Endless belt power transmission systems or components – Positive drive belt – Belt formed of rigid links
Reexamination Certificate
2001-04-19
2004-09-28
Charles, Marcus (Department: 3682)
Endless belt power transmission systems or components
Positive drive belt
Belt formed of rigid links
C474S212000
Reexamination Certificate
active
06796920
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in a silent chain power transmission apparatus for use as a timing chain for timed power transmission in an automobile, a power transmitting chain in an industrial machine, or the like.
2. Description of the Related Art
In a conventional silent chain power transmission apparatus, an endless silent chain is employed which comprises a multiplicity of link plates interleaved by a multiplicity of connecting pins in a fingers-crossed fashion, as illustrated in
FIG. 8
hereof. Each link plate
100
has a pair of V-shaped teeth
10
each defined by inside and outside faces
1
,
2
for meshing with teeth of a sprocket S as shown in
FIG. 8
hereof. As can be clearly seen from
FIG. 7
, the inside tooth faces
1
are scooped out deeper inwardly than the profiles, symmetrical with the profiles of the outside tooth faces
2
, of imaginary inside tooth faces
1
′ so that their interference with the teeth of the sprocket upon intermeshing can be prevented. Accordingly, pitch line Li of the inside tooth faces is positioned closer to the pin center line Lp than a pitch line Lo of the outside tooth faces. The pitch line Li is a line passing parallel to pin center line Lp over two inside tooth faces
1
of the link plate at points where a distance between those two points becomes 1/2 of the chain pitch
2
, which is equal to the distance between two pins of the link plate. Similarly, the pitch line Lo of the outside tooth faces is a line passing parallel to the pin center line Lp over the two outside tooth faces
2
at points where the distance between the two points becomes 3/2 of the chain pitch P.
More specifically, the profiles of the V-shaped link teeth
10
of the Link plate
100
are interrelated to each other to satisfy Hi≦Ho, where Hi is a distance from the pin center line Lp to the pitch line Li of the inside tooth faces and Ho is a distance from the pin center line Lp to the pitch line Lo of the outside tooth profiles.
Though not shown, the sprocket S to be intermeshed with the silent chain C has teeth of profiles formed in a hobbing process using a hob cutter.
It has been known that when the silent chain arranged as explained above is brought into meshing engagement with the sprocket S, the silent chain C is wound around the sprocket in a polygonal manner and used practically in such manner.
However, since the link plates
100
of the silent chain C mesh at their outside tooth faces alone with the teeth of the sprocket S, the silent chain makes, upon commencement of and release from meshing engagement with the sprocket, a polygonal motion involving up and down movements radial of the sprocket.
A quantitative analysis of the polygonal motion may be made. As can be appreciated from
FIG. 8
, since a pitch angle of the silent chain C and the number of teeth N of the sprocket S have relations expressed by &agr;=(360°/N), the followings may be established.
First, when the chain pitch is P and the center of the sprocket S, the connecting pin
200
a
and a free-span part of the chain C following the link plate
100
b
are arranged to form a right angle, the distance from the center of the sprocket S to the connecting pin
200
a
on the free-span part of the chain becomes U=P/2 sin(&agr;/2). The term “free-span part of the chain” used herein represents a chain portion not completely engaged with the sprocket but being in a process of engaging with the sprocket. In other words, the free-span part of the chain is that part of the chain which is not completely constricted by the sprocket and is thus placed in a relatively free state.
Next, as shown in
FIG. 9
, when the sprocket S is rotated half a pitch angle &agr;/2 and the centers of the sprocket S and the link plate
100
b
and the free-span part of the chain are positioned to form a right angle, the distance from the center of the sprocket S to the pitch line of the free-span part of the chain is expressed by V=P/2 tan(&agr;/2).
As can be readily appreciated from the above discussion, the silent chain C just started meshing with the sprocket S makes a polygonal motion of amplitude Hs=U−V involving up and down movements during half pitch angle (&agr;/2) rotation of the sprocket S.
Consequently, in the thus-arranged conventional silent chain power transmission apparatus, the polygonal motion of amplitude Hs=U−V and associated up and down movements cause the link plates
100
a
,
100
b
,
100
c
to hit the teeth of the sprocket S, resulting in an undesired motion. In addition, when the silent chain apparatus is operated at a high speed, undesired vibratory and impact sounds are produced at the start of meshing of the silent chain with the sprocket. Further, impact of the chain C against the sprocket S shortens the lives of the chain and sprocket. Moreover, the polygonal motion causes the tension of the chain to change, thereby further decreasing durability of the silent chain.
To this end, an improved silent chain power transmission apparatus has been proposed in Japanese Patent Laid-Open Publication No. HEI-8-184348 in which arrangements are made to reduce vibrations, sounds and chain tension fluctuations arising owing to the polygonal motion of the chain. The disclosed apparatus comprises a silent chain having rows of interleaved link plates with teeth defined by inner and outer flank surfaces, and a sprocket having teeth for meshing with the link plate teeth. The sprocket is gear-cut by using a rack cutter having teeth of profiles identical to the profiles of the link plates upon linear stretching of the silent chain. As a result, the silent chain can mesh with the sprocket teeth smoothly, thereby minimizing polygonal motion of the chain and thus reducing noisy impact sounds.
In the thus-arranged silent chain power transmission apparatus, upon commencement of intermeshing, since the link plates of the silent chain come into meshing engagement with the sprocket in a similar manner as the tooth profiles of the rack cutter, the chain polygonal motion can be minimized. However, when the link plates of the silent chain wind around and get seated on the sprocket, the chain polygonal motion arises as in the conventional power transmission apparatus. Thus, it is not possible for the proposed power transmission apparatus to completely kill the chain polygonal motion throughout the course of meshing of the chain with the sprocket. Consequently, vibrations, noisy sounds and chain tension fluctuations produced in the proposed power transmission apparatus cannot be reduce to substantially zero.
Moreover, due to the polygonal motion of the chain, a concave bottom surface defined between the opposed inner flanks or tooth faces of each link plate interferes with the edges of the teeth of the sprocket. Similarly, the edges of the V-shaped teeth of the link plates interfere with the root bottoms of the sprocket. As a result, partial wear and breakage are inevitable at the interfering parts of the chain and sprocket.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a silent chain power transmission apparatus which can prevent up and down movements of a silent chain thereof, which are due to polygonal motion of the chain when the chain intermeshes with, and becomes seated on, a sprocket, and thereby substantially reduce vibratory and impact sounds and fluctuation in tensioning of the chain, and which can prevent wear of concave bottom surfaces of link plates forming the chain, edges of V-shaped teeth of the link plates and the root bottom of the sprocket and thereby improve durability of the apparatus.
According to the present invention, there is provided a silent chain power transmission apparatus which comprises: an endless silent chain comprised of a multiplicity of link plates interleaved by a multiplicity of connecting pins, each of the link plates having a pair of V-shaped teeth and a pair of pinholes for fitting the connecting pins, each of the V-shaped l
Fukuda Shigekazu
Funamoto Takayuki
Horie Hiroshi
Iwasaki Yoshinori
Matsuno Kazumasa
Charles Marcus
Howson and Howson
Tsubakimoto Chain Co.
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