Abstract:
A longitudinal adjuster ( 3 ), for a vehicle seat ( 1 ), includes a lower rail ( 9 ), an upper rail ( 11 ), moveable in relation to the lower rail ( 9 ) in a longitudinal direction (x), and a locking unit ( 13 ) for locking the upper rail ( 11 ) to the lower rail ( 9 ). The locking unit ( 13 ) includes two locking elements (VR), which, in order to lock the upper rail ( 11 ) and the lower rail ( 9 ), engage in the upper rail and the lower rail in a blocking manner in steps such that one of the locking elements (VR) pre-locks the upper rail ( 11 ) and the lower rail ( 9 ) with play in a pre-locking step and one of the locking elements (VR) locks the upper rail ( 11 ) and the lower rail ( 9 ) without play in a locking step. A vehicle seat ( 1 ) including such a longitudinal adjuster ( 3 ) is provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase Application of International Application PCT/EP2015/073785, filed Oct. 14, 2015, and claims the benefit of priority under 35 U.S.C. §119 of German Applications 10 2014 221 229.4, filed Oct. 20, 2014 and 10 2014 225 426.4 filed Dec. 10, 2014, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a longitudinal adjuster for a vehicle seat. Furthermore, the invention relates to a vehicle seat comprising such a longitudinal adjuster. 
       BACKGROUND OF THE INVENTION 
       [0003]    DE 10 2008 056 683 B4 discloses a longitudinal adjuster which comprises at least one lower rail and at least one upper rail which is displaceable in the longitudinal direction relative to the lower rail, and, for the play-free locking of said lower and upper rails, comprises at least two locking units for locking the upper rail in relation to the lower rail. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an object of the present invention to specify a longitudinal adjuster for a vehicle seat, said longitudinal adjuster being improved in relation to the prior art, and an improved vehicle seat. 
         [0005]    The object is achieved according to the invention with a longitudinal adjuster for a vehicle seat, wherein the longitudinal adjuster comprises at least one lower rail, at least one upper rail which is displaceable in the longitudinal direction in relation to the lower rail, and at least one locking unit for locking the upper rail in relation to the lower rail with at least two locking mechanisms arranged on the upper rail, wherein, for locking upper rail and lower rail, the locking mechanisms engage in the upper rail and lower rail in a stepwise blocking manner such that, in a prelocking step, the locking elements prelock the upper rail and lower rail with respect to each other with play, and in that, in a locking step, at least one of the locking mechanism locks the upper and lower rail to each other in a manner free from play (without play). 
         [0006]    The advantages achieved with the invention consist in particular in that deformation travel customary in the prior art for a first locking element in order to shift a further locking element in a load path is not required. 
         [0007]    In a refinement of the longitudinal adjuster, the locking mechanism is designed as a substantially plate-like (plate-shaped) locking element and/or a lever-shaped locking element. By means of a design of the locking mechanism as a substantially plate-shaped locking element, an outlay of production and installation is low. By means of a design of the locking mechanism is a substantially lever-shaped locking element, a nested or intermeshing arrangement of a plurality of lever-shaped locking elements is possible, wherein an advantage of a small construction space arises here. 
         [0008]    A further refinement of the longitudinal adjuster provides an actuating element for locking or unlocking the locking unit, wherein, when the actuating element is actuated, the locking unit is bringable from a locking position into an unlocked position, and, after adjustment of the vehicle seat and with the actuating element unactuated, the locking unit is adjustable in a stepwise manner from the unlocked position via a prelocking position into the locking position. Simple actuation of the locking unit is possible by means of the actuating element, wherein when the actuating element is unactuated, secure locking of the upper and lower rails is ensured in all positions of the locking unit. 
         [0009]    In another refinement of the longitudinal adjuster, when the actuating element is unactuated, one of the locking mechanisms is arranged in a prelocking position. When the actuating element is unactuated, a relative movement of upper rail and lower rail in the prelocking position is therefore always restricted and an adjustment of the vehicle seat beyond the restricted relative movement is no longer possible. The restricted movement of one of the rails in relation to the other rail then leads to locking of both rails by one of the locking mechanisms then dropping into the locking position. 
