U.S. patent application number 10/310852 was filed with the patent office on 2003-06-12 for apparatus for controlling engine.
Invention is credited to Kondo, Wakichi.
Application Number | 20030106515 10/310852 |
Document ID | / |
Family ID | 27482721 |
Filed Date | 2003-06-12 |
United States Patent
Application |
20030106515 |
Kind Code |
A1 |
Kondo, Wakichi |
June 12, 2003 |
Apparatus for controlling engine
Abstract
An engine has variable-valve mechanisms. An engine control
system has an engine control unit for executing automatic stop and
start control. At an automatic-stop, the variable-valve mechanisms
are controlled to obtain a valve operation characteristic suitable
for a restart of the engine. When a catalyst is in an inactivated
state, the variable-valve mechanisms are controlled to reduce the
amount of residual gas leaking out from cylinders. At an
automatic-start, the control of the variable-valve mechanism is
prohibited and an intake air is adjusted by using a throttle valve.
At an automatic-stop, the engine speed is abruptly reduced so that
the engine speed passes through a resonant revolution speed area in
a short period of time. When the voltage of a battery is low, the
control of the variable-valve mechanism may be prohibited.
Inventors: |
Kondo, Wakichi;
(Kariya-City, JP) |
Correspondence
Address: |
Larry S. Nixon, Esq.
NIXON & VANDERHYE P.C.
8th Floor
1100 North Glebe Rd.
Arlington
VA
22201-4714
US
|
Family ID: |
27482721 |
Appl. No.: |
10/310852 |
Filed: |
December 6, 2002 |
Current U.S.
Class: |
123/179.4 ;
123/198DB |
Current CPC
Class: |
F02D 2041/0092 20130101;
F02N 2200/102 20130101; F01L 13/0021 20130101; F02D 13/0211
20130101; F02N 11/0818 20130101; F02D 2200/0404 20130101; Y02T
10/48 20130101; F02D 41/187 20130101; F02D 2200/602 20130101; F02D
41/042 20130101; F01L 1/185 20130101; Y02T 10/18 20130101; F01L
1/053 20130101; F01L 2800/00 20130101; F02N 2200/0801 20130101;
F02D 2041/001 20130101; F02N 2200/103 20130101; F02D 41/1456
20130101; F02D 2200/503 20130101; F02D 41/062 20130101; F02D
2041/0095 20130101; Y02T 10/40 20130101; F01L 2013/0068 20130101;
Y02T 10/12 20130101; F02D 2200/0406 20130101 |
Class at
Publication: |
123/179.4 ;
123/198.0DB |
International
Class: |
F02N 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2001 |
JP |
2001-372259 |
Dec 14, 2001 |
JP |
2001-381015 |
Dec 18, 2001 |
JP |
2001-383898 |
Jan 22, 2002 |
JP |
2002-12924 |
Claims
What is claimed is:
1. A control apparatus for an internal combustion engine,
comprising: variable-valve control means for controlling at least
an intake airflow by adjusting valve operation characteristics of
the intake valve, exhaust valve or both the intake and exhaust
valves of the engine; an automatic-stop control means, which is
used for automatically stopping the engine when a predetermined
automatic stop condition is satisfied in the course of an operation
of the engine; and an automatic-stop valve control means, which is
used for computing target valve operation characteristics for an
automatic-stop time on the basis of present states of the engine
and/or a vehicle employing the engine and for controlling the valve
operation characteristics to the target valve operation
characteristics for an automatic-stop time right after the
automatic-stop control means automatically stops the engine.
2. A control apparatus for an internal combustion engine according
to claim 1, further comprising: an automatic-start control means,
which is used for automatically starting the engine when a
predetermined automatic-start condition is satisfied in an
automatic-stop state of the engine; and an automatic-start valve
control means, which is used for computing target valve operation
characteristics for an automatic-start time on the basis of present
states of the engine and/or the vehicle and for controlling the
valve operation characteristics to the target valve operation
characteristics for an automatic-start time when the
automatic-start control means automatically starts the engine.
3. A control apparatus for an internal combustion engine according
to claim 1, wherein the automatic-stop valve control means computes
valve operation characteristics presumed to be proper for the next
automatic start as the target valve operation characteristics for
an automatic-stop time.
4. A control apparatus for an internal combustion engine according
to claim 1, wherein the automatic-stop valve control means computes
valve operation characteristics, which sets valve lift quantities
at 0 or minimum values, as the target valve operation
characteristics for an automatic-stop time.
5. A control apparatus for an internal combustion engine according
to claim 1, wherein the automatic-stop valve control means computes
the target valve operation characteristics for an automatic-stop
time on the basis of at least one of an automatic-stop count, a
cooling-water temperature, an intake-air temperature, an oil
temperature and information having correlations with any one of the
automatic-stop count, the cooling-water temperature, the intake-air
temperature, and the oil temperature.
6. A control apparatus for an internal combustion engine,
comprising: a variable-valve control means for controlling at least
an intake airflow by adjusting valve operation characteristics of
the intake valve, exhaust valve or both the intake and exhaust
valves of the engine; an automatic-start control means, which is
used for automatically starting the engine when a predetermined
automatic-start condition is satisfied in an automatic-stop state
of the engine; and an automatic-start valve control means, which is
used for computing target valve operation characteristics for an
automatic-start time on the basis of present states of the engine
and/or a vehicle employing the engine and for controlling the valve
operation characteristics to the target valve operation
characteristics for an automatic-start time when the
automatic-start control means automatically starts the engine.
7. A control apparatus for an internal combustion engine according
to claim 6, wherein the automatic-start valve control means
computes the target valve operation characteristics for an
automatic-start time on the basis of at least one of an
automatic-stop count, an automatic-stop time, a cooling-water
temperature, an intake-air temperature, an oil temperature and
information having correlations with the automatic-stop count, the
automatic-stop time, the cooling-water temperature and the oil
temperature.
8. A control apparatus for an internal combustion engine according
to claim 6, wherein, in the event of an engine stall caused by a
failure of an automatic start of the engine, the automatic-start
valve control means controls the valve operation characteristics to
increase the intake airflow and the automatic-start control means
restarts the engine.
9. A control apparatus for an internal combustion engine,
comprising: a variable-valve control means for controlling at least
an intake airflow by adjusting valve operation characteristics of
the intake valve, exhaust valve or both the intake and exhaust
valves of the engine; an automatic-start control means, which is
used for automatically starting the engine when a predetermined
automatic-start condition is satisfied in an automatic-stop state
of the engine; a variable-valve control prohibition means for
fixing the valve operation characteristics at predetermined
conditions during a variable-valve control prohibition period,
which is a predetermined period after the automatic start of the
engine carried out by the automatic-start control means; and a
throttle-valve control means for controlling the intake airflow
during the variable-valve control prohibition period by adjusting
the opening of a throttle valve provided on an intake path of the
engine.
10. A control apparatus for an internal combustion engine according
to claim 9, wherein, during the variable-valve control prohibition
period, the variable-valve control prohibition means fixes the
valve operation characteristics each at a target valve operation
characteristic for an automatic start of the engine.
11. A control apparatus for an internal combustion engine according
to claim 9, wherein the variable-valve control prohibition means
sets the variable-valve control prohibition period at a value
dependent on the automatic-stop count or automatic-start count of
the engine.
12. A control apparatus for an internal combustion engine,
comprising: a variable-valve mechanism for varying valve operation
characteristics of the intake valve, exhaust valve or both the
intake and exhaust valves of the engine in control of an intake
airflow by; and an automatic-stop control means, which is used for
adjusting the intake airflow by controlling the variable-valve
mechanism and/or controlling a throttle valve so as to gradually
reduce a torque output by the engine and stop the engine when a
predetermined automatic-condition is satisfied during an operation
of the engine, wherein, in a process to gradually reduce a torque
output by the engine and stop the engine, the automatic-stop
control means executes torque abrupt reduction control to abruptly
reduce the intake airflow by controlling the variable-valve
mechanism so as to abruptly reduce the torque output by the engine
with a timing with which an engine speed is about to pass through a
predetermined revolution speed range.
13. A control apparatus for an internal combustion engine according
to claim 12, wherein the predetermined revolution speed range is
set to include a resonant revolution speed zone in which vibration
of the engine is resonant with vibration of a vehicle-driving
system.
14. A control apparatus for an internal combustion engine according
to claim 12, wherein the automatic-stop control means controls the
variable-valve mechanism so as to put the intake valve in a
completely closed state during the torque abrupt reduction
control.
15. A control apparatus for an internal combustion engine according
to claim 12, wherein the automatic-stop control means controls the
variable-valve mechanism and completely closes the throttle valve
so as to minimize the intake airflow during the torque abrupt
reduction control.
16. A control apparatus for an internal combustion engine according
to claim 12, wherein the automatic-stop control means terminates
injection of fuel during the torque abrupt reduction control.
17. A control apparatus for an internal combustion engine according
to claim 12, wherein, in a process to gradually reduce a torque
output by the engine and stop the engine, the automatic-stop
control means controls a fuel injection volume so as to sustain an
air-fuel ratio at a target air-fuel ratio till the engine speed is
reduced to the predetermined revolution speed range.
18. A control apparatus for an internal combustion engine,
comprising: a variable-valve control means for by varying valve
operation characteristics of the intake valve and/or exhaust valve
of the engine in accordance with a voltage output by a battery
mounted on a vehicle employing the engine and controlling at least
an intake airflow into a combustion chamber of the engine; an
automatic-start control means, which is used for automatically
starting the engine when a predetermined automatic-restart
condition is satisfied in an automatic-stop state of the engine; a
battery-voltage detection means for detecting a voltage output by
the battery; and a variable-valve control prohibition means, which
is used for prohibiting variable control executed by the
variable-valve control means on the intake valve and/or the exhaust
valve in dependence on the voltage of the battery detected by the
battery-voltage detection means after the engine is automatically
started by the automatic-start control means.
19. A control apparatus for an internal combustion engine according
to claim 18, wherein the variable-valve control prohibition means
prohibits the variable control executed by the variable-valve
control means on the intake valve and/or the exhaust valve till the
voltage of the battery detected by the battery-voltage detection
means reaches a predetermined level.
20. A control apparatus for an internal combustion engine according
to claim 18, wherein the variable-valve control means is a means
for setting valve lift quantities of the intake valve and/or the
exhaust valve by utilizing a voltage output by the battery.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on Japanese Patent Applications
No. 2001-372259 filed on Dec. 6, 2001, No. 2001-381015 filed on
Dec. 14, 2001, No. 2001-383898 filed on Dec. 18, 2001 and No.
2002-12924 filed on Jan. 22, 2002 the contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an apparatus for
controlling an internal combustion engine, which is also referred
to hereafter simply as an engine. More particularly, the present
invention relates to an apparatus for controlling an engine having
a variable-valve mechanism.
[0004] 2. Related Art
[0005] In the conventional engine, a throttle valve is provided on
an intake pipe of the engine. The throttle valve adjusts the
opening thereof in order to control an intake airflow. The driver
depresses an accelerator pedal connected to the throttle valve by
an electrical link mechanism so that the valve operates in
accordance with a pedal-depression quantity. In addition, the
throttle valve can also be controlled by an electrical control unit
and a motor. The control of intake airflow executed by using the
throttle valve is referred to as the throttle-valve control. Since
a volume exists between the throttle valve and a cylinder, a
response to a control command in the control of the intake airflow
lags behind the command. In addition, a negative pressure is built
up the downstream of the throttle valve. For this reason, a
relatively large pumping loss is incurred.
[0006] The engine also has an intake valve and an exhaust valve.
The intake valve and the exhaust valve are driven by a
valve-driving mechanism such as a cam or by an electrical actuator.
Operating characteristics of al least one of the intake valve and
the exhaust valve are prescribed in terms of its attributes such as
an opening timing, a closing timing, a valve opening, a valve lift
quantity and a lift-quantity waveform. There is known a
variable-valve mechanism for varying the operation characteristics
of the valves. For example, there is a variable-valve mechanism for
adjusting the opening and the closing timings in an advance or
retard direction. Another example is a variable-valve mechanism for
adjusting the opening of the valve to a value between a zero and a
maximum. Another typical variable-valve mechanism adjusts the
operation characteristics with a high degree of freedom. In an
engine having such a variable-valve mechanism, the intake airflow
can be adjusted by using the variable-valve mechanism. The control
of intake airflow executed by the variable-valve mechanism is
referred to as variable-valve control. Typically, the operation
characteristics of the valve are adjusted in accordance with an
acceleration operation quantity and the operating state of the
engine. The variable-valve control generates a small response lag
in comparison with the throttle-valve control. In addition, in the
case of the variable-valve control, the magnitude of an incurred
pumping loss can be reduced. For example, by execution of
variable-valve control, the throttle valve can be opened
relatively. In a typical engine, the execution of variable-valve
control makes it unnecessary to install a throttle valve.
[0007] JP-A-8-193531 discloses an apparatus for automatically
stopping the engine temporarily. Such an apparatus is referred to
as an automatic stop and start apparatus or an idling stop control
apparatus. Control executed by the apparatus is known as automatic
stop and start control. When the vehicle is halted, for example,
the engine is automatically stopped without the need for an
operation to be carried out by the driver. Such control is referred
to as automatic stop control. When the driver makes an attempt to
drive the vehicle after the automatic stop control, the engine is
automatically started. In response to an operation carried out by
the driver to depress the accelerator pedal, for example, a start
motor is automatically activated to start the engine automatically.
The start motor can also be automatically activated to start the
engine when the driver carries out an operation to release the
brake pedal. Such control is referred to as automatic start control
or automatic restart control. The automatic stop and start control
is a means capable for effectively reducing the fuel consumption,
exhaust emissions and noises.
[0008] By execution of the automatic stop and start control, on the
other hand, a transient state such as the start or stop of the
engine occurs very frequently. For this reason, there is demanded
proper control of the engine also in the transient state such as
the start or stop of the engine.
[0009] Assume for example that, in automatic stop control, a valve
operation characteristic prior to the automatic stop control is
saved. In this case, in the next automatic start control based on
the saved valve operation characteristic, it is feared that a
smooth start of the engine is obstructed.
[0010] As another example, assume that the lift quantity of the
exhaust valve is set at a large value in automatic stop control. In
this case, residual gas left in the engine flows out from the
cylinder to the exhaust pipe when the engine is halted temporarily.
