U.S. patent application number 09/735480 was filed with the patent office on 2001-06-28 for valve timing control system for internal combustion engine.
This patent application is currently assigned to HONDA GIKEN KOGYO KABUSHIKI KAISHA. Invention is credited to Furukawa, Tomoya, Masuda, Shun, Suzuki, Junichi, Tachibana, Yosuke.
Application Number | 20010004884 09/735480 |
Document ID | / |
Family ID | 18490792 |
Filed Date | 2001-06-28 |
United States Patent
Application |
20010004884 |
Kind Code |
A1 |
Tachibana, Yosuke ; et
al. |
June 28, 2001 |
Valve timing control system for internal combustion engine
Abstract
There is provided a valve timing control system for an internal
combustion engine, which is capable of enhancing the accuracy of
valve timing control. The valve timing control system 1 for the
internal combustion engine 3 changes the cam phase of an intake cam
6a relative to a crankshaft 9, to thereby control the valve timing
of an intake valve 4. The valve timing control system 1 fixes a
desired cam phase CAINCMD at a value CAINCMDFC during an fuel
cut-off, and controls a cam phase change mechanism 8 such that from
a time t2 during the fuel cut-off, the cam phase is held at a value
assumed at the time t2. Further, the valve timing control system 1
calculates a learned value DCALEARN of the amount of deviation of
an actual cam phase CAIN based on a plurality of values of the
actual cam phase CAIN detected at and after the time t2, and the
constant value CAINCMDFC of the desired cam phase CAINCMD (step
S5).
Inventors: |
Tachibana, Yosuke;
(Wako-shi, JP) ; Suzuki, Junichi; (Wako-shi,
JP) ; Furukawa, Tomoya; (Wako-shi, JP) ;
Masuda, Shun; (Wako-shi, JP) |
Correspondence
Address: |
ARENT FOX KINTNER PLOTKIN & KAHN, PLLC
Suite 600
1050 Connecticut Avenue, N.W.
Washington
DC
20036-5339
US
|
Assignee: |
HONDA GIKEN KOGYO KABUSHIKI
KAISHA
|
Family ID: |
18490792 |
Appl. No.: |
09/735480 |
Filed: |
December 14, 2000 |
Current U.S.
Class: |
123/90.15 ;
123/90.17 |
Current CPC
Class: |
F01L 1/34 20130101; F02D
41/2441 20130101; F02D 13/0219 20130101; Y02T 10/12 20130101; F02D
41/2464 20130101; F02D 41/2438 20130101; F02D 41/123 20130101; F02D
2041/001 20130101; Y02T 10/18 20130101 |
Class at
Publication: |
123/90.15 ;
123/90.17 |
International
Class: |
F01L 001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 24, 1999 |
JP |
368025/1999 |
Claims
What is claimed is:
1. A valve timing control system for an internal combustion engine
having a crankshaft, an intake valve, an exhaust valve, an intake
cam for opening and closing said intake valve, and an exhaust cam
for opening and closing said exhaust valve, the valve timing
control system controlling valve timing of at least one of said
intake valve and said exhaust valve by changing a cam phase which
is a phase of at least one of said intake cam and said exhaust cam,
relative to said crankshaft, the valve timing control system
comprising: actual cam phase-detecting means for detecting said cam
phase as an actual cam phase: a cam phase change mechanism for
changing said cam phase: operating condition-detecting means for
detecting operating conditions of said engine; fuel cut-off
determination means for determining whether or not fuel cut-off is
being carried out for cutting off supply of fuel to said engine;
desired cam phase-setting means for setting a desired cam phase
according to said detected operating conditions of said engine, and
fixing said desired cam phase at a constant value during said fuel
cut-off; cam phase control means for controlling said cam phase
change mechanism such that said cam phase change mechanism causes
said cam phase to become equal to said desired cam phase, and holds
said cam phase at and after a predetermined timing during said fuel
cut-off; and actual cam phase deviation calculation means for
calculating an amount of deviation of said actual cam phase based
on a plurality of values of said actual cam phase detected at and
after said predetermined timing during said fuel cut-off, and said
constant value of said desired cam phase.
2. A valve timing control system according to claim 1, further
including: actual cam phase-integrating means for integrating an
amount of change in said actual cam phase before said fuel cut-off
to obtain an integrated value; and calculation-permitting means for
permitting said actual cam phase deviation calculation means to
calculate said amount of deviation of said actual cam phase when
said integrated value is equal to or larger than a predetermined
value.
