U.S. patent application number 11/988864 was filed with the patent office on 2009-06-11 for control apparatus for an internal combustion engine and method for controlling the same.
This patent application is currently assigned to TOYOTA JIDOSHA KABUSHIKI KAISHA. Invention is credited to Takashi Kawai.
Application Number | 20090145382 11/988864 |
Document ID | / |
Family ID | 38513296 |
Filed Date | 2009-06-11 |
United States Patent
Application |
20090145382 |
Kind Code |
A1 |
Kawai; Takashi |
June 11, 2009 |
Control apparatus for an internal combustion engine and method for
controlling the same
Abstract
In a control apparatus for an internal combustion engine having
a valve timing control portion controlling the timing opening and
closing of an intake valve disposed in an intake port communicating
with a cylinder of the internal combustion engine, when the
internal combustion engine is being started from a cold condition,
multi-stroke operation is set, in which one combustion cycle of the
internal combustion engine includes two or more intake and
compression strokes, formed by a first intake stroke and the first
compression stroke and a second intake stroke and compression
stroke, followed by a combustion stroke and an exhaust stroke. The
valve timing control portion controls a lift of the intake valve
during the first intake stroke and the first compression stroke to
a low lift amount, which is smaller than the normal lift amount
required for intake of a requested intake air amount, and controls
the lift of the intake valve in a second intake and a second
compression stroke to the normal lift amount.
Inventors: |
Kawai; Takashi; (Susono-shi,
JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
TOYOTA JIDOSHA KABUSHIKI
KAISHA
TOYOTA-SHI
JP
|
Family ID: |
38513296 |
Appl. No.: |
11/988864 |
Filed: |
May 8, 2007 |
PCT Filed: |
May 8, 2007 |
PCT NO: |
PCT/IB2007/001188 |
371 Date: |
January 16, 2008 |
Current U.S.
Class: |
123/90.16 ;
123/406.53; 701/113 |
Current CPC
Class: |
F02D 13/0273 20130101;
F01L 1/34 20130101; F01L 2800/01 20130101; F02D 2200/0611 20130101;
Y02T 10/36 20130101; F02D 41/068 20130101; F02D 41/0002 20130101;
F02D 41/064 20130101; Y02T 10/18 20130101; F02D 41/0025 20130101;
F02D 13/0226 20130101; F02D 41/3058 20130101; F02D 19/084 20130101;
F02D 2041/001 20130101; Y02T 10/30 20130101; F01L 1/36 20130101;
F01L 2800/00 20130101; Y02T 10/12 20130101; F02D 2013/0292
20130101 |
Class at
Publication: |
123/90.16 ;
701/113; 123/406.53 |
International
Class: |
F01L 1/34 20060101
F01L001/34 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2006 |
JP |
2006-131880 |
Claims
1. A control apparatus for an internal combustion engine
comprising: a variable valve driving device that changes the timing
of the opening and closing and lift amount of an intake valve
disposed in an intake port that communicates with a cylinder of the
internal combustion engine; a valve timing control portion that
controls the timing of the opening and closing and lift amount of
the intake valve by the variable valve driving device; a cold start
determining portion that determines whether the internal combustion
engine is being started from a cold start; and a multi-stroke
operation setting portion that sets a multi-stroke operation, in
which one combustion cycle of the internal combustion engine
includes two or more intake and compression strokes, when the cold
start determining portion determines that the internal combustion
engine is being started from the cold start, wherein the
multi-stroke operation is formed by a first intake stroke and a
first compression stroke and a second intake stroke and a second
compression stroke, followed by a combustion stroke and an exhaust
stroke, wherein the valve timing control portion controls the lift
of the intake valve during the first intake and the compression
strokes to a low lift amount, which is smaller than the normal lift
amount required for intake of a requested intake air amount, and
controls the lift of the intake valve in the second intake and the
second compression stroke to the normal lift amount.
2. The control apparatus according to claim 1, wherein the low lift
amount is the lift at which the pumping loss during the first
intake and the first compression stroke is maximized.
3. The control apparatus according to claim 1, further comprising:
an ignition timing control portion that controls ignition timing by
a spark plug disposed in the cylinder, wherein the ignition timing
control portion prohibits ignition during the first intake and the
first compression stroke.
4. The control apparatus according to claim 1, wherein the
multi-stroke operation setting portion sets the execution of,
during one combustion cycle, a plurality of repetitions of the
first intake stroke and the first compression stroke, followed by
performing the second intake stroke and the second compression
stroke.
5. The control apparatus according to claim 1, further comprising:
a multi-stroke operation termination determining portion that
determines whether or not multi-stroke operation is to be
terminated; and a four-stroke operation setting portion that sets
one combustion cycle of the combustion of the internal combustion
engine to four-stroke operation, which includes an intake stroke, a
compression stroke, an expansion stroke, and an exhaust stroke, if
the multi-stroke operation termination determining portion
determines that multi-stroke operation is to be terminated.
6. The control apparatus according to claim 5, further comprising:
a temperature detector that detects a temperature in the cylinder
wherein the multi-stroke operation termination determining portion
determines that multi-stroke operation is to be terminated if a
temperature in the cylinder is greater than or equal to a threshold
cylinder temperature.
7. The control apparatus according to claim 5, further comprising:
a coolant temperature detector that detects a temperature of the
coolant of the internal combustion engine wherein the multi-stroke
operation termination determining portion determines that
multi-stroke operation is to be terminated if the temperature of
the coolant is greater than or equal to a threshold coolant
temperature.
8. The control apparatus according to claim 5, further comprising:
a requested load calculation portion that calculates a requested
load on the internal combustion engine wherein the multi-stroke
operation termination determining portion determines that
multi-stroke operation is to be terminated if the calculated
requested load is greater than or equal to a threshold engine
load.
9. The control apparatus according to claim 5, further comprising:
a cylinder temperature predicting portion that predicts, before
starting the first intake stroke and the first compression stroke,
in one combustion cycle, a temperature in a cylinder after
performing the second intake stroke and the second compression
stroke wherein the multi-stroke operation termination determining
portion determines that multi-stroke operation is to be terminated
if the predicted temperature in the cylinder is greater than or
equal to a threshold predicted cylinder temperature.
10. The control apparatus according to claim 6, wherein the
internal combustion engine uses a fuel including alcohol as a fuel,
and the control apparatus further includes a determining value
setting portion that sets any one of the threshold cylinder
temperature, the threshold coolant temperature, the threshold
engine load, and the threshold predicted cylinder temperature in
accordance with the concentration of alcohol in the fuel.
11. The control apparatus according to claim 1, wherein the
internal combustion engine has a first cylinder group and a second
cylinder group, and wherein the control apparatus operates only
cylinders belonging to the first cylinder group and includes a
reduced-cylinder operation setting portion that sets cylinders
belonging to the second cylinder group to reduced cylinder
operation, in which the cylinders are stopped, and an all-cylinder
operation setting portion that sets all cylinders belonging to the
first cylinder group and cylinders belonging to the second cylinder
group to all-cylinder operation, in which all cylinders are
operated, wherein the cold start determining portion determines
whether restoration of operation of the cylinders belonging to the
second group of cylinders is a cold start when the engine
transitions from reduced-cylinder operation to all-cylinder
operation, and the multi-stroke operation setting portion sets the
operation of cylinders belonging to the second cylinder group to
multi-stroke operation when the cold start determining portion
determines that restoration of operation of the cylinders belonging
to the second cylinder group of cylinders is the cold start.
12. The control apparatus according to claim 1, wherein the
variable valve driving device has an intake cam that drives the
opening and closing of the intake valve and an electrical motor
rotationally driving the intake cam, wherein the valve timing
control portion controls the valve timing by controlling the
rotational drive of the intake cam using the electrical motor.
13. A method for controlling an internal combustion engine
comprising: determining whether the internal combustion engine is
being started from a cold start; executing multi-stroke operation,
which includes, in one combustion cycle in the internal combustion
engine, two or more intake and compression strokes, formed by a
first intake stroke and a first compression stroke and a second
intake stroke and compression stroke, followed by a combustion
stroke and an exhaust stroke; and controlling a lift of an intake
valve during the first intake stroke and the first compression
stroke to a low lift amount, which is smaller than the normal lift
amount required for intake of a requested intake air amount, and
controlling the lift of the intake valve in the second intake
stroke and the second compression stroke to the normal lift
amount.
14. The control apparatus according to claim 7, wherein the
internal combustion engine uses a fuel including alcohol as a fuel,
and the control apparatus further includes a determining value
setting portion that sets any one of the threshold cylinder
temperature, the threshold coolant temperature, the threshold
engine load, and the threshold predicted cylinder temperature in
accordance with the concentration of alcohol in the fuel.
15. The control apparatus according to claim 8, wherein the
internal combustion engine uses a fuel including alcohol as a fuel,
and the control apparatus further includes a determining value
setting portion that sets any one of the threshold cylinder
temperature, the threshold coolant temperature, the threshold
engine load, and the threshold predicted cylinder temperature in
accordance with the concentration of alcohol in the fuel.
16. The control apparatus according to claim 9, wherein the
internal combustion engine uses a fuel including alcohol as a fuel,
and the control apparatus further includes a determining value
setting portion that sets any one of the threshold cylinder
temperature, the threshold coolant temperature, the threshold
engine load, and the threshold predicted cylinder temperature in
accordance with the concentration of alcohol in the fuel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a control apparatus for an
internal combustion engine and a method for controlling an internal
combustion engine. More specifically, it relates to a control
apparatus for an internal combustion engine and a method for
controlling an internal combustion engine capable of controlling
the timing of the opening and closing and the lift amounts of
individual intake valves of an internal combustion engine.
[0003] 2. Description of the Related Art
[0004] The Japanese Patent Application Publication No.
JP-A-10-252511 discloses a system that controls the opening and
closing of the intake valve and exhaust valve by a valve driving
mechanism capable of variably adjusting the timing of the opening
and closing of intake and exhaust valves disposed in each cylinder
of an internal combustion engine. In this system, during normal
operation, in which combustion in the internal combustion engine is
stable, the internal combustion engine is operated by a four-stroke
combustion cycle comprising an intake stroke, a compression stroke,
an expansion stroke, and an exhaust stroke. In doing this, control
is performed to open and close the intake valve at a prescribed
timing in the intake stroke, and control is performed to open and
close the exhaust valve at a prescribed timing in the exhaust
stroke.
[0005] However, in the case, for example, of a cold start of the
internal combustion engine, in which there is a tendency for
incomplete combustion to occur, there are cases in which the fuel
is not completely combusted and non-combusted fuel remains that is
exhausted from the cylinder in the exhaust stroke. Therefore, in
the above-noted system, in the case in which it is determined that
incomplete combustion is occurring in the internal combustion
engine, the following control is performed. Specifically, the
opening of the intake valve and the exhaust valve is stopped for a
prescribed period of time during operation of the internal
combustion engine. As a result, during the time that the valves are
stopped, both the intake and the exhaust valves are closed, and the
up and down motion of the piston repeatedly performs the
compression stroke and the expansion stroke only. In this
condition, ignition is done each time between the compression
stroke and the expansion stroke.
[0006] During this repetition of the compression and
explosion/expansion strokes in this manner, non-combusted fuel in
the cylinder is completely combusted. Subsequently, when complete
combustion of the non-combusted fuel is verified, normal valve
opening and closing operation is again permitted and normal
operation resumes. By doing this, the system enables complete fuel
combustion and suppression of exhausting of non-combusted fuel in
an operating condition in which there is a tendency for incomplete
combustion to occur.
[0007] During the time when an internal combustion engine is being
started from the cold condition of the internal combustion engine,
in order to stabilize combustion and to improve starting
characteristics, the fuel injection amount is increased by
performing control to achieve a fuel-rich condition. From the
standpoint of improving fuel economy and exhaust emissions,
however, it is desirable to further expand the lean limit of the
internal combustion engine even during the cold start. With regard
to this point, when incomplete combustion occurs, the above-noted
system performs repeated compression and expansion strokes with
both the intake valve and the exhaust valve closed, performing
ignition each time to complete combust the non-combusted fuel. That
is, according to the system, by repeating the compression and
explosion/expansion strokes, fuel that fills the closed cylinder is
completely combusted, and is not related to control of the air-fuel
ratio toward the lean side during operation when the internal
combustion engine is cold started, nor is it related to extending
the lean limit.
SUMMARY OF THE INVENTION
[0008] The present invention has an object to provide a control
apparatus for an internal combustion engine and a method for
controlling an internal combustion engine improved to achieve an
extension of the lean limit, even when the internal combustion
engine is being started from the cold start.
[0009] A first aspect of the present invention is a control
apparatus for an internal combustion engine having a variable valve
driving means for changing the timing of the opening and closing
and lift amount of an intake valve disposed in an intake port
communicating with a cylinder of the internal combustion engine; a
valve timing control means for controlling the timing of the
opening and closing and lift amount of the intake valve by the
variable valve driving means; a cold start determining means for
determining whether the internal combustion engine is being started
from a cold start; and a multi-stroke operation setting means for
setting, in which one combustion cycle of the internal combustion
engine includes two or more intake and compression strokes, when
the cold start determining means determines that the internal
combustion is being started from the cold start, wherein the
multi-stroke operation is formed by a first intake stroke and a
first compression stroke and a second intake stroke and a second
compression stroke, followed by a combustion stroke and an exhaust
stroke. In this aspect, the valve timing control means controls a
lift of the intake valve during the first intake stroke and the
first compression stroke to a low lift amount, which is smaller
than the normal lift amount required for intake of a requested
intake air amount, and controls the lift of the intake valve in a
second intake stroke and a second compression stroke to the normal
lift amount.
[0010] According to the first aspect, by performing two or more
intake and compression strokes, and making the lift amount in the
first intake stroke small, it is possible to raise the intake
temperature when an intake air flows into a combustion chamber.
Even when the temperature of the internal combustion engine is low,
therefore, as during cold starting, it is possible to more quickly
raise the temperature in the combustion chambers and stabilize
combustion.
[0011] In a second aspect, the low lift amount may be the lift
amount at which the pumping loss during the first intake stroke and
the first compression stroke is maximum.
[0012] According to the second aspect, when intake is done in the
first intake stroke and the first compression stroke, it is
possible to more effectively raise the temperature of the intake
gas, enabling not only an improvement in combustion
characteristics, but also earlier warm-up of the internal
combustion engine.
[0013] A third embodiment is the control apparatus of either the
first or second aspect, which may further have an ignition timing
control means for controlling ignition timing by a spark plug
disposed in the cylinder, wherein the ignition timing control means
prohibits ignition during the first intake stroke and the first
compression stroke.
[0014] According to the third aspect, in addition to effectively
raising the temperature of the intake gas during the first intake
stroke and the first compression strokes, it is possible to perform
intake in accordance with a requested intake air amount in the
second intake and the second compression stroke, enabling
generation of a torque as required for the requested load.
[0015] A fourth aspect is a-control apparatus of any one of the
first to third aspects, wherein the multi-stroke operation setting
means may perform, during one combustion cycle, a plurality of
repetitions of the first intake stroke and the first compression
stroke, followed by performing the second intake stroke and the
second compression stroke.
[0016] According to the fourth aspect, the intake temperature is
more reliably raised and it is possible to warm up the internal
combustion engine at an earlier stage.
[0017] A fifth aspect is the control apparatus according to any of
the first to fourth aspects, which may further have a multi-stroke
operation termination determining means for determining whether
multi-stroke operation is to be terminated; and a four-stroke
operation setting means for setting one combustion cycle of the
combustion of the internal combustion engine to four-stroke
operation comprising an intake stroke, a compression stroke, an
expansion stroke, and an exhaust stroke, if the multi-stroke
operation judges that multi-stroke operation is to be
terminated.
[0018] The above-noted multi-stroke operation is advantageous in
improving the combustion characteristics when the internal
combustion engine is cold. However, because the lift amount of the
intake valve becomes small in the first intake stroke and the first
compression stroke, so that the intake resistance becomes large,
the torque loss is large. Therefore, after combustion stabilizes, a
switch may be made to normal four-stroke operation. With regard to
this point, according to the sixth through ninth aspects as noted
below, it is possible to reliably determine the timing of this
switching and, when it is determined that the multi-stroke
operation is to be terminated, it is possible to switch to
four-stroke operation, in which the normal intake stroke,
compression stroke, expansion stroke, and exhaust stroke are
performed.
[0019] A sixth aspect is the control apparatus of the fifth aspect,
which may further have a temperature detecting means for detecting
a temperature in the cylinder, wherein the multi-stroke operation
termination determining means determines that multi-stroke
operation is to be terminated if a temperature in the cylinder
reaches a threshold cylinder temperature.
[0020] A seventh aspect is the control apparatus of the fifth
aspect, which may further comprise a water temperature detection
means for detecting the temperature of the coolant of the internal
combustion engine, wherein the multi-stroke operation termination
determining means determines that multi-stroke operation is to be
terminated if the coolant temperature reaches a threshold coolant
temperature.
[0021] An eighth aspect is the control apparatus of the fifth
aspect, which may further have a requested load calculation means
for calculating a requested load on the internal combustion engine,
wherein the multi-stroke operation termination determining means
determines that multi-stroke operation is to be terminated if the
calculated requested load reaches or exceeds a threshold engine
load.
[0022] A ninth aspect is the control apparatus of the fifth aspect,
which may further have a cylinder temperature predicting means for
predicting, before starting the first intake stroke and the first
compression stroke in one combustion cycle, a temperature in a
cylinder after performing the second intake stroke and the second
compression stroke, wherein the multi-stroke operation termination
determining means determines that multi-stroke operation is to be
terminated if the predicted temperature in the cylinder reaches a
threshold predicted cylinder temperature.
[0023] In the case of the multi-stroke operation noted above, if
intake and compression strokes are repeated, the intake gas
temperature will raise excessively. When the intake gas temperature
rises excessively, it is also possible to envision this as a cause
of abnormal combustion. With regard to this point, according to the
ninth aspect, the temperature in the cylinder is predicted, and it
is determined whether to switching from multi-stroke operation to
six-stroke operation based on the predicted temperature. Therefore,
even in the case of performing multi-stroke operation, it is
possible to more reliably prevent the intake gas from reaching an
excessively high temperature.
[0024] Also, in the case in which the fuel of the internal
combustion engine includes an alcohol, because the volatility of
the fuel will differ depending on the concentration of the alcohol
fuel in the fuel, the combustion characteristics will also change.
That is, even for the same operating condition, the time from
starting to reach stabilized combustion will differ.
[0025] A tenth aspect is the control apparatus of any one of the
sixth to ninth aspects, wherein the internal combustion engine may
use a fuel including alcohol as a fuel, and the control apparatus
may set any one of the threshold cylinder temperature, the
threshold coolant temperature, the threshold engine load, and the
threshold predicted engine temperature in accordance with the
concentration of alcohol fuel in the fuel.
[0026] According to the tenth aspect, the determination value of
the threshold cylinder temperature, the threshold coolant
temperature, the threshold engine load, or the threshold predicted
engine temperature used as a reference in determining whether to
switch from multi-stroke operation to four-stroke operation in
accordance with the concentration of alcohol fuel in the fuel. It
is therefore possible to perform the switching determination
reliably, in accordance with the fuel that is used.
[0027] An eleventh aspect is the control apparatus of any one of
the first to tenth aspects, wherein the internal combustion engine
may a first cylinder group and a second cylinder group, and wherein
the control apparatus may operate only cylinders belonging to the
first cylinder group and may include a reduced-cylinder operation
setting means for setting cylinders belonging to the second
cylinder group to reduced cylinder operation, in which the
cylinders are stopped, and an all-cylinder operation setting means
for setting all cylinders belonging to the first cylinder group and
cylinders belonging to the second cylinder group to all-cylinder
operation, in which all cylinders are operated, wherein the cold
start determination means determines whether restoration of
operation of the cylinders belonging to the second group of
cylinders is a cold start when an engine transition is made from
reduced-cylinder operation to all-cylinder operation, and the
multi-stroke operation setting means sets the operation of
cylinders belonging to the second cylinder group to multi-stroke
operation when the cold start determining means determines that
restoration of operation of the cylinders belonging to the second
group of cylinders is the cold start.
[0028] According to the eleventh aspect, when return is being made
from so-called reduced-cylinder operation to all-cylinder
operation, even in the case in which the cylinders that had be
stopped during reduced-cylinder operation are to be restored to
operation when cold, it is possible to apply the above-noted
multi-stroke operation. It is therefore possible to more quickly
stabilize the combustion in cylinders that had been stopped, and
possible to more quickly return from reduced-cylinder operation to
all-cylinder operation.
[0029] A twelfth aspect is the control apparatus of any one of the
first to eleventh aspects, wherein the variable valve driving means
may have an intake cam driving the opening and closing of the
intake valve and an electrical motor rotationally driving the
intake cam, wherein the valve timing control means may control the
valve timing by controlling the rotational drive of the intake cam
using the electrical motor.
[0030] According to the twelfth aspect, because it is possible to
control the valve timing of the intake valve using an electrical
motor, it is possible to reliably control the intake valve to a set
lift amount, and possible to reliably achieve control of the lift
amount in the above-noted six-stroke operation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The foregoing and further objects, features, and advantages
of the invention will become apparent from the following
description of preferred embodiments with reference to the
accompanying drawings, wherein like numerals are used to represent
like elements, and wherein:
[0032] FIG. 1 is a schematic view describing the configuration of a
system according to the first embodiment of the present
invention;
[0033] FIG. 2 is a drawing describing the relationship between the
lift amount of an intake valve and the pumping loss;
[0034] FIG. 3A and FIG. 3B are drawings describing the opening and
closing timing and the lift amounts of the intake and exhaust
valves;
[0035] FIG. 4 is a flowchart describing a control routine executed
by the system in the first embodiment of the present invention;
[0036] FIG. 5 is a graph describing the relationship between the
coolant temperature and the threshold engine load in a second
embodiment of the present invention;
[0037] FIG. 6 is a flowchart describing a control routine executed
by the system in the second embodiment of the present
invention;
[0038] FIG. 7 is a flowchart describing a control routine executed
by the system in the third embodiment of the present invention;
[0039] FIG. 8 is a graph describing the relationship between the
alcohol concentration in the fuel and the threshold coolant
temperature in a fourth embodiment of the present invention;
[0040] FIG. 9 is a flowchart describing a control routine executed
by the system in the fourth embodiment of the present invention;
and
[0041] FIG. 10 is a flowchart describing a control routine executed
by the system in a fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0042] Embodiments of the present invention are described in detail
below, with references made to the accompanying drawings. In the
drawings, elements that are the same or corresponding elements to
elements earlier described are assigned the same reference numerals
and the descriptions thereof are either simplified or omitted.
[0043] FIG. 1 is a schematic view showing the configuration of the
first embodiment of the present invention. The system shown in FIG.
1 has an internal combustion engine 10. The internal combustion
engine 10 has a cylinder 12. Although only the cross-section of
only one cylinder 12 is shown in FIG. 1, the internal combustion
engine 10 actually has a plurality of cylinders 12. A piston 14 is
disposed within the cylinder 12. The piston 14 is connected to a
crankshaft 18 via a connecting rod 16. A rotational speed sensor 20
that generates an output responsive to the rotational speed of the
crankshaft is disposed in the vicinity of the crankshaft 18. A
coolant temperature sensor 22 that detects the temperature of the
coolant for the internal combustion engine is provided in the
internal combustion engine. A combustion chamber 24 is provided at
the top of the piston 14. A temperature sensor 26 (temperature
detecting means) that generates an output responsive to the
temperature within the combustion chamber 24 is disposed in the
combustion chamber 24. A spark plug 28 is inserted with the head
thereof exposed into the combustion chamber 24.
[0044] The internal combustion engine 10 has an intake port 30 and
an exhaust port 32 that communicate with the combustion chamber 24.
An injector 34 is built into the intake port 30. The intake port 30
is connected to an intake passage 36. An air flow meter 38 is
disposed in the intake passage 36.
[0045] The intake port 30 of each cylinder 12 of the internal
combustion engine 10 has an intake valve 40 that opens and closes
the intake port 30. An intake valve shaft 42 is fixed to the intake
valve 40. A valve lifter 44 is mounted to the top end of the intake
valve shaft 42. The impelling force of a valve spring 46 acts on
the intake valve shaft 42, and the intake valve 40 is impelled in
the valve-closing direction by the impelling force. An intake cam
50 is disposed above the valve lifter 44. The intake cams 50 of
each cylinder 12 are connected two each to one and the same
camshaft (not shown), and are linked to a variable valve timing
mechanism 52 via the camshaft and the like. A cam position sensor
54 is mounted in the vicinity of the camshaft of the intake cams.
The cam position sensor 54 generates an output responsive to the
rotational angle and the rotational speed of the intake cam 50.
[0046] The internal combustion engine 10 has, on the exhaust ports
32 of each cylinder 12, an exhaust valve 60 that opens and closes
the exhaust port 32. The exhaust valve 60 has the same
configuration as the intake valve 40. That is, the exhaust valve 60
has an exhaust valve shaft 62 fixed to the exhaust valve 60, a
valve lifter 64 mounted at the top of the exhaust valve shaft 62,
and a valve spring 66 mounted so as to impel the exhaust valve
shaft 62 in the valve-closing direction. An exhaust cam 70 is
disposed at the top of the valve lifter 64. The exhaust cams 70 of
each cylinder 12 are connected two each to one and the same
camshaft (not shown), and are linked to a variable valve timing
mechanism 72 via the camshaft and the like. A cam position sensor
74 is mounted in the vicinity of the camshaft of the exhaust cams
70. The cam position sensor 74 generates an output responsive to
the rotational angle and the rotational speed of the exhaust cam
70.
[0047] The variable valve timing mechanism 52 for the intake valve
40 side utilizes a motor to control the rotational speed and
rocking of the camshaft to control the rotation an the rocking of
the intake cam 50. As a result, the phase, operating angle, and
lift amount of the intake valve 40 can be varied independently for
each cylinder 12. The variable valve timing mechanism 72 for the
exhaust valve 70 utilizes a motor or the like to control the
rotation and rocking of the camshaft to control the rotation and
rocking of the exhaust cam 70. As a result, the phase, operating
angle, and lift amount of the exhaust valve 70 can be varied
independently for each cylinder 12.
[0048] By varying the phase of the intake and exhaust valves 40,
60, it is possible to change the timing of the opening and the
closing of the intake and exhaust valves 40, 60. By varying the
operating angle, it is possible to change the period of time of
opening of the intake and exhaust valves 40, 60. By varying the
lift amount, it is possible to change the size of the passage
formed between the valves and the intake and output ports 30, 32
when the intake and exhaust valves 40, 60 are open. This type of
control can be performed for each intake valve 40 and exhaust valve
60 of each individual cylinder 12. Because the mechanism to control
the rotating and rocking of the camshaft so as to control the
phase, operating angle, and lift amount of the intake valves 40 or
the exhaust valve 60 is not particularly novel, it will not be
described here in detail.
[0049] The internal combustion engine 10 has an ECU (electronic
control unit) 80 as a control apparatus for the internal combustion
engine. The ECU 80 acquires information required for control of the
internal combustion engine 10 from such sensors as the rotational
speed sensor 20, the coolant temperature sensor 22, the temperature
sensor 26, the air flow meter 38, and the cam position sensors 54,
74, and controls the spark plug 28, the injector 34, an the
variable valve timing mechanisms 52, 72, based on the acquired
information.
[0050] In cases, for example, in which the internal combustion
engine 10 is cold started, in which the internal combustion engine
10 has not yet been warmed up, the temperatures of various parts of
the internal combustion engine 10 are low. For this reason, the
intake air temperature when the engine is cold started is low. It
is therefore difficult for fuel to be atomized, and the condition
occurs in which there is low mixture of air and fuel, making it
difficult to achieve stable combustion. For this reason, control is
generally performed to increase the amount of fuel injection amount
at the cold start. If this control is performed, however, the
air-fuel ratio during the cold start becomes rich, and the amount
of non-combusted fuel that is exhausted increases. In order to
extend the lean limit and improve the fuel economy and exhaust
emissions characteristics, therefore, it is desirable that the
control to increase the fuel injection amount during a cold start
be done over a short period of time, or be avoided. For this
reason, it is desirable in cold starting that, at an earlier stage
after the starting of the internal combustion engine 10 the intake
air temperature is increased, atomization is promoted, and
combustion is stabilized.
[0051] If the intake resistance in the intake stroke of the
internal combustion engine 10 increases, heat of friction occurs
when the intake gas is taken into the cylinder 12. Therefore, by
making the intake resistance in the intake stroke, that is, the
pumping loss, large it is possible to raise the temperature of the
gas taken into the cylinder 12 by increasing heat of friction.
[0052] FIG. 2 is a drawing describing the relationship between the
lift amount of the intake valve 40 and the pumping loss. In FIG. 2,
the horizontal axis represents the lift amount of the intake valve
40, and the vertical axis represents the pumping loss. The solid
line (i) in FIG. 2 shows the case in which the internal combustion
engine 10 is in a lower rotational speed region than shown by the
solid line (ii). As shown in FIG. 2, as the lift of the intake
valve 40 increased from the condition in which the lift amount is
zero, the pumping loss also increases, and becomes maximum at some
lift amount (low lift amount). The pumping loss gradually decreases
as the lift amount becomes larger than the low lift amount. The low
lift amount at which the pumping loss is maximum is different
depending upon the engine rotational speed and, as shown by the
solid lines (i) and (ii) of FIG. 2, as the engine rotational speed
increases, the low lift amount tends to increase.
[0053] The heat of friction generated when the intake gas flows in
cylinder is higher, the greater is the pumping loss in the intake
stroke. Therefore, by setting the lift amount to the low lift
amount and making the pumping loss maximum, it is possible to more
quickly raise the temperature of the intake gas when making a cold
start.
[0054] In contrast, the lift amount of the intake valve 40 is set
to the lift amount (normal lift amount) required to reliable intake
the requested air into the cylinder 12. With regard to this point,
even when the internal combustion engine is cold started, in order
to generate the torque required for starting, it is necessary to
intake the requested amount of air, and necessary to perform intake
by controlling the lift amount of the intake valve 40 to the normal
lift amount. Therefore, if the compression stroke and the
explosion/combustion stroke are performed after completing the
intake stroke with the control remaining at the low lift amount in
order to raise the temperature as noted above, it can be presumed
that the amount of intake gas filling the cylinder 12 is
insufficient, so that the combustion is actually decreased.
[0055] The system of the first embodiment, in order to
simultaneously achieve a rise of the intake gas temperature and a
sufficient gas intake amount in performing a cold start, after
repeating the intake stroke and the compression stroke two times in
one combustion cycle of the internal combustion engine 10, executes
a combustion stroke and an exhaust stroke. FIG. 3A and FIG. 3B
describe the opening and closing timing and lift amounts of the
intake and exhaust valves in the internal combustion engine 10,
FIG. 3A showing operation at the time of cold starting and FIG. 3B
showing the operation after combustion stabilizes.
[0056] As shown in FIG. 3A, when the intake temperature is low
during a cold start, one combustion cycle is formed by the six
strokes of the first intake stroke, a first compression stroke, a
second intake stroke, a second compression stroke, an expansion
stroke, and an exhaust stroke, with one ignition occurring with a
prescribed timing in the second compression stroke. In this
embodiment, this operating condition of the internal combustion
engine 10 will be referred to as "six-stroke operation." During
six-stroke operation, in the initial intake stroke (first intake
stroke), in order to raise the intake temperature with the pumping
loss at a maximum, the lift amount of the intake valve 40 is
controlled to be the low lift amount. The relationship between the
low lift amount and the pumping loss differs, depending upon the
timing of the opening and closing and the operating angle of the
intake valve. Therefore, the low lift amount that is set at this
point is the lift amount that maximizes the pumping loss under a
condition in which the opening and closing timing and operating
angle are set to appropriate timing and angle in relationship to
other operating conditions. The intake temperature rises because of
the heat of friction generated during the first intake stroke.
Although the temperature rise will differ depending upon the
temperature of the gas that is taken in and the engine rotational
speed at that time, it is, for example, approximately 50.degree. C.
to 60.degree. C. After performing intake in the condition of this
lift amount, the intake valve 40 is closed, and the first
compression stroke is entered.
[0057] After the above, the second intake stroke is entered without
performing ignition. When this occurs, the lift amount of the
intake valve 40 is controlled to the normal lift amount required to
intake the requested air amount. The normal lift amount also
differs depending upon the timing of the opening and closing and
the operating angle of the intake valve 40. Therefore, the normal
lift amount is set to a lift amount to intake the requested amount
of air in the case in which the lift amount, the opening and
closing timing, and the operating angle are properly set. With the
valve timing set in this manner, the piston 14 is lowered in the
second intake stroke and intake is performed. By doing this, the
required amount of intake air can be acquired. The piston 14 begins
to rise and the second compression stroke starts, and in the second
compression stroke ignition is performed at the optimum timing.
After that, the expansion stroke and the exhaust stroke are
performed.
[0058] During the six-stroke operation, the exhaust valve 60 is
closed during a period from the first intake stroke to the second
compression stroke and during the compression stroke in the same
manner as a period from the normal intake stroke to the expansion
stroke. That is, during the six-stroke operation control is
performed so that the exhaust valve 60 is first opened and then
closed at an appropriate time in the region of the start of the
exhaust stroke.
[0059] The two intake and compression strokes causes the
temperature of the intake gas to raise, and enables intake of the
required amount of intake gas. Therefore, it is possible to acquire
the air required for combustion while promoting the mixing of fuel
and air, and possible to improve the combustion condition during
the cold start. Also, by a temperature rise of the intake gas, it
is possible to more quickly warm-up the internal combustion engine
and stabilize combustion. Because the raising of the intake gas
temperature at the time of cold start stabilizes combustion, it is
possible to suppress an increase in the fuel injection amount, and
extend the lean limit.
[0060] A map establishing the relationship between the low lift
amount and engine rotational speed at which the pumping loss is
maximum and the timing of the opening and closing of the intake
valve 40, and a map establishing the relationship between the lift
amount, the requested air intake amount and timing of the opening
and closing of the intake valve 40 are stored in the ECU 80. The
low lift amount and normal lift amount in the case of six-stroke
operation are established in accordance with these maps, and the
ECU 80 performs control of the intake valve 40, via the variable
valve timing mechanism 52, in accordance with the set low lift
amount and normal lift amount.
[0061] After the internal combustion engine 10 is warmed up and
combustion has stabilized, a transition is made to operation
(four-stroke operation) in which one combustion cycle is formed by
the normal four strokes. That is, the intake stroke is performed so
that the lift amount of the intake valve 40 is controlled to the
normal lift amount in response to the requested amount of intake
air. After that, the intake valve 40 is closed and, after
performing the compression stroke, ignition is performed at an
appropriate timing, immediately after which the expansion stroke
and exhaust stroke are performed. The exhaust valve 60, similar to
the case of normal control, is first opened and then closed at an
appropriate time in the exhaust stroke of the four strokes to
perform exhausting.
[0062] The ECU 80 stores a map establishing the relationship
between the normal lift amount, the amount of requested air intake,
and the timing of the opening and closing and the operating angle
of the intake valve 40. In the case of performing four-stroke
operation, the normal lift amount is calculated using the map and,
in response to the calculated normal lift amount, the ECU 80
controls the intake valve 40 via the variable valve timing
mechanism 52.
[0063] The six-stroke operation is effective in the case in which,
for example, during cold starting, when raising the intake
temperature has priority. However, in the condition in which
control is performed to the low lift amount at which the pumping
loss is maximum, because two intakes are performed the torque loss
increases. If the internal combustion engine 10 has been warmed up
and the combustion has been stabilized, a switch is made
immediately to four-stroke operation. For this reason, it is
determined in the system of the first embodiment that combustion
has stabilized, a transition is made from six-stroke operation to
four-stroke operation.
[0064] Specifically, when the temperature in the combustion chamber
24 has risen sufficiently, it can be determined that combustion in
the internal combustion engine 10 has stabilized. Therefore, the
temperature in the combustion chamber 24 is detected from the
output of the temperature sensor 26 mounted in the combustion
chamber 24, and if the detected temperature is sufficiently high,
it is determined that combustion has stabilized. The ECU 80 has
stored a threshold cylinder temperature that is the minimum
temperature in the combustion chamber 24 to determine that the
internal combustion engine 10 has warmed up and the combustion has
stabilized. If the detected temperature has reached at least the
threshold cylinder temperature, the ECU 80 determines that
combustion in the internal combustion engine 10 has stabilized and
switches from six-stroke operation to four-stroke operation.
[0065] FIG. 4 is a flowchart describing a control routine executed
by the ECU 80 in the first embodiment of the present invention. The
flowchart shown in FIG. 4 is a routine that executed each time the
internal combustion engine 10 is started. In the flowchart shown in
FIG. 4, the temperature of the coolant in the internal combustion
engine 10 is first detected (step S100). The coolant temperature is
determined based on the output of the coolant temperature sensor
22. Next, it is determined whether or not cold start of the
internal combustion engine 10 has been requested (step S102).
Whether or not cold start has been requested is determined, for
example, based on whether or not the coolant temperature determined
in step S100 is below a prescribed range when starting of the
internal combustion engine 10 is requested.
[0066] If it is determined at step S102 that the cold start has
been requested, required information regarding the current
operating condition is detected (step S104). For example,
information such as the engine rotational speed, the accelerator
operating amount, and the temperature in the combustion chamber 24
is detected in accordance with the output from various sensors.
Next, the requested intake air amount is calculated (step S106).
The requested intake air amount is calculated in accordance with
requested load determined based on the output of an accelerator
operating sensor.
[0067] Next, it is determined whether or not the temperature T24 in
the combustion chamber 24 is greater than or equal to the threshold
cylinder temperature T0 (step S108). If at step S108 the
temperature T24 in the combustion chamber 24 is greater than or
equal to the threshold cylinder temperature T0, it is determined
that the internal combustion engine 10 has not warmed up and that
combustion has not stabilized, resulting in execution of six-stroke
operation (step 110).
[0068] Specifically, using a map stored in the ECU 80, the low lift
amount at which the pumping loss is maximum for the current engine
rotational speed is determined, and the lift amount of the intake
valve 40 for the first intake stroke is determined. Using a map
stored in the ECU 80, the normal lift amount for the second intake
stroke is determined in accordance with the requested intake air
amount determined in step S106. In accordance with the current
operating condition detected in step S104, the operating angle and
phase of the intake valve 40 at the time of engine starting are
determined. In accordance with the valve timing, such as the
calculated lift amount and the like, control of the intake valve 40
is performed by the variable valve timing mechanism 52. In this
condition, the first intake stroke, the first compression stroke,
the second intake stroke, and the second compression stroke are
performed, after which the compression stroke and exhaust stroke
are performed. Control is performed so that ignition is done at an
appropriate time during the second compression stroke. During this
period of time, control is performed to close the exhaust valve 60
from the first intake stroke to the second compression stroke and
during the expansion stroke, and to open the exhaust valve 60 at
the normal valve timing in the exhaust stroke to perform
exhausting.
[0069] Return is made again to step S104, at which information
regarding the current operating condition is detected after the
requested amount of intake air is calculated (steps S104 and S106),
at step S108 the temperature T24 in the combustion chamber 24 is
compared with the threshold cylinder temperature T0. If it is not
determined that the temperature T24 is greater than or equal to the
threshold cylinder temperature T0 at step S108, six-stroke
operation is performed (step S110), and the processing of steps
S104 to S108 is performed. That is, six-stroke operation (step
S110) and the processing of steps S104 to S108 are repeated until
it is determined that the temperature T24 in a combustion chamber
temperature reaches the threshold cylinder temperature T0 at step
S108.
[0070] If, however, it is not determined at step S102 that a cold
start had been requested, and if it is determined at step S108 that
the temperature T24 in the combustion chamber 24 is greater than or
equal to the threshold cylinder temperature T0, it is determined
that the temperature T24 in the combustion chamber 24 has reached
the temperature T0 at which the internal combustion engine is
assumed to have already warmed up. Therefore, normal four-stroke
operation is executed (step S112). Specifically, using a map stored
in the ECU 80, the normal lift amount of the intake valve 40 is set
in accordance with the requested amount of intake air. The opening
and closing timing and operating angles of the exhaust valve 60 and
the intake valve 40 are set in accordance with the current
condition of the internal combustion engine. In this condition, the
normal intake stroke, compression stroke, expansion stroke, and
exhaust stroke are performed, and control is done to perform
ignition between the compression stroke and the expansion stroke.
Next, the processing is ended.
[0071] As described above, according to the first embodiment when
performing cold starting, control is performed so that after
performing the first intake stroke and the first compression stroke
at the low lift amount at which the pumping loss is maximum, the
second intake stroke and the second compression stroke are
performed, after which the expansion stroke and the exhaust stroke
are performed. By doing this, it is possible to raise the
temperature of the intake air from the condition in which the
intake temperature is low, such as when doing cold starting,
thereby enabling both an improvement in the combustion condition,
early warm-up of the internal combustion engine, and stabilization
of combustion.
[0072] In the first embodiment, the temperature T24 in the
combustion chamber 24 is directly detected and, based on whether
this temperature T24 has reached the threshold temperature T0, it
is determined whether to switch between six-stroke operation and
four-stroke operation. The present invention, however, is not
limited to performing the determination of switching between
six-stroke operation and four-stroke operation in this manner. This
determination can be made if it is possible to determine with some
accuracy the stabilization of combustion when cold starting is
done. The determination of whether or not to switch, therefore, can
be made, for example, by detecting the temperature of the coolant
for the internal combustion engine 10 and basing the judgment on
whether or not the coolant temperature is higher than or equal to
the threshold coolant temperature at which the internal combustion
engine 10 is assumed to have warmed up. The threshold coolant
temperature can be set based on a temperature by experimentally
determining a value which is experimentally determined and whish
indicates that the internal combustion engine 10 has warmed up and,
based on that value, in consideration of what extent of warm-up the
six-stroke operation is to be continued.
[0073] The first embodiment of the present invention is described
for the case in which it is determined that a cold start has been
requested. The present invention is not, however, limited in this
manner, and may perform six-stroke operation in other cases in
which it is effective to give priority to raising the intake
temperature. Therefore, for example, six-stroke operation may be
started even in cases in which it is determined that the internal
combustion engine 10 is not warmed up. Also, six-stroke operation
may also be performed only in a case, of a so-called fast idling
condition, in which the internal combustion engine is operating at
a rotational speed higher than a normal idling speed, such as
during catalyst warm-up or during a cold start.
[0074] The low lift amount in the first intake stroke of six-stroke
operation was described for the case of a lift amount at which the
pumping loss is maximum. In the present invention, however, the low
lift amount is not limited in this manner, and may be set as a
small lift amount at which the pumping loss is larger than at a
lift amount that is normally set in accordance with a requested
amount of intake air. This is a reason why, even if two intake
strokes are performed at a lift amount that is the same as the
normal lift amount, it is possible to raise the intake temperature
slightly.
[0075] The first embodiment was described for the case in which the
lift amount in the second intake stroke during six-stroke operation
and the lift amount in four-stroke operation are set in accordance
with the requested amount of intake air, and valve timing control
including this lift amount is performed to control the intake air
amount. The present invention is not limited in this manner,
however, and an electronically controlled throttle valve may be
disposed in the intake passage 36 and the air intake amount may be
controlled by the degree of opening of the throttle valve. In this
case, the lift of the intake valve in the first intake stroke can
be controlled to the low lift amount, and the normal lift amount in
the second intake stroke and in four-stroke operation can be set to
the maximum lift amount for the case in which the intake cam 50 is
rotated one time, instead of the lift amount set in accordance with
the requested amount of intake air.
[0076] Also, the first embodiment is described for case in which,
during the cold start of the internal combustion engine, the first
combustion cycle is performed with six-stroke operation, which
includes a first intake stroke, a first compression stroke, a
second intake stroke, a second compression stroke, an expansion
stroke, and an exhaust stroke. However, the present invention is
not limited in this manner, and multi-stroke operation may be
performed that includes a plurality of repetitions of a first
intake stroke and a first compression stroke, followed by
performing of a second intake stroke, a second compression stroke,
an expansion stroke, and an exhaust stroke. In this case, pumping
loss during the first intake stroke increases, thereby enabling of
effectively raising the intake temperature during one combustion
cycle.
[0077] The first embodiment was described for the case in which the
means for changing the valve timing of the intake valve 40 is that
of connecting two intake cams 50 each to one and the same camshaft,
the rotation and rocking of the camshaft being controlled by the
variable valve timing mechanism 52, and value timing including the
phase, lift amount, and operating angles of the intake valves 40
being controlled independently for each cylinder 12. The present
invention, however, is not limited to this method of controlling
the intake valve 40. In the present invention, the means for
changing the valve timing of the intake valve 40 may be a different
configuration that is capable of opening and closing the valve at
least two times, in the intake strokes during one combustion cycle,
and also changing the lift of the intake valve. Specifically, for
example, by using an electromagnetically driven valve, the lift and
opening and closing timing of the intake valve 40 may be
independently controlled for each intake valve 40. In the same
manner, the means for changing the valve timing of the exhaust
valve 60 is not limited to the means described with regard to the
first embodiment, and may be a different configuration that is
capable of controlling the timing of the one opening and closing at
appropriate times within the exhaust stroke, in accordance with the
condition in six-stroke operation (or multi-stroke operation).
[0078] Although the first embodiment was described for the case in
which the internal combustion engine 10 is a gasoline engine, there
is no limitation in this manner, and the internal combustion engine
10 may also be, for example, a diesel engine. Although the example
given is that of fuel injection by port injection, the engine may
be an internal combustion engine that uses cylinder injection.
[0079] For example, in the first embodiment by executing step S102
the "cold starting determining means" may implemented, by executing
step S110 the "multi-stroke operation setting means," the "valve
timing control means," and the "ignition timing control means" may
be implemented, by executing step S108 the "multi-stroke operation
termination determining means" may be implemented, by executing
step S110 the "four-stroke operation setting means" is implemented,
and by executing step S104 the "temperature detection means" and
"coolant temperature detection means" are implemented.
[0080] The second embodiment of the present invention is described
below, with reference to FIG. 5 and FIG. 6. The description of the
second embodiment will focus on the only the characteristic parts
of the second embodiment, and the descriptions of parts that are
the same as the first embodiment will be either simplified or
omitted. The system in the second embodiment has the same type of
configuration as the system of the first embodiment. In the system
of the second embodiment, with the exception of the method for
determining timing of switching from six-stroke operation to
four-stroke operation being different from the method in the first
embodiment, control is performed in the same manner as in the first
embodiment.
[0081] Specifically, in the system of the second embodiment, the
determination of the switching from six-stroke operation to
four-stroke operation is made in accordance with an engine load.
FIG. 5 is a graph describing the relationship between the coolant
temperature and the threshold engine load to determine whether to
switch from six-stroke operation to four-stroke operation in the
second embodiment. In FIG. 5, the horizontal axis represents the
coolant temperature and the vertical axis represents the threshold
engine load. As noted above, in the six-stroke operation, the
intake stroke are performed two times and, of the two intake
strokes, intake is performed in the first intake stroke with the
lift amount set to the lift amount at which the pumping loss is
maximum. For this reason, compared with the case of normal
four-stroke operation, the generated torque is small. Therefore, in
the case in which the load becomes large, it is difficult to
generate a torque in accordance with that load with six-stroke
operation. Therefore, regardless of whether the internal combustion
engine 10 has warmed up, in the case in which the requested load is
above a given load, in order to generate a torque in accordance
with the requested load, switching is done from the six-stroke
operation to the four-stroke operation. That is, the rise of the
requested load of the internal combustion engine 10 above the solid
line (i) (threshold engine load (i)) in FIG. 5 is a first condition
for switching from six-stroke operation to four-stroke
operation.
[0082] In six-stroke operation, an increase in the intake
temperature makes it easier to burn the fuel. If the engine load
becomes large under this condition, abnormal combustion tends to
cause knocking. Also, if such abnormal combustion occurs, it can be
assumed that the warm-up of the internal combustion engine 10 has
progressed to some extent. In the second embodiment, therefore, in
order to give priority to suppression of knocking, six-stroke
operation is only permitted only when the engine load is within a
range that does not cause knocking. The limit value of requested
load set in consideration of occurrence of knocking, as indicated
by the solid line (ii) in FIG. 5, is smaller than when the
temperature of the coolant for the internal combustion engine 10 is
high, and becomes higher when the coolant temperature is low. In
consideration of suppression of knocking, the rise above the solid
line (ii) in FIG. 5 (threshold engine load (ii)) is a second
condition for switching from six-stroke operation to four-stroke
operation.
[0083] From the above, in the second embodiment six-stroke
operation is executed at the cold start, and a transition is made
to four-stroke operation if either of the following first and
second conditions is satisfied. The first condition is (requested
load).gtoreq.(threshold engine load (i)) and the second condition
is (requested load).gtoreq.(threshold engine load (ii)).
[0084] That is, when the coolant temperature and the requested load
are in the region below the thick line (I), six-stroke operation is
executed and continued, and the value of the solid line (I) is a
threshold engine load for switching from six-stroke operation to
four-stroke operation. The threshold engine load is the value that
is the smaller of the threshold engine load (i) and the threshold
engine load (ii) at the coolant temperature at that time. The ECU
80 has stored map establishing the relationship between the coolant
temperature and the threshold engine load, based on the
relationship such as shown in FIG. 5. The threshold engine load is
calculated using the map, based on the detected coolant
temperature.
[0085] FIG. 6 is a flowchart describing a control routine executed
by the ECU 80 in the second embodiment of the present invention.
The routine of FIG. 6 is the same as the routine of FIG. 4, with
the exception that, after step S104 of FIG. 4, step S202 is
executed, and after step S106 step S204 is executed, and in place
of step S108, steps S204 and S206 are executed.
[0086] Specifically, it is determined the internal combustion
engine is being started from the cold condition, i.e. a cold start,
at step S102 and then information regarding the operating condition
is detected (step S104). In this case, the engine rotational speed,
the accelerator operating amount and, in place of the coolant
temperature of the combustion chamber 24, the coolant temperature
are detected in accordance with outputs from various sensors. Next,
the engine load is calculated (step S202). The engine load is
calculated based on information regarding the operating condition
of the internal combustion engine 10 detected in step S104. Next,
the requested intake air amount is calculated (step S106), and the
threshold engine load is calculated (step S204). The threshold
engine load is determined using a map (refer to FIG. 5) stored in
the ECU 80, in accordance with the coolant temperature calculated
at step S104.
[0087] Next, it is determined whether or not the current load is
greater than or equal to the threshold engine load (step S206).
That is, the load calculated at step S202 and the load calculated
at step S204 are compared, and it is determined whether the engine
load is greater than or equal to the threshold engine load. At step
S206 if it is determined that the engine load is greater than or
equal to the threshold engine load, six-stroke operation is
performed (step S110). That is, control is performed so that the
first intake stroke is performed with the intake valve 40 at the
low lift amount and the first compression stroke is performed, and
the second intake stroke is performed with the intake valve 40 at
the normal lift amount condition, the second compression stroke,
and ignition are performed, followed by the expansion stroke and
the exhaust stroke. The processing of steps S104, S202, S106, S204,
S206, and S110 is repeated until it is determined that the engine
load is greater than or equal to the threshold engine load at step
S206.
[0088] If, however, it is not determined that the internal
combustion engine is being started from the cold condition at step
S102, or if at step S206 it is determined the engine load is
greater than or equal to the threshold engine load, four-stroke
operation is set (step S112), and the processing is ended.
[0089] As described above, in the second embodiment the threshold
engine load for switching from six-stroke operation to four-stroke
operation is set in accordance with the coolant temperature, and
the engine operation is switched from six-stroke operation to
four-stroke operation in accordance with the set threshold engine
load. Therefore, if the requested engine load is large and the
internal combustion engine can not generate an output torque in
corresponding to the requested load with six-stroke operation, or
if knocking is expected to occur because of abnormal combustion, it
is possible to avoid six-stroke operation and perform four-stroke
operation. Also, six-stroke operation is continued until either the
first or second above-noted condition is satisfied. For this
reason, if the intake temperature is low at the cold start of the
internal combustion engine, it is possible to reliably raise the
temperature of the intake gas and improve the combustion
condition.
[0090] The second embodiment is described for the case in which the
switching load is set to the smaller of the first condition that
considers the requested engine load and the second condition that
considers the occurrence of knocking. In the present invention,
however, the threshold engine load need not take into consider both
of these, and may be set with consideration given to either one of
the first condition and the second condition.
[0091] In the second embodiment, by executing step S202 the
"requested load calculation means" may be implemented, and by
executing step S206, the "multi-stork operation termination
determining means" may be implemented.
[0092] The third embodiment of the present invention is described
below, with reference made to FIG. 7. The description as follows
will focus on the only the characteristic parts of the third
embodiment, and the descriptions of parts that are the same as the
first embodiment will be either simplified or omitted. The system
in the third embodiment has the same type of configuration as the
system of the first embodiment. In the system of the third
embodiment, with the exception of predicting the temperature in the
combustion chamber 24 and switching from four-stroke operation to
six-stroke operation based on the predicted temperature, control is
performed in the same manner as in the first embodiment.
[0093] Specifically, in the system of the third embodiment as well,
six-stroke operation is performed at the cold start. It is possible
to predict the temperature rise .DELTA.T after the intake stroke in
six-stroke operation, based on the air intake amount detected
during the six-stroke operation. Therefore, the predicted
temperature Tp in the combustion chamber 24 after the second intake
stroke in six-stroke operation can be expressed by the current
temperature T24 in the combustion chamber and the temperature rise
.DELTA.T in the form of Equation (1).
Predicted combustion chamber temperature Tp=Combustion chamber
temperature T24+.DELTA.T (1)
[0094] Before starting six-stroke operation, even if the
temperature in the combustion chamber 24 is lower than the
threshold engine load, there are cases in which an excessive rise
occurs in the intake temperature when six-stroke operation is
actually performed. If ignition is done under the condition,
because it may cause abnormal combustion or knocking to occur, it
is preferable to avoid this condition. Therefore, in the third
embodiment, as noted above, the temperature Tp in the combustion
chamber 24 after the second intake stroke in six-stroke operation
is predicted and, if the predicted temperature Tp is at least the
threshold engine load T0, a switch is made to four-stroke
operation.
[0095] FIG. 7 is a flowchart describing a control routine executed
by the ECU 80 in the third embodiment. The flowchart shown in FIG.
7, with the exception of having steps S302 to S310 after the step
S110 of the flowchart shown in FIG. 4, is the same as the routine
shown in FIG. 4. Specifically, in the first combustion when the
cold start is determined at step S102, if at step S108 it is
determined that the current temperature T24 in the combustion
chamber 24 is lower than the threshold cylinder temperature T0,
six-stroke operation is performed (step S110), after which
information regarding the operating condition, such as the
temperature T24 in the combustion chamber 24 or the intake air
amounts and the like in the first and second intake strokes is
again detected (step S302).
[0096] Next, the requested intake air amount is calculated (step
S304). After that, based on the intake air amounts in the first and
second intake strokes detected at step S302, the temperature rise
.DELTA.T is calculated (step S306). The temperature rise .DELTA.T
can be determined from a map establishing the relationship between
the intake air amount and the temperature rise. Next, the predicted
temperature Tp after the second intake stroke in the combustion
chamber 24 is calculated (step S308). The combustion chamber
predicted temperature Tp is calculated in accordance with the
above-noted Equation (1).
[0097] Next, it is determined whether the combustion chamber
predicted temperature Tp is greater than or equal to the threshold
predicted cylinder temperature T0 (step S310). If it is determined
that the combustion chamber predicted temperature Tp is greater
than or equal to the threshold cylinder temperature T0, six-stroke
operation is again performed at step S110, and the processing of
steps S302 to S310 is performed. That is, as long as it is not
determined that the condition combustion chamber predicted
temperature Tp is greater than or equal to the threshold predicted
cylinder temperature T0 at step S310, six-stroke operation is
performed at step S110. If, however, it is determined that the
combustion chamber predicted temperature Tp is greater than or
equal to the threshold predicted cylinder temperature T0 at step
S310, four-stroke operation is set and processing is ended.
[0098] As described above, according to the third embodiment, when
the internal combustion engine 10 is being started from the cold
condition, i.e. cold start, when six-stroke operation is performed,
the combustion chamber temperature after performing six-stroke
operation is predicted, and it is determined whether to switch to
four-stroke operation based on the predicted temperature. It is
therefore possible to suppress an excessive rise in the temperature
in the combustion chamber 24, and possible to effectively prevent
knocking due to abnormal combustion.
[0099] The third embodiment is described for the case in which the
temperature in the combustion chamber 24 is detected by the
temperature sensor 26, and the predicted temperature is calculated
from the detected temperature and the temperature rise predicted
from the intake air amount. However, the method for calculating the
predicted temperature Tp in the combustion chamber 24 is not
limited to this method, and may be a calculation by another method.
For example, the initial value of the temperature in the combustion
chamber 24 may be predicted from the coolant temperature at the
time of starting, after which the temperature rise .DELTA.T is
calculated from the intake air amounts for the intake strokes
(first intake stroke and second intake stroke) for each combustion
cycle, and the temperature rise .DELTA.T may be successively added
to the initial value of the temperature in the combustion chamber
24 to predict the temperature in the combustion chamber 24. Also,
for example, a combustion pressure sensor that detects the
combustion pressure is provided and the temperature in the
combustion chamber may be predicted from the combustion pressure
and the intake air amount. Additionally, the temperature in the
combustion chamber 24 is directly detected and the temperature at
the next time may be predicted from the amount of variation.
Alternatively, a temperature sensor is provided in the vicinity of
the intake valve to directly detect the intake temperature and the
temperature in the combustion chamber 24 is predicted based on the
intake temperature.
[0100] The third embodiment was described for the case in which a
switch is made to four-stroke operation if the predicted
temperature in the combustion chamber 24 reaches or exceeds the
threshold predicted cylinder temperature. The present invention,
however, is not limited in this manner, and if the predicted
temperature in the combustion chamber 24 is at least the threshold
predicted cylinder temperature, the lift amount may be increased by
a prescribed amount from the low lift amount, the low lift amount
being gradually changed until it reaches the normal lift amount
during which time six-stroke operation is continued. By doing this,
it is possible to suppress the torque variation to a small amount
when the switch is made to four-stroke operation. When such control
is performed, the threshold predicted cylinder temperature may be
set to lower than the normal. Additionally, amount of gradual
change of the lift amount during six-stroke operation is not
limited to being a fixed amount of change.
[0101] In the third embodiment, by executing steps S306 and S308,
the "cylinder internal temperature predicting means" may be
implemented, and by executing step S310 the "multi-stroke operation
termination determining means" may be implemented.
[0102] The fourth embodiment of the present invention is described
below, with reference made to FIG. 8 and FIG. 9. The description of
the fourth embodiment will focus on the only the characteristic
parts of the fourth embodiment, and the descriptions of parts that
are the same as the first to third embodiments will be either
simplified or omitted. The system in the fourth embodiment has the
same type of configuration as the system of the first embodiment,
with the exception that it is used as a flexible fuel vehicle
(FFV). Specifically, the system of the fourth embodiment can use
alcohols such as ethanol, methanol, bio-ethanol, or bio-methanol,
or a mixture of these alcohols and gasoline as a fuel. Use as a
fuel is possible regardless of the proportion of alcohol fuel in
the fuel that is used.
[0103] The system in the fourth embodiment performs six-stroke
operation at the cold start. The control executed by the system of
the fourth embodiment, with the exception of the threshold cylinder
temperature, the threshold coolant temperature, the threshold
engine load or the threshold predicted cylinder temperature being
set in accordance with the alcohol concentration in the fuel when
determining whether to switch from six-stroke operation to
four-stroke operation, is the same as in the first embodiment. FIG.
8 is a graph describing the relationship between the alcohol
concentration in the fuel and the threshold coolant temperature for
switching to four-stroke operation in a fourth embodiment of the
present invention.
[0104] The proportion of alcohol fuel in the fuel used the system
of the fourth embodiment as described above is not fixed. However,
the concentration of alcohol included in the fuel used is a factor
affecting the atomization of fuel when taken into the cylinder 12.
Specifically, atomization of the fuel occurs easily even at a
relatively low temperature in the case in which the alcohol
concentration is low and the gasoline concentration is high,
whereas, as the alcohol concentration in the fuel increases, it
becomes difficult for the fuel to atomize. For this reason, the
temperature at which a given amount of fuel can be atomized is
higher, the higher is the alcohol concentration.
[0105] Therefore, particularly when the temperature in various
parts of the internal combustion engine 10 is low at the cold
start, the higher the alcohol concentration is, in order to achieve
stable combustion, the more it is necessary raise the temperature
of the intake gas to make it easier to atomize the fuel. For this
reason, when six-stroke operation is performed for raising the
intake temperature, the intake temperature is made higher, the
higher is the concentration of the alcohol fuel. That is, as shown
in FIG. 8, control in which the threshold coolant temperature for
switching from six-stroke operation to four-stroke operation is
made higher, the higher is the alcohol fuel concentration, to raise
the intake temperature in six-stroke operation, is continued until
the inside of the combustion chamber 24 reaches a higher
temperature.
[0106] The ECU 80 has stored map establishing the relationship, as
shown in FIG. 8, between alcohol concentration in the fuel and the
threshold coolant temperature. When making a cold start of the
internal combustion engine 10, the alcohol concentration of the
fuel is detected and the threshold coolant temperature is
calculated in accordance with the map, in accordance with the
detected alcohol concentration. If the temperature of the coolant
in the internal combustion engine 10 reaches or exceeds the
threshold coolant temperature, a switch is made from six-stroke
operation to four-stroke operation.
[0107] FIG. 9 is a flowchart describing a control routine executed
by the ECU 80 in the fourth embodiment. The routine of FIG. 9, with
the exception of execution of steps S402 to S406 in place of step
S108 after step S106 of FIG. 4, is the same as the routine of FIG.
4. Specifically, if it is determined at step S102 that the internal
combustion engine is being started from the cold condition,
information regarding the operating condition is detected, the
requested intake air amount is calculated (steps S104 and S106),
and the alcohol concentration of the currently used fuel is read
out (step S402). The alcohol concentration of the fuel is stored in
the ECU 80. At this point, instead of reading out the alcohol
concentration from the ECU, a concentration meter that detects the
concentration of the alcohol fuel may be installed to detect the
alcohol concentration.
[0108] Next, the threshold coolant temperature is calculated (step
S404). The threshold coolant temperature is calculated as a value
corresponding to the alcohol concentration read out in step S402,
in accordance with the map stored beforehand in the ECU 80. Next,
it is determined whether the coolant temperature detected at step
S104 is greater than or equal to the threshold coolant temperature
(step S406) and, if it is not determined that the coolant
temperature is greater than or equal to the threshold coolant
temperature, six-stroke operation is performed (step S110).
Six-stroke operation is repeated in the steps S104, S106, S402 to
S406 and S110 until it is determined at step S406 that the coolant
temperature is greater than or equal to the threshold coolant
temperature. If it is determined that the coolant temperature is
greater than or equal to the threshold coolant temperature at step
S406, a switch is made to four-stroke operation (step S112).
[0109] As described above, in the fourth embodiment the threshold
coolant temperature is calculated in accordance with the alcohol
concentration in the fuel. For this reason, it is possible to
continue six-stroke operation until the coolant temperature reaches
a temperature, at which the combustion stabilizes, set in
accordance with the alcohol concentration, and possible to reliably
perform warm-up to the required temperature. It is also possible to
accommodate combustibility in accordance with the concentration of
the alcohol fuel. When it is difficulty to achieve stable
combustion due to the high alcohol concentration, it is possible to
raise the temperature more quickly to achieve stable combustion by
continuing six-stroke operation to a higher temperature. In
particular when a fuel is used that includes an alcohol fuel,
although there are cases in which the cold start is difficult, it
is possible to raise the temperature in the combustion chamber 24
more quickly by performing six-stroke operation as in the
above-described fourth embodiment. Therefore, because the
temperature in the combustion chamber becomes a temperature at
which the fuel can be atomized more quickly, it is possible to
improve the starting characteristics of the internal combustion
engine. In an engine using a fuel with a low volatility, such as in
an FFV, the fourth embodiment can effectively improve starting
characteristics.
[0110] The fourth embodiment is described for the case of using an
alcohol fuel or a fuel mixture of an alcohol fuel and gasoline. The
present invention, however, is not limited in this manner, and may
also use a fuel including a so-called bio-alcohol or a light oil in
place of gasoline. In this case as well, in general if the alcohol
concentration is high, the threshold coolant temperature will be
set to high. In this manner, by experimentally setting the
relationship between the threshold coolant temperature and the
alcohol concentration for each fuel beforehand, the forth
embodiment can be applied to other alcohol fuels as well.
[0111] The fourth embodiment is described for the case in which the
threshold coolant temperature is set in accordance with the alcohol
concentration. The fourth embodiment, however, is not limited in
this manner. For example, the threshold coolant temperature T0 with
respect to the combustion chamber temperature T24 in the first
embodiment, the threshold engine load in the second embodiment, and
the threshold predicted coolant temperature T0 with respect to the
combustion chamber predicted temperature Tp in the third embodiment
may each be set in accordance with the alcohol concentration. Each
of these thresholds can be made based on experimental maps in
accordance with the alcohol concentration.
[0112] Also, for example, in the fourth embodiment by executing
step S302 and step S304, the "determination value setting means"
may be implemented.
[0113] The fifth embodiment of the present invention is described
below, with reference made to FIG. 10. The description of the fifth
embodiment will focus on the only the characteristic parts of the
fifth embodiment, and the descriptions of parts that are the same
as the first through the fourth embodiments will be either
simplified or omitted. The system of the fifth embodiment, with the
exception that the engine is a so-called V-type engine having a
plurality of cylinders, is the same as the system of FIG. 1.
[0114] Specifically, the internal combustion engine 10 of the fifth
embodiment has two groups (hereinafter "banks") of cylinders. In
this system, if the requested load is large, the internal
combustion engine 10 is operated with all of the cylinders 12
operating (all-cylinder operation). In contrast, if the requested
load is small, only one bank of cylinders is operated, with
cylinders belonging to the other bank being stopped
(reduced-cylinder operation).
[0115] In the case of reduced-cylinder operation, in which only one
bank is operating, the cylinders belonging to the other bank are
stopped. In this condition, if the requested load becomes large,
transition is made from the reduced-cylinder operation to
all-cylinder operation. That is, the bank that is stopped
(auxiliary bank) is started. Then, even if the cylinders 12 on the
operating bank side, which are operating during reduced-cylinder
operation, are warm up, if the reduced-cylinder operation continued
for a long period of time and when starting cold in the
reduced-cylinder operation, the cylinders 12 of the auxiliary bank
that are stopped during reduced-cylinder operation might not be
sufficiently warmed up. In such cases, immediately after switching
from reduced-cylinder operation to all-cylinder operation, it can
be envisioned that a raise in the temperature of the intake air in
the auxiliary bank is not sufficient, and combustion in the
cylinders of the auxiliary bank degrades.
[0116] In the above-noted situation, it cylinders 12 of the
auxiliary bank are not warmed up and are still cold, the system of
the fifth embodiment makes one combustion cycle of temperature
six-stroke operation when the auxiliary bank is returned to
operation. That is, with regard to the auxiliary bank, the low lift
amount at which the pumping loss is maximum is set, and the first
intake stroke and the first compression stroke are performed, after
which the lift amount is set to the normal lift amount and then the
second intake stroke, the second compression stroke, the expansion
stroke, and the exhaust stroke are performed. After that, if the
temperature T24 in the combustion chambers 24 of the auxiliary bank
reaches or exceeds the threshold cylinder temperature T0, the
six-stroke operation is ended and the four-stroke operation is
performed.
[0117] During this period, the current operating condition on the
operating bank that is operating during the reduced-cylinder
operation is maintained. That is, in the case of performing
four-stroke operation, four-stroke operation is performed, and in
the case of performing six-stroke operation, six-stroke operation
is performed, for example, in accordance with the routine shown in
FIG. 4. If it is determined that the six-stroke operation is to be
terminated, a switch is made to four-stroke operation. When the
operation of the auxiliary bank is restored by four-stroke
operation, the internal combustion engine 10 starts to operate with
all of the cylinders 12 operating. When the stopped bank is
returned to four-stroke operation, the ignition timing is switched
to ignition timing that is set for all-cylinder operation
beforehand, and then, the timing of the intake valves 40 and the
exhaust valves 60 of each cylinder 12 is switched to the valve
timing set beforehand.
[0118] FIG. 10 is a flowchart describing a control routine executed
by the system of the fifth embodiment. The routine of FIG. 10, is
repeatedly executed during operation of the internal combustion
engine 10. Specifically, it is determined at step S502 whether or
not reduced-cylinder operation is in progress. If it is not
determined that reduced-cylinder operation is in progress, the
current operation is continued and processing ends.
[0119] If, however, it is determined at step S502 that
reduced-cylinder operation is in progress, next information
regarding the operating condition is detected (step S504). Required
information, for example the engine rotational speed and intake air
amount, and the coolant temperature and the like is detected based
on outputs from various sensors. Next, the current requested load
is calculated (step S506). The requested load is calculated based
on the accelerator operating amount. Next, it is determined whether
there is a request to transition from reduced-cylinder operation to
all-cylinder operation (step S508). Whether or not there is a
request to transition from reduced-cylinder operation to
all-cylinder operation is determined, for example, based on whether
the load calculated at step S506 is higher than a prescribed load.
If a request for transition to all-cylinder operation is determined
at step S508, the current operation is continued and processing is
ended.
[0120] If it is not determined that there is a request for
transition to all-cylinder operation at step S508, however, it is
determined whether the cold start of the auxiliary bank is carried
out (step S510). Specifically, the determination is made based on
whether the temperature of the coolant in the auxiliary bank
detected at step S504 is lower than a prescribed coolant
temperature.
[0121] If it is determined at step S510 that the auxiliary bank is
being restored from a cold start, the temperature T24 in the
combustion chamber 24 of the cylinders 12 in the auxiliary bank is
detected (step S512). Then, it is determined whether the
temperature T24 is greater than or equal to the threshold cylinder
temperature T0 for switching from the six-stroke operation to the
four-stroke operation (step S514). If it is not determined that the
temperature T24 is greater than or equal to the threshold cylinder
temperature T0 at step S514, at step S516 the auxiliary bank is set
to six-stroke operation. That is, the first intake stroke is
performed with the intake valve 40 set to the low lift amount, and
the first compression stroke are performed. After the first intake
stroke and compression stroke, the second intake stroke is
performed with the intake valve 40 set to the normal lift amount
and second compression stroke are performed, after which the
expansion stroke and exhaust stroke are performed. After that,
processing returns to step S512. The six-stroke operation of steps
S512, S514, and S516 is repeated until it is determined step S514
that the temperature T24 in the combustion chamber 24 reaches or
exceeds the threshold cylinder temperature T0.
[0122] It is not determined at step S510 that the auxiliary bank of
cylinders 12 is being restored from the cold condition, and it is
determined at step S514 that the temperature T24 is greater than or
equal to the threshold cylinder temperature T0, at step S518 normal
four-stroke operation is executed, and all-cylinder operation is
performed immediately. After that, the processing is ended.
[0123] As described above, according to the fifth embodiment, even
when restoring the operation of the auxiliary bank that had been
stopped, by performing six-stroke operation to raise the
temperature, it is possible to more quickly raise the temperature
in the combustion chambers 24 on the auxiliary bank, enabling
stabilization of combustion.
[0124] In the system of the fifth embodiment, it is possible to
start with reduced-cylinder operation even when the cold start of
the internal combustion engine 10 is carried out. In the case of
performing a cold start with reduced-cylinder operation, the
routine of FIG. 4 is performed in the same manner as in the first
embodiment, and the auxiliary bank only is operated in six-stroke
operation until the temperature T24 in the combustion chambers 24
on the auxiliary bank rises to the threshold cylinder temperature
T0. In this manner, even when cold start of the internal combustion
engine 10 is carried out, it is possible by performing six-stroke
operation to raise the temperature in the combustion chambers 24 on
the auxiliary bank to more quickly stabilize combustion. Because it
is possible in this manner to perform reduced-cylinder operation
even in the cold condition, it is possible to improve fuel
economy.
[0125] In the fifth embodiment, for example, by executing step S510
the "cold starting determining means" may be implemented, and by
executing step S516 the "multi-stroke operation means" may be
implemented.
[0126] In the case in which references are made to numbers of
elements, quantities, and ranges in the like in the foregoing
embodiments, unless the numbers are explicitly stated or clear in
principle as specific numbers, there is no restriction to the
stated numbers. Additionally, the structures and methods of steps
described in the embodiments, unless explicitly stated or clear in
principle as specified structures and methods, are not necessarily
essential to the present invention.
* * * * *