U.S. patent application number 09/732347 was filed with the patent office on 2002-06-13 for variable displacement engine control for fast catalyst light-off.
Invention is credited to Glugla, Christopher P., Michelini, John Ottavio.
Application Number | 20020069638 09/732347 |
Document ID | / |
Family ID | 24943178 |
Filed Date | 2002-06-13 |
United States Patent
Application |
20020069638 |
Kind Code |
A1 |
Glugla, Christopher P. ; et
al. |
June 13, 2002 |
VARIABLE DISPLACEMENT ENGINE CONTROL FOR FAST CATALYST
LIGHT-OFF
Abstract
A system and method for controlling a variable displacement
engine include starting the engine with at least one bank of
cylinders deactivated to increase load on at least one other bank
of activated cylinders and reduce time required for an engine
and/or vehicle component to reach a desired operating temperature.
In one embodiment, ignition timing or spark is retarded and
air/fuel ratio is biased lean for the activated cylinder bank
during and shortly after starting to further reduce the time
required for catalyst light off and closed loop operation. During
activation of a deactivated bank of cylinders, air/fuel ratio of
one or more activated cylinders is biased rich with air/fuel ratio
of the deactivated cylinders biased lean. In addition, spark is
retarded during activation of the deactivated cylinders to reduce
the time necessary for components associated with the deactivated
cylinders to reach desired operating temperatures.
Inventors: |
Glugla, Christopher P.;
(Macomb, MI) ; Michelini, John Ottavio; (Sterling
Heights, MI) |
Correspondence
Address: |
David S. Bir
Brooks & Kushman
Twenty-Second Floor
1000 Town Center
Southfield
MI
48075-1351
US
|
Family ID: |
24943178 |
Appl. No.: |
09/732347 |
Filed: |
December 7, 2000 |
Current U.S.
Class: |
60/284 ; 60/274;
60/285 |
Current CPC
Class: |
F01N 2430/02 20130101;
Y02T 10/26 20130101; F01N 13/107 20130101; Y02T 10/12 20130101;
F01N 2430/06 20130101; F02D 41/1443 20130101; F02D 17/02 20130101;
Y02A 50/2322 20180101; F01N 13/011 20140603; F01N 3/20 20130101;
F02D 41/0087 20130101; Y02A 50/20 20180101; F02B 75/22 20130101;
F01N 13/009 20140601; F01N 2430/08 20130101; F02D 41/024 20130101;
F02B 2075/184 20130101 |
Class at
Publication: |
60/284 ; 60/285;
60/274 |
International
Class: |
F01N 003/00 |
Claims
What is claimed:
1. A method for controlling an internal combustion engine having a
plurality of cylinders, at least some of which are selectively
deactivated in a variable displacement operating mode, the method
comprising: controlling the engine during starting to deactivate at
least one cylinder to increase load on activated cylinders; and
biasing air/fuel ratio lean relative to stoichiometry for the
activated cylinders to reduce time required for at least one engine
component to reach a desired operating temperature.
2. The method of claim 1 further comprising retarding ignition
timing for the activated cylinders.
3. The method of claim 1 wherein the steps of controlling and
biasing are performed until a catalyst reaches light-off
temperature.
4. The method of claim 1 wherein the steps of controlling and
biasing are performed until an exhaust gas oxygen sensor reaches a
desired operating temperature for closed loop control of the
engine.
5. The method of claim 1 further comprising: biasing air/fuel ratio
rich relative to stoichiometry for the activated cylinders; biasing
air/fuel ratio lean for at least one deactivated cylinder during
activation after at least one emission control device associated
with the activated cylinders has reached a desired operating
temperature.
6. The method of claim 5 wherein the step of controlling activation
comprises: activating the deactivated cylinders and controlling
air/fuel ratio to the cylinders during activation to provide a lean
air/fuel ratio; and controlling air/fuel ratio for a corresponding
number of activated cylinders during activation of the deactivated
cylinders provide a rich air/fuel ratio.
7. The method of claim 6 further comprising retarding ignition
timing for the at least one deactivated cylinder during
activation.
8. A method for controlling a variable displacement internal
combustion engine having cylinders grouped into first and second
banks with associated separate first and second upstream emission
control devices and first and second exhaust gas oxygen sensors and
at least a third downstream emission control device, at least one
bank being selectively activated and deactivated to provide
variable displacement, the method comprising: deactivating the
second bank during and after starting until the first emission
control device and first exhaust gas oxygen sensor reach associated
desired operating temperatures.
9. The method of claim 8 further comprising retarding ignition
timing for the first bank during and after starting.
10. The method of claim 8 further comprising biasing air/fuel ratio
lean for the first bank during and after starting.
11. The method of claim 8 further comprising: activating the second
bank after the first emission control device and first exhaust gas
oxygen sensor reach associated desired operating temperatures until
the second emission control device and second exhaust gas oxygen
sensor reach associated desired operating temperatures.
12. The method of claim 11 further comprising: biasing air/fuel
ratio rich for the first bank and lean for the second bank until
the second emission control device and second exhaust gas oxygen
sensor reach associated desired operating temperatures.
13. The method of claim 11 further comprising: retarding ignition
timing for the second bank until the second emission control device
and second exhaust gas oxygen sensor reach associated desired
operating temperatures.
14. The method of claim 8 wherein the third downstream emission
control device is a shared emission control device positioned
downstream of both upstream emission control devices.
15. A system for controlling an internal combustion engine having
at least first and second cylinder banks, at least one of which is
selectively deactivated in a variable displacement operating mode,
the system comprising: first and second upstream emission control
devices; first and second exhaust gas oxygen sensors having
associated heaters and positioned downstream relative to the first
and second upstream emission control devices, respectively; at
least a third emission control device positioned downstream
relative to at least one of the first and second upstream emission
control devices; and an engine controller for deactivating the
first bank after starting the engine until the second upstream
emission control device and the second exhaust gas oxygen sensor
have attained minimum desired operating temperatures.
16. The system of claim 15 wherein the controller retards ignition
timing for the second bank during and after starting.
17. The system of claim 15 wherein the controller biases air/fuel
ratio lean for the second bank during and after starting.
18. The system of claim 15 wherein the controller: activates the
first bank after the second emission control device and second
exhaust gas oxygen sensor reach associated desired operating
temperatures until the first emission control device and first
exhaust gas oxygen sensor reach associated desired operating
temperatures.
19. The system of claim 15 wherein the controller biases air/fuel
ratio rich for the second bank and lean for the first bank until
the first emission control device and first exhaust gas oxygen
sensor reach associated desired operating temperatures.
20. The system of claim 19 wherein the controller retards ignition
timing for the first bank until the first emission control device
and first exhaust gas oxygen sensor reach associated desired
operating temperatures.
21. A computer readable storage medium having stored data
representing instructions executable by a computer to control a
variable displacement internal combustion engine having cylinders
grouped into first and second banks with associated separate first
and second upstream emission control devices and first and second
exhaust gas oxygen sensors and at least a third downstream emission
control device, at least one bank being selectively activated and
deactivated to provide variable displacement, the computer readable
storage medium comprising: instructions for deactivating the first
bank after starting the engine until the second upstream emission
control device and the second exhaust gas oxygen sensor have
attained minimum desired operating temperatures.
22. The computer readable storage medium of claim 21 further
comprising instructions for retarding ignition timing for the
second bank during and after starting.
23. The computer readable storage medium of claim 21 further
comprising instructions for biasing air/fuel ratio lean for the
second bank during and after starting.
24. The computer readable storage medium of claim 21 further
comprising: instructions for activating the first bank after the
second emission control device and second exhaust gas oxygen sensor
reach associated desired operating temperatures until the first
emission control device and first exhaust gas oxygen sensor reach
associated desired operating temperatures.
25. The computer readable storage medium of claim 21 further
comprising: instructions for biasing air/fuel ratio rich for the
second bank and lean for the first bank until the first emission
control device and first exhaust gas oxygen sensor reach associated
desired operating temperatures.
26. The computer readable storage medium of claim 25 further
comprising: instructions for retarding ignition timing for the
first bank until the first emission control device and first
exhaust gas oxygen sensor reach associated desired operating
temperatures.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a system and method for
controlling a multi-cylinder internal combustion engine operable in
a variable displacement mode to reduce the time required for a
catalyst to reach a desired operating efficiency.
