U.S. patent application number 11/447249 was filed with the patent office on 2006-12-07 for compression ignition engine.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to Seinosuke Hara, Tomio Hokari, Makoto Nakamura, Seiji Suga, Masahiko Watanabe.
Application Number | 20060272608 11/447249 |
Document ID | / |
Family ID | 37440189 |
Filed Date | 2006-12-07 |
United States Patent
Application |
20060272608 |
Kind Code |
A1 |
Hara; Seinosuke ; et
al. |
December 7, 2006 |
Compression ignition engine
Abstract
In a compression ignition engine employing a variable valve
actuation mechanism variably adjusting an intake valve
characteristic including at least one of an intake valve lift and
an intake valve closure timing, a control system operates to
temporarily lower an effective compression ratio of the engine by
controlling the intake valve characteristic during a cranking
period of cold starting operation. At a point of time when a
predetermined cranking speed threshold value has been reached owing
to a cranking speed rise, the effective compression ratio is risen
by controlling the intake valve characteristic. After combustion of
the engine has been stabilized, the intake valve characteristic is
brought closer to a desired value determined based on engine
operating conditions by way of closed-loop control.
Inventors: |
Hara; Seinosuke; (Kanagawa,
JP) ; Hokari; Tomio; (Kanagawa, JP) ; Suga;
Seiji; (Kanagawa, JP) ; Nakamura; Makoto;
(Kanagawa, JP) ; Watanabe; Masahiko; (Yokohama,
JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
37440189 |
Appl. No.: |
11/447249 |
Filed: |
June 6, 2006 |
Current U.S.
Class: |
123/182.1 |
Current CPC
Class: |
F01L 2001/34469
20130101; F01L 13/0015 20130101; F01L 2001/34479 20130101; F01L
2001/34423 20130101; F02D 41/064 20130101; F01L 2001/34483
20130101; F01L 2001/34426 20130101; F01L 2001/0476 20130101; F01L
13/08 20130101; F01L 1/3442 20130101; F02N 19/004 20130101 |
Class at
Publication: |
123/182.1 |
International
Class: |
F01L 13/08 20060101
F01L013/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 7, 2005 |
JP |
2005-166538 |
Claims
1. A compression ignition-engine comprising: sensors that detect
engine operating conditions; a variable valve operating system
comprising at least a variable valve actuation mechanism variably
adjusting an intake valve characteristic including at least one of
a valve lift of an intake valve and a valve closure timing of the
intake valve and actuated by an actuator; and a control unit
configured to be electrically connected to the sensors and the
actuator for controlling the variable valve actuation mechanism via
the actuator to bring the intake valve characteristic closer to a
desired value determined based on the engine operating conditions
detected by the sensors; said control unit comprising a processor
programmed to perform the following, (a) temporarily lowering an
effective compression ratio of the engine by controlling the intake
valve characteristic during a cranking period of cold starting
operation; (b) rising the effective compression ratio by
controlling the intake valve characteristic at a point of time when
a predetermined cranking speed threshold value has been reached
owing to a cranking speed rise; and (c) bringing the intake valve
characteristic closer to the desired value determined based on the
engine operating conditions by way of closed-loop control, after
combustion of the engine has been stabilized.
2. The compression ignition engine as claimed in claim 1, wherein:
the variable valve actuation mechanism of the variable valve
operating system is able to vary the intake valve characteristic,
before cranking operation of the engine is started or
simultaneously with the engine cranking operation; and the variable
valve operating system further comprises a sensor that is able to
detect information regarding an operating state of the intake valve
from a substantially zero engine speed value.
3. The compression ignition engine as claimed in claim 1, further
comprising: a sensor that is able to detect information regarding
an operating state of the intake valve from a substantially zero
engine speed value; and a sensor that detects information regarding
a quantity of air charged into an engine cylinder, wherein the
processor is further programmed for: (d) compensating for, based on
at least one of the information regarding the intake valve
operating state and the information regarding the quantity of air
charged into the cylinder, at least one of a fuel injection amount
and a fuel injection timing, both determined based on the engine
operating conditions including engine speed and engine load.
4. The compression ignition engine as claimed in claim 1, further
comprising: a sensor that is able to detect information regarding
an operating state of the intake valve from a substantially zero
engine speed value, wherein the processor is further programmed
for: (e) gradually controlling the intake valve operating state
including at least an actual intake valve closure timing, to a
normal intake valve operating state, when restarting the engine by
either one of a starter and a motor generator.
5. The compression ignition engine as claimed in claim 1, wherein
the processor is further programmed for: (f) generating a control
command signal to the actuator for controlling at least the intake
valve closure timing to a desired standby timing spaced apart from
a piston bottom dead center position during a stopping period of
the engine; and (g) generating an engine stop signal after
generating the control command signal.
6. The compression ignition engine as claimed in claim 1, wherein
the processor is further programmed for: (h) temporarily shutting
off or reducing electric power supply to either one of a glow plug
and an electric heater, during the cranking period of cold starting
operation.
7. A compression ignition engine (1) comprising: sensors that
detect engine operating conditions; a variable valve operating
system comprising at least a variable valve actuation mechanism
variably adjusting an intake valve characteristic including at
least one of a valve lift of an intake valve and a valve closure
timing of the intake valve and actuated by an actuator; a
decompression device provided to operate an exhaust valve in a
decompression mode corresponding to a constantly-opened valve
operating state during a cranking period of cold starting
operation; and a control unit configured to be electrically
connected to the sensors and the actuator for controlling the
variable valve actuation mechanism via the actuator to bring the
intake valve characteristic closer to a desired value determined
based on the engine operating conditions detected by the sensors;
said control unit also configured to be electrically connected to
the decompression device for switching the exhaust valve to the
decompression mode during the cranking period; and said control
unit comprising a processor programmed to perform the following,
(a) temporarily lowering an effective compression ratio of the
engine by maintaining the exhaust valve in the decompression mode
corresponding to the constantly-opened valve operating state during
the cranking period; (b) inhibiting the decompression mode and
returning the exhaust valve to a normal operating state at a point
of time when a predetermined cranking speed threshold value has
been reached owing to a cranking speed rise; (c) rising the
effective compression ratio by controlling the intake valve
characteristic substantially at the point of time when the
predetermined cranking speed threshold value has been reached owing
to the cranking speed rise; and (d) bringing the intake valve
characteristic closer to the desired value determined based on the
engine operating conditions by way of closed-loop control, after
combustion of the engine has been stabilized.
8. A compression ignition engine comprising: sensor means for
detecting engine operating conditions; a variable valve operating
system comprising at least a variable valve actuation mechanism
variably adjusting an intake valve characteristic including at
least one of a valve lift of an intake valve and a valve closure
timing of the intake valve and actuated by an actuator; and a
control unit configured to be electrically connected to the sensor
means and the actuator for controlling the variable valve actuation
mechanism via the actuator to bring the intake valve characteristic
closer to a desired value determined based on the engine operating
conditions detected by the sensor means; said control unit
comprising (a) means for temporarily lowering an effective
compression ratio of the engine by controlling the intake valve
characteristic during a cranking period of cold starting operation;
(b) means for rising the effective compression ratio by controlling
the intake valve characteristic at a point of time when a
predetermined cranking speed threshold value has been reached owing
to a cranking speed rise; and (c) means for bringing the intake
valve characteristic closer to the desired value determined based
on the engine operating conditions by way of closed-loop control,
after combustion of the engine has been stabilized.
9. A compression ignition engine comprising: sensor means for
detecting engine operating conditions; a variable valve operating
system comprising at least a variable valve actuation mechanism
variably adjusting an intake valve characteristic including at
least one of a valve lift of an intake valve and a valve closure
timing of the intake valve and actuated by an actuator; a
decompression device provided to operate an exhaust valve in a
decompression mode corresponding to a constantly-opened valve
operating state during a cranking period of cold starting
operation; and a control unit configured to be electrically
connected to the sensor means and the actuator for controlling the
variable valve actuation mechanism via the actuator to bring the
intake valve characteristic closer to a desired value determined
based on the engine operating conditions detected by the sensor
means; said control unit also configured to be electrically
connected to the decompression device for switching the exhaust
valve to the decompression mode during the cranking period; and
said control unit comprising (a) means for temporarily lowering an
effective compression ratio of the engine by maintaining the
exhaust valve in the decompression mode corresponding to the
constantly-opened valve operating state during the cranking period;
(b) means for inhibiting the decompression mode and returning the
exhaust valve to a normal operating state at a point of time when a
predetermined cranking speed threshold value has been reached owing
to a cranking speed rise; (c) means for rising the effective
compression ratio by controlling the intake valve characteristic
substantially at the point of time when the predetermined cranking
speed threshold value has been reached owing to the cranking speed
rise; and (d) means for bringing the intake valve characteristic
closer to the desired value determined based on the engine
operating conditions by way of closed-loop control, after
combustion of the engine has been stabilized.
10. A method for controlling a compression ignition engine
employing a variable valve actuation mechanism variably adjusting
an intake valve characteristic including at least one of a valve
lift of an intake valve and a valve closure timing of the intake
valve, the method comprising: (a) temporarily lowering an effective
compression ratio of the engine by controlling the intake valve
characteristic during a cranking period of cold starting operation;
(b) rising the effective compression ratio by controlling the
intake valve characteristic at a point of time when a predetermined
cranking speed threshold value has been reached owing to a cranking
speed rise; and (c) bringing the intake valve characteristic closer
to a desired value determined based on engine operating conditions
by way of closed-loop control, after combustion of the engine has
been stabilized.
11. A method for controlling a compression ignition engine
employing a variable valve actuation mechanism variably adjusting
an intake valve characteristic including at least one of a valve
lift of an intake valve and a valve closure timing of the intake
valve and a decompression device provided to operate an exhaust
valve in a decompression mode corresponding to a constantly-opened
valve operating state during a cranking period of cold starting
operation, the method comprising: (a) temporarily lowering an
effective compression ratio of the engine by maintaining the
exhaust valve in the decompression mode corresponding to the
constantly-opened valve operating state during the cranking period;
(b) inhibiting the decompression mode and returning the exhaust
valve to a normal operating state at a point of time when a
predetermined cranking speed threshold value has been reached owing
to a cranking speed rise; (c) rising the effective compression
ratio by controlling the intake valve characteristic substantially
at the point of time when the predetermined cranking speed
threshold value has been reached owing to the cranking speed rise;
and (d) bringing the intake valve characteristic closer to the
desired value determined based on the engine operating conditions
by way of closed-loop control, after combustion of the engine has
been stabilized.
Description
TECHNICAL FIELD
[0001] The present invention relates to a compression ignition
engine employing a variable valve operating system for at least one
of intake and exhaust valves, and specifically to the improvement
of a compression ignition engine control technology suited to
compression ignition engines such as a four-stroke-cycle Diesel
engine, a two-stroke-cycle Diesel engine, a premix compression
ignition engine, and the like.
BACKGROUND ART
[0002] In recent years, there have been proposed and developed
various engine control technologies for compression ignition
engines with variable valve operating systems. Generally, a
variable valve operating system, capable of variably adjusting a
valve lift and valve timing of at least one of intake and exhaust
valves of a reciprocating internal combustion engine depending on
engine operating conditions, is widely utilized for controlling a
charging efficiency, an effective compression ratio, and an amount
of residual gas of the engine, thereby enhancing the engine power
performance and exhaust emission control performance. In Diesel
engines or premix compression ignition engines, air alone is
compressed during the compression stroke, and then fuel, which is
sprayed or injected into the cylinder, is self-ignited due to a
temperature rise of the compressed air (heat produced by
compressing the incoming air). That is, such self-ignition of the
sprayed fuel can be performed under a high-temperature
high-pressure condition where the pressure and temperature of the
compressed air are high enough to ignite spontaneously the sprayed
fuel. The spontaneous ignition temperature and spontaneous ignition
pressure needed for self-ignition both change depending on sorts of
fuel that is sprayed into the compressed air. Generally, unless the
temperature of the compressed air is more than 1000 degrees K
(Kelvin temperature) and the pressure of the compressed air is more
than 1 MPa (mega Pascal), it does not result in spontaneous
ignition of the sprayed fuel.
[0003] For the reasons discussed above, the compression ratio of
the engine has to be set to a high ratio of 15:1 or more, so that
the in-cylinder pressure and in-cylinder temperature become high
enough to spontaneously ignite the sprayed fuel and to achieve the
combustion of the sprayed fuel, for instance, even when the engine
cylinder wall temperature is still low during cold starting and
thus heat of the compressed air is taken by the cylinder wall.
