Back drive type silent chain

Details Back drive type silent chain Back drive type silent chain

1999-01-21

2001-01-09

Bucci, David A. (Department: 3682)

Endless belt power transmission systems or components

Positive drive belt

Belt formed of rigid links

C474S212000

Reexamination Certificate

active

06171209

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a back-driving silent chain, and in particular, it relates to a guide link for a back-driving silent chain that has window portions to reduce the stiffness or rigidity of the link. The chain has a plurality of rows of links that are interleaved and connected by a connecting pin inserted in the apertures of each of the link plates. In its preferred embodiment each row comprises multiple link plates, each with a pair of apertures and a pair of teeth on both sides of the aperture or pinhole center line. The link plates have guide links positioned on the outermost side of the link plates. The invention relates to an improvement in the construction of the guide links.
Silent chains are used conventionally as power transmission chains for automobiles and motorcycles in transmissions and transfer cases for four-wheel drive vehicles. In general, a silent chain is comprised of multiple link plates, each of which has a pair of teeth. Each link typically includes a pair of apertures. The links are interleaved and are connected by connecting pins placed in the apertures. Guide links are positioned on the outermost side of the link plates and the ends of the connecting pins are press fit into apertures in the guide links.
FIGS. 7 and 8
show examples of a conventional low-rigidity or low stiffness guide links.
FIG. 7
shows the guide link disclosed in Japanese Utility Model No. 4-52641 ('641) (U.S. Pat. No. 5,176,586). In this case, guide link
100
has pinholes
101
,
102
and window hole
103
. As is clear from the shape of pinholes
101
,
102
and lines
1
-
2
of the '641 specification, the silent chain with guide link
100
is the rocker joint-type silent chain that uses a rocker joint composed of a pair of long and short connecting pins and pinholes
101
,
102
that secure the press-fit end of the longer pin of the rocker joint. Incidentally, single-dot line
110
in the figure indicates the pinhole center line.
When the silent chain comprising multiple link plates and guide links such as guide link
100
is operated, tension acts along the entire length of the chain. Tensile force applied through the connecting pins, in the direction to expand the aperture center distance (or pitch), acts on the apertures
101
,
102
of the guide links and on the apertures of the link plates. Because the rigidities or stiffness of the inner links differs from the stiffness of the guide links, the connecting pins of a conventional silent chain can be deformed or possibly fractured.
Therefore, various ideas have been implemented in the past to equalize the elongation of the guide links and inner links caused by the tensile load (tensile rigidity). The tensile load is applied during chain operation or, more commonly, during a preloading or pre-stressing operation after assembly of the chain.
FIG. 8
shows the guide link disclosed in Japanese Laid-Open Patent Heisei 4-210144 ('144) (U.S. Pat. No. 5,345,753) and guide link
200
has pinholes
201
,
202
and slit
203
. As is clear from the shape of pinholes
201
,
202
, the silent chain with this guide link
100
, too, is a rocker-joint-type silent chain and the end of the longer pin of the rocker joint is press-fit in apertures
201
,
202
. Incidentally, single-dot line
210
in the figure indicates the pinhole center line.
For these guide links, the tensile rigidity of the guide link is lowered by formation of a window hole
103
,
203
or slit. That is, the guide link is made to deform or elongate equally with the link plate against the tensile load, to prevent deformation of the rocker joint.
However, the conventional guide links are guide links for the rocker joint, as shown in
FIGS. 7 and 8
. Material thickness d at the edge of pinholes
101
,
102
and window hole
103
differs from material thickness d′ at the pinholes
201
,
202
and slit
203
. Depending on the position of the pinhole, the press-fit between the end of the pin of the rocker joint and pinhole may not be secure.
In the example in
FIG. 8
, although the material thickness d′ at the edges of slit
203
, pinholes
201
,
202
looks sufficient in the figure, the material thickness can be considerably less locally at the edges of the pinhole and slit as shown in FIG.
7
. If the round pinhole of the guide link
200
is changed to receive a round pin, while a similar slit,
203
, is utilized, decrease of the force that secures the end of the rocker joint pin in the pinhole can occur easily.
On the other hand, in the case of the back-driving silent chain, which includes links with pairs of teeth on both sides of the centerline between the apertures, the thickness of the guide link must be sufficient to ensure the contact area between the chain and the shoe of an associated chain tensioner arm. Thus, the rigidity of the guide link is higher than that of the normal guide link. Therefore, a low-rigidity guide is strongly needed, especially for the back-driving silent chain.
This invention addresses the above-described situations and its purpose is to offer a back-driving silent chain of low rigidity that does not result in the decrease of the fitting force between the pinhole of the guide link and the connecting pin.
SUMMARY OF THE INVENTION
In its preferred embodiments, the silent chain or power transmission device of the present invention comprises a silent chain having multiple rows of links. Each of the link rows is comprised of multiple link plates each having a pair of circular apertures formed at both ends thereof and a pair of teeth on each of the opposite sides of the center line extending between the center of the apertures. The link plates are connected with one another by round pins received in the pair of apertures.
Guide links are placed on the outer edges of the rows of links of the chain in the transverse direction and the ends of the round pins are press-fit into the apertures of the guide links. Each of the guide links include a pair of flat outside surfaces at the upper and lower edges of the guide links in the vertical direction. The flat outside surfaces are formed on the opposite sides of the center line between the apertures. A chain guide or tensioner arm shoe contacts the flat outside surfaces. The guide links also include window holes with the edge portions of the window holes in the vicinity of the apertures being formed of arcuate surfaces equally spaced apart from the edge portions of the apertures.
In another embodiment, the back-driving silent chain of this invention comprises multiple link plates having a pair of circular apertures at both ends thereof and a pair of teeth on the opposite sides of the center line of the apertures. The link plates are connected with one another by round pins received in the apertures. Guide links are press-fit on the outer edges of the rows of plates. The ends of the round pins are press-fit into the apertures of the guide links. Each of the guide links include a pair of flat outside surfaces and a pair of slits formed on the opposite sides of the center line of the apertures. A chain guide or tensioner arm shoe contacts the flat outside surfaces of the guide links. The edge portions of the slits are in the vicinity of the apertures and are formed of arcuate surfaces equally spaced apart from the edge portions of the apertures.
In the silent chain of this invention, the end of the round connecting pin is press-fit into a corresponding round pinhole of the guide link. Window holes or slits are formed on both sides of the center line of the pinholes of the guide link. The edge in the vicinity of such a window hole or slit is formed by arcuate surfaces which arc at equal distances from the edge of the pinhole.
The contact area between the guide link and chain guide or shoe of the chain tensioner is along the outside edges of the guide link. At the same time, the rigidity of the guide link is reduced and the material thickness at the edges of the window hole or pinhole in the vicinity of the slit can be made uniform. As a result, the fitting

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