Abstract:
A headrest adjustment assembly is disclosed for adjusting the position of a headrest relative to a seatback. The headrest adjustment assembly includes a guide disposed in the seat back, at least one holding bar disposed within the guide, the guide and holding bar being configured with sufficient clearance to allow selective relative longitudinal and transverse sliding, the holding bar being fixed to the headrest, and a clamping element mounted to the seat back for selectively applying a transverse force to the holding bar to thereby fix the position of the holding bar within the guide and prevent relative transverse or longitudinal sliding.

Description:
FIELD OF INVENTION  
       [0001]     The invention concerns a vehicle seat with a headrest having at least one holding bar, which is height-adjustably secured on at least one support base, which itself is enclosed within a reclinable seat back and affixed to a carrying structure, as well as a headrest adjustment assembly.  
       BACKGROUND OF INVENTION  
       [0002]     In order to hold to the lowest possible level the force necessary for the elevation or lowering of a rear seat headrest, whether this be done manually or by remotely actuated, automatic means, it is of advantage if the holding bars of said head rest move within a guide component wherein a radial clearance is present. Counter to this concept, the danger is present, that where such play exists between a holding bar and its support, that the headrest will wobble during driving periods and emit rattling noises. A secure retention of the headrest in the reclining seat back requires, further, auxiliary aids such as springs or motor powered drives, in order to be able to remotely allow the headrest to move into its lowest position. In a backseat arrangement made known by DE 195 32 260 C2, the holding bar of a headrest is held by force in its lowest position of elevation by means of a compression spring acting in that direction. The spring becomes active, if an arresting means, in the form of a spring projection obstructingly resting within a notch in the holder rod is removed therefrom by remote action. The problem which arises is that a wobble-free seating of the headrest is dependent upon friction, whereby high adjusting forces become necessary. From this situation, a large adjustment force of the spring is required, which in turn demands a spring of correspondingly large dimensions. This disadvantage brings in turn, the problem that the user, upon the lifting of the headrest by hand, must overcome not only the frictional resistance between the holding bar and the support, but also force of the spring, which exercises this force in a downward direction. Yet another problem in the described arrangement, and also in the case of a motor powered lowering, is that the active connection between the spring or the drive must finally be dismantled, when the headrest is to be removed from the reclining seat back.  
       SUMMARY  
       [0003]     Based on this background, it is the purpose of the invention to propose a vehicle seat, wherein a headrest of said seat is so supported, that, during operational periods, it is free from play and the therewith associated wobbling and is noiselessly secured in the reclining seat back, and will allow itself to be lowered, without the aid of springs or motor drives, by no more force than its own weight.  
         [0004]     This purpose is achieved in accord with certain aspects of the present disclosure, in that a tubular support affixed within the reclined seat back encompasses the holding bar with radial clearance. Further, a clamping element, made movable between a fixed position and a released situation by a remote controlled drive is installed. In addition, when the said clamping element is in its fixed position, a holding bar is subjected to a clamping force impelling it transversely to its longitudinal direction. In this way, the holding bar, with the outer surface of its circumference, is pressed against its support in such a manner, that it now, loaded with its said longitudinally transverse clamping force, becomes stationarily affixed within its support.  
         [0005]     By means of this arrangement, a nearly frictionless axial movement, especially during the lowering of the headrest, assures that, between the headrest and one of the guiding supports a completely circumferentially located, radial clearance exists. When the holding bar is not loaded with a clamping force, then the headrest, by virtue of its own weight is free to move unhindered in a downward direction. A fixed and wobble-free seat of the headrest when in use is thereby achieved, in that the mentioned circumferential radial clearance is removed by a clamping mechanism, while the holding bar, upon loading by a clamping force having a frictional contact acting in an axial direction, is pressed into a support. The shape closure between the holding bar and its support is advantageously, thereby effected, in that the support forms a receiving type, circumferential zone, which accepts the holding bar in a form-fit manner. Consideration can also be granted to an embodiment wherein the support possesses a projection, which protrudes radially inward and engages itself in a complementary recess of the holding bar. In spite of the said radial clearance between the support and the holding bar, the said holding bar cannot avoid, during its operational time, coming into contact with a support, especially if the holding bar, for instance, is subject to fabrication tolerances deviating from specified dimensioning and structure. In order to hold the friction to the lowest possible level, the proposal is, in the case of a preferred arrangement, that a protruding receiving element with a point or linear contact zone of the support acts against the circumferential surface of the holding bar.  
         [0006]     Normally, in the case of a headrest, a hand-operated arresting agent for the position setting of the headrest at various levels of elevation is present. In order to be able to undertake, in spite of such a design, a remote actuated lowering of the headrest, in a preferred embodiment variant, provision is made that the arresting agent is to be so coupled with the clamping element, relative to movement, that the arresting agent of the holding bar becomes suspended during a released condition of the clamping element. Also, in that state of the clamping element wherein a fixing position is possible, a release is effected of the arresting agent, and therewith the said elevation adjustment of the head rest by hand becomes possible. At the same time, the clamping elements exert their force on the holding bars.  
