WO2009005414A1

WO2009005414A1 - A seat back support mechanism

Info

Publication number: WO2009005414A1
Application number: PCT/SE2007/000639
Authority: WO
Inventors: Lennart Simonsson; Ola BOSTRÖM
Original assignee: Autoliv Development Ab
Priority date: 2007-07-02
Filing date: 2007-07-02
Publication date: 2009-01-08
Also published as: WO2009005463A1; EP2162314A1; EP2162315A1; EP2162314A4; EP2162315A4

Abstract

A seat back support mechanism supports the back of a seat in a motor vehicle. The mechanism comprises at least one first component (2,3) which is adapted to be connected to the squab of a seat, and at least one further component (32) which is adapted to be connected to the back of the seat. The components (2,3,32) are connected together by a connection arrangement. The mechanism comprises a deformable element (23) which is configured to break when subjected to a force in excess of a predetermined level which is exerted on the lower part of the back of the seat. The mechanism is configured to permit the lower part of the back of the seat to be displaced when the deformable element (23) is broken. The connection arrangement is configured to permit the further component (32) to pivot relative to the first component (2,3) without deforming the deformable element (23).

Description

"ASEAT BACKSUPPORTMECHANISM'

Description

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.

A prior proposed seat back support mechanism of the type described above is disclosed in GB-A-2316442. This prior proposed seat back support mechanism incorporates a pivot link arrangement which is configured to permit the lower part of a seat back to be displaced rearwardly. The pivot link arrangement is locked normally by a frangible pin. The frangible pin is configured to break to allow the pivot link arrangement to displace the lower part of the seat back when the lower part of the seat back is subjected to a force by a seat occupant which is in excess of a predetermined threshold. As the lower part of the seat back moves rearwardly the upper part of the seat back moves forwardly to a position which is closer to the head of the seat occupant to offer support to the head of the seat occupant. After the lower part of the seat back has been displaced the mechanism is configured to pivot rearwardly under the influence of forces exerted by the seat occupant on the seat back whilst absorbing energy from the seat occupant.

After the mechanism has been actuated the frangible pin must be replaced before the seat back can be returned and locked in its normal position. A problem with this prior proposed mechanism is that the frangible pin can become deformed and broken by forces other than the forces exerted by the seat occupant in a rear impact, such as forces arising from cargo or a rear seat passenger striking the rear of the seat back during a frontal impact. Forces exerted on the rear of the seat back during a frontal impact may cause the frangible pin to become deformed or to break unnecessarily. The frangible pin must then be replaced to return and lock the seat back in its normal position and the replacement can be expensive and time consuming.

The present invention seeks to provide an improved seat back support mechanism. According to one aspect of the present invention, there is provided a seat 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; at least one further component adapted to be connected to the back of the seat, the further component being connected to the first component by a connection arrangement which comprises a deformable element, the deformable element being configured to resist displacement of the further component relative to the first component, the deformable element being configured to deform in the event that a force which is in excess of a predetermined level is exerted on the further component to permit displacement of the further component relative to the first component; wherein the connection arrangement is configured to permit the further component to pivot relative to the first component from a first orientation to a second orientation in response to fulfilment of a first criterion without deforming the deformable element; the mechanism further comprising return means which is configured to act on the further component to return the further component from the second orientation to the first orientation in response to fulfilment of a second criterion.

Preferably the further component is provided with an elongate guide slot, the guide slot receiving slideably a guide member, the further component being configured to move relative to the guide member when the further component pivots relative to the first component, the guide member being positioned at a first position along the length of the guide slot when the further component is in the first orientation and the guide member is positioned at a second position along the length of the guide slot when the further component is in the second orientation.

Conveniently the length of the guide slot is from 10 to 40 mm. Advantageously the connection arrangement further comprises a blocking element which blocks movement of the further component relative to the guide member, the blocking element being releasable in response to fulfilment of the first criterion to permit movement of the further component relative to the guide member.