However, such a high compression ratio causes excessively high
pressures acting on the piston after the engine warm-up has been
completed, thus resulting in the increased mechanical friction loss
and reduced engine power performance. To avoid this (for avoidance
of undesirable mechanical friction loss), it is effective to reduce
the compression ratio to 15:1 or less after completion of the
engine warm-up, in other words, after the engine starting operation
has been completed, thereby enhancing the engine performance. After
completion of the starting operation, the cylinder wall temperature
becomes high, and thus the heat produced by compressing the air is
hard to be taken by the cylinder wall even at a comparatively low
compression ratio. As a result, the temperature and pressure of the
compressed air easily become high during the compression stroke,
thus ensuring self-ignition of the sprayed fuel. As is generally
known, the variable compression ratio adjustment can be achieved by
mechanically varying the clearance volume, that is, the air volume
with the piston at top dead center (TDC). Alternatively, the
variable compression ratio adjustment can be achieved by
mechanically varying the piston stroke characteristic. However,
such variable compression ratio devices, for example, a multi-link
variable compression ratio device and the like, capable of
mechanically varying the clearance volume or mechanically varying
the piston stroke characteristic, have complicated mechanical
configuration and structure. In lieu thereof, it is possible to
variably adjust the mass of air entering the engine cylinder at the
beginning of the compression stroke by retarding or advancing the
intake-valve closure timing, denoted by "IVC" and expressed in
terms of crank angle. In such a case, it is possible to retard a
rise in in-cylinder pressure and a rise in in-cylinder temperature
with respect to a predetermined crank angle. In other words, it is
possible to lower the effective compression ratio by retarding an
in-cylinder pressure rise and/or an in-cylinder temperature rise by
way of variable adjustment of intake valve closure timing IVC. One
such IVC adjustment type variable compression ratio device for a
compression ignition engine has been disclosed in Japanese Patent
Provisional Publication No. 1-315631 (hereinafter is referred to as
"JP1-315631"). In the case of JP1-315631, the IVC adjustment type
variable compression ratio device is exemplified in a
two-stroke-cycle Diesel engine. Concretely, when it is determined
that the current operating condition of the two-stroke-cycle Diesel
engine corresponds to an engine starting period, intake valve
closure timing IVC is phase-advanced towards a timing value near
bottom dead center (BDC) by means of an electric-motor driven
variable valve operating device (or a motor-driven variable valve
timing control (VTC) system), thereby increasing an effective
compression ratio and consequently enhancing the self-ignitability
during the starting period. In contrast, during engine normal
operation, intake valve closure timing IVC is phase-retarded to
decrease the effective compression ratio and consequently to reduce
a fuel consumption rate. The motor-driven VTC system of JP1-315631
uses a rotary-to-linear motion converter, such as a ball-bearing
screw mechanism, for changing relative phase of an intake-valve
camshaft to an engine crankshaft. The rotary-to-linear motion
converter (the ball-bearing screw mechanism) of JP1-315631 is
comprised of a warm shaft (i.e., a ball bearing shaft with helical
grooves) driven by a step motor, an inner slider (i.e., a
recirculating ball nut), recirculating balls provided in the
helical grooves, and an outer slider axially movable together with
the inner slider and rotatable relative to the inner slider. The
other types of variable valve operating devices have been disclosed
in (i) Japanese document "JSAE Journal Vol. 59, No. 2, 2005"
published by Society of Automotive Engineers of Japan, Inc. and
titled "Gasoline Engine: Recent Trends in Variable Valve Actuation
Technologies to Reduce the Emission and Improve the Fuel Economy"
and written by two authors Yuuzou Akasaka and Hajime Miura, and
(ii) Japanese document "Proceedings JSAE 9833467, May, 1998"
published by Society of Automotive Engineers of Japan, Inc. and
titled "Reduction of the engine starting vibration for the Parallel
Hybrid System" and written by four authors Hiroshi Kanai, Katsuhiko
Hirose, Tatehito Ueda, and Katsuhiko Yamaguchi. The Japanese
document "JSAE Journal Vol. 59, No. 2, 2005" discloses various
types of variable valve operating systems, such as a helical gear
piston type two-stepped phase control system, a rotary vane type
continuously variable valve timing control (VTC) system, a
swing-arm type stepped valve lift and working angle variator, a
continuously variable valve event and lift (VEL) control system,
and the like. The VTC and VEL control systems are operated by means
of respective actuators for example electric motors or
electromagnets, each of which is directly driven in response to a
control signal (a drive signal) from an electronic control unit
(ECU). Alternatively, the VTC and VEL control systems are often
operated indirectly by means of a hydraulically-operated device,
which is controllable electronically or electromagnetically. On the
other hand, the Japanese document "Proceedings JSAE 9833467, May,
1998" teaches the use of a variable valve timing control system
installed on the intake valve side of an engine of a hybrid vehicle
employing a parallel hybrid system, for prevention of rapid engine
torque fluctuations, which may occur during engine stop and start
operation.
SUMMARY OF THE INVENTION
[0004] In the case of the compression ignition engine with the
variable valve operating device, as disclosed in JP1-315631, the
effective compression ratio is controlled to a relatively high
ratio by means of the variable valve operating device during the
engine starting period. After the starting operation has been
completed, the effective compression ratio is controlled to a
relatively low ratio by means of the variable valve operating
device. In such an engine control system, there is an increased
tendency for the work of compression to increase during the engine
starting period. The increased work of compression leads to a drop
in cranking speed, thereby resulting in an increased heat loss of
the compressed air (compressed gas). As a result of this, a
compression temperature, i.e., a temperature of the compressed gas,
tends to drop, thus deteriorating the engine startability.
According to the engine control system as disclosed in JP1-315631,
the effective compression ratio is lowered and decreasingly
compensated for, just after the starting operation has been
completed. That is to say, the effective compression ratio is
controlled to a relatively low ratio, though there is a possibility
that the combustion stability is still insufficient just after
completion of the starting operation. This leads to the problem of
deteriorated combustion stability. Additionally, in order to
increase cranking speed, the compression ignition engine as
disclosed in JP1-315631 often uses an engine starter of a high
torque capacity (a motor generator of a high torque capacity in
case of a hybrid vehicle). This leads to another problem of
increased manufacturing costs and increased weight. Instead of
using an engine starter of a high torque capacity, a so-called
decompression device can be used to increase cranking speed. The
decompression device is often used for an engine for a two-wheeled
vehicle, so as to constantly open an exhaust valve during cranking,
thus reducing the work of compression and consequently increasing
the cranking speed. However, the decompression device itself does
not have an effective-compression-ratio reducing function that
reduces the effective compression ratio after completion of the
starting operation. Thus, it is difficult to realize the improved
fuel economy (i.e., the reduced fuel consumption rate) during
normal engine operation, by the use of the decompression
device.
[0005] In more detail, in the VTC system disclosed in JP1-315631,
when there is no application of electric current to the step motor
of the VTC system and thus the step motor is de-energized (OFF),
intake valve closure timing IVC is automatically controlled to a
timing value near bottom dead center (BDC), for example, 20 degrees
of crank angle after BDC, under an unfailed condition of the VTC
system. Conversely when the step motor is energized (ON), intake
valve closure timing IVC is controlled to a timing value retarded
from the piston BDC position, for example, 60 degrees of crank
angle after BDC. JP1-315631 teaches the phase-advance of intake
valve closure timing IVC to a timing value near BDC during the
engine starting period, and also teaches the phase-retard of intake
valve closure timing IVC after completion of the starting
operation. However, according to the system of JP1-315631, the
effective compression ratio remains high during cranking, thus
resulting in an undesirable drop in cranking speed.
[0006] In the case of the system as disclosed in the Japanese
document "JSAE Journal Vol. 59, No. 2, 2005", intake valve closure
timing IVC is not phase-retarded from BDC during cranking and cold
starting with a starter energized. The effective compression ratio
remains high during the cranking and starting period. This also
leads to the problem of reduced cranking speed.
[0007] In the case of the system as disclosed in the Japanese
document "Proceedings JSAE 9833467, May, 1998", intake valve
closure timing IVC of the starting period is phase-retarded to
reduce the quantity of air charged in the engine, thus preventing a
rapid rise in torque generated by the engine. However, even after
cranking operation, intake valve closure timing IVC remains
retarded, thus deteriorating the engine startability or
self-ignitability during start operation.
[0008] It is, therefore, in view of the previously-described
disadvantages of the prior art, an object of the invention to
provide a compression ignition engine, capable of avoiding the
aforementioned problem that spontaneous ignition of fuel does not
take place owing to a drop in cranking speed during a starting
period.
[0009] In order to accomplish the aforementioned and other objects
of the present invention, a compression ignition engine comprises
sensors that detect engine operating conditions, a variable valve
operating system comprising at least a variable valve actuation
mechanism variably adjusting an intake valve characteristic
including at least one of a valve lift of an intake valve and a
valve closure timing of the intake valve and actuated by an
actuator, and a control unit configured to be electrically
connected to the sensors and the actuator for controlling the
variable valve actuation mechanism via the actuator to bring the
intake valve characteristic closer to a desired value determined
based on the engine operating conditions detected by the sensors,
the control unit comprising a processor programmed to perform the
following, temporarily lowering an effective compression ratio of
the engine by controlling the intake valve characteristic during a
cranking period of cold starting operation, rising the effective
compression ratio by controlling the intake valve characteristic at
a point of time when a predetermined cranking speed threshold value
has been reached owing to a cranking speed rise, and bringing the
intake valve characteristic closer to the desired value determined
based on the engine operating conditions by way of closed-loop
control, after combustion of the engine has been stabilized.
[0010] According to another aspect of the invention, a compression
ignition engine comprises sensors that detect engine operating
conditions, a variable valve operating system comprising at least a
variable valve actuation mechanism variably adjusting an intake
valve characteristic including at least one of a valve lift of an
intake valve and a valve closure timing of the intake valve and
actuated by an actuator, a decompression device provided to operate
an exhaust valve in a decompression mode corresponding to a
constantly-opened valve operating state during a cranking period of
cold starting operation, and a control unit configured to be
electrically connected to the sensors and the actuator for
controlling the variable valve actuation mechanism via the actuator
to bring the intake valve characteristic closer to a desired value
determined based on the engine operating conditions detected by the
sensors, the control unit also configured to be electrically
connected to the decompression device for switching the exhaust
valve to the decompression mode during the cranking period, and the
control unit comprising a processor programmed to perform the
following, temporarily lowering an effective compression ratio of
the engine by maintaining the exhaust valve in the decompression
mode corresponding to the constantly-opened valve operating state
during the cranking period, inhibiting the decompression mode and
returning the exhaust valve to a normal operating state at a point
of time when a predetermined cranking speed threshold value has
been reached owing to a cranking speed rise, rising the effective
compression ratio by controlling the intake valve characteristic
substantially at the point of time when the predetermined cranking
speed threshold value has been reached owing to the cranking speed
rise, and bringing the intake valve characteristic closer to the
desired value determined based on the engine operating conditions
by way of closed-loop control, after combustion of the engine has
been stabilized.
[0011] According to a further aspect of the invention, a method for
controlling a compression ignition engine employing a variable
valve actuation mechanism variably adjusting an intake valve
characteristic including at least one of a valve lift of an intake
valve and a valve closure timing of the intake valve, the method
comprises temporarily lowering an effective compression ratio of
the engine by controlling the intake valve characteristic during a
cranking period of cold starting operation, rising the effective
compression ratio by controlling the intake valve characteristic at
a point of time when a predetermined cranking speed threshold value
has been reached owing to a cranking speed rise, and bringing the
intake valve characteristic closer to a desired value determined
based on engine operating conditions by way of closed-loop control,
after combustion of the engine has been stabilized.
[0012] According to a still further aspect of the invention, a
method for controlling a compression ignition engine employing a
variable valve actuation mechanism variably adjusting an intake
valve characteristic including at least one of a valve lift of an
intake valve and a valve closure timing of the intake valve and a
decompression device provided to operate an exhaust valve in a
decompression mode corresponding to a constantly-opened valve
operating state during a cranking period of cold starting
operation, the method comprises temporarily lowering an effective
compression ratio of the engine by maintaining the exhaust valve in
the decompression mode corresponding to the constantly-opened valve
operating state during the cranking period, inhibiting the
decompression mode and returning the exhaust valve to a normal
operating state at a point of time when a predetermined cranking
speed threshold value has been reached owing to a cranking speed
rise, rising the effective compression ratio by controlling the
intake valve characteristic substantially at the point of time when
the predetermined cranking speed threshold value has been reached
owing to the cranking speed rise, and bringing the intake valve
characteristic closer to the desired value determined based on the
engine operating conditions by way of closed-loop control, after
combustion of the engine has been stabilized.
[0013] The other objects and features of this invention will become
understood from the following description with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a system block diagram illustrating an embodiment
of a compression ignition engine.
[0015] FIG. 2 is a construction drawing showing an electric-motor
driven variable valve operating system, which is applicable to the
compression ignition engine of the embodiment.
[0016] FIG. 3 is a construction drawing showing another
electric-motor driven variable valve operating system, which is
applicable to the compression ignition engine of the
embodiment.
[0017] FIG. 4 is a construction drawing showing a camshaft sensor
incorporated in the engine control system of the compression
ignition engine of the embodiment.
[0018] FIG. 5 is a construction drawing showing another camshaft
sensor incorporated in the engine control system of the compression
ignition engine of the embodiment.
[0019] FIG. 6 is a crank-angle versus camshaft sensor signal
characteristic diagram.
[0020] FIG. 7 is a diagram of intake valve open timing (IVO),
intake valve closure timing (IVC), exhaust valve opening timing
(EVO), and exhaust valve closure timing (EVC) in a
four-stroke-cycle compression ignition engine.
[0021] FIG. 8 is a diagram of intake valve open timing (IVO),
intake valve closure timing (IVC), exhaust valve opening timing
(EVO), and exhaust valve closure timing (EVC) in a two-stroke-cycle
compression ignition engine.
[0022] FIG. 9 is a time chart showing one phase-control
characteristic of a variable valve operating system (a VTC system)
incorporated in the engine control system of the compression
ignition engine of the embodiment.
[0023] FIG. 10 is a phase-control characteristic diagram showing
phase changes attained by the intake-valve VTC system, for
effective compression ratio changes under various operating
conditions, such as during cranking, after engine warm-up, and at
maximum phase-advance timing.
[0024] FIG. 11 is a flow chart showing a starting-period VTC
control routine executed within an electronic control unit
incorporated in the engine control system of the compression
ignition engine of the embodiment.
[0025] FIG. 12 is a disassembled view showing the detailed
structure of a hydraulically-operated rotary vane type VTC
mechanism, which is applicable to the engine control system of the
compression ignition engine of the embodiment.
[0026] FIGS. 13A-13C are explanatory views showing the operation of
a hydraulic control system for the hydraulically-operated rotary
vane type VTC mechanism shown in FIG. 12.
[0027] FIG. 14A is an explanatory view showing the operating
angular range of the rotary vane of the hydraulically-operated VTC
mechanism shown in FIG. 12.
[0028] FIGS. 14B-14C respectively show the maximum phase-advance
position and the maximum phase-retard position with regard to the
rotary vane of the hydraulically-operated VTC mechanism shown in
FIG. 12.
[0029] FIG. 15 is a time chart showing another phase-control
characteristic of the VTC system.
[0030] FIG. 16 is a time chart showing another phase-control
characteristic in the case of a combination of the VTC system and a
decompression device.
[0031] FIG. 17 is a time chart showing another phase-control
characteristic of the VTC system.
[0032] FIG. 18 is a valve event and lift control characteristic
diagram showing valve event and lift characteristics attained by a
continuously variable valve event and lift control (VEL) system,
for effective compression ratio changes under various operating
conditions, such as during cranking, after engine warm-up, and at
maximum phase-advance timing.
[0033] FIG. 19 is a flow chart showing a glow-plug/electric-heater
control routine.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] Referring now to the drawings, particularly to FIG. 1, the
variable valve operating system incorporated in the compression
ignition engine of the embodiment is exemplified in a
four-stroke-cycle engine. As indicated by the arrow in the system
block diagram of FIG. 1, a crankshaft 2 of an engine 1 rotates
clockwise. As is generally known, a piston position at which a
piston 3 has moved to the bottom of the cylinder of engine 1,
corresponds to 180 degrees of crank angle. The lowest piston
position is called "bottom dead center (BDC)". A piston position
obtained when engine crankshaft 2 further rotates and thus piston 3
has reached the top of the engine cylinder, corresponds to 360
degrees of crank angle. The highest piston position is called "top
dead center (TDC)".
[0035] In the case of usual diesel combustion, diesel fuel (fuel
oil) is sprayed or injected via a fuel injection valve 4 into the
cylinder during the compression stroke. Then, the sprayed fuel is
self-ignited and combusted due to the high-temperature
high-pressure compressed gas (heat produced by compressing the
incoming air). On the other hand, in the case of premix compression
ignition, fuel is sprayed or injected via fuel injection valve 4
into the cylinder during the intake stroke so that the sprayed fuel
is sufficiently premixed with air charged in the cylinder. Residual
gas is set to a comparatively large amount for a temperature rise
in air-fuel mixture. When piston 3 moves up, a temperature rise and
a pressure rise in premixed air-fuel mixture occur, thereby
resulting in spontaneous ignition of the air-fuel mixture so that
the mixture is combusted. A fuel injection amount and injection
timing of fuel injection valve 4 included in the electronic
injection control system are both controlled, responsively to a
sensor signal from a crank angle sensor 5, by means of an
electronic control unit (ECU) 6. The purpose of crank angle sensor
5 is to inform the ECU 6 of engine speed Ne as well as the relative
position of crankshaft 2.
[0036] During start operation, an engine starter 7 is operated to
crank the engine 1 or to turn the crankshaft 2. In the case of a
hybrid-vehicle engine, rather than using starter 7, engine 1 is
rotated by means of a motor generator. Additionally, during the
starting period, an electric current is applied to a glow plug 8
for a temperature rise in glow plug 8 and for promotion of
vaporization of fuel, thus supporting or assisting spontaneous
ignition. Harmful exhaust emission gases such as carbon monoxide
(CO), hydrocarbons (HCs), soot (particulate matter), nitrogen
oxides (NOx), and the like, are filtered out and purified by means
of a catalytic converter 301.
[0037] An intake valve 9 and an exhaust valve 10 are installed in
the upper part of engine 1. Intake valve 9 is driven by an intake
cam 11, whereas exhaust valve 10 is driven by an exhaust cam 12.
Intake cam 11 is mechanically linked via a variable valve actuation
mechanism (or a variable valve characteristic adjustment mechanism)
13 to a camshaft timing pulley 14. In the embodiment shown in FIG.
1, a hydraulically-operated rotary vane type variable valve timing
control (VTC) mechanism is used as variable valve actuation
mechanism 13. In lieu thereof, a variable valve lift (VVL)
mechanism or a continuously variable valve event and lift (VEL)
control mechanism may be used as variable valve actuation mechanism
13. Rotation of crankshaft 2 is transmitted via a timing belt, a
timing chain or the like to camshaft timing pulley 14. In the shown
embodiment, exhaust cam 12 is linked directly to camshaft timing
pulley 14. Alternatively, exhaust cam 12 may be linked to camshaft
timing pulley 14 through the VTC mechanism for intake cam 11. In
lieu thereof, exhaust cam 12 may be linked to camshaft timing
pulley 14 through a separate VTC mechanism differing from the VTC
mechanism for intake cam 11.
[0038] A sensor signal from an engine temperature sensor (a water
temperature sensor or an engine coolant temperature sensor) 15,
which detects engine temperature Te, is input into ECU 6. A sensor
signal from a camshaft sensor 16 of the VTC system is also input
into ECU 6. Camshaft sensor 16 is located near the intake camshaft
associated with intake cam 11. Camshaft timing pulley 14 is driven
by the engine crankshaft at 1/2 the revolution speed of crankshaft
2. In the variable valve operating system of FIG. 1, intake cam 11
is rotated with a phase difference between an angular phase
detected by crank angle sensor 5 and an angular phase detected by
camshaft sensor 16. The valve-opening action of intake valve 9 is
performed once for each two revolutions of crankshaft 2, for entry
of air into the cylinder.
[0039] During rotation of camshaft timing pulley 14, exhaust cam 12
linked to camshaft timing pulley 14 is also driven. The
valve-opening action of exhaust valve 12 is performed once for each
two revolutions of crankshaft 2, for exhausting burned gas from the
engine cylinder. As can be seen from the left-hand side of FIG. 1,
an air flow sensor 17, a turbo charger 18, and an exhaust gas
recirculation (EGR) valve 19 are installed in an induction system
20 and arranged upstream of intake valve 9. Air flow sensor 17 is
provided for measuring the quantity Qa of air entering the engine
cylinder. Additionally, as input information indicative of engine
load, the input interface of ECU 6 receives a sensor signal from an
accelerator position sensor 100 that detects an amount APS of
depression of an accelerator pedal.
[0040] Variable valve actuation mechanism 13 (or the
hydraulically-operated rotary vane type VTC mechanism in the engine
control system of the compression ignition engine of the embodiment
shown in FIG. 1) is a variable phase control means, which is
operable simultaneously with cranking operation of engine 1. In the
case of the hydraulically-operated VTC mechanism of the compression
ignition engine of the embodiment shown in FIG. 1, the VTC
mechanism is operated by hydraulic pressure produced by an oil pump
of engine 1, and therefore the hydraulic pressure produced by the
engine oil pump tends to drop during cranking operation. Due to
such a drop in the supplied hydraulic pressure, the VTC system has
uncertainty in controlling the valve timing (IVC and/or IVO) of
intake valve 9. Under a particular condition where the VTC system
has uncertainty in controlling the valve timing due to a drop in
hydraulic pressure produced by the engine oil pump, for example,
during cranking, a separate electric-motor driven hydraulic oil
pump 302 is driven simultaneously with the ignition-switch turn-ON
operation so as to quickly satisfactorily feed or deliver hydraulic
pressure to the VTC mechanism.
[0041] As shown in FIG. 2, a relative phase change of a camshaft
310 to camshaft timing pulley 14, that is, a valve timing change of
intake valve 9, may be achieved by using a motor-driven spiral disk
type VTC mechanism, rather than using the hydraulically-operated
rotary vane type VTC mechanism, whose detailed construction will be
described later in reference to the disassembled view of FIG. 12.
Actually, in the case of the motor-driven spiral disk type VTC
mechanism of FIG. 2, the phase difference between camshaft 310 and
camshaft timing pulley 14 can be varied by means of a linkage (a
motion converter) 312. The radial outside portion of linkage 312 is
mechanically linked to both of camshaft timing pulley 14 and a
spiral disk 311, such that the radial outside portion of linkage
312 slides along a guide groove 313 formed in camshaft timing
pulley 14 and also slides along a guide groove 314 formed in spiral
disk 311. On the other hand, the radial inside portion of linkage
312 is fixedly connected to camshaft 310. When the phase angle of
spiral disk 311 relative to camshaft timing pulley 14 varies, the
radial position of the outside portion of linkage 312 with respect
to the axis of camshaft 310 varies, and thus a phase change of
camshaft 310 relative to camshaft timing pulley 14 occurs. There
are various methods to vary the phase angle of spiral disk 311
relative to camshaft 310. In the case of the motor-driven spiral
disk type VTC mechanism shown in FIG. 2, a hysteresis motor 315 is
used as an actuator (a driving power source or an
electrically-controlled actuator means). Hysteresis motor 315 can
apply torque to a hysteresis member 316 in a spaced, contact-free
relationship with hysteresis member 316, for varying the phase
angle of spiral disk 311 relative to camshaft timing pulley 14.
Assuming that the car battery voltage is higher than a specified
voltage value, the motor-driven VTC mechanism can be certainly
operated by means of hysteresis motor 315 from the time when engine
1 is cranked. As is generally known, the magnitude of torque acting
on hysteresis member 316 increases, as the applied electric current
to hysteresis motor 311 increases. The increased torque acts to
rotate hysteresis member 316 against the spring force of a biasing
means (a return spring). As a result, it is possible to
continuously vary the relative phase of camshaft 310 to camshaft
timing pulley 14 responsively to the current value of the applied
current to hysteresis motor 311. Therefore, it is possible to
accurately control or adjust the actual relative phase of camshaft
310 to camshaft timing pulley 14 to a desired value by controlling
the applied current by way of closed-loop control (feedback
control) in response to the sensor signal from camshaft sensor
16.
[0042] Referring now to FIG. 3, there is shown a modification of
the motor-driven VTC mechanism, which is applicable to the
compression ignition engine of the embodiment. In the modified VTC
mechanism of FIG. 3, relative phase of camshaft 310 to camshaft
timing pulley 14, in other words, relative phase of camshaft 310 to
crankshaft 2 is varied by means of a helical spline mechanism 320.
Helical spline mechanism 320 is comprised of a substantially
ring-shaped axially-movable helical-gear nut having an internal
helically-splined groove portion, and an external helically-splined
shaft end portion of camshaft 310. The internal helically-splined
groove portion of the nut is in meshed-engagement with the external
helically-splined shaft end portion of camshaft 310. Axially
leftward movement or axially rightward movement of the nut of
helical spline mechanism 320 causes a change in relative phase of
camshaft 310 to camshaft timing pulley 14. As an actuator (a
driving power source or an electrically-controlled actuator means)
that creates axial movement of the nut of helical spline mechanism
320, a reversible motor 321 is used. As clearly shown in FIG. 3, a
rotary-to-linear motion converter 322 is interleaved or provided
between the motor shaft of motor 321 and the nut of helical spline
mechanism 320, for converting rotary motion of the motor shaft in a
normal-rotational direction or in a reverse-rotational direction
into axial movement of the nut of helical spline mechanism 320. In
the shown embodiment, motor 321 is installed on the cylinder head
of engine 1. In lieu thereof, motor 321 may be installed on
camshaft timing pulley 14. In the case of motor 321 installed on
the cylinder head of engine 1, a bearing has to be attached to the
rotary-to-linear motion converter 322. In this case, rotary motion
of the motor shaft of motor 321 is converted into axial movement
(linear motion) of the nut of helical spline mechanism 320 through
the bearing. With the previously-noted arrangement of FIG. 3, the
variable valve timing control function of the VTC system can be
achieved or realized simultaneously with the start of cranking, by
electrically controlling motor 321. In more detail, the actual
relative phase of camshaft 310 to camshaft timing pulley 14 can be
controlled or adjusted to a desired value by controlling rotary
motion (or an applied current value) of motor 321 by way of
closed-loop control responsively to the sensor signal from camshaft
sensor 16. As a reversible motor that creates axial movement of the
nut of helical spline mechanism 320, the VTC system may use a D. C.
motor, a stepping motor, a synchronous motor with a permanent
magnet, or the like. In the case of the use of rotary-to-linear
motion converter 322 having a design speed reduction ratio set to a
comparatively great value, it is more desirable or preferable that
the VTC mechanism is conditioned in its maximum phase-retard state,
in advance, before the start of cranking, so that the VTC mechanism
can be kept at the maximum phase-retard state, even under a
condition where a drop in battery voltage occurs during the
cranking period.
[0043] In the engine control system of the compression ignition
engine of the embodiment, it is necessary to control relative phase
of camshaft 310 to camshaft timing pulley 14 by means of the VTC
mechanism during the cranking period. Therefore, even at very low
engine speeds, substantially corresponding to zero, the engine
control system uses information concerning the actual relative
phase of the VTC mechanism. For the reasons discussed above, the
engine control system of the compression ignition engine of the
embodiment uses the high-precision camshaft sensor 16 having a high
detection accuracy at which camshaft sensor 16 is able to detect
the angular phase of camshaft 310 (in other words, the operating
state of intake valve 9) even at very low engine speeds,
substantially corresponding to zero.
[0044] Referring to FIG. 4, there is shown the detailed
construction of high-precision camshaft sensor 16. As shown in FIG.
4, camshaft sensor 16 is comprised of a toothed portion 330
attached to camshaft 310, a bridge circuit having magnetic
resistance elements 331 located close to the toothed portion 330,
and a magnet 332. The bridge circuit, having magnetic resistance
elements 331, is disposed between the toothed portion 330 and
magnet 332. The strength of magnetic flux 333 produced by magnet
332 varies depending on the relative position of each tooth of
toothed portion 330 to magnet 332. When an electric resistance of
each of magnetic resistance elements 331 varies owing to a change
in magnetic flux 333, a change in electric voltage in the bridge
circuit occurs. One pair of diagonally opposite corners of the
bridge circuit is connected to a first one of two input terminals
of each of a difference circuit (DIFF circuit) 334 and a summation
circuit (SUM circuit) 335, whereas the other pair of the bridge
circuit is connected to the second input terminal of each of DIFF
circuit 334 and SUM circuit 335. The output terminal of DIFF
circuit 334 generates a differential signal (simply, a DIFF
signal), whereas the output terminal of SUM circuit 335 generates a
summation signal (simply, a SUM signal). Based on the DIFF signal
and the SUM signal, it is possible to detect or determine whether
the toothed portion 330 of camshaft 310 is rotating or
stationary.
[0045] Referring to FIG. 5, there is shown the detailed
construction of another type of high-precision camshaft sensor 16.
As shown in FIG. 5, camshaft 310 has a cam 343. A rotor 341 is
installed on or fixedly connected to the left-hand side (the
crankshaft side or the camshaft timing pulley side) of a VTC
mechanism 342, whereas a rotor 344 is installed on or fixedly
connected to the right-hand side of cam 343 of camshaft 310. Rotor
341 has a leaf 340, which is integrally connected onto or
integrally formed with the outer periphery of rotor 341 and whose
radial height varies according to its rotational directions. In a
similar manner, rotor 344 has a leaf 345, which is integrally
connected onto or integrally formed with the outer periphery of
rotor 344 and whose radial height varies according to its
rotational directions. The radial height of leaf 340 is detected by
a gap sensor 346, and then the detected radial height of leaf 340
is converted into an analogue voltage signal (output signal from
gap sensor 346). In a similar manner, the radial height of leaf 345
is detected by a gap sensor 350, and then the detected radial
height of leaf 345 is converted into an analogue voltage signal
(output signal from gap sensor 350). The analogue voltage signal
from gap sensor 346 is converted into an angular signal via a
signal converter (or an arithmetic circuit) 347, whereas the
analogue voltage signal from gap sensor 350 is converted into an
angular signal via a signal converter (or an arithmetic circuit)
349. These angular signals are input from signal converters 347 and
349 into a cam rotation angle arithmetic unit 348. Within cam
rotation angle arithmetic unit 348, the valve timing of intake
valve 9, for example, intake valve closure timing IVC is calculated
based on the angular signal from signal converter 347 and the
angular signal from signal converter 349, and thereafter the
calculated signal (IVC signal) is generated from the output
terminal of cam rotation angle arithmetic unit 348.
[0046] Referring to FIG. 6, there is shown the relationship between
a crank angle and a camshaft sensor signal output value of the
camshaft sensor of FIG. 5, exactly, the crank-angle versus first
gap sensor voltage signal characteristic of gap sensor 346 and the
crank-angle versus second gap sensor voltage signal characteristic
of gap sensor 350. On the basis of the output voltage signal from
the 1.sup.st gap sensor 346, a reference cam rotation angle signal
(see the output voltage signal characteristic indicated by the
solid line in FIG. 6) is generated within signal converter 347. On
the basis of the output voltage signal from the 2.sup.nd gap sensor
350, a camshaft rotation angle signal, that is, a cam rotation
angle signal (see the output voltage signal characteristic
indicated by the broken line in FIG. 6) is generated within signal
converter 349. Cam rotation angle arithmetic unit 348
arithmetically calculates or computes a cam timing controlled
variable (i.e., a cam timing advance amount) based on the generated
reference cam rotation angle signal and the generated camshaft
rotation angle signal. Thus, intake valve closure timing IVC of
intake valve 9 can be controlled in response to the output signal,
generated from cam rotation angle arithmetic unit 348 and
representative of the calculated cam timing advance amount.
[0047] In the case that the engine control system of the
compression ignition engine of the embodiment uses camshaft sensor
16, which is comprised of the toothed portion 330, the bridge
circuit having magnetic resistance elements 331, and magnet 332 and
shown in FIG. 4, the sensor signal from crank angle sensor 5 of
FIG. 1 is utilized as the reference cam rotation angle signal of
the crank-angle versus camshaft sensor signal characteristic as
shown in FIG. 6. As the camshaft rotation angle signal (the cam
rotation angle signal), the DIFF signal and the SUM signal
generated from camshaft sensor 16 of FIG. 4 are utilized. After the
toothed portion 330 of camshaft 310 starts to rotate, the DIFF
signal and the SUM signal are generated from camshaft sensor 16.
Concretely, the DIFF signal and the SUM signal are outputted each
time each of teeth of the toothed portion 330 approaches close to
magnet 332. A specified one of teeth of the toothed portion 330,
corresponding to the zero camshaft rotation angle of camshaft 310,
is cut out, to provide a reference point of camshaft rotation
angle. Thus, the number of pulses of each of the DIFF signal and
the SUM signal can be counted from the cut-out portion serving as
the reference point (the reference camshaft angular position).
Based on the counted value of pulses of each of the DIFF signal and
the SUM signal, the camshaft rotation angle signal is
generated.
[0048] Referring now to FIG. 7, there are shown the timings IVO and
IVC of intake valve 9 and the timings EVO and EVC of exhaust valve
10 during normal engine operation in a four-stroke-cycle
compression ignition engine, such as a four-stroke-cycle Diesel
engine. Exhaust valve 10 starts to open substantially at minus 180
degrees of crank angle at the beginning of exhaust stroke. The
timing where exhaust valve 10 starts to open is called as "exhaust
valve open timing EVO". Exhaust valve 10 starts to close at the end
of exhaust stroke. The timing where exhaust valve 10 starts to
close is called as "exhaust valve closure timing EVC". On the other
hand, intake valve 9 starts to open at a timing value near
0.degree. crank angle at the beginning of intake stroke. The timing
where intake valve 9 starts to open is called as "intake valve open
timing IVO". Intake valve 9 starts to close at a timing value near
BDC (corresponding to 180 degrees of crank angle) at the end of
intake stroke. The timing where intake valve 9 starts to close is
called as "intake valve closure timing IVC". Diesel fuel (fuel oil)
is sprayed or injected into the cylinder at the end of compression
stroke. Self-ignition of the sprayed fuel occurs before or after
TDC (corresponding to 360 degrees of crank angle). When intake
valve closure timing IVC is phase-advanced from BDC, the quantity
of gas (air) charged in the cylinder tends to reduce, thus
resulting in a reduced effective compression ratio. Conversely when
intake valve closure timing IVC is phase-retarded from BDC, reflux
of gas (air), charged into the cylinder once, back to induction
system 20 occurs, and thus the mass of gas charged into the
cylinder is reduced, thereby resulting in a reduced effective
compression ratio.
[0049] Referring now to FIG. 8, there are shown the timings IVO and
IVC of intake valve 9 and the timings EVO and EVC of exhaust valve
10 during normal engine operation in a two-stroke-cycle compression
ignition engine, such as a two-stroke-cycle Diesel engine. One
operating cycle of events, namely the intake and compression
strokes as well as the power and exhaust strokes, is completed for
every crankshaft revolution (360 degrees of-crank angle). During
the first 180 degrees crank angle range (in a crank angle range
from 0.degree. to 180.degree.), the intake and compression strokes
are produced. During the subsequent 180 degrees crank angle range
(in a crank angle range from 180.degree.to 360.degree.), the power
and exhaust strokes are produced. Self-ignition of the sprayed fuel
occurs before TDC, corresponding to 180 degrees of crank angle. The
valve-opening action of intake valve 9 and the valve-opening action
of exhaust valve 10 are performed once for each crankshaft
revolution. Thus, in the two-stroke-cycle engine, in FIG. 1
camshaft timing pulley 14 is driven by the crankshaft at the same
revolution speed of crankshaft 2. The other structure of the
two-stroke-cycle compression ignition engine is similar to that of
the four-stroke-cycle compression ignition engine. In the
two-stroke-cycle compression ignition engine, when intake valve
closure timing IVC is brought closer to BDC, gas (air) charged in
the cylinder is compressed under a condition where the mass of the
charged gas is great, thus increasing or rising the effective
compression ratio. On the contrary, when intake valve closure
timing IVC is phase-retarded with respect to BDC, for the same
internal pressure in induction system 20, there is a tendency for
the quantity of gas (air) charged into the cylinder to be reduced,
thus lowering or decreasing the effective compression ratio.
[0050] Referring to FIG. 9, there is shown a phase-control
characteristic obtained by means of the VTC system of the
compression ignition engine of the embodiment during a cranking and
starting period. When the latest up-to-date informational data of
engine speed Ne, determined based on the sensor signal from crank
angle sensor 5, indicates a very low engine speed substantially
corresponding to zero during the starting period of engine 1, or
when the latest up-to-date informational data of engine temperature
Te, determined based on the sensor signal from engine temperature
sensor 15, indicates a low engine temperature value less than or
equal to 40.degree. C. with the ignition switch turned ON, the
processor of ECU 6 determines that engine 1 is in a cold starting
state. At the time ta at which the engine starter becomes energized
(ON), the phase of variable valve actuation mechanism 13
(hereinafter referred to as "VTC phase") is retarded from a phase
suited to normal engine operation of engine 1. As can be seen from
the phase-change characteristic curves of FIG. 10 attained by the
intake-valve VTC system, intake valve closure timing IVC is
phase-retarded from BDC during cranking. As a result, the effective
compression ratio is lowered, thus reducing the work of
compression. This contributes to the increased cranking speed and
enhanced startability. Suppose that the VTC phase has been retarded
in advance, before the start of cranking. In such a case, starter 7
becomes energized (ON) at once without VTC phase-retard
control.
[0051] Returning to FIG. 9, at the time tb at which the cranking
speed begins to exceed 400 rpm, the VTC mechanism is controlled so
that the VTC phase (that is, intake valve closure timing IVC) is
brought closer to the phase corresponding to the maximum
phase-advance state. Therefore, as can be seen from the
intake-valve phase changes shown in FIG. 10, intake valve closure
timing IVC is brought closer to a timing value near BDC. As a
result, the effective compression ratio is raised, and thus
in-cylinder gas temperature becomes high. Thereafter, at the time
tc at which the VTC phase becomes the phase corresponding to the
maximum phase-advance state, fuel injection starts. At the time tc,
by virtue of the high effective compression ratio and high
temperature gas, the injected fuel is certainly combusted. Owing to
the combustion energy, a rapid rise in engine speed Ne occurs. At
the same time, in order to adjust the fuel-injection amount, the
electronic fuel injection system is controlled by means of ECU 6 of
FIG. 1, such that engine speed Ne is maintained at a specified
idling speed for example 600 rpm. In this manner, in the engine
control system of the compression ignition engine of the
embodiment, the VTC phase (i.e., intake valve closure timing IVC)
can be controlled temporarily to the phase corresponding to the
phase-advance state during the starting period. Therefore, suppose
that the engine control system of the compression ignition engine
of the embodiment, capable of varying the effective compression
ratio by a change in the IVC phase (a change in intake valve
closure timing IVC), is applied to a fixed compression-ratio
compression-ignition internal combustion engine (of a low
geometrical compression ratio) in which intake valve closure timing
IVC is generally controlled to a timing value phase-retarded from
BDC by way of feedback control after engine warm-up. It is possible
to adjust the effective compression ratio temporarily to a high
ratio by controlling intake valve closure timing IVC to a timing
value phase-advanced from BDC during the starting and warm-up
period, as if the geometrical compression ratio has been varied to
a high ratio for example by means of a multi-link variable
compression ratio device. That is to say, the variable valve
operating system (variable valve actuation mechanism 13)
incorporated in the compression ignition engine of the embodiment,
capable of varying the effective compression ratio by
phase-changing intake valve closure timing IVC, has a variable
compression ratio function just like a multi-link variable
compression ratio device (or a multi-link piston crank mechanism)
capable of varying a geometrical compression ratio, defined-as a
ratio (V1+V2)/V1 of the full volume (V1+V2) existing within the
engine cylinder and combustion chamber with the piston at BDC to
the clearance-space volume (V1) with the piston at TDC, by varying
a piston stroke characteristic (at least one of the piston TDC
position and the piston BDC position). Generally, the
low-geometrical-compression-ratio compression-ignition engine (the
fixed geometrical-compression-ratio engine) itself has merits,
namely light weight and reduced cost. In the case of a combination
of the low-geometrical-compression-ratio compression-ignition
engine and the variable valve operating system (variable valve
actuation mechanism 13) incorporated in the compression ignition
engine of the embodiment capable of varying the effective
compression ratio by phase-changing intake valve closure timing
IVC, there are several advantages, that is, light-weight, simple
construction, and reduced cost. As discussed above, the geometrical
compression ratio often denoted by Greek letter ".epsilon." is
generally defined as a ratio (V1+V2)/V1 of the full volume (V1+V2)
existing within the engine cylinder and combustion chamber with the
piston at BDC to the clearance-space volume (V1) with the piston at
TDC. On the other hand, the effective compression ratio denoted by
Greek letter ".epsilon.'" is generally defined as a ratio of the
effective cylinder volume corresponding to the maximum working
medium volume to the effective clearance volume corresponding to
the minimum working medium volume. These two compression ratios
.epsilon. and .epsilon.' are thermodynamically distinguished from
each other.
