Abstract:
A damper assembly for a marine vessel propulsion unit or a motor vehicle drive train is provided. The damper assembly includes a damper hub rotatably with respect to a center axis, a damper flange fixed for rotation on an outer surface of the damper hub, a cover plate coupled to the damper hub via the damper flange, an elastic element axially pressing against the cover plate, and a friction assembly axially fixed to the cover plate. The friction assembly supports the elastic element and maintains an orientation of the elastic element with respect to the cover plate during movement of a center axis of damper hub.

Description:
[0001]    This claims the benefit to U.S. Provisional Patent Application No. 62/030,976 filed on Jul. 30, 2014, which is hereby incorporated by reference herein. 
         [0002]    The present disclosure relates generally to damper assemblies and more specifically to damper assemblies for marine vessel propulsion units or motor vehicle drive trains. 
     
    
     BACKGROUND 
       [0003]    In marine vessel propulsion units, a rubber coupling damper is generally applied on a damper hub for connecting the damper hub to an engine crankshaft. Rubber coupling has no durability issue due to its excellent energy absorption for axial cycling from the drive train due the nature of rubber mass used. However, rubber coupling dampers are less capable of good NVH performance. 
         [0004]    U.S. Pat. No. 8,454,446 discloses a damper mechanism for a clutch that is provided with a friction generating mechanism contrived to generate a hysteresis torque using a frictional resistance in order to absorb and attenuate torsional vibrations effectively. The friction generating mechanism has a first friction washer, a second friction washer, and a third friction washer. 
         [0005]      FIG. 1  shows a conventional motor vehicle drive train damper assembly  10 . Damper assembly  10  includes a damper hub  12  for connection to a transmission shaft and a damper flange  14  fixed for rotation with damper hub  12  by a splined connection. Damper assembly  10  further includes a cover plate  16  and a retainer plate  18  fixed together by spacers  20 . An attachment element  22 , for example a clutch disc, is fixed to the retainer plate. Attachment element  22  is configured for connecting damper hub  12  to an engine via plates  16 ,  18  and springs  24  held in circumferentially extending spaces of plates  16 ,  18 . Plates  16 ,  18  are arranged to drive springs  24  during operation of damper assembly  10 . Damper flange  14  extends into circumferential spaces between springs  24  such that springs  24  are arranged to drive damper flange  14  during operation of damper assembly  10 , which in turn drives damper hub  12 . An idle damper  26  is provided between retainer plate  18  and damper flange  14  and an axial spring  28 , in the form of a diaphragm spring, is provided between damper flange  14  and cover plate  16 . A washer  30  is provided between axial spring  28  and damper flange  14 . Washer  30  is rotationally fixed to cover plate  16 , but is not axially fixed to cover plate  16 . 
       SUMMARY OF THE INVENTION 
       [0006]    Applying the conventional motor vehicle drive train damper assembly  10  to a marine vessel propulsion unit provides improved NVH performance, but excessive axial movements of the transmission input shaft during operation cause very high stress on axial spring  28  within damper assembly  10  due to axial cycling experienced by axial spring  28 , which has been shown to lead to cracking of axial spring  28 . Embodiments of the invention may reduce the axial cycling to an axial spring to zero or close to zero, which may keep the cycling stress as a possible to achieve intended durability with maximum possible spring energy allowed by the installation space. In addition to marine vessel propulsion units, embodiments of the damper assembly of the present invention may also be used in motor vehicle drive trains. 
         [0007]    A damper assembly for a marine vessel propulsion unit or a motor vehicle drive train is provided. The damper assembly includes a damper hub rotatably with respect to a center axis, a damper flange fixed for rotation on an outer surface of the damper hub, a cover plate coupled to the damper hub via the damper flange, an elastic element axially pressing against the cover plate, and a friction assembly axially fixed to the cover plate. The friction assembly supports the elastic element and maintains an orientation of the elastic element with respect to the cover plate during movement of a center axis of damper hub. 
