Abstract:
A stowable rear seat, wherein a seat back section comprises: a seat back body stood in a floor surface so as to tilt freely; a seat back locking mechanism that locks the tilting of the seat back body; and a swinging member that swings in the forward/backward direction in conjunction with the tilting movement of the seat back body when the lock of the seat back locking mechanism is released and the seat back body tilts. The seat cushion section of the stowable rear seat comprises: a seat cushion body freely housed in the underfoot floor surface and arranged horizontally in the floor surface in front of the seat back body, and a seat cushion locking mechanism that locks the seat cushion body in a horizontal state on the floor surface.

Description:
TECHNICAL FIELD 
     The present invention relates to a stowable rear seat. 
     BACKGROUND ART 
     Some conventional vehicles include stowable rear seats so as to extend the space of rear passenger rooms in the case of no passengers in the rear passenger spaces (for example, refer to Patent Document 1). The stowable rear seat includes a seat cushion and a seat back. In a seatable state, the seat cushion is placed in a substantially horizontal posture relative to a floor surface while the seat back is positioned in an upright state at the rear of the seat cushion. Ina stowed state, the seat cushion is placed on a foot floor surface at a lower position than the floor surface in a substantially horizontal posture while the seat back is folded in a substantially horizontal posture relative to the floor surface. In order to change the seatable state to the stowed state, a user releases the locks for the seat cushion and for the seat back and then moves the seat cushion to the foot floor surface and then tilts the seat back. 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. H9-30303 
       
    
     SUMMARY OF INVENTION 
     Problems to be Solved by the Invention 
     In recent years, simplified stowing operations have been awaited in order to improve the usability. 
     Accordingly, it is an object of the present invention to provide a simplified stowing operation for the stowable rear seat. 
     Means for Solving the Problem 
     On order to solve the above problems, the invention described in claim  1  is a stowable rear seat, including:
         a seat back unit; and   a seat cushion unit, wherein   the seat back unit including:
           a tiltable seat back body erecting on a floor surface;   a seat back locking mechanism for locking a tilt of the seat back body; and   a rocking member provided at a lower end of the seat back body which rocks in an anteroposterior direction in cooperation with a tilting operation of the seat back body after locking of the seat back locking mechanism is unlocked;   
           the seat cushion unit including:
           a seat cushion body horizontally placed on the floor surface in front of the seat back body, the seat cushion body being foldable on a foot floor surface at a lower position than the floor surface; and   a seat cushion locking mechanism provided in the floor surface, the seat cushion locking mechanism engaging with a back end of the seat cushion body to lock a horizontal state of the seat cushion body on the floor surface, and   
           the rocking member is detached from the seat cushion locking mechanism when the seat back body is in an upright state, and is in contact with the seat cushion locking mechanism when the seat back body is in a tilted state to release the lock of the seat cushion locking mechanism.       

     The invention described in claim  2  is the stowable rear seat according to claim  1 , wherein
         the seat cushion unit includes:
           a shifting mechanism which shifts the seat cushion body between the horizontal state on the floor surface and a folded state on the foot floor surface, and   
           the shifting mechanism shifts the seat cushion body from the horizontal state on the floor surface to the folded state on the foot floor surface when the seat cushion locking mechanism is unlocked.       

     The invention described in claim  2  is the stowable rear seat according to claim  1 , further including:
         a lock shaft provided at the back end of the seat cushion body, the lock shaft engaging with the seat cushion locking mechanism to lock the horizontal state of the seat cushion body on the floor surface, wherein   the seat cushion locking mechanism comprises:
           a base plate having a cutout which is extended vertically and an upper part thereof opened such that the lock shaft is capable of moving forward and backward;   a regulation pawl rotatably attached to the base plate, the regulation pawl being rotated urged by the lock shaft entering the cutout, occluding an upside of the lock shaft after entry of the lock shaft up to a lower end of the cutout to regulate upward movement of the lock shaft and maintaining the horizontal state of the seat cushion body; and   a ratchet unit rotatably attached to the base plate and engaging with the regulation pawl to thereby lock/release the regulated state of the regulation pawl, wherein   
           the ratchet unit has one end engaging with the regulation pawl and the other end placed on a rocking path of the rocking member, the other end rotating the ratchet unit urged by the rocking member and releasing the regulated state of the regulation pawl;   the one end of the ratchet unit engages with the regulation pawl;   the ratchet unit is urged in a locking direction of the regulation pawl; and   the other end of the ratchet unit is configured to rotate the ratchet unit in a direction opposite to the urging direction so as to retract the ratchet unit from the rocking path when the rocking member urges one of a first urging surface placed on the rocking path of the rocking member and urged by the rocking member when the seat back body is tilted from the upright state and a second urging surface urged by the rocking member when the seat back body erects from the tilted state.       

     The invention described in claim  4  is the stowable rear seat according to claim  3 , wherein
         the one end of the ratchet unit engages with the regulation pawl by coming into contact with respective cam surfaces provided therein; and   at least one of the cam surfaces of the one end of the ratchet unit and the regulation pawl has such a shape that the ratchet unit pushes the regulation pawl toward the cutout when the regulated state of the regulation pawl is to be locked.       

     The invention described in claim  5  is the stowable rear seat according to claim  4 , wherein
         a distance from the cam surface of the one end of the ratchet unit to a rotational shaft of the ratchet unit is shorter than a distance from a position of the rocking member contacting the first urging surface to the rotational shaft of the ratchet unit.       

     The invention described in claim  6  is the stowable rear seat according to claim  3 , wherein
         the first urging surface is closer to a rotational shaft of the ratchet unit than the second urging surface;   the other end of the ratchet unit has the first urging surface projecting outward from the base plate; and   the rocking member rocks outside the base plate.       

     The invention described in claim  7  is the stowable rear seat according to claim  3 , wherein
         the second urging surface is provided on the tip surface of the other end of the ratchet unit; and   the other end of the ratchet unit has a larger width at a position that is further distant from a rotational shaft of the ratchet unit.       

     The invention described in claim  8  is the stowable rear seat according to claim  1 , further including:
         a shifting mechanism for shifting the seat cushion body between the horizontal state on the floor surface and a folded state on the foot floor surface, wherein   the shifting mechanism includes:
           a pair of parallel legs rotatably attached to the seat cushion body and the foot floor surface and supporting the seat cushion body so as to guide the seat cushion body between a horizontal state on the floor surface and a folded state on the foot floor surface; and   a guide member rotatably attached to the seat cushion body and the foot floor surface and comprising a rod member for guiding the seat cushion body between the horizontal state on the floor surface and the folded state on the foot floor surface together with the paired legs.   
               

     The invention described in claim  9  is the stowable rear seat according to claim  8 , wherein
         both ends of the rod member comprise rotational shafts.       

     The invention described in claim  10  is the stowable rear seat according to claim  8 , wherein
         a rotational shaft of the guide member adjacent to the seat cushion body is placed further forward than rotational shafts of the paired legs adjacent to the seat cushion body; and   a rotational shaft of the guide member adjacent to the foot floor surface is placed further forward and downward than rotational shafts of the paired legs adjacent to the foot floor surface.       

     The invention described in claim  11  is the stowable rear seat according to claim  8 , wherein
         the guide member is placed outside the paired legs.       

     The invention described in claim  12  is the stowable rear seat according to claim  1 , further including:
         a shifting mechanism for shifting the seat cushion body between the horizontal state on the floor surface and a folded state on the foot floor surface, wherein   the shifting mechanism includes:
           a pair of right and left legs rotatably attached to the seat cushion body and the foot floor surface and rotating relative to the foot floor surface in the anteroposterior direction to support the seat cushion body so as to guide the seat cushion body between the horizontal state on the floor surface and the folded state on the foot floor surface; and   a rotation urging unit for applying rotational force to at least one of the paired legs when the seat cushion body is guided from the horizontal state on the floor surface to a folded state on the foot floor surface.   
               

     The invention described in claim  13  is the stowable rear seat according to claim  12 , wherein
         connection between the rotation urging unit and at least one of the legs is released before the seat cushion body reaches the folded state on the foot floor surface.       

     The invention described in claim  14  is the stowable rear seat according to claim  12 , wherein
         the rotation urging unit is placed inside the paired legs.       

     The invention described in claim  15  is the stowable rear seat according to claim  12 , wherein
         the rotation urging unit is placed adjacent to the foot floor surface in the leg.       

     The invention described in claim  16  is the stowable rear seat according to claim  1 , further comprising:
         a shifting mechanism for shifting the seat cushion body between the horizontal state on the floor surface and a folded state on the foot floor surface, wherein   the shifting mechanism comprises:
           a pair of right and left legs rotatably attached to the seat cushion body and the foot floor surface and rotating relative to the foot floor surface in the anteroposterior direction to support the seat cushion body so as to guide the seat cushion body between the horizontal state on the floor surface and the folded state on the foot floor surface; and   a first rotation urging unit for applying rotational force to at least one of the paired legs when the seat cushion body is guided from the folded state on the foot floor surface to the horizontal state on the floor surface.   
               

     The invention described in claim  17  is the stowable rear seat according to claim  16 , further comprising:
         a second rotation urging unit for applying rotational force to at least the other of the paired legs when the seat cushion body is guided from the horizontal state on the floor surface to the folded state on the foot floor surface.       

     The invention described in claim  18  is the stowable rear seat according to claim  17 , wherein
         the first rotation urging unit is placed adjacent to the seat cushion body in the leg; and   the second rotation urging unit is placed adjacent to the foot floor surface in the leg.       

     The invention described in claim  19  is the stowable rear seat according to claim  17 , wherein
         the first and second rotation urging units are placed inside the paired legs.       

     The invention described in claim  20  is the stowable rear seat according to any one of claims  17  to  19 , wherein
         connection between the first rotation urging unit and at least one of the legs is released before the seat cushion body reaches the horizontal state on the floor surface; and   connection between the second rotation urging unit and at least the other of the legs is released before the seat cushion body reaches the folded state on the foot floor surface.       

     Effects of Invention 
     According the invention described in claim  1 , the seat cushion locking mechanism is unlocked when the rocking member rocks in cooperation with the tilting of the seat back body from the upright state. As a result, the seat cushion locking mechanism is unlocked in cooperation with the tilting operation of the seat back body. This can eliminate a manual unlocking operation for the seat cushion locking mechanism and simplify the stowing operation compared to manual unlocking for each of the seat back unit and the seat cushion unit. 
     The rocking member is detached from the seat cushion locking mechanism in the upright state of the seat back body and comes into contact with the seat cushion locking mechanism to unlock the seat cushion locking mechanism in the tilted state of the seat back body. This can provide an allowance required for the unlocking operation. The unlocking can thereby be prevented even if the seat back body tilts slightly by, for example, the vibration of the vehicles. 
     Additionally, the rocking member is detached from the seat cushion locking mechanism in the upright state of the seat back body to prevent abnormal noise caused by the contact between these two components. 
     According to the invention described in claim  2 , if the seat cushion locking mechanism is unlocked, the shifting mechanism shifts the seat cushion body from the horizontal state on the floor surface to the folded state on the foot floor surface. This also allows a folding operation for the seat cushion body in cooperation with the tilt of the seat back body. The stowing operation can thereby be further simplified. 
     According to the invention described in claim  3 , the rocking member urges one of the first and second urging surfaces to rotate the ratchet unit in a direction opposite to the urged direction to retract the ratchet unit from the rocking path, the first urging surface being urged by the rocking member when the seat back body is tilted from the upright state, the second urging surface being urged by the rocking member when the seat back body erects from the tilted state. As a result, the ratchet unit can be retracted from the rocking path when the seat back body is tilted from the upright state or when it erects from the tilted state. In other words, even if the rocking member contacts the other end of the ratchet unit on the rocking path during the erection of the seat back body from the tilted state, the ratchet unit can be smoothly retracted from the rocking path and enables a smooth erection operation. That is, the stowable rear seat can smoothly be returned to the upright state even before the seat back body is folded completely. 
     According to the invention described in claim  4 , at least one of the cam surface of the regulation pawl and the cam surface of the end of the ratchet unit has such a shape that the ratchet unit pushes the regulation pawl toward the cutout to lock the regulated state of the regulation pawl; hence, the lock shaft can be firmly held by the regulation pawl pushed toward the cutout during the locking. 
     According to the invention described in claim  5 , the distance from the cam surface of the end of the ratchet unit to the rotational shaft of the ratchet unit is shorter than the distance from a position of the rocking member contacting the first urging surface to the rotational shaft; hence, the principle of leverage can be applied to reduce the urging force from the rocking member required for the operation of the ratchet unit. This configuration can release the lock by the seat cushion locking mechanism with small force. 
     According to the invention described in claim  6 , the first urging surface urged by the rocking member rocking outside the base plate can project outward from the base plate to prevent the interference of the rocking member with the base plate. A configuration including the rocking member coming into contact with the first urging surface inside the base plate requires such a large base plate as to allow entry of the rocking member. In contrast, a rocking member coming into contact with the first urging surface outside the base plate can avoid an increase in the size of the base plate with no need to consider the entering of the rocking member. 
     According to the invention described in claim  7 , the other end of the ratchet unit has a larger width at a position that is further distant from the second rotational shaft. This configuration can increase the area of the second urging surface provided on the tip surface of the other end. The surface for guiding the rocking member thereby increases when the rocking member urges the second urging surface during shifting from the tilted state to the upright state. This can stabilize the operation of the ratchet unit. 
     According to the invention described in claim  8 , the guide member guides the seat cushion body between the horizontal state on the floor surface and the folded state on the foot floor surface together with the paired legs. This can prevent the rattle of the seat cushion body in the folding operation. As a result, the seat cushion body can be smoothly folded to reduce the manual adjustment. 
     According to the invention described in claim  9 , both ends of the rod member composed of the guide member function as the rotational shafts; hence, the guide member can be integrated with the rotational shafts to enhance the stability of the operation. This can also reduce the number of parts and improve the assembling work efficiency. 
     According to the invention described in claim  10 , the rotational shaft of the guide member adjacent to the seat cushion body is placed further forward than the rotational shafts of the paired legs adjacent to the seat cushion body while the rotational shaft of the guide member adjacent to the foot floor surface is placed further forward and downward than the rotational shafts of the paired legs and adjacent to the foot floor surface. This geometry enables the seat cushion body to be smoothly disposed at a substantially horizontal posture during the folded state on the foot floor surface. 
     According to the invention described in claim  11 , the guide member is provided outside the paired legs; hence, the paired legs do not interfere with the guide member to secure a smooth operation. 
     According to the invention described in claim  12 , the rotation urging unit applies rotational force to at least one of the legs in order to guide the seat cushion body from the horizontal state on the floor surface to the folded state on the foot floor surface. The rotational force can automatically move the seat cushion body to the folded state on the foot floor surface. This configuration can provide a smooth folding operation of the seat cushion unit. 
     According to the invention described in claim  13 , the connection between the rotation urging unit and at least one of the legs is released before the seat cushion body reaches the folded state on the foot floor surface. This configuration can intercept the transmission of the biasing force halfway through the folding operation of the seat cushion body to shift the seat cushion body to the folded state on the foot floor surface by the remaining force. As a result, shock can be eased during the contact of the seat cushion body with the foot floor surface. 
     According to the invention described in claim  14 , the rotation urging unit is placed inside the paired legs and can therefore be protected by the legs. This configuration can stabilize the operation over a long period of time. 
     According to the invention described in claim  15 , the rotation urging unit can be placed adjacent to the foot floor surface in the legs to therefore connect the rotation urging unit to a portion having high rigidity in the legs. This configuration can stabilize the operation of the rotation urging unit. 
     According to the invention described in claim  16 , the first rotation urging unit applies rotational force to at least one of the legs in order to guide the seat cushion body from the folded state on the foot floor surface to the horizontal state on the floor surface. As a result, the rotational force of the first rotation urging unit can serve as auxiliary force to raise the seat cushion body with smaller force when the seat cushion body folded on the foot floor surface is returned to the floor surface. This configuration allows the seat cushion body to be returned more easily. 
     According to the invention described in claim  17 , the second rotation urging unit applies rotational force to at least the other leg in order to guide the seat cushion body from the horizontal state on the floor surface to the folded state on the foot floor surface. The rotational force can automatically move the seat cushion body to the folded state on the foot floor surface. This configuration can provide a smooth folding operation of the seat cushion unit. 
     According to the invention described in claim  18 , the first rotation urging unit is placed adjacent to the seat cushion body in the leg while the second rotation urging unit is placed adjacent to the foot floor surface in the leg. This configuration can prevent interference between both the units to stabilize the operation. 
     According to the invention described in claim  19 , the first and second rotation urging units are placed inside the paired legs and can therefore be protected by the legs. This configuration can stabilize the operation over a long period of time. 
     According to the invention described in claim  20 , the connection between the first rotation urging unit and at least one of the legs is released before the seat cushion body reaches the horizontal state on the floor surface. As a result, the seat cushion body starts to move from the horizontal state, while the rotational force of the second rotation urging unit is applied without application of the rotational force of the first rotation urging unit. This configuration can achieve quick start-up of the folding operation. 
     Additionally, the connection between the second rotation urging unit and at least the other leg is released before the seat cushion body reaches the folded state on the foot floor surface. This configuration can intercept the transmission of the biasing force halfway through the folding operation of the seat cushion body to shift the seat cushion body to the folded state on the foot floor surface by the remaining force. As a result, shock can be eased during the contact of the seat cushion body with the foot floor surface. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  This is a side view illustrating an outline configuration of a stowable rear seat according to the present embodiment. 
         FIG. 2  This is a side view illustrating an internal configuration of the stowable rear seat in  FIG. 1 . 
         FIG. 3  This is a perspective view illustrating the internal configuration of the stowable rear seat in  FIG. 1 . 
         FIG. 4  This is a perspective view illustrating an outline configuration of a reinforcing member according to the present embodiment. 
         FIG. 5  This is a perspective view illustrating an outline configuration of another reinforcing member according to the present embodiment. 
         FIG. 6  This is a perspective view illustrating an outline configuration of a seat cushion locking mechanism according to the present embodiment. 
         FIG. 7  This is a side view illustrating an outline configuration of the seat cushion locking mechanism according to the present embodiment. 
         FIG. 8  This is a side view illustrating the relationship between a locus of a lock shaft and a regulation pawl according to the present embodiment. 
         FIG. 9A  This is a schematic diagram illustrating the relationship between a cam surface of a ratchet unit and a cam surface of the regulation pawl according to the present embodiment. 
