U.S. patent application number 10/802987 was filed with the patent office on 2005-09-22 for increasing the duration of peak combustion pressure in cylinders of a diesel engine using fuel injection control strategies.
Invention is credited to Liu, Zhengbai.
Application Number | 20050205053 10/802987 |
Document ID | / |
Family ID | 34862008 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050205053 |
Kind Code |
A1 |
Liu, Zhengbai |
September 22, 2005 |
INCREASING THE DURATION OF PEAK COMBUSTION PRESSURE IN CYLINDERS OF
A DIESEL ENGINE USING FUEL INJECTION CONTROL STRATEGIES
Abstract
A diesel engine fuel injection strategy comprises injecting fuel
into a cylinder (28) during a compression upstroke of a piston (30)
that reciprocates within the cylinder and creating pressure
sufficient to initiate combustion of the injected fuel. As the fuel
is combusting, more fuel is injected at a controlled rate of
injection to cause further combustion of fuel in a manner that upon
substantially peak in-cylinder pressure being attained is effective
to prolong that peak in-cylinder pressure such that a trace (62B)
of pressure vs. crank angle would contain a distinct plateau (62P)
representing the prolonged peak pressure.
Inventors: |
Liu, Zhengbai; (Naperville,
IL) |
Correspondence
Address: |
INTERNATIONAL ENGINE INTELLECTUAL PROPERTY COMPANY
4201 WINFIELD ROAD
P.O. BOX 1488
WARRENVILLE
IL
60555
US
|
Family ID: |
34862008 |
Appl. No.: |
10/802987 |
Filed: |
March 17, 2004 |
Current U.S.
Class: |
123/299 |
Current CPC
Class: |
Y02T 10/123 20130101;
F02M 45/02 20130101; Y02T 10/12 20130101; F02B 3/06 20130101; Y02T
10/40 20130101; F02D 41/402 20130101; F02B 2275/14 20130101; F02D
35/023 20130101; Y02T 10/44 20130101 |
Class at
Publication: |
123/299 |
International
Class: |
F02B 003/00 |
Claims
What is claimed is:
1. A method for prolonging peak in-cylinder pressure in a diesel
comprising: a) injecting fuel into a cylinder during a compression
upstroke of a piston that reciprocates within the cylinder and
creating pressure sufficient to initiate combustion of the injected
fuel, and b) as the fuel is combusting, injecting more fuel at a
controlled rate of injection to cause further combustion of fuel in
a manner that upon substantially peak in-cylinder pressure being
attained is effective to prolong that peak in-cylinder pressure
such that a trace of pressure vs. crank angle would contain a
distinct plateau representing the prolonged peak pressure, wherein
c) the combined injections of a) and b) comprise at least two
discrete injection pulses.
2. A method as set forth in claim 1 wherein step a) is performed by
at least one of the discrete injection pulses that begins and ends
before top dead center in the engine cycle and step b) is performed
by another of the discrete injection pulses that begins before top
dead center and ends after top dead center.
3. A method as set forth in claim 1 wherein steps a) and b) are
collectively effective to advance the timing of peak pressure such
that the peak pressure is achieved slightly before top dead center
in the engine cycle.
4. A diesel engine comprising: a) multiple cylinders into which a
fueling system injects fuel during engine cycles; and b) an engine
control system that controls the fueling system and causes the
fueling system to inject fuel into each cylinder during a
compression upstroke of a respective piston that reciprocates
within the respective cylinder so that combustion of the injected
fuel will be initiated by in-cylinder pressure created by the
upstroking piston, and as the fuel is combusting, injects more fuel
at a controlled rate of injection to cause further combustion of
fuel in a manner that upon substantially peak in-cylinder pressure
being attained is effective to prolong that peak in-cylinder
pressure such that a trace of pressure vs. crank angle would
contain a distinct plateau representing the prolonged peak
pressure, wherein c) the combined injections of a) and b) comprise
at least two discrete injection pulses.
5. A diesel engine as set forth in claim 4 wherein at least one of
the discrete injection pulses begins and ends before top dead
center in the engine cycle and another of the discrete injection
pulses begins before top dead center and ends after top dead
center.
