JPH06123252A - Misfire detection method for engine - Google Patents

Abstract

PURPOSE:To detect a misfire surely by preventing an error diagnosis because of an influence of rotational change in an engine. CONSTITUTION:It is determined whether a postcorrection differential rotation DELNA #n-1 of the #n-1 cylinder reaches a determination level (a snatch determination level) KXLVLMIS or the more, by which an engine rotational change due to a disturbance is determined (S202), and when DELNA n-1) KXLVLMIS is found, it is determined that a snatch is generated, so that a snatch flag FLGSN is set (S203). On the other hand, when DELNA n-1< KXLVLMIS and FLGSN=1 are found, it is determined whether a count value TMSNC reaches the predetermined value (an ignition number) KTSNC or not, and when the predetermined time has passed in TMSNC #KTSNC after the postcorrection differential rotation DELNA n-1 of the #n-1 cylinder passes across the snatch determination level. KXLVLMIS, it is determined that the snatch is finished to clear the snatch flag FLGSN (S207). In a subroutine of the continuous misfire diagnosis, an erroneous diagnosis is prevented, as the misfire diagnosis is not carried out when FLGSN=1.

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 engine speed fluctuations.

[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 rotational speed fluctuation due to the torque fluctuation due to misfire and comparing the rotational speed fluctuation with a predetermined determination level. For example, JP-A-62-118
In Japanese Patent Publication No. 031, the intervals of a plurality of pulse signals generated for each revolution of the crankshaft are measured, the maximum value of the rotational fluctuation of the engine is discriminated from the time change of the pulse intervals, and the maximum value and the pulse signal A technique for determining an abnormal combustion cylinder based on a count value 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 the case where a large rotation fluctuation, so-called snatch, occurs in the engine due to a disturbance other than misfire, such as a rotation fluctuation associated with torque fluctuation during rapid acceleration or during gear shifting, etc. In such a case, if the misfire determination is performed by simply comparing the engine speed fluctuation amount with the misfire determination level, there is a possibility that a non-misfire rotation fluctuation is erroneously determined as misfire.

The present invention has been made in view of the above circumstances, and provides an engine misfire detection method capable of eliminating the influence of engine speed fluctuations due to disturbances to prevent erroneous diagnosis and reliably detecting misfires. Is intended.

[0008]

An engine misfire detection method according to the present invention is an engine misfire detection method for detecting an engine misfire by using a difference in engine speed between two cylinders whose combustion stroke order is reversed. The determination level for determining the engine rotation fluctuation due to is set based on the engine operating state, and when the difference is equal to or higher than the determination level, and after the difference crosses the determination level from top to bottom, If the time has not elapsed, the diagnosis for detecting misfire is stopped.

[0009]

In the engine misfire detection method according to the present invention, the difference in engine speed between the two cylinders whose combustion stroke order is changed is higher than the judgment level for judging the engine speed fluctuation due to the disturbance, and a large engine speed fluctuation occurs. if you did this,
In order to stop the diagnosis for misfire detection, and also to wait for the convergence of the engine speed fluctuation, even when the above-mentioned difference has crossed the above-mentioned judgment level from above to below and a predetermined time has not passed,
Stop diagnostics for misfire detection.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. The drawings relate to an embodiment of the present invention, FIG. 1 is a flowchart showing a subroutine for snatch determination, FIG. 2 is a flowchart 1 showing a misfire diagnosis routine, FIG. 3 is a flowchart 2 showing a misfire diagnosis routine, and FIG. 5 is a flowchart showing a subroutine for misfire diagnosis, FIG. 5 is a flowchart showing a subroutine for misfire determination, FIG. 6 is a schematic configuration diagram of an engine control system, FIG. 7 is a front view of a crank rotor and a crank angle sensor, and FIG. 8 is a cam rotor and a cam angle. A front view of the sensor, FIG. 9 is a circuit configuration diagram of an electronic control system, and FIG.
Is a time chart showing the relationship among crank pulse, cam pulse, combustion stroke cylinder, and ignition timing, FIG. 11 is an explanatory diagram showing differential rotation before correction, FIG. 12 is an explanatory diagram showing differential rotation after correction, and FIG. 13 is misfire. Explanatory drawing of judgment level, FIG.
Is an explanatory diagram showing differential rotation when a snatch occurs, and FIG. 15 is an explanatory diagram showing differential rotation when a continuous misfire occurs.

