Patent Publication Number: US-2022234477-A1

Title: Seat sliding device and method of manufacturing the seat sliding device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority under 35U.S.C. § 119 from Japanese Patent Application No. 2021-008671 filed on Jan. 22, 2021, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a seat sliding device and a method of manufacturing the seat sliding device. 
     BACKGROUND 
     In an electric seat sliding device, Japanese Patent Application Laid-Open No. 2009-241698 discloses a reinforcing plate provided inside an upper rail in order to prevent breakage of a gear box fixed to the upper rail when a large load acts on the upper rail. The reinforcing plate includes a projecting upper end fixed to a top wall of the upper rail by staking. In this case, a staked portion of the reinforcing plate projects from the top wall of the upper rail, which makes it difficult to be applied to a structure in which a mounting bracket on the seat side is directly fixed to the top wall of the upper rail by welding. Meanwhile, Japanese Patent Application Laid-Open No. 2018-30475 discloses a structure in which a reinforcing plate is attached to a side wall of an upper rail using an elastically deformable holding member, and European Patent No. 1033278 discloses a structure in which a side wall of an upper rail projects inward or is bent to fix a fixing element such as a nut to the upper rail. 
     SUMMARY 
     In Japanese Patent Application Laid-Open No. 2018-30475, when the reinforcing plate is attached to the upper rail, a separate component, which is the holding member, is used, which results in an increase in the number of components. In European Patent No. 1033278, a high-tension material (high-tensile steel) used for the upper rail has a large springback, and thus gap is easily generated. As a result, it is difficult to fix the reinforcing plate to the side wall of the upper rail without gap. 
     Accordingly, an object of the present invention is to prevent an increase in the number of components, and to allow a reinforcing member to be attached without gap by using the side wall of the upper rail. 
     A seat sliding device of the present invention includes: a lower rail extending along a front-rear direction of a vehicle body; an upper rail moving relative to the lower rail along a longitudinal direction of the lower rail; a screw shaft rotatably attached to the upper rail and extending along a direction of the relative movement; a nut member attached to the lower rail and screwed onto the screw shaft; and at least one reinforcing member attached to the upper rail and having a through-hole through which the screw shaft passes. The upper rail includes a pair of right and left engagement holes formed in a pair of right and left side walls and with which right and left side edges of the reinforcing member are engaged, and a pair of right and left locking-pieces formed on the pair of right and left side walls so as to be positioned higher than the engagement holes and in which an upper end surface enters within the upper rail. The reinforcing member includes a pair of right and left locking portions formed at lower portions of the right and left side edges and engaged with the pair of right and left engagement holes, and a pair of right and left recesses formed at upper portions of the right and left side edges and with which the pair of right and left locking-pieces are engaged. The locking-piece enters the recess in a state where an upper end surface abuts an inner side surface of the recess and is bent into an S-shape in the recess and engaged with the recess. 
     In a method for manufacturing a seat sliding device of the present invention, the seat sliding device includes: a lower rail extending along a front-rear direction of a vehicle body; an upper rail moving relative to the lower rail along a longitudinal direction of the lower rail; a screw shaft rotatably attached to the upper rail and extending along a direction of the relative movement; a nut member attached to the lower rail and screwed onto the screw shaft; and at least one reinforcing member attached to the upper rail and having a through-hole through which the screw shaft passes. The method includes a fitting step of fitting a locking portion formed in right and left side edges of the reinforcing member into a pair of right and left engagement holes formed in a pair of right and left side walls of the upper rail; and a pushing step of, in a pair of right and left locking-pieces formed on the pair of right and left side walls so as to be positioned higher than the engagement holes, pushing a vertically intermediate position of the locking-piece so as to push the locking-piece into a recess in a state where an upper end surface of the locking-piece abuts an upper side surface of the recess, whereby the locking-piece is bent into an S-shape in the recess and engaged with the recess subsequent to the fitting step. 
     The present invention makes it possible to prevent an increase in the number of components, and to allow a reinforcing member to be attached without gap by using the side wall of the upper rail. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of a seat sliding device according to an embodiment of the present invention. 
         FIG. 2  is a perspective view of the seat sliding device according to the embodiment. 
         FIG. 3  is a cross-sectional view taken from line of  FIG. 2 . 
