U.S. patent application number 17/190712 was filed with the patent office on 2022-09-08 for systems and methods for fuel post injection timing.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Eric Kurtz, Jason Martz, Michiel J. Van Nieuwstadt.
Application Number | 20220282678 17/190712 |
Document ID | / |
Family ID | 1000006549540 |
Filed Date | 2022-09-08 |
United States Patent
Application |
20220282678 |
Kind Code |
A1 |
Kurtz; Eric ; et
al. |
September 8, 2022 |
SYSTEMS AND METHODS FOR FUEL POST INJECTION TIMING
Abstract
Methods and systems are provided for fuel post injection for
diesel particulate filter (DPF) regeneration. In one example, a
method may include, responsive to a request for generating
exotherms in an exhaust system of an engine while combustion is
discontinued in at least one cylinder of the engine, injecting fuel
into a cylinder within a threshold crank angle range around top
dead center (TDC) of a compression stroke of the cylinder and also
within the threshold crank angle range around top dead center of an
exhaust stroke of the cylinder, the threshold crank angle range
extending from no more than 40 crank angle degrees before TDC to no
more than 40 crank angle degrees after TDC. In this way, fuel post
injections may be injected +/-40 crank angle degrees after TDC of
the compression and exhaust strokes to increase exhaust temperature
while avoiding wall wetting and oil-in-fuel dilution.
Inventors: |
Kurtz; Eric; (Dearborn,
MI) ; Van Nieuwstadt; Michiel J.; (Ann Arbor, MI)
; Martz; Jason; (Canton, MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
1000006549540 |
Appl. No.: |
17/190712 |
Filed: |
March 3, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02D 13/0215 20130101;
F02D 41/405 20130101; F02D 41/027 20130101; F02D 13/04 20130101;
F02B 37/24 20130101; F02D 41/0002 20130101; F02D 41/0077 20130101;
F02D 41/009 20130101; F02D 13/06 20130101; F01N 3/023 20130101 |
International
Class: |
F02D 41/02 20060101
F02D041/02; F02D 41/40 20060101 F02D041/40; F02D 41/00 20060101
F02D041/00; F02D 13/02 20060101 F02D013/02; F02D 13/06 20060101
F02D013/06; F02B 37/24 20060101 F02B037/24; F02D 13/04 20060101
F02D013/04; F01N 3/023 20060101 F01N003/023 |
Claims
1. A method, comprising: responsive to a request for generating
exotherms in an exhaust system of an engine while combustion is
discontinued in at least one cylinder of the engine, injecting fuel
into a cylinder within a threshold crank angle range around top
dead center of a compression stroke of the cylinder and also within
the threshold crank angle range around top dead center of an
exhaust stroke of the cylinder, the threshold crank angle range
extending from no more than 40 crank angle degrees before top dead
center to no more than 40 crank angle degrees after top dead
center.
2. The method of claim 1, further comprising: adjusting an air flow
through the engine responsive to the request for generating the
exotherms in the exhaust system of the engine.
3. The method of claim 2, wherein injecting fuel into the cylinder
within the threshold crank angle range around top dead center of
the compression stroke of the cylinder and also within the
threshold crank angle range around top dead center of the exhaust
stroke of the cylinder comprises: determining an amount of fuel to
inject based on the adjusted air flow through the engine;
determining a first timing for injecting the fuel within the
threshold crank angle range around top dead center of the
compression stroke and a second timing for injecting the fuel
within the threshold crank angle range around top dead center of
the exhaust stroke based on a desired air-fuel mixing relative to a
desired decreased ignition probability; and injecting the
determined amount of fuel at the first timing and at the second
timing.
4. The method of claim 3, wherein determining the first timing for
injecting the fuel within the threshold crank angle range around
top dead center of the compression stroke and the second timing for
injecting the fuel within the threshold crank angle range around
top dead center of the exhaust stroke based on the desired air-fuel
mixing relative to the desired decrease ignition probability
comprises: setting the first timing and the second timing to be
earlier within the threshold crank angle range responsive to the
desired air-fuel mixing being greater than the desired decreased
ignition probability; and setting the first timing and the second
timing to be later within the threshold crank angle range
responsive to the desired decreased ignition probability being
greater than the desired air-fuel mixing.
5. The method of claim 2, wherein adjusting the air flow through
the engine comprises at least one of adjusting a vane position of a
variable geometry turbine to a further closed position and
adjusting an intake throttle to a further closed position.
6. The method of claim 2, wherein combustion is discontinued in the
at least one cylinder of the engine responsive to an engine braking
condition, and adjusting the air flow through the engine comprises
operating a decompression device.
7. The method of claim 2, wherein combustion is discontinued in the
at least one cylinder of the engine responsive to a cylinder
deactivation condition, and adjusting the air flow through the
engine comprises maintaining an exhaust valve or an intake valve of
each deactivated cylinder open.
8. The method of claim 1, wherein the threshold crank angle range
extends from 30 crank angle degrees before top dead center to 30
crank angle degrees after top dead center.
9. The method of claim 1 wherein the request for generating the
exotherms in the exhaust system of the engine is responsive to a
soot load of a particulate filter positioned in the exhaust system
of the engine being greater than a threshold soot load, and the
method further comprises fully closing an exhaust gas recirculation
(EGR) valve positioned in a passage coupled between the exhaust
system of the engine and an intake of the engine in response to the
request for generating the exotherms in the exhaust system of the
engine.
10. A method, comprising: responsive to a request to regenerate a
particulate filter while combustion is discontinued in at least one
cylinder of an engine: determining a first timing of a first fuel
post injection within a first threshold timing range of no more
than 80 crank angle degrees and a second timing of a second fuel
post injection within a second threshold timing range of no more
than 80 crank angle degrees based on a desired exhaust gas
condition, the first threshold timing range extending from a
compression stroke of a cylinder to a power stroke of the cylinder
and the second threshold timing range extending from an exhaust
stroke of the cylinder to an intake stroke of the cylinder; and
delivering the first fuel post injection to the cylinder at the
first timing and the second fuel post injection to the cylinder at
the second timing.
11. The method of claim 10, further comprising adjusting an amount
of each of the first fuel post injection and the second fuel post
injection based on an air flow through the engine.
12. The method of claim 11, wherein combustion is discontinued in
the at least one cylinder of the engine responsive to a request for
engine braking, and the method further comprises adjusting the air
flow through the engine via a decompression device responsive to
the request for engine braking.
13. The method of claim 11, wherein combustion is discontinued in
the at least one cylinder of the engine responsive to a cylinder
deactivation condition, and wherein the air flow through the engine
is adjusted via a variable geometry turbine during the cylinder
deactivation condition.
14. The method of claim 10, wherein the first timing of the first
fuel post injection is earlier within the first threshold timing
range and the second timing of the second fuel post injection is
earlier within the second threshold timing range when the desired
exhaust gas condition is an increased mixing of fuel with air, and
wherein the first timing of the first fuel post injection is later
within the first threshold timing range and the second timing of
the second fuel post injection is later within the second threshold
timing range when the desired exhaust gas condition is decreased
ignitability.
15. The method of claim 10, wherein the cylinder receiving the
first fuel post injection and the second fuel post injection is
included in the at least one cylinder having discontinued
combustion.
16. The method of claim 10, wherein the cylinder receiving the
first fuel post injection and the second fuel post injection is not
included in the at least one cylinder having discontinued
combustion.
17. A system, comprising: an engine including a plurality of
cylinders; and a controller storing executable instructions in
non-transitory memory that, when executed, cause the controller to:
inject fuel into at least one of the plurality of cylinders each
revolution of the engine during a threshold post injection timing
range extending from no more than 40 degrees before top dead center
to no more than 40 degrees after top dead center while particulate
filter regeneration is requested during an engine operating
condition where combustion is discontinued.
18. The system of claim 17, further comprising a particulate filter
coupled in an exhaust system of the engine, and wherein the
particulate filter regeneration is requested responsive to a soot
load of the particulate filter being greater than a threshold soot
load.
19. The system of claim 17, wherein the engine operating condition
where combustion is discontinued is one of an engine braking
condition and a cylinder deactivation condition.
20. The system of claim 17, wherein to inject the fuel into the at
least one of the plurality of cylinders each revolution of the
engine during the threshold post injection timing range, the
controller includes further instructions stored in the
non-transitory memory that, when executed, cause the controller to:
set a timing to inject the fuel into the at least one of the
plurality of cylinders each revolution of the engine during the
threshold post injection timing range to be before top dead center
within the threshold post injection timing range as a desired
amount of heat production increases; and set the timing to inject
the fuel to be after top dead center within the threshold post
injection range as a desired amount of mixing increases.
Description
FIELD
[0001] The present description relates generally to methods and
systems for controlling fuel post injection timing in a vehicle
engine during diesel particulate filter regeneration.
BACKGROUND/SUMMARY
[0002] Combustion in an engine of a vehicle using diesel or
gasoline fuel may generate particulate matter (PM) (such as soot
and aerosols) that can be exhausted to the atmosphere. Emission
after-treatment devices may be used to treat exhaust gases before
the exhaust gases leave the vehicle. In particular, the emission
after-treatment devices may include particulate filters, oxidation
catalysts, and nitrogen oxide (NOx) catalysts. Particulate matter,
which is largely made up of carbon particles from incomplete
combustion, may be collected in particulate filters and may
gradually restrict a flow of exhaust gas as the particulate matter
accumulates in the particulate filters. In order to periodically
regenerate or purge the particulate filter of particulate matter,
measures may be taken that result in an increase of the exhaust gas
temperature above a predetermined level (e.g., above 600 K) in
order to incinerate the carbon particles accumulated in the
filter.
[0003] In some cases, a particulate filter reaches high enough
temperatures during normal vehicle operation to passively perform a
particulate filter regeneration. However, some vehicles may not
reach passive regeneration conditions (e.g., vehicle speeds above
40 mph), and the particulate filter may become fouled.
[0004] In some cases, the vehicle may perform active particulate
filter regeneration based on an estimated soot load, for example.
The estimated soot load may be based on an exhaust backpressure
measured upstream of the particulate filter. The active particulate
filter regeneration may include post combustion fuel injection,
referred to herein as "post injection," which increases the
temperature of the exhaust by producing exotherms. In some
examples, the active particulate filter regeneration may occur
while the vehicle slows down and combustion is discontinued. Air
continues to be pumped by the engine, but a relatively small amount
of fuel post injection may be provided. As a result, the exhaust
system may cool off during the active regeneration, and the
particulate filter may not be adequately emptied. As another
example, the engine may be operated with one or more cylinders
deactivated. The post injections may become larger as fewer
cylinders are active, increasing a likelihood of wall wetting and
fuel in-oil dilution.
[0005] Other attempts to increase exhaust gas temperatures for a
diesel particulate filter (DPF) regeneration include a fuel post
injection after a main fuel injection within cylinders of the
engine. One example approach is shown by Tonetti et al. in U.S.
Pat. No. 6,666,020 B2. Therein, to initiate regeneration in a DPF,
a fuel injection strategy is performed in each cylinder in which a
main fuel injection occurs followed by two fuel post
injections.
[0006] However, the inventors herein have recognized potential
issues with such systems. As one example, a fuel post injection
strategy for cylinder deactivation or engine braking is not
discussed, and without precise timing of the post injection and
controlling the amount of fuel post injection, wall wetting and
fuel in-oil dilution may still occur.
[0007] In one example, the issues described above may be addressed
a method, comprising responsive to a request for generating
exotherms in an exhaust system of an engine while combustion is
discontinued in at least one cylinder of the engine, injecting fuel
into a cylinder within a threshold crank angle range around top
dead center of a compression stroke of the cylinder and also within
the threshold crank angle range around top dead center of an
exhaust stroke of the cylinder, the threshold crank angle range
extending from no more than 40 crank angle degrees before top dead
center to no more than 40 crank angle degrees after top dead
center. In this way, fuel post injection may be used to create
exotherms in a diesel oxidation catalyst (DOC) for DPF regeneration
while reducing oil-in-fuel dilution and bore washing within the
cylinder.
[0008] As one example, the request for generating the exotherms in
the exhaust system of the engine may be responsive to a soot load
of a particulate filter positioned in the exhaust system of the
engine being greater than a threshold soot load, and the method may
further include adjusting an air flow through the engine responsive
to the request for generating the exotherms in the exhaust system
of the engine. In some examples, injecting fuel into the cylinder
within the threshold crank angle range around top dead center of
the compression stroke of the cylinder and also within the
threshold crank angle range around top dead center of the exhaust
stroke of the cylinder may include determining an amount of fuel to
inject based on the adjusted air flow through the engine,
determining a first timing for injecting the fuel within the
threshold crank angle range around top dead center of the
compression stroke, determining a second timing for injecting the
fuel within the threshold crank angle range around top dead center
of the exhaust stroke, and injecting the determined amount of fuel
at the first timing and the second timing. The first timing and the
second timing may each be determined based on desired exhaust gas
properties. For example, the first timing and the second timing may
be earlier within the threshold crank angle range responsive to
increased mixing being desired relative to a reduced ignition of
the fuel, and the second timing to be later within the threshold
crank angle range responsive to the reduced ignition of the fuel
being more desired than the increased mixing. Further, an exhaust
gas recirculation (EGR) valve of the engine may be fully closed to
prevent recirculation of the injected fuel.
[0009] In some examples, the air flow may be adjusted by adjusting
a vane position of a variable geometry turbine. Additionally or
alternatively, the air flow through the engine may be adjusted by
operating a decompression device. The decompression device may be a
continuously variable valve lift (CVVL) system, and operating the
decompression device may include adjusting an exhaust valve opening
timing or an intake valve opening timing, for example. In such an
example, combustion may be discontinued in the at least one
cylinder of the engine responsive to an engine braking condition.
In other examples, combustion may be discontinued in the at least
one cylinder of the engine responsive to a cylinder deactivation
condition, and adjusting the air flow through the engine may
include maintaining an exhaust valve of each deactivated cylinder
open.
[0010] By injecting the fuel post injection within the threshold
crank angle range, mixing of the fuel post injection with the air
within the cylinder may be increased. As such, when the fuel post
injection reaches an oxidation catalyst positioned in the exhaust
system upstream of the particulate filter, an increased amount of
exotherms may be created to increase the temperature of the
particulate filter. Additionally, with increasing the air and fuel
mixing and basing the amount of fuel post injection on the amount
of air flow through the cylinder, oil-in-fuel dilution and bore
washing may be reduced or avoided. As a result, particulate filter
regeneration may occur with reduced fuel usage even during exhaust
cooling events such as cylinder deactivation and engine
braking.
[0011] It should be understood that the summary above is provided
to introduce in simplified form a selection of concepts that are
further described in the detailed description. It is not meant to
identify key or essential features of the claimed subject matter,
the scope of which is defined uniquely by the claims that follow
the detailed description. Furthermore, the claimed subject matter
is not limited to implementations that solve any disadvantages
noted above or in any part of this disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 schematically depicts an example cylinder of an
internal combustion engine.
[0013] FIG. 2 shows a method for diesel particulate filter (DPF)
regeneration during a cylinder deactivation event.
[0014] FIG. 3 shows a method for DPF regeneration during an engine
braking event.
[0015] FIG. 4 shows a method for controlling fuel post injection
during DPF regeneration when combustion is discontinued in at least
one cylinder.
[0016] FIG. 5 displays a first example timing chart for increased
mixing of air with fuel from a fuel post injection during DPF
regeneration by injecting a fuel post injection earlier within a
threshold timing range.
[0017] FIG. 6 displays a second example timing chart for decreasing
a probability of fuel from a fuel post injection igniting during
DPF regeneration by injecting the fuel post injection later within
the threshold timing range.
[0018] FIG. 7 displays an example timeline of adjustments to engine
operating parameters for DPF regeneration.
DETAILED DESCRIPTION
[0019] The following description relates to systems and methods for
fuel post injection during diesel particulate filter regeneration.
Fuel post injection may occur in an engine, such as the engine
schematically shown in FIG. 1, for example, which includes a diesel
oxidation catalyst (DOC) and a diesel particulate filter (DPF) to
reduce emissions from the engine. In some examples, DPF
regeneration may occur while one or more cylinders are deactivated,
which may cause a temperature of the DPF to decrease. A method for
DPF regeneration during cylinder deactivation is shown in FIG. 2,
while a method for DPF regeneration during engine braking is shown
in FIG. 3. In each example, the fuel post injection may be
precisely timed in order to increase an amount of heat produced via
the post injection and/or increase mixing of air and fuel while
also decreasing wall wetting, such as according to the method shown
in FIG. 4. A first example timing chart for performing the fuel
post injection is shown in FIG. 5, with the post injection
occurring while the air within the cylinder is at the highest
temperature in order to increase mixing of air and the post
injected fuel by enhancing evaporation of the fuel with the hotter
air. A second example timing chart is shown in FIG. 6, with the
fuel post injection occurring while the air mass within the
cylinder is increasing and at lower temperatures in order to
decrease a probability of the fuel igniting prior to generating an
exotherm for DPF regeneration. Additionally, a prophetic example
timeline for adjusting operation of the engine during DPF
regeneration is shown in FIG. 7. In this way, exhaust system
cooling while combustion is discontinued in at least one engine
cylinder (e.g., due to cylinder deactivation or engine braking) may
be reduced, enabling effective and efficient DPF regeneration with
reduced cylinder wall wetting.
[0020] Turning now to the figures, FIG. 1 depicts an example of a
cylinder 14 of an internal combustion engine 10, which may be
included in a vehicle 5. Engine 10 may be controlled at least
partially by a control system, including a controller 12, and by
input from a vehicle operator 130 via an accelerator pedal 132 and
an accelerator pedal position sensor 134 for generating a
proportional pedal position signal PP. Cylinder (herein, also
"combustion chamber") 14 of engine 10 may include combustion
chamber walls 136 with a piston 138 positioned therein. Piston 138
may be coupled to a crankshaft 140 so that reciprocating motion of
the piston is translated into rotational motion of the crankshaft.
Crankshaft 140 may be coupled to at least one vehicle wheel 55 via
a transmission 54, as further described below. Further, a starter
motor (not shown) may be coupled to crankshaft 140 via a flywheel
to enable a starting operation of engine 10.
[0021] In some examples, vehicle 5 may be a hybrid vehicle with
multiple sources of torque available to one or more vehicle wheels
55. In other examples, vehicle 5 is a conventional vehicle with
only an engine. In the example shown, vehicle 5 includes engine 10
and an electric machine 52. Electric machine 52 may be a motor or a
motor/generator. Crankshaft 140 of engine 10 and electric machine
52 are connected via transmission 54 to vehicle wheels 55 when one
or more clutches 56 are engaged. In the depicted example, a first
clutch 56 is provided between crankshaft 140 and electric machine
52, and a second clutch 56 is provided between electric machine 52
and transmission 54. Controller 12 may send a signal to an actuator
of each clutch 56 to engage or disengage the clutch, so as to
connect or disconnect crankshaft 140 from electric machine 52 and
the components connected thereto, and/or connect or disconnect
electric machine 52 from transmission 54 and the components
connected thereto. Transmission 54 may be a gearbox, a planetary
gear system, or another type of transmission.
[0022] The powertrain may be configured in various manners
including as a parallel, a series, or a series-parallel hybrid
vehicle. In electric vehicle embodiments, a system battery 58 may
be a traction battery that delivers electrical power to electric
machine 52 to provide torque to vehicle wheels 55. In some
embodiments, electric machine 52 may also be operated as a
generator to provide electrical power to charge system battery 58,
for example, during a braking operation. It will be appreciated
that in other embodiments, including non-electric vehicle
embodiments, system battery 58 may be a typical starting, lighting,
ignition (SLI) battery coupled to an alternator.
[0023] Vehicle wheels 55 may include mechanical brakes 59 to slow
the rotation of vehicle wheels 55. Mechanical brakes 59 may include
friction brakes, such as disc brakes or drum brakes, or
electromagnetic (e.g., electromagnetically-actuated) brakes, for
example, both friction brakes and electromagnetic brakes configured
to slow the rotation of vehicle wheels 55, and thus the linear
motion of vehicle 5. As an example, mechanical brakes 59 may
include a hydraulic brake system comprising brake calipers, a brake
servo, and brake lines configured to carry brake fluid between the
brake servo and the brake calipers. Mechanical brakes 59 may be
configured such that a braking torque applied to wheels 55 by the
brake system varies according to the pressure of brake fluid within
the system, such as within the brake lines. Furthermore, vehicle
operator 130 may depress a brake pedal 133 to control an amount of
braking torque supplied by mechanical brakes 59, such as by
controlling the pressure of brake fluid within the brake lines, to
slow vehicle 5 and/or hold vehicle 5 stationary. For example, a
brake pedal position sensor 137 may generate a proportional brake
pedal position signal BPP, which may be used to determine the
amount of braking torque requested by vehicle operator 130.
[0024] Cylinder 14 of engine 10 can receive intake air via a series
of intake passages 142 and 144 and an intake manifold 146. Intake
manifold 146 can communicate with other cylinders of engine 10 in
addition to cylinder 14. In some examples, one or more of the
intake passages may include a boosting device, such as a
turbocharger or a supercharger. For example, FIG. 1 shows engine 10
configured with a turbocharger 170, including a compressor 174
arranged between intake passages 142 and 144 and an exhaust turbine
176 arranged along an exhaust passage 135. Compressor 174 may be at
least partially powered by exhaust turbine 176 via a shaft 180. In
examples where turbocharger 170 is a variable geometry turbocharger
(VGT), an effective aspect ratio of exhaust turbine 176 may be
varied.
[0025] In some examples, a throttle 162 including a throttle plate
164 may be provided in the engine intake passages for varying a
flow rate and/or pressure of intake air provided to the engine
cylinders. For example, throttle 162 may be positioned downstream
of compressor 174, as shown in FIG. 1, or may be alternatively
provided upstream of compressor 174. A throttle position sensor may
be provided to measure a position of throttle plate 164. However,
in other examples, engine 10 may not include throttle 162.
[0026] An exhaust manifold 148 can receive exhaust gases from other
cylinders of engine 10 in addition to cylinder 14. An exhaust gas
sensor 128 is shown coupled to exhaust manifold 148 upstream of a
plurality of emission control devices. Exhaust gas sensor 128 may
be a temperature sensor positioned to measure a temperature of the
exhaust gases. In the example shown, the plurality of emission
control devices includes a diesel oxidation catalyst (DOC) 178 and
a diesel particulate filter (DPF) 181. DOC 178 may be a
stainless-steel canister that contains a honeycomb structure (to
increase surface area within DOC 178) coated with catalytic metals
such as platinum or palladium. When exhaust gases such as carbon
monoxide or hydrocarbons touch the inner surfaces of DOC 178, the
gases are oxidized and may produce water and small amounts of
carbon dioxide. DPF 181 may be a ceramic filter with a honeycomb
structure used to capture particulate matter (e.g., soot). After
capturing soot, DPF 181 is heated up to high temperatures (e.g.,
around 600 Kelvin) by the exhaust gases to oxidize and burn the
soot within DPF 181. The oxidation and burning of the soot from DPF
181 is an event herein referred to as regeneration. In some
examples, additional emission control devices may be included in
the plurality of emission control devices, such as a NOx trap
and/or a selective catalytic reduction (SCR) system. Although
exhaust gas sensor 128 is shown coupled upstream of DOC 178, in
other examples, exhaust gas sensor 128 may be coupled between DOC
178 and DPF 181, downstream of DPF 181, or in one or more of the
three locations.
[0027] Each cylinder of engine 10 may include one or more intake
valves and one or more exhaust valves. For example, cylinder 14 is
shown including at least one intake poppet valve 150 and at least
one exhaust poppet valve 156 located at an upper region of cylinder
14. In some examples, each cylinder of engine 10, including
cylinder 14, may include at least two intake poppet valves and at
least two exhaust poppet valves located at an upper region of the
cylinder. Intake valve 150 may be controlled by controller 12 via
an actuator 152. Similarly, exhaust valve 156 may be controlled by
controller 12 via an actuator 154. The positions of intake valve
150 and exhaust valve 156 may be determined by respective valve
position sensors (not shown) and/or camshaft position sensors (not
shown).
[0028] During some conditions, controller 12 may vary the signals
provided to actuators 152 and 154 to control the opening and
closing of the respective intake and exhaust valves. The valve
actuators may be of an electric valve actuation type, a cam
actuation type, or a combination thereof. The intake and exhaust
valve timing may be controlled concurrently, or any of a
possibility of variable intake cam timing, variable exhaust cam
timing, dual independent variable cam timing, or fixed cam timing
may be used. Each cam actuation system may include one or more cams
and may utilize one or more of cylinder deactivation valve control
(CDVC), cam profile switching (CPS), variable cam timing (VCT),
variable valve timing (VVT), variable valve lift (VVL), and/or a
continuous variable valve lift (CVVL) systems that may be operated
by controller 12 to vary valve operation. For example, cylinder 14
may alternatively include an intake valve controlled via electric
valve actuation and an exhaust valve controlled via cam actuation,
including CPS and/or VCT. In other examples, the intake and exhaust
valves may be controlled by a common valve actuator (or actuation
system) or a variable valve timing actuator (or actuation system).
Actuator 152 and/or actuator 154 may be included in a decompression
device 153. In one example, decompression device 153 may be the
CVVL system and may be used to control valve lift during engine
braking, such as to release compressed gas from cylinder 14 by
opening exhaust valve 156 near top dead center. In other examples,
decompression device 153 may be another type of compression release
engine brake, such as a Jacobs (e.g., Jake) brake.
[0029] As further described herein, intake valve 150 and/or exhaust
valve 156 may be deactivated during selected conditions, such as
when decreased torque demand is requested and one or more cylinders
of engine 10 are operated unfueled. The number and identity of
cylinders operated unfueled may be symmetrical or asymmetrical,
such as by selectively discontinuing fueling to one or more
cylinders on only a first engine bank, selectively discontinuing
fueling to one or more cylinders on only a second engine bank, or
selectively discontinuing fueling to one or more cylinders on each
of the first and second engine banks. As another example,
combustion may be discontinued in one or more cylinders of engine
10 during engine braking. In the case of engine braking, intake
valve 150 and/or exhaust valve 156 may be adjusted by decompression
device 153.
[0030] Cylinder 14 can have a compression ratio, which is a ratio
of volumes when piston 138 is at bottom dead center (BDC) to top
dead center (TDC). In one example, the compression ratio is in the
range of 14:1 to 25:1. However, in some examples, such as where
different fuels are used, the compression ratio may be
increased.
[0031] In some examples, each cylinder of engine 10 may be
configured with one or more fuel injectors for providing fuel
thereto. As a non-limiting example, cylinder 14 is shown including
one fuel injector 166. Fuel injector 166 is shown coupled directly
to cylinder 14 for injecting fuel directly therein in proportion to
the pulse-width of signal FPW received from controller 12 via an
electronic driver 168. In this manner, fuel injector 166 provides
what is known as direct injection (hereafter also referred to as
"DI") of fuel into combustion cylinder 14. While FIG. 1 shows
injector 166 as a side injector, it may also be located overhead of
the piston, such above the piston between intake valve 150 and
exhaust valve 156. Alternatively, the injector may be located
overhead and near the intake valve to increase mixing. Fuel may be
delivered to fuel injector 166 from a high pressure fuel system 8
including fuel tanks, fuel pumps, and a fuel rail. Alternatively,
fuel may be delivered by a single stage fuel pump at lower
pressure, in which case the timing of the direct fuel injection may
be more limited during the compression stroke than if a high
pressure fuel system is used. Further, while not shown, the fuel
tanks may have a pressure transducer providing a signal to
controller 12.
[0032] It will be appreciated that in an alternative embodiment,
fuel injector 166 may be a port injector providing fuel into the
intake port upstream of cylinder 14. Further, while the example
embodiment shows fuel injected to the cylinder via a single
injector, the engine may alternatively be operated by injecting
fuel via multiple injectors, such as one direct injector and one
port injector. In such a configuration, the controller may vary a
relative amount of injection from each injector.
[0033] Fuel may be delivered by fuel injector 166 to the cylinder
during a single cycle of the cylinder. Further, the distribution
and/or relative amount of fuel delivered from the injector may vary
with operating conditions, such as air charge temperature, as
described herein below. Furthermore, for a single combustion event,
multiple injections of the delivered fuel may be performed per
cycle. The multiple injections may be performed during the
compression stroke, intake stroke, or any appropriate combination
thereof.
[0034] Fuel tanks in fuel system 8 may hold fuels of different fuel
types, such as fuels with different fuel qualities and different
fuel compositions. The differences may include different cetane
numbers, different heats of vaporization, different fuel blends,
different additives, and/or combinations thereof, etc. A few
examples of different fuels includes diesel as a first fuel type,
biodiesel as a second fuel type, and kerosene as a third type.
Moreover, fuel characteristics of one or all fuel tanks may vary
frequently, for example, due to day to day variations in tank
refilling, and/or seasonally, such as due to different seasonal
fuel blends. However, in an alternative embodiment, engine 10 is a
gasoline engine, and the fuels held in fuel system 8 may include
one or more gasoline blends.
[0035] External exhaust gas recirculation (EGR) may be provided to
the engine via a high pressure EGR system 83, delivering exhaust
gas from a zone of higher pressure in exhaust passage 135 to a zone
of lower pressure in intake manifold 44, via an EGR passage 81.
However, in other examples, EGR system 83 may be a low pressure EGR
system, where EGR passage 81 is coupled between exhaust passage 135
downstream of turbine 176 and intake passage 142 upstream of
compressor 174. In still other examples, both high pressure EGR and
low pressure EGR loops may be included.
[0036] An amount EGR provided to intake manifold 44 may be varied
by controller 12 via an EGR valve 80. For example, controller 12
may be configured to actuate and adjust a position of EGR valve 80
to adjust the amount of exhaust gas flowing through EGR passage 81.
EGR valve 80 may be adjusted between a fully closed position, in
which exhaust gas flow through EGR passage 81 is blocked, and a
fully open position, in which exhaust gas flow through the EGR
passage is maximally enabled. As an example, EGR valve 80 may be
continuously variable between the fully closed position and the
fully open position. As such, the controller may increase a degree
of opening of EGR valve 80 to increase an amount of EGR provided to
intake manifold 44 and decrease the degree of opening of EGR valve
80 to decrease the amount of EGR provided to intake manifold 44. As
an example, EGR valve 80 may be an electronically activated
solenoid valve. In other examples, EGR valve 80 may be positioned
by an incorporated stepper motor, which may be actuated by
controller 12 to adjust the position of EGR valve 80 through a
range of discreet steps (e.g., 52 steps), or EGR valve 80 may be
another type of flow control valve. Further, EGR may be cooled via
passing through an EGR cooler 85 within EGR passage 81. EGR cooler
85 may reject heat from the EGR gases to engine coolant, for
example.
[0037] Under some conditions, EGR system 83 may be used to regulate
a temperature of an air and fuel mixture within the combustion
chamber. Further, EGR may be desired to attain a desired engine
dilution, thereby increasing fuel efficiency and emissions quality,
such as emissions of nitrogen oxides. As an example, EGR may be
requested at low-to-mid engine loads. Thus, it may be desirable to
measure or estimate an EGR mass flow. EGR sensors may be arranged
within EGR passage 81 and may provide an indication of one or more
of mass flow, pressure, and temperature of the exhaust gas, for
example. An amount of EGR requested may be based on engine
operating conditions, including engine load (as estimated via
accelerator pedal position sensor 134), engine speed (as estimated
via a crankshaft acceleration sensor), engine temperature (as
estimated via an engine coolant temperature sensor 116), etc. For
example, controller 12 may refer to a look-up table having the
engine speed and load as the input and output a desired amount of
EGR corresponding to the input engine speed-load. In another
example, controller 12 may determine the desired amount of EGR
(e.g., desired EGR flow rate) through logic rules that directly
take into account parameters such as engine load, engine speed,
engine temperature, etc. In still other examples, controller 12 may
rely on a model that correlates a change in engine load with a
change in a dilution request, and further correlates the change in
the dilution request with a change in the amount of EGR requested.
For example, as the engine load increases from a low load to a mid
load, the amount of EGR requested may increase, and then as the
engine load increases from a mid load to a high load, the amount of
EGR requested may decrease. Controller 12 may further determine the
amount of EGR requested by taking into account a best fuel economy
mapping for a desired dilution rate. After determining the amount
of EGR requested, controller 12 may refer to a look-up table having
the requested amount of EGR as the input and a signal corresponding
to a degree of opening to apply to EGR valve 80 (e.g., as sent to
the stepper motor or other valve actuation device) as the
output.
[0038] Controller 12 is shown in FIG. 1 as a microcomputer,
including a microprocessor unit 106, input/output ports 108, an
electronic storage medium for executable programs (e.g., executable
instructions) and calibration values shown as non-transitory
read-only memory chip 110 in this particular example, random access
memory 112, keep alive memory 114, and a data bus. Controller 12
may receive various signals from sensors coupled to engine 10,
including the signals previously discussed and additionally
including a measurement of inducted mass air flow (MAF) from a mass
air flow sensor 122; an engine coolant temperature (ECT) from a
temperature sensor 116 coupled to a cooling sleeve 118; a profile
ignition pickup signal (PIP) from a Hall effect sensor 120 (or
other type) coupled to crankshaft 140; a temperature signal from
exhaust gas sensor 128, which may be used by controller 12 to
determine the temperature of the exhaust gas; a signal from an
exhaust differential pressure sensor 182 that measures a pressure
difference between upstream of DPF 181 and downstream of DPF 181;
and an absolute manifold pressure signal (MAP) from a MAP sensor
124. An engine speed signal, RPM, may be generated by controller 12
from signal PIP. The manifold pressure signal MAP from MAP sensor
124 may be used to provide an indication of vacuum or pressure in
the intake manifold. Controller 12 may infer an engine temperature
based on the engine coolant temperature.
[0039] Controller 12 receives signals from the various sensors of
FIG. 1 and employs the various actuators of FIG. 1 to adjust engine
operation based on the received signals and instructions stored on
a memory of the controller. For example, upon receiving a signal
from accelerator pedal position sensor 134 or brake pedal position
sensor 137 indicating that braking is requested, controller 12 may
discontinue fueling to cylinder 14 by discontinuing signal FPW from
electronic driver 168 so that fuel is not delivered via fuel
injector 166 and may further adjust intake valve 150 and exhaust
valve 156 via actuators 152 and 154, respectively.
[0040] As described above, FIG. 1 shows only one cylinder of a
multi-cylinder engine. As such, each cylinder may similarly include
its own set of intake/exhaust valves, fuel injector(s), etc. It
will be appreciated that engine 10 may include any suitable number
of cylinders, including 2, 3, 4, 5, 6, 8, 10, 12, or more cylinders
in various configurations. Further, each of these cylinders can
include some or all of the various components described and
depicted by FIG. 1 with reference to cylinder 14.
[0041] As elaborated above, DPF 181 captures soot to reduce an
amount of particulate matter emitted from vehicle 5. DPF
regeneration (oxidization and burning of the soot to empty DPF 181)
is used to reduce exhaust backpressure, for example, and to enable
DPF 181 to continue capturing soot. In order to burn the soot from
DPF 181, it is desired for the exhaust gases flowing through the
exhaust system to reach temperatures around 600 K. However, the
exhaust gases may not reach the desired temperatures for
regeneration during nominal engine operation. For example, extended
high speed operation of vehicle 5 may result in exhaust gases being
hot enough to passively regenerate DPF 181, but when vehicle 5 is
not driven at high speeds for extended periods (e.g., due to
in-town driving), the exhaust gases may not be hot enough to
regenerate DPF 181. Therefore, active DPF regeneration may be
triggered once the amount of soot captured surpasses a soot load
threshold, which will be elaborated below in regard to FIG. 2.
Active DPF regeneration includes post combustion fuel injection,
referred to herein as "post injection," wherein unburnt fuel is
delivered to DOC 178, where the oxidation of the unburnt fuel
produces an increase in the exhaust gas temperature (e.g.,
exotherms) at an inlet of DPF 181. However, fuel post injection
increases fuel consumption and cylinder wall wetting.
[0042] Further, combustion may be discontinued in one or more
cylinders during some engine operating conditions, which may
further reduce exhaust gas temperatures and/or reduce air flow
through the engine, which may in turn reduce an amount of fuel that
can be delivered via post injection. For example, due to a low
torque demand, one or more cylinders (e.g., cylinder 14) within the
engine may be deactivated to increase fuel economy. Since
combustion is occurring in fewer cylinders, the exhaust gas
temperature may decrease. As another example, engine braking, which
may be facilitated by decompression device 153, may be used to slow
vehicle 5, causing the cylinders to be used for decompression
braking instead of for combustion. As such, similar to deactivating
cylinders, the exhaust gas temperatures may not reach the desired
600 K for DPF regeneration. As such, control methods that enable
robust DPF regeneration while combustion is discontinued may
increase an efficiency of DPF regeneration, thereby decreasing the
exhaust backpressure for more efficient engine operation and
enabling DPF 181 to capture additional soot particulates.
[0043] Therefore, FIG. 2 shows an example method 200 for operating
an engine with post fuel injection for DPF regeneration during a
cylinder deactivation event in a vehicle. For example, the DPF may
be DPF 181 of vehicle 5 shown in FIG. 1, and an example cylinder
that may be deactivated may be cylinder 14, also shown in FIG. 1.
Although method 200 will be described with respect to the engine
system and components shown in FIG. 1, method 200 may be applied to
other engine systems without departing from the scope of this
disclosure. Instructions for carrying out method 200 and the rest
of the methods included herein may be executed by a controller
(e.g., controller 12 of FIG. 1) based on instructions stored on a
memory of the controller and in conjunction with signals received
from sensors of the engine system, such as the sensors described
above with reference to FIG. 1 and elaborated below. The controller
may employ actuators of the engine system to adjust engine
operation, such as by adjusting operation of a fuel injector (e.g.,
fuel injector 166 of FIG. 1) to perform the post injection of
fuel.
[0044] At 202, method 200 includes estimating operating conditions.
The operating conditions may include, for example, an exhaust gas
temperature, an accelerator pedal position (e.g., signal PP output
by a pedal position sensor), an engine temperature (e.g., as
estimated from an output of an engine coolant temperature sensor,
such as engine coolant temperature sensor 116 of FIG. 1), a mass
air flow of intake air provided to the engine (e.g., MAF), a torque
demand, a boost demand, a fuel injection amount and timing, a
position of an EGR valve (e.g., EGR valve 80 of FIG. 1), cylinder
valve lift and timing settings, and an exhaust gas pressure. As an
example, the exhaust gas pressure may be a differential pressure
measured by an exhaust differential pressure sensor (e.g., exhaust
differential pressure sensor 182 of FIG. 1). A signal received by
the controller from the exhaust differential pressure sensor may
indicate a difference in exhaust pressure between a position
upstream of the DPF, before the exhaust gases flow through the DPF,
and a position downstream of the DPF, after the exhaust gases flow
through the DPF. Further, the controller may use the differential
pressure to estimate a soot load of the DPF. As another example,
the soot load may be measured virtually by the controller
inputting, for example, the engine speed and the exhaust
temperature into a look-up table, algorithm, or map, which may
output the estimated soot load. As another example, the exhaust gas
temperature may be measured by an exhaust gas sensor (e.g., exhaust
gas sensor 128 shown in FIG. 1) and indicates the temperature of
the exhaust gas.
[0045] At 204, method 200 includes determining if DPF regeneration
is requested. DPF regeneration may be requested when the soot load
increases above an upper soot load threshold. The upper soot load
threshold may be a positive non-zero value stored within a memory
of the controller. This non-zero value may be a percentage of the
DPF covered in soot. In one example, at the upper soot load
threshold may be approximately 45% of a soot holding capacity of
the DPF. In other examples, the upper soot load threshold may be
higher than 45% (e.g., 60%) or lower than 45% (e.g., 40%) of the
soot holding capacity of the DPF. If the soot load is not at or
above the upper soot load threshold, then DPF regeneration may not
be requested, although passive DPF regeneration may still occur
while the vehicle is driven at highway speeds (e.g., 60-70 mph) for
extended periods (e.g., 20-30 minutes). Due to the high
temperatures used for DPF regeneration, the request for DPF
regeneration is a request for generating exotherms in the exhaust
system (e.g., at the DOC).
[0046] If DPF regeneration has not been requested, such as when the
soot load does not increase above the upper soot load threshold,
method 200 proceeds to 206 and includes not increasing the exhaust
gas temperature via adjustments to engine operation. As such,
engine operating parameters will not be adjusted to facilitate
active regeneration. For example, post fuel injection will not be
performed, as raising the DPF temperature by generating exotherms
in the exhaust system is not desired, and the EGR valve may
adjusted based on a desired engine dilution. Method 200 may then
end.
[0047] Returning to 204, if DPF regeneration has been requested,
method 200 proceeds to 208 and includes determining if cylinder
deactivation has been requested. For example, conditions for
cylinder deactivation may be met if the torque demand, or engine
load, is below a threshold torque demand (or engine load). The
threshold torque demand (or engine load) may be a pre-determined,
non-zero value stored in controller memory below which a subset of
cylinders may be able to produce the demanded torque, enabling the
engine to operate at higher efficiency and increased fuel economy.
For example, the engine may be a variable displacement engine
(VDE). Further, deactivating cylinders may be enabled only if the
engine coolant temperature is above a threshold to preempt cold
cylinder related issues, which may result in higher particulate
matter generation.
[0048] If cylinder deactivation has not been requested, method 200
proceeds to 210 and includes providing main injection fueling to
each cylinder. For example, a fuel injector (e.g., fuel injector
166 shown in FIG. 1) coupled to each cylinder may be actuated
within a compression stoke of the corresponding cylinder to deliver
the main injection fueling. An amount of fuel injected may be
determined based on the torque demand. For example, when the torque
demand is higher, more fuel may be provided to the cylinder to
increase the amount of torque produced during combustion. As one
example, the controller may input the torque demand into a look-up
table, algorithm, or map, which may output the amount of fuel to
inject. Further, the amount to fuel to inject may be delivered via
one or more injections. In this way, the main fuel injection
provides fuel for combustion in every cylinder, thereby producing
engine torque in every cylinder during an engine cycle.
[0049] At 212, method 200 includes increasing the exhaust gas
temperature via adjustments to engine operation. For example, to
increase the exhaust gas temperature, additional oxygen may be
provided to the cylinders by adjusting the intake valve timing or
positioning the VGT vanes to increase boost, and post fuel
injections may be provided to react with the additional oxygen at a
DOC positioned upstream of the DPF (e.g., DOC 178 of FIG. 1) to
generate exotherms for heating the DPF. In another example, the EGR
valve may be closed to increase an amount of hot exhaust gas
flowing to the DPF. For regeneration to occur, a temperature of the
DPF may be increased to at least a threshold temperature. The
threshold temperature may be a non-zero, positive temperature value
stored in controller memory at or above which soot is burned from
the DPF. As one example, the threshold temperature is within a
range between 550 and 650 K. For example, the threshold temperature
may be 600 K. With the DPF temperature reaching the threshold
temperature, regeneration may occur, and soot trapped within the
DPF may be burned to reduce the soot load of the DPF.
[0050] Further, the DPF regeneration may be continued until the
soot load of the DPF is decreased to a lower threshold soot load
(e.g., lower than the upper threshold soot load). The lower
threshold soot load may be a pre-determined value stored in the
memory of the controller that corresponds to the DPF being
substantially empty. For example, the lower threshold soot load may
be in a range from 0-10% of the DPF soot holding capacity. As an
example, the lower threshold soot load may be 5%. Additionally,
fuel post injection may occur in active cylinders close to the
exhaust valve opening. Once the DPF regeneration reaches the lower
threshold soot load, the engine may be operated as described above
at 206, for example.
[0051] Method 200 may then end. For example, method 200 may be
repeated at a pre-determined frequency during engine operation to
provide DPF regeneration responsive to the soot load reaching the
upper threshold load, for example.
[0052] Returning to 208, if cylinder deactivation is requested,
then method 200 proceeds to 216 and includes selecting cylinder(s)
for deactivation. For example, the number of cylinders to be
deactivated may increase as the driver torque demand decreases. In
still other examples, the controller may determine a desired
induction ratio (a total number of cylinder firing events divided
by a total number of cylinder compression strokes) based at least
on torque demand. The controller may determine the number of
cylinders to deactivate (or the desired induction ratio) by
inputting the operating conditions, such as one or more of the
torque demand and the engine load, into one or more look-up tables,
maps, or algorithms and outputting the number of cylinders to
deactivate for the given conditions.
[0053] In some examples, the controller may select a group of
cylinders and/or an engine bank to deactivate based on the
operating conditions. The selection may be based on, for example,
which group of cylinders was deactivated during a previous cylinder
deactivation event. For example, if during the previous cylinder
deactivation event, a first group of cylinders were deactivated,
then the controller may select a second group of cylinders that is
different than the first group of cylinders for deactivation during
the present cylinder deactivation event. In still another example,
cylinder deactivation may be restricted to specific cylinders due
to hardware of the engine. Using a V-8 engine as an example, the
hardware may restrict deactivation to two specific cylinders from
each engine bank, for example. In still other examples, a cylinder
deactivation pattern may be selected based on the torque demand in
order to maintain vehicle operability and driveability, as the
remaining fueled cylinders provide all of the engine torque.
Further, the cylinder deactivation pattern may be selected in order
to mitigate engine noise, vibration, and harshness (NVH) depending
on a configuration of the engine (e.g., a layout and a total number
of cylinders) and may include determining a duration of
deactivation of each cylinder in the selected pattern.
[0054] At 218, the method 200 includes deactivating the selected
cylinder(s). Deactivating the selected cylinder(s) refers to
discontinuing combustion in the selected cylinder(s). Deactivating
the selected cylinder(s) includes discontinuing the main injection
fueling of the selected cylinder(s), as indicated at 220. Main
injection fueling of the cylinders is stopped by the controller
discontinuing a fuel pulse-width signal to the fuel injector
coupled to the each of the selected cylinder(s). As such, there is
no longer fuel available to the cylinder for combustion.
[0055] In addition to discontinuing main injection fueling of the
cylinder(s) selected for deactivation, deactivating the selected
cylinder(s) further includes maintaining the intake or exhaust
valve of the selected cylinder(s) open, as indicated at 222.
Depending on a desired fuel post injection timing, the controller
may select between maintaining open the exhaust and maintaining
open the intake valve. The exhaust valve may be held open for later
fuel post injection timings while the intake valve may be held open
during earlier fuel post injection timings, which will be further
elaborated with respect to FIG. 4.
[0056] At 224, method 200 includes performing post injection of the
fuel during a threshold timing range each engine revolution. As
will be elaborated with respect to FIG. 4, the threshold timing
range may reduce wall wetting, bore washing, and fuel-in-oil
dilution while still enabling exotherms to be generated at the DOC
to increase the DPF temperature to the temperature threshold for
DPF regeneration during cylinder deactivation. In some examples,
performing the post injection of fuel during the threshold timing
range each engine revolution (e.g., a 360.degree. revolution of a
crankshaft of the engine) includes performing the post injection in
one or more deactivated cylinder(s) and not in active cylinder(s),
as optionally indicated at 226. For example, active cylinder(s) may
not receive any fuel post injection, but still may receive main
injections of fuel for producing engine torque via combustion. As
such, the fuel injectors of the active cylinder(s) may be actuated
during the compression stroke for main injection fueling, but may
not be actuated for any additional fuel injections during the
compression stroke or during the exhaust stroke. In other examples,
performing the post injection of fuel during the threshold timing
range each engine revolution includes preforming the post injection
in one or more deactivated cylinder(s) and also in active
cylinder(s), as optionally indicated at 228. In such examples, the
fuel post injection, described in method 400 of FIG. 4, may be
injected into a selected number of active and deactivated
cylinder(s). For example, some or all active cylinder(s) may first
receive the main fuel injection close to BDC of the compression
stroke and then receive additional fuel injections within the
threshold timing range that will be described with respect to FIG.
4. The controller may determine to increase or decrease the number
of cylinder(s) receiving the post injection, both active and
deactivated, based on if the temperature of the exhaust gas. For
example, the controller may increase the number of cylinder(s)
receiving the fuel post injection to increase the exhaust gas
temperature.
[0057] Method 200 may then end. For example, method 200 may be
repeated responsive to a change in the operating conditions in
order to reactivate deactivated cylinders (e.g., responsive to an
increased torque demand) or to discontinue DPF regeneration
responsive to the soot load of the DPF decreasing below the lower
threshold soot load. Note that in some examples, cylinder
deactivation may already be occurring before DPF regeneration is
requested. In such cases, the selected cylinder(s) may be
deactivated before regeneration is requested at 202. However, post
fuel injection may not occur in these cylinders until DPF
regeneration is requested.
[0058] Turning now to FIG. 3, an example method 300 for operating
an engine with post fuel injection for DPF regeneration during an
engine braking event in a vehicle is shown. For example, the DPF
may be DPF 181 shown in FIG. 1. As another example, engine braking
may be performed by a decompression device, such as decompression
device 153 shown in FIG. 1. Although method 300 will be described
with respect to the engine system and components shown in FIG. 1,
method 300 may be applied to other engine systems without parting
from the scope of this disclosure. Instructions for carrying out
method 300 may be executed by a controller (e.g., controller 12 of
FIG. 1) based on instructions stored on a memory of the controller
and in conjunction with signals received from sensors of the engine
system, such as the sensors described above with reference to FIG.
1 and elaborated below. The controller may employ actuators of the
engine system to adjust engine operation, such as by adjusting
operation of fuel injectors to inject fuel post injections within
cylinders of the engine.
[0059] Method 300 starts at 302, which includes estimating
operating conditions. The operating conditions may include, for
example, an engine speed, an intake manifold pressure (e.g., MAP),
a mass air flow of intake air provided to the engine (e.g., MAF),
an engine temperature, a torque demand, a boost demand, a fuel
injection amount and timing, cylinder valve lift and timing
settings, an exhaust gas temperature, a desired engine dilution, a
soot load of the DPF, a brake pedal position, an accelerator pedal
position, etc., such as elaborated above with respect to 202 of
FIG. 2. As one example, the brake pedal position and the
accelerator pedal position may be determined based on signals
received from respective pedal position sensors (e.g., brake pedal
position sensor 137 and accelerator pedal position sensor 134 of
FIG. 1, respectively). Together, the accelerator pedal position and
the brake pedal position may be used by the controller to determine
the torque demand, which may be a positive torque demand or a
negative (e.g., braking) torque demand.
[0060] At 304, method 300 includes determining if DPF regeneration
is requested. As described above at 204 of method 200, DPF
regeneration may be requested if the soot load has surpassed the
upper soot load threshold.
[0061] If DPF regeneration is not requested at 304, method 300
proceeds to 306 and includes not increasing the exhaust gas
temperature via adjustments to engine operation. Similar to 206 of
method 200, if the soot load has not surpassed the upper soot load
threshold, engine operating parameters will not be adjusted to
facilitate active regeneration. For example, post fuel injection
will not be performed, and an EGR valve may be adjusted to provide
the desired engine dilution.
[0062] The method 300 may then end. For example, method 300 may be
repeated at a pre-determined frequency during engine operation
and/or responsive to a change in the operating conditions in order
to provide efficient DPF regeneration responsive to the soot load
exceeding the upper soot load threshold, for example.
[0063] If DPF regeneration is requested at 304, then method 300
continues to 308, which includes determining if engine braking is
requested. For example, engine braking may be requested responsive
to a change in one or more of the accelerator pedal position and
the brake pedal position. As an example, engine braking may be
requested responsive to a tip-out event, where the accelerator
pedal position changes from a depressed position to an undepressed,
neutral position or a less depressed position. As another example,
engine braking may be requested responsive to the brake pedal
position increasing (e.g., being further depressed). As still
another example, engine braking may be requested responsive to a
decrease in the demanded torque and/or in response to a non-zero
requested brake torque, as determined from the accelerator pedal
position and the brake pedal position. Further, engine braking may
be requested when the engine speed is greater than a threshold
engine speed. The threshold engine speed may be a pre-determined,
non-zero engine speed stored in memory below which further slowing
the engine (e.g., via engine braking) may result in the engine
inadvertently shutting off.
[0064] If engine braking is not requested, method 300 continues to
310, which includes not operating the decompression device. As
described above with respect to FIG. 1, the decompression device
may be a CVVL system used to control intake and exhaust valves for
engine braking or may be a Jake brake. For example, when the CVVL
system is not operated as a decompression device, it may be used to
facilitate combustion in the cylinders by opening and closing the
intake and exhaust valves during intake and exhaust strokes,
respectively.
[0065] At 312, the method 300 includes providing main injection
fueling to each cylinder. Similar to 210 of method 200, a fuel
injector (e.g., fuel injector 166 shown in FIG. 1) coupled to each
cylinder is actuated by the controller within the compression stoke
of the corresponding cylinder. In this way, the main fuel injection
provides fuel to mix with air introduced to the cylinder by an
intake valve opening, and both are compressed by a piston until
combustion occurs, producing torque to power the vehicle.
[0066] At 314, the method 300 includes increasing the exhaust gas
temperature via adjustment to engine operation, as explained above
at 212 of method 200. Method 300 may then end. For example, method
300 may be repeated responsive to the operating conditions changing
so that active DPF regeneration may be discontinued once the soot
load decreases below a lower soot load threshold (e.g., the lower
soot load threshold discussed above with respect to FIG. 2).
[0067] Returning to 308, if engine braking is requested, then
method 300 continues to 316 and includes discontinuing main
injection fueling. Main injection fueling of the cylinders is
stopped by the controller discontinuing a fuel pulse-width signal
to the fuel injector coupled to each cylinder. As such, there is no
longer fuel available to the cylinder for combustion.
[0068] At 318, method 300 includes operating the decompression
device to control air flow through the engine. As described above
with respect to FIG. 1, the decompression device may be the CVVL
system and may be operated to slow down the vehicle by reducing
compression temperatures and pressures within the cylinder. In one
example, one or more exhaust valves of each cylinder may be held
open throughout the four-stroke engine cycle by the decompression
device, while the intake valve may be operated with a conventional
intake valve timing for the four-stroke cycle, as will be
elaborated herein. As such, the gas within the cylinder is
compressed, but the compression does not create pressures and
temperatures high enough to cause ignition. Around TDC of the
conventional expansion (e.g., power) stroke, the decompression
device allows high pressure gas to flow out of the cylinder via the
open exhaust valve. This outflow, along with the piston moving to
BDC, causes the cylinder pressure to decrease and fall below an
exhaust manifold pressure. Due to the pressure difference between
the cylinder and the exhaust manifold, the cylinder fills with
exhaust gases entering through the opening created by the exhaust
valve during the conventional exhaust stroke. As the intake valve
is opened before TDC of the exhaust stroke, gas in the cylinder
flows into the exhaust manifold via the open exhaust valve and into
the intake manifold via the open intake valve as the cylinder
pressure equilibrates with the exhaust and intake manifold
pressures. During the conventional intake stroke, gas may again
fill the cylinder as the piston moves from TDC to BDC. In this way,
power is not generated in the cylinder as the piston uses energy to
compress the air, and the compressed air is released without
combustion occurring, resulting in a net loss of energy.
[0069] In other examples, one or more intake valves of each
cylinder may be held open while the exhaust valve is operated with
a conventional exhaust valve timing for a four-stroke engine cycle,
as will be elaborated herein. Maintaining the intake valve open
(instead of the exhaust valve) may allow any fuel-rich leakage
across the open valve to flow into the intake manifold, where it
can be re-inducted into the cylinder instead of flowing to the
exhaust manifold. In particular, the intake valve may be held open
when a desired fuel post injection timing is earlier, and the
exhaust valve may be held open when the desired fuel post injection
timing is later, which will be elaborated below with respect to
FIG. 4.
[0070] At 320, the method 300 includes performing a post injection
of fuel during a threshold timing range during each engine
revolution, as will be described in detail with respect to FIG. 4.
As mentioned above with respect to FIG. 2, the threshold timing
range may enable an amount of fuel delivered via post injection
during DPF regeneration while combustion is discontinued to be
increased without increasing wall wetting, for example. The fuel
delivered via the post injection may then flow through the exhaust
system to a DOC (e.g., DOC 178 shown in FIG. 1) to generate
exotherms, increasing the temperature of the exhaust gases at an
inlet of the DPF for DPF regeneration.
[0071] Method 300 may then end. For example, method 300 may be
repeated responsive to a change in the operating conditions so that
combustion may be resumed in each cylinder when engine braking is
no longer requested.
[0072] Continuing now to FIG. 4, an example method 400 for
providing fuel post injection is shown. Although method 400 will be
described with respect to the engine system and components shown in
FIG. 1, method 400 may be applied to other engine systems without
departing from the scope of this disclosure. As an example, method
400 may be performed by a controller (e.g., controller 12 of FIG.
1) as a part of method 200 of FIG. 2 (e.g., at 224) or as a part of
method 300 of FIG. 3 (e.g., at 320). Additionally or alternatively,
method 400 may be performed responsive to a request for fuel post
injection for DPF regeneration while combustion is discontinued in
at least one cylinder of the engine.
[0073] At 402, method 400 includes fully closing an EGR valve. For
example, the EGR valve may be EGR valve 80 of EGR system 83 shown
in FIG. 1. The EGR may be in various open positions that enable
exhaust gases to flow to an intake manifold of the engine before
the controller closes the EGR valve for performing the fuel post
injection. As such, the controller may then send a signal to the
EGR valve to adjust the EGR valve to a fully closed position, where
the exhaust gases are blocked from flowing to the intake manifold.
As another example, the EGR valve may already be in a fully closed
position (e.g., during high engine loads). Instead of closing the
EGR valve, the controller maintains the EGR valve in the fully
closed position. With the EGR valve fully closed, more exhaust
gases reach the DPF, and the fuel provided via the post injection
is prevented from recirculating through the engine and causing
fouling in the intake system.
[0074] At 404, method 400 includes adjusting a VGT based on a
desired air flow through the engine. By adjusting vanes of a
turbine of the VGT, an effective aspect ratio of the turbine is
adjusted. For example, adjusting the VGT turbine vanes to a more
open position enables less flow restriction through the turbine but
may reduce boost at lower engine speeds, while adjusting the vanes
to a more closed position may increase the speed of the turbine
while restricting flow through the turbine. For DPF regeneration,
the VGT is used to adjust the backpressure of the exhaust. In
conditions of decompression braking with all cylinders deactivated,
there is no boost produced. Increasing the exhaust backpressure by
closing the VGT will increase backflow from the exhaust, into the
cylinder and in part into the intake manifold in and around BDC
when the exhaust valve first opens. This will reduce an exhaust
mass flow rate.
[0075] In other embodiments, an intake throttle can be used to
control air flow through the engine. Closing the intake throttle
may decrease the intake manifold pressure and lead to lower initial
and final compression pressures. Backflows from the exhaust,
through the cylinder, and into the intake will also increase during
the period when the exhaust valve is open due to the lower intake
manifold pressure and larger pressure difference across the engine.
This will also reduce the exhaust mass flow rate. Reducing the
exhaust mass flow rate may reduce an occurrence of hydrocarbon slip
(e.g., from the fuel delivered via the post injection) through a
DOC (e.g., DOC 178 shown in FIG. 1). For example, hydrocarbon slip
may refer to hydrocarbons that escape oxidation at the DOC and pass
through the DOC unchanged, which may increase vehicle emissions
and/or cause uncontrolled DPF regeneration.
[0076] At 406, method 400 includes setting a post injection timing
within a threshold timing range (e.g., the threshold timing range
described with respect to FIGS. 2 and 3) relative to TDC of both
compression and exhaust strokes based on desired exhaust gas
properties. As mentioned above, injecting the post injection fuel
during the threshold timing range reduces wall wetting, bore
washing, and fuel-in-oil dilution while still providing additional
heat to the exhaust gas by producing exotherms in the DOC, and thus
to the DPF. As one example, the threshold timing range may
encompass timings between 30 crank angle degrees before TDC of the
compression stroke and 30 degrees after TDC of the compression
stroke and may also encompass timings between 30 crank angle
degrees before TDC of the exhaust stroke and 30 crank angle degrees
after TDC of the exhaust stroke. Thus, the threshold timing range
may be centered at TDC during each engine revolution and span 60
crank angle degrees. In other examples, the threshold timing range
may be larger or smaller than 60 crank angle degrees. For example,
the threshold timing range may span from 40 crank angle degrees
before TDC to 40 degrees after TDC. Further, the threshold timing
range may be stored in non-transitory memory. In some examples, it
may be desirable to favor increased mixing of air with the fuel
delivered via the fuel post injection, which will be described in
further detail with respect to FIG. 5. In such examples, the fuel
post injection may occur earlier within the threshold timing range.
For example, injection may occur before TDC of the compression
stroke and before TDC of the exhaust stroke, both times being when
the temperature of the cylinder is increased allowing for increased
fuel evaporation and mixing with the air. In other examples, it may
be desirable to decrease a likelihood of ignition of the fuel
delivered via the fuel post injection, which will be described in
further detail with respect to FIG. 6. In such examples, the fuel
post injection may occur later within both threshold timing ranges,
after TDC of the compression stroke and after TDC of the exhaust
stroke.
[0077] Therefore, as one example, the controller may set the post
injection timing based on at least an exhaust gas temperature
(e.g., as measured at 202 of method 200 or 302 of method 300). For
example, the controller may input the exhaust gas temperature into
a look-up table, algorithm, or map stored in memory, which may
output the specific post injection timing to use within the
threshold timing range relative to TDC of both the compression
stroke and the exhaust stroke.
[0078] At 408, the method 400 includes determining a post injection
amount based on an air flow through the engine. For example, the
air flow through the engine may be measured by a mass air flow
sensor (e.g., MAF sensor 122 shown in FIG. 1). Increasing the air
flow through the engine may increase the amount of fuel that can be
delivered to the cylinder via post injection since there is more
air available to react with the fuel to generate exotherms at the
DOC. As one example, the controller may input the mass air flow
into a look-up table, algorithm, or map stored in memory, which may
output the post injection amount to use for each post
injection.
[0079] At 410, the method 400 includes injecting the determined
post injection amount at the set post injection timing once per
engine revolution. To inject the fuel for the post injection, the
controller transmits a fuel pulse-width signal corresponding to the
determined post injection amount at the determined timing to the
fuel injector of the cylinder receiving fuel post injection. In
some examples, all cylinders of the engine may receive the fuel
post injection while in other examples, a subset of cylinders may
receive the fuel post injection, such as described above at 224 of
method 200 of FIG. 2. In some examples, the injection of fuel may
be a continuous stream of fuel while in others the fuel may be
injected in multiple, quick pulses. Further, because the fuel post
injection is performed once per engine revolution, two post
injections are performed per cylinder per engine cycle (e.g., one
in the threshold timing range relative to TDC of the compression
stroke and one in the threshold timing range relative to TDC of the
exhaust stroke), as will be further described with respect to FIGS.
5 and 6.
[0080] The method 400 may then end. As one example, method 400 may
be repeated at a pre-determined frequency so that the post
injection amount or timing may be adjusted based on, for example,
changes to the engine air flow or changes to the exhaust gas
temperature. In this way, the controller may accurately maintain
the exhaust gas temperature over a threshold temperature for DPF
regeneration without increasing wall wetting and fuel-in-oil
dilution.
[0081] Together, FIGS. 2-4 provide a method for maintaining DPF
regeneration during events that cool the exhaust system.
Specifically, FIGS. 2 and 4 provide a control routine for
increasing or maintaining the exhaust temperature while cylinders
are deactivated within the engine for increasing engine efficiency,
and FIGS. 3 and 4 provide a control routine for increasing or
maintaining the exhaust temperature while the engine is used to
slow down the vehicle. As a result, the exhaust temperature may
enable DPF regeneration without increasing intake system fouling
and fuel wetting in the cylinder, such as bore washing and
oil-in-fuel dilution.
[0082] Turning now to FIG. 5, a first exemplary timing chart 500
demonstrating fuel post injection timing during DPF regeneration is
shown. In particular, first exemplary timing chart 500 shows a fuel
post injection timing that prioritizes mixing between air and fuel
from the fuel post injection. For exemplary timing chart 500, a
piston position is shown in a plot 502, an exhaust valve lift is
shown in a dashed plot 503, an intake valve lift is shown in a plot
505, an in-cylinder pressure is shown in a plot 504, a cylinder air
mass is shown in a plot 506, a cylinder temperature is shown in a
plot 508, and a fuel injector status is shown in a plot 510. In
addition to the plots, a first crank angle range 512 is indicated
between 150 crank angle degrees (CAD) and 210 CAD, and a second
crank angle range 514 is indicated between 510 CAD and 570 CAD.
[0083] For all of the above, the horizontal axis represents engine
position (in CAD), with the engine position increasing along the
horizontal axis from left to right. For example, one four-stroke
engine cycle is shown, which occurs from 0 to 720 CAD (e.g., two
full rotations of an engine crankshaft). In the example timing
charts, the compression stroke corresponds to an interval from 0
CAD to 180 CAD, the power stroke corresponds to an interval from
180 CAD to 360 CAD, the exhaust stroke corresponds to an interval
from 360 CAD to 540 CAD, and the intake stroke corresponds to an
interval from 540 CAD to 720 CAD. The vertical axis of each plot
represents the labeled parameter. For plot 502, the vertical axis
shows piston position relative to TDC. For plots 504, 506, and 508,
the labeled parameter increases up the vertical axis from bottom to
top. For plots 503 and 505, the valve lift amount increases up the
vertical axis from a fully closed position. For plot 510, the
vertical axis indicates whether the fuel injector is open (e.g.,
the fuel injector is actuated) or closed (e.g., the fuel injector
is not actuated), as labeled.
[0084] First crank angle range 512 begins at 150 CAD, which is
within the compression stroke near TDC, and ends at 210 CAD, which
is within the power stroke near TDC (e.g., ranging between +/-30
CAD ATDC of the compression stroke). Thus, first crank angle range
512 spans 60 CAD. In other examples, the first crank angle range
may begin 40 CAD before TDC of the compression stroke and end 40
CAD after TDC of the compression stroke (e.g., ranging between
+/-40 CAD ATDC of the compression stroke). For example, first crank
angle range 512 may extend from 140 CAD to 220 CAD, spanning 80
CAD. In still other examples, first crank angle range 512 may begin
at another crank angle that is in a range between 30 and 40 CAD
before TDC of the compression stroke and may end at another crank
angle that is in a range between 30 and 40 CAD after TDC of the
compression stroke for range that is between 60 and 80 CAD. The
first crank angle range 512 indicates when in the engine cycle a
first fuel post injection may occur in the cylinder in order to
reduce wall wetting, for example.
[0085] In the example of timing chart 500, the intake valve (plot
505) is maintained open throughout the four-stroke cycle with
relatively low valve lift by a decompression device (e.g.,
decompression device 153 shown in FIG. 1). As the piston rises
toward TDC (plot 502) and compresses the air within the cylinder,
pressure increases within the cylinder (plot 504). Further, the
in-cylinder pressure peaks within first crank angle range 512,
shortly before TDC. As the pressure builds up in the cylinder, the
temperature (plot 508) also increases within the cylinder. However,
a peak in-cylinder pressure and a peak in-cylinder temperature may
be lower than when the intake valve is not held open via the
decompression device.
[0086] In the example shown in FIG. 5, the first fuel post
injection timing is determined based on a desire to increase mixing
between post injected fuel and air. As such, the first fuel post
injection occurs at CAD1, which is near the beginning of first
crank angle range 512 and while the in-cylinder temperature is
peaking (plot 508), as indicated by the fuel injector opening (plot
510). By starting the fuel injection at CAD1, the fuel delivered
via the first fuel post injection may more readily evaporate due to
the high the temperatures of the cylinder (plot 508) caused by the
increasing pressure of the cylinder (plot 504). The evaporation of
the fuel from the first fuel post injection allows for increased
mixing with air in the cylinder. Note that while first exemplary
timing chart 500 shows the fuel injector as continuously open, the
fuel injector may be alternatively pulsed open and closed within
the shown open range. A change in air flow is indicated by the drop
in air mass (plot 506) within the first 30 CAD of the first crank
angle range 512, as the higher pressure gas flows out of the
cylinder via the open intake valve.
[0087] The intake valve is maintained open (instead of the exhaust
valve) when the first fuel post injection is earlier within first
crank angle range 512 to reduce leakage of the injected fuel
through the exhaust valve while the air mass (plot 506) is rapidly
decreasing between approximately 150 CAD and approximately 210 CAD.
Instead, any rich gas outflow may occur through the open intake
valve and may be reintroduced into the cylinder as the air mass
(plot 506) increases after approximately 210 CAD. Further, at least
a portion of the fuel injected during the first fuel post injection
may flow out of the cylinder via the open exhaust valve (dashed
plot 503) during the exhaust stroke.
[0088] In addition to first crank angle range 512, timing chart 500
includes a second crank angle range 514, which indicates a range
during which a second fuel post injection may occur in order to
again reduce wall wetting. The second crank angle range starts at
510 CAD, 30 CAD before TDC of the intake stroke, and ends at 570
CAD, 30 CAD after TDC of the intake stroke. Thus, second crank
angle range 514 is centered on TDC of the exhaust stroke in the
same manner that first crank angle range 512 is centered on TDC of
the compression stroke. In other examples, the second crank angle
range may vary similarly to that described above with respect to
first crank angle range 512, such as beginning at another crank
angle that is in a range between 30 and 40 CAD before TDC of the
exhaust stroke and may end at another crank angle that is in a
range between 30 and 40 CAD after TDC of the exhaust stroke.
[0089] In the example shown in FIG. 5, the second fuel post
injection occurs at CAD2 (plot 510), near the beginning of second
crank angle range 514. By injecting fuel at CAD2, the fuel may be
heated by the temperature of the air within the cylinder (plot 508)
before the temperature decreases due to the air mass (plot 506) in
the cylinder increasing. During the second fuel post injection and
within second crank angle range 514, the in-cylinder pressure (plot
504) is relatively low since the exhaust valve (dashed plot 503) is
partially open at the start of the crank angle range and the intake
valve (plot 505) remains open. With the low pressures, combustion
of the fuel injected during the second fuel post injection will not
occur (e.g., has a decreased probability to occur), and the
injected fuel may enter the exhaust system via the open exhaust
valve and reach the DOC to generate exotherms for DPF regeneration.
For example, the injected fuel may preferentially flow to the
exhaust system instead of the intake system because the valve lift
of the exhaust valve (dashed plot 503) is greater than the valve
lift of the intake valve (plot 505). Further, the air mass (plot
506) flows out of the cylinder during the start of the second crank
angle range 514 until the exhaust valve closes, and the air mass
may again increase within the cylinder during the intake stroke as
air flows into the cylinder via the open intake valve (plot 505) as
the piston moves from TDC to BDC (plot 502). Due to the relatively
high temperatures, the fuel may evaporate and prevent wall wetting
within the cylinder, and the fuel may be exhausted when the exhaust
valve opens during the subsequent exhaust stroke.
[0090] Continuing to FIG. 6, a second exemplary timing chart 600
demonstrates fuel post injection timing during DPF regeneration. In
particular, second exemplary timing chart 600 shows a fuel post
injection timing for decreasing the likelihood of fuel delivered
via the fuel post injection igniting within the cylinder. For
example, the fuel post injection timing shown in FIG. 5 may have a
higher probability of igniting than the fuel post injection timing
described below with respect to FIG. 6 due to the higher
temperatures and pressures present while the fuel is injected at
the timing described with respect to FIG. 5. As similar parameters
are numbered the same in FIG. 6 as in FIG. 5, the parameters will
not be reintroduced.
[0091] In the example shown in FIG. 6, the exhaust valve (dashed
plot 503) is maintained open throughout the four-stroke cycle with
relatively low valve lift by a decompression device, and the first
fuel post injection timing is determined based on the air mass
(plot 506) flowing into and out of the cylinder. In this example,
the first fuel post injection occurs at CAD3, which is near the end
of the first crank angle range 512, as indicated by the fuel
injector opening (plot 510). By starting the first fuel post
injection at CAD3, after the air has flowed out of the cylinder via
the open exhaust valve (dashed plot 503), the fuel may have time to
mix with air within the cylinder, but the temperature of the
cylinder (plot 508) may not be high enough to cause the fuel to
evaporate. Near BDC of the exhaust stroke, the air fuel mixture
flows out of the cylinder and into an exhaust system (e.g., exhaust
manifold 148 shown in FIG. 1), eventually reaching the DOC to
generate exotherms for DPF regeneration.
[0092] The second fuel post injection occurs near the end of the
second crank angle range 514 at CAD4. At TDC of the intake stroke,
the intake valve (plot 503) is opened, allowing air to flow into
the cylinder, as shown by the increasing air mass (plot 506). The
fuel injector (plot 510) is opened at CAD4, providing the second
fuel post injection as the air mass (plot 506) is increasing in the
cylinder. By starting the second post fuel injection at CAD4,
temperatures in the cylinder (plot 508) are low enough that
ignition of the injected fuel will not occur. The fuel delivered
via the second fuel post injection may flow out of the cylinder as
the air mass subsequently decreases during the compression stroke
(plot 506) through the open exhaust valve (plot 505), and may be
oxidized in the DOC to produce exotherms for DPF regeneration.
[0093] Turning now to FIG. 7, an example timeline 700 for a DPF
regeneration during passive regeneration, cylinder deactivation,
and engine braking is shown. For example, the DPF may be DPF 181
and the engine may be engine 10, both shown in FIG. 1. An engine
speed is shown in a plot 702, a DPF soot load is shown in a plot
704, a DPF temperature is shown in a plot 708 while a potential DPF
temperature is shown by a dashed plot 710, a cylinder fueling state
is shown in a plot 712, a decompression mode is shown in a plot
714, a VGT (e.g., VGT 170 shown FIG. 1) position is shown in a plot
716, and an EGR valve position is shown in a plot 718. Further, an
upper soot threshold is shown by a dashed line 706, and a lower
soot threshold is shown by a dashed line 707. The upper soot load
threshold is a higher threshold percentage of the DPF covered by
soot above which active DPF regeneration is requested to reduce
exhaust backpressure, for example (e.g., 45%). The lower soot load
threshold is a lower threshold percentage of the DPF covered in
soot below which active DPF regeneration is discontinued and the
DPF is considered emptied. Further still, a DPF temperature
threshold is shown by a dashed line 709, at or above which soot may
be burned from the DPF. For example, the DPF temperature threshold
may be at least 600 K.
[0094] For all of the above, the horizontal axis represents time,
with time increasing along the horizontal axis from left to right.
The vertical axis represents each labeled parameter. For plots 702,
704, 708, and 710, the labeled parameter increases up the vertical
axis from bottom to top. For plot 712, the vertical axis shows the
cylinder fueling state ranging from all unfueled to all fueled. For
example, the number of fueled cylinder(s) increases up the vertical
axis until all of the cylinders are fueled. As a further example,
fueled in this example means the cylinders are receiving main fuel
injections that are used for combustion within the cylinder. As
such, unfueled cylinders are not receiving main fuel injections,
but the cylinders may receive fuel post injections. For plot 714,
the vertical axis indicates whether the decompression mode is on or
off. For example, when the decompression mode is on, a
decompression device (e.g., decompression device 153 of FIG. 1) is
operated to perform decompression engine braking. As a further
example, when the decompression mode is off, the decompression
device is not operated for decompression engine braking. For plots
716 and 718, the vertical axis shows the position of the VGT and
the EGR valve, respectively, from a fully closed position
("closed") to a fully open position ("open"), as labeled.
[0095] At time t0, all cylinders are fueled and active (plot 712).
The DPF soot load (plot 704) is less than the upper soot load
threshold (dashed line 706), indicating that active DPF
regeneration is not requested. However, the engine is operated at a
relatively high speed (plot 702) and load (not shown), which
increases from time t0 to time t1. Because of the high load
operation, EGR is not requested, and the EGR valve is fully closed
(plot 718). Further, the decompression mode is off (plot 714), as
engine braking is not desired, and the VGT is operated with the VGT
vanes in the fully open position (plot 716) to prevent engine choke
due to the high operating speed. Due to the high operating speed
and load, the exhaust system is relatively hot, and the temperature
of the DPF increases between time t0 and time t1 (plot 708) until
it reaches the threshold DPF temperature (dashed line 709) at time
t1. Because the temperature of the DPF has reached the threshold
DPF temperature at time t1, the DPF soot load (plot 704) begins to
decrease at time t1. Thus, passive DPF regeneration occurs between
time t1 and time t2, as the heat generated through engine operation
alone raises the temperature of the DPF (plot 708) above the
threshold DPF temperature (dashed line 709).
[0096] From time t2 to time t3, a duration in time elapses, as
indicated by the break in the horizontal axis. The duration in time
may be one day or several days, for example, or another period.
From time t3 to time t4, all cylinders are fueled, the
decompression mode (plot 714) is off, as engine braking is not
requested, and the VGT and the EGR valve are each in an open
position (plots 716 and 718, respectively). However, after the
engine speed (plot 702) decreases between time t3 and time t4, the
engine load has also decreased, and conditions for cylinder
deactivation are met. In response, half of the engine cylinders are
deactivated (plot 712) at time t4. Since fewer cylinders are
active, the EGR valve decreases in openness to allow less exhaust
gases to recirculate to the cylinders. Additionally, the VGT is
moved to a more open position at time t4 to allow more air to flow
through the cylinders.
[0097] At time t5, the soot load in the DPF (plot 704) increases
past the upper soot load threshold (dashed line 706). As such, DPF
regeneration is requested at time t5. In response, the EGR valve
(plot 718) is fully closed to prevent any fuel from the post
injection from recirculating to the cylinders and fouling the
intake system, and thus not allowing the fuel from the post
injection to reach the DOC to generate exotherms for heating and
regenerating the DPF. The VGT (plot 716) moves to a more closed
position, increasing the exhaust backpressure and decreasing an
exhaust mass flow rate. Further, fuel post injection is performed
within a threshold timing range each engine revolution, such as
described above with respect to FIGS. 2 and 4. With the changes
made to the engine operation, the DPF temperature (plot 708)
increases until DPF temperature surpasses the temperature threshold
(dashed line 709) for DPF regeneration. Note that the dashed plot
710 shows the potential temperature if the post injection routine
(e.g., closing the EGR valve, controlling air flow with the VGT,
and providing fuel post injection twice within a four-stroke engine
cycle) were not performed to increase the DPF temperature. At time
t4, dashed line 710 remains below the temperature threshold and,
without closing the EGR valve, closing the VGT, and performing fuel
post injection, the DPF would not be able to perform regeneration,
as the DPF temperature is below the temperature threshold. At time
t7, the soot load (plot 704) reaches the lower soot load threshold
(dashed line 707). As such, the DPF is regenerated at time t7, and
the fuel post injections are discontinued.
[0098] Again, a time lapse occurs from time t7 to time t8,
indicated by the break in the horizontal axis, during which the
soot load in the DPF builds up. Similar to the first time lapse
between time t2 to time t3, one or more days may have passed since
the DPF regeneration that occurred from time t3 to time t7.
[0099] At time t8, the soot load of the DPF (plot 704) increases
past the upper soot load threshold. With the upper soot load
threshold surpassed, DPF regeneration is requested. All of the
cylinders are fueled (plot 712) due to the high engine load at time
t8 (not shown), and the VGT is open at a partially open position
(plot 716) due to the high engine load. Further, the EGR valve may
be closed (plot 718) due to the high load operation and to prevent
the fuel from the post injection from being recirculated. In
addition to main fuel injections, one or more cylinder(s) also
receive post fuel injections, creating already hot exhaust gases
that heat the DPF temperature (plot 708) to above the temperature
threshold (dashed line 709).
[0100] At time t9, the DPF regeneration is interrupted by an engine
braking event. In response to the engine braking event, all of the
cylinders are unfueled (plot 712), and the decompression mode (plot
714) is turned on. With the decompression mode on, the intake and
exhaust valves are managed by a decompression device (e.g.,
decompression device 153 shown in FIG. 1) to help slow down the
vehicle, an example of which is shown within FIGS. 5 and 6. The VGT
(plot 716) is moved from the partially open to the closed position.
The closed VGT facilitates braking in addition to the decompression
device by increasing the pressure in the cylinders and also reduced
the exhaust mass flow rate. Further, the EGR valve is maintained
fully closed (plot 718) in response to the engine braking event
while DPF regeneration is requested in order to prevent the fuel
from the post injection from being recirculated.
[0101] As braking occurs and main injection fueling is discontinued
in the cylinders, fuel post injection is performed within the
threshold timing range each engine revolution, such as described
above with respect to FIGS. 3 and 4. As a result, the DPF
temperature (plot 708) remains above the threshold temperature
(dashed line 709), enabling DPF regeneration to continue even while
combustion is discontinued in the engine. If the fuel post
injection were not performed, the temperature of the exhaust gases
and consequently the DPF temperature (plot 708) would drop, as
indicated by the dashed plot 710.
[0102] At time t10, the soot load of the DPF decreases below the
lower soot load threshold (dashed line 707). As such, DPF
regeneration has concluded, and the post injection is discontinued.
Further, the EGR valve (plot 718) is moved from a closed position
to a partially open position to allow exhaust gases to recirculate
back to the braking engine. Since braking is still occurring by
time t10, the decompression mode (plot 714) remains on and the VGT
position (plot 716) remains closed.
[0103] In this way, exhaust temperatures may be increased or
maintained during active DPF regeneration while combustion is
discontinued in at least one cylinder, such as during engine
braking or during a cylinder deactivation condition. Further, by
adjusting the air flow through the engine via the decompression
device and/or the VGT, the overall amount of post injection fuel
may be increased while the post injection quantity per engine
revolution per cylinder may be minimized. Further still, by
injecting the fuel for the post injections within the two timing
ranges of no more than 80 crank angle degrees centered on TDC of
each of the compression stroke and the exhaust stroke, oil-in fuel
dilution and bore washing may be reduced or avoided. As a result,
exhaust temperatures can be increased or maintained during
conditions in which exhaust system occurring may occur without
undesired effects to the cylinder.
[0104] The technical effect of injecting fuel post injections
within two timing ranges of no more than 80 crank angle degrees
centered on TDC during particulate filter regeneration while at
least one cylinder of the engine is unfueled is that a soot load of
the particulate filter may be decreased while cylinder wall wetting
is reduced.
[0105] The disclosure also provides support for a method,
comprising: responsive to a request for generating exotherms in an
exhaust system of an engine while combustion is discontinued in at
least one cylinder of the engine, injecting fuel into a cylinder
within a threshold crank angle range around top dead center of a
compression stroke of the cylinder and also within the threshold
crank angle range around top dead center of an exhaust stroke of
the cylinder, the threshold crank angle range extending from no
more than 40 crank angle degrees before top dead center to no more
than 40 crank angle degrees after top dead center. In a first
example of the method, the method further comprises: adjusting an
air flow through the engine responsive to the request for
generating the exotherms in the exhaust system of the engine. In a
second example of the method, optionally including the first
example, injecting fuel into the cylinder within the threshold
crank angle range around top dead center of the compression stroke
of the cylinder and also within the threshold crank angle range
around top dead center of the exhaust stroke of the cylinder
comprises: determining an amount of fuel to inject based on the
adjusted air flow through the engine, determining a first timing
for injecting the fuel within the threshold crank angle range
around top dead center of the compression stroke and a second
timing for injecting the fuel within the threshold crank angle
range around top dead center of the exhaust stroke based on a
desired air-fuel mixing relative to a desired decreased ignition
probability, and injecting the determined amount of fuel at the
first timing and at the second timing. In a third example of the
method, optionally including one or both of the first and second
examples, determining the first timing for injecting the fuel
within the threshold crank angle range around top dead center of
the compression stroke and the second timing for injecting the fuel
within the threshold crank angle range around top dead center of
the exhaust stroke based on the desired heat generation relative to
the desired air-fuel mixing comprises: setting the first timing and
the second timing to be earlier within the threshold crank angle
range responsive to the desired air-fuel mixing being greater than
the desired decreased ignition probability, and setting the first
timing and the second timing to be later within the threshold crank
angle range responsive to the desired decreased ignition
probability being greater than the desired air-fuel mixing. In a
fourth example of the method, optionally including one or more or
each of the first through third examples, adjusting the air flow
through the engine comprises at least one of adjusting a vane
position of a variable geometry turbine to a further closed
position and adjusting an intake throttle to a further closed
position. In a fifth example of the method, optionally including
one or more or each of the first through fourth examples,
combustion is discontinued in the at least one cylinder of the
engine responsive to an engine braking condition, and adjusting the
air flow through the engine comprises operating a decompression
device. In a sixth example of the method, optionally including one
or more or each of the first through fifth examples, combustion is
discontinued in the at least one cylinder of the engine responsive
to a cylinder deactivation condition, and adjusting the air flow
through the engine comprises maintaining an exhaust valve or an
intake valve of each deactivated cylinder open. In a seventh
example of the method, optionally including one or more or each of
the first through sixth examples, the threshold crank angle range
extends from 30 crank angle degrees before top dead center to 30
crank angle degrees after top dead center. In an eighth example of
the method, optionally including one or more or each of the first
through seventh examples, the request for generating the exotherms
in the exhaust system of the engine is responsive to a soot load of
a particulate filter positioned in the exhaust system of the engine
being greater than a threshold soot load, and the method further
comprises fully closing an exhaust gas recirculation (EGR) valve
positioned in a passage coupled between the exhaust system of the
engine and an intake of the engine in response to the request for
generating the exotherms in the exhaust system of the engine.
[0106] The disclosure also provides support for a method,
comprising: responsive to a request to regenerate a particulate
filter while combustion is discontinued in at least one cylinder of
an engine: determining a first timing of a first fuel post
injection within a first threshold timing range of no more than 80
crank angle degrees and a second timing of a second fuel post
injection within a second threshold timing range of no more than 80
crank angle degrees based on a desired exhaust gas condition, the
first threshold timing range extending from a compression stroke of
a cylinder to a power stroke of the cylinder and the second
threshold timing range extending from an exhaust stroke of the
cylinder to an intake stroke of the cylinder, and delivering the
first fuel post injection to the cylinder at the first timing and
the second fuel post injection to the cylinder at the second
timing. In a first example of the method, the method further
comprises: adjusting an amount of each of the first fuel post
injection and the second fuel post injection based on an air flow
through the engine. In a second example of the method, optionally
including the first example, combustion is discontinued in the at
least one cylinder of the engine responsive to a request for engine
braking, and the method further comprises adjusting the air flow
through the engine via a decompression device responsive to the
request for engine braking. In a third example of the method,
optionally including one or both of the first and second examples,
combustion is discontinued in the at least one cylinder of the
engine responsive to a cylinder deactivation condition, and wherein
the air flow through the engine is adjusted via a variable geometry
turbine during the cylinder deactivation condition. In a fourth
example of the method, optionally including one or more or each of
the first through third examples, the first timing of the first
fuel post injection is earlier within the first threshold timing
range and the second timing of the second fuel post injection is
earlier within the second threshold timing range when the desired
exhaust gas condition is an increased mixing of the fuel with air,
and wherein the first timing of the first fuel post injection is
later within the first threshold timing range and the second timing
of the second fuel post injection is later within the second
threshold timing range when the desired exhaust gas condition is
decreased ignitability. In a fifth example of the method,
optionally including one or more or each of the first through
fourth examples, the cylinder receiving the first fuel post
injection and the second fuel post injection is included in the at
least one cylinder having discontinued combustion. In a sixth
example of the method, optionally including one or more or each of
the first through fifth examples, the cylinder receiving the first
fuel post injection and the second fuel post injection is not
included in the at least one cylinder having discontinued
combustion.
[0107] The disclosure also provides support for a system,
comprising: an engine including a plurality of cylinders, and a
controller storing executable instructions in non-transitory memory
that, when executed, cause the controller to: inject fuel into at
least one of the plurality of cylinders each revolution of the
engine during a threshold post injection timing range extending
from no more than 40 degrees before top dead center to no more than
40 degrees after top dead center while particulate filter
regeneration is requested during an engine operating condition
where combustion is discontinued. In a first example of the system,
the system further comprises: a particulate filter coupled in an
exhaust system of the engine, and wherein the particulate filter
regeneration is requested responsive to a soot load of the
particulate filter being greater than a threshold soot load. In a
second example of the system, optionally including the first
example, the engine operating condition where combustion is
discontinued is one of an engine braking condition and a cylinder
deactivation condition. In a third example of the system,
optionally including one or both of the first and second examples,
to inject the fuel into the at least one of the plurality of
cylinders each revolution of the engine during the threshold post
injection timing range, the controller includes further
instructions stored in the non-transitory memory that, when
executed, cause the controller to: set a timing to inject the fuel
into the at least one of the plurality of cylinders each revolution
of the engine during the threshold post injection timing range to
be before top dead center within the threshold post injection
timing range as a desired amount of heat production increases, and
set the timing to inject the fuel to be after top dead center
within the threshold post injection range as a desired amount of
mixing increases.
[0108] In another representation, a method comprises: responsive to
a request for particulate filter regeneration while combustion is
discontinued in at least one cylinder of an engine, determining a
timing for performing a fuel post injection in the at least one
cylinder each revolution of the engine based on a desire for
increased mixing relative to a desire for decreased ignitability.
In the preceding example, additionally or optionally, the timing
for performing the fuel post injection is earlier within a
threshold crank angle range when the desire for increased mixing is
greater than the desire for decreased ignitability. In one or both
of the preceding examples, additionally or optionally, the
threshold crank angle range extends from no more than 40 crank
angle degrees before top dead center to no more than 40 crank angle
degrees after top dead center. In any or all of the preceding
examples, additionally or optionally, the threshold crank angle
range extends from 30 crank angle degrees before top dead center to
30 crank angle degrees after top dead center. In any or all of the
preceding examples, additionally or optionally, the timing for
performing the fuel post injection is before top dead center when
the desire for increased mixing is greater than the desire for
decreased ignitability and after top dead center when the desire
for decreased ignitability is greater than the desire for increased
mixing. In any or all of the preceding examples, the method
additionally or optionally further comprises maintaining a valve of
the at least one cylinder open throughout each revolution of the
engine responsive to the request for particulate filter
regeneration while combustion is discontinued in the at least one
cylinder. In any or all of the preceding examples, additionally or
optionally, the valve is an intake valve responsive to the desire
for increased mixing being greater than the desire for decreased
ignitability. In any or all of the preceding examples, additionally
or optionally, the valve is an exhaust valve responsive to the
desire for decreased ignitability being greater than the desire for
increased mixing. In any or all of the preceding examples, the
method additionally or optionally further comprises restricting
flow through an exhaust turbine responsive to the request for
particulate filter regeneration while combustion is discontinued in
the at least one cylinder. In any or all of the preceding examples,
the method additionally or optionally further comprises fully
closing an exhaust gas recirculation valve responsive to the
request for particulate filter regeneration while combustion is
discontinued in the at least one cylinder.
[0109] Note that the example control and estimation routines
included herein can be used with various engine and/or vehicle
system configurations. The control methods and routines disclosed
herein may be stored as executable instructions in non-transitory
memory and may be carried out by the control system including the
controller in combination with the various sensors, actuators, and
other engine hardware. The specific routines described herein may
represent one or more of any number of processing strategies such
as event-driven, interrupt-driven, multi-tasking, multi-threading,
and the like. As such, various actions, operations, and/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 features and
advantages of the example embodiments described herein, but is
provided for ease of illustration and description. One or more of
the illustrated actions, operations, and/or functions may be
repeatedly performed depending on the particular strategy being
used. Further, the described actions, operations, and/or functions
may graphically represent code to be programmed into non-transitory
memory of the computer readable storage medium in the engine
control system, where the described actions are carried out by
executing the instructions in a system including the various engine
hardware components in combination with the electronic
controller.
[0110] It will be appreciated that the configurations and routines
disclosed herein are exemplary in nature, and that these specific
embodiments are not to be considered in a limiting sense, because
numerous variations are possible. For example, the above technology
can be applied to V-6, I-4, I-6, V-12, opposed 4, and other engine
types. Moreover, unless explicitly stated to the contrary, the
terms "first," "second," "third," and the like are not intended to
denote any order, position, quantity, or importance, but rather are
used merely as labels to distinguish one element from another. The
subject matter of the present disclosure includes all novel and
non-obvious combinations and sub-combinations of the various
systems and configurations, and other features, functions, and/or
properties disclosed herein.
[0111] As used herein, the term "approximately" is construed to
mean plus or minus five percent of the range unless otherwise
specified.
[0112] The following claims particularly point out certain
combinations and sub-combinations regarded as novel and
non-obvious. These claims may refer to "an" element or "a first"
element or the equivalent thereof. Such claims should be understood
to include incorporation of one or more such elements, neither
requiring nor excluding two or more such elements. Other
combinations and sub-combinations of the disclosed features,
functions, elements, and/or properties may be claimed through
amendment of the present claims or through presentation of new
claims in this or a related application. Such claims, whether
broader, narrower, equal, or different in scope to the original
claims, also are regarded as included within the subject matter of
the present disclosure.
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