U.S. patent application number 09/879229 was filed with the patent office on 2002-02-07 for engine valve drive control apparatus and method.
Invention is credited to Fuwa, Toshio.
Application Number | 20020014213 09/879229 |
Document ID | / |
Family ID | 26594966 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014213 |
Kind Code |
A1 |
Fuwa, Toshio |
February 7, 2002 |
Engine valve drive control apparatus and method
Abstract
A drive control apparatus and method control driving of an
engine valve of an internal combustion engine based on
electromagnetic force generated by a certain electromagnet. A
controller of the apparatus sets a target drive velocity in
accordance with a displacement of the engine valve, such that the
target drive velocity corresponds to a velocity of the engine valve
when there is no engine load. The controller then controls a
magnitude of the electromagnetic force by controlling current
applied to the electromagnet, depending upon a degree of separation
between an actual drive velocity of the engine valve and the target
drive velocity, so that the actual drive velocity is made
substantially equal to the target drive velocity.
Inventors: |
Fuwa, Toshio; (Nagoya-shi,
JP) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET, N.W., SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
26594966 |
Appl. No.: |
09/879229 |
Filed: |
June 13, 2001 |
Current U.S.
Class: |
123/90.11 |
Current CPC
Class: |
F01L 2820/02 20130101;
F02D 13/0253 20130101; F02D 2200/0602 20130101; Y02T 10/12
20130101; F01L 9/20 20210101; F02D 13/0203 20130101 |
Class at
Publication: |
123/90.11 |
International
Class: |
F01L 009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 29, 2000 |
JP |
2000-196120 |
Feb 16, 2001 |
JP |
2001-40685 |
Claims
What is claimed is:
1. A drive control apparatus for controlling driving of an engine
valve of an internal combustion engine based on an electromagnetic
force generated by at least one electromagnet, comprising: a
setting unit that sets a target drive velocity of the engine valve
in accordance with a displacement of the engine valve, such that
the target drive velocity corresponds to a velocity of the engine
valve when there is no engine load; and a control unit that
controls a magnitude of the electromagnetic force by controlling
current applied to the at least one electromagnet, depending upon a
degree of separation between an actual drive velocity of the engine
valve and the target drive velocity, so that the actual drive
velocity is made substantially equal to the target drive velocity
set by the setting unit.
2. A drive control apparatus according to claim 1, wherein the
engine valve is able to displace between a first position and a
second position, and wherein a magnitude of the target drive
velocity is set to a minimum when the engine valve reaches one of
the first position and the second position during displacement
thereof.
3. A drive control apparatus according to claim 1, wherein: the
internal combustion engine further includes at least one spring
that exerts an elastic force on the engine valve, such that the
engine valve is driven by the elastic force of the spring in
addition to the electromagnetic force of the at least one
electromagnet; and the target drive velocity is determined so as to
coincide with a velocity of displacement of the engine valve when
the engine valve freely oscillates between opposite ends of a
stroke thereof under the elastic force of the spring.
4. A drive control apparatus according to claim 1, wherein the
control unit comprises: a feed-forward current setting unit that
calculates a feed-forward current for driving the engine valve so
that the actual drive velocity is made substantially equal to the
target drive velocity when there is no engine load; and a feed-back
current setting unit that calculates a feedback current depending
upon the degree of separation between the actual drive velocity and
the target drive velocity, and wherein the control unit controls
exciting current applied to the at least one electromagnet, based
on the feed-forward current and the feedback current.
5. A drive control apparatus according to claim 4, wherein the
exciting current applied to the at least one electromagnet is
substantially equal to a sum of the feed-forward current and the
feedback current.
6. A drive control apparatus according to claim 4, wherein when an
air gap formed between the engine valve and a selected one of the
at least one electromagnet is greater than a predetermined value
during a movement of the engine valve toward the selected
electromagnet, the feedback current setting unit sets the feedback
current to 0 without regard to the degree of separation between the
actual drive velocity and the target drive velocity.
7. A drive control apparatus according to claim 4, wherein a
feedback gain used when calculating the feedback current increases
with an increase in an air gap formed between the engine valve and
a selected one of the at least one electromagnet during a movement
of the engine valve toward the selected electromagnet.
8. A drive control apparatus according to claim 4, wherein the
engine valve is able to displace between a first position and a
second position, and wherein a magnitude of the target drive
velocity is set to a minimum when the engine valve reaches one of
the first position and the second position during displacement
thereof.
9. A drive control apparatus according to claim 4, wherein: the
internal combustion engine further includes at least one spring
that exerts an elastic force on the engine valve, such that the
engine valve is driven by the elastic force of the spring in
addition to the electromagnetic force of the at least one
electromagnet; and the target drive velocity is determined so as to
coincide with a velocity of displacement of the engine valve when
the engine valve freely oscillates between opposite ends of a
stroke thereof under the elastic force of the spring.
10. A drive control apparatus according to claim 1, wherein: the
control unit comprises an electromagnetic force required value
calculating unit that constructs a physical model of the engine
valve that includes a drive velocity of the engine valve as a model
variable, and calculates a required value of the electromagnetic
force that is needed for making the actual drive velocity
substantially equal to the target drive velocity, based on the
physical model, the actual drive velocity and the target drive
velocity; and the control unit controls exciting current applied to
the at least one electromagnet based on the electromagnetic force
required value calculated by the electromagnetic force required
value calculating unit.
11. A drive control apparatus according to claim 10, wherein: the
electromagnetic force required value calculating unit comprises an
acceleration required value calculating unit that calculates a
required value of an acceleration of the engine valve that is
needed for making the actual drive velocity substantially equal to
the target drive velocity, and an external force estimating unit
that estimates an external force that acts on the engine valve
depending upon an engine operating state; and the electromagnetic
force required value calculating unit calculates the required value
of the electromagnetic force based on the required value of the
acceleration calculated by the acceleration required value
calculating unit, the external force estimated by the external
force estimating unit, and an equation of motion of the engine
valve that describes the physical model.
12. A drive control apparatus according to claim 11, wherein the
external force estimating unit estimates the external force based
on at least one pressure that acts on the engine valve, and a
frictional resistance at each sliding portion of the engine
valve.
13. A drive control apparatus according to claim 11, wherein the
control unit sets an observer that observes an internal state of
the engine valve based on a vibration model thereof, and wherein
the actual drive velocity of the engine valve and the external
force that acts on the engine valve are estimated by using the
observer.
14. A drive control apparatus according to claim 10, wherein: the
electromagnetic force required value calculating unit comprises an
energy amount deviation calculating unit that calculates an energy
amount deviation between an actual energy amount of the engine
valve based on the actual drive velocity and a target energy amount
of the engine valve based on the target drive velocity; and the
electromagnetic force required value calculating unit calculates
the required value of the electromagnetic force based on the energy
amount deviation, and an equation of conservation of energy of the
engine valve that describes the physical model.
15. A drive control apparatus according to claim 10, wherein the
engine valve is able to displace between a first position and a
second position, and wherein a magnitude of the target drive
velocity is set to a minimum when the engine valve reaches one of
the first position and the second position during displacement
thereof.
16. A drive control apparatus according to claim 10, wherein: the
internal combustion engine further includes at least one spring
that exerts an elastic force on the engine valve, such that the
engine valve is driven by the elastic force of the spring in
addition to the electromagnetic force of the at least one
electromagnet; and the target drive velocity is determined so as to
coincide with a velocity of displacement of the engine valve when
the engine valve freely oscillates between opposite ends of a
stroke thereof under the elastic force of the spring.
17. A method for controlling driving of an engine valve of an
internal combustion engine based on an electromagnetic force
generated by at least one electromagnet, comprising the steps of:
setting a target drive velocity of the engine valve in accordance
with a displacement of the engine valve, the target drive velocity
corresponding to that of the engine valve when there is no engine
load; and controlling a magnitude of the electromagnetic force by
controlling current applied to the at least one electromagnet,
depending upon a degree of separation between an actual drive
velocity of the engine valve and the target drive velocity, so that
the actual drive velocity is made substantially equal to the target
drive velocity.
Description
INCORPORATION BY REFERENCE
[0001] The disclosures of Japanese Patent Applications Nos.
2000-196120 and 2001-40685 filed on Jun. 29, 2000 and Feb. 16,
2001, respectively, including the specifications, drawings and
abstracts, are incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to engine valve drive control
apparatus and method for controlling driving of engine valves of an
internal combustion engine based on electromagnetic force generated
by electromagnets.
[0004] 2. Description of Related Art
[0005] Valve drive apparatuses for driving engine valves, such as
intake valves and exhaust valves, of internal combustion engines,
by controlling electromagnetic force of electromagnets have been
known. The valve drive apparatus of this type is desired to ensure
high operating stability when driving the engine valves.
Furthermore, it is desirable to minimize the amount of electric
power that is consumed for driving the engine valves, and to
suppress occurrence of noises upon opening and closing of each
engine valve by reducing its drive velocity when the engine valve
reaches either one of the opposite ends of its stroke (or a range
of its displacement), namely, the fully closed position or the
fully open position.
[0006] In a conventional apparatus as disclosed in Japanese Patent
laid-open Publication No. 9-217859, the actual operating state of
the engine valve is detected, and the electromagnetic force
generated by an appropriate electromagnet is controlled so that the
actual operating state coincides with a target operating state of
the valve. In this manner, the electromagnetic force of the
electromagnet is controlled to a magnitude that meets various
requirements as mentioned above.
[0007] When controlling the electromagnetic force generated by the
electromagnet, the apparatus as disclosed in the above-identified
publication operates to determine a positional deviation between
the actual position of an engine valve and a target position
thereof (e.g., a fully open position or a fully closed position),
and apply a controlled current to the electromagnet so that the
resulting electromagnetic force has a magnitude suitable for
displacing or moving the engine valve to the target position. If
the positional deviation is large, for example, the exciting
current applied to the electromagnet is increased so that the
engine valve is opened or closed with accordingly increased
electromagnetic force.