[0052] Hereupon, it is necessary to care the fact that the quantity
of air charged into the cylinder of engine 1 changes depending on
intake valve closure timing IVC. When intake valve closure timing
IVC is retarded, the quantity of air charged into engine 1 becomes
small. Therefore, it is desirable to properly control the
fuel-injection amount, fully taking into account the intake valve
closure timing IVC. For this reason, the fuel-injection amount is
compensated for responsively to at least sensor signals from
camshaft sensor 16 and air flow sensor 17 in addition to engine
speed Ne and engine load (e.g., the amount APS of depression of the
accelerator pedal), thereby preventing or suppressing the
generation of soot.
[0053] Thereafter, as can be seen from the A characteristic curve
(indicated by the solid line in FIG. 9), at the time td at which a
stable combustion state has been reached, for example, when the
engine temperature (engine coolant temperature) exceeds 60.degree.
C., the VTC phase is controlled or adjusted from the phase
corresponding to the maximum phase-advance state in the
phase-retard direction (that is, toward a phase suited to the
normal engine operation of engine 1). In lieu of the VTC phase
control based on the A characteristic curve of FIG. 9, the VTC
phase control based on the B characteristic curve indicated by the
broken line in FIG. 9 may be applied. According to the VTC phase
control based on the B characteristic curve of FIG. 9, during the
warm-up time period tc-td from tc to td, intake valve closure
timing IVC may be retarded gradually to the phase suited to the
normal engine operation of engine 1, depending on the combustion
stability. As can be seen from the phase-change characteristic
curves of FIG. 10 attained by the intake-valve VTC system, the VTC
phase suited after completion of engine warm-up, is set to an
intermediate phase, which is advanced from the VTC phase suited for
the early stage (see the time period ta-tb in FIG. 9) of engine
cranking and retarded from the maximum phase-advanced VTC phase of
the starting and warm-up period (in particular, see the warm-up
time period tc-td in FIG. 9). By way of the proper setting of the
VTC phase (i.e., the previously-noted intermediate phase) suited
after completion of engine warm-up, it is possible to properly
lower the effective compression ratio to such an extent that does
not cause any trouble in combustion, thereby effectively lowering
the work of compression and ensuring a reduction in mechanical
friction loss of engine 1, a decrease in fuel consumption rate
(improved fuel economy), and reduced NOx (nitrogen oxides)
emissions. Additionally, by virtue of the properly lowered
effective compression ratio after engine warm-up, it is possible to
effectively reduce a peak value of combustion pressure, thereby
ensure a reduction in combustion noise and vibrations. Suppose that
the engine control system of the compression ignition engine of the
embodiment is applied to a hybrid vehicle employing an automatic
engine stop-restart system frequently executing engine stop and
restart operation even after completion of engine warm-up. It is
possible to reconcile the enhanced startability and the reduced
electric power consumption, by virtue of the properly lowered
effective compression ratio after engine warm-up. From the time td
after completion of engine warm-up, intake valve closure timing IVC
is optimally controlled usually by way of closed-loop control
depending on engine operating conditions such as engine speed Ne
and engine load (accelerator-pedal depression amount APS).
[0054] Referring now to FIG. 11, there is shown the starting-period
VTC control routine executed within ECU 6 incorporated in the
engine control system of the compression ignition engine of the
embodiment. The routine of FIG. 11 is executed as time-triggered
interrupt routines to be triggered every predetermined time
intervals for example 10 milliseconds.
[0055] After an ignition switch (an engine key switch) is turned ON
at step 360, a check or a determination for the current VTC phase
is made through step 361. Actually, at step 362 just after step
361, the processor of ECU 6 executes a comparative check for the
current VTC phase (that is, the current intake valve closure timing
IVC) with respect to a first predetermined phase angle. More
concretely, when step 362 determines that the current VTC (i.e.,
the latest up-to-date informational data of intake valve closure
timing IVC) is phase-retarded with respect to the first
predetermined phase angle, the routine proceeds to step 363.
Conversely when step 362 determines that the current intake valve
closure timing IVC is not phase-retarded with respect to the first
predetermined phase angle, the routine proceeds to step 364.
[0056] At step 363, starter 7 becomes energized (ON).
[0057] At step 364, starter 7 becomes energized (ON).
[0058] Subsequently to step 364, step 365 occurs to initiate VTC
phase-retard control for variable valve actuation mechanism 13 (the
VTC mechanism). In the control routine of FIG. 11, step 365 (that
is, VTC phase-retard control) is executed just after step 364 (that
is, starter energizing operation). In lieu thereof, step 365 (VTC
phase-retard control) may be executed just before step 364 (starter
energizing operation).
[0059] At step 367, a comparative check similar to step 362 is made
again to determine whether the current VTC phase (that is, the
current intake valve closure timing IVC) is phase-retarded with
respect to the first predetermined phase angle. When the answer to
step 367 is affirmative (YES), that is, when the current intake
valve closure timing IVC has been phase-retarded with respect to
the first predetermined phase angle, the routine proceeds to step
368. Conversely when the answer to step 367 is negative (NO), the
routine returns to step 365. The return from step 367 to step 365
is repeatedly executed until the actual intake valve closure timing
IVC has been retarded with respect to the first predetermined phase
angle. In other words, after a specified time period has expired
from the initial execution of step 367, the routine shifts from
step 367 to step 368. The current timing value of intake valve
closure timing IVC, needed for the comparative check of step 367,
is detected or determined based on the sensor signal from camshaft
sensor 16.
[0060] At step 368, a check is made to determine whether the latest
up-to-date informational data of engine speed Ne, determined based
on the sensor signal from crank angle sensor 5, is greater than or
equal to a first predetermined speed value such as 400 revolutions
per minute. When the answer to step 368 is affirmative (YES), that
is, when the current engine speed is greater than or equal to the
first predetermined speed value (e.g., 400 rpm), the routine
proceeds from step 368 to step 369. Conversely when the answer to
step 368 is negative (NO), step 368 is repeatedly executed, until
the current engine speed exceeds the first predetermined speed
value owing to a rise in cranking speed.
[0061] At step 369, VTC phase-advance control for variable valve
actuation mechanism 13 (the VTC mechanism) is executed. After step
369, step 370 occurs.
[0062] At step 370, a comparative check is made to determine
whether the current VTC phase (that is, the current intake valve
closure timing IVC) is phase-advanced with respect to a second
predetermined phase angle. When the answer to step 370 is
affirmative (YES), that is, when the current intake valve closure
timing IVC has been phase-advanced with respect to the second
predetermined phase angle, the routine proceeds to step 371.
Conversely when the answer to step 370 is negative (NO), step 370
is repeatedly executed, until the current intake valve closure
timing IVC has been phase-advanced with respect to the second
predetermined phase angle by way of the VTC phase-advance
control.
[0063] At step 371, fuel injection starts. At this time, the
fuel-injection amount is compensated for responsively to at least
the sensor signal from camshaft sensor 16 and the sensor signal
(representative of the quantity of air charged into the cylinder)
from air flow sensor 17 in addition to engine speed Ne and engine
load (e.g., accelerator-pedal depression amount APS). After step
371, step 372 occurs.
[0064] At step 372, a check is made to determine whether the latest
up-to-date informational data of engine speed Ne (i.e., the current
engine speed) is greater than or equal to a second predetermined
speed value such as 500 revolutions per minute. When the answer to
step 372 is affirmative (YES), that is, when the current engine
speed is greater than or equal to the second predetermined speed
value (e.g., 500 rpm), the routine proceeds from step 372 to step
373. Conversely when the answer to step 372 is negative (NO), step
372 is repeatedly executed, until the current engine speed exceeds
the second predetermined speed value.
[0065] At step 373 a check is made to determine whether the latest
up-to-date informational data of engine temperature, determined
based on the sensor signal from engine temperature sensor 15, is
greater than or equal to a predetermined temperature value (a
temperature threshold) such as 60.degree. C. When the answer to
step 373 is affirmative (YES), that is, when the current engine
temperature is greater than or equal to the predetermined
temperature value (,e.g., 60.degree. C.), the routine proceeds from
step 373 to step 374. Conversely when the answer to step 373 is
negative (NO), step 373 is repeatedly executed, until the current
engine temperature exceeds the predetermined temperature value
owing to an engine temperature rise after the fuel injection
operation.
[0066] At step 374, VTC phase-retard control for variable valve
actuation mechanism 13 (the VTC mechanism) is executed so that the
actual VTC phase (that is, the actual intake valve closure timing
IVC) is retarded towards a phase suited to the normal engine
operation of engine 1. After step 374, step 375 occurs.
[0067] At step 375, a check is made to determine whether the
current VTC phase (i.e., the actual intake valve closure timing
IVC) is brought closer to the desired phase (the desired timing)
suited for the normal engine operation and determined based on the
up-to-date informational data of engine speed Ne and engine load
APS, by way of closed-loop control for the VTC phase. In this
manner, through step 375, the intermediate VTC phase control suited
for the normal engine operation is executed within an intermediate
phase-angle range phase-advanced from the maximum phase-retarded
VTC phase and retarded from the maximum phase-advanced VTC
phase.
[0068] According to the control routine of FIG. 11, only during the
early stage (see the time period ta-tb in FIG. 9) of engine
cranking, intake valve closure timing IVC is retarded from BDC, and
thereafter intake valve closure timing IVC is adjusted
(phase-advanced) to a timing value near BDC so that engine 1 is
operated in a high effective compression ratio mode. After this,
immediately when engine speed Ne reaches and exceeds the second
predetermined speed value, for example, 500 rpm, the processor of
ECU 6 determines that the engine starting operation has been
completed. After completion of engine starting operation, in other
words, after completion of engine warm-up, intake valve closure
timing IVC is,retarded by a predetermined phase angle .DELTA.
(corresponding to a phase difference between the actual intake
valve closure timing IVC and its desired value) from BDC. In order
to properly lower the effective compression ratio after completion
of engine starting operation, in the case of the four-stroke-cycle
compression ignition engine, intake valve closure timing IVC may be
phase-advanced from BDC.
[0069] In the engine stopped state, as can be supposed, there are
two cases, namely one being a case that intake valve closure timing
IVC (VTC phase) has already been set to the maximum phase-retard
timing under the engine stopped state, and the other being a case
that intake valve closure timing IVC (VTC phase) is controlled to
the maximum phase-retard timing simultaneously with the turned-ON
operation of the ignition switch. Therefore, in the case that
intake valve closure timing IVC (VTC phase) has to be controlled to
the maximum phase-retard timing simultaneously with the ignition
switch turned-ON operation, through steps 365 and 367 the current
intake valve closure timing IVC (or the actual IVC) is detected or
determined based on the sensor signal from camshaft sensor 16, and
then a phase-angle difference (a deviation or an error signal)
between the detected actual intake valve closure timing IVC and the
desired value (e.g., the maximum phase-retard timing) is
determined. In order to adjust the phase-angle difference to zero,
VTC phase control (IVC control) is performed. On the contrary, in
the case that intake valve closure timing IVC (VTC phase) has
already been set to the maximum phase-retard timing under the
engine stopped state, the routine of FIG. 11 flows from step 362
(only the comparative check for the current VTC phase (the current
IVC) with respect to the first predetermined phase angle) through
step 363 (starter energizing operation) quickly to step 368,
bypassing steps 365 and 367.
[0070] In the starting-period VTC control system of FIG. 11, after
step 371 (the fuel-injection starting step), (i) the first check
for an engine speed rise above the second predetermined speed value
(e.g., 500 rpm) and (ii) the second check for an engine temperature
rise above the predetermined temperature value (e.g., 60.degree.
C.) are both made. In lieu thereof, only the first check may be
executed, without executing the second check. In such a case,
immediately when an engine speed rise above the second
predetermined speed value is detected, the routine advances from
step 372 quickly to step 374 without executing a check for an
engine temperature rise, so that the actual intake valve closure
timing IVC can be quickly retarded by the predetermined phase angle
.DELTA., corresponding to the phase difference between the actual
intake valve closure timing IVC and the desired value,
corresponding to the intermediate VTC phase angle suited for the
normal engine operation. This is because, in the case of engine
speeds above the second predetermined speed value (e.g., 500 rpm)
during the last stage of engine starting, the quantity of heat
generated by combustion of the injected fuel tends to be greater
than the quantity of heat radiated from the cylinder wall, even
under a comparatively low engine-temperature condition, and thus
stable combustion can be ensured. As soon as the processor of ECU 6
determines, based on only the check for the engine speed rise above
the second predetermined speed value (500 rpm), that a stable
combustion state has been reached and achieved, the routine
proceeds to step 375 to initiate the intermediate VTC phase control
suited for the normal engine operation.
[0071] In the case that intake valve closure timing IVC is not set
to the maximum phase-retard timing in the engine stopped state,
through step 365 of the control routine of FIG. 11, the VTC
phase-retard control, in other words, IVC phase-control to the
maximum phase-retard timing is executed. As discussed previously,
the quantity of air charged into the cylinder changes depending on
intake valve closure timing IVC. Thus, fully taking into account
the air-fuel mixture (A/F) ratio, the fuel-injection amount must be
varied responsively to the VTC phase change (i.e., IVC phase
change). Actually, the mass of fuel, injected from fuel injection
valve 4, is controlled or changed depending on various factors,
that is, the quantity Qa of air entering the engine cylinder,
measured by air flow sensor 17, the accelerator-pedal depression
amount APS, and engine speed Ne detected by crank angle sensor 5.
In addition to the aforementioned sensor signals, preferably, the
state of EGR valve 19 (i.e., the EGR valve opening) and the
turbo-charging state (e.g., boost pressure) of turbo charger 18 may
be taken into account for determining the mass of the injected fuel
and injection timing. As a matter of course, in the case of the
occurrence of a change in VTC phase, that is, a change in intake
valve open timing IVO as well as a change in intake valve closure
timing IVC, it is necessary to properly change the fuel injection
timing as well as fuel-injection amount. For the reasons discussed
above, the sensor signal input from camshaft sensor 16 into the
input interface of ECU 6 is important to execute the VTC phase
control (that is, IVC phase control) and also to execute the
electronic fuel injection control. For instance, in the case of
one-stroke injection of the Diesel engine, a fuel injection pattern
is classified into a pilot-injection area, a main-injection area,
an after-injection area, and a post-injection area. The fuel
injection pattern changes depending on engine operating conditions.
In step 371 of the flow chart shown in FIG. 11, the fuel injection
pattern is given as a function of intake valve closure timing IVC.
By the use of the predetermined or preprogrammed function
representative of the relationship between the fuel injection
pattern and intake valve closure timing IVC, a change in intake
valve closure timing IVC can be remarkably reflected as a change in
the fuel injection pattern (containing a fuel injection amount and
the number of fuel injections).
[0072] Instead of executing (i) a check for the necessity for VTC
phase retard and (ii) VTC phase-retard control (see the flow from
step 361 via steps 362 and 364 to step 365 in FIG. 11) during the
early stage of the engine starting period, the control routine as
shown in FIG. 11 may be somewhat modified, so that the VTC phase
control (i.e., the IVC control) to a desired phase (i.e., a desired
standby timing suited for the early stage of engine cranking) is
executed for each transition to an engine stopped state. In this
case, it is possible to easily adjust intake valve closure timing
IVC to a desired standby timing spaced apart from BDC for each
transition to an engine stopped state, by slightly modifying step
365 of FIG. 11. Concretely, at the modified step 365, a control
command signal (or a drive signal or an electric signal) is applied
to the actuator (or the electrically-controlled actuator means) of
the VTC mechanism during the early stage of the engine stopping
period in such a manner as to control or adjust the intake valve
closure timing IVC to the desired standby timing spaced apart from
BDC, that is, to the desired phase-change state remarkably
phase-retarded or phase-advanced from BDC. After completion of the
IVC phase-adjustment to the desired standby timing, at the last
stage of the engine stopping period, an engine stop signal is
output. By the use of the modified step 365, it is possible to
efficiently achieve the IVC phase-adjustment to the desired standby
timing spaced apart from BDC during the engine stopping period
rather than the engine starting period. This eliminates (i) a check
for the current VTC phase and (ii) VTC phase-retard control during
the early stage of the engine starting period. This contributes to
the shortened engine starting time.
[0073] The combustion stability of engine 1 is affected by various
control parameters, namely, engine temperature, fuel property (for
example, cetane value), intake air temperature (charge air
temperature), residual gas ratio, EGR rate, boost pressure, and the
like. In the engine control system of the compression ignition
engine of the embodiment, it is preferable that a plurality of
control parameters, directly participating in combustion stability,
are detected and intake valve closure timing IVC is controlled,
fully taking into account the detected control parameters. As the
control parameters, directly participating in combustion stability,
the following parameters are exemplified. [0074] (1) In-cylinder
pressure; [0075] (2) Vibrations of cylinder head, caused by gas
vibrations of controlled or uncontrolled burning [0076] (3)
Rotational-speed fluctuations in crankshaft [0077] (4) Ionic
current arising from combustion [0078] (5) Emission intensity of
flame A threshold value for each of the above-mentioned control
parameters, suited for engine speed and engine load after engine
warm-up, is experimentally measured and determined beforehand.
Thus, it is possible to determine, based on the comparison result
of the detected value of the control parameter and its threshold
value, whether or not a stable combustion state has been reached.
Based on such a decision result concerning a stable/unstable
combustion state, it is possible to prevent forcible phase-advance
of intake valve closure timing IVC during the starting period, thus
enabling intake valve closure timing IVC to timely control in the
phase-retard direction. At this time, it is necessary to
experimentally measure and determine the threshold value of each of
the control parameters in the VTC phase-advance state with a target
engine, beforehand. The threshold values for these control
parameters can be used for fuel-injection amount control and
fuel-injection timing control in real time.
[0079] Referring now to FIG. 12, there is shown the disassembled
view of the electronically-controlled hydraulically-operated rotary
vane type VTC mechanism, capable of executing the VTC phase-retard
control of steps 365 and 374 and VTC phase-advance control of step
369. As can be seen from the disassembled view of FIG. 12, a
hydraulically-operated vane body 22 of a four-blade vane unit 105
is fixedly connected or bolted to the shaft end of an intake
camshaft 200 having intake cam 11, by means of a center bolt (or a
vane mounting bolt) 21. Camshaft timing pulley 14 is formed with a
sprocket 103, which serves as a rotary member driven by the engine
crankshaft via a timing chain 131 (see FIG. 14A). Camshaft timing
pulley 14 is fixedly connected to a substantially cylindrical
hydraulic housing 23 integrally formed with four partition wall
portions (simply, four shoes), each protruding radially inwards
from and integrally formed with the inner periphery of the
cylindrical housing. Vane body 22 is operably accommodated in
hydraulic housing 23. The front end of vane body 22 is hermetically
covered in a fluid-tight fashion by a front cover 24. Vane body 22
is formed integral with four vanes. Application of hydraulic
pressure to one sidewall of each of the vanes causes relative
rotary motion of vane body 22 to housing 23, thereby resulting in a
phase difference (a change in relative phase) between vane body 22
and housing 23. Thus, it is possible to vary intake valve closure
timing IVC during operation of engine 1 by controlling the phase
difference between vane body 22 and housing 23. In the case of the
electronically-controlled hydraulically-operated rotary vane type
VTC mechanism shown in FIG. 12, intake valve open timing IVO varies
simultaneously with a change in intake valve closure timing
IVC.
[0080] As clearly shown in FIG. 12, two rows of return springs
(biasing means) 25, 25 are disposed between one sidewall surface of
each of the vanes and a stopper surface of each of the partition
wall portions of housing 23. In total, eight return springs 25 are
arranged in housing 23. Spring forces of return springs 25
permanently bias vane body 22 to cause relative rotary motion of
vane body 22 to housing 23 in a clockwise direction, that is, in a
phase-advance direction of camshaft 200. Alternatively, return
springs 25 may be arranged in housing 23, so that spring forces of
the return springs permanently bias vane body 22 to cause relative
rotary motion of vane body 22 to housing 23 in a counterclockwise
direction, that is, in a phase-retard direction of camshaft 200.
Front cover 24 is secured to or fixedly connected to housing 23 by
means of mounting bolts 117. Although it is not clearly shown in
FIG. 12, front cover 24 is formed with an air bleeder hole 128. As
described later in reference to FIGS. 14A-14C, to create rotary
motion of each of the vanes of vane body 22 relative to housing 23,
for phase advance, working fluid (hydraulic oil) is supplied into a
variable-volume phase-advance hydraulic chamber 30 through a
phase-advance hydraulic line 32 and a phase-advance oil hole 106.
Conversely for the purpose of phase retard, working fluid
(hydraulic oil) is supplied into a variable-volume phase-retard
hydraulic chamber 31 through a phase-retard hydraulic line 33 and a
phase-retard oil hole 107. The four vane blades of vane body 22 and
housing 23 cooperate with each other to define four variable-volume
phase-retard chambers 31 and four variable-volume phase-advance
chambers 30. In the shown embodiment, the two rows of springs (25,
25) are disposed in the associated phase-advance chamber 30.
[0081] Phase-advance hydraulic line 32 and phase-retard hydraulic
line 33 are formed or defined in intake camshaft 200 shown in FIG.
12. Working fluid discharged from the engine oil pump, provided for
lubricating oil supply into the engine, or working fluid discharged
from separate electric-motor driven hydraulic oil pump 302, is
delivered through a phase-advance oil-delivery groove 35 and a
phase-retard oil-delivery groove 34 into the respective hydraulic
lines 32 and 33. Phase-advance oil-delivery groove 35 and
phase-retard oil-delivery groove 34 are located in a cam journal
bearing portion 108. The shaft end of intake camshaft 200 has a
female screw-threaded portion 118 into which center bolt 21 is
screwed. Working fluid flow of the previously-noted hydraulic
circuit for the hydraulically-operated rotary vane type VTC
mechanism is controlled by an oil control valve 39 whose operation
is hereunder described in reference to FIGS. 13A-13C. Oil control
valve 39 is comprised of an electromagnetic solenoid 40, a spool
41, and a spool-biasing spring 42. In FIGS. 13A-13C, a port denoted
by "A" is connected to phase-advance hydraulic line 32, whereas a
port denoted by "B" is connected to phase-retard hydraulic line 33.
The axial position of solenoid 40 is controlled in response to a
control signal (or a drive signal) applied from the output
interface (or the drive circuit) of ECU 6 to the solenoid. That is,
solenoid 40 serves as an actuator (a driving power source or an
electrically-controlled actuator means) for the
hydraulically-operated rotary vane type VTC mechanism.
[0082] As shown in FIG. 13A, when solenoid 40 is de-energized (OFF)
and thus spool 41 is held at its spring-loaded position by the
spring force of spool-biasing spring 42, hydraulic pressure in
phase-advance hydraulic line 32 becomes high, while hydraulic
pressure in phase-retard hydraulic line 33 becomes low. As a result
of this, vane body 22 moves in the phase-advance direction, and
then vane body 22 is held at an angular position corresponding to
the maximum phase-advanced VTC phase, in other words, the maximum
phase-advance intake valve closure timing substantially
corresponding to BDC (that is, IVC.apprxeq.BDC). The phase-advance
state (IVC.apprxeq.BDC) of the VTC mechanism, created by the
spring-loaded axial position of spool 41, corresponds to an
operating mode important to the starting and warm-up period of
engine 1. Even in the presence of a failure in the engine control
system such as a control signal line failure, it is possible to
certainly start the engine 1 by the phase-advance state
(IVC.apprxeq.BDC) of the VTC mechanism, created by the
spring-loaded axial position (the de-energized state) of spool
41.
[0083] As shown in FIG. 13B, when spool 41 moves axially leftwards
against the spring force of spool-biasing spring 42 with solenoid
40 energized (ON) and then spool 41 is held at the leftmost spool
position (viewing FIG. 13B), hydraulic pressure in phase-advance
hydraulic line 32 becomes low, while hydraulic pressure in
phase-retard hydraulic line 33 becomes high. As a result of this,
vane body 22 moves in the phase-retard direction, and then vane
body 22 is held at an angular position corresponding to the maximum
phase-retarded VTC phase, in other words, the maximum phase-retard
intake valve closure timing retarded from and spaced apart from
BDC.
[0084] As shown in FIG. 13C, when spool 41 is held at a specified
intermediate spool position, phase-advance hydraulic line 32 and
phase-retard hydraulic line 33 are blocked by the two lands of
spool 41. Hydraulic pressure in variable-volume phase-advance
hydraulic chamber 30 and hydraulic pressure in variable-volume
phase-retard hydraulic chamber 31 are held constant. That is, the
VTC mechanism is held at its pressure-hold mode. As a result, the
relative position of vane body 22 to housing 23 can be held at a
desired angular position, in other words, at a balanced position of
torque acting on vane body 22 due to the spring force of each of
return springs 25 and torque acting on vane body 22 due to the
differential pressure between phase-advance and phase-retard
hydraulic chambers 30 and 31 defined on both sides of each of the
vanes. Therefore, by properly controlling the axial position of
spool 41, it is possible to hold intake valve closure timing IVC at
an arbitrary timing value between the maximum phase-retard timing
and the maximum phase-advance timing. The spool position control is
executed by ECU 6 by way of closed-loop control (feedback control)
based on the sensor signal from camshaft sensor 16. As discussed
previously, during engine cranking, in particular, during the early
stage (see the time period ta-tb in FIG. 9) of cranking, intake
valve closure timing IVC is controlled to the maximum phase-retard
timing, corresponding to the rightmost spool position shown in FIG.
13A. This results in the reduced work of compression, the increased
cranking speed, and the ease of engine starting. Owing to the
reduced work of compression, it is possible to easily crank the
engine, in spite of setting of the applied electric current to
starter 7 to a comparatively low level. This eliminates the
necessity for an engine starter of a high torque capacity.
[0085] As set forth above, by way of the axial position control for
spool 41, in other words, by way of applied current control for
solenoid 40, as can be seen from the phase-change characteristic
curves of FIG. 10, intake valve closure timing IVC can be
controlled to an arbitrary timing value, ranging from the maximum
phase-advance timing substantially corresponding to BDC to the
maximum phase-retard timing retarded by approximately 40 degrees of
crank angle from BDC. Intake valve open timing IVO also varies
simultaneously with a change in intake valve closure timing IVC
(see the intake-valve phase-change characteristic curves of FIG.
10). Approaching intake valve closure timing IVC closer to BDC
results in a rise in effective compression ratio, thereby enhancing
the startability of engine 1.
[0086] Additionally, during the cranking period, intake valve
closure timing IVC is considerably phase-retarded from BDC, and as
a result the work of compression is effectively reduced and a
cranking speed increase occurs, thus ensuring enhanced
startability. After completion of engine warm-up, the effective
compression ratio is lowered by slightly retarding intake valve
closure timing IVC from BDC, thus effectively reducing a fuel
consumption rate after engine starting. Additionally, owing to the
lowered effective compression ratio, an excessive rise in
combustion temperature will be effectively suppressed, thus
reducing NOx (nitrogen oxides) emissions.
[0087] Returning to FIG. 12, one of the four vane blades of vane
body 22 has an axial bore that slidably accommodating therein a
hydraulic lock piston 110. Piston 110 is arranged to selectively
engaged with or disengaged from a seat 111 (having a lock-piston
hole) of camshaft timing pulley 14, depending on engine operating
conditions. With piston 110 in fitted-engagement with seat 111,
vane body 22 is coupled to cam timing pulley 14, so that vane body
22 rotates together with cam timing pulley 14 during operation. For
instance, when hydraulic pressure to be supplied to vane body 22 is
insufficient due to a failure in separate electric-motor driven
hydraulic oil pump 302 during a starting period, lock piston 110 is
brought into engagement with seat 111 of camshaft timing pulley 14,
thus constraining rotary motion (free rotation) of vane body 22
relative to the cylindrical housing 23 and consequently preventing
the camshaft from rotating relative to the crankshaft.
[0088] As best seen from FIG. 14A, the position of
fitted-engagement of piston 110 with seat 111, is set or designed
to provide the maximum phase-advanced VTC phase, in other words,
the maximum phase-advance intake valve closure timing substantially
corresponding to BDC (i.e., IVC.apprxeq.BDC). When engine 1 starts
to rotate and thus hydraulic pressure acting on vane body 22
becomes high, piston 110 moves against the spring force of a piston
return spring 112 in a direction disengaging of piston 110 from
seat 111, under pressure of working fluid fed via phase-advance oil
hole 106 and phase-retard oil hole 107. As a result, vane body 22
is uncoupled from camshaft timing pulley 14, thereby enabling vane
body 22 to be controlled hydraulically.
[0089] As shown in FIG. 12, in addition to return springs 25, it is
more preferable to further provide a torsion coil spring 120
between vane body 22 and front cover 24. There is no risk of
interference between each of return springs 25 and torsion coil
spring 120, since the installation position of each return spring
25 arranged in housing 23 differs from the installation position
off torsion coil spring 120. A combination of return springs 25 and
torsion coil spring 120 realizes a great magnitude of spring bias
permanently biasing vane body 22 in a clockwise direction.
Concretely, as appreciated from the disassembled view of FIG. 12,
the left-hand hook end of torsion coil spring 120 is fitted into a
torsion-spring hook insertion hole 122 bored in front cover 24,
whereas the right-hand hook end of torsion coil spring 120 is
fitted into a torsion-spring hook insertion hole 121 bored in vane
body 22. In the same manner as return springs 25, a spring force of
torsion coil spring 120 permanently biases vane body 22 to cause
relative rotary motion of vane body 22 to housing 23 in a clockwise
direction, that is, in a phase-advance direction of camshaft
200.
[0090] In FIG. 12, a member denoted by reference sign 104 is a
positioning pin included in a positioning mechanism for the purpose
of positioning between housing 23 and camshaft timing pulley 14
when assembling these component parts by means of bolts 117. The
positioning means is effective to easily determine the specified
angular position of housing 23 relative to camshaft timing pulley
14, in other words, the specified angular position of lock piston
110, which is slidably accommodated in the axial bore of vane body
22 circumferentially movable in housing 23 within limits, relative
to the lock-piston hole of seat 111, when assembling the two
component parts.
[0091] Referring to FIG. 14A, hydraulic housing 23 is driven by the
engine crankshaft via a crankshaft timing pulley 132 and timing
chain 131. In the case of the four-stroke-cycle engine, housing 23
is driven by the crankshaft at 1/2 the revolution speed of
crankshaft 2. In the case of the two-stroke-cycle engine, housing
23 is driven by the crankshaft at the same revolution speed as
crankshaft 2. As described previously, working fluid is supplied
into variable-volume phase-advance hydraulic chamber 30 through
phase-advance hydraulic line 32, whereas working fluid is supplied
into variable-volume phase-retard hydraulic chamber 31 through
phase-retard hydraulic line 33. When hydraulic pressure in
phase-advance hydraulic chamber 30 is equal to or higher than that
in phase-retard hydraulic chamber 31, phase-advance hydraulic
chamber 30 is filled with working fluid (hydraulic oil). Under
these conditions, vane body 22 is conditioned in its maximum
phase-advance state (the maximum phase-advance angular position)
shown in FIG. 14B. The valve-opening action and valve-closing
action of intake valve 9 are made at the earliest timing with
respect to a rotation angle of camshaft timing pulley 14, in other
words, with respect to a crank angle. That is, intake valve closure
timing IVC and intake valve open timing IVO are both set to their
maximum phase-advance timings. When there is no application of
hydraulic pressure to both of phase-advance hydraulic chamber 30
and phase-retard hydraulic chamber 31, the VTC phase (intake valve
closure timing IVC and intake valve open timing IVO) is
automatically controlled to the phase corresponding to the maximum
phase-advance state shown in FIG. 14B by the spring forces produced
by springs 25.
[0092] On the contrary, when hydraulic pressure in phase-retard
hydraulic chamber 31 is higher than that in phase-advance hydraulic
chamber 30, phase-retard hydraulic chamber 31 is filled with
working fluid. Under these conditions, vane body 22 is conditioned
in its maximum phase-retard state (the maximum phase-retard angular
position) shown in FIG. 14C. The valve-opening action and
valve-closing action of intake valve 9 are made at the latest
timing with respect to a crank angle. That is, intake valve closure
timing IVC and intake valve open timing IVO are both set to their
maximum phase-retard timings.
[0093] As set forth above, by means of springs 25 disposed in
respective phase-advance chambers 30, it is possible to
automatically set intake valve closure timing IVC to the maximum
phase-advance timing (i.e., IVC.apprxeq.BDC) shown in FIG. 14B by
the spring forces produced by springs 25, under a particular
condition where there is no application of hydraulic pressure to
both of phase-advance hydraulic chamber 30 and phase-retard
hydraulic chamber 31. In the rotary vane type VTC mechanism of FIG.
12, return springs are exemplified in compression coil springs.
Instead of using a compression coil spring as return spring 25, a
tensile coil spring or a leaf spring may be used. By means of
torsion coil spring 120 further provided in addition to springs 25,
it is possible to automatically set intake valve closure timing IVC
to the maximum phase-advance timing (i.e., IVC.apprxeq.BDC) by the
spring force produced by torsion coil spring 120, under a
particular condition where there is no hydraulic-pressure
application to both of phase-advance hydraulic chamber 30 and
phase-retard hydraulic chamber 31.
[0094] In the case of the motor-driven spiral disk type VTC
mechanism shown in FIG. 2, it is possible to automatically control
or set the VTC phase, in particular, intake valve closure timing
IVC to the maximum phase-advance state (i.e., IVC.apprxeq.BDC) by a
spring force produced by biasing means, even if there is no torque
application to hysteresis member 316 owing to a failure in
hysteresis motor 315. In this case, the biasing means is attached
to helical spline mechanism 320 shown in FIG. 3, in such a manner
as to enable automatic adjustment of the VTC phase, in particular,
intake valve closure timing IVC to the phase corresponding to the
maximum phase-advance state (i.e., IVC.apprxeq.BDC) by the spring
force produced by the biasing means attached to helical spline
mechanism 320, even when reversible motor 321 is failed. By the
provision of the biasing means, even in the presence of a failure
in reversible motor 321, it is possible to certainly attain engine
starting operation.
[0095] According to the VTC phase control shown in FIG. 9, by means
of the variable valve actuation mechanism 13 (phase-change means),
intake valve closure timing IVC is phase-retarded from BDC during
cranking (see the time period ta-tb in FIG. 9), thereby reducing
the work of compression. As shown in FIG. 15, another method of
reducing the work of compression during cranking is to adjust or
control intake valve closure timing IVC to a timing value
phase-advanced from BDC. As can be seen from another phase-control
characteristic of FIG. 15, as soon as engine cranking operation is
initiated at the time point ta, the VTC phase is controlled to a
phase advanced from BDC, and thus intake valve closure timing IVC
of intake valve 9 is controlled to a timing value considerably
phase-advanced from BDC. After the time tb at which the cranking
speed begins to exceed 400 rpm, intake valve closure timing IVC is
phase-retarded toward BDC. Thereafter, at the time tc, fuel
injection starts. After this, at the time td when engine
temperature Te exceeds a predetermined temperature value such as
60.degree. C., intake valve closure timing IVC is retarded from BDC
to a timing value suited to the normal engine operation of engine
1.
[0096] As another method of reducing the work of compression during
cranking, a starting-period decompression device may be combined
with phase change means or phase control means, such as the VTC
mechanism, the VVL mechanism, the VEL mechanism or the like. The
decompression device is provided to constantly open exhaust valve
10 during a cranking period, thereby permitting a reduction in the
work of compression even when intake valve closure timing IVC of
intake valve 9 has been phase-advanced to a timing value
substantially corresponding to a phase-advance state. For instance,
by pushing exhaust valve 10 downwards by means of an electromagnet,
it is possible to slightly open exhaust valve 10, thus realizing a
decompressing function. FIG. 16 shows the phase-control
characteristic obtained by the combined system of the decompression
device and the phase change means (the VTC mechanism).
[0097] Returning to FIG. 16, at the time ta, the starter becomes
energized (ON) for engine cranking. At the same time, the VTC phase
(intake valve closure timing IVC) is controlled to a phase
substantially corresponding to a phase-advance state (=BDC), and
additionally the decompression device is energized (ON) for
maintaining exhaust valve 10 in its constantly-opened valve
operating state (i.e., in a decompression mode). The decompression
device may be energized (ON) before the time ta. As soon as the
cranking speed begins to exceed 400 rpm at the time tb, the
decompression device is de-energized (OFF) to inhibit the
exhaust-valve decompression mode. And thus, the operating mode of
exhaust valve 10 returns to a normal valve operating state.
Thereafter, at the time tc, fuel injection starts. At the time tc1
after tc, an increase in fuel injection amount is inhibited or
stopped, so as to control or maintain engine speed Ne to a
specified idling speed for example 600 rpm. Thereafter, at the
warm-up completion time point td at which combustion has been
stabilized, for example, when engine temperature Te exceeds
60.degree. C., the VTC phase is controlled from the phase
substantially corresponding to the phase-advance state in the
phase-retard direction (that is, toward a phase suited to the
normal engine operation of engine 1). In the case of the VTC phase
control shown in FIG. 16, the VTC mechanism is merely switched from
one of the relatively phase-retarded position and the relatively
phase-advanced position to the other. The VTC phase control system
is simple in phase-control components. This contributes to the
reduced cost of the VTC mechanism. Additionally, in the case of the
combined system of the starting-period decompression device and the
phase change means (the VTC mechanism), it is possible to
completely control or adjust the work of compression to zero during
the cranking and starting period. Therefore, the cranking process
can be passed early, and the engine starting time can be shortened,
thus reducing exhaust emissions such as soot.
[0098] On automotive vehicles, owing to a rapid engine torque rise,
the vehicle body tends to vibrate undesirably. To avoid this, as
can be seen from the phase-control characteristic of FIG. 17, the
VTC phase is first controlled to a phase-retard state (considerably
retarded from BDC) simultaneously with the start of cranking (see a
rapid fall in the VTC phase from the time ta), and thereafter the
VTC phase is gradually controlled moderately toward a phase
corresponding to a phase-advance state (=BDC) from the time tb at
which the cranking speed begins to exceed 400 rpm. Thereafter, at
the time tc when the VTC phase is advanced up to a predetermined
phase, fuel injection starts. The phase-advancing operation of the
VTC phase (intake valve open timing IVO as well as intake valve
closure timing IVC) is continued until the time tc1, thus resulting
in a gradual increase in the quantity of air charged into the
cylinder. As a consequence, as can be appreciated from a moderate
engine speed rise from the time tc in FIG. 17, it is possible to
realize a gradual rise in engine power output or engine torque. As
a matter of course, simultaneously with a change in the VTC phase
(timing changes for IVO and IVC), the fuel injection amount and
injection timing are both controlled properly by means of ECU 6. At
the time td that engine temperature Te exceeds the predetermined
temperature value, for example 60.degree. C., and engine warm-up
has been completed and combustion has been stabilized, the
processor of ECU 6 inhibits the VTC phase from being held at the
phase-advance state, substantially corresponding to BDC. From
immediately after the time td, the VTC phase is controlled in the
phase-retard direction (that is, toward a phase suited to the
normal engine operation of engine 1), thus ensuring a drop in the
effective compression ratio, in other words, improved fuel
economy.
[0099] On hybrid vehicles employing an automatic engine
stop-restart system capable of temporarily automatically stopping
an internal combustion engine under a specified condition where a
selector lever of an automatic transmission is kept in its neutral
position, the vehicle speed is zero, the engine speed is an idle
speed, and the brake pedal is depressed, and automatically
restarting the engine from the vehicle standstill state, the engine
stop and restart operation is frequently executed even after
completion of engine warm-up. In the case of engine restart
operation, engine 1 has already been warmed up and thus engine 1 is
in the stable combustion state without executing phase-advance
control for the IVC phase. Therefore, it is possible to omit the
phase-advancing process of the VTC phase to a phase corresponding
to a phase-advance state (=BDC) from the time tb in FIG. 17. As can
be seen from the B characteristic curve indicated by the broken
line in FIG. 17, with the lapse of time, the VTC phase is gradually
shifted or controlled from the phase-retard state (considerably
retarded from BDC and corresponding to the low effective
compression ratio) to the phase suited to the normal engine
operation of engine 1 without the phase-advancing process to the
phase-advance state (=BDC). As a result of this, it is possible to
prevent uncomfortable noise and vibrations of the vehicle,
occurring owing to a rapid engine-torque rise at the beginning of
fuel injection during engine startup under the in-cylinder pressure
substantially identical to atmospheric pressure. Additionally, by
omitting or eliminating the phase-advancing process to the
phase-advance state (=BDC), it is possible to effectively reduce an
electric power consumption rate of the engine starter or the motor
generator.
[0100] The effective compression ratio can be controlled by means
of either one of the VTC mechanism, the VVL mechanism, and the VEL
mechanism. FIG. 18 shows the intake valve lift and event
characteristic, which is obtained by the continuously variable
valve event and lift (VEL) control mechanism, capable of
continuously varying both of valve lift and event from a short
event (small working angle) and low valve lift characteristic to a
long event (large working angle) and high valve lift
characteristic. As can be seen from the characteristic curves of
FIG. 18 attained by the intake-valve VEL system, during a cranking
period, the intake valve lift is set to the maximum lift state and
thus intake valve closure timing IVC is phase-retarded to reduce
the work of compression. As soon as the cranking speed exceeds the
predetermined speed value such as 400 rpm (see step 368 of FIG.
11), the intake valve lift is set to the minimum lift state and
thus intake valve closure timing IVC is phase-advanced to its
maximum phase-advance timing to increase certainty in stable
combustion. Thereafter, at a point of time at which engine warm-up
has been completed and combustion has been stabilized, the intake
valve lift is set to an intermediate lift value between the maximum
lift value and the minimum lift value, so as to properly retard
intake valve closure timing IVC from BDC, and whereby a mechanical
friction loss is reduced and fuel economy is improved.
[0101] On compression ignition engines, glow plug (a small electric
heater) 8 shown in FIG. 1 is located inside the engine cylinder or
an electric heater is often provided in the induction system, for
preheating the air or promotion of vaporization of the fuel,
thereby assisting spontaneous ignition and promoting combustion
during an engine starting period, and consequently enhancing the
engine startability. Electric power consumed by the electric heater
or glow plug 8 is great (e.g., several amperes). When supplying
electric power to the electric heater or glow plug 8 during
cranking, there is an increased tendency for the cranking speed to
be fallen, thereby deteriorating the engine startability. As a
countermeasure for a fall in cranking speed, occurring owing to
electric power consumed by the electric heater or glow plug 8, the
glow-plug/electric-heater control routine shown in FIG. 19 is
executed.
[0102] Returning to FIG. 19, at step 391, an ignition switch (an
engine key switch) is turned ON. At step 392, electric power supply
to glow plug 8 (electric heater) is enabled, and thus electric
power is supplied to glow plug 8 (electric heater) to energize it.
Subsequently to step 392, step 393 occurs. At step 393, starter 7
becomes energized (ON). At the same time, at step 394, electric
power supply to glow plug 8 (electric heater) is shut off
(disabled) or reduced to a low level. At step 395 after step 394, a
check is made to determine whether the latest up-to-date
informational data of engine speed Ne, determined based on the
sensor signal from crank angle sensor 5, exceeds a first
predetermined speed value such as 400 rpm. When the answer to step
395 is affirmative (YES), that is, when the current engine speed
exceeds the first predetermined speed value (e.g., 400 rpm), the
routine proceeds from step 395 to step 396. Conversely when the
answer to step 395 is negative (NO), step 395 is repeatedly
executed, until the current engine speed exceeds the first
predetermined speed value owing to a rise in cranking speed. Under
the condition of cranking speed above 400 rpm, through step 396
electric power is supplied again to glow plug 8 (electric heater)
to energize it, and simultaneously fuel injection starts. At this
time (at step 396), in s similar manner to step 369 of FIG. 11,
phase-advance control for variable valve actuation mechanism 13
(the VTC mechanism) is executed. Thereafter, at step 397, a check
is made to determine whether the latest up-to-date informational
data of engine speed Ne exceeds a second predetermined speed value
such as 600 revolutions per minute. When the answer to step 397 is
affirmative (YES), that is, when the current engine speed exceeds
the second predetermined speed value (e.g., 600 rpm), the routine
proceeds from step 397 to step 398. Conversely when the answer to
step 397 is negative (NO), step 397 is repeatedly executed, until
the current engine speed exceeds the second predetermined speed
value (e.g., 600 rpm). Immediately when the current engine speed
exceeds the second predetermined speed value (e.g., 600 rpm),
electric power supply to glow plug 8 (electric heater) is shut off
(disabled) through step 398.
[0103] By way of execution of the glow-plug/electric-heater control
routine shown in FIG. 19, electric power supply to glow plug 8
(electric heater) can be temporarily shut off (disabled) or reduced
to a low level, until the cranking speed reaches the first
predetermined speed value such as 400 rpm. This increases certainty
in sufficient electric power supply to starter 7, thus more
certainly enhancing the engine startability.
[0104] As will be appreciated from the above, according to the
compression ignition engine of the embodiment, employing a variable
valve operating system being responsive to a control signal from an
electronic control unit for variably adjusting or bringing an
intake valve characteristic including at least one of an intake
valve lift and an intake valve closure timing IVC closer to a
desired value (a desired valve characteristic value determined
based on engine operating conditions) via an actuator
(electrically-controlled actuator means), during a cranking period
of cold starting operation with a starter energized (ON), an
effective compression ratio of an engine is temporarily decreased
or lowered by controlling the intake valve characteristic. At a
point of time when a predetermined cranking speed threshold value
(e.g., 400 revolutions per minute) has been reached owing to a
cranking speed rise, the effective compression ratio is increased
or risen by controlling the intake valve characteristic. After
combustion of the engine has been stabilized, the intake valve
characteristic is brought closer to the desired value (the desired
valve characteristic value) determined based on the engine
operating conditions by way of closed-loop control. Thus, it is
possible to reconcile the enhanced engine startability during
cranking and cold starting operation and improved fuel economy
during normal engine operation (after engine warm-up). Suppose that
the compression ignition engine of the embodiment, capable of
properly controlling the effective compression ratio by varying the
intake valve characteristic depending on engine operating
conditions, such as during a cranking period of cold starting
operation, during an engine warm-up period, and after engine
warm-up, is combined with an engine starter of a low torque
capacity (or a motor generator of a low torque capacity) and a
fixed compression-ratio compression-ignition internal combustion
engine of a low geometrical compression ratio. This contributes to
the reduced engine gross weight. Thus, the compression ignition
engine of the embodiment is suitable for the engine for hybrid
vehicles.
[0105] Furthermore, according to the compression ignition engine of
the embodiment, the variable valve operating system is comprised of
a variable valve actuation mechanism capable of varying the intake
valve characteristic including at least one of the intake valve
lift and intake valve closure timing IVC, before the start of
cranking operation or simultaneously with cranking operation, and
an engine sensor (concretely, a camshaft sensor) that is able to
detect information regarding an intake valve operating state (i.e.,
the actual intake valve lift and the actual intake valve closure
timing) from a substantially zero engine speed value. Thus, even
when a temporary drop in battery voltage is occurring during
operation of the engine starter, it is possible to satisfactorily
adjust (phase-advance or phase-retard) or bring the actual intake
valve characteristic, in particular, intake valve closure timing
IVC, closer to the desired value, according to various situations,
that is, during cranking and starting operation and after warm-up
(in a stable combusting state).
[0106] Additionally, according to the compression ignition engine
of the embodiment, by means of the electronic control unit, at
least one of a fuel injection amount and a fuel injection timing,
both determined based on engine speed and engine load (e.g., an
accelerator-pedal depression amount), can be compensated for based
on at least one of information regarding a quantity of air charged
into an engine cylinder and information regarding an intake valve
operating state (i.e., the actual intake valve lift and the actual
intake valve closure timing). Thus, it is possible to compensate
for at least one of the fuel injection amount and fuel injection
timing in real time responsively to a change in the intake valve
operating state, and whereby the generation of soot and unstable
combustion can be prevented beforehand.
[0107] Additionally, according to the compression ignition engine
of the embodiment, when restarting the engine by either one of a
starter and a motor generator, an intake valve operating state
including at least an actual intake valve closure timing, is
gradually shifted or controlled from a phase-retard state to a
normal intake valve operating state with the lapse of time. This
results in a compression pressure fall of the engine during
cranking. Thus, it is possible to reduce the electric power
consumption during the cranking period of engine restarting
operation, and also to avoid a rapid engine torque rise and
uncomfortable noise and vibrations of the vehicle during the
restarting operation.
[0108] Preferably, during an engine stopping period, the electronic
control unit generates a control command signal to the
electrically-controlled actuator means for controlling at least the
intake valve closure timing IVC to a desired standby timing spaced
apart from BDC, and thereafter generates an engine stop signal.
During the next starting operation, (i) a check for a current phase
of the variable valve actuation mechanism and (ii) phase-retard
control of the variable valve actuation mechanism can be
eliminated, thereby shortening the engine starting time.
[0109] More preferably, during the cranking period of cold starting
operation, the electronic control unit operates to temporarily shut
off (disable) or reduce electric power supply to either one of glow
plug 8 and an electric heater. The temporary shut-off/reduction
operation of electric power supply to glow plug 8 or the electric
heater, contributes to the increased certainty in sufficient
electric power supply to the starter, thereby ensuring the enhanced
engine startability.
[0110] Moreover, in the case of a starting-period decompression
device is combined with the variable valve actuation mechanism,
during a cranking period of cold starting operation an exhaust
valve is maintained in a constantly-opened valve operating state
(i.e., in a decompression mode) to decrease an effective
compression ratio by way of decompression for in-cylinder pressure
during the cranking period for a smooth cranking speed rise. At a
point of time when a predetermined cranking speed threshold value
(e.g., 400 revolutions per minute) has been reached owing to the
smooth cranking speed rise, the decompression mode is inhibited and
the exhaust valve is returned to a normal valve operating state.
Additionally, substantially at the point of time when the
predetermined cranking speed threshold value (400 rpm) has been
reached owing to the smooth cranking speed rise, the effective
compression ratio is increased or risen by controlling an intake
valve characteristic including at least one of an intake valve lift
and intake valve closure timing IVC, for enhancing the
self-ignitability of fuel, which is injected after the
predetermined cranking speed threshold value (e.g., 400 rpm) has
been reached. After combustion of the engine has been stabilized,
the intake valve characteristic is brought closer to a desired
value (a desired valve characteristic value) determined based on
engine operating conditions by way of closed-loop control. By such
a combination of the decompression device and the variable valve
actuation mechanism, the control system for the variable valve
actuation mechanism employed in the variable valve operating system
can be simplified, thus ensuring the reduced control system cost.
Additionally, by way of an adequate decompressing function of the
decompression device, the work of compression can be remarkably
reduced, thus enabling a smooth cranking speed rise, that is, a
shortened engine starting time.
[0111] The entire contents of Japanese Patent Application No.
2005-166538 (filed Jun. 7, 2005) are incorporated herein by
reference.
[0112] While the foregoing is a description of the preferred
embodiments carried out the invention, it will be understood that
the invention is not limited to the particular embodiments shown
and described herein, but that various changes and modifications
may be made without departing from the scope or spirit of this
invention as defined by the following claims.
* * * * *