JP2001055967A - Ignition plug incorporating pressure sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ignition plug incorporating a pressure sensor which shows widely ranged use temperature and fastening load, excellent durability and high accuracy in sensing pressure. SOLUTION: An ignition plug 1 incorporating a pressure sensor has a main body metal fitting 17 inside which a pressure sensor 41 is arranged so as to be in contact with an internal combustion engine main body 25 through a gasket 33 for securing airtightness. The pressure sensor 41 has an piezoelectric element composed of polycrystalline PbNb2O6, and senses pressure inside a cylinder of the internal combustion engine from fluctuation of plug fastening load. Adopting polycrystalline PbNb2O6 as the piezoelectric element, the ignition plug 1 incorporating the pressure sensor shows a widely ranged use temperature and fastening load, excellent durability, and accuracy in sensing pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spark plug with a built-in pressure sensor having a built-in pressure sensor for detecting the in-cylinder pressure of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, in an internal combustion engine, in order to comprehensively control the operation of the engine, the operating state of each part of the internal combustion engine is detected. By using (in-cylinder pressure), misfire and knocking are detected, and fuel efficiency is improved. This in-cylinder pressure is obtained by providing a through hole communicating with the cylinder in the cylinder head of the internal combustion engine, providing a pressure sensor in the through hole, and detecting a change in pressure of the combustion gas propagated through the through hole by the pressure sensor. Can be measured.

[0003] However, this measuring method requires a special processing operation for providing a conductive hole in the cylinder head.
Further, there is a problem that the structure of the internal combustion engine becomes complicated. In order to solve such a problem, there has been proposed a seat-type pressure sensor which is disposed between an ignition plug and an internal combustion engine and detects an in-cylinder pressure based on a change in a tightening load of the ignition plug. As an example of a seat-type pressure sensor, there is a sensor mounted on an internal combustion engine as a spark plug (a spark plug with a built-in pressure sensor) in which a piezoelectric element is built in a mounting seat of a metal shell of the spark plug.

The piezoelectric element has a characteristic of outputting electric charge in accordance with the applied pressure. The pressure applied to the piezoelectric element is determined based on the amount of the output electric charge, and the in-cylinder pressure is detected. I have. Since the ignition plug with a built-in pressure sensor can be mounted on the internal combustion engine without specially processing the cylinder head, the in-cylinder pressure can be easily measured. Further, since the shape of the internal combustion engine is not complicated, it is possible to secure a wide space for installing other devices such as an intake valve and an exhaust valve.

Conventionally, as a piezoelectric element provided in an ignition plug with a built-in pressure sensor, a polycrystalline PbTi
O ₃ (lead titanate; hereinafter also referred to as PT) and polycrystalline Pb (Zr, Ti) O ₃ (zirconium / lead titanate; hereinafter also referred to as PZT) have been frequently used.

[0006]

However, PT and P
Piezoelectric elements including ZT have the characteristic that the element deteriorates with the progress of use and the output decreases. If the deterioration progresses excessively, the output ratio of electric charge decreases, and pressure is detected normally. I can't do anything.

[0007] The rate of progress of the deterioration of the piezoelectric element differs for each piezoelectric element. In addition, even when the ambient temperature is high or the pressure applied is large, the rate of progress of the deterioration of the piezoelectric element is low. It is known to be faster. In particular, the seat-type pressure sensor receives heat from the combustion of the air-fuel mixture in the internal combustion engine, and is always in a state in which a pressure (tightening load) is applied.

For this reason, it is desirable to use a piezoelectric element having a wide range of usable temperature and a tightening load as the piezoelectric element used for the ignition plug with a built-in pressure sensor. It is desirable to use a piezoelectric element having excellent durability.

On the other hand, the piezoelectric element has a characteristic (temperature characteristic) that the output charge constantly changes due to a different ambient temperature even when the applied pressure is the same. Further, the piezoelectric element has a characteristic (pyroelectric characteristic) in which the output charge fluctuates transiently due to expansion or contraction of a crystal constituting the piezoelectric element due to a rapid temperature change.

Therefore, when the temperature changes due to a change in the operation state of the internal combustion engine, an error may occur in the pressure signal due to the temperature characteristic, or the ground level of the pressure signal may fluctuate due to the pyroelectric characteristic. . In order to solve such a problem, for example, in an electronic control unit (ECU) that takes in a pressure signal, the dynamic range of the input pressure signal is set to be wide, and the input range of the pressure signal is controlled according to a temperature change at the time of detection. Then, by correcting the error and the ground level, an accurate pressure is detected.

However, the range width recognized internally by the ECU is a fixed value determined by the hardware specifications of each ECU. Therefore, if the dynamic range of the pressure signal is set to be large, the ECU internally recognizes the input signal. The smallest unit of recognizable pressure becomes relatively large. For this reason,
This causes a problem that the resolution of the pressure signal is reduced and the accuracy of the detected pressure is reduced.

The present invention has been made in order to solve the above problems, and has a pressure sensor having a wide range of usable temperature and tightening load, excellent durability, and high pressure detection accuracy. To provide a spark plug with a built-in pressure sensor.

[0013]

According to a first aspect of the present invention, there is provided a piezoelectric element provided in a mounting seat of a metal shell of a spark plug which generates spark discharge between electrodes. A pressure sensor built-in ignition plug that detects the in-cylinder pressure of the internal combustion engine by detecting a change in the plug tightening load with the piezoelectric element and outputs an electric signal corresponding to the detected pressure from a sensor output cable. And polycrystalline PbNb ₂ O ₆ is used.

Since the spark plug with a built-in pressure sensor of the present invention uses polycrystalline PbNb ₂ O ₆ as the piezoelectric element, the rate of decrease in output with time is smaller than in the prior art. It becomes a pressure sensor with excellent durability. Here, the rate of decrease in output of polycrystalline PbNb ₂ O ₆ with time can be determined from the measurement result when the output change rate with time is measured, which will be described later. The measurement result is shown in FIG. Show. In this measurement, in addition to the polycrystalline PbNb ₂ O ₆ (lead niobate) applied as the piezoelectric element of the present invention, the polycrystalline PbTiO ₃ (lead titanate) used conventionally as the piezoelectric element was used. , PT) and polycrystalline Pb (Zr, Ti) O ₃ (zirconium lead titanate; hereinafter also referred to as PZT).

From the measurement results shown in FIG. 3, when the temperature and the tightening load are used under the same conditions,
Polycrystalline PbNb ₂ O ₆ is compared to PT and PZT.
It can be seen that the time until the output drops to the same level is long. Therefore, the ignition plug with a built-in pressure sensor of the present invention is excellent in durability because the rate of decrease in output over time is reduced and the time until the pressure sensor becomes unusable becomes longer as compared with the related art. It will be.

By the way, in a pressure sensor using a piezoelectric element, an output error occurs due to a temperature change due to a temperature characteristic of the piezoelectric element. For this reason, for example, in an electronic control unit (ECU) that takes in a pressure signal, a dynamic range of the input pressure signal is set wide, and processing such as controlling the input range of the pressure signal according to a temperature change at the time of detection is performed. And corrects an output error due to a temperature change to detect an accurate pressure.

However, the range width recognized internally by the ECU is a fixed value determined by the hardware specifications of each ECU. Therefore, when the dynamic range of the pressure signal is set to be large, the ECU internally recognizes the input signal. The minimum unit of the recognizable pressure becomes relatively large, and the resolution of the pressure signal decreases.

However, since the spark plug with a built-in pressure sensor of the present invention uses polycrystalline PbNb ₂ O ₆ as the piezoelectric element, the rate of decrease in output due to temperature change is small, so that the dynamic plug is more dynamic than in the past. The range can be set small. The rate of decrease in output of the polycrystalline PbNb ₂ O ₆ due to a change in temperature can be determined from a measurement result obtained when an output change rate (temperature characteristic) due to a temperature change is measured, and the measurement result is shown in FIG. . This measurement was performed on PT and PZT in addition to polycrystalline PbNb ₂ O ₆ .

From the measurement results shown in FIG. 4, the polycrystalline PbN
It can be seen that b ₂ O ₆ has a smaller output change rate (lower temperature characteristic) due to the same temperature change than PT and PZT. Therefore, the spark plug with a built-in pressure sensor of the present invention can set the dynamic range of the pressure signal to be smaller than before, so that the resolution of the pressure signal can be increased and the pressure detection accuracy can be increased.

Since the piezoelectric element has a pyroelectric property,
When a rapid temperature change occurs, the ground level of the pressure signal fluctuates. For this reason, similarly to the above-described measures against the temperature characteristics, for example, by setting a wide dynamic range of the pressure signal input to the ECU and controlling the input range of the pressure signal according to a temperature change at the time of detection, the ground level is reduced. The fluctuation of the level is corrected, and an accurate pressure is detected.

The spark plug with a built-in pressure sensor of the present invention is a polycrystalline PbN having a low pyroelectric characteristic as a piezoelectric element.
Since b ₂ O ₆ is used, the fluctuation of the ground level is reduced, and the dynamic range can be set smaller than in the conventional case. The fluctuation of the ground level when polycrystalline PbNb ₂ O ₆ is used can be determined from a measurement result when a change in the in-cylinder pressure of an actual internal combustion engine, which will be described later, is measured. 6 is shown. This measurement was performed on PT in addition to polycrystalline PbNb ₂ O ₆ .

