U.S. patent application number 10/281936 was filed with the patent office on 2004-04-29 for control system for direct injection spark ignition engines with a cam profile switching device.
Invention is credited to Kim, Yong-Wha, Kolmanovsky, Ilya V., Sun, Jing.
Application Number | 20040079326 10/281936 |
Document ID | / |
Family ID | 32107277 |
Filed Date | 2004-04-29 |
United States Patent
Application |
20040079326 |
Kind Code |
A1 |
Kolmanovsky, Ilya V. ; et
al. |
April 29, 2004 |
Control system for direct injection spark ignition engines with a
cam profile switching device
Abstract
A system and method for controlling air charge motion in the
cylinder of a direct injection spark ignition engine during
transitions between different combustion modes is provided. The
system includes a cam profile switching device that controls the
position of an intake valve for the cylinder. The system further
includes an electronic control unit configured to control the cam
profile switching device to position the intake valve in a first
position in advance of the transition and to move the intake valve
to a second position when a predetermined condition for
transitioning between the two combustion modes is met.
Inventors: |
Kolmanovsky, Ilya V.;
(Ypsilanti, MI) ; Sun, Jing; (Bloomfield, MI)
; Kim, Yong-Wha; (Ann Arbor, MI) |
Correspondence
Address: |
DYKEMA GOSSETT PLLC
39577 WOODWARD AVENUE
SUITE 300
BLOOMFIELD HILLS
MI
48304
US
|
Family ID: |
32107277 |
Appl. No.: |
10/281936 |
Filed: |
October 29, 2002 |
Current U.S.
Class: |
123/306 ;
123/308 |
Current CPC
Class: |
F02D 41/3064 20130101;
Y02T 10/18 20130101; Y02T 10/12 20130101; F02D 13/0234
20130101 |
Class at
Publication: |
123/306 ;
123/308 |
International
Class: |
F02B 031/00 |
Claims
We claim:
1. A method for controlling air charge motion in a cylinder of an
internal combustion engine during a transition between a first
combustion mode and a second combustion mode, comprising the steps
of: positioning an intake valve for said cylinder in a first
position in advance of said transition using a cam profile
switching device; and, moving said intake valve to a second
position using said cam profile switching device when a
predetermined condition for transitioning between said first and
second combustion modes is met.
2. The method of claim 1 wherein said engine comprises a direct
injection spark ignition engine.
3. The method of claim 1 wherein one of said first and second
combustion modes comprises a homogenous mode wherein a homogenous
mixture of air and fuel is present in said cylinder and another of
said first and second combustion modes comprises a stratified mode
wherein a stratified mixture of air and fuel is present in said
cylinder.
4. The method of claim 1 wherein said positioning step includes the
substeps of: determining whether said intake valve is in said first
position; and, moving said intake valve to said first position if
said intake valve is in a position other than said first
position.
5. The method of claim 1 wherein said predetermined condition for
transitioning between said first and second combustion modes is
whether a torque demand for said engine meets a predetermined
relationship.
6. The method of claim 1, further comprising the step of adjusting
a time at which fuel is injected into said cylinder concurrently
with said moving step.
7. The method of claim 1, further comprising the steps of:
determining whether said intake valve is in a steady state position
once a desired pressure in an intake manifold of said engine is
obtained and a desired air-fuel ratio in said cylinder is obtained;
moving said intake valve to said steady state position if said
intake valve is in a position other than said steady state
position.
8. A system for controlling air charge motion in a cylinder of an
internal combustion engine during a transition between a first
combustion mode and a second combustion mode, comprising: a cam
profile switching device coupled to an intake valve for said
cylinder; and, an electronic control unit configured to control the
cam profile switching device to position said intake valve in a
first position in advance of said transition and move said intake
valve to a second position when a predetermined condition for
transitioning between said first and second combustion modes is
met.
9. The system of claim 8 wherein said engine comprises a direct
injection spark ignition engine.
