U.S. patent application number 17/452101 was filed with the patent office on 2022-05-12 for method of controlling engine, and engine system.
The applicant listed for this patent is Mazda Motor Corporation. Invention is credited to Yoshihisa Nou, Noriyuki Ota.
Application Number | 20220145825 17/452101 |
Document ID | / |
Family ID | |
Filed Date | 2022-05-12 |
United States Patent
Application |
20220145825 |
Kind Code |
A1 |
Ota; Noriyuki ; et
al. |
May 12, 2022 |
METHOD OF CONTROLLING ENGINE, AND ENGINE SYSTEM
Abstract
A method of controlling an engine is provided, the method
including the steps of injecting main fuel by a fuel injector
during an intake stroke or a compression stroke, providing a
mixture gas containing fuel and air inside a cylinder, applying by
an ignition device a high voltage between electrodes of a spark
plug at a timing when the mixture gas is not ignited, detecting a
parameter related to a current value of an electric-discharge
channel generated between the electrodes, determining whether the
detected parameter is within a range between a first threshold and
a second threshold to determine a flowing state of a vortex inside
the cylinder, injecting supplemental fuel by the fuel injector
after the main fuel injection when the parameter is determined to
be outside the range, and igniting the mixture gas by the ignition
device using the spark plug after the supplemental fuel
injection.
Inventors: |
Ota; Noriyuki; (Aki-gun,
JP) ; Nou; Yoshihisa; (Aki-gun, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mazda Motor Corporation |
Aki-gun |
|
JP |
|
|
Appl. No.: |
17/452101 |
Filed: |
October 25, 2021 |
International
Class: |
F02D 41/40 20060101
F02D041/40; F02D 41/18 20060101 F02D041/18; F02D 41/00 20060101
F02D041/00; F02P 5/145 20060101 F02P005/145; F02P 17/12 20060101
F02P017/12 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 10, 2020 |
JP |
2020-187350 |
Claims
1. A method of controlling an engine by using a controller, the
engine including a cylinder with a pentroof ceiling, air being
introduced into the cylinder through an intake valve provided to
the ceiling; an ignition device including a spark plug provided at
or near the center axis of the cylinder; and a fuel injector
provided at or near the center axis of the cylinder, the method
comprising the steps of: injecting main fuel by the fuel injector
during one of an intake stroke and a compression stroke, and
providing a mixture gas containing fuel and air inside the
cylinder; applying by the ignition device a high voltage between
electrodes of the spark plug at a timing when the mixture gas is
not ignited, and detecting a parameter related to a current value
of an electric-discharge channel generated between the electrodes;
determining by the controller whether the detected parameter is
within a range between a first threshold and a second threshold to
determine a flowing state of a vortex inside the cylinder;
injecting supplemental fuel by the fuel injector after the
injecting the main fuel, when the parameter is determined to be
outside the range; and igniting the mixture gas by the ignition
device using the spark plug after the injecting the supplemental
fuel.
2. The method of claim 1, wherein the injecting the supplemental
fuel includes, when the parameter is determined to be below the
first threshold, injecting the supplemental fuel at a first
injection timing, and when the parameter is determined to be above
the second threshold, injecting the supplemental fuel at a second
injection timing retarded from the first injection timing.
3. The method of claim 2, wherein the applying the high voltage
includes detecting the parameter by the ignition device at a timing
between an opening of the intake valve and a closing of the intake
valve, and wherein the determining whether the detected parameter
is within the range includes determining by the controller a
flowing state of a swirl vortex inside the cylinder based on the
parameter.
4. The method of claim 3, wherein the applying the high voltage
includes detecting the parameter by the ignition device after a
given time constant passes from the opening of the intake
valve.
5. The method of claim 2, wherein the applying the high voltage
includes detecting the parameter by the ignition device after the
closing of the intake valve, and wherein the determining whether
the detected parameter is within the range includes determining by
the controller a flowing state of a tumble vortex inside the
cylinder based on the parameter.
6. The method of claim 2, wherein the applying the high voltage
includes detecting the parameter by the ignition device during the
intake stroke and during the compression stroke.
7. An engine system, comprising: an engine including: a cylinder
with a pentroof ceiling, air being introduced into the cylinder
through an intake valve provided to the ceiling; an ignition device
including a spark plug provided at or near the center axis of the
cylinder; and a fuel injector provided at or near the center axis
of the cylinder; and a controller electrically connected to the
ignition device and the fuel injector, wherein the controller
includes a processor configured to execute: a main fuel injection
module to control the fuel injector to inject main fuel during one
of an intake stroke and a compression stroke, and provide a mixture
gas containing fuel and air inside the cylinder; a determination
module to control the ignition device to apply a high voltage
between electrodes of the spark plug at a timing when the mixture
gas is not ignited, and detect a parameter related to a current
value of an electric-discharge channel generated between the
electrodes, and to determine whether the parameter detected by the
ignition device is within a range between a first threshold and a
second threshold to determine a flowing state of a vortex inside
the cylinder; a supplemental fuel injection module to control the
fuel injector to inject supplemental fuel after the injection of
the main fuel, when the determination module determines that the
parameter is outside the range; and a main ignition control module
to control the ignition device to ignite the mixture gas by the
spark plug after the fuel injector injects the supplemental
fuel.
8. The engine system of claim 7, wherein when the determination
module determines that the parameter is below the first threshold,
the fuel injector injects the supplemental fuel at a first
injection timing, and when the determination module determines that
the parameter is above the second threshold, the fuel injector
injects the supplemental fuel at a second injection timing retarded
from the first injection timing.
9. The engine system of claim 8, wherein the ignition device
detects the parameter at a timing between an opening of the intake
valve and a closing of the intake valve, and wherein the controller
determines a flowing state of a swirl vortex inside the cylinder
based on the parameter.
10. The engine system of claim 9, wherein the ignition device
detects the parameter after a given time constant passes from the
opening of the intake valve.
11. The engine system of claim 8, wherein the ignition device
detects the parameter after the closing of the intake valve, and
wherein the controller determines a flowing state of a tumble
vortex inside the cylinder based on the parameter.
12. The engine system of claim 8, wherein the ignition device
detects the parameter during the intake stroke and during the
compression stroke.
13. The method of claim 1, wherein the applying the high voltage
includes detecting the parameter by the ignition device at a timing
between an opening of the intake valve and a closing of the intake
valve, and wherein the determining whether the detected parameter
is within the range includes determining by the controller a
flowing state of a swirl vortex inside the cylinder based on the
parameter.
14. The method of claim 1, wherein the applying the high voltage
includes detecting the parameter by the ignition device after the
closing of the intake valve, and wherein the determining whether
the detected parameter is within the range includes determining by
the controller a flowing state of a tumble vortex inside the
cylinder based on the parameter.
15. The method of claim 1, wherein the applying the high voltage
includes detecting the parameter by the ignition device during the
intake stroke and during the compression stroke.
16. The engine system of claim 7, wherein the ignition device
detects the parameter at a timing between an opening of the intake
valve and a closing of the intake valve, and wherein the controller
determines a flowing state of a swirl vortex inside the cylinder
based on the parameter.
17. The engine system of claim 7, wherein the ignition device
detects the parameter after the closing of the intake valve, and
wherein the controller determines a flowing state of a tumble
vortex inside the cylinder based on the parameter.
18. The engine system of claim 7, wherein the ignition device
detects the parameter during the intake stroke and during the
compression stroke.
19. An engine system, comprising: an engine mounted on an
automobile and including: a cylinder with a pentroof ceiling, air
being introduced into the cylinder through an intake valve provided
to the ceiling; an ignition device including a spark plug provided
at or near the center axis of the cylinder; and a fuel injector
provided at or near the center axis of the cylinder; and a
controller electrically connected to the ignition device and the
fuel injector, wherein the controller includes a processor
configured to execute: a main fuel injection module to control the
fuel injector to inject main fuel during one of an intake stroke
and a compression stroke, and provide a mixture gas containing fuel
and air inside the cylinder; a determination module to control the
ignition device to apply a high voltage between electrodes of the
spark plug at a timing when the mixture gas is not ignited, and
detect a parameter related to a current value of an
electric-discharge channel generated between the electrodes, and to
determine whether the parameter detected by the ignition device is
within a range between a first threshold and a second threshold so
as to determine a flowing state of a vortex inside the cylinder; a
supplemental fuel injection module to control the fuel injector to
inject supplemental fuel after the injection of the main fuel, when
the determination module determines that the parameter is outside
the range; and a main ignition control module to control the
ignition device to ignite the mixture gas by the spark plug after
the fuel injector injects the supplemental fuel.
20. The engine system of claim 19, wherein the fuel of the engine
is gasoline.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to control of an engine
according to a flow inside a cylinder.
BACKGROUND OF THE DISCLOSURE
[0002] Increasing combustion speed is beneficial to improve the
fuel efficiency of an engine. In an engine provided with spark
plugs, each spark plug ignites a mixture gas inside a cylinder to
generate a flame around the spark plug. Then, the flame is
propagated entirely inside the cylinder while causing a reaction of
unburned mixture gas, and the combustion for one cycle finishes.
Therefore, in order to accelerate the reaction of the unburned
mixture gas to the flame and to increase the combustion speed, it
is preferable to increase a contacting area between the flame and
the unburned mixture gas, and to generate a strong turbulence.
Conventionally, a swirl flow and a tumble flow are generated inside
the cylinder in order to accelerate the generation of the
turbulence inside the cylinder.
[0003] Although it is known that the turbulence is generated when
the flow inside the cylinder is crushed (broken) before a piston
reaches a top dead center during a compression stroke, the state of
the intake flow may vary between cycles. Therefore, conventionally,
various methods are examined for estimating the in-cylinder
flow.
[0004] For example, JP2014-145306A discloses a technology to cause
a spark plug provided to a combustion chamber to ignite a plurality
of times so as to detect a current value of an electric-discharge
channel of the spark plug, and control an ignition timing according
to an in-cylinder flow which is estimated based on the detected
current value.
[0005] Here, the present inventors conducted a diligent study for
improving the combustion according to the flow estimated based on
the current value of the electric-discharge channel as described in
JP2014-145306A. As a result, it became apparent that the state of
the in-cylinder flow in a latter half of a compression stroke
varies according to a position of the center of a vortex formed
inside the cylinder by the intake flow, and this fluctuation in the
flowing state may be one factor for combustion variation.
[0006] A tumble-vortex component and a swirl-vortex component are
combined in the intake flow to form an oblique in-cylinder flow.
When the centers of the vortexes exist around the central part of
the cylinder in the side view and the plan view, respectively, the
rotating flow is maintained also in the latter half of the
compression stroke. As a result, the turbulence becomes uniform or
substantially uniform entirely inside the cylinder. In this case,
the flame is uniformly or substantially uniformly propagated from
around the center toward a peripheral part inside the cylinder.
[0007] However, the present inventors found that, when the center
of the tumble vortex deviates downward of the cylinder in the side
view, the vortex center contacts a top surface of the piston and a
lower half of the tumble vortex is broken, which causes the
in-cylinder flow to form a forward one-way flow from an
intake-valve side to an exhaust-valve side. With the forward
one-way flow, the turbulence in an area inside the cylinder on the
exhaust-valve side is strong whereas the turbulence in an area on
the intake-valve side is weak. In such a case, although the flame
is easily propagated toward the exhaust-side area, the propagation
toward the intake-side area is difficult.
[0008] Moreover, when the center of the tumble vortex deviates
upward of the cylinder in the side view, the vortex center contacts
a ceiling of the cylinder, and an upper half of the tumble vortex
is broken, which causes the in-cylinder flow to form a backward
one-way flow from the exhaust-valve side to the intake-valve side.
With the backward one-way flow, the turbulence in the intake-side
area of the cylinder is strong whereas the turbulence in the
exhaust-side area is weak. In such a case, although the flame is
easily propagated toward the intake-side area, the propagation
toward the exhaust-side area is difficult.
[0009] On the other hand, the present inventors found that, when
the center of the swirl vortex deviates outward of the cylinder in
the plan view, part of the flame under the propagation from the
central part toward the peripheral part inside the cylinder is
disturbed by the swirl flow deviated from the center of the
cylinder, and thus, the propagation of the flame toward a specific
area is difficult.
[0010] The obstruction of the flame propagation toward the partial
area inside the cylinder lowers the combustion speed, and causes
combustion variation. Therefore, in order to reduce the combustion
variation of the engine, it is necessary to accelerate the flame
propagation toward the partial area according to the state of the
in-cylinder flow. When the combustion variation of the engine is
reduced, fuel efficiency of the engine improves.
SUMMARY OF THE DISCLOSURE
[0011] Therefore, the present disclosure is made in view of the
above situation, and one purpose thereof is to provide a method of
controlling an engine, capable of reducing combustion variation by
estimating a state of a flow inside a cylinder and controlling a
fuel injector according to the flowing state.
[0012] As a result of further diligent study to solve the problem,
the present inventors found that the position of the vortex inside
the cylinder can be estimated by detecting a current value of an
electric-discharge channel which is generated between electrodes of
a spark plug during an intake stroke or a compression stroke before
starting the combustion of the mixture gas, and thus, the flowing
state in a latter half of the compression stroke can be
estimated.
[0013] According to one aspect of the present disclosure, a method
of controlling an engine by using a controller is provided. The
engine includes a cylinder with a pentroof ceiling, air being
introduced into the cylinder through an intake valve provided to
the ceiling, an ignition device including a spark plug provided at
or near the center axis of the cylinder, and a fuel injector
provided at or near the center axis of the cylinder. The method
includes the steps of injecting main fuel by the fuel injector
during one of an intake stroke and a compression stroke, and
providing a mixture gas containing fuel and air inside the
cylinder, applying by the ignition device a high voltage between
electrodes of the spark plug at a timing when the mixture gas is
not ignited, and detecting a parameter related to a current value
of an electric-discharge channel generated between the electrodes,
determining by the controller whether the detected parameter is
within a range between a first threshold and a second threshold to
determine a flowing state of a vortex inside the cylinder,
injecting supplemental fuel by the fuel injector after the
injecting the main fuel, when the parameter is determined to be
outside the range, and igniting the mixture gas by the ignition
device using the spark plug after the injecting the supplemental
fuel.
[0014] Here, for convenience, a "forward one-way flow" indicates a
flow from an intake-valve side to an exhaust-valve side, and a
"backward one-way flow" indicates a flow from the exhaust-valve
side to the intake-valve side; however, they may be the
opposite.
[0015] The engine of this configuration includes the cylinder with
the pentroof ceiling, the spark plug provided at or near the center
axis of the cylinder, and the fuel injector provided at or near the
center axis of the cylinder. Since the ceiling is the pentroof
type, the intake air introduced into the cylinder forms a tumble
vortex, and the intake air introduced into the cylinder through the
intake valve also forms a swirl vortex. The flow inside the
cylinder becomes oblique with respect to the cylinder axis.
[0016] During the intake stroke or the compression stroke, the
mixture gas is formed inside the cylinder by the injecting main
fuel by the fuel injector, and the ignition device applies the high
voltage between the electrodes of the spark plug at the timing when
the mixture gas is not ignited, and generates the
electric-discharge channel between the electrodes. In the detecting
the parameter, the parameter related to the current value of the
electric-discharge channel generated at the spark plug is detected.
Note that the detecting the parameter may be after or before the
main fuel injection.
[0017] The electric-discharge channel generated between the
electrodes by energy being applied to the spark plug, is extended
as the intensity of the flow around the spark plug increases. The
extension of the electric-discharge channel increases the
resistance between the electrodes, which accelerates a decrease in
the voltage applied between the electrodes. As a result, a period
of time required for the consumption of the energy applied to the
spark plug (i.e., a discharge duration) becomes shorter. The
present inventors found that the ignition device can measure the
intensity of the flow around the spark plug by detecting the
discharge duration of the current as the parameter related to the
current value, and can estimate, based on the measured intensity,
the center of the vortex inside the cylinder.
[0018] In more detail, when the center of the tumble vortex
positions around the center of the combustion chamber in a side
view, since the center of the tumble vortex separates from the
spark plug to a certain extent, the intensity of the flow around
the spark plug becomes moderate. In this case, the parameter falls
within the range between the first threshold and the second
threshold. When the center of the tumble vortex deviates upward in
the cylinder, since the center of the tumble vortex is near the
spark plug, the intensity of the flow around the spark plug becomes
weak (i.e., the flow is slow). In this case, the parameter exceeds
the second threshold. When the center of the tumble vortex deviates
downward in the cylinder, since the center of the tumble vortex is
far from the spark plug, the intensity of the flow around the spark
plug becomes strong (i.e., the flow is fast). In this case, the
parameter falls below the first threshold. The controller
determines whether the detected parameter is below the first
threshold or above the second threshold. According to this, the
controller can estimate, before igniting the mixture gas inside the
cylinder, whether the flow is the forward one-way flow or the
backward one-way flow and whether an area where the turbulence is
weak exists.
[0019] Moreover, when the center of the swirl vortex positions
around the center of the cylinder in a plan view, the intensity of
the flow around the spark plug becomes moderate, and the parameter
falls within the range between the first threshold and the second
threshold. When the center of the swirl vortex deviates from the
center of the cylinder, the intensity of the flow around the spark
plug becomes weak and the parameter exceeds the second threshold,
and alternatively, the intensity of the flow around the spark plug
becomes strong and the parameter falls below the first threshold.
The controller determines whether the detected parameter is below
the first threshold or above the second threshold so that it can
estimate whether an area where the flame is difficult to propagate
exists before igniting the mixture gas inside the cylinder.
[0020] Moreover, when the parameter is determined to be below the
first threshold or above the second threshold, the fuel injector
injects the supplemental fuel, in the injecting the supplemental
fuel, at an injection timing retarded from the main fuel. The
supplemental fuel makes the fuel concentration higher at the area
where the turbulence is weak or the area where the flame is
difficult to propagate (hereinafter, referred to as a "specific
area"). Therefore, in a latter half of the compression stroke, a
normal mixture gas can be positioned in areas other than the
specific area, whereas the mixture gas with the relatively high
fuel concentration can be positioned in the specific area. After
the injecting the supplemental fuel, the ignition device uses the
spark plug to ignite the mixture gas to accelerate the flame
propagation toward the specific area, and the flame is uniformly or
substantially uniformly propagated entirely inside the cylinder. As
a result, the combustion speed increases.
[0021] As described above, by the fuel injector injecting the
supplemental fuel as needed according to the flowing state inside
the cylinder of each cycle, the combustion speed is made to be
constant or substantially constant between the cycles, and thus,
combustion variation is reduced. The fuel efficiency of this engine
improves.
[0022] The injecting the supplemental fuel may include, when the
parameter is determined to be below the first threshold, injecting
the supplemental fuel by the fuel injector at a first injection
timing, and when the parameter is determined to be above the second
threshold, injecting the supplemental fuel at a second injection
timing retarded from the first injection timing.
[0023] When the parameter is determined to be below the first
threshold, the tumble vortex flows as the forward one-way flow from
the intake-valve side to the exhaust-valve side in the latter half
of the compression stroke, and thus, the turbulence on the
intake-valve side is not likely be generated. When the parameter is
determined to be below the first threshold, by the fuel injector
injecting the supplemental fuel at the relatively advanced timing,
the supplemental fuel does not receive high compression pressure
inside the cylinder, and rides on the flow of the tumble vortex to
be carried from the exhaust-valve side to the intake-valve side
area. Thus, the mixture gas with the high fuel concentration can be
positioned on the intake-valve side at the ignition timing.
[0024] On the other hand, when the parameter is determined to be
above the second threshold, the tumble vortex becomes the backward
one-way flow from the exhaust-valve side to the intake-valve side
in the latter half of the compression stroke, and thus, the
turbulence on the exhaust-valve side is not likely be generated.
When the parameter is determined to be above the second threshold,
by the fuel injector injecting the supplemental fuel at the
relatively retarded timing, the supplemental fuel receives high
compression pressure inside the cylinder, and stays in the central
part inside the cylinder when seen in a side view, and then flows
toward the exhaust valve where the flow is weak. Thus, the mixture
gas with the high fuel concentration can be positioned on the
exhaust-valve side at the ignition timing.
[0025] Moreover, when the parameter is determined to be below the
first threshold, the center of the swirl vortex deviates toward the
intake valve. This is because the maximum flow velocity of the
intake flow introduced into the cylinder is comparatively low in
the velocity distribution in the radial direction, and a kurtosis
of the flow velocity distribution is low. In this case, the flame
is difficult to propagate toward the intake-valve side area. When
the parameter is determined to be below the first threshold, the
fuel injector injects the supplemental fuel at the relatively
advanced timing. The supplemental fuel rides on the flow of the
swirl vortex to be carried to the intake-valve side area taking a
long time. Thus, the mixture gas with the high fuel concentration
can be positioned near the intake valve at the ignition timing.
[0026] On the other hand, when the parameter is determined to be
above the second threshold, the center of the swirl vortex deviates
toward the exhaust valve. This is because the flow velocity of the
intake flow introduced into the cylinder is extremely high near a
liner. Also in this case, the flame is difficult to propagate
toward the intake-valve side area. When the parameter is determined
to be above the second threshold, the fuel injector injects the
supplemental fuel at the relatively retarded timing. The
supplemental fuel rides on the fast flow near the liner to be
carried to the intake-valve side area quickly. Thus, the mixture
gas with the high fuel concentration can be positioned near the
intake valve at the ignition timing.
[0027] The applying the high voltage may include detecting the
parameter by the ignition device at a timing between an opening of
the intake valve and a closing of the intake valve. The determining
whether the detected parameter is within the range may include
determining by the controller a flowing state of a swirl vortex
inside the cylinder based on the parameter.
[0028] The oblique flow generated by the tumble flow and the swirl
flow can be divided into the tumble vortex and the swirl vortex.
The center of the swirl vortex mainly caused by the swirl flow
stabilizes in a period during the intake stroke between the opening
and the closing of the intake valve. Thus, by the ignition device
detecting the parameter in the period between the opening and the
closing of the intake valve, the controller can accurately estimate
the flowing state including the center of the swirl vortex.
[0029] The applying the high voltage may include detecting the
parameter by the ignition device after a given time constant passes
from the opening of the intake valve.
[0030] The intake air easily varies for a certain period from the
moment when the intake valve opens. Thus, by not allowing the
ignition device to detect the parameter for the certain period, the
controller can further accurately estimate the center of the swirl
vortex.
[0031] The applying the high voltage may include detecting the
parameter by the ignition device after the closing of the intake
valve. The determining whether the detected parameter is within the
range may include determining by the controller a flowing state of
a tumble vortex inside the cylinder based on the parameter.
[0032] The center of the tumble vortex mainly caused by the tumble
flow stabilizes in a period during the compression stroke after the
closing of the intake valve. Thus, by the ignition device detecting
the parameter after the closing of the intake valve, the controller
can accurately estimate the flowing state including the center of
the tumble vortex.
[0033] The applying the high voltage may include detecting the
parameter by the ignition device during the intake stroke and
during the compression stroke.
[0034] That is, by the ignition device detecting the parameter
during both of the intake stroke and the compression stroke, as
described above, the controller can estimate the positions of the
center of the vortex comprised of the swirl vortex component and
the center of the vortex comprised of the tumble vortex component,
and thus, the state of the oblique flow inside the cylinder can be
estimated accurately.
[0035] According to another aspect of the present disclosure, an
engine system is provided, which includes an engine and a
controller. The engine includes a cylinder with a pentroof ceiling,
air being introduced into the cylinder through an intake valve
provided to the ceiling, an ignition device including a spark plug
provided at or near the center axis of the cylinder, and a fuel
injector provided at or near the center axis of the cylinder, and
the controller is electrically connected to the ignition device and
the fuel injector. The controller includes a processor configured
to execute a main fuel injection module to control the fuel
injector to inject main fuel during one of an intake stroke and a
compression stroke, and provide a mixture gas containing fuel and
air inside the cylinder, a determination module to control the
ignition device to apply a high voltage between electrodes of the
spark plug at a timing when the mixture gas is not ignited, and
detect a parameter related to a current value of an
electric-discharge channel generated between the electrodes, and to
determine whether the parameter detected by the ignition device is
within a range between a first threshold and a second threshold to
determine a flowing state of a vortex inside the cylinder, a
supplemental fuel injection module to control the fuel injector to
inject supplemental fuel after the injection of the main fuel, when
the determination module determines that the parameter is outside
the range, and a main ignition control module to control the
ignition device to ignite the mixture gas by the spark plug after
the fuel injector injects the supplemental fuel.
[0036] Such an engine system is based on the knowledge of the
present inventors that the center of the vortex inside the cylinder
can be estimated when the ignition device detects the parameter
related to the current value of the electric-discharge channel
generated between the electrodes of the spark plug, as described
above.
[0037] The controller causes the fuel injector to inject the
supplemental fuel as needed according to the estimated center of
the vortex, after the injection of the main fuel and before the
ignition. Thus, the mixture gas with the high fuel concentration
can be positioned in the specific area in the latter half of the
compression stroke.
[0038] The controller then controls the ignition device so that the
spark plug ignites the mixture gas, which increases the combustion
speed at the area where the mixture gas with the high fuel
concentration is positioned.
[0039] As described above, by injecting the supplemental fuel as
needed in each cycle, the combustion speed is made to be constant
or substantially constant between the cycles, and thus, combustion
variation is reduced.
[0040] When the determination module determines that the parameter
is below the first threshold, the fuel injector may inject the
supplemental fuel at a first injection timing, and when the
determination module determines that the parameter is above the
second threshold, the fuel injector may inject the supplemental
fuel at a second injection timing retarded from the first injection
timing.
[0041] By changing the injection timing of the supplemental fuel
based on the magnitude relationship between the parameter, and the
first threshold and the second threshold, the mixture gas with the
high fuel concentration can be positioned in the specific area.
[0042] The ignition device may detect the parameter at a timing
between an opening of the intake valve and a closing of the intake
valve. The controller may determine a flowing state of a swirl
vortex inside the cylinder based on the parameter.
[0043] As described above, by the ignition device detecting the
parameter during the intake stroke between the opening and the
closing of the intake valve, the controller can accurately estimate
the center of the swirl vortex.
[0044] The ignition device may detect the parameter after a given
time constant passes from the opening of the intake valve.
[0045] As described above, the intake air easily varies for a
certain period from the moment when the intake valve opens. Thus,
by not allowing the ignition device to detect the parameter for the
certain period, the controller can further accurately estimate the
center of the vortex of the swirl vortex.
[0046] The ignition device may detect the parameter after the
closing of the intake valve. The controller may determine a flowing
state of a tumble vortex inside the cylinder based on the
parameter.
[0047] As described above, by the ignition device detecting the
parameter during the compression stroke after the closing of the
intake valve, the controller can accurately estimate the center of
the tumble vortex.
[0048] The ignition device may detect the parameter during the
intake stroke and during the compression stroke.
[0049] As described above, by the ignition device detecting the
parameter during both of the intake stroke and the compression
stroke, the controller can estimate the positions of the center of
the vortex comprised of the swirl vortex component and the center
of the vortex comprised of the tumble vortex component, and thus,
the state of the oblique flow inside the cylinder can be estimated
accurately.
[0050] According to still another aspect of the present disclosure,
an engine system is provided, which includes an engine and a
controller. The engine is mounted on an automobile and includes a
cylinder with a pentroof ceiling, air being introduced into the
cylinder through an intake valve provided to the ceiling, an
ignition device including a spark plug provided at or near the
center axis of the cylinder, and a fuel injector provided at or
near the center axis of the cylinder. The controller is
electrically connected to the ignition device and the fuel
injector. The controller includes a processor configured to execute
a main fuel injection module to control the fuel injector to inject
main fuel during one of an intake stroke and a compression stroke,
and provide a mixture gas containing fuel and air inside the
cylinder, a determination module to control the ignition device to
apply a high voltage between electrodes of the spark plug at a
timing when the mixture gas is not ignited, and detect a parameter
related to a current value of an electric-discharge channel
generated between the electrodes, and to determine whether the
parameter detected by the ignition device is within a range between
a first threshold and a second threshold so as to determine a
flowing state of a vortex inside the cylinder, a supplemental fuel
injection module to control the fuel injector to inject
supplemental fuel after the injection of the main fuel, when the
determination module determines that the parameter is outside the
range, and a main ignition control module to control the ignition
device to ignite the mixture gas by the spark plug after the fuel
injector injects the supplemental fuel.
[0051] The fuel of the engine may be gasoline.
BRIEF DESCRIPTION OF DRAWINGS
[0052] FIG. 1 is a view illustrating an engine system.
[0053] FIG. 2 is a view illustrating a configuration of a
combustion chamber of an engine, where an upper part of this figure
is a plan view of the combustion chamber and a lower part of this
figure is a cross-sectional view taken along a line II-II in the
upper part.
[0054] FIG. 3 is a block diagram of the engine system.
[0055] FIG. 4 is a view illustrating an ignition device.
[0056] FIG. 5 is a block diagram illustrating functional blocks
related to control of the engine.
[0057] FIG. 6 is a view illustrating the center of a tumble vortex
and a state of flow inside a cylinder in a latter half of a
compression stroke.
[0058] FIG. 7 is a view illustrating a time-series change in
voltage and current between electrodes of a spark plug at different
flow intensities around the spark plug.
[0059] FIG. 8 is a view illustrating a duration of an electric
discharge detected by the ignition device, and the center of the
tumble vortex.
[0060] FIG. 9 is a view illustrating a relationship between the
center of a swirl vortex and a propagation state of flame inside
the cylinder.
[0061] FIG. 10 is a view illustrating a relationship between the
duration of the electric discharge detected by the ignition device,
and the center of the swirl vortex.
[0062] FIG. 11 is a time chart illustrating an injection timing of
main fuel, a timing of the electric discharge, an injection timing
of supplemental fuel, and a timing of a main ignition.
[0063] FIG. 12 is a view illustrating a change in a flow and
distribution of the supplemental fuel inside the cylinder when the
center of the tumble vortex is near a piston.
[0064] FIG. 13 is a view illustrating the change in the flow and
the distribution of the supplemental fuel inside the cylinder when
the center of the tumble vortex is near a ceiling.
[0065] FIG. 14 is a view illustrating the change in the flow and
the distribution of the supplemental fuel inside the cylinder when
the center of the swirl vortex deviates toward an exhaust valve,
and when the center of the swirl vortex deviates toward an intake
valve.
[0066] FIG. 15 is a flowchart illustrating a process for
controlling the engine executed by an ECU.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0067] Hereinafter, one embodiment of a method of controlling an
engine, and an engine system is described with reference to the
accompanying drawings. The engine, the engine system, and the
engine control method described herein are merely illustration.
[0068] FIG. 1 is a view illustrating the engine system. FIG. 2 is a
view illustrating a configuration of a combustion chamber of the
engine. An intake side and an exhaust side illustrated in FIG. 1
are opposite from the intake side and the exhaust side illustrated
in FIG. 2. FIG. 3 is a block diagram illustrating a control device
for the engine.
[0069] The engine system includes an engine 1. The engine 1
includes cylinders 11, and is a four-stroke engine in which an
intake stroke, a compression stroke, an expansion stroke, and an
exhaust stroke are repeated in each cylinder 11. The engine 1 is
mounted on a four-wheeled automobile, and the automobile travels
according to the operation of the engine 1. Fuel of the engine 1 is
gasoline in this example.
(Configuration of Engine)
[0070] The engine 1 is provided with a cylinder block 12 and a
cylinder head 13. The cylinder head 13 is placed on the cylinder
block 12. A plurality of cylinders 11 are formed inside the
cylinder block 12. The engine 1 is a multi-cylinder engine. In FIG.
1, only one cylinder 11 is illustrated.
[0071] A piston 3 is inserted into each cylinder 11. The piston 3
is coupled to a crankshaft 15 through a connecting rod 14. The
piston 3 reciprocates inside the cylinder 11. The piston 3, the
cylinder 11, and the cylinder head 13 define a combustion chamber
17.
[0072] As illustrated in the lower part of FIG. 2, a lower surface
of the cylinder head 13 (i.e., a ceiling of the cylinder 11) is
constituted by a sloped surface 1311 and a sloped surface 1312. The
sloped surface 1311 is a slope on a side of an intake valve 21
(described later), and inclines upwardly toward a central part of
the ceiling of the cylinder 11. The sloped surface 1312 is a slope
on a side of an exhaust valve 22 (described later), and inclines
upwardly toward the central part of the ceiling of the cylinder 11.
The ceiling of the cylinder 11 is a so-called pentroof type.
[0073] The cylinder head 13 is formed with intake ports 18 for the
cylinders 11 such that each intake port 18 communicates with the
inside of the corresponding cylinder 11. Although detailed
illustration is omitted, the intake port 18 is a so-called tumble
port. That is, the intake port 18 has a shape which generates a
tumble flow inside the cylinder 11. The pentroof ceiling of the
cylinder 11 and the tumble port generate the tumble flow inside the
cylinder 11.
[0074] Each intake port 18 is provided with the intake valve 21.
The intake valve 21 opens and closes the intake port 18. A valve
operating mechanism opens and closes the intake valve 21 at a given
timing. The valve operating mechanism may be a variable valve
operating mechanism which varies a valve timing and/or a valve
lift. As illustrated in FIG. 3, the valve operating mechanism
includes an intake S-VT (Sequential-Valve Timing) 23 of an electric
type or a hydraulic type. The intake S-VT 23 continuously changes a
rotational phase of an intake camshaft within a given angle range.
A valve opening period of the intake valve 21 does not change.
[0075] The cylinder head 13 is formed with exhaust ports 19 for the
cylinders 11 such that each exhaust port 19 communicates with the
inside of the corresponding cylinder 11.
[0076] Each exhaust port 19 is provided with the exhaust valve 22.
The exhaust valve 22 opens and closes the exhaust port 19. A valve
operating mechanism opens and closes the exhaust valve 22 at a
given timing. The valve operating mechanism may be a variable valve
operating mechanism which varies a valve timing and/or a valve
lift. As illustrated in FIG. 3, the valve operating mechanism
includes an exhaust S-VT 24 of an electric type or a hydraulic
type. The exhaust S-VT 24 continuously changes a rotational phase
of an exhaust camshaft within a given angle range. A valve opening
period of the exhaust valve 22 does not change.
[0077] Injectors 6 are attached to the cylinder head 13 for the
respective cylinders 11. As illustrated in FIG. 2, each injector 6
is provided to the central part of the cylinder 11 in the plan view
(at or near a center axis X1 of the cylinder). In detail, the
injector 6 is disposed in a valley part of the pentroof where the
sloped surface 1311 and the sloped surface 1312 intersect with each
other.
[0078] The injector 6 directly injects fuel into the cylinder 11.
The injector 6 is one example of a fuel injector, and is of a
multiple nozzle hole type having a plurality of nozzle holes (not
illustrated in detail). As illustrated by two-dot chain lines in
FIG. 2, the injector 6 injects fuel radially outwardly from the
central part to a peripheral part of the cylinder 11. Although, in
this example, the injector 6 has ten nozzle holes which are
circumferentially disposed at an equal angle, the number of nozzle
holes and the positions thereof are not particularly limited to
this configuration.
[0079] The injector 6 is connected to a fuel supply system 61. The
fuel supply system 61 is comprised of a fuel tank 63 which stores
fuel, and a fuel supply passage 62 which couples the fuel tank 63
to the injector 6. A fuel pump 65 and a common rail 64 are
interposed in the fuel supply passage 62. The fuel pump 65 pumps
fuel to the common rail 64. The fuel pump 65 is a plunger-type pump
driven by the crankshaft 15 in this example. The common rail 64
stores at a high fuel pressure the fuel pumped from the fuel pump
65. When the injector 6 is valve-opened, the fuel stored in the
common rail 64 is injected into the cylinder 11 from the nozzle
holes of the injector 6. The pressure of the fuel supplied to the
injector 6 may be changed according to the operating state of the
engine 1. Note that the configuration of the fuel supply system 61
is not limited to the configuration described above.
[0080] Spark plugs 25 are attached to the cylinder head 13 for the
respective cylinders 11. Each spark plug 25 forcibly ignites a
mixture gas inside the cylinder 11. Although detailed illustration
is omitted, a center electrode and a ground electrode of the spark
plug 25 are positioned at the central part of the cylinder 11 in
the plan view, near the ceiling.
[0081] As illustrated in FIGS. 1 and 3, the spark plug 25 is
electrically connected to an ignition device 7. The ignition device
7 applies voltage between the electrodes of the spark plug 25 to
cause an electric discharge (arc discharge) so as to ignite the
mixture gas inside the cylinder 11. The ignition device 7 also
causes the spark plug 25 to discharge the electricity when the
mixture gas is not ignited, and detects a parameter related to a
current value of an electric-discharge channel, which is generated
between the electrodes in the electric discharge (details will be
described later). The detected parameter is used to estimate a
state of flow inside the cylinder 11. The configuration of the
ignition device 7 will be described later.
[0082] The engine 1 is connected at one side to an intake passage
40. The intake passage 40 communicates with the intake ports 18 of
the cylinders 11. Air to be introduced into the cylinders 11 flows
through the intake passage 40. The intake passage 40 is provided at
its upstream-end part with an air cleaner 41. The air cleaner 41
filters the air. The intake passage 40 is provided, near its
downstream end, with a surge tank 42. A part of the intake passage
40 downstream of the surge tank 42 constitutes independent passages
branching for the respective cylinders 11. Downstream ends of the
independent passages are connected to the intake ports 18 of the
cylinders 11, respectively.
[0083] The intake passage 40 is provided, between the air cleaner
41 and the surge tank 42, with a throttle valve 43. The throttle
valve 43 adjusts the opening of the valve to control an amount of
air to be introduced into the cylinder 11.
[0084] The engine 1 is provided with a swirl generator which
generates a swirl flow inside the cylinders 11. Although detailed
illustration is omitted, the swirl generator has a swirl control
valve 56 attached to the intake passage 40. The intake passage 40
includes a first intake passage 18a and a second intake passage 18b
(see FIG. 2) which are parallelly provided downstream of the surge
tank 42, and the swirl control valve 56 is provided to the second
intake passage 18b. The swirl control valve 56 is an opening
control valve which is capable of choking a cross-section of the
second intake passage 18b. When the opening of the swirl control
valve 56 is small, a flow rate of the intake air flowing into the
cylinder 11 from the first intake passage 18a is relatively large,
and a flow rate of the intake air flowing into the cylinder 11 from
the second intake passage 18b is relatively small, which increases
the swirl flow inside the cylinder 11. On the other hand, when the
opening of the swirl control valve 56 is large, the flow rate of
the intake air flowing into the cylinder 11 from the first intake
passage 18a and the flow rate of the intake air flowing from the
second intake passage 18b are substantially equal, which reduces
the swirl flow inside the cylinder 11. When the swirl control valve
56 is fully opened, the swirl flow is not generated. Note that as
illustrated by white arrows in FIG. 2, the swirl flow circles in
the counterclockwise direction.
[0085] Note that instead of generating the swirl flow by the swirl
control valve 56, the intake port 18 of the engine 1 may be
configured to be a helical port capable of generating the swirl
flow.
[0086] The engine 1 is connected at the other side to an exhaust
passage 50. The exhaust passage 50 communicates with the exhaust
ports 19 of the cylinders 11. The exhaust passage 50 is a passage
through which exhaust gas discharged from the cylinders 11 flows.
Although detailed illustration is omitted, an upstream part of the
exhaust passage 50 constitutes independent passages branching for
the respective cylinders 11. Upstream ends of the independent
passages are connected to the exhaust ports 19 of the cylinders 11,
respectively.
[0087] The exhaust passage 50 is provided with an exhaust gas
purification system having a plurality of catalytic converters. An
upstream catalytic converter includes a three-way catalyst 511 and
a GPF (Gasoline Particulate Filter) 512. A downstream catalytic
converter includes a three-way catalyst 513. Note that the exhaust
gas purification system is not limited to the illustrated
configuration. For example, the GPF may be omitted. Moreover, the
catalytic converter is not limited to the one including the
three-way catalyst. Further, the disposed order of the three-way
catalyst and the GPF may be changed suitably.
[0088] An exhaust gas recirculation (EGR) passage 52 is connected
between the intake passage 40 and the exhaust passage 50. The EGR
passage 52 is a passage through which a part of exhaust gas
recirculates to the intake passage 40. An upstream end of the EGR
passage 52 is connected to a part of the exhaust passage 50 between
the upstream and downstream catalytic converters. A downstream end
of the EGR passage 52 is connected to a part of the intake passage
40 between the throttle valve 43 and the surge tank 42.
[0089] The EGR passage 52 is provided with an EGR cooler 53 of a
water-cooled type. The EGR cooler 53 cools exhaust gas. The EGR
passage 52 is also provided with an EGR valve 54. The EGR valve 54
controls a flow rate of exhaust gas flowing through the EGR passage
52. The EGR valve 54 changes its opening to control a recirculating
amount of the cooled exhaust gas.
[0090] As illustrated in FIG. 3, the control device for the engine
1 is provided with an ECU (Engine Control Unit) 10 to operate the
engine 1. The ECU 10 is a controller based on a well-known
microcomputer, and includes a processor (e.g., a central processing
unit (CPU)) 101 which executes a program, memory 102 which is
comprised of, for example, RAM (Random Access Memory) and ROM (Read
Only Memory), and stores the program and data, and an interface
(I/F) circuit 103 which inputs and outputs an electric signal. The
ECU 10 is one example of a "controller."
[0091] As illustrated in FIGS. 1 and 3, various kinds of sensors
SW1-SW9 are connected to the ECU 10. The sensors SW1-SW9 output
signals to the ECU 10. The sensors include the following sensors.
An airflow sensor SW1 is provided to the intake passage 40
downstream of the air cleaner 41, and measures the flow rate of air
flowing through the intake passage 40. An intake temperature sensor
SW2 is provided to the intake passage 40 downstream of the air
cleaner 41, and measures the temperature of the air flowing through
the intake passage 40. An intake pressure sensor SW3 is attached to
the surge tank 42, and measures the pressure of the air to be
introduced into the cylinder 11. An in-cylinder pressure sensor SW4
is attached to the cylinder head 13 for each cylinder 11, and
measures the pressure inside the cylinder 11. A water temperature
sensor SW5 is attached to the engine 1, and measures the
temperature of coolant. A crank angle sensor SW6 is attached to the
engine 1, and measures a rotational angle of the crankshaft 15. An
accelerator opening sensor SW7 is attached to an accelerator pedal
mechanism, and measures an accelerator opening corresponding to an
operation amount of an accelerator pedal. An intake cam angle
sensor SW8 is attached to the engine 1, and measures a rotational
angle of the intake camshaft. An exhaust cam angle sensor SW9 is
attached to the engine 1, and measures a rotational angle of the
exhaust camshaft.
[0092] The ECU 10 determines the operating state of the engine 1
based on the signals of the sensors SW1-SW9, and also calculates a
control amount of each device based on a given control logic stored
in the memory 102. The control logic includes calculating a target
amount and/or the control amount by using a map stored in the
memory 102.
[0093] The ECU 10 outputs electric signals related to the
calculated control amounts to the injectors 6, the spark plugs 25,
the intake S-VT 23, the exhaust S-VT 24, the fuel supply system 61,
the throttle valve 43, the EGR valve 54, and the swirl control
valve 56.
[0094] The ECU 10 electrically connected to the various sensors and
devices constitutes a plurality of functional blocks to operate the
engine 1, which will be described later.
(Configuration of Ignition Device)
[0095] FIG. 4 illustrates a configuration of the ignition device 7.
The ignition device 7 applies voltage between a center electrode
251 and a ground electrode 252 of the spark plug 25 so as to cause
the electric discharge inside the cylinder 11. The ignition device
7 includes an ignition coil 70 having a primary coil 70a, a
secondary coil 70c, and an iron core 70b. The ignition device 7 is
also provided with a capacitor 72, a transistor 73, an energy
generator 74, and an ignition controller 75.
[0096] The center electrode 251 is connected to the secondary coil
70c of the ignition coil 70, and the ground electrode 252 is
connected to the ground. When a secondary voltage applied between
the electrodes by the secondary coil 70c reaches a voltage required
for electrical breakdown, the electric discharge occurs at a gap
between the center electrode 251 and the ground electrode 252.
[0097] One end of the primary coil 70a is connected to the
capacitor 72. The capacitor 72 stores electrical energy to supply a
primary current to the primary coil 70a. The energy generator 74
includes a power source, and charges the capacitor 72.
[0098] The other end of the primary coil 70a is connected to a
collector of the transistor 73. The transistor 73 switches between
supplying or not supplying the primary current to the ignition coil
70.
[0099] As described above, one end of the secondary coil 70c is
connected to the center electrode 251, and the other end is
connected to the ignition controller 75.
[0100] The ignition controller 75 controls the energy generator 74
and the transistor 73 so that the spark plug 25 ignites the mixture
gas inside the cylinder 11 at a given timing.
[0101] Moreover, the ignition controller 75 can measure the
secondary voltage applied between the electrodes of the spark plug
25 by the secondary coil 70c, and a secondary current flown from
the secondary coil 70c to the spark plug 25. As described above,
the ignition device 7 causes the spark plug 25 to discharge the
electricity when the mixture gas is not ignited, and detects the
parameter related to the current value at the time of the electric
discharge.
(Operation Control for Engine)
[0102] Next, operation control for the engine 1 by the ECU 10 is
described. The engine 1 is a spark-ignition engine. The injector 6
injects fuel into the cylinder 11 during an intake stroke or a
compression stroke by an amount corresponding to the operating
state of the engine 1 to form mixture gas inside the cylinder 11,
and the spark plug 25 ignites the mixture gas at a given timing
near a compression top dead center (TDC) to combust the mixture
gas.
[0103] The engine 1 generates a turbulence inside the cylinder 11
to improve fuel efficiency. When the turbulence is generated inside
the cylinder 11, combustion speed increases. In detail, the engine
1 is provided with the cylinder 11 with the pentroof ceiling, and
the intake port 18 of the tumble-port type. The intake air
introduced into the cylinder 11 generates a tumble flow. The engine
1 also includes the swirl control valve 56. When the swirl control
valve 56 is closed, the intake air introduced into the cylinder 11
generates a swirl flow. By the tumble flow and the swirl flow being
combined together, an oblique flow in which a tumble vortex and a
swirl vortex are combined, is generated inside the cylinder 11.
[0104] Here, the state of the intake flow inside the cylinder 11 is
not the same in every cycle, but may vary depending on various
factors. The change in the state of the intake flow may lead to the
change in the combustion speed. When the combustion speed varies
between cycles, combustion variation of the engine 1 may be caused.
The engine system and the method of controlling the engine 1
disclosed herein reduce the combustion variation of the engine 1 by
reducing the variations in the combustion speed between the
cycles.
[0105] In more detail, in this engine system, the state of the flow
inside the cylinder 11 is estimated every cycle, as well as
supplemental fuel being injected into the cylinder 11 as needed
based on the estimated flowing state.
[0106] FIG. 5 is a block diagram illustrating a configuration of
the control device for the engine 1, which executes the control for
reducing the combustion variation. FIG. 5 illustrates functional
blocks of the ECU 10. The ECU 10 includes a main fuel injection
module 81 and a main ignition control module 82 executed by the
processor 101 to perform their respective functions. These modules
stored in the memory 102 as software modules. The main fuel
injection module 81 sets an injection amount and an injection
timing of main fuel corresponding to a demanded torque of the
engine 1, and causes the injector 6 to inject the main fuel. The
main ignition control module 82 causes the spark plug 25 to ignite
the mixture gas inside the cylinder 11 at a given timing after the
injection of the main fuel.
[0107] The ECU 10 also includes a determination module 83 and a
supplemental fuel injection module 84. As will be described later,
the determination module 83 determines the flowing state inside the
cylinder 11 based on the parameters detected by using the ignition
device 7 and the spark plug 25. The supplemental fuel injection
module 84 injects supplemental fuel inside the cylinder 11 as
needed before the spark plug 25 ignites the mixture gas, based on
the flowing state inside the cylinder 11 determined by the
determination module 83.
[0108] Below, the estimation of the flowing state inside the
cylinder 11, which is executed by the engine control device
illustrated in FIG. 5, is described. Then, injection control of the
supplemental fuel based on the estimated flowing state is
described.
(Estimation of Flowing State)
[0109] FIG. 6 is a view illustrating the center of the tumble
vortex in an early half of a compression stroke and the flowing
state inside the cylinder 11 in a latter half of the compression
stroke. Chart 601 in FIG. 6 illustrates the flowing state inside
the cylinder 11 in the early half of the compression stroke, where
the center of the tumble vortex is near the piston 3 inside the
cylinder 11. Chart 604 illustrates the flowing state inside the
cylinder 11 in the latter half of the compression stroke, in which
the crank angle progressed from the state of chart 601.
[0110] Similarly, chart 602 illustrates the flowing state inside
the cylinder 11 in the early half of the compression stroke, where
the center of the tumble vortex is at the middle between the piston
3 and the ceiling inside the cylinder 11. Chart 605 illustrates the
flowing state inside the cylinder 11 in the latter half of the
compression stroke, in which the crank angle progressed from the
state of chart 602.
[0111] Moreover, chart 603 illustrates the flowing state inside the
cylinder 11 in the early half of the compression stroke, where the
center of the tumble vortex is near the ceiling inside the cylinder
11. Chart 606 illustrates the flowing state inside the cylinder 11
in the latter half of the compression stroke, in which the crank
angle progressed from the state of chart 603.
[0112] Note that the early half and the latter half of the
compression stroke correspond to the early half and the latter half
when the compression stroke is equally divided, respectively.
[0113] First, as illustrated in chart 602, when the center of the
tumble vortex inside the cylinder 11 is located around the center
of the combustion chamber 17 in the side view, the rotating flow is
maintained also in the latter half of the compression stroke as
indicated by a solid arrow in chart 605. As a result, the
turbulence is uniform or substantially uniform entirely inside the
cylinder. In this case, the flame is uniformly or substantially
uniformly propagated from around the center toward the peripheral
part inside the cylinder 11. Since the propagation of the flame is
accelerated by the turbulence inside the cylinder 11, the
combustion speed is comparatively high.
[0114] As illustrated in chart 601, when the center of the tumble
vortex deviates downward inside the cylinder 11 in the side view,
the vortex center contacts the top surface of the piston 3 and a
lower half of the tumble vortex is broken in the latter half of the
compression stroke as illustrated in chart 604. Accordingly, as
indicated by an arrow in chart 604, the flow inside the cylinder 11
becomes a one-way flow from the intake valve 21 toward the exhaust
valve 22. Hereinafter, this one-way flow is referred to as a
"forward one-way flow." When the flow inside the cylinder 11 is the
forward one-way flow, the turbulence inside the cylinder 11 is
uneven. In detail, while the turbulence in an area on the
exhaust-valve side is strong, the turbulence in an area on the
intake-valve side (the area surrounded by a one-dot chain line in
chart 604) is weak. In such a case, although the flame generated by
the ignition of the mixture gas at the central part of the cylinder
11 is easily propagated toward the exhaust-side area, the
propagation toward the intake-side area is difficult. The
combustion speed in the case of chart 604 is lower than the case of
chart 605.
[0115] As illustrated in chart 603, when the center of the tumble
vortex deviates upward inside the cylinder 11 in the side view, the
vortex center contacts the ceiling of the cylinder 11 and an upper
half of the tumble vortex is broken in the latter half of the
compression stroke as illustrated in chart 606. Accordingly, as
indicated by arrows in chart 606, the flow inside the cylinder 11
becomes a one-way flow from the exhaust valve 22 toward the intake
valve 21. Hereinafter, this one-way flow is referred to as a
"backward one-way flow." When the flow inside the cylinder 11 is
the backward one-way flow, the turbulence inside the cylinder 11 is
uneven. In detail, while the turbulence in the area on the
intake-valve side is strong, the turbulence in the area on the
exhaust-valve side (the area surrounded by a one-dot chain line in
chart 606) is weak. In such a case, although the flame is easily
propagated toward the intake-side area, the propagation toward the
exhaust-side area is difficult. The combustion speed in the case of
chart 606 is lower than the case of chart 605.
[0116] In the engine system, the ignition device 7 detects the
flowing state inside the cylinder 11. In detail, the ignition
device 7 causes the electric discharge inside the cylinder 11 at a
timing when the mixture gas is not ignited, and detects a period of
time for which the electric discharge continues (discharge
duration). The determination module 83 estimates the intensity of
the flow around the spark plug 25 based on the detected discharge
duration, and determines the center of the tumble vortex based on
the estimated flow intensity.
[0117] FIG. 7 illustrates a time-series change 701 in the voltage
and a time-series change 702 in the current between the electrodes
of the spark plug 25 at different flow intensities around the spark
plug 25. When the spark plug 25 is applied with energy and voltage
is applied between the electrodes, an electric-discharge channel is
formed between the center electrode 251 and the ground electrode
252 (see charts 703 and 704). As the intensity of the flow around
the spark plug 25 increases, the electric-discharge channel is
blown and extended by the flow. The extension of the
electric-discharge channel increases the resistance between the
electrodes, which accelerates a decrease in the voltage applied
between the electrodes. As the intensity of the flow around the
spark plug 25 increases, a period of time required for the
consumption of the energy applied to the spark plug 25 (i.e., the
discharge duration) becomes shorter.
[0118] In more detail, as indicated by solid lines in FIG. 7, when
there is no flow around the spark plug 25, the electric-discharge
channel is hardly extended (see chart 703), and thus, the discharge
duration is long. Since the electric-discharge channel extends as
the intensity of the flow around the spark plug 25 increases (see
chart 704), the discharge duration becomes shorter as illustrated
by broken lines and dotted lines in charts 701 and 702. That is,
the discharge duration of the current between the electrodes of the
spark plug 25 is in proportion to the intensity of the flow around
the spark plug 25. When the ignition device 7 detects the discharge
duration, the determination module 83 can estimate the intensity of
the flow (i.e., a flow velocity) around the spark plug 25.
[0119] FIG. 8 illustrates a relationship between the discharge
duration detected by the ignition device 7, and the center of the
tumble vortex inside the cylinder 11. Chart 800 of FIG. 8
illustrates a relationship between the discharge duration and a
flow velocity Vp around the spark plug 25. As described above, the
discharge duration is in proportion to the flow velocity Vp, and
the flow velocity Vp increases as the discharge duration is
shorter, and the flow velocity Vp decreases as the discharge
duration is longer.
[0120] As illustrated in chart 802 of FIG. 8, when the center of
the tumble vortex is at the middle between the piston 3 and the
ceiling inside the cylinder 11 in the early half of the compression
stroke, the center of the vortex is separated from the spark plug
25 to some extent. Therefore, the flow velocity Vp around the spark
plug 25 is between V1 and V2.
[0121] On the other hand, as illustrated in chart 801, when the
center of the tumble vortex is near the piston 3 in the early half
of the compression stroke, the center of the vortex is largely
separated from the spark plug 25. Therefore, the flow velocity Vp
around the spark plug 25 is higher than V1.
[0122] Moreover, as illustrated in chart 803, when the center of
the tumble vortex is near the ceiling in the early half of the
compression stroke, the center of the vortex is near the spark plug
25. Therefore, the flow velocity Vp around the spark plug 25 is
lower than V2.
[0123] The tumble vortex which is formed inside the cylinder 11
mainly by a tumble flow, becomes stable and the center of the
tumble vortex is defined during the compression stroke after the
intake valve 21 is closed. Therefore, the center of the tumble
vortex can be estimated by the spark plug 25 carrying out the
electrical discharge (a second electric discharge described later)
and the ignition device 7 detecting the discharge duration (a
second discharge duration described later) in the early half of the
compression stroke. If the discharge duration is shorter than a
first threshold corresponding to the velocity V1, the center of the
tumble vortex can be estimated to be near the piston 3. If the
discharge duration is longer than a second threshold corresponding
to the velocity V2, the center of the tumble vortex can be
estimated to be near the ceiling. If the discharge duration is
between the first threshold and the second threshold, the center of
the tumble vortex can be estimated to be at the middle of the
combustion chamber 17 in the side view.
[0124] FIG. 9 is a view illustrating a relationship between the
center of the swirl vortex during the intake stroke and the flowing
state inside the cylinder 11 in the latter half of the compression
stroke. Chart 901 of FIG. 9 illustrates the flowing state inside
the cylinder 11 when the center of the swirl vortex deviates to the
exhaust-valve side inside the cylinder 11 during the intake stroke.
Chart 904 illustrates a propagation state of the flame after the
latter half of the compression stroke, in which the crank angle
progressed from the state of chart 901.
[0125] Similarly, chart 902 illustrates the flowing state inside
the cylinder 11 when the center of the swirl vortex is almost on
the axis of the cylinder 11 at the central part of the cylinder 11
during the intake stroke. Chart 905 illustrates the propagation
state of the flame after the latter half of the compression stroke,
in which the crank angle progressed from the state of chart
902.
[0126] Moreover, chart 903 illustrates the flowing state inside the
cylinder 11 when the center of the swirl vortex deviates to the
intake-valve side inside the cylinder 11 during the intake stroke.
Chart 906 illustrates the propagation state of the flame after the
latter half of the compression stroke, in which the crank angle
progressed from the state of chart 903.
[0127] First, as illustrated in chart 902, when the center of the
swirl vortex inside the cylinder 11 is located on the axis at the
central part of the cylinder 11 in the plan view, the center of the
swirl vortex is located near the axis also in the latter half of
the compression stroke. The turbulence inside the cylinder 11 is
uniform or substantially uniform entirely inside the cylinder 11.
When the spark plug 25 ignites the mixture gas at the central part
of the cylinder 11, the flame is propagated from the central part
toward the peripheral part inside the cylinder 11 while being
curved in the circumferential direction by the swirl vortex as
indicated by broken arrows in chart 905. The flame is uniformly or
substantially uniformly propagated from around the center toward
the peripheral part inside the cylinder 11. Since the propagation
of the flame is accelerated by the turbulence inside the cylinder
11, the combustion speed is comparatively high.
[0128] As illustrated in chart 901, when the center of the swirl
vortex deviates to the exhaust-valve side in the plan view, the
center of the swirl vortex deviates from the center of the cylinder
11. The turbulence inside the cylinder 11 becomes uneven entirely
inside the cylinder 11. Moreover, when the spark plug 25 ignites
the mixture gas at the central part of the cylinder 11 near the
compression TDC in the latter half of the compression stroke, the
flame is propagated from the central part toward the peripheral
part inside the cylinder 11 while being curved (turned) in the
circumferential direction by the swirl vortex as indicated by
broken arrows in chart 904. Here, the flow velocity of the swirl
vortex is higher as being separated from the center of the swirl
vortex (see concentric circles in chart 904). That is, the flow
velocity of the swirl vortex is relatively high on the intake-valve
side which is far from the center of the swirl vortex. Although the
flame propagating from the central part of the cylinder 11 to the
exhaust-valve side propagates radially outwardly while being curved
in the circumferential direction, the flame propagating from the
central part of the cylinder 11 to the intake-valve side is
intensely curved by the swirl vortex at the high flow velocity,
thus the radially outward propagation being difficult. As a result,
the flame propagation in the intake-side area is difficult as
indicated by the one-dot chain line in chart 904. In this case, the
combustion speed is lower than the case of chart 905.
[0129] As illustrated in chart 903, also when the center of the
swirl vortex deviates to the intake-valve side in the plan view,
the center of the swirl vortex deviates from the center of the
cylinder 11. The turbulence inside the cylinder 11 becomes uneven
entirely inside the cylinder 11. Moreover, when the spark plug 25
ignites the mixture gas at the central part of the cylinder 11 near
the compression TDC in the latter half of the compression stroke,
the flame is propagated from the central part toward the peripheral
part inside the cylinder 11 while being curved in the
circumferential direction by the swirl vortex as indicated by
broken arrows in chart 906. Here, the direction from the central
part to the intake-valve side of the cylinder 11 is the direction
opposite from the flow of the swirl vortex in the counterclockwise
direction indicated by solid lines in chart 906. As a result,
although the flame propagating from the central part of the
cylinder 11 to the exhaust-valve side propagates radially outwardly
while being curved in the circumferential direction, the flame
propagating from the central part of the cylinder 11 to the
intake-valve side is pushed back by the flow of the swirl vortex,
thus the radially outward propagation being difficult. As a result,
the flame propagation in the intake-side area is difficult as
indicated by the one-dot chain line in chart 906. In this case, the
combustion speed is lower than the case of chart 905.
[0130] FIG. 10 illustrates a relationship between the duration of
the electric discharge detected by the ignition device 7, and the
center of the swirl vortex inside the cylinder 11. Chart 1000 of
FIG. 10 illustrates a relationship between the discharge duration
and the flow velocity around the spark plug 25.
[0131] The intake air is flown into the cylinder 11 mainly from the
first intake passage 18a to generate the swirl flow. As illustrated
in chart 1002 of FIG. 10, a flow-velocity distribution occurs
inside the cylinder 11 during the intake stroke by the intake air
which is introduced mainly from the first intake passage 18a. The
center of the swirl vortex is located on the axis around the
central part of the cylinder 11 when the velocity distribution
during the intake stroke is as illustrated in chart 1002, in which
the flow velocity is the maximum at a certain position in the
radial direction between the central part and a liner of the
cylinder 11, and the flow velocity decreases toward the central
part and toward the liner from the certain position. In this case,
the flow velocity around the spark plug 25 is between V3 and
V4.
[0132] On the other hand, as illustrated in chart 1001, in a case
of the flow-velocity distribution in which the flow velocity near
the liner is extremely high during the intake stroke, the center of
the swirl vortex deviates to the exhaust-valve side. In this case,
the flow velocity around the spark plug 25 is lower than V4.
[0133] Moreover, as illustrated in chart 1003, when the maximum
flow velocity is comparatively low, and a kurtosis of the flow
velocity is small in the flow-velocity distribution during the
intake stroke, the center of the swirl vortex deviates to the
intake-valve side. In this case, the flow velocity around the spark
plug 25 is higher than V3.
[0134] The swirl vortex formed mainly by a swirl flow inside the
cylinder 11 becomes stable during the intake stroke between the
opening and closing of the intake valve 21. The ignition device 7
causes the spark plug 25 to carry out the electrical discharge (a
first electric discharge described later) and detects the discharge
duration (a first discharge duration described later) during the
intake stroke. In detail, the flow of the intake air easily changes
for a certain period from the opened timing of the intake valve 21.
The swirl vortex stabilizes after the certain period from the
opening of the intake valve 21, before the closing of the intake
valve 21. The ignition device 7 causes the spark plug 25 to carry
out the electric discharge after a given period (a time constant
.DELTA.t described later) from the opening of the intake valve 21,
and detects the discharge duration.
[0135] The determination module 83 can determine that the center of
the swirl vortex deviates to the intake-valve side when the
discharge duration is shorter than the first threshold
corresponding to the velocity V3. The determination module 83 can
determine that the center of the swirl vortex deviates to the
exhaust-valve side when the discharge duration is longer than the
second threshold corresponding to the velocity V4. The
determination module 83 can determine that the center of the swirl
vortex is on the axis at the central part of the cylinder 11 when
the discharge duration is between the first threshold and the
second threshold. Note that the velocity V3 corresponding to the
first threshold and the velocity V1 described above are not
necessarily the same. Similarly, the velocity V4 corresponding to
the second threshold and the velocity V2 described above are not
necessarily the same.
(Injection Control of Supplemental Fuel)
[0136] FIG. 11 is a time chart illustrating the timing of the fuel
injection by the injector 6, and the timings of the electric
discharge and the ignition by the spark plug 25. The crank angle
progresses from the left to the right in FIG. 11.
[0137] As described above, when the center of the tumble vortex
and/or the swirl vortex deviate due to the variation in the intake
flow, the area with a small turbulence and/or the area with
difficulty in the flame propagation are generated inside the
cylinder 11. The supplemental fuel makes the mixture gas of which
the fuel concentration is locally high be positioned in the area
with the small turbulence and/or the area with the difficulty in
the flame propagation so as to accelerate the flame propagation
toward such specific areas.
[0138] First, the main fuel injection module 81 causes the injector
6 to inject the main fuel inside the cylinder 11 in a period during
the intake stroke between the opening and closing of the intake
valve 21 (see a main fuel injection 1104). The main fuel is spread
inside the cylinder 11 by the flow, and the mixture gas is
generated inside the cylinder 11.
[0139] As illustrated in chart 1102, the determination module 83
causes the ignition device 7 and the spark plug 25 to carry out a
first electric discharge 1105 at a timing during the intake stroke
after the given time constant .DELTA.t passes from the opening of
the intake valve 21. The first electric discharge 1105 is the
electric discharge which is performed when the mixture gas is not
ignited. The ignition device 7 detects the first discharge duration
of the first electric discharge. The determination module 83
estimates the center of the swirl vortex based on the first
discharge duration detected in the first electric discharge
1105.
[0140] The determination module 83 also causes the ignition device
7 and the spark plug 25 to carry out a second electric discharge
1106, for example, in the early half of the compression stroke
after the closing of the intake valve 21. Also the second electric
discharge 1106 is the electric discharge which is performed when
the mixture gas is not ignited. The ignition device 7 detects the
second discharge duration of the second electric discharge. The
determination module 83 estimates the center of the tumble vortex
based on the second discharge duration detected in the second
electric discharge 1106.
[0141] When both of the first discharge duration and the second
discharge duration detected by the ignition device 7 are between
the first threshold and the second threshold, the center of the
tumble vortex is located at the middle between the piston 3 and the
ceiling inside the cylinder 11, and the center of the swirl vortex
is located on the axis at the central part of the cylinder 11. In
this case, the injection of the supplemental fuel is unnecessary.
As illustrated in chart 1102 of FIG. 11, the supplemental fuel
injection module 84 suspends the injection of the supplemental
fuel, and the main ignition control module 82 causes the spark plug
25 to ignite the mixture gas at the given timing near the
compression TDC in the latter half of the compression stroke (see a
main ignition 1107 of FIG. 11). In this case, since the centers of
the swirl vortex and the tumble vortex are located at the central
part of the cylinder 11 when seen in a plan view and a side view,
respectively, the turbulence is uniform or substantially uniform
entirely inside the cylinder 11. The flame uniformly or
substantially uniformly propagates from the central part toward the
peripheral part of the cylinder 11. The combustion speed is
comparatively high.
[0142] Next, the case where the second discharge duration detected
by the ignition device 7 is below (shorter than) the first
threshold is described. In this case, the center of the tumble
vortex is near the piston 3 inside the cylinder 11, and the forward
one-way flow is generated inside the cylinder 11 in the latter half
of the compression stroke. As illustrated in chart 1101 of FIG. 11,
the supplemental fuel injection module 84 causes the injector 6 to
inject a given amount of supplemental fuel (a first supplemental
fuel 1108). The injector 6 injects the first supplemental fuel 1108
at a first injection timing, for example, in the early half of the
compression stroke or the latter half of the compression
stroke.
[0143] FIG. 12 is a view illustrating the flow change and
distribution of the first supplemental fuel inside the cylinder 11
when the center of the tumble vortex is near the piston 3 inside
the cylinder 11. As described above, when the center of the tumble
vortex is near the piston 3, the center of the vortex contacts the
top surface of the piston 3 and the lower half of the tumble vortex
is broken as the piston 3 ascends as illustrated in P1201, P1202,
P1203, and P1204, in this order. Accordingly, as indicated by a
black arrow in P1205, the flow inside the cylinder 11 becomes the
forward one-way flow from the intake valve 21 toward the exhaust
valve 22 in the latter half of the compression stroke.
[0144] The first supplemental fuel is injected inside the cylinder
11 at a relatively early timing (P1203) during the compression
stroke, and since the pressure inside the cylinder 11 is not
relatively high at that early timing, the injected first
supplemental fuel rides on the tumble vortex to be carried from the
exhaust-valve side to the intake-valve side (see hatched areas in
P1203, P1204, and P1205) before the vortex is broken. As a result,
the mixture gas with the high fuel concentration can be positioned
around the intake valve.
[0145] After the injection of the first supplemental fuel 1108, the
main ignition control module 82 causes the spark plug 25 to ignite
the mixture gas at the given timing near the compression TDC in the
latter half of the compression stroke (see the main ignition 1107
in chart 1101). Although the flame is difficult to be propagated
toward the intake-valve side due to the forward one-way flow, since
the fuel concentration of the mixture gas is high on the
intake-valve side, the flame propagation toward the intake-valve
side is accelerated. Accordingly, the combustion speed is increased
to the extent similar to the case where the discharge duration is
between the first threshold and the second threshold. Therefore,
combustion variation of the engine 1 is reduced.
[0146] Next, the case where the second discharge duration detected
by the ignition device 7 is above (longer than) the second
threshold is described. In this case, the center of the tumble
vortex is near the ceiling inside the cylinder 11, and the backward
one-way flow is generated inside the cylinder 11 in the latter half
of the compression stroke. As illustrated in chart 1103 of FIG. 11,
the supplemental fuel injection module 84 causes the injector 6 to
inject a given amount of supplemental fuel (a second supplemental
fuel 1109). The injector 6 injects the second supplemental fuel
1109 at a second injection timing in the latter half of the
compression stroke. The injection timing of the second supplemental
fuel 1109 is later than the injection timing of the first
supplemental fuel 1108.
[0147] FIG. 13 is a view illustrating the flow change and
distribution of the second supplemental fuel inside the cylinder 11
when the center of the tumble vortex is near the ceiling inside the
cylinder 11. As described above, when the center of the tumble
vortex is near the ceiling, the center of the vortex contacts the
ceiling and the upper half of the tumble vortex is broken as the
piston 3 ascends as illustrated in P1301, P1302, P1303, and P1304,
in this order. Accordingly, as indicated by black arrows in P1305,
the flow inside the cylinder 11 becomes the backward one-way flow
from the exhaust valve 22 toward the intake valve 21 in the latter
half of the compression stroke.
[0148] The injector 6 injects the second supplemental fuel in the
latter half of the compression stroke (see P1304). Since the
pressure inside the cylinder 11 is high in the latter half of the
compression stroke, when seen in a side view, the second
supplemental fuel injected inside the cylinder 11 stays at the
central part inside the cylinder 11 by receiving the high
compression pressure, as well as flowing to the exhaust-valve side
where the flow is relatively weak (see hatched areas in P1304 and
P1305). As a result, the mixture gas with the high fuel
concentration can be positioned around the exhaust valve.
[0149] After the injection of the second supplemental fuel 1109,
the main ignition control module 82 causes the spark plug 25 to
ignite the mixture gas at the given timing near the compression TDC
in the latter half of the compression stroke (see the main ignition
1107 in chart 1103). Although the flame is difficult to be
propagated toward the exhaust-valve side due to the backward
one-way flow, since the fuel concentration of the mixture gas is
high on the exhaust-valve side, the flame propagation toward the
exhaust-valve side is accelerated. Accordingly, the combustion
speed is increased to the extent similar to the case where the
discharge duration is between the first threshold and the second
threshold. Therefore, combustion variation of the engine 1 is
reduced.
[0150] Therefore, by injecting the supplemental fuel according to
the flowing state inside the cylinder 11, even when the center of
the tumble vortex varies due to the variation in the state of the
intake flow between the cycles, the ECU 10 can make the combustion
speed to be the same or substantially the same. Thus, the
combustion variation can be reduced.
[0151] Next, the case where the first discharge duration detected
by the ignition device 7 is below (shorter than) the first
threshold is described. In this case, the center of the swirl
vortex deviates to the intake-valve side inside the cylinder 11. As
illustrated in chart 1101 of FIG. 11, the supplemental fuel
injection module 84 causes the injector 6 to inject the given
amount of supplemental fuel (i.e., the first supplemental fuel
1108). The injector 6 injects the first supplemental fuel 1108 at
the first injection timing, for example, in the early half of the
compression stroke or the latter half of the compression
stroke.
[0152] P1401 and P1402 of FIG. 14 are views illustrating the flow
change and distribution of the first supplemental fuel inside the
cylinder 11 when the center of the swirl vortex deviates to the
intake-valve side. When the center of the swirl vortex deviates to
the intake-valve side, as illustrated in P1401, the kurtosis of the
flow velocity distribution inside the cylinder 11 during the
compression stroke is low. Therefore, an area where the flow
velocity is extremely high does not exist.
[0153] The first supplemental fuel radially injected from the
central part inside the cylinder 11 in the early or latter half of
the compression stroke after the second electric discharge, rides
on the flow to be carried in the circumferential direction. Since
the injection timing of the supplemental fuel is relatively
advanced, a long period of time is spent for the spray of the
supplemental fuel injected to the exhaust-valve side to be carried
to the intake-valve side. As a result, the fuel concentration of
the mixture gas on the intake-valve side is increased at the
ignition timing (P1402).
[0154] After the injection of the first supplemental fuel, the main
ignition control module 82 causes the spark plug 25 to ignite the
mixture gas at the given timing near the compression TDC in the
latter half of the compression stroke (see the main ignition 1107
of chart 1101). As described above, since the radially outward
flame propagation is disturbed by the swirl vortex with the
deviated center, the propagation toward the intake-valve side is
difficult. However, since the fuel concentration of the mixture gas
on the intake-valve side is high, the flame propagation toward the
intake-valve side is accelerated. Accordingly, the combustion speed
is increased to the extent similar to the case where the discharge
duration is between the first threshold and the second threshold.
Therefore, combustion variation of the engine 1 is reduced.
[0155] Next, the case where the first discharge duration detected
by the ignition device 7 is above (longer than) the second
threshold is described. In this case, the center of the swirl
vortex deviates to the exhaust-valve side inside the cylinder 11.
As illustrated in Chart 1103 of FIG. 11, the supplemental fuel
injection module 84 causes the injector 6 to inject the given
amount of supplemental fuel (i.e., the second supplemental fuel
1109). The injector 6 injects the second supplemental fuel 1109 at
the second injection timing in the latter half of the compression
stroke. The injection timing of the second supplemental fuel 1109
is later than the injection timing of the first supplemental fuel
1108.
[0156] P1403 and P1404 of FIG. 14 are views illustrating the flow
change and distribution of the second supplemental fuel inside the
cylinder 11 when the center of the swirl vortex deviates to the
exhaust-valve side. When the center of the swirl vortex deviates to
the exhaust-valve side, as illustrated in P1403, the velocity
distribution inside the cylinder 11 in the latter half the
compression stroke includes an area near the liner where the flow
velocity is extremely high.
[0157] Among the second supplemental fuel radially injected from
the central part inside the cylinder 11 at the late timing in the
latter half of the compression stroke, the supplemental fuel
injected to the intake-valve side rides on the flow at the low
velocity, thus moving a little and staying on the intake-valve
side. On the other hand, the supplemental fuel injected to the
exhaust-valve side rides on the flow at the high velocity, thus
being carried promptly to the intake-valve side in the
circumferential direction. As a result, the sprays of the
supplemental fuel are overlapped with each other, and the fuel
concentration of the mixture gas on the intake-valve side is
increased at the ignition timing (P1404).
[0158] After the injection of the second supplemental fuel 1109,
the main ignition control module 82 causes the spark plug 25 to
ignite the mixture gas at the given timing near the compression TDC
in the latter half of the compression stroke (see the main ignition
1107 of chart 1103). As described above, the flame is difficult to
be propagated toward the intake-valve side since the propagating
direction is curved by the swirl vortex with the deviated center.
However, since the fuel concentration of the mixture gas is high on
the intake-valve side, the flame propagation toward the
intake-valve side is accelerated. Accordingly, the combustion speed
is increased to the extent similar to the case where the discharge
duration is between the first threshold and the second threshold.
Therefore, combustion variation of the engine 1 is reduced.
[0159] Therefore, by injecting the supplemental fuel according to
the flowing state inside the cylinder 11, even when the center of
the swirl vortex varies due to the variation in the state of the
intake flow between the cycles, the ECU 10 can make the combustion
speed to be constant or substantially constant. Thus, the
combustion variation can be reduced.
[0160] Note that the energies applied to the spark plug 25 in the
first electric discharge, the second electric discharge, and the
main ignition may be the same as, or different from each other.
(Controlling Process of Engine Control Device)
[0161] Next, a controlling process of the control device of the
engine 1 described above is described with reference to the
flowchart of FIG. 15. First, at step S1, the ECU 10 acquires the
sensor values of the sensors SW1 to SW9. Next, at step S2, the ECU
10 calculates the demanded torque of the engine 1 based on the
acquired sensor values. At step S3, the ECU 10 determines the
injection amount and injection timing of the main injection, which
can achieve the demanded torque. The ECU 10 also determines the
main ignition timing.
[0162] At step S4, the ECU 10 determines the timings of the first
electric discharge and the second electric discharge. At this step,
the ECU 10 also determines the time constant .DELTA.t for the
execution of the first electric discharge. For example, the ECU 10
may adjust the time constant .DELTA.t according to the operating
state of the engine 1 (i.e., the load and/or the speed of the
engine 1)
[0163] Next, at step S5, the ECU 10 causes the injector 6 to carry
out the main injection 1104 based on the injection amount and
injection timing determined at step S3. As illustrated in FIG. 11,
the injector 6 performs the main injection 1104 during the intake
stroke.
[0164] At step S6, the ECU 10 causes the ignition device 7 to carry
out the first electric discharge 1105. The ignition device 7
performs the first electric discharge 1105 during the intake
stroke, and detects the first discharge duration. Moreover, at step
S7, the ECU 10 causes the ignition device 7 to carry out the second
electric discharge 1106. The ignition device 7 performs the second
electric discharge 1106 in the early half of the compression
stroke, and detects the second discharge duration.
[0165] At step S8, the ECU 10 determines whether the first
discharge duration is below the first threshold, and whether the
second discharge duration is below the first threshold. When the
ECU 10 determines as YES at step S8 (when the first discharge
duration or the second discharge duration is below the first
threshold), the process proceeds to step S10. When the ECU 10
determines as NO at step S8, the process proceeds to step S9.
[0166] At step S9, the ECU 10 determines whether the first
discharge duration is above the second threshold, and whether the
second discharge duration is above the second threshold. When the
ECU 10 determines as YES at step S9 (when the first discharge
duration or the second discharge duration is above the second
threshold), the process proceeds to step S11. When the ECU 10
determines as NO at step S9, the supplemental fuel is not
injected.
[0167] At step S10, the ECU 10 determines the injection amount and
injection timing of the first supplemental fuel 1108. As described
above, the injection timing of the first supplemental fuel 1108 is
advanced compared with the injection timing of the second
supplemental fuel 1109. At step S11, the ECU 10 determines the
injection amount and injection timing of the second supplemental
fuel 1109. The injection timing of the second supplemental fuel
1109 is retarded compared with the injection timing of the first
supplemental fuel 1108. The injection amount and injection timing
of the first supplemental fuel 1108, and the injection amount and
injection timing of the second supplemental fuel 1109 may be
determined according to the operating state of the engine 1.
[0168] After the ECU 10 determines the injection amount and
injection timing of the supplemental fuel, at step S12, the ECU 10
executes the injection of the supplemental fuel in the early or
latter half of the compression stroke (in the case of the first
supplemental fuel 1108), or in the latter half of the compression
stroke (in the case of the second supplemental fuel 1109). Then, at
step S13, the ECU causes the spark plug 25 to ignite the mixture
gas.
[0169] Note that, preferably, the injection amount of the
supplemental fuel is suppressed to an amount which will not degrade
an emission performance, for example. The reduction in the
injection amount of the supplemental fuel can maintain the
favorable emission performance, as well as suppressing the
degradation in fuel efficiency.
[0170] The injector 6 is not limited to inject the main fuel during
the intake stroke, but may inject the main fuel during the
compression stroke. The spark plug 25 may perform the first
electric discharge before or after the injection of the main fuel.
Similarly, the spark plug 25 may perform the second electric
discharge before or after the injection of the main fuel.
[0171] Moreover, the technology disclosed herein is applicable not
only to the engine 1 with the configuration described above, but to
engines with various configurations.
[0172] It should be understood that the embodiments herein are
illustrative and not restrictive, since the scope of the invention
is defined by the appended claims rather than by the description
preceding them, and all changes that fall within metes and bounds
of the claims, or equivalence of such metes and bounds thereof, are
therefore intended to be embraced by the claims.
DESCRIPTION OF REFERENCE CHARACTERS
[0173] 1 Engine [0174] 10 ECU (Controller) [0175] 11 Cylinder
[0176] 1311 Sloped Surface (Ceiling) [0177] 1312 Sloped Surface
(Ceiling) [0178] 25 Spark Plug [0179] 6 Injector (Fuel Injector)
[0180] 7 Ignition Device [0181] 81 Main Fuel Injection Module
[0182] 82 Main Ignition Control Module [0183] 83 Determination
Module [0184] 84 Supplemental Fuel Injection Module
* * * * *