JPH0642398A - Misfire detecting method for engine - Google Patents

Abstract

PURPOSE:To perform accurate detection of the misfire state of a cylinder with out being influence by the error of a rotation detecting means to detect rotation of an engine. CONSTITUTION:From difference rotation DELNEn between the number MNXn of revolutions of engine corresponding to a #n cylinder and the number of MNXn-1 of revolutions of an engine corresponding to a #n-l cylinder, a weighted means AVEDNnOLD of difference rotation classified by a cylinder obtained through statistical processing of the difference rotation DELNEn is subtracted and calculated as difference rotation DELNAn after correction at S106. By comparing the difference rotation DELNAn after correction with a miss fire decision level LVLMIS set by means of the number NE of revolutions of an engine and a fundamental fuel injection pulse width Tp serving as a parameter at S112, accurate detection of misfire is practicable without being influenced by the position of the protrusions of a crank rotor corresponding to the crank position of an engine, an allowable error in a shape from the viewpoint of manufacture, and an allowable error in the mounting position of a crank angle sensor to an engine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine misfire detection method for detecting misfire based on an output from a rotation detection means for detecting engine rotation.

[0002]

2. Description of the Related Art Generally, it is ideal that combustion in a multi-cylinder engine is performed through the same process every cycle in order to obtain a stable output. However, in a multi-cylinder engine, a complicated intake pipe shape and a cylinder are used. Due to synergistic effects such as non-uniform intake distribution ratio due to air intake interference between the cylinders, slight difference in combustion temperature between cylinders caused by cooling path, variation in combustion chamber volume of each cylinder, manufacturing variation such as piston shape, etc. , Combustion tends to vary.

Conventionally, the combustion fluctuation between the cylinders has been suppressed to a minimum by the air-fuel ratio control and the ignition timing control for each cylinder. However, in the high performance engine which has a tendency toward high output and low fuel consumption recently, When the injector, the spark plug, or the like is deteriorated or malfunctions, it causes intermittent misfires, and the output is easily reduced.

Generally, whether or not a cylinder is in a misfire state is
It can be detected by detecting the engine speed variation and comparing the engine speed variation with a predetermined determination level. For example, in Japanese Unexamined Patent Publication No. 62-118031, the intervals of a plurality of pulse signals generated for each revolution of the crankshaft are measured, and the maximum value of the engine rotational fluctuation is determined from the time change of the pulse intervals. A technique for determining an abnormal combustion cylinder based on the maximum value and the count value of the pulse signal is disclosed.

Further, in Japanese Patent Laid-Open No. 2-112646, a plurality of angular positions are detected per revolution of a multi-cylinder internal combustion engine, and the instantaneous rotational speed at a specific rotational position of each cylinder is detected from the detected angular position intervals. However, there is disclosed a technique for detecting an abnormal cylinder from the variation of the instantaneous rotation speed.

[0006]

However, in general,
In order to detect the number of revolutions of the engine, for example, a rotation detecting means including a rotor that rotates in conjunction with the rotation of the engine and a sensor for detecting a predetermined position corresponding to the crank position of the rotor is used. It is necessary, and the rotor and the sensor forming this rotation detecting means have a slight error in the mounting position for each engine, and also have an allowable error in manufacturing each component.

Therefore, the rotation speed fluctuation detected by the rotation detecting means includes the above-mentioned error which differs from engine to engine, and if misfire determination is carried out with the determination level set uniformly, it will be an erroneous determination. There is a risk.

The present invention has been made in view of the above circumstances, and when detecting a misfire based on the output from the rotation detecting means for detecting the rotation of the engine, an error relating to the rotation detecting means for detecting the rotation of the engine. It is an object of the present invention to provide an engine misfire detection method capable of accurately detecting the misfire state of a cylinder by eliminating the influence of the above.

[0009]

According to a first aspect of the present invention, there is provided a method for detecting engine misfire, which is based on an output from a rotation detecting means for detecting the rotation of the engine, the engine speed of a cylinder in a combustion stroke, and The differential rotation with respect to the engine speed of the cylinder one combustion stroke before is obtained, and the differential rotation is statistically processed to correct the error related to the rotation detection means, and then compared with the determination level set based on the engine operating state. It is characterized by detecting a misfire.