         [0007]     In order to reduce the expenditure of force upon the lifting of the headrest, a clamping element can be aided in the direction of subject securement by a spring element, which can also be designed as a gas-spring and be activated in an opposite direction by a servomotor. This has the advantage, that the clamping element presses the holding bar permanently and with nearly the same clamping force against its circumferential surface, even if this, for instance, depends under the condition of tolerances on the lifting of the headrest. Consideration can also be given to a bidirectional movement coupling between the arresting apparatus and a clamping element. With the release of the arresting apparatus by hand, then also, the clamping on the holding bar is relieved, so that, upon the lifting of the headrest, only the weight thereof need be overcome.  
         [0008]     In the case of headrests, which posses a second holding bar in connection with the first holding bar, provision has been made, that in a cross direction, that is, in a direction running transverse to the longitudinal axis of the vehicle, at least one of the two holding bars is subjected to the force of a clamping element. Since both holding bars are, movementwise, coupled together, then the release of the radial clearance between the holding bars and their support is carried out in a first embodiment variant, so that both holding bars, simultaneously are impelled in a transverse direction and, with the aid of one clamping element, are actively form-fit pressed into a corresponding, vehicle axis following the direction of the vehicle. As this is done, it suffices when only one holding bar is retainingly loaded by one clamping element. In a second method variant the necessary radial clearance for lowering the headrest is released, in that both holding bars, by a change in their separating distance, are elastically deformed and are pressed into a recess of a ring bearing thereby. By means of the elastic deformation, the holding bars are brought out of their original parallel alignment and assume a converging mutual position.  
         [0009]     In the case of embodiment variants, wherein at least one holding bar is subjected to force in the transverse direction by a clamping element, provision is advantageously made, that in the fixed position, between the clamping element and a holding bar, an effective form-fit is achieved in the longitudinal direction of the vehicle. The clamping element takes over, when this is done, the function of a basic support in the said longitudinal direction of the vehicle. Should, for example, there be a headrest with two holding bars, a three-point support could be provided, and it would be sufficient, if a clamping element fulfills one support function and yet additionally, for each holding bar, there would still be one support of the above described kind. The form-fit between the holding bar and the clamping element is, advantageously, so carried out, that that surface, which is coacting with the circumferential surface of the holding bar, has a complementary concave shape, whereby a receiving zone for the said holding bar is formed.  
         [0010]     In the case of one embodiment example, wherein, principally, a holding bar is subjected to force by a clamping element, provision is made, that a drive of a spring element exerts itself on the clamping element in the direction of the desired fixation, while an oppositely directed servomotor seeks to place the holding bar in its release position. Such a drive can easily be installed within the reclining seat back between the two holding bars, whereby the outside dimension in the direction of travel can be held to relatively small proportions. This reduction of installation space is generally the case, if a leaf spring is employed as the said spring element, the one end of which leaf spring abuts a stationary base and the free end thereof is connected with the clamping element. As a servomotor, there is provided on a flat side of the leaf spring an air spring with a controllable filling capability, which is changeable with the curvature of the leaf spring.  
         [0011]     The advantage of that said drive is that it is comprised of only two, simply made components, which run reliably, for a long operational life. These two components consist of the said leaf spring and air spring. Likewise, there can be considered a membrane cylinder, that is, a so-called pressure cylinder, which is spring induced to move in the affixing direction.  
         [0012]     In an additional advantageous, variant embodiment, each holding bar is assigned one clamping element, whereby the holding bars, when in a fixed position, are subjected to forces acting in the opposite direction from that of the clamping forces. The clamping elements and a common, servo drive assigned to them, in this arrangement, are advantageously placed between the holding bars. In other words, the holding bars are bent away from each other, causing an increase in their separating distance and are respectively conducted into a ring bearing.  
         [0013]     This said bearing arrangement assures a form-fit, which is transverse to the clamping force, i.e., thus an effective connection in the longitudinal direction of the vehicle. Advantageous to this application of force from the clamps, is that upon a failure of the clamping elements, the holding bars spring back into their original parallel alignment, whereby the original radial clearance between them and the supports, that is the clamping elements is again established, so that a nearly frictionless lowering of the head is enabled. To reduce the driving force of the two clamping elements, provision has been made that these are bound together by a knee linkage with a servomotor.  
