Patent Publication Number: US-10328825-B2

Title: Vehicle seat

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a Divisional of U.S. application Ser. No. 14/791,928 filed on Jul. 6, 2015, which claims priority under 35 USC 119 from Japanese Patent Application, No. 2014-140919 filed Jul. 8, 2014, the disclosure of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Technical Field 
     The present invention relates to a vehicle seat. 
     Related Art 
     International Publication (WO) No. 2013/021497 describes an invention relating to a vehicle seat device. To explain briefly, a vehicle seat is provided with a seat frame configured including a first seat frame portion disposed at a seat cushion side, and a second seat frame portion disposed at a seatback side. A seat portion support mechanism that employs bearings to rotatably support a seat portion, on which an occupant sits, is provided at the center of a front portion of the first seat frame portion. The axial line of a rotation axis of the seat portion support mechanism is oriented in a direction tilted at a specific angle, such that the rear is higher than the front in the seat front-rear direction. The seat portion is accordingly capable of swaying by rotating the seat portion about the rotation axis of the seat portion support mechanism. 
     Moreover, a seatback support mechanism in which bearings are employed to rotatably support a seatback that supports the back of the occupant, is provided at a height direction intermediate portion of the second seat frame portion. The axial line of a rotation axis of the seatback support mechanism is oriented toward the seat front-rear direction. Thus the seatback is capable of swaying about the rotation axis of the seatback support mechanism. 
     In the above configuration, the driver consciously or unconsciously attempts to rotate (swing) their pelvis and shoulders in opposite directions when the vehicle turns. When this occurs, the seat portion sways, and the seatback also sways, such that the seat portion and the seatback follow the movement of the occupant. 
     SUMMARY 
     However, in the case of the related art described above, configuration is made such that the swaying action of the seat portion is realized by the seat portion support mechanism, and issues thereby arise in that there is a large number of components, and the structure is complex. 
     In consideration of the above circumstances, a subject of the present invention is to obtain a vehicle seat capable of allowing the lumbar region of an occupant to sway during lateral acceleration of the vehicle, using a simple configuration. 
     A vehicle seat of a first aspect of the present invention includes a seat cushion frame configuring a frame member of a seat cushion, and a seat unit that is supported by the seat cushion frame and on which an occupant sits, that has a higher seating face rigidity in a seat front-rear direction than a seating face rigidity in a seat width direction, and that has the seating face rigidity in the seat width direction set lower at a seat front-rear direction rear side than at a seat front-rear direction front side. 
     The vehicle seat of the first aspect operates as follows. In general, during lateral acceleration of a vehicle, such when the vehicle turns, an inertial force also acts on the occupant in the vehicle width direction. Thus the head of the seated occupant is apt to move in the application direction of the inertial force, direction of their vision moves greatly in the application direction of the inertial force, and steering operation performance is affected. 
     In contrast thereto, the present inventors have found from their research that, if, during lateral acceleration of the vehicle, the seating face can function so as to roll-rotate the lumbar region of the occupant about a hypothetical rotation axis, which passes through the vicinity of the lumbar spine of the seated occupant and tilts downward toward the front (hereafter referred to as “seating face rotation axis”), the movement of the head of the seated occupant can be suppressed to a minimal amount, and the burden on the occupant seated in a front seat (particularly the driver) is greatly reduced. 
     In the first aspect, the seat unit supported by the seat cushion frame is set with higher seating face rigidity in the seat front-rear direction than the seating face rigidity in the seat width direction. Namely, the rigidity distribution of the seating face of the seat unit is anisotropic. Thus, first, a hypothetical rotation axis (a roll axis, lateral rotation axis of the lumbar region) is formed running along the seat front-rear direction in a space above the seat unit. Furthermore, the seating face rigidity in the seat width direction of the seat unit is set lower at the seat front-rear direction rear side than at the front side, such that a front side of the hypothetical rotation axis (roll axis of the lumbar region) drops down toward the seating face side, and rises at a rear side. The seating face rotation axis is accordingly formed passing through the vicinity of the lumbar spine of the seated occupant tilting downward toward the front. Namely, in the present aspect, rather than setting a complex configuration using bearings or the like between the seat cushion frame and the seat unit in order to allow the seat unit to sway, the seat unit itself has a function of allowing the lumbar region to sway about the seating face rotation axis. 
     A vehicle seat of a second aspect of the present invention is the first aspect, wherein the seat unit is formed in a net form including plural longitudinal direction fiber members extending along the seat front-rear direction, and plural lateral direction fiber members extending along the seat width direction, and the respective fiber members are disposed more sparsely at the seat front-rear direction rear side than at the seat front-rear direction front side of the seat unit. 
     In the vehicle seat of the second aspect, the seat unit is formed in a net form including the plural longitudinal direction fiber members and the plural lateral direction fiber members. Furthermore, the fiber members are disposed more sparsely at the seat front-rear direction rear side than at the front side of the seat unit, such that the rigidity of the seat unit at the seat front-rear direction rear side is comparatively lower than the rigidity at the front side. Thus in the present aspect, the seating face rigidity of the seat unit is realized by the placement density of the longitudinal direction fiber members and the lateral direction fiber members. In other words, the rigidity distribution of the seat unit can be set to a desired distribution, simply by changing the placement density of the longitudinal direction fiber members and the lateral direction fiber members. 
     A vehicle seat of a third aspect of the present invention is the second aspect, wherein the longitudinal direction fiber members are thinner at the seat front-rear direction rear side than at the seat front-rear direction front side. 
     In the vehicle seat of the third aspect, the longitudinal direction fiber members are thinner at the seat front-rear direction rear side than at the seat front-rear direction front side, thereby enabling a difference in rigidity to be created in the seat unit by the longitudinal direction fiber members themselves. This enables both the number of longitudinal direction fiber members used and the number of lateral direction fiber members used to be reduced. 
     A vehicle seat of a fourth aspect of the present invention is the second aspect, wherein the lateral direction fiber members disposed at the seat front-rear direction rear side are thinner than the lateral direction fiber members disposed at the seat front-rear direction front side. 
     In the vehicle seat of the fourth aspect, the lateral direction fiber members disposed at the seat front-rear direction rear side are thinner than the lateral direction fiber members disposed at the seat front-rear direction front side, thereby enabling a difference in rigidity to be created in the seat unit by the lateral direction fiber members themselves. This enables the number of lateral direction fiber members used to be reduced. 
