Vehicle seat and method of production thereof

End portions of elastic fibers are fixed to a holder plate as well as a holder cover constituting a seat surface of a vehicle seat, thereby spanning the elastic fibers. A net-shaped seat portion is thus formed of the elastic fibers. The holder plate and the holder cover are suspended on the elastic fibers in the upper-diagonal direction. The elastic fibers thus strained are overlaid with urethane foam, and a cushion member is formed by a urethane pad. Meanwhile, the holder cover is pulled by a spring in the lower-diagonal direction so as to impart an initial tensile force to the elastic fibers, whereby deflections are eliminated. When an occupant's weight acts on the vehicle seat with the above construction, the vehicle seat deflects downward, with a predetermined deflection curve being drawn. However, both end portions of the elastic fibers are suspended on the elastic fibers in the upper-diagonal direction. This provides a substantially linear deflection curve, and a feeling of sitting-on-the-bottom is eliminated. The elastic fibers and the urethane pad can be formed integrally by means of a mold, thereby allowing a shorter manufacturing process.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a vehicle seat and a method of production 
thereof. 
2. Description of the Related Art 
Vital cushion characteristics of a vehicle seat are a proper degree of 
flexibility, strength enough to carry a load, and durability. 
In order to insure such cushion characteristics, conventional vehicle seats 
have been made up of: a seat frame formed of steel pipe and the like; a 
spring member such as a urethane pad and a S-shaped spring, which is 
mounted to the seat frame; and, a covering material such as tricot, 
moquette, and woven fabrics, which surrounds the surface of the seat frame 
and the spring member. 
However, the spring member formed of the urethane pad, the S-shaped spring 
and the like requires a large amount of urethane foam, which makes savings 
in manufacturing costs of the vehicle seat difficult to achieve. 
As shown in FIG. 11, a vehicle seat 100 has been proposed for solving this 
problem (Japanese Utility Model Application Laid-Open No. 61-172560). In 
the vehicle seat 100, a seat frame 102 is provided with elastic fibers 104 
which are spanned in the form of cross stripes. Urethane foam 106 is then 
integrally overlaid on both upper and lower surfaces of the elastic fibers 
104. The elastic fibers 104 acting as a spring layer and the urethane foam 
106 acting as a cushion layer are integrally formed into the vehicle seat 
100. Therefore, a proper degree of flexibility is thereby expected. In 
addition, the vehicle seat with a simplified structure and the use of the 
urethane foam 106 in a reduced amount can be attained. 
However, in the above vehicle seat 100, the elastic fibers 104 are spanned 
in a flat plane with respect to the surface of the seat frame 102. 
Accordingly, a non-linear deflection curve is drawn in which the amount of 
deflection in the elastic fibers 104 relative to a load is greatest 
immediately when the elastic fibers 104 receives a load, and thereafter 
reduces gradually. (See a solid line in FIG. 9.) 
As a result, with this vehicle seat 100, a so-called feeling of 
sitting-on-the-bottom occurs (by which is meant a feeling of being seated 
in the bottom of the seat due to unsteady variations of deflections). 
SUMMARY OF THE INVENTION 
In view of the above-described fact, an object of the present invention is 
to provide both a vehicle seat designed to eliminate a so-called feeling 
of sitting-on-the-bottom and a method for producing the vehicle seat which 
allows for fewer components and a shorter manufacturing process. 
The vehicle seat according to the present invention comprises: a holding 
member which forms a seat surface for an occupant; an elastic material of 
which an end portion is secured to the holding member, thereby spanning 
the elastic material; an elastic suspending means that suspends the 
holding member from a central portion thereof in the upper-diagonal and 
outward direction relative to the seat surface formed by the holding 
member; a urethane pad integrally overlays the holding member, the elastic 
material, and the elastic suspending means; and, a tension means that 
strains the holding member from a central portion thereof in the 
lower-diagonal and outward direction relative to the seat surface formed 
by the holding member. 
According to the present invention, the method for producing the vehicle 
seat comprises: a first process comprising the mounting of the holding 
member and an outer frame, which is disposed on the outer periphery of the 
holding member so as to constitute the elastic suspending means, to a mold 
which forms a cushion member for the vehicle seat; a second process 
comprising the spanning of the elastic material between the outer frame 
and the holding member so as to form the elastic suspending means; a third 
process comprising the spanning of the elastic material between the 
holding members in the form of a net; and, a fourth process including 
injecting urethane foam into the mold. 
