JP2844841B2 - Misfire detection device for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a device for detecting misfire using a filter in a multi-cylinder internal combustion engine.

[Conventional technology]

Conventionally, an angle signal output from a rotation angle sensor of an internal combustion engine is digitally calculated by a microcomputer or the like to calculate an instantaneous rotational speed, and the instantaneous rotational speed is statistically processed. There is something that detects

[Problems to be Solved by the Invention] However, in the above-described apparatus, the load on the digital operation is large, so that when the engine rotates at a high speed, the operation time is restricted and the digital operation processing is restricted. There is a problem that it is no longer possible to detect a misfire.

An object of the present invention is to detect a misfire reliably even at a high rotation speed by reducing the processing amount of digital computation.

[Means for solving the problem]

As means for solving the above-mentioned problems, the present invention provides a rotation detecting means for detecting rotation of an engine, and according to the rotation of the engine so as to be a filter frequency band obtained by dividing the ignition frequency of the engine by the number of cylinders of the engine. And a misfire detecting means for detecting a misfire based on a rotation signal from the rotation detecting means passing through the filter means. .

[Action]

As a result, the rotation signal from the rotation detecting means is passed through a filter that uses a frequency band obtained by dividing the ignition frequency by the number of cylinders of the engine, that is, a frequency band of a signal component of the rotation signal generated at the time of misfire as a filter frequency band, thereby causing misfire Only the signal components generated at the time are passed. The misfire of the engine is detected based on the passed signal.

〔The invention's effect〕

As described above, according to the present invention, a filter that uses a frequency band obtained by dividing an engine rotation signal by an ignition frequency by the number of cylinders of an engine, that is, a frequency band of a signal component of a rotation signal generated at the time of misfire as a filter frequency band. , A signal component generated at the time of misfire is detected by analog calculation. Therefore, there is an excellent effect that misfire can be reliably detected even at a high rotation speed.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

This embodiment relates to a four-cylinder internal combustion engine, and FIG. 1 shows an overall configuration diagram. 1 is a reference position sensor that outputs a signal every 720 ° CA of the engine crankshaft, 2 is a waveform shaping circuit that shapes the signal from the reference position sensor 1, and 3 is a slit that rotates in synchronization with the crankshaft of the internal combustion engine. The disk is provided with slits at every 1 CA and at every 180 CA of the crankshaft. A rotation sensor that detects a slit position of each 1 ゜ CA of the slit disk 3 and generates a rotation signal for each 1 ゜ CA of the crankshaft;
Is a cylinder discrimination sensor that detects a slit position of the slit disk 3 at every 180 ° CA and generates a cylinder discrimination signal at every 180 ° CA of the crankshaft. Reference numeral 6 denotes a frequency dividing circuit, which outputs a signal every 30 ° CA of the crankshaft by counting rotation signals based on the cylinder discrimination signal.

Reference numeral 7 denotes a variable filter module serving as a filter means, which receives a rotation signal and outputs a misfire signal component signal of the rotation signal. Numeral 8 denotes a maximum value minimum value holding circuit which holds the maximum value and the minimum value of the misfire component signal from the filter module 7, and receives a signal of 30 ° by a clear signal from the ECU 9 described later.
The maximum and minimum values are cleared for each CA.

Reference numeral 9 denotes an engine control computer (ECU) that controls ignition timing and fuel injection amount based on signals from the shaping circuit 2, the frequency dividing circuit 6, the variable filter module 7, and the like, and determines misfire. 10 is a warning lamp for warning of misfire, 11 is an injector, and 12 is an igniter.

FIG. 2 is a configuration diagram of the variable filter module 7 serving as a filter unit. 7a is an FV converter that converts a rotation signal for each 1 CA into an analog voltage signal corresponding to a frequency, and 7b is a switched capacitor filter, which inputs a filter frequency (passing frequency band) to a CLK terminal 7b-2. The frequency can be changed according to the frequency of the signal. The analog voltage signal is input to the IN terminal 7b-1,
A misfire component signal of the rotation signal is output from the terminal 7b-3. 7c
Is a low-pass filter, which cuts high frequency components of the analog voltage signal from the FV converter 7a. 7d is a forward amplifier for amplifying the analog voltage signal, 7e is a VF converter for converting the analog voltage signal from the amplifier 7d to a frequency signal, and the frequency signal from the VF converter 7e is a switched capacitor filter 7b. Is input to the CLK terminal 7b-2.

