U.S. patent application number 09/104933 was filed with the patent office on 2002-02-07 for combustion state diagnosing system and combustion state diagnosing method for diagnosing engine and recording medium.
This patent application is currently assigned to Hitachi, Ltd.. Invention is credited to ISHII, TOSHIO, KIMURA, HIROSHI, KURIHARA, NOBUO, TAKAKU, YUTAKA.
Application Number | 20020014113 09/104933 |
Document ID | / |
Family ID | 15937351 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014113 |
Kind Code |
A1 |
TAKAKU, YUTAKA ; et
al. |
February 7, 2002 |
COMBUSTION STATE DIAGNOSING SYSTEM AND COMBUSTION STATE DIAGNOSING
METHOD FOR DIAGNOSING ENGINE AND RECORDING MEDIUM
Abstract
It is an object of the present invention to provide a low-cost
combustion state diagnosing system and a combustion state
diagnosing method capable of accurately detecting misfires which
occur at a low frequency while a multiple-cylinder engine is
operating at a high engine speed under a low load. The object can
be achieved, when diagnosing combustion state, by extracting
specific rotation period component of a period synchronous with
rotation from a combustion state parameter for at least two
rotations, and judging combustion state on the basis of the
extracted specific rotation period component. The combustion state
parameter may be the engine speed or the output torque of a
multiple-cylinder engine which varies according to the combustion
state of the engine.
Inventors: |
TAKAKU, YUTAKA; (MITO-SHI,
JP) ; ISHII, TOSHIO; (MITO-SHI, JP) ;
KURIHARA, NOBUO; (HACHINOHE-SHI, JP) ; KIMURA,
HIROSHI; (HITACHINAKA-SHI, JP) |
Correspondence
Address: |
EVENSON MCKEOWN EDWARDS & LENAHAN
1200 G STREET NW
SUITE 700
WASHINGTON
DC
20005
|
Assignee: |
Hitachi, Ltd.
|
Family ID: |
15937351 |
Appl. No.: |
09/104933 |
Filed: |
June 26, 1998 |
Current U.S.
Class: |
73/114.07 ;
73/114.14 |
Current CPC
Class: |
G01M 15/11 20130101 |
Class at
Publication: |
73/116 |
International
Class: |
G01L 003/26 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 27, 1997 |
JP |
9-172195 |
Claims
What is claimed is:
1. A combustion state diagnosing system for diagnosing a combustion
state of a multiple-cylinder engine by measuring a parameter of the
combustion state varying according to the combustion state of the
engine, such as engine speed or output torque, diagnosing the
combustion state on the basis of the parameter of the combustion
state, said diagnostic system comprising: a combustion state
parameter measuring means which measures values of parameter of the
combustion state N times (at least once) in one ignition cycle of
the multiple-cylinder engine at times corresponding to a
predetermined crank angle; a specific rotation period component
extracting means for extracting a specific rotation period
component of a period synchronous with rotation of a crankshaft
from values of the parameter of the combustion state measured by
the combustion state parameter measuring means at least in two
rotations of a crankshaft; and a combustion state judging means for
judging the combustion state on the basis of the specific rotation
period component extracted by the specific rotation period
component extracting means.
2. The combustion state diagnosing system for diagnosing combustion
state of a multiple-cylinder engine according to claim 1, wherein
the combustion state parameter measuring means measures necessary
times T(i) each necessary for the crankshaft to turn through an
angle between predetermined crank angles N times in each ignition
cycle of the engine, and the specific rotation period component
extracting means is provided with a high-pass filter means which
filters out low-frequency components of the necessary times T(i) to
calculate filtered necessary times Tf(i) to extract specific
rotation period components of a period synchronous with the
rotation of the crankshaft from the filtered necessary times
Tf(i).
3. The combustion state diagnosing system for diagnosing combustion
state of a multiple-cylinder engine according to claim 2, wherein
the high-pass filer means filters out the components of periods
longer than a time necessary for two rotations of the crankshaft of
the engine.
4. The combustion state diagnosing system for diagnosing combustion
state of a multiple-cylinder engine according to claim 2, wherein
the high-pass filter means calculates the difference [T(i)-T(i-N)]
from the necessary times T(i) corresponding to the cylinders
successive in ignition order to use the same as the filtered
necessary time Tf(i).
5. The combustion state diagnosing system for diagnosing combustion
state of a multiple-cylinder engine according to claim 1, wherein
the measured varying values of torque are used directly as those of
the combustion state parameter.
6. The combustion state diagnosing system for diagnosing combustion
state of a multiple-cylinder engine according to claims 1, wherein
the specific rotation period component extracting means is provided
with an arithmetic means which extracts a specific rotation period
component which is a variable component of X (=Tf) of a period
synchronous with the rotation of the crankshaft from the sum of the
products of values of the combustion state parameter for at least
two rotations of the crankshaft or Tf (=X), i.e., X(i), X(i-1), . .
. , X(i-c+1), where c is greater than or equal to the product of N
and the number of cylinders of the engine, and at least two sets
each of c pieces of weighting coefficients.
7. The combustion state diagnosing system for diagnosing combustion
state of a multiple-cylinder engine according to claim 6, wherein
the weighting coefficients are set so as to extract a two-rotation
period component of a period synchronous with two rotations of the
crankshaft of the engine.
8. The combustion state diagnosing system for diagnosing combustion
state of a multiple-cylinder engine according to claims 1, wherein
the specific rotation period component extracting means extracts
components synchronous with two rotations of the crankshaft of the
engine.
9. The combustion state diagnosing system for diagnosing combustion
state of a multiple-cylinder engine according to claim 1, wherein
the specific rotation period component extracting means extracts
components synchronous with one rotation of the crankshaft of the
engine.
10. The combustion state diagnosing system for diagnosing
combustion state of a multiple-cylinder engine according to claim
1, wherein the combustion state judging means counts the frequency
of successive values of the specific rotation period component
exceeding a predetermined value, judges that a misfire occurred
every ignition cycle if the count of the frequency is greater than
a predetermined number, and judges that a misfire occurred at
intervals if the count of the frequency is not greater than the
predetermined value.
11. The combustion state diagnosing system for diagnosing
combustion state of a multiple-cylinder engine according to claims
1, wherein the specific rotation period component extracting means
includes a phase calculating means for calculating the phase of the
specific rotation period component, and the combustion state
judging means includes a misfiring cylinder identifying means for
finding the number of misfiring cylinders and/or misfiring
cylinders on the basis of at least the phase of the specific
rotation period component.
12. The combustion state diagnosing system for diagnosing
combustion state of a multiple-cylinder engine according to claim
1, wherein the combustion state judging means specifies a pattern
indicating a maximum from the sum of the products of a plurality of
values of the combustion state parameters or Tf (=X), i.e., X(i),
X(i-1), . . . , X(i-d+1), where d is a constant, and d pieces of
weighting coefficients for a plurality of predetermined patterns
when it is judged that a misfire occurred, and identifies a
misfiring cylinder on the basis of the maximum and the specified
pattern.
13. The combustion state diagnosing system for diagnosing
combustion state of a multiple-cylinder engine according to claim 1
further comprising a misfire counting means for counting the
frequency of judgement that a misfire occurred made by the
combustion state judging means in a predetermined period, and an
alarm means for giving an alarm to the driver when the frequency
exceeds a predetermined number and/or a misfire information storage
means for storing misfire information.
