U.S. patent application number 09/509304 was filed with the patent office on 2001-06-07 for method for evaluating the march of pressure in a combustion chamber.
Invention is credited to BELLMANN, HOLGER, WALTER, KLAUS.
Application Number | 20010002587 09/509304 |
Document ID | / |
Family ID | 7843251 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010002587 |
Kind Code |
A1 |
WALTER, KLAUS ; et
al. |
June 7, 2001 |
METHOD FOR EVALUATING THE MARCH OF PRESSURE IN A COMBUSTION
CHAMBER
Abstract
A method for evaluating the combustion chamber pressure in an
internal combustion engine is described, in which the output signal
of at least one cylinder pressure sensor and one crankshaft angle
sensor is performed by the control unit of the engine. By analysis
of the course of combustion chamber pressure over the crankshaft
angle, characteristic pressure courses are obtained for certain
valve control times. From these characteristic pressure courses, a
conclusion can be drawn as to the valve control times "outlet
opens", "outlet closes", "inlet opens", and "inlet closes",
referred to the crankshaft angle.
Inventors: |
WALTER, KLAUS;
(BIETIGHEIM-BISSINGEN, DE) ; BELLMANN, HOLGER;
(ADOLF-GESSWEIN-STR., DE) |
Correspondence
Address: |
STRIKER STRIKER & STENBY
103 EAST NECK ROAD
HUNTINGTON
NY
11743
US
|
Family ID: |
7843251 |
Appl. No.: |
09/509304 |
Filed: |
March 23, 2000 |
PCT Filed: |
September 22, 1998 |
PCT NO: |
PCT/DE98/02809 |
Current U.S.
Class: |
123/90.15 ;
123/435; 123/90.1; 73/114.16 |
Current CPC
Class: |
F01L 1/34 20130101; F02D
13/0215 20130101; F01L 2201/00 20130101; F02D 2041/001 20130101;
F02D 35/023 20130101; F02D 41/009 20130101; F02D 13/0261
20130101 |
Class at
Publication: |
123/90.15 ;
123/90.1; 123/435; 73/117.3 |
International
Class: |
F01L 001/34; G01L
005/13 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 23, 1997 |
DE |
197 41 820.1 |
Claims
1. A method for evaluating the combustion chamber pressure in an
internal combustion engine having at least one cylinder pressure
sensor and one crankshaft angle sensor, which outputs a signal
representative of the crankshaft position, and an evaluation device
to which the signals of the sensors are supplied, characterized in
that from the course of the combustion chamber pressure as a
function of the crankshaft angle position, it is concluded that at
least one of the valve control times "outlet opens", "outlet
closes", "inlet opens", "inlet closes" exists with respect to the
crankshaft angle position, to which end the events characterizing
the valve control times are evaluated.
2. The method of claim 1, characterized in that it is concluded
that the valve control time "outlet opens" exists, if the expansion
line of the course of combustion chamber pressure is varying in
such a way that the change in the pressure gradient changes its
sign with increasing volume or with an increasing crankshaft
angle.
3. The method of claim 1, characterized in that to detect "inlet
closes", the volume or the crankshaft angle at which the
compression pressure is equal to the pressure that prevailed during
the expulsion at the same distance from top dead center is
detected.
4. The method of claim 1 or 2, characterized in that to ascertain
the valve control time "inlet closes", the volume or the crankshaft
angle at which the compression pressure is equal to the ambient
pressure is detected.
5. The method of claim 1 or 2, characterized in that to detect the
valve control time "inlet closes", the volume or the crankshaft
angle at which the compression pressure is equal to a
predeterminable fixed pressure is detected.
6. The method of claim 1, characterized in that to determine the
valve control times "outlet closes", "inlet closes" or "inlet
opens", the absolute pressure level during the compression before
the onset of combustion is evaluated, and either from a single
pressure course or from a pressure course averaged over multiple
cycles, by comparison with engine-specifically ascertained data
stored in memory in the form of a performance graph or
characteristic curve or engine-specifically ascertained
mathematical relationships or adapted conversion factors, a
conclusion as to the valve control times is drawn.
7. The method of claim 1, characterized in that to detect at least
one valve control time, the combustion pressure gradient during the
compression before the onset of combustion or a polytropic exponent
calculated from it is evaluated, and from the single pressure
course or from a pressure course averaged over multiple cycles, via
engine- specifically ascertained conversions stored in memory in
the form of a performance graph or characteristic curve or
engine-specifically ascertained mathematical relationships or
adapted conversion factors, a conclusion as to the valve control
time is drawn.
8. The method of claim 1, characterized in that from the absolute
pressure level or from the pressure gradient during the expansion
before the opening of the outlet valve or from a polytropic
exponent calculated from the pressure gradients, either from a
single pressure course or from a pressure course averaged over
multiple cycles, via engine- specifically ascertained conversions
stored in memory in the form of a performance graph or
characteristic curve, engine-specifically ascertained mathematical
relationships or adapted conversion factors, a conclusion is drawn
as to the valve control times "outlet closes", "inlet opens" or
"inlet closes".
9. The method of claim 1, characterized in that from the location
of the maximum pressure increase, either from a single pressure
course or from a pressure course averaged over multiple cycles, via
engine-specifically ascertained conversions stored in memory in the
form of a performance graph or characteristic curve,
engine-specifically ascertained mathematical relationships or
adapted conversion factors, a conclusion is drawn as to the valve
control times "outlet closes", "inlet opens" or "inlet closes".
10. The method of claim 1, characterized in that to detect the
valve control times, at least one of the following variables is
employed: deviation of the location of the maximum pressure
increase over multiple cycles, the maximum incident pressure
gradient from a single pressure course or from a pressure course
averaged over multiple cycles; deviation of the maximum incident
pressure gradient over multiple cycles; location of the maximum
pressure from a single pressure course or from a pressure course
averaged over multiple cycles; deviation of the location of the
maximum pressure over multiple cycles; level of the maximum
pressure from a single pressure course or from a pressure course
averaged over multiple cycles; deviation of the location of the
maximum pressure over multiple cycles; wherein additionally,
engine-specifically ascertained conversions stored in memory in the
form of a performance graph or characteristic curve,
engine-specifically ascertained mathematical relationships or
adapted conversion factors are also taken into account to determine
the valve control times.
11. The method of claim 1, characterized in that a conclusion as to
the valve control times is drawn from one of the following
variables: deviation of the location of certain portions of the
energy conversion over multiple cycles; location of the maximum
energy conversion from a single pressure course or from a pressure
course averaged over multiple cycles; deviation of the location of
the maximum energy conversion over multiple cycles; maximum
gradient of the energy conversion from a single pressure course or
from a pressure course averaged over multiple cycles; and taking
into account engine-specifically ascertained conversions stored in
memory in the form of a performance graph or characteristic curve,
engine-specifically ascertained mathematical relationships or
adapted conversion factors.
12. The method of claim 1, characterized in that one of the
following variables is evaluated: indicated work from a single
pressure course or from a pressure course averaged over multiple
cycles; deviation in the indicated work over multiple cycles;
indicated high-pressure work from a single pressure course or from
a pressure course averaged over multiple cycles; deviation of the
indicated high-pressure work over multiple cycles; indicated
low-pressure work from a single pressure course or from a pressure
course averaged over multiple cycles; deviation in the indicated
low-pressure work over multiple cycles, and a conclusion as to the
valve control times is drawn via engine-specifically ascertained
conversions stored in memory in the form of a performance graph or
characteristic curve, engine-specifically ascertained mathematical
relationships or adapted conversion factors.
13. The method of claim 1, characterized in that the combustion
chamber pressure is integrated over a predeterminable range, or
that the differential combustion chamber pressure is integrated
over a predeterminable range, and either the integral from a single
pressure course or from a pressure course averaged over multiple
cycles is formed, and a conclusion as to the valve control times is
drawn via engine-specifically ascertained conversions stored in
memory in the form of a performance graph or characteristic curve,
engine-specifically ascertained mathematical relationships or
adapted conversion factors.
