U.S. patent application number 09/943023 was filed with the patent office on 2002-03-07 for self-igniting engine.
This patent application is currently assigned to Fuji Jukogyo Kabushiki Kaisha. Invention is credited to Itoh, Jin, Kaneko, Makoto, Kani, Nobumasa, Morikawa, Koji, Saisyu, Youhei.
Application Number | 20020026924 09/943023 |
Document ID | / |
Family ID | 18757028 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020026924 |
Kind Code |
A1 |
Morikawa, Koji ; et
al. |
March 7, 2002 |
Self-igniting engine
Abstract
In a self-igniting possible range, both intake and exhaust
valves are placed in a closure condition for a period from the end
of an exhaust stroke and the beginning of an intake stroke for
establishing a negative overlap period in which a residual gas is
pressurized to increase its temperature, thus raising the air fuel
mixture temperature in a combustion chamber up to a self-igniting
possible temperature. In addition, when a crank angle reaches a
predetermined crank angle in the first half of an intake stroke, a
fuel is injected from an in-cylinder injector into the combustion
chamber. This fuel injected becomes a premixed air fuel because of
being evaporated by the gas temperature in the combustion chamber,
and on shifting to a compression stroke afterwards, the temperature
in the combustion chamber reaches the self-igniting possible
temperature.
Inventors: |
Morikawa, Koji; (Tokyo,
JP) ; Kaneko, Makoto; (Tokyo, JP) ; Kani,
Nobumasa; (Tokyo, JP) ; Saisyu, Youhei;
(Tokyo, JP) ; Itoh, Jin; (Tokyo, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN &
LANGER & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
Fuji Jukogyo Kabushiki
Kaisha
1-7-2, Nishishinjuku, Shinjuku-ku
Tokyo
JP
160-8316
|
Family ID: |
18757028 |
Appl. No.: |
09/943023 |
Filed: |
August 30, 2001 |
Current U.S.
Class: |
123/305 ;
123/90.15 |
Current CPC
Class: |
F02D 2041/001 20130101;
F02B 2275/18 20130101; F02D 13/0215 20130101; F02M 26/01 20160201;
Y02T 10/44 20130101; F02B 1/12 20130101; F02D 13/0265 20130101;
F02B 2023/102 20130101; F02D 41/402 20130101; Y02T 10/123 20130101;
F02D 13/0219 20130101; F02D 41/3029 20130101; Y02T 10/128 20130101;
F02B 23/101 20130101; F02D 41/401 20130101; Y02T 10/18 20130101;
F02B 2275/14 20130101; F02B 75/00 20130101; F02D 41/3035 20130101;
Y02T 10/12 20130101; Y02T 10/40 20130101; F02B 3/06 20130101; Y02T
10/125 20130101; F02D 41/3047 20130101; F02B 23/104 20130101; F02B
17/005 20130101 |
Class at
Publication: |
123/305 ;
123/90.15 |
International
Class: |
F01L 001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 6, 2000 |
JP |
270614\2000 |
Claims
What is claimed is:
1. A self-igniting engine comprising: fuel injection means for
injecting a fuel directly into a combustion chamber; temperature
increasing means for increasing a temperature of an air fuel
mixture, by evaporating said fuel to a self-igniting possible
temperature causing a multi-point ignition; and injection timing
control means for setting a fuel injection start timing in the
middle of an intake stroke for a low-load operating condition and
for setting said fuel injection start timing in the first half of a
compression stroke for a high-load operating condition.
2. The self-igniting engine according to claim 1, wherein said
temperature increasing means includes a variable valve timing
mechanism for operating an intake/exhaust valve into a closing
condition for a predetermined period from the end of an exhaust
stroke to the beginning of said intake stroke.
3. The self-igniting engine according to claim 1, wherein said
injection timing control means variably sets said fuel injection
start timing in accordance with engine driving conditions.
4. A self-igniting engine comprising: fuel injection means for
injecting a fuel directly into a combustion chamber; temperature
increasing means for increasing a temperature of an air fuel
mixture by evaporating said fuel to a self-igniting possible
temperature causing a multi-point ignition; and injection timing
control means for setting a fuel injection start timing in a
compression ignition driving range, wherein said injection timing
control means sets first fuel injection in the middle of an intake
stroke and sets second fuel injection in the second half of a
compression stroke for high-load operating condition.
5. The self-igniting engine according to claim 4, wherein said
temperature increasing means includes a variable valve timing
mechanism for operating an intake/exhaust valve into a closing
condition for a predetermined period from the end of an exhaust
stroke to the beginning of said intake stroke.
6. The self-igniting engine according to claim 4, wherein said
injection timing control means variably sets said fuel injection
start timing in accordance with engine driving conditions.
Description
[0001] This application claims benefit of Japanese Application
Number 2000-270614 filed on Sep. 6, 2000, the contents of which are
incorporated by this reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a self-igniting engine by
igniting an air fuel mixture at multi-points.
[0004] 2. Description of the Related Art
[0005] So far, there have been studied various types of engine
operating techniques, for example, not only operating by a spark
ignition but also by a self-igniting engine using a compression
heat in dependency on a driving range for controlling an emission
of toxic gases from a gasoline engine. In the case of such a
self-igniting engine, although the quantity of NOx to be generated
in an emission gas is considerably reducible, difficulty is
encountered in positively controlling the ignition timing as well
as an ordinary spark ignition type gasoline engine because the
combustion depends on the self-igniting method.
[0006] Such a conventional self-igniting type engine has been
disclosed in Japanese Unexamined Patent Publication No. 11-210539.
In the case of the self-igniting type gasoline engine disclosed in
this Publication, the gas temperature (air fuel mixture
temperature) for igniting the air fuel mixture within a combustion
chamber is set to a little lower temperature than a temperature
causing the self-igniting, and the air fuel mixture is ignited by
spark plug within that range by increasing the internal pressure in
the cylinder by the combustion of the air fuel mixture around the
spark plug for increasing the gas temperature therein as whole,
thereby multi-point-igniting the entire air fuel mixture.
[0007] However, in a case where the self-igniting timing is
controlled by the ignition timing of the spark plug like this as
disclosed in the aforesaid publication, there is a need to control
the air fuel mixture temperature to be within a ignition
temperature range which is impossible for self-igniting. For
example, in a case where the air fuel mixture temperature reaches
the temperature which does not rely on sparking, knocking occurs
due to early ignition. On the other hand, when the air fuel mixture
temperature falls below that temperature relying on the sparking, a
misfire occurs. For this reason, difficult is the control of the
air fuel mixture temperature. In addition, difficulty is
experienced in changing the air fuel temperature rapidly, which
makes it difficult to offer a stable combustion state.
SUMMARY OF THE INVENTION
[0008] Accordingly, it is an object of the present invention to
provide a self-igniting engine capable of achieving a stable
combustion state in a self-igniting operation range by controlling
the fuel injection timing to overcome a difficulty of controlling
the air fuel mixture temperature.
[0009] In accordance with the present invention, there is provided
a self-igniting engine including fuel injection means for injecting
a fuel directly into a combustion chamber, temperature increasing
means for increasing a temperature of an air fuel mixture by
evaporating the fuel to a self-igniting possible temperature
causing a multi-point ignition, and injection timing control means
for setting a fuel injection start timing in the middle of an
intake stroke for a low-load operating condition and for setting
the fuel injection start timing in the first half of a compression
stroke for a high-load operating condition.
[0010] In this configuration, in a compression ignition driving
range where there occurs multi-point ignition of premixed air fuel
made by the evaporation of a fuel directly injected from the fuel
injection means into the combustion chamber, temperature increasing
means increases the air fuel mixture up to a compression ignition
possible temperature, while the injection timing control means sets
the fuel injection start timing in the middle of an intake stroke
at a low-load driving and sets it in the first half of a
compression stroke at high-load driving.
[0011] The above and other objects, features and advantages of the
invention will become more clearly understood from the following
description referring to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is an illustration of the entire structure of a
self-igniting engine according to a first embodiment;
[0013] FIG. 2A is an illustration for explaining the control of
valve opening time periods of an intake valve and an exhaust valve
according to the first embodiment;
[0014] FIG. 2B is an illustration for explaining the control of
valve opening time periods of an intake valve and an exhaust valve
according to the first embodiment;
[0015] FIG. 3 is an illustration of a driving range according to
the first embodiment;
[0016] FIG. 4 is a flow chart showing a combustion mode setting
routine according to the first embodiment;
[0017] FIG. 5 is a flow chart showing an injection control routine
at a self-igniting combustion according to the first
embodiment;
[0018] FIG. 6 is an illustration for explaining a fuel injection
timing according to the first embodiment;
[0019] FIG. 7 is an illustration for explaining the relationship
between a top surface of a piston and fuel injection at an intake
stroke according to the first embodiment;
[0020] FIG. 8 is an illustration for explaining a combustion
pressure at the self-igniting combustion according to the first
embodiment;
[0021] FIG. 9 is a flow chart showing an injection control routine
at the self-igniting combustion according to a second
embodiment;
[0022] FIG. 10A is an illustration for explaining a fuel injection
timing at a high-load driving condition according to the second
embodiment;
[0023] FIG. 10B is an illustration for explaining a fuel injection
timing at a low-load driving condition according to the second
embodiment; and
[0024] FIG. 11 is an illustration for explaining a driving range
according to the second embodiment.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] A first embodiment of the present invention is shown in
FIGS. 1 to 8. In FIG. 1, reference numeral 1 represents an engine
body, numeral 2 represents a piston, numeral 3 represents a
combustion chamber, numeral 4 designates an intake port, numeral 5
designates an exhaust port, numeral 6 designates an intake valve,
and numeral 7 denotes an exhaust valve. A throttle valve 9 is
placed in an intake passage 8 communicating with the intake port
4.
[0026] In addition, an injection nozzle for an injector 11 of an
in-cylinder injection, serving as fuel injection means, is arranged
to face the center of a top surface of the combustion chamber 3.
And a curved concave piston cavity 2a is formed in a top surface of
the piston 2 which is in opposed relation to the in-cylinder
injector 11 in its injecting direction. Additionally, a sparking
portion of a spark plug 12 is placed to face one side of the
combustion chamber 3.
[0027] Moreover, an intake cam 13a and an exhaust cam 13b for
opening/closing the intake valve 6 and the exhaust valve 7 are
placed in a state connected to a variable valve timing (VVT)
mechanism 14a or 14b. These VVT mechanisms 14a and 14b changes the
rotational phase of the intake cam 13a or the exhaust cam 13b
respectively through such an actuator as a hydraulic solenoid (or a
solenoid valve) to perform variable control of the opening/closing
timing of the intake valve 6 or the exhaust valve 7, each being
operated under control of an actuating pressure (or an actuating
signal) outputted from such an actuator 15 as a solenoid valve.
[0028] Incidentally, in the illustration, numeral 16 denotes a
knock sensor, numeral 17 depicts a water temperature sensor and
numeral 18 depicts an 0.sub.2 (Oxygen) sensor.
[0029] Signals obtained as the detection results by these sensors
are inputted to an electronic control unit (ECU) 20. The electronic
control unit (ECU) 20 basically comprises a microcomputer composed
of a CPU 21, a ROM 22, a RAM 23, an input port 24, an output port
25 and other devices which are interconnected through a two-way bus
26 to each other.
[0030] In addition to the aforesaid sensors, a crank angle sensor
31, which generates a crank pulse at every crank angle, is
connected to the input port 24, and a load sensor 33, which
generates an output voltage proportional to an actuating (pressing,
stepping) quantity of an accelerator pedal 32, is connected through
an A/D converter 34 to the input port 24.
[0031] Moreover, the output port 25 is connected through a drive
circuit 35 to the in-cylinder injector 11, and is further connected
through actuator drive circuits 36a and 36b to an actuator 15 which
is made to individually operate the VVT mechanisms 14a and 14b.
[0032] In this embodiment, as FIG. 3 shows, the driving range is
divided into a driving range I at idling operation or low-speed and
low-load operation, a compression ignition possible driving range
II and a driving range III other than these ranges I and II in a
manner that an engine speed Ne and an engine load Lo are used as
parameters. In addition, as FIG. 2A shows, the valve timings in the
driving ranges I and III are controlled so that a positive overlap
period BVO for which both the valves 6 and 7 take the opening
conditions is set up for a period from the late part of an exhaust
stroke to the early part of an intake stroke. On the other hand, as
FIG. 2B shows, in the driving range II, a negative overlap period
BVC for which both the valves 6 and 7 take the closure conditions
is set up for a period from the end of an exhaust stroke and the
beginning of an intake stroke.
[0033] Furthermore, as combustion modes, a stratified combustion
control is implemented in the driving range I, the compression
ignition combustion control is implemented in the driving range II,
and uniform combustion control is executed in the driving range
III.
[0034] Under the stratified combustion control, a fuel is injected
from the in-cylinder injector 11 toward the piston cavity 2a made
in the piston 2 at a relatively late timing such as a late part of
a compression stroke, and the injected fuel rises along the curved
concave surface of the piston cavity 2a so that a relatively rich
air fuel mixture gathers around the sparking portion of the spark
plug 12 to provide a satisfactory ignition characteristic.
[0035] Under the uniform combustion control, the fuel is injected
from the in-cylinder injector 11 into the combustion chamber at
such a relatively early timing as the beginning of an intake stroke
to promote to mix the fuel injected and fresh air so that a
homogenized air fuel mixture is produced at the ignition by the
spark plug 12.
[0036] On the other hand, in the driving range II, during the
negative overlap period BVC (see FIG. 2B) for which both the intake
valve 6 and exhaust valve 7 are in the closing condition, or during
a period from an intake stroke to the first half of a compression
stroke, the fuel is injected from the injector 11 to produce a
uniform premixed air fuel mixture before the gas temperature in the
combustion chamber 3 reaches the self-igniting condition possible
temperature. So that, when the gas temperature reaches the
self-igniting temperature, the air fuel mixture in the combustion
chamber 3 is ignited simultaneously, thereby realizing multi-point
ignition combustion, that is, the combustion that the flame does
not propagate, so to speak, the combustion made by an infinity
number of spark plugs.
[0037] More concretely, in the driving range II, during the
negative overlap period BVC for which both the intake valve 6 and
exhaust valve 7 are in the closing condition, the residual gas kept
in the combustion chamber 3 is pressurized to rise in temperature
in accordance with the lifting of the piston 2, and the temperature
of fresh air taken in the subsequent intake stroke increases due to
the residual gas, and further the temperature of this fresh air
increases by the subsequent compression stroke, then reaching the
self-igniting possible temperature.
[0038] The combustion temperature of the air fuel mixture by the
self-igniting combustion is approximately 1800.degree. C., and is
lower by approximately 200.degree. C. than the combustion based on
the ordinary ignition. In addition, since the air fuel mixture is
ignited simultaneously, rapid low-temperature combustion becomes
feasible. In consequence, owing to the low-temperature combustion,
the discharging quantity of NOx is reducible, and because of the
simultaneous ignition, the thermal efficiency becomes high and the
lean combustion becomes possible accordingly so that the exhaust
gas can substantially become clean while the fuel consumption being
kept close to that of a diesel engine.
[0039] In this connection, low-cetane-value gasoline or methanol is
used. It has been known that even such a low-cetane-value fuel, for
example, gasoline, allows the self-igniting condition when the gas
temperature in the combustion chamber 3 exceeds approximately
900.degree. C. In this embodiment, the temperature increase by the
pressurization of the residual gas and the normal compression ratio
are used as temperature increasing means, and the gas temperature
is set through the use of these functions to reach the compression
ignition possible temperature.
[0040] That is, in the case of the constant volume cycle, the
theoretical thermal efficiency .eta.th is given by the following
equation:
.eta.th=1-(1/.epsilon..sup..kappa.-1)
[0041] where .epsilon.: compression ratio and .kappa.: ratio of
specific heat.
[0042] Accordingly, when the ratio .kappa. of specific heat is
increased by the pressurization temperature increase of the
residual gas, it is possible to raise the gas temperature up to the
self-igniting temperature within a practical range without
increasing the compression ratio .epsilon. considerably. In this
embodiment, the compression ratio is set to be in a range of 14 to
20.
[0043] In this case, it is said that, as indicated by a solid line
in FIG. 8, if the maximum value of the combustion is set at a
portion passing by the compression top dead center, the ideal
combustion, which does not produce the knocking, is attainable.
Naturally, the self-igniting timing at this time is immediately
before the end of the compression stroke. The electronic control
unit (ECU) 20 controls the self-igniting timing on the premixed air
fuel through the control of the fuel injection timing.
[0044] Concretely, the process is conducted as shown in the flow
charts of FIGS. 4 and 5. FIG. 4 shows a combustion mode setting
routine. In this routine, in step S1, with reference to a map shown
in FIG. 3, the driving range is determined on the basis of engine
driving condition detecting parameters such as an engine speed Ne
and an engine load Lo.
[0045] If a decision is made that the driving condition is a
low-speed low-load state, including an idling driving state, which
exists in the driving range I, the operational flow advances to a
step S2 to output, to the actuator 15, drive signals for changing
the rotational phases of the intake cam 13a and the exhaust cam 13b
so that both the intake valve 6 and exhaust valve 7 take the
opening condition for a period from a late part of an exhaust
stroke to an early part of an intake stroke by the VVT mechanisms
14a and 14b to establish the positive overlap period BVO (see FIG.
2A). Following this, the operational flow advances to a step S3 for
setting the combustion mode at stratified combustion control based
on the ignition by the spark plug 12. Thereafter, this routine
comes to an end.
[0046] Incidentally, a well-known technique is employed for the
fuel injection timing at the stratified combustion control, and the
description thereof will be omitted for brevity.
[0047] On the other hand, when the driving condition is in the
driving range III, the operational flow goes to a step S4 in which,
as well as the step S2, drive signals for changing the rotational
phases of the intake cam 13a and the exhaust cam 13b are outputted
to the actuator 15 so that both the intake valve 6 and exhaust
valve 7 take the opening condition for a period from a late part of
an exhaust stroke to an early part of an intake stroke by means of
the VVT mechanisms 14a and 14b to set up the positive overlap
period BVO (see FIG. 2A). Following this, the operational flow
advances to a step S5 for setting the combustion mode at uniform
combustion control based on the self-igniting by the spark plug 12.
Thereafter, this routine comes to an end.
[0048] Incidentally, a well-known technique is employed for the
fuel injection timing at the uniform combustion control, and the
description thereof will be omitted for brevity.
[0049] Furthermore, when the driving condition is in the
self-igniting range forming the driving range II, the operational
flow proceeds to a step S6 in which drive signals for changing the
rotational phases of the intake cam 13a and the exhaust cam 13b are
outputted to the actuator 15 so that both the intake valve 6 and
exhaust valve 7 take the closure condition for a period from the
end of an exhaust stroke to the beginning of an intake stroke by
means of the VVT mechanisms 14a and 14b to set up the negative
overlap period BVC (see FIG. 2B). Following this, the operational
flow advances to a step S7 for setting the combustion mode at the
self-igniting combustion control. Thereafter, this routine comes to
an end.
[0050] In the combustion mode setting routine shown in FIG. 4, upon
the selection of the self-igniting combustion, the self-igniting
injection control routine as shown in FIG. 5 is initiated, and a
step S11 is first implemented to make a decision on the driving
condition on the basis of engine driving condition detecting
parameters such as an engine speed Ne and an engine load Lo. If the
decision shows low-load driving, the operational flow proceeds to a
step S12 to implement the intake stroke injection control, and then
this routine comes to an end. On the other hand, if the decision
shows high-load driving, the operational flow proceeds to a step
S13 to execute the first-half injection control of the compression
stroke, and then this routine comes to an end.
[0051] Upon the implementation of the intake stroke injection
control in the step S12, an injection start signal is outputted
when the piston 2 in the cylinder undergoing the fuel injection
reaches a set crank angle in the first half of the intake stroke
(see FIG. 6).
[0052] Since the fuel injection start timing at low-load driving is
set in the first half of the intake stroke, the fuel injected
entirely evaporates to produce premixed air fuel up to the
self-igniting timing, thus promoting the self-igniting. In this
case, as FIG. 7 shows, preferably, the fuel injection start timing
is set at a timing that the tip portion of the fuel spray toward
the top surface T of the piston 2 at the intake stroke follows the
piston 2 without coming into contact with the top surface T of the
piston. In this embodiment, it is set at approximately 60.degree.
CA (Cam Angle) after the top dead center of the exhaust stroke.
[0053] Since the injection is conducted in a state where the tip
portion of the fuel spray at the lowering stroke follows the piston
2 without attaching itself to the piston top surface T, the fuel is
efficiently diffused to produce the homogenized and premixed air
fuel mixture within the combustion chamber 3.