         FIG. 9B  This is a schematic diagram illustrating the relationship between the cam surface of the ratchet unit and the cam surface of the regulation pawl according to the present embodiment. 
         FIG. 9C  This is a schematic diagram illustrating the relationship between the cam surface of the ratchet unit and the cam surface of the regulation pawl according to the present embodiment. 
         FIG. 10  This is a sideview illustrating the relationship between the rocking path of the rocking member and the ratchet unit according to the present embodiment. 
         FIG. 11  This is a front view illustrating an outline configuration of a shifting mechanism in a horizontal state of the seat cushion body according to the present embodiment. 
         FIG. 12  This is a perspective view as diagonally viewed from the left front, illustrating the outline configuration of the shifting mechanism in the horizontal state of the seat cushion body according to the present embodiment. 
         FIG. 13  This is a perspective view as diagonally viewed from the right front, illustrating the outline configuration of the shifting mechanism in the horizontal state of the seat cushion body according to the present embodiment. 
         FIG. 14A  This illustrates an outline configuration of a frame unit according to the present embodiment and a sectional view of the unit taken along a line a-a in  FIG. 14B . 
         FIG. 14B  This is a front view illustrating the outline configuration of the frame unit according to the present embodiment. 
         FIG. 15  This is a schematic side view illustrating the operation of the shifting mechanism according to the present embodiment. 
         FIG. 16  This is a schematic side view illustrating the operation of a seat back unit and a seat cushion unit according to the present embodiment. 
         FIG. 17  This is a side view illustrating a modification of a hamper in  FIG. 8 . 
         FIG. 18  This is a side view illustrating a modification of a base plate in  FIG. 8 . 
         FIG. 19  This is a front view illustrating a modification of the shifting mechanism. 
         FIG. 20  This is a perspective view as diagonally viewed from the left front, illustrating the modification of the shifting mechanism. 
         FIG. 21  This is a perspective view as diagonally viewed from the right front, illustrating the modification of the shifting mechanism. 
         FIG. 22A  This illustrates an outline configuration of a frame unit of the shifting mechanism in  FIG. 19  and is a sectional view of the unit taken along a line a-a in  FIG. 22B . 
         FIG. 22B  This is a front view illustrating the outline configuration of the frame unit in  FIG. 22A . 
         FIG. 23  This is a schematic side view illustrating the operation of the shifting mechanism in  FIG. 19 . 
         FIG. 24  This is a schematic side view illustrating the operation of the seat back unit and the seat cushion unit including the shifting mechanism in  FIG. 19 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Exemplary embodiments according to the present invention will now be described with reference to the accompanying drawings. Although various preferred technical limitations are applied to the following embodiments according to the present invention, the scope of the present invention should not be limited to these embodiments and examples illustrated in these drawings. 
       FIG. 1  is a side view illustrating an outline configuration of a stowable rear seat according to the present embodiment.  FIG. 2  is a side view illustrating an internal configuration of the stowable rear seat.  FIG. 3  is a perspective view illustrating the internal configuration of the stowable rear seat. As illustrated in  FIG. 3 , a pair of right and left stowable rear seats  1 A and  1 B is provided so as to be stowable independently. The right stowable rear seat  1 A has a smaller width than that of the left stowable rear seat  1 B. 
     As illustrated in  FIG. 1 , the stowable rear seats  1 A and  1 B each include a seat back unit  2  and a seat cushion unit  3 , which are covered with the seat pads  21  and  31 , respectively. 
     The seat back unit  2  will now be described. The seat back unit  2  includes a tiltable seat back body  4  erecting on a floor surface  100  of a vehicle body and a seat back locking mechanism  5  which locks the tilt of the seat back body  4 . 
     As illustrated in  FIGS. 2 and 3 , the seat back body  4  includes a seat back frame  41  functioning as the outer periphery of the seat back body  4 , a back board  42  attached to the seat back frame  41 , and hinge units  43  and  44  provided at the right and left lower ends of the seat back frames  41 . The hinge units are rotatably supported by the floor surface  100  such that the seat back frame  41  can be tilted. 
     The seat back frame  41  of the right stowable rear seat  1 A has a different configuration from that of the left stowable rear seat  1 B. The seat back frame  41   a  of the right stowable rear seat  1 A will now be described. 
     As illustrated in  FIG. 3 , the right seat back frame  41   a  includes a first pipe unit  411   a  formed by bending one pipe so as to surround the upper, right, and left sides of the back board  42   a , and a second pipe unit  412   a  having a linear shape placed on the lower side of the back board  42   a  so as to be connected to both ends of the first pipe unit  411   a . As a result, the entire seat back frame  41   a  surrounds the outer periphery of the back board  42   a.    
     Inside the right and left corners between the first and second pipe units  411   a  and  412   a , wires  45   a  and  46   a  for mounting a child safety seat (not illustrated) are provided. 
     Among the hinge units  43   a  and  44   a , the hinge unit  43   a  adjacent to the outside of the vehicle is a rotatable hinge shaft engaging with a support bracket  101  provided on the floor surface  100 , and is welded to the second pipe unit  412   a.    
     The other hinge unit  44   a  adjacent to the center of the vehicle is a rotatable hinge bracket engaging via a hinge shaft  441  with a center hinge bracket  102  provided on the floor surface  100 . The hinge unit  44   a  is attached to the left lower corner of the back board  42   a . In the left lower corner of the back board  42   a , a reinforcing member  47   a  is provided so as to surround the hinge unit  44   a  and the wire  46   a.    
       FIG. 4  is a perspective view illustrating an outline configuration of the reinforcing member  47   a.    
     The reinforcing member  47   a  has a larger thickness than that of the back board  42   a  and is welded to the first and second pipe units  411   a  and  412   a . The reinforcing member  47   a  has welded portions  471   a  and  472   a  having ribs in order to assure high welding strength. Screw units  473   a  for fixing the hinge  44   a  are provided in the upper and lower portions of the reinforcing member  47   a . The hinge  44   a  is fixed to the back board  42   a  via the reinforcing member  47   a  to enhance the attachment strength of the hinge  44   a.    
     The seat back frame  41   b  of the left stowable rear seat  1 B will now be described. 
     As illustrated in  FIG. 3 , the left seat back frame  41   b  includes a pipe unit  411   b  formed by bending a single pipe so as to surround the entire periphery of the back board  42   b . The pipe unit  411   b  is bent so as to chamfer its right lower corner and surround the back board  42   b  except for its right lower corner. Both ends of the pipe unit  411   b  are welded at the left lower corner of the back board  42   b . Inside the pipe unit  411   b , a reinforcing pipe  412   b  bridges between the upper and lower sides of the pipe unit  411   b.    
     In the left corner between the reinforcing pipe  412   b  and the lower side of the pipe unit  411   b  and in the corner between the left and lower sides of the pipe unit  411   b , wires  45   b  and  46   b  are provided for mounting a child safety seat (not illustrated). 
     Among hinge units  43   b  and  44   b , the hinge unit  43   b  adjacent to the outside of the vehicle is a rotatable hinge shaft engaging with a support bracket  101  provided on the floor surface  100 , and is welded to the left lower corner of the pipe unit  411   b.    
     The other hinge unit  44   b  adjacent to the center of the vehicle is a rotatable hinge bracket engaging via a hinge shaft  441  with a center hinge bracket  102  provided on the floor surface  100 . The hinge unit  44   b  is attached to the right lower corner of the back board  42   b . In the left lower corner of the back board  42   b , a reinforcing member  47   b  is provided so as to surround the hinge unit  44   b.    
       FIG. 5  is a perspective view illustrating an outline configuration of the reinforcing member  47   b.    
     The reinforcing member  47   b  has a larger thickness than that of the back board  42   b  and is welded to the right lower corner of the pipe unit  411   b . The reinforcing member  47   b  has a rib  471   b  along its entire periphery to enhance its entire strength. Screw units  473   b  for fixing the hinge unit  44   b  are provided in the upper and lower portions of the reinforcing member  47   b . The hinge unit  44   b  is fixed to the back board  42   b  via the reinforcing member  47   b  to enhance the attachment strength of the hinge  44   b.    
     As illustrated in  FIG. 3 , the seat back locking mechanism  5  includes a lever unit  51  provided in the upper outside of the seat back body  4 , and a lock unit  52  provided in the outside of the seat back body  4  and engaging with a latched portion  115  (refer to  FIG. 1 ) of a vehicle body. In an upright state of the seat back body  4 , the lock unit  52  engages with the latched portion of the vehicle body and locks the upright state. In response to the operation of the lever unit  51 , the locking between the lock unit  52  and the latched portion is released to shift the seat back body  4  to a tiltable state. 
     At the lower end of each of the seat back bodies  4  of the right and left stowable rear seats  1 A and  1 B, a rocking member  6  is provided and the rocking member  6  rocks in the anteroposterior direction in cooperation with a tilting operation of the seat back body  4  after locking of the seat back locking mechanism  5  is released. The rocking member  6  is formed by bending a metal rod into a rectangle frame extending downward. The rocking member  6  is welded at a substantial center of each of the second pipe unit  412   a  and the pipe unit  411   b.    
     Each seat cushion unit  3  includes a seat cushion body  7 , a seat cushion locking mechanism  8 , and a shifting mechanism  9 . In these components, only the seat cushion bodies  7  have different widths between the right and left stowable rear seats  1 A and  1 B while the seat cushion locking mechanisms  8  and the shifting mechanisms  9  have the same configurations in the right and left stowable rear seats  1 A and  1 B. 
     Each seat cushion body  7  is horizontally placed on the floor surface  100  in front of the seat back body  4  and is foldable on a foot floor surface  110  at a lower position than the floor surface  100 . Hereafter, a state of the seat cushion body  7  positioned horizontally on the floor surface  100  is called a horizontal state, and a state of the seat cushion body  7  folded on the foot floor surface  110  is called a folded state. In the center back end of the seat cushion body  7 , a lock shaft  71  engaging with the seat cushion locking mechanism  8  extends in the lateral direction. On the front undersurface of the seat cushion body  7 , a posture maintaining unit  72  is provided to maintain the posture of the seat cushion body  7 , the posture maintaining unit  72  being in contact with the foot floor surface  110  in the folded state. 
