Seat slide device

Abstract

Provided is a seat slide device capable of absorbing a deviation of a rail member to smoothly move a seat. A lower rail (30R) on the rear side has first slides (38aR, 38bR) respectively attached to edge portions of a pair of rail top walls (34R) and contacts an upper rail (50R) on the rear side to restrict the front and rear movement of the upper rail (50R) on the rear side. A lower rail (30F) on the front side has a gap portion between an edge portion of one rail top wall (34F) and an upper rail (50F) on the front side to allow the front and rear movement of the upper rail (50F) on the front side.

Description

Technical Field

[0001] This invention relates to a seat sliding device. Background Technology

[0002] For example, Patent Document 1 discloses a seat sliding device comprising a lower guide rail and an upper guide rail that moves along the lower guide rail. Furthermore, in recent years, seat sliding devices have been known that allow a vehicle seat to move in the left-right direction by arranging a lower guide rail and an upper guide rail that extend in the left-right direction separately.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. 2016 / 157409 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] However, due to dimensional and parallelism deviations in the lower and upper guide rails, the sliding position of the lower guide rail relative to the upper guide rail may sometimes shift on one or both sides of the front and rear sides. Although this deviation can be absorbed by shifting the sliding position, if the guide rails interfere with each other, causing a deterioration in sliding performance, the seat cannot move smoothly.

[0008] Methods for solving problems

[0009] The present invention was made in view of the above-mentioned problems, and its object is to provide a seat sliding device that can absorb the deviation of the guide rail components and enable the seat to move smoothly.

[0010] The first embodiment of this invention includes a seat sliding device comprising: a seat for an occupant to sit on; and a lateral sliding mechanism for sliding the seat in the left-right direction; the lateral sliding mechanism comprising: front and rear lower guide rails arranged separately in the front-rear direction and provided with guide rail grooves extending in the left-right direction; and front and rear upper guide rails arranged separately in the front-rear direction in a manner corresponding to the front and rear lower guide rails and guided by the front and rear lower guide rails to move in the left-right direction; the front and rear lower guide rails each include a pair of guide rail top walls extending in the front-rear direction in a manner facing each other across the guide rail grooves, the rear lower guide rail having a first slide block respectively mounted on the edge portion of the pair of guide rail top walls, contacting the rear upper guide rail and restricting the front-rear movement of the rear upper guide rail, and the front lower guide rail having a gap portion between the edge portion of the pair of guide rail top walls and the front upper guide rail allowing the front upper guide rail to move back and forth.

[0011] The effects of the invention

[0012] According to the present invention, deviations in the frame components can be absorbed, allowing the seat to move smoothly. Attached Figure Description

[0013] Figure 1 This is a perspective view of a vehicle seat that utilizes a seat sliding mechanism.

[0014] Figure 2 This is a perspective view showing the horizontal sliding mechanism and the side beams of the seat cushion.

[0015] Figure 3 This is a side view showing the front and rear sliding mechanism.

[0016] Figure 4 This is a side view showing the main part of the rear sliding mechanism in an enlarged manner.

[0017] Figure 5 This is a side view showing the main part of the front sliding mechanism in an enlarged manner. Detailed Implementation

[0018] Hereinafter, with reference to the accompanying drawings, the vehicle seat sliding device according to the embodiment will be described. In this specification, the left-right, front-back, and up-down directions of the seat sliding device are defined based on the left-right, front-back, and up-down directions of the vehicle. The left-right and front-back directions correspond to two orthogonal directions in the horizontal plane, and the up-down direction corresponds to the vertical direction.

[0019] Figure 1 In this context, the seat sliding device 1 is a device that moves the vehicle seats at the vehicle floor. This seat sliding device 1 is applied to multiple rows of seats arranged in the front-rear direction of a car (an example of a vehicle), such as the second row of seats 100 in a three-row vehicle.

[0020] Seat 100 is a single-person seat. Although in Figure 1 Only one seat 100 is shown in the drawing, but a pair of seats 100 are arranged in the vehicle at a predetermined distance in the left-right direction. Seat sliding device 1 is provided in each seat 100.

[0021] Seat 100 has a seat cushion 110, a seat back 120, and a headrest 130. The seat cushion 110 supports the buttocks of the seated occupant from below, and the seat back 120 supports the lumbar and back of the seated occupant. The headrest 130 is installed on the upper part of the seat back 120 to support the head of the seated occupant.