In particular, in an inactivated state of a catalyst for cleaning
exhaust gas, the state of the exhaust emissions is worsened.
[0011] For example, the intake change of intake airflow resulting
from the variable-valve control can be detected by an
intake-air-flow sensor or an intake-airflow meter only after a
fixed delay. Right after the engine has been automatically started,
on the other hand, the operating state of the engine changes
abruptly. Thus, there is a case in which, by execution of the
variable-valve control, the intake airflow cannot be adjusted
properly. As a result, a torque shock is generated. In addition, a
change in air-fuel ratio is resulted in.
[0012] In a process wherein the engine speed becomes lower than an
idle speed due to the automatic stop control, for example, the
engine speed temporarily matches the characteristic frequency of
the engine itself or the characteristic frequency of the driving
system of the vehicle. As a result, resonance occurs, temporarily
increasing the amplitude of vibration and the magnitude of
noise.
[0013] In the automatic stop control, for example, a starter is
used frequently. As a result, there appears a tendency to reduction
of the battery voltage. In particular, the voltage of the battery
decreases at an automatic-start time. When the voltage of the
battery decreases, the variable-valve mechanism does not operate in
a stable manner in some cases. When the voltage of the battery
decreases, for example, it is quite within the bounds of
possibility that the operation characteristic of the valve cannot
be controlled to follow a target operation characteristic. As a
result, it is feared that the exhaust emissions deteriorate.
SUMMARY OF THE INVENTION
[0014] It is thus an object of the present invention to provide a
control apparatus, which is capable of properly controlling an
engine having a variable-valve mechanism when the engine is
automatically stopped.
[0015] It is another object of the present invention to provide a
control apparatus, which is capable of properly controlling an
engine having a variable-valve mechanism when the engine is
automatically started.
[0016] It is a further object of the present invention to provide a
control apparatus, which is capable of smoothly starting an engine
having a variable-valve mechanism when the engine is automatically
started.
[0017] It is a still further object of the present invention to
provide a control apparatus, which is capable of reducing emissions
exhausted from an engine having a variable-valve mechanism right
after the engine is stopped.
[0018] It is a still further object of the present invention to
provide a control apparatus, which is capable of controlling the
intake airflow of an engine having a variable-valve mechanism in a
stable manner right after the engine is automatically stopped.
[0019] It is a still further object of the present invention to
provide a control apparatus, which is capable of suppressing
uncomfortable vibration caused by a low speed of an engine having a
variable-valve mechanism right after the engine is stopped.
[0020] It is a still further object of the present invention to
provide a control apparatus, which is capable of controlling the
intake airflow of an engine having a variable-valve mechanism in a
stable manner in automatic start control.
[0021] In accordance with a first aspect of the present invention,
right after an automatic stop control means automatically stops the
engine, an automatic stop valve control means computes a target
valve operation characteristic on the basis of the present state of
the engine and/or the present state of the vehicle, and controls a
valve operation characteristic to the target valve operation
characteristic for an automatic-stop time.
[0022] An automatic-stop time is defined as a time between an
automatic stop of the engine and an automatic start of the engine.
In general, the automatic-stop time such as a time of waiting for a
traffic light to turn to a green color is relatively short in many
cases. Thus, while the engine is in an automatically stopped state,
the state of the engine and/or the state of the vehicle such as the
temperature of the cooling water do not change much in many cases.
Accordingly, it is possible to find a valve operation
characteristic in which the state of the engine and/or the state of
the vehicle at an automatic start of the engine after an automatic
stop of the engine are the same as the state of the engine and/or
the state of the vehicle right after the automatic stop so that the
state of the engine and/or the state of the vehicle right after the
automatic stop can be applied to the automatic start after the
automatic stop.
[0023] Thus, right after the engine is automatically stopped, it is
possible to find a valve operation characteristic, which is
presumed to be proper for an automatic start after the automatic
stop from the present state of the engine and/or the present state
of the vehicle right after the automatic stop, as a target valve
operation characteristic, and control the valve operation
characteristic to the target valve operation characteristic while
the engine is in an automatically stopped state. At the next
automatic-start time, the engine can be automatically started under
a valve operation characteristic approximately proper for an
automatic start so that an automatic-start characteristic of the
engine can be improved and exhaust emissions at the automatic-start
time can be reduced.
[0024] By the way, if an exhaust valve of any cylinder is largely
opened in an automatically stopped state of the engine, resulting
in a state in which residual gas remaining in the cylinder leaks
out to an exhaust pipe with ease, it is quite within the bounds of
possibility that the residual gas leaking out from the cylinder is
discharged to the atmosphere without being cleaned by a catalyst
provided on the exhaust pipe as a means for cleaning exhaust gas
provided that the catalyst is in a pre-warmed state or an
inactivated state.
[0025] In order to solve the above problem, if the catalyst is
presumed to be in a state of being warmed or activated
insufficiently on the basis of the present state of the engine
and/or the present state of the vehicle, which is detected right
after the engine is stopped automatically, a valve operation
characteristic making residual gas left in a cylinder difficult to
leak out is found and set as a target valve operation
characteristic for an automatic-stop time. An example of such a
condition is a condition in which the lift quantity of the valve is
0 or a minimum. If the catalyst is presumed to be in a state of
being warmed or activated insufficiently, the engine can be stopped
into an automatic stopped state by using a valve operation
characteristic making residual gas left in a cylinder difficult to
leak out as a target valve operation characteristic for the
automatic stop. Thus, exhaust emissions can be reduced during an
automatic stop.
[0026] When an automatic start control means automatically starts
the engine, an automatic start valve control means computes a
target valve operation characteristic on the basis of the present
state of the engine and/or the present state of the vehicle, and
controls a valve operation characteristic to the target valve
operation characteristic for an automatic start time. When the
engine is automatically started, a target valve operation
characteristic optimum for an automatic start is found on the basis
of the present state of the engine and/or the present state of the
vehicle, and used as a target valve operation characteristic when
the engine is automatically started. Thus, at an automatic-start
time of the engine, the engine can be automatically started under a
target valve operation characteristic optimum for an automatic
start. As a result, an automatic-start characteristic of the engine
can be improved and exhaust emissions at the automatic-start time
can be reduced.
[0027] Right after an automatic stop of the engine, a target valve
operation characteristic for an automatic-stop time is found on the
basis of the present state of the engine and/or the present state
of the vehicle, and the valve operation characteristic is
controlled to the target valve operation characteristic for the
automatic-stop time. In addition, a target valve operation
characteristic for an automatic-start time is found on the basis of
the present state of the engine and/or the present state of the
vehicle, and the valve operation characteristic is controlled to
the target valve operation characteristic for the automatic-start
time.
[0028] In this configuration, right after an automatic stop of the
engine, a target valve operation characteristic for an
automatic-stop time is found on the basis of the present state of
the engine and/or the present state of the vehicle, and the valve
operation characteristic is controlled in advance for the time
being to the target valve operation characteristic for the
automatic-stop time. In addition, a target valve operation
characteristic for an automatic-start time is found on the basis of
the present state of the engine and/or the present state of the
vehicle, and the valve operation characteristic is controlled to
the target valve operation characteristic for the automatic-start
time. When the engine is automatically started, the magnitude of
correction of the valve operation characteristic can be reduced so
that the valve operation characteristic can be corrected to a valve
operation characteristic optimum for an automatic start in a short
period of time. In addition, even if the valve operation
characteristic set during the automatic stop is inevitably shifted
from the valve operation characteristic optimum for the current
automatic start due to a large change in engine state and/or a
change in vehicle state during the automatic stop, the valve
operation characteristic can be corrected to a valve operation
characteristic optimum for an automatic start at an automatic-start
time.
[0029] It is to be noted that, if the catalyst is presumed to be in
a state of being warmed or activated insufficiently on the basis of
the state of the engine and/or the state of the vehicle right after
an automatic stop of the engine, right after the automatic stop of
the engine, first of all, the valve operation characteristic is
controlled in advance to a valve operation characteristic making
residual gas left in a cylinder difficult to leak out and, then,
when the engine is automatically started, the valve operation
characteristic can be corrected to a valve operation characteristic
optimum for an automatic start. An automatic-start characteristic
of the engine can be improved and, at the same time, exhaust
emissions at the automatic stop of the engine can be reduced.
[0030] By the way, in general, the lower the temperature of the
engine and/or the lower the temperature of the battery mounted on
the vehicle, the poorer the performance of the battery. The poorer
the performance of the battery, the smaller the driving power of a
starter. The smaller the driving power of a starter, the lower the
flowability of the engine oil. The lower the flowability of the
engine oil, the greater the frictions among movable parts. Thus,
the cranking of the automatic-start time is prone to variations and
the automatic-start characteristic of the engine tends to
deteriorate. In addition, the number of automatic stops or the
number of automatic starts increases and the automatic-stop time is
lengthened so that the consumption of the battery power during an
automatic stop rises. With the increased consumption of the battery
power during an automatic stop, the start power decreases due to
the consumption of power from the battery, and the automatic-start
characteristic of the engine tends to deteriorate.
[0031] A target valve operation characteristic for an
automatic-stop time can be found on the basis of at least one of an
automatic-stop count (or the number of previous automatic stops or
the number of automatic stops carried out so far, a cooling-water
temperature, an intake-air temperature, an oil temperature and
pieces of information having correlations with the automatic-stop
count, the cooling-water temperature, the intake-air temperature
and the oil temperature. By the automatic-stop count, the number of
previous automatic stops or the number of automatic stops carried
out so far is meant. As an alternative, a target valve operation
characteristic for an automatic-start time is found on the basis of
at least one of an automatic-stop count, an automatic-stop time, a
cooling-water temperature, an intake-air temperature, an oil
temperature and pieces of information having correlations with the
automatic-stop count, the automatic-stop time, the cooling-water
temperature, the intake-air temperature and the oil temperature. If
a target valve operation characteristic for an automatic-stop time
and/or a target valve operation characteristic for an
automatic-start time are found using at least one of information
for determining a warming state of the engine (that is,
temperatures of the engine such as a cooling-water temperature, an
intake-air temperature and an oil temperature) and information for
determining the performance of the battery such as the
automatic-stop count and the automatic-stop time, the valve
operation characteristic can be controlled in a direction of
stabilizing the cranking of the engine occurring at an
automatic-start time in order to cope with a state of easy-to-occur
cranking variations caused by a reduced driving power of the
starter and increased frictions among movable components. As a
result, the automatic-start characteristic of the engine can be
further improved. The reduced driving power of the starter is
attributed to the deterioration of performance of battery occurring
at a low temperature of the engine and/or a low temperature of the
battery. An example of the direction of stabilizing the cranking of
the engine is a direction of increasing the intake airflow.
[0032] When an engine stall occurs due to a failure of an automatic
start of the engine, the valve operation characteristic can be
controlled in a direction of increasing the intake airflow prior to
a restart of the engine. In an operation to start the engine, the
engine can be restarted with an intake airflow greater than the
valve operation characteristic for an engine-stall state after the
engine stall due to a failure of an automatic start of the engine.
Thus, the engine stall is prevented from being generated several
times consecutively. As a result, the engine can be restarted
successfully at an early time.
[0033] In accordance with a second aspect of the present invention,
a variable-valve control prohibition means fixes the valve
operation characteristic at a predetermined valve operation
characteristic during a predetermined period after an automatic
start of the engine, and a throttle-valve control means controls
the opening of a throttle valve provided on the intake pipe of the
engine in order to adjust the intake airflow. The predetermined
period is referred to hereafter as a variable-valve control
prohibit period.
[0034] In this configuration, during the variable-valve control
prohibit period, that is, during a period including complicated and
much variable transient times following an automatic start of the
engine, the valve operation characteristic is fixed and the
variable-valve control for adjusting the intake airflow is
prohibited. Instead, throttle-valve control is executed to adjust
the intake airflow. In comparison with the variable-valve control,
the throttle-valve control exhibits a small delay of detection of
an intake airflow at a transient time. Thus, during a period of an
unstable operating state following an automatic start of the
engine, the throttle-valve control is executed to stabilize the
intake airflow so that it is possible to prevent the drivability
following an automatic start of the engine and exhaust emissions
following the automatic start of the engine from deteriorating.
[0035] In this case, if a difference between a target valve
operation characteristic set initially at an automatic start of the
engine and a valve operation characteristic fixed during the
variable-valve control prohibit period following the completion of
the automatic start of the engine is large, the valve operation
characteristic prior to the completion of the automatic start of
the engine greatly changes in an abrupt manner to a valve operation
characteristic after the completion of the automatic start of the
engine so that it is quite within the bounds of possibility that
the abrupt change in valve operation characteristic appears as a
torque shock and/or a deterioration of exhaust emissions.
[0036] In order to solve the above problem, during the
variable-valve control prohibit period following the completion of
the automatic start of the engine, the valve operation
characteristic is fixed at a target valve operation characteristic
for an automatic-start time of the engine. Since the valve
operation characteristic is sustained and fixed prior to and after
the completion of the automatic start of the engine, variations in
valve operation characteristic can be eliminated. Thus, a torque
shock and/or deterioration of exhaust emissions can be prevented
from occurring due to an abrupt change in valve operation
characteristic.
[0037] In addition, while the variable-valve control prohibit
period following the automatic start of the engine can be set at a
fixed value determined in advance, the variable-valve control
prohibit period following the automatic start of the engine can be
set at a value dependent on the number of previous engine automatic
stops or the number of previous engine automatic starts. If the
number of previous engine automatic stops after a start of a
vehicle run or the number of previous engine automatic starts after
the start of the vehicle run is small, the number of times an
adverse effect is experienced can be determined to be small as
well. Examples of the adverse effect are deteriorations caused by
the variable-valve control such as a deterioration of the
drivability and a deterioration of exhaust emissions. Since the
number of times an adverse effect is experienced is small, the
variable-valve control prohibit period can be shortened and the
variable-valve control can thus be started at an early time after
the automatic start of the engine. Thus, control to let the
improvement of the performance take precedence of others can be
executed. Typically, the performance such as fuel economy can be
improved by execution of the variable-valve control. If the number
of previous engine automatic stops after a start of a vehicle run
or the number of previous engine automatic starts after the start
of the vehicle run is large, on the other hand, the number of times
an adverse effect is experienced can be determined to be large as
well. In this case, the variable-valve control prohibit period is
lengthened. Thus, control can be executed to let avoidance of the
adverse effect caused by the variable-valve control take precedence
of others rather than letting the improvement of the performance
take precedence of others.
[0038] In accordance with a third aspect of the present invention,
there is provided a variable-valve mechanism capable of controlling
the intake airflow by varying valve operation characteristics of
the intake valve or exhaust valve or both the valves of the engine.
An intake airflow is controlled by adjusting the variable-valve
mechanism and/or a throttle valve so as to gradually reduce a
torque output by the engine and stop the engine when a
predetermined condition for an automatic stop of the engine is
satisfied during an operation of the engine. In addition, during
the process to reduce the torque output by the engine, torque
abrupt reduction control is executed to abruptly decrease the
intake airflow by controlling the variable-valve mechanism so as to
abruptly reduce the torque output by the engine with a timing with
which the engine speed is about to pass through a predetermined
speed zone. In this case, it is preferable to set the predetermined
speed zone for execution of the torque abrupt reduction control to
include a resonance speed area in which vibration of the engine is
resonant with vibration of a vehicle-driving system.
[0039] Thus, when the engine is automatically stopped, if the
variable-valve mechanism is controlled to abruptly decrease the
intake airflow with a timing with which the engine speed is about
to pass through the predetermined speed zone including the
resonance speed area, the intake airflow into a cylinder abruptly
decreases, exhibiting good responsiveness also with the timing with
which the engine speed is about to pass through the predetermined
speed zone. Thus, the engine speed can be reduced abruptly, passing
through the predetermined speed zone including the resonance speed
zone. As a result, at the time of the automatic stop control, the
engine speed can be changed through the resonance speed zone in a
short period of time so that noises and vibration, which are caused
by the resonance phenomenon, can be reduced with a high degree of
reliability without making the driver feel a sense of
incompatibility.
[0040] In the case of a system having a variable-valve mechanism
capable of controlling an intake valve to a completely closed state
or a state with a valve lift quantity of 0, it is preferable to
control the variable-valve mechanism to put the intake valve in the
completely closed state at the time of the torque abrupt reduction
control. At the time of the torque abrupt reduction control, it is
possible to reduce the intake airflow into a cylinder to 0
instantaneously and, hence, to abruptly decrease the engine speed.
Thus, the engine speed can be changed to pass through the resonance
speed zone in a short period of time. As a result, noises and
vibration, which are caused by the resonance phenomenon, can be
reduced substantially.
[0041] In the case of a system having a variable-valve mechanism
not capable of controlling an intake valve to a completely closed
state, on the other hand, it is preferable to control the
variable-valve mechanism to minimize the intake valve at the time
of the torque abrupt reduction control and to control a throttle
valve to a completely closed state. Even in the case of a system
having a variable-valve mechanism not capable of controlling an
intake valve to a completely closed state, both the variable-valve
control and the throttle-valve control are effectively executed at
the time of the torque abrupt reduction control to set the intake
airflow at 0 quickly in order to reduce the engine speed abruptly.
Thus, in the case of a variable-valve mechanism not capable of
controlling an intake valve to a completely closed state, the
engine speed can be changed to pass through the resonance speed
zone in an extremely short period of time. As a result, noises and
vibration, which are caused by the resonance phenomenon, can be
reduced effectively.
[0042] In addition, injection of fuel can also be stopped at the
time of the torque abrupt reduction control. Thus, the engine speed
can be abruptly reduced with a high degree of effectiveness by
reducing the intake airflow as well as stopping the injection of
fuel at the time of the torque abrupt reduction control.
[0043] In addition, in a process to gradually reduce a torque
output by the engine and stop the engine at the time of the
automatic-stop control, the fuel injection volume can be controlled
so as to maintain an air-fuel ratio at a target air-fuel ratio till
the engine speed is reduced to a predetermined speed zone. The
air-fuel ratio can be maintained at the target air-fuel ratio in a
process to gradually reduce the torque output by the engine at the
time of the automatic-stop control. Thus, it is possible to
gradually reduce the engine speed without deteriorating exhaust
emissions.
[0044] In accordance with a fourth aspect of the present invention,
there is provided a variable-valve control prohibition means for
prohibiting control executed by a variable-valve control means to
open and close an intake valve and/or an exhaust valve on the basis
of a battery voltage detected by a battery-voltage-driving means
after the engine is automatically started by an automatic-start
control means.
[0045] Thus, if the voltage of a battery decreases after the engine
is automatically started so that the control response
characteristics of the intake valve and/or the exhaust valve
deteriorate, making it impossible to follow target valve lift
quantities and follow valve opening/closing timings with a high
degree of precision, the control of the intake valve and/or the
exhaust valve is prohibited and, instead, the valve positions are
fixed so as to stabilize a target intake airflow and, hence,
suppress deteriorations of exhaust emissions.
[0046] In addition, it is preferable to have the variable-valve
control prohibition means prohibit intake-air-flow control executed
by using the intake valve and/or the exhaust valve till the voltage
of the battery reaches a predetermined level.
[0047] In control of the intake airflow by varying a lift quantity
variable through the use of electric power, in particular, the
intake airflow at a location in close proximity to a combustion
chamber of the engine can be adjusted. It is thus unnecessary to
take a delay of an air system into consideration in comparison with
the intake-airflow control by using a throttle valve. As a result,
the control of the intake airflow can be executed with a high
degree of precision. When the voltage of the battery decreases,
however, a response delay is incurred in the control of the intake
valve and/or the exhaust valve so that the precision of the control
of the intake airflow and the exhaust emissions inevitably
deteriorate. Thus, when the voltage of the battery decreases, the
valve lift quantity is held at a fixed value and the control of the
intake airflow is prohibited in order to suppress the
deteriorations of the exhaust emissions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] Features and advantages of embodiments will be appreciated,
as well as methods of operation and the function of the related
parts, from a study of the following detailed description, the
appended claims, and the drawings, all of which form a part of this
application. In the drawings:
[0049] FIG. 1 is a block diagram of the configuration of an engine
control system according to a first embodiment of the present
invention;
[0050] FIG. 2 is a diagram of the configuration of a variable valve
according to the first embodiment of the present invention;
[0051] FIG. 3 is a graph representing a state of a large lift
quantity of a variable-valve mechanism according to the first
embodiment of the present invention;
[0052] FIG. 4 is a graph representing a state of a small lift
quantity of the variable-valve mechanism according to the first
embodiment of the present invention;
[0053] FIG. 5 is a graph representing operation characteristics of
the variable-valve mechanism according to the first embodiment of
the present invention;
[0054] FIG. 6 is a flowchart representing engine control according
to the first embodiment of the present invention;
[0055] FIG. 7A is a graph representing relations between an engine
cooling water temperature Tw and a basic valve lift quantity Bstop
in the first embodiment of the present invention;
[0056] FIG. 7B is a graph representing a relation between an
engine-automatic-stop count NS or an engine-automatic-start count
NR and a valve-lift-quantity correction coefficient Cstop in the
first embodiment of the present invention;
[0057] FIG. 8 is a flowchart representing other engine control
according to the first embodiment of the present invention;
[0058] FIG. 9A is a graph representing other relations between the
engine cooling water temperature Tw and the basic valve lift
quantity Bstart in the first embodiment of the present
invention;
[0059] FIG. 9B is a graph representing another relation between the
engine-automatic-stop count NS or the engine-automatic-start count
NR and a first valve-lift-quantity correction coefficient C1start
in the first embodiment of the present invention;
[0060] FIG. 9C is a graph representing a relation between an
engine-automatic-stop time Ts and a second valve-lift-quantity
correction coefficient C2start in the first embodiment of the
present invention;
[0061] FIG. 10 is a flowchart representing further engine control
according to the first embodiment of the present invention;
[0062] FIG. 11 is a graph representing a relation between an
engine-stall count Nes and a valve lift quantity increase .DELTA.VL
in the first embodiment of the present invention;
[0063] FIG. 12 is a time chart representing engine control
according to the first embodiment of the present invention;
[0064] FIG. 13 is a time chart representing other engine control
according to the first embodiment of the present invention;
[0065] FIG. 14 is a time chart representing further engine control
according to the first embodiment of the present invention;
[0066] FIG. 15 is a flowchart representing engine control according
to a second embodiment of the present invention;
[0067] FIG. 16 is a graph representing a relation between the
engine-automatic-stop count NS or the engine-automatic-start count
NR and a prohibition time KCAST of variable-valve control in the
second embodiment of the present invention;
[0068] FIG. 17 is a time chart representing the engine control
according to the second embodiment of the present invention;
[0069] FIG. 18 is a flowchart representing engine control according
to a third embodiment of the present invention;
[0070] FIG. 19 is a time chart representing the engine control
according to the third embodiment of the present invention;
[0071] FIG. 20 is a flowchart representing engine control according
to a fourth embodiment of the present invention;
[0072] FIG. 21 is a flowchart representing other engine control
according to the fourth embodiment of the present invention;
[0073] FIG. 22 is a map for setting a target intake airflow excess
reduction quantity FQA in the fourth embodiment of the present
invention;
[0074] FIG. 23 is a map for setting a target lift quantity VL in
the fourth embodiment of the present invention;
[0075] FIG. 24 is a flowchart representing further engine control
according to the fourth embodiment of the present invention;
[0076] FIG. 25 is a flowchart representing still further engine
control according to the fourth embodiment of the present
invention;
[0077] FIG. 26 is a time chart representing engine control
according to the fourth embodiment of the present invention;
and
[0078] FIG. 27 is a graph representing a relation between an engine
speed NE and the magnitude of a noise in the fourth embodiment of
the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0079] First Embodiment
[0080] Some preferred embodiments of the present invention are
explained by referring to diagrams as follows. First of all, a
rough configuration of an entire engine control system is explained
by referring to FIG. 1. An air cleaner 13 is provided at the upper
end of the upstream side of an intake pipe 12 employed in an
internal combustion engine 11. An airflow meter 14 for detecting an
intake airflow is provided the downstream of the air cleaner 13.
Downstream of the airflow meter 14, there are provided a throttle
valve 15, the opening of which can be adjusted by typically a DC
motor, and a throttle-opening sensor 16 for detecting an opening of
the throttle valve 15.
[0081] A surge tank 17 is further provided downstream of the
throttle valve 15. On the surge tank 17, there is provided an
intake-pipe-pressure sensor 18 for detecting a pressure of air in
the intake pipe 12. In addition, on the surge tank 17, there is
provided an intake manifold 19 for introducing air into cylinders
employed in the engine 11. At locations in close proximity to an
intake port of the intake manifold 19, there are provide fuel
injection valves 20 for injecting fuel into their respective
cylinders. Ignition plugs 21 each provided for one of the cylinders
are installed on cylinder heads of the engine 11. Mixed gas in a
cylinder is ignited by a spark electric discharge of the ignition
plug 21 provided for the cylinder.
[0082] On an intake valve 28 employed in the engine 11, there is
provided a variable-valve lift mechanism 30 for changing the lift
quantity of the intake valve 28. By the same token, on an exhaust
valve 29 employed in the engine 11, there is provided a
variable-valve lift mechanism 31 for changing the lift quantity of
the exhaust valve 29. In addition, on the intake valve 28, it is
possible to provide a variable-valve lift mechanism for changing
the valve timing of the intake valve 28. In the same way, on the
exhaust valve 29, it is possible to provide a variable-valve lift
mechanism for changing the valve timing of the exhaust valve
29.
[0083] On the other hand, on an exhaust pipe 22 employed in the
engine 11, there is provided a catalyst 23 such as a 3-way catalyst
for reducing the amounts of emissions such as CO, HC and NOx
contained in exhaust gas. Upstream of the catalyst 23, there is
provided an air-fuel-ratio sensor 24 such as a linear
air-fuel-ratio sensor or an oxygen sensor for detecting an air fuel
ratio of exhaust gas or determining whether the air fuel ratio is
on the rich or lean side. In addition, on a cylinder block of the
engine 11, there are provided a cooling-water-temperature sensor 25
for detecting a temperature of cooling water and a crank-angle
sensor 26 for detecting an engine speed.
[0084] Signals generated by these sensors are supplied to an engine
control circuit 27 referred to hereafter as an ECU. The ECU 27 has
a configuration including a microcomputer as a core component. The
microcomputer executes a variety of control programs stored in an
embedded ROM, which serves as a storage medium, in order to control
fuel injection volumes of the fuel injection valves 20 and ignition
timings of the ignition plugs 21 in accordance with an operating
state of the engine 11.
[0085] Next, the configuration of the variable-valve mechanism 30
of the intake valve 28 is explained by referring to FIGS. 2 to 5.
It is to be noted that, since the configuration of the
variable-valve mechanism 31 of the exhaust valve 29 is the same as
the configuration of the variable-valve mechanism 30 of the intake
valve 28, the configuration of the variable-valve mechanism 31 is
not explained specially.
[0086] As shown in FIG. 2, a link arm 34 is provided between a
rocker arm 33 and a cam shaft 32 for driving the intake valve 28.
Above the link arm 34, there is provided a control shaft 35 rotated
by a stepping motor not shown in the figure. On the control shaft
35, there is provided an eccentric cam 36 rotatable with the
control shaft 35 as a single body. The link arm 34 is supported at
an eccentric position relative to the axis of the eccentric cam 36
by a support shaft not shown in the figure in such a manner that
the link arm 34 can be reciprocated. A reciprocating cam 38 is
provided at the center of the link arm 34. A side surface of the
reciprocating cam 38 is in contact with an outer circumferential
surface of a cam 37 provided on the cam shaft 32. A pressure cam 39
is provided on the lower end of the link arm 34. The lower-end
surface of the pressure cam 39 is in contact with the upper-end
surface of a roller 40 provided at the center of the rocker arm
33.
[0087] With the above configuration, when the cam 37 is rotated by
the rotation of the cam shaft 32, the reciprocating cam 38 of the
link arm 34 reciprocates horizontally in accordance with the outer
circumferential shape of the cam 37, causing the link arm 34 to
also reciprocate horizontally as well. When the link arm 34
reciprocates horizontally, the pressure cam 39 also reciprocates
horizontally so that the roller 40 of the rocker arm 33 moves up
and down in accordance with the lower-end surface shape of the
pressure cam 39, causing the rocker arm 33 also to move up and down
as well. When the rocker arm 33 moves up and down, the intake valve
28 also moves up and down as well.
[0088] When the eccentric cam 36 is rotated by the rotation of the
control shaft 35, on the other hand, the position of the support
shaft of the link arm 34 moves, changing an initial contact point
position between the pressure cam 39 of the link arm 34 and the
roller 40 of the rocker arm 33. For the initial contact point
position, refer to FIGS. 3 and 4. In addition, as shown in FIG. 2,
the lower-end surface of the pressure cam 39 of the link arm 34
comprises a base surface 39a formed at such a curvature that the
magnitude of a pressure of the rocker arm 33 at a left-side portion
is 0, that is, the valve lift quantity of the intake valve 28 is 0,
and a base surface 39b formed at such a curvature that the
magnitude of a pressure of the rocker arm 33 increases when moving
in the right direction starting from the base surface 39a, that is,
the valve lift quantity of the intake valve 28 increases when
moving in the direction.
[0089] In a large lift mode in which the valve lift quantity of the
intake valve 28 is increased, the rotation of the control shaft 35
moves the initial contact point position between the pressure cam
39 of the link arm 34 and the roller 40 of the rocker arm 33 in the
right direction as shown in FIG. 3. Thus, when the pressure cam 39
is reciprocated horizontally due to the rotation of the cam 37, a
particular portion of the lower-end surface of the pressure cam 39
is moved to the right. Accordingly, the largest magnitude of a
pressure of the rocker arm 33 increases, raising the largest valve
lift quantity of the intake valve 28 and lengthening a period in
which the rocker arm 33 is pressed. As a result, an opened-valve
period of the intake valve 28 is also lengthened as well. By the
particular portion, the portion of lower-end surface in contact
with the roller 40 is meant.
[0090] In a small lift mode in which the valve lift quantity of the
intake valve 28 is decreased, on the other hand, the rotation of
the control shaft 35 moves the initial contact point position
between the pressure cam 39 of the link arm 34 and the roller 40 of
the rocker arm 33 in the left direction as shown in FIG. 4. Thus,
when the pressure cam 39 is reciprocated horizontally due to the
rotation of the cam 37, a particular portion of the lower-end
surface of the pressure cam 39 is moved to the left. Accordingly,
the largest magnitude of a pressure of the rocker arm 33 decreases,
reducing the largest valve lift quantity of the intake valve 28 and
shortening a period in which the rocker arm 33 is pressed. As a
result, an opened-valve period of the intake valve 28 is also
shortened as well. By the particular portion, the portion of
lower-end surface in contact with the roller 40 is meant as
described above.
[0091] In the variable-valve lift mechanism 30 described above, if
the initial contact point position between the pressure cam 39 of
the link arm 34 and the roller 40 of the rocker arm 33 is moved
continuously by rotating the control shaft 35 by using the stepping
motor, it is possible to continuously change the largest valve lift
quantity of the intake valve 28 and the opened-valve period of the
intake valve 28 as shown in FIG. 5.
[0092] Driven by power generated by a battery 41 mounted on the
vehicle, the ECU 27 executes a variable-valve lift control program
stored in the ROM, controlling the variable-valve lift mechanism 30
of the intake valve 28 and the variable-valve lift mechanism 31 of
the exhaust valve 29 on the basis of an accelerator position, an
operating state of the engine 11 and other information in order to
continuously change the valve lift quantities of the intake valve
28 and the exhaust valve 29. In this case, the ECU 27 functions as
a variable-valve control means for controlling the intake airflow.
It is to be noted that, in a system employing a variable valve
timing mechanism in conjunction with the variable-valve lift
mechanisms 30 and 31, both the valve lift quantities and the valve
timings may be continuously changed in order to control the intake
airflow.
[0093] In addition, the ECU 27 executes the automatic-stop control
program of ROM shown in FIG. 6 to automatically stop the engine 11
if a predetermined automatic-stop condition is satisfied during an
operation of the engine 11. Right after the automatic stop, the ECU
27 finds a target valve lift quantity VLstop of an engine
automatic-stop time for the intake valve 28 and a target valve lift
quantity VLstop of an engine automatic-stop time for the exhaust
valve 29 on the basis of a state of the engine 11 and a state of
the vehicle, controlling the valve lift quantities of the intake
valve 28 and the exhaust valve 29 to their respective target valve
lift quantities VLstop. The target valve lift quantity VLstop is a
valve lift quantity presumed to be suitable for the next automatic
start of the engine 11 or a valve lift quantity making it difficult
for residual gas left in the cylinders to leak out. At a point of
time the valve lift quantities of the intake valve 28 and the
exhaust valve 29 become equal to their respective target valve lift
quantities VLstop, the control of the variable-valve lift
mechanisms 30 and 31 is discontinued.
[0094] Furthermore, the ECU 27 executes the automatic-start control
program of ROM shown in FIG. 8 to first find a target valve lift
quantity VLstart of an engine automatic-start time for the intake
valve 28 and a target valve lift quantity VLstart of an engine
automatic-start time for the exhaust valve 29 on the basis of a
state of the engine 11 and a state of the vehicle, controlling the
valve lift quantities of the intake valve 28 and the exhaust valve
29 to their respective target valve lift quantities Vlstart if a
predetermined automatic-start condition is satisfied in an
automatic-stop state of the engine 11. The target valve lift
quantity VLstart is a valve lift quantity optimum for an automatic
start of the engine 11. Then, at a point of time the valve lift
quantities of the intake valve 28 and the exhaust valve 29 become
equal to their respective target valve lift quantities VLstart, the
ECU 27 automatically starts the engine 11.
[0095] Moreover, the ECU 27 executes the
engine-stall-generation-time control program of ROM shown in FIG.
10 to correct a target valve lift quantity VLstart of an engine
automatic-start time for the intake valve 28 in a direction of
increasing an intake airflow in the event of the so-called engine
stall caused by a failure of an automatic start of the engine 11,
and control the valve lift quantity of the intake valve 28 to the
corrected target valve lift quantity VLstart of an engine
automatic-start time for the intake valve 28. Then, at a point of
time the valve lift quantity of the intake valve 28 becomes equal
to the corrected target valve lift quantity VLstart of an engine
automatic-start time for the intake valve 28, the ECU 27
automatically restarts the engine 11.
[0096] The following description explains the processing of the
control programs executed by the ECU 27 by referring to flowcharts
shown in FIGS. 6, 8 and 10.
[0097] Automatic-Stop Control
[0098] The automatic-stop control program represented by the
flowchart shown in FIG. 6 is executed repeatedly at predetermined
time intervals during the operation of the engine 11. When this
program is invoked, the flowchart begins with a step 101 to
determine whether or not automatic-stop conditions are satisfied.
Typically, the automatic-stop conditions include conditions (1) to
(3) described as follows.
[0099] (1): The speed of the vehicle shall be 0 km/h. That is, the
vehicle shall be in a stopped state.
[0100] (2): The accelerator pedal shall not be depressed.
[0101] (3): The brake pedal shall be in a state of being
depressed.
[0102] If conditions (1) to (3) are all satisfied, the
automatic-stop conditions are considered to hold true. If even only
one of conditions (1) to (3) is not satisfied, on the other hand,
the automatic-stop conditions are considered not to hold true. It
is to be noted that the automatic-stop conditions can be modified
if necessary.
[0103] If the automatic-stop conditions are satisfied during the
operation of the engine 11, a request for an engine stop is
determined to exist. In this case, the flow of the program goes on
to a step 102 at which automatic stop control or idling stop
control is executed. In this automatic stop control, a fuel cut
operation and an ignition cut operation are carried out to
automatically stop the engine 11. The processing of the step 102 is
carried out to play the role of an automatic stop control
means.
[0104] Then, the flow of the program goes on to a step 103 to
determine whether or not the automatic stop of the engine 11 has
been completed by for example determining whether or not the engine
speed NE has decreased to 0. At a point of time the automatic stop
of the engine 11 is completed, the flow of the program goes on to a
step 104 at which target valve lift quantities VLstop of the intake
valve 28 and the exhaust valve 29 for the engine automatic-stop
time are each computed in accordance with an equation given below.
As described above, the target valve lift quantity VLstop is a
valve lift quantity presumed to be suitable for the next automatic
start of the engine 11 or a valve lift quantity making it difficult
for residual gas left in the cylinders to leak out.
VLstop=Bstop.times.Cstop
[0105] where reference notation Bstop is a basic valve lift
quantity for the engine automatic-stop time and reference notation
Cstop is a valve-lift-quantity correction coefficient for
correcting the basic valve lift quantity Bstop.
[0106] A basic valve lift quantity Bstop is set in dependence on an
engine-cooling-water temperature detected right after the automatic
stop of the engine 11 by using a formula or a map prepared for the
basic valve lift quantity Bstop for the engine automatic-stop time
like one shown in FIG. 7A.
[0107] In accordance with the map of basic valve lift quantity
Bstop shown in FIG. 7A, in a zone where the engine-cooling-water
temperature detected right after the automatic stop of the engine
11 is lower than a predetermined value and the catalyst 23 can be
assumed to be in an inactivated state, the basic valve lift
quantity Bstop used as a base value for the target valve lift
quantity VLstop for the engine automatic-stop time is set at 0 or a
minimum in order to attach importance to reduction of exhaust
emissions during the automatic stop of the engine 11 and to set the
target valve lift quantity VLstop at a valve lift quantity making
it difficult for residual gas left in the cylinders to leak out
during the automatic stop of the engine 11.
[0108] In accordance with the map of basic valve lift quantity
Bstop shown in FIG. 7A, in a zone where the engine-cooling-water
temperature detected right after the automatic stop of the engine
11 is at least equal to the predetermined value and the catalyst 23
can be assumed to be in an activated state, on the other hand, the
basic valve lift quantity Bstop used as a base value for the target
valve lift quantity VLstop for the engine automatic-stop time is
set in accordance with an engine-cooling-water temperature Tw
detected right after the automatic stop in order to attach
importance to the next automatic start characteristic or the
restart characteristic of the engine 11 and to set the target valve
lift quantity VLstop at a valve lift quantity presumed to be proper
for the next automatic start of the engine 11 from a standpoint of
the engine-cooling-water temperature Tw detected right after the
automatic stop.
[0109] In general, the lower the temperature of the engine and/or
the lower the temperature of the battery mounted on the vehicle,
the poorer the performance of the battery. The poorer the
performance of the battery, the smaller the driving power of a
starter not shown in the figure. The smaller the driving power of
the starter, the lower the flowability of the engine oil. The lower
the flowability of the engine oil, the greater the frictions among
movable parts. Thus, the cranking of the automatic-start time is
prone to variations and the automatic-start characteristic of the
engine tends to deteriorate. Since the battery is mounted in the
same room as the engine 11, the temperature of the battery changes
due to heat dissipated by the engine 11 in accordance with the
temperature of the engine 11. From this relation, when the engine
cooling-water temperature representing the temperature of the
engine 11 is low, the temperature of the engine 11 can be presumed
to be also low as well.
[0110] In accordance with the map of basic valve lift quantity
Bstop shown in FIG. 7A, in the zone where the engine-cooling-water
temperature detected right after the automatic stop of the engine
11 is at least equal to the predetermined value and the catalyst 23
can be assumed to be in an activated state, the lower the engine
cooling-water temperature representing the temperature of the
engine 11, the larger the value at which the basic valve lift
quantity Bstop is set. Thus, in order to cope with the fact that
the driving power of the starter is small at a low temperature of
the battery, causing greater frictions among movable parts and,
hence, making the cranking of the automatic-start time of the
engine 11 prone to variations, the basic valve lift quantity Bstop
is set at a relatively large value in order to change the target
valve lift quantity VLstop in a direction of stabilizing the
cranking such as a direction of increasing the intake airflow at
the automatic-start time of the engine 11.
[0111] On the other hand, the valve lift quantity correction
coefficient Cstop is a correction coefficient, which is used for
correcting the basic valve lift quantity Bstop for the engine
automatic-stop time when the performance of the battery
deteriorates due to a large number of operations carried out so far
to automatically start the engine 11. A valve lift quantity
correction coefficient Cstop is determined in dependence on the
number of engine automatic stops carried out so far or the number
of engine automatic starts carried out so far by using a formula or
the map of valve lift quantity correction coefficient Cstop shown
in FIG. 7B.
[0112] In general, the larger the number of engine automatic stops
carried out so far or the number of engine automatic starts carried
out so far, the larger the consumption of power from the battery
and, hence, the lower the performance of the battery. Thus, the
larger the number of engine automatic stops carried out so far or
the number of engine automatic starts carried out so far, the
smaller the driving power of the starter. As a result, as the
number of engine automatic stops carried out so far or the number
of engine automatic starts carried out so far increases, the
automatic start characteristic of the engine 11 tends to
deteriorate.
[0113] From the relation described above, the map of valve lift
quantity correction coefficient Cstop shown in FIG. 7B is created
so that, in a zone where the number of engine automatic stops
carried out so far or the number of engine automatic starts carried
out so far is greater than a predetermined value, that is, in a
zone where the deterioration of performance of battery caused by
the increased number of operations carried out so far to
automatically start the engine 11 cannot be ignored, the larger the
number of engine automatic stops carried out so far or the number
of engine automatic starts carried out so far, the larger the value
at which the valve lift quantity correction coefficient Cstop is
set. Thus, the larger the number of engine automatic stops carried
out so far or the number of engine automatic starts carried out so
far, the smaller the driving power of the starter and, hence, the
more the cranking at the automatic-start time of the engine 11 is
prone to variations, the larger the value at which the valve lift
quantity correction coefficient Cstop is set. A large valve lift
quantity correction coefficient Cstop changes the target valve lift
quantity VLstop in a direction of stabilizing the cranking or a
direction of increasing the intake airflow. In a zone where the
number of engine automatic stops carried out so far or the number
of engine automatic starts carried out so far is smaller than the
predetermined value, that is, in a zone where the deterioration of
performance of battery caused by the increased number of operations
carried out so far to automatically start the engine 11 can be
almost ignored, on the other hand, the valve lift quantity
correction coefficient Cstop is set at 1.0. In this zone, the
target valve lift quantity VLstop is equal to the basic valve lift
quantity Bstop.
[0114] In the map of basic valve lift quantity Bstop shown in FIG.
7A, as temperature information for determining a temperature of the
engine 11 and/or a temperature of the battery, an engine
cooling-water temperature Tw is used. It is to be noted, however,
that another temperature such as an intake air temperature Ti, an
ambient temperature Ta or an oil temperature To can also be used as
well. In a word, it is preferable to find a basic valve lift
quantity Bstop on the basis of one, two or more pieces of such
temperature information.
[0115] At the step 104, the basic valve lift quantity Bstop is
corrected by multiplying the basic valve lift quantity Bstop by the
valve lift quantity correction coefficient Cstop to find a target
valve lift quantity VLstop for the automatic-stop time of the
engine 11. However, the basic valve lift quantity Bstop can also be
used as a target valve lift quantity VLstop for the automatic-stop
time of the engine 11 as it is without correction of the basic
valve lift quantity Bstop by multiplying the basic valve lift
quantity Bstop by the valve lift quantity correction coefficient
Cstop.
[0116] After finding the target valve lift quantity VLstop for the
automatic-stop time of the engine 11, the flow of the program goes
on to a step 105 at which variable-valve lift control is executed
to control the variable-valve lift mechanism 30 of the intake valve
28 and the variable-valve lift mechanism 31 of the exhaust valve 29
so that the valve lift quantities of the intake valve 28 and the
exhaust valve 29 are adjusted to their respective target valve lift
quantities VLstop. The processing of the steps 104 and 105 is
carried out to play the role of an automatic-stop-time valve
control means.
[0117] The flow of the program goes on to a step 106 to determine
whether or not the valve lift quantities of the intake valve 28 and
the exhaust valve 29 have each been adjusted to the target valve
lift quantity VLstop. At a point of time the valve lift quantities
of the intake valve 28 and the exhaust valve 29 become equal to
their respective target valve lift quantities VLstop, the flow of
the program goes on to a step 107 at which conductions of currents
to the driving motors of the variable-valve lift mechanisms 30 and
31 are halted.
[0118] By carrying out the processing described above, the
variable-valve lift mechanisms 30 and 31 are halted with the valve
lift quantities of the intake valve 28 and the exhaust valve 29 set
at their respective target valve lift quantities VLstop, which are
each a valve lift quantity presumed to be suitable for the next
automatic start or a valve lift quantity making it difficult for
residual gas left in the cylinders to leak out.
[0119] It is to be noted that, in a system employing a variable
valve timing mechanism in conjunction with the variable-valve lift
mechanisms 30 and 31, when the engine 11 is automatically stopped,
control can be executed to adjust the valve lift quantities to
their respective target valve lift quantities for the automatic
stop of the engine 11 and the valve timings to their respective
target valve timings for the automatic stop of the engine 11.
[0120] Automatic Start Control
[0121] The automatic-start control program represented by the
flowchart shown in FIG. 8 is executed repeatedly at predetermined
time intervals during an automatic stop of the engine 11. When this
program is invoked, the flowchart begins with a step 201 to
determine whether or not automatic-start conditions are satisfied.
In the case of a manual-transmission car (an MT car), typically,
the automatic-start conditions include conditions (1) to (3)
described as follows.
[0122] (1): The speed of the vehicle shall be 0 km/h. That is, the
vehicle shall be in a stopped state.
[0123] (2): The clutch pedal shall be in a state of being
depressed.
[0124] (3): The brake pedal shall be in a state of not being
depressed.
[0125] If conditions (1) to (3) are all satisfied, the
automatic-start conditions are considered to hold true. If even
only one of conditions (1) to (3) is not satisfied, on the other
hand, the automatic-start conditions are considered not to hold
true.
[0126] It is to be noted that the automatic-start conditions can be
modified if necessary. In the case of an automatic-transmission car
(an AT car), on the other hand, the automatic-start conditions are
typically considered to be satisfied when the shift lever has been
shifted to a drive range or the like with the brake pedal put in a
state of being depressed. In a word, the automatic-start conditions
are considered to be satisfied when the driver has carried out
operations in a preparation for running the vehicle, be the vehicle
an AT car or an MT car.
[0127] If the automatic-start conditions are satisfied in an
automatic-stop state of the engine 11, a request for an engine
start is determined to exist. In this case, the flow of the program
goes on to a step 202 at which target valve lift quantities VLstart
of the intake valve 28 and the exhaust valve 29 for the engine
automatic-start time are each computed in accordance with an
equation given below. As described above, the target valve lift
quantity VLstart is a valve lift quantity presumed to be optimum
for the automatic-start time of the engine 11.
VLstart=Bstart.times.C1start.times.C2start
[0128] where reference notation Bstart is a basic valve lift
quantity for the engine automatic-start time whereas reference
notations C1start and C2start are respectively first and second
valve-lift-quantity correction coefficients for correcting the
basic valve lift quantity Bstart.
[0129] A basic valve lift quantity Bstart is set in dependence on
an engine-cooling-water temperature Tw detected immediately before
an automatic start of the engine 11 by using a formula or a map
prepared for the basic valve lift quantity Bstart for the engine
automatic-start time like one shown in FIG. 9A.
[0130] In accordance with the basic valve lift quantity Bstart's
map shown in FIG. 9A, the lower the engine cooling-water
temperature Tw used as temperature information indicating the
temperatures of the engine 11 and the battery, the larger the value
at which the basic valve lift quantity Bstart is set. Thus, in
order to cope with the fact that the driving power of the starter
is small at a low temperature of the engine 11 or the battery,
causing greater frictions among movable parts and, hence, making
the cranking of the automatic-start time of the engine 11 prone to
variations, the basic valve lift quantity Bstart is set at a
relatively large value in order to change the target valve lift
quantity VLstart in a direction of stabilizing the cranking such as
a direction of increasing the intake airflow at the automatic-start
time of the engine 11.
[0131] On the other hand, the first valve lift quantity correction
coefficient C1start is a correction coefficient, which is used for
correcting the basic valve lift quantity Bstart for the engine
automatic-start time when the performance of the battery
deteriorates due to a large number of operations carried out so far
to automatically start the engine 11. A first valve lift quantity
correction coefficient C1start is determined in dependence on the
number of engine automatic stops carried out so far or the number
of engine automatic starts carried out so far by using a formula or
the map of first valve lift quantity correction coefficient C1start
shown in FIG. 9B. In the following description, the number of
engine automatic stops carried out so far and the number of engine
automatic starts carried out so far are also referred to as an
engine automatic stop count NS and an engine automatic start count
NR respectively. The map of first valve lift quantity correction
coefficient C1start shown in FIG. 9B is created so that, in a zone
where the number of engine automatic stops carried out so far or
the number of engine automatic starts carried out so far is smaller
than a predetermined value, that is, in a zone where the
deterioration of performance of battery caused by the increased
number of operations carried out so far to automatically start the
engine 11 can be almost ignored, the first valve lift quantity
correction coefficient C1start is set at 1.0. In a zone where the
number of engine automatic stops carried out so far or the number
of engine automatic starts carried out so far is greater than the
predetermined value, that is, in a zone where the deterioration of
performance of battery caused by the increased number of operations
carried out so far to automatically start the engine 11 cannot be
ignored, on the other hand, the larger the number of engine
automatic stops carried out so far or the number of engine
automatic starts carried out so far, the larger the value at which
the first valve lift quantity correction coefficient C1start is
set.
[0132] In addition, the second valve lift quantity correction
coefficient C2start is a correction coefficient, which is used for
correcting the basic valve lift quantity Bstart for the engine
automatic-start time when the performance of the battery
deteriorates due to a long automatic-stop time Ts of the engine 11
or large consumption of power from the battery during the automatic
stop of the engine 11. A second valve lift quantity correction
coefficient C2start is determined in dependence on the
automatic-stop time Ts of the engine 11 by using a formula or the
map of second valve lift quantity correction coefficient C2start
shown in FIG. 9C. The map of second valve lift quantity correction
coefficient C2start shown in FIG. 9C is created so that, in a zone
where the automatic-stop time Ts of the engine 11 is smaller than a
predetermined value, that is, in a zone where the deterioration of
performance of battery caused by the large consumption of power
from the battery during the automatic stop of the engine 11 can be
almost ignored, the second valve lift quantity correction
coefficient C2start is set at 1.0 meaning no correction of the
basic valve lift quantity Bstart. In a zone where the
automatic-stop time Ts of the engine 11 is greater than the
predetermined value, that is, in a zone where the deterioration of
performance of battery caused by the large consumption of power
from the battery during the automatic stop of the engine 11 cannot
be ignored, on the other hand, the longer the automatic-stop time
Ts of the engine 11, the larger the value at which the second valve
lift quantity correction coefficient C2start is set.
[0133] When the number of engine automatic stops carried out so far
or the number of engine automatic starts carried out so far
increases or when the automatic-stop time Ts of the engine 11
becomes long, the driving power of the starter decreases, making
the cranking of the automatic-start time of the engine 11 prone to
variations. In this case, the first valve lift quantity correction
coefficient C1start or the second valve lift quantity correction
coefficient C2start is set at a large value, which changes the
target valve lift quantity VLstart in a direction of stabilizing
the cranking or a direction of increasing the intake airflow at the
automatic start of the engine 11.
[0134] In the basic valve lift quantity Bstart map shown in FIG.
9A, as temperature information for determining a temperature of the
engine 11 and/or a temperature of the battery, an engine
cooling-water temperature Tw is used. It is to be noted, however,
that another temperature such as an intake air temperature Ti, an
ambient temperature Ta or an oil temperature To can also be used as
well. In a word, it is preferable to find a basic valve lift
quantity Bstart on the basis of one, two or more pieces of such
temperature information.
[0135] Then, at the step 202, the basic valve lift quantity Bstart
is corrected by multiplying the basic valve lift quantity Bstart by
the first valve lift quantity correction coefficient C1start and
the second valve lift quantity correction coefficient C2start to
find a target valve lift quantity VLstart for the automatic-start
time of the engine 11. However, one of the first valve lift
quantity correction coefficient C1start and the second valve lift
quantity correction coefficient C2start or both can be eliminated
from the formula for computing a target valve lift quantity
VLstart.
[0136] After finding the target valve lift quantity VLstart for the
automatic-start time of the engine 11, the flow of the program goes
on to a step 203 at which variable-valve lift control is executed
to control the variable-valve lift mechanism 30 of the intake valve
28 and the variable-valve lift mechanism 31 of the exhaust valve 29
so that the valve lift quantities of the intake valve 28 and the
exhaust valve 29 are adjusted to their respective target valve lift
quantities VLstart. The processing of the steps 202 and 203 is
carried out to play the role of an automatic-start-time valve
control means.
[0137] The flow of the program goes on to a step 204 to determine
whether or not the valve lift quantities of the intake valve 28 and
the exhaust valve 29 have been adjusted to their respective target
valve lift quantities VLstart. At a point of time the valve lift
quantities of the intake valve 28 and the exhaust valve 29 become
equal to their respective target valve lift quantities VLstart, the
flow of the program goes on to a step 205 at which automatic start
control is executed to turn on the starter and to start the engine
11 automatically. The processing of the step 205 is carried out to
play the role of an automatic-start control means.
[0138] By carrying out the processing described above, the engine
11 is automatically started with the valve lift quantities of the
intake valve 28 and the exhaust valve 29 set at their respective
target valve lift quantities Vlstart.
[0139] It is to be noted that, in a system employing a variable
valve timing mechanism in conjunction with the variable-valve lift
mechanisms 30 and 31, when the engine 11 is automatically started,
control can be executed to adjust the valve lift quantities to
their respective target valve lift quantities for the
automatic-start time of the engine 11 and the valve timings to
their respective target valve timings for the automatic-start time
of the engine 11.
[0140] Engine-Stall-Generation-Time Control
[0141] The engine-stall-generation-time control program represented
by the flowchart shown in FIG. 10 is executed repeatedly at
predetermined time intervals after the start of automatic-start
control. When this program is invoked, the flowchart begins with a
step 301 to determine whether or not the engine so-called engine
stall has been generated due to a failure of an automatic start of
the engine 11 by, typically, determining whether or not the engine
speed NE has decreased to 0. If no engine stall has been generated,
the execution of the program is ended without doing anything.
[0142] If an engine stall has been generated, on the other hand,
the flow of the program goes on to a step 302 at which the target
valve lift quantity VLstart set for the intake valve 28 to be used
at an automatic-start time of the engine 11 is increased by a
predetermined valve lift quantity increment .DELTA.VL in a
correction process to increase the intake airflow as follows:
VLstart=VLstart+.DELTA.VL
[0143] A valve lift quantity increment .DELTA.VL is determined in
dependence on the number of previous engine stalls by using a
formula or the valve lift quantity increment .DELTA.VL's map like
one shown in FIG. 11. In accordance with the valve lift quantity
increment .DELTA.VL's map, the larger the number of previous engine
stalls, the larger the value at which a valve lift quantity
increment .DELTA.VL is set.
[0144] After correcting the target valve lift quantity VLstart for
the automatic-start time of the engine 11, the flow of the program
goes on to a step 303 at which variable-valve lift control is
executed to control the variable-valve lift mechanism 30 of the
intake valve 28 so that the valve lift quantity of the intake valve
28 is adjusted to the corrected target valve lift quantity
VLstart.
[0145] The flow of the program goes on to a step 304 to determine
whether or not the valve lift quantities of the intake valve 28 and
the exhaust valve 29 have been adjusted to their respective
corrected target valve lift quantities VLstart. At a point of time
the valve lift quantities of the intake valve 28 and the exhaust
valve 29 become equal to their respective corrected target valve
lift quantities VLstart, the flow of the program goes on to a step
305 at which automatic start control is re-executed to
automatically start the engine 11.
[0146] It is to be noted that, in a system employing a variable
valve timing mechanism in conjunction with the variable-valve lift
mechanisms 30 and 31, when an engine stall is generated, the target
valve lift quantities for the automatic-start time of the engine 11
and the target valve timings for the automatic-start time of the
engine 11 can each be corrected to increase the intake airflow.
[0147] FIGS. 12 to 14 show time charts for the programs represented
by the flowcharts shown in FIGS. 6, 8 and 10.
[0148] The time charts shown in FIG. 12 are time charts of typical
control, which is executed when an engine cooling-water temperature
Tw is determined to be higher than a predetermined value and the
catalyst 23 is determined to have been activated. In this case,
when the automatic stop conditions are satisfied during an
operation of the engine 11, the engine 11 is automatically stopped.