[0003] 2. Background Art
[0004] Fuel economy for a multi-cylinder internal combustion engine
can be improved by deactivating some of the engine cylinders under
certain operating conditions. Reducing the number of operating
cylinders reduces the effective displacement of the engine such
that it is sometimes referred to as a variable displacement engine.
Mechanisms which reduce the effective stroke of one or more
cylinders may also be used to provide a variable displacement mode
of operation. Depending upon the particular configuration of the
variable displacement engine, one or more cylinders may be
selectively deactivated to improve fuel economy under light load
conditions, for example. In some engine configurations, a group of
cylinders, which may be an entire bank of cylinders, is selectively
activated and deactivated.
[0005] Reducing the effective displacement by reducing the number
of operating cylinders may also reduce the operating temperature of
various engine and/or vehicle components which may adversely affect
desired engine control or operation. For example, emission control
devices, such as catalytic converters, and associated exhaust gas
oxygen (EGO) sensors require a minimum operating temperature to
function as desired. In the case of some EGO sensors, a reliable
indication of oxygen content (or air/fuel ratio) which may be used
for more efficient closed loop control of the engine requires a
minimum operating temperature. Likewise, emission control devices
having catalysts require a minimum operating temperature for
efficient operation. For variable displacement engines configured
to selectively operate an entire bank of cylinders, sensors and
catalysts associated with the deactivated bank may cool below the
desired operating temperature. Likewise, emission control devices
and related sensors require some period of time after a cold start
to operate efficiently. It is desirable to minimize the time
required for these components to reach associated desired operating
temperatures after starting the engine.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide a system
and method for controlling an engine operable in a variable
displacement mode during and shortly after starting to reduce the
time necessary for emission control devices and related sensors to
reach a desired minimum operating temperature. Another object of
the present invention is to reduce or eliminate the time required
to achieve a desired minimum operating temperature for components
associated with one or more deactivated cylinders operating in a
variable displacement mode.
[0007] In carrying out the above objects and other objects,
advantages, and features of the invention, a system and method for
controlling an internal combustion engine having at least one bank
of cylinders operable in a variable displacement mode include
starting the engine with at least one bank of cylinders deactivated
to increase load on at least one other bank of activated cylinders
and reduce time required for an engine and/or vehicle component to
reach a desired operating temperature. In one embodiment, ignition
timing or spark is retarded and air/fuel ratio is operated lean for
the activated cylinder bank during and shortly after starting to
further reduce the time required for catalyst light off and closed
loop operation. During activation of a deactivated bank of
cylinders, air/fuel ratio of one or more activated cylinders is
biased rich with air/fuel ratio of the deactivated cylinders biased
lean. In addition, spark is retarded during activation of the
deactivated cylinders to reduce the time necessary for components
associated with the deactivated cylinders to reach desired
operating temperatures.
[0008] The present invention provides a number of advantages. For
example, the present invention controls the engine during and
shortly after starting to reduce the time necessary for emission
control devices to reach a desired operating efficiency.
Furthermore, the present invention, reduces the time after starting
or activating a deactivated bank of cylinders to operate in the
more efficient closed loop mode.
[0009] The above advantage and other advantages, objects, and
features of the present invention will be readily apparent from the
following detailed description of the preferred embodiments when
taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is a block diagram illustrating operation of one
embodiment for a system or method for controlling a variable
displacement engine during starting or reactivation of deactivated
cylinders according to the present invention;
[0011] FIG. 2 is a block diagram illustrating operation of another
embodiment for a system or method for controlling a variable
displacement engine according to the present invention;
[0012] FIG. 3 is a flow diagram illustrating operation of one
embodiment for a system or method for controlling a variable
displacement engine during starting according to the present
invention; and
[0013] FIG. 4 is a logic diagram illustrating a reactivation
strategy for cylinders of a variable displacement engine according
to one embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0014] A block diagram illustrating an engine control system for a
representative internal combustion engine operable in a variable
displacement mode to reduce the time for engine/vehicle components
to achieve a desired minimum operating temperature according to the
present invention is shown in FIG. 1. System 10 preferably includes
an internal combustion engine 12 having a plurality of cylinders,
represented by cylinder 14. In one preferred embodiment, engine 12
includes ten cylinders arranged in a "V" configuration having two
cylinder banks with five cylinders each. As used herein, a cylinder
bank refers to a related group of cylinders having a common
characteristic, such as being located proximate one another or
having a common emission control device (ECD) or exhaust manifold
for example. As such, cylinder banks can also be defined for
in-line cylinder configurations which are within the scope of the
present invention.
