Abstract:
A pendulum damper fixed to a rotating element of an engine comprises a pendulum anchor, a pendulum, and a flexible metal strap attaching the pendulum and pendulum anchor. The strap is wound around the pendulum and pendulum anchor to define a bifilar pendulum. A pendulum clamp is attached to the pendulum such that part of the strap is captured between the pendulum clamp and the pendulum. A pendulum anchor clamp is attached to the pendulum anchor such that a portion of the strap is captured between the pendulum anchor clamp and the pendulum anchor. The pendulum includes a pendulum anchor-facing, flexible strap-supporting cam surface. The pendulum anchor includes a pendulum-facing, flexible strap-supporting cam surface. The surfaces of the pendulum and the pendulum anchor that face each other are mutually conjugant so that at all positions of normal pendulum motion there is only a small running clearance between the two surfaces.

Description:
TECHNICAL FIELD 
       [0001]    The disclosed inventive concept relates generally to dampers to reduce torsional vibration in an internal combustion engine. More particularly, the disclosed inventive concept relates to pendulum dampers mounted by straps to the engine flywheel. 
       BACKGROUND OF THE INVENTION 
       [0002]    Torsional vibration in the internal combustion engine is a well-known problem. This vibration is the consequence of a variation in the crankshaft speed of rotation, driven by fluctuations in the delivery of torque from the pistons to the crankshaft. The firing frequency of the engine is usually the largest constituent of the crankshaft torsional vibration. 
         [0003]    One response to torsional vibration in the internal combustion engine has been the provision of vibration dampers. A common choice of vibration damper is the pendulum damper. This type of damper has been used in aircraft engines and, more recently, has been used in the torque converters of production automotive engines. The pendulum damper is thus well known for suppressing engine vibrations. This suppression is accomplished by tuning the pendulum to resonate at the engine firing frequency. In particular, pendulum dampers have been employed to balance or cancel out undesirable order vibrations of an engine. In these cases, the crankshaft is connected to the pendulum mass by rollers that in different ones of the references move in circular, cycloidal, or other paths in an attempt to keep the pendulums&#39; resonant frequency in accordance with the engine&#39;s firing frequency at all engine speeds. 
         [0004]    Known pendulum dampers are designed to prevent mechanical damage to the engine by preventing swing amplitudes of the pendulum masses beyond their mechanical limits or capacity. In these known dampers the pendulum masses at low amplitude swing angles almost completely cancel engine vibrations by tracking of the rollers along a path which generates approximately tautochronic motion of the pendulums. At higher or greater amplitudes, these arrangements provide a method of automatically detuning the pendulums whereby they progressively become less and less tuned to the excitation frequency of the crankshaft. This results in a progressive decrease in the response of the pendulum to the vibrational impulses, which limits the swing amplitude at higher torsional vibration excitation levels to maintain the pendulum mass within the mechanical limits of its swing angle capacity. 
         [0005]    While pendulum dampers have proven effective at reducing torsional vibration in the internal combustion engine, known pendulum dampers do not provide a perfect solution to the vibration problem. Of particular concern is the fact that the placement of the rollers is generally limited to lubricated environments. However, placement of the rollers in a non-lubricated environment such as on the flywheel of a dry clutch may result in early failure and thus raises durability concerns. 
         [0006]    As in so many areas of vehicle technology there is always room for improvement related to the systems and methods to reduce the amount of torsional vibration produced by the internal combustion engine. 
       SUMMARY OF THE INVENTION 
       [0007]    The disclosed inventive concept overcomes the problems associated with known approaches to reducing torsional vibrations generated in operating internal combustion engines. The disclosed inventive concept accomplishes this step by providing a pendulum damper for an internal combustion engine. The damper is fixed to a rotating element such as the engine&#39;s flywheel. 
         [0008]    The pendulum damper of the disclosed inventive concept includes a pendulum having first and second ends and a pendulum anchor fixedly attached to the rotating element. The pendulum anchor also has first and second ends. 
         [0009]    A flexible strap is wound around the pendulum and the pendulum anchor such that the strap connects the first end of the pendulum to the first end of the pendulum anchor and connects the second end of the pendulum to the second end of the pendulum anchor. The strap is composed of any of a variety of flexible materials appropriate for such an application, including stainless steel. Preferably the flexible strap is formed from a plurality of layered straps. This arrangement defines a bifilar pendulum damper. 
         [0010]    A pendulum clamp is attached to the pendulum by mechanical fasteners such that a portion of the flexible strap is captured between the pendulum clamp and the pendulum. In the same manner a pendulum anchor clamp is attached to the pendulum anchor by mechanical fasteners such that a portion of the flexible strap is captured between the pendulum anchor clamp and the pendulum anchor. 
         [0011]    The pendulum includes a pendulum anchor-facing surface having active regions that define flexible strap-supporting cam surfaces. In the same way the pendulum anchor includes a pendulum-facing surface having active regions that define flexible strap-supporting cam surfaces. 
         [0012]    The disclosed pendulum damper may be tuned to reduce torsional vibrations of different orders by adjusting the cam surface configurations to change the lengths of the actively flexing portions of the flexible strap. The pendulum damper disclosed herein may be used in a non-lubricated environment. Thus the disclosed pendulum damper offers several advantages over known roller systems by providing better durability and a reduction in material, manufacturing and assembly costs. 
         [0013]    The above advantages and other advantages and features will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a more complete understanding of this invention, reference should now be made to the embodiments illustrated in greater detail in the accompanying drawings and described below by way of examples of the invention wherein: 
           [0015]      FIG. 1  is an end view of a bifilar pendulum damper constructed according to the disclosed inventive concept assembled to an engine flywheel; 
           [0016]      FIG. 2  is an enlarged view of the bifilar pendulum damper shown in  FIG. 1 ; and 
           [0017]      FIG. 3  is a cross-sectional view taken on a plane indicated by and viewed in the direction of line  3 - 3  of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    In the following figures, the same reference numerals will be used to refer to the same components. In the following description, various operating parameters and components are described for different constructed embodiments. These specific parameters and components are included as examples and are not meant to be limiting. 
         [0019]    An assembly for dampening torsional vibration according to the disclosed inventive concept, generally illustrated as  10 , is shown in  FIG. 1 , which illustrates an end view of the assembly  10 , and  FIG. 2 , which illustrates an enlarged view of the assembly  10 . The assembly  10  includes at least one bifilar pendulum damper assembly  12  fastened to an automotive engine flywheel  14  with the engine flywheel having an axial direction  16  (shown in  FIG. 3 ). The bifilar pendulum damper assembly  12  is shown in greater detail in  FIG. 2 . 
         [0020]    It is to be understood that while a single bifilar pendulum damper assembly  12  is shown attached to the engine flywheel  14  preferably four such assemblies would be attached to the engine flywheel  14 , although other numbers of assemblies such as three and five may be possible depending on the number of engine cylinders and other variables. By way of preferred example, by placing one bifilar pendulum damper assembly  12  on each quadrant of the engine flywheel  14  a turning order of 1.5 could be achieved to correspond to the firing frequency of a three cylinder engine. 
         [0021]    The bifilar pendulum damper assembly  12  basically comprises a fixed portion and a movable portion. The fixed portion is a pendulum anchor  18  while the movable portion is a pendulum  20 . The pendulum anchor  18  is fixedly attached to the engine flywheel  14 . A plurality of mounting bores  22 ,  22 ,′ and  22 ″ are formed in the pendulum anchor  18  although a greater or lesser number of bores may be formed. A like number of fasteners (fasteners  24 ,  24 ′, and  24 ″, shown in  FIG. 1 ) fix the pendulum anchor  18  to the engine flywheel  14 . Attachment of the pendulum anchor  18  to the engine flywheel  14  may be controlled by use of dowels or similar location tools to more precisely control the actual location of the pendulum anchor  18  relative to the engine flywheel  14 . 
         [0022]    The pendulum  20  is attached to the pendulum anchor  18  by a flexible strap  26 . The flexible strap  26  may be formed from any of a variety of suitable materials which may include, but not be limited to, stainless steel shim stock. The shim stock would preferably be wound in multiple layers to form the flexible strap  26  thereby achieving the desired tensile strength. The shim stock forming the flexible strap  26  may be of any suitable thickness but in any event must be thin enough so that it does not undergo excessive bending stress from wrapping and flexing during engine operation. 
         [0023]    The flexible strap  26  includes two free ends including a first end  28  that is slotted into a saw cut  30  formed in the pendulum anchor  18 . A pin or set screw  32  anchors the end  28  within the saw cut  30 . On assembly, once the end  28  of the flexible strap  26  is positioned within the saw cut  30  and the pin or set screw  32  is adjusted so as to hold the end  28  in place, the flexible strap  26  is then wrapped around the pendulum anchor  18  and the pendulum  20  multiple times until the desired number of wraps (and thus the desired tensile strength) is achieved. The pendulum  20  and the pendulum anchor  18  may be held in place relative to each other during the wrapping of the flexible strap  26  by mounting both pieces in a fixture that precisely locates and holds the pieces by engaging dowels or other fasteners into holes  22 ,  22 ′, and  22 ″ in the pendulum anchor  18  and holes  24  and  24 ′ in the pendulum  20 . 
         [0024]    Once the flexible strap  26  has been wrapped as desired, it is held in tension while fastener holes are formed through an appropriate process that would not result in excessive weakening of the flexible strap  26  in the areas adjacent to the fastener holes. Particularly, fastener holes  34 ,  34 ′,  34 ″, and  34 ″′ are formed through the area of the flexible strap  26  adjacent to the pendulum anchor  18  while fastener holes  36 ,  36 ′,  36 ″, and  36 ″′ are formed through the area of the flexible strap  26  adjacent to the pendulum  20 . 
         [0025]    Following formation of the fastener holes  34 ,  34 ′,  34 ″, and  34 ″′, a pendulum anchor clamp  38  is positioned so that fasteners  40 ,  40 ′,  40 ″, and  40 ″′ are located through the fastener holes  34 ,  34 ′,  34 ″, and  34 ″′ to thereby fasten the pendulum anchor clamp  38  to the pendulum anchor  18 , capturing therebetween a portion of the flexible strap  26 . Similarly, following formation of the fastener holes  36 ,  36 ′,  36 ″, and  36 ″′, a pendulum clamp  42  is positioned so that fasteners  44 ,  44 ′,  44 ″, and  44 ″′ are located through the fastener holes  36 ,  36 ′,  36 ″, and  36 ″′ to thereby fasten the pendulum clamp  42  to the pendulum  20 , capturing therebetween a portion of the flexible strap  26 . Excess shim stock at the second end  31  would then be removed. 
         [0026]    It should be noted that at the end holes  34 ,  34 ′″,  36 , and  36 ′″ where the flexible strap  26  transitions from being clamped between the pendulum  20  and the pendulum clamp  42 , and between the pendulum anchor  18  and the pendulum anchor clamp  38 , material has been removed from the pendulum  20 , the pendulum clamp  42 , the pendulum anchor  18  and the pendulum anchor clamp  38  at the surfaces that mate the flexible strap  26  so that most of the clamping loads generated by the fasteners  40 ,  40 ′″,  44 , and  44 ′″ are transferred to the portion of the flexible strap  26  located between the flexing portion between the pendulum  20  and the pendulum anchor  18  that has not been weakened by the formation of holes  34 ,  34 ′″,  36 , and  36 ′″. The clamping load on these portions of the flexible strap  26  will generate friction between the flexible strap  26  and the pendulum  20 , the pendulum clamp  42 , the pendulum anchor  18 , and the pendulum anchor clamp  38  so that the tensile load carried by the flexing portions of the flexible strap  26  will not be transferred to the portion of the flexible strap  26  that has been weakened by the formation of holes  34 ,  34 ′″,  36 , and  36 ′″. 
         [0027]    The pendulum anchor  18  includes an active region in the form of a pendulum-facing surface  48 . A first shaped curve  50  forms a first cam surface while a second shaped curve  52  forms a second cam surface. The pendulum-facing surface  48  further includes a series of peaks  54 ,  54 ′, and  54 ″ and valleys  56  and  56 ′. 
         [0028]    The pendulum  20  includes an active region in the form of a pendulum anchor-facing surface  58 . A first shaped curve  60  forms a first cam surface while a second shaped curve  62  forms a second cam surface. The pendulum-facing surface  58  further includes a series of peaks  64 ,  64 ′ and  64 ″ and valleys  66  and  66 ′. Elastomeric bumpers  68  and  68 ′ are provided adjacent the peaks  64  and  64 ″ respectively. The elastomeric bumpers  68  and  68 ′ are provided to reduce the impact of metal to metal contact between the pendulum anchor  18  and the pendulum at both ends of the swinging of the pendulum  20  relative to the pendulum anchor  18 . 
         [0029]    It is to be understood that the shapes of the pendulum-facing surface  48  of the pendulum anchor  18  and the pendulum anchor-facing surface  58  of the pendulum  20  are shown in suggested forms that are not intended as being limiting. Rather, the surface configurations are contoured such that the cam surfaces provide effective wrapping and unwrapping surfaces for the flexible strap  26 , while the peaks and valleys of the pendulum  20  and the pendulum anchor  18  are configured to be mutually conjugant. At all positions of the pendulum&#39;s swing relative to the pendulum anchor  18  there is only a small running clearance between the surface  48  of the pendulum anchor  18  and the surface  58  of the pendulum  20 . This conjugant relationship between the two surfaces ensures that the pendulum motion cannot deviate from its prescribed path, the flexible strap  26  will never see any compressive load that could distort it, and the pendulum  20  cannot impact against the pendulum anchor  18  at any location except at the elastomeric bumpers  69  and  68 ′. Specifically, and as shown in  FIG. 1 , the position of the pendulum  20  relative to the pendulum anchor  18  is shown at the middle of its allocated travel between the ends of the swing where the elastomeric bumpers  68  and  68 ′ would make contact against the pendulum anchor  18 . 
         [0030]    However, in operation, the pendulum  20  would swing to one side or the other relative to the pendulum anchor  18  as illustrated in broken lines in  FIG. 3 . By moving toward the right of center relative to the pendulum anchor  18  as depicted by the broken lines the flexible strap  26  has wrapped around the first shaped curve  50  of the pendulum anchor  18  and the second shaped curve  62  of the pendulum  20  while at the same time the flexible strap  26  has unwrapped around the second shaped curve  52  of the pendulum anchor  28  and the first shaped curve  60  of the pendulum  20 . 
         [0031]    Thus the cam surfaces are contoured so that the unwrapping end of the flexible strap  26  experiences a constant or a progressively decreasing radius while the wrapping end experiences a constant or a progressively increasing radius. In this way the lengths of the actively flexing strap  26  between the pendulum  20  and the pendulum anchor  18  remain constant or decrease as the angle of the swing of the pendulum  20  increases. This geometry will allow the pendulum resonance frequency at high amplitude to be forced sufficiently high so that the pendulum  20  will be less responsive to receiving additional energy from crankshaft vibration before the elastomeric bumpers  68  and  68 ′ attached to pendulum anchor-facing surface  58  of the pendulum  20  come into contact with the pendulum-facing surface  48  of the pendulum anchor  18 . 
         [0032]    The bifilar pendulum damper assembly  12  of the disclosed inventive concept may be employed in a lubricant-free environment. However, this environment should be free from dirt or debris. 
         [0033]    One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the true spirit and fair scope of the invention as defined by the following claims.