The measurement results shown in FIGS. 5 and 6 indicate that polycrystalline PbNb ₂ O ₆ has a smaller ground level fluctuation (smaller pyroelectric characteristic) than PT. Therefore, the spark plug with a built-in pressure sensor of the present invention can set the dynamic range of the pressure signal to be smaller than before, so that the resolution of the pressure signal can be increased and the pressure detection accuracy can be increased.

On the other hand, the output deterioration rate of the piezoelectric element changes depending on the magnitude of the applied pressure, but the spark plug with a built-in pressure sensor of the present invention has a small output deterioration rate with respect to the plug tightening load. This can be determined from the measurement result obtained when the output deterioration rate with respect to the magnitude of the tightening load is measured, which will be described later, and the measurement result is shown in FIG. This measurement was also performed on PT and PZT in addition to polycrystalline PbNb ₂ O ₆ .

From the measurement results shown in FIG. 7, it can be seen that polycrystalline PbNb
It can be seen that ₂ O ₆ has a smaller output deterioration rate with respect to the same tightening load than PT and PZT. Therefore, the spark plug with a built-in pressure sensor of the present invention can suppress the deterioration of the output with respect to the tightening load as compared with the conventional one, so that the range of the usable tightening load is widened,
It can be widely used in many types of internal combustion engines. Further, in an environment in which the same tightening load is applied, the detection accuracy can be kept high since the output deterioration rate is smaller than in the conventional case. Further, since the deterioration of the output due to the use progress under the environment where the tightening load is the same is reduced, the device can be used for a longer time than before, and the durability is excellent.

Although the output degradation rate of the piezoelectric element changes depending on the ambient temperature, the output plug degradation rate of the spark plug with a built-in pressure sensor according to the present invention is small relative to the ambient temperature. This can be determined from the measurement result when the output deterioration rate with respect to the ambient temperature is measured, which will be described later, and the measurement result is shown in FIG. In addition, this measurement was performed using polycrystalline PbNb.
_In addition to ₂ O ₆ , PT and PZT were also performed.

From the measurement results shown in FIG. 8, the polycrystalline PbNb
It can be seen that ₂ O ₆ has a smaller output deterioration rate at the same ambient temperature than PT and PZT. Therefore, the spark plug with a built-in pressure sensor of the present invention can suppress the deterioration of the output with respect to the ambient temperature as compared with the related art, so that the usable temperature range is wide, and it can be widely used in many types of internal combustion engines. . Further, in an environment where the ambient temperature is the same, the detection accuracy can be kept high because the output deterioration rate is smaller than in the conventional case. Further, the deterioration of the output due to the lapse of use in an environment having the same ambient temperature is reduced, so that the device can be used for a longer time than before, and the durability is excellent.

From the above measurement results, the usable range of temperature and tightening load of the spark plug with a built-in pressure sensor of the present invention is wider than that of a conventional spark plug with a built-in pressure sensor using PT and PZT. A pressure sensor having excellent durability and high pressure detection accuracy.

Further, in order to suppress the deterioration of the output due to an increase in the ambient temperature, it is preferable to use a piezoelectric element having a high Curie point. Note that, in a piezoelectric element whose temperature has exceeded the Curie point, the polarization inside the element collapses, so that even if pressure is applied, no charge is output and the pressure cannot be detected.

Here, as a piezoelectric element having a high Curie point, for example, single-crystal LINbO ₃ (lithium niobate) is known, and thus each of the above-described piezoelectric elements (polycrystalline PbNb ₂ O ₆ , PT, PZT) is used. Table 1 shows a comparison of characteristics including the above. Table 1 shows the piezoelectric constant d for each piezoelectric element.
33 [pC / N], Curie point [° C], temperature characteristic [% /
° C] and pyroelectricity [pC / ° C].

[0030]

[Table 1]

From Table 1, it can be seen that the single crystal LINbO ₃ has an extremely high Curie point compared to other piezoelectric elements, and is the most suitable piezoelectric element for suppressing the deterioration of the output with respect to the ambient temperature. However, when the piezoelectric elements are compared with each other in terms of piezoelectric constant, the single crystal LINbO ₃ has a smaller piezoelectric constant than the other piezoelectric elements. The piezoelectric constant is a value representing the magnitude of the output charge with respect to the applied pressure. A piezoelectric element with a small piezoelectric constant has a small S / N ratio because the magnitude of the pressure signal with respect to noise is small. More easily. In particular, since the internal combustion engine uses a large voltage in an ignition system or the like, a large noise is generated from these devices, and it is difficult to accurately detect a pressure signal with a piezoelectric element having a small piezoelectric constant.

Further, since the manufacturing cost of a single crystal is considerably higher than that of a polycrystal (for example, about 10 times), a spark plug with a built-in pressure sensor using a single crystal piezoelectric element has a low price competitiveness. Would. Therefore, the single crystal LINbO ₃
Is the most suitable piezoelectric element to suppress deterioration due to ambient temperature, but considering the piezoelectric constant and cost,
It is difficult to use it for a spark plug with a built-in pressure sensor. The inhibition of degradation (endurance), the detection accuracy, when comprehensively judging the piezoelectric constant and cost, as the piezoelectric element used in the pressure sensor, than a single crystal LiNbO _3,
It can be determined that polycrystalline PbNb ₂ O ₆ is suitable.

As described above, the spark plug with a built-in pressure sensor of the present invention using polycrystalline PbNb ₂ O ₆ as the piezoelectric element can suppress the influence of noise on the pressure signal and realize low cost. A spark plug with a built-in pressure sensor having a pressure sensor with excellent durability and high pressure detection accuracy.

[0034]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an external view showing a configuration of an ignition plug with a built-in pressure sensor (hereinafter, also referred to as an ignition plug) according to an embodiment to which the present invention is applied. In order to show the internal structure, a left half surface of the ignition plug is sectioned. It is shown as a diagram.

As shown in FIG. 1, the ignition plug 1 with a built-in pressure sensor of this embodiment has a terminal electrode 11 for receiving a high voltage for ignition supplied from the outside, and a center electrode electrically connected to the terminal electrode 11. Electrode 13, terminal electrode 11 and center electrode 13
Insulator 15 made of an insulator covering a connection path connecting
Metal shell 1 covering the portion of insulator portion 15 on the side of center electrode 13
7 and a central electrode 13 extending from an end of the metal shell 17.
And an outer electrode 19 facing the same.

A resistor 21 for preventing noise is provided in a connection path connecting the terminal electrode 11 and the center electrode 13 with the resistor 21 sandwiched between conductive glass seals 23. The metal shell 17 has a hexagonal portion 3 for fitting with a fastening tool when the spark plug 1 is mounted.
1, a mounting seat 35 in contact with the internal combustion engine main body 25 via a gasket 33 for ensuring airtightness, and a screw portion 37 provided with a screw groove for screw connection to the internal combustion engine. .

The mounting seat 35 has a pressure sensor 41 inside, and the terminal electrode 1 in the mounting seat 35 is provided.
From one end, a sensor output cable 43 composed of a conductor for outputting a pressure signal output from the pressure sensor 41 to an external device is led out in a direction toward the terminal electrode 11. In this embodiment, the pressure signal is output to an electronic control unit (ECU) via the sensor output cable 43.

Here, the configuration of the pressure sensor 41 provided inside the mounting seat 35 will be described below. Also,
FIG. 2 is an enlarged view of a cross section of the mounting seat 35. As shown in FIG. 2, the pressure sensor 41 provided inside the mounting seat portion 35 includes an annular piezoelectric element 51 centered on the insulator portion 15.
An insulator 53 provided at an end of the piezoelectric element 51 on the terminal electrode 11 side;
The plate packing 55 provided at the end on the third side and the piezoelectric element 5
1 and a connection terminal 59 that penetrates through the insulator 53 to electrically connect the piezoelectric element 51 and the sensor output cable 43. It is composed of The lower end 57a and the upper end 57b of the case 57 are fixed by laser welding. The piezoelectric element 51 is made of polycrystalline PbN.
consisting of b ₂ O _6.

The pressure sensor 41 thus configured is
Spark plug 1 that changes due to fluctuations in the in-cylinder pressure of an internal combustion engine
Is detected via the gasket 33 to detect the in-cylinder pressure of the internal combustion engine. That is, the tightening load applied to the gasket 33 fluctuates due to the fluctuation of the in-cylinder pressure, and the fluctuation of the tightening load is transmitted to the piezoelectric element 51 via the case 57 and the plate packing 55 as the fluctuation of the pressure, and transmitted. Piezoelectric element 51 according to pressure
Outputs the charge. Then, when the electric charge is output according to the fluctuation of the pressure transmitted by the piezoelectric element 51, the output electric charge is supplied to the sensor output cable 43 through the connection terminal 59, and the pressure signal generated by the output electric charge is It is output to an electronic control unit (ECU) which is an external device through the sensor output cable 43.

As described above, the ignition plug with a built-in pressure sensor detects the in-cylinder pressure of the internal combustion engine based on the fluctuation of the plug tightening load, and outputs a pressure signal to the ECU. The ECU that has received the pressure signal controls the internal combustion engine based on the operating state of the internal combustion engine in addition to the in-cylinder pressure obtained from the pressure signal.

Next, in order to clarify the features of the ignition plug with a built-in pressure sensor of the present embodiment, measurement results of pressure detection performed under various conditions will be described below. The measurement is
In addition to a spark plug with a built-in pressure sensor having polycrystalline PbNb ₂ O ₆ (lead niobate) as the piezoelectric element 51 which is a feature of the present invention, a conventional piezoelectric element is provided for comparison. The test was also performed for the spark plug with a built-in pressure sensor. As a conventional ignition plug with a built-in pressure sensor, polycrystalline PbTiO ₃ (lead titanate; hereinafter also referred to as PT) and polycrystalline Pb (Z
r, Ti) O ₃ (zirconium lead titanate, hereinafter PZ
T).

First, FIG. 3 shows a measurement result when the output change rate with time is measured. The measurement was performed at an ambient temperature of 18
In an environment of 0 ° C., the electric charge output from the ignition plug with a built-in pressure sensor tightened with a tightening torque of 40 Nm was measured. The measurement result is based on the magnitude of the output charge in the initial state (when the time is 0 [Hr]) as a reference (100%), and the ratio of the magnitude of the output charge that changes with time (output change rate). This is shown for each piezoelectric element.

The normal ambient temperature of the piezoelectric element of the ignition plug with a built-in pressure sensor in a general internal combustion engine is 1
The temperature is about 20 ° C., and the normal tightening torque of the spark plug is 25 Nm. This measurement was performed as an accelerated test under more severe conditions than usual. FIG. 3 shows the measurement results, with the horizontal axis representing the durability time [Hr] and the vertical axis representing the output change rate [%].

According to the measurement results shown in FIG. 3, the time required for the output change rate to decrease to 90% is equal to that of the polycrystalline PbNb.
₂ O ₆ is 300 [Hr], PT is 150 [Hr], PZT
Is 60 [Hr]. From this, when used under the same conditions with respect to temperature and tightening load, polycrystalline PbNb ₂ O ₆ takes twice or more times as long as PT and PZT until the output decreases to the same level. You can see that.

Therefore, the polycrystalline PbNb ₂ O ₆ used as the piezoelectric element 51 in the present invention has a longer time to deteriorate to the same degree as PT and PZT which have been conventionally used, and thus has excellent durability. Will be. Next, FIG. 4 shows a measurement result when an output change rate (temperature characteristic) due to a temperature change is measured. The measurement is based on the output charge when the ambient temperature is 25 ° C. as a reference (0%), and the ratio of the magnitude of the output charge that changes with the rise in the ambient temperature (output change rate).
Was measured for each piezoelectric element. FIG. 4 shows the measurement results, where the horizontal axis represents the ambient temperature [° C.] and the vertical axis represents the output change rate [%].

According to the measurement results shown in FIG. 4, when the ambient temperature is 120 ° C., the output change rate is polycrystalline PbNb.
₂ O ₆ is 24 [%], PT is 34 [%], and PZT is 37 [%].
[%]. From this, polycrystalline PbNb
It can be seen that ₂ O ₆ has a smaller output change rate (lower temperature characteristic) due to the same temperature change than PT and PZT.

Since the output change (temperature characteristic) of the piezoelectric element 51 due to such a temperature change also occurs in the spark plug 1 of the present embodiment, in an internal combustion engine equipped with the spark plug 1, for example, an electronic control unit (ECU) In), the in-cylinder pressure is detected by correcting the pressure signal based on the ambient temperature at the time of detection. That is, the ECU sets a wide dynamic range of the input pressure signal, performs processing such as controlling the input range of the pressure signal according to a temperature change at the time of detection, and corrects an error due to temperature characteristics. . At this time, as the temperature characteristic of the piezoelectric element 51 increases, the output change rate increases, so that it is necessary to set a wide dynamic range.

However, the range width recognized internally by the ECU is a fixed value determined by the hardware specifications of each ECU. Therefore, if the dynamic range of the pressure signal is set to be large, the ECU internally recognizes the input signal with respect to the input signal. The smallest unit of recognizable pressure becomes relatively large. For this reason,
The resolution of the pressure signal decreases, and the accuracy of the detected pressure decreases. Therefore, in order to increase the detection accuracy, the piezoelectric element 51 having a small temperature characteristic is desirable.

Then, from the measurement results shown in FIG.
Since polycrystalline PbNb ₂ O ₆ has smaller temperature characteristics than PT and PZT conventionally used as piezoelectric elements, using the spark plug 1 of the present embodiment
The dynamic range can be set smaller than before.

Therefore, according to the ignition plug 1 of the present embodiment, the resolution of the pressure signal can be made higher than before, and the pressure detection accuracy can be made higher. continue,
FIGS. 5 and 6 show measurement results when the actual change in the in-cylinder pressure of the internal combustion engine is measured by the ignition plug 1 with the built-in pressure sensor. FIG. 5 shows a measurement result when polycrystalline PbNb ₂ O ₆ is used as the piezoelectric element 51 of the ignition plug 1 with a built-in pressure sensor, and FIG. 6 shows a measurement result when PT is used as the piezoelectric element.

