Abstract:
A torsional vibration damper with a friction device. The friction device is formed on at least one friction surface on two contra-rotationally and oppositely disposed disc parts that are in frictional contact with one another. In order to propose how to determine the initial stressing effect of the frictional action independently of external support of the disc parts, the frictional surfaces are pressurized against one another by means of at least one spring element.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority from German Patent Application No. 10 2009 008 670.6, filed Feb. 12, 2009, and German Patent Application No. 10 2009 042 051.7, filed Sep. 17, 2009, which applications are incorporated herein by reference in their entirety. 
     FIELD OF THE INVENTION 
     The invention relates to a torsional vibration damper. 
     BACKGROUND OF THE INVENTION 
     Torsional vibration dampers with friction devices have been available for a long time, and are used particularly in the drive trains of motor vehicles with a drive unit such as an internal combustion engine subjected to torsional-vibration stress. To generate frictional torque, diaphragm springs find application; they are supported on a component that is axially fixed and axially pressurizes two disc parts with friction surfaces against one another, wherein one disc part can be assigned to the output part and the other disc part respectively assigned to the input part, or at least to an intermediate part that is a multi-stage series-connected torsional-vibration damper. Alternatively, the diaphragm spring can be accommodated on a disc part fixed in circumferential direction and its force-transmitting edge may feature a friction surface that generates frictional torque on a friction surface of the other disc part. In this case, the disc parts must be supported axially, respectively, on other components in order to counteract the axial force of the diaphragm spring and centering means for the diaphragm spring must be provided. Furthermore, the unit costs of the diaphragm springs are high because of large amounts of punching scrap incurred because the diaphragm spring must be disposed on a large circumference to achieve high frictional torque. 
     BRIEF SUMMARY OF THE INVENTION 
     Object of the invention is therefore to propose a torsional vibration damper that features a friction device without a diaphragm spring. 
     In view of that, a torsional vibration damper according to the invention is proposed with two disc parts disposed oppositely to one another, against the effect of at least one energy accumulator in a rotatably limited manner, and a friction device is interposed between the latter, which is effective under relative rotation of the disc parts, wherein the friction device is formed by at least a friction surface provided on either disc part and which pressurizes two friction surfaces at least axially against one another, by means of at least a spring element, wherein the extension of the spring element in circumferential direction assumes an angle range less than 360°; thus dispensing with a diaphragm spring in the friction device. In this manner, the extension of the spring element in circumferential direction entails the arch length that corresponds to the maximum dimension of the spring element in circumferential direction, with an angular range that corresponds to the length of said arch. Preferably, the spring element has at least a support surface on which the spring force exerted by the spring element is transmitted into a disc part. 
     The torsional vibration damper can feature several damper stages, for instance two working in series, which can be formed by energy accumulators with different stiffness coefficients active in circumferential direction. Said stages can be flange parts mounted as discs that rotate relative to one another; they can respectively pressurize energy accumulators, for instance, in one direction, and upon rotation of flange parts relative to one another, the energy accumulator, for instance, compresses the coil springs via their face side. A flange part can be captured by the input part and the other by the output part and the friction device can be interposed between the two flange parts. To manufacture a multiple-stage serially connected damper, in which one damper stage is activated at greater angles than the other one, a floating, intermediate flange can be provided between the output- and input side flange parts. The friction device can be provided between the output side and the intermediate flange and/or the input side and the intermediate flange. 
     In one embodiment, the spring element exerts spring force on both disc parts in such a manner that the latter are pressed against each other, and hence, in case of relative rotation of both disc parts, frictional torque is generated depending on the spring force, among others. The spring element is advantageously disposed in the external circumference area of the disc parts, wherein the frictional torque can be increased among others. 
