JP2006112858A - Piezoelectric acceleration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric acceleration sensor capable of detecting accurately and precisely engine knocking in consideration of a temperature characteristic. <P>SOLUTION: In a knocking sensor 100, an insulating sleeve 131, the first insulating plate 130, the first electrode plate 140, a piezoelectric element 150, the second electrode plate 160, the second insulating plate 135, a weight 170, and a disc spring 180 are fitted in this order onto a collar part 122 and fixed by a nut 185, on the outer circumference of a cylindrical part 121 of a main metal fitting 120. A lead wire 200b is fixed to the first thermistor connection part 142 and a lead wire 200c is fixed to the second thermistor connection part 162 respectively, and a thermistor 200 is placed. Signals output from the first and second terminals 141, 161 include a detected vibration signal by the piezoelectric element 150 and a detected temperature signal by the thermistor 200. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric acceleration sensor, and more particularly to a piezoelectric acceleration sensor that detects a knocking phenomenon in a combustion chamber of an automobile or the like with a piezoelectric element.

  Conventionally, a piezoelectric acceleration sensor using a piezoelectric element is known as a device for detecting a knocking phenomenon in a combustion chamber of an automobile or the like, and the ignition timing of the ignition plug is optimally controlled by a control system using the piezoelectric acceleration sensor. The time is adjusted. As such a piezoelectric acceleration sensor, for example, a so-called center-hole type non-resonant knock sensor having a mounting hole for mounting to a cylinder block or the like of an internal combustion engine at the center can be cited. The center hole type non-resonant knock sensor includes a metal shell including a cylindrical portion and a flange portion located at one end thereof, an annular piezoelectric element fitted on the outer periphery of the cylindrical portion of the metal shell, and a metal shell. A sensor body having an annular weight that is fitted on the outer periphery of the cylindrical portion and sandwiching the piezoelectric element between the flange portion and a resin molded body that covers the sensor body is known (for example, , See Patent Document 1).

In recent years, the use temperature of the knocking sensor tends to be increased with the space saving around the engine, and the necessity of highly accurate knocking control for high-efficiency combustion is increasing. By the way, the output characteristics of the knocking sensor change depending on the temperature dependence of the piezoelectric element. Therefore, when it is determined that the current operation region is the knock zone based on the engine speed and the engine load, the vibration level from the vibration sensor (knock sensor) is corrected based on the engine water temperature output from the water temperature sensor. A knock detection device that detects engine knock based on the corrected vibration level is known. Thus, by considering the temperature characteristics of the knocking sensor, it is possible to detect knocking of the engine more accurately and accurately (see, for example, Patent Document 2).
JP 2004-93197 A Japanese Utility Model Publication No. 2-122330

  However, in the above prior art, the temperature of the knocking sensor is monitored from the outside of the knocking sensor in order to correct the temperature of the knocking sensor. For example, in the invention described in Patent Document 2, the engine water temperature is monitored by a water temperature sensor. However, if such a monitoring means is provided outside the knocking sensor, the knocking sensor is enlarged, and the space around the engine is saved. However, there is a problem that the manufacturing cost is increased due to the complexity of the configuration.

  In addition, with the recent high performance of the engine, it is necessary to control the combustion timing of the engine more accurately. However, if the temperature of the knocking sensor is monitored from the outside, high-precision monitoring cannot be performed due to the influence of the external environment, etc. In this case, there is a problem that it is difficult to accurately control the combustion timing of the engine.

  It is an object of the present invention to provide a piezoelectric acceleration sensor that can execute high-precision temperature monitoring with a simple configuration that does not increase the size of a casing and enables accurate control of engine combustion timing. To do.

  In order to achieve the above object, a piezoelectric acceleration sensor according to a first aspect of the present invention is a piezoelectric acceleration sensor comprising a piezoelectric element and a casing that houses the piezoelectric element. A thermistor electrically connected in parallel with the element was provided.

  According to a second aspect of the present invention, in addition to the configuration of the first aspect of the invention, the piezoelectric acceleration sensor is attached to an acceleration detection object whose temperature varies.

  A piezoelectric acceleration sensor according to a third aspect of the invention is characterized in that, in addition to the configuration of the invention according to the second aspect, the acceleration detection object whose temperature varies is an internal combustion engine.