[0022] The seat sliding device 1 includes a longitudinal sliding mechanism 2 for moving the seat 100 in the front-back direction.

[0023] The longitudinal sliding mechanism 2 has left and right lower guide rails 20Lt and 20Rt and left and right upper guide rails (not shown) corresponding to the left and right lower guide rails 20Lt and 20Rt.

[0024] The left and right lower guide rails 20Lt and 20Rt are installed on the vehicle floor at a predetermined distance apart in the left-right direction. The left and right lower guide rails 20Lt and 20Rt extend in the front-back direction and are arranged in parallel.

[0025] The lower guide rails 20Lt and 20Rt have a rectangular cross-sectional shape. Guide rail grooves 21Lt and 21Rt extending in the front-to-back direction are provided on the upper surface of the lower guide rails 20Lt and 20Rt. The lower guide rails 20Lt and 20Rt are formed by extrusion molding using metal materials such as aluminum.

[0026] The upper guide rail is slidably mounted on the lower guide rails 20Lt and 20Rt. The upper guide rail moves in the back-and-forth direction by being guided by the lower guide rails 20Lt and 20Rt. The upper guide rail is formed by extrusion molding using a metal material such as aluminum.

[0027] like Figure 2 As shown, the seat sliding device 1 includes a lateral sliding mechanism 3 for moving the seat 100 in the left-right direction. The lateral sliding mechanism 3 is connected to the left and right upper guide rails in the longitudinal sliding mechanism 2, and can move in the forward and backward direction in conjunction with the forward and backward movement of the left and right upper guide rails.

[0028] The horizontal sliding mechanism 3 has front and rear lower guide rails 30F and 30R and front and rear upper guide rails 50F and 50R corresponding to the front and rear lower guide rails 30F and 30R.

[0029] The front and rear lower guide rails 30F and 30R are arranged at a predetermined distance in the front-rear direction. The front and rear lower guide rails 30F and 30R extend in the left-right direction and are arranged in parallel. Each lower guide rail 30F and 30R is fixed to the left and right upper guide rails by straddling them.

[0030] Guide rail grooves 36F and 36R extending in the left-right direction are provided on the upper surface of the lower guide rails 30F and 30R. The lower guide rails 30F and 30R are formed by extrusion molding using metal materials such as aluminum.

[0031] The front and rear upper guide rails 50F and 50R are slidably mounted on the front and rear lower guide rails 30F and 30R. Specifically, the front upper guide rail 50F is slidably mounted on the front lower guide rail 30F. The front upper guide rail 50F moves in the left-right direction by being guided by the front lower guide rail 30F. The rear upper guide rail 50R is slidably mounted on the rear lower guide rail 30R. The rear upper guide rail 50R moves in the left-right direction by being guided by the rear lower guide rail 30R.

[0032] The seat cushion 110 has left and right side beams 111Lt and 111Rt arranged separately in the left-right direction. The left and right side beams 111Lt and 111Rt are connected to the front frame 112, which extends left and right at the front of the seat cushion 110, and extend from the front to the rear. The front and rear upper guide rails 50F and 50R extend from the left side beam 111Lt to the right side beam 111Rt in the left-right direction, and are connected to the left and right side beams 111Lt and 111Rt by fasteners such as bolts and nuts (not shown).

[0033] Thus, the upper guide rails 50F and 50R extend in the left-right direction and are connected to the left and right seat cushion side beams 111Lt and 111Rt, respectively. The left and right seat cushion side beams 111Lt and 111Rt are connected by the upper guide rails 50F and 50R, thereby providing rigidity to the seat cushion 110 and, consequently, the seat 100. Furthermore, the upper guide rails 50F and 50R support the seat cushion side beams 111Lt and 111Rt from below. The front and rear upper guide rails 50F and 50R are formed using aluminum or other metal materials through extrusion molding.

[0034] See below. Figure 3 and Figure 4 The detailed structure of the rear lower guide rail 30R and the rear upper guide rail 50R will be described below. Assuming the center of gravity of the seat 100 and the occupant seated there (e.g., a standard-sized occupant), the rear lower guide rail 30R and the rear upper guide rail 50R are positioned below or near this center of gravity. That is, the rear lower guide rail 30R and the rear upper guide rail 50R are configured to be closer to the center of gravity than the front lower guide rail 30F and the front upper guide rail 50F.

