U.S. patent application number 11/946083 was filed with the patent office on 2008-06-12 for controller for internal combustion engine and method for variable valve timing control for the same.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Toshifumi Hayami, Naoki Yoshiume.
Application Number | 20080135002 11/946083 |
Document ID | / |
Family ID | 39496505 |
Filed Date | 2008-06-12 |
United States Patent
Application |
20080135002 |
Kind Code |
A1 |
Yoshiume; Naoki ; et
al. |
June 12, 2008 |
CONTROLLER FOR INTERNAL COMBUSTION ENGINE AND METHOD FOR VARIABLE
VALVE TIMING CONTROL FOR THE SAME
Abstract
A controller is provided to an engine including a variable valve
timing unit for manipulating a valve timing of an intake valve of
the engine. The controller includes an idle-continuation
determining unit for determining whether an idling operation of the
engine is in a continued state. The controller further includes a
torque reserve control unit for executing a torque reserve control
to advance the valve timing and increase an intake air quantity of
the engine within a combustion limit of the engine when the
idle-continuation determining unit determines that the idling
operation is in the continued state. The controller further
includes a torque correction unit for executing a torque correction
control to retard the valve timing in the torque reserve control in
at least one of conditions where: an auxiliary device exerts a
load; the load is increased; and a vehicle starts moving.
Inventors: |
Yoshiume; Naoki;
(Takahama-city, JP) ; Hayami; Toshifumi;
(Kariya-city, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
39496505 |
Appl. No.: |
11/946083 |
Filed: |
November 28, 2007 |
Current U.S.
Class: |
123/90.12 ;
123/90.15 |
Current CPC
Class: |
F02D 2041/001 20130101;
F02D 41/083 20130101; F02D 2250/22 20130101; F01L 1/3442
20130101 |
Class at
Publication: |
123/90.12 ;
123/90.15 |
International
Class: |
F01L 1/34 20060101
F01L001/34; F01L 9/02 20060101 F01L009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2006 |
JP |
2006-329062 |
Claims
1. A controller for an engine of a vehicle, the engine including a
variable valve timing unit for manipulating an intake valve timing
including opening and closing timings of an intake valve of the
engine, the controller comprising: an idle-continuation determining
unit for determining whether an idling operation of the engine is
in a continued state; a torque reserve control unit for executing a
torque reserve control for advancing the intake valve timing and
increasing an intake air quantity of the engine within a combustion
limit of the engine when the idle-continuation determining unit
determines that the idling operation is in the continued state; and
a torque correction unit for executing a torque correction control
to retard the intake valve timing in the torque reserve control in
at least one of conditions where: an auxiliary device of the
vehicle exerts a load; the load is increased; and the vehicle
starts moving.
2. The controller according to claim 1, wherein the torque reserve
control unit regulates an advance in the intake valve timing such
that a pressure in an intake pipe of the engine is equal to or less
than a predetermined pressure in the torque reserve control.
3. The controller according to claim 1, wherein the torque reserve
control unit sets an advance in the intake valve timing and an
increase in the intake air quantity such that a variation in an
actual speed of the engine is within a predetermined range relative
to the target idling speed in the torque reserve control.
4. The controller according to claim 1, wherein the torque reserve
control unit determines the combustion limit on the basis of a
fluctuation in a speed of the engine in the torque reserve
control.
5. The controller according to claim 1, wherein the torque reserve
control unit determines the combustion limit on the basis of an
air-fuel ratio of the engine in the torque reserve control.
6. The controller according to claim 1, further comprising: a unit
for gradually shifting a target throttle position to an accelerator
demand throttle position, which is set on the basis of an
accelerator position, after the torque correction unit retards the
intake valve timing when the vehicle starts moving.
7. The controller according to claim 1, further comprising: a unit
for shifting a target throttle position to an accelerator demand
throttle position, which is set on the basis of the accelerator
position, since the accelerator demand throttle position becomes
greater than a throttle position demanded by the torque reserve
control unit, after the torque correction unit retards the intake
valve timing when the vehicle starts moving.
8. The controller according to claim 1, wherein the
idle-continuation determining unit determines whether the idling
operation is in the continued state on the basis of the accelerator
position.
9. The controller according to claim 8, wherein the
idle-continuation determining unit determines that the idling
operation is in the continued state in a condition where: the
accelerator position is equal to or less than a predetermined
threshold; and a deviation between an actual speed of the engine
and the target idling speed is equal to or less than a
predetermined threshold.
10. The controller according to claim 1, wherein the
idle-continuation determining unit determines whether the idling
operation is in the continued state on the basis of a deviation
between a throttle position, which produces the target idling
speed, and one of an actual throttle position and a target throttle
position.
11. The controller according to claim 1, wherein the variable valve
timing unit includes: a housing; a vane that partitions an interior
of the housing into an advance chamber and a retard chamber
respectively connected with hydraulic passages; a pair of check
valves respectively provided to the hydraulic passages for
restriction of a counterflow of a working fluid from the advance
chamber and the retard chamber, and the hydraulic passages are
respectively provided with drain passages being respectively in
parallel with the hydraulic passages to respectively bypasses the
check valves; and a pair of drain change-over valves respectively
provided to the hydraulic passages for communicating and blocking
the hydraulic passages.
12. A method for a variable valve timing control for an engine of a
vehicle, the method comprising: determining whether an idling
operation of the engine is in a continued state; executing a torque
reserve control for advancing an intake valve timing, which
includes opening and closing timings of an intake valve of the
engine, and increasing an intake air quantity of the engine within
a combustion limit of the engine when the idling operation is in
the continued state; and executing a torque correction control to
retard the intake valve timing in the torque reserve control in at
least one of conditions where: an auxiliary device of the vehicle
exerts a load to the engine; the load is increased; and the vehicle
starts moving.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on and incorporates herein by
reference Japanese Patent Application No. 2006-329062 filed on Dec.
6, 2006.
FIELD OF THE INVENTION
[0002] The present invention relates to a controller for an
internal combustion engine provided with a variable valve timing
unit for varying opening and closing timings of an intake valve of
the internal combustion engine The present invention further
relates to a method for a variable valve timing control for the
internal combustion engine.
BACKGROUND OF THE INVENTION
[0003] For example, when an auxiliary device applies a load to an
internal combustion engine during an idling operation of the
engine, or when the load is increased during the idling operation,
an increase in a torque of the engine is demanded. Alternatively,
when a vehicle starts during the idling operation, an increase in
the torque of the engine is also demanded. The auxiliary device may
be an air conditioner, a power steering, and the like.
[0004] Conventionally, in such a demand in torque, throttle
positions of a throttle valve and an idling speed control valve
(ISC valve) are corrected to increase an intake air quantity,
whereby a torque loss caused by the load of the auxiliary device
are compensated for and the torque of the engine can be increased
at the start of the vehicle. In this correction of the throttle
positions, a torque fluctuation (torque reduction) caused by the
load of the auxiliary device and a torque shortage at the start of
the vehicle are suppressed so as to reduce a lag in an actual
torque relative to a demand torque.
[0005] However, an actual change in the in-cylinder charging air
delays relative to the manipulation of the throttle valve and the
ISC valve. In addition, a response of the torque of the engine
caused by the charging air also delays relative to the
manipulation. Therefore, only with the manipulation of the
positions of the throttle valve and the ISC valve, the actual
torque cannot be controlled with good response relative to the
fluctuation in the demand torque. Thus, the idling speed cannot be
sufficiently maintained.
[0006] An in-cylinder charging efficiency can be changed with good
response by switching over opening and closing characteristics such
as a working angle and a lift of an intake valve and an exhaust
valve of an internal combustion engine. Therefore, a torque in a
system provided with the variable valve unit can be manipulated
with good response by switching over the opening and closing
characteristics. U.S. Pat. No. 5,446,359 (JP-A-H8-338273) discloses
a variable valve unit that manipulates a valve opening
characteristic and a valve closing characteristic by switching
cams, which drive an intake valve and an exhaust valve of an
internal combustion engine. Specifically, in U.S. Pat. No.
5,446,359, a normal cam is switched to an auxiliary device
actuation cam to switch over the valve opening and closing
characteristics, when the auxiliary device such as an air
conditioner and the like operates during the idling operation. The
torque can be increased by switchover of the valve opening and
closing characteristics. Thus, a torque loss caused by a load of
the auxiliary device can be compensated for with good response to
maintain the idling speed.
[0007] However, the system provided with the variable valve timing
involves a problem. Specifically, when the load caused by the
auxiliary device is applied or increased during the idling
operation, or when the vehicle is started, torque may not be
produced sufficient to compensate for a demand for an increase in
torque or to maintain the idling speed, even manipulating opening
and closing timings of an intake valve from an advance angle
position suited to the idling operation at the normal idling.
SUMMARY OF THE INVENTION
[0008] In view of the foregoing and other problems, it is an object
of the present invention to produce a controller for an internal
combustion engine of a vehicle, the controller being adapted to
suppressing torque fluctuation to maintain an engine speed. It is
another object of the present invention to produce a method for a
variable valve timing control for the internal combustion
engine.
[0009] According to one aspect of the present invention, a
controller for an engine of a vehicle, the engine including a
variable valve timing unit for manipulating an intake valve timing
including opening and closing timings of an intake valve of the
engine, the controller comprising an idle-continuation determining
unit for determining whether an idling operation of the engine is
in a continued state. The controller further comprises a torque
reserve control unit for executing a torque reserve control for
advancing the intake valve timing and increasing an intake air
quantity of the engine within a combustion limit of the engine when
the idle-continuation determining unit determines that the idling
operation is in the continued state. The controller further
comprises a torque correction unit for executing a torque
correction control to retard the intake valve timing in the torque
reserve control in at least one of conditions where: an auxiliary
device of the vehicle exerts a load; the load is increased; and the
vehicle starts moving.
[0010] According to another aspect of the present invention, a
method for a variable valve timing control for an engine of a
vehicle, the method comprising determining whether an idling
operation of the engine is in a continued state. The method further
comprising executing a torque reserve control for advancing an
intake valve timing, which includes opening and closing timings of
an intake valve of the engine, and increasing an intake air
quantity of the engine within a combustion limit of the engine when
the idling operation is in the continued state. The method further
comprising executing a torque correction control to retard the
intake valve timing in the torque reserve control in at least one
of conditions where: an auxiliary device of the vehicle exerts a
load to the engine; the load is increased; and the vehicle starts
moving.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The above and other objects, features and advantages of the
present invention will become more apparent from the following
detailed description made with reference to the accompanying
drawings. In the drawings:
[0012] FIG. 1 is a view showing an outline of a whole engine
control system in an embodiment;
[0013] FIG. 2 is a view schematically showing a variable valve
timing unit and its hydraulic control circuit;
[0014] FIG. 3 is a view illustrating a retard angle operation, a
holding operation, and an advance angle operation of the variable
valve timing unit;
[0015] FIG. 4 is a time chart illustrating a determination of an
idle-continuation;
[0016] FIG. 5 is a time chart illustrating a determination of a
starting condition:
[0017] FIG. 6 is a time chart illustrating a torque reserve
control;
[0018] FIG. 7 is a time chart illustrating the torque reserve
control;
[0019] FIG. 8 is a time chart illustrating a torque correction
control;
[0020] FIG. 9 is a time chart illustrating the torque correction
control;
[0021] FIG. 10 is a flowchart illustrating a VVT control
routine;
[0022] FIG. 11 is a flowchart illustrating a target advance angle
calculating routine;
[0023] FIG. 12 is a flowchart illustrating an idle-continuation
target advance angle calculating routine;
[0024] FIG. 13 is a flowchart illustrating the idle-continuation
target advance angle calculating routine;
[0025] FIG. 14 is a flowchart illustrating a throttle position
control routine;
[0026] FIG. 15 is a flowchart illustrating a target throttle
position calculating routine;
[0027] FIG. 16 is a flowchart illustrating an idle-continuation
target throttle position calculating routine;
[0028] FIG. 17 is a flowchart illustrating the idle-continuation
target throttle position calculating routine;
[0029] FIG. 18 is a flowchart illustrating an idle-continuation
determining routine; and
[0030] FIG. 19 is a flowchart illustrating a combustion limit
determining routine.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Embodiment
[0031] First, an outline of a whole engine control system is
described with reference to FIG. 1. An air cleaner 53 is provided
upstreammost of an intake pipe 52 of an internal combustion engine
51. An air flowmeter 54 is provided downstream of the air cleaner
53 to detect an intake air quantity. A throttle valve 56 and a
throttle position sensor 57 are provided downstream of the air
flowmeter 54. A motor 55 is provided to control an opening, i.e.,
position of the throttle valve 56. The throttle position sensor 57
detects the opening (throttle position) of the throttle valve
56.
[0032] A surge tank 58 is provided downstream of the throttle valve
56. An intake-pipe pressure sensor 59 is provided to the surge tank
58 to detect pressure in an intake pipe. The surge tank 58 is
provided with intake manifolds 60, which lead air into respective
cylinders of the engine 51. Fuel injection valves 61 are
respectively provided in the vicinity of intake ports of the intake
manifolds 60 for respective cylinders of the engine to inject fuel.
Ignition plugs 62 are mounted to a cylinder head of the engine 51
to ignite air-fuel mixture in the cylinders by generating spark
discharge.
[0033] The engine 51 is provided with a vane type variable valve
timing unit 11, which varies a valve timing (opening and closing
timing) of an intake valve 67. An exhaust pipe 63 of the engine 51
is provided with an exhaust gas sensor 64 such as an air-fuel ratio
sensor and an oxygen sensor for detecting an air-fuel ratio of
exhaust gas or rich and lean conditions of exhaust gas. A catalyst
65 such as a three-way catalyst is provided downstream of the
exhaust gas sensor 64 for purification of exhaust gas.
[0034] A cylinder block of the engine 51 is provided with a
cooling-water temperature sensor 66 and a crank angle sensor 44.
The cooling-water temperature sensor 66 detects temperature of
cooling water of the engine 51. The crank angle sensor 44 outputs a
pulse signal each time where the engine 51 rotates by a
predetermined crank angle. The crank angle and an engine speed are
detected on the basis of an output signal from the crank angle
sensor 44. Further, an accelerator position corresponding to
depression of an accelerator pedal is detected by an accelerator
sensor 68.
[0035] Outputs of such various sensors are input into an electronic
control unit (ECU) 43. The ECU 43 is constructed mainly of a
microcomputer to execute various engine control programs stored in
a built-in ROM (memory medium) to control fuel injection quantities
of the fuel injection valves 61 and ignition timings of the
ignition plugs 62 according to an engine operating state.
[0036] Subsequently, the construction of the vane type variable
valve timing unit 11 is described with reference to FIG. 2. A
housing 12 of the vane type variable valve timing unit 11 is
screwed and fixed to a sprocket by bolts 13. The sprocket is
rotatably supported on an outer periphery of a camshaft (not shown)
of the intake valve. In this structure, rotation of a crankshaft of
an engine is transmitted to the sprocket and the housing 12 via a
timing chain, so that the sprocket and the housing 12 rotate in
synchronism with the crankshaft. A vane rotor 14 is received in the
housing 12 such that the vane rotor 14 is rotatable relative to the
housing 12. The vane rotor 14 is screwed and fixed to an end of the
camshaft by a bolt 15.
[0037] Multiple vane chambers 16 are formed in the housing 12. The
vane chambers 16 respectively receive multiple vanes 17 provided to
an outer periphery of the vane rotor 14. The vanes 17 are rotatable
in the vane chambers 16 in both advance and retard angle
directions. Each of the vane chambers 16 is partitioned into an
advance angle chamber 18 and a retard angle chamber 19 by each of
the vanes 17.
[0038] When hydraulic pressure equal to or greater than a
predetermined pressure is exerted to both the advance angle
chambers 18 and the retard angle chambers 19, the vanes 17 are held
by the hydraulic pressure. In this condition, rotation of the
housing 12 caused by rotation of the crankshaft is transmitted to
the vane rotor 14 via the hydraulic pressure, and the camshaft is
rotationally driven integrally with the vane rotor 14. While the
engine operates, a hydraulic control valve 21 controls hydraulic
pressure in the advance angle chambers 18 and the retard angle
chambers 19 to turn the vane rotor 14 relative to the housing 12,
thereby controlling a displacement angle (camshaft phase) of the
camshaft relative to the crankshaft to vary a valve timing of the
intake valve 67.
[0039] One of the vanes 17 has both sides provided with stopper
portions 22, 23 for restriction of a rotative range, in which the
vane rotor 14 turns relative to the housing 12. Specifically, the
stopper portions 22, 23 restricts an aftermost retard angle
position and a foremost advance angle position of a displacement
angle of the camshaft. One of the vanes 17 is provided with a lock
pin 24, which locks the displacement angle of the camshaft at a
predetermined locked position when the engine stops, or the like.
When the lock pin 24 is locked, the lock pin 24 is fitted into a
lock hole (not shown) provided to the housing 12 to hold the
displacement angle of the camshaft at the predetermined locked
position. The locked position is set at a position suited to
starting of the vehicle. The locked position is, for example, a
substantially intermediate position in a controllable range, in
which the displacement angle of the camshaft can be controlled.
[0040] Working oil in an oil pan 26 is fed through the hydraulic
control valve 21 to a hydraulic control circuit of the variable
valve timing unit 11 by an oil pump 27. The hydraulic control
circuit is provided with hydraulic pressure feed passages 28, 29.
Oil is discharged from an advance angle pressure port of the
hydraulic control valve 21, and is fed to the advance angle
chambers 18 through the hydraulic pressure feed passages 28. Oil is
discharged from a retard angle pressure port of the hydraulic
control valve 21, and is fed to the retard angle chambers 19
through the hydraulic pressure feed passages 29.
[0041] Check valves 30, 31 are provided for restriction of a
counterflow of the working oil from the respective chambers 18, 19.
