Rocker joint silent chain having a joint pin thicker than a...

Endless belt power transmission systems or components – Positive drive belt – Belt formed of rigid links

Reexamination Certificate

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Details

C474S212000

Reexamination Certificate

active

06186921

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a silent chain, or chain with links having inverted teeth. More particularly, the invention related to a silent chain with a rocker-joint and, in particular, to a rocker joint having improved resistance to fracture as a result of usage and wear.
Generally, silent chains are used with sprockets as the power transmission chain in transmissions, transfer cases, engine timing systems, and the like, for automobiles and motorcycles. Silent chains are formed by the assembly of rows of link plates in transverse and longitudinal directions. Conventionally, the direction along the length of chain as it travels between the sprockets is referred to as the longitudinal direction. The links are interlaced and joined by connecting pins. Each link plate has a pair of teeth and a pair of pin apertures. The links are connected to each other by connecting pins inserted in each pin aperture. Guide links are utilized to maintain the chain on the sprockets when the chain is wrapped around the sprockets during operation. Guide link plates are typically installed in the center or at both outer edges of the row of link plates arranged in the lateral direction. The guide links are conventionally press fit over pins, which connect the interlaced inside or articulating links. Guide links typically do not include inverted teeth.
Conventionally, a rocker joint is used as the connecting pin. The rocker joint is comprised of a pair of long and short pins, i.e., a rocker pin and a joint pin that is longer than the rocker pin and both ends of which are fixed to guide links. The pins connect the links across the width of the chain in the transverse direction, i.e., at right angles to the longitudinal direction.
Damage to a chain may first occur during the press-stress operation, where the newly-assembled chain is subjected to a high load. During the pre-stress operation, cracks may be formed in a link plate or pin shortening the operational life of the chain. After undergoing normal usage and wear, the silent chain typically fails due to fracture of the connecting pin due to the rocker joint structure. This fracture often occurs at the attachment of the guide link to the rocker joint, where the effective cross-sectional area of the rocker joint decreases.
Examined Japanese Patent Application 1-55821 proposes a silent chain in which the joint pin is reinforced by placing one link plate on the inside of the guide link to prevent contact damage or breakage of the joint pin. However, in this case, the overall width of the chain is increased by the thickness of the additional link plate. Therefore, the most effective means to prevent breakage of the joint pin without increasing the chain width is to increase the cross-sectional area of the overall rocker joint and to decrease the shear stress that acts on the joint pin.
Another prior art patent has proposed the silent chain disclosed in Japanese Laid-Open Patent 6-207643. In this silent chain, the pin aperture formed in the link plate has a long-circular shape to increase the cross-sectional area of the overall rocker joint, which includes a rocker pin and joint pin. The aperture results in the increased breaking strength of the joint pin. However, the special shape of the pin aperture must be formed in the link plate.
The present invention provides an improved silent chain by increasing the wear resistance of the joint pin without employing a special pin aperture shape.
SUMMARY OF THE INVENTION
The silent chain of one embodiment of the present invention comprises multiple link plates, each having an aperture formed at each end thereof. The link plates are connected to one another by rocker pins and joint pins received in the apertures. The joint pins are longer than the rocker pins. Guide links are press fit on both ends of the joint pins. The cross-sectional area of the joint pins is larger than that of the rocker pins.
The silent chain of a second embodiment of the present invention has a joint pin that has a thickness that is greater than that of the rocker pin.
In the silent chain of a third embodiment of the present invention, the center of the curvature of the rolling surface of the joint pin and the center of curvature of the rolling surface of the corresponding rocker pin are asymmetrical with respect to the centerline of the aperture and the radius of the curvature of the rolling surface of the joint pin is greater than that of the rocker pin.
In the present invention, the breaking strength of the joint pin is increased without employing a special pin-aperture shape because the cross-sectional area of the joint pin is made larger than that of the rocker pin.
Although the cross-sectional shape of the rocker pin is relatively smaller because the cross-sectional area of the joint pin is increased, in the case of the rocker pin, its overall effective cross-sectional area is not changed. Even if the cross-sectional area of the rocker pin is decreased, the corresponding cross-sectional area of the joint pin is increased by the same amount so that the shear stress is borne across the rocker pin in cooperation with the joint pin. Therefore, the shear stress generated in the rocker pin changes very little, even if the cross-sectional area of the rocker pin is decreased and, as a result, the breaking strength of the rocker pin is maintained.
For a better understanding of these and other aspects and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.


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European Search Report in EPO 99303938.7, dated Oct. 18, 1999.

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