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
2001-01-12
2002-10-29
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
C474S109000
Reexamination Certificate
active
06471612
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a closed hydraulic tensioner used for applying an appropriate tension to a timing belt or a timing chain of an automobile engine.
2. Description of the Related Art
Hydraulic tensioners used to apply an appropriate tension to a timing chain or belt of an automobile engine include a closed hydraulic tensioner having an oil previously sealed therein, and an open hydraulic tensioner containing an oil supplied from an oil pump of the engine. The latter-mentioned open hydraulic tensioner further includes a reservoir-equipped type hydraulic tensioner in which an oil supplied from the oil pump is stored in a reservoir provided in the tensioner.
FIG. 3
is a longitudinal cross-sectional view showing one example of the conventional closed hydraulic tensioners. The hydraulic tensioner
1
shown in
FIG. 3
comprises a housing
2
, a flanged cylinder
3
mounted in the housing
2
, and a piston rod
4
slidably fitted in the cylinder
3
from an end thereof, with a small clearance defined between the cylinder
3
and the piston rod
4
. A ball seat
5
A forming part of a check valve
5
is press-fitted in the opposite end of the cylinder
3
so that a high-pressure chamber
6
is defined interiorly of the cylinder
3
. A circular rod guide
7
has an axial connecting hole
7
A formed therein and is mounted on the piston rod
4
by means of a stop ring
7
B. By the rod guide
7
, the piston rod
4
is aligned with the axis of the cylinder
3
. A compression coil sprig
8
is disposed in a pre-loaded or compressed condition between a flange of the flanged cylinder
3
and the rod guide
7
so that the spring
8
urges the piston rod
4
in a direction to project outward from the housing
2
.
The housing
2
has an intermediate partition wall
2
A. The flanged cylinder
3
is disposed on a forward side of the partition wall
2
A within the housing
2
. An oil seal
9
and a dust seal
10
are disposed between an outer circumferential surface of the piston rod
4
and an inner circumferential surface of the housing
2
. The piston rod
4
, the flanged cylinder
3
, the housing
2
and the oil seal
9
jointly define therebetween a space and this space forms a low-pressure chamber
11
. A second stop ring
12
is attached to the inner circumferential surface of the housing
2
at a position behind the oil seal
9
. The stop ring
12
limits the forward stroke of the rod guide
7
. The partition wall
2
A has a central oil passage
2
B and a connecting passage
2
C located radially upward of the oil passage
2
B. The flange of the flanged cylinder
3
has two axial oil passages
3
A formed in an outer circumferential surface thereof and spaced at an angle of 180 degrees. The flanged cylinder
3
further has a radial oil passage
3
B formed in an end face thereof which is held in abutment with the partition wall
2
A. The housing
2
further has a reservoir
15
formed on the rearward side of the partition wall
2
A. The reservoir
15
is defined by a diaphragm
14
attached to the housing
2
by means of a diaphragm clamp
13
. The diaphragm
14
is urged toward the reservoir
15
by means of a loading spring
18
. The high-pressure chamber
6
, low-pressure chamber
11
and the reservoir
15
are previously filled with an oil. The low-pressure chamber
11
communicates with the reservoir
15
through the oil passages
3
A and
3
B and the connecting passage
2
C.
In operation, when a shoe (not shown) is subjected to an impact force applied from a belt or a chain (not shown), the piston rod
4
moves backward against the force of the spring
8
. With this backward movement of the piston rod
4
, the hydraulic pressure within the high-pressure chamber
6
increases to thereby close the check valve
5
. Thus, the oil inside the high-pressure chamber
4
leaks out to the low-pressure chamber
11
through the small clearance between the outer circumferential surface of the piston rod
4
and the inner circumferential surface of the flanged cylinder
3
. During that time, the impact force applied to the shoe from the belt or chain is dampened or otherwise absorbed by a flow resistance produced when the oil passes through the small clearance.
When the piston rod
4
moves forward in the projecting direction under the force of the spring
8
, the oil inside the reservoir
15
is introduced into the high-pressure chamber
6
through the check valve
5
. In this instance, since the amount of oil held inside the reservoir
15
decreases, the diaphragm
14
is displaced toward the reservoir
15
side by the force of the loading spring
18
to thereby follow up the change in content volume of the reservoir
15
.
FIG. 4
is a longitudinal cross sectional view showing another example of the conventional closed hydraulic tensioners. The hydraulic tensioner
21
includes a housing
22
in the form of a bottomed cylinder, a plunger
26
slidably fitted in the cylindrical housing
22
and having one end facing toward the bottom of the housing
22
with a first oil chamber
23
defined therebetween, the plunger
26
having the opposite end facing a second oil chamber
24
and being urged by a spring
25
toward the second oil chamber
24
, a rod portion
27
formed integrally with the plunger
26
and projecting outward from the housing
22
, a free piston
31
sealed from the rod portion
27
by means of an oil seal
28
and slidably fitted in the cylindrical housing
22
via a packing
29
, the free piston
31
having one end facing the second oil chamber
24
and being urged by a loading spring
30
toward the second oil chamber
24
, and an oil passage
33
formed in the plunger
26
and equipped with a check valve
32
which allows the oil to flow from the second oil chamber
24
into the first oil chamber
23
and blocks reverse flow of the oil.
In operation, when the tension in a belt or a chain (not shown) increases, the load exerted via the rod portion
27
onto the plunger
26
increases to thereby increase the hydraulic pressure within the first oil chamber
23
. With this pressure rise, the oil inside the first oil chamber
23
flows through a small clearance between the plunger
26
and the housing
22
into the second oil chamber
24
, thereby permitting the plunger
26
to move backward. With this backward movement of the plunger
26
, the increased tension in the belt or chain is absorbed. In this instance, the free piston
31
moves forward to an extent corresponding to the amount of oil flown into the second oil chamber
24
.
When the tension in the belt or chain decreases, the force or pressure applied to the rod portion
27
decreases. Accordingly, the plunger
26
moves forward by the force of the spring
25
to thereby cancel out the reduction in tension of the belt or chain. In this instance, the oil in the second oil chamber
24
flows through the oil passage
33
and the check valve
32
into the first oil chamber
23
, and the loading spring
30
moves the free piston
31
backward by a distance corresponding to the amount of oil flown out from the second oil chamber
24
.
FIG. 5A
is a side view illustrating one example of the conventional reservoir-equipped hydraulic tensioners, and
FIG. 5B
is a front cross-sectional view of the hydraulic tensioner. As shown in these figures, the reservoir-equipped hydraulic tensioner
41
includes a housing
42
having formed therein a reservoir
43
open upward and a plunger accommodating hole
44
(
FIG. 5B
) extending in a horizontal direction with respect to the reservoir
43
. A hollow plunger
45
having an open inner end is slidably inserted into the plunger accommodating hole
44
and resiliently urged by a spring
46
in a direction to project from the housing
42
. An outer end (projecting end) of the hollow plunger
45
has an orifice
47
. A check valve
48
is provided at the bottom of the plunger accommodating hole
44
. The plunger accommodating hole
44
and the hollow plunger
45
jointly form a pressure chamber
49
. The reservoir
43
and the c
Bucci David A.
Charles Marcus
Dann Dorfman Herrell and Skillman
Skillman Henry H.
Tsubakimoto Chain Co.
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