10. The system of claim 8 wherein said one of said first and second
combustion modes comprises a homogenous mode wherein a homogenous
mixture of air and fuel is present in said cylinder and another of
said first and second combustion modes comprises a stratified mode
wherein a stratified mixture of air and fuel is present in said
cylinder.
11. The system of claim 8 wherein said electronic control unit is
further configured, in positioning said intake valve in a first
position in advance of said transition, to determining whether said
intake valve is in said first position and to move said intake
valve to said first position if said intake valve is in a position
other than said first position.
12. The system of claim 8 wherein said predetermined condition for
transitioning between said first and second combustion modes is
whether a torque demand for said engine meets a predetermined
relationship.
13. The system of claim 8, wherein said electronic control unit is
further configured to adjust a time at which fuel is injected into
said cylinder concurrently with moving said intake valve to said
second position.
14. The system of claim 8 wherein said electronic control unit is
further configured to determine whether said intake valve is in a
steady state position once a desired pressure in an intake manifold
of said engine is obtained and a desired air-fuel ratio in said
cylinder is obtained and to move said intake valve to said steady
state position if said intake valve is in a position other than
said steady state position.
15. An article of manufacture, comprising: a computer storage
medium having a computer program encoded thereon for controlling
air charge motion in a cylinder of an internal-combustion engine
during a transition between a first combustion mode and a second
combustion mode, said computer program including code for:
positioning an intake valve for said cylinder in a first position
in advance of said transition using a cam profile switching device;
and, moving said intake valve to a second position using said cam
profiled switching device when a predetermined condition for
transitioning between said first and second combustion modes is
met.
16. The article of manufacture of claim 15 wherein said engine
comprises a direct injection spark ignition engine
17. The article of manufacture of claim 15 wherein one of said
first and second combustion modes comprises a homogenous mode
wherein a homogenous mixture of air and fuel is present in said
cylinder and another of said first and second combustion modes
comprises a stratified mode wherein a stratified mixture of air and
fuel is present in said cylinder.
18. The article of manufacture of claim 15 wherein said code for
positioning said intake valve includes: code for determining
whether said intake valve is in said first position; and, code for
moving said intake valve to said first position if said intake
valve is in a position other than said first position.
19. The article of manufacture of claim 15 wherein said computer
program further includes code for adjusting a time at which fuel is
injected into said cylinder concurrently with moving said intake
valve to said second position.
20. The article of manufacture of claim 15 wherein said computer
program further includes: code for determining whether said intake
valve is in a steady state position once a desired pressure in an
intake manifold of said engine is obtained and a desired air-fuel
ratio in said cylinder is obtained; and, code for moving said
intake valve to said steady state position if said intake valve is
in a position other than said steady state position.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to engine control systems and, in
particular, to a method and system for controlling air charge
motion in the cylinders of a direct injection spark ignition (DISI)
engine.
[0003] 2. Discussion of Related Art
[0004] In a DISI engine, the fuel injection nozzle is located
inside the combustion chamber rather than the induction pipe as in
conventional multi-port or throttle body fuel injection engines.
This allows a DISI engine to form a stratified air charge
composition in the engine cylinders and to burn air-fuel mixtures
having air-fuel ratios that deviate substantially from the
stoichiometric air-fuel ratio (14.7:1). DISI engines also have
improved thermal efficiency and reduced engine knock as compared to
conventional multi-port or throttle body fuel injected engines.
[0005] DISI engines are capable of operating in a plurality of
different combustion modes including a homogenous combustion mode,
a stratified combustion mode, and a hybrid combustion mode. In a
homogenous combustion mode, a homogenous air-fuel mixture is
present within a cylinder during a combustion event. In a
stratified combustion mode, a stratified air-fuel mixture is
present within the cylinder. Depending upon the mode of operation,
the air charge composition and air charge motion must be adjusted
to optimize the combustion process.
[0006] In most conventional DISI engines, a swirl control valve
actuated by a stepper motor is used to control air charge motion.
These conventional engines have a significant drawback. During a
transition between combustion modes, the air charge composition
changes. For example, when transitioning from a stratified
combustion mode to a homogenous combustion mode, there is typically
an air-fuel ratio gap (e.g., from >22:1 to <20:1). As a
result, a step change in the fueling rate frequently occurs at the
switching instant between combustion modes. The step change in the
fueling rate can cause a significant torque disturbance.
[0007] The inventors herein have recognized a need for a method and
system for controlling air charge motion in a cylinder of an
internal combustion engine during a transition between two
combustion modes that will minimize and/or eliminate one or more of
the above-identified deficiencies.
SUMMARY OF THE INVENTION
[0008] The present invention provides a method and system for
controlling air charge motion in a cylinder of an internal
combustion engine during a transition between first and second
combustion modes.
[0009] A method in accordance with the present invention includes
the step of: positioning an intake valve for the cylinder in a
first position in advance of the transition using a cam profile
switching device. For example, during a transition from a
stratified combustion mode to a homogenous combustion mode, the
intake valve may be placed in a long valve lift position to hasten
egress of air from the engine's intake manifold. The method may
further include the step of moving the intake valve to a second
position using the cam profile switching device when a
predetermined condition for transitioning between the first and
second combustion modes is met. Continuing with the above example,
the cam profile switching device may move the intake valve to a
short valve lift position to reduce air induction into the
cylinder.
[0010] A system in accordance with the present invention may
include a cam profile switching device coupled to an intake valve
for the cylinder. The system may further include an electronic
control unit configured to control the cam profile switching device
to position the intake valve in a first position in advance of the
transition and move the intake valve to a second position when a
predetermined condition for transitioning between the first and
second combustion modes is met.
[0011] A system and method in accordance with the present invention
is advantageous. Control of the cylinder intake valve using a cam
profile switching device allows changes in valve lift during a
single engine event. As a result, air charge motion can be directly
and more quickly controlled than by using a swirl control valve or
electronic throttle. The transition between combustion modes is
therefore accomplished more quickly and LNT purge efficiency and
fuel economy is improved. Further, a step change in the air charge
can be effected during the transition between combustion modes
thereby avoiding the need for a step change in the fueling rate and
reducing torque disturbance and increasing drivability
performance.
[0012] These and other advantages of this invention will become
apparent to one skilled in the art from the following detailed
description and the accompanying drawings illustrating features of
this invention by way of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic diagram illustrating an internal
combustion engine incorporating a system for controlling air charge
motion in a cylinder of the engine during a transition between
first and second combustion modes in accordance with the present
invention.
[0014] FIG. 2 is a perspective view illustrating a cam profile
switching device.
[0015] FIGS. 3A-B are flow chart diagrams illustrating several
embodiments of a method for controlling air charge motion in a
cylinder of the engine during a transition between first and second
combustion modes in accordance with the present invention.
[0016] FIGS. 4A-B are timing diagrams illustrating values for
several variables in the engine of FIG. 1 over time during
implementation of the method of FIGS. 3A-B.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0017] Referring now to the drawings wherein like reference
numerals are used to identify identical components in the various
views, FIG. 1 illustrates an internal combustion engine 10 and a
system 12 in accordance with the present invention for controlling
air charge motion in a cylinder 14 of engine 10 during a transition
between first and second combustion modes. The air charge motion is
controlled to quicken the transition between combustion modes and
to reduce torque disturbances occurring during the transition.
[0018] Engine 10 is designed for use in a motor vehicle. It should
be understood, however, that engine 10 may be used in a wide
variety of applications. Engine 10 comprises a direct injection
spark ignition (DISI) engine. Engine 10 provides motive energy to a
motor vehicle or other device and is conventional in the art.
