JPH086676B2 - Misfire diagnosis device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention relates to a misfire diagnosis device for an internal combustion engine, and more specifically,
The present invention relates to a technique for preventing a misdiagnosis during coasting, particularly in a misfire diagnostic device configured to perform a misfire diagnosis based on a crank angular velocity.

<Prior Art> As a device for diagnosing a misfire of an internal combustion engine, a device for directly detecting an in-cylinder pressure for each cylinder and diagnosing a misfire has been proposed. A device capable of diagnosing misfire from changes in crank angular velocity (engine speed fluctuation) was previously proposed as a device that can be used (IS IS in 1979).
ATA-Paper `` Experiences with a new method for meas
uring the engine roughness '' by R. Latsch, E. Mausner,
See V. Bianchi and Japanese Patent Application No. 1-275046).

<Problems to be Solved by the Invention> By the way, under normal operating conditions, as shown in FIG. 8, a large change appears in the crank angular velocity depending on the presence or absence of a misfire. In the case of the figure, misfire diagnosis can be performed by measuring 1/2 rotation cycle.

However, when the vehicle is coasting,
As shown in the figure, when the indicated mean effective pressure Pi is in the same condition when all cylinders are misfiring, even if there is a misfiring cylinder, there is almost no step in the indicated mean effective pressure Pi between the cylinders, so during coasting As shown in FIG. 9, the crank angular velocity does not change depending on whether or not there is a misfire, and even if there is a misfiring cylinder, a diagnosis of no misfiring may be made, and the cause of impairing the reliability of the misfire diagnosis based on the crank angular speed. It was.

The present invention has been made in view of the above problems, by prohibiting the misfire diagnosis based on the crank angular speed during coasting, by allowing the misfire diagnosis only in the operating conditions that can accurately perform the misfire diagnosis based on the crank angular speed, The purpose is to improve the reliability of misfire diagnosis based on the crank angular velocity.

<Means for Solving the Problem> Therefore, in the present invention, as shown in FIG. 1, an internal combustion engine including a misfire diagnosis means for performing a misfire diagnosis based on the crank angular speed of the internal combustion engine detected by the crank angular speed detection means. In the misfire diagnosis device, if the throttle valve fully closed detection means detects the fully closed state of the throttle valve interposed in the intake system of the engine and the crank angular velocity is equal to or higher than a predetermined value, the misfire diagnosis is prohibited. The means is configured to prohibit the misfire diagnosis by the misfire diagnosis means.

<Operation> With such a configuration, when the throttle valve is fully closed and the crank angular speed is equal to or higher than a predetermined value, the misfire diagnosis based on the crank angular speed is prohibited, and the accuracy of the misfire diagnosis based on the crank angular speed is reduced during coasting. By avoiding erroneous diagnosis, the misfire diagnosis based on the crank angular velocity is performed in an operating state other than coasting.

That is, the boost during coasting changes as shown in FIG. 6, and it can be considered that the boost and the indicated mean effective pressure Pi are in a substantially proportional relationship. Therefore, even when the throttle valve is fully closed, At lower rotation speeds, the step of the indicated mean effective pressure Pi may become large enough to allow misfire diagnosis due to misfire occurrence.Therefore, the throttle valve is fully closed and the crank angular velocity ( The engine misfire diagnosis based on the crank angular speed is prohibited when the engine speed) is above a predetermined level.

<Examples> Examples of the present invention will be described below.

In FIG. 2 showing an embodiment, a crankshaft (not shown) of a 4-cycle 4-cylinder internal combustion engine 1 is made of a magnetic material and is surrounded by 120 at every crank angle of 3 ° (3 ° CA).
The signal disc plate 2 having a plurality of convex portions is pivotally supported, and the magnet open end of the electromagnetic pickup 3 for 3 ° CA detection fixed near the periphery of the signal disc plate 2 is used for rotation of the crankshaft. Along with this, the convex portion is opened and closed to obtain an induced electromotive force pulse, and the signal disk plate 2 and the electromagnetic pickup 3 for detecting 3 ° CA are used to obtain detection signals at every 3 ° CA. There is.

Further, a pair of protrusions 2a and 2b are provided on one end face of the signal disc plate 2 on the same circumference with the rotating shaft interposed therebetween, and an electromagnetic pickup for detecting TDC for detecting the protrusions 2a and 2b. Induced electromotive force pulse is obtained every 180 ° CA by 4 and the protrusions 2a, 2b of the signal disk plate 2 are obtained.
And 180 ° C depending on the combination with the electromagnetic pickup 4.
The detection signal of A is obtained. Here, the detection position of the protrusions 2a, 2b by the electromagnetic pickup 4 is
By aligning with the top dead center position (TDC), the compression T of each cylinder is detected by, for example, an ignition signal and the TDC position detection.
DC position can be detected.

The induced electromotive force output from each of the electromagnetic pickups 3 and 4 is input to the zero-cross comparators 5 and 6, respectively, and converted into a pulse wave of 0 V center based on the magnitude with respect to the 0 V level, and further, the following waveform shaping circuit 7, At 8, it is shaped into a pulse wave whose low level is 0V.

The output pulse of the waveform shaping circuit 7 that rises (falls) every 3 ° CA (hereinafter abbreviated as 3 ° CA pulse) is a built-in computer control that performs misfire diagnosis and controls fuel supply to the engine 1. It is input to the timer 1 of the unit 9, and the timer 1 counts the number of 3 ° CA pulses. Also, the output pulse of the waveform shaping circuit 8 that rises (falls) every 180 ° CA at the TDC position of each cylinder (hereinafter referred to as TDC
Abbreviated as pulse. ) Is input to the trigger 1 of the control unit 9.

Further, the control unit 9 receives an ON / OFF signal from the idle switch 11 which is turned on at the fully closed position of the throttle valve 10 interposed in the intake system of the engine 1, that is, at the idle position. ing.

The control unit 9 measures the cycle of the TDC pulse input to the trigger 1, that is, the 180 ° CA (TDC) cycle in the four-cylinder engine 1 of the present embodiment, and the 3 ° CA pulse is triggered by the TDC pulse. Counting, for example
Detect the interrupt execution timing of the misfire diagnosis program at around ATDC 15 °, and perform misfire diagnosis at 180 ° CA cycle.

The means for detecting the rotational position of the crankshaft is, in addition to the type of device for obtaining the induced electromotive force pulse, an optical type for detecting the light passing through a slit provided in the signal disk plate to detect the rotational position of the crankshaft. However, the device is not limited to the device of this embodiment.

Next, the misfire diagnosis program which is executed at the execution timing (ATDC 15 °) immediately after TDC detected by counting 3 ° CA pulses from the TDC pulse will be described with reference to the flowchart of FIG.

In this embodiment, the functions as the misfire diagnosis means and the misfire diagnosis prohibition means are provided by software as shown in the flow chart of FIG. Further, the throttle valve fully closed detecting means in this embodiment corresponds to the idle switch 11, and the crank angular velocity detecting means is a combination of the protrusions 2a and 2b of the signal disk plate 2 and the electromagnetic pickup 4. Sensor part,
This is realized by the time measurement function of the control unit 9.

First, in step 1 (indicated as S1 in the figure. The same applies hereinafter), it is determined whether the idle switch 11 is ON or OFF.
Here, if it is determined that the idle switch 11 is ON and the throttle valve 10 is in the fully closed state, the routine proceeds to step 2, where the engine speed N calculated based on the 180 ° C cycle is N.
It is determined whether (crank angular velocity) exceeds a predetermined velocity (for example, 1200 rpm).

When it is determined in step 2 that the engine rotation speed N exceeds the predetermined speed, this program is terminated and the misfire diagnosis is prohibited. This is because when the vehicle is coasting (during coasting with the transmission in the neutral position and the throttle valve fully closed), there is almost no step in the indicated mean effective pressure Pi between the cylinders even if there is a misfire. This is because the crank angular velocity is not affected by the misfire and the accurate misfire diagnosis cannot be performed based on the crank angular velocity (7th example).
(See Figures and 9).

Even when the throttle valve 10 is fully closed, when the engine speed N is below a predetermined value, as shown in FIG. 6, the boost which is substantially proportional to the indicated mean effective pressure Pi increases. Since a step difference between the cylinders of the indicated mean effective pressure Pi is generated to such an extent that the occurrence of misfire can be distinguished, such an operation region is set as a misfire diagnosis region, and the operation region where the misfire diagnosis is performed is expanded as much as possible.

In this way, when the throttle valve 10 is fully closed, and
If the misfire diagnosis is prohibited when the engine rotation speed N (crank angular velocity) exceeds a predetermined speed, it is possible to avoid the diagnosis of no misfire even though the misfire has occurred, and the reliability of the misfire diagnosis is improved. It is possible to improve the engine speed, and by adding the condition of the engine rotation speed N, the diagnosis is not prohibited in a useless area, and the operation area in which the diagnosis is prohibited is locally limited to a wide range. Misfire diagnosis is possible.

