BRIEF DESCRIPTION OF DRAWINGS
The invention comprises various components and arrangements of components, preferred embodiments of which are illustrated in the accompanying drawings wherein:
FIG. 1 is a partial front view of a conventional ISO 606 compliant roller chain sprocket;
FIG. 1A is an enlarged illustration of the FIG. 1 sprocket showing a roller at the onset of meshing;
FIG. 2 partially illustrates a sprocket with root relief formed in accordance with one aspect of the present development;
FIG. 2A is an enlarged illustration of the FIG. 2 sprocket showing a roller at the instant of 2-point meshing impact;
FIG. 3 is an overlay of the ISO 606 tooth form shown in FIG. 1 with the tooth form shown in FIG. 2;
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;
FIG. 5 is an overlay of the ISO 606 tooth form shown in FIG. 1 with the tooth form shown in FIG. 4;
FIG. 6A is an enlarged illustration of the FIG. 4 tooth form showing a roller at the onset of meshing having initial meshing contact;
FIG. 6B is an enlarged illustration of the FIG. 4 tooth form showing a roller at the instant of 2-point meshing impact;
FIG. 7 shows a chain drive system in accordance with the present development.
DETAILED DESCRIPTION OF THE INVENTION
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.
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 22a,22b when a chain roller 15 is fully seated in the root of the tooth space TS20 (those of ordinary skill in the art will understand that locations 22a,22b 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 22a,22b. A reference line L1 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 TS20 and symmetrically bisects distance between the roller seating locations 22a,22b.
Referring now also to FIG. 2A, the roller 15 is shown in a fully meshed (2-point) driving position and the next meshing roller 15a is shown at the instant of meshing impact at locations 22a,22b. The 2-point contact at these contact locations 22a,22b effectively serves to spread the initial radial impact IR over a larger contact area as compared to the sprocket 10 which will exhibit single-point contact for the radial impact IR.
As shown in the FIG. 3 overlay of the tooth forms T,T20 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 Rf for both convex flanks 26a,26b, the outside diameter OD, and the pitch diameter PD for the tooth form T20 are respectively identical to the tooth form T for the ISO 606 compliant sprocket 10. Referring now to all of FIGS. 2, 2A, 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 22a,22b of the sprocket 20. As such, the root diameter RD20 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 22a,22b 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 22a,22b, 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 RD20 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 22a,22b 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 22a,22b 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 TS20 of the sprocket 20 as defined by the flank radii Rf 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 Rf at the points TP so that the tooth form T20 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.
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.
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 T30 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 P30 as shown in FIG. 5 with chordal pitch P30 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 P30 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.
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 P30 of the sprocket 30 on the smaller pitch diameter PD30. The magnitude of the radial difference 23 between the standard pitch diameter PD of a standard ISO sprocket 10 and the pitch diameter PD30 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 Rf 30 for the flanks 36a,36b may or may not be the same as the magnitude of the radii Rf of the corresponding flanks 16a,16b for the sprocket 10. Referring again to FIG. 4, roller 15 is shown to be fully meshed and seated on contact points 32a,32b with its center C shifted radially inward on the smaller diameter pitch diameter PD30, 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 32a,32b. The root diameter R30 of the sprocket 30 is smaller than the root diameter R20 of the root relief sprocket 20 without the added CPR.
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 32a,32b. The meshing roller 15a is shown at an instant of single-point meshing impact IC at an initial contact point 33a as a result of the pitch mismatch. The initial contact point 33a is located radially outward from the trailing roller seating locations 32a. As the roller engagement phenomenon continues as shown in FIG. 6B, the meshing roller 15a will then make 2-point radial impact IR at contact points 32a,32b, and may rebound and have multiple impacts before finally moving into driving position. Owing to the pitch mismatch, as the roller 15a meshes in this staged manner, the preceding roller 15 is pushed forward slightly into single point contact at point 33b located slightly radially outward from the leading roller seating location 32b 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.
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.
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.
Patent Application
20080081719
