Title: Control apparatus for internal combustion engine
Abstract: Based on results of a knock control for adjusting ignition timing in accordance with the occurrence of knocking, an electronic control unit computes deposit required ignition timing akgrg, which is ignition timing determined by taking adhesion of deposits in an internal combustion engine into consideration. Based on the deposit required ignition timing akgrg, the electronic control unit reduces a vvt allowable variable range of a target VVT advancement amount, which is a control target value of a variable valve timing mechanism. The electronic control unit corrects a required ignition timing based on the actual VVT advancement amount vt, which is chanted according to the reduction of the allowable variable range of the target VVT advancement amount. As a result, problems resulting from the adhesion of deposits are effectively avoided.
Patent Number: 6,910,461 Issued on 06/28/2005 to Tanei, et al.
| Inventors:
|
Tanei; Katsutoshi (Aichi-ken, JP);
Idogawa; Masanao (Toyota, JP);
Kaneko; Rihito (Aichi-ken, JP);
Kasashima; Kenji (Aichi-ken, JP);
Takagi; Noboru (Toyota, JP);
Takagi; Isao (Okazaki, JP)
|
| Assignee:
|
Toyota Jidosha Kabushiki Kaisha (Toyota, JP)
|
| Appl. No.:
|
845163 |
| Filed:
|
May 14, 2004 |
Foreign Application Priority Data
| May 15, 2003[JP] | 2003-137288 |
| Oct 21, 2003[JP] | 2003-361077 |
| Dec 12, 2003[JP] | 2003-414982 |
| Current U.S. Class: |
123/406.29; 123/90.15; 123/406.33; 123/406.45; 123/568.14 |
| Intern'l Class: |
F02D 013/02; F01L013/00; F02P005/15.2 |
| Field of Search: |
123/40629,406.33,406.45,406.48,901.1,901.5,901.6,901.7,568.14
|
References Cited [Referenced By]
U.S. Patent Documents
| 6105552 | Aug., 2000 | Arisawa et al.
| |
| 6769404 | Aug., 2004 | Aoyama et al.
| |
| 6848422 | Feb., 2005 | Hashizume et al.
| |
| Foreign Patent Documents |
| 275043 | Nov., 1990 | JP.
| |
| A-08-3382/72 | Dec., 1996 | JP.
| |
| A-09-3031/65 | Nov., 1997 | JP.
| |
| A-11-1902/36 | Jul., 1999 | JP.
| |
| 130027 | May., 2002 | JP.
| |
Other References
U.S. Appl. No. 10/745,555, filed Jan. 12, 2004, Tanei et al.
|
Primary Examiner: Huynh; Hai
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
1. A control apparatus for an internal combustion engine, the engine generating
power by combusting mixture of air and fuel, wherein the apparatus performs a knock
control for adjusting an ignition timing, at which the air-fuel mixture is ignited,
and a variable valve actuation control for adjusting a valve actuation, which is
actuation of a valve of the engine, in accordance with the occurrence of knocking
in the engine,
wherein the apparatus determines the magnitude of a change in the ignition timing
due to adhesion of deposits in the engine based on the results of the knock control,
and wherein, based on the magnitude of the change in the ignition timing, the apparatus
changes a set value of the valve actuation in the variable valve actuation control.
2. The apparatus according to claim 1, wherein the apparatus determines the magnitude
of the change in the ignition timing based on the difference in required ignition
timing between a case where no deposits are present and the current state of deposits.
3. The apparatus according to claim 2, wherein the apparatus determines the magnitude
of the change in the ignition timing based on the difference in the required ignition
timing under a predetermined engine operating condition where deposits produces
a marked adverse effect.
4. The apparatus according to claim 1, wherein, to change the set value of the
valve actuation, the apparatus reduces an allowable variable range of the valve
actuation as the magnitude of the change in the ignition timing is increased.
5. The apparatus according to claim 1, wherein the apparatus corrects required
ignition timing according to the set value of the valve actuation that has been
changed based on the magnitude of the change in the ignition timing.
6. The apparatus according to claim 5, wherein the variable valve actuation control
includes adjusting the valve timing of the valve, and wherein the apparatus sets
a correction amount used for correcting the ignition timing such that the correction
amount is proportional to the square of the ratio of the set value of the valve
timing that has been changed based on the magnitude of the change in the ignition
timing to a set value of the valve timing in a state where no deposits collect.
7. The apparatus according to claim 5, wherein the valve is one of an intake
valve and an exhaust valve, wherein the variable valve actuation control includes
adjusting the valve overlap amount of the valves, and wherein the apparatus sets
a correction amount used for correcting the ignition timing such that the correction
amount is proportional to the square of the ratio of the set value of the valve
overlap amount that has been changed based on the magnitude of the change in the
ignition timing to a set value of the valve overlap amount in a state where no
deposits collect.
8. The apparatus according to claim 5, wherein the variable valve actuation control
includes adjusting the valve timing of the valve, and wherein the apparatus sets
a correction amount used for correcting the ignition timing such that the correction
amount varies in a quadratic curve form with a bottom point with respect to the
set value of the valve timing that has been changed based on the magnitude of the
change in the ignition timing.
9. The apparatus according to claim 5, wherein the valve is one of an intake
valve and an exhaust valve, wherein the variable valve actuation control includes
adjusting the valve overlap amount of the valves, and wherein the apparatus sets
a correction amount used for correcting the ignition timing such that the correction
amount varies in a quadratic curve form with a bottom point with respect to the
set value of the valve overlap amount that has been changed based on the magnitude
of the change in the ignition timing.
10. The apparatus according to claim 9, wherein the valve overlap amount when
the correction amount of the ignition timing exhibits the bottom point is set to
have a greater value as the engine load increases.
11. The apparatus according to claim 1, wherein the apparatus corrects maximum
torque ignition timing, at which the engine generates the maximum torque, according
to the set value of the valve actuation that has been changed based on the magnitude
of the change in the ignition timing.
12. The apparatus according to claim 1, wherein the apparatus corrects knock
limit point ignition timing according to the set value of the valve actuation that
has been changed based on the magnitude of the change in the ignition timing.
13. The apparatus according to claim 1, wherein the apparatus corrects at least
one of maximum advanced ignition timing and maximum retarded ignition timing in
the knock control according to the set value of the valve actuation that has been
changed based on the magnitude of the change in the ignition timing.
14. The apparatus according to claim 1, wherein, when the degree of deposits
is expressed as a rate, the rate having a value of 0 in a state where no deposits
collect and a value of 1 in a state where the amount of deposits reaches an assumed
maximum value, the apparatus computes a rate learning width, which is an amount
of retardation of the ignition timing that corresponds to engine operating conditions
when the amount of deposits reaches the assumed maximum value, and wherein the
apparatus multiplies the rate learning width by the rate expressing the degree
of deposits, and sets the result of the multiplication as a retardation amount
of the ignition timing that corresponds to the present level of deposits, and
wherein the apparatus corrects the rate learning width according to the set value
of the valve actuation that has been changed based on the magnitude of the change
in the ignition timing.
15. The apparatus according to claim 1, wherein, in the knock control, the apparatus
separately learns a first learning value, which reflects the magnitude of the change
in the ignition timing made to deal with deposits, and a second learning value,
which reflects the magnitude of the change in the ignition timing made to deal
with a factor other than deposits.
16. The apparatus according to claim 15, wherein, when updating the first leaning
value and the second learning value, the apparatus computes a learning update amount,
which is the total amount of update amount required for the feedback start point
of the knock control, and determines a distribution ratio of the learning update
amount, which ratio represents the rate of the learning update amount reflected
in the first learning value and the rate of the learning update amount reflected
in the second learning value, and wherein the apparatus determines an update amount
of the first learning value and an update amount of the second learning value according
to the learning update amount and the distribution ratio.
17. The apparatus according to claim 16, wherein the distribution ratio is changed
in accordance with the engine operating conditions.
18. The apparatus according to claim 16, wherein the distribution ratio is changed
in accordance with the engine load.
19. The apparatus according to claim 16, wherein the update of the first learning
value and the update of the second learning value are each restricted to a predetermined
update range, wherein, if one of the learning values cannot be updated as required
owing to the restriction of the update range, the apparatus reflects all of the
learning update amount in the other learning value regardless of the setting of
the distribution ratio.
20. The apparatus according to claim 15, wherein the apparatus sets an engine
operation region in which the first learning value is prohibited from being updated,
and changes the engine operation region according to the amount of the change in
the set value of the valve actuation based on the magnitude of the change in the
ignition timing.
21. The apparatus according to claim 20, wherein the engine operation region
is a region in which the load acting on the engine is higher than a predetermined
load, and wherein the apparatus changes the predetermined load to a lower load
as the amount of the change in the set value of the valve actuation based on the
magnitude of the change in the ignition timing is increased.
22. The apparatus according to claim 15, wherein, when the degree of deposits
is expressed as a rate, the rate having a value of 0 in a state where no deposits
collect and a value of 1 in a state where the amount of deposits reaches an assumed
maximum value, the apparatus computes a rate learning width, which is an amount
of retardation of the ignition timing that corresponds to engine operating conditions
when the amount of deposits reaches the assumed maximum value, and wherein the
apparatus multiplies the rate learning width by the rate expressing the degree
of deposits, and sets the result of the multiplication as a retardation amount
of the ignition timing that corresponds to the present level of deposits,
wherein the apparatus corrects the rate learning width according to the set value
of the valve actuation that has been changed based on the magnitude of the change
in the ignition timing, and
wherein, when the corrected rate learning width is no more than a predetermined
determination value, the apparatus prohibits the first learning value from being
updated.
23. A method for controlling an internal combustion engine, the engine generating
power by combusting mixture of air and fuel, the method comprising:
performing a knock control for adjusting an ignition timing, at which the air-fuel
mixture is ignited, in accordance with the occurrence of knocking in the engine;
performing a variable valve actuation control for adjusting a valve actuation,
which is actuation of a valve of the engine in accordance with the occurrence of
knocking in the engine;
determining the magnitude of a change in the ignition timing due to adhesion
of deposits in the engine based on the results of the knock control; and
changing a set value of the valve actuation in the variable valve actuation control
based on the magnitude of the change in the ignition timing.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a control apparatus for an internal combustion
engine, and in particular, to a control apparatus suitably applicable to an internal
combustion engine that performs both knock control for adjusting an ignition timing
and a variable valve actuation control for an engine valve in accordance with the
occurrence of knocking.
In an internal combustion engine, depending on its use, deposits originating
from
an unburned fuel, a blow-by gas, a lubricant, or the like may be gradually deposited
on an intake port, an intake valve, a piston, or the like. It is known that such
an increase in the amount of deposits leads to, for example, a decrease in the
substantial volume of a combustion chamber and an associated increase in in-cylinder
compression pressure during burning, thus increasing the possibility of knocking.
In general, for the internal combustion engine, knock control is preformed to
detect the occurrence of knocking using a knock sensor and adjust the ignition
timing on the basis of the results of the detection. The knock control suppresses
the occurrence of knocking by retarding the ignition timing when the incidence
of knocking is high, while advancing the ignition timing when the incidence is low.
On the other hand, in recent years, internal combustion engines with a variable
valve actuation mechanism that can vary the valve actuation of engine valves, that
is, intake or exhaust valves, have been put to practical use, for example, a variable
valve timing mechanism that can vary a valve timing for the engine valves and a
variable valve lift mechanism that can vary the valve lift amount of the engine
valves. Such an internal combustion engine with a variable valve actuation mechanism
can reduce the actual compression ratio of the engine by adjusting the valve actuation
of the engine valves. Thus, the internal combustion engine with the variable valve
actuation mechanism can also suppress the occurrence of knocking by allowing the
variable valve actuation mechanism to reduce the actual compression ratio to prevent
an increase in in-cylinder compression pressure caused by deposits.
Thus, in the prior art, a control apparatus for an internal combustion engine
has been proposed which performs knock control for the ignition timing based on
the results of the detection by the knock sensor and which also allows the variable
valve actuation mechanism to perform the variable control of the valve actuation
on the basis of the results of the detection by the knock sensor as set forth in
Japanese Patent Laid-Open No. 8-338272.
With the control apparatus described in Japanese Patent Laid-Open No. 8-338272,
the ignition timing is retarded on the basis of the detection of the occurrence
of knocking by the knock sensor. On the other hand, the amount of retardation of
the valve timing for the intake valve carried out by the variable valve timing
mechanism is set in accordance with the intensity of the knocking detected by the
knock sensor. Such a control apparatus can effectively inhibit the occurrence of
knocking on the basis of the multiplier effect of the retardation of the ignition
timing and the valve timing.
Once the ignition timing has been changed by the knock control, the appropriate
values of the valve actuation of the engine valves are also changed. Thus, once
the ignition timing and the valve actuation have been individually changed as in
the case of the above conventional control apparatus, the set values of the valve
actuation may deviate from the appropriate values in the present engine operating
state. As a result, the performance of the engine otherwise successfully provided
may not be adequately enjoyed to its limit. Thus, although the conventional control
apparatus is effective on the inhibition of the occurrence of knocking, the valve
actuation is not sufficiently optimized so as to deal with changes in engine operating
state accompanying changes in ignition timing. Therefore, the conventional control
apparatus still has room for improvement in terms of mileage or the like.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control apparatus for an
internal combustion engine that more effectively solves problems associated with
the deposits.
To achieve the foregoing and other objectives and in accordance with the purpose
of the present invention, a control apparatus for an internal combustion engine
is provided. The engine generates power by combusting mixture of air and fuel.
The apparatus performs a knock control for adjusting an ignition timing, at which
the air-fuel mixture is ignited, and a variable valve actuation control for adjusting
a valve actuation, which is actuation of a valve of the engine, in accordance with
the occurrence of knocking in the engine. The apparatus determines the magnitude
of a change in the ignition timing due to adhesion of deposits in the engine based
on the results of the knock control. Based on the magnitude of the change in the
ignition timing, the apparatus changes a set value of the valve actuation in the
variable valve actuation control.
The present invention also provides a method for controlling an internal combustion
engine. The engine generates power by combusting mixture of air and fuel. The method
includes: performing a knock control for adjusting an ignition timing, at which
the air-fuel mixture is ignited, in accordance with the occurrence of knocking
in the engine; performing a variable valve actuation control for adjusting a valve
actuation, which is actuation of a valve of the engine in accordance with the occurrence
of knocking in the engine; determining the magnitude of a change in the ignition
timing due to adhesion of deposits in the engine based on the results of the knock
control; and changing a set value of the valve actuation in the variable valve
actuation control based on the magnitude of the change in the ignition timing.
Other aspects and advantages of the invention will become apparent from the
following description, taken in conjunction with the accompanying drawings, illustrating
by way of example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention, together with objects and advantages thereof, may best be understood
by reference to the following description of the presently preferred embodiments
together with the accompanying drawings in which:
FIG. 1 is a schematic view showing the configurations of an internal combustion
engine and its control system according to a first embodiment of the present invention;
FIG. 2 is a perspective view of a variable valve timing mechanism provided in
the internal combustion engine in FIG. 1;
FIG. 3 is a graph showing the relationship between an MBT point and a knock
limit point and the most retarded ignition timing with respect to an engine speed;
FIG. 4 is a time chart showing an example of knock control;
FIG. 5 is a graph showing an example of valve timing control;
FIG. 6 is a diagram showing an example of a calculation map for an upper limit
VVT advancement amount;
FIG. 7 is a diagram showing an example of a calculation map for a base second
knock limit point;
FIG. 8 is a graph showing the relationship between a VVT advancement correction
factor and a actual VVT advancement amount;
FIG. 9 is a graph showing the relationship between parameters relating to ignition
timing setting control and the actual VVT advancement amount;
FIGS. 10(
a) to 10(
e) are graphs illustrating the
effect of variations in valve timing for an intake valve on the knock limit point;
FIG. 11 is a graph illustrating variations in knock limit point with respect
to the valve timing for the intake valve;
FIG. 12 is a graph illustrating variations in MBT limit point with respect to
the valve timing for the intake valve;
FIG. 13 is a graph illustrating variations in knock limit point and MBT point
with respect to valve timing for an exhaust valve;
FIG. 14 is a graph illustrating a calculation of a MPT point variation amount
according to a second embodiment of the present invention;
FIG. 15(
a) is a graph illustrating a calculation of a knock limit
point variation amount in a low to medium load region;
FIG. 15(
b) is a graph illustrating a calculation of the knock
limit point variation amount in a high load region;
FIG. 16 is a chart conceptually showing the manner of distributing a learning
value update amount according to a third embodiment of the present invention;
FIG. 17 is a graph illustrating setting of a rate learning prohibited region;
FIG. 18 is a flow chart of a learning value updating process; and
FIG. 19 is a graph illustrating setting of the rate learning prohibited region
according to a fourth embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
(First Embodiment)
A control apparatus for an internal combustion engine according to a first embodiment
of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, an internal combustion engine
10 to which the present
embodiment is applied comprises a variable valve timing mechanism
11 that
can vary a valve timing for an intake valve
12, as an adjustable mechanism
that can vary a valve actuation (dynamic behavior) of engine valves. A combustion
chamber
13 of the internal combustion engine
10 is provided with
an ignition plug
14 that ignites and burns a mixture of air and fuel sucked
into the combustion chamber
13, and a knock sensor
15 that detects
the occurrence of knocking accompanying the burning of the mixture.