On the other hand, when it is determined in step 1 that the idle switch 11 is off, or in step 2 the engine speed N
If it is determined that the engine speed is less than the predetermined speed, a large step difference between the cylinders is generated in the indicated mean effective pressure Pi due to the occurrence of misfire, and the misfire diagnosis based on the 180 ° CA cycle (crank angular velocity) can be performed. Then, perform a misfire diagnosis.

In step 3, the latest value Tnew of the TDC cycle (180 ° cycle for four cylinders) measured as the input interval of the TDC pulse to the value Told4 four times before is updated and stored.

That is, the latest value of the 180 ° cycle, which is obtained as the time from the TDC immediately before the interrupt execution of this program to the previous TDC, is set in Tnew, and it is obtained in the previous execution of this program and set in Tnew. One cycle before (180 ° C
A)) to Told1 as the cycle data, and similarly, the cycle Told1 one time before in the previous time is set to the cycle Told2 two times before (one rotation before) and set to 2 in the previous time.
The previous cycle Told2 is the cycle To three times before (540 ° CA)
Set to ld3, and the cycle 3 times before the previous cycle Told3
Is set to the cycle Told4 four times before (two times before).

In the next step 4, the latest cycle Tn obtained in step 3
ew One cycle before (1/2 cycle before) the cycle Told2, two cycles before (one cycle before) the cycle Told4, according to the following formula, the misfire judgment approximately equivalent to the step difference of the indicated mean effective pressure Pi between the cylinders. Calculate the value LU.

A value approximately corresponding to the step of the indicated average effective pressure Pi is calculated in the part excluding the multiplication term of the rotation speed ² / predetermined value in the above equation, but the correction term (revolution speed ² / predetermined value) according to the rotation speed is calculated. The level of the misfire determination value LU calculated according to an arithmetic expression not provided largely differs depending on the engine rotation speed N, and the absolute value level of the determination value LU tends to increase as the engine speed decreases. Therefore, the discriminant value LU is increased and corrected as the rotational speed is higher, and the discriminant value LU is calculated to be approximately the same in each rotational range, so that the misfire discriminant value LU is not affected by the engine rotational speed N. The accuracy of misfire diagnosis based on is maintained. The predetermined value for dividing the square value of the rotation speed is for adjusting the digits of the determination value LU when the digits of the rotation speed are different.

In this way, if the substantially same discriminant value LU is calculated in each rotation range, the slice level SL used for the level determination of this discriminant value LU is changed according to the engine speed,
The slice level SL can be set to a constant level irrespective of the engine rotation speed without having to deal with the level change of the discrimination value LU depending on the rotation speed. Therefore, the slice level
It is possible to reduce the matching man-hours for making SL correspond to the change in the discriminant value LU level, and at the rotation speed, slice level SL
Since it is not necessary to change, it is possible to save the memory capacity related to the slice level SL setting.

When the discriminant value LU is corrected and set in accordance with the engine speed in step 4, in the next step 5, the discriminant value LU calculated in step 4 is a negative value, and the indicated mean effective pressure decreases and changes. Is indicated.

When the discriminant value LU is a negative value and indicates a decrease change in the average effective pressure, the routine proceeds to step 6, where a slice level SL that is constant regardless of the engine rotation speed and step 4
The discriminant value LU calculated in step 3 is compared to determine whether the discriminant value LU calculated this time is smaller than the slice level SL.

Here, if it is determined that the determination value LU is smaller than the slice level SL, the process proceeds to step 7 to determine the flag flag. When the discriminant value LU is determined to be negative, the flag flag is set to 1 in step 18 which will be described later, and when the discriminant value LU is zero or more, it is set to 0 in step 19. When it is determined that the flag flag is zero in step 7, it is determined that the determination value LU is less than the slice level SL in the first time when the determination value LU becomes negative. It is estimated that the cylinder in which the decrease in average effective pressure Pi has been decreased is misfiring, and the routine proceeds to step 8.

In step 8, the cylinder in the combustion stroke that has affected the TDC cycle sampled recently is specified according to which cylinder the previous TDC is the compression TDC, and that cylinder is designated as the misfire detection cylinder based on the present discrimination value LU. To do. That is, for example, when the compression TDC of this time is for the # 2 cylinder, if the ignition order is # 1 → # 3 → # 4 → # 2, there is combustion in the # 4 cylinder immediately before. Since the cycle is measured under the influence of combustion and the discriminant value LU is calculated, the misfire occurrence of the # 4 cylinder is discriminated based on the discriminant value LU which is discriminated to be less than the slice level SL this time, and the step Go to 9 # 4
The count value C4 that counts the number of cylinder misfires is incremented by 1. Similarly, it is assumed that a misfire has occurred in the cylinder that was in the combustion stroke immediately before the cylinder to which the current compression TDC corresponds, and the misfire detection count C1 to C3 is incremented for each cylinder (steps 10 to 12). ).

