Abstract:
An automobile seat is composed of a seat cushion, seat back, and supporting element. The seat cushion supports the hip portion of a vehicle occupant at its normal position. The seat cushion is disposed so that the seat cushion may be freely movable while being forwardly rotated about a front end supporting fulcrum from the normal position to an inverted position. The seat cushion has a reverse surface which is made substantially horizontal at its inverted position. The seat back supports the back of the vehicle occupant at its normal position. The seat back is disposed so that the seat back may be freely movable while being forwardly fallen down from the normal position to a fall-down position. The seat back has a rear surface which is made substantially horizontal at its fall-down position. The reverse surface of the seat cushion at the inverted position and the rear surface of the seat back at the fall-down position are located at substantially the same height level. By the movements of the seat cushion and seat back to their respective inverted position and fall-down position, the seat has its attitude changed from its ordinary state to its flat state. The supporting element fixes the seat cushion and seat back to an automobile body. The supporting element supports the seat cushion and seat back so that the seat cushion and seat back may be freely backwardly slidable from a first position for the ordinary state to a second position for the flat state.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an automobile seat whose attitude is freely changeable from an ordinary state to a flat state. 
     Japanese Utility Model Application Laid-Open Publication No. H7-27239 discloses a seat that is freely changeable from an ordinary state to a flat state. A seat cushion is forwardly rotated about a front end supporting fulcrum and moved to a substantially horizontal inverted position. A seat back is forwardly inclined about a lower end supporting fulcrum and moved to a substantially horizontal fall-down position. In the flat state, a reverse surface of the seat cushion at the inverted position and a rear surface of the seat back at the fall-down position form the flat surfaces that are substantially at the same height level. 
     SUMMARY OF THE INVENTION 
     However, in the above-described conventional technique, the seat cushion is forwardly inverted about the front end supporting fulcrum. Therefore, the seat in the flat state forwardly protrudes by the entire length of the seat cushion. For this reason, it is difficult to apply the seat to an automobile having no sufficient space in front of the seat. 
     An object of the present invention is to provide an automobile seat which even when no sufficient space exists in front of the seat can be changed to a flat state. 
     To attain the above object, an automobile seat according to the present invention is composed of a seat cushion, seat back, and supporting element. The seat cushion supports the hip portion of a vehicle occupant at its normal position. The seat cushion is disposed so that the seat cushion may be freely movable while being forwardly rotated about a front end supporting fulcrum from the normal position to an inverted position. The seat cushion has a reverse surface which is made substantially horizontal at its inverted position. The seat back supports the back of the vehicle occupant at its normal position. The seat back is disposed so that the seat back may be freely movable while being forwardly fallen down from the normal position to a fall-down position. The seat back has a rear surface which is made substantially horizontal at its fall-down position. The reverse surface of the seat cushion at the inverted position and the rear surface of the seat back at the fall-down position are located at substantially the same height level. By the movements of the seat cushion and seat back to their respective inverted position and fall-down position, the seat has its attitude changed from its ordinary state to its flat state. The supporting element fixes the seat cushion and seat back to an automobile body. The supporting element supports the seat cushion and seat back so that the seat cushion and seat back may be freely backwardly slidable from a first position for the ordinary state to a second position for the flat state. 
     When changing the seat from its ordinary state to its flat state for the purpose of a break or quiet sleep or of widely using the interior of an automobile compartment, the seat cushion and seat back are slid from the first position to the second backward position and are then moved to the inverted position and fall-down position to thereby dispose the reverse surface of the seat cushion and the rear surface of the seat back in substantially the same plane. Therefore, the amount of forward protrusion of the seat cushion at the inverted position is decreased. Accordingly, it is possible to obtain a seat that can be applied to an automobile having no sufficient space in front of the seat. 
     The supporting element may be composed of a fixed rail fixed to the floor of an automobile body and a movable rail for supporting the seat cushion and seat back, and the movable rail may be freely slidably engaged with the fixed rail. 
     In the above-described construction, by moving the movable rail, the seat cushion and seat back are moved from the first positions to the second positions. 
     The seat may further comprise a seat frame for supporting the seat cushion and seat back, the seat frame may comprise the front end supporting fulcrum and rear end supporting fulcrum, and the supporting element may support the seat frame so that the seat frame may be freely backwardly slidable from a first position for the ordinary state to a second position for the flat state. 
     In the above-described construction, by moving the seat frame, the seat cushion and seat back are moved from the first position to the second position. 
     Further, the supporting element may be composed of a fixed rail fixed to the floor of an automobile body and rollers provided on the seat frame, and the rollers may be freely slidably engaged with the fixed rail. 
     Also, the rollers may protrude laterally from both sides of the seat frame. 
     The seat may further comprise a first lock mechanism for unlockably locking the seat cushion at the normal position thereof, a second lock mechanism for unlockably locking the seat back at the normal position thereof, a first unlocking mechanism for unlocking the locked state of the first lock mechanism with the movement of the seat cushion toward the second position, and a second unlocking mechanism for unlocking the locked state of the second lock mechanism with the movement of the seat back toward the second position. 
     According to the above-described construction, when retreating the seat frame up to the second position, the locked states of the first and second lock mechanisms are automatically released. Accordingly, the operation for releasing the locked states of the first and second lock mechanisms becomes unnecessary, with the result that the operating efficiency becomes high. 
     The seat frame may have a slide lock freely engageable with the fixed rail and an operating lever for moving the slide lock, and the slide lock having been engaged with the fixed rail may the seat frame to the fixed rail. 
     In the above-described construction, the seat frame is fixed to the first and second position by the slide lock. Further, by moving the operating lever, the engagement of the slide lock with the fixed rail is released, with the result that the seat frame becomes freely slidable. 
     In a case where the supporting element is composed of a fixed rail fixed to the floor of an automobile body and a movable rail for supporting the seat cushion and seat back and when the movable rail is freely slidably engaged with the fixed rail, the seat cushion may include, when the seat cushion is located at its normal position, an intermediate supporting fulcrum located backwardly from the front end supporting fulcrum, and the intermediate supporting fulcrum is freely rotatably connected through a link to a fixed supporting fulcrum located backwardly from the intermediate supporting fulcrum and fixed to the floor of the automobile body. 
     Also, the fixed supporting fulcrum may be provided on the fixed rail. 
     In the above-described construction, when changing the seat from the ordinary state to the flat state, the seat cushion is moved to the inverted position and the seat back is moved to the fall-down position. When the seat cushion is moved while being rotated about the front end supporting fulcrum, the front end supporting fulcrum itself is backwardly moved using the fixed supporting fulcrum as a basis. The amount of forward protrusion of the seat cushion at the inverted position is decreased by the length which is twice as large as that corresponding to the spacing between the front end supporting fulcrum and fixed supporting fulcrum as compared with that when the seat cushion is in the ordinary state. Accordingly, the seat has a wider range of applicability to an automobile having no sufficient space in front thereof. Also, the position in the back-and-forth direction of the seat is fixed by the intermediate supporting fulcrum of the seat cushion being connected through a link to the fixed supporting fulcrum. For this reason, a lock mechanism for regulating the position in the back-and-forth direction of the seat becomes unnecessary. This is advantageous for a decrease in the weight of an automobile body as well as for a decrease in the cost. In addition, a mechanism for stopping a further rotation of the seat cushion from the inverted position thereof and thereby maintaining the seat cushion substantially at the horizontal level also becomes unnecessary. 
     Also, the movable rail is automatically slid from the first position to the second position that is rear from this first position through the movement of the seat cushion to the inverted position. Accordingly, the seat has an excellent operating efficiency. 
     The seat back may include an intermediate supporting fulcrum, and the intermediate supporting fulcrum may be connected to the fixed rail through a link that is freely foldable. 
