Abstract:
A reduced noise and vibration chain drive system includes a sprocket with a plurality of symmetrical teeth and tooth spaces. A chain is engaged with the sprocket and includes rollers received in the tooth spaces. The root surface of each tooth space includes a modified root surface portion defined with root relief so that a roller fully seated in said tooth space contacts the root surface at first and second circumferentially spaced apart roller-seating locations but is spaced from the root surface between the first and second roller-seating locations. The sprocket is optionally defined with a reduced chordal pitch as compared to the as-built link pitch of the chain. The roller seating diameter of an inscribed circle tangent to a fully seated roller is greater than a root diameter of the sprocket.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from and benefit of the filing date of U.S. provisional patent application Ser. No. 60/827,920 filed Oct. 3, 2006, and this prior application Ser. No. 60/827,920 is hereby expressly incorporated by reference into the present specification. This application is also a continuation-in-part of U.S. patent application Ser. No. 11/541,210 filed Sep. 29, 2006, and this prior application Ser. No. 11/541,210 is hereby expressly incorporated by reference into the present specification. 
     
     BACKGROUND 
       [0002]    Roller chain sprockets used in automotive engine chain drive systems are typically manufactured according to ISO 606: 2004(E) standard (International Organization for Standardization). The ISO 606 standard specifies requirements for short-pitch precision roller chains and associated chain wheels or sprockets. As shown in  FIG. 1 , the sprocket  10  includes only an ISO 606 tooth form T that is symmetrical with respect to the tooth space TS and has a constant root or roller seating surface  14  which is concave and defined as a circular arc segment by a radius R i  extending from one convex tooth flank  16   a  to the adjacent or facing convex tooth flank  16   b  as defined by the roller seating angle α. Accordingly, each flank radius R f  is tangent to R i  at the opposite tangency points TP. A chain (shown diagrammatically in  FIG. 1A ) with a link pitch P has rollers  15 , 15   a  of diameter D R  in contact with the tooth root surface  14  at the root diameter RD (the diameter of an inscribed circle tangent to the radially innermost location on the root surface  14 ), and the fully meshed or seated roller  15  is tangent to the root diameter RD. The ISO sprocket  10  has a chordal pitch also of length P. The pitch circle diameter PD, tip or outside diameter OD, and tooth angle A (equal to 360°/N; N=tooth count) further define the ISO 606 compliant sprocket. For a given direction of sprocket rotation  11 , the leading flank  16   a  of a tooth T is referred to herein as an engaging flank and the trailing flank  16   b  of that same tooth T is referred to as the disengaging flank, and each tooth T is defined symmetrically about a tooth center TC. 
         [0003]    Roller-sprocket impact at the onset of meshing is the dominant noise source associated with roller chain drive systems and it occurs when a chain link row leaves the span and its meshing roller collides with the sprocket tooth. It is believed that multiple roller-sprocket tooth impacts occur during the meshing phenomena and these impacts contribute to the undesirable noise levels associated with roller chain drives. There will be at least two impacts at the onset of meshing, a radial impact as the roller  15  collides with the root surface  14  and a tangential impact as the roller moves into its driving position. It is believed that radial impact(s) will occur first, followed closely by tangential impact(s). Referring to  FIG. 1A , the radial impact I R  for roller  15   a , which is shown at the onset of meshing, is believed to be the major contributor to the chain drive noise level. Accordingly, it is desirable to develop a new and improved roller chain sprocket tooth form to reduce the noise levels associated with roller-sprocket impact at the onset of meshing. 
       SUMMARY 
       [0004]    In accordance with one aspect of the present development, a chain drive system includes a sprocket comprising a plurality of teeth with tooth spaces defined between each circumferentially successive pair of teeth. Each of the tooth spaces defined at least by opposing first and second convex tooth flanks and a concave root surface extending between the convex tooth flanks. The plurality of teeth are symmetrically defined about respective tooth centers evenly spaced from each other at a tooth angle such that each of the tooth spaces is symmetrically defined. A chain is engaged with the sprocket, and the chain includes rollers that are respectively received in the tooth spaces. The root surface of each tooth space comprises a modified root surface portion defined with root relief so that a roller fully seated in the tooth space contacts the root surface at first and second circumferentially spaced apart roller-seating locations, but is spaced from the root surface between the first and second circumferentially spaced apart locations. The fully seated roller includes a roller center located on a pitch diameter. 