         [0008]    A method of forming a damper assembly for a marine vessel propulsion unit or a motor vehicle drive train is also provided. The method includes fixing a cover plate, an elastic element axially pressing against the cover plate and a friction assembly axially together such that the friction assembly supports the elastic element and maintains an orientation of the elastic element with respect to the cover plate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention is described below by reference to the following drawings, in which: 
           [0010]      FIG. 1  shows a conventional damper assembly; 
           [0011]      FIG. 2  shows a damper assembly in accordance with an embodiment of the present invention; 
           [0012]      FIGS. 3   a  to  3   h  schematically illustrate the formation of a first washer and fixing of a cover plate, an elastic element and a friction assembly axially together; 
           [0013]      FIG. 4  shows a damper assembly in accordance with another embodiment of the present invention; and 
           [0014]      FIG. 5  shows a damper assembly in accordance with another further embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The present disclosure provides embodiments of damper assemblies with a friction package protected from axial cycling loads. This arrangement may advantageously improve durability by preventing axial cycling of the elastic element, e.g. a diaphragm spring, and improve performance by limiting the stackup and tolerance on a height of the spring. In a first embodiment, the spring is contained in a space formed by a cover plate on one side and a steel washer on the other side. The steel washer includes shoulders to prevent further compression of the spring via the contact thickness of the package, which prevents cycling of the diaphragm spring in the axial direction, and is expanded into slots in the cover plate so that the friction package is self-contained. A friction washer, which may be plastic, splined to the damper hub, is compressed between the spring and steel washer, and drivingly engaged with the flange by axial protrusions. 
         [0016]      FIG. 2  shows a damper assembly  40  in accordance with a first embodiment of the present invention. Damper assembly  40  includes a damper hub  42  for connection to a transmission shaft and a damper flange  44  fixed for rotation with damper hub  42  by a splined connection. Damper assembly  40  further includes a cover plate  46  and a retainer plate  48  fixed together by spacers. An attachment element, for example a clutch disc or a spring plate, is fixed to an outer radial portion of retainer plate  48  for connecting damper hub  42  to an engine via plates  46 ,  48  and springs  54  held in circumferentially extending spaces of plates  46 ,  48 . Plates  46 ,  48  are arranged to drive springs  54  during operation of damper assembly  40 . Damper flange  44  extends into circumferential spaces between springs  54  such that springs  54  are arranged to drive damper flange  44  during operation of damper assembly  40 , which in turn drives damper hub  42 . 
         [0017]    An idle damper  56  is provided between retainer plate  48  and damper flange  44 . Idle damper  56  includes a radially inner portion  62  contacting an outer radial surface of damper hub  42 , a radially outer portion  64  and a spring  66  held between portions  62 ,  64 . An axial spring  68  contacts an engine-side axial surface  70  of damper flange  44  and an axial surface of radially inner portion  62  of idle damper  56 . Axial spring  68 , which may be a diaphragm spring, is compressed to press idle damper  56  against retainer plate  48 . At radially outer portion  64 , idle damper  56  includes axially extending protrusions  72  extending past axial surface  70  into spaces formed in damper flange  44  such that protrusions  72  are drivingly engaged with flange  44 . 
         [0018]    Damper assembly  40  is also is provided with an elastic element  58 , in the form of an axial spring, e.g., a diaphragm spring, between damper flange  44  and cover plate  46 . A radially outer end of elastic element  58  contacts an engine-side axial surface  76  of cover plate  46 . A friction assembly  80  axially fixed to cover plate supports elastic element  58  and maintains an orientation of elastic element  58  with respect to cover plate  46  during movement of a center axis of damper hub  42 , about which damper hub  42  rotates during operation. As schematically shown in  FIG. 2 , when damper hub  42  is perfectly aligned, the center axis of damper hub  42  has an untilted orientation  90 . When a transmission shaft received inside of damper hub  42  is tilted axially, the center axis of damper hub  42  may have a tilted orientation  90 ′ that is angled with respect to untilted orientation  90 . Friction assembly  80  is provided to maintain an orientation of elastic element  58  with respect to cover plate  46  when the center axis of damper hub  42  has a tilted orientation  90 ′ to prevent elastic element  58  from being cycled, which can cause breakage. 
         [0019]    Friction assembly  80  includes a first washer  82  and a second washer  84 . First washer  82  is formed of metal, which in a preferred embodiment is steel, and second washer  84  is a friction washer forming a transmission-side axial friction surface  85  for contacting a radially inner end of elastic element  58 . In a preferred embodiment, friction washer  84  is formed of plastic; however, friction washer  84  may be formed of any material having a lower coefficient of friction than a coefficient of friction of the material forming damper flange  44 , which is generally steel. Axial friction surface  85  is formed on a radially extending annular plate portion  83  of friction washer  84 . 
