U.S. patent application number 12/269948 was filed with the patent office on 2009-05-21 for internal combustion engine electric discharge structure.
This patent application is currently assigned to NISSAN MOTOR CO., LTD.. Invention is credited to Taisuke SHIRAISHI, Eiji TAKAHASHI, Tomonori URUSHIHARA.
Application Number | 20090126668 12/269948 |
Document ID | / |
Family ID | 40350117 |
Filed Date | 2009-05-21 |
United States Patent
Application |
20090126668 |
Kind Code |
A1 |
SHIRAISHI; Taisuke ; et
al. |
May 21, 2009 |
INTERNAL COMBUSTION ENGINE ELECTRIC DISCHARGE STRUCTURE
Abstract
An internal combustion engine electric discharge structure is
provided which comprises a first electrode and a dielectric
material. The first electrode includes a first voltage receiving
end and a second engine attachment end with a long thin conductive
material that discharges non-equilibrium plasma. The dielectric
material covers the first electrode.
Inventors: |
SHIRAISHI; Taisuke;
(Yokohama-shi, JP) ; TAKAHASHI; Eiji;
(Yokosuka-shi, JP) ; URUSHIHARA; Tomonori;
(Yokohama-shi, JP) |
Correspondence
Address: |
GLOBAL IP COUNSELORS, LLP
1233 20TH STREET, NW, SUITE 700
WASHINGTON
DC
20036-2680
US
|
Assignee: |
NISSAN MOTOR CO., LTD.
Yokohama
JP
|
Family ID: |
40350117 |
Appl. No.: |
12/269948 |
Filed: |
November 13, 2008 |
Current U.S.
Class: |
123/145A |
Current CPC
Class: |
H01T 13/50 20130101;
F02P 3/01 20130101 |
Class at
Publication: |
123/145.A |
International
Class: |
F23Q 7/22 20060101
F23Q007/22 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 16, 2007 |
JP |
2007-298294 |
Claims
1. An internal combustion engine electric discharge structure
comprising: a first electrode including a first voltage receiving
end and a second engine attachment end with a long thin conductive
material that discharges non-equilibrium plasma by a barrier
discharge; and a dielectric material covering the first
electrode.
2. The internal combustion engine electric discharge structure of
claim 1, further comprising a second electrode facing the first
electrode on a periphery of the dielectric material.
3. The internal combustion engine electric discharge structure of
claim 2, wherein the second electrode includes a tubular electrode
surrounding at least a portion of the first electrode.
4. The internal combustion engine electric discharge structure of
claim 3, further comprising a cylinder head having the second
electrode attached thereto, with the first electrode including a
linear central electrode.
5. The internal combustion engine electric discharge structure of
claim 2, wherein the first electrode includes a linear central
electrode; and the second electrode is disposed as at least part of
one of a wall surface of a combustion chamber and a top surface of
a piston.
6. The internal combustion engine electric discharge structure of
claim 2, further comprising a fuel injection valve for supplying
fuel into a combustion chamber of an internal combustion engine;
and a voltage application device operatively coupled to the first
voltage receiving end of the first electrode for applying a voltage
between the first electrode and the second electrode, such that the
non-equilibrium plasma generates radicals within the combustion
chamber before an air-fuel mixture in the combustion chamber
undergoes autoignition.
7. The internal combustion engine electric discharge structure of
claim 6, further comprising a control unit operatively coupled to
the voltage application device to vary a discharge start timing of
the non-equilibrium plasma discharge in accordance with a
mechanical load of the internal combustion engine.
8. The internal combustion engine electric discharge structure of
claim 7, wherein the control unit sets the discharge start timing
of the non-equilibrium plasma discharge to occur during an intake
stroke when the mechanical load of the internal combustion engine
is comparatively low.
9. The internal combustion engine electric discharge structure of
claim 8, wherein the control unit sets the discharge start timing
of the non-equilibrium plasma discharge to be increasingly advanced
as the mechanical load of the internal combustion engine becomes
lower.
10. The internal combustion engine electric discharge structure of
claim 7, wherein the control unit sets the discharge start timing
of the non-equilibrium plasma discharge to occur during a
compression stroke when the mechanical load of the internal
combustion engine is comparatively high.
11. The internal combustion engine electric discharge structure of
claim 10, wherein the control unit sets the discharge start timing
of the non-equilibrium plasma discharge to be increasingly delayed
as the mechanical load of the internal combustion engine
increases.
12. The internal combustion engine electric discharge structure of
claim 6, further comprising a control unit operatively coupled to
the voltage application device to set a discharge start timing of
the non-equilibrium plasma discharge to occur after an intake valve
has opened.
13. The internal combustion engine electric discharge structure of
claim 6, further comprising a control unit operatively coupled to
the voltage application device to set a discharge ending timing of
the non-equilibrium plasma discharge to occur before an intake
valve has closed.
14. The internal combustion engine electric discharge structure of
claim 6, further comprising a control unit operatively coupled to
the voltage application device to set a discharge energy of the
non-equilibrium plasma discharge such that the discharge energy
increases as the mechanical load of the internal combustion engine
becomes lower when the mechanical load of the internal combustion
engine is in a low load range.
15. The internal combustion engine electric discharge structure of
claim 14, wherein the control unit increases the discharge energy
of non-equilibrium plasma discharge by at least one method selected
from increasing a voltage value of an AC voltage applied between
the first and second electrodes, increasing a frequency of the AC
voltage applied between the first and second electrodes, and
increasing an application duration of the AC voltage applied
between the first and second electrodes.
16. The internal combustion engine electric discharge structure of
claim 6, further comprising a variable compression ratio mechanism
arranged to change a mechanical compression ratio of the internal
combustion engine; and a control unit operatively coupled to the
variable compression ratio mechanism to reduce the mechanical
compression ratio so that an air-fuel mixture does not undergo
compression ignition when a mechanical load of the internal
combustion engine is in a high load range, and volumetric ignition
is performed.
17. The internal combustion engine electric discharge structure of
claim 6, further comprising a fuel injection control unit
operatively coupled to the fuel injection valve to control
injection of fuel directly into a cylinder of the internal
combustion engine such that a stratified air-fuel mixture is formed
in the cylinder when a mechanical load of the internal combustion
engine is in a low load range.
18. An internal combustion engine control method for controlling an
operating state of an internal combustion engine, comprising:
determining a mechanical load of the internal combustion engine;
injecting fuel into a combustion chamber of the internal combustion
engine; applying a voltage to an electric discharge device having a
first electrode and a second electrode to produce a non-equilibrium
plasma discharge generating radicals within the combustion chamber
before an air-fuel mixture of the fuel undergoes autoignition; and
setting a discharge start timing of the non-equilibrium plasma
discharge such that the discharge start timing varies in accordance
with the mechanical load.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to Japanese Patent
Application No. 2007-298294, filed on Nov. 16, 2007. The entire
disclosure of Japanese Patent Application No. 2007-298294 is hereby
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to an internal
combustion engine electric discharge structure. More specifically,
the present invention relates to an electric discharge structure
which discharges non-equilibrium plasma in order to increase a
number of radicals and thereby improve autoignition properties of
the internal combustion engine.
[0004] 2. Background Information
[0005] An electric discharge device has been proposed for an
internal combustion engine in which the air-fuel mixture is ignited
in an assisted manner by a sparkplug. In this electric discharge
device radicals are generated in a cylinder and the autoignition
properties of the air-fuel mixture are improved (see, Japanese
Laid-Open Patent Application No. 2001-20842). The radicals tend to
induce oxidation reactions (i.e., combustion), and the oxidation
reactions (combustion) tend to become chain reactions. Therefore,
when radicals are generated in the cylinder, the autoignition
properties of the air-fuel mixture are improved.
[0006] In view of the above, it will be apparent to those skilled
in the art from this disclosure that there exists a need for an
improved internal combustion engine electric discharge structure.
This invention addresses this need in the art as well as other
needs, which will become apparent to those skilled in the art from
this disclosure.
SUMMARY OF THE INVENTION
[0007] As mentioned above, it has been discovered that, in order to
improve the autoignition properties of the air-fuel mixture, a
sparkplug can be used to generate radicals in the cylinder.
However, since spark ignition is a thermal plasma discharge, the
efficiency of radical generation is low even if spark ignition is
induced by a sparkplug as in the conventional apparatus previously
described. Moreover, in this conventional apparatus the amount of
radicals generated is limited. It is therefore believed that the
effects of improving the autoignition properties are small.