The engine misfire detection method according to the second aspect of the present invention is the method of the first aspect of the present invention, in which an error relating to the rotation detecting means is corrected by subtracting a value based on a weighted average value of the differential rotation from the differential rotation. It is characterized by doing.

[0011]

In the engine misfire detection method according to the first aspect of the present invention, the differential rotation speed between the engine speed of the combustion stroke cylinder and the engine speed of the cylinder before the first combustion stroke is determined based on the output from the rotation detection means. The difference rotation is statistically processed to correct the error related to the rotation detecting means. Then, the determination level set based on the engine operating state is compared with the corrected differential rotation speed to detect misfire.

In the engine misfire detection method according to the second aspect of the invention, in the first aspect of the invention, the rotation detecting means is used as a differential rotation after correction by weighting the differential rotations and subtracting a value based on the weighted average value. Error related to.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. The drawings relate to one embodiment of the present invention, FIG. 1 is a flowchart 1 showing a misfire diagnosis routine, FIG. 2 is a flowchart 2 showing a misfire diagnosis routine, FIG. 3 is a flowchart showing a misfire determination routine, and FIG. 4 is an engine control. FIG. 5 is a front view of a crank rotor and a crank angle sensor, FIG. 6 is a front view of a cam rotor and a cam angle sensor,
7 is a circuit diagram of the electronic control system, FIG. 8 is a time chart showing the relationship among crank pulse, cam pulse, combustion stroke cylinder, and ignition timing, FIG. 9 is an explanatory diagram showing differential rotation before correction, and FIG. 10 is correction. Explanatory diagram showing the differential rotation after that, FIG.
1 is an explanatory diagram of a misfire determination level, and FIG. 12 is an explanatory diagram showing a differential rotation when a misfire occurs.

In FIG. 4, reference numeral 1 is an engine,
In the figure, a horizontally opposed four cylinder engine is shown. An intake manifold 3 is communicated with each intake port 2a formed in a cylinder head 2 of the engine 1, a throttle chamber 5 is communicated with the intake manifold 3 through an air chamber 4, and an intake pipe is provided upstream of the throttle chamber 5. An air cleaner 7 is attached via 6.

Further, the air cleaner 7 of the intake pipe 6
An intake air amount sensor (a hot wire type intake air amount sensor in the figure) 8 is installed immediately downstream of the throttle valve 5 provided in the throttle chamber 5.
A throttle sensor 9 is connected to a.

Further, an idle speed control (ISC) valve 11 is provided in a bypass passage 10 that connects the upstream side and the downstream side of the throttle valve 5a.
Each intake port 2 of each cylinder of the intake manifold 3
The injector 12 is exposed immediately upstream.

Further, an ignition plug 13a whose tip is exposed to the combustion chamber is attached to each cylinder of the cylinder head 2 and is connected to the ignition plug 13a.
The igniter 14 is connected to b.

The injector 12 has a fuel supply path 15
The fuel tank 16 is communicated with the fuel tank 16 through the fuel tank 16. An in-tank type fuel pump 17 is provided in the fuel tank 16. The fuel from the fuel pump 17 is pressure-fed to the injector 12 and the pressure regulator 19 through the fuel filter 18 provided in the fuel supply passage 15, and is returned from the pressure regulator 19 to the fuel tank 16 to a predetermined position. Adjusted to pressure.

Further, a knock sensor 25 is attached to the cylinder block 1a of the engine 1, a cooling water temperature sensor 27 is exposed to a cooling water passage 26 which communicates the left and right banks of the cylinder block 1a, and the cylinder head 2 is also provided. The O2 sensor 29 is exposed to the gathering portion of the exhaust manifold 28 communicating with the exhaust port 2b. Reference numeral 30 is a catalytic converter.

A crank rotor 31 is mounted on a crank shaft 1b supported by the cylinder block 1a, and a crank angle sensor 32 including a magnetic sensor such as an electromagnetic pickup or an optical sensor is provided on the outer periphery of the crank rotor 31. Are arranged opposite to each other to constitute rotation detecting means for detecting the rotation of the engine. Further, a cam rotor 33 is connected to the cam shaft 1c of the cylinder head 2, and a cam angle sensor 34 for discriminating a cylinder including a magnetic sensor such as an electromagnetic pickup or an optical sensor is provided on the outer periphery of the cam rotor 33 so as to be opposed thereto. There is.