     A vehicle seat of a fifth aspect of the present invention is any one of the second aspect to the fourth aspect, wherein a number of seating face regions partitioned by the longitudinal direction fiber members, and the lateral direction fiber members or the seat cushion frame is smaller at the seat front-rear direction rear side than at the seat front-rear direction front side. 
     In the vehicle seat of the fifth aspect, the number of seating face regions partitioned by the longitudinal direction fiber members, and the lateral direction fiber members or the seat cushion frame is smaller at the seat front-rear direction rear side than at the seat front-rear direction front side, such that the seating face rigidity of the seat unit is lower at the seat front-rear direction rear side than at the front side. 
     A vehicle seat of a sixth aspect of the present invention is any one of the second aspect to the fifth aspect, wherein both end portions of the lateral direction fiber members that are disposed at the seat front-rear direction front side of the seat unit are fixed to the seat cushion frame, and both end portions of the lateral direction fiber members that are disposed at a rear side of the lateral direction fiber members, which are disposed at the front side of the seat unit, are fixed to the longitudinal direction fiber members. 
     In the vehicle seat of the sixth aspect, both end portions of the lateral direction fiber members disposed at the seat front-rear direction front side of the seat unit are fixed to the seat cushion frame, such that the supporting rigidity of the lateral direction fiber members at this portion is comparatively high. In contrast thereto, both end portions of the lateral direction fiber members that are disposed at rear side of the lateral direction fiber members, which are disposed at the front side of the seat unit, are fixed to the longitudinal direction fiber members, such that the supporting rigidity of the lateral direction fiber members at this portion is comparatively low. 
     A vehicle seat of a seventh aspect of the present invention is any one of the second aspect to the fifth aspect, wherein both end portions of the lateral direction fiber members that are disposed at the seat front-rear direction front side of the seat unit are fixed to the seat cushion frame, and a lateral direction fiber member non-placement region in which the lateral direction fiber members are not disposed is provided at the seat front-rear direction rear side of the seat unit. 
     In the vehicle seat of the seventh aspect, both end portions of the lateral direction fiber members that are disposed at the seat front-rear direction front side of the seat unit are fixed to the seat cushion frame, such that the supporting rigidity of the lateral direction fiber members at this portion is comparatively high. In contrast thereto, the lateral direction fiber member non-placement region in which the lateral direction fiber members are not disposed is provided at the seat front-rear direction rear side of the seat unit, such that the supporting rigidity of the lateral direction fiber members at this portion is equivalent to zero. 
     A vehicle seat of an eighth aspect of the present invention is the first aspect, wherein the seat unit is configured by a resin seat cushion pad that has cushioning properties, and plural thinned portions are formed at a seating face side of the seat cushion pad, such that the rigidity of the seat cushion pad is lower at the seat front-rear direction rear side than at the seat front-rear direction front side. 
     In the vehicle seat of the eighth aspect, the seat unit is configured by the resin seat cushion pad that has cushioning properties. Moreover, the plural thinned portions are formed at the seating face side of the seat cushion pad, such that the rigidity of the seat cushion pad is lower at the seat front-rear direction rear side than at the seat front-rear direction front side. Thus in the present aspect, the seating face rigidity of the seat unit is realized by the shape (placement, shape, and size, etc. of the thinned portions) at the seating face side of the seat cushion pad. In other words, the rigidity distribution of the seat unit can be set to a desired distribution simply by changing the shape of the resin at the seating face side of the seat cushion pad. Thus the seat unit is easy to make, and the rigidity is easy to adjust. 
     A vehicle seat of a ninth aspect of the present invention is the eighth aspect, wherein the thinned portions are formed by recessed grooves extending along the seat front-rear direction, and a greater number of the recessed grooves are formed at the seat front-rear direction rear side than at the seat front-rear direction front side. 
     In the vehicle seat of the ninth aspect, the thinned portions are formed by the recessed grooves extending along the seat front-rear direction, and there are a greater number of the recessed grooves at the seat front-rear direction rear side than at the front side, such that the rigidity of the seat unit is lower at the seat front-rear direction rear side than at the front side. Configuration is made such that the rigidity of the seat unit changes according to the number of recessed grooves. Thus, in a hypothetical case in which the rigidity of the seat front-rear direction rear side of the seat unit is lowered to a particular rigidity, the depth of the recessed grooves can be made shallower by increasing the number of recessed grooves. This configuration is therefore suitable for cases in which the thickness of the seat unit is comparatively thin. 
     A vehicle seat of a tenth aspect or an eleventh aspect of the present invention is the eighth aspect or the ninth aspect, wherein the thinned portions are formed by recessed grooves extending along the seat front-rear direction, and a groove depth of each recessed groove is set deeper at the seat front-rear direction rear side than at the seat front-rear direction front side. 
     In the vehicle seat of the tenth aspect or the eleventh aspect, the thinned portions are formed by the recessed grooves extending along the seat front-rear direction, and the groove depth is deeper at the seat front-rear direction rear side than at the front side, such that the rigidity of the seat unit is lower at the seat front-rear direction rear side than at the front side. Configuration is made such that the rigidity of the seat unit changes according to the depth of the recessed grooves. In a hypothetical case in which the rigidity of the seat front-rear direction rear side of the seat unit is lowered to a particular rigidity, the number of recessed grooves can be reduced by making the recessed grooves deeper. 
     As explained above, the vehicle seat of the first aspect of the present invention exhibits an excellent advantageous effect of enabling the lumbar region of an occupant to sway during lateral acceleration of the vehicle, using a simple structure. 
     The vehicle seat of the second aspect of the present invention exhibits an excellent advantageous effect of enabling design to optimize seating face rigidity to be achieved comparatively easily. 
     The vehicle seat of the third aspect of the present invention exhibits an excellent advantageous effect of enabling a reduction in costs by reducing both the number of longitudinal direction fiber members used, and the number of lateral direction fiber members used. 
     The vehicle seat of the fourth aspect of the present invention exhibits an excellent advantageous effect of enabling a contribution to a reduction in costs by reducing the number of lateral direction fiber members used. 
