U.S. patent application number 11/033770 was filed with the patent office on 2006-07-13 for method for controlling engine air/fuel ratio.
Invention is credited to Brian Kenneth Bolton, Anne-Lise Grosmougin, Kevin Dean Sisken.
Application Number | 20060150628 11/033770 |
Document ID | / |
Family ID | 35911651 |
Filed Date | 2006-07-13 |
United States Patent
Application |
20060150628 |
Kind Code |
A1 |
Bolton; Brian Kenneth ; et
al. |
July 13, 2006 |
METHOD FOR CONTROLLING ENGINE AIR/FUEL RATIO
Abstract
A system for controlling engine air/fuel ratio includes an
engine, a compressor having an inlet receiving air. The compressor
discharges air to the engine intake. A recirculation path is
provided from the compressor discharge to the compressor inlet. A
controllable valve is located along the recirculation path. A
controller is programmed to control the valve to vary the air flow
to the engine intake, thereby controlling the air/fuel ratio.
Various applications for the compressor recirculation arrangement
are possible.
Inventors: |
Bolton; Brian Kenneth;
(Birmingham, MI) ; Sisken; Kevin Dean; (Saline,
MI) ; Grosmougin; Anne-Lise; (Birmingham,
MI) |
Correspondence
Address: |
BROOKS KUSHMAN P.C.
1000 TOWN CENTER
TWENTY-SECOND FLOOR
SOUTHFIELD
MI
48075
US
|
Family ID: |
35911651 |
Appl. No.: |
11/033770 |
Filed: |
January 12, 2005 |
Current U.S.
Class: |
60/605.2 |
Current CPC
Class: |
F02B 29/0406 20130101;
F02M 26/05 20160201; F02B 37/16 20130101; F02D 41/0245 20130101;
F01N 2430/06 20130101; F02M 26/23 20160201; F01N 3/023 20130101;
F02D 41/0007 20130101; F02D 41/0275 20130101; F01N 3/206 20130101;
Y02T 10/144 20130101; F02D 41/029 20130101; Y02T 10/12 20130101;
F02D 23/02 20130101; F02D 41/0235 20130101; Y02T 10/26 20130101;
F02D 41/0065 20130101 |
Class at
Publication: |
060/605.2 |
International
Class: |
F02B 33/44 20060101
F02B033/44 |
Goverment Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0001] This invention was made with Government support under
Contract No. DE-FC02-99EE50575. The Government may have certain
rights to this invention.
Claims
1.-3. (canceled)
4. A system for controlling engine air/fuel ratio, the system
comprising: an engine including a plurality of cylinders fed by
fuel injectors, an intake, and an exhaust; a compressor having an
inlet receiving air, the compressor discharging air to the engine
intake; a recirculation path from the compressor discharge to the
compressor inlet; a controllable valve along the recirculation
path; a controller programmed to control the valve to vary the air
flow to the engine intake, thereby controlling the air/fuel ratio;
a lean NOx trap receiving the engine exhaust, the lean NOx trap
requiring a rich fuel mixture for regeneration; and wherein the
controller is programmed to periodically regenerate the lean NOx
trap by controlling the valve to reduce the air/fuel ratio.
5. A system for controlling engine air/fuel ratio, the system
comprising: an engine including a plurality of cylinders fed by
fuel injectors, an intake, and an exhaust; a compressor having an
inlet receiving air, the compressor discharging air to the engine
intake; a recirculation path from the compressor discharge to the
compressor inlet; a controllable valve along the recirculation
path; a controller programmed to control the valve to vary the air
flow to the engine intake, thereby controlling the air/fuel ratio;
a diesel particulate filter receiving the engine exhaust, the
diesel particulate filter requiring a high temperature for
regeneration; and wherein the controller is programmed to
periodically regenerate the diesel particulate filter by
controlling the valve to reduce the air/fuel ratio, thereby
increasing exhaust temperature.
