Patent Application
20050020392
The invention relates to a sprocket and more particularly to a composite sprocket comprising a polymer ring mounted to a metallic hub with retaining members and a transverse lug.
Sprockets are well known in the art of power transmission. Two or more sprockets may be connected by a belt, chain or other flexible member suitable for bearing a tensile load. A sprocket may have a flat belt bearing surface or comprise transversely mounted teeth, gears or grooves.
Prior art sprockets are generally homogeneous, meaning the body of the sprocket and the teeth are made or cut out of the same material. The material may comprise metal, plastic, or other suitably tough material. In other instances the sprocket teeth are removable. This allows the teeth to be individually replaced, allowing the sprocket to remain in service during maintenance. The prior art sprockets of this type comprise metal such as steel and are used in severe duty applications such as on earth moving equipment.
Representative of the art is U.S. Pat. No. 4,752,281 (1988) to Lammers which discloses a drive sprocket assembly having a support hub and a plurality of replaceable teeth.
Also representative of the art is GB 2064708 (1980) to Berg which discloses a composite gear or sprocket wheel, the outer toothed portion is formed of a piece of continuously moulded flexible gear belting attached to the rim of the gear or sprocket wheel center blank or disc.
Reference is also made to copending application Ser. No. 10/404,181 filed Mar. 31, 2003 by the same inventor as the instant invention which discloses a composite sprocket having a non-metallic ring for engaging a driving member.
The prior art sprockets do not teach a hub having a removable wear surface attached to the hub using a retaining ring and transverse lugs to prevent rotation.
What is needed is a composite sprocket having a hub with a removable wear surface attached to the hub by retaining members and having transverse lugs to prevent rotation between the hub and the removable wear surface. The present invention meets this need.
The primary aspect of the present invention is to provide a composite sprocket having a hub with a removable wear surface attached to the hub by retaining members and having transverse lugs to prevent rotation between the hub and the removable wear surface.
Other aspects of the invention will be pointed out or made apparent by the following description of the invention and the accompanying drawings.
The invention comprises a composite sprocket. The sprocket comprises a polymer outer ring mounted to a metallic inner hub. The outer ring has a profile, for example, a toothed profile. The toothed ring comprises a thermoset material such as polyurethane. The hub comprises any suitable metallic or non-metallic material sufficient for transmitting a torque from the ring to a shaft. A retaining ring or adhesives or both are used to lock the ring in place on the hub. Cooperating transverse lugs on the ring and grooves in the hub prevent the ring from rotating when subjected to a torque. A retaining member or members are used to prevent lateral movement of the ring.
Description of the Preferred Embodiment of the Invention
Hub 10 has an outer rim 11. Outer rim 11 comprises radial projection or shoulder 12. Hub 10 may comprise any suitable material for transmitting a torque such as metallic or non-metallic material, for example but not by way of limitation steel, stainless steel with hardening on the belt bearing surface, aluminum, as well as their equivalents, or a combination thereof.
Circular member or ring 20 comprises a flange 21 disposed on one side of the ring for keeping a belt trained thereon. Ring 20 also comprises an outer profile, for example, a toothed profile for engaging a belt comprising grooves 21 between teeth 22, see
Ring 20 comprises a polymeric material, namely, molded thermoset or thermoplastic including but not limited to polyurethane, polyamide, polystyrene, polyethylene, and a combination of two or more of the foregoing, and their equivalents. For example, ring 20 may comprise Adiprene L-325, which is a liquid urethane elastomer that can be cured to a strong, rubbery solid by reaction of its terminal isocyanate groups with polyamine or polyol compounds. Properly cured L-325 yields hard tough products that approach the strength of structural plastics. L-325 typically has high impact strength and resistance to abrasion and deformation with resilience and extensibility. L-325 vulcanizite is resistant to heat, water, ozone, oils and most solvents.
Use of a thermoset or thermoplastic material has the advantage of improving resistance to the effects of debris caught between a belt and ring 20. The ring is more compliant than prior art metal sprockets allowing the ring to partially absorb part of a debris penetrating force which otherwise would be absorbed solely by a belt, thereby facilitating a belt failure. Ring 20 may also comprise a metallic material.
Ring 20 is molded having a radius ID1 under ambient conditions. An outer surface 16 of outer rim 11 is fabricated with a radius ID2. Shoulder 12 has a radius ID3. Radius ID3 is greater than ID1. The relationship between ID1, ID2 and ID3 is a function of the coefficient of thermal expansion of the ring 20. It is desirable that the ring be expandable just enough so that after it is heated it can be slipped or pressed onto rim 11 to bear upon surface 16. Upon cooling the ring shrinks back to ID1.
Retaining member or retaining ring 13 is engaged with circumferential groove 14 in rim 11. Retaining ring 13 prevents lateral movement and retains ring 20 on outer surface 16. By way of example and not of limitation, a retaining ring manufactured by Smalley Steel Ring Company, part number WS-1100 may be used in the invention.
