JPH10148153A - Misfire diagnostic device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To positively prevent erroneous diagnosis due to snatch or disturbance to improve the misfire diagnostic accuracy. SOLUTION: The engine speed is calculated for every a specified crank angle between cylinders, the last engine speed is subtracted from the present engine speed to calculate a difference rotation, a correction value of the difference rotation is subtracted from the difference rotation to calculate a corrected difference rotation, and the corrected difference rotation of an object cylinder #n-1 prior to one combustion process, is subtracted from the corrected difference rotation to calculate a corrected difference rotation-change DDNEAn of a cylinder #n. A false judgement preventing-judging level LVLMISL for judging the rotational variations due to a misfire judging level LVLMISH and factors other than misfire, is set based on the engine speed NE and the basic fuel injection pulse width Tp (S42, 43). When the corrected difference rotation-change DDNEAn-1 in relation to the object cylinder #n-1 is a minus misfire judging level or less (S44) and a minus false judgment preventing-judging level or above (S46), and when the corrected difference rotation- change DDNEAn in relation to the cylinder #n in the present process is a misfire judging level or above (S46), the diagnostic object cylinder #n-1 is judged to be misfired (S47).

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 diagnosing a misfire based on a change in an engine rotation state quantity for each predetermined crank angle. The present invention relates to an engine misfire diagnosis device that improves misfire diagnosis accuracy.

[0002]

2. Description of the Related Art Conventionally, an engine misfire diagnosis apparatus for diagnosing engine misfire based on a change in an engine rotation state quantity for each predetermined crank angle has been employed.

[0003] However, since the engine rotational state quantity also changes due to snatching, disturbance, or the like, erroneous diagnosis occurs if the misfire of the engine is simply diagnosed based on the change in the engine rotational state quantity for each predetermined crank angle.

To cope with this, the present applicant has disclosed in
No. 4,423,972.

In this prior art, an engine speed is used as an engine speed state quantity, and a difference in engine speed between cylinders at each predetermined crank angle, that is, a differential speed DELN.
E is calculated and the differential rotation DELN of the current combustion stroke cylinder #n is calculated.
The crank angle is calculated by subtracting the differential rotation correction value AVEDNX for the cylinder #n calculated one cycle (720 ° CA) earlier by a statistical process using a weighted average from En to calculate the corrected differential rotation DELNAn for the cylinder. Eliminate the effects of manufacturing tolerances, mounting tolerances, etc. of the crank rotor and crank angle sensor for detection. Further, the corrected differential rotation change DDNEA for the cylinder #n is subtracted from the corrected differential rotation DELNAn by subtracting the corrected differential rotation DELNAn-1 of the misfire diagnosis target cylinder # n-1 one combustion stroke before.
n, and calculates the corrected differential rotation change DDNEAn based on the engine operating state.
In addition to the comparison with IS, the correction difference rotation change DDNEAn-1 for the misfire diagnosis target cylinder # n-1 one combustion stroke before calculated at the time of execution of the previous routine is minus the misfire determination level minus.
Compare with LVLMIS. Then, the current change in the correction difference rotational speed DDNEAn of the combustion stroke cylinder #n is determined by the misfire determination level L.
When VLMIS or more and the correction differential rotation change DDNEAn-1 of the misfire diagnosis target cylinder # n-1 is equal to or less than the minus misfire determination level, it is determined that misfire of the misfire diagnosis target cylinder # n-1 is misfired. Eliminates the effects of dynamic rotation fluctuations,
Prevents misdiagnosis due to snatching.

In other words, if an intermittent rotation fluctuation such as a snatch occurs in the engine, the intermittent rotation fluctuation due to the snatch or the like is erroneously diagnosed as a misfire simply by comparing the corrected differential rotation DELNA with a predetermined misfire determination level. Would. For this reason, in each of the preceding examples, the correction difference rotation DEL of the front and rear cylinders
By determining the misfire based on the change in NA, that is, the corrected differential rotation change DDNEA, the influence of intermittent rotation fluctuation such as a snatch is eliminated, and the misfire diagnosis accuracy is improved.

[0007]

However, in the above-mentioned prior art, the present and previous correction difference rotation change DDNE
An, DDNEAn-1 is a single misfire determination level L for judging misfire set based on the engine operating state.
Positive / negative misfire determination level LVLMI based on VLMIS
S, -LVLMIS are compared with each other to determine the misfire of the cylinder # n-1 for which misfire is to be diagnosed. Since the snatch, disturbance, and the like are not necessarily directly determined, there is a limit to the improvement of the misfire diagnostic accuracy. There is.

The present invention has been made in view of the above circumstances, and has as its object to provide an engine misfire diagnosis device capable of reliably preventing misdiagnosis due to snatching, disturbance, or the like and further improving misfire diagnosis accuracy.

[0009]

In order to achieve the above object, an engine misfire diagnosis apparatus according to the first aspect of the present invention, as shown in the basic configuration diagram of FIG. A rotational state quantity change detecting means for detecting a change in the rotational state quantity, a cylinder discriminating means for discriminating a current combustion stroke cylinder and judging a cylinder one combustion stroke earlier as a misfire diagnosis target cylinder, and a cylinder discriminating means for judging misfire. A misfire determination level setting means for setting a misfire determination level based on an engine operation state; and an erroneous determination prevention determination level for determining a change in the rotational state amount due to a factor other than a misfire with a value larger than the misfire determination level. An erroneous determination prevention determination level setting means that is set based on the state; and a change in the engine rotation state amount with respect to the misfire diagnosis target cylinder is equal to or less than the negative misfire determination level. Misfire determination means for determining that a misfire diagnosis target cylinder is misfired when the change in the engine rotation state quantity for the current combustion stroke cylinder is equal to or greater than the misfire determination level when the eggplant misjudgment prevention determination level is equal to or greater than the misjudgment prevention determination level. It is characterized by the following.

The engine misfire diagnosis apparatus according to the second aspect of the present invention, as shown in FIG. 1 (b), has an engine rotation state quantity detecting means for detecting an engine rotation state quantity at every predetermined crank angle between cylinders. A difference rotation state amount calculation means for calculating a difference between the rotation state amounts by subtracting the engine rotation state amount detected this time from the engine rotation state amount detected last time, and a current combustion stroke cylinder, and a cylinder one combustion stroke earlier. And a cylinder discriminating means for judging the cylinder as a misfire diagnosis target cylinder, and subtracting a differential rotation state amount correction value for the cylinder calculated one cycle before by a statistical process using a weighted average from the current rotation state amount of the combustion stroke cylinder, A correction difference rotation state amount calculation means for calculating a correction difference rotation state amount for the cylinder; and a correction difference rotation state amount of the misfire diagnosis target cylinder one combustion stroke prior to the correction difference rotation state amount. Correction difference rotation state amount change calculating means for calculating a change in the correction difference rotation state amount for the cylinder, misfire determination level setting means for setting a misfire determination level for determining misfire based on the engine operating state, Erroneous determination prevention determination level setting means for setting an erroneous determination prevention determination level for determining a change in the rotational state amount due to a factor other than misfire with a value larger than the misfire determination level based on the engine operation state; The change in the correction difference rotational state amount for the misfire diagnosis target cylinder is equal to or less than the negative misfire determination level and equal to or greater than the negative misjudgment prevention determination level, and the change in the engine rotational state amount for the current combustion stroke cylinder is A misfire determining means for determining that a misfire has occurred in the cylinder to be misfired when the misfire is at or above the misfire determination level.

According to a third aspect of the present invention, in the engine misfire diagnosis apparatus according to the first or second aspect, the engine rotation state quantity is an engine speed.

That is, according to the first aspect of the present invention, a change in the amount of engine rotation for each predetermined crank angle is detected, the current combustion stroke cylinder is determined, and the cylinder one combustion stroke earlier is determined as the misfire diagnosis target cylinder. to decide. Then, a misfire determination level for determining misfire and a misjudgment prevention determination level for determining a change in the rotational state amount due to a factor other than misfire with a value larger than the misfire determination level are set to the engine operating state, respectively. Set based on: The change in the amount of engine rotation for the misfire diagnosis target cylinder is equal to or less than the negative misfire determination level and equal to or greater than the negative misjudgment prevention determination level, and the change in the amount of engine rotation for the current combustion stroke cylinder is misfired. When it is equal to or higher than the determination level, it is determined that a misfire has occurred in the cylinder subject to misfire diagnosis. Here, an erroneous determination prevention determination level for determining a change in the engine rotation state amount due to a factor other than misfire based on the engine operating state is set, and the change in the engine rotation state amount for the misfire diagnosis target cylinder is determined as a negative erroneous determination. If it is less than the prevention determination level, it is determined that there is a factor other than misfire, that is, engine rotation fluctuation due to snatch or disturbance, and in this case, misfire diagnosis is excluded. On the other hand, when the change in the engine rotation state amount for the misfire diagnosis target cylinder is equal to or greater than the negative misjudgment prevention determination level, the change in the engine rotation state amount for the misfire diagnosis target cylinder is equal to or less than the negative misfire determination level, and
Only when the change in the amount of engine rotation with respect to the current combustion stroke cylinder is equal to or greater than the misfire determination level is determined to be misfire of the cylinder subject to misfire diagnosis, so that misdiagnosis due to snatch or disturbance is reliably prevented to improve misfire diagnosis accuracy. It is possible to improve.