Engine 10 may define a plurality of combustion chambers or
cylinders 14 and may also include a plurality of pistons 16,
coolant passages 18, a throttle assembly 20, an intake manifold 22,
an exhaust manifold 24, and engine gas recirculation (EGR) system
26, fuel injectors 28, spark plugs 30, an ignition system 32,
intake valves 34, exhaust valves 36, camshaft 38, and one or more
cam profile switching devices 40.
[0019] Cylinders 14 provide a space for combustion of an air/fuel
mixture to occur and are conventional in the art. In the
illustrated embodiment, only one cylinder 14 is shown. It will be
understood, however, that engine 10 may define a plurality of
cylinders 14 and that the number of cylinders 14 may be varied
without departing from the spirit of the present invention.
[0020] Pistons 16 are coupled to a crankshaft (not shown) and drive
the crankshaft responsive to an expansion force of the air-fuel
mixture in cylinders 14 during combustion. Pistons 16 are
conventional in the art and a piston 16 may be disposed in each
cylinder 14.
[0021] Coolant passages 18 provide a means for routing a heat
transfer medium, such as a conventional engine coolant, through
engine 10 to transfer heat from cylinders 14 to a location external
to engine 10. Passages 18 are conventional in the art.
[0022] Throttle assembly 20 controls the amount of air delivered to
intake manifold 22 and cylinders 14. Assembly 20 is conventional in
the art and may include a throttle body 42 and a throttle plate 44
disposed therein for regulating the amount of airflow through body
42 to manifold 22. It should be understood that assembly 20 may be
electronically controlled.
[0023] Intake manifold 22 provides a means for delivering charged
air to cylinders 14. Manifold 22 is conventional in the art. An
inlet port 46 is disposed between manifold 22 and each cylinder
14.
[0024] Exhaust manifold 24 is provided to vent exhaust gases from
cylinders 14 after each combustion event. Manifold 24 is also
conventional in the art and may deliver exhaust gases to a
catalytic converter (not shown). An exhaust port 48 is disposed
between manifold 24 and each cylinder 14.
[0025] EGR system 26 is provided to return a portion of the exhaust
gases to cylinders 14 in order to reduce emissions of combustion
byproducts. EGR system 26 includes a passage 50 that extends from
exhaust manifold 24 to intake manifold 20 and an EGR valve 52 that
may be disposed within passage 50 to control the delivery of
recirculated exhaust gases to intake manifold 22.
[0026] Fuel injectors 28 are provided to deliver fuel in controlled
amounts to cylinders 14 and are conventional in the art. Although
only one fuel injector 28 is shown in the illustrated embodiment,
it will again be understood that engine 10 will include additional
fuel injectors for delivering fuel to other cylinders 14 in engine
10.
[0027] Spark plugs 30 are provided to ignite the air/fuel mixture
in cylinders 14. Spark plugs 30 are also conventional in the art.
Although only one spark plug is shown in the illustrated
embodiment, it should be understood that each cylinder 14 will
include at least one spark plug 30.
[0028] Ignition system 32 delivers electrical current to spark
plugs 30. System 32 is conventional in the art and may comprise a
solid-state ignition system (i.e., a distributor-less system).
[0029] Intake valves 34 open and close each intake port 46 to
control the delivery of air to the respective cylinder 14. Intake
valves 34 are conventional in the art. Although only one intake
valve is shown in the illustrated embodiment, it should be
understood that multiple intake valves may be used for each
cylinder 14.
[0030] Exhaust valves 36 open and close each exhaust port 48 to
control the venting of exhaust gases from the respective cylinder
14 and are also conventional in the art. Again, although only one
exhaust valve is shown in the illustrated embodiment, it should be
understood that multiple exhaust valves may be used for each
cylinder 14.
[0031] Camshaft 38 is provided to control the opening and closing
of intake valves 34 and exhaust valves 36 in each of cylinders 14.
Camshaft 38 is conventional in the art and may be controlled by an
actuator (not shown) responsive to control signals generated by the
vehicle's electronic control unit (ECU). Camshaft 38 may have
multiple cams disposed thereon having different cam profiles for
variable control of intake valves 34 and exhaust valves 36. It will
be understood that more than one camshaft may be used to control
the opening and closing of intake valves 34 and exhaust valves
36.
[0032] Cam profile switching devices 40 are provided to allow the
use of multiple cam profiles on camshaft 38 to control actuation of
intake valves 34 and exhaust valves 36. Devices 40 are conventional
in the art. See, e.g., Dopson et al., "Emissions Optimisation by
Camshaft Profile Switching" SAE 910838 pp. 195-205 (1991), the
entire disclosure of which is incorporated herein by reference.
Referring to FIG. 2, one example of a device 40 is illustrated.
Camshaft 38 may include three cams 54, 56, 58 disposed thereon with
cams 54, 58 having identical profiles and cam 56 having a different
profile. A hydraulic switch 60 is used to selectively couple intake
valve to cam 56 thereby enabling variable valve lift. Switch 60 may
be controlled responsive to a signal from the vehicle's electronic
control unit.
[0033] System 12 is provided to control air charge motion in
cylinder 14 of engine 10 during a transition between first and
second combustion modes. System 12 may form part of a larger system
for controlling engine 10. System 12 may include cam profile
switching devices 40 and an electronic control unit (ECU) 62.
[0034] ECU 62 is provided to control engine 10. ECU 62 may comprise
a programmable microprocessor or microcontroller or may comprise an
application specific integrated circuit (ASIC). ECU 62 may include
a central processing unit (CPU) 64 and an input/output (I/O)
interface 66. Through interface 66, ECU 62 may receive a plurality
of input signals including signals generated by conventional
sensors such as a profile ignition pickup (PIP) sensor 68, a engine
coolant temperature sensor 70, a cylinder identification (CID)
sensor 72, an air temperature sensor 74, a mass air flow (MAF)
sensor 76, a manifold absolute pressure (MAP) sensor 78, and a
Heated Exhaust Gas Oxygen (HEGO) sensor 80. Also through interface
66, ECU 62 may generate a plurality of output signals including one
or more signals used to control fuel injectors 28, spark plugs 30,
camshaft 38, EGR valve 52, and cam profile switching devices 40.
ECU 62 may also include one or more memories including, for
example, Read Only Memory (ROM) 82, Random Access Memory (RAM) 84,
and a Keep Alive Memory (KAM) 86 to retain information when the
ignition key is turned off.
[0035] Referring now to FIGS. 3A-B and 4A-B, several embodiments of
a method in accordance with the present invention for controlling
air charge motion in cylinder 14 during a transition from one
combustion mode to another combustion mode will be described in
detail. FIG. 3A illustrates a method for controlling air charge
motion in cylinder 14 during a transition from a stratified
combustion mode to a homogenous combustion mode with FIG. 4A
illustrating the values of several variables in engine 10 over time
during the transition. Conversely, FIG. 3B illustrates a method for
controlling air charge motion in cylinder 14 during a transition
from a homogenous combustion mode to a stratified combustion mode
with FIG. 4B illustrating the values of the same variables in
engine 10 over time during the transition. The inventive method or
algorithm may be implemented by system 12 wherein ECU 62 is
configured to perform several steps of the method by programming
instruction or code (i.e., software). The instructions may be
encoded on a computer storage medium such as a conventional
diskette or CD-ROM and may be copied into one of memories 82, 84,
86 of ECU 62 using conventional computing devices and methods.
[0036] Referring again to FIGS. 3A-B, the inventive method may
begin with several steps to preposition the components of engine 10
for the transition between combustion modes. These steps may
include the step 88A, 88B of adjusting the position of throttle
plate 44 and/or EGR valve 52. Referring to FIG. 1, ECU 62 may
generate control signals to control plate 44 and valve 52.