An electronic control unit
16 performs various types of control relating
to the operation of the internal combustion engine
10. The electronic control
unit
16 is a computer, which comprises a CPU that performs the various types
of control, a memory that stores information required for the control, an output
port through which an instruction signal is outputted to external equipment, and
other components.
Various sensors are connected to the input port of the electronic control
unit
16 to detect an engine operating state. The sensors include, for example,
the knock sensor
15, a crank sensor
17 detecting a crank angle that
is the rotation phase of a crank shaft, a cam sensor
18 detecting a cam
angle that is the rotation angle of an intake camshaft, and a throttle sensor
19
detecting a throttle opening degree ta. Detection signals from these sensors are
inputted to the electronic control unit through the input port. An engine speed
ne is determined from a detection signal from the crank sensor
17.
On the other hand, the output port of the electronic control unit
16 connects
to a drive circuit for actuators required to control the engine, such as the variable
valve timing mechanism
11 and an igniter
14a that generates
a high voltage current required to cause the ignition plug
14 to ignite
a mixture. The electronic control unit
16 controls the engine by controlling
the actuators on the basis of detection signals from the sensors.
Now, the variable timing mechanism
11 will be described with reference
to FIG.
2. FIG. 2 is a perspective view showing the sectional structure
of the variable valve timing mechanism
11.
As shown in the figure, the variable valve timing mechanism
11 is disposed
at one end of an intake camshaft
30 on which cams
30a opening
and closing an intake valve
12 are disposed. The variable valve timing mechanism
11 is roughly composed of a vane rotor
31 and a housing
32.
A cam sprocket
33 is disposed at the end of the intake camshaft
30
at which the variable valve timing mechanism
11 is disposed so that the
cam sprocket
33 is rotatable relative to the intake camshaft
30.
The cam sprocket
33 is coupled to the crank shaft via a timing belt
33a.
The housing
32 is integrally rotatably fixed to the cam sprocket
33.
The vane rotor
31 is disposed inside the housing
32 so as to be
rotatable relative to the housing
32. The vane rotor
31 is integrally
rotatably fixed to the intake camshaft
30. A plurality of vanes
34
are formed on the outer periphery of the vane rotor
31. The vanes
34
are accommodated in respective concave portions
35 formed around the inner
periphery of the housing
32 so as to be movable in a circumferential direction.
Pressure chambers
36 and
37 are formed at the respective sides of
each vane
34 and are partitioned by the outer peripheral surface of the
vane rotor
31, the inner peripheral surface of the housing
32, and others.
Oil is fed into each of the pressure chambers
36 and
37 so that
its pressure acts on the circumferential sides of the corresponding vane
34.
Depending on a difference in oil pressure between the pressure chambers
36
and
37, power is generated to rotatably move the vane rotor
31 relative
to the housing
32.
The rotation of the vane rotor
31 relative to the housing
32 changes
the relative rotation phase of the intake camshaft
30 with respect to the
cam sprocket
33. This in turn changes the rotation phase of the cams
30a,
which open and close the intake valve
12, relative to the crank shaft. Thus,
on the basis of the control of the oil pressure in the pressure chambers
36
and
37, the valve timing for the intake valve
12 is changed.
<1> Summary of Knock Control
In the internal combustion engine
10 configured as described above, the
electronic control unit
16 performs knock control that adjusts an ignition
timing in accordance with the occurrence of knocking detected by the knock sensor
15. Now, a brief description will be given of the knock control according
to the present embodiment.
The knock control according to the present embodiment is performed by setting
a required ignition timing afin that is a control instruction value for the ignition
timing, as described below. Here, the ignition timing is expressed as the advancement
amount [°CA] of the crank angle with respect to the top dead center of a cylinder
that is a firing target.
(Calculation of Maximum Retardation Amount akmax)
To set the required ignition timing afin, a maximum advanced ignition timing
absef
and a maximum retarded ignition timing almf are first calculated; the maximum advanced
ignition timing is a limit value on the advancement side of the setting range of
the required ignition timing afin for the knock control, the maximum retarded ignition
timing akmf being a limit value on the retardation side. Then, on the basis of
these values, the maximum retardation amount akmax for the required ignition timing
afin with respect to the maximum advanced ignition timing absef during the knock
control is calculated.
The maximum advanced ignition timing absef is calculated on the basis of an MBT
point ambt and a first knock limit point aknok
1. Specifically, as shown
in Equation (1) below, one of the MBT point ambt and the first knock limit point
aknok
1 which is closer to the point of the most significant retardation
is set as the maximum advanced ignition timing absef.
The MBT point indicates the ignition timing (maximum torque ignition timing)
that provides the maximum torque under the present engine operating conditions.
The first knock limit point aknok
1 indicates the advancement limit value
(knock limit point ignition timing) of the ignition timing at which knocking can
be reduced to an allowable level or lower under the assumed best conditions when
a large-octane-number fuel, having a large knock limit value, is used. The MBT
point ambt and the first knock limit point aknok
1 are set taking into account
the present engine speed ne, an engine load, the setting of the valve timing for
the intake valve
12 executed by the variable valve timing mechanism
11,
and the like. Specific manners of calculating these values will be described later.
On the other hand, the maximum retarded ignition timing akmf is set as the index
value of the ignition timing with which knocking can be adequately reduced to the
allowable level or lower even under the assumed worst conditions. Specifically,
as shown in Equation (2) below, the maximum retarded ignition timing akmf is set
as a value obtained by retarding a second knock limit point aknok
2 for the
ignition timing by an amount equal to the sum of a deposit correction term depvt
and a present constant RTD.
The second knock limit point aknok
2 indicates the advancement limit (knock
limit point ignition timing) of the ignition timing at which knocking can be reduced
to an allowable level or lower under the assumed best conditions when a low-octane-number
fuel, having a low knock limit value, is used. The value of the second knock limit
point aknok
2 is set taking into account the present engine speed ne, the
engine load, the setting of the valve timing for the intake valve
12 executed
by the variable valve timing mechanism
11, and the like. Specific manners
of calculating these values will be described later.
The deposit correction item adepvt is an index value indicative of the retardation
amount of the ignition timing based on the present level of deposits in the current
internal combustion engine
10. A specific manner of calculating the deposit
correction term adepvt will also be described later.
The maximum retardation amount akmax is calculated from the maximum advanced
ignition timing absef and maximum retarded ignition timing akmf calculated as described
above, on the basis of Equation (3) below.
FIG. 3 shows the relationship between the engine speed ne and each of the maximum
advanced ignition timing absef, maximum retarded ignition timing akmf, maximum
retardation amount akmax, and others, in which deposits described above is not
occurring. As shown in this figure, these values vary with the engine speed in
a knocking region in which knocking exceeds the allowable level. In the present
embodiment, when deposits start to be deposited, the setting of the valve timing
for the intake valve
12 provided by the variable valve timing mechanism
11 is correspondingly changed. This correspondingly changes the above set values.
(Calculation of Required Ignition Period afin)
The required ignition timing afin is calculated by determining a ignition timing
retardation amount aknk that is the retardation amount of the required ignition
timing afin with respect to the maximum advanced ignition timing absef. The value
of the ignition timing retardation amount aknk is set on the basis of the maximum
retardation amount akmax, a KCS learning value agknk, and a KCS feedback correction
value akcs as shown in Equation (4).
Then, as shown in Equation (5) below, the required ignition timing afin is
set by subtracting the ignition timing retardation amount aknk from the maximum
advanced ignition timing absef. That is, the required ignition timing afin is obtained
by advancing the maximum retarded ignition timing akmf by the KCS learning value
agknk and retarding it by the KCS feedback correction value akcs as shown in Equation
(6) below. An upper limit value and a lower limit value are set for the required
ignition timing afin so that it increases above the maximum advanced ignition timing
absef or decreases below the maximum retarded ignition timing akmf.
The KCS feedback correction value akcs is set in accordance of the occurrence
of knocking detected by the knock sensor
15. Specifically, if it is determined
that the detected magnitude of knocking is greater than a predetermined determination
value and is thus equal to or lower than the allowable level, the KCS feedback
correction value akcs is gradually reduced. On the other hand, if the detected
magnitude of knocking is equal to or greater than the determination value, the
KCS feedback correction value akcs is increased by a predetermined value.
On the other hand, if the absolute KCS feedback correction value akcs remains
greater than a predetermined value (|akcs|>A) for a predetermined time or
longer the KCS feedback correction value akcs is updated so that its absolute value
decreases gradually. Specifically, if the KCS feedback correction value akcs remains
greater than a certain positive value (akcs>A), a predetermined value B is
subtracted from the KCS learning value agknk. Furthermore, the predetermined value
B is also subtracted from the KCS feedback correction value akcs. On the other
hand, if the KCS feedback correction value akcs remains less than a certain negative
value (akcs<-;A), the predetermined value B is added to each of the KCS learning
value agknk and KCS feedback correction value akcs. The thus updated KCS learning
value agknk is stored in a backup memory of the electronic control unit
16.
This value is retained even while the engine is stopped.
During knock control, a rate learning value rgknk is updated in accordance
with the occurrence of knocking. The rate learning value rgknk is set as an index
value indicative of the degree of deposits to the internal combustion engine
10
described above. In this case, the state in which no deposits collect in the internal
combustion engine is set to a value 0. The state in which the amount of deposits
reaches an assumed maximum value is set to a value 1. Thus, the degree of deposits
is expressed by the rate learning value rgknk.
The rate learning value rgknk is set to 0 as an initial value before shipment,
that is, when no deposits collects in the internal combustion engine. Subsequently,
the rate learning value rgknk increases or decreases gradually in accordance with
the incidence of knocking within the range from 0 to 1, inclusive. Specifically,
the rate learning value rgknk is gradually increased consistently with the incidence
of knocking. The rate learning value rgknk is gradually reduced consistently with
the incidence of knocking. Like the KCS learning value agknk, the updated rate
learning value rgknk is stored in the backup memory of the electronic control unit
16. This value is retained even while the engine is stopped.
FIG. 4 shows an example of the manner of such knock control. In the illustrated
example, the adjustment of the ignition timing is started at a time t
0 in
accordance with the occurrence of knocking on the basis of knock control. When
the knock control is started, the KCS feedback correction value akcs has been set
to 0, which is its initial value. The required ignition timing afin has been set
to a value obtained by advancing the maximum retarded ignition timing akmf by the
KCS learning value agknk.
In the illustrated example, during the period between the time t
0, at
which
the knock control is started, and a time t
1, the occurrence of knocking
at a level equal to or higher than the determination value is not detected. Thus,
the KCS feedback correction value akcs is gradually reduced from the initial value
0, set at the start of the knock control. Accordingly, after the time t
0,
the required ignition timing afin is gradually advanced.
Subsequently, after the time t
1, every time the occurrence of
knocking at a level equal to or higher than the determination value is detected,
the KCS feedback correction value akcs is increased by a predetermined value in
increments. Thus, while the occurrence of such knocking is continually detected,
the required ignition timing afin is advanced in increments of a predetermined time.
Subsequently, after a time t
2, once the detection of occurrence
of knocking is stopped, the KCS feedback correction value is gradually reduced.
The required ignition timing afin is thus gradually advanced.
The above knock control advances the required ignition timing afin so as to obtain
a larger torque, to the extent that knocking exceeding the allowable level does
not occur.
<2> Setting VVT Advancement Amount
On the other hand, in the present embodiment, the electronic control unit
16
determines the magnitude of a change in the required ignition timing afin made
to deal with deposits in the internal combustion engine
10, on the basis
of the results of the knock control. Then, on the basis of the magnitude of the
variations, the electronic control unit
16 changes the settings of the valve
timing for the intake valve
12 provided by the variable valve timing mechanism
11.
Specifically, in accordance with an increase in the amount of collecting
deposits, the electronic control unit
16 limits the advancement amount for
the valve timing for the intake valve
12 provided by the variable valve
timing mechanism
11, that is, maintains the valve timing at a value of retardation.
This serves to reduce the actual compression ratio to suppress an increase in in-cylinder
compression pressure caused by deposits. As a result, a favorable burning state
is maintained.
With reference to FIGS. 5 and 6, a detailed description will be given of the
valve timing control according to the present embodiment.
FIG. 5 shows an example of the manner executed by the variable valve timing
mechanism
11 to variably set the valve timing. In the present embodiment,
the valve timing for the intake valve
12, which can be varied by the variable
valve timing mechanism
11, is expressed as an advancement amount [°CA]
with reference to the retardation limit (0) of the variable setting range of the
valve timing for the intake valve
12, shown by the alternate long and two
short dashes line in the figure. In the present embodiment, the advancement amount
for the valve timing for the intake valve
12 is a parameter corresponding
to a "set value of the valve actuation of the engine valve in the variable valve
actuation control".
(Calculation of Deposit Required Ignition Period akgrg)
In the valve timing control according to the present embodiment, the deposit
required
ignition timing akgrg is first calculated on the basis of the KCS learning value
agknk and rate learning value rgknk, set for the above knock control. The value
of the deposit required ignition timing akgrgr is the index value of the present
required ignition timing afin retarded to deal with deposits (precisely speaking,
the advancement amount for the present required ignition timing with respect to
the maximum retarded ignition timing akmf).
To calculate deposit required ignition timing akgrg, the deposit ignition timing
retardation amount adep is first, determined by multiplying the rate learning value
rgknk by maximum ignition timing retardation amount DLAKNOK as shown in Equation
(7) below. The maximum ignition timing retardation amount DLANKNOK is a constant
for the retardation amount for the required ignition timing required to deal with
the assumed maximum amount of deposits under predetermined engine operating conditions
under which the effect of the deposits is most marked. This value is predetermined
through experiments or the like. The level of the effect of the deposits on the
required ignition timing afin, that is, the retardation amount for the required
ignition timing afin required to deal with the deposits, varies depending on the
engine speed ne.
As shown in Equation (8) below, the deposit required ignition timing akgrg is
calculated by subtracting the deposit ignition timing retardation amount adep from
the KCS learning value agknk.
As the amount of deposits increases to increase the amount of retardation of
the
required ignition timing afin executed to deal with the deposits, the thus calculated
deposit required ignition timing akgrg is further retarded, that is, has a smaller
value. Thus, the value of the deposit required ignition timing akgrg can be used
as the index value of the amount of deposits.
In the present embodiment, the amount of retardation of the required ignition
timing afin executed to deal with the deposits is reflected in the maximum retardation
amount akmax using the deposit correction item adepvt. Thus, in the present embodiment,
the KCS learning value is the index value of the magnitude of a change in required
ignition timing afin made to deal with a factor other than the deposits.
In the present embodiment, as shown in Equation (8) above, the deposit required
ignition timing akgrg, obtained by subtracting the deposit ignition timing retardation
amount adep from the KCS learning value agknk, is the index value of the present
required ignition timing afin retarded to deal with the deposits. That is, the
value of the deposit required ignition timing akgrg enables the determination of
the magnitude of a change in ignition timing made to deal with the deposits to
the present internal combustion engine
10.
(Calculation of VVT Advancement Amount vt)
Subsequently, a target VVT advancement amount vtt that is a control
target value for the valve timing for the intake valve
12 is calculated
on the basis of the deposit required ignition timing akgrg determined as described above.
First, as shown in Equation (9) below, an upper limit VVT advancement amount
vtlmt is determined on the basis of the deposit required ignition timing akgrg
and a throttle opening degree ta that is the index value of an engine load. The
upper limit VVT advancement amount vtlmt is set as the advancement side limit value
of the setting range of the target VVT advancement amount vtt.
In this case, the value of the upper limit VVT advancement amount vtlmt is set
as described below.
As the amount of deposits increases, the substantial volume of the combustion
chamber
13 decreases to increase the in-cylinder compression pressure during
burning. This increases the possibility of knocking. On the other hand, the normal
valve timing for the intake valve
12 is set for the period in which an intake
efficiency is highest.
By reducing the present allowable setting range of the target VVT advancement
amount vtt to retard the valve timing for the intake valve
12 compared to
the inherent set period, it is possible to reduce the intake efficiency and thus
the actual compression ratio. Consequently, the in-cylinder compression pressure
during burning can be reduced. Thus in the present embodiment, when the deposit
required ignition timing akgrg has decreased to indicate that the amount of deposits
has increased, the value of the upper limit VVT advancement amount vtlm is reduced
to narrow the allowable setting range of the target VVT advancement amount vtt.
However, when a heavy load is being imposed on the engine and a large amount
of air is being taken in, the in-cylinder compression pressure during burning is
high. Accordingly, the effect of the deposits is relatively insignificant. Thus,
when the engine load is heavy, the magnitude of a reduction in upper limit VVT
advancement amount vtlmt carried out to cope with the reduced value of the deposit
required ignition timing akgrg is reduced compared to the case in which the engine
load is light.
FIG. 6 shows an example of a calculation map used to calculate the upper limit
VVT advancement amount vtlmt as described above. As shown in this figure, when
the deposit required ignition timing akgrgr has a large value to indicate that
almost no deposits are present, the value of the upper limit VVT advancement amount
vtlmt is set at a maximum advancement amount vtmax that is the advancement side
limit of the variable setting range of the valve timing for the intake valve
12
provided by the variable valve timing mechanism
11. In contrast, when the
deposit required ignition timing akgrgr has a small value to indicate that the
amount of deposits has increased, the value of the upper limit VVT advancement
amount vtlmt is set at as small a value as that set when the engine load is light.
Moreover, when the target VVT advancement amount vtt is calculated, not
only the upper limit VVT advancement amount vtlmt but also a base VVT advancement
amount vtbase are calculated. The value of the base VVT advancement amount vtbase
is set as a control target value for the optimum valve timing for the intake valve
12 used when no deposits collect in the internal combustion engine. In this
case, the base VVT advancement amount vtbase is calculated on the basis of the
engine speed ne and engine load (in this case, the throttle opening degree ta is
used as the index value of the engine load) as shown in Equation (10) below.
Then, as shown in Equation (11) below, one of the calculated upper limit VVT
advancement amount vtlm and base VVT advancement amount vtbase which is closer
to the point of most significant retardation is set as the target VVT advancement
amount vtt.
The electronic control unit
16 controls the variable valve timing mechanism
11 using the thus calculated target VVT advancement amount vtt as a control
target value for the valve timing for the intake valve
12. Specifically,
the variable valve timing mechanism
11 is controlled so as to make an actual
VVT advancement amount vt equal to the calculated target VVT advancement amount
vtt, the actual VVT advancement amount vt being the measured value of the advancement
amount for the valve timing for the intake valve
12 determined from the
results of detections by the crank sensor
17 and cam sensor
18. Thus,
the valve timing for the intake valve
12 is controlled so as to reduce the
effect of the deposits to retain a favorable burning state.
<3> Details of Ignition Timing Setting Control in Accordance with Valve
Timing Setting
Once the valve timing for the intake valve
12 is thus changed, the optimum
ignition timing is correspondingly changed. For example, if the valve timing for
the intake valve
12 is retarded, the valve overlap between the intake valve
and the exhaust valve decreases to reduce the amount of internal EGR present in
the cylinder during burning. Accordingly, if the valve timing for the intake valve
12 is retarded, the speed of burning in the cylinder increases to retard
the optimum ignition timing.
In the present embodiment, the required ignition timing afin and others are set
as described below to obtain the optimum ignition timing regardless of changes
in the valve timing for the intake valve
12. With reference to FIGS. 7 to
9, a detailed description will be given of ignition timing setting control
according to the present invention
(Calculation of Base MBT Point and Base Knock Limit Point)
In the present embodiment, for the ignition timing setting control, a base MBT
point ambtvof, a first base knock limit point aknokvof, and a second base knock
limit point aknokbse are calculated.
The base MBT point ambtvof indicates a ignition timing with which the maximum
torque is obtained at the present values of the engine speed and engine load when
the valve timing for the intake valve
12 is set at the position of the most
significant retardation in the allowable setting range. The first base knock limit
point aknokvof indicates the advancement limit value of the ignition timing which
enables knocking to be reduced to an allowable level or lower, the knocking possibly
occurring at the present values of the engine speed ne and engine load when the
valve timing for the intake valve
12 is set at the position of the most
significant retardation in the allowable setting range. The second base knock limit
point aknokbse indicates the advancement limit value of the ignition timing which
enables knocking to be reduced to an allowable level or lower, the knocking possibly
occurring at the present values of the engine speed ne and engine load when the
above low-octane-number fuel is used and when the valve timing for the intake valve
12 is set equal to the position of the most significant retardation in the
allowable setting range. These calculated values are used as base values to calculate
the MBT point ambt, first knock limit point aknok
1, and second knock limit
point aknok
2.