According to the second aspect of the present invention, the amount of engine rotation is detected at each predetermined crank angle between cylinders, and the amount of rotation of the engine is detected by subtracting the amount of engine rotation detected this time from the previously detected amount of engine rotation. The difference is calculated, the current combustion stroke cylinder is determined, and the cylinder one combustion stroke earlier is determined as the misfire diagnosis target cylinder. Then, by subtracting the differential rotation state amount correction value for the cylinder calculated one cycle ago by statistical processing using a weighted average from the current rotation stroke amount of the cylinder in the combustion stroke cylinder, a corrected differential rotation state amount for the cylinder is calculated. Then, the change in the corrected differential rotation state amount for the cylinder is calculated by subtracting the corrected differential rotation state amount of the misfire diagnosis target cylinder one combustion stroke before from the corrected differential rotation state amount. Then, a misfire determination level for determining misfire and a misjudgment prevention determination level for determining a change in the rotational state amount due to a factor other than misfire with a value larger than the misfire determination level are set to the engine operating state, respectively. Set based on: Then, the change in the corrected difference rotational state amount with respect to the misfire diagnosis target cylinder one combustion stroke before is equal to or less than the negative misfire determination level and equal to or greater than the negative misjudgment prevention determination level, and the current combustion stroke cylinder is changed. When the change of the engine rotation state quantity with respect to the engine is equal to or more than the above-mentioned misfire determination level, it is determined that the misfire diagnosis target cylinder is misfired.

At this time, according to the third aspect of the invention, the engine speed is used as the rotational state quantity.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

First, the overall structure of the engine will be described with reference to FIG. In the figure, reference numeral 1 denotes an engine, which in this embodiment is a horizontally opposed four-cylinder gasoline engine. The cylinder block 1a of this engine 1
In each of the left and right banks, a cylinder head 2 is provided, and an intake port 2a and an exhaust port 2b are formed in each cylinder head 2.

In the intake system of the engine 1, an intake manifold 3 communicates with each intake port 2a, and a throttle chamber 5 communicates with the intake manifold 3 via an air chamber 4 in which intake passages of respective cylinders are gathered. . An air cleaner 7 is attached to the upstream side of the throttle chamber 5 via an intake pipe 6, and the air cleaner 7 is communicated with the air intake chamber 8.

The throttle chamber 5 is provided with a throttle valve 5a linked to an accelerator pedal. The intake pipe 6 is connected to a bypass passage 9 that bypasses the throttle valve 5a.
At the time of idling, the bypass passage 9 depends on the valve opening.
An idle speed control valve (ISC valve) 10 for controlling the idle speed by adjusting the amount of bypass air flowing through the engine is provided.

Further, an injector 11 is disposed immediately upstream of the intake port 2a of each cylinder of the intake manifold 3. The injector 11 has a fuel supply path 12
The fuel tank 13 is provided with an in-tank type fuel pump 14. The fuel from the fuel pump 14 is pressure-fed to the injector 11 and the pressure regulator 16 via the fuel filter 15 interposed in the fuel supply path 12, and is returned from the pressure regulator 16 to the fuel tank 13, where The fuel pressure to the injector 11 is adjusted to a predetermined pressure.

On the other hand, for each cylinder of the cylinder head 2, a spark plug 17 for exposing the discharge electrode at the tip to the combustion chamber is provided.
The ignition plug 17 is connected to an igniter 19 via an ignition coil 18 provided for each cylinder.

In the exhaust system of the engine 1, an exhaust pipe 21 is communicated with a collection portion of an exhaust manifold 20 communicating with each exhaust port 2b of the cylinder head 2, and a catalytic converter 22 is interposed in the exhaust pipe 21. And is communicated with the muffler 23.

Next, sensors for detecting the operating state of the engine will be described. Immediately downstream of the air cleaner 7 in the intake pipe 6, a thermal intake air amount sensor 24 using a hot wire or a hot film is interposed, and a throttle valve 5a provided in the throttle chamber 5 is provided with a throttle valve 5a. A throttle sensor 25 having a built-in opening sensor 25a and an idle switch 25b that is turned on when the throttle valve 5a is fully closed is connected in series.

The cylinder block 1a of the engine 1
A knock sensor 26 is mounted on the cooling water passage 2 which communicates the left and right banks of the cylinder block 1a.
7, a cooling water temperature sensor 28 is provided, and an O2 for detecting an air-fuel ratio state is provided upstream of the catalytic converter 22.
A sensor 29 is provided.

The crankshaft 30 of the engine 1
A crank angle sensor 32 is provided on the outer periphery of a crank rotor 31 that is axially mounted on the cam shaft 33. Further, a cam rotor 34 connected to a cam shaft 33 that makes a half turn with respect to the crank shaft 30 has a cam angle for cylinder identification. A sensor 35 is provided opposite.

As shown in FIG. 16, the crank rotor 31 has projections 31a, 31b and 31c formed on its outer periphery, and these projections 31a, 31b and 31c are connected to the cylinders (# 1 and # 2 cylinders). (# 3, # 4 cylinders) before compression top dead center (BTDC) θ1, θ2, θ3.
In the present embodiment, θ1 = 97 ° CA, θ2 = 65
° CA, θ3 = 10 ° CA.

As shown in FIG. 17, on the outer periphery of the cam rotor 34, projections 34a, 34b,
The protrusion 34a is formed at a position θ4 after the compression top dead center (ATDC) of the # 3 and # 4 cylinders.
b is composed of three protrusions, and the first protrusion is A of the # 1 cylinder.
It is formed at the position of TDCθ5. Further, the protrusion 34c
Is composed of two projections, and the first projection is the AT of the # 2 cylinder.
It is formed at the position of DCθ6. In the present embodiment, θ4 = 20 ° CA, θ5 = 5 ° CA, θ6 = 20 °
CA.

As shown in the time chart of FIG. 7, the crank rotor 31 and the cam rotor 34 are rotated by the rotation of the crankshaft 30 and the camshaft 33 in association with the operation of the engine. Detected by the angle sensor 32 and detected from the crank angle sensor 32 by θ1, θ2, θ3 (BTDC97
°, 65 °, 10 °) of the engine 1
Output every 1/2 rotation (180 ° CA). On the other hand, θ3
Each protrusion of the cam rotor 34 is detected by the cam angle sensor 35 between the crank pulse and the θ1 crank pulse, and a predetermined number of cam pulses are output from the cam angle sensor 35.

Then, an electronic control unit 40 described later (FIG. 1)
8), the engine speed NE is calculated based on the input interval time Tθ of the crank pulse output from the crank angle sensor 32, and the order of combustion stroke of each cylinder (for example, # 1 cylinder → # 3 cylinder) → # 2 cylinder → # 4 cylinder)
Based on the pattern of the cam pulse from the cam angle sensor 35 and the value counted by the counter, the cylinders such as the fuel injection target cylinder and the ignition target cylinder are determined.

The injector 11, the spark plug 17,
The calculation of control amounts for actuators such as the ISC valve 10 and the output of control signals, that is, engine control such as fuel injection control, ignition timing control, idle speed control, etc.
Is performed by an electronic control unit (ECU) 40 shown in FIG.

The ECU 40 includes a CPU 41, a ROM 4
2, RAM 43, backup RAM 44, counter
A timer group 45 and an I / O interface 46 are mainly configured by a microcomputer connected to each other via a bus line, and are connected to the constant voltage circuit 47 for supplying a stabilized power to each unit, and to the I / O interface 46. And a peripheral circuit such as an A / D converter 49.

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 (cam pulse), a fuel injection timer, an ignition timer, and a timer for generating a periodic interrupt. Various timers such as a periodic interrupt timer, a timer for measuring the input interval of a crank angle sensor signal (crank pulse), and a watchdog timer for monitoring a system abnormality are collectively referred to for convenience. Is used.

The constant voltage circuit 47 is connected to a battery 51 via a first relay contact of a power supply relay 50 having two relay contacts, and a relay coil of the power supply relay 50 is connected to the ignition switch 52 by the battery 51.
Connected through. The constant voltage circuit 47
When the ignition switch 52 is turned on and the contact of the power supply relay 50 is closed, power is supplied to each unit in the ECU 40 while the ignition switch 52 is turned on and the ignition switch 52 is turned on and off. Instead, the backup power is always supplied to the backup RAM 44. Further, the fuel pump 14 is connected to the battery 51 via a relay contact of a fuel pump relay 53. The power supply relay 50
A power line for supplying power from the battery 51 to each actuator is connected to the second relay contact.

