1. Field of the Invention
The invention pertains to the field of sprockets for roller or bush chains. More particularly, the invention pertains to a sprocket that reduces the noise generated when the roller or bush chain and the sprocket mesh.
2. Description of Related Art
Conventional chain sprocket interfaces seat the roller or bush in the root of the sprocket tooth as if the sprocket is held stationary and a taut chain is wrapped around it. A roller swinging-on an arc the length of a chain pitch around the center of the previous roller, located on the pitch circle of the sprocket, contacts the root of the sprocket tooth when reaching the pitch circle of the sprocket.
The prior art discloses attempts to reduce the noise created by rollers impacting a sprocket. Some sprocket designs have attempted to decrease the impact noise of roller chain drives by altering the sprocket tooth profile. One attempt to reduce roller chain and sprocket noise using a modified sprocket tooth profile is described by U.S. Pat. No. 5,921,877. A sprocket tooth profile having three sections is described as making the roller of a chain come into engagement with the teeth of the sprocket without generating a large noise. However, this design is limited to a unidirectional roller chain drive because of the asymmetry of the tooth profile as generally shown by
Other designs also utilized an asymmetrical tooth design in an effort to reduce the noise generated by the impact of the rollers as they strike the sprocket. U.S. Pat. Nos. 5,921,878 and 5,993,344 disclose an asymmetrical tooth profile that incorporates a flank flat that is tangential to an engaging flank radius and a first root radius, and a pitch mismatch, where the sprocket chordal pitch is less than the chain chordal pitch. This arrangement is described as facilitating a staged roller tooth contact with the sprocket. Again, the asymmetry of the tooth profile mandates a unidirectional roller chain drive system.
Other asymmetrical tooth designs provide a tooth space clearance between the roller and a portion of the tooth root in an attempt to reduce the noise generated by the vibrational contact of unseated rollers with the sprocket teeth as the rollers wear.
U.S. Pat. No. 6,736,744 discloses a sprocket that substantially avoids radial impact of chain rollers with the sprocket. The tooth root radius of the sprocket is increased while the sprocket pitch circle diameter is maintained. Thus, a clearance between the roller and the tooth root is created, which allows rollers of a chain of like pitch to impact the sprocket teeth in a substantially tangential fashion on their flanks, rather than substantially radially on the tooth root. Backlash is not minimized with this design.
Similarly, U.S. Publication No. 2003/0186766 discloses an engaging flank profile with seating, impact and distal portions, all with arcs with well-defined radii and arc centers. The profile of the disengaging flank is determined in accordance with a modified form of the JIS standard, in which the sprocket pitch is smaller than the roller chain pitch. The impact point is located at the tangent point to permit a gradual change in the roller velocity. Backlash is not minimized with this design.
Therefore, there is a need in the art for a multi-directional sprocket that substantially minimizes the noise generated by the substantially radial impacts between the rollers of a roller chain and a sprocket, while minimizing backlash.
An improved sprocket profile engages a roller or bush chain smoothly and prevents radial impact with the root of the tooth during engagement. Teeth on the sprocket have a root radius equivalent to that of the chain engaging component, with the center point of the root radius located one chordal distance inside the sprocket's pitch circle. This profile allows chain rollers or bushings to impact sprocket teeth tangentially on their flanks rather than radially on their tooth root. The present invention is applicable to both roller and bush chains.
The present invention alters the contact between the sprocket teeth and the roller or bush chain by providing teeth with a root radius equivalent to that of the chain engaging component, with the center point of the root radius located one chordal distance inside the sprocket pitch circle. The present invention uses the standard root radius from ISO, but, unlike the prior art, the root radius is located one chordal distance inside the pitch circle. The present invention decreases noise and backlash.
Chordal distance (also known as chordal rise and fall) is defined as the difference between the distance from the center of the sprocket to the centerline of the chain that is perpendicular to the centerline of the sprocket when a chain roller member (for a roller chain) or a chain bushing member (for a bush chain) is on the sprocket centerline and the distance when two roller members or two bushing members are equally spaced about the sprocket centerline. This value, or radial difference, varies with the chain and/or sprocket pitch.
In
The chordal distance determines the amount of backlash and, for a given number of teeth, the chordal distance increases as the diameter of the pitch circle decreases. Table 1 shows two examples of sprocket profiles.
In both examples, the pitch has been arbitrarily chosen as 8 mm. In the first example, the sprocket has ten teeth. The pitch circle radius with ten teeth is 12.944 mm. The corresponding chordal distance is 0.634 mm, which is quite large and may cause excessive backlash. Excessive backlash has been shown to be a very important contributor to the level and type of noise produced by a chain and sprocket interface. Therefore, as shown in
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.
Number | Name | Date | Kind |
---|---|---|---|
2667792 | Bendall | Feb 1954 | A |
2725755 | Riopelle et al. | Dec 1955 | A |
3448629 | Pfrank et al | Jun 1969 | A |
4036071 | McKnight et al. | Jul 1977 | A |
4099424 | Pemberton | Jul 1978 | A |
4116081 | Luttrell et al. | Sep 1978 | A |
RE30018 | Clemens et al. | Jun 1979 | E |
4738653 | Riewerts et al. | Apr 1988 | A |
4758209 | Ledvina | Jul 1988 | A |
5192252 | Skurka et al. | Mar 1993 | A |
5397278 | Suzuki et al. | Mar 1995 | A |
5419743 | Takeda et al. | May 1995 | A |
5848948 | Allen | Dec 1998 | A |
5876295 | Young | Mar 1999 | A |
5921877 | Suzuki | Jul 1999 | A |
5921878 | Young | Jul 1999 | A |
5993344 | Young | Nov 1999 | A |
5997424 | Young | Dec 1999 | A |
6030306 | Young | Feb 2000 | A |
6036614 | Baddaria | Mar 2000 | A |
6179741 | Young | Jan 2001 | B1 |
6325734 | Young | Dec 2001 | B1 |
6736744 | Wigsten et al. | May 2004 | B1 |
6761657 | Young | Jul 2004 | B2 |
20030186766 | Wang et al. | Oct 2003 | A1 |
20050009655 | Kubo et al. | Jan 2005 | A1 |
Number | Date | Country |
---|---|---|
55024203 | Feb 1980 | JP |
56150655 | Nov 1981 | JP |
09042423 | Feb 1997 | JP |
2002340142 | Nov 2002 | JP |
Number | Date | Country | |
---|---|---|---|
20070087880 A1 | Apr 2007 | US |