[0054] In this case, if the fuel is injected at the vicinity of the
end of the intake stroke as indicated by, for example, a dashed
line in the same illustration, since the gas within the combustion
chamber 3 is compressed by lifting the piston 2 at the compression
stroke, the fuel injected from the in-cylinder injector 11 is not
sufficiently diffused, which makes it difficult to offer the
homogenized and premixed air fuel mixture. Moreover, if the fuel is
injected at the beginning of the intake stroke, since the injected
fuel comes into collision (abutting condition) with the top surface
of the piston 2 to drop therefrom, it is difficult that the fuel
evaporates entirely.
[0055] In addition, upon the implementation of the first-half
injection control in the compression stroke in the step S13, an
injection start signal is outputted when the position 2 in the
cylinder undergoing the fuel injection reaches a set crank angle in
the first half of the compression stroke.
[0056] Since the fuel injection start timing at high-load driving
is set in the first half of the compression stroke, only a portion
of the fuel produces the premixed air fuel mixture while the
remaining fuel is dispersed within the combustion chamber 3 in the
form of fuel-drop (liquid form) and hence, when the premixed air
fuel mixture is compression-ignited, this acts as a heat source to
successively combust the fuel produced by the evaporation of the
fuel-drop, thereby suppressing the preignition indicated by a
dashed line in FIG. 8 and achieving the self-igniting combustion at
a combustion position indicated by a solid line in the same
illustration. In this connection, in this embodiment, the fuel
injection start timing is set at approximately 240.degree. CA after
the top dead center of the exhaust stroke.
[0057] In this case, it is also possible that the fuel injection
start timing assumes a variable value setted previously according
to the driving conditions.
[0058] As stated above, in this embodiment, since the fuel
injection timing is variably setted according to the driving
conditions, it is possible to realize the optimum self-igniting
combustion for obtaining stable combustion in the self-igniting
possible range. In addition, in the driving range II (self-igniting
possible range), both the valves 6 and 7 take the closing condition
for a period from the end of the exhaust stroke to the early part
of the intake stroke to set up the negative overlap period BVC for
which the residual gas is pressurized by the temperature increase;
therefore, it is possible to provide a high ratio of the specific
heat and to easily raise the gas temperature in the combustion
chamber 3 up to the self-igniting possible temperature, which can
control the temperature of the combustion chamber 3.
[0059] Furthermore, a second embodiment of the present invention
will be described hereinbelow with reference to FIGS. 9 to 11. In
this embodiment, the fuel is injected twice during one cycle to
expand the driving range II forming the self-igniting possible
range.
[0060] That is, when the self-igniting combustion control is
selected in the combustion mode setting routine of the first
embodiment shown in FIG. 4, an injection control routine at the
self-igniting combustion is initiated, and a step S21 is first
implemented to check whether or not the cylinder to be subjected to
fuel injection has shifted to an intake stroke. When it has shifted
to the intake stroke, the operational flow goes to a step S22 to
implement the first injection control.
[0061] In this first injection control, the crank angle is counted
from when the top dead center of the exhaust stroke has been
passed, or the elapsed time is measured, and the fuel injection is
initiated when it reaches a predetermined crank angle (in this
embodiment, approximately 60.degree. CA) in the first half of the
intake stroke.
[0062] As in the case of the first embodiment, the fuel first
injected enables the production of the uniform premixed air fuel
mixture before the gas temperature in the combustion chamber 3
reaches the self-igniting possible temperature.
[0063] Subsequently, a step S23 follows to make a decision on a
driving condition on the basis of engine driving condition
detecting parameter such as an engine load Lo and an engine speed
Ne. If the decision shows a low-load driving, the operational flow
advances to a step S24 so that a standby condition is taken until
the cylinder to be subjected to the fuel injection shifts to the
expansion stroke. When it has shifted to the expansion stroke, the
operational flow advances to a step S25 to implement the second
injection control, and then this routine comes to an end.
[0064] In the second injection control, the crank angle is counted
from when the top dead center of the compression stroke has been
passed, or the elapsed time is measured, and the fuel injection is
initiated when it reaches a predetermined crank angle in the first
half of the expansion stroke (see FIG. 10B).