The input port of the I / O interface 46 includes an idle switch 25b, a knock sensor 2
6. A crank angle sensor 32, a cam angle sensor 35, a vehicle speed sensor 36 for detecting a vehicle speed, and a starter switch 37 for detecting a starting state are connected, and further, via the A / D converter 49. And the intake air amount sensor 24, the throttle opening degree sensor 25a, the cooling water temperature sensor 2
8 and the O2 sensor 29 are connected, and the battery voltage VB is input and monitored.

On the other hand, an output port of the I / O interface 46 is disposed on the relay coil of the fuel pump relay 53, the ISC valve 10, the injector 11, and an instrument panel (not shown) to display various alarms in a centralized manner. The alarm lamp 38 is connected via the drive circuit 48 and the igniter 19 is connected.

An external connector 55 is connected to the I / O interface 46. A serial monitor (portable failure diagnostic device) 60 is connected to the external connector 55 to provide a serial monitor. 60, input / output data in the ECU 40 and the ECU 40
A misfire determination NG flag FLGNG, which indicates that a misfire stored in the backup RAM 44 has been diagnosed by the self-diagnosis function described below, a failed part including misfire cylinder data,
Trouble data indicating the content of the failure is read out to enable diagnosis. Further, the serial monitor 60 allows the trouble data to be initially set (cleared).

The diagnosis of trouble data by the serial monitor 60 and the initial set are described below.
It is described in detail in Japanese Patent Publication No. 7-76730 by the present applicant.

In accordance with the control program stored in the ROM 42, the CPU 41 processes the detection signals from the sensors and switches, which are input via the I / O interface 46, the battery voltage, etc., and stores them in the RAM 43. Based on various data, various learning value data stored in the backup RAM 44, fixed data stored in the ROM 42, and the like, a fuel injection amount, an ignition timing, a duty ratio of a drive signal for the ISC valve 10, and the like are calculated. It performs engine control such as injection control, ignition timing control, and idle speed control.

In such an engine control system, EC
In U40, misfire diagnosis is performed based on the change in the engine rotation state quantity. That is, using the engine rotational speed NE as an example of the engine rotational state amount, a change in the engine rotational speed for each predetermined crank angle is detected, and the crank pulse and the cam pulse output from the crank angle sensor 32 and the cam angle sensor 35 are detected. Based on current combustion stroke cylinder #
n is determined, and cylinder # n−1 one combustion stroke before is determined as a misfire diagnosis target cylinder. A misfire determination level LVLMISH for determining misfire and the misfire determination level LV
A misjudgment prevention judgment level LVLMI for judging rotation fluctuation caused by factors other than misfire with a value larger than LMISH
SL is set based on the engine operating state. Then, the change in the engine speed for the misfire diagnosis target cylinder # n-1 is represented by a minus misfire determination level-LVLMI.
SH or less and a negative erroneous determination prevention determination level -LVL
MISL or more, and the change in the engine speed for the current combustion stroke cylinder #n is the misfire determination level LVLM.
If ISH or more, it is determined that the misfire of the misfire diagnosis target cylinder # n-1 has occurred.

That is, an erroneous judgment prevention judgment level LVLMISL for judging a change in the engine speed due to factors other than the misfire based on the engine operating state is set, and the change in the engine speed for the misfire diagnosis target cylinder # n-1 is set. Is less than the negative erroneous determination prevention determination level -LVLMISL, it is determined that a factor other than misfire, that is, engine rotation fluctuation due to snatch, disturbance, or the like, and in this case, misfire diagnosis is excluded.

When the change in the engine speed with respect to the misfire diagnosis target cylinder # n-1 is equal to or more than the minus erroneous judgment prevention judgment level -LVLMISL, the misfire diagnosis target cylinder # n-
Only when the change in the engine speed with respect to 1 is equal to or less than the negative misfire determination level -LVLMISH and the change in the engine speed with respect to the current combustion stroke cylinder #n is equal to or greater than the misfire determination level LVLMISH, the misfire diagnosis target cylinder # n-
Judge as 1 misfire. Therefore, it is possible to reliably prevent erroneous diagnosis due to rotation fluctuations caused by snatches, disturbances and the like other than misfires, and to further improve misfire diagnosis accuracy.

More specifically, in the present embodiment,
The engine speed between BTDC θ2 and θ3, that is, the engine speed between θ2 and θ3 crank pulse inputs is adopted as the engine speed between cylinders for each predetermined crank angle, and the engine speed in the same section last time is calculated from the engine speed MNXn calculated this time. MNXn-1 is subtracted to calculate the difference between the rotation speeds, that is, the difference rotation DELNEn. Further, based on the crank pulse and the cam pulse respectively output from the crank angle sensor 32 and the cam angle sensor 35, the current combustion stroke cylinder #
n is determined, and cylinder # n−1 one combustion stroke before is determined as a misfire diagnosis target cylinder. Then, the current cylinder #n calculated one cycle (720 ° CA) earlier by the statistical processing based on the weighted average from the differential rotation DELNEn of the cylinder #n of the combustion stroke cylinder #n
Is subtracted from the differential rotation correction value AVEDNXn−4 to calculate a corrected differential rotation DELNAn for the cylinder #n.
The correction differential rotation change DDNEAn for the cylinder #n is calculated by subtracting the correction differential rotation DELNAn-1 of the misfire diagnosis target cylinder # n-1 one combustion stroke earlier from the corrected differential rotation DELNAn. A misfire determination level LVLMISH for determining misfire and the misfire determination level LVLMI
Misjudgment prevention judgment level LVLMISL for judging rotation fluctuation caused by factors other than misfire with a value larger than SH
Are set based on the respective engine operating conditions. The correction difference rotation change DDNEAn-1 for the misfire diagnosis target cylinder # n-1 is equal to the minus misfire determination level -LVLM.
ISH or less, and minus erroneous judgment prevention judgment level -LV
LMISL or higher and the current combustion stroke cylinder #n
Is greater than or equal to the misfire determination level LVLMISH, it is determined that the misfire diagnosis target cylinder # n-1 has misfired.

Therefore, as described above, the effects of the manufacturing tolerance, the mounting tolerance, and the like of the crank rotor 31 and the crank angle sensor 32 for detecting the crank angle which is the basis for detecting the engine speed are eliminated. Correction difference rotation DEL
NA, the change in the corrected differential rotation DELNA, that is, the corrected differential rotation change DDNEA is determined by the misfire determination level LVLM.
Compared with ISH and the erroneous determination prevention determination level LVLMISL, the correction difference rotation change DDNEAn, DDN of the front and rear cylinders is compared.
By determining the misfire of the cylinder # n-1 to be misfire-diagnosed by EAn-1, the synergy between the elimination of the tolerance of the crank rotor 31 and the crank angle sensor 32 and the prevention of the misdiagnosis due to the snatch, disturbance, and the like is further improved. Improve misfire diagnosis accuracy.

That is, the ECU 40 has the functions of the rotational state amount change detecting means, the cylinder determining means, the misfire determination level setting means, the erroneous determination prevention determination level setting means, and the misfire determination means according to the present invention. State quantity detection means,
It also implements functions as a difference rotation state amount calculation unit, a correction difference rotation state amount calculation unit, and a correction difference rotation state amount change calculation unit.

Hereinafter, the misfire diagnosis processing according to the present invention executed by the ECU 40 will be described with reference to the flowcharts shown in FIGS.

First, the ignition switch 52 is turned on.
Then, when the power is supplied to the ECU 40, the system is initialized, and each flag and each counter are initialized except for trouble data and data such as various learning values stored in the backup RAM 44. And
When the starter switch 37 is turned on and the engine is started, a cylinder discrimination / engine speed calculation routine shown in FIG. 2 is executed every time a crank pulse is input from the crank angle sensor 32.

In this cylinder discriminating / engine speed calculating routine, when the crank rotor 31 rotates with the engine operation and the crank pulse from the crank angle sensor 32 is input, first, in step S1, the crank input at this time is input. Whether the pulse corresponds to the crank angle of θ1, θ2, or θ3 is identified based on the input pattern of the cam pulse from the cam angle sensor 35. In step S2, the current combustion is determined based on the input pattern of the crank pulse and the cam pulse. The cylinders such as the stroke cylinder, the misfire diagnosis target cylinder, the ignition target cylinder, and the fuel injection target cylinder are determined.

That is, as shown in the time chart of FIG. 7, for example, if there is a cam pulse input between the input of the previous crank pulse and the input of the current crank pulse, the current crank pulse will be θ1 crank It can be identified as a pulse, and the crank pulse input next time can be identified as a θ2 crank pulse.