In FIG. 6, 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 the 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.

Also, 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 connecting 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 in 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 around 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. 7, 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. 8, a cylinder discriminating projection (or 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.

Each protrusion 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. 10, 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. 9, reference numeral 41 is an electronic control unit (ECU) composed of a microcomputer, etc., and the CPU 42, ROM 43, RAM 44, backup RAM 44a, 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.

The ROM 43 stores a control program and various fixed data for control, and the RAM 44 outputs the output signals of the sensors and switches after data processing and the CPU 42 calculates the data. 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.

The CPU 42 calculates the fuel injection amount, the ignition timing, the duty ratio of the drive signal of the ISC valve 11, etc. in accordance with the control program stored in the ROM 43, and controls the air-fuel ratio, the ignition timing, and the idle speed. 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. 2 and 3 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 during the execution of the previous routine is executed. Is stored in the work area, and in step S102, θ2, θ3
From the input interval time between crank pulses and the included angle (θ2-θ3) of the crank rotor 31, which indicates θ2 and θ3,
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.

In the following description, each parameter,
The subscripts n, n-1, n-2, ... Of each flag represent each cylinder number.

Next, in step S103, the engine speed M corresponding to the #n cylinder calculated in step S102 is calculated.
The difference between NXn and the engine speed MNXn-1 corresponding to the # n-1 cylinder one combustion stroke before (calculated at the time of the previous routine execution) is calculated as the differential rotation speed DELNEn corresponding to the #n cylinder (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, respectively, 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. 10, 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. When 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 the θ6 cam pulse is input 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.

In the embodiment, the ignition order is # 1 → # 3.
→ # 2 → # 4. For example, when the misfire diagnosis routine is executed in synchronization with the θ3 crank pulse of BTDCθ3 of the # 3 cylinder, the combustion stroke cylinder #n is the # 1 cylinder,
Cylinder # n-1 before one combustion stroke is # 4 cylinder, and cylinder # n-2 before one combustion stroke is # 2 cylinder.

Here, the detected position of the crank angle by the crank angle sensor 32 is a manufacturing tolerance of the positions and shapes of the protrusions 31a, 31b, 31c of the crank rotor 31, the crank angle sensor 32 is directed to the engine 1. There is an error in the mounting position of each engine.

Therefore, the differential rotation speed DELNE calculated based on the crank pulse from the crank angle sensor 32.
Include variations due to these errors, and in particular, at the time of high engine speed, apparently relatively small engine speed fluctuations are uniformly generated as shown in FIG.

Therefore, from step S105 to step
When proceeding to S106, the differential rotation DE calculated in the above step S103
The differential rotation correction value AVEDN0 of the #n cylinder up to the last time calculated by statistically processing the differential rotation DELNEn from LNEn.
n is subtracted and the corrected differential rotation DELNAn is calculated (DELNAn ← DELNEn-AVEDN0n).

As a result, as shown in FIG. 11, the rotation fluctuation due to the misfire and the protrusions 31a of the crank rotor 31,
From the uncorrected differential rotation speed DELNEn in which the manufacturing tolerances of the positions and shapes of 31b and 31c, the apparent rotation fluctuation due to the tolerance of the mounting position of the crank angle sensor 32 to the engine 1, and the like are mixed, An accurate difference in engine speed between the # 1 and # n-1 cylinders, that is, the corrected differential rotation speed DELNA can be obtained, and as shown in FIG. 12, rotational fluctuation due to misfire can be accurately extracted. .

Incidentally, FIG. 11, FIG. 12, and FIG.
In FIG. 5, differential rotation data calculated in the ECU 41 is shown by setting one scale on the vertical axis to 50 rotations and one scale on the horizontal axis (1 div) to 720 ° CA.

As described above, for example, when this misfire diagnosis routine is executed in synchronization with the BTDCθ3 crank pulse of the # 3 cylinder, the cylinder # 4, which is the cylinder # n-1 one combustion stroke before, is the cylinder subject to the misfire diagnosis. And the # 1 cylinder BTD
The rotation speed MNX4 (= MNXn-1) of the # 4 cylinder (# n-1 cylinder) before one combustion stroke calculated from the input interval time between the C2 and θ3 crank pulses of Cθ2 and θ3 to the B of the # 4 cylinder.
Rotational speed MNX of the # 2 cylinder (# n-2) before two combustion strokes based on the input interval time between the TDC θ2 and θ3 crank pulses
2 (= MNXn-2) is subtracted and statistically processed to obtain the corrected differential rotation speed DELNA4 (= DELNAn-1) of the # 4 cylinder (# n-1 cylinder) and the BT of the # 3 cylinder obtained in the previous routine execution.
DCθ2, θ3 From the rotational speed MNX1 (= MNXn) based on the input interval time between crank pulses, the BTDCθ of the # 1 cylinder
Rotational speed MNX4 (= MNXn-1) based on the input interval time between 2 and θ3 crank pulses is subtracted and statistically processed to obtain the corrected differential rotation speed DELNA1 (# 1 cylinder (#n cylinder) obtained in this routine. = DELNAn), the misfire diagnosis for the corresponding cylinder # 4 (# n-1 cylinder) is performed in the subsequent processing.

Next, from step S106 to step S107
Then, the difference between the corrected differential rotation speed DELNAn of the #n cylinder and the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder calculated during the execution of the previous routine is calculated.
Is calculated as (DDNEAn ←← DELNAn−DEL
NAn-1). That is, by catching the change in the corrected differential rotation speed DELNA, the influence of a relatively small engine speed fluctuation caused by a cause other than misfire is eliminated, and accurate misfire detection is possible.

After that, the above steps S107 to S1
After 08, it is determined whether or not the misfire diagnosis condition is satisfied in each of steps S108, S109, and S110. That is,
In step S108, it is checked whether fuel is being cut, and step S1
At 09, it is checked whether the basic fuel injection pulse width Tp is smaller than the set value TpLWER. In step S110, it is checked whether the engine speed NE is equal to or higher than the set speed NEUPER.

After the steps S108, S109, S110, the fuel is not being cut, Tp ≧ TpLWER, and N
If E <NEUPER, it is determined that the diagnostic condition is satisfied, and step S1
At 11, the diagnosis permission flag FLGDIAG is set (FLGDIG
AG ← 1) On the other hand, when the fuel is being cut in step S108, Tp <TpLWER in step S109, or NE ≧ NEUPER in step S110, it is determined that the diagnostic condition is not satisfied and the process branches from step S112 to step S112. Then, the diagnosis permission flag FLGDIAG is cleared (FLGDI
AG ← 0).

When the process proceeds from step S111 or step S112 to step S113, a subroutine for snatch determination, which will be described later, is executed to determine engine speed fluctuation due to disturbance, that is, whether or not snatch is generated. If snatch is generated, As will be described later, the snatch flag FL
Set GSN to 1. Then, in step S114, a subroutine for continuous misfire diagnosis, which will be described later, is executed, and when the snatch is not generated by referring to the value of the snatch flag FLGSN, the start and end of continuously occurring misfires are detected.

Next, the above steps S114 to S115.
To the misfire flag FL of the # n-1 cylinder before one combustion stroke.
Refer to the value of GMISn-1. This misfire flag is set to FLGMISn-1 = 1 when the misfire is determined in the continuous misfire diagnosis in step S114, and FLGMISn-1 = 0, that is, misfire occurs in the # n-1 cylinder. If not, the process proceeds from step S115 to step S116, and the differential rotation DELNE of the # n-1 cylinder is performed.
n-1 and differential rotation weighted average value AVED of all cylinders up to the previous time
The difference Δ with N0 (= DELNEn-1 −AVEDN0) is
Upper and lower set values MINDN, MAXDN (MINDN <M
AXDN) is determined to be within a predetermined setting range.

In step S116, MINDN <Δ <M
When AXDN is within the set range, it is determined that the differential rotation speed DELNEn is fluctuating due to an error related to the crank rotor 31 or the crank angle sensor 32, and the differential rotation speed DELNEn-1 is statistically processed in steps S120 and S121. Then, the process proceeds to step S122.

That is, in step S120, in order to correct the differential rotation variation due to the error, the differential rotation weighted average value AVEDN0 of all cylinders up to the previous time and the corrected differential rotation DELNAn-1 of the # n-1 cylinder are newly added. When calculating the all-cylinder differential rotation weighted average value AVEDN (AVEDN ← (3/4) ×
AVEDN0 + (1/4) × DELNAn-1), in step S121, this new all cylinder differential rotation weighted average value AVED
The difference between N and the differential rotation speed DELNEn-1 of the # n-1 cylinder, and the differential rotation correction value AVEDN of the # n-1 cylinder up to the previous time.
0n-1 to new # n-1 cylinder difference Rotation correction value AVE
Calculate DNn-1 (AVEDNn-1 ← (7/8) x AV
EDN0n-1 + (1/8) × (DELNEn-1-AVED
N)).

On the other hand, in step S115, FLGMIS
When n-1 = 1, that is, when # n-1 cylinder misfires,
In step S117, the misfire count value MISCNTn-
Count up 1 (MISCNTn-1 ← MISCN
Tn-1 + 1) The process proceeds to step S118.

Further, in step S116, Δ ≦ MIND
When N or Δ ≧ MAXDN, not the fluctuation of the differential rotation speed DELNEn−1 due to an error relating to the crank rotor 31 or the crank angle sensor 32, but the fluctuation of the differential rotation speed DELNEn−1 due to the variation of the combustion state of the # n−1 cylinder. And proceeds to step S118.

In step S118, the all-cylinder differential rotation weighted average value AVEDN0 up to the previous time is set as the current all-cylinder differential rotation weighted average value AVEDN (AVEDN ← AVEDEN0). In step S119, the difference between the # n-1 cylinders up to the previous time is calculated. The rotation correction value AVEDN0n-1 is set as a new differential rotation correction value AVEDNn-1 for the # n-1 cylinder (AVEDENn-1 ← AVEDN0n-
1), proceed to step S122.

When the process proceeds from step 119 or step S121 to step S122, the value of the diagnosis permission flag FLGDIAG is referred to. When FLGDIAG = 0,
If the flag jumps to step S128 and FLGDIAG = 1, then in step S123, the count value CRACNT that is counted each time the misfire diagnosis is executed is incremented (CR
(ACNT ← CRACNT + 1), and it is determined in step S124 whether the count value CRACNT has reached 2000.

As described above, this misfire diagnosis routine is executed every θ3 crank pulse input, that is, the engine 1
Since it is executed every / 2 rotations, the above count value CRAC
An NT value of 2000 indicates 1000 engine revolutions.

In step S124, CRACNT <2
When the value is 000, the process branches to step S128 and CRACNT ≧
If 2000, a misfire determination subroutine to be described later is executed in step S125, and in steps S126 and S127, the count value CRACNT and the misfire count values MISCNT1 to 4 for all cylinders are cleared (CRACNT ← 0. , MISCNT1 to 4 ← 0), and proceeds to step S128. In step S128, each data such as the differential rotation speed DELNEn calculated this time, the corrected differential rotation speed DELNAn, the differential rotation weighted average value AVEDN of all cylinders, and the differential rotation correction value AVEDNn-1 of # n-1 cylinder is stored in the RAM 44 as monitoring data. Set and exit the routine.

Next, each subroutine in the above misfire diagnosis routine (snatch determination in step S113, step
The continuous misfire diagnosis in S114 and the misfire determination in step S125) will be described.

First, in the snatch determination subroutine shown in FIG. 1, in step S201, the misfire determination level map is referenced with interpolation calculation using the engine speed NE and the basic fuel injection pulse width Tp as parameters to determine the misfire determination level. Set LVLMIS based on engine operating conditions.

The misfire determination level LVLMIS is shown in FIG.
As shown in Fig. 3, 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.

Next, from step S201 to step S2
Proceeding to 02, in order to determine the presence or absence of so-called snatch, which is the engine speed fluctuation associated with torque fluctuations due to disturbances during sudden acceleration or gear shifting, the above misfire judgment level LVLMIS is multiplied by K (depending on engine characteristics, etc. K = 1 to
2) The judgment level obtained by doing (hereinafter, “snatch judgment level”)
), And the corrected differential rotation speed DELNAn- of the # n-1 cylinder.
When DELNAn-1 ≧ K × LVLMIS is compared with 1, it is determined that a large engine speed fluctuation due to disturbance, so-called snatch, is detected, the process branches to step S203, and the snatch flag FLGSN is set (FLGSN ← 1). In step S208, a count value TMSNC to be described later is cleared (TMSNC ← 0) and the routine exits.

On the other hand, in step S202, DELNAn-
When 1 <K × LVLMIS, the process proceeds from step S202 to step S204, and it is determined whether or not the snatch flag FLGSN is cleared. If FLGSN = 0, the routine exits through the above step S208 and F
When LGSN = 1, that is, when the previous routine was executed, DELNAn-1 ≧ K × LVMLMIS, the snatch flag FLGSN is set, and this time, DELNAn-1 <
When K × LVLMIS is reached and within a predetermined time thereafter, the process proceeds from step S204 to step S205,
Count up the count value TMSNC (TMSN
C ← TMSNC + 1).

The count value TMSNC is temporarily set to #n.
-When the corrected differential rotation speed DELNAn-1 of the -1 cylinder becomes higher than the snatch judgment level (K x LVLMIS) and then becomes smaller than the snatch judgment level (K x LVLMIS), counting is started and the elapsed time thereafter is measured. If the count value TMSNC is counted up in step S205, step S206 is performed.
Then, the count value TMSNC is the set value (the number of ignitions) K
It is determined whether TSNC has been reached.

The set value KTSNC is calculated, for example, from the engine speed NE (KTSNC = NE / 100),
In step S206, TMSNC <KTSNC, that is, after the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder crosses the snatch determination level (K × LVLMIS) from top to bottom, a predetermined value indicated by the set value KTSNC is given. When the time of has not elapsed, the routine is exited as it is.

On the other hand, in step S206, TMSNC ≧
KTSNC, that is, the corrected differential rotation D of the # n-1 cylinder
ELNAn-1 is the snatch judgment level (K x LVLMI
When the predetermined time indicated by the set point value KTSNC has passed after the step S) is crossed, it is determined that the snatch (engine rotation fluctuation due to disturbance) has ended, the process proceeds to step S207, and the snatch flag FLGSN is cleared (FLG).
SN ← 0), the count value TMSN in step S208 described above.
Clear C and exit the routine.

The value of the snatch flag FLGSN is referred to in the subroutine for continuous misfire diagnosis in FIG. 4. In this subroutine, the value of the diagnosis permission flag FLGDIAG is referenced in step S301, and when FLGDIAG = 0, in step S311. # N-1 cylinder misfire flag FLGMISn-1
Is cleared (FLGMISn-1.rarw.0) and the routine exits, and when FLGDIAG = 1, the value of the snatch flag FLGSN is referred to in step S302.

Then, in step S302, the FLGSN
When = 1, there is an engine speed fluctuation (switch) due to disturbance, so the misfire diagnosis is not executed and the above steps are executed.
Exit the routine via S311. That is, as shown in FIG. 14, when the throttle opening suddenly increases due to sudden acceleration or the like, the fuel injection amount (basic fuel injection pulse width Tp) is immediately increased accordingly, and the engine speed NE and the vehicle speed are delayed. Rise. At this time, the difference in the engine speed between the cylinders fluctuates greatly, and a snatch occurs in which the longitudinal acceleration fluctuates greatly.Therefore, during rotation fluctuations due to this snatch, the diagnosis for misfire is stopped and misdiagnosis is prevented. Of.

On the other hand, in step S302, FLGSN =
When the value is 0, the rotation fluctuation due to the snatch has subsided, so the process proceeds from step S302 to step S303 and thereafter.
Perform a continuous misfire diagnosis. In this continuous misfire diagnosis, first, in step S303, the negative misfire determination level-LVMLMI is set.
S is compared with the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder.

The comparison result in step S303, DELN
An-1> -LVMLMIS, and the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder is negative. Misfire determination level -LVLM
If it has not fallen below the IS, it is judged that there is no misfire, the process branches to step S311, the misfire flag is cleared (FLGMISn-1 ← 0), and the routine exits.

The comparison result in step S303, D
ELNAn-1 ≤ -LVMLMIS, and the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder is negative.
If it is below VLMIS, follow the steps above.
The routine proceeds from step S303 to step S304, and the corrected differential rotation change DDNEAn of the #n cylinder and the negative misfire determination level-LVMLMI.
By comparing with S, the change in the corrected differential rotation speed DELNA from the # n−1 cylinder to the #n cylinder is examined.

Then, in step S304, DDNEA
When n ≦ −LVMLMIS, and when the corrected differential rotation speed DELNA gradually decreases from the # n−1 cylinder to the #n cylinder, it is determined that the rotation fluctuation is due to a cause other than misfire, and the routine proceeds through step S311 described above. Exit through D DN
EAn> -LVMLMIS and a negative misfire determination level-
If the post-correction differential rotation speed DELNA dropped below LVLMIS fluctuates near the negative misfire determination level −LVMLMIS from the # n−1 cylinder to the #n cylinder,
In S305, the corrected differential rotation change DDNEAn of the # n-1 cylinder
-1 is compared with the negative misfire determination level-LVMLMIS, and #
Corrected differential rotation D from the n-2 cylinder to the # n-1 cylinder
Investigate changes in ELNA.

As a result, in the above step S305, DDNE
An-1 ≤ -LVMLMIS, and the above steps S303 and S304
Compensated differential rotation DELNA
However, it falls below the negative misfire determination level −LVMLMIS from the # n−2 cylinder to the # n−1 cylinder, and the negative misfire determination level −LVLM from the # n−1 cylinder to the #n cylinder.
When it is near the IS, it is determined that the misfire has started from the # n-1 cylinder, and the steps S305 to S308 are performed.
Go to.

In step S308, the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder is set as the minimum value DNEAMS (DNEAMS ← DELNAn-1), and then the routine proceeds to step S310 to misfire the # n-1 cylinder. Flag FLGM
Set ISn-1 (FLGMISn-1 ← 1) and exit the routine.

On the other hand, in step S305, DDNEAn-
1> -LVMLMIS, and when the corrected differential rotation speed DELNA has not dropped below the negative misfire determination level -LVMLMIS from the # n-2 cylinder to the # n-1 cylinder,
The process branches from step S305 to step S306, # n-2.
It is determined whether or not the cylinder misfire flag FLGMISn-2 is set, that is, whether or not the # n-2 cylinder is in the misfire state.

At step S306, FLGMISn-2
= 0, and when the # n-2 cylinder does not misfire,
After the above step S311, the routine is exited and FLGMI
When Sn-2 = 1 and # n-2 cylinder is misfiring, the routine proceeds from step S306 to step S307, where #n
Check the drop level of the corrected differential rotation speed DELNAn-1 for the -1 cylinder.

That is, in step S307, the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder and the minimum differential rotation speed DNE are calculated.
Compared with AMS, DELNAn-1 <DNEAMS, and when the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder is lower than the minimum differential rotation speed DNEAMS at the time of misfire, # n-2 cylinder To # n-1 cylinder, it is determined that the misfires are continuously occurring, and the above-mentioned step S308 is executed.
Then, the minimum value DNEAMS is updated, the misfire flag FLGMISn-1 is set in step S310, and the routine exits.

On the other hand, in step S307, DELNAn-
When 1 ≧ DNEAMS and the corrected differential rotation speed DELNAn−1 of the # n−1 cylinder is equal to or larger than the minimum value DNEAMS, the routine proceeds from step S307 to step S309, where # n−
The corrected differential rotation speed DELNAn-1 of one cylinder is compared with the value obtained by adding the minimum value DNEAMS to the misfire determination level LVLMIS to determine whether or not the drop of the corrected differential rotation speed DELNA has recovered to a predetermined level. To do.

Then, in step S309, DELNA
When n-1 <DNEAMS + LVLMIS, and when the drop in the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder has not recovered, it is similarly determined that the misfire continues in the # n-1 cylinder. In step S310, the misfire flag FLGMISn-1 is set and the routine exits.

On the other hand, in step S309, DELNAn-
When 1 ≧ DNEAMS + LVMLMIS and the drop of the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder is recovered, it is determined that the misfire has ended, and the misfire flag FLGMISn-1 is cleared in step S311 described above to execute the routine. Exit through.

That is, from the # n-2 cylinder to the # n-1 cylinder, the corrected differential rotation speed DELNA is the misfire determination level LV.
In the negative direction below LMIS, from # n-1 cylinder to #
When the state continues for n cylinders, # n-
By determining that the misfire has started from one cylinder, determining that the misfire has occurred, and determining that the misfire has ended when the corrected differential rotation speed DELNA has recovered to a predetermined level or higher, as shown in FIG. It is possible to reliably detect misfires that continuously occur in the two cylinders, # 1 and # 3 cylinders.

In the misfire determination subroutine of FIG. 5, the total number of misfires ΣMIS for four cylinders is determined in step S401.
CNTn (n = 1 to 4) is divided by the count value CRACCNT (= 2000) in the above-mentioned misfire diagnosis routine to calculate the misfire rate MISCN T per 1000 revolutions of the engine.
Calculate (%) (MISCNT ← ΣMISCNTn /
CRACNT x 100).

