U.S. patent number RE40,439 [Application Number 11/583,382] was granted by the patent office on 2008-07-22 for method to control electromechanical valves.
This patent grant is currently assigned to Ford Global Technologies, LLC. Invention is credited to Diana D. Brehob, Eric Warren Curtis, William Francis Stockhausen.
United States Patent |
RE40,439 |
Brehob , et al. |
July 22, 2008 |
Method to control electromechanical valves
Abstract
A system for controlling electromechanical of an internal
combustion has a valve-closing electromagnet for attracting the
armature coupled to the valve to close the valve, a valve-opening
electromagnet for attracting the armature to open the valve, a
valve-opening spring for biasing the valve open, and a
valve-closing spring for biasing the valve closed. The method
includes de-energizing the valve-closing electromagnet for a
predetermined time, enabling the valve to oscillate by the valve
springs, and then energizing the valve-closing electromagnet to
close the valve. Consequently, only the valve-closing electromagnet
is energized to open and close the valve. The valve biasing springs
force the valve to a location at which the valve-closing
electromagnet can close the valve. This provides an electrical
energy over prior methods in which both the valve-opening and
valve-closing electromagnets are energized to actuate the
valve.
Inventors: |
Brehob; Diana D. (Dearborn,
MI), Curtis; Eric Warren (Milan, MI), Stockhausen;
William Francis (Northville, MI) |
Assignee: |
Ford Global Technologies, LLC
(Dearborn, MI)
|
Family
ID: |
33132108 |
Appl.
No.: |
11/583,382 |
Filed: |
October 18, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
09682959 |
Nov 2, 2001 |
06805079 |
Oct 19, 2004 |
|
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Current U.S.
Class: |
123/90.11;
251/129.07; 123/90.24; 123/90.15 |
Current CPC
Class: |
F01L
9/20 (20210101); F02B 1/12 (20130101); F01L
2009/2169 (20210101); F01L 2009/2136 (20210101) |
Current International
Class: |
F01L
9/04 (20060101) |
Field of
Search: |
;123/90.11 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Denion; Thomas
Assistant Examiner: Riddle; Kyle M.
Attorney, Agent or Firm: Brehob; Diana Alleman Halt McCoy
Russell & Tuttle LLP
Claims
What is claimed is:
1. A method for actuating .[.a.]. .Iadd.an intake .Iaddend.valve
disposed in a cylinder head of an internal combustion engine by an
electromechanical valve system having an armature operatively
connected to the valve, a valve closing electromagnet capable of
exhibiting an electromagnetic force for attracting the armature to
close the valve, a valve opening spring for biasing the armature in
a direction to open the valve, and a valve closing spring for
biasing the armature in a direction to close the valve, comprising
the steps of: de-energizing the valve closing electromagnet when
said valve is in a substantially fully closed position; maintaining
the valve closing electromagnet in said de-energized state for a
predetermined time enabling the valve to oscillate by force of the
valve opening spring and the valve closing spring .Iadd.while
inducting air past the valve as it oscillates.Iaddend.; and
energizing the valve closing electromagnet after said predetermined
time to close the valve.
2. The method of claim 1, said predetermined time is based on
oscillation characteristics of the valve when the valve closing
electromagnet is de-energized.
3. The method of claim 1 wherein said valve is one of an intake
valve and an exhaust valve.
4. The method of claim 1, wherein said predetermined time is
approximately a valve period, said valve period is the time elapsed
between de-energizing the valve closing electromagnet until the
valve returns to a nearly closed position for a first time.
5. The method of claim 4, wherein said valve period is based on the
spring constant of the valve opening spring, the spring constant of
the valve closing spring, a mass of the valve, and a mass of the
armature, and damping coefficients of the valve opening spring, the
armature, and the valve.
6. The method of claim 1, wherein said predetermined time is
substantially an integral number of valve periods, said valve
period is the time elapsed between de-energizing the valve closing
electromagnet until the valve returns to a nearly closed
position.
7. The method of claim 6, wherein said integral number is less than
a predetermined number.
8. The method of claim .[.6.]. .Iadd.7.Iaddend., wherein said
predetermined number is the number of a first occurring oscillation
of the armature at which a trajectory of the armature fails to
attain a predetermined distance away from said fully closed
position, said predetermined distance is a maximum distance that
the armature may be away from the valve closing electromagnet while
being capable of being attracted by the valve closing
electromagnet.
9. The method of claim 1, wherein said predetermined time is a time
when the valve is closer to a fully closed position of the valve
than a distance at which the valve closing electromagnet is capable
of attracting the armature and causing the valve to close.
