Note: Descriptions are shown in the official language in which they were submitted.
l663
- 1 -
BACKGROUND OF THE INVE~TION
.. . .. __
This invention relates to vehicle seats of the type in
which a seat part (normally comprising a seat rest and a back
rest) is supported and guided for upward and downward movement
relative to a base part by means of a spring suspension. The
suspension includes spxing means capable of counterbalancing
the load of the seat part and its occupant so that the seat
part, under static conditions, is located at a mid-ride position
substantially midway between UP-stop and DOWN-stop positions.
Said spring means can comprise any means of taking up, storing
and giving out energy so that the seat and its occupant can
oscillate between the UP-stop and DOWN-stop positions when
subjected to external forces.
Such a vehicle seat assists in i.solating the occupant
from vibrations transmitted from the vehicle wheels, particu-
larly as the vehicle passes over rough terrain. However, the
necessary freedom of the seat part to move up and down carries
with it the danger, in the case of a driver's seat, of the
driver's feet losing correct contact with the control pedals.
Previous attempts to overcome this difficulty have largely
been based on the concept that the seat part of a suspension
seat should move pivotally about a horizontal axis through the
knee-hinges of the driver, since if such a knee-hinge axis
(sometimes referred to herein as the K axis) is fixed relative
to the base part of the seat, the lower leg, and hence the ankles,
'~
L6~3
-- 2
of the driver can remain stationary irrespective of the movemen~s
of the seat. However, if the seat rest and back rest of a
seat part move in this way, the driver's back inclination
will vary with rise and fall of the seat. This difficulty
can be overcome by incorporating a linkage to change the
inclination of the back rest with changes in the inclination
of the seat rest. ~n example of a suspension seat designed
in th.is way is found in British Patent Specification 1,156,942.
Such suspension seats have the disadvantage of a rela-
tively large fore and aft movement of the entire part of the
driver's body above his hip (H axis) since the knee hinge axis
is the axis about which the seat rest and the hip region of his
body must swing.
The present invention is based on the realisation that
if a suspension seat can be designed to move in such a way that
the seat occupant's lower leg will move about a horizontal
transverse axis through the occupantls ankle hinges (A axis),
the knee hinge axis accordingly being free to swing about
the ankle hinge axis, such a seat will a~ford the driver a
high degree of control over the vehicle over a wide range of
seat movemen~. Moreover, it is found that a seat movable in
this way affords a high degree of comfort to the driver.
Accordingly an object of the invention is to provide a
uspension seat capable of moving the seat occupant's lower leg
about a
~59~6~i3
horizontal transverse axis through his ankle hinges, at the
same time causing the seat occupantls back to move up and
down with the back res-t ol the seat at a substantially
constant inclination to the vertical. References herein to
'the ver-tical' assume the vehicle to be on horizontal ground.
In the present invention a suspended vehicle seat
provides isolation from vertical vibrations to an occupant
thereof and includes a seat part, which includes a seat rest
which is mounted for tilting movement and a back rest, a base
part, and means connecting the seat part to the base part.
The means connecting the spring part to the base part includes
a spring suspension by which the back rest is supported on the
base part and which is effective to restrict movement of the
back rest to a substantially vertical direction. The suspension
includes a spring,and a plurality of relatively movable
structural elements, certain of the elements connecting to
the seat rest and to the back rest for providing pivotal
movement of the seat rest about at least two spaced apart
horizontal transverse axes through instantaneous centers of
rotation. The centers are the instan,taneous centers of
rotation of the thigh of a seat occupant for whom the seat
is designed which is positioned on the seat rest relative
to any two of the structural elements of the seat which move
relative to each other during upward and downward movement
of the seat part relative to the base part. The pivotal
movement of the seat rest causes the thigh of a seat occupant
to remain in contact with the seat rest and to be movable
longitudinally and pivotally in such a way that the ankle
- 3~
66~
hinge axis of the seat occupant will remain stationary
relative to the base part as the seat moves above and below
its mid ride position in response to vertical vibrations.
A specific embodiment of the present invention also
provides a vehicle seat comprising a seat part having a
seat frame mounted for upward and downward movement relative
to a base part by means of a spring-biased scissor-action
suspension (as
- 3a -
~S~L663
-- 4 --
defined) the linkage arms of the suspension being arranged
to effect upward and downward movement of the seat frame
substantially without tilting movement, the seat part
further having a seat pan for supporting a seat cushion,
the seat pan having pivot connections to the seat suspension
such that during upward and downward movement of the seat,
movement of the rearward part of the seat pan takes place
in an upward and downward direction such that the movement
of the H axis is vertical, and the seat pan tilts to cause
the K axis to move along an arc permitting the A axis to
remain stationary, the H, K and A axes being as herein
defined.