     The spring force and hence the frictional torque can be influenced by the stiffness of spring element or its geometry, if necessary. For instance, the stiffness depends on the spring element material as well as on spring element&#39;s geometrical formation, among others, and determines the spring force depending on the deflection of supporting surface relative to a basic state of the spring element, which then exists when the spring force is zero. Furthermore, the spring rate can be influenced by the grip length, as the distance between projected mid-point of supporting surface on the fixing plane and the mid-point of supporting surface facing the fastening element. In a further embodiment, several spring elements are purposefully distributed over the circumference. In particular, at least two spring elements have the same radial distance from a common rotation axis. Furthermore, at least two spring elements disposed over the circumference produce equal magnitudes of frictional torque. In a further advantageous embodiment, at least two spring elements can produce different magnitudes of frictional torque. Through the spring force applied to the disc parts by several spring elements, resultant frictional torque is developed as total of the respective individual frictional torque values, thus increasing the effectiveness of the friction device. 
     In a further embodiment, the frictional torque of the friction device can be influenced by the relative rotation angle of both disc parts. By introducing a changing thickness on one disc part, for instance, in the form of a ramp-shaped embossing change of depth in the mating area, thus meaning, on the surface of respective disc parts swept through by the support surface of the spring element during relative rotation of both disc parts, it is possible to vary the spring force in dependence upon the angle of relative rotation of both disc parts. Thickness change in contact area should be continuous in an ideal case, so that the spring element can slide on corresponding surfaces of the disc parts. Advantageously, the cross-sectional shape of the spring element is rounded in the supporting surface area in order to provide wear-resistant connection between spring element and disc part as well as sliding-capability with respect to relative rotation. 
     In one embodiment, the spring element is a kind of clamp in particular with U-shaped form. The clamp, for instance, consisting of spring steel is pushed over two axially adjacent components of the disc parts, with a friction surface respectively, and exerts spring force on the latter, with which frictional torque can be developed, which does not require additional external disc parts&#39; axial support. On the contrary, the parts are subjected to mutual bracing. At the same time, the clamp is preferably disposed with its opening pointing outwards radially, so that loss of the clamp under the effect of centrifugal force is ruled out. 
     In one embodiment, the spring element is punched, such that its manufacture is cost-effective because of reduced punching scrap in comparison with the manufacture of conventional diaphragm springs. The spring elements are formed advantageously after punching and then hardened subsequently. The assembly of clamps on input- or output part undercut and, if necessary, formation of positive locking can be facilitated by introducing feed slants at the ends of clamp chicks. 
     In one embodiment, the spring element is indirectly or directly fixed on a disc part particularly by a person skilled in the art of interconnection technology known for this purpose, for instance, clamping-, riveting- or screw connection with suitable fastening elements. In doing so, the spring element can be fixed advantageously on corresponding components by form closure to develop the friction device even under low bracing so that the possibility is ruled out that a spring element may fall off. Furthermore, the spring element can be disposed on the side surface of a disc part. Advantageously, the spring element is disposed on a rivet element, for instance, on a rivet element formed as spacing part. 
     In order to dispose the spring element non-rotatably relative to at least one disc part advantageously, two fastening elements spaced apart can be provided on the spring element. Thereby, the two fastening elements can also have different shapes, in that, for instance, the one, a rivet and the other, a fastening element together depict a lift-up in the disc part and a complementary recess in the spring element. Alternatively, a limit stop can be provided, for instance, on a disc part such that the spring element is connected rotatably relative to the corresponding disc part, within defined limits and that rotary motion beyond the limits is limited by the limit stop. 