14. The method of claim 13, characterized in that from the
deviation in the integral or integrals over multiple cycles, a
conclusion as to the valve control times is drawn.
15. The method of claim 1, characterized in that from the
occurrence of oscillations in the course of the combustion chamber
pressure caused by knocking combustion or from the necessity of
counterprovisions to avoid knocking combustion, which in turn are
taken on the basis of pressure oscillations in the course of the
combustion chamber pressure, a conclusion as to the valve control
times is drawn either from a single pressure course or from a
pressure course averaged over multiple cycles, via
engine-specifically ascertained conversions stored in memory in the
form of a performance graph or characteristic curve,
engine-specifically ascertained mathematical relationships or
adapted conversion factors.
Description
[0001] The invention relates to a method for evaluating the course
of the combustion chamber pressure and internal combustion engines,
as generically defined by the preamble to the main claim.
PRIOR ART
[0002] It is known to ascertain the course of the combustion
chamber pressures in the cylinders of an internal combustion engine
with the aid of suitable sensors, and from this course to detect
operating states of the engine and obtain trigger signals for
controlling the engine. Typically, each cylinder of the engine is
assigned a combustion chamber pressure sensor. A crankshaft sensor
is also used, which furnishes an output signal that is
representative for the crankshaft position. The two signals are
evaluated jointly in the engine control unit. A camshaft sensor is
no longer needed, since it is possible, especially after starting,
to synchronize the crankshaft and camshaft position by linking the
course of the combustion chamber pressure and the crankshaft sensor
signal. A method in which the course of combustion chamber pressure
is evaluated as a function of the crankshaft position, for the sake
of cylinder detection and to generate signals required for
ignition, is known from published, unexamined German Patent
Application DE-OS 44 05 015. The cylinder detection and the
detection of the crankshaft revolution in which the engine is
located in a combustion cycle is performed in the known method by
evaluating the pressure increase in a certain cylinder, for
instance, and distinguishing between a pressure increase in the
compression stroke and a pressure increase in the ensuing
combustion. Since these values are different, the crankshaft
revolution in which the engine is located can be ascertained.
>From this finding, control signals for the engine can be
generated.
[0003] In the known method, an evaluation of the course of
combustion chamber pressure to detect the valve control times, that
is, in order to detect whether the outlet valve is opening or
closing or whether the inlet valve is opening or closing, is not
performed.
ADVANTAGES OF THE INVENTION
[0004] The method of the invention having the characteristics of
the main claim has the advantage over the prior art that precise
analysis of the course of combustion chamber pressure is performed,
so that the valve control times can be ascertained with reference
to the crankshaft position. To that end, characteristic events are
evaluated from which unambiguously determined valve control times
can be detected. For the valve control times of "outlet opens",
"outlet closes", "inlet opens", "inlet closes", characteristic
pressure courses are obtained which according to the invention are
advantageously extracted from the course of the combustion chamber
pressure.
[0005] Further advantages of the invention are attained by the
provisions recited in the dependent claims. It is especially
advantageous that various valve control times can be ascertained by
detecting the various associated characteristic events. Some valve
control times can also be detected from a similar evaluation of the
course of the combustion chamber pressure. A comparison with
engine- typical characteristic variables stored in memory makes it
possible to determine valve control times for a specific
engine.
[0006] Further processing of the combustion chamber pressure signal
before further evaluation, such as a differentiation or integration
of the course of combustion chamber pressure, makes further
ascertainments of valve control times advantageously possible.
Taking additional engine operating conditions into account, such as
the incidence of knocking combustion, and the ensuing additional
signal processing, such as averaging, advantageously makes it
possible to ascertain valve control times even if difficult
conditions or operating states of the engine are occurring.