         [0005]    In accordance with another aspect of the present development, a sprocket includes a plurality of teeth with tooth spaces defined between each circumferentially successive pair of teeth. Each of the tooth spaces is defined at least by opposing first and second convex tooth flanks and a concave root surface extending between the convex tooth flanks. The plurality of teeth are symmetrically defined about respective tooth centers evenly spaced from each other at a tooth angle such that each of the tooth spaces is symmetrically defined. The sprocket is adapted to mesh with an associated chain such that rolling or non-rolling rollers of the associated chain are received in respective ones of said tooth spaces. Each of said tooth spaces is defined with a modified root surface portion adapted to contact a fully seated roller of the associated chain at first and second circumferentially spaced apart roller-seating locations, and adapted to be spaced from the fully seated roller between the first and second roller seating locations. 
         [0006]    In accordance with another aspect of the present invention, a sprocket includes a plurality of teeth with tooth spaces defined between each circumferentially successive pair of teeth. Each of the tooth spaces is defined at least by opposing first and second convex tooth flanks and a concave root surface extending between the convex tooth flanks. The plurality of teeth are symmetrically defined about respective tooth centers evenly spaced from each other at a tooth angle such that each of the tooth spaces is symmetrically defined. The sprocket defines a roller seating diameter that is greater than a root diameter. 
     
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0007]    The invention comprises various components and arrangements of components, preferred embodiments of which are illustrated in the accompanying drawings wherein: 
           [0008]      FIG. 1  is a partial front view of a conventional ISO 606 compliant roller chain sprocket; 
           [0009]      FIG. 1A  is an enlarged illustration of the  FIG. 1  sprocket showing a roller at the onset of meshing; 
           [0010]      FIG. 2  partially illustrates a sprocket with root relief formed in accordance with one aspect of the present development; 
           [0011]      FIG. 2A  is an enlarged illustration of the  FIG. 2  sprocket showing a roller at the instant of 2-point meshing impact; 
           [0012]      FIG. 3  is an overlay of the ISO 606 tooth form shown in  FIG. 1  with the tooth form shown in  FIG. 2 ; 
           [0013]      FIG. 4  is a partial front view of a sprocket defined with chordal pitch reduction and root relief in accordance with another aspect of the present development; 
           [0014]      FIG. 5  is an overlay of the ISO 606 tooth form shown in  FIG. 1  with the tooth form shown in  FIG. 4 ; 
           [0015]      FIG. 6A  is an enlarged illustration of the  FIG. 4  tooth form showing a roller at the onset of meshing having initial meshing contact; 
           [0016]      FIG. 6B  is an enlarged illustration of the  FIG. 4  tooth form showing a roller at the instant of 2-point meshing impact; 
           [0017]      FIG. 7  shows a chain drive system in accordance with the present development. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The present invention is directed to a new sprocket for a roller chain and a drive system including one or more sprockets formed in accordance with the present invention drivingly engaged with a roller chain. The chain and portions thereof described herein are conventional in all respects unless otherwise noted or shown. The term “roller” as used herein with respect to a chain encompasses both rotating and non-rotating members, e.g., a rotatable sleeve carried on a non-rotatable bushing or other location/member, or simply a non-rotatable bushing or other member itself without any rotatable sleeve carried thereon such as used for a bush chain. Accordingly, the term “roller chain” is intended to encompass a chain with rotatable rollers or a “bush chain” wherein the “rollers” are merely non-rolling bushings or other non-rotatable members. 
