JP2002256960A - Detecting method for knocking - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the background level for detecting knocking with good accuracy without any increase in sampling speed. SOLUTION: Out of output signals from a pressure sensor S, a signal where no vibration component due to knocking is superimposed is filtered by a band- pass filter 6, and further the output signal of the band-pass filter 6 is filtered by a low-pass filter 10. According to the output signal of the low-pass filter 10, the background level is detected. Sampling for obtaining the background level is performed for a signal passed through the low-pass filter, and in the signal, high frequency component is suppressed for equalization, whereby the background level can be obtained with good accuracy without any increase in sampling speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for detecting a background level from an output signal of a pressure sensor for detecting an in-cylinder pressure in a combustion chamber of an internal combustion engine and detecting knocking based on the background level.

[0002]

2. Description of the Related Art Conventionally, knocking has been detected in order to control ignition timing while suppressing occurrence of knocking. When knocking occurs, abnormal pressure waves are generated in the combustion chamber, and knocking-specific vibration occurs in the internal combustion engine.Therefore, by examining the knocking-specific frequency component of the vibration generated in the internal combustion engine,
Knocking is detected. For detecting the vibration state of the internal combustion engine, various sensors such as a knock sensor and a pressure sensor for detecting an in-cylinder pressure in the combustion chamber are used. From the output signal (sensor signal), a knock-specific signal is detected via a filter circuit. Extract signal components in the frequency band.

When extracting a vibration frequency component unique to knocking from an output signal of a sensor, a vibration component (hereinafter referred to as "background component") generated due to a factor other than knocking is also extracted. Therefore, in order to suppress a decrease in the knocking detection accuracy, it is necessary to consider the signal level of the background component when performing the knocking determination based on the extracted vibration frequency component.

[0004] The signal level of this background component (hereinafter referred to as "background level").
For example, the following method can be considered. First,
A background component is extracted from the sensor signal by performing filtering using a filter having a pass band specific to knocking (hereinafter referred to as “knocking frequency band”) as a pass band. Then, from the extracted background component, sampling and A / D conversion are performed over a predetermined section in the combustion cycle, and the average value of the data values obtained as a result is obtained as a background level (for example, Japanese Patent Laid-Open No. 4-244933). Reference).

[0005]

However, in the method of detecting the background level in this manner, the value obtained varies depending on the width of the sampling interval. In order to reduce the error, a method of performing sampling at a high speed (about 50 kHz to 100 kHz), and holding and averaging a large amount of data may be considered. However, hardware for realizing high-speed A / D conversion is considered. And a large-capacity memory is required, which increases the manufacturing cost, which is not preferable.

[0006] The present invention has been made in view of such a background, and without increasing the sampling speed,
It is an object of the present invention to provide a knocking detection method capable of accurately obtaining a background level.

[0007]

In order to solve the above-mentioned problems, in the knocking detecting method according to the first aspect, a signal from a pressure sensor for detecting an in-cylinder pressure in a combustion chamber of an internal combustion engine is used for knocking. During the period in which the resulting vibration component is not superimposed, the signal is filtered by a band-pass filter having a knocking frequency band as a pass band, and the signal filtered by the band-pass filter is equal to or higher than the cutoff voltage level or equal to or lower than the cutoff voltage level. Filter with a voltage cut filter that passes only
The signal filtered by the voltage cut filter is filtered by a low pass filter having a pass band equal to or lower than a cutoff frequency lower than the knocking frequency band. Then, based on the output signal of the low-pass filter, a background level which is a level of a signal generated by a factor other than knocking included in the signal of the pressure sensor is detected.

As described above, in the first aspect of the present invention, the detection of the background level is performed on the output signal of the low-pass filter. Since the high-frequency component is suppressed and averaged in the output signal of the low-pass filter, the background level can be obtained stably without speeding up the sampling, and the knocking can be detected accurately. .

Further, in order to detect the background level from the output signal of the low-pass filter, the output signal of the pressure sensor is filtered by a band-pass filter during a period in which vibration components due to knocking are not superposed. Do. To this end, the filtering time (window) may be set to a period in which knocking is not feared, but may overlap with the knocking-prone period, and even in such a case, the vibration component due to knocking may be generated. It is possible to detect the background level from a signal that is not superposed. For example,
The output signal of the low-pass filter is acquired irrespective of the presence or absence of knocking, and if knocking is determined to be absent as a result of knocking determination (knocking determination based on a background level in the past), back-up based on the output signal of the low-pass filter is performed. What is necessary is just to detect the ground level.

[0010] The above-mentioned object can also be solved by the present invention. In the knocking detection method according to the second aspect, the signal of the pressure sensor is set such that the knocking frequency band is a pass band and the output is equal to or higher than the cutoff voltage level during a period in which the vibration component due to knocking is not superposed. Filtering is performed by a band-pass filter set so as to be only the off-voltage level or lower, and the signal filtered by the band-pass filter is filtered by a low-pass filter having a pass band equal to or lower than a cutoff frequency lower than the knocking frequency band. . Then, the background level is detected based on the output signal of the low-pass filter.

According to such a knocking detection method,
The same effect as the first aspect can be obtained. According to the second aspect of the present invention, the output of the band-pass filter is cut off so as to be only at or above the cutoff voltage level or below the cutoff voltage level. That is, the bandpass filter is integrated with the voltage cut filter, and has a function of the voltage cut filter. Therefore, there is no need to provide an independent voltage cut filter,
This is preferable in that the circuit configuration is simplified.

The above object can also be solved by the invention described in claim 3. In the knocking detection method according to the third aspect, the signal of the pressure sensor is filtered by a bandpass filter having a knocking frequency band as a pass band during a period in which a vibration component due to knocking is not superimposed. The signal filtered by the band-pass filter is filtered by a low-pass filter whose pass band is lower than the cutoff frequency lower than the knocking frequency band and whose output is set to only the cutoff voltage level or higher or the cutoff voltage level only. The background level is detected based on the output signal of the low-pass filter.

According to such a knocking detection method,
The same effect as the first aspect can be obtained. According to the third aspect of the present invention, the output of the low-pass filter is cut off so as to be only at or above the cutoff voltage level or below the cutoff voltage level. That is, it is integrated with the low-pass filter voltage cut filter and has the function of the voltage cut filter. Therefore, similarly to the second aspect of the invention, there is no need to provide an independent voltage cut filter, and the circuit configuration is simplified.

It is preferable that the cutoff voltage is set to the earth ground of the measuring system. That is, the output signal of the bandpass filter is
Since the signal has an amplitude centered on the earth ground of the measurement system including the bandpass filter, the background level can be detected with high accuracy by setting the cutoff voltage to the earth ground.

The cut-off frequency of the low-pass filter may be, for example, 10
The frequency is preferably set to 0 Hz or less, and the detection accuracy of the background level becomes extremely high as described later. In the above invention, a so-called seat-type pressure sensor (where the pressure sensor is provided on a mounting seat of a spark plug of an internal combustion engine, and a change in a tightening load of the spark plug is provided). It is preferable to apply the present invention to a method of detecting the in-cylinder pressure of an internal combustion engine by detecting the pressure. In the output signal of such a seat-type pressure sensor, there is a high possibility that signal components due to piston slap, distortion of the cylinder head, seating of the intake valve and the exhaust valve, etc. are superimposed and become a background component, It is preferable to obtain the background level with high accuracy by applying the present invention.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram of an internal combustion engine control device (ECU) 2 having a configuration for realizing the present invention. The ECU 2 controls an internal combustion engine having a plurality of cylinders, and receives an output signal of the pressure sensor S as shown in FIG.

The ECU 2 includes a charge amplifier 4 for outputting a signal corresponding to the charge generated by the pressure sensor S, a background level detection circuit 5 for processing the output signal of the charge amplifier 4, an ignition timing of the internal combustion engine 21, A CPU 12 for executing a control process for comprehensively controlling an idle rotation speed and the like.

The pressure sensor S is, as shown in FIGS.
It is provided on a mounting seat of the ignition plug 23 of the internal combustion engine 21. The pressure sensor S detects a change in the tightening load of the ignition plug 23 on the internal combustion engine 21 to detect the change in the internal combustion engine 2.
The internal pressure (in-cylinder pressure) of the first combustion chamber 25 is detected, and a charge corresponding to the magnitude of the in-cylinder pressure in the combustion chamber is output as a detection signal.

As shown in FIG. 3, the spark plug 23 has a metal shell 23a formed with a thread for attaching the spark plug 23 to the body of the internal combustion engine 21.
The metal shell 23a is a mounting seat for the spark plug 23, and the spark plug 23 is fastened to the body of the internal combustion engine 21 via the metal shell 23a.

The pressure sensor S has a piezoelectric element (not shown) built in the metal shell 23a, and has an electric charge corresponding to a tightening load of the ignition plug 23 which changes according to a change in the in-cylinder pressure. The generated charges corresponding to the internal pressure are output via the output cable 23b. Charge amplifier 4
Converts the charge generated by the pressure sensor S into a voltage signal,
Output as a sensor signal of the pressure sensor S.

