U.S. patent application number 12/952033 was filed with the patent office on 2012-05-24 for four stroke internal combustion engine having variable valve timing and method.
This patent application is currently assigned to CATERPILLAR INC.. Invention is credited to Darryl Baldwin, Willibald Berlinger, Rohit Menon.
Application Number | 20120125276 12/952033 |
Document ID | / |
Family ID | 46063122 |
Filed Date | 2012-05-24 |
United States Patent
Application |
20120125276 |
Kind Code |
A1 |
Baldwin; Darryl ; et
al. |
May 24, 2012 |
FOUR STROKE INTERNAL COMBUSTION ENGINE HAVING VARIABLE VALVE TIMING
AND METHOD
Abstract
A four stroke internal combustion includes at least one cylinder
and at least one intake valve associated with the cylinder. The
intake valve is configured to open and close over a predetermined
range of crankshaft rotation in accordance with a Miller
thermodynamic cycle. An electronic controller receives at least one
input signal indicative of an amount of air and/or an amount of
air/fuel mixture in cylinder. The electronic controller is
configured to provide a timing phase signal that operates to adjust
a timing of operation of the intake valve based on the input
signal(s) such that a torque output of the engine is maintained
substantially constant over a predetermined range of engine speed
by shifting the predetermined range of crankshaft rotation.
Inventors: |
Baldwin; Darryl; (Lafayette,
IN) ; Menon; Rohit; (Lafayette, IN) ;
Berlinger; Willibald; (Peoria, IL) |
Assignee: |
CATERPILLAR INC.
Peoria
IL
|
Family ID: |
46063122 |
Appl. No.: |
12/952033 |
Filed: |
November 22, 2010 |
Current U.S.
Class: |
123/90.17 |
Current CPC
Class: |
F01L 1/3442 20130101;
Y02T 10/12 20130101; F01L 2820/041 20130101; F02D 13/0269 20130101;
Y02T 10/142 20130101 |
Class at
Publication: |
123/90.17 |
International
Class: |
F01L 1/34 20060101
F01L001/34 |
Claims
1. A four stroke internal combustion engine, comprising: at least
one cylinder having a piston reciprocable between top dead center
(TDC) and bottom dead center (BDC) positions; at least one intake
valve associated with the at least one cylinder and operable by a
camshaft, the at least one valve being configured to open and close
over a predetermined range of crankshaft rotation, wherein the
intake valve operates in accordance with a Miller thermodynamic
cycle; an electronic controller disposed to receive at least one
input signal indicative of at least one of an amount of air and an
amount of air/fuel mixture in the at least one cylinder; wherein
the electronic controller is configured to provide a timing phase
signal that operates to adjust a timing of operation of the at
least one intake valve based on the at least one input signal such
that a torque output of the engine is maintained substantially
constant over a predetermined range of engine speed by shifting the
predetermined range of camshaft rotation with respect to a
crankshaft position.
2. The engine of claim 1, wherein the timing phase signal causes a
phase shift in the predetermined range of camshaft.
3. The engine of claim 2, further comprising a phaser associated
with the camshaft and disposed to index the camshaft in response to
the timing phase signal.
4. The engine of claim 1, wherein the at least one input includes
at least one of engine speed, engine load, charge air oxygen
concentration, altitude, and fuel quality.
5. The engine of claim 1, wherein a ratio of air to fuel in the at
least one cylinder is maintained constant during engine operation
to yield at least one of a rich-burn stoichiometric combustion and
a lean burn stoichiometric combustion.
6. The engine of claim 5, wherein the timing phase signal operates
to decrease a Miller effect of the engine when at least one of the
engine speed is low, the engine load is low, the altitude is high,
the fuel quality is high, and the engine is in a startup mode.
7. The engine of claim 1, wherein the engine is fueled by at least
one or natural gas, propane, field gas, biogas, and producer
gas.
8. The engine of claim 1, wherein at least one of the torque output
and a speed of the engine is maintained within a range of +/-10% of
a target torque output value.
9. The engine of claim 1, wherein the engine is configured to, at
times, admit and compress an intake charge for combustion in the at
least one cylinder that is within the range of between 20 and 80%
of a total possible intake charge, which is defined as an intake
charge that would have been admitted into the at least one cylinder
had the intake valve been opened substantially at TDC and closed
substantially at BDC during an intake stroke.
10. The engine of claim 9, wherein a volumetric efficiency of the
engine is within the range of 45-60%.
11. The engine of claim 1, wherein the at least one cylinder is
configured to operate at a compression ratio 10:1 and 15:1.
12. A method for operating a four-stroke internal combustion
engine, comprising: operating the engine at a stoichiometric air to
fuel ratio and at an engine valve timing in a fashion consistent
with a Miller thermodynamic combustion cycle; receiving operating
parameters at an electronic controller, the operating parameters
being indicative of an amount of an air and fuel combustion mixture
present in at least one engine cylinder; processing the operating
parameters in the electronic controller to determine at least one
of a desired valve timing and a timing phase variation, wherein the
operating parameters include at least one of engine speed, engine
load, altitude, and fuel quality; determining a valve phase signal
based on at least one of the desired valve timing and the timing
phase variation; and changing a valve timing based on the valve
phase signal to selectively adjust the amount of the combustion
mixture such that an engine torque output is maintained
substantially constant over an engine speed range.
13. The method of claim 12, wherein the processing of the operating
parameters involves determining the at least one of desired valve
timing and timing phase variation based on a then-present engine
speed and engine load.
14. The method of claim 13, wherein the processing of the operating
parameters involves compensating the at least one of desired valve
timing and timing phase variation based on altitude.
15. The method of claim 13, wherein the processing of the operating
parameters involves compensating the at least one of desired valve
timing and timing phase variation based on fuel quality.
16. The method of claim 12, wherein changing the valve timing is
accomplished by indexing a camshaft in response to the valve phase
signal.
17. The method of claim 16, wherein the valve phase signal is
provided to a phaser device that operates to adjust the indexing of
the camshaft in response to the valve phase signal.
18. The method of claim 12, wherein operating the engine consistent
with the Miller thermodynamic combustion cycle is accomplished by
at least one of: maintaining at least one intake valve associated
with a cylinder of the engine open beyond a BDC position of a
piston such that an intake stroke is generally prolonged and a
compression stroke is generally abridged under a late inlet closing
(LIC) type of engine operation, and closing the at least one intake
valve before the BDC position of the piston such that the intake
stroke is generally abridged and the compression stroke is
generally prolonged under an early inlet closing (EIC) type of
engine operation.
19. The method of claim 18, wherein determining the at least one of
desired valve timing and timing phase variation is consistent with:
quickening the closing of the at least one intake valve when the
engine is operating under a LIC type of operation, or delaying the
closing of the at least one intake valve when the engine is
operating under an EIC type of operation, such that an effect of
the Miller cycle is decreased when the operating parameters are
indicative of at least one of a low engine speed, a low engine
load, a high altitude, or a high fuel quality, or when the engine
is in a startup mode.
20. The method of claim 18, wherein determining the at least one of
desired valve timing and timing phase variation is consistent with:
delaying the closing of the at least one intake valve when the
engine is operating under a LIC type of operation, or quickening
the closing of the at least one intake valve when the engine is
operating under an EIC type of operation, such that an effect of
the Miller cycle is increased when the operating parameters are
indicative of at least one of a high engine speed, a high engine
load, or a low fuel quality.
Description
TECHNICAL FIELD
[0001] This patent disclosure relates generally to spark ignition
internal combustion engines and, more particularly to engines
having variable valve timing capability.
BACKGROUND
[0002] The Miller cycle is a combustion process used in a type of
four-stroke internal combustion engine. A traditional Otto cycle
engine uses four "strokes," two of which have the greatest impact
on the engine's power output--the compression stroke, during which
power is used to compress a fuel and air mixture, and the power
stroke, during which the mixture combusts to produce power. An
appreciable portion of an engine's power output depends on the
amount of power internally consumed by the engine during the
compression cycles of the various engine cylinders.
[0003] In an engine operating under a Miller cycle, one or more
intake valves of a combustion cylinder are left open for a longer
period after bottom dead center (BDC) or are closed sooner, i.e.
before BDC, when compared to a corresponding engine operation in an
Otto cycle. In this way, a smaller amount of charge air is
compressed in the cylinder than what would otherwise have been
admitted into the cylinder had the intake valve timing been
performed in the standard Otto cycle operation.
[0004] When operating in a late intake valve closing fashion (LIC),
the charge is partially expelled back out the still-open intake
valve as the piston initially moves upwards in what is
traditionally the compression stroke. Similarly, when the intake
valve is closed early (EIC), the charge admitted in the cylinder is
expanded as the piston approaches BDC before being compressed.
Typically this loss of charge air would result in a loss of power.
However, in the Miller cycle, the reduction in charge air is
compensated for by the use of a supercharger or a turbocharger. One
aspect of the Miller cycle is that the compression stroke actually
starts in LIC engines only after the piston has pushed out this
"extra" charge and the intake valve closes, or in EIC engines after
the piston has passed BDC and begins to compress the charge in the
cylinder.
