Abstract:
A fitting ( 10 ), in particular for a motor vehicle seat, having a first fitting part ( 11 ), on which a gear rim ( 17 ) is formed and a second fitting part ( 12 ) on which a gearwheel ( 16 ) is formed. The gearwheel meshes with the gear rim ( 17 ), whereby the two fitting parts ( 11, 12 ) are in geared connection with each other. The fitting also has a rotatably mounted, revolving eccentric driven by a driving element for driving a relative rolling motion of gearwheel ( 16 ) and gear rim ( 17 ). During this rolling motion a tooth flank ( 16   d ) of a tooth ( 16   a ) of the gearwheel ( 16 ) rests against a tooth flank ( 17   d ) of a tooth ( 17   a ) of the gear rim ( 17 ) at a contact point (K). The tooth flanks ( 16   d,    17   d ) of the teeth ( 16   a,    17   a ) of the gearwheel ( 16 ) and gear rim ( 17 ) resting against each other at the contact point (K) each follow the course of a portion of a respective logarithmic spiral.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a United States National Phase application of International Application PCT/EP2010/005103 and claims the benefit of priority under 35 U.S.C. §119 of German Patent Application DE 10 2009 040 453.8 filed Aug. 28, 2009, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     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 
     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 
     An object of the invention is to create a fitting of the type mentioned in the introduction with an alternative toothing. 
     According to the invention, a fitting is provided comprising a first fitting part having a toothed ring and a second fitting part having a toothed wheel which meshes with the toothed ring, as a result of which the first fitting part and the second fitting part are in gear connection with each other. A rotatably supported circumferential eccentric is driven by a driver for driving a relative rolling movement of the toothed wheel and the toothed ring. During this rolling movement, at a contact point a tooth flank of a tooth of the toothed wheel bears against a tooth flank of a tooth of the toothed ring, wherein the tooth flanks of the teeth of the toothed wheel and the tooth flanks of the teeth of the toothed ring, which bear against each other at the contact point, each follow the course of a section of one logarithmic spiral. 
     Due to the fact that the tooth flanks of the teeth of toothed wheel and toothed ring such tooth flanks bearing against one another in the contact point, follow the course of a section of a logarithmic spiral, the contact force in the contact point can circulate almost uniformly in a defined direction and with a defined effective lever arm. Tooth tips and tooth roots adjoin as gently as possible, i.e. continuously and differentiably. The section of the logarithmic spiral can lead to indentations within the area of the tooth flanks, i.e. in sections, the teeth have a smaller width radially more inside and a bigger width radially more outside. 
     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. 
     Alternatively to the known solutions, in which either the basic geometric shapes straight line, circular arc, cycloid, trochoid or flank forms (evolvents) which have been developed and optimized for other gear applications with other boundary conditions are used and adapted to real conditions as good as possible in a gear fitting, the solution according to the invention makes it possible to preset the desired force conditions in the gear unit during the rolling movement, to determine from this the surface contour of the teeth required for the respective situation and to form the overall contour of the teeth step by step by sequencing the required single geometry pieces. 
     An essential reason for the fact that conditions are usually not ideal and not physically exactly correct when using flank forms of conventional gear teeth are the special requirements of an adjustable gear unit which, in addition to the usual task of translating a torque, also must fulfill the requirement of being self-locking and consequently blocking in both directions of load in its idle state and of being free of backlash at the same time. Known gear units and flank shapes which have been developed for them usually dispose of one single contact point or contact area between toothed wheel and toothed ring. This rolling area is nearly always close to the extension of eccentricity, i.e. to the line connecting the axes. With the generic gear fittings, the backlash free state during idle state is obtained by a change of the axes distance, i.e. by moving toothed wheel and toothed ring—in most cases by means of spring-loaded systems in the eccentric—towards each other, as far as this is possible in the corresponding state. In the extreme case, in a known tooth configuration, one single tooth bears with both of its flanks exactly in the extension of eccentricity. This state, during which the axis-reducing force and the contact points are nearly on the same line, naturally is rather instable and is therefore avoided according to the invention. For a very stable position, the teeth are configured in such a way that, in the backlash-free state, there is an angle in the order of a right angle between the contact points. 
     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 
       In the drawings: 
         FIG. 1  is view of a radial cut through toothed wheel and toothed ring of the exemplary embodiment; 
         FIG. 2  is an enlarged sectional view of  FIG. 1 ; 
         FIG. 3  is an axial cut through view of the exemplary embodiment; 
         FIG. 4  is an exploded view of the fitting; 
         FIG. 5  is a schematic view of a vehicle seat; and 
         FIG. 6  is an exploded view of a modified fitting. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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. 
     The fitting  10  has a first fitting part  11  and a second fitting part  12  which are rotatable relative to one another. 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 which, at least in some areas, can be hardened. In order to absorb the axially acting forces, i.e. in order to hold the fitting parts  11  and  12  axially 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 B2. The enclosing ring  13  is preferably composed of metal, in particular of steel, which is preferably unhardened. The enclosing ring  13  has a substantially flat ring shape. 
     The enclosing ring  13  is (in the present case in an outer edge section) connected tightly to one of the two fitting parts  11  and  12 , in the present case to the first fitting part  11 , for example welded or beaded (at least partially in the circumferential direction). By means of an end section which is facing radially inwards, the enclosing ring  13  engages over the other one of the two fitting parts  11  and  12  radially outwards, optionally with the interposition of a separate sliding ring, without impeding the relative rotation of the two fitting parts  11  and  12 . Moreover, the inner surfaces of the two fitting parts  11  and  12  which face one another are protected from the intrusion of foreign material and from impurities and damage. 
     The enclosing ring  13  and the fitting part  11  or  12  which is tightly connected with it consequently enclose the other one of the two fitting parts  11  and  12  which is movable relative to them. From a structural point of view, the two fitting parts  11  and  12  together (with the enclosing ring  13 ) consequently form a disk-shaped unit. 
     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  can, however, 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 fitting  10  consequently is located in the force flow between backrest  4  and seat part  3 . 
     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. 
     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 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 . The toothed wheel  16  and the toothed ring  17  are formed preferably by means of one single stamping process which simultaneously punches the fitting parts  11  and  12  from their initial material. Alternatively, the fitting parts  11  and  12  can be manufactured—with similar geometries and same functions—by massive forming (preferably cold-flow forming or hot-flow forming). In the present case, the toothed wheel  16  forms the radially outer edge of the second fitting part  12 , i.e. radially outward the second fitting part  12  is flush with the toothed wheel  16 . 
     One of the two fitting parts  11  and  12 , has a collar  19 , in the present case the second fitting part  12 , concentrically to the toothed wheel  16 . The collar  19  can be integrally formed on (i.e. formed in one piece with) said fitting part as a collar formation or 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  22 . 
     Supported on the collar  19 —with their curved inner surfaces—are two wedge segments  27  which bear—with their curved outer surfaces—the other of the two fitting parts  11  and  12 , in the present case the first fitting part  11 . For this purpose, a receptacle of the last-named fitting part is coated (covered) with a slide bearing bush  28  which is preferably pressed in to be rotationally fixed, and against which the outer surfaces of the wedge segments  27  bear. The concepts “support” and “bear” shall not be limited to a defined direction of the flow of forces by the fitting  10 , since this direction depends on the mounting of the fitting  10 . 
     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  35   a  of an omega spring  35 . The spring  35  acts upon the wedge segments  27  in the circumferential direction, in particular in order to press them apart, it being possible during operation for the broad sides of the wedge segments  27  to touch and act on each other. 
     The driver  21  is secured axially on the outside of the fitting part provided with the collar  19  by a securing ring  43  which is preferably clipped on. The securing ring  43  extends in the axial direction along a part of the hub  22 , so that the hub  22  does not directly bear against the inside of the collar  19  but, with the interposition of the securing ring  43 , is supported in the collar  19  (and consequently the driver  21  is supported on the second fitting part  12 ). On the outside of the fitting part provided with the slide bearing bush  28  (in the present case of the first fitting part  11 ), a sealing ring  44  is provided between its radially outermost edge and the covering disk  25 , such sealing ring being composed for example of rubber or of soft plastic material and being connected with, in particular clipped to, the covering disk  25 . The sealing ring  44  can also be composed of metal and be tightly connected, for example welded, to the first fitting part  11 , the covering disk  25  then being movable relative to the sealing ring  44 . Within the installation space between the two fitting parts  11  and  12 , a separating ring  45 , composed for example of plastic material, is optionally provided as internal sealing. 
     The wedge segments  27  (and the spring  35 ) define an eccentric which, in the extension of the direction of eccentricity, presses the toothed wheel  16  into the toothed ring  17  at an engagement site. When drive is effected by means of the rotating drive shaft  7  which rotates (several times), a torque is first of all transmitted onto the driver  21  and then, by means of the driver segment  29 , onto the eccentric which is so defined and 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. 
     To improve the dynamic operating characteristics, a retaining spring  51  as has been disclosed, for example in DE 195 48 809 C1, the disclosure of which is expressly incorporated herein (and corresponding U.S. Pat. No. 5,871,414 is incorporated by reference), is still provided preferably as locking element. The retaining spring  51  in the present case cooperates with a toothing  55 , which is configured as a further toothed ring at the first fitting part  11 . The retaining spring  51 —which is preferably supported on an axial projection of the slide bearing bush  28 —each time locks the wedge segments  27  in the non-driven state (by the retaining spring  51  locking the spring  35  by bearing against the end fingers  35   a ) and is released by the driven driver  21 . 
     Each of the 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 concentric, 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. 
     The course of two adjacent tooth roots  16   b  results, for example, from a radius adjoining the one tooth flank  16   d  (continuous and differentiable), an arc-shaped piece of the root circle or a straight piece which is adjacent tangentially to the root circle, and a mirror-symmetrical radius which is adjoining the next tooth flank  16   d . The tooth roots  16   b  merge in the point of contact to the root circle. The course of a tooth tip  16   c  results, for example, from a radius adjoining the one tooth flank  16   d  (continuous and differentiable), a piece bearing against the tip circle and a mirror-symmetrical radius which is adjoining the other tooth flank  16   d . The tooth tips  16   c  touch the tip circle at their radially outermost point. 