     In one embodiment, at least two cutouts can be provided in the spring element in which at least two rivets of an element can be added complementarily, while the rivet element on the other hand is fixed at least on one disc part. The spring element can at the same time be clamped advantageously between the disc part and rivet element. In a preferred embodiment, the spring element is formed such that it can be fixed on the spacing part between two disc parts and the latter spacing part upheld at a definite distance. In particular, the spring element can be attached to several spacing parts. Further advantages and advantageous embodiments of the invention are object of the following figures as well as their descriptive parts in whose depiction scaled reproduction was dispensed with for the sake of clarity. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       The nature and mode of operation of the present invention will now be more fully described in the following detailed description of the invention taken with the accompanying drawing figures, in which: 
         FIG. 1  shows a partial section through a hydrodynamic torque converter with torsional vibration dampers according to the invention, 
         FIG. 2  shows a detail of the torsional vibration damper depicted in  FIG. 1  with a friction device according to the invention, 
         FIG. 3  shows a partial section through a hydrodynamic torque converter with a further torsional vibration damper according to the invention, 
         FIG. 4  shows a detail of the torsional vibration damper depicted in  FIG. 3  with a friction device according to the invention, 
         FIG. 5  shows a cross-sectional view of the spring element depicted in  FIGS. 3 and 4   
         FIG. 6  shows a partial view of a further torsional vibration damper according to the invention in two different embodiments, 
         FIG. 7  shows a cross section through the torsional vibration damper along B-C from  FIG. 6  in a first embodiment, 
         FIG. 8  shows a cross section through the torsional vibration damper along B-B from  FIG. 6  in a second embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows the upper half of a hydrodynamic torque converter  1  disposed around a rotation axis  40  with a torsional vibration damper  2  disposed in its housing in sectional view. The torsional vibration damper  2  features an input part  3  formed by two disc parts  4 ,  5 , which is connected with the turbine wheel  6  and the output part  7  of the converter lock-up clutch  8 . The output part  9  of the torsional vibration damper  2  is formed by the disc part  10  formed as a hub-flange and fixedly connected with the hub  11  that feeds the torque into the transmission input shaft (not shown). The disc part  13  formed as an intermediate flange  12  is disposed floating between the disc parts  4 ,  5 ,  10  and accommodates the energy accumulators  14  that are respectively distributed over the circumference and which can be disposed in different manners to form several damper stages, for instance, they can be pressurized for different torsional angles of disc parts  4 ,  5 ,  10 , or they can feature different stiffness values and/or they can be nested inside one another. 
     In order to prevent the torsional vibration damper  2  from swinging up, in particular in the depicted exemplary embodiment of the intermediate flange  12  under rotational irregularities of engine torque, a friction device  15  is provided between the disc parts  10 ,  13 , thus between the output part  9  of the torsional vibration damper  2  and the intermediate flange  12 . The friction device  15  is formed by a spring element  30  in form of a clamp  16  that axially braces both disc parts  10 ,  13  with one another and develops frictional torque between the friction surfaces provided on the disc parts  10 ,  13 , as soon as both disc parts  10 ,  13  are rotated against one another, as this is the case, for instance, upon introduction of rotational irregularities in the torsional vibration damper  2 . At the same time, the frictional torque is developed in parallel to the effect of the energy accumulators  14 , so that a hysteresis in their load characteristic is developed versus the torsional distance that counteracts a swing up of the intermediate flange  12 , since the latter is retarded relative to the output part  9 . 
       FIG. 2  shows a cutout from  FIG. 1  for detailed illustration of the friction device  15 . The two disc parts  10 ,  13  disposed coaxially contrarotatably feature friction surfaces  17 ,  18  respectively, facing one another and tensioned by several clamps  16  axially pre-stressed and distributed over the circumference. The clamps  16  are accommodated in cutouts  19 ,  20  of the disc parts  10 ,  13  and at least suspended on a disc part  10 ,  13  secured against rotation and loss. As such, they are fitted preferably—as depicted—with their opening outwards, so that they can be supported radially on the cutout  19  by means of the clasp  21  under the effect of centrifugal force. The chicks  22 ,  23  exert the pre-stressing force against both friction surfaces  17 ,  18 . In disc parts  10 ,  13 , undercuts  24 ,  25  are provided to secure the clamp  16  from getting lost. For easy assembly, the chicks  22 ,  23  of the clamp  16  feature insertion slants  26 ,  27 .  FIG. 3  shows the upper sectional half of a hydrodynamic torque converter  1  disposed around a rotation axis with a torsional vibration damper  2  disposed in its housing according to a further embodiment. The spring element  30  is connected with the disc part  13  in a form-closed manner, by means of a fastening element  32 , on the side surface  42  in the radial outer area. Thus, on the spring element  30 , a cutout is provided, through which the fastening element  32  extends. In order to establish a non-rotatable link to the disc part  13 , a further fastening element  33  is provided in the form of a pick-up on the side surface  42  of the disc part  13 , said pick-up fits in a complementary recess on the spring element  30 . For axial centering of the disc parts  10 ,  13  is an additional spring element  31  disposed in the radial inner area of the side disc parts  10 ,  13 , for instance, the latter is formed as a diaphragm spring. In doing so, the spring element  31  should be disposed possibly radially inside in order to keep its dissipated foreign friction, in the torsional vibration dampers,  2  low. 
       FIG. 4  shows a detail of the torsional vibration damper  2  depicted in  FIG. 3  with a friction device according to the invention. The spring element  30  is attached to the disc part  13  with the help of the fastening element  32 . As such, it is disposed sunken in a cutout  48  of the disc part  13  in order to obtain a possibly small axial assembly space of the torsional vibration damper  2 . The spring element  30  presses the disc part  13  with a spring force on the disc part  10  in order to generate frictional toque resulting from relative rotation of the two disc parts  10 ,  13 . Since the frictional torque increases proportionally to the increase of the radial distance of the supporting surface  52  from the rotation axis and because it is advantageous to maximize the frictional torque with low pre-stress of the spring element, the spring element  30  and its support surface  52  is disposed in a radial outer area of both disc parts  10 ,  13 . 
     To reduce the axial assembly space of the friction device  15 , the support area  50  on the disc part  10 , on which the support surface  52  of the spring element  30  slides during relative rotation of both disc parts  10 ,  13 , is incorporated, sunken in the disc part  10 . In that case, the incorporated, sunken support area  50  can feature different depths of sink, circumferentially, so that the spring element  30 , when sliding on the support surface  52  depending on the contarotational angle of the two disc parts  10 ,  13  relative to one another, exerts a different spring force on both disc parts  10 ,  13 . This angular dependency of spring force, for instance, is established by a ramp-shaped and particularly continuous changing thickness  34  in the disc part  10  when sliding on the support surface  52 . In doing so, the formation of changing thickness  34  should possibly be continuous circumferentially, so that small shearing forces act on the spring element  30  in the plane, normal to the spring force. In the support surface  52  of spring element  30 , circumferentially opposite, respectively in the side area  56 , minted forms  54 , for instance, spoon-shaped are provided, which facilitate perfect sliding of the support surface  52  on the support area  50  without the spring element  30  jamming particularly in the ramp-shaped area—changing thickness  34 . 
       FIG. 5  depicts the spring element  30  from  FIG. 4  in a radial cross-section view. The set-up height h of the spring element  30  as the distance between the plane of the support surface  58  and the fixing plane  38  can be subdivided first of all such that a set-up height denotes the basic state of the spring element  30  without pre-stress spring force, thus the non-deformed state and not the state when it is mounted on the disc part, which depends on the initial bent form of the spring element. 
     Furthermore, the set-up height changes through the assembly of the spring element  30  on the two disc parts  10 ,  13  and during relative rotation of the two disc parts  10 ,  13  through the ramp-shaped—changing thickness  34 —section. In that case, the set-up height h in basic spring element state should be chosen such that adequate spring force acts on both disc parts whilst accounting for component tolerances, particularly of both disc parts  10 ,  13  and, thus, sufficient frictional torque is generated by the friction device  15 . 
     Furthermore, the sensitivity of the spring force may be influenced depending, for instance, on the set-up height h by means of the grip length l as the distance between the mid-point of the support surface  52  projected on the fixing plane  38  and the mid-point of the fastening element facing the support surface or if necessary its complementary cutout  46  in spring element  30 . The thickness of the spring element d is selected suitably based on the requirements with respect to assembly space dimensions, the production method based on spring element  30  and the material properties as well as the desired stiffness of the spring element. A rounded surface  36  of spring element  30  provided on the support surface  52  causes wear-resistant and smooth connection with respect to relative rotation of both disc parts  10 ,  13 , between the spring element  30  and disc part  10 . 
     In  FIG. 6 , the cutout of a torsional vibration damper  2  with two other different embodiments according to the invention is depicted in plan.  FIG. 7  shows a cross-section of the torsional vibration damper  2  along the line B-C from  FIG. 6  in the first embodiment. The torsional vibration damper  2  features an input part  3  formed by two disc parts  4 ,  13  that accommodates the energy accumulator  14   s  that are distributed over the circumference. The output part  9  of the torsional vibration damper  2  consists of the disc part  10 , which is formed as a hub-flange. 
     To prevent swing up of the torsional vibration damper  2  in the event of rotational irregularities of engine torque, a friction device  15  is disposed between the disc parts  10 ,  13 , thus between the output part  9  of the torsional vibration damper  2  and the input part  3 . The friction device  15  is formed by a spring element  30  and a rivet element  60  in the form of a spacing element that axially connects both disc parts  4 ,  13  with one another whilst the spring element  30  braces both disc parts  10 ,  13  axially and frictional torque is generated between friction surfaces  17 ,  18  provided on the disc parts  10 ,  13 , as soon as both disc parts  5 ,  10  are contra-rotated; this, for instance, is the case when rotational irregularities are input into the torsional vibration damper  2 . At the same time, the frictional torque is developed parallel to the effect of the energy accumulator  14 , so that a hysteresis in its force characteristic is developed versus the torsional distance that counteracts a swing up effect of the output part  9 , since the latter is retarded relative to the input part  3 . 
     The spring element  30  has two recesses in which two rivets  62  can be impressed complementarily in order to dispose the spring element  30  non-rotatably. The rivets  62  are again attached to the rivet element  60 , and they particularly form a common part with the latter. The rivet element  60  serves as spacing part in order to hold both disc parts  4 ,  13  at a definite axial distance apart and is particularly connected non-rotatably with the latter. The spring element  30  is clamped between the disc part  4  and the rivet element  60  with which the latter is fixed indirectly or if necessary directly on both disc parts  4 ,  13 . The set-up height of the spring element must thereby be suitably selected in order to be able to develop an adequate spring force on the disc part  10  despite spacing between the disc part  4  and the disc part  10  defined by the rivet element  60 . To keep the axial assembly space of the torsional vibration damper  2  as small as possible, axially viewed, suitably small spacing parts in the form of rivet elements  60  can be used, since the thickness of the spring element  30  in the assembly shown here still flows into the overall axial assembly length. The radially required assembly space of the spring element  30  can be reduced in that this is punched in a manner that it obtains an arched shape when viewed in plan.  FIG. 8  shows a cross-section of the torsional vibration damper  2  along the line B-B from  FIG. 6  in a further second embodiment of the friction device. 
     The spring element  30  is disposed on several rivet elements  60  and has a wavy structure when viewed in cross-section, in order to increase the spring force and the support surface  52  on the disc part  10 ,  11 . 
     LIST OF REFERENCE SYMBOLS 
     
         
           1  torque converter 
           2  torsional vibration damper 
           3  input part 
           4  disc part 
           5  disc part 
           6  turbine wheel 
           7  output part 
           8  converter lock-up clutch 
           9  output part 
           10  disc part 
           11  hub 
           12  intermediate flange 
           13  disc part 
           14  energy accumulator 
           15  friction device 
           16  clamp 
           17  friction surface 
           18  friction surface 
           19  cutout 
           20  cutout 
           21  clasp 
           22  chick 
           23  chick 
           24  undercut 
           25  undercut 
           26  feed slant 
           27  feed slant 
           30  spring element 
           31  spring element 
           32  fastening element 
           33  fastening element 
           34  thickness change 
           36  rounded surface 
           38  fixing plane 
           40  rotation axis 
           42  side surface 
           44  recess 
           46  recess 
           48  depression 
           50  support area 
           52  support surface 
           54  embossing 
           56  side area of spring element 
           58  plane of support surface 
           60  rivet element 
           62  rivet 
         h set-up height 
         l grip length 
         d thickness of spring element