         [0019]      FIG. 2  partially shows a sprocket  20  formed in accordance with a first embodiment of the present development. As compared to the sprocket  10  shown in  FIGS. 1 and 1A , the sprocket  20  is modified to include “root relief,” i.e., to define a modified concave root surface  24  that provides 2-point contact at roller seating locations  22   a , 22   b  when a chain roller  15  is fully seated in the root of the tooth space TS 20  (those of ordinary skill in the art will understand that locations  22   a , 22   b  are lines of contact that extend across a thickness of the root surface  24 ). A clearance space  21  is thus defined between the fully seated roller  15  and the modified root surface  24  between the contact locations  22   a , 22   b . A reference line L 1  that passes through the center C of the fully seated roller  15  and also through the sprocket axis of rotation X (see  FIG. 7 ) symmetrically bisects the tooth space TS 20  and symmetrically bisects distance between the roller seating locations  22   a , 22   b.    
         [0020]    Referring now also to  FIG. 2A , the roller  15  is shown in a fully meshed (2-point) driving position and the next meshing roller  15   a  is shown at the instant of meshing impact at locations  22   a , 22   b . The 2-point contact at these contact locations  22   a , 22   b  effectively serves to spread the initial radial impact I R  over a larger contact area as compared to the sprocket  10  which will exhibit single-point contact for the radial impact I R . 
         [0021]    As shown in the  FIG. 3  overlay of the tooth forms T,T 20  of the sprockets  10 , 20 , respectively, it is apparent that the profile difference is in the roller seating angle α region only, radially inward from and circumferentially between the tangency points TP. The flank radii R f  for both convex flanks  26   a , 26   b , the outside diameter OD, and the pitch diameter PD for the tooth form T 20  are respectively identical to the tooth form T for the ISO 606 compliant sprocket  10 . Referring now to all of  FIGS. 2 ,  2 A, and  3 , there is “root relief” or an open clearance space  21  defined between a roller  15  and the modified root surface  24  when the roller  15  is fully seated and in contact with roller seating locations  22   a , 22   b  of the sprocket  20 . As such, the root diameter RD 20  of the sprocket  20  is smaller than the root diameter RD of the sprocket  10  owing to this root relief, but the radial position of the fully seated roller  15  is unchanged as between the sprockets  10 , 20 . The angle φ ( FIG. 2 ) has a vertex at the roller center C and locates the roller seating locations  22   a , 22   b  between which the roller  15  bridges the root surface  24 , and this angle is preferably 90°, but may be in the range of 75° to 100°. It is important to note that the roller  15  is in the same radial position (with its center C also on the pitch circle PD) as a fully meshed roller with the ISO 606 compliant sprocket tooth form  10 . Accordingly, the sprocket  20  defines or exhibits a roller seating diameter  25 , which is defined as the diameter of the inscribed circle tangent to a roller  15  seated on roller-seating locations  22   a , 22   b , and this roller seating diameter  25  is equal to the root diameter RD of a standard ISO sprocket  10 , but is larger than the root diameter RD 20  of the sprocket  20 . In other words, the only functional difference for sprocket  20  as compared to the conventional sprocket  10  is the 2-point roller contact at points  22   a , 22   b  and the related root relief clearance space  21 , without any radial inward movement of the fully-meshed roller  15  as compared to the standard ISO sprocket  10 . The modification to the roller seating angle α region to provide the 2-point contact at locations  22   a , 22   b  and related root relief  21  may be accomplished by combining straight line segments with circular arc segments, and/or involute segments, i.e., the shape of the root surface  24  between the contact points  22  can vary given that the roller  15  makes no contact with this surface. The tooth space TS 20  of the sprocket  20  as defined by the flank radii R f  and modified root surface  24  is symmetrical, with all line segments, etc. being tangent to adjacent segments in order to provide a smooth transition and tooth form, and this modified root surface  24  will also be tangent to the flank radii R f  at the points TP so that the tooth form T 20  for the sprocket  20  will precisely overlay the tooth T form for the sprocket  10  outward from the tangency points TP to the tip or outside diameter OD. 
         [0022]    As shown above in  FIGS. 1 and 1A , the chain link pitch P for a minimum “as-manufactured” (new or unworn) roller chain is equal to the chordal pitch P for a roller chain sprocket such as the sprocket  10  having a maximum as-manufactured tooth form. This equality for chain pitch P and sprocket chordal pitch P exists only at the aforementioned limits of the manufacturing tolerance range, and as the relevant chain and sprocket tolerances vary toward the opposite end of their respective manufacturing limits, there will be a pitch mismatch between chain link pitch and sprocket chordal pitch, with the chain link pitch being greater than the sprocket chordal pitch. In other words, the chain link pitch will always be slightly greater than sprocket chordal pitch except at the specified manufacturing tolerance limits as noted. 