[0065] The fuel injection quantity under the second injection
control is set to be smaller than the first fuel injection
quantity. In this embodiment, the ratio of the first fuel injection
quantity and the second fuel injection quantity is set to be 7:3.
Incidentally, the air fuel ratio A/F is based on the sum total of
the first and second fuel injection quantities.
[0066] Since the second fuel injection timing at low-load operation
is set in the first half of the expansion stroke, the exhaust gas
temperature rises. And consequently, the residual gas temperature
further rises during the next negative overlap period BVC (see FIG.
2B) for which both the intake valve 6 and exhaust valve 7 take the
closure condition between the end of the exhaust stroke and the
beginning of the intake stroke, and a higher ratio of specific heat
is obtainable accordingly, which promoting the next self-igniting
combustion.
[0067] When the decision in the step S23 shows high-load driving,
the operational flow advances to a step S26 where the standby
condition is taken until the cylinder to be subjected to the fuel
injection has shifted to the compression stroke, and when it has
shifted to the compression stroke, the operational flow advances to
a step S27 to implement the second fuel injection control, and then
this routine comes to an end.
[0068] In the second injection control at the high-load driving,
the crank angle is counted from when the piston 2 has passed
through the bottom dead center of the intake stroke, or the elapsed
time is measured, and the fuel injection is conducted when it
reaches a predetermined crank angle in the second half of the
compression stroke (see FIG. 10A).
[0069] The second fuel injection quantity at high-load operating
condition is set to form a ratio similar to that of the fuel
injection quantities at the low-load operating condition, and
naturally, the air fuel ratio A/F is based on the sum total of the
first and second fuel injection quantities.
[0070] Since, at the low-load operating condition, the second fuel
injection timing is set in the second half of the compression
stroke, liquid-drop-like fuel is dispersed in the combustion
chamber 3 in the middle of self-igniting combustion, and the fuel
generated by the evaporation of the fuel-drop is combusted (burnt)
consecutively, thereby suppressing the preignition and to offer the
ideal self-igniting combustion.
[0071] As stated above, since the fuel injection is made in two
stages during one cycle, the self-igniting combustion is promoted
at the low-load driving while the self-igniting combustion is
suppressed at the high-load operating condition to prevent the
preignition; in consequence, as shown in FIG. 11, as compared with
the range of the first embodiment indicated by a broken line, the
driving range II forming a self-igniting possible range can be
expanded by a driving range IV defined at the outside thereof. This
not only achieves further improvement of the fuel consumption but
also realizes the reduction of the exhaust emission, and even
provides the stable combustion.
[0072] In addition, as in the case of the first embodiment, in the
driving range II (compression ignition possible range), since both
the valves 6 and 7 are set in the closure condition for a period
from the end of the exhaust stroke to the beginning of the intake
stroke to establish the negative overlap period BVC for which the
residual gas is temperature-increased by pressurization, the ratio
of specific heat becomes higher, and the gas temperature in the
combustion chamber 3 can easily be increased up to the
self-igniting possible temperature, thus enable the temperature
control of the combustion chamber 3.
[0073] The present invention is not limited to the above-described
embodiments, but for example, the intake valve 6 and the exhaust
valve 7 can be adaptable of an electromagnetic controlled valve,
and in this case, the valve opening/closing timings can be
controlled variably without using the VVT mechanism.
[0074] In addition, it is also appropriate that the exhaust
throttle valve is placed in the exhaust passage, and in the
self-igniting possible range, a portion of the exhaust gas is
restricted by the exhaust throttle valve in the second half of the
exhaust stroke, and at the beginning of the intake stroke, the
exhaust valve is opened, thereby producing the internal EGR. In
this case, there is no need to establish the negative overlap
period BVC.
[0075] Still additionally, it is also possible that the first fuel
injection timing and the second fuel injection timing are set as a
fixed value or that they assume a variable value set on the basis
of driving parameters.
[0076] As described above, according to the present invention, it
is possible to acquire stable combustion conditions in
self-igniting driving range by additionally implementing the fuel
injection timing control so as to overcome the difficulty in the
control of the air fuel mixture temperature.
[0077] Having described the preferred embodiments of the invention
referring to the accompanying drawings, it should be understood
that the present invention is not limited to those precise
embodiments and various changes and modifications thereof could be
made by one skilled in the art without departing from the spirit or
scope of the invention as defined in the appended claims.
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