JP2006119035A - Knocking sensor and knocking detection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect highly accurately the sensor temperature of a knocking sensor, while maintaining compactness. <P>SOLUTION: A thermistor 17 is connected in parallel with an output terminal of a piezoelectric element 12 of the knocking sensor 1, and low-frequency components similar to a direct current are extracted from a sensor output by a low-pass filter 33. Since the low-frequency components are proportional to the resistance value of the thermistor 17 that changes according to the temperature, the sensor temperature can be detected with high accuracy by the low-frequency components by a microcomputer 36, and high-frequency components are extracted from the sensor output as a vibration signal by a high-pass filter 32. The vibration signal is subjected to frequency analysis by the microcomputer 36, while the level of knocking components is corrected corresponding to the detected sensor temperature; and by comparing the corrected knocking component level with the determination level, the presence of knocking is determined. <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, as in the patent literature, there is a difference between the sensor temperature and the temperature detected at a location other than the water temperature or other knocking sensor, so that the determination accuracy cannot be sufficiently improved.
Although it is conceivable to incorporate a temperature sensor in the knocking sensor, it is necessary to increase the number of connector terminals and signal lines (harness) for taking out a temperature detection signal from the temperature sensor, resulting in high costs.

  The present invention has been made in view of such conventional problems, and is capable of detecting a sensor temperature with high accuracy with a low-cost configuration without increasing the number of output terminals and signal lines of the knocking sensor, and providing high accuracy. The purpose is to make a simple knocking determination.

For this reason, the knocking sensor for an internal combustion engine according to the present invention has a configuration in which a temperature sensitive resistance element having a large temperature coefficient is connected in parallel to the output terminal of the piezoelectric element.
The knock detection device for an internal combustion engine according to the present invention includes a knock sensor configured by connecting a piezoelectric element and a temperature-sensitive resistance element having a large temperature coefficient in parallel, and a high-frequency component including a knock vibration component from the output of the knock sensor. And a frequency separation circuit that separates and extracts a low frequency component close to a direct current for detecting the sensor temperature.

  With such a configuration, since the low frequency component of the output of the knocking sensor changes depending on the sensor temperature due to the configuration in which the temperature sensing resistance element having a large temperature coefficient is connected in parallel to the output terminal of the knocking sensor, the low frequency component is changed based on the low frequency component. The sensor temperature can be detected, and it is possible to improve the knocking determination accuracy by correcting the temperature of the sensor output (high frequency component) based on the sensor temperature.

  Further, since the number of output terminals of the sensor does not increase, it is possible to maintain low cost and compactness without increasing the number of output signal lines (harnesses).

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 positive side of the input terminal is connected to the power supply VCC via a resistor (RL) 34, and the negative side is grounded via 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 low-pass filter 33 extracts a low-frequency component close to direct current from the output of the knocking sensor 1.
Here, since the low frequency component close to the direct current extracted by the low pass filter 33 depends on the temperature by the temperature-resistance characteristic of the thermistor 17, the sensor temperature can be detected in accordance with the low frequency component level. Therefore, the signal from the low-pass filter 33 is input to the microcomputer 36 as a sensor temperature signal. The high frequency component from the high pass filter 32 is amplified by an amplifier (AMP) 37 and then input to the microcomputer 36 as a vibration signal.

  The microcomputer 36 corrects the level of the knocking component according to the detected sensor temperature while performing frequency analysis of the vibration signal, and compares the corrected knocking component level with the determination level, thereby performing knocking. Determine presence or absence. 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.

Specifically, the sensor (piezoelectric element) output decreases as the sensor temperature increases, and the resonance point shifts to the low frequency side. Therefore, the temperature depends on the temperature characteristic in the frequency band used for knocking determination. Perform temperature correction in a direction that eliminates the effects of changes due to.
As the thermistor 17, a thermistor having a stable characteristic and maintaining a high resistance so as to reduce the influence on the high frequency component in the detection temperature range is used. Currently, NTC thermistors having negative temperature-resistance characteristics are suitable, but PTC thermistors having positive temperature-resistance characteristics can be used as long as they have stable characteristics. In this embodiment, an NTC thermistor is used.

In this manner, since the thermistor 17 for detecting the sensor temperature is built in the housing 16 in the knocking sensor 1, the sensor temperature can be detected with higher accuracy compared to a substitute for the water temperature or the like, so that the knocking determination can be performed with high accuracy. Can be done.
Further, the compactness of the sensor itself can be maintained without changing the outer shape of the knocking sensor 1 and the number of output terminals of the knocking sensor 1 does not increase. Therefore, the number of harnesses connecting the knocking sensor 1 and the engine control unit 31 is also increased. It does not increase, can maintain the compactness of the entire apparatus, and can be implemented at low cost. It is also possible to use a thermocouple or the like as a temperature sensor that detects the sensor temperature built in the knocking sensor. However, when an element that detects temperature by electromotive force, such as a thermocouple, is used, it is connected in parallel with the output terminal. The number of output terminals and the number of harnesses increase. Such a problem can be solved by connecting the temperature-sensitive resistance element in parallel to the output terminal as in the present invention.

