U.S. patent application number 10/225897 was filed with the patent office on 2004-02-26 for method of determining valve events to optimize engine operating parameters.
This patent application is currently assigned to Visteon Global Technologies, Inc.. Invention is credited to Collins, Brett Denton, Mianzo, Lawrence Andrew.
Application Number | 20040035402 10/225897 |
Document ID | / |
Family ID | 31887106 |
Filed Date | 2004-02-26 |
United States Patent
Application |
20040035402 |
Kind Code |
A1 |
Collins, Brett Denton ; et
al. |
February 26, 2004 |
METHOD OF DETERMINING VALVE EVENTS TO OPTIMIZE ENGINE OPERATING
PARAMETERS
Abstract
A method for determining valve timing events to optimize
operating parameters of an engine having a variable valve timing
system over an entire operating range of the engine. The method
includes setting combinations of intake valve opening and closing
timing events and exhaust valve opening and closing timing events
for a given engine speed. For each combination, a fuel conversion
efficiency measure and an emissions measure of the engine at the
given engine speed is obtained. Combinations which optimize a
weighted cost function of the fuel conversion efficiency measure
and the emission measure for a range of engine output torque
settings at the given engine speed are then selected. This is
repeated for each given engine speed across a range of engine
speeds. A feed-forward map based on the selected combinations for
the entire operating range of the engine is then assembled.
Inventors: |
Collins, Brett Denton;
(Tucson, AZ) ; Mianzo, Lawrence Andrew; (Plymouth,
MI) |
Correspondence
Address: |
BROOKS KUSHMAN P.C.
1000 TOWN CENTER
TWENTY-SECOND FLOOR
SOUTHFIELD
MI
48075
US
|
Assignee: |
Visteon Global Technologies,
Inc.
Dearborn
MI
|
Family ID: |
31887106 |
Appl. No.: |
10/225897 |
Filed: |
August 22, 2002 |
Current U.S.
Class: |
123/568.14 ;
123/90.15; 701/115 |
Current CPC
Class: |
F02D 13/0215 20130101;
Y02T 10/42 20130101; Y02T 10/47 20130101; F02D 41/2451 20130101;
F02M 26/01 20160201; Y02T 10/12 20130101; F02D 13/0265 20130101;
F02D 41/2425 20130101; F02D 41/006 20130101; F02D 41/0002 20130101;
F02D 41/2464 20130101; Y02T 10/18 20130101; Y02T 10/40 20130101;
F02D 41/2432 20130101; F02D 2041/001 20130101 |
Class at
Publication: |
123/568.14 ;
123/90.15; 701/115 |
International
Class: |
F02M 025/07 |
Claims
What is claimed is:
1. A method for determining valve timing events to optimize
operating parameters of an engine having a variable valve timing
system over an entire operating range of the engine, the method
comprising the steps of: (A) setting combinations of intake valve
opening and closing timing events and exhaust valve opening and
closing timing events for a given engine speed; (B) for each
combination, obtaining a fuel conversion efficiency measure and an
emissions measure of the engine at the given engine speed; (C)
selecting combinations which optimize a weighted cost function of
the fuel conversion efficiency measure and the emission measure for
a range of engine output torque settings at the given engine speed;
(D) repeating steps A, B, and C for each given engine speed across
a range of engine speeds; and (E) assembling a feed-forward map
based on the selected combinations for the entire operating range
of the engine.
2. The method of claim 1 wherein: the fuel conversion efficiency
measure includes a fuel consumption measure.
3. The method of claim 1 wherein: the emissions measure includes an
estimated NO.sub.X measure.
4. The method of claim 1 wherein: the emissions measure includes an
internal exhaust gas re-circulation measure.
5. The method of claim 1 further comprising: controlling the engine
in accordance with the selected combination for an engine output
torque setting at a given engine speed.
