U.S. patent application number 11/090216 was filed with the patent office on 2005-10-20 for valve actuation controlling apparatus and method for engine.
Invention is credited to Hashizume, Akira.
Application Number | 20050229880 11/090216 |
Document ID | / |
Family ID | 34940770 |
Filed Date | 2005-10-20 |
United States Patent
Application |
20050229880 |
Kind Code |
A1 |
Hashizume, Akira |
October 20, 2005 |
Valve actuation controlling apparatus and method for engine
Abstract
After commanding an engine to stop, an electronic controller
controls a variable working-angle control mechanism to increase the
working angle of an intake valve in preparation for restarting of
the engine. In the case of an automatic stop, which is followed by
restarting of the engine in a relatively short time, the working
angle of the intake valve is set to the maximum working angle of
the variable working-angle control mechanism, which maximizing
decompression. In a manual stop, it is necessary to allow for both
hot start and cold start. Also, in the manual stop, a target
working angle when the engine is stopped is set less than that of a
case of the automatic stop. Thus, the starting characteristic is
prevented from being degraded by increased friction of engine parts
during a cold start, and knocking is prevented from occurring due
to a high compression ratio in a cylinder during a hot start.
Inventors: |
Hashizume, Akira;
(Yokohama-shi, JP) |
Correspondence
Address: |
KENYON & KENYON
1500 K STREET NW
SUITE 700
WASHINGTON
DC
20005
US
|
Family ID: |
34940770 |
Appl. No.: |
11/090216 |
Filed: |
March 28, 2005 |
Current U.S.
Class: |
123/90.15 |
Current CPC
Class: |
Y02T 10/12 20130101;
F02D 2041/001 20130101; F02D 41/0005 20130101; Y02T 10/42 20130101;
F01L 2800/03 20130101; F02D 13/0234 20130101; F01L 13/00 20130101;
Y02T 10/18 20130101; Y02T 10/40 20130101; F02D 41/042 20130101;
F01L 1/34 20130101 |
Class at
Publication: |
123/090.15 |
International
Class: |
F01L 001/34 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 2004 |
JP |
2004-120486 |
Claims
1. A valve actuation controlling apparatus applied to an engine
equipped with a variable working-angle control mechanism which
varies working angle of an intake valve, wherein, after commanding
the engine to stop, the valve actuation controlling apparatus
controls the variable working-angle control mechanism to increase
the working angle of the intake valve in preparation for restarting
of the engine.
2. The valve actuation controlling apparatus according to claim 1,
wherein the apparatus adjusts a throttle opening of the engine in
accordance with the increase in the working angle of the intake
valve after commanding the engine to stop.
3. A valve actuation controlling apparatus applied to an engine
equipped with a variable working-angle control mechanism which
varies working angle of an intake valve, wherein, after commanding
the engine to stop, the valve actuation controlling apparatus
controls the variable working-angle control mechanism to increase
the working angle of the intake valve in preparation for restarting
of the engine, and varies the increased working angle according to
whether a stopping requirement of the engine is satisfied.
4. The valve actuation controlling apparatus according to claim 3,
wherein the increased working angle is varied within a range where
the valve closing time of the intake valve coincides with a middle
period of a compression stroke.
5. The valve actuation controlling apparatus according to claim 3,
wherein the engine includes an ignition switch and performs
automatic stop/restart control, wherein the engine stopping
requirement comprises: an automatic stopping requirement that is
satisfied when the engine is stopped by the automatic stop/restart
control; and a manual stopping requirement that is satisfied when
the ignition switch has been turned off, and the engine is stopped
by the manual stopping requirement is satisfied, accordingly.
6. The valve actuation controlling apparatus according to claim 5,
wherein the increased working angle that has been varied in
accordance with the automatic stopping requirement is larger than
the increased working angle that has been varied in accordance with
the manual stopping requirement.
7. The valve actuation controlling apparatus according to claim 6,
wherein the engine includes a cylinder, and wherein the increased
working angle that has been varied in accordance with the automatic
stopping requirement is set to a maximum working angle of the
variable working-angle control mechanism, and wherein the increased
working angle that has been varied in accordance with the manual
stopping requirement is equal to or lower than an upper limit of a
range in which a compression ratio of air in the cylinder does not
cause knocking during a hot start of the engine, and is equal to or
higher than a lower limit of a range in which a compression ratio
of air in the cylinder permits a torque sufficient for a cold start
of the engine to be generated.
8. The valve actuation controlling apparatus according to claim 3,
wherein the engine further includes a variable phase mechanism that
varies a center of the working angle of the intake valve, wherein,
after commanding the engine to stop, the valve actuation
controlling apparatus, in preparation for restarting of the engine,
sets the working angle center of the intake valve to a phase that
is set according to the stopping requirement of the engine.
