Seat suspension device

A seat suspension device which comprises an upper frame, a lower frame, a pair of linkage mechanisms provided between the upper and lower frames, and a torsion bar which elastically supports the seat upon the suspension device. The torsion bar is so arranged that it extends along the lateral bar section of one of the upper and lower frames, with its support end portion being secured at the other of the upper and lower frames, so as to resiliently support the upper frame. Further, the linkage mechanisms have downwardly arced upper portions in each of their links. Thus, these structures permit the lowering of the upper frame or the seat down to a lowest possible degree without interference of the parts of the linkage mechanisms and torsion bar.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a seat suspension device for use in an 
automotive seat. 
2. Description of the Prior Art 
In general, jolting or rolling experienced during driving an automobile on 
a rough road is reduced by use of a seat suspension device which is 
installed beneath the seat for resiliently bearing the same. 
A typical example of conventional seat suspension device of this kind is 
shown in FIG. 1 of the accompanying drawings, wherein the device as a 
whole is generally designated by (1), which has a lower frame (2) fixed to 
the floor (not shown) of an automobile, and an upper frame (3) bearing a 
seat cushion frame (not shown) to which an automotive seat is mounted. 
As shown, a pair of X-shaped links (5)(5') are provided between the lower 
and upper frames (2)(3) to permit vertical movement of the upper frame (3) 
relative to the lower one (2). Each of the X-shaped links (5)(5') is 
composed of two links (6)(7) crossed at a pivot point (8) in a manner 
rotatable thereabout, such that the first link (6) is at its lower end 
fixed to a lower fixed spindle (9) rotatably supported on the lower frame 
(2) and at its upper end connected to an upper movable spindle (10) which 
is provided with a pair of rollers (10a) for allowing the upper end of the 
link (6) to move in the longitundinal direction of the lateral bar 
sections of the upper frame (3), whereas the second link (7) is at its 
upper end rotatably connected to an upper fixed spindle (11) journalled at 
the upper frame (3) and at its lower end connected to a lower movable 
spindle (12) which is also provided with a pair of rollers (12a) for 
movements of the lower end of the link (7) in a same direction as in the 
upper end of the first link (6). A torsion bar (13) is arranged centrally 
of the thus-constructed X-shaped links (5)(5'), passing through the pivot 
portions (8), with its one terminal portion (13a) being curved and secured 
at the first link (6) of the X-shaped link (5) in a direction opposite the 
other terminal portion (13a') which is secured via an adjustment mechanism 
(15) at the upper part of the second link (7) of the opposed X-shaped link 
(5). 
According to this prior art, when a downward load is applied to the seat 
suspension device (1), the X-shaped links (5) are lowered, causing both 
terminal portions (13a)(13a') of the torsion bar (13) to move away from 
each other, whereby the torsion bar (13) produces an elastic repercussive 
force via its terminal portions (13a)(13a') against the lowering of the 
X-shaped links (5) so as to absorb a jolt or vibration of the automobile. 
However, such structure of the prior art suspension device is not adaptable 
for use in a small automobile with limited space and a truck whose floor 
is generally higher, in that the torsion bar (13) extends transversely and 
centrally of the suspension device (1), which is a limit against the 
bottom line of a cushion body laying centrally of the device (1). This 
means that the bottom line of the cushion body can not be further lowered 
into the central portion of the suspension device (1), as a result of 
which the buttocks position of an occupant sitting on the seat is not 
lowered to a lowest possible level, and therefore it is impossible to 
design a seat of low seating level that is suitable for use in the small 
automobile or truck. 
SUMMARY OF THE INVENTION 
In order to eliminate the above-stated drawback, it is a purpose of the 
present invention to provide an improved seat suspension device which 
allows for receiving a seat cushion body therein so that the bottom of the 
seat cushion body may be lowered at a lowest possible degree. 
In achieving this purpose, the present invention comprises a seat 
suspension device of such linkage type wherein an upper frame bearing a 
seat is movable vertically relative to a lower frame fixed on the floor of 
an automobile via a pair of link mechanisms interposed between the upper 
and lower frames, and a torsion bar arranged on the lower frame such that 
it extends along the longitudinal direction of the lateral bar section of 
the lower frame, with its base end portion being secured on the lower 
frame side and its support end portion being disposed externally of the 
link mechanisms and secured at the upper frame side, whereby the upper 
frame is resiliently supported in a manner movable vertically relative to 
the lower frame. 