6. A diesel engine as set forth in claim 4 wherein the discrete
injection pulses are collectively effective to advance the timing
of peak pressure such that the peak pressure is achieved slightly
before top dead center in the engine cycle.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to internal combustion
engines. More specifically it relates to increasing the power
output of a diesel engine by increasing the duration of peak
combustion pressure in the cylinders through the use of fuel
injection control strategies.
BACKGROUND OF THE INVENTION
[0002] At some crank angle in an engine cycle after the beginning
of combustion in a cylinder, cylinder pressure reaches a maximum,
or peak, value. Typically, that peak pressure exists for only a
minute fraction of the engine cycle, and in a trace of cylinder
pressure vs. crank angle, the duration of peak pressure would
appear essentially as a single point of the trace, as shown for
example in FIG. 3 of U.S. Pat. No. 4,397,285. It is known that the
area under such a pressure trace at least approximates the engine
power output. Prolonging the duration of peak pressure could be an
effective way to increase the area under the pressure trace, and
hence power output, if that extended duration does not cause
offsetting power loss due to post-peak decreases in pressure.
[0003] The nature of a diesel engine and its fuel injection system
allows fuel to be injected even after combustion has commenced
within a cylinder. The fuel injection process during an engine
cycle is some generally described in terms of phases, such as pilot
injection, main injection, and post-injection. Any particular fuel
injection process typically always comprises a main fuel injection,
with pilot and post-injection being optional possibilities.
[0004] Contemporary fuel injection systems allow injection
pressure, injection rate, and injection timing to be fairly
accurately controlled. The inventor has recognized that such
control capabilities can be used to accomplish the goal of
prolonging the duration of peak pressure for increasing the power
output of a diesel engine.
[0005] U.S. Pat. No. 5,522,359 describes a method of fueling a
diesel engine in a manner that limits peak pressure in order to
limit in-cylinder temperature rise for the purpose of limiting
NO.sub.X formation. A single pulse is used for an injection, and
its timing occurs so as to cause combustion to occur during the
downward expansion stroke.
[0006] Principles of the present invention can be embodied in fuel
injection control strategies that use more than one discrete
injection pulse, in particular by implementing such strategies in
the processing system that processes various data to control the
operation of the fuel injectors that inject fuel into the engine
cylinders.
[0007] Controlling fuel injections in a manner that properly
controls the rate at which fuel is being injected as a function of
crank angle can be effective to accomplish the desired goal.
Exactly how fuel injections will be controlled in any given engine
depends on specifics of the engine, the fuel injection system, and
the processing system that controls the fuel injection system. For
example, fuel must obviously be injected at a pressure greater than
in-cylinder pressure, but control of injection pressure by itself
may not necessarily control the instantaneous rate of fuel
injection because of other factors that are present, such as the
design of the particular fuel injectors or the crank angle at which
fuel actually beings to combust and release energy into a
cylinder.
[0008] For certain engines, fuel injection systems, and processing
systems, the control of fuel injection pressure and the number of
fuel injections, including the timing and duration of each
injection, may be sufficient to at least approximately define a
desired trace of rate of fuel injection vs. crank angle that will
result in prolonging the duration of peak cylinder pressure in a
way that increases per-cylinder power output.
[0009] Because an engine that powers a motor vehicle will run at
different speeds depending on how the vehicle is being driven, the
crank angle at which peak pressure occurs may change with engine
speed. Hence, the task of successfully prolonging peak pressure at
different engine speeds depends on the capacity of the processing
system to store a number of data maps that will store data that can
be used in the calculation of fueling data to assure proper control
of the fuel injection system within each of multiple speed ranges.
The data stored in the maps is obtained by mapping a base engine
for various combinations of engine speed and load to develop the
data that needs to be stored in the processing system for use in
calculating engine fueling data. The engine fueling data will cause
the engine to be fueled in such a way that the rate at which the
combusting fuel is releasing energy will cause the peak in-cylinder
pressure to be prolonged for a greater fraction of an engine cycle
than has heretofore been possible.
