Abstract:
A headrest in a vehicle seat includes an inflatable protective cushion in which the contact surface area is increased and caused to approach the head without needing to provide burst seams in the upholstery or in the cover or to make use of an elastic covering material. The protective cushion is arranged between the headrest frame member and the upholstery. The cover or the upholstery is joined at its outer circumference by jointing means to the headrest frame member. The jointing means maintain the cover, or the upholstery, tensioned in the non-activated condition of the protective cushion and permit a limited displacement of the outer circumference of the cover, or upholstery, from the headrest frame member in the activated condition of the protective cushion. The upholstery may thus be brought by the protective cushion nearer to the head and the contact surface area may be enlarged without destroying the cover or upholstery.

Description:
The present invention relates to a headrest including an inflatable protective cushion activated in the case of a rear-end impact. 
     BACKGROUND OF THE INVENTION 
     In a rear-end impact a vehicle occupant is exposed to added risk of injury in the region of the nape of the neck due to shear and bending forces when the head is not in contact with the headrest. This is, however, mostly the case since the vehicle occupant when on the move often shifts to a more comfortable seating position which is not always an optimum from the safety point of view. To reduce this risk of injury headrests have been developed with which by means of an inflatable protective cushion the contact surface area of the upholstery of the headrest is increased whilst being caused to approach the head. So that a movement of the headrest upholstery is possible, known headrests are provided with either an elastic covering material or seams in the covering material which burst on inflation of the protective cushion to thus deploy a folded portion of the cover and thereby permit expansion of the protective cushion. This results in the cover being irreversibly damaged once the protective cushion has been deployed. Apart from this, providing these burst seams constitutes an additional, not inconsiderable complication in fabricating the headrest. When employing an elastic covering material the choice of material is substantially restricted due to the required elastic properties which affects the costs and freedom in visual design of the headrest. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention provides a headrest including an inflatable protective cushion in which the contact surface area is increased and caused to approach the head without needing to provide burst seams in the upholstery or in the cover or to make use of an elastic covering material. 
     The protective cushion is arranged between the headrest frame member and the upholstery. The cover or the upholstery is joined at its outer circumference by jointing means to the headrest frame member. The jointing means maintain the cover, or the upholstery, tensioned in the non-activated condition of the protective cushion and permit a limited displacement of the outer circumference of the cover, or upholstery, from the headrest frame member in the activated condition of the protective cushion. Thus, the upholstery may be brought by the protective cushion nearer to the head and the contact surface area may be enlarged without destroying the cover or upholstery. The upholstery and/or the cover may be returned to their original positions after having been activated. 
     Furthermore, the invention provides an activating means which on detection of a rear-end impact activates a gas source for inflating the protective cushion, the activating means comprising a pressure sensor responding to the pressure exerted by the occupant on the backrest of the vehicle seat, and an acceleration sensor applied to the vehicle body or to the seat and which activates the gas source only when pressure is exerted by the occupant on the backrest and simultaneously the acceleration sensor signals a rear-end impact. It is this activating means that prevents the protective cushion in the headrest from being inflated when despite pressure being exerted on the backrest no rear-end impact is involved or when the corresponding vehicle seat is not occupied. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention read from the following description and from the drawings illustrating embodiments of the invention by way of example and to which reference is made, in which 
     FIG. 1 is a section through a headrest in accordance with a first embodiment of the invention in the non-activated condition; 
     FIG. 2 is a section through the headrest as shown in FIG. 1 but in the activated condition: 
     FIG. 3 is a section through a headrest in accordance with a second embodiment of the invention in the non-activated condition; 
     FIG. 4 is a view of the headrest as shown in FIG. 3 from the rear; 
     FIG. 5 is a section through a headrest in accordance with a third embodiment of the invention in the non-activated condition; 
     FIG. 6 illustrates the headrest as shown in FIG. 5 but in the activated condition; 
     FIG. 7 a  is a view of a headrest in accordance with a fourth embodiment of the invention in an inclined front view; 
     FIG. 7 b  is a view of a headrest as shown in FIG. 7 a  in an inclined rear view in the non-activated condition; 
     FIG. 7 c  is a section through the headrest as shown in FIG. 7 a;    
     FIG. 7 d  is a view of the headrest as shown in FIG. 7 a  in the activated condition; 
     FIG. 7 e  is a section through the headrest as shown in FIG. 7 a  in the activated condition. 