By the expression 'scissor-action suspension' is
meant a suspension which comprises a pair of rigid links
having a common pivot connection in the manner of a pair of
scissors,or a plurality of pairs of such links having a
common pivot axis, one end of each link of the or each pair
having a pivot connection to a seat part of the seat and the
opposite end of each link of the pair having a pivot connec-
tion to the base part of the seat, the axes of the pivot
connections all being parallel to one another, some of the
pivot connections being fixed pivot connections but the
others being sliding or rolling connections sufficient to
give freedom of movement to the suspension in a substantially
vertical direction only, an example being described in British
.. ~
Patent No. 957,332.
~L154~;;63
-- 5 --
B~IEF SUMMARY ~F THE DRAWINGS
Figure 1 is a diagrammatic representation oE a vehicle
seat suspension of the scissor-action linkage type formed by
two transversely spaced pairs of crossed arm linkages having
cornmon pivotal axes to the base part, to the seat part and
to each other, and showing the instantaneous centres of
rotation of the moving parts of the suspension and of links
representing the upper and lower leg portions of a seat occu-
pant;
Figure 2 is a diagrammatic side elevation, part
sectional, of a vehicle seat constructed in accordance with
the invention;
Figure 2A shows a modification of the vehicle
seat of Figure 2 which involves a different instantaneou~s
centre of rotation;
Figure 3 is a diagrammatic representation of the
movement o-E the vehicle seat of Figure 2;
Figures 4 and 5 are diagrammatic illustrations of the
combination respectively of the seat rest mounting of Fig.
2A with other types of suspension;
Figures 6 to 11, are diagramrnatic illustrations of
suspensions in which the seat rest is pivoted about a pair of
instantaneous centres of rotation different from that of Figure
, .
' ' .
~5g~6~3~
2; Figure 8 and Figure 2~ utilising the same instantaneous
centres of rotation;
Figure 12 is a diagrammatic representation, corres-
poncling to that of Figure 1, of the instantaneous centres
of rotation of the parts of another type of suspension, and
Figure 13 is a diagrammatic representation of a seat
suspension in which the seat rest is pivoted at instan-
taneous centres of rotation shown in Figure 12.
DESCRIPTION OF PREFERRED EMBODIMENTS
In each of the drawings, the seat part is shown to be
supported by links lying in the plane of the drawing, and
normally a second set of links or more than two sets of links
of the same construction will be located in parallel relation-
ship to the first set of links in order to provide stable
support for the seat part. ~lowever it will be appreciated
that if the single set of linlcs appearing in the plane of the
drawing can be provided with adequa~e depth in a direction
perp~ndicular to the plane of the drawing, only one such
set of links may be needed to provide adequate support.
Before describing the invention in detail, it is
necessary to consider the basic design concepts of a seat for
achieving the object of the invention. In order to achieve
rise and fall of the driver's back without variation of its
inclination, it will normally be necessary to adopt one of
a663
- 7 -
three well-k~own basic seat suspension designs For con-
venience these will be referred to as types A, B and C in
which:-
Type A provides a back rest mounted on a seat frame,the seat frame being guided for vertical movement by a
system of scissor-action linkages, such as are described
in detail in British Patent Specification No. 957,332 and
shown in Figure 1 of the drawings accompanying the present
Specification.
Type B provides a back rest which is mounted for
upward and downward sliding movement on one or more supports
extending upwardly from the base part substantially vertically
and located behind the back rest.
Type C provides a back rest ~ ich is connected by a
parallelogram linkage system to a ~jupport upstanding from
the base part, the links of the system being horizontal or
at an angle ~o the horizontal sufficiently small ~o minimise
~ore and aft movement of the back rest with rise and fall of
the seat. An example of such a suspension can be seen in
United States Patent Specification 3,788,697.
Since, in accordance with the invention, the seat
rest must rise and fall as the back rest rises and falls,
but with a desired relative movement between the seat rest
~L5~6~i~
- 8 -
and back rest to maintain the A axis stationary, the means
for achieving this movement of the seat rest will utilise
as much as possible of the Type A, B or C suspension means
on which the back rest is supported, but with additional
supporting means to effect said desired relative movement.
