Abstract:
A sprocket is provided with a plurality of teeth spaced about its periphery, the sprocket including roots located between pairs of adjacent 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. Roots have three distinct radii. a cushioning material for receiving the impact while engaging a chain has a geometry means substantially following the contours of the sprocket teeth geometry.

Description:
FIELD OF THE INVENTION  
       [0001]     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 random tooth roller chain sprocket  
       BACKGROUND OF THE INVENTION  
       [0002]     Randomized sprockets for roller chain 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 and 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.  
         [0003]     It is also known to use roller chain sprockets, which are oriented to minimize strand length variation of the chain. 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 orientation of the sprockets are adjusted to provide favorable dynamics to the drive. This can include the minimization of the strand variation and providing the maximum strand variation for each chain strand to be phased differently than other strands.  
         [0004]     Elastomer cushion rings are also known for conventional, equally tooth spaced sprockets. United States patent application No.20030176251 teaches a method for installing a cushion ring on a sprocket body to construct a sprocket assembly includes applying a deforming force to a cushion ring so that an opening therein is deformed to a shape that accommodate passage of a non-circular flange of a sprocket body therethrough. When the cushion ring is deformed, the non-circular flange of the sprocket body is inserted through the opening of the cushion ring. The deforming force is then 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.  
         [0005]     United States patent application No.20020169044 teaches a sprocket includes a hub and a plurality of teeth projecting radially outwardly from the hub. At least one cushion ring is located adjacent 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. When part of a sprocket with symmetric tooth spaces, the cushion ring is being 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, wherein the leading end and trailing end are located a common radial distance from a center of the hub about which the sprocket rotates. The tooth spaces of the sprocket can be symmetric, asymmetric and the root surface can be relieved. The sprocket can include multiple tooth profiles distributed randomly about the hub.  
         [0006]     U.S. Pat. No. 6,371,875 discloses a roller chain sprocket includes a number of sprocket teeth each having an engaging flank and a disengaging flank. An engaging flank of a first tooth of the sprocket cooperates with a 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 being positioned at least proximate a radial line extending between a center of the sprocket and the arc center of the first root surface portion. A first compression pad having 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.  
         [0007]     U.S. Pat. No. 6,179,741 discloses a roller chain sprocket includes a number of sprocket teeth each having an engaging flank and a disengaging flank. An engaging flank of a first tooth of the sprocket cooperates with a 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 being positioned at least proximate a radial line extending between a center of the sprocket and the arc center of the first root surface portion. A first compression pad having 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.  
         [0008]     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.  
         [0009]     Therefore, it is desirable to have cushion ring material to follow the irregular geometry of the random sprocket teeth such that each chain engagement has a predetermined amount of interference with the roller chain pin links and bush links.  
       SUMMARY OF THE INVENTION  
       [0010]     A random tooth sprocket having contoured elastomer cushion ring having elastomer material affixed onto each side of a random tooth roller chain sprocket is provided.  
         [0011]     A random tooth sprocket having contoured elastomer cushion ring having at least one cushion ring geometry each having a predetermined amount of interference with the roller chain pin links and bush links is provided. The different cushion ring geometries each changes the amount of interference with the chain for each incremental rotation of the sprocket. Full interference occurs at full chain engagement. The interference can occur abruptly or gradually during chain engagement. This can be used for tuning the noise, vibration and harshness (NVH) levels while minimizing negative effects. Negative effects includes durability concerns (e.g. tearing of the cushioning means) from too large an interference or applying the interference abruptly.  
         [0012]     A random tooth sprocket having contoured elastomer cushion ring having chain pin and bush links compress the elastomer material during chain engagement to the sprocket is provided.  
         [0013]     A random tooth sprocket having contoured elastomer cushion ring having the elastomer material reduces chain roller and/or bushing engagement impact forces thereby reducing noise and increases roller/bushing fatigue life.  
         [0014]     Accordingly, a sprocket comprising a plurality of teeth spaced about its periphery, said sprocket including roots located between pairs of adjacent teeth is provided. Each of said roots have a root radius defined as the distance between the center of said sprocket and the point along said root closest to the sprocket center in the radial direction, and at least one of said roots have a first root radius, at least one of said roots have a second root radius, said second root radius being less than said first root radius. The first root radius and the second root radius are defined so that the distance between the centers of adjacent rollers will be substantially equal along the rollers seated in the sprocket roots. The sprocket further includes a cushioning material for receiving the impact while engaging a chain having a geometry means substantially following the contours of the sprocket teeth geometry.  
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0015]      FIG. 1  shows a frontal view random tooth sprocket having contoured elastomer cushion ring of the present invention.  
         [0016]      FIG. 2  shows a first alternative embodiment of the present invention.  
         [0017]      FIG. 3  shows a second alternative embodiment of the present invention.  
         [0018]      FIG. 4  shows a third alternative embodiment of the present invention.  
         [0019]      FIG. 5  shows a fourth alternative embodiment of the present invention.  
         [0020]      FIG. 6  shows a fifth alternative embodiment of the present invention.  
         [0021]      FIG. 7  shows a sixth alternative embodiment of the present invention.  
         [0022]      FIG. 8  shows a seventh alternative embodiment of the present invention.  