DRAWING
[0007] One exemplary embodiment of the invention is shown in the
drawing Figs. and will be described in further detail in the
ensuing description. Specifically, FIG. 1 shows a system, already
known per se, for detecting the pressure course in the cylinders of
an internal combustion engine. In FIG. 1a, relevant parts of the
internal combustion engine are shown. FIG. 2 shows a characteristic
course of combustion chamber pressure over the crankshaft angle.
FIG. 3 is a flow chart of an evaluation method according to the
invention, and FIGS. 4, 5 and 6 show various relationships among
the combustion chamber pressure, combustion chamber volume, and
crankshaft angle.
[0008] In FIG. 1, the most essential components of an apparatus for
ascertaining the combustion chamber pressure in each cylinder of an
internal combustion engine are shown. In each of the cylinders 10,
11, 12 and 13 of a four-cylinder engine, respective cylinder
pressure sensors 14, 15, 16 and 17 are disposed, which ascertain
the pressure courses P1, P2, P3 and P4. A crankshaft sensor 18 is
also present, which outputs an output signal S1 that is
characteristic for the crankshaft position.
[0009] Both the output signals of the cylinder pressure sensors 14,
15, 16 and 17 and the output signal of the crankshaft sensor 18 are
delivered to the engine control unit 19, which processes these
signals. Via inputs 20, further signals (such as a temperature T,
load L and so forth) can be supplied to the control unit and can be
further processed in the control unit as well.
[0010] The control unit 19 includes a multiplexer 21, by way of
which the output signal of the cylinder pressure sensors is sent
selectively to an analog/digital converter 22. The switchover of
the multiplexer 11 is done as a function of crankshaft angle and is
tripped by suitable triggering actions on the part of the control
unit 19. The actual evaluation of the signals is done in a
microprocessor 23 of the control unit 19; via an output unit 23a,
as a function of the variables ascertained, this microprocessor can
output control signals S2 and S3, such as ignition or injection
signals, to various components of the engine.
[0011] The signal processing takes place in the microprocessor 23
of the control unit 19, and on the basis of this processing, a
conclusion can be drawn as to the valve control times, or the valve
control times can be ascertained.
[0012] FIG. 3 shows an evaluation flow chart, in which in step SCH
1 the pressure is calculated from the sensor signal. In step SCH 2,
the crankshaft angle is written in, so that in step SCH 3 the
reference pressure P( ) is present. In step SCH 4, the pressure
course is evaluated, optionally taking data stored in memory into
account, and in step SCH 5, a conclusion as to the applicable valve
control unit is drawn.
[0013] By opening the inlet valve 24, the fuel-air mixture is
supplied to the cylinder of an engine, for instance to cylinder 10
(FIG. 1a). In a known manner, the fuel is injected by the injection
valve 25 before the injection valve 24 into the intake tube 26, and
ignited via the spark plug 27 and via the spark plug 27. Via an
outlet valve 28, the gas generated in the cylinder can be let out.
The triggering of the inlet and outlet valves is done in a known
manner with the aid of the camshaft or camshafts, not shown. The
camshaft or camshafts are driven in a known manner by the
crankshaft. The location of the camshaft or camshafts relative to
the crankshaft can be varied by the control unit 19 as a function
of rpm, by means of suitable trigger signals S3. By the detection
according to the invention of the valve control times as a function
of the crankshaft angle, the association between the camshaft
position and the crankshaft position can be determined.
[0014] In FIG. 2, the course of the combustion chamber pressure P1
of the cylinder 10 is plotted over the crankshaft angle. The
cylinder pressure attains two maximum values, which are one cycle
or 720 KW apart. The maximum combustion chamber pressure in the
range in which a combustion occurs is higher than in the range in
which only a compression occurs. In the example of FIG. 2, a
combustion takes place in the phase Ve. In the phase Ko only a
compression occurs.
[0015] The combustion chamber pressure course schematically shown
in FIG. 2 is evaluated according to the invention by various
criteria, in order from them to draw conclusions as to events that
are characteristic for the camshaft position relative to the
crankshaft position and thus for the valve seat control times. One
such event can for instance be the crankshaft position at which the
inlet valve closes. Other valve control times are the control times
designated as "outlet opens", "inlet opens", and "outlet closes".
For each valve control time, there are characteristic or definitive
features in the pressure course, the evaluation of which features
will be described in further detail below.
[0016] To detect the valve control time "outlet opens", the
expansion line of the combustion chamber pressure course can be
evaluated. As long as the outlet valve is closed, the events
occurring in the cylinder involve a thermodynamically closed
system, so that the events can be calculated in accordance with
thermodynamic principles. As the volume increases, a pressure
decrease occurs, which is established similarly to a polytropic
expansion. It is characteristic of this that the amount of the
pressure gradient decreases with increasing volume. If the outlet
valve is opened, then dictated by the pressure that is elevated
relative to the environment, gas flows out of the cylinder. As a
result, the amount of the pressure gradient increases. The
evaluation of the pressure gradient for the outlet opening that has
occurred can thus utilized as a definitive or characteristic
behavior of the pressure course. If the pressure gradient has a
behavior which is distinguished by a lessening decrease and a
sudden increase in the amount of the pressure gradient then it can
be concluded that the outlet has opened. Mathematically, the
evaluation can be done by checking for instance for a change of
sign in the second derivation of the pressure in accordance with
the volume. If such a change of sign occurs in the second
derivation of the pressure in accordance with the crankshaft angle,
then it can be concluded that an outlet opening has taken place. In
FIG. 4, which shows the relationship between the pressure P and the
volume V between top dead center OT and bottom dead center UT, the
point A1 would characterize the outlet opening that has occurred.
At this point, it is true that the second derivation of the
pressure in accordance with the volume d.sup.2P/dv has a change of
sign. This is also true for the relationship d.sup.2P/d.sup.2.
[0017] To detect the valve control time "inlet closes", the volume
or the crankshaft angle at which the compression curve passes
through a known, fixed level is detected. In the simplest case,
this comparison level is obtained from the pressure course during
expulsion. The location of the intersection A2 between the
compression pressure course and the pressure course during the
expulsion in the crankshaft angle pattern or the course of volume
can be learned from FIG. 5. It is admittedly not a direct measure
of the valve control time "inlet closes", but it does shift upon a
change in the closure of the inlet valve. Thus a desired value for
the location of point A2 can be applied in engine-dependent fashion
as a function of the load and rpm. For a diagnosis, the deviation
of the actual value for the point A2 from the desired value is then
used. The recording of the engine- specific data can be done before
the engine is put into operation, for instance on a test bench. The
data obtained are then stored in memories, for instance of the
control unit, which can access these data at any time.
[0018] The evaluation of the course of combustion chamber pressure
is not limited to only the pressure-volume relationship; an
evaluation on the basis of the pressure and crankshaft angle
relationship is also possible. By evaluating the location of points
A3 and A4 in FIG. 6, corresponding conclusions can be drawn. Also
plotted in FIG. 6 is the combustion chamber pressure P over the
crankshaft angle. In addition, the load change top dead center
points LWOT, an ignition top dead center point ZOT, bottom dead
center points UT, and angles .alpha.3, .beta.3, .alpha.4, .beta.4
are plotted; the angle .alpha.3 and .alpha.4 respectively defines
the distance between bottom dead center UT and the respective point
A3 and A4; the angle .beta.3 defines the distance between A3 and
ZOT; and the angle .beta.4 defines the distance between A4 and
LWOT. It the pressure at point A3 is equal to the pressure at point
A4, than for the angles the applicable equations are
.alpha.3=.alpha.4 and .beta.3=.beta.4.
[0019] If it is not possible to evaluate the course of combustion
chamber pressure during the expulsion of the combustion gases
located in the cylinder, for instance if because of the high
combustion temperature, from transient drifting caused by thermal
shock, the combustion chamber pressure sensor furnishes only
imprecise signals, then the evaluation of the course of combustion
chamber pressure can also be performed as a substitute by
comparison with the ambient pressure. For instance, to detect the
valve control time "inlet valve closes inlet valve", the volume or
the crankshaft angle at which the compression pressure is equal to
the ambient pressure can be detected. In that case, the point A3 is
defined as the intersection of the compression pressure course and
the ambient pressure. Then, however, a zero level correction of the
pressure course will be necessary, which increases the effort and
expense of calculation and under some circumstances can lead to
incorrect measurements.
