U.S. patent application number 11/879454 was filed with the patent office on 2009-01-22 for apparatus and method for controlling maximum cylinder pressure in an internal combustion engine.
Invention is credited to Gerald T. Fattic.
Application Number | 20090020102 11/879454 |
Document ID | / |
Family ID | 39663453 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090020102 |
Kind Code |
A1 |
Fattic; Gerald T. |
January 22, 2009 |
APPARATUS AND METHOD FOR CONTROLLING MAXIMUM CYLINDER PRESSURE IN
AN INTERNAL COMBUSTION ENGINE
Abstract
An Engine Control Module includes an electronic controller for
controlling the position of an EGR valve, the timing of opening and
closing of the engine combustion valves, and the timing of the
individual cylinder fuel injectors of an engine. Each engine
cylinder includes a pressure sensor. Peak cylinder pressure is sent
to the ECM during each firing cycle. The ECM is programmed with
required maximum percentages of EGR and optimal combustion valve
timing for each engine operating condition, and sets the EGR valve
and/or the camshaft phaser accordingly to adjust combustion in all
the engine cylinders. The ECM also compares the measured peak
pressure for each cylinder and adjusts the timing of fuel injection
for the next firing cycle to trim the measured peak pressure in
each cylinder to a predetermined level at or below the maximum
allowable peak firing pressure for the engine.
Inventors: |
Fattic; Gerald T.; (Fishers,
IN) |
Correspondence
Address: |
DELPHI TECHNOLOGIES, INC.
M/C 480-410-202, PO BOX 5052
TROY
MI
48007
US
|
Family ID: |
39663453 |
Appl. No.: |
11/879454 |
Filed: |
July 17, 2007 |
Current U.S.
Class: |
123/472 ;
60/278 |
Current CPC
Class: |
Y02T 10/44 20130101;
F02D 43/00 20130101; Y02T 10/47 20130101; F02D 41/0085 20130101;
F02D 41/40 20130101; F02D 21/08 20130101; F02D 41/005 20130101;
F02D 35/023 20130101; F02D 37/00 20130101; Y02T 10/40 20130101 |
Class at
Publication: |
123/472 ;
60/278 |
International
Class: |
F02D 41/30 20060101
F02D041/30; F02M 25/07 20060101 F02M025/07 |
Claims
1. A method for controlling pressure in a cylinder of an internal
combustion engine below a maximum allowable firing pressure,
comprising the steps of: a) measuring a peak firing pressure in
said cylinder during a firing cycle thereof; b) comparing said
measured peak firing pressure against said maximum allowable firing
pressure to determine a pressure difference; c) calculating from
said pressure difference an amount of recirculated exhaust gas to
be added in dilution to a fuel-air mixture for said cylinder to
reduce the resulting peak firing pressure in said cylinder in a
subsequent firing cycle to a pressure value no more than said
maximum allowable firing pressure; and d) providing said calculated
diluted fuel-air mixture to said cylinder.
2. A method in accordance with claim 1 wherein said engine has a
plurality of cylinders, and wherein each of said cylinders is
provided with a pressure sensor, and wherein said measured peak
firing pressure is an average of the measured peak firing pressures
in said plurality of cylinders, and wherein said calculating and
providing steps are provided to all of said plurality of
cylinders.
3. A method in accordance with claim 2 comprising the further steps
of: a) calculating from said pressure difference an amount of fuel
to be added to an incoming air charge to provide an adjusted
fuel-air mixture for said cylinder to reduce the resulting peak
firing pressure in said cylinder in a subsequent firing cycle to a
pressure value no more than said maximum allowable firing pressure;
and b) providing said adjusted fuel-air mixture to said
cylinder.
4. A method in accordance with claim 2 comprising the further steps
of: a) calculating from said pressure difference an optimum timing
schedule for energizing of a plurality of fuel injectors for said
plurality of cylinders to reduce the resulting peak firing pressure
in said cylinder in a subsequent firing cycle to a pressure value
no more than said maximum allowable firing pressure; and b)
energizing said plurality of fuel injectors according to said
calculated optimum timing schedule.
