Abstract:
Radial vibration dampers (RVD&#39;s) press-fittable to a shaft and shaft systems incorporating RVD&#39;s are disclosed herein. The RVD&#39;s include a first inertia member and a second inertia member fixedly connected to one another to define an annular channel having a radially facing, open side and a spring damper material seated in the annular chamber and axially compressed between the two inertia members. The spring damper material has a compressible portion protruding from the radially facing, open side so that, when the compressible portion is compressed against a shaft, the spring damper material defines a gap between the shaft and the inertia members. The RVD may be press-fittable inside a hollow shaft or to the outside of a hollow or solid shaft. The RVD&#39;s disclosed herein have first vibration mode shapes that are radial in nature and decoupled from latter vibration modes.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/974,202, filed Apr. 2, 2014, which is incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to radial vibration dampers, more particularly, to radial vibration dampers press-fittable to shafts such as, but not limited to, drive-shafts, prop-shafts, and half-shafts. 
       BACKGROUND 
       [0003]    Radial vibration dampers are used to reduce radial vibrations in rotating shaft systems. radial vibration dampers can be mounted internally or externally relative to the shaft. The most desirable radial vibration damper for inside a hollow shaft is one that has its first mode shape being radial in nature while being sufficiently decoupled from latter modes. The device must also be easy to insert into the shaft at a designated axial location, and hold its position throughout its operating life. Such a radial vibration damper is typically expensive because the construction is complex and it is unrealistic to invest in expensive injection molds for smaller production runs. 
         [0004]    An additional problem encountered while assembling these devices is that the inner diameter of the hollow shaft that receives them generally has loose tolerances that do not allow a robust metal-to-metal press-fit. 
       SUMMARY 
       [0005]    The present disclosure is directed to radial vibration dampers that are simpler in construction and eliminate the need for the expensive rubber to metal mold-bonded parts as present in commercially available radial vibration dampers. According to one aspect, a radial vibration damper is disclosed that includes a first inertia member and a second inertia member fixedly connected to one another to define an annular channel having a radially facing, open side. A spring damper material is seated in the annular channel in axial compression between the first inertia member and the second inertia member, and the spring damper material has a compressible portion thereof protruding from the radially facing, open side a sufficient distance that, once the compressible portion is compressed against a shaft, the spring damper material defines a gap between the shaft and the first and second inertia members. In another aspect, the radial vibration damper further includes a fastener connecting the first inertia member to the second inertia member. 
         [0006]    According to another aspect of the previous embodiments, the spring damper material includes a first rib protruding therefrom compressed by contact with the first inertia member and a second rib protruding therefrom compressed by contact with the second inertia member. In another aspect of the previous embodiments, the spring damper material includes a main body between the first rib and the second rib that includes a stiffness portion and the compressible portion, wherein the compressible portion is more proximal to the radially facing, open side of the annular channel. In another aspect, the first inertia member and the second inertia member each include a groove shaped and sized to receive the first rib and the second rib, respectively, of the spring damper material. In another aspect, the radial vibration damper of claim  1 , wherein the first inertia member and the second inertia member each include an alignment fixture to hold the spring damper material in its position. 
         [0007]    In another aspect of the previous embodiments, the spring damper material of the radial vibration damper includes a compressible material in at least the first rib, the second rib, and the compressible portion. The compressible material includes one or more of an elastomeric material, a hyperfoam material, and a nylon. The stiffness portion includes one or more of the same materials as the compressible portion but has a higher modulus. In another aspect, the spring damper material is a monolithic body. 
         [0008]    In another aspect of the previous embodiments, the spring damper material of the radial vibration damper comprises a main body defined by a first ring of a compressible material in contact with a surface of the shaft, a second ring of a stiffness material seated adjacent to the first ring, a third ring compressed between the main body and the first inertia member, and a fourth ring compressed between the main body and the second inertia member. 
         [0009]    In another aspect of the previous embodiments, the radial vibration damper has a first mode shape of vibration that is radial. In another aspect, the first mode shape of vibration is decoupled from a second mode of vibration. 
         [0010]    In another aspect of the previous embodiments, the radial vibration damper is press-fittable into a hollow shaft with the compressible portion of the spring damper material compressed against an inner surface of the hollow shaft. In another aspect, the radial vibration damper is press-fittable over a shaft with the compressible portion of the spring damper material compressed against an exterior surface of the shaft. 
         [0011]    A system is also disclosed that includes a shaft having press-fit thereto a radial vibration damper according to any of the previous embodiments. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0012]    The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. 
           [0013]    Many aspects of the disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0014]      FIG. 1  is a side perspective view, with a portion cut away, of a radial vibration damper seated within a hollow shaft. 
           [0015]      FIG. 2  is a side perspective view, with a portion cut away, of a second embodiment of a radial vibration damper. 
           [0016]      FIG. 3  is a grid showing four Modal responses, in color, of the radial vibration damper of  FIG. 1  as modeled using finite element modeling. 
           [0017]      FIG. 4  is perspective longitudinal cross-sectional view of a third embodiment of a radial vibration damper, seated about the outside of a shaft 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Reference is now made in detail to the description of the embodiments as illustrated in the drawings. While several embodiments are described in connection with these drawings, there is no intent to limit the disclosure to the embodiment or embodiments disclosed herein. On the contrary, the intent is to cover all alternatives, modifications, and equivalents. 
         [0019]    Referring now to  FIG. 1 , an example of one embodiment of a system  100  that includes a hollow shaft  104  with radial vibration damper  102  press fit therein is shown. The hollow shaft  104  may be any shaft intended to rotate during use, such as a drive shaft, prop-shaft, half-shafts, or the like used in automotive applications, but is not limited thereto. As seen in  FIG. 3 , the results of finite element modeling demonstrate that the radial vibration damper  102  has a first mode of vibration that is radial in shape with sufficient separation between the first mode and the second mode of vibration, which in this illustration is axial (known as modal decoupling). In  FIG. 3 , the color scale correlates color along the visible spectrum with the magnitude of the stress experienced at specific locations within the radial vibration damper  102 , with red tones representing the largest magnitude values and violet tones representing the smallest magnitude values. The radial vibration damper  102  may be tuned to have a modal decoupling of 20 Hz or greater (a generally accepted industrial standard) by changing various parameters of the radial vibration damper  102 , which will be better understood after an explanation of the structure of the damper itself. 
         [0020]    Two embodiments of a radial vibration damper, generally designated by reference  102  are provided in  FIGS. 1 and 2 . As explained above, the radial vibration dampers  102 ,  102 ′ are press-fittable into a hollow shaft  104 . The radial vibration dampers  102 ,  102 ′ both include a first inertia member  106  and a second inertia member  108  fixedly connected to one another, thereby defining a central longitudinal axis A and an annular channel  152  having at least one radially facing open side  154 , which faces radially outward towards an inner surface  105  of a hollow shaft  104  for a radial vibration damper  102 ,  102 ′ press-fit to the inside of the hollow shaft  104 . The first and second inertia members  106 ,  108  may define an annular channel  152  that extends part-way, in the radial direction, between the first and second inertia members  106 ,  108 . The first and second inertia members  106 ,  108  may also define an annular channel  152  that extends radially all the way between the first and second inertia members  106 ,  108 . A spring damper material  112  is disposed at least partially within the annular channel  152  and is axially compressed between the first inertia member  106  and the second inertia member  108 . 
         [0021]    The spring damper material  112  is an annular body disposed about the central longitudinal axis A at a position that places a compressible portion  114  of the spring damper material  112  beyond the outer diameter of the first inertia member  106  and the second inertia member  108 , which places at least part of the compressible portion  114  outside of the annular channel  152 . Described another way, the compressible portion  114  of the spring damper material  112  extends from the annular channel  152 , through the radially facing open side  154 , and into contact with the inner surface  105  of the hollow shaft  104 . The annular body of the spring damper material  112  also includes a first rib  116  protruding therefrom compressed by contact with the first inertia member  106  and a second rib  118  protruding therefrom compressed by contact with the second inertia member  108 . The first rib  116  and second rib  118  extend axially from opposing sides of the spring damper material  112 . 