3. A valve timing control system according to claim 1, further
including: follow-up delay determination means for determining
based on a difference between said desired cam phase and said
actual cam phase whether or not there occurs a follow-up delay of
said actual cam phase with respect to said desired cam phase; and
second calculation-permitting means for permitting said actual cam
phase deviation calculation means to calculate said amount of
deviation of said actual cam phase when it is determined by said
follow-up delay determination means that there does not occurs said
follow-up delay.
4. A valve timing control system according to claim 2, further
including: follow-up delay determination means for determining
based on a difference between said desired cam phase and said
actual cam phase whether or not there occurs a follow-up delay of
said actual cam phase with respect to said desired cam phase; and
second calculation-permitting means for permitting said actual cam
phase deviation calculation means to calculate said amount of
deviation of said actual cam phase when it is determined by said
follow-up delay determination means that there does not occurs said
follow-up delay.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a valve timing control system for
an internal combustion engine, which varies the cam phase, i.e. the
phase angle of at least one of an intake cam and an exhaust cam for
opening and closing an intake valve and an exhaust valve,
respectively, relative to a crankshaft of the engine, to thereby
control valve timing of corresponding one(s) of the intake valve
and the exhaust valve.
[0003] 2. Description of the Prior Art
[0004] Conventionally, a valve timing control system of the
above-mentioned kind was proposed in Japanese Laid-Open Patent
Publication (Kokai) No. 7-269380. This valve timing control system
includes a solenoid control valve, and a cam phase change mechanism
to which oil pressure is supplied via the solenoid control valve.
In this valve timing control system, an operation amount is output
to the solenoid control valve, whereby the oil pressure is supplied
to the cam phase change mechanism via the solenoid control valve.
The cam phase change mechanism includes two hydraulic chambers i.e.
an advance chamber and a retard chamber. The oil pressure from the
solenoid control valve is selectively supplied to one of the two
hydraulic chambers, whereby the phase angle (hereinafter simply
referred to as "the cam phase") of an intake cam relative to a
crankshaft is advanced or retarded to thereby change the valve
timing (opening/closing timing) of an intake valve.
[0005] Further, desired valve timing is calculated based on engine
rotational speed and the amount of intake air, and the solenoid
control valve is feedback-controlled such that detected valve
timing becomes coincident with the desired valve timing. During the
feedback control, a hold operation amount (operation amount at
which the cam phase change mechanism neither advances nor retards
the cam phase) is learned to enhance the accuracy of feedback
control, and a leaned value of the hold operation amount is used to
calculate the operation amount. The learned value is calculated by
adding an amount of deviation of the operation amount to the
current operation amount when the rate or speed of change in the
valve timing is within a predetermined small range, and at the same
time the amount of change in the operation amount is within a
predetermined small range, that is, when the valve timing undergoes
very small changes. The amount of deviation of the operation amount
is read from a map set in advance such that values of the amount of
deviation are indexed by respective values of the rate of change in
the valve timing.
[0006] According to the above conventional valve timing control
system, so long as the condition that the valve timing undergoes
very small changes is satisfied, the calculation of the learned
value is carried out irrespective of whether or not the cam phase
change mechanism is in normal operation, or irrespective of whether
or not the desired valve timing is being changed. Hence, it is
sometimes impossible to obtain an appropriate learned value,
resulting in the degraded accuracy of the feedback control.
Further, although the calculation of the learned value is carried
out when the valve timing undergoes very small changes, such a
state of the valve timing is often terminated in a short time
during actual operation of the internal combustion engine. This
sometimes causes the learning process to be terminated before
obtaining a sufficient number of samplings to calculate the
appropriate learned value. In such a case, the use of the learned
value results in the degraded accuracy of the feedback control.
SUMMARY OF THE INVENTION
[0007] It is an object of the invention to provide a valve timing
control system for an internal combustion engine, which is capable
of enhancing the accuracy of valve timing control.
[0008] To attain the above object, the present invention provides a
valve timing control system for an internal combustion engine
having a crankshaft, an intake valve, an exhaust valve, an intake
cam for opening and closing the intake valve, and an exhaust cam
for opening and closing the exhaust valve, the valve timing control
system controlling valve timing of at least one of the intake valve
and the exhaust valve by changing a cam phase which is a phase of
at least one of the intake cam and the exhaust cam, relative to the
crankshaft.