[0035] like Figure 3 As shown, the lower guide rail 30R on the rear side has a lower guide rail body 31R and a base 40R.

[0036] like Figure 4 As shown, the lower guide rail body 31R has a space SR for guiding the movement of the upper guide rail 50R on the rear side. The lower guide rail body 31R is mainly composed of a guide rail bottom wall 32R, a pair of guide rail side walls 33R, and a pair of guide rail top walls 34R. The guide rail bottom wall 32R, the pair of guide rail side walls 33R, and the pair of guide rail top walls 34R are integrally formed.

[0037] The bottom wall 32R of the guide rail is fixed to the upper end 40aR of the base 40R. The bottom wall 32R of the guide rail has inclined surfaces 32aR and 32bR that slope downward toward the center in the front-back direction.

[0038] A roller mechanism 35R is provided on the bottom wall 32R of the guide rail for moving the upper guide rail 50R on the rear side. The roller mechanism 35R includes a front roller 35aR rotatably disposed on the front inclined surface 32aR and a rear roller 35bR rotatably disposed on the rear inclined surface 32bR. The front and rear rollers 35aR and 35bR are formed of, for example, polyacetal resin.

[0039] The upper ends of the front and rear rollers 35aR and 35bR protrude into the space SR through openings provided on the front and rear inclined surfaces 32aR and 32bR. The upper guide rail 50R within the space SR is supported by the upper ends of the front and rear rollers 35aR and 35bR. The rotation axes CaR and CbR of the front and rear rollers 35aR and 35bR are arranged along the inclination of the front and rear inclined surfaces 32aR and 32bR. Thus, the front and rear rollers 35aR and 35bR are configured in an inclined state such that the upper ends of the rollers supporting the lower guide rail 30R are close to each other.

[0040] A pair of guide rail sidewalls 33R rise vertically upwards from the front and rear edges of the guide rail bottom wall 32R, respectively. One guide rail sidewall 33R is located at the front edge of the guide rail bottom wall 32R, and the other guide rail sidewall 33R is located at the rear edge of the guide rail bottom wall 32R.

[0041] A pair of guide rail top walls 34R are disposed on the upper edges of a pair of guide rail side walls 33R, extending in the front-rear direction in a mutually facing manner. A certain gap is provided between the edges 34aR and 34bR of each guide rail top wall 34R, through which a guide rail groove 36R is formed. The width of the guide rail groove 36R in the front-rear direction is set to be greater than the thickness of the upper guide rail 50R.

[0042] The base 40R supports the lower guide rail body 31R. The base 40F is a plate-shaped component used to fix the lower guide rail 30R to the longitudinal sliding mechanism 2.

[0043] like Figure 3 As shown, the upper guide rail 50R on the rear side has an upper guide rail body 51R and a beam support 55R integrally formed with the upper end of the upper guide rail body 51R.

[0044] like Figure 4 As shown, the upper guide rail body 51R is formed as a longitudinal wall extending upward through the guide rail groove 36R of the lower guide rail 30R. The lower end portion 52R of the upper guide rail body 51R is housed within the space SR of the lower guide rail body 31R.

[0045] At the lower end 52R of the upper guide rail body 51R, there are front and rear bearing surfaces 52aR and 52bR for the upper ends of the front and rear rollers 35aR and 35bR to abut against. The front and rear bearing surfaces 52aR and 52bR are formed into inclined surfaces that slope downward toward the center in the front and rear directions, respectively.

[0046] like Figure 3 As shown, the beam support 55R supports the left and right side beams 111Lt and 111Rt of the seat cushion. The beam support 55R is composed of a first support surface 55aR located on the front side and a second support surface 55bR located on the rear side. The first support surface 55aR supports the lower edge E1 of the rear end portion E of the side beams 111Lt and 111Rt, and is formed as a surface shape along the lower edge E1. The second support surface 55bR supports the rear edge E2 of the rear end portion E of the side beams 111Lt and 111Rt, and is formed as a sloping surface shape that rises along the rear edge E2.

