Abstract:
A torsion damper including: a plurality of springs; a first plate with a central axis; and a second plate with a central axis. The plurality of springs displaces the first and second plates so that the central axis for the first plate is radially offset from the central axis for the second plate. In one embodiment, the radial offset between the central axis for the first plate and the central axis for the second plate is fixed. In another embodiment, the first plate comprises a central bore and the second plate comprises an extruded cylinder; and the fixed alignment is maintained by contact between the central bore and the extruded cylinder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Application No. 61/210,203, filed Mar. 16, 2009, which application is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to a torsion damper, and more specifically to a torsion damper with induced imbalance. 
     BACKGROUND OF THE INVENTION 
     The prior art teaches torsion dampers with springs for providing torsional flexibility, cover plates for containing the springs and receiving torque from an input element (i.e., an engine crankshaft), and flanges for transmitting torque from the springs to an output element (i.e., a transmission input shaft). Flanges for conventional dampers are usually engaged, often by a spline connection, with a hub disposed on the input shaft. The spline connection adequately centers the flange relative to a central axis of the damper. 
     Prior art series dampers offer improved torsional isolation by increasing rotational travel of the damper. Series dampers often have two flanges, one of which is a floating flange. Prior art floating flanges are usually positioned by the springs. That is, the flanges have cutouts for receiving the springs which are, in turn, positioned in formed cover plate windows. The geometrical position of the springs maintains the flange in a generally centered position with regards to a central axis of the damper without additional centering features. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention broadly comprises a torsion damper including: a plurality of springs; a first plate with a central axis; and a second plate with a central axis. The plurality of springs displaces the first and second plates so that the central axis for the first plate is radially offset from the central axis for the second plate. In one embodiment, the radial offset between the central axis for the first plate and the central axis for the second plate is fixed. In another embodiment, the first plate comprises a central bore and the second plate comprises an extruded cylinder; and the fixed alignment is maintained by contact between the central bore and the extruded cylinder. 
     In one embodiment, the first plate comprises a central bore and the second plate comprises an extruded cylinder and the plurality of springs displaces the first and second plates so that the central bore and the extruded cylinder are in contact. In another embodiment, the first or second plate exhibits rotational imbalance when rotated about its central axis. In one embodiment, the first or second plate includes a respective cutout and under rotation, the respective cutout unbalances the first or second plate. In another embodiment, the first or second plate includes a respective mass element attached to the plate and wherein, under rotation, the respective mass element unbalances the first or second plate. In one embodiment, the first plate includes an outer circumference and a central bore forming an inner circumference and a radial distance between the inner and outer circumferences is non-uniform. 
     The present invention also broadly comprises a torsion damper including: a first plate with an outer diameter; a first plurality of apertures disposed in the first plate; and a central bore in the first plate. Prior to forming the central bore and the first plurality of apertures in the first plate, the first plate has a first center of mass and the first plate with the central bore has a second center of mass radially displaced from the first center of mass. In one embodiment, the first plate with the central bore and the first plurality of apertures has the second center of mass. 
     In one embodiment, the torsion damper includes: a second plate with a second plurality of apertures; and a plurality of springs disposed in the first and second pluralities of apertures. In another embodiment, the first plate includes a first central axis passing through the second center of mass, the second plate includes a center of mass and a second central axis parallel to the first central axis and passing through the center of mass for the second plate, and the first central axis and the second central axis are radially offset. In one embodiment, the first central axis and the second central axis are in a fixed radial alignment. In another embodiment, the second plate comprises an extruded cylinder and the fixed alignment is maintained by contact between the first plate central bore and the second plate extruded cylinder. 
     In one embodiment, the torsion damper includes: a second plate with an extruded cylinder and a second plurality of apertures; and plurality of springs disposed in the first and second apertures. The plurality of springs displaces the first and second plates so that the central bore and the extruded cylinder are in contact. In another embodiment, the first plate includes an outer circumference and the central bore forms an inner circumference and a radial distance between the inner and outer circumferences is non-uniform. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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  is a cross-sectional view of a torque converter with a torsional damper according to an example aspect of the invention; 
         FIG. 2  is a front view of a torsional damper according to an example aspect of the invention; 
         FIG. 3  is a cross-sectional view of the torsional damper shown in  FIG. 2  generally along line  3 - 3  in  FIG. 2 ; 
         FIG. 4  is a simplified view of the torsion damper shown in  FIG. 2 ; 
         FIG. 5  is a cross-sectional view of the torsion damper shown in  FIG. 4  generally along line  5 - 5  in  FIG. 4 ; 
         FIG. 6  is a front view of the torsion damper shown in  FIG. 4  with the cover plates and flange displaced by force from the springs; and, 
         FIG. 7  is a cross-sectional view of a cover plate shown in  FIG. 4 , generally along line  7 - 7  in  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     At the outset, it should be appreciated that like drawing numbers appearing in different drawing views identify identical, or functionally similar, structural elements. Furthermore, it is understood that this invention is not limited only to the particular embodiments, methodology, materials and modifications described herein, and as such may, of course, vary. It is also understood that the terminology used herein is for the purpose of describing particular aspects only, and is not intended to limit the scope of the present invention, which is limited only by the appended claims. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs. Although any methods, devices or materials similar or equivalent to those described herein can be used in the practice or testing of the invention, the following example methods, devices, and materials are now described. 
     The following description is made with reference to  FIG. 1 .  FIG. 1  is a cross-sectional view of a torque converter with a torsional damper according to an example aspect of the invention. Torque converter  10  includes impeller assembly  12 , turbine assembly  14  and stator assembly  16 . Cover  18  is drivingly engaged with impeller  12  at weld  20  and with a prime mover (not shown) at lugs  22 . Turbine assembly  14  is fixedly connected to torsion damper  24  and drive plate  26  via rivet  28 , for example. Piston plate  30  is drivingly engaged with torsion damper  24  at tabs  32 . Piston plate  30  is engageable with cover  18  at friction interface, or clutch,  34 . 
     The following description is made with reference to  FIGS. 1-3 .  FIG. 2  is a front view of torsion damper  24  shown in  FIG. 1  according to an example aspect of the invention.  FIG. 3  is a cross-sectional view of torsion damper  24  generally along line  3 - 3  in  FIG. 2 . Torsion damper  24  includes outer cover plates  36  and  38  fixedly connected by rivet  40 . Torsion damper  24  further includes inner cover plates  42  and  44  and flange  46 . Flange  46  is drivingly engaged with hub  48  at rivets  50 , for example. Hub  48  is engaged with and radially positioned by an output element such as an input shaft of a transmission (not shown). By radial, we mean orthogonal to axial axis  11  in  FIG. 1 . 
     Torsion damper  24  further includes outer plurality  52  of springs disposed between cover plates  36  and  38 , and inner plurality  54  of springs disposed between cover plates  42  and  44 . Although the foregoing description and example figures describe a particular number and configuration of springs, the scope of the present invention is not limited to that number and/or configuration only, and broadly construed, alternatively can also include different numbers and/or configurations of springs. 
     Radial position of cover plate  36  is adjusted by pilot interface  56  defined by axially extending portion  58  of cover plate  36  and pilot surface  60  of hub  48 . By axial, we mean parallel to axis  11 . Unless stated otherwise, an axis in the discussion below is parallel to axis  11 . Radial position of flange  46  is adjusted by rivets  50  and hub  48 . That is, radial positions of cover plate  36  and flange  46  are controlled by hub  48 , which is in turn radially positioned by an input shaft (not shown) as described above. 
     Cover plates  42  and  44  include plurality  62  of outer spring windows, or cutouts, for receiving plurality  52  of outer springs and plurality  64  of inner spring windows, or cutouts, for receiving plurality  54  of inner springs. Radial position of cover plates  42  and  44  is adjusted by force of spring pluralities  52  and  54  engaged with window pluralities  62  and  64 . That is, radial position of cover plates  42  and  44  is not adjusted by a direct interface with hub  48 . 
     The following description is made with reference to  FIGS. 4 and 5 .  FIG. 4  is a simplified front view of torsion damper  24  shown in  FIG. 2  showing a portion of cover plates  42  and  44 , and flange  46 , for example.  FIG. 5  is a cross-sectional view of torsion damper  24  generally along line  5 - 5  in  FIG. 4 . Cover plates  42  and  44  each include central axis  94  parallel to damper axis  66  and passing through the center of bores  68  and  70 , respectively. Flange  46  includes a central axis  96  parallel to damper axis  66  and passing through the center of extruded cylinder  72 . 
     Cover plates  42  and  44  include respective outer diameters  74  and  76 . Flange  46  includes outer diameter  78  (shown as a dashed line in  FIG. 4 ).  FIG. 4  shows cover plates  42  and  44 , and flange  46  with central axes  94  and  96  aligned and coincident with damper axis  66 . However, as can be seen in  FIG. 4 , outer diameters  74 ,  76 , and  78  do not share a center point disposed along damper axis  66 . For example, offset axis  80  passing through the center of outer diameters  74  and  76  is disposed to the right of damper axis  66  and offset axis  82  passing through the center of outer diameter  78  is disposed to the left of damper axis  66 . By offset axis we mean an axis centered with respect to an outer diameter. 
     Blanks for cover plates  42  and  44  with outer diameters  74  and  76  have a center of mass CM 1  disposed along offset axis  80 . Material removal for central bores  68  and  70  adjusts the center of mass for cover plates  42  and  44 , respectively, because central bores  68  and  70  are not radially aligned with offset axis  80 . Likewise, the center of mass for a flange blank having outer diameter  78  prior to material removal for central bore  72  is disposed along offset axis  82 . After material removal for central bores  68 , and  70 , center of mass CM 2  for plates  42  and  44  is aligned with central axis  94 . After material removal for central bore  72 , center of mass CM 3  for flange  46  is aligned with central axis  96 . Thus, centers of mass disposed along offset axis  80  of cover plates  42  and  44  prior to material removal for central bores  68  and  70 , respectively, and center of mass disposed along offset axis  82  of flange  46  prior to material removal for central bore  72 , are radially displaced from respective centers of mass along central axes  94  and  96 , respectively, after material removal for central bores  68 ,  70 , and  72 . Alternately stated, the respective centers of mass for the cover plates and the flange are different before and after the formation of the respective center bores. 
     Material removed to create pluralities  64  of spring windows may also adjust the respective centers of mass. For example, the center of mass for cover plates  42  and  44  resulting from windows  64  (individually labeled  64 A) may be disposed along offset axis  80 . Likewise, the center of mass for flange  46  resulting from windows  64  (shown as dashed lines in  FIG. 4  and individually labeled  64 B) may be disposed along offset axis  82 . Plates  42 ,  44 , and/or  46  may include additional mass or material removal at positions  88  with a center of mass disposed along axis  90 , for example. 
     The following description is made with reference to  FIGS. 4-6 .  FIG. 6  is a simplified front view of torsion damper  24  with a portion of cover plates  42  and  44 , and flange  46 , shown displaced by force from plurality  54  of springs, for example. Spring force is indicated by arrows  92 . Spring force  92  urges cover plates  42  and  44  to the left and urges flange  46  to the right, as shown in  FIG. 6 . As a result, offset axes  80  and  82  for cover plates  42  and  44 , and flange  46 , respectively, move towards and are nearly coincident with damper axis  66 . Likewise, central axis  94  for cover plates  42  and  44  moves to the left, and central axis  96  for flange  46  moves to the right. That is, the springs urge central axis  94  to radially displace from central axis  96 . 
     Central axes  94  and  96  are in a fixed alignment. That is, repeated rotational acceleration and deceleration about damper axis  66  leaves central axes  94  and  96  in a consistent radial position relative to one another. The relative displacement between axes  94  and  96  may be limited, or fixed, by the configuration of torsion damper  24 . For example, contact between central bore  70  of cover plate  44  and extruded cylinder  72  of flange  46  may limit radial displacement of axes  94  and  96 . For example, force applied to the cover plates by springs  54  causes the cover plates to radially displace with respect to each other until central bore  70  of cover plate  44  and extruded cylinder  72  of flange  46  come into contact. Advantageously, this contact occurs at substantially the same respective points on the central bore and the cylinder, essentially fixing the alignment between the axes. 
       FIG. 7  is a cross-sectional view of a cover plate shown in  FIG. 4 , generally along line  7 - 7  in  FIG. 4 . Offset axes  80  and  82  are not coincident with respective central axes  94  and  96 . Cover plates  42  and  44  exhibit rotational imbalance when rotated about central axis  94 . Likewise, flange  46  exhibits rotational imbalance when rotated about central axis  96 . Cutouts  85  and/or attached mass elements  87  at location  88  unbalances plates  42 ,  44 , and/or  46 . Imbalance from offset centers of mass imparts a dynamic force to the flange and cover plates, and keeps central bore  70  and extruded cylinder  72  in contact when damper  24  is under rotation. 
     The disclosed plate designs introduce a consistent imbalance to torsion damper  24 . Force  92  of springs misaligns cover plates  42  and  44 , and flange  46  so that their centers of mass are radially offset from damper axis  66 . The imbalance is exaggerated by additional mass or mass removal at locations  88 . Because the imbalance is consistent, it can be corrected for in assembly  10  by attaching balance weight  102  to turbine  14  ( FIG. 1 ) for example. Furthermore, the disclosed plate designs improve measurement repeatability by maintaining the components in a consistent position when assembly  10  is rotated. 
     It should be understood that a present invention torsional damper is not limited to the number, size, shape, or configuration of components shown and that other numbers, sizes, shapes, or configurations of components are included in the spirit and scope of the claimed invention. It also should be understood that a present invention torsional damper is not limited to use in the torque converter shown and that a present invention torsional damper can be used in other types and configurations of torque transfer devices. 
     Of course, changes and modifications to the above examples of the invention should be readily apparent to those having ordinary skill in the art, without departing from the spirit or scope of the invention as claimed. Although the invention is described by reference to specific preferred and/or example embodiments, it is clear that variations can be made without departing from the scope or spirit of the invention as claimed.