If there is no cam pulse input between the previous and current crank pulse inputs and there is a cam pulse input between the last and previous crank pulse inputs, the current crank pulse can be identified as a θ2 crank pulse, and The input crank pulse can be identified as a θ3 crank pulse. Further, when there is no cam pulse input between the previous and current times and between the last and last crank pulse inputs, the currently input crank pulse can be identified as the θ3 crank pulse, and the next input crank pulse is It can be identified as a θ1 crank pulse.

Further, three cam pulses are input between the previous and current crank pulse inputs (θ corresponding to the projection 34b).
(5 cam pulses), the next compression top dead center is # 3 cylinder, the current combustion stroke cylinder is # 1 cylinder, the misfire diagnosis target cylinder is # 4 cylinder one combustion stroke earlier, and the ignition target cylinder is # 3 cylinder.
It can be determined that the cylinder and the fuel injection target cylinder are the # 4 cylinder that is two cylinders behind the cylinder. When two cam pulses (θ6 cam pulse corresponding to the projection 34c) are input between the previous and current crank pulse inputs, the next compression top dead center is #
There are four cylinders. The current combustion stroke cylinder is # 2 cylinder, the misfire diagnosis target cylinder is # 3 cylinder, the ignition target cylinder is # 4 cylinder, and the fuel injection target cylinder is # 3 cylinder.

One cam pulse is input between the previous and current crank pulse inputs (θ4 corresponding to the projection 34a).
When the previous compression top dead center determination is # 4 cylinder, the next compression top dead center is # 1 cylinder, the current combustion stroke cylinder is # 4 cylinder, and the misfire diagnosis target cylinder is # 2. The cylinder and the cylinder to be ignited can be determined as # 1 cylinder, and the fuel injection cylinder can be determined as # 2 cylinder. Similarly, when one cam pulse is input between the previous and current crank pulse inputs, and the previous compression top dead center determination was # 3 cylinder, the next compression top dead center is # 2 cylinder, and the current compression top dead center is # 2 cylinder. The combustion stroke cylinder can be determined to be # 3 cylinder, the misfire diagnosis target cylinder is # 1 cylinder, the ignition target cylinder is # 2 cylinder, and the fuel injection target cylinder is # 1 cylinder.

In the four-stroke four-cylinder engine 1 of the present embodiment, the combustion strokes are in the order of # 1 → # 3 → # 2 → # 4, and as shown in the time chart of FIG. Assuming that the combustion stroke cylinder #n is the # 1 cylinder, the misfire diagnosis target cylinder is the immediately preceding # n-1 cylinder, that is, the # 4 cylinder.
Cylinder, and the cylinder to be ignited reaches the compression top dead center # n + 1
= # 3 cylinder, the fuel injection target cylinder #i at this time is part 2
The subsequent # n + 3 = # 4 cylinder. The cylinder discrimination results of the current combustion stroke cylinder #n and the misfire diagnosis target cylinder # n-1 are referred to in the misfire diagnosis routine shown in FIGS. Misfire diagnosis is performed for the target cylinder # n-1.

Although not described in detail here, the ignition timing for the cylinder # n + 1 is set in accordance with the result of the determination of the cylinder # n + 1 to be ignited, and the ignition timing is controlled for each cylinder. Further, the determination result of the fuel injection target cylinder #i (# n + 3 cylinder) is referred to in a fuel injection amount setting routine (not shown) executed every predetermined cycle, and the fuel injection amount is set for each cylinder.

Thereafter, the process proceeds from step S2 to step S3, in which the time from the previous crank pulse input to the present crank pulse input measured by the crank pulse input interval timer, that is, the crank pulse input interval time (θ1 crank pulse And the input interval time Tθ12 of the θ2 crank pulse, the input interval time Tθ23 of the θ2 crank pulse and the θ3 crank pulse, or the input interval time Tθ31 of the θ3 crank pulse and the θ1 crank pulse), and the crank pulse input interval time Tθ is detected.

Next, the routine proceeds to step S4, where the angle between the crank pulses corresponding to the crank pulse identified this time is read out, and the current engine speed N is determined based on the angle between the crank pulses and the crank pulse input interval time Tθ.
E is calculated, stored at a predetermined address in the RAM 43, and the routine exits. The angle between the crank pulses is known and is stored in advance in the ROM 42 as fixed data. In the present embodiment, the angle between the θ1 crank pulse and the θ2 crank pulse is 32 ° CA.
The angle between the θ2 crank pulse and the θ3 crank pulse is 55 ° CA, and the angle between the θ3 crank pulse and the θ1 crank pulse is 93 ° CA. Further, in consideration of the engine start, the engine speed NE is calculated at, for example, 150 rpm or more.

In the misfire diagnosis routine shown in FIGS. 3 and 4 executed every time the θ3 crank pulse is input, the misfire diagnosis target cylinder # n-1, the current combustion stroke cylinder #n,
And the respective data of the engine speed NE are read out, and misfire diagnosis is performed for the cylinder # n-1 for misfire diagnosis.

The misfire diagnosis routine is executed in response to the input of the θ3 crank pulse. At this time, the input interval time Tθ2 between the θ2 crank pulse and the θ3 crank pulse is obtained by the cylinder discrimination / engine speed calculation routine.
The engine speed NE between the BTDCs θ2 and θ3 is calculated based on (3), and the misfire diagnosis of the corresponding cylinder is performed based on the engine speed NE between the BTDCs θ2 and θ3.

In this misfire diagnosis routine, first,
In step S11, each data obtained in the previous execution of the routine is stored in the work area. In step S12, the current engine speed NE, that is, the latest BTDC θ2, θ
The engine speed NE between 3 is read and the current cylinder #n
(MNXn ←←)
NE).

Next, the process proceeds to step S13, and the process proceeds to step S12.
From the engine speed MNXn corresponding to the current cylinder #n set in the above, the engine speed MNXn-1 corresponding to the cylinder # n-1 one combustion stroke earlier set in the previous routine and stored in the work area is set. A subtraction is performed to calculate a change in the engine speed between cylinders at each predetermined crank angle, that is, a differential rotation DELNEn (DELNEn ← MNXn).
-MNXn-1).

In steps S14 and S15, the present combustion stroke cylinder data #n and misfire diagnosis target cylinder data # n-1 determined in the cylinder determination / engine speed calculation routine are read out, and the current combustion is performed. The stroke cylinder #n and the misfire diagnosis target cylinder # n-1 (= 1 cylinder before the combustion stroke) are specified.

Next, at step S16, the differential rotation DEL
A difference rotation correction value AVEDNXn−4 for the cylinder #n calculated at the time of execution of this routine four times before, that is, one cycle (720 ° CA) ago by statistical processing in steps S26 and S27 described later is subtracted from NEn, Correction difference rotation DE
Calculate LNAn (DELNAn ← DELNen-A
VEDNXn-4). This difference rotation correction value AVEDNX is
As will be described in detail later, the corrected differential rotation DELNA of all cylinders is weighted and averaged to calculate an all cylinder differential rotation weighted average value AVEDN, and further, the differential rotation DELNEn of the cylinder #n with respect to this all cylinder differential rotation weighted average value AVEDN. Is a weighted average.

That is, the crank angle detected by the crank angle sensor 32 includes manufacturing tolerances, such as the position and shape of each of the projections 31a, 31b, 31c of the crank rotor 31, and the crank angle sensor 32 to the engine 1. There is a permissible error or the like in the mounting position of each engine. Therefore, the difference rotation DELNE calculated based on the crank pulse from the crank angle sensor 32 includes variations due to these errors. For this reason, especially at the time of high engine rotation, as shown in FIG.
As a result, large engine speed fluctuations occur uniformly. If the misfire diagnosis is made directly by this differential speed DELNE, an erroneous diagnosis will occur.

Therefore, by subtracting the differential rotation correction value AVEDNXn-4 for the cylinder #n calculated one cycle earlier by the statistical processing from the differential rotation DELNEn, and calculating the corrected differential rotation DELNAn, the crank rotor 31
Of the projections 31a, 31b, and 31c, and the tolerance of the mounting position of the crank angle sensor 32 to the engine 1 and the like.
, And an accurate difference between the engine speed MNXn-1 for the cylinder # n-1 one combustion stroke before and the engine speed MNXn-1 for the cylinder # n-1 one combustion stroke earlier. In the timing chart of FIG.
The correction differential rotation DELNA is shown. Differential rotation D shown in FIG.
With respect to ELNE, as shown in FIG.
It can be seen that in the case of NA, an accurate differential rotation in which the influence of the above-described tolerance is eliminated is obtained.

In FIGS. 8, 9 and FIG. 10, which will be described later, the differential rotation data calculated by the ECU 40 is shown with one scale on the vertical axis being 50 rpm and one scale (1 div) on the horizontal axis being 720 ° CA. Show.

