Patent Publication Number: US-11654798-B2

Title: Vehicle seat

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 17/203,970 filed on Mar. 17, 2021, which is a Continuation of U.S. patent application Ser. No. 16/498,037 filed on Sep. 26, 2019, which is the U.S. National Stage entry of International Application No. PCT/JP2018/011654 filed under the Patent Cooperation Treaty having a filing date of Mar. 23, 2018, which claims priority to Japanese Patent Application No. 2017-073464 having a filing date of Apr. 3, 2017, all of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a vehicle seat provided with a height-adjustable seat cushion. 
     BACKGROUND ART 
     A vehicle seat provided with a height-adjustable seat cushion is known. For instance, Patent Document 1 discloses a seat cushion that can be moved up and down by means of links, in which a torsion bar is placed in a pipe connecting a pair of left and right links such that the upward movement of the seat cushion is assisted by the biasing force of the torsion bar. On one end of the torsion bar and the pipe, a position holding member for holding the torsion bar is fitted into the inner hole of the pipe to align the axis of the torsion bar with the central axis of the pipe. Also, Patent Document 2 discloses a cylindrical position holding member consisting of two semi-cylindrical parts. 
     PRIOR ART DOCUMENT(S) 
     Patent Document(s) 
     Patent Document 1: JP2007-230253A 
     Patent Document 2: JP2015-3577A 
     SUMMARY OF THE INVENTION 
     Task to be Accomplished by the Invention 
     However, the prior art position holding member may rotate relative to the torsion bar such that the position of the position holding member which receives a transverse force from the torsion bar may change. Therefore, it was necessary to secure the strength of the position holding member over a wide angular range, which hindered the reduction in size and weight of the position holding member. 
     In addition, when the end portion of the torsion bar is bent, assembly is difficult with the position holding member described in Patent Document 1. With the position holding member described in Patent Document 2 which consists of two parts, assembly is possible but the number of component parts becomes large and the assembling work is complicated. 
     In view of such prior art problems, a primary object of the present invention is to provide a vehicle seat provided with a height-adjustable seat cushion including a position holding member that does not rotate relative to the torsion bar. Also, at least some of the embodiments of the present invention are aimed to provide a position holding member that can be assembled easily. 
     Means to Accomplish the Task 
     A vehicle seat ( 1 ) in at least some of the embodiments of the present invention is a vehicle seat provided with a height-adjustable seat cushion, comprising: a base member ( 2 ) supported by a vehicle body; a cushion frame ( 5 ) constituting a frame of the seat cushion ( 3 ); a link mechanism ( 6 ) that supports the cushion frame to be movable up and down relative to the base member; a drive mechanism ( 7 ) that drives the cushion frame in a vertical direction via the link mechanism; and a torsion bar ( 14 ) that, to urge the cushion frame upward, extends between left and right side portions of the cushion frame and has lateral first and second ends ( 17 ,  16   b ) respectively joined to a first portion ( 12 ) and a second portion ( 8 ) that rotate relative to each other in a pivot portion of the link mechanism, wherein the torsion bar includes a shaft portion ( 15 ) extending in a lateral direction and an extension portion ( 16 ) at least partially extending in a direction intersecting the shaft portion and joined to the second portion on a side of the second end, the first portion unrotatably supports the first end of the torsion bar and supports a part of the shaft portion of the torsion bar adjacent to the second end via a position holding member ( 24 ,  41 ) for suppressing displacement of the axis of the torsion bar, and the position holding member includes a main body ( 25 ,  42 ) supported to be rotatable relative to the first portion and provided with a through-hole ( 27 ) for insertion of the shaft portion and an engagement portion ( 26 ,  43 ) engaging with the extension portion so as to rotate integrally. 
     According to this configuration, because the position holding member does not rotate relative to the torsion bar around the axis but rotates relative to the first portion, the position on the position holding member where the transverse force of the torsion bar is applied is fixed, and therefore, it is sufficient that the position holding member has a strength withstanding the transverse force in a narrow angular range. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in the foregoing configuration, one of the cushion frame and the link mechanism includes a connection pipe ( 12 ) that is rotatable relative to the other, the connection pipe constitutes the first portion, and the main body of the position holding member has a cylindrical contour and is rotatably received in an inner hole ( 13 ) of the connection pipe. 