[0020] If measurement values for the ambient pressure and the
compression curve, which is the case in supercharged engines, for
instance, than an evaluation of the combustion chamber pressure
course can also be done on the basis of a fixed pressure value. In
that case, however, special diagnostic strategies that prevent
misdiagnosis from a strong change in the ambient pressure, for
instance when driving at relatively high altitudes, are necessary.
If the control unit detects this kind of high altitude travel, for
instance in conjunction with other evaluations for regulating the
engine, then a detection of valve control times can be suppressed
at least intermittently.
[0021] If valve control times change, for instance because of a
corresponding change in the camshaft positions, once again this
leads to a change in the combustion chamber pressure course during
the compression phase, the combustion phase, and the expansion
phase. From a change in the camshaft position, the valve control
times are for instance changed in such a way that the residual gas
content in the cylinder charge varies in a characteristic way. A
relatively high residual gas content, which can be caused for
instance by late closure of the outlet valve or early opening of
the inlet valve, in each case relative to the crankshaft angle,
increases both the absolute pressure and the pressure gradient
during the compression phase, assuming that the same quantity of
fresh air is delivered. If the same instant of ignition is assumed,
the combustion will begin late, with the attendant effects on the
characteristic values that describe the combustion and the
expansion. If various engine-specific characteristic values or
performance graphs are stored in memories of the control unit, than
these characteristic values or performance graphs can be accessed
at any time. A comparison with the measured cylinder pressure
course, with knowledge of the engine-specifically present
relationships, for instance also including ascertained mathematical
relationships, yields a conclusion as to which of the valve control
times is present. During engine operation, characteristic values
can be adapted. From the adapted characteristic values, once again
a conclusion as to the current valve control times can be drawn. A
further evaluation option for the course of combustion pressure can
also be obtained from the deviation from cycle to cycle in the
variables characterizing combustion, in externally ignited engines,
with an increasing residual gas content. This affords the
opportunity of making a conclusion about the valve control times
from the deviation in the characteristic values via
engine-specifically ascertained performance graphs or
characteristic curves, engine-specifically ascertained mathematical
relationships, or characteristic values adapted during engine
operation.
[0022] A combination of the aforementioned evaluation options can
be made at any time. It is also possible, both in evaluating the
pressure gradients and in evaluating the maximum pressure, the
location of the maximum pressure, and in general in the evaluation
of single pressure courses, first to perform averaging, for
instance over multiple engine cycles, and then to examine the
average values of the combustion chamber pressure course for
variables that characterize certain valve control times. Once
again, engine-specifically ascertained relationships, stored in
memory as a performance graph or characteristic curve, or
mathematical relationships should be taken into account. To detect
at least one of the valve control times "outlet opens", "outlet
closes", "inlet closes", "inlet opens", a defined combustion
chamber pressure integral or a differential combustion chamber
pressure integral can also initially be formed; the integration
limits should be selected in a suitable way and in particular
designed such that valve control time-typical phases are
combined.
[0023] A further option for detecting the valve control times is to
derive characteristic variables for certain valve control times
from the occurrence of oscillations in the combustion chamber
pressure course as a consequence of knocking combustion or from the
necessity of counterprovisions to avoid knocking combustion, which
provisions are in turn taken on the basis of pressure oscillations
in the course of the combustion chamber pressure. Once again, an
additional averaging can be performed.
[0024] The invention can be used in engines with an arbitrary
number of cylinders; the number of cylinder pressure sensors is for
instance equal to the number of cylinders or to half the number of
cylinders. In a simplified version, at least one sensor can be
employed. As the sensors, knocking sensors can also be used, or
arbitrary combustion sequence sensors, from whose output signal
characteristic features for valve control times can be
obtained.
* * * * *