6. A method for determining valve timing events to optimize
operating parameters of an engine having a variable valve timing
system over an entire operating range of the engine, the method
comprising the steps of: (A) setting combinations of intake valve
and exhaust valve closing timing events for a given engine speed;
(B) for each combination, obtaining a fuel conversion efficiency
measure and an emissions measure of the engine at the given engine
speed; (C) selecting combinations which optimize a weighted cost
function of the fuel conversion efficiency measure and the emission
measure for a range of engine output torque settings at the given
engine speed; (D) repeating steps A, B, and C for each given engine
speed across a range of engine speeds; and (E) assembling a
feed-forward map based on the selected combinations for the entire
operating range of the engine.
7. The method of claim 6 further comprising: setting exhaust valve
opening timing events as a function of engine speed.
8. The method of claim 6 further comprising: setting intake valve
opening timing events as a function of exhaust valve closing timing
events.
9. The method of claim 6 further comprising: controlling the engine
in accordance with the selected combination for an engine output
torque setting at a given engine speed.
10. A method for determining valve timing events to optimize
operating parameters of an engine having a variable valve timing
system over an entire operating range of the engine, the method
comprising the steps of: (A) setting combinations of intake valve
and exhaust valve closing timing events for a given engine speed;
(B) for each combination, obtaining an exhaust gas residual
measurement and an air charge measurement of the engine at the
given engine speed; (C) selecting combinations which optimize a
weighted cost function of the exhaust gas residual measurement and
the air charge measurement for a range of engine output torque
settings at the given engine speed; (D) repeating steps A, B, and C
for each given engine speed across a range of engine speeds; and
(E) assembling a feed-forward map based on the selected
combinations for the entire operating range of the engine.
11. The method of claim 10 further comprising: setting exhaust
valve opening timing events as a function of engine speed.
12. The method of claim 10 further comprising: setting intake valve
opening timing events as a function of exhaust valve closing timing
events.
13. The method of claim 10 further comprising: controlling the
engine in accordance with the selected combination for an engine
output torque setting at a given engine speed.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method of determining
valve events to optimize engine operating parameters for a given
engine speed/load point.
[0003] 2. Background Art
[0004] An engine equipped with a variable valve timing system has
the potential to effectively manage exhaust gas re-circulation
without the need for external equipment and to effectively control
the cylinder charge, thus determining the operating point of the
engine. Variable valve timing systems provide an opportunity to
select the best valve timing events for a desired engine operating
condition. However, given a variable valve event timing system
capable of this flexibility, a valve timing event control method
providing a comprehensive valve timing event strategy is necessary
for these potentials to be realized.
[0005] Such a desired comprehensive valve timing event strategy
would control the aspiration of the engine without the need for
external gas re-circulation or throttling while providing the
highest level of exhaust gas residual reasonable for a desired
engine operating condition, minimizing NO.sub.X formation, and
maximizing fuel economy. In essence, the desired comprehensive
valve timing event strategy would manage internal exhaust gas
re-circulation and cylinder air charge for an engine equipped with
a variable valve timing event system.
[0006] In general, the valve timing event control method providing
the desired comprehensive valve timing event strategy would
implement real time valve timing event control as a mechanism for
managing cylinder charge, thereby eliminating the need for a
conventional throttle body which is a source of considerable
pumping losses. Thus, given an engine without a throttle, a
camshaft drive mechanism, and an external exhaust gas
re-circulation equipment, the desired comprehensive valve timing
event strategy would ideally optimize fuel economy; minimize
emissions; not preclude implementation of other advanced control
strategies; be conductive to continuous, transient engine control;
be generic enough to be easily applied to any naturally aspirated
four stroke engine; and make physical sense.
SUMMARY OF THE INVENTION
[0007] Accordingly, it is an object of the present invention to
provide a method for determining valve events to optimize engine
operating parameters for a given engine speed/load point.
[0008] In carrying out the above objects and other objects, the
present invention provides a method for determining valve timing
events to optimize operating parameters of an engine having a
variable valve timing system over an entire operating range of the
engine. The method includes the steps of (A) setting combinations
of intake valve opening and closing timing events and exhaust valve
opening and closing timing events for a given engine speed; (B) for
each combination, obtaining a fuel conversion efficiency measure
and an emissions measure of the engine at the given engine speed;
(C) selecting combinations which optimize a weighted cost function
of the fuel conversion efficiency measure and the emission measure
for a range of engine output torque settings at the given engine
speed; (D) repeating steps A, B, and C for each given engine speed
across a range of engine speeds; and (E) assembling a feed-forward
map based on the selected combinations for the entire operating
range of the engine.
[0009] The optimization algorithm employed by the method generally
includes the following steps. First, at each engine speed, the
intake valve opening and closing timing events (IVO, IVC) and the
exhaust valve opening and closing timing events (EVO, EVC) are
swept. The spark and fuel are adjusted to maintain the best mean
engine torque output (i.e., engine load) and the desired air-fuel
ratio at each valve setting. The next step is that at each engine
speed/load point, the valve timing events are selected from all
possible valve timing event combinations which minimize a cost
function of fuel consumption and emissions. From a local
optimization perspective, one approach is to choose the minimum
NO.sub.X (i.e., emissions) production allowable without degradation
of combustion stability, sacrificing some degradation in fuel
conversion efficiency. Globally, a later trade-off may be made
between emissions and fuel economy and a cycle basis.
[0010] Unfortunately, accurate NO.sub.X formulation from simulation
is difficult as is predicting combustion stability. So instead, in
simulation, burnt exhaust gas residual is used as an indicator of
NO.sub.X (cylinder temperature could be used alternatively). In the
laboratory, a NO.sub.X measurement and an indicator of combustion
stability, such as covariance of indicated mean effective pressure,
could be used to refine the optimization.
[0011] The next step is to determine the valve timing events to
obtain the desired engine load and the desired exhaust gas
residual. It is desirable and sometimes necessary to have high
exhaust gas residual at low engine loads (for desirable NO.sub.X
emissions), low exhaust gas residual (for good performance), and a
smooth transition in between. It is also desirable to have minimal
exhaust gas residual at engine idling for proper combustion
stability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 illustrates an exemplary internal combustion engine
having a variable valve timing event system for variably
controlling valve timing events in accordance with the method of
the present invention;
[0013] FIG. 2 illustrates a data map plotting contour lines of
engine brake torque versus EVC and IVC timing events at a given
engine speed;
[0014] FIG. 3 illustrates a data map plotting contour lines of
engine fuel conversion efficiency versus EVC and IVC timing events
at the given engine speed;
[0015] FIG. 4 illustrates a data map plotting contour lines of
engine NO.sub.X formation versus EVC and IVC timing events at the
given engine speed;
[0016] FIG. 5 illustrates a data map plotting contour lines of
engine exhaust gas re-circulation versus EVC and IVC timing events
at the given engine speed;
[0017] FIG. 6 illustrates a feed-forward table of EVC and IVC
timing events for engine speed/load points across the operating
range of the engine in which the engine has a first set of
operating parameters;
[0018] FIG. 7 illustrates a map plotting IVO and EVC mirrored
timing events for each engine speed/load point in which the engine
has a second set of operating parameters;
[0019] FIG. 8 illustrates a map plotting IVC timing events for each
engine speed/load point in which the engine has the second set of
operating parameters; and
[0020] FIGS. 9A, 9B, 9C, and 9D illustrate timing sequences for
EVO, EVC, IVO, and IVC timing events in accordance with the method
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0021] Referring now to FIG. 1, an exemplary internal combustion
engine 10 having a variable valve timing event system 12 for
variably controlling valve timing events in accordance with the
method of the present invention is shown. Engine 10 includes a
cylinder block having at least one cylinder 14. Cylinder 14
includes a combustion chamber 16 which houses a movable piston 18.
A connecting rod 20 connects piston 18 to a crankshaft (not shown).
Piston 18 moves up and down within combustion chamber 16 to move
connecting rod 20 up and down in order to rotate the crankshaft
and, consequently, power the vehicle having engine 10.
