Abstract:
A dual mass flywheel for a drivetrain of a motor vehicle includes a primary flywheel mass, a secondary flywheel mass and a coupling device. The coupling device includes at least two pivot levers associated with the secondary flywheel mass that interact with a control profile formed on the primary flywheel mass. The pivot levers are pretensioned against the control profile in a radial direction by an elastic element. A control segment of the elastic element is disposed radially inside the control profile.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a 371 U.S. National Stage of International Application No. PCT/EP2010/000632, filed Feb. 2, 2010, which claims priority to German Patent Application No. 10 2009 007 373.6, filed Feb. 4, 2009. The disclosures of the above applications are incorporated by reference herein. 
     FIELD 
     The present invention relates to a dual mass flywheel for a drive train of a motor vehicle. 
     BACKGROUND 
     Such a dual mass flywheel serves in a motor vehicle for the intermediate storage of kinetic energy during the idle strokes of the engine and for the taking up and damping of rotational vibrations between the engine and the drive train. For this purpose, the dual mass flywheel has a primary flywheel mass and a secondary flywheel mass which are rotatable with respect to an axis of rotation of the dual mass flywheel and which are rotationally elastically coupled to one another by a coupling device. The coupling device has at least two pivot levers which are associated with one of the two flywheel masses and which cooperate with a control section associated with the other flywheel mass. The pivot levers are in this respect biased from the outside to the inside toward the control section by elastic elements in a radial direction with respect to the axis of rotation. 
     A dual mass flywheel is, for example, known from WO 2004/016968 whose coupling device includes pivot levers which are pressed from the outside to the inside toward an inner cam by spring elements arranged in the radial direction. 
     DE 32 13 748 A1 describes a somewhat differently structured coupling device for a clutch disk. The spring elements provided for the biasing of the pivot levers toward an inner cam are here arranged tangentially to the axis of rotation about an inner cam. 
     It is disadvantageous with the known dual mass flywheels that on their operation an unwanted speed dependence of the coupling characteristics of the respective coupling device occurs due to the centrifugal forces acting on the individual components. 
     SUMMARY 
     An object of the present invention is to provide a dual mass flywheel having a coupling device which has fewer speed dependent coupling characteristics. 
     This object is satisfied by a dual mass flywheel having such a coupling device configured such that at least one respective middle section of the elastic elements is arranged within the control section in the radial direction with respect to the axis of rotation. 
     In the dual mass flywheel in accordance with the invention, the centrifugal forces acting on the elastic elements in operation are minimized in that the elastic elements are arranged more closely to the axis of rotation of the dual mass flywheel than previously usual. In the known designs, the minimal spacing of the elastic elements from the axis of rotation is limited by the embodiment of an inner cam cooperating with the pivot lever and having a specific control section. Provision is in contrast made in accordance with the invention to design the dual mass flywheel such that the elastic elements are arranged substantially further inwardly in the radial direction relative to the control section. This does not preclude that sections of the elastic elements project beyond the control section in the radial direction. It is only important that at least one respective center section or one center region of the elastic elements, i.e. for example, the center of gravity of the elastic elements, is arranged more closely to the axis of rotation of the dual mass flywheel than a surface of the control section cooperating with the pivot levers. 
     The elastic elements and/or the pivot levers cooperating with them can be made relatively short due to the inwardly disposed arrangement of the elastic elements. The reduction of the masses of the components used associated with this (compared with conventional concepts) additionally reduces the disturbing influence of the centrifugal forces acting on the individual components. 
     Since the elastic elements are particularly prone to centrifugal forces occurring during operation of the dual mass flywheel, this concept minimizes speed dependent effects in a particularly efficient manner. It is additionally simultaneously achieved that more construction space is available in the radial direction for the design of the control section. In other words, the design of the control section is only limited to a smaller degree by components disposed further outwardly. The dual mass flywheel in accordance with the invention can therefore also be given a more compact construction. 
     The control section is preferably formed at an inner cam. 
     In accordance with an embodiment, the elastic elements each extend substantially in a tangential direction, in particular with an—almost—complete compression of the elastic elements. “Substantially in a tangential direction” is to be understood such that even slight deviations from a tangential alignment are covered which, for example, occur on increasing extensions of the respective elastic elements. 
     The elastic elements can have a smaller spacing from the axis of rotation than the pivot axles of the pivot levers about which the pivot levers are pivotable. This means that not necessarily all sections of the pivot levers are always further away from the axis of rotation of the dual mass flywheel during operation than each section of the elastic elements. It is rather decisive in this embodiment that the pivot axles supporting the pivot levers are arranged radially further outwardly than the elastic elements. The elastic elements are in particular arranged within a circle in the radial direction which is arranged concentrically to the axis of rotation of the dual mass flywheel and whose radius is defined by the spacing of the pivot axles to the axis of rotation. 
     Provision can be made to associate a support means with each of the elastic elements, said support means being arranged at the flywheel mass with which the pivot levers are associated and being suitable for the support of the respective elastic element in a radial direction. The support means holds the elastic elements in its position intended for use during the operation of the dual mass flywheel and counters the occurring centrifugal forces. The support means is in particular molded directly at the corresponding flywheel mass. Since the support means and the elastic elements are associated with each flywheel mass, relative wear movements between these components are avoided. The support means can in particular be segments which—viewed from the axis of rotation—are slightly convexly curved to be able to accept a deformation of the elastic elements occurring in specific operating states in a radial direction in an improved manner. 
     It is furthermore possible that each of the elastic elements is in contact with a pair of pivot levers. Such a construction is simple to solve from a construction aspect and only requires a small number of components. The control section can be divided into a plurality of identical sections, with each pair of pivot levers being associated with one of the sections or cooperating with it. 
     The elastic elements are preferably springs, in particular helical springs. 
     An arrangement of the elastic elements radially within the control section can be implemented particularly advantageously when, in contrast to a conventional design, the elastic elements are arranged axially offset from the control section with respect to the axis of rotation of the dual mass flywheel, with this applying at least to the center plane of the elastic elements relative to the center plane of the control section. 
     At least one driver element (for example a roller device) can be associated with each pivot lever and is in contact with a control surface associated with the control section, with a first plane in which the driver element and the control surface are in contact being arranged axially offset with respect to the axis of rotation from a second plane in which the pivot levers are arranged. In other words, the elastic elements and the control section are arranged behind one another—optionally also partly overlapping in the axial direction—in the axial direction of the dual mass flywheel. Under certain circumstances, a space can be utilized in the radial direction within the control section for the arrangement of components of the coupling device, whereby the space requirements of the dual mass flywheel is reduced in the axial direction. 
     In accordance with an advantageous further development, a separate driver element is associated with each pivot lever. The elastic elements can furthermore be arranged in the second plane. 
     Provision can be made for the optimized transmission of the torque generated by the elastic elements and acting on the individual pivot levers onto the control section that the pivot levers each have two arms which include an angle which is smaller than 180°. This means that the two arms of the individual pivot levers are not arranged parallel to one another. The pivot axle of the pivot levers is in particular disposed between the end of the pivot lever which is acted on by the corresponding elastic element and the end which is in contact with the control section. 
     The pivot levers are in particular in contact with the control surface of the control section via a respective roller device. The pivot levers can be pivotally connected to the one of the two flywheel masses. 
     Further areas of applicability will become apparent from the description herein. The description and specific example in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present invention. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible embodiments such that the drawings are not intended to limit the scope of the present invention, wherein: 
         FIG. 1  shows a cross-section through a dual mass flywheel in accordance with the invention along the axis of rotation; and 
         FIG. 2  shows a section through the dual mass flywheel in accordance with the invention of  FIG. 1  perpendicular to the axis of rotation. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a cross-section through a dual mass flywheel  10  along its axis of rotation R. The dual mass flywheel  10  has a housing  11 , a primary flywheel mass  12  and a secondary flywheel mass  14 . The primary flywheel mass  12  is rotationally fixedly connected to a crankshaft  16  of an engine, not shown, of a motor vehicle, whereas the secondary flywheel mass  14  is rotatably supported by a bearing  18  on a transmission input shaft  20  of a transmission, now shown, of the motor vehicle. The secondary flywheel mass  14  can selectively be connected in a drive effective manner to the transmission input shaft  20  by means of a clutch  22  which is only shown in part in  FIG. 1 . The transmission input shaft  20  is supported by a second bearing  18 ′ in a recess  24  of the crankshaft  16 . To take up axial forces acting on the secondary flywheel mass  14  which occur in specific operating states of the dual mass flywheel  10 , a third bearing  18 ″ is provided which is axially supported on the crankshaft  16  via a radially inwardly disposed section of the primary flywheel mass  12 . 
     The flywheel masses  12 ,  14  are rotationally elastically coupled to one another by a coupling device  26 . 
       FIG. 2  shows a section through the dual mass flywheel  10  perpendicular to the axis of rotation R along the line AA, with the representation of details of the support in the region about the transmission input shaft  20  having been omitted for reasons of clarity. 
     The individual components of the coupling device  26  can be seen from  FIG. 2 . They include a plurality of pivot levers  28  which are pivotably supported with respect to a respective pivot axle  30 . Each of the pivot levers  28  has a driver arm  32  and a lever arm  34 . The two arms  32 ,  34  include an angle which is smaller than 180° and larger than 90°. The geometry of the pivot levers  28  can, however, also have characteristics differing therefrom if other circumstances are present in the dual mass flywheel  10  due to the construction. 
     The respective driver arm  32  of the pivot levers  28  extends from the corresponding pivot axle  30  toward an end of the pivot lever  28  which is in contact via a driver roll  38  with a control surface on a control section  36  formed at the primary flywheel mass  12 . The control section  36  is shown formed on an inner cam associated with the primary flywheel mass  12 . The lever arm  34 , in contrast, is in contact at its end remote from the pivot axle  30  with an end of an elastic element, shown herein as a helical spring  40 . The other end of the respective spring  40  is in turn in contact with the lever arm  34  of an adjacent pivot lever  28 ′. The adjacent pivot lever  28 ′ is substantially of the same function and construction as the pivot lever  28 . It is, however, arranged with mirror symmetry—with respect to a plane of symmetry disposed between adjacent pivot axles  30 . As such, the following description of the operation of pivot levers  28  is also applicable to the adjacent pivot lever  28 ′. 
     The active principle of the dual mass flywheel  10  can be explained in an illustrative manner with reference to  FIG. 2 . As already described above, the control section  36  is formed at the primary flywheel mass  12 . The pivot levers  28  are, in contrast, pivotably supported at a respective hollow bolt  41  of the secondary flywheel mass  14  with respect to the pivot axles  30 . To increase the stability, the pivot levers  28  can be engaged around in the manner of a cage and can hereby be supported at both sides (not shown). 
     It is stated in the following for the example of the pivot levers  28  upwardly disposed in  FIG. 2  how a relative rotation of the two flywheel masses  12 ,  14  can result in different positions of the pivot levers  28 . A first state is shown in which the driver rolls  38  of the pivot levers  28  are arranged at a maximum distance from the axis of rotation R due to the embodiment of the control section  36 . The spring  40  is maximally compressed in this state. On a change of the relative position of the two flywheel masses  12 ,  14  with respect to one another—for example on a rotation of the primary flywheel mass  12  clockwise relative to the secondary flywheel mass  14 —the driver rolls  38  run through a central region of the control surface on the control section  36  associated with them. A position of the primary flywheel mass  12  relative to the secondary flywheel mass  14  is shown by dashed lines in  FIG. 2  and defines a second state in which the driver rolls  38  approach closest to the axis of rotation R. The spring  40  is minimally compressed in this second state as is likewise indicated by dashed lines. The spring  40  also deforms slightly on the extension due to the pivoting of the pivot levers  28  and presses snugly at a support segment  42  which holds the spring  40  in its radial position against the centrifugal forces acting thereon. To take up the curvature of the spring  40  ideally on its extension, the support segment  42  is slightly convexly curved viewed from the axis of rotation. 
     When the primary flywheel mass  12  rotates further clockwise relative to the secondary flywheel mass  14 , the driver rolls  38  are pressed outwardly again by the control surface of the control section  36 , whereby a compression of the spring  40  takes place via the pivot levers  28  which generates a force acting against the relative rotation of the flywheel masses  12 ,  14 . 
     In other words, a respective spring  40  and a segment of the control section  36  are associated with each pair of pivot levers  28  and  28 ′, whereby a threefold symmetry of the coupling device  236  results with respect to the axis of rotation R. More or fewer pivot lever pairs can generally also be provided. It is also possible not to provide any pivot lever pairs, but rather to support one end of the springs  40  at the secondary flywheel mass  14 . 
       FIG. 2  illustrates the advantage which results due to the arrangement of the springs  40  substantially radially within the control section  36 . Due to the arrangement of the springs  40  more closely to the axis of rotation R, the centrifugal forces acting on them are minimized. In addition, construction space is saved in the radial direction or the control section  36  can extend further outwardly in the radial direction than with conventional dual mass flywheels. A greater freedom of design is hereby present with respect to the pitches of the control section  36 . In addition, the arms  32 ,  34  of the pivot levers  28  and the springs  40  can be made relatively short, which likewise has a positive effect on a reduction of the changes of the coupling characteristics depending on the centrifugal force. 
     Again with reference to  FIG. 1 , it will be described in the following how the construction space disposed within the control section  36  is used for the arrangement of the springs  40 . To design the construction of the pivot levers  28  in as simple a manner as possible and to avoid a mutual blocking of the pivot levers  28  and of the control section  36 , these components are arranged offset in the axial direction. The pivot levers  28  and the springs  40  are substantially disposed in a plane which corresponds to the section plane AA. A plane BB which extends centrally through the control surface of the control section  36  extending perpendicular thereto is disposed in the direction toward the crankshaft  16  offset parallel thereto. The section plane BB also extends substantially centrally through the driver rolls  38 . In other words, the driver roller  38  does not lie in the plane which is spanned by the arms  32 ,  34  of the pivot levers  28  (plane AA). The driver rollers  38  are rather supported laterally at the pivot levers  28 . 
     The arrangement of individual components of the coupling device  26  offset in the axial direction of the dual mass flywheel  10  only results in a slightly larger extent of the dual mass flywheel  10  in the axial direction since the control section  26  and the driver rolls  38  in contact therewith only have a small axial extent. The parallel offset resulting therefrom between the pivot levers  28  and the springs  40 , on the one hand, and the control section  26  and the driver rolls  38 , on the other hand, is therefore only small, whereas the construction space saving in the radial direction is significant. As shown, a compact dual mass flywheel  10  is thus provided which is additionally less influenced by centrifugal forces occurring in operation. 
     REFERENCE NUMERAL LIST 
     
         
           10  dual mass flywheel 
           11  housing 
           12  primary flywheel mass 
           14  secondary flywheel mass 
           16  crankshaft 
           18 ,  18 ′,  18 ″ bearings 
           20  transmission input shaft 
           22  clutch 
           24  recess 
           26  coupling device 
           28  pivot lever 
           30  pivot axle 
           32  driver arm 
           34  lever arm 
           36  control section 
           38  driver roll 
           40  spring 
           41  bolt 
           42  support segment 
         R axis of rotation 
         AA section plane 
         BB driver roller/control section plane