U.S. patent application number 10/788431 was filed with the patent office on 2004-10-21 for engine valve actuator.
Invention is credited to Leman, Scott A..
Application Number | 20040206331 10/788431 |
Document ID | / |
Family ID | 27658792 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040206331 |
Kind Code |
A1 |
Leman, Scott A. |
October 21, 2004 |
Engine valve actuator
Abstract
An engine with a lockable valve actuator and method of
controlling an engine with such an actuator are disclosed. The
actuator may include an actuator cylinder with an actuator piston
reciprocatingly disposed therein. The actuator piston may be moved
by directing pressurized fluid into the actuator cylinder, and
locked into a given position by maintaining the pressurized fluid
in the actuator cylinder. The actuator may be used in conjunction
with a mechanically driven actuator used to move a valve, with the
fluidically driven actuator being used to maintain the valve into a
desired position.
Inventors: |
Leman, Scott A.; (Eureka,
IL) |
Correspondence
Address: |
MARSHALL, GERSTEIN & BORUN LLP
6300 SEARS TOWER
233 S. WACKER DRIVE
CHICAGO
IL
60606
US
|
Family ID: |
27658792 |
Appl. No.: |
10/788431 |
Filed: |
February 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10788431 |
Feb 27, 2004 |
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10067030 |
Feb 4, 2002 |
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6732685 |
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Current U.S.
Class: |
123/321 ;
123/90.16 |
Current CPC
Class: |
F01L 2800/10 20130101;
F01L 9/10 20210101; Y02T 10/12 20130101; F01L 2800/00 20130101;
F02B 2275/32 20130101; F01L 2305/00 20200501; F01L 13/065
20130101 |
Class at
Publication: |
123/321 ;
123/090.16 |
International
Class: |
F02D 013/04; F01L
001/34 |
Claims
What is claimed is:
1. An engine valve assembly, comprising: a valve seat; an engine
valve element adapted to move relative to the valve seat between an
open position and a closed position; a mechanically driven actuator
being adapted to move the valve element to the open position; a
fluidically driven actuator being adapted to prevent the valve
element from moving to the closed position, the fluidically driven
actuator including an actuator piston reciprocatingly disposed in
an actuator cylinder, the actuator piston adapted to maintain the
engine valve element in an intermediate position between the closed
position and the open position, the actuator cylinder being in
fluid communication with a source of pressurized fluid, the source
of pressurized being insufficient to move the valve element toward
the open position in an internal combustion engine; and a control
valve adapted to pass the flow of the pressurized fluid to the
actuator cylinder during movement of the valve element toward the
open position, and maintain the fluid in the actuator cylinder
during movement of the valve element toward the closed position to
maintain the valve at the intermediate position.
2. The engine valve assembly of claim 1, including a spring
connected to the engine valve element and biasing the engine valve
element toward the closed position.
3. An engine valve assembly, comprising: an engine valve element
disposed in a port connected to an engine cylinder; a fluidically
driven valve actuator; a source of low pressure fluid in fluid
communication with the valve actuator, a force generated by the
source of low pressure fluid being sufficient to move the valve
element and take up lash associated with the valve element and the
valve actuator; an engine driven mechanical linkage mounted
proximate the engine valve element and adapted to move the engine
valve element to an open position; and a control valve adapted to
control flow of the pressurized fluid from the source of low
pressure fluid to the valve actuator.
4. The engine valve assembly of claim 3, wherein the valve actuator
includes an actuator cylinder and an actuator plunger
reciprocatingly disposed in the actuator cylinder.
5. The engine valve assembly of claim 3, wherein the valve actuator
includes an actuator piston reciprocatingly disposed in an actuator
cylinder, the actuator piston having a rod operatively associated
therewith and being adapted to maintain the engine valve element in
an intermediate position between a closed position and the open
position.
6. The valve assembly of claim 3, including a coil spring mounted
about the valve element to bias the valve element toward a closed
position.
7. The valve assembly of claim 3, wherein the source of low
pressure fluid is a lubrication oil system of the engine.
8. The valve assembly of claim 3, wherein the mechanical linkage is
actuated by a cam shaft.
9. A variable valve actuator system, comprising: a valve positioned
adjacent an engine cylinder; an engine driven mechanical actuator
system adapted to move the valve between first and second
positions; a fluid pressurization source; a fluidically driven
valve actuator in predetermined intermittent fluid communication
with the fluid pressurization source, the fluidically driven
actuator adapted to prevent the valve from moving to the second
position for a predetermined period of time; a control valve
adapted to shut off fluid communication between the fluid
pressurization source and the fluidically driven valve actuator and
to prevent fluid from back flowing out of the fluidically driven
actuator causing the fluidically driven actuator to become
hydraulically locked.
10. The variable valve actuator system of claim 9, wherein the
source of pressurized fluid is a lubrication oil system for an
engine.
11. The variable valve actuator system of claim 9, wherein the
mechanical actuation system includes a cam shaft to move the valve
from the first position to the second position; and a compression
spring to move the valve from the second position to the first
position when the fluidically driven actuator is not hydraulically
locked.
12. A method of controlling an engine having at least one valve,
comprising: moving the valve from a first position to a second
position with a mechanically driven actuator; moving the valve from
the second position to an intermediate position between the first
and second positions; and holding the valve in the intermediate
position with a fluidically driven actuator in a hydraulically
locked configuration.
13. The method of claim 12, wherein holding the valve in the
intermediate position comprises: transporting pressurized fluid
from a fluid pressurization source to the fluidically driven
actuator; removing fluid communication between the fluid source and
the fluidically driven actuator; and hydraulically locking the
fluid in the fluidically driven actuator by preventing fluid
backflow from the fluidically driven actuator.
14. The method of claim 13, wherein preventing backflow is
performed by a control valve.
15. The method of claim 12, including holding an intake valve in
the intermediate position with the hydraulically locked
actuator.
16. The method of claim 12, including holding an exhaust valve in
the intermediate position with the hydraulically locked
actuator.
17. The method of claim 12, wherein moving the valve from the first
position to the second position includes using a mechanical
linkage.
18. The method of claim 12, wherein moving the valve from the first
position to the second position includes the step of using a
mechanical linkage having a cam.
19. The method of claim 12, wherein holding the valve in the
intermediate position includes using a hydraulically locked
actuator having an actuator cylinder and an actuator piston
reciprocatingly disposed in the actuator cylinder, and wherein
holding the valve in the open position includes directing fluid to
the actuator cylinder, and preventing backflow of the fluid out of
the actuator cylinder.
20. The method of claim 12, wherein the pressurized fluid is
lubrication oil of the engine.
Description
CROSS-REFERENCE
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/067,030, which was filed on Feb. 4,
2002.
TECHNICAL FIELD
[0002] This disclosure relates generally to internal combustion
engines and, more particularly, to engine valve actuators.
BACKGROUND
[0003] The operation of an internal combustion engine requires,
among other things, the timed opening and closing of a plurality of
valves. For example, with a typical four-stroke, diesel engine, one
of ordinary skill in the art will readily recognize such an engine
operates through four distinct strokes of a piston reciprocating
through a cylinder, with intake and exhaust valves operating in
conjunction with the piston. In an intake stroke, the piston
descends through the cylinder while an intake valve is open. The
resulting vacuum draws air into the cylinder. In a subsequent
compression stroke, the piston reverses direction while the intake
valve and an exhaust valve are closed, thereby compressing the air
within the cylinder. This is followed by a combustion or power
stroke wherein fuel is injected into the compressed air and thereby
ignited, with the resulting force pushing the piston again in the
descending direction while both the intake and exhaust valves are
closed. Finally, the piston reverses direction with the exhaust
valve open, thereby pushing the combustion gases out of the
cylinder.
[0004] In certain variations on the typical diesel or Otto cycle,
it is desirable to open or close one of the intake and/or exhaust
valves at alternative times. For example, in a compression release
braking mode, the exhaust valve is opened as the piston approaches
a top dead center position during the compression stroke to, in
effect, increase engine braking operation. In so doing the engine
cylinders draw in air during the intake stroke, compress the air,
and then vent the compressed air out of the exhaust valve near top
dead center of the piston.
[0005] Another mode of engine operation requiring atypical valve
sequencing is known as the Miller cycle. During the Miller cycle,
the intake valve is held open during the initial stages of the
compression stroke. Such operation reduces the effective
compression ratio of the engine and results in a more mechanically
efficient power producing engine. Alternatively, the intake valve
is closed prior to completion of a normal intake stroke to provide
Miller cycle benefits.
[0006] One other situation modifying typical valve operation is
internal exhaust gas recirculation. One disadvantage of diesel or
Otto cycle engine operation is that all of the fuel brought into
the cylinder and compressed may not entirely combust. Among other
things, this phenomenon may be undesirable due to an unacceptably
high level of pollutants, such as nitrous oxide (NOx) and
particulates, being released during the exhaust stroke.
[0007] Exhaust gas recirculation (hereinafter referred to as "EGR")
attempts to curtail such drawbacks of conventional engine
operation. With EGR, at least a portion of the exhaust gases is not
exhausted to the atmosphere, but rather is introduced back into the
engine cylinder to be combusted in subsequent power or combustion
strokes of the engine. With typical internal EGR, the exhaust gases
are expelled through the exhaust valve and reintroduced to the
cylinder through the exhaust valve itself. Such a process requires
that the exhaust valve stay open not only through the exhaust
stroke, but also on the intake stroke, after the piston reverses
direction, thereby creating a vacuum and drawing a portion of the
exhaust gases back into the cylinder through the still open exhaust
valve.
[0008] One of ordinary skill in the art will readily appreciate
that a substantial force is required to open the exhaust valve and
maintain the valve in an open position as the piston reciprocates
through the cylinder toward the top dead center position. A valve
actuator employing highly pressurized oil may be used to apply this
force to open the exhaust valve.
[0009] However, holding an exhaust valve in an open position by a
valve actuator employing highly pressurized oil requires, for
example, pressurized oil on the order of fifteen hundred to five
thousand pounds per square inch (10.34 to 34.4 MPa). The engine or
machine in which the engine has been mounted therefore has had to
provide a high pressure source or high pressure rail and be able to
supply the high pressure oil to the actuator when desired. Such a
requirement has, among other things, the disadvantage, at least
with respect to Miller cycle and EGR operation, of decreasing the
engine efficiency in that the engine must continually direct usable
work to the high pressure rail to maintain such pressures even
though the high pressure oil is only required for a relatively
short duration during the engine operation. Not only is the
provision of such pressurized fluid taxing on the efficiency of the
engine, but with certain machines the provision of such a high
pressure rail is simply not available or desirable.
[0010] The present disclosure is directed to overcoming one or more
of the problems or disadvantages associated with the prior art.
SUMMARY
[0011] In accordance with one aspect of the disclosure, an engine
valve assembly includes a valve seat and an engine valve element
adapted to move relative to the valve seat between an open position
and a closed position. A mechanically driven actuator can be
adapted to move the valve element to the open position. A
fluidically driven actuator can be adapted to prevent the valve
element from moving to the closed position. The fluidically driven
actuator can include an actuator piston reciprocatingly disposed in
an actuator cylinder. The actuator piston can be adapted to
maintain the engine valve element in an intermediate position
between the closed position and the open position. The actuator
cylinder is in fluid communication with a source of pressurized
fluid. The source of pressurized is insufficient to move the valve
element toward the open position in an internal combustion engine.
A control valve can be adapted to pass the flow of the pressurized
fluid to the actuator cylinder during movement of the valve element
toward the open position. The valve is operable for maintaining the
fluid in the actuator cylinder during movement of the valve element
toward the closed position to maintain the valve at the
intermediate position.
[0012] In accordance with another aspect of the disclosure, a valve
assembly includes an engine cylinder and an engine piston
reciprocatingly movable relative to the engine cylinder. An engine
valve element is disposed in a port that is connected to the engine
cylinder. A source of low pressure fluid is in fluid communication
with a fluidically driven valve actuator. A force generated by the
source of low pressure fluid is sufficient to move the valve
element and take up lash associated with the valve element and the
valve actuator. An engine driven mechanical linkage mounted
proximate the engine valve element is adapted to move the engine
valve element to an open position. A control valve is adapted to
control flow of the pressurized fluid from the source of low
pressure fluid to the valve actuator.
[0013] In accordance with another aspect of the disclosure, a
variable valve actuator includes a valve positioned adjacent an
engine cylinder and an engine driven mechanical actuator system
adapted to move the valve between first and second positions. A
fluidically driven valve actuator in predetermined intermittent
fluid communication with a fluid pressurization source is provided.
The fluidically driven actuator is adapted to prevent the valve
from moving to the second position for a predetermined period of
time. A control valve is adapted to shut off fluid communication
between the fluid pressurization source and the fluidically driven
valve actuator and to prevent fluid from back flowing out of the
fluidically driven actuator causing the fluidically driven actuator
to become hydraulically locked.
[0014] In accordance with yet another aspect of the disclosure, a
method of controlling an engine having at least one valve includes
moving the valve from a first position to a second position with a
mechanically driven actuator, moving the valve from the second
position to an intermediate position between the first and second
positions, and holding the valve in the intermediate position with
a fluidically driven actuator in a hydraulically locked
configuration.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagrammatic cross-sectional view of an
embodiment of an internal combustion engine showing an engine
block, cylinder head and engine valve actuator;
[0016] FIG. 2 is cross-sectional view of the engine of FIG. 1,
taken along line 2-2 of FIG. 1;
[0017] FIG. 3 is a schematic representation of an engine valve
actuator shown in a first position;
[0018] FIG. 4 is a schematic representation of an engine valve
actuator shown in a second position;
[0019] FIG. 5 is a schematic representation of an engine valve
actuator shown in a third position;
[0020] FIG. 6 is a flow chart depicting a sample sequence of steps
which may be taken to operate an internal combustion engine valve
actuator;
[0021] FIG. 7 is a graph plotting valve lift vs. engine crank angle
during normal operation;
[0022] FIG. 8 is a graph plotting valve lift vs. engine crank angle
during internal exhaust gas recirculation operation;
[0023] FIG. 9 is a graph plotting valve lift vs. engine crank angle
during Miller cycle operation; and
[0024] FIG. 10 is a schematic representation of an alternative
engine valve actuator configuration.
DETAILED DESCRIPTION
[0025] Referring now to the drawings, and with specific reference
to FIG. 1, an embodiment of an internal combustion engine is
generally referred to by reference numeral 20. While the engine 20
is depicted and will be described in further detail herein with
reference to a four stroke, internal combustion diesel engine, it
is to be understood that the teachings of the disclosure can be,
employed in conjunction with any other type of engine as well.
[0026] The engine 20 may include a plurality of engine cylinders 22
in each of which is reciprocatingly mounted an engine piston 24. In
the depicted embodiment, six such engine cylinders 22 and six
engine pistons 24 are depicted in aligned fashion, but it is to be
understood that a greater or lesser number are possible, and that
engine cylinder orientations other than in-line, such as, for
example, a "V" configuration, are possible as well. A connecting
rod 26 may be connected to each engine piston 24, and in turn be
connected to a crank shaft 27 so as to capitalize on the motion of
the engine piston 24 to produce useful work in a machine (not
shown) with which the engine 20 is associated. Each engine cylinder
24 may be provided within an engine block 28 having a cylinder head
30, and may further include at least one intake valve 32, and an
exhaust valve 34.
[0027] Referring now to FIGS. 2-5, the cylinder head 30, and a pair
of exhaust valves 34 are shown in greater detail for one of the
engine cylinders 22. As shown therein, a pair of exhaust ports 38
may be provided in the cylinder head 30 to allow for fluid
communication into and out of the engine cylinder 22. In addition,
while FIG. 1 depicts only one intake port 36 per cylinder 22, it is
to be understood that a pair of intake ports 36 are typically
provided in each cylinder 22 in a manner similar to the exhaust
ports 38 depicted in FIG. 2. In normal engine operation, air may be
allowed to enter the engine cylinder 22 through the intake ports
36, while combustion or exhaust gases may be allowed to exit the
engine cylinder 22 through the exhaust ports 38. An intake valve
element 40 may be provided within each intake port 36, while an
exhaust valve element 42 may be provided within each exhaust port
38.