Right after the engine 11 is automatically stopped, since the
engine cooling-water temperature Tw is determined to be higher than
the predetermined value and the catalyst 23 is determined to have
been activated, the target valve lift quantities VLstop of the
intake valve 28 and the exhaust valve 29 for the engine
automatic-stop time are set in accordance with an
engine-cooling-water temperature Tw detected right after the
automatic stop and in accordance with other information in order to
attach importance to the next automatic start characteristic or the
restart characteristic of the engine 11. After the valve lift
quantities VLstop for the intake valve 28 and the exhaust valve 29
are controlled to their respective target valve lift quantities
VLstop for the engine automatic-stop time, which have each been set
at a valve lift quantity presumed to be suitable for the next
automatic start, the execution of the control of the variable-valve
lift mechanisms 30 and 31 is ended. In this way, during the
automatic stop of the engine 11, the variable-valve lift mechanisms
30 and 31 are halted with the valve lift quantities of the intake
valve 28 and the exhaust valve 29 set at their respective target
valve lift quantities VLstop, which are each a valve lift quantity
presumed to be suitable for the next automatic start.
[0149] When the automatic start conditions are satisfied during the
automatic stop of the engine 11, target valve lift quantities
VLstart of the intake valve 28 and the exhaust valve 29 for the
engine automatic-start time are each set at a valve lift quantity
presumed to be optimum for the automatic start on the basis of an
engine-cooling-water temperature Tw detected immediately before the
automatic start and on the basis of other information. Then, after
the valve lift quantities of the intake valve 28 and the exhaust
valve 29 are corrected from their respective target valve lift
quantities VLstop for the engine automatic-stop time to their
respective target valve lift quantities VLstart for the engine
automatic-start time, the engine 11 is automatically started. The
target valve lift quantities VLstop for the engine automatic-stop
time are each a valve lift quantity presumed to be suitable for an
automatic start. On the other hand, the target valve lift
quantities VLstart for the engine automatic-start time are each a
valve lift quantity optimum for an automatic start. In this way, at
an automatic-start time of the engine 11, the engine 11 can be
automatically started at a valve lift quantity suitable for the
automatic start. It is thus possible to improve the automatic-start
characteristic of the engine 11 and reduce exhaust emissions at the
automatic-start time.
[0150] As described above, right after an automatic stop of the
engine 11, first of all, the valve lift quantities of the intake
valve 28 and the exhaust valve 29 are each set at a valve lift
quantity presumed to be suitable for a next automatic start. Then,
right before the automatic start of the engine 11, the valve lift
quantities of the intake valve 28 and the exhaust valve 29 are each
corrected to a valve lift quantity optimum for the automatic start.
Thus, when the engine 11 is automatically started, the magnitudes
of corrections for correcting the valve lift quantities are small
so that the valve lift quantities of the intake valve 28 and the
exhaust valve 29 can each be corrected to a valve lift quantity
optimum for an automatic start in a short period of time. In
addition, even if the valve lift quantities each set during the
automatic stop of the engine 11 at a valve lift quantity presumed
to be suitable for the next automatic start inevitably deviates
from a condition optimum for the next automatic start due to the
fact that the state of the engine 11 and/or the state of the
vehicle have greatly changed during the automatic stop of the
engine 11, the valve lift quantities of the intake valve 28 and the
exhaust valve 29 can each be corrected to a valve lift quantity
optimum for the automatic start when the engine 11 is automatically
started.
[0151] On the other hand, the time charts shown in FIG. 13 are time
charts of typical control, which is executed when an engine
cooling-water temperature Tw is determined to be lower than a
predetermined value and the catalyst 23 is determined to have not
been activated. In this case, when the automatic stop conditions
are satisfied during an operation of the engine 11, the engine 11
is automatically stopped. Right after the engine 11 is
automatically stopped, since the engine cooling-water temperature
Tw is determined to be lower than the predetermined value and the
catalyst 23 is determined to have not been activated, the target
valve lift quantities VLstop of the intake valve 28 and the exhaust
valve 29 for the engine automatic-stop time are set at a valve lift
quantity such as 0 or a minimum value making it difficult for
residual gas left in the cylinders to leak, out in order to attach
importance to reduction of exhaust emissions generated during the
automatic stop of the engine 11. After the valve lift quantities
VLstop for the intake valve 28 and the exhaust valve 29 are
controlled their respective target valve lift quantities VLstop for
the engine automatic-stop time, which have each been set at a valve
lift quantity making it difficult for residual gas left in the
cylinders to leak out, the execution of the control of the
variable-valve lift mechanisms 30 and 31 is ended. In this way,
during the automatic stop of the engine 11 with the catalyst 23 put
in an inactivated state, the variable-valve lift mechanisms 30 and
31 are halted with the valve lift quantities of the intake valve 28
and the exhaust valve 29 set at their respective target valve lift
quantities VLstop, which have each been set at a valve lift
quantity making it difficult for residual gas left in the cylinders
to leak out. Thus, when the catalyst 23 is still in an inactivated
state, residual gas left in the cylinders can be prevented from
leaking out during the automatic stop of the engine 11 so that it
is possible to reduce exhaust emissions generated during the
automatic stop of the engine 11.
[0152] When the automatic start conditions are satisfied during the
automatic stop of the engine 11, target valve lift quantities
VLstart of the intake valve 28 and the exhaust valve 29 for the
engine automatic-start time are each set at a valve lift quantity
presumed to be optimum for the automatic start on the basis of an
engine-cooling-water temperature Tw detected immediately before the
automatic start and on the basis of other information. Then, after
the valve lift quantities of the intake valve 28 and the exhaust
valve 29 are corrected from their respective target valve lift
quantities VLstop for the engine automatic-stop time to their
respective target valve lift quantities VLstart for the engine
automatic-start time, the engine 11 is automatically started. The
target valve lift quantities VLstop for the engine automatic-stop
time are each a valve lift quantity presumed to be suitable for an
automatic start. On the other hand, the target valve lift
quantities VLstart for the engine automatic-start time are each a
valve lift quantity optimum for the automatic start. In this way,
at an automatic-start time of the engine 11, the engine 11 can be
automatically started at a valve lift quantity suitable for the
automatic start. When the catalyst 23 is still in an inactivated
state, it is thus possible to improve the automatic-start
characteristic of the engine 11 while reducing exhaust emissions at
the automatic-start time.
[0153] The time charts shown in FIG. 14 are time charts of typical
control executed in the event of an engine stall caused by a
failure of an automatic start of the engine 11. In this case, in
the event of an engine stall, the target valve lift quantity
VLstart set for the intake valve 28 to be used at an
automatic-start time of the engine 11 is increased by a
predetermined valve lift quantity increment .DELTA.VL in a
correction process to increase the intake airflow. Then, after
correcting the target valve lift quantity VLstart for the
automatic-start time of the engine 11, variable-valve lift control
is executed to control the variable-valve lift mechanism 30 of the
intake valve 28 so that the valve lift quantity of the intake valve
28 is adjusted to the corrected target valve lift quantities
VLstart. At a point of time the valve lift quantity of the intake
valve 28 becomes equal to the corrected target valve lift quantity
VLstart, automatic start control is re-executed to automatically
start the engine 11.
[0154] Thus, even in the event of an engine stall caused by a
failure of an automatic start of the engine 11, at an automatic
restart time, automatic start control of the engine 11 can be
executed with a valve lift quantity corrected to a value greater
than a valve lift quantity at the time of the engine stall, that
is, corrected in a direction of increasing the intake airflow. As a
result, the engine stall can be prevented from being generated
several times consecutively, and the engine can therefore be
restarted successfully at an early time.
[0155] In addition, in this embodiment, by using at least one of
pieces of temperature information for determining a temperature of
the engine 11 or the battery and pieces of information for
determining performance of the battery, a target valve lift
quantity VLstop for an engine automatic-stop time and a target
valve lift quantity VLstart for an engine automatic-start time are
found. The pieces of temperature information include the
temperature of the engine cooling water, the temperature of intake
air, the ambient temperature and the temperature of the oil while
the pieces of information for determining performance of the
battery include the number of engine automatic stops carried out so
far or the number of engine automatic starts carried out so far. As
described above, the target valve lift quantity VLstop for an
engine automatic-stop time is a valve lift quantity presumed to be
suitable for the next automatic start. Thus, in order to cope with
the fact that the performance of the battery is poor at a low
temperature of the battery, decreasing the driving power of the
starter, causing greater frictions among movable parts and, hence,
making the cranking of the automatic-start time of the engine 11
prone to variations, the target valve lift quantity is corrected in
a direction of stabilizing the cranking such as a direction of
increasing the intake airflow at the automatic-start time of the
engine 11.
[0156] As described above, in this embodiment, the target valve
lift quantity VLstop for an engine automatic-stop time is changed
from a valve lift quantity presumed to be suitable for the next
automatic start to a valve lift quantity making it difficult for
residual gas left in the cylinders to leak out and vice versa in
dependence on an activation state of the catalyst 23 or a
temperature of the engine cooling-water. It is to be noted,
however, that the target valve lift quantity VLstop for an engine
automatic-stop time can also be fixed at a valve lift quantity
presumed to be suitable for the next automatic start or a valve
lift quantity making it difficult for residual gas left in the
cylinders to leak out.
[0157] In addition, this embodiment executes both the control to
adjust the valve lift quantity to the target valve lift quantity
VLstop for an engine automatic-stop time in an automatic stop of
the engine 11 and the control to adjust the valve lift quantity to
the target valve lift quantity VLstart for an engine
automatic-start time in an automatic start of the engine 11.
However, only one of them can also be executed.
[0158] Furthermore, this embodiment uses a stepping motor as a
means for driving the variable-valve lift mechanisms 30 and 31.
However, as the means for driving the variable-valve lift
mechanisms 30 and 31, a means other than the stepping motor can
also be employed. Examples of the other means are an
electromagnetic actuator and an oil-pressure actuator. As an
alternative, by directly driving the intake valve and/or the
exhaust valve by using an electromagnetic actuator, valve operation
characteristics can be changed. The valve operation characteristics
include the valve lift quantity and the valve timing.
[0159] Moreover, while this embodiment applies the present
invention to a system for changing the operation characteristics of
the intake valve and the exhaust valve, this embodiment may also
apply the present invention to a system for changing the operation
characteristics of the intake valve only.
[0160] Second Embodiment
[0161] Next, a second embodiment of the present invention is
explained. The second embodiment has the same configuration as that
shown in FIG. 1. In the case of the second embodiment, however,
processing represented by a flowchart shown in FIG. 15 is carried
out as a substitute for the first embodiment's processing
represented by the flowchart shown in FIG. 8. The other control
processing of the first embodiment is also carried out by the
second embodiment.
[0162] An automatic-start control program stored in a ROM and
represented by the flowchart shown in FIG. 15 is executed by the
ECU 27 to automatically start the engine 11 when predetermined
automatic-start conditions are satisfied in an automatic-stop state
of the engine 11 with a timing shown in time charts of FIG. 17.
Then, till the time lapsing since the completion of the automatic
start of the engine 11 exceeds a variable-valve control prohibition
time KCAST, the valve lift quantities of the intake valve 28 and
the exhaust valve 29 are fixed at their respective target valve
quantities for the automatic-start time, and the control of the
intake airflow based on the intake the variable-valve lift control
is prohibited. Instead, the intake airflow is controlled by
adjusting the opening of the throttle valve 15 in the mean
time.
[0163] The following description explains processing carried out by
the ECU 27 by execution of the automatic-start control program
represented by the flowchart shown in FIG. 15. The automatic-start
control program represented by the flowchart shown in FIG. 15 is
executed repeatedly at predetermined time intervals during an
automatic stop of the engine 11. The processing carried out at the
steps 201 to 205 is the same as that carried out at the steps 201
to 205 of the first embodiment.
[0164] After completion of the step 203, the flow of the program
goes on to a step 204 to determine whether or not the valve lift
quantities of the intake valve 28 and the exhaust valve 29 have
been adjusted to their respective target valve lift quantities
VLstart. At a point of time the valve lift quantities of the intake
valve 28 and the exhaust valve 29 become equal to their respective
target valve lift quantities VLstart, the flow of the program goes
on to a step 205 at which automatic start control is executed to
turn on the starter and to start the engine 11 automatically. The
processing of the step 205 is carried out to play the role of an
automatic-start control means.
[0165] At the next step 226, the valve lift quantities of the
intake valve 28 and the exhaust valve 29 are fixed at their
respective target valve quantities for the automatic-start time
after completion of the automatic start of the engine 11. The
control of the intake airflow based on the intake the
variable-valve lift control is prohibited. Instead, throttle-valve
control is started to control the intake airflow by adjusting the
opening of the throttle valve 15.
[0166] The flow of the program goes on to a step 227 to determine
whether or not the time CAST lapsing since the completion of the
automatic start of the engine 11 has exceeded the variable-valve
control prohibition time KCAST. The variable-valve control
prohibition time KCAST is set at a period of time it takes to
stabilize the operating state to a certain degree. The time
required to stabilize the operating state is a period of time
lapsing since the completion of the automatic start of the engine
11. This period includes complicated and much variable transient
times. In this case, in order to make the processing simple, the
variable-valve control prohibition time KCAST can be set at a fixed
value determined in advance. As an alternative, a variable-valve
control prohibition time KCAST can be determined by searching the
variable-valve control prohibition time KCAST's map like one shown
in FIG. 16 for a particular value dependent on the number of
automatic stops carried out so far since the start of the running
state of the vehicle (that is, an automatic stop count NS) or the
number of automatic starts carried out so far since the start of
the running state of the vehicle (that is, an automatic start count
NR). That is, the variable-valve control prohibition time KCAST is
set at the particular value.
[0167] The larger the automatic stop count NS or the automatic
start count NR, the more frequently adverse effects such as
deterioration of the drivability and deterioration of exhaust
emissions are experienced. Such deteriorations are caused by the
variable-valve lift control. In accordance with the map shown in
FIG. 16, the larger the automatic stop count NS or the automatic
start count NR, the larger the value at which the variable-valve
control prohibition time KCAST is set. Thus, the number of adverse
effects caused by the variable-valve lift control can be reduced.
It is to be noted that, in accordance with the typical map shown in
FIG. 16, in a zone where the automatic stop count NS or the
automatic start count NR is smaller than a predetermined value A,
the variable-valve control prohibition time KCAST is set at a fixed
value, which is a lower limit. In a zone where the automatic stop
count NS or the automatic start count NR is greater than another
predetermined value B, on the other hand, the variable-valve
control prohibition time KCAST is set at another fixed value, which
is an upper limit.
[0168] If the determination result obtained at the step 227
indicates that the time CAST lapsing since the completion of the
automatic start of the engine 11 has not exceeded the
variable-valve control prohibition time KCAST, the flow of the
program goes back to the step 226. The processing of the steps 226
and 227 is carried out to play the roles of a variable-valve
control prohibition means and a throttle-valve control means.
[0169] At a point of time the determination result obtained at the
step 227 indicates that the time CAST lapsing since the completion
of the automatic start of the engine 11 has exceeded the
variable-valve control prohibition time KCAST, the flow of the
program goes back to the step 228 at which the variable-valve
control is permitted and the throttle-valve control is ended. In
consequence, after the time CAST lapsing since the completion of
the automatic start of the engine 11 exceeds the variable-valve
control prohibition time KCAST, the valve lift quantities of the
intake valve 28 and the exhaust valve 29 are continuously changed
in accordance with information such as an accelerator position and
an operating state of the engine 11 in order to control the intake
airflow. In the course of the intake-air-flow control based on the
control of the variable-valve lift quantities, the throttle valve
15 is fixed typically at a completely opened position to reduce the
resistance of intake air.
[0170] It is to be noted that, in a system employing a variable
valve timing mechanism in conjunction with the variable-valve lift
mechanisms 30 and 31, before the time CAST lapsing since the
completion of the automatic start of the engine 11 exceeds the
variable-valve control prohibition time KCAST, the valve lift
quantities can be fixed at their respective target valve lift
quantities for the automatic-start time of the engine 11 and the
valve timings can be fixed at their respective target valve timings
for the automatic-start time of the engine 11.
[0171] In the case of the embodiment described above, before the
time CAST lapsing since the completion of the automatic start of
the engine 11 exceeds the variable-valve control prohibition time
KCAST, the valve lift quantities of the intake valve 28 and the
exhaust valve 29 are fixed and the intake-air-flow control based on
the control of the variable-valve lift quantities is prohibited.
Instead, the intake airflow is controlled by adjusting the opening
of the throttle valve 15. Thus, during a period including
complicated and much variable transient times right after an
automatic start of the engine 11, by using the conventional system,
the field-proven throttle-valve control can be executed as the
control of the intake airflow in order to adjust the intake airflow
in a stable manner. As a result, after the automatic start of the
engine 11, deterioration of the drivability and deterioration of
exhaust emissions can be avoided.
[0172] In addition, in the case of this embodiment, after
completion of an automatic start of the engine 11, the valve lift
quantities of the intake valve 28 and the exhaust valve 29 are
fixed at their respective target valve lift quantities for the
automatic-start time of the engine 11 or for a time prior to the
completion of the automatic start of the engine 11. Thus, before
and after the completion of the automatic start of the engine 11,
the valve lift quantities can each be sustained at a fixed value to
eliminate variations in valve lift quantities. As a result, a
torque shock and/or deterioration of exhaust emissions can be
prevented from occurring due to changes in valve lift
quantities.
[0173] It is to be noted that the fixed values at which the valve
lift quantities are sustained after the automatic start of the
engine 11 do not have to be the target valve lift quantities for
the automatic-start time of the engine 11. Instead, the fixed
values at which the valve lift quantities are sustained after the
automatic start of the engine 11 can be each a constant determined
in advance or found by using a map, a formula or the like in
dependence on operating states for the automatic-start time of the
engine 11, which include a temperature of the cooling water, a
temperature of the oil, an ambient temperature and an automatic
halt period of the engine 11.
[0174] In addition, in the case of this embodiment, a map used for
finding a variable-valve control prohibition time KCAST is created
in such a way that, the larger the automatic stop count NS or the
automatic start count NR, the larger the value at which the
variable-valve control prohibition time KCAST is set. After the
start of a running state of the vehicle, the automatic stop count
NS or the automatic start count NR is small so that adverse effects
such as deterioration of exhaust emissions and deterioration of the
drivability, which are caused by the variable-valve lift control,
are experienced less frequently. Thus, after the start of a running
state of the vehicle, the variable-valve control prohibition time
KCAST is set at a small value so as to start the variable-valve
lift control from an early time after an automatic start of the
engine 11. By starting the variable-valve lift control from an
early time, it is possible to let the improvement of the
performance such as improvement of the fuel economy resulting from
the variable-valve lift control take precedence of others. Then, as
the automatic stop count NS or the automatic start count NR
increases after the start of a running state of the vehicle so that
the adverse effects caused by the variable-valve lift control are
experienced more frequently, the variable-valve control prohibition
time KCAST is set at a large value so as to let avoidance of the
adverse effects caused by the variable-valve lift control take
precedence of the improvement of the performance by execution the
variable-valve lift control.
[0175] As described above, this embodiment uses a stepping motor as
a means for driving the variable-valve lift mechanisms 30 and 31.
It is to be noted, however, that, as the means for driving the
variable-valve lift mechanisms 30 and 31, a means other than the
stepping motor can also be employed. Examples of the other means
are an electromagnetic actuator and an oil-pressure actuator. As an
alternative, by directly driving the intake valve and/or the
exhaust valve by using an electromagnetic actuator, valve operation
characteristics can be changed. The valve operation characteristics
include the valve lift quantity and the valve timing.
[0176] In addition, while this embodiment applies the present
invention to a system for changing the operation characteristics of
the intake valve and the exhaust valve, this embodiment may also
apply the present invention to a system for changing the operation
characteristics of the intake valve only.
[0177] Third Embodiment
[0178] Next, a third embodiment of the present invention is
explained. The third embodiment has the same configuration as that
shown in FIG. 1. In the case of the third embodiment, however,
processing represented by a flowchart shown in FIG. 18 is carried
out as a substitute for the first embodiment's processing
represented by the flowchart shown in FIG. 8. The other control
processing of the first embodiment is also carried out by the third
embodiment.
[0179] An automatic-start control program stored in a ROM and
represented by the flowchart shown in FIG. 18 is executed by the
ECU 27 to automatically start the engine 11 when predetermined
automatic-start conditions are satisfied in an automatic-stop state
of the engine 11. It is to be noted that, at that time, the
variable-valve lift mechanisms 30 and 31 are each set at a position
proper for a restart operation.
[0180] The ECU 27 executes the automatic-start control program
represented by the flowchart shown in FIG. 18 to accompany an
automatic stop of the engine 11. The automatic-start control
program represented by the flowchart shown in FIG. 18 is executed
repeatedly at predetermined time intervals based on a count value
of typically a counter not shown in the figure. When the program is
invoked, the flowchart begins with a step 201 to determine whether
or not the automatic-start conditions are satisfied.
[0181] If a determination result obtained at the step 201 is an
acknowledgement, the flow of the program goes on to a step 232. At
the step 232, the voltage VB of the battery 41 mounted on the
vehicle is compared with a voltage criterion value KVBAT.
[0182] The voltage criterion value KVBAT is a value set for the
following reason. If the voltage VB of the battery 41 is low so
that a voltage applied to a stepping motor for rotating the control
shaft 35 is not sufficient, the responsiveness of the stepping
motor deteriorates even if valve lift control is executed on the
basis of, among others, an operating state. If the responsiveness
of the stepping motor deteriorates, the rotation of the control
shaft 35 is inevitably late, being incapable of following a target
valve lift quantity. Thus, a target intake airflow cannot be
obtained. As a result, exhaust emissions unavoidably worsen. For
this reason, the voltage criterion value KVBAT is set at a value to
be used as a criterion for determining whether or not the problem
described above arises.
[0183] If a comparison result obtained at the step 232 indicates
that the voltage VB of the battery 41 is equal to or higher than
the voltage criterion value KVBAT, the flow of the program goes on
to a step 234 by way of a step 233. The processing of these steps
is carried out to execute variable-valve lift quantity control
right after the restart of the engine 11. The variable-valve lift
quantity control can be executed right after the restart of the
engine 11 because the voltage VB of the battery 41 is sufficiently
high. Specifically, first of all, target positions of the intake
and exhaust valves 28 and 29 are found at the step 233. The target
positions of the intake and exhaust valves 28 and 29 are target
valve lift positions of the intake and exhaust valves 28 and 29 for
the restart time of the engine 11. The target positions of the
intake and exhaust valves 28 and 29 are found by using typically a
map or a formula in dependence on operating states for the restart
time of the engine 11. The operating states include a temperature
of the cooling water, a temperature of the oil, an ambient
temperature and a stop period of the engine 11.
[0184] After the target positions of the intake and exhaust valves
28 and 29 are found, the variable-valve lift quantity control is
executed at the step 234. Specifically, the variable-valve lift
mechanism 30 of the intake valve 28 and the variable-valve lift
mechanism 31 of the exhaust valve 29 are controlled so that the
valve lift positions of the intake and exhaust valves 28 and 29 are
brought to the target positions of the intake and exhaust valves 28
and 29 for the restart time of the engine 11 before the execution
of the program is ended.
[0185] If the comparison result obtained at the step 232 indicates
that the voltage VB of the battery 41 is lower than the voltage
criterion value KVBAT, on the other hand, the flow of the program
goes on to a step 236 by way of a step 235. At the step 235, the
variable-valve lift quantity control is prohibited before the flow
of the program goes on to the step 236. At the step 236, a target
intake airflow is found by using typically a map or a formula in
dependence on operating states for the restart time of the engine
11. The operating states include a temperature of the cooling
water, a temperature of the oil, an ambient temperature and a stop
period of the engine 11. Then, control is executed to drive the
throttle valve 15 so that the intake airflow into a combustion
chamber is brought to the target intake airflow.
[0186] As described above, if the voltage VB of the battery 41 is
lower than the voltage criterion value KVBAT, the intake airflow
control by using the intake valve 28 is prohibited. Instead,
control by using the throttle valve 15 is executed.
[0187] Next, typical operations of the embodiment are explained by
referring to time charts shown in FIG. 19. An idle stop execution
flag shown in a column (a) in FIG. 19 is a flag indicating an
automatic stop operation or a restart operation of the engine 11.
First of all, at a time T1, the idle stop execution flag is turned
on and the engine 11 is automatically stopped by halting operations
such as the fuel injection control and the ignition control. The
engine speed NE decreases to 0 rpm at a time T2 as shown in a
column (b) in FIG. 19. At the time T1, the opening of the throttle
valve 15 is restored to a completely closed position as shown in a
column (d) in FIG. 19.
[0188] At the time T2, when the engine 11 is stopped as evidenced
by an engine speed NE of 0 rpm, the variable-valve lift mechanism
30 is set to take the lift quantity of the intake valve 28 to a
lift quantity suitable for a restart of the engine 11 as shown in a
column (d) in FIG. 19. Then, at a time T3, when the lift quantity
of the intake valve 28 is set at a position suitable for a restart
of the engine 11, a variable-valve lift quantity control execution
flag is set at an OFF state as shown in a column (f) in FIG.
19.
[0189] Then, at a time T4, the engine 11 is automatically started
at a request made by the driver. For example, when a starter flag
is turned on as shown in a column (g) in FIG. 19, the idle stop
execution flag shown in the column (a) in FIG. 19 is turned off to
commence the restart operation of the engine 11. In the case of
this embodiment, if the voltage VB of the battery 41 is lower than
the voltage criterion value KVBAT as shown in a column (c) in FIG.
19, the variable-valve lift quantity control of the intake valve 28
is prohibited and the intake airflow control is executed by using
the throttle valve 15 as shown in a column (e) in FIG. 19. Then, as
the voltage VB of the battery 41 exceeds the voltage criterion
value KVBAT at a time T6, the throttle valve 15 is fixed at a
predetermined opening and the variable-valve lift quantity control
of the intake valve 28 is executed. In this way, it is possible to
implement intake airflow control with good responsiveness.
[0190] As described above, if the voltage VB of the battery 41 is
lower than the voltage criterion value KVBAT, the variable-valve
lift quantity control of the intake valve 28 is prohibited to
inhibit the execution of the intake airflow control based on the
variable-valve lift quantity control. Thus, even if the precision
of the variable-valve lift quantity control becomes poor due to a
low voltage VB of the battery 41, deteriorations of exhaust
emissions can be suppressed because the variable-valve lift
mechanisms 30 and 31 are fixed.
[0191] Fourth Embodiment
[0192] Next, a fourth embodiment of the present invention is
explained. The fourth embodiment has the same configuration as that
shown in FIG. 1. In the case of the fourth embodiment, however,
processing represented by a flowchart shown in FIG. 20 is carried
out as a substitute for the first embodiment's processing
represented by the flowchart shown in FIG. 6. The other control
processing of the first embodiment is also carried out by the
fourth embodiment.
[0193] The ECU 27 executes automatic stop control programs shown in
FIGS. 20, 21, 24 and 25. In an operation to automatically stop the
engine 11, the engine speed NE is gradually reduced as shown in
time charts of FIG. 26 in order to give no sense of incompatibility
to the driver. In order to gradually reduce the engine speed NE, it
is necessary to gradually decrease a torque output by the engine
11. In order to gradually decrease the torque output by the engine
11, it is necessary to gradually reduce the input airflow QA and
the fuel injection volume TAU as shown in the same flowcharts. When
the engine speed NE is decreased to a resonant revolution speed
zone, torque abrupt reduction control is executed to abruptly
decrease the torque output by the engine 11. The torque abrupt
reduction control is executed by abruptly reducing the input
airflow QA and ending the injection of fuel by adjustment of the
variable-valve mechanism 30 and the throttle valve 15. By executing
the torque abrupt reduction control at the time the engine speed NE
is decreased to the resonant revolution speed zone, the engine
speed NE can pass through the resonant revolution speed zone in a
short period of time. The resonant revolution speed zone is the
engine speed NE's zone in which the vibration of the engine 11 is
resonant with the vibration of the vehicle-driving system. The
resonant revolution speed zone is typically the revolution speed
range 300 to 400 rpm. FIG. 27 shows a graph representing a relation
between the engine speed NE and the magnitude of a noise.
