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
2000-06-21
2002-03-05
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
06352487
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic chain tensioner for use with an associated chain or belt that drives an engine camshaft, balance shaft drive or the like. In particular, the hydraulic tensioner of the present invention is directed to an improvement of the construction of a hydraulic tensioner to prevent errors in the assembly of the vent device.
In general, a hydraulic tensioner includes a housing, a plunger inserted into a bore formed in the housing, and a spring that biases the plunger in the projecting or protruding direction. In the housing, a chamber is formed by assembling a hollow plunger into the bore of the housing. Oil is supplied to the chamber from an external oil pressure source. The pressurized oil acts on the plunger to cause the plunger to protrude from the housing bore and provide tension to an associated chain.
In a hydraulic tensioner, when air mixes with oil in the chamber, the plunger can be forced inwardly toward the housing due to compression of the mixed air and oil. The air/oil mixture compresses when the tension of the chain or belt increases and, as a result, the chain or belt tension can vary due to the reduced effectiveness of the tensioner.
A hydraulic tensioner, as disclosed in Japanese Laid-Open Patent No. 7-158703, discloses one proposed solution of such a problem. This hydraulic tensioner has a disc as a vent device inside the plunger. A spiral groove is formed on the disc surface. The starting end of the groove is located on the outer peripheral side of the disc surface and the terminal end is located at the center of the disc surface.
FIG. 10
shows the enlarged plunger tip portion of the hydraulic tensioner disclosed in the above-mentioned prior art patent publication. In the Figure, a hole
100
a
is formed at the tip of plunger
100
and disc
110
is inserted in inner chamber
100
b
formed inside hollow plunger
100
. Spiral groove
110
a
is formed on one of the main surfaces (top surface) of disc
110
. On a portion of the outer periphery of disc
110
a groove
110
b
is formed that extends in the direction of the center axis of the plunger and connects to the starting end of groove
110
a.
In such a hydraulic tensioner, air mixed into the chamber passes to spiral groove
110
a
from groove
110
b
on the outer periphery of disc
110
and leaks out to the outside air together with hydraulic oil after passing through hole
100
a
of plunger
100
. At such time, leakage of the oil in the chamber to the outside of the tensioner is controlled by the spiral form of groove
110
a
on the main surface of disc
110
.
Typically, product inspection after assembly of the hydraulic tensioner involves checking the ability of the chamber to retain oil pressure by introducing hydraulic oil into the chamber and measuring the rate of leakage of oil from the hole at the plunger tip.
However, in a conventional hydraulic tensioner, a disc
110
that functions as a vent device is in a single round plate shape, so that, as shown in
FIG. 11
, disc
110
can be assembled in an up/down reversed fashion. When such assembly error occurs, air mixed into the chamber cannot be discharged outside of the tensioner because spiral groove
110
a
of disc
110
is not connected to hole
110
a
. of plunger
100
. On the other hand, when such a hydraulic tensioner, assembled in error, is inspected in the same manner as above, the hydraulic oil in the chamber can pass groove
110
b
on the outer periphery of disc
110
, pass through the gap between the disc's main surface and the plunger and leak out of the tensioner. The product can be judged to be acceptable, even in such case of incorrect assembly.
The objective of this invention is to offer a hydraulic tensioner that prevents incorrect assembly of the vent device and that eliminates such a conventional problem.
SUMMARY OF THE INVENTION
It is a first object of the present invention to provide a hydraulic chain tensioner including a housing with a bore formed therein. A hollow plunger is inserted slidably into the housing. The plunger has a tip with an open vent hole or aperture and a spring member that biases the plunger in the protruding direction. A vent device or disc is provided inside the hollow portion of the plunger. The vent device is composed of disc first and second portions. The first portion has a first main surface on which the vent channel is formed and the said second portion is provided on the second main surface which is on the opposite side to the first main surface. The second portion has a passage, the outer diameter of which is larger than the open vent hole in the plunger that connects to a hole in the center axis direction and extends to intersect the center axis and opens on the outer peripheral surface. The vent device is assembled into the plunger with the first main surface having a vent channel facing toward the tip of the plunger.
When the assembly is correct, fluid in the chamber passes the vent channel on the first main surface of the vent device, passes the open hole at the plunger tip and is discharged from the tensioner if fluid in the chamber is pressurized during product inspection. Air mixed in the chamber passes the vent channel on the first main surface of the vent device and leaks out to the outside air from the hole at the plunger tip.
On the other hand, when the second portion on the second main surface side of the vent device is facing the side of the plunger tip during assembly, that is, the top and bottom of the vent device are reversed in an incorrect orientation of assembly, a gap is formed between the second main surface of the vent device and the inner wall of the plunger tip because the outer diameter of the second portion of the vent device is larger than the open hole of the plunger.
When fluid is supplied to the chamber and pressure is applied inside the chamber, the fluid in the chamber flows into the passage from its opening on the outer surface of the second portion of the vent device, passes the hole in the center axis direction and is discharged in a large quantity to the outside of the tensioner.
The volume of fluid discharged from the hole at the plunger tip is large when incorrectly assembled, so that it can be separated from correctly assembled devices and, thereby, erroneous assembly of the vent device can be prevented.
It is a second object of the invention to provide a hydraulic tensioner with a vent disc having, a first portion with an outer diameter which is slightly smaller than the inner diameter of the plunger. The outer diameter of the first portion of the vent device is slightly smaller than the inner diameter of the plunger, so that a gap is formed between the outer diameter of the first portion of the vent device and the inner diameter of the plunger, and, thereby, the air mixed in the chamber passes the gap and moves to the side of the first main surface of the vent device and is discharged outside of the vent channel on the first main surface.
It is a third object of the invention to provide a hydraulic tensioner with a vent disc having a first portion with an outer diameter which is substantially equal to the inner diameter of the plunger and a groove in the center axis direction that connects to the starting end of the vent channel on the outer surface of the first portion. The outer diameter of the first portion of the vent device is substantially equal to the inner diameter of the plunger, so that when the vent device is assembled into the plunger, the outer diameter of the first portion of the vent device fits the inner diameter of the plunger without clearance. An axial groove connected to the starting end of the vent channel is formed on the outer periphery of the first portion of the vent device. Therefore, the air mixed in the chamber moves to the side of the first main surface of the vent device through the groove and is discharged outside from the vent channel on the first main surface.
It is a fourth object of the invention to provide a hydraulic tensioner which has a vent channel with a tortu
Borg-Warner Automotive K.K.
Bucci David A.
Dziegielewski Greg
McAnulty Timothy
Sidley Austin Brown & Wood
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