     As illustrated in  FIG. 3 , the seat cushion locking mechanism  8  is provided in the floor surface  100  so as to be placed below the seat back body  4  and in the back side of the seat cushion body  7  in the horizontal state. The seat cushion locking mechanism  8  can engage with the lock shaft  71  to lock the horizontal state of the seat cushion body  7 . 
     The seat cushion locking mechanism  8  will now be explained in detail.  FIG. 6  is a perspective view illustrating an outline configuration of the seat cushion locking mechanism  8  while  FIG. 7  is a side view thereof. As illustrated in  FIGS. 6 and 7 , the seat cushion locking mechanism  8  includes a pair of the right and left base plates  81 , a regulation pawl  82 , and a ratchet unit  83 . The interval H 1  between the right and left base plates  81  is shorter than the width H 2  of the rocking member  6 . This configuration reduces the width of the base plate  81 . 
     Each base plate  81  includes a plate board  811  having a bottom  813  fixed to the floor surface  100  with a screw  812  and a plate body  814  erecting from the inner side of the bottom  813 . The plate body  814  has a cutout  815  which is vertically extending and the upper part thereof is opened. 
       FIG. 8  is a side view illustrating the relationship between a locus R of a lock shaft  71  and the regulation pawl  82 . As illustrated in  FIG. 8 , the cutout  815  is provided along the locus R of the lock shaft  71 . Upon shifting between the horizontal state and the folded state of the seat cushion body  7 , the lock shaft  71  moves forward and backward within the cutout  815 . Lines R 1  and R 2  in  FIG. 8  indicate a variation in the locus R of the lock shaft  71 . The width of the cutout  815  is determined such that the cutout  815  can fit with the lock shaft  71  despite slight shift of the locus R in the anteroposterior direction. At the lower end of the cutout  815 , an auxiliary cutout  816  extends forward in continuation from the cutout  815 . 
     Behind the cutout  815 , a first rotational shaft  817  rotatably holding the regulation pawl  82  and a second rotational shaft  818  rotatably holding the rachet unit  83  bridge between the pair of the base plates  81 . 
     At the bottom  813  of at least one base plate of the pair of the base plates  81 , a hamper  84  occluding the auxiliary cutout  816  is provided in order to prevent the lock shaft  71  from entering the auxiliary cutout  816 . The hamper  84  is a reversed V-shaped plate spring. The hamper  84  is placed in the anteroposterior direction so that one side  841  of the reversed V-shape occludes the portion of the auxiliary cutout  816  adjacent to the cutout  815 . One end  842  of the hamper  84  is fixed at the center of the bottom  813  of the base plate  81  while the other end  843  is separated from the bottom  813 . For example, if a luggage on a loading space collides with the seat back body  4  from the back due to head-on collision, the lock shaft  71  comes into contact with the side  841  of the hamper  84 . If a load greater than or equal to a predetermined level is applied to the hamper  84  at this time, the hamper  84  deforms and opens the auxiliary cutout  816  (refer to a dotted line T in  FIG. 8 ). A predetermined load required for deforming the hamper  84  can be adjusted by varying the thickness or elastic modulus of the plate spring of the hamper  84 . 
     On the bottom  813  of the base plate  81 , a detachment stopper  85  is attached for preventing the detachment of the hamper  84  from the plate body  814  of the base plate  81  due to the deformation of the hamper  84 . The detachment stopper  85  is a plate member and extends in the anteroposterior direction beside the other end  843  of the hamper  84 . The other end  843  of the hamper  84  is disposed between the plate body  814  and the detachment stopper  85 . If the hamper  84  deforms to move in the anteroposterior direction, the detachment stopper  85  prevents the hamper  84  from shifting in the direction away from the plate body  814 . 
     If a luggage clashes with the back side of the stowable rear seats  1 A and  1 B to move the entire rear seats forward, the lock shaft  71  deforms the hamper  84  to enter the auxiliary cutout  816 . Since upward movement of the lock shaft  71  is regulated by entering into the auxiliary cutout  816 , the seat cushion body  7  itself is also locked in the horizontal state. In this way, even if a luggage clashes with the back side to tilt the seat back body  4 , the seat cushion body maintains the locked state. This can prevent unlocking in cooperation with the tilt of the seat back body  4 . 
     The regulation pawl  82  is rotatably attached to the base plate  81  by the first rotational shaft  817 . The regulation pawl  82  has a concave portion  821  at its tip to engage with the lock shaft  71 . A state of the lock shaft  71  engaged into the concave portion  821  and the tip oriented substantially frontward is called a regulated state (refer to a chain line T 1  illustrated in  FIG. 8 ). A state of the lock shaft  71  detached from the inside of the concave portion  821  and the tip oriented substantially upward is called a released state (refer to a solid line T 2  illustrated in  FIG. 8 ). The regulation pawl  82  is always applied with a biasing force by the biasing spring  822  in a direction Y 1  enabling the released state. 
     The base end of the regulation pawl  82  is provided with a cam surface  823  to engage with the ratchet unit  83 . The cam surface  823  includes a first arcuate cam surface  824  and a second flat cam surface  825  continuously extending downward from the first cam surface  824 . In the regulated state, the second cam surface  825  is latched by the ratchet unit  83  to regulate further rotation caused by the biasing spring  822 . In the released state, the second cam surface  825  is latched by a stopper  819  provided on the bottom  813  of the base plate  81  to regulate further rotation caused by the biasing spring  822 . 
     If the lock shaft  71  guided by the cutout  815  engages with the concave portion  821  of the regulation pawl  82  in the released state, the regulation pawl  82  is rotated urged by the lock shaft  71 . This rotation causes the regulation pawl  82  to occlude the upside of the lock shaft  71 , regulating the upward movement of the lock shaft  71  to lead to the regulated state. At this time, the regulated state is locked by the ratchet unit  83 . 
     The ratchet unit  83  is rotatably attached to the base plate  81  by the second rotational shaft  818 . The ratchet unit  83  engages with the regulation pawl  82  to thereby lock/release the regulated state of the regulation pawl  82 . The end  831  of the ratchet unit  83  engages with the cam surface  823  of the regulation pawl  82  and has an end surface functioning as the cam surface  832 . The ratchet unit  83  is always urged in a direction Y 2  locking the regulation pawl  82  by a biasing spring  89  functioning as a biasing member. The biasing spring  89  is a torsion spring attached to the second rotational shaft  818 . 
       FIG. 9  shows schematic diagrams illustrating the relationship between the cam surface  832  of the ratchet unit  83  and the cam surface  823  of the regulation pawl  82 . The cam surface  832  of the ratchet unit  83  has an upper portion  833  inclined so as to project from a lower portion  834  towards the regulation pawl  82 . During the rotation of the regulation pawl from the released state to the regulated state, the engagement position of the cam surface  832  of the ratchet unit  83  shifts from the first cam surface  824  to the second cam surface  825  of the regulation pawl  82 , as illustrated in  FIG. 9A . At this time, if the cam surface  832  of the ratchet unit  83  is flat, the rotation path of the regulation pawl  82  after the shifting is indicated by two-dot chain lines t 1  in  FIGS. 9B and 9C . If the upper portion  833  of the cam surface  832  of the ratchet unit  83  is further inclined so as to project from the lower portion  834  towards the regulation pawl  82  as described above, the regulation pawl  82  after the shifting is further rotated along the rotation path than those indicated by the two-dot chain lines t 1  in  FIGS. 9B and 9C . That is, the ratchet unit  83  pushes the regulation pawl  82  toward the cutout  815  to lock the regulated state of the regulation pawl  82 , enabling a more robust regulated state. 
       FIG. 10  is a side view illustrating the relationship between the rocking path K of the rocking member  6  and the ratchet unit  83 . As illustrated in  FIG. 10 , the rocking member  6  rocks just outside of the base plate  81  on the rocking path K without interference with the base plate  81 . The other end  835  of the ratchet unit  83  is placed on the rocking path K of the rocking member  6 . In the other end  835  including the upper surface having a substantially reversed V-shape, a surface adjacent to the second rotational shaft  818 , i.e., the inner surface is called a first urging surface  836 , the outer surface that is the tip surface of the other end  835  is called a second urging surface  837 , and the lower surface facing the first urging surface  836  is called an opposite surface  838 . The other end  835  of the ratchet unit  83  has such a shape that a part of the first urging surface  836  projects outward from the base plate  81 . With respect to the other end  835  of the ratchet unit  83 , the width between the first urging surface  836  and the opposite surface  838  becomes wider gradually as the distance from the second rotational shaft  818  becomes further. The opposite surface  838  is provided with a concave portion  839  for latching one end  891  of the biasing spring  89 . The concave portion  839  is formed in a portion wider than the basis end of the other end  835  of the ratchet unit  83 . This can prevent a decrease in the rigidity of the ratchet unit  83  due to the provision of the concave portion  839 . The concave portion  839  is placed outside the base plate  81 . This configuration can prevent the base plate  81  from obstructing the attachment of the biasing spring  89 . 
     When the seat back body  4  is tilted from the upright state, the first urging surface  836  traverses the rocking path K 1  of the rocking member  6  in the tilted state so as to be pushed by the rocking member  6 . In contrast, when the seat back body  4  erects from the tilted state, the second urging surface  837  traverses the rocking path K 2  of the rocking member  6  in the upright state so as to be pushed by the rocking member  6 . The rocking member  6 , which is a downward rectangle frame as described above, can stably urges the first and second urging surfaces  836  and  837  compared to, for example, an L-shaped or rod rocking member. 
     The first and second urging surfaces  836  and  837  urged by the rocking member  6  rotate the rachet unit  83  in a direction opposite to the urged direction Y 2  to retract the rachet unit  83  from the rocking path K. As a result, the rachet unit  83  can be retracted from the rocking path K when the seat back body  4  is tilted from the upright state or when it erects from the tilted state. In other words, even if the rocking member  6  contacts the other end  835  of the rachet unit  83  on the rocking path K during the erection of the seat back body  4  from the tilted state, the rachet unit  83  can be smoothly retracted from the rocking path K and enables a smooth erection operation. 
     In the upright state of the seat back body  4 , the rocking member  6  is detached from the rachet unit  83  of the seat cushion locking mechanism  8 . In the tilted state of the seat back body  4 , the rocking member  6  contacts the other end  835  of the rachet unit  83  and releases the lock of the seat cushion locking mechanism  8 . 