[0008] The present invention was designed in view of such
conventional problems. One object of the present invention is to
provide an electric discharge structure which is used in an
internal combustion engine and which can improve the autoignition
properties of an air-fuel mixture beyond that of conventional
practice, and to provide a method for controlling the operation of
the internal combustion engine.
[0009] In accordance with a first aspect, an internal combustion
engine electric discharge structure is provided which basically
comprises a first electrode and a dielectric material. The first
electrode includes a first voltage receiving end and a second
engine attachment end with a long thin conductive material that
discharges non-equilibrium plasma. The dielectric material covers
the first electrode.
[0010] These and other objects, features, aspects and advantages of
the present invention will become apparent to those skilled in the
art from the following detailed description, which, taken in
conjunction with the annexed drawings, discloses preferred
embodiments of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Referring now to the attached drawings which form a part of
this original disclosure:
[0012] FIG. 1 is a simplified schematic cross-sectional view of a
portion of a multi-link engine that is part of an electric
discharge structure in accordance with a first embodiment;
[0013] FIG. 2A is a partial cross-sectional view of the electric
discharge structure of the engine shown in FIG. 1;
[0014] FIG. 2B is a cross-sectional view of the electric discharge
structure illustrated in FIG. 2A, taken along section line 2B-2B of
FIG. 2A;
[0015] FIG. 3A is a diagram showing the electric discharges
obtained when an AC voltage (electric potential) is applied to a
spark ignition discharge mechanism in accordance with a comparative
example of a conventional discharge mechanism;
[0016] FIG. 3B is a diagram showing the electric discharges
obtained when an AC voltage (electric potential) is applied to the
electric discharge structure in accordance with the first
illustrated embodiment;
[0017] FIG. 4 is a diagram showing various methods for increasing
the discharge energy of the electric discharge structure;
[0018] FIG. 5 is a graph showing the problems with forming
non-equilibrium plasma by the application of short pulses in
accordance with a comparative example of a conventional discharge
mechanism;
[0019] FIG. 6A is a simple link diagram showing the arrangement of
a multi-link variable compression ratio mechanism at a high
compression ratio;
[0020] FIG. 6B is a simple link diagram showing the arrangement of
the multi-link variable compression ratio mechanism at a low
compression ratio;
[0021] FIG. 6C is a simple link diagram showing the method for
varying the compression ratio using the multi-link variable
compression ratio mechanism;
[0022] FIG. 7 is a perspective view of a variable valve timing
mechanism for adjusting the opening and closing timing of a
valve;
[0023] FIG. 8A is a simplified elevational view of the variable
valve timing mechanism when valves are in a closed state;
[0024] FIG. 8B is a simplified elevational view of the variable
valve timing mechanism when the valves are in a state of maximum
lift;
[0025] FIG. 8C is a simplified elevational view showing the
variable valve timing mechanism when the stroke amount of cam
followers is minimized, cam noses are at the highest position, and
the valves are in a closed state;
[0026] FIG. 8D is a simplified elevational view of the variable
valve timing mechanism when the stroke amount of cam followers is
minimized, the cam noses are at the lowest position, and the valves
are in a closed state;
[0027] FIG. 9 is a graph showing the valve lift amount and the
opening and closing timings in the variable valve timing
mechanism;
[0028] FIG. 10A is a graph showing the relationship of an air-fuel
ratio to various operational states of the engine having the
electric discharge structure in accordance with the first
embodiment;
[0029] FIG. 10B is a graph showing the relationship of a barrier
discharge start timing to various operational states of the engine
having the electric discharge structure in accordance with the
first embodiment;
[0030] FIG. 10C is a graph showing the relationship of discharge
energy to various operational states of the engine having the
electric discharge structure in accordance with the first
embodiment;
[0031] FIG. 10D is a graph showing the relationship of an intake
valve close timing to various operational states of the engine
having the electric discharge structure in accordance with the
first embodiment;
[0032] FIG. 10E is a graph showing the relationship of a mechanical
compression ratio to various operational states of the engine
having the electric discharge structure in accordance with the
first embodiment;
[0033] FIG. 11 is a graph showing the variation in the heat
generation rate depending on if and when the barrier discharge
start timing begins;
[0034] FIG. 12A is a drawing schematically depicting the state in
which radicals are distributed within the cylinder when barrier
discharge does not occur;
[0035] FIG. 12B is a drawing schematically depicting the state in
which radicals are distributed within the cylinder when barrier
discharge is initiated during compression stroke;
[0036] FIG. 12C is a drawing schematically depicting the state in
which radicals are distributed within the cylinder when barrier
discharge is initiated during intake stroke;
[0037] FIG. 13 is a graph showing the relationship between the
barrier discharge start timing and the crank angle at which the
mass combustion ratio is 50%;
[0038] FIG. 14 is a graph showing the piston behavior in a
multi-link variable compression ratio mechanism;
[0039] FIG. 15 is a graph showing the relationship between the
air-fuel ratio and combustion stability;
[0040] FIG. 16 is a graph showing the problems due to the heat
generation rate suddenly increasing to an excessive degree, and the
effects of the illustrated embodiment;
[0041] FIG. 17A is a graph showing the correlation between an
air-fuel ratio and a fluctuation rate of the depicted average
effective pressure;
[0042] FIG. 17B is a graph showing that a fuel consumption rate can
be reduced if a lean combustion limit is expanded;
[0043] FIG. 18 is a simplified schematic cross-sectional view of a
portion of an engine that is part of an electric discharge
structure in accordance with a second embodiment;
[0044] FIG. 19 is a simplified schematic cross-sectional view of a
portion of the engine showing the manner in which fuel is injected
into the engine in accordance with the second embodiment;
[0045] FIG. 20A is a graph showing the relationship of an air-fuel
ratio to various operational states of the engine having the
electric discharge structure in accordance with the second
embodiment;
[0046] FIG. 20B is a graph showing the relationship of a barrier
discharge start timing to various operational states of the engine
having the electric discharge structure in accordance with the
second embodiment;
[0047] FIG. 20C is a graph showing the relationship of discharge
energy to various operational states of the engine having an
electric discharge structure in accordance with the second
embodiment;
[0048] FIG. 20D is a graph showing the relationship of an intake
valve close timing to various operational states of the engine
having an electric discharge structure in accordance with the
second embodiment;
[0049] FIG. 20E is a graph showing the relationship of a mechanical
compression ratio to various operational states of the engine
having an electric discharge structure in accordance with the
second embodiment;
[0050] FIG. 21 is a partial cross-sectional view showing the
operational configuration of the engine having an electric
discharge structure in accordance with a third embodiment;
[0051] FIG. 22A is a partial cross-sectional view showing the
operational configuration of the engine having an electric
discharge structure in accordance with a fourth embodiment where a
barrier discharge is formed within a combustion chamber;
[0052] FIG. 22B is a partial cross-sectional view showing the
operational configuration of the engine having an electric
discharge structure in accordance with a fourth embodiment where a
barrier discharge is formed within a concave part of a top surface
of a piston;
[0053] FIG. 23A is a partial cross-sectional view showing the
operational configuration of the engine having an electric
discharge structure in accordance with a fifth embodiment where a
barrier discharge is formed within a combustion chamber;
[0054] FIG. 23B is a partial cross-sectional view showing the
operational configuration of the engine having an electric
discharge structure in accordance with a fifth embodiment where a
barrier discharge is formed within a concave part of a top surface
of a piston;
[0055] FIG. 24A is a diagram showing a waveform of an alternating
current as a sine curve applied to the electric discharge
structure; and
[0056] FIG. 24B is a diagram showing a waveform of an alternating
current as a bipolar multiple pulse applied to the electric
discharge structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0057] Selected embodiments of the present invention will now be
explained with reference to the drawings. It will be apparent to
those skilled in the art from this disclosure that the following
descriptions of the embodiments of the present invention are
provided for illustration only and not for the purpose of limiting
the invention as defined by the appended claims and their
equivalents.
[0058] First, the essential technological ideas relating to the
internal combustion engine electric discharge structure will be
described.
[0059] As described above, an engine has been proposed in which
spark ignition generates radicals (chemically active species which
are in a state wherein molecular dissociation is induced by the
collision of high-energy electrons with fuel or air molecules, and
which promote ignition of an air-fuel mixture) in a cylinder and in
which the autoignition properties (compression ignition properties)
of the air-fuel mixture are improved.
[0060] However, the effects of improving ignition properties in
such an engine have been small. Specifically, spark ignition
involves a thermal plasma discharge. In a thermal plasma discharge,
kinetic energy is adequately exchanged among electrons, ions, and
molecules. The result is an establishment of a state of thermal
equilibrium in which the electron energy, the ion energy, and the
neutral particle energy are in equilibrium with each other.
Radicals are chemically active species which are in a state wherein
molecular dissociation is induced by collisions of high-energy
electrons with fuel or air molecules, and which promote ignition of
the air-fuel mixture. In spark ignition, energy is also imparted to
ions and molecules which do not contribute to the generation of
radicals, and the efficiency of conversion of input energy to
electron energy is low. When the input energy is increased in order
to increase the amount of radicals, there is a possibility that the
electrodes will melt. Therefore, it is difficult to increase the
amount of radicals.
[0061] In view of this, a non-equilibrium plasma discharge is
preferred. In a non-equilibrium plasma discharge, a thermally
non-equilibrium state is achieved in which the electron temperature
(electron energy) alone is extremely high (specifically, electron
energy is much higher than ion energy and ion energy is equal to
neutral particle energy), and the efficiency of converting input
energy to electron energy is high. Heat loss is small in a
non-equilibrium plasma discharge because the gas temperature is not
increased. The danger that the electrodes will melt is also
small.
[0062] Because of such reasons, radicals can be generated
comparatively easily if a non-equilibrium plasma discharge is used.
In view of this, a non-equilibrium plasma discharge mechanism for
an engine is proposed herein. To conduct a non-equilibrium plasma
discharge, possibilities include methods using a barrier discharge
and methods using short pulse application. It has been discovered
that of these methods, a barrier discharge is particularly
preferable.
[0063] Now referring to FIG. 1, a simplified schematic
cross-sectional view of a portion of a multi-link engine 1 is
illustrated that forms a part of an electric discharge structure in
accordance with a first embodiment. As explained hereinafter, the
multi-link engine 1 utilizes a non-equilibrium plasma discharge
function, preferably barrier discharge, to improve the autoignition
properties of the multi-link engine 1.
[0064] The engine 1 is provided with a barrier discharge device 70.
The barrier discharge device 70 is provided between an intake port
60a and an exhaust port 60b, substantially in the center of a
combustion chamber of a cylinder head. The barrier discharge device
70 generates radicals through barrier discharge, which is a
non-equilibrium plasma discharge. The barrier discharge device 70
is also capable of igniting an air-fuel mixture through barrier
discharge at a comparatively high load (when the air-to-fuel ratio
of the air-fuel mixture is comparatively rich). The detailed
structure of the barrier discharge device 70 will be described
hereinafter with reference to an enlarged view (FIG. 2).
[0065] The engine 1 having a barrier discharge function according
to the present embodiment has a variable compression ratio
mechanism (hereinafter referred to as a "multi-link variable
compression ratio mechanism"), which uses a multi-link mechanism
for connecting a piston 32 to a crankshaft 33 by two links. The
multi-link variable compression ratio mechanism connects the piston
32 to the crankshaft 33 by an upper (first) link 11 and a lower
(second) link 12. The multi-link variable compression ratio
mechanism also controls the lower link 12 by using a control
(third) link 13 to vary the mechanical compression ratio.
[0066] The upper link 11 is connected at the top end to the piston
32 via a piston pin 21. The upper link 11 is connected at the
bottom end to one end of the lower link 12 via a connecting pin 22.
The piston 32 receives combustion pressure that moves the piston 32
within a cylinder 31a of a cylinder block 31 back and forth.
[0067] The lower link 12 is connected at one end to the upper link
11 via the connecting pin 22. The lower link 12 is connected at the
other end to the control link 13 via a connecting pin 23. The lower
link 12 also has a substantially central connecting hole in which
crank pins 33b of the crankshaft 33 are disposed. Thus, the lower
link 12 oscillates around the crank pins 33b as a center axis. The
lower link 12 is divided into two left and right members. The
crankshaft 33 comprises a plurality of crank journals 33a and a
plurality of crank pins 33b for each cylinder. The journals 33a are
rotatably supported by the cylinder block 31 and a ladder frame 34.
The crank pins 33b are eccentric relative to the crank journals 33a
by a predetermined amount, and the lower link 12 is oscillatably
connected thereto.
[0068] The control link 13 is connected to the lower link 12 via
the connecting pin 23. The control link 13 is also connected at the
other end to a control shaft 25 via a connecting pin 24. The
control link 13 oscillates or rocks around the connecting pin 24. A
gear is formed on the control shaft 25, and this gear meshes with a
pinion 53 provided to a rotating axle 52 of an actuator 51. The
control shaft 25 is rotated by the actuator 51 to move the
connecting pin 24.
[0069] Various sensors are provided for sensing the operating state
of the engine, including the engine rotation speed and the engine
load. The signals of various sensors are inputted to a controller
90. The controller 90 controls the actuator 51 to rotate the
control shaft 25 and vary the compression ratio. The controller 90
also controls a high-voltage high-frequency generator 80 so that
the AC voltage value, the application duration, the AC frequency,
the application timing, and other parameters corresponding to the
operating state of the engine are applied. Thus, the controller 90
may be considered to constitute a non-equilibrium plasma discharge
control unit. In addition, the high-voltage high-frequency
generator 80 constitutes a voltage application device. Furthermore,
the controller 90 controls the fuel injection of a fuel injection
valve 65 provided to the intake port 60a. An intake valve 61 is
capable of varying the opening and closing timings thereof, as is
described hereinafter. The controller 90 determines the engine load
and performs control according to the load. The controller 90 is
configured from a microcomputer comprising a central processing
unit (CPU), a read-only memory (ROM), a random access memory (RAM),
and an input/output interface (I/O interface). The controller 90
can also be configured from a plurality of microcomputers.
[0070] FIGS. 2A and 2B contain enlarged cross-sectional views of
the barrier discharge device 70. The barrier discharge device 70 of
the illustrated embodiment discharges non-equilibrium plasma by
using a barrier discharge. Non-equilibrium plasma can also be
formed by applying a short pulse instead of forming a barrier
discharge, but barrier discharge is preferred in the illustrated
embodiment. The reasons for this are described hereinafter.
[0071] The barrier discharge device 70 comprises a central
electrode 71 and a tubular electrode 72. The central electrode 71
is a rod-shaped electrical conductor. The entire periphery of the
central electrode 71 is covered by a dielectric material
(insulating material) 73. The central electrode 71 is connected to
the high-voltage high-frequency generator 80 via a terminal 71a. An
AC voltage is applied to the central electrode 71 upon being
generated by the high-voltage high-frequency generator 80. The
value, application duration, AC frequency, application timing, and
other characteristics of the AC voltage are controlled (set)
according to the operating state of the engine 1,
[0072] The tubular electrode 72 is a tubular electrical conductor.
The tubular electrode 72 is attached to the cylinder head. The
inner periphery side of the tubular electrode 72 is a discharge
chamber 72a. The central electrode 71 protrudes into the discharge
chamber 72a. The central electrode 71 is provided on the top side
of the substantial center of the fuel chamber. The center of the
central electrode is substantially parallel to a line extending
through the center of the fuel chamber. The distance from the
central electrode 71 to the dielectric material and the distance
from the dielectric material to the tubular electrode 72 are set to
be substantially the same.
[0073] When an AC voltage is applied to the central electrode 71
from the high-voltage high-frequency generator 80, streamers S are
generated between the tubular electrode 72 and the dielectric
material 73 as shown in FIG. 2A. A plurality of streamers S is
generated in the vertical direction as shown in FIG. 2A. The
streamers are branched into thin streaks, and FIG. 2A shows a state
in which six streamers are generated on both the right and left
sides of the dielectric material 73. The streamers are also formed
in a radial pattern about the dielectric material 73, as shown in
FIG. 2B. FIG. 2B shows a state in which twelve streamers are formed
in a radial pattern about the dielectric material 73. The barrier
discharge device 70 can generate a large amount of radicals in the
discharge chamber 72a by forming a plurality of streamers S. It is
also possible for multipoint simultaneous ignition, i.e., a
volumetric ignition (hereinafter referred to as "volume ignition"),
to occur within the discharge chamber.
[0074] The barrier discharge device 70 can perform multiple
electric discharges within a predetermined time, whereby a large
amount of radicals can be generated in the discharge chamber 72a.
This will be described with reference to FIGS. 3A and 3B. FIGS. 3A
and 3B contain views showing the electric discharge obtained when
an AC voltage (electric potential) is applied. FIG. 3A is a diagram
showing the electric discharges obtained when an AC voltage
(electric potential) is applied by a spark ignition discharge
mechanism in accordance with a comparative example of a
conventional discharge mechanism. FIG. 3B is a view showing the
electric discharges obtained when an AC voltage (electric
potential) is applied by the electric discharge structure in
accordance with the illustrated embodiment.
[0075] First, as a comparison, a case will be described in which an
AC voltage is applied to the spark ignition discharge mechanism of
a conventional sparkplug. In cases in which an AC voltage is
applied to the sparkplug, an arc discharge occurs between the
electrodes when the absolute value of an electric potential V.sub.0
formed between the electrodes by the applied voltage reaches a
discharge voltage (insulation breakdown electric potential) Va, as
shown in FIG. 3A. Arc discharge similarly occurs when the polarity
is inverted. With this sparkplug, four arc discharges occur within
the discharge time t as shown in FIG. 3A. A discharge takes place
in one location, and the form of the discharge is either point or
linear.
[0076] In the barrier discharge device 70, the dielectric material
(insulating material) 73 covers the central electrode 71. The
dielectric material 73 acts as a capacitor. After a barrier
discharge (non-equilibrium plasma discharge) has occurred, an
electric charge is accumulated on the surface of the dielectric
material 73. The barrier discharge (non-equilibrium plasma
discharge) occurs between the dielectric material 73 and the
tubular electrode 72 when the absolute value of the difference
between the electric potential V.sub.0 created by the applied
voltage and the electric potential Vw created by the surface
electric charge of the dielectric material 73 reaches a discharge
voltage Vd, as shown in FIG. 3B. Therefore, streamers S are formed
at a plurality of locations in the discharge chamber 72a in the
barrier discharge device 70, and eight barrier discharges
(non-equilibrium plasma discharges) occur within the discharge time
t, as shown in FIG. 3B.
[0077] Thus, the barrier discharge device 70 can increase the
number of discharges in the same time (discharge time t) to a
greater level than that obtained with a sparkplug in a conventional
method.
[0078] Though not shown in the drawings, increasing the voltage
value of the AC voltage in the barrier discharge device 70 also
makes more likely that the absolute value of the difference between
the electric potential V.sub.0 created by the applied voltage and
the electric potential Vw created by the surface electric charge of
the dielectric material 73 will reach the discharge voltage Vd, and
makes it possible to increase the number of discharges.
[0079] FIG. 4 is a diagram showing various methods for increasing
the discharge energy of the electric discharge structure.
[0080] The discharge energy of the barrier discharge device 70 is
controlled by the voltage value, application duration, and AC
frequency of the AC voltage from the high-voltage high-frequency
generator 80. One possibility for increasing the discharge energy
of the barrier discharge device 70 is a method for increasing the
voltage value of the AC voltage in the manner shown in plot (B-1)
of FIG. 4 relative to the waveform of a reference AC applied
voltage (plot (A) of FIG. 4). The discharge energy of the barrier
discharge part can also be increased by increasing the frequency of
the AC voltage, the applied duration as in plot (B-2) of FIG. 4, or
the AC frequency as in plot (B-3) of FIG. 4.
[0081] As described above, another method for forming
non-equilibrium plasma aside from initiating a barrier discharge is
a method for forming non-equilibrium plasma by applying a short
pulse between the electrodes and blocking the electric potential
before the transition to an arc discharge. However, a barrier
discharge is preferred in the illustrated embodiment. The reasons
for this are described with reference to FIG. 5 which is a graph
showing the problems with forming non-equilibrium plasma by the
application of short pulses in accordance with a comparative
example of a conventional discharge mechanism.
[0082] To form non-equilibrium plasma by the application of short
pulses, the required voltage (electric potential) corresponding to
the discharge location (density, air-fuel mixture composition, and
the like) must be applied. Non-equilibrium plasma is generated if
the voltage V1 is applied at a pressure P0, but when the voltage V2
is applied, thermal plasma is generated, as shown in FIG. 5. Thus,
non-equilibrium plasma or thermal plasma is generated merely by
slight variations in the applied voltage, and the discharge lacks
robustness with short pulse application.
[0083] By contrast, with a barrier discharge, the electrodes are
originally covered on one side with a dielectric material, and the
voltage is kept substantially within a range that extends from the
discharge start voltage (lower limit of voltage) to a voltage at
which the withstand-voltage properties of the dielectric material
can be ensured (upper limit of voltage), whereby non-equilibrium
plasma can always be maintained regardless of the voltage. An arc
transition does not take place because the electrodes are covered
by a dielectric material. Thus, discharge robustness is high. In an
internal combustion engine, the potential required for a discharge
varies extensively, and it is difficult to form non-equilibrium
plasma by the application of short pulses. Therefore,
non-equilibrium plasma based on a barrier discharge is preferable
for application in an internal combustion engine.
[0084] FIGS. 6A-6C are simple link diagrams showing the arrangement
of a multi-link variable compression ratio mechanism. With a
multi-link variable compression ratio mechanism, the mechanical
compression ratio can be varied by rotating the control shaft 25
and varying the position of the connecting pin 24. For example, if
the connecting pin 24 is at position A as shown in FIG. 6C, the top
dead center (TDC) is at a high level, resulting in a high
compression ratio. If the connecting pin 24 is at position B as
shown in FIGS. 6B and 6C, the control link 13 is pushed upward, and
the position of the connecting pin 23 rises. The lower link 12 is
thereby rotated counterclockwise around the crank pins 33b, the
connecting pin 22 moves down, and the piston 32 in the piston top
dead center (TDC) moves to a lower position. Therefore, the
compression ratio is low.
[0085] FIG. 7 is a perspective view showing a variable valve timing
mechanism for adjusting the opening and closing timing of a valve.
The engine 1 having a barrier discharge function comprises a
variable valve timing mechanism 200. The mechanism disclosed, for
example, in Japanese Laid-Open Patent Application No. 11-107725 can
be used as the variable valve timing mechanism 200. This is
described with reference to the drawings.
[0086] The variable valve timing mechanism 200 comprises a camshaft
210, a link arm 220, a valve lift control shaft 230, a rocker arm
240, a link member 250, and oscillating cams 260. Cam followers 63
are pushed by the oscillation of the oscillating cams 260, thus
opening and closing valves (intake valves) 61.
[0087] The camshaft 210 is rotatably supported at the top part of
the cylinder head along the longitudinal direction of the engine.
One end of the camshaft 210 is inserted through a cam sprocket 270.
The cam sprocket 270 is rotated by the transmission of torque from
a crank axle of the engine. The camshaft 210 rotates together with
the cam sprocket 270. The camshaft 210 can rotate relative to the
cam sprocket 270 by hydraulic pressure, and the phase of the
camshaft 210 relative to the cam sprocket 270 can be varied. This
type of structure makes it possible to vary the rotational phase of
the camshaft 210 relative to the crank axle. A cam 211 is fixed to
the camshaft 210. The cam 211 rotates integrally with the camshaft
210. The pair of oscillating cams 260 connected by pipes is
inserted through the camshaft 210. The oscillating cams 260
oscillate around the camshaft 210 as a rotational center, and the
cam followers 63 perform a stroke.
[0088] The link arm 220 is supported by the insertion of the cam
211. The valve lift control shaft 230 is disposed parallel to the
camshaft 210. A cam 231 is formed integrally on the valve lift
control shaft 230. The valve lift control shaft 230 is controlled
by an actuator 280 so as to rotate within a predetermined range of
rotational angles.
[0089] The rocker arm 240 is supported by the insertion of the cam
231 and is connected to the link arm 220. The link member 250 is
connected to the rocker arm 240.
[0090] The camshaft 210 is inserted through the oscillating cams
260, which can oscillate around the camshaft 210. The oscillating
cams 260 are connected to the link member 250. The oscillating cams
260 move up and down, pushing down on the cam followers 63 and
opening and closing the valves 61.
[0091] Next, the action of the variable valve timing mechanism 200
will be described with reference to FIGS. 8A-8D.