         [0023]      FIG. 9  shows a side view of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]     Referring to  FIGS. 1-9 , a random tooth chain sprocket  10  having a set of teeth  12  circumferentially distributed upon its circumference is shown. Random tooth chain sprocket  10  may be used in conjunction with a roller chain  13  having random tooth chain sprocket  10  with a plurality of roots with the first root radius and a plurality of roots with the second root radius. The roots having the first root radius are randomly arranged with the roots having the second root radius in a predetermined pattern about the random tooth chain 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. For detailed description of the random tooth sprocket, refer to 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. In the preferred embodiment of the present invention, three tooth roots are used.  
         [0025]     As the rollers of a known roller chain  13  move from seat to seat between the set of teeth  12 , the radial position at which the rollers seat varies from maximum radius to nominal radius to 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 chain sprocket  10 . The roller chain  13  comprises chain pin and bush links.  
         [0026]     Cushion material  14  is affixed onto such as bonded to at least one side of random tooth chain sprocket  10 . Cushion material  14  geometry has 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 to the sprocket. The elastomer material  14  reduces chain roller and/or bushing engagement impact forces which reduces noise and increases roller/bushing fatigue life. The elastomer material  14  may include, but are not limited to, various heat- and oil-resistant nonhalogen synthetic rubbers, hydrogenated nitrile butadiene rubber (HNBR), partially or completely hydrogenated acrylonitrile-butadiene rubber, or polyacrylate (ACM).  
         [0027]     Elastomer material  14  has a contoured edge or circumference, which is termed cushioning means  16 . The geometry of the cushioning means  16  material 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 geometry of the cushioning means  16  is also designed to vary the rate of chain interference as the chain enters and exits engagement with the sprocket  10 . Therefore, cushioning means  16  may have various geometric shapes or contours. For example, see respectively the first shape  16   a  of  FIG. 2 , second shape  16   b  of  FIG. 3 , third shape  16   c  of  FIG. 4 , fourth shape  16   d  of  FIG. 5 , fifth shape  16   e  of  FIG. 6 , sixth shape  16   f  of  FIG. 7 , and seventh shape  16   g  of  FIG. 8 . The purpose of the various shapes of cushioning means  16  is to tune the sprocket and chain engagement system. Tuning may be necessary to achieve optimum noise, vibration and harshness (NVH) levels improvement and at the same time minimize any negative effects such as increased chain load or cushion means  16  durability or elastomer material  14  compression set from chain  13  engagement forces necessary to compress the cushion ring. Clearance relief geometry is positioned adjacent to each interference geometry. Each adjacent clearance relief provides a space to accept the deflected cushion ring material  14  especially the cushioning means  16  portion. The geometry and amount of cushioning means  16  interference as well as the geometry and amount of cushioning means  16  clearance relief may be altered to achieve optimum system performance. As can be seen, the various cushion ring geometries affects the rate of interference as the chain comes into and out of sprocket engagement as well as total interference with a fully engaged chain.  
         [0028]     Cushioning means  16  of  FIG. 9  may have a first thickness  20  and a second thickness  22  on each side of random tooth chain sprocket  10  respectively. Thickness  20  and thickness  22  must be 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 random tooth chain sprocket  10  may be provided for the cushioning material  14  to pass through random tooth chain sprocket  10 .  
         [0029]     At least two radii, radius  1  and radius  2  are provided for random tooth chain sprocket  10 . A third radii  3  may also be provided. One relationship between the three radii is that radius  1  is greater in length than radius  2 . Radius  2  is greater in length than radius  3 . The geometry of random tooth chain sprocket  10  substantially follows the relationship between the three radii.  
         [0030]     It should be noted that the pitch distance (or chordal length) between seated rollers remains constant. 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 noise produced by the chain drive.  
         [0031]     The design of the present invention is directed to maintaining the engagement (or seating) of the roller with the root of the sprocket  10 , but changing the position of the root radially from tooth to tooth is random. That is, it varies irregularly around the sprocket.  10  Preferably, the pattern does not contain any abrupt transitions from the upper seating or the lower seating positions to the other extreme position without passing through the nominal seating position for at least one tooth. Avoidance of abrupt transitions should contribute to the smooth running of the chain  13  and reduce the generation of mechanical noise and reduce wear on the rollers.  
         [0032]     In other words, the present invention provides a contoured cushioning material geometry means  16 - 16   g  to substantially follow the contours of the sprocket teeth  12  geometry. the contoured cushioning material geometry mean  16 - 16   g  has uneven edges circumferentially following the first, the second radii, and the third radii.  
         [0033]     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) must be determined. While locating the seating position of each roller, the pitch distance between seated rollers must remain constant.  
         [0034]     Elastomer material  14  may be bonded to each side of a random tooth roller chain  13  sprocket  10 . The cushion ring geometry  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 geometry  16  portion during chain  13  engagement to the sprocket  10 . The elastomer material  14  reduces chain roller and/or bushing engagement impact forces which reduces noise and increases roller/bushing fatigue life.  
         [0035]     Conventional sprocket tooth (not shown) angular spacing 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. 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]     Random sprocket  10  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.  
         [0037]     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.