Abstract:
A fitting ( 10 ), in particular for a motor vehicle seat, includes a first fitting part ( 11 ), on which a ring gear ( 17 ) is formed, a second fitting part ( 12 ), on which a gear ( 16 ) is formed, which meshes with the ring gear ( 17 ), whereby the two fitting parts ( 11, 12 ) are in a transmission connection with each other, and a rotatably mounted, revolving eccentric for driving a relative rolling motion of the gear ( 16 ) and the ring gear ( 17 ). The eccentric is driven by a carrier, wherein during said rolling motion, a tooth flank ( 16   d ) of a tooth ( 16   a ) of the gear ( 16 ) contacts a tooth flank ( 17   d ) of a tooth ( 17   a ) of the ring gear ( 17 ) at a pitch point (W). The radius of curvature (K 1 ) of the tooth flank ( 16   d ) of the tooth ( 16   a ) of the gear ( 16 ) at the pitch point (W) and the radius of curvature (K 2 ) of the tooth flank ( 17   d ) of the tooth ( 17   a ); of the ring gear ( 17 ) at the pitch point (W) are at least approximately equal.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States National Phase application of International Application PCT/EP2010/004719 and claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2009 039 648.9 filed Aug. 28, 2009, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a fitting for a vehicle seat, in particular for a motor vehicle seat, having a first fitting part on which is formed a toothed ring, a second fitting part on which is formed a toothed wheel which meshes with the toothed ring, as a result of which the two fitting parts are in gear connection with each other, a rotatably supported circumferential eccentric, driven by a driver, for driving a relative rolling movement of the toothed wheel and the toothed ring. 
       BACKGROUND OF THE INVENTION 
       [0003]    A fitting of this type is known from DE 40 34 843 C2, such fitting serving as a backrest adjusting mechanism. The tooth flanks of toothed wheel and toothed ring which come to bear against one another are configured according to an evolvent toothing. 
       SUMMARY OF THE INVENTION 
       [0004]    An object of the invention is to create a fitting of the type mentioned in the introduction with an alternative toothing. 
         [0005]    According to the invention, a fitting is provided comprising a first fitting part with a toothed ring, a second fitting part with a toothed wheel which meshes with the toothed ring to provide a gear connection, a rotatably supported circumferential eccentric and a driver. The eccentric is driven by the driver for driving a relative rolling movement of the toothed wheel and the toothed ring. During this rolling movement a tooth flank of a tooth of the toothed wheel bears against a tooth flank of a tooth of the toothed ring at a pitch point and a radius of curvature of the tooth flank of the tooth of the toothed wheel at the pitch point and the radius of curvature of the toothed flank of the tooth of the toothed ring at the pitch point are approximately identical. 
         [0006]    Due to the fact that the radius of curvature of the tooth flank of the tooth of the toothed wheel at the pitch point and the radius of curvature of the tooth flank of the tooth of the toothed ring at the pitch point are at least approximately identical, a more extensive contact surface is possible, increasing the stability under load. A constant radius of curvature (circular-arc-shaped curvature) represents a simple geometry which is easy to manufacture and can be configured for different versions. Preferred geometric relations of the pitch point, of the center points of toothed wheel and toothed ring and of an instantaneous center of rotation improve the properties of this toothing. 
         [0007]    The use of an eccentric epicyclic gear system in a fitting enables the inclination of the backrest of a vehicle seat to be adjusted continuously. The saving of a central pinion compared with a planetary gear system leads to the occurrence of a wobbling movement which is superimposed on the relative rotation of the fitting parts. The eccentric which comprises, for example, two wedge segments braced apart by means of a spring, or a sickle-shaped member, is preferably supported, on its side opposing the slide bearing, for example on the inside, on a collar of the other fitting part. 
         [0008]    The invention is explained in more detail hereinafter with reference to an exemplary embodiment shown in the drawings. 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 
         [0009]    In the drawings: 
           [0010]      FIG. 1  is a side view of an only partially represented cut through toothed wheel and toothed ring of the exemplary embodiment; 
           [0011]      FIG. 2  is an axial cut through view of the exemplary embodiment; 
           [0012]      FIG. 3  is an exploded view of the fitting; and 
           [0013]      FIG. 4  is a schematic representation of a vehicle seat according to the invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    Referring to the drawings in particular, a vehicle seat  1  for a motor vehicle has a seat part  3  and a backrest  4 , the inclination of which is adjustable relative to the seat part  3 . In order to adjust the inclination of the backrest  4 , a drive shaft  7 , which is arranged horizontally in the transition region between the seat part  3  and the backrest  4 , is rotated manually, for example, by means of a handwheel  5 , or in a motor-driven manner, for example by means of an electrical motor. On both sides of the vehicle seat  1 , the drive shaft  7  engages in a fitting  10  so that it is rotationally secure, in a manner which will be described later. The drive shaft  7  defines the adopted directional data of a cylinder coordinate system. 
         [0015]    The fitting  10  is in the form of a gear fitting in which a first fitting part  11  and a second fitting part  12  are connected to each other by means of a gear unit for displacement and fixing in position, to be more precise, by means of an eccentric epicyclic gear system, which in the present case is self-locking, as described, for example, in DE 44 36 101 A1, the relevant disclosure of which is expressly incorporated herein (and corresponding U.S. Pat. No. 5,634,689 is hereby incorporated by reference in its entirety). 
         [0016]    With the mounting of the fitting  10 , the first fitting part  11  is, for example, connected tightly to the structure of the backrest  4 , i.e. it is fixed with respect to the backrest part. The second fitting part  12  is then connected tightly to the structure of the seat part  3 , i.e. it is fixed with respect to the seat part. Those assignments of the fitting parts  11  and  12  are preferred when the drive shaft  7  and the backrest  4  are to have the same direction of rotation, or when the position of the drive shaft  7  relative to the backrest  4  is to be constant in order, for example, to be able to fit to the structure of the backrest  4  an electrical motor rotating the drive shaft  7 . However, the assignments of the fitting parts  11  and  12  can also be exchanged, i.e. the first fitting part  11  would then be fixed with respect to the seat part and the second fitting part  12  would be fixed with respect to the backrest. The latter assignments of the fitting parts  11  and  12  are preferred when the radial spacings of the fastening points between the fitting  10  and a relatively thin metal backrest sheet are to be as large as possible. 
         [0017]    Each of the two fitting parts  11  and  12  can be approximately inscribed in a circular disk shape. The two fitting parts  11  and  12  are preferably composed of metal, in particular steel. In order to absorb the axially acting forces, i.e. in order to hold the fitting parts  11  and  12  together, an enclosing ring  13  is provided. Such a method of holding parts together by means of an enclosing ring is described, for example, in U.S. Pat. No. 6,799,806 A, the relevant disclosure of which is expressly incorporated herein. The preferably metal enclosing ring  13  is, with the mounting of the fitting  10 , connected tightly to the second fitting part  12 , being preferably first of all pressed on and then welded. Alternatively, the enclosing ring  13  is beaded, engaging over the second fitting part  12 . At one of its end faces, the enclosing ring  13  has an edge bent radially inwards by means of which it engages radially over the outside of the first fitting part  11 , optionally with the interposition of a sliding ring, without impeding the relative movement of the two fitting parts  11  and  12 . From a structural point of view, the two fitting parts  11  and  12  therefore together form a disk-shaped unit. 
         [0018]    In order to form the gear unit, an externally toothed wheel  16  is formed on the second fitting part  12 , and an internally toothed ring  17  is formed on the first fitting part  11 , the toothed wheel and the toothed ring meshing with each other. The diameter of the tip circle of the external toothing of the toothed wheel  16  is smaller by at least the depth of one tooth (of the toothed ring  17 ) than the diameter of the root circle of the internal toothing of the toothed ring  17 . A corresponding difference in the number of teeth of the toothed wheel  16  and the toothed ring  17  of at least one tooth permits a rolling movement of the toothed ring  17  on the toothed wheel  16 . 
         [0019]    On the side facing the toothed wheel  16 , the first fitting part  11  has, concentrically with the toothed ring  17 , a collar  19  which can be integrally formed on (i.e. formed in one piece with) the first fitting part  11  as a collar formation or which can be secured thereto in the form of a separate sleeve. A driver  21  is supported rotatably in the collar  19  by means of a hub  22 . The driver  21  is preferably composed of plastic material. The hub  22  of the driver  21  is provided centrally with a bore  23  for receiving the drive shaft  7 . The profile of the bore  23  is configured to fit the profile of the drive shaft  7 , in the present case a splined shaft profile. Adjoining its hub  22 , the driver  21  has a covering disk  25  which is formed in one piece with the hub  22  and which has a larger diameter than the hub. 
         [0020]    Supported on the collar  19  (with their curved inner surfaces) are two wedge segments  27  which support (with their curved outer surfaces) the second fitting part  12  by means of a slide bearing bush  28  which is pressed into the second fitting part  12  in a rotationally secure manner. The driver  21  has—spaced radially from the hub  22 —a driver segment  29  which engages with clearance between the narrow sides of the wedge segments  27  and which is formed in one piece with the covering disk  25  and the hub  22 . The mutually facing broad sides of the wedge segments  27  each receive, with a respective recess defined by projecting sections of material, a respective angled end finger of an omega spring  35  which presses the wedge segments  27  apart in the circumferential direction, it being possible during operation for the projecting material sections of the wedge segments  27  to touch and act on each other. 
         [0021]    The driver  21  is secured axially to the outside of the first fitting part  11  by a clipped-on securing ring  43 . Provided on the outside of the second fitting part  12 , between the radially outer edge thereof and the covering disk  25 , is a sealing ring  44  which is composed, for example, of rubber or soft plastic material and which is connected, especially clipped, to the covering disk  25 . 
         [0022]    The wedge segments  27  (and the omega spring  35 ) define an eccentric which, in extension of the direction of eccentricity (i.e. the line connecting the axes), presses the toothed wheel  16  into the toothed ring  17  at an engagement site so defined. When drive is effected by means of the rotating drive shaft  7 , a torque is first of all transmitted onto the driver  21  and then, by means of the driver segment  29 , onto the eccentric which slides along the slide bearing bush  28 , shifting the direction of eccentricity and thus shifting the site of engagement of the toothed wheel  16  in the toothed ring  17 , this presenting itself as a wobbling rolling movement, i.e. as a relative rotation with a superimposed wobbling movement. As a result, the inclination of the backrest  4  is continuously adjustable between several use positions. 
         [0023]    Depending on the mounting of the fitting  10 , the eccentric (i.e. the wedge segments  27 ) is supported by the second fitting part  12 , while the eccentric, for its part, supports the first fitting part  11 , or the relationships are exactly reversed, i.e. the eccentric rests on the first fitting part  11  and supports the second fitting part  12 . 
         [0024]    Each of the—in the present case thirty three—teeth  16   a  of the toothed wheel  16  has radially inward on both sides a tooth root  16   b,  radially outward a tooth tip  16   c  and, between them on both sides, one tooth flank  16   d  each. The tip circle circumscribing the tooth tips  16   c  and the root circle inscribed by the tooth roots  16   b  are concentrical, in the present case to the receptacle for the eccentric, such receptacle being coated with the slide bearing bush  28 , a center point M 16  and a radial orientation (in cylinder coordinates) of the toothed wheel  16  thus being defined. 
         [0025]    The course of two adjacent tooth roots  16   b  results, for example, from a radius (quarter arc) of approximately 1 mm, adjoining the one tooth flank  16   d  (continuous and differentiable), a straight piece of 1 to 2 mm which is adjacent tangentially to the root circle, and a mirror-symmetrical radius (quarter arc) of approximately 1 mm, which is adjoining the next tooth flank  16   d.  The tooth roots  16   b  merge in the point of contact to the root circle (radius for example approximately 31 mm). The course of a tooth tip  16   c  results, for example, from a radius (quarter arc) of approximately 1 mm, adjoining the one tooth flank  16   d  (continuous and differentiable), a tangential piece of 1 to 2 mm and a mirror-symmetrical radius (quarter arc) of approximately 1 mm, which is adjoining the other tooth flank  16   d.  The tooth tips  16   c  touch the tip circle (radius, for example, approximately 34 mm) at their radially outermost point. 
         [0026]    Correspondingly, each of the—in the present case thirty-four—teeth  17   a  of the toothed ring  17  has a tooth root  17   b,  a tooth tip  17   c  and two tooth flanks  17   d.  The tip circle which is inscribed by the tooth tips  17   c  and the root circle which circumscribes the tooth roots  17   b  are concentrical, in the present case with respect to the collar  19 , thus defining a center point M 17  and a radial orientation (in cylinder coordinates) of the toothed ring  17 . The courses of the tooth roots  17   b  and of the tooth tips  17   c  preferably correspond to those of the tooth roots  16   b  and of the tooth tips  16   c.  The straight piece which bears against the root circle (radius for example approximately 36 mm) can be a little longer than that of the toothed wheel  16 . The radius at the tooth tip  17   c  can be a little larger than that of the tooth tip  16   c,  resulting in the piece adjoining the tip circle (radius, for example, approximately 33 mm) being a little shorter than with the toothed wheel  16 . The tooth roots of adjacent teeth  17   a  merge in their point of contact with the root circle (their radially outermost point), thus defining the tooth base enclosed by them. The tooth tips  17   c  touch the tip circle at their radially inmost point. The eccentricity e (of the eccentric) is the distance between the center point M 17  of the toothed ring  17  and the center point M 16  of the toothed wheel  16 . It amounts, for example to 1 to 2 mm. 
         [0027]    It results from the exact configuration of the teeth  16   a  and  17   a,  how the teeth  16   a ,  17   a  can come into contact, in particular along which contact lines and contact surfaces. In the pole toothing of the present embodiment, the tooth flanks  16   d  and  17   d —subsequently at one pitch point W each—get to bear against one another, i.e. they serve for the rolling movement, while the tooth tips  16   c,    17   c,  and the tooth roots  16   b,    17   b  can be configured independently of this. When the fitting  10  is driven, that is to say during the rolling movement, the pitch point W is not exactly in the extension of the eccentricity e, but—relative to the center point M 16  of the toothed wheel  16 —it is at a first angle α of 10° to 50°, in particular approximately 45°, over the extension of the eccentricity e. The contact of these tooth flanks  16   d  and  17   d  at the pitch point W has the same effect as if the toothed wheel  16  and the toothed ring  17  rotated relative to one another around an instantaneous center of rotation P. The first angle a depends on the shape of the wedge segments  27 , in particular of the wedge angle, and of their position during the rolling movement. With respect to the extension of the eccentricity e, a further pitch point occurs on the side opposing pitch point W, so that the toothed wheel  16  is supported, i.e. stabilized at three points (eccentric and the two pitch points). 
         [0028]    The instantaneous center of rotation P is, in every case, in the extension of the eccentricity e. Moreover, the instantaneous center of rotation P—with respect to the pitch point W—is located at a second angle β of 80° to 100°, in particular approximately 90°, with respect to the straight line connecting the pitch point W and the center point M 16  of the toothed wheel  16 . The toothed flanks  16   d  and  17   d  are configured as circular-arc pieces around the instantaneous center of rotation P, i.e. the center point of their curvature is the same point, namely the instantaneous center of rotation P, and the (constant) radius of curvature K 1  of the tooth flank  16   d  and the (constant) radius of curvature) K 2  of the tooth flank  17   d  are identical as well (for example approximately 33 mm). 
         [0029]    The identical radius of curvature K 1 =K 2  for the tooth flanks  16   d  and  17   d  is an ideal radius of curvature for perfectly worked teeth  16   a  and  17   a.  In practice, there are tolerances in production. To compensate them, it is advantageous, if the actual radius of curvature K 2  of the tooth flank  17   d  is slightly smaller and/or the actual radius of curvature K 1  of the tooth flank  16   d  is slightly larger than the ideal radius of curvature, i.e. the radius of curvature K 1  of the tooth flank  16   d  at the pitch point W and the radius of curvature K 2  of the tooth flank  17   d  at the pitch point W are (only) at least approximately identical. Since the tooth flanks  16   d,    17   d  are only very short circular-arc pieces it can be sensible—depending on the production tolerances—that the actual radii of curvature K 1 , K 2  of the tooth flanks  16   d,    17   d  are within a range of ±10%, preferably ±4%, particularly preferably ±1%, each time, for example, referred to their common mean value (K 1 +K 2 )/2. The named ranges are consequently considered to be still approximate. Preferably, both centers of curvature are located on the straight line connecting pitch point W and the instantaneous center of rotation P. 
         [0030]    While specific embodiments of the invention have been 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.