Abstract:
A sprocket includes a plurality of teeth spaced about its periphery, roots located between pairs of adjacent teeth, and a cushion ring contacted by a chain engaging the sprocket teeth. The roots have root radii defined as the distance between the center of sprocket and the point along the root closest to the sprocket center in the radial direction. In some embodiments, the roots have three distinct radii. The cushioning material of the cushion ring receives the impact while engaging the chain. In some embodiments, the cushion ring has a contour substantially following the contours of the sprocket teeth geometry. In some embodiments, the cushion ring has a randomized contour to provide predetermined cushioning that varies from tooth to tooth around the sprocket.

Description:
REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part patent application of co-pending application Ser. No. 10/959,738, filed Oct. 6, 2004, entitled “ELASTOMER CUSHION RING FOR A RANDOM TOOTH ROLLER CHAIN SPROCKET”. 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 cushion rings. More particularly, the invention pertains to elastomer cushion rings that are bonded to at least one side of a sprocket. 
         [0004]    2. Description of Related Art 
         [0005]    Randomized sprockets for roller chains are known. U.S. Pat. No. 6,155,943, which is hereby incorporated herein by reference, discloses a roller chain and sprocket drive with a randomized sprocket which modulates the roller position on the sprocket by varying the radial seating position of the roller while maintaining a constant chordal dimension between seated rollers. The roots between teeth of the sprocket have radii that vary between a nominal radius, a maximum radius, and a minimum radius. This variation or randomization is intended to provide a noise modulation effect while avoiding the negative effects of high impact from conventional randomized sprockets. 
         [0006]    Roller chain sprockets oriented to minimize strand length variation of the chain are also known. U.S. Pat. No. 6,213,905, which is hereby incorporated herein by reference, discloses a roller chain and sprocket drive which has at least two sprockets with varied radial seating positions. The relative orientations of the sprockets are adjusted to provide favorable dynamics to the drive. This includes minimizing strand variation and providing the maximum strand variation for each chain strand to be phased differently than other strands. 
         [0007]    Elastomer cushion rings are also known for conventional sprockets with equally spaced teeth. U.S. Patent Application Publication No. 2003/0176251 discloses a method of installing a cushion ring on a sprocket body that includes applying a force to the cushion ring so that an opening in the cushion ring is deformed to a shape that accommodates passage of a non-circular flange of the sprocket body through the cushion ring. After the non-circular flange of the sprocket body is inserted through the opening of the cushion ring, the deforming force is released from the cushion ring so that the cushion ring is trapped between the flange and another portion of the sprocket body. The sprocket assembly includes at least one and typically two cushion rings trapped by respective non-circular flanges. 
         [0008]    U.S. Patent Application Publication No. 2002/0169044 discloses a sprocket with a hub and a plurality of teeth projecting radially outwardly from the hub. At least one cushion ring is located adjacent to the teeth, and the cushion ring defines a plurality of compression pads separated from each other by transverse grooves. Each of the compression pads is defined symmetrically about a circumferential mid-point. The cushion ring, when part of a sprocket with symmetric tooth spacings, is operable identically in first and second opposite rotational directions. In one arrangement, the compression pads each include a planar outer surface having a leading and a trailing end, where the leading end and trailing end are located a common radial distance from the center of the hub about which the sprocket rotates. The tooth spaces of the sprocket may be symmetric or asymmetric, and the root surface may be relieved. The sprocket may include multiple tooth profiles distributed randomly about the hub. 
         [0009]    U.S. Pat. Nos. 6,179,741 and 6,371,875 disclose a roller chain sprocket with sprocket teeth each having an engaging flank and a disengaging flank. The engaging flank of a first tooth of the sprocket cooperates with the disengaging flank of a second tooth to define a tooth space having a root surface extending between the engaging flank and the disengaging flank. The root surface has a first root surface portion defined by a first radius extending from an arc center of the first root surface portion. A cushion ring is mounted to a first face of the sprocket and has a number of alternating compression pads and grooves. A first groove has a first groove portion defined by a second radius extending from an arc center of the first groove portion. The arc center of the first groove portion is positioned at least proximate to a radial line extending between a center of the sprocket and the arc center of the first root surface portion. A first compression pad has an inclined outer surface defined by a leading edge that is spaced radially inward relative to a trailing edge. The leading edge is also positioned radially inward from the engaging flank of the first tooth, and the trailing edge is positioned radially inward from a disengaging flank of the first tooth. 
         [0010]    As can be seen, the above listed prior art sprocket tooth angular spacing is repetitive and is equal to 360 degrees divided by the number of sprocket teeth. Repetitive sprocket tooth spacing is known to create undesirable chain engagement noise having orders that are related to the number of sprocket teeth. A random tooth sprocket has both irregular angular spacing and varying pitch radii of the sprocket teeth which disrupts the repetitive chain engagement noise orders. 
       SUMMARY OF THE INVENTION 
       [0011]    A sprocket includes a plurality of teeth spaced about its periphery, roots located between pairs of adjacent teeth, and a cushion ring contacted by a chain engaging the sprocket teeth. The roots have root radii defined as the distance between the center of sprocket and the point along the root closest to the sprocket center in the radial direction. In some embodiments, the roots have three distinct radii. The cushioning material of the cushion ring receives the impact while engaging the chain. In some embodiments, the cushion ring has a contour substantially following the contours of the sprocket teeth geometry. In some embodiments, the cushion ring has a randomized geometry to provide predetermined cushioning that varies from tooth to tooth around the sprocket. 
         [0012]    In some embodiments, the sprocket includes a contoured elastomer cushion ring of an elastomer material affixed onto each side of the random tooth roller chain sprocket. In some embodiments, the sprocket includes a contoured elastomer cushion ring having at least one cushion ring contour, each contour having a predetermined amount of interference with the roller chain pin links and bush links. The different cushion ring geometries each change the amount of interference with the chain for each incremental rotation of the sprocket. Full interference occurs at full chain engagement. The interference may occur abruptly or gradually during chain engagement. This is preferably used for tuning the noise-vibration-harshness (NVH) levels while minimizing negative effects. Negative effects include durability concerns, such as tearing of the cushioning material, from too large an interference or applying the interference too abruptly. The elastomer material reduces chain roller or bushing engagement impact forces, thereby reducing noise and increasing roller/bushing fatigue life. 
         [0013]    Accordingly, a sprocket of the present invention includes a plurality of teeth spaced about its periphery with roots located between pairs of adjacent teeth. The sprocket further includes a cushion ring including a cushioning material for receiving the impact while engaging a chain. Each root has a root radius defined as the distance between the center of the sprocket and the point along the root closest to the sprocket center in the radial direction. In some embodiments, at least one of the roots has a first root radius, and at least one of the roots has a second root radius, the second root radius being greater than the first root radius. The first root radius and the second root radius are defined so that the distance between the centers of adjacent rollers are substantially equal along the rollers seated in the sprocket roots. In other embodiments, the tooth spacings are all equal and the root radii are all equal. In some embodiments, the cushion ring has a contour substantially following the contours of the sprocket teeth geometry. In other embodiments, the cushion ring has a randomized geometry to provide predetermined cushioning that varies from tooth to tooth around the sprocket. 
         [0014]    In some embodiments, the sprocket for a roller chain includes a plurality of rollers connected by links. The sprocket includes a chain driving body. A plurality of teeth are spaced about a periphery of the body, with roots located between pairs of adjacent teeth, each root serving as a seat for a roller of a link engaged with the sprocket. The sprocket further includes a cushion ring affixed onto the chain-driving body for receiving an impact of the links of the roller chain driven by the body. The cushion ring has a plurality of contoured edges, each contoured edge corresponding to one of the seats, the contoured edges being arranged in a random sequence around the sprocket. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0015]      FIG. 1  shows a side view of a random tooth sprocket including a contoured elastomer cushion ring with a first geometry in an embodiment of the present invention. 
           [0016]      FIG. 2  shows a sprocket with a second cushion ring geometry in an embodiment of the present invention. 
           [0017]      FIG. 3  shows a sprocket with a third cushion ring geometry in an embodiment of the present invention. 
           [0018]      FIG. 4  shows a sprocket with a fourth cushion ring geometry in an embodiment of the present invention. 
           [0019]      FIG. 5  shows a sprocket with a fifth cushion ring geometry in an embodiment of the present invention. 
           [0020]      FIG. 6  shows a sprocket with a sixth cushion ring geometry in an embodiment of the present invention. 
           [0021]      FIG. 7  shows a sprocket with a seventh cushion ring geometry in an embodiment of the present invention. 
           [0022]      FIG. 8  shows a sprocket with an eighth cushion ring geometry in an embodiment of the present invention. 
           [0023]      FIG. 9  shows a cross sectional view of a sprocket in an embodiment of the present invention. 
           [0024]      FIG. 10  shows a side view of a sprocket including a cushion ring with interference pads located at random radial positions in an embodiment of the present invention. 
           [0025]      FIG. 11  shows a side view of a sprocket including a cushion ring with interference pads located at random angular positions in an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0026]    In a first set of embodiments, the sprocket is a random tooth sprocket including a cushion ring with a contour substantially following the contours of the sprocket teeth geometry. Referring to  FIG. 1 , the random tooth sprocket  10  includes a set of teeth  12  circumferentially distributed upon its circumference. The random tooth sprocket  10  is preferably used in conjunction with a roller chain  13 , as shown in  FIGS. 2-8 . The random tooth sprockets of  FIGS. 1-8  are described herein for clockwise rotation of the sprockets during use, but the geometries of  FIGS. 1-8  may also be used with counterclockwise rotation within the spirit of the present invention. The random tooth sprocket  10  includes a plurality of roots with a first root radius and a plurality of roots with a second root radius greater than the first root radius. In the embodiments of  FIGS. 1-9 , the roots with the first root radius are randomly arranged with the roots with the second root radius in a predetermined pattern about the random tooth sprocket  10  periphery. By randomly arranged, it is meant that the pattern is staggered between first and second radii, and not a pure alternating pattern between first and second radii. A random tooth sprocket is described in more detail in U.S. Pat. No. 6,155,943, which is hereby incorporated herein by reference. A random sprocket comprises two or more radii for locating the tooth roots. Preferably, three tooth roots are used, as denoted by the numbers  1 ,  2 , and  3  in  FIGS. 2-8 . 
         [0027]    As the rollers of the roller chain  13  move from seat to seat between the set of teeth  12 , the radial position at which the rollers seat varies from a maximum radius to a nominal radius to a minimum radius. The angular displacement of the sprocket is the angular distance between the center of the roller in one seat and the center of the roller in an adjacent seat. The angular displacement is effectively altered from seat to seat around the random tooth sprocket  10 . The roller chain  13  includes chain pins and bush links. 
         [0028]    The cushion material  14  of the cushion ring is affixed, preferably by bonding, onto at least one side of the random tooth sprocket  10 . The contour of the cushion material  14  provides a predetermined amount of interference with the roller chain  13  pin links and bush links. The chain pin and bush links compress the elastomer material  14  during chain  13  engagement with the sprocket. The elastomer material  14  reduces the chain roller or bushing engagement impact forces, which reduces noise and increases the roller/bushing fatigue life. The cushion ring includes an elastomeric material, which may include, but is not limited to, various heat-resistant and oil-resistant non-halogen synthetic rubbers, hydrogenated nitrile butadiene rubber (HNBR), partially or completely hydrogenated acrylonitrile-butadiene rubber, or polyacrylate (ACM). 
         [0029]    The elastomer material  14  of the cushion ring has a contoured edge or circumference  16 . The geometry of the contoured edge  16  follows the irregular geometry of the random sprocket teeth  12  such that each chain  13  engagement has a predetermined amount of fully engaged chain interference with the chain pin links and bush links. The contoured edge  16  is preferably designed to provide a substantially equivalent chain interference at each seating of the chain. The geometry of the contoured edge  16  is also preferably designed to vary the rate of chain interference as the chain enters and exits engagement with the sprocket  10 . Therefore, contoured edge  16  may have various geometric shapes or contours. For example, see respectively the first contoured edge  16  of  FIG. 1 , the second contoured edge  16   a  of  FIG. 2 , the third contoured edge  16   b  of  FIG. 3 , the fourth contoured edge  16   c  of  FIG. 4 , the fifth contoured edge  16   d  of  FIG. 5 , the sixth contoured edge  16   e  of  FIG. 6 , the seventh contoured edge  16   f  of  FIG. 7 , and the eighth contoured edge  16   g  of  FIG. 8 . The various shapes of the contoured edge  16  are preferably used to tune the sprocket and chain engagement system. Tuning may be necessary to achieve improvement or optimization of noise-vibration-harshness (NVH) levels and at the same time to minimize any negative effects such as increased chain load or elastomer material  14  durability or compression set from chain  13  engagement forces necessary to compress the cushion ring. A clearance relief contour is preferably positioned adjacent to each interference geometry. Each adjacent clearance relief provides a space to accept the deflected cushion ring material  14  especially the contoured edge  16  portion. The geometry and amount of contoured edge  16  interference as well as the geometry and amount of contoured edge  16  clearance relief may be altered to achieve optimum system performance. As can be seen in  FIGS. 1-9 , the various cushion ring geometries affect the rate of interference as the chain comes into and out of sprocket engagement as well as the total interference with a fully engaged chain. The contoured cushioning material edge  16 - 16   g  preferably has uneven edges circumferentially following the first radii, the second radii, and the third radii of the random sprocket. 