         [0023]      FIG. 4  illustrates a sprocket  30  formed in accordance with an alternative embodiment, which includes added chordal pitch reduction (referred to herein as “added CPR”) i.e., sprocket chordal pitch reduction that is greater than the inherent pitch mismatch between the sprocket and chain as described above, in addition to the previously defined root relief  21 . This sprocket  30  is identical to the sprocket  20  except the tooth profile T 30  is also shifted radially inward (see the overlay with the conventional sprocket  10  in  FIG. 5 ) as a result of the added CPR, thereby introducing pitch mismatch between the chain link pitch P and sprocket chordal pitch P 30  as shown in  FIG. 5  with chordal pitch P 30  being shorter than the standard chain and sprocket chordal pitch P by an amount greater than that resulting from manufacturing tolerances. The sprocket chordal pitch P 30  is less than the chain link pitch P by an amount equal to at least 0.4% up to 1% of the as-built (unworn) chain link pitch P. 
         [0024]    Referring to  FIG. 5 , the added chordal pitch reduction in accordance with the present development is diagrammatically illustrated in which a standard ISO 606 chordal pitch P on pitch diameter PD is compared to the reduced chordal pitch P 30  of the sprocket  30  on the smaller pitch diameter PD 30 . The magnitude of the radial difference  23  between the standard pitch diameter PD of a standard ISO sprocket  10  and the pitch diameter PD 30  of the sprocket  30  provides another means for measuring the magnitude of the added chordal pitch reduction. The outside diameter OD and roller seating angle α of the sprocket  30  are identical to the standard sprocket  10 , and the magnitude of the flank radii R f 30  for the flanks  36   a , 36   b  may or may not be the same as the magnitude of the radii R f  of the corresponding flanks  16   a , 16   b  for the sprocket  10 . Referring again to  FIG. 4 , roller  15  is shown to be fully meshed and seated on contact points  32   a , 32   b  with its center C shifted radially inward on the smaller diameter pitch diameter PD 30 , which is smaller than the standard ISO 606 pitch diameter PD of the sprockets  10  and  20 . A root relief clearance  31  is defined between the roller  15  and the relieved root surface  34  so that the roller  15  bridges the root surface  34  between trailing and leading roller seating locations  32   a , 32   b . The root diameter R 30  of the sprocket  30  is smaller than the root diameter R 20  of the root relief sprocket  20  without the added CPR. 
         [0025]    Referring now to  FIG. 6A , the sprocket  30  is rotating in direction  11  and the leading roller  15  is seated in 2-point contact at trailing and leading roller-seating locations  32   a , 32   b . The meshing roller  15   a  is shown at an instant of single-point meshing impact IC at an initial contact point  33   a  as a result of the pitch mismatch. The initial contact point  33   a  is located radially outward from the trailing roller seating locations  32   a . As the roller engagement phenomenon continues as shown in  FIG. 6B , the meshing roller  15   a  will then make 2-point radial impact I R  at contact points  32   a , 32   b , and may rebound and have multiple impacts before finally moving into driving position. Owing to the pitch mismatch, as the roller  15   a  meshes in this staged manner, the preceding roller  15  is pushed forward slightly into single point contact at point  33   b  located slightly radially outward from the leading roller seating location  32   b  on the disengaging (trailing) side of the preceding sprocket tooth. This staged meshing phenomenon leads to reduced noise and vibration as the chain meshes with the sprocket  20 . 
         [0026]      FIG. 7  shows a chain drive system in accordance with the present development. The chain C is conventional in all respects and includes rows R of link plates L and (rotatable or non-rotatable) rollers  15 . The chain is drivingly engaged with the sprocket  30 , with rollers  15  received in the tooth spaces TS thereof. The sprocket  30  rotates about an axis of rotation X. 
         [0027]    The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein.