JP2006118449A - Knocking detection device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform accurate knocking determination without being influenced by temperature change. <P>SOLUTION: Vibration signal (level) in a frequency band used for knocking determination obtained by frequency analysis of high frequency component of output of a knocking sensor is determined. Temperature correction coefficient corresponding to frequency band used for the knocking determination is selected from temperature correction coefficient characteristics established for each frequency band. A thermistor is connected to output terminal of the knocking sensor in parallel to detect temperature of the sensor from low frequency (direct current) component of out put of the knocking sensor. Temperature correction coefficient is determined from the temperature correction coefficient characteristics selected based on temperature of the sensor. Temperature correction is performed by multiplying the level of the vibration signal and the temperature correction coefficient together. Knocking determination is performed by comparing the vibration signal level subjected to temperature correction and a determination threshold. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a technique for detecting knocking of an internal combustion engine.

Patent Document 1 discloses a technique for improving the knocking determination accuracy by correcting the output from the knocking sensor or the knocking determination value with the sensor temperature estimated based on the water temperature detected by the water temperature sensor. ing.
Japanese Utility Model Publication No. 2-122330

However, the inventor of the present application does not determine the change characteristic of the knocking sensor output due to the temperature only by the uniform change due to the temperature change of the piezoelectric element or the like that is the sensor body. It was found that the difference in the frequency band of the vibration was caused by shifting in the direction.
In Patent Document 1, since the correction is performed with the temperature correction characteristic uniquely set for the temperature, when the vibration frequency used for the knocking determination is switched, the temperature may not be corrected correctly and an erroneous determination may be made. In some cases, accurate knocking determination could not be made.

  The present invention has been made in view of such a conventional problem, and an object thereof is to perform accurate knocking determination by correctly performing temperature correction regardless of the difference in frequency band.

  Therefore, the present invention provides a knocking detection device that detects the presence or absence of knocking based on a vibration signal from a knocking sensor, the frequency band separation means for separating the vibration signal from the knocking sensor by frequency band, and the knocking Sensor temperature detecting means for detecting the temperature of the sensor, temperature correction coefficient calculating means for calculating a temperature correction coefficient of the knocking sensor output for each frequency band based on the detected knocking sensor temperature, and for each calculated frequency band And a knocking determination means for performing the knocking determination by correcting the temperature using the temperature correction coefficient.

  With such a configuration, the knocking determination is performed by the temperature correction process using the temperature correction coefficient for each frequency band in response to the fact that the output change characteristic with respect to the temperature varies depending on the vibration frequency. It is possible to make an accurate determination while avoiding the influence as much as possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
In FIG. 1, a knocking sensor 1 includes a cylindrical member 11 having a flange portion 11a with a bottom portion protruding outward, and a cylinder block of an engine through a fastening bolt 3 in a central hole of the cylindrical member 11. 2 is fastened.
On the outside of the cylindrical member, an annular piezoelectric element (piezo element) 12 is fitted and joined to the upper surface of the flange portion, and a mass member 13 is placed on the piezoelectric element 12. A plate spring 14 that elastically urges the plate spring 14 and a presser plate 15 of the plate spring 14 are mounted.

Further, a housing 16 is formed by resin molding of these outer circumferences, and a connector portion 16a is formed by projecting end portions of the two output terminals 12a of the piezoelectric element 12.
When the vibration acceleration of the engine is applied to the piezoelectric element 12, an output voltage corresponding to the vibration acceleration is generated, and knocking can be detected based on the high frequency component of the output voltage.
In the piezoelectric element type knocking sensor 1, as a configuration according to the present invention, a thermistor (temperature sensitive resistance element) 17 having a large temperature coefficient is connected in parallel to the output terminal 12 a of the piezoelectric element 12. The thermistor 17 is embedded in the housing 16 by the resin mold.

FIG. 2 shows a circuit configuration of a knocking detection device including the knocking sensor 1.
The output of the knocking sensor 1 (piezoelectric element 12) is input to the high pass filter (HPF) 32 and the low pass filter (LPF) 33 of the engine control unit (ECU) 31 via the harness 21. The + side of the input terminal is connected to the power supply VCC through a resistor (RL) 34, and the-side is grounded through a capacitor (CL) 35.

The high-pass filter 32 extracts a high-frequency component for knocking determination from the output of the knocking sensor 1, and the high-frequency component is amplified by an amplifier (AMP) 37 and then input to the microcomputer 36 as a vibration signal.
On the other hand, the low-pass filter 33 extracts a low frequency component close to a direct current from the output of the knocking sensor 1. Here, the low frequency component close to the direct current depends on the temperature depending on the temperature-resistance characteristic of the thermistor 17, and is input to the microcomputer 36 as a sensor temperature signal.

FIG. 3 shows functional blocks of knocking determination processing by the microcomputer 36.
The frequency analysis (FFT) unit A performs frequency analysis on the vibration signal of the high frequency component extracted from the high pass filter 32, and calculates the vibration signal level in the frequency band used for knocking determination. Note that the high-pass filter 32 may have a frequency analysis function by narrowing the band to the knocking frequency component. Alternatively, a signal subjected to frequency analysis via a dedicated frequency analysis circuit may be input to the microcomputer 36.

The sensor temperature detection unit B detects the sensor temperature based on the low frequency (direct current) component extracted from the low pass filter 33.
A memory C of the microcomputer 36 stores a temperature correction coefficient characteristic map for each frequency band. Here, the change in the output of the knocking sensor due to the temperature change has a characteristic that the output decreases as the temperature rises when considering only the characteristic of the piezoelectric element, but the vibration system configured by the entire sensor (mass-spring-damper). When the frequency-output characteristic of the frequency shifts in the frequency direction due to a temperature change, the output (sensor sensitivity) may increase with a predetermined temperature rise depending on the frequency (see FIG. 4). Therefore, the temperature correction characteristic is set so as to eliminate the output change with respect to the temperature change for each frequency band.

Based on the sensor temperature detected by the temperature detection unit B from the characteristic map of the temperature correction coefficient of the corresponding frequency band, the correction unit D uses the frequency band vibration signal level used for knocking determination analyzed by the FFT unit A. The temperature is corrected by multiplying the searched temperature correction coefficient.
The knock determination unit E performs knock determination by comparing the temperature-corrected vibration level with a determination threshold value. The determination threshold value may be temperature corrected. When the temperature correction coefficient is set in the same manner as described above, the same knocking determination result can be obtained by dividing the determination threshold value by the corresponding temperature correction coefficient. Further, one or a plurality of vibration signals for each frequency band used for knocking determination can be switched and used.

  In this way, even if the frequency band used for the knocking determination is switched depending on the operating conditions, the output change of the knocking sensor 1 is correctly corrected for the temperature change that differs depending on the frequency band by using the temperature correction characteristic for each frequency band. Therefore, knocking determination can be performed accurately by reducing the setting margin as an error factor of the determination threshold.

  In this embodiment, the thermistor 17 for detecting the sensor temperature is connected to the output terminal in parallel in the knocking sensor 1, and the sensor temperature is detected by separating the low frequency component close to the direct current. High-accuracy temperature detection can be performed, sensor connectors and wire harnesses can be shared, and both the knocking sensor and the determination circuit can be realized at low cost while maintaining compactness.

  However, the sensor temperature may be detected by the engine coolant temperature detected by the water temperature sensor or the lubricant temperature detected by the lubricant temperature sensor.

Sectional drawing which shows the internal structure of the knocking sensor in embodiment Circuit diagram of knock detection device using knock sensor Functional block diagram of knock determination processing by microcomputer in the knock detection device Diagram showing different temperature-sensor sensitivity characteristics in different frequency bands

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Knocking sensor 12 Piezoelectric element 12a Output terminal 17 Thermistor 21 Harness 31 Engine control unit 32 High pass filter 33 Low pass filter A Frequency analysis part B Temperature detection part C Memory D Correction part E Determination part

Claims (6)

A knocking detection device that detects the presence or absence of knocking based on a vibration signal from a knocking sensor,
Frequency separation means for separating the vibration signal from the knocking sensor by frequency band;
Sensor temperature detecting means for detecting the temperature of the knocking sensor;
A temperature correction coefficient calculating means for calculating a temperature correction coefficient of the knocking sensor output for each frequency band based on the detected knocking sensor temperature;
Using the calculated temperature correction coefficient for each frequency band, knocking determination means for performing knocking determination with temperature correction;
A knock detection device for an internal combustion engine, comprising:   2. The knock detection device for an internal combustion engine according to claim 1, wherein the knocking determination unit performs knocking determination by comparing a value obtained by correcting a vibration signal for each frequency band with a temperature correction coefficient with a threshold value. 3. .   2. The knock detection device for an internal combustion engine according to claim 1, wherein the knocking determination unit performs knocking determination by comparing a vibration signal for each frequency band with a threshold value corrected with a temperature correction coefficient. 3. The knocking sensor is configured by connecting a piezoelectric element and a temperature-sensitive resistance element having a large temperature coefficient in parallel.
The said sensor temperature detection means isolate | separates and extracts the low frequency component close | similar to direct current | flow from the output of the said knocking sensor, and detects sensor temperature based on the level of this low frequency component. Item 4. The knocking detection device for an internal combustion engine according to any one of Items 3 to 4.   The knock detection device for an internal combustion engine according to any one of claims 1 to 3, wherein the sensor temperature detection means is means for detecting an engine coolant temperature as a substitute value of the sensor temperature.   The knock detection device for an internal combustion engine according to any one of claims 1 to 3, wherein the sensor temperature detection means is means for detecting a lubricating oil temperature as a substitute value of the sensor temperature.