Abstract:
A cushion ring ( 102 ) is received in a concentric groove in a sprocket ( 112 ) with teeth and a hub. More specifically, the groove is defined between an annular portion of the hub and the teeth. The cushion ring has an inner ring ( 106 ) and an outer ring ( 104 ). The outer ring is made of an incompressible material that has a load bearing area for receiving load from the links of the chain. The load and engagement noise energy of the chain links are combined and distributed over a large area of the outer ring. The inner ring receives this distributed load and noise energy from the outer ring and absorbs most of such energy. This improved distribution decreases wear and increases life of the resilient material while also providing for a reduced level of chain engagement noise.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims an invention which was disclosed in Provisional Application No. 60/784,431, filed Mar. 21, 2006, entitled “CHAIN NOISE REDUCTION DEVICE”. The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention pertains to the field of chain noise reduction devices. More particularly, the invention pertains to cushion or damping rings in chain sprockets. 
         [0004]    2. Description of Related Art 
         [0005]    Chains and sprockets have long been used as a means for transmitting power, timing rotary components and the like. One difficulty associated with such chain and sprocket arrangements is the impact of the chain rollers or links on the sprocket as they engage. This impact creates excessive noise and excessive wear. This impacting and the noise associated therewith are shown in  FIG. 1  as resulting from the roller  10  of a chain  12 , impacting against the tooth  14  of a sprocket  16 . The loudest noise occurs at the engagement starting point  18 , which occurs as indicated by the distribution curve  20  along the travel path of the chain. 
         [0006]    As a result of the noise and wear associated with conventional roller chain and sprocket couplings, devices have been developed in an effort to reduce these problems as discussed in Oonuma et al.&#39;s U.S. Pat. No. 4,348,199 and shown in prior art  FIGS. 1-7 . These devices have attempted to buffer the chain at the range of points  18  where the loudest noise occurs. A first buffer ring is illustrated in  FIGS. 2 and 3  and includes circular peripheral grooves  22  and  24  on a sprocket  26  on either side of the sprocket tooth  28 . Located within the grooves  22  and  24  are resiliently compressible buffer rings  30  and  32 . These buffer rings  30  and  32  fit snugly in grooves  22  and  24  due to their resilient nature. The buffer rings in  FIGS. 2 and 3  provide the buffering effect, reducing noise through the resilient restoring force against compression of the rings  30  and  32  in resisting the link plates  34  of chain  36 . However, because of the fixed location of the buffer rings  30  and  32  relative to the sprocket  26  and the sprocket teeth  28 , rapid wear and fatigue is experienced at fixed points on the rings  30  and  32 , rendering the device as relatively impractical. 
         [0007]    A second type of buffer ring is illustrated in  FIGS. 4 and 5 . The sprocket  26  again includes circular peripheral grooves  22  and  24  on either side of sprocket tooth  28  to accommodate metallic buffer rings  38  and  40 . These buffer rings have an inner diameter which is larger than the outer diameter of either of the grooves  22  and  24 . Also, the buffer rings  38  and  40  have a radial thickness which is less than or equal to the depth of the bottom of the grooves  22  and  24  below the inscribed circle  42  of the link plates  34  of the roller chain where it engages the sprocket. The inscribed circle  42  is shown in  FIG. 4 . 
         [0008]    The buffer ring shown in  FIGS. 4 and 5  either functions by deforming the ring from its circular shape or remaining circular. The ring material itself is not compressed between the link plates of the chain  36  and the bottom of the grooves  22  and  24  as in the device of  FIGS. 2 and 3 . An advantage of the metallic buffer rings is that they constantly change position with respect to the teeth  28  of the sprocket  26  and hence do not have fixed wear spots. However, because there is still metallic on metallic contact between the rings  38  and  40  and the grooves  22  and  24 , maximum noise abatement cannot be achieved. 
         [0009]      FIGS. 6 ,  7 , and  8  show another type of buffer ring. The buffer ring  62  consists of an outer resiliently compressible ring  64  made out of rubber and an inner spring-like ring  66  that is not compressible, made of steel. The buffer ring  62  resides between the sprocket  50  and a circular flange member  56  in a circular peripheral groove  54 . The circular flange member  56  is bolted to the sprocket  50  by fasteners  58 . The circular flange member  56  also has a radial flange  60  that forms circular peripheral groove  54  with the side of the sprocket. The roller chain  44  is comprised of link plates  46  having rollers  48  that engage the teeth  52  of a sprocket  50 . 
