Abstract:
In a gear train ( 10, 30 ) for an actuator, in particular of a vehicle seat ( 2 ), the gear train comprises a drive ( 11 ) that can be rotated about a rotational axis (A), at least one eccentric cam ( 12, 13 ) that is driven by the drive ( 11 ), a pinion ( 14, 15 ) that is driven by the eccentric cam ( 12, 13 ), a gear ring ( 16 ), which meshes with the pinion ( 14, 15 ) and in relation to which the pinion ( 14, 15 ) executes a rolling motion that defines a point of rolling contact (W), and a take-off drive ( 18 ) that taps the relative rolling motion. At least some sections of the material of the pinion ( 14, 15 ) and/or the ring gear ( 16 ) in the vicinity of the point of rolling contact (W) are elastically deformable, in order to produce surface contact at the point of rolling contact (W).

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a continuation of International Application PCT/EP2007/003885, which was filed May 3, 2007. The entire disclosure of International Application PCT/EP2007/003885, which was filed May 3, 2007, is incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a gear train for an actuator, in particular of a vehicle seat, comprising a drive for being rotated about a rotational axis; at least one eccentric for being driven by the drive; a ring gear; a pinion that is meshed with the ring gear and is for being driven by the eccentric so that, relative to the ring gear, the pinion carries out a rolling motion defining a point of rolling contact; and an output for rotating in response to the rolling motion of the pinion. 
       BACKGROUND 
       [0003]    A gear train of the type described in the Technical Field section of this disclosure is known from DE 28 49 542 A1. The gear train of DE 28 49 542 A1 is used as a load-bearing gear unit in a backrest inclination adjuster. The pinion and the ring gear are, therefore, respectively formed on a fitting and are driven by a manually driven eccentric for the relative rolling motion thereof. The tooth geometries partially incorporate an arcuate cycloid. 
       BRIEF SUMMARY OF SOME ASPECTS OF THE INVENTION 
       [0004]    An object of the present invention is the provision of improvements to a gear train of the type described in the Technical Field section of this disclosure. In accordance with one aspect of the present invention, a gear train for an actuator in a vehicle, in particular a gear train for an actuator of a vehicle seat, comprises a drive for being rotated about a rotational axis; at least one eccentric for being driven by the drive; a ring gear; a pinion that is meshed with the ring gear and is for being driven by the eccentric so that, relative to the ring gear, the pinion carries out a rolling motion defining a point of rolling contact; and an output for rotating in response to the rolling motion of the pinion, wherein the pinion&#39;s material that is proximate the point of rolling contact is at least partially elastically deformable and/or the ring gear&#39;s material that is proximate the point of rolling contact is at least partially elastically deformable, so that there is surface contact at the point of rolling contact. 
         [0005]    Because the material of the pinion and/or the ring gear in the region of the point of rolling contact is at least partially elastically deformable, a surface contact (e.g., a broad area of contact) is generated at the point of rolling contact, by way of which large lubricating gap lengths and small lubricating gap thicknesses are achieved for a highly viscous lubricant film on the components, which markedly improves the damping effect of the lubricant film. Where there is a small space requirement, a high gear ratio is achieved. Without the elastic deformation of the material according to the exemplary embodiment of the invention, there would be substantially only one point or line contact at the point of rolling contact. 
         [0006]    The region of the rolling contact is the region of the pinion and/or the ring gear where the two components mesh with one another, i.e. preferably the region of the toothing. Apart from the rolling contact itself which is planar, the directly adjacent material region, i.e. the radially externally located region of the pinion and/or the radially internally located region of the ring gear, forms part of the region of the rolling contact. The radial depth of the region relative to the rolling contact depends on the material selected and the geometric and elastic properties thereof, i.e. the possible depth of deformation in the material due to the forces present at the point of rolling contact. 
         [0007]    In order to produce the partial elastic deformation, the pinion, on the one hand, and the ring gear, on the other hand, may consist at least partially of different material, so that at the point of rolling contact a variable resilience and thus material displacement occurs. For example, the pinion and/or the ring gear may be configured from plastics, and in particular may be produced as a plastics injection-molded part, while the other component is less resilient and, for example, consists of metal. It is also possible that the pinion and/or the ring gear comprise recesses in the material, which increase the resilience of the material and at the same time receive the elastically displaced material. It is, however, also possible that the pinion and/or the ring gear are mounted in a resilient bed, which ensures the resilience. The partial use of a cycloid or approximately cycloid shape as the tooth geometry with a similar curvature and the resulting convex-concave support simplifies the configuration of the surface contact. 
         [0008]    During operation, and also with regard to local stresses and wear, it is advantageous if eccentricities of motion and asymmetries of bearing forces as a result of the operation are compensated for. Thus, compensation of the wobbling portion of the rolling motion when transmitted to the output is carried out by a circular sliding gear or a compensation stage with a gear ratio of one. In particular by way of the circular sliding gear, the output may be acted upon approximately symmetrically, by two pinions that are mounted eccentrically relative to the rotational axis, are offset relative to one another in the peripheral direction by 180°, are axially adjacent to one another, and that both cooperate with the common ring gear and the common output. 
         [0009]    For tapping (e.g., harnessing) the rolling motion by the output, preferably a circular sliding gear (surface pressure gear) with guide elements is provided for the pinion, as is disclosed for example in U.S. Pat. No. 4,228,698 A, or alternatively an Oldham coupling (double slider crank mechanism) is provided, as is disclosed for example in EP 0 450 324 B1. 
         [0010]    In order to achieve a greater reduction between the motor speed and the speed of the output, two gear trains may be arranged in series. The two gear trains may be axially and/or radially nested. Coaxial rotations of the drive and output of the gear trains require no compensation elements and allow simple bearing ratios. Accordingly, the eccentrics may be formed on the respective outputs of the preceding gear trains, i.e. integrally configured therewith, which also reduces the number of components required. 
         [0011]    When the eccentric is defined by at least one rolling body, which is respectively in contact with (or may be indirectly in contact with) a round geometry of the drive and a round geometry of the pinion, and rolls therebetween, a simple eccentric is produced which, by way of the rolling body and as a result of rolling friction (i.e. substantially devoid of friction), transmits the drive motion with a high degree of efficiency. During this rolling motion, therefore, the drive, rolling body and pinion rotate relative to one another. In the relative system of the pinion, the rolling body is only able to follow the drive at half speed due to the mutual rolling, i.e. the eccentric rotates only approximately half as rapidly as the drive. Thus the eccentric already represents per se a gear train with a gear ratio of at least two. One or more rolling bodies, in particular balls, cylindrical rollers or hollow cylinders, may be provided. In the radial sequence in the region of the eccentric, a further component, for example a ring, may be arranged on which the contact takes place and which, for example, may carry out a compensating motion. 
         [0012]    The gear train according to the invention may be combined with a brush commutated motor or electronically commutated motor, to which the gear train is attached on the output side, to form a motorized actuator. A preferably common housing of the motorized actuator may be of sealed construction, possibly by including covers or the like, which allows easy handling of the motorized actuator in a dipping bath. 
         [0013]    Such a motorized actuator may, for example, be incorporated in a load-bearing gear unit of an adjuster of a vehicle seat. Due to the high step-down ratio, the load-bearing gear unit may be prevented from wearing out by a wrap-spring brake or the like on the rotor, if required. A hollow shaft construction allows a simple connection of a transmission rod between both sides of the vehicle seat, preferably by a profiled central receiver in the drive component for the load-bearing gear unit, i.e. in the exemplary embodiment in the output of the gear train. 
         [0014]    Other aspects and advantages of the present invention will become apparent from the following. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The invention is described in more detail hereinafter with reference to an exemplary embodiment and modifications thereof shown in the drawings, in which: 
           [0016]      FIG. 1  shows a cross section through the exemplary embodiment along the line I-I in  FIG. 2 , 
           [0017]      FIG. 2  shows a longitudinal section through the exemplary embodiment used in a motorized actuator, 
           [0018]      FIG. 3  shows a schematic side view of a vehicle seat, 
           [0019]      FIG. 4  shows an enlarged, schematic partial view of  FIG. 1 , 
           [0020]      FIG. 5  shows a partial view of a modification with recesses in the pinion, 
           [0021]      FIG. 6  shows a partial view of a modification with a resilient bed, 
           [0022]      FIG. 7  shows a schematic representation of a modification comprising radially nested gear trains, and 
           [0023]      FIG. 8  shows a schematic representation of a modification comprising an improved rolling eccentric. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    A motorized actuator  1  of a vehicle seat  2 , for example of a motor vehicle, comprises a motor  5  and at least one gear train  10  attached to the output side of the motor  5 . The (first) gear train  10  comprises: a drive  11  that is attached to the motor  5 , configured as a hollow shaft, and rotatable about a rotational axis A; a first eccentric  12  driven by the drive  11 ; a second eccentric  13  coupled to the first eccentric  12  for rotating therewith; a first pinion  14  driven by the first eccentric  12 ; a second pinion  15  driven by the second eccentric  13 ; a ring gear  16 ; and an output  18 . The rotational axis A defines the following directional information used in this disclosure. 
         [0025]    The two eccentrics  12  and  13  may respectively be fixed eccentrics. For each of these two fixed eccentrics, the fixed eccentric is located fixedly in terms of rotating with the drive  11 , with the (radial) inner face of the fixed eccentric being on the (radial) outer face of the drive  11 , and the radial outer face of the fixed eccentric sliding along the radial inner face of the associated pinion  14  or  15  (respectively). Such a fixed eccentric is disclosed in DE 28 49 542 A1, the entire disclosure of which is incorporated herein by reference. The eccentrics  12  and  13  may also be defined by a wedge system, as is disclosed in DE 44 36 101 A1, the entire disclosure of which is incorporated herein by reference. 
         [0026]    In  FIG. 1 , the first eccentric  12  is defined by a rolling body  12   a , for example a ball, a cylindrical roller or a hollow cylinder. On the one hand, the rolling body  12   a  is located at one point of the periphery of the drive  11 , on the outer face of the drive  11 , and rolls on the drive  11 . On the other hand, the rolling body  12   a  rolls in an annular groove along the inner face of the first pinion  14 . As a result, the center point of the first pinion  14  is located on an eccentric axis B, which is offset from, parallel to, and rotates around the rotational axis A. The rotation of the eccentric axis B around the rotational axis A is at a rotational speed which is less than half of the rotational speed of the drive  11 . 
         [0027]    The above-mentioned rolling eccentric, which is defined by the rolling body  12   a , thus forms a gear train with a gear ratio of at least two, with the efficiency thereof being very high due to the pure rolling contact. The above-mentioned rolling eccentric, which is defined by the rolling body  12   a , also simultaneously serves as a bearing for the first pinion  14 . The exemplary embodiment shown in  FIG. 1 , in which the radial forces acting on the rolling body  12   a  for its frictionless (e.g., substantially frictionless) rolling are produced by the radial forces of the first pinion  14  at the point of the external rolling contact W, represents only the basic principle.  FIG. 8  shows a preferred improvement, in which the “rolling eccentric—gear train” is implemented as a closed functional unit with internal force management (e.g., a spring), by two rolling bodies  12   a  pretensioned against one another (e.g., biased away from one another) being used between the round rolling geometries and the radial forces being absorbed in an opposing manner by further rolling bodies  12   b.    
         [0028]    Any combinations of the aforementioned types of eccentric are possible. A preferred bearing of the pinions  14  and  15  on the eccentrics  12  and  13  by way of a plain bearing, ball bearing or rolling bearing is schematically shown in  FIG. 2 . With such a bearing arrangement, the rolling contact W is moved to a separately configured component. In the exemplary embodiment, the two eccentrics  12  and  13  are located in a fixed phase relationship with one another and are offset relative to one another about the rotational axis A in the peripheral direction by 180°, and arranged fixedly in terms of rotation relative to one another. The pinions  14 ,  15  are eccentrically mounted relative to the rotational axis A (i.e., they are driven by the eccentrics  12 ,  13 ), are arranged axially adjacent to one another, and carry out movements offset relative to one another by 180°; therefore, initially only the motion of the first pinion  14  is described in the following. 
         [0029]    The first pinion  14  carries out a rolling motion on the ring gear  16 . In the exemplary embodiment, the ring gear  16  is fixed. Regarding the rolling motion of the first pinion  14  on the ring gear  16 , the first pinion  14  meshes with the ring gear  16 . That is, a radially outwardly located external toothing  14   a  of the first pinion  14  meshes with a radially inwardly located internal toothing  16   a  of the ring gear  16 . The outside diameter of the external toothing  14   a  is smaller than the root diameter of the internal toothing  16   a  by at least the height of one tooth. The number of teeth of the external toothing  14   a  is less than the number of teeth of the internal toothing  16   a  by one. The tooth geometry both of the external toothing  14   a  and also of the internal toothing  16   a  is a partial cycloid or an approximate cycloid shape, i.e. the tooth flanks may possibly be reduced and/or contain intermediate portions, preferably circular arcs. 
         [0030]    During the rolling motion of the first pinion  14  on the ring gear  16 , the point of the external toothing  14   a  of the first pinion  14  located in the extension of the eccentricity of the first eccentric  13 , i.e. the connecting line between the rotational axis A and the eccentric axis B, is in contact with the current facing point of the internal toothing  16   a  of the ring gear  16 . The contact point might be denoted as the point of rolling contact W. While with known solutions a linear contact between the two components takes place at the point of rolling contact W, for example due to slightly different radii of curvature of the two sets of teeth, according to the exemplary embodiment of the invention a surface contact is provided at the point of rolling contact W. Therefore, for a highly viscous lubricant film on the components, large lubricant gap lengths and small lubricant gap thicknesses may be achieved, which markedly improves the damping effect. 
         [0031]    In order to achieve the surface contact at the point of rolling contact W, the material of the ring gear  16  radially outside the point of rolling contact W, i.e. the material at least indirectly bearing the external toothing  16   a , is at least partially elastically deformable. In the exemplary embodiment ( FIG. 1 ), recesses  20  are provided in the material of the ring gear  16  which create space for receiving the material which is elastically displaced at the point of rolling contact W. The recesses  20  may additionally or alternatively be provided in the first pinion  14  ( FIG. 5 ). The material may naturally also be more flexible, for example by the first pinion  14  being metallic and the ring gear  16  being plastic, with the plastic ring gear  16  preferably being produced as a plastic injection-molded part. In a modification ( FIG. 6 ), the ring gear  16  is metallic, but mounted in a resilient bed  21  inside a fixed housing  22 ; therefore, overall, a layered, resilient arrangement is provided. The different possibilities for generating the surface contact may also be combined. 
         [0032]    In order to tap (e.g., harness) the rolling motion of the first pinion  14  and to compensate for the wobbling portion thereof, a circular sliding gear (surface pressure gear) is configured between the first pinion  14  and the output  18 . The circular sliding gear is mounted for rotating about the rotational axis A. Further regarding the circular sliding gear, at least two, in the exemplary embodiment eight, approximately cylindrical guide elements  24  project axially from a disc-shaped base body of the output  18 , for example the guide elements  24  may be stamped-out cams or pins. The first pinion  14  has at least two, in the exemplary embodiment eight, guide openings  25  around the eccentric axis B, according to the number of guide elements  24 , into which the guide elements  24  engage with clearance. The clearance is slightly greater than double the distance of the eccentric axis B from the rotational axis A. With the rolling motion of the first pinion  14 , the output  18  carries out a reduced rotational motion about the rotational axis A. 
         [0033]    As compared to the first pinion  14 , the second pinion  15 , which is driven by the second eccentric  13 , carries out the same rolling motion on the common ring gear  16 , also with surface contact at a point of rolling contact W. The surface contact between the second pinion  15  and the common ring gear  16  is produced by the same means as for the first pinion  14 . By the offset arrangement of the two pinions  14  and  15 , the similarly common output  18  is acted upon symmetrically and as a result is free of transverse forces. 
         [0034]    In accordance with the exemplary embodiment, the motorized actuator  1  according to  FIG. 2  has a second gear train  30  that is arranged, with respect to the rotational axis A, axially offset to the above-described first gear train  10 , and the second gear train  30  is attached to the output side of the first gear train  10 . The components of the second gear train  30  are configured the same or almost the same as those of the first gear train  10 , in particular with regard to the geometric dimensions of the cooperating regions, i.e. the two gear trains  10  and  30  provide the same reduction ratio. For forming a common housing  22 , the ring gear  16  extends axially throughout both gear trains  10  and  30 , possibly by the radial interposition of the resilient bed  21  and/or steps of (e.g., discontinuities of) the teeth in the axial direction. 
         [0035]    The common housing  22  of the motorized actuator  1  also supports the motor  5 , which is arranged axially offset on the side (e.g., at the end) of the first gear train remote from the second gear train  30 . In the exemplary embodiment, a stator  5   a  of the motor  5  is fixedly mounted in the housing  22 , while a rotor  5   b  is mounted for rotating about the rotational axis A and is connected fixedly in terms of rotation to the drive  11  of the first gear train  10 . The motor  5  is preferably electronically commutated. In this regard, the magnetic field of the stator  5   a  circulates and the rotor  5   b  carries permanent magnets  5   c  which for example contain metals from the group of rare earth metals. The necessary electronics  5   d  are preferably arranged on the front face of the motor  5  remote from the first gear train  10 . The output  18  of the second gear train  30  forms at the same time the entire output of the motorized actuator  1 . This output  18  is configured as a hollow shaft. The hollow shaft, which serves as the output  18 , extends for the entire axial length of the motorized actuator  1 , and is profiled on its inner face for receiving a transmission rod fixedly in terms of rotation. The hollow shaft, which serves as the output  18 , has an outer face that rotatably supports both: the rotor  5  with the drive  11  of the first gear train  10 ; and the output  18  of the first gear train  10  with the drive  11  of the second gear train. 
         [0036]    In a modified embodiment ( FIG. 7 ), two radially nested gear trains are provided instead of the axially nested gear trains. The radial external first gear train  10  corresponds to the aforementioned gear trains  10  and  30 , i.e. a first pinion  14  is driven to create a rolling motion on a fixed ring gear  16 , the two cycloid toothings meshing. For the sake of clarity, the output  18  is not shown in the drawings. For driving the first eccentric  12 , a modified radial internal gear train  32  is arranged upstream. In the internal gear train  32 , on a fixed bearing  34  provided on its (radial) outer face with a cycloid toothing, a ring  36  carries out a rolling motion with a cycloid toothing on its (radial) inner face driven by an eccentric arranged axially offset to the plane of the drawing. As a compensation stage for compensating for the wobbling motion, a further cycloid toothing is provided on the (radial) outer face of the ring  36  which carries out a rolling motion on a cycloid toothing on the (radial) inner face of the first eccentric  12 . This compensation stage has, however, a gear ratio of one, as the number of teeth is selected to be the same. With the two reduction gear trains  10  and  32 , as described above, measures are implemented for surface contact at the point of rolling contact W of the components rolling against one another. 
         [0037]    The motorized actuator  1  according to the invention, for example, may be used for the inclination adjustment of a backrest  42  of the vehicle seat  2  relative to a seat part  43  of the vehicle seat  2 . To this end, the motorized actuator  1  drives a load-bearing gear unit located in the force flux between the backrest  42  and the seat part  43 , for example a geared fitting such as, for example, as disclosed in DE 199 38 666 A1, the entire disclosure of which is incorporated herein by reference. The motorized actuator  1  may, by forming an integrated adjuster, be completely or partially integrated in the load-bearing gear unit, as is disclosed in DE 10 2004 019 466 A1, the entire disclosure of which is incorporated herein by reference. 
         [0038]    The motorized actuator  1  may, however, also be used for height adjustment of the seat part  43 , by the motorized actuator  1  for example being effective between a rocker (e.g., a pivotable, supporting linkage), on the one hand, and a seat frame or a seat rail, on the other hand, and also being integrated in the adjuster. Further possibilities for use of the motorized actuator  1  are possible between further components of the vehicle seat  2  which are movable relative to one another. 
         [0039]    It will be understood by those skilled in the art that while the present invention has been discussed above with reference to an exemplary embodiment and modifications, various additions, modifications and changes can be made thereto without departing from the spirit and scope of the invention as set forth in the following claims.