         [0014]     In the case of the embodiment examples described up to this point, the clamping of the holding bars is carried out in a transverse direction. In an additional embodiment, one holding bar is subjected to a clamping force exercised in the direction of travel. The holding bar is also held in an upper and a lower ring bearing, whereby the clamping force will now be applied at a location underneath the two said ring bearings. The holding bar, in this arrangement, receiving force over a circumferential area facing the direction of travel, is pressed into a recess within the lower ring bearing and simultaneously receives force over a circumferential area facing away from the direction of travel, whereby it is pressed into a recess within an upper ring bearing. Upon the application of a clamping force, thus the holding bar secures itself on the lower ring bearing in the manner of a whip, whereby the holding bar in the upper ring bearing is stationary and under pressure. In this way, without even an elastic deformation, the holding bar assures a sufficient fixation of the headrest in the axial direction. A clearance-free seat in the transverse direction is achieved therein, in that the ring bearings, as in the case of the above described embodiment examples, work in form-fit combination with the holding bar. This form-fit is, however, only provided by one holding bar. In the possible case that a second holding bar is involved, then the receiving recesses of the ring bearings are so adapted, that these enable a clearance for the holding bar in the transverse direction. In this arrangement, it is of advantage, that in a case of a failure of parallelism, this failure being possibly a diverging alignment of the two holding bars, the second bar can execute a sideways movement, during the lifting and the lowering of the headrest in the supports provided for this purpose. A error in the parallel alignment of the holding bars does not increase either the friction or the therewith associated adjustment force during a gravity based lowering nor by a manual lifting of the headrest.  
         [0015]     Advantageously the desired clearance in the transverse direction is achieved, in that the receiving recesses possess a detent surface active in the transverse direction as well as in the longitudinal direction.  
         [0016]     The available installation space of a reclining seat back in the longitudinal direction of the vehicle is, by its nature, very limited. In the case of a preferred variant, on this account, the clamping elements are also designed as lever arms, which are pivotal about an axle running in the transverse direction, and can coact, with their downward pointing free ends with a holding bar. The lever arms run in a space-saving manner in the longitudinal direction of the said holding bars. For the movement of the clamping elements, in their released state, these elements possess extended projections, which extend themselves in the direction of travel, as well as, again in a space-saving manner, into the space existing between the holding bars. The free ends of the said extended projection are bound to one another by means of a bridge section, which can be hingedly swung downward by a servomotor. The said servomotor can be installed with little demand of space in the reclining seat back in the vehicle longitudinal direction. 
     
    
     BRIEF SUMMARY OF THE DRAWINGS  
       [0017]     In the following, with the aid of the attached figures showing one advantageous embodiment, the invention will be described and explained in greater detail. There is shown in:  
         [0018]      FIG. 1 a  perspective of a first embodiment of a vehicle seat with a headrest, whereby, principally a carrier structure of the reclining seat back is visible,  
         [0019]      FIG. 2 a  cross-section of the assembly of  FIG. 1 , taken along line II-II of  FIG. 4 ,  
         [0020]      FIG. 3 a  cross-section of the assembly of  FIG. 1 , taken along line III-III of  FIG. 6 ,  
         [0021]      FIG. 4 a  cross-section of the assembly of  FIG. 1 , taken along line IV-IV in  FIG. 2 ,  
         [0022]      FIG. 4   a  a cross-section of the assembly of  FIG. 1 , taken along line IVA-IVA of  FIG. 4 ,  
         [0023]      FIG. 5 a  cross-section of the assembly of  FIG. 1 , taken along line V-V in  FIG. 2 ,  
         [0024]      FIG. 6 a  cross-section of the assembly of  FIG. 1 , taken along line VI-VI of  FIG. 3   
         [0025]      FIG. 7  an enlarged view of detail VII of  FIG. 4 ,  
         [0026]      FIG. 8 a  perspective of a variant of the embodiment of  FIG. 1   
         [0027]      FIG. 9 a  cross-section of a second embodiment in a situation wherein the headrest is fixed, and is also found in it used condition,  
         [0028]      FIG. 10 a  cross-section of the assembly of  FIG. 9 , wherein the headrest is not fixed, and can be raised by hand or can be lowered by gravity,  
         [0029]      FIG. 11 a  cross-section of the assembly of  FIG. 9 , taken along line XI-XI of the  FIGS. 9 and 10 ,  
         [0030]      FIG. 12 a  cross section of the assembly of  FIG. 9 , taken along line XII-XII of the  FIGS. 9 and 10 ,  
         [0031]      FIG. 13 a  perspective of a third embodiment,  
         [0032]      FIG. 14 a  cross-section of the assembly of  FIG. 13 , taken along line XVI-XVI in  FIG. 16 , which shows the head rest in its operating state,  
         [0033]      FIG. 15  an enlarged view of a portion of  FIG. 14 ,  
         [0034]      FIG. 16 a  cross-section of the assembly of  FIG. 13 , taken along line XVI-XVI of  FIG. 13 ,  
         [0035]      FIG. 17 a  cross-section of the assembly of  FIG. 13 , taken along line XVII-XVII of  FIG. 14 ,  
         [0036]      FIG. 18 a  cross section of the assembly of  FIG. 13 , taken along line XVIII-XVIII of  FIG. 14 ,  
         [0037]      FIG. 19 a  cross-section of the assembly of  FIG. 13 , taken along line XIX-XIX of  FIG. 14 ,  
         [0038]      FIG. 20 a  cross-section of the assembly of  FIG. 13 , taken along line XX-XX of  FIG. 15 ,  
         [0039]      FIG. 21 a  cross-section of the assembly of  FIG. 13 , taken along line XXI-XXI of  FIG. 15 ,  
         [0040]      FIG. 22 a  cross-section of the assembly of  FIG. 13 , taken along line XXII-XXII of  FIG. 15 ,  
         [0041]      FIG. 23 a  cross-section of the assembly of  FIG. 13 , which shows a head rest in the released condition,  
         [0042]      FIG. 24  an enlarged view of detail XXIV of  FIG. 16 , and  
         [0043]      FIG. 25  an enlarged view of detail XXV of  FIG. 23 . 