14. An engine combustion state diagnosing program storage medium
storing a program for measuring a combustion state parameter
varying according to the combustion state of a multiple-cylinder
engine, such as engine speed at which the multiple-cylinder engine
is operating or output torque of the multiple-cylinder engine and
judging combustion state on the basis of the combustion state
parameter; wherein the program specifies steps of: measuring the
combustion state parameter N times (at least once) in one ignition
cycle of each cylinder at a predetermined crank angle, extracting a
specific rotation period component of a period synchronous with
rotation from at least the two values of the combustion state
parameter, and judging combustion state on the basis of the
extracted specific rotation period component.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a combustion state
diagnosing system for diagnosing the combustion state of a
multiple-cylinder engine and, more particularly, to a combustion
state diagnosing system and a combustion state diagnosing method
capable of accurately finding the occurrence of a misfire.
[0002] If an engine misfires, expected energy of combustion cannot
be produced, the output of the engine decreases, and unburned
gasses are discharged into an exhaust system to cause various
problems. For example, the unburned gasses discharged into the
atmosphere cause air pollution. Furthermore, part of the unburned
gases burn in a catalytic unit included in the exhaust system and
heats the exhaust system at an abnormally high temperature, which
may possibly cause the catalytic unit to melt. If the catalytic
unit melts, the exhaust gas cannot be purified, causing air
pollution.
[0003] To prevent such air pollution, the ARB (Air Resources Board)
of California, USA provides by regulations that misfires shall be
detected and, if the frequency of misfires exceeds a predetermined
value, malfunction codes shall be stored and information shall be
given to that effect to the driver by lighting up a malfunction
indicator light. A threshold frequency of misfires in such a case
must be determined taking into consideration a frequency
detrimental to the exhaust gas (frequency of misfires in 1000
rotations of the crankshaft of the engine) and a frequency
detrimental to the catalytic unit (frequency of misfires in 200
rotations of the crankshaft of the engine). The concrete value of
the threshold frequency of misfires is dependent on the type of the
vehicle and the property of the exhaust gas provided by relevant
regulations. For example, about 2% of a low frequency of misfires
must be sensed, which corresponds to 80 misfires per 1000 rotations
of the crankshaft of an 8-cylinder engine. Suppose that misfires
occur in such a frequency in one cylinder, a malfunction indicator
light must be turned on if the frequency of misfires in 500
ignition cycles is eighty. The upper limit of an operating range in
which misfires must be detected was raised from an upper limit on
the order of 3000 rpm to the maximum engine speed on the order of
6000 rpm. The regulations require the detection of misfires in a
wide range of a no-load condition to a full-load condition.
[0004] The following prior arts are available for detecting
misfires in engines.
[0005] Disclosed in Japanese Patent Laid-open No. 4-19344 is an
apparatus which detects abnormal combustion on the basis of the
magnitudes of components for frequencies determined through the
frequency analysis of engine speed information.
[0006] Disclosed in Japanese Patent Laid-open No. 6-58196 is an
apparatus for detecting misfires and judging cylinders in which
misfires occurred, in which the apparatus comprises a torque
measuring means for measuring the instantaneous magnitude of the
output torque of an engine, a specific frequency component
extracting means for extracting a predetermined specific frequency
component from the measured output torque measured by the torque
measuring means, a misfire pattern judging means for judging if any
misfire occurred in a cylinder on the basis of the specific
frequency component and judging a misfire pattern if a misfire
occurred, a storage means for storing data representing the
relation between a misfired cylinder and the phase shift of the
specific frequency component for each misfire pattern, and a
misfired cylinder judging means for judging a misfired cylinder by
comparing the phase shift of the specific frequency component and a
phase shift stored in the storage means according to the judged
misfire pattern.
[0007] Disclosed in Japanese Patent Laid-open No. 6-26996 is a
technique for judging a combustion state from the variation of
rotating speed. This known technique in order to eliminate the
error factor due to the error caused by the measuring system,
measures a time necessary for the crankshaft to turn through a
predetermined angle, extracts a characteristic component from
values of combustion state parameter measured every one or more
rotations, calculates a combustion state parameter by using the
extracted characteristic component or on the basis of an extracted
characteristic component extracted from a value for the necessary
time in one or a plurality of rotations, and judges the combustion
state of each cylinder on the basis of the combustion state
parameter.
[0008] Japanese Patent Laid-open No. 4-19344 discusses misfire
detection when misfires occur successively (every ignition cycle),
but does not discuss the detection of misfires that occur at a low
frequency necessary to meet the above-mentioned regulations. Since
the two-rotation period component of the output of the rotation
signal output means (a component of a frequency equal to a quarter
of a frequency fTDC corresponding to the ignition period of a
specific cylinder in Japanese Patent Laid-open No. 4-19344, which
is equal to two-rotation period component for two rotations of the
crankshaft of the engine) or a component of a period equal to a
integral multiple of period (a frequency of fTDC/4m, m is a natural
number) is extracted in a fixed period, the extraction frequency
varies according to the engine speed. Therefore, the power of a
frequency component extracted while the engine speed is momentarily
varying disperses on frequency basis and hence the accuracy in
misfire detection is reduced. Since a frequency analysis window
(sampling frequency) must be longer than the period of a component
to be extracted, sampling must be repeated many times. The period
of rotation is especially long while the engine speed is low and
hence the frequency analysis window must be of a long time. The
period of rotation is short while the engine speed is high, the
frequency analysis window is, for example, for at least several
tens rotations. Therefore, if misfires occur at a low frequency,
the frequency component produced by misfires is small and it is
difficult to discriminate between misfiring and normal firing.
Since specific frequency components must be extracted from many
sampled data, load on the arithmetic unit increases and a special,
expensive CPU or the like will be necessary.
[0009] Japanese Patent Laid-open No. 6-58196 discusses cases where
a specific cylinder misfires every ignition cycle, but nothing is
taken into consideration about the detection of misfires that occur
at a low frequency necessary to meet the above-mentioned
regulations. Also, expensive torque measuring means is required.
Periodic extraction of rotation 1/2-order and 1-order components
from the output signal of the torque sensor entails the
above-mentioned technical problems.
[0010] A combustion state detecting technique based on rotating
speed information does not need any expensive sensor and is
prevalently used for detecting the combustion state of automobile
engines. However, it is difficult to detect the combustion state of
an engine having a large number of cylinders or a large rotative
inertia in a high accuracy because the engine speed varies scarcely
when a misfire occurs while the engine is operating at a high
engine speed under a low load.
[0011] Experiments proved that it is difficult to achieve accurate
misfire detection by a prior art proposed by the applicant of the
present patent application in Japanese Patent Laid-open No. 6-26996
when an 8-cylinder engine is operating at 6000 rpm under a low
load.
[0012] It is an object of the present invention to provide a
low-cost combustion state diagnosing system and a combustion state
diagnosing method capable of accurately detecting misfires which
occur at a low frequency while a multiple-cylinder engine is
operating at a high engine speed under a low load.
SUMMARY OF THE INVENTION
[0013] The object can be achieved, when diagnosing combustion
state, by extracting specific rotation period component of a period
synchronous with rotation from a combustion state parameter for at
least two rotations, and judging combustion state on the basis of
the extracted specific rotation period component. The combustion
state parameter may be the engine speed or the output torque of a
multiple-cylinder engine which varies according to the combustion
state of the engine. More concretely, the present invention solves
the foregoing problem by the following system.
[0014] A combustion state diagnosing system for diagnosing the
combustion state of a multiple-cylinder engine by measuring a
parameter of combustion state varying according to the combustion
state of the engine, such as engine speed or output torque,
diagnosing combustion state on the basis of the parameter of the
combustion state, comprises: a combustion state parameter measuring
means which measures a parameter of the combustion state N times
(at least once) in one ignition cycle of the multiple-cylinder
engine at times corresponding to a predetermined crank angle; a
specific rotation period component extracting means for extracting
a specific rotation period component of a period synchronous with
rotation of a crankshaft from values of the parameter of the
combustion state measured by the combustion state parameter
measuring means at least in two rotations of a crankshaft; and a
combustion state judging means for judging the combustion state on
the basis of the specific rotation period component extracted by
the specific rotation period component extracting means.
