Conveyors: power-driven – Conveyor section – Endless conveyor
Reexamination Certificate
2001-09-26
2003-03-18
Ellis, Christopher D. (Department: 3651)
Conveyors: power-driven
Conveyor section
Endless conveyor
C198S851000, C474S156000, C474S157000, C474S212000
Reexamination Certificate
active
06533107
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a silent chain power transmitting apparatus for transmitting power between sprockets with different numbers of teeth as achieved when driving camshafts or a balancer shaft from a crankshaft of a four-stroke engine.
In a four-stroke engine shown in
FIG. 10
hereof, a silent chain power transmitting apparatus used for driving intake valves, exhaust valves and a balancer from a crankshaft has a valve driving crankshaft sprocket
11
a
, an intake valve driving camshaft sprocket
12
a
, an exhaust valve driving camshaft sprocket
12
b
, a balancer driving crankshaft sprocket
11
b
, a balancer shaft sprocket
13
, a camshaft driving silent chain
20
a
, a balancer shaft driving silent chain
20
b
, a tensioner device composed of a tensioner lever L and a tensioner T cooperative to apply an appropriate tension on the silent chain
20
, and a chain guide G for guiding the silent chain
20
a
against oscillation.
The intake and exhaust valves are designed to complete a single cycle of operation while the crankshaft makes two revolutions. Thus, the number of teeth of the camshaft sprockets
12
a
,
12
b
is twice the number of teeth of the camshaft driving crankshaft sprocket
11
a
. The sprockets
11
a
.
12
a
,
12
B and the silent chain
20
a
form a speed decreasing power transmitting mechanism.
The balancer is designed to cancel out high-order unbalance by completing two revolutions while the crankshaft makes a single turn or revolution. To this end, the number of teeth of the balancer shaft sprocket
13
is half the number of teeth of the balancer driving crankshaft sprocket
11
b
. The sprockets
11
b
,
13
and the silent chain
20
b
form a speed increasing power transmitting mechanism.
The camshaft driving silent chain
20
a
and the balancer shaft driving silent chain
20
b
are substantially identical in construction, and though not shown in detail, they are constructed such that when the silent chain
20
a
,
20
b
is stretched straight under tension, respective central swelled portions of the inside flanks of a pair of link teeth of each link plate project outward from rectilinear outside flanks of the link teeth of the preceding link plate. With this construction, when the link plates of the silent chain
20
a
,
20
b
start to mesh with teeth of the sprocket
11
a
,
11
b
,
12
a
,
12
b
,
13
, the inside flanks of the link plates come into contact with the sprocket teeth. This engagement is taken over by subsequent engagement of the outside flanks with the sprocket teeth, as achieved when the link plates of the silent chain are wrapped around the sprocket. When the link plates are placed in full meshing engagement with the sprocket teeth, the outside flanks are completely seated on the sprocket teeth. By way of the meshing engagement between the outside flanks of the link plates and the sprocket teeth, the silent chain transmits power between the crankshaft and the camshafts or between the crankshaft and the balancer shaft.
The crankshaft sprockets
11
a
,
11
b
, the camshaft sprockets
12
a
,
12
b
and the balancer shaft sprocket
13
are formed by a sprocket tooth hobbing process. In the hobbing process, a hob cutter with teeth profiled similarly with the profile of a series of trapezoidal teeth formed by the rectilinear outside flanks of the longitudinally overlapping link plates described previously is used to cut the periphery of a cylindrical workpiece with an amount of addendum modification set in such a manner that the silent chain
20
a
,
20
b
, as it is wrapped around the sprocket, forms an equilateral polygon with one side equal in length to a pitch of the silent chain. Thus, an involute tooth form is produced.
Operation of the conventional silent chain power transmitting apparatus of the foregoing construction will be described in conjunction with one of the sprockets
11
a
,
11
b
,
12
a
,
12
b
and
13
with different numbers of teeth.
In the conventional silent chain power transmitting apparatus, the silent chain
20
a
,
20
b
, as it is wrapped around the sprocket, forms an equilateral polygon while the outside flanks of each pair of link teeth are being seated on tooth flanks or surfaces of alternate sprocket teeth. In this instance, since the central swelled portion of the inside flanks of one link plate projects outward from the rectilinear outside flank of the preceding link plate, the inside flank of the link plate come into contact with the sprocket tooth flank and temporarily raises or lifts up the silent chain before the outside flank is seated on the same sprocket tooth flank Such temporary chain lifting seeks to suppress the equilateral polygonal chain motion, generally called “chordal action” of the silent chain, which involves up and down movement or oscillation of the chain in a radial direction of the sprocket when the chain starts to mesh with the sprocket.
However, due to a great difference in the number of teeth between the crankshaft sprocket
11
a
and the camshaft sprockets
12
a
,
12
b
, or between the crankshaft sprocket
11
b
and the balancer shaft sprocket
13
, the angles of rotation of the sprockets
11
a
,
11
b
;
12
a
,
12
b
and
13
, which cause the silent chain to advance by one chain pitch, are different from one another. Consequently, the amplitudes of the chordal actions occurring at the respective sprockets vary to a considerable extent.
In the case where a silent chain having link teeth formed with centrally swelled inside flanks is used, the silent chain approaching a sprocket is lifted up by a constant amount of distance. Accordingly, the chordal action with respect to a selected one of the sprockets
11
a
,
11
b
,
12
a
,
12
b
and
13
can be suppressed. However, it is extremely difficult to suppress all of the chordal actions associated with these sprockets
11
a
,
11
b
,
12
a
,
12
b
and
13
.
Furthermore, even when the chordal action occurring with respect to one of the
11
a
,
11
b
,
12
a
,
12
b
and
13
is suppressed, it is not considered from the viewpoint of the silent chain power transmitting apparatus as a whole that vibration and noises resulting from the chordal action are effectively reduced. Rather, when the central swelled portions of the inside flanks impinge against the sprocket tooth flanks, a beating motion of the silent chain occurs, producing additional sorts of vibration and noise and fluctuating the chain tension.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a silent chain power transmitting apparatus for transmitting power between sprockets with different numbers of teeth, as achieved when camshafts or a balancer shaft is driven by a crankshaft of a four-stroke engine via a silent chain, in which the chordal action of the silent chain is completely suppressed with respect to all of the sprockets to thereby reduce vibration and noises caused the chordal action, and the changes in the chain tension is suppressed to thereby improve the driving performance and the durability of the silent chain power transmitting apparatus.
To achieve the foregoing object, according to the present invention, there is provided a silent chain power transmitting apparatus comprising; an endless silent chain composed of a multiplicity of link plates interleaved and articulately connected together by connecting pins, each link plate having a pair of generally V-shaped link teeth and a pair of pin holes for fitting the connecting pins, the V-shaped link teeth having inside and outside flanks; and at least two sprockets spaced from each other and having different numbers of teeth for mesh with the V-shaped link teeth of the link plates. When the silent chain starts to mesh with each of the sprockets, the inside flank of one link plate comes in contact with a tooth of the sprocket, and as the silent chain is wrapped around and subsequently placed in full meshing with the sprocket, the outside flank of the preceding link plate comes in contact with and subsequently becomes completely seated on the s
Horie Hiroshi
Sonoda Masatoshi
Suzuki Kenshi
Deuble Mark A.
Ellis Christopher D.
Howson & Howson
Tsubakimoto Chain Co.
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