[0015] As one of ordinary skill in the art will appreciate, system
10 includes various sensors and actuators to effect control of the
engine. One or more sensors or actuators may be provided for each
cylinder 14, or a single sensor or actuator may be provided for the
engine. For example, each cylinder 14 may include four actuators
which operate corresponding intake and exhaust valves, while only
including a single engine coolant temperature sensor for the entire
engine. However, the block diagrams of the Figures generally
illustrate only a single type of sensor for ease of illustration
and description.
[0016] System 10 preferably includes a controller 16 having a
microprocessor 18 in communication with various computer-readable
storage media, indicated generally by reference numeral 20. The
computer readable storage media preferably include a read-only
memory (ROM) 22, a random-access memory (RAM) 24, and a keep-alive
memory (KAM) 26. As known by those of ordinary skill in the art,
KAM 26 is used to store various operating variables while
controller 16 is powered down but is connected to the vehicle
battery. Computer-readable storage media 20 may be implemented
using any of a number of known memory devices such as PROMs,
EPROMs, EEPROMs, flash memory, or any other electric, magnetic,
optical, or combination memory device capable of storing data, some
of which represent executable instructions, used by microprocessor
18 in controlling the engine. Microprocessor 18 communicates with
the various sensors and actuators via an input/output (I/O)
interface 32. Of course, the present invention could utilize more
than one physical controller, such as controller 16, to provide
engine/vehicle control depending upon the particular
application.
[0017] In operation, air passes through intake 34 where it may be
distributed to the plurality of cylinders via an intake manifold,
indicated generally by reference numeral 36. System 10 preferably
includes a mass airflow sensor 38 which provides a corresponding
signal (MAF) to controller 16 indicative of the mass airflow. If no
mass airflow sensor is present, a mass airflow value may be
inferred from various engine operating parameters. A throttle valve
40 may be used to modulate the airflow through intake 34 during
certain operating modes. Throttle valve 40 is preferably
electronically controlled by an appropriate actuator 42 based on a
corresponding throttle position signal generated by controller 16.
A throttle position sensor provides a feedback signal (TP)
indicative of the actual position of throttle valve 40 to
controller 16 to implement closed loop control of throttle valve
40.
[0018] As illustrated in FIG. 1, a manifold absolute pressure
sensor 46 may be used to provide a signal (MAP) indicative of the
manifold pressure to controller 16. Air passing through intake 34
enters the combustion chambers or cylinders 14 through appropriate
control of one or more intake valves. The intake and exhaust valves
may be controlled directly or indirectly by controller 16 along
with ignition timing (spark) and fuel to selectively
activate/deactivate one or more cylinders 12 to provide variable
displacement operation. Alternatively, variable displacement
operation may be provided by selectively modifying the effective
stroke of one or more cylinders. Variable displacement operation
may be selectively used to quickly achieve a minimum operating
temperature for one or more exhaust gas oxygen sensors and emission
control devices during starting of the engine or during activation
of cylinders after operating in the variable displacement mode
according to the present invention as explained in greater detail
below.
[0019] A fuel injector 48 injects an appropriate quantity of fuel
in one or more injection events for the current operating mode
based on a signal (FPW) generated by controller 16 processed by an
appropriate driver. Control of the fuel injection events is
generally based on the position of the pistons within respective
cylinders 14. Position information is acquired by an appropriate
crankshaft sensor which provides a position signal (PIP) indicative
of crankshaft rotational position. At the appropriate time during
the combustion cycle, controller 16 generates a spark signal (SA)
which is processed by ignition system 58 to control spark plug 60
and initiate combustion within an associated cylinder 14.
[0020] Controller 16 (or a camshaft arrangement) controls one or
more exhaust valves to exhaust the combusted air/fuel mixture of
activated or running cylinders through an associated exhaust
manifold, indicated generally by reference numeral 28. Depending
upon the particular engine configuration, one or more exhaust
manifolds may be used. In one preferred embodiment, engine 12
includes an exhaust manifold 28 associated with each bank of
cylinders as illustrated in FIG. 1.
