Driving unit and tensioner

Details Driving unit and tensioner Driving unit and tensioner

2001-07-26

2004-02-24

Fenstermacher, David (Department: 3682)

Endless belt power transmission systems or components

Means for adjusting belt tension or for shifting belt,...

C474S110000

Reexamination Certificate

active

06695730

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tensioner for maintaining constant tension of a non-ended belt, a chain, or the like.
2. Description of the Related Art
A tensioner is a device for maintaining constant tension of a chain, timing belt, or the like that is used, for example, for an engine of an automobile or a motorbike, by pushing or pulling the chain or timing belt in a certain direction if the chain or timing belt becomes loose or slack.
FIG. 18
is an illustration showing an example of a tensioner that is actually installed in the main body of an engine
100
. In this engine
100
, a non-ending chain
103
encircles a set of two cam sprockets
101
and a crank sprocket
102
. The tensioner A has a curve-shaped chain guide
104
that makes contact with the aforementioned timing chain
103
and guides that chain. This chain guide
104
is installed in a free-moving condition with a base portion
105
as a supporting point. Then, by the moving of the chain guide
104
by a retractable and extensible drive shaft
106
of the tensioner A, the tension of the timing chain
103
is adjusted.
FIG.
17
(
a
) shows a conventional tensioner. Such a tensioner A is inserted into a case
51
along with a rotating shaft
52
and a drive shaft
53
. The case
51
is to be installed in an apparatus such as an engine, and a flange
51
b
is formed with an external protrusion in which a hole
51
a
is formed for the purpose of such installation.
In order to connect the rotating shaft
52
to the drive shaft
53
, a male screw portion is formed on the outer surface of the rotating shaft
52
while a female screw portion is formed on the inner surface of the drive shaft
53
, and said imposition is done by engaging said screw portions. The rotating shaft
52
and the drive shaft
53
, which are connected to each other, are supported inside the case
51
by the back-end portion
52
a
of the rotating shaft
52
being connected with the case
51
by interfitting said back-end portion
52
a
with an interfitting hole
59
of the case
51
. Also, when the drive shaft
53
is connected with the rotating shaft
52
it is engaged on the front-side part of the rotating shaft
52
to approximately one-half of the overall length of said rotating shaft
52
, and a torsion spring
54
is installed at the back-side part of the rotating shaft
52
for the approximately one-half of the overall length of said rotating shaft
52
with which the drive shaft
53
is not engaged.
One end
54
a
of the torsion spring
54
is fastened onto the rotating shaft
52
from the direction crossing the axial direction while the other end
54
b
is fastened onto the case
51
. Accordingly, when assembled under the condition that the torsion spring is twisted to have a specified torque, the rotating shaft
52
rotates due to the loaded strength of the torsion spring
54
.
The drive shaft
53
is in a tube whose cross-section is not circular and into which the approximately front half of the rotating shaft
52
is inserted in the condition of engagement. The part of the drive shaft
53
that engages with the rotating shaft
52
is supported by a bearing
55
. This bearing
55
is fixed on the tip part of the case
51
.
FIG.
17
(
b
) is a cross-section view of such a bearing
55
, and in which in this example has a drive-shaft hole
55
a
(a hole in which the drive shaft
53
slides while contacting the inner surface thereof) that has a noncircular, approximately oval shape. The peripheral cross-section of the drive shaft
53
has the same shape as the drive-shaft hole
55
a
, and by inserting said drive shaft
53
into said drive-shaft hole
55
a
bearing
55
the rotation of the drive shaft
53
is stopped.
In the constitution described above, even if the loaded strength of the torsion spring
54
acts upon the rotating shaft
52
so as to rotate the rotating shaft
52
, the drive shaft
53
, which is engaged with the rotating shaft
52
, does not rotate. Therefore, the loaded strength of the torsion spring
54
that rotates the rotating shaft
52
is converted into the driving force of the drive shaft
53
and the drive shaft
53
moves forward. By this movement, because the drive shaft
53
constantly presses against the timing belt and the chain, they are maintained at a constant level of tension.
In such a structure, on the front-end tip of the aforementioned shaft
53
a cap
56
is installed, and this cap
56
contacts directly or indirectly with the chain or the timing belt as shown in the aforementioned FIG.
17
(
a
). Though not shown in the figures, the back-end portion of the case
51
is sealed by the engagement of a sealing bolt so as to prevent the invasion of dust, water, or other undesired substances. Further, the aforementioned tensioner A is a tensioner of a pushing-type, but a tensioner of a pulling type also is also available.
In the tensioner A of which the structure is described above, if the rotating shaft
52
and the drive shaft
53
are removed from the case
51
by mistake, the initial load previously given to the torsion spring
54
becomes zero, because one end of the torsion spring
54
is fastened on the rotating shaft
52
while the other end is fastened on the case
51
, as described above. Accordingly, the reassembly of the rotating shaft
52
and the drive shaft
53
and the reinserting of them into the case
51
is to be done after the torsion spring
54
is wound a specified number of times in order to have an initial load, but sometimes the appropriate number of windings of the torsion spring to have the initial load for such a tensioner is not known. Also, it is extremely difficult to latch both ends of the torsion spring
54
in the condition that the initial load is given as described above.
Also, in the tensioner A, of which the structure is as described above, for converting the rotation torque by the torsion spring
54
into driving force in the axial direction, it is necessary to stop the rotation of the drive shaft
53
by the restraining force of the bearing
55
. Therefore, the drive shaft
53
, of which the surrounding cross-section shape is formed to be in an approximately oval shape, is inserted into the bearing
55
, which has a similar oval-shaped engagement hole, as a result of which the rotation of the drive shaft
53
is stopped, as shown in FIG.
17
(
b
).
However, the problem is that, in order to stop the rotation of the drive shaft, it is necessary to form the cross-section shape thereof into such a noncircular shape as an oval shape, which takes time to do and is troublesome.
Furthermore, the aforementioned bearing
55
is of a plate-shaped member a few millimeters thick, to be manufactured by a press, pattern molding, or the like. The thicker the bearing
55
is, the more steadily the same supports the drive shaft
53
so as to stabilize the operation thereof However, the problem is that, when the bearing
55
is thicker, either the effective stroke length of the drive shaft
53
is forced to be reduced or the storage space of the torsion spring
54
is reduced in the axial direction by the increased thickness.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the aforementioned problems, and its purposes are (1) is to provide a drive shaft that enables the initial load of the torsion spring to be retained when the tensioner is removed for maintenance purposes or the like, and also that does not need a bearing to stop the rotation of the drive shaft as is conventionally done, that does not need processing to form the cross-section of the drive shaft to be in a noncircular shape, and does not need to reduce the effective stroke length of the drive shaft or the storage space of the torsion spring; and (2) to provide a tensioner using such a drive shaft.
To attain the aforementioned purposes, the invention set forth in claim
1
is characterized such that it has two shaft portions that compose a set and that are engaged by two screw members, and a spring that has at each of its two ends a hook

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