     
    
     DETAILED DESCRIPTION  
       [0044]     Reference will now be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, and not meant as a limitation of the invention. For example, features illustrated or described as part of one embodiment may be used with another embodiment to yield a third embodiment. It is intended that the present disclosure include these and other modifications and variations. In discussing various embodiments, like or similar reference numbers are used below to refer to like or similar parts of the various embodiments.  
         [0045]     The headrest of the embodiments shown in FIGS.  1  to  8 , possess the following basics of construction, which are also to be found in the embodiments shown in FIGS.  9  to  12 , as well as in FIGS.  13  to  25 . Each headrest, all designated with the reference number  1 , comprises a head-cushion (not shown), which extends from a first holding bar  2  to a second holding bar  3 . The two holding bars, seen in cross-section as being rounded, are separated from one another at a predetermined distance by a cross bar  4  and run, at least in accord with the specifications, parallel to one another. In the reclining back  5  of the seat (shown in  FIG. 14 ) is a carrying structure  6  for the said reclining back  5 , whereby this, in turn, is itself affixed to a seat framing  7 . The carrier structure  6  consists of two guide parts  8 ,  9 , which respectively circumferentially enclose a holding bar  2 , 3 . The open channel  10 ,  11 , which is bounded by a guide part  8 , 9  is again formed above, within a tube section  12 , which is affixed on the carrier structure  6  and bears on its upper end face a covering cap  13 , which lies on the upper side of the reclining seat back  5  (see also  FIG. 14 ). The inside diameter of a channel  10 ,  11  is greater than the outside diameter  14  of the holding bars  2 ,  3 . Between these and a guide part  8 ,  9  exists, on this account, a fully circumferential radial clearance, which principally permits a movement of the holding bar in a transverse direction. A transverse direction is that direction which extends at right angles to the longitudinal axis  16  of the vehicle. The channel  10  is extended in the transverse direction  15 , and is also shaped in cross-section more or less extended, lengthened, oval opening (see  FIG. 4A ).  
         [0046]     For a secure and radial fixation of the holder bars  2 , 3 , a clamping device is present. This clamping means includes, essentially, a narrow, slat shaped clamping element  18 , which is placed in channel  10  and extends generally along the entire length of the guide part  8 . The side of the clamping element  18 , which is proximal to the holding bar  2  is complementary to the outside shape of the holding bar  2 . In the “in use” position of the headrest  1 , the clamping element  18 , by means of a drive, is under pressure in a transverse direction  15  with one side  19  facing against the holding bar  2 . The side  19  is within a recess  20  wherein the holding bar  2  lies, having therein a form-fit connection, transverse to the direction of the clamping force F, that is to say, at right angles to the transverse direction  15 . The so form-fitted fixation of the holding bar  3  is reinforced, in that the inner side of the channel  10 , which side is remote from the clamping element  18 , is likewise curved complementary to the circumferential surface of the holding bar  2  and creates as shown in  FIGS. 2, 3  a recess  21  to receive in a form-fitting manner, the holding bar  2  when the clamping element  18  is fixed. The clamping element  18  is freed from its state of fixation, as this fixation is shown in  FIGS. 2, 4  and, as again shown in  FIGS. 3, 6 , becomes movable in a released condition. In this said released condition, the two recesses  20 ,  21  radially retract from the holding bar and allow movement of the holding bar  2  both transversely and longitudinally. The recesses  20 ,  21  form, when this is done, a support to guide the holding rod  2 . As may be inferred from the cross-section of  FIG. 5 , the separating distance in the longitudinal direction of the vehicle  16 , between opposite sides of the channel  10 , from the top down, continually diminishes, which, further, is also the case with the channel  11  of the guide part  9 . This condition assures, that in the case of unfavorable tolerances, the holding bars  2 ,  3  do not come into contact with the lower wall zones of the guide parts  8  and  9 .  
         [0047]     When the affixing element  18  finds itself in its fixed state, then also the second holding bar  3  presses with a circumferential surface against a recess  22  constructed within channel  11 . This recess, which, together with the remaining inner circumferential zone of the guide part  9  forms a support, is also shaped by means of a wall area, which is curved to be complementary to the circumferential surface of the holding bar  3 . During the released state of the clamping element  18 , in accord with  FIGS. 3, 6 , between the holding bars  2 , 3  and the guide parts  8 ,  9  exists an all-around radial clearance  17 . The holding bars  2 ,  3  are thus conducted into the channels  10 ,  11  with only minimal friction, so that the headrest, with no other agent than its weight can move into the lowest position of elevation.  