As shown in FIG. 5, the crank rotor 3
Around the outer periphery of 1 are projections (or slits) 31a, 31
b and 31c are formed. Each protrusion 31a, 31b,
31c is before compression top dead center (BTDC) θ1, θ of each cylinder
The detection signals of the respective projections 31a, 31b, 31c output from the crank angle sensor 32 are formed in the positions of 2 and θ3, and the detected signals are input to the ECU 41 as θ1, θ2, and θ3 crank pulses, and the engine rotation speed is increased. The number is calculated, and the control timings of the ignition timing control and the fuel injection control are obtained.

Further, as shown in FIG. 6, a cylinder discriminating projection (which may be a slit) 3 is provided on the outer periphery of the cam rotor 33.
3a, 33b, 33c are formed. The projection 33a is formed at the position of the compression top dead center (ATDC) θ4 of the # 3 and # 4 cylinders, and the projection 33b is composed of three projections, and the first projection is the compression top dead of the # 1 cylinder. After the point (ATD
C) It is formed at the position of θ5. Furthermore, the protrusion 33c
Is formed by two projections, and the first projection is formed at the position of the compression dead center (ATDC) θ6 of the # 2 cylinder.

The projections 33a, 33 of the cam rotor 33
b, 33c are detected by the cam angle sensor 34, the waveform is shaped, and the ECU 41 determines θ4, θ for cylinder discrimination.
It is input to the ECU 41 as a 5 and θ6 cam pulse.

As a result, when the engine is in operation, a cam pulse is generated at a position where it does not overlap the crank pulse as shown in FIG. 8, and it becomes possible to discriminate the cylinder from the number and generation state of this cam pulse.

In the illustrated embodiment, θ1 = 97 ° C. A, θ
2 = 65 ° C A, θ3 = 10 ° C A, θ4 = 20 ° C A, θ5
= 5 ° C.A, θ6 = 20 ° C.A.

On the other hand, in FIG. 7, reference numeral 41 is an electronic control unit (ECU) composed of a microcomputer, etc., and the CPU 42, ROM 43, RAM 44, backup RAM 44 a, and I / O interface 45 are mutually connected via a bus line 46. Connected, constant voltage circuit 4
A predetermined stabilizing voltage is supplied from 7.

The constant voltage circuit 47 includes an ECU relay 48.
Is connected to the battery 49 via the relay contact of the ECU and directly connected to the battery 49.
When the ignition switch 50 connected between the relay coil of the relay 48 and the battery 49 is turned on and the relay contact of the ECU relay 48 is closed, the control power is supplied to each part and the ignition is also performed. When the switch 50 is turned off, the backup RA
Supply backup power to M44a.

The battery 49 is connected to the fuel pump 17 via a relay coil of the fuel pump relay 51 and a relay contact of the fuel pump relay 51.

Further, the input port of the I / O interface 45 has an intake air amount sensor 8, a throttle sensor 9, a knock sensor 25, a cooling water temperature sensor 27, an O 2 sensor 29, a crank angle sensor 32, a cam angle sensor 34,
The vehicle speed sensor 35 and the like are connected, and the battery 49 is connected to monitor the battery voltage.

The igniter 14 is connected to the output port of the I / O interface 45, and further,
Via the drive circuit 52, the ISC valve 11, the injector 12, the relay coil of the fuel pump relay 51, and
ECS installed on an instrument panel (not shown)
An (Electronic Control System) lamp 53 is connected.

A control program and various fixed data for control are stored in the ROM 43, and output signals of the sensors and switches after data processing are carried out in the RAM 44 and calculations by the CPU 42. Stores processed data. Further, the backup RAM 44a is constantly supplied with power regardless of the ignition switch 50. Even if the ignition switch 50 is turned off and the operation of the engine is stopped, the stored contents are not lost, and the faulty part detected by the self-diagnosis function is detected. The trouble codes etc. corresponding to are stored.

The trouble data can be read out to the outside by connecting the serial monitor 54 to the ECU 41 via the connector 55. This serial monitor 5
Regarding No. 4, JP-A-2-73 previously filed by the applicant.
No. 131 is described in detail.

In the CPU 42, the fuel injection amount, the ignition timing, the duty ratio of the drive signal of the ISC valve 11, etc. are calculated according to the control program stored in the ROM 43, and the air-fuel ratio control, the ignition timing control and the idle speed control are performed. Each cylinder #n (n
= 1 to 4) misfires are individually judged.

Next, the misfire detection procedure executed by the ECU 41 will be described with reference to the flow charts of FIGS.

The flowcharts of FIGS. 1 and 2 show a misfire diagnosis routine which is interrupted in synchronism with the θ3 crank pulse from the crank angle sensor 32. First, in step S101, each data obtained when the routine is executed last time is executed. Is stored in the work area, and in step S102, from the input interval time between the θ2 and θ3 crank pulses and the included angle (θ2−θ3) of the crank rotor 31 indicating θ2 and θ3, #n
The engine speed MNXn corresponding to the (n = 1, 3, 2, 4) cylinder is calculated in the range of, for example, 150 rpm or more in consideration of the misfire in the low engine speed region.

Then, the process proceeds to step S103, and the above step
Engine speed MN corresponding to #n cylinder calculated in S102
From Xn, the engine speed MNXn-1 (calculated during the previous routine execution) corresponding to the # n-1 cylinder one combustion stroke before is subtracted to calculate the differential rotation speed DELNEn (DELNEn ←
MNXn-MNXn-1).

Next, at step S104, based on the crank pulse and the cam pulse output from the crank angle sensor 32 and the cam angle sensor 34, the #n cylinder which is the combustion stroke cylinder this time is n = 1, 3, 2, 4 It is determined which of the two is # n- before one combustion stroke in step S105.
Determine one cylinder.

For example, as shown in FIG. 8, when a crank pulse is input from the crank angle sensor 32 after the θ5 cam pulse is input from the cam angle sensor 34, this crank pulse indicates the crank angle of the # 3 cylinder. If the θ4 cam pulse is input after the θ5 cam pulse, it can be determined that the subsequent crank pulse indicates the crank angle of the # 2 cylinder.

Similarly, the crank pulse after inputting the θ 6 cam pulse indicates the crank angle of the # 4 cylinder, and
When the θ4 cam pulse is input after the θ6 cam pulse, it can be determined that the subsequent crank pulse indicates the crank angle of the # 1 cylinder.

Further, after the cam pulse is input from the cam angle sensor 34, it can be determined that the crank pulse input from the crank angle sensor 32 indicates the reference crank angle (θ1) of the corresponding cylinder.

For example, when the misfire diagnosis routine is executed in synchronism with the θ3 crank pulse of BTDCθ3 of the # 3 cylinder, the combustion stroke cylinder #n is the # 1 cylinder and # n-1 before the first combustion stroke. The cylinder is the # 4 cylinder. Then, in this case, the # 1 cylinder as the combustion stroke cylinder #n is the cylinder subject to the misfire diagnosis, and the BTDC θ2 and θ3 of the # 3 cylinder are θ2 and θ3.
From the rotational speed MNX1 (= MNXn) calculated based on the input interval time Tθ23 between crank pulses, the rotational speed MNX4 based on the input interval time between the BTDC θ2, θ3 θ2, θ3 crank pulses of the # 1 cylinder calculated during the previous routine execution.
Differential rotation DELNE1 obtained by subtracting (= MNXn-1)
By (= DELNEn), the misfire diagnosis for the corresponding cylinder (# 1 cylinder in this case) is performed in the subsequent processing.

Here, the detected position of the crank angle by the crank angle sensor 32 is the manufacturing tolerance of the positions and shapes of the protrusions 31a, 31b, 31c of the crank rotor 31, and the crank angle sensor 32 to the engine 1. There is an error in the mounting position of each engine. Therefore,
The differential rotation speed DELNEn calculated based on the crank pulse from the crank angle sensor 32 includes variations due to these errors. Particularly, when the engine speed is high, as shown in FIG. The result is that engine speed fluctuations occur uniformly.

Therefore, if the misfire determination is performed by using the differential rotation speed DELNEn calculated in the above step S103 as it is, an erroneous determination is caused.
Differential rotation weighted average value AVED for each cylinder obtained by statistically processing NEn
NnOLD (calculated at the previous routine execution) is the differential rotation DE
Subtract from LNEn and calculate as corrected differential rotation DELNAn (DELNAn ← DELNEn-AVEDNnOL
D).