         [0010]    In a development of the longitudinal adjuster, a locking mechanism has a multiplicity of latching teeth and, for example, is configured in such a manner that at least one of the latching teeth is wider than all of the other latching teeth. It is possible by means of the latching teeth to produce a connection of the locking mechanism at least to the upper rail, wherein the at least one wide latching tooth is provided for transmitting force between the locking mechanism associated therewith and the lower rail since a play-free connection (without play) is produced only between the wide latching tooth and the lower rail. When a play-free connection is present, movement of the wide latching tooth in an associated recess is not possible. A movement clearance between a latching tooth and the associated recess is accordingly referred to as play. 
         [0011]    In another development of the longitudinal adjuster, the upper rail is provided with a number of recesses which corresponds at least to the number of latching teeth of the locking mechanisms. One latching tooth is assigned to precisely one recess. By means of the recesses accommodating the latching teeth, a permanent connection of the upper rail to the locking mechanisms even during the adjustment of the seat is provided. 
         [0012]    According to an embodiment of the longitudinal adjuster, the upper rail has a number of recesses in mutually opposite side walls per locking mechanism. For example, here, the recesses in the one side wall are identical and the recesses in the opposite side wall differ at least in one parameter. A design of the locking mechanism with latching teeth of differing width is therefore possible, wherein the locking mechanism accordingly has latching teeth of identical design on one side. 
         [0013]    In another embodiment of the longitudinal adjuster, the recesses differing at least in one parameter are introduced into the upper rail in a manner lying diagonally opposite one another. A resulting arrangement of the locking mechanisms which is laterally reversed in the longitudinal direction is therefore possible, as a result of which the locking mechanisms are arrangeable in such a manner that they always take up different positions in the locking direction. 
         [0014]    In another development of the longitudinal adjuster, the respective locking element, in particular the respective substantially plate-shaped locking element, is designed as a latching plate with latching teeth which are arranged one behind another in the longitudinal direction on both longitudinal edges and are arranged moveably in the locking direction at least in corresponding recesses of the upper rail. The movability of the locking element in the locking direction permits simple actuation of same, wherein, with the design of the latching plate, an outlay on production and installation is straight-forward and cost-effective. The respective latching plate is expediently oriented substantially horizontally, i.e. a normal vector of the respective latching plate is expediently oriented substantially parallel to the locking direction and therefore expediently substantially parallel to the vertical axis of the vehicle. The actuating direction is the direction in which the locking mechanisms or at least the teeth thereof are substantially moved for locking and unlocking. In the case of the substantially lever-shaped locking mechanisms, the latter are expediently pivoted in such a manner that the teeth thereof move substantially upward or downward in order to lock or to unlock. Said up and down movement of the teeth in the case of the lever-shaped locking mechanisms can be a partial movement of a pivoting movement of the teeth because of the pivoting movement of the lever-shaped locking mechanisms, i.e. the teeth pivot laterally and upward or laterally and downward in the opposite direction in order to lock or to unlock. 
         [0015]    In a further embodiment of the longitudinally adjuster, the one locking element is arranged in relation to the other locking element adjacent and laterally reversed in the longitudinal direction. It is therefore possible for the locking elements always to take up different positions in the locking direction. This is likewise possible if the locking elements are arranged precisely one behind another. 
         [0016]    According to a development of the longitudinal adjuster, the upper rail has, per locking mechanism at least one recess which is wider in the longitudinal direction than the other recesses. The at least one wider recess is therefore designed as a receptacle for the wide latching tooth and ensures guidance of the latter in the locking direction. The already described play-free connection of the wide latching tooth to the lower rail is not restricted. 
         [0017]    In another development of the longitudinal adjuster, the upper rail has, per locking mechanism, at least one recess which is of conical design in contrast to the other recesses. By means of the conical design of the recess, the latter in the locking position accommodates a latching tooth in such a manner that force can be transmitted from the upper rail to the locking mechanism. 
         [0018]    In a further refinement of the longitudinal adjuster, the recess is of conical design in the locking direction in such a manner that said recess guides a latching tooth of the associated locking mechanism such that said latching tooth latches in the locking position without play or in a manner free from play. Therefore, only the conically designed recess and one latching tooth per locking mechanism are in force-transmitting engagement with the upper rail, wherein only one of the two locking mechanisms ever latches in a manner free from play. The second locking mechanism serves only to absorb collision loads after a slight deformation because of a force acting due to a collision. 
