Endless belt power transmission systems or components – Positive drive belt – Belt formed of rigid links
Reexamination Certificate
2000-02-16
2002-01-01
Marmor, Charles A (Department: 3681)
Endless belt power transmission systems or components
Positive drive belt
Belt formed of rigid links
C474S226000, C474S233000
Reexamination Certificate
active
06334828
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in a power transmitting silent chain apparatus for use as a timing chain for 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 power transmitting silent chain apparatus, a silent chain comprises a plurality of link plates each having a pair of teeth profiled as shown in
FIG. 5
hereof so that it starts meshing with a sprocket at outer flanks
15
forming outer sides of the link teeth
14
. Inner flanks
16
forming inner sides of the link teeth
14
are provided to extend deeper inward than an imaginary profile symmetrical with the outer flanks
15
forming the outer sides of the link teeth
14
so that they do not interfere with involute teeth of the sprocket during meshing of the chain with the sprocket.
Consequently, as shown in
FIG. 5
, an inner flank pitch line PL
2
, passing parallel to a chain pitch line PL
1
(line passing over the centers of apertures
12
of the link plate
13
) over the inner flanks
16
at points where the distance between the points becomes ½ of a chain pitch P (distance between the centers of the link apertures
12
), is positioned closer to the chain pitch line PL
1
than an outer flank pitch line PL
3
, passing parallel to the chain pitch line PL
1
over the outer flanks
15
at points where the distance between those points becomes {fraction (3/2)} of the chain pitch P. That is, the profiles of the teeth of the link plate
13
are Hi≦Ho, where Hi is a distance from the chain pitch line PL
1
to the inner flank pitch line PL
2
, and Ho is a distance from the chain pitch line to the outer flank pitch line PL
3
.
Referring next to
FIG. 6
, the sprocket
11
has involute teeth for meshing with the silent chain. These teeth are formed by an ordinary sprocket teeth hobbing process in which a hob cutter with teeth
17
profiled correspondingly to the outer configurations of the outer flanks is used to cut a peripheral portion of the sprocket by an amount of addendum modification Hf between a gear cutting center line (tangential to a pitch radius of the sprocket) and a hob center line (tangential to an intermeshing radius of the sprocket).
It has been known that when the silent chain comprising the link plates arranged as shown in
FIG. 5
is placed in meshing engagement with the sprocket having the involute teeth arranged as explained above, the silent chain is wound around the sprocket in a polygonal fashion and practically used in this manner.
However, since the link plates of the above silent chain mesh at their outer flanks alone with the involute teeth of the sprocket, the silent chain makes, upon commencement of meshing, a polygonal motion involving up and down movements radial of the sprocket.
Then, a quantitative analysis was made on the polygonal motion. As can be appreciated from
FIG. 7
, since a pitch angle &agr; of the silent chain and the number of teeth N of the sprocket
11
have relations expressed by &agr;=(360°/N), the followings may be established.
First, when the chain pitch is P and a free span of the chain following the link
13
b
is positioned at a right angle to a line passing over the centers of the sprocket
11
and a pin
12
a
, the distance from the center of the sprocket
11
to the pin
12
a
of the chain free span is expressed by U=P/2 sin(&agr;/2). The term “free span of the chain” used herein represents a chain portion not completely engaged with the sprocket but being in progress of engaging with the sprocket. In other words, the chain free span is a chain portion not completely restrained by the sprocket and is thus placed in a relatively free state.
Next, as shown in
FIG. 8
, when the sprocket
11
is rotated a half pitch angle &agr;/2 and the chain free span is positioned at a right angle to a line passing over the centers of the sprocket
11
and the link
13
b
, the distance from the center of the sprocket
11
to the chain pitch line PL
1
of the chain free span is expressed by V=P/2 tan(&agr;/2).
As can be readily appreciated from the above discussion, the silent chain just started meshing engagement with the sprocket
11
makes a polygonal motion of Amplitude Hs=U−V involving up and down movements during half pitch angle (&agr;/2) rotation of the sprocket
11
.
Consequently, in the thus-arranged conventional power transmitting silent chain apparatus, the polygonal motion of Amplitude Hs=U−V and associated up and down movements cause the link plates
13
a
,
13
b
,
13
c
to hit the involute teeth of the sprocket
11
, resulting in an undesired beating 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 silent chain against the sprocket shortens the lives of the chain and the sprocket. Moreover, the polygonal motion causes the tension of the chain to change, thereby further decreasing the durability of the silent chain.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a power transmitting silent chain apparatus in which vibratory sounds and impact sounds produced by up and down movements involved in the polygonal motion of the silent chain are reduced and the changes in the chain tension are alleviated, and in which the silent chain and sprocket have increased durability.
To attain the above object, there is provided, in accordance with the present invention, a power transmitting silent chain apparatus which comprises: a silent chain comprised of a plurality of link plates interconnected by connector pins, each link plate having a pair of teeth; and a sprocket having a plurality of involute teeth for meshing with the link plate teeth, the link plate teeth having inner and outer flanks profiled to satisfy the expression
Hi=Ho+Hs
where Hi is a distance from a pitch line of the chain to a pitch line of the inner flanks, Ho is a distance from the chain pitch line to a pitch line of the outer flanks, and Hs is an amplitude of a polygonal motion of the chain.
In the thus-arranged silent chain apparatus, the distance from the center of the sprocket to a free span of the chain is kept constant throughout the course of meshing of a link plate immediately before the chain free span, that is, from the start of meshing until seating on the sprocket of that link plate, thereby preventing the silent chain from making vertical movements resulting from the polygonal motion of the chain. This leads to the further advantage that vibratory sounds and impact sounds produced upon meshing of the chain with the sprocket can be alleviated and hence the silent chain apparatus is imparted with increased durability.
Preferably, engaging or bearing surfaces of the link plates are processed by shaving or fine-blanking so that they have a shear plane length of more than 70% of the thickness of the link plate. As a result, it becomes possible to reduce impact sounds produced upon meshing of the chain with the sprocket and wear of the sprocket teeth. This further prolongs the lives of the chain and sprocket and prevents stiffening of the chain links.
Each of the connector pins may comprise either a round pin or a locker pin.
REFERENCES:
patent: 4915676 (1990-04-01), Komeya
patent: 5267910 (1993-12-01), Maruyama et al.
patent: 5419743 (1995-05-01), Takeda et al.
patent: 5628702 (1997-05-01), Kotera
patent: 5651746 (1997-07-01), Okuda
patent: 5758484 (1998-06-01), Ledvina et al.
patent: 5803854 (1998-09-01), Tada et al.
British Search Report dated Jun. 16, 2000.
Armstrong Westerman Hattori McLeland & Naughton LLP
Ho Ha
Marmor Charles A
Tsubakimoto Chain, CO
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