Seat back support mechanism

A back support mechanism for supporting the back of a seat in a motor vehicle, wherein the seat back support mechanism includes at least one first component adapted to be connected to the squab of the seat or to a frame supporting the squab of the seat, and at least one further component adapted to be connected to the back of the seat. A connection between the components includes a linkage to permit the further component to move with first and second pivotal actions relative to the first component. The linkage includes two pivot link elements which are respectively mounted to effect a pivotal movement relative to the at least one first component. The pivot link elements directly or indirectly support the further component. The pivot link elements permit the further component to effect an initial rearward pivotal movement which constitutes the first pivotal action before effecting the second pivotal action. The connection includes a deformable element which resists the second pivotal action. The deformable element is adapted to deform to permit the second pivotal action when subjected to a force in excess of a predetermined threshold.

BACKGROUND OF THE INVENTION 
The present invention relates to a seat back support mechanism and more 
particularly, relates to a seat back support mechanism for supporting the 
back of a seat intended to be mounted in a vehicle. A preferred seat back 
support mechanism in accordance with the invention may incorporate a 
recliner mechanism. 
When a vehicle with a conventional seat is involved in a rear impact, the 
seat may be accelerated with a substantial forward acceleration since the 
seat is secured to the floor of the vehicle. The posterior and torso of an 
occupant of the vehicle sitting on the seat will consequently be 
accelerated, because of the intimate contact between the seat, and the 
back of the seat, and the posterior and torso of the occupant. The head of 
the occupant, however, is not in direct contact with the seat and, due to 
its inertia, will tend to remain stationary. Since the posterior and torso 
are being accelerated forwardly, this means that effectively the head of 
the occupant may move rearwardly relative to the torso, thus bending the 
neck of the occupant. This can cause injury to the occupant. 
It is now believed that the risk of injury to an occupant of a vehicle can 
be diminished if the back of the seat is mounted in such a way that the 
top part of the seat back can move forwardly to support the head of the 
occupant and also in such a way that the seat back can subsequently 
"yield", at least to a predetermined extent, during a rear impact. In this 
way, the torso of the occupant can be caused to accelerate in a more 
gradual manner, and the head of the occupant can be supported thus 
reducing the risk of injury. 
SUMMARY OF THE INVENTION 
The present invention seeks to provide a seat back support mechanism which 
is adapted to permit the back of the seat to yield when subjected to a 
predetermined minimum force. 
According to this invention there is provided a back support mechanism for 
supporting the back of a seat in a motor vehicle, the seat back support 
mechanism comprising at least one first component adapted to be connected 
to the squab of the seat or to a frame supporting the squab of the seat, 
and at least one further component adapted to be connected to the back of 
the seat, the mechanism comprising a connection between the components, 
the connection including means to permit the further component to move 
with a first pivotal action relative to the first component, and also with 
a second pivotal action relative to the first component, there being an 
element which resists second pivotal action, element being adapted to 
deform to permit the second pivotal action when subjected to a force in 
excess of a predetermined threshold. 
Preferably the element is of arcuate form, each of the opposed ends of the 
element being connected to a respective one of components, the two ends 
being adapted to be moved towards one another, with a consequent 
collapsing of the arcuate element, as the further component effects the 
second pivotal movement relative to the first component. 
Conveniently the arcuate element is provided with a notch on the interior 
of the arc to assist in the defortmation of element. The notch may be a 
"v"-shaped notch. 
Advantageously a linkage is provided comprising two pivot link elements, 
the pivot link elements each being mounted to effect a pivotal movement 
relative to at least one first component, the pivot link elements directly 
or indirectly supporting further component, the pivot link elements 
permitting further component to effect an initial rearward pivotal 
movement which constitutes first pivotal action before effecting second 
pivotal action. 
Conveniently one of the pivot link elements comprises the deformable 
element. 
Preferably the deformable element is connected by a pivot pin to an integer 
supporting the further component, the pivot pin extending into a guide 
aperture which is fixed in position. 
Advantageously the integer supporting the further component comprise a 
recliner support plate which supports a recliner mechanism, the recliner 
mechanism comprising a support arm which constitutes the further 
component. 
Conveniently release means are provided to prevent premature movement of 
the pivot links. The release means may comprise a frangible means, adapted 
to break when subjected to a predetermined force. Alternatively, the 
release means may comprise mechanically or electro-mechanically operated 
release means in the form of a retractable locking pin or the like, the 
retractable locking means being retracted in response to a predetermined 
acceleration of the vehicle being sensed by an appropriate sensor. The 
sensor may effect retraction of the retractable pin or may control a 
solenoid or the like. 