[0005] One example of a known engine operation mode can be seen in
U.S. Pat. No. 7,178,492, which issued on Feb. 20, 2007. Here, a
mixture of pressurized air and recirculated exhaust gas is fed from
intake manifold to an intake port of a combustion chamber. An air
intake valve can be selectively operated to open the port to allow
the mixture of pressurized air and recirculated exhaust gas to flow
between the combustion chamber and the intake manifold during a
major portion of the compression stroke of the piston. A fuel
supply system is controlled to inject fuel into the combustion
chamber after the intake valve is closed. In this engine
application, a variable intake valve closing mechanism selectively
interrupts the closing timing of the intake valve such that the
intake valve is held open for a desired period. Fuel, in this case
diesel, is injected into the combustion chamber when the intake
valve is closed, and the engine has a compression ratio of about
4/1.
SUMMARY
[0006] The disclosure describes, in one aspect, a four stroke
internal combustion engine. The engine includes at least one
cylinder and at least one intake valve associated with the
cylinder. The intake valve is configured to open and close over a
predetermined range of crankshaft rotation in accordance with a
Miller thermodynamic cycle. An electronic controller receives at
least one input signal indicative of an amount of air and/or an
amount of air/fuel mixture in cylinder. The electronic controller
is configured to provide a timing phase signal that operates to
adjust a timing of operation of the intake valve based on the input
signal(s) such that a torque output of the engine is maintained
substantially constant over a predetermined range of engine speed
by shifting the predetermined range of crankshaft rotation.
[0007] In another aspect, the disclosure describes a method for
operating a four-stroke internal combustion engine. The method
includes operating the engine at a stoichiometric air to fuel ratio
and at an engine valve timing in a fashion consistent with a Miller
thermodynamic combustion cycle. Operating parameters are received
at an electronic controller. The operating parameters are
indicative of an amount of an air and fuel combustion mixture
present in at least one engine cylinder. The operating parameters
are processed in the electronic controller to determine a desired
valve timing and/or a timing phase variation. The operating
parameters include engine speed, engine load, altitude, and/or fuel
quality. A valve phase signal is determined based on the desired
valve timing and/or the timing phase variation. A valve timing of
the engine is changed based on the valve phase signal to
selectively adjust the amount of the combustion mixture such that
an engine torque output is maintained substantially constant over
an engine speed range.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a block diagram of an engine in accordance with
the disclosure.
[0009] FIG. 2 is a partial cross section of a combustion cylinder
of an engine in accordance with the disclosure.
[0010] FIGS. 3 and 4 are perspective and section views of a phaser
in accordance with the disclosure.
[0011] FIG. 5 is a block diagram for an engine controller in
accordance with the disclosure.
[0012] FIG. 6 is a block diagram of a phaser controller in
accordance with the disclosure.
[0013] FIG. 7 is a qualitative chart illustrating various engine
operating conditions in accordance with the disclosure.
[0014] FIG. 8 is a flowchart for a method in accordance with the
disclosure.
[0015] FIG. 9 is a valve timing diagram in accordance with the
disclosure.
DETAILED DESCRIPTION
[0016] This disclosure relates to internal combustion engines
having variable valve and fuel injection and/or spark timing
capability. Although the disclosed embodiment describes a spark
ignition engine operating on gaseous hydrocarbon fuel, such as
natural gas, compression ignition engines or engines operating on
gasoline or any other hydrocarbon fuel are contemplated and are
well suited for the devices and methods disclosed herein.
[0017] In various engine applications such as those operating at
various speeds while maintaining a constant torque output, as speed
is reduced, the effective "amount" of Miller changes depending on
the LIC or EIC type of Miller mode of operation of the engine.
Typically, the air charge of the engine is maintained constant by
appropriate compensation of intake manifold pressure or boost and
intake valve timing. In most engine applications, such additional
boost is not readily attainable, which results in those engines
being unable to maintain their constant torque output when
operating at lower speeds. Having identified this problem, the
present disclosure proposes a method and system for controlling the
amount of Miller that an engine uses dynamically based on engine
operating parameters, which include engine speed as well as other
parameters. These parameters are processed in a controller which,
in one embodiment, is configured to control the operation of a cam
phaser. The cam phaser operates to change the valve timing and thus
adjust the amount of Miller depending on engine speed, which
permits the engine to operate at lower speeds than the speeds that
were previously possible.
[0018] FIG. 1 shows a block diagram for an internal combustion
engine 100. The internal combustion engine 100 includes a crankcase
102 forming a plurality of cylinders 104. Each cylinder 104 is
operably associated with an injector 106, an intake runner 108, and
an exhaust runner 110. During operation of the engine 100, air
enters each cylinder 104 via its respective intake runner 108.