     The vehicle seat of the fifth aspect of the present invention exhibits an excellent advantageous effect of enabling the rigidity distribution of the seat unit to be set to a desired distribution, simply by changing the number of seating face regions. 
     The vehicle seat of the sixth aspect of the present invention exhibits an excellent advantageous effect of enabling the rigidity distribution of the seat unit to be easily changed, by fixing both end portions of the lateral direction fiber members either to the seat cushion frame, or fixing both end portions of the lateral direction fiber members to the longitudinal direction fiber members. 
     The vehicle seat of the seventh aspect of the present invention exhibits an excellent advantageous effect of enabling a large difference in the rigidity distribution of the seat unit to be easily provided depending on the range over which the lateral direction fiber member non-placement region is provided. 
     The vehicle seat of the eighth aspect of the present invention exhibits an excellent advantageous effect of enabling design to optimize seating face rigidity to be performed comparatively easily, of enabling productivity to be improved, and also of enabling the rigidity to be easily adjusted. 
     The vehicle seat of the ninth aspect of the present invention exhibits an excellent advantageous effect of being suitable for adjusting the rigidity distribution in cases in which the seat unit is wide in the seat width direction. 
     The vehicle seat of the tenth aspect and the eleventh aspect of the present invention exhibit an excellent advantageous effect of being suitable for adjusting the rigidity distribution in cases in which the thickness of the seat unit is comparatively thick. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a perspective view of a seat cushion of a vehicle seat according to a first exemplary embodiment; 
         FIG. 2  is a schematic side view of a vehicle seat provided with the seat cushion illustrated in  FIG. 1 ; 
         FIG. 3A  is an enlarged cross-section of relevant portions, illustrating a fixing structure of a longitudinal direction fiber member to a seat cushion frame; 
         FIG. 3B  is an enlarged cross-section of relevant portions, illustrating a modified example of the fixing structure in  FIG. 3A ; 
         FIG. 4A  is an enlarged perspective view of relevant portions, illustrating a connection structure of longitudinal direction fiber members and a lateral direction fiber member; 
         FIG. 4B  is an enlarged perspective view of relevant portions, illustrating a modified example of the connection structure in  FIG. 4A ; 
         FIG. 5  is a perspective view illustrating a vehicle seat according to a modified example 1 of the first exemplary embodiment; 
         FIG. 6  is a plan view illustrating a seat cushion of a vehicle seat according to a modified example 2 of the first exemplary embodiment; 
         FIG. 7  is a plan view illustrating a seat cushion of a vehicle seat according to a modified example 3 of the first exemplary embodiment; 
         FIG. 8A  is an enlarged perspective view of relevant portions illustrating an example of a branched structure of a longitudinal direction fiber member of the seat cushion illustrated in  FIG. 7 ; 
         FIG. 8B  is an enlarged perspective view of relevant portions illustrating an example of a branched structure of a longitudinal direction fiber member of the seat cushion illustrated in  FIG. 7 ; 
         FIG. 9A  is a plan view illustrating a seat cushion of a vehicle seat according to a modified example 4 of the first exemplary embodiment; 
         FIG. 9B  is a plan view illustrating a seat cushion of a vehicle seat according to a modified example 5 of the first exemplary embodiment; 
         FIG. 9C  is a plan view illustrating a seat cushion of a vehicle seat according to a modified example 6 of the first exemplary embodiment; 
         FIG. 10A  is a perspective view of a seat unit of a seat cushion of a vehicle seat according to a second exemplary embodiment; 
         FIG. 10B  is a horizontal cross-section illustrating a state of the seat unit taken along line  10 (B)- 10 (B) in  FIG. 10A ; 
         FIG. 10C  is a horizontal cross-section illustrating a state of the seat unit taken along line  10 (C)- 10 (C) in  FIG. 10A ; 
         FIG. 11A  is a perspective view of a seat unit, illustrating a seat unit according to a modified example 1 of the second exemplary embodiment; 
         FIG. 11B  is a horizontal cross-section illustrating a state of the seat unit taken along line  11 (B)- 11 (B) in  FIG. 11A ; 
         FIG. 11C  is a horizontal cross-section illustrating a state of the seat unit taken along line  11 (C)- 11 (C) in  FIG. 11A ; and 
         FIG. 12  is a side view illustrating a configuration of a seat cushion according to a modified example 2 of the second exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Exemplary Embodiment 
     Explanation follows regarding a first exemplary embodiment of a vehicle seat according to the present invention, with reference to  FIG. 1  to  FIG. 9 . Note that in each of the drawings, the arrow FR indicates the vehicle front side, the arrow UP indicates the vehicle upper side, and the arrow IN indicates the vehicle width direction inside as appropriate. 
     As illustrated in  FIG. 2 , a vehicle seat  10  is configured including a seat cushion  12  supporting the buttocks and thighs of an occupant, a seatback  14  (tiltably) supported at a rear end portion of the seat cushion  12  and supporting the back of the occupant, and a headrest (not illustrated in the drawings) provided with adjustable height at an upper end portion of the seatback  14  and supporting the head of the occupant. Note that only a seatback frame  16  of the seatback  14  is illustrated in  FIG. 2 , and that a seatback pad supporting the back of the occupant, a cover, and the like, are omitted from the drawings. 
     As illustrated in  FIG. 1 , the seat cushion  12  includes a metal seat cushion frame  18  configuring a frame member of the seat cushion  12 . The seat cushion frame  18  is configured in a rectangular frame shape in plan view. The seat cushion frame  18  is moreover configured by a front side frame  18 A and a rear side frame  18 B, disposed running parallel to each other along the seat width direction, and a pair of left and right side frames  18 C disposed running parallel to each other along the seat front-rear direction. The front side frame  18 A, the rear side frame  18 B, and the pair of left and right side frames  18 C are each configured by a pipe member. 
     Note that although the seat cushion frame  18  is configured by metal pipe members in the present exemplary embodiment, configuration is not limited thereto, and the seat cushion frame may be configured by a different material or different structural members. For example, the seat cushion frame may be configured by joining press-formed components made of steel plates formed with U shaped or C shaped cross-sections, by welding or joining by bolts, etc. Alternatively, the seat cushion frame may be configured by extrusion-formed aluminum alloy components, or resin-molded components made of a fiber reinforced plastic such as CFRP. Note that this point similarly applies to the seatback frame  16  of the seatback  14 . 