     According to this configuration, the first portion can be achieved with a simple structure. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in any of the foregoing configurations, the engagement portion ( 26 ) of the position holding member ( 24 ) includes an engagement protrusion ( 30 ) that protrudes from the main body ( 25 ) and an engagement claw ( 29 ) that protrudes from the main body and resiliently holds the extension portion in cooperation with the engagement protrusion or the engagement portion ( 43 ) of the position holding member ( 41 ) includes a pair of engagement claws ( 44 ) that protrude from the main body ( 42 ) and resiliently sandwich the extension portion. 
     According to this configuration, the engagement portion can be achieved with a simple structure. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in the foregoing configuration, the engagement claw retains the extension portion by overhanging the same and is positioned above the engagement protrusion. 
     According to this configuration, the engagement state of the engagement portion can be checked easily. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in any of the foregoing configurations, the engagement portion is positioned more laterally outward than the second portion. 
     According to this configuration, the engagement state of the engagement portion can be checked easily. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in any of the foregoing configurations, the position holding member is provided, on a laterally inner end surface thereof, with a receiving groove ( 35 ) recessed to extend in a radial direction so as to be capable of receiving the extension portion, and consists of an integrally molded article. 
     According to this configuration, when the torsion bar is inserted into the through-hole of the position holding member and the position of the position holding member relative to the torsion bar is shifted, the bent extension portion of the torsion bar is received in the receiving groove so that the shifting of the position of the position holding member is allowed. Thus, by inserting the end portion of the torsion bar into the through-hole of the position holding member consisting of an integrally molded article and shifting the position holding member, they can be assembled together. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in the foregoing configuration, the receiving groove is provided at a position circumferentially shifted from a side where a transverse force that the position holding member receives from the torsion bar becomes maximum. 
     According to this configuration, because the receiving groove is not provided at the position where the transverse force of the torsion bar is applied, it is possible to secure the strength of the position holding member. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in the foregoing configuration, the side where the transverse force that the position holding member receives from the torsion bar becomes maximum is reinforced preferentially. 
     According to this configuration, since the part that receives the transverse force and requires a strength is reinforced preferentially, another part that may have a low strength is given less reinforcement and the position holding member can be reduced in size and weight. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in any of the foregoing configurations, multiple ribs ( 34 ) extending along an axial direction are provided on an outer circumferential surface of the main body of the position holding member. 
     According to this configuration, because the ribs slidably contact the connection pipe that serves as the first portion, the frictional resistance when the position holding member slides relative to the connection pipe can be reduced. 
     A vehicle seat according to at least some of the embodiments of the present invention is characterized in that, in the foregoing configuration, a side circumferential wall of the main body includes an inner circumferential wall ( 31 ) defining the through-hole, an outer circumferential wall ( 32 ) rotatably supported by the first portion, and multiple reinforcement walls ( 33 ) extending in a radial direction and connecting between the inner circumferential wall and the outer circumferential wall, and at least some of the reinforcement walls are provided at positions aligned with the ribs in the radial direction. 
     According to this configuration, because the position holding member has a hollowed structure, the weight of the position holding member can be reduced, and because the ribs and the reinforcement walls are mutually aligned in the radial direction, the reinforcement against the transverse force of the torsion bar can be achieved efficiently. 
     Effect of the Invention 
     According to the present invention, because the position holding member does not rotate relative to the torsion bar but rotates relative to the first portion, the position on the position holding member where the transverse force of the torsion bar is applied is fixed, and therefore, it is only required that the holding member has a strength that withstands the transverse force in a narrow angular range. 
     In the configuration in which the first portion is constituted of a connection pipe, the structure can be simplified. 
     In the configuration in which the engagement portion includes an engagement claw, the structure can be simplified. 
     In the configuration in which the engagement claw overhangs the extension portion, the engagement state of the engagement portion can be checked easily. 