[0022] Combustion chamber 16 includes an intake port 22 and an
exhaust port 24. An intake runner 26 is connected to intake port
22. An exhaust runner 28 is connected to exhaust port 24. Intake
runner 26 introduces an air/fuel mixture into combustion chamber 16
through intake port 22. (In a direct fuel injection system, the
fuel is injected directly into combustion chamber 16 and intake
runner 26 introduces air into the combustion chamber.) Exhaust
runner 28 discharges an exhaust gas of the combusted air/fuel
mixture in combustion chamber 16 from exhaust port 24.
[0023] During operation of engine 10, air enters intake runner 26.
A fuel injector 30 injects fuel into intake runner 26 (or directly
into combustion chamber 16 if the fuel injector is part of a direct
fuel injection system). The injected fuel mixes with the air in
intake runner 26 to form an air/fuel mixture. An intake valve 32
moves from a closed position to an opened position with respect to
intake port 22 to enable the air/fuel mixture to be drawn into
combustion chamber 16. Intake valve 32 then moves to its closed
position with respect to intake port 22 to seal off combustion
chamber 16.
[0024] Piston 18 then moves up within combustion chamber 16 to
compress the air/fuel mixture in the combustion chamber. A spark
plug 34 then provides a spark within combustion chamber 16 to
ignite the compressed air/fuel mixture. The compressed air/fuel
mixture then combusts to produce power which causes piston 18 to
move downward.
[0025] An exhaust valve 36 then moves from a closed position to an
opened position with respect to exhaust port 24 to discharge at
least a portion of the combusted air/fuel mixture (i.e., exhaust
gas) into exhaust runner 28. Exhaust valve 36 then moves back to
its closed position with respect to exhaust port 24 to seal off
combustion chamber 16 and the cycle repeats.
[0026] Variable valve timing event system 12 includes a controller
(power train module) 38. Based on desired engine condition inputs,
controller 38 controls the air/fuel mixture injected into
combustion chamber 16, the ignition timing of spark plug 34, and
the opening and closing valve timing events of intake valve 32 and
exhaust valve 36. The desired engine condition inputs include at
least an engine speed or RPM (revolutions per minute) input 40 and
an engine brake torque (i.e., engine load) input 42. Engine speed
input 40 indicates a desired speed of engine 10 during operation.
Engine brake torque input 42 indicates a desired load provided by
engine 10 during operation.
[0027] In accordance with the method of the present invention,
controller 38 controls the opening and closing valve timing events
of intake valve 32 and exhaust valve 36 to optimize parameters of
engine 10 for a desired engine speed and a desired engine load,
i.e., a desired engine speed/load point. Controller 38 uses the
method of the present invention to control the valve timing events
in order to provide a comprehensive valve timing event strategy
which manages the cylinder air charge and the exhaust gas mass
residual in combustion chamber 16 for each engine cycle to obtain
optimal operating parameters of engine 10 for a desired engine
speed/load point.
[0028] An infinite number of valve timing event combinations of
intake valve 32 and exhaust valve 36 exist for a given engine
speed/load point. As such, the method of the present invention
provides a continuous and transient variation of the valve timing
events across different engine speed/load points such that the
method physically accommodates the mechanical response limitations
of the elements of engine 10. The optimal engine parameters
generally include maximal fuel conversion efficiency and minimal
emissions (i.e., minimal NO.sub.X formation) of engine 10 for a
desired engine speed/load point. Typically, such optimal engine
parameters occur when the highest level of residual gas (i.e.,
exhaust gas) is retained in combustion chamber 16 for the next
cycle. This is because the presence of inert gas such as retained
exhaust gas in combustion chamber 16 reduces the peak temperature
during combustion, and hence retards the formation of NO.sub.X
particles. However, there is an upper limit of retained exhaust
gas, dictated by combustion stability that begins to deteriorate in
the presence of excessive exhaust gas. Thus, it is generally
beneficial to have the most retained exhaust gas reasonable,
without endangering combustion stability.
[0029] As such, controller 38 uses the method of the present
invention to provide real-time valve timing event control in order
to control cylinder air charge and exhaust gas residual. The method
contains two general parts which function together in order to
manage the cylinder air charge and the exhaust gas residual. First,
the method provides times for closing intake valve 32 and exhaust
valve 36 in order to trap a desired amount of exhaust gas residual
in combustion chamber 16 for the next combustion stroke. Second,
the method provides a time for closing intake valve 32 to enable
enough time for a desired amount of fresh air/fuel (or just fresh
air if direct injection engine) to be introduced into combustion
chamber 16.
