U.S. patent application number 16/225565 was filed with the patent office on 2019-04-25 for control of airflow in a uniflow-scavenged, two-stroke cycle, opposed-piston engine during transient operation.
This patent application is currently assigned to ACHATES POWER, INC.. The applicant listed for this patent is ACHATES POWER, INC.. Invention is credited to Nishit Nagar, Suramya D. Naik, Daniel Schum, ARUNANDAN SHARMA.
Application Number | 20190120164 16/225565 |
Document ID | / |
Family ID | 57882185 |
Filed Date | 2019-04-25 |
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United States Patent
Application |
20190120164 |
Kind Code |
A1 |
SHARMA; ARUNANDAN ; et
al. |
April 25, 2019 |
CONTROL OF AIRFLOW IN A UNIFLOW-SCAVENGED, TWO-STROKE CYCLE,
OPPOSED-PISTON ENGINE DURING TRANSIENT OPERATION
Abstract
Control of airflow in a uniflow-scavenged, two-stroke cycle,
opposed-piston engine during transient operation includes
monitoring at least one operating parameter of the engine to
recognize a transition to a transient state of engine operation. If
a transient state of operation is detected, fuel injection and
airflow into to the cylinders of the engine are controlled to
optimize combustion and limit emissions. Airflow into cylinders of
the engine may be controlled by increasing a scavenging ratio of
the engine or by increasing a trapping efficiency of the
engine.
Inventors: |
SHARMA; ARUNANDAN; (San
Diego, CA) ; Nagar; Nishit; (Issaquah, WA) ;
Naik; Suramya D.; (Milpitas, CA) ; Schum; Daniel;
(Vista, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ACHATES POWER, INC. |
San Diego |
CA |
US |
|
|
Assignee: |
ACHATES POWER, INC.
San Diego
CA
|
Family ID: |
57882185 |
Appl. No.: |
16/225565 |
Filed: |
December 19, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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15173478 |
Jun 3, 2016 |
10161345 |
|
|
16225565 |
|
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62279301 |
Jan 15, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02B 37/24 20130101;
F02D 2200/1002 20130101; F02B 2075/025 20130101; F02D 41/182
20130101; F02D 13/0284 20130101; F02M 55/025 20130101; F02B 25/08
20130101; F02M 35/1038 20130101; F02D 41/2451 20130101; F02B 75/282
20130101; F02D 2200/602 20130101; F01B 7/14 20130101; F02D 2400/04
20130101; F02D 41/1458 20130101; F02D 41/0007 20130101; F02D
41/3064 20130101; Y02T 10/12 20130101; Y02T 10/144 20130101; F02B
75/02 20130101; F02D 2200/101 20130101; F02D 41/10 20130101 |
International
Class: |
F02D 41/30 20060101
F02D041/30; F02D 41/00 20060101 F02D041/00; F02B 75/02 20060101
F02B075/02; F02D 41/24 20060101 F02D041/24; F02D 13/02 20060101
F02D013/02; F02B 37/24 20060101 F02B037/24; F02M 35/10 20060101
F02M035/10; F02M 55/02 20060101 F02M055/02; F02B 75/28 20060101
F02B075/28; F01B 7/14 20060101 F01B007/14; F02B 25/08 20060101
F02B025/08; F02D 41/18 20060101 F02D041/18; F02D 41/14 20060101
F02D041/14; F02D 41/10 20060101 F02D041/10 |
Claims
1. A method of controlling operations of a uniflow-scavenged,
two-stroke cycle, opposed-piston engine during transient modes of
engine operation, comprising: monitoring a transient indication
parameter of the engine; determining, based on the transient
indication parameter, whether the engine is in a transient state of
operation; if the engine is in a transient state of operation:
controlling fuel injection into to the cylinders of the engine by
changing one or more of a common-rail pressure and a fuel injection
duration; controlling unidirectional airflow through cylinders of
the engine by increasing a scavenging ratio of the engine or by
increasing a trapping efficiency of the engine; determining when
the transient mode ends; and, transitioning the engine to a steady
state of operation; otherwise, operating the engine in a steady
state of operation if the engine is not in a transient state of
operation.
2. The method of claim 1, wherein the transient indication
parameter comprises an accelerator position.
3. The method of claim 1, wherein controlling unidirectional
airflow through cylinders of the engine comprises changing one or
more of a supercharger shunt valve setting, a supercharger drive
ratio setting, and a turbine vane setting.
4. The method of claim 1, wherein increasing a scavenge ratio of
the engine comprises: decreasing an exhaust backpressure of the
engine; and, increasing a velocity of unidirectional airflow
through the cylinders of the engine.
5. The method of claim 4, wherein increasing a scavenge ratio of
the engine further comprises, after increasing the scavenge ratio
for a calibration period, increasing a compressor outlet pressure
of the engine.
6. The method of claim 1, wherein increasing a trapping efficiency
of the engine comprises: decreasing an exhaust backpressure of the
engine; increasing a velocity of unidirectional airflow through the
cylinders of the engine; and, increasing a compressor outlet
pressure of the engine.
7. The method of claim 6, wherein increasing a trapping efficiency
of the engine further comprises, after increasing the trapping
efficiency for a calibration period, reducing a compressor outlet
pressure of the engine.
8. The method of claim 1, wherein the engine comprises active air
handling devices including at least one valve, a supercharger
drive, and a variable geometry turbine, and transitioning the
engine to a steady state of operation comprises issuing a transient
command .theta..sub.2 for an actuator of at least one air handling
device from an engine control unit (ECU), monitoring an elapse of
time from the issuing step, and transitioning the engine to a
steady state of operation in response to an elapse of a calibration
time.
9. The method of claim 8, wherein the engine comprises a steady
state control process in which an airflow parameter comprising one
of mass airflow, boost pressure, exhaust and back-pressure in the
air handling system is sensed and an error value is determined by
subtracting the sensed parameter value from a desired set-point
value for the airflow parameter, and transitioning the engine to a
steady state of operation comprises transitioning the engine to a
steady state of operation response when: an elapse of a calibration
time occurs; or, the error value is less than a calibration
value.
10. The method of claim 9, wherein controlling unidirectional
airflow through cylinders of the engine comprises changing one or
more of a supercharger shunt valve setting, a supercharger drive
ratio setting, and a turbine vane setting.
11. A method of controlling operations of an air handling system of
uniflow-scavenged, two-stroke cycle, opposed-piston engine equipped
with at least one cylinder with a bore and axially-spaced exhaust
and intake ports that communicate with the bore, a pair of pistons
disposed in opposition in the bore and operative to open and close
the exhaust and intake ports during operation of the engine, the
air handling system including a charge air subsystem to provide
charge air to the intake port, an exhaust subsystem to receive
exhaust gas from the exhaust port, and a supercharger operable to
pump charge air in the charge air subsystem, comprising: monitoring
a transient indication parameter of the engine; determining, based
on the transient indication parameter, whether the engine is in a
transient state of operation; if the engine is in a transient state
of operation: at an onset of the transient state, opening a
backpressure valve in the exhaust subsystem to reduce backpressure
resistance to airflow through the air handling system; at the onset
of the transient state, controlling unidirectional airflow through
cylinders of the engine by changing a supercharger shunt valve
setting to increase a supercharger pressure ratio of the engine or
by changing a supercharger drive ratio setting to increase the
supercharger pressure ratio of the engine; determining when the
transient state of operation ends; and then, transitioning the
engine to a steady state of operation; otherwise, operating the
engine in a steady state of operation if the engine is not in a
transient state of operation.
12. The method of claim 11, wherein the transient indication
parameter comprises an accelerator position or an engine load.
13. The method of claim 11, wherein the engine further includes a
turbocharger with a turbine in the exhaust subsystem and a
compressor in the charge air subsystem, upstream of the
supercharger, and controlling unidirectional airflow through
cylinders of the engine further comprises one or more of decreasing
an exhaust backpressure of the air handling system, and increasing
a compressor outlet pressure of the air handling system.
14. An airflow control combination for a uniflow-scavenged,
two-stroke cycle, opposed-piston engine equipped with at least one
cylinder with a bore and axially-spaced exhaust and intake ports
that communicate with the bore, a pair of pistons disposed in
opposition in the bore and operative to open and close the exhaust
and intake ports during operation of the engine, and an air
handling system including a charge air subsystem to provide charge
air to the intake port, an exhaust subsystem to receive exhaust gas
from the exhaust port, a supercharger operable to pump charge air
in the charge air subsystem, and a command-controlled shunt valve
which promotes a charge air pressure ratio across the supercharger,
the airflow control combination comprising: a sensor that senses
one of engine acceleration and engine load of the engine; a sensor
that detects charge air pressure at the intake of the supercharger;
a sensor that detects charge air pressure at the outlet of the
supercharger; and, a control unit programmed to: determine the
occurrence of a torque demand for the engine, the torque demand
having an intensity based on an intensity of a rate of change of
engine acceleration or engine load with respect to a transient
intensity threshold value; produce a transient command for the
shunt valve to increase the charge air pressure ratio across the
supercharger when the intensity of the torque demand exceeds the
transient intensity threshold; and produce a steady state command
to control the charge air pressure ratio across the supercharger to
a desired setpoint when the intensity of the torque demand falls
below the transient intensity threshold.
15. The airflow control combination of claim 14, further comprising
a backpressure valve in the exhaust subsystem to control a
backpressure in the air handling system, in which the control unit
is further programmed to produce a transient command to open the
backpressure valve when the intensity of the torque demand exceeds
the transient intensity threshold.
16. An airflow control combination for a uniflow-scavenged,
two-stroke cycle, opposed-piston engine equipped with at least one
cylinder with a bore and axially-spaced exhaust and intake ports
that communicate with the bore, a pair of pistons disposed in
opposition in the bore and operative to open and close the exhaust
and intake ports during operation of the engine, a charge air
channel to provide charge air to the intake port, an exhaust
channel to receive exhaust gas from the exhaust port, a
supercharger operable to pump charge air in the charge air channel,
and a command-controlled supercharger drive which promotes a charge
air pressure ratio across the supercharger, the airflow control
combination comprising: a sensor that senses one of engine
acceleration and engine load of the engine; a sensor that detects
charge air pressure at the intake of the supercharger; a sensor
that detects charge air pressure at the outlet of the supercharger;
and, a control unit programmed to: determine the occurrence of a
torque demand for the engine, the torque demand having an intensity
based on an intensity of a rate of change of engine acceleration or
engine load with respect to a transient intensity threshold value;
produce a transient command supercharger drive to increase the
charge air pressure ratio across the supercharger when the
intensity of the torque demand exceeds the transient intensity
threshold; and produce a steady state command to control the charge
air pressure ratio across the supercharger to a desired setpoint
when the intensity of the torque demand falls below the transient
intensity threshold.
17. The airflow control combination of claim 16, further comprising
a backpressure valve in the exhaust channel to control a
backpressure in the air handling system, in which the control unit
is further programmed to produce a transient command to open the
backpressure valve when the intensity of the torque demand exceeds
the transient intensity threshold.
18. A control process of a uniflow-scavenged, two-stroke cycle,
opposed-piston engine equipped with one or more cylinders, each
cylinder having a bore and axially-spaced exhaust and intake ports
that communicate with the bore, a pair of pistons disposed in
opposition in the bore and operative to open and close the exhaust
and intake ports during operation of the engine, an air handling
system of the engine including a charge air subsystem to provide
charge air to the intake ports, an exhaust subsystem to receive
exhaust gas from the exhaust ports, and a plurality of
command-controlled air flow devices positioned in the charge air
and exhaust subsystems to establish and sustain a unidirectional
flow of gas through the cylinders, in which the control process is
executable by a programmed control unit of the engine, and
comprises: a steady-state control portion operable to control an
airflow device in a steady state mode of engine operation with a
steady-state command .theta..sub.1; a transient control portion
operable to control the airflow device in a transient mode of
engine operation by means of a transient command .theta..sub.2;
and, a transition portion operable to initiate steady state control
for issuing a steady-state command .theta..sub.1, and to transition
control of the airflow device to transient control for issuing a
transient command .theta..sub.2 when an onset of a transient
condition of the engine is detected by the programmed control
unit.
19. The control process of claim 18, in which the transition
portion is further operable to determine when to transition control
of the airflow device from transient control to steady state
control.
20. The control process of claim 19, in which the steady-state
control portion comprises a feedback controller and a feedforward
controller, wherein the feedback controller generates a set-point
correction value (c) to correct a current position of the airflow
device, the device feedforward controller generates a device
position command, and the set-point correction value (c) and the
device position command are added to generate the steady state
command .theta..sub.1.
21. The control process of claim 20, in which the transient control
portion comprises a feedforward device controller that generates a
transient command .theta..sub.2' in response to a level of
transient intensity or a rate of change of air/fuel ratio (AFR) and
a gate that provides a final transient command .theta..sub.2 on the
basis of elapsed time since the transient condition has been
detected.
22. The control process of claim 21, in which the transition
portion changes control from transient to steady state if either
the transient command .theta..sub.2' has been active for a
calibration time, or if an error value (e) representing a
difference between a desired set-point of an airflow parameter and
a sensed value of the airflow parameter is less than a calibration
value.
23. The control process of claim 21, in which the programmed
control unit generates an on-board diagnostic (OBD) fault if the
error value (e) is greater than the calibration value after a
calibration time, and is not changing.
24. The control process of claim 19, in which the control process
is executable by the programmed control unit of the engine to
control one of a supercharger shunt valve of the air handling
system, a supercharger drive of the air handling system, a variable
geometry turbine of the air handling system, an exhaust
backpressure valve of the air handling system, and a wastegate
valve of the air handling system.
25. The control process of claim 19, in which a plurality of
control processes are executable by the programmed control unit of
the engine to control a supercharger shunt valve of the air
handling system, an exhaust backpressure valve of the air handling
system, and a wastegate valve of the air handling system.
26. The control process of claim 19, in which a plurality of
control processes are executable by the programmed control unit of
the engine to control a supercharger drive of the air handling
system and a variable geometry turbine of the air handling system.
Description
PRIORITY
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 62/279,301 filed in the United States Patent
and Trademark Office on 15 Jan. 2016.
RELATED APPLICATIONS
[0002] This application contains subject matter related to the
subject matter of the following US applications, which are commonly
owned herewith: U.S. patent application Ser. No. 13/654,340, filed
Oct. 17, 2012, published as US 2013/0104848 A1; U.S. patent
application Ser. No. 13/926,360 filed on Jun. 25, 2013, published
as US 2014/0373814 A1, and issued as U.S. Pat. No. 9,206,751 B2 on
Dec. 8, 2015; U.S. patent application Ser. No. 14/039,856, filed on
Sep. 27, 2013, published as US 2014/0026563 A1; U.S. patent
application Ser. No. 14/378,252, filed on Aug. 12, 2014, published
as US 2015/0033736 A1; and, U.S. patent application Ser. No.
15/062,868, filed on Mar. 7, 2016.
FIELD
[0003] The field is control and operation of air handling systems
for two-stroke cycle, opposed-piston engines.
BACKGROUND
[0004] A two-stroke cycle engine is an internal combustion engine
that completes a cycle of operation with a single complete rotation
of a crankshaft and two strokes of a piston connected to the
crankshaft. The strokes are typically denoted as compression and
power strokes. In a two-stroke cycle, opposed-piston ("OP2S")
engine two pistons are disposed crown-to-crown in the bore of a
cylinder for reciprocating movement in opposing directions along
the central axis of the cylinder. The cylinder has
longitudinally-spaced inlet and exhaust ports formed in the
cylinder sidewall near respective ends of the cylinder. Each of the
opposed pistons controls a respective one of the ports, opening the
port as it moves toward a bottom dead center (BDC) location during
a power stroke (also called an expansion stroke), and closing the
port as it moves from BDC toward a top dead center (TDC) location
during a compression stroke. One of the ports provides passage for
the products of combustion out of the bore, the other serves to
admit pressurized air into the bore; these are respectively termed
the "exhaust" and "intake" ports (in some descriptions, intake
ports are referred to as "air" ports or "scavenge" ports).
[0005] OP2S engines typically operate according to the
compression-ignition principle. During a compression stroke,
turbulent pressurized air ("charge air") enters the bore of a
cylinder through the intake port and is compressed between the end
surfaces of the two pistons as they move from BDC toward TDC. Fuel
directly injected into the cylinder between the approaching piston
end surfaces mixes with the turbulent air. The fuel is ignited by
the heat of the compressed air, and combustion follows. Fuel is
provided by an engine fuel handling system that includes one or
more fuel injectors mounted to the cylinder between the TDC
locations of the piston end surfaces.
[0006] In a uniflow-scavenged OP2S engine, near the end of a power
stroke, charge air entering a cylinder through the intake port
displaces exhaust gas flowing out of the cylinder through the
exhaust port. Thus gas flows through the cylinder in one direction
("uniflow")--from intake port to exhaust port. A continuous
positive pressure differential must exist from the intake ports to
the exhaust ports of the engine in order to maintain the desired
unidirectional flow of gas in the cylinders. Further, a high air
mass density must be provided to the intake ports because of the
short time that they are open; this need is especially acute during
engine start, acceleration, and load increases. This requires
pumping work.
[0007] In an opposed-piston engine, the pumping work is done by an
air handling system (also called a "gas exchange" system) which
moves fresh air into and transports combustion gases (exhaust) out
of the engine. The pumping work may be done by a gas-turbine driven
compressor (e.g., a turbocharger), and/or by a mechanically-driven
pump, such as a supercharger (also called a "blower"). In some
instances, the compressor may be located upstream or downstream of
a supercharger in a two-stage pumping configuration. The pumping
arrangement (single stage, two-stage, or otherwise) can drive the
scavenging process, which is critical to ensuring effective
combustion, increasing the engine's indicated thermal efficiency,
and extending the lives of engine components such as pistons,
rings, and cylinder.
[0008] During steady state performance of an OP2S engine,
operational parameters change slowly, if at all. Thus, for example,
when propelling a vehicle on a highway at a steady speed, the
transport of gasses (charge air and exhaust) through, and provision
of fuel in, the vehicle's OP2S engine can be maintained at a
slowly-changing pace. This translates to stable control with enough
time to optimize engine performance in terms of fuel efficiency and
emissions. However, vehicle operation frequently subjects the
engine to sudden demands for torque, especially in urban driving or
during operation in industrial conditions. Such demands may come
from acceleration, deceleration, switching accessories (like air
conditioning) on or off, pulling a trailer, climbing a hill, and so
on. A sudden demand for torque associated with an abrupt change in
engine load or engine speed is considered to be a transient event.
Such a demand is hereinafter referred to as a "torque request."
During a transient event, a demand for increased torque generates a
requirement to quickly increase the supply of fuel to the engine in
order to raise the level of energy released by combustion. This
requires a concurrent provision of additional air in order to burn
the additional fuel.
[0009] It is desirable to limit the production of emissions during
engine operation. Consequently, during a transient event, a
limiting factor for OP2S engine response may be defined by how
rapidly the air handling system can change the flow of charge air
through the engine in support of a torque request while keeping
engine emissions under control. During the period of the torque
request, a low air/fuel ratio (AFR) value due to the lack of charge
air can result in incomplete combustion, leading to particulate
matter (PM) emissions, such as soot. On the other hand, reducing
the fuel supply to maintain a target AFR can result in poor engine
response.
[0010] In a uniflow-scavenged OP2S engine, some of the air
delivered to a cylinder during a cycle of engine operation
("delivered air") flows out of the exhaust port during scavenging
and thus is not available for combustion. An accurate measure of
AFR for use in controlling combustion uses the mass of charge air
retained ("trapped") in the cylinder when the last port of the
cylinder is closed. Depending on engine design either the exhaust
port or the intake port may be the last to close; in many
instances, the intake port is the last to close. It is further the
case that, in addition to the trapped charge air, a measurable mass
of residual exhaust gas may sometimes be trapped in the cylinder by
closure of the exhaust port and/or by recirculation into the
cylinder with the charge air.
[0011] Provision of fuel and air in the engine is governed by an
engine control mechanization that senses various engine operating
parameters and regulates the flow of gasses (air and exhaust)
through the engine and the injection of fuel into the engine. It is
particularly desirable that the engine control mechanization be
able to recognize transient events of an OP2S engine so as to
rapidly configure the air handling system for increasing the amount
of delivered and/or retained charge air provided to the cylinders
in response to torque requests.
[0012] The gas pressure differential across the engine that is
necessary to sustain the unidirectional flow of charge air and
exhaust is generated and sustained by air handling elements of the
air handling system, which may include a supercharger and one or
more turbochargers. During steady state operation the engine
control mechanization governs these elements in a closed-loop mode
by continuous adjustments that seek desired target values
("setpoints") for particular air flow parameters in order to
maintain efficient operation with low emissions. When a demand for
increased torque is made, the charge air pressure must be rapidly
increased ("boosted").
[0013] Therefore, it is desirable that the air handling system of a
uniflow-scavenged, OP2S engine respond to a torque request without
significant delay, while maintaining control of emissions during
transient operation.
SUMMARY
[0014] In a turbocharged, uniflow-scavenged, OP2S engine with a
crankshaft-driven supercharger disposed in the air handling system
between a compressor and engine intake ports, torque requests
initiate transient modes of operation during which provision of
fuel and charge air are increased or decreased while desired modes
of control over emissions are maintained.
[0015] Thus, when a transient event occurs, fuel injection into the
cylinders of the engine is controlled. For example, with a common
rail direct injection fuel handling system, fuel injection is
increased (or decreased) by changing one or more of a fuel rail
pressure and a fuel injection duration in response to an increase
in engine load. Concurrently, airflow into cylinders of the engine
is increased (or decreased) by controlling an airflow parameter
representing charge air that is trapped or retained in the
cylinders by last port closings.
[0016] One airflow parameter representing charge air that is
trapped or retained in a cylinder by last port closing is a
scavenging ratio (SR) of the engine, which is the ratio between a
mass of delivered air and a mass of trapped charge which includes
trapped charge air, and which may include residual or recirculated
exhaust. For example, by increasing SR, the mass of charge air
flowing through a cylinder increases, thereby reducing charge air
exhaust residuals in the cylinder, which results in less PM
generation since there is more fresh charge for combustion. The
trade-off can possibly be an increase in nitrous oxide (NOx)
emissions due to more fresh charge air available for
combustion.
[0017] Another airflow parameter representing charge air that is
trapped or retained in a cylinder by last port closing is a
trapping efficiency (TE) of the engine, which is the ratio between
a mass of delivered charge air and a mass of trapped charge air.
For example, a higher compressor outlet pressure will result in
more volumetric flow across a supercharger, thereby increasing the
boost pressure and resulting in more trapped mass (charge air and
exhaust) in the cylinders. More trapped mass may result in higher
PM but with more trapped exhaust, NOx emissions can be lowered.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic illustration of a uniflow-scavenged,
two-stroke cycle, opposed-piston (OP2S) engine of the prior
art.
[0019] FIG. 2 is a schematic diagram illustrating a fuel injection
system embodiment for the OP2S engine of FIG. 1.
[0020] FIG. 3 is a schematic diagram illustrating an air handling
system embodiment for the OP2S engine of FIG. 1.
[0021] FIG. 4. is a schematic diagram illustrating a control
mechanization embodiment for the OP2S engine of FIG. 1.
[0022] FIG. 5 is a flow diagram illustrating a transient control
algorithm implemented by operation of a control mechanization
embodiment according to FIG. 4.
[0023] FIG. 6 is a flow diagram illustrating an air handling
configuration step of the transient control algorithm by which
scavenging ratio is prioritized.
[0024] FIG. 7 is a flow diagram illustrating an air handling
configuration step of the transient control algorithm by which
trapping efficiency is prioritized.
[0025] FIG. 8 shows a process for controlling active airflow
devices of the air handling system of FIG. 3 during steady state
and transient modes of engine operation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] FIG. 1 is a schematic representation of a uniflow-scavenged,
two-stroke cycle opposed-piston (OP2S) engine 8 of the compression
ignition type that includes at least one cylinder. Preferably, the
engine 8 has two or more cylinders. In any event, the cylinder 10
represents both single cylinder and multi-cylinder configurations
of the OP2S engine 8. The cylinder 10 includes a bore 12 and
longitudinally displaced intake and exhaust ports 14 and 16
machined or formed in the cylinder, near respective ends thereof.
An air handling system 15 of the engine 8 manages the transport of
charge air into, and exhaust out of, the engine. Each of the intake
and exhaust ports includes one or more circumferential arrays of
openings in which adjacent openings are separated by a solid
portion of the cylinder wall (also called a "bridge"). In some
descriptions, each opening is referred to as a "port"; however, the
construction of a circumferential array of such "ports" is no
different than the port constructions in FIG. 1. Fuel injectors 17
include nozzles that are secured in threaded holes that open
through the sidewall of the cylinder. A fuel handling system 18 of
the engine 8 provides fuel for direct side injection by the
injectors 17 into the cylinder. Two pistons 20, 22 are disposed in
the bore 12 with their end surfaces 20e, 22e in opposition to each
other. For convenience, the piston 20 is referred to as the
"intake" piston because it opens and closes the intake port 14.
Similarly, the piston 22 is referred to as the "exhaust" piston
because it opens and closes the exhaust port 16. Preferably, but
not necessarily, the intake piston 20 and all other intake pistons
are coupled to a crankshaft 30 disposed along one side of the
engine 8; and, the exhaust piston 22 and all other exhaust pistons
are coupled to a crankshaft 32 disposed along the opposite side of
the engine 8.
[0027] Operation of the OP2S engine 8 is well understood. In
response to combustion the opposed pistons move away from
respective TDC locations where they are at their innermost
positions in the cylinder 10. While moving from TDC, the pistons
keep their associated ports closed until they approach respective
BDC locations where they are at their outermost positions in the
cylinder and the associated ports are open. The pistons may move in
phase so that the intake and exhaust ports 14, 16 open and close in
unison. Alternatively, one piston may lead the other in phase, in
which case the intake and exhaust ports have different opening and
closing times.
[0028] As charge air enters the cylinder 10 through the intake port
14, the shapes of the intake port openings cause the charge air to
rotate in a vortex 34 about the cylinder's longitudinal axis, which
spirals in the direction of the exhaust port 16. A swirl vortex 34
promotes air/fuel mixing, combustion, and suppression of
pollutants. Swirl velocity increases as the end surfaces 20e and
22e move together.
[0029] FIG. 2 shows the fuel handling system 18 embodied as a
common rail direct injection fuel handling system. The fuel
handling system 18 delivers fuel to each cylinder 10 by injection
into the cylinder. Preferably, each cylinder 10 is provided with
multiple fuel injectors mounted for direct injection into cylinder
space between the end surfaces of the pistons. For example, each
cylinder 10 has two fuel injectors 17. Preferably, fuel is fed to
the fuel injectors 17 from a fuel source 40 that includes at least
one rail/accumulator mechanism 41 to which fuel is pumped by a fuel
pump 43. A fuel return manifold 44 collects fuel from the fuel
injectors 17 and the fuel source 40 for return to a reservoir from
which the fuel is pumped. Elements of the fuel source 40 are
operated by respective computer-controlled actuators that respond
to fuel commands issued by an engine control unit. Although FIG. 2
shows the fuel injectors 17 of each cylinder disposed at an angle
of less than 180.degree., this is merely a schematic representation
and is not intended to be limiting with respect to the locations of
the injectors or the directions of the sprays that they inject. In
a preferred configuration, best seen in FIG. 1, the injectors 17
are disposed for injecting fuel sprays in diametrically opposing
directions of the cylinder 8 along an injection axis. Preferably,
each fuel injector 17 is operated by a respective
computer-controlled actuator that responds to injector commands
issued by an engine control unit.
[0030] FIG. 3 shows an embodiment of the air handling system 15
that manages the transport of charge air provided to, and exhaust
gas produced by, the OP2S engine 8. A representative air handling
system construction includes a charge air subsystem 38 and an
exhaust subsystem 40. In the air handling system 15, a charge air
source receives fresh air and processes it into charge air. The
charge air subsystem 38 receives the charge air and transports it
to the intake ports of the engine 8. The exhaust subsystem 40
transports exhaust products from exhaust ports of the engine for
delivery to other exhaust components.
[0031] The air handling system 15 includes a turbocharger system
that may comprise one or more turbochargers. For example, a
turbocharger 50 includes a turbine 51 and a compressor 52 that
rotate on a common shaft 53. The turbine 51 is disposed in the
exhaust subsystem 40 and the compressor 52 is disposed in the
charge air subsystem 38. The turbocharger 50 extracts energy from
exhaust gas that exits the exhaust ports and flows into the exhaust
subsystem 40 directly from engine exhaust ports 16, or from an
exhaust manifold assembly 57 that collects exhaust gasses output
through the exhaust ports. Preferably, in a multi-cylinder OP2S
engine, the exhaust manifold 57 comprises an exhaust plenum or
chest that communicates with the exhaust ports 16 of all cylinders
10, which are supported in a cylinder block 75. The turbine 51 is
rotated by exhaust gas passing through it to an exhaust outlet 58.
This rotates the compressor 52, causing it to generate charge air
by compressing fresh air.
[0032] Exhaust gasses from the exhaust ports of the cylinders 50
flow from the exhaust manifold assembly 57 into the inlet of the
turbine 51, and from the turbine's outlet into an exhaust outlet
channel 55. In some instances, one or more after-treatment devices
79 are provided in the exhaust outlet channel 55. While the air
handling system 15 may be constructed to reduce NOx emissions
produced by combustion by recirculating exhaust gas through the
ported cylinders of the engine, the details of an exhaust gas
recirculation (EGR) loop are not necessary to an understanding of
transient response according to this disclosure.
[0033] The charge air subsystem may provide inlet air to the
compressor 52 via an air filter 80. As the compressor 52 rotates it
compresses inlet air, and the compressed inlet air flows into the
inlet 71 of a supercharger 60. Air pumped by the supercharger 60
flows through the supercharger's outlet 72 into the intake manifold
62. Pressurized charge air is delivered from the intake manifold 62
to the intake ports 14 of the cylinders 10. Preferably, in a
multi-cylinder OP2S engine, the intake manifold 68 comprises an
intake plenum or chest that communicates with the intake ports 14
of all cylinders 10.
[0034] The charge air subsystem may further include at least one
cooler coupled to receive and cool charge air before delivery to
the intake ports of the engine 8. In these instances, charge air
output by the compressor 52 flows through a cooler 67, whence it is
pumped by the supercharger 60 to the intake ports. A second cooler
69 may be provided between the output of the supercharger 60 and
the intake manifold 68.
[0035] With further reference to FIG. 3, the air handling system 15
is equipped for control of gas flow at separate control points in
the charge air and exhaust subsystems.
[0036] In the charge air subsystem, charge air flow and boost
pressure are controlled by operation of a shunt path 80 coupling
the output 72 of the supercharger to the supercharger's input 71.
The shunt path 80 includes a shunt valve 82 that governs the flow
of charge air into, and thus the pressure in, the intake manifold
68. More precisely, the shunt valve 82 shunts the charge air flow
from the supercharger's outlet 72 (high pressure) to its inlet 71
(lower pressure). Sometimes those skilled in the art refer to the
shunt valve 82 as a "bypass" valve or a "recirculation" valve. A
backpressure valve 90 in the exhaust channel 55 governs the flow of
exhaust out of the turbine and thus the backpressure in the exhaust
subsystem for various purposes, including modulation of the exhaust
temperature. As per FIG. 3, the backpressure valve 90 is positioned
in the exhaust channel 55, between the output 58 of the turbine 51
and the after-treatment devices 79. A wastegate valve 92 diverts
exhaust gasses around the turbine, which enables control of the
speed of the turbine. Regulation of the turbine speed enables
regulation of the compressor speed which, in turn, permits control
of charge air boost pressure. The valves 82, 90, and 92 are opened
and closed by respective computer-controlled actuators that respond
to rotational commands issued by an engine control unit. In some
cases, these valves may be controlled to two states: fully opened
or fully closed. In other cases, any one or more of the valves may
be variably adjustable to a plurality of states between fully
opened and fully closed.
[0037] In some instances, additional control of gas flow and
pressure is provided by way of a variable speed supercharger. In
these aspects, the supercharger 60 is coupled by a drive mechanism
95 (Drive) to a crankshaft 30 or 32 of the engine 8, to be driven
thereby. The drive mechanism 95 may comprise a stepwise
transmission device, or a continuously variable transmission device
(CVD), in which cases charge air flow, and boost pressure, may be
varied by varying the speed of the supercharger 60 in response to a
speed control signal provided to the drive mechanism 95. In other
instances, the supercharger may be a single-speed device with a
mechanism to disengage the drive, thus giving two different drive
states. In yet other instances, a disengagement mechanism may be
provided with a stepwise or continuously variable drive. In any
event, the drive mechanism 95 is operated by a computer-controlled
actuator that responds to drive commands issued by an engine
control unit.
[0038] In some aspects, the turbine 51 may be a variable-geometry
turbine (VGT) device having an effective aspect ratio that may be
varied in response to changing speeds and loads of the engine.
Alteration of the aspect ratio enables control of the speed of the
turbine. Regulation of the turbine speed enables regulation of the
compressor speed which, in turn, permits control of charge air
boost pressure. Thus, in many cases, a turbocharger comprising a
VGT does not require a wastegate valve. A VGT device is operated by
a computer-controlled actuator that responds to turbine commands
issued by an engine control unit.
[0039] In this disclosure, an engine control mechanization is a
computer-based system that governs the operations of various engine
systems, including the fuel handling system, the air handling
system, a cooling system, a lubrication system, and other engine
systems. The engine control mechanism includes one or more
electronic control units coupled to associated sensors, actuators,
and other machine devices throughout the engine. As per FIG. 4,
control of the fuel handling system of FIG. 2 and the air handling
system of FIG. 3 (and, possibly, other systems of the OP2S engine
8) is implemented by a control mechanization 93 that includes a
programmable engine control unit (ECU) 94 programmed to execute
fuel handling algorithms and air handling algorithms under various
engine operating conditions. Such algorithms are embodied in
control modules that are part of an engine systems control program
executed by the ECU 94 while the engine is operating. For the
common rail direct injection system, the ECU 94 controls injection
of fuel into the cylinders by issuing rail pressure (Rail) commands
to the fuel source 40, and by issuing injector (Injector) commands
for operation of the injectors 17. For the air handling system the
ECU 94 controls the transport of gas (charge air and exhaust)
through the engine by issuing backpressure (Backpressure),
wastegate (Wastegate) and shunt (Shunt) commands to open and close
the exhaust backpressure valve 90, the wastegate valve 92, and the
supercharger shunt valve 82, respectively. In cases where the
supercharger 60 is operated by a variable drive, the ECU 94 also
controls gas transport by issuing drive (Drive) commands to actuate
the supercharger drive 95. And, in those instances where the
turbine 51 is configured as a variable geometry device, the ECU 94
also controls the transport of gas by issuing VGT commands to set
the aspect ratio of the turbine.
[0040] When the OP2S engine 8 runs, the ECU 94 determines the
current engine operating state based on engine load and engine
speed, and governs the amount, pattern, and timing of fuel injected
into each cylinder 10 by control of common rail fuel pressure and
injection duration, based on the current operating state. For this
purpose, the ECU 94 receives signals from an accelerator sensor 96
(or a speed governor or a cruise control system, or equivalent
means) that detects accelerator position, an engine speed sensor 97
that detects the rotational speed of the engine, and a sensor 98
that detects rail pressure. At the same time, the ECU 94 configures
the air handling system 15 to provide the optimal AFR for the
current operational state. For this purpose, the ECU receives
signals from air flow sensors that may include one or more of a
mass air flow sensor 100 that detects the mass flow of air into the
inlet of the compressor 52, an intake manifold pressure sensor 101
that detects charge air pressure in the intake manifold 68, an
exhaust manifold pressure sensor 102 that detects exhaust pressure
in the exhaust manifold 57, a supercharger intake pressure sensor
103 that detects charge air pressure at the intake of the
supercharger 60, a supercharger outlet pressure sensor 104 that
detects charge air pressure at the outlet of the supercharger 60,
and, possibly other sensors.
[0041] During engine operation, the ECU 94 monitors a transient
indication parameter which indicates changes in the engine load
and/or the engine speed. A sudden change in the transient
indication parameter, at a rate that indicates a transient state,
causes the ECU 94 to invoke a transient control module. In this
regard, a transient indication parameter may be based on or derived
from sensor information including, without limitation, one or more
of accelerator (gas pedal) movement, engine speed, engine
acceleration, crankshaft angle, and fuel demand. The ECU 94
determines a transient indication parameter value (from gas pedal
movement, for example) and also measures, estimates, or calculates
(hereinafter, "calculates") a rate of change of the transient
indication parameter value.
[0042] The ECU 94 is programmed to execute a transient control
algorithm via the control mechanization 93 of FIG. 4. The transient
control algorithm enables the ECU 94 to monitor and respond to
transient activity of the OP2S engine. An exemplary embodiment of
the transient control algorithm is illustrated in FIG. 5. With
reference to FIGS. 4 and 5, presume that the engine is operating in
a steady state when the ECU 94 initiates a monitoring process at
step 120. The monitoring process enables the ECU 94 to detect and
respond to a torque demand. In decision step 122, the ECU monitors
the engine load and speed parameters for change. An increase in
engine load (such as would be indicated by movement of an
accelerator pedal, for example) indicates a positively-directed
torque demand. Conversely, a decrease in engine load indicates a
negatively-directed torque demand. If the ECU detects no torque
demand in decision step 122, steady state operation is maintained
at 123. However, if a torque demand is detected, the positive exit
from decision step 122 is followed to decision step 124.
[0043] In decision step 124, the ECU 94 monitors the rate of change
of the transient indication parameter (hereinafter "transient
intensity") with respect to a transient intensity calibration
threshold value for an indication of a transient state of
operation. If transient intensity does not reach the transient
intensity calibration threshold value, the ECU 94 follows the
negative exit from decision step 126 and exercises steady state
control to configure the fuel and air handling systems for optimal
AFR. However, if the transient intensity exceeds the calibration
threshold value, the ECU 94 follows the positive exit from decision
step 126 and initiates a transient mode of operation in steps 126
and 128. At step 126, a demanded fuel quantity is calculated from
the demanded torque. In some instances the calculated fuel demand
may differ from the amount of fuel actually delivered. In this
regard, the ECU 94 may execute a fuel limiter or smoke limiter
routine which limits the delivered fuel based on current airflow
and current AFR. See, for example, the fuel limiter for a
uniflow-scavanged, two-stroke cycle, opposed-piston engine
described in commonly-owned, co-pending U.S. patent application
Ser. No. 15/062,868. In response to a demand for increased torque,
ECU 94 determines a required increase (or decrease) in the amount
of delivered fuel, and adjusts the common rail pressure and
injection duration, as necessary to satisfy the demand.
[0044] At step 128, the ECU 94 exercises a transient control
process to configure the air handling system for controlling
unidirectional airflow through cylinders of the engine as required
to support combustion of the demanded fuel. In some aspects, when a
low-to-high transition in torque demand signals the onset of a
transient condition such control is exercised by reducing airflow
resistance and increasing charge air velocity. In some other
aspects, when a high-to-low transition in torque demand signals the
onset of a transient condition such control is exercised by
increasing airflow resistance and decreasing charge air
velocity.
[0045] For example, in responding to a demand for increased torque,
the ECU 94 may implement an air handling strategy that ensures the
airflow path from the intake ports of the engine to the exhaust
channel 55 is configured to prioritize the scavenging ratio of the
engine by increasing the flow of charge air delivered to the
cylinders, as is desirable to maintain the positive pressure drop
and a high air flow rate from intake to exhaust for the OP2S. In
this case, the ECU 94 increases charge air flow by reducing exhaust
flow resistance and increasing the pressure drop across the engine.
Depending upon a desired emissions result, the ECU 94 either
continues to give priority to the scavenging ratio or transitions
priority to trapping efficiency by increasing the compressor outlet
pressure, thereby increasing the mass flow rate of charge air.
[0046] The ECU 94 continues to execute the monitoring process by
continuing to decision step 130 where the ECU 94 maintains
transient control over the air handling system through the loop
130, 131 until the torque demand is met, at which time the ECU
takes the positive exit from decision step 130, reasserts
steady-state control and returns to monitoring engine load and/or
engine speed via decision step 122.
[0047] In response to a demand for increasing torque at a rate that
indicates transient control, the ECU 94 may be programmed to
operate according to a scavenging ratio (SR) preference strategy in
configuration step 128 of FIG. 5 by executing the process
illustrated in FIG. 6. Referring to FIGS. 4 and 6, in step 150, the
ECU 94 calculates a level of transient intensity and detects a
transient condition when the transient intensity level meets or
exceeds a transient intensity calibration threshold value, at which
point the ECU 94 switches to transient control of the supercharger
drive 95, the valves 82, 90, and 92, and the turbine 51 (if
configured as a VGT device).
[0048] In step 152, the ECU 94 opens the backpressure valve 90 to a
setting calibrated for the calculated level of transient intensity.
This reduces the resistance of the exhaust subsystem to the
delivery of charge air, which increases the scavenging ratio.
[0049] In step 154, the ECU 94 increases the velocity of charge air
provided to the intake ports of the engine in order to accelerate
the unidirectional flow of gas in the engine. Charge air velocity
is increased by increasing the supercharger pressure ratio (outlet
pressure/inlet pressure), which further increases the scavenging
ratio. This can be done by closing the supercharger shunt valve 82
to a value calibrated for the calculated transient intensity. This
can also be done by changing the setting of the supercharger drive
95 to a value calibrated for the level of transient intensity. In
some aspects, the ECU 94 may control both the shunt valve and the
drive in order to achieve a finer control over the operation of the
supercharger 60.
[0050] In step 156, the ECU 94 further reduces the resistance of
the exhaust subsystem to the delivery of charge air by reducing the
resistance of the turbine 51 to the flow of exhaust, which further
increases the scavenging ratio. If the turbine 51 is a
fixed-geometry device, the ECU 94 opens the wastegate valve 92 to a
value calibrated for the measured transient intensity. On the other
hand, if the turbine 51 is a variable-geometry device, the ECU 94
opens the vanes of the turbine 52 to a value calibrated for the
measured transient intensity.
[0051] The changes made to the configuration of the air handling
system by the ECU 94 in steps 152, 154, and 156 are initiated
substantially simultaneously, at the onset of the transient
condition, and the ECU 94 measures time from the point of onset.
Upon elapse of a period of time calibrated for the level of
transient intensity, the ECU 94, in step 158, activates the turbine
51 in order to increase the compressor outlet pressure, thereby
resulting in an increase in boost pressure. This is done either by
closing the wastegate valve 92 to a calibrated position (if the
turbine is a fixed-geometry device) or by opening the turbine vanes
to a calibrated position (if the turbine is a VGT device).
[0052] In step 160, once the airflow demand is met, the ECU 94
returns to steady-state control of the air handling system.
[0053] In response to a demand for increasing torque at a rate that
indicates transient control, the ECU 94 may be programmed to
operate according to a trapping efficiency (TE) preference strategy
in configuration step 128 of FIG. 5 by executing the process the
process illustrated in FIG. 7. Referring to FIGS. 4 and 7, in step
170, the ECU 94 calculates a level of transient intensity and
detects the onset of a transient condition when the transient
intensity level meets or exceeds a transient intensity calibration
threshold value, at which point the ECU 94 switches to transient
control of the supercharger drive 95, the valves 82 and 90, and 92,
and the turbine 51 (if configured as a VGT device).
[0054] In step 172, the ECU 94 opens the backpressure valve 90 to a
value calibrated for the calculated intensity of the torque demand.
This reduces the resistance of the exhaust subsystem to the
delivery of charge air, which increases the scavenging ratio.
[0055] In step 174, the ECU 94 accelerates the delivery of charge
air to the intake ports of the engine by increasing the
supercharger pressure ratio, which further increases the scavenging
ratio. This can be done by closing the supercharger shunt valve 82
to a value calibrated for the calculated intensity of the torque
demand. This can also be done by changing the setting of the
supercharger drive 95 to a value calibrated for the calculated
intensity of the torque demand. In some aspects, both the shunt
valve and the drive may be controlled to achieve a finer control
over the speed of the supercharger 60.
[0056] In step 176, the ECU 94 activates the turbine 52, which
increases the mass and velocity of the compressed air delivered by
the compressor 52 to the supercharger 60. The increased mass of
charge delivered to the cylinders increases the trapping efficiency
of the OP2S engine. If the turbine 51 is a fixed-geometry device,
the ECU 94 closes the wastegate valve 92 to a value calibrated for
the measured intensity of the torque demand. On the other hand, if
the turbine 51 is a variable-geometry device, the ECU 94 closes the
vanes of the turbine 52 to a value calibrated for the measured
intensity of the torque demand.
[0057] The changes made to the configuration of the air handling
system by the ECU 94 in steps 174 and 176 are initiated
substantially simultaneously, and time is measured from the point
of initiation. Upon elapse of a period of time calibrated for the
measured intensity of the torque demand, the ECU 94, in step 178,
reduces the speed of the turbine 52 in order to reduce the
compressor outlet pressure, thereby resulting in an increase in
scavenging ratio. This is done either by opening the wastegate
valve 92 to a calibrated position (if the turbine is a
fixed-geometry device) or by closing the turbine vanes to a
calibrated position (if the turbine is a VGT device).
[0058] In step 180, once the airflow demand is met, the ECU 94
returns to steady-state control of the air handling system.
[0059] The ECU 94 executes the air handling algorithms illustrated
in FIGS. 5-7 using various configurations of a device control
process 199 illustrated by the schematic diagram of FIG. 8. In this
regard, the ECU executes respective adaptations of the device
control process for a plurality of active airflow devices
comprising the backpressure valve 90, the supercharger shunt valve
82, the supercharger drive 95, the wastegate valve 92 (for a fixed
geometry turbine), the turbine vanes (for a VGT device), and
possibly other active airflow devices. In each case, the respective
device control process comprises a steady state control portion 200
operable to control the active airflow device in a steady state
mode of engine operation by means of a steady-state command
.theta..sub.1, a transient control portion 220 operable to control
the active airflow device in a transient mode of engine operation
by means of a transient command .theta..sub.2, and a transition
portion 230. The transition portion 230 is operable to initiate
steady state control by default and to transition control of the
device to transient control at the point when an onset of a
transient condition is detected. The transition portion 230
monitors various parameters during the transient condition in order
to determine when to transition control of the device from
transient control to steady state control. In each device control
process, the steady state control portion 200 and the transient
control portion 220 run simultaneously. Thus, at the points of
transition there is no delay in formulating the appropriate
command.
[0060] In each device control process, the steady state control
portion 200 includes a feedback controller 201 and a device
feedforward controller 202. The feedback controller 201 receives
engine speed and engine load command-based control variables that
are output as desired air parameter set-points (mass airflow, boost
pressure, exhaust back-pressure, etc.) from a map or look-up table
203A indexed by engine load and engine speed (RPM) parameter
values. A desired parameter set-point for current values of engine
speed and current engine load is corrected at 204 for ambient
condition factors that are output from a map or look-up table 203B
indexed by ambient conditions. A parameter value of the
corresponding component of actual airflow (mass airflow, boost
pressure, exhaust back-pressure, etc.) in the air handling system
is sensed (which may include measurement, estimation, or
calculation) at 206 and an error value (e) is determined at 207 by
subtracting the sensed parameter value from the desired set-point.
The error value is input to the feedback controller 201, which
generates a device set-point correction (c). The device feedforward
controller 202 generates device actuator position commands in
response to engine speed and engine load parameter values. The
output of the feedback controller 201 and the output of the
feedforward device controller 202 are added at 209 to generate a
steady state device actuator command .theta..sub.1 output by the
ECU 94 to a device actuator.
[0061] The transient control portion 220 includes a feedforward
device controller 221 that generates a transient device actuator
command in response to the level of transient intensity or the rate
of change of AFR resulting from the change in amount of fuel being
injected. Using the transient intensity and the current position of
an active actuator (valve, supercharger drive, VGT), a feedforward
actuator command, .theta..sub.2', is generated. This command can be
modified (or gated) at 222 on the basis of a elapsed time (obtained
from a counter 223) since the transient has been detected, thereby
resulting in a final device actuator command (.theta..sub.2) from
transient controller 220.
[0062] By way of the transition portion 230, the ECU 94 changes
control from steady state to transient if transient intensity is
greater than a calibration value. The ECU 94 changes control from
transient to steady state if either the elapsed time exceeds a
limit, or the error value e drops below a calibration value level.
Thus, at decision step 231, the ECU 94 tests the transient
intensity level against the transient intensity calibration
threshold value. When the test indicates the positive exit from
decision step 231, the ECU 94, in step 232, enables transient
control of the air handling system and issues the transient device
actuator command .theta..sub.2 to the active device. Otherwise,
following the negative exit from decision step 231, the ECU 94, in
step 233, issues the steady-state device actuator command,
.theta..sub.1. In decision step 234, if a transient device actuator
command has been active for a calibration period, or if the
air-handling set-points (mass airflow, boost, exhaust
back-pressure, etc.) are met (e<calibration value), then the
control process transitions via step 235 to steady-state control
and issues a steady state device actuator command, .theta..sub.1.
If the air-handling set-points are not met after elapse of a
calibration period, and the error between set-point and measured
value is not changing, then the ECU 94 may raise an
under-performance on-board diagnostic (OBD) fault via an OBD
indicator 300 (seen in FIG. 4) during the transition 235 to steady
state control.
[0063] In view of the examples and embodiments described in
connection with FIGS. 3-8, several airflow control combinations
have been described for a uniflow-scavenged, two-stroke cycle,
opposed-piston engine 8 equipped with at least one cylinder 10 with
a bore 12 and axially-spaced exhaust and intake ports 16 and 14
that communicate with the bore, a pair of pistons 22 and 20
disposed in opposition in the bore and operative to open and close
the exhaust and intake ports during operation of the engine, an air
handling system 15 that includes a charge air subsystem 38 to
provide charge air to the intake port, an exhaust subsystem 40 to
receive exhaust gas from the exhaust port, and a supercharger 60
that is operable to pump charge air in the charge air
subsystem.
[0064] According to this specification, and with reference to FIGS.
4, 5, and 6, a first airflow control combination includes a
command-controlled shunt valve 82 which promotes a charge air
pressure ratio across the supercharger, a sensor 96 or 97 that
senses one of engine acceleration and engine load of the engine, a
sensor 103 that detects charge air pressure at the intake of the
supercharger, a sensor 104 that detects charge air pressure at the
outlet of the supercharger, and, a programmed control unit 94. The
control unit is programmed to determine the occurrence of a torque
demand for the engine, the torque demand having an intensity based
on an intensity of a rate of change of engine acceleration or
engine load with respect to a transient intensity threshold value
(step 124), produce a transient command for the shunt valve to
increase the charge air pressure ratio across the supercharger when
the intensity of the torque demand exceeds the transient intensity
threshold (step 154), and produce a steady state command to control
the charge air pressure ratio across the supercharger to a desired
setpoint when the intensity of the torque demand falls below the
transient intensity threshold (step 160).
[0065] According to this specification, and with reference to FIGS.
4, 5, and 7, a second airflow control combination includes a
command-controlled supercharger drive 95 which promotes a charge
air pressure ratio across the supercharger, a sensor 96 or 97 that
senses one of engine acceleration and engine load of the engine, a
sensor 103 that detects charge air pressure at the intake of the
supercharger, a sensor 104 that detects charge air pressure at the
outlet of the supercharger, and, a programmed control unit 94. The
control unit is programmed to determine the occurrence of a torque
demand for the engine, the torque demand having an intensity based
on an intensity of a rate of change of engine acceleration or
engine load with respect to a transient intensity threshold value
(step 124), produce a transient command for the supercharger drive
to increase the charge air pressure ratio across the supercharger
when the intensity of the torque demand exceeds the transient
intensity threshold (step 154), and produce a steady state command
to control the charge air pressure ratio across the supercharger to
a desired setpoint when the intensity of the torque demand falls
below the transient intensity threshold (step 160).
[0066] As will be evident to the reasonably skilled craftsman, the
principles of transient air handling control set forth herein may
be practiced in various control configurations of the air handling
system of a uniflow-scavanged, two-stroke cycle, opposed-piston
engine. For example, transient control of the air handling system
may be bidirectional. That is to say transient control may occur in
response to low-load to high-load transitions that exceed a
threshold positive rate of change (as presented and described
hereinabove), and also may occur in response to high-load to
low-load transitions that exceed a threshold negative rate of
change. Further, the air handling system may be configured with a
supercharger alone or a turbocharger alone, as well as the
supercharger/turbocharger examples described above. Therefore,
although control of airflow and fuel flow in a uniflow-scavanged,
two-stroke cycle, opposed-piston engine during transient operation
has been described with reference to presently preferred examples
and embodiments, it should be understood that various modifications
can be made without departing from the scope of the following
claims.
* * * * *