     In the above-described construction, when the seat back is moved to the fall-down position, the foldable link is accommodated compactly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side view showing an ordinary state of a seat according to a first embodiment: 
     FIG. 2 is a side view showing a flat state of the seat in FIG. 1; 
     FIG. 3 is a sectional view taken along line III—III of FIG. 1; 
     FIG. 4 is a sectional view taken along line IV—IV of FIG. 1; 
     FIG. 5 is a side view showing an ordinary state of a seat according to a second embodiment; 
     FIG. 6 is a side view showing a flat state of the seat in FIG. 5; 
     FIG. 7 is a sectional view taken along line IIV—IIV of FIG. 5; 
     FIG. 8 is a side view showing an ordinary state of a seat according to a third embodiment; 
     FIG. 9 is a side view showing a flat state of the seat in FIG. 8; 
     FIG. 10 is a sectional view taken along line X—X of FIG. 9; 
     FIG. 11 is a sectional view taken along line XI—XI of FIG. 8; 
     FIG. 12 is a sectional view taken along line XII—XII of FIG. 9; 
     FIG. 13 is a side view showing an ordinary state of a seat according to a fourth embodiment; 
     FIG. 14 is a side view showing an middle way of movement of a seat cushion of FIG. 13; 
     FIG. 15 is a side view showing a flat state of the seat in FIG. 13; 
     FIG. 16 is a sectional view taken along line XVI—XVI of FIG. 13; 
     FIG. 17 is a sectional view taken along line XVII—XVII of FIG. 13; and 
     FIG. 18 is a sectional view taken along line XVIII—XVIII of FIG.  13 ; 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described with reference to the drawings below. 
     FIGS. 1 to  4  show a first embodiment of the present invention. The first embodiment relates to a seat in the third row (third seat) of a wagon vehicle and has a movable structure of a slide rail system. 
     A pair of fixed rails  1  are fixed on a left side portion and a right side portion of a vehicle body floor  2  in the drawings, respectively. Each fixed rail  1  has an opening  3  formed along its longitudinal direction on an upper face thereof. An inverse T-shaped movable rail  4  is fitted in each fixed rail  1  slidably in a longitudinal direction of a vehicle through rollers (not shown). 
     The fixed rail  1  is formed with a front latch hole  5  provided at a first position for sitting and a rear latch hole  6  provided at a second position for changing the seat to a flat state, respectively. An upper portion of the movable rail  4  which projects upward from the opening  3  of the fixed rail  1  is provided with a latch piece  8  rotatably supported by a pin of a latch plate  7 . The latch piece  8  is biased to rotate toward the fixed rail  1  side by a spring (not shown). When a tip end  8   a  of the latch piece  8  is engaged in the latch hole  5  or  6 , the movable rail  4  at the first or second position is prevented from moving in a sliding manner. When the other end  8   b  of the latch piece  8  is pressed, the latch piece  8  rotates to be released from the latch hole  5  or  6 . 
     A front end portion of the movable rail  4  is fixed with a front plate  9 . A rear end portion of the movable rail  4  is fixed with a device plate  10 . An intermediate portion of the movable rail  4  is fixed with a U-shaped striker  11  (shown in FIG.  4 ). 
     A front end portion of a seat cushion  12  is ratatably connected to and supported at a front end supporting fulcrum  101  of the front plate  9 . A side face of the rear end portion of the seat cushion  12  is provided with a hook  13  engageable with the striker  11  and rotatable about a supporting fulcrum  13   a . The hook  13  is biased by a spring  14  in a direction in which it is engaged with the striker  11 . When the hook is rotated in a disengaging direction against a biasing force of the spring  14 , the engaging state between the hook  13  and the striker  11  is cancelled or disengaged. A rear end portion of the seat cushion  12  is provided rotatably with an approximately U-shaped large leg member  15  covering the rear end portion. 
     A device arm  17  fixed to a side face of the seat back  16  is mounted to the device plate  10  rotatably about a lower end supporting fulcrum  102 . The seat back 16  can be rotated forward and rearward about the lower end supporting fulcrum  102 . Aside face of an upper end portion of the seat back  16  is provided with a pin  18  (shown in FIG.  2 ). A stopper  19  engaging a lower end portion of the device arm  17  to prevent the device arm  17  from rotating is provided rotatably about a supporting fulcrum  19   a  below the device arm  17 . The stopper  19  is biased in a direction in which it is engaged with the device arm  17  by a spring (not shown). A lower edge of the stopper  19  is formed with a notch  20 . 