To assemble the composite sprocket, ring 20 is heated as necessary in order to slightly soften and expand the ring. The temperature range to which the ring is heated is approximately 65° C. to 175° C. Heating the ring expands the radius ID1 according to the coefficient of thermal expansion of the ring material. Ring 20 is then pressed over and engaged with surface 16. Lugs 17 are aligned with and engage grooves 15. Hub 10 is maintained at an ambient temperature, approximately 23° C., during this process. As ring 20 cools it shrinks, returning the ring to ID1, thereby mechanically locking ring 20 into hub 10. Retaining ring 13 is then snapped in place in groove 14.
In another embodiment, no retaining ring is used. Ring 20 is retained by the radial dimensional difference between ID1 and ID3. Namely ID3 is of a sufficient magnitude to prevent ring 20 from coming off the sprocket once it cools by creating an interference fit between the ring and the hub.
A metallic ring may also be installed in a like manner, that is by heating to partially expand the ring and then sliding it on the hub while the hub is maintained at an ambient temperature. Retaining ring 13 is used to hold metallic ring 20 in place. The metallic embodiment may comprise stainless steel with a hardened belt bearing surface. Bolts (not shown) are engaged through holes 19 to attach hub 10 to a known motorcycle wheel W.
Ring 20 comprises lugs 17 which extend transversely across a ring width on a ring inner surface 18. Lug receiving grooves 15 are disposed about outer surface 16. Lug grooves 15 are transversely oriented in order to cooperatively engage lugs 17 when ring 20 is pressed onto outer surface 16. Grooves 15 are slightly deeper than a lug height in order to facilitate installation and to eliminate radial interference between the lug and the groove, see gap G. Lugs 17 lock the ring in place on the hub so that an excessive torque does not result in a relative rotational movement of the ring and the hub.
Certain pairs of lugs 17 and grooves 15 may be circumferentially spaced so as to create a particular keyed arrangement whereby a certain orientation may be realized between ring 20 and hub 10. For example, a spacing between two lug and groove set may be less than a spacing between another lug and groove set. This keyed feature can be used to assure a desired relationship between the ring and sprocket.
Surface 16 may be treated with a known adhesive to bind ring 20 to hub 10. For example, any epoxy adhesive suitable for the temperature and materials can be used, including but not limited to the 3M series 800 epoxies such as 3M DP810™. Further, an interference fit may be created by making ID2 greater than ID1 in an ambient temperature condition. Either method of fixing the ring to the hub serves to lock the ring in place on the hub, thereby preventing it from moving relative to the hub while transmitting a torque.
The inventive sprocket facilitates maintenance of the sprocket. Once the toothed profile has worn a predetermined amount, the outer ring 20 can easily be removed and replaced. This eliminates the need to replace the entire sprocket, as well as eliminating the need to remove the entire sprocket from a wheel.
The sprocket, wheel and tire represent a significant part of the unsprung weight of the rear suspension of a motorcycle. Reducing the unsprung weight can significantly improve the handling characteristics of a motorcycle. The inventive sprocket serves such a purpose. Use of a thermoplastic ring 20 significantly reduces a sprocket weight. For example, an average density for high speed tool steel is ˜8.7 gm/cc, or 546 lb/ft3. An average density for polyurethane is ˜1.3 g/cc, or, 82 lb/ft3. This difference in density represents a significant weight reduction in a single composite pulley system, as well as a significant weight reduction in a system utilizing multiple composite pulleys.
Using the inventive sprocket in a typical motorcycle rear suspension this can result in an unsprung weight reduction of approximately 676 grams. For example, a known aluminum sprocket, wheel, brake disc, mounting bolts (5) and tire combination weighs 21.12 kilograms. The same combination using the inventive composite sprocket weighs 20.45 kilograms. More particularly, the known metal sprocket used in the foregoing system weighs 2,832 grams. A composite sprocket of identical physical design weighs 2,147 grams, a sprocket weight reduction of approximately 25%. This also directly affects the suspension components such as the shocks and springs by a reduction in service conditions and thereby overall cost.
Surface 16 may be treated with a known adhesive to further bind ring 20 to hub 10. For example, any epoxy adhesive suitable for the temperature and materials can be used, including but not limited to the 3M series 800 epoxies such as 3M DP810™. Further, an interference fit may be created by making ID2 greater than ID1 in an ambient temperature condition. Either method of fixing the ring to the hub serves to lock the ring in place on the hub, thereby preventing it from moving relative to the hub while transmitting a torque.
In an alternate embodiment ring 20 is cast in place on rim 11 using known techniques.
Although forms of the invention has been described herein, it will be obvious to those skilled in the art that variations may be made in the construction and relation of the parts without departing from the spirit and scope of the invention described herein.
| Number | Date | Country | |
|---|---|---|---|
| 60489407 | Jul 2003 | US |