         [0022]    As represented by dashed lines in  FIGS. 1 and 2 , the annular body of the spring damper material  112  includes a main body  120  between the first rib  116  and the second rib  118  that includes a stiffness portion  122  more proximate an inner surface  124  thereof and the compressible portion  126 . The stiffness portion  122  enables the compression portion  126  to be compressed against an inner surface  105  of a hollow shaft  104  ( FIG. 1 ) for a press-fit. More particularly, the stiffness portion  122  provides a hydrostatic radial force to define a joint  130  between the compressible portion  126  and the inner surface  105  of the hollow shaft  104  and the compressible portion  126  has a coefficient of friction, which, combined, hold the radial vibration damper  102  in place within the hollow shaft  104  without axial movement (creep). The outer diameters of the first inertia member  106  and second inertia member  108  are generally less than a diameter of the inner surface  105  of the hollow shaft  104  such that when radial vibration damper  102  is press fit into the hollow shaft  104 , which compresses the compressible portion  126  against the inner surface  105  of the shaft  104 , the spring damper material  112  defines a gap  128  between the first and second inertia members  106 ,  108  and the inner surface  105  of the hollow shaft  104 . This gap  128  allows some amount of movement of the first and second inertia members  106 ,  108  relative to the rotation of the hollow shaft  104 . 
         [0023]    As seen in  FIGS. 1 and 2 , the spring damper material  112  may be a monolithic body. However, in an alternate embodiment, not shown, the spring damper material  112  may be made up of multiple parts including any one or more of the following: (1) a main body  120  having a stiffness portion and a compressible portion as a single unit or, alternately, defined by a first ring of stiffness providing material having a second ring seated thereabout that includes a compressible material (or a plurality of either of such rings), (2) a compressible ring (in place of the first rib  116 ) compressed between the main body  120  and the first inertia member  106  (or a plurality of such rings), and (3) a second compressible ring (in place of the second rib  118 ) compressed between the main body  120  and the second inertia member  108  (or a plurality of such rings). 
         [0024]    In  FIGS. 1 and 2 , the main body  120  is shown as being generally toroidally-shaped, in particular as a rectangular toroid body, but is not limited thereto. In other embodiments, the main body may have a trapezoidal, a circular, or any other acceptable shaped transverse cross-section. 
         [0025]    Still referring to  FIGS. 1 and 2 , the spring damper material  112  includes a compressible material in at least the first rib  116 , the second rib  118 , and the compressible portion  126 . The compressible material includes one or more of an elastomeric material, a hyperfoam material, and a nylon. Each of these materials may be any such materials that are suitable to absorb and/or damp the vibrations generated by the shaft and can withstand the general conditions experienced by the shaft such as temperature changes, road conditions, etc. The elastomeric material may be or include one or more of a styrene-butadiene rubber, a natural rubber, a nitrile butadiene rubber, an ethylene propylene diene rubber (EPDM), an ethylene acrylic elastomer, a hydrogenated nitrile butadiene rubber, and a polycholoroprene rubber. One example of an ethylene acrylic elastomer is VAMAC® ethylene acrylic elastomer from E. I. du Pont de Nemours and Company. The hyperfoam material may be or include one or more of micro cellular urethane, sponge, or the like. The nylon may be or include nylon 6, nylon 6/6, or the like. The spring damper material  112  may be a composite that optionally includes a plurality of fibers dispersed therein. The fibers may be continuous or fragmented (chopped) aramid fibers like the fibers sold under the name TECHNORA® fiber and/or carbon fibers, for example. 
         [0026]    The spring damper material  112  also includes the stiffness portion  122 , which may be or include one or more of the materials listed above for the compressible portion  126  and/or the ribs  116 ,  118 , but have a higher modulus than the material selected for at least one of the first and second ribs  116 ,  118  and the compressible portion  126 . 
         [0027]    As seen in  FIGS. 1 and 2 , a fastener  110  may be used to fixedly connect the first inertia member  106  to the second inertia member  108  (and vice versa). The fastener  110  may be a bolt, screw, rivet, or the like. As shown in  FIG. 1 , the fastener is a shoulder bolt having a first shoulder  170  seated against a stop  172  in the first inertia member  106  and a second shoulder  174  seated against the second inertia member  108 . The second shoulder  174  is positioned at a distance from the first shoulder  170  that defines the amount of axial compression applied to the spring damper material  112 . This distance is adjustable to change the amount of axial compression. One of the first and second inertia members  106 ,  108  includes a threaded bore  176  when the shoulder bolt has a threaded end  178 . The fasteners  110  may be such that a head portion, if present, is counter-bored into one of the inertia member  106 ,  108 . 
         [0028]    In the embodiment of  FIG. 2 , rather than having the fastener  110  control the distance defining the axial compression of the spring damper material  112 , one or more of the first and second inertia members  106 ,  108  may include an arm  132  extending toward the other inertia member when fixedly connected thereto that defines the distance the inertia members will remain from one another and thereby define the axial compression of the spring damper material  112 . In  FIG. 2 , both the first inertia member  106  and the second inertia member  108  include an arm  132  that are mateable with one another. When viewed in a longitudinal cross-section the inertia members are generally T-shaped when the arms  132  are present. In  FIG. 2 , the first and second inertia member  106 ,  108  are still fixedly connected by a fastener  110 , but the fastener could be omitted if the arm  132  of one of the inertia members,  106 ,  108  terminated with a male member and the other terminated with a female member that were mateable together with a secure connection, such as, but not limited to, a press-fit. In another embodiment (not shown), only one of the first and second inertia members  106 ,  108  may have an arm  132  extending therefrom and ending in a male fitting, which may be press fit with a female fitting disposed in the other of the first or second inertia members  106 ,  108 . In another embodiment, the first and second inertia members  106 ,  108  may each have multiple arms  132  distributed radially to maintain a balanced shaft system  100 . 
         [0029]    Referring to both  FIG. 1  and  FIG. 2 , the first and second inertia members  106 ,  108  may be made from any material having a sufficient mass, usually a cast iron metal, and may be cast, spun, forged, machined, or molded using known or hereinafter developed techniques. The first and second inertia members  106 ,  108  may include a groove  134  shaped and sized to receive the first rib  116  and the second rib  118 , respectively therein, in a surface thereof that is facing the spring damper material  112 . Since the ribs are annular rings disposed about the central longitudinal axis A, the grooves  134  are likewise annular rings disposed about the central longitudinal axis. The first rib  116  and the second rib  118  may be continuous or discontinuous rings and likewise the grooves  134  may be continuous or discontinuous rings. The grooves  134  act to position the spring damper material  112  in a predetermined position, determined to be appropriate to form the joint  130  ( FIG. 1 ). In another embodiment, in addition to the grooves  134  or as an alternative to the grooves  134 , the first inertia member  106  and/or the second inertia member  108  may include an alignment fixture  180  ( FIG. 1 ) that protrudes therefrom toward the spring damper material  112  and at least a portion of the alignment fixture is juxtaposed to the spring damper material  112  or could be inserted into the spring damper material  112  (not shown). 
         [0030]    The radial vibration dampers  102 ,  102 ′ may be tuned by changing the mass of the first and second inertia members, by changing the geometry of the first and second ribs  116 ,  118  individually or collectively, changing the thickness of the stiffness portion  122 , changing the compressible nature of the first and second ribs  116 ,  118  and/or the compressible portion  126 , and/or changing the distance of separation between the first and second inertia members  106 ,  108  thereby changing the axial compression of the spring damper material. 
         [0031]    The radial vibration dampers  102 ,  102 ′ disclosed herein provide a radial vibration damper with a first mode of vibration that is purely radial in character and adequately separated from subsequent vibration modes. The radial vibration dampers  102 ,  102 ′ disclosed herein also involve fewer parts and eliminates the need for over-molding and mold-bonding processes for constructing the elastomeric parts. This results in reducing manufacturing costs and easier installation, among other benefits. 
         [0032]    Referring now to  FIG. 4 , an example of a system  200  is illustrated that includes a shaft  204  with a radial vibration damper  202  press-fit thereon (i.e. disposed about the shaft). In system  200 , the shaft  204  may be either solid or hollow, and the radial vibration damper  202  is press-fittable to an outer, exterior surface  203  of the shaft  204 . The radial vibration damper  202  includes a first inertia member  206  and a second inertia member  208  fixedly connected to one another, thereby defining a central longitudinal axis A′ and an annular channel  252  having at least one radially facing open side  254 , which faces radially inward towards the shaft for a radial vibration damper  202  press-fit to an exterior surface  203  of a shaft  204 . The first and second inertia members  206 ,  208  may define an annular channel  252  to extend part-way, in the radial direction, between the first and second inertia members  206 ,  208 . The first and second inertia members  252  may alternatively define an annular channel  252  to extend radially all the way between the first and second inertia members  252 . A spring damper material  212  is disposed at least partially within the annular channel  252  and is axially compressed between the first inertia member  206  and the second inertia member  208 . The central longitudinal axis A′ may generally coincide with an axis B of rotation of the shaft  204 . 
