Abstract:
A torsional vibration damper includes front and rear hub members with an inertia mass between the two hub members. Annular elastomeric rings are positioned between the front and rear hub members and the inertia mass holding the inertia mass. Fasteners extend through the front hub member, the inertia mass, and fixed to the rear hub member. A clearance between the fastener and the inertia mass allows relative motion to absorb torsional vibration.

Description:
FIELD OF THE INVENTION 
     The invention relates to torsional vibration dampers and, in particular, to vibration dampers adapted to be mounted on rotatable shafts such as the crankshaft of an internal combustion engine. 
     BACKGROUND OF THE INVENTION 
     Torsional vibration dampers are employed extensively in internal combustion engines to reduce torsional vibrations delivered to rotatable shafts. The torsional vibrations may have a considerable amplitude and, if not abated, can potentially damage gears or similar structures attached to the rotatable shaft and cause fatigue failure of the rotatable shaft. Torsional vibration dampers absorb vibration and, to a certain extent, reduce the amplitude of the vibrations by converting the vibrational energy to thermal energy as a result of the damping action. The absorption of the vibrational energy lowers the strength requirements of the rotatable shaft and, therefore, lowers the required weight of the shaft. The torsional vibration damper also has a direct effect on inhibiting vibration of nearby components of the internal combustion engine which would be affected by the vibration. 
     Virtually all motor vehicles with internal combustion engines incorporate a “serpentine” drive belt system consisting of a single endless drive belt and a series of pulleys. The pulleys derive power from the endless drive belt and operate to drive the various vehicle accessories such as the engine fan, power steering pump, air pumps, air conditioning unit, and the alternator. The endless drive belt that drives each of these pulleys is driven by a drive pulley connected to the crankshaft of the internal combustion engine. To reduce the transfer of vibrations between the crankshaft and the serpentine drive belt system, the drive pulley may comprise a torsional vibration damper that functions to absorb vibration and reduce the amplitude or magnitude of the angular vibrations delivered by the crankshaft. 
     With torsional vibration dampers it is generally desirable to maximize the inertia within the space permitted. Typically, torsional vibration dampers rely on an annular inertia member that rests on an elastomeric ring compressed between the inertia ring and a hub. With such a design, if one is to replace the rubber component, one must remove the damper from the crankshaft of the engine. This is relatively labor intensive. Further, with this design, assembly is problematic. The elastomer must be compressed during assembly of the damper. This requires special equipment which, in turn, increases the cost of the damper. 
     SUMMARY OF THE INVENTION 
     The present invention is premised on the realization that a torsional vibration damper with a large inertia in a minimal space can be formed by having an inertia member that extends approximately from the central opening of hub of the damper to the perimeter of the damping/absorption. Separate front and rear hub members are fastened together with the inertia mass held between the hub members. Annular elastomeric rings are located between the hub members and the inertia mass to provide the vibration damping. Fasteners extend through the hub members and the inertia member with a clearance provided between the inertia mass and the fasteners. This allows movement of the inertia mass relative to the hub members. 
     This design increases the inertia mass within the space provided, and allows the elastomeric members to be replaced without removing the entire damper. Further, when this damper is initially assembled, no special equipment is required to attach the inertia mass to the hub member because the elastomeric members are compressed by simply tightening the fasteners. 
     The objects and advantages of the present invention will be further appreciated in light of the following detailed description and drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded perspective view of the present invention; 
         FIG. 2  is a cross sectional view of the present invention; 
         FIG. 3  is a cross sectional view of an alternate embodiment of the present invention partially broken away; and 
         FIG. 4  is a cross sectional view of a second alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     As shown in  FIGS. 1 and 2 , damper  10  includes a first hub member  12 , a second hub member  14 , an inertia mass  16 , and first and second compressible or elastomeric rings  18  and  20 . This damper  10  is held together with shoulder bolts  22  and attaches to crankshaft  24 . 
     The first hub member  12  includes a first central hub  26  having a first central opening  28  with spokes  30  extending radially outwardly from hub  26  to an annular ring  32 . There are a series of holes or openings  34  between spokes  30 . 
     Likewise, second hub member  14  includes a second hub  36  with a second central opening  38 . The hub member  14  further includes spokes  40  that extend radially outward from the second hub  36  and extend to an outer annular ring  42 . Internally threaded holes  44  extend through the spokes  40 . As shown, the second hub  36  of second hub member  14  is axially elongated to provide an engaging surface  27  with a shaft (not shown). 
     In turn, the inertia mass  16  includes a central opening  46  that is slightly larger than the first and second central openings  28  and  38 , respectively. A central annular mass  48  extends from the central opening  46  peripherally outward to a peripheral annular ring  50 . The thickness and size of annular ring  50  can be established to create the necessary mass for the inertia mass  16 . 
     Extended from the central annular mass  48  are rounded trapezoidal protrusions  52 . These protrusions  52  extend from first and second sides  54  and  56  of inertia mass  16  and occupy spaces  57  and  59  between spokes  30  and  40 , respectively. These protrusions  52  increase the inertia of the ring without increasing its outer peripheral dimension. Between the protrusions  52  and annular mass  48  of inertia mass  16  are narrow portions  58  which are slightly larger than the size of spokes  30  and  40 , permitting movement of the inertia mass  16  relative to the first and second hub members  12  and  14 . Likewise, these narrow portions  58  include holes  60  which are slightly larger than the holes  34  and  44  in spokes  30  and  40 , again, to permit relative movement of the inertia mass  16  relative to the first and second hub members  12 , 14  as is discussed hereinafter. 
     The inertia mass  16  includes a narrowed annular portion  65 , which accommodates the elastomeric rings  18  and  20 . As shown, the first and second elastomeric rings  18  and  20  are located or held in compression between ring  32  and ring  42 , and the first and second sides  54  and  56  of the inertia mass  16  at the annular portions  65 . Annular portions  65  narrow from the central annular mass  48  to the peripheral annular ring  50 . 
     The bolts  22  include a head portion  66 , a shaft  68  and a threaded portion  70 , which is narrower than shaft  68 , leaving a shoulder  72 . The bolts  22  extend through the holes  34  in the first hub member  12 , through the holes  60  in the inertia mass, and are threaded into internally threaded holes  44  in the second hub member  14  with the shoulder  72  engaging the interior side of spoke  40 . The length of the shaft  68  is designed so that when nut  22  is fully threaded into hole  44 , the elastomeric rings  18  and  20  are compressed between the rings  32  and  42 , and the narrow ring portion  65  of inertia mass  16 , but no part of the first or second hub members  12 , 14  is in contact with the inertia mass  16 . The diameter of shaft  68  is equal to the inner diameter of the holes  34  in spokes  30 , but is narrower than the holes  60  in the inertia mass  16 . The size differential is a matter of choice, but is generally designed to allow for 1 to 3 degrees of relative motion between the inertia mass and the first and second hub members  12  and  14 . 
     The elastomeric rings  18  and  20  are generally identical and are formed from any desired elastomeric material that is suitable for automotive applications. Generally, SBR, EPDM or Vamac is suitable for rings  18  and  20 . The hardness of the rings is chosen to meet the end use requirements of the damper  10 . 
     This product can be assembled using an assembly fixture with locators to properly position the first and second hub members. The assembled damper can be fixed to the crankshaft in any manner, such as press fitting, fasteners, or the like. This assembly method is very simple and does not require any special apparatus to compress the elastomeric vibration absorbing material used in the damper  10 , significantly reducing the cost of the damper. Further, if the elastomeric member must be removed, the hub member  14  does not have to be removed from the crankshaft, significantly reducing the cost of repairing a damper. 
     The embodiments shown in the present invention can obviously be modified. For example, the outer surface of the inertia mass  16  can be configured to drive a serpentine belt, as desired. Further, the shoulder bolts  22  can be replaced by standard bolts with sleeves. 
     An alternate embodiment of the present invention in which the second hub member  14  is eliminated is shown in  FIG. 3 . In this embodiment, damper  80  is fixed to a rotating plate  82 , such as the outer surface of a viscous damper. The hub member  84  includes a hub  86  with spokes  88  and ring  90 , which presses elastomeric ring  92  against the inertia mass  96 , which, in turn, forces the inertia mass  96  against the second elastomeric ring  98  into compression between the inertia mass  96  and the plate  82 . Shoulder bolts  100  screw into internally threaded holes  104  of plate  82  with the shoulders  106  engaging the plate  82 , stopping further movement. This provides space  109  between the inertia mass  96  and the plate  82  to permit relative movement. Spacing is also provided between shoulder bolts  100  and the inertia mass  96 , to, again, provide for 1 to 3 degrees relative movement of the inertia mass relative to the hub. This embodiment has the same advantages as the embodiment shown in  FIGS. 1 and 2 , and allows the invention to be attached, for example, to a viscous damper. 
       FIG. 4  shows an alternate embodiment in which the first hub  112  contacts the second hub  114 . In this embodiment, the inertia mass  118  extends from the second hub  114  outwardly with a slight clearance between the second hub and the inertia mass. Thus, the hubs establish the desired separation of the hub members  112  and  114  from the inertia mass  118 , as well as the compression of rings  122  and  124 . 
     Each of these embodiments provide the advantages of the present invention, including ease of assembly and ease of repair, and with the savings and costs associated therewith. 
     This has been a description of the present invention along with the preferred method of practicing the present invention. However, the invention itself should only be defined by the appended claims.