The check valves 30, 31 respectively have the hydraulic pressure
feed passages 28 of the advance angle chambers 18 and the hydraulic
pressure feed passages 29 of the retard angle chambers 19.
According to the embodiment, the check valves 30, 31 are provided
to the hydraulic pressure feed passages 28, 29 of the advance angle
chamber 18 and the retard angle chamber 19 of only one vane chamber
16. Alternatively, the check valves 30, 31 may be provided to the
hydraulic pressure feed passages 28, 29 of the advance angle
chambers 18 and the retard angle chambers 19 of two or greater vane
chambers 16.
[0042] Drain oil passages 32, 33 are respectively provided in
parallel with the hydraulic pressure feed passages 28, 29 of the
respective chambers 18, 19. The drain oil passages 32, 33
respectively bypass the check valves 30, 31. Drain change-over
valves 34, 35 are provided respectively to the drain oil passages
32, 33. Each of the drain change-over valves 34, 35 include a spool
valve operated in a valve closing direction by being exerted with
hydraulic pressure (pilot pressure) from a hydraulic change-over
valve 38. The drain change-over valves 34, 35 are respectively held
at valve open positions by springs 41, 42 when not being exerted
with the hydraulic pressure. When the drain change-over valves 34,
35 are opened, the drain oil passages 32, 33 are opened, thereby
defeat operations of the check valves 30, 31. By contrast, when the
drain change-over valves 34, 35 are closed, the drain oil passages
32, 33 are closed, thereby enabling the check valves 30, 31. In
this condition, the check valves 30, 31 respectively restrict
counterflow of oil from the chambers 18, 19, thereby maintaining
hydraulic pressure in the chambers 18, 19.
[0043] Since the respective drain changeover valves 34, 35 need not
electric wiring, the drain change-over valves 34, 35 are assembled
compactly to the vane rotor 14 in the vane type variable valve
timing unit 11 together with the check valves 30, 31. Thereby, the
drain change-over valves 34, 35 are arranged near the respective
chambers 18, 19 to enable opening and closing of the respective
drain oil passages 32, 33 near the respective chambers 18, 19 with
good response at the time of advance angle and retard angle
operations.
[0044] The hydraulic control valve 21 includes an advance and
retard angle hydraulic control function 37 and the hydraulic
change-over valve (drain change-over control function) 38
integrated with each other. The advance and retard angle hydraulic
control function 37 includes a spool valve driven by a linear
solenoid 36 for control of hydraulic pressure fed to the advance
angle chambers 18 and the retard angle chambers 19. The hydraulic
change-over valve (drain change-over control function) 38 is
provided for change-over of hydraulic pressure for driving the
respective drain change-over valves 34, 35. The ECU 43 controls an
electric current (control duty) carried to the linear solenoid 36
of the hydraulic control valve 21.
[0045] The ECU 43 calculates an actual valve timing (actual
displacement angle) of the intake valve 67 on the basis of output
signals from the crank angle sensor 44 and a cam angle sensor 45.
The ECU 43 further calculates a target valve timing (target
displacement angle) of the intake valve 67 on the basis of outputs
from various sensors such as the intake-pipe pressure sensor 59 and
the cooling-water temperature sensor 66 for detecting an engine
operating state. The ECU 43 executes routines for control of a
variable valve timing to perform a feedback control of a drive
current of the hydraulic control valve 21 of the variable valve
timing unit 11 such that the actual valve timing agrees with the
target valve timing. Hydraulic pressure in the advance angle
chambers 18 and the retard angle chambers 19 is controlled to turn
the vane rotor 14 relative to the housing 12, thereby changing the
displacement angle of the camshaft such that the actual valve
timing agrees with the target valve timing.
[0046] When the intake valve 67 is driven to open and close while
the engine operates, a torque fluctuation is applied to the
camshaft from the intake valve 67 and is transmitted to the vane
rotor 14, whereby torque fluctuation in the advance and retard
angle directions acts on the vane rotor 14. Therefore, when the
torque fluctuation is applied to the vane rotor 14 in the retard
angle direction, the working oil in the advance angle chambers 18
is applied with pressure and pushed out from the advance angle
chambers 18. When torque fluctuation is applied to the vane rotor
14 in the advance angle direction, the working oil in the retard
angle chambers 19 is applied with pressure and pushed out from the
retard angle chambers 19. When rotation speed of the oil pump 27
being a hydraulic pressure supply source is low, hydraulic pressure
of the oil pump 27 becomes low. In this condition, in a structure
where the check valves 30, 31 are not provided, the vane rotor 14
is pushed back to the retard angle direction by the torque
fluctuation even when the oil pump 27 feeds the hydraulic pressure
to the advance angle chambers 18 to advance the displacement angle
of the camshaft. As a result, controlling of the vane rotor 14 at
the target displacement angle takes long, and a response of the
control becomes low.
[0047] In contrast, according to the embodiment, the check valves
30, 31 are respectively provided to the hydraulic pressure feed
passages 28 of the advance angle chambers 18 and the hydraulic
pressure feed passages 29 of the retard angle chambers 19 for
restriction of the counterflow of oil from the respective chambers
18, 19. In addition, the drain oil passages 32, 33, which bypass
the check valves 30, 31, are respectively provided in parallel with
the hydraulic pressure feed passages 28, 29 of the respective
chambers 18, 19. Further, the drain change-over valves 34, 35 are
respectively provided to the drain oil passages 32, 33. In this
structure, as shown in FIG. 3, hydraulic pressure in the respective
chambers 18, 19 is controlled in the following retard angle
operation, the holding operation, and the advance angle
operation.
[0048] (Retard Angle Operation)
[0049] In the retard angle operation, the actual valve timing is
caused to retard toward the target valve timing on the retard angle
side. In this retard angle operation, feeding of hydraulic pressure
to the drain change-over valve 34 of the advance angle chamber 18
is stopped to open the drain change-over valve 34 of the advance
angle chamber 18, thereby defeating the function of the check valve
30 of the advance angle chamber 18. Further, in this retard angle
operation, hydraulic pressure is applied to the drain change-over
valve 35 of the retard angle chamber 19 from the hydraulic
change-over valve 38 to close the drain change-over valve 35 of the
retard angle chamber 19, thereby enabling the function of the check
valve 31 of the retard angle chamber 19. In this operation, the
check valve 31 restricts counterflow of oil from the retard angle
chamber 19, and the hydraulic pressure is efficiently fed to the
retard angle chamber 19 to enhance a response in the retard angle
operation, regardless of torque the fluctuation of the vane rotor
14 in the advance angle direction even when the hydraulic pressure
is low.
[0050] (Holding Operation)
[0051] In the holding operation, the actual valve timing is held at
the target valve timing. In this holding operation, hydraulic
pressure is applied to both the drain change-over valves 34, 35 of
the advance angle chamber 18 and the retard angle chamber 19 from
the hydraulic change-over valve 38 to close both the drain
change-over valves 34, 35. In this condition, the functions of both
the check valves 30, 31 of the advance angle chamber 18 and the
retard angle chamber 19 are enabled. When torque applied from the
intake valve 67 to the camshaft fluctuates, torque fluctuating in
the retard and advance angle directions is applied to the vane
rotor 14. In the state of the holding operation, even when the
fluctuating torque is applied to the vane rotor 14, the check
valves 30, 31 restrict counterflow of oil from both the advance
angle chamber 18 and the retard angle chamber 19 to restrict a
decrease in hydraulic pressure holding the vanes 17 from both sides
thereof. Thus, the holding stability of the vanes 17 can be
enhanced.
[0052] (Advance Angle Operation)
[0053] In the advance angle operation, the actual valve timing is
advanced toward the target valve timing on the advance angle side.
In this advance angle operation, hydraulic pressure is applied to
the drain change-over valve 34 of the advance angle chamber 18 from
the hydraulic change-over valve 38 to close the drain change-over
valve 34 of the advance angle chamber 18, thereby enabling the
function of the check valve 30 of the advance angle chamber 18.
Further, in this advance angle operation, feeding of hydraulic
pressure to the drain change-over valve 35 of the retard angle
chamber 19 is stopped to open the drain change-over valve 35 of the
retard angle chamber 19, thereby defeating the function of the
check valve 31 of the retard angle chamber 19. In this operation,
the check valve 30 restricts counterflow of oil from the advance
angle chamber 18, and the hydraulic pressure is efficiently fed to
the advance angle chamber 18 to enhance a response in the advance
angle operation, regardless the torque fluctuation of the vane
rotor 14 in the retard angle direction even when the hydraulic
pressure is low.
[0054] When an auxiliary device such as an air conditioner and a
power steering are operated in a condition where the engine 51 is
in an idling operation or the vehicle starts, torque produced by
the engine 51 fluctuates and decreases. As a result, the engine
speed may decrease due to the load of the auxiliary device and the
starting of the vehicle.
[0055] As a countermeasure to the decrease in the engine speed, the
ECU 43 executes routines for control of the variable valve timing
(VVT) and the throttle position shown in FIGS. 10 to 19. The ECU 43
and the routines for control of the VVT and the throttle position
shown in FIGS. 10 to 19 serve as a torque reserve control unit and
a torque compensation unit.
[0056] As shown in a time chart of FIG. 4, at a time point t1, an
actual accelerator position AP is less than an idle threshold ID1.
The idle threshold ID1 is in the vicinity of a full-close position,
for example. In addition, an actual engine speed NE becomes equal
to or less than an idle threshold ID2, and a deviation between the
actual engine speed NE and a target idling speed is equal to or
less than a predetermined value. In this condition, an
idle-continuation counter CIDL begins counting. At a time point t2,
the idle-continuation counter CIDL exceeds a predetermined value
kIDL. In this condition, the idling operation of the engine 51 is
determined to be continued, and an idle-continuation flag XIDL is
set to 1. This function serves as an idle-continuation determining
unit.
[0057] Thereafter, as shown in a time chart of FIG. 5, at a time
point t3 or at a time point where an actual engine speed NE exceeds
the idle threshold 102, when the actual accelerator position AP
exceeds the idle threshold ID1, it is determined that the idling
operation terminates and a starting condition of the vehicle comes
out. In this condition, the idle-continuation flag XIDL is set to
0, and the idle-continuation counter CIDL is set to 0. The
idle-continuation counter CIDL may be subjected to a
guard-processing with a predetermined upper limit guard value.
[0058] In addition, as shown in time charts of FIGS. 6 and 7, at a
time point t4, when the idle-continuation flag XIDL is set to 1 and
a predetermined condition for executing a VVT in-idling advance
control is met, a torque reserve control is executed. In the torque
reserve control, an intake valve timing, which is the valve timing
of the intake valve 67, is advanced, and an increase correction of
the throttle position is performed to increase the intake air
quantity. In this operation a decrease in torque caused by the
advance of the intake valve timing cancels an increase in torque
caused by an increase in intake air quantity. Therefore, the torque
can be maintained substantially constant. In addition, to the
canceling of the increase in torque, a retard-angle correction of
the intake valve timing is executed to increase the torque
sufficiently to compensate for a torque loss caused by the load of
the auxiliary device and the like. In this state, the decrease in
torque by the advance of the intake valve timing is equivalent to a
reserve torque, which can be generated by the retard-angle
correction of the intake valve timing. In addition, in the course
of the torque reserve control, the ignition timing, an in-cylinder
charging efficiency, and the like may be corrected according to the
advance angle of the intake valve timing in the same manner as at
the time of normal operation. The in-cylinder charging efficiency
can be corrected by manipulating the exhaust valve timing,
correcting the EGR rate, and the like.
[0059] In the torque reserve control, as shown in the time chart of
FIG. 6, the advance angle of the intake valve timing and the
throttle position are regulated such that an intake pressure PM
does not exceed a predetermined pressure kPM. In this operation,
the intake pressure PM is regulated below a predetermined pressure
kVVTPM to be maintained in a negative pressure state, in which a
sufficient brake performance for a brake device can be ensured, in
the course of torque reserve control. Here, the intake pressure PM
of the engine 51 is used to actuate the brake device.
[0060] The predetermined pressure kPM is an upper limit value of
the intake pressure PM, which can ensure a sufficient brake
performance. The predetermined pressure kPM may be set slightly
less than the upper limit value.
[0061] Further, as shown in the time chart of FIG. 7, in the torque
reserve control, a combustion limit of the engine 51 is determined
on the basis of a fluctuation in the engine speed NE. The advance
angle of the intake valve timing and the throttle position are
limited such that a combustion condition of the engine 51 does not
exceed the combustion limit, i.e., within the combustion limit.
[0062] In the torque reserve control, the advance angle of the
intake valve timing and the increase in intake air quantity may be
set such that the actual engine speed NE does not fluctuate a
predetermined value or greater beyond a target idling speed. In
this operation, it is possible to restrict the actual engine speed
NE from fluctuating beyond the target idling speed in the torque
reserve control. Thus, the idling speed can be stabilized.
[0063] Thereafter, as shown in time charts of FIGS. 8, 9, at a time
point t5, the auxiliary device is turned ON to apply the load in
the course of the torque reserve control. In this condition, an
auxiliary device flag XLOAD is set to 1, and a torque correction
control is executed.
[0064] In this torque correction control, as shown in the time
chart of FIG. 8, in the case where the reserve torque is equal to
or greater than an auxiliary device demand torque, the retard-angle
correction of the intake valve timing is performed by the retard
angle corresponding to the auxiliary device demand torque. The
reserve torque is the torque, which can be generated by the
retard-angle correction of the intake valve timing. The auxiliary
device demand torque is a torque required to compensate for the
torque loss caused by the load of the auxiliary device. The
retard-angle correction of the intake valve timing is performed
with good response, so as to temporarily compensate the torque loss
caused by the load of the auxiliary device. Thereby, the idling
speed can be maintained with good response by suppressing torque
fluctuation caused by the load of the auxiliary device in the
idling operation.
[0065] At a time point t5, the retard-angle correction of the
intake valve timing is performed in order to compensate for the
torque loss caused by the load of the auxiliary device. In
addition, at the time point t5, an increase correction of the
throttle position begins to gradually increase the throttle
position to regularly compensate for the torque loss caused by the
load of the auxiliary device. At the time point t6, a predetermined
time kLOAD has elapsed since the time point t5, in which the
retard-angle correction of the intake valve timing is performed and
the increase correction of the throttle position begins. At the
time point t6, the in-cylinder charging air is determined to be
actually increasing, and the torque is determined to be also
increasing since the increase correction of the throttle position.
Therefore, at the time point t6, the advance-angle correction of
the intake valve timing is again performed. In this operation, the
torque loss is once caused by the load of the auxiliary device, and
the torque loss is compensated for by the increase in torque by
performing the retard-angle correction of the intake valve timing.
The torque compensated for by the retard-angle correction is
further compensated for by the increase correction of the throttle
position. At that time, the throttle position or the increase
correction of the throttle position is stored immediately before
the beginning of the increase correction of the throttle
position.
[0066] Thereafter, at a time point t7, the auxiliary device is
turned OFF, and hence the auxiliary device does not apply the load.
At the time point t7, a decrease correction of the throttle
position is performed to return the throttle position to the
throttle position immediately before the starting of the increase
correction of the throttle position, and the auxiliary device flag
XLOAD is set to 0.
[0067] As shown in the time chart of FIG. 9, at a time point t5,
the reserve torque is equal to or less than the auxiliary device
demand torque, and the auxiliary device flag XLOAD is set to 1
since the auxiliary device is turned ON. At the time point t5, in
this condition, a retard-angle correction of the intake valve
timing is performed by a retard angle corresponding to the reserve
torque. The reserve torque corresponds to the advance-angle
correction in the torque reserve control. At the time point t5, in
this condition, the increase correction of the throttle position is
further performed by a transient correction opening of the throttle
valve 56. The transient correction opening of the throttle valve 56
corresponds to a difference between the auxiliary device demand
torque and reserve torque. The difference between the auxiliary
device demand torque and the reserve torque is a short relative to
the auxiliary device demand torque. Thereby, the torque loss caused
by the load of the auxiliary device is temporarily compensated for
with good response by the retard-angle correction of the intake
valve timing and the increase in torque by the increase correction
of the throttle position.
[0068] In addition, when the idling operation is terminated and
starting of the vehicle is detected in the course of the torque
reserve control, the retard-angle correction of the intake valve
timing is performed by the retard angle corresponding to the
reserve torque. The retard angle corresponds to the advance-angle
correction by the torque reserve control. Thus, a torque loss
caused by the starting of the vehicle is temporarily compensated
for with good response by the increase in torque by the
retard-angle correction of the intake valve timing. Thereby, the
engine speed NE can be maintained with good response by suppressing
torque fluctuation caused by the load of the auxiliary device in
the idling operation. Thus, torque fluctuation cause by the
starting of the vehicle is suppressed with good response and the
engine speed NE can be maintained.
[0069] The torque reserve control and the torque correction control
are executed by the ECU 43 according to the respective programs
shown in FIGS. 10 to 19. The processings in the respective routines
shown in FIGS. 10 to 19 is described below.
[0070] (VVT Control)
[0071] A VVT control routine shown in FIG. 10 is executed at a
predetermined interval when the ECU 43 is turned ON. When the
routine is started up, an operating state, which includes the
engine speed NE, the load, the in-cylinder charging efficiency, the
cooling-water temperature, and the like, are detected in STEP 101.
Thereafter the procedure proceeds to STEP 102 to determine whether
a predetermined condition for executing the VVT control is met on
the basis of the detected operating state. Consequently, in the
case where it is determined that the predetermined condition for
executing the VVT control is not met, the routine is terminated
without performing processings subsequent to STEP 103.
[0072] In contrast, in the case where it is determined that the
predetermined condition for executing the VVT control is met in
STEP 102, the procedure proceeds to STEP 103. In STEP 103, an
actual advance angle of the intake valve timing is calculated in
accordance with a phase difference between an output signal of the
crank angle sensor 44 and a subsequently generated output signal of
the cam angle sensor 45. The actual advance angle corresponds to a
present position relative to a most retard angle position.
Subsequently, the procedure proceeds to STEP 104. In STEP 104, a
target advance angle calculating routine shown in FIG. 11 is
executed to calculate a target advance angle VTT of the intake
valve timing on the basis of the present operating state and the
like.
[0073] Thereafter, the procedure proceeds to STEP 105 to execute a
VVT control mode determining routine (not shown) to determine
whether the VVT control mode is any one of a feedback control mode,
a retention control mode, a cleaning mode, and the like, on the
basis of the present operating state and the like.
[0074] Thereafter, the procedure proceeds to STEP 106 to calculate
an OCV target current according to a present VVT control mode such
that the actual advance angle of the intake valve timing agrees
with the target advance angle VTT Subsequently, the procedure
proceeds to STEP 107 to calculate a control duty for controlling
the control current of the hydraulic control valve 21 (OCV) at the
OCV target current, and the routine is terminated.
[0075] (Target Advance Angle Calculation)
[0076] A target advance angle calculating routine shown in FIG. 11
is a sub-routine executed in STEP 104 of the VVT control routine
shown in FIG. 10. When the routine is started up, the engine speed
NE and a load, which corresponds to the intake air quantity and the
intake pressure PM, are first detected in STEP 201. The procedure
proceeds to STEP 202, in which a reference target advance angle
VTTbs corresponding to the engine speed NE and the load is obtained
referring to a data map of the reference target advance angle
VTTbs. The data map of the reference target advance angle VTTbs is
defined such that the reference target advance angle VTTbs becomes
0 at the time of the idling operation.
[0077] Thereafter, the procedure proceeds to STEP 203 to execute an
idle-continuation target advance angle calculating routine shown in
FIGS. 12 and 13 to calculate an idle-continuation target advance
angle VTTid at the time of an idle-continuation, in which the
idling continues. The procedure proceeds to STEP 204 to add the
idle-continuation target advance angle VTTid at the time of the
idle-continuation to the reference target advance angle VTTbs to
obtain a final target advance angle VTT
VTT=VTTbs+VTTid
[0078] (Idle-Continuation Target Advance Angle Calculation)
[0079] An idle-continuation target advance angle calculating
routine shown in FIGS. 12 and 13 is a sub-routine executed in STEP
203 of the target advance angle calculating routine shown in FIG.
11. When the routine is started up, an operating state, which
includes the engine speed NE, the load, the in-cylinder charging
efficiency, the cooling-water temperature, and the like, is first
detected in STEP 301. The procedure proceeds to STEP 302 to execute
an idle-continuation determining routine shown in FIG. 18 to
determine whether the idling operation continues. The
idle-continuation flag XIDL is set to 1, which indicates that the
idling operation continues, or 0 according to the results of
determination.
[0080] Thereafter, the procedure proceeds to STEP 303 to determine
whether the VVT in-idling advance control executing condition is
met, depending upon whether the idle-continuation flag XIDL is set
to 1 and a normal idling speed control (ISC) executing condition is
met.
[0081] In the case where it is determined in STEP 303 that the VVT
in-idling advance control executing condition is met, the procedure
proceeds to STEP 304 to determine whether the auxiliary device is
turned ON to apply the load. In the case where it is determined in
STEP 304 that the auxiliary device is turned OFF and does not apply
the load, the procedure proceeds to STEP 313 to maintain or reset
the auxiliary device flag XLOAD to 0 and reset a retard angle
shortage .DELTA.VTload to 0.
[0082] Thereafter, the procedure proceeds to STEP 314 in FIG. 13 to
determine whether the intake pressure PM is less than a
predetermined pressure kPM. The predetermined pressure kPM is set
to an upper limit value of the intake pressure, which can ensure a
sufficient brake negative pressure, or a value slightly less than
the upper limit value.
[0083] In the case where it is determined in STEP 314 that the
intake pressure PM is less than the predetermined pressure kPM, it
is determined that a sufficient brake negative pressure can be
ensured. In this condition, the procedure proceeds to STEP 315 to
perform the increase correction of the idle-continuation target
advance angle VTTid by a predetermined value .DELTA.VT1.
VTTid=VTTid+.DELTA.VT1
[0084] Thereafter, the procedure proceeds to STEP 316 to execute a
combustion limit determining routine shown in FIG. 19 to determine
whether a combustion limit is reached on the basis of fluctuation
in the engine speed NE. A combustion limit flag XBRNLMT is set to
1, which indicates the combustion limit, or 0 according to the
results of the determination.
[0085] Thereafter, the procedure proceeds to STEP 317 to determine
whether the combustion limit flag XBRNLMT is set to 1. In the case
where it is determined that the combustion limit flag XBRNLMT is 0,
the idle-continuation target advance angle VTTid is gradually
increased by repeating the increase correction of the
idle-continuation target advance angle VTTid by the predetermined
value .DELTA.VT1. The idle-continuation target advance angle VTTid
is gradually increased until it is determined in STEP 314 that the
intake pressure PM is equal to or greater than the predetermined
pressure kPM, or it is determined in STEP 317 that the combustion
limit flag XBRNLMT is set to 1. Thereby, the intake valve timing is
gradually advanced when the idle-continuation is determined.
[0086] Thereafter, when it is determined in STEP 314 that the
intake pressure PM is equal to or greater than the predetermined
pressure kPM, the procedure proceeds to STEP 318. In STEP 318, the
advance angle of the intake valve timing is limited by performing a
decrease correction of the idle-continuation target advance angle
VTTid by the predetermined value .DELTA.VT2 to limit the
idle-continuation target advance angle VTTid such that the intake
pressure PM does not increase beyond the predetermined pressure
kPM.
[0087] When it is determined in STEP 317 that the combustion limit
flag XBRNLMT is set to 1, the procedure proceeds to STEP 318. In
STEP 318, the advance angle of the intake valve timing is limited
by performing the decrease correction of the idle-continuation
target advance angle VTTid by the predetermined value VT2 to
regulate the idle-continuation target advance angle VTTid, such
that the idle-continuation target advance angle VTTid does not
exceed the combustion limit.
[0088] After performing the increase correction of the
idle-continuation target advance angle VTTid to advance the intake
valve timing, when it is determined in STEP 304 shown in FIG. 12
that the auxiliary device is turned ON, the procedure proceeds to
STEP 305. In STEP 305, when it is determined that the auxiliary
device has just been turned to ON from the OFF state, the procedure
proceeds to STEP 306. In STEP 306, an auxiliary device demand
retard angle VTload is calculated to conform to the operating state
of the auxiliary device and the like with reference to a data map,
for example. The data map may be created for each auxiliary device.
The auxiliary device demand retard angle VTload is a retard angle
of the intake valve timing, which produces the auxiliary device
demand torque, which is a torque required to compensate for the
torque loss caused by the load of the auxiliary device.
[0089] Thereafter, the procedure proceeds to STEP 307 to determine
whether the present idle-continuation target advance angle VTTid is
equal to or greater than the auxiliary device demand retard angle
VTload. That is, in step 307, it is determined whether the reserve
torque is equal to or greater than the auxiliary device demand
torque. In the case where it is determined in STEP 307 that the
idle-continuation target advance angle VTTid is equal to or greater
than the auxiliary device demand retard angle VTload, that is, the
reserve torque is equal to or greater than the auxiliary device
demand torque, the procedure proceeds to STEP 308. In STEP 308, the
decrease correction of the idle-continuation target advance angle
VTTid is performed by the auxiliary device demand retard angle
VTload, and the auxiliary device flag XLOAD is set to 1.
VTTid=VTTid-VTload
XLOAD=1
[0090] Thereby, when it is determined that the auxiliary device is
turned ON, the retard-angle correction of the intake valve timing
is performed by the auxiliary device demand retard angle VTload
corresponding to the auxiliary device demand torque. Thus, the
torque loss caused by the load of the auxiliary device is
temporarily compensated for with good response by the increase in
torque by the retard-angle correction of the intake valve
timing.
[0091] By contrast, in the case where it is determined in STEP 307
that the idle-continuation target advance angle VTTid is less than
the auxiliary device demand retard angle VTload, that is, the
reserve torque is less than the auxiliary device demand torque, the
auxiliary device demand retard angle VTload cannot be ensured even
by performing the decrease correction of the idle-continuation
target advance angle VTTid to 0. In this condition, the procedure
proceeds to STEP 309. In STEP 309, the idle-continuation target
advance angle VTTid is subtracted from the auxiliary device demand
retard angle VTload to obtain the retard angle shortage
.DELTA.VTload for the auxiliary device demand retard angle VTload.
The decrease correction of the idle-continuation target advance
angle VTTid to 0 is performed, and the auxiliary device flag XLOAD
is set to 1.
.DELTA.VTload=VTload-VTTid
VTTid=0
XLOAD=1
[0092] Thereby, when it is determined that the auxiliary device is
turned ON, the retard-angle correction of the intake valve timing
is performed by the retard angle, which is the idle-continuation
target advance angle VTTid corresponding to the reserve torque.
[0093] In this manner, after the decrease correction of the
idle-continuation target advance angle VTTid is performed to retard
the intake valve timing, the procedure proceeds to STEP 310. In
STEP 310, a counter CLOAD is set to a predetermined count value
kLOAD, and then proceeds to STEP 311 to count down the count value
of the counter CLOAD by 1 to count the time lapsed after the
auxiliary device is turned ON. Thereafter, in the case where it is
determined in STEP 305 that the auxiliary device has not just been
turned ON, the procedure jumps over the processings of STEPS 306 to
310 to proceed to STEP 311 to count down the counter CLOAD 1 by 1.
At this time, the counter CLOAD may be subjected to a guard
processing at a lower limit guard value such as 0.
[0094] Thereafter, the procedure proceeds to STEP 312 shown in FIG.
13 to determine whether the counter CLOAD is equal to or less than
0. In the case where it is determined that the counter CLOAD is
greater than 0, the routine is terminated without performing the
processings subsequent to STEP 314. Thereby, another of the
advance-angle correction of the intake valve timing is inhibited
until beginning of an increase in the torque by increase in the in
in-cylinder charging air by the increase correction of the throttle
position.
[0095] When it is determined in STEP 312 that the counter CLOAD is
equal to or less than 0, that is, at the time point when the
predetermined time kLOAD lapses, the increase correction of the
throttle position leads to an actual increase in the in-cylinder
charging air to increase the torque. In this condition, another of
the advance-angle correction of the intake valve timing is
performed by executing processings of STEP 314 to STEP 318. Thus,
the intake pressure PM does not increase beyond the predetermined
pressure kPM, and the combustion limit is not exceeded.
[0096] In the case where it is determined in STEP 303 shown in FIG.
12 that the VVT in-idling advance control executing condition is
not met, it is determined that the idling operation terminates and
the vehicle is started, and the procedure proceeds to STEP 319. In
STEP 319, the idle-continuation target advance angle VTTid is set
to 0, the auxiliary device flag XLOAD is set to 0, and the retard
angle shortage .DELTA.VTload is reset to 0. Thereby, the
retard-angle correction of the intake valve timing is performed by
the retard angle, which is the idle-continuation target advance
angle VTTid corresponding to the reserve torque, and the torque
loss caused by the starting of the vehicle is temporarily
compensated for with good response by the increase in torque by the
retard-angle correction of the intake valve timing.
[0097] (Throttle Position Control)
[0098] The throttle position control routine shown in FIG. 14 is
executed at a predetermined interval when the ECU 43 is turned ON.
When the routine is started up, an operating state is detected in
STEP 401, and then the procedure proceeds to STEP 402 to determine
whether a predetermined throttle control executing condition is
met, on the basis of the detected operating state. In this
condition, the operating state includes the accelerator position,
the engine speed NE, an abnormal flag, and the like. Consequently
in the case where it is determined that the throttle control
executing condition is not met, the routine is terminated without
performing the processings subsequent to STEP 403.
[0099] In contrast, in the case where it is determined that the
throttle control executing condition is met in STEP 402, the
procedure proceeds to STEP 403. In STEP 403, the actual throttle
position is detected on the basis of the output signal from the
throttle position sensor 57. In STEP 404, a target throttle
position calculating routine shown in FIG. 15 is executed to
calculate a target throttle position TA on the basis of a present
operating state and the like.
[0100] In STEP 405, a throttle position control mode determining
routine (not shown) is executed to determine whether a throttle
position control mode is any one of a normal control mode, a limp
home control mode, and the like, on the basis of the present
operating state and the like. In STEP 406, the control duty of the
motor 55 of the throttle valve 56 is calculated according to a
present throttle position control mode such that the actual
throttle position agrees with the target throttle position TA.
Thus, the routine is terminated.
[0101] (Target Throttle Position Calculation)
[0102] A target throttle position calculating routine shown in FIG.
15 is a sub-routine executed in STEP 404 of the throttle position
control routine shown in FIG. 14. When the routine is started up,
an accelerator sensor detection value APmad based on an output
signal from the accelerator sensor 68 is obtained in STEP 501. In
STEP 502, an accelerator full-close position learning routine (not
shown) is executed to learn an accelerator full-close position
AP0.
[0103] Thereafter, the procedure proceeds to STEP 503 to correct
the accelerator sensor detection value APmad by using the
accelerator full-close position AP0 as learnt to obtain an actual
accelerator position AP.
AP=APmad-AP0
[0104] Thereafter, the procedure proceeds to STEP 504 to execute an
accelerator demand throttle position calculating routine (not
shown) to calculate an accelerator demand throttle position TAap
conformed to the actual accelerator position AP and the like.
[0105] Thereafter, the procedure proceeds to STEP 505 to execute an
ISC demand air calculating routine (not shown) to calculate an ISC
demand air quantity Qisc on the basis of the target idling speed
and the like. The procedure proceeds to STEP 506 to execute an ISC
demand throttle position calculating routine (not shown) to
calculate an ISC demand throttle position TAisc conformed to the
ISC demand air quantity Qisc, and the like.
[0106] Thereafter, the procedure proceeds to STEP 507 to execute an
idle-continuation target throttle position calculating routine
shown in FIGS. 16 and 17 to calculate the idle-continuation target
throttle position TAvvt at the time of the idle-continuation.
[0107] Thereafter, the procedure proceeds to STEP 508 to obtain a
throttle sensor detection value TAmad based on an output signal
from the throttle position sensor 57. The procedure proceeds to
STEP 509 to execute a throttle full-close position learning routine
(not shown) to learn a throttle full-close position TA0.
[0108] Thereafter, the procedure proceeds to STEP 510 to calculate
a final target throttle position TA by substituting the accelerator
demand throttle position TAap, the ISC demand throttle position
TAisc, the idle-continuation target throttle position TAvvt, and
the throttle full-close position TA0 to the following formula.
TA=TAap+TAisc+TAvvt+TA0
[0109] (Idle-Continuation Target Throttle Position Calculation)
[0110] An idle-continuation target throttle position calculating
routine shown in FIGS. 16 and 17 is a sub-routine executed in STEP
507 of the target throttle position calculating routine shown in
FIG. 15. When the routine is started up, an operating state, which
includes the engine speed NE, the load, the in-cylinder charging
efficiency, the cooling-water temperature, and the like, is first
detected in STEP 601. The procedure proceeds to STEP 602 to execute
an idle-continuation determining routine shown in FIG. 18 to
determine whether the idling operation continues. The
idle-continuation flag XIDL is set to 1, which indicates that the
idling operation continues, or 0 according to the results of
determination.
[0111] Thereafter, the procedure proceeds to STEP 603 to determine
whether the VVT in-idling advance control executing condition is
met, depending upon whether the idle-continuation flag XIDL is set
to 1 and a normal idling speed control (ISC) executing condition is
met.
[0112] In the case where it is determined in STEP 603 that the VVT
in-idling advance control executing condition is met, the procedure
proceeds to STEP 604 to determine whether the auxiliary device is
turned ON to apply the load. In the case where it is determined in
STEP 604 that the auxiliary device is turned OFF and the auxiliary
device does not apply the load, the procedure proceeds to STEP 612
to perform the decrease correction of an auxiliary device
correction opening TAload by a predetermined value .DELTA.TA3.
[0113] Thereafter, the procedure proceeds to STEP 613 shown in FIG.
17 to determine whether the intake pressure PM is less than the
predetermined pressure kPM. When it is determined that the intake
pressure PM is less than the predetermined pressure kPM, the
procedure proceeds to STEP 614 to perform the increase correction
of a VVT interlocking opening TAvvtb, which is conformed to the
advance-angle correction (idle-continuation target advance angle
VTTid) of the intake valve timing, by a predetermined value
.DELTA.TA4.
TAvvtb=TAvvtb+.DELTA.TA4
[0114] Thereafter, the procedure proceeds to STEP 615 to execute a
combustion limit determining routine shown in FIG. 19 to determine
whether a combustion limit is reached on the basis of fluctuation
in the engine speed NE. The combustion limit flag XBRNLMT is set to
1, which indicates the combustion limit, or 0 according to the
results of the determination.
[0115] Thereafter, the procedure proceeds to STEP 616 to determine
whether the combustion limit flag XBRNLMT is set to 1. In the case
where it is determined that the combustion limit flag XBRNLMT is
set to 0, the VVT interlocking opening TAvvtb is gradually
increased by repeating the increase correction of the VVT
interlocking opening TAvvtb by the predetermined value .DELTA.TA4,
until it is determined in STEP 614 that the intake pressure PM is
equal to or greater than the predetermined pressure kPM, or it is
determined in STEP 616 that the combustion limit flag XBRNLMT is
set to 1. Hereby, the throttle position is gradually increased when
the idle-continuation is determined.
[0116] Thereafter, when it is determined in STEP 614 that the
intake pressure PM is equal to or mort than the predetermined
pressure kPM, the procedure proceeds to STEP 617. In STEP 617, the
throttle position is limited by performing the decrease correction
of the VVT interlocking opening TAvvtb by a predetermined value
.DELTA.TA5 to limit the VVT interlocking opening TAvvtb such that
the intake pressure PM does not increase beyond the predetermined
pressure kPM.
[0117] When it is determined in STEP 616 that the combustion limit
flag XBRNLMT is set to 1, the procedure proceeds to STEP 617. In
STEP 617, the throttle position is limited by performing the
decrease correction of the VVT interlocking opening TAvvtb by the
predetermined value .DELTA.TA5 to limit the VVT interlocking
opening TAvvtb such that the combustion limit is not exceeded.
[0118] Thereafter, the procedure proceeds to STEP 618 to add the
auxiliary device correction opening TAload to the VVT interlocking
opening TAvvtb to obtain the idle-continuation target throttle
position TAvvt.
TAvvt=TAvvtb+TAload
[0119] In the case where it is determined in STEP 604 shown in FIG.
16 that the auxiliary device is turned ON after performing the
increase correction of the idle-continuation target throttle
position TAvvt to increase the throttle position, the procedure
proceeds to STEP 605. In STEP 605, it is determined whether the
retard angle shortage .DELTA.VTload of VVT calculated in STEP 309
shown in FIG. 12 is greater than 0, that is, it is determined
whether the idle-continuation target advance angle VTTid is less
than the auxiliary device demand retard angle VTload and the
reserve torque is equal to or less than the auxiliary device demand
torque.
[0120] In the case where it is determined in STEP 605 that the
retard angle shortage .DELTA.VTload of VVT is greater than 0, the
auxiliary device demand retard angle VTload cannot be ensured even
when the decrease correction of the idle-continuation target
advance angle VTTid is performed to 0. In this condition, the
procedure proceeds to STEP 606 to obtain a transient correction
opening TAloadc conformed to the retard angle shortage
.DELTA.VTload of VVT from a data map or the like. The transient
correction opening TAloadc is a throttle position correction
magnitude corresponding to torque of the retard angle shortage
.DELTA.VTload of VVT and serves to compensate for an intake
response delay.
[0121] Thereafter, the procedure proceeds to STEP 607 to perform
the increase correction of the auxiliary device correction opening
TAload by the transient correction opening TAloadc to reset the
retard angle shortage .DELTA.VTload of VVT to 0.
TAload=TAload+TAloadc
.DELTA.VTload=0
[0122] Thereby, in the case where it is determined that the retard
angle shortage .DELTA.VTload of VVT is greater than 0, that is, the
reserve torque is less than the auxiliary device demand torque, the
retard-angle correction of the intake valve timing by a retard
angle (the idle-continuation target advance angle VTTid)
corresponding to the reserve torque is performed. In addition, the
increase correction of the throttle position is performed by the
transient correction opening TAloadc corresponding to the shortage
(shortage of VVT in retard angle) in the reserve torque relative to
the auxiliary device demand torque. Thus, the torque loss caused by
the auxiliary device load is temporarily compensated for with good
response by the retard-angle correction of the intake valve timing
and the increase in the torque by the increase correction of the
throttle position.
[0123] Thereafter, the procedure proceeds to STEP 608 to obtain a
steady condition auxiliary device demand opening TAloadb conformed
to an operating state of the auxiliary device and the like with
reference to a data map. The data map may be created for each
auxiliary device. The steady condition auxiliary device demand
opening TAloadb is the throttle position, which corresponds to the
auxiliary device demand torque, which is a torque required to
compensate for the torque loss caused by the load of the auxiliary
device. The throttle position is to be converged to the steady
condition auxiliary device demand opening TAloadb when a steady
condition comes out.
[0124] Thereafter, the procedure proceeds to STEP 609 to determine
whether the auxiliary device correction opening TAload is less than
the steady condition auxiliary device demand opening TAloadb. In
the case where it is determined that the auxiliary device
correction opening TAload is less than the steady condition
auxiliary device demand opening TAloadb, the procedure proceeds to
STEP 610 to perform the increase correction of the auxiliary device
correction opening TAload by a predetermined value .DELTA.TA1. At
this time, the auxiliary device correction opening TAload may be
subjected to a guard processing at an upper limit guard value. The
upper limit guard value may be the steady condition auxiliary
device demand opening TAloadb, for example.
TAload=TAload+ATA1
[0125] Thereafter, in the case where it is determined in the
above-mentioned STEP 609 that the auxiliary device correction
opening TAload is equal to or greater than the steady condition
auxiliary device demand opening TAloadb, the procedure proceeds to
STEP 611 to perform the decrease correction of the auxiliary device
correction opening TAload by a predetermined value .DELTA.TA2. At
this time, the auxiliary device correction opening TAload may be
subjected to a guard processing at a lower limit guard value. The
lower limit guard value may be 0, for example.
TAload=TAload-.DELTA.TA2
[0126] In this manner the increase correction of the auxiliary
device correction opening TAload is performed such that the
auxiliary device correction opening TAload agrees substantially
with the steady condition auxiliary device demand opening TAloadb.
Thereby, the increase correction of the throttle position is
performed. In this condition, the torque loss, which is compensated
for so far by the increase in torque by the retard-angle correction
of the intake valve timing, is compensated by the increase in
torque by the increase correction of the throttle position.
[0127] Thereafter, when it is determined in STEP 604 that the
auxiliary device is turned OFF, and the auxiliary device does not
apply the load, the procedure proceeds to STEP 612 to perform the
decrease correction of the auxiliary device correction opening
TAload by the predetermined value .DELTA.TA3. At this time, the
auxiliary device correction opening TAload may be subjected to a
guard processing at a lower limit guard value. The lower limit
guard value may be 0, for example.
TAload=TAload-.DELTA.TA3
[0128] Thereby, the decrease correction of the throttle position is
performed to return the throttle position to the throttle position
immediately before the increase correction of the throttle position
begins.
[0129] Thereafter, in the case where it is determined in STEP 603
that the VVT in-idling advance control executing condition is not
met, it is determined that the idling operation terminates and the
starting condition of the vehicle comes out, and the procedure
proceeds to STEP 619. In STEP 619, it is determined whether an
accelerator demand throttle position TAap, which is conformed to
the actual accelerator position AP and the like, is equal to or
greater than the idle-continuation target throttle position
TAvvt.
[0130] In the case where it is determined in STEP 619 that the
accelerator demand throttle position TAap is less than the
idle-continuation target throttle position TAvvt, the procedure
proceeds to STEP 620 to perform the decrease correction of the
idle-continuation target throttle position TAvvt by a predetermined
value .DELTA.TA6.
TAvvt=TAvvt-ATA6
[0131] Thereafter, when it is determined in STEP 619 that the
accelerator demand throttle position TAap is equal to or greater
than the idle-continuation target throttle position TAvvt, the
procedure proceeds to STEP 621 to reset the idle-continuation
target throttle position TAvvt to 0.
[0132] After the intake valve timing is caused to retard when the
starting condition of the vehicle is detected, the
idle-continuation target throttle position TAvvt is set to 0 after
the accelerator demand throttle position TAap becomes equal to or
greater than the idle-continuation target throttle position TAvvt.
Thereafter, the final target throttle position TA is set to the
accelerator demand throttle position TAap. Thus, the actual
throttle position is smoothly controlled to the accelerator demand
throttle position TAap at the starting.
[0133] In addition, after the intake valve timing is caused to
retard when the starting condition of the vehicle is detected, the
actual throttle position may be smoothly controlled to the
accelerator demand throttle position TAap by shifting the final
target throttle position TA to the accelerator demand throttle
position TAap after the accelerator demand throttle position TAap
becomes greater than the actual throttle position.
[0134] Alternatively, after the intake valve timing is caused to
retard when the starting condition of the vehicle is detected, the
final target throttle position TA may be gradually shifted to the
accelerator demand throttle position TAap by delaying in the
control or the like.
[0135] (Idle-Continuation Determination)
[0136] The idle-continuation determining routine shown in FIG. 18
is a sub-routine executed in STEP 302 shown in FIG. 12 and STEP 602
shown in FIG. 16. When the routine is started up, the actual
accelerator position AP is first detected in STEP 701. The
procedure proceeds to STEP 702 to determine whether the actual
accelerator position AP is equal to or less than the idle threshold
ID1, which is, for example, a position in the vicinity of the
full-close position.
[0137] In the case where it is determined in STEP 702 that the
actual accelerator position AP is equal to or less than the idle
threshold ID1, the procedure proceeds to STEP 703 to detect the
actual engine speed NE. The procedure proceeds to STEP 704 to
determine whether the actual engine speed NE is equal to or less
than an idle threshold ID2. That is, in STEP 704, it is determined
whether a deviation between the actual engine speed NE and the
target idling speed is equal to or less than a predetermined
value.
[0138] When it is determined in STEP 702 that the actual
accelerator position AP is equal to or less than the idle threshold
ID1, and it is determined in STEP 704 that the actual engine speed
NE is equal to or less than the idle threshold ID2, the procedure
proceeds to STEP 705 to begin the processing of counting up the
idle-continuation counter CIDL 1 by 1.
[0139] Thereafter, the procedure proceeds to STEP 706 to determine
whether the count value of the idle-continuation counter CIDL is
equal to or greater than the predetermined value kIDL. When it is
determined that the count value of the idle-continuation counter
CIDL is equal to or greater than the predetermined value kIDL, the
procedure proceeds to STEP 707, determining that the idling
operation of the engine 51 continues, and the idle-continuation
flag XIDL is set to 1.
[0140] In contrast, in the case where it is determined in STEP 702
that the actual accelerator position AP is greater than the idle
threshold ID1, the procedure proceeds to STEP 708. Alternatively,
in the case where it is determined in STEP 704 that the actual
engine speed NE is greater than the idle threshold ID2, that is,
the deviation between the actual engine speed NE and the target
idling speed is greater than the predetermined value, the procedure
proceeds to STEP 708. In STEP 708, the idle-continuation counter
CIDL is reset to 0, and the idle-continuation flag XIDL is
maintained or reset to 0.
[0141] In the routine shown in FIG. 18, it is determined that the
idling operation is in the continued state, when the state, in
which the actual accelerator position AP is equal to or less than
the idle threshold ID1 and the actual engine speed NE is equal to
or less than the idle threshold ID2, that is, the deviation between
the actual engine speed NE and the target idling speed is equal to
or less than the predetermined value, continues for a predetermined
period. The method for determination of the state, in which the
idling operation continues, may be appropriately modified. For
example, the state, in which the idling operation continues, may be
determined when the state, in which the actual accelerator position
AP is equal to or less than the idle threshold ID1, continues for a
predetermined period. When the accelerator position is returned to
the vicinity of the full-close position, the state of idling
operation is brought about. Therefore, it possible to accurately
determine whether the idling operation continues by monitoring the
accelerator position.
[0142] The state, in which the idling operation continues, may be
determined when a state, in which a deviation between an ISC demand
throttle position and the actual throttle position, continues for a
predetermined period. Alternatively, the state, in which the idling
operation continues, may also be determined when the target
throttle position becomes equal to or less than a predetermined
value, continues for a predetermined period.
[0143] When the target throttle position is set to the ISC demand
throttle position and the actual throttle position is controlled at
the ISC demand throttle position, the state of idling operation is
brought about. Therefore, it possible to accurately determine
whether the idling operation continues by evaluating of the
deviation between the ISC demand throttle position and the actual
throttle position or a target throttle position.
[0144] (Combustion Limit Determination)
[0145] The combustion limit determining routine shown in FIG. 19 is
a sub-routine executed in STEP 316 shown in FIG. 13 and STEP 615
shown in FIG. 17. When the routine is started up, the actual engine
speed NE is first detected in STEP 801 and then the procedure
proceeds to STEP 802 to calculate an engine speed fluctuation
NEfluct. The engine speed fluctuation NEfluct may be calculated by,
for example, assuming that a difference between the actual engine
speed NE at the last time and the actual engine speed NE at the
present time is the engine speed fluctuation NEfluct.
Alternatively, the engine speed fluctuation NEfluct may be
calculated by assuming that a difference between the maximum value
of the actual engine speed NE and the minimum value of the actual
engine speed NE in a predetermined period is the engine speed
fluctuation NEfluct.
[0146] The combustion state of the engine 51 becomes unstable in
the vicinity of the combustion limit of the engine 51, and the
engine speed fluctuation NEfluct increases. Therefore, it is
possible to accurately determine the combustion limit by monitoring
the engine speed fluctuation NEfluct.
[0147] Thereafter, the procedure proceeds to STEP 803 to determine
whether the engine speed fluctuation NEfluct is equal to or greater
than the combustion limit determination value kBRN. In the case
where it is determined that the engine speed fluctuation NEfluct is
equal to or greater than the combustion limit determination value
kBRN, the procedure proceeds to STEP 804, determining that the
combustion limit of the engine 51 is reached, to set the combustion
limit flag XBRNLMT to 1.
[0148] In contrast, in the case where it is determined in STEP 803
that the engine speed fluctuation NEfluct is less than the
combustion limit determination value kBRN, the procedure proceeds
to STEP 805 to maintain or reset the combustion limit flag XBRNLMT
at 0.
[0149] In the routine shown in FIG. 19, the combustion limit is
determined on the basis of the engine speed fluctuation NEfluct.
Alternatively, a method for determination of the combustion limit
may be appropriately modified, and for example, the combustion
limit may be determined on the basis of the air-fuel ratio of the
engine 51. The combustion state of the engine 51 becomes unstable
in the vicinity of the combustion limit of the engine 51, and the
air-fuel ratio of exhaust gas is considerably varied. Therefore, it
is possible to accurately determine the combustion limit by, for
example, monitoring the variation in air-fuel ratio of exhaust
gas.
[0150] In the embodiment described above, when it is determined
that the idling operation continues, the torque reserve control is
executed. In the torque reserve control, the intake valve timing is
once advanced, and the increase correction of the throttle position
is performed to increase the intake air quantity. Therefore, the
torque reserve control enables the retard-angle correction of the
intake valve timing to increase the torque enough to compensate for
the torque loss caused by the load of the auxiliary device and the
like. The torque reserve control performs the retard-angle
correction of the intake valve timing, while maintaining the torque
substantially constant by decreasing the torque by the advance of
the intake valve timing to cancel the increase in torque by the
increase in intake air quantity. In this operation, simply
advancing of the intake valve timing may lead to deterioration in
combustion, nevertheless, the increase in intake air quantity can
restrict the deterioration in combustion caused by the advance of
the intake valve timing. Thus, a favorable state of combustion can
be maintained. Furthermore, a loss in pumping can be decreased by
the increase in intake air quantity and/or the increase in intake
pressure, so that it is possible to enhance a fuel consumption
during the idling operation.
[0151] The torque correction control for causing the intake valve
timing to retard is executed when the auxiliary device and the like
apply the load or the starting condition of the vehicle is detected
in the course of the torque reserve control. Therefore, the torque
loss caused by the load of the auxiliary device and the starting of
the vehicle can be compensated for with good response by increase
in the torque by the retard-angle correction of the intake valve
timing. Thereby, it is possible to suppress torque fluctuation
caused by the load of the auxiliary device at the time of idling
operation and starting of the vehicle with good response. Thus, it
is possible to effectively restrict a drop in rotating speed at the
time of idling operation and at the start.
[0152] The torque correction control may be executed when the load
of the auxiliary device and the like quickly increases in the
course of the torque reserve control.
[0153] Here, in a system, in which an intake pressure of the engine
51 is used to actuate a brake device, a sufficient brake negative
pressure may not be ensured when the intake pressure excessively
increases in torque reserve control.
[0154] In this respect, according to the embodiment, the advance
angle of the intake valve timing and the throttle position are
restricted such that the intake pressure does not exceed a
predetermined pressure in the torque reserve control. Therefore, it
is possible to restrict the intake pressure to a predetermined
pressure or less in the torque reserve control to maintain the
intake pressure in a state of negative pressure, such that a
sufficient brake performance can be ensured.
[0155] In addition, the variable valve timing unit 11 includes the
check valves 30, 31, the drain change-over valves 34, 35, and the
like being capable of ensuring the responsibility thereof even at
low hydraulic pressure. Therefore, the torque reserve control can
be executed with good response for advancing the intake valve
timing and the torque correction control for causing the intake
valve timing to retard, even in the idling operation in the
low-speed operation, in which the hydraulic pressure fed from the
oil pump 27 is low.
[0156] In addition, the variable valve timing unit 11 may be
appropriately modified in construction. The variable valve timing
unit 11 may be applied to a system mounting thereon various
hydraulically driven variable valve timing units such as a vane
type variable valve timing unit, in which the check valves 30, 31,
the drain change-over valves 34, 35, and the like are omitted. The
variable valve timing unit 11 may be applied to a variable valve
timing unit other than a vane type variable valve timing unit. For
example, the variable valve timing unit 11 may be applied to a
helical type variable valve timing unit, and the like.
[0157] Further, the invention is not limited to a system mounting
thereon a vane type variable valve timing unit but can be variously
modified and embodied in application to a system mounting thereon
an electrically-driven variable valve timing unit.
[0158] The above processings such as calculations and
determinations are not limited being executed by the ECU 43. The
control unit may have various structures including the ECU 43 shown
as an example.
[0159] It should be appreciated that while the processes of the
embodiments of the present invention have been described herein as
including a specific sequence of steps, further alternative
embodiments including various other sequences of these steps and/or
additional steps not disclosed herein are intended to be within the
steps of the present invention.
[0160] Various modifications and alternations may be diversely made
to the above embodiments without departing from the spirit of the
present invention.
* * * * *