         [0019]    According to another development of the longitudinal adjuster, the lower rail has a multiplicity of formations spaced apart at equal distances, wherein a formation expediently in each case has a projection, a web and a catch. The formations are designed as receptacles for the latching teeth, wherein the projection, the web and the catch expediently have different heights in the locking direction. They are expediently arranged in a step-shaped manner one behind the other in the longitudinal direction of the lower rail. In the locking direction, i.e. expediently in a direction parallel to a vertical axis of the vehicle, the projection here forms the lowest step and the catch the highest step or vice versa. A latching tooth which is dropped or latched into the catch is arranged here in the locking position, and a latching tooth arranged on the web is arranged in the prelocking position. The formations are expediently formed in one side wall or in opposite side walls of the lower rail. 
         [0020]    In a refinement of the longitudinal adjuster, the catch is of conical design at its flanks in such a manner that only the wide latching tooth of one of the locking mechanisms latches without play. The other latching teeth latch here in the catch with play. The transmission of force is therefore ensured exclusively by means of the wide latching tooth. 
         [0021]    By means of the play-free connection of the wide latching tooth to the lower rail and the play-free connection of the latching tooth to the conical recess of the upper rail, a force only from the upper rail onto the latching tooth in the conical recess is therefore transmitted via the wide latching tooth to the lower rail. The latching teeth arranged with play in the other recesses of the upper rail and in the formations in the lower rail are not force-transmitting in a normal operation of the longitudinal adjuster. They are provided exclusively for a collision situation of the vehicle. Forces acting during the collision may result in deformation of the latching teeth arranged without play, wherein the latching teeth arranged up to now with play are shifted because of the deformation onto the respective recess or formation in a force-transmitting manner. 
         [0022]    A vehicle seat comprising such a longitudinal adjuster is always in a locked state when the actuating element is unactuated, wherein a longitudinal displacement of the vehicle seat not desired by the user is avoided in an advantageous manner. 
         [0023]    Exemplary embodiments of the invention are explained in more detail with reference to drawings. The present invention is described in detail below with reference to the attached figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    In the drawings: 
           [0025]      FIG. 1  is a schematic side view showing a vehicle seat with a longitudinal adjuster; 
           [0026]      FIG. 2  is a schematic perspective view showing a pair of rails of the longitudinal adjuster; 
           [0027]      FIG. 3  is a schematic partially sectioned perspective partial view showing the pair of rails in the region of a locking unit of the longitudinal adjuster which is in a prelocked state; 
           [0028]      FIG. 4A  is a schematic partially sectioned perspective partial view showing the pair of rails illustrated in  FIG. 3 ; 
           [0029]      FIG. 4B  is a schematic view showing the opposite side of the partial view illustrated in  FIG. 4A  of the pair of rails; 
           [0030]      FIG. 5  is a schematic view showing the partial view illustrated in  FIG. 3  of the pair of rails of the longitudinal adjuster in the locked state, wherein another locking element is latched in a locking position; 
           [0031]      FIG. 6  is a schematic view showing a vertical section of the pair of rails in the y-z plane; 
           [0032]      FIG. 7  is a schematic view showing in side view a detail of a latching geometry on a lower rail of the pair of rails illustrated in  FIG. 5 ; 
           [0033]      FIG. 8A  is a schematic view showing in top view a first load path of the locking element; 
           [0034]      FIG. 8B  is a schematic view showing in top view a second load path of the locking element; 
           [0035]      FIG. 9  is a schematic view showing a further exemplary embodiment of a locking unit; 
           [0036]      FIG. 10  is a schematic view showing components of the locking unit shown in  FIG. 9 ; 
           [0037]      FIG. 11  is a schematic view showing a partially sectioned perspective partial view of the further exemplary embodiment; and 
           [0038]      FIG. 12  is a schematic view showing in side view a latching hole of a further lower rail. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0039]    Referring to the drawings, mutually corresponding parts are provided with the same reference signs throughout the Figures. 
         [0040]      FIG. 1  shows a vehicle seat  1  of a vehicle in a side view. The vehicle seat  1  has an actuating element  5  which is connected to a longitudinal adjuster  3  and upon actuation of which the longitudinal adjuster  3  permits the vehicle seat  1  to be displaced along a longitudinal direction x, wherein the latter runs substantially parallel to the direction of travel. The vehicle seat  1  has a respective pair of rails  7  (illustrated in more detail in  FIG. 2 ) on both vehicle seat sides in the longitudinal direction x. 