10. An electromagnetic valve apparatus for actuating a valve
disposed in a cylinder head of an internal combustion engine, the
engine having at least one cylinder, comprising: an armature
operatively connected to the valve; a valve closing electromagnet
capable of exhibiting an electromagnetic force for attracting said
armature to close the valve; .Iadd.a valve opening electromagnet
capable of exhibiting an electromagnetic force for attracting said
armature to open the valve;.Iaddend. a valve opening spring coupled
to said armature for biasing said armature in a direction to open
the valve; a valve closing spring coupled to said valve for biasing
the valve to a closed position; and an electronic control unit
operably connected to said valve closing electromagnet de-energizes
said valve closing electromagnet allowing the valve to oscillate by
force of said valve opening spring and said valve closing spring
and maintains said valve closing electromagnet in said de-energized
state at least until the valve travels to a nearly open position
and returns to a nearly closed position .Iadd.without energizing
the valve opening electromagnet.Iaddend..
11. The system of claim 10 further comprising a position sensor
coupled to said armature providing an indication of a position of
the valve with respect to the cylinder head, said position sensor
is connected to said electronic control unit.
12. The system of claim 11 wherein said electronic control unit
energizes said valve closing electromagnet to cause the valve to
close when said position sensor indicates that the valve is within
a predetermined distance from said cylinder head.
13. The system of claim 12 wherein said predetermined distance is a
maximum distance that said armature may be away from the valve
closing electromagnet while being capable of being attracted by the
valve closing electromagnet.
14. The system of claim 10 wherein said electronic control unit
energizes said valve closing electromagnet at a predetermined time
after said valve closing electromagnet is de-energized to cause the
valve to close.
15. The system of claim 14, said predetermined time is based on
dynamic characteristics of the valve and the electromagnetic valve
apparatus.
16. The system of claim 14 wherein the valve is an intake
valve.
17. The system of claim 16 wherein said predetermined time is
determined so as to provide a desired quantity of air to one
cylinder of the engine.
18. The system of claim 17 further comprising a piston disposed in
the cylinder which reciprocates within the cylinder, wherein a time
of performing said de-energizing step which enables oscillation of
the valve is based on the position of said piston in the
cylinder.
19. The system of claim 16, further comprising a throttle valve
disposed in the intake duct of the engine, wherein a time of
performing said de-energizing step which enables oscillation of the
valve and a position of said throttle valve are determined to
provide a desired quantity of air to one cylinder of the
engine.
20. The system of claim 10 wherein the valve is an exhaust
valve.
21. The system of claim 20 wherein the engine is a homogeneous
charge compression ignition engine and an opening time and a
closing time of the valve is based on a desired portion of exhaust
gases to retain in one cylinder.
22. A method for actuating an intake valve disposed in a cylinder
head of an internal combustion engine by an electromagnetic valve
apparatus having a valve closing electromagnet capable of
exhibiting an electromagnetic force for attracting the armature to
close the valve, the valve opening electromagnet capable of
exhibiting an electromagnetic force for attracting the armature to
open the valve, a valve opening spring for biasing the armature in
a direction to open the valve, a valve closing spring for biasing
the armature in a direction to close the valve, comprising the
steps of: actuating the valve according to a first mode when a
first set of engine operating conditions are detected, said first
mode further comprises the steps of de-energizing the valve closing
electromagnet; maintaining the valve closing electromagnet in said
de-energized state for a first predetermined time enabling the
valve to oscillate by force of the valve opening spring and the
valve closing spring; and energizing the valve closing
electromagnet after said first predetermined time to close the
valve; and actuating the valve according to a second mode when a
second set of engine operating conditions are detected, said second
mode further comprises the steps of de-energizing the valve closing
electromagnet to allow the valve to open, energizing the valve
opening electromagnet in response to said de-energizing step to
attract the armature to the valve opening electromagnet thereby
causing the valve to open; de-energizing the opening electromagnet
after a second predetermined time has elapsed since the valve
opening electromagnet has been energized; and energizing the valve
closing electromagnet in response to said de-energizing step of the
valve opening electromagnet to attract the armature to the valve
closing electromagnet thereby causing the valve to close.
23. The method of claim 22, wherein said first predetermined time
is based on oscillation characteristics of the valve when the valve
opening electromagnet is de-energized and the valve closing
electromagnet is de-energized.
24. The method of claim 22, wherein the valve is an intake valve,
said first set of engine operating conditions are those indicating
a lower flow rate of air through the valve, and said second set of
engine operating conditions are those indicating a higher flow rate
of air through the valve.
25. The method of claim 22, further comprising the step of
inducting air past the valve as it oscillates, when the valve is
operated according to said first mode.