9. The valve actuation controlling apparatus according to claim 3,
wherein the apparatus adjusts a throttle opening of the engine in
accordance with the increase in the working angle of the intake
valve after commanding the engine to stop.
10. An engine having a variable working-angle control mechanism
which varies working angle of an intake valve and a valve actuation
controlling apparatus, wherein, after commanding the engine to
stop, the valve actuation controlling apparatus controls the
variable working-angle control mechanism to increase the working
angle of the intake valve in preparation for restarting of the
engine.
11. The engine according to claim 10, wherein the valve actuation
controlling apparatus adjusts a throttle opening of the engine in
accordance with the increase in the working angle of the intake
valve after commanding the engine to stop.
12. An engine having a variable working-angle control mechanism
which varies working angle of an intake valve and a valve actuation
controlling apparatus, wherein, after commanding the engine to
stop, the valve actuation controlling apparatus controls the
variable working-angle control mechanism to increase the working
angle of the intake valve in preparation for restarting of the
engine, and varies the increased working angle according to whether
a stopping requirement of the engine is satisfied.
13. The engine according to claim 12, wherein the increased working
angle is varied within a range where the valve closing time of the
intake valve coincides with a middle period of a compression
stroke.
14. The engine according to claim 12, further comprising an
ignition switch, wherein the engine performs automatic stop/restart
control, wherein the engine stopping requirement comprises: an
automatic stopping requirement that is satisfied when the engine is
stopped by the automatic stop/restart control; and a manual
stopping requirement that is satisfied when the ignition switch has
been turned off, and the engine is stopped by the manual stopping
requirement is satisfied, accordingly.
15. The engine according to claim 14, wherein the increased working
angle that has been varied in accordance with the automatic
stopping requirement is larger than the increased working angle
that has been varied in accordance with the manual stopping
requirement.
16. The engine apparatus according to claim 15, further comprising
a cylinder, wherein the increased working angle that has been
varied in accordance with the automatic stopping requirement is set
to a maximum working angle of the variable working-angle control
mechanism, and wherein the increased working angle that has been
varied in accordance with the manual stopping requirement is equal
to or lower than an upper limit of a range in which a compression
ratio of air in the cylinder does not cause knocking during a hot
start of the engine, and is equal to or higher than a lower limit
of a range in which a compression ratio of air in the cylinder
permits a torque sufficient for a cold start of the engine to be
generated.
17. The engine according to claim 12, further comprising a variable
phase mechanism that varies a center of the working angle of the
intake valve, wherein, after commanding the engine to stop, the
valve actuation controlling apparatus, in preparation for
restarting of the engine, sets the working angle center of the
intake valve to a phase that is set according to the stopping
requirement of the engine.
18. The engine according to claim 12, wherein the valve actuation
controlling apparatus adjusts a throttle opening of the engine in
accordance with the increase in the working angle of the intake
valve after commanding the engine to stop.
19. A valve actuation controlling method applied to an engine
equipped with a variable working-angle control mechanism which
varies working angle of an intake valve, the method comprising:
controlling the variable working-angle control mechanism to
increase the working angle of the intake valve in preparation for
restarting of the engine, after commanding the engine to stop.
20. The valve actuation controlling method according to claim 19,
further comprising adjusting a throttle opening of the engine in
accordance with the increase in the working angle of the intake
valve after commanding the engine to stop.
21. A valve actuation controlling method applied to an engine
equipped with a variable working-angle control mechanism which
varies working angle of an intake valve, the method comprising:
controlling the variable working-angle control mechanism to
increase the working angle of the intake valve in preparation for
restarting of the engine, after commanding the engine to stop; and
varying the increased working angle according to whether a stopping
requirement of the engine is satisfied.
22. The valve actuation controlling method according to claim 21,
wherein said varying the increased working angle includes varying
the increased working angle within a range where the valve closing
time of the intake valve coincides with a middle period of a
compression stroke.
23. The valve actuation controlling method according to claim 21,
wherein the engine includes an ignition switch and performs
automatic stop/restart control, wherein the engine stopping
requirement comprises: an automatic stopping requirement that is
satisfied when the engine is stopped by the automatic stop/restart
control; and a manual stopping requirement that is satisfied when
the ignition switch has been turned off, and the engine is stopped
by the manual stopping requirement is satisfied, accordingly.
24. The valve actuation controlling method according to claim 23,
wherein the increased working angle that has been varied in
accordance with the automatic stopping requirement is larger than
the increased working angle that has been varied in accordance with
the manual stopping requirement.
25. The valve actuation controlling method according to claim 24,
wherein the engine includes a cylinder, and wherein the increased
working angle that has been varied in accordance with the automatic
stopping requirement is set to a maximum working angle of the
variable working-angle control mechanism, and wherein the increased
working angle that has been varied in accordance with the manual
stopping requirement is equal to or lower than an upper limit of a
range in which a compression ratio of air in the cylinder does not
cause knocking during a hot start of the engine, and is equal to or
higher than a lower limit of a range in which a compression ratio
of air in the cylinder permits a torque sufficient for a cold start
of the engine to be generated.
26. The valve actuation controlling method according to claim 21,
wherein the engine further includes a variable phase mechanism that
varies a center of the working angle of the intake valve, the
method comprising: setting, in preparation for restarting of the
engine, the working angle center of the intake valve to a phase
that is set according to the stopping requirement of the engine
after commanding the engine to stop.
27. The valve actuation controlling method according to claim 21,
further comprising adjusting a throttle opening of the engine in
accordance with the increase in the working angle of the intake
valve after commanding the engine to stop.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a valve actuation
controlling apparatus and method applied to an engine equipped with
a variable working-angle control mechanism which varies the working
angle of intake valves.
[0002] Engines such as vehicle engines are equipped with variable
valve mechanisms which vary valve characteristics of intake valves
and exhaust valves. Among variable valve mechanisms proposed
recently, there are variable valve lift and working-angle control
mechanisms which vary valve lifts and working angles of intake and
exhaust valves.
[0003] Japanese Laid-Open Patent Publications No. 2002-89303 and
No. 2002-61522 each disclose a valve actuation controlling
apparatus that presets the valve actuation of intake valves to be
suitable for securing engine starting characteristics immediately
before the engine stops, thereby preparing for a next engine start.
As shown in FIG. 8, immediately before the engine stops, that is
after commanding the engine to stop, the valve actuation
controlling apparatus as disclosed in Japanese Laid-Open Patent
Publications No. 2002-89303 and No. 2002-61522 reduces the valve
lift and the working angle .theta. of the intake valves compared to
those during idling of the engine, and advances the center .phi. of
the working angle. If the working angle .theta. is reduced and the
working angle center .phi. is advanced, intake valve closing time
IVC is advanced far ahead of a bottom dead center BDC and a
compression ratio of air in a cylinder is reduced, causing
decompression to occur during starting of the engine. Also, if the
lift is reduced and valve-opening area of the intake valve when
opened is reduced, velocity of air flow into the cylinder is
increased, thereby intensifying air flow in the cylinder during
starting of the engine.
[0004] It is true that decompression and intensified cylinder air
flow are favorable to improvement of engine starting
characteristics. However, the above setting of the valve actuation
of intake valves does not always ensure proper engine starting
characteristics depending on engine starting conditions.
[0005] For example, during a very cold start in which engine parts
encounter high friction, working angle .theta. that is less than
that of idling may result in a shortage of intake air, making it
impossible to generate sufficient torque to counteract the
increased friction. On the other hand, an attempt to intensify air
flow in the cylinder will cause heat from friction between air and
the intake valve, etc. to raise compression end temperature
(temperature at the top dead center) of the air drawn into the
cylinder, increasing the likelihood of knocking during a hot start.
Thus, reducing the lift and working angle .theta. of the intake
valves immediately before the engine stops do not always ensure
proper engine starting characteristics.
SUMMARY OF THE INVENTION
[0006] Accordingly, it is an objective of the present invention to
provide valve actuation controlling apparatus and method that
improve engine starting characteristics.
[0007] To achieve the foregoing and other objectives and in
accordance with the purpose of the present invention, a valve
actuation controlling apparatus applied to an engine equipped with
a variable working-angle control mechanism which varies working
angle of an intake valve is provided. After commanding the engine
to stop, the valve actuation controlling apparatus controls the
variable working-angle control mechanism to increase the working
angle of the intake valve in preparation for restarting of the
engine.
[0008] The present invention provides anther valve actuation
controlling apparatus applied to an engine equipped with a variable
working-angle control mechanism which varies working angle of an
intake valve. After commanding the engine to stop, the valve
actuation controlling apparatus controls the variable working-angle
control mechanism to increase the working angle of the intake valve
in preparation for restarting of the engine, and varies the
increased working angle according to whether a stopping requirement
of the engine is satisfied.
[0009] The present invention also provides an engine having a
variable working-angle control mechanism which varies working angle
of an intake valve and a valve actuation controlling apparatus.
After commanding the engine to stop, the valve actuation
controlling apparatus controls the variable working-angle control
mechanism to increase the working angle of the intake valve in
preparation for restarting of the engine.
[0010] The present invention provides another engine having a
variable working-angle control mechanism which varies working angle
of an intake valve and a valve actuation controlling apparatus.
After commanding the engine to stop, the valve actuation
controlling apparatus controls the variable working-angle control
mechanism to increase the working angle of the intake valve in
preparation for restarting of the engine, and varies the increased
working angle according to whether a stopping requirement of the
engine is satisfied.
[0011] Further, the present invention provides a valve actuation
controlling method applied to an engine equipped with a variable
working-angle control mechanism which varies working angle of an
intake valve. The method includes controlling the variable
working-angle control mechanism to increase the working angle of
the intake valve in preparation for restarting of the engine, after
commanding the engine to stop.