         [0010]    One of the problems associated with the buffer ring  62  is that the sharp edges of the link plates of the chain  46  contact a very small surface of the rubber outer portion  64  of the buffer ring  62 . Since the surface area in which the edges of the links  46  contact the outer portion  64  of the buffer ring  62  is small, the sharp edges of the links  46  are forced to continuously contact the rubber outer portion  64  of the ring at the same place, indenting and wearing the rubber, resulting in a chewing of the outer portion  64  of the buffer ring  62  at the contact places between the sharp links of the chain and the rubber outer ring  64 . The indentations to the rubber and the high localized stress that occurs at these points is shown in  FIG. 9  by arrows  69 . 
         [0011]    Another example of a cushion ring is shown in Watanabe et al.&#39;s U.S. Pat. No. 4,261,214, which discloses a ring formed with a multilayer structure of an inner spirally winding body with the layers of the body being close together and an outer periphery with a cushioning material. The body may be made of spring steel or a strengthened plastic. The cushioning material contacts the roller chain guides. 
         [0012]    Another cushion ring made of steel is shown in Hamilton&#39;s US Published Application 2003/0176251, which discloses a sprocket assembly with two cushion rings trapped by respective non-circular flanges. The cushion rings are steel. The cushion rings are installed on the sprocket body by deforming the cushion rings and then inserting the non-circular flange of the sprocket body through the opening of the cushion ring. 
         [0013]    Kawashimi et al.&#39;s U.S. Pat. No. 4,227,422 discloses a buffer spring plate or cushion ring with an inner member that is a steel spring plate and an outer member that has flexibility and elastibility like rubber or plastic. The outer member contacts the roller chain guides. 
         [0014]    Therefore there is a need in the art for a cushion ring that has a long life, resists wear and decreases the noise from the impact of the chain with the sprocket. 
       SUMMARY OF THE INVENTION 
       [0015]    A cushion ring is received in a concentric groove in a sprocket with teeth and a hub. More specifically, the groove is defined between an annular portion of the hub and the teeth, for contacting link chain strands of a chain. The cushion ring has an inner ring and an outer ring. The outer ring is made of an incompressible material that has a load bearing area for receiving the load from links of the chain. The load and engagement noise energy of the chain links is combined and distributed over a large area of the outer ring. The inner ring receives this distributed load and noise energy from the outer ring and absorbs most of the energy. This improved distribution decreases wear and increases life of the resilient material while also providing for a reduced level of chain engagement noise. 
         [0016]    The inner ring may be bonded to the outer ring, or it may be bonded to the sprocket hub or it may float relative to the groove between the annular portion of the hub and the teeth and the outer ring. 
         [0017]    The outer ring is preferably made of steel or spring steel and the inner ring is preferably made of plastic or rubber, although other materials may also be used. 
         [0018]    The cushion ring may be used with a roller chain, a silent chain, a toothed chain, and/or a power transmission chain with pins and links. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0019]      FIG. 1  shows a schematic of the coupling between a roller chain and a sprocket. 
           [0020]      FIG. 2  shows a side view of a first prior art buffer ring interacting with a roller chain. 
           [0021]      FIG. 3  shows a cross-section of  FIG. 2 . 
           [0022]      FIG. 4  shows a side view of a second prior art buffer ring interacting with a roller chain. 
           [0023]      FIG. 5  shows a cross-section of  FIG. 4 . 
           [0024]      FIG. 6  shows a side view of another prior art buffer ring interacting with a roller chain and sprocket. 
           [0025]      FIG. 7  shows a cross-sectional view taken along line  7 - 7  of  FIG. 6 . 
           [0026]      FIG. 8  shows a schematic of a prior art buffer ring of  FIG. 6 . 
           [0027]      FIG. 9  shows a schematic of the force impacts on the prior art buffer ring of  FIG. 6 . 
           [0028]      FIG. 10  shows a schematic of the force impacts on a cushion ring of a first embodiment of the present invention. 
           [0029]      FIG. 11  shows a side view of the cushion ring of the first embodiment with a sprocket. 
           [0030]      FIG. 12  shows a schematic of the cushion ring of the first embodiment mounted on a sprocket and engaging a roller chain. 
           [0031]      FIG. 13  shows a section view of the cushion ring of the first embodiment with a sprocket. 
           [0032]      FIG. 14  shows a schematic of a cushion ring of a second embodiment with a sprocket. 
