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
2000-02-16
2002-05-07
Hannon, Thomas R. (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
C474S109000
Reexamination Certificate
active
06383103
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hydraulic tensioner used for applying an appropriate tension to a timing belt or a timing chain of a vehicle engine.
2. Description of the Related Art
Conventionally, a timing belt or a timing chain is used in a drive system for transmitting rotational motion from a crankshaft to a camshaft of an automobile engine, and a hydraulic tensioner is widely used to suppress vibration, which would otherwise occur in the timing belt or chain when the timing belt or chain travels, and to maintain a proper tension in the timing belt or chain.
FIG. 4
schematically illustrates a chain transmitting device for an engine in which a hydraulic tensioner is used. The hydraulic tensioner
41
is mounted on an engine body on the slack side of a chain (timing chain)
62
. The chain
62
is fitted around and extends between a driving sprocket
59
rotated by a crankshaft
58
of the engine and a driven sprocket
61
fixed on a camshaft
60
.
The hydraulic tensioner
41
includes a plunger
43
projecting from the front face of a tensioner housing
42
such that the plunger
43
can undergo reciprocating motion. A tip portion of the plunger
43
presses the rear side of a tension lever
64
at a position near the free end thereof. The tension lever
64
is pivotally supported on the engine body by means of a support shaft
63
. Through such an arrangement, a shoe surface
65
of the tension lever
64
is brought into slidable contact with the slack side of the chain
62
to thereby apply tension to the chain
62
.
Most conventional hydraulic tensioners have a relief valve or an orifice provided alone. The hydraulic tensioner equipped with only the relief valve has a problem that air staying in the plunger cannot escape until the air pressure goes up to a predetermined pressure. On the other hand, the hydraulic tensioner equipped with the orifice alone would encounter a problem that the hydraulic pressure is likely to becomes extremely high or extremely low, making it difficult to achieve an accurate pressure setting. To deal with these problems, attempts have been made to provide hydraulic tensioners equipped with both a relief valve and an orifice.
One example of the proposed hydraulic tensioners is shown in
FIG. 5
, which includes a relief valve and an orifice. provided seperately, as discussed below.
The hydraulic tensioner
41
includes a plunger
43
slidably mounted in a housing
42
so that a high-pressure oil chamber
44
is defined between the housing
42
and an inner part of the plunger
43
. The plunger
43
is urged in a direction to project from the housing
42
by means of a spring
45
. A tip end of the plunger
43
is provided with an end plug
55
.
Between the housing
42
and the high-pressure oil chamber
44
, there is provided a check valve mechanism
47
including a check ball
46
. The check valve mechanism
47
permits oil to flow into the high-pressure chamber
44
while blocking the oil from flowing out from the high-pressure oil chamber
44
. The high-pressure oil chamber
44
is always filled with the oil which is supplied to an oil supply passage
48
from an oil supply source (not shown) via the check valve mechanism
47
.
The plunger
43
is also formed with a secondary oil chamber
50
communicating with the high-pressure oil chamber
44
through an oil passage
49
. A sleeve
51
is slidably received in the secondary oil chamber
50
and urged in an axial inward direction by a spring
52
. The plunger
43
further has a discharge port
53
normally closed by the sleeve
51
. The discharge port
53
is opened when the sleeve
51
is displaced in an axial outward direction past the discharge port
53
against the force of the spring
52
. The spring-loaded sleeve
51
assembled in the plunger
43
forms a relief valve
54
.
The housing
42
of the tensioner
41
further includes an orifice member
56
having a peripheral helical orifice
56
A designed to communicate with an upper part of the high-pressure oil chamber
44
for allowing the leakage of air or oil from the high-pressure oil chamber
44
.
While the chain
43
is running, the plunger
43
of the foregoing conventional hydraulic tensioner
41
may be subjected to a force or load applied from the chain
62
in a direction to move the plunger
43
backward against the force of the spring
45
whereupon the hydraulic pressure in the high-pressure oil chamber
47
increases. In this instance, air or oil leaks from the orifice
56
A of the orifice member
56
to thereby absorb an impact force applied to the plunger
43
. At the same time, a pressure rise is developed in the pressure in the secondary oil chamber
50
, which forces the sleeve
51
of the relief valve
54
to gradually move backward away from the secondary oil chamber
50
against the force of the spring
52
. As the pressure in the secondary oil chamber
50
further increases, the sleeve
51
is caused to move backward past the discharge port
53
whereupon the discharge port
53
is opened, allowing the oil to flow out from the secondary oil chamber
50
to thereby relieve the pressure in the high-pressure oil chamber
44
.
FIG. 6
shows in cross section another example of the conventional hydraulic tensioner which includes a relief valve and an orifice member provided separately.
The hydraulic tensioner
41
′ is equipped with an oil supply passage
48
and a check valve mechanism
47
, a plunger
43
′, a high-pressure oil chamber
44
′ and an orifice member
56
that are similar to those of the tensioner
41
shown in FIG.
5
. The conventional tensioner
41
′ is substantially the same in function and operation as the conventional tensioner shown in
FIG. 5
but differs from the latter in the respective positions of the relief valve
54
and orifice member
56
.
More specifically, the relief valve
54
is disposed inside the housing
42
and located above the high-pressure oil chamber
44
. The orifice member
55
is provided at a tip end of the plunger
42
.
The operation and function of the hydraulic tensioner
41
′ are the same as those of the hydraulic tensioner
41
of FIG.
5
and a further description thereof can, therefore, be omitted.
As discussed above, in the foregoing examples of the conventional hydraulic tensioners, the relief valve
54
which is adapted to be opened to release the pressure of the high-pressure oil chamber beyond a predetermined limit, and the orifice member
56
which is designed to vent air or leak the oil from the high-pressure oil chamber to thereby absorb an impact force applied to the plunger are provided separately. Thus, it has been conventionally impossible to integrate these two functionally different components into a single unit. Since the relief valve and the orifice member are arranged separately, the conventional hydraulic tensioners are relatively large in size and hence require a large space for installation, and are expensive to manufacture.
SUMMARY OF THE INVENTION
It is accordingly a general object of the present invention to solve the foregoing problems associated with the prior art.
A more specific object of the present invention is to provide a hydraulic tensioner including a relief valve and an orifice member integrated into a single operating unit which is capable of achieving both a pressure-releasing function and a fluid-leaking function with respect to a high-pressure oil chamber, occupies only a small space in the housing and hence is contributive to the downsizing of the tensioner, and adds to reduction of the manufacturing cost of the tensioner.
To achieve the foregoing objects, there is provided, according to the present invention, a hydraulic tensioner comprising: a tensioner housing having a plunger accommodation bore formed therein, a plunger slidably fitted into the plunger accommodation bore of the tensioner housing and urged by a spring such that a tip portion of the plunger is projected to the exterior of the plunger accommodation bore, the plunger having a ho
Fujimoto Nobuyuki
Suzuki Tadasu
Dann Dorfman Herrell and Skillman, P.C.
Hannon Thomas R.
Johnson Vicky A.
Skillman Henry H.
Tsubakimoto Chain Co.
LandOfFree
Hydraulic tensioner does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Hydraulic tensioner, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hydraulic tensioner will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2834872