in fig1 the essential components for understanding an embodiment of the invention are shown in a roughly schematic manner in a type of cross - sectional illustration of the upper section of the backrest of a passenger - car seat 1 . the passenger - car seat 1 comprises the backrest 3 having approximately vertically aligned head restraint guides 5 for supporting a head restraint 7 . the latter essentially comprises a head restraint rear part 9 , which is connected fixedly to head restraint rods 11 for the vertically displaceable mounting in the head restraint guides 5 of the backrest 3 , and a head restraint front part 13 which is movable with respect to the head restraint rear part 9 . the head restraint front part 13 can be pivoted about a horizontal rotational axis 15 at the upper , forwardly bent end of the head restraint rear part 9 , whereupon its lower end can be effectively moved in the direction of the arrow x towards the back of a vehicle occupant &# 39 ; s head ( not illustrated ) or away from the latter . in the figure , a first rotational position of the head restraint front part 13 is illustrated by solid lines and a second rotational position by dashed lines . a spreading - lever arrangement 17 which fixes the front part with respect to the rear part is provided between the head restraint rear part 9 and the head restraint front part 13 . the said spreading - lever arrangement is assigned a spring element 18 which prestresses the spreading levers , and therefore the head restraint front part 13 , with respect to the rear part 9 . a bowden cable 19 is fastened by the one end to a linkage point 17 a of the spreading - lever arrangement 17 . in an alternative embodiment , the spring element 18 may be replaced by a compression spring which acts in cooperation with a motor - powered or hydraulically - actuated bowden cable which selectively pulls the front part 13 toward the rear part 9 against the force of the compression spring , or releases the front part 13 so that it may be moved away from the rear part 9 by the compression spring . in a further embodiment , a damper element may be provided obliquely extending between the rear part 9 and the front part 13 to damp and retard reversing of the head restraint front part 13 when the back of the occupant &# 39 ; s head impacts against it . the damper element may be frictional , hydraulic or pneumatic . in a coupling element 20 , which is illustrated more precisely in fig1 a , the bowden cable 19 branches into a first and second bowden cable branch 19 . 1 and 19 . 2 . as can be seen in fig1 a , the coupling element 20 essentially comprises a wire connector 20 a which connects the ends of the inner wires of the single - piece bowden cable section 19 and of the two branches 19 . 1 and 19 . 2 fixedly to one another in such a manner that — in the manner of an or element — a tensile force acting on one of the branches 19 . 1 , 19 . 2 is passed on into the single - piece section 19 . a first end of the bowden cable ( put more precisely : of an inner wire ) is wound around a reel 21 a which is seated on the shaft of an electric motor 21 for adjustment of the inclination . the electric motor is activated — which is not illustrated in the figure — by an actuating switch or via an electronic control unit . the second end of the bowden cable is connected ( which is not illustrated , however , in fig1 ) to a drive for release in the event of a crash , which drive is described more precisely further below with reference to examples . when the electric motor is activated via a corresponding control signal (“ head restraint forwards ” or “ head restraint rearwards ”), the reel 21 a is rotated in one of the two rotational directions and the inner wire of the bowden cable 19 is tightened or relaxed , whereupon the head restraint front part 13 is moved forwards or backwards with respect to the head restraint rear part 9 as symbolized by the arrow via the spreading - lever arrangement 17 in interaction with the spring element 18 . in a manner which is similar in principle , the driving force applied during a release in the event of a crash is transmitted to the head restraint front part , but in this case the transmission of force takes place very rapidly , and the spreading - lever arrangement is stretched until it reaches the position beyond the dead center , which is illustrated by dashed lines in fig1 . in this position , the lever arrangement acts in a self - locking manner , i . e . when the back of the vehicle occupant &# 39 ; s head impacts against it is unable to recede into its originally set position , and , as a result , securely intercepts the head . after the accident , it has to be unlocked manually in a suitable manner ( known per se ) and can then be returned into the set position of inclination . attention has to be given to the fact that the spring element 18 has to have such a spring constant that the set angular position of the head restraint front part is retained even when the back of the vehicle occupant &# 39 ; s head is laid violently against it . fig2 shows , in a perspective illustration depicted by dashed lines , a front seat 100 of a passenger car having a seat part 101 , a backrest 103 and a head restraint 105 in which a driving device 107 for an adjusting mechanism ( not illustrated ) is installed , which adjusting mechanism can be used to adjust the head restraint 105 in the event of a rear - end crash and optionally also a frontal crash . the seat part 101 and the backrest 103 have separate frame parts 109 and 111 , respectively , made of metal sections . the head restraint 105 has the construction described further above and of which the head restraint rear part 105 a , the horizontal rotational axis 105 b and the pivotable head restraint front part 105 c can be seen in this figure . the driving device 107 comprises , for example , a total of five steel wires 113 which are fastened in each case by one end to one of the upright sections of the frame part 111 of the backrest 103 and at the other end have a hook 113 a . the steel wires 113 run essentially horizontally and transversely with respect to the longitudinal axis of the vehicle and therefore with respect to the direction of movement of a vehicle occupant ( not illustrated ) in the event of a rear - end impact , and grip with their hooks 113 a in an alternating manner from both sides around a bowden cable 115 which runs essentially vertically . the bowden cable 115 is fastened by the one end to a lower transverse support 117 of the frame 111 , and its upper end is connected — which is not illustrated in greater detail in the figure — to the head restraint front part 105 c or to a lever / joint mechanism assigned thereto . the steel wires 113 and the bowden cable 115 are each embedded over the greater part of their longitudinal extent in a movable manner in a load distributor plate 119 which , in particular , also covers the engagement points of the hooks 113 a with the bowden cable 115 from the abovementioned vehicle occupant &# 39 ; s body . if , in the event of a sufficiently severe rear - end impact or a “ rebound ” after a frontal impact , the vehicle occupant &# 39 ; s body is pressed from the front against the backrest 103 by an acceleration which exceeds the absorption capacity of the upholstery ( not illustrated ), then it is pushed , in particular , also against the steel wires 113 , and the latter pull the hook 113 a towards them at the respective point at which the hook engages with the bowden cable 115 , since the steel wires are themselves inextensible . as a consequence of the tension exerted by the steel wires 113 in an alternating manner from both sides , the flexible bowden cable 115 takes on a zigzag or meandering form . its ( upper ) free end is thereby pulled downwards in the direction of the arrow in the figure by an amount which substantially exceeds the amount of displacement of the vehicle occupant in the direction of the backrest and in the process releases a pivoting movement of the head restraint front part , which pivoting movement can be driven , for example , by means of a compression - spring device , which is released by means of the bowden cable , between the head restraint rear part and head restraint front part . fig3 sketches a further driving device 207 in a front seat 200 of a passenger car corresponding in respect of the rest of its construction to the seat according to fig2 . the driving device 207 here comprises a total of six fibre - reinforced , for example kevlar reinforced plastic strips 213 which are looped in an alternating manner from both sides around a plastic cable 215 , which is used as the secondary tension element and is likewise fibre - reinforced , and are in each case fastened by both ends in corresponding slots in the upright sections of the frame part 211 . the function of this arrangement basically corresponds entirely to that according to the first embodiment . the plastic strips 213 and the plastic cable 215 interact in a manner which is low in friction and in a similar way as the wires according to fig2 interact with the bowden cable provided therein as the secondary tension element . the design of the primary tension elements as nets or strips according to fig2 and 3 , which design is flatter than steel wires , enables a separate load - distributing element to be omitted in the last - mentioned designs . while the best mode for carrying out the invention has been described in detail , those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims .