U.S. patent application number 15/050308 was filed with the patent office on 2016-06-16 for method and system for binary flow turbine control.
The applicant listed for this patent is Ford Global Technologies, LLC. Invention is credited to Brad Alan Boyer, Julia Helen Buckland, Jeffrey Allen Doering.
Application Number | 20160169131 15/050308 |
Document ID | / |
Family ID | 52004250 |
Filed Date | 2016-06-16 |
United States Patent
Application |
20160169131 |
Kind Code |
A1 |
Doering; Jeffrey Allen ; et
al. |
June 16, 2016 |
METHOD AND SYSTEM FOR BINARY FLOW TURBINE CONTROL
Abstract
Methods and systems are provided for adjusting the opening of a
scroll valve of a binary flow turbine. Scroll valve adjustments are
used at different engine operating conditions to improve engine
performance and boost response. Scroll valve adjustments are
coordinated with wastegate and EGR valve adjustments for improved
engine control.
Inventors: |
Doering; Jeffrey Allen;
(Canton, MI) ; Buckland; Julia Helen; (Commerce
Township, MI) ; Boyer; Brad Alan; (Canton,
MI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Ford Global Technologies, LLC |
Dearborn |
MI |
US |
|
|
Family ID: |
52004250 |
Appl. No.: |
15/050308 |
Filed: |
February 22, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14053525 |
Oct 14, 2013 |
9267450 |
|
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15050308 |
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61833377 |
Jun 10, 2013 |
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Current U.S.
Class: |
60/605.2 |
Current CPC
Class: |
F02P 5/045 20130101;
F02B 37/22 20130101; F02M 26/04 20160201; Y02T 10/40 20130101; F02D
2200/1002 20130101; F02D 13/02 20130101; F02D 13/0215 20130101;
F02D 2041/001 20130101; F02P 5/04 20130101; F02D 41/0007 20130101;
F02D 41/005 20130101; F02M 26/01 20160201; F02D 41/022 20130101;
F02B 37/18 20130101; F02B 37/183 20130101; F02D 41/062 20130101;
F02M 26/07 20160201; Y02T 10/144 20130101; F02B 37/12 20130101;
F02D 41/04 20130101; F02D 41/0052 20130101; F02M 26/05 20160201;
F02B 37/025 20130101; F02M 26/06 20160201; Y02T 10/12 20130101;
F02B 37/02 20130101; Y02T 10/47 20130101; F02D 41/023 20130101;
F02D 2200/0404 20130101 |
International
Class: |
F02D 41/00 20060101
F02D041/00; F02B 37/18 20060101 F02B037/18; F02M 26/07 20060101
F02M026/07; F02D 41/02 20060101 F02D041/02; F02D 41/06 20060101
F02D041/06; F02B 37/02 20060101 F02B037/02; F02D 13/02 20060101
F02D013/02 |
Claims
1. A method for an engine, comprising: adjusting, via a controller,
an engine torque actuator including a scroll valve coupled to an
inlet of one scroll of a multi-scroll exhaust turbine and coupled
to each cylinder exhaust port of the engine; the adjusting
including moving the scroll valve towards a closed position in
response to an indication of engine deactivation while the engine
still rotates; directly injecting fuel to cylinders of the engine
via direct injectors coupled directly to the cylinders; and
adjusting cylinder intake and/or exhaust valve timing responsive to
an operating parameter during engine operation.
2. The method of claim 1, wherein the indication of engine
deactivation includes a deceleration fuel shut-off, and wherein
valve timing is adjusted based on a position of the scroll valve
position to adjust an amount of internal EGR delivered to the
engine.
3. The method of claim 1, wherein the one scroll is a first, outer
scroll, the multi-scroll exhaust turbine including a second, inner
scroll, the scroll valve not coupled to an inlet of the second
scroll.
4. The method of claim 1, wherein the scroll valve is coupled
downstream of an exhaust manifold coupled to each cylinder of the
engine.
5. The method of claim 4, wherein moving the scroll valve to the
closed position includes moving the scroll valve to the closed
position based on one or more of turbine speed or boost pressure
during the indication of engine deactivation.
6. The method of claim 5, wherein the moving based on turbine speed
includes moving the scroll valve based on a difference between an
estimated or measured turbine speed during the indication of engine
deactivation relative to a turbine speed deceleration profile and a
difference between measured and desired boost pressure, the scroll
valve moved towards a fully closed position as the difference
increases.
7. The method of claim 6, further comprising moving a wastegate
coupled across the exhaust turbine to a more closed position in
response to the indication of engine deactivation, the wastegate
position based on the scroll valve position.
8. The method of claim 7, wherein moving the wastegate includes,
during a first condition, moving the wastegate to the more closed
position as the scroll valve is moved to the closed position;
during a second condition, moving the wastegate to the more closed
position after the scroll valve is moved to the closed position;
and during a third condition, moving the wastegate to the more
closed position before the scroll valve is moved to the closed
position.
9. The method of claim 6, further comprising adjusting intake
throttle position during the indication of engine deactivation
based on the moving of the scroll valve.
10. The method of claim 4, wherein a timing of moving the scroll
valve to the closed position is based on a transmission event.
11. A method for a boosted engine, comprising: via a controller:
deactivating direct fuel injection to an engine; while the engine
spins towards rest, adjusting a scroll valve coupled to an outer
scroll of a multi-scroll exhaust turbine based on deviation of
estimated turbine speed relative to a turbine speed deceleration
profile; and adjusting cylinder valve timing.
12. The method of claim 11, wherein deactivating fuel injection to
the engine includes deactivating in response to a tip-out, and
wherein the cylinder valve timing is adjusted responsive to scroll
valve position.
13. The method of claim 11, wherein the adjusting includes, as the
deviation of the estimated or measured turbine speed from the
turbine speed deceleration profile increases, moving the scroll
valve towards a fully closed position.
14. The method of claim 11, wherein a timing of adjusting the
scroll valve is based on a transmission event during the engine
spin-down.
15. The method of claim 13, further comprising moving a wastegate
coupled across the exhaust turbine towards a more closed position
while the engine spins towards rest, the position of the wastegate
based on the scroll valve position.
16. The method of claim 15, further comprising adjusting, intake
throttle position, while the engine spins towards rest, the
adjusting based on the scroll valve adjustment.
17. An engine system, comprising: an engine including selectively
deactivatable fuel injectors; a turbocharger for providing a
boosted aircharge to the engine, the turbocharger including an
intake compressor and an exhaust turbine, the exhaust turbine
including a first outer scroll and a second inner scroll; a scroll
valve coupled between an exhaust manifold of the engine and an
inlet of the first outer scroll; a variable cylinder valve timing
system coupled to the engine to adjust intake and/or exhaust valve
timing; a wastegate included in a bypass coupled between an inlet
and an outlet of the exhaust turbine; and a controller with
computer readable instructions for, adjusting the cylinder valve
timing responsive to an operating parameter; and in response to
torque demand being lower than a threshold, selectively
deactivating fuel injection to the engine; and while the engine
spins down to rest, decreasing an opening of the scroll valve, the
decreasing based on a difference between an estimated or measured
turbine speed and a desired spin-down turbine speed profile during
the spin-down.
18. The system of claim 17, wherein the controller includes further
instructions for coordinating an opening of the wastegate during
the engine spin-down based on the decreasing an opening of the
scroll valve to further reduce the difference between the estimated
or measured turbine speed and the desired spin-down turbine speed
profile.
19. The system of claim 17, further comprising an EGR system
configured to recirculate exhaust gas from the exhaust manifold to
an intake manifold of the engine, wherein the controller includes
further instructions for adjusting an EGR valve of the EGR system
to decrease an amount of EGR during the decreasing of an opening of
the scroll valve.
20. The system of claim 17, wherein the controller includes further
instructions for, during a first engine restart from the spin-down,
restarting the engine with the scroll valve closed; and during a
second engine restart from the spin-down, restarting the engine
with the scroll valve open, a duration of engine deactivation
preceding the first engine restart longer than a duration of engine
deactivation preceding the second engine restart.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/053,525, entitled "METHOD AND SYSTEM FOR
BINARY FLOW TURBINE CONTROL," filed on Oct. 14, 2013, which claims
priority to U.S. Provisional Patent Application Ser. No.
61/833,377, entitled "METHOD AND SYSTEM FOR BINARY FLOW TURBINE
CONTROL," filed on Jun. 10, 2013, the entire contents of which are
hereby incorporated by reference for all purposes.
FIELD
[0002] The present application relates to controlling a scroll
valve coupled to a binary flow turbine in a boosted engine
system.
BACKGROUND AND SUMMARY
[0003] In vehicles having internal combustion engines, it can be
beneficial to discontinue fuel injection to all or some of the
engine cylinders during certain operating conditions, such as
during vehicle deceleration or braking. For example, one or more
cylinder fuel injectors may be selectively deactivated while the
engine is rotating. Such an operation is also known as a
deceleration fuel shut-off (DFSO) event. The larger the number of
cylinders that are deactivated, and/or the longer the cylinders are
deactivated, the greater the fuel economy improvement that can be
achieved.
[0004] However, there may be poor drivability issues during an
engine reactivation following the DFSO. As such, following fuel
deactivation, the engine may start spinning towards rest. In
addition, where the engine is turbocharged, the turbine may also
start spinning towards rest. If a vehicle operator tips-in during
the engine spin-down, the time taken to spool up the turbine may be
substantial, and the operator torque demand may not be timely met.
As such, this may degrade engine performance and vehicle
driveability. In addition, while the engine spins down, air may
continue to flow through the cylinders towards an exhaust catalyst
causing catalyst cooling as well as oxidizing catalytic sites. When
combustion is re-initiated, additional fuel may be required to
reduce and reactivate the exhaust catalyst. During some conditions,
this fuel penalty may even outweigh the fuel economy benefits of
the DFSO.
[0005] The inventors herein have recognized that such drivability
issues may be overcome in a boosted engine system that uses a
binary flow turbine. In one example, engine performance may be
improved by a method comprising adjusting a scroll valve coupled to
an inlet of one scroll of a multi-scroll exhaust turbine responsive
to an indication of engine deactivation. By closing the scroll
valve during a DFSO, turbine speed can be maintained elevated for a
duration, enabling faster turbine spool-up upon subsequent engine
reactivation, and reducing catalyst cooling.
[0006] In one example, in response to a DFSO event, a scroll valve
coupled to only an outer scroll of a multi-scroll exhaust turbine
may be moved to a more closed position. For example, the scroll
valve may be moved, gradually or immediately, to a fully closed
position. The moving of the scroll valve may be based on the
turbine speed so that the turbine speed follows a desired
deceleration profile. The scroll valve may then be maintained at
the closed (e.g., fully closed) position during a subsequent engine
restart. As such, by closing the scroll valve, the exhaust manifold
pressure can be increased, allowing the turbine to keep spinning at
or above a threshold speed while the engine spins towards rest. By
enabling the turbine speed to follow a desired speed profile, in
response to a sudden request for torque, such as due to a tip-in
during the engine spin-down, the turbine may be quickly spooled up
and the boost levels can be elevated. This allows drivability
issues during a DFSO to be reduced. In addition, by closing the
scroll valve, the elevated exhaust manifold pressure may reduce
fresh air flow through the engine, decreasing the extent of exhaust
catalyst cooling and oxidation. As such, this also lowers the fuel
penalty required for reducing the exhaust catalyst upon engine
reactivation. Wastegate and EGR valve adjustments may be
coordinated with the scroll valve adjustments to further improve
turbine speed control.
[0007] In this way, scroll valve adjustments in a binary flow
turbine can be advantageously used to improve turbine speed control
during an engine deactivation as well as during the subsequent
engine reactivation. By improving turbine speed control, boost
performance of the engine during the reactivation is improved. In
addition, losses in exhaust catalyst performance during the DFSO,
due to catalyst cooling and oxidation, are lowered. Overall, engine
performance and fuel economy is improved.
[0008] 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
[0009] FIG. 1 shows a schematic diagram of a boosted engine system
including a binary flow turbine and an exhaust gas recirculation
(EGR) system.
[0010] FIGS. 2-3 show example maps of engine operating conditions
that may be used to determine when to transition the binary flow
turbine of FIG. 1 between one scroll or two scroll
configurations.
[0011] FIG. 4 shows a map depicting differences in transient torque
response when operating the binary flow turbine of FIG. 1 with one
or two scrolls.
[0012] FIGS. 5-11 depict example flowcharts for adjusting the
position of a scroll valve based on various engine operating
conditions.
[0013] FIGS. 12-17 depict example scroll valve adjustments
commanded responsive to various engine operating conditions to
improve engine performance and boost response.
DETAILED DESCRIPTION
[0014] The following description relates to systems and methods for
operating a boosted engine including a binary flow turbine and an
exhaust gas recirculation (EGR) system, as shown in FIG. 1. A
controller may be configured to perform a routine, such as the
routine of FIG. 5, to adjust a position of a scroll valve of the
turbine (such as from an initial position) based on various engine
operating conditions. Selection of an initial scroll valve schedule
may be based on engine speed-load maps such as those shown at FIGS.
2-3. For example, the scroll valve position may be adjusted during
engine starts (FIG. 6) to reduce engine start emissions and
turbocharger whine. The valve position may be adjusted during
torque transients (FIG. 7), such as a tip-in, to reduce turbo lag.
The valve position may also be adjusted responsive to combustion
stability limits (FIG. 8), abnormal combustion events (FIG. 9), and
engine deactivation (FIG. 10). Various engine actuators may be
adjusted based on the scroll valve adjustment, such as a turbine
wastegate, VCT, spark, EGR valves, etc. For example, as elaborated
at FIG. 11, torque disturbances associated with the scroll valve
transition may be compensated for using concomitant adjustments to
one or more engine actuators. The scroll valve adjustments may
improve boost response (FIG. 4). Example scroll valve adjustments
are described with reference to FIGS. 12-17. In this way, the
horsepower capability of a turbocharged engine, and overall engine
performance, can be improved during various engine operating
conditions.
[0015] FIG. 1 shows a schematic diagram of an engine 10, which may
be included in a propulsion system of an automobile. Engine 10 may
be controlled at least partially by a control system including
controller 12 and by input from a vehicle operator 14 via an input
device 16. In this example, input device 16 includes an accelerator
pedal and a pedal position sensor 18 for generating a proportional
pedal position signal PP.
[0016] Engine 10 may include a plurality of combustion chambers
(i.e., cylinders). In the example shown in FIG. 1, Engine 10
includes combustion chambers 20, 22, 24, and 26, arranged in an
inline-4 configuration. It should be understood, however, that
though FIG. 1 shows four cylinders, engine 10 may include any
number of cylinders in any configuration, e.g., V-6, I-6, V-12,
opposed 4, etc.
[0017] Though not shown in FIG. 1, each combustion chamber (i.e.,
cylinder) of engine 10 may include combustion chamber walls with a
piston positioned therein. The pistons may be coupled to a
crankshaft so that reciprocating motions of the pistons are
translated into rotational motion of the crankshaft. The crankshaft
may be coupled to at least one drive wheel of a vehicle via an
intermediate transmission system, for example. Further, a starter
motor may be coupled to the crankshaft via a flywheel to enable a
starting operation of engine 10.
[0018] Each combustion chamber may receive intake air from an
intake manifold 28 via an air intake passage 30. Intake manifold 28
may be coupled to the combustion chambers via intake ports. For
example, intake manifold 28 is shown in FIG. 1 coupled to cylinders
20, 22, 24, and 26 via intake ports 32, 34, 36, and 38
respectively. Each respective intake port may supply air and/or
fuel to the respective cylinder for combustion.
[0019] Each combustion chamber may exhaust combustion gases via an
exhaust port coupled thereto. For example, exhaust ports 40, 42, 44
and 46, are shown in FIG. 1 coupled to cylinders 20, 22, 24, 26,
respectively. Each respective exhaust port may direct exhaust
combustion gases from a respective cylinder to an exhaust manifold
or exhaust passage.
[0020] Each cylinder intake port can selectively communicate with
the cylinder via an intake valve. For example, cylinders 20, 22,
24, and 26 are shown in FIG. 1 with intake valves 48, 50, 52, and
54, respectively. Likewise, each cylinder exhaust port can
selectively communicate with the cylinder via an exhaust valve. For
example, cylinders 20, 22, 24, and 26 are shown in FIG. 1 with
exhaust valves 56, 58, 60, and 62, respectively. In some examples,
each combustion chamber may include two or more intake valves
and/or two or more exhaust valves.
[0021] Though not shown in FIG. 1, in some examples, each intake
and exhaust valve may be operated by an intake cam and an exhaust
cam. Alternatively, one or more of the intake and exhaust valves
may be operated by an electromechanically controlled valve coil and
armature assembly. The position of an intake cam may be determined
by an intake cam sensor. The position of exhaust cam may be
determined by an exhaust cam sensor.
[0022] Intake passage 30 may include a throttle 64 having a
throttle plate 66. In this particular example, the position of
throttle plate 66 may be varied by controller 12 via a signal
provided to an electric motor or actuator included with throttle
64, a configuration that is commonly referred to as electronic
throttle control (ETC). In this manner, throttle 64 may be operated
to vary the intake air provided the combustion chambers. The
position of throttle plate 66 may be provided to controller 12 by
throttle position signal TP from a throttle position sensor 68.
Intake passage 30 may include a mass air flow sensor 70 and a
manifold air pressure sensor 72 for providing respective signals
MAF and MAP to controller 12.
[0023] In FIG. 1, fuel injectors are shown coupled directly to the
combustion chambers for injecting fuel directly therein in
proportion to a pulse width of a signal FPW received from
controller 12 via an electronic driver, for example. For example,
fuel injectors 74, 76, 78, and 80 are shown in FIG. 1 coupled to
cylinders 20, 22, 24, and 26, respectively. In this manner, the
fuel injectors provide what is known as direct injection of fuel
into the combustion chamber. Each respective fuel injector may be
mounted in the side of the respective combustion chamber or in the
top of the respective combustion chamber, for example. In some
examples, one or more fuel injectors may be arranged in intake
passage 28 in a configuration that provides what is known as port
injection of fuel into the intake ports upstream of the respective
combustion chambers. Though not shown in FIG. 1, fuel may be
delivered to the fuel injectors by a fuel system including a fuel
tank, a fuel pump, a fuel line, and a fuel rail.
[0024] The combustion chambers of engine 10 may be operated in a
compression ignition mode, with or without an ignition spark. In
some examples, a distributorless ignition system (not shown) may
provide ignition sparks to spark plugs coupled to the combustion
chambers in response to controller 12. For example, spark plugs 82,
84, 86, and 88 are shown in FIG. 1 coupled to cylinders 20, 22, 24,
and 26, respectively.
[0025] Engine 10 may include a turbocharger 90. Turbocharger 90 may
include an exhaust turbine 92 and an intake compressor 94 coupled
on a common shaft 96. The blades of exhaust turbine 92 may be
caused to rotate about the common shaft as a portion of the exhaust
gas stream discharged from engine 10 impinges upon the blades of
the turbine. Intake compressor 94 may be coupled to turbine 92 such
that compressor 94 may be actuated when the blades of turbine 92
are caused to rotate. When actuated, compressor 94 may then direct
pressurized gas to air intake manifold 28 from where it may then be
directed to engine 10. In this way, turbocharger 90 may be
configured for providing a boosted aircharge to the engine
intake.
[0026] Turbocharger 90 may be configured as a multi-scroll
turbocharger wherein the exhaust turbine includes a plurality of
scrolls. In the depicted embodiment, turbine 92 includes two
scrolls including a first outer scroll 95 and a second inner scroll
97. Each scroll may receive exhaust gas from exhaust manifold 29
via distinct inlets. Specifically, exhaust gas may flow along a
first exhaust gas entry path 102 into first outer scroll 95 and
along a second exhaust gas entry path 104 into second inner scroll
97. A scroll valve 106 may be coupled in first exhaust gas entry
path 102 between engine exhaust manifold 29 and an inlet of the
first outer scroll 95. In this way, exhaust turbine 92 is
configured as a binary flow turbine. As elaborated below, by
adjusting a position of the scroll valve 106, an amount of exhaust
gas directed to the turbine can be varied. As such, the scroll
valve is not coupled to an inlet of the second inner scroll.
[0027] A wastegate 110 may be coupled across turbine 92.
Specifically, wastegate 110 may be included in a bypass 108 coupled
between an inlet and outlet of the exhaust turbine. By adjusting a
position of wastegate 110, an amount of boost provided by the
turbine may be controlled.
[0028] Exhaust gases exiting turbine 92 and/or wastegate 110 may
pass through an emission control device 112. Emission control
device 112 can include multiple catalyst bricks, in one example. In
another example, multiple emission control devices, each with
multiple bricks, can be used. In some examples, emission control
device 112 may be a three-way type catalyst. In other examples,
emission control device 112 may include one or more of a diesel
oxidation catalyst (DOC), selective catalytic reduction catalyst
(SCR), and a diesel particulate filter (DPF). After passing through
emission control device 112, exhaust gas may be directed to a
tailpipe 114.
[0029] Engine 10 may include one or more exhaust gas recirculation
(EGR) systems for recirculating an amount of exhaust gas exiting
engine 10 back to the engine intake. For example, engine 10 may
include a first, low pressure EGR (LP-EGR) system 116 for
recirculating a portion of exhaust gas from the exhaust manifold to
the intake manifold, specifically, from the engine exhaust,
downstream of turbine 92, to the engine intake, upstream of
compressor 94. The LP-EGR system may include an LP-EGR conduit 118,
an LP-EGR valve 120 configured to control an amount of exhaust gas
recirculated along LP-EGR conduit 118, and an LP-EGR cooler 122 for
cooling the exhaust gas before delivery to the intake.
[0030] Engine 10 may further include a second, high pressure EGR
(HP-EGR) system 126 for recirculating a portion of exhaust gas from
the exhaust manifold to the intake manifold, specifically, from the
engine exhaust, upstream of turbine 92, to the engine intake,
downstream of compressor 94. The HP-EGR system may include an
HP-EGR conduit 128, an HP-EGR valve 130 configured to control an
amount of exhaust gas recirculated along HP-EGR conduit 128, and an
HP-EGR cooler 132 for cooling the exhaust gas before delivery to
the intake.
[0031] In some examples, controller 12 may be a conventional
microcomputer including: a microprocessor unit, input/output ports,
read-only memory, random access memory, keep alive memory, and a
conventional data bus. Controller 12 is shown in FIG. 1 receiving
various signals from sensors coupled to engine 10, in addition to
those signals previously discussed, including: engine coolant
temperature (ECT) from a temperature sensor 138; an engine position
sensor 140, e.g., a Hall effect sensor sensing crankshaft position.
Barometric pressure may also be sensed (sensor not shown) for
processing by controller 12. In some examples, engine position
sensor 140 produces a predetermined number of equally spaced pulses
every revolution of the crankshaft from which engine speed (RPM)
can be determined. Additionally, various sensors may be employed to
determine turbocharger boost pressure. For example, a pressure
sensor 133 may be disposed in the engine intake downstream of
compressor 94 to determine boost pressure. Additionally, at least
the exhaust passage routing exhaust to outer scroll 95 may include
various sensors for monitoring operating conditions of the
multi-scroll turbocharger. Exhaust gas sensor 134 may be any
suitable sensor for providing an indication of exhaust gas air/fuel
ratio such as a linear oxygen sensor or UEGO (universal or
wide-range exhaust gas oxygen), a two-state oxygen sensor or EGO, a
HEGO (heated EGO), a NOx, HC, or CO sensor.
[0032] Based on the input from the various sensors, controller 12
may be configured to perform various control routines (such as
those described with reference to FIGS. 5-11) and actuate one or
more engine actuators. The actuators may include, for example,
intake throttle 64, EGR valves 120 and 130, wastegate 110, and
scroll valve 106.
[0033] As such, by adjusting scroll valve 106 based on engine
operating conditions, the turbine may be operated in different
modes, and the dynamic range over which boost can be provided by
the turbocharger is enhanced. For example, the turbocharger may be
operated in a first mode with the scroll valve closed (e.g., fully
closed) during selected conditions, such as at low engine speeds,
during engine cold-starts, and in response to an increased demand
for torque. When operating in the first mode with the scroll valve
closed, the turbine behaves like a small mono-scroll turbine,
providing faster spin-up and BMEP. Herein, the closing of the
scroll valve shuts off exhaust flow to the first scroll. The
resulting limited flow of exhaust through only one of the scrolls
increases exhaust manifold pressure and turbine inlet pressure (and
engine backpressure). By raising the pressure of exhaust flowing
through the turbine, turbine speed and power in increased,
particularly when the engine is operating at low speeds and during
transient performance. When coordinated with adjustments to the
wastegate, as well as one or both EGR systems (to provide cooled
EGR benefits), the time to desired torque and turbine spin-up can
be substantially improved.
[0034] As another example, the turbocharger may be operated in a
second mode with the scroll valve open (e.g., fully open) during
selected conditions. When operating in the second mode with the
scroll valve open, the turbine behaves like a large mono-scroll
turbine, providing improved peak power. Herein, the opening of the
scroll causes exhaust to flow through both the first and second
scroll. The resulting drop in exhaust manifold pressure allows more
fresh air to be drawn into the engine intake. The increased flow of
exhaust through the turbine also increases the driving of the
turbine. When coordinated with adjustments to the wastegate, as
well as one or both EGR systems, boosted engine performance is
improved, a stoichiometric window is enlarged and the fuel economy
benefits of cooled EGR are achieved. Example scroll valve
adjustments responsive to operating conditions are described with
reference to the routines of FIGS. 5-11 and with reference to the
examples of FIGS. 12-17.
[0035] While the above modes describe the scroll valve as being
either fully open or fully closed, it will be appreciated that in
still other modes, the scroll valve may be adjusted to any
(variable) position between the fully open and fully closed states,
based on engine operating conditions. For example, based on engine
operating conditions, the scroll valve may be opened or closed
incrementally (e.g., in 20% increments).
[0036] Now turning to FIG. 2, map 200 depicts an example scroll
valve schedule (and coordination with a wastegate schedule) that
may be implemented to optimize fuel economy and torque production
during boosted engine operation. The map depicts speed-load regions
wherein the scroll valve may be operated closed versus where the
scroll valve may be operated open. Specifically, map 200 shows
engine speed along the x-axis and engine load (as BMEP) along the
y-axis.
[0037] As shown, when operating in a first region 202, defined by
low load conditions (at low speed as well as at high speed), the
engine may be operated with the scroll valve open as well as the
wastegate open. By opening the scroll valve during the low
speed-low load conditions the engine pumping losses can be reduced
by reducing the exhaust manifold pressure.
[0038] In comparison, when operating in a second region 204,
defined by low speed and high load conditions, the engine may be
operated with the scroll valve closed. By closing the scroll valve
during the high load conditions, exhaust flow may be restricted to
only the inner scroll of the turbine. As a result, turbine inlet
pressures may be increased, reducing turbo lag and improving low
speed transient performance.
[0039] During high speed and high load conditions, such as when the
engine is operating in third region 206, the engine may be operated
with the scroll valve open and the wastegate partially or fully
closed. By opening the scroll valve while closing the wastegate
during the high speed and high load conditions, a larger portion of
exhaust flow may be directed to both the scrolls to expedite
turbine spin-up and boost delivery. As a result, turbine inlet
pressure is reduced, reducing engine backpressure and improving
fuel efficiency.
[0040] During cold-start conditions, such as when operating in
fourth region 208, the engine may be started with the scroll valve
closed and exhaust flow directed through only one of the scrolls.
By closing the scroll valve during at least an early portion of an
engine start operation, catalyst warming to light-off temperatures
can be improved. Specifically, by closing the scroll valve during
the cold-start, and restricting exhaust gas flow to be through only
one of the multiple scrolls, thermal losses at the turbine (through
part of the turbine housing and a portion of the turbine wheel) are
reduced. As such, this allows a higher exhaust gas temperature to
be retained, the higher exhaust gas temperature then directed to
the exhaust catalyst.
[0041] During the cold-start conditions, the wastegate may be open
or closed, depending on the prevalent engine operating conditions,
so as to maximize the temperature of exhaust gas directed to the
catalyst and/or optimize turbo speed for NVH. For example, during
an engine cold-start the engine may be started with the scroll
valve closed and the wastegate closed to increase the temperature
of exhaust gas directed to the catalyst. As another example, during
an engine cold-start the engine may be started with the scroll
valve closed and the wastegate open to increase the temperature of
exhaust gas directed to the catalyst by minimizing the heat
transfer to the exhaust components. In some embodiments, additional
combustion strategies may be implemented with the scroll valve and
wastegate adjustments to reduce time to catalyst light-off. For
example, retarded spark ignition timing and valve timing
adjustments can be used to complement the reduced exhaust
temperature losses associated with the closed scroll valve.
[0042] Map 300 of FIG. 3 depicts an alternate scroll valve schedule
that may be implemented to optimize fuel economy and torque
production during boosted engine operation. As with the map of FIG.
2, map 300 depicts speed-load regions (with engine speed shown
along the x-axis and engine load (as BMEP) shown along the y-axis)
wherein the scroll valve may be operated closed versus where the
scroll valve may be operated open.
[0043] In the depicted map, when operating in a first region 302,
defined by low load conditions (at medium to high speeds), the
engine may be operated with the scroll valve open as well as the
wastegate open. By opening the scroll valve and the wastegate
during the low load conditions, exhaust manifold pressure and
engine pumping losses are minimized while meeting demanded engine
torque.
[0044] In comparison, when operating in a second region 304,
defined by low speed conditions, including low load and high load
conditions, the engine may be operated with the scroll valve
closed. By closing the scroll valve during the low speed-low load
conditions, turbocharger transient response from a low load to a
high load condition can be improved.
[0045] For example, during a transient increase in torque demand
(e.g., a tip-in or a change in speed-load conditions from operating
region 302 to 304, or from 202 to 204), where the torque request
increases beyond a calibratable threshold, the scroll valve may be
commanded closed. This improves turbocharger response and results
in a faster delivery of torque. This action may be coordinated with
the wastegate, with the wastegate moved towards a closed position
when the scroll valve is closed to further improve turbocharger
response. Alternatively, the wastegate may be used to initially
manage the residuals (e.g., by initially being opened) and then be
closed to facilitate boost production. Further still, the scroll
valve and the wastegate may be coupled (electrically or
mechanically) such that they close or open together.
[0046] As with the schedule of FIG. 2, during high speed and high
load conditions, such as when the engine is operating in third
region 306, the engine may be operated with the scroll valve open
and the wastegate partially or fully closed. In 302, neither the
scroll valve nor the wastegate needs to be closed to meet required
boost for engine torque demand. In region 306, some closing of the
wastegate is required to meet demanded torque but the torque demand
can be met with an open scroll valve. By opening the scroll valve
while closing the wastegate during the high speed and high load
conditions, a larger portion of exhaust flow may be directed to
both the scrolls to expedite turbine spin-up and boost delivery
while reducing exhaust manifold pressure, residuals and engine
pumping losses compared to an open scroll valve. As a result,
higher peak power can be achieved.
[0047] As engine operating conditions change, a position of the
scroll valve may be adjusted. For example, as engine speed-load
conditions change, based on the schedules shown at maps 200 and
300, the scroll valve may be moved from a fully closed to a fully
open position (or vice versa). Further, a wastegate schedule may be
coordinated with the scroll valve adjustments. Further still, EGR
valve adjustments may be coordinated with the scroll valve
adjustments to improve cooled EGR delivery. Example adjustments are
described herein with reference to FIGS. 12-17.
[0048] Now turning to FIG. 4, plot 400 depicts the improvement in
transient response obtained by moving the scroll valve to a closed
position. Plot 400 depicts a change in engine torque output (as
BMEP) along the y-axis, over time along the x-axis. At t1, a
transient increase in torque demand may be requested, such as due
to a tip-in event. In response to the tip-in, turbine operation may
be initiated with the scroll valve open (as shown by dashed line
402) or with the scroll valve closed (as shown by solid line 404).
Between t1 and t2, while the turbine spins up, there may be no
substantial difference between turbocharger output with the scroll
valve open or closed, as this response is dictated by manifold
filling. However, after t2, the lower engine backpressure
experienced when operating with the scroll valve open reduces the
transient response of the turbocharger. In comparison, when
operating with the scroll valve closed, higher torque is achieved,
as well as faster attainment of the higher torque. Further, the
closed scroll valve allows for increased flexibility for trade-offs
that may be required during the transient response, such as tumble,
EGR, etc. If so equipped, an engine with variable charge motion
(tumble) may be used to optimize burn rates for each condition.
[0049] FIG. 5 depicts an example routine 500 that may be performed
to adjust the position of a scroll valve coupled to an outer scroll
of a multi-scroll exhaust turbine based on engine operating
conditions. Specifically, the routine may determine an initial
scroll valve position and schedule, and then based on engine
operating conditions, including based on engine limitations,
transients, EGR valve limits, etc., the initial scroll valve
position and schedule may be further modified via the specific
routines and sub-routines of FIGS. 6-11. The routine may further
enable wastegate adjustments and EGR valve adjustments (including
HP-EGR and LP-EGR adjustments) to be coordinated with the scroll
valve adjustments to improve engine performance, torque output, and
fuel economy.
[0050] At 502, the routine includes estimating and/or measuring
engine operating conditions. These may include, for example, engine
speed, torque demand, catalyst temperature, engine temperature,
exhaust air-fuel ratio, MAP, MAF, barometric pressure, etc. At 504,
based on the estimated engine operating conditions, an initial
scroll valve position and schedule may be determined. As used
herein, the scroll valve schedule may include determining how and
when to transition the scroll valve to the initial position.
[0051] At 506, it may be determined if engine start conditions are
present. For example, it may be determined if the engine is being
started from an engine shutdown condition and/or while an exhaust
catalyst is below a light-off temperature. If yes, then at 508, the
routine includes further adjusting the scroll valve schedule and
position (from the initial position determined at 504) based on the
temperature conditions to reduce cold-start emissions, expedite
catalyst heating, as well as to reduce the occurrence of any
turbocharger whine. As elaborated with reference to FIG. 6, this
may include starting the engine with the scroll valve open during
some start conditions and starting the engine with the scroll valve
closed during other start conditions. In particular, the scroll
valve is adjusted to keep the turbocharger speed outside a
resonance zone where turbo whine can occur. Wastegate adjustments
may be coordinated with, and based on, the corresponding scroll
valve adjustments. Example scroll valve adjustments performed
during engine start conditions are described with reference to FIG.
14.
[0052] After an engine start has been completed (hot start or cold
start), the routine proceeds to 514, where it may be determined if
there are any transients. For example, it may be determined if
there is a sudden increase in torque demand (e.g., due to an
operator pedal tip-in). If yes, then at 516, the routine includes
further adjusting a scroll valve schedule and position based on the
transient conditions to meet the transient torque demand and reduce
turbo lag. As elaborated with reference to FIG. 7, this may include
moving the scroll valve to a more closed position in response to an
increased torque demand. Wastegate adjustments may be coordinated
with, and based on, the corresponding scroll valve adjustments.
Example scroll valve adjustments performed during transient changes
in torque demand are described with reference to FIG. 17.
[0053] At 518 (from 514 or 516), it may be determined if the engine
is combustion stability limited. If yes, then at 520, the routine
includes further adjusting a scroll valve schedule and position
based on engine dilution and the combustion stability limits to
decrease the amount of residuals in the combustion chamber. As
elaborated with reference to FIG. 8, this may include moving the
scroll valve to a position that enables less engine dilution to be
provided. Wastegate adjustments as well as EGR valve adjustments
(to the HP-EGR valve and/or the LP-EGR valve) may be coordinated
with, and based on, the corresponding scroll valve adjustments.
Example scroll valve adjustments performed during engine operation
where combustion stability is limited are described with reference
to FIG. 15.
[0054] At 522 (from 518 or 520), it may be determined if an engine
hardware limit has been reached. For example, it may be determined
if there is any indication of pre-ignition. If yes, then at 524,
the routine includes further adjusting the scroll valve schedule
and position based on the engine hardware limits to reduce an
engine load. As elaborated with reference to FIG. 9, this may
include moving the scroll valve to a more open position to rapidly
reduce an engine load below engine hardware limits. Wastegate
adjustments may be coordinated with, and based on, the
corresponding scroll valve adjustments. Furthermore, other
pre-ignition mitigating steps, such as fuel enrichment, may be used
concurrently with the scroll valve adjustment to further expedite
mitigation of the pre-ignition. Example scroll valve adjustments
performed in response to an indication of pre-ignition are
described with reference to FIG. 13.
[0055] At 526 (from 522 or 524), it may be determined if engine
deactivation conditions have been met. For example, it may be
determined if a deceleration fuel shut-off (DFSO) event is being
performed. If yes, then at 528, the routine includes further
adjusting the scroll valve schedule and position based on the
engine deceleration indication to reduce turbine speed as per a
desired deceleration speed profile and any potential torque
disturbance. As elaborated with reference to FIG. 10, this may
include adjusting the scroll valve to a more closed position based
on turbine speed. Wastegate adjustments, as well as EGR valve
adjustments, may be coordinated with, and based on, the
corresponding scroll valve adjustments. Example scroll valve
adjustments performed during engine deactivation are described with
reference to FIG. 16.
[0056] At 530 (from 526 or 528), it may be determined if a torque
disturbance (e.g., torque surge or dip) is expected due to the
scheduled scroll valve adjustments (such as due to any of the
scheduled scroll valve adjustments at 508-528). If yes, then at
532, the routine includes adjusting one or more engine torque
actuators, as well as further adjusting a timing of the scroll
valve transition (e.g., when the scroll valve is transitioning to
or from an open or a closed position) to reduce the impact of the
imminent torque surge/dip. By adjusting the valve schedule, the
torque disturbance may be better masked, improving the vehicle
operator's drive feel. Further, a timing of the scroll valve
transition may be adjusted to overlap a transmission event. Example
torque actuator adjustments and scroll valve timing adjustments
performed to mask torque disturbances are described with reference
to FIG. 12.
[0057] In this way, by using scroll valve adjustments, alone or in
combination with wastegate and EGR valve adjustments, a range of
engine operation over which boost benefits can be provided is
enhanced. Further, the engine's tolerance to trade-offs performed
as operating conditions vary is increased. Overall, engine
performance is enhanced while also improving fuel economy.
[0058] Now turning to FIG. 6, an example routine 600 that may be
performed during start conditions is described. The routine enables
cold-start emissions to be reduced, exhaust catalyst light-off to
be expedited and turbocharger speed related NVH issues to be
avoided.
[0059] At 602, the routine includes estimating and/or measuring
engine operating conditions such as engine coolant temperature,
exhaust catalyst temperature, torque demand, BP, MAP, MAF, etc. In
addition, an initial scroll valve position may be determined based
on the estimated operating conditions. At 604, the routine includes
confirming an engine start condition. For example an engine start
may be confirmed by engine speed being below a threshold. If engine
start conditions are not confirmed, the routine may end. The engine
start may include an engine hot start or an engine cold start. As
such, turbocharger NVH concerns may not necessarily be temperature
dependent and may need to be managed regardless of the exhaust
catalyst temperature and light off state.
[0060] At specific turbocharger rotational speeds in turbocharged
engine systems, NVH issues may occur. For example, a whine can be
heard. The NVH issues may be particularly objectionable during
engine starts when the overall engine system noise is not
sufficient to mask any audible resonance at the turbocharger. Thus,
at 606, it may be determined if selected engine start conditions
are present, for example, start conditions that can lead to
objectionable audible resonance at the turbocharger. Specifically,
at 606, a turbine speed may be estimated and it may be determined
if the turbine speed is within a range R1. In one example, the
turbine speed range R1 may be based on turbine resonance and may
correspond to a turbine speed range where turbocharger whine during
a start is likely. The threshold range may be based on one or more
manifold pressure, airflow, engine speed, estimated or measured
exhaust gas temperature, and spark timing. In alternate
embodiments, the selected start conditions may be further
identified based on engine speed, intake manifold pressure,
etc.
[0061] If the turbine speed is not inside range R1, the routine
proceeds to 607, which includes confirming engine cold-start
conditions. For example, an engine cold-start condition may be
confirmed when an exhaust catalyst temperature is less than a
threshold temperature (e.g., a catalyst light-off temperature). As
another example, an engine cold-start condition may be confirmed
when an exhaust temperature is less than a threshold temperature.
As still another example, an engine cold-start condition may be
confirmed when the engine has been shut-down for more than a
threshold duration. Further considerations in assessing an engine
cold-start condition may include ambient conditions (such as
ambient temperature conditions), and engine temperature conditions
(e.g., based on engine coolant temperature). If engine cold-start
conditions are not confirmed, the routine may end.
[0062] If cold-start conditions are confirmed, the routine proceeds
to 608 wherein the engine is started with a scroll valve coupled to
an inlet of one scroll of a multi-scroll exhaust turbine adjusted
to expedite catalyst warm-up. Herein, the one scroll may be a
first, outer scroll, the turbine further including a second, inner
scroll, the scroll valve not coupled to an inlet of the second
scroll. The adjusting includes, in one example, moving the scroll
valve to a more closed position. In one example, moving the scroll
valve to a more closed position includes moving the scroll valve to
a fully closed position. By closing the scroll valve, the turbine
surface area for maximum heat flux to an exhaust catalyst is
minimized, expediting catalyst warm-up. In addition, the time
required to build boost on a subsequent tip-in is reduced.
[0063] The adjusting of the scroll valve may be based on exhaust
temperature. For example, when the exhaust temperature at the
cold-start is below a threshold, the valve may be moved to a more
closed position (e.g., to a fully closed position), the valve then
moved to a more open position (e.g., towards the fully open
position) as the exhaust temperature moves above the threshold. In
the depicted example, the threshold may be an exhaust catalyst
light-off temperature. The scroll valve may then be maintained in
the more closed position for a threshold number of combustion
events since the engine cold-start. Then, after the threshold
number of combustion events has elapsed, the scroll valve may be
moved to a more open position.
[0064] Next, at 610, the routine includes adjusting a turbine
wastegate position based on the scroll valve position to expedite
catalyst heating. The adjusting includes, as an example, moving the
wastegate to a more closed position as the scroll valve is moved to
a more closed position, to pre-position the wastegate to improve
boost response on possible subsequent tip-ins. In some embodiments,
the wastegate position may be further adjusted based on the exhaust
temperature at the cold-start. For example, the wastegate may be
moved to a more open position as the exhaust temperature moves
above the threshold. The routine may further include adjusting
various engine operating parameters responsive to the scroll valve
(and wastegate) adjustment to reduce torque transients during the
scroll valve adjustments. For example, one or more of spark
ignition timing, VCT, EGR and intake throttle position may be
adjusted while moving the scroll valve based on the scroll valve
position.
[0065] One or more additional steps may be taken to further
expedite exhaust catalyst heating during the cold-start. For
example, at 612, the routine includes retarding spark ignition
timing based on the scroll valve opening. Herein, an amount of
spark retard applied may be based on a difference between the
exhaust temperature and a light-off temperature. However, by using
the scroll valve adjustment, the amount of spark retard required
may be less than the amount required when no scroll valve
adjustment is used. Thus, by reducing the amount of spark retard
required, fuel economy is improved.
[0066] At 614, the routine includes adjusting the scroll valve
opening based on the exhaust temperature. Specifically, as the
exhaust temperature increases (e.g., above a threshold temperature,
such as a light-off temperature), the scroll valve opening may be
increased. That is, as the catalyst warms up, the scroll valve is
gradually moved from the fully closed to the fully open position,
allowing more exhaust gas to flow through both scrolls of the
turbine.
[0067] Next, at 630, and as further elaborated with reference to
FIG. 11, the routine includes adjusting one or more engine torque
actuators, as well as a timing of the scroll valve transition, to
reduce the impact of any torque surge/dip caused by the scroll
valve adjustment. By adjusting the engine torque actuators, any
torque disturbance may be better masked, and the vehicle operator's
drive feel may be improved. In one example, the adjusting includes
adjusting a timing of the scroll valve based on a transmission
event to better mask the torque surge.
[0068] Returning to 606, if the turbine speed is in range R1, then
the routine proceeds to 616 wherein in response to selected engine
start conditions being met (wherein the turbine speed is within a
threshold range), the engine is started with the scroll valve
coupled to the outer scroll of the exhaust turbine open. For
example, when a cold-start condition includes an exhaust catalyst
temperature being less than a threshold temperature and a turbine
speed being below a threshold speed, the scroll valve is adjusted
by moving the scroll valve to a more closed position. In
comparison, when the cold-start condition includes the exhaust
catalyst temperature being less than the threshold temperature and
the turbine speed being above the threshold speed, the scroll valve
is adjusted by moving the scroll valve to a more open position. As
such, an opening of the scroll valve may be adjusted based on each
of the turbine speed and an exhaust temperature.
[0069] While a nominal scroll valve position that is closed is
advantageous for expediting catalyst light-off and reducing time to
build boost, during some conditions, the closed position of the
scroll valve can result in a turbocharger speed that elicits the
audible resonance that is objectionable to the driver and/or
passengers of the vehicle. In such instances, by commanding the
scroll valve to the open position, the turbocharger speed is
reduced, thereby moving the turbocharger out of the resonance
conditions, and mitigating the objectionable noise. As such, the
conditions at which the scroll valve may be opened may depend on,
in addition to catalyst temperature and turbine speed, factors such
as engine speed, air flow, intake manifold pressure, engine coolant
or cylinder head temperature, air-fuel ratio, spark retard, torque
reserve, exhaust manifold temperature and pressure and other
similar parameters that are indicative of a cold start and which
define the energy delivered by the turbine.
[0070] At 618, the routine includes adjusting an opening of a
wastegate coupled across the exhaust turbine. Specifically, the
controller may increase an opening of the wastegate while an
opening of the scroll valve is increased to further reduce
turbocharger speed and improve NVH. An order of opening of the
wastegate and the scroll valve may be based on, for example, a
relative authority of each of the wastegate and the scroll valve at
the given operating conditions. For example, when turbine energy
changes sufficiently, one or the other may be opened initially,
while the other is closed. By coordinating the action of the scroll
valve with the action of the wastegate, both the wastegate and the
scroll can be used to mitigate the NVH issues that arise as turbine
energy changes. Further, while the depicted example suggests
opening the scroll valve and closing the wastegate, in alternate
examples, the wastegate may be opened while the scroll valve is
closed. One or the other may be closed to pre-position the
wastegate to improve boost response on possible subsequent tip-ins
and/or manage turbo speed for NVH and/or maximize heat flux to the
exhaust catalyst.
[0071] At 620, it may be determined if the turbine speed is outside
range R1. If not, then at 622, the controller may maintain each of
the scroll valve and wastegate open until the turbine speed is
outside of the threshold range. Else, after the turbine speed is
outside of the threshold range, the controller may adjust a
position of each of the scroll valve and the wastegate based on
exhaust temperature. Specifically, upon confirming that the turbine
speed is outside range R1, at 624, the routine determines if the
exhaust temperature is above the catalyst light-off temperature. If
yes, then the routine moves to 626 wherein the scroll valve is
moved to a scheduled position that is based on engine operating
conditions. If not, the routine moves to 628, wherein the scroll
valve is moved to a more closed position to expedite catalyst
heating, the scroll valve opening then increased as the exhaust
temperature increases and the exhaust catalyst becomes sufficiently
warmed. In other words, the controller maintains each of the scroll
valve and wastegate open until the turbine speed is outside of the
threshold range. Then, after the turbine speed is outside of the
threshold range, a position of each of the scroll valve and the
wastegate is adjusted based on exhaust temperature.
[0072] From both 626 and 628, the routine proceeds to 630 wherein,
as elaborated with reference to FIG. 11, the routine includes
adjusting one or more engine torque actuators to better mask any
torque disturbances caused by the scroll valve adjustment.
Specifically, one or more of EGR, VCT, spark timing, and intake
throttle position is adjusted during the engine cold-start based at
least on the scroll valve adjustment.
[0073] It will be appreciated that while the depicted routine is
ended in response to start conditions not being confirmed, in
alternate embodiments, if no scroll valve adjustment is confirmed,
an engine hot-start condition may be further confirmed. For
example, based on whether the engine is already sufficiently heated
(where one or more of engine temperature, exhaust temperature, and
exhaust catalyst temperature are sufficiently high) or based on the
engine being shut-down for less than a threshold duration, a hot
start condition may be confirmed. During engine hot-start
conditions, the scroll valve may be adjusted to expedite turbine
spin-up and/or manage turbo speed for NVH. For example, the engine
may be started with the scroll valve moved to a more open
position.
[0074] It will also be appreciated that while the example of
routine 600 discusses scroll valve adjustments used to manage turbo
whine at low speed conditions of engine starts, similar turbo whine
may be experienced at other low engine speed conditions not
associated with a start. During such low speed conditions not
associated with a start, the scroll valve may be similarly adjusted
to a position that removes the turbine from a speed range that
produces whine. The scroll valve position that avoids such a
turbine speed may change based on the engine operating conditions,
especially based on air-flow rate, exhaust gas pressure, and
wastegate position.
[0075] In one example, during a first engine start conditions
(e.g., a first engine cold-start condition), the engine may be
started with the scroll valve open for a first, larger number of
combustion events, while during a second engine start condition
(e.g., a second, different engine cold start condition or an engine
hot-start condition), the engine is started with the scroll valve
more open for a second, smaller number of combustion events. The
first engine start condition may include an exhaust catalyst
temperature being lower than a threshold temperature, while the
second engine start condition may include the exhaust catalyst
temperature being higher than the threshold temperature. During the
first engine start condition, an opening of the scroll valve may be
adjusted based on the exhaust catalyst temperature while during the
second engine start condition, the opening of the scroll valve may
be adjusted based on the catalyst temperature, as well as
turbocharger speed. The adjusting of the scroll valve during the
first engine start may include, as an example, for a first number
of combustion events, starting the engine with the scroll valve
moved to a more closed position (e.g., fully closed) and as the
exhaust catalyst temperature increases, increasing an opening of
the scroll valve. Then, after the first number of combustion
events, moving the scroll valve to a fully open position. In
comparison, adjusting of the scroll valve during the second engine
start may include, as an example, for a second number of combustion
events, starting the engine with the scroll valve moved to a more
open position (e.g., partially closed or fully open) and as the
exhaust catalyst temperature increases, increasing an opening of
the scroll valve. Then, after the second number of combustion
events, moving the scroll valve to a fully open position. In one
example, each of the first number and second number of combustion
events may be based on an exhaust temperature at engine start.
Alternatively, the number of combustion events may be based on
engine coolant temperature upon start-up.
[0076] Further, during the first engine start condition, the engine
may be started with a wastegate coupled to the exhaust turbine more
open for the first, number of combustion events while during the
second engine start condition, the engine is started with the
wastegate more open for a second number of combustion events.
Herein, during each of the first and second engine start conditions
(e.g., cold-start and hot-start conditions), the opening of the
wastegate may be based on the opening of the scroll valve.
[0077] In one example, an engine system comprises an engine, and a
turbocharger for providing a boosted aircharge to the engine,
wherein the turbocharger includes an intake compressor and an
exhaust turbine. The exhaust turbine may include a first outer and
a second inner scroll, and a scroll valve may be coupled between an
engine exhaust manifold and an inlet of the first outer scroll. The
engine system may further include a wastegate in a bypass coupled
between an inlet and an outlet of the turbine. A controller of the
engine system may be configured with computer readable instructions
for, during an engine start (e.g., cold-start) condition, starting
the engine with an opening of the scroll valve adjusted responsive
to exhaust temperature for a number of cylinder events since a
first combustion event. The adjusting may include, starting the
engine with the scroll valve more closed, and increasing an opening
of the scroll valve as the exhaust temperature rises.
Alternatively, the controller may be configured with computer
readable instructions for, during an engine start (e.g., hot start
or cold-start) condition, where turbine speed is lower than a
threshold speed, starting the engine with an opening of the scroll
valve increased based on the turbine speed. Then, after the turbine
speed is higher than the threshold, decreasing the opening of the
scroll valve (e.g., based on exhaust temperature. The controller
may include further instructions for adjusting the wastegate while
adjusting the scroll valve during the cold-start, the wastegate
adjustment based on the scroll valve adjustment to expedite exhaust
catalyst heating during the cold-start.
[0078] In this way, adjustments to a scroll valve position may be
used during engine start conditions to move turbine speed out a
speed range that produces turbo whine. Scroll valve position
adjustments may also be advantageously used during the engine start
to expedite catalyst heating and reduce cold-start emissions. An
example scroll valve adjustment is now described with reference to
FIG. 14.
[0079] Map 1400 of FIG. 14 depicts adjusting of a scroll valve
coupled to an inlet of an outer scroll of a multi-scroll exhaust
turbine responsive to engine start conditions, specifically,
responsive to an engine hot-start, or different engine cold-start
conditions. Map 1400 depicts exhaust temperature at plot 1402,
scroll valve adjustments at plot 1404, and engine conditions (on or
off) at plot 1406. All plots are depicted over time, plotted along
the x-axis.
[0080] Prior to t1, the engine may be shutdown. At t1, an engine
restart request may be received. The engine restart at t1 may be an
engine cold-start due to the engine being shut-down for a duration
that is longer than a threshold. As such, over the duration of the
engine shutdown, an exhaust catalyst may have cooled (plot 1402) to
below a light-off temperature (Tcat). Thus, at t1, an engine
cold-start may be initiated wherein the engine is spun up. In the
depicted example, the cold-start condition at t1 may be a first
cold-start condition, where the turbine speed is outside a
threshold range where turbo whine can occur. As such, the threshold
range may be based on one or more of manifold pressure, engine
speed, and spark timing. Thus, the first cold-start condition may
include no indication of turbocharger resonance. Accordingly, at
t1, the engine may be started (plot 1405) with the scroll valve
moved to a more closed position (plot 1404). In the depicted
example, the scroll valve may be moved to a fully closed position.
By closing the scroll valve, heat loss through the turbine is
reduced, increasing the exhaust heat transferred to the exhaust
catalyst. As such, this expedites exhaust warm-up.
[0081] The engine may be started with the scroll valve in the more
closed position for a first, larger number of combustion events
since the engine start. In the depicted example, the scroll valve
is maintained closed for a duration between t1 and t2. Then, after
the threshold number of combustion events have elapsed, at t2, the
scroll valve opening may be adjusted based on the exhaust
temperature. In the depicted example, at t2, the exhaust may also
be at the light-off temperature. Thus, as the exhaust temperature
increases above the threshold temperature after t2, the scroll
valve opening may be gradually increased until it is fully open. In
alternate examples, the scroll valve may be immediately moved to a
fully open position. Then engine may then be operated with the
scroll valve fully open. By opening the scroll valve, engine
pumping losses are reduced.
[0082] After t2 and before t3, the engine may be shut-down
temporarily. For example, the engine may be in an idle-stop
condition, where the engine is selectively deactivated. The engine
deactivation may be short enough that the exhaust catalyst is not
sufficiently cooled and is at or above Tcat (plot 1402). At t3, an
engine restart request is received. In response to the engine
hot-start condition at t3, the engine may be restarted (plot 1406)
with the scroll valve open (in the depicted example, fully
open).
[0083] After t3 and before t4, the engine may be shut-down. At t4,
an engine restart request may be received. The engine restart at t4
may also be an engine cold-start due to the engine being shut-down
for a duration that is longer than a threshold. As such, over the
duration of the engine shutdown, an exhaust catalyst may have
cooled (plot 1402) to below a light-off temperature (Tcat). In
addition, the scroll valve may be closed during the shut-down.
Thus, at t4, an engine cold-start may be initiated wherein the
engine is spun up. In the depicted example, the cold-start
condition at t4 may be a second cold-start condition, where the
turbine speed is inside a threshold range where turbo whine can
occur. As such, the threshold range may be based on one or more of
manifold pressure, engine speed, and spark timing. Thus, the second
cold-start condition may include an indication of potential
turbocharger resonance. Accordingly, at t4, the engine may be
started (plot 1405) with the scroll valve moved to a more open
position (plot 1404), such as a fully open position. By opening the
scroll valve, exhaust manifold pressure is reduced, and turbine
speed is reduced. This brings the turbine speed out of the range
where whine can occur. In the depicted example, the scroll valve
may be moved to a fully open position.
[0084] The engine may be started with the scroll valve in the more
open position for a second, smaller number of combustion events
since the engine start (as compared to the first number of
combustion events at the first cold start at t1). In the depicted
example, the scroll valve is maintained open for a duration between
t4 and t5. Then, after the threshold number of combustion events
have elapsed, at t5, the scroll valve opening may be adjusted based
on the exhaust temperature. In the depicted example, at t5, the
exhaust may still be below the light-off temperature. Thus, after
t5, the scroll valve is gradually closed to expedite catalyst
warm-up until the scroll valve is fully closed before t6. At t6,
the exhaust temperature increases above the threshold temperature
responsive to which the scroll valve opening is increased to a
fully open position. Then engine may then be operated with the
scroll valve fully open.
[0085] While not depicted in the example of FIG. 14, in further
examples, a controller may adjust a wastegate coupled across the
exhaust turbine responsive to the cold-start or hot start
condition. The controller may also adjust various engine torque
actuators, such as one or more of spark ignition timing, VCT, and
intake throttle position based on the scroll valve adjustment. In
this way, by adjusting a scroll valve adjustment during an engine
cold-start, catalyst warm-up is expedited, cold-start exhaust
emissions and turbo whine are reduced.
[0086] Now turning to FIG. 7, an example routine 700 is shown for
adjusting a scroll valve coupled to an inlet of an outer scroll of
a multi-scroll exhaust turbine responsive to an increased torque
demand, such as following a tip-in. The approach allows turbo lag
to be reduced.
[0087] At 702, the routine includes estimating and/or measuring
engine operating conditions such as engine coolant temperature,
exhaust catalyst temperature, torque demand, BP, MAP, MAF, etc. In
addition, an initial scroll valve position may be determined based
on the estimated operating conditions.
[0088] At 704, a tip-in may be confirmed. For example, it may be
determined if the torque demand has increased by more than a
threshold amount, and/or whether an accelerator pedal has been
depressed by more than a threshold amount. If tip-in conditions are
not confirmed, at 720, the routine includes moving the scroll valve
to the initial position, as determined and scheduled at 702.
Further, at 722, a position of a wastegate coupled across the
exhaust turbine may be adjusted based on the scheduled scroll valve
position so that the engine torque demand estimated at 702 can be
provided. Further still, residuals may be recirculated from the
engine exhaust to the engine intake via the EGR system(s), with the
valves adjusted to settings determined at 702, to meet the torque
demand. This includes adjusting an LP-EGR valve if the engine
system include an LP-EGR system and an HP-EGR valve if the engine
system includes an HP-EGR system to provide the determined amount
of exhaust gas recirculation.
[0089] If a tip-in is confirmed, then at 706, the routine includes,
in response to the tip-in, adjusting an opening of a scroll valve
coupled to the outer scroll of a multi-scroll exhaust turbine to
reduce turbo lag. Specifically, the adjusting includes reducing the
opening of the scroll valve. That is, the scroll valve may be moved
to a more closed position. In one example, the scroll valve may be
moved to a fully closed position. The scroll valve closing may be
based on the torque demanded at the tip-in. For example, the scroll
valve closing may be based on a difference between the torque
demanded and the torque that can be provided at the engine
operating conditions existing at the tip-in. As the difference
increases, the scroll valve may be moved closer to a fully closed
position to improve turbine spin-up. In an alternate example, the
reducing the opening of the scroll valve may be based on an
estimated or measured turbine speed at the tip-in. Therein, as a
difference between the estimated or measured turbine speed and a
requested turbine speed (based on the torque demanded) increases,
the scroll valve towards may be moved towards the fully closed
position. In still a further example, the reducing the opening of
the scroll valve may be based on an estimated or measured boost
pressure at the tip-in. Therein, as a difference between the
estimated or measured boost pressure and a requested boost pressure
(based on the torque demanded) increases, the scroll valve towards
may be moved towards the fully closed position. By closing the
scroll valve responsive to the tip-in, exhaust manifold pressure
may be increased, thereby expediting turbine spin-up. As such, this
reduces turbo lag and allows the increased torque demand to be
quickly met. In some examples, the scroll valve opening may also be
adjusted based on ambient air density, such as during the tip-in,
the valve moved towards a fully closed position as the ambient air
density decreases.
[0090] At 708, the routine includes, adjusting an opening of a
wastegate coupled across the exhaust turbine in response to the
tip-in, the wastegate opening based on the scroll valve opening. By
closing the wastegate, exhaust manifold pressure can be further
increased. For example, the wastegate may be moved towards a fully
closed position as the scroll valve is moved towards the fully
closed position. A timing of the wastegate adjustment may be based
on a timing of the scroll valve adjustment and further based on an
authority of the wastegate relative to the authority of the scroll
valve. For example, when the wastegate has lower authority relative
to the scroll valve, the wastegate adjustment may follow the scroll
valve adjustment. That is, first the wastegate may be kept open
while the scroll valve is moved to the closed position, and then
the scroll valve may be opened while the wastegate is closed. In
another example, when the wastegate has higher authority relative
to the scroll valve, the wastegate adjustment may lead or be
concurrent with the scroll valve adjustment. That is, first the
scroll valve may be kept open while the wastegate is moved to the
closed position, and then the wastegate may be opened while the
scroll valve is closed. Alternatively, they may be concurrently
closed.
[0091] At 710, the routine includes adjusting an amount of exhaust
gas recirculated to the engine intake. Specifically, an amount of
EGR may be reduced as the scroll valve moves towards the fully
closed position. In some embodiments, the engine may include an EGR
system having an LP-EGR valve in an LP-EGR passage for
recirculating exhaust gas from the exhaust manifold, downstream of
the turbine, to the intake manifold, upstream of the compressor, as
well as an HP-EGR valve in an HP-EGR passage for recirculating
exhaust gas from the exhaust manifold, from upstream of the
turbine, to the intake manifold, downstream of the compressor. The
engine controller may adjust each of the LP-EGR valve and the
HP-EGR valve in response to the tip-in to vary a ratio of HP-EGR to
LP-EGR based on the scroll valve closing. As one example, the
controller may increase an opening of the LP-EGR valve while
decreasing an opening of the HP-EGR valve to increase a ratio of
LP-EGR to HP-EGR. In another example, the controller may decrease
the opening of each of the LP-EGR valve and the HP-EGR valve to
reduce engine dilution.
[0092] At 712, it may be confirmed if the elevated torque demand
(responsive to the tip-in) has been met. In one example, it may be
determined that the torque demand has been met if the turbine has
sufficiently spun up. Thus, at 712, it may be determined if the
turbine speed is above the threshold. If not, then at 716, the
controller may maintain the scroll valve closed until the turbine
speed is at or above the threshold speed (or boost pressure is at
or above a requested boost pressure). Alternatively, the controller
may continue reducing the opening of the scroll valve (towards the
fully closed position), or maintain the scroll valve at a closed
position, until the turbine speed is at or above the threshold
speed (or boost pressure is at or above the requested boost
pressure).
[0093] At 714, after the turbine speed, or in another example boost
pressure, is at or above a threshold, the routine includes opening
the scroll valve. For example, the scroll valve may be fully
opened.
[0094] At 716, as further elaborated with reference to FIG. 11, the
routine includes adjusting one or more engine torque actuators, as
well as a timing of the scroll valve transition, to reduce the
impact of any torque surge/dip caused by the scroll valve
adjustment. By adjusting the engine torque actuators, any torque
disturbance may be better masked, and the vehicle operator's drive
feel may be improved. In one example, the adjusting includes
adjusting a timing of the scroll valve based on a transmission
event following the tip-in to better mask the torque
disturbance.
[0095] In this way, adjustments to a scroll valve during a tip-in
may be advantageously used to expedite turbine spin-up and improve
boost performance during the tip-in. An example scroll valve
adjustment is now described with reference to FIG. 17.
[0096] Map 1700 of FIG. 17 depicts adjusting of a scroll valve
coupled to an inlet of an outer scroll of a multi-scroll exhaust
turbine responsive to increased torque demand, specifically,
responsive to a tip-in. Map 1700 depicts an engine torque at plot
1702, turbine speed at plot 1704, scroll valve adjustments at plot
1706, wastegate adjustments at plot 1708, HP-EGR valve adjustments
at plot 1710, and LP-EGR valve adjustments at plot 1712. All plots
are depicted over time, plotted along the x-axis.
[0097] Prior to t1, the engine may be operating with each of the
scroll valve (plot 1706) and the wastegate (plot 1708) at least
partially open to provide engine torque (plot 1702) control. At t1,
a tip-in event may be confirmed. In response to the tip-in event,
the scroll valve coupled to an outer scroll of a multi-scroll
turbine is moved to a more closed position. In the depicted
example, closing the scroll valve includes fully closing the scroll
valve. As such, the scroll valve may be kept closed for a duration
following the tip-in until the turbine speed (plot 1704) is at or
above a threshold speed. In the depicted example, the scroll valve
is maintained closed from t1 to t2. At t2, when the turbine speed
is sufficiently high (e.g., above a threshold speed), the scroll
valve is opened. In the depicted example, opening the scroll valve
includes fully opening the scroll valve.
[0098] In one example, the duration of scroll valve closing may be
based on turbine speed following the tip-in, with the duration
increased as the turbine speed following the tip-in decreases. In
other words, if a larger spin-up is required, the scroll valve may
be moved to a more closed position, while if a smaller spin-up is
required, the scroll valve may be moved to a relatively less closed
position. By closing the scroll valve responsive to a tip-in, an
exhaust manifold pressure can be rapidly increased, thereby
enabling the turbine to quickly spin-up. As such, this reduces
turbo lag and allows transients to be better addressed. In
comparison, if the scroll valve was not closed following the
tip-in, an amount of time taken to spin up the turbine may be
longer, as shown by plot 1703 (dashed line), and as also shown at
FIG. 4.
[0099] At t1, while closing the scroll valve, a net amount of EGR
delivered to the engine may also be reduced. This may include
reducing an opening of an LP-EGR valve coupled to an LP-EGR system,
or reducing an opening of an HP-EGR valve coupled to an HP-EGR
system. Further still, the controller may adjust the opening of
each of the LP-EGR valve and the HP-EGR valve to vary a ratio of
LP-EGR to HP-EGR delivered to the engine. In the depicted example,
an opening of the HP-EGR valve (plot 1710) is decreased to reduce
an amount of residuals recirculated from upstream of the turbine to
downstream of the compressor. At the same time, an opening of the
LP-EGR valve (plot 1712) is increased to increase an amount of
residuals recirculated from downstream of the turbine to upstream
of the compressor. As such, the net amount of EGR and engine
dilution may be reduced. In alternate embodiments, the net amount
of EGR may be maintained while the scroll valve is closed.
[0100] At t1, to further assist in turbine spin-up, the wastegate
is kept closed responsive to the closing the scroll valve. Herein,
the wastegate has higher, or comparable authority and therefore is
adjusted concurrent to the scroll valve. However in alternate
examples, such as when the wastegate has lower authority, the
wastegate adjustment may follow the scroll valve adjustment. The
wastegate may also be controlled to intermediate positions to
actively control boost to a desired set point. In some examples,
the timing of the scroll valve adjustment may be further based on a
transmission event following the tip-in.
[0101] At t3, in response to sufficient turbine and engine spin-up,
the wastegate may be opened after the scroll valve is opened. In
addition, at t3, an opening of the LP-EGR valve may be reduced
while an opening of the HP-EGR valve is increased, so as to
increase the net amount of engine dilution. In an alternate
example, a controller may open the scroll valve while maintaining
the amount of EGR delivered to the engine. In yet another example,
the opening of the HP-EGR valve may be reduced while an opening of
the LP-EGR valve is increased, so as to increase the net amount of
engine dilution.
[0102] While not depicted in the example of FIG. 17, in further
examples, a controller may adjust various engine torque actuators,
such as one or more of spark ignition timing, VCT, valve overlap,
and an intake throttle position based on the scroll valve
adjustment, the measured boost pressure and the torque transients.
In this way, scroll valve adjustments may be performed responsive
to transient torque demands. By closing the scroll valve when
torque demand increases, turbine spin up can be expedited. By
adjusting the engine dilution (via EGR valve adjustments) based on
the scroll valve adjustment, torque transients and combustion
stability concerns can be better addressed, improving engine
performance.
[0103] Now turning to FIG. 8, an example routine 800 is shown for
adjusting a scroll valve coupled to an inlet of an outer scroll of
a multi-scroll exhaust turbine responsive to engine dilution. The
approach allows combustion stability limits for engine combustion
to be improved.
[0104] At 802, the routine includes estimating and/or measuring
engine operating conditions such as engine coolant temperature,
exhaust catalyst temperature, torque demand, BP, MAP, MAF, etc. In
addition, an initial scroll valve position may be determined based
on the estimated operating conditions.
[0105] At 804, the routine includes determining an engine dilution
required based on the estimated operating conditions. The engine
dilution request may include a request for LP-EGR and/or a request
for HP-EGR. Further, an amount of residuals to be recirculated from
the engine exhaust manifold to the engine intake manifold, such as
via an EGR system, may be determined based on the required dilution
and the estimated operating conditions. As used herein,
recirculating via an EGR system may include recirculating via a
low-pressure EGR system coupled between the engine exhaust,
downstream of the turbine, and the engine intake, upstream of an
intake compressor, by opening a first EGR valve and/or
recirculating via a high-pressure EGR system coupled between the
engine exhaust, upstream of the turbine, and the engine intake,
downstream of the intake compressor, by opening a second, different
EGR valve. Further, residuals may be recirculated from the engine
exhaust to the engine intake via the EGR system(s) to provide the
desired dilution until a combustion stability limit is reached
[0106] At 806, it may be determined if an engine combustion
stability has been reached, or is being approached. Fuel economy
and emissions can be improved at many engine operating conditions
by increasing the amount of burned gas trapped in a cylinder (also
referred to as residuals). This burned gas can be introduced during
a valve overlap period (internal EGR), or by recirculating exhaust
gas to the engine intake (external EGR). The recirculated exhaust
gas can be taken from the exhaust path upstream (HP-EGR) or
downstream (LP-EGR) of the turbine, and may or may not be cooled.
However, there may be limits to the amount of residuals that can be
tolerated due to combustion stability constraints. For example,
residuals may need to be limited at high load conditions to allow
the demanded torque to be delivered. In one example, it may be
determined at 806 if the engine will operate at or near combustion
stability limits when operating with the EGR valves and the scroll
valve at the initially scheduled position. Herein, the combustion
stability limits may have been previously determined based on the
engine operating conditions and parameters.
[0107] If combustion stability limits have not been reached, then
at 816, the routine includes moving the scroll valve to the initial
position, as determined and scheduled at 802. Further, at 818, a
position of a wastegate coupled across the exhaust turbine may be
adjusted based on the scheduled scroll valve position and the
engine dilution request so that the required engine dilution can be
provided. Further still, residuals may be recirculated from the
engine exhaust to the engine intake via the EGR system(s), with the
valves adjusted to settings determined at 802, to provide the
desired dilution until a combustion stability limit is reached.
[0108] If combustion stability limits have been reached, then at
808, the routine includes, adjusting the scroll valve position
responsive to the engine dilution request relative to the engine
combustion stability limits. This includes moving the scroll valve
to a more closed position as a request for engine dilution
increases, and moving the scroll valve towards a more open position
as a request for engine dilution decreases (to reduce internal
residuals). For example, the scroll valve schedule may be adjusted
based on intake manifold pressure. Therein, as the manifold
pressure increases (above a threshold pressure), the scroll valve
may be moved towards the more open position.
[0109] The scroll valve adjustment may be further based on whether
the dilution request was for LP-EGR or HP-EGR. For example, when
the dilution request is for increased HP-EGR, the scroll valve may
be moved to a more closed position to ensure that the exhaust
manifold pressure is sufficiently high to flow EGR to the intake
manifold (e.g., the exhaust manifold pressure is higher than the
intake manifold pressure). In comparison, when the dilution request
is for increased LP-EGR, the scroll valve may be moved to a more
open position.
[0110] As such, the position of the scroll valve affects the amount
of internal EGR delivered to the cylinders through its impact on
the exhaust manifold pressure during the valve overlap period.
Further, for engine systems configured with LP-EGR, the position of
the scroll valve affects the maximum turbine energy. This, in turn,
dictates the maximum amount of air and/or EGR that can be delivered
to the engine system through the compressor. Further still, for
engine systems configured with HP-EGR, the position of the scroll
valve affects EGR delivery via its impact on the exhaust manifold
pressure. It also changes the available turbine energy, thereby
also dictating the maximum amount of air that can be delivered to
the engine system through the compressor.
[0111] At 810, an intake and/or exhaust valve timing may be
adjusted based on the scroll valve position to adjust an amount of
internal EGR delivered to the engine. For example, where the valve
timing is adjusted via a variable cam timing (VCT) device, VCT
adjustments may be used to decrease an amount of intake to exhaust
valve overlap to decrease an amount of residuals delivered via
internal EGR. Valve timing adjustments may include retarding intake
valve opening and/or advancing exhaust valve closing. By opening
the intake valve later and/or closing the exhaust valve earlier,
while the scroll valve is at the more closed position, internal EGR
is reduced.
[0112] At 812, one or more of the LP-EGR valve and the HP-EGR valve
may be adjusted based on the scroll valve position to adjust an
amount of external EGR delivered to the engine. As one example,
while moving the scroll valve to the more closed position, an
opening of the first LP-EGR valve and/or the second HP-EGR valve
may be reduced to reduce an amount of residuals delivered to the
engine via external EGR. As another example, the controller may
maintain the first LP-EGR valve and/or the second HP-EGR valve open
while decreasing the opening of the scroll valve. It will be
appreciated that while the above routine discusses making scroll
valve adjustments to meet engine dilution needs when the engine
reaches combustion stability limits, in still further embodiments,
the scroll valve adjustments may be made to meet engine dilution
needs when at least one of the LP-EGR valve and the HP-EGR valve
reaches a limit. This may include, for example, an opening limit
(beyond which the valve cannot be opened any further) or a closing
limit (beyond which the valve cannot be closed any further) of the
EGR valves. As such, when any of the EGR valves reach their opening
or closing limit, further changes to residual amounts, as well as a
further change in LP-EGR to HP-EGR ratio may be provided by
corresponding adjustments to the scroll valve. Wastegate
adjustments may be concomitantly used with, and based on the scroll
valve adjustments, to meet the engine dilution requirement.
[0113] At 814, the routine includes adjusting one or more engine
actuators during the scroll valve transition to reduce any impact
of a torque disturbance resulting from the scroll valve adjustment.
For example, the routine may include adjusting one or more of a
wastegate coupled to the exhaust turbine, spark ignition timing,
VCT, positive valve overlap, and intake throttle opening while
moving the scroll valve to the more closed position wherein the
adjusting is based on each of the scroll valve position and engine
dilution. As elaborated with reference to FIG. 11, the actuator
adjustment may be used to better mask any torque surge/dip that may
arise during the scroll valve adjustment, thereby improving the
vehicle operator's drive feel. In one example, a timing of the
scroll valve adjustment is based on a transmission event to better
mask the torque disturbance.
[0114] In this way, adjustments to the LP-EGR valve and HP-EGR
valve can be coordinated with wastegate and scroll valve actions so
as to manage residuals. Then, as turbine energy changes, one of the
wastegate and the scroll valve can be opened to manage boost
response while using the other to manage exhaust pressure for
residual control. Alternatively, one of the wastegate and the
scroll valve may be opened initially, while the other is maintained
closed. Then, as the turbine energy changes sufficiently, the other
which was closed may be opened, while the first one is closed. An
order of opening and closing may depend on the relative authority
of each device at the various operating conditions.
[0115] In one example, an engine system comprises an engine, and a
turbocharger for providing a boosted aircharge to the engine,
wherein the turbocharger includes an intake compressor and an
exhaust turbine. The exhaust turbine may include a first outer and
a second inner scroll with a scroll valve coupled to an inlet of
the first outer scroll but not to an inlet of the second inner
scroll. A wastegate may be included in a bypass coupled between an
inlet and an outlet of the turbine. A first EGR passage may be
coupled between an engine exhaust, downstream of the turbine, and
an engine intake, upstream of the compressor, the first EGR passage
including a first EGR valve. A second EGR passage may be coupled
between the engine exhaust, upstream of the turbine, and the engine
intake, downstream of the compressor, the second EGR passage
including a second EGR valve. The engine system may further include
a controller with computer readable instructions for, opening one
or more of the first EGR valve and the second EGR valve to provide
engine dilution, and upon reaching a limit, providing further
engine dilution by decreasing an opening of the scroll valve. The
limit may include one of an opening limit of the first EGR valve
and/or an opening limit of the second EGR valve. The controller may
be configured to maintain the first and/or second EGR valve open
while increasing the opening of the scroll valve. Alternatively,
the controller may be configured to decrease the opening of the
first and/or second EGR valve while increasing the opening of the
scroll valve. The controller may be further configured to adjust
the opening of each of the first and second EGR valve while
decreasing the opening of the scroll valve to vary a ratio of
high-pressure EGR to low-pressure EGR delivered to the engine.
[0116] In another example, a method for an engine may include
recirculating residuals from an engine exhaust to an engine intake
via an EGR system until a combustion stability is reached, and
after the limit, reducing internal residuals by moving a scroll
valve coupled to an outer scroll of a multi-scroll turbine to a
more open position. The method further includes, while moving the
scroll to the more open position, reducing an opening of a first
LP-EGR valve and/or a second HP-EGR valve.
[0117] An example adjustment is now described with reference to
FIG. 15. Map 1500 of FIG. 15 depicts adjusting of a scroll valve
coupled to an inlet of an outer scroll of a multi-scroll exhaust
turbine responsive to engine dilution. Map 1500 depicts an engine
dilution requested at plot 1501 (dashed line) and an engine
dilution provided at plot 1502 (solid line). Map 1500 further
depicts EGR valve adjustments at plot 1504 and scroll valve
adjustments at plot 1506. All plots are depicted over time, plotted
along the x-axis.
[0118] Prior to t1, the engine may be operating with the scroll
valve (plot 1506) at a more open position (e.g., at a fully open
position). Further, the EGR valve (plot 1504) may be at a position
that is based on the engine dilution needed (plot 1501) so that the
requested engine dilution is provided (plot 1502). As such, the
engine dilution request may include one or more of a low-pressure
EGR request and a high-pressure EGR request. In one example, the
engine dilution request may also include a ratio of LP-EGR to
HP-EGR. In still another example, the engine dilution request may
also include a ratio of internal EGR to external EGR.
[0119] At t1, based on a change in engine operating conditions,
there may be an increased request for engine dilution. For example,
there may be an increased demand for LP-EGR and/or HP-EGR. As such,
the engine dilution needed may be within an engine combustion
stability limit 1503. Accordingly, an opening of the EGR valve may
be increased at t1, while maintaining a position of the scroll
valve, to meet the increased engine dilution need. Increasing an
opening of the EGR valve may include increasing an opening of a
LP-EGR valve when the engine dilution request includes a request
for more LP-EGR. Alternatively, the increasing may include
increasing an opening of a HP-EGR valve when the engine dilution
request includes a request for more HP-EGR. Further still, while
plot 1504 shows a single EGR valve, the opening of the EGR valve
may include opening of each of a LP-EGR valve and a HP-EGR valve to
vary a ratio of LP-EGR and HP-EGR provided based on the engine
dilution request. Then, at t2, when the engine dilution request
decreases, the EGR valve opening may be correspondingly
decreased.
[0120] At t3, based on a change in engine operating conditions,
there may again be an increased request for engine dilution.
However, to provide the desired engine dilution, at t3, the EGR
valve may need to be opened beyond its opening limit 1505. Since
this is not possible, the EGR valve may be fully opened and
maintained at its opening limit 1505 and the remaining engine
dilution need may be met by decreasing an opening of the scroll
valve at t3. As such, by closing the scroll valve and using scroll
valve adjustments to provide the desired dilution, engine
combustion stability limits may be met, thereby improving engine
performance. Then, at t4, when the engine dilution request
decreases, the EGR valve opening may be decreased and the scroll
valve opening may be correspondingly increased.
[0121] Herein, adjusting the scroll valve responsive to engine
dilution includes adjusting the scroll valve responsive to an EGR
request, the EGR request including one or more of LP-EGR, HP-EGR,
or a ratio of LP-EGR to HP-EGR, the ratio based on the requested
engine dilution. Further still, the scroll valve opening may be
adjusted responsive to a ratio of internal EGR to external EGR, the
ratio based on the requested engine dilution.
[0122] As used herein, the adjusting responsive to engine dilution
includes adjusting responsive to the engine dilution request
relative to the engine combustion stability limit. For example, the
scroll valve may be moved to a more closed position as a request
for engine dilution increases while the scroll valve is moved to a
more open position as a request for engine dilution decreases.
[0123] While the depicted example suggests closing the scroll
valve, in alternate examples, the scroll valve may be opened in
response to the engine dilution, the adjustment (opening or
closing) based not only on the engine dilution request but also on
the engine EGR system configuration. In one example, wherein the
engine includes an EGR system configured to recirculate exhaust gas
from an engine exhaust to an engine intake, the adjusting may
include, in response to an engine dilution request being higher
than an engine dilution that can be provided by the EGR system,
increasing an opening of the scroll valve, and in response to the
engine dilution request being lower than the engine dilution that
can be provided by the EGR system, decreasing the opening of the
scroll valve. Herein, the EGR system may include one or more of a
low-pressure EGR system including a first EGR valve and a
high-pressure EGR system including a second EGR valve, and wherein
one or more of the first EGR valve and the second EGR valve is
adjusted based on the engine dilution request and the scroll valve
adjustment. In another example, the adjusting of the scroll valve
responsive to engine dilution may include increasing engine
dilution by increasing opening of a valve coupled to the EGR system
while increasing an opening of the scroll valve, the increasing
based on each of an engine dilution request and an opening limit of
the EGR valve. The adjusting responsive to engine dilution may
further include decreasing engine dilution by decreasing opening of
the valve coupled to the EGR system while decreasing the opening of
the scroll valve, the decreasing based on each of the engine
dilution request and a closing limit of the EGR valve.
[0124] In engine systems configured with an LP-EGR system, the
scroll valve can be positioned to provide the turbine power
required to deliver the air and external EGR to the engine. At low
engine loads, the turbine power is higher with the scroll valve
closed due to higher exhaust manifold pressure. At some higher
engine loads (system dependent), the open scroll valve may produce
more turbine power due to increased mass flow.
[0125] In the depicted embodiment, cylinder valve timing may be
maintained during the increasing and decreasing opening of the
scroll valve. However, in alternate embodiments, valve timing
adjustments may be concurrently used alongside scroll valve
adjustments to also meet the engine dilution. For example, valve
timing may be adjusted to reduce valve overlap while the scroll
valve opening is increased.
[0126] While not depicted in the example of FIG. 15, in further
examples, a controller may adjust a wastegate coupled across the
exhaust turbine responsive to the engine dilution, the wastegate
adjusted based on the scroll valve adjustment and the engine
dilution. The controller may also adjust various engine torque
actuators, such as one or more of spark ignition timing, VCT, and
intake throttle position based on the scroll valve adjustment and
the engine dilution.
[0127] In this way, scroll valve adjustments may be performed
responsive to engine dilution. By closing the scroll valve when EGR
valve limits are reached, or opening the scroll valve when engine
combustion stability is limited, an amount of residuals delivered
to the engine can be managed and engine dilution can be provided
without degrading engine performance.
[0128] Now turning to FIG. 9, an example routine 900 is shown for
adjusting a scroll valve coupled to an inlet of an outer scroll of
a multi-scroll exhaust turbine in response to an indication of
pre-ignition to reduce engine load and mitigate engine damage. The
routine allows engine hardware to be protected from pre-ignition
and other hardware limits.
[0129] At 902, the routine includes estimating and/or measuring
engine operating conditions such as engine coolant temperature,
exhaust catalyst temperature, torque demand, BP, MAP, MAF, etc. In
addition, an initial scroll valve position may be determined based
on the estimated operating conditions.
[0130] At 904, it may be determined if there is an indication of
knock (without pre-ignition). If there is no indication of knock,
then at 906, it may be determined if there is an indication of
pre-ignition. As such, at 904 and 906, engine knock and
pre-ignition may be identified and distinguished from one another.
If neither knock nor pre-ignition is determined at 904 and 906, the
routine proceeds to 926 wherein the scroll valve is moved to the
initial position, as determined and scheduled at 902. Further, at
928, a position of a wastegate coupled across the exhaust turbine
may be adjusted based on the scheduled scroll valve position and
further based on the engine operating conditions so that a desired
boost can be provided. Further still, the position of an EGR valve
of the EGR system (including a LP-EGR valve of the LP-EGR system
and an HP-EGR valve of the HP-EGR system) may be adjusted based on
the scheduled scroll valve position, the wastegate position, and
the engine operating conditions to provide a desired engine
dilution.
[0131] In one example, the indication of knock and the indication
of pre-ignition may be identified and distinguished based on the
output of a knock sensor coupled to the engine block. Based on a
comparison of the output relative to a threshold, and further based
on a timing (e.g., in crank angle degrees) of the output, a knock
or pre-ignition event may be determined. As such, engine knock may
be due to an abnormal combustion event occurring in a cylinder
after a spark ignition event of the cylinder while engine
pre-ignition may be due to an abnormal combustion event occurring
in the cylinder before a spark ignition event of the cylinder. As
an example, the indication of pre-ignition at 906 may include a
knock sensor output that is higher than a threshold and that is
received before a cylinder ignition event. In comparison, the
indication of knock at 904 may include a knock sensor output that
is higher than the threshold and that is received after the
cylinder ignition event. In still another example, the knock sensor
output may be compared to different thresholds for identifying
knock and pre-ignition. For example, the indication of knock may be
based on a knock sensor output that is higher than a first
threshold received in a first window while the indication of
pre-ignition is based on a knock sensor output that is higher than
a second threshold and that is received in a second window, the
second threshold higher than the first threshold, and the second
window earlier than the first window. That is, pre-ignition may
result in an earlier and relatively stronger vibration, received in
the cylinder before the spark event, while knock may result in a
later and relatively softer vibration, received in the cylinder
after the spark event.
[0132] In still further examples, the indication of pre-ignition
may be based on the output of one or more of a knock sensor, a
torque sensor, and a crank acceleration sensor. Further still, the
indication of knock or pre-ignition may include an indication
regarding the likelihood of knock or pre-ignition. For example,
based on engine operating conditions and further based on engine
knock or pre-ignition history, it may be inferred whether
pre-ignition or knock is likely and the routine of FIG. 9 may be
executed in response to the likelihood of knock or pre-ignition
being higher than a threshold.
[0133] At 904, in response to the indication of knock without
pre-ignition, the routine includes increasing an opening of the
scroll valve to a less open position (that is, more open that the
initial position but relatively more closed relative to an opening
used in response to pre-ignition) so to reduce exhaust manifold
pressure and internal residuals. The adjusting in response to the
indication of knock may be based on a measurement of knock
intensity from a knock sensor, in-cylinder pressure measurements or
other means with an opening of the scroll valve increased as the
knock intensity increases. At 910, the routine includes further
adjusting one or more of VCT, throttle position, spark timing,
cylinder fueling and EGR delivered to the knock-affected cylinder,
while adjusting the scroll valve, the adjusting based on the scroll
valve adjustment. As such, these may include actuator adjustments
used to address knock. For example, in response to the indication
of knock, spark timing may be retarded, with the amount of spark
retard applied adjusted based on the opening of the scroll valve.
Thus, as the scroll valve opening is increased in response to
knock, an amount of spark retard that needs to be applied to
address the knock may be decreased. By using the scroll valve to
address the knock, the amount of spark retard required is
decreased, thereby enabling knock mitigation with reduced fuel loss
and improved fuel economy.
[0134] Further still, a wastegate coupled across the exhaust
turbine may be adjusted based on the scroll valve adjustment. For
example, as the scroll valve is moved to a more open position, the
wastegate may also be moved to a more open position. This further
assists in reducing residuals and in-cylinder temperature to
mitigate the knock.
[0135] At 912, it may be determined if knock has been mitigated.
For example, it may be determined if the indication of knock is
less than the threshold. If yes, the routine may proceed to 914 to
resume the initial settings, including the initial position of the
scroll valve. Alternatively, engine actuator settings and scroll
valve settings may be re-adjusted based on the prevalent engine
operating conditions following the mitigation of knock. If knock
has not been sufficiently mitigated at 912, then at 916, the
routine includes maintaining the scroll valve position. For
example, the controller may maintain the scroll valve at the more
open position for a duration until an in-cylinder temperature is
below a threshold, and then move the scroll valve to a more closed
position if desired.
[0136] Returning to 906, in response to the indication of
pre-ignition, at 918, the routine includes adjusting the scroll
valve to a more open position to reduce engine load. The opening of
the scroll valve responsive to the indication of pre-ignition is
more than the opening responsive to the indication or knock. In one
example, adjusting the scroll valve to the more open position
includes fully opening the scroll valve. Alternatively, the scroll
valve may be opened in discrete increments (e.g., in step-wise
increments of 20%). By opening the scroll valve in response to the
indication of pre-ignition, exhaust manifold pressure can be
reduced, thereby reducing an amount of trapped residuals in the
cylinder that can contribute to further pre-ignition events. In one
example, by opening the scroll valve in response to pre-ignition,
engine load can be lowered from an elevated 17.5 bar level to a
safer and more stable 16 bar load level within 1-2 seconds.
[0137] In one example, the adjusting of the scroll valve in
response to the indication of pre-ignition may be based on exhaust
manifold pressure with an opening of the scroll valve increased as
the exhaust manifold pressure exceeds a threshold pressure. In
another example, the adjusting of the scroll valve in response to
the indication of pre-ignition may be based on a turbine inlet
temperature with an opening of the scroll valve increased as the
turbine inlet temperature exceeds a threshold temperature. For
example, if the turbine inlet temperature is determined to be
beyond a threshold temperature corresponding to a material
durability limit for more than a specified duration (e.g., at or
above 950.degree. C. for more than 0.3 seconds), the scroll valve
may be at least partially opened in order to rapidly reduce engine
load to a safer level where engine hardware will not be
degraded.
[0138] As such, the threshold temperature at which the turbine
inlet is limited may vary at different scroll openings. For
example, the thermal stresses may be higher when the scroll valve
is fully closed. Accordingly, a lower temperature threshold may be
applied (e.g., 850.degree. C.) when the scroll valve is closed
while a higher temperature threshold is applied (e.g.,
950-1000.degree. C.) when the scroll valve is open.
[0139] In a further example, the adjusting of the scroll valve in
response to the indication of pre-ignition may be based on the
intensity or frequency of the pre-ignition, an opening of the
scroll valve increased as the intensity or frequency of
pre-ignition increases. In yet another example, the adjusting of
the scroll valve in response to the indication of pre-ignition may
be based on engine speed with the opening of the scroll valve
increased as the engine speed decreases. Further still, the
adjusting of the scroll valve in response to the indication of
pre-ignition may be based on an air temperature including an
ambient air temperature or a manifold air temperature, the opening
of the scroll valve increased as the air temperature increases. In
still another example, the adjusting of the scroll valve in
response to the indication of pre-ignition may be based on one or
more of ambient humidity and fuel octane content, the opening of
the scroll valve increased as the humidity decreases, the opening
of the valve increased as the fuel octane content/rating
decreases.
[0140] At 920, the routine includes further adjusting one or more
of VCT, throttle position, spark timing, cylinder fueling and EGR
delivered to the knock-affected cylinder, while adjusting the
scroll valve, the adjusting based on the scroll valve adjustment.
As such, these may include actuator adjustments used to address
pre-ignition. For example, in response to the indication of knock,
cylinder fuel injection may be enriched the cylinder, with the
cylinder enrichment adjusted based on the opening of the scroll
valve. Thus, as the scroll valve opening is increased in response
to pre-ignition, an amount cylinder fuel enrichment that needs to
be applied to address the pre-ignition may be decreased. By using
the scroll valve to address the pre-ignition, the amount of
enrichment required is decreased, thereby enabling pre-ignition
mitigation with reduced fuel loss and improved fuel economy.
[0141] Further still, a wastegate coupled across the exhaust
turbine may be adjusted based on the scroll valve adjustment. For
example, as the scroll valve is moved to a more open position, the
wastegate may also be moved to a more open position. This further
assists in reducing engine load, exhaust manifold pressure, and
turbine inlet temperature to mitigate the pre-ignition.
[0142] It will be appreciated that there may be selected engine
operating conditions, such as selected engine speed-load
conditions, wherein only a wastegate adjustment can be used (in
place of, and similar to a scroll valve adjustment) to control the
exhaust manifold pressure. For example, in response to the
indication of pre-ignition, only a wastegate adjustment can be used
to reduce exhaust manifold pressure and engine load to mitigate the
pre-ignition. However, even if wastegate adjustments are possible,
scroll valve adjustments may be advantageous even in those
operating conditions. As one example, scroll valve adjustments may
enable the active controls of the wastegate to be decoupled from
the control of the scroll valve and the pre-ignition mitigation.
For example, based on control forces and valve authority (that is,
based on authority of wastegate relative to scroll valve), one or
the other of the scroll valve and the wastegate may be selected for
pre-ignition control. For example, during a first pre-ignition
condition, where the wastegate has higher authority, the wastegate
may be opened to reduce engine load and mitigate the pre-ignition
while during a second, different pre-ignition condition, where the
scroll valve has higher authority, the scroll valve may be opened
to reduce engine load and mitigate the pre-ignition. During a third
pre-ignition condition, where the wastegate and the scroll valve
have substantially similar authority, one of the two may be
selected (e.g., the scroll valve is opened while the wastegate is
closed or the wastegate is opened while the scroll valve is
closed). Alternatively, each of the scroll valve and the wastegate
may be at least partially opened to reduce the engine load. This
provides less boost, lowers the engine load and mitigates the
occurrence of pre-ignition.
[0143] At 922, it may be determined if pre-ignition has been
mitigated and there is no further indication of pre-ignition. For
example, it may be determined if the turbine inlet temperature is
less than a threshold. Alternatively, it may be determined if the
exhaust manifold pressure is less than a threshold. If yes, the
routine may proceed to 914 to resume the initial settings,
including the initial position of the scroll valve. For example,
the controller may open the scroll valve in response to the
indication of pre-ignition, maintain the scroll valve at the more
open position for a duration until the exhaust manifold pressure is
below a threshold, and after the exhaust manifold pressure has been
lowered and if there is no further indication of pre-ignition, move
the scroll valve to a more closed position. Alternatively, engine
actuator settings and scroll valve settings may be re-adjusted
based on the prevalent engine operating conditions following the
mitigation of pre-ignition.
[0144] If pre-ignition has not been sufficiently mitigated at 922,
then at 916, the routine includes maintaining the scroll valve
position. For example, the controller may maintain the scroll valve
at the more open position for a duration until the turbine inlet
temperature, or the exhaust manifold pressure, is below the
respective threshold. Then, after the temperature or pressure has
been sufficiently lowered, the scroll valve may be moved to a more
closed position. For example, after the turbine inlet temperature
is below the threshold temperature, the controller may at least
partially close the scroll valve, with the scroll valve closing
based on turbine speed or measured boost pressure. In one example,
at least partially closing the scroll valve includes moving the
scroll valve from the more open position to a fully closed
position.
[0145] From 914 or 916, the routine proceeds to 924 where the
routine includes adjusting one or more engine actuators during the
scroll valve transition to reduce any impact of a torque
disturbance resulting from the scroll valve adjustment. For
example, the routine may include adjusting one or more of a
wastegate coupled to the exhaust turbine, spark ignition timing,
VCT, positive valve overlap, and intake throttle opening while
moving the scroll valve to the more open position. As elaborated
with reference to FIG. 11, the actuator adjustment may be used to
better mask any torque surge/dip that may arise during the scroll
valve adjustment, thereby improving the vehicle operator's drive
feel. In one example, a timing of adjusting the scroll valve is
based on a transmission event to reduce the torque impact.
[0146] In some embodiments, the scroll valve may be opened
responsive to both engine pre-ignition and knock, however the
opening responsive to pre-ignition may be more than the opening
responsive to knock. For example, in response to the indication of
pre-ignition, the scroll valve may be adjusted to a first open
position while in response to an indication of knock, the scroll
valve is adjusted to a second open position, the second position
less open than the first position.
[0147] It will be appreciated that while the routine of FIG. 9
describes scroll valve adjustments responsive to knock or
pre-ignition, similar scroll valve adjustments may be applied in
response to other engine hardware limits being met or approached.
For example, scroll valve adjustments may be used in response to a
turbine inlet temperature (e.g., as estimated by a thermocouple)
approaching a limit determined by the material of the turbine, an
exhaust valve temperature approaching a limit determined by the
material of the exhaust valve, a peak cylinder pressure (e.g., as
estimated by a cylinder pressure transducer) approaching a limit
determined by the combination of temperature and material of the
exhaust valve, or a turbocharger speed (e.g., as estimated by a
proximity sensor) approaching a limit. As such, each parameter may
be estimated or inferred based on a model. In each case, when the
limit is met or approached, the scroll valve may be adjusted in a
direction that reduces engine load, thereby reducing engine damage.
Further, wastegate adjustments may be coordinated with the scroll
valve adjustment to reduce degradation of the engine, turbocharger,
and catalyst.
[0148] In one example, an engine system comprises an engine and a
turbocharger for providing a boosted aircharge to the engine, the
turbocharger including an intake compressor and an exhaust turbine.
The exhaust turbine may include a first outer and a second inner
scroll and a scroll valve may be coupled between an engine exhaust
manifold and an inlet of the first outer scroll, but not the inner
scroll. A wastegate may be included in a bypass coupled between an
inlet and an outlet of the turbine. A knock sensor may be coupled
to the engine for identifying and differentiating cylinder knock
and cylinder pre-ignition. An engine controller may be configured
with computer readable instructions for indicating cylinder
pre-ignition based on an output of the knock sensor, and in
response to the indication of pre-ignition, the controller may
increase an opening of the scroll valve based on turbine inlet
temperature. The increasing may include, as the turbine inlet
temperature exceeds a threshold, increasing an opening of the
scroll valve towards a fully open position, and as the turbine
inlet temperature falls below the threshold, decreasing the opening
of the scroll valve towards a fully closed position. Further, the
controller may adjust an opening of the wastegate based on the
opening of the scroll valve, the wastegate moved to a more open
position as the opening of the scroll valve is increased.
[0149] In this way, scroll valve adjustments may be advantageously
used to rapidly reduce engine load in response to engine hardware
limits being reached. By opening the scroll valve and optionally a
wastegate in response to an indication of pre-ignition (such an
indication regarding a likelihood of pre-ignition), exhaust
manifold pressures and turbine inlet temperatures can be quickly
decreased, reducing the risk of imminent pre-ignition and engine
damage.
[0150] An example adjustment is now described with reference to
FIG. 13. Map 1300 of FIG. 13 depicts adjusting of a scroll valve
coupled to an inlet of an outer scroll of a multi-scroll exhaust
turbine responsive to engine hardware limit (specifically, in
response to knock and pre-ignition in the present example). Map
1300 depicts a knock sensor output at plot 1302, scroll valve
adjustments at plot 1304, and changes to an engine load at plot
1306. All plots are depicted over time, plotted along the
x-axis.
[0151] Prior to t1, the engine may be operating with the scroll
valve (plot 1304) at a more closed position (e.g., at a fully
closed position). At t1, in response to an engine knock sensor
output (plot 1302) being higher than a first threshold Thr1 but
lower than a second threshold Thr2, knock may be determined. In
response to the indication of engine knock, the scroll valve may be
moved to a more open position and may be maintained in the more
open position for a duration until the indication of knock is below
the first threshold. After the duration has elapsed and the
indication of knock is below the first threshold, the scroll valve
may be returned to the more closed position. As such, by opening
the scroll valve in response to knock, the engine load may be
reduced. In addition to the scroll valve adjustment, the engine
knock may be mitigated by retarding spark timing (not shown).
[0152] Between t1 and t2, engine speed-load conditions may change
and the engine may be operating at high engine load conditions
where knock is likely. At t2, in response to the engine knock
sensor output again being higher than the first threshold Thr1 but
lower than a second threshold Thr2, knock may be determined. The
indication of knock at t2 may be higher than the indication of
knock at t1. In response to the indication of engine knock at t2,
the scroll valve may be moved to a more open position (e.g., the
same more open position as in response to the indication of knock
at t1) and may be maintained in the more open position for a
duration until the indication of knock is below the first
threshold. Herein, due to the indication of knock at t2 being
higher than the corresponding indication at t1, the scroll valve
may be kept open for a longer duration. Then, after the duration
has elapsed, the scroll valve may be returned to the more closed
position. In addition to the scroll valve adjustment, the engine
knock may be mitigated by retarding spark timing (not shown).
[0153] Between t2 and t3, engine speed-load conditions may change
and the engine may be operating at low speed and high engine load
conditions where pre-ignition is likely. At t3, in response to the
engine knock sensor output (plot 1302) being higher than each of
the first threshold Thr1 and second threshold Thr2, pre-ignition
may be determined. In response to the indication of engine
pre-ignition, the scroll valve may be moved to a more open position
and may be maintained in the more open position for a duration
until the indication of pre-ignition is below each of the first and
second threshold. Specifically, an opening of the scroll valve
responsive to the indication of pre-ignition may be higher (that
is, more open) than the opening of the scroll valve responsive to
the indication of knock. For example, in response to knock, the
scroll valve may be partially opened while in response to
pre-ignition, the scroll valve may be fully opened. Further, the
duration for which the scroll valve is opened responsive to the
indication of pre-ignition may be longer than the duration of
scroll valve opening responsive to the indication of knock. For
example, in response to knock, the scroll valve may be opened until
the indication of knock has reduced and then the valve may be
closed. In comparison, in response to pre-ignition, the scroll
valve may be maintained open for a while even after the indication
of pre-ignition has reduced, as shown.
[0154] After the longer duration has elapsed and the indication of
pre-ignition is below each of the first and second threshold, the
scroll valve may be returned to the more closed position. As such,
by opening the scroll valve in response to pre-ignition, the engine
load may be quickly reduced from the higher load region to a
medium-low load region. In doing so, the likelihood of further
pre-ignition events is reduced. In addition to the scroll valve
adjustment, the pre-ignition may be mitigated by enriching cylinder
fuel injection for the duration (not shown).
[0155] While not depicted in the example of FIG. 13, in further
examples, a controller may adjust a wastegate coupled across the
exhaust turbine responsive to the indication of pre-ignition or
knock, the wastegate adjusted based at least on the scroll valve
adjustment. The controller may also adjust various engine torque
actuators, such as one or more of spark ignition timing, VCT, EGR
(LP-EGR and/or HP-EGR), and intake throttle position based on the
scroll valve adjustment.
[0156] In this way, scroll valve adjustments may be performed
responsive to engine hardware limits being met or approached. By
opening the scroll valve to immediately reduce an engine load,
engine components may be protected from degradation and engine life
may be extended.
[0157] Now turning to FIG. 10, an example routine 1000 is shown for
adjusting a scroll valve coupled to an inlet of an outer scroll of
a multi-scroll exhaust turbine in response to an indication of
engine deactivation. The adjustment enables turbine response during
a subsequent tip-in to be improved. By closing the scroll valve and
wastegate during DFSO, the turbine speed is maximized and the
actuators are pre-positioned for best transient response on tip-in.
Because the fuel is off, the increase in exhaust manifold pressure
does not result in higher fuel consumption
[0158] At 1002, the routine includes estimating and/or measuring
engine operating conditions such as engine coolant temperature,
exhaust catalyst temperature, torque demand, BP, MAP, MAF, etc. In
addition, an initial scroll valve position may be determined based
on the estimated operating conditions. At 1004, an indication of
engine deactivation may be confirmed. In the depicted example, the
indication of engine deactivation includes a deceleration fuel
shut-off event (DFSO). The DFSO event may be in response to torque
demand being lower than a threshold, such as during a tip-out.
Therein, cylinder fuel injection may be selectively stopped. In an
alternate example, where the engine is configured to be selectively
deactivated in response to idle-stop conditions, engine
deactivation may be confirmed in response to an idle-stop operation
being performed where cylinder fuel injection is deactivated while
spark is also deactivated. As such, following engine deactivation,
the engine may still be rotating, the vehicle may still be
traveling, and the torque demand at the vehicle wheels may be
negative. Further, the engine may spin towards rest un-fueled.
[0159] If engine deactivation is not confirmed, the routine
proceeds to 1016 wherein the scroll valve is moved to the initial
position, as determined and scheduled at 1002. Further, at 1018, a
position of a wastegate coupled across the exhaust turbine may be
adjusted based on the scheduled scroll valve position and further
based on the engine operating conditions so that a desired turbine
and/or engine speed deceleration profile can be provided. Further
still, the position of an EGR valve of the EGR system (including a
LP-EGR valve of the LP-EGR system and an HP-EGR valve of the HP-EGR
system) may be adjusted based on the scheduled scroll valve
position, the wastegate position, and the engine operating
conditions to provide a desired engine deceleration profile.
[0160] If engine deactivation is confirmed, then at 1006, the
routine includes in response to the indication of engine
deactivation, moving the scroll valve to a more closed position.
For example, the scroll valve may be moved to a fully closed
position. As such, the scroll valve may be coupled to only a first,
outer scroll of the multi-scroll exhaust turbine but not to a
second inner scroll of the turbine. In one example, the valve may
be moved to the more closed position based on one or more of
turbine speed and boost pressure during the engine deactivation.
Specifically, the valve may be moved based on a difference between
an estimated or measured turbine speed during the engine
deactivation relative to a desired turbine speed deceleration
profile and/or the difference between a measured or estimated boost
pressure relative to a desired boost pressure, the valve moved to a
more closed position (e.g., towards the fully closed position) as
the difference increases. The desired turbine speed deceleration
profile may allow the turbine speed to be maintained above a
threshold level for a duration of the engine spin-down. By
maintaining the turbine speed, exhaust manifold pressure can be
maintained elevated during the spin-down. The increased exhaust
manifold pressure reduces the air flow through the engine during
the deceleration, thereby reducing exhaust catalyst cooling. As
such, this reduces an amount of fuel enrichment required during a
subsequent engine operation to reactivate the exhaust catalyst,
providing fuel economy improvements.
[0161] At 1008, the routine further includes moving a wastegate
coupled across the exhaust turbine to a more closed position, the
position of the wastegate based on the position of the scroll
valve. Moving the wastegate may include moving the wastegate
concurrently with the scroll valve or sequentially with the scroll
valve, an order of the sequential moving based at least on a
relative authority of the wastegate and the scroll valve under the
given engine operating conditions. For example, during a first
condition where both the scroll valve and the wastegate have
comparable authorities, the controller may move the wastegate to a
more closed position as the scroll valve is moved to the more
closed position. During a second condition, where the scroll valve
has higher authority, the controller may move the wastegate to the
more closed position after the valve is moved to the more closed
position. During a third condition, where the wastegate has higher
authority, the routine includes moving the wastegate to the more
closed position before the scroll valve is moved to the more closed
position.
[0162] In addition, at 1008, the routine may include adjusting one
or more of VCT, valve timing, EGR, and an intake throttle position
during the engine deactivation based on the moving of the scroll
valve. For example, the controller may adjust intake and exhaust
valve timing during the deceleration to decrease valve overlap. The
controller may also adjust the EGR valves to reduce an amount of
residuals delivered to the engine intake during the deceleration.
The engine settings may be adjusted to maximize engine torque
response after exit from DFSO. These may include reducing or
stopping EGR, and moving VCT to a timing for optimum combustion
stability with scroll valve closed.
[0163] At 1010, it may be determined if the turbine speed is below
a threshold speed. During a DFSO, the scroll valve and wastegate
may be closed to maximize turbocharger response on exit from DFSO.
In alternate embodiments, it may be determined if the engine speed
is below a threshold speed. For example, it may be determined if
the engine has spun substantially to rest. If the turbine speed has
not reduced below the threshold, then at 1011, the routine includes
maintaining the scroll valve in the closed position or continuously
adjusting the scroll valve position until the turbine speed has
reduced according to the desired deceleration profile.
[0164] As an example, as a difference between an estimated or
measured turbine speed and a desired spin-down turbine speed
profile increases, the closing of the scroll valve towards a fully
closed position may be increased (that is, the valve may be moved
to a more closed position). A closing of the wastegate may be
coordinated during the engine spin-down based on the closing of the
scroll valve to further reduce the difference between the estimated
or measured turbine speed and the desired spin-down turbine speed
profile. Likewise, where the engine system include an EGR system
for recirculating exhaust gas from the exhaust manifold to an
intake manifold of the engine, the controller may further adjust an
EGR valve of the EGR system to decrease an amount of EGR during the
closing of the scroll valve (and/or the wastegate). In addition cam
timing will be adjusted for optimum combustion stability, this
lowers fresh air flow through the unfueled cylinders thereby
reducing exhaust catalyst cooling. As such, adjusting VCT for lower
volumetric efficiency may also reduce catalyst cooling, but EGR may
not have that effect because the EGR is fresh air when in DFSO.
Further, by enabling the turbine speed to be maintained above a
threshold speed for a duration of the engine deactivation (and
spin-down), turbine spin-up during a subsequent engine activation
can be expedited, enabling better boost control.
[0165] If the turbine speed has reduced below the threshold speed,
then at 1012, an initial scroll valve position may be resumed.
Alternatively, a default engine rest or DFSO scroll valve position
may be resumed. In one example, this includes moving the scroll
valve to a fully closed position (if it has not already reached
that position). Alternatively, if the scroll valve is already at
the fully closed position, the routine includes maintaining the
scroll valve at the fully closed position. In still other examples,
the scroll valve may be moved to a fully open position, at least
temporarily.
[0166] In one embodiment, the position resumed at 1012 may be based
on the duration of the DFSO. For example, in response to DFSO
conditions being met, while fuel is deactivated, a timer may be
started. In the event of a shorter DFSO, where the duration elapsed
on the timer is less than a threshold amount of time, the
controller may temporarily move the scroll valve to a fully open
position to clear out residuals from the cylinder, and then return
the scroll valve to the fully closed position. During a subsequent
engine restart, the engine may be started with the scroll valve
closed to improve boost response (such as responsive to a tip-in,
as elaborated in the routine of FIG. 7). In the event of a longer
DFSO, where the duration elapsed on the timer is more than a
threshold amount of time, the controller may maintain the scroll
valve at a fully closed position so that the turbine is maintained
at a speed range from where the turbine can be quickly spun-up
during a subsequent engine start. For example, during a first
engine restart from the engine spin-down, a controller may restart
the engine with the scroll valve closed while during a second
engine restart from the spin-down, the controller may restart the
engine with the scroll valve open. Herein, a duration of engine
deactivation preceding the first engine restart may be longer than
the duration of engine deactivation preceding the second engine
restart. This allows boost response during the engine restart to be
improved.
[0167] At 1014, the routine includes adjusting one or more engine
actuators during the scroll valve transition to reduce any impact
of a torque surge/dip resulting from the scroll valve adjustment.
For example, the routine may include adjusting one or more of a
wastegate coupled to the exhaust turbine, VCT, positive valve
overlap, and intake throttle opening while moving the scroll valve
to the more closed position. As elaborated with reference to FIG.
11, the actuator adjustment may be used to better mask any torque
disturbances that may arise during the scroll valve adjustment,
thereby improving the vehicle operator's drive feel. In one
example, a timing of adjusting the scroll valve is based on a
transmission event during the engine spin-down to better mask the
impact of a torque surge.
[0168] An example adjustment responsive to engine deactivation is
now described with reference to FIG. 16. Map 1600 of FIG. 16
depicts adjusting of a scroll valve coupled to an inlet of an outer
scroll of a multi-scroll exhaust turbine responsive to engine
deactivation, specifically, in response to a DFSO event in the
present example. Map 1600 depicts turbine speed at plot 1602,
engine speed at plot 1604, cylinder fueling at plot 1606, scroll
valve adjustments at plot 1608, and wastegate adjustments at plot
1610. All plots are depicted over time, plotted along the
x-axis.
[0169] Prior to t1, the engine may be operating fueled (plot 1606)
and each of the scroll valve and wastegate may be at a more open
position. For example, each of the scroll valve and the wastegate
may be at a fully open position. At t1, engine deactivation
conditions may be met. For example, at t1, a vehicle operator may
tip-out and/or apply wheel brakes. In response to the reduced
torque demand, fuel injection to the engine cylinders may be
selectively deactivated. Due to the deactivation, the engine may
start spinning towards rest (plot 1604).
[0170] While the engine is spinning down, the scroll valve may be
moved towards a more closed position (e.g., towards a fully closed
position). In the depicted example, the scroll valve is shown being
gradually moved to the fully closed position. However, in alternate
examples, the scroll valve may be immediately moved to a fully
closed position, concurrent with the cylinder fuel deactivation.
The closing of the scroll valve (plot 1608) may be adjusted based
on turbine speed (plot 1602) so that a desired turbine speed
deceleration profile can be provided. As such, the desired turbine
speed deceleration profile enables the turbine speed to remain
above a threshold speed for a longer duration of the engine
deactivation. In other words, turbine spin-down to rest following
engine deactivation is slowed down. By keeping the turbine
spinning, an exhaust manifold pressure can be maintained, which in
turns reduces air flow through the engine. The reduced air flow
decreases cooling of the exhaust catalyst and depletion of
catalytic sites with oxygen.
[0171] The scroll valve closing is gradually increased (as
depicted, or immediately decreased in an alternate example) after
t1 until the scroll valve is at a fully closed position, after
which the scroll valve is maintained at the fully closed position.
In addition to scroll valve adjustments, wastegate adjustments may
be used to assist in providing the desired turbine speed
deceleration profile. In the depicted example, the wastegate may
also be closed in response to the engine deactivation, the closing
of the wastegate following the closing of the scroll valve.
Specifically, due to a higher authority of the scroll valve, the
scroll valve may start being moved towards a fully closed position
at t1 while the wastegate may start being moved towards a fully
closed position shortly after t1 (after a delay since the moving of
the scroll valve towards the closed position). While the example
shows the wastegate being gradually closed, in alternate examples,
the wastegate may be immediately closed. In still further examples,
such as where the wastegate has higher authority, the wastegate may
be immediately closed concurrently with the immediate closing of
the scroll valve and the deactivating of fuel to the cylinders
(e.g., at t1).
[0172] Just before t2, the engine may have spun to rest. In
addition, each of the scroll valve and the wastegate may be at the
fully closed position. At t2, engine reactivation conditions may be
met. For example, the vehicle operator may tip-in and/or release
wheel brakes. In response to the increased torque demand, cylinder
fueling may be resumed (plot 1606). In addition, the scroll valve
may be kept closed for a duration of the restart, between t2 and
t3, until the turbine speed has been raised above a threshold
speed. By keeping the scroll valve closed during an early part of
the restart, turbine spin-up is expedited, reducing turbo lag and
improving turbocharger performance upon restart. Then, at t3, the
scroll valve may be gradually moved to a more open position, for
example, towards a fully open position.
[0173] The wastegate may also be kept closed during the early part
of the restart to further assist in expediting turbine spin-up.
Then, once the turbine has sufficiently spun up, the wastegate may
be opened. In the depicted example, the wastegate is kept closed
during the engine restart. Then, shortly after t3 (after a delay
since the moving of the scroll valve towards the more open
position), the wastegate is also moved towards the more open
position.
[0174] As such, if the scroll valve was not closed during the
engine deactivation and maintained closed during at least a portion
of the subsequent engine reactivation, the turbine speed may drop
faster during the engine deactivation and take a longer time to
spin-up during the subsequent engine reactivation, as shown by
segment 1603 (dashed line). The delay in spinning up the turbine
may result in turbo lag that reduces turbocharger performance
during the restart.
[0175] While the depicted example shows wastegate adjustments
succeeding scroll valve adjustments, in alternate embodiments,
based on engine operating conditions, wastegate adjustments may be
concurrent with or may precede scroll valve adjustments. Further,
while not depicted in the example of FIG. 16, in other examples, a
controller may adjust various engine torque actuators, such as one
or more of VCT, valve overlap, EGR and intake throttle position
based on the scroll valve adjustment during the engine spin-down
and the subsequent restart.
[0176] In this way, scroll valve adjustments may be performed
responsive to engine deactivation conditions. By closing the scroll
valve while the engine spins down, turbine speed may be better
managed and turbocharger control may be improved.
[0177] Now turning to FIG. 11, an example routine 1100 is shown for
adjusting a timing of a scroll valve adjustment based on an engine
transmission event to reduce the impact, if any, of a torque surge
associated with the scroll valve adjustment. The routine allows
such a torque surge to be better masked, improving the quality of
the vehicle operator's drive experience.
[0178] At 1102, the routine includes determining the scroll valve
adjustment requested. For example, the controller may determine
whether the scroll valve is to be moved to a more open position
(e.g., to a fully open position) or to a more closed position
(e.g., to a fully closed position). As previously elaborated, the
engine may include a second scroll inner to the first scroll, the
scroll valve coupled only to the first scroll. The scroll valve
adjustment may lead to transitioning of a restriction in exhaust
upstream of the first scroll. As such, a transitioning of an
opening of the scroll valve based on various operating conditions
and operating limits leads to a transitioning in a restriction in
exhaust upstream of a first scroll of a multi-scroll exhaust
turbine based on various operating conditions and operating limits.
These may include, for example, as elaborated with reference to
FIGS. 5-10, cold-start conditions, engine dilution conditions,
pre-ignition conditions, combustion stability limits, hardware
limits, etc. Scroll valve adjustments may include, at lower turbine
speeds, closing the scroll valve to increase restriction in exhaust
upstream of the first scroll, and at higher turbine speeds, opening
the scroll valve to decrease the restriction.
[0179] At 1104, a torque change associated with the scheduled
scroll valve adjustment is determined. As such, the torque change
may include a torque surge or a torque dip. For example, at
moderate to high boost flow and airflow conditions, when the scroll
valve is opened (at constant cam timing), exhaust flow is allowed
to go through both scrolls. As a result the exhaust manifold
pressure rapidly decreases, causing more fresh air to be trapped in
the cylinders. If this increase in airflow is matched by fuel to
maintain constant air-fuel ratio and ignition timing, the opening
of the scroll valve produces a "bump" up in engine torque, herein
also referred to as a torque bump or torque surge. In a similar
fashion, if the engine is at a moderate to high airflow, and the
scroll valve is closed to help spool up the turbine, the elevated
exhaust manifold pressure will cause the trapped aircharge to
suddenly decrease, while also reducing further fresh air flow into
the engine. If this decrease in airflow is matched by fuel to
maintain constant air-fuel ratio and ignition timing, the closing
of the scroll valve produces a "bump" down in engine torque, herein
also referred to as a torque bump or torque dip. In either case,
the torque disturbance, or torque bump, leads to poor drivability.
As elaborated below, an engine controller may be configured to
adjust an engine actuator during the scroll valve transition to
maintain engine torque and reduce the impact of the torque
bump.
[0180] At 1106, it may be determined if a torque bump is expected.
Specifically, based on the estimation of a torque change associated
with the scheduled scroll valve adjustment, it may be determined if
a torque surge or torque dip is expected. In one example, a torque
surge may be confirmed if the torque change associated with the
scheduled scroll valve adjustment is a positive change that is more
than a threshold amount. In another example, a torque dip may be
confirmed if the torque change associated with the scheduled scroll
valve adjustment is a negative change that is more than a threshold
amount.
[0181] If a torque bump is not expected, then at 1108, the routine
includes maintaining the position of one or more engine actuators.
Further, the scroll valve adjustment is performed as scheduled
(e.g., at a timing based on the estimated operating
conditions).
[0182] If a torque bump is expected, then at 1110, it may be
determined if there is an upcoming transmission event. The
controller may determine if there is an upcoming transmission event
based on the shift schedule of the transmission. The upcoming
transmission event may include an upcoming transmission upshift
event or an upcoming transmission downshift event. As such, the
engine transmission may include a manual transmission or an
automatic transmission. The transmission may further include one or
more clutches such as a torque converter clutch, and a forward
clutch. The one or more clutches may include a mechanical clutch
that is mechanically actuated, as well as an "e-clutch" that is
electronically actuated (that is, a clutch-by-wire).
[0183] In some embodiments, in determining if there is an upcoming
transmission event, the controller may determine a duration between
the upcoming transmission event (based on a shift schedule of the
transmission) and a time when a request for transitioning
restriction at the scroll valve is received. If the duration is
sufficiently long (e.g., longer than a threshold duration), an
upcoming transmission event may not be confirmed. If the duration
is sufficiently short (e.g., shorter than a threshold duration), an
upcoming transmission event may be confirmed.
[0184] If an upcoming transmission event is confirmed, then at
1116, the routine includes adjusting a timing of the transitioning
based on a transmission event. The adjusting may include, in
response to an upcoming transmission event, timing the
transitioning to at least partially overlap the transmission event.
For example, if a duration between the transmission event and a
request for transitioning restriction is smaller than a threshold,
the timing of the scroll valve transitioning may be adjusted to be
during the transmission event (e.g., concurrent with the
transmission event). In another example, the timing may be adjusted
so that the timing of the transitioning immediately follows the
transmission event. By timing the transitioning to at least
partially overlap the transmission event, the impact of the torque
bump can be better masked, thereby improving driveability.
[0185] At 1118, the routine includes adjusting an engine actuator
during the scroll valve transition to maintain engine torque and
reduce the impact of a torque bump that would have been experienced
during the transition. The engine actuator adjusted may include one
or more of VCT, EGR, valve timing (including adjusting a valve
overlap), intake throttle position, wastegate, and transmission
shift schedule. In each case, the engine actuator adjustment may be
based on the transitioning of the scroll valve opening and the
change in restriction in exhaust upstream of the first scroll. For
example, the engine actuator may be adjusted to transiently
increase engine airflow when the scroll valve is closed to increase
restriction, and the engine actuator may be adjusted to transiently
decrease engine airflow when the scroll valve is opened to decrease
restriction. Alternatively, the engine actuator may be adjusted to
increase engine airflow when the scroll valve is transitioned by a
large amount to a more open position or to a more closed position.
In this way, a restriction in exhaust upstream of a first scroll of
a multi-scroll exhaust turbine may be transitioned based on
operating conditions while adjusting an engine actuator during the
transition to maintain engine torque during the transition.
[0186] As another example, when closing the scroll valve to
increase restriction, an engine actuator may be adjusted to
transiently increase engine air flow. This transient increase in
engine air flow may compensate for the transient drop in air flow
experienced when the scroll valve is closed and the exhaust
manifold pressure is increased. As another example, when opening
the scroll valve to decrease restriction, the engine actuator may
be adjusted to transiently decrease engine air flow. This transient
decrease in engine air flow may compensate for the transient rise
in air flow experienced when the scroll valve is opened and the
exhaust manifold pressure is decreased. As one example, when the
scroll valve is closed, the intake throttle opening may be
temporarily increased to transiently increase the engine air flow
while when the scroll valve is opened, the intake throttle opening
may be temporarily decreased to transiently decrease the engine air
flow.
[0187] As another example, when closing the scroll valve to
increase restriction, the engine actuator may be adjusted to
decrease engine dilution, to compensate for higher internal
residuals due to higher exhaust manifold pressure. In comparison,
when opening the scroll valve to decrease restriction, the engine
actuator may be adjusted to increase engine dilution. As still
another example, when timing the transitioning during the
transmission event, clutch slippage and/or spark retard may be
adjusted (e.g., increased) during the transitioning, the increasing
based on the transitioning. Therein, the amount of clutch slippage
may be increased as the transitioning of the scroll valve
increases. Likewise, an amount of spark retard applied may be
increased as the transitioning of the scroll valve increases.
[0188] If an upcoming transmission event is not confirmed at 1110,
for example, if the duration between the transmission event and the
request for transitioning restriction is larger than the threshold,
at 1112, the routine includes performing the scroll valve
adjustment as scheduled. This may include timing the transitioning
to be before any (subsequent) transmission event.
[0189] An example adjustment to the timing of a scroll valve
transition is described with reference to FIG. 12. Specifically,
map 1200 of FIG. 12 depicts a desired scroll valve schedule at plot
1202, a transmission shift schedule at plot 1204, and an actual or
commanded scroll valve schedule at plot 1206. Actuator adjustments
(herein intake throttle adjustments) applied during the scroll
valve transition are described at plot 1208. All plots are shown
over time (along the x-axis).
[0190] Prior to t1, the engine may be operating with the scroll
valve more open (plot 1206). For example, the scroll valve may be
fully open. Based on engine operating conditions before t1, a
controller may determine at t1 that the scroll valve is to be
transitioned to a more closed position (e.g., a fully closed
position). For example, in response to an increase in torque
demand, boost may need to be increased at or after t1. Accordingly,
a scroll valve transition request (plot 1202) may be made at t1.
The controller may further determine that the scroll valve
adjustment needs to be performed between t1 and t3. In other words,
if the scroll valve adjustment is performed after t3, engine
performance will be degraded. The controller may further determine
if there is an upcoming transmission event, such as where a
transmission gear is engaged. Based on the engine operating
conditions, it may be determined that a transmission upshift or
gear engagement (plot 1204) is scheduled to start at t2. In view of
the upcoming transmission event, the scroll valve transition
requested at t1 may be actually commanded shortly after t2,
specifically, during the transmission upshift or gear engagement.
In the depicted example, the transmission upshift may be performed
in multiple upshift steps and the scroll valve closing may be
transitioned to occur after the first upshift step has been
completed.
[0191] As such, if a transmission event is not confirmed between t1
and t3, then the scroll valve transition commanded at t1 may be
actually performed at t1 (see dashed segment 1207). As another
example, at t4, based on engine operating conditions, a request to
open the scroll valve may be made. Since no transmission events are
expected soon after t4, the controller may command the requested
scroll valve transition at t4. Thus, at t4, the scroll valve may be
transitioned from the more closed position to the more open
position.
[0192] By timing a scroll valve transition to at least partially
overlap the transmission event (as occurs between t2 and t3),
driveability is improved. Further driveability improvements during
scroll valve transition are achieved by engine actuator adjustments
that increase engine airflow during the closing of the scroll
valve. Specifically, closing of the scroll valve causes exhaust
manifold pressure to rise, which in turn reduces fresh air flow
into the cylinders for a few engine cycles following the closing of
the scroll valve. Then, as the turbine speed picks up due to the
rise in exhaust manifold pressure, boost is increased and fresh air
flow to the engine cylinders increases. Thus, to compensate for the
torque dip resulting from the reduced airflow, upon receiving the
request for scroll valve closing and before the scroll valve is
closed, specifically between t1 and t2, the opening of an intake
throttle may be increased. Then, during the first few cycles
following the closing of the scroll valve, specifically between t2
and t3, the intake air throttle opening may be further increased
(more than the opening between t1 and t2). For example, between t1
and t2, the throttle may be partially open and between t2 and t3,
the throttle may be fully open. Then, as the turbine speed and
boost level picks up, specifically after t3, the intake air
throttle may resume its original position.
[0193] Likewise, engine actuator adjustments that decrease engine
airflow during the scroll valve transition at t4 may be used to
improve driveability during scroll valve opening. Specifically,
opening of the scroll valve causes exhaust manifold pressure to
drop, which in turn increases fresh air flow into the cylinders for
a few engine cycles following the opening of the scroll valve.
Then, as the turbine speed drops due to the drop in exhaust
manifold pressure, boost is decreased and fresh air flow to the
engine cylinders decreases. Thus, to compensate for the torque
surge resulting from the increased airflow, during the first few
cycles following the opening of the scroll valve, specifically
immediately after t4, an intake air throttle may be temporarily
opened. For example, the intake throttle opening may be gradually
increased (in the depicted example, stepwise increased). Then, as
the turbine speed and boost level drops, the intake air throttle
may be resume its original position (that is, the opening of the
intake throttle may be increased).
[0194] Wastegate adjustments (not shown) may also be used during
each of the scroll valve transitions to further assist in
turbocharger control. For example, the wastegate may be opened when
the scroll valve is opened and the wastegate may be closed when the
scroll valve is closed. In this way, actuator adjustments may be
used to improve driveability during a scroll valve transition.
[0195] In this way, a binary flow turbine may be advantageously
used to improve boost control at various engine operating
conditions. By adjusting the valve during cold-start conditions,
increased manifold pressure can be used to expedite catalyst
warm-up as well as turbine spin-up during the cold-start. In
addition, scroll valve adjustments may be used to bring turbine
speed out of a speed range where audible resonance can occur,
improving drive feel. By adjusting the valve responsive to
transient changes in torque demand, turbo lag can be reduced,
improving the engine's boost response. Furthermore, by adjusting
the valve responsive to engine deactivation, turbine spin-up upon
engine reactivation is also improved. By adjusting the valve
responsive to engine dilution, residuals can be delivered to the
engine without degrading combustion, thereby extending the benefits
of EGR to a wider range of operating conditions. By adjusting the
valve when engine hardware limits are reached, such as responsive
to pre-ignition, engine load can be quickly lowered and component
damage can be reduced. By using one or more engine actuators to
compensate for the torque impact of the scroll valve adjustment,
the torque impact felt by a vehicle operator is reduced. In
addition, by adjusting the timing based on a transmission event,
the torque impact is better masked. Overall, engine performance and
boost response is improved, exhaust emissions are reduced, and
vehicle driveability is improved.
[0196] 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. 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.
[0197] 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. 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.
[0198] 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.
* * * * *