Then, the procedure proceeds to step S402, where the misfire rate MISCNT calculated in step S401 is the set value LMSC.
It is determined whether it is smaller than NT. This set value LMSC
NT is the engine speed NE and the basic fuel injection pulse width Tp
These are constants previously stored in the ROM 43 with and as parameters.

As a result of the determination in step S402, MI
When SCNT ≧ LMSCNT, in step S403,
The misfire rate MISCNT is stored in a predetermined address of the backup RAM 44a, and the backup R is stored in step S404.
It is checked whether or not the first misfire determination NG flag FLGNG1 stored in the predetermined address of the AM 44a is set.

Then, in step S404, the first misfire determination NG flag FLGNG1 has not been set and F
When LGNG1 = 0, the routine jumps from step S404 to step S406, and the first misfire determination NG flag FLG
When NG1 is set and FLGNG1 = 1, the process proceeds from step S404 to step S405 to set the second misfire determination NG flag FLGNG2 stored in a predetermined address of the backup RAM 44a (FLGNG2 ←
1) A warning is given to the user by turning on or blinking the ECS lamp 53, and the process proceeds to step S406.

In step S406, the first misfire determination NG flag FLGNG1 is set (FLGNG1 ← 1), and the step
In S412, the misfire OK counter for counting the number of times of determination of no abnormality is cleared (CNTOK ← 0) and the routine is exited.

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 is stored in, and the trouble data stored in the backup RAM 44a is read by the blinking code of the monitor lamp of the ECU 41 or the serial monitor 54 at the time of troubleshooting in the dealer. After the misfiring cylinder is discriminated and repaired, the trouble data in the backup RAM 44a is cleared via the serial monitor 54 or the like.

On the other hand, in step S402, MISCNT
<When LMSCNT, it is judged that there is no abnormality, and the step
In S407, if the misfire OK counter CNTOK is incremented (CNTOK ← CNTOK + 1), step S408
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 S409, S410, and S411, clearing the first misfire determination NG flag FLGNG1, the second misfire determination NG flag FLGNG2, and the misfire rate MISCNT (FLGNG1 ← 0, F
LGNG2 ← 0, MISCNT ← 0), step S41 described above.
In 2, clear the misfire OK counter CNTOK (CN
TOK ← 0) Exit the routine.

[0090]

As described above, according to the present invention, the difference in engine speed between the two cylinders whose combustion stroke order is changed is greater than or equal to the determination level for determining the engine rotation fluctuation due to the disturbance, and the large engine rotation is performed. If fluctuations occur,
Stop the diagnosis for misfire detection, and also stop the diagnosis for misfire detection when the difference crosses the judgment level from top to bottom and the predetermined time has not passed, and Since it waits for the fluctuations to converge, erroneous diagnosis can be prevented, and an excellent effect such as reliable detection of misfire can be obtained.

[Brief description of drawings]

FIG. 1 is a flowchart showing a subroutine for snatch determination.

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

FIG. 3 is a flowchart 2 showing a misfire diagnosis routine.

FIG. 4 is a flowchart showing a subroutine for continuous misfire diagnosis.

FIG. 5 is a flowchart showing a subroutine for misfire determination.

FIG. 6 is a schematic configuration diagram of an engine control system.

FIG. 7 is a front view of a crank rotor and a crank angle sensor.

FIG. 8 is a front view of a cam rotor and a cam angle sensor.

FIG. 9 is a circuit configuration diagram of an electronic control system.

FIG. 10 is a time chart showing the relationship between crank pulse, cam pulse, combustion stroke cylinder, and ignition timing.

FIG. 11 is an explanatory diagram showing a differential rotation before correction.

FIG. 12 is an explanatory diagram showing a differential rotation after correction.

FIG. 13 is an explanatory diagram of a misfire determination level.

FIG. 14 is an explanatory diagram showing a differential rotation when a snatch occurs.

FIG. 15 is an explanatory diagram showing a differential rotation when a continuous misfire occurs.

[Explanation of symbols]

 1 Engine DELNA Corrected differential rotation (difference) K × LVMLMIS Snatch judgment level (judgment level)

Claims (1)

[Claims] 1. A method for detecting misfire of an engine, which detects a misfire by using a difference in engine speed between two cylinders whose combustion stroke order is different from each other. Set based on the state, if the difference is above the judgment level, and if the predetermined time has not elapsed after the difference crosses the judgment level from top to bottom, for misfire detection A method for detecting engine misfire, characterized by stopping diagnosis.