           [0033]      FIG. 15  shows a section view of the cushion ring of a second embodiment with a sprocket. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]      FIG. 12  shows a schematic of the cushion or buffer ring  102  of the present invention mounted to a sprocket  112  and engaging a roller chain of chain links  108  and rollers  110 . The cushion ring  102  of the present invention includes an outer ring  104  made of a spring-like steel or a material that is not compressible and an inner ring  106  of a compressible or resilient material such as rubber or plastic. In this embodiment, the outer ring  104  and the inner ring  106  are bonded together as shown in  FIG. 11 . The cushion ring  102  has a larger outside diameter than the inscribed circle  142  created by the chain link plates  108  when engaged with the sprocket  112 . The cushion ring  102  acts as a force balance between the entrance and exit chain strands  101 ,  103  on a single sprocket. The cushion ring  102  interferes with the chain path at the engagement point by an amount approximately equal to the chordal amplitude of the sprocket. If the tension of the entrance and exit strands of the chain  101 ,  103  are equal, the cushion ring  102  cancels the chordal action of the chain. If the tension in the entrance and exit strands  101 ,  103  is not equal, the cushion ring  102  momentarily transfers load from the tight strand  103  to the loose or slack strand  101  of the chain. 
         [0035]    The cushion ring  102  receives load at three points. The first load R H  at point  105  is on the inner diameter of the inner ring  106  of the cushion ring which runs on the sprocket hub  120 . The second and third loads R 1N , R 2N  are produced at the entrance and exit positions where the chain contacts the outer diameter of the outer ring  104  of the cushion ring  102 . The cushion ring  102  contacts the chain over a short distance near the engagement points. The cushion ring  102  may or may not contact the chain over the effective wrap angle depending on the compressibility of the resilient material. As the tensions T 1  and T 2  of the entrance and exit strands  101 ,  103  of the chain vary, the cushion ring  102  rocks at a pivot point  105 , to transfer the strand tension from the tight strand  103  to the loose strand  101 , momentarily decreasing the tension and the ring interference or contact of the tight strand  103 , while the ring interference with the loose side  101  of the chain and tension increases. The forces R 1N  and R 2N  are relatively small for large strand tensions because the interference is small compared to the chain strand length. 
         [0036]    By having the outer ring  104  of the cushion ring  102  be spring-like steel, the cushion ring of the present invention reduces the impact energy of the chain&#39;s links  108  seating on the sprocket  112 . The inner ring  106 , made of a resilient material such as rubber or plastic, softens the impact of the links  108  even further and adds additional cushion and sound deadening between the cushion ring  102  and the sprocket  112 , where damage to and/or wear of the resilient inner ring  106  is less likely. Damage to and/or wear of the cushion ring  102  is also less likely because of the significant increase in the load bearing portion in which the links  108  of the chain contact, the smoothness of the outer ring surface  104   a  that mates with the links  108 , and the elimination of contact between the resilient inner ring  106  and the cutting edges of the roller chain guide links  108 . 
         [0037]    As previously stated, the cushion ring  102  of the present invention has an outer ring  104  of an incompressible material, preferably steel, and an inner ring  106  of a compressible material, preferably rubber or plastic. With the outer ring  104  and contact surface of the chain being incompressible (steel), the load generated by the chain over the effective wrap angle is distributed along the outer surface  104  of the cushion ring  102 , meaning not in pockets of point loads as in the prior art, increasing the life of the cushion ring  102 . The load transmitted to the inner ring  106  at the entrance and exit points of the chain strands is very small and the load increases as the top dead center and point  105  is approached. The highest load on the inner ring  106  is at the top dead center at R H  and point  105  and the least amount of load present at the entrance and exit points R 1N , R 2N  of the chain strands  101 ,  103  as shown in  FIGS. 10 and 12 . Furthermore, with the inner ring  106  made of compressible material (rubber), any load spikes on the steel outer ring  104  is further absorbed and damped by the inner ring  106 . 
         [0038]    In the prior art, specifically U.S. Pat. No. 4,348,199 and shown in prior art  FIGS. 6 through 8 , where the cushion ring has an outer ring of rubber or compressible material and an inner ring of an incompressible material of steel, the wear and the stress on the outer ring is significantly high. In the prior art, the edges of the links  46  of the chain contact a small surface of the outer portion  64  of the buffer ring  62 . With the contact area being so small, and easily displaceable due to characteristics of the material used, the sharp edges of the links  46  of the chain continuously contact the outer ring  64  not necessarily at the same places, indenting and displacing the rubber when contact with the chain is made, eventually resulting in a chewing up of the rubber. Referring to  FIG. 9 , the rubber outer ring  64  of the cushion ring  62  receives point load stress, shown by arrows  69  along the effective wrap angle. The point load stress would be heaviest at the entrance and exit contact points with the chain and decrease as approach, but are still present near top dead center. With the point stress as shown in  FIG. 9  and the increased wear of the rubber, the prior art cushion rings are not as effective at balancing the forces of the entrance and exit strands of the chain and have a very short wear life. 