Further, since the low-pass filter is generally provided in order to separate low-frequency components even in a normal knocking determination circuit, the low-pass filter can be used as it is for sensor temperature detection, and an increase in cost can be avoided.
Further, a failure diagnosis of the knocking sensor can be performed based on the sensor temperature. That is, as described above, since the knocking sensor 1 is mounted on the cylinder block 2 of the engine, the knocking sensor 1 is substantially the same as the engine coolant temperature (water temperature). Using the water temperature, when the temperature difference between the sensor temperature obtained from the low frequency component of the sensor output and the water temperature (sensor mounting portion temperature) becomes larger than a predetermined value, it is diagnosed that the knocking sensor 1 has failed.

For the fault diagnosis, the microcomputer 36 uses a water temperature signal input from a water temperature sensor 41 provided for engine control.
FIG. 3 shows a flowchart of the knocking sensor failure diagnosis.
In step 1, the counter that measures the abnormal state duration is reset to the initial value.
In step 2, it is determined whether the water temperature Tw is equal to or higher than the diagnosis permission water temperature Tw0. When the water temperature is low, the temperature difference between the water temperature and the sensor temperature is small even when the sensor is normal, so failure diagnosis accuracy based on the temperature difference is reduced, so diagnosis is prohibited, and accuracy is achieved by performing diagnosis on the condition that the diagnosis allowable water temperature is Tw0 or higher. Secure.

In step 3, a temperature value obtained by subtracting a predetermined temperature from the water temperature Tw is calculated as a threshold value Td for disconnection failure determination, and a temperature value obtained by adding the predetermined temperature to the water temperature Tw is calculated as a threshold value Tt for short-circuit failure determination. Calculate as The predetermined temperature may be set to a higher value as the water temperature Tw is higher.
In step 4, it is determined whether the sensor temperature Ts is less than the threshold value Td for determining the disconnection failure. If it is determined that the sensor temperature Ts is less than the threshold value Td, it is determined that the disconnection is abnormal, and the process proceeds to step 5. In order to measure the duration of the disconnection abnormality state, the value of the counter is decremented.

In step 6, it is determined whether the value of the counter has become 0. Before it becomes 0, the process returns to step 2, and when the disconnection abnormality determination continues, the counter is decremented repeatedly to measure the duration of the disconnection abnormality state. To do.
In this way, when it is determined in step 6 that the counter value has become 0, that is, the disconnection abnormality state has continued for a predetermined time, the process proceeds to step 7 to establish a diagnosis that knocking has failed. To do. Here, in this embodiment, since the thermistor 17 has a negative temperature-resistance characteristic, if the wire breaks, the resistance between the output terminals becomes extremely large, and the sensor temperature is detected as an extremely low temperature compared to the water temperature Tw. Since it is less than the value Td, it can be determined that the disconnection is abnormal.

  If it is determined in step 4 that the sensor temperature Ts is equal to or higher than the disconnection failure determination threshold value Td, the process proceeds to step 8 to check whether the sensor temperature Ts is higher than the short-circuit failure determination threshold value Tt. Determine. If it is determined that the value is higher than the threshold value Tt, it is determined that the short circuit is abnormal, and the process proceeds to step 9 where the counter value is decremented. In step 10, it is determined whether the counter value becomes 0. Before that, the process returns to Step 2 and becomes 0, that is, when it is determined that the short-circuit abnormality state has continued for a predetermined time, the process proceeds to Step 11 to establish a diagnosis that knocking has a short-circuit disconnection failure. Here, when the short circuit occurs, the resistance between the output terminals becomes extremely small, and the sensor temperature is detected as an extremely high temperature as compared with the water temperature Tw and becomes higher than the threshold value Tt.

When these disconnection failure or short circuit failure diagnosis results (flag setting) are issued, the reliability of knocking determination is lost, and therefore knocking determination is prohibited in step 12.
FIG. 4 shows a comparison between the normal state of the knocking sensor and the disconnection failure when this failure diagnosis is performed.
As described above, it is possible to perform a failure diagnosis of the knocking sensor that cannot be performed when the sensor temperature is substituted by the water temperature or the like. In addition, by establishing diagnosis when an abnormal state continues for a predetermined time, erroneous determination due to a transient temperature shift can be prevented. The precondition for permitting the diagnosis is that the sensor for detecting the temperature of the sensor mounting portion for comparison, such as the water temperature sensor 41, is normal. That is, when the failure diagnosis of the water temperature sensor 41 is performed first and the failure is diagnosed, the knocking sensor failure diagnosis is prohibited.

Lubricating oil temperature may be used as the sensor mounting portion temperature from the outside of the knocking sensor. Further, when a thermistor having a positive temperature-resistance characteristic is used as the temperature sensitive resistance element connected in parallel to the output terminal, the diagnosis result based on the comparison between the sensor temperature and the temperature of the sensor mounting portion such as the water temperature is as above. May be reversed (disconnection → short circuit, short circuit → disconnection).
Next, another embodiment of failure diagnosis with different diagnosis permission conditions will be described.

In this embodiment, as shown by a dotted line in FIG. 2, an outside air temperature sensor 42 that detects the outside air temperature (or intake air temperature) is provided, and an outside air temperature signal is input to the microcomputer 36. In addition to the water temperature sensor 41, the microcomputer 36 receives an engine rotation signal from an engine control crank angle sensor 43.
FIG. 5 shows a flowchart of failure diagnosis according to the present embodiment.

In step 21, it is determined based on the engine rotation signal from the crank angle sensor 43 whether the engine is stopped.
When it is determined in step 21 that the engine is stopped, the process proceeds to step 22 where it is determined whether the water temperature Tw and the outside air temperature Ta are substantially the same temperature (deviation | ΔT | is within a predetermined value).
When it is determined that the water temperature Tw and the outside air temperature Ta are substantially the same temperature, it is determined that the failure diagnosis permission condition for the knocking sensor 1 is satisfied, and the process proceeds to step 23 to perform step 3 of the first embodiment. Failure diagnosis similar to that performed thereafter is executed.

  By performing failure diagnosis in a stable state where the temperature when the engine is stopped is in an equilibrium state and the outside air temperature and the engine temperature (sensor temperature such as water temperature) are substantially the same as in this embodiment, Accurate failure determination can be performed.

Sectional drawing which shows the internal structure of the knocking sensor in embodiment Circuit diagram of knock detection device using knock sensor The flowchart which shows the knocking sensor failure diagnostic routine in a knocking detection apparatus same as the above. Same as above Time chart showing failure A flowchart showing a routine of another method of knocking failure diagnosis

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 41 Water temperature sensor 42 Outside temperature sensor 43 Crank angle sensor

Claims (11)

  A knocking sensor for an internal combustion engine, wherein a temperature-sensitive resistance element having a large temperature coefficient is connected in parallel to an output terminal of a piezoelectric element.   A knocking sensor configured by connecting a piezoelectric element and a temperature sensitive resistance element having a large temperature coefficient in parallel; a high-frequency component including a knocking vibration component from an output of the knocking sensor; and a low-frequency component close to a direct current for detecting the knocking sensor temperature; A knocking detection apparatus comprising: a frequency separation circuit that separates and extracts the signal.   The vibration signal is extracted based on the high frequency component from the frequency classification circuit, while the sensor temperature is detected based on the low frequency component from the frequency classification circuit, and the vibration signal is knocked based on the signal corrected by the sensor temperature. The knocking detection apparatus according to claim 2, further comprising a determination circuit that determines whether or not there is any.   A sensor failure that compares the sensor mounting part temperature detected based on a signal from the outside of the knocking sensor and the detected sensor temperature and diagnoses that the knocking sensor has failed when the difference between the two is equal to or higher than a predetermined level. The knocking detection device according to claim 3, comprising a diagnostic circuit.   5. The knocking detection device according to claim 4, wherein the signal from the outside of the knocking sensor is a detection signal of an engine coolant temperature or a lubricating oil temperature.   When the temperature of the knocking sensor mounting part is low and the sensor temperature is high, if the temperature sensitive resistance element has a negative temperature-resistance characteristic, the knocking sensor output terminal is short-circuited. 6. The diagnosis according to claim 4, wherein when the temperature sensitive resistance element has a positive temperature-resistance characteristic, a failure diagnosis is made if the knocking sensor output terminals are disconnected. The knocking detection apparatus as described.   When the temperature of the knocking sensor mounting part is high and the sensor temperature is low, if the temperature sensitive resistance element has a negative temperature-resistance characteristic, the knocking sensor output terminal is broken. 7. The diagnosis according to claim 4, wherein when the temperature-sensitive resistance element has a positive temperature-resistance characteristic, a failure diagnosis is made if the knocking sensor output terminals are short-circuited. The knocking detection device according to any one of the above.   The knocking detection device according to any one of claims 4 to 7, wherein a failure diagnosis of the knocking sensor is permitted when the temperature of the knocking sensor attachment portion is equal to or higher than a predetermined temperature.   When the outside air temperature or intake air temperature detection signal and the engine operation stop determination signal are input and the outside air temperature or the intake air temperature is substantially equal to the knocking sensor mounting portion temperature and it is determined that the engine operation is stopped, the knocking is performed. The knock detection device according to any one of claims 4 to 8, wherein a failure diagnosis of the sensor is permitted.   10. The knocking detection device according to claim 4, wherein a failure diagnosis of the knocking sensor is prohibited while the means for detecting the temperature of the sensor attachment portion is out of order.   The knocking detection device according to any one of claims 4 to 10, wherein knocking determination is prohibited when it is diagnosed that the knocking sensor is malfunctioning.