         [0041]      FIG. 2  shows one of the pairs of rails  7  of the longitudinal adjuster  3  in a perspective illustration. The two pairs of rails  7  are constructed analogously here. 
         [0042]    The illustrated pair of rails  7  comprises a lower rail  9  and an upper rail  11 , wherein the lower rail  9  is connected to a vehicle structure of the vehicle and the upper rail  11  is arranged on the lower rail  9 . 
         [0043]    The upper rail  11  is displaceable in the longitudinal direction x relative to the lower rail  9  and is lockable to the lower rail  9  by means of a locking unit  13 . In this case, the lower rail  9  and the upper rail  11  engage around each other with their substantially U-shaped profiles having respectively inwardly and outwardly bent longitudinal edges. 
         [0044]      FIG. 3  shows a partially sectioned perspective partial view of the pair of rails  7  in the region of the locking unit  13  in a prelocked state. 
         [0045]    For the stepwise locking—prelocking and locking—of lower rail  9  and upper rail  11 , the locking unit  13  has two locking elements  17 ,  19 . The locking elements  17 ,  19  are arranged one behind another in the longitudinal direction x and are identical in construction and manner of operation, wherein the one locking element  17  is arranged rotated by 180° about an axis of the locking direction z in relation to the further locking element  19  in a fitted position. 
         [0046]    The locking unit  13  comprises at least the two locking elements  17 ,  19 . However, the number of locking elements  17 ,  19  and the arrangement thereof can also vary, i.e. can be at least two or more than two. 
         [0047]    For the longitudinal adjustment of the vehicle seat  1 , the actuating element  5  is actuated, as a result of which the longitudinal adjuster  3  is unlocked by the locking unit  13  being brought from a locking position P 2  into an unlocked position P 0  and, after adjustment of the vehicle seat  1  and with the actuating element  5  unactuated, is adjusted in a stepwise manner from the unlocked position P 0  via the illustrated prelocking position P 1  into the locking position P 2  or, in a corresponding position of the lower rail  9  and the upper rail  11  with respect to each other, is brought directly from the unlocked position P 0  into the locking position P 2 . 
         [0048]    After adjustment of the vehicle seat  1  and release of the actuating element  5 , the two locking elements  17 ,  19  in the example illustrated are adjusted from the unlocked position P 0  of the locking unit  13  in such a manner that one of the locking elements  17 ,  19 , namely the locking element  19 , takes up the prelocking position P 1  with play, and the other locking element  17  still remains in the unlocked position P 0 . By this means, in the prelocking position of the locking unit  13 , movement of the upper rail  11  relative to the lower rail  9  in both directions is possible to a limited extent before the upper and lower rail  11 ,  9  are blocked with respect to each other. In other examples, with a corresponding position of the lower rail  9  and of the upper rail  11  with respect to each other, one of the locking elements  17 ,  19  can also take up the prelocking position P 1  and the other locking element  17 ,  19  can directly take up the locking position P 2 . 
         [0049]    In the example illustrated, it is ensured by further movement of the vehicle seat  1  from the prelocking position of the locking unit  13  forward or rearward in the longitudinal direction x that one of the locking elements  17 ,  19  securely drops or latches into the locking position P 2 , as illustrated in  FIG. 4A or 5 , wherein the situation after the movement of the vehicle seat  1  to the rear, i.e. counter to the direction of travel, is illustrated in this exemplary embodiment in  FIG. 4A , and the situation after movement of the vehicle seat  1  forward, i.e. in the direction of travel and therefore in the longitudinal direction x, is illustrated in  FIG. 5 . 
         [0050]    Stepless locking of the longitudinal adjuster  3  is therefore made possible, wherein, in the respective locking steps—prelocking step or locking step only one of the locking elements  17 ,  19  is in the respective step, the prelocking position P 1  or the locking position P 2 . However, the longitudinal adjuster  3  is designed in such a manner that all of the locking elements  17 ,  19 , the two locking elements  17 ,  19  in the example illustrated, can take up both the prelocking position P 1  and the locking position P 2 , wherein it depends in each case on the orientation of the upper rail  11  and the lower rail  9  with respect to each other whether the particular locking element  17 ,  19  is in the prelocking position P 1  or in the locking position P 2 . 
         [0051]    Various locking steps are possible here: 
         [0052]    locking movement of one of the locking elements  17 ,  19  from the unlocked position P 0  directly into the locking position P 2 ; 
         [0053]    locking movement of one of the locking elements  17 ,  19  from the unlocked position P 0  via the prelocking position P 1  into the locking position P 2 , or 
         [0054]    locking movement of one of the locking elements  17 ,  19  from the unlocked position P 0  into the prelocking position P 1 . 
         [0055]    The two locking elements  17 ,  19  here are always in different locking steps and not in one and the same step. 
         [0056]      FIG. 3  shows the one locking element  17  in the unlocked position P 0  and the further locking element  19  in the prelocking position P 1 , and therefore the locking unit  13  is prelocked. That is to say, the upper rail  11  and the lower rail  9  are adjustable to a restricted extent with respect to each other. 
         [0057]    Since the locking elements  17 ,  19  have an identical construction, a detailed description of them is undertaken below only with reference to the locking element  17 , wherein structural features relating to the lower rail  9  and/or the upper rail  11  are designed identically for the locking element  19  on the lower rail  9  and on the upper rail  11 . 
         [0058]    The locking element  17  has a basic body  17   a  which is of plate-shaped design in the form of a latching plate. On the longitudinal side, the basic body  17   a  has a number of protruding latching teeth  17   b , of which, in the example illustrated, at least one—the latching tooth  17   b ′—is of a different size from the remaining latching teeth  17   b.    
         [0059]    In the exemplary embodiment shown, the latching tooth  17   b ′ has a greater width than the remaining latching teeth  17   b . Furthermore, the latching tooth  17   b ′ is referred to as the wider latching tooth  17   b ′. The wider latching tooth  17   b ′ is in particular an outer tooth of the latching plate, as seen in the longitudinal direction x. 
         [0060]    In the exemplary embodiment shown, five latching teeth  17   b  and the wider latching tooth  17   b ′ are formed on the longitudinal edges of the basic body  17   a . The outer position of the wider latching tooth  17   b ′ in the longitudinal direction x is in particular formed to the rear in the direction of travel and, adjacent thereto, two latching teeth  17   b  are formed to the front in the direction of travel. Opposite thereto, three identical latching teeth  17   b  are formed on the right longitudinal edge. 
         [0061]    Analogously to the construction of the locking element  17 , the locking element  19  has a basic body  19   a  and latching teeth  19   b ,  19   b′.    
         [0062]    In other words: the two locking elements  17 ,  19  have a number of identical latching teeth  17   b ,  19   b  on one longitudinal side and a corresponding number of latching teeth  17   b ,  19   b  on the opposite longitudinal side, wherein, in this example, one of said latching teeth  17   b ′,  19   b ′ is of wider design and all of the other latching teeth  17   b ,  19   b  are of identical design. 
         [0063]    The number of latching teeth  17   b  can vary, wherein the latter can be formed on one side or both sides of a longitudinal edge of the basic body  17   a.    
         [0064]    The two locking elements  17 ,  19  are held in the upper rail  11 . For this purpose, the upper rail  11  has corresponding dimensions and shapes. 
         [0065]    In particular, the upper rail  11  has a number of recesses  11   a  to  11   a ″ corresponding to the number of latching teeth  17   b ,  19   b . That flank or side of the upper rail  11  which lies opposite the longitudinal side of the latching plate with the identical latching teeth  17   b ,  19   b  has correspondingly designed and identical recesses  11   a  in which the identical latching teeth  17   b ,  19   b  engage with play (tolerance). 
         [0066]    On the opposite flank or side of the upper rail  11  that, in this example, lies opposite the longitudinal side of the latching plate with different latching teeth  17   b ,  17   b ′,  19   b ,  19   b ′, the upper rail  11  has differently designed recesses  11   a  to  11   a ″ in a manner corresponding to the different latching teeth  17   b ,  17   b ′,  19   b ,  19   b ′ in this example. If, in other examples, all of the latching teeth  17   b ,  17   b ′,  19   b ,  19   b ′ are of identical design, this expediently also applies to the recesses  11   a  to  11   a″.    
         [0067]    In detail, the upper rail  11  has, on the right in the direction of travel, three recesses  11   a  which guide the latching teeth  17   b  and are designed in such a manner that the latching teeth  17   b  are movable in the locking direction z. 
         [0068]    On the left in the direction of travel, the upper rail  11  in this example has at the rear a recess  11   a ′ which guides the wider latching tooth  17   b ′ and is wider in the longitudinal direction x than the recess  11   a  which is adjacent at the front in the direction of travel. In this example, in contrast to the recess  11   a , a left front recess  11   a ″ in the direction of travel is of conical design at the closed locking end in the locking direction z and guides the latching tooth  17   b  in such a manner that the latter latches in the locking position P 2  without play (into the recess  11   a ″) and therefore the upper rail  11  is locked merely by means of engagement of the latching tooth  17   b  in the recess  11   a ″ without play. In a travel mode, a force acting on the upper rail  11  is therefore transmitted exclusively by the latching tooth  17   b  and the recess  11   a ″ to the locking element  17 . 
         [0069]    A vertical offset V between the recesses  11   a ,  11   a ′,  11   a ″ of the one locking element  17  and the recesses  11   a  of the further locking element  19  is provided in order to facilitate installation of the locking element  17 ,  19  in the upper rail  11 . 
         [0070]    The lower rail  9  has a multiplicity of formations  9   a , wherein each formation  9   a  has a projection  9   b , or web  9   c  and a catch  9   d . The lower rail  9  preferably has the formations  9   a  distributed over the entire longitudinal extent and spaced apart from one another at equal distances. 
         [0071]    In this example, the catch  9   d  is of conical design at its flanks F 1 , F 2 , illustrated in more detail in  FIG. 7 , such that the respective latching tooth  17   b  latches with play, and the wide latching tooth  17   b ′ latches without play, into the catch  9   d . The force is therefore transmitted from the locking element  17  to the lower rail  9  exclusively by the wide latching tooth  17   b ′ in the catch  9   d . In the travel mode, the remaining latching teeth  17   b  are not in force-transmitting engagement with the rails  9 ,  11 . If the force exceeds a predetermined limit value, the two force-transmitting latching teeth  17   b ,  17   b ′ are deformed. Owing to this deformation, the play between the further latching teeth  17   b  and the recesses  11   a ,  11   a ′ is reduced until said latching teeth and recesses are in contact. The further latching teeth  17   b  therefore transmit the force to the locking element  17  and act in a supporting manner in a crash situation. 
         [0072]    The at least two locking elements  17 ,  19  are arranged in such a manner that, when the actuating element  5  is released, the two locking elements  17 ,  19  are always in engagement with the rails  9 ,  11  in different positions of the locking action (P 0 , P 1 , P 2 ). 
         [0073]    In the unlocked position P 0 , the latching teeth  17   b ,  17   b ′ rest on an associated projection  9   b  of the lower rail  9 . A movement of the vehicle seat  1  is possible in both directions along the longitudinal direction x. 
         [0074]    In the prelocking position P 1 , the vehicle seat  1  has been displaced further in the direction of travel in relation to the unlocked position P 0 . The latching teeth  17   b ,  17   b ′ rest on the respective web  9   c  and strike against the respective projections  9   b  which only permit a further movement in the direction of travel. This prelocking position therefore prevents movement of the vehicle seat  1  counter to the direction of travel. 
         [0075]    In the prelocking position P 1  or else in a first step of a locking mechanism of the longitudinal adjuster  3 , safety locking takes place which ensures a load absorption capability in both loading directions of the longitudinal direction x immediately after the actuating element  5  is released. This first step of the locking mechanism has play and therefore no inclined flanks F 3 , F 4  (vertical flanks or stops) which would assist an opening due to a crash load or crash impulses. That is to say, the third flank F 3  and/or the fourth flank F 4  are not inclined in the same manner as the first flank F 1  and/or the second flank F 2 . The first step of the locking mechanism or load absorption step is therefore free from influences of a chain of tolerances. In a further embodiment, the third flank F 3  and/or the fourth flank F 4 , in particular the third flank F 3 , can be slightly inclined, for example at an angle of 0° to 6°, in particular 0° to 3°, in particular 3°. 
         [0076]    In the locking position P 2 , the vehicle seat  1  has been displaced further in the direction of travel in relation to the prelocking position P 1 , as a result of which the latching teeth  17   b ,  17   b ′ engage in a latching manner in the associated catch  9   d . The latching teeth  17   b ,  17   b ′ are latched in the respective catch  9   d , wherein here only the wide latching tooth  17   b ′ latches without play in the associated catch  9   d.    
         [0077]    From the basic body  17   a ,  19   a , a guide pin  17   c ,  19   c  penetrates upward in the locking direction z through an opening O 1  in the upper rail  11 . An opening O 2  serves as a receptacle for a tension spring  21  which is illustrated in more detail in  FIG. 6  and prestresses the locking element  17 ,  19  in the locking direction z. The opening O 1  has a larger diameter than the diameter of the guide pin  17   c ,  19   c . The tension spring  21  is hooked on the locking element  17 ,  19 , which is designed as the latching plate, and the upper rail  11 , wherein the tension spring  21  does not have any contact with the guide pin  17   c ,  19   c.    
         [0078]    Under a maximum action of force by means of the actuating element  5  on the guide pins  17   c ,  19   c , the locking elements  17 ,  19  are pressed downward in the locking direction z in such a manner that contact with the lower rail  9  is interrupted and therefore the displacement of the upper rail  11  in relation to the lower rail  9  can be carried out. 
         [0079]    When the actuating element  5  is released, the latter does not exert any further force on the guide pins  17   c ,  19   c  of the locking elements  17 ,  19 , said guide pins being pulled upward in the locking direction z owing to the prestress of the respective tension springs  21 . 
         [0080]    Alternatively, in embodiments (not illustrated) of what is referred to as a “PEL” locking mechanism (PEL=permanent engaged locking), two and more locking elements  17 ,  19  are possible. Customarily, two to five locking elements are used. 
         [0081]      FIG. 4A  shows a partially sectioned perspective partial view of the pair of rails  7  illustrated in  FIG. 3 , wherein the locking element  17  latches in the locking position P 2 . The upper rail  11  of the pair of rails  7  illustrated in  FIG. 3  has been displaced to the left. The locking element  17  is latched in the locking position P 2 , and the further locking element  19  is in the prelocking position P 1 . By the latching teeth  17   b ,  17   b ′ dropping into the associated catches  9   d  and by the latching teeth  19   b  striking against the respective projection  9   b , the displacement is restricted, wherein the upper rail  11  and the lower rail  9  are locked without play. The locking element  17  is arranged in a manner free from play (=without play) by means of the latching tooth  17   b ′ because of the latching geometry (illustrated in  FIG. 7 ) of the catches  9   d.    
         [0082]      FIG. 4B  shows the opposite side of the partial view illustrated in  FIG. 4A  of the pair of rails  7 . Additionally to the illustration shown in  FIG. 4A , the lower rail  9  is illustrated interrupted in a region B, wherein the conical formation at the locking end of the recess  11   a  can be seen. 
         [0083]      FIG. 5  shows a further exemplary embodiment of the pair of rails  7  illustrated in  FIG. 3 , wherein the further locking element  19  is latched in the locking position P 2 . The upper rail  11  has been displaced to the right from the first state illustrated in  FIG. 3 . Unlike in  FIG. 4A , the displacement is restricted by the latching teeth  19   b ,  19   b ′ of the locking element  19  dropping into the respective catch  9   d  and is subsequently prevented by the latching engagement. Although the latching teeth  17   b  of the other locking element  17  come into engagement with the respective web  9   c  during the shifting of the upper rail  11 , said latching teeth do not transmit any force in this direction. 
         [0084]      FIG. 6  shows a vertical section of a possible exemplary embodiment in the y-z plane. Arranged between the lower rail  9  and the upper rail  11  are balls  15  for the mutual guidance of the rails  9 ,  11 , and therefore friction between said rails is reduced. 
         [0085]    The connecting elements  17 ,  19  have a respective tension spring  21 , wherein, in the section shown here, only the locking element  17  is illustrated. The locking elements  17 ,  19  are arranged in the upper rail  11  in the locking direction z. The tension spring  21  is arranged on the associated locking element  17 ,  19  and on the upper rail  11  and prestresses the locking element  17 ,  19  in the locking direction z. 
         [0086]      FIG. 7  shows, in a side view, a detail of a latching geometry on the lower rail  9  of the pair of rails  7 , illustrated in  FIG. 3 , with reference to the illustration shown in  FIG. 5  in a transition region of the locking elements  17 ,  19 . The latching tooth  19   b  has dropped into the catch  9   d  and is therefore in the locking position P 2 . The latching tooth  17   b  is arranged on the web  9   c  and is therefore in the prelocking position P 1 . 
         [0087]    The first flank F 1  belonging to the catch  9   d  has a very small inclination with an angle, for example, of 0° to 6°, in particular 3°, wherein a configuration for a particularly high level of crash safety and smaller tolerance compensation is possible. 
