Hydraulic tensioner

Details Hydraulic tensioner Hydraulic tensioner

1999-05-27

2001-03-20

Bucci, David A. (Department: 3682)

Endless belt power transmission systems or components

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

Tension adjuster or shifter driven by electrical or fluid motor

Reexamination Certificate

active

06203461

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a hydraulic tensioner for imparting an appropriate tension to, for example, a timing belt or chain in a vehicular engine.
2. Description of the Related Art:
For a timing belt or chain which transmits rotation between a crank shaft and a cam shaft in an engine, a hydraulic tensioner is in wide use for suppressing vibrations generated from the timing belt or chain during vehicular running and for maintaining an appropriate tension.
FIG. 5
shows a chain drive in an engine for which a conventional hydraulic tensioner is used. In this figure, a hydraulic tensioner A
1
is attached to an engine body on a slack side of a chain A
6
. The chain A
6
is entrained on both a driving sprocket A
3
which is rotated by a crank shaft A
2
of the engine and a driven sprocket A
5
which is fixed onto a cam shaft A
4
.
In the hydraulic tensioner A
1
, a plunger A
8
projects retractably from the front side of a tensioner body A
7
. The plunger A
8
pushes the back side of a tensioner lever A
10
at a position near a free end of the same lever. The tensioner lever A
10
is pivotally connected to the engine body through a pivot shaft A
9
, so that a shoe surface A
11
of the tensioner lever A
10
comes into sliding contact with the slack side of the chain A
6
and thereby imparts a tension to the chain.
In the interior of the tensioner body A
7
, as shown in
FIG. 6
, there is formed a plunger receiving hole A
12
into which is inserted the plunger A
8
in a protrudable and retractable manner. A ball check valve A
13
is provided at the bottom of the hole A
12
.
The plunger A
8
has a hollow portion A
14
which is open at its end face opposed to the ball check valve A
13
. A plunger spring A
15
is disposed in both the hollow portion A
14
and the plunger receiving hole A
12
. Thus, the plunger spring A
15
acts between the tensioner body A
7
and the plunger A
8
to urge the plunger A
8
at all times so that a front end portion of the plunger projects to the exterior of the tensioner body A
7
.
A high-pressure chamber H is formed by a space which is defined by both the plunger receiving hole A
12
and the hollow portion A
14
of the plunger A
8
. The interior of the high-pressure chamber H is always filled with oil which is fed from an oil supply source (not shown) through an oil passage A
16
and a ball check valve A
13
.
In the hydraulic tensioner A
1
constructed as above, when an impact force is exerted on the plunger A
8
from the chain A
6
side through the tensioner lever A
10
shown in
FIG. 5
, the internal oil pressure of the high-pressure chamber H rises and the a check ball A
17
in the ball check valve A
13
blocks an opening of the oil passage A
16
which extends through a ball seat A
18
, thereby preventing a reverse flow of oil to the oil supply source side.
As a result, the internal pressure of the high-pressure chamber H further increases and leaks to the exterior of the tensioner body A
7
through a slight gap formed between the outer peripheral surface of the plunger A
8
and the inner peripheral surface of the plunger receiving hole A
12
. At this time, the impact force acting on the plunger A
8
is buffered by the resulting flow resistance of oil.
According to a standard construction of the conventional hydraulic tensioner A
1
referred to above, a seating surface A
19
of the ball seat in the ball check valve A
13
in which the oil passage A
16
opens as in
FIG. 7
is formed as an outwardly expanded tapered surface having a divergent angle of about 90°, and the inside diameter of the oil passage A
16
is 2.5 mm, while the outside diameter of the check ball A
17
is 3.97 mm.
The check ball A
17
having the above outside diameter is made of steel and has a mass of about 0.26 g. When the pressure of oil supplied through the oil passage A
16
to the high-pressure chamber H side in
FIG. 6
is low and when a load imposed on the plunger A
8
from the chain side pulsates with a cycle exceeding 100 Hz, the check ball A
17
can no longer follow up the variation in the load due to its inertia, with consequent leakage of oil from the high-pressure chamber H side to the oil passage A
16
, thus causing the backstop force of the plunger A
8
to be deteriorated markedly and intensifying the vibration of the chain.
On the other hand, if the pressure of the oil fed to the high-pressure chamber H is increased, it will become possible to suppress the vibration of the chain during vehicular running, but because of an increase in the tension acting on the chain a beat noise is apt to occur between the driving sprocket and the driven sprocket. For this reason it has so far been difficult to satisfy the performance required from the engine side.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to solve the above-mentioned problems of the prior art and provide a hydraulic tensioner capable of affording a sufficient backstop force without increasing the supplied oil pressure even in the event the load acting on the plunger varies at a high frequency.
To attain the foregoing object, a hydraulic tensioner of the present invention includes a tensioner body having a plunger receiving hole, and a plunger slidably fitted in the plunger receiving hole and urged by a spring so that one end of the plunger projects outwards from the plunger receiving hole, the plunger defining within the plunger receiving hole a high-pressure chamber. The tensioner further includes a ball check valve having an oil passage allowing oil to be introduced into the high-pressure chamber, and a check ball disposed between the oil passage and the high-pressure chamber to permit only the flow of oil in a direction from the oil passage toward the high-pressure chamber. The ball check valve further has a valve seat on which the check ball rests when closed. The oil passage extending through the valve seat. The valve seat has an outwardly diverging tapered surface having a divergent angle of 60° to 110°. The check ball has a mass of 0.1 g or less.
With this construction, the check ball is superior in its performance of following up oil pressure variations of high frequencies, and even in a region wherein the load acting on the plunger varies at high frequencies it is possible to ensure a sufficient backstop force without increasing the oil pressure supplied.
The above and other object and advantages of the present invention will become apparent from the following detailed description of the preferred embodiment when read in conjunction with the accompanying drawings.


REFERENCES:
patent: 4881927 (1989-11-01), Suzuki
patent: 5181889 (1993-01-01), Maruyama et al.
patent: 5366415 (1994-11-01), Church et al.
patent: 5653651 (1997-08-01), Kawashima et al.
patent: 5713809 (1998-02-01), Yamamoto et al.
patent: 5785619 (1998-07-01), Nakakubo et al.
patent: 5908363 (1999-06-01), Suzuki
patent: 5913742 (1999-06-01), Nakamura et al.
patent: 0 110 061 (1984-06-01), None
patent: 0 459 798 (1991-12-01), None
patent: 0 834 678 (1998-04-01), None
patent: 91/12450 (1991-08-01), None

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