Abstract:
A motor vehicle seat having a seat frame; a pivotally mounted seat back of the seat frame that, on the one hand, can be displaced within an area of use between two different positions of use and, on the other hand, can be tilted forward toward the seat surface of the seat frame by being pivoted; a seat longitudinal guide for adjusting the longitudinal position of the seat; a fixing device for locking a previously adjusted longitudinal position of the seat, and; a coupling mechanism via which the back seat back is coupled to the fixing device whereby enabling the fixing device to be released when tilting the seat back forward toward the seat surface. Compensating features are provided for preventing the fixing device from releasing when the seat back pivots at least over a portion of the area of use.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a National Phase Patent Application of International Application Number PCT/DE02/01910, filed on May 22, 2002, which claims priority of German Patent Application Number 101 27 067.4, filed on May 23, 2001. 
   BACKGROUND 
   The invention relates to a motor vehicle seat. 
   A motor vehicle seat of this kind comprises a seat frame; a pivotally mounted back rest of the seat frame which can be adjusted on one side (by pivoting) in an area of use between different useful positions and which on the other side—after releasing the backrest, for example by means of a release lever normally provided for this on the backrest—can be folded forwards (by pivoting) steplessly towards the seat surface of the seat frame; a seat longitudinal guide for adjusting the seat longitudinal position of the seat frame; a fixing device for locking a previously set seat longitudinal position; a coupling mechanism through which the backrest is coupled to the fixing device so that when the backrest is folded forwards towards the seat surface the fixing device can be released by an output side of the coupling mechanism; as well as a tumbler fitment of the backrest which when pivoting the backrest tumbles about a tumbler axis and to which an input side of the coupling mechanism is connected. 
   The different useful positions which the seat back can occupy in the area of use serve to support the back of a person seated on the seat. Further useful positions can also serve to support the back of a person reclining on the seat. 
   Folding the backrest onto the seat surface, on the other hand, serves to release the fixing device of the seat longitudinal guide through the coupling mechanism which is connected on the input side to the tumbler fitment and on the output side to the fixing device. Folding the backrest forwards is normally accomplished by actuating a lever provided for this purpose on the backrest which enables the backrest to be folded effortlessly forwards onto the seat surface whilst at the same time releasing the useful position of the vehicle seat which previously existed. 
   After releasing the fixing device by folding the backrest forwards the seat can be easily moved forwards, for example, to facilitate ease of entry into the back of the vehicle in the case of a two-door cabriolet vehicle. This is the so-called easy-entry function which is to make access to the back seat of a two-door vehicle that much easier. This easy-entry function is often coupled to a memory device through which the original seat position is automatically relocated when subsequently sliding back the vehicle seat. 
   In the case of a known vehicle seat of the type mentioned at the beginning, the coupling mechanism comprises a Bowden cable whose core is connected on one side to the tumbler fitment and on the other side (if necessary through further coupling elements) to the fixing device of the seat longitudinal guide. The problem here is that as a result of the tumbler movement of the tumbler fitment when swiveling the seat—depending upon the useful position in which the seat is already located—there is a different lengthening of the Bowden cable and thus different operating paths arise for releasing the fixing device by means of the Bowden cable. In order to solve this problem it is known to integrate an elastic element in the form of a tensile spring into the core of the Bowden cable whereby the spring constant of this spring is so great that it does not impair the actuation of the fixing device by means of the Bowden cable. The action of this spring must thus overcome the action of the spring elements normally integrated into the fixing device whose function is to pretension the fixing device into its locked state. (Through this pretensioning of the fixing device into its locked state it is to be guaranteed for safety reasons that the seat longitudinal guide is always then automatically locked unless an occupant actively actuates the release of the fixing device). Only if the fixing device is fully unlocked and further actuation of the fixing device by means of the coupling mechanism is no longer possible does the tensile spring expand and thus permit compensation of the overtravel which can happen as a result of the previously mentioned different actuating paths for releasing the fixing device—depending on the position of the seat back and thus the tumbler fitment at the start of folding the backrest forwards. 
   The known coupling mechanism for the easy-entry function has the drawback that as a result of the large spring constant required the spring which is to be integrated for this into the Bowden cable takes up some structural space and significantly increases the weight of the assembly. 
   SUMMARY 
   The object of the invention is to improve a motor vehicle seat of the type already mentioned so that with simple means it is possible to couple the backrest through the tumbler fitment and a coupling mechanism to the fixing device of the seat longitudinal guide. 
   According to this, compensating means are provided which when pivoting the back rest (for the purpose of adjusting the useful position of the backrest or for folding the backrest forwards) prevent a release of the fixing device at least over a partial area of the area of use. 
   With the solution according to the invention—unlike the prior art—not simply is the overtravel compensated which can occur after releasing the fixing device, but rather compensation of the tolerances which are due to the tumbler motion of the tumbler fitment already takes place before the release of the fixing device. For this, compensating means are provided which prevent the release from already taking place whilst the backrest during folding forwards is still located in its area of use or at least in a certain predeterminable portion of this area of use. 
   The portion of the area of use can, on the one hand, be smaller than the latter; these two areas can however also coincide so that release of the fixing device is impossible so long as the seat back is still located in its area of use when folding forwards. 
   The compensating means can be formed in particular for compensating the action of the backrest on the coupling mechanism when pivoting the backrest in the said portion of the area of use. In other words, the compensating means compensate the action of the backrest (through the tumbler fitment) on the coupling mechanism so that no such action of the coupling mechanism on the fixing device can take place which would lead to a release of the fixing device. 