  According to a fourth aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the piezoelectric element and the thermistor are electrically connected inside the casing. It is characterized by being connected.

  According to a fifth aspect of the present invention, in addition to the configuration of the first aspect of the invention, the thermistor is in thermal contact with the piezoelectric element. It is characterized by.

  According to a sixth aspect of the present invention, in addition to the configuration of the first aspect of the present invention, the piezoelectric acceleration sensor detects knocking of the internal combustion engine. In addition, the thermistor is a thermistor having a negative temperature resistance coefficient.

  In the piezoelectric acceleration sensor according to the first aspect of the invention, the piezoelectric element and the thermistor are electrically connected in parallel to the terminal, and the terminal is shared by the piezoelectric element and the thermistor, thereby With a simple configuration that does not increase the size, high-precision temperature monitoring can be performed, and accurate control of engine combustion timing can be realized.

  Further, in the piezoelectric acceleration sensor of the invention according to claim 2, in addition to the effect of the invention of claim 1, the piezoelectric acceleration sensor is attached to the acceleration detection object whose temperature fluctuates, so that the piezoelectric acceleration sensor is influenced by the temperature fluctuation of the acceleration detection object. The temperature of the type acceleration sensor is detected, and highly accurate temperature monitoring can be realized.

  Further, in the piezoelectric acceleration sensor of the invention according to claim 3, in addition to the effect of the invention of claim 2, since the acceleration detection object is an internal combustion engine, the piezoelectric acceleration sensor of the piezoelectric acceleration sensor due to the influence of temperature fluctuations of the internal combustion engine. The temperature is detected and high-precision temperature monitoring can be realized.

  In the piezoelectric acceleration sensor of the invention according to claim 4, in addition to the effect of the invention according to any one of claims 1 to 3, the piezoelectric element and the thermistor are electrically connected inside the casing. Therefore, the harness from the piezoelectric acceleration sensor to the receiving circuit can be reduced, and the cost and layout can be improved.

  Further, in the piezoelectric acceleration sensor of the invention according to claim 5, in addition to the effect of the invention according to any one of claims 1 to 4, the thermistor is in thermal contact with the piezoelectric element, so that it is in the vicinity of the piezoelectric element. By installing the thermistor in the high-temperature, highly accurate temperature monitoring can be performed, and temperature correction can be performed more accurately.

  Further, in the piezoelectric acceleration sensor of the invention according to claim 6, in addition to the effect of the invention according to any one of claims 1 to 5, the piezoelectric acceleration sensor detects knocking of the internal combustion engine, and the thermistor Since is a thermistor having a negative temperature resistance coefficient, practical accuracy can be ensured by using a thermistor capable of measuring temperature with high accuracy at high temperatures.

  Hereinafter, a knocking sensor 100 which is an embodiment of a piezoelectric acceleration sensor according to the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of the knocking sensor 100. FIG. 2 is an exploded perspective view of an assembly part of the knocking sensor 100.

  The knocking sensor 100 of the present embodiment is a so-called center-hole type non-resonant knocking sensor having a mounting hole 120b at the center as shown in the sectional view of FIG. As shown in an exploded perspective view in FIG. 2, the knocking sensor 100 includes a cylindrical tubular portion 121 and an annular flange portion that is located at the one end 121 c and protrudes radially outward of the tubular portion 121. And a metal shell 120 made of 122.

  On the outer periphery of the cylindrical portion 121 of the metal shell 120, an annular first insulating plate 130, an annular first electrode plate 140, an annular piezoelectric element 150, and an annular first electrode are sequentially arranged from the flange 122 side. A two-electrode plate 160, an annular second insulating plate 135, an annular weight 170, and a disc spring 180 are fitted. Further, a nut 185 having an inner peripheral surface formed with a screw portion 185b is screwed into a screw portion 121b formed on the outer peripheral surface of the cylindrical portion 121, and the first and second insulating plates 130 and 135, first and first The two-electrode plates 140 and 160, the piezoelectric element 150, the weight 170, and the disc spring 180 are sandwiched and fixed between the flange portion 122 and the nut 185 to form the sensor body 190.