[0030] That is, the method of the present invention is based on two
principles. One, selecting an early closing timing event for
exhaust valve 36 before top dead center thereby trapping residual
gas in combustion chamber to control exhaust gas residual. Two,
selecting a closing timing event for intake valve 32 to control
cylinder air charge. The method may select fixed times for intake
valve 32 opening (IV) and exhaust valve 36 opening (EVO) such that
only two valve timing events (i.e., the two valve timing events for
exhaust valve closing (EVC) and intake valve closing (IVC)) are
selected for a given engine speed/load point.
[0031] The method selects an IVO timing event to take place
approximately opposite the EVC timing event with respect to top
dead center (TDC). This is because a mass of exhaust gas is trapped
in combustion chamber 16 due to early EVC, and unnecessarily
pumping gas through a valve orifice creates pumping losses. As a
result, it makes physical sense to select an IVO timing event that
is opposite the EVC timing event. This reflection of IVO and EVC
timing events about TDC is referred to as an "EVC/IVO mirror."
[0032] As an example, if the EVC timing event is 20.degree. before
TDC then the IVO timing event should be 20.degree. after TDC
because it is at this point in the cycle that the cylinder pressure
at EVC and IVO will be approximately equal, and minimal gas
exchange will occur. However, it may be more beneficial to have
some amount of blowback from combustion chamber 16 into intake
runner 26 to promote fuel vaporization and mixing. In the instance,
the IVO timing event is fixed to be slightly earlier. As such, this
leaves the IVC timing event as the main mechanism for limiting air
charge.
[0033] For a given engine speed, the method of the present
invention may select a fixed EVO timing event as the EVO timing
event is a function of engine speed (and to a lesser extent, engine
load) and, as such, can be chosen independent of the other valve
timing events (EVC, IVC, and IVO). Thus, the method fixes the EVO
timing event to provide the best EVO timing event for each engine
speed.
[0034] For a given engine speed/load point, there are an infinite
number of possible EVC and IVC timing events. Taking into the
considerations mentioned above regarding exhaust gas residual, the
method selects appropriate EVC and IVC timing events which yield a
continuous valve event surface across an array of engine speed/load
points and which generally provide high fuel conversion efficiency
and minimal undesired emissions.
[0035] In order to provide optimal engine parameters for a given
engine speed/load point, the method chooses appropriate EVC and IVC
timing events from an EVC and IVC feed-forward table. EVC and IVC
feed-forward tables are assembled from EVC and IVC data maps in
accordance with the present invention as explained below.
[0036] FIGS. 2, 3, 4, and 5 illustrate such EVC and IVC data maps
for assembling an EVC and IVC feed-forward table. FIGS. 2, 3, 4,
and 5 respectively illustrate EVC and IVC data maps 60, 70, 80, and
90. Each data map 60, 70, 80, and 90 includes contour lines which
are plotted at a given engine speed such as 1000 rpms. In each of
data maps 60, 70, 80, and 90, the x-axis is the IVC timing event
measured in crank angle (CA) degrees after TDC and the y-axis is
the EVC timing event (i.e., EVC/IVO mirrored timing event) measured
in crank angle degrees after TDC.
[0037] Data map 60 illustrated in FIG. 2 illustrates the brake
torque of engine 10 produced by EVC and IVC timing event
combinations at the given engine speed. Data map 60 includes three
brake torque contour lines 62, 64, and 66. Brake torque contour
lines 62, 64, and 66 represent EVC and IVC timing event
combinations which respectively produce 120 N-m, 130 N-m, and 140
N-m of brake torque. Data map 60 includes more brake torque contour
lines (not shown) for other brake torque values. On brake contour
line 64, point 67 represents the EVC and IVC combination of
400.degree., 550.degree. which produces 130 N-m of brake torque at
the given engine speed. Similarly, on brake contour line 64, point
68 represents the EVC and IVC combination of 450.degree.,
475.degree. which produces 130 N-m of brake torque at the given
engine speed.
[0038] Data map 70 illustrated in FIG. 3 illustrates the fuel
conversion efficiency of engine 10 produced by EVC and IVC timing
event combinations at the given engine speed. Data map 70 includes
two fuel conversion efficiency contour lines 72 and 74. Fuel
conversion efficiency contour lines 72 and 74 represent EVC and IVC
timing event combinations which respectively produce 25% and 30%
fuel conversion efficiency. Data map 70 includes more fuel
conversion efficiency contour lines (not shown) for other fuel
conversion efficiency values.
[0039] On fuel conversion efficiency contour line 72, point 76
represents the EVC and IVC combination of 350.degree., 500.degree.
which produces 25% fuel conversion efficiency at the given engine
speed. Similarly, on fuel conversion efficiency contour line 74,
point 78 represents the EVC and IVC combination of 450.degree.,
475.degree. which produces a fuel conversion efficiency of 30% at
the given engine speed.
[0040] Brake torque contour line 64 is plotted in a dotted line on
data map 70. As can be seen on data map 70, point 78 intersects
brake contour line 64 and fuel conversion efficiency contour line
74. As such, point 78 represents the EVC and IVC combination of
450.degree., 475.degree. which produces a brake torque of 130 N-m
and a fuel conversion efficiency of 30% at the given engine
speed.
[0041] Data map 80 illustrated in FIG. 4 illustrates the estimated
NO.sub.X formation in particles per minute (ppm) of engine 10
produced by EVC and IVC timing event combinations at the given
engine speed. Data map 80 includes three NO.sub.X contour lines 82,
84, and 86. NO.sub.X formation contour lines 82 and 84 represent
EVC and IVC timing event combinations which respectively produce
2000 ppm, 2427 ppm, and 3000 rpm. Data map 80 includes more
NO.sub.X formation contour lines (not shown) for other NO.sub.X
formation rates.
[0042] On NO.sub.X formation contour line 82, point 87 represents
the EVC and IVC combination of 350.degree., 500.degree. which
produces 2000 ppm at the given engine speed. Similarly, on NO.sub.X
formation contour line 84, point 88 represents the EVC and IVC
combination of 450.degree., 475.degree. which produces 2427 ppm at
the given engine speed.
[0043] Brake torque contour line 64 is plotted in a dotted line on
data map 80. As can be seen on data map 80, point 88 intersects
brake contour line 64 and NO.sub.X formation contour line 84. As
such, point 88 represents the EVC and IVC combination of
450.degree., 475.degree. which produces a brake torque of 130 N-m
and an estimated NO.sub.X formation of 2427 ppm at the given speed.
As point 88 represents the same EVC and IVC combination as point 78
in data map 70, the fuel conversion efficiency is 30%. Thus,
selecting an EVC and IVC combination of 450.degree., 475.degree.
for engine 10 produces a brake torque of 130 N-m at the given
engine speed with the operating parameters of the engine including
a fuel conversion efficiency of 30% and an estimated NO.sub.X
formation of 2427 ppm.
[0044] Data map 90 illustrated in FIG. 5 illustrates the percent
exhaust gas re-circulation (EGR) of engine 10 produced by EVC and
IVC timing event combinations at the given engine speed. Data map
90 includes two EGR contour lines 92 and 94. EGR contour lines 92
and 94 represent EVC and IVC timing event combinations which
respectively produce 10% and 15% EGR. Data map 90 includes more EGR
contour lines (not shown) for other percent EGR values.
[0045] On EGR contour line 94, point 98 represents the EVC and IVC
combination of 450.degree., 475.degree. which produces a 15% EGR at
the given engine speed. Brake torque contour line 64 is plotted in
a dotted line on data map 90. As can be seen on data map 90, point
88 intersects brake contour line 64 and EGR contour line 94. As
such, point 98 represents the EVC and IVC combination of
450.degree., 475.degree. which produces a brake torque of 130 N-m
and a 15% at the given speed. As point 98 represents the same EVC
and IVC combination as point 78 in data map 70, the fuel conversion
efficiency is 30%. Similarly, as point 98 represents the same EVC
and IVC combination as point 88 in data map 80, the estimated
NO.sub.X formation is 2427 ppm. Thus, selecting an EVC and IVC
combination of 450.degree., 475.degree. for engine 10 produces a
brake torque of 130 N-m at the given engine speed with the
operating parameters of the engine including a fuel conversion
efficiency of 30%, an estimated NO.sub.X formation of 2427 ppm, and
a 15% EGR.
[0046] Data maps 60, 70, 80, and 90 represent respective engine
operating parameters for EVC and IVC timing event combinations at
the given engine speed. Thus, each engine speed has an associated
set of data maps. For instance, a second set of data maps are
assembled for an engine speed of 2000 rpm, a third set of data maps
are assembled for an engine speed of 3000 rpm, etc. At any given
engine speed, the method of the present invention uses the
corresponding feed-forward tables derived as explained below from
the associated data maps to select the EVC and IVC timing events
which produce a desired brake torque and optimal fuel conversion
efficiency, NO.sub.X formation, and percent EGR.
[0047] FIG. 6 illustrates a feed-forward table 100 derived from
data maps 60, 70, 80, and 90 for the given engine speed of 1000 rpm
and associated data maps for other engine speeds such as 2000 rpm
and 3000 rpm. Feed-forward table 100 lists EVC and IVC combinations
for respective engine speed/load points in which the operating
parameters of engine 10 include a fuel conversion efficiency of
30%, an estimated NO.sub.X formation of 2427 ppm, and a 15% EGR.
For instance, the engine speed/load point of 130 N-m at 1000 rpm
lists the EVC and IVC combination of 450.degree., 475.degree. which
produces these operating parameters of engine 10. Thus, if these
engine operating parameters are desired for the engine speed/load
point of 130 N-m and 1000 rpm, then the method of the present
invention selects the EVC and IVC combination of 450.degree.,
475.degree. from feed-forward table 100.
[0048] Other feed-forward tables are derived from data maps 60, 70,
80, and 90 for the given engine speed of 1000 rpm and associated
data maps for other engine speeds. These other feed-forward tables
list EVC and IVC combinations for respective engine speed/load
points for different operating parameters of engine 10. Thus, for a
given engine speed/load point, the method of the present invention
selects the appropriate EVC and IVC combination from the
appropriate feed-forward table associated with desired engine
operating parameters.
[0049] FIGS. 7 and 8 illustrate three-dimensional data maps which
plot the EVC and IVC combinations for the data contained in a
feed-forward table. FIG. 7 illustrates a data map 100 which plots
mirrored EVC/IVO timing events for each engine speed/load point. As
described above, the mirrored EVC/IVO timing event is a function of
the EVC timing event as the IVO timing event is generally selected
to mirror the EVC timing event. FIG. 8 illustrates a data map 110
which plots the IVC timing event for each engine speed/load point.
In data maps 100 and 110, brake torque (i.e., engine load) is along
x-axis 102 and engine speed is along y-axis 104. The mirrored
EVC/IVO timing events and the IVC timing events are plotted along
z-axis 106.
[0050] With reference to the contour lines contained in data maps
60, 70, 80, and 90, it is apparent that the engine operating
parameters, i.e., fuel conversion efficiency, the NO.sub.X
formulation, and the percent EGR, vary differently from one another
between EVC and IVC timing event combinations. As such, for a given
engine speed/load point, the method of the present invention may
select the EVC and IVC timing event combination as a function of a
weighting between the engine operating parameters. For instance,
the method may select the EVC and IVC timing event combination from
the feed-forward map associated with a relatively lesser fuel
conversion efficiency but a relatively much greater reduction in
the NO.sub.X formulation as a result of a higher percentage EGR for
the given engine speed/load point.