Accordingly, when an occupant sits on the seat, the link mechanisms and the 
upper frame are lowered due to his or her weight, while simultaneously the 
upper frame is applied an elastic repercussive force from the torsion bar 
which is twisted by the lowering upper frame, and supported resiliently 
thereby, and it will be appeciated that since the torsion bar is arranged 
laterally of the device, the bottom of the seat cushion body is lowered 
through the center of the seat suspension device without interference of 
the torsion bar, whereupon the buttocks position of the occupant can be 
lowered at a desired low level or down to a lowest possible degree towards 
the floor of the automobile.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION 
With reference to FIGS. 2-5, one preferred embodiment of the present 
invention will be described hereinafter. 
At first, in this embodiment, many of the reference numerals and characters 
used in the above-stated description of the prior art will be used, in 
view of a similar structure of seat suspension device to the prior art 
one, and as such all like reference numerals and characters in the former 
correspond to all like ones that will be indicated hereinafter, so that 
the specific description is eliminated thereof. 
A seat suspension device (1) comprises an upper frame (3), lower frame (2), 
and a pair of X-shaped links (5)(5') interposed between the upper and 
lower frames (3)(2) such that the upper frame (3) is movable vertically 
relative to the lower frame (2) in a manner similar to the conventional 
device (1) as stated above. 
It should be noted here that the upper frame (3) in the present embodiment 
also constitutes a seat cushion frame associated with a seat cushion body 
(4). This is intended to provide a single frame between the seat 
suspension device (1) and the seat cushion body (4) with a view to 
reducing the height of the seat cushion body (4) with respect to the floor 
of the automobile (not shown). 
With respect to a pair of the X-shaped links (5)(5'), a description will be 
given mainly of the X-shaped link (5). Link (5) comprises a first link 
member (6) and second link member (7) such that the crossing point or 
pivot portion (8) of those two link members (6)(7) is located lower; in 
other words, the first and second link members (6)(7) respectively have 
upper long arcuate sections (6a)(7a) that extend upwardly away from each 
other at the pivot portion (8), and further respectively have lower short 
rectilinear sections (7a)(7b) that extend downwardly away from each other 
at the pivot portion (8), with the former sections (6a)(7a) being longer 
than the latter sections (6b) (7b), respectively. 
The upper long arcuate sections (6a)(7a) are at their respective lower 
edges formed with semicircular cut-away portions (6a1)(7a1) which are so 
disposed as to be engagable with the upper surface of a lower movable 
spindle (12) and that of a lower fixed spindle (9), respectively. The 
lower movable and lower fixed spindles (12)(9) are provided on the lower 
frame (2), and also provided on the lower frame (2) are the lower ends of 
the first and second link members (6)(7), in the same manner as in the 
above-stated prior art. 
The other opposite X-shaped link (5') is constructed in a similar way to 
the above-mentioned X-shaped link (5) with its members or elements 
designated by numerals or characters with dashes being formed and 
assembled in the same manner with those of the X-shaped link (5), and so, 
specific description thereof is omitted. 
On the lower frame (2), a torsion bar (13) is mounted such that it extends 
along the lateral bar section of the lower frame (2), which comprises a 
support end portion (13a), an intermediate portion (13b) and a base end 
portion (13c) in an integral manner. As best seen in FIG. 2, those three 
integral portions of the torsion bar (13) are of such structure that the 
support end portion (13a) is bent externally of the lower frame (2) at a 
substantially right angle relative to the intermediate portion (13b) in a 
sense to direct inwardly of the lower frame (2) and further twisted in an 
upwardly inclined manner from the intermediate portion (13b). This 
particular intermediate portion (13b) is secured on the upper surface of 
the lateral bar section (2a) of the lower frame in a manner to be 
explained later, extending along the longitudinal direction of that 
lateral bar section (2a), and the base end portion (13c) is bent at a 
substantially right angle relative to the intermediate portion (13b), 
extending horizontally therefrom in a direction inwardly of the lower 
frame (2). The support end portion (13a) is secured at the side of the 
upper frame (3) in such a manner as to be disposed externally of the 
X-shaped link (5) through a torsion force adjustment mechanism (15) 
provided on the lateral surface of the upper frame (3) adjustment 
mechanism (15) will be described later. On the other hand, the base end 
portion (13c) is secured by a bolt-like headed extension (9a) of the fixed 
spindle (9) which is projected at the rearward portion of the lower frame 
(2). 