6. A system for controlling engine air/fuel ratio, the system
comprising: an engine including a plurality of cylinders fed by
fuel injectors, an intake, and an exhaust; a compressor having an
inlet receiving air, the compressor discharging air to the engine
intake; a recirculation path from the compressor discharge to the
compressor inlet; a controllable valve along the recirculation
path; a controller programmed to control the valve to vary the air
flow to the engine intake, thereby controlling the air/fuel ratio;
a diesel oxidation catalyst receiving the engine exhaust; and
wherein the controller is programmed to control the valve to reduce
air/fuel ratio, thereby increasing exhaust temperature and
affecting the diesel oxidation catalyst.
7. The system of claim 6 wherein the valve is controlled so as to
increase exhaust temperature for more rapid catalyst light off.
8. The system of claim 6 wherein the valve is controlled so as to
increase exhaust temperature to a range where catalyst efficiency
is higher.
9.-11. (canceled)
12. A method for controlling engine air/fuel ratio wherein an
engine includes a plurality of cylinders fed by fuel injectors, an
intake, and an exhaust, a compressor has an inlet receiving air,
the compressor discharging air to the engine intake, the method
comprising: providing a recirculation path extending from the
compressor discharge to the compressor inlet, wherein a
controllable valve is located along the recirculation path;
controlling the valve to vary the air flow to the engine intake,
thereby controlling the air/fuel ratio; wherein a lean NOx trap
receives the engine exhaust, the lean NOx trap requiring a rich
fuel mixture for regeneration; and periodically regenerating the
lean NOx trap by controlling the valve to reduce the air/fuel
ratio.
13. A method for controlling engine air/fuel ratio wherein an
engine includes a plurality of cylinders fed by fuel injectors, an
intake, and an exhaust, a compressor has an inlet receiving air,
the compressor discharging air to the engine intake, the method
comprising; providing a recirculation path extending from the
compressor discharge to the compressor inlet, wherein a
controllable valve is located along the recirculation path;
controlling the valve to vary the air flow to the engine intake,
thereby controlling the air/fuel ratio; wherein a diesel
particulate filter receives the engine exhaust, the diesel
particulate filter requiring a high temperature for regeneration;
and periodically regenerating the diesel particulate filter by
controlling the valve to reduce the air/fuel ratio, thereby
increasing exhaust temperature.
14. A method for controlling engine air/fuel ratio wherein an
engine includes a plurality of cylinders fed by fuel injectors, an
intake, and an exhaust, a compressor has an inlet receiving air,
the compressor discharging air to the engine intake, the method
comprising: providing a recirculation path extending from the
compressor discharge to the compressor inlet, wherein a
controllable valve is located along the recirculation path;
controlling the valve to vary the air flow to the engine intake,
thereby controlling the air/fuel ratio; wherein a diesel oxidation
catalyst receives the engine exhaust; and controlling the valve to
reduce air/fuel ratio, thereby increasing exhaust temperature and
affecting the diesel oxidation catalyst.
15. The method of claim 14 wherein the valve is controlled so as to
increase exhaust temperature for more rapid catalyst light off.
16. The method of claim 14 wherein the valve is controlled so as to
increase exhaust temperature to a range where catalyst efficiency
is higher.
Description
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method for controlling engine
air/fuel ratio.
[0004] 2. Background Art
[0005] After-treatment devices such as Lean NOx Traps (LNT) are
being devised to adsorb NOx emissions from diesel engines in an
effort to meet future emission standards. LNTs can be very
effective in trapping NOx but need to be periodically cleaned
through a regeneration process. A rich environment (close to an
air/fuel ratio of 14) is required to regenerate the trap. While
fuel injection in the combustion chamber and/or fuel injection in
the exhaust stream can effectively reduce the exhaust air/fuel
ratio, they both present some limitations in terms of how much fuel
can be injected. Too much fuel injected in the combustion chamber
after the main combustion event (late post injection) can result in
wall wetting and engine damage or affect the engine torque curve
when injected too early. Injecting large quantities of fuel in the
exhaust stream could require large and bulky injectors.
[0006] For the foregoing reasons, there is a need for an improved
method for controlling engine air/fuel ratio.
SUMMARY OF THE INVENTION
[0007] It is an object of the invention to provide an improved
method for controlling engine air/fuel ratio.
[0008] The invention comprehends bringing the air/fuel ratio down
to an intermediate level through engine air flow management during
the LNT regeneration process. More specifically, in a supercharged
or turbocharged engine including a compressor at the intake,
recirculating some air from the compressor discharge back to the
compressor inlet reduces the engine air/fuel ratio. This approach
alleviates much of the requirements on the fuel injection side that
are typically associated with LNT regeneration. Further reduction
of the air/fuel ratio can be achieved via fuel injection into the
combustion chamber and/or fuel injection in the exhaust stream.
[0009] Further, in accordance with the invention, this same method
of recirculating some air from the compressor discharge back to the
compressor inlet to reduce the engine air/fuel ratio can be used to
increase the engine's exhaust temperature to promote regeneration
of a diesel particulate filter (DPF). For example, if the DPF is
full of exhaust particles and requires regeneration, this
compressor recirculation can be used to increase the exhaust
temperature. The amount of air being recirculated is selected as a
function of the required exhaust temperature increase.
[0010] Similarly, this approach can be used to increase exhaust
temperature for more rapid catalyst light off or move the exhaust
temperature to a range where catalyst efficiency is higher.
[0011] Further, this approach can be used for optimization of
turbocharger operation, by either moving the compressor operation
away from the surge line (safety feature), or bringing it to a
higher efficiency line (performance feature).
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates modulated compressor recirculation to
control engine air/fuel ratio in accordance with a preferred
embodiment of the invention; and
[0013] FIG. 2 illustrates a method of the invention in the
preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] With reference to FIG. 1, an engine 10 includes a plurality
of cylinders fed by fuel injectors. The engine intake is indicated
at 14 while the engine exhaust is indicated at 16. In the
illustrated preferred embodiment, the engine is equipped with an
exhaust gas recirculation (EGR) system. The EGR system recirculates
a portion of the exhaust gases back to the engine intake 14, as
needed, to avoid excessively high combustion temperatures which
cause NOx creation. EGR cooler 18 cools the recirculated exhaust
gas prior to introduction at engine intake 14.
[0015] As shown, the engine is equipped with a turbocharger system
20. System 20 includes turbine 22 driven by exhaust gases. Turbine
22 drives compressor 24. Charge air cooler (CAC) 26 cools the
charge air from compressor 24 prior to introduction at engine
intake 14.
[0016] According to the invention, engine air flow management is
utilized to reduce the engine air/fuel ratio. More specifically, a
recirculation path 30 from the compressor discharge to the
compressor inlet is provided, and a controllable valve 32 is
located along this recirculation path 30. A controller 33 is
programmed to modulate controllable valve 32 to vary the airflow to
the engine intake 14, thereby varying the air/fuel ratio.
[0017] In more detail, a modulated compressor recirculation flow
can, for instance, bring the engine air/fuel ratio from 25 down to
17 (arbitrary numbers selected as an example), and then fuel
injection strategies may be employed to further lower the exhaust
air/fuel ratio from 17 down to 14 where regeneration becomes
effective. In FIG. 1, the Lean NOx Trap (LNT) is indicated at 36.
The innovative approach of the invention involves recirculating
some air flow (charge air) from the compressor outlet back into the
compressor inlet. The amount of air available in each cylinder of
engine 10 is reduced, resulting in richer fuel combustion in the
engine. Exhaust gases reaching LNT 36 are fuel rich and promote the
regeneration process. At the end of LNT regeneration, compressor
recirculation is disabled, bringing the engine back to lean
operating conditions where it runs most effectively.
[0018] The invention is applicable to supercharged or turbocharged
engines. In the preferred embodiment illustrated in FIG. 1,
recirculation path 30 is composed of an external tube introduced
between the compressor outlet and the compressor inlet of the
turbocharger system 20. The purpose of the tube is to recirculate
compressed air from the compressor outlet back into the compressor
inlet. The tube (recirculation passage) can also be directly
incorporated into the compressor housing. Air will naturally flow
from the compressor outlet (high pressure side) into the compressor
inlet (low pressure side).
[0019] Modulator valve 32 is capable of modulating the air flow,
and is installed in the tube, creating a compressor bleed line. The
amount of air going through the bypass tube is defined by the size
of the tube and the valve position (full open, or modulated). The
valve is electronically modulated by controller 33 to provide
variable and controllable air/fuel ratio. It is appreciated that
controller 33 may be any suitable controller as understood by those
of ordinary skill in the art of engine control systems. That is,
controller 33 may be the engine controller or a different
controller that controls one or more subsystems of the engine.
[0020] When regeneration is required at LNT 36 (possibly defined by
the NOx conversion rate of the LNT), bypass valve 32 is opened and
high pressure air (charge air) circulates through the bypass tube
and is fed back to the compressor inlet, thereby lowering the
amount of air going into the engine intake 14 and the engine
cylinders, thus creating rich combustion in the cylinders. The
exhaust gases that are fed to the after-treatment devices (that is,
LNT 36 in FIG. 1) are fuel rich and contain high thermal mass. Such
conditions promote LNT regeneration.
[0021] The amount of air flow bled around compressor 24 can be
modulated based on a targeted air/fuel ratio. Once regeneration is
achieved, bypass valve 32 is closed and the engine returns to
normal lean operating conditions. Engine fueling and timing
adjustments may be made during the regeneration phase to maintain
the torque at the same level as under normal lean operating
conditions, resulting in a minimum fuel economy penalty. Under
recirculation conditions, the compressor pressure ratio and speed
drop and the air mass flow rate displaced by the compressor
increases. Those characteristics result in safe compressor
operating conditions, as the operating point is moving away from
the compressor surge line.
[0022] To get air fuel ratios of 14 (in the example), fuel
injection strategies will also be employed. The operation and
strategy of these fuel injection strategies may vary depending on
the implementation as understood by those of ordinary skill in the
art of engine control systems.
[0023] With continuing reference to FIG. 1, the primary application
of this modulated compressor recirculation arrangement is to
provide a targeted air/fuel ratio for LNT regeneration. The
operation of valve 32 can be electronically controlled by
controller 33 based on LNT regeneration needs and engine operating
conditions at that time. Bleed modulation, engine fueling and
timing strategies can all be optimized to provide the required
air/fuel ratio and exhaust temperature for LNT regeneration, while
maintaining engine torque for good drivability and minimizing fuel
economy impact.
[0024] Another application of the invention is the temporary
increase of engine exhaust temperature to promote diesel
particulate filter regeneration. FIG. 1 illustrates a diesel
particulate filter at 34.
[0025] Another application of the invention is to increase exhaust
temperature to promote faster catalyst light off or to increase
exhaust temperature to a level where catalyst efficiency is higher,
resulting in overall lower tailpipe emissions. FIG. 1 illustrates a
diesel oxidation catalyst at 38.
[0026] Yet another application of the invention is the optimization
of turbocharger operation, by either moving the compressor
operation away from the surge line (safety feature), or bringing it
to a higher efficiency line (performance feature).
[0027] FIG. 2 illustrates a method of the invention in the
preferred embodiment. According to the method for controlling
engine air/fuel ratio, a recirculation path extending from the
compressor discharge to the compressor inlet is provided (block
50). A controllable valve is provided at a location along the
recirculation path (block 52). According to the method, the valve
is controlled to vary the air flow to the engine intake, thereby
controlling the air/fuel ratio (block 54). The method may be
utilized for a variety of different applications.
[0028] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
* * * * *