         [0030]    The contoured edge  16  as shown in cross section in  FIG. 9  may have a first thickness  20  and a second thickness  22  different from the first thickness on opposite side of the random tooth sprocket  10 . The first thickness  20  and the second thickness  22  are preferably wide enough to allow sufficient contact of the chain  13  bush link plates and pin link plates within the permissible side to side movement of the chain  13  on the sprocket  10 . A set of holes in a flange of the random tooth sprocket  10  may be provided for the cushioning material  14  to pass through random tooth sprocket  10 . 
         [0031]    At least two radii are provided for the random tooth sprocket  10 . A third radius may also be provided. As shown in  FIGS. 2-8 , one relationship between the three radii is that radius  3  is greater in length than radius  2  and radius  2  is greater in length than radius  1 . The geometry of the random tooth sprocket  10  preferably substantially follows the relationship between the three radii to provide predetermined substantially equivalent amounts of chain interference and cushioning at each roller seating. 
         [0032]    It should be noted that the pitch distance or chordal length between seated rollers preferably remains constant around the sprocket. Maintaining a constant chordal length reduces the impact load of the rollers against the teeth. The variation in the seating position from tooth to tooth results in a modulation of the timing of successive impacts. This modulation reduces the pitch frequency of the noise produced by the chain drive. 
         [0033]    The design of the sprockets of  FIGS. 1-9  is preferably directed to maintaining the engagement or seating of the roller with the root of the sprocket  10 , but the radial position of the root varies irregularly from tooth to tooth around the sprocket  10 . Preferably, the pattern does not contain any abrupt transitions from the upper seating positions to the lower seating positions, or vice versa, without passing through the nominal seating position for at least one tooth. The avoidance of abrupt transitions contributes to the smooth running of the chain  13  and reduce the generation of mechanical noise and reduce wear on the rollers. 
         [0034]    In order to generate the profile of the sprocket  10  of the present invention, the location of the seating radius of each root, or the space between sprocket teeth  12  in which the rollers seat, is first determined. While locating the seating position of each roller, the pitch distance between seated rollers is kept constant. The elastomer material  14  may be bonded to each side of the random tooth sprocket  10 . The cushion ring contour  16  has a predetermined amount of interference with the roller chain pin links and bush links. The chain pin and bush links compress the elastomer material  14  especially the ring contour edge  16  portion during chain  13  engagement to the sprocket  10 . The elastomer material  14  reduces chain roller or bushing engagement impact forces, which reduces noise and increases roller/bushing fatigue life. 
         [0035]    The random sprocket  10  of the embodiments of  FIGS. 1-9  is not limited to three different radii. A random sprocket such as sprocket  10  can have as few as two radii or a plurality of radii greater than three. A random tooth sprocket  10  has both irregular angular spacing and varying pitch radii of the sprocket teeth  12  which disrupts the repetitive chain engagement noise orders. 
         [0036]    In some embodiments of the present invention, the sprocket is a conventional sprocket with a randomized cushion ring. The angular spacing of the teeth of a conventional sprocket is repetitive and is equal to 360 degrees divided by the number of sprocket teeth. Repetitive sprocket tooth spacing creates undesirable chain engagement noise orders that are related to the number of sprocket teeth. Conventional cushion rings do not change the repetitive chain engagement noise orders. In some embodiments of the present invention, elastomer cushion rings with random interference pads are bonded to each side of a conventional roller chain sprocket. 