[0092] FIGS. 8A and 8B are views showing the manner in which the
stroke amount of the cam followers 63 is maximized to maximize the
lift amount of the valves 61. FIG. 8A shows the manner in which cam
noses 262 are at their highest positions, and the oscillation
direction of the oscillating cams 260 is inverted. At this time,
the cam followers 63 are at top end positions, and the valves 61
are in a closed state. FIG. 8B shows the manner in which the cam
noses 262 are at their lowest positions, and the oscillation
direction of the oscillating cams 260 is inverted. At this time,
the cam followers 63 are at bottom end positions, and the valves 61
are in a state of maximum lift.
[0093] FIGS. 8C and 8D are views showing the manner in which the
stroke amount of the cam followers 63 is minimized. FIG. 8C shows
the manner in which the cam noses 262 are at their highest
positions and the oscillating direction of the oscillating cams 260
is inverted. FIG. 8D shows the manner in which the cam noses 262
are at their lowest positions and the oscillation direction of the
oscillating cams 260 is inverted. In the present embodiment, the
stroke amount of the cam followers 63 is zero, and the lift amount
of the valves 61 is also zero. Therefore, in FIGS. 8C and 8D, the
valves 61 are always in a closed state regardless of the action of
the oscillating cams 260.
[0094] To increase the stroke amount of the cam followers 63 and
the lift amount of the valves 61, the valve lift control shaft 230
is rotated to lower the position of the cam 231 and to set the
axial center P1 below the axial center P2, as shown in FIGS. 8A and
8B. The entire rocker arm 240 is thereby moved downward.
[0095] When the camshaft 210 is rotatably driven in this state, the
drive force is transmitted first to the link arm 220 and then to
the rocker arm 240, the link member 250, and the oscillating cams
260.
[0096] When the cam 211 is to the left of the camshaft 210, as
shown in FIG. 8A, the base-circle parts 261 of the oscillating cams
260 are in contact with the cam followers 63, at which time the cam
followers 63 are at the top end position and the valves 61 are in a
state of maximum lift.
[0097] When the cam 211 is to the right of the camshaft 210, as
shown in FIG. 8B, the cam noses 262 of the oscillating cams 260 are
in contact with the cam followers 63, at which time the cam
followers 63 are at the bottom end positions and the valves 61 are
in an opened state.
[0098] To reduce the stroke amount of the cam followers 63 and the
lift amount of the valves 61, the valve lift control shaft 230 is
rotated to raise the position of the cam 231, and the axial center
P1 is set above and to the right of the axial center P2, as shown
in FIGS. 8C and 8D. The entire rocker arm 240 is thereby moved
upward. When the camshaft 210 is rotatably driven in this state,
the drive force is transmitted first to the link arm 220 and then
to the rocker arm 240, the link member 250, and the oscillating
cams 260. When the cam 211 is to the left of the camshaft 210, as
shown in FIG. 8C, the base-circle parts 261 of the oscillating cams
260 are in contact with the cam followers 63. When the cam 211 is
to the right of the camshaft 210, as shown in FIG. 8D, the
base-circle parts 261 of the oscillating cams 260 are still in
contact with the cam followers 63.
[0099] Thus, in cases in which the valve lift control shaft 230 is
rotated, the position of the cam 231 is raised, and the axial
center P1 is set above and to the right of the axial center P2, the
cam followers 63 do not perform a stroke and the valves 61 remain
closed, even though the camshaft 210 rotates and the oscillating
cams oscillate.
[0100] FIG. 9 is a graph showing the valve lift amount and the
opening and closing timings in the variable valve timing mechanism
200. The solid lines indicate the lift amount and the opening and
closing timings of the valves 61 when the valve lift control shaft
230 is rotated. The dashed lines indicate the opening and closing
timings of the valves 61 when the phase of the camshaft 210 is
varied relative to the cam sprocket 270.
[0101] According to the structure of the variable valve timing
mechanism 200 described above, the lift amount and operating angle
of the valves 61 can be continually varied. Thus, the lift amount
and operating angle of the valves 61 can be continually and freely
varied by varying the angle of the valve lift control shaft 230 and
the phase of the camshaft 210 relative to the cam sprocket 270.
[0102] FIGS. 10A-10E are graphs showing an example of an operation
map of the engine having a barrier discharge function. The range of
extremely low load (for example, engine is an idol state) will now
be discussed. When the load is in a range of extremely low load,
the air-fuel ratio A/F is set to a constant value (FIG. 10A). Also,
the barrier discharge start timing is set to a constant timing of
the intake stroke (FIG. 10B). The constant timing is a timing in
which the setting is made near the most advanced angle within the
low load range described hereinafter. The discharge energy is set
to a level that increases the lower the load is (FIG. 10C). The
intake valve close timing (IVC) is set to be nearer to the advance
angle than the bottom dead center (BDC), and the operation proceeds
according to the Miller cycle. This timing is set to an angle that
is more advanced the lower the load is (FIG. 10D). The mechanical
compression ratio is set to a high level (FIG. 10E).
[0103] The range of low load will now be discussed. In a low load
range in which the load is greater than in the extremely low load
range, the air-fuel ratio A/F is set to decrease (i.e., become
richer) as the load increases (FIG. 10A). The barrier discharge
start timing is set to the intake stroke when the load is low, is
set to approach the retard angle as the load increases, and is set
to the compression stroke when the load is high (FIG. 10B). The
reasons for these settings are described hereinafter. The discharge
energy is set to a constant value (FIG. 10C). The intake valve
close timing (IVC) is set to a constant value nearer the retard
angle than the bottom dead center (BDC) (FIG. 10D). The mechanical
compression ratio is set to a high level (FIG. 10E).
[0104] The range of low to moderate load will now be discussed. In
a low-to-moderate load range in which the load is greater than in
the low load range, the air-fuel ratio A/F is set to decrease
(i.e., become richer) as the load increases (FIG. 10A). The barrier
discharge start timing is set to lag much more than in the low load
range, and is also set to approach the retard angle as the load
increases (FIG. 10B). The discharge energy is set to a constant
value (FIG. 10C). The intake valve close timing (IVC) is set to a
constant value nearer to the lag angle than the bottom dead center
(BDC) (FIG. 10D). The mechanical compression ratio is set to be
much less than in the extremely low load range or the low load
range, and is also set to decrease as the load increases (FIG.
10E).
[0105] The range of moderate to high load will now be discussed. In
a moderate-to-high load range in which the load is greater than in
the low-to-moderate load range, the air-fuel ratio A/F is set to
decrease (i.e., become richer) as the load increases (FIG. 10A).
The barrier discharge start timing is set to approach the retard
angle as the load increases (FIG. 10B). The discharge energy is set
to a constant value (FIG. 10C). The intake valve close timing (IVC)
is set to a constant value nearer to the retard angle than the
bottom dead center (BDC) (FIG. 10D). The mechanical compression
ratio is set to be even less than in the low-to-moderate load
range, and is also set to decrease as the load increases (FIG.
10E).
[0106] The reasons for setting the control map in the above manner
will be described herein. In the low load range, the barrier
discharge start timing is set to the intake stroke when the load is
low, is set to approach the retard angle as the load increases, and
is set to the compression stroke when the load is high (FIG. 10B).
The reasons for these settings will be explained with reference to
FIG. 11.
[0107] FIG. 11 is a graph showing the variation in the heat
generation rate outside of the barrier discharge start timing. Line
A in the diagram is shown as a comparative example, and is a line
indicating variation in the heat generation rate when a barrier
discharge is not performed (i.e., radicals are not generated). It
can be seen from line A that the peak of the heat generation rate
is suppressed at the crank angle .theta.a. The heat generation rate
is substantially symmetrical before and after this peak, and the
crank angle MB.theta.50% (discussed below) at which the mass
combustion ratio is 50% substantially coincides with .theta.a.
[0108] Line B in the diagram is a line indicating variation in the
heat generation rate when a barrier discharge is initiated during
the compression stroke (for example, 135 deg BTDC). It can be seen
from line B that the peak of the heat generation rate is suppressed
at the crank angle .theta.b nearer to the advance angle than when
the barrier discharge was not performed (line A), and the heat
generation rate rises more rapidly than when the barrier discharge
was not performed (line A). The heat generation rate is
substantially symmetrical before and after this peak, and the crank
angle MB.theta. 50%, at which the mass combustion ratio is 50%,
substantially coincides with .theta.b.
[0109] Line C in the diagram is a line indicating variation in the
heat generation rate when a barrier discharge is initiated during
the intake stroke (for example, 270 deg BTCD). It can be seen from
line C that the peak of the heat generation rate is suppressed at
the crank angle .theta.c even nearer to the advance angle than when
the barrier discharge was initiated during the compression stroke
(line B), and the variation is steep. The heat generation rate is
substantially symmetrical before and after this peak, and the crank
angle MB.theta. 50%, at which the mass combustion ratio is 50%,
substantially coincides with .theta.c.
[0110] FIGS. 12A-C contain drawings schematically depicting the
state in which radicals are distributed within the cylinder, which
is the result of analyzing the reasons that bring about a state
such as in FIG. 11. The radicals are schematically depicted by the
dots in the drawings. Research has shown that differences in the
variation in the heat generation rate brought about by the barrier
discharge start timing are caused by the state in which radicals
are distributed within the cylinder, as shown in FIG. 11.
[0111] When a barrier discharge is not performed (i.e., when
radicals are not generated), there is naturally no distribution of
radicals in the cylinder 31a (FIG. 12A). When the air-fuel mixture
undergoes compression ignition while no radicals are distributed,
the heat generation rate varies comparatively slowly, as shown by
line A in FIG. 11.
[0112] In cases in which a barrier discharge is initiated during
the intake stroke, it can be seen that radicals are distributed
throughout substantially the entire cylinder 31a immediately before
ignition, as shown in FIG. 12C. This is because there is a long
timing from the time when the barrier discharge device 70 performs
a barrier discharge to generate radicals until the time of
ignition, and the radicals are therefore carried by the intake flow
to be widely dispersed throughout the cylinder 31a. When
compression ignition takes place in the state in which the radicals
are widely distributed, the air-fuel mixture combusts substantially
all at once throughout the entire cylinder 31a. The radicals are in
a state in which molecular dissociation is induced by collisions of
high-energy electrons with fuel or air molecules. Such radicals
have the characteristic of readily inducing oxidation reactions
(i.e., combustion) and creating chain oxidation reactions. The
radicals undergo combustion substantially all at once throughout
the entire cylinder 31a when the pressure in the cylinder increases
while radicals having such characteristics are dispersed throughout
the entire cylinder 31a. Research has shown that the heat
generation rate also rises suddenly because a combustion reaction
takes place in this manner throughout the entire cylinder 31a.
[0113] Initiating a barrier discharge during the compression stroke
brings about an intermediate state in the cylinder 31a immediately
before ignition, that is, a state between the case of no barrier
discharge (FIG. 12A) and the case in which a barrier discharge is
initiated during the intake stroke (FIG. 12C). In the intermediate
state, fewer radicals are distributed in the vicinity of the
barrier discharge device 70 (FIG. 12B). This is because there is a
short timing from the time when the barrier discharge device 70
performs a barrier discharge to generate radicals until the time of
ignition, and the radicals are therefore unable to widely disperse.
When compression ignition takes place in the state in which the
radicals are dispersed in the vicinity of the barrier discharge
device 70, the combustion process first involves the radicals and
then spreads to the surrounding radical-free air-fuel mixture. It
is because of this type of mechanism that line B is an intermediate
line between line A and line C.
[0114] FIG. 13 is a graph showing the relationship between the
barrier discharge start timing and the crank angle at which the
mass combustion ratio is 50%.
[0115] As described above, varying the barrier discharge start
timing causes a change in the crank angle MB.theta. 50% at which
the mass combustion ratio is 50%. In other words, the autoignition
properties change. This relationship is plotted in FIG. 13. Up
until the barrier discharge start timing reaches approximately 270
deg BTDC, the crank angle MB.theta. 50% at which the mass
combustion ratio is 50% advances as the barrier discharge start
timing is advanced. In other words, autoignition properties are
improved. When the barrier discharge start timing is advanced to
270 deg BTDC or greater, the crank angle MB.theta. 50% at which the
mass combustion ratio is 50% lags behind as the barrier discharge
start timing is advanced.
[0116] The following are thought to be the reasons that the crank
angle MB.theta. 50% at which the mass combustion ratio is 50%
advances the farthest (i.e., autoignition properties are best) when
the barrier discharge start timing is approximately 270 deg BTDC.
Specifically, there is an overlap between timings in which the
intake valve and exhaust valve of the engine are normally opened
and closed. It is believed that initiating a barrier discharge
after the exhaust valve has closed causes the air-fuel mixture
drawn in through the intake valve to scatter more readily and
autoignition properties to improve in comparison with a case in
which a barrier discharge is initiated during the timing in which
the exhaust valve has not yet closed. It is also believed that the
air-fuel mixture readily scatters and autoignition properties
improve because the rate of air intake is higher during the latter
half of the downward movement of the piston than the first half.
The barrier discharge part continuously performs a barrier
discharge for a predetermined time (predetermined crank angle
timing) following discharge initiation. The air flow rate decreases
after the intake valve is closed. When a non-equilibrium plasma
discharge is performed while the air flow rate has decreased, the
radicals do not disperse as readily as when the air flow rate is
high. Therefore, to efficiently disperse radicals within the
cylinder, the end timing of the non-equilibrium plasma discharge is
preferably before the closing of the intake valve.
[0117] As can be seen from FIG. 13, the heat generation timing (the
crank angle MB.theta. 50% at which the mass combustion ratio is
50%) can be controlled by adjusting the barrier discharge start
timing. In other words, the autoignition properties of the air-fuel
mixture can be controlled by adjusting the barrier discharge start
timing. As the autoignition properties improve, the operability at
a lean air-fuel ratio improves as well. However, if the
autoignition properties improve excessively when the air-fuel ratio
is not particularly lean, there is a danger that knocking will
occur. In view of this, the barrier discharge start timing is
preferably adjusted according to the air-fuel ratio (load).
[0118] As a comparative example, FIG. 13 also shows a case in which
radicals are generated by a sparkplug. It is clear from the diagram
that even if radicals are generated by a sparkplug, there is little
difference from cases in which radicals are not generated.
[0119] Based on the above knowledge, an electric discharge
structure is provided which causes a barrier discharge to be
initiated during the intake stroke so that radicals are widely
distributed within the cylinder when the air-fuel ratio corresponds
to an extremely diluted (lean) condition.
[0120] Depending on the operating state, there is a danger that the
autoignition properties will be improved to an excess and that
knocking will occur if the amount of radicals generated within the
cylinder is too great or the radicals are too widely distributed.
In view of this, the autoignition properties are adjusted by
delaying the barrier discharge start timing as the load increases
(as the amount of fuel increases and the air-fuel ratio corresponds
to a richer mixture). The above factors are the reasons that the
barrier discharge start timing is set to occur during the intake
stroke when the load is low, is set to approach a retard angle as
the load increases, and is set to occur during the compression
stroke when the load is high (FIG. 10B).
[0121] The mechanical compression ratio is set to a high level in a
load range at or below a low load (FIG. 10E). The reasons for these
settings will now be described.
[0122] An engine having a multi-link variable compression ratio
mechanism has the characteristic of having a longer timing in which
the piston stays in proximity to the top dead center in comparison
with a common engine in which the compression ratio is constant
(hereinafter referred to as a "normal engine"). Due to this
characteristic, an engine having a multi-link variable compression
ratio mechanism, even at a high compression ratio, is less
susceptible to knocking than a common engine is, comparatively high
combustion energy can be obtained even with ultra-lean combustion,
and stable combustion can be maintained.
[0123] This aspect is described with reference to FIG. 14. FIG. 14
contains a graph showing the piston behavior in a multi-link
variable compression ratio mechanism, wherein the upper portion of
FIG. 14 is an enlarged view of the dotted line portion of the lower
portion of the figure. In FIG. 14, the thin solid lines indicate
the piston behavior in the multi-link variable compression ratio
mechanism engine having the same compression ratio as a normal
engine.
[0124] If the time in which the piston is within a predetermined
distance from the top dead center is defined as the timing in which
the piston is in proximity to the top dead center, it is clear from
FIG. 14 that the multi-link variable compression ratio mechanism
engine has a longer timing in which the piston is in proximity to
the top dead center than does a normal engine having the same
compression ratio. Specifically, in the multi-link variable
compression ratio mechanism engine, the timing L1 in which the
piston is in proximity to the top dead center at a high compression
ratio is longer than the timing L2 in which the piston is in
proximity to the top dead center at a low compression ratio. In
other words, the inequality L1>L2 is true in FIG. 14.
[0125] Thus, the multi-link variable compression ratio mechanism
engine has a longer timing in which the piston is in proximity to
the top dead center than does a normal engine. Furthermore, the
timing in which the piston is in proximity to the top dead center
is longer than that observed at a high compression ratio. The fact
that the piston is in proximity to the top dead center for a long
time means that a high compression state is maintained for a long
time during combustion. When a high compression state is maintained
for a long time, knocking does not readily occur, and combustion is
stable because comparatively high combustion energy can be obtained
even during ultra-lean combustion.
[0126] Because of such characteristics, the multi-link variable
compression ratio mechanism engine has the characteristics shown in
FIG. 15. FIG. 15 is a graph showing the relationship between the
air-fuel ratio and combustion stability. The thin line in the
diagram denotes a normal engine, and the thick line denotes a
multi-link variable compression ratio mechanism engine.
[0127] As can be seen from FIG. 15, in a normal engine (compression
ratio: about 8 to 12), the air-fuel ratio which can ensure
combustion stability is about 22.
[0128] According to the multi-link variable compression ratio
mechanism engine, the combustion stability limit is not compromised
because the piston remains in proximity to the top dead center for
a long time. Increasing the compression ratio (e.g., to about 18)
makes it possible to obtain stable combustion even at an air-fuel
ratio A/F of about 30. The above are the reasons the mechanical
compression ratio is set to a high level in a load range at or
below a low load (FIG. 10E). The map load range in FIG. 10 was set
based on this knowledge.
[0129] Next, the reasons for selecting the settings in the
extremely low load range in the control map will be described. In
the extremely low load range, as described above, the intake valve
close timing (IVC) is set nearer to the advance angle than in the
bottom dead center (BDC), and the operation proceeds according to
the Miller cycle. The timing is set nearer to the advance angle at
lower loads (FIG. 10D). The filling efficiency of intake air is
thereby reduced, the effective compression ratio is lowered, and
pump loss is reduced. Since the combustion amount decreases with
decreased load (the air-fuel ratio is substantially constant
because the air intake amount also decreases), the air-fuel mixture
loses autoignition properties. In view of this, the discharge
energy is greatly increased at lower loads (FIG. 10C). The map of
the extremely low load range in FIG. 10 was set based on the above
knowledge. As shown, operation is possible even at extremely low
load ranges.
[0130] Next, the reasons for the settings in the low-to-moderate
load range of the control map will be described. In the
low-to-moderate load range, as described above, the barrier
discharge start timing lags to a considerably greater extent than
in the low load range (FIG. 10B). The mechanical compression ratio
is set to be much lower than in the extremely low and low load
ranges (FIG. 10E).
[0131] In cases in which radicals are generated and combustion
takes place by compression ignition, the air-fuel mixture has
better autoignition properties. Therefore, when the load is greater
and the amount of combustion increases, there is a possibility that
the heat generation rate will suddenly increase to an excessive
degree, as shown by line A in FIG. 16. When the heat generation
rate suddenly increases to an excessive degree in this manner,
there is a danger that knocking will occur.
[0132] In view of this, in the present embodiment, when the load
increases to within a low-to-moderate load range, the compression
ratio is reduced so that the air-fuel mixture does not undergo
compression ignition. It is designed so that volumetric ignition is
performed by the barrier discharge part during the compression
stroke. The fuel in the vicinity of the barrier discharge part
thereby undergoes flame propagation. The remaining unburned
air-fuel mixture is adiabatically compressed by the burned air-fuel
mixture and is made to undergo autoignition. As a result, the heat
generation rate varies as shown by line B in FIG. 16 and does not
suddenly increase to an excessive degree, and knocking does not
occur. The map of the low-to-moderate load range in FIG. 10 is set
based on the above. Operation is thereby made possible even in a
low-to-moderate load range.
[0133] Spark ignition is performed by the barrier discharge part at
a moderate-to-high load or greater, whereby operation is possible
even in a moderate-to-high load range.
[0134] FIGS. 17A and 17B contain graphs showing various effects of
the present embodiment. In the present embodiment, it is possible
to greatly expand the lean combustion limit because the barrier
discharge start timing is appropriately controlled according to the
operating state as described above.
[0135] In FIG. 17A, plotting the correlation between the air-fuel
ratio A/F (horizontal axis) and the fluctuation rate CPi (vertical
axis) of the depicted average effective pressure results in line A
in normal combustion by compression ignition. The lean combustion
limit is the air-fuel ratio AFa.
[0136] Line B depicts cases in which radicals are generated by a
sparkplug, and combustion occurs by compression ignition. The lean
combustion limit is the air-fuel ratio of AFb, and is somewhat
leaner than the air-fuel ratio AFa of the lean combustion limit in
normal cases.
[0137] Line C depicts cases in which radicals are generated by the
barrier discharge part, and combustion occurs by compression
ignition. The lean combustion limit is the air-fuel ratio of AFc.
The lean combustion limit can be greatly expanded in comparison
with the air-fuel ratio AFa of the lean combustion limit in normal
cases and in comparison with the air-fuel ratio AFb of the lean
combustion limit in generation of radicals by a sparkplug and
combustion by compression ignition. As described above, the
operation shown by the dashed lines can be arbitrarily selected
because it is possible to control the crank angle MB.theta. 50% at
which the mass combustion ratio is 50% by adjusting the barrier
discharge start timing. If the lean combustion limit is expanded,
the fuel consumption rate ISFC can be reduced as shown in FIG. 17B.
The present embodiment makes it possible to reduce the fuel
consumption rate regardless of the load, and to improve fuel
consumption.
[0138] In the present embodiment, the first electrode composed of a
long thin conductive material and the dielectric material for
covering the first electrode allow a barrier discharge to be
performed in which non-equilibrium plasma is discharged and
radicals can be generated within a cylinder. Therefore, the
autoignition properties of an air-fuel mixture during the
compression stroke can be improved, the fuel consumption rate can
consequently be reduced regardless of the load, and fuel
consumption can also be improved.
Second Embodiment
[0139] Referring now to FIG. 18, an internal combustion engine
electric discharge structure in accordance with a second embodiment
will now be explained. Basically, in this second embodiment, the
internal combustion engine electric discharge structure of the
first embodiment is replaced in FIG. 1 with a modified structure as
discussed below. In view of the similarity between the first and
second embodiments, the parts of the second embodiment that are
identical to the parts of the first embodiment will be given the
same reference numerals as the parts of the first embodiment.
Moreover, the descriptions of the parts of the second embodiment
that are identical to the parts of the first embodiment can be
omitted for the sake of brevity.
[0140] FIG. 18 is a simplified schematic cross-sectional view
showing the operational configuration of the engine having an
electric discharge structure in accordance with a second
embodiment. The engine 1 having a barrier discharge function of the
first embodiment was a so-called port-injection engine in which the
fuel injection valve 65 was provided to the intake port, but the
electric discharge structure can also be applied to a direct
fuel-injection engine such as the one shown in FIG. 18, in which
fuel is directly injected into the cylinder.
[0141] In this type of direct fuel-injection engine, the air-fuel
mixture is stratified only in the vicinity of the barrier discharge
device 70 as shown in FIG. 19 to make operation possible even with
a lean air-fuel ratio. Generating radicals in this type of lean
air-fuel mixture allows the lean combustion limit to be expanded,
the fuel consumption rate to be reduced, and fuel consumption to be
improved.
[0142] An example of an operation map for the engine having such a
barrier discharge function is shown in FIGS. 20A-20E. An interval
in which a barrier discharge is not performed is provided in the
vicinity of a comparatively high load within the low load range
(FIGS. 20A and 20B). In the low load range, a high compression
ratio is set by the variable compression ratio mechanism, and
knocking does not readily occur. Therefore, there is an operation
range in which lean combustion is possible even though a barrier
discharge is not performed. When a barrier discharge is performed
in such an operating range, there is a danger that autoignition
properties will improve excessively and that knocking will occur.
In view of this, a barrier discharge is not performed in the
vicinity of comparatively high loads within the low load range.