The background level detection circuit 5
Is to improve the detection accuracy of the background level by the CPU 12 by performing filtering or the like on the output signal output from the pressure sensor S. As shown in FIG. 1, the background level detection circuit 5 includes a bandpass filter 6, an amplification circuit 8,
A low-pass filter 10.

The band-pass filter 6 uses a knocking frequency band as a pass band (in the present embodiment, the band-pass filter 6 is used).
kHz to 10 kHz), and includes a high-pass filter 6a and a low-pass filter 6b. As shown in FIG. 4, the high-pass filter unit 6a includes an operational amplifier OP1.
And its non-inverting input terminal (+)
Is supplied with an output signal of the charge amplifier 4 via the capacitors C1 and C2 connected in series. Also,
This non-inverting input terminal (+) is connected to GN via a resistor R1.
It is connected to the D line (0 [V]). Operational amplifier O
The inverting input terminal (-) of P1 is connected to GN via a resistor R2.
It is connected to the D line and to the output terminal of the operational amplifier OP1 via the resistor R4.

The output terminal of the operational amplifier OP1 is connected to a resistor R
3, the output terminal of the operational amplifier OP1 is connected to the non-inverting input terminal (+) of the operational amplifier OP1 via the capacitor C2 and the resistor R3. It is in a state of being left. The output terminal of the operational amplifier OP1 is
It is connected to the GND line via a resistor R5.

The high-pass filter section 6a configured as described above allows a frequency component higher than a predetermined cutoff frequency (6 kHz in the present embodiment) of the output signal of the charge amplifier 4 to pass therethrough, and passes through the output terminal of the operational amplifier OP1. Works to output. On the other hand, the low-pass filter unit 6b
It has an operational amplifier OP2, and its non-inverting input terminal (+) has a resistor R6 connected in series,
The output terminal of the operational amplifier OP1 is connected via R7,
The output signal of the high-pass filter unit 6a is input. The non-inverting input terminal (+) is connected to the GND line via the capacitor C3. Operational amplifier OP2
Is connected to the GND line via a resistor R8 and to the output terminal of the operational amplifier OP2 via a resistor R9.

The output terminal of the operational amplifier OP2 is connected to the connection point between the resistor R6 and the resistor R7 via the capacitor C4, whereby the output terminal of the operational amplifier OP2 is connected via the capacitor C4 and the resistor R7. It is connected to the non-inverting input terminal (+) of the operational amplifier OP2. The output terminal of the operational amplifier OP2 is connected to the GND line via a resistor R10.

The low-pass filter 6b configured as described above functions to pass a frequency component equal to or lower than a predetermined cutoff frequency (10 kHz in this embodiment) in the output signal of the high-pass filter 6a. That is, the band-pass filter 6 outputs a predetermined pass band (6 kHz to 10 kHz in the present embodiment) of the output signal of the charge amplifier 4.
The frequency component of (kHz) passes, and the function of outputting the output signal Va from the output terminal of the operational amplifier OP2 is achieved.

In the operational amplifiers OP1 and OP2 constituting the band-pass filter 6, each operational amplifier OP
A positive power supply (+5 V in this embodiment) is connected to one of a pair of power supply input terminals 1 and OP2, and a GND line is connected to the other power supply input terminal. That is, since the operational amplifier OP1 and the operational amplifier OP2 are provided to operate with a single power supply, they each function as a voltage cut filter that passes only a cutoff voltage level or more that is the earth ground (0 V) of the measurement system. . Therefore, the output signal Va of the band-pass filter 6
Is a signal rectified so that its signal level is equal to or higher than the cutoff voltage level.

In this embodiment, as described above, the band-pass filter 6 is set so that the knocking frequency band is set as the pass band and the output is set to only the cut-off voltage level or higher.
, Filtering the signal of the pressure sensor S. Next, the amplifying circuit 8 is configured to include an operational amplifier OP3, and the non-inverting input terminal (+) is connected to the output terminal of the operational amplifier OP2 via a resistor R12 connected in series. The output signal Va of the filter 6 is input. The non-inverting input terminal (+) of the operational amplifier OP3 is connected to the GND line via the resistor R11, and is connected to the operational amplifier O3 via the resistor R13.
It is connected to the output terminal of P3. That is, the amplifier circuit 8
It is configured as a non-inverting amplifier circuit, and simply amplifies the output signal Va of the band-pass filter 6 at a magnification determined by the ratio between the resistors R11 and R13.

The low-pass filter 10 comprises a resistor R14 and a capacitor C5.
4 is connected to an output terminal of an operational amplifier OP3, and the other end of the resistor R14 is connected to G via a capacitor C5.
Connected to ND line. With this configuration, the low-pass filter 10 allows the frequency component below a predetermined cutoff frequency (a frequency lower than the knocking frequency band) to pass through the output signal of the amplifier circuit 8, and the resistor R 14 and the capacitor From the connection point with C5, the output signal Vb
Works as output.

The CPU 12 samples the signal from the background level detection circuit 5 during the period in which it is known that knocking has not occurred, and subjects it to A / D.
Convert to determine the background level. Also CP
U12 is not only a background level detection circuit 5, but also a peak hold circuit for detecting a peak value of an output signal obtained by passing an output signal of the pressure sensor S through a band-pass filter or a high-pass filter, or an output after passing the filter. Signals are also input / output to / from an integrating circuit for integration. Then, the CPU 12 determines the occurrence of knocking based on, for example, a peak value obtained via a peak hold circuit (not shown) during the occurrence of knocking and a background level.

Although not shown, since the pressure sensors S of the present embodiment are provided for each cylinder of the internal combustion engine 21, if there are a plurality of pressure sensors S in accordance with the number of cylinders, each pressure sensor S Each time, a charge amplifier 4 and a background level detection circuit 5 are provided.

FIG. 5 shows an output signal () of the charge amplifier 4 and an output signal Va () of the band-pass filter 6.
And an output signal Vb () of the low-pass filter 10. One scale on the horizontal axis shown in FIG. 5 corresponds to 2 ms.
The knocking frequency component of the output signal () of the charge amplifier 4 is converted into an output signal Va by the bandpass filter 6.
(), And further passed through the low-pass filter 10 to suppress the output signal V in which high frequency components are suppressed.
b (). The output signal Vb shown in FIG.
() Shows the case where the cutoff frequency of the low-pass filter 10 is set to 500 Hz.

As described above, in the method of the present embodiment, among the output signals from the pressure sensor S, the signal in which the vibration component caused by knocking is not superimposed is filtered by the band-pass filter 6, and further filtered. The output signal of the band pass filter 6 is filtered by the low pass filter 10. Then, a background level is detected based on the output signal of the low-pass filter 10. That is, the sampling for obtaining the background level is performed on the signal passed through the low-pass filter, and the high-frequency component is suppressed and averaged in the signal. The background level can be obtained with high accuracy.

In FIG. 6, the output signal Va of the band-pass filter 6 is shown at the top, and the cut-off frequencies of the low-pass filter 10 are set to 1 kHz, 500 Hz, and 100 Hz in order from the top below. The output signal Vb in each of the above cases is shown. FIG. 7 shows the relationship between the cutoff frequency of the low-pass filter 10 and the detection result of the background level.

6 and 7, the lower the cut-off frequency of the low-pass filter 10, the higher the output signal Vb from which the high-frequency component has been further removed. As a result, the variation in the background level converges. (This is shown by the solid line in FIG. 7).
In other words, the background level can be accurately obtained without increasing the sampling frequency.
It is understood that the variation is extremely small below Hz.

The pressure sensor S is configured as a so-called seat type pressure sensor, and its output signal includes signal components caused by piston slap, distortion of the cylinder head, seating of the intake valve and the exhaust valve, and the like. Therefore, the level of the signal component caused by the background component is high, and the level of the signal component resulting therefrom can be accurately obtained as the background level.

As described above, one embodiment of the present invention has been described. However, the present invention is not limited to the above embodiment, and can take various forms. For example, in the above-described embodiment, the band-pass filter 6 has been described as being integrated with the voltage cut filter. However, the present invention is not limited to this. For example, the operational amplifier OP1 and the operational amplifier OP2 are operated with both power supplies (a power supply having a pair of positive and negative power supplies; for example, ± 5 V), a function as a voltage cut filter is removed from the band pass filter 6, and the band pass filter 6 and the low pass A voltage cut filter may be provided between the filter 10 and the band-pass filter 6.

When the voltage cut filter is separate from the band-pass filter 6, the voltage cut filter may be formed integrally with the low-pass filter at the subsequent stage. For example, it is possible to replace the amplifier circuit 8 and the low-pass filter 10 in FIG. 4 with the low-pass filter unit 6b.

Further, in the above-described embodiment, the description has been made as to passing or outputting only a signal having a cut-off voltage (earth ground in the above-described embodiment). However, the present invention is not limited to this. It may be configured to pass or output. This is because G is connected to one power input terminal of the operational amplifiers OP1 and OP2.
This can be realized by connecting an ND line and connecting a minus power supply (for example, -5 V) to the other power supply input line.