On the other hand, when it is determined in step 7 that the flag flag is set to 1, the determination value LU continues to be negative, and in this case, the determination value LU that was first negative. It is correct to identify the misfiring cylinder based on
In step 13, it is determined that the cylinder burned two times before the combustion cylinder specified as the latest compression TDC has misfired.

That is, when the current compressed TDC is the # 4 cylinder, the immediately preceding combustion cylinder is the # 3 cylinder, and the previous time is the # 1 cylinder. Therefore, in step 13, the combustion cylinder is the # 4 cylinder. If it is determined, it is estimated that the # 1 cylinder has misfired, and the routine proceeds to step 14, where C1 for counting up the number of misfires of the # 1 cylinder is incremented by 1. Combustion cylinder is # 2, #
Similarly, when the number of cylinders is # 1 and # 3, the misfires of the # 3, # 4, and # 2 cylinders are estimated and the number of misfire detections for each cylinder is counted up (steps 15 to 17).

In this way, when the misfiring cylinder is identified and the number of misfirings of that cylinder is counted up, and when it is judged in step 6 that the judgment value LU is negative but is equal to or higher than the slice level SL, step 18 is executed. The flag flag is set to 1.

If it is determined in step 5 that the determination value LU is greater than or equal to zero, the process proceeds to step 19 and the flag flag is set to zero.

When the flag flag is set in step 18 or step 19, the process proceeds to step 20. In step 20, it is determined whether or not the count value cnt for counting the number of times the program is executed has reached a predetermined value (for example, 1000). Here, when the count value cnt is not counted up to the predetermined value, the routine proceeds to step 21, where the count value cnt is incremented by 1 to end the program, but when it is the predetermined value, the count value is counted at step 22. After the cnt is reset to zero, the misfire occurrence display for each cylinder is performed in step 23 to step 30 based on the misfire occurrence rate for each cylinder.

In step 23, C1 in which the number of misfire detections for the # 1 cylinder is set is compared with a predetermined value (for example, 40), so that the count value cnt is counted up to a predetermined value during a predetermined period or more. When the misfire of the # 1 cylinder is detected at a certain ratio, the routine proceeds to step 24, where the occurrence of the misfire of the # 1 cylinder is displayed and warned, for example, on the dashboard of the vehicle in which the engine 1 is mounted.

Similarly, by comparing C2 to C4 in which the number of misfire detections of the # 2 cylinder to # 4 cylinder is set with a predetermined value, it is determined whether or not the misfire frequency is high for each cylinder.
For cylinders that have misfired more than a predetermined frequency,
Display the occurrence of misfire as above (step 25 ~
30).

After determining the misfire occurrence frequency by comparing each of the misfire count values C1 to C4 with a predetermined value, C1 to C4 in step 31.
Is reset to zero, and the number of misfire detections for each cylinder is newly set to each of the misfire count values C1 to C4 during the predetermined period in which the count value cnt is again counted up to the predetermined value.

By the way, the misfire diagnosis is not limited to the one based on the above misfire discrimination value LU, but as shown in the flowchart of FIG. 4, the misfire is diagnosed by whether or not the rotation cycle T has increased more than a predetermined value. It may be configured to.

The program shown in the flowchart of FIG. 4 is similar to the program shown in the flowchart of FIG.
First, in step 51 and step 52, the throttle valve 10 is fully closed and the engine speed N is equal to or higher than the predetermined speed in the same manner as in step 1 and step 2 above. It is determined whether or not there is.

When the throttle valve 10 is fully closed and the engine speed N is equal to or higher than a predetermined speed, the misfire diagnosis cannot be accurately performed based on the crank angular speed. Therefore, the program is ended as it is, and the diagnosis without misfire is made when the misfire occurs. Prevent that.

Then, only when the misfire prohibition condition is not satisfied, the routine proceeds to step 53 and thereafter to perform the misfire diagnosis.

In step 53, the values from the latest value Tnew of the TDC cycle (180 ° cycle for four cylinders) measured as the input interval of the TDC pulse to the value Told4 four times before are updated and stored in step 53.

Then, in the next step 54, four times before the latest value Tnew
The average value of the TDC cycle up to Told4 is calculated, and the result is set in the slice level SL.

In the next step 55, a value obtained by adding a predetermined deviation α variably set with the engine load and the engine speed as parameters to the slice level SL obtained as the average cycle, and the latest cycle
Compare with Tnew.