     In the configuration in which the engagement portion is positioned more laterally outward than the second portion, the engagement state of the engagement portion can be checked easily. 
     In the configuration in which the position holding member is provided with a receiving groove, by inserting the end portion of the torsion bar into the through-hole of the position holding member and shifting the position holding member, they can be assembled together. 
     In the configuration in which the receiving groove is provided at a position circumferentially shifted from a side where a transverse force received from the torsion bar becomes maximum, the receiving groove is not provided at the position where the transverse force of the torsion bar is applied, and therefore, it is possible to secure the strength of the position holding member. 
     In the configuration in which the side where the transverse force that the position holding member receives from the torsion bar becomes maximum is reinforced preferentially, the part that receives the transverse force and requires a strength is reinforced preferentially, and therefore, it is possible to give less reinforcement to another part that may have a low strength and to reduce the size and weight of the position holding member. 
     In the configuration in which multiple ribs extending along an axial direction are provided on an outer circumferential surface of main body of the position holding member, the ribs slidably contact the connection pipe that serves as the first portion, and therefore, the frictional resistance when the position holding member slides relative to the connection pipe can be reduced. 
     In the configuration in which the position holding member includes an inner circumferential wall, an outer circumferential wall, reinforcement walls, and at least some of the reinforcement walls are provided at positions aligned with the ribs in the radial direction, the position holding member has a hollowed structure, and therefore, the weight of the position holding member can be reduced, and also, because the ribs and the reinforcement walls are mutually aligned in the radial direction, the reinforcement against the transverse force of the torsion bar can be achieved efficiently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a perspective view showing a vehicle seat according to the first embodiment; 
         FIG.  2    is a horizontal sectional view showing a vicinity of a torsion bar of the vehicle seat according to the first embodiment; 
         FIG.  3    is a perspective view showing the torsion bar and a position holding member according to the first embodiment; 
         FIG.  4    is a perspective view showing an assembled state of the position holding member according to the first embodiment to the torsion bar; 
         FIG.  5    is a perspective view showing the position holding member according to the first embodiment; 
         FIG.  6    is a perspective view the position holding member according to the first embodiment as viewed from another direction; 
         FIG.  7    is a perspective view showing an assembled state of a position holding member according to the second embodiment to the torsion bar; 
         FIG.  8    is a perspective view showing the position holding member according to the second embodiment; and 
         FIG.  9    is a perspective view showing the position holding member according to the second embodiment as viewed from another direction. 
     
    
    
     MODES FOR CARRYING OUT THE INVENTION 
     In the following, a. vehicle seat according to the first embodiment of the present invention will be described with reference to the drawings. As shown in  FIG.  1   . the vehicle seat  1  is to be installed as a driver&#39;s seat or a passenger seat of a vehicle and includes a pair of left and right base members  2 ,  2  supported by a vehicle body, a seat cushion  3  supported by the pair of left and right base members  2 ,  2 , a seat back  4  connected to the seat cushion  3 , and a headrest (not shown in the drawings) connected to the seat back  4 . The position of the seat cushion  3  is adjustable in a height direction owing to a link mechanism  6  that supports a cushion frame  5 , which constitutes a frame of the seat cushion  3 , to be movable up and down relative to the base members  2  and a drive mechanism  7  that drives the cushion frame  5  in the vertical direction via the link mechanism  6 . Further, the vehicle seat  1  is preferably supported on the vehicle body via rails (not shown in the drawings) extending in the fore-and-aft direction so that the position thereof is adjustable in the fore-and-aft direction. 
     The cushion frame  5  includes a pair of left and right side frames  8 ,  8  and a front frame  9  connecting between the pair of left and right side frames  8 ,  8  on a front side. 
     The link mechanism  6  includes a pair of left and right front links  10 ,  10  respectively connecting between the pair of left and right base members  2 ,  2  and the pair of left and right side frames  8 ,  8  on a front side and a pair of left and right rear links  11 ,  11  respectively connecting between the pair of left and right base members  2 ,  2  and the pair of left and right side frames  8 ,  8  on a rear side, and each link  10 ,  10 ,  11 ,  11  is pivoted to the corresponding base member  2  and the corresponding side frame  8  about laterally extending axes. In the pair of left and right rear links  11 ,  11 , the rotation axes of the left pivot portions and the corresponding right pivot portions are coaxial. 
     The link mechanism  6  further includes a connection pipe  12  extending laterally and having left and right end portions secured to the respective rear links  11 . As shown in  FIGS.  1  and  2   , the connection pipe  12  has a central axis coaxial with the rotation axes of the pair of left and right side frames  8 ,  8  and the pair of left and right rear links  11 , and the end portions  12   b  of the connection pipe  12  secured to the rear links  11  are rotatably pivoted to the side frames  8 , whereby the pair of left and right rear links  11 ,  11  and the connection pipe  12  together can rotate relative to the pair of left and right side frames  8 ,  8  about an axis extending in the lateral direction. The left and right end portions  12   b ,  12   b  of the connection pipe  12  constituting the pivot portions are members separate from the main body  12   a  and respectively joined by welding to the left and right ends of the main body  12   a  after processing so that the shape of the end portions  12   b ,  12   b  is not changed by the processing of the main body  12   a.    
     A torsion bar  14  inserted in an inner hole  13  of the connection pipe  12  is formed by bending both end portions of a steel rod having a circular cross-section. As shown in  FIG.  3   , the torsion bar  14  includes a shaft portion  15  that extends laterally, an extension portion  16  having a first extension portion  16   a  extending from the right end of the shaft portion  15  orthogonally to the shaft portion  15  and a second extension portion  16   b  extending leftward from a tip end of the first extension portion  16   a  in parallel with the shaft portion  15 , and a fold-back portion  17  formed by folding back the left end portion of the steel rod so that the rotation about the axis can be easily restricted. 
     As shown in  FIG.  2   , the extension portion  16  is positioned outside of the inner hole  13  of the connection pipe  12 . The second extension portion  16   b  is positioned forward of the shaft portion  15  and is engaged with an engagement hole  18  provided in the right side frame  8 . To prevent the second extension portion  16   b  from getting out of the engagement hole  18  rightward, an upper surface of the second extension portion  16   b  is provided with an engagement groove  19  for engaging with a part of the side frame  8  defining the engagement hole  18 . Since the extension portion  16  is engaged with the right side frame  8 , the right end side of the torsion bar  14  is restricted from rotating relative to the right side frame  8  about the axis. 
     A left end side of the main body  12   a  of the connection pipe  12  is provided with a flattened pipe portion  20  formed by denting the main body  12   a  from front and back to narrow the inner hole  13 . The fold-back portion  17  of the torsion bar  14  is sandwiched at the flattened pipe portion  20  in the inner hole  13 , whereby the left end side of the torsion bar  14  is restricted from rotating relative to the connection pipe  12  about the axis. 
     The torsion bar  14  is retained by the right side frame  8  and the flattened pipe portion  20  in a twisted state. When the cushion frame  5  is moved up and down, the angle between the right side frame  8  and the pair of left and right rear links  11 ,  11  as well as the connection pipe  12  changes, and therefore, the twist angle of the torsion bar  14 , which is engaged with the right side frame  8  on the right end side thereof and with the connection pipe  12  on the left end side thereof changes. The torsion bar  14  is installed such that when the cushion frame  5  is moved down, the twist angle of the torsion bar  14  increases, and when the cushion frame  5  is moved up, the twist angle of the torsion bar  14  decreases, and therefore, the biasing force produced by the twisting of the torsion bar  14  acts in the direction to move the cushion frame  5  upward. 
     The drive mechanism  7  includes an electric motor  21  secured to the left side frame  8 , a pinion  22  that is rotated by the rotation of the electric motor  21 , and a gear  23  secured to the left rear link  11  and meshing with the pinion  22 . The electric motor  21  drives the cushion frame  5  in the vertical direction via the pinion  22 , the gear  23 , and the left rear link  11 . At this time, the right rear link II operates in linkage with the left rear link  11  via the connection pipe  12 , and the pair of left and right front links  10 ,  10  operate in linkage with the pair of left and right rear links as the pair of left and right side frames  8 ,  8  and the front frame  9  are rigidly connected with each other. Instead of the electric motor  21 , a configuration may be made such that the cushion frame  5  is driven manually. 
