JPH1077899A - Missfire diagnosing device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve diagnosing precision and reliability by a method wherein a missfire is reliably detected without being influenced by the rotation fluctuation of an engine due to other cause than a missfire and in an operation region wherein erroneous decision is apt to occur. SOLUTION: A missfire decision level LVLMIS and the differential rotation change DDNEAn after correction of a #n cylinder are compared with each other at a step S204. In a case of DDNEAn >=LVLMIS, a negative missfire decision level (-LVMIS) and the differential rotation change DDNEAn-1 after correction of a #n-1 cylinder are compared with each other at a step S205. In a case of DDNEAn >=LVLMIS and DDNEAn <=LVLMIS, further, an intake pipe pressure change (NEWPINTn-1 -OLDPINTn-1 ) is compared with an intake pipe pressure missfire decision value PINTMIS at a step S206. In a case of (NEWPINTn-1 -OLDPINTn-1 )>=PINTMIS, by deciding that the #n-1 cylinder is in a missfire state, erroneous decision is prevented regardless of an operation state, a missfire is accurately detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine misfire diagnosis apparatus for detecting misfire from fluctuations in engine rotation.

[0002]

2. Description of the Related Art In general, it is ideal for combustion to be performed through the same process in each cycle in order to obtain a stable output. However, in a multi-cylinder engine, the shape of the intake pipe becomes complicated, and Due to the non-uniformity of the intake air distribution ratio due to intake interference between the cylinders, the slight difference in combustion temperature between the cylinders caused by the cooling route, the variation in the production of the combustion chamber volume, the piston shape, etc. of each cylinder. , Combustion tends to vary.

Heretofore, combustion fluctuations between cylinders have been minimized by air-fuel ratio control and ignition timing control for each cylinder. However, in recent high-performance engines, which tend to have high output and low fuel consumption, When the injector, the spark plug, or the like is deteriorated or malfunctions, it causes intermittent misfiring, which tends to lower the output.

In general, whether a cylinder is in a misfire state is determined by
It can be detected by detecting a rotation speed variation due to misfire and comparing the rotation speed variation with a predetermined determination level. For example, Japanese Patent Application Laid-Open No. Sho 62-118031 measures the interval between a plurality of pulse signals generated for each rotation of a crankshaft, and determines the maximum value of the engine speed fluctuation from the time change of the pulse interval. A technique for determining an abnormal combustion cylinder based on the maximum value and the count value of the pulse signal is disclosed.

Japanese Patent Application Laid-Open No. 2-112646 discloses a method of detecting a plurality of angular positions per one rotation of a multi-cylinder internal combustion engine, and detecting an instantaneous rotational speed of a specific rotational position of each cylinder from the detected angular position intervals. However, there is disclosed a technology for detecting an abnormal cylinder from the fluctuation of the instantaneous rotational speed.

However, in some cases, the engine may fluctuate in rotation due to causes other than misfire. Therefore, simply comparing the fluctuation in engine speed with the misfire determination level may not be sufficient.
For example, if the rotation fluctuation occurs continuously for a predetermined time due to a snatch or the like, it becomes difficult to distinguish between the rotation fluctuation due to the snatch and the rotation fluctuation due to a misfire, and an erroneous determination may occur.

[0007] For this reason, the present applicant has previously disclosed in
In Japanese Patent No. 42397, the difference between the engine speed of the cylinder in the combustion stroke and the engine speed of the cylinder one combustion stroke before is obtained as a difference rotation, and the difference rotation is statistically processed to correct the error. The change in the differential rotation becomes a negative value equal to or less than the misfire determination level between the cylinder before the two combustion strokes and the cylinder before the one combustion stroke, and misfires between the cylinder one combustion stroke before and the combustion stroke cylinder. When it becomes a positive value equal to or higher than the judgment level, 1
A technique has been proposed that determines a cylinder misfire state before a combustion stroke, and thereby can accurately detect a cylinder misfire state without being affected by fluctuations in engine rotation caused by causes other than misfire.

[0008]

Problems to be Solved by the Invention JP-A-6-423
According to the proposal of Japanese Patent Publication No. 97, although the diagnosis accuracy can be improved by removing the influence of engine rotation fluctuation due to causes other than misfire, it is affected by the rotation fluctuation due to snatch and disturbance during high rotation and low load operation. In an easy specific operation region, there is no possibility of erroneous determination, and there is a problem of further improving diagnostic accuracy.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to reliably detect a misfire without being affected by fluctuations in engine rotation due to causes other than a misfire and in an operating region where misjudgment is likely to occur. It is an object of the present invention to provide an engine misfire diagnosing device capable of improving the diagnostic accuracy and reliability.

[0010]

According to the first aspect of the present invention,
As shown in the basic configuration diagram of FIG. 1, the difference between the engine speed of the cylinder in the combustion stroke and the engine speed of the cylinder one combustion stroke before is based on the output from the rotation detecting means for detecting the rotation of the engine. Differential rotation calculating means for determining as a differential rotation,
Statistical processing of the differential rotation calculated by the differential rotation calculating means, and a corrected differential rotation calculating means for calculating a corrected differential rotation by correcting an error relating to the rotation detecting means, and a pressure detecting means for detecting an intake pipe pressure. An intake pipe pressure change calculating means for calculating a change in the intake pipe pressure corresponding to the cylinder one combustion stroke before, based on the output of the engine, and a misfire determination based on a change in the engine speed based on the engine operating state. Misfire determination level setting means for setting a misfire determination level; intake pipe pressure misfire determination value setting means for setting an intake pipe pressure misfire determination value for misfire determination due to intake pipe pressure change according to an engine operating region; The change in the corrected differential rotation calculated by the post differential rotation calculating means is a negative value equal to or less than the misfire determination level between the cylinder before the two combustion strokes and the cylinder before the one combustion stroke, and the cylinder before the one combustion stroke. When When a positive value equal to or more than the misfire determination level between the combustion cylinder and the intake pipe pressure change calculated by the intake pipe pressure change calculation means is equal to or greater than the intake pipe pressure misfire determination value, one combustion cycle is performed. A misfire determination unit that determines that the cylinder before the stroke is in a misfire state.

