Information
-
Patent Grant
-
6619249
-
Patent Number
6,619,249
-
Date Filed
Tuesday, January 22, 200222 years ago
-
Date Issued
Tuesday, September 16, 200321 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Denion; Thomas
- Corrigan; Jaime
Agents
-
CPC
-
US Classifications
Field of Search
US
- 123 9012
- 123 9015
- 123 9016
- 123 9017
- 123 198 F
- 123 40623
- 123 481
- 091 520
- 091 440
-
International Classifications
-
Abstract
A hydraulic control system for an internal combustion engine is provided which comprises a first hydraulic operating mechanism and a second hydraulic operating mechanism, the first hydraulic operating mechanism and the second hydraulic operating mechanism being operated independently by oil pressure of a common oil press source, and a circulation line that supplies pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a hydraulic control system for an internal combustion engine, which has two hydraulic operating mechanisms operated independently by oil pressure of a common oil pressure source. The present invention further relates to a hydraulic control system for an internal combustion engine, which has two variable valve timing control mechanisms capable of varying lift characteristics of at least one of an intake valve and an exhaust valve.
In the field of internal combustion engines, it is a common practice to actuate various kinds of hydraulic operating mechanisms by using an oil pump for circulation of lubrication oil as an oil pressure source. Examples of such hydraulic operating mechanism are a variable valve timing control mechanism for varying the opening and closing timings and the lift of the intake and exhaust valves in accordance with the operating condition of the engine and a variable compression ratio control mechanism for varying the piston stroke of each cylinder and thereby varying the compression ratio in accordance with the operation condition of the engine.
An example of a hydraulic variable valve timing control mechanism is disclosed in Japanese Patent Provisional Publication No. 5-248217. This variable valve timing control mechanism is capable of varying the opening and closing timings of the intake and exhaust valves in two steps by switching from one of a low-speed rocker arm and a high-speed rocker arm to another. Other variable valve timing control mechanisms are a variable phase control mechanism for varying the operation angle phase (i.e., maxim lift phase) of the intake and exhaust valves, an operation angle varying mechanism for varying the operation angles and valve lifts of the intake and exhaust valves and a valve stop mechanism for temporarily stopping the intake and exhaust valves of some of the cylinders.
SUMMARY OF THE INVENTION
In this connection, in case two hydraulic operating mechanisms which are operated independently by oil pressure of a common oil pressure source e used in an internal combustion engine, there is a possibility of causing the following problems. Namely, In case the operating conditions of both of the hydraulic operating mechanisms are changed simultaneously, particularly at a low-speed engine operating condition where the oil pressure produced by the oil pump is low, there is a possibility that the hydraulic operating mechanisms become poor in responsiveness due to a lack of the oil pressure supplied thereto. To prevent such deterioration of the responsiveness, it is considered to use an oil pump, accumulator or the like for the hydraulic operating mechanisms' exclusive use. However, in this instance, a hydraulic circuit of the hydraulic control system becomes complicated in structure, thus causing a possibility of increasing the weight and the cost.
Particularly, in case the two hydraulic operating mechanisms are variable valve timing control mechanisms for varying the lift characteristics of the intake and exhaust valves, it is highly necessitated to change the operating conditions of the variable valve timing control mechanisms at the same timing so as to attain the required lifts which vary largely in accordance with the operating conditions of the engine at idling or at full-throttle operation.
For example, in case a variable phase control mechanism for varying the operation angle phase of an intake valve and a valve stop mechanism for temporarily stopping the intake and exhaust valves of some of the cylinders are used, it is desirable, when the valve stop mechanism is operated to stop the intake and exhaust valves of some of the cylinders, to advance the operation angle phase of the intake valve by the variable phase control mechanism so that a predetermined torque can be attained by the remaining cylinders. In this instance, the delay of the responsiveness of the valve stop mechanism becomes a particularly large problem. Namely, in the cylinders where the intake and exhaust valves are stopped, it is necessitated to inhibit injection of fuel. If there is a difference between the period during which the intake and exhaust valves are actually stopped and the period during which injection of fuel is actually inhibited, it is possible that fuel is injected during the time of the valves being stopped. This is particularly not desirable.
It is accordingly an object of the present invention to provide a hydraulic control system for an internal combustion engine, which has two hydraulic operating mechanisms operated independently by oil pressure of a common oil pressure source and which is simple in structure and has an improved responsiveness.
To accomplish the above object, there is provided according to an aspect of the present invention a hydraulic control system for an internal combustion engine comprising a first hydraulic operating mechanism, a second hydraulic operating mechanism, the first hydraulic operating mechanism and the second hydraulic operating mechanism being operated independently by oil pressure of a common oil pressure source, and a circulation line that supplies pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism.
According to another aspect of the present invention, there is provided a hydraulic control system for an internal combustion engine comprising an oil pressure source, an oil sump, a first hydraulic operating mechanism, a second hydraulic operating mechanism, a first hydraulic control valve for selectively communicating the first hydraulic operating mechanism with one of the oil pressure source and the oil sump thereby controlling an operation of the first hydraulic operating mechanism, a second hydraulic control valve for selectively communicating the second hydraulic operating mechanism with one of the oil pressure source and the oil sump, a control line fluidly connecting between the second hydraulic control valve and the second hydraulic operating mechanism for conducting pressure oil supplied to and discharged from the second hydraulic operating mechanism, and a circulation line connecting between the first hydraulic control valve and the control line for supplying pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism.
According to a further aspect of the present invention, there is provided a hydraulic control system for an internal combustion engine comprising a phase control mechanism for varying a phase of an intake valve, a valve stop mechanism for temporarily stopping intake and exhaust valves of some of cylinders, the phase control mechanism and the valve stop mechanism being operated by oil pressure of a common oil pressure source, and means for supplying pressure oil discharged from the phase control mechanism to the valve stop mechanism in addition to pressure oil supplied from the oil pressure source to the valve stop mechanism when the phase of the intake valve is advanced by the phase control mechanism and the intake and exhaust valves of some of the cylinders are stopped by the valve stop mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a hydraulic control system for an internal combustion engine according to an embodiment of the present invention;
FIGS. 2A
to
2
C are schematic views for illustrating operations of a variable phase control mechanism and a hydraulic control valve for phase control, which are used in the hydraulic control system of
FIG. 1
;
FIG. 3
is a perspective view of a valve stop mechanism used in the hydraulic control system of
FIG. 1
;
FIGS. 4A and 4B
are schematic views for illustrating operations of a hydraulic control valve for valve stop, used in the hydraulic control system of
FIG. 1
; and
FIGS. 5A and 5B
are graphs for showing an advanced valve timing operation range and a part cylinder operation range, respectively.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to
FIG. 1
, a hydraulic control system for an internal combustion engine includes first hydraulic operating mechanism
12
and second hydraulic operating mechanism
14
that are fluidly connected to oil pump
10
serving as a anon oil pressure source. In this embodiment, hydraulic operating mechanism
12
and
14
are embodied in valuable valve timing control mechanisms capable of varying lift characteristics of at least one of an intake valve and an exhaust valve of each cylinder. More specifically, hydraulic operating mechanisms
12
and
14
are embodied in a variable phase control mechanism for continuously varying the phase of an intake valve and a valve stop mechanism for temporarily stopping the intake and exhaust valves of some (e.g., a half) of the cylinders, respectively.
Further, the hydraulic control system includes hydraulic control valve
16
for phase control, that controls oil pressure supplied from oil pump
10
to variable phase control mechanism
12
, and hydraulic control valve
18
for valve stop, that controls oil pressure supplied from oil pump
10
to valve stop mechanism
14
.
Variable phase control mechanism
12
is of the type having been already proposed and described briefly with reference to
FIGS. 2A
to
2
C. Variable phase control mechanism
12
includes outer circumferential side gear potion
22
rotatable together with cam sprocket
21
which is in turn rotatable in timed relation with a crank shaft (not shown), inner circumferential side gear portion
24
disposed concentrically with and inside of cam sprocket
21
and rotatable together with intake cam shaft
23
, annular piston
25
meshed with the inner and outer circumferential surfaces of outer circumferential side gear portion
22
and inner circumferential side gear portion
24
by means of splines, and return spring
26
for urging piston
25
toward the retard side.
The opposite ends of piston
25
are associated with retard side oil pressure chamber
27
and advance side oil pressure chamber
28
, respectively. By axial movement of piston
25
in response to oil pressures in oil pressure chambers
27
and
28
, the phase of intake camshaft
23
relative to cam sprocket
21
is varied thereby varying the phase of the intake valve continuously.
Details of such a phase control mechanism are disclosed in Japanese Patent Provisional Publication Nos. 2000-073797, 2000-145487 and 2000-234533.
Valve stop mechanism
14
is of the type having been already proposed and described briefly with reference to FIG.
3
. When the oil pressure in valve stop oil pressure chamber
31
is low, coupling
33
is urged by the bias of a spring (not shown) disposed inside thereof so as to protrude into a position where it contacts auxiliary rocker arm
36
a
having roller bearing
34
. This causes rotational power to be transmitted to the intake and exhaust valves by way of auxiliary rocker arm
36
a
, coupling
33
and rocker arm
36
thereby causing all the cylinders to operate. On the other hand, when a predetermined oil pressure is supplied to valve stop oil pressure chamber
31
, piston
38
pushes coupling
33
against the bias of the spring disposed inside coupling
33
and causes coupling
33
to move apart from auxiliary rocker arm
36
a
. This shuts off transmission of power from auxiliary rocker arm
36
a
to coupling
33
thereby performing a part cylinder operation where the intake and exhaust valves of some of the cylinders are stopped. Details of such a valve stop mechanism are disclosed in Pages 56 to 58 of Auto Motor and Sport (German car magazine) No. 15, published on Jul. 14, 1999.
Referring to
FIGS. 1
to
4
A and
4
B, a hydraulic circuit of the hydraulic control system will be described. The hydraulic circuit includes first supply line
41
for supplying oil pressure from oil pumps
10
to hydraulic control valve
16
for phase control, second supply line
42
for supplying oil pressure fan oil pump
10
to hydraulic control valve
18
for valve stop, retard side control line
43
connecting between control valve
16
and retard side oil pressure chamber
27
, advance side control line
44
connecting between control valve
16
and advance side oil pressure fiber
28
, valve stop control line
45
connecting between control valve
18
and valve stop oil pressure chamber
45
, retard side drain line
46
for conducting pressure oil discharged from control valve
16
to oil sump or oil pan
11
, and drain line
47
for valve stop for conducting pressure oil discharged from control valve
18
to oil pan
11
.
In the embodiment, circulation line
48
is provided which is fluidly connected at one end to retard side oil pressure chamber
27
of phase control mechanism
12
and at another end to valve stop oil pressure chamber
31
of valve stop mechanism
14
so as to supply pressure oil discharged from retard side oil pressure chamber
27
to valve stop oil pressure chamber
31
. More specifically, circulation line
48
is connected at one end to control valve
16
so as to communicate with retard side oil pressure chamber
27
of phase control mechanism
12
by way of retard side control line
43
and at another end (downstream side) to valve stop control line
45
so as to communicate therethrough with valve stop oil pressure chamber
31
of valve stop mean
14
. Namely, circulation line
48
is constructed so that it can supply pressure oil discharged from retard side oil pressure chamber
27
not through control valve
18
but directly to valve stop oil pressure chamber
31
.
In circulation line
48
is disposed check valve
49
for preventing reverse flow of pressure oil from valve stop mechanism
14
to phase control mechanism
12
. Further, control valve
51
is disposed in advance side drain line
50
branching off from circulation line
48
at a location upstream of check valve
49
(i.e., on phase control mechanism
12
side of check valve
49
) and extending up to oil pan
11
. The valve opening pressure of check valve
49
is set at a value lower than that of control valve
51
. For example, the valve opening pressure of check valve
49
is set at about 0.1 kgf/cm
2
and the valve opening pressure of control valve
51
is set at about 0.3 kgf/cm
2
.
The operation of the hydraulic control system will now be described.
Phase control mechanism
12
supplies a duty signal to a solenoid (not show) for driving spool
16
a
of control valve
16
thereby feedback controlling the operation angle phase of the intake valve corresponding to the position of piston
25
.
More specifically, upon retard, i.e., when the operation angle phase of the intake valve is retarded, spool
16
a
of phase control valve
16
is placed in the position shown in FIG.