In one embodiment the connection arrangement further comprises a motor which is connected to the blocking element to release and move the blocking element in response to fulfilment of the first criterion.

Preferably the first criterion is a force exerted on the further component which is in excess of a predetermined level.

In another embodiment the first criterion is a signal generated by a crash sensor which is indicative of a crash situation.

In a further embodiment the first criterion is a signal generated by a pre-crash sensor which is indicative of an anticipated crash situation.

Preferably the second criterion is a force exerted on the return means which is in excess of a predetermined level.

Conveniently the return means comprises a Bowden cable which has an outer sheath fixed relative to the further component and an inner cable fixed relative to the guide member such that the inner cable moves the further component relative to the guide member when a force which is in excess of a predetermined level is exerted on one end of the inner cable.

Advantageously the connection arrangement further comprises a biasing element which biases the further component towards the first orientation.

In one embodiment the biasing element is a torsion spring.

Preferably the deformable element is a frangible release element.

Alternatively the deformable element is a spring.

Conveniently the further component comprises a recliner support plate which supports a recliner mechanism.

According to another aspect of the present invention, there is provided a vehicle seat comprising the support mechanism as defined in the claims hereinafter.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

Figure 1 is a perspective view of a seat back support mechanism in accordance with a preferred embodiment of the invention,

Figure 2 is an exploded view of the seat back support mechanism of figure 1 ,

Figure 3 is a plan view of four co-operating parts of a movement arrangement which forms part of the mechanism shown in figures 1 and 2 in a first condition,

Figure 4 is a view corresponding to figure 3 showing the four parts in a second condition, Figure 5 is a view corresponding to figures 3 and 4 showing the four parts in a third and final condition,

Figure 6 is a plan view of parts of a pivoting arrangement which forms part of the mechanism shown in figures 1 and 2 in an unactuated condition,

Figure 7 is a view corresponding to figure 6 with the parts of the pivoting arrangement in an actuated condition,

Figure 8 is a plan view of part of the pivoting arrangement shown in figures 6 and 7 with a return mechanism in an unactuated condition,

Figure 9 is a view corresponding to figure 8 with the return mechanism in an actuated condition,

Figure 10 is a view corresponding to figure 6 following actuation of the pivoting arrangement and the movement arrangement,

Figure 11 is a view corresponding to that of figure 3, but illustrating an alternative embodiment;

Figure 12 is a view corresponding to that of figure 4, illustrating the embodiment of figure 11 , and

Figure 13 is a view corresponding generally to that of figure 5, illustrating the embodiment of figures 11 and 12.

Referring initially to figures 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 1 includes a movement arrangement which, when actuated, allows the back of the seat to be displaced to 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 rearward Iy and the top part of the back of the seat moves forwardly. Subsequently the back of the seat may effect a second 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.

As will be described below, the seat back support mechanism 1 also includes a connection arrangement which permits the back of the seat to pivot forwardly without necessarily displacing the lower part of the back of the seat.

Considering the components that together constitute the mechanism 1 as illustrated in figures 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 at least partly 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 17. 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 18 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, 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 recess, thus permitting the intermediate support plate 15 to pivot in a forward direction (i.e. a counter clockwise direction as viewed in figures 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 deformable 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 guide member in the form of a pivot pin 36, the pivot pin 36 also being received in an elongate guide slot 37 provided in the recliner support plate 32. The length of the guide slot 37 is preferably from 10 to 40 mm, although it should be appreciated that a longer, or generally larger slot may be appreciated depending upon the nature of the seat. 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.

A return means 46 is mounted to the recliner support plate 32. In this preferred embodiment, the return means 46 comprises a blocking element 47 in the form of a pin which is connected to a Bowden cable 48. The Bowden cable 48 comprises an inner cable 49 and an outer sheath 50. The blocking element 47 is connected to one end of the inner cable 49 of the Bowden cable 48 and the corresponding end of the outer sheath 50 is fixed to the recliner support plate 32 by a fixture 51. A coil spring 52 is fitted around the blocking element 47 and the coil spring biases the pivot pin 36 and the fixture 51 away from one another, to bias the recliner support plate 32 towards its normal orientation, as seen in figure 6. However, alternative arrangements may not use a Bowden cable arrangement and could, for example, instead use a pneumatically or motor-driven return means.

