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.