         FIG. 4  is a side sectional view of an upper rail shown in  FIG. 1 . 
         FIG. 5  is an enlarged view showing the periphery of a tongue-piece of the upper rail of  FIG. 4 . 
         FIG. 6  is a front view of a reinforcing plate used in the seat sliding device of FIG. 
         FIG. 7  is an enlarged view showing the periphery of the tongue-piece of the upper rail of  FIG. 3 . 
         FIG. 8A  is an explanatory diagram showing an operation sequence for attaching the reinforcing plate to the upper rail. 
         FIG. 8B  is an explanatory diagram showing an operation sequence for attaching the reinforcing plate to the upper rail. 
         FIG. 8C  is an explanatory diagram showing an operation sequence for attaching the reinforcing plate to the upper rail. 
         FIG. 8D  is an explanatory diagram showing an operation sequence for attaching the reinforcing plate to the upper rail. 
         FIG. 8E  is an explanatory diagram showing an operation sequence for attaching the reinforcing plate to the upper rail. 
         FIG. 9  is a sectional view showing an attachment state of a nut member used for the seat sliding device of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will be described below with reference to the drawings. In the drawings, a direction indicated by an arrow FR is the front of a vehicle body, a direction indicated by an arrow RR is the rear of a vehicle body, a direction indicated by an arrow LH is the left side of a vehicle body, and a direction indicated by an arrow RH is the right side of a vehicle body. In the following description, a “front-rear direction” and a “right-left direction” correspond to a “front-rear direction of a vehicle body” and a “right-left direction of a vehicle body” respectively, unless otherwise specified. 
     As shown in  FIGS. 1 and 2 , an electric seat sliding device mounted on an automobile is provided with a lower rail  1  fixed to a floor surface of a vehicle body and extending along a front-rear direction of the vehicle, and an upper rail  3  moving relative to the lower rail  1  along a longitudinal direction inside the lower rail  1 . The upper rail  3  is attached to a lower surface of a seat (not shown). Accordingly, the seat, together with the upper rail  3 , moves in a front-rear direction with respect to the lower rail  1  attached to the floor surface of the vehicle body. The lower rail  1  and the upper rail  3  constitute a rail body. 
     The lower rail  1  includes inclined walls  1   b  and  1   c  extending outward obliquely upward from both right and left ends of a bottom wall  1   a . The lower rail  1  also includes right and left side walls  1   d  and  1   e  extending upward from upper ends of the inclined walls  1   b  and  1   c . The lower rail  1  also includes upper walls  1   f  and  1   g  extending inward from the upper ends of the right and left side walls  1   d  and  1   e , and inner walls  1   h  and  1   i  extending downward from inner ends of the upper walls  1   f  and  1   g  substantially parallel to the side walls  1   d  and  1   e . In the lower rail  1 , the bottom wall  1   a  is fixed to the floor surface of the vehicle body via a plurality of fixtures (not shown). 
     As shown in  FIG. 3 , the upper rail  3  includes right and left side walls  3   b  and  3   c  extending downward from both right and left sides of a top wall  3   a , and folded portions  3   d  and  3   e  bent outward from lower ends of the right and left side walls  3   b  and  3   c . In the upper rail  3 , the top wall  3   a  is fixed to the lower surface of the seat via a plurality of fixtures (not shown) on the seat side. 
     A lower guide ball and an upper guide ball (not shown) are rotatably stored between: a lower ball holding portion and an upper ball holding portion formed in the folded portions  3   d  and  3   e  of the upper rail  3 ; and the lower rail  1 . The lower guide ball and the upper guide ball are supported by a ball retainer (not shown). When the upper rail  3  moves in a front-rear direction with respect to the lower rail  1 , the lower guide ball and the upper guide ball rotate to suppress friction between the rails and enable smooth movement. 
     As shown in  FIGS. 1 and 2 , respective fixed stoppers is are formed on the right and left sides near the front and rear ends of the lower rail  1 . The fixed stoppers  1   s  are engaged with the ball retainer to prevent the plurality of lower guide balls and the upper guide balls from being disengaged from the lower ball holding portion and the upper ball holding portion as well as a positional deviation in the front-rear direction. 
