Abstract:
A spindle drive for a vehicle seat connected with an upper rail. According to this invention, an upper rail slides on the surface of a drive nut preferably made of plastic whose internal thread is engaged by the spindle. Advantageous further developments deal with improving the longitudinal guidance of the upper rail on the drive nut as well as with preventing the upper rail from radially moving away from the drive nut.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a spindle drive for an adjusting mechanism for vehicle seats. Such a drive is known, for instance, from DE-OS (German Patent Application) No. 37 25 158. In this literature of reference, a rail firmly connected with the vehicle seat is driven via a rotating spindle which, in the axial direction, is firmly connected with the seat. The drive is effected through a regulating unit which makes the spindle rotate, with the rotation of the spindle being transformed into a longitudinal motion of the seat. 
     From DE-OS (German Patent Application) No. 39 19 398 it is known to provide a vehicle seat adjusting mechanism with a drive nut formed fast with the vehicle whereon a rotating spindle connected with the seat supports itself and which thus, by means of its rotation, moves the seat in its longitudinal direction. 
     SUMMARY OF THE INVENTION 
     This invention thus proceeds from an adjusting mechanism of the type for a vehicle seat including a spindle engaging a drive nut to move the vehicle seat. It is an object of this invention to simplify the known design of such a spindle drive and to improve it, in particular with regard to the guidance of the upper rail as well as with regard to a protection against any possible tilting of the seat guideway relative to the guideway parts formed fast with the vehicle. 
     Thus, on principle, this invention consists in simultaneously using the drive nut, held fast to the vehicle, also for guiding the upper rail of the seat. This provides the possibility to improve and simplify the guideway of the upper rail. 
     A particularly effective support of the upper rail and, thus, of the seat will be achieved via the drive nut, the seat being supported in the vertical direction, i.e., in the direction of the biggest load. 
     A considerably improved guiding behavior will be achieved between the drive nut and the upper rail by means of longitudinal recesses and projections thereon which form a guideway for the upper rail in the longitudinal direction of the spindle. Thereby, the upper rail will be largely prevented from being displaced sideways, i.e., in the direction transverse to the longitudinal axis of the spindle. Thus, the drive nut not only will take care of conveying the seat in the longitudinal direction of the spindle but will additionally take care of receiving the load of the seat in the horizontal direction as well as of guiding the upper rail in the lateral direction. 
     It is recommended to use a guide rail in the upper rail which runs in the longitudinal direction of the upper rail and which plunges into a longitudinal groove in the drive nut if the action of the lateral guidance of the drive nut is to be symmetrical. The additional advantage of such a type of guidance lies in that the cross-sectional surface of the rail guided in the groove is relatively small as compared with the cross-sectional surface of the drive nut itself so that the thus created guideway system is likewise relatively indifferent to temperature variations, in particular to a strong change in temperature. This particularly applies to the dimensions in the lateral direction. 
     In developing this invention further, the guide rail can be connected with the upper rail in one piece. This can be done by means of a cupping process, by means of casting or by means of extrusion. 
     However, the rail may also be of a separate material, in particular of a slidable material which furthers and supports the sliding properties of the upper rail on the drive nut. 
     A particularly simple design is rendered by having the guide rail essentially extending over the entire length of the upper rail and slidingly projecting into a corresponding recess of the drive nut. The guide rail can be of a separate slidable material improving the slidability of the upper rail on the drive nut. 
     If the guideway is subjected to less heavy use it is also possible to use a combination of characteristics in which the drive nut has a projection which may be connected firmly with the nut or even may be formed in one piece with it and which engages a corresponding longitudinal groove of the upper rail, thus guiding the same. In order to improve the sliding properties of the drive it is possible to manufacture the drive nut of a slidable plastic material so that this part of the guideway system will not require separate greasing. Such a drive nut has the further advantage of being manufacturable at relatively low cost even in case of a more complicated design. 
     In order to save weight upon manufacturing the seat it is possible to form the drive nut of plastic and the upper rail of aluminum. In accordance therewith, it is in particular the sliding properties of the plastic that are of importance in a drive nut made of plastic material. The guiding properties of the inventive design also make themselves most excellently noted in an aluminium rail as, due to the relatively small width of the guideway, the effects of the different shrinkage properties of the two materials deviating from each other will be less embarrassing in case of major temperature differences. 
     In developing this invention further, the nut is rotatably supported in the horizontal and transverse direction to the longitudinal axis of the spindle is recommended if the upper rail is swivelling horizontally--for example, due to a corresponding sequence of motions during its axial motion or else, because of a swivelling motion permitted for the seat surface in the rest condition. 
     It is possible to adapt the abutment surface of the drive nut in a simple manner to the varying angle of inclination of the upper rail. 
     An additional lateral support of the upper rail is achievable by means of front faces of pivots supported on side walls of the upper rail. Thereby, the free ends of the comparatively strong pivots are additionally made use of so as to receive forces which are essentially horizontal and which are transverse to the longitudinal axis of the spindle and to divert them into the bottom of the motor vehicle via the support of the drive nut. In doing so, however, it will have to be taken into consideration that the tolerance-ratings between the ends of the pivots and the side walls of the upper rail will not be too close as in case of low temperatures the upper rail will undergo a considerable shrinkage, particularly so if it is of aluminium, so that then the seat may be given to jamming. On the other hand, with this required wide tolerance-rating it is to be feared that there will be an expansion in the lateral dimensions of the rail in case of high temperatures, thus a considerable play existing between the pivots and the adjacent side walls of the upper rail. This may cause an embarrassing drawer effect in that the upper rail will tilt in respect of the guide surfaces of the drive nut. In this case, the inventive design&#39;s guiding properties are extremely valuable as they are largely indifferent to temperatures due to the little expansion of these guideways. 
     In developing this invention advantageously further, it is possible, to use suitable measures in order to prevent the upper rail from being lifted out vertically upwards relative to the drive nut. Horizontally extending projections of the upper rail reach behind corresponding projections of the drive nut, in particular behind the pivots projecting in the horizontal directions. These projections preferably extend over the entire motion travel of the upper rail or over its entire length. 
     It is also possible by the present invention to enlarge the abutment surfaces of the pivots for the projections and in order to improve the guiding behavior of the drive nut relative to swivelling motions of the upper rail. Thus an enlarged abutment surface of the projections will be achieved on the pivots while, otherwise, the pivots would only have a line-shaped contact with the projections. 
     An additional safety measure against any undesired vertical motion of the upper rail, such as in case of an accident, can be achieved by means of safety lugs which are shaped to project horizontally out of the cage and which, if the case may be such, engage the projections of the upper rail, with the effective surface of these lugs as a rule lying above the effective surface of the pivots relative to the rail projections. In the normal case, the projections are slidingly guided in this way on the pivots which, in many cases, are of plastic. However, if these plastic pivots are torn out during an accident the safety lugs on the cage will become effective relative to the projections moving vertically upwards. Preferably, these safety lugs will be shaped in one piece out of the steel cage. 
     The cage itself will receive a particularly simple and inexpensive design in which the cage is formed of two parts, one of which is fastened to the vehicle bottom. Thereby, the assembly of the nut into the cage will become relatively simple by way of inserting the pivot of a nut into a corresponding opening of the one part of the cage, subsequently the corresponding opening of the second cage part being sled onto the opposite pivot and, thereupon, the second cage part being connected with the first one. A further simplification with regard to the cage can be achieved by shaping one side surface of the cage out of a lower rail, with the lower rail not absolutely having to extend over a major part of the possible motion travel of the upper rail. It will be sufficient to provide some individual posts projecting into the upper rail so as to serve as a guide and to support the upper rail. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, one example of an embodiment of this invention will be explained, reference being made to the drawing, wherein: 
     FIG. 1 shows the broken-off, perspective and--in part--symbolical representation of the type of fastening of the upper rail on the drive nut arranged in the cage; 
     FIG. 2 shows, in partial section, the representation of the nut arranged in the side walls of the cage as seen in the longitudinal direction of the spindle; 
     FIG. 3 shows the drive nut fixed to the one part of the cage, with the second cage part being left away for the sake of an enhanced clarity; 
     FIG. 4 shows a section above the drive nut through the upper rail in the horizontal direction, with the cage being left away which holds the nut from below; 
     FIG. 5 as seen in the longitudinal direction of the spindle, shows a section through a first embodiment of the spindle drive; 
     FIG. 6 shows a section on the same level through a second embodiment of the spindle drive; and 
     FIG. 7 shows a section through a third embodiment of the inventive spindle drive. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an upper rail 1 in respect of which (not illustrated in the drawing) a spindle 2 provided with an external thread is rotatably supported, yet not axially displaceably. Thus, the upper rail 1 follows a longitudinal motion of the spindle 2. The spindle 2 penetrates through a drive nut 4 provided with an internal thread 3 and supported in a cage 5 hereinafter often denominated as a nut holder. The cage 5 is bolted to the bottom of an automotive vehicle in that a corresponding bolt penetrates through the elongated hole 6 and engages the bottom of the vehicle. 
     The internal thread 3 of the drive nut 4 engages the external thread of the spindle 2 so that, upon a rotation of the spindle 2, the nut 4 formed fast with the vehicle exerts a kinetic force on the spindle 2, thereby the same being moved in its longitudinal direction and--in doing so--carrying along the upper rail 1 together with the vehicle seat. A gear unit 7 connected with the spindle or a manual drive which may be fastened to the vehicle seat may serve the performance of a rotary motion through the spindle. 
     FIG. 2, in sectional position, shows two side surfaces 8 and 9, one of which can be lower rail, of the cage 5 which have two circular openings 10 and 11 penetrated by two essentially cylinder-shaped pivots 12 and 13 connected with the drive nut 4 in one piece. Thereby, the nut 4 is rotatably supported in the openings 10, 11 of the cage 5. Safety lugs 39 are shown schematically in FIG. 2 with respect to the cage 5. 
     The cage itself is composed of two cage parts 14, 15 undetachably joined together by means of welding, riveting or some other type of connection after the nut has been introduced between the side surfaces 8 and 9 of the right-angled cage parts 14, 15. 
     FIG. 3 shows the cage part 15 without the front cage part 14 and without the upper rail 1, yet with the nut 4 inserted into the opening 10. The double arrow H is to indicate the rotatability of the nut 4 within the circular opening 10. 
     With regard to the mode of operation of this invention it now is very important that the upper rail 1 rests with the lower surface of its mid-section 16 of FIG. 1 on the abutment surface 17 of the nut 4 and thus transmits a force acting vertically on the mid-section 16 to the abutment surface 17 and, via the pivots 12, 13 as well as via the cage 5, to the bottom of the vehicle. Because of the design of the nut 4 so as to be of plastic the upper rail 1 will slide in a comparatively easy way, without being greased, on the abutment surface of the nut 4. 
     Further, it is important for the inventive design that the side walls 21, 22 adjacent to the mid-section 16 support themselves on the front faces 19, 20 of the pivots 12, 13 so that the upper rail 1 will be guided by the nut 4 also transversely to the longitudinal axis of the spindle. In this respect attention will have to be paid to the fact that, in case of high temperatures, a comparatively large play D (see FIG. 7) will be required between the front faces 19, 20 of the pivots 12 and 13 and the inside surfaces of the side walls 21, 22 of the upper rail 1 so as to prevent the side walls 21, 22 from getting jammed in respect of the nut 4 in case of very low temperatures. This will in particular be the case if the nut 4 inclusive of the pivots is exclusively made from plastic, the upper rail 1 being made of aluminium since in such a case the temperature expansion behavior of the two materials is very different. Moreover, the distance of the two side walls 21, 22 is comparatively large so that the shrinkage processes will make themselves felt even more noticeably. 
     In order to achieve a better guidance in this respect, a longitudinal through groove has been inserted into the abutment surface of the nut 4 in the longitudinal direction of the spindle wherein a guide rail 24 is sliding with comparatively narrow tolerance-rating. The guide rail 24 may be a projection essentially extending over the entire length of the upper rail 1 and formed in one piece together with the same so that the guide rail 24 is formed together with the upper rail 1 when the same is extruded or cast and will not need a separate working operation. 
     However, as can be seen from FIG. 6, it also may be a separate part which, for instance, is inserted permanently into a corresponding groove 23 of the nut 4 and is connected with the same in a comparatively firm manner. Thus, the guide rail 24 will slide in the longitudinal groove 23 of the nut 4. Such a design will be of particular advantage when a special material is to be used for the guide rail so as to simplify the tolerance-rating, for instance. It is the particular duty of the guide rail 24 to prevent the upper rail 1 from jamming (drawer effect) in respect of the front faces 19, 20 of the nut 4 which, otherwise, might easily happen due to the large tolerance distance D (see, e.g., FIG. 7). 
     FIG. 5 largely coincides with the design of FIG. 7, with the exception of the projection 24 not being shaped by means of extrusion or casting (as is possible with aluminium) so as to form one piece with the upper rail 1, such as is the case in FIG. 7, but--by means of a drawing process--is subsequently shaped out of an upper rail 1 preferably made of steel. 
     For the further development of this invention it is also important that the projections 25, 26 which--for example, in FIG. 4--extend horizontally from the side walls 21, 22 towards the central plane of the upper rail 1 and preferably run over the entire length of the upper rail 1. As can be seen from FIGS. 1 and 5 through 7, these projections 25, 26 reach behind the peripheries of the pivots 12, 13, thus preventing the upper rail from being lifted upwards (e.g., FIG. 5) even in case of strong vertical forces (an accident), since the pivots will prevent any such motion. 
     In particular in such cases when the nut 4--as described further above--is rotatably supported in the cage 5 it is recommendable to enlarge the abutment surfaces of the projections 25, 26 on the pivots 12, 13. This is done, for instance, in that--as can be seen in particular from FIGS. 1 through 3--the pivots have a rectangular recess 27, 28 which provide wide abutment surfaces 30, 31 whereon the abutment surfaces of the projections 25, 26 may support themselves. In FIG. 1 as well as in FIGS. 2 and 3 the widened abutment surface 31 is sketched out; the broken-line-type representation in FIG. 1 is to indicate that this surface lies invisibly behind the side wall 21 of the upper rail 1. 
     In order to generate a higher elasticity of the pivots, the same are provided with circular-sector-shaped impressions 32 pointing towards the longitudinal axis of the pivot and, as explained with reference to FIG. 1, lying behind the side wall (21), thus not being visible when the upper rail is mounted. 
     As the rail 1 of FIG. 5 which was formed by way of cupping does not permit the projections 25, 26 to be attached at right angles to the side walls 21, 22, to this end--over the length of the nut--a section 33, 34 was cut off from each of the pivots 12, 13 of the nut 4. 
     In FIG. 7, vertically upwards projecting projections 35, 36 serve an improved type of fastening of the automotive vehicle seat. 
     FIG. 4 shows a section on the level of line G-E of FIG. 7, in this section the guide rail 24 and the side walls 21, 22 are discernible. 
     The design of the lateral guidance by means of the guide rail 24 or rather by means of the recess may be varied within the scope of this invention by means of a different type of shape, for instance, by using a plurality of rails and grooves or by changing their profiles. 
     On principle, it is also possible to switch the functions of the drive nut and the spindle in that the spindle and the rail will be firmly mounted with regard to the vehicle bottom and in that the nut will move together with the seat.