5. A method in accordance with claim 4 wherein said calculating and
energizing steps are carried out for each individual fuel injector.
Description
TECHNICAL FIELD
[0001] The present invention relates to internal combustion
engines; more particularly, to means for controlling maximum
cylinder pressure in an internal combustion engine; and most
particularly, to apparatus and method for controlling cylinder
pressure wherein either the amount of exhaust gas recirculated into
the combustion mixture or the valve actuation timing is regulated
to globally limit combustion, and wherein fuel injection timing is
regulated on an individual cylinder basis, hence to limit the
maximum cylinder pressure obtainable in any individual
cylinder.
BACKGROUND OF THE INVENTION
[0002] Excessively high pressure in an operating cylinder of an
internal combustion engine may cause damage to the engine pistons,
cylinder heads, and other components. Peak firing pressure is
affected by the combustion process and the conditions of the
incoming combustion air. In addition, the operation of a
turbo-charger increases peak firing pressure by increasing the
temperature and pressure of the incoming air.
[0003] Internal combustion engines, and especially diesel engines,
encounter a variety of operational conditions ranging from extreme
cold at sea level to high temperatures at high altitudes. These
conditions may induce various engine parameters to exceed designed
engine limits, for example, peak firing pressure (PFP),
turbocharger speed (TS), and preturbine temperature (PTT). More
specifically, the parameters are more susceptible to being exceeded
when the engine is running at full load at extreme ambient
temperature and/or altitude conditions.
[0004] There is also a continued demand for improved performance of
diesel engines, in terms of fuel economy, component loading, power
output, and reduced emissions. To facilitate optimized engine
performance, conditions of combustion within the internal
combustion engine should be controlled. However, engine designs are
limited because of the extremes of environmental conditions under
which an engine must operate. For example, cylinder PFP may become
too high when an engine is operating during cold days and when the
inlet air temperature is low, thus generating excessive stress on
engine components. Alternatively, cylinder exhaust temperatures may
become too high when the engine is operated during hot days and
when the inlet air temperature is very high, thus causing
turbocharger damage due to overheating and overspeed.
[0005] U.S. Pat. No. 6,557,347 discloses methods and apparatus for
controlling peak firing pressure for turbo-charged diesel engines.
The method includes determining an allowable peak firing pressure,
determining an actual peak firing pressure, and comparing the two
firing pressures to control the operation of a turbocharger for
controlling peak firing pressure. The rotational speed of the
turbocharger is varied to vary intake pressure and hence
combustion. A controller continuously monitors intake air manifold
pressure and fuel injection timing and outputs a signal to the
motor-generator driving the turbocharger. This method reduces
engine torque output and is applicable only globally to all the
engine cylinders equally.
[0006] What is needed in the art is a method and apparatus for
controlling peak firing pressure in an internal combustion engine
that does not substantially reduce output torque and that can
control peak firing pressure in individual cylinders of the
engine.
[0007] It is a principal object of the present invention to control
peak cylinder pressure in an internal combustion engine.
SUMMARY OF THE INVENTION
[0008] Briefly described, a fuel-injected internal combustion
engine is provided with means for recirculating a portion of the
engine exhaust gas (EGR) into the intake manifold as is know in the
prior art. An Engine Control Module (ECM) includes an electronic
controller for controlling the position of an EGR valve, the timing
of opening and closing of the engine combustion valves, and the
timing of the individual cylinder fuel injectors of the engine.
Each engine cylinder is provided with a pressure sensor, and a peak
cylinder pressure signal is sent to the ECM during each firing
cycle. The ECM is programmed with required maximum percentages of
EGR for each of the various engine operating conditions, and sets
the EGR valve and/or adjusts the fueling rate accordingly to adjust
globally the combustion in all the cylinders of the engine.