[0143] In an extremely low load range in which the load is lower
than in the low load range, a stratified operation is performed
(FIG. 20D) and the air-fuel ratio A/F is made leaner (sparser)
according to the load (FIG. 20A). A barrier discharge is performed
because the autoignition properties must be improved along with the
increase in sparseness. The barrier discharge start timing is set
to occur during the intake stroke, wherein the effects of
autoignition properties improvement are high (FIG. 20B). The
autoignition properties are improved by increasing the discharge
energy along with the increase in sparseness (FIG. 20C).
[0144] By using the present embodiment, the invention can be
carried out even with a direct fuel-injection engine, the fuel
consumption rate can be reduced regardless of the load, and fuel
consumption can be improved.
Third Embodiment
[0145] Referring now to FIG. 21, an internal combustion engine
electric discharge structure in accordance with a third embodiment
will now be explained. Basically, in this third embodiment, the
internal combustion engine electric discharge structure of the
first embodiment is replaced in FIG. 1 with a modified structure as
discussed below. In view of the similarity between the first and
second embodiments, the parts of the third embodiment that are
identical to the parts of the first embodiment will be given the
same reference numerals as the parts of the first embodiment.
Moreover, the descriptions of the parts of the third embodiment
that are identical to the parts of the first embodiment can be
omitted for the sake of brevity.
[0146] FIG. 21 is a simplified schematic cross-sectional view
showing the third embodiment of an engine having a barrier
discharge function. In the barrier discharge device 70 of the
present embodiment, a dielectric layer (insulating layer) 73 is
formed on the inner periphery of the tubular electrode 72, and the
central electrode 71 is exposed. The distal end of the dielectric
layer (insulating layer) 73 preferably protrudes farther toward the
combustion chamber than does the distal end of the tubular
electrode 72 or the distal end of the central electrode 71. This is
because such a configuration makes it possible to suppress the
occurrence of a thermal plasma discharge between the distal end of
the tubular electrode 72 and the distal end of the central
electrode 71, even in cases in which the discharge energy of a
non-equilibrium plasma discharge has been increased. The dielectric
layer 73 acts as a capacitor in the configuration of the present
embodiment as well, and the same effects as in the first embodiment
are obtained.
Fourth Embodiment
[0147] Referring now to FIGS. 22A and 22B, an internal combustion
engine electric discharge structure in accordance with a fourth
embodiment will now be explained. Basically, in this fourth
embodiment, the internal combustion engine electric discharge
structure of the first embodiment is replaced in FIG. 1 with a
modified structure as discussed below. In view of the similarity
between the first and fourth embodiments, the parts of the fourth
embodiment that are identical to the parts of the first embodiment
will be given the same reference numerals as the parts of the first
embodiment. Moreover, the descriptions of the parts of the fourth
embodiment that are identical to the parts of the first embodiment
can be omitted for the sake of brevity.
[0148] FIGS. 22A and 22B contain simplified schematic
cross-sectional views showing the fourth embodiment of the engine
having a barrier discharge function. In the barrier discharge
device 70 of the present embodiment, in contrast to the first
embodiment, the central electrode 71 protrudes into the combustion
chamber.
[0149] Thus, the barrier discharge device 70 forms a barrier
discharge within the combustion chamber as shown in FIG. 22A. In
the present embodiment, the top surface of the piston 32 or the
inside wall surface of the cylinder head functions as an electrode.
Specifically, in the present embodiment, a barrier discharge is
performed and radicals are generated in the area A between the top
surface of the piston 32 and the dielectric layer (insulating
layer) 73 of the central electrode 71, or in the area B between the
inside wall surface of the cylinder head and the dielectric layer
(insulating layer) 73. Whether the barrier discharge is performed
in area A or B is determined by the position of the piston 32 when
an AC voltage is applied to the barrier discharge device 70. In
view of this, the discharge area of barrier discharge can be
selected by controlling the application timing of the AC voltage
applied to the barrier discharge device 70.
[0150] A concave part can be formed in the top surface of the
piston 32 as shown in FIG. 22B, and the configuration can be
designed so that barrier discharge is performed between the concave
part and the distal end of the dielectric material (insulating
material) 73 of the central electrode 71.
Fifth Embodiment
[0151] Referring now to FIGS. 23A and 23B, an internal combustion
engine electric discharge structure in accordance with a fifth
embodiment will now be explained. Basically, in this fifth
embodiment, the internal combustion engine electric discharge
structure of the first embodiment is replaced in FIG. 1 with a
modified structure as discussed below. In view of the similarity
between the first and fifth embodiments, the parts of the fifth
embodiment that are identical to the parts of the first embodiment
will be given the same reference numerals as the parts of the first
embodiment. Moreover, the descriptions of the parts of the fifth
embodiment that are identical to the parts of the first embodiment
can be omitted for the sake of brevity.
[0152] FIGS. 23A and 23B contain simplified schematic
cross-sectional views showing the fifth embodiment of the engine
having a barrier discharge function. In the barrier discharge
device 70 of the present embodiment, the dielectric material
(insulating material) 73 is shorter in comparison with the fourth
embodiment, and the central electrode 71 is exposed within the
combustion chamber. A dielectric layer (insulating layer) 32a is
also formed on the top surface of the piston 32.
[0153] Thus, the barrier discharge device 70 performs a barrier
discharge within the combustion chamber as shown in FIG. 23A.
Specifically, a barrier discharge is performed and radicals are
generated in the area A between the distal end of the central
electrode 71 and the dielectric layer (insulating layer) 32a on the
top surface of the piston 32.
[0154] If a concave part is formed in the top surface of the piston
32, and the dielectric layer (insulating layer) 32a is formed in
the inner periphery of the concave part as shown in FIG. 23B, a
barrier discharge is performed between the dielectric layer
(insulating layer) 32a and the distal end of the central electrode
71.
[0155] Although alternating current corresponding to the operating
state of the engine is applied to the barrier discharge device 70,
but the alternating current is not limited to a sine curve (FIG.
24A). A bipolar multiple pulse power source can also be used, such
as is shown in FIG. 24B.
[0156] Also in the above descriptions, a multi-link mechanism was
exemplified as the variable compression ratio mechanism, but other
possible examples include, e.g., a mechanism in which a hydraulic
device is incorporated into the piston as such to adjust the height
of the top surface of the piston, a mechanism in which the distance
between the cylinder head and the cylinder block can be adjusted,
and a mechanism in which the piston height can be adjusted by
offsetting the center of the crankshaft.
[0157] Furthermore, the mechanism for adjusting the valve timing of
the intake valve can also be, e.g., an oscillating cam which uses a
link (Japanese Laid-Open Patent Application No. 2000-213314), a
mechanism in which the cam is twisted in the manner of a vane-type
variable valve timing system (Japanese Laid-Open Patent Application
No. 9-60508), a system in which a switch is made between two types
of cams having different timings in the manner of a direct variable
valve timing system (Japanese Laid-Open Patent Application No.
4-17706), or the like.
GENERAL INTERPRETATION OF TERMS
[0158] In understanding the scope of the present invention, the
term "comprising" and its derivatives, as used herein, are intended
to be open ended terms that specify the presence of the stated
features, elements, components, groups, integers, and/or steps, but
do not exclude the presence of other unstated features, elements,
components, groups, integers and/or steps. The foregoing also
applies to words having similar meanings such as the terms,
"including", "having" and their derivatives. Also, the terms
"part," "section," "portion," "member" or "element" when used in
the singular can have the dual meaning of a single part or a
plurality of parts. The terms of degree such as "substantially",
"about" and "approximately" as used herein mean a reasonable amount
of deviation of the modified term such that the end result is not
significantly changed.
[0159] While only selected embodiments have been chosen to
illustrate the present invention, it will be apparent to those
skilled in the art from this disclosure that various changes and
modifications can be made herein without departing from the scope
of the invention as defined in the appended claims. For example,
the size, shape, location or orientation of the various components
can be changed as needed and/or desired. Components that are shown
directly connected or contacting each other can have intermediate
structures disposed between them. The functions of one element can
be performed by two, and vice versa. The structures and functions
of one embodiment can be adopted in another embodiment. It is not
necessary for all advantages to be present in a particular
embodiment at the same time. Every feature which is unique from the
prior art, alone or in combination with other features, also should
be considered a separate description of further inventions by the
applicant, including the structural and/or functional concepts
embodied by such features. Thus, the foregoing descriptions of the
embodiments according to the present invention are provided for
illustration only, and not for the purpose of limiting the
invention as defined by the appended claims and their
equivalents.
* * * * *