[0008] It should be noted, however, that the engine valves are
subjected to external forces that vary depending upon the engine
load. The external forces exerted on each engine valve are produced
by, for example, the internal pressure (or in-cylinder pressure)
within a corresponding combustion chamber, and the intake pressure
or the exhaust pressure. Therefore, if the electromagnetic force of
the electromagnet(s) is controlled based solely on information on
the position of the engine valve in question (e.g., a positional
deviation), the electromagnetic force may become insufficient when
the drive force required to drive the engine valve is increased due
to the influence of the external forces. In this case, the engine
valve may not exhibit sufficiently high operating stability. If the
electromagnetic force is set in advance to be sufficiently large so
as to avoid the above situation, on the other hand, the engine
valve may be driven by an excessively large electromagnetic force,
depending on the condition of the engine load. This may result in
increased power consumption, and occurrence of noise and vibrations
at the time of opening and closing of the engine valve. In order to
appropriately control the electromagnetic force for driving the
engine valve, therefore, it is necessary to control electric
current applied to the selected electromagnet in accordance with
the engine load so that the influence of the external forces is
taken into consideration.
[0009] To control current applied to the electromagnet in
accordance with the engine load, it is necessary to obtain the
relationship between the engine load and the electromagnetic force
suitable for the engine load through experiments or the like, in
addition to the information in the position of the engine valve,
and to pre-set the relationship in the form of a control map, for
example. Thus, it takes a great amount of time to perform
operations to correlate control constants or parameters.
SUMMARY OF THE INVENTION
[0010] It is therefore an object of the invention to provide an
engine valve drive control apparatus and method which enable an
engine valve to be driven with an appropriate electromagnetic force
that is controlled in accordance with the engine load, and which
permits a significantly simplified operation to correlate control
constants used for control of driving of the engine valve.
[0011] To accomplish the above and/or other object(s), one aspect
of the invention provides a drive control apparatus for controlling
driving of an engine valve of an internal combustion engine based
on an electromagnetic force generated by at least one
electromagnet. The apparatus includes a controller that sets a
target drive velocity of the engine valve in accordance with a
displacement of the engine valve, such that the target drive
velocity corresponds to a velocity of the engine valve when there
is no engine load. The controller then controls a magnitude of the
electromagnetic force by controlling current applied to the
electromagnet, depending upon a degree of separation between an
actual drive velocity of the engine valve and the target drive
velocity, so that the actual drive velocity is made substantially
equal to the target drive velocity set by the setting unit.
[0012] When the drive force required to stably or reliably drive
the engine valve changes in accordance with the external force that
depends upon the engine load, the actual drive velocity deviates or
separates from the target drive velocity that corresponds to the
velocity of the engine valve in a no-engine-load state, because of
the influence of the external force.
[0013] With the drive control apparatus constructed as described
above, if the actual drive velocity deviates from the target drive
velocity (in a no-engine-load state) due to the influence of the
engine load, electric current applied to an appropriate
electromagnet is controlled depending upon the degree of separation
between the actual and target drive velocities. In this manner, the
electromagnetic force of the electromagnet is controlled so that
the actual drive velocity substantially coincides with the target
drive velocity. Thus, even if the external force acting on the
engine valve varies depending upon the engine load, the engine
valve is driven with a suitably controlled electromagnetic force
that corresponds to the engine load, so as to ensure opening and
closing characteristics that are equivalent to those provided when
there is no engine load. Furthermore, when controlling the
electromagnetic force of the electromagnet depending upon the
engine load as described above, there is no need to perform an
operation to empirically determine the relationship between the
engine load and the electromagnetic force suitable for the engine
load, through experiments or the like. Rather, it is simply
required to set the target drive velocity in a no-engine-load state
in accordance with the displacement (or position) of the engine
valve. It is, therefore, possible to greatly simplify an operation
to correlate control constants.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The foregoing and/or further objects, features and
advantages of the invention will become apparent from the following
description of preferred embodiments of the invention with
reference to the accompanying drawings, wherein like numerals are
used to represent like elements and wherein:
[0015] FIG. 1 is a schematic diagram illustrating an exhaust valve
and a drive control apparatus thereof;
[0016] FIG. 2 is a timing chart illustrating time-dependent changes
in the valve displacement and other parameters during a
no-engine-load state;
[0017] FIG. 3 is a map used in arithmetic operations, which
indicates a relationship between the target drive velocity and the
valve displacement;
[0018] FIG. 4 is a map used in arithmetic operations, indicating a
relationship between the valve displacement and the level of
feed-forward current supplied to a lower coil;
[0019] FIG. 5 is a map used in arithmetic operations, indicating a
relationship between the valve displacement and the level of
feed-forward current supplied to an upper coil;
[0020] FIG. 6 is a graph showing changes of the actual drive
velocity and the target drive velocity with the valve
displacement;
[0021] FIG. 7 is a flowchart illustrating a procedure of valve
drive control according to a first embodiment of the invention;
[0022] FIG. 8 is a timing chart indicating time-dependent changes
of the valve displacement, the feedback current, the feed-forward
current, and the command current;
[0023] FIG. 9 is a map that is referred to when a feedback gain is
determined;
[0024] FIG. 10 is a schematic diagram illustrating the construction
of an internal combustion engine that employs a valve drive control
apparatus according to a third embodiment of the invention;
[0025] FIG. 11 is a flowchart illustrating a procedure of valve
drive control according to the third embodiment of the
invention;
[0026] FIG. 12 is a graph showing changes of the actual drive
velocity and the target drive velocity with the valve
displacement;
[0027] FIG. 13 is a graph indicating a relationship among the
required acceleration, the air gap, and the command current "I";
and
[0028] FIG. 14 is a flowchart illustrating a procedure of valve
drive control according to a fifth embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
First Embodiment
[0029] A first embodiment in which the invention is applied to a
drive control apparatus for intake valves and exhaust valves of an
internal combustion engine will be described.
[0030] In this embodiment, all of the intake valves and the exhaust
valves are formed as electromagnetically driven valves that are
opened and closed by using electromagnetic force generated by
electromagnets. The intake valves and the exhaust valves are
identical in construction and are controlled in the same manner
when they are driven. In the following, therefore, the construction
and operation of, for example, an exhaust valve will be described
in detail.
[0031] Referring to FIG. 1, an exhaust valve 10 includes a valve
shaft 20, a valve body 16 provided at one of axially opposite ends
of the valve shaft 20, and an electromagnetic drive portion 21 for
driving the valve shaft 20. The valve shaft 20 is supported by the
cylinder head 18 to be allowed to reciprocate by means of the
electromagnetic drive portion 21. The cylinder head 18 has an
exhaust port 14 that communicates with a combustion chamber 12 of
the engine. A valve seat 15 is formed near an opening of the
exhaust port 14. As the valve shaft 20 is reciprocated, the valve
body 16 rests or abuts upon the valve seat 15 to close the exhaust
port 14, and is moved away from the valve seat 15 to open the
exhaust port 14.
[0032] A lower retainer 22 is provided on an end portion of the
valve shaft 20 remote from the valve body 16. A lower spring 24 is
disposed in a compressed state between the lower retainer 22 and
the cylinder head 18. The valve body 16 and the valve shaft 20 are
urged in a valve closing direction (i.e., upward in FIG. 1) under
elastic force of the lower spring 24.
[0033] The electromagnetic drive portion 21 has an armature shaft
26 that is disposed coaxially with the valve shaft 20. A disc-like
armature 28 made of a high-magnetic-permeability material is fixed
to a substantially middle portion of the armature shaft 26, and an
upper retainer 30 is fixed to an end of the armature shaft 26. The
other end of the armature shaft 26 remote from the upper retainer
30 abuts on the end portion of the valve shaft 20 provided with the
lower retainer 22.
[0034] In a casing (not shown) of the electromagnetic drive portion
21, an upper core 32 is fixedly positioned between the upper
retainer 30 and the armature 28, and a lower core 34 is fixedly
positioned between the armature 28 and the lower retainer 22. Each
of the upper core 32 and the lower core 34 is made of a
high-magnetic-permeability material, and assumes an annular shape.
The armature shaft 26 extends through a central portion of each
annular core 32, 34 such that the shaft 26 can reciprocate relative
to the cores 32, 34.
[0035] An upper spring 38 is disposed in a compressed state between
the upper retainer 30 and an upper cap 36 that is provided in the
casing. The elastic force of the upper spring 38 urges the armature
shaft 26 toward the valve shaft 20. In turn, the armature shaft 26
urges the valve shaft 20 and the valve body 16 in a valve opening
direction (i.e., downward in FIG. 1).
[0036] A displacement sensor 52 is attached to the upper cap 36.
The displacement sensor 52 outputs a voltage signal that varies in
accordance with the distance between the displacement sensor 52 and
the upper retainer 30. It is thus possible to detect a displacement
of the armature shaft 26 or the valve shaft 20, that is, a
displacement of the exhaust valve 10, based on the voltage signal
of the displacement sensor 52.
[0037] An annular groove 40 having a center located on the axis of
the armature shaft 26 is formed in a lower surface of the upper
core 32 that faces the armature 28. An upper coil 42 is received in
the annular groove 40. The upper coil 42 and the upper core 32 form
an electromagnet 61 for driving the exhaust valve 10 in the valve
closing direction.
[0038] An annular groove 44 having a center located on the axis of
the armature shaft 26 is formed in a upper surface of the lower
core 34 that faces the armature 28. A lower coil 46 is received in
the annular groove 44. The lower coil 46 and the lower core 34 form
an electromagnet 62 for driving the exhaust valve 10 in the valve
opening direction.
[0039] In operation, electric current is applied to the coils 42,
46 of the electromagnets 61, 62 under control of an electronic
control unit 50 that governs various controls of the internal
combustion engine. The electronic control unit 50 includes a CPU, a
memory, and a drive circuit for supplying exciting current to the
coils 42, 46 of the electromagnets 61, 62. The electronic control
unit 50 further includes an input circuit (not shown) for receiving
a detection signal from the displacement sensor 52, an A/D
converter (not shown) that converts the detection signal as an
analog signal into a digital signal, and so on.
[0040] FIG. 1 shows a state of the exhaust valve 10 in which
neither the upper coil 42 nor the lower coil 46 is supplied with
exciting current, and therefore no electromagnetic force is
generated by the electromagnets 61, 62. In this state, the armature
28 is not attracted by electromagnetic force of either of the
electromagnets 61, 62, but rests at an intermediate position
between the cores 32, 34 at which the elastic forces of the springs
24, 38 are balanced with each other. With the exhaust valve 10 held
in the state of FIG. 1, the valve body 16 is spaced apart from the
valve seat 15 so that the exhaust port 14 is in a half-open state.
Hereinafter, the position of the exhaust valve 10 in the state of
FIG. 1 will be referred to as "neutral position".
[0041] Next, the operation of the exhaust valve 10 that is driven
through control of current applied to the coils 42, 46 will be
described.
[0042] Before driving of the exhaust valve 10 in the opening and
closing directions is started, a process (which will be called
"initial driving process") is implemented to displace or move the
exhaust valve 10 from the neutral position to a fully closed
position corresponding to an end of the stroke of the valve shaft
20, and hold the exhaust valve 10 still in this position. In the
initial driving process, exciting current is applied from the drive
circuit of the electronic control unit 50 alternately to the coils
42, 46 at predetermined time intervals. With the current applied to
the coils 42, 46 thus controlled, the armature 28, the armature
shaft 26, the valve shaft 20, etc. are forcibly oscillated under
the influences of the elastic forces of the springs 24, 38 and the
electromagnetic forces generated alternately by the electromagnets
61, 62. Then, the amplitude of the oscillation of the armature 28
gradually increases until the armature 28 is brought into abutment
with the upper core 32. At the moment when the armature 28 abuts on
the upper core 32, the current application to the lower coil 46 is
stopped, and the upper coil 42 is continuously supplied with a
constant exciting current. As a result, the armature 28 is
attracted to the upper core 32 by the electromagnetic force
generated by the electromagnet 61, and is maintained in this state
in which the armature 28 rests upon the upper core 32. Thus, the
exhaust valve 10 is held in the fully closed position, which is the
initial operating state that permits subsequent opening and closing
actions of the valve 10.
[0043] In order to open and close the exhaust valve 10 initially
placed in the fully closed position, in synchronism with the
operation of the engine, an exciting current, which is set as a sum
of a feed-forward current component (hereinafter referred to as "FF
current If") and a feedback current component (hereinafter referred
to as "FB current Ib"), is supplied from the drive circuit of the
electronic control unit 50 selectively to the coils 42, 46 of the
electromagnets 61, 62.
[0044] The driving force for opening and closing the exhaust valve
10 is basically determined by the elastic forces of the springs 24,
38, the masses of the valve body 16, the valve shaft 20, the
armature 28, the armature shaft 26, etc. The driving force also
varies depending on the magnitudes of frictional resistance at
various sliding portions including, for example, interfaces between
the armature shaft 26 and the cores 32, 34, an interface between
the valve shaft 20 and the cylinder head 18, etc. Furthermore,
since the valve body 16 receives external force based on exhaust
pressures in the combustion chamber 12 and the exhaust port 14 (or
intake pressures in the case of an intake valve), the driving force
on the exhaust valve 10 changes under the influence of the external
force.
[0045] In order to ensure a sufficiently high operating stability
of the exhaust valve 10, it is necessary to set the magnitudes of
the electromagnetic force generated by the electromagnets 61, 62,
in other words, the amounts of exciting current supplied to the
coils 42, 46, to appropriate values so that the resulting driving
force reflects the frictional resistance at various sliding
portions, and the external force due to the in-cylinder pressure
and other factors.
[0046] While the magnitude of frictional resistance at each sliding
portion is regarded as being substantially constant regardless of
the engine load, the magnitude of external force due to the
in-cylinder pressure and other factors is likely to change greatly
in accordance with the engine load. For example, when the engine
load is increased, the combustion pressure is increased, and the
in-cylinder pressure or the exhaust pressure at the time of opening
of the exhaust valve 10 is accordingly increased, resulting in an
increase in the external force due to the aforementioned pressures.
Therefore, if the exciting current applied to the coils 42, 46 is
determined without taking the external force into consideration,
the electromagnetic force for driving the exhaust valve 10 may
become insufficient, resulting in a reduction in the operating
stability of the exhaust valve 10, or the exhaust valve 10 may be
driven by excessively large electromagnetic force, which may result
in an increase in the power consumption, and/or cause vibrations
and noises (due to contacts between the armature 28 and the cores
32, 34, and collision between the valve seat 15 and the valve body
16, etc.) upon opening and closing of the exhaust valve 10.
[0047] According to the embodiment of the invention, therefore, the
FF current "If" and the FB current "Ib" are appropriately set so as
to reflect the frictional resistance and the external force due to
the in-cylinder pressure and other factors, so that the exhaust
valve 10 operates with a sufficiently high stability, and does not
suffer from the above-described problems, such as increased power
consumption and the noises and vibrations occurring upon opening
and closing thereof.
[0048] A procedure of setting the FF current "If" and the FB
current "Ib" will be hereinafter described in detail. A target
drive velocity Vt of the exhaust valve 10 that is referred to upon
setting of the FF current "If" and the FB current "Ib" will be
initially described.
[0049] If the supply of exciting current to the upper coil 42 is
stopped while the exhaust valve 10 is held at the fully closed
position through the initial driving process, the armature 28 is
moved away from the upper core 32, and the armature 28, the
armature shaft 26, the retainers 22, 30, the valve shaft 20 and the
valve body 16 (which will be generally called "a movable portion")
are oscillated by the elastic forces of the springs 24, 38.
[0050] Assuming that the operation of the engine is stopped and no
external force based on the in-cylinder pressure acts on the valve
body 16, and that no frictional resistance is present at each
sliding portion, the movable portion as indicated above is caused
to freely oscillate under the elastic forces of the springs 24,
38.
[0051] In this embodiment, the velocity of the movable portion of
the exhaust valve 10 when it is freely oscillated as described
above is determined as a target drive velocity "Vt" used when
driving the exhaust valve 10, and the target drive velocity "Vt" is
set in accordance with the displacement of the exhaust valve 10
(hereinafter, referred to as "valve displacement") "X". By setting
the target drive velocity "Vt" in this manner, the elastic energies
stored in the springs 24, 38 can be converted into kinetic energy
of the movable portion, and the energy loss in driving the exhaust
valve 10 can be minimized.
[0052] FIG. 3 shows a map indicating a relationship between the
target drive velocity "Vt" and the valve displacement "X". The
relationship indicated in this map is stored in advance as function
data in a memory of the electronic control unit 50.
[0053] As shown in the map, in the case where the exhaust valve 10
displaces from the fully closed position to a fully open position
(i.e., when the position of the exhaust valve 10 changes from point
A to point C and then to point B along a solid line in FIG. 3), the
magnitude of the target drive velocity "Vt"
(=.vertline.Vt.vertline.) takes a minimum value "0" when the
exhaust valve 10 is at the fully closed position (point A) or the
fully open position (point B). When the exhaust valve 10 is at the
neutral position (point C), the magnitude of the target drive
velocity "Vt" takes a maximum value (.vertline.-Vtmax.vertline.).
During displacement of the exhaust valve 10 from the fully open
position to the fully closed position (i.e., a change in the
position from point B to point D, and further to point A, along the
solid line in FIG. 3), the magnitude of the target drive velocity
Vt takes the minimum value "0" when the exhaust valve 10 is at the
fully open position (point B) or the fully closed position (point
A). When the exhaust valve 10 is at the neutral position (point D),
the magnitude of the target drive velocity "Vt" takes a maximum
value (.vertline.Vtmax.vertline.).
[0054] A procedure of setting the FF current "If" will be described
with reference to FIGS. 2, 4 and 5. FIG. 2 is a timing chart
indicating time-dependent changes in the valve displacement "X"
((a) in FIG. 2), the FF currents "If" supplied to the coils 42, 46
of the electromagnets 61, 62 ((b), (c) in FIG. 2), and the actual
drive velocity Va of the exhaust valve 10 when there is no engine
load. In FIG. 2, section (b) indicates time-dependent changes in
the FF current "If" supplied to the upper coil 42, and section (c)
indicates time-dependent changes in the FF current "If" supplied to
the lower coil 46.
[0055] The FF current "If" supplied to the upper coil 42 during a
period between time t0 and time t1 in FIG. 2 is set to a value
(hold current value) "If2" such that the armature 28 is held in
contact with the upper core 32. Thus, the exhaust valve 10 is held
at the fully closed position during this period.
[0056] To open the exhaust valve 10 from the aforementioned state,
the supply of the FF current "If" to the upper coil 42 is stopped
at point of time t1. As a result, the movable portion of the
exhaust valve 10 starts moving in the valve opening direction under
the elastic force of the upper spring 38. Subsequently, the
magnitude (absolute value) of the actual drive velocity "Va"
gradually increases, and reaches the maximum at a point of time t2
when the exhaust valve 10 reaches the neutral position. When the
exhaust valve 10 further moves beyond the neutral position, the FF
current "If" starts being supplied to the lower coil 46.
[0057] FIG. 4 shows a map indicating a relationship between the FF
current "If" supplied to the lower coil 46 and the valve
displacement "X". The relationship between the FF current "If" and
the valve displacement "X" indicated in this map is stored in
advance as function data in the memory of the electronic control
unit 50.
[0058] As indicated in the map, the FF current "If" is set to a
constant value "If1" during a period of time in which the exhaust
valve 10 moves from position "X1" to position "X2" that is closer
to the fully open position than position "X1" (i.e., a period
between time t3 and time t4 in FIG. 2). The position "X1" is
shifted a certain distance from the neutral position toward the
fully open position, as shown in FIG. 4. As the FF current "If" is
supplied to the lower coil 46, the armature 28 is attracted toward
the lower core 34 by the electromagnetic force of the electromagnet
62.
[0059] Then, during a period in which the exhaust valve 10 moves
from the position "X2" to the fully open position (period between
time t4 and time t5), the FF current "If" is gradually reduced as
the exhaust valve 10 approaches the fully open position. Therefore,
the electromagnetic force generated by the electromagnet 62
gradually decreases. The bias force of the lower spring 24 for
biasing or urging the movable portion of the exhaust valve 10 in
the valve closing direction is increased as the exhaust valve 10
approaches the fully open position. Thus, the bias force of the
lower spring 24 increases while the electromagnetic force of the
electromagnet 62 decreases, and consequently the magnitude of the
actual drive velocity "Va" gradually decreases.
[0060] When the exhaust valve 10 reaches the fully open position,
the FF current "If" is set to a value (hold current value) If2 such
that the armature 28 is held in contact with or rests upon the
lower core 34. As a result, the exhaust valve 10 is held at the
fully open position.
[0061] To close the exhaust valve 10 from the above state, the
supply of the FF current "If" to the lower coil 46 is stopped at a
point of time t6. As a result, the movable portion of the exhaust
valve 10 starts moving in the valve closing direction due to the
elastic force of the lower spring 24. Subsequently, the magnitude
of the actual drive velocity "Va" gradually increases, and reaches
the maximum at a point of time t7 at which the exhaust valve 10
reaches the neutral position. As the exhaust valve 10 is further
moved beyond the neutral position, the FF current "If" starts being
supplied to the upper coil 42.
[0062] FIG. 5 shows a map indicating a relationship between the FF
current "If" supplied to the upper coil 42 and the valve
displacement "X". The relationship between the FF current "If" and
the valve displacement "X" indicated in this map is stored in
advance as function data in the memory of the electronic control
unit 50.
[0063] As indicated in the map, during a period in which the
exhaust valve 10 moves from position "X3" to position "X4" that is
closer to the fully closed position that position "X3" (i.e., a
period between time t8 and time t9 in FIG. 2), the FF current "If"
is set to a constant value If1. The position "X3" is shifted a
certain distance from the neutral position toward the fully closed
position, as shown in FIG. 5. As the FF current "If" is supplied to
the upper coil 42, the armature 28 is attracted toward the upper
core 32 under the electromagnetic force of the electromagnet
61.
[0064] Then, during a period in which the exhaust valve 10 moves
from the position "X4" to the fully closed position (i.e., a period
between time t9 and time t10), the FF current "If" is gradually
reduced as the exhaust valve 10 approaches the fully closed
position. Therefore, the electromagnetic force generated by the
electromagnet 61 gradually decreases. The bias force of the upper
spring 38 for biasing or urging the movable portion of the exhaust
valve 10 in the valve opening direction is increased as the exhaust
valve 10 approaches the fully closed position. Thus, since the bias
force of the upper spring 38 increases while the electromagnetic
force of the electromagnet 61 decreases, the magnitude of the
actual drive velocity "Va" gradually decreases.
[0065] When the exhaust valve 10 reaches the fully closed position,
the FF current "If" is set to the hold current value "If2" and is
kept at this value. As a result, the exhaust valve 10 is held at
the fully closed position.
[0066] It should be noted herein that the FF current "If" supplied
to the coils 42, 46 is set to a minimum magnitude that is needed in
order to make the actual drive velocity "Va" equal to the target
drive velocity "Vt" when there is no engine load, while taking
account of frictional resistance at various sliding portions in the
exhaust valve 10.
[0067] For example, if the FF current "If" supplied to the lower
coil 46 is not sufficient when the exhaust valve 10 is to be
opened, the electromagnet 62 does not generate electromagnetic
force large enough to stably drive the exhaust valve 10, and the
armature 28 cannot be brought into abutment or contact with the
lower core 34. This results in a generally-termed loss of
synchronism with which the exhaust valve 10 does not reach the
fully open position but settles toward the neutral position as
indicated by a one-dot chain line in (a) in FIG. 2. If such loss of
synchronism occurs, it becomes necessary to perform the initial
driving process again, and the exhaust valve 10 can no longer
operate with a sufficiently high stability.
[0068] If the FF current "If" supplied to the lower coil 46 is set
to be excessively large, on the other hand, the magnitude of the
actual drive velocity "Va" (measured at time t4') immediately
before the exhaust valve 10 reaches the fully closed position
becomes relatively large, as indicated by two-dot chain lines in
(a), (c) and (d) in FIG. 2. As a result, an increased quantity of
energy is lost at the time of abutment of the armature 28 with the
lower core 34, resulting in increased power consumption and
increased noise and vibrations caused by the abutment. Furthermore,
the armature 28 may collide with the lower core 34 and rebound, and
loss of synchronism may result if the armature 28 rebounds to a
large extent.
[0069] In this embodiment, the FF current "If" supplied to the
coils 42, 46 is controlled to a minimum level that is needed to
make the actual drive velocity "Va" equal to the target drive
velocity "Vt" when there is no engine load. Accordingly, the
exhaust valve 10 operates with a sufficiently high stability, and
is substantially free from otherwise possible problems, such as an
increase in the power consumption, and noise and vibrations that
would occur upon opening or closing of the valve 10.
[0070] Next, a procedure of setting the FB current "Ib" will be
described with reference to FIGS. 6 to 8.
[0071] When there is no engine load, the actual drive velocity "Va"
can be made equal to the target drive velocity "Vt" by supplying
the FF current "If" set as described above to the coils 42, 46 for
opening and closing the exhaust valve 10 . In contrast, during an
actual operation of the engine, namely, when a load is applied to
the engine, external forces based on the in-cylinder pressure and
the exhaust pressure act on the valve body 16 of the exhaust valve
10 . Due to the influence of such external forces, the actual drive
velocity "Va" tends to deviate from the target drive velocity
"Vt".
[0072] FIG. 6 indicates the actual drive velocity "Va" and the
target drive velocity "Vt" having a tendency as mentioned above, in
relation to the valve displacement "X". As the exhaust valve 10 is
opened, the target drive velocity "Vt" changes from point A to
point B along a solid line in FIG. 6 whereas the actual drive
velocity "Va" cannot follow the changes of the target drive
velocity "Vt", and becomes smaller in magnitude than the target
drive velocity "Vt" (.vertline.Va.vertline..ltoreq..vertline.V-
t.vertline.) as indicated by a two-dot chain line in FIG. 6 under
the influence of the aforementioned external force. In this
embodiment, a velocity deviation ".DELTA.V" between the actual
drive velocity "Va" and the target drive velocity "Vt" is detected
as a degree by which the actual drive velocity "Va" deviates or
separates from the target drive velocity "Vt". Then, the FB current
"Ib" is set based on the detected velocity deviation
".DELTA.V".
[0073] A procedure or process of controlling driving (i.e., opening
and closing) of the engine valve based on the FB current "Ib" and
the FF current "If" will be described with reference to the
flowchart shown in FIG. 7. The process or series of steps as
illustrated in the flowchart is performed after the supply of the
hold current "If2" to the coil 42 or 46 is stopped to drive (i.e.,
open or close) the exhaust valve 10. The process is repeatedly
executed by the electronic control unit 50 at predetermined time
intervals ".DELTA.t".
[0074] In the process of FIG. 7, step 100 is initially executed to
read the valve displacement "X" based on the detection signal from
the displacement sensor 52. Then, step 110 is executed to calculate
an actual drive velocity "Va" of the exhaust valve 10 according to
expression (1) as indicated below. In this embodiment, an actual
drive velocity detecting unit that detects the actual drive
velocity "Va" of the exhaust valve 10 is constituted by a portion
of the electronic control unit 50 that executes step S110 and the
displacement sensor 52.
Va=(X.sub.(i)-X.sub.(i-1)/.DELTA.t (1)
[0075] In the above expression (1), subscript "(i)" indicates a
value (of the displacement "X") detected in the present control
cycle, and "(i-1)" indicates a value (of the displacement "X")
detected in the previous control cycle, while "(i+1)" indicates an
estimated value to be obtained in the next control cycle.
[0076] After the actual drive velocity "Va" is calculated as
described above, step 120 is executed to calculate an FF current
"If" based on the valve displacement "X", with reference to the map
as indicated in FIG. 4 or 5.
[0077] Step 130 is then executed to determine whether an air gap
"G" between the armature 28 and the electromagnet 61 or 62 is equal
to or less than a predetermined value "G1" (step 130).
[0078] The air gap "G" is defined as a distance between the
armature 28 and one of the upper core 32 and the lower core 34
toward which the armature 28 is moving. More specifically, the air
gap "G" corresponds to a distance between the armature 28 and the
lower core 34 when the exhaust valve 10 is about to be fully
opened. When the exhaust valve 10 is about to be closed., on the
other hand, the air gap "G" corresponds to a distance between the
armature 28 and the upper core 32.
[0079] In step 130, it is determined whether to start feedback
control based on the FB current "Ib" depending upon the size of the
air gap "G". Here, the size of the air gap "G" is used as a basis
for determining whether to start the feedback control for the
following reason.
[0080] Assuming that substantially the same level of exciting
current is supplied to the electromagnet 61 or 62, the
electromagnetic force acting on the armature 28 is reduced with an
increase in the air gap "G". In other words, as the air gap "G"
increases, an increased proportion of the electric energy supplied
to the electromagnet 61 or 62 is likely to be wastefully consumed
without contributing to attraction (or driving) of the armature 28
toward the corresponding core. In the above-described process,
therefore, the feedback control based on the velocity deviation
".DELTA.V" is performed only after it is determined that the air
gap "G" is equal to or less than the predetermined value "G1". If
the air gap "G" is greater than the predetermined value "G1", which
means that the armature 28 is driven by the electromagnet 61 or 62
to be attracted to the corresponding core 32 or 34 with a reduced
electric efficiency, the feedback control is substantially stopped
by setting the FB current "Ib" to "0", so as to minimize the
increase in the power consumption.
[0081] If it is determined in step 130 that the air gap "G" is
equal to or less than the predetermined value "G1" ("YES" in step
130), step 140 is executed to calculate a target drive velocity
"Vt" with reference to the map as indicated in FIG. 3. Step 150 is
then executed to calculate the velocity deviation ".DELTA.V"
according to the following expression (2):
.DELTA.Va=.vertline.Vt.vertline.-.vertline.Va.vertline. (2)
[0082] In the above expression (2), ".vertline.Vt.vertline." and
".vertline.Va.vertline." represent the magnitudes (absolute values)
of the target drive velocity "Vt" and the actual drive velocity
"Va", respectively.
[0083] In step 160, the FB current "Ib" is calculated according to
the following expression (3), based on the velocity deviation
.DELTA.V obtained in step 150.
Ib=K.multidot..DELTA.V (3)
[0084] In the above expression (3), "K" is a feedback gain, and is
set to a constant value in this embodiment.
[0085] It is to be noted that if the magnitude of the external
force acting on the valve body 16 of the exhaust valve 10 increases
in accordance with the engine load, the velocity deviation
".DELTA.V" increases with an increase in the degree of deviation of
the actual drive velocity "Va" from the target drive velocity "Vt".
Therefore, the FB current "Ib", which is equal to the product of
the velocity deviation ".DELTA.V" and the feedback gain "K", is set
to a level that can compensate for the influence of the engine
load.
[0086] Conversely, if it is determined in step 130 that the air gap
"G" is greater than the predetermined value "G1" ("NO" in step
130), step 165 is executed to set the FB current "Ib" to "0".
[0087] After the FB current "Ib" is thus determined in step 160 or
step 165, a final command current "I", which is to be applied to
the electromagnet 61 or 62, is calculated according to the
following expression (4) in step 170.
I=Ib+If (4)
[0088] If the magnitude .vertline.Va.vertline. of the actual drive
velocity "Va" is greater than the magnitude .vertline.Vt.vertline.
of the target drive velocity "Vt", and the calculated FB current
"Ib" becomes a negative value whereby the command current "I"
calculated according to the above expression (4) would be a
negative value, the command current "I" is set to "0".
[0089] In step 180, the command current "I" thus determined is
applied to a selected one of the electromagnets 61, 62. More
specifically, the command current "I" is supplied to the lower coil
46 so as to open the exhaust valve 10, while the command current
"I" is supplied to the upper coil 42 so as to close the exhaust
valve 10 . In this manner, the magnitude of the electromagnetic
force generated by each electromagnet 61, 62 is controlled through
control of electric current applied to the corresponding
electromagnet 61, 62. The process of FIG. 7 is then terminated
after execution of step 180.
[0090] FIG. 8 indicates time-dependent changes in the valve
displacement "X" ((a) in FIG. 8), the FB current "Ib" ((b) in FIG.
8), the FF current "If" ((c) in FIG. 8), and the sum (command
current "I") of the FB current "Ib" and the FF current "If" ((d) in
FIG. 8) in the case where the exhaust valve 10 is driven to the
fully open position in accordance with the process of FIG. 7. Each
of the FB current "Ib", FF current "If" and the command current "I"
is applied to the lower coil 46 so that the exhaust valve 10 is
opened. In the section (a) of FIG. 8, a solid line indicates the
actual valve displacement "X", and a one-dot chain line indicates
the valve displacement "X" in the case where the exhaust valve 10
is moved such that the actual drive velocity "Va" is kept equal to
the target drive velocity "Vt".
[0091] As indicated in FIG. 8, during a period between a point of
time (t1) when the supply of the FF current "If" to the upper coil
42 (which is not shown in FIG. 8) is stopped and the exhaust valve
10 starts being driven in the opening direction, and a point of
time (t2) when the air gap "G" reaches the predetermined value
"G1", all of the FF current "If", the FB current "Ib" and the
command current "I" applied to the lower coil 46 are equal to"0",
and therefore the movable portion of the exhaust valve 10 is moved
toward the fully open position under the bias force of the upper
spring 38.
[0092] Subsequently, when the air gap "G" decreases to be equal to
the predetermined value "G1" at time t2, the FB current "Ib" is
calculated from that point on as a value corresponding to the
velocity deviation ".DELTA.V". Therefore, the command current I is
calculated as a value equal to the FB current "Ib", and thus the
feedback control alone is executed in the period between t2 and
t3.
[0093] When the valve displacement X then reaches the predetermined
value "X1" at a point of time t3, the FF current "If" starts being
calculated as a value corresponding to the valve displacement "X".
Accordingly, the command current "I" is calculated as the sum of
the FF current "If" and the FB current "Ib", so that the
feed-forward control and the feedback control are both executed in
the period between t3 and t4.
[0094] Subsequently, when the actual drive velocity "Va" of the
exhaust valve 10 settles to be equal to the target drive velocity
"Vt", the velocity deviation ".DELTA.V" naturally becomes "0", and
the FB current "Ib" also becomes equal to "0". Thus, as long as
this condition (Va=Vt) is satisfied, the command current "I" is set
equal to the FF current "If", so that only the feed-forward control
is substantially executed (in the period between t4 and t5).
Subsequently, when the valve displacement "X" reaches the fully
open position at a point of time t5, the FF current "If" is set
equal to the hold current value "If2" from that point on, so that
the exhaust valve 10 is held at the fully open position.
[0095] This embodiment, in which the driving of the engine valve
(an intake valve or an exhaust valve) is controlled in the
above-described manner, yields the following advantages.
[0096] (1) Even when the external force that acts on the engine
valve changes in accordance with the engine load, the engine valve
is driven with a suitable electromagnetic force corresponding to
the engine load, so that the engine valve exhibits substantially
the same opening and closing characteristics as when no load is
applied to the engine.
[0097] Furthermore, since the influence of the engine load is
compensated for or cancelled through the feedback control, the FF
current in the feed-forward control can be set as a value that
enables the actual drive velocity to coincide with the target drive
velocity set for a no-load state, without regard to the actual
engine load. Accordingly, there is no need to consider the
influence of the engine load when setting the FF current, thus
eliminating the correlating or matching operation to determine a
relationship between the engine load and the electromagnetic force
suitable for the engine load through experiments, or the like.
Hence, the operation to correlate control constants can be
considerably simplified.
[0098] (2) Furthermore, the target drive velocity of the engine
valve is set so that the magnitude of the drive velocity decreases
to a minimum immediately before the valve reaches one end of its
stroke, that is, the fully closed position or the fully open
position. With this arrangement, it is possible to reduce noise and
vibrations at the time of opening or closing of the engine valve,
and achieve a reduction in the consumption of electric power
required for driving the engine valve.
[0099] (3) Still further, the target drive velocity is set to be
equal to the velocity of displacement of the engine valve when it
is freely oscillated between the opposite ends of the stroke of the
valve shaft under elastic forces of the upper and lower springs.
Thus, the engine valve can be driven in a manner that minimizes the
energy loss, and therefore the power consumption can be
reduced.
[0100] (4) When it is determined that the air gap "G" is greater
than the predetermined value "G1" and the armature 28 is attracted
to the upper or lower core by the corresponding electromagnet 61,
62 with a relatively low electric efficiency, the feedback control
is substantially stopped by setting the FB current to "0", thereby
suppressing an otherwise possible increase in the power
consumption.
Second Embodiment
[0101] A second embodiment of the invention will be described
mainly with regard to differences of this embodiment from the first
embodiment.
[0102] In the first embodiment, the feedback gain "K" used in the
calculation of the FB current "Ib" based on the velocity deviation
".DELTA.V" is set to a constant value. In the second embodiment,
the feedback gain "K" can be varied depending upon the size of the
air gap "G" and the magnitude of the velocity deviation
".DELTA.V".
[0103] A procedure of setting the feedback gain "K" in this manner
will be described with reference to FIG. 9. FIG. 9 shows a map
indicating a relationship among the air gap "G", the velocity
deviation ".DELTA.V" and the feedback gain "K". The relationship
indicated in the map is stored in advance as function data in the
memory of the electronic control unit 50.
[0104] As indicated in the map, the feedback gain "K" is set to one
of predetermined values K1, K2, K3, K4 and K5 corresponding to
respective regions A, B, C, D and E that are determined in
accordance with the air gap "G" and the velocity deviation
".DELTA.V". With regard to the predetermined values K1 to K5, the
relationship as indicated in the following expression (5) is
established in advance.
K1>K2>K3>K4>K5 (5)
[0105] (1) Region A
[0106] If the velocity deviation ".DELTA.V" is equal to or greater
than a predetermined value ".DELTA.V1" (>0), the feedback gain
"K" is set to the predetermined value "K1" without regard to the
size of the air gap "G". In the region A, the magnitude
.vertline.Va.vertline. of the actual drive velocity "Va" is
considerably less than the magnitude .vertline.Vt.vertline. of the
target drive velocity "Vt", and the exhaust valve 10 may suffer
from loss of synchronism.
[0107] In the region A, the electromagnetic force of each
electromagnet 61, 62 is increased by setting the feedback gain "K"
to the maximum value, so that the actual drive velocity "Va" will
be quickly settled to be equal to the target drive velocity
"Vt".
[0108] (2) Region B
[0109] If the velocity deviation ".DELTA.V" is less than "0", the
feedback gain "K" is set to the predetermined value "K5" regardless
of the size of the air gap "G". In the region B, the magnitude
.vertline.Va.vertline. of the actual drive velocity "Va" is greater
than the magnitude .vertline.Vt.vertline. of the target drive
velocity "Vt", and there is a possibility that the velocity of the
movable portion becomes high at the moment when the exhaust valve
10 reaches the fully open position or the fully closed position.
Furthermore, in the region B, the FB current "Ib" is calculated as
a negative value. If the feedback gain K is large, therefore, the
FF current "If" is substantially reduced due to this negative FB
current "Ib", whereby the command current "I" becomes excessively
small, which may result in a loss of synchronism of the exhaust
valve 10.
[0110] In the region B, the feedback gain "K" is set to the
smallest value among all the regions A-E, for example, is set to
"0". As a result, the feedback control term (FB current "Ib") of
the command current "I" is reduced to suppress an increase in the
actual drive velocity "Va". At the same time, a suitable amount of
feed-forward control term (FF current "If" ) of the command current
"I" is secured so that a loss of synchronism that would be
otherwise caused by an excessively reduced command current "I" can
be avoided or suppressed as much as possible.
[0111] (3) Regions C. D. E
[0112] If the velocity deviation ".DELTA.V" is equal to or greater
than "0" but is less than the predetermined value ".DELTA.V1", the
feedback gain "K" is set to one of the predetermined values K2, K3,
K4 corresponding to the regions C, D, E that are defined depending
upon the size of the air gap "G". That is, in the regions C, D, E,
the feedback gain "K" is set to greater values as the air gap "G"
increases. Assuming that the same exciting current is supplied to
the electromagnet 61 or 62, the magnitude of the electromagnetic
force that acts on the armature 28 is reduced with an increase in
the air gap "G". In general, the magnitude of the electromagnetic
force is inversely proportional to the size of the air gap "G".
[0113] In the regions C, D, E, the feedback gain "K" is set to
larger values as the air gap G increases, so as to cause the
electromagnet 61 or 62 to generate an appropriate magnitude of
electromagnetic force in accordance with the size of the air gap
"G". Thus, the actual drive velocity "Va" can be controlled to
reliably follow the target drive velocity "Vt" to be equal to this
value "Vt" in a relatively short time.
[0114] In step 160 in the flowchart of FIG. 7, the feedback gain
"K" is set to one of the predetermined values K1 to K5 based on the
air gap "G" and the velocity deviation ".DELTA.V", and then the FB
current "Ib" is determined from the above-indicated expression
(3).
[0115] This embodiment yields the advantages (1) to (4) as
described above in conjunction with the first embodiment, and
yields an additional advantage as follows.
[0116] (5) Since the feedback gain is set to greater values as the
air gap increases, an appropriate magnitude of the electromagnetic
force that is suitable for the size of the air gap can be generated
at the electromagnet 61 or 62. Thus, the actual drive velocity can
be controlled to reliably follow the target drive velocity to be
equal to this target value in a relatively short time.
Third Embodiment
[0117] A third embodiment of the invention will be described mainly
with regard to differences of this embodiment from the first and
second embodiments.
[0118] In the second embodiment, the feedback gain K is set to one
of different values corresponding to the regions A to E that are
defined depending upon the air gap "G" and the velocity deviation
".DELTA.V". Therefore, even if there is a strong non-linearity in
the relationship between the air gap "G" and the magnitude of the
electromagnetic force that acts on the engine valve, an
approximately linear relationship can be established between the
air gap "G" and the electromagnetic force in each of the regions
A-E, and the feedback gain "K" can be thus set to an optimal value
in each region A-E.
[0119] Although the aforementioned gain scheduling is effective to
cause the actual drive velocity "Va" to quickly follow and coincide
with the target drive velocity Vt, the gain scheduling requires a
correlating or matching operation for pre-setting an optimal
feedback gain K for each region.
[0120] In the third embodiment, therefore, a physical model is
constructed which includes the engine valve drive velocity as a
model variable. By using the physical model, a required value of
electromagnetic force needed to make the actual drive velocity "Va"
equal to the target drive velocity "Vt" is calculated. More
specifically, an equation of motion that simulates the behavior of
an engine valve during the opening and closing thereof is
determined. Based on the equation of motion, a response analysis of
the engine valve is conducted so as to calculate the aforementioned
required value of the electromagnetic force.
[0121] FIG. 10 illustrates an internal combustion engine that
employs a drive control apparatus for controlling engine valves (an
intake valve 11 and an exhaust valve 10) according to the third
embodiment. The engine of FIG. 10 includes an in-cylinder pressure
sensor 54 that detects the pressure in the combustion chamber
(which will be called "in-cylinder pressure"), an intake pressure
sensor 56 that detects the internal pressure of an intake passage
13 (which will be called "intake pressure"), and an exhaust
pressure sensor 58 that detects the internal pressure of an exhaust
passage 17 (which will be called "exhaust pressure"). The intake
pressure sensor 56 may also be used as a sensor for detecting the
amount of the intake air, or the flow rate of the intake air, based
on the intake pressure and the engine speed, during the air-fuel
ratio control, for example. Furthermore, the in-cylinder pressure
sensor 54, which is used for estimating an external force that acts
on each engine valve, may be eliminated if the internal combustion
engine is equipped with a combustion pressure sensor that detects
the combustion pressure, namely, the maximum in-cylinder pressure
during the combustion stroke. In this case, the combustion pressure
sensor also performs the function of the in-cylinder pressure
sensor 54.
[0122] A procedure of calculating a required value of
electromagnetic force in an exemplary case in which the exhaust
valve 10 is opened and closed will be described with reference to
the flowchart shown in FIG. 11 and the graph as shown in FIG.
12.
[0123] The process as illustrated in the flowchart of FIG. 11 is
implemented after the supply of hold current to one of the upper
and lower coils 42, 46 is stopped upon opening or closing the
exhaust valve 10 (for example, after time t1 or time t6 in FIG. 2).
The process is repeatedly executed by the electronic control unit
50 in at predetermined time intervals .DELTA.t. FIG. 12, which is
similar to FIG. 6, indicates the actual drive velocity "Va" and the
target drive velocity "Vt" in relation to the valve displacement
"X". In the following, there will be described the case where the
target drive velocity "Vt" changes from point A to point B via
point D along a solid line in FIG. 12 as the exhaust valve 10 is
opened.
[0124] In the process of FIG. 11, step 200 is initially executed to
read the valve displacement "X(i)" in the current control cycle
based on a detection signal from the displacement sensor 52. Step
210 is then executed to calculate an actual drive velocity "Va(i)"
(that corresponds to point C in FIG. 12) according to the
above-indicated expression (1). In order to reduce the influence of
noise on the detection signal of the displacement sensor 52, it is
preferable to perform a filtering process, such as a first-order
lag process, for removing a high-frequency component(s) emphasized
by the noise , on the actual drive velocity "Va" calculated as
described above.
[0125] Subsequently, step 220 is executed to estimate a valve
displacement "X(i+1)" to be attained in the next control cycle
according to the following expression (6), and read a target drive
velocity "Vt(i+1)" (refer to point D in FIG. 12) corresponding to
the valve displacement "X(i+1)" based on the relationship between
the valve displacement "X" and the target drive velocity "Vt" as
indicated in FIG. 12.
X.sub.(i+1)=X.sub.(1)+Va.sub.(i).multidot..DELTA.t (6)
[0126] Next, a required value of acceleration (required
acceleration "a") of the exhaust valve needed to make the actual
drive velocity "Va" (=Va(i)) of the exhaust valve 10 equal to the
target drive velocity "Vt" (=Vt(i+1)) is calculated in step 230
according to the following expression (7).
a=(Vt.sub.(i+1)-Va.sub.(i))/.DELTA.t (7)
[0127] After the required acceleration "a" is calculated, an
external force "F" that acts on the exhaust valve 10 is estimated
in step 240 according to the following expression (8).
F=fa-fb (8)
[0128] In the above expression (8), "fa" represents the force that
acts on the exhaust valve 10, and particularly, on the valve body
16, in accordance with a pressure difference between the
in-cylinder pressure and the exhaust pressure. For example, "fa" is
calculated according to the following expression (9). For the
estimation of an external force that acts on the intake valve 11 as
an engine valve, the intake pressure detected by the intake
pressure sensor 56 is used in place of the exhaust pressure as
described below.
fa=K1.multidot.(Pc-Pe) (9)
[0129] K1: constant
[0130] Pc: in-cylinder pressure
[0131] Pe: exhaust pressure
[0132] Furthermore, in the above expression (8), "fb" represents
frictional resistance at various sliding portions of the exhaust
valve 10, and is set to a constant value that is predetermined
through experiments or the like. Since the magnitude of the
frictional resistance changes depending upon the state of
lubrication at each sliding portion, in particular, upon the
temperature of the lubricant, the frictional resistance "fb" may be
estimated or determined as a function of the engine temperature.
For example, the frictional resistance "fb" is set to larger values
as the engine temperature (estimated from, e.g., the temperature of
the engine cooling water) is lower.
[0133] By modeling the exhaust valve 10 as a spring-mass vibration
system, an equation of motion (10) as indicated below is obtained.
In the following expression (10), the valve displacement "X(i)" is
equal to 0 at a reference position when the exhaust valve 10 is
positioned at the aforementioned neutral position.
m.multidot.a+c.multidot.Va.sub.(i)+k.multidot.X.sub.(i)=F+Fem
(10)
[0134] In the above expression (10), "m" represents the mass of the
vibration model, and is set based on, for example, the mass of the
movable portion of the exhaust valve 10, and "c" represents the
damping coefficient of the vibration model, and is set based on,
for example, the resisting force generated at various sliding
portions of the exhaust valve 10 depending upon the sliding speed
thereof. Furthermore, "k" represents the spring coefficient of the
vibration model, and is set based on the elastic characteristics of
the upper spring 38 and the lower spring 24, and "Fem" represents a
required value of the electromagnetic force of the electromagnet 61
or 62 needed to make the actual drive velocity "Va" of the exhaust
valve 10 equal to the target drive velocity "Vt".
[0135] From the equation of motion (10), an expression (11) as
indicated below is derived. In step 250, the required
electromagnetic force value "Fem" is calculated according to the
expression (11).
Fem=m.multidot.a+c.multidot.Va.sub.(i)+k.multidot.X.sub.(i)-F
(11)
[0136] Subsequently, step 260 is executed to calculate the command
current "I" supplied to the coil 42, 46 of the electromagnet 61, 62
based on the required electromagnetic force "Fem". FIG. 13 shows a
map that is referred to when calculating the command current "I".
The map indicates a relationship among the required electromagnetic
force "Fem", the air gap "G" and the command current "I". The
relationship indicated in this map is pre-stored as function data
in the memory of the electronic control unit 50.
[0137] As indicated in FIG. 13, the command current "I" is set to
greater values as the required electromagnetic force "Fem"
increases and the air gap "G" increases. The command current "I" is
set as indicated in the map of FIG. 13 since a relationship as
represented by expression (12) below is established among the
required electromagnetic force "Fem", the air gap "G" and the
command current "I".
Fem.varies.(I/G).sup.2 (12)
[0138] After the command current "I" is thus calculated, step 270
is executed to apply the command current "I" to a selected one of
the electromagnets 61, 62. More specifically, the command current
"I" is supplied to the lower coil 46 when the exhaust valve 10 is
to be opened, and the command current "I" is supplied to the upper
coil 42 when the exhaust valve 10 is to be closed. After the
magnitude of the electromagnetic force of each of the
electromagnets 61, 62 is controlled through control of current
applied to each electromagnet 61, 62 in this manner, the process of
FIG. 11 is once terminated.
[0139] The third embodiment, in which driving of the engine valve
is controlled in the above manner, yields the advantages (2) to (4)
stated above in conjunction with the first embodiment, and further
yields an advantage as follows.
[0140] (6) Even in the case where the external force that acts on
the engine valve changes depending upon the engine load, the engine
valve is driven with suitable electromagnetic force that is
controlled in accordance with the engine load, so as to assure
opening and closing characteristics that are equivalent to those
obtained when there is no engine load.
[0141] Furthermore, using a model in which the engine valve is
modeled as a spring-mass vibration system, the opening and closing
behavior of the engine valve is simulated in order to calculate a
required value of the electromagnetic force. Therefore, it is not
necessary to perform a correlating or matching operation in advance
so as to empirically obtain a relationship between the engine load
and the electromagnetic force suitable for the engine load through
experiments, or the like. Accordingly, the correlating operation
with respect to control constants can be greatly simplified. Still
further, the modeling of the engine valve as described above
eliminates the need to set an optimal feedback gain in accordance
with the air gap, thus further simplifying the correlating
operation.
Fourth Embodiment
[0142] A fourth embodiment of the invention will be described
mainly with regard to differences of this embodiment from the third
embodiment.
[0143] In the third embodiment, the actual drive velocity "Va" is
calculated based on the above-indicated expression (1) (in step 210
in FIG. 11). Also, the force that acts on the engine valve in
accordance with the engine load, namely, the force that acts on the
exhaust valve 10 in accordance with a pressure difference between
the in-cylinder pressure and the exhaust pressure, or the force
that acts on the intake valve 11 in accordance with a pressure
difference between the in-cylinder pressure and the intake
pressure, is estimated (in step 240 in FIG. 11) based on the
in-cylinder pressure, the exhaust pressure and the intake pressure
detected by the pressure sensors 54, 56, 58, respectively.
[0144] In the fourth embodiment, on the other hand, an observer is
set which observes an internal state of the engine valve based on a
vibration model of a spring-mass system used for simulating the
opening and closing behavior of the engine valve. The observer is
used for estimating an actual drive velocity of the engine valve,
and also estimating a resultant force, which is a sum of the force
that acts on the engine valve due to the pressure difference
between the in-cylinder pressure and the exhaust pressure or the
intake pressure, and the frictional resistance at the sliding
portions of the engine valve. Accordingly, the in-cylinder pressure
sensor 54 and the exhaust pressure sensor 58, out of the
aforementioned pressure sensors 54, 56, 58, are omitted or
eliminated from the engine valve drive control apparatus according
to this embodiment.
[0145] A procedure of estimating the external force that acts on an
engine valve, for example, the exhaust valve 10 in this case, by
means of the aforementioned observer will be described below.
[0146] By modeling the exhaust valve 10 as a spring-mass vibration
system, an equation of motion (13) is obtained. In the equation of
motion (13), the parameters "m", "c" and "k" are the same as those
as defined in the aforementioned expression (10). Also, "x"
represents a valve displacement of the exhaust valve 11, and "u"
represents a control input applied to the vibration model, namely,
the electromagnetic force of each electromagnet 61, 62.
Furthermore, "w" represents an external force that acts on the
exhaust valve 10, which is a resultant force that is a sum of the
force "fa" that acts on the exhaust valve 10 due to the pressure
difference between the in-cylinder pressure and the exhaust
pressure, and the frictional resistance "fb" that arises at the
sliding portions of the exhaust valve 10.
m.multidot.{dot over (x)}+c.multidot.{dot over
(x)}+k.multidot.x=w+u (13)
[0147] Here, a state variable "X" is defined as indicated in the
following expression (14). 1 X = ( x x .degree. w ) ( 14 )
[0148] From the above-indicated expressions (13) and (14), the
state equation (15) is obtained with respect to the vibration model
of the exhaust valve 10.
{dot over (X)}=A.multidot.X+B.multidot.u (15)
[0149] 2 A = ( 0 1 0 - k m - c m 1 m 0 0 0 ) B = ( 0 1 m 0 )
[0150] An output equation with respect to the vibration model of
the exhaust valve 10 is given as indicated in the following
expression (16).
Y=C.multidot.X (16)
[0151] C=(100)
[0152] Next, an observer for determining an estimated value "Z" of
the valve displacement "X" is written as indicated in the following
expression (17). In the expression (17), "L" represents an observer
gain.
{dot over (Z)}A.multidot.Z+B.multidot.u+L(Y-C.multidot.Z) (17)
[0153] 3 Z = ( x _ x . _ w _ ) ( x _ , x . _ , w _ are estimated
values of x , x .degree. , w , respectively . )
[0154] An estimated error "e" between the valve displacement "X"
and an estimated value "Z" thereof (e=X-Z) can be determined from
the following expression (18) derived from the above-indicated
expressions (15) to (17).
{dot over (e)}=(A-L.multidot.C)e (18)
[0155] By suitably designing the observer gain "L" so that the
estimated error "e" determined according to the expression (18)
converges or settles to "0", the estimated value "Z" can be
determined from the above expression (17). In other words, it
becomes possible to estimate the drive velocity (actual drive
velocity "Va") of the exhaust valve 10. If the control input "u" is
set to "0" in the above-indicated expressions (15) and (17), for
example, the external force "w" can be estimated. The thus
estimated external force "w" includes the electromagnetic force of
each electromagnet 61, 62, in addition to the force "fa" that acts
on the exhaust valve 10 due to the pressure difference between the
in-cylinder pressure and the exhaust pressure, and the frictional
resistance "fb". Therefore, by subtracting the electromagnetic
force currently generated at the electromagnet 61 or 62 from the
estimated external force "w", it is possible to estimate the
resultant force "F" of the frictional resistance "fb" and the force
"fa" that acts on the valve due to the pressure difference between
the in-cylinder pressure and the exhaust pressure.
[0156] In this embodiment, the required acceleration "a" is
calculated (in step 230 in FIG. 11) from the actual drive velocity
"Va" of the exhaust valve 10 estimated through the use of the
observer and the target drive velocity "Vt" set based on the map
shown in FIG. 12, and the required electromagnetic force "Fem" is
calculated (in step 250) based on the required acceleration "a" and
the external force "F" estimated through the observer.
Subsequently, the command current I is calculated (in step 260)
based on the required electromagnetic force "Fem". Then, the
command current "I" is applied to a selected one of the
electromagnets 61, 62 (in step 270).
[0157] The fourth embodiment, in which driving of the engine valve
is controlled in the above-described manner, yields substantially
the same advantages as those of the third embodiment, and further
yields advantages as follows.
[0158] (7) The observer that observes an internal state of the
engine valve is set based on the vibration model of the spring-mass
system that simulates the opening and closing behavior of the
engine valve is set. Since the external force that acts on the
engine valve is estimated by using the observer, there is no need
to newly provide sensors, such as an in-cylinder pressure sensor
and an exhaust pressure sensor, for estimating the external force.
Hence, the construction of the engine valve drive control apparatus
can be simplified.
[0159] (8) Even in the case where the frictional resistance at the
sliding portions of the engine valve changes depending upon, for
example, the engine temperature, not to mention the force that
changes depending upon the engine load, the external force can be
accurately estimated in accordance with variations in the
frictional resistance. Thus, the external force can be estimated
with improved accuracy, whereby the actual drive velocity can be
more favorably controlled to quickly follow the target drive
velocity to coincide with the target value in a short time.
[0160] (9) According to the above-indicated expression (1), the
actual drive velocity of the engine valve is calculated by
differentiating the detection signal of the displacement sensor 52.
In this case, if noise is mixed into the detection signal of the
displacement sensor 52, the influence of the noise is emphasized by
the differentiation process, and therefore the accuracy with which
the actual drive velocity is calculated tends to be reduced. In
this respect, this embodiment utilizes the observer for estimating
the actual drive velocity of the engine valve as well as the
external force. This makes it possible to reduce an adverse
influence of the noise, and control the drive velocity of the
engine valve so that the actual drive velocity quickly follows the
target drive velocity to coincide with the target value in a short
time.
Fifth Embodiment
[0161] A fifth embodiment of the invention will be described mainly
with regard to differences of this embodiment from the third
embodiment.
[0162] The fifth embodiment differs from the third embodiment in
that a physical model of the engine valve is described based on an
equation of conservation of energy instead of the equation of
motion. More specifically, an amount of actual kinetic energy of
the engine valve is calculated based on the actual drive velocity
of the engine valve while an amount of target kinetic energy of the
engine valve is calculated based on the target drive velocity, and
a deviation of the actual kinetic energy amount from the target
kinetic energy amount is calculated. Furthermore, a required value
of electromagnetic force is calculated based on the energy amount
deviation and the equation of conservation of energy with regard to
the engine valve. Among the respective pressure sensors 54, 56, 58,
the in-cylinder pressure sensor 54 and the exhaust pressure sensor
58 are omitted or eliminated from an engine valve drive control
apparatus according to this embodiment of the invention.
[0163] A procedure of calculating the required electromagnetic
force in an exemplary case where the exhaust valve 10 is opened and
closed will be described with reference to the flowchart shown in
FIG. 14.
[0164] A series of steps as illustrated in the flowchart of FIG. 14
are executed after the supply of hold current to the upper or lower
coil 42 or 46 is stopped upon opening or closing of the exhaust
valve 10 (for example, after time t1 or time t6 in FIG. 2). The
process of FIG. 14 is repeatedly executed by the electronic control
unit 50 at predetermined time intervals .DELTA.t.
[0165] Initially, steps 300 to 320 are executed to calculate the
actual drive velocity "Va(i)" of the exhaust valve 10 in the
current control cycle, and read a target drive velocity "Vt(i+1)"
to be achieved in the next control cycle. The contents of the
operations of steps 300 to 320 are the same as those of steps 200
to 220 in FIG. 11, and therefore will not be described herein.
