Endless belt power transmission systems or components – Positive drive pulley or guide roll – With particular belt
Reexamination Certificate
1999-08-11
2001-06-12
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Positive drive pulley or guide roll
With particular belt
C474S156000, C474S212000, C474S213000
Reexamination Certificate
active
06244983
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is related to a silent chain power transmitting device formed by a combination of a silent chain and sprocket. The silent chain is formed of a plurality of interleaved links. Each link has a pair of depending teeth joined at a crotch. Each tooth has an inside flank and an outside flank. The links are interleaved and are connected by connecting pins inserted through pin holes or apertures formed in each link. The teeth of the silent chain engage with teeth formed on an associated sprocket. In particular, this invention is related to a silent chain transmission device with reduced noise from impact engagement and vibration during operation.
Silent chain is typically used in automobiles, motorcycles and other vehicles to transmit power. The silent chain usually includes rows of multiple links interleaved in an endless loop wrapped around a pair of sprockets. During operation, one of the flank sides of the teeth on the link engages with the teeth on the sprocket to transmit power from the driving sprocket to the driven sprocket.
When using a conventional silent chain, engagement between the chain and the sprocket generates noise. In order to reduce noise, it is preferable to have smooth contact between the link and the sprocket. The engaging vibration or chordal action of the chain during engagement is also one of the causes of noise. In order to reduce the engaging vibration, the chain should maintain a linear movement until it engages with the sprocket. Therefore, it is believed that chain noise can be significantly reduced if the chain can maintain its linear movement and then smoothly engage with the sprocket.
In other words, the movement of the silent chain and the sprocket are very like the movement of a rack-type cutter. The linear part of the silent chain can be considered similar to a rack cutter that moves across a sprocket and the sprocket can be considered as the gear cut by the rack cutter.
Based on the above consideration, the inventor proposed a silent chain transmission device in Japanese laid-open application no. (Kokai) Hei 8-184348. In that silent chain, the flank side of the tooth on each link series which engages with a sprocket when the silent chain is extended in a linear form has the same shape as the part of the tooth shape of a rack cutter capable of generating the sprocket, and the sprocket has a tooth shape generated by such a rack cutter. As a result, the silent chain is able to maintain its linear movement and contact smoothly and then engage with the sprocket with minimal vibration during engagement.
By using such a silent chain transmission device, the noise generated by the impact of the chain on the sprocket and the engaging vibration, including the low-frequency noise, can be suppressed. In addition, since the rotation of the links within the link rows is proportional to the angle of rotation of the sprocket, the irregularity in angular velocity can be prevented.
In a series of studies on the reduction of the noise generated by a silent chain during operation it was found that the noise is generated not only in the initial stage of the engagement but also when the chain and the sprocket are fully engaged.
Especially for the silent chain with a structure using the inside flank for initial engagement but the outside flank for full engagement, the noise level reaches its peak when the chain and the sprocket are fully engaged. This may be explained by sudden increase of the load on the engaging point when the engaging point shifts from the inside flank to the outside flank.
However, the silent chain proposed in the prior art laid-open publication mentioned above has been designed to reduce the noise only in the initial stage of the engagement. The noise problem when the chain and the sprocket are fully engaged is not addressed by that chain.
In consideration of the situation described above, the purpose of this invention is to reduce the noise for a silent chain transmission device not only in the initial stage of the engagement but also when the chain and the sprocket are fully engaged, and to provide a silent chain with minimal vibration during engagement.
SUMMARY OF THE INVENTION
In a first embodiment, the present invention includes a silent chain comprising multiple interleaved links. Each link has a pair of teeth with an inner flank and an outer flank. The links are interconnected by connecting pins. A sprocket is used together with the silent chain.
In one embodiment, the inner flank of the link tooth contacts the tooth of the sprocket when the silent chain is extended in a linear direction as well as when the chain is wound on the sprocket. The first part of the tooth surface on the sprocket which contacts the silent chain in the initial stage of the engagement has a tooth shape the same as the envelope for the locus of the lower part of the inner flank of the chain link which engages the sprocket when the silent chain has a linear movement with minimal engaging vibration. The second part of the tooth surface on the sprocket which contacts the silent chain at the full engagement or seating in the sprocket has a tooth shape the same as the envelope for the locus of the upper part of the inner flank of the chain link which engages with the sprocket when the silent chain is wound on the sprocket and the link has a rotary movement.
As noted above, the first part of the tooth surface on the sprocket, which contacts the silent chain in the initial stage of the engagement, has a tooth shape which is the same as the envelope for the locus of the lower part of the inner flank which engages with the sprocket when the silent chain has a linear movement without engaging vibration. As a result, when the silent chain maintains a linear movement towards the sprocket, the link has a smooth contact with the sprocket and is able to engage with the sprocket with minimal impact and causing minimal engaging vibration. Therefore, the noise caused by the impact of the link on the sprocket during the initial stage of the engagement can be minimized.
Next, as the engagement progresses and the silent chain is wound or seated on the sprocket, the upper part of the inner flank of the link contacts the second part of the tooth surface on the sprocket, due to the rotation of the link around the tooth of sprocket. In other words, the silent chain has a structure using the inside for both initial engagement and full engagement. In this case, the engaging point between the link and the sprocket is always on the inner flank from initial engagement to full engagement. As a result, the chain of this invention will not have the sudden increase of load on the engaging point due to the shift of the engaging point observed for the chain structure using the inside flank for initial engagement but the outside flank for full engagement.
In addition, the loading on each tooth of the sprocket can be decreased and the lifetime of the sprocket can be extended. Moreover, the second part of the tooth surface on the sprocket has a tooth shape which is the same as the envelope for the locus of the upper part of the inner flank when the link has a rotary movement. As a result, when the silent chain is wound on the sprocket, the upper part of the inner flank engages with the second part of the tooth surface on the sprocket as the link rotates around the tooth of the sprocket. Therefore, the impact of the link on the tooth of the sprocket at full engagement can be minimized and the noise generated can be minimized.
A second embodiment of the present invention concerns a silent chain described in the first embodiment and is further characterized by the fact that the first part and the second part of the tooth surface on the sprocket are connected through a curved surface.
According to the present invention, the noise generated by the silent chain transmission device can be reduced not only in the initial stage of the engagement but also when the chain and the sprocket are fully engaged, and the vibration properties of the silent chain transmission device
Borg-Warner Automotive K.K.
Bucci David A.
Charles Maran
Dziegielewski Greg
McAndrews Held & Malloy Ltd.
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