         [0039]      FIGS. 11 and 13  show another schematic of a cushion ring of the first embodiment with a sprocket. The sprocket comprises a hub  120 , an annular portion with radial flanges  114  and a continuous circumferential row of spaced apart radially projecting teeth  112 . The annular portion is fastened or welded onto the hub  120  and the radial flanges  114  define circular outer diameters or concentric grooves  118  that are larger than the cushion ring inner diameter, trapping the cushion ring  102  loosely within the concentric groove  118 . The grooves  118  are positioned coaxially with the sprocket  112  and are adjacent to the sprocket teeth  112   a . A small space  107  (see  FIG. 10 ) is present between the groove  118  and the resilient inner ring  106  of the cushion ring  102  to allow the resilient component of the inner ring  106  to displace as necessary. The links  108  of chain run along the outer surface or load bearing portion  104   a  of the outer ring  104 . 
         [0040]      FIGS. 14 and 15  show a cushion ring of a second embodiment with a sprocket. The cushion ring  202  is comprised of an outer ring  204  made of spring-like steel that is not compressible and an inner ring  206  made of a resilient material such as rubber or plastic. In this embodiment, the outer ring  204  and the inner ring  206  are not bonded together and are independent of each other or separate. The inner ring  206  has a smaller diameter than the outer ring  204  and a space  207  is present between the inner ring  206  and the outer ring  204 . The inner ring  206  is preferably an O-ring. The sprocket comprises a hub  120 , an annular portion with radial flanges  114  and a continuous circumferential row of spaced apart radially projecting teeth  112   a . The annular portion is fastened or welded onto the hub  120  and the radial flanges  114  define circular outer diameters or concentric grooves  218  that are larger than the cushion ring inner diameter, trapping the cushion ring  202  loosely within the concentric groove  218 . The grooves are positioned coaxially with the sprocket  112  and are adjacent to the sprocket teeth  112   a.    
         [0041]    With the inner ring  206  separate from the outer ring  204  and having a smaller diameter than the outer ring  204 , and the inner ring  206  floats within the concentric groove  218  independent of the outer ring  204 . The outer ring  204  rotates or floats independent of the inner ring around the outer diameter of the inner ring  206 . With the inner ring  206  and the outer ring  204  floating or rotating independent of each other, the outer diameter of the inner ring  206  will contact the same place on the inner diameter of the outer ring  204  with an extremely low frequency, distributing the wear of the cushion ring evenly or continuously. 
         [0042]    The links  108  of chain run along the outer surface or load bearing portion  204   a  of the outer ring  204 . With the outer ring  204  and contact surface of the chain being incompressible (steel), the load generated on the chain over the effective wrap angle is distributed along the outer surface  204  of the cushion ring  202 , meaning not in pockets of point loads as in the prior art, increasing the life of the cushion ring  202 . The load transmitted to the inner ring  106  at the entrance and exit points of the chain stands is very small and the load increases as the top dead center and point  105  is approached. The highest load on the inner ring  106  is at the top dead center at R H  and point  105  and the least amount of load present at the entrance and exit points R 1N , R 2N  of the chain strands  101 ,  103  similar to the first embodiment shown in  FIGS. 10 and 12 . Furthermore, with the inner ring  206  made of compressible material (rubber), any load spikes on the steel outer ring  204  is further absorbed and damped by the inner ring  206 . 
         [0043]    As in the first embodiment, damage and wear is decreased due to the significant increase in the load bearing portion in which the links of the chain contact, the smoothness of the outer ring  204  surfaces that mate with the chain&#39;s links  108  and the resilient inner ring  206 , the elimination of contact between the resilient inner ring  206  and the cutting edges of the chain links  108 , and the cycling of the load bearing area of the inner ring  206 . The force distribution of cushion ring  202  is improved similarly to cushion ring  102  of  FIGS. 10 and 11 . 
         [0044]    In either embodiment, the cushion rings  102 ,  202  are not limited to one side or the other of the sprocket teeth  112 , but may be applied to each side of the sprocket hub  120 . 
         [0045]    The inner ring  106 ,  206  is preferably HNBR rubber. The outer ring  104 ,  204  is preferably high carbon or alloy steel with a hardness similar to the links  108  of the chain. 
         [0046]    The cushion ring  102 ,  202  of the present invention may also be used with toothed chains, silent chains, and other power transmission chains with pins and links. 
         [0047]    Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.