It therefore can be seen that the torsion bar (13) thus constructed, 
resiliently urges, at its support end portion (13), the upper frame (3) in 
an upward direction away from the lower frame (2), thereby offering a 
cushiony effect to the upper frame (3) and thus to the seat cushion body 
(4), and the torsion bar (13) as a whole is positioned distant from the 
X-shaped links (5)(5') so as to avoid the interference of the former with 
the latter. 
As shown in FIG. 5, the torsion bar (13) is secured by means of a pair of 
spaced retaining members (16)(16') which are fixed on the upper surface of 
the aforementioned lateral bar section (2a) of the lower frame (2) such 
that the torsion bar (13) is rotatable via a pair of spilt bushes 
(17)(17') within the retaining members (16)(16'). Specifically, the two 
retaining members (16)(16') are respectively formed with circular bores 
(16a)(16a') each having an inner diameter generally equal to the 
respective outer diameters of the two spilt bushes (17)(17') firmly 
encircling the outer surface of the intermediate portion (13b) of the 
torsion bar (13), and are further respectively formed with opened portions 
(16a)(16a') which extend along the longitudinal direction of the 
respective circular bores (16a)(16a'), establishing opened communication 
with those bores (16a)(16a'), whereupon each of the retaining members 
(16)(16') assumes a substantially shaped configuration in section. The 
thus-formed retaining members (16)(16') are arranged such that the opened 
portions (16a)(16a') thereof face in a direction opposite to each other in 
order to resist a component force generated from a load (P) applied to the 
support end portion (3a) of the torsion bar (13). Specifically, the first 
retaining member (16) receiving the intermediate portion (13b) adjacent to 
the support end portion (13a) is so arranged that its opened portion (16a) 
faces inwardly of the lower frame (2) to thereby resist an outwardly 
exerted component force (F1) generated through the torsion bar (13) from 
the load (P) in a direction outwardly of the lower frame (2). In contrast, 
as to the second retaining member (16') receiving the intermediate portion 
(13b) adjacent to the base end portion (13c), its opened portion (16a') 
faces outwardly of the lower frame (2) to thereby resist an inwardly 
exerted component force (F2) which is further produced through the torsion 
bar (13) due to the resistance of the first retaining member (16) in a 
direction inwardly of the lower frame (2). (See FIG. 1) 
The foregoing two split bushes (17)(17') are spaced from each other on the 
intermediate portion (13b) at a distance equal to that of the two spaced 
retaining members (16)(16'). 
Securing the intermediate portion (13b) of the torsion bar (13) on the 
lower frame (2) is effected by inserting the same at its two spaced split 
bushes (17)(17') into the opened portions (16b)(16b') of the retaining 
members (16)(16') and then snap fitting it in the bores (16a)(16a') 
thereof, respectively. 
The torsion force adjustment mechanism (15) to which the support end 
portion (13a) of the torsion bar (13) is operatively connected is a 
conventional one that has been commonly used in this particular field, and 
no specific description thereon is included. But, for the sake of 
understanding, the basic construction of the adjustment mechanism (15) is 
such that there is provided an operation knob (15a) and a cam member (15b) 
having plural discrete cam surfaces, which is rotated by operation of the 
knob (15a) to provide varied heights of the cam surface. Against one of 
those plural cam surfaces of the cam member (15b), is abutted the support 
end portion (13a) of the torsion bar (13). By operation of the knob (15), 
the cam member (15b) is caused to rotate, changing its cam surface to 
another different one, whereby such variation of cam surface height causes 
the corresponding variation of torsion angle of the support end portion 
(13a), thus enabling adjustment in the elastic repercussive force of the 
torsion bar (13) against the upper frame (3). 
Between the upper and lower frames (3)(2), a shock absorber (18) is 
obliquely provided for the purpose of absorbing a sudden great load such 
that its upper end is pivotally fixed on the rear surface of the upper 
frame (3) and its lower end is pivotally fixed on the latteral surface of 
the lower frame (2). 