     A seat unit  20 , on which the occupant sits, is installed at an upper end side of the seat cushion frame  18  described above. Configuration of the seat unit  20  in the present exemplary embodiment includes features explained in detail below. 
     The seat unit  20  is configured by a net strung over the entire seat cushion frame  18  along the seat front-rear direction. Structurally, the seat unit  20  is configured including plural longitudinal direction fiber members  22  extending along the seat front-rear direction, and plural lateral direction fiber members  24  extending along the seat width direction. Each of the longitudinal direction fiber members  22  and lateral direction fiber members  24  is configured as a collective body of thin fibers, and is made of resin. 
     More specifically, the plural longitudinal direction fiber members  22  are configured by plural first longitudinal direction fiber members  22 A strung between the front side frame  18 A and the rear side frame  18 B, and plural second longitudinal direction fiber members  22 B strung between the front side frame  18 A and the lateral direction fiber members  24 . Each of the first longitudinal direction fiber members  22 A and the second longitudinal direction fiber members  22 B is disposed at a specific pitch in the seat width direction. Longer second longitudinal direction fiber members  22 B are disposed at intermediate positions between adjacent first longitudinal direction fiber members  22 A, and shorter second longitudinal direction fiber members  22 B are disposed at the outsides of the first longitudinal direction fiber members  22 A disposed at both sides in the seat width direction. 
     As illustrated in  FIG. 3A , an inverted triangle shaped attachment portion  26  is provided protruding out toward the seat lower side at an outer peripheral lower end portion of the front side frame  18 A. The attachment portion  26  is formed in a plate shape, with an attachment hole  28  formed at a center portion thereof. Plural attachment portions  26  are disposed running along the width direction of the front side frame  18 A at a specific pitch. Note that although the attachment portions  26  are disposed protruding out toward the seat lower side in the configuration illustrated in  FIG. 3A , it is sufficient that the attachment portion does not have a configuration protruding out toward the seat upper side or the seat front side, and the attachment portion may protrude out toward the seat rear side. 
     A front end portion of each first longitudinal direction fiber member  22 A is wound about an outer peripheral front side portion of the front side frame  18 A, and then inserted through the attachment hole  28  of the respective attachment portion  26 . The end portion of the first longitudinal direction fiber member  22 A inserted through the attachment hole  28  is then folded back over the attachment portion  26 , and then fixed to the first longitudinal direction fiber member  22 A by a fixing means such as an adhesive. An attachment structure of a rear end portion of each first longitudinal direction fiber member  22 A to the rear side frame  18 B is similar to the attachment structure of each first longitudinal direction fiber member  22 A to the front side frame  18 A. Note that the attachment structure of the first longitudinal direction fiber member  22 A to the attachment portion  26  is not limited thereto, and a different structure may be applied. For example, a hook may be attached to an end portion of the first longitudinal direction fiber member  22 A, and the hook may be anchored to the attachment hole  28  of the attachment portion  26 . 
     Moreover, in the attachment structure of the front end portion of the first longitudinal direction fiber member  22 A illustrated in  FIG. 3A , the front end portion of the longitudinal direction fiber member  22 A is directly wound around the outer peripheral front side portion of the front side frame  18 A. However, configuration is not limited thereto, and as illustrated in  FIG. 3B , the front end portion of the first longitudinal direction fiber member  22 A may be wound around the outer peripheral front side portion of the front side frame  18 A with a member interposed therebetween. In the example illustrated in  FIG. 3B , a covering layer  30 , configured from urethane or the like, is provided at an outer peripheral portion of the front side frame  18 A, at least in a range contacting the longitudinal direction fiber member  22 . Such a configuration enables damage of the first longitudinal direction fiber member  22 A due to wear, and the occurrence of abnormal noise due to the front end portion of the first longitudinal direction fiber member  22 A directly rubbing against the front side frame  18 A, to be suppressed or prevented. 
     The attachment structure of the front end portions of the first longitudinal direction fiber members  22 A has been explained above, and front end portions of the second longitudinal direction fiber members  22 B are attached to the respective attachment portions  26  of the front side frame  18 A, in a similar manner to the front end portions of the first longitudinal direction fiber members  22 A. 
     As illustrated in  FIG. 1 , the plural lateral direction fiber members  24  are configured by plural first lateral direction fiber members  24 A and second lateral direction fiber members  24 B disposed at a specific pitch in the seat front-rear direction. The first lateral direction fiber members  24 A are strung along the seat width direction between the left and right side frames  18 C at a front side in the seat front-rear direction of the seat cushion frame  18  (see the X portion). The second lateral direction fiber members  24 B are strung along the seat width direction between the outermost first longitudinal direction fiber members  22 A at an intermediate portion in the seat front-rear direction of the seat cushion frame  18  (see the Y portion). Note that a lateral direction fiber member non-placement region  32 , in which any lateral direction fiber members  24  are not disposed, is provided at a rear side in the seat front-rear direction of the seat cushion frame  18  (see the Z portion). 
     Both end portions of each first lateral direction fiber member  24 A are attached to the respective left and right side frames  18 C. An attachment structure of the end portions of the first lateral direction fiber members  24 A to the side frames  18 C is similar to the attachment structure of the front end portions of the first longitudinal direction fiber members  22 A to the front side frame  18 A. Both end portions of each second lateral direction fiber member  24 B are attached to the pair of first longitudinal direction fiber members  22 A positioned adjacent to the respective side frames  18 C by a fixing means such as an adhesive. 
     Rear end portions of the second longitudinal direction fiber members  22 B previously described are attached to the respective first lateral direction fiber member  24 A or second lateral direction fiber member  24 B disposed at the rear most position, by a fixing means such as an adhesive (see  FIG. 4A ).  FIG. 4A  illustrates connection locations between the second longitudinal direction fiber members  22 B and the second lateral direction fiber member  24 B. In the configuration illustrated in  FIG. 4A , the second lateral direction fiber member  24 B passes to the upper side or the lower side of the first longitudinal direction fiber members  22 A, without being adhered thereto. However configuration is not limited thereto, and as illustrated in  FIG. 4B , the second lateral direction fiber member  24 B may be adhered not only to the second longitudinal direction fiber members  22 B, but also to the first longitudinal direction fiber members  22 A, at intersection portions therewith. 