     A rotary plate  21  is provided rotatably about a supporting fulcrum  21   a  below the stopper  19 . A lower end portion of the rotary plate  21  is provided with a spring  22  biasing the rotary plate  21  in a counterclockwise direction in FIG.  1 . An upper end of the rotary plate  21  is formed with a pin  23  corresponding to the notch  20  of the stopper  19 . An operating lever  24  integrated with the rotary plate  21  is provided at supporting the fulcrum  21   a  of the rotary plate  21 . When the operating lever  24  is lifted upwardly, the rotary plate  21  rotates in a clockwise direction against the spring  22 , the pin  23  enters into the notch  20  and the pin pushes the stopper  19  upwardly, so that the engagement between the stopper  19  and the device arm  17  is cancelled. 
     Next, procedures for changing the seat from an ordinary state to a flat state will be explained. 
     First, the latch piece  8  of the movable rail  4  is released from the latch hole  5  of the fixed rail  1  and the movable rail  4  together with the seat cushion  12  and the seat back  16  is slid rearward. After the movable rail  4  is moved rearward from the first position to the second position, the latch piece  8  is engaged with the corresponding latch hole  6 , so that the movable rail  4  is fixed at the second position. 
     Secondly, the hook  13  is rotated to cancel the engagement between the hook  13  and the striker  11 , the seat cushion  12  as a whole is rotated forward about the front end fulcrum  101  while it is being lifted up, and the seat cushion  12  is moved up to a inverted position where a back face  12   a  of the seat cushion  12  faces upward. A substantially horizontal state of the seat cushion  12  is maintained by the leg member  15  which has been put in a standing-up state. 
     Thirdly, the operating lever  13  is lifted upward. Thereby, the rotary plate  21  Is rotated and the pin  23  enters into the notch  20  to press the stopper  19  downward, so that the engagement between the stopper  19  and the device arm  17  is cancelled. Then, the seat back  16  is rotated forward about the lower end supporting fulcrum  102  to be moved to a substantially horizontally fall-down position. The pin  18  at the upper end portion of the seat back  16  is engaged with the upper edge of the front plate  9  so that the seat back  16  is maintained in the substantially horizontal state, A back face  16   a  of the seat back  16  maintained in the substantially horizontal state is put in the same height as that of the back face  12   a  of the seat cushion  12 , so that a flat continuous face is formed by the rear face  16   a  and the back face  12   a.    
     In this embodiment, as the seat cushion  12  and the seat back  16  are rotated forward, respectively, after they are moved to the second position rearward of the first position, a relative forward-projecting amount of the seat cushion  12  is reduced, so that the structure of the embodiment is applicable to an automobile where a sufficient space is not provided ahead of a seat. 
     FIGS. 5 to  7  show a second embodiment of the present invention. The second embodiment has a movable structure of a roller type. 
     A pair of fixed rails  25  are fixed on a left side portion and a right side portion of the vehicle body floor  2  in the drawings. Each fixed rail  25  has an approximately C-shaped sectional configuration and is formed on its upper face with an opening  27  along the longitudinal direction thereof. 
     The seat cushion  12  and the seat back  16  are supported by a seat frame  28 . Rollers  29  projecting in a vehicle transverse outer side direction are provided at a front end and a rear end of the seat frame  28  (shown in FIG.  7 ). Each roller  29  is fitted in the fixed rail  25  movably in a sliding manner along the longitudinal direction of the fixed rail  25 . The seat cushion  12  and the seatback  16  together with the seat frame  28  are provided movably in a sliding manner between the front first position for sitting and the rear second position for changing the seat to the flat state. It is to be noted that a locking mechanism (not shown) is provided between the seat frame  28  and the fixed rail  25 . The seat frame  28  is fixed at the first position or the second position by the locking mechanism. 
     Next, a structure for supporting the seat cushion  12  and the seat back  16  to the seat frame  28  will be explained. 
     A front end portion of the seat frame  28  is provided with a front end supporting fulcrum  101 , a rear end portion thereof is provided with a lower end supporting fulcrum  102 , and a middle portion thereof is fixed with a U-shaped striker  11 . 
     A front end portion of the seat cushion  12  is rotatably supported at the front end supporting fulcrum  101  of the seat frame  28 . A rear end portion of the seat cushion  12  is engaged with the striker  11  by a locking mechanism  31 . The locking mechanism  31  includes the hook  13  disposed on a side face of a rear end portion of the seat cushion  12 . The hook  13  is provided rotatably about a supporting fulcrum  13   a  and is engaged with the striker  11 . The hook  13  is biased in an engaging direction by a spring  14 . When the hook  13  is rotated in a disengaging direction, the engagement between the hook  13  and the striker  11  is cancelled. 
     A lower end supporting fulcrum  102  of the seat frame  28  is mounted rotatably on a lower end portion of the seat back  16  through a locking mechanism  32 . The locking mechanism  32  includes the stopper  19  and the rotary plate  21 . The device arm  17  fixed to a side face of the seat back  16  is mounted rotatably to the lower end supporting fulcrum  102 , and the seat back  16  is rotatable forward and rearward about the lower end supporting fulcrum  102 . The pin  18  is provided on a side face of an upper end portion of the seat back  16  (shown in FIG.  6 ). A stopper  19  engaged with a lower end portion of the device arm  17  to prevent the device arm  17  from rotating is provided rotatably about the supporting fulcrum  19   a . The stopper  19  is biased in an engaging direction by a spring (not shown), and is formed at its lower edge with a notch  20 . 
     The rotary plate  21  rotating about the supporting fulcrum  21   a  is provided below the stopper  19 . A spring  22  biasing the rotary plate  21  in a counterclockwise direction in the FIG. 5 is provided at a lower end portion of the rotary plate  21 . A pin  23  corresponding to the notch  20  of the stopper  19  is formed at an upper end portion of the rotary plate  21 . U- 205  When the rotary plate  21  is rotated against the spring  22  in a clockwise direction in FIG. 5, the pin  23  enters into the notch  20  to press the stopper  19  downward. Thereby, the engagement between the stopper  19  and the device arm  17  is cancelled. 
     In a case where the seat is changed from an ordinary state to a flat state, the seat cushion  12  and the seat back  16  are slid from the first position to the rear second position and then are individually rotated forward, like the first embodiment. Accordingly, a relative forward-projecting amount of the seat cushion  12  is reduced, and the structure of the embodiment is applicable to an automobile where a sufficient space can not be provided ahead of a seat. 
     FIGS. 8 to  12  show a third embodiment of the present invention. In the third embodiment, the same structures as those in the second embodiment are attached with the same reference numerals as those in the second embodiment, and explanation thereof is omitted. 
     A guide plate  36  having an upper edge higher than an upper face portion of the fixed rail  25  is provided at a rear end portion of the fixed rail  25 . The guide plate  36  is provided at its front end with a slanting face contiguous to the upper face portion of the fixed rail  25 . 
     A sliding lock  34  entering into the fixed rail  25  from the opening  27  to engage a locking hole (not shown) positioned at a lower face of the fixed rail  25  is provided at a front end of the seat frame  28 . When the sliding lock  34  is engaged with the lower face of the fixed rail  25 , the seat frame  28  is locked to the fixed rail  25  and, when the former is disengaged from the latter, it is made slidable in a longitudinal direction of the fixed rail  25 . Locking holes (not shown) are provided at the first and second positions, and the seat frame  28  is fixed at the first position or the second position by the sliding lock  34 . When an operating lever  35  extending from an upper portion of the sliding lock  34  is lifted up, the sliding lock  34  rotates to be disengaged from the engagement with the fixed rail  25 . 
     A pin  13   b  which can ride on the guide plate  36  is provided at a lower end portion of the hook  13 . An approximately U-shaped large leg member  15  is rotatably provided at a rear end portion of the seat cushion  12 . 
     An operating lever  33  integrated with the rotary plate  21  is provided at the supporting fulcrum  21   a  of the rotary plate  21 . When the operating lever  33  is rotated so as to ride on the guide plate  36 , the rotary plate  21  rotates against the spring  22  in a clockwise direction in FIG.  8  and the pin  23  enters into the notch  20  to press up the stopper  19 . Thereby, the engagement between the stopper  19  and the device arm  17  is cancelled. 
     Next, procedures for changing the seat from the ordinary state to the flat state will be explained. 
     First, the operating lever  35  is lifted up to rotate the sliding lock  34 , and the engagement between the seat frame  28  and the fixed rail  25  is cancelled. Then, the seat frame  28  is slid rearward together with the seat cushion  12  and the seat back  16 . When the seat frame  28  is moved rearward to the second position, the sliding lock  34  is again engaged with the fixed rail  25 . 
     Secondly, when the seat frame  28  reaches to the rear second position, the pin  13   b  of the hook  13  of the locking mechanism  31  rides on the guide plate  36  and the hook  13  rotates. Thereby, the engagement between the hook  13  and the striker  11  Is automatically cancelled. Then, the seat cushion  12  as a whole is moved up to the inverted position in a rotating manner, 
     Simultaneously, when seat frame  28  reaches to the rear second position, the operating lever  33  of the locking mechanism  32  rides on the guide plate  36  and the rotary plate  21  rotates. Thereby, the pin  23  enters into the notch  20  to press down the stopper  19 , so that the engagement between the rotary plate  21  and the device arm  17  is automatically cancelled. Then, the seat back  16  is fall-down to the fall-down position. The pin  18  at the upper end portion is engaged with the upper edge of the seat frame  28  so that the seat back  16  is maintained in the substantially horizontal state. 
     Thus, in the case that the seat is changed from the ordinary state to the flat state, the seat cushion  12  and the seat back  16  are rotated forward, respectively, while they are being slid from the first position to the rear second position in the same manner as the first and second embodiments. As a result, a relative forward-projecting amount of the seat cushion  12  is reduced, so that the structure in the embodiment is applicable to an automobile where a sufficient space is not provided ahead of a seat. 
     Furthermore, as each of the looking mechanisms  31  and  32  is unlocked by merely moving the seat frame  28  rearward up to the second position, it becomes unnecessary to perform an unlocking operation on the locking mechanism  31 , which results in improvement in operation performance. 
     FIGS. 13 to  18  show a fourth embodiment of the present invention. 
     Front and rear end portions of a fixed rail  41  are fixed on a vehicle body floor  44  by brackets  42  and  43 , each comprising a pair of upper and lower parts. The front bracket  42  projects above the fixed rail  41  and an upper end portion thereof is provided with a fixed supporting fulcrum (hinge pin)  103 . 
     A movable rail  45  has a C-shaped configuration opened outwardly and is engaged with the fixed rail  41  movably in a sliding manner along the longitudinal direction of the fixed rail  41 . A front end of the movable rail  45  is provided with a supporting plate  46 . A front end portion of a seat cushion  47  put in an ordinary state is connected to an upper end portion of the supporting plate  46  rotatably through a front end supporting fulcrum (hinge pin)  104 . A hook  48  is provided at a rear end portion of the seat cushion  47 . The hook  48  is engaged with a pin  49  of the movable rail  45 , so that an ordinary state of the seat cushion  47  is maintained. In the ordinary state, the fixed supporting fulcrum  103  is positioned by a length  108  rearward from the front end supporting fulcrum  104  of the seat cushion. 
     The seat cushion  47  includes an intermediate supporting fulcrum (hinge pin)  105  positioned rearward from the front end supporting fulcrum  104  and forward from the fixed supporting fulcrum  103 . A link  50  connects the intermediate supporting fulcrum  105  and the fixed fulcrum  103  to each other. A clearance  109  (shown in FIG. 17) between a side face of the seat cushion  47  and the link  50  in the intermediate supporting fulcrum  105  is set to be smaller than a projecting amount  110 (shown in FIG. 16) of the front end supporting fulcrum  104 . 