         [0033]    As shown in  FIG. 4 , the first inertia member  206  and the second inertia member  208  are generally annular in shape and each has an inner radial surface  246  that has a diameter generally greater than a diameter of the exterior surface  203  of the shaft  204 . Each of the first and second inertia members  206 ,  208  may be characterized as having a flange portion  242  extending radially inward and terminating in the inner radial surface  246  of the first or second inertia members  206 ,  208 . The flange portions  242  of the first and second inertia members  206 ,  208  have inner axial faces  248  that define axial boundaries of the annular channel  252 , which is defined having the radially facing, open side  254  oriented radially inward toward central longitudinal axis A′. With the flange portions  242  extending therefrom, each of the first and second inertia members  206 ,  208  may have a longitudinal cross-section that is generally L-shaped, and the longitudinal cross-section of the first inertia member  206  may be a mirror image thereof. In one embodiment (not shown), the first and second inertia members  206 ,  208  may be annular discs having inner axial faces which define an annular channel  252  extending therebetween along the entire radial distance between the first and second inertia members  206 ,  208 . The spring damper material  212  may be seated within the annular channel  252  and compressed between the first and second inertia members  206 ,  208 . 
         [0034]    The spring damper material  212  is an annular body at least partially seated in the annular channel  252  and extending inward from the annular channel  252 , through the radially facing open side  254 , and into contact with the exterior surface  203  of the shaft  204 . At least a portion of the spring damper material  212  may be disposed within the annular channel  252  and is positioned to place a compressible portion  214  of the spring damper material  212  closer to the central longitudinal axis A′ than the inner radial surfaces  246  of the first and second inertia members  206 ,  208  such that the compressible portion  214  is in contact with the exterior surface  203  of the shaft  204 . The annular body of the spring damper material  212  also includes a first rib  216  protruding therefrom compressed by contact with the first inertia member  206  and a second rib  218  protruding therefrom compressed by contact with the second inertia member  218 . The spring damper material  212  is secured in the annular channel  252  through compression of the first rib  216  and second rib  218  by the first inertia member  206  and second inertia member  208 , respectively. 
         [0035]    As represented by the dashed lines in  FIG. 4 , the annular body of the spring damper material  212  includes a main body  220  between the first rib  216  and the second rib  218  that includes a stiffness portion  222 , which is more proximate an outer radial surface  225  of the spring damper material  212 , and the compressible portion  226 , which is positioned more proximate the shaft  204 . The stiffness portion  222  enables the compressible portion  226  to be compressed against the exterior surface  203  of the shaft  204  ( FIG. 1 ) for a press-fit. More particularly, the stiffness portion  222  provides a hydrostatic radial force to define a joint  230  between an inner radial surface  224  of the compressible portion  226  and the exterior surface  203  of the shaft  204 , and the compressible portion  226  has a coefficient of friction, which combined hold the radial vibration damper  202  in place on the exterior surface  203  of the shaft  204  without axial movement (creep). The inner diameters of the first and second inertia members  206 ,  208  are generally greater than a diameter of the exterior surface  203  of the shaft  204  such that when radial vibration damper  202  is press fit to the exterior surface  203  of the shaft  204 , which compresses the compressible portion  226  against the exterior surface  203  of the shaft  204 , the spring damper material  212  defines a gap  228  between the first and second inertia members  206 ,  208  and the exterior surface  203  of the shaft  204 . This gap  228  allows some amount of movement of the first and second inertia members  206 ,  208  relative to the rotation of the shaft  204 . 
         [0036]    As seen in  FIG. 4 , the spring damper material  212  may be a monolithic body, may be made up of multiple parts, or may have any shape previously described above in relation to  FIGS. 1-2 . Additionally, the spring damper material  212 —including the compressible portion  226 , the stiffness portion  222 , and the ribs  216 ,  218 —may be made of any of the aforementioned materials described in relation to  FIGS. 1-2 . The stiffness portion of the spring damper material  212  may be or include one or more of the materials listed above for the compressible portion  226  and/or the ribs  216 ,  218 , but have a higher modulus than the material selected for at least one of the first and second ribs  216 ,  218  and the compressible portion  226 . 
         [0037]    As seen in  FIG. 4 , fasteners  210  may be used to fixedly connect the first inertia member  206  to the second inertia member  208  (and vice versa). The fasteners  210  may be bolts, screws, rivets, or the like. As shown in  FIG. 4 , the fasteners  210  may be bolts having a first shoulder  270  seated against a stop  272  in the first inertia member  206 . The second inertia member  208  may have a threaded bore  276  to receive a threaded end of the fastener  210 . In one embodiment, the fasteners  210  may be shoulder bolts (not shown) having a first shoulder and a second shoulder such that an amount of axial compression on the spring damper material  212  is limited by the distance between the first shoulder and the second shoulder, as described in conjunction with the embodiments depicted in  FIGS. 1-2 . The fasteners  210  may be such that a head portion, if present, is counter-bored into one of the first or second inertia members  206 ,  208 . The fasteners  210  may be distributed radially to maintain a balanced rotating system. 
         [0038]    In the embodiment of  FIG. 4 , rather than having the fastener  210  control the distance defining the axial compression of the spring damper material  212 , the first and second inertia members  206 ,  208  may define an axial dimension of the annular channel  252 , which defines the axial compression of the spring damper material  212 . The first inertia member  206  or the second inertia member  208  may abut as shown in  FIG. 4  or may have arms (not shown) extending toward the other inertia member  206 ,  208  to define the axial compression of the spring damper material  212 . In one embodiment, the first inertia member  206  and the second inertia member  208  both have arms (not shown) extending toward the other inertia member to define the axial compression of the spring damper material  212 . In another embodiment, the arms of one of the first and second inertia members  206 ,  208  may terminate in a male member and the arms of the other one of the first and second inertia members  206 ,  208  may terminate in a female member, such that the male member and female member are mateable to create a secure press fit, which may eliminate the need for fasteners  210  to couple together the first and second inertia members  206 ,  208 . 
         [0039]    Referring to  FIG. 4 , the first and second inertia members  206 ,  208  may be made from any material having a sufficient mass, usually a cast iron metal, and may be cast, spun, forged, machined, or molded using known or hereinafter developed techniques. The first and second inertia members  206 ,  208  may include a groove  234  shaped and sized to receive the first rib  216  and the second rib  218 , respectively therein. The groove  234  may be disposed in the inner axial faces  248  of the first and second inertia members  206 ,  208 . Since the first and second ribs  216 ,  218  are annular rings disposed about the central longitudinal axis A′, the grooves  234  are likewise annular rings disposed about the central longitudinal axis A′. The first rib  216  and the second rib  218  may be continuous or discontinuous rings and likewise the grooves  234  may be continuous or discontinuous rings. The grooves  234  act to position the spring damper material  212  in a predetermined position determined to be appropriate to form the joint  230  ( FIG. 4 ). In another embodiment, in addition to the grooves  234  or as an alternative to the grooves  234 , the first inertia member  206  and/or the second inertia member  208  may include an alignment fixture (not shown) that protrudes therefrom toward the spring damper material  212  and at least a portion of the alignment fixture is juxtaposed to the spring damper material  212  or could be inserted into the spring damper material  212  (not shown). 
         [0040]    The radial vibration damper  202  may be tuned by changing the mass of the first and second inertia members  206 ,  208 , by changing the geometry of the first and second ribs  216 ,  218  individually or collectively, changing the thickness of stiffness portion  222 , changing the compressible nature of the first and second ribs  216 ,  218  and/or the compressible portion  226 , and/or changing the distance of separation between the first and second inertia members  206 ,  208  thereby changing the axial compression of the spring damper material. 
         [0041]    Radial vibration damper  202  disposed on the exterior surface  203  of the shaft  204  provides easier access to the radial vibration damper  202  for tuning and service. In addition, the external radial vibration damper  202  allows for easy addition of more weight to the first and second inertia members  206 ,  208 , as well as the same advantages pointed out above for the embodiments described with reference to  FIGS. 1-2 . 
         [0042]    Although the invention is shown and described with respect to certain embodiments, it is obvious that modifications will occur to those skilled in the art upon reading and understanding the specification, and the present invention includes all such modifications.