If however a Type B suspension is employed to support the
back rest, the means for supporting the seat rest can con-
veniently include a Type A or Type C suspension or parts
thereof
It is now necessary to consider the way in which a
driver's body will move in relation to the parts of such
suspension in order to achieve the objective o~ the inven-
tion. Use will be made in this connection of the Method of
Instantaneous Centres o~ Rotation in considering the move-
ment of the upper leg or thigh of the seat occupant relative
to the parts of the suspension
It is considered, in this connection, that the thigh of
the seat occupant extends between point K, which is the knee
hinge, and point H which is either the hip joint or preferably
a point (sometimes referred to as PPP meaning "pre~erred
pivot point") which is somewhat behind the true hip joint.
This is the point about which the thigh effectively rotates
6~i3
g
as it rocks with the seat rest It is assumed that point H
is relatively stationary with respect to the seat frame.
It should be borne in mind
1) that the Method of Instantaneous Centres of Rotation is
based on the concept that any displacement of a body,
movable in a plane, between two positions may be
considered as a purely rotational movement about some
centre;
2) that the centre of rotation of a first link of a
mechanism relative to a second link of the mechanism
to which it is pivoted lies at the pivot;
3) that the centre of rotation of a body having linear
movement lies at infinity on a line perpendicular to
the direction of movement and
4) that if the instantaneous centre of rotation of any part x re-
lative to any part ~ is defined as the point Ix then if the
mechanism has relatively moving parts a, b, c and d,
the lnstantaneous centre I is at the intersection
a.d.
of the line connecting Ia b and Ib d with the line
connecting la.c. c.d. -
Considering first the A type suspension1 shown in Flg. 1,
this will be seen to comprise a base part 1, and two pairs of
. ~
663
-- 10 -
scissor links spaced transversely of the seat, only one being
visibleg this pair consisting of first and second links 2, 3.
Link 3 is connected at its forward end by a roller or slider 4
to the base part 1 and by a fixed pivot ~ at its rearward end
to a seat frame 6. Link 2 is connected at its forward end by
a roller or slider 5 to the seat frame 6 and by a fixed pivot
P2 at its rearward end to the base part 1. Links 2 and 3 have
a pivotal interconnection P3 at their intersection. The upper
leg or thigh of the seat occupant will be looked upon as a link
7,and the lower leg as a linlc 8 pivoted at the ankle hinge
point A to the floor, and thu~ to the base part 1. Point ~l
is regarded as Eixed relative to Erame 6
It will readily be seen from concept (2) above that the
instantaneous centres I2 1~ I4 3~ I~.3~ I5.2 and I3.2 are
established at the pivot points of the respective parts of the
suspension. Similarly from concept (3) above, it will be seen
that instantaneous centres I6 5 and I4 1 will be at infinity
on lines perpendicular to the respective guide tracks of sliders
5 or 4, or at the point of contact of guide track and rollers
5 or 4, and I6 1 will be at infinity on lines normal to the
direction of travel of seat frame 6.
By use of concept (4) above, the other instantaneous
centres can be established, the most important ones being
7.1' I7.2, I7.3~ I7 4, I7 5 and I7 6.
It will be appreciated from this that if the thigh
., - .:
~5g~63
represented by link 7 can be supported on at least two parts of
~he suspension (including the base part) at the respective
instantaneous centres of rotation of the link 7 relative
to such parts, the thigh or link 7 will move as a link of
the suspension mechanism in such a way that no displacement
of the ankle point A will occur, since point A is a fixed
point by.definition in establishing the instantaneous centres.
Since the thigh 7 can only be supported relative to
the parts of the suspension by supporting it on a seat rest,
reference will now be made to Figures2 and 3 which illustrate
a practical form of seat constructed in accordance with the
teaching of the present i.nvention,
Reference has already been made to the base part 1,
links 2, 3, roller or slider members 4, 5, and seat frame 6,
The seat part is seen to consist o the seat frame 6 together
with the seat rest 10 and back rest 11, back rest 11 being
supported on frame 6. The seat rest 10 consists of a pan or
frame 12 covered by a seat cushion 13, and back rest 11 con-
sists of a back pan 14 and back cushion 15.
The spring means for supporting the seat part 6, 10, 11
on the base part 1 is a torsion bar 17 extending within a
tube 18 to which the upper rearward end of each link 3 is
secured, The tube 18 is journalled at its ends in the seat
frame 6. One end of bar 17 is secured to one end of tube
~ 5~663
18 and the opposite end of bar 17 is connected to the frame
6 via a preload adjustment mechanism (not shown~, Manual
Operation of this mechanism by the seat occupant enables
the preload in the torsion bar 17 to be varied.