[0021] An exhaust gas oxygen sensor 62 is preferably associated
with each bank of cylinders and provides a signal (EGO) indicative
of the oxygen content of the exhaust gases to controller 16. As
known by those of ordinary skill in the art, the EGO signal may be
used as feedback in a closed loop controller to control the
air/fuel ratio provided to the one or more cylinders. Closed loop
operation is generally more efficient than open loop operation
under similar operating conditions. However, a reliable EGO signal
for use in closed loop operation generally requires the EGO sensor
to be above a minimum operating temperature. As such, the present
invention provides a system and method for reducing or eliminating
open loop operation time during and shortly after starting the
engine or activating a deactivated cylinder by appropriate engine
control to quickly achieve and a desired minimum operating
temperature of the exhaust gas oxygen sensor(s) and associated
emission control device(s).
[0022] The present invention is independent of the particular type
of emission control device and/or exhaust gas oxygen sensor
utilized, which may depend on the particular application. In one
embodiment, heated exhaust gas oxygen sensors (HEGO) are used in
combination with a three-way catalyst. Of course, various other
air/fuel ratio indicators or sensors and emission control devices
may be used such as a universal exhaust gas oxygen sensor (UEGO),
for example. The exhaust gas oxygen sensor signals may be used to
independently adjust the air/fuel ratio, or control the operating
mode of one or more cylinders or banks of cylinders. In one
preferred embodiment, during activation or reactivation of a group
or bank of cylinders, the air/fuel ratio is biased rich for the
activated cylinders and lean for the deactivated cylinders to
balance the feedgas emissions associated with each group or bank of
cylinders provided to a downstream or underbody catalyst while
reducing the time required for the components associated with the
deactivated cylinders to reach desired operating temperatures.
[0023] With continuing reference to FIG. 2, the exhaust gas passes
through the exhaust manifolds 28 to associated upstream emission
control devices (ECDs) 64A and 64B which may be catalytic
converters, for example. After passing through the associated
upstream ECDs, the exhaust gas is combined and flows past an
underbody exhaust gas oxygen sensor 66 and through a downstream or
underbody emission control device 68 before flowing past a catalyst
monitoring sensor 70 (typically another exhaust gas oxygen sensor)
and being exhausted to atmosphere.
[0024] A temperature sensor 72 may be provided to monitor the
temperature of a catalyst within emission control device 68,
depending upon the particular application. Alternatively, the
temperature may be estimated using an appropriate temperature model
based on various other sensed or estimated engine/vehicle
parameters which may include mass airflow, manifold absolute
pressure or load, engine speed, air temperature, engine coolant
temperature, and/or engine oil temperature, for example. Likewise,
temperature of exhaust gas oxygen sensors 62A, 62B and/or 66 can be
measured or estimated using an appropriate model. A representative
temperature model is described in U.S. Pat. No. 5,956,941, for
example.
[0025] According to the present invention, controller 16 controls
selective operation in the variable displacement mode for one or
more cylinders to reduce the time required for catalyst light-off
and closed loop control after starting the engine and activating or
reactivating one or more cylinders. In a preferred embodiment,
engine 12 is a V-10 engine with variable displacement operation
provided by selectively deactivating one bank of cylinders under
appropriate engine and/or vehicle operating conditions, such as
during starting and under light load, for example. Deactivating one
or more cylinders during starting increases the load on the
activated or operating cylinders and provides additional heat flux
to the corresponding sensors and emission control devices to more
quickly attain catalyst light-off and closed loop operation. The
present invention controls the engine to similarly reduce the time
to attain a desired minimum operating temperature during activation
of the remaining group(s) or bank(s) of cylinders after starting
the engine or after operating in the variable displacement mode for
a period of time where the components may cool to below the desired
minimum operating temperature.