As a result, the differential rotation D before correction shown in FIG.
From ELNEn, each protrusion 31a of the crank rotor 31,
The influences of manufacturing tolerances of the positions and shapes of 31b and 31c, the tolerances of the mounting position of the crank angle sensor 32 on the engine 1 and the like are eliminated, and as shown in FIG. Number and # n-1 before 1 combustion stroke
It is possible to obtain an accurate differential rotation speed with respect to the engine speed corresponding to the cylinder.

Incidentally, FIGS. 9 and 10 and FIG. 12 which will be described later.
In, the vertical axis has a scale of 50, and the horizontal axis has a scale of 720 ° CA (720 ° CA / div).
The differential rotation data calculated in the CU 41 is shown.

After that, the above steps S106 to S1
It is determined whether or not the misfire diagnosis condition is satisfied through the steps of 07, S108, and S109. That is, in step S107, it is checked whether or not the fuel is being cut, and in step S108, the basic fuel injection amount T
It is checked whether p is smaller than the set value TpLWER. In step S109, it is checked whether the engine speed NE is equal to or higher than the set speed NEUPER.

When the fuel is being cut in step S107, Tp <TpLWER in step S108, or NE ≧ NEUPER in step S109, it is determined that the diagnostic condition is not satisfied, and the process branches from step S114 to the diagnostic permission flag. When FLGDIAG is cleared (FLGDIAG ← 0),
In step S115, the misfire flag F for each cylinder indicating the occurrence of misfire
LGMISn is cleared (FLGMISn ← 0) and the process proceeds to step S116 and thereafter.

On the other hand, through the steps S107, S108 and S109, when Tp ≧ TpLWER and NE <NEUPER are not set during the fuel cut, the diagnosis condition is satisfied and the process proceeds to step S110 to set the diagnosis permission flag FLGDIAG. Set (FLGDIAG ← 1) and proceed to step S111.

In step S111, the engine speed NE and the basic fuel injection pulse width Tp are used as parameters to refer to the misfire determination level map with interpolation calculation. When the misfire determination level LVLMIS is set, the process proceeds to step S112, and the above step S106 is performed. It is determined whether or not the post-correction differential rotation speed DELNAn calculated in step 1 is smaller than the negative misfire determination level (-LVMLMIS).

The misfire determination level LVLMIS is shown in FIG.
As shown in 1, the engine low load region where the basic fuel injection pulse width Tp is small is set as a non-diagnosable region, and the slice level increases as the basic fuel injection pulse width Tp increases and the load increases. Is stored in the ROM 43 as a map, and as shown in FIG. 12, the misfire can be correctly detected for the differential rotation (the corrected differential rotation DELNAn) whose level changes according to the engine operating condition at the time of the misfire. You can do it.

Then, in step S112, DELNA
When n ≧ −LVMLMIS, it is determined that there is no misfire, and the process branches to step S115, where DELNAn <−LVLM
If it is IS, it is determined that a misfire has occurred and the process proceeds to step S113,
Set the misfire flag FLGMISn (FLGMISn
← 1) Proceed to step S116.

In step S116, the misfire flag FLGMI is set.
Referring to the value of Sn, FLGMISn = 0, that is, when no misfire has occurred in the cylinder #n subject to misfire diagnosis, in step S117, the difference Δ () between the differential rotation speed DELNEn and the differential rotation weighted average value AVEDNOLD of all cylinders = DELEN-AV
EDNOLD) is the upper and lower set values MINDN, MAXDN
It is determined whether or not it is within a predetermined setting range between (MINDN <MAXDN).

Then, in step S117, MINDN
<Δ <MAXDN, and when it is within the set range, it is determined that the differential rotation speed DELNEn is fluctuating due to an error relating to the crank rotor 31 or the crank angle sensor 32, and the differential rotation speed DELNEn is statistically processed in steps S121 and S122. Then, the process proceeds to step S123.