[0047] The first support surface 55aR is fastened to the lower edge E1 of the seat cushion side beams 111Lt and 111Rt. The second support surface 55bR is fastened to the rear edge E2 of the seat cushion side beams 111Lt and 111Rt. The first support surface 55aR is also used as a fixing part for installing the seat belt anchor.

[0048] like Figure 2 As shown, a locking mechanism 57R is provided on the upper guide rail 50R to lock the movement of the upper guide rail 50R in the left and right directions. The locking mechanism 57R is fixed to the upper guide rail 50R via a steel base plate (not shown).

[0049] The locking mechanism 57R includes a rotatably supported shaft 58R and a locking pawl 59R mounted on the shaft 58R. The movement of the upper guide rail 50R is locked by engaging the locking pawl 59R into the engaging hole 37R provided in the lower guide rail 30R. The shaft 58R rotates in response to the operation of a lever operable by the occupant. If the shaft 58R rotates, the locking pawl 59R also rotates, disengaging from the engaging hole 37R of the lower guide rail 30R. This allows for left-right movement relative to the upper guide rail 50R.

[0050] like Figure 4 As shown, first slides 38aR and 38bR are provided at the edges 34aR and 34bR of the guide rail top wall 34R facing each other across the guide rail groove 36R. The first slides 38aR and 38bR are formed, for example, by polyacetal resin.

[0051] The first slide blocks 38aR and 38bR are arranged to cover the edge portions 34aR and 34bR, and the outer periphery of the first slide blocks 38aR and 38bR contacts the upper guide rail body portion 51R. Each slide block 38aR and 38bR is clamped in such a way that it fills the gap between the upper guide rail body portion 51R and the edge portions 34aR and 34bR, thereby restricting the forward and backward movement of the upper guide rail 50R.

[0052] Next, see Figure 3 and Figure 5 The detailed structure of the lower guide rail 30F and the upper guide rail 50F on the front side is explained below. Figure 3 As shown, the lower guide rail 30F on the front side has a lower guide rail body part 31F and a base part 40F.

[0053] like Figure 5 As shown, the lower guide rail body 31F has a space SF for guiding the movement of the upper guide rail 50F on the front side. The lower guide rail body 31F is mainly composed of a guide rail bottom wall 32F, a pair of guide rail side walls 33F, and a pair of guide rail top walls 34F. The guide rail bottom wall 32F, the pair of guide rail side walls 33F, and the pair of guide rail top walls 34F are integrally formed.

[0054] The bottom wall 32F of the guide rail is fixed to the upper end 40aF of the base 40F. The bottom wall 32R of the guide rail has a planar shape along the horizontal plane.

[0055] A roller mechanism 35F is provided on the bottom wall 32R of the guide rail for moving the upper guide rail 50F on the front side. The roller mechanism 35F consists of a rotatably configured roller 35aF. The roller 35aF is formed of, for example, polyacetal resin. The upper end of the roller 35aF protrudes into the space SF through an opening provided in the bottom wall 32F of the guide rail. The upper guide rail 50F in the space SF is supported by the upper end of the roller 35aF. The rotation axis CaF of the roller 35aF is arranged horizontally. Thus, the roller 35aF is configured in a vertically upright state.

[0056] A pair of guide rail sidewalls 33F rise upwards from the front and rear edges of the guide rail bottom wall 32F, respectively. One guide rail sidewall 33F is located at the front edge of the guide rail bottom wall 32F, and the other guide rail sidewall 33F is located at the rear edge of the guide rail bottom wall 32F.

[0057] A pair of guide rail top walls 34F are located on the upper edges of a pair of guide rail side walls 33F, extending forward and backward in a mutually opposing manner. A certain gap is provided between the edges 34aF and 34bF of each guide rail top wall 34F, and a guide rail groove 36F is formed by this gap. The width of the guide rail groove 36F in the forward and backward direction is set to be greater than the thickness of the upper guide rail 50F.

[0058] The base 40F supports the lower guide rail body 31F. The base 40F is a plate-shaped component used to fix the lower guide rail 30F to the longitudinal sliding mechanism 2.

[0059] like Figure 3 As shown, the upper guide rail 50F on the front side has an upper guide rail body part 51F and a beam support part 55F integrally formed with the upper end of the upper guide rail body part 51F.

