Abstract:
A vehicle seat including at least two components connected, directly or indirectly, by an adjustment mechanism. A locking means is provided, arranged to lock the two components relative to each other when predetermined conditions are experienced, to restrict relative movement of the two components. The locking means may be arranged to engage when a vehicle in which the seat is mounted is involved in an impact. The locking means reduces the amount of relative movement of seat components owing to compliance in seat adjustment mechanism in the event of a vehicle impact.

Description:
TECHNICAL FIELD 
     The present invention relates to a vehicle seat, and particularly but not exclusively to an automotive vehicle seat. 
     BACKGROUND OF THE INVENTION 
     Automotive vehicle seats typically provide for a whole range of adjustments aimed at enhancing occupant comfort and safety. These adjustments typically include forwards and backwards movement to enable the position of the seat on the longitudinal axis of a vehicle to be adjusted, upward and downward movement to enable the position of the seat on the vertical axis of a vehicle to be adjusted and pivotal movement of a seat squab part relative to the cushion part to enable rake of the squab relative to the seat to be adjusted. 
     The mechanisms inherent to the provision of these adjustments impart a degree of play or compliance to a seat. This presents a problem under vehicle impact conditions in that movement of a seat relative to a vehicle as a result of compliance in its adjustment mechanisms will contribute to movement of an occupant of the seat relative to the vehicle during impact conditions. This movement generally counters the intended effects of safety devices such as seat belts and airbags intended to restrain and control movement of vehicle occupant during an impact and can therefore increase the risk of an occupant incurring an injury. 
     As automotive vehicle seats have become more complex so their mass has increased and this exacerbates the problem since the increased mass results in increased forces being generated by the seat when a vehicle is involved in an impact. The problem is further exacerbated where a vehicle seat is provided with an integrated seat belt mounted on the seat rather than directly to the vehicle. With this arrangement force applied to the seat belt by an occupant during a vehicle impact is transmitted to the vehicle seat rather than directly to the vehicle. This further increases the load upon the seat and generates further movement of the seat relative to the vehicle. 
     Embodiments of the present invention have been made in consideration of these problems. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a vehicle seat comprising at least two components connected, directly or indirectly, by an adjustment mechanism enabling adjustment of the relative positions of the two components, wherein at least one locking means is provided arranged to lock the two components relative to each other when predetermined conditions are experienced, thereby restricting relative movement of the two components. 
     Preferably the locking means is arranged to engage in the event of a vehicle on which the seat is mounted being involved in an impact. This may be characterised by deceleration of the vehicle at a rate greater than a predetermined value. Thus, the locking means will be activated to limit relative movement of components of the vehicle seat in a vehicle impact. The locking means may be resiliently biased against engagement, for example by a spring. 
     The locking means may be provided between any two relatively adjustable components of the seat. More than one locking means may be provided on the vehicle seat. For example, one or more locking means could be provided between any two of the following seat components: seat squab, seat cushion, moveable rail and fixed rail. One of the seat components may be fixed relative to the vehicle. 
     The locking means may be separate to the adjustment mechanism. Alternatively, the locking means may form part of the adjustment mechanism. 
     The locking means may comprise two mutually engageable components mounted respectively to the two seats components. One component could comprise teeth, and the other a pawl or teeth. 
     The locking means may be activated by any suitable arrangement. In one embodiment a component of the locking means is connected to a seat belt anchorage and the locking means is arranged to lock when a force applied to the seat belt anchorage by a seat belt exceeds a predetermined threshold. In another embodiment a component of the locking means is arranged to move from a first position to a second position as a result of inertial forces acting on the mass of the component resulting from deceleration of the vehicle in an impact, and movement of the component causing the locking means to lock. Other arrangements are, of course, possible. For example the locking means could be brought into operation by an actuator under control of an electronic control unit programmed to determine deployment of the locking means in dependence upon impact conditions as sensed by one or more impact sensors. 
     The locking means may be arranged to continue to lock the two components relative to each other even though the predetermined conditions no longer apply. 
     Means may be provided to release the locking means, to enable relative movement of components of the seat following an impact. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In order that the invention may be more clearly understood embodiments thereof will now be described, by way of example, with reference to the accompanying drawings of which: 
         FIG. 1  shows a diagrammatic perspective view of a vehicle seat according to the invention; 
         FIG. 2  shows a partial cut-away left side view of the seat of  FIG. 1  in a fully raised position; 
         FIG. 3  shows the view of  FIG. 2  with the seat in a mid-position; 
         FIG. 4  shows the view of  FIG. 3  with the seat in a fully lowered position; 
         FIG. 5  shows a detailed view of the locking means shown in  FIGS. 2 to 4  in a locked state; 
         FIG. 6  shows a partial cut-away right side view of the seat of  FIG. 1 ; 
         FIG. 7  shows a detailed view of the locking means shown in  FIG. 6  in an unlocked state; and 
         FIG. 8  shows the view of  FIG. 7  with the locking means in a locked state. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the figures an automotive vehicle seat comprises a cushion part  1  and a squab part  2 , each having respective metal frames  3 ,  4  supporting upholstery  5 . 
     The cushion  1  and squab  2  are pivotally connected together by a pivot  6  enabling the rake of the squab relative to the cushion  1  to be adjusted. A mechanism is provided to one side of the seat for adjustment of the rake of the squab  2 . 
     The cushion frame  3  is mounted by way of a height adjustment mechanism, generally  7 , to a moveable slide  8 . The moveable slide  8  is slidably mounted on a fixed slide  9  which is in turn fixed to the vehicle floor. The moveable and fixed slide arrangement allows fore and aft movement of the seat relative to the vehicle. The height adjustment mechanism provides for heightwise movement of the seat relative to the floor and roof of the vehicle. The seat is shown in a fully raised position in  FIG. 2 , a fully lowered position in  FIG. 4  and an intermediate position in  FIG. 3 . 
     The seat includes a seat belt comprising a webbing strap  11 . The seat belt is shown in a fastened state in  FIG. 1 , although no occupant is shown in the seat. The webbing is stored on a conventional reel housed in the seat squab  2  and pays out of an opening  12  towards the top of the seat squab  2  and can be drawn in a diagonal fashion across an occupant of the seat so that a fitting  13  slidably mounted on the webbing  11  can be engaged into a latch fastened to an anchor point towards the bottom of the squab and on the opposite side of the squab to the aperture  12  through which the webbing strap  11  is paid out. The webbing strap  11  continues from the fastening to an anchor point  14  on the cushion frame  3 . The reel is of the ‘inertia’ type and arranged to lock under impact conditions to prevent further retraction of the seat belt from the reel and thus restrain movement of the seat occupant. 
     The seat belt anchor point  14  is provided on a locking member  15  comprising a metal plate mounted on the cushion frame  3  by a pivot  16  enabling the locking member to rotate relative to the cushion frame  3 . Under normal circumstances rotation of the locking member is inhibited by a resilient member, in this case a helical tension spring,  17  extending from the seat belt anchor point  14  on the locking member  15  to the cushion frame  3 . The locking member  15  is arranged such that a force, which exceeds a predetermined threshold, exerted on the seat belt by an occupant during rapid deceleration of the vehicle when the seat belt reel has locked, in particular as a result of an impact, will cause the locking member  15  to rotate in an anti-clockwise direction (as viewed in  FIGS. 2 to 5 ) against the action of the resilient member  17 . The general direction of a force applied to the seat belt anchor point  14  as a result of a vehicle impact is shown by arrow  18  in  FIG. 5 . 
     The locking member  15  has a toothed edge  19  and is intended to cooperate with a locking rack  20 . The locking rack  20  is mounted by way of a pivot  21  to the moveable slide  8  of the seat. The locking rack  20  is generally elongate and curved with a toothed edge  22 . The locking rack  20  is connected at one end to the pivot  21  and extends upwardly from the pivot with its toothed edge facing the toothed edge  19  of the locking member  15 . 
     A guide bracket  23  is also mounted to the cushion frame  3  (not shown in  FIG. 5 ). The guide bracket is arranged to support the locking rack  20  against the effects of gravity so that the toothed edge of the locking rack  20  remains a predetermined distance from the toothed edge  19  of the locking member  15  throughout the full range of height adjustment of the seat. 
     When the seat is in its fully raised position, as shown in  FIG. 2 , the support bracket  23  supports the locking rack  20  in an upright position and the toothed edge  19  of the locking member is adjacent the free end of the locking rack  20 . When the seat is in its lowermost position, as shown in  FIG. 4 , the free end of the locking rack  20  extends almost horizontally and the toothed edge  19  of the locking member  15  faces the toothed edge of the rack near to the pivot  21 . Throughout the full range of height adjustment of the seat the distance between the toothed edge of the locking member  15  and the toothed edge  19  of the rack  20  is approximately constant. 
     In the event of an impact condition resulting in a force being exerted by the seat belt on the seat belt anchor point  14  sufficient to overcome tension in the resilient means  17  the locking means  15  will rotate until its toothed edge  19  contacts and engages with the toothed edge of the locking rack  20 . As the locking member  15  is mounted to the cushion frame  3  and the rack  20  to the moveable rail  8  engagement of the locking member  15  and locking rack  20  serves to inhibit, and preferably substantially prevent, movement of the cushion frame  3  relative to the moveable rail  8  as a result of compliance in the seat height adjustment mechanism. As a result, under impact conditions, movement of the seat, and hence its occupant, relative to the vehicle as a result of compliance in the height adjustment mechanism is reduced. When force applied to the seat belt anchor point  14  reduces below a predetermined level, below which tension in the resilient means  17  is no longer overcome, the resilient means causes the locking member  15  to disengage from the locking rack  20  again allowing for heightwise adjustment of the seat. 
     The seat height adjustment mechanism is provided to the opposite side of the seat rails  8 , 9  to the locking member  15  and rack  20 . 
     On the opposite side of the seat to the locking means  15  and rack  20  the cushion frame  3  is provided with an arcuate rack  24  extending partially around the pivot  6  between the cushion frame  3  and squab frame  4 . 
     Mounted to the squab frame  4  is a locking arrangement, generally indicated by reference numeral  25 , arranged to engage with the arcuate rack  24 . 
     The locking arrangement comprises a locking pawl  26  mounted to the squab frame  4  by way of a pivot  27 . The pawl comprises an arm having a toothed edge arranged to engage with the arcuate rack  24  when the locking pawl  26  is rotated in a clockwise direction (as viewed in  FIGS. 6 to 8 ) about pivot  27 . Movement of the locking pawl  26  is controlled by an associated locking plate  28  which cooperates with the locking pawl  26 . The locking plate  28  is mounted to the squab frame  4  by pivot  29  from which it is freely suspended. The centre of gravity of the locking plate  28  is indicated at  30 . 
     For normal operation of the seat the locking plate  28  and locking pawl  26  are arranged in the configuration shown in  FIGS. 6 and 7 . In this configuration the centre of gravity  30  of the locking plate  28  lies substantially vertically below the pivot  29  and the locking plate  28  engages with the locking pawl  26  to retain the pawl  26  in a raised position such that the toothed edge of the pawl is separated from the arcuate rack  24 . A calibration spring (not shown) holds the locking plate  28  in position. In the event of a vehicle impact rapid deceleration of the vehicle will result in inertial forces urging the centre of gravity  30  of the locking plate  28  in the direction indicated by arrow  31  in  FIG. 7 . This causes the locking plate  28  to swing forwards against the action of the calibration spring to the position illustrated in  FIG. 8 . On doing so the locking plate  28  releases the locking pawl  26  and bears against the locking pawl  26  urging the toothed edge of the pawl  26  into engagement with the arcuate rack  24 . The surface  32  of the locking pawl  26  against which the locking plate  28  bears is shaped such that the locking plate  28  engages the locking pawl  26  with an over centre action so that the locking plate  28  and pawl  26  remain in the configuration illustrated in  FIG. 8  following an impact. 
     Engagement of the locking pawl  26  with the arcuate rack  24  provides a connection between the cushion frame  3  and squab frame  4  inhibiting pivotal movement between the two frames about pivot  6  and thereby limiting forward movement of the seat squab  2  during a vehicle impact as a result of compliance in the seat squab adjustment mechanism. 
     The arcuate rack  24  and locking arrangement  25  are provided on the opposite side of the seat to the seat squab  2  adjustment mechanism thereby limiting the greater movement of that side of the seat squab  2  which would result if the locking means were not present. 
     The fact that the seat squab  2  locking arrangement remains locked after a vehicle impact could cause difficulties, in particular for a two door vehicle where the vehicle seat is arranged so that its squab  2  can be moved forward into a so-called “dumped” position to enable access to rear seats of the vehicle. To overcome this problem an arrangement for releasing the locking means is provided. A pin mounted (at point  33 ) to the reverse side of the locking plate  28  to that shown in  FIGS. 6 to 8  projects from the plate and through an arcuate slot  34  in the squab frame  4 . As is conventional with seats for two door vehicles a squab release latch is provided to enable the squab  2  to be released from the seat so that it can be moved to the dumped position. The squab release latch is released by operation of a squab release lever mounted on the seat. In this arrangement the squab release lever is arranged not only to operate the squab release latch but also to move the locking plate  28  from the locked position shown in  FIG. 8  (if it is in that position) and return it to the normal position shown in  FIG. 7  by moving the pin projecting from the locking plate  28 . Thus, following a vehicle impact which has caused the locking plate  28  to engage with the locking pawl  26 , the locking arrangement is unlocked on operation of the squab release lever enabling the squab to be moved to the dumped position allowing rear seat passengers to exit the vehicle or emergency services to gain access to the rear seats of the vehicle. 
     The above embodiments of the invention both act to reduce vehicle seat movement under vehicle impact conditions resulting from compliance in vehicle seat adjustment mechanisms. This allows for better function of vehicle occupant safety systems, improving vehicle occupant safety. 
     The above embodiments are described by way of example only. Many variations are possible without departing from the scope of the invention.