That is, in step S121, in order to correct the differential rotation variation due to an error, the total cylinder differential rotation weighted average is calculated from the all-cylinder differential rotation weighted average value AVEDNOLD calculated during the previous routine execution and the corrected differential rotation DELNAn calculated this time. When the value AVEDN is calculated (AVEDN ← (3/4)
X AVEDNOLD + (1/4) x DELNAn), in step S122, from the difference between this all-cylinder difference rotation weighted average value AVEDN and the difference rotation DELNEn, and the cylinder-by-cylinder difference rotation weighted average value AVEDNnOLD calculated from the previous routine execution,
Calculate the differential rotation weighted average value AVEDNn for each cylinder this time (AVEDNn ← (7/8) × AVEDNnOLD + (1 /
8) x (DELNEn-AVEDN)).

On the other hand, in step S116, FLGMIS
When n = 1, that is, when the misfire diagnosis target cylinder #n has misfired, in step S118, the misfire count value MISC is counted.
Count up NTn (MISCNT NT ←← MISC
NTn + 1) Proceed to step S119, and again step S119 above.
At 117, when Δ ≦ MINDN or Δ ≧ MAXDN, the crank rotor 31 or the crank angle sensor 3
It is the fluctuation of the differential rotation speed DELNEn that is not related to the error of 2 and is caused by another factor (snatch, etc.).
It is discriminated that there is a fluctuation of and the process proceeds to step S119.

In step S119, the previously calculated all-cylinder differential rotation weighted average value AVEDNOLD is set as the current all-cylinder differential rotation weighted average value AVEDN (AVEDN ← AVEDENOL
D), in step S120, the previously calculated cylinder-by-cylinder differential rotation weighted average value AVEDNnOLD is set as the current cylinder-by-cylinder differential rotation weighted average value AVEDNn (AVEDNn ← AVEDENnOLD),
Proceed to step S123.

When the process proceeds from step 120 or step S122 to step S123, the value of the diagnosis permission flag FLGDIAG is referred to. When FLGDIAG = 0,
When the program jumps to step S129 and FLGDIAG = 1, in step S124 the count value CRACCNT is incremented (CRACNT ← CRACNT + 1), and in step S125 whether or not the count value CRACCNT reaches 2000, that is, this misfire detection. Since the routine is executed every 1/2 revolution of the engine for each θ3 crank pulse input, it is determined whether or not the count value CRACNT has reached a value for 1000 revolutions of the engine.

In step S125 above, CRACNT <2
When 000, the process branches to step S129 and CRACNT ≧.
If 2000, a misfire determination subroutine described below is executed in step S126, and in steps S127 and S128, the count value CRACNT and the count value M of all misfire counts are executed.
Clear ISCNT1 to 4 respectively (CRACNT ←
0, MISCNT1 to 4 ← 0), and proceeds to step S129. In step S129, the differential rotation DELNEn calculated this time, the corrected differential rotation DELNAn, and the differential rotation weighted average value AV for all cylinders AV
Each data of EDN and cylinder-by-cylinder differential rotation weighted average value AVEDNn is set in the RAM 44 as monitor data, and the routine is exited.

Steps in the above misfire diagnosis routine
The subroutine for misfire determination in S126 is shown in FIG. 3. In this routine, first, in step S201, the total number of misfires ΣMISCNTn (n = 1 to 4) for four cylinders is set to the count value CRACCNT (in the misfire detection routine described above. = 20
00) to calculate the misfire rate MISCNT (%) per 1000 engine revolutions (MISCNT ← ΣMI
SCNTn / CRACNT × 100).

Then, the procedure proceeds to step S202, where the misfire rate MISCNT calculated in step S201 is the set value LMSC.
It is determined whether it is smaller than NT. This set value LMSC
NT is a constant previously stored in the ROM 43 with the engine speed NE and the basic fuel injection amount Tp as parameters.

As a result of the discrimination in step S202, M
If ISCNT ≧ LMSCNT, step S203
Then, the misfire rate MISCNT is stored in a predetermined address of the backup RAM 44a, and it is checked in step S204 whether the first misfire determination NG flag FLGNG1 stored in the predetermined address of the backup RAM 44a is set.

In step S204, the first misfire determination NG flag FLGNG1 has not been set and F
When LGNG1 = 0, the routine jumps from step S204 to step S206, and the first misfire determination NG flag FLG
When NG1 is set and FLG NG1 = 1, the process proceeds from step S204 to step S205 and backup R
The second misfire determination NG flag FLGNG2 stored in the predetermined address of the AAM 44a is set (FLGNG2 ←
1) A warning is given to the user by turning on or blinking the ECS lamp 53, and the process proceeds to step S206.