In the vehicle seat with the above construction, the urethane pad is 
integrally overlaid with: the elastic material spanned between the holding 
members; and, the elastic suspending mean that suspends the holding member 
in the upper-diagonal direction. The seat surface of the vehicle seat is 
thereby formed. 
When an occupant's weight acts on the seat surface, the elastic material 
deflects downward, with a predetermined deflection curve being drawn. At 
this time, one end of the elastic member is suspended by the elastic 
suspending means through the holding member. This elastic suspending means 
imparts a predetermined tensile force to the holding member from the 
central portion of the holding member in an upper-diagonal and outward 
direction, whereby the elastic material is suspended. This provides a 
substantially linear deflection curve of the elastic material, and a 
feeling of sitting-on-the-bottom is eliminated, as compared with the 
elastic material spanned in a flat plane. The holding member, in which the 
elastic material is fixed, is also strained by the tension means from the 
central portion of the holding member in the lower-diagonal and outward 
direction. An initial tensile force is thereby imparted to the elastic 
material. As a result, an initial deflection acting downward is 
eliminated, and the elastic material is prevented from leaving the holding 
member when a fixed portion of the elastic material is pulled upward. 
In the method for producing the vehicle seat, the holding member and the 
outer frame, which is disposed on the outer periphery of the holding 
member so as to constitute the elastic suspending means, are mounted into 
the mold forming the cushion member for the vehicle seat. The elastic 
material is then spanned between the outer frame and the holding member so 
as to form the elastic suspending means. The other elastic material is 
spanned between the holding members in the form of a net. Subsequently, a 
covering material is applied or fitted to the mold, into which urethane 
foam is injected, whereby the elastic material and the holding member are 
integrally formed with the urethane pad. In this way, a one-piece body is 
formed with the elastic material acting as a spring member, the urethane 
pad acting as the cushion member, and the covering material. This allows 
for fewer components and a shorter manufacturing process.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a cushion member 12 and a seat frame 14 for a vehicle seat 10 
according to the present invention. 
Construction of the Cushion Member 
A cushion member 12 is formed of: elastic fibers 24 and 26, of which end 
portions are held both between holder plates 16 and holder covers 20 and 
between holder plates 18 and holder covers 22 so as to span the elastic 
fibers 24 and 26 into the form of a net; and, a urethane pad 44 and a 
covering material 61 which are together combined with the former 
components so as to form a seat portion. 
The holder plates 16 constitute an outer frame of the seat portion. On the 
outer periphery of the holder plates 16, holder plates 18 are disposed to 
form banked portions 28 of the cushion member 12. When curvature of the 
buttocks of a seated occupant is taken into account, the holder plates 16 
and 18 are flexed at a given curvature in the longitudinal direction of a 
vehicle. 
As shown in FIG. 2, the holder plate 16 is bent at its center line, which 
is the longitudinal axis of the holder plate 16, and directed upwardly 
toward the holder plate 18. On the upper surface of the holder plate 16, 
bosses 30 are vertically provided at predetermined intervals. The bosses 
30 fit into circular holes 31 formed in the holder cover 20, thereby 
allowing both end portions of the elastic fibers 24 and 26 to be held 
between the holder plate 16 and the holder cover 20. In each of the bosses 
30, a through hole 32 is formed into which a positioning pin 56 mounted in 
an upper mold 52 is inserted, as shown in FIG. 5. The holder cover 20 has 
hooking members 34 provided downwardly for insertion into and through 
holes 36 formed in the holder plate 16 so as to protrude from the lower 
surface of the holder plate 16. Similarly, on the holder plate 18 and in 
the holder cover 22, bosses 38 and circular holes 40 are respectively 
formed for holding end portions of the elastic fibers 26 therein. 
The elastic fibers 24 and 26 use porous polypropylene or polyester fibers 
to permit continual use as an elastic material and to prolong life cycle 
of the elastic fibers 24 and 26 because of reduced creeps. As shown in 
FIG. 3, a urethane pad 44 forms the banked portion 28 rising toward the 
holder plate 18, which is disposed outwardly at an upper portion of the 
holder plate 16 constituting the cushion member 12. The urethane pad 44 
further forms a side portion 48 which bends downwardly from the banked 
portion 28. At an end portion of the side portion 48, a side holder 50 is 
provided so as to mount the cushion member 12 onto a seat frame 14 fixed 
to a vehicle body. As illustrated in FIG. 4, the side holder 50 has a 
substantially U-shaped cross-section, with circular holes 51 formed in its 
side surface at predetermined intervals. When urethane foam is injected, 
the circular holes 51 have a provision whereby the urethane foam enters 
therein so as to secure the side holder 50 to the end portion of the side 
portion 48 of the cushion member 12. 