Here, for example, if the misfire diagnosis routine is executed by inputting the BTDCθ3 crank pulse of the # 3 cylinder, the current combustion stroke cylinder #n is the # 1 cylinder, and the cylinder # n- one cylinder before the combustion stroke is executed. As # 1, cylinder # 4 becomes a cylinder subject to misfire diagnosis (see FIG. 7). In the current routine, the rotation speed MNX # 1 (= MNXn) of the # 1 cylinder (#n cylinder) in the current combustion stroke calculated based on the BTDC θ2 and θ3 crank pulse input interval times of the # 3 cylinder.
Is subtracted from the rotational speed MNX # 4 (= MNXn-1) of the # 4 cylinder (# n-1 cylinder) one combustion stroke before, based on the BTDC .theta.2, .theta.3 crank pulse input interval time of the # 1 cylinder.
DELNE # 1 (DELNEn = MN)
Xn-MNXn-1) is calculated. And this differential rotation D
Subtract the differential rotation correction value AVEDNX # 1 (AVEDNXn-4) for the # 1 cylinder calculated at the time of execution of this routine four times before, that is, one cycle before, from ELNE # 1.
The correction differential rotation DELNA # 1 (DELNAn) for one cylinder is calculated (see FIG. 11).

Then, in the processing after step S17, FIG.
As shown in FIG. 1, the corrected differential rotation DELNA of the # 1 cylinder
# 1 (DELNAn) is subtracted from the corrected differential rotation DELNA # 4 (DELNAn-1) of the # 4 cylinder, which is the cylinder # n-1 to be diagnosed one combustion stroke before, calculated at the time of execution of the previous routine. Cylinder correction differential rotation change DDNEA # 1 (DDNEA # 1)
An) is calculated. Then, the corrected differential rotation change DDNEA # 1 (DDNEAn) of the # 1 cylinder and the corrected differential rotation change DDNEA # 4 of the # 4 cylinder calculated at the time of execution of the previous routine.
A misfire diagnosis is performed for the # 4 cylinder (# n-1 cylinder) to be subjected to the misfire diagnosis based on the change state with (DDNEAn-1).

That is, in step S17, the corrected differential rotation DELNAn-1 of the # n-1 cylinder calculated in the previous execution of the routine and stored in the work area is calculated from the corrected differential rotation DELNAn of the #n cylinder calculated in step S16. Is subtracted to obtain the corrected differential rotation change DDNEA for the #n cylinder.
n (DDNEAn ← DELNAn−DELN)
An-1).

The behavior of the corrected differential rotation change DDNEA is
This is shown in the timing chart of FIG.

Here, if an intermittent rotation fluctuation such as a snatch occurs in the engine 1, the intermittent rotation fluctuation due to the snatch or the like can be regarded as a misfire simply by comparing the corrected differential rotation DELNA with a predetermined misfire determination level. Misdiagnosed,
Accurate misfire diagnosis cannot be performed. Therefore, by diagnosing misfire based on the change in the corrected differential rotation DELNA of the front and rear cylinders, that is, the corrected differential rotation change DDNEA, the differential rotation (corrected differential rotation DELNA) whose level changes according to the engine operating state at the time of the misfire occurs. On the other hand, the influence of intermittent rotation fluctuations such as snatches is eliminated to enable accurate misfire diagnosis.

Next, the process proceeds to step S18, and steps S18 to S18 are performed.
In S20, it is determined whether a misfire diagnosis condition is satisfied.

That is, it is determined in step S18 whether or not the fuel cut is being performed. If the fuel cut is not being performed, in step S19, the basic fuel which is set in a fuel injection amount setting routine described later and determines the basic fuel injection amount is determined. The injection pulse width Tp is compared with the lower limit value TpLWER, and it is determined whether or not the current engine operation region is in the misfire diagnosable region. Then, when Tp ≧ TpLWRE, in a succeeding step S20, the current engine speed NE is compared with an upper limit value NEUPER.

Here, during fuel cut, no fuel is injected, and each cylinder is in a forced misfire state, so that misfire diagnosis cannot be performed. In addition, when Tp <TpLWRE and the fuel injection amount is small, a rotational fluctuation component other than misfire is large, and misfire diagnosis is performed if misfire diagnosis is performed based on a change in engine speed. Further, in a high rotation range of NE ≧ NEEUPER, the rotation fluctuation is moderated, and a misfire diagnosis cannot be performed in this range.

Therefore, during fuel cut, or when Tp
<TpLWRE misfire diagnosable area, or NE> NE
If the UPER is in the high rotation range, the process proceeds from the relevant step to step S21 due to the failure of the misfire diagnosis condition, clears the diagnosis permission flag FLGDIAG (FLGDIAG ← 0), prohibits the misfire diagnosis, and proceeds to step S23.

On the other hand, when fuel injection is performed, Tp ≧ T
When the current engine operating state is in the misfire diagnosable area in pLWRE and is in the area excluding high revolutions with NE <NEEUPER, it is determined that the misfire diagnosing condition is satisfied, and the routine proceeds to step S22, where the diagnosis permission flag FLGDIAG is set (FLGDIAG ← 1) to permit misfire diagnosis, and proceed to step S23.

Then, in step S23, a single-fire misfire diagnosis subroutine shown in FIG. 5 is executed, and a single-fire misfire diagnosis for the cylinder # n-1 to be subjected to the misfire diagnosis, that is, a single-fire misfire for each cylinder is determined.

In this single-shot misfire diagnosis subroutine, in step S41, the diagnosis permission flag FLGDIAG is referred to.
If FLGDIAG = 0 and the misfire diagnosis is not satisfied and the misfire diagnosis is prohibited, the process jumps to step S48, and clears the cylinder-specific misfire flag FLGMISn-1 indicating the single-shot misfire of the cylinder # n-1 to be misfire-diagnosed ( FLGMISn
-1 ← 0), and proceeds to step S24 of the misfire diagnosis routine (FIG. 4).

On the other hand, in step S41, FLGDIA
If G = 1 and the misfire diagnosis is permitted, the process proceeds to step S42, where the misfire determination level map is referred to based on the current engine speed NE and the basic fuel injection pulse width Tp representing the engine load, and interpolation calculation is performed. To set the misfire determination level LVLMISH.

The misfire determination level LVLMISH is used for judging misfire by comparing with the above-described corrected differential rotation change DDNEA, and differs depending on the engine characteristics for each engine type and the engine operating state. Therefore, the engine speed N is determined in advance by an experiment or a simulation.
For each operation region based on E and the basic fuel injection pulse width Tp,
The correction difference rotation change DDNEA when a misfire occurs is obtained,
The corresponding misfire determination level LVLMISH is shown in FIG.
As shown in FIG. 2A, a misfire determination level map is set using the engine speed NE and the basic fuel injection pulse width Tp as parameters (in the present embodiment, it is set as an 8 × 8 grid map). ), And stored in a series of addresses in the ROM 42.

As shown in FIG. 13, the misfire determination level LVLMISH is set when the basic fuel injection pulse width Tp is less than the lower limit as a non-diagnosable area. The value is set to a higher value as the pulse width Tp increases and the engine load increases.

In the following step S43, a basic fuel injection pulse width T representing the current engine speed NE and the engine load is set.
Referring to the erroneous determination prevention determination level map based on p and
An erroneous determination prevention determination level LVLMISL is set by interpolation calculation.

This erroneous judgment prevention judgment level LVLMISL
Is the correction difference rotation change D for the misfire diagnosis target cylinder # n-1.
This is for judging factors other than misfire, that is, engine rotation fluctuations due to snatch, disturbance, and the like, by comparing with DNEAn-1.

Here, when the engine speed fluctuates due to snatching or disturbance, the engine speed temporarily drops significantly. Therefore, the erroneous determination prevention determination level L
VLMISL is set to a value larger than the misfire determination level LVLMISH. It should be noted that when the engine speed fluctuates due to snatching or disturbance,
When the engine rotational speed temporarily drops greatly and the corrected differential rotation change DDNEAn-1 of the misfire diagnosis target cylinder # n-1 includes the engine rotation fluctuation due to snatch, disturbance, or the like, the corrected differential rotation change DDNEAn- 1 indicates a negative value. Therefore, the erroneous diagnosis prevention determination level LVLMI
In order to make a determination based on SL, it is actually necessary to give the erroneous determination prevention determination level LVLMISL as a negative value. Further, the magnitude of the rotation fluctuation due to snatch, disturbance, and the like differs depending on the engine characteristics and the engine operating state for each engine type.

For this reason, a misfire diagnosis target cylinder #n when a rotational fluctuation occurs due to a snatch, a disturbance, or the like in each operating region based on the engine rotational speed NE and the basic fuel injection pulse width Tp through experiments or simulations in advance. A correction differential rotation change DDNEAn-1 of -1 is obtained, and a negative value erroneous diagnosis prevention determination level -LVLMISL corresponding to this is set. Then, the plus value erroneous diagnosis prevention determination level LVLMISL from which the minus sign is deleted is shown in FIG.
As shown in (b), an erroneous diagnosis prevention determination level map is set using the engine speed NE and the basic fuel injection pulse width Tp as parameters (in the present embodiment, consistency with the misfire determination level map is obtained). Therefore, it is set as an 8 × 8 grid map) and stored in a series of addresses in the ROM 42.

The erroneous diagnosis prevention judgment level LVL read out together with the interpolation calculation from the erroneous diagnosis prevention judgment level map
In step S45 to be described later, the MISL is provided with a minus sign, and a negative value erroneous diagnosis prevention determination level -LV
LMISL, and the corrected differential rotation change DDNEAn-1 of the misfire diagnosis target cylinder # n-1 is compared with the minus erroneous diagnosis prevention determination level -LVLMISL to obtain the corrected differential rotation change of the misfire diagnosis target cylinder # n-1. It is determined whether or not DDNEAn-1 is due to engine rotation fluctuation due to snatch, disturbance, or the like.

Then, the process proceeds to a step S44, wherein the corrected differential rotation change DDN for the cylinder # n-1 to be subjected to the misfire diagnosis calculated in the previous execution of the routine and stored in the work area.
EAn-1 is read out and the correction difference rotation change DDNEAn
-1 is compared with a minus misfire determination level -LVLMISH in which the misfire determination level LVLMISH is given a negative sign. When DDNEAn-1> -LVLMISH, it is determined that no misfire has occurred in the cylinder # n-1 to be subjected to misfire diagnosis, and the routine jumps to step S48 to cause misfire in the cylinder # n-1 to be subjected to misfire diagnosis. Clears the misfire flag FLGMISn-1 indicating that (FLGMISn-1 ←
0), and proceed to step S24 of the misfire diagnosis routine.

On the other hand, DDNEAn-1 ≦ −LVLM
In the case of ISH, in the following step S45, the correction difference rotation change DDNEAn-1 of the cylinder # n-1 corresponding to the misfire diagnosis is calculated as
Erroneous judgment prevention judgment level LV set in step S43
By comparing the LMISL with a minus misjudgment prevention determination level −LVLMISL in which a negative sign is added to the LMISL, the corrected differential rotation change DDNEAn−1 of the misfire diagnosis target cylinder is caused by a rotation change caused by a factor other than the misfire, that is, a snatch or disturbance. It is determined whether it is a thing.

Then, DDNEAn-1 ≧ -LVLMIS
L, the correction difference rotation change DDN of the misfire diagnosis target cylinder # n-1
EAn-1 is a negative erroneous determination prevention determination level -LVLMI.
If not less than SL, it is determined that the corrected differential rotation change DDNEAn-1 is not a rotation fluctuation caused by snatch, disturbance, or the like, and the process proceeds to step S46, where the currently calculated corrected differential rotation change DDNEAn for the #n cylinder is determined as the misfire determination level. LVL
By comparing with the MISH, the cylinder # n-
Verify misfire for 1.

When DDNEAn ≧ LVLMISH, it is determined that the misfire diagnosis target cylinder # n-1 is misfired, and the routine proceeds to step S47, where the misfire diagnosis target cylinder # n-
A misfire flag FLGMISn-1 for 1 is set (FLGMISn-1 ← 1), and the routine proceeds to step S24 of the misfire diagnosis routine.

On the other hand, in step S45, DDNEAn-
When 1 <-LVLMISL, it is determined that the correction difference rotation change DDNEAn-1 of the cylinder # n-1 to be misfire-diagnosed is due to a rotation fluctuation caused by a factor other than misfire, that is, a snatch or disturbance, and the above-described step S48 is performed. To the misfire flag FLGMISn of the cylinder # n-1 to be misfired.
-1 is cleared (FLGMISn-1 ← 0), and the routine proceeds to step S24 of the misfire diagnosis routine.

Further, as a result of the verification in step S46,
If DDNEAn <LVLMISH, and it is determined that the misfire diagnosis target cylinder # n-1 has not suffered a misfire, similarly, in step S48, the misfire flag FLGMISn-1 for the relevant misfire diagnosis target cylinder # n-1 Is cleared, and the routine proceeds to step S24 of the misfire diagnosis routine.

Here, as shown by the broken line in FIG. 14, when a snatch, disturbance, or the like occurs, the engine speed is greatly reduced, and the correction difference rotation change DDNEAn-1 is set to a value less than the minus erroneous determination determination level -LVLMISL. Show. That is,
A misjudgment prevention judgment level LVLMISL for judging engine revolution fluctuations due to factors other than misfire is set based on the engine operating state based on the engine speed NE and the basic fuel injection pulse width Tp representing the engine load, and the misfire diagnosis target cylinder is set. When the correction differential rotation change DDNEAn-1 of # n-1 is less than the negative erroneous determination prevention determination level -LVLMISL, it is determined that the engine rotation has fluctuated due to a factor other than misfire, that is, a snatch, disturbance, or the like. By exclusion, it is possible to reliably prevent erroneous determination due to rotation fluctuation such as snatch or disturbance.

When the correction difference rotation change DDNEAn-1 for the misfire diagnosis target cylinder # n-1 is equal to or more than the minus erroneous determination prevention determination level -LVLMISL, the correction difference rotation change DDNEAn-1 is caused by a snatch, disturbance, or the like. It can be determined that the rotation does not fluctuate. In this state, when the misfire diagnosis target cylinder # n-1 misfires, as shown by the solid line in FIG. 14, the effective pressure due to combustion cannot be obtained in the corresponding cylinder # n-1. Engine speed MNXn before combustion stroke of cylinder # n-1
In contrast to -2, the engine speed MNXn-1 at the end of the combustion stroke in which the exhaust valve of the corresponding cylinder # n-1 opens decreases, the corrected differential speed change DDNEAn-1 becomes a negative value, and a negative misfire occurs Indicates a value equal to or less than the judgment level -LVLMISH. Then, for the engine speed MNXn-1, the next cylinder #
n increases MNXn in the next section, and
The correction difference rotation change DDNEAn for the #n cylinder is a positive value, and indicates a value equal to or higher than the misfire determination level LVLMISH. Therefore, this causes the misfire diagnosis target cylinder #n
Therefore, it is possible to properly diagnose misfire for -1, and to surely prevent misdiagnosis due to rotation fluctuation caused by snatch or disturbance other than misfire, and to further improve misfire diagnosis accuracy.

When the single-fire misfire diagnosis subroutine is completed and the process proceeds to step S24 of the misfire diagnosis routine (see FIG. 4), the processing of steps S24 to S30 prepares for the next misfire diagnosis, and the statistical processing performs the relevant cylinder #. A difference rotation correction value AVEDNXn-1 for n-1 is calculated.

In step S24, referring to the misfire flag FLGMISn-1 of the cylinder # n-1 to be subjected to misfire diagnosis this time,
FLGMISn-1 = 0, cylinder # n-1 to be misfired this time
If no misfire has occurred, the process proceeds to step S25. Then, the corresponding cylinder # n-1 stored in the work area
AVE of all cylinders at the time of execution of the previous routine in which the differential rotation of DELNEn-1 and the differential rotation of all cylinders are weighted and averaged.
By calculating the difference (DELNEn-1-AVEDNn-1) from DNn-1 and comparing it with the lower limit value MINDN and the upper limit value MAXDN, each of the protrusions 31a, 3 of the crank rotor 31 is calculated.
It is determined whether or not rotational variations due to manufacturing tolerances such as the position and shape of the 1b and 31c, and tolerances for mounting the crank angle sensor 32 to the engine 1 are included in the differential rotation DELNEn-1. .

Then, MINDN <DELNEn-1-A
If VEDNn-1 <MAXDN, the differential rotation DELNEn-1 of the relevant cylinder # n-1 and the average differential weight ADVDNn of all the cylinder differential rotations
When the difference from -1 is within a set range determined by the upper and lower limits MAXDN and MINDN, the differential rotation DELNE is caused by an error relating to the crank rotor 31 and the crank angle sensor 32.
Since it is determined that n-1 has fluctuated, the process proceeds to step S26, where the weighted average of the all cylinder difference rotation weighted average value AVEDNn-1 up to the previous time and the correction difference rotation DELNAn-1 of the corresponding cylinder # n-1 is calculated. To calculate the current all-cylinder differential rotation weighted average value AVEDNn (AVEDNn ← (3/4) × AVEDNn−1).
+ (1/4) * DELNAn-1).

Next, at step S27, the cylinder # n-1 (four cylinder engine in the present embodiment, the cylinder # n-1 and the cylinder # n-5 are the same cylinder) calculated in the present routine five times before. The differential rotation correction value AVEDNXn-5 for the cylinder # n-1 stored in the work area is stored in the work area.
The above-described step S26 is performed when ELNEn-1 and the previous routine are executed.
AVENn-1
Weighted average using the difference (DELNEn-1 -AVEDNn-1) with respect to the difference rotation correction value AVE for the corresponding cylinder # n-1.
DNXn-1 (AVEDNXn-1 ← (7/8) × AV
EDNXn-5 + (1/8) × (DELNEn-1-AVE
DNn-1)), and proceeds to the step S31.

Then, the next time (when this routine is executed three times later), the corrected differential rotation DE for the corresponding cylinder # n-1 (#n) will be described.
When calculating LNAn-1 (DELNAn), the difference rotation correction value AVEDNXn-1 (AVEDNXn-4) is used, and the projections 31a,
Manufacturing tolerances such as the position and shape of 31b and 31c,
Influences such as a permissible error in the mounting position of the crank angle sensor 32 to the engine 1 are eliminated.

On the other hand, in step S24, FLGMIS
If n-1 = 1 and a misfire has occurred in the corresponding cylinder # n-1, the process proceeds from step S24 to step S28, in which the corresponding cylinder #n
The misfire frequency count value MISCNTn-1 for counting the misfire frequency of -1 is counted up, and step S29 is performed.
And the weighted average value AV of all cylinder difference rotations at the time of execution of the previous routine
EDNn-1 is the weighted average value of all cylinder differential rotation AVEDN
n (AVEDNn ← AVEDNn−1), and in a succeeding step S30, the differential rotation correction value AVENDXn−5 calculated in the present routine five times before is set as the differential rotation correction value AVEDNn−1 for the relevant cylinder # n−1 (AVEDNXn). -1 ← AVED
NXn-5), and it proceeds to step S31.

In step S25, MIN
When DN ≧ DELNEn−1−AVEDnn−1, it is determined that the influence of the error relating to the crank rotor 31 and the crank angle sensor 32 included in the differential rotation DELNEn−1 is negligible, and DELNEn−1−AVEDnn−1 ≧ MAX
When the rotation fluctuation is large in DN, it is determined that the rotation fluctuation is caused by snatching or the like, and similarly, the processing proceeds to step S31 via steps S29 and S30.

Then, in the processing after step S31, comprehensive misfire determination is performed.

In step S31, the diagnosis permission flag F
Referring to LGDIAG, if FLGDIAG = 0 and the misfire diagnosis is prohibited due to the failure of the diagnostic conditions, step S3
Jump to 7.

On the other hand, when FLGDIAG = 1 and misfire diagnosis is permitted, the flow advances to step S32 to count up the count value CRACNT, and then to step S33.
Then, the count value CRACNT is set to a set value (2000).
To determine whether the set value has been reached. That is, whenever FLGDIAG = 1, the misfire diagnosis for each cylinder is performed a set number of times (2000 times) determined by the above set value by the single-shot misfire diagnosis subroutine, a comprehensive misfire determination is performed by a misfire determination subroutine shown in FIG. .

If CRACNT <2000 and the set number of times has not yet been reached, the routine jumps to step S37 without making a comprehensive misfire determination, and CRACNT ≧ 2.
When the misfire diagnosis for each cylinder has reached the set number of times (2000 times) at 000, the process proceeds to step S34. Then, step S34
Then, the misfire determination subroutine shown in FIG. 6 is executed to make a comprehensive misfire determination.

In the misfire determination subroutine, first, in step S51, the misfire counts MISCNT # 1 to # 4 for each cylinder counted up in step S28 are summed up, and the total value of all cylinder misfire counts ΣMISCNT # 1 to # 4 Is calculated,
The misfire rate MISPCNT during this period is calculated (MISPC
NT ← ΣMISCNT # 1 to # 4 × 100/2000).

Next, in step S52, the misfire rate MIS
By comparing PCNT with the set value LMSCNT, it is determined whether or not misfire has occurred constantly. And MI
If SPCNT ≧ LMSCNT and a misfire occurs constantly, it is determined that the engine is abnormal due to the misfire, and the process proceeds to step S 53, where the misfire rate MISPCNT is stored at a predetermined address in the backup RAM 44.

In the following step S54, the backup RA
First misfire determination NG flag FLGNG stored in M44 and set when it is determined that the engine is abnormal due to misfire
Referring to FIG. 1, if FLGNG1 = 1 and it is already determined that the engine is abnormal due to a misfire, the process proceeds to step S55, in which a second misfire determination NG flag FLGNG2 stored in the backup RAM 44 and determined to be an engine abnormality due to the misfire is set (FLGNG2). ← 1), proceed to step S56. The alarm lamp 38 is turned on or blinks when the misfiring engine abnormality is determined, and the driver is notified of the misfiring engine abnormality. That is, when it is determined that a permanent misfire has occurred twice consecutively, the reliability of the misfire diagnosis is improved by determining that the engine is abnormal due to the misfire.

In step S54, FLGNG1 = 0.
At the first time when it is determined that the engine is abnormal due to misfire, the process jumps to step S56.

Then, in step S56, the first-time misfire determination NG flag FLGNG1 is set (FLGNG1 ← 1), and in the following step S57, the count value CNTOK for determining the absence of abnormality for determining the cancellation of the misfire abnormality determination is cleared. (CNTOK ← 0), the routine proceeds to step 35 of the misfire diagnosis routine (FIG. 4).

On the other hand, in step S52, the MIS
If PCNT <LMSCNT, it is determined that no permanent misfire has occurred or that a temporary misfire has occurred due to acceleration or deceleration, etc., and the process proceeds to step S58, where the count value CNTOK for determining the absence of abnormality is counted up ( CNTOK ← CN
TOK + 1). In a succeeding step S59, the condition for canceling the misfire abnormality determination is determined by comparing the determination count value CNTOK with a set value (80).

When CNTOK <80, it is determined that the condition for canceling the misfire abnormality has not been satisfied, and the routine proceeds directly to step S35 of the misfire diagnosis routine.

When CNTOK ≧ 80 and the judgment of no abnormality continues for the set number of times (80 times) determined by the set value,
It is determined that there is no misfire abnormality, and the process proceeds from step S59 to step S60 when the condition for canceling the misfire abnormality determination is satisfied.
In S60 to S62, the first misfire determination NG flag FLGNG1,2
Second misfire determination NG flag FLGNG2, misfire rate MISPC
Clear each NT, proceed to the above step S57,
The above-mentioned determination count value CNTOK is cleared, and the routine proceeds to step S35 of the misfire diagnosis routine.

When the misfire determination subroutine ends and the process proceeds to step S35 of the misfire diagnosis routine (see FIG. 4), the count value CR is prepared for the next total misfire determination.
The ACNT is cleared, and in the following step S36, the number of misfires MISCNT # 1 to # 4 for each cylinder is cleared, and the process proceeds to step S37.

Then, in step S37, the above data is stored as monitor data, and the routine exits.

In the present embodiment, the engine speed is used as the engine speed state quantity, and the misfire is detected based on the engine speed change amount for each predetermined period. However, the present invention is not limited to this. Instead, an engine rotation cycle, an engine rotation angular velocity, or an engine rotation angular acceleration may be used instead of the engine rotation speed.

[0114]

As described above, according to the first aspect of the present invention, a change in the engine rotation state quantity is detected at every predetermined crank angle, and the current combustion stroke cylinder is determined.
The cylinder before the combustion stroke is determined to be the cylinder to be misfired. Then, a misfire determination level for determining misfire and a misjudgment prevention determination level for determining a change in the rotational state amount due to a factor other than misfire with a value larger than the misfire determination level are set to the engine operating state, respectively. The change of the engine rotation state amount for the misfire diagnosis target cylinder is equal to or less than the negative misfire determination level and equal to or greater than the negative misjudgment prevention determination level, and the engine rotation state amount for the current combustion stroke cylinder is set. When the change is equal to or higher than the misfire determination level, it is determined that the misfire diagnosis target cylinder is misfired.Therefore, it is determined whether or not the change in the engine rotational state quantity of the misfire diagnosis target cylinder is due to rotation fluctuation due to a factor other than misfire, that is, a snatch or disturbance. , Which can be directly determined by comparison with the erroneous determination prevention determination level, and the engine rotational state quantity for the misfire diagnosis target cylinder When the change is less than the negative of erroneous determination prevention determination level, it is determined that the engine rotational fluctuations due to factors other than misfire i.e. snatch or disturbance, at this time may be excluded misfire diagnostics.

If the change in the engine rotational state quantity for the cylinder subject to misfire diagnosis is equal to or greater than the negative erroneous determination prevention determination level, it is determined that the change in the rotational state quantity is not due to snatching or disturbance, and the misfire diagnosis is made. Only when the change in the engine rotation state quantity for the target cylinder is equal to or less than the negative misfire determination level and the change in the engine rotation state quantity for the current combustion stroke cylinder is equal to or greater than the misfire determination level,
Since it is determined that the misfiring diagnosis target cylinder is misfiring, it is possible to properly diagnose misfiring for the relevant misfiring diagnosis target cylinder, and to reliably prevent erroneous diagnosis due to rotation fluctuations caused by snatches and disturbances other than misfiring. Thus, the misfire diagnosis accuracy can be further improved.