In step S206, the first misfire determination NG flag FLGNG1 is set (FLGNG1 ← 1), and the step
In S212, the misfire OK counter for counting the number of times of determination of no abnormality is cleared (CNTOK ← 0), and the routine exits.

That is, in order to avoid erroneous diagnosis due to noise or the like, the misfire rate MISCNT is set to the set value L in the first judgment.
No warning is issued immediately even if it becomes MSCNT or higher. 2
The misfire rate MISCNT is set value LMS continuously in the second judgment.
When the number of cylinders exceeds CNT, it is determined that the cylinder is abnormal and a warning is issued.

At this time, the backup RAM 44a
The trouble data of the misfiring cylinder #n is stored in, and when the dealer troubleshoots, the blinking code of the monitor lamp of the ECU 41 or the serial monitor 54.
The trouble data stored in the backup RAM 44a is read at. After the misfiring cylinder is discriminated and repaired, the backup RAM 44a is
The trouble data is cleared via the serial monitor 54 or the like.

On the other hand, in step S202, MISCNT
<When LMSCNT, it is judged that there is no abnormality, and the step
When the misfire OK counter CNTOK is incremented in S207 (CNTOK ← CNTOK + 1), step S208
Then, it is determined whether or not the value of the misfire OK counter CNTOK exceeds 80 times. When CNTOK <80, the routine is exited as it is, and when CNTOK ≧ 80, the step is executed.
In S209, S210, 211, if the first misfire determination NG flag FLGNG1, the second misfire determination NG flag FLGNG2, and the misfire rate MISCNT are cleared (FLGNG1 ← 0, F
LGNG2 ← 0, MISCNT ← 0), step S21 described above.
In 2, clear the misfire OK counter CNTOK (CN
TOK ← 0) Exit the routine.

[0067]

As described above, according to the present invention, when the misfire is detected based on the output from the rotation detecting means for detecting the rotation of the engine, the engine speed of the cylinder in the combustion stroke and the cylinder After statistically processing the rotational speed difference from the engine speed of the cylinder one combustion stroke earlier, the misfire is detected by comparing with the determination level set based on the engine operating state. It can be eliminated, and an excellent effect can be obtained such that the misfire state of the cylinder can be accurately detected.

[Brief description of drawings]

FIG. 1 is a flowchart showing a misfire diagnosis routine.

FIG. 2 is a flowchart 2 showing a misfire diagnosis routine.

FIG. 3 is a flowchart showing a misfire determination routine.

FIG. 4 is a schematic configuration diagram of an engine control system.

FIG. 5 is a front view of a crank rotor and a crank angle sensor.

FIG. 6 is a front view of a cam rotor and a cam angle sensor.

FIG. 7 is a circuit configuration diagram of an electronic control system.

FIG. 8 is a crank pulse, a cam pulse, a combustion stroke cylinder,
And time chart showing the relationship of ignition timing

FIG. 9 is an explanatory diagram showing a differential rotation before correction.

FIG. 10 is an explanatory diagram showing a differential rotation after correction.

FIG. 11 is an explanatory diagram of a misfire determination level.

FIG. 12 is an explanatory diagram showing a differential rotation when a misfire occurs.

[Explanation of symbols]

 1 engine 31 crank rotor (rotation detecting means) 32 crank angle sensor (rotation detecting means) DELNEn differential rotation DELNAn corrected differential rotation LVLMIS determination level

Claims (2)

[Claims] 1. A differential rotation between an engine speed of a cylinder in a combustion stroke and an engine speed of a cylinder one combustion stroke before the cylinder is obtained based on an output from a rotation detecting means for detecting the rotation of the engine. A method for detecting misfire of an engine, which comprises statistically processing the differential rotation to correct an error relating to the rotation detecting means, and then detecting a misfire by comparing with a determination level set based on an engine operating state. 2. The misfire detection method for an engine according to claim 1, wherein an error relating to the rotation detecting means is corrected by subtracting a value based on a weighted average value of the differential rotation from the differential rotation. .