         [0020]    Friction washer  84  includes a radially inner splined surface formed by axially extending splines  86  extending radially inward from an axially extending base portion  87  for mating with axially extending splines  88  formed on the outer radial surface of damper hub  42  for fixing friction washer  84  for rotation with damper hub  42 . Axially extending base portion  87  including an axial friction surface  93  for axially contacting damper flange  44  to minimize the friction transmitted to elastic element  58  from damper hub  42  and damper flange  44 . In order to prevent splines  88  of damper hub  42 , which are steel, from damaging the plastic splines  86  of friction washer  84 , splines  88  include a tapered outer radial surface  75 , which is angled with respect to the center axis of damper hub  42 . Friction washer  84  also includes axially and radially extending projections  89 , which are formed at an intersection of plate portion  83  and base portion  87 , for mating with spaces formed at the radially inner end of elastic element  58  such that elastic element  58  is mechanically connected for rotation with friction washer  84 . Friction washer  84  includes axially extending protrusions  91  extending past a transmission-side axial surface  71  of damper flange  44  into spaces formed in damper flange  44  such that protrusions  91  are drivingly engaged with flange  44 . 
         [0021]    First washer  82  includes a radially extending annular plate portion  92  axially between plate portion  83  of friction washer  84  and transmission-side axial surface  71  of damper flange  44 . First washer  82  further includes a plurality of axially extending tabs  94  axially extending from a radially outer end of plate portion  92  completely through corresponding slots  96  formed in cover plate  46 . Tabs  94  also extend through spaces formed in the radially outer end of elastic element  58 . As discussed further below with respect to  FIGS. 3   a  to  3   h , in this embodiment, tabs  94  include fingers  98  at an axially outer end thereof for axially fixing friction assembly  80  to cover plate  46 . Fingers  98  contact a transmission-side axial surface  81  of cover plate  46 , and along with shoulders  99  of tabs  94 , prevent axial movement between first washer  82  and cover plate  46 . 
         [0022]    If possible, a small gap G between plate portion  92  of first washer  82  and damper flange  44  is kept larger than zero (i.e., no contact between plate portion  92  of first washer  82  and damper flange  44  under axial loading of elastic element  58 ), such that surface  72  of washer  84  contacts surface  71  of flange  44  to minimize the friction transmitted from flange  44  to elastic element  58 . In this case, the cycling amplitude to elastic element  58  is zero. With a zero cycling amplitude, the mean stress level may be increased accordingly for the same durability requirement and the elastic energy of elastic element  58  may be increased with given installation limitation. 
         [0023]      FIGS. 3   a  to  3   h  schematically illustrate the formation of first washer  82  and the fixing of cover plate  46 , elastic element  58  and friction assembly  80  axially together such that friction assembly  80  supports elastic element  58  and maintains an orientation of elastic element  58  with respect to cover plate  46 . 
         [0024]      FIG. 3   a  shows a partial plan view of first washer  82  in a flat orientation, before tabs  94  are bent to extend axially away from annular plate portion  92 . In a preferred embodiment, first washer  82  is a flat piece stamped out from sheet metal. In this exemplary embodiment, first washer  82  includes four tabs  94 , each being spaced from the circumferentially adjacent tabs by an angle a of 90 degrees. As shown in  FIG. 3   a , each tab  94  includes two fingers  98  at the outer end thereof that are separated from each other by a gap. Outer lateral edges of fingers  98  are separated from each other by a distance w. Each tab  94  also includes two shoulders  99  positioned between plate portion  92  and fingers  98 . Outer lateral edges of shoulders are separated from each other by a distance s, which is greater than distance w. 
         [0025]      FIG. 3   b  shows a partial plan view of first washer  82  after tabs  94  are bent to extend axially away from annular plate portion  92 . In a preferred embodiment, tabs  94  are bent to extend at an angle of approximately ninety degrees with to an axial surface  100  of plate portion  92 . As shown in  FIG. 3   b , shoulders  99  extend laterally wider than fingers  98  at this point in the formation process.  FIG. 3   c  shows a cross-sectional view of first washer  82  along T-T in  FIG. 3   b . As shown in  FIG. 3   c , tabs  94  and plate portion  92  are of a same uniform thickness t. 
         [0026]      FIG. 3   d  shows a partial plan view of cover plate  46 . Slots  96  in cover plate  46  are formed to have a width d that is greater than or equal to distance w and less than distance s. 
         [0027]      FIG. 3   e  shows a cross-sectional side view of cover plate  46 , elastic element  58  and friction assembly  80  assembled as a unit before friction assembly  80  is axially fixed to cover plate  46 . Elastic element  58  and plate portion  83  of friction washer  84  are sandwiched axially between plate portion  92  of first washer  82  and cover plate  46  such that axial surface  100  of plate portion  92  contacts an axial surface  102  of plate portion  83 , the radially inner end of elastic element  58  contacts axial surface  85  of plate portion  83  and the radially outer end of elastic element contacts axial surface  76  of cover plate  46 . Tabs  94  of first washer  82 , specifically fingers  98 , extend through holes  96  in cover plate  46  and shoulders  99  of tabs  94  contact axial surface  76  of cover plate  46 . 
         [0028]      FIGS. 3   f  to  3   h  schematically illustrate a sequence of fixing tool  104  being applied to one of tabs  94  to axially fix friction assembly  80  to cover plate  46 . Fixing tool  104  is forced in the axial direction Dl in between fingers  98  such that fingers  98  are forced laterally away from each other such that lateral edges  106  of fingers  98  are forced laterally outward to contact axial surface  81  of cover plate  46  such that cover plate  46  is wedged between fingers  98  and shoulders  99  to axially fix first washer  82  to cover plate  46 , and thereby axially fix friction assembly  80  to cover plate  46 .  FIG. 3   f  shows fixing tool  104  before it contacts tab  94 .  FIG. 3   g  shows fixing tool  104  as fixing tool  104  initially contacts tab  94 , with a tip of fixing tool  104  extending into a gap between fingers  98 .  FIG. 3   h  shows fixing tool  104  after fixing tool  104  has axially fixed first washer  82  to cover plate  46  by causing lateral edges  106  to extend outward and contact cover plate  46 . As shown in  FIG. 3   h , after applying fixing tool  104  to friction assembly  80 , lateral edges  106  of tab  94  are spaced from each other by a distance w′ that is greater than the width d of holes  96 . 
         [0029]    The height of shoulders  99  of tabs  94  do not change under axial loading of damper flange  44 , which follows the axial motion of hub  42  caused by the excessive axial input shaft movements. This may ensure a constant space for the friction elements (i.e., elastic element  58  and friction washer  84 ) for all loading conditions. 
         [0030]      FIG. 4  shows a damper assembly in accordance with a further embodiment of the present invention. Damper assembly  110  is formed in a similar manner to damper assembly  40 , with the differences being that friction washer  84  and elastic element  58  are replaced by a friction washer  112  and an elastic element  114 . 
         [0031]    Damper assembly  110  is also is provided elastic element  114 , in the form of an axial spring, e.g., a diaphragm spring, on a transmission side of cover plate  46 . More specifically, elastic element  114  is held inside of a friction assembly  116  axially fixed to cover plate  46  such that friction assembly  116  maintains an orientation of elastic element  114  with respect to cover plate  46  during movement of a center axis of damper hub  42  (i.e., when the center axis of damper hub  42  has an untilted orientation). Friction assembly  116  is provided to maintain an orientation of elastic element with respect to cover plate  46  when the center axis of damper hub  42  has a tilted orientation to prevent elastic element  114  from being damaged. 
         [0032]    Friction assembly  116  includes first washer  82  and a second washer in the form of friction washer  112 . In a preferred embodiment, friction washer  112  is formed of plastic; however, friction washer  112  may be formed of any material having a lower coefficient of friction than a coefficient of friction of the material forming damper flange  44 , which is generally steel. Friction washer  112  includes an axial friction surface  119  for contacting a radially inner end of elastic element  114 , which is positioned axially between washers  82 ,  112 . Friction washer  112  also includes an axial friction surface  120  for axially contacting damper flange  44 , minimizing the friction transmitted from flange  44  to elastic element  114 . 
         [0033]    Friction washer  112  includes a radially inner splined surface formed by axially extending splines  121  extending radially inward from an axially extending base portion  122  for mating with axially extending splines  88  formed on the outer radial surface of damper hub  42  for fixing friction washer  112  for rotation with damper hub  42 . In order to prevent splines  88  of damper hub  42 , which are steel, from damaging the plastic splines  121  of friction washer  112 , splines  88  include a tapered outer radial surface  75 , which is angled with respect to the center axis of damper hub  42 . Friction washer  112  further includes a radially extending plate portion  123  for contacting axial surface  76  of cover plate  46 . 
         [0034]      FIG. 5  shows a damper assembly  140  in accordance with another further embodiment of the present invention. Damper assembly  140  is formed in a similar manner to damper assembly  40 , with one difference being a friction assembly  180  and an elastic element  158  being fixed to an outer axial surface (i.e., transmission-side axial surface) of a cover plate  146 . 
         [0035]    Damper assembly  140  includes a damper hub  142  for connection to a transmission shaft and a damper flange  144  fixed for rotation with damper hub  142  by a splined connection. Damper assembly  140  further includes a cover plate  146  and a retainer plate  148  fixed together by spacers  150 . An attachment element, for example a clutch disc or a spring plate, may be fixed to an outer radial portion of retainer plate  148  for connecting damper hub  142  to an engine via plates  146 ,  148  and springs held in circumferentially extending spaces of plates  146 ,  148 . Similar to the embodiment described in  FIG. 2 , plates  146 ,  148  are arranged to drive springs held in circumferentially extending spaces of plates  146 ,  148  during operation of damper assembly  140 . 
         [0036]    Additionally, an idle damper  156  and an axial spring  68  are provided between damper flange  144  and retainer plate  148  in essentially the same manner as described above with respect to  FIG. 2 . 
         [0037]    Damper assembly  140  is also is provided with an elastic element  158 , in the form of an axial spring, e.g., a diaphragm spring, on a transmission side of cover plate  146 . More specifically, a radially outer end of elastic element  158  contacts a transmission-side axial surface  181  of cover plate  146 . A friction assembly  180  axially fixed to cover plate  146  supports elastic element  158  and maintains an orientation of elastic element  158  with respect to cover plate  146  during movement of a center axis of damper hub  142  (i.e., when the center axis of damper hub  142  has an untilted orientation). Friction assembly  180  is provided to maintain an orientation of elastic element with respect to cover plate  146  when the center axis of damper hub  142  has a tilted orientation to prevent elastic element  158  from being damaged. 
         [0038]    Friction assembly  180  includes a first washer  182  and a second washer  184 . First washer  182  is formed of metal, which in a preferred embodiment is steel, and second washer  184  is a friction washer forming an engine-side axial friction surface  185  for contacting a radially inner end of elastic element  158 . In a preferred embodiment, friction washer  184  is formed of plastic; however, friction washer  184  may be formed of any material having a lower coefficient of friction than a coefficient of friction of the material forming damper flange  144 , which is generally steel. Axial friction surface  185  is formed on a radially extending annular plate portion  183  of friction washer  184 . 
         [0039]    Friction washer  184  includes a radially inner splined surface formed by axially extending splines  186  extending radially inward from an axially extending base portion  187  for mating with axially extending splines  188  formed on the outer radial surface of damper hub  142  for fixing friction washer  184  for rotation with damper hub  142 . Axially extending base portion  187  includes an axial friction surface  193  for axially contacting damper flange  144  to minimize the friction transmitted to elastic element  158  from damper hub  142  and damper flange  144 . In order to prevent splines  188  of damper hub  142 , which are steel, from damaging the plastic splines  186  of friction washer  184 , splines  188  include a tapered outer radial surface  175 , which is angled with respect to the center axis of damper hub  142 . Friction washer  184  further includes an axial projection  189  on an outer edge thereof for supporting a radially inner end of first washer  182 . 
         [0040]    In this embodiment, first washer  182  is formed by an annular plate that is axially fixed to cover plate  146  by rivets  194  extending axially through corresponding holes formed in first washer  182  and cover plate  146  and corresponding spaces formed in elastic element  158 . Accordingly, this embodiment, friction assembly  180  is axially fixed to cover plate  146  by rivets  194 . 
         [0041]    Damper assemblies  40 ,  110 ,  140  provide a main damper friction package that may advantageously reduce the axial cycling to axial springs  58 ,  158  to zero or close to zero, which may keep the cycling stress as low as design possible to achieve intended durability with maximum possible spring energy allowed by the installation space. 
         [0042]    In the preceding specification, the invention has been described with reference to specific exemplary embodiments and examples thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative manner rather than a restrictive sense.