[0028] Each of the valve elements 40, 42 may include a valve head
44 from which a valve stem 46 extends. The valve head 44 includes a
sealing surface 48 adapted to seal against a valve seat 50 about a
perimeter 52 of the valve ports 36, 38. The valve elements 40, 42
further include a bridge 54 adapted to contact the valve stems 46
associated with each engine cylinder 22. A valve spring 56 imparts
force between the top of each valve stem 46 and the cylinder head
30, thereby biasing the stem 46 away from the cylinder head 30 and
thus biasing the valve head 44 into seating engagement with the
corresponding valve seats 50 to close the intake and exhaust valves
32, 34.
[0029] As shown best in FIG. 2, movement of the valve elements 40,
42 is controlled not only by the springs 56, but by a cam assembly
58 as well. As one of ordinary skill in the art will readily
recognize, rotation of the cam 60 periodically causes a push rod 62
to rise, thereby causing a rocker arm 64, connected thereto, to
pivot about a pivot 66. In so doing, an end 68 of the rocker arm 64
is caused to move downwardly and thereby open the exhaust valve
element 42. Under normal engine operation, the cam 60 imparts
sufficient force to the valve stem 46 to overcome the biasing force
of the spring 56 and thereby push the valve head 44 away from the
valve seat 50, to open the exhaust valves 34 (or intake valve 32).
Further rotation of the cam 60 allows the spring 56 to push the end
68 of the rocker arm 64 upward and the push rod 62 downward until
the cam 60 completes another revolution.
[0030] In certain modes of engine operation, such as with the
compression release braking, Miller cycle operation, and EGR
referenced above, it is desirable for the intake and/or exhaust
valves 32, 34 to be held open for longer periods, or at a timing
sequence other than that dictated by the cam 60. In such
situations, a valve actuator 70 may be used to so hold the intake
valve 32 and/or exhaust valve 34 open. As shown in FIGS. 3-5, one
example of the valve actuator 70 includes an actuator cylinder 72
in which an actuator piston 74 is reciprocatingly disposed. The
actuator cylinder 72 may include an opening 79, through which an
actuator rod 78 may extend in the direction of the rocker arm 64
and the valve stem 46 as well.
[0031] The actuator cylinder 72 may also include a port 80
providing access to an actuation chamber 82. The port 80 is adapted
to place the actuation chamber 82 into fluid communication with a
low pressure fluid source 84. In one embodiment, the pressurized
fluid may be lubrication oil of the engine 20 (typically at a
pressure level less than one hundred pounds per square inch, for
example, on the order of sixty to ninety pounds per square inch
(413.7 KPa to 620.5 KPa)). Placement of the fluid source 84 into
fluid communication with the actuation chamber 82 may be provided
through a fluid passage 85 and be controlled by a control valve 88.
The control valve 88 may include an inlet 92 and an outlet 94. The
control valve 88 may be biased into a first position connecting the
port 80 to the low pressure fluid source 84 and be actuated by a
solenoid 95 to a second position disconnecting the port 80 from the
low pressure fluid source 84. The solenoid 95 may itself be
actuated upon receipt of a control signal or the like from a main
control or processor 96 (FIG. 1) of the engine 20. The fluid source
84 may be in fluid communication with an oil drain, sump, or
accumulator 97, for example, via a check valve.