As will become clear from the description below, the blocking element 47 is positioned normally so as to resist movement of the support plate 32 relative to the pivot pin 36. The Bowden cable 48 manages the blocking element 47 and the bias provided by the spring 52 to control their combined blocking and biasing effects to prevent or allow movement of the recliner support plate 32 relative to the pivot pin 36. The function of the return mechanism 46 will be described in further detail below.

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 defines 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 earner plates 41 ,42. The carrier plate 42 is formed integrally with a support arm 43 that is adapted to be connected 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 figures 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 is disengaged from the intermediate support plate 15, the back of the seat may be tilted forwardly.

Referring now to figures 3 to 5, which illustrate 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.

Figure 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 deform and 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 figure 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 displaced 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 figure 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 figure 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. The connection arrangement which permits the back of the seat to pivot forwardly will now be described. In the preferred embodiment of the invention the connection arrangement comprises the support plates 2,3, the recliner support plate 32, the pivot pin 36, the guide slot 37 and the return means 46. The way that these components co-operate will now be described with reference to figures 6 to 10 of the accompanying drawings.

When the seat back is in its normal, upright, position the recliner support plate 32 is positioned so that the pivot pin 36 sits at the lower end of the guide slot 37, as seen in figure 6. The blocking element 47 and the spring 52 of the return means 46 act to retain the recliner support plate 32 in the normal position relative to the pivot pin 36 so that the seat back remains upright during normal vehicle operation. The blocking element 47 and the spring 52 hold the recliner support plate 32 yieldably so that if a force in excess of a predetermined level is exerted on the recliner support plate 32 then the spring 52 yields to allow the recliner support plate 32 to pivot about the pivot pin 30. The biasing force exerted by the spring 52 in this preferred embodiment represents a first criterion. It is to be appreciated that the first criterion may be fulfilled if a force is exerted on the recliner support plate 32 which overcomes the biasing force exerted by the spring 52. The connection arrangement permits the recliner support plate 32 to pivot relative to the support plates 2,3 in response to this first criterion being fulfilled. The force exerted on the rear of the seat back might, for instance, result from cargo in the rear of the vehicle or a rear passenger striking the seat back during a frontal impact. As the seat back pivots forwardly the recliner support plate 32 pivots about pivot pin 30 and moves such that the pivot pin 36 is positioned at the upper end of the guide slot 37, as shown in figure 7.

As the recliner support plate 32 moves relative to the pivot pin 36, the blocking element 47 pushes one end of the inner cable 49 back into the outer sheath 50 of the Bowden cable 48 which results in the other end of the inner cable 49 moving outwardly from the outer sheath 50 as shown generally by the arrow 53 in figure 8. The recliner support plate 32 moves until the pivot pin 36 is positioned at the upper end of the guide slot 37, as shown in figure 9, where further movement of the recliner support plate 32 is prevented by the pivot pin 36 acting on the upper end of the guide slot 37.

It is to be appreciated that the connection arrangement permits the recliner support plate 32 to pivot relative to the support plates 2,3 from a first orientation to a second orientation without the deformation of the frangible element 23. The connection arrangement thus allows for a component which supports a seat back to pivot without breaking or plastically deforming any elements.