The operation of the variable filter module will be described with reference to FIGS.

First, the rotation signal from the rotation sensor 5 shown in FIG.
The signal is input to the V converter 7a and converted into an analog voltage signal. The analog voltage signal in a normal state has a sine wave as shown in FIG. 4, and at the time of misfiring, a waveform having a longer cycle in the misfiring cylinder as shown in FIG.

By the way, when the analog voltage signals shown in FIGS. 4 and 5 are subjected to frequency analysis, they show frequency characteristics as shown in FIGS. 8 and 9, respectively. Here, fign is the ignition frequency, and a large amplitude appears in a frequency band around fign / N (N is the number of cylinders, N = 4 in this embodiment) in addition to the ignition frequency fign at the time of misfire (FIG. 9). During normal ignition, a large amplitude appears only at the ignition frequency fign.

The switched capacitor filter 7b is a filter for passing only a signal in the frequency band of fign / 4,
gn is to vary the engine speed, it is necessary to center frequency f ₀ of the filter 7b is always fign / 4.

Meanwhile switched capacitor filter 7b is using MF10 manufactured by National Semiconductor Corporation, of the signal input to the center frequency f ₀ of the filter and the CLK terminal 7b-2 frequency f
_CLK has the following relationship.

In addition, the following formula is established to set the center frequency f ₀ to a value obtained by dividing the ignition frequency fign by the number of cylinders (N) in order to detect misfire.

From the above equations (A) and (B), f _CLK = 25 · fign (C) is obtained.

Meanwhile firing frequency fign is 1/180 of the frequency f ₁ ° _CA of the rotation signal to be input to the F-V converter 7a. (∵720
た め Because CA fires 4 times) From the above formulas (C) and (D) As described above, if a signal having a frequency obtained by multiplying the frequency f ₁゜_CA of the rotation signal input to the FV converter 7a by 0.139 is input to the CLK terminal 7b-2, the center frequency f ₀ of the switched capacitor filter 7b is always fig / 4. become.

Now, assuming that the conversion ratio between the FV converter 7a and the VF converter 7e is 1: 1, the analog voltage signal from the FV converter 7a passes through a low-pass filter 7c to remove high frequency components, and It is amplified 0.139 times by 7d.
This amplified analog voltage signal is supplied to a VF converter 7e.
Is converted into a frequency signal. Frequency f _CLK of the frequency signal is 0.139 times the frequency f ₁ ° _CA of the rotation signal. When the frequency signal of this frequency f _CLK is input to the CLK terminal,
The center frequency f ₀ of the switched capacitor filter 7b is fign
Set to / 4. When an analog voltage signal from the FV converter 7a is input to the IN terminal 7b-1, a signal component of the analog voltage signal in a frequency band of fign / 4 is output from the OUT terminal 7b-3. 6 and 7 show output waveforms from the OUT terminal 7b-3, FIG. 6 shows the case of normal ignition, and FIG. 7 shows the case of misfire. Since the misfire occurs when a waveform having a large amplitude is output to, ECU maximum value _max and minimum value _min of the cycle (720 ° CA) for each of the output signals of the combustion
9 detects and determines misfire.

FIG. 10 is a flowchart showing the operation of the ECU 9 constituting the misfire detecting means, and the operation of the ignition discrimination in the ECU 9 will be described based on the flowchart.

The ECU 9 sends a reference signal from the reference sensor 2 for every 720 CA
The maximum value and the minimum value of the interrupt signal for every 30 ° CA from the frequency dividing circuit 6 and the misfire component signal from the switched capacitor filter 7b for every 30 ° CA are input via the maximum value / minimum value holding circuit 8, respectively. .

The misfire determination routine shown in FIG.
The following processing is executed only when an interrupt signal is input for each.