     As shown in  FIGS.  1  and  2   , a position holding member  24  is mounted between the right end side of the connection pipe  12  and the right end side of the shaft portion  15  of the torsion bar  14  to align the axis of the torsion bar  14  with the central axis of the connection pipe  12  and to maintain that state. 
     As shown in  FIGS.  3  to  6   , the position holding member  24  is an integrally molded article including a main body  25  configured to hold the shaft portion  15  of the torsion bar  14  and to be attached to the connection pipe  12  and an engagement portion  26  configured to engage with the first extension portion  16   a  of the torsion bar  14 . 
     The main body  25  has a cylindrical contour formed with a through-hole  27  extending along the lateral direction. The shaft portion  15  of the torsion bar  14  is inserted into and held by the through-hole  27  and the cylindrical outer circumferential surface of the main body  25  contacts the inner circumferential surface of the inner hole  13  of the connection pipe  12 , whereby the position of the axis of the shaft portion  15  of the torsion bar  14  is maintained. if the position of the axis of the shaft portion  15  shifts relative to the connection pipe  12 , the biasing force of the torsion bar  14  deviates from the designed value, but the position holding member  24  can prevent this shifting. The right end of the main body  25  is provided with a flange  28  that extends from the side circumferential surface in the radial direction, and the left surface of the flange  28  abuts against the right end of the connection pipe  12  to determine the lateral position of the position holding member  24  relative to the connection pipe  12  (see  FIG.  2   ). 
     As shown in  FIG.  5   , the engagement portion  26  includes an engagement claw  29  and an engagement protrusion  30  that are provided on the right end surface of the main body  25  and oppose each other. The free end side of the engagement claw  29  is bent toward the engagement protrusion  30  so as to overhang the first extension portion  16   a  (see  FIG.  3   ) and the distance between the right end surface of the main body  25  and the surface of the free end side of the engagement claw  29  facing is substantially the same as the diameter of the first extension portion  16   a  of the torsion bar  14 . The surface of the engagement claw  29  opposite to the surface facing the first extension portion  16   a  is provided with ribs  29   a  extending along the respective side edges thereof for reinforcing the strength. The top of the engagement protrusion  30  does not protrude from the main body  25  more than the free end of the engagement claw  29 , and the distance between the top of the engagement protrusion  30  and the free end of the engagement claw  29  is usually smaller than the diameter of the first extension portion  16   a  but, with resilient deformation of the engagement claw  29 , the first extension portion  16   a  can pass between the top of the engagement protrusion  30  and the free end of the engagement claw  29 . A configuration is made such that, after assembly, the engagement claw  29  is positioned above the engagement protrusion  30  and/or the engagement portion  26  is positioned more laterally outward than the side frame  8 , the engagement state can be checked easily. 
     The engagement protrusion  30  exhibits a triangular shape as seen in the radial direction, and includes a guide surface  30   a  that extends away from the main body  25  toward the engagement claw  29  and a retaining surface  30   b  that is provided at a position closer to the guide surface  30   a  than the engagement claw  29  is and approaches the main body  25  toward the engagement claw  29 . The guide surface  30   a  guides the first extension portion  16   a  when the position holding member  24  is assembled to the torsion bar  14 , and the retaining surface  30   b  cooperates with the engagement claw  29  and the right end surface of the main body  25  to hold the first extension portion  16   a  in the assembled state. The angle of the retaining surface  30   b  relative to the right end surface of the main body  25  is steeper than the angle of the guide surface  30   a  relative to the right end surface of the main body  25 , and therefore, it requires a larger force when reverse-rotating the position holding member  24  to release the engagement between the position holding member  24  and the first extension portion  16   a . than when rotating the position holding member  24  to make them engage with each other. It is to be noted that, instead of the engagement claw  29  and the engagement protrusion  30 , the engagement portion  26  may be constituted of a recess (not shown in the drawings) provided on the main body  25  or a combination of the engagement claw  29  and the recess. 