     FIG. 8 is a schematic section through a vehicle seat including an activating means in accordance with a first embodiment of the invention in the non-activated condition of the headrest; 
     FIG. 9 is a schematic section through a vehicle seat as shown in FIG. 8 in the activated condition of the headrest; 
     FIG. 10 is a schematic section through a vehicle seat including an activating means in accordance with a second embodiment of the invention in the non-activated condition of the headrest; and 
     FIG. 11 illustrates the vehicle seat as shown in FIG. 10 but in the activated condition of the headrest. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIGS. 1 and 2 there is illustrated the headrest comprising a gas source  1 , for example a pyrotechnic gas generator or a compressed gas cartridge, and an inflatable protective cushion  2 , all of which are provided between an upholstery  3  and a headrest frame member  7 . A cover  4  covers the upholstery  3 . The cover  4  is extended in length by a jointing means configured as a jointing hem  5  folded into a recess in the rear side of the headrest frame member  7  and is held in place by means of a clamping strip  6  in a groove in the headrest frame member  7 . Applied to the jointing hem  5  is a circumferential seam  10  by means of which the jointing hem  5  is clasped by a flange  9  applied to a panel  8  on the headrest frame member  7 . The panel  8  is held in place on the headrest frame member  7  by a holding device comprising latching hooks  11  configured on the panel  8  each constituting a stop  16  and a dome  12  configured on the frame member  7  with a pin  13  slidingly guided therein. The two pins  13  are connected via traction means  14 , for example a traction tape which is guided through openings  15  in the frame member  7  and extending between the protective cushion  2  and the upholstery  3 . The frame member  7  is secured by a clip fastener  17  to a headrest bracket  18 . 
     In a rear-end impact the gas source  1  is activated to inflate the protective cushion  2 . The enlargement of the protective cushion  2  draws the pins  13  from the domes  12  by the traction tape  14 , as a result of which the stops  16  of the latching hooks  11  are released. The protective cushion simultaneously generates via the upholstery  3  and the cover  4  in the jointing hem  5  a tractive stress, resulting in the seam  10  clasped by the flange  9  pulling the panel  8  from the frame member  7  to the rear until the panel  8  is retained by the stops  16  of the latching hooks  11  at the domes  12  (see FIG.  2 ). The protective cushion  2  moves the upholstery  3  away from the frame member  7  until the jointing hem  5  is totally removed from the rear side recess in the frame member  7  and is extended. Due to the expansion of the protective cushion  2  vertically the upholstery  3  is simultaneously extended and thus the contact surface area enlarged for the head. 
     It is thus clearly evident that activation of the headrest causes damage neither to the cover nor to the upholstery since no burst seams are provided. All that is required to reinstate the headrest is to change the gas source  1  and, if need be, the protective cushion  2 . All other components can be simply returned to their original condition by folding the loop  5  back in the rear side recess in the frame member  7  in the headrest, the pins threaded in place and the panel  8  refitted. Due to the panel  8  being arrested by means of the stops  16  to the latching hooks  11  there is no danger of the vehicle occupants being injured by loose parts. Instead of the upholstery  3  with the cover  4  an upholstery may also be employed in which the cover is worked into the surface, or the surface of which does away with the need of a separate cover, the jointing hem  5  then being directly tacked to the upholstery. 
     In the description of the following embodiments like components are identified by like reference numerals so that reference can be made to the above description as regards the components concerned. 
     Referring now to FIGS. 3 and 4 there is illustrated a headrest in which the cover is extended in length beyond the end of the upholstery  3  and secured by means of the clamping strip  6  directly in the groove in the headrest frame member  7 . The cover  4  forms a loop  21  which is maintained tensioned by a traction means located therein in the form of a tensioning cord  22 . The tensioning cord  22  is brought out at two openings  23  in the loop  21  and wrapped around a pin  24  which is shiftingly mounted in an indent in the frame member  7 . Applied to the pin  24  is a traction means  25 , for instance a tape, which is guided through an opening  26  in the frame member between the protective cushion  2  and the upholstery  3  and secured at the other end to the frame member  7 . The rear side recess of the frame member  7  is closed off by a panel  31  secured to the frame member  7  by latching hooks  32 . Activation of the gas source  1  pulls the pin  24  from its guide due to inflation of the protective cushion  2  and releases the tensioning cord  22 , as a result of which the loop  21  is released and the upholstery extended and moved away from the frame member as already described with reference to FIG.  1 . 
     In addition to the advantages already described with reference to FIG. 1 this embodiment has the added advantage that the panel  31  remains on the frame member  7  and the headrest thus comprises a closed surface on the rear side even in the activated condition. The loop  21  may also be formed by a jointing hem directly stitched to the cover  4  for which a more moderately priced material may be used to advantage. 
     Referring now to FIGS. 5 and 6 there is illustrated a headrest in which the loop  21  is maintained tensioned by an elastic traction means  40 . This elastic traction means may be, for example, a coil-spring tape which is expanded on inflation of the protective cushion  2  by the tension in the cover  4  so that the upholstery  3  is extended and can be moved away from the frame member  7 . When the pressure in the protective cushion  2  drops, the loop  21  of the cover  4  is drawn back under the panel  31  by the tension of the coil-spring tape so that the upholstery reassumes its original shape. It is particularly of advantage in this embodiment that the headrest reassumes its original shape by itself. 
     Referring now to FIGS. 7 a  to  7   e  there is illustrated a headrest  80  in accordance with a fourth embodiment of the invention in which the upholstery consists of a fixed part  88  and a movable part  83 . The fixed part  83  of the upholstery surrounds the headrest in the non-activated condition (FIGS. 7 a ,  7   b  and  7   c ) for the most part. The upper end and lower end of the movable part  83  of the upholstery are each joined to the frame member  86  of the headrest by an elastic fabric  84 ,  85 . This elastic fabric  84 ,  85  is accommodated in a recess in the frame member  86  where it is looped about reversing rods. In the activated condition (FIGS. 7 d  and  7   e ) the upholstery part  83  is extended and moved away from the frame member  86  by the inflation of the protective cushion  2  the same as described before, the elastic fabric  84 ,  85  being thereby expanded. With the drop in pressure in the protective cushion  2  the upholstery is caused to reassume its original shape by the tension in the elastic fabric  84 ,  85 . Due to the tape  84 ,  85  being looped about the reversing rods a sufficient length of the elastic tape  84 ,  85  is made available to permit the necessary expansion for the travel of the upholstery part  83 . 
     In this embodiment no additional tensioning means are needed, there also being no need for a separate panel on the rear side since the headrest in the non-activated condition is totally enclosed by the upholstery parts  83  and  88 . This has the added advantage that the headrest comprises a closed and upholstered surface on all sides. Instead of the looped elastic tape it is here also possible to use one or more traction springs, this necessitating, however, reinforcement of the upper and lower edge of the movable upholstery  83  at the fastening points of the springs. 
     Referring now to FIGS. 8 and 9 there is illustrated a vehicle seat  50  including a backrest  53  and a headrest  51 . The headrest comprises an inflatable protective cushion  60  and a gas source  59  which is activated by an activating means. The activating means comprises an opening mechanism  58 , a pressure sensor  54  configured as a pressure plate and an acceleration sensor  57  each connected to the other by a traction means  56 , for example a wire cable or Bowden cable. When involved in a rear-end impact a vehicle occupant  52  seated in the vehicle seat  50  is urged against the backrest  52  due to the mass inertia to thereby displace the pressure plate  54  against the force of the return springs  55 . The acceleration sensor  57  does not release the traction cable  56  until the acceleration corresponds to the value of a rear-end impact so that the movement of the supporting plate is then passed on via the traction cable into the opening mechanism  58  which opens the gas source  59 , for instance a gas cartridge, and thus inflate the protective cushion  60 . Due to the function of the acceleration sensor  57  the traction means  56  is clamped in place as long as no rear-end impact is detected so that the gas source is unable to be activated solely by the pressure plate  54  being impressed which, for example, would be the case were the vehicle occupant to allow himself to drop into the seat heavily. 
     The invention thus also provides an activating means for an inflatable headrest without electronic or pyrotechnic components which reliably prevents activation as long as no rear-end impact is involved or the corresponding seat is unoccupied. Due to the absence of electronic and pyrotechnic components the means is not dependent on an external energy source and is accordingly less susceptible to trouble, although, of course, there is no problem in making use of a pyrotechnic gas generator as an alternative for inflating the protective cushion. 
     Referring now to FIGS. 10 and 11 there is illustrated the pressure sensor configured as a gas bladder  74  in the backrest  53  connected by tubing  75  via the acceleration sensor  76  to the inflatable protective cushion  77  in the headrest  51 . The acceleration sensor  76  comprises a valve  78  which shuts off the tubing  75  until an acceleration is sensed corresponding to a rear-end impact. In a rear-end impact (FIG. 11) the vehicle occupant  52  is urged into the backrest  53  and forces the gas from the gas bladder  74  through the tubing  75  via the opened valve  78  into the protective cushion  77  causing it to inflate and enabling it to develop its protective effect by enlargement and approximation of the headrest, as already described. Due to the activating means as described with reference to FIGS. 8 to  11  it is also prevented that the protective cushion  77  is inflated in the headrest  51  when the corresponding seat is unoccupied. 
     In this embodiment too, the absence of electronic and pyrotechnic components makes it independent of an external energy supply, it being even simpler and thus less susceptible to trouble due to the small number of mechanical components required, although, here too, there is no problem in making use of a pyrotechnic gas generator as an alternative for inflating the protective cushion.