         [0037]    The elastomer material of random cushion rings of the present invention is preferably compressed unequally and non-repetitively during chain engagement to the sprocket. The cushion ring randomness modulates the angular position where each chain roller impacts a sprocket tooth and disrupts the repetitive chain engagement noise orders. This variation or randomization preferably provides a noise modulation effect. The compression of the elastomer material reduces chain roller or bushing engagement impact forces which, in turn, reduces noise and increases roller/bushing fatigue life. Random cushion rings of the present invention may have compression pads of irregular geometry, angular positioning, radial positioning, or chain interference. The cushion ring randomness modulates the angular position where each chain roller impacts a sprocket tooth and disrupts the repetitive chain engagement noise orders. 
         [0038]    A clearance relief geometry is preferably positioned adjacent to each interference geometry. Each adjacent clearance relief provides a space to accept the deflected cushion ring material. In at least some embodiments the cushion ring material is deflected into both the clearance relief space immediately before and the clearance relief space immediately after the compression pad. The geometry, angular position, radial position, and amount of the cushion ring interference as well as the geometry, angular position, radial position, and amount of cushion ring clearance relief may be altered to tune the sprocket and chain engagement system. Tuning may be necessary to achieve optimum NVH improvement and at the same time minimize any negative effects from engagement forces necessary to compress the cushion ring. The sprockets of  FIGS. 10 and 11  are described herein for clockwise rotation of the sprockets during use, but the geometries of  FIGS. 10 and 11  may also be used with counterclockwise rotation within the spirit of the present invention. 
         [0039]      FIG. 10  shows a side view of a sprocket  30  including a random cushion ring  34 , where the interference pads  35  are located in a random sequence of three radial positions  4 ,  5 , and  6  with respect to the center of the sprocket. The radial distances are indicated as dashed lines in  FIG. 10 . The sprocket  30  includes a plurality of teeth  32 , which are equally shaped and equally spaced around the perimeter of the sprocket. A roller seat  33  is located between each pair of adjacent teeth of the sprocket. The contoured edge  37  of the cushion ring is formed to provide a compression pad  35  with a clearance relief geometry  36  for each roller seat. Preferably, the pattern does not contain any abrupt transitions from the upper radial positions  6  to the lower radial positions  4 , or vice versa, without passing through the intermediate radial position for at least one tooth. Although the interference pads are shown at three radial positions in  FIG. 10 , two radial positions or more than three radial positions may be used in the random sequence within the spirit of the present invention. 
         [0040]      FIG. 11  shows a side view of a sprocket  30  including a random cushion ring  44 , where the interference pads  45  are located in a random sequence of three angular positions  7 ,  8 , and  9  with respect to the center of the sprocket. In  FIG. 11 , the angular positions are indicated as rotations from alignment of the center of the sprocket tooth and the center of the contoured edge at the tooth, and for each angular position the center of the contoured edge is rotated clockwise with respect to the center of the tooth. In other embodiments, the angular positions may include the center of a contoured edge aligned with the center of a sprocket tooth and/or one, more than one, or all centers of contoured edges rotated counterclockwise with respect to the center of the sprocket tooth within the spirit of the present invention. The sprocket  30  includes a plurality of teeth  32 , which are equally shaped and equally spaced around the perimeter of the sprocket. A roller seat  33  is located between each pair of adjacent teeth of the sprocket. The contoured edge  47  of the cushion ring is formed to provide a compression pad  45  with a clearance relief geometry  46  for each roller seat. Preferably, the pattern does not contain any abrupt transitions from the maximum angular positions  9  to the minimum angular positions  7 , or vice versa, without passing through the intermediate angular position for at least one tooth. Although the interference pads are shown at three angular positions in  FIG. 11 , two angular positions or more than three angular positions may be used in the random sequence within the spirit of the present invention. 
         [0041]    In another embodiment of the present invention, the random cushion ring includes a random sequence of at least two contoured edges. The contoured edges may vary in the shape of the compression pad or the clearance relief geometry. The contoured edges preferably are selected from the geometries  16 - 16   g  shown in  FIGS. 1-8 . 
         [0042]    Alternatively, a random cushion ring of the present invention may be used in combination with a random sprocket of the present invention. Finally, a random cushion ring may include a random sequence consisting of contoured edges of any combination of variations in geometry, angular position, and radial position within the spirit of the present invention. 
         [0043]    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.