While in the cylinder 104, the air mixes with fuel injected from
the injector 106 to form a combustible mixture. In an alternative
embodiment, the fuel is mixed with intake air before it enters the
engine cylinders to yield a combustible mixture. In either engine
configuration, the combustible mixture is compressed via a piston
(not shown) and is ignited by a spark producing power. Exhaust gas
remaining in the cylinder 104 is evacuated via the respective
exhaust runner 110 and the process is repeated. Air entering each
cylinder via its respective intake runner 108 is supplied to the
intake runners 108 through an intake manifold 112. Similarly,
exhaust gas from the cylinders 104 is collected in an exhaust
manifold 114. The fuel supplied to each injector 106 is compressed
by a fuel pump 116, which supplies compressed fuel to a common rail
118 that is in fluid communication with each of the injectors 106.
Alternatively, the fuel is provided to a mixing valve (not shown)
that mixes fuel with incoming engine air in a predetermined
ratio.
[0019] A detail section view of a cylinder 104 of the engine 100 is
shown in FIG. 2. In the description that follows, elements and
features that are the same or similar to corresponding elements and
features previously described are denoted with the same reference
numerals as previously used for simplicity. Accordingly, the
cylinder 104 includes a piston 202 reciprocally mounted therewithin
and eccentrically connected to a rotating crankshaft (not shown)
via a connecting rod 204 (partially shown). A cylinder head 206
forms portions of the intake runner 108 and the exhaust runner 110.
An intake valve 208 is reciprocally mounted in the cylinder head
206 and disposed to selectively fluidly block air entering the
cylinder 104 from the intake runner 108. Similarly, an exhaust
valve 210 selectively fluidly blocks exhaust gas present in the
cylinder 104 after a power stroke of the engine from entering the
exhaust runner 110. Although single intake and exhaust valves are
shown for simplicity, the engine 100 may include multiple valves
per cylinder 104.
[0020] The opening and closing of the intake and exhaust valves 208
and 210 in the illustrated embodiment is accomplished by two
overhead cams, but other configurations may be used. Moreover,
although dedicated intake and exhaust cams are shown, alternate
engine configurations may include a single cam operating both the
intake and exhaust valves of the engine. In the illustrated
embodiment, an intake valve cam 212 includes a plurality of intake
lobes 214 that form eccentric features configured to push the
intake valve 210 open through a corresponding intake valve bridge
216 as the intake cam 212 rotates. Similarly, an exhaust valve cam
218 includes exhaust lobes 220 that push the exhaust valve 210 open
through a corresponding exhaust valve bridge 222. Although the
illustration in FIG. 2 is simplified, similar structures operating
valves for cylinders arranged in any inline, V, or any other
configuration are contemplated.
[0021] The engine 100 is a four stroke engine, which means that
four strokes of the piston 202 are successively performed to
produce power. In the illustrated embodiment, the engine 100 is
operating under a Miller thermodynamic cycle, in which the intake
valve 208 is kept open after the piston 202 has passed its BDC
position longer or shorter than what a typical engine running an
Otto or Diesel cycle would have. More specifically, a qualitative
valve timing chart 300 is shown in FIG. 9. Although typical valve
timing charts are configured based on the particular structures of
each engine, the chart 300 is shown simplified and without valve
lead, lag, or overlap effects for simplicity.
[0022] The chart 300 represents various intake and exhaust valve
opening events with respect to the rotation of the engine's
crankshaft, which is viewed from the front as it rotates in the
direction of the arrow, R. Accordingly, TDC is shown at the top of
the chart 300 and represents the crankshaft position (0 degrees) at
which the piston 202 is at the topmost position in the cylinder 104
as shown in FIG. 2. Similarly, BDC is shown at the bottom of the
chart 300 and represents the position at which the piston 202 is at
the bottommost position in the cylinder 104 (180 degrees). In the
chart, an intake stroke 302 extends from TDC, at which the intake
valve 208 is assumed to instantaneously open for purposes of the
present disclosure, to an angle belonging in the range of about 1
to 100 degrees before or after BDC over an angle, .alpha. (alpha),
which is generically illustrated. The compression stroke 304 begins
when the intake valve has closed, which in the present discussion
is assumed to occur instantaneously, and extends up to TDC. A
combustion or power stroke 306 immediately follows until about BDC,
and is followed by an exhaust stroke 308. The initiation of the
power stroke 306 can be selectively advanced or retarded by either
providing a spark in a spark ignition engine or by permitting
auto-ignition to occur in a compression ignition engine by creating
appropriate conditions within the combustion cylinder.
[0023] As shown by the shaded area 310 in the chart 300, the
opening and closing of the intake valve prolongs the intake stroke
302 past the BDC position, which delays the compression stroke 304
in a fashion that is characteristic of one type of the Miller cycle
(LIC). It should be appreciated that in an EIC type of Miller
cycle, the valve timing chart would be different. The actuation of
the intake valve is advantageously variable based on other engine
operating and environmental conditions such that engine operation
may be optimized under most operating conditions. The point of
ignition or initiation of the power stroke 306 can also be
selectively controlled in the engine 100 of the present disclosure.
The duration of the intake stroke and/or the initiation of the
combustion stroke are two parameters that can be actively
controlled in the engine 100. Such control is effective in
improving fuel economy, extending the constant torque engine speed
operating range of the engine, adjusting for altitude effects,
compensating for different fuel types, and generally providing
other advantages to the operation of the engine 100 as is described
in further detail in the paragraphs that follow.
[0024] One embodiment of a component configuration used to
selectively adjust the timing of the opening and closing of the
intake and exhaust valves of the engine 100 is shown in FIGS. 3 and
4. Accordingly, a perspective view of the intake cam 212 is shown
in FIG. 3. The intake cam shown includes twelve lobes 214 but other
configurations may be used.
[0025] The intake cam 212 includes a timing wheel 224 that forms a
plurality of notches 226, and a phaser 228. In the illustrated
embodiment, and exemplary phaser 228 includes a housing 230 forming
four internal chambers 231, but other phaser configurations having
fewer or more chambers. In general, any appropriate type of rotary
actuator may be used. The exemplary phaser 228 further includes a
cam rotor 232. The cam rotor 232 forms four arms 234, one
corresponding to each chamber 231, sealably disposed to rotate
within the chambers 231. The cam rotor 232 further includes a
network of fluid passages 236 configured to provide pressurized
fluid between the walls of the chambers 231 and the arms 234 such
that the relative angular position of the cam rotor 232 relative to
the housing 230 may be adjusted.
[0026] The angular adjustment of the cam rotor 232 relative to the
housing 230 during operation of the engine 100 creates an offset or
phase difference in the rotational position of the lobes 214, which
in turn yields a phase shift in the opening and closing of the
intake valves relative to the rotational position of the crankshaft
and thus the position of the pistons within their respective engine
cylinders. This phase shift may be accomplished by appropriately
adjusting the pressure of fluid in the fluid passages 236.
[0027] A block diagram of the PCM 254 is shown in FIG. 5. As shown,
the PCM 254 is disposed to receive various inputs indicative of
engine operating parameters and other parameters. Specifically, the
PCM 254 receives an engine speed signal (RPM) 402, an engine load
signal (LOAD) 404, which may be expressed as a torque applied to
the engine, an actual intake valve phase or intake cam timing
signal (I_TIM) 406, an exhaust cam timing signal (E_TIM) 408, a
fuel methane or octane rating signal (METH) 410, an altitude signal
(ALT) 412, and other parameters that are not shown here, such as
intake manifold pressure, exhaust pressure, engine oil or coolant
temperature, ignition timing (IGN 444 as shown in FIG. 6) and the
like. Of the illustrated signals, the RPM 402 may be provided as an
engine speed value in revolutions per minute, or it may
alternatively be provided as a raw series of pulses from the
crankshaft position sensor, which are then used to derive the
engine speed. The LOAD 404 may be provided directly by a load
sensor (not shown), or it may alternatively be calculated
indirectly from other parameters, such as the current and voltage
output of a generator or alternator connected to the engine (not
shown), a pressure and flow of hydraulic fluid provided by a fluid
pump connected to the engine (not shown), or any other appropriate
parameters indicative of the load applied to the engine during
operation. The I-TIM and E-TIM 406 and 408 respectively may be
provided from cam position sensors associated with the intake and
exhaust valves of the engine. The ALT 412 may be provided by a
barometric pressure sensor (not shown), while the METH 410 may be
provided automatically by a fuel quality sensor (not shown) and/or
provided by a manually selectable mechanical or electronic switch,
which can be set by an operator if the fuel quality provided to the
engine is known.
[0028] The PCM 254 includes various sub-modules as shown and
described here, but it should be appreciated that the functionality
of the modules illustrated is not exhaustive. Accordingly, fewer or
more functions than those shown may be integrated with the PCM 254.
Moreover, the PCM 254 shown here is an electronic control device
or, stated differently, an electronic controller. As used herein,
the term electronic controller may refer to a single controller or
may include more than one controller disposed to control various
functions and/or features of the engine. For example, a master
controller, used to control systems associated with the engine,
such as a generator or alternator, may be cooperatively implemented
with a motor or engine controller, used to control the engine 100.
In this embodiment, the term "controller" is meant to include one,
two, or more controllers that may be associated with one another
and that may cooperate in controlling various functions and
operations of the engine 100. The functionality of the controller,
while shown conceptually in FIGS. 5-6 to include various discrete
functions for illustrative purposes only, may be implemented in
hardware and/or software without regard to the discrete
functionality shown. Accordingly, various interfaces of the
controller are described relative to components of the engine. Such
interfaces are not intended to limit the type and number of
components that are connected, nor the number of controllers that
are described.
[0029] Accordingly, the PCM 254 includes an intake valve timing
module 414, which receives at least the intake valve timing signal
406, the load 404, and the engine speed 402. The intake valve
timing module 414 performs calculations to provide an intake valve
phase signal 416. The intake valve phase signal 416 may be the same
as or provide a basis for determination of a signal controlling the
operation of the phaser device, for example, the phaser 228, as was
shown and previously described. Although any suitable
implementation may be used for the intake valve timing module 414,
a specific implementation is shown in FIG. 6.
[0030] In reference to FIG. 6, the intake valve timing module 414
includes a lookup table 418 that is populated by valve timing
values or, in the illustrated embodiment, valve phase signals that
are tabulated against engine speed 402, engine load 404 and,
optionally, the ignition timing value (IGN) 444. The timing values
in the table 418 are arranged to provide timing advance or retard,
depending on the type of Miller operation used, for decreasing
engine speed and/or for decreasing engine load to provide a
lessened or decreased effect of Miller operation of the engine. In
other words, when the constant torque operating range of the engine
is expanded to encompass lower engine speeds, the table 418 may be
arranged to provide a larger air charge in the cylinder by changing
the timing of the intake valves to account for the lower intake air
pressure of the engine when operating at low engine speeds. A
similar strategy may be used when the engine operates at higher
altitudes.
[0031] Thus, the table 418 receives the engine speed 402 and load
404 during operation, and uses these parameters to lookup,
interpolate, or otherwise determine a desired intake timing value
420. In one embodiment, the ignition timing 444 is also used to
determine the intake timing value 420. The desired intake timing
value 420 is compared to the actual intake timing 406 at a summing
junction 422 to provide an intake timing error 423. The intake
timing error 423 is provided to a control algorithm 424, which
yields an intake valve timing command signal 426. The control
algorithm 424 may be any suitable algorithm such as a
proportional-integral-derivative (PID) controller or a variation
thereof, a model based algorithm, a single or multidimensional
function and the like. Moreover, the control algorithm 424 may
include scheduling of various internal terms thereof, such as
gains, to enhance its stability.
[0032] Returning now to FIG. 5, the intake valve timing command
signal 426 is optionally compensated by the addition of
compensation terms at a junction 428. In the illustrated
embodiment, the compensation terms are an altitude compensation
term 430 and a fuel quality compensation term 432. These
compensation terms are optional and augment the flexibility of
engine operation under different environmental conditions. More
specifically, the altitude compensation term 430 is a timing
advance or retard value that depends on the altitude 412 of
operation of the engine. The altitude signal 412 is provided to an
altitude compensation module 434. In the illustrated embodiment,
the altitude compensation module 434 may include a function that
provides an appropriate timing advance or retard value based on the
expected air density at various altitudes. In this way, the
altitude compensation module 434 may provide a term tending to
change intake valve timing, which results in a lessened Miller
effect for higher altitudes.
[0033] In a similar fashion, the fuel quality compensation term 432
is a timing advance or retard value that depends on the measured or
provided fuel methane or octane number. In the illustrated
embodiment, the fuel quality compensation term 432 is provided by a
fuel quality timing module 436 based on the fuel quality signal
410. In one embodiment, the fuel quality timing module 436 may
provide a compensation term tending to change the intake valve
timing, thus decreasing the Miller effect of the engine for fuels
having relatively high methane or octane numbers. The intake valve
timing command signal 426 is thus compensated to provide the intake
valve phase signal 416.
[0034] In engines having separate intake and exhaust valve
camshafts, the PCM 254 may be further configured to provide a
separate exhaust valve phase signal 438. The exhaust valve phase
signal 438 in the embodiment illustrated is determined in a fashion
similar to that of the intake valve phase signal 416. Accordingly,
the exhaust valve phase signal 438 is determined by an altitude and
fuel quality compensated exhaust valve timing signal 440 that is
provided by an exhaust valve timing module 442. The exhaust valve
timing module 442 receives as inputs the engine speed 402 and load
404 as well as the exhaust valve timing 408. The exhaust valve
timing module 442 may operate similar to the intake valve timing
module 414 and include similar elements and algorithms. The exhaust
valve timing signal 440 may be compensated by use of the same or
different compensation terms as used for the intake valve timing
command, namely the altitude compensation term 430 and the fuel
quality compensation term 432. It should be appreciated that in
engines having a single camshaft operating both intake and exhaust
valves, a separate exhaust valve phase signal will not be
required.
[0035] A qualitative graph illustrating certain advantages that can
be realized by the selective adjustment of the intake and exhaust
valve opening duration as disclosed herein is shown in FIG. 7. More
specifically, FIG. 7 is a graph of engine operating points with and
without timing compensation that are plotted for specific
conditions of engine speed 502. In this way, engine speed 502 is
plotted against the horizontal axis and engine volumetric
efficiency 504 is plotted along the vertical axis. For internal
combustion engines, volumetric efficiency typically refers to the
efficiency with which the engine can move the charge into and out
of the cylinders. More specifically, volumetric efficiency is a
ratio, which can be expressed as a percentage, of what quantity of
fuel and air actually enters the cylinder during induction over the
actual capacity of the cylinder under static conditions. Relevant
to the present disclosure, the ability to achieve high volumetric
efficiencies for lower engine speeds is desired such that an engine
speed range over which an engine can operate at constant torque
conditions may be increased.
[0036] In the chart shown in FIG. 7, a baseline engine operating
point 506 is plotted to serve as a baseline for comparison of the
effect on volumetric efficiency of valve phase shifting for engine
operation at lower speeds. The baseline operating point 506
includes engine operation under the Miller cycle. A second engine
operating point 508 is plotted for a lower engine speed, which is
about 6% lower than the baseline engine speed and, which was
acquired with no adjustment being performed to intake or exhaust
valve timing as compared to the baseline point 506. Operation at
the lower engine speed provides a reduction in the volumetric
efficiency of the engine by about 0.5% at the second point 508. A
third point 510 was acquired at an even lower engine speed, which
was about 11.5% lower than the baseline engine speed. Unlike the
second point, the intake timing at the third point 510 was advanced
by fewer than 10 degrees. The volumetric efficiency at the third
point 510 increased by about 3% relative to the baseline volumetric
efficiency.
[0037] The increase in volumetric efficiency by timing adjustment
for lower engine speeds enables the constant torque operation of
the engine over a broader range of engine speeds. This engine
operating ability is advantageous for various engine applications,
such as generator sets, work machines, stationary compressors,
hybrid electric drive systems and the like. In general,
applications that can use engines operating at nearly constant
engine speeds stand to benefit from the systems and methods
disclosed herein because operation at reduced engine speeds while
maintaining constant or nearly constant torque as higher engine
speeds presents advantages such as improved fuel consumption and
reliability, reduced noise and emissions, and others
[0038] A flowchart for a method of operating an engine is shown in
FIG. 8. The engine is operated at a fuel-rich stoichiometric air
mixture at 602. Such air mixture may be expressed or considered as
a desired air to fuel ratio (AFR) of a mixture of charge air and
fuel present in the engine cylinder when combustion is initiated,
which may be further maintained substantially constant over the
engine operating range. An electronic controller is disposed to
receive various engine and other operating parameters at 604 that
are indicative of the amount of charge air or the amount of the air
and fuel mixture that is ingested in the engine's cylinders during
operation. The electronic controller processes the parameters
received to determine a timing phase variation at 606. The timing
phase variation is configured to provide relatively high Miller
effects during operation of the engine such that the amount of
fuel/air mixture in the engine cylinders is sufficient to yield a
desired torque output while the engine operates under fuel-rich
stoichiometric combustion conditions.
[0039] In one embodiment, the valve phase changes are variable
depending on the engine load and engine speed, altitude, fuel
quality, and other parameters. In general, any parameter that is
indicative of the concentration of oxygen, which is required for
combustion, and/or fuel, may be used as an indication of the amount
of fuel/air mixture in the engine during combustion. In one
embodiment, the valve timing is adjusted at 608 based on engine
speed and load. Optionally, the valve timing is also adjusted or
compensated at 610 based on altitude, and at 612 based on fuel
quality. Such adjustments are used to provide a valve phase signal
at 614 by the electronic controller. The phase signal may be any
appropriate type of signal that can effect a change in the valve
timing of the engine during operation. In the illustrated
embodiment, for example, the valve phase signal is a PWM signal
that is provided to a control valve. The control valve selectively
adjusts the flow of fluid into and out from a phaser device. The
phaser device is in turn configured to adjust its position to
provide a timing phase shift to a camshaft operating the
valves.
[0040] Accordingly, the timing of the engine valves is changed
based on the valve phase signal at 616, for example, by indexing
the camshaft at the phaser device. In this way, the cam is indexed
to appropriately change the Miller effect depending on the type of
Miller operation of the engine based on engine speed, engine load,
altitude, and other conditions. In the disclosed embodiment, the
valve phase signal is provided to at least one control valve. The
control valve operates to adjust the timing or phase of a set of
valves by indexing a camshaft. The process may be repeated
continuously to adjust or shift the timing phase of the engine
valves during operation of the engine.
[0041] By shifting the timing phase of the engine valves, an engine
operating in accordance with the disclosed method is advantageously
capable of extending its engine speed operating range while
maintaining a nearly constant engine torque output for a controlled
engine speed, such as for electric power generation applications, a
controlled engine speed, such as for compressor applications, and
so forth. Such engine operating capability is advantageous for
certain engine applications, such as those used in hybrid electric
drive systems, generator sets, compressors and the like, in which
the engine speed may be adjusted in response to load changes.
INDUSTRIAL APPLICABILITY
[0042] The present disclosure is applicable to internal combustion
engines of any type and, more particularly, to stationary engines
that operate on natural gas. The disclosed devices and methods are
unique in that the timing of lean or rich burning engine is
adjusted to include a substantial Miller effect in the range of
about 20-80%, with most applications operating in a range of about
40-50%. The valve phasing is variable and dynamically adjusted
during engine operation based on various operating parameters such
as engine speed, engine load, altitude, fuel quality, and others.
In this way, the timing of the intake valves is changed for
decreasing engine speed and load and/or increasing altitude, and
also for decreasing fuel quality such that sufficient air and fuel
is present in the cylinders over a wide operating range. In the
illustrated embodiments, the engine 100 operates at a compression
ratio of 13/1 or greater.
[0043] In previously proposed engines using the Miller cycle, some
of which are gasoline engines for automotive applications using
compression ratios of 14.7 or greater, efficiency of the engine is
increased by raising the compression ratio of the cylinders.
Although the compression ratio is limited in a typical gasoline
engine due to self-ignition of the compressed fuel and air mixture
in the cylinder, a higher overall cylinder pressure is possible due
to the reduced compression stroke of a Miller cycle engine.
[0044] When the Miller cycle is used on certain stationary engine
applications, such as a generator set, the engine speed may be kept
constant and the engine's ability to increase or decrease its load
output quickly may be advantageously improved by the methods
described herein. For other stationary engine applications, such as
engines driving gas compressors, the engine may be required to run
at different speeds but maintain constant torque. For these engine
applications, the reduced intake air compression that occurs at low
engine speeds causes the Miller effect to be more pronounced but
also to be limiting to the engine's effective speed range. This is
especially pronounced for engines having turbochargers because of
the generally inadequate exhaust gas power available at low engine
speeds to drive sufficiently high intake air pressure for engine
operation. By implementing the engine structures and methods
disclosed herein, the engine effective speed range may be increased
at a nearly constant engine torque output by shifting the engine
valve phases appropriately such that the enthalpy of reaction of a
fuel and air mixture in the combustion chambers of the engine may
be maintained within a desired range.
[0045] Moreover, additional benefits may be realized by use of a
engine having a phaser for selectively controlling the amount of
Miller effect of the engine as described herein. For example,
engine applications having residual load on the engine at startup,
such as engines used to drive gas compressors in the petroleum
industry, may include functionality that reduces the Miller effect
for engine operation at and/or immediately following engine
startup. In this way, the engine is able to overcome the residual
load of the driven equipment, hence enabling the engine and
associated engine components to achieve engine startup. In one
embodiment, an engine in accordance with the foregoing disclosure
may further include a control routine that is activated when the
engine is at condition for startup, for example, when the engine
ignition switch is in a mode indicating that the ignition is on but
the engine is not running. At such condition, the control routing
may command a predetermined phase signal to the phaser of the
engine that will result in a reduced Miller effect of the engine
until the engine has started as indicated, for example, by the
engine speed exceeding a predetermined low engine speed threshold
or any other appropriate parameter.
[0046] It will be appreciated that the foregoing description
provides examples of the disclosed system and technique. However,
it is contemplated that other implementations of the disclosure may
differ in detail from the foregoing examples. All references to the
disclosure or examples thereof are intended to reference the
particular example being discussed at that point and are not
intended to imply any limitation as to the scope of the disclosure
more generally. All language of distinction and disparagement with
respect to certain features is intended to indicate a lack of
preference for those features, but not to exclude such from the
scope of the disclosure entirely unless otherwise indicated.
[0047] Recitation of ranges of values herein are merely intended to
serve as a shorthand method of referring individually to each
separate value falling within the range, unless otherwise indicated
herein, and each separate value is incorporated into the
specification as if it were individually recited herein. All
methods described herein can be performed in any suitable order
unless otherwise indicated herein or otherwise clearly contradicted
by context.
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