26. The method of claim 22, said first set of operating conditions
is indicated by a lower engine speed and a lower engine torque.
27. A computer readable storage medium having stored data
representing instructions executable by a computer to open a valve
disposed in a cylinder of an internal combustion engine, the valve
is actuated by an electromechanical valve apparatus having an
armature operatively connected to the valve, a valve closing
electromagnet capable of exhibiting an electromagnetic force for
attracting said armature to close the valve, a valve opening spring
for biasing said armature in a direction to open the valve, and a
valve closing spring for biasing the valve closed, comprising:
instructions to de-energize the valve closing electromagnet; and
instructions to energize the valve closing electromagnet at a
predetermined time after said de-energizing instructions, wherein
said predetermined time is based on an integral number of valve
periods, said valve period is the time elapsed between
de-energizing the valve closing electromagnet until the valve
returns to a nearly closed position for a first time when the valve
closing electromagnet is maintained de-energized.
28. The computer readable storage medium of claim 27 wherein the
valve is an intake valve, further comprising: instructions to
determine a desired amount of air to induct into said cylinder; and
instructions to determine said integral number of valve periods to
cause said desired amount of air to be inducted into said
cylinder.
29. The computer readable storage medium of claim 28, further
comprising instructions to determine an initiation time to
de-energize the valve closing electromagnet to provide said desired
amount air to said cylinder, said initiation time is based on a
position of a piston disposed in the cylinder.
30. The computer readable storage medium of claim 27, further
comprising: instructions to determine a desired amount of air to
induct into the cylinder; instructions to determine a desired
amount of burned gases to trap in said cylinder; instructions to
determine said integral number of valve periods during which the
valve is allowed to oscillate and to determine an initiation time
to de-energize the valve closing electromagnet based on said
desired amount of air and said desired amount of burned gases, said
initiation time is based on a position of a piston disposed in the
cylinder.
31. The computer readable storage medium of claim 27, further
comprising: instructions to determine a desired amount of air to
induct into the cylinder; instructions to determine a desired
turbulence level of the gases trapped in the combustion chamber;
and instructions to determine said integral number of valve periods
during which the valve is allowed to oscillate and to determine an
initiation time to de-energize the valve closing electromagnet
based on said desired amount of air and said desired turbulence
level, said initiation time is based on a position of a piston
disposed in the cylinder.
32. The computer readable storage medium of claim 27 wherein said
integral number of valve periods is less than a predetermined
number of valve periods.
.Iadd.33. A method for actuating a valve disposed in a cylinder
head of an internal combustion engine by an electromechanical valve
system having an armature operatively connected to the valve, a
valve closing electromagnet capable of exhibiting an
electromagnetic force for attracting the armature to close the
valve, a valve opening spring for biasing the armature in a
direction to open the valve, and a valve closing spring for biasing
the armature in a direction to close the valve, comprising the
steps of: de-energizing the valve closing electromagnet when said
valve is in a substantially fully closed position; maintaining the
valve closing electromagnet in said de-energized state to open the
valve while the valve oscillates by force of the valve opening
spring and the valve closing spring, without energizing an
electromagnet to hold open the valve; and energizing the valve
closing electromagnet after said maintaining to close the
valve..Iaddend.
.Iadd.34. The method of claim 33 further comprising varying a
timing of said energizing to vary the closing timing of the
valve..Iaddend.
.Iadd.35. The method of claim 33, wherein a time that the valve
closing magnet is maintained in said de-energized state is based on
oscillation characteristics of the valve when the valve closing
electromagnet is de-energized..Iaddend.
.Iadd.36. The method of claim 33, wherein said valve is one of an
intake valve and an exhaust valve..Iaddend.
.Iadd.37. The method of claim 33, wherein a time that the valve
closing magnet is maintained in said de-energized state is
approximately a valve period and where said valve period is the
time elapsed between de-energizing the valve closing electromagnet
until the valve returns to a nearly closed position for a first
time..Iaddend.
.Iadd.38. The method of claim 37, wherein said valve period is
based at least on the spring constant of the valve opening spring,
the spring constant of the valve closing spring, a mass of the
valve, and a mass of the armature, and damping coefficients of the
valve opening spring, the armature, and the valve..Iaddend.
.Iadd.39. The method of claim 33, wherein a time that the valve
closing magnet is maintained in said de-energized state is
substantially an integral number of valve periods, and where said
valve period is the time elapsed between de-energizing the valve
closing electromagnet until the valve returns to a nearly closed
position..Iaddend.
.Iadd.40. The method of claim 39, wherein said integral number is
less than a predetermined number..Iaddend.
.Iadd.41. The method of claim 40, wherein said predetermined number
is the number of a first occurring oscillation of the armature at
which a trajectory of the armature fails to attain a predetermined
distance away from said fully closed position, said predetermined
distance is a maximum distance that the armature may be away from
the valve closing electromagnet while being capable of being
attracted by the valve closing electromagnet..Iaddend.
.Iadd.42. The method of claim 33, wherein a time that the valve
closing magnet is maintained in said de-energized state is a time
when the valve is closer to a fully closed position of the valve
than a distance at which the valve closing electromagnet is capable
of attracting the armature and causing the valve to
close..Iaddend.
.Iadd.43. The method of claim 33, wherein the electromechanical
valve system further comprises a valve opening electromagnet
capable of exhibiting an electromagnetic force for attracting the
armature to open the valve..Iaddend.
.Iadd.44. The method of claim 1, wherein the electromechanical
valve system further comprises a valve opening electromagnet
capable of exhibiting an electromagnetic force for attracting the
armature to open the valve..Iaddend.
.Iadd.45. A method for actuating an intake valve disposed in a
cylinder head of an internal combustion engine by an
electromagnetic valve apparatus having a valve closing
electromagnet capable of exhibiting an electromagnetic force for
attracting the armature to close the valve, a valve opening
electromagnet capable of exhibiting an electromagnetic force for
attracting the armature to open the valve, a valve opening spring
for biasing the armature in a direction to open the valve, a valve
closing spring for biasing the armature in a direction to close the
valve, comprising the steps of: actuating the valve according to a
first mode when a first set of engine operating conditions are
detected, said first mode further comprising the steps of
de-energizing the valve closing electromagnet; maintaining the
valve closing electromagnet in said de-energizing state to enable
the valve to oscillate by force of the valve opening spring and the
valve closing spring without energizing the valve opening
electromagnet; and energizing the valve closing electromagnet to
close the valve; and actuating the valve according to a second mode
during a second set of engine operating conditions, said second
mode further comprising the steps of de-energizing the valve
closing electromagnet to allow the armature to open, energizing the
valve opening electromagnet thereby causing the valve to open;
de-energizing the valve opening electromagnet to allow the valve to
close; and energizing the valve closing electromagnet thereby
causing the valve to close..Iaddend.
.Iadd.46. The method of claim 45, wherein the valve is an intake
valve, said first set of engine operating conditions are those
indicating a lower flow rate of air through the valve, and said
second set of engine operating conditions are those indicating a
higher flow rate of air through the valve..Iaddend.
.Iadd.47. The method of claim 45, further comprising inducting air
past the valve as it oscillates, when the valve is operated
according to said first mode..Iaddend.
.Iadd.48. The method of claim 45, wherein the first set of
operating conditions is indicated by lower engine speed and a lower
engine torque..Iaddend.
Description
BACKGROUND OF INVENTION
1. Field of the Invention
The present invention relates generally to a method for controlling
electromechanical valves in an internal combustion engine.
2. Background of the Invention
An electromechanically operated poppet valve in the cylinder head
of an internal combustion, as disclosed in U.S. Pat. No. 4,455,543,
is actuated by energizing and de-energizing electromagnets acting
upon an armature coupled to the poppet valve. Because the actuation
of the electromagnets is controlled by an electronic control unit,
valve opening and closing events occur independently of engine
rotation. In conventional engines with camshaft actuated valves,
which have timings based on engine rotation, air delivery to the
cylinders is controlled by a throttle valve placed in the inlet
duct of the engine. In contrast, electromechanical valves are
capable of controlling air delivery based on valve timing, thereby
providing a thermal efficiency improvement over throttled operation
of a conventional engine.
However, a drawback to electromechanical valves is the amount of
electrical energy consumed in actuating them. The inventors of the
present invention have recognized a method to operate
electromechanical valves in a manner which consumes less electrical
energy than prior methods.
SUMMARY OF INVENTION
Disadvantages of prior methods are overcome by a method for
actuating an intake valve disposed in a cylinder head of an
internal combustion engine by an electromagnetic valve apparatus.
The apparatus has a valve closing electromagnet capable of
exhibiting an electromagnetic force for attracting the armature to
close the valve, a valve opening electromagnet capable of
exhibiting an electromagnetic force for attracting the armature to
open the valve, a valve opening spring for biasing the armature in
a direction to open the valve, and a valve closing spring for
biasing the armature in a direction to close the valve. The method
includes the steps of actuating the valve according to a first mode
when a first set of engine operating conditions are detected and
actuating the valve according to a second mode when a second set of
engine operating conditions are detected. The first mode further
includes the steps of de-energizing the valve closing
electromagnet, maintaining the valve closing electromagnet in the
de-energized state for a first predetermined time enabling the
valve to oscillate by force of the valve opening spring and the
valve closing spring, and energizing the valve closing
electromagnet after the first predetermined time to close the
valve. The second mode further includes the steps of de-energizing
the valve closing electromagnet to allow the valve to open,
energizing the valve opening electromagnet in response to said
de-energizing step to attract the armature to the valve opening
electromagnet thereby causing the valve to open, de-energizing the
opening electromagnet after a second predetermined time has elapsed
since the valve opening electromagnet has been energized, and
energizing the valve closing electromagnet in response to the
de-energizing step of the valve opening electromagnet to attract
the armature to the valve closing electromagnet thereby causing the
valve to close.
An electromagnetic valve apparatus for actuating a valve disposed
in a cylinder head of a multi-cylinder internal combustion engine
is disclosed which has an armature operatively connected to the
valve, a valve closing electromagnet capable of exhibiting an
electromagnetic force for attracting said armature to close the
valve, a valve opening spring coupled to the armature for biasing
the armature in a direction to open the valve, a valve closing
spring coupled to the valve for biasing the valve to a closed
position, and an electronic control unit operably connected to the
valve closing electromagnet. The electronic control unit
de-energizes the valve closing electromagnet allowing the valve to
oscillate by force of the valve opening spring and the valve
closing spring and maintains the valve closing electromagnet in the
de-energized state at least until the valve travels to a nearly
open position and returns to a nearly closed position. The
predetermined time is based on dynamic characteristics of the valve
and the electromagnetic valve apparatus. The valve is an intake
valve of the engine. Intake air flows past an oscillating intake
valve.
A primary advantage of the present invention is that the amount of
energy utilized in actuating a valve is approximately half of prior
art actuation methods.
According to an aspect of the present invention, the valve may be
opened for a period of time over which the valve oscillates between
a nearly open position and a nearly closed position. Compared with
prior methods in which the valve is maintained in a fully open
position for the entire duration of opening, the present invention
provides more intake turbulence to the incoming air stream by
virtue of the air being inducted past an intake valve which is at a
half open position, on average.
BRIEF DESCRIPTION OF DRAWINGS
The advantages described herein will be more fully understood by
reading an example of an embodiment in which the invention is used
to advantage, referred to herein as the Detailed Description, with
reference to the drawings wherein:
FIG. 1 is a schematic of an engine equipped with
electromechanically-actuated poppet valves;
FIG. 2 is a detail of an example of an electromechanically-actuate
poppet valve in a closed position;
FIG. 3 is a detail of an example of an electromechanically-actuated
poppet valve in an open position;
FIG. 4 is a graph of valve position over time for an
electromechanically-actuated valve operating according to an aspect
of the present invention;
FIG. 5 is a graph of valve position according to prior art and a
graph of valve position according to an aspect of the present
invention;
FIG. 6 is a graph of air flow inducted as piston position is
varied; and
FIG. 7 is a flowchart indicating valve operating procedure.
DETAILED DESCRIPTION
In FIG. 1, a single cylinder 13 of an internal combustion engine 10
with an electromechanical intake valve 20 and exhaust valve 19 is
shown. Engine 10 contains a piston 14 which reciprocates within
cylinder 13. Intake valve 20, disposed in cylinder head 22, is
opened to allow gases to communicate between the combustion chamber
(the volume enclosed by cylinder 13, piston 14, and cylinder head
22) and intake port 70. When exhaust valve 19 is opened, gases are
released from the combustion chamber into exhaust port 72. In the
embodiment shown in FIG. 1, fuel is injected into intake port 70 by
injector 16, a configuration commonly called port fuel injection.
However, the present invention applies to any fuel delivery method,
including direct injection, central injection, and carburetion.
Intake valve 20 and exhaust valve 19 are actuated
electromechanically by valve actuators 18 and 17, respectively. In
a preferred embodiment, engine 10 is a spark-ignited engine, spark
plug 12 initiates combustion in the combustion chamber. The present
invention also applies to engines with other types of ignitors and
to compression ignition engines in which the fuel and air
spontaneously ignite due to a compression generated temperature
rise in the combination chamber. Both diesel and homogeneous charge
compression ignition are examples of the latter type of engine.
Continuing to refer to FIG. 1, electronic control unit (ECU) 60 is
provided to control engine 10. ECU 60 has a microprocessor 46,
called a central processing unit (CPU), in communication with
memory management unit (MMU) 48. MMU 48 controls the movement of
data among the various computer readable storage media and
communicates data to and from CPU 46. The computer readable storage
media preferably include volatile and nonvolatile storage in
read-only memory (ROM) 50, random-access memory (RAM) 54, and
keep-alive memory (KAM) 52, for example. KAM 52 may be used to
store various operating variables while CPU 46 is powered down. The
computer-readable storage media may be implemented using any of a
number of known memory devices such as PROMs (programmable
read-only memory), EPROMs (electrically PROM), EEPROMs
(electrically erasable PROM), flash memory, or any other electric,
magnetic, optical, or combination memory devices capable of storing
data, some of which represent executable instructions, used by CPU
46 in controlling the engine or vehicle into which the engine is
mounted. The computer-readable storage media may also include
floppy disks, CD-ROMs, hard disks, and the like. CPU 46
communicates with various sensors and actuators via an input/output
(I/O) interface 44. Examples of items that are actuated under
control by CPU 46, through I/O interface 44, are fuel injection
timing, fuel injection rate, fuel injection duration, throttle
valve position, spark plug 12 timing, actuation of valve actuators
18 and 17 to control opening and closing of intake valve 20 and
exhaust valve 19, respectively, and others. Sensors 42
communicating input through I/O interface 44 may be indicating
piston position, engine rotational speed, vehicle speed, coolant
temperature, intake manifold pressure, pedal position, throttle
valve position, air temperature, exhaust temperature, exhaust
stoichiometry, exhaust component concentration, and air flow. Some
ECU 60 architectures do not contain MMU 48. If no MMU 48 is
employed, CPU 46 manages data and connects directly to ROM 50, RAM
54, and KAM 52. Of course, the present invention could utilize more
than one CPU 46 to provide engine control and ECU 60 may contain
multiple ROM 50, RAM 54, and KAM 52 coupled to MMU 48 or CPU 46
depending upon the particular application.
In FIG. 2, an example of an electromechanical valve actuator 18 is
shown in which intake valve 20 is in a closed position. Intake
valve 20 closes off port 70 in cylinder head 22. Valve actuator 18
is shown in detail in FIG. 2. A valve closing spring 24 biases
valve 20 to the closed position. Armature 30 is disposed between
two electromagnets: a valve closing electromagnet 32 and valve
opening electromagnet 28. Armature 30 is connected to shafts 26 and
34. As shown in FIG. 2, armature 30 is next to valve closing
electromagnet 32. For this position to prevail, valve closing
electromagnet 32 is energized. Otherwise, armature 30 would act
under the influence of valve closing spring 24 and valve opening
spring 36. In the embodiment shown in FIG. 2, valve opening spring
is attached to shaft 34 at the lower end of valve opening spring
36. Other alternative configurations may also provide the same
functionality. If both electromagnets 28 and 32 are de-energized,
armature 30 is influenced by springs 24 and 36 and attains a
neutral position in between electromagnets 28 and 34. Valve
actuator 17 and exhaust valve 19 can also be represented by FIG. 2,
by way of example.
Continuing to refer to FIG. 2, valve actuator 18 preferably
includes a valve position sensing device, such as a linear variable
differential transformer (LVDT) 38. The tip of shaft 34 forms the
core of the position sensor. The inductance of the LVDT varies when
the position of the shaft 34 is altered with respect to the LVDT 38
windings. LVDT 38 is connected to ECU 60 (connection not shown).
LVDT 38 is shown by way of example; other types of position sensing
devices may also be used.
FIG. 3 shows the same hardware as shown in FIG. 2 with the
difference being that FIG. 2 shows valve 20 in the fully closed
position and FIG. 3 shows valve 20 in the fully open position.
Thus, in FIG. 2, valve closing electromagnet 32 is energized and,
in FIG. 3, valve closing electromagnet 28 is energized. In FIG. 2,
valve opening spring 36 is compressed. Holding current is applied
to valve closing electromagnet 32 to act against the spring tension
of valve opening spring 36. Analogously, in FIG. 3, valve closing
spring 24 is compressed. Holding current is applied to valve
opening electromagnet 28 to act against the spring tension of valve
closing spring 24.
Before discussing aspects of the present invention, an example of
prior art control of an electromechanical valve is described.
Typically, a valve, whether an intake or exhaust valve, of an
internal combustion engine is normally closed, i.e., the valve is
in the closed position for more of the time than the open position.
Thus, the description of valve opening begins with a closed valve,
i.e., with a holding current be applied to valve closing
electromagnet 32. Actuating the valve proceeds by: de-energizing
valve closing electromagnet 32 which causes the valve to open under
the influence of valve opening spring 36; applying a peak current
to valve opening electromagnet 28 to grab armature 30 when it is
near its fully open position; applying a holding current to valve
opening electromagnet 28 after armature 30 is attracted to valve
opening electromagnet 28); applying holding current for as long as
the desired open duration of the valve; de-energizing valve opening
electromagnet 28 which causes the valve to close under the
influence of valve spring 24; and, applying a peak current to valve
opening electromagnet 32 to grab armature 30 when it is near its
fully closed position. The terms peak current and holding current
are concepts known to those skilled in the art and refer to a
higher current level (peak current) used to catch a moving armature
30 and a lesser current (holding current) used to prevent a
stationary armature 30 from moving.
The neutral position, i.e., the position that valve 20 attains when
both electromagnets 28 and 34 are de-energized, is about halfway
between the fully closed position, FIG. 2, and fully open position,
FIG. 3. The exact neutral position would depend, though, on the
relative spring tensions of valve opening spring 36 and valve
closing spring 24. In FIG. 4, a plot of valve position as a
function of time is shown for valve 20 under the situation that the
valve at time T0 is at the fully closed position by virtue of
holding current being applied to valve closing electromagnet 32. At
time T0+, valve closing electromagnet 32 is de-energized. The valve
lifts from the fully closed position and proceeds to a nearly open
position by action of the valve opening spring 36. As valve 20
progresses to a nearly open position, valve closing spring 24
becomes compressed. Valve 20 then returns to a nearly closed
position under the influence of the valve closing spring 24. The
period of time that it takes for the valve to leave the fully
closed position, travel to a nearly open position, and return to a
nearly closed position is called a valve period and is indicated as
T1 in FIG. 4. The oscillation of valve 20 continues, with each
successive peak and trough being closer to the neutral position
than the prior peak or trough, due to irreversibilities in the
system. Eventually, valve 20 stops oscillating and attains the
neutral position (not shown in FIG. 4). Period T2 is twice period
T1 and period T3 is three times period T1, etc. The first three
troughs of the curve in FIG. 4 are lower than the maximum grabbing
distance dotted line with the 4.sup.th trough being above the
maximum grabbing distance. The maximum grabbing distance is the
maximum distance away from the fully closed position that armature
30 may be and still allow valve closing electromagnet 32 to attract
armature 30. If armature 30 is farther away from the fully closed
position than the maximum grabbing distance, valve closing
electromagnet 32 cannot attract armature 30, that is, at the peak
current of the driving system (not shown). For the example shown in
FIG. 4, after de-energizing valve closing electromagnet 32,
armature 30 may be allowed to oscillate three periods and still
allow valve closing electromagnet 32 to catch armature 30 at around
the end of period T3. If valve closing electromagnet were not
caught before valve 20 begins the fourth oscillation, valve 20
would not come to a position where valve closing electromagnet 32
could exert enough attractive force to catch valve 20.
As mentioned above, the power consumption in performing a valve
catching, i.e., applying the peak current, is the predominant
energy consuming function. In performing one cycle of valve open
and close, prior art methods perform two such valve catching
events:
valve grabbing near the fully open position and valve grabbing near
the fully closed position. The present invention, in contrast,
performs only one valve catching event, valve grabbing near the
closed position. As a consequence, about a 50% electrical energy
savings in electromechanical valve actuations is realized by
practicing the present invention.
The valve lift profiles and open duration provided by prior art are
quite different from the present invention and are illustrated in
FIG. 5. In the upper graph of FIG. 5 showing prior art, the valve
opens and is held open for a variable duration and then the valve
is closed. Three example durations are shown in FIG. 5. However,
the minimum duration is the sum of the opening time and the closing
time and the maximum duration is infinite. Referring now to the
lower portion of FIG. 5, according to an aspect of the present
invention, the valve opens and then the valve is grabbed to
re-close at times near T1, T2, and T3 only in the example shown.
Valve closing electromagnet 32 is not capable of grabbing armature
30, except when armature 30 is within the maximum grabbing distance
(shown in FIG. 4), which occurs at discrete times after the valve
is released by valve closing electromagnet 32. These discrete times
are designated with an X on the abscissa of the lower graph of FIG.
5.
Comparing the valve profile of prior art, upper graph in FIG. 5,
and that provided by the present invention, lower graph in FIG. 5,
shows that the valve is retained in a fully open position in
between valve opening and valve closing; whereas, the valve
oscillates between nearly closed and nearly open according to the
present invention. Actuation of intake valve 20, according to prior
art, is preferred for inducting large quantities of air into the
combustion chamber of engine 10. It is known to those skilled in
the art that at engine operating conditions in which a lesser
amount of air is desired, that opening intake valve 20 to less than
the fully open position provides advantages. Specifically, intake
turbulence is enhanced when air is drawn into cylinder 13 past a
less open intake valve 20. Intake turbulence is known to those
skilled in the art to accelerate the ensuing combustion event and
to aid in ensuring robust combustion. Thus, the present invention,
in which the valve is oscillating between a nearly open position
and a nearly closed position is preferred in situations in which a
lesser amount of air is to be inducted into cylinder 13.
When intake valve 20 is operated according to prior art approaches,
the amount of air inducted can be determined by controlling the
opening and closing time of the valve, as shown in the upper graph
of FIG. 5. According to an aspect of the present invention, intake
valve 20 is opened at any time; however, the closing occurs at
predetermined intervals only. In the example shown in FIG. 4,
intake valve 20 may be closed at times T1, T2, or T3. To induct the
desired amount of air into the cylinder, the timing of intake valve
20 opening is adjusted, as shown in FIG. 6. The opening time, with
respect to crank position (which is related to piston position), is
shown in FIG. 6 on the abscissa and the mass of air inducted on the
ordinate. The family of curves in FIG. 6 indicates the amount of
air inducted if intake valve 20 were closed at times T1, T2, and
T3. If, for example, the desired amount of air to be inducted is an
amount Ma, shown in FIG. 6 by a dotted line, only T2 and T3
closings can be used to provide Ma. To provide exactly Ma, intake
valve 20 would be opened at CP3, if it were being closed after the
T3 interval and would be opened at CP2, if it were being closed
after the T2 interval. In this example, the curve related to the T1
closing does not cross the dotted line indicating that a T1 closing
cannot provide Ma.
According to an aspect of the present invention discussed above,
closing of the valve occurs based on a number of valve periods or
oscillations of the valve, i.e., based on a time. Alternatively, if
the valve apparatus is equipped with a valve position sensor, such
as a LVDT as shown in FIGS. 2 and 3, the valve closing may be
initiated based on the position of the valve. As an example, the
valve closing electromagnet is energized based on an indication
from the LVDT that the valve is within the maximum grabbing
distance of the valve closing electromagnet. The valve period is a
function of the valve apparatus characteristics. If the
characteristics change due to: deposits forming on the valve
affecting the mass of the system, temperature changes affecting
valve tension, lengths of system members, or other characteristics
of the system, or aging affects such as wear, then the valve period
may be affected. The position sensor on valve 20 could be used to
determine the valve period at the particular set of conditions, to
update the valve period in ECU 60 as the valve period changes, or
to supplant the use of valve period in determining when to close
the valve.
A method of operating an engine according to an aspect of the
present invention is shown in FIG. 7. The procedure begins in step
100. Control passes to step 102 in which it is determined how much
air, Ma, should be trapped in the cylinder. This is based on driver
demand for power. Control passes to step 104 in which it is
determined whether the desired amount of air, Ma, can be provided
by practicing the present invention. If not, control passes to step
120, in which prior art methods are used. The valve trajectory of
prior art is shown in the upper half of FIG. 5 and is described
above. From step 120, control returns to step 100, where a
determination of valve procedure is determined for the next valve
opening cycle. If a positive result in step 104, control passes to
step 106 in which the minimum number of valve oscillations that can
be used to provide Ma is determined. The minimum number is an
integral number and is less than the number of oscillations in
which the trajectory of armature 30 fails to attain the minimum
valve grabbing distance. Control passes to step 108 in which the
timing to initiate valve opening is determined. Constraints placed
on the initiation time are that the number of oscillations is that
which was found in step 106 and Ma is to be provided to the
cylinder. Control is passed to step 110 in which the valve is
opened starting at the initiation time found in block 108 and is
open for the minimum number of oscillations. Control then returns
to block 100.
In the above discussion of determining a valve opening time in step
108, the constraints discussed are the number of valve periods or
oscillations over which the valve is open and providing the desired
air, Ma.
Alternatively, the opening time could be constrained by a desired
turbulence level of the inducted gases or a desired level of
exhaust gases to trap in the cylinder. These alternative
constraints could preferably be used in lean burn engines, that is,
engines in which the amount of air delivered to the cylinder is
more than that for fully combusting the fuel that is supplied to
the cylinder.
While several modes for carrying out the invention have been
described in detail, those familiar with the art to which this
invention relates will recognize alternative designs and
embodiments for practicing the invention. The above-described
embodiments are intended to be illustrative of the invention, which
may be modified within the scope of the following claims.
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