After the seat back has pivoted forwardly, for instance following a frontal impact, the seat back may be returned to its normal, upright, position by fulfilling a second criterion. In this preferred embodiment the second criterion is fulfilled by exerting a force on the free end of the inner cable 49 of the Bowden cable 48 which is in excess of a predetermined level. The predetermined level is the level of force required to pivot the recliner support plate 32 back to its normal orientation. If a force is exerted on the free end of the inner cable 49 then the other end of the inner cable 49 acts on the pivot pin 36 via the blocking element 47 and the corresponding end of the outer sheath 50 acts on the recliner support plate 32 via the fixture 51. The forces exerted by the inner cable 49 on the pivot pin 36 and the recliner support plate 32 cause the recliner support plate 32 to pivot about the pivot pin 30 and to move relative to the pivot pin 36 to return the recliner support plate 32 to its initial position, as shown in figure 6. The force which must be exerted on the free end of the inner cable 49 is representative of a second criterion which must be fulfilled to permit the return means 46 to return the recliner support plate 32 from the second orientation to the first orientation. The pivoting arrangement is thus resetable so that the seat back may be returned to its normal position without having to replace components of the movement arrangement which might otherwise have been deformed unnecessarily.

If, following forward pivoting of the seat back by the pivoting arrangement, the seat occupant exerts a force on the seat back which is in excess of a predetermined level then the frangible release element 23 of the movement arrangement can still break to permit displacement of the recliner support plate 32, as shown in figure 10. Actuation of the movement arrangement following forward pivoting of the seat back could, for instance, become necessary if the vehicle is involved in a frontal impact and then is subsequently struck from the rear.

In other embodiments of the invention the blocking element 47 may be controlled by an electrical motor. In these other embodiments the electrical motor moves the blocking element 47 to permit movement of the recliner support plate 32 relative to the pivot pin 36.

It is also envisaged that in alternative embodiments, the deformable element 23 could take a different form. For example, whilst the embodiment has been described above with reference to the deformable release element 23 being engaged with the aperture 22 in the intermediate guide plate 15, and having a small extending fungible stud which locates in the aperture 28 formed in the pivot link 27, in the embodiment illustrated in figures 11 to 13, the deformable element takes the form of a spring 123. The spring 123 is formed from an elongate piece of spring wire and has a hooked end region 124 which is hooked over, and engages the upper edge of the intermediate support plate 15. From this point, the spring 123 extends towards the pivot pin 25 and is wrapped so as to take a single turn around the pivot pin 25, behind the plate 15 as shown. The spring then extends generally downwardly towards the pivot pin 30 where it terminates with a bent end region 125 bearing against the pivot 30.

In the initial condition illustrated in figure 3, with the pivot pin 36, at the lower end of the second pivot link 33 being located at a forward position within the generally triangular aperture 21 formed in the intermediate support plate 15, the spring 123 is effective, by virtue of its resiliency, to retain the support plate 15 and pivot link 27 in position relative to one another.

If the vehicle is subjected to a rear impact, a substantially 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 deform the spring 123 in the manner illustrated in figure 12. Thus, if the rear impact is only a very gentle rear impact, the seat remains in its initial condition, without any deformation of the spring 123. However, if the impact is of a predetermined severity, the spring 123 will deform, thus permitting the pivot links to move to the condition illustrated in figure 12.

It is to be understood that should a sufficient continuing rearward force be applied to the back of the seat to cause the second pivot link 33 to collapse, then the spring 123 is allowed to relapse slightly as the components assume the position illustrated in figure 13. Nevertheless, it remains the case that the predetermined threshold for the force that must be applied to the back of the seat to cause the second pivot link 33 to collapse is still greater than the force necessary to be applied to the back of the seat to deform the spring 123 thus permitting movement of the first pivot link from the position illustrated in figure 11.

As would be appreciated, by replacing the fungible release element 23 of the earlier embodiment with the deformable spring 123, the apertures 22, 28 formed in the intermediate support plate 15 and the first pivot link 27 respectively are no longer required and so these holes are not illustrated in the arrangement of figures 11 to 13.

Whilst in the embodiments described above the first criterion is represented by a predetermined level of force which must be exerted on the back of the seat, in another embodiment the first criterion is fulfilled by the generation of a crash signal by a crash sensor. In a further embodiment, the first criterion is fulfilled by the generation of a signal by a pre-crash sensor which is indicative of an anticipated crash situation.