         [0048]     The drive, with which the clamping element  18  can toggle back and forth between its fixed position and its freed position, encompasses, as its principal components, a leaf spring  23  and an air spring  24 , of which the content of air is adjustable. The leaf spring  23  and the air spring  24  are placed in a space  25  which extends nearly to the fullest extent of the width and height of the carrier structure  6 . This opens with its one end in the channel  10  of the guide part  8 . The width  27  ( FIG. 6 ) of the leaf spring  23  is somewhat less than the length of the clamping element  18  and represents, to a certain extent, the height of the space  25 . The end  26  of the leaf spring  23 , which is proximal to the guide part  8  is bent into a hooklike shape and lies in a correspondingly shaped groove  28  within the clamping element  18 . The space  25  extends on and beyond the forward or back side of the guide part  9  and tapers down to an opening  29 , which opening, when seen in cross-section is somewhat hook shaped, in which opening the leaf spring, with its other, likewise hook shaped end  30 , lies stationarily affixed. In the fixed position of the clamping element  18  ( FIGS. 2, 4 ), the leaf spring  28  is seen as tensioned, and presses the clamping element  18  against the holding bar  2 . This runs somewhat parallel to a wall  31  of the space  25 . Between the wall  31  and the leaf spring  23  is placed the said air spring  24 . By means of a control connection  32  ( FIG. 1 ) the air spring can be filled with air. When this occurs, its side, which is remote from the wall, bulges out, whereby the leaf spring  23  is correspondingly compressed. The end  26 , at this point, is moved away from the holding bar  2  and takes the clamping element  18  along with it. Between the holding bars  2 ,  3  and the guide parts  8 ,  9  is now so much clearance available, that the headrest  1 , as discussed above, for no other reason than its own weight can slide downward into its lowest possible position of elevation.  
         [0049]     The clamping element is swingingly supported about a pivot axle  34 , which extends in a longitudinal bar direction  33 . The said pivot axle  34  is located in a receiver channel  35 , which stands in communication with the channel  10  of the guide part  8  by means of a connection channel  36 . The pivot axle  34  is bound to the clamping element  18  by means of a lever arm  37 . In order to enable a swing movement of the lever arm  37  in the connection channel  36 , this widens in the direction of the channel  10 .  
         [0050]     The filling and the emptying of the air spring  24  is remotely controllable from the driver&#39;s seat. The driver can, accordingly, lower the headrest of the back seats, in order to maintain a free sight line to the rear. Independently of the remote controlled, gravity actuated lowering of the headrest  1  are also elevation adjustments provided, namely a lowering or raising of the head rest by hand. For this activity, the clamping force F must be so designed, that first, a loose and shaky installation of the headrest is avoided and second, the least possible bodily exertion for the elevation adjustment of the said headrest is assured. This is achieved, in that a plastic material is exclusively chosen for the clamping element, which material exhibits a low degree of friction against the metallic holding bar. Particularly adaptable for this application are the so-called alloyed plastics, also such plastic materials into which friction reducing agents have been incorporated, namely Teflon-particulate, talcum, or the like.  
         [0051]     In another way, the friction can be reduced, in that the receiving surfaces  20 ,  21 ,  22  are so designed, that these coact with the circumferential surfaces of the holding bars  2 , 3  at point or linear contacts  38 , which are apportioned about the circumference, (see  FIG. 4A ). This arrangement, to a certain extent, can be achieved, in that the receivers  20 ,  21 ,  22  are aligned to be tangential to the circumferential surfaces of the holding bars  2 ,  3  and possess a flat area  39 , running in the longitudinal direction  33 . In  FIG. 4A  appears the right side view of the headrest  1  in its in-use positioning. The holding bar  2  is pressed by the clamping element  18  (this element not shown) to bring its circumferential surface against the flat surface  39 . In this way, a linear contact zone  38  is created with extends itself in the longitudinal direction  38  of the said holding bar. On the left side of  FIG. 4A , the situation is shown, wherein the clamping element  18 , is to be found in its released condition. By this design, a radial clearance  17  on all sides, which enables a nearly friction-free lowering of the headrest  1  is made available.  
         [0052]     On the inner side of the holding bar  2  is incised a plurality of notches  40 , into which a locking wire  41  is inserted in the area of the of the cover plate  13 . The locking wire  41  is can be ejected from one of the notches  40  by means of a pusher  42 , which said pusher is on the cover plate  13  and acts in a transverse direction. The headrest  1  can then be brought into another position of elevation, whereby, after the release of the pusher  42 , the locking wire  41  then engages in the next successive notch. So that, a remote controlled lowering of the headrest becomes possible, a movement-coupling between the clamping element  18  and the locking wire  41  is provided, in such a manner, that the restraining of the holding bar in the released state of the clamping element is removed, and in that, in the affixed state of the clamping element  18  a release of the restraint and an elevation adjustment of the headrest  1  by hand is made possible. The movement-coupling is assured by a lever arm  43 , which is pivotally swingable about an axle  44  placed within the carrier structure  6 . The lever arm  43 , engages, with its free end  45 , in a recess  46  in the pusher  42 . In the holding position of the locking wire  41  ( FIG. 7 ) the free end  45  lies in the recess  46  on that wall  47 , which is remote from the locking wire  41 . The other wall (not shown in  FIG. 7 ) lies on the locking wire  41 . An activation of the pusher  42 , thus moves the locking wire  41  out of the notch  40 . The lever arm  43  is not affected by the movement of the pusher  42 , due to the presence of the recess  46 . If the clamping element  18  is caused to leave its fixed position and enter into its released position, then the lever arm  43  swings to the left by means of a projection  48  protruding from the clamping element  18 . When this occurs, the free-end  45  of the lever arm  43  carries with it the pusher  42 . The holding bar  2  is thereby unlocked and can drop into its lowest position.  
         [0053]     In the case of the variant shown in  FIG. 8 , provided as a drive in the direction of fixation of the clamping element  18 , is a spring loaded membrane cylinder, or a pneumatic container  49 . This is placed within the carrier structure  6  and activates the clamping element  18  by a spring loaded plunger  50  (not shown in  FIG. 8 ). The movement of the clamping element  18  into its released state is done by charging the said pneumatic container  49  with compressed air, which is available from the connection fitting  32 . Not only in the case of the variant of  FIG. 8 , but also regarding that in  FIG. 1 , the clamping force F is generated by a spring. This has the advantage, that during a deviation of the holding bars  2 ,  3  from their intended specified alignment, such as, for example, a fault in their being parallel, during the manual operated elevation adjustment, the holding bar  2  is always loaded with the same clamping force F. If during an elevation adjustment, the holding bar moves itself away from the clamping element  18 , then this is immediately corrected by the spring action. If the holding bar approaches the clamping element  18 , then it is made to retract by the spring force. Accordingly, even in the case of the tolerance deviations, there is no significant increasing of the frictional force between the holding bar  3  and the guide part  8 , or the clamping element  18 , so that an easy height adjustment by hand can be carried out with an equally continuing expenditure of force. Consequently, similar inherent correction actions serve as well for embodiments which are described hereunder.  
         [0054]     Considering now the FIGS.  9  to  12 , showing another embodiment, the two holding bars  2 ,  3 , on their mutual, proximal inner sides, although in opposite directions, are subjected to force from a clamping element  118 ,  118   a . The upper end section  88  of the guide parts  108 ,  109  form a guiding support for the holding bars  2 ,  3 .  
         [0055]     The application of force onto the holding bars  2 ,  3  is carried out at a lower position of the guide parts  108 ,  109  or on a position lying underneath the guide elements. Further, the said application of force is of such a nature that the holding bars  2 ,  3 , upon the increasing of their separating distance, become deformed, and consequently, the separation is widened. As this occurs, the holding bars  2 ,  3 , fronted by circumferential surface sections, which face in the transverse direction  15 , are pressed into a recess  51  in the end sections  88 , which, for the diminishing of frictional force, possesses two flat, inside surfaces  139 . The in-use state of the headrest, that is, its condition, when the clamping elements  118 ,  118   a  find themselves in their clamping condition, is made clear in  FIGS. 11 and 12  to the right, particularly for the holding bar  2 . These lie with their circumferential surfaces defining touching lines  138  on the flat surfaces  139 . The fixation in the transverse direction  15  is executed thus on the holding bars  2 ,  3  by clamping force F and in the longitudinal vehicle direction  16  by means of the form-fit between the receiving surfaces  51  and the holding bars  2 ,  3 . A form-fit of this kind also exists between the clamping elements  118 ,  118   a  and the holding bars  2 ,  3 , as may be inferred from  FIG. 12 . Also, in this case, the right portion of the illustration presents the fixed and the left portion shows the released state of the headrest  1 . That side of the clamping element  118 ,  118   a , which coacts with the holding bars  2 ,  3 , is concavely curved and possesses two flat surfaces  52 , tangential to the outside circumference of the holding bars  2 ,  3  and running in the longitudinal direction  33  of the bars.  
         [0056]     That part of a clamping element  118 ,  188   a , which coacts with a holding bar  2 ,  3 , is subdivided by means of an axial slot  53  into at least into two extending prongs, wherein each prong  54  carries a flat surface  52 . The clamping elements  118 ,  118   a  are within a housing  55  of the carrier structure  6 , having small clearance  56  allowed to the housing wall  57  ( FIG. 12 , top view). By means of the said clearance  56 , assurance is provided, that the clamping elements  118 ,  188   a  can move unhindered within the housing  55 . In their closed position, the clamping elements  118 ,  188   a  are pressed against the holding bars  2 ,  3 , with the result that these said bars are slightly and elastically bent away from one another. By means of this application of force, in the one abutting flat surface, which is inclined at an angle of 90°, the said prongs  54  are spread in the longitudinal direction  16  of the vehicle, and accordingly press against the inner surface of the housing wall  57 . Thereby, a zero-clearance, form-fit between the holding bars  2 ,  3  and the clamping elements  118 ,  118   a , acting in the longitudinal direction  16  of the vehicle is assured. The clamping elements  118 ,  118   a  are connected by means of a knee joint linkage  58  to the plunger  59 , which is actuated by an electric motor  60 . In order to assure the continuity of a constantly equal clamping force onto the holding bars  2 ,  3 , it is possible to place in the force transmission line between the knee joint  58  and the plunger  59  a spring element, preferably in the form of a torsion spring (not shown).  
         [0057]     As is especially to be learned from  FIG. 12 , the holding bars  2 ,  3  are not pressed by the clamping elements  118 ,  118   a  against a solid, mechanical detent, such as the wall of a guide part  108 ,  109 , but a separating distance  61  remains thereinbetween, which is shown for clarity, in a somewhat exaggerated manner, in  FIG. 12 . The holding bars  2 ,  3  lie, not only on the clamping elements  118 ,  188   a , but also on the recess  51  of the guide parts  108 ,  109 . Furthermore, the clear inside width of the guide parts  108 ,  109  are so dimensioned, that a contact between the holding bars  2 ,  3  and the guide part  108 ,  109  is prevented. The guidance of the holding bars  2 ,  3  is carried out exclusively in the area of the end section  88  and proximal to the clamping element  118 , and moreover with an elevation adjustment without radial clearance  17  and having a gravity lowering with a radial clearance  17 . The clamping elements  118 ,  118   a  are designed as lever arms  89 ,  90 , which extend in the longitudinal direction  33  of the bars.  
         [0058]     On their lower ends, the lever arms  89 ,  90  are bound by linkage to the knee joint  58 . The lever arm  89  is further bound on its upper end by means of a linkage  92  with the carrier structure  6 . The lever arm  90  is longer than the lever arm  89 , but however, at the same connection elevation as the lever arm  89 , and is connected by means of a linkage  93  to be pivotal with the carrier structure  6 . The axles of the stated linkages  91 ,  92 ,  93  run in the longitudinal direction of the vehicle. The lever arm  90  acts with its upper end together with an adjacent lever arm  95 , which is pivotally carried by a centrally placed axle  94 , which axle extends in the longitudinal direction of the vehicle. In the released position of the clamping elements  118 ,  118   a  the said lever arm  90 , with its upper end, applies pressure on the lower end of the lever arm  95 . This then rotates to the extent, that its upper end, which coacts on a detent  96  of the pusher  42 , and brings this into a position, in which a locking wire  41  is brought out of its engagement in a notch  40  in the holding bar  3 . The head rest  1  is then freely movable with its holding bars  2 ,  3  in the guide parts  108 ,  109 . In the fixed position of the clamping elements  118 ,  118   a , the lever arm  95  is retracted into its starting position by the pusher  42 , in which the lever arm  95  lies with its under end on the upper end of the lever arm  90 . The sides of the clamping elements  218 ,  218   a  which coact with the holding bars are designed as flat surfaces which extend in the transverse direction  15 .  
         [0059]     In FIGS.  13  to  25 , another embodiment is presented, wherein, contrary to the above described embodiments, the holding bars  2  and  3  are to be found not in the transverse direction  15 , but rather in the longitudinal direction  16  of the vehicle, more exactly in the travel direction  62 . Accordingly, an efficient form-fit is made in the transverse direction, between the guide parts  208 ,  209  and the holding bars  2 ,  3 . The clamping elements  218 ,  218   a  are constructed of two lever arms  63  extending themselves approximately in the same direction as the holding arms, which clamping elements, respectively are pivotally carried about a respective axle  64  which is affixed to the carrier structure  6 . The downward pointing free ends  65  of the lever arms  63  are respectively under pressure from the arms  66  of a spring extension  66   a , which referred pressure works against the circumferential surface of each of the holding bars  2 ,  3 . These bars, again can be slightly, elastically deformed thereby, which, however, for a secure fixation of the headrest  1  is not necessary. In the guide parts  208 ,  209  is to be respectively found for the holding arms  2 ,  3  an upper bearing, made from a first projecting ring  70  extending itself radially inward and also a lower bearing, made from a second projecting ring  69 , again extending itself inward. In the inside circumferences of the projecting rings  69 ,  70  are located the recesses  67 ,  68 . The recess  67  of the upper projecting ring  70  is located on that side of a holding bar  2 ,  3 , which faces into the direction of travel  62 , where, conversely, the recess  68  of the lower projecting ring  69  is to be found on that side of the holding bar  2 ,  3  which faces contrary to the direction of travel  62 . The recesses  67 ,  68  which coact with the holding bar  2  comprise flat surfaces  239 , which are tangential to the circumferential surface of the holding bar  2  and run in the longitudinal direction  33  thereof and enclose an angle. In the fixed position of the clamping element  218 , the holding bar  2  acts to form a contact line  238  together with the flat surfaces  239 . Thereby, an active form-fit, in the transverse direction  15  is made between the holding bar  2  and the guide part  208 .  
         [0060]     The receiving recesses  67   a ,  68   a  of the guide part  109 , which coact with the holding bars  2 ,  3 , possess a flat surface  72  which extends in the transverse direction  15 , onto which the holding bar  3  lies with a line shaped contact position  238 . This arrangement assures, that, in the case of a manual elevation adjustment, when a faulty parallel alignment of the holding bars  2 ,  3  exists, the holding bar  3  can carry out a movement in the transverse direction  15  while the holding bar  2  is guided without clearance in the transverse direction  15  within the recesses  67  and  68 .  
         [0061]     On the inner sides of the lever arms  63 , which face one another, is placed an extension piece  73 , which runs in the direction of travel  62 . The pivoting of this extension piece  73  downward so acts, that the clamping elements  218 ,  218   a  are moved into their released condition. For the pivoting, the free ends of the extension piece  73  are bound together by a somewhat strip shaped bridge component  74 . On its upper edge, the bridge  74  possesses a projecting detent  75 , which acts counter to the travel direction  62 . On the carrier structure  6  is linkedly connected a lever  76 , which extends in a transverse direction  15 . The free end of the lever  76  is in turn bound by a connection piece  77  to a plunger  79 , which is moved by an electric motor  78  in, somewhat, the direction  33  of a holding bar. If the plunger  79  is moved downward by the electric motor  78 , then the lever  76  takes the bridge component  74  along with it. When this occurs, the extension piece  73  swings downward and accordingly, the thereon attached lever arm  63  enters into its released position (see  FIGS. 15 and 20  to  23 ). In the released position the holding bars  2 ,  3  are conducted through the bearings made by the ring projections  69 ,  70  with a radial clearance  17  on all sides. The radial clearance, in this instance, is so dimensioned, that even a curved holding bar  2 ,  3 , as in the previous embodiment, is so guided, that a lowering of the headrest  1  is possible because of its weight.  
         [0062]     A restraining of the headrest  1  at various positions of elevation is realized in the same manner and way as has been described previously for the embodiments explained above. This restraint would be by means of a locking wire  411  which has engaged in a notch  40 . Such a restraint can be relieved by a pusher  42 . The moving-coupling between the clamping elements  218 ,  218   a  and the pusher  42  is done by means of a plunger  80  ( FIGS. 13, 24 ,  25 ) which is located somewhat in the upper area, extending in the holding bar direction  33 , but only up to just below the cover plate  13 . At the upper end of the said plunger  80 , are two angle levers  81 , which border the guide part  208  on both sides. Further, the angle levers are connected together by a linkage  97 . Each of which levers  81  possesses a first arm  82  which extends somewhat in a transverse direction  15  and a second arm  83 , which is affixed to the free end of the said first arm  82 . The second arm  83  extends approximately in a direction  33  parallel to the longitudinal axis of the holding rod. At the connection point between the arms  82 ,  83 , the angle levers are bound together by an axle  84  running in the longitudinal direction  16  of the vehicle. The axle  84  is turnably enclosed in a bearing  85 , which is an integral element of the of the guide part  208 . With its free end (not shown) the arm  83  engages itself in a recess  27  of the pusher  42 . The recess  27  is located in underside location and extends itself in the transverse direction. Further, the arm  83 , with its side which faces the holding bar  2 , coacts with a detent surface  86 .  
         [0063]     Upon a manual positional adjustment of the headrest  1 , the pusher  42  would be activated in order to free the restraints to the movement thereof, that is, in  FIG. 24  the pusher  42  would be pushed to the left. When this occurs, then the locking wire  41  is ejected from its enclosure in the notch  40 . On the account of the recess  87 , the arm  83 , which is engaged in the underside of the pusher  42 , does not obstruct the pushing movement. If, however, starting considerations from the situation shown in  FIG. 24 , the clamping elements  218 ,  218   a  occupy their released position, in which the lever  76  has been pivoted down by the electric motor, then the plunger  80 , because of its drive-like connection with the lever  76  is also moved down along with the angle lever  81  on its end, which is connected to the said plunger  60 . The result is, that the arm  83  of the angle lever  81  abuts against the detent surface  86  of the pusher  42 , so that this is activated and the locking wire is expelled from its engagement in the notch  40 . The headrest, accordingly, can drop into its lowest position by the force of gravity.  
         [0064]     It should be understood that various modifications and variations of the above are possible within the scope of the invention, as defined by the following claims and their equivalents.