In the above-described embodiment, the so-called plug-integrated pressure sensor (PGPS) provided integrally with the ignition plug 23 is used as the seat-type pressure sensor. However, the present invention is not limited to this. For example, FIG.
As shown in the above, the present invention can be applied to a case in which a washer-type combustion pressure sensor (GPS) S ′ formed separately from a spark plug is used as a seat-type pressure sensor.

The washer-type combustion pressure sensor S 'is fixed between the mounting seat of the spark plug and the engine 21 by tightening the spark plug, and detects a change in the tightening load of the spark plug in that state. This detects the in-cylinder pressure of the internal combustion engine. The washer-type combustion pressure sensor S '
A gasket 201 and the like for sealing between the mounting seat for the ignition plug and the engine head are provided.
Is configured to output the electric charge generated in the piezoelectric element to the outside via the.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an internal combustion engine control device.

FIG. 2 is an explanatory diagram showing an arrangement position of a pressure sensor in an internal combustion engine.

FIG. 3 is an explanatory diagram showing an ignition plug provided with a pressure sensor.

FIG. 4 is a circuit diagram showing a configuration of a background level detection circuit.

FIG. 5 is a diagram illustrating waveforms of an output signal of a pressure sensor and a signal in a background level detection circuit.

FIG. 6 is a diagram showing output signals of a band-pass filter and a low-pass filter.

FIG. 7 is a diagram illustrating a relationship between a cutoff frequency of a low-pass filter 10 and a detection result of a background level.

FIG. 8 is an explanatory view showing a modification of the seat-type pressure sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 4 ... Charge amplifier 5 ... Background level detection circuit 6 ... Band pass filter 10 ... Low pass filter 21 ... Internal combustion engine 23 ... Ignition plug 25 ... Combustion chamber S ... Pressure sensor Va ... Band pass filter output signal Vb ... Low pass filter output signal

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masayuki Motomura 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi F-term (reference) 3G019 GA14 KA28 3G084 BA00 BA16 DA04 DA13 DA38 EA01 EA11 FA21 FA25

Claims (6)

[Claims] 1. A signal from a pressure sensor for detecting an in-cylinder pressure in a combustion chamber of an internal combustion engine is filtered by a band-pass filter having a knock band as a pass band during a period in which vibration components due to knock are not superposed. The signal filtered by the band-pass filter is filtered by a voltage cut filter that allows only the cut-off voltage level or higher or the cut-off voltage level to pass, and the signal filtered by the voltage cut filter is shifted from the knocking frequency band. Filtering with a low-pass filter having a low cut-off frequency or lower as a pass band, and detecting a background level which is a level of a signal generated by a factor other than knocking included in a signal of the pressure sensor by an output signal of the low-pass filter. Special A method of detecting knocking as a feature. 2. A knock sensor according to claim 1, wherein a signal from a pressure sensor for detecting an in-cylinder pressure in a combustion chamber of the internal combustion engine is set such that a knock frequency band is a pass band and an output is a cut-off voltage in a period in which vibration components due to knock are not superposed. Filtering with a band-pass filter set to only the level or higher or lower than the cut-off voltage level, and filtering the signal filtered by the band-pass filter with a low-pass filter having a pass band equal to or lower than the cut-off frequency lower than the knocking frequency band. A knocking detection method characterized by detecting a background level which is a level of a signal generated by a factor other than knocking included in a signal of the pressure sensor, based on an output signal of the low-pass filter. 3. A signal from a pressure sensor for detecting an in-cylinder pressure in a combustion chamber of an internal combustion engine is filtered by a band-pass filter having a knocking frequency band as a pass band during a period in which vibration components due to knocking are not superposed. A signal filtered by the band-pass filter is filtered by a low-pass filter having a cut-off frequency lower than a knocking frequency band as a pass band and whose output is set only at a cut-off voltage level or higher or a cut-off voltage level or lower. A knocking detection method characterized by detecting a background level which is a level of a signal generated by a factor other than knocking included in a signal of the pressure sensor, based on an output signal of the low-pass filter. 4. The knocking detection method according to claim 1, wherein the cutoff voltage is an earth ground of a measurement system. 5. The knocking detection method according to claim 1, wherein a cutoff frequency of the low-pass filter is 100 Hz or less. 6. The pressure sensor is provided on a mounting seat of an ignition plug used in an internal combustion engine, and detects a pressure in a cylinder of the internal combustion engine by detecting a change in a tightening load of the ignition plug. The knocking detection method according to claim 1, wherein the knocking is detected.