Silent chain

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

06743134

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a silent chain used for power transmission, in applications such as the timing drive of automobiles or motorcycles, or as a chain drive in a general purpose engine, a diesel engine or an industrial machine or the like. More specifically, the invention relates to a silent chain used as a timing chain in an engine.
An example of a conventional silent chain a bush-type silent chain
1
is shown in FIGS.
3
(A) and
3
(B). In this silent chain
1
, guide plates
2
, link assemblies
3
and intermediate link plates
6
are disposed adjacent one another in the direction of the width of the chain, but shifted longitudinally so that they are interleaved. The interleaved members are articulably connected with one another by connecting pins
7
.
The guide plates
2
do not have teeth, but each guide plate has a pair of pin holes
2
a
as shown in FIG.
4
. Each link assembly
3
comprises two inner link plates
4
each having a pair of teeth
4
a
, which mesh with the teeth of a sprocket, a pair of bushing holes
4
b,
and a pair of bushings
5
, each press-fit into a bushing hole
4
b,
as shown in FIGS.
5
(A) and
5
(B). In the link assembly
3
, the two inner link plates
4
are integrally connected and fixed to each other by two bushings
5
. Further, each intermediate link plate
6
includes a pair of teeth
6
a,
which mesh with the teeth of a sprocket, and a pair of pin holes
6
b,
as shown in FIG.
6
.
In the inner link plate
4
, as shown in FIG.
5
(A) and
FIG. 7
, a pair of teeth
4
a
are formed, each having an outside surface portion
4
c
and an inside surface portion
4
d,
a pair of bushing holes
4
b
, into each of which a bushing
5
is press-fit and fixed, a back surface portion
4
e
formed on the side opposite to the side where the pair of teeth
4
a
is formed, and a pair of shoulder portions
4
f,
each of which connects an outside surface portion
4
c
to the back surface portion
4
e.
The broken line P in
FIG. 7
is a pitch line, which passes through the centers of the bushing holes
4
b.
In the particular chain shown in FIG.
3
(A), two intermediate link plates
6
are disposed centrally with respect to the width direction of the chain, link assemblies
3
are disposed on both outer sides of the intermediate link plates
6
, and the guide plates
2
are disposed on both of the outermost sides of the chain. These elements are longitudinally shifted with respect to one another, and thereby interleaved, and are articulably connected to one another by connecting pins
7
. In this case, the connecting pin
7
is press-fit into and fixed to the pin holes
2
a
of the guide plates
2
on both outermost sides in the chain, and in the intermediate link plates
6
, the connecting pin
7
can extend through the pin holes
6
b
with play, or can be press-fit and fixed into the pin hole
6
b.
Since the link assembly
3
is composed of plural link plates
4
, the problem arises that, if the inner link plates are not light in weight, the weight of the silent chain becomes excessive. Further, the rigidity of the teeth of the inner link plates is high. Thus, when the chain meshes with the teeth of a sprocket during operation, tooth surfaces of each inner link plate collide with tooth surfaces of the sprocket and the collision shock is dispersed to the entire inner link plate, generating meshing noises of large amplitude.
In the inner link plates
4
, which form the link assembly
3
, the bushing
5
is press-fit into, and fixed to, the bushing hole
4
b
. Thus, the bushing hole
4
b
, formed in the inner link plate
4
, is a size larger than the pin hole
6
b
in the intermediate link plate
6
. As a result, the distance between the bushing hole
4
b
and the adjacent outer side portion of the inner link plate
4
becomes smaller than the corresponding distance in the intermediate link plate
6
. In this case, as shown in
FIG. 7
, the shortest distance k′ between the bushing hole
4
b
and the outside surface portion
4
c
, and the shortest distance l′ between the bushing hole
4
b
and the inside surface portion
4
d
are comparatively small. However, the shortest distance w′ between the bushing hole
4
b
and the tip of the tooth of the inner link plate is still relatively large. Accordingly, the distances l′, k′ and w′ become unbalanced.
When the bushing
5
is press-fit into the bushing hole
4
b
in the inner link plate
4
to form a link assembly, the inner link plate
4
is usually deformed in the areas where the distance between the bushing hole
4
b
and the outer side portion is small. Accordingly, strain is generated in the inner diameter of the press-fit bushing
5
. Since the back surface portion
4
e
and the shoulder portions
4
f
of the inner link plate
4
have no direct relationship to the meshing of the link plate teeth with the teeth of a sprocket, it is possible to suppress the strain generated in the inner diameter of the press-fit bushing by increasing the shortest distance m′ between the bushing hole
4
b
, and the back surface portion
4
e
and the shortest distance n′ between the bushing hole
4
b
, and the shoulder portions
4
f
. However, in the teeth
4
a
, the distances k′ and l′ cannot be correspondingly increased without affecting the meshing relationship between the teeth
4
a
and the teeth of the sprocket. Thus, when the distances k and l are small, and the distance w′ is large, the inner diameter of the press-fit bushing
5
has different degrees of deformation in the areas corresponding to the distances k′ and 1′ and the area corresponding to the distance w′. As a result nonuniform strains are generated, and the inside of the bushing deviates from true roundness. This problem arises because the relationships between the shortest distances and the plate thickness of the inner link plate have not been noted. Thus, the distances k′ and l′ may be too small compared to the plate thickness of the inner link plate. However, these problems can arise even when the plate thickness is increased.
When the roundness of the inner diameter of the bushing press-fit into the bushing hole deteriorates, if the link assembly is incorporated into a chain, the interfacial pressure between the surface of the connecting pin and the inner periphery of the bushing becomes nonuniform, or the connecting pin makes contact with the inner periphery of the bushing only on one side. Consequently, wear of the connecting pin and bushing, and resulting wear elongation of the chain are both accelerated.
SUMMARY OF THE INVENTION
Accordingly, a general object of this invention is to overcome the problems associated with the above-described conventional silent chain.
A more specific object of the invention is to provide a silent chain in which wear of the connecting pins and bushings, and wear elongation of the chain can be suppressed.
According to one aspect of the invention, the silent chain comprises a link assembly including at least two inner link plates, each link plate having a pair of teeth and a pair of bushing holes, the link plates being connected and fixed to one another by a pair of bushings, each said bushing being press-fit into bushing holes of all of said link plates of the link assembly, wherein each of the teeth of the inner link plates has a through-hole approximately in its center.
According to the invention, the deformation of the inside of a press-fit bushing can be made more uniform compared to the deformation in the case of conventional inner link plate lacking the through-holes. Accordingly, deviation from roundness in the inside of the bushing can be prevented.
Further, the through-holes reduce the weight of the inner link plates, and as a result, a weight reduction of the a reduction in the overall weight of the silent chain can be realized. Because of this weight reduction, when the silent chain meshes with the sprocket teeth the shock energy due to the collision between the tooth faces of the i

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