2
A. This causes the oil pressure from oil pump
10
to be supplied to retard side oil pressure chamber
27
by way of first supply line
41
and retard side control line
43
, while causing pressure oil in advance side oil pressure chamber
28
to be discharged through retard side drain line
46
into oil pan
11
. As a result, piston
25
is pushed toward the retard side (i.e., to the left-hand side in FIG.
2
A). In the meantime, in
FIG. 2A
are shown the lift characteristics of the intake and exhaust valves that are retarded maximumly.
Upon advance. i.e., when the operation angle phase of the intake valve is advanced, spool
16
a
is placed in the position shown in FIG.
2
B. This causes oil pressure to be supplied to advance side oil pressure chamber
28
by way of first supply line
41
and advance side control line
44
, while causing pressure oil in retard side oil pressure chamber
27
to be discharged through retard side control line
43
and circulation line
48
. As a result, piston
25
is pushed to the advance side (i.e., to the right-hand side in
FIG. 2B
) . In the meantime, in
FIG. 2B
are shown the lift characteristics of the intake and exhaust valve that are advanced maximumly.
When the operation angle phase of the intake valve is to be held at any given phase, spool
16
a
is placed in the position shown in
FIG. 2C
to close both of the ports connected to retard side control line
43
and advance side control line
44
. By this, the oil pressure in both oil pressure chambers
27
and
28
is confined therewithin, thus allowing piston
25
to be held at the present position, i.e., making it possible to hold piston
25
at any given position.
Valve stop mechanism
14
performs switching between full cylinder operation with all cylinders in operation and part cylinder operation with some of the cylinders kept out of operation, by switching the positions of spool
18
a
of control valve
18
according to the operating condition of the engine as shown in
FIGS. 4A and 4B
. Specifically, at the time of full cylinder operation. spool
18
a
of control valve
18
is placed at the position shown in FIG.
4
A. This causes pressure oil in valve stop oil pressure chamber
31
to be discharged through valve stop control line
45
and valve stop drain line
47
into oil pan
11
. On the other hand, at the time of port cylinder operation, spool
18
a
is placed at the position shown in
FIG. 4B
thereby causing oil pressure of oil pump
10
to be supplied through second supply line
42
and valve stop control line
45
to valve stop oil pressure chamber
31
.
In case oil pressure is supplied to valve stop mechanism
14
to start part cylinder operation at the time of advance, i.e., under the condition where pressure oil is discharged from retard side oil pressure chamber
27
into circulation line
48
, pressure oil is supplied through circulation line
48
to valve stop oil pressure chamber
31
rapidly. Namely, in addition to pressure oil supplied from oil pump
10
to valve stop oil pressure chamber
31
by way of second supply line
42
, control valve
18
and valve stop control line
45
, pressure oil is supplied from retard side oil pressure chamber
27
to valve stop oil pressure chamber
31
by way of circulation line
48
. Accordingly, retard side oil pressure chamber
27
functions as a kind of accumulator, so that it becomes possible to improve the responsiveness of valve stop mechanism
14
without using an additional accumulator or the like. As a result, it becomes possible to make longer the time of part cylinder operation and therefore it becomes possible to further improve the fuel consumption.
In other words, if the responsiveness of valve stop mechanism
14
is lowered, fuel will possibly be injected into a cylinder whose valves are stopped and therefore will possibly deteriorate the exhaust efficiency. However, since valve stop mechanism
14
starts part cylinder operation with an improved responsiveness, such a deterioration of the exhaust efficiency can be effectively suppressed.
Particularly, at low-speed engine operation, the oil pressure supplied by oil pump
10
is low so that the responsiveness of valve stop mechanism
14
tends to be lowered. However, according to the present invention, additional pressure oil is supplied from retard side oil pressure chamber
27
thereby enabling valve stop mechanism
14
to attain a good responsiveness even in an operation range where the oil pressure supplied to valve stop mechanism
14
is low.
Further, circulation line
48
is joined to valve stop control line
45
connecting between control valve
18
and valve stop oil pressure chamber
31
and is therefore constructed so as to supply pressure oil not through control valve
18
but directly to valve stop oil pressure chamber
31
.