[0194] The following description explains processing carried out by
the ECU 27 by execution of the programs.
[0195] Automatic Stop Control
[0196] The automatic stop control program represented by the
flowchart shown in FIG. 20 is executed repeatedly at predetermined
intervals after a request for a stop of the engine 11 is made when
predetermined automatic stop control conditions are satisfied
during an operation of the engine 11. The program is executed to
play the role of an automatic stop control means. When the program
is invoked, the flowchart begins with a step 141 to determine
whether or not the engine 11 is in a state prior to an automatic
stop process of the engine 11 or prior to completion of the an
automatic stop process of the engine 11 by typically determining
whether or not the engine speed NE is higher than a criterion value
for the completion of the automatic stop. If the engine 11 is in an
automatic stop process of the engine 11, the flow of the program
goes on to a step 142 to determine whether or not the engine speed
NE is in the resonant revolution speed zone or even lower than the
zone. A criterion range used in the determination of the step 142
can be made greater than the resonant revolution speed zone to a
certain degree in order to provide a small margin to the
determination. In a word, the criterion range needs to include a
resonant revolution speed, which increases the amplitude of
vibration of the engine 11, the amplitude of vibration of the
vehicle-driving system and the magnitude of a noise when the
frequency of the vibration of the engine 11 matches the
characteristic frequency of the vibration of the vehicle-driving
system.
[0197] If a determination result obtained at the step 142 indicates
that the engine speed NE has not decreased to a value in the
resonant revolution speed zone, torque gradual reduction control is
executed at steps 143 and 144. The torque gradual reduction control
begins with the step 143 at which an intake airflow gradual
reduction control program represented by the flowchart shown in
FIG. 21 is executed to gradually reduce the intake airflow QA.
Then, at the next step 144, a fuel injection volume gradual
reduction control program represented by the flowchart shown in
FIG. 24 is executed to gradually reduce the fuel injection volume
TAU. In this way, the torque output by the engine 11 can be
gradually decreased to gradually reduce the engine speed NE without
providing a sense of incompatibility to the driver.
[0198] If a determination result obtained at the step 142 in a
later execution of the automatic stop control program represented
by the flowchart shown in FIG. 20 indicates that the engine speed
NE has decreased to a value in the resonant revolution speed zone
or a value lower than the zone, on the other hand, torque abrupt
reduction control is executed at steps 145 and 146. The torque
abrupt reduction control begins with the step 145 at which an
intake airflow abrupt reduction control program represented by the
flowchart shown in FIG. 25 is executed to abruptly reduce the
intake airflow QA. Then, at the next step 146, injection of fuel is
ended. In this way, the torque output by the engine 11 can be
abruptly decreased to abruptly reduce the engine speed NE so that
the engine speed NE can pass through resonant revolution speed zone
in a short period of time.
[0199] Intake Airflow Gradual Reduction Control
[0200] When the intake airflow gradual reduction control program
represented by the flowchart shown in FIG. 21 is invoked at the
step 143 of the flowchart shown in FIG. 20, the flowchart shown in
FIG. 21 begins with a step 143a at which a target intake airflow
gradual reduction quantity FQA is found for the present engine
speed NE and the present intake airflow QA by using a formula or a
map prepared for the target intake airflow gradual reduction
quantity FQA as shown in FIG. 22. The map of target intake airflow
gradual reduction quantity FQA shown in FIG. 22 is created so that,
the lower the engine speed NE, the smaller the target intake
airflow gradual reduction quantity FQA and, the smaller the intake
airflow QA, the smaller the target intake airflow gradual reduction
quantity FQA.
[0201] After a target intake airflow gradual reduction quantity FQA
is found, the flow of the program goes on to a step 143b at which a
target valve lift quantity VL of the intake valve 28 is found for
the present engine speed NE and a target intake airflow by using a
formula or a map prepared for the target valve lift quantity VL of
the intake valve 28 as shown in FIG. 23. The target intake airflow
is a difference between the present intake airflow QA and the
target intake airflow gradual reduction quantity FQA. The target
valve lift quantity VL's map shown in FIG. 23 is created so that,
the lower the engine speed NE, the smaller the target valve lift
quantity VL and, the smaller the target intake airflow, that is,
the smaller the difference between the present intake airflow QA
and the target intake airflow gradual reduction quantity FQA, the
smaller the target valve lift quantity VL.
[0202] After the target valve lift quantity VL is computed, the
flow of the program goes on to a step 143c at which the
variable-valve control is executed to control the variable-valve
lift mechanism 30 of the intake valve 28 so as to take the valve
lift quantity of the intake valve 28 to the target valve lift
quantity VL.
[0203] It is to be noted that, in a system employing a variable
valve timing mechanism in conjunction with the variable-valve lift
mechanism 30, at a step 202, a target valve lift quantity VL and a
target valve timing VT are computed. Then, at the next step 203,
the variable-valve lift mechanism 30 of the intake valve 28 is
controlled so as to take the valve lift quantity of the intake
valve 28 to the target valve lift quantity VL and the variable
valve timing mechanism of the intake valve 28 can be controlled so
as to take the variable valve timing of the intake valve 28 to the
target variable valve timing VT.
[0204] By carrying the processing described above repeatedly, the
variable-valve lift mechanism 30 of the intake valve 28 or both the
variable-valve lift mechanism 30 and the variable valve timing
mechanism of the intake valve 28 are controlled so as to gradually
reduce the input airflow QA by the target intake airflow gradual
reduction quantity FQA at one time.
[0205] Fuel Injection Volume Gradual Reduction Control
[0206] When the fuel injection volume gradual reduction control
program shown in FIG. 24 is invoked at the step 144 of the
flowchart shown in FIG. 20, a fuel injection volume TAU that takes
the air-fuel ratio to a target air-fuel ratio A/F is computed by
using the present intake airflow QA and the target air-fuel ratio
A/F, which is typically set at the stoichiometric air-fuel ratio.
Thus, when the intake airflow gradual reduction control program
represented by the flowchart shown in FIG. 21 is executed to
gradually reduce the intake airflow, the fuel injection volume TAU
is also gradually reduced while the air-fuel ratio is being
sustained at the target air-fuel ratio A/F, which is typically the
stoichiometric air-fuel ratio, so that the torque output by the
engine 11 and, hence, the engine speed NE are gradually
reduced.
[0207] Intake Airflow Abrupt Reduction Control
[0208] When the fuel injection volume abrupt reduction control
program shown in FIG. 25 is invoked at the step 145 of the
flowchart shown in FIG. 20, first of all, at a step 145a, the
target valve lift quantity VL of the intake valve 28 is set at a
minimum value (>0). Then, at the next step 145b, the
variable-valve control is executed to control the variable-valve
lift mechanism 30 of the intake valve 28 so as to take the valve
lift quantity of the intake valve 28 to the target valve lift
quantity VL, which has been set at the minimum value.
[0209] It is to be noted that, in a system employing a variable
valve timing mechanism in conjunction with the variable-valve lift
mechanism 30, at a step 145a, a target valve lift quantity VL and a
target valve timing VT that minimize the intake airflow QA are
computed. Then, at the next step 145b, the variable-valve lift
mechanism 30 of the intake valve 28 is controlled so as to take the
valve lift quantity of the intake valve 28 to the target valve lift
quantity VL and the variable valve timing mechanism of the intake
valve 28 can be controlled so as to take the variable valve timing
of the intake valve 28 to the target variable valve timing VT.
[0210] Then, the flow of the program goes on to a step 145c at
which the target throttle opening of the throttle valve 15 is set
at 0 to completely close the throttle valve 15. Subsequently, at
the next step 145d, throttle-valve control is executed to adjust
the throttle valve 15 so as to take the throttle opening to the
target throttle opening of the throttle valve 15, which has been
set at 0 to completely close the throttle valve 15. By carrying out
the above processing, the intake airflow QA can be reduced
abruptly.
[0211] In the case of the embodiment described above, in the intake
air quantity control based on the variable-valve control, attention
paid to the fact that the responsiveness of the intake air quantity
control is improved without incurring a response delay of an air
system leads to abrupt reduction of the intake airflow QA by
execution of the variable-valve control at the time the engine
speed NE decreases to the resonant revolution speed area in the
course of an operation to automatically stop the engine 11. The air
system starts from the throttle valve 15 and ends at the cylinders.
Thus, with a timing of the engine speed NE decreasing to the
resonant revolution speed area, the intake airflow QA into a
cylinder can be decreased abruptly with good responsiveness so that
the engine speed NE can also be abruptly decreased in the resonant
revolution speed area. Thus, at an execution time of the automatic
stop control, the engine speed NE can pass through the resonant
revolution speed area in a short period of time. As a result, it is
possible to reduce the amplitude of vibration and the magnitude of
a noise, which are caused by the resonance phenomenon, as well as
make the driver feel no sense of incompatibility.
[0212] In addition, in the case of this embodiment, at an execution
time of torque abrupt reduction control, the variable-valve lift
mechanism 30 is controlled to establish a valve operation
characteristic minimizing the intake airflow QA, and the throttle
valve 15 is completely closed. An example of the valve operation
characteristic minimizing the intake airflow QA is a state in which
the valve lift quantity is equal to a minimum value. Thus, both the
variable-valve control and the throttle-valve control can be
effectively utilized to set the intake airflow QA into a cylinder
at 0 quickly and, hence, reduce the output torque abruptly. By
adopting this control technique, even in a system incapable of
controlling the intake valve 28 to a completely closed state, the
resonant revolution speed area can be passed through in a short
period of time so that it is possible to reduce the amplitude of
vibration and the magnitude of a noise, which are caused by the
resonance phenomenon.
[0213] Furthermore, in the case of this embodiment, injection of
fuel is halted at an execution time of the torque abrupt reduction
control. Thus, both the abrupt reduction of the intake airflow and
the termination of the fuel injection can effectively decrease the
engine speed abruptly.
[0214] Moreover, in the case of this embodiment, the fuel injection
volume is adjusted so as to take the air-fuel ratio to a target
air-fuel ratio A/F at an execution time of the torque gradual
reduction control. Thus, at the execution time of the torque
gradual reduction control, the air-fuel ratio can be sustained at
the target air-fuel ratio A/F. As a result, the engine speed can be
reduced gradually without deteriorating exhaust emissions.
[0215] In addition, in the case of this embodiment, the intake
airflow QA is gradually decreased by execution of the
variable-valve control at an execution time of the torque gradual
reduction control. Thus, the intake airflow QA into a cylinder can
be gradually reduced with good responsiveness at the execution time
of the torque gradual reduction control in order to decrease the
output torque gradually with a high degree or reliability.
[0216] It is to be noted that the torque gradual reduction control
raises a small problem of a response delay incurred in the air
system in comparison with the torque abrupt reduction control.
Thus, the intake airflow QA can be gradually reduced by executing
only the torque gradual reduction control. It is needless to say,
nevertheless that, at an execution time of the torque gradual
reduction control, both the variable-valve control and the
throttle-valve control can be executed to reduce the intake airflow
QA gradually.
[0217] Moreover, this embodiment has a configuration wherein the
variable-valve lift mechanism 30 cannot be controlled to put the
intake valve 28 in a completely closed state, that is, a state with
a valve lift quantity of 0. In the case of a system having a
variable-valve lift mechanism controllable to put the intake valve
28 in a completely closed state, however, the variable-valve lift
mechanism can be controlled to put the intake valve 28 in a
completely closed state, that is, a state with a valve lift
quantity of 0, at an execution time of the torque abrupt reduction
control. The intake airflow QA into a cylinder can be set at 0
instantaneously to abruptly reduce the engine speed at an execution
time of the torque abrupt reduction control. Thus, the resonant
revolution speed area can be passed through in a short period of
time so that it is possible to substantially reduce the amplitude
of vibration and the magnitude of a noise, which are caused by the
resonance phenomenon.
[0218] It is to be noted that, in the case of this embodiment, in a
small lift mode, the position of the control shaft 35 is set so as
to set a point of contact with the link arm 34 at the position of
the eccentric cam 36, that is, a position at a shortest distance
from the axial center of the control shaft 35 as shown in FIG. 4.
For this small lift mode, the curvature of the bottom surface range
of the pressure cam 39, that is, the bottom surface range in
contact with the roller 40, is designed into a curvature at which
the pressure cam 39 does not bend the roller 40 downward. Thus, in
the small lift mode, the pressure cam 39 never bends the roller 40
downward even when the cam 37 of the cam shaft 32 shifts the
reciprocating cam 38 horizontally. As a result, the lift quantity
of the intake valve 28 can be set at 0. In such a configuration, by
setting the variable-valve lift mechanism 30 in the small lift mode
when the engine speed NE passes through the resonant revolution
speed area in an operation to automatically stop the engine 11, the
intake airflow can be set at 0 so that the resonant revolution
speed area can be passed through in a short period of time.
[0219] Furthermore, in the case of this embodiment, the throttle
valve 15 is provided on the intake pipe 12. However, the throttle
valve 15 can be eliminated and the intake airflow can be controlled
by using only the variable-valve mechanism.
[0220] In addition, in the case of this embodiment, a stepping
motor is used as a means for driving the variable-valve lift
mechanism 30. However, as the means for driving the variable-valve
lift mechanism 30, a means other than the stepping motor can also
be employed. Examples of the other means are an electromagnetic
actuator and an oil-pressure actuator. As an alternative, by
directly driving the intake valve and/or the exhaust valve by using
an electromagnetic actuator, valve operation characteristics can be
changed. The valve operation characteristics include the valve lift
quantity and the valve timing.
[0221] Moreover, while this embodiment applies the present
invention to a system for changing the operation characteristics of
the intake valve and the exhaust valve, this embodiment may also
apply the present invention to a system for changing the operation
characteristics of the intake valve only.
[0222] Furthermore, the scope of the present invention is not
limited to a vehicle run by only a driving power output by the
engine. Instead, the present invention can also be applied to a
hybrid car run by both a driving power output by the engine and a
driving power output by a driving-power source other than the
engine. An example of the other driving-power source is a
motor.
[0223] Although the present invention has been described in
connection with the preferred embodiments thereof with reference to
the accompanying drawings, it is to be noted that various changes
and modifications will be apparent to those skilled in the art.
Such changes and modifications are to be understood as being
included within the scope of the present invention as defined in
the appended claims.
* * * * *