[0009] The valve timing control system according to the invention
is characterized by comprising:
[0010] actual cam phase-detecting means for detecting the cam phase
as an actual cam phase:
[0011] a cam phase change mechanism for changing the cam phase:
[0012] operating condition-detecting means for detecting operating
conditions of the engine;
[0013] fuel cut-off determination means for determining whether or
not fuel cut-off is being carried out for cutting off supply of
fuel to the engine;
[0014] desired cam phase-setting means for setting a desired cam
phase according to the detected operating conditions of the engine,
and fixing the desired cam phase at a constant value during the
fuel cut-off;
[0015] cam phase control means for controlling the cam phase change
mechanism such that the cam phase change mechanism causes the cam
phase to become equal to the desired cam phase, and holds the cam
phase at and after a predetermined timing during the fuel cut-off;
and
[0016] actual cam phase deviation calculation means for calculating
an amount of deviation of the actual cam phase based on a plurality
of values of the actual cam phase detected at and after the
predetermined timing during the fuel cut-off, and the constant
value of the desired cam phase.
[0017] According to this valve timing control system, it is
determined whether or not fuel cut-off is being carried out, and
during the fuel cut-off, the desired cam phase is fixed at a
constant value. Further, the cam phase change mechanism is
controlled such that it causes the cam phase to become equal to the
desired cam phase, and holds the cam phase at and after a
predetermined timing during the fuel cut-off. The amount of
deviation of the actual cam phase is calculated based on a
plurality of values of the actual cam phase detected at and after
the predetermined timing during the fuel cut-off and the constant
value of the desired cam phase. Since fuel is not burned during the
fuel cut-off, there is no need to change the desired cam phase, and
hence the desired cam phase can be fixed to the constant value, as
described above. Further, the fuel cut-off is not terminated
immediately but often continues over a certain time period.
Therefore, since the amount of deviation of (a detected value of)
the actual cam phase from a correct value to be detected is
calculated in a state in which the desired cam phase is fixed, and
the cam phase is held after the predetermined timing, it is
calculated not only based on the actual cam phase which has
sufficiently converged on the desired cam phase but also when the
converged state of the actual cam phase continues over a certain
time period, differently from the conventional valve timing control
system in which learning is carried out on condition that the valve
timing undergoes very small changes, irrespective of whether or not
the desired cam phase is being changed. This makes it possible to
calculate a learned value of the amount of deviation more
accurately reflecting an actual amount of deviation of the actual
cam phase, whereby the amount of deviation of the actual cam phase
can be calculated with higher accuracy. This makes it possible to
correct the actual cam phase during the valve timing control by
using a thus accurately calculated and hence a reliable learned
value of the amount of deviation of the actual cam phase, and
thereby enhance the accuracy of the valve timing control.
[0018] Preferably, the valve timing control system further includes
actual cam phase-integrating means for integrating an amount of
change in the actual cam phase before the fuel cut-off to obtain an
integrated value, and calculation-permitting means for permitting
the actual cam phase deviation calculation means to calculate the
amount of deviation of the actual cam phase when the integrated
value is equal to or larger than a predetermined value.
[0019] According to this preferred embodiment, the calculation of
the amount of deviation is permitted on condition that the
integrated value of the amount of change in the actual cam phase
before the fuel cut-off is equal to or larger than the
predetermined value. Generally, when the cam phase change mechanism
is in operation without being inoperatively fixed, the integrated
value of the amount of change in the actual cam phase becomes
larger with the lapse of operation time of the mechanism.
Therefore, by permitting the calculation of the amount of deviation
of the actual cam phase on condition that the integrated value is
equal to or larger than the predetermined value, it is possible to
sample only data of the actual cam phase when the cam phase change
mechanism is in operation while eliminating data of the same when
the mechanism is inoperatively fixed. This makes it possible to
fully enhance the reliability of the learned value of the amount of
deviation of the actual cam phase, and hence further increase the
accuracy of the valve timing control.
[0020] Preferably, the valve timing control system further includes
follow-up delay determination means for determining based on a
difference between the desired cam phase and the actual cam phase
whether or not there occurs a follow-up delay of the actual cam
phase with respect to the desired cam phase, and second
calculation-permitting means for permitting the actual cam phase
deviation calculation means to calculate the amount of deviation of
the actual cam phase when it is determined by the follow-up delay
determination means that there does not occurs the follow-up
delay.
[0021] According to this preferred embodiment, the calculation of
the amount of deviation of the actual cam phase is permitted when
it is determined based on the difference between the desired cam
phase and the actual cam phase that there does not occur a
follow-up delay of the latter with respect to the former. In
general, when the cam phase change mechanism is in normal
operation, there does not occur the follow-up delay or the like, so
that the difference between the desired cam phase and the actual
cam phase is small, and a state, for instance, in which the
difference is excessively large cannot continue for a long time
period. Hence, it is possible to determine, based on the
difference, whether or not there occurs the follow-up delay, i.e.
delay of the actual cam phase in following up the desired cam
phase. Therefore, by permitting the calculation of the amount of
deviation of the actual cam phase when there occurs no follow-up
delay, as described above, it is possible to sample data of the
actual cam phase when the cam phase change mechanism is in normal
operation, in other words, when the actual cam phase has converged
on the desired cam phase. This makes it possible to further enhance
the reliability of the learned value of the amount of deviation of
the actual cam phase, and hence further increase the accuracy of
the valve timing control.
[0022] The above and other objects, features, and advantages of the
invention will become more apparent from the following detailed
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a block diagram schematically showing the
arrangement of an internal combustion engine incorporating a valve
timing control system according to an embodiment of the
invention;
[0024] FIG. 2 is a flowchart showing a learned value-calculating
process carried out by the valve timing control system for
calculating a leaned value of an amount of deviation of an actual
cam phase;
[0025] FIG. 3 is a timing chart showing an example of changes in
cam phase which occur during an F/C operation of the engine
and;
[0026] FIG. 4 is a timing chart showing an example of changes in an
actual cam phase CAIN and corresponding changes in an integrated
value CAINX.
DETAILED DESCRIPTION
[0027] The invention will now be described in detail with reference
to the drawings showing an embodiment thereof. Referring first to
FIG. 1, there is schematically shown the arrangement of an internal
combustion engine incorporating a valve timing control system
according to an embodiment of the invention. As shown in the
figure, the valve timing control system 1 includes an ECU 2 that
carries out cam phase control, fuel cut-off control, and so forth
in dependence on operating conditions of an internal combustion
engine (hereinafter simply referred to as "the engine") 3.
[0028] The engine 3 is a four-stroke cycle DOHC (double overhead
camshaft) gasoline engine, which includes an intake camshaft 6 and
an exhaust camshaft 7. The intake camshaft 6 has intake cams 6a
(only one of them is shown) for opening and closing respective
intake valves 4 (only one of them is shown) during operation of the
engine 3. The exhaust camshaft 7 includes exhaust cams 7a (only one
of them is shown) for opening and closing respective exhaust valves
5 (only one of them is shown). The intake and exhaust camshafts 6,
7 are connected to a crankshaft 9 by a timing belt, not shown, for
rotating through 360 degrees as the crankshaft 9 rotates through
720 degrees. A cam phase change mechanism 8 (VTC) is arranged at
one end of the intake camshaft 6.
[0029] The cam phase change mechanism 8 includes two hydraulic
chambers, i.e. an advance chamber, not shown, and a retard chamber,
not shown. Oil pressure is selectively supplied to one of these two
hydraulic chambers, whereby the phase angle (hereinafter simply
referred to as "the cam phase") of the intake cam 6a relative to
the crankshaft 9 is continuously advanced or retarded. This
advances or retards the opening/closing timing of the intake valves
4. Further, the cam phase change mechanism 8 is connected to a
solenoid control valve 10 (cam phase control means) which is
responsive to a drive signal from the ECU 2 for being driven
thereby to selectively supply the oil pressure from an hydraulic
pump, not shown, of a lubricating system of the engine 3 to one of
the advance chamber and the retard chamber, according to the duty
ratio DOUT (%) of the drive signal. This causes the cam phase
change mechanism 8 to advance or retard the cam phase. The angle
between the most retarded position and the most advanced position
of the cam phase change mechanism 8 is set to a predetermined value
(e.g. 30 degrees of cam angle).