[0012] The present invention provides another valve actuation
controlling method applied to an engine equipped with a variable
working-angle control mechanism which varies working angle of an
intake valve. The method includes: controlling the variable
working-angle control mechanism to increase the working angle of
the intake valve in preparation for restarting of the engine, after
commanding the engine to stop; and varying the increased working
angle according to whether a stopping requirement of the engine is
satisfied.
[0013] Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with
the accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The invention, together with objects and advantages thereof,
may best be understood by reference to the following description of
the presently preferred embodiments together with the accompanying
drawings in which:
[0015] FIG. 1 is a schematic diagram showing an engine control
system according to one embodiment of the present invention;
[0016] FIG. 2(a) is a graph showing changes in valve actuation in a
variable phase mechanism;
[0017] FIG. 2(b) is a graph showing changes in valve actuation in a
variable working-angle control mechanism;
[0018] FIG. 3 is a diagram outlining automatic stop/restart
control;
[0019] FIG. 4 is a flowchart of a working angle setting process
during engine stopping period;
[0020] FIG. 5(a) is a diagram showing a setting of working angle of
the intake valve after a manual engine stop made by the automatic
stop/restart control;
[0021] FIG. 5(b) is a diagram showing a setting of the working
angle of the intake valve after an automatic engine stop made by
the automatic stop/restart control;
[0022] FIG. 6 is a time chart showing a control in a case where the
ignition switch is turned off;
[0023] FIG. 7 is a time chart showing a control in a case where the
engine is automatically stopped; and
[0024] FIG. 8 is a diagram showing valve actuation setting of an
intake valve when an engine stops in a case of a prior art valve
actuation controlling apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] An embodiment of the present invention will be described in
detail below with reference to the drawings.
[0026] As shown in FIG. 1, an engine 10 includes an intake passage
11, a combustion chamber 12, and an exhaust passage 13. Installed
in the intake passage 11 are an air flowmeter 14 which detects an
air flow rate in the intake passage 11 and a throttle valve 15
which changes the air flow rate by changing the flow area of the
intake passage 11. The intake passage 11 is connected to the
combustion chamber 12 via an intake valve 16. The combustion
chamber 12 is connected to the exhaust passage 13 via an exhaust
valve 17. The intake valve 16 and exhaust valve 17 are driven
according to rotation of the engine 10. The intake valve 16 opens
and closes the intake passage 11 to the combustion chamber 12, and
the exhaust valve 17 opens and closes the exhaust passage 13 to the
combustion chamber 12.
[0027] A valve operating system of the intake valve 16 has a
variable phase mechanism 18 and a variable working-angle control
mechanism 19. The variable phase mechanism 18 continuously changes
a working angle center .phi. of the intake valve 16 as shown in
FIG. 2 (a). The variable phase mechanism 18 employed in this engine
10 changes the working angle center .phi. by changing a rotational
phase of a camshaft with respect to a crankshaft. The variable
working-angle control mechanism 19 continuously changes the working
angle .theta. of the intake valve 16 as shown in FIG. 2(b). The
variable working-angle control mechanism 19 increases the lift of
the intake valve 16 in accordance with an increase of the working
angle .theta., and decreases the lift of the intake valve 16 in
accordance with a decrease of the working angle .theta.. The
working angle of the intake valve 16 is the number of degrees the
intake valve 16 stays open.
[0028] Both of the variable phase mechanism 18 and the variable
working-angle control mechanism 19 are driven hydraulically. The
hydraulic power is supplied from an oil pump that is driven by
rotation of the crankshaft of the engine 10.
[0029] Various types of control over the engine 10 configured as
described above are performed by an electronic controller 20. The
electronic controller 20 is equipped with a central processing unit
(CPU) which runs various computational processes for controlling
the engine 10, a read-only memory (ROM) which stores control
programs and data, a random access memory which records
computational results from the CPU and data from sensors, and input
and output ports used to exchange data with external devices.
[0030] The input ports of the electronic controller 20 are
connected with the air flowmeter 14, a throttle sensor 21, a valve
timing sensor 22 (VT sensor 22), and a valve lift sensor (VL sensor
23). The throttle sensor 21 detects the opening degree (throttle
opening degree Ta) of the throttle valve 15. The VT sensor 22
detects the current working angle center .phi. of the intake valve
16. The VL sensor 23 detects the current working angle .theta. of
the intake valve 16. The input ports of the electronic controller
20 are connected with various sensors which detect operating
condition of the engine 10 and driving-condition of the
vehicle.
[0031] The output ports of the electronic controller 20 are
connected with various actuators used to control the engine 10 as
well as with the throttle valve 15, the variable phase mechanism
18, and the variable working-angle control mechanism 19. The
electronic controller 20 controls the actuators based on detection
results produced by the various sensors, and thereby performs
various types of control over the engine 10.
[0032] For example, valve actuation control of the intake valve 16
is performed as follows. First, the electronic controller 20
calculates target values for the working angle center .phi. and the
working angle .theta. of the intake valve 16 suitable for the
current operating state based on the rotational speed of the engine
and depression of an accelerator pedal detected by sensors. The
electronic controller 20 performs feedback control of the variable
phase mechanism 18 and the variable working-angle control mechanism
19 such that the current working angle center .phi. and working
angle .theta. detected by the VT sensor 22 and the VL sensor 23 of
the intake valve 16 seek the calculated respective target values.
This makes it possible to obtain optimum valve actuation of the
intake valve 16 according to the current operating state of the
engine.
[0033] If the working angle .theta. and the lift of the intake
valve 16 are changed by the variable working-angle control
mechanism 19, the volume of air introduced into the combustion
chamber 12 (intake air amount Ga) is changed as well. To deal with
this situation, the electronic controller 20 controls the opening
degree of the throttle valve 15 along with control of the working
angle .theta.. This secures a required intake air amount Ga
regardless of changes made by the variable working-angle control
mechanism 19 to the working angle .theta. and the lift of the
intake valve 16.
[0034] If idling continues for a relatively long period of time
while waiting for traffic lights to change, automatic stop/restart
control, i.e., "automatic idling stop control", is performed, which
involves stopping the engine 10 automatically, waiting in a stopped
state, and restarting the engine in response to the driver's action
to start the vehicle. The automatic stop/restart control is
performed by the electronic controller 20, and will be outlined
below with reference to FIG. 3.
[0035] When the driver turns on an ignition switch, so that the
electronic controller 20 is activated, the electronic controller 20
sets control mode to Mode 0, which represents normal engine-stopped
state. In Mode 0, if the driver sets the ignition switch to a Start
position, the engine 10 starts being cranked. When the engine 10 is
started successfully, the control mode of the electronic controller
20 shifts to Mode 1, which represents normal engine-operating
state.
[0036] If the ignition switch is turned off during normal operation
of the engine 10 in Mode 1, the electronic controller 20 performs a
normal engine stopping process to stop the engine 10 and shifts to
Mode 0. After performing necessary stop processes, the electronic
controller 20 cuts off power to itself.
[0037] On the other hand, if automatic stopping requirements of the
engine 10 are satisfied during normal engine operation in Mode 1,
the electronic controller 20 shifts to Mode 2 in which it performs
an engine stop process to stop the engine 10 automatically. With
the engine 10 of this embodiment, the automatic stopping
requirements are satisfied, for example, if all the following
conditions (a1) to (a6) are met.
[0038] (a1) The depression of the accelerator pedal is 0.
[0039] (a2) The vehicle speed is equal to or lower than a
predetermined speed.
[0040] (a3) The brake pedal is depressed.
[0041] (a4) Coolant temperature is equal to or higher than a
predetermined temperature Ta and the engine 10 has been warmed
up.
[0042] (a5) Hydraulic fluid temperature of an automatic
transmission is equal to or higher than a predetermined
temperature.
[0043] (a6) Car battery level is equal to or above a predetermined
value.
[0044] As the control mode shifts to Mode 2, the electronic
controller 20 stops fuel supply, and thereby stops the engine 10.
When it is confirmed that the engine 10 has stopped completely, the
control mode of the electronic controller 20 shifts to Mode 3,
which represents engine-stopped state brought about by the
automatic stop/restart control.
[0045] In Mode 3, when the engine 10 is on standby and in a stopped
state, if restart requirements of the engine 10 are satisfied, the
electronic controller 20 shifts to Mode 4 in which it performs a
restart process to restart the engine 10 automatically. With the
engine 10 of this embodiment, the restart requirements are
satisfied, for example, if any of the following conditions (b1) to
(b4) is met.
[0046] (b1) The brake pedal is released.
[0047] (b2) The accelerator pedal is depressed.
[0048] (b3) A shift is made from P (parking) or N (neutral) range
to another range.
[0049] (b4) The car battery level is below a predetermined
value.
[0050] As the control mode shifts to Mode 4, the engine 10 is
restarted. When the engine 10 is restarted successfully, the
control mode of the electronic controller 20 shifts to Mode 1.
[0051] In Mode 3, i.e., in an engine-stopped state brought about by
the automatic stop/restart control, if a malfunction occurs during
restarting of the engine 10 in Mode 4 due to turning off of the
ignition switch or an abnormality in the system, the electronic
controller 20 shifts forcibly to Mode 0. In that case, the engine
10 is restarted only if the driver operates the ignition switch
directly. That is, the engine 10 is not restarted
automatically.
[0052] (Engine Stop Time Working Angle Setting Process)
[0053] With the engine 10 of this embodiment, when the engine 10
stops, the working angle .theta. of the intake valve 16 is set to
an optimum value in preparation for the next restarting of the
engine 10. Details of the stop-time working angle setting process
will be described below with reference to FIGS. 4 to 7.
[0054] The engine 10 of this embodiment can be stopped in two ways:
manual stop via deactivation of the ignition switch and automatic
stop via the automatic stop/restart control. In the case of the
automatic stop, which is followed by restarting in a relatively
short time, the restarting is a hot start in which the engine 10 is
restarted in a sufficiently hot state. On the other hand, in the
case of the manual stop, which is made through deactivation of the
ignition switch, it is necessary to allow for both hot start and
cold start because it is difficult to predict situations in which
the engine is started.
[0055] Thus, according to this embodiment, the working angle
.theta. of the intake valve 16 is varied between the automatic stop
based on automatic stop/restart control and manual stop based on
deactivation of the ignition switch. Thus, an optimum working angle
.theta. is preset for the intake valve 16 according to expected
situations in which the engine 10 will be started, taking into
consideration the difference between automatic stop and manual
stop.
[0056] FIG. 4 shows a flowchart of the stop-time working angle
setting process according to this embodiment. The electronic
controller 20 determines in Step 100 whether the engine 10 is in an
automatically stopped state. If the engine 10 is in an
automatically stopped state (S100: YES), the electronic controller
20 sets the target value of the working angle .theta. of the intake
valve 16, i.e., a stop-time target working angle .theta.t which is
set during a stop, to a maximum working angle .theta.max
(.theta.max=260.degree. CA in this engine 10) which is the upper
limit of a working angle range of the variable working-angle
control mechanism 19 in step 102. Thereafter, the electronic
controller 20 proceeds to step 110. If the engine 10 is not in an
automatically stopped state (S100: NO), the electronic controller
20 goes to step 104.
[0057] At step 104, the electronic controller 20 determines whether
the engine 10 is currently in a manually stopped state based on
deactivation of the ignition switch. If the engine 10 is in a
manually stopped state (S104: YES), the electronic controller 20
sets the stop-time target working angle .theta.t to a relatively
large value (e.g., 200.degree. CA) in step 106, and then it goes to
step 110. If the engine 10 is not in a manually stopped state
(S104: NO), i.e., if the engine 10 is not currently stopped, the
electronic controller 20 temporarily suspends the routine. In this
case, normal working angle control is performed according to the
engine-operating state as described above.
[0058] In step 110, the electronic controller 20 controls the
variable working-angle control mechanism 19 such that the current
working angle .theta. of the intake valve 16 seeks the target
working angle .theta.t set in step 102 or step 106. Immediately
before a stop, the engine 10 is normally operated under low loads
and the working angle .theta. of the intake valve 16 is set to a
relatively small value. Thus, the working angle .theta. of the
intake valve 16 is increased through the working angle control. At
the same time, the electronic controller 20 also changes the
working angle center .phi. of the intake valve 16 as required.
[0059] If the working angle .theta. of the intake valve 16 is
increased, the intake air amount Ga changes accordingly. This
increases or decreases compression torque of the air in the
cylinder, and may cause variations in rotational speed of the
engine. To deal with this situation, the electronic controller 20
performs cooperative control in step 112 to regulate the throttle
opening Ta in response to increases in the working angle .theta. of
the intake valve 16, and then the electronic controller 20
temporarily suspends the routine. The cooperative control involves
decreasing the throttle opening Ta to curb any increase in the
intake air amount Ga resulting from increases in the working angle
.theta. of the intake valve 16, and increasing the throttle opening
Ta to check any decrease in the intake air amount Ga resulting from
increases in the working angle .theta. of the intake valve 16.
[0060] Even if the intake air amount Ga is not kept constant by the
cooperative control of the throttle opening Ta while the engine is
stopped, it is possible to reduce variations in the rotational
speed of the engine, provided that the changes in the intake air
amount Ga resulting from increases in the working angle .theta. is
curbed through changes in the throttle opening Ta. The electronic
controller 20 executes the above routine periodically while it is
active.
[0061] After a manual stop, the working angle .theta. of the intake
valve 16 is set to a relatively large value (e.g., 200.degree. CA)
by the stop-time working angle setting process. In so doing, the
valve closing time IVC of the intake valve 16 is set to a point
relatively early in the middle period of the compression stroke as
shown in FIG. 5(a). Since both hot start and cold start are
anticipated in the case of restarting after a manual stop as
described above, it is necessary to set working angle .theta. which
can accommodate both hot start and cold start properly.
[0062] In the case of a hot start, an excessive volume of the
intake air amount Ga raises the compression end temperature, i.e.,
an excessive volume of the intake air amount Ga increases a
temperature rise in the cylinder due to adiabatic compression in
the cylinder when the top dead center is reached. This may cause
knocking. To deal with this situation, it is necessary to lower the
compression ratio of air in the cylinder by delaying the valve
closing time IVC of the intake valve 16 relative to the bottom dead
center BDC and thereby returning part of the air drawn once into
the cylinder to the intake passage 11 along with ascent of the
piston during the compression stroke.
[0063] In the case of a cold start, it is necessary to secure an
intake air amount Ga equal to or larger than a certain volume in
order to generate sufficient torque to counteract the friction of
parts of the engine 10 increased by decreased lubricant viscosity
and the like. That is, even when reducing the compression ratio of
air in the cylinder, the delay in the valve closing time IVC of the
intake valve 16 caused by an increase in the working angle .theta.
should be kept within certain limits in order to secure the
sufficient volume of intake air needed to make a cold start.
[0064] Thus, at the time of a manual stop of the engine 10, the
target working angle .theta.t of the intake valve 16 is set such
that a compression ratio of air in the cylinder (combustion chamber
12) is equal to or lower than the upper limit of a range in which
knocking is avoided during a hot start of the engine 10, and is
equal to or higher than the lower limit of a range in which
sufficient torque is generated during a cold start of the engine
10. Consequently, during restarting, the engine 10 can be started
under increased friction in case of a cold start, and knocking can
be avoided in case of a hot start. Also, decompression occurs due
to the reduced compression ratio.
[0065] In order to permit a delay in the valve closing time IVC,
the working angle center .phi. of the intake valve 16 is delayed
more than during low-load operation of the engine 10 such as
idling.
[0066] On the other hand, after an automatic stop of the engine 10,
the working angle .theta. of the intake valve 16 is set to the
maximum working angle .theta.max by the stop-time working angle
setting process. The valve closing time IVC of the intake valve 16
is set in the middle period of the compression stroke, lagging
greatly behind the bottom dead center BDC as shown in FIG.
5(b).
[0067] After an automatic stop, since the engine 10 is restarted in
a relatively short time, the restarting is expected to be a hot
start. Since only a hot start is expected, the engine 10 requires
only small torque during starting, obviating the need to secure a
large intake air amount Ga. Consequently, the valve closing time
IVC of the intake valve 16 is allowed to be delayed greatly in
order to maximize decompression. Thus, the working angle .theta. of
the intake valve 16 is set to the maximum working angle .theta.max,
allowing the valve closing time IVC to be delayed to the maximum
extent possible. Incidentally, the working angle center .phi. of
the intake valve 16 is set to the same phase as during the manual
stop.
[0068] FIG. 6 shows in a manual stop in the stop-time working angle
setting process. As shown in FIG. 6, if the ignition switch is
turned off at time t1, i.e., if an engine stop command is given
manually, the working angle .theta. of the intake valve 16 is
increased gradually to the target working angle .theta.t
(200.degree. CA) . At the same time, the valve closing time IVC of
the intake valve 16 is gradually delayed toward the bottom dead
center BDC.
[0069] At this time, if the throttle opening Ta is fixed, increases
in the working angle .theta. result in increases in the intake air
amount Ga as indicated by an alternate long and short dash line in
FIG. 6. However, since the throttle opening Ta is decreased
gradually by the cooperative control with increases in the working
angle .theta., the increases in the intake air amount Ga are
curbed.
[0070] When the valve closing time IVC of the intake valve 16 is
delayed relative to the bottom dead center BDC at time t2, the
intake air amount Ga decreases with further increases in the
working angle .theta.. However, after time t2, the cooperative
control gradually increases the throttle opening Ta in accordance
with increases in the working angle .theta., and thereby curbs the
decreases in the intake air amount Ga.
[0071] At time t3, when the working angle .theta. of the intake
valve 16 reaches the target working angle .theta.t (e.g.,
200.degree. CA), the working angle .theta. stops increasing and is
held at the target working angle .theta.t. When it is confirmed
that the working angle .theta. has stopped increasing to the target
working angle .theta.t and that the engine 10 has stopped
completely, the electronic controller 20 finishes the engine stop
process and cuts off power to itself.
[0072] FIG. 7 shows in an automatic stop in the stop-time working
angle setting process. As shown in FIG. 7, at time t4, if the
automatic stopping requirements are satisfied and the electronic
controller 20 shifts from Mode 1 to Mode 2, i.e., if an engine stop
command is given by the automatic stop/restart control, the working
angle .theta. of the intake valve 16 increases gradually to the
maximum working angle .theta.max (260.degree. CA), i.e., to the
target working angle .theta.t. At the same time, the valve closing
time IVC of the intake valve 16 is delayed toward the bottom dead
center BDC, and the intake air amount Ga is increased accordingly.
Thus, the cooperative control gradually decreases the throttle
opening Ta to curb the increases in the intake air amount Ga.
[0073] When the valve closing time IVC of the intake valve 16 is
delayed relative to the bottom dead center BDC at time t5, the
intake air amount Ga decreases with further increases in the
working angle .theta.. Thus, the cooperative control gradually
increases the throttle opening Ta to curb the decreases in the
intake air amount Ga.
[0074] At time t6, when the working angle .theta. of the intake
valve 16 reaches the maximum working angle .theta.max, the working
angle .theta. stops increasing and is held at the maximum working
angle .theta.max. When it is confirmed that the working angle
.theta. has stopped increasing to the target working angle .theta.t
and that the engine 10 has stopped completely, the electronic
controller 20 switches to Mode 3 and makes the engine 10 standby in
a stopped state until the restart requirements are satisfied.
[0075] The embodiment described above has the following
advantages.
[0076] (1) After commanding the engine 10 to stop, the electronic
controller 20 according to this embodiment increases the working
angle .theta. of the intake valve 16 far more greatly than for a
low-load operation, in preparation for restarting the engine 10.
Specifically, the working angle .theta. of the intake valve 16 is
increased to such an extent that the valve closing time IVC of the
intake valve 16 coincides with the middle period of the compression
stroke. Consequently, the compression ratio of air in the cylinder
is reduced, causing decompression to occur. This reduces the torque
required for the crankshaft to rotate. The restart of the engine 10
is therefore facilitated. Also, since decompression occurs even if
intake air is not throttled by the intake valve 16, it is possible
to prevent compression end temperature from rising due to
frictional heat and to avoid eventual knocking during a hot start
of the engine 10.
[0077] (2) According to this embodiment, the target working angle
.theta.t for increases in the working angle .theta. is varied
between automatic stop and manual stop of the engine 10. More
specifically, in the case of the automatic stop of the engine 10,
the target working angle .theta.t is set to the maximum working
angle .theta.max of the variable working-angle control mechanism
19. In the case of the manual stop of the engine 10, the target
working angle .theta.t is set such that the compression ratio of
air in the cylinder is equal to or lower than the upper limit of a
range in which knocking can be avoided during a hot start of the
engine, and is equal to or higher than the lower limit of a range
in which sufficient torque can be generated during a cold start of
the engine. This makes it possible to set a desirable working angle
according to conceivable situations in which the engine 10 will be
started in the case of both automatic stop and manual stop.
[0078] (3) According to this embodiment, cooperative control of the
intake valve 16 is performed in response to increases in the
working angle .theta. of the intake valve 16 at the time of an
engine stop. This reduces variations in the intake air amount Ga
resulting from increases in the working angle .theta. of the intake
valve 16 during the engine stop, making it possible to reduce
variations in the rotational speed of the engine 10 caused by
changes in the compression ratio.
[0079] (4) According to this embodiment, the working angle center
.phi. of the intake valve 16 is changed along with increases in the
working angle .theta. of the intake valve 16 at the time of the
engine stop. This makes the valve actuation of the intake valve 16
at the time of restarting more suitable for starting the engine
10.
[0080] The above embodiments may be modified as follows.
[0081] The settings of the target working angle .theta.t in the
stop-time working angle setting process at the time of both manual
stop and automatic stop may be changed as required according to the
characteristics of the given engine. If the target working angle
.theta.t of the intake valve 16 at the time of a manual stop is set
to such a value which allows for conceivable situations in which
the engine will be restarted after both automatic stop and manual
stop, it is possible to ensure proper engine starting
characteristics.
[0082] The working angle center .phi. may be varied between
automatic stop and manual stop. This permits the valve actuation of
the intake valve 16 at restart of the engine 10 to be finely
adjusted. Consequently, the starting characteristics of the engine
10 can be further improved depending on the adjustment.
[0083] The target working angle .theta.t at the stop-time working
angle setting process of the above embodiments may be varied
according to the engine stopping requirements in the automatic stop
and manual stop. For example, if outside air temperature is very
low when the engine stops, it is expected that the engine 10 is
restarted at a very low temperature, and thus the target working
angle .theta.t may be set to a smaller value than when temperature
is relatively high. In such a case, the present invention is also
applicable to engines which do not perform automatic stop/restart
control.
[0084] It may be after the engine 10 stops completely that the
stop-time working angle setting process increases the working angle
.theta. in preparation for restarting. In this case, the
cooperative control of the throttle opening Ta performed along with
increases in the working angle .theta. may be omitted. Also, the
cooperative control of the throttle opening Ta may also be omitted
if variations in the rotational speed of the engine resulting from
increases in the working angle .theta. are small.
[0085] The control for increasing the working angle .theta. when
the engine stops can be applied, in the same or similar manner as
the above embodiments, to an engine which has only a variable
working-angle control mechanism 19, but does not have a variable
phase mechanism 18.
[0086] The present examples and embodiments are to be considered as
illustrative and not restrictive and the invention is not to be
limited to the details given herein, but may be modified within the
scope and equivalence of the appended claims.
* * * * *