It is to be appreciated that whilst the biasing and blocking configuration described above is in the form of a pin and a coil spring, in other embodiments the biasing and blocking effect may be obtained by equivalent means. For instance, in further embodiments the biasing could be achieved by the provision of a torsion spring.

In the present Specification "comprises" means "includes or consists of and "comprising" means "including or consisting of.

Claims

1. A seat 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 (2,3) adapted to be connected to the squab of the seat or to a frame supporting the squab of the seat; at least one further component (32) adapted to be connected to the back of the seat, the further component (32) being connected to the first component (2,3) by a connection arrangement which comprises a deformable element (23), the deformable element (23) being configured to resist displacement of the further component (32) relative to the first component (2,3), the deformable element being configured to deform in the event that a force which is in excess of a predetermined level is exerted on the further component (32) to permit displacement of the further component (32) relative to the first component (2,3); characterised in that the connection arrangement is configured to permit the further component (32) to pivot relative to the first component (2,3) from a first orientation to a second orientation in response to fulfilment of a first criterion without deforming the deformable element (23); the mechanism further comprising return means (46) which is configured to act on the further component (32) to return the further component (32) from the second orientation to the first orientation in response to fulfilment of a second criterion.

2. A mechanism according to claim 1 , wherein the further component (32) is provided with an elongate guide slot (37), the guide slot (37) receiving slideably a guide member (36), the further component (32) being configured to move relative to the guide member (36) when the further component (32) pivots relative to the first component (2,3), the guide member (36) being positioned at a first position along the length of the guide slot (37) when the further component (32) is in the first orientation and the guide member (36) is positioned at a second position along the length of the guide slot (37) when the further component (32) is in the second orientation.

3. A mechanism according to claim 2, wherein the length of the guide slot (37) is from 10 to 40 mm.

4. A mechanism according to claim 2 or claim 3, wherein the connection arrangement further comprises a blocking element (47) which blocks movement of the further component (32) relative to the guide member (36), the blocking element (47) being releasable in response to fulfilment of the first criterion to permit movement of the further component (32) relative to the guide member (36).

5. A mechanism according to claim 4, wherein the connection arrangement further comprises a motor which is connected to the blocking element (47) to release and move the blocking element (47) in response to fulfilment of the first criterion.

6. A mechanism according to claim 4 or claim 5, wherein the first criterion is a force exerted on the further component (32) which is in excess of a predetermined level.

7. A mechanism according to claim 4 or claim 5, wherein the first criterion is a signal generated by a crash sensor which is indicative of a crash situation.

8. A mechanism according to claim 4 or claim 5, wherein the first criterion is a signal generated by a pre-crash sensor which is indicative of an anticipated crash situation.

9. A mechanism according to any one of the preceding claims, wherein the second criterion is a force exerted on the return means (46) which is in excess of a predetermined level.

10. A mechanism according to claim 9 as dependent upon any one of claims 2 to 8, wherein the return means (46) comprises a Bowden cable (48) which has an outer sheath (50) fixed relative to the further component (32) and an inner cable (49) fixed relative to the guide member (36) such that the inner cable (49) moves the further component (32) relative to the guide member (36) when a force which is in excess of a predetermined level is exerted on one end of the inner cable (49).

11. A mechanism according to any one of claims 2 to 10, wherein the connection arrangement further comprises a biasing element (52) which biases the further component (32) towards the first orientation.

12. A mechanism according to claim 11 , wherein the biasing element (52) is a torsion spring.

13. A mechanism according to any one of the preceding claims, wherein the defoimable element (23) is a frangible release element.

14. A mechanism according to any one of the preceding claims, wherein the defoimable element (123) is a spring.

15. A mechanism according to any one of the preceding claims, wherein the further component (32) comprises a recliner support plate which supports a recliner mechanism (42).

16. A vehicle seat incorporating a support mechanism according to any one of the preceding claims.

17. A support mechanism substantially as hereinbefore described with reference to and as shown in the accompanying drawings.