveyance seat is already known and is described in Japanese Patent Application Publication No. 2006-290131 (JP 2006-290131 A), for example. With this technology, an electric drive mechanism  130  that electrically slides an upper rail  120  with respect to a lower rail  110  mainly includes a motor  132 , a shaft  134  that rotates when the motor  132  is driven, a screw  136  that is assembled to the upper rail  120 , a nut (not shown) that screws onto the screw  136 , and a gear subassembly  140  that transmits the rotation of the shaft  134  to the nut (not shown), as shown in  FIG. 5 . When the motor  132  is driven, the upper rail  120  is electrically slid with respect to the lower rail  110  by the nut (not shown) and the screw  136  moving relative to one another. As a result, the conveyance seat is able to be slid easily. 
     However, with the technology described in JP 2006-290131 A, the motor  132  is assembled to the upper rail  120  via a bracket  124 , as shown in  FIG. 6 . Therefore, if there is variation in the lower rail  110  or the upper rail  120  due to an offset or error in a vehicle body (not shown), the height position of both ends of the shaft  134  may be off (i.e., the shaft  134  may be inclined). 
     SUMMARY OF THE INVENTION 
     The invention thus provides a conveyance seat that includes an electric drive mechanism that electrically slides an upper rail with respect to a lower rail, in which an offset in a height position of both ends of a shaft that rotates when a drive source of the electric drive mechanism is driven is able to be inhibited, even if there is variation in a lower rail or an upper rail. 
     One aspect of the invention relates to a conveyance seat including: a pair of lower rails that are assembled to a floor-side member; a pair of upper rails, each of which is slidably assembled to the corresponding lower rail; an electric drive mechanism that electrically slides each upper rail with respect to the corresponding lower rail; a pair of brackets, each of which is assembled to an upper surface of the corresponding upper rail; and a pair of buffer members, each of which is arranged between the upper surface of the upper rail and the bracket. The electric drive mechanism includes a drive source that is fastened to one of the brackets; a shaft that rotates by driving force of the drive source; a pair of screws that are assembled one to each rail of the lower rails or the upper rails (i.e., a pair of the screws that are assembled to one of the pairs of the rails, either the lower rails or the upper rails, one of the screw being assembled to each of the rails); a pair of nuts, each of which screws onto the corresponding screw; and a pair of gear subassemblies, each of which transmits rotation of the shaft to the corresponding nut. The electric drive mechanism electrically slides the upper rail with respect the lower rail by the screw moving relative to the nut or by the nut moving relative to the screw, by rotation of the shaft when the drive source is driven. 
     According to this structure, the height position of the drive source with respect to the upper rail is able to be adjusted by deformation of the buffer member. Therefore, even if there is variation in the lower rail or the upper rail clue to an offset or error in the vehicle body, the buffer member absorbs this variation, thereby enabling an offset in the height position of both ends of the shaft to be inhibited (i.e., enabling the shaft to be inhibited from inclining). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: 
         FIG. 1  is an overall perspective view of a conveyance seat according to an example embodiment of the invention; 
         FIG. 2  is an enlarged view of a power slide device in  FIG. 1 ; 
         FIG. 3  is an exploded view of  FIG. 2 ; 
         FIG. 4  is a sectional view taken along line IV-IV in  FIG. 2 ; 
         FIG. 5  is an exploded view of a portion of a power slide device according to related art; 
         FIG. 6  is a longitudinal sectional view of the power slide device in  FIG. 5  in an assembled state; and 
         FIG. 7  is a sectional view of a conveyance seat according to an example embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, example embodiments of the invention will be described with reference to  FIGS. 1 to 4 . In the description below, a vehicle seat  1  is given as an example of the conveyance seat of the invention. Also, directions of up, down, front, rear, left, and right in the description below indicate directions of up, down, front, rear, left, and right in the drawings that will be described later, i.e., indicate directions of up, down, front, rear, left, and right based on the vehicle seat  1  in a state arranged inside a vehicle (not shown) such as an automobile. 