Further, the accuracy of misfire diagnosis can be improved only by adding a process of setting an erroneous determination prevention determination level and a process of comparing a change in the amount of engine rotation with respect to the erroneous determination prevention determination level. It has an effect that can be easily realized.

According to the second aspect of the present invention, the engine rotation state amount is detected at every predetermined crank angle between the cylinders,
The engine rotation state quantity detected this time is subtracted from the engine rotation state quantity detected last time to calculate the difference in the rotation state quantity, the current combustion stroke cylinder is determined, and the cylinder one combustion stroke earlier is set as the misfire diagnosis target cylinder. to decide. Then, by subtracting the differential rotation state amount correction value for the cylinder calculated one cycle ago by statistical processing using a weighted average from the current rotation stroke amount of the cylinder in the combustion stroke cylinder, a corrected differential rotation state amount for the cylinder is calculated. Then, the change in the corrected differential rotation state amount for the cylinder is calculated by subtracting the corrected differential rotation state amount of the misfire diagnosis target cylinder one combustion stroke before from the corrected differential rotation state amount. Then, a misfire determination level for determining misfire and a misjudgment prevention determination level for determining a change in the rotational state amount due to a factor other than misfire with a value larger than the misfire determination level are set to the engine operating state, respectively. Set based on 1
The change in the corrected difference rotational state amount for the misfire diagnosis target cylinder before the combustion stroke is equal to or less than the negative misfire determination level and equal to or greater than the negative misjudgment prevention determination level, and the engine rotational state amount for the current combustion stroke cylinder is changed. When the change is equal to or greater than the misfire determination level, it is determined that the cylinder to be misfired is misfired.Therefore, in the misfire diagnosis, a crank rotor or a crank angle for detecting a crank angle which is a basis for detecting an engine rotation state quantity. Using the corrected differential rotation state amount excluding the effects of the sensor manufacturing tolerance and the mounting tolerance error, the change in the corrected differential rotation state amount is compared with the misfire determination level and the erroneous determination prevention determination level to correct the front and rear cylinders. In order to determine the misfire of the cylinder for which misfire is to be diagnosed based on the change in the differential rotation amount, the tolerance of the crank rotor and the crank angle sensor must be eliminated and snatching must be performed. By the synergistic effect with the prevention of erroneous diagnosis due to disturbance or the like, it is possible to further improve the misfire diagnostic accuracy.

In this case, in the invention according to claim 3, the engine speed is used as the rotational state quantity, so that the invention described in claim 1 or 2 can be applied to a conventional engine misfire diagnosis apparatus very easily. It can be incorporated and has the effect of improving the misfire diagnosis accuracy.

[Brief description of the drawings]

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

FIG. 2 is a flowchart of a cylinder discrimination / engine speed calculation routine.

FIG. 3 is a flowchart of a misfire diagnosis routine.

FIG. 4 is a flowchart of a misfire diagnosis routine (continued).

FIG. 5 is a flowchart of a single-shot misfire diagnosis subroutine.

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

FIG. 7 shows a crank pulse, a cam pulse, a combustion stroke cylinder,
Time chart showing the relationship between ignition timing and fuel injection timing

FIG. 8 is a timing chart showing a differential rotation behavior.

FIG. 9 is a timing chart showing the behavior of the correction differential rotation.

FIG. 10 is a timing chart showing a behavior of a change in the correction difference rotation when a misfire occurs.

FIG. 11 is an explanatory diagram showing a calculation relationship of a differential rotation, a corrected differential rotation, and a corrected differential rotation change.

FIG. 12 is an explanatory diagram of a misfire determination level map and an erroneous determination prevention determination level map.

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

FIG. 14 is an explanatory diagram showing a relationship between a change in correction difference rotation when a snatch occurs and a misfire occurs, and an erroneous determination prevention determination level and a misfire determination level.

FIG. 15 is an overall schematic diagram of an engine.

FIG. 16 is a front view of a crank rotor and a crank angle sensor.

FIG. 17 is a front view of a cam rotor and a cam angle sensor.

FIG. 18 is a circuit configuration diagram of an electronic control system.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Engine 32 Crank angle sensor 40 Electronic control device (rotational state amount change detecting means, cylinder determining means, misfire determination level setting means, misjudgment prevention determining level setting means, misfire determining means, engine rotational state quantity detecting means, differential rotation state Amount calculating means, correction difference rotation state quantity calculation means, correction difference rotation state quantity change calculation means) NE engine speed (engine rotation state quantity; engine operating state) #n current combustion stroke cylinder # n-1 misfire diagnosis target cylinder (Cylinder before one combustion stroke) LVLMISH misfire determination level Tp Basic fuel injection pulse width (engine operating state) LVLMISL misjudgment prevention judgment level -LVLMISH minus misfire judgment level -LVLMISL minus misjudgment prevention judgment level MNXn-1 one combustion stroke before Engine speed corresponding to cylinder # n-1 (engine rotation state detected last time) Amount) MNXn Engine speed (currently detected engine rotation amount) corresponding to current combustion stroke cylinder #n DELNE Differential rotation (change in engine rotation state amount; difference in rotation state amount) DELNEn Current combustion stroke cylinder #n Differential rotation (current differential rotation state amount of combustion stroke cylinder) AVEDNX differential rotation correction value (differential rotation state correction value) DELNA correction differential rotation (corrected differential rotation state amount) DELNAn Correction difference of current combustion stroke cylinder #n Rotation (current difference rotational state quantity of the combustion stroke cylinder) DELNAn-1 Misfire diagnosis target cylinder #n one combustion stroke before
Correction differential rotation of -1 (correction differential rotation state amount of cylinder subject to misfire diagnosis before one combustion stroke) DDNEA Correction differential rotation change (change of correction differential rotation state amount) DDNEAn-1 Correction for misfire diagnosis target cylinder # n-1 Change in differential rotation (change in corrected differential rotation state quantity for cylinder subject to misfire diagnosis before one combustion stroke) DDNEAn Change in corrected differential rotation for current combustion stroke cylinder #n (change in engine rotation state quantity for current combustion stroke cylinder)

Claims (3)

[Claims] The present invention is characterized in that a rotation state quantity change detecting means for detecting a change in an engine rotation state quantity for each predetermined crank angle, a current combustion stroke cylinder is determined, and a cylinder one combustion stroke before is determined as a misfire diagnosis target cylinder. Cylinder discrimination means, misfire judgment level setting means for setting a misfire judgment level for judging misfire based on the engine operating state, and judging a change in the rotational state amount due to factors other than misfire with a value larger than the misfire judgment level Error determination prevention determination level setting means for setting an error determination prevention determination level for performing a misfire determination based on the engine operating state, and a change in the engine rotation state amount for the misfire diagnosis target cylinder is equal to or less than the negative misfire determination level, and is negative. The change in the amount of engine rotation with respect to the current combustion stroke cylinder is equal to or greater than the erroneous determination prevention determination level and is equal to or less than the misfire determination level. An engine misfire diagnosis device comprising: a misfire determining means for determining that a misfire has occurred in a cylinder subject to misfire diagnosis. 2. An engine rotation state amount detecting means for detecting an engine rotation state amount at each predetermined crank angle between cylinders, and a rotation state amount by subtracting a currently detected engine rotation state amount from a previously detected engine rotation state amount. Differential rotation state quantity calculation means for calculating the difference between the cylinders, cylinder determination means for determining the current combustion stroke cylinder, and determining the cylinder one combustion stroke before as the misfire diagnosis target cylinder, and current difference rotation state of the combustion stroke cylinder A correction difference rotation state amount calculating means for subtracting the difference rotation state amount correction value for the cylinder calculated one cycle ago by a statistical process using a weighted average from the amount to calculate a correction difference rotation state amount for the cylinder; A corrected differential rotation state quantity for subtracting the corrected differential rotation state quantity of the cylinder subject to misfire diagnosis one combustion stroke before from the differential rotation state quantity to calculate a change in the corrected differential rotation state quantity for the cylinder concerned A change calculation means; a misfire determination level setting means for setting a misfire determination level for determining misfire based on the engine operating state; and determining a change in rotation state amount due to a factor other than misfire with a value larger than the misfire determination level. Means for setting an erroneous determination prevention determination level based on the engine operating state, and a correction difference rotation state quantity for the cylinder subject to misfire diagnosis one combustion stroke before which the change in the rotation amount is minus. A misfire determination that determines that a misfire diagnosis target cylinder is misfired when the engine misfire determination cylinder level is equal to or less than the negative misjudgment prevention determination level and the change in the engine rotation state quantity for the current combustion stroke cylinder is equal to or greater than the misfire determination level. And a means for diagnosing misfire of an engine. 3. The engine misfire diagnosis apparatus according to claim 1, wherein the engine rotation state quantity is an engine speed.