[0030] Further, the solenoid control valve 10 simultaneously closes
the advance chamber and the retard chamber when the received drive
signal has a predetermined hold duty ratio (e.g. 50%). This causes
the cam phase change mechanism 8 to hold (fix) the cam phase
assumed when the chambers were closed, without retarding or
advancing the same any longer.
[0031] A cam angle sensor 20 (actual cam phase-detecting means) is
arranged at the other end of the intake camshaft 6, opposite to the
one end at which the cam phase change mechanism 8 is arranged. The
cam angle sensor 20 is comprised e.g. of a magnet rotor and an MRE
(magnetic resistance element) pickup, and delivers a cam signal,
which is a pulse signal, to the ECU 2 whenever the camshaft 6
rotates through a predetermined angle (e.g. one degree). The ECU 2
calculates an actual cam phase CAIN, i.e. a detected cam phase,
based on the cam signal and a CRK signal, referred to
hereinafter.
[0032] The engine 3 has an intake pipe 11 having a throttle valve
12 arranged in an intermediate portion thereof and a throttle valve
opening sensor 21 (operating condition-detecting means) inserted
into the intermediate portion. The throttle valve 12 is driven by
the ECU 2 via a solenoid actuator, not shown, to have an opening
degree .theta.TH thereof (hereinafter referred to as "the throttle
valve opening .theta.TH) varied between a fully open position and a
fully closed position. Further, the throttle valve opening sensor
21 detects the throttle valve opening .theta.TH (parameter
representative of an operating condition of the engine 3) to
deliver a signal indicative of the sensed throttle valve opening
.theta.TH to the ECU 2.
[0033] Further, injectors 13 (only one of them is shown) and an
intake pipe absolute pressure sensor 22 (operating
condition-detecting means) formed e.g. by a semiconductor pressure
sensor are inserted into the intake pipe 11 at respective locations
downstream of the throttle valve 12. Each injector 13 is driven by
a drive signal from the ECU 2, and injects fuel into the intake
pipe 11 only during a fuel injection time period TOUT over which it
is driven by the drive signal. The intake pipe absolute pressure
sensor 22 senses an intake pipe absolute pressure PBA (parameter
representative of an operating condition of the engine 3) within
the intake pipe 11, and delivers a signal indicative of the sensed
absolute pressure PBA to the ECU 2.
[0034] The engine 3 has the crankshaft 9 to which is mounted a
crank angle position sensor 23 (cam phase detection means,
operating condition-detecting means). The crank angle position
sensor 23 is constructed e.g. similarly to the above cam angle
sensor 20, and delivers the CRK signal, which is a pulse signal, to
the ECU 2 whenever the crankshaft 9 rotates through a predetermined
angle (e.g. one degree). The ECU 2 determines an engine rotational
speed NE (parameter representative of an operating condition) of
the engine 3, based on the CRK signal. Further, the ECU 2
determines the actual cam phase CAIN based on the CRK signal and
the cam signal from the cam angle sensor 20, as described
hereinabove.
[0035] The ECU 2 (actual cam phase-detecting means, operating
condition-detecting means, fuel cut-off determination means,
desired cam phase-setting means, cam phase control means, actual
cam phase deviation calculation means, actual cam phase-integrating
means, calculation-permitting means, follow-up delay determination
means, second calculation-permitting means) is formed by a
microcomputer including an I/O interface, a CPU, a RAM, and a ROM,
none of which are specifically shown. The signals from the sensors
20 to 23 are each input to the CPU after A/D conversion and
waveform shaping by the I/O interface. The CPU determines an
operating condition of the engine 3 based on these signals, and
sets the duty ratio DOUT of the solenoid control valve 10, the fuel
injection time period TOUT of the injectors 13, and so forth,
according to a control program stored beforehand in the ROM, and
data stored in the RAM. Further, the CPU outputs drive signals
indicative of the duty ratio DOUT, the fuel injection time period
TOUT, etc. to thereby carry out cam phase control, fuel cut-off
(hereinafter referred to as "F/C operation") control, and a
deviation amount calculation process for calculating an amount of
deviation of (detected value of) the actual cam phase CAIN from a
correct value to be detected, during the F/C operation.
[0036] In the cam phase control, a desired cam phase CAINCMD is
calculated based on operating conditions (e.g. the engine
rotational speed NE, the intake pipe absolute pressure PBA, etc.)
of the engine 3, and the cam phase change mechanism 8 is controlled
in a feedback or feedforward manner such that the actual cam phase
CAIN which is corrected as described hereinafter becomes equal to
the desired cam phase CAINCMD. Further, as described hereinafter,
during the F/C operation, the desired cam phase CAINCMD is fixed at
a value CAINCMDFC assumed at a time point of the start of the F/C
operation (time t1 shown in FIG. 3), and the feedback control of
the cam phase is executed over a predetermined time period tset
from the start of the F/C operation. Further, when the
predetermined time period tset has elapsed (at a time t2 shown in
FIG. 3), the duty ratio of the solenoid control valve 10 is set to
the predetermined hold duty ratio, whereby the cam phase is held at
a value assumed when the predetermined time period tset has elapsed
(at the time t2 shown in FIG. 3).
[0037] In the following, a learned value-calculating process
carried out by the ECU 2 during the F/C operation for calculating a
learned value of the amount of deviation of the actual cam phase
CAIN will be described. FIG. 2 shows a flowchart for a routine of
the learned value-calculating process which is executed at
predetermined time intervals (e.g. every 10 msec.) according to the
settings of a timer.
[0038] As shown in FIG. 2, in the learned value-calculating
process, first, it is determined at a step S1 whether or not the
integrated value CAINX of the amount of change in the actual cam
phase CAIN is equal to or larger than a predetermined value
CAINREF. The integrated value CAINX is obtained by integrating or
adding up absolute values of the amount of change in the actual cam
phase CAIN occurring in the retarding or advancing direction over a
time period from the start of the engine 3 to the present time
point. Generally, when the cam phase change mechanism 8 is in
proper operation without being inoperatively fixed, the integrated
value CAINX becomes larger with the lapse of operation time of the
mechanism. Therefore, the determination at the step S1 permits
sampling of data of the actual cam phase CAIN only when the cam
phase change mechanism 8 is in proper operation while eliminating
data of the same when the cam phase change mechanism 8 is
inoperatively fixed. Further, the predetermined value CAINREF is
set to a value (e.g. 60 degrees of cam angle) large enough to
consider that the cam phase change mechanism 8 has been operating
without being inoperatively fixed from the start of the engine 3 to
the present time point.
[0039] A timing chart shown in FIG. 4 illustrates an example of
changes in the actual cam phase CAIN and corresponding changes in
the integrated value CAINX. In the illustrated example, as the
actual cam phase CAIN changes with the lapse of time, the
integrated value CAINX of the amount of change in the actual cam
phase CAIN is increased to become equal to the predetermined value
CAINREF at a time t0 after the start of the engine 3, and larger
thereafter.
[0040] If the answer to the question of the step S1 is negative
(No), i.e. if CAINX<CAINREF holds, the program is immediately
terminated. On the other hand, if the answer to the question of the
step S1 is affirmative (Yes), i.e. if CAINX.gtoreq.CAINREF holds,
the program proceeds to a step S2, wherein it is determined whether
or not there is a follow-up delay of the cam phase change mechanism
8. This determination is carried out in the following manner: Time
periods are integrated or added up over which the difference DCAIN
between the desired cam phase CAINCMD and the actual cam phase CAIN
calculated during the cam phase control before the start of the F/C
operation is equal to or larger than a predetermined value #DCAIN
to obtain an integrated time tint, and if the integrated time tint
is smaller than a predetermined value tref, it is determined that
there is no follow-up delay of the cam phase change mechanism,
whereas if the integrated time tint is equal to or larger than the
predetermined value tref, it is determined that there is the
follow-up delay. The integrated time tint is reset when the value
of a F/C flag, referred to hereinafter, is set to "1". The
determination at the step S2 permits the amount of deviation of the
actual cam phase CAIN to be calculated only when the cam phase
change mechanism 8 is in normal operation, in other words, when the
actual cam phase CAIN has converged on the desired cam phase
CAINCMD.
[0041] If the answer to the question of the step S2 is negative
(No), i.e. if it is determined that there is the follow-up delay,
the program is immediately terminated. On the other hand, if the
answer to the question of the step S2 is affirmative (Yes), i.e. if
it is determined that there is no follow-up delay, the program
proceeds to a step S3, wherein it is determined whether or not the
engine 3 is in the F/C operation. This determination is carried out
with reference to the value of the F/C flag. The F/C flag is set to
"1" by the F/C operation control when the throttle valve opening
.theta.TH is in the fully closed position, and at the same time the
engine 3 is in a decelerating condition at an engine rotational
speed NE equal to or smaller than a predetermined value #NE (e.g.
4000 rpm), determining that the F/C operation should be carried
out. If any of these conditions is not satisfied, the F/C flag is
set to "0".
[0042] If the answer to the question of the step S3 is negative
(No), i.e. if it is determined that the engine 3 is not in the F/C
operation, the program is immediately terminated. On the other
hand, if the answer to the question of the step S3 is affirmative
(Yes), i.e. if the engine 3 is in the F/C operation, the program
proceeds to a step S4, wherein it is determined whether or not an
F/C timer has timed out. The F/C timer is a downcount timer for
measuring a time period elapsed after the start of the F/C
operation and set to the predetermined time period tset in
synchronism with the timing of the above F/C flag being set to "1"
to start measuring the elapsed time. The predetermined time period
tset is provided for determining whether or not the feedback
control of the cam phase is carried out over a sufficiently long
time period after the start of the F/C operation for the cam phase
to converge on a desired cam phase CAINCMDFC set at a time point of
the start of the F/C operation, and set to a value large enough to
properly carry out the determination.
[0043] If the answer to the question of the step S4 is negative
(No), i.e. if it is determined that the F/C timer has not timed
out, the program is immediately terminated. On the other hand, if
the answer to the question of the step S4 is affirmative (Yes),
i.e. if the above predetermined time period tset has elapsed, it is
determined that the cam phase has sufficiently converged, and the
program proceeded to a step S5, wherein a learned value-calculating
routine is carried out for calculating the learned value of the
amount of deviation of the actual cam phase CAIN, followed by
terminating the program.
[0044] In the learned value-calculating routine, values of the
actual cam phase CAIN detected during the F/C operation are
averaged to thereby obtain an average value CAINAVE of the actual
cam phase CAIN, and a difference between the average value CAINAVE
and the desired cam phase CAINCMD is calculated as the learned
value DCALEARN of the amount of deviation of the actual cam phase
CAIN. More specifically, a present value CAIN(n) of the actual cam
phase CAIN and an immediately preceding value CAINAVE (n-1) of the
average value CAINAVE obtained in the immediately preceding loop
are multiplied by respective predetermined weighting coefficients
and added up to calculate the present value CAINAVE(n) of the
average value CAINAVE. Then, a difference between the present value
CAINAVE(n) of the average value and the predetermined value
CAINCMDFC of the desired cam phase CAINCMD fixed at the time point
of the start of the F/C operation is stored in the RAM as the
learned value DCALEARN of the amount of deviation of the actual cam
phase CAIN. The learned value DCALEARN stored in the RAM at the
time point (time t3 shown in FIG. 3) of completion of the F/C
operation is used as a correction value for correcting the actual
cam phase CAIN in cam phase control carried out thereafter.
[0045] FIG. 3 is an example of a timing chart showing changes in
the cam phase which occur during the F/C operation. As shown in the
figure, when the F/C flag is set to "1" at the time t1, the F/C
timer is set to the predetermined time period tset in synchronism
with the setting of the F/C flag, and starts measuring elapsed
time. Simultaneously, the desired cam phase CAINCMD is fixed at the
value CAINCMDFC assumed at the time t1. Form this time, the
feedback control of the cam phase continues to be carried out until
the F/C timer times out, whereby the cam phase is caused to
converge on the value CAINCMDFC. At the time t2 when the F/C timer
times out, the feedback control is terminated, and the drive signal
having the predetermined hold duty ratio, referred to hereinabove,
is supplied to the solenoid control valve 10, whereby the cam phase
change mechanism 8 holds (fixes) the cam phase at a value assumed
at the time t2.