According to a second aspect of the present invention, in the first aspect of the present invention, the intake pipe pressure change calculating means calculates a difference between the intake pipe pressure at a current crank angle and the intake pipe pressure before a predetermined crank angle. It is characterized in that it is calculated as a pipe pressure change.

According to a third aspect of the present invention, in the first aspect of the present invention, the intake pipe pressure change calculating means calculates a difference between the intake pipe pressure at a current crank angle and a statistically processed value of the intake pipe pressure. It is characterized in that it is calculated as a pressure change.

That is, according to the first aspect of the present invention, the difference between the engine speed of the cylinder in the combustion stroke and the engine speed of the cylinder one combustion stroke before is defined as the differential rotation based on the output from the rotation detecting means. This differential rotation is statistically processed to calculate a corrected differential rotation in which an error relating to the rotation detecting means is corrected, and 1 based on the output from the pressure detecting means.
The change of the intake pipe pressure corresponding to the cylinder before the combustion stroke is calculated. Then, a change in the post-correction differential rotation is a misfire determination level for a misfire determination based on a change in the engine speed set based on the engine operating state between the cylinder before the two combustion strokes and the cylinder before the one combustion stroke. The following negative value is a positive value equal to or higher than the misfire determination level between the cylinder one combustion stroke before and the cylinder in the combustion stroke, and is used for misfire determination based on a change in intake pipe pressure set according to the engine operation region. It is determined that the cylinder before one combustion stroke is in a misfire state when the intake pipe pressure misfire determination value becomes equal to or more than the intake pipe pressure misfire determination value.

In this case, the intake pipe pressure misfire determination value is calculated as the difference between the intake pipe pressure at the current crank angle and the intake pipe pressure at a certain crank angle before the present invention. In the described invention, it is calculated as the difference between the intake pipe pressure at the current crank angle and the statistically processed value of the intake pipe pressure.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. 2 to 18 relate to the first embodiment of the present invention, FIG. 2 is a flowchart of a single-fire misfire diagnosis subroutine, FIGS. 3 to 5 are flowcharts of a misfire diagnosis routine, FIG. 6 is a flowchart of a misfire determination subroutine, and FIG. 8 is a schematic configuration diagram of an engine control system, FIG. 8 is a front view of a crank rotor and a crank angle sensor, FIG. 9 is a front view of a cam rotor and a cam angle sensor, FIG. 10 is a circuit configuration diagram of an electronic control system, and FIG. FIG. 12 is an explanatory diagram showing the differential rotation of
Is an explanatory diagram showing a differential rotation after correction, FIG. 13 is an explanatory diagram showing a differential rotation when a misfire occurs, FIG. 14 is an explanatory diagram of a misfire determination level, FIG. 15 is an explanatory diagram of a misfire determination level map, and FIG. FIG. 17 is an explanatory diagram of a pipe pressure misfire determination value map, FIG. 17 is an explanatory diagram showing an operation state and a differential rotation when a snatch occurs, and FIG. 18 is a time chart showing a relationship among a crank pulse, a cam pulse, a combustion stroke cylinder, and ignition timing. .

In FIG. 7, reference numeral 1 denotes an engine,
The figure shows a horizontally opposed four-cylinder engine. In both left and right banks of the cylinder block 1a of the engine 1,
Each of the cylinder heads 2 is provided with an intake port 2a and an exhaust port 2b.

An intake manifold 3 communicates with the intake port 2a, and a throttle chamber 5 communicates with an upstream gathering portion of the intake manifold 3 via an air chamber 4. An air cleaner 7 is attached via a pipe 6.

The air cleaner 7 of the intake pipe 6
A suction air amount sensor 8 of a hot wire type or a hot film type is interposed immediately downstream of the throttle chamber 5 and a throttle valve 5 a interposed in the throttle chamber 5.
And a throttle opening sensor 9 for detecting the throttle opening.
a and a throttle sensor 9 having a built-in idle switch 9b that is turned on when the throttle valve is fully closed.

An idle speed control (ISC) valve 11 for adjusting the amount of idle air is interposed in a bypass passage 10 communicating the upstream side and the downstream side of the throttle valve 5a. An intake pipe pressure sensor (absolute pressure sensor) 13 as a pressure detecting means is connected to a passage communicating with 3.

Further, an injector 14 is provided immediately upstream of each intake port 2a of each cylinder of the intake manifold 3.
A spark plug 15a having a tip exposed to the combustion chamber is attached to the cylinder head 2 for each cylinder. An ignition coil 15b is connected to the ignition plug 15a, and an igniter 16 is connected to the ignition coil 15b.

The injector 14 is connected to a fuel tank 18 via a fuel supply passage 17, and an in-tank type fuel pump 19 is provided in the fuel tank 18. The fuel from the fuel pump 19 is pumped from the injector 14 to the pressure regulator 21 via the fuel filter 20 interposed in the fuel supply passage 17, and the excess fuel is returned from the pressure regulator 21 to the fuel tank 18. The above injector 1
The fuel pressure to 4 is regulated to a predetermined pressure.

On the other hand, a knock sensor 22 is attached to the cylinder block 1a of the engine 1, and a cooling water temperature sensor 24 faces a cooling water passage 23 which connects the left and right banks of the cylinder block 1a. Further, an O2 sensor 2 is connected to a collecting portion of the exhaust manifold 25 communicating with the exhaust port 2b of the cylinder head 2.
6, a catalytic converter 27 is provided downstream of the O2 sensor 26.

A crank rotor 28 is mounted on a crankshaft 1b supported by the cylinder block 1a. A crank angle sensor 29 comprising a magnetic sensor (such as an electromagnetic pickup) is mounted on the outer periphery of the crank rotor 28.
And rotation detection means for detecting the rotation of the engine. Further, a cam rotor 30 is connected to the camshaft 1c of the cylinder head 2, and a cam angle sensor 31 for cylinder identification, which is also a magnetic sensor, is provided opposite to the cam rotor 30.

As shown in FIG. 8, the crank rotor 28 has projections 28a, 28b and 28c formed on the outer periphery thereof, and these projections 28a, 28b and 28c are connected to the cylinders (# 1, # 2 and # 2). 3, # 4) before compression top dead center (BTD
C) It is formed at the positions of θ1, θ2, θ3. In this embodiment, θ1 = 97 ° CA, θ2 = 65 ° CA, θ3 = 1
0 ° CA.

As shown in FIG. 9, on the outer periphery of the cam rotor 30, protrusions 30a, 30b, 3 for cylinder discrimination are provided.
0c is formed, and the projection 30a is formed at the position θ4 after the compression top dead center (ATDC) of the # 3 and # 4 cylinders, and the projection 30b is formed.
Is composed of three protrusions and the first protrusion is the AT of the # 1 cylinder.
It is formed at the position of DCθ5. Further, the protrusion 30c
Is formed by two projections, and the first projection is the AT of the # 2 cylinder.
It is formed at the position of DCθ6. In this embodiment,
θ4 = 20 ° CA, θ5 = 5 ° CA, θ6 = 20 ° CA.

As shown in the time chart of FIG. 18, each protrusion of the crank rotor 28 is detected by the crank angle sensor 29, and θ1, θ2, θ3 (BTDC 97
°, 65 °, 10 °) crank pulse
While output every two rotations (every 180 ° CA), each protrusion of the cam rotor 30 is detected by the cam angle sensor 31 between the θ3 crank pulse and the θ1 crank pulse, and a predetermined number of cam pulses are output. .

An electronic control unit (ECU; see FIG. 10) 40, which will be described later, calculates the engine speed NE based on the input interval time of the crank pulse output from the crank angle sensor 29, and calculates the combustion of each cylinder. Based on the pattern of the stroke order (for example, # 1 cylinder → # 3 cylinder → # 2 cylinder → # 4 cylinder) and the value of the cam pulse from the cam angle sensor 31 counted by the counter, the fuel injection target cylinder and ignition The cylinder of the target cylinder is determined.

Next, an electronic control unit (ECU) 40 for electronically controlling the engine 1 will be described with reference to FIG. The ECU 40 includes a CPU 41, a ROM 42,
The RAM 43, the backup RAM 44, the counter / timer group 45, and the I / O interface 46 are constituted mainly by microcomputers connected to each other via a bus line, and a constant voltage circuit 47 for supplying a stabilized voltage to each unit. Peripheral circuits such as a drive circuit 48 for driving actuators by a signal from an output port of the I / O interface 46 and an A / D converter 49 for converting an analog signal from a sensor to a digital signal are incorporated. .

The counter / timer group 45 includes various counters such as a free-run counter, a counter for counting the input of a cam angle sensor signal, a fuel injection timer, an ignition timer, and a periodic interrupt for generating a periodic interrupt. Various timers such as a timer, a timer for measuring an input interval of a crank angle sensor signal, and a watchdog timer for monitoring a system abnormality are collectively referred to for convenience.
, Various software counters and timers are used.

The constant voltage circuit 47 is connected to a battery 51 via a relay contact of a power relay 50, and a relay coil of the power relay 50 is connected to the battery 51 via an ignition switch 52. The constant voltage circuit 47 is directly connected to the battery 51, and the ignition switch 52 is
When N is turned on and the relay contact of the power supply relay 50 is closed, the power is supplied from the constant voltage circuit 47 to each unit, and the power is always backed up to the backup RAM 44 regardless of whether the ignition switch 52 is ON or OFF. Power is supplied.

The fuel pump 19 is connected to the battery 51 via a relay contact of a fuel pump relay 53. One end of the fuel coil of the fuel pump relay 53 is connected to the battery 51 via the ignition switch 52. The other end of the relay coil is connected to the drive circuit 48.

The input port of the I / O interface 46 includes an idle switch 9b and a knock sensor 2
2, crank angle sensor 29, cam angle sensor 31, and
A vehicle speed sensor 32 is connected, an intake air amount sensor 8, a throttle opening sensor 9a, an intake pipe pressure sensor 1
3. The cooling water temperature sensor 24 and the O2 sensor 26 are connected via the A / D converter 49, and
The voltage VB from the battery 51 is input to the D converter 49 and monitored.

On the other hand, the igniter 16 is connected to the output port of the I / O interface 46,
An MIL lamp 54, which is disposed on the ISC valve 11, the injector 14, and an instrument panel (not shown), and displays various alarms in a concentrated manner, is connected via the drive circuit 48.

The ROM 42 stores engine control programs, various failure diagnosis programs, and fixed data such as maps, and the RAM 43 processes output signals of the sensors and switches. The subsequent data and the data processed by the CPU 41 are stored. Further, the backup RAM 44 stores various learning maps, trouble codes corresponding to the failed parts detected by the self-diagnosis function, and the like, and retains data even when the ignition switch 52 is turned off. .

The trouble data stored in the backup RAM 44 is read out by connecting a select monitor 60, which is a portable failure diagnosis device, to the I / O interface 46 of the ECU 40 via a connector 55. be able to. This select monitor 60 is described in detail in Japanese Patent Application Laid-Open No. 2-73131 filed earlier by the present applicant.