     A screw shaft  17  extending along a movement direction of the upper rail  3  is disposed inside the upper rail  3 . The screw shaft  17  has almost the same length as the upper rail  3  and is supported by the upper rail  3 . Meanwhile, a nut member  19  is attached to the bottom wall  1   a  slightly to the rear side of the longitudinal center of the lower rail  1 . The nut member  19  includes a female screw  19   a  into which a male screw  17   a  of the screw shaft  17  is screwed. That is, when the screw shaft  17  rotates, the screw shaft  17  (upper rail  3 ) moves in the front-rear direction with respect to the nut member  19  (lower rail  1 ). 
     The screw shaft  17  is rotationally driven by a drive unit  25  having a motor (not shown) and a gear box  23 . The drive unit  25  is attached to a pair of right and left mounting plates  3   f  formed on the front side end of the upper rail  3  in the longitudinal direction. The drive unit  25  is attached to the mounting plates  3   f  by mounting holes  3   fh  formed in the mounting plates  3   f  and by a fastener  27  (rivet, bolt nut, etc.). 
     As shown in  FIG. 1 , a serration  17   b  is formed at a front end of the screw shaft  17 . The serration  17   b  is meshed with a worm wheel (not shown) rotatably supported in a gear box  23 , so that the screw shaft  17  and the drive unit  25  are connected. Electric seat sliding devices except for a motor are provided at the right and left positions of the seat. An output shaft of a single motor provided in one of the electric seat sliding devices of the seat is connected to an input shaft (not shown) of the gear box  23  of the other electric seat sliding device by a connecting member (not shown). Thus, the screw shafts  17  of the right and left electric seat sliding devices are driven synchronously. 
     Reinforcing plates  29  and  31  as reinforcing members are attached to the front and rear sides of the upper rail  3 . The reinforcing plates  29  and  31  are formed substantially in a plate shape orthogonal to the screw shaft  17 , and attached inside the upper rail  3  so as to straddle between the right and left side walls  3   b  and  3   c  of the upper rail  3 . 
     A slit  3   g  is formed long in a vertical direction as shown in  FIGS. 4 and 5 . The slit  3   g  extends from the lower ends of the side walls  3   b  and  3   c  to a vertically intermediate position of the side walls  3   b  and  3   c  along a direction orthogonal to the longitudinal axis of the upper rail  3  (vertical direction). 
     As shown in  FIGS. 4 and 5 , a pair of holes  3   i  and  3   i  are formed in the right and left side walls  3   b  and  3   c  of the upper rail  3  so as to be positioned higher than the slits  3   g . The pair of holes  3   i  and  3   i  are formed in the side walls  3   b  and  3   c  with an interval therebetween in the front-rear direction, and a bridging portion is formed between the pair of holes  3   i  and  3   i . A tongue-piece  3   j  serving as a locking-piece is formed by separating an upper end of the bridging portion from the side walls  3   b  and  3   c  by shearing. 
       FIG. 6  shows a rear reinforcing plate  29  of the two front and rear reinforcing plates  29  and  31  attached in the slits  3   g . Since the two reinforcing plates  29  and  31  have the same shape, only the rear reinforcing plate  29  will be described hereinafter. 
     In the reinforcing plate  29 , a through-hole  29   b  is formed in the center of a plate portion  29   a  and the screw shaft  17  is inserted into the through-hole  29   b . An inner diameter of the through-hole  29   b  is larger than an outer diameter of the screw shaft  17 . Accordingly, the screw shaft  17  is rotatable with respect to the reinforcing plate  29  in a state where the screw shaft  17  is inserted into the through-hole  29   b . When the screw shaft  17  moves in the front-rear direction together with the upper rail  3  with respect to the nut member  19  (lower rail  1 ) by rotation, an upper rail projection  3   p  shown in  FIG. 4  abuts a pair of front and rear lower rail projections  1   p  shown in  FIG. 1 . This restricts the upper rail  3  from moving in the front-rear direction. 
     As shown in  FIG. 4 , the upper rail projection  3   p  projects downward at a position slightly rearward of the center of the upper rail  3  in the front-rear direction. Upper rail projections  3   p  project downward continuing from the right and left side walls  3   b  and  3   c  by leaving portions between the right and left side walls  3   b  and  3   c  and the folded portions  3   d  and  3   e  unbent, and are formed on both the right and left sides. As shown in  FIG. 1 , the lower rail projections  1   p  provided in the front and the rear are formed by cutting and raising the bottom wall  1   a  of the lower rail  1  upward, and are formed on both the right and left sides corresponding to the right and left upper rail projections  3   p.    
     A bearing nut  33  is disposed on the rear side of the rear reinforcing plate  29 , and a bearing nut  35  is disposed on the front side of the front reinforcing plate  31 . The bearing nuts  33  and  35  are lock nuts with some of threads crushed in advance. The bearing nuts  33  and  35  are screwed into a predetermined position of the male screw  17   a  of the screw shaft  17  and fixed thereto. With a state where a conventional nut is screwed into a predetermined position of the male screw  17   a  of the screw shaft  17 , the nut may be fixed to the screw shaft  17  by means of staking by pushing a plurality of portions of the nut from the outer periphery of the nut toward the axial center. 
     When an impact load directed to the front of a vehicle body acts on the upper rail  3  due to a vehicle collision or the like, the reinforcing plate  31  at the front of the vehicle body moves to the front of the vehicle body, so that the reinforcing plate  31  collides with the bearing nut  35  at the front of the vehicle body. Accordingly, it is possible to prevent an impact load from being directly transmitted from the upper rail  3  to the gear box  23  connected to the upper rail  3 . For this reason, this prevents an impact load which would separate the gearbox  23  from the screw shaft  17 , caused by the transmission of the impact load to the gear box  23 , from acting. At this time, a tensile force acts on the screw shaft  17 . 
     When an impact load directed to the rear of the vehicle body acts on the upper rail  3 , the reinforcing plate  29  at the rear of the vehicle body collides with the bearing nut  33  at the rear of the vehicle body. Accordingly, it is possible to prevent an impact load from being directly transmitted from the upper rail  3  to the gear box  23  connected to the upper rail  3 . Thus, this prevents the gear box  23  from pushing the screw shaft  17 , caused by the transmission of the impact load to the gear box  23 . A tensile force also acts on the screw shaft  17 . 
     With the screw shaft  17  disposed in the upper rail  3 , a rear end  17   c  on the rear side is rotatably supported by a bearing portion  37   a  of an end cap  37 . The end cap  37  is attached by engaging with engagement holes  3   h  formed in the side walls  3   b  and  3   c  of the upper rail  3 . This attachment is performed by means of a pair of right and left engagement claws  37   b  provided so as to sandwich the bearing portion  37   a . A male screw is formed at a front end  17   d  formed further forward than the serration  17   b  of the screw shaft  17 . A washer  34  is inserted in contact with an end face of the male screw  17   a  of the screw shaft  17 . As shown in  FIG. 2 , when the nut  36  is screwed onto the male screw, a worm wheel (not shown) in the gear box  23  is fixed so as to be sandwiched between the washer  34  (end surface of the male screw  17   a ) and the nut  36 , and the screw shaft  17  is fixed in the axial direction to the worm wheel (not shown) in the gear box  23 . 
     As shown in  FIG. 6 , in the reinforcing plate  29 , lower locking portions (locking portions)  29   c  and  29   d  projecting outward in the right-left direction are formed at lower portions on both sides of the plate portion  29   a  in the right-left direction. The lower locking portions  29   c  and  29   d  are engaged with the slits  3   g  at the lower portions of the side walls  3   b  and  3   c  of the upper rail  3 . 
     The reinforcing plate  29  has a recess  29   e  formed in upper portions of both sides of the plate portion  29   a  in the right-left direction, in such a way as to be recessed toward the inner side in the right-left direction. The recess  29   e  is engaged with the tongue-piece  3   j  formed in upper portions of the side walls  3   b  and  3   c  of the upper rail  3 . An upper tapered surface  29   tu  inclining downward as moving inward in the right-left direction is formed on an upper side surface (upper inner surface) of the recess  29   e , and a lower tapered surface  29   tb  inclining upward as moving inward in the right-left direction is formed on a lower side surface (lower inner surface) of the recess  29   e . An inclination angle θ 1  of the upper tapered surface  29   tu  with respect to a horizontal plane is set smaller than an inclination angle θ 2  of the lower tapered surface  29   tb  with respect to the horizontal plane. 
     Further, the reinforcing plate  29  includes an upper locking portion  29   f  projecting upward from an upper end of the plate portion  29   a . The reinforcing plates  29  and  31  are attached to an upper engagement hole  3   ah  formed in the top wall  3   a  of the upper rail  3  by fitting the upper locking portion  29   f  formed in an upper end into the upper engagement hole  3   ah  formed in the top wall  3   a  of the upper rail  3 . The height of the upper locking portion  29   f  is set so as not to project upward from the top wall  3   a  of the upper rail  3 . 
     As shown in  FIG. 7 , the upper rail  3  includes the tongue-piece  3   j  that engages with the recess  29   e  of the reinforcing plate  29 . The tongue-piece  3   j  is formed on the pair of right and left side walls  3   b  and  3   c . The tongue-piece  3   j  enters the recess  29   e  in a state where an upper end surface (tip surface)  3   ju  abuts the upper tapered surface  29   tu  of the recess  29   e , and is bent into an S-shape in the recess  29   e  to be engaged with the recess  29   e . The tongue-piece  3   j  includes a first bent portion  3   j  a bent inward in the right-left direction at a portion lower than a vertically intermediate portion (pushing position of a jig  40  described later), and a second bent portion  3   jb  bent to the opposite side to the bending direction of the first bent portion  3   ja , at a portion higher than the vertically intermediate portion (pushing position of the jig  40  described later). In addition, the tongue-piece  3   j  is formed into an S-shape. 
     The upper end surface  3   ju  of the tongue-piece  3   j , with respect to the upper tapered surface  29   tu , enters the inner side in the right-left direction further than a position P 1 , which passes through a base end of the tongue-piece  3   j  and is orthogonal to the upper tapered surface  29   tu  of the recess  29   e . In  FIG. 7 , a virtual line X passing through the base end of the tongue-piece  3   j  and orthogonal to the upper tapered surface  29   tu  of the recess  29   e  is shown with respect to an inner surface of the side walls  3   b  and  3   c , and a corner portion P 2  at the inner end of the upper end surface  3   ju  in the right-left direction enters the inner side in the right-left direction further than the virtual line X. In this state, the corner portion P 2  of the tongue-piece  3   j  is positioned outside a circle Cr up to the position P 1  centered on the base end of the tongue-piece  3   j . Accordingly, the corner portion P 2  of the tongue-piece  3   j  catches on the upper tapered surface  29   tu  of the recess  29   e , and thus this prevents the corner portion P 2  of the tongue-piece  3   j  from further moving outward in the right-left direction beyond the position P 1 . 
     After the tongue-piece  3   j  has been pushed by the jig  40 , which will be described later, when the jig  40  is removed, the tongue-piece  3   j  bent into an S-shape tries to move outward in the right-left direction at the first bent portion  3   ja  due to elastic recovery (springback), while trying to move inward in the right-left direction at the second bent portion  3   jb , and thus the tongue-piece  3   j  tries to return to being straight. Accordingly, the corner portion P 2  of the tongue-piece  3   j  pushes up the upper tapered surface  29   tu  of the recess  29   e , and thus this prevents the contact (engagement) between the upper end surface  3   ju  of the tongue-piece  3   j  and the upper tapered surface  29   tu  of the recess  29   e  from disengaging. 
     In order for the contact between the upper end surface  3   ju  of the tongue-piece  3   j  and the upper tapered surface  29   tu  of the recess  29   e  not to disengage while the tongue-piece  3   j  is pushed by the jig  40 , an upper end position Pu before the tongue-piece  3   j  is pushed is set, a start position Pr of the upper tapered surface  29   tu  is set and an inclination angle θ 1  of the upper tapered surface  29   tu  is set. 