[0046] From the time t2, the learned value-calculating routine for
calculating the learned value of the amount of deviation of the
actual cam phase CAIN continues to be carried out until the time t3
at which the F/C operation is completed. In other words, at the
time t3, the F/C flag is set to "0" to terminate the F/C operation,
and the learned value-calculating routine is terminated. From the
time t3 on, the desired cam phase CAINCMD is calculated based on
operating conditions of the engine 3, and the actual cam phase CAIN
is corrected based on the learned value DCALEARN of the amount of
deviation of the actual cam phase CAIN, while the feedback control
or feedforward control of the cam phase is executed such that the
actual cam phase CAIN corrected as above becomes equal to the
desired cam phase CAINCMD.
[0047] As described in detail heretofore, according to the valve
timing control system of the present embodiment, the desired cam
phase CAINCMD is fixed at the predetermined value CAINCMDFC during
the F/C operation, and the cam phase is held at a value assumed (at
the time t2) at a predetermined timing event during the F/C
operation, by the cam phase change mechanism. The learned value
DCALEARN of the amount of deviation of the actual cam phase CAIN is
calculated as a difference between the average value CAINAVE of a
plurality of values of the actual cam phase CAIN detected after the
predetermined timing event, and the fixed value CAINCMDFC of the
desired cam phase CAINCMD. In many cases, the fuel cut-off is not
terminated immediately but often continued for a certain time
period.
[0048] Therefore, differently from the conventional control system
in which learning is carried out on condition that the valve timing
undergoes very small changes, irrespective of whether or not a
desired cam phase CAINCMD is being changed, the learned value
DCALEARN is calculated not only based on the actual cam phase CAIN
having sufficiently converged on the fixed value CAINCMDFC of the
desired cam phase CAINCMD but also when the converged state of the
actual cam phase CAIN continues for a certain time period. This
makes it possible to calculate the leaned value DCALEARN more
accurately reflecting the actual amount of deviation of the actual
cam phase CAIN, whereby the amount of deviation of the actual cam
phase CAIN due to the aging or variation among lots of component
parts of the system can be calculated with higher accuracy. This
makes it possible to correct the actual cam phase CAIN by using the
learned value DCALEARN of the amount of deviation calculated as
above with accuracy in execution of valve timing control, thereby
enhancing the accuracy of the valve timing control.
[0049] Further, calculation of the learned value DCALEARN of the
amount of deviation is permitted, when the integrated value CAINX
of the amount of change in the actual cam phase CAIN before an F/C
operation is equal to or larger than the predetermined value
CAINREF, and at the same time when the integrated value tint of
time periods over which the difference DCAIN between the desired
cam phase CAINCMD and the actual cam phase CAIN is equal to or
larger than the predetermined value #DCAIN is smaller than a
predetermined value tref. In other words, the learned value
DCALEARN is calculated only when the cam phase change mechanism 8
is operating without being inoperatively fixed, and without
follow-up delay. This makes it possible to further enhance the
reliability of the calculated learned value DCALEARN of the amount
of deviation of the actual cam phase CAIN, and hence further
increase the accuracy of the valve timing control. Further, the
amount of deviation of the actual cam phase CAIN is not learned
before the F/C timer times out, that is, until a time period has
elapsed which is long enough to assume that the actual cam phase
CAIN has sufficiently converged on the fixed value CAINCMDFC. This
makes it possible to further increase the reliability of the
calculated learned value DCALEARN of the amount of deviation of the
actual cam phase CAIN.
[0050] Although the above-mentioned embodiment is applied to a
valve timing control system for controlling the cam phase of each
intake cam 6a, this is not limitative, but the same may be applied
to a valve-timing control system for controlling the cam phase of
each exhaust cam 7a, or for controlling the cam phase of each
intake cam 6a and the cam phase of each exhaust cam 7a. That is,
the amount of deviation of the actual cam phase of the exhaust cam
7a or the amounts of deviation of the actual cam phases of the
intake and exhaust cams may be calculated. Either of the these
systems makes it possible to obtain the same advantageous effect as
provided by the valve timing control system which calculates the
amount of deviation of the actual cam phase CAIN of the intake cam
6a, described above.
[0051] Further, the parameters for detecting operating conditions
of the engine are not limited to the engine rotational speed NE,
the throttle valve opening .theta.TH, and the intake pipe absolute
pressure PBA, but a parameter, such as an intake air temperature TA
or the like, may be also used so long as it is representative of an
operating condition of the engine.
[0052] It is further understood by those skilled in the art that
the foregoing is a preferred embodiment of the invention, and that
various changes and modifications may be made without departing
from the spirit and scope thereof.
* * * * *