Fluid handling – Line condition change responsive valves – Direct response valves
Reexamination Certificate
2002-10-03
2004-11-02
Krishnamurthy, Ramesh (Department: 3753)
Fluid handling
Line condition change responsive valves
Direct response valves
C474S110000
Reexamination Certificate
active
06810907
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to hydraulic tensioners used to apply proper tension to a timing chain, belt, or the like in a vehicle engine, and more particularly to a tensioner having a relief valve mechanism.
BACKGROUND OF THE INVENTION
These tensioners are typically installed in the manner depicted in
FIG. 9
, where a hydraulic tensioner
50
is shown in conjunction with a timing transmission in FIG.
9
. The tensioner
50
adjusts chain tension through a tension lever TL, and a relief valve (not shown in
FIG. 9
) is provided in the tensioner to relieve excess tension generated in the timing chain TC, when the timing chain is stretched as it transmits power.
The relief valve mechanism is shown in a cross-sectional view of the tensioner in FIG.
10
. The tensioner comprises a housing, or tensioner body,
51
, and a hollow plunger
52
, slidably fitting into a blind plunger-accommodating hole
51
a
formed in the housing
51
. An end wall
52
a
of the plunger
52
is outside the housing. A spring
53
, inside the plunger
52
, biases the plunger in the projecting direction. A high pressure oil chamber
54
is constituted by the interior of the plunger and a part of the blind hole
51
a
behind the plunger. A check valve mechanism
55
is provided at the bottom of the plunger-accommodating hole
51
a
, and a relief valve mechanism
57
is provided in the housing
51
at a location such that it communicates with the oil chamber
54
through a passage
57
b
, which leads to an opening in the side wall of the plunger-accommodating hole
51
a
, near the bottom of the hole.
The check valve mechanism
55
comprises a ball seat
55
b
having an oil passage
55
a
. The seat
55
b
is press-fit into a hole
51
b
formed at a bottom portion of the plunger-accommodating hole
51
a
. A check ball
55
c
, which can abut the ball seat
55
b
, is held in close proximity to the seat by a retainer
55
d
. A spring
55
e
, shown schematically, biases the check ball
55
c
toward the ball seat
55
b
. An oil supply passage (not shown), for supplying oil from a source of oil under pressure to the high pressure oil chamber
54
, communicates with hole
51
b
in the housing
51
. The check valve mechanism
55
permits the flow of oil into the high-pressure oil chamber
54
, but blocks flow out of the high pressure oil chamber
54
in the reverse direction.
The relief valve mechanism
57
comprises a valve element fitting recess
57
a
formed in the housing
51
, the oil passage
57
b
, which provides fluid communication between the high pressure oil chamber
54
and the valve element fitting recess
57
a
, a cup-shaped valve element
57
c
slidably fitting into the recess
57
a
with the bottom surface of the valve element
57
c
facing the oil passage
57
b
, a spring
57
d
, which biases the valve element
57
c
toward the oil passage
57
b
, a relief hole
57
e
, provided near the oil passage
57
b
in a side wall of the valve element fitting recess
57
a
, and a plug
57
f
press-fit into the recess
57
a
from the outside. The relief hole
57
e
provides fluid communication between the inside of the valve element fitting recess
57
a
and the outside of the housing
51
.
When the oil pressure in the high pressure oil chamber
54
exceeds a predetermined pressure, the valve element
57
c
is moved backward against the biasing force of the spring
57
d
, and the oil passage
57
b
communicates with the relief hole
57
e
, thereby reducing the oil pressure in the high pressure chamber
54
. The inside of the valve element fitting recess
57
a
is filled with oil to ensure smooth operation of the valve element
57
c
, and the oil is supplied and discharged through an oil hole
57
h
bored in the plug
57
f
as the valve element
57
c
moves backward and forward.
With the engine operating normally, when the timing chain loosens, the biasing force of the spring
53
in the above-described hydraulic tensioner
50
causes the plunger
52
to project. As the plunger projects, the check ball
55
c
separates from the seat
55
b
, and oil, supplied from an oil pressure source such as an oil pump or the like, flows into the oil chamber
54
through the oil supply passage (not shown). The oil supply passage communicates with the hole
51
b
and the oil passage
55
a
in the ball seat
55
b
, so that the oil supplied to the oil chamber
54
maintains tension in the timing chain.
When the chain is under excess tension, the plunger
52
receives a thrust load from the tensioner lever (
FIG. 9
) in a direction opposite to the direction in which the plunger is biased by spring
53
. The check valve mechanism
55
then prevents backflow of oil from the high pressure oil chamber
54
, and the oil, being non-compressible, prevents the return of the plunger
52
. However, the valve element
57
c
of the relief valve mechanism
57
responds to the excess oil pressure in chamber
54
by sliding against the biasing force of spring
57
d
. A slight backward movement of the valve element
57
c
absorbs a small amount of excess tension in the timing chain.
When the thrust applied to the plunger
52
further increases, causing the valve element
57
c
to move farther in recess
57
a
, the oil passage
57
b
communicates with the relief hole
57
e
, permitting discharge of oil from the high pressure oil chamber
54
to the outside of the tensioner
50
. Thus, the oil pressure in the high pressure oil chamber
54
decreases, and excessive tension of the timing chain is absorbed.
When the oil pressure in chamber
54
decreases as oil is discharged from the tensioner, the biasing force of the spring
57
d
causes the valve element
57
c
to close the relief hole
57
e
, to maintain the oil pressure in chamber
54
at a preset value. If the oil pressure in chamber
54
decreases excessively, the check valve mechanism
55
allows oil to flow into chamber
54
, to return the oil pressure to a normal level.
In the conventional hydraulic tensioner
50
, as shown in
FIG. 10
, a condition of excess tension can occur while oil continues to flow from the high pressure oil chamber to the relief valve mechanism. When this condition occurs, the valve element
57
c
of the relief valve mechanism
57
moves backward rapidly and collides with the plug
57
f
, generating hitting sounds.
The spring
57
d
, which biases the valve element
57
c
, can also become compressed past its elastic limit, with the result that the biasing force exerted by the spring
57
d
gradually decreases, and the relief valve ceases to function properly. To avoid these problems, it has been proposed to provide a buffer of rubber or the like between the valve element
57
c
and the plug
57
f
in the valve element fitting recess
57
a
. However, this has not proven to be an effective solution, since the insertion of the buffer required additional assembly manpower and increases production cost.
Accordingly, the objects of the invention are to overcome the above-mentioned problems, and to provide an inexpensive, hydraulic tensioner with a structurally simple relief valve mechanism capable of avoiding hitting sounds in the relief valve structure, and avoiding wearing out and breakage of the biasing spring in the relief valve. It is also an object of the invention to provide a hydraulic tensioner which instantaneously adjusts to rapid variations in chain tension, and operates reliably when excess oil has been supplied, when tension in the timing chain increases rapidly, and when the oil pressure inside the high pressure oil chamber has reached an excessive level.
SUMMARY OF THE INVENTION
The hydraulic tensioner in accordance with the invention comprises a tensioner housing, and a plunger for exerting a tensioning force on a flexible transmission medium. The plunger projects from a blind hole in the tensioner housing, and the blind hole and the plunger together define a high pressure oil chamber. A passage is provided for delivering oil into the high pressure chamber from a high pressure oil supply, and a relief valve is connected to the high pressur
Fujimoto Nobuyuki
Hashimoto Hiroshi
Kurokawa Yoshio
Namie Tsutomu
Howson and Howson
Krishnamurthy Ramesh
Tsubakimoto Chain Co.
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