When an interrupt signal is input, it is determined in step 20 whether or not a reference signal has been input. When it is determined that the reference signal has been input, that is, when the first cylinder is at the top dead center (TDC) timing, the process proceeds to step 30. In step 30,
The RAM (d _max ) storing the maximum value of the misfire component signal and the RAM (d _min ) storing the minimum value are initialized, and the process proceeds to step 40. If it is determined in step 20 that the reference signal has not been input, the process proceeds to step 40 without initializing d _max and d _min . In step 40, the analog-to-digital converter is activated to digitally convert the maximum value and the minimum value of the misfire component signal from the maximum value / minimum value holding circuit 8. Next step
The maximum value and the minimum value of the misfire component signal digitally converted at 50 are read, and at step 60, when the maximum value of the misfire component signal read at step 50 is larger than the value stored in d _max
Update the value of d _max . Further, when the minimum value of the misfire component signal read in step 50, step 70 is less than the value stored in the d _min updates the value of d _min. Next, in step 75, a clear signal is output to the maximum value minimum value holding circuit 8 to clear the maximum value and the minimum value held by the holding circuit. Steps
At step 80, it is determined whether or not 720 ° CA has elapsed since the input of the reference signal. When 720 ° CA has elapsed, that is, when one cycle of combustion is completed, at step 90, the misfire component in one cycle of combustion is determined. The difference Range (amplitude of the misfire component signal) between the maximum value d _max and the minimum value d _min of the signal is calculated. This Range
Is larger than a predetermined value, it means that the engine has misfired. Next, in order to determine the misfire in step 100, compares the Range misfire determination value T _0. Range is determined that a misfire when greater than T ₀ has occurred, in step 110, outputs a warning lamp point No.燈信the driver informing misfire. If it is determined in step 80 that 720 CA has not elapsed, the misfire determination routine ends without performing the processing in steps 90 to 110. Also when the Range in step 100 determines that ie misfire is smaller than T ₀ has not occurred without the process of step 110, and terminates the engine misfire detection routine.

As described above, every time an interrupt signal is input every 30 ° CA, the misfire determination routine shown in FIG. 4 is executed, and the difference between the maximum value and the minimum value of the misfire component signal in one cycle of combustion of the engine is calculated.
That is, the occurrence of a misfire of the engine is determined from the magnitude of the amplitude of the misfire component signal.

Note that the above-described determination value T ₀ may be varied depending on the engine speed and the engine load, and when the engine speed is rapidly changing, and when the engine load is rapidly changing, it is easy to make a misfire misjudgment. Therefore, the output of the warning lamp lighting signal in step 110 may be canceled. In step 110, the warning lamp is turned on and step 6 is performed.
A misfire cylinder may be determined based on the crank angle at which the maximum value and minimum value obtained in steps 0 and 70 occur, and fuel supply to the cylinder may be stopped to prevent deterioration of the emission.

Further, in the present embodiment, misfire is determined based on the magnitude of the amplitude of the misfire component signal. However, misfire may be determined when the maximum value of the misfire component signal exceeds a predetermined value.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a block diagram showing the configuration of a variable filter in the above embodiment, FIG.
FIG. 5 is an analog voltage waveform diagram at normal time, FIG. 5 is an analog voltage waveform diagram at misfire, FIG. 6 is a filter output waveform diagram at normal time, FIG. 7 is a filter output waveform diagram at misfire, and FIG. FIG. 9 is a frequency characteristic diagram of a normal analog voltage waveform, FIG. 9 is a frequency characteristic diagram of a misfire analog voltage waveform, and FIG. 10 is a flowchart showing the operation of the ECU. 4 ... A rotation angle sensor as a rotation detecting means, 7b ... A switched capacitor filter as a filtering means, 8 ... ECU as a misfire detecting means.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 45/00 F02P 17/00

Claims (1)

(57) [Claims] 1. A rotation detecting means for detecting rotation of an engine, and a filter frequency band varies according to the rotation of the engine so as to be a filter frequency band obtained by dividing an ignition frequency of the engine by the number of cylinders of the engine. A misfire detection device for an internal combustion engine, comprising: filter means; and misfire detection means for detecting misfire based on a rotation signal from the rotation detection means passing through the filter means.