The CPU 41 calculates the fuel injection amount, the ignition timing, the duty ratio of the drive signal of the ISC valve 11 and the like according to the control program stored in the ROM 42, and controls the air-fuel ratio, the ignition timing and the idle speed. And various other controls, and each cylinder #n (n = 1
4) Misfires are individually judged. That is, the ECU 40 and the sensors / actuators connected to the ECU 40 provide the differential rotation calculating means, the corrected differential rotation calculating means, the intake pipe pressure change calculating means, the misfire determination level setting means, The functions of the pipe pressure misfire determination value setting means, the misfire determination means, and other control functions are realized.

Next, regarding the processing relating to the misfire detection executed by the ECU 40, the misfire diagnosis routine of FIGS. 3 to 5, the single-shot misfire diagnosis subroutine of FIG. 2 called from the misfire diagnosis routine, and the misfire determination subroutine of FIG. Will be described with reference to a flowchart.

The misfire diagnosis routine of FIGS. 3 to 5 is interrupted and executed in synchronization with the θ3 crank pulse from the crank angle sensor 29. First, in step S101, each data obtained during the previous execution of the routine is stored in the work area. Then, in step S102, #n (n = 1, 3, 2, 4) is obtained from the input interval time between the .theta.2 and .theta.3 crank pulses and the angle (.theta.2 -.theta.3) of the crank rotor 31 indicating .theta.2 and .theta.3. ) The engine speed MNXn corresponding to the cylinder is calculated in a range of, for example, 150 rpm or more in consideration of misfire in the low engine speed range.

Next, the routine proceeds to step S103, in which the # n-1 cylinder one combustion stroke before is set as the misfire diagnosis target cylinder, and the intake pipe pressure P based on the output of the intake pipe pressure sensor 13 at the current crank angle is set to #. Intake pipe pressure NEWP corresponding to n-1 cylinder
INTn-1 (NEWPINTn-1 ← P), and step S1
Proceeding to 04, the engine speed MNX corresponding to #n cylinder
From n, the engine speed MNXn corresponding to the # n-1 cylinder
-1 (calculated at the previous execution of the routine) is subtracted, and the differential rotation DE
Calculate LNEn (DELNEn ← MNXn−MNXn−
1).

Next, the process proceeds to step S105, and based on the crank pulse and the cam pulse output from the crank angle sensor 29 and the cam angle sensor 31, respectively, the current combustion stroke cylinder #n cylinder is n = 1, 3, 2, 4 is determined, and in step S106, # before the first combustion stroke is determined.
The n-1 cylinder is determined.

For example, as shown in FIG. 18, when a crank pulse is input from the crank angle sensor 29 after the θ5 cam pulse is input from the cam angle sensor 31, the crank pulse is used to determine 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 the input of the θ6 cam pulse indicates the crank angle of the # 4 cylinder.
When a 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 31, it can be determined that the crank pulse input from the crank angle sensor 29 indicates the reference crank angle (θ1) of the corresponding cylinder.

In this embodiment, the ignition order is # 1 → # 3 →
# 2 → # 4, for example, the misfire diagnosis routine is now #
When executed in synchronization with the θ3 crank pulse of the BTDC θ3 of the three cylinders, the combustion stroke cylinder #n is the # 1 cylinder, and
Cylinder # n-1 before the combustion stroke is # 4 cylinder, and cylinder # n-2 before the combustion stroke is # 2 cylinder.

Here, the detected position of the crank angle by the crank angle sensor 29 is determined by the manufacturing tolerance of the position and the shape of each of the projections 31a, 31b, 31c of the crank rotor 31, and the position of the crank angle sensor 29 to the engine 1. There is a permissible error of the mounting position of each engine.

Therefore, the differential rotation DELNE calculated based on the crank pulse from the crank angle sensor 29 is calculated.
n includes the variation due to these errors,
In particular, when the engine is running at high speed, as shown in FIG. 11, the result is that apparently large engine rotation fluctuations occur uniformly.

For this reason, the steps from step S106
In S107, the differential rotation DE calculated in step S104 is calculated.
From LNEn, the differential rotation correction value AVEDN0 of the #n cylinder up to the previous time calculated by statistically processing this differential rotation DELNEn.
By subtracting n and calculating as a corrected differential rotation DELNAn (DELNAn ← DELNEn−AVEDN0n), the differential rotation before correction DELNEn shown in FIG.
Manufacturing tolerance of the position and shape of each projection 31a, 31b, 31c of the crank rotor 31, crank angle sensor 2
As shown in FIG. 12, the engine rotation speed corresponding to the #n cylinder and the engine rotation speed corresponding to the # n-1 cylinder one combustion stroke before were removed, as shown in FIG. Find the exact difference rotation between numbers.

Note that FIGS. 11 and 12 and FIGS.
In the graph, the difference rotation data calculated in the ECU 40 is shown with one graduation on the vertical axis being 50 rotations and one graduation (1 div) on the horizontal axis being 720 ° CA.

Then, steps S107 to S1 are performed.
Proceeding to 08, the corrected differential rotation DELNAn of the #n cylinder is
The difference between the corrected differential rotation speed DELNAn-1 of the # n-1 cylinder calculated at the time of execution of the previous routine and the corrected differential rotation change DDN
Calculated as EAn (DDNEAn ← DELNAn−DE
LNAn-1), a misfire diagnosis for the # n-1 cylinder is performed in the subsequent processing.