     In this embodiment, the distance m from the cam surface  832  of the end  831  of the rachet unit  83  to the center of the second rotational shaft  813  is shorter than the distance n from a position of the rocking member  6  contacting the first urging surface  836  of the rachet unit  83  to the center of the second rotational shaft  818 . 
     As illustrated in  FIG. 7 , the regulation pawl  82  in the regulated state is locked since the second cam surface  825  of the regulation pawl  82  engages with the cam surface  832  of the ratchet unit  83 . When the seat back body  4  is tilted from the upright state in the locked state, the rocking member  6  rocks in the direction of the arrow Y 3 , urges the first urging surface  836  of the ratchet unit  83  against the biasing force of the biasing spring, and rotates the ratchet unit  83  in the direction of the arrow Y 4 . This rotation releases the lock to rotate the regulation pawl  82  in the direction of the arrow Y 5  due to the biasing force of the biasing spring  822 , releases the regulation of the lock shaft  71 , and leads to the released state. 
     The shifting mechanism  9  shifts the seat cushion body  7  between the horizontal state and the folded state.  FIG. 11  is a front view illustrating an outline configuration of the shifting mechanism  9  in the horizontal state of the seat cushion body  7 .  FIG. 12  is a perspective view as diagonally viewed from the left front.  FIG. 13  is a perspective view as diagonally viewed from the right front. As illustrated in  FIGS. 11 to 13 , the shifting mechanism  9  includes a frame unit  91 , foot-side bearing units  92 , seat-side bearing units  93 , a guide member  94 , and a rotation urging unit  95 . 
       FIG. 14A  illustrates an outline configuration of the frame unit  91 .  FIG. 14A  is a sectional view of the unit taken along a line a-a in  FIG. 14B  while  FIG. 14B  is a front view thereof. As illustrated in  FIGS. 14A and 14B , the frame unit  91  includes a pair of parallel legs  911  and  912  and a connection frame  913  connecting the pair of legs  911  and  912 . 
     At the lower end of each of the legs  911  and  912  composed of a metal pipe, a rotational shaft unit  914  is supported by a foot-side bearing unit  92 . At each upper end of the legs  911  and  912 , a pivot hole  915  is rotatably supported by the seat-side bearing unit  93 . 
     The connection frame  913  is attached at the longitudinal center of the paired legs  911  and  912 . As illustrated in  FIGS. 12 and 13 , the connection frame  913  curves so as to project forward in the horizontal state of the seat cushion body  7 . As illustrated in  FIG. 14A , both ends of the connection frame  913  are fixed by, for example, welding at the position shifted in the projecting direction of the connection frame  913 , from the center S of the cross section orthogonal to the longitudinal direction of the legs  911  and  912 . 
     A bias engagement member  96  for engaging with the rotation urging unit  95  has a substantial L shape viewed from the front and is attached to the left leg  911  and the connection frame  913  by, for example, welding. 
     As illustrated in  FIGS. 11 to 13 , a pair of foot-side bearing units  92  is provided for each of the paired legs  911  and  912  and mounted on the foot floor surface  110  with a predetermined interval between the foot-side bearing units  92  in the lateral direction. Seat-side bearing units  93  are provided for the respective paired legs  911  and  912  and fixed to the undersurface of the seat cushion body  7  with a predetermined interval in the lateral direction. This enables guiding between the horizontal state and the folded state while the paired legs  911  and  912  support the seat cushion body  7 . 
     A guide member  94  is placed outside the paired legs  911  and  912 , that is on the right side of the paired legs  911  and  912 , i.e., adjacent to the center of the vehicle. The guide member  94  guides the seat cushion body  7  between the horizontal state and the folded state together with the paired legs  911  and  912 . The guide member  94  is formed by bending both ends of a metal round rod. The upper end of the guide member  94  serves as a rotational shaft  941  by being supported by the seat-side bearing unit  93  in the horizontal position. The lower end of the guide member  94  serves as a rotational shaft  942  by being supported by the foot-side bearing units  92  in the horizontal position. The rotational shaft  941  of the guide member  94  adjacent to the seat cushion body  7  is placed further forward than the rotational shafts of the paired legs  911  and  912  adjacent to the seat cushion body  7 . In contrast, the rotational shaft  942  of the guide member  94  adjacent to the foot floor surface  110  is placed further forward and downward than the rotational shafts of the paired legs  911  and  912  adjacent to the foot floor surface  110 . This geometry enables smooth folding of the seat cushion body  7  into a substantially horizontal posture during the folded state. 
     The rotation urging unit  95  applies rotational force to at least one leg  911  of the paired legs  911  and  912  when guiding the seat cushion body  7  from the horizontal state to the folded state. The rotation urging unit  95  is a flat spiral spring placed inside the paired legs  911  and  912  and at a portion of the leg  911  adjacent to the foot floor surface  110 . The rotation urging unit  95  has an inner end fixed to the left foot-side bearing units  92  and an outer end engaging with the bias engagement member  96 . In the horizontal state of the seat cushion body  7 , the outer end of the rotation urging unit  95  engages with the bias engagement member  96  to apply biasing force to the left leg  911 . The outer end of the rotation urging unit  95  is detached from the bias engagement member  96  halfway through guiding of the seat cushion body  7  from the horizontal state to the folded state. 
     A detailed operation of the shifting mechanism  9  will be explained.  FIG. 15  is a schematic side view illustrating the operation of the shifting mechanism  9 . Solid lines in  FIG. 15  indicate the seat cushion body  7  and the shifting mechanism  9  in the horizontal state while two-dot chain lines indicate the seat cushion body  7  and the shifting mechanism  9  during a shifting operation. The seat cushion locking mechanism  8  is unlocked from the horizontal state to then release the rotation urging unit  95 . As a result, biasing force of the rotation urging unit  95  rotates the legs  911  and  912  forward and also moves the seat cushion body  7  forward. During this movement, the guide member  94  reduces the rattle of the seat cushion body  7 . Additionally, since the connection frame  913  has such a curved shape as to project forward in the horizontal state of the seat cushion body  7 , the space at the center between the connection frame  913  and the seat cushion body  7  can be secured before the paired legs  911  and  912  guide the seat cushion body  7  from the horizontal state to the folded state. This can prevent contact of the connection frame  913  with the seat cushion body  7  in a folding operation and enables to perform a smooth folding operation for the seat cushion body  7 . Since the connection frame  913  projects downward after the folding, the seat cushion body  7  can be placed downward to use a space more effectively. 
     Since the rotation urging unit  95  is detached from the bias engagement member  96  halfway through guiding of the seat cushion body  7  from the horizontal state to the folded state, no biasing force is applied to the paired legs  911  and  912  after the detaching to move the seat cushion body  7  with a decrease in the rotational force. As a result, the posture maintenance unit  72  comes into contact with the foot floor surface  110  to then complete the shifting operation and lead to the folded state of the seat cushion body  7 . During the folded state, the seat cushion body  7  is maintained in a substantially horizontal posture by the guide member  94  and the posture maintenance unit  72 . 
     The cooperation of the seat back unit  2  and the seat cushion unit  3  during the folding operation will be explained.  FIG. 16  is a schematic side view illustrating the operation of the seat back unit  2  and the seat cushion unit  3 . Solid lines in  FIG. 16  indicate the seat back unit  2  and the seat cushion unit  3  in the seatable state (horizontal state) while two-dot chain lines indicate the seat back unit  2  and the seat cushion unit  3  during the folding operation. If the seat back locking mechanism  5  is unlocked from the seatable state to tilt the seat back body  4 , the rocking member  6  unlocks the seat cushion locking mechanism  8  before the complete folding. This applies the biasing force of the rotation urging unit  95  to the paired legs  911  and  912  to rotate the paired legs  911  and  912 . Thereby, the seat cushion body  7  shifts from the horizontal state to the folded state. If the seat cushion body  7  reaches the folded state, a user folds the seat back body  4  completely to finish the folding operation. 
     According to the present embodiment as described above, the seat cushion locking mechanism  8  is unlocked when the rocking member  6  rocks in cooperation with the tilting of the seat back body  4  from the upright state. As a result, the seat cushion locking mechanism  8  is unlocked in cooperation with the tilting operation of the seat back body  4 . This can eliminate a manual unlocking operation of the seat cushion locking mechanism  8  and simplify the stowing operation compared to manually unlocking each of the seat back unit  2  and the seat cushion unit  3 . 
     The rocking member  6  is detached from the seat cushion locking mechanism  8  in the upright state of the seat back body  4  and comes into contact with the seat cushion locking mechanism  8  to unlock the seat cushion locking mechanism  8  when the seat back body  4  is to be tilted. This can provide an allowance required for the unlocking operation. The unlocking can thereby be prevented even if the seat back body  4  tilts slightly by, for example, the vibration of the vehicle. 
     If the seat cushion locking mechanism  8  is unlocked, the shifting mechanism  9  shifts the seat cushion body  7  from the horizontal state to the folded state. This also allows a folding operation for the seat cushion body  7  in cooperation with the tilting of the seat back body  4 . The stowing operation can thereby be further simplified. 
     Additionally, the rocking member  6  is detached from the seat cushion locking mechanism  8  in the upright state of the seat back body  4  to prevent abnormal noise caused by the contact between these two components. 
     In recent years, it has been awaited for a technique to smoothly return a seat back to the upright state even when the seat back is halfway tilted from a perspective of improvement in usability. 
     That is, it has been awaited for a stowable rear seat which can smoothly be returned to the upright state even before the seat back is folded completely to be provided. 
     In the present embodiment to meet this request, the rocking member  6  urges one of the first and second urging surfaces  836  and  837  to rotate the ratchet unit  83  in a direction opposite to the urged direction to retract the ratchet unit  83  from the rocking path K, the first urging surface  836  being urged by the rocking member  6  when the seat back body  4  is tilted from the upright state, the second urging surface  837  being urged by the rocking member  6  when the seat back body  4  erects from the tilted state. As a result, the ratchet unit  83  can be retracted from the rocking path K when the seat back body  4  is tilted from the upright state or when it erects from the tilted state. In other words, even if the rocking member  6  contacts the other end  835  of the ratchet unit  83  on the rocking path K during the erection of the seat back body  4  from the tilted state, the ratchet unit  83  can be smoothly retracted from the rocking path K and enables a smooth erection operation. That is, the stowable rear seat can smoothly be returned to the upright state even just before the seat back body  4  is folded completely. 