Method for Producing the Cushion Member 
A method for producing a cushion member will now be described with 
reference to FIG. 5. 
As a first step, holder plates 16 and 18 are fixed to a upper mold 52 into 
which the shape of a cushion member 12 is impressed. The upper mold 52 is 
provided with holes 54 punched for positioning. Into the holes 54, 
positioning pins 56 are anchored so as to fit into through-holes 32 and 42 
of bosses 30 and 38 respectively. A side holder 50 is fixed to a groove 60 
formed in each side surface portion of the upper mold 52. 
Subsequently, elastic fibers 24 and 26 are wound around the bosses 30 and 
38 to form a seat surface and elastic suspending means. A method will now 
be given for spanning the elastic fibers 24 and 26. As illustrated in FIG. 
2, one end portions of the elastic fibers 26 are first wound around the 
bosses 38 of the holder plate 18 in spiral fashion. The end portions 
thereof are extended through circular holes 40 of the holder cover 22. The 
end portions of the elastic fibers 26 are thereby held between the holder 
cover 22 and the holder plate 18. Deflections are thereby eliminated. 
Next, the elastic fibers 26 are spanned between and wound around the 
bosses 38 and 30 in the transverse direction of a vehicle. The other 
elastic fibers 24 are then wound between the bosses 30 disposed in the 
lateral direction of the vehicle seat 10. (See FIG. 5.) Similarly, this 
spanning operation is also performed in the longitudinal direction of the 
vehicle, whereby a net-shaped seat surface is formed. When the spanning 
operation is completed, the holder covers 20 and 22 are fitted into the 
respective holder plates 16 and 18 so as to rigidly secure the end 
portions of the elastic fibers 24 and 26 therebetween. The elastic fibers 
24 and 26 are thus securely anchored at a given pitch by both the holder 
covers 20 and 22 and the holder plates 16 and 18 so that variations in 
seat pressure distribution due to the misalignment of the windings are 
prevented. Because the spanning operation is simple, thereby allowing the 
use of robots or the like in the course of assembling work to achieve a 
labor saving. Furthermore, the breaking of the elastic fibers 24 and 26 
caused by intensive, localized stress can be prevented because the contact 
surfaces of the elastic fibers 24 and 26 extend around the side surfaces 
of the bosses 30 and 38. 
In addition, the elastic fibers 26 spanned between the bosses 38 and 30 are 
separated from the elastic fibers 24 spanned between the bosses 30 
disposed in the lateral direction of a vehicle seat 10. 
After the above spanning operation is completed, a urethane cover 61 is 
either sprayed or pasted over a lower mold 62. Urethane foam is then 
charged to effect mold-matching of the upper and lower molds 52 and 62. 
Thereafter, the urethane foam is expanded, and the molds are released 
after a predetermined period of time (for ten minutes at 60.degree. C. in 
this embodiment). The cushion member 12 fitted within the upper mold 52 
are removed therefrom, and production work is now completed. As can be 
seen from the above description, in the method for producing the cushion 
member 12 according to this embodiment, the upper and lower molds 52 and 
62 alone can be used to form the cushion member 12, thereby allowing for 
fewer components and a shorter manufacturing process. Furthermore, this 
allows for both lighter weight and a smaller-sized design of the cushion 
member 12, thereby providing a wider space within the vehicle. 
Cushion Member Installation Work 
As shown in FIG. 1, fixing pins 64 are provided on a seat frame 14 which is 
fixed to a vehicle body (not shown). These pins 64 are fitted into holes 
42 formed in bosses 38 of holder plates 18 so as to mount a cushion member 
12 onto the seat frame 14. At the same time, a side holder 50 is 
interlocked with each L-shaped hook 66 provided on side portions of the 
seat frame 14. (See FIG. 3.) As illustrated in FIG. 6, in the longitudinal 
direction of a vehicle, there is an axis 65 disposed in the transverse 
direction of the seat frame 14, and a cross member 70 is connected to the 
axis 65 and is equipped with fixing pins 68. The axis 65 and the cross 
member 70 are covered by a urethane pad 72 having an elliptical 
cross-section. The fixing pins 68 are fitted into holes 78 formed in 
bosses 76 of a holder plate 74 disposed in the transverse direction, 
whereby a position of the seat frame 14 in the longitudinal direction 
thereof is assumed. 
Thereafter, a hooking member 34 and a stopper portion 80 are connected to 
one another via a spring 82, as shown in FIG. 3. The mounting operation of 
the vehicle seat 10 is now completed. 