[0060] like Figure 5 As shown, the upper guide rail body 51F is formed as a longitudinal wall extending upward through the guide rail groove 36F of the lower guide rail 30F. The lower end portion 52F of the upper guide rail body 51F is housed within the space SR of the lower guide rail body 31R.

[0061] At the lower end 52F of the upper guide rail body 51F, a receiving surface 52aF is formed that abuts against the roller 35aF. The receiving surface 52aF is formed into a planar shape along the horizontal direction.

[0062] like Figure 3 As shown, the beam support 55F supports the left and right side beams 111Lt and 111Rt of the seat cushion. The beam support 55F is composed of a first support surface 55aF located at the rear and a second support surface 55bF located at the front. The first support surface 55aF is the portion supporting the lower edge B1 of the front end portion B of the side beams 111Lt and 111Rt, and is formed into a surface shape along the lower edge portion B1. The second support surface 55bF is the portion supporting the front edge B2 of the front end portion B of the side beams 111Lt and 111Rt, and is formed into a slope shape that rises along the inclination of the front edge portion B2.

[0063] The first support surface 55aF is fastened to the lower edge B1 of the side beams 111Lt and 111Rt of the seat cushion. The second support surface 55bF is fastened to the front edge B2 of the side beams 111Lt and 111Rt of the seat cushion.

[0064] The upper guide rail 50F is equipped with a locking mechanism 57F that locks the movement of the upper guide rail 50F in the left and right directions. The locking mechanism 57F is fixed to the upper guide rail 50F via a steel base plate (not shown). The locking mechanism 57F has the same structure as the locking mechanism 57R, and has a shaft 58F supported by a rotatable shaft and a locking pawl 59F mounted on the shaft 58F.

[0065] like Figure 5 As shown, second slides 38aF and 38bF are provided at the edges 34aF and 34bF of the guide rail top wall 34F facing each other across the guide rail groove 36F. The second slides 38aF and 38bF are formed, for example, by polyacetal resin.

[0066] The second slides 38aF and 38bF are arranged to cover the edge portions 34aF and 34bF. The outer periphery of the second slides 38aF and 38bF is separated from the upper guide rail body portion 51F. That is, a certain gap portion GP is provided between the second slides 38aF and 38bF provided on the edge portions 34aF and 34bF and the upper guide rail body portion 51F.

[0067] In this type of sliding mechanism 3, the seat 100 can slide in the left and right directions by moving the upper guide rails 50F and 50R at the front and rear while being guided by the lower guide rails 30F and 30R at the front and rear.

[0068] In the seat sliding device 1 of this embodiment, the rear lower guide rail 30R has first slide blocks 38aR and 38bR, which are respectively mounted on the edge portions 34aR and 34bR of a pair of guide rail top walls 34R, and contact the rear upper guide rail 50R to restrict the forward and backward movement of the rear upper guide rail 50R. The front lower guide rail 30F has a gap portion GP between the edge portion 34aF and 34bF of a guide rail top wall 34F and the front upper guide rail 50F, allowing the forward and backward movement of the front upper guide rail 50F.

[0069] According to this structure, the forward and backward movement of the rear upper guide rail 50R is restricted by the first slide blocks 38aR and 38bR. Therefore, even if there are deviations in the dimensions and parallelism of the guide rail components, positional displacement of the rear upper guide rail 50R can be suppressed within the rear lower guide rail 30R. Since the sliding position of the rear upper guide rail 50R is maintained in the correct position, interference between the rear upper guide rail 50R and the lower guide rail 30R can be suppressed. On the other hand, the gap portion GP provided on the front lower guide rail 30F allows for forward and backward movement of the front upper guide rail 50F. This absorbs deviations in the forward and backward direction of the front upper guide rail 50F caused by deviations. At this time, even if the sliding position of the front upper guide rail 50F deviates, interference between the front upper guide rail 50F and the lower guide rail 30F is suppressed due to the presence of the gap portion GP. As a result, the upper guide rails 50F and 50R can move smoothly in the left and right directions, thus enabling the seat 100 to move smoothly.

[0070] In this embodiment, the rear roller mechanism 35R has a pair of rollers 35aR and 35bR that are arranged front to back and tilted together with their upper ends close to each other, separated by the rear upper guide rail 50R.