[0009] Further, the ECM compares the measured peak pressure for
each firing of each cylinder and adjusts, by delay or advance, the
timing of fuel injection for the next firing cycle to trim the
measured peak pressure in each cylinder to a predetermined level at
or below the maximum allowable peak firing pressure for the
engine.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
[0011] FIG. 1 is a schematic drawing of a combustion control system
in accordance with the invention for a V-8 diesel engine;
[0012] FIG. 2 is an idealized graph showing the effect on cylinder
pressure of varying the EGR content of the combustion mixture;
[0013] FIG. 3 is an idealized graph showing the amount of EGR
correction required as a function of the difference between maximum
allowable peak pressure and average peak pressure (pressure
error);
[0014] FIG. 4 is an algorithm for varying EGR percentage and rate
of fueling in the combustion mixture as shown in FIG. 3 to control
globally the average peak pressure;
[0015] FIG. 5 is an algorithm including the algorithm shown in FIG.
4, showing control of fuel injection to each cylinder to trim the
individual cylinder peak pressures;
[0016] FIG. 6 is an idealized graph showing the effect of varying
fuel injection timing on control of cylinder pressure; and
[0017] FIG. 7 is an algorithm for varying fuel injection timing to
trim the maximum pressure in each individual cylinder.
[0018] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set out
herein illustrate preferred embodiments of the invention and such
exemplifications are not to be construed as limiting the scope of
the invention in any manner.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] In a first step in a method for controlling an engine
cylinder pressure at or below an allowable PFP, such a pressure is
determined for an engine design based upon design parameters of the
engine. The allowable pressure may be a fixed maximum value or may
be calculated as a function of throttle setting signal, since in
some applications the desired allowable pressure may vary during
different engine operating conditions. The PFP may also define a
desired peak firing pressure, which may be the same or a different
value from a maximum allowable peak firing pressure, depending on
for, example, operation needs of the engine.
[0020] Referring to FIG. 1, a V8 diesel engine 10 includes cylinder
pressure sensors 12a-12h disposed in the firing chambers of the
eight cylinders, respectively. A crankshaft angular position sensor
(encoder) 14 is mounted on the end of the engine crankshaft to
continuously indicate the angular position thereof during operation
of the engine. A cylinder pressure controller 16 receives signals
from the individual pressure sensors 12a-12h and also from the
crankshaft sensor 14 and performs combustion calculations for each
cylinder in the engine firing sequence. An engine control module
18, which may include pressure controller 16, provides overall
monitoring and control of all engine functions, including, for
example, timing and duty cycle of the fuel injectors and EGR valve
(not shown), and feeds back relevant engine data to controller 16
for making the combustion calculations. For exemplary purposes, the
engine shown is a diesel V8, but the invention is applicable to any
form of spark-ignited or compression-ignited engine.
[0021] In accordance with the present invention, EGR may be added
to the air intake manifold of engine 10 to limit globally the peak
pressures in all the cylinders of a multi-cylinder engine during
combustion, as described above. Referring now to FIG. 2, Curve 20
represents the cylinder pressure during the compression and exhaust
stroke as a function of crankshaft angle, for combustion of a
mixture having a relatively low EGR content. Curve 22 represents
the same cylinder wherein the EGR content of the mixture is
substantially increased. It is seen that as EGR is increased, the
peak pressure in the cylinder decreases because the combustion rate
is reduced; hence, the combustion process is spread over a wider
angular range. As the cylinder pressure approaches a maximum
pressure limit, the EGR level can be increased to limit the
pressure, in accordance with the invention. Using EGR to control
the peak cylinder pressure allows the same fueling rate and
approximately the same torque production, when the combustion angle
is held relatively constant, both of which are significant
improvements upon the prior art.
[0022] The amount of EGR correction can be a function of the
difference of the maximum peak pressure and the average peak
pressure of all the cylinders. Referring to Curve 24 in FIG. 3, as
the average peak pressure approaches the maximum peak pressure, as
in Region 26, the amount of required EGR correction will increase
rapidly. When the difference is large, as in Region 28, the amount
of correction can be zero. The function can be tailored to prevent
the EGR from causing engine surge by the tailoring the slope of the
function.