     As shown in  FIG.  6   , the cylindrical main body  25  of the position holding member  24  is hollowed to have a two-layer structure, and includes an inner circumferential wall  31  defining the through-hole  27 , an outer circumferential wall  32  slidably contacting an inner circumferential surface of the connection pipe  12  defining the inner hole  13  and rotatably supported by the connection pipe  12 , and multiple reinforcement walls  33  extending in the radial direction to connect between the inner circumferential wall  31  and the outer circumferential wall  32 . To reduce the frictional resistance when the position holding member  24  rotates relative to the connection pipe  12  about the axis, the outer circumferential surface of the outer circumferential wall  32  is provided with multiple ribs  34  along the axial direction so that the ribs  34  slidably contact the inner circumferential surface of the connection pipe  12 . The multiple ribs  34  are arranged at a substantially regular interval in the circumferential direction over a prescribed area on the side that receives the transverse force from the torsion bar  14 . The multiple reinforcement walls  33  are arranged at a substantially regular interval in the circumferential direction, and the reinforcement walls  33  positioned on the side where the ribs  34  are provided are aligned with the ribs  34  in the radial direction, and thereby, the reinforcement against the transverse force from the torsion bar  14  is achieved efficiently. 
     The inner circumferential wall  31  and the outer circumferential wall  32  of the position holding member  24  are respectively provided, in the left end surfaces thereof, with an inner receiving groove  35   a  and an outer receiving groove  35   b  which are recessed to extend in the radial direction. The inner receiving groove  35   a  and the outer receiving groove  35   b  are provided at positions on the circumferentially opposite side of the ribs  34  and mutually aligned with each other in the radial direction. The circumferential width of the inner receiving groove  35   a  and the outer receiving groove  35   b  is substantially the same as the diameter of the torsion bar  14 . The depth of the inner receiving groove  35   a  and the outer receiving groove  35   b  in the lateral direction is set such that a receiving groove  35  constituted of the inner receiving groove  35   a  and the outer receiving groove  35   b  can receive the extension portion  16  of the torsion bar  14  when the position holding member  24  is assembled to the torsion bar  14 . The receiving groove  35  is provided at a position displaced from the engagement portion  26  in the circumferential direction by about 90 degrees. It is to be noted that the angle of the position of the receiving groove  35  relative to the engagement portion  26  may be changed within a range in which they are misaligned with each other in the circumferential direction. Further, because the strength is lowered around the receiving groove  35 , the receiving groove  35  is provided at a position circumferentially displaced from the side where the transverse force that the position holding member  24  receives from the torsion bar becomes the maximum; for example, at a diagonal position. 
     Now, a description will be made of the assembly method and the advantages. The worker inserts the free end of the second extension portion  16   b  of the torsion bar  14  into the through-hole  27  from the left end side of the position holding member  24  and moves the position holding member  24  to the right end side of the shaft portion  15 . At this time, since the position holding member  24  is provided with the receiving groove  35 , the extension portion  16  that is bent relative to the shaft portion  15  can be passed. 
     Then, the worker rotates the position holding member  24  relative to the shaft portion  15  of the torsion bar  14  about the axis. At this time, the first extension portion  16   a  slides along the guide surface  30   a  of the engagement protrusion  30  while resiliently deforming the engagement claw  29 , and thereafter, is disposed between the engagement claw  29  and the engagement protrusion  30 . The engagement claw  29  cooperates with the engagement protrusion  30  to resiliently hold the first extension portion  16   a.    
     Thereafter, the worker inserts the torsion bar  14  to which the position holding member  24  has been mounted into the inner hole  13  of the connection pipe  12  and make the fold-back portion  17  and the second extension portion  16   b  of the torsion bar  14  engage with the flattened pipe portion  20  and the right side frame  8 , respectively. 