[0032] The low pressure fluid source 84, when the control valve 88
is in the first position (FIG. 4), is able to fill the actuator
chamber 82 sufficiently to move the actuator piston 74 so as to
take up any lash 98 (FIG. 3) existing in the system, such as that
between the actuator rod 78 and the valve stem 46 or between the
actuator rod 78 and the rocker arm 64. "Taking up any lash in the
system" is defined herein to mean removing any space between
movable components. In so doing, when it is desired to hold the
exhaust valve 34 in an open position, the control valve 88 can be
moved to the second position (FIG. 5) thereby disconnecting the
inlet 92 and hydraulically locking the actuator 70. Pressure within
the engine cylinder 22 imparts force on the exhaust valve 34, and
in turn the actuator rod 78, but the fluid within the actuator
cylinder 72, being incompressible and locked, holds the actuator
piston 74, and thus the exhaust valve 34 (or intake valve 32), in
the open position.
Industrial Applicability
[0033] In operation, the engine 20 can be used in a variety of
applications. For example, the engine 20 may be provided on board a
prime-mover, vehicle or the like, or any type of machine requiring
the provision of mechanical or electrical energy. Such machines may
include, but are not limited to, earth moving machines, backhoes,
graders, rock crushers, pavers, skid-steer loaders, cranes, trucks,
and the like.
[0034] Referring now to FIG. 6, in conjunction with FIGS. 2-5, the
engine 20 can be operated so as to open an engine valve and hold an
engine valve open in the following manner. By way of background,
one of ordinary skill in the art will understand that a typical
four-stoke, diesel cycle, internal combustion engine operates
through four distinct strokes of the piston 24 through the cylinder
22.
[0035] In a first or intake stroke, the engine piston 24 descends
through the engine cylinder 22 away from the cylinder head 30 while
the intake valve 32 is opened by the cam assembly 58, as indicated
in steps 99 and 100, respectively. FIG. 7 depicts the intake valve
32 and exhaust valve 34 lift of a typical diesel cycle engine
wherein engine operation is plotted as seven hundred and twenty
degrees of engine crank angle, and with each of the four strokes
representing 180.degree. of rotation of the crank shaft 27. In so
doing, air is drawn into the engine cylinder 22, as indicated in a
step 102.
[0036] In a second or compression stroke, the engine piston 24
reverses its motion, at the direction of the rod 26, while the
intake valve 32 and exhaust valve 34 are closed with springs 56.
Such steps are indicated by reference numerals 104 and 106,
respectively in FIG. 6. As the engine piston 24 ascends through the
engine cylinder 22 toward the cylinder head 30, air is compressed
(as indicated by a step 110).
[0037] In a third or combustion stroke, fuel is injected directly
into the compressed air and thereby is ignited, as indicated by a
step 112. The resulting explosion and expanding gases push the
engine piston 24 again in a descending direction (as indicated by a
step 113) through the engine cylinder 22, while the intake and
exhaust valves 32, 34 remain closed.
[0038] In a fourth or exhaust stroke, the engine piston 24 again
reverses and ascends through the engine cylinder 22, but with the
exhaust valve 34 open by the cam assembly 58, thereby pushing the
combustion gases out of the engine cylinder 22. Such steps are
indicated in FIG. 6 as steps 114 and 116, respectively.
[0039] With certain engine operation variations, such as
compression release braking, Miller cycle operation, and EGR, it
may be desirable to alter the above valve timing and hold one or
more valves open against substantial cylinder pressures. The
teachings of the present disclosure enable such operation, without
resort to highly pressurized oil rails, thereby preserving engine
efficiency and simplicity. Taking internal EGR as an example, it is
necessary in such operation for the exhaust valve 34 (or intake
valve 32) to remain open throughout not only the exhaust stroke,
but during an interim period between when the exhaust valve 34 is
normally closed and when the intake valve 32 opens to conduct the
intake stroke. FIG. 8 depicts such altered valve timing in
graphical form.
[0040] This can be accomplished by allowing the cam assembly 58 to
open the exhaust valve 34 according to a normal exhaust stroke as
indicated above (step 116), and then using the actuator 70 to
maintain the exhaust valve 34 in an open position. More
specifically, as the cam assembly 58 moves to open the exhaust
valve 34, the rocker arm 64 pivots downwardly compressing the
spring 56. With the spring pressure overcome by the cam assembly
58, the pressurized fluid flowing from the low pressure source 84
and filling the actuation chamber 82 is able to move the piston 74.