     First, the structure of the vehicle seat  1  will be described with reference to  FIG. 1 . This vehicle seat  1  includes a seat cushion  2 , a seatback  3 , and a power slide device  4 . Of the scat cushion  2 , the seatback  3 , and the power slide device  4 , the seat cushion  2  and the seatback  3  are well known, so only the power slide device  4  will be described below. 
     As shown in  FIGS. 2 to 4 , the power slide device  4  includes left and right lower rails  10  that are assembled to a floor of a vehicle (not shown), left and right upper rails  20  that are slidably assembled to these left and right lower rails  10 , and an electric drive mechanism  30  that electrically slides these left and right upper rails  20  with respect to the left and right lower rails  10 . Hereinafter, the left and right lower rails  10 , the left and right upper rails  20 , and the electric drive mechanism  30  will be described separately. In the description below, parts such as the lower rails and upper rails that are provided in plurality may be described in the singular to simplify the description. 
     First, the lower rails will be described. The lower rail  10  is formed in a long shape that extends in a longitudinal (front-rear) direction of the vehicle, not shown. Each end portion (i.e., a front end portion and a rear end portion) of this lower rail  10  is fastened to the vehicle body, not shown, via a leg, also not shown. The left and right lower rails  10  are formed in a pair. 
     Next, the upper rails  20  will be described. The upper rail  20  is also formed in a long shape that extends in the longitudinal (front-rear) direction of the vehicle, not shown, similar to the lower rail  10  described above. This upper rail  20  is formed so as to be able to slide in the longitudinal direction with respect to the lower rail  10 . Also, an opening  22  is formed in an upper surface of this upper rail  20 . This opening  22  is used to fasten an end of a shaft  34  to a worm gear  40   a  of a gear subassembly  40 , as will be described later. 
     This opening  22  is covered by a generally T-shaped bracket  24 . In this state, rivets B that hold this bracket  24  in place pass through the upper rail  20  and are fastened to a holder  54 , described later, that is assembled inside this upper rail  20 . That is, the bracket  24  is assembled to an upper surface of the upper rail  20 , and the holder  54  is assembled inside the upper rail  20 , by these rivets B. 
     The rivet B is inserted through a rubber member G via a collar C. This collar C makes it possible to obtain axial force with the inserted rivet B, even when the rivet B is inserted into the rubber members G. The rubber member G is provided sandwiching an edge of a mounting hole  24   a  into which the rivet B is inserted, from both surface sides. Therefore, the rubber member G is arranged between the upper surface of the upper rail  20  and the bracket  24 . The left and right upper rails  20  are also formed in a pair, similar to the lower rails  10 . 
     Last, the electric drive mechanism  30  will be described. This electric drive mechanism  30  includes a motor  32 , a shaft  34  that includes a left shaft  34   a  and a right shaft  34   b , left and right screws  36 , left and right nuts  38 , and left and right gear subassemblies  40  each of which has a worm gear  40   a  and a wheel gear  40   b . A reduction unit  32   a  that has a mounting bracket  32   b  is provided on the motor  32 . This mounting bracket  32   b  is fastened by crimping to a tip end of the right bracket  24  that will be described later. 
     The left shaft  34   a  is connected at one end to the reduction unit  32   a , and fastened at the other end to the worm gear  40   a  of the left gear subassembly  40 . Meanwhile, the right shaft  34   b  is also connected at one end to the reduction unit  32   a , and fastened at the other end to the worm gear  40   a  of the right gear subassembly  40 , similar to the left shaft  34   a . The left screw  36  is assembled inside the left lower rail  10 , while the right screw  36  is assembled inside the right lower rail  10 , similar to the left screw  36 . 
     The left nut  38  is assembled in a state screwed onto the left screw  36 . The wheel gear  40   b  of the left gear subassembly  40  is assembled to an outer surface of this left nut  38 . Meanwhile, the right nut  38  is assembled in a state screwed onto the right screw  36 , similar to the left nut  38 . The wheel gear  40   b  of the right gear subassembly  40  is assembled to an outer surface of this right nut  38 . 