     Owing to the provision of the receiving groove  35 , though the torsion bar  14  is bent it is possible to fit the position holding member  24  onto the torsion bar  14  from the end portion thereof and to move it to a prescribed position, and therefore, the assembly is easy and the position holding member  24  can consist of an integrally molded article such that the number of components is reduced. 
     Once the engagement portion  26  engages with the first extension portion  16   a , the rotation of the position holding member  24  relative to the torsion bar  14  about the axis and the lateral movement of the position holding member  24  relative to the torsion bar  14  are restricted, and the position and the attitude of the position holding member  24  are stabilized. Therefore, even if the position holding member  24  assembled to the torsion bar  14  is shipped, the risk that the position holding member  24  may move out of place or suffer damage is small. 
     Due to the engagement of the engagement portion  26  with the first extension portion  16   a , the position holding member  24  will rotate relative to the connection pipe  12  together with the right end side of the shaft portion  15  of the torsion bar  14 . Therefore, the position on the position holding member  24  where the transverse force of the torsion bar  14  is applied is fixed, whereby it is sufficient that the position holding member  24  has a strength withstanding the transverse force in a narrow angular range. Thus, it is possible to reduce the size and weight of the position holding member  24  and to provide the receiving groove  35  in a part where the influence of the transverse force is small. 
     Next, with reference to  FIGS.  7  to  9   , the second embodiment of the present invention will be described. In the following description, the parts common with the first embodiment will be denoted by the same reference numerals and the description thereof will be omitted. In the second embodiment, the shape and the assembling method of the position holding member  41  are different from those of the first embodiment. 
     The position holding member  41  according to the second embodiment is an integrally molded article including a main body  42  configured to hold the shaft portion  15  of the torsion bar  14  and to be attached to the connection pipe  12  and an engagement portion  43  configured to engage with the first extension portion  16   a  of the torsion bar  14 . 
     As in the first embodiment, the main body  42  has a cylindrical shape provided with a through-hole  27  extending along the lateral direction and includes an inner circumferential wall  31 , an outer circumferential wall  32 , and reinforcement walls  33 . It is to be noted that the main body  42  does not include a structure corresponding to the ribs  34  in the first embodiment. 
     As shown in  FIG.  8   , the engagement portion  43  includes a pair of engagement claws  44 ,  44  that are provided on the right end surface of the main body  42  and oppose each other. The pair of engagement claws  44 ,  44  are mirror symmetric to each other. Each engagement claw  44  includes an engagement piece  45  configured to engage with the extension portion  16  of the torsion bar  14  and ribs  46  provided on the side of the engagement piece  45  opposite from the side facing the first extension portion  16   a  to extend along the respective lateral edges thereof for reinforcing the strength. A flange  47  that radially extends from the side circumferential surface of the right end of the main body  42  extends to a part where the ribs  46  are provided and supports the ribs  46 . 
     The rightward protruding length of the engagement piece  45  is greater than the radius of the first extension portion  16   a , and preferably is greater than or equal to the diameter of the first extension portion  16   a . The side of the engagement piece  45  facing the first extension portion  16   a  is provided with a ridge  48  extending along the extension direction of the first extension portion  16   a  at a part protruding from the main body  25  beyond the radius of the first extension portion  16   a . The distance between the pair of engagement pieces  45 ,  45  is substantially the same as the diameter of the first extension portion  16   a . Also, the distance between the pair of ridges  48 ,  48  is smaller than the diameter of the first extension portion  16   a  so that the tip end of each ridge  48  press-contacts the first extension portion  16   a . Thereby, the pair of engagement claws  44 ,  44  resiliently hold the first extension portion  16   a.    
     Now, a description will be made of the assembly method and the advantages. The worker inserts the free end of the second extension portion  16   b  of the torsion bar  14  into the through-hole  27  from the left end side of the position holding member  41  and moves the position holding member  41  to the right end side of the shaft portion  15 . At this time, the position holding member  41  is positioned more leftward than the target lateral position of the position holding member  41  by a degree equivalent to or greater than the rightward protruding length of the engagement claws  44 . As in the first embodiment, the position holding member  41  is provided with the receiving groove  35 , and therefore, the extension portion  16  that is bent relative to the shall portion  15  can be passed. 
     Then, the worker rotates the position holding member  41  relative to the shaft portion  15  of the torsion bar  14  about the axis to align the gap between the pair of engagement claws  44 ,  44  with the first extension portion  16   a  of the torsion bar  14  in the lateral direction, and thereafter, moves the position holding member rightward. At this time, the pair of ridges  48  are pushed  1   w  the first extension portion  16   a  to move away from each other and the pair of engagement claws  44 ,  44  deform resiliently, whereby the first extension portion  16   a  can pass between the pair of engagement claws  44 ,  44 . Once the central axis of the first extension portion  16   a  passes between the pair of ridges  48 ,  48 , the pair of engagement claws  44 ,  44  partially recover from the resilient deformation, whereby the pair of engagement claws  44 ,  44  resiliently hold the first extension portion  16   a.    
     Thereafter, as in the first embodiment, the worker inserts the torsion bar  14  to which the position holding member  41  has mounted into the inner hole  13  of the connection pipe  12  and make the fold-hack portion  17  and the second extension portion  16   b  of the torsion bar  14  engage with the flattened pipe portion  20  and the right side frame  8 , respectively. 
     Even though the position holding member  41  is an integrally molded article, owing to the provision of the receiving groove  35 , the assembly to the bent torsion bar  14  is easy as in the first embodiment. 
     Once the engagement portion  43  engages with the first extension portion  16   a , the position holding member  41  does not rotate relative to the torsion bar  14  about the axis owing to the retention by the pair of engagement pieces  45 ,  45 , and also the movement in the lateral direction is restricted owing to the retention by the pair of ridges  48 ,  48  and right surface of the main body  42 . Therefore, even if the position holding member  24  assembled to the torsion bar  14  is shipped, the risk that the position holding member  24  may move out of place or suffer damage is small. 
     As in the first embodiment, due to the engagement of the engagement portion  43  with the first extension portion  16   a , the position holding member  41  will rotate relative to the connection pipe  12  together with the right end side of the shaft portion  15  of the torsion bar  14 . Therefore, the position on the position holding member  41  where the transverse force of the torsion bar  14  is applied is fixed, whereby it is sufficient that the position holding member  41  has a strength withstanding the transverse force in a narrow angular range. Thus, it is possible to reduce the size and weight of the position holding member  41  and to provide the receiving groove  35  in a part that does not receive the transverse force. 
     The concrete embodiments have been described in the foregoing, but various modifications of the present invention are possible without being limited to the above embodiments. In the above embodiments, left and right may be reversed. The connection pipe may be formed as a part of the cushion frame and be pivotally supported by the pair of left and right rear links, with the extension portion of the torsion bar being engaged with one of the rear links. It is also possible to provide the connection pipe and the torsion bar coaxially with the pivot portions between the base members and the rear links, secure the connection pipe to one of the base members and the rear links, and make the extension portion of the torsion bar engage with the other of the base members and the rear links. The connection pipe may have any shape so long as the part receiving the position holding member has a circular inner circumferential surface, and the other part may have a rectangular pipe shape or a rod-like shape. The connection pipe and the torsion bar may be attached to the front links instead of the rear links. The prior art referred to in the present application is incorporated herein by reference in its entirety. 
     Glossary 
     
         
           1 : vehicle seat 
           2 : base member 
           3 : seat cushion 
           5 : cushion frame 
           6 : link mechanism 
           7 : drive mechanism 
           8 : side frame (second portion) 
           11 : rear link 
           12 : connection pipe (first portion) 
           13 : inner hole 
           14 : torsion bar 
           15 : shaft portion 
           16 : extension portion 
           24 ,  41 : position holding member 
           25 ,  42 : main body 
           26 : engagement portion 
           27 : through-hole 
           29 ,  44 : engagement claw 
           30 : engagement protrusion 
           31 : inner wall 
           32 : outer circumferential wall 
           33 : reinforcement wall 
           34 : rib 
           35 : receiving groove