Further, as seen from
FIGS. 5A and 5B
, the region H
2
where pressure oil is supplied to valve stop mechanism
14
to perform part cylinder operation with some of the cylinders kept out of operation is nearly included with the region H
1
where the operation angle phase of the intake valve is advanced from the maximumly retarded phase by phase control mechanism
12
thereby performing an advanced timing engine operation. Namely, when part cylinder operation is performed, it is desirable to advance the operation angle phase of the intake valve thereby retaining a predetermined torque by means of the remaining cylinders, while increasing an internal EGR thereby improving the fuel consumption and reducing the NOx emission. Accordingly, when oil pressure is supplied to valve stop mechanism
14
to start part cylinder operation, it is highly possible that phase control mechanism
12
is in a state of operation where the operation angle phase is advanced.
As indicated by arrows A
1
in
FIGS. 5A and 5B
, under an engine operating condition where the engine speed increases from the low-speed low-load range, the operating condition of phase control mechanism
12
is switched to the advance side simultaneously with switching to part cylinder operation. Further, as indicated by arrows A
2
, under an engine operating condition where the engine speed decreases from the high-speed low-load range, switching to the part cylinder operation is started during switching of phase control mechanism
12
to the advance side. Further, as indicated by arrows A
3
, even under an engine operating condition where the torque decreases from the high load range, switching to the part cylinder operation is started during switching of phase control mechanism
12
to the advance side. In this manner, when part cylinder operation is started, it is highly possible that phase control mechanism
12
has been switched to the advance side, i.e., it is highly possible that pressure oil is supplied through circulation line
48
to valve stop oil pressure chamber
31
, so that it becomes possible to make effectively higher the responsiveness of the hydraulic control system at the time of start of part cylinder operation.
In the meantime, in case phase control mechanism
12
is switched to the advance side under a condition where the oil pressure downstream of check valve
49
is high so that check valve
49
cannot be opened, such as the case where part cylinder operation is performed continuously, control valve
51
is adapted to open to enable pressure oil in retard side oil pressure chamber
27
to be discharged through advance side drain line
50
to oil pan
11
.
Further, at the time of full cylinder operation, the valve opening load of check valve
49
is lower than that of control valve (check valve)
51
and the oil pressure downstream of check valve
49
is low, so that when phase control mechanism
12
is switched to the advance side only check valve
49
is opened. Accordingly, pressure oil in retard side oil pressure chamber
27
is discharged through circulation line
48
, valve stop control line
45
and valve stop drain line
47
to oil pan
11
.
The entire contents of Japanese Patent Application P2001-12557 (filed Jan. 22, 2001) are incorporated herein by reference.
Although the invention has been described above by reference to a certain embodiment of the invention, the invention is not limited to the embodiment described above. Modifications and variations of the embodiment described above will occur to those skilled in the art, in light of the above teachings. For example, a flow restriction or orifice that generates a differential pressure can replace control valve
51
. The scope of the invention is defined with reference to the following claims.
Claims
- 1. A hydraulic control system for an internal combustion engine comprising:a first hydraulic operating mechanism; a second hydraulic operating mechanism, wherein the first hydraulic operating mechanism and the second hydraulic operating mechanism are adapted to operate independently by oil pressure of a common oil pressure source; and a circulation line that supplies pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism; wherein the first hydraulic operating mechanism and the second hydraulic operating mechanism are valve control mechanisms adapted to vary lift characteristics of one of an intake valve and an exhaust valve.
- 2. A hydraulic control system according to claim 1, wherein the first hydraulic operating mechanism is a phase control mechanism for varying a phase of one of an intake valve and an exhaust valve.
- 3. A hydraulic control system according to claim 2, adapted so that the pressure oil discharged from the phase control mechanism when the phase of the intake valve is advanced by the phase control mechanism is supplied through the circulation line to the second hydraulic operating mechanism.
- 4. A hydraulic control system according to claim 1, wherein the second hydraulic operating mechanism is a valve stop mechanism for temporarily stopping intake and exhaust valves of some of cylinders when supplied with pressure oil.
- 5. A hydraulic control system according to claim 1, further comprising a check valve disposed in the circulation line adapted to prevent reverse flow of pressure oil from the second hydraulic operating mechanism to the first hydraulic operating mechanism.
- 6. A hydraulic control system according to claim 5, further comprising a drain line branching off from the circulation line at a location upstream of the check valve and a control valve disposed in the drain line, a valve opening load of the control valve being set at a value higher than that of the check valve.
- 7. A hydraulic control system according to claim 6, wherein the control valve is a check valve.
- 8. A hydraulic control system according to claim 5, further comprising a drain line branching off from the circulation line at a location upstream of the check valve and a flow restriction disposed in the drain line.
- 9. A hydraulic control system for an internal combustion engine comprising:an oil pressure source; an oil sump; a first hydraulic operating mechanism; a second hydraulic operating mechanism; a first hydraulic control valve adapted to selectively communicate the first hydraulic operating mechanism with one of the oil pressure source and the oil sump thereby controlling an operation of the first hydraulic operating mechanism; a second hydraulic control valve adapted to selectively communicate the second hydraulic operating mechanism with one of the oil pressure source and the oil sump thereby controlling an operation of the second hydraulic operating mechanism; a control line fluidly connecting between the second hydraulic control valve and the second hydraulic operating mechanism adapted to conduct pressure oil supplied to and discharged from the second hydraulic operating mechanism; and a circulation line connecting between the first hydraulic control valve and the control line adapted to supply pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism; wherein the first hydraulic operating mechanism is a phase control valve adapted to vary a phase of one of an intake valve and an exhaust valve, and the second hydraulic operating mechanism is a valve stop mechanism adapted to temporarily stop intake and exhaust valves of some of cylinders.
- 10. A hydraulic control system according to claim 9, further comprising a check valve disposed in the circulation line adapted to prevent reverse flow of pressure oil from the second hydraulic operating mechanism to the first hydraulic operating mechanism.
- 11. A hydraulic control system according to claim 10, further comprising a drain line branching off from the circulation line at a location upstream of the check valve and a check valve disposed in the drain line, a valve opening load of the check valve disposed in the drain line being set at a value higher than that of the check valve disposed in the circulation line.
- 12. A hydraulic control system according to claim 10, further comprising a drain line branching off from the circulation line at a location upstream of the check valve and a flow restriction disposed in the drain line.
- 13. A hydraulic control system according to claim 9, wherein the oil pressure source comprises an oil pump driven by the engine.
- 14. A hydraulic control system for an internal combustion engine comprising:a phase control mechanism for varying a phase of an intake valve; a valve stop mechanism for temporarily stopping intake and exhaust valves of some of cylinders; the phase control mechanism and the valve stop mechanism being operated independently by oil pressure of a common oil pressure source; and means for supplying pressure oil discharged from the phase control mechanism to the valve stop mechanism in addition to pressure oil supplied from the oil pressure source to the valve stop mechanism when the phase of the intake valve is advanced by the phase control mechanism and the intake and exhaust valves of some of the cylinders are stopped by the valve stop mechanism.
- 15. A hydraulic control system according to claim 14, wherein the means comprises a circulation line that fluidly connects between the phase control mechanism and the valve stop mechanism.
- 16. A hydraulic control system according to claim 15, further comprising a check valve disposed in the circulation line adapted to prevent reverse flow of pressure oil from the valve stop mechanism to the phase control valve.
- 17. A hydraulic control system according to claim 16, further comprising a drain line branching off from the circulation line at a location upstream of the check valve and a check valve disposed in the drain line, a valve opening load of the check valve disposed in the drain line being set at a value higher than that of the check valve disposed in the circulation line.
- 18. A hydraulic control system according to claim 16, further comprising a drain line branching off from the circulation line at a location upstream of the check valve and a flow restriction disposed in the drain line.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2001-012577 |
Jan 2001 |
JP |
|
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Number |
Name |
Date |
Kind |
3303753 |
McCay, Jr. |
Feb 1967 |
A |
4622886 |
Imada et al. |
Nov 1986 |
A |
4977928 |
Smith et al. |
Dec 1990 |
A |
5335499 |
Thompson et al. |
Aug 1994 |
A |
5460129 |
Miller et al. |
Oct 1995 |
A |
Foreign Referenced Citations (4)
Number |
Date |
Country |
5-248217 |
Sep 1993 |
JP |
2000-73797 |
Mar 2000 |
JP |
2000-145487 |
May 2000 |
JP |
2000-234533 |
Aug 2000 |
JP |