[0051] Using the method of the present invention, for low and upper
engine load conditions, controller 38 selects EVC event just prior
to the top center of piston 18 thus trapping a mass of exhaust gas
in combustion chamber 16. Piston 18 continues to move upward within
cylinder 14 towards the top center and compresses the trapped
exhaust gas. After reaching the top center, piston 18 moves
downwardly within cylinder 14, subsequently decompressing the
trapped exhaust gas and recovering the work originally done during
compression. Controller 38 then selects IVO to allow the air/fuel
mixture to enter combustion chamber 16. Controller 38 maintains
intake valve 32 open long enough to draw in a desired fresh mass of
air and fuel into combustion chamber 16 at which point the
controller selects the IVC timing event. Piston 18 continues its
motion until it is once again compressing the contents of
combustion chamber 16 to produce combustion. Controller 38 then
selects EVO timing event for the given engine speed and engine load
with consideration given to optimizing the fuel conversion
efficiency and minimizing undesired emissions. The cycle then
repeats.
[0052] At high engine load conditions, at or near the maximum
torque limits of engine 10 for a given engine speed, controller 38
selects EVC and IVO timing events to overlap near the top center of
piston 18. Controller 38 overlaps these times to use the momentum
of the fluid being expelled from cylinder 14 to assist in drawing
the air/fuel mixture for combustion into the cylinder and further
purging exhaust gas present in the cylinder which may become a
limitation at high loads.
[0053] An embodiment of the timing strategy provided by the method
of the present invention is to have controller 38 select EVC and
IVO timing events to provide a desired or constant amount of
exhaust gas mass residual at or near the maximum value (determined
by combustion stability) over the low to mid load engine range. As
the engine load increases, the timing strategy is selected such
that the exhaust gas mass residual gradually tapers off. The
exhaust gas mass residual is tapered off because of the limited
volume of cylinder 14. That is, to make room for more air/fuel
mixture it is necessary to decrease the amount of exhaust gas.
[0054] FIGS. 9A, 9B, 9C, and 9D illustrate EVO, EVC, IVO, and IVC
timing event sequences selected by controller 38 using the method
of the present invention. FIG. 9A illustrates the valve event
timing sequence for low engine loads. FIG. 9B illustrates the valve
event timing sequence for mid-range engine loads. FIG. 9C
illustrates the valve event timing sequence for high engine loads.
FIG. 9D illustrates the valve event timing sequence for maximum
engine loads.
[0055] In general, the valve event timing sequences illustrated in
FIGS. 9A, 9B, 9C, and 9D represent how the valve events vary at a
given engine speed as a function of engine load. At low engine load
conditions (FIG. 9A) there is less total mass trapped in cylinder
14. Thus, controller 38 selects IVC at a mid-range value after the
top center of the piston stroke, selects EVC just prior to top
center, and selects IVO just after top center.
[0056] As the engine load increases (FIG. 9B) the desired amount of
exhaust gas retained in cylinder 14 increases so controller 38
selects EVC and IVO to move farther away from top center.
Controller 38 also selects IVC relatively later to allow the
induction of more fresh air/fuel charge into cylinder 14.
[0057] When the engine load reaches a higher range (FIG. 9C)
controller 38 selects IVC at a time even later with respect to FIG.
9B to maximize the amount of gas trapped in cylinder 14. Likewise,
controller 38 selects EVC and IVO back towards top center to reduce
the amount of residual exhaust gas and make room for more fresh
air/fuel mixture.
[0058] Finally, at the maximum engine load (FIG. 9D) controller 38
selects IVC at the same time with respect to FIG. 9C. Controller 38
selects EVC and IVO further towards the top center such that these
events slightly overlap to allow for the small amount of blow
available, thus reducing the amount of the residual gas trapped as
much as possible and consequently maximizing the fresh air/fuel
charge.
[0059] Of course, as described above, controller 38 may select EVO
and IVO events at fixed times while varying EVC and IVC events. In
this way, controller 38 removes two degrees of freedom in order to
simply control.
[0060] While embodiments of the invention have been illustrated and
described, it is not intended that these embodiments illustrate and
describe all possible forms of the invention. Rather, the words
used in the specification are words of description rather than
limitation, and it is understood that various changes may be made
without departing from the spirit and scope of the invention.
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