     In the thus configured seat unit  20 , the fiber members strung along the seat front-rear direction are disposed across the entire seat cushion frame  18 , as previously described. However, the fiber members strung along the seat width direction are mainly disposed at the seat front-rear direction front side of the seat cushion frame  18 . Fiber members generally have high rigidity with respect to the application direction of tensile force, but have low rigidity with respect to bending. Thus in the case of the seat unit  20  of the present exemplary embodiment, in which the fiber members are strung along the seat front-rear direction across the entire seat cushion frame  18 , rigidity is comparatively high in the seat front-rear direction, this being the application direction of tensile force on the longitudinal direction fiber members  22 , and rigidity is comparatively low in the seat width direction, this being an axis-orthogonal direction to the longitudinal direction fiber members  22 . Namely, in the seat unit  20 , the rigidity of a seating face is set higher in the seat front-rear direction than the rigidity of the seating face in the seat width direction. 
     Furthermore, in the seat unit  20  with the above configuration, the fiber members are more sparsely disposed at the seat front-rear direction rear side than at the front side. To explain this point with reference to  FIG. 1 , the fiber members are densely disposed at the seat front-rear direction front side of the seat unit  20  (see the X portion), the fiber members are disposed to an intermediate extent at the seat front-rear direction intermediate portion of the seat unit  20  (see the Y portion), and the fiber members are sparsely disposed at the seat front-rear direction rear side of the seat unit  20  (see the Z portion). Namely, the density of the fiber members, which are configured by the longitudinal direction fiber members  22  and the lateral direction fiber members  24 , changes from dense to sparse in stages on progression from the seat front-rear direction front side toward the rear side of the seat unit  20 . To explain this from a different perspective, the seat unit  20  is partitioned into multiple rectangular shaped regions by the longitudinal direction fiber members  22 , the lateral direction fiber members  24 , or the seat cushion frame  18 . The regions are collectively referred to below as “seating face regions  34 ”, and when referring to each region individually, the regions are referred to as “seating face regions  34 A,  34 B,  34 C,  34 D” in sequence from the smallest area. Considering the number of seating face regions  34 , there is a large number of seating face regions  34 , configured by a dense concentration of the seating face regions  34 A and the seating face regions  34 B with small areas, at the seat front-rear direction front side of the seat unit  20 , an intermediate number of seating face regions  34  at the seat front-rear direction intermediate portion of the seat unit  20 , configured by the seating face regions  34 A with the small areas and front sides of the seating face regions  34 D with the largest areas, and a small number of seating face regions  34  at the seat front-rear direction rear side of the seat unit  20 , configured by the seating face regions  34 C with large areas and rear sides of the seating face regions  34 D. Thus the seat unit  20  is set with lower seating face rigidity in the seat width direction at the rear side than at the front side in the seat front-rear direction. To refer to a relationship with a seating face rotation axis θ 2 , described later, as illustrated in  FIG. 2 , rigidity distribution of the seat unit  20  is set in inverse proportion to a distance from the seating face rotation axis θ 2  to the seating face (rotation radius R 1 &lt;R 2 ). 
     Operation and Advantageous Effects of Present Exemplary Embodiment 
     Explanation follows regarding operation and advantageous effects of the present exemplary embodiment. 
     In the seat unit  20  supported by the seat cushion frame  18  in the vehicle seat  10  according to the present exemplary embodiment, the seating face rigidity in the seat front-rear direction is set higher than the seating face rigidity in the seat width direction. Namely, the rigidity distribution of the seating face in the seat unit  20  is anisotropic. Thus the lumbar region of a seated occupant is susceptible to sway in the seat width direction. First, a hypothetical rotation axis (a roll axis, lateral rotation axis of the lumbar region) θ 1  is accordingly formed running along the seat front-rear direction in a space above the seat unit  20  (see  FIG. 2 ). Furthermore, the seating face rigidity in the seat width direction of the seat unit  20  is set lower at the rear side than at the front side in the seat front-rear direction. Namely, the lumbar region of the seated occupant sways more easily at the seat rear side than at the front side, such that the hypothetical rotation axis (roll axis of the lumbar region) θ 1  drops down toward the seating face side at a front side, and rises at a rear side. The seating face rotation axis θ 2  is accordingly formed passing through the vicinity of the lumbar spine of the seated occupant, and tilts downward toward the front. Namely, in the vehicle seat  10  according to the present exemplary embodiment, rather than setting a complex configuration using bearings or the like between the seat cushion frame  18  and the seat unit  20  so as to allow the seat unit  20  to sway, the seat unit  20  itself has a function of allowing the lumbar region of the seated occupant to sway about the seating face rotation axis θ 2 . Thus the present exemplary embodiment enables swaying of the lumbar region of the occupant during lateral acceleration of the vehicle, using a simple configuration. 
     To consider this in an actual situation in which the vehicle is traveling, when the vehicle turns, a force toward outside of the turning direction due to inertial force acts on the seated occupant. Thus in the vehicle seat  10  according to the present exemplary embodiment, the lumbar region sways about the seating face rotation axis θ 2  at the seat unit  20 . Note that a shear moment from the seatback  14  toward an initial posture retention direction side acts directly on the back of the seated occupant at the seatback  14  side (even when there is no rotation mechanism provided to the seatback). Thus the seated occupant forms a sideways V shaped posture, namely, a posture in which a portion between the head and the lumbar region is curved, in a vehicle back face view, and the movement amount of the head is suppressed (to a minimum). This thereby enables a stable driving posture to be maintained, without direction of vision moving greatly. This enables the steering operation performance of the driver to be improved, and also enables the burden on the body of an occupant seated in a front seat (particularly the driver) to be greatly reduced. Furthermore, since the lumbar region of the occupant is allowed to sway, a similar movement to that when walking is performed without effort, particularly by the driver. This thereby enables the occurrence of lower back pain, or further worsening of lower back pain due to a long period of driving, to be suppressed or prevented, and driving comfort and steering satisfaction can be improved. 
     In the present exemplary embodiment, the seat unit  20  is configured in a net form, and includes the plural longitudinal direction fiber members  22  and lateral direction fiber members  24 . Furthermore, the fiber members are more sparsely disposed at the seat front-rear direction rear side than at the front side of the seat unit  20 , such that the rigidity at the seat front-rear direction rear side of the seat unit  20  is comparatively lower than at the front side. Thus in the present exemplary embodiment, the seating face rigidity of the seat unit  20  is realized by the placement density of the longitudinal direction fiber members  22  and the lateral direction fiber members  24 . In other words, the rigidity distribution of the seat unit  20  can be set to a desired distribution, simply by changing the placement density of the longitudinal direction fiber members  22  and the lateral direction fiber members  24 . The present exemplary embodiment thereby enables design to optimize seating face rigidity to be performed comparatively easily. 
     In the present exemplary embodiment, the number of the seating face regions  34  partitioned by the longitudinal direction fiber members  22 , and the lateral direction fiber members  24  or the seat cushion frame  18  is smaller at the seat front-rear direction rear side than at the front side, such that seating face rigidity of the seat unit  20  is lower at the seat front-rear direction rear side than at the front side. The present exemplary embodiment thereby enables the rigidity distribution of the seat unit  20  to be set to a desired distribution, simply by changing the number of seating face regions  34 . 
     In the present exemplary embodiment, both end portions of the first lateral direction fiber members  24 A disposed at the seat front-rear direction front side of the seat unit  20  are fixed to the side frames  18 C of the seat cushion frame  18 , such that the supporting rigidity of the first lateral direction fiber members  24 A at this portion is comparatively high. In contrast thereto, both end portions of the second lateral direction fiber members  24 B disposed at the seat front-rear direction rear side of the first lateral direction fiber members  24 A are fixed to the first longitudinal direction fiber members  22 A, such that the supporting rigidity of the second lateral direction fiber members  24 B at this portion is comparatively low. Fixing both end portions of the lateral direction fiber members  24  either to the side frames  18 C of the seat cushion frame  18 , or to the longitudinal direction fiber members  22  in this manner thereby enables the rigidity distribution of the seat unit  20  to be easily changed. 
     Similarly, in the present exemplary embodiment, both end portions of the first lateral direction fiber members  24 A disposed at the seat front-rear direction front side of the seat unit  20  are fixed to the side frames  18 C of the seat cushion frame  18 , such that the supporting rigidity of the first lateral direction fiber members  24 A at this portion is comparatively high. In contrast, the lateral direction fiber member non-placement region  32  in which the lateral direction fiber members  24  are not disposed, is provided at the seat front-rear direction rear side of the seat unit  20  (the seat front-rear direction rear side of the second lateral direction fiber members  24 B), such that the supporting rigidity of the lateral direction fiber members  24  at this portion is equivalent to zero. Thus a large difference in the rigidity distribution of the seat unit  20  can be simply provided depending on the range over which the lateral direction fiber member non-placement region  32  is provided. 
     Variations 
     Explanation follows regarding several variations of the first exemplary embodiment. 
     Modified Example 1 
     The example illustrated in  FIG. 5  is similar to the previously described seat unit  20  illustrated in  FIG. 1 , in that a seat unit  40  is configured by plural longitudinal direction fiber members  42  and lateral direction fiber members  44 ; however the seat unit  40  is configured differently from the seat unit  20  in the following respects. 
     In the seat unit  40 , the longitudinal direction fiber members  42  are strung in a radial shape from the center of the front side frame  18 A of the seat cushion frame  18 . There are two types of longitudinal direction fiber members  42 , these being first longitudinal direction fiber members  42 A strung from the front side frame  18 A to the rear side frame  18 B, and second longitudinal direction fiber members  42 B strung from the front side frame  18 A to the respective side frames  18 C. Thus the longitudinal direction fiber members  42  are strung between any two side frames of the seat cushion frame  18 . 
     The lateral direction fiber members  44  are configured by first lateral direction fiber members  44 A strung between the first longitudinal direction fiber members  42 A at the left and right, and second lateral direction fiber members  44 B strung between the second longitudinal direction fiber members  42 B at the left and right, without being fixed to the seat cushion frame  18 . The pitch of the lateral direction fiber members  44  is set to increase on progression from the seat front-rear direction front side toward the rear side. Thus the fiber members of the seat unit  40  are more sparsely disposed at the seat front-rear direction rear side than at the front side, and the number of seating face regions  46  is smaller at the seat front-rear direction rear side than at the front side. Thus in the seat unit  40 , the seating face rigidity at the seat front-rear direction rear side is lower than the seating face rigidity at the seat front-rear direction front side. 
     In the seat unit  40 , disposing the longitudinal direction fiber members  42  in a shape radiating out from the front side frame  18 A of the seat cushion frame  18  enables all the longitudinal direction fiber members  42  to be strung between the any two side frames of the seat cushion frame  18 , whereby a swaying amount of a seated occupant in the seat width direction is suppressed at a location at the seat front-rear direction front side, and the swaying amount in the seat width direction is increased at a location at the seat front-rear direction rear side. This enables the longitudinal direction fiber members  42  to be stably supported. 
     Modified Example 2 
     Configuration of a seat unit  48  illustrated in  FIG. 6  is substantially similar to that of the seat unit  40  illustrated in  FIG. 5 , differing in that one of each of the second longitudinal direction fiber members  42 B is disposed at the left and right. Since the overall number of longitudinal direction fiber members  42  is accordingly reduced compared to in the seat unit  40  illustrated in  FIG. 5 , the placement interval between the longitudinal direction fiber members  42  is wider. Adjustment of the seating face rigidity of the seat unit  48  is accordingly cruder than in the seat unit  40  illustrated in  FIG. 5 ; however costs can be reduced by reducing the number of fiber members used, while retaining the advantageous effects of the seat unit  40  illustrated in  FIG. 5 , as described above. 
     Modified Example 3 
     A seat unit  50  illustrated in  FIG. 7  and  FIG. 8  includes features that the placement density of the fiber members is set by branching partway along longitudinal direction fiber members  52 . Specifically, a pair of left and right first longitudinal direction fiber members  52 A extends in parallel to each other from the rear side frame  18 B of the seat cushion frame  18  toward the seat front-rear direction front side. Front end portions of the pair of left and right first longitudinal direction fiber members  52 A are coupled together in the seat width direction by a first lateral direction fiber member  54 A. The front end portions of the pair of left and right first longitudinal direction fiber members  52 A then branch into two forks to form respective second longitudinal direction fiber members  52 B extending in a V shape, and the second longitudinal direction fiber members  52 B then extend in parallel along the seat front-rear direction. The total of four second longitudinal direction fiber members  52 B are coupled together in the seat width direction by a second lateral direction fiber member  54 B. A front end portion of each second longitudinal direction fiber member  52 B then branches into two forks to form respective third longitudinal direction fiber members  52 C extending in a V shape. Front end portions of each of the third longitudinal direction fiber members  52 C are fixed to the front side frame  18 A of the seat cushion frame  18 . In the above configuration, the seat unit  50  is formed with isosceles triangle shaped, isosceles trapezoid shaped, and rectangular shaped seating face regions  58 . 
     Note that the following configurations may be applied as configurations of the branched portions. As illustrated in  FIG. 8A , a first example is a configuration in which two second longitudinal direction fiber members  52 B branch directly from one first longitudinal direction fiber member  52 A. In this example, the two second longitudinal direction fiber members  52 B after branching are thinner than the first longitudinal direction fiber member  52 A prior to branching. In this example, the fiber members become thinner at each branching; however an advantage is that a small number of components suffices. As illustrated in  FIG. 8B , in a second example, the one first longitudinal direction fiber member  52 A prior to branching, and the two second longitudinal direction fiber members  52 B after branching are each fixed to respective apex portions of a coupling member  56  formed in an inverted triangular plate shape. In this example, the number of components increases; however an advantage is that the thickness of the fiber members does not change. 
     The seat unit  50  enables the number of seating face regions to be regularly increased between before and after branching of the longitudinal direction fiber members  52 . In this example, the number of seating face regions after branching increases to (2n+1), where n is the number of seating face regions prior to branching. This enables the rigidity distribution of the seating face to be changed by branching the longitudinal direction fiber members  52  at locations where a change in the rigidity distribution of the seating face is desired. 
     Modified Example 4 
     A seat unit  60  illustrated in  FIG. 9A  is configured by plural longitudinal direction fiber members  62  strung between the front side frame  18 A and the rear side frame  18 B of the seat cushion frame  18 , and plural lateral direction fiber members  64  strung between the pair of left and right longitudinal direction fiber members  62  disposed at both sides in the seat width direction. The plural longitudinal direction fiber members  62  are disposed at a uniform pitch in the seat width direction. In contrast thereto, the plural lateral direction fiber members  64  are disposed at a non-uniform pitch, such that the pitch widens on progression from the seat front-rear direction front side toward the rear side of the seat unit  60 . Thus in the seat unit  60 , the fiber members are more sparsely disposed at the seat front-rear direction rear side than at the front side, and the number of seating face regions  66  is smaller at the seat front-rear direction rear side than at the front side. The seating face rigidity at the seat front-rear direction rear side is accordingly lower than the seating face rigidity at the seat front-rear direction front side of the seat unit  60 . In the seat unit  60 , preparation of one type of the longitudinal direction fiber member  62  and one type of the lateral direction fiber member  64  suffices, thereby enabling the manufacturing cost to be reduced. 
     Modified Example 5 
     Similarly to the seat unit  60 , a seat unit  70  illustrated in  FIG. 9B  is configured by plural longitudinal direction fiber members  72  strung between the front side frame  18 A and the rear side frame  18 B of the seat cushion frame  18 , and plural lateral direction fiber members  74  strung between the pair of left and right longitudinal direction fiber members  72  disposed at both sides in the seat width direction. Out of these fiber members, the cord diameter of each longitudinal direction fiber member  72  increases on progression from a rear end portion toward a front end portion. Note that the lateral direction fiber members  74  are all formed with the same cord diameter, and are disposed at a uniform pitch in the seat front-rear direction. 
     In the above configuration, the cord diameter of the longitudinal direction fiber member  72  increases on progression from the seat front-rear direction rear side toward the front side, thereby enabling a difference in rigidity to be created by the longitudinal direction fiber member  72  itself. Namely, the seating face rigidity at the seat front-rear direction rear side is lower than the seating face rigidity at the seat front-rear direction front side in the seat unit  70 . Moreover, both the number of longitudinal direction fiber members  72  used and the number of lateral direction fiber members  74  used can be reduced compared to the seat unit  60  illustrated in  FIG. 9A , this being an effective way to reduce costs. 
     Modified Example 6 
     Similarly to the seat unit  60 , a seat unit  80  illustrated in  FIG. 9C  is configured by plural longitudinal direction fiber members  82  strung between the front side frame  18 A and the rear side frame  18 B of the seat cushion frame  18 , and plural lateral direction fiber members  84  strung between the pair of left and right longitudinal direction fiber members  82  disposed at both sides in the seat width direction. Out of these fiber members, there are four types of lateral direction fiber members  84 , each with a different cord diameter, these being a first lateral direction fiber member  84 A, a second lateral direction fiber member  84 B, a third lateral direction fiber member  84 C, and a fourth lateral direction fiber member  84 D. The first lateral direction fiber member  84 A to the fourth lateral direction fiber member  84 D are disposed such that the cord diameter gradually increases on progression from the seat front-rear direction rear side toward the front side. Note that the longitudinal direction fiber members  82  are all formed with the same cord diameter, and are disposed at a uniform pitch in the seat width direction. 
     In the above configuration, the cord diameter of the lateral direction fiber members  84  increases on progression from the seat front-rear direction rear side toward the front side, thereby enabling a difference in rigidity to be created by the lateral direction fiber members  84  themselves. Namely, the seating face rigidity at the seat front-rear direction rear side is lower than the seating face rigidity at the seat front-rear direction front side in the seat unit  80 . Moreover, the number of lateral direction fiber members  84  used can be reduced compared to the seat unit  60  illustrated in  FIG. 9A , thereby contributing to a reduction in cost. 
     Second Exemplary Embodiment 
     Explanation follows regarding a second exemplary embodiment of the vehicle seat of the present invention, with reference to  FIG. 10A  to  FIG. 12 . Note that the same reference numerals are applied to configuration portions that are similar to those of the first exemplary embodiment previously described, and explanation thereof is omitted. 
     As illustrated in  FIG. 10A , in a vehicle seat according to the second exemplary embodiment, a seat unit  90  of a seat cushion is configured by a resin seat cushion pad that has cushioning properties. Specifically, the seat unit  90  is configured, for example, from urethane foam. 
     Plural thinned portions are formed to a seating face side of the seat unit  90 , such that the seat unit  90  has lower rigidity at the seat front-rear direction rear side than at the front side. Specifically, plural recessed grooves  92 , serving as thinned portions, are formed running along the seat front-rear direction at the seating face side of the seat unit  90 . The recessed grooves  92  are configured by three first recessed grooves  92 A formed spanning from a rear end portion to a front end portion of the seat unit  90  (see  FIG. 10C ), and a total of four second recessed grooves  92 B, disposed extending from the rear end portion of the seat unit  90  to a front-rear direction intermediate portion of the seat unit  90 , at both sides in the seat width direction of the first recessed grooves  92 A (see  FIG. 10B ). Thus a greater number of recessed grooves  92  are set at the seat front-rear direction rear side than at the front side in the seat unit  90 , and the seat unit  90  is set with a lower rigidity at the seat front-rear direction rear side than at the front side. Note that the recessed grooves  92  are formed running along the seat front-rear direction, such that the seating face rigidity of the seat unit  90  is set higher in the seat front-rear direction than seating face rigidity in the seat width direction. 
     Operation and Advantageous Effects 
     In the above configuration, the seat unit  90  is configured by a resin seat cushion pad that has cushioning properties. Moreover, in the present exemplary embodiment, plural of the recessed grooves  92 , these being thinned portions, are formed to the seating face side of the seat unit  90 , such that the rigidity of the seat unit  90  is lower at the seat front-rear direction rear side than the rigidity at the front side. Thus in the present exemplary embodiment, the difference in rigidity provided by the seating face of the seat unit  90  is realized by the shape of the seating face side of the seat cushion pad (the number of recessed grooves  92 ). In other words, the rigidity distribution of the seat unit  90  can be set to a desired distribution simply by changing the shape of the resin at the seating face side of the seat unit  90 . The seat unit  90  is accordingly easy to make, and the rigidity is easy to adjust. The present exemplary embodiment accordingly enables design to optimize seating face rigidity to be performed comparatively easily, enables productivity to be improved, and also enables the rigidity to be easily adjusted. 
     In the above configuration, the thinned portions are configured by the recessed grooves  92  extending along the seat front-rear direction, and the number of recessed grooves  92  is greater at the seat front-rear direction rear side than at the front side, such that the rigidity of the seat unit  90  is lower at the seat front-rear direction rear side than at the front side. In short, configuration is made such that the rigidity of the seat unit  90  changes according to the number of recessed grooves  92 . Thus, in a hypothetical case in which the rigidity of the seat front-rear direction rear side of the seat unit  90  is lowered to a particular rigidity, the depth of the recessed grooves  92  can be made shallower by increasing the number of the recessed grooves  92 . This configuration is therefore suitable for adjusting the rigidity distribution in cases in which the seat unit  90  is wide in the seat width direction, and the thickness of the seat unit  90  is comparatively thin. 
     Variations 
     Explanation follows regarding several variations of the second exemplary embodiment. 
     Modified Example 1 
     The example illustrated in  FIG. 11A  is similar to the seat unit  90  illustrated in  FIGS. 10  in the respect that a seat unit  96  of a seat cushion is configured by a resin seat cushion pad that has cushioning properties. 
     Plural recessed grooves  98 , serving as thinned portions, are formed running along the seat front-rear direction at the seating face side of the seat unit  96 . The recessed grooves  98  are disposed at a uniform pitch in the seat width direction. All the recessed grooves  98  are formed spanning from a rear end portion to a front end portion of the seat unit  96 , and are set with the same length direction dimension as each other. However, as illustrated in  FIGS. 11A, 11B, and 11C , the groove depth of each recessed groove  98  is set so as to gradually become deeper on progression from the seat front-rear direction front side toward the rear side. 
     In the above configuration, the thinned portions are configured by the recessed grooves  98  extending along the seat front-rear direction, and the groove depth is deeper at the seat front-rear direction rear side than at the front side, such that the rigidity of the seat unit  96  is lower at the seat front-rear direction rear side than at the front side. In short, configuration is made such that the rigidity of the seat unit  96  changes according to the depth of the recessed grooves  98 . Thus, in a hypothetical case in which the rigidity of the seat front-rear direction rear side of the seat unit  96  is lowered to a particular rigidity, the number of recessed grooves  98  can be reduced by making the recessed grooves  98  deeper. This configuration is therefore suitable for adjusting the rigidity distribution in cases in which the seat unit  96  is narrow in the seat width direction, but the thickness of the seat unit  90  is comparatively thick. 
     Note that the configuration illustrated in  FIG. 11A  may be combined with the configuration illustrated in  FIG. 10A , previously described. 
     Modified Example 2 
     In the example illustrated in  FIG. 12 , the thickness of a seat unit  100  is set thicker at the seat front-rear direction rear side, and thinner at the seat front-rear direction front side, while retaining the configuration illustrated in  FIGS. 11 , previously described. Thus the thickness of the seat unit does not necessarily need to be uniform. This point similarly applies to the second exemplary embodiment illustrated in  FIG. 10A . 
     Note that in the exemplary embodiment illustrated in  FIG. 10A  to  FIG. 12 , are formed with the recessed grooves  92 ,  98 , serving as thinned portions; however configuration is not limited thereto, and recessed portions, through-holes, or the like, that do not fall into the category of “grooves”, may be formed instead. 
     Supplementary Explanation of Exemplary Embodiments 
     In the first exemplary embodiment and the second exemplary embodiment explained above, a support face of the seatback  14  is configured as a non-rotating structure; however configuration is not limited thereto, and the support face of the seatback may be provided with a mechanism that actively enables rotation of a seated occupant toward an upright direction from a direction in which the occupant is swung due to inertial force, when the vehicle is turning. As an example, the configuration described in the publication cited as related art, a configuration in which the support face of the seatback is supported by a resilient body disposed in a spider-web shape, or another configuration may be applied.