Sprocket equipped with cushion body

Details Sprocket equipped with cushion body Sprocket equipped with cushion body

2000-05-25

2002-04-16

Hannon, Thomas R. (Department: 3682)

Endless belt power transmission systems or components

Positive drive pulley or guide roll

With particular belt

C474S161000

Reexamination Certificate

active

06371874

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a sprocket equipped with cushion body, and more particularly to such a sprocket which is equipped with a cushion body capable of reducing striking noise at the engagement points between a sprocket and a chain when a wrapping angle of the chain relative to the sprocket exceeds 180°.
2. Description of the Related Art
In an automobile engine, for example, in order to drive a camshaft, a chain is trained around a crank sprocket and a cam sprocket.
FIG. 4
shows the relationship between such camshaft-driving chain C and the crank sprocket
50
. In the sprocket
50
of this type, a cushion body
52
may be sometimes used as a noise suppression measure. The cushion body
52
is mounted on the sprocket
50
in such a manner that it comes in contact with the chain C at both an engagement start point and an engagement finish point of the chain C relative to the sprocket
50
.
The chain C, as it is in the position indicated by the solid lines shown in
FIG. 4
, has a wrapping angle smaller than 180°. In this position, the cushion body
52
comes into contact with the chain C at the two engagement points (i.e., the engagement start point and the engagement finish point) of the chain C relative to the sprocket
50
. The cushion body
52
has a ring-like shape with uniform thickness and is floatingly mounted on a boss
54
of the sprocket
50
. The cushion body
52
endeavors to reduce striking noise at the engagement points between the chain C and the sprocket
50
while it is constrained in position relative to the sprocket
50
at three points, one being a contact point between the cushion body
52
and the boss
54
and the other two being contact points between the cushion body
52
and the chain C.
However, since the cushion body
52
is not prevented from moving in a direction perpendicular to the axis the sprocket
50
, the position of the cushion body
52
relative to the engagement points between the chain C and the sprocket
50
is not always constant. This may lead to an insufficient noise-reducing effect achieved by the cushion body
52
.
In the case where a crank sprocket of a smaller diameter is used, a greater chain wrapping angle may become necessary. In addition, when the chain C is arranged to further drive an oil pump, an alternator or the like auxiliary device disposed near the crank sprocket
50
, the resulting arrangement may necessary have a greater chain wrapping angle. In these cases, the wrapping angle of the chain C exceeds 180°, as indicated by the phantom lines shown in FIG.
4
. While the phantom-lined chain C is running, a downward force is applied from the chain C to the cushion body
52
, tending to separate the cushion body
52
from the boss
54
. The cushion body
52
thus displaced or offset downward from predetermined position is no longer possible to redice striking noise at the engagement points between the chain C and the sprocket
50
. Rather, the downwardly offset cushion member per se forms an additional noise source. This problem becomes critical as the diameter of the sprocket becomes small because a sprocket of a smaller diameter is accompanied by a greater chordal action (also called “chordal effect”) of the chain.
In the general engine mounting structure, the crank sprocket
50
is disposed at a lower position in the vertical direction. In this case, the cushion body
52
is mounted such that a space is defined between the cushion body
52
and the chain C at a position below the sprocket
50
. Since the cushion body
52
has an own weight which acts in the same direction as the downward force applied from the chain C, the cushion body
52
is likely to move in an offset direction. Especially if the cushion body
52
is displaced or offset from the redetermined position due to its own weight and a downward component force of the chain tension after the engine is stopped, restarting of the engine will immediately produce great striking noise caused due to direct contact between the chain C and the sprocket
50
and floating movement of the cushion body
50
.
In addition, since the cushion body
52
is not fixed in position relative to the sprocket
50
, the cushion body
52
needs to be displaced in a predetermined position when the chain C is set or trained around the sprocket
50
. Thus, the efficiency of a chain-and-sprocket assembling work is low.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a sprocket equipped with a cushion body which is set in a predetermined position and, hence, is capable of surely reducing noise at engagement points between a chain and the sprocket when a wrapping angle of the chain relative to the sprocket exceeds 180°.
To achieve the object, there is provided according to the present invention a sprocket equipped with a cushion body mounted on the cylindrical outer surface of a coaxial boss of the sprocket for reducing striking noise at engagement points between the sprocket and a chain wound around the sprocket, wherein the cushion body has a solid structure including a cylindrical inner surface slidable on the cylindrical outer surface of the boss and a cylindrical outer surface eccentric to the cylindrical outer surface of the boss, the cylindrical outer surface of the cushion body being in contact with the chain at the engagement points between the sprocket and the chain.
In the state where the chain is wound around the sprocket equipped with the cushion body, the chain is in contact with the cushion body at the engagement points between the sprocket and the chain. When the wrapping angle of the chain relative to the sprocket exceeds 180°, the cushion body is subjected to a component force of the chain tension acting on each engagement point in a direction toward a top of the sprocket. In this instance, however, since the cushion body has a solid structure, movement of the cushion member is prohibited in all directions except the circumferential direction even if any force is applied to the cushion body. Thus, the cushion body can retain its prescribed posture or position.
When the sprocket starts rotation, the chain comes into meshing engagement with the sprocket at the engagement points. At the same time, the cushion body is in contact with the chain at the engagement points between the chain and the sprocket to thereby reduce striking noise between the chain and the sprocket. The cushion body is in sliding contact with the boss so that it can retain its prescribed position in which the cushion body is always in contact with the chain at the engagement points.
Even if the wrapping angle of the chain relative to the sprocket exceeds 180°, the cushion body, owing to its solid structure as opposed to the hollow structure of the conventional cushion body, can retain its prescribed position against forces (including a component force of the chain tension and the action of the gravity) tending to move the cushion body in a direction perpendicular to the axis of the sprocket. Thus, the cushion body achieves its prescribed function to reduce striking noise at the engagement points between the chain and the sprocket.
The cushion body may be comprised of a single cushion member of a disk-like configuration having an eccentric through-hole defined by the cylindrical inner surface of the cushion body and an outer peripheral surface forming the cylindrical outer surface of the cushion body. The single cushion member is simple in construction and can be produced at a relatively low cost.
As an alternative, the cushion body may be comprised of an annular bearing slidably mounted on the cylindrical outer surface of the boss and having a cylindrical outer surface, and an eccentric cushion member attached to the cylindrical outer surface of the bearing and having a cylindrical outer surface forming the cylindrical outer surface of the cushion body.
The cushion body is slidable relative to the boss and hence is not fully prevented from moving in the circumferential direction of the boss

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