   In a further embodiment, the compensating means are formed and provided to prevent, during pivoting of the backrest, at least in the portion of the compensating area, any action of the coupling mechanism on the fixing device. 
   In a preferred embodiment the compensating means are formed and provided to only permit an action of the coupling mechanism on the fixing device when the backrest when folding forwards for the purpose of releasing the easy-entry function has reached the fully folded forwards position (corresponding to the backrest resting on the seat surface) except for a predetermined angular difference. In this case it is ensured that irrespective of the useful position in which the vehicle seat is located during release of the easy-entry function, the action of the coupling mechanism on the fixing device always starts at the same forward rake angle of the backrest. 
   According to a variation of the invention the compensating means are mounted in or on the coupling mechanism. It can hereby be proposed that the compensating means during pivoting of the backrest at least in the portion of the compensation area compensate an action of the backrest or tumbler fitment on the coupling mechanism so that the coupling mechanism on the output side does not act on the fixing device. 
   The solution according to the invention can be applied in particular to a coupling mechanism having traction means, which during pivoting of the backrest and the tumbler movement of the fitment involved therewith, transfers forces to the output side of the coupling mechanism so that the coupling mechanism can act on the fixing device. The core of a Bowden cable is thereby particularly suitable as traction means. 
   According to an embodiment of the invention the traction means are dimensioned so that they are slack when the backrest is swiveled in the area of use or at least a portion of same. No forces can then be transferred through the traction means so long as the backrest when folding forwards is still located in the area of use or the said portion of the area of use. Thus, so long as the backrest when folding forwards for the purpose of releasing the easy-entry function is still in the said swivel range (area of use or a portion thereof), the corresponding movement only leads to a breakdown of the cable slack, thus not however to a release of the fixing device. This only starts when the cable slack has completely broken down and, thus, only at a defined swivel position of the backrest behind the area of use or a portion hereof. 
   With a further development of the invention an elastic element additionally acts on the coupling mechanism in order to hold the traction means during swiveling of the backrest in the area of use or a portion thereof under a slight pretension which is sufficient to prevent the coupling mechanism from rattling. A very small cost-effective lightweight spring is adequate for this since it can be considerably weaker than the spring elements used to pretension the fixing device. The spring can, on the one hand, act on the traction means directly, or on the other hand, act through at least one further component on the traction means. 
   According to a further embodiment of the invention the traction means are fixed on a holder which is mounted to pivot about an axis, more particularly the tumbler axis, whereby this holder is then not entrained by the tumbler fitment when the backrest during folding forwards for the purpose of releasing the easy-entry function is located in its area of use or at least a portion thereof. Then during pivoting of the backrest in the area of use, or at least a portion thereof, no action takes place on the traction means through the tumbler fitment. This only happens after the backrest has been pivoted (folded forwards) beyond its area of use towards the seat surface. 
   In a further development of this embodiment of the invention when using a Bowden cable as the component of the coupling mechanism for fixing the sleeve of the Bowden cable on the tumbler fitment side, on the one hand, and the core on the other, two relatively rotatable holders are provided which can pivot about an axis (more particularly the tumbler axis) and which when folding the backrest forwards are only then turned relative to each other when the backrest is located outside of the area of use or at least a predetermined portion thereof. Only then by turning, the core of the Bowden cable on the one holder, and the sleeve on the other opposite holder, does the core become taut which leads to action of the fixing device. 
   It can hereby be further proposed that when folding the backrest forwards outside of the area of use or at least a portion thereof the one holder is moved in unison with the tumbler fitment and the other holder is blocked on a structural group of the seat frame which cannot pivot together with the backrest. 
   In a further embodiment of the invention, the coupling mechanism comprises a coupling lever (or release lever) which when the backrest pivots in its area of use or at least in a portion thereof does not act on the element of the coupling mechanism mounted on the output side towards the fixing device, so that the forces which are introduced on the input side into the coupling mechanism when the backrest is pivoted are not transferred towards the fixing device and thus no locking of the fixing device can take place. The release of the fixing device thus only takes place when the backrest has been folded forwards beyond its area of use or at least a defined portion thereof. 
   In a further development, the element of the coupling mechanism on the output side of the lever has an outward bulge in which one end of the coupling lever can move when the backrest is pivoted without acting on the element on the output side. The end of the coupling lever moves into the bulge when the release of the fixing device has concluded and thus serves for compensating the overtravel. 
   For compensating the overtravel generally, compensating means are provided which when folding the backrest forwards beyond the position in which the release of the fixing device has concluded, counteract any interaction of two elements of the coupling mechanism so that an additional action of the coupling mechanism on the fixing device is avoided. It should thus be prevented that when folding the backrest forward beyond the position at which the fixing device is fully released, there results a further additional action on the actuating element of the fixing device (to be deflected for unlocking the fixing device). I.e. it is prevented that the actuating element after complete release of the fixing device is deflected still further (additionally). Damage to the fixing device, for example by its resetting springs through overstraining as a result of folding the backrest forwards is hereby to be prevented. 
   The compensating means can be formed by an outward bulge in one of the elements of the coupling mechanism, e.g. by the second element of the coupling mechanism on the output side having a bulge in which a section of the element connected on the input side can move without acting on the element on the output side. For this the contour of the bulge has at least in part a curvature, more particularly a radius, such that a section of the element on the input side, more particularly in the form of a coupling or release lever, can move therein without acting on the element on the output side, whereby the section of the coupling lever then moves into the bulge when the release of the fixing device is completed. 
   In another variation of the invention the compensating means are not integrated in the coupling mechanism but rather in the fixing device of the seat longitudinal guide. For this for example the locking teeth which are normally provided in a fixing device are over long so that when the coupling mechanism acts on the fixing device the first part of the movement of the locking teeth only serves for compensating tolerances as a result of different positions of the tumbler fitment and the release effects, i.e. the lifting of the locking teeth from the associated ratchet openings of the seat longitudinal guide only then follow on. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features and advantages of the invention will now be explained with reference to an embodiment illustrated in the drawings. 
       FIGS. 1   a  and  1   b  are diagrammatic illustrations of the seat frame of a motor vehicle seat with a backrest in two different settings of the backrest rake; 
       FIGS. 2   a  and  2   b  are diagrammatic views of a coupling mechanism through which the backrest of  FIGS. 1   a  and  1   b  is coupled to the fixing device of a seat longitudinal guide, each in a situation which is produced through the rake of the backrest according to  FIGS. 1   a  and  1   b;    
       FIG. 3  is a perspective view of two retaining discs which are rotatable relative to each other of which one disc serves to hold the end of the Bowden cable sleeve on the backrest side and the other disc serves to hold the end of the Bowden cable core on the backrest side, forming a component of the coupling mechanism for coupling a seat back to the fixing device of a seat longitudinal guide; 
       FIGS. 4   a  to  4   d  are side views of an exemplary lever assembly coupled through a Bowden cable to the seat back of a seat frame for releasing the fixing device of a seat longitudinal guide with four different settings of the backrest rake; 
       FIGS. 5   a  to  5   c  are detailed perspective illustrations of an exemplary assembly according to  FIG. 4   a  with three different settings of the backrest rake; 
       FIG. 6  is a perspective view of a part of a seat frame known from the prior art with a seat longitudinal guide, a fixing device of the seat longitudinal guide, a seat side part on which a backrest is swivel mounted as well as with a programmable memory device for automatically finding a predetermined seat longitudinal position; 
       FIG. 6   a  is a rear view of the illustration of  FIG. 6 ; 
       FIG. 7  is a perspective view according to  FIG. 6  in a situation in which the backrest has been folded forwards so that the seat can be moved with the backrest folded forwards; 
       FIG. 8  is a perspective view according to  FIG. 6  in a situation in which with the backrest raised up in the memory position an actuating lever was actuated in order to set the memory position anew; 
       FIG. 9  is a perspective view according to  FIG. 6  in a situation in which the memory position of the seat with the backrest raised up is approached; 
       FIG. 10  is a perspective view according to  FIG. 6  in a situation in which the memory position of the seat with the raised up backrest is reached; 
       FIG. 11  is a side view of a frame of a motor vehicle seat. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The seat frame G (seat lower frame) illustrated in side view in  FIG. 11  comprises a seat longitudinal guide SLF with a seat rail which is mounted movable in the seat longitudinal direction L on an under rail to be fixed on the vehicle body, and a seat side part  8  which is attached vertically adjustable on the seat rail through front and rear articulated levers  9   a  and  9   b . On its other longitudinal side, which cannot be seen in  FIG. 11 , the seat frame G has a corresponding arrangement. Between the two seat side parts of the seat frame G extends a seat surface F which holds a seat cushion on which a vehicle occupant can sit. 
   Furthermore the side parts  8  of the seat frame G each have a tumbler fitment T for supporting a pivotal backrest R which is shown in dotted lines in  FIG. 11 . 
   Here, parts of the seat frame are to mean all those components which are movable in the seat longitudinal direction on the lower rail which is fixed on the body, thus in particular the seat rail, the seat side part  8  and the further components of the seat connected thereto. 
   If a vehicle seat of this kind which is adjustable in the longitudinal direction L is used for a two-door vehicle then it is known in order to make it easier to enter the back of the vehicle to couple the backrest to the seat longitudinal adjuster, namely so that when folding the backrest R forwards towards the seat surface F which extends between the seat side parts  8 , a fixing device associated with the seat longitudinal guide SLF is released and the seat can be pushed forwards with the backrest folded forwards. This is the so-called easy-entry function. 
   In the following discussion, the basic principle of the easy entry function when using a programmable memory device for automatically seeking a predeterminable seat longitudinal position will first be explained with reference to a seat arrangement illustrated in  FIGS. 6 to 10  and known from WO 00/55002 (see corresponding U.S. Pat. No. 6,631,952). For further details on this reference is made to WO 00/55002 which expressly relates to the subject of the present description. 
   The perspective front view according to  FIG. 6  and the associated rear view in  FIG. 6   a  show a rail  101  fixed on the body and a seat rail  102  movably guided thereon in the seat longitudinal direction L whereby a ratchet rail  107  having several ratchet openings  170  arranged in succession in the longitudinal direction L of the seat is fixed on the rail  101  which is fixed on the body. The seat rail  102  supports the remaining components of the seat frame, see  FIG. 11 . 
   The seat rail  102  is lockable by means of a fixing device  120  in respect of the rail  101  fixed on the body. The fixing device can be any conventional fixing device used for longitudinally adjusting the seat.  FIGS. 6 and 6   a  show the housing, a swivel mounted actuating element  120   b  and a torsion spring assembly (shown in  FIG. 7 ) of a known fixing device  120  acting on the actuating element  120   b , with its housing fixed on the seat rail  102 . The torsion spring serves inter alia to remove the play from the assembly so as to prevent any rattling noises. 
   This fixing device comprises for example according to DE 299 10 720 U1 a number of locking teeth arranged inside the housing and elastically pretensioned—by means of springs mounted in the form of coil springs in the housing—towards a ratchet device (not shown in  FIGS. 6 and 6   a ) fixed on the body-side rail  101 . As a result of the pretension acting on the locking teeth the locking teeth which are associated with the seat rail  102  automatically engage in the ratchet device fixed on the body so that the seat longitudinal adjustment is locked unless the locking teeth are brought out of engagement with the ratchet device by means of the actuating element  120   b  provided for this purpose (see  FIG. 7 ). 
   Since the actuating element  120   b  ( FIG. 7 ) of the fixing device  120  is pretensioned by means of the spring assembly  120   a  which consists of the springs mounted inside the housing and acting on the locking teeth, as well as the torsion spring mounted outside of the housing, opposite the direction into which it has to pivot in order to release the fixing device  120 , the fixing device  120  can only then be released when a force is exerted on the actuating element  120   b  against the action of the spring assembly  120   a.    
   In order to release the fixing device  120  the actuating element  120   b  can be actuated on one side by a seat user directly by seizing an actuating lever  109  swivel mounted on the seat frame and having a cross bar  190  by an actuating handle provided for this purpose (and not shown in  FIGS. 6 and 6   a ) and swiveling it counter-clockwise whereby the actuating element  120   b  is moved down against the pretension of the spring assembly  120   a . On the other hand the fixing device  120  can also be released by folding the seat back forwards whereby the seat back is coupled to the actuating lever  109  through a Bowden cable which has a cable  121   b  and whose Bowden cable (not shown) is supported on a Bowden support  121 . Furthermore a gearing part  122  which has a guide  122   a  and a mounting  122   b  for the cable  121   b  of the Bowden cable is mounted on the swivel axis of the actuating lever  109  by means of an axle shaft  124 . This gearing part  122  converts tightening of the cable  121   b  which happens when the backrest is folded forwards into a swivel movement which in turn is transferred by two arms  123  of the gearing which engage round the actuating lever  109  to said lever. The actuating lever  109  thereby swivels clockwise when the backrest is folded forwards and releases the fixing device  120  through the actuating element  120   b.    
   Furthermore a cable nipple  168  is fixed, for example squashed on the cable  121   b  of the Bowden cable between the Bowden cable support  121 , which is fixed on the seat rail by means of a fixing plate  121   a , and the gearing  122 . The cable nipple  168  is associated with a switch element in the form of a switch lever  106  which is mounted by means of a bearing bushing  165 , a stepped bolt  165   a  and a screw  166  for swivel movement about an axis formed through the longitudinal axis of the stepped bolt  165   a , and at the same time is fixed on the seat frame or its seat rail  102 . The switch lever  106  has in its upper section  161  a stop  162  which is mounted directly adjacent the cable nipple  168  and on which the cable nipple  168  can act in the seat longitudinal direction whereby the switch lever  106  is swiveled. 
   The second end section of the switch lever  106  mounted underneath the bearing bush  165  and the stepped bolt  165   a  forms an actuating section  160  which is associated with an actuating section of a locking pawl  104  of the memory device. The actuating section of the locking pawl  104  is thereby formed by an actuating face  140  on the top side of the locking pawl. 
   The switch lever  106  is here locked by a projection  191  of the actuating lever  109  on which the upper section  161  of the switch lever  106  is vertically supported with a stop  163  (transversely to the longitudinal direction L of the seat), in the position illustrated in  FIGS. 6 and 6   a  in which its actuating section  160  acts on the actuating face  140  of the locking pawl  104 . The torque required for this is applied through the spring assembly  120   a  of the fixing device  120  which acts through the actuating element  120   b  and actuating lever  109  on the lever projection  191 . 
   As an alternative or in addition, the perpendicular position of the switch lever  106  can also be assisted through a spring mounted directly on the switch lever  106  (not shown) or by the switch lever  106  being mounted with sufficient friction which cannot be overcome through the action of the compression spring  400  of the locking pawl  104 . 
   The locking pawl  104  itself is as can be seen in particular from  FIG. 6   a  swivel mounted on a bearing stud  155  of a slider  105  which is guided with a base body  150  movable in the seat longitudinal direction L next to the ratchet openings  170  of the ratchet rail  107 . The slider has in its base body  150  a recess  152  in which a compression spring  400  is mounted which is underneath the actuating face  140  of the locking pawl  104  and acts on the latter whereby the locking pawl  104  is pretensioned so that a ratchet hook  141  mounted at the other end of the locking pawl  104  has the tendency to engage in the ratchet rail  107 . In the situation illustrated in  FIGS. 6 and 6   a  in which the seat is locked in the memory position with the backrest not folded forwards the locking pawl is prevented from this tendency to engage, in that the actuating section  160  of the switch lever  106  is supported on the actuating face  140  of the locking pawl  104  so that the latter cannot pivot about the bearing stud  155  in order to bring the ratchet hook  141  into engagement with the ratchet rail  107 . 
   In the situation illustrated in  FIGS. 6 and 6   a , a counter stop  144  of the locking pawl  104  is furthermore in contact with the stop  132  of a stop element  103  which is fixed by fixing screws  136  on the seat rail  102 . Furthermore, a follower  143  of the locking pawl  104  which at the top adjoins the stop  144  is located in engagement with an engagement area  134  of the stop element  103 . 
   If, in the position of the seat illustrated in  FIGS. 6 and 6   a  in which the seat is locked in the memory position, the backrest is folded forwards then the cable  121   b  of the Bowden cable is tensioned and moved towards the rear (backrest side) seat end. 
   According to  FIG. 7 , on the one hand, the actuating lever  109  is hereby swiveled counter-clockwise through the gearing part  122  and arms  123  whereby it acts on the actuating element  120   b  and releases the fixing device  120 . On the other hand the cable nipple  168  which is squashed with the cable  121   b  is moved towards the rear seat end and thereby acts on the stop  162  in the upper section  161  of the switch lever  106 . The switch lever  106  is thereby pivoted counter-clockwise whereby its actuating section  160  is lifted from the associated actuating face  140  of the locking pawl  104 . This swivel movement of the switch lever  106  is possible since the latter is no longer blocked by the lever projection  191  which was swiveled down together with the actuating lever  109 . Since the switch lever  106  has released the locking pawl  104  the latter now swivels as a result of the action of the compression spring  400  (see  FIG. 6   a ) about the bearing stud  155  of the slider  105  until the ratchet hook  141  engages in an opening  170  of the ratchet rail  107 . The locking pawl  104  and thus the memory device as a whole is thereby locked. 
   The swivel movement of the locking pawl  104  furthermore has the result that the follower  143  of the locking pawl  104  as well as the engagement area  134  of the stop element  103  move out of engagement. This is necessary so that the seat frame can move since otherwise movement of the seat would be blocked by the locked memory device. 
   The cable nipple  168  thereby serves as the locking means which when the backrest is folded forwards acts on the switch lever  106  so that the locking pawl  104  cannot be released by means of the switch lever  106 . 
   The arrangement is designed so that when folding the backrest forwards the ratchet hook  141  can engage already under the action of the compression spring  400  into a ratchet opening  170  before the fixing device  120  is released so far that the seat rail  102  can be displaced relative to the rail  101  fixed on the body. A permissible storage of the actual seat longitudinal position as the memory position is hereby guaranteed. If, however the ratchet hook  141  cannot immediately engage in a ratchet opening  170  because the seat is positioned so that the ratchet hook  141  under the action of the compression spring  400  stops on a web between two ratchet openings  170 , then the ratchet hook  141  only engages in the next ratchet opening  170  which it passes after a slight displacement of the seat frame in the seat longitudinal direction L. In such a case there is a slight deviation between the seat longitudinal position when folding the backrest forwards, and the subsequently stored memory position. 
   In the situation shown in  FIG. 7  which was reached by folding the backrest forwards, the seat frame can now be pushed forwards in the seat longitudinal direction with the backrest folded forwards in order to make it easier for a passenger to climb into the back of the vehicle or to place an object in the back of the vehicle. 
   If the seat is then moved back again with the backrest still folded forward it is then automatically stopped at the latest in the memory position defined by the locking pawl  104 . For on reaching the memory position the stop  132  of the seat frame moves into contact with the stop  144  of the memory device whereby further movement of the seat frame backwards is prevented. 
   If then the backrest is again folded back into its function position then the tension of the cable  121   b  is released and the switch lever  106  and the actuating lever  109  with the projection  191  fixed thereon return to the position illustrated in  FIGS. 6 and 6   a . If then the actuating lever  109  is swiveled counter-clockwise to release the fixing device  120  the position shown in  FIG. 8  is automatically set. 
   When manually swiveling the actuating lever  109  by means of an actuating handle provided for this purpose the fixing device  120  is indeed released through the actuating element  120   b  so that the seat frame can be moved in the seat longitudinal direction L on the rail  101  fixed on the body; however—unlike when folding the backrest forwards the switch lever  106  hereby remains in its upright position in which its actuating section  160  acts vertically on the actuating face  140 . This prevents the locking pawl  104  from being locked under the action of the compression spring  400 . 
   As a result of the lever projection  191  which is swiveled down according to  FIG. 8  and which consequently does not bear against the associated stop  163  of the switch lever  106  the vertical position of the switch lever  106  must be secured for example by a suitable design of the actuating face  140  of the locking pawl  104 . The actuating face  140  can hereby be curved so that it under the action of the compression spring  400  of the locking pawl  104  exerts no moment on the actuating section  160  of the switch lever  106  which would result in a swivel movement of the switch lever  106  counter-clockwise. Expressed in other terms, the interaction of the actuating face  140  of the locking pawl  104  with the actuating section  160  of the switch lever  106  must be designed so that no counter-clockwise swivel movement of the switch lever  106  is triggered through the forces introduced by means of the compression spring  400  from the locking pawl  104 . A swivel movement of the switch lever  106  clockwise is, however, blocked by the cable nipple  168 . 
   Alternatively the upright position of the switch lever  106 —as already mentioned above—can also be secured by a suitable spring element (not shown) or by sufficiently adequate friction forces. 
   In short, the actuation of the actuating lever  109  in the memory position of the seat (with the backrest not folded forwards) leads on the one hand to the fixing device  120  being released whilst at the same time the locking pawl  104  and thus the memory device overall remains in the released state which already existed prior to swiveling the actuating lever  109 , see  FIGS. 6 and 6   a . Furthermore the follower  143  of the memory device engages in the engagement area  134  of the stop element  103  on the seat rail side. 
   In this situation any movement of the seat frame in the seat longitudinal direction L leads to the locking pawl  140  being entrained at the same time so that when sliding the seat a new memory position is set also at the same time. The newly set memory position which corresponds to the seat longitudinal position newly set by sliding the seat frame is however not already locked when the actuating lever  109  is finally let go. For this initially only has the result according to  FIGS. 6 and 6   a  that the fixing device  120  is locked and thus the seat rail  102  is locked relative to the rail  101  fixed on the body. Locking of the memory device however according to  FIG. 7  only takes place when in the new seat longitudinal position the seat back is folded forwards. Thus, with the present embodiment, the memory device is only always then locked when the seat is moved forwards with the backrest folded forwards within the scope of the easy-entry function. 
     FIG. 9  shows the seat frame after it was initially pushed forwards in the seat longitudinal direction L with the backrest folded forwards whereby the locking pawl  104  has been left back locked in the original seat position, and after then the backrest was folded back up into its function position. Furthermore the actuating lever  109  is swiveled so that the fixing device  120  is unlocked and the seat frame can be displaced selectively forwards or backwards in the seat longitudinal direction. In each seat longitudinal position which is hereby reached the seat frame can be locked relative to the rail  101  fixed on the body by means of the fixing device  120  by letting go the actuating lever  109 . 
     FIG. 10  finally shows the position of the seat frame when the latter is moved back to the memory position with the backrest upright. The switch lever  106  thereby stops with its actuating section  160  against a projection  140   a  which protrudes vertically up from the actuating face  140  of the locking pawl  104 . This is due to the fact that the locking pawl  104  is located in the locked state in which it engages by its ratchet hook  141  (see  FIG. 6   a ) in a ratchet opening  170  of the ratchet rail  107 . Through the inclined position of the actuating face  140  of the locking pawl  104  linked with this the latter exerts on the actuating section  160  of the switch lever  106  a torque with a component both parallel and perpendicular to the seat longitudinal direction L. As a result of this the switch lever  106  is swiveled counter-clockwise and its actuating section  160  moves to stop with the projection  140   a  of the locking pawl  104 . This has the effect that the locking pawl  104  remains locked when the seat lower frame reaches the memory position illustrated in  FIG. 10 . 
   In short the actuating face  140  in the locked state of the locking pawl  104  interacts with the actuating section  160  of the switch lever  106  so that the latter is swiveled when the seat is pushed with the backrest upright into the memory position whereby release of the locking pawl  104  is prevented. (If the seat is pushed back into the memory position with the backrest folded forwards, then the switch lever  106  as a result of the action of the cable nipple  168  is readily swiveled, see  FIG. 7 , so that even in this case no release of the memory device can take place). On the other hand the actuating face  140  of the locking pawl  104  and the actuating section  160  of the switch lever  106  interact in the released state of the locking pawl  104 , see  FIG. 6 , so that the locking pawl  104  remains unlocked, as detailed above with reference to  FIG. 6 . 
   Owing to the locked state of the locking pawl  104  the seat frame on reaching the memory position is automatically stopped when the stop  132  of the stop element  103  on the seat frame side becomes blocked with the counter stop  144  of the memory device (see  FIG. 6   a ). 
   If then in the memory position the actuating lever  109  is let go then this is swiveled clockwise under the action of the spring assembly  120   a  of the fixing device  120  until the fixing device  120  is again locked. At the same time through the projection  191  of the actuating lever  109  which acts on the angled stop  163  in the upper section  161  of the switch lever  106  the switch lever  106  is swiveled clockwise into its upright position whereby the switch lever  106  acts by its actuating section  160  on the actuating face  140  of the locking pawl  104  and releases this (against the action of the compression spring  400 )—which requires a corresponding design of the spring assembly  120   a . The seat is then located again in the position explained with reference to  FIGS. 6 and 6   a  with the backrest raised up in the memory position. 
   Different embodiments will now be explained with reference to  FIGS. 1   a  to  4   d  showing how according to the present invention folding the backrest forwards onto the seat face of the seat frame is transferred through the coupling mechanism which then releases the fixing device of the longitudinal guide. 
   The following comments on  FIGS. 1   a  to  4   d  are substantially restricted to the construction and function of the coupling mechanism  1 . Further details will not be provided on the remaining structural groups of the seat assembly, such as e.g. the rail longitudinal guide, the fixing device of the rail longitudinal guide, the memory device as well as the interaction of these groups. For this reference is made to the above details relating to  FIGS. 6 to 10 . 
     FIG. 1   a  shows diagrammatically the seat frame G illustrated in  FIG. 11  now in a position where the backrest R is set vertical. This corresponds as a rule to the front most position of use of the backrest, i.e. the front most position of the area of use in which the incline of the backrest R is adjustable in order to be able to adapt to the different needs of a person seated on a corresponding seat. 
     FIG. 1   b  shows the seat frame of  FIG. 1   a  in a position in which the backrest R has been moved from the vertical position about an angle α into an incline position in which the backrest R is inclined sharply backwards. 
   With the coupling according to the invention it is possible—as will be explained below with reference to  FIGS. 2   a  and  2   b —to reach the situation where when folding the backrest forwards for the purpose of triggering the easy-entry function both from the position illustrated in  FIG. 1   a  (substantially upright backrest R) and also from the position illustrated in  FIG. 1   b  (sharply backwards inclined backrest R) the release of the fixing device takes place for the seat longitudinal guide with the same incline of the backrest R forwards; in the example here the rake angle is about 20° relative to the vertical. This means that the release of the fixing device by folding the backrest forwards takes place each time when the backrest is a defined angle β away from the swivel position in which it rests on the seat face F of the seat frame. 
     FIG. 2   a  shows diagrammatically a Bowden cable  10  which is a constituent part of the coupling mechanism  1  for coupling the backrest to the fixing device of the seat longitudinal guide. The Bowden cable  10  comprises a Bowden sleeve  11  and core  15 . The Bowden sleeve  11  is fixable by its backrest end  12  by means of a Bowden cable block to a side part of the seat frame. The other end  13  of the Bowden sleeve  11  facing the fixing device which is to be released is fixed on a Bowden cable block of the seat-side rail (top rail) of the seat longitudinal guide. 
   The core  15  of the Bowden cable extends from a tumbler fitment T of the seat back R (see  FIG. 11 ) up to an actuating lever H—shown symbolically in  FIG. 2   a —for releasing the fixing device of the seat longitudinal guide. Correspondingly the core  15  of the Bowden cable  10  is fixed by its end  16  associated with the seat back and representing the input side of the coupling mechanism, on the tumbler fitment T of the seat back R (see  FIG. 11 ) and by its other end  17  which is provided on the output side of the coupling mechanism to the actuating lever H. K in  FIG. 2   a  designates a curve along which the backrest-side end  16  of the core  15  of the Bowden cable  10  moves when adjusting the rake of the backrest. This curve K thus represents the tumbler movement of the tumbler fitment and the movement hereby triggered of the backrest-side end  16  of the core  15  of the Bowden cable  10 . 
   It can be seen that the backrest side end  16  of the core  15  in the situation of the coupling mechanism  1  represented in  FIG. 2   a  (corresponding to a vertically set backrest R according to  FIG. 1   a ) has the greatest possible distance from the actuating lever H which can happen when this end  16  of the core  15  moves along the curve K. 
     FIG. 2   b  shows on the other hand the coupling mechanism  1  in the situation where the backrest R has been set into a sharply rearwardly inclined position. In this position the backrest-side end  16  of the core  15  of the Bowden cable  10  has the smallest possible spacing from the actuating lever H. 
   According to the invention the core  15  of the Bowden cable  10  has in the position of the coupling mechanism  1  shown in  FIG. 2   b  a slack which is dimensioned so that the core  15  during swivel movement of the backrest R from the swivel position inclined sharply back shown in  FIG. 2   b  into the vertical position shown in  FIG. 1   a  is just lifted, thus the cable begins to tighten on reaching the vertical position. The release of the fixing device of the seat longitudinal guide by means of the coupling mechanism  1 , more particularly the Bowden cable  10  starts by the core  15  acting with increasing tightening through the actuating lever H on the fixing device until this is released. The release is terminated when the backrest R has been folded forwards about 20° relative to the vertical. The seat can then be moved forwards to execute the easy-entry function in order to make it easier for a person to enter the back of the vehicle. 
   Means are thereby provided for guiding the Bowden cable  10 , more particularly the core  15  which ensure that when the backrest R is folded forwards beyond the position shown in  FIG. 1   a  the core is guided so that it actually results in further tightening of the core  15 . 
   The coupling mechanism illustrated in  FIGS. 2   a  and  2   b  has the advantage that a compensation of the tumbler movement is carried out through a simple slack in the core of the Bowden cable. This has the positive side effect that wear on the Bowden cable is minimised since the Bowden cable is tightened only in a single useful position (namely the foremost useful position, for example vertical position); the wear involved with permanent tightening of the core is hereby avoided. 
   In order to prevent chattering noises of the coupling mechanism during operation of the vehicle as a result of slack in the core of the Bowden cable a small weakly dimensioned spring is sufficient either to engage directly on the core  15  of the Bowden cable  10  (not shown) or to act on another part of the coupling mechanism such as e.g. the actuating lever H. 
   With the embodiment illustrated in  FIG. 3  the end  12  of the Bowden sleeve  11  on the backrest side as well as the end  16  of the core  15  of the Bowden cable  10  on the backrest side are each fixed on one of two relatively rotatable retaining discs (or holders)  21 ,  22  which are mounted for example loosely on the tumbler axis A of the backrest fitment (tumbler fitment). As a result of the loose bearing of the two retaining discs  21 ,  22  on a common axis, any adjustment of the backrest rake or folding the backrest forwards for the purpose of triggering the easy-entry function initially has no effect on the tightening of the core  15  of the Bowden cable  10  so that no release of the fixing device can take place through the Bowden cable or through the tightening of the core of the Bowden cable  10 . 
   If however on folding the backrest forwards for the purpose of triggering the easy-entry function the foremost useful position of the backrest or the foremost position of the area of use of the backrest R is exceeded (see  FIG. 1   a ) then, on the one hand, a locking element in the form of a locking pin  27  moves from the tumbler fitment into the retaining disc  22  which holds the one end  16  of the cable  15 . This is entrained further by the tumbler fitment which in turn results in entrainment of the backrest side end  16  of the core  15  of the Bowden cable  10  fixed on the retaining disc  22 . 
   At the same time the other retaining disc  21  on which the backrest end  12  of the Bowden sleeve  11  is fixed is blocked by means of a blocking element  26  which is mounted for example on a seat side part. This retaining disc  21  can therefore execute no further movement. As a result therefore during further swivel movement of the backrest there is a relative movement between the backrest side end  16  of the core  15  and the backrest end  12  of the sleeve  11  of the Bowden cable  10 . The core is hereby increasingly tightened and triggers the release of the fixing device of the seat longitudinal guide. 
   As a result therefore even with this embodiment it is reached that the release of the fixing device when folding the backrest forwards—independently of the previously set useful position of the backrest—always starts with a defined position of the back rest and is thus reached with a defined folding angle of the backrest forwards. 
     FIGS. 4   a  to  4   d  show an embodiment of the coupling mechanism  1  in which the end  17  of the core  15  of the Bowden cable  10  associated with the fixing device of the seat longitudinal guide or the actuating lever provided for releasing this fixing device engages on an end  31  of a release lever  30  which is swivel mounted on the seat-side rail of the rail longitudinal guide (top rail  102 ). The other end  32  of this release lever  30  interacts with a further lever  35  on the output side which in turn can act with an actuating section  36  on the fixing device of the seat longitudinal guide in order to release same. This further lever  35  on the output side is also mounted for swivel movement on the seat-side rail (top rail  102 ) of the seat longitudinal guide. The release lever  30  is thereby pretensioned by a spring  34  against the active direction of the core  15  of the Bowden cable  10  when the core is tightened. 
     FIG. 4   a  shows this coupling mechanism  1  in a state in which the backrest R—for example according to  FIG. 1   b —is set inclined backwards. The lower end  32  of the release lever  30  is hereby out of engagement with the actuating section  36  of the further lever  35  on the output side. When the backrest is folded forwards for the purpose of triggering the easy-entry function, forces introduced into the Bowden cable  10  therefore initially do not result in release of the fixing device of the seat longitudinal guide. 
   On folding the backrest further forwards the release lever  30  moves into contact by its lower end  32  with the actuating section  36  of the further lever  35  on the output side as soon as the backrest R is located in its front useful position (see  FIG. 1   a ). At this moment the release lever  30  starts to act on and thus release the fixing device through the further lever  35  mounted on the output side. This situation is shown in  FIG. 4   b.    
   The release of the fixing device is concluded when the lever  35  on the output side has been swiveled sufficiently far through the release lever  30 , as shown in  FIG. 4   c.    
   With any possible further folding forwards of the backrest R the release lever  30  then engages by its lower end  32  into a bulge  37  of the actuating section  36  of the lever  35  on the output side. The rounded area of this bulge  37  is selected so that the lower end  32  of the release lever  30  when swiveling the release lever  30  can move therein without triggering any further movement of the lever  35  on the output side. The overtravel when folding the backrest beyond the point in which the fixing device is completely released can be compensated hereby, see  FIG. 4   d.    
   An overtravel compensation of this kind by means of two interacting levers  30 ,  35  can also be combined with the embodiment according to  FIGS. 2   a ,  2   b  and  FIG. 3  in that the actuating lever H provided there is replaced each time by the levers  30 ,  35 . This arrangement for the overtravel compensation is even independent of whether according to the present invention compensating means are provided for compensating the tumbler movement before releasing the fixing device. The overtravel compensation by means of the levers  30 ,  35  thus represents an independent inventive idea. 
   According to  FIG. 5   a  the embodiment of a coupling mechanism shown in  FIG. 4   a  is integrated into a rail assembly with easy-entry mechanism, as shown in  FIGS. 6 to 10 . This arrangement comprises in particular a rail  101  fixed on the body (lower rail) and a seat rail  102  (top rail) which is guided movable in the seat longitudinal direction L relative to the rail  101  fixed on the body and which can be locked by means of a fixing device  120  on the rail  101  fixed on the body. This fixing device  120  is coupled in the manner previously described with reference to  FIGS. 6 to 10  to the backrest of a motor vehicle seat through a Bowden cable  121   a ,  121   b  with a Bowden support  121  and a cable  121   b  (as core) guided in the Bowden sleeve  121   a  in order to be able to release the fixing device  120  for triggering the easy-entry function when folding the backrest forwards. 
   The coupling mechanism which serves to couple the fixing device  120  to the backrest of the motor vehicle seat has in addition to the Bowden cable with the core  121   b  an actuating lever  109  with projection  191 , as described with reference to  FIGS. 6 to 10 , and which here corresponding to the details on  FIGS. 4   a  to  4   d  serves as a lever  35  provided on its actuating section  36  with a bulge  37 . Connected in front of this lever  35  is a release lever  30  which is coupled to the core  121   b  of the Bowden cable corresponding to the release lever  30  of  FIGS. 4   a  to  4   d  so that when the backrest of the vehicle seat is folded forwards it can be swiveled to release the fixing device  120 . This release lever  30  corresponds to the gearing part  122  of  FIGS. 6 to 10 , but with the important difference that the release lever  30  engages not directly on the actuating lever  109  but rather acts by one end  32  on the actuating section  36  of the projection  191  which is provided on the actuating lever  109 . 
     FIG. 5   a  shows the coupling mechanism for coupling the backrest to the fixing device  120 —corresponding to the illustration in  FIG. 4   b —in a situation where the backrest R—for example according to  FIG. 1   a —runs substantially perpendicular, thus is located in its front position of use. 
   If the backrest is folded forward from this position then the cable  121   b  of the Bowden cable is tightened and the release lever  30  swivels counter-clockwise whereby it bears with its one end  32  on the actuating section  36  of the lever  35  on the output side, so that the latter, more particularly its actuating lever  109 , is swiveled to release the fixing device  120 . 
   The release of the fixing device is concluded when the lever  35  on the output side and thus the actuating lever  109  as a component part of the lever  35  on the output side has been swiveled so far that the locking teeth (not shown) of the fixing device  120  have completely lifted out from the associated ratchet device which is fixed on the body. 
   With any possible further folding forward of the backrest the release lever  30  then engages by its lower end  32  in the bulge  37  of the actuating section  36  of the lever  35  on the output side. This bulge is designed so that the lower end  32  of the actuating lever  30  can move therein without releasing any further movement of the lever  35  on the output side. The overtravel when folding the backrest forwards beyond the point at which the fixing device  120  be completely released, can hereby be compensated, see  FIG. 5   c . More particularly it is prevented that when the backrest is folded forwards beyond the point at which the fixing device  120  is completely released there is further additional action on the actuating element  120   b  (see  FIG. 6 ) of the fixing device  120 , i.e. it is prevented that the actuating element  120   b  after complete release of the fixing device  120  is deflected still further (additionally). Damage to the fixing device  120 , for example by its resetting springs, through overstrain as a result of folding the backrest forwards is hereby prevented.