  A cylindrical insulating sleeve 131 is interposed between the cylindrical portion 121, the first and second electrode plates 140 and 160, and the piezoelectric element 150, and these insulations are maintained. The first and second electrode plates 140 and 160 are extended with first and second terminals 141 and 161, respectively, for outputting the voltage generated between the electrodes to the outside. In addition, at a substantially intermediate position between the end portion where the first and second terminals 141 and 161 are extended and the ring-shaped portion engaged with the metal shell 120, a first horizontal plane is formed to fix the thermistor 200. First and second thermistor connection portions 142 and 162 are formed.

  A thermistor 200 for measuring the temperature of the knocking sensor 100 is provided so as to be placed on the first and second thermistor connecting portions 142 and 162. The thermistor 200 is composed of a main body portion 200a in which a temperature sensitive element is coated with a glass material or an epoxy material, and lead wires 200b and 200c connected to the temperature sensitive element. The lead wires 200b and 200c form ring-shaped leg portions in a direction orthogonal to the main body portion 200a, and the leg portions formed by the lead wires 200b and 200c are the first and second thermistor connection portions 142, respectively. , 162. The thermistor 200 is electrically connected to the first and second thermistor connecting portions 142 and 162 by lead wires 200b and 200c, and the detected temperature signal is transmitted to the lead wires 200b and 200c and the first and second terminals 141 and 161. Is output to the outside.

  That is, the piezoelectric element 150 and the thermistor 200 are electrically connected in parallel to the first and second electrode plates 140 and 160 (first and second terminals 141 and 161). The second electrode plates 140 and 160 (first and second terminals 141 and 161) are commonly used for the piezoelectric element 150 and the thermistor 200. Further, the piezoelectric element 150 and the thermistor 200 are provided in the vicinity of the position, and the thermistor 200 can sense the temperature of the piezoelectric element 150, and the two are in thermal contact with each other.

  The thermistor 200 is an NTC (Negative Temperature Coefficient) type thermistor having a negative temperature resistance coefficient. Since knocking tends to occur more easily at higher temperatures, it is preferable that the thermistor 200 can accurately measure the temperature even at higher temperatures. Therefore, the thermistor 200 generally uses a NTC thermistor that can secure a resistance value that is somewhat large up to 100 ° C. or higher, thereby ensuring practical accuracy.

  As shown in FIG. 1, such a sensor main body 190 is covered with a resin molded body 110 to constitute the knocking sensor 100. However, the mounting hole 120b for mounting the knocking sensor 100 to a cylinder block or the like of the internal combustion engine is exposed without being covered with the resin molding 110. In addition, the connector part 113 is formed by this resin molding 110, and the one end part of the 1st, 2nd terminals 141 and 161 is arrange | positioned in the form which protrudes inside the connector part 113. FIG. Knocking sensor 100 is connected to the outside through this connector portion 113.

  Next, a method for manufacturing the knocking sensor 100 will be described with reference to the drawings. FIG. 3 is a side view of the sensor main body 190. FIG. 4 is a front view of the sensor main body 190.

  First, brass is processed into a cylindrical shape to form a weight 170 as shown in FIG. Further, as shown in FIG. 2, a soft iron metal shell 120 having a cylindrical tubular portion 121 and an annular flange 122 at one end 121c thereof is prepared. Next, on the outer periphery of the cylindrical portion 121 of the metallic shell 120, an insulating sleeve 131 made of PET, a first insulating plate 130 made of PET, a first electrode plate 140 made of 42Ni—Fe alloy, and piezoelectric elements 150, 42Ni made of PZT. The second electrode plate 160 made of Fe alloy, the second insulating plate 135 made of PET, the weight 170 made of brass, and the disc spring 180 are fitted in this order. Next, a soft iron nut 185 is screwed into the screw part 121b of the cylindrical part 121 and tightened until a predetermined load is applied to the piezoelectric element 150, and the first and second insulating plates 130 and 135, the first and second electrodes are tightened. The plates 140 and 160, the piezoelectric element 150, the weight 170, and the disc spring 180 are sandwiched and fixed between the flange 122 and the nut 185. Then, as described above, the thermistor 200 is fixed to be mounted on the first and second thermistor connecting portions 142 and 162. As a method for fixing the thermistor 200, any method such as laser welding or soldering may be used. Thereby, the sensor main body 190 is formed.

  As a result, as shown in FIGS. 3 and 4, in the sensor body 190 formed as described above, the ring-shaped leg of the lead wire 200b of the thermistor 200 is fixed on the first thermistor connecting portion 142, and The ring-shaped leg of the lead wire 200 c is fixed on the second thermistor connection portion 162. Then, the thermistor 200 is placed so that the main body 200a stands upward from the first and second thermistor connecting portions 142, 162.