[0166] Step 330 is then executed to calculate an actual kinetic
energy amount "Ea" of the exhaust valve 10 in the current control
cycle according to the following expression (19).
Ea=(1/2)m.multidot.Va.sup.2(i)+(1/2) k.multidot.X.sup.2(i) (19)
[0167] The first term in the right-hand side of the expression (19)
is the amount of kinetic energy of the modeled exhaust valve 10,
and "m" in the same term is a coefficient set based on, for
example, the mass of the movable portion of the exhaust valve 10.
The second term in the right-hand side of the above expression (19)
is the amount of elastic energy of the modeled exhaust valve 10,
and "k" in the same term is a coefficient set based on the elastic
characteristics of the armature 28, the lower spring 24, and the
like.
[0168] Subsequently, step 340 is executed to calculate a target
kinetic energy amount "Et" of the exhaust valve 10 for the next
control cycle according to the following expression (20).
Et=(1/2) m.multidot.Vt.sup.2(i+1)+(1/2)k.multidot.X.sup.2(i+1)
(20)
[0169] After the actual kinetic energy amount "Ea" and the target
kinetic energy amount "Et" are calculated as described above, step
350 is executed to calculate a deviation ".DELTA.E" of the actual
kinetic energy "Ea" from the target kinetic energy "Et" according
to the following expression (21).
.DELTA.E=Et-Ea (21)
[0170] The deviation ".DELTA.E" of the energy amount varies
depending upon the external force that acts on the exhaust valve
10, including the force that acts on the valve 10 depending upon
the engine load, and the frictional resistance at sliding portions
of the valve 10. Namely, if there is no such external force on the
exhaust valve 10, the amount of kinetic energy of the exhaust valve
10 will be always constant and will not change. In an actual
operation, however, the amount of kinetic energy of the exhaust
valve 10 changes due to the influence of the external force, and a
deviation arises between the actual kinetic energy amount "Ea" and
the target kinetic energy amount "Et". Therefore, by determining
the deviation ".DELTA.E" between the amounts of kinetic energy "Ea"
and "Et", and setting a required value of the electromagnetic force
based on the deviation ".DELTA.E" of energy amount, it is possible
to control electromagnetic force so as to reflect the influence of
the external force, without directly determining the magnitude of
the external force.
[0171] A specific manner of control of electromagnetic force in the
above case will be described. In order to make the actual kinetic
energy amount "Ea" equal to the target kinetic energy amount "Et"
in the next control cycle, the amount of work "Fem(X(i+1)-X1(i))"
that is done by use of the electromagnetic force of the
electromagnet 61, 62 during a period between the current control
cycle and the next control cycle, that is, the amount of energy
given to the exhaust valve 10 during that period, needs to be equal
to the deviation .DELTA.E of energy amount that occurs due to the
external force acting on the exhaust valve 10 . Namely, the
relationship as represented by the following expression (22) needs
to be established between the deviation ".DELTA.E" and the
aforementioned amount of work Fem(X(i+1)-X1(i)).
.DELTA.E=Fem(X(i+1)-X1(i)) (22)
[0172] Accordingly, the required electromagnetic force "Fem" is
finally calculated in step 360 based on the expression (23) that is
derived from the expression (22).
Fem=.DELTA.E/(X(i+1)-X1(i)) (23)
[0173] After the required electromagnetic force "Fem" is calculated
in this manner, steps 370 and 380 are executed to calculate the
command current "I" supplied to the upper or lower coil 42, 46 of
the electromagnet 61, 62, and apply the thus obtained command
current "I" to a selected one of the electromagnets 61, 62. The
contents of the operations of steps 370, 380 are the same as those
of steps 260, 270 in FIG. 11, and will not be described herein.
[0174] The fifth embodiment, in which driving of the engine valve
is controlled in the above-described manner, yields substantially
the same advantages as those of the third embodiment, and further
yields an advantage as described below, which is substantially the
same as the advantage (7) of the fourth embodiment.
[0175] (10) In the fifth embodiment, the required electromagnetic
force is calculated by using the equation of conservation of energy
with regard to the engine valve. In this calculation, the magnitude
of the energy amount deviation reflects the influences of external
forces that act on the engine valve, including the force that acts
on the valve depending upon the engine load and the frictional
resistance at the sliding portions of the valve. Thus, there is no
need to directly calculate the external force. This makes it
unnecessary to newly provide a sensor or sensors, such as an
in-cylinder pressure sensor and an exhaust pressure sensor, for
estimating the external force, which may lead to further
simplification of the construction of the engine valve drive
control apparatus.
[0176] The invention may also be carried out by changing or
modifying the embodiments as illustrated above.
[0177] In the second embodiment, the feedback gain "K" is variably
set to one of the predetermined values "K1" to "K5" corresponding
to the regions A to E that are defined in accordance with the
feedback gain "K" and the air gap "G". It is, however, possible to
select a manner of setting the feedback gain "K" as desired. For
example, the feedback gain "K" may be set based solely on the air
gap "G" such that the feedback gain "K" stepwise increases as the
size of the air gap "G" increases. Alternatively, the feedback gain
"K" may be set so as to continuously change in accordance with the
air gap "G", by using the following expression (24) instead of a
map.
K=Ka.multidot.G+Kb (24)
[0178] G: air gap
[0179] Ka, Kb: constants
[0180] While the feedback gain "K" is set to the predetermined
value "K1" in the region "A" in the second embodiment, it is
possible to set the feedback gain "K" to a value that is greater
than the predetermined value "K1" in the region "A" when the air
gap "G" is small, namely, when the exhaust valve 10 is close to the
fully open position or the fully closed position. Namely, if the
velocity deviation ".DELTA.V" is greater than the predetermined
value ".DELTA.V1" when the exhaust valve 10 is approaching the
fully open position or the fully closed position, the actual drive
velocity "Va" may become 0 before the exhaust valve 10 reaches the
fully open position or the fully closed position, resulting in a
loss of synchronism. By setting the feedback gain "K" in the
above-described manner, such a loss of synchronism is avoided as
much as possible.
[0181] In the first and second embodiments, both the feedback
control and the feed-forward control are carried out by setting the
command current "I" to be applied to the electromagnet 61 or 62,
based on the FB current "Ib" and the FF current "If". It is,
however, also possible to perform the feedback control alone, for
example, to apply only the FB current "Ib" to a selected one of the
electromagnets 61, 62.
[0182] While only the P term (proportional term) of the PID control
is calculated when calculating the FB current "Ib" based on the
velocity deviation ".DELTA.V" in the first and second embodiments,
it is also possible to calculate the I term (integral term) and the
D term (differential term) as well.
[0183] While the feedback control is started when the air gap "G"
decreases to or below the predetermined value "G1" in the
illustrated embodiments, it is also practicable to always perform
the feedback control regardless of the size of the air gap "G".
[0184] While the velocity deviation ".DELTA.V" between the actual
drive velocity "Va" and the target drive velocity "Vt" is
calculated as a parameter that indicates the degree of separation
between the actual drive velocity "Va" and the target drive
velocity "Vt" in the first and second embodiments, it is also
possible to evaluate the degree of separation using the ratio of
the actual velocity "Va" to the target velocity "Vt", i.e.,
Va/Vt.
[0185] In the third embodiment, the required acceleration "a" is
calculated based on the actual drive velocity "Va(i)" in the
current control cycle and the target drive velocity "Vt(i+1)"
(estimated value) corresponding to the valve displacement "X(i+1)"
(estimated value) for the next control cycle, it is also possible
to calculate the required acceleration "a" based on the actual
drive velocity "Va(i)" in the current control cycle and the target
drive velocity "Vt(i)" corresponding to the valve displacement
"X(i)" (actually measured value) in the current control cycle.
[0186] In the third embodiment, the force that acts on the exhaust
valve 10 in accordance with the engine load is estimated based on
the pressure difference between the in-cylinder pressure and the
exhaust pressure. Here, it is to be noted that the in-cylinder
pressure greatly changes in accordance with the operating state of
the engine whereas the exhaust pressure does not change so much as
compared with the in-cylinder pressure. Therefore, the exhaust
pressure may be regarded as a constant pressure, and the force that
acts on the exhaust valve 10 may be estimated based solely on the
in-cylinder pressure. Furthermore, since the in-cylinder pressure
and the exhaust pressure are related with each other, the exhaust
pressure may be estimated based on the in-cylinder pressure. In
this case, the exhaust pressure sensor 58 may be eliminated, and
the construction of the drive control apparatus can be
simplified.
[0187] While the intake pressure used for the estimation of the
exhaust pressure is directly detected by the intake pressure sensor
56, the intake pressure may be estimated based on, for example, the
amount of intake air (or the flow rate of intake air) detected by
an air flow meter, the engine speed, and other parameters.
[0188] While the required electromagnetic force "Fem" is calculated
based on the above-indicated expression (23) in the fifth
embodiment, it is also possible to estimate the external force
acting on the engine valve in the current control cycle, and to add
the force that cancels out the estimated external force, that is,
the force applied in the direction opposite to the direction of the
estimated external force, to the value obtained from the expression
(23), and set the result of the addition as the required
electromagnetic force value "Fem". With this arrangement, the
energy amount deviation caused by the external force is cancelled
out in a feed-forward manner by the canceling force, so that the
actual drive velocity "Va" follows the target drive velocity "Vt"
with improved accuracy to coincide with the target value in a
relatively short time. In this modified example, the external force
may be estimated based on the detection signals from the pressure
sensors 54, 55, 58 as described above in the third embodiment, or
may be estimated by using an observer as in the fourth
embodiment.
[0189] While the command current "I" is calculated based on the
graph of FIG. 13 in the third to fifth embodiments, the command
current "I" may be calculated by any other method provided that the
command current "I" is set to greater values with increases in the
required electromagnetic force "Fem" and in the size of the air gap
"G". For example, the command current "I" may be calculated based
on a function expression (25) by way of example.
I=Kc.multidot.G.multidot.{square root}{square root over (Fem)}+Kd
(25)
[0190] where Kc, Kd: constants.
* * * * *