[0026] Referring now to FIG. 2, an alternative embodiment for
controlling a variable displacement engine to reduce the time for
catalyst light-off and/or closed loop operation according to the
present invention is shown. As will be recognized by those of
ordinary skill in the art, system 100 includes similar components
as described with reference to the embodiment illustrated in FIG. 1
and incorporated here by reference. Internal combustion engine 102
includes two cylinder banks 104, 106. Each cylinder bank includes
an associated upstream or close-coupled emission control device 108
and 110, respectively. In addition, rather than combining the
exhaust and using a common third emission control device as
illustrated in FIG. 1, each bank 104, 106 also has an associated
downstream or underbody emission control device 112, 114,
respectively. In one embodiment, the emission control devices 108,
110, 112, and 114 are three-way catalysts.
[0027] As also illustrated in FIG. 2, each ECD has an associated
exhaust gas oxygen sensor 116, 118, 120, 122, respectively, which
are preferably HEGO sensors. Additional exhaust gas oxygen sensors
124, 126 may be provided downstream relative to downstream ECDs
112, 114, respectively, to provide a conversion efficiency
indication and monitor operation of the emission control devices.
Downstream ECDs 112, 114 preferably include associated temperature
sensors 128, 130 to provide an indication of the catalyst
temperature which may be used to determine or estimate the
temperature of associated exhaust gas oxygen sensors. It should be
recognized by those of ordinary skill in the art that the
temperature of the emission control devices and/or the temperature
of one or more exhaust gas oxygen sensors can be modeled as
described above with reference to the embodiment illustrated in
FIG. 1. Sensor and emission control device temperature modeling may
be used alone or in combination with one or more temperature
sensors to quickly attain associated desired minimum operating
temperatures according to the present invention.
[0028] Of course, one of ordinary skill in the art will recognize
that a variety of engine/vehicle operating parameters influence the
current operating mode and selective activation/deactivation of one
or more cylinders to provide variable displacement operation. These
parameters may affect or override the decision to
activate/deactivate cylinders to provide the temperature control
features in accordance with the present invention.
[0029] The diagrams of FIGS. 3 and 4 generally represent control
logic for embodiments of a system or method according to the
present invention. As will be appreciated by one of ordinary skill
in the art, the diagrams may represent any one or more of a number
of known processing strategies such as event-driven,
interrupt-driven, multi-tasking, multi-threading, and the like. As
such, various steps or functions illustrated may be performed in
the sequence illustrated, in parallel, or in some cases omitted.
Likewise, the order of processing is not necessarily required to
achieve the objects, features, and advantages of the invention, but
is provided for ease of illustration and description. Although not
explicitly illustrated, one of ordinary skill in the art will
recognize that one or more of the illustrated steps or functions
may be repeatedly performed depending upon the particular
processing strategy being used.
[0030] Preferably, the control logic is implemented primarily in
software executed by a microprocessor-based engine controller. Of
course, the control logic may be implemented in software, hardware,
or a combination of software and hardware depending upon the
particular application. When implemented in software, the control
logic is preferably provided in a computer-readable storage medium
having stored data representing instructions executed by a computer
to control the engine. The computer-readable storage medium or
media may be any of a number of known physical devices which
utilize electric, magnetic, and/or optical devices to temporarily
or persistently store executable instructions and associated
calibration information, operating variables, and the like.
[0031] A flow diagram illustrating operation of one embodiment for
a system or method for controlling a variable displacement engine
to reduce the time for catalyst light-off and/or closed loop
operation according to the present invention is shown in FIG. 3.
Block 150 determines whether the engine is being started. If the
engine is starting, block 152 deactivates one or more cylinders to
increase the load of the activated cylinders and reduce the time
for the various components to reach a desired minimum operating
temperature. In one embodiment, block 152 represents deactivation
of a cylinder bank such that the close-coupled catalyst of the
activated bank reaches light-off more quickly. Depending upon the
particular engine configuration and operating mode, one or more
groups of cylinders may be selectively deactivated in accordance
with the present invention.
[0032] Block 154 represents monitoring of the associated catalyst
and exhaust gas oxygen sensor temperatures for the activated
cylinders. Temperatures may be determined using an appropriate
model as represented by block 156. Alternatively, or in
combination, temperatures for the EGO sensor(s) and/or emission
control devices may be monitored using one or more associated
temperature sensors as represented by block 158. Signal attributes
of signals provided by the EGO sensors may also be used to provide
an indication of the associated sensor temperature as represented
by block 160. However, the use of the sensor signal to infer
whether or not the sensor is ready is generally only valid if
operating in a narrow window and modulating fuel about the
stoichiometric air/fuel ratio.
[0033] Block 162 determines whether the EGO sensor has reached a
desired minimum operating temperature such that it provides a
reliable signal for closed-loop air/fuel ratio control. If the EGO
sensor is not ready for closed-loop as determined by block 162, the
engine is operated open-loop with a lean air/fuel ratio as
represented by block 167. Block 164 determines whether the
associated close-coupled catalyst has reached a desired minimum
operating temperature corresponding to the catalyst light-off
temperature, for example. If the EGO sensor is ready but the
catalyst has not reached an appropriate temperature, the engine
controller may operate the activated cylinders closed-loop with a
lean biased air/fuel ratio as represented by block 168. In
addition, emission timing or spark is preferably retarded from MBT
for the activated cylinders as represented by block 170. The
controller continues to monitor the associated temperatures as
indicated by block 154.
[0034] Once the EGO sensor(s) and associated catalyst have reached
their corresponding desired minimum operating temperatures as
represented by blocks 162 and 164, additional cylinders or cylinder
banks may be activated as represented by block 166. Preferably
cylinder activation or reactivation is controlled according to the
strategy illustrated and described with reference to FIG. 4.
[0035] FIG. 4 provides a block diagram illustrating a cylinder
activation/deactivation strategy according to one embodiment of the
present invention. Block 180 of FIG. 4 represents monitoring of at
least one engine or vehicle component such as an emission control
device (ECD). In this embodiment, block 180 determines whether an
upstream or close coupled ECD is above a corresponding or
associated temperature threshold. For example, the temperature
threshold may correspond to the light-off temperature of a
three-way catalyst. Block 182 determines whether a downstream or
underbody ECD is above a corresponding temperature. The downstream
ECD may be associated with a single upstream device, as illustrated
in FIG. 2, or shared by multiple upstream devices as illustrated in
FIG. 1. If the upstream ECD is above the corresponding temperature
threshold as determined by block 180 and the downstream ECD is
above its associated temperature threshold as determined by block
182, all cylinders are operated under closed-loop control with a
normal scheduled air/fuel ratio and spark or ignition timing as
represented by block 184.
[0036] If the upstream component is below its associated
temperature threshold as indicated by block 180, or the downstream
component is below its associated temperature threshold as
indicated by block 182, block 186 determines whether an associated
exhaust gas oxygen sensor is available for providing information
sufficient to operate in closed-loop mode. In this particular
embodiment, block 186 determines whether an associated HEGO sensor
has reached an appropriate operating temperature to provide
reliable information with respect to the oxygen content of the
exhaust gas. If the associated HEGO sensor is ready for closed-loop
operation as determined by block 186, the previously deactivated
cylinders are activated with a lean bias on the air/fuel ratio and
spark is retarded from MBT. The previously running or activated
cylinders are operated with a rich bias air/fuel ratio. All
cylinders are operated using closed-loop control of air/fuel ratio
based on the HEGO sensor reading with appropriate lean/rich bias as
represented by block 188. In one embodiment, an entire bank of
cylinders is activated and operated with a lean bias and retarded
spark until the downstream ECD reaches its temperature threshold as
determined by block 182.
[0037] If the HEGO sensor associated with the ECD is not ready for
closed-loop operation, as may occur during and shortly after a cold
start, as determined by block 186, the engine is controlled to
activate the deactivated cylinders and operate them open-loop with
a lean air/fuel ratio and spark retarded from MBT. The previously
activated or running cylinders may be operated with a rich bias
air/fuel ratio in closed-loop mode depending upon the particular
exhaust configuration. For exhaust configurations as illustrated in
FIG. 1, the number of cylinders operating with a lean bias during
activation or deactivation preferably corresponds to the number of
cylinders operating with a rich bias such that the combined feedgas
emissions are near the stoichiometric ratio prior to entering the
downstream or underbody catalyst.
[0038] Thus, the present invention provides a system and method for
controlling a variable displacement engine to reduce the time
necessary for catalyst light-off and/or closed loop operation after
engine starting or operating in the variable displacement mode.
[0039] While the best mode for carrying out the invention has been
described in detail, those familiar with the art to which this
invention relates will recognize various alternative designs and
embodiments for practicing the invention as defined by the
following claims.
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