  Then, nylon resin is injection-molded by a known resin mold forming technique to form a resin molded body 110 having a connector portion 113 as shown in FIG. At this time, the sensor main body 190 is covered with the resin molded body 110. However, the mounting hole 120b for mounting the knocking sensor 100 to a cylinder block or the like of the internal combustion engine is exposed without being covered. In this way, the knocking sensor 100 as shown in FIG. 1 is completed.

  In the completed knocking sensor 100, since the piezoelectric element 150 and the thermistor 200 are integrally molded by the resin molded body 110, the thermal conductivity is higher than that through a gas such as air, and the temperature of the piezoelectric element 150 is in the thermistor 200. It is easy to communicate. Note that, similarly to the mounting hole 120b, one end portions of the first and second terminals 141 and 161 are not covered for signal output to the outside.

  Next, the function of the knocking sensor 100 will be described. The knocking sensor 100 attached to the cylinder block or the like of the internal combustion engine via the attachment hole 120b receives a detection vibration signal about vibration detected by the piezoelectric element 150 from the first and second terminals 141, 161 from an external receiving circuit (illustrated). To the outside). In an external receiving circuit (not shown), if an AC component is extracted from a signal output from the knocking sensor 100 through a bandpass filter or the like, only the detected vibration signal output by the piezoelectric element 150 can be obtained. A knocking phenomenon can be detected based on the detected vibration signal.

  On the other hand, when the knocking sensor 100 is heated by a cylinder block or the like of the internal combustion engine, the detected temperature signal about the temperature of the knocking sensor 100 (particularly the piezoelectric element 150) detected by the thermistor 200 is used as the first and second terminals 141, 141. 161 to an external receiving circuit (not shown). In an external receiving circuit (not shown), if a DC component is extracted from a signal output from the knocking sensor 100 through a band pass filter or the like, only the detected temperature signal output by the thermistor 200 can be obtained. Based on the temperature signal, the temperature of knocking sensor 100 (piezoelectric element 150) can be detected.

  Therefore, it is possible to detect knocking with high accuracy by performing predetermined temperature correction in consideration of the temperature characteristics of the knocking sensor 100 (piezoelectric element 150) based on the detected vibration signal and detected temperature signal output from the knocking sensor 100. Therefore, the combustion timing of the engine can be accurately controlled based on the detection result of knocking.

  As described above, according to the knocking sensor 100 according to the present embodiment, the piezoelectric element 150 and the thermistor 200 are connected to the first and second electrode plates 140 and 160 (first and second terminals 141 and 141 in the resin molded body 110. 161) is electrically connected in parallel. Therefore, the knocking sensor 100 allows the first and second electrode plates 140 and 160 (first and second terminals 141 and 161) to be shared by the piezoelectric element 150 and the thermistor 200 so that the thermistor 200 can be used without increasing the number of components. It has a built-in structure. Therefore, highly accurate temperature monitoring can be executed with a simple configuration without increasing the size of the casing, and accurate control of the combustion timing of the engine can be realized. Further, the harness from the knocking sensor 100 to the external receiving circuit (not shown) can be reduced, and the cost and layout can be improved.

  Conventionally, when the temperature of the sensor mounting portion on the internal combustion engine side for mounting the knocking sensor fluctuates, the temperature of the piezoelectric element and the temperature of the sensor mounting portion may not always match. In general, the internal combustion engine is provided with means for detecting the cooling water temperature, but the cooling water temperature may be greatly different from the temperature of the piezoelectric element. For this reason, the temperature of the piezoelectric element cannot be monitored with high accuracy. On the other hand, in the knocking sensor 100, the thermistor 200 that detects the temperature is installed inside the knocking sensor 100. Therefore, since the thermistor 200 detects the temperature of the knocking sensor 100 (piezoelectric element 150) itself, highly accurate temperature monitoring can be performed even when the temperature of the sensor mounting portion varies.