Referring to FIGS. 3A and 4A, when transitioning from a stratified
combustion mode to a homogenous combustion mode, plate 44 and valve
52 are moved from relatively open positions
.theta..sub.thr.sub..sub.--.sub.s,
.theta..sub.egr.sub..sub.--.sub.s, respectively, to relatively
closed positions .theta..sub.thr.sub..sub.--.- sub.h,
.theta..sub.egr.sub..sub.--.sub.h, to decrease the pressure in
intake manifold 22 and the air charge in cylinder 14. Referring to
FIGS. 3B and 4B, when transitioning from a homogenous combustion
mode to a stratified combustion mode, plate 44 and valve 52 are
moved in the opposite direction to achieve an increase in intake
manifold pressure and cylinder air charge.
[0037] The inventive method may continue with the step 90A, 90B of
positioning the intake valve 34 in cylinder 14 in a predetermined
position in advance of the transition. Step 90A, 90B may include
the substeps 92A, 92B and 94A, 94B of determining whether intake
valve 34 is in the predetermined position and moving intake valve
34 to the predetermined position if intake valve 34 is in a
position other than the predetermined position. Referring to FIGS.
3A and 4A, during a transition from a stratified combustion mode to
a homogenous combustion mode, system 12 will actuate device 40 to
move intake valve 34 to a long valve lift position v.sub.long if
valve 34 is in a different position (e.g., a short valve lift
position v.sub.short). This action expedites removal of air from
intake manifold 22. Referring to FIGS. 3B and 4B, during a
transition from a homogenous combustion mode to a stratified
combustion mode, system 12 will actuate device 40 to move intake
valve 34 to a short valve lift position v.sub.short if valve 34 is
in a different position (e.g., a long valve lift position
v.sub.long). This action slows removal of air from intake manifold.
Step 90A, 90B is advantageous because it quickens the transition
between combustion modes.
[0038] The inventive method may continue with the step 96A, 96B of
adjusting the rate or amount of fuel injected by fuel injector 28
and/or the spark timing of spark plug 30. ECU 62 may generate
control signals to fuel injector 28 and/or spark plug 30 to control
fuel injection and spark timing, respectively, relative to a
demanded torque for engine 10.
[0039] As set forth above, intake valve 34 is prepositioned in a
first predetermined position prior to the transition between
combustion modes. The inventive method then continues with the step
98A, 98B of moving intake valve 34 to a second predetermined
position when a predetermined condition for transitioning between
two combustion modes is met. Steps 98A, 98B may include substeps
100A, 100B and 102A, 102B. In substeps 10A, 100B, the predetermined
condition is evaluated. In accordance with the illustrated
embodiment of the invention, the predetermined condition is whether
a torque demand for engine 10 and in-cylinder conditions meet a
predetermined relationship. In the case of a transition from a
stratified combustion mode to a homogenous combustion mode, the
predetermined relationship is:
Tq.sup.dmdf.sub.tq.sup.h(N,P,.lambda..sub.hll,.delta..su-
b.max-retard, v.sub.short) where f.sub.tq.sup.h is the torque
regression for homogenous operation of engine 10, N is engine
speed, P is pressure in intake manifold 22, .lambda..sub.hll is the
homogenous lean limit air fuel ratio, .delta..sub.max-retard is the
maximum spark retard and v.sub.short is the condition where intake
valve 34 is in a short lift position. In the case of a transition
from a homogenous combustion mode to a stratified combustion mode,
the predetermined relationship is:
Tq.sup.dmd.ltoreq.f.sub.tq.sup.s(N,P,.lambda..sub.srl,
.delta..sub.MBT, v.sub.long) where f.sub.tq.sup.s is the torque
regression for stratified operation of engine 10, N is engine
speed, P is pressure in intake manifold 22, .lambda..sub.srl is the
stratified rich limit air fuel ratio, .delta..sub.MBT is the
maximum brake torque and v.sub.long is the condition where intake
valve 34 is in a long lift position.
[0040] If the predetermined condition for transitioning between the
two combustion modes is not met, the method returns to step 96A,
96B and repeats. If the predetermined condition is met, substep
102A, 102B occurs in which intake valve 34 is moved to the second
predetermined position. ECU 62 may generate control signals to cam
profile switching devices 40 to move intake valve 34 to the second
predetermined position. In the case of a transition from a
stratified combustion mode to a homogenous combustion mode, intake
valve 34 is moved from a long lift position v.sub.long to a short
lift position v.sub.short to reduce air induction into cylinder 14
as shown in FIGS. 3A and 4A. In the case of a transition from a
homogenous combustion mode to a stratified combustion mode, intake
valve 34 is moved from a short lift position v.sub.short to a long
lift position v.sub.long to increase air induction into cylinder 14
as shown in FIGS. 3B and 4B. Concurrently with the movement of
intake valve 34, ECU 62 may generate control signals to adjust the
fuel injection timing of fuel injector 28. In the case of a
transition from a stratified combustion mode to a homogenous
combustion mode, ECU 62 may move the injection timing from late to
early as shown in FIG. 4A. In the case of a transition from a
homogenous combustion mode to a stratified combustion mode, ECU 62
may move the injection timing from early to late as shown in FIG.
4B.
[0041] The method may continue with the step 104A, 104B of
adjusting the rate or amount of fuel injected by fuel injector 28
and/or the spark timing of spark plug 30. ECU 62 may generate
control signals to fuel injector 28 and/or spark plug 30 to control
fuel injection and spark timing, respectively, relative to a
demanded torque for engine 10 and an optimal spark timing.
[0042] The method may then continue with the step 106A, 106B of
determining whether one or more predetermined conditions are met.
In the illustrated embodiment, ECU 62 determines whether engine
torque Tq is equal to a demanded torque Tq.sup.dmd, whether the
pressure P in intake manifold 22 is equal to a desired intake
manifold pressure P.sup.dsd and whether the air-fuel ratio X is
equal to a desired air-fuel ratio .lambda..sup.dsd. If any one of
these conditions is not met in the transition from a homogenous
combustion mode to a stratified combustion mode, the method returns
to step 104B. If any one of these conditions is not met in the
transition from a stratified combustion mode to a homogenous
combustion mode, ECU 62 performs the step 108A in which ECU 62
compares the air-fuel ratio .lambda. to the homogenous lean limit
air-fuel ratio .lambda..sub.hll. If the air-fuel ratio .lambda. is
at the homogenous lean limit air-fuel ratio .lambda..sub.hll and
the demanded torque Tq.sup.dmd cannot be met, the method continues
with the step 110A in which ECU 62 retards the timing of spark plug
30, and returns to step 106A.
[0043] Once the desired pressure P.sup.dsd in intake manifold 22
and air-fuel ratio .lambda..sup.dsd are obtained, the method may
continue with the step 112A, 112B of determining whether intake
valve 34 is in a desired steady state position v.sup.dsd. If intake
valve 34 is in the desired steady state position v.sup.dsd, the
algorithm terminates. If intake valve 34 is not in a position other
than the desired steady state position v.sup.dsd, ECU 62 may
perform the step 114A, 114B by actuating cam profile switching
devices 40 to move intake valve 34 to the desired steady state
position v.sup.dsd. Following step 114A, 114B, the method returns
to step 104A, 104B.
[0044] A system and method in accordance with the present invention
offer significant advantages. By using a cam profile switching
device, the system can change intake valve lift during a single
engine event. As a result, air charge motion can be directly and
more quickly controlled than by using a swirl control valve or
electronic throttle. The transition between combustion modes is
therefore accomplished more quickly and LNT purge efficiency and
fuel economy is improved. Further, and with reference to FIGS. 4A
and 4B, a step change in the air charge can be effected during the
transition between combustion modes thereby eliminating the need
for a step change in the fueling rate and reducing torque
disturbance and increasing drivability performance.
* * * * *