Since the scissor action links 2, 3 provide for vertical
upward and downward movement of the seat ~rame 6, the back
rest 11 can be mounted directly on the seat frame 6 to
achieve its desired upward and downward movement at a con-
stant inclination to the vertical.
Since however the seat rest 10 supports the thigh 7, it
is required, in accordance with the invention that the seat
rest shall be supported at at least two of the points I7 1
to I7 6~ Since I7 1 is close to the knee axis IC this is an
inconvenient centre at which to actually support the seat rest.
Among the most convenient instantaneous centres Eor this purpose
are I7 2' I7 3 and I7.6-
The support between the thigh 7 and link 2 is providedby a pivotal connection 20 at I7 2 between the seat pan 12
and link 2. Since however I7 3 is at a relatively long
distance from the seat~ pivotal movement of the seat pan 12
about I7 3 is simulated by mounting a plate 21 on link 3,
the plate 21 being part cylindrical about a horizontal axis
through I7 3, and mounting a roller 22 on seat pan 12 to roll
on plate 21,
663
An even more convenient pair of centres are I7 2 and I7 6
Mounting of the seat pan for movement about I7 6 is simulated,
as seen in the fragmentary illustration in Fig. 2A, by causing
roller 22 to roll on a plate 23 fixed directly to the seat
frame 6 and curved about the horiæontal axis through I7 ~.
Alternatively, the seat pan 12 could be positively
supported on the transverse horizontal axis through I7 ~ by
providing arms (as in Figs. 6 and 10) connec-ted to and projecting
from seat frame 6 and seat pan 12 alongside the seat occupant,
the respective arms being interconnected by pivots on the
said transverse axis through I7 6. The connections from the
arms to the seat frame 6 and seat pan 12 will be such as to
support the seat pan on the seat frame.
The manner in which the seat rest moves when supported
at I7 2 and I7 3 is illustrated in Fig. 3, the Eull line of
the seat part correspondlng to the mid-ride position, and the
UP- and DOWN-stop positions being shown in chain-dotted lines.
In the description which follows,reference n~tmerals 1
to 8 will be retained so far as possible to represent the
same type of parts shown in Figure 2 in spite of minor
variations in the shape and function of the parts, in order
to avoid the confusion which would occur from the adoption
of different references. References 2 and 3 wlll denote
any two links by means of which the seat part is mounted on
the base part.
Thus in Figure 4 there is shown,in skeleton form, a
- l4 -
~ 5~ 66~
type B suspension in which the back rest 11 is guided for
vertical movement by sliding on a vertical rod la forming
part of the base part I9 and the seat rest 10 is supported
by links 2 and 3 of a modified type A suspension. Since the
links 2 and 3 are no longer required to maintain the vertical
movement of the seat, the type A suspension has been modified
by omitting the lower rearward half of link 2 Alternatively
the link 3 could hav~ been omitted, (as in Fig. 8). The seat
rest 10 in this case is supported, as in Fig. 2 ~, at the
instantaneous centres of rotation I7 2 and I7 6.
Figure S illustrates a modification of the seat suspen-
sion of Figure 4 in that the type B suspension has been replaced
by a type C suspension. In this case, the links of the
modified type A suspension on which the seat rest is supported
are indicated by re~erences 2A, 3A. The linlcs of the type C
suspension by which the seat frame 6 is mounted on the base l
are indicated by references 2C and 3C.
Figure 6 shows in skele~on form a modified type A
suspension on which the seat part 10 is supported at instan-
taneous centres of rotation I7 5 and I7 6. The support at
I7 5 is achieved by providing a rigid link 30 connecting slider
or roller 5 to a slider or roller 31 movable in a horizontal
guide on the seat frame 6 and a part 30a upstanding from
link 30 having a pivotal and sliding connection at point I7 5
:`
~ '`' ' ' ' .~;
~59L~i63
- 15 -
to the seat part 10~ A rigid link 32 rigidly connected to the
seat frame 6 extends therefrom to a pivot connection 33 on an
upstanding side member lOa of the seat part 10 at I7 6. Alter-
natively, instead of allowing link 30a to slide relative to pivot
34, the link 32 coul~ be pivoted to seat frame 6 instead of being
rigidly fixed. As shown a type B suspension is used to maintain
the vertical movement of the seat frame 6. Alternatively, the
vertical movement could be achieved by converting the modified
type A suspension, on which the seat part 10 is supported, to
a full type A suspension.
Figure 7 is a diagrammatic view, in skeleton form, of a
modified type A suspension supporting a seat rest 10, with a
type B suspe~sion supporting the back rest, and in which the
seat rest 10 is pivoted at I7 2 and I7 5. ~he pivot connection
at I7 2 is achieved as shown in Fig. 2. The I7 5 connection
however is provided by a rigid link 40 connected between slider
or roller 5 and a slider or roller 41 both moving in horizontal
guides on frame 6, with a link ~2, pivotally connected to and
upstanding from link 40, the link 42 having a pivotal connec-
tion 43 to the seat rest 10 at I7 5.
As an alternative to the modified type A suspension as shown,
one could us~ a different modified type A suspension, for example
as in Fig. 6. A full type A suspension could be used for
controlling the movement of the back rest.
Figure 8 is a representation9 in skeleton form, of a modified
type A suspension on which the seat rest 10 is supported at I7 2~
~5~66
- 16 -
as described in connection with the embodiment of Fig. 7, andat I7 6 as described in connection with the embodiment of
Fig. 6.
Figure 9 i9 a representation, in skel.eton form, of a
seat part 10 supported a~ I7 6 as in Figure 8, and also at
I7 1 In view of the difficulty of providing actual support
at the point I7 1' the desired effect is achieved by pivotally
connecting first and second rods 45, 46, at one end thereof
to base part 1 and at their opposite end to a coupling rod 47
such that, as the system of rod 45-47 is moved pivotally a
point on the rod 47 moves along an arc of a circle centred at
point I7 1 An arm 48 rigidly fixed to the underside of the
seat part 10 has a pivotal connection 49 to the above mentioned
point on rod 47 so that pivotal connection 49 moves instan
taneously about centre I7
Figure 10 is a representation, in skeletob form, of a
seat part lO supported at I7 6 ànd at I7 1 by means different
from those sho~n in Figure 9. In the present case, the
support at I7 6 differs from that of Figure 9 in that a
swinging link 50 depends from pivot connection 33 to a pivot
connection 51 on the seat part 10. The support at I7 1 is
provided by an assymetric scissor-action linlcage in which iinks
52, 53 of the linkage have roller connections 54, 55 on the
base 1 and seat part 10 respectively, and fixed pivot connections
56, 57 on the seat part 10 and base part 1 respectively.
,
~59L66~
- 17 -
Figure 11 is a representation, in skeleton form, oE a
seat part 10 supported at I7 6 as in Figures 8 and 9, and at
I7 1 In this case, the support at I7 1 is provided by an arm
60 rigidly fixed to the seat part 10 and carrying a roller 61
at its lower end, the roller rolling on a part-cyclindrical
sur~ace lb on base 1, the surface lb being arcuate about a
horizontal axis through I7 l
Figure 12 shows diagrammatically a type C suspension
on which a seat -frame 6 i9 supported ~or vertical movement
relative to a base 1 by two parallel links 2, 3 pivoted
at their opposite ends to frame 6 and base 1. By the same
method as was used in relation to Figure 1, the instantaneous
centres of rotation of the thigh 7 of the seat occupant to
parts 1, 2 and 6 have been plotted to provide four centres
I7 1' I7 2' I7 3 and I7 6 at any two of which a seat rest could
be pivoted .
Figure 13 shows diagrammatically a type C suspension in
accordance with the teaching5 o~ Figure 12, in which an arm 65
~1~ii4~i3
upstanding from link 3 has a pivo-tal connection 66 at I7 3
with the seat part 10. A further arm 67 upstanding from
link 2 has a pivotal connec-tion 68 at I7 2 with the seat
part lOo The pivotal connection 66 (as shown) or 68 may
need to be received in a slot in the associated arm to permit
some freedom for relative translational movement.between
connections 66 and 68.
If the two instantaneous centres of rotation selected
as pivot axes of the seat rest do not at all times provide
stable support for the seat rest, the latter can be supported
at one or more further instantaneous centres of rotation.
For example, two separate arcuate surface and roller connections
at the front and rear of the seat part could be provided to
permit rotation of the seat part about centre I7 6.
A closely related invention is disclosed and claimed
in applicant's copending Canadian P~atent Application serial
no. 347,272, filed March 7 r 1980 .
The description and teaching oE the invention given
above will enable those skilled in the art to devise many
other alternative embodiments within the scope of the
invention~ and these various supporting means can be combined
together in many different ways which will equally be apparent
to those skilled in the art.
- 18 -