  In addition, in order to accurately perform temperature correction for realizing highly accurate knocking detection, it is particularly necessary to grasp the temperature of the piezoelectric element 150 itself having temperature characteristics. Therefore, in the knocking sensor 100, the thermistor 200 is installed in the vicinity of the piezoelectric element 150 so that the two are in thermal contact with each other. Therefore, the thermistor 200 can perform highly accurate temperature monitoring for the piezoelectric element 150, and can perform temperature correction more accurately.

  In the above embodiment, the piezoelectric element 150 corresponds to the “piezoelectric element” of the present invention, the resin molded body 110 corresponds to the “casing” of the present invention, and the thermistor 200 corresponds to the “thermistor” of the present invention. .

  The present invention is not limited to the embodiment described in detail above, and it goes without saying that various modifications are possible.

  In the above-described embodiment, the main body portion 200a of the thermistor 200 is placed so as to stand upward from the first and second thermistor connection portions 142 and 162. However, if the thermistor 200 is electrically connected in parallel with the piezoelectric element 150 and the temperature of the knocking sensor 100 (piezoelectric element 150) can be detected effectively, it can be installed in another manner. For example, as shown in another longitudinal sectional view of the knocking sensor 100 of FIG. 5, the ring-shaped leg of the lead wire 200b of the thermistor 200 is fixed on the first thermistor connecting portion 142, and the ring-shaped of the lead wire 200c. The thermistor 200 may be mounted such that the legs are fixed on the second thermistor connection part 162 and the main body part 200a is directed downward from the first and second thermistor connection parts 142, 162.

  Further, the thermistor 200 is not limited to the NTC type having a negative temperature resistance coefficient, but may be a PTC (Positive Temperature Coefficient) type having a positive characteristic in which the resistance value increases as the temperature rises. In this case, both may be properly used depending on the region in which the temperature characteristic is to be corrected and the frequency to be measured. That is, the NTC type is particularly easy to accurately measure the temperature on the high temperature side, but since the resistance value decreases at high temperatures, the cutoff frequency of the high-pass filter may increase due to parallel connection. On the other hand, although it is difficult to measure the temperature on the high temperature side in the PTC type, the resistance value increases at a high temperature, so that the cut-off frequency of the high pass filter at a high temperature decreases. In consideration of the characteristics of each of the NTC type and the PTC type, a sensor corresponding to the mounting position and purpose of use of the knocking sensor 100 may be used.

  Moreover, in the said embodiment, although the piezoelectric element 150 and the thermistor 200 are integrally molded with the resin molding 110, if the thermistor 200 can detect the temperature of the piezoelectric element 150 effectively, both will be provided in another form. Also good.

  The piezoelectric acceleration sensor of the present invention can be applied to a knocking detection device for an internal combustion engine such as an engine.

2 is a longitudinal sectional view of the knocking sensor 100. FIG. FIG. 3 is an exploded perspective view of an assembly component of knock sensor 100. 4 is a side view of a sensor main body 190. FIG. 3 is a front view of a sensor main body 190. FIG. 4 is another longitudinal sectional view of the knocking sensor 100. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Knock sensor 110 Resin molding 120 Main metal fitting 130 1st insulating board 131 Insulating sleeve 135 2nd insulating board 140 1st electrode board 141 1st terminal 142 1st thermistor connection part 150 Piezoelectric element 160 2nd electrode board 161 2nd terminal 162 Second thermistor connection 170 Weight 180 Disc spring 185 Nut 190 Sensor body 200 Thermistor 200a Body 200b, 200c Lead wire

Claims (6)

In a piezoelectric acceleration sensor comprising a piezoelectric element and a casing containing the piezoelectric element,
A piezoelectric acceleration sensor comprising a thermistor electrically connected in parallel with the piezoelectric element in the casing.   The piezoelectric acceleration sensor according to claim 1, wherein the piezoelectric acceleration sensor is attached to an acceleration detection object whose temperature varies.   The piezoelectric acceleration sensor according to claim 2, wherein the acceleration detection object whose temperature varies is an internal combustion engine.   4. The piezoelectric acceleration sensor according to claim 1, wherein the piezoelectric element and the thermistor are electrically connected inside the casing. 5.   5. The piezoelectric acceleration sensor according to claim 1, wherein the thermistor is in thermal contact with the piezoelectric element. 6. The piezoelectric acceleration sensor detects knocking of an internal combustion engine,
The piezoelectric thermistor according to any one of claims 1 to 5, wherein the thermistor is a thermistor having a negative temperature resistance coefficient.

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