In the measurement, the operating state of the internal combustion engine was set to "1500
When the state was rapidly changed from "rpm / no load" to "1500 rpm / full load", the in-cylinder pressure was detected by the ignition plug 1 with a built-in pressure sensor. Further, for a comparative experiment, an in-cylinder pressure when the operating state was similarly changed was also detected by using a tonometer which directly detects an in-cylinder pressure from a conduction hole communicating with the cylinder. In the detection by the spark plug 1, the time constant τ of the charge amplifier circuit for amplifying the sensor output signal is set to 75 [msec] and 210 [ms].
ec]. In addition, the time constant τ of the charge amplifier circuit used for detection by the tonometer is
In all, the cylinder pressure was detected as 10 [sec].

FIG. 5 (a) and FIG. 6 (a)
FIGS. 5B and 6B show the measurement results when the time constant τ of the charge amplifier circuit is 75 msec, and FIGS. 5B and 6B show the measurement results when the time constant τ is 210 msec. , The horizontal axis is time [sec], and the vertical axis is the cylinder pressure Pmax [kg / c].
m ² ]. The upper part of each measurement result is the measurement result by the ignition plug with the built-in pressure sensor, and the lower part is the measurement result by the acupressure meter. FIGS. 5C and 6C show a change in the temperature of the spark plug mounting seat 35 at the time of measurement. The horizontal axis represents time [sec], and the vertical axis represents seat temperature [° C.]. It is expressed as

According to the measurement results shown in FIGS. 5 and 6,
The in-cylinder pressure detected by the tonometer (lower row of each measurement result) has almost no fluctuation in the ground level, while the in-cylinder pressure detected by the spark plug with a built-in pressure sensor (upper row of each measurement result) is all at the ground level. Is fluctuating.

Such a difference occurs because the spark plug 1
Is located closer to the combustion chamber than the tonometer,
This is because the operating state of the internal combustion engine was affected by a temperature change due to a sudden change. That is, the ground level of the in-cylinder pressure detected by the ignition plug 1 fluctuates because the output charge fluctuates transiently due to a rapid temperature change due to the pyroelectric characteristics of the piezoelectric element 51.

Assuming that the magnitude of the fluctuation of the ground level in each measurement result is a drift amount, each drift amount is 9 [kg / cm ² ] in the upper part of FIG. 5A and 1 in the upper part of FIG.
6 [kg / cm ² ], 10 [kg / cm ² ] in the upper part of FIG. 6 (a), and 20 [kg / cm ² ] in the upper part of FIG. 6 (b).

Here, when the polycrystalline PbNb ₂ O ₆ is compared with PT based on the measurement results when the time constant τ of the charge amplifier circuit is the same, the drift amount of the polycrystalline PbNb ₂ O ₆ is smaller than that of PT. I understand. This is a polycrystalline PbNb ₂ O
No. ₆ is because the pyroelectric property is smaller than that of PT.

Note that such fluctuations in the ground level are caused by the spark plug 1 of the present embodiment, as in the case of the above-described temperature characteristics.
Therefore, in an internal combustion engine equipped with the spark plug 1, for example, in an electronic control unit (ECU),
The pressure in the cylinder is detected by correcting the pressure signal based on the ambient temperature at the time of detection. In other words, the ECU sets a wide dynamic range of the input pressure signal, performs processing such as controlling the input range of the pressure signal according to a temperature change at the time of detection, and suppresses ground level fluctuation due to pyroelectric characteristics. Has been corrected. At this time, the larger the pyroelectric characteristic of the piezoelectric element 51 is, the larger the fluctuation of the ground level becomes. Therefore, it is necessary to set a wide dynamic range.

However, the range width that the ECU internally recognizes is a fixed value determined by the hardware specifications of each ECU. Therefore, if the dynamic range of the pressure signal is set to be large, the ECU internally responds to the input signal. The smallest unit of recognizable pressure becomes relatively large. For this reason,
The resolution of the pressure signal decreases, and the accuracy of the detected pressure decreases. Therefore, in order to increase the detection accuracy, a piezoelectric element having a small pyroelectric characteristic is desirable.

From the measurement results shown in FIGS. 5 and 6, polycrystalline PbNb ₂ O ₆ has a smaller drift amount than PT conventionally used as a piezoelectric element.
It can be seen that the pyroelectric characteristics are small. Also, from the above-mentioned Table 1 showing the characteristics of each piezoelectric element, the polycrystalline PbNb ₂ O ₆ is PZT
It can be seen that the pyroelectric characteristics are smaller than those of the first embodiment.

Therefore, the polycrystalline PbNb ₂ O ₆ is
By using the spark plug 1 of the present embodiment used as 1, the dynamic range can be set smaller than before. Therefore, the spark plug 1 of this embodiment
According to the method, the resolution of the pressure signal can be made higher than before, and the pressure detection accuracy can be made higher.