As described above, for example, when this misfire diagnosis routine is executed in synchronization with the BTDC θ3 crank pulse of the # 3 cylinder, the # 4 cylinder as the cylinder # n−1 one combustion stroke before is subjected to the misfire diagnosis. Become a cylinder, BT of # 1 cylinder
The # 4 cylinder (# n-1) one combustion stroke before, which was calculated based on the input interval time between the θ2 and θ3 crank pulses of DC θ2 and θ3.
The rotation speed MN of the # 2 cylinder (# n-2) two combustion strokes before based on the input interval time between the BTDC θ2 and θ3 crank pulses of the # 4 cylinder based on the rotation speed MNX4 (= MNXn-1) of the #cylinder)
X2 (= MNXn-2) is subtracted, statistically processed, and the corrected differential rotation speed DELNA4 (= DELNAn-1) of the # 4 cylinder (# n-1 cylinder) obtained at the time of execution of the previous routine, and the # 3 cylinder BTDC θ2, θ3 Based on the input interval time between crank pulses, the rotation speed MNX1 (= MNXn) to the BTD of the # 1 cylinder
The rotational speed MNX4 (= MNXn-1) based on the input interval time between Cθ2 and θ3 crank pulses is subtracted, statistically processed, and the corrected differential rotation DELNA1 of the # 1 cylinder (#n cylinder) obtained in this routine is obtained. (= DELNAn), a misfire diagnosis is performed on the corresponding cylinder # 4 (# n-1 cylinder).

That is, when an intermittent rotation fluctuation such as a snatch occurs in the engine, it is difficult to make an accurate misfire determination only by comparing the corrected differential rotation DELNAn with a predetermined misfire determination level. By capturing the change in the differential rotation after the correction, as shown in FIG. 13, the difference in the rotation of the engine due to the snatch or the like is changed, as shown in FIG. Eliminate the effects and enable accurate misfire detection.

Next, steps S108 to S109 are performed.
When proceeding to the subsequent steps, it is determined whether or not the misfire diagnosis condition is satisfied in each of steps S109, S110, and S111. That is,
In step S109, it is checked whether or not the fuel is being cut.
At 10, it is checked whether the basic fuel injection pulse width Tp is smaller than the set value TpLWER. In step S111, it is determined whether or not the engine speed NE is equal to or higher than a set speed NEUPER.

After the steps S109, S110, and S111, the fuel cut is not being performed, and Tp ≧ TpLWER and N
If E <NEUPER, step S1
Proceed to 12 to set the diagnosis permission flag FLGDIAG (FL
GDIAG ← 1) On the other hand, when fuel cut is being performed in step S109, when Tp <TpLWER in step S110, or when NE ≧ NEUPER in step S111, the diagnostic condition is not satisfied and the process branches from step S113 to step S113. And clears the diagnosis permission flag FLGDIAG (FLGDIAG
AG ← 0).

Then, when the process proceeds from step S112 or step S113 to step S114, a single-shot misfire diagnosis subroutine described later is executed. In step S115, the value of the misfire flag FLGMISn-1 of the # n-1 cylinder one combustion stroke before is performed. See The misfire flag FLGMISn-1 is set to FLGMISn-1 = 1 when it is determined that a misfire has occurred in the single-shot misfire diagnosis in step S114, and FLGMISn-1 = 0, that is, # as the misfire diagnosis target If no misfire has occurred in the n-1 cylinder, the process proceeds from step S115 to step S116, where # n-
The difference Δ (= DELNE) between the differential rotation DELNEn-1 of one cylinder and the differential rotation weighted average value AVEDN0 of all cylinders up to the previous time.
n−1−AVEDN0) is the upper and lower set values MINDN, M
It is determined whether it is within a predetermined setting range between AXDN (MINDN <MAXDN).

As a result, in step S116, MI
NDN <Δ <MAXDN, and when it is within the set range, the crank rotor 28 or the crank angle sensor 29
It is determined that the differential rotation DELNEn is fluctuating due to the error related to the differential rotation DELNEn−1 in steps S120 and S121.
Is statistically processed, and the process proceeds to step S122.

That is, in step S120, in order to correct the differential rotation fluctuation due to the error, a new differential rotation weighted average value AVEDN0 of all the cylinders up to the previous time and the corrected differential rotation DELNAn-1 of the # n-1 cylinder are newly obtained. Calculating the total cylinder difference rotation weighted average AVEDN, (AVEDN ← (3/4) × A
VEDN0 + (1/4) × DELNAn-1), step S
At 121, this new all-cylinder differential rotation weighted average value AVEDN
And the differential rotation DELNEn-1 of the # n-1 cylinder and
The differential rotation correction value AVEDN0n- of the # n-1 cylinder up to the previous time
From 1, the differential rotation correction value AVEDNn for the new # n-1 cylinder
-1 is calculated (AVEDnn-1 ← (7/8) × AVED
N0n-1 + (1/8) x (DELNEn-1-AVED
N)).

On the other hand, in step S115, FLGMIS
When n-1 = 1, that is, when the # n-1 cylinder misfires,
The process branches from step S115 to step S117 to count up the misfire count MISCNTn-1 (M
ISCNTn-1 ← MISCNTn-1 + 1), step S118
Proceed to. When Δ ≦ MINDN or Δ ≧ MAXDN in step S116, the crank rotor 28
Alternatively, it is determined that the change is the fluctuation of the differential rotation DELNEn-1 irrespective of the error of the crank angle sensor 29, and the fluctuation of the differential rotation DELNEn-1 is caused by another factor such as snatching, acceleration and deceleration, and the process proceeds to step S118.

In step S118, the weighted average value of all cylinder difference rotations AVEDN0 up to the previous time is set as the current weighted average value of all cylinder difference rotations AVEDN (AVEDN ← AVEDN0), and in step S119, the difference between the # n-1 cylinder and the previous time is determined. The rotation correction value AVEDN0n-1 is set as a new # n-1 cylinder difference rotation correction value AVEDNn-1 (AVEDNn-1 ← AVEDN0n-).
1), and 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.
The process jumps to step S128, and when FLGDIAG = 1, in step S123, the count value CRACNT, which is counted each time misfire diagnosis is performed, is incremented (CRACNT).
← CRACNT + 1), count value CR in step S124
It is determined whether or not ACNT has reached a set value, for example, 2000. As described above, this misfire detection routine is based on θ
Since the process is executed every three crank pulse inputs, that is, every 1/2 engine revolution, CRACNT = 2000 indicates 1000 engine revolutions.

In step S124, CRACNT <2
000, the flow branches to step S128, and CRACNT ≧
At the time of 2000, a misfire determination subroutine described later is executed in step S125, and in steps S126 and S127, the count value CRACNT and the count values MISCNT1 to MISCNT4 of the number of misfires for all cylinders are cleared (CRA).
CNT ← 0, MISCNT1 to 4 ← 0), and the process proceeds to step S128.

In step S128, the intake pipe pressure NEWPINTn-1 corresponding to the current # n-1 cylinder is set to the old data OL.
DPINTn-1 (OLDPINTn-1 ← NEWPIN
Tn-1), in step S129, the differential rotation DEL calculated this time
NEn, corrected differential rotation DELNAn, corrected differential rotation change D
DNEAn, all cylinder difference rotation weighted average value AVEDN, #n
The data of the -1 cylinder differential rotation correction value AVEDNn-1 is set in the RAM 43 as monitoring data, and the routine exits.

Next, the single-fire misfire diagnosis subroutine of step S114 in the above misfire diagnosis routine and step S1
The 25 misfire determination subroutines will be described.

First, in the single-shot misfire diagnosis subroutine shown in FIG. 2, in step S201, a diagnosis permission flag FLGDI
Referring to the value of AG, when FLGDIAG = 0, step
At S208, misfire flag F for cylinder # n-1 one combustion stroke before
LGMISn-1 is cleared (FLGMISn-1 ← 0), and the process returns to step S115 of the misfire diagnosis routine, where FLGDI
When AG = 1, the process proceeds to step S202.

In step S202, the misfire determination level LVLMIS is referenced by referring to the misfire determination level map using the engine speed NE and the basic fuel injection pulse width Tp as parameters.
Set. This misfire determination level LVLMIS is shown in FIG.
As shown in FIG. 4, the engine low load region where the basic fuel injection pulse width Tp is small is set as a non-diagnosable region, and the level of misfire determination is increased as the basic fuel injection pulse width Tp increases and the load increases. Are set, for example,
As shown in FIG. 15, a misfire determination level map composed of an 8 × 8 grid is stored in the ROM 42, and the misfire determination level LVLMIS is set by referring to the misfire determination level map with interpolation calculation.

Then, the process proceeds to step S203, and similarly, using the engine speed NE and the basic fuel injection pulse width Tp as parameters, for example, the intake pipe stored in the ROM 42 having an 8 × 8 grid as shown in FIG. When the intake pipe pressure misfire determination value PINTMIS is set by referring to the pressure misfire determination value map with interpolation calculation, the process proceeds to step S204 and thereafter, and the single-shot misfire is performed using the misfire determination level LVLMIS and the intake pipe pressure misfire determination value PINTMIS. Make a decision.

That is, the intake pipe pressure is generated when air is sucked into the cylinder within a certain unit time. However, if a misfire occurs in the corresponding cylinder, the engine speed decreases and the intake valve is opened. The time is relatively long, and the time for sucking air into the cylinder is long, and the ventilation efficiency between intake and exhaust in the cylinder is reduced. The intake air amount of the corresponding cylinder decreases.

Therefore, when the variation in the rotational speed of a certain cylinder exceeds the level determined to be misfire, and the intake pipe pressure at the crank angle at that time becomes higher than the intake pipe pressure before a certain crank angle (atmospheric pressure). Is approached), it is possible to determine that a misfire has occurred, and it is possible to reliably detect a misfire even in an operation region in which erroneous determination is likely to occur, such as during high-speed low-load operation.

After step S204, first, in step S2
In 04, the corrected differential rotation change DDN of the #n cylinder from the RAM 43 is read.
EAn is read, and the corrected differential rotation change DD of the #n cylinder is read.
NEAn is compared with the misfire determination level LVLMIS.
When DDNEAn <LVLMIS, it is determined that no misfire has occurred, and the process returns from step S204 to step S115 of the misfire diagnosis routine via step S208 described above.
If DNAnn ≧ LVLMIS, the process proceeds to step S205, where the negative misfire determination level (−LVLMIS) and the RAM 43
Differential rotation change DDNE of cylinder # n-1 read from
Compare with An-1.

Then, in the above step S205, DDNEA
If n-1> -LVLMIS, it is determined that there is no misfire, and the process branches to step S208 described above, where DDNEAn-1 ≦ −LV.
In the case of the LMIS, further, in step S206, a change in the intake pipe pressure (NEWPINTn-1−OLDPINTn-1) which is a difference between the current intake pipe pressure NEWPINTn-1 corresponding to the # n-1 cylinder and the old data OLDPINTn-1 is obtained. Is compared with the intake pipe pressure misfire determination value PINTMIS. This intake pipe pressure change (NEWPINTn-1-OLDPINTn-1)
As described above, the execution cycle of the misfire determination routine is θ
The old data OLDPINTn-1 of the intake pipe pressure corresponding to the # n-1 cylinder is 720 ° every 3 crank pulse inputs.
Since it is before, the change is from the crank angle of 720 ° before the intake pipe pressure corresponding to the # n-1 cylinder to the current crank angle.

As a result of the comparison in step S206, (NEW
If (PINTn-1-OLDPINTn-1) <PINTMIS, it is determined that no misfire has occurred, and the aforementioned step S208 is performed.
And returns to step S115 of the misfire diagnosis routine through
(NEWPINTn-1−OLDPINTn-1) ≧ PINT
At the time of MIS, it is finally determined that a single-shot misfire has occurred in the # n-1 cylinder, and the routine proceeds to step S207, where the misfire flag F
After setting LGMISn-1 (FLGMISn-1 ← 1), the process returns to step S115 of the misfire diagnosis routine.

That is, after the corrected differential rotation decreases in the negative direction below the misfire determination level LVLMIS from the # n-2 cylinder to the # n-1 cylinder, the corrected differential rotation from the # n-1 cylinder to the #n cylinder. Is increased in the positive direction above the misfire determination level LVLMIS, it is considered that a misfire has occurred in the # n-1 cylinder. Cannot be said that there is no possibility of erroneous determination.

Therefore, only when it is determined that there is a possibility of a misfire based on the change in the corrected differential rotation and the change in the intake pipe pressure is equal to or greater than the intake pipe pressure misfire determination value PINTMIS, # n−1 By determining that a misfire has occurred in the cylinder, as shown in FIG. 17, it can be distinguished from an engine rotation fluctuation such as a snatch in which the differential rotation continuously changes for a predetermined time,
It is possible to prevent misjudgment and accurately detect misfire regardless of the driving state.

In the misfire determination subroutine shown in FIG. 6, in step S301, the total number of misfires of the four cylinders detected by the single-fire misfire diagnosis subroutine is divided by MIS.
CNTn (n = 1 to 4) is used as the count value CRACNT (= 2000) in step S123 of the misfire diagnosis routine.
MISC misfire rate per 1000 engine revolutions
Calculate NT (%) (MISCNT ← ΣMISCNT
n / CRACNT × 100).

Next, the process proceeds to step S302, in which the misfire rate MISCNT calculated in step S301 is set to 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
Is a constant stored in the ROM 42 in advance with the parameters as parameters.

As a result of the determination in step S302, M
If ISCNT ≧ LMSCNT, step S303
Then, the misfire rate MISCNT is stored at a predetermined address of the backup RAM 44, and at step S304, it is checked whether or not the first misfire determination NG flag FLGNG1 stored at the predetermined address of the backup RAM 44 is set.

Then, in step S304, the first-time misfire determination NG flag FLGNG1 has not been set, and F
When LGNG1 = 0, the process jumps from step S304 to step S306, and the first misfire determination NG flag FLG
When NG1 is set and FLGNG1 = 1, the process proceeds from step S304 to step S305, where the backup R
The second misfire determination NG flag FLGNG2 stored at a predetermined address of the AM 44 is set (FLGNG2 ←
1) A warning is issued to the user by turning on or blinking the MIL lamp 54, and the process proceeds to step S306.

In step S306, the first-time misfire determination NG flag FLGNG1 is set (FLGNG1 ← 1).
In S312, the misfire OK counter for counting the number of determinations of no abnormality is cleared (CNTOK ← 0), and the process returns to step S126 of the misfire diagnosis routine.

That is, in order to avoid erroneous diagnosis due to noise or the like, the misfire rate MISCNT is set to the set value LM in the first determination.
Even if SCNT or more, the warning is not immediately issued, and the misfire rate MISCNT continues to be the set value LMSC in the second determination.
When it becomes NT or more, the cylinder is determined to be abnormal and a warning is issued.

At this time, the trouble data of the misfiring cylinder is stored in the backup RAM 44, and when troubleshooting at the dealer, the backup RAM 44 is operated by the blinking code of the monitor lamp of the ECU 40 or by the above-mentioned select monitor 60. By reading the trouble data stored in the storage device, the contents of the trouble can be known. Then, after the misfire cylinder is determined and repaired, the trouble data in the backup RAM 44 is cleared via the select monitor 60 or the like.

On the other hand, in step S302, the MISCNT
If <LMSCNT, it is determined that there is no abnormality, and step
When the misfire OK counter CNTOK is incremented in step S307 (CNTOK ← CNTOK + 1), step S308 is performed.
Then, it is determined whether or not the value of the misfire OK counter CNTOK has exceeded 80 times. If CNTOK <80, the flow directly returns to step S126 of the misfire diagnosis routine, and CN
When TOK ≧ 80, the first misfire determination NG flag FLGNG1, the second misfire determination NG flag FLGNG2, and the misfire rate MISCNT are cleared in steps S309, S310, and S311, respectively (FLGNG1 ← 0, FLGNG2 ← 0, MISC).
NT ← 0), the misfire OK counter C in step S312 described above.
NTOK is cleared (CNTOK ← 0), and the routine returns to step S126 of the misfire diagnosis routine.

FIGS. 19 and 20 relate to the second embodiment of the present invention. FIG. 19 is a partial flowchart of a misfire diagnosis routine, and FIG. 20 is a flowchart of a single-shot misfire diagnosis subroutine.

This embodiment is different from the first embodiment in which misfire is determined based on the intake pipe pressure change from a certain crank angle before to the current crank angle to the intake pipe pressure change based on the weighted average value of the intake pipe pressure. The misfire determination is performed based on the above, and the corresponding steps of the misfire diagnosis routine and the single-shot misfire diagnosis routine are changed.

That is, in the misfire diagnosis routine of this embodiment, as shown in FIG. 19, step S128 in FIG. 5 is changed to step S1280, and in this step S1280, the current value corresponding to the # n-1 cylinder in step S103 is changed. From the intake pipe pressure NEWPINTn-1 and the intake pipe pressure weighted average value DPINTn-1 corresponding to the cylinder # n-1 up to the previous time.
A new weighted average value DPINTn-1 is calculated (DPINTn
-1 ← (7/8) × DPINTn−1 + (1/8) × NEW
PINTn-1), and the weighted average value DPINTn-1 is used in a single misfire diagnosis.

In the single misfire diagnosis subroutine, as shown in FIG. 20, the step S206 of the single misfire diagnosis subroutine of the first embodiment shown in FIG. 2 is changed to step S2060, and in this step S2060, the # n-1 cylinder is set. The intake pipe pressure change (NE) which is the difference between the corresponding current intake pipe pressure NEWPINTn-1 and the intake pipe pressure weighted average value DPINTn-1.
WPINTn-1-DPINTn-1) is compared with an intake pipe pressure misfire determination value PINTMIS.

Then, (NEWPINTn-1-DPIN
If (Tn-1) <PINTMIS, it is determined that no misfire has occurred, and the process returns from step S2060 to step S208 to the misfire diagnosis routine, where (NEWPINTn-1-DPIN).
If (Tn-1) ≥PINTMIS, it is finally determined that a single-shot misfire has occurred in the # n-1 cylinder, and step S2060 is performed.
From step S207 to the misfire flag FLGMISn-1.
And returns to the misfire diagnosis routine.

In this embodiment, since the intake pipe pressure weighted average value is used, misfire can be reliably detected even if misfires occur continuously in the same cylinder, and the misfire diagnosis accuracy is further improved as compared with the first embodiment. Can be improved.

[0087]

As described above, according to the present invention, the difference between the engine speed of the cylinder in the combustion stroke and the engine speed of the cylinder one combustion stroke before is obtained as the difference rotation, and this difference rotation is statistically calculated. The corrected differential rotation obtained by processing and correcting the error relating to the rotation detecting means is calculated, and based on the output from the pressure detecting means, the change in the intake pipe pressure corresponding to the cylinder one combustion stroke before is calculated and corrected. The change in the rear differential rotation is less than or equal to a negative value equal to or less than the misfire determination level for misfire determination based on a change in the engine speed set based on the engine operation state between the cylinder before the two combustion strokes and the cylinder before the one combustion stroke. Is a positive value equal to or higher than the misfire determination level between the cylinder one combustion stroke before and the combustion stroke cylinder, and an intake pipe for misfire determination based on a change in intake pipe pressure set according to the engine operation region. Pressure misfire judgment value or less When it becomes, for determining that before one combustion stroke of the cylinder is misfiring state, without being affected by rotation fluctuation of the engine due to causes other than misfire, and,
Excellent effects can be obtained, for example, a misfire can be reliably detected even in an operation region where misjudgment is likely to occur, and diagnostic accuracy and reliability can be improved.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is a flowchart of a single-shot misfire diagnosis subroutine according to the first embodiment of the present invention;

FIG. 3 is a flowchart of a misfire diagnosis routine (part 1);

FIG. 4 is a flowchart showing a misfire diagnosis routine (part 2);

FIG. 5 is a flowchart showing a misfire diagnosis routine (part 3);

FIG. 6 is a flowchart showing a misfire determination subroutine.

FIG. 7 is a schematic configuration diagram of an engine control system according to the first embodiment;

FIG. 8 is a front view of the crank rotor and the crank angle sensor according to the first embodiment;

FIG. 9 is a front view of the cam rotor and the cam angle sensor according to the first embodiment;

FIG. 10 is a circuit diagram of an electronic control system according to the first embodiment;

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

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

FIG. 13 is an explanatory diagram showing a differential rotation when a misfire occurs.

FIG. 14 is an explanatory diagram of a misfire determination level according to the first embodiment;

FIG. 15 is an explanatory diagram of a misfire determination level map according to the embodiment;

FIG. 16 is an explanatory diagram of an intake pipe pressure misfire determination value map;

FIG. 17 is an explanatory diagram showing an operation state and a differential rotation when a snatch occurs

FIG. 18 is a time chart showing a relationship among a crank pulse, a cam pulse, a combustion stroke cylinder, and an ignition timing.

FIG. 19 is a partial flowchart of a misfire diagnosis routine according to the second embodiment of the present invention.

FIG. 20 is a flowchart of a single-fire misfire diagnosis subroutine;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine 13 ... Intake pipe pressure sensor (pressure detecting means) 28 ... Crank rotor (rotation detecting means) 29 ... Crank angle sensor (rotation detecting means) DELNEn ... Differential rotation DELNAn ... Corrected differential rotation DDNEAn ... Corrected differential rotation change LVLMIS: misfire determination level PINTMIS: intake pipe pressure misfire determination value NEWPINTn-1: intake pipe pressure (intake pipe pressure at current crank angle) OLDPINTn-1: intake pipe pressure (intake pipe pressure before a certain crank angle) DPINTn-1 … Intake pipe pressure weighted average

Claims (3)

[Claims] 1. A method for calculating a difference between an engine speed of a cylinder in a combustion stroke and an engine speed of a cylinder one combustion stroke before as a differential rotation based on an output from rotation detection means for detecting engine rotation. Rotation calculating means, statistically processing the differential rotation calculated by the differential rotation calculating means, and a corrected differential rotation calculating means for calculating a corrected differential rotation by correcting an error relating to the rotation detecting means; and detecting an intake pipe pressure. Pipe pressure change calculating means for calculating a change in the intake pipe pressure corresponding to the cylinder one combustion stroke before, based on the output from the pressure detecting means, and a change in the engine speed based on the engine operating state. A misfire determination level setting means for setting a misfire determination level for misfire determination; and an suction setting unit for setting an intake pipe pressure misfire determination value for misfire determination based on a change in intake pipe pressure in accordance with an engine operating region. The change in the corrected differential rotation calculated by the pipe pressure misfire determination value setting means and the corrected differential rotation calculation means is equal to or less than the misfire determination level between the cylinder before the two combustion strokes and the cylinder before the one combustion stroke. The negative value is a positive value equal to or higher than the misfire determination level between the cylinder one combustion stroke before and the combustion stroke cylinder, and the change in the intake pipe pressure calculated by the intake pipe pressure change calculating means is the same as the intake pipe pressure change. An engine misfire diagnosis device, comprising: misfire determination means for determining that a cylinder before a combustion stroke is in a misfire state when a pressure misfire determination value is equal to or more than a pressure misfire determination value. 2. The intake pipe pressure change calculating means calculates a difference between an intake pipe pressure at a current crank angle and an intake pipe pressure before a predetermined crank angle as an intake pipe pressure change. An engine misfire diagnosis device according to the above. 3. The intake pipe pressure change calculating means calculates a difference between an intake pipe pressure at a current crank angle and a statistically processed value of the intake pipe pressure as an intake pipe pressure change. Engine misfire diagnostic device.