In the present embodiment, the base MBT point ambtvof, first knock limit point
aknokvof, and second knock limit point aknokbse are calculated as functions of
the engine speed ne and engine load as shown in Equations (11) to (13) below. In
the present embodiment, the throttle opening degree ta is used as the index value
of the present engine load.
FIG. 7 shows an example of a calculation map used to calculate the second base
knock limit point aknokbse. As shown in this figure, as the engine speed ne and
the engine load increase, the second base knock limit point aknokbse is set at
a smaller value. A similar calculation map is used to set the base MBT point ambtvof
and the first base knock limit point aknokvof. In spite of different set values,
these calculation maps exhibit similar tendencies in terms of the engine speed
ne and engine load. The second base knock limit point aknokbse may be set at a
smaller value as the engine speed ne decreases.
(Calculation of VVT Advancement Correction Coefficient kavvt)
Then, a VVT advancement correction coefficient kavvt is calculated on the basis
of the present valve timing (actual VVT advancement amount vt). The VVT advancement
correction coefficient kavvt indicates the ratio of a value X to a value Y (X/Y).
- Value X: difference in the internal EGR amount of the internal combustion
engine 10 between the case in which the valve timing for the intake valve
12 is at the present value (actual VVT advancement amount vt) and the case
in which it is at the position of the most significant retardation.
- Value Y: difference in the internal EGR amount of the internal combustion
engine 10 between the case in which the valve timing for the intake valve
12 is set equal to the base VVT advancement amount vtbse and the case in
which it is at the position of the most significant retardation.
On the other hand, it has been confirmed that the amount of internal EGR present
in the cylinder during burning when the engine speed ne and the engine load have
specific values is almost proportional to the square of the amount of valve overlap
between the intake valve and the exhaust valve. On the other hand, with the variable
valve timing mechanism
11 according to the present embodiment, the variable
range of the intake valve
12 is set so that the amount of valve overlap
between the intake valve and the exhaust valve is 0 when the actual VVT advancement
amount vt is 0 as shown in FIG.
5. Thus, in the internal combustion engine
10, with the specific engine speed ne and engine load, the internal EGR
amount is proportional to the square of the advancement amount for the valve timing
for the intake valve
12. Thus, in the present embodiment, the VVT advancement
correction coefficient kavvt is determined on the basis of Equation (15) below.
##EQU1##
FIG. 8 shows the relationship between the actual VVT advancement amount vt and
the VVT advancement correction coefficient kavvt. As shown in this figure, the
VVT advancement correction coefficient kavvt is proportional to the square of the
value of the actual VVT advancement amount vt. Furthermore, when the actual VVT
advancement amount vt is equal to the base VVT advancement amount vtbse, the VVT
advancement correction coefficient kavvt has a value of 1. As shown in FIG. 8,
when the actual VVT advancement amount vt has a predetermined value v
1,
the value of the VVT advancement correction coefficient kavvt is the square of
the ratio (v
1/vtbse) of the predetermined value v
1 to the base VVT
advancement amount vtbse.
In the present embodiment, the VVT advancement correction coefficient kavvt is
a parameter corresponding to the square of the ratio of the set value of the valve
timing after a change based on the magnitude of a change in ignition timing made
to deal with deposits to the set value before the change. The valve timing before
the change corresponds to the valve timing in a state where there is no deposit.
That is, the VVT advancement correction coefficient kavvt is proportional to the
square of the ratio of the set value of the valve timing that has been changed
based on the magnitude of a change in the ignition timing to the set value of the
valve timing in a state where there is no deposit.
(Calculation of MBT Point and Knock Limit Point)
On the other hand, in the present embodiment, not only the VVT advancement correction
coefficient kavvt is calculated but also a base MBT point difference kambt and
a base knock limit point difference kaknk are determined. The base MBT point difference
kambt and the base knock limit point difference kaknk indicate a difference in
MBT point and a difference in knock limit point, respectively, between the case
in which at the present values of the engine speed ne and engine load, the valve
timing of the intake valve
12 is set equal to the base VVT advancement amount
vtbse and the case in which at the present values of the engine speed ne and engine
load, the valve timing of the intake valve
12 is set at the position of
the most significant retardation.
The values of the base MBT difference kambt and base knock limit point difference
kaknk at each engine speed ne and engine load can be predetermined through experiments
or the like. Accordingly, as shown in Equations (16) and (17) below, the base MBT
difference kambt and the base knock limit point difference kaknk are determined
as functions of the engine speed ne and engine load (in this case, the throttle
opening degree ta is used as an index value).
kaknk=f7(
ne,ta) (17)
As described above, with the variable valve timing mechanism
11 according
to the present embodiment, when the advancement amount is 0, the amount of valve
overlap between the intake valve and the exhaust valve is 0, with the internal
EGR amount almost 0. Accordingly, the base MBT difference kambt and base knock
limit point difference kaknk calculated herein are advancement correction amounts
at the MBT point and knock limit point corresponding to the internal EGR amount
observed when the base VVT advancement amount vtbase is set at the present values
of the engine speed ne and engine load.
On the other hand, the advancement correction amounts at the MBT point and knock
limit point can be considered to be proportional to the internal EGR amount. Consequently,
the advancement correction amount kvtmbt at