         [0088]    The second flank F 2  belonging to the catch  9   d  has a somewhat greater inclination of, for example, 3° to 10°, in particular 6°, in comparison to the flank F 1 . By this means, the configuration for traveling mode loads and a great tolerance compensation is achieved, and a disengaging of the locking position P 2  in the event of crash impulses cannot be entirely ruled out. Crash loads in this direction are taken over after a small displacement by the illustrated latching tooth  17   b  of the locking element  17 , in particular when the latching tooth  17   b  is in contact with the flank F 4 , in the prelocking position P 1 . 
         [0089]    The flanks F 3 , F 4  are what are referred to as load absorption flanks for the prelocking step and, at high impulses, absorb the resulting force before the locking position P 2  arises. They are therefore not inclined in one embodiment and are therefore designed as vertical flanks or stops. In a further embodiment, the third flank F 3  and/or the fourth flank F 4 , in particular the third flank F 3 , can be slightly inclined, for example at an angle of 0° to 6°, in particular 0° to 3°, in particular 3°. 
         [0090]      FIG. 8A  shows a first load path L 1  of a locking element  17  which has two latching teeth  17   b  and a latching tooth  17   b ′. The latching teeth  17   b  on the right side in the longitudinal direction x and the central latching tooth  17   b  on the left side are latched in the recesses  11   a . The vehicle front-side latching tooth  17   b  on the left side in the longitudinal direction x is latched into the conical recess  11   a ″, and the rear-side latching tooth  17   b ′ is latched into the wider recess  11   a ′ and at the same time into the catch  9   d . The force is therefore transmitted only from the upper rail  11  to the latching tooth  17   b  in the conical recess  11   a ″ via the wide latching tooth  17   b ′ to the lower rail  9 . 
         [0091]      FIG. 8B  shows a second load path L 2  of the locking element  17  illustrated in  FIG. 8A , wherein the upper rail  11  is shifted to the right. The force is transmitted from the upper rail  11  to the latching tooth  17   b  in the conical recess  11   a ″ via the wide latching tooth  17   b ′ to the lower rail  9 . 
         [0092]      FIGS. 9 to 11  show a further possible exemplary embodiment of a locking unit  13  in various views. 
         [0093]    The locking unit  13  comprises locking elements  23 ,  25  which are of offset design in such a manner that they are arrangeable so as to movable by means of a locking rod  27  about the latter in the longitudinal direction x. A rail  29 , in particular a lower rail  9 , has a multiplicity of latching holes  31  in which the locking elements  23 ,  25  engage and permit locking of the rail  29 . In this embodiment, the locking elements  23 ,  25  can be nested one inside the other in order to reduce the overall length of the locking unit  13 . 
         [0094]    The locking elements  23 ,  25  are of lever-shaped design. On the locking element  23 , four latching teeth  23   a  are arranged at equal distances one behind another at the front in the direction of travel on the right longitudinal edge. One latching tooth  23   a ′ is arranged adjacent to a latching tooth  23   a  at the rear in the direction of travel. The latching tooth  23   a ′ is designed to be wider in the longitudinal direction x than the other latching teeth  23   a.    
         [0095]    On the locking element  25 , four latching teeth  25   a  are arranged at equal distances one behind another at the front in the direction of travel on the right longitudinal edge. One latching tooth  25   a ′ is arranged adjacent to a latching tooth  25   a  at the rear in the direction of travel. The latching tooth  25   a ′ is designed to be wider in the longitudinal direction x than the other latching teeth  25   a.    
         [0096]    The latching teeth  23   a ,  25   a  of the locking elements  23 ,  25  are of identical design, and the latching teeth  23   a ′,  25   a ′ of the locking elements  23 ,  25  are of identical design. 
         [0097]      FIG. 12  shows the latching hole  31  of the rail  29  in a side view. The latching hole  31  is of L-shaped design and has a catch  31   b , the flanks F 1 , F 2  of which are of conical design in such a manner that the latching tooth  25   a  latches with play. The latching tooth  23   a  rests on a web  31   b , wherein the latter is therefore arranged in the prelocking position P 1 . 
         [0098]    An upper rail which is not illustrated in this exemplary embodiment has a number of formations receiving the latching teeth  23   a ,  23   a ′,  25   a ,  25   a ′, and therefore a force can be transmitted from the upper rail to the lower rail. 
         [0099]    While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.