Advantageously the means to permit the further component to move with a 
first and second pivotal action are connected to a support plate which is 
mounted to effect a pivotal motion relative to the first component, means 
being provided to lock the support plate in position. 
Preferably the means provided to lock the support plate in position 
comprise a pivotally mounted lever which initially engages the support 
plate to lock the support plate in position, and is movable to a position 
in which the lever is disengaged from the support plate to permit a 
pivoting movement of the support plate. 
The invention also relates to a vehicle seat incorporating a seat back 
support mechanism as described above.

DETAILED DESCRIPTION OF THE INVENTION 
Referring initially to FIGS. 1 and 2 of the accompanying drawings, a seat 
back support mechanism 1 is adapted to be mounted between the squab of the 
seat, or a frame supporting the squab of the seat, which is connected to 
the floor of the motor vehicle, and the back of the seat. The mechanism is 
adapted to provide a "recliner" effect and is also provided with means 
which can be actuated to permit the back of the seat to be tilted 
forwardly, which may prove convenient if, for example, the seat is the 
front seat in a two-door motor car. As will be described, the support 
mechanism is so designed, that during a rear impact, the back of the seat 
may effect a first movement relative to the squab of the seat, if the 
force applied to the back of the seat exceeds a certain limit in which the 
lower part of the back of the seat moves rearwardly and the top part of 
the back of the seat moves forwardly. Subsequently the back of the seat 
may effect a movement, if the force applied to the back of the seat is in 
excess of a predetermined threshold, during which the back of the seat 
effectively tilts rearwardly, with the bottom part of the back of the seat 
remaining substantially stationary and the top part of the back of the 
seat moving rearwardly. 
Considering the components that together constitute the mechanism 1 as 
illustrated in FIGS. 1 and 2, it is to be understood that the mechanism 
comprises a front main support plate 2 of substantially triangular form, 
and a rear main support plate 3 of a substantially corresponding form, the 
plates 2 and 3 forming the outer parts of the mechanism, the remaining 
components being located between the outer plates 2 and 3. 
The front main support plate 2 is provided with a first aperture 4 
co-aligned with a corresponding first aperture 5 formed in the rear main 
support plate 3. A bearing 6 passes through these apertures and pivotally 
supports two intermediate components as will be described hereinafter. 
The front main support plate 2 defines a further aperture 7 which is 
co-aligned with a corresponding further aperture 8 formed in the rear main 
support plate 3. A bolt 9 is provided which passes through the co-aligned 
apertures 7 and 8, the bolt 9 being associated with a nut 10 located 
adjacent the rear main support plate 3. One intermediate element is 
pivotally mounted on a bearing surface provided on the bolt 9, as will be 
described hereinafter. 
The front main support plate 2 defines two further apertures 11, and the 
rear main support plate defines two further co-aligned apertures 12. Each 
pair of apertures 11,12 receives a respective spacer element 13,14, the 
spacer elements being located between the front and rear main support 
plates. 
The front and rear main support plates 2,3 are provided with means to mount 
the described mechanism in position on the squab of a vehicle seat or on a 
frame which supports the squab of a vehicle seat. 
The bearing 6 pivotally supports an intermediate support plate 15. The 
intermediate support plate 15 defines a first aperture 16 which receives 
the bearing 6. The intermediate support plate 15 can thus pivot about an 
axis defined by the aperture 16 and the bearing 6. The lower part of the 
intermediate support plate defines a recess 37. A locking lever 18 is 
provided having a forward end 19 which has an exterior profile 
corresponding to the profile of the recess 17. The locking lever 18 has 
formed therein an aperture 20 which is located between the forward end 19 
and a protruding handle portion, The aperture 20 of the locking lever 18 
receives the bearing on the bolt 9 so the locking lever is pivotally 
mounted for pivotal rotation about the axis defined by the bolt 9. The 
locking lever 18 is mounted in a position which is co-planar with the 
intermediate support plate 15. The locking lever 18 may move from a first 
position, in which the forward end 19 of the locking lever is snugly 
received within the recess 17 engaging the intermediate support plate 15, 
thus preventing rotation of the intermediate support plate 15 in either 
sense about the axis defined by the bearing 6 and the aperture 16, and a 
release position, in which the forward end 19 of the locking lever 18 is 
disengaged from the intermediate support plate 15, thus permitting the 
intermediate support plate 15 to pivot in a forward direction (i.e. a 
counter clockwise direction as viewed in FIGS. 1 and 2) about the axis 
defined by the bearing 6 and the aperture 16. This movement can be 
effected when it is desired to tilt the back of the seat forwardly. 
The intermediate support plate 15 defines a substantially triangular guide 
aperture 21, the function of which will become clear from the following 
description. 
The intermediate guide plate 15 defines an aperture 22 which receives part 
of a release element 23, the function of which will become clear from the 
following description. 
The intermediate support plate 15 defines a further aperture 24 which 
receives a pivot pin 25 which is also received in an aperture 26 formed in 
one end of an elongate pivot link 27. The link 27 is thus mounted for 
pivotal movement about an axis defined by the pivot pin 25. 
The pivot link 27 is of elongate form. At the centre of the pivot link 27 
is an aperture 28. In an initial position of the pivot link, the aperture 
28 in the link 27 is co-aligned with the aperture 22 in the intermediate 
support plate 15. The release element 23 which is engaged with the 
aperture 22 has a small extending frangible stud which is located in the 
aperture 28. The stud thus serves to maintain the pivot link 27 in its 
initial position. The pivot link 27 defines, at the end remote from the 
aperture 26, a further aperture 29, that further aperture 29 receiving a 
further pivot pin 30 The pivot pin 30 is received in an aperture 31 formed 
in a recliner support plate 32. The recliner support plate 32 will be 
described in greater detail hereinafter. 
A second pivot link 33 is provided which effectively co-operates with the 
first pivot link 27 to provide a parallel linkage between the intermediate 
support plate 15 and the recliner support plate 32. The second pivot link 
33 is of arcuate form having a first aperture 34 at one end, which 
receives the bearing 6, and having a second aperture 35 at the other end, 
which receives a pivot pin 36, the pivot pin 36 also being received in an 
aperture 37 provided for that purpose in the recliner support plate 32. It 
is to be noted, however, that part of the pivot pin 36 extends to the 
other side of the second pivot link 33 and is received within the 
triangular guide aperture 21 formed in the intermediate support plate 15. 
The second pivot link 33 is of arcuate form, A "V" notch or recess 38 is 
provided substantially at the mid point of the link on the interior side 
of the arc. 
The recliner support plate 32 comprises a component that is adapted to be 
connected to the back of a seat and is, of itself, of substantially 
conventional form, defining an aperture 39 that is provided, about its 
periphery, with a plurality of inwardly directed teeth 40. The aperture 
thus effectively forms the ring gear for a planetary gear system. The 
planetary gear system is mounted between two carrier plates 41,42. The 
carrier plate 42 is formed integrally with a support arm 43 that is 
adapted to be connected directly to the frame forming the back of a seat 
It is to be appreciated that a seat back support mechanism, as described 
with reference to FIGS. 1 and 2, will be provided on each side of the 
seat, the support arms 43 engaging two arms of an inverted "U"-shaped 
frame that forms an essential component of the back of the seat. 
It is to be appreciated that the planetary gear mechanism comprising the 
aperture 39, the carrier plates 41 and 42 and the associated co-operating 
gears may be provided with an adjusting knob, to enable the degree of 
inclination of the back of the seat to be adjusted, and is conventional. 
It will now be understood more clearly that when the locking lever 18 is 
moved, by actuating the handle, to a position in which the forward end 19 
is disengaged from the recess 17, the intermediate plate 15 can be tilted 
forwardly, effecting a pivotal motion about the axis defined by the 
bearing 6. The pivot link 27 is locked to the intermediate plate 15 by the 
release element 23 and consequently, when the lock lever 18 is disengaged 
from the intemediate support plate 15, the back of the seat may be tilted 
forwardly. 
Referring now to FIGS. 3 to 5, there is illustrated the relative position 
of the intermediate support plate 15, the first pivot link 27 and the 
second pivot link 33 together with the position of the recliner support 
plate 32. These four components together effect a predetermined movement 
when a vehicle in which the seat back support mechanism is provided is 
involved in a rear impact. 
FIG. 3 illustrates the four components of interest, when in an initial 
condition. It is to be observed that the pivot pin 36, at the lower end of 
the second pivot link 33, is located at a forward position within the 
generally triangular aperture 21 formed in the intermediate support plate 
15. The recliner support plate 32 is in such an orientation that the back 
of the seat (with the particular adjustment of the recliner mechanism 
illustrated) is vertical, as indicated by the line 45. 