[0071] According to this structure, since the pair of rollers 35aR and 35bR are tilted close together, the upper guide rail 50R on the rear side can be positioned in the center of the pair of rollers 35aR and 35bR. As a result, the movement of the upper guide rail 50R on the rear side in the front-back direction can be suppressed.

[0072] In this embodiment, the front roller mechanism 35F includes a roller 35aF disposed below the front upper guide rail 50F and with the rotation axis CaF horizontally disposed.

[0073] This structure allows for forward and backward movement of the upper guide rail 50F on the front side. Therefore, it can absorb positional shifts in the forward and backward directions of the upper guide rail 50F caused by misalignment.

[0074] The lower guide rail 30R and the upper guide rail 50R on the rear side are positioned below the seat 100 and the center of gravity of the occupant sitting in the seat 100.

[0075] According to this structure, forward and backward movement is restricted at the lower guide rail 30R and upper guide rail 50R, which are located near the center of gravity. This restricts positional deviation on the upper guide rail 50R side, which bears a larger load. Consequently, the seat 100 can move smoothly in the left and right directions, allowing for smooth forward and backward movement of the upper guide rails 50F and 50R.

[0076] In the above embodiment, the seat sliding device was described with reference to the second-row seats. However, the seat sliding device can also be applied to seats other than the second-row seats. Furthermore, it is not limited to seats for single occupants, but can also be used for seats for multiple occupants.

[0077] Explanation of reference numerals in the attached figures

[0078] 1. Seat sliding mechanism

[0079] 2. Longitudinal sliding mechanism

[0080] 20Lt, 20Rt lower guide rails

[0081] 21Lt, 21Rt guide rail grooves

[0082] 3 Horizontal sliding mechanism

[0083] 30F, 30R lower guide rails

[0084] 31F, 31R Lower Guide Rail Body

[0085] 35F and 35R roller mechanisms

[0086] 35aF, 35aR, 35bR rollers

[0087] 38aF, 38bF second slide

[0088] 38aR, 38bR First Slide

[0089] 40F, 40R base

[0090] 50F, 50R upper guide rail

[0091] 51F and 51R upper guide rail body

[0092] 57F and 57R locking mechanisms

[0093] 58F and 58R axes

[0094] 59F and 59R card jaws

[0095] 100 seats

[0096] 110 Seat Cushions

[0097] 111Lt, 111Rt Seat Cushion Side Beams

[0098] 112 Front Architecture

[0099] 120 seat back

[0100] 130 headrest

[0101] GP gap

Claims

1. A seat sliding device, characterized in that, have: Seats, the seats being provided for occupants to sit on; and A lateral sliding mechanism that allows the seat to slide in the left-right direction; The lateral sliding mechanism has: The front and rear lower guide rails are arranged separately in the front-rear direction and are provided with guide rail grooves extending in the left-right direction; and The front and rear upper guide rails are arranged separately in the front and rear direction in a manner corresponding to the front and rear lower guide rails, and are guided by the front and rear lower guide rails to move in the left and right direction. The front and rear lower guide rails each include a pair of guide rail top walls that extend in the front-rear direction in a manner that faces each other across the guide rail grooves. The lower guide rail on the rear side has a first slide block, which is respectively installed on the edge of the top wall of the pair of guide rails and contacts the upper guide rail on the rear side to restrict the forward and backward movement of the upper guide rail on the rear side. The lower guide rail on the front side has a gap between the edge of the top wall of the pair of guide rails and the upper guide rail on the front side, which allows the upper guide rail on the front side to move back and forth.

2. The seat sliding device according to claim 1, characterized in that, The lower rear guide rail has a rear roller mechanism that supports the lower end of the upper rear guide rail from below and rotates as the upper rear guide rail moves left and right. The rear roller mechanism has a pair of rollers arranged at an angle, one on each side, separated by the upper guide rail on the rear side, with their upper ends close to each other.

3. The seat sliding device according to claim 1 or 2, characterized in that, The lower guide rail on the front side has a front roller mechanism, which supports the lower end of the upper guide rail on the front side from below and rotates as the upper guide rail on the front side moves in the left and right direction. The front roller mechanism includes rollers disposed below the upper guide rail on the front side and whose rotation axis is horizontally arranged.

4. The seat sliding device according to claim 1 or 2, characterized in that, The lower rear guide rail and the upper rear guide rail are positioned below the center of gravity of the seat and the occupant sitting in the seat.

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