[0010] It is to be understood that the mapping of an engine that
achieves this goal results from investigation and analysis of many
factors. Knowledge of the combustion chamber design and of the
capabilities of the fuel injection system and the associated
processing system forms a starting point in mapping an engine. As
long as the fuel injection and processing systems are capable of
providing the necessary degree of control accuracy, the goal of
prolonging peak in-cylinder pressure becomes attainable, albeit
that different factors might be used for control in different
systems depending on specifics of those systems.
[0011] With knowledge of how a given fuel injection system and
associated processing system perform, and with knowledge of how
combustion occurs within the cylinders of a particular engine, it
becomes possible to correlate in-cylinder pressure resulting from
combustion of injected fuel with the rate at which the combusting
fuel is releasing energy. A peak pressure can be prolonged for a
limited fraction of the engine cycle in an engine cylinder by
controlling the rate at which additional fuel is injected into the
cylinder once fuel already in the cylinder has started to combust
and is releasing energy.
[0012] For any given speed and load the data entered into a map can
be obtained through from engineering analysis and/or actual data
from a running engine.
[0013] For certain speeds and loads, only two discrete injection
pulses, each of suitable timing and duration, may be sufficient for
initiating combustion within a cylinder to the point of maximum
pressure and prolonging that maximum pressure for a limited
fraction of the engine cycle in a way that increases the power
output. Such a combination of pulses may be a main pulse that is
preceded by a pilot injection pulse or a main pulse that is
followed by a post-injection pulse.
[0014] For other speeds and loads, more than two discrete injection
pulses may be required, such as one or more pilot injections and/or
one or more post-injections accompanying a main fuel injection, may
be needed in order to cause the combusting fuel to reach maximum
pressure and then prolong that maximum pressure for a limited
fraction of the engine cycle so as to increases the power output.
Moreover, each such injection, whether it be a pilot injection, a
main injection, or a post-injection, must be defined by timing,
duration, and fuel pressure.
[0015] Consequently, the task of mapping an engine requires a
developmental effort where multiple solutions become entirely
possible due to the number of variables and possible combinations
of those variables. However, once a base engine has been mapped and
appropriate solutions selected as a result of the development
effort, the mapping may be used in the mass production of the
engine to the benefit of end users of the engines.
SUMMARY OF THE INVENTION
[0016] The present invention relates to a method for prolonging
peak in-cylinder pressure in a diesel engine. Diesel fuel is
injected into a cylinder during a compression upstroke of a piston
that reciprocates within the cylinder and creates pressure
sufficient to initiate combustion of the injected fuel. As the fuel
is combusting, more fuel is injected at a controlled rate of
injection to cause further combustion of fuel in a manner that upon
substantially peak in-cylinder pressure being attained is effective
to prolong that peak in-cylinder pressure such that a trace of
pressure vs. crank angle would contain a distinct plateau
representing the prolonged peak pressure. At least two discrete
fuel injections are used to accomplish this.
[0017] The invention also relates to an engine that embodies the
described strategy.
[0018] The foregoing, along with further features and advantages of
the invention, will be seen in the following disclosure of a
presently preferred embodiment of the invention depicting the best
mode contemplated at this time for carrying out the invention. This
specification includes drawings, now briefly described as
follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a general schematic diagram of a portion of an
exemplary diesel engine.
[0020] FIG. 2 is a graph comparing representative fuel injection
strategies to illustrate accomplishment of the objective of
prolonging peak in-cylinder pressure by the inventive strategy.
[0021] FIG. 3 is a graph showing in-cylinder pressure traces
resulting from the respective strategies of FIG. 2.
[0022] FIG. 4 is another graph comparing other representative fuel
injection strategies to illustrate accomplishment of the objective
of prolonging peak in-cylinder pressure by the inventive
strategy.
[0023] FIG. 5 is a graph showing in-cylinder pressure traces
resulting from the respective strategies of FIG. 4.
[0024] FIG. 6 is a graph showing in-cylinder pressure traces
resulting from other respective fuel strategies.
[0025] FIG. 7 is a graph showing in-cylinder pressure traces
resulting from still other respective fuel strategies.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] FIG. 1 shows a schematic diagram of a portion of an
exemplary diesel engine 20 for powering a motor vehicle. A
processor-based electronic engine control system 22 processes data
from various sources to develop various control data for
controlling various aspects of engine operation. The data processed
by control system 22 may originate at external sources, such as
sensors, and/or be generated internally.
[0027] Control system 22 includes an injector driver module 24 for
controlling the operation of electric-actuated fuel injection
devices 26. Each device 26 mounts on the engine in association with
a respective engine combustion chamber illustrated by an engine
cylinder 28 within which a piston 30 reciprocates. Intake air is
delivered to cylinder 28 through an intake system when an intake
valve 31 is open. Each piston is coupled to a crankshaft 32 by a
corresponding connecting rod 34. A processor of control system 22
can process data sufficiently fast to calculate, in real time, the
timing and duration of device actuation to set both the timing and
the amount of fueling.
[0028] Engine 20 further comprises an oil system 36 having a pump
38 for drawing oil from a sump and delivering the oil under
pressure to an oil rail 40 that serves in effect as a manifold for
supplying oil, as a control fluid, to the individual devices 26. An
injection pressure regulator (IPR) valve 42 is under the control of
control system 22 via an IPR driver 44 to regulate the hydraulic
pressure of oil in oil rail 40.
[0029] Each device 26 comprises a body 46 that mounts on engine 20
in association with oil rail 40, a respective cylinder 28, and a
source of fuel 48. Device 26 has an electrical connector 50 that
provides for the electrical connection of its actuator to injector
driver module 24. Fuel source 48 supplies liquid fuel to a fuel
inlet port 52 of body 46. Body 46 further comprises a fuel outlet
port, i.e. a nozzle 54, through which fuel is injected into
cylinder 28, and a control fluid inlet port 56 that is communicated
to the oil in oil rail 40.
[0030] The hydraulic pressure of the oil in rail 40 provides
injector control pressure, or ICP. Control system 22 establishes a
desired set-point for ICP and causes valve 42 to operate in a way
that forces actual ICP in rail 40 to the desired set-point. As
engine 20 runs and changing conditions call for change in the ICP
set-point, the strategy continues to force actual ICP to follow the
changing desired set-point for ICP.
[0031] Each device 26 has a plunger that, during the injecting
phase of device operation, is displaced within an internal pumping
chamber by oil at ICP from oil rail 40 to force fuel out of the
pumping chamber. The timing and the stroke of the plunger are also
controlled by control system 22. ICP applied through the plunger to
act on the fuel in the pumping chamber, amplifying the pressure of
fuel to a magnitude large enough for forcing a normally closed
control valve in nozzle 54 to open so that the amplified fuel
pressure forces the fuel through the nozzle into cylinder 28 as the
plunger is being displaced. Actual ICP in rail 40 is controlled by
control system 22 acting on IPR valve 42 via driver 44.
[0032] Control of ICP and of the timing and stroke of the injector
device plunger controls how fuel is injected into cylinder 28 and
such control capability can therefore be used to implement the
inventive strategy. In a diesel engine it is the pressure within
cylinder that is effective to initiate combustion of fuel, and it
is to an exhaust system that diesel exhaust gases resulting from
combustion pass when an exhaust valve 57 is open.
[0033] A first example of inventive strategy is described with
reference to FIGS. 2 and 3. A broken line trace 60A in FIG. 2 shows
rate of fueling, or rate of injection ROI, as a single main fuel
injection pulse that begins just slightly earlier than 0.degree.
crank angle (top dead center or TDC) Crank angle data is supplied
to control system 22 from a sensor 64. The amount of fuel
introduced is at least approximately represented by the area under
the pulse.
[0034] A broken line trace 60B in FIG. 3 is a trace of in-cylinder
pressure during the same engine cycle as trace 60A. The portion of
trace 60B that occurs earlier than the beginning of pulse 60A
corresponds to intake air being compressed within cylinder 28. As
fuel begins to be injected into cylinder 28, a point is reached
where the fuel begins to combust. This increases the in-cylinder
pressure even more as piston 30 moves through TDC and begins the
power downstroke. As the effective cylinder volume increases during
the downstroke, the in-cylinder pressure falls off. Trace 60B has a
peak pressure that is essentially just a single point 60P shortly
after TDC.