If the vehicle is subjected to a rear impact, a substantial rearwardly 
directed force is applied to the back of the seat. This initially causes 
the pivot links 27,33, to commence a rearward pivoting motion. The 
rearward pivoting motion of the links is only permitted to proceed if the 
force applied to the back of the seat is sufficiently large to break the 
frangible part of the release element 23 that is received within the 
aperture 28 of the first link 27. Thus, if the rear impact is only a very 
gentle rear impact, the seat remains in its initial condition. However, if 
the impact is of a predetermined severity, the frangible part will break, 
thus permitting the pivot links to move. The pivot links then move to the 
condition illustrated in FIG. 4. 
It is to be observed that the pivot pin 36, provided at the lower end of 
the pivot link 33, has now moved to a rearward position at the bottom of 
the generally triangular aperture 21 formed in the intermediate support 
plate 15 The first pivot link 27 has effected a rearward swinging motion 
about the axis defined by the pivot pin 25 which is received in the 
aperture 24 of the intermediate support plate 15 and the aperture 26 of 
the pivot link 27. 
As a consequence the recliner support plate 32 has moved rearwardly, and 
the inclination of the recliner support plate 32 has changed so that the 
seat back is now inclined slightly forwardly, as can be seen from the 
orientation of the line 45 in FIG. 4. 
It is to be understood that during this movement of the back of the seat, 
the lower part of the torso of the occupant has effectively engaged the 
lower part of the back of the seat and moved the lower part of the back of 
the seat rearwardly. Consequently, the top of the back of the seat is 
moved forwardly and either the top of the back of the seat or a head-rest 
carried by the top of the back of the seat will be brought into engagement 
with the head of the occupant to support the head of the occupant. 
Should a continuing rearward force be applied to the back of the seat, that 
force will tend to pivot the recliner support plate 32 about the axis of 
the pivot pin 30 which is provided at the lower end of the pivot link 27. 
This movement with a pivotal action is initially resisted by the second 
pivot link 33. However, because the second pivot link 33 is of arcuate 
form, and especially because of the provision of the "V" notch 38 on the 
inner surface of the arc, the second pivot link 33 can only withstand a 
predetermined force tending to compress that pivot link. If the force 
applied to the back of the seat is beyond a predetermined threshold, the 
second pivot link 33 will collapse and deform, permitting the recliner 
support plate 32 to pivot about the axis defined by the pivot pin 30. 
It is to be understood that the predetermined threshold for the force that 
must be applied to the back of the seat to cause the second pivot link to 
collapse is greater than the force necessary to be applied to the back of 
the seat to cause the frangible part of the release element 23 to break, 
thus permitting movement of the first pivot link 27. 
The pivot pin 36 provided at the lower end of the second pivot link 33 thus 
moves upwardly, within the triangular aperture 21 formed in the 
intermediate support plate 15, to occupy a position adjacent the 
upper-most corner of that triangular aperture. As can be seen in FIG. 5, 
the second pivot link 33 has collapsed, but it is to be understood that in 
collapsing, the second pivot link has absorbed energy. 
In an alternative embodiment, an additional element may absorb the energy. 
This element may comprise a spring or other flexible element. In such a 
case forward movement of the back of the seat after impact has to be 
prevented. It is to be appreciated also that during the first movement of 
the back of the seat, an energy absorbing element can be used to absorb 
energy. 
It is to be appreciated that whilst, in the described embodiment, an 
intermediate support plate 15 is provided, the only real function of the 
intermediate support plate 15 is to permit a forward-tilting of the entire 
back of the seat. If a seat back support mechanism is to be provided in a 
seat which is not present in a two-door car, then the intermediate support 
plate could be omitted. In such a case, the apertures 21, 22 and 24 could 
be formed in the rear main support plate 3. The locking lever 18 would 
also be omitted. 
Whilst the release element 23 has been described as being a frangible pin, 
the release element 23 could constitute a mechanical or electro-mechanical 
arrangement adapted to retract a pin in response to a signal from an 
appropriate sensor. The sensor may comprise a sensor adapted to respond to 
a an acceleration of the vehicle in excess of the predetermined threshold. 
The sensor may automatically retract a pin which initially engages the 
aperture 28 in the pivot link 27, thus releasing the pivot link 27. 
Alternatively, a retractable pin may be retracted by means of a solenoid. 
It is to be appreciated that further modifications may be effected to the 
invention without departing from the scope of the following claims.