From the measurement results shown in FIGS. 5 and 6, it can be seen that the smaller the time constant τ of the charge amplifier circuit, the smaller the amount of change (drift amount) of the ground level. For this reason, in order to suppress the drift amount, the time constant τ may be reduced, whereby the dynamic range can be set smaller and the detection accuracy can be increased.

However, on the other hand, it has been found that when the time constant τ is set small, the pressure waveform detected by the charge amplifier circuit is distorted. Therefore, the time constant τ of the charge amplifier circuit is preferably set in consideration of both the drift amount and the distortion of the pressure waveform.

Next, FIG. 7 shows a measurement result when the output deterioration rate with respect to the magnitude of the tightening load of the ignition plug with the built-in pressure sensor was measured. As a value indicating the tightening load, an axial stress which is a pressure per unit area generated between the mounting seat portion 35 of the ignition plug and the internal combustion engine main body 25 is used.

In the measurement, the deterioration rate of the output when 400 [Hr] was passed with the ambient temperature set to 180 [° C.]
The measurement was performed for each axial stress. FIG. 7 shows the measurement results, with the horizontal axis representing the axial stress [kgf / cm ² ] and the vertical axis representing the output charge deterioration rate [%]. According to the measurement results shown in FIG. 7, the axial stress when the output deterioration rate is 10% is:
Polycrystalline PbNb ₂ O ₆ is about 1250 [kgf / cm ² ], PT is about 700 [kgf / cm ² ], and PZT is about 400 [kgf / cm ² ].
It has become. Generally, in order to maintain the detection accuracy within an allowable range, the output deterioration rate is desirably within 10%. From the above measurement results, it is found that the ignition plug 1 of this embodiment using polycrystalline PbNb ₂ O ₆ Can maintain the detection accuracy within an allowable range even when the tightening load is increased, as compared with a conventional ignition plug with a built-in pressure sensor using PT and PZT.

In addition, the spark plug 1 of this embodiment has a smaller output deterioration rate with respect to the same tightening load than the conventional spark plug with a built-in pressure sensor, so that the usable tightening load range is widened. It can be widely used in many types of internal combustion engines.

Further, since the output is less deteriorated due to the lapse of use in an environment where the tightening load is the same, the device can be used for a longer time than before, and the durability is excellent. Therefore, the spark plug 1 of the present embodiment can suppress the deterioration of the output with respect to the change in the tightening load, has high detection accuracy, can be applied to many internal combustion engines, and has excellent durability, as compared with the related art. Become.

Next, FIG. 8 shows the measurement results when the output deterioration rate with respect to the ambient temperature was measured. The measurement was performed by measuring the rate of deterioration of the output when 400 [Hr] was passed with the axial stress set to 1000 [kgf / cm ² ] at each ambient temperature. FIG. 8 shows the measurement results, where the horizontal axis represents the ambient temperature [° C.] and the vertical axis represents the output charge deterioration rate [%].

According to the measurement results shown in FIG. 8, the ambient temperature at which the output deterioration rate is 10% is lower than that of the polycrystalline PbNb.
₂ O ₆ has a temperature of about 205 ° C., PT has a temperature of 155 ° C., and PZT has a temperature of 130 ° C. From this, polycrystalline Pb
It can be seen that Nb ₂ O ₆ has a smaller output deterioration rate at the same ambient temperature than PT and PZT.

Therefore, the spark plug 1 of this embodiment is
Since the deterioration of the output with respect to the ambient temperature can be suppressed as compared with the related art, the usable temperature range is widened, and it can be widely used for many types of internal combustion engines. Further, in an environment where the ambient temperature is the same, the detection accuracy can be kept high because the output deterioration rate is smaller than in the conventional case. Further, the deterioration of the output due to the lapse of use in an environment having the same ambient temperature is reduced, so that the device can be used for a longer time than before, and the durability is excellent.

As described above, the normal ambient temperature of the piezoelectric element portion of the ignition plug with a built-in pressure sensor in a general internal combustion engine is about 120 ° C. It may rise to about ° C. On the other hand, in order to prevent the deterioration of the piezoelectric element, it is possible to increase the cooling efficiency of the internal combustion engine and suppress the temperature rise.However, the design change and additional equipment are required, which increases the cost. Would.

However, the spark plug 1 of this embodiment has a deterioration rate of less than 5% even in an environment where the ambient temperature is 150 ° C. from the measurement results shown in FIG. It is not necessary to take measures to increase the cooling efficiency, and the cost of the entire internal combustion engine can be reduced.

From the above measurement results, the usable range of the temperature and the tightening load of the ignition plug 1 with a built-in pressure sensor of this embodiment is wider than that of the conventional ignition plug with a built-in pressure sensor using PT and PZT. At the same time, the pressure sensor is excellent in durability and has high detection accuracy of pressure detection.

Note that, from the measurement results shown in FIG.
bNb ₂ O ₆ has a small output deterioration rate of 1% or less even when the axial stress is 500 [kgf / cm ² ], and has a considerably high output deterioration rate compared with conventionally used PT and PZT. It turns out that it is small. Thus, the ignition plug with the built-in pressure sensor of the present invention has an axial stress of 500 when the plug is attached.
When used in an environment of [kgf / cm ² ] or more, excellent durability can be exhibited as compared with a conventionally used piezoelectric element.

Further, from the measurement results shown in FIG.
bNb ₂ O ₆ can be used even when the ambient temperature is 120 ° C.
It can be seen that the output deterioration rate is as small as about 2%, and the output deterioration rate is considerably smaller than the conventionally used PT and PZT. Therefore, when the spark plug with a built-in pressure sensor of the present invention is used in an environment in which the element temperature is 120 ° C. or higher, excellent durability can be exhibited as compared with a conventionally used piezoelectric element. Can be.

In order to prevent the output from deteriorating due to an increase in ambient temperature, it is preferable to use a piezoelectric element having a high Curie point. Note that, in a piezoelectric element whose temperature has exceeded the Curie point, the polarization inside the element collapses, so that even if pressure is applied, no charge is output and the pressure cannot be detected.

From Table 1 above, which shows the characteristics of each piezoelectric element, it can be seen from Table 1 that the single crystal LINbO ₃ has an extremely high Curie point as compared with other piezoelectric elements, and is optimal for suppressing the deterioration of the output with respect to the ambient temperature. It turns out that it is a piezoelectric element.
However, when the piezoelectric elements are compared with each other in terms of piezoelectric constant, the single crystal LINbO ₃ has a smaller piezoelectric constant than the other piezoelectric elements. Since a piezoelectric element having a small piezoelectric constant has a small pressure signal with respect to noise, the S / N ratio becomes small, and the piezoelectric element is easily affected by noise. In particular, since the internal combustion engine uses a large voltage in an ignition system or the like, a large noise is generated from these devices, and it is difficult to accurately detect a pressure signal with a piezoelectric element having a small piezoelectric constant.

Further, since the manufacturing cost of a single crystal is considerably higher than that of a polycrystal (for example, about 10 times), a spark plug with a built-in pressure sensor using a single crystal piezoelectric element has a low price competitiveness. Would. Therefore, the single crystal LINbO ₃
Is the most suitable piezoelectric element to suppress deterioration due to ambient temperature, but considering the piezoelectric constant and cost,
It is difficult to use it for a spark plug with a built-in pressure sensor. The inhibition of degradation (endurance), the detection accuracy, when comprehensively judging the piezoelectric constant and cost, as the piezoelectric element used in the pressure sensor, than a single crystal LiNbO _3,
It can be determined that polycrystalline PbNb ₂ O ₆ is suitable.

As described above, the ignition plug 1 with a built-in pressure sensor of this embodiment using polycrystalline PbNb ₂ O ₆ as the piezoelectric element can suppress the influence of noise on the pressure signal and realize low cost. While excellent in durability,
A spark plug with a built-in pressure sensor having a pressure sensor with high pressure detection accuracy is obtained.

While the embodiment of the present invention has been described above, the present invention is not limited to such an embodiment.
Various aspects can be taken. For example, an ignition coil for generating a high voltage for ignition may be integrally formed above the terminal electrode. As a result, the ignition plug with a built-in pressure sensor can effectively use the space in the plug hole of the internal combustion engine.

[Brief description of the drawings]

FIG. 1 is an external view illustrating a configuration of an ignition plug with a built-in pressure sensor according to an embodiment.

FIG. 2 is an enlarged view of a cross section of a mounting seat of a spark plug with a built-in pressure sensor.

FIG. 3 is a graph showing a measurement result when an output change rate of a piezoelectric element over time is measured.

FIG. 4 is a graph showing measurement results when an output change rate (temperature characteristic) due to a temperature change of a piezoelectric element is measured.

FIG. 5 is a graph showing a measurement result when a change in in-cylinder pressure is measured using polycrystalline PbNb ₂ O ₆ as a piezoelectric element.

FIG. 6 is a graph showing a measurement result when a change in an in-cylinder pressure is measured using polycrystalline PbTiO ₃ as a piezoelectric element.

FIG. 7 is a graph showing a measurement result when an output deterioration rate due to a change in plug tightening load is measured.

FIG. 8 is a graph showing a measurement result when an output deterioration rate due to a change in an ambient temperature is measured.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Spark plug with a built-in pressure sensor, 11 ... Terminal electrode, 13
... Center electrode, 15 ... Insulