Abstract:
A motor-vehicle headrest has a head part and a base part, the latter being surrounded by and shiftable on the head part in a predetermined direction. A pair of inner racks on the base part are directed oppositely outward toward the head part and each have an array extending in the direction of gear teeth. Similarly, a pair of outer racks on the base part are directed toward each other inward, confront the inner racks, and are formed with respective arrays extending in the direction of gear teeth. Respective gears each mesh with a respective one of the outer racks and the respective inner rack so that on movement between the inner and outer positions the gears roll between the respective racks. A play compensator between one of the racks and the respective part biases the racks and gears into tight engagement with one another.

Description:
FIELD OF THE INVENTION 
     The invention relates primarily to a vehicle-seat headrest having a base part and a headrest part movable relative to the base part between a back position and a front position by a bearing assembly comprising a first bearing element associated with the base part and a second bearing element associated with the headrest part, the first bearing element and the second bearing element forming respective bearing surfaces that are interconnected and form at least one bearing-surface pair. 
     BACKGROUND OF THE INVENTION 
     A headrest is known from DE 10 2004 059 237 [US 2006/0119150] where the head casing can be adjusted between a first and a second position relative to the support rods. Three column-like guides are anchored in the head casing and held in sliding guides that are firmly connected to the support rods. 
     A headrest is known from DE 10 2007 002 615 where a headrest part can be moved relative to a base part that is firmly connected to the support rods. A tubular guide is integrally molded to the headrest part can telescope in a sleeve integrally molded on the base part. The further the headrest part is offset from the base part, the smaller the effective contact surface by means of which the headrest part is supported on the base part. 
     A headrest is known from DE 10 2006 016 270 where the headrest part has two posts supported in guide sleeves of the base part. In this manner the headrest part can be horizontally adjusted relative to the base part. For quick forward movement of the headrest part in case of a crash, a spring is connected to a gear assembly. When the spring is released the spring travel x causes movement of the headrest part of 2×. 
     OBJECT OF THE INVENTION 
     Based on this prior art it is the object of the invention to create a headrest that is very stable in any position. Furthermore, the headrest should not make any annoying noise, and be precisely guided. 
     SUMMARY OF THE INVENTION 
     The object is primarily attained according to by a headrest having a base part and a headrest part that can be moved relative to the base part between a back position and a front position. A first bearing element is attached to the base part and is coupled with a second bearing element of the headrest part. The first bearing element and the second bearing element form bearing surfaces that directly or indirectly are coupled with each other while forming at least one bearing-surface pair. The bearing surfaces of the second bearing element are supported on the bearing surfaces of the first bearing element. The bearing surfaces of the bearing-surface pair are in contact with each other. 
     The term bearing element as used in the present application means bearing and guide elements. The term bearing surfaces as used in the present application means bearing and guide surfaces. 
     For example, the first bearing element and the second bearing element may be coupled with each other via a force-transmitter engaging into both bearing elements. The force-transmitter may be formed, for example, by one or more toothed sleeve gears. In this case, the bearing surfaces of the first bearing element and of the second bearing element mesh with the toothed sleeve gear. Together with the surface of the toothed sleeve gear, the bearing surfaces of the first bearing element and the bearing surfaces of the second bearing element form a pair of bearing surfaces that are in contact with each other. 
     A gear may be connected between the first bearing element and the second bearing element by means of which the first bearing element and the second bearing element operate together. 
     The headrest has a play compensator by means of which at least one bearing-surface pair is biased into engagement. The coupled-together surfaces of the first bearing element and of the second bearing element are biased into engagement such that forces can be transferred between the first bearing element and the second bearing element. If, for example, the bearing surfaces of the bearing-surface pair are associated with interacting positive fit means, the positive fit means are biased into positive engagement. If, for example, the bearing surfaces of the bearing-surface pair is formed by coupled-together gears, the gears are biased into engagement with each other. The first bearing element and/or the second bearing element and/or at least one force-transmitting element may be supported, for example, with movement clearance. The bearing surfaces of the bearing-surface pair are kept in contact by the play compensator such that the headrest part is precisely guided despite the movement clearance. The play compensator prevents any undesired movements of the headrest part, which would cause, for example, annoying noise. 
     In addition the play compensator may comprise means ensuring that the bearing surfaces of the bearing-surface pair, which engage each other in a positive fit such as via coupled-together gears, cannot move out of engagement. 
     The headrest part is therefore supported on the base body without play. The headrest part causes no annoying noise caused by movement clearance. More precise guiding is achieved due to the interconnection of the bearing surfaces of the bearing-surface pairs that is free of any play. Furthermore, any manufacturing tolerances of the coupled-together bearing surfaces may be compensated for by this embodiment. 
     According to one embodiment of the invention the play compensator comprises at least one elastic support. Due to deformation of the elastic support a return force may be applied to the elements that engage with the elastic support. The elastic support may be prestressed, for example, such that a force is continuously applied to the elements coupled-together by the elastic support. The elastic support may apply, for example, a force to the first bearing element and/or to the second bearing element and/or to the force-transmitter. For example, teeth of the headrest part may be held in engagement with teeth of a toothed gear of the force-transmitter by the elastic support. As an alternative, or in addition, teeth of the base body, for example, may be held in mesh with the teeth of the toothed gear of the force-transmitter by the elastic support. For example, the elastic support may be formed by a spring or an elastically deformable plastic. 
     According to a further embodiment of the invention the play compensator comprises at least one force deflector by means of which a first force having a first effective direction can be converted into a second force having a second effective direction. The force deflector makes it possible, for example, to use the return force of an elastic support to prestress multiple bearing-surface pairs while in contact with each other. 
     According to another embodiment the force deflector comprises at least one deflecting element biased by the elastic return force of the elastic support against a bearing surface positioned at an angle to the first effective direction. The bearing surface may be, for example, a surface of the base body, or for example, a surface of the headrest part. The deflecting element is associated with, for example, a primary bearing surface of a bearing-surface pair and biases a secondary bearing surface of the bearing-surface pair while in contact with the primary bearing surface. The primary bearing surface and the secondary bearing surface may be, for example, bearing surfaces of the first or of the second bearing element, or a bearing surface of the force-transmitter. A first deflection element and a second deflection element may be supported, for example, on the force-transmitter. The first deflection element may, for example, bias a bearing surface of the first bearing element into engagement with the force-transmitter. The second deflection element may, for example, bias a bearing surface of the second bearing element into contact with the force-transmitter. 
     According to a further embodiment of the invention the deflection element is formed by a ball half. The ball half has a convex surface making point contact with the bearing surface. 
     Regarding the characteristics of the generic part, reference is made to the explanations given as to the first-discussed aspect of the invention. 
     According to the second-discussed aspect of the invention the bearing assembly comprises first gear teeth associated with the first bearing element and second gear teeth associated with the second bearing element. The first gear teeth are connected with the second gear teeth. The first gear teeth and the second gear teeth may be connected with each other directly or indirectly. Pivoting of the headrest part about at least one axis may be prevented by the first gear teeth and the second gear teeth. The first gear teeth and the second gear teeth may form, for example, bearing-surface pairs whose contact surfaces in a straight line. 
     The coupled-together first gear teeth and the second gear teeth may form a force-transmitter of the head part. 
     The first gear teeth and the second gear teeth may, for example, be associated with a guide. At least one primary guide may, for example, prevent pivoting about a first axis of the headrest part. At least one secondary guide may prevent pivoting of the headrest part about a second spatial axis. In addition the guide may, for example, prevent straight-line movement in at least one direction. A precise and jam-free guiding of the headrest part is possible by the coupled-together gears. 
     Gears enable the transmission of large forces and guarantee precise guiding without the risk of jamming. Furthermore, gears may formed any desired transmission ratios for the gear teeth. The gear teeth may be any type of teeth, such as a gear rod, toothed rod, or the like. The coupled-together gear teeth may form a gear transmission. A step up or down may be done by the coupled-together gear teeth; in particular, the coupled-together gear teeth may at least partially produce different travels upon the movement of the headrest part between the back position and the front position. Furthermore, a supporting that is free of clearance is possible in any position of the headrest part, for example, by providing elastic supports, which stress the is coupled-together gears during engagement. 
     The effective length of the coupled-together gear teeth, e.g. the length over which forces from the gear teeth may be absorbed, is significant for the quality of the guide. The longer the length over which a bearing-surface pair of coupled-together gear teeth is in contact, the better the quality of the supporting and guiding, and the more effectively pivoting of the headrest part is prevented. The bearing-surface pair may, for example, use line contact. 
     According to a further embodiment of the invention the first bearing element and the second bearing element are coupled to each other via at least one force-transmitter. A transmission ratio can be created by the force-transmitter. As an alternative, a spacing between the first bearing element and the second bearing element may be bridged, for example, by the force-transmitter. As an alternative or in addition it is possible, for example, to provide the force-transmitter with a manual or motor drive in order to move the headrest part in this manner. The force-transmitter is in contact with the first gear teeth and the second gear teeth. 
     According to a further embodiment the force-transmitter may comprise at least one toothed gear. If the force-transmitter comprises at least one toothed gear, the toothed gear is in contact, for example, with the first gear teeth and with the second gear teeth. The teeth of the gear are engaged in the first gear teeth and the second gear teeth. If the force-transmitter is formed by at least one toothed gear it is possible that the first gear teeth and the second gear teeth are formed by a rack. 
     According to another embodiment the first gear teeth and the second gear teeth form a gear transmission. In this manner it is possible to provide a transmission ratio between movable parts of the headrest. For example, the headrest part may be supported on the base body by a gear transmission. For example, a different movement may be carried out between the headrest part and a rear cover of the headrest by the gear transmission. For example, the rear cover may move half of the travel of the headrest part on movement of the headrest part between the back position and the front position. 
     For example, the first bearing element comprises at least one first rack that is planar or arcuate, and the second bearing element comprises a second rack that is planar or arcuate, at least one toothed gear being provided that meshes with both the first rack and the second rack. The axial length by means of which the toothed gear engages the first rack and the second rack is substantial for the effectiveness of the guide of the headrest part. Upon the movement of the headrest part between the back position and the front position the toothed gear rolls off on both the first rack and on the second rack, the center of rotation of the toothed gear moving half of the travel relative to the headrest part. Depending on the shape and size of the toothed gear the path of travel of the headrest part may vary with the movement from the back position into the front position. Furthermore, it is possible with this embodiment to make the headrest small since the secondary bearing element moves twice the travel as the toothed gear upon the movement between the back position and the front position. 
     The bearing assembly may comprise, for example, at least one first guide that prevents pivoting of the headrest part about a horizontal axis extending transverse to a seat direction. The guide has, for example, first gear teeth in the form of at least one first vertical rack and second gear teeth in the form of at least a second vertical rack. The first rack and the second rack are parallel to each other. At least one toothed gear is between the first rack and the second rack, in mesh with the first rack and with the second rack. A shaft of the toothed gear may be guided, for example, in a groove of the base body. The teeth of the first rack, the second rack, and the toothed gear may be formed such that movement of the headrest part in the seat direction and against the seat direction is possible between a back position and a front position, however, pivoting about the horizontal axis mentioned above transverse to the seat direction is prevented. The gears of the first rack, the second rack, and of the toothed gear are aligned, for example, vertically. 
     The bearing assembly may comprise, for example, at least one second guide that prevents pivoting of the headrest part about a vertical axis. The guide has, for example, first gear teeth in the form of at least one first horizontal rack and second gear teeth in the form of at least one second horizontal rack. The first rack and the second rack are parallel to each other. For example, at least one toothed gear is between the first rack and the second rack and meshes with the first rack and with the second rack. The teeth of the first rack, the second rack, and the toothed gear may be formed such that movement of the headrest part is possible toward the seat direction and away from of the seat direction between a back position and a front position, however, pivoting about the vertical axis is prevented. The gears of the first rack, the second rack, and the toothed gear are aligned, for example, horizontally transverse to the seat direction. 
     According to a further embodiment the toothed gear of the force-transmitter is a cylinder. For example, the travel of the headrest part may be straight-line, if the toothed gear is cylindrical. The toothed gear and the racks may be equipped, for example, with straight teeth that extend parallel to the pivot axis of the toothed gear. The toothed gear may mesh, for example, with one or more racks, and particularly make line contact with the rack. 
     According to another embodiment, the toothed gear is frustoconical. The travel of the headrest part may be, for example, circular arc if the toothed gear is formed frustoconical. In this case the racks may be equipped with angled teeth that are aligned with a rotational center of the headrest part. In this embodiment the toothed gear may be equipped, for example, with straight teeth. A frustoconical set of teeth may also be engaged in a rack, and particularly form line contact with the rack. 
     If the headrest part is to have an arcuate travel path between the back position and the front position, a first guide comprises, for example, first gear teeth in the form of at least one first vertical rack and second gear teeth in the form of at least one second vertical rack. The first rack and the second rack are parallel to each other. For example, at least one toothed gear is between the first rack and the second rack and meshes with the first rack and with the second rack. The teeth of the first rack, the second rack, and the toothed gear are formed such that, for example, an arcuate movement of the headrest part in the seat direction and opposite the seat direction is possible between a back position and a front position. The arcuate movement has, for example, a vector in the seat direction, and a vertical vector. However, pivoting about the horizontal axis transverse to the seat direction is prevented. The gears of the first rack and of the second rack are stellate and are centered on the center point of the arcuate travel. The toothed gear is formed, for example, frustoconical, the gears of the toothed gear radiating from the center point of the arcuate travel. 
     For arcuate movement of the headrest part a second guide has, for example, first gear teeth in the form of at least one first rack formed convexly arcuate and extending horizontally and a second gear teeth in the form of at least one second rack formed convexly arcuate and extending horizontally. The arcuate shape of the first rack and of the second rack corresponds, for example, to the arcuate travel of the headrest part. The first rack and the second rack are parallel to each other. For example, at least one cylindrical toothed gear is between the first rack and the second rack and meshes with the first rack and with the second rack. A shaft of the toothed gear may be guided, for example, in a groove of the base body. The teeth of the first rack, the second rack, and of the toothed gear may be formed such that movement of the headrest part in the seat direction and opposite the seat direction is possible between a back position and a front position, however, pivoting about the vertical axis is prevented. The gears of the first rack, the second rack, and of the toothed gear are aligned, for example, horizontally transverse to the seat direction. 
     According to a further embodiment the first bearing element and the second bearing element can move relative to each other in a telescoping manner. For this purpose the first bearing element and the second bearing element are, for example, coaxial to each other in each position, and can be displaced coaxially relative to each other. Being coaxial may mean in the sense of the invention that the second bearing element can be moved relative to the first bearing element traveling parallel to a common axis. The travel may be straight or bent. Movable in a telescoping manner means in the sense of the invention that the first and the second bearing element can be displaced relative to each other between a nested position and an extended position. 
     According to another embodiment a housing-like cover is provided that is movable on the base part and operatively connected to the headrest part. The cover closes an area of the headrest that may be, for example, a back face relative to the travel direction. The cover may be movable into the same direction as the headrest part, or as an alternative, in a different direction. The cover may traverse the same travel during movement of the headrest part, or as an alternative, a different travel. Furthermore, the cover may have, for example, the same travel as the headrest part, or as an alternative, a different travel. 
     According to a further embodiment the cover is is operatively connected to an element of the force-transmitter. The element may be, for example, the pivot axis of the toothed gear that meshes with a rack of the first bearing element and with a rack of the second bearing element. 
     The first bearing element comprises first gear teeth, and the second bearing element comprises second gear teeth. The first gear teeth and the second gear teeth are coupled to each other. The gear teeth can be interconnected directly or indirectly. The first gear teeth and the second gear teeth embody surfaces, which form a bearing-surface pair of coupled-together gears. If, for example, a force-transmitter, particularly at least one toothed gear, is between the first gear teeth and the second gear teeth, for example, a first bearing-surface pair may be formed between the first gear teeth and the force-transmitter, and a second bearing-surface pair may be formed between the second gear teeth and the force-transmitter. The elements embodying the bearing-surface pair have surfaces being in contact with each other. According to the invention the contact surface between the surfaces of the bearing-surface pair is substantially constant in each position of the headrest part. In particular the contact surface between the surfaces of each bearing-surface pair is constant in each position of the headrest part. 
     This way, the headrest part has the same stability in all positions. Furthermore, no different friction forces occur in the positions of the headrest part. The displacement force necessary to move the headrest part is therefore constant. 
     Point contact is formed between the bearing surfaces of at least one bearing-surface pair. Point contact in the sense of the invention means that the contact surface between the elements forming the bearing-surface pair is as small as a point, for example at least one bearing surface of the bearing-surface pair may be convexly arcuate. 
     A low coefficient of friction is formed between the headrest part and the base part due to the point contact. The headrest part can be easily moved between the back position and the front position by the characteristics according to the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       Further advantages of the invention are obvious from the description of the shown embodiments shown in the figures. Therein: 
         FIG. 1  is a perspective schematic rear view of the headrest according to the invention, 
         FIG. 2  is a perspective schematic rear view of the headrest without a cover, 
         FIG. 3  is a schematic longitudinal sectional view of the headrest in a first plane, the support rods not being shown for reasons of clarity, 
         FIG. 4  is a schematic cross-sectional view of the headrest, the headrest part being in the back position, 
         FIG. 5  shows the headrest according to  FIG. 4 , the headrest part being in an intermediate position, 
         FIG. 6  shows the headrest according to  FIG. 4 , the headrest part being in a front position, 
         FIG. 7  is an enlarged cutout view of the detail indicated at VII in  FIG. 5 , 
         FIG. 8  is a schematic longitudinal sectional view of the headrest in a second section plane, the headrest being in the back position, 
         FIG. 9  is a view like  FIG. 8 , the headrest part being in the intermediate position, 
         FIG. 10  is a view like  FIG. 8 , the headrest part being in the front position, 
         FIG. 11  is a view of a second embodiment of the headrest according of the invention according to  FIG. 8 , the gears of the guides Fa and Fb being frustoconical, and the racks of the guides Fa and Fb being equipped with teeth oriented in a star shape, 
         FIG. 12  is an enlarged view of the guide Fa according to  FIG. 11 , the headrest part not being shown, and 
         FIG. 13  a longitudinal section like  FIG. 3  of the headrest according to  FIGS. 11 and 12 , 
         FIG. 14  is a schematic rear view of a third embodiment of the headrest, a rear cover not being shown, 
         FIG. 15  is a schematic perspective rear view of the headrest, the rear cover and cushion not being shown, 
         FIG. 16  is a schematic perspective rear view of the headrest, a rear cover and the headrest part not being shown, 
         FIG. 17  is a schematic longitudinal sectional view of the headrest, 
         FIG. 18  is a sectional view according to section line XIX-XIX of  FIG. 14 , and 
         FIG. 19  is a horizontal section view through the headrest of the embodiment of  FIGS. 14-18 . 
     
    
    
     DETAILED DESCRIPTION 
     A headrest is shown generally at  10 . The same reference numerals in different figures refer to similar parts, lower case letters being added or omitted. 
     The headrest  10  is anchored to the backrest of a vehicle seat (not shown) by two support rods  11 . End parts  12  of the support rods  11  each fit in a respective bearing sleeve  13  of a base body  14  of the headrest  10 , not shown in  FIG. 1 . The base body  14  is closed by a cover  38  in  FIG. 1 . 
     A bearing assembly  16  supports the headrest part  15  on the base body  14  so as to move relative to the base body  14 . The headrest part  15  carries a cushion P. In the embodiment according to  FIGS. 2 to 10  the headrest part  15  can be moved in a straight-line in the direction x 1  and x 2  between a back position shown, for example, in  FIG. 4 , and a front position shown in  FIG. 6 . In the front position the headrest part  15  is shifted relative to the back position toward the head of an unillustrated passenger in the seat. 
     In  FIG. 2  the headrest  10  is shown without its cover  38 . The bearing assembly  16  comprises three guides Fa, Fb, and Fc. The guides Fa and Fb prevent pivoting or canting of the headrest part  15  about the y-axis and straight-line movement in directions y 1  and y 2  relative to the base part  14 . The guide Fc prevents pivoting or canting of the headrest part  15  about the z-axis, and straight-line movement in directions z 1  and z 2 . A respective carriage  17   a ,  17   b , and  17   c  (see  FIG. 3 ) is associated with each guide Fa, Fb, and Fc. Each of the carriages  17   a ,  17   b , and  17   c  is attached to the headrest part  15  such that it can move somewhat elastically relative to the headrest part  15 . The base part  14 , however, is substantially rigid. 
     Since the construction of the three guides Fa, Fb, and Fc is substantially the same, only one guide Fa is described by way of example. 
     The carriage  17   a  comprises a plate  66  and side parts  20 . The side parts  20  extend approximately at right angles to the plane of the plate  66 . Two bar-shaped bearing bases  26  of a rack  18  are supported in a seat  31  of the carriage  17   a . The bearing bases  26  extend parallel to the direction x 1 -x 2 . The rack  18  lies in a plane that is approximately parallel to the plane formed by the plate  66 . 
     The rack  18  has teeth  40  on its edge turned toward a sleeve gear  23 . The teeth  40  have surfaces  78 . 
     An elastic support  19  is provided in a seat  25  of each bearing base  26  between the respective rack  18  and the carriage  17 . In the embodiment according to  FIGS. 2 to 10  the elastic support  19  is formed by an approximately cylindrical, rod-shaped elastic body made, for example, from plastic, rubber, or the like. 
     Slots  21  (see  FIG. 4 ) formed in each of the side parts  20  of the carriage  17   a  are traversed by a shaft  22  having a center axis M. In this manner the carriage  17   a  can move relative to the shaft  22  in the direction x 1 -x 2 . The shaft  22  is supported in the base body  14  in grooves  24  that also extend parallel to the x-axis. The shaft  22  can therefore move in the direction x 1 -x 2  relative to the base body  14 . The sleeve gear  23  is rotationally fixed on the shaft  22 . The sleeve gear  23  meshes with the rack  18 . 
     A rack  32  is associated with and positioned opposite the rack  18  relative to the center axis M of the shaft  22 , and has two bar-like bearing bases  26  fitted in grooves  33  of the base body  14 . The rack  32  is movable parallel to the y-axis relative to the base body  14 . An elastic support  19  is mounted in a seat  25  of each bearing base  26  between the respective rack  32  and the base body  14 . The rack  32  also meshes with the sleeve gear  23 . 
     Movement of the rack  18  of the guide F is possible only within the limits of the clearance between outer surface  36  of the bearing base  26  and an outer surface  79  of the sleeve gear  23 . Movement of the rack  32  of the guides F is possible within the limits of the clearance between an outer surface  34  of the base body  14  and an outer surface  79  of the sleeve gear  23 . 
     The headrest  10  has a play compensator E described below. The elastic support  19  biases the teeth  40  of the rack  18  in play-free engagement with the teeth  83  of the sleeve gear  23 . The outer surface  78  of the rack  18  and the outer surface  79  of the sleeve gear  23  are kept in contact by the elastic support  19 . Further-more, the elastic support  19  biases the teeth  82  of the rack  32  into play-free engagement with the teeth  83  of the sleeve gear  23 . An outer surface  81  of the rack  32  and the outer surface  79  of the sleeve gear  23  are maintained in contact by the elastic support. Any gear flange clearance is therefore excluded. 
     The clearance between the rack  32  and the base body  13 , and the clearance between the shaft  22  and the groove  24  are such that the teeth  82  of the rack  32  may not move out of engagement with the teeth  83  of the sleeve gear  23  if the outer surface  35  of the bearing base  26  abuts a groove base  67  of the groove  33 , and an outer surface  71  of the shaft abuts an inner surface  68  of the groove  24 . Furthermore, the clearance between the shaft  22  and the slot  21 , and between the outer surface  36  of the rack  18  and an abutment surface  37  of the carriage  17   a  are such that the teeth  40  of the rack  18  may not move out of engagement with the teeth of the sleeve gear  23  if the outer surface  71  of the shaft  22  abuts an inner surface  69  of the groove  24 , an inner surface  70  of the slot  21  abuts the outer surface  71  of the shaft  22 , and the outer surface  36  abuts the contact surface  37 . 
     In the embodiment shown in  FIGS. 1 to 10  the teeth  40  of the racks  18  and  32 , and of the sleeve gear  23  in the guides Fa and Fb extend parallel to the z-axis and in the guide Fc parallel to the y-axis. Each gear tooth  40  of the racks  18  and  32 , and of the sleeve gear  23  of the guides Fa and Fb has an approximate length A 1 . Each gear of the racks  18  and  32 , and of the sleeve gear  23  of the guide Fc has an approximate length A 2 . The racks  18  and  32  of the guides Fa and Fb are in contact with the respective sleeve gear  23  approximately over the entire length A 1 . The racks  18  and  32  of the guide Fc are in contact with the respective sleeve gear  23  approximately over the entire length A 2 . The racks  18  and  32 , and of the sleeve gear  23  of the guides Fa and Fb are roughly at a right angle to the guide Fc. 
     White the guides Fa and Fb prevent rotation of the headrest part  15  about the y-axis, rotation about the z-axis is prevented by the guide Fc. The headrest part  15  is therefore solidly supported in any position. 
     The contact between the outer surface  71  of the shaft  22  and the outer surface of the groove  24  is the same in any position of the headrest part  15 . Furthermore, the contact between the rack  18  and the sleeve gear  23 , and between the rack  32  and the sleeve gear  23  is the same in any position of the headrest part  15  in all the guides Fa, Fb, and Fc. 
     If the headrest part  15  is in the back position according to  FIGS. 4 and 8 , the sleeve gear  23  is in contact with a front end  27  of the rack  18  and with a rear end  29  of the rack  32 . 
     In  FIGS. 5 and 9  the headrest part  15  is shown in an intermediate position between the back position and the front position. The sleeve gear  23  is in contact with the center of the rack  18  and of the rack  32  in the intermediate position. 
     In  FIGS. 6 and 10  the headrest part  15  is shown in the front position, in which it is located at the furthest spacing from the base body  14 . In the front position the sleeve gear  23  is in contact with a rear end  28  of the rack  18  and a front end  30  of the rack  32 . 
     If the sleeve gear  23  has traversed a length l from the rear end  29  to the front end  30  of the rack  25  (between the back position and the front position) in the direction x 1 , the headrest part  15  has moved by a travel equal to 2l in the direction x 1  (see  FIG. 6 ). 
     In the embodiment shown in  FIGS. 1 to 10  the cover  38  is firmly connected to the shafts  22 . Hence, if the headrest part  15  moves forward by a travel  21  in the direction x 1 , the cover  38  moves by a travel l in the direction x 1 . On rearward movement of the headrest part  15  in the direction x 2  from the front position into the back position the cover  38  also covers half of the travel of the headrest part  15  due to the connection. 
     It is obvious from the figures as described above that the racks  18  of the guides Fa, Fb, and Fc are parallel to the respective racks  32  and can move parallel to each other. Thus the racks  18  can be displaced parallel to the racks  32 . In the back position according to  FIG. 4  the racks  18  are next to the racks  32 , while the racks  18  and  32  are offset relative to each other in the front position according to  FIG. 6 . The headrest  10  therefore requires only a small installation space. 
     According to  FIGS. 11 to 13  a second shown embodiment is show that differs from the first embodiment of  FIGS. 1 to 10  in that a gear  39  of the guides Fa and Fb is frustoconical. Teeth  41  of the rack  18  meshing with the gear  39  are arrayed like a star in the guide Fa. Teeth of the rack  32  meshing with the gear  39  are also arrayed like a star (not shown). The star-shaped gears taper toward the center point of an arcuate path. The guide Fb corresponds to the illustrated guide Fa. 
     The sleeve gear  23  (not shown) of the guide Fc is cylindrical. The racks (also not shown) of the guide Fc are provided with straight teeth that extend parallel to the y-axis. The racks  18  and  32  of the guide Fc are arcuate corresponding to a longitudinal axis  1  of the slots  21 . 
     In the headrest  10  according to this second embodiment the headrest part  15  moves through an arcuate path about a pivot center point (not shown) defined by a cone angle α between the longitudinal axis M of the shaft  22  and a longitudinal axis  72  of the teeth of the gear  39 . It is clear that according to the invention headrests can be made that have different movement characteristics of the headrest part  15 . 
     It should be noted that the headrest part  15  can be locked in different positions, or as an alternative in any desired position between the back position and the front position, and in the back position and the front position. 
     A third embodiment is shown in  FIGS. 14 to 19 .  FIG. 14  is a rear view of the headrest  10  where a rear cover is not shown. Like the first shown embodiment, the headrest part  15  can move relative to the base body  14  from a back position (see for example  FIG. 19 ) in the direction x 1  into a front position (not shown), and from the front position in the direction x 2  into the back position. The base body  14  is supported on a backrest (not shown) of a vehicle seat together with support rods  11 . End parts  12  of the support rods  11  fit in bearing sleeves  13  of the base body  14 . 
     The bearing assembly  16  for supporting the headrest part  15  on the base body  14  comprises guides Fa, Fb, and Fc (see for example  FIGS. 14 and 17 ). The guides Fa and Fb prevent pivoting or canting of the headrest part  15  about the y-axis of the headrest part  15  and straight-line movement in the directions y 1  and y 2 . The guide Fc prevents pivoting or canting of the headrest part  15  about the z-axis and straight-line movement into the directions z 1  and z 2 . 
     The guides Fa, Fb, and Fc each comprise a carriage  17 . The carriages  17   a ,  17   b , and  17   c  are attached to the headrest part  15 . Each carriage  17   a ,  17   b , and  17   c  (see for example  FIG. 15 ) has a plate  66  and side parts  20 . Teeth  44  forming racks are formed on the plate  66 . The teeth  44  form an outer surface  84 . In this shown embodiment two gears  44  that are spaced from each other are integrally molded on each carriage  17   a ,  17   b , and  17   c . The gears  44  of the guides Fa and Fb are set at an outer spacing A 1  from each other. The gears  44  of the guide Fc are set at an outer spacing A 2  from each other. The greater the outer spacing A 1  and A 2  of the gears, the better pivoting of the headrest part  15  about the y-axis, or about the z-axis is prevented. 
     A pin  54  is held in a bore  53  of the shaft  22  at each end  47  and  48  of the shaft  22 . The bore  53  is coaxial to the axis M of the shaft  22 . The pin  54  has a head  61  set in a groove  52  of the base body  14 . The diameter of the head  61  is larger than the diameter of the bore  53 . The head  61  can move in the groove  52  in the directions x 1  and x 2 . An outer surface  86  of the head  61  is positioned at a slight spacing to an outer surface  87  of the groove. The shaft  22  may therefore move within the limits of the longitudinal extension of the groove  52  relative to the base body  14  in the directions x 1  and x 2 . 
     A slot  21  is formed in each side part  20  of the carriage  17   a  of the guide Fa, Fb, and Fc. A longitudinal axis q of the slot  21  extends parallel to the x-axis. Each slot  21  receives a respective one of the pins  54 . The carriage  17   a  can therefore move relative to the shaft  22  in the directions x 1  and x 2 . 
     Each array of teeth  44  meshes with teeth  46  (see for example  FIG. 15  and  FIG. 16 ) rotationally fixed on the shaft  22 . Therefore, two sets of teeth  46  are formed on each shaft  22 . The teeth  46  may, for example, be integrally molded on the shaft  22 . An approximate outer spacing A 1  is formed between the pinion-like gears in the guides Fa and Fb, and an approximate outer spacing A 2  is formed in the guide Fc. 
     Each set of teeth  46  of the shaft  22  further meshes with teeth  45  forming as a rack and firmly connected to the base body  14 . The teeth  45  form an outer surface  84 . Each guide Fa and Fb comprises two sets of teeth  45  integrally molded on the base body  14  and set at an outer spacing A 1  to each other. Each guide Fc comprises two sets of teeth  45  integrally molded on the base body  14  and set at an outer spacing A 2  to each other. 
     As an alternative to the two gears  44 , the two sets of teeth  46 , and the two sets of teeth  45  of the guides Fa, Fb, and Fc, each guide Fa, Fb, and Fc may be provided with only one teeth  44 ,  45 , or one set of teeth  46 , wherein the teeth  44 ,  45  and the teeth  46  in the guides Fa and Fb have a length A 1  and a length A 2  in the guide Fc. 
     The racks  44  of the carriages  17   a ,  17   b , and  17   c  are, for example, clear in  FIG. 15 , the teeth  45  of the base body  14  are, for example, obvious in  FIG. 16 . For reasons of clarity the headrest part  15  is not shown in  FIG. 15 , and the headrest part  15  and the carriages  17   a ,  17   b , and  17   c  are not shown in  FIG. 16 . 
     The carriage  17   a  and the shaft  22  of the guides Fa, Fb, and Fc are supported with play. A play compensator E of the headrest  10  is described below by way of example with reference to the guide Fc. The end  48  of the shaft  22  of the guide Fc is shown in  FIG. 18 . Movement of the shaft  22  of the guide Fc in the direction z 1  relative to the base body  22  is possible until a side surface  51  of the head  61  of the pin  54  stops at an end surface  75  of the groove  52 . Movement of the carriage  17   a  relative to the shaft  22  in the direction z 1  can therefore occur only until an inner end  74  of the slot  21  stops at an outer surface  76  of the pin  54 . On contact between the outer surface  51  of the head  61  and the side surface  75  of the groove  52 , the teeth  46  engage into the teeth  45  of the base body  14 . Furthermore, the teeth  44  of the carriage  17   c  and the teeth  46  of the pinion engage when the inner end  74  of the slot  21  stops the outer surface  76  of the pin  54 . 
     Like to the guide Fc the guides Fa and Fb also have play, movement of the shaft  22  and of the carriage  17   a  being possible parallel to the y-axis. 
     The pin  54  extends through a bore  55  of a first ball half  58 . A cavity for a spring  59  is adjacent the bores  55  and  56 . The spring  59  is biased in the shown installation situation, and is supported on an annular shoulder  60  of the ball halves  57 ,  58 . thus it biases the ball half  57  of the guide Fc shown, for example, in  FIG. 18 , in the direction y 1 , and the ball half  58  in the opposite direction y 2 . 
     The ball half  58  engages a bearing surface  62  of the base body  14 . The bearing surface  62  is inclined toward the longitudinal axis M of the shaft  22  at an angle β. Due to the inclination of the bearing surface  62  a portion of the spring force of the spring  59  acts at a right angle to the longitudinal axis M of the shaft  22  and biases the pin  54 , and thus the teeth  46  in the direction z 2  into engagement with the teeth  45  of the base body  14 . The force by means of which the teeth  46  are biased while being in engagement with the teeth  45  depends on the angle β and on the force of the spring  59 . 
     The ball half  57  is supported on a bearing surface  63  of the carriage  17   c . The ball half  63  (see  FIG. 18 , guide Fc, end part  48  of the shaft  22 ) is biased by the spring  59  in the direction z 1 . The bearing surface  63  of the carriage  17   c  is inclined toward the center axis a at an angle δ. A portion of the spring force of the spring  59  acts perpendicular to the center axis a of the shaft  22  and biases the carriage Fc in the direction z 2  so that the rack  44  is spring-loaded into engagement with the teeth  46  of the pinion. 
     The ball halves  57  and  58  therefore represent deflection elements for the spring force of the spring  59  that acts parallel to the longitudinal axis a of the shaft  22 . 
     The outer surface  64  of the ball half  57  is in point contact with the bearing surface  63 . The outer surface  65  of the ball half  58  is in point contact with the bearing surface  63 . In this manner sliding friction during movement of the headrest part  15  is low between the back position and the front position. 
     The contact between the outer surface  62  of the base body  14  and the outer surface  65  of the ball half  58 , and the contact between the outer surface  63  of the carriage  17   a  and the outer surface  64  of the ball half  57  are constant in any position of the headrest part  15 . Furthermore, the contact between the gears  44 ,  45 , and  46  of each guide Fa, Fb, and Fc is constant in any position of the headrest part  15 . The teeth  44  of each guide Fa, Fb, and Fc form a bearing-surface pair together with the teeth  46  of the shaft  22 . Furthermore, the teeth  45  of each guide Fa, Fb, and Fc form a bearing-surface pair together with the teeth  46  of the shaft  22 . The contact of each bearing-surface pair  44 / 46  and  45 / 46  of each guide Fa, Fb, and Fc is formed as a line contact having the long contact length of the bearing element being engaged. The headrest part  15  is therefore supported on the base body  14  with the same bearing surface in any position. 
     Like the first shown embodiment shown in  FIGS. 1 to 10  the headrest part  15  traverses twice the travel relative the shaft  22  during movement between the back and the front position. 
     For the sake of completeness it should be noted that sets of teeth  77  are formed on each carriage  17   a  and  17   b . Two sets of teeth  77  that are spaced to each other are formed on the carriage  17   c . The sets of teeth  77  are part of a latch that enables movement of the headrest part  15  in the direction x 1 , but prevents return movement in the direction x 2 . Return movement of the headrest part  15  in the direction x 2  is possible only if the latch is unlocked, for example by a pushbutton.