     At least one of the cam surface  823  of the regulation pawl  82  and the cam surface  832  of the end  831  of the ratchet unit  83  has such a shape that the ratchet unit  83  pushes the regulation pawl  82  toward the cutout  815  to lock the regulated state of the regulation pawl  82 ; hence, the lock shaft  71  can be firmly held by the regulation pawl  82  being pushed toward the cutout  815  during the locking. 
     The distance m from the cam surface  832  of the end  831  of the rachet unit  83  to the center of the second rotational shaft  813  of the rachet unit  83  is shorter than the distance n from a position of the rocking member  6  contacting the first urging surface  836  to the second rotational shaft  818 ; hence, the principle of leverage can be applied to reduce the urging force from the rocking member  6  required for the operation of the rachet unit  83 . This configuration can release the lock by the seat cushion locking mechanism  8  with small force. 
     The first urging surface  836  urged by the rocking member  6  rocking outside the base plate  81  projects outward from the base plate  81  to prevent the interference of the rocking member  6  with the base plate  81 . A configuration including the rocking member  6  coming into contact with the first urging surface  836  inside the base plate  81  requires such a large base plate  81  as to allow entry of the rocking member  6 . In contrast, a rocking member  6  coming into contact with the first urging surface  836  outside the base plate  81  can avoid an increase in the size of the base plate with no need to consider the entry of the rocking member  6 . 
     The width of the other end  835  of the rachet unit  83  becomes wider as distancing away from the second rotational shaft  818 . This configuration can increase the area of the second urging surface  837  formed on the tip surface of the other end  835 . The surface for guiding the rocking member  6  thereby increases when the rocking member  6  urges the second urging surface  837  during shifting from the tilted state to the upright state. This can stabilize the operation of the rachet unit  83 . 
     In recent years, mechanisms have been developed which move a seat cushion to a foot floor surface in cooperation with the tilting operation of a seat back. Manual adjustment is however necessary even after the folding operation depending on the state of the seat cushion. 
     That is, it is awaited for a technique to provide a smooth folding operation of a seat cushion and reduce the manual adjustment when the seat cushion is moved in cooperation with the tilting operation of a seat back. 
     In order to meet this request, the present embodiment includes the guide member  94  guiding the seat cushion body  7  between the horizontal state and the folded state together with the paired legs  911  and  912 . This can prevent the rattle of the seat cushion body  7  during the folding operation. As a result, when the seat cushion body  7  is moved in cooperation with the tilting operation of the seat back unit  2 , the seat cushion body  7  can be smoothly folded and the manual adjustment can be reduced. 
     Both ends of the rod member forming the guide member  94  function as the rotational shafts  941  and  942 ; hence, the guide member  94  can be integrally formed with the rotational shafts  941  and  942  to enhance the stability of the operation. This can also reduce the number of parts and improve the assembling work efficiency. 
     The rotational shaft  941  of the guide member  94  adjacent to the seat cushion body  7  is placed further forward than the rotational shafts of the paired legs  911  and  912  adjacent to the seat cushion body  7 . Additionally, the rotational shaft  942  of the guide member  94  adjacent to the foot floor surface  110  is placed further forward and downward than the rotational shafts of the paired legs  911  and  912  adjacent to the foot floor surface  110 . This geometry enables the seat cushion body  7  to be smoothly disposed at a substantially horizontal posture during the folded state on the foot floor surface  110 . 
     The guide member  94  is provided outside the paired legs  911  and  912 ; hence, the paired legs  911  and  912  do not interfere with the guide member  94  to secure a smooth operation. 
     Because the guide member  94  is placed outside the paired legs  911  and  912  and adjacent to the center of the vehicle body, a passenger can be prevented from contacting the guide member  94 . 
     The rotation urging unit  95  applies rotational force to at least one leg  911  when the seat cushion body  7  is guided from the horizontal state to the folded state. Therefore, the rotational force can automatically move the seat cushion body  7  to the folded state. This configuration can provide a smooth folding operation of the seat cushion unit  3 . 
     The connection between the rotation urging unit  95  and at least one leg  911  is released before the seat cushion body  7  reaches the folded state. This configuration can intercept the transfer of biasing force halfway through the folding operation of the seat cushion body  7  to transit the seat cushion body  7  to the folded state by remaining force. As a result, shock can be eased when the seat cushion body  7  contacts with the foot floor surface  100 . 
     The rotation urging unit  95  is placed inside the paired legs  911  and  912  and can therefore be protected by the legs  911  and  912 . This configuration can stabilize the operation over a long period of time. 
     The rotation urging unit  95  is placed adjacent to the foot floor surface  110  in the legs  911  and  912  to therefore connect the rotation urging unit  95  to a portion having high rigidity in the legs  911  and  912 . This configuration can stabilize the operation of the rotation urging unit  95 . 
     The present invention can also be applicable to any other embodiment other than the above embodiments. Proper modifications can be applied without departing from the scope and spirit of the present invention. 
     For example, the embodiment described above exemplifies the auxiliary cutout  816  extending forward. Alternatively, if the direction of the load by shock from the back of the seat back body  4  is different from the anteroposterior direction, the auxiliary cutout  816  is preferably parallel to the direction of the load. Thereby, when the entire stowable rear seat  1  moves forward in response to shock from the back, the lock shaft  71  can easily be fit into the auxiliary cutout  816 . 
     As illustrated in  FIG. 17 , the reversed V-shape hamper  84  can be replaced with at least a hamper  84   a  including a plate spring projecting upwards so as to occlude the auxiliary cutout  816 . 
     If collision from the back is ignored, the auxiliary cutout  816  and the hamper  84  may be omitted as illustrated in  FIG. 18 . This can reduce the production steps and the parts of the base plate  81 . 
     The preceding embodiment exemplifies the guide member  94  composed of a round rod, but may be any rod such as a square rod or a pipe beside the round rod. 
     Although the preceding embodiment exemplifies the shifting mechanism  9  including a single rotation urging unit  95 , multiple rotation urging units may be provided. A shifting mechanism  9 C including multiple rotation urging units will now be explained in detail. In the following description, the same elements as those in the preceding embodiment are designated with the same reference numerals. 
       FIG. 19  is a front view illustrating an outline configuration of the shifting mechanism  9 C in the horizontal state of the seat cushion body  7 .  FIG. 20  is a perspective view as diagonally viewed from the left front.  FIG. 21  is a perspective view as diagonally viewed from the right front. As illustrated in  FIGS. 19 to 21 , the shifting mechanism  9 C includes a frame unit  91   c , a foot-side bearing unit  92   c , a seat-side bearing unit  93   c , a guide member  94   c , a first rotation urging unit  95   c , and a second rotation urging unit  96   c.    
       FIG. 22  illustrates outline configurations of the frame unit  91   c .  FIG. 22A  is a sectional view of the unit taken along a line a-a in  FIG. 22B  while  FIG. 22B  is a front view thereof. As illustrated in  FIGS. 22A and 22B , the frame unit  91   c  includes a pair of parallel legs  911   c  and  912   c  and a connection frame  913   c  connecting the paired legs  911   c  and  912   c.    
     In the lower end of each of the legs  911   c  and  912   c  composed of a metal pipe, a rotational shaft unit  914   c  is supported by a foot-side bearing unit  92   c . In the upper end of each of the legs  911   c  and  912   c , a pivot hole  915   c  is rotatably supported by the seat-side bearing unit  93   c.    
     The connection frame  913   c  is attached at the longitudinal centers of the paired legs  911   c  and  912   c . As illustrated in  FIGS. 20 and 21 , the connection frame  913   c  curves so as to project forward in the horizontal state of the seat cushion body  7 . As illustrated in  FIG. 22A , both ends of the connection frame  913   c  are fixed by, for example, welding at the position shifted in the projecting direction of the connection frame  913 , from the center S of the cross section orthogonal to the longitudinal direction of the legs  911   c  and  912   c.    
     Adjacent to the foot floor surface  110  in the left leg  911   c , a substantially U-shaped bias engagement member  97   c  for engaging with the second rotation urging unit  96   c  is attached by, for example, welding. 
     As illustrated in  FIGS. 19 to 21 , a pair of foot-side bearing units  92   c  is provided for each of the paired legs  911   c  and  912   c  and mounted on the foot floor surface  110  with a predetermined interval between the foot-side bearing units  92   c  in the lateral direction. Seat-side bearing units  93   c  are provided for the respective legs  911   c  and  912   c  and fixed to the undersurface of the seat cushion body  7  with a predetermined interval in the lateral direction. This enables guiding between the horizontal state and the folded state while the paired legs  911   c  and  912   c  support the seat cushion body  7 . 
     A guide member  94   c  is placed outside the paired legs  911   c  and  912   c , and on the right side of the paired legs  911   c  and  912   c , i.e., adjacent to the center of the vehicle. The guide member  94   c  guides the seat cushion body  7  between the horizontal state and the folded state together with the paired legs  911   c  and  912   c . The guide member  94   c  is formed by bending both ends of a metal round rod. The upper end of the guide member  94   c  serves as a rotational shaft  941   c  supported by the seat-side bearing unit  93  in the horizontal position. The lower end of the guide member  94   c  serves as a rotational shaft  942   c  supported by the foot-side bearing units  92   c  in the horizontal position. The rotational shaft  941   c  of the guide member  94   c  adjacent to the seat cushion body  7  is placed further forward than the rotational shafts of the paired legs  911   c  and  912   c  adjacent to the seat cushion body  7 . In contrast, the rotational shaft  942   c  of the guide member  94   c  adjacent to the foot floor surface  110  is placed further forward and downward than the rotational shafts of the paired legs  911   c  and  912   c  adjacent to the foot floor surface  110 . This geometry enables the seat cushion body  7  to be smoothly folded into a substantially horizontal posture during the folded state. 