With the present invention constructed as above, the upper frame (3), when 
a downward load is applied, in case of an occupant sitting on the seat 
thereon, is lowered towards the lower frame (2), with the lowering of the 
X-shaped links (5)(5'), which causes the twistingly rotation of the 
support end portion (13a) of the torsion bar (13) in a downward direction 
in relation to the intermediate portion (13a) thereof, with the result 
that the torsion bar (13) creates an elastic repersussive force at its 
support end portion (13a) so sufficiently as to support the upper frame 
(3) resiliently at a given level determined by the torsion adjustment 
mechanism (15). 
Further, in accordance with the present invention, the torsion bar (13) is 
provided along one lateral bar section (2a) of the upper frame (2) with 
its support end portion (13a) disposed externally of the X-shaped link 
(5), and the shock absorber (18) is so arranged that it is disposed 
externally of the seat suspension device (1), and therefore, the bottom of 
the seat cushion body (4), when lowered down, is not contacted with those 
torsion bar (13) and shock absorber (18). 
Still further, in the present invention, the downwardly arced shape of the 
upper arcuate sections (6a)(6a')(7a)(7a') of the X-shaped links (5)(5') is 
advantageous in that, when the X-shaped links (5)(5') are lowered, the 
upper arcuate sections (6a)(6a') (7a)(7a') thereof are displaced outwardly 
at a far distance as compared with merely rectilinearly formed link 
members of the previously stated prior-art X-shaped links, to thereby 
ensure preventing those sections (6a)(6a')(7a)(7a') from contact with the 
bottom portion of the seat cushion body (4) being lowered. Accordingly, 
there is no possibility of the seat cushion body (4) being contacted with 
the X-shaped links (5)(5'). 
Thus, it will be appreciated that the seat cushion body (4) on the 
above-described suspension device (1) can be lowered down to a lowest 
possible degree without any obstruction of surrounding elements of the 
suspension device (1) as such, in conjunction with the simple provision of 
the upper frame (3) between the seat cushion body (4) and the X-shaped 
links (5)(5'), it is readily possible that the buttocks position (a) of an 
occupant on the seat cushion body (4) can be lowered to a lowest possible 
level, as seen in FIG. 3(B). Moreover, the provision of the semi-circular 
cut-away portions (6a1)(7a1)(6a1') (7a1') in the X-shaped links (5)(5') 
allows further lowering of the seat cushion body (4) as well as the 
buttocks position (a) of the occupant thereon, by the reason of the fact 
that when those cut-away portions (6a1)(7a1)(6a1')(7a1') are nearly 
engaged with the lower fixed and lower movable spindles (9) (12), 
respectively, as in FIG. 3(B), the X-shaped links (5)(5') are further 
lowered to a degree substantially corresponding to the depth of the 
cutaway portions (6a1)(7a1)(6a1')(7a1'). Accordingly, the seat suspension 
device (1) in accordance with the present invention can readily be 
installed in a small automobile with limited interior space or in a truck 
having a relatively high floor. 
Another advantage of the present invention is that the torsion bar (13) is 
secured on the lower frame (2) simply by the two retaining members 
(16)(16') of which opened portions (16b)(16b') receiving the torsion bar 
(13) are directed opposite to each other, which expedites the mounting of 
the torsion bar (13) to the lower frame (2) with far more ease. 
In addition, the fact that the torsion bar (13) is directly connected with 
the upper and lower frames (3)(2) at its support end portion (13a) and 
base end portion (13c), respectively, not through the X-shaped links 
(5)(5'), serves to avoid the hard frictional contact of the torsion bar 
(13) with the parts of the X-shaped links (5)(5'), thus resulting in a 
much more increased length of use life of the torsion bar (13). 
While in the above-described embodiment the torsion bar (13) is mounted on 
the lower frame (2) with its support end portion (13a) being secured at 
the upper frame (2), it may be arranged, reversely, that the torsion bar 
(13) is mounted on the upper frame (3) with its support end portion (13a) 
being secured at the lower frame (2). 
Also, while in the embodiment the X-shaped links (5)(5') are used, yet 
another kinds of linkage mechanisms such a parallel linkage structure may 
be provided for vertical movements of the seat suspension device (1). 
Finally, it should be understood that the present invention is not limited 
to the illustrated embodiments but other replacements, modifications, and 
additions may structurally be possible without departing from the spirit 
and scope of the appended claims for the invention.