[0035] The solid line trace 62A in FIG. 2 represents a strategy
that embodies principles of the present invention. Fueling occurs
as several distinct pulses 62A1, 62A2, 62A3. The former two could
be considered pilot pulses and the latter one as a main pulse. The
amount of fuel injected as a result of each pulse 62A1, 62A2, 62A3
corresponds at least approximately to the area under the respective
pulse.
[0036] A solid line trace 62B in FIG. 3 is a trace of in-cylinder
pressure during the same portion of the engine cycle as trace 62A.
Early pilot injection of fuel creates an in-cylinder fuel-air
charge that begins to combust earlier in the engine cycle than is
the case for trace 60A. The combustion is augmented by the second
pilot pulse 62A2 and thereafter by main pulse 62A3. This control of
the combustion process releases energy into cylinder 28 in a
controlled way that prolongs the duration of peak pressure, as
portrayed by the distinct substantially flat plateau 62P of trace
62B. Comparison of traces 60B and 62B discloses that the area under
trace 62B is greater than that under trace 60B, indicating greater
power output. In this instance, the attainment of peak pressure
occurs earlier in the engine cycle with the inventive strategy, and
although the inventive strategy provides lower pressure in that
portion of the cycle after the point where the two traces cross,
some 6.degree. or so after TDC, the earlier prolonged increase in
pressure more than makes up for that later lower pressure,
resulting in power gain.
[0037] It is also to be noted that the total amounts of fuel
injected during the respective traces are same. Although trace 62A
contains two pilot injections, the amount of fuel introduced during
the main injection 62A3 is less than that introduced during the
single pulse of trace 60A.
[0038] FIG. 4 shows a comparison of respective injection strategies
similar to the comparison of FIG. 2. The inventive strategy of FIG.
4 differs from the corresponding one of FIG. 2 in that two pilot
pulses 62A1a and 62A1b replace the single pilot pulse 62A1. The
resulting pressure trace 62B in FIG. 5 is essentially the same as
trace 62B in FIG. 3.
[0039] The current invention has the following unique features:
[0040] 1) It can be used in heavy-duty, medium-duty, and light-duty
diesel engines.
[0041] 2) It is very flexible, meaning it can be implemented in
various combinations of injection pulses, based on various engine
requirements.
[0042] 3) The injection strategy will include at least one main
injection and one or more pilot or/and post-injections.
[0043] 4) The pilot injection number could be equal to one or
greater than one.
[0044] 5) The post injection number could be equal to one or
greater than one.
[0045] 6) The main injection number could also be greater than
one.
[0046] 7) The invention can be implemented in the processor alone,
provided that the processor has sufficient capacity, and this makes
the invention quite cost-effective.
[0047] FIGS. 6 and 7 illustrate two more examples. The solid line
trace 70A in FIG. 6 is a representative in-cylinder pressure trace
using a strategy that does not use the present invention. The
broken line trace 70B shows a prolonging of peak pressure using the
inventive strategy. The extension occurs in the forward crank angle
direction. The same solid line trace 70A is present in FIG. 7. The
broken line trace 80B shows a prolonging of peak pressure using the
inventive strategy, but with the extension occurring in the
backward crank angle direction. In both examples the inventive
strategy is effective to increase the power output.
[0048] Unlike the method of U.S. Pat. No. 5,522,359, the present
invention does not involve increasing the engine compression ratio
so that combustion can occur as the downstroke commences while the
expanding cylinder volume limits the in-cylinder pressure as the
combustion process continues. By contrast, the present invention
allows pressure to increase after the commencement of combustion to
a maximum, or peak, and thereafter prolong that peak pressure so
that in a pressure trace, a distinct substantially flat plateau,
rather than just a single point, defines the peak pressure.
[0049] While a presently preferred embodiment of the invention has
been illustrated and described, it should be appreciated that
principles of the invention apply to all embodiments falling within
the scope of the following claims.
* * * * *