     The first rotation urging unit  95   c  applies rotational force to at least one leg  912   c  of the paired legs  911   c  and  912   c  when the seat cushion body  7  is guided from the folded state to the horizontal state. The first rotation urging unit  95   c  is a flat spiral spring placed inside the paired legs  911   c  and  912   c  and at a portion of the leg  912   c  adjacent to the seat cushion body  7 . The first rotation urging unit  95   c  has an inner end fixed to the right seat-side bearing unit  93   c  and an outer end engaging with the connection frame  913   c . In the folded state of the seat cushion body  7 , the outer end of the first rotation urging unit  95   c  engages with the connection frame  913   c  to apply biasing force to the right leg  912   c . The outer end of the first rotation urging unit  95   c  is detached from the connection frame  913   c  halfway through guiding of the seat cushion body  7  from the folded state to the horizontal state. 
     The second rotation urging unit  96   c  applies rotational force to at least the other leg  911   c  of the paired legs  911   c  and  912   c  when the seat cushion body  7  is guided from the horizontal state to the folded state. The second rotation urging unit  96   c  is a flat spiral spring placed inside the paired legs  911   c  and  912   c  and at a portion of the leg  911   c  adjacent to the foot floor surface  110 . The second rotation urging unit  96   c  has an inner end fixed to the left foot-side bearing units  92   c  and an outer end engaging with the bias engagement member  97   c . In the horizontal state of the seat cushion body  7 , the outer end of the second rotation urging unit  96   c  engages with the bias engagement member  97   c  to apply biasing force to the left leg  911   c . The outer end of the second rotation urging unit  96   c  is detached from the bias engagement member  97   c  halfway through guiding of the seat cushion body  7  from the horizontal state to the folded state. 
     A detailed operation of the shifting mechanism  9 C will be explained.  FIG. 23  is a schematic side view illustrating the operation of the shifting mechanism  9 C. Solid lines in  FIG. 23  indicate the seat cushion body  7  and the shifting mechanism  9 C in the horizontal state while two-dot chain lines indicate the seat cushion body  7  and the shifting mechanism  9 C during a shifting operation. The seat cushion locking mechanism  8  is unlocked from the horizontal state to release the connection between the first rotation urging unit  95   c  and the connection frame  913   c . As a result, biasing force of the second rotation urging unit  96   c  rotates the legs  911   c  and  912   c  forward and also moves the seat cushion body  7  forward. During this movement, the guide member  94   c  reduces the rattle of the seat cushion body  7 . Additionally, since the connection frame  913   c  has a curved shape projecting forward in the horizontal state of the seat cushion body  7 , the space at the center between the connection frame  913   c  and the seat cushion body  7  can be secured while the paired legs  911   c  and  912   c  guide the seat cushion body  7  from the horizontal state to the folded state. This can prevent contact of the connection frame  913   c  with the seat cushion body  7  in a folding operation and a smooth folding operation for the seat cushion body  7  can be performed. Since the connection frame  913   c  projects downward after the folding, the seat cushion body  7  can be placed downward to use a space more effectively. 
     Since the first rotation urging unit  95   c  is connected to the connection frame  913   c  while the second rotation urging unit  96   c  is detached from the bias engagement member  97   c  halfway through guiding of the seat cushion body  7  from the horizontal state to the folded state, biasing force of the first rotation urging unit  95   c  is applied to the paired legs  911   c  and  912   c  after the detaching. Since the biasing force counteracts the biasing force of the second rotation urging unit  96   c , the seat cushion body  7  moves with a decrease in the rotational force of the paired legs  911   c  and  912   c . As a result, the posture maintenance unit  72  comes into contact with the foot floor surface  110  to then complete the shifting operation and lead to the folded state of the seat cushion body  7 . During the folded state, the seat cushion body  7  is maintained in a substantially horizontal posture by the guide member  94   c  and the posture maintenance unit  72 . 
     In order to prevent the seat cushion body  7  in the folded state from moving upward freely, it is preferable that the biasing force of the first rotation urging unit  95  is at a level that does not raise the seat cushion body  7 . 
     In order to return the seat cushion body  7  in the folded state to the horizontal state, the seat cushion body  7  is raised from the folded state by a user and moved to the horizontal state so as to be locked by the seat cushion locking mechanism  8 . The biasing force applied by the first rotation urging unit  95   c  at this time allows the user to move the seat cushion body  7  with smaller force than the case where there is no biasing force. 
     The cooperation during the folding operation of the seat back unit  2  and the seat cushion unit  3  will be explained.  FIG. 24  is a schematic side view illustrating the operation of the seat back unit  2  and the seat cushion unit  3 . Solid lines in  FIG. 24  indicate the seat back unit  2  and the seat cushion unit  3  in the seatable state (horizontal state) while two-dot chain lines indicate the seat back unit  2  and the seat cushion unit  3  during the folding operation. If the seat back locking mechanism  5  is unlocked from the seatable state to tilt the seat back body  4 , the rocking member  6  unlocks the seat cushion locking mechanism  8  before the complete folding. This applies the biasing force of the first and second rotation urging units  95   c  and  96   c  to the paired legs  911   c  and  912   c  to rotate the paired legs  911   c  and  912   c , respectively. Thereby, the seat cushion body  7  shifts from the horizontal state to the folded state. If the seat cushion body  7  reaches the folded state, the user folds the seat back body  4  completely to complete the folding operation. 
     In order to return the seat cushion folded on the foot floor surface to the floor surface, the user has to troublesomely raise the seat cushion in a stooping posture. 
     That is, it is awaited for a technique to return a seat cushion more easily. 
     In order to meet such a request, this modification includes the first rotation urging unit  95   c  applying rotational force to at least one leg  912   c  when the seat cushion body  7  is guided from the folded state to the horizontal state. As a result, the rotational force of the first rotation urging unit  95   c  can serve as auxiliary force to raise the seat cushion body  7  with smaller force when the seat cushion body  7  folded on the foot floor surface  110  is returned to the floor surface  100 . This configuration allows the seat cushion body  7  to be returned more easily. 
     The second rotation urging unit  96   c  applies rotational force to at least the other leg  911   c  when the seat cushion body  7  is guided from the horizontal state to the folded state. The rotational force can automatically move the seat cushion body  7  to the folded state. This configuration can provide a smooth folding operation of the seat cushion unit  7 . 
     The first rotation urging unit  95   c  is placed adjacent to the seat cushion body  7  in the leg  912   c  while the second rotation urging unit  96   e  is placed adjacent to the foot floor surface  110  in the leg  911   c . This configuration can prevent interference between both the units to stabilize the operation. 
     The first and second rotation urging units  95   c  and  96   c  are placed inside the paired legs  911   c  and  912   c  and can therefore be protected by the legs  911   c  and  912   c . This configuration can stabilize the operation over a long period of time. 
     The connection between the first rotation urging unit  95   c  and at least one leg  912   c  is released before the seat cushion body  7  reaches the horizontal state. As a result, the seat cushion body  7  starts to move from the horizontal state, while the rotational force of the second rotation urging unit  96   c  is applied without application of the rotational force of the first rotation urging unit  95   c . This configuration can achieve quick start-up of the folding operation. 
     The connection between the second rotation urging unit  96   c  and at least the other leg  911   c  is released before the seat cushion body  7  reaches the folded state. This configuration can intercept the transmission of the biasing force halfway through the folding operation of the seat cushion body  7  to shift the seat cushion body  7  to the folded state by the remaining force. As a result, shock can be eased when the seat cushion body  7  contacts with the foot floor surface  110 . 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               1  stowable rear seat 
               2  seat back unit 
               3  seat cushion unit 
               4  seat back body 
               5  seat back locking mechanism 
               6  rocking member 
               7  seat cushion body 
               8  seat cushion locking mechanism 
               9  shifting mechanism 
               21 ,  31  seat pad 
               41  seat back frame 
               42  back board 
               43 ,  44  hinge unit 
               45   a ,  46   a  wire 
               45   b ,  46   b  wire 
               47   a  reinforcing member 
               47   b  reinforcing member 
               51  lever unit 
               52  lock unit 
               71  lock shaft 
               72  posture maintenance unit 
               81  base plate 
               82  regulation pawl 
               83  ratchet unit 
               84  hamper 
               85  detachment stopper 
               91  frame unit 
               92  foot-side bearing unit 
               93  seat-side bearing unit 
               94  guide member 
               95  rotation urging unit 
               96  bias engagement member 
               100  floor surface 
               101  support bracket 
               102  center hinge bracket 
               110  foot floor surface 
               115  latched portion 
               811  plate board 
               812  screw 
               813  bottom 
               814  plate body 
               815  cutout 
               816  auxiliary cutout 
               817  first rotational shaft 
               818  second rotational shaft 
               819  stopper 
               821  concave portion 
               822  biasing spring 
               823  cam surface 
               824  first cam surface 
               825  second cam surface 
               831  one end 
               832  cam surface 
               833  upper portion 
               834  lower portion 
               835  other end 
               836  first urging surface 
               837  second urging surface 
               841  one side 
               842  one end 
               843  other end 
               911 ,  912  leg 
               913  connection frame 
               914  rotational shaft unit 
               915  pivot hole 
               941  rotational shaft 
               942  rotational shaft