[0015] In the combustion state diagnosing system, the combustion
state parameter measuring means may measure necessary times T(i)
each necessary for the crankshaft to turn through an angle between
predetermined crank angles N times every ignition cycle of the
engine, and the specific rotation period component extracting means
may be provided with a high-pass filter means which filters out
low-frequency components of the necessary times T(i) to calculate
filtered necessary times Tf(i) to extract specific rotation period
components of a period synchronous with the rotation of the
crankshaft from the necessary times Tf(i).
[0016] In the combustion state diagnosing system, the high-pass
filter means may filter out the components of periods longer than a
time necessary for two rotations of the crankshaft of the
engine.
[0017] In the combustion state diagnosing system, the high-pass
filter means may calculate the difference [T(i)-T(i-N)] from the
necessary times T(i) corresponding to the cylinders successive in
ignition order to use the same as the filtered necessary time
Tf(i).
[0018] In the combustion state diagnosing system, the measured
varying values of torque may be used directly as those of the
combustion state parameter.
[0019] In the combustion state diagnosing system, the specific
rotation period component extracting means may be provided with an
arithmetic means which extracts specific rotation period component
which is a variable component of X (=Tf) of a period synchronous
with the rotation of the crankshaft from the sum of the products of
values of the combustion state parameter for at least two rotations
of the crankshaft or Tf (=X), i.e., X(i), X(i-1), . . . , X(i-c+1),
where c is not less than the product of N and the number of
cylinders of the engine, and at least two sets each of c pieces of
weighting coefficients.
[0020] In the combustion state diagnosing system, the weighting
coefficients may be set so as to extract a two-rotation period
components of a period synchronous with two rotations of the
crankshaft of the engine.
[0021] In the combustion state diagnosing system, the specific
rotation period component extracting means may extract components
synchronous with two rotations of the crankshaft of the engine. A
one-rotation period component may be used.
[0022] In the combustion state diagnosing system, the specific
rotation period component extracting means may extract components
synchronous with one rotation of the crankshaft of the engine.
[0023] In the combustion state diagnosing system, the combustion
state judging means may count the frequency of successive values of
the specific rotation period component exceeding a predetermined
value, may judge that a misfire occurred every ignition cycle if
the count of the frequency is greater than a predetermined number,
and may judge that a misfire occurred at intervals if the count of
the frequency is not greater than the predetermined value.
[0024] In the combustion state diagnosing system, the specific
rotation period component extracting means may include a phase
calculating means for calculating the phase of the specific
rotation period component, and the combustion state judging means
may include a misfiring cylinder identifying means for finding the
number of misfiring cylinders and/or misfiring cylinders on the
basis of at least the phase of the specific rotation period
component.
[0025] In the combustion state diagnosing system, the combustion
state judging means may specify a pattern indicating a maximum from
the sum of the products of a plurality of values of the combustion
state parameters or Tf (=X), i.e., X(i), X(i-1), . . . , X(i-d+1),
where d is a constant, and d pieces of weighting coefficients for a
plurality of predetermined patterns when it is judged that a
misfire occurred, and may identify a misfiring cylinder on the
basis of the maximum and the specified pattern.
[0026] Preferably, the combustion state diagnosing system further
comprises a misfire counting means for counting the frequency of
judgements that a misfire occurred made by the combustion state
judging means in a predetermined period, and an alarm means for
giving an alarm to the driver when the frequency exceeds a
predetermined number and/or a misfire information storage means for
storing misfire information.
[0027] The present invention provides an engine combustion state
diagnosing program storage medium storing a program for measuring a
combustion state parameter varying according to the combustion
state of a multiple-cylinder engine, such as engine speed at which
the multiple-cylinder engine is operating or output torque of the
multiple-cylinder engine and judging the combustion state on the
basis of the combustion state parameter; in which the program
specifies measuring the combustion state parameter N times (at
least once) in one ignition cycle of each cylinder at a
predetermined crank angle, extracting a specific rotation period
component of a period synchronous with rotation from at least the
two values of the combustion state parameter, and judging the
combustion state on the basis of the extracted specific rotation
period component.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] [FIG. 1]
[0029] FIG. 1 is a block diagram of a combustion state diagnosing
system in a preferred embodiment according to the present
invention.
[0030] [FIG. 2]
[0031] FIG. 2 is a block diagram of an arithmetic circuit.
[0032] [FIG. 3]
[0033] FIG. 3 is a timing diagram showing signals.
[0034] [FIG. 4]
[0035] FIG. 4 is a diagrammatic view of assistance in explaining an
engine speed measuring section.
[0036] [FIG. 5]
[0037] FIG. 5 is a block diagram of assistance in explaining the
functions of a preferred embodiment according to the present
invention.
[0038] [FIG. 6]
[0039] FIG. 6 is a flow chart of a procedure in a preferred
embodiment according to the present invention.
[0040] [FIG. 7]
[0041] FIG. 7 is a graph showing the magnitudes of various rotation
period components.
[0042] [FIG. 8]
[0043] FIG. 8 is table of misfiring patterns.
[0044] [FIG. 9]
[0045] FIG. 9 is a diagrammatic view of assistance in explaining
weighting coefficients.
[0046] [FIG. 10]
[0047] FIG. 10 is a diagrammatic view of assistance in explaining
weighting coefficients.
[0048] [FIG. 11]
[0049] FIG. 11 is a diagrammatic view of assistance in explaining
weighting coefficients.
[0050] [FIG. 12]
[0051] FIG. 12 is a diagrammatic view of assistance in explaining
weighting coefficients.
[0052] [FIG. 13]
[0053] FIG. 13 is a diagrammatic view of assistance in explaining
the behavior of specific rotation period components when a misfire
occurred.
[0054] [FIG. 14]
[0055] FIG. 14 is a diagrammatic view of assistance in explaining
the behavior of specific rotation period components when a misfire
occurred.
[0056] [FIG. 15]
[0057] FIG. 15 is a diagrammatic view of assistance in explaining
the behavior of specific rotation period components when a misfire
occurred.
[0058] [FIG. 16]
[0059] FIG. 16 is a diagrammatic view of assistance in explaining
the behavior of specific rotation period components when a misfire
occurred.
[0060] [FIG. 17]
[0061] FIG. 17 is a diagrammatic view of assistance in explaining
the behavior of two-rotation period component when a misfire
occurred.
[0062] [FIG. 18]
[0063] FIG. 18 is a diagrammatic view of assistance in explaining
the behavior of specific rotation period components and such.
[0064] [FIG. 19]
[0065] FIG. 19 is a diagrammatic view of assistance in explaining
the behavior of two-rotation period component when a misfire
occurred.
[0066] [FIG. 20]
[0067] FIG. 20 is a diagrammatic view of assistance in explaining
the behavior of two-rotation period component when a misfire
occurred.
[0068] [FIG. 21]
[0069] FIG. 21 is a diagrammatic view of assistance in explaining
Tf and such.
[0070] [FIG. 22]
[0071] FIG. 22 is a diagrammatic view of assistance in explaining
the behavior of two-rotation period component when a misfire
occurred.
[0072] [FIG. 23]
[0073] FIG. 23 is a diagrammatic view of assistance in explaining
the behavior of a specific rotation period component when a misfire
occurred.
[0074] [FIG. 24]
[0075] FIG. 24 is a graph of assistance in explaining a misfired
cylinder identifying method.
[0076] [FIG. 25]
[0077] FIG. 25 is part of a flow chart of a procedure in another
embodiment according to the present invention.
[0078] [FIG. 26]
[0079] FIG. 26 is a diagrammatic view of assistance in explaining a
method of interrupting diagnosis.
[0080] [FIG. 27]
[0081] FIG. 27 is a diagram showing the behavior of Tf, by way of
example, when the engine undergoes disturbance.
[0082] [FIG. 28]
[0083] FIG. 28 is a flow chart of a procedure in a further
embodiment according to the present invention.
[0084] [Reference Characters]
DESCRIPTION FO THE PREFERRED EMBODIMENTS
[0085] Preferred embodiments of the present invention will be
described hereinafter with reference to the accompanying
drawings.
[0086] FIG. 1 is a block diagram of a combustion state diagnosing
system in a preferred embodiment according to the present invention
for diagnosing the combustion state of an engine. An engine 1 is
provided with a position sensor 5 for measuring crank angle, a
phase sensor 3 for finding a reference position. In this
embodiment, the position sensor 5 detects electromagnetically the
teeth of a ring gear 4 included in an engine starting mechanism for
starting the engine 1, and provides a number of signals equal to
that of the teeth of the ring gear 4 every rotation of a crankshaft
7. A reference sensor 6 detects electromagnetically a projection 4a
formed on the ring gear 4 to provide a signal indicating a specific
crank angle once every one rotation of the crankshaft 7. The phase
sensor 3 which generates a signal for identifying cylinders once
every two rotations of the crankshaft 7 is combined with a cam
shaft 2. The present invention may be provided with sensors other
than those sensors. Detection signals provided by the sensors 3, 5
and 6 are given to an arithmetic circuit 8, and the arithmetic
circuit 8 calculates a crank angle, an engine speed and such. In
FIG. 1, indicated at 9 are pistons, at 10 are connecting rods
connecting the pistons 9 to the crankshaft 7.
[0087] The oxygen concentration of the exhaust gas flowing through
an exhaust pipe 11 is measured by an oxygen concentration sensor
12, and the exhaust gas is purified by a catalytic unit 13. If a
misfire occurs, unburned gases are discharged from the engine 1
into the exhaust pipe 11 and burn in the catalytic unit 13.
Consequently, the catalytic unit 13 is heated at an abnormally high
temperature, the catalyst of the catalytic unit 13 is deteriorated,
and the unburned gases are discharged into the atmosphere to cause
air pollution. In the nature of things various injurious gases
cannot be removed from the exhaust gas and cause air pollution if
the catalyst of the catalytic unit 13 is deteriorated even if
misfires do not occur.
[0088] FIG. 2 is a block diagram of an arithmetic circuit 8 shown
in FIG. 1. An output signal 3a of the phase sensor 3, an output
signal 5a of the position sensor 5, an output signal 6a of the
reference sensor 6, and respective output signals of an air flow
sensor, not shown, and a water temperature sensor, not shown, are
given to the arithmetic circuit 8. Ignition, fuel supply and such
are controlled according to a control program stored in a ROM 11 on
the basis of those output signals of the sensors.
[0089] FIG. 3 is a timing diagram of signals for an eight cylinder
engine. FIG. 3 shows the waveform of the output signal 3a of the
phase sensor 3 shaped by a waveform shaping circuit, not shown, and
the output signal 3a has one pulse every two rotations of the
crankshaft 7. The output signal 3a has a pulse provided at time
corresponding to, for example, time when the piston of the first
cylinder is at the combustion top dead center. FIG. 3 shows the
waveform of the output signal 6a of the reference sensor 6 shaped
by a waveform shaping circuit, not shown. The output signal 6a has
one pulse every one rotation of the crankshaft 7 and the pulse is
provided at time corresponding to, for example, when the piston of
first cylinder is at the top dead center. FIG. 3 shows the waveform
of the output signal 5a of the position sensor 5 shaped by a
waveform shaping circuit, not shown. The output signal 5a has
pulses provided at times corresponding to fixed crank angles
corresponding to the teeth of the ring gear 4.
[0090] A curve 14 indicates the variation of the count of the
pulses of the signal 5a with time. The count indicated by the curve
14 is reset when the AND signal between the signals 3a and 6a is
true. A crank angle with reference to, for example, the combustion
top dead center of the piston of the first cylinder can be known
from the count indicated by the curve 14. A curve 15 represents a
signal indicating engine speed measuring sections, and, on the
basis of the counted value 14, has pulses each corresponding to an
angular range around a crank angle corresponding to the combustion
top dead center of the piston of each cylinder. In this example,
the ignition order is the first, the second, the third, . . . and
the eighth cylinder. Engine speed measuring sections corresponding
to the cylinders are designated by the numbers of the cylinders.
Time T necessary for the crankshaft 7 to rotate through the engine
speed measuring section is measured by a timer. A curve 16
represents the operation of the timer. The time T is stored
temporarily in a RAM or the like before the same is applied to a
processing routine. Although dependent on the variation of the
engine speed when a misfire occurs, the resolution of the time is 1
.mu.s at most, preferably, in the range of 0.05 to 0.2 .mu.s. The
time T may be measured by any other suitable method provided that a
time necessary for the crankshaft 7 to turn through a predetermined
angle can be measured.
[0091] FIG. 4 is a diagram of assistance in explaining the engine
speed measuring section. Suppose that a misfire occurred in the
second cylinder, a drop in the engine speed increases to a maximum
at time when the piston of the third cylinder is near the
combustion top dead center. Each of the engine speed measuring
sections (the curve 15) corresponds to, for example, an angular
range Wn from a crank angle Wsn with respect to the combustion top
dead center of the piston of each cylinder, where n=1, 2, . . . or
8. To facilitate calculation, it is desirable that all the angular
ranges Wn (n=1, 2, 3, . . . and 8) are equal. It is preferable that
WS1=WS5, W1=W5, . . . , and WS4=WS8 and W4=W8 to eliminate the
influence of pitch errors in the ring gear 4. Thus the same engine
speed measuring sections are used every rotation of the crankshaft
7. It is preferable that all the angular ranges Wn are a fixed
value; otherwise the following normalizing process must be carried
out before a filtering process using a high-pass filter.
T'=T.times.W/Wn
[0092] where T' corresponds to a necessary time for turning through
the engine speed measuring section of the width W.
[0093] Although one engine speed measuring section is determined
for each cylinder, two engine speed measuring sections may be
determined for each cylinder. Although operations necessary for the
arithmetic process increases if the number of engine speed
measuring sections increases, the influence of pitch errors in the
ring gear 4 is reduced and accuracy in misfire detection is
improved. The position and the width of the engine speed measuring
section are not limited to those employed in this embodiment.
[0094] FIG. 5 is a block diagram showing the functions of the
embodiment. A necessary time measuring unit 16 measures the
necessary time T necessary for the crankshaft to turn through a
predetermined angle for each cylinder. A high-pass filter unit 17
filters out low-frequency components of the necessary time T to
calculate a filtered necessary time Tf. A specific rotation period
component extracting unit 19 extracts a specific rotation period
component of a period synchronous with rotation of the crankshaft
from the filtered necessary times Tf for two rotations. A
combustion state judging unit 20 judges a combustion state on the
basis of the specific rotation period component extracted by the
specific rotation period component extracting unit 19.
[0095] FIG. 6 is a flow chart of a procedure to be carried out by
the embodiment of the present invention. This procedure uses a
recording medium storing a program specifying operations for
measuring the value of a combustion parameter which varies
according to the combustion state of the engine, and judging a
combustion state on the basis of the combustion parameter. For
example, the procedure shown in FIG. 6 is started every time the
necessary time is measured. It is to be noted that the following
processes are executed in synchronism with ignition cycles. Thus a
specific rotation period component synchronous with the rotation
can be easily extracted.
[0096] In step S1, a measured necessary time T is read. This step
is executed every time a necessary time T is measured. Therefore,
if N necessary time measuring sections are set for each cylinder,
the step is executed for each necessary time measuring section.
[0097] Then step S2 is executed. Basically, above processes may be
executed once every ignition cycle.
[0098] The accuracy of misfire detection is affected by pitch
errors in the ring gear 4 if one-rotation period component is used.
The necessary time T is subjected to pitch error correction in step
S2. As mentioned in, for example, Japanese Patent Laid-open No.
5-332189, pitch error correction is achieved by measuring the
necessary time T during operation under a specific operating
condition, such as during fuel cut control, errors in the width of
each desired time measuring section are determined to learn a
correction coefficient. The necessary time T is multiplied by the
correction coefficient for the necessary time measuring section
corresponding to the necessary time T to correct errors
attributable to the pitch errors.
[0099] In step S3, low-frequency components of the necessary time T
are filtered out to calculate a filtered necessary time Tf. The
filtered necessary time Tf is calculated by using the following
expressions.
Tf(n)=T(n)-T(n-1) (1)
Tf(n)=T(n)-T(n-1)/Tn.sup.3 (2)
[0100] where n is the number of the cylinder.
[0101] Expression (1) expresses the function of a most simple
differentiation filter for removing low-frequency components. The
variation of the filtered necessary time Tf calculated by using
Expression (1) due to a misfire is greatly dependent on the engine
speed and hence it is preferable to use Expression (2). If the
filtered necessary time Tf is calculated by using Expression (2),
the variation of the filtered necessary time Tf due to a misfire is
not dependent on the engine speed (inversely proportional to T) and
is substantially proportional to load on the engine (output
torque).
[0102] It is essential to remove low-frequency components of
periods not smaller than an analysis window (the number of sampling
operations) for extracting specific rotation period components. For
example, the moderate variation of the engine speed during
acceleration or deceleration causes errors when extracting specific
rotation period components and, therefore, such low-frequency
components must be removed. Therefore, the low-frequency components
may be removed by means other than the foregoing high-pass
filter.
[0103] The analysis window can be narrowed without increasing
errors if such low-frequency components are removed, and hence
misfires that occur at a low frequency can be detected.
[0104] The filtered necessary times Tf for two rotations, i.e., for
eight ignition cycles, are stored in step S4.
[0105] Specific rotation period components are extracted from the
filtered necessary times Tf in step S5.
[0106] Kinds of specific rotation period components to be extracted
will be explained. FIG. 7 shows the magnitudes of rotation period
components when a misfire occurred repeatedly in each of various
misfiring patterns. Misfiring patterns designated by misfiring
pattern numbers are shown in FIG. 8. All the components are zero in
the not misfiring state as pattern No. 1. If misfires occur, the
magnitudes of the rotation period components correspond to a value
corresponding to the number of the cylinders in which misfires
occurred. The misfiring pattern No. 2 is for the specific rotation
period components when a misfire occurred in one cylinder, the
misfiring patterns Nos. 3 to 6 are for the specific rotation period
components when misfires occurred in two cylinders, and misfiring
patterns Nos. 7 to 13 are for the specific rotation period
components when misfires occurred in three cylinders. The
distribution of the components is dependent on misfiring pattern.
Basically, this embodiment extracts two-rotation period components,
and one-rotation period components as auxiliary components for the
following reasons. One of the reasons for extracting two-rotation
period components and one-rotation period components is that
extraction is hardly subject to the influence of measuring errors
in the necessary time T due to the width of the necessary time
measuring section. The width of the necessary time measuring
section is affected directly by pitch errors in the ring gear 4. As
mentioned above, errors in T and Tf attributable to pitch errors in
the ring gear 4 include only components of periods shorter than the
one rotation period if the same engine speed measuring section is
used every rotation; that is, the two-rotation period components
are not affected by pitch errors in the ring gear 4. Variation of
the engine speed due to differences in mass between operating
members, such as the pistons of the engine includes only components
of periods shorter than that of the one-rotation period components.
Thus, the two-rotation period components are hardly subject to the
influence of various errors. Although the one-rotation period
components are subject to the influence of the errors, the same are
less susceptible to the errors than the 2/3-rotation period
components and 1/2-rotation period components. As shown in FIG. 7,
it is difficult to discriminate the misfiring patterns Nos. 6 to 13
in which misfires occur every rotation from a normal pattern by the
two-rotation period components. Therefore one-rotation period
components different from normal components in such misfiring
patterns are selected.
[0107] The specific rotation period components for the 8-cylinder
engine are calculated by using the following expressions. 1 P
.times. r ( n ) = = 0 7 Tf ( n - k ) .times. W .times. r ( k ) P
.times. i ( n ) = = 0 7 Tf ( n - k ) .times. W .times. i ( k ) P
.times. ( n ) = P .times. r ( n ) 2 + P .times. i ( n ) 2 ( 3 )
[0108] P.times.r and P.times.i are the real parts and the imaginary
parts of the x-rotation period components, and P.times. is the sum
of squares of the real parts and the imaginary parts signifying the
power of the x-rotation period components.
[0109] W.times.r and W.times.i are weighting coefficients for
extracting the real parts and the imaginary parts of the x-rotation
period components. FIGS. 9 and 10 show weighting coefficients for
extracting one-rotation period components and two-rotation
components, respectively. These weighting coefficients are
determined on the basis of the position of the necessary time
measuring section. The extraction of the specific rotation period
components is achieved by using Expression (3) and two rotations
(eight data) as an analysis window, and by shifting the window by
one step corresponding to one data every ignition cycle.
[0110] If N necessary time measuring sections are set for all the
cylinders, weighting coefficients respectively for those necessary
time measuring sections are necessary. If N=2, the following
expression is used for calculating specific rotation period
components. 2 P .times. r ( n ) = = 0 15 Tf ( n - k ) .times. W
.times. r ( k ) P .times. i ( n ) = = 0 15 Tf ( n - k ) .times. W
.times. i ( k ) P .times. ( n ) = P .times. r ( n ) 2 + P .times. r
( n ) 2 ( 4 )
[0111] FIGS. 11 and 12 show weighting coefficients for extracting
one-rotation period components and two-rotation period components,
respectively. The weighting coefficients are determined on the
basis of the position of the necessary time measuring section. The
weighting coefficients shown in FIGS. 11 and 12 applied to a case
where the necessary time measuring sections are arranged at equal
intervals.
[0112] The specific rotation period component extracting unit 19 is
provided with an arithmetic device which extracts the specific
rotation period components, i.e., variable components of Tf, i.e.,
X, of a period synchronous with rotation from the sum of the
products of the combustion parameter for two rotations or Tf (X),
i.e., X(i), X(i-1), . . . and X(i-c+1), where c is greater than or
equal to the product of N and at least two predetermined sets each
of C pieces of weighting coefficient. For example, the weighting
coefficients are determined so as to extract one-rotation period
components of a period synchronous with one rotation and
two-rotation period components of a period synchronous with two
rotations of the crankshaft.
[0113] The number of Tf corresponding to two rotations (8.times.N
for 8-cylinder engine) is used for extracting the specific rotation
period components of Tf because the number is the least necessary
number for extracting two-rotation period components. Although the
number of Tf may be greater than that corresponding to two
rotations, frequent misfiring and each-ignition-cycle misfiring
differ from each other in the magnitude of the specific rotation
period components and different thresholds may be necessary. Since
any decision need not be made by using two rotations as a unit to
cancel out the pitch errors, load on calculation will be doubled,
tripled, . . . if two rotations, four rotations, six rotations, . .
. are used. Accordingly, it is most preferable that the number of
Tf for extracting the specific rotation period components of Tf
corresponds to two rotations.
[0114] FIGS. 13 and 14 show Tf in cases where one of the cylinders
is misfiring (the misfiring pattern No. 2) every ignition cycle and
at a low frequency, and the modes of behavior of power P1 for one
rotation period components and power P2 for tow rotation period
components. If a misfire occurs every ignition cycle, P1 and P2
remain substantially constant regardless of misfiring pattern. If
misfires occur at a low frequency, P1 and P2 increase temporarily
and returns to the former levels for normal combustion pattern
after eight combustion cycles. If misfires occur at a low
frequency, the behavior of P1 and P2 assume greatly different modes
for different misfiring patterns. FIGS. 15 and 16 show Tf and the
modes of behavior of P1 and P2 for the misfiring patterns Nos. 4
and 6, respectively. It is to be noted that there is little
difference between P2 for the normal combustion pattern and P2 for
the misfiring pattern No. 6 when the engine misfires in a regular
misfiring mode in which a misfire occurs every ignition cycle, and
there is a significant difference between P2 for the normal
combustion pattern and P2 for the misfiring pattern No. 6 when the
engine misfires in a low-frequency misfiring mode in which misfires
occur at a low frequency.
[0115] In step S6, a query is made to see if diagnostic conditions
necessary for the proper diagnosis of combustion state are
fulfilled. If the response in step S6 is affirmative, step S7 is
executed. If the response in step S6 is negative, the procedure is
ended without judging any combustion state. The diagnostic
conditions include the sensors including the reference sensor 6
being functional, the fuel cut control is not in operation, and the
engine speed is in a predetermined engine speed range and neither
excessively high nor excessively low. A transient state where the
operation of the engine changes sharply, such as a state in which
the engine is sharply accelerated or decelerate or the transmission
is shifted, or the vehicle is traveling on a rough road, the engine
speed varies and it is possible that the engine is misfiring even
if the engine is in the normal combustion state. Therefore, it is
preferable to exclude such a state from the diagnostic
conditions.
[0116] In step S7, the combustion state is judged on the basis of
the specific rotation period components.
[0117] Condition (A) that the two-rotation period component P2 is
not smaller than a predetermined threshold KL2 and, if the learning
of the pitch errors in the ring gear has been completed, a
condition (B) that the one-rotation period component P1 is not
smaller than a predetermined threshold KL1 are examined. If either
the condition (A) or (B) is fulfilled, it is judged that the engine
is misfiring and then step S8 is executed. If neither the condition
(A) nor (B) is fulfilled, it is judged that the engine is not
misfiring and it is judged that the engine is operating in the
normal combustion state in step S9. If either the condition (A) or
(B) is fulfilled in the preceding diagnosing cycle and neither the
condition (A) nor (B) is fulfilled in the succeeding diagnosing
cycle, step S8 is executed.
[0118] In step S8, the number of successive diagnosing cycles in
which either the condition (A) or (B) is fulfilled is examined. If
the number is greater than a predetermined number, for example
sixteen, it is judged that the engine is misfiring every ignition
cycle and step S10 is executed. If a state in which the number of
successive diagnosing cycles in which either the condition (A) or
(B) is fulfilled is below the predetermined number is followed by a
state in which neither the condition (A) nor (B) is fulfilled, it
is judged that misfires are occurring at a low frequency and step
S11 is executed. The procedure advances from step S10 to step S12
to identify cylinders misfiring every ignition cycle, and then the
respective counts of a misfire counter for the relevant cylinder
and a total misfire counter are incremented.
[0119] In step S14, a query is made to see if the plurality of
cylinders misfired. A method of determining whether or not the
plurality of cylinders misfired will be described by way of
example. FIG. 17 shows the behavior of P2r and P2i when a specific
cylinder misfired only once. A point moves along a path
substantially resembling a circle of a fixed radius in steps of
45.degree. starting from a position (1) through positions (2), (3),
. . . and (8). An angle between an axis P2r and a vector (P2r, P2i)
is A.sub.base. The behavior of the one-rotation period component P1
is different and a point revolves two times in steps of about
90.degree.. FIG. 18 shows the same case as that shown in FIG. 17.
In FIG. 18, ignition cycles are plotted on the horizontal axis. If
a counter CYLCNT which counts 0 to 7 for the first to the eighth
cylinder every ignition cycle is used, and:
A=A.sub.base-CYLCNT.times.45 (5)
[0120] the value of A is substantially constant. In the normal
combustion state, P2 is approximately 0, the calculation of A and
A.sub.base is insignificant and hence A and A.sub.base are not
calculated. FIG. 19 shows the behavior of and A when each of the
first, the second and the third cylinder misfires once on a polar
coordinate system. A point lies near the origin in the normal
combustion state. Point appears eight times at an angular position
dependent on the number of the cylinder outside the threshold KL2,
and returns to the origin when a misfire occurs. Suppose that the
difference between the maximum and the minimum of A is DA when the
value increases beyond the threshold KL2 due to a misfire. Then,
the difference DA is substantially 0 in this case. FIG. 20 shows
some examples of the behavior of P2 and A on a polar coordinate
system when each of the plurality of cylinders misfires once. For
example, if the first and the second cylinder misfire, a point
appears once at a position for first cylinder misfiring shown in
FIG. 19, seven times at a position for the vector sum of first
cylinder misfiring and second cylinder misfiring (more precisely, a
position substantially corresponding to the vector sum when the
behavior of {square root}P2 and A is shown on a polar coordinate
system), and a point appears once at a position for second cylinder
misfire shown in FIG. 19. This behavior is greatly dependent on the
pattern of misfiring. In this case, the difference DA is defined as
mentioned above. When the plurality cylinders misfire, the
difference DA is far greater than 45.degree.. Accordingly, the
procedure advances to step S16 if DA is not smaller than, for
example, 25.degree. and it is judged that the plurality of
cylinders misfired, or the procedure advances to step S15 and it is
judged that one of the cylinders misfired.
[0121] Then, the procedure advances from step S15 to step S17 to
identify the misfired cylinder. For example, since the different
misfired cylinders have different values of A as shown in FIG. 19,
the mean of the values of A is calculated, and it is judged that
the first cylinder misfired if the mean is in the range of
0.degree..+-.22.5.degree., the second cylinder misfired if the mean
is in the range of -45.degree..+-.22.5.degree., . . . . After
judging the misfired cylinder, the respective counts of a misfire
counter for the relevant cylinder and the total misfire counter are
incremented.
[0122] The procedure advances from step S16 to step S19 to identify
the misfired cylinder. For example, the first and the last misfired
cylinder can be identified by the values of A as sown in FIG. 20.
Although it is impossible to identify the misfired cylinders, the
number of the misfired cylinders (the frequency of misfires) can be
found from the frequency of changes of the point A (twice if the
two cylinders misfired and three times if the three cylinders
misfired). If the number of times of existence of point at the
position every change of A is used, the intermediate misfired
cylinders can be identified. For example, if the first and the
third cylinder misfire, the point appears twice at the initial
position. Therefore it is judged that the first cylinder
(A.apprxeq.0) and the cylinder in which ignition occurred two
ignition cycles later, namely, the third cylinder, misfired. If the
first and the fourth cylinder misfired, a point appears three times
at the initial position. Therefore it is judged that the first
cylinder (A.apprxeq.0) and the cylinder in which ignition occurred
three ignition cycles later, namely, the third cylinder,
misfired.
[0123] After the decision has been made, the count of the total
misfire counter is incremented by the number of the misfired
cylinders (the number of misfires), and the count of a counter for
the relevant cylinder is incremented in step S20.
[0124] In step S21, the count of the total misfire counter is
checked, for example, every 1000 rotations of the crankshaft (4000
ignition cycles). If the count is not smaller than a threshold CR,
step S22 is executed to give a warning to the driver, and
information about misfiring including the numbers of the misfired
cylinders, the operating condition of the engine when a decision is
made that the engine is misfiring and the mode of misfiring
(regular misfiring mode or low-frequency misfiring mode), and then
the procedure is ended. When the count of the total misfire counter
is less than the threshold CR, the procedure is ended.
[0125] A method of identifying the misfiring cylinders when the
engine is operating in the regular misfiring mode in an embodiment
will be described hereinafter. If Tf exceeds a threshold TfSL1 as
shown in FIG. 21, it is judged that the cylinder is misfiring, and
the misfired cylinder is identified by CYLCNT. The number of the
identified misfired cylinders is regarded as the number of
misfires. This misfired cylinder identifying operation is executed
every two rotations of the crankshaft (eight ignition cycles). The
threshold TfSL1 is determined on the basis of engine speed and
load. Since the threshold TfSL1 is not greatly dependent on engine
speed, the threshold TfSL1 may be determined on the basis of only
load. Since this operation is susceptible to the pitch errors in
the ring gear when engine speed is high, the method is carried out
after the completion of leering the pitch errors or TfSL1 is
increased by corrections proportional to engine speed until the
learning of the pitch errors is completed. The threshold TfSL1 is
set to a relatively large value even if the learning of the pitch
errors is completed to avoid judging that the normally operating
cylinders are misfiring because the accuracy of misfire detection
is not very high while the engine is operating at a high engine
speed under a low load. If any cylinders exceeding TfSL1 are not
found, it is judged that the number of misfired cylinders (the
number of misfires) is 1 because it has been found that at least
one of the cylinders is misfiring in the regular misfiring mode,
and the misfired cylinder identifying operation is not
executed.
[0126] If the cylinder is misfiring in the regular misfiring mode,
the misfired cylinder is identified, and if misfiring is due to the
malfunction of the ignition system, the unburned fuel is discharged
into the exhaust system, burns in the catalytic unit. Consequently,
the catalytic unit is heated excessively and deteriorated and the
unburned gas is discharged into the atmosphere. Therefore, it is
preferable to stop supplying the fuel to the cylinder misfiring in
the regular misfiring mode. When the engine is operating under a
high load, it is preferable to supply the fuel at an increased rate
to the cylinders not misfiring to reduce the No.sub.x concentration
of the exhaust gas, because only intake air is discharged into the
exhaust system, surplus oxygen is supplied to the catalytic unit to
reduce No.sub.x conversion efficiency if the supply of the fuel to
the misfiring cylinder is stopped and hence it is preferable to
reduce the No.sub.x concentration of the exhaust gas before the
exhaust gas flows into the catalytic unit.
[0127] A method of identifying the cylinder misfiring in the
regular misfiring mode in another embodiment will be described
hereinafter.
[0128] The sum of the 1/2-rotation period component, the
2/3-rotation period component, the one-rotation period component
and the two-rotation period component is equal to a value
corresponding to the number of misfiring cylinders. Therefore, the
sum is compared with a Predetermined threshold to judge the number
of the misfiring cylinders. Since the sum is dependent on engine
speed and load, the threshold is determined on the basis of engine
speed and load. If it is known that one of the cylinders is
misfiring in the regular misfiring mode, the misfiring cylinder is
identified by the phase angle A of P2 because different misfiring
cylinders have different phase angles A of P2, respectively, as
shown in FIG. 22. If it is judged that the two cylinders are
misfiring, the misfiring pattern is judged by comparing P2 with a
predetermined threshold because the different misfiring pattern
Nos. 3 to 6 have different P2, respectively. Since the value of P2
is dependent on engine speed and load, the threshold is determined
on the basis of engine speed and load. Since the different
misfiring cylinders have different phase angles of P1 and P2,
respectively, for each misfiring pattern as shown in FIG. 23, the
misfiring cylinder is identified by the phase angles of P1 and P2
after the misfiring pattern has been judged. If the three or more
cylinders are misfiring, the misfiring cylinders are not identified
and only the number of the misfiring cylinders are judged.
[0129] A method of identifying the misfiring cylinder misfiring in
the regular misfiring mode in a third embodiment will be described
hereinafter. After a decision has been made that some cylinders are
misfiring in the regular misfiring mode, the supply of furl to the
cylinders is stopped for one cylinder at a time and the variation
of P2 and P1 is examined. If P2 and P1 do not vary, it is judged
that the associated cylinder is misfiring.
[0130] The foregoing methods may be used in combination. For
example, the number of the misfiring cylinders may be judged on the
basis of the sum of the 1/2-rotation period component, the
2/3-rotation period component, the one-rotation period component
and the two-rotation period component, the supply of the fuel to
the cylinders which are identified to be misfiring cylinders is
stopped to examine the variation of P2 and P1, and a final decision
that the cylinder is misfiring may be made when P2 and P1 do not
vary or that the cylinder is not misfiring and the former misfiring
cylinder identification may be canceled when P2 and P1 vary.
[0131] A misfiring cylinder identifying method for the
low-frequency misfiring mode (step S19 in FIG. 6) in another
embodiment will be described hereinafter. This method determines
only the number of the misfiring cylinders. FIG. 24 is a graph
showing the relation between the quotient of division of .SIGMA.P2,
i.e., the sum of the values of P2 in the preceding eight ignition
cycles, by load and the phase angle change DA of P2. In FIG. 24,
the range of phase angle change is divided into sections by the
number of the misfiring cylinders (the number of misfires).
Therefore, the number of the misfiring cylinders can be known from
the section in which the chase angle change. As mentioned above, it
is judged that only one of the cylinders is misfiring if DA is less
than, for example 25.degree.. Therefore it is judged that the
plurality of cylinders are misfiring if DA is not smaller than
25.degree., and the number of the misfiring cylinders is judged on
the basis of the region shown in FIG. 24.
[0132] A method of identifying the misfired cylinders in an
embodiment will be described hereinafter. This method is applicable
to either the low-frequency misfiring mode (one of the cylinders is
misfiring or the plurality of cylinders are misfiring) or the
regular misfiring mode. A plurality of weighting coefficients are
determined beforehand for various misfiring patterns as shown in
FIG. 8. For example, the coefficient for the misfiring state is 1
and the coefficient for the normal combustion state is 0 to
facilitate calculations. Then, the coefficient for the misfiring
pattern No. 2 is 1,0,0,0,0,0,0,0, and the coefficient for the
misfiring pattern No. 3 is 1,1,0,0,0,0,0,0. The sum of the products
of the coefficients and Tf(i) are calculated every two rotations of
the crankshaft, and a decision is made that the pattern having the
maximum sum is the actual misfiring pattern. The cylinder having
the coefficient corresponding to 1 is identified to be a misfiring
cylinder. The pattern need not be the two rotations of the
crankshaft and may a pattern for one rotation of the crankshaft,
and the identification of the misfiring cylinders may be identified
every rotation of the crankshaft. Weighting coefficients other than
the foregoing weighting coefficients may be used. The use of
weighting coefficients determined on the basis of data about actual
misfires will improve the identification accuracy. Although this
embodiment was explained as applied to the identification of the
misfired cylinders after misfires have occurred, the method can be
applied to the detection of misfires when combustion state
diagnosis is executed on the basis of torque, in which the
influence of measuring errors is not significant. It is judged that
the engine is in the normal combustion state if all the sums of
products for the patterns are within a predetermined range, and a
decision is made that the pattern having the maximum sum among the
misfiring patterns other than predetermined patterns is the actual
misfiring pattern if all the sums of products for the patterns are
outside the predetermined range.