     Correspondingly, each of the 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 concentric, 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 piece which bears against the root circle can be a little longer than that of the toothed wheel  16 . The trajectories of the edges of the tooth tips  16   c  of the toothed wheel  16  define an envelope during a complete rotation of the toothed wheel  16 . Preferably, the tooth tip  17   c  of the toothed ring  17 —at least in sections—passes radially equidistant to this envelope. The tooth roots  17   b  of adjacent teeth  17   a  merge in their point of contact (of their radially outermost point) with the root circle, 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 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 spiral toothing of the present embodiment, the tooth flanks  16   d  and  17   d —subsequently at one contact point K 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 contact point K is not exactly at 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 55°, in particular approximately 35° to 50°, relative to the extension of the eccentricity e. The first angle α 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 contact point occurs on the side opposing contact point K, so that the toothed wheel  16  is supported, i.e. stabilized at three points (eccentric and the two contact points). 
     At the contact point K, each of the two tooth flanks  16   d  and  17   d  follows the course of a section, preferably of a logarithmic spiral each. In the following, this is explained by means of the logarithmic spiral for tooth flank  16   d , a corresponding explanation applying to the logarithmic spiral of tooth flank  17   d . In a special case, both logarithmic spirals correspond to one another. 
     With respect to an asymptotic point O, said logarithmic spiral runs according to the formula (in polar coordinates r, φ)
 
r=ae kφ 
 
     The asymptotic point O, which can, for example, be arranged within the root circle of the toothed wheel  16 , in general is, as shown in  FIG. 1 , at an angle over the extension of eccentricity e, such angle differing from the first angle α—with respect to the center point M 16  of the toothed wheel  16 . Combined with the parameters a, k, several possibilities of choice are thus available. 
     Parameters a,k are chosen in such a way that the direction of contact force F in the contact point K points into a defined direction. This defined direction is at a second angle β to the line connecting the center point M 16  of the toothed wheel  16  and contact point K. The second angle β changes when the contact point K moves along the tooth flank  16   d , the direction of contact force F at the last contact point of the tooth flank  16   d  of a tooth  16   a  corresponding to the orientation of contact force F at the first contact point of the tooth flank  16   d  of the next tooth. The second angle β can amount, for example, to 90° to 120°. The change of the second angle β preferable corresponds to the partition angle γ of the toothed wheel  16 , i.e. 2π divided by the number of teeth  16   a . The effective lever arm is perpendicular to the direction of contact force F, i.e. it deviates from the line connecting center point M 16  and contact point K. 
     Parameters a, k besides can be chosen in such a way that the asymptotic point O is on the straight line connecting center point M 16  of the toothed wheel  16  and contact point K. k then becomes k=−tan β (the algebraic sign depends on which of the two mirror symmetrical flanks  16   d  is regarded). 
     The arc length of the section of the logarithmic spiral which serves as tooth flank  16   d  preferably corresponds to the partition angle γ of the toothed wheel  16  (i.e. 2π divided by the number of teeth  16   a ). The angle φ of the logarithmic spiral then runs, for example, at an angle range of −γ/2 to +γ/2, what is indicated in  FIG. 2 . The contact point K in  FIG. 2  then corresponds to φ=0. An arc length which is bigger than γ, for example 2γ can, however, also be chosen. 
     The previously mentioned relationships of parameters a, k and angles and angle areas β, γ and φ correspondingly apply to the logarithmic spiral of the tooth flanks  17   d  of the teeth  17   a  of toothed ring  17 . 
     Depending on the choice of the section of the logarithmic spiral (i.e. of the angle range for φ), indentations can occur at the tooth flanks  16   d  of the toothed wheel and/or at the tooth flanks  17   d  of the toothed ring  17 , so that (approximately) trapezoidal (dovetail) teeth  16   a  and/or  17   a  result. Such shapes favor a clear, secure establishing of contact in the area of a larger first angle α at a high solidity since, with a very small first angle α, which is built due to known flank shapes, undesired secondary contacts would occur, which could be avoided only by a reduction of tooth width which reduces solidity. 
     The toothing according to invention can be used also in a modified fitting  10 ′ (with inverse bearing of the eccentric), the first fitting part  11 ′ of which is provided with the toothed ring  17  and the collar  19  and the second fitting part  12 ′ of which is provided with the toothed wheel  16  and the receptacle (coated with the slide bearing bush  28 ) for the eccentric. It can be used also in a modified fitting, the fitting parts of which are provided with radially protruding flanges, as it is described, for example, in DE 44 36 101 A1 (corresponding to U.S. Pat. No. 5,634,689) or DE 199 38 666 A1 (corresponding to U.S. Pat. No. 6,619,743). 
     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.