As can be seen from the above description, mounting is completed by only 
fitting the cushion member 12 into the seat frame 14, thereby allowing for 
fewer mounting processes. In addition, initial tension is imparted to 
elastic fibers 24 by the springs 82, thereby eliminating initial 
downwardly deflections. Furthermore, the hooking members 34 of the holder 
covers 20 are pulled downward by the springs 82, thereby preventing the 1 
if ting-off of the holder covers 20 due to forces acting on the end 
portions of the elastic fibers 24 when the vehicle seat 10 is used. The 
end portions of the elastic fibers 24 are securely fixed, thereby 
eliminating the chance that the holder covers 20 and the holder plates 16 
break loose from one another. 
Deflection Characteristics of the Cushion Member 
FIG. 7 shows experimental values in which a deflection curve of a single 
elastic fiber 24 varies according to a tensile force in the upper-diagonal 
direction imparted to both end portions of the elastic fiber 24 forming a 
seat surface. 
As illustrated in FIG. 8, point 0 at the center between points B and C 
receives load F.sub.x. At this time, the positions of points A and D 
supporting both end portions of the elastic fiber 24 are graded upwardly 
from 0.degree. to 45.degree. through 22.5.degree. in relation to straight 
line B-C. Furthermore, points B and C are influenced by tensile forces in 
the lower-diagonal direction, which are caused by springs. 
As can be judged from FIG. 7, when the elastic fiber 24 is spanned in a 
flat plane, i.e. , points A and D are at an angle of 0.degree., the 
initial deflection X given is large, thus resulting in a non-linear 
deflection curve. As load F.sub.x further increases, the deflection curve 
gradually approaches a straight line. When a vehicle seat 10 in which the 
elastic fibers 24 have a deflection curve as drawn in the above manner is 
employed, a momentary sense of softness is felt when an occupant is 
seated, and a so-called feeling of sitting-on-the-bottom occurs as 
occupant's weight is applied. 
When points A and D are at an angle of 22.5.degree. and 45.degree. 
respectively, substantially linear deflection curves are drawn. This means 
that the amount of deflection increases at a given ratio. Accordingly, an 
occupant has no feeling of sitting-on-the-bottom when seated in the 
vehicle seat 10 in which the elastic fibers 24 having the deflection curve 
as drawn in the above manner are employed. 
FIG. 9 shows one hysteresis loop of a cushion member 12 in which the 
elastic fibers are spanned in a flat plane (solid line), and another 
hysteresis loop of the cushion member 12 in which those fibers are spanned 
between points A and D at an angle of 22.5.degree. (dashed line). 
As can be determined from this graph, the hysteresis loop drawn in 
accordance with the cushion member 12 (the dashed line) of the present 
embodiment is closer to a linear state when compared with the solid line. 
Accordingly, a cushion member producing no feeling of 
sitting-on-the-bottom is achievable. 
FIG. 10 shows a graph illustrating results from experiments to determine a 
critical point, at which the degree of each angle for points A and D must 
be established in order to secure benefits from the present invention. 
On the basis of experimental results in FIG. 10, it can be determined that 
the optimum cushion characteristics are obtained when points A and D are 
at angles of about 5.degree. each. That is, when points A and D are at an 
angle of 0.degree., load F.sub.x, where corresponding deflection X is 40 
mm, 60 mm, and 80 mm, is now given 0.05 kg, 0.09 kg, and 0.13 kg. As a 
result, F.sub.x1 .noteq.F.sub.x2, indicates a non-linear deflection curve. 
When points A and D are each at an angle of 5.degree., the result is that 
0.068 kg, 0.102 kg, and 0.14 kg, and F.sub.x1 .apprxeq.F.sub.x2. This 
indicates a substantially constant variation in deflection X in relation 
to load F.sub.x, i.e., a substantially linear deflection curve. It can 
thereby be determined that proper critical value is five degrees and more 
preferably ten degrees or greater so as to attain benefits from the 
present invention. 
With the cushion member 12 according to this embodiment, although the 
elastic fibers 24 are wound an equal number of times, cushion 
characteristics adapted for the bodily shape of each occupant can readily 
be provided by an increased or decreased number of times of winding. 
An aeratable cushion member as high as 200 to 300 ml/cm.sup.2 /s can be 
provided by mesh-shaped grooves cut in the surface of the cushion member 
12 along the elastic fibers 24, while permeability in conventional 
urethane pads is 30 ml/cm.sup.2 /s. 
Furthermore, with a covering material 61 being made of urethane elastomers 
and the like, the cushion member 12 is washable because it is easy of 
loading and unloading.