[0133] Another embodiment will be described. Basically, step S7' of
this embodiment differs from step S7 of the embodiment previously
described with reference to FIG. 6. FIG. 25 shows part of the
embodiment different from that shown in FIG. 6. The following
conditions are used for judging combustion state on the basis of
the specific rotation period components. Queries are mode in step
S7' to see (a) if the two-rotation period component P2 is not
smaller than the predetermined threshold KL2, (b) if the
one-rotation period component P1 is not smaller than the
predetermined threshold KL1 when the engine is operating at a low
engine speed, and (c) if the one-rotation period component P1 is
not smaller than the predetermined threshold KL1 when the learning
of the pitch errors in the ring gear is completed and the engine is
operating at a high engine speed. If the response to any one of the
queries about (a), (b) and (c) is affirmative, it is judged that
the engine is misfiring and the procedure goes to step S8. If the
response to none of the queries about (a), (b) and (c) is
affirmative, it is judged that the engine is not misfiring and the
procedure goes to step S9, in which it is judged that the engine is
operating in the normal combustion mode. Because the influence of
the pitch errors in the ring gear on P1 is insignificant when the
engine speed is low and P1 can be used for making the decision even
if the learning of the pitch errors is not completed. Low engine
speeds are in the range of 2000 to 3000 rpm.
[0134] It is preferable to change the width and the position of the
engine speed measuring section according to the specific rotation
period components to be extracted. For example, the width is
reduced to place importance on the gain for P2 because the
two-rotation period component P2 is not susceptible to the
influence of the pitch errors in the ring gear, and the width is
increased for the one-rotation period component P1 to place
importance on the reduction of errors.
[0135] An embodiment to interrupt diagnosis will be explained
hereinafter. The following method is proposed in addition to the
foregoing diagnostic conditions.
[0136] FIG. 26 is a graph showing the relation between the
frequency of decisions that P2 is greater than the predetermined
threshold made in step S7 of FIG. 6 when misfires occur at a low
frequency, and the phase angle change DA of P2 during that time. In
FIG. 26, numbers are the misfiring pattern numbers shown in FIG. 8.
In an ordinary misfiring mode, points indicating misfiring patterns
are outside a shaded region, and the points often lie in the shaded
region if the engine undergoes disturbance in such a case where the
vehicle travels on a rough road. Therefore, it is judged that
faulty misfire detection is made due to disturbance and the
procedure is interrupted to suspend the diagnosis for a
predetermined time. Points when a misfire occurred shown in FIG. 26
are at positions in an ideal state. Actually, the points are
scattered and an allowance is set so that the points may not lie in
the shaded region when a misfire occurs. The shape of the shaded
region may be determined so that the points may not lie therein
when a misfire occurs and may be other than that shown in FIG.
26.
[0137] Another embodiment to interrupt diagnosis will be explained.
When the engine undergoes disturbance, Tf leans to the negative
side (accelerating side) as shown in FIG. 27. If Tf leans to the
negative side beyond a threshold TfSL2, the diagnostic operation is
interrupted. Basically, Tf leans only to the positive side
(decelerating side) when a misfire occurs and leans scarcely to the
negative side. Accordingly, the absolute value of the threshold
TfSL2 must be greater than that of Tf when a misfire occurs. The
variation of Tf when a misfire occurs is dependent on engine speed
and load, the threshold TfSL2 is determined on the basis of engine
speed and load. Since Tf is not greatly dependent on engine speed,
the threshold TfSL2 may be determined only on the basis of load.
The base phase angle A.sub.base of P2 explained with reference to
FIG. 18 starts from 0.degree. when a misfire occurs, but the same
starts from, for example, -180.degree. when the engine undergoes
disturbance. Therefore, the diagnosis may be interrupted if the
base phase angle A.sub.base is greater than a predetermined angle
than 0.degree..
[0138] The method of diagnosing a combustion state in the foregoing
embodiment diagnosis a combustion state on the basis of engine
speed. A method of diagnosing a combustion state in another
embodiment which diagnosis a combustion state on the basis of
torque will be described hereinafter. The method in this embodiment
is similar to the previously described method in the foregoing
embodiment in many respects and hence only functions of the former
different from the latter will be described. FIG. 28 is a flow
chart of a procedure to be executed by the method in this
embodiment. The procedure is started, similarly to that shown in
FIG. 6, in synchronism with a combustion cycle.
[0139] Torque is measured in step S101. Torque may be an
instantaneous torque measured when the crankshaft is at a
predetermined crank angle, such as a crank angle 30.degree. after
the combustion top dead center, or the mean of torque measured
while the crankshaft turns through an angular range between
predetermined crank angles. Torque may be measured once or N times
every one combustion cycle. In step S102, the specific rotation
period component is extracted. If torque is used as data for
combustion state diagnosis, combustion state diagnosis is not
affected by the pitch errors in the ring gear, and the correction
for the necessary time can be ignored and the measured torque may
be used for directly combustion state diagnosis. The torque is
substantially zero if a misfire occurs and is a positive value
corresponding to the load while the engine is operating in the
normal combustion mode. The torque increases monotonously during
acceleration or decreases monotonously during deceleration. Since
the effect of components of long periods on the torque is
insignificant unless the torque changes sharply, low-frequency
components need not be removed. Naturally, it is preferable to
remove low-frequency components.
[0140] The measured values of torque measured in step S102 while
the crankshaft rotates twice are stored in a storage device, and
the specific rotation period component is extracted in step S103.
If it is judged in step S104 that diagnostic conditions are
fulfilled, the combustion state of the engine is diagnosed on the
basis of the specific rotation period component in step S105. Since
the influence of the pitch errors in the ring gear on the measured
torque is insignificant as mentioned above, the one-rotation period
component may be used without learning the pitch errors.
[0141] The rest of steps of the procedure are the same as those of
the previously described procedure for combustion state diagnosis
based on engine speed. When a misfire occurs, Tf is a positive
value (T increases) and torque decreases. Thus, Tf and torque lean
toward opposite directions, the phase angle A.sub.base of P2 and
the value of A in this procedure are different from those in the
previously described procedure.
[0142] Although the misfire diagnosing methods have been described
as the preferred embodiments of the combustion state diagnosing
method of the present invention, the present invention is not
limited in its practical application to those embodiments. For
example, the threshold employed in judging a combustion state on
the basis of the specific rotation period component may be smaller
than the threshold for judging if a misfire occurred to enable the
decision of a state in which the engine is not misfiring but the
mode of combustion is unsatisfactory.
[0143] Although the foregoing embodiments employ information about
engine speed or torque as a parameter characterizing combustion
state, the parameter need not be limited thereto. For example, the
pressure in the combustion chamber of the engine, the oxygen
concentration of the exhaust gas (output signal of an oxygen
concentration sensor) or the vibration of the engine may be used as
the parameter.
[0144] The combustion state diagnosing system extracts the specific
rotation period component relating to abnormal combustion including
misfiring from the parameter of combustion state, such as
information about the variation of engine speed, and judges a
combustion state on the basis of the extracted specific rotation
period component in a high accuracy.
* * * * *