     A rear side supporting plate  51  is provided at a rear end portion of the movable rail  45 . A lower end supporting fulcrum  106  of the seat back  52  Is supported on the supporting plate  51 . A two-foldable link  53  extending obliquely connects an intermediate supporting fulcrum  107  of the seat back  52  and the movable rail  45  to each other. 
     Next, procedures for changing the seat from an ordinary state to a flat state. 
     First, the hook  48  of the seat cushion  47  is released from the pin  49 , and the seat cushion  47  is rotated as a whole forward about the front end supporting fulcrum  104 . At this time, as the intermediate supporting fulcrum  105  is connected to the fixed supporting fulcrum  103  via the link  50 , the front end supporting fulcrum  104  is moved rearward while being rotated. As a result, both the seat cushion  47  and the seat back  52  are moved rearward. When the front end supporting fulcrum  104  is moved rearward, the front end supporting fulcrum  104  passes through inside of the link  50 . At this time, since the clearance  109  between the link  50  and the seat cushion  47  is larger than the projecting amount  110  of the front end supporting fulcrum  104 , the front end supporting fulcrum  104  securely passes through the link  50  without interfering with the link  50 . The fixed supporting fulcrum  103 , the front end supporting fulcrum  104  and the intermediate supporting fulcrum  105  must be set to be a positional relationship where they do not form an equilateral triangle, namely, a relationship where the seat cushion  47  is smoothly rotated. 
     When the seat cushion  47  is put to a substantially horizontal inverted position, the forward-projecting amount of the seat cushion  47  is moved rearward by an amount corresponding to two times a distance  108  between the front end supporting fulcrum  104  and the fixed supporting fulcrum  103 . The seat cushion  47  put in the inverted position is maintained in the substantially horizontal state by a two-point support of the front end supporting fulcrum  104  and the intermediate supporting fulcrum  105 . 
     Secondly, the seat back  52  is fell forward and is put in a substantially horizontal fall-down position. At this time, the foldable link  53  is folded at its intermediate portion, and it is accommodated compactly in a space corresponding to a side face of the seat back  52 . A rear face  52   a  of the seat back  52  at the fall-down position is positioned in the same height as that of the back face  47   a  of the seat cushion  47 , and the rear face  52   a  and the back face  47   a  forms a contiguous flat face. 
     As in the fourth embodiment the seat cushion  47  and the seat back  52  are positioned at the inverted position and the fall-down position, respectively, in the state where they are put in the second position rearward of the first position in the same manner as the first embodiment, a relative forward-projecting amount of the seat cushion  47  is reduced, and the structure of the fourth embodiment is applicable to an automobile where a sufficient space is not provided ahead of a seat. 
     Also, since the intermediate supporting fulcrum  105  of the seat cushion  47  is coupled to the fixed supporting fulcrum  103  via the link  50 , the position of the seat along the longitudinal direction of the vehicle body floor  44  is locked. As a result, a locking mechanism for restraining the position of the seat along the longitudinal direction becomes unnecessary. Furthermore, as the seat cushion  47  and the seat back  52  are automatically moved rearward in a sliding manner by only rotating the seat cushion  47  forward, the fourth embodiment has an excellent operation performance. 
     It is to be noted that the fixed supporting fulcrum  103  is set to the bracket  42  of the fixed rail  41  in the above explanation, but it may be set to another bracket mounted to the vehicle body floor  44  independently. Also, in the structure of the embodiment, a boss is provided in a projecting manner at a side portion of the seat cushion  47  and an arm for receiving the boss is provided in a projecting manner at the front bracket  42 , so that a supporting force for supporting the seat cushion  47  at the inverted position is supplemented so that a range of durable weight can be enlarged. Furthermore, similarly, an arm member contacting with the vehicle body floor  44  is provided at the hook  48  or the like, so that a supporting force for supporting the seat cushion  47  can be supplemented by the arm member. Also, these two techniques can simultaneously be applied to the structure of the embodiment.