       FIG. 8A ,  FIG. 8B ,  FIG. 8C ,  FIG. 8D  and  FIG. 8E  show an operation sequence for attaching the reinforcing plate  29  to the upper rail  3 . As shown in  FIG. 8A , the reinforcing plate  29  is inserted into the slit  3   g  from the lower side of the upper rail  3 . At this time, the upper locking portion  29   f  of the reinforcing plate  29  is fitted into the upper engagement hole  3   ah  and the lower locking portions  29   c  and  29   d  are fitted into the slit  3   g . In this state, a staking process by the jig (pushing jig)  40  is performed. During the staking process, a vertically almost-intermediate portion of the tongue-piece  3   j  is pushed from both right and left sides in the horizontal direction by the jig  40 , whereby the tongue-piece  3   j  is formed into an S-shape. In the jig  40 , for example, an abutting surface  40   a  that abuts the tongue-piece  3   j  is formed in a cross-sectional arc shape in the vertical direction. 
     Here, as shown in  FIG. 8B ,  FIG. 8C , and  FIG. 8D , the jig  40  pushes a vertically almost-intermediate portion of the tongue-piece  3   j  so as to push the tongue-piece  3   j  to a predetermined position in the recess  29   e . As a result, the first bent portion  3   ja  lower than the vertically intermediate portion (pushing position of the jig  40 ) is bent by being pushed inward in the right-left direction. Meanwhile, the upper end surface  3   ju  of the tongue-piece  3   j  is pushed while being maintained in contact with the upper tapered surface  29   tu , and thus the second bent portion  3   jb  higher than the vertically intermediate portion (pushing position of the jig  40 ) is bent to the opposite side (outer side in the right-left direction) to the bending direction of the first bent portion  3   ja.    
     In this state, when the tongue-piece  3   j  is released from being pushed by the jig  40 , as shown in  FIG. 8E , the first bent portion  3   ja  of the tongue-piece  3   j  bent into an S-shape returns slightly outward in the right-left direction due to elastic recovery (springback), and the second bent portion  3   jb  returns slightly outward in the right-left direction due to elastic recovery (springback). In this state, a force acts in a direction in which the tongue-piece  3   j  pushes up the upper tapered surface  29   tu  of the recess  29   e , thereby making it possible to attach the reinforcing plate  29  to the side walls  3   b  and  3   c  of the upper rail  3  without gap. The reinforcing plate  31  is attached to the upper rail  3  in the same manner as the reinforcing plate  29 . 
     Further, the upper end surface  3   ju  of the tongue-piece  3   j , with respect to the upper tapered surface  29   tu , enters the inner side in the right-left direction further than the position P 1 , which passes through the base end of the tongue-piece  3   j  and is orthogonal to the upper tapered surface  29   tu  of the recess  29   e  (see  FIG. 7 ). Accordingly, it is possible to prevent the upper end (tip portion) of the tongue-piece  3   j  from moving toward the opening side of the recess  29   e  (outer side in the right-left direction) and the tongue-piece  3   j  disengaging from the recess  29   e.    
     Next, the attachment structure of the nut member  19  to the lower rail  1  will be described. 
     As shown in  FIG. 9 , the nut member  19  is attached to the lower rail  1  by a bracket  39 . The bracket  39  is fixed to the lower rail  1  so as to cover the upper side of the nut member  19 . An elastic member  45  is interposed between the bracket  39  and the nut member  19 . The elastic member  45  is made of an elastically deformable material such as rubber and is formed into a U-shape in a side view. 
     The nut member  19  includes an upper surface  19   b , a lower surface  19   c , a left side surface  19   d , a right side surface  19   e , a front surface  19   f  and a rear surface  19   g , and is formed into a substantially rectangular parallelepiped shape as a whole. The female screw  19   a  is formed passing through between the front surface  19   f  and the rear surface  19   g  in the front-rear direction. 
     The respective restriction projections  19   h  projecting forward and backward are formed on the front surface  19   f  side and the rear surface  19   g  side of the left side surface  19   d . The respective restriction projections  19   i  projecting forward and backward are formed on the front surface  19   f  side and the rear surface  19   g  side of the right side surface  19   e . Each of the restriction projections  19   h  and  19   i  is formed over the entire length of the nut member  19  in the vertical direction. The restriction projections  19   h  and  19   i  are disposed so as to sandwich the elastic member  45  from both the right and left sides in a state where the elastic member  45  is mounted on the nut member  19 . 
     The bracket  39  includes a flat portion  39   a  facing the upper surface  19   b  of the nut member  19 , and a pair of wall surface portions  39   b  extending downward from both ends, in the front-rear direction, of the flat portion  39   a  and facing the front and rear surfaces of the nut member  19 . The bracket  39  is provided with a pair of attachment surface portions  39   c  extending in directions mutually separating from the lower ends of the pair of wall surface portions  39   b  (front-rear direction). 
     An insertion hole  39   bh  into which the screw shaft  17  is inserted is formed in the wall surface portion  39   b . An inner diameter of the insertion hole  39   bh  is larger than an outer diameter of the screw shaft  17 . An anti-rotation projection  39   d  is formed on a portion lower than the insertion hole  39   bh  of the wall surface portion  39   b . An attachment hole  39   ch  for attaching the bracket  39  to the bottom wall  1   a  of the lower rail  1  is formed in the attachment surface portion  39   c.    
     The bracket  39  is formed of a metal plate, and as shown in  FIG. 9 , with the attachment surface portion  39   c  of the bracket  39  overlaid on the bottom wall  1   a  of the lower rail  1 , a rivet is inserted as a fixture  47  into the insertion hole  39   ch  from the lower side, thereby fixing the bracket  39  by staking from the attachment surface portion  39   c  side. 
     As shown in  FIG. 9 , the elastic member  45  includes a damper lower surface  45   a  in contact with the lower surface  19   c  of the nut member  19 . A damper front surface  45   b  and a damper rear surface  45   c  are formed extending upward from a front end edge and a rear end edge of the damper lower surface  45   a , respectively. Damper through-holes penetrating in the front-rear direction are formed in the damper front surface  45   b  and the damper rear surface  45   c . The screw shaft  17  is inserted into the damper through-holes. An inner diameter of the damper through-hole is larger than an outer diameter of the screw shaft  17  and is almost equal to that of the insertion hole  39   bh  of the bracket  39 . 
     End edges of the damper front surface  45   b  and the damper rear surface  45   c  in the right-left direction are positioned further on the inner side in the right-left direction than the end edges of the damper lower surface  45   a  in the right-left direction. In other words, the respective end edges of the damper lower surface  45   a  on both the right and left sides project more outwardly in the right-left direction than the respective end edges of the damper front surface  45   b  and the damper rear surface  45   c  on both the right and left sides. 
     Next, the operation and effect of the present embodiment will be described. 
     (1) A seat sliding device of the present embodiment includes: a lower rail  1  extending along a front-rear direction of a vehicle body; an upper rail  3  moving relative to the lower rail  1  along a longitudinal direction of the lower rail  1 ; a screw shaft  17  rotatably attached to the upper rail  3  and extending along a direction of the relative movement; a nut member  19  attached to the lower rail  1  and screwed onto the screw shaft  17 ; and reinforcing plates  29  and  31  attached to the upper rail  3  and having a through-hole  29   b  through which the screw shaft  17  passes. The upper rail  3  includes a pair of right and left slits  3   g  formed in a pair of right and left side walls  3   b  and  3   c  and with which right and left side edges of the reinforcing plates  29  and  31  are engaged, and a pair of right and left tongue-pieces  3   j  formed on the pair of right and left side walls  3   b  and  3   c  so as to be positioned higher than the slits  3   g  and in which an upper end surface  3   ju  enters within the upper rail  3 . The reinforcing plates  29  and  31  include a pair of right and left lower locking portions  29   c  and  29   d  formed at lower portions of the right and left side edges and engaged with the pair of right and left slits  3   g , and a pair of right and left recesses  29   e  formed at upper portions of the right and left side edges and with which the pair of right and left tongue-pieces  3   j  are engaged. The tongue-piece  3   j  enters the recess  29   e  in a state where an upper end surface  3   ju  abuts an upper side surface of the recess  29   e  and is bent into an S-shape in the recess  29   e  and engaged with the recess  29   e.    
     The tongue-piece  3   j  provided in the upper rail  3  is engaged with the recess  29   e  of the reinforcing plates  29  and  31  engaged with the slits  3   g  of the upper rail  3 . The tongue-piece  3   j  enters the recess  29   e  in a state where the upper end surface  3   ju  abuts the upper side surface of the recess  29   e , and is bent into an S-shape in the recess  29   e  and engaged with the recess  29   e . Accordingly, the reinforcing plates  29  and  31  can be attached to the side walls  3   b  and  3   c  of the upper rail  3  without gap because a force acts in a direction pushing up the tongue-piece  3   j.    
     (2) A pair of holes  3   i  and  3   i  are formed in the side walls  3   b  and  3   c  with an interval therebetween in the front-rear direction of the vehicle body, a bridging portion is formed between the pair of holes  3   i  and  3   i , and the upper end surface  3   ju  of the tongue-piece  3   j  is formed by separating an upper end of the bridging portion from the side walls  3   b  and  3   c.    
     The tongue-piece  3   j  structured in this manner makes it possible to form the tongue-piece  3   j  to be long. 
     (3) The upper side surface of the recess  29   e  is formed as an upper tapered surface  29   tu  inclining downward as moving inward in the right-left direction, and the upper end surface  3   ju  of the tongue-piece  3   j , with respect to the upper tapered surface  29   tu , enters an inner side in the right-left direction further than a position P 1  that passes through a base end of the tongue-piece  3   j  and is orthogonal to the upper tapered surface  29   tu  of the recess  29   e.    
     The tongue-piece  3   j  structured in this manner makes it possible to prevent the upper end (tip portion) of the tongue-piece  3   j  from moving toward the opening side of the recess  29   e  (outer side in the right-left direction) and the tongue-piece  3   j  disengaging from the recess  29   e.    
     (4) A method for manufacturing a seat sliding device of the present embodiment includes: a fitting step of fitting lower locking portions  29   c  and  29   d  formed in right and left side edges of reinforcing plates  29  and  31  into a pair of right and left slits  3   g  formed in a pair of right and left side walls  3   b  and  3   c  of an upper rail  3 ; and a pushing step of, in a pair of right and left tongue-pieces  3   j  formed on the pair of right and left side walls  3   b  and  3   c  so as to be positioned higher than the slits  3   g , pushing a vertically intermediate position of the tongue-piece  3   j  so as to push the tongue-piece  3   j  into a recess  29   e  in a state where an upper end surface  3   ju  of the tongue-piece  3   j  abuts an upper side surface of the recess  29   e , whereby the tongue-piece  3   j  is bent into an S-shape in the recess  29   e  and engaged with the recess  29   e  subsequent to the fitting step. 
     The tongue-piece  3   j  provided in the upper rail  3  is engaged with the recess  29   e  of the reinforcing plates  29  and  31  engaged with the slits  3   g  of the upper rail  3 . The tongue-piece  3   j  enters the recess  29   e  in a state where the upper end surface  3   ju  abuts the upper side surface of the recess  29   e , and is bent into an S-shape in the recess  29   e  and engaged with the recess  29   e . Even if springback of the tongue-piece  3   j  is generated after the pushing step, the reinforcing plates  29  and  31  can be attached to the side walls  3   b  and  3   c  of the upper rail  3  without gap because a force acts in the direction pushing up the tongue-piece  3   j.    
     (5) In the pushing step, a jig  40  pushes a vertically intermediate portion of the tongue-piece  3   j  so as to push the tongue-piece  3   j  into the recess  29   e , whereby the tongue-piece  3   j  is bent into an S-shape in the recess  29   e  and engaged with the recess  29   e . The jig  40  has an abutting surface  40   a  that abuts the tongue-piece  3   j , formed in a cross-sectional arc shape in the vertical direction. 
     When the jig  40  moves inward in the right-left direction to push the tongue-piece  3   j , there is no concentration in stress even if the contact point with the tongue-piece  3   j  changes, thereby making it possible to prevent the tongue-piece  3   j  from breaking or being damaged. 
     Although the embodiments of the present invention have been described above, these embodiments are merely illustrative examples that have been described to facilitate understanding of the present invention, and the present invention is not limited to the embodiments. The technical scope of the present invention is not limited to the specific technical matters disclosed in the above embodiments, but also includes various modifications, alternations, alternative techniques, and the like which can be easily derived therefrom. 
     For example, although the screw shaft  17  is attached to the upper rail  3  and the nut member  19  is attached to the lower rail  1  in the above embodiment, the screw shaft  17  may be attached to the lower rail  1  and the nut member  19  may be attached to the upper rail  3 . In this case, the reinforcing plates  29  and  31  are attached to the lower rail  1  side.