The predetermined deviation α is set by background processing by the program shown in the flowchart of FIG. 5, and is a parameter representative of the engine load such as the basic fuel injection amount Tp set by the electronically controlled fuel injection device. And the engine speed N is used as a parameter for each operating region, and a map in which the predetermined deviation α is stored is searched based on the latest engine load and engine speed N.
This predetermined deviation α corresponds to the difference in the periodic fluctuation level when the misfire occurs due to the difference in the operating conditions, and the accuracy of the misfire diagnosis is ensured for each operating condition.

When it is determined in step 55 that Tnew> SL + α, Tnew has a deviation of a predetermined value or more and exceeds the average cycle, and at this time, the latest cycle Tnew becomes a predetermined value or more due to a decrease in cylinder pressure due to misfire. Since it is estimated that the extension has occurred, the occurrence of misfire is determined, and the routine proceeds to step 56.

In step 56, the cylinder in the combustion stroke at the present time is determined, and the cylinder ignited before this cylinder is set as the misfiring cylinder.

That is, assuming that the ignition order is # 1 → # 3 → # 4 → # 2, for example, if the current combustion stroke cylinder is # 2, the latest cycle Tnew is the TDC that overlaps the combustion stroke of the previous # 4 cylinder. Since the cycle has been measured, the misfiring cylinder is determined to be the # 4 cylinder, and, like C1 to C4 shown in the flowchart of FIG. Count up (step 57 ~
60).

On the other hand, when it is determined in step 55 that Tnew ≦ SL + α, the latest cycle Tnew does not extend with a deviation of a predetermined value or more from the average cycle, so it is determined that there is no misfire, and steps 56-60 are jumped. And proceed to step 61.

After step 61, the misfiring cylinder is displayed based on the misfire detection rate as in steps 20 to 31 in the flowchart of FIG. 3, and the description thereof is omitted here.

In the present embodiment, when the misfire occurrence frequency for each cylinder is equal to or higher than a predetermined value, the cylinder is displayed and a warning is given. However, a failsafe such as stopping the fuel supply to the cylinder together with the warning is given. The control may be executed.

Further, in the above, the misfire diagnosis of the 4-cylinder internal combustion engine has been described as an embodiment, but it may be a 6-cylinder engine or an 8-cylinder engine, and a more complicated judgment logic is used in the misfire diagnosis based on the judgment value LU. The misfire diagnosis may be based on the crank angular velocity.

<Effects of the Invention> As described above, according to the present invention, when the throttle valve is fully closed and the coasting speed is equal to or higher than a predetermined value during coasting, the accuracy of the misfire diagnosis based on the crank angular speed decreases. Since the misfire diagnosis is prohibited, for example, even if a misfire occurs during coasting, the diagnosis of no misfire does not occur, the reliability of the misfire diagnosis is improved, and the crank angular velocity ( By including the condition that the engine rotation speed) is equal to or higher than a predetermined value, it is possible to prevent the misfire diagnosis from being prohibited in an unnecessary operation region, and to reduce the operation region in which the diagnosis is prohibited as much as possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of the present invention, FIG. 2 is a system schematic diagram showing an embodiment of the present invention, and FIG. 3 is a flow chart showing contents of misfire diagnosis control in the same embodiment.
4 and 5 are flowcharts showing other embodiments of the misfire diagnosis control, FIG. 6 is a diagram showing boost change with respect to engine speed during coasting, and FIG. 7 is an indicated average during coasting. Time charts showing changes in effective pressure, and FIGS. 8 and 9 are diagrams showing changes in crank angular velocity depending on the presence or absence of misfire. 1 ... Engine, 2 ... Signal disk plate 3,4 ... Electromagnetic pickup, 5,6 ... Zero cross comparator, 7,8 ... Wave shaping circuit 9 ... Control unit, 10 ... Throttle valve 11 ... Idle switch

Claims (1)

[Claims] 1. A crank angular velocity detecting means for detecting a crank angular velocity of an internal combustion engine, a misfire diagnosing means for performing a misfire diagnosis based on the crank angular velocity detected by the crank angular velocity detecting means, and an intake system of the engine. A throttle valve fully closed detection means for detecting a fully closed state of the throttle valve; and a fully closed state of the throttle valve detected by the throttle valve fully closed detection means, and the crank angular velocity is not less than a predetermined value. A misfire diagnosis device for an internal combustion engine, comprising: a misfire diagnosis prohibition means for prohibiting the misfire diagnosis by the misfire diagnosis means.