[0023] Referring to FIG. 4, an algorithm 30 is shown for management
of EGR addition. The amount of additional EGR introduced cannot
exceed an EGR Limit established for the engine. The Pressure Error
is the difference between the Maximum Peak Pressure (also referred
to herein as the Maximum Allowable Pressure) and the Average Peak
Pressure (see FIG. 3) as determined by controller 16 (FIG. 1). The
EGR Correction is a pressure correction of the calculated amount of
EGR for a specific peak pressure. When the total amount of EGR
introduced for purposes of controlling the average cylinder
pressure is less than or equal to the EGR limit, the fueling rate
need not be changed from the commanded fuel amount. That is, no
fueling adjustment will be made to the commanded fuel quantity to
trim the average cylinder pressure. However, when the total amount
of EGR that is to be introduced is greater than the EGR limit, then
the EGR is commanded to only the EGR limit, and fueling adjustment
can intervene to prevent the cylinder pressure from exceeding the
pressure limit. The command EGR is held at the EGR limit while the
Command Fuel is reduced to prevent the cylinder pressure from
exceeding the Maximum Peak Pressure.
[0024] The fuel correction can also be applied to an individual
cylinder control 38 as shown in algorithm 40 in FIG. 5. The EGR
limit is calculated from the engine parameters to prevent the
air/fuel ratio from going rich. Using an oxygen sensor in the
exhaust to derive an Air/Fuel ratio can also be used to calculate
the EGR limit.
[0025] The individual cylinder control can always monitor each
cylinder, while the EGR control can monitor only the average
pressure operation.
[0026] Referring now to FIGS. 6 and 7, the combustion phase angle
can also control the value of peak pressure of the combustion
process. Curve 50 shows the cylinder pressure curve for a normal
timing of fuel injection in engine 10 (FIG. 1). A 50% heat release
angle is defined in the art as the crank angle, relative to Top
Dead Center (TDC), at which the heat release value in the
particular cylinder is one-half the total heat release of the
cylinder during its cylinder event. If the 50% heat release angle
is delayed after TDC, the maximum cylinder pressure will decrease,
as shown in Curve 52. If the range of delay is limited to a
predetermined value, the torque production may be reduced slightly.
This is a method to control the peak cylinder pressure without
reducing the fueling quantity or causing a large change in torque
production, again an important improvement over methods of the
prior art. By delaying 54 the fuel injection timing until after
TDC, the cylinder pressure is increasing when the cylinder is
moving down on the power stroke of the engine. As shown in
algorithm 60, if the 50% heat release angle can be maintained
within a specified number of degrees of TDC, for example, 15
degrees, the torque production from combustion will be only
slightly reduced.
[0027] If the peak cylinder pressure is still above the pressure
limit and the 50% heat release angle is at 15 degrees or greater,
then the fuel amount can be reduced to maintain a cylinder pressure
at or below the maximum cylinder pressure.
[0028] Other combustion angles can be modulated for purposes of
controlling individual cylinder pressure, other than the 50% heat
release angle. For examples, instead of adjusting a 50% heat
release angle, a 50% mass fraction burn angle (a 50% mass fraction
burn angle is defined in the art as the crank angle, relative to
TDC, at which the Mass Fraction Burn exceeds 0.5) or a start of
combustion angle can be adjusted. Further, instead of a 50% heat
release angle, a 10% heat release angle can be used; and instead of
a 50% mass fraction burn angle, a 10% mass fraction burn angle can
be used.
[0029] Variable valve timing, as is well known in the prior art,
can be substituted as the control variable in place of EGR. Again,
the control is global control of maximum cylinder pressure in all
cylinders, like EGR control.
[0030] While the invention has been described by reference to
various specific embodiments, it should be understood that numerous
changes may be made within the spirit and scope of the inventive
concepts described. Accordingly, it is intended that the invention
not be limited to the described embodiments, but will have full
scope defined by the language of the following claims.
* * * * *