     The worm gear  40   a  of the left gear subassembly  40  is fastened to the other end of the left shaft  34   a , as described above. The worm gear  40   a  and the wheel gear  40   b  of this left gear subassembly  40  are able to be connected such that the rotational directions of the two are orthogonal to each other. Meanwhile, the worm gear  40   a  of the right gear subassembly  40  is fastened to the other end of the right shaft  34   b , as described above, similar to the worm gear  40   a  of the left gear subassembly  40 . The worm gear  40   a  and the wheel gear  40   b  of this right gear subassembly  40  are able to be connected such that the rotational directions of the two are orthogonal to each other. 
     The left and right gear subassemblies  40  structured in this way are retained by left and right housings  42 , respectively. Also, the left housing  42  is housed in a recess  54   a  of the U-shaped left holder  54 , via a left damper rubber  52 , in a state sandwiching the worm gear  40   a  and the wheel gear  40   b  of the left gear subassembly  40 . The same applies to the right housing  42 . 
     Then, the left holder  54  within which the left housing  42  is housed is assembled inside the left upper rail  20 , as described above. When this left holder  54  is assembled inside the left upper rail  20  in this way, the worm gear  40   a  of the left gear subassembly  40  protrudes from the opening  22 , and the other end of the left shaft  34   a  is able to be fastened to this protruding worm gear  40   a . The same applies to the right holder  54 . The left and right lower rails  10 , the left and right upper rails  20 , and the electric drive mechanism  30  together form the power slide device  4 . 
     Continuing on, the operation of the vehicle seat  1  provided with this power slide device  4  will now be described. When the motor  32  is driven, the left and right nuts  38  rotate via the left and right shafts  34  (i.e., the left shaft  34   a  and the right shaft  34   b ), and the left and right gear subassemblies  40  (i.e., the left worm gear  40   a  and the left wheel gear  40   b , and the right worm gear  40   a  and the right wheel gear  40   b ). As a result, the rotated left and right nuts  38  move with respect to the left and right screws  36 , so the left and right upper rails  20  are able to be electrically slid with respect to the left and right lower rails  10 . 
     The vehicle seat  1  according to this example embodiment of the invention is structured as described above. According to this structure, the opening  22  for fastening an end of the shaft  34  to the worm gear  40   a  of the gear subassembly  40  is formed in the upper surface of the upper rail  20 . This opening  22  is covered by the generally T-shaped bracket  24 . In this state, the rivets B that hold this bracket  24  in place pass through the upper rail  20 , and are fastened to the holder  54  that is assembled inside the upper rail  20 . The rubber members G through which the rivets B are inserted are arranged between the upper surface of the upper rail  20  and the bracket  24 . Thus, the height position of the motor  32  with respect to the left and right upper rails  20  is able to be adjusted by the deformation of these rubber members G. Therefore, even if there is variation (a left-right difference) in the left and right lower rails  10  and the left and right upper rails  20  due to an error or offset in the vehicle body, not shown, the rubber members G will absorb this variation, so an offset in the height position of both ends of the shaft  34  is able to be inhibited (i.e., the shaft  34  is able to be inhibited from inclining). 
     The content described above only relates to one example embodiment of the invention. The invention is not limited to this content. In the example embodiment, the vehicle seat  1  is described as an example of the conveyance seat, but the conveyance seat is not limited to the vehicle seat  1 . That is, the conveyance seat may also be a seat of any of a variety of types of conveyance, such as a scat of a marine vessel, a seat of an aircraft, or a seat of a railcar, for example. 
     Also, in the example embodiment, the left and right screws  36  are described as being assembled to the left and right lower rails  10 , but they are not limited to this. That is, the left and right screws  36  may alternatively be assembled to the left and right upper rails  20 , as shown in  FIG. 7 . In this case, the left and right screws  36  are rotated by driving the motor  32 .