The piston 74 moves through the lash 98 until the actuator rod 78
engages the rocker arm 64. This step is indicated by reference
numeral 118 in FIG. 6.
[0041] In order to hold the exhaust valve 34 in such a position
even after the cam 60 rotates to another position, the control
valve 88 is switched from the first position (shown in FIG. 4) to
the second position (shown in FIG. 5), as indicated by a step 120.
In so doing, the fluid is locked from escaping the actuation
chamber 82 and, due to its incompressibility, prevents the actuator
piston 74 from moving and, thus, prevents the exhaust valve 34 from
closing. As used herein, a "hydraulically locked" device is defined
as a device having substantially no fluid flow and substantially no
fluid leakage, and "backflow" is defined as fluid flow from the
actuator 70 to the low pressure fluid source 84.
[0042] In addition to the above example, the actuator 70 may be
hydraulically locked using any number of other devices including,
but not limited to, check valves. For example, as shown in FIG. 10,
a check valve 121 can be provided between the actuator 70 and the
low pressure source 84. The check valve allows the fluid from
source 84 to enter the actuator cylinder 72 and move the actuator
piston 74, but not flow back to the source 84. In conjunction with
such structure, a normally closed control valve 122 may be provided
also in communication with the low pressure source 84 (or drain 97
or atmosphere). Upon actuation of solenoid 123 of the control valve
122, the fluid pressure with the actuator cylinder 72 is able to
flow to the low pressure source 84 or drain 97. In so doing, the
actuator piston 74 is able to move up, closing the valve 32,
34.
[0043] Continuing with the example of EGR, the exhaust valve 34 is
held open as the engine piston 24 ascends to a top dead center
position, and remains open after the engine piston 24 reverses and
descends while the intake valve 32 is opened, as indicated by steps
124 and 126, respectively. A portion of the exhaust gases vented
from the engine cylinder 22 through the exhaust valve 34 are
thereby reintroduced to the engine cylinder 22 by the resulting
pressure differential. This step is indicated by reference numeral
128. After a predetermined stroke length (e.g., ninety degrees of a
seven hundred and twenty degree four stroke cycle as shown in FIG.
8), the exhaust valve 34 is closed as indicated by a step 130,
while the intake valve 32 remains open to complete the intake
stroke as explained above. The exhaust valve 34 can be closed by
switching the control valve 88 back to the first position (shown in
FIG. 4) and thereby enabling the spring 56 to push the actuator
piston 74 up, and the pressurized fluid out of, the actuator
cylinder 72. Normal engine operation may then resume, beginning
with the compression stroke as indicated in FIG. 6.
[0044] The teachings of the present disclosure can also be used to
provide Miller cycle benefits. As illustrated in FIG. 9, the intake
valve 32 (or exhaust valve 34) may be held open during the initial
stages of the compression stroke to thereby reduce the compression
ratio of the engine and provide the engine efficiencies of the
Miller cycle as well known by those of ordinary skill in the art.
The intake valve 32 could be so held by employing the actuator 70
after the cam assembly 58 opens the intake valve during the intake
stroke. More specifically, as the intake valve 32 is about to be
closed by the spring 56 at the conclusion of a normal intake
stroke, the control valve 88 could be actuated so as to prevent
fluid flow from the actuator 72 back to the low pressure fluid
source 84. In so doing, the actuator piston 74 is locked in
position, as is the intake valve 32 as depicted in FIG. 9.
[0045] One of ordinary skill in the art will understand that
significant force is required to open the intake and exhaust valves
32, 34, and hold the valves open, during the compression and
exhaust strokes, due to the ascending piston and pressurized gases
being pushed out of the engine cylinder 22 and thus against the
valves 32, 34. The actuator 70, and its ability to become
hydraulically locked, is able to hold the valves 32, 34 open under
such conditions, without resort to high pressure rails and the
drops in engine efficiency incumbent with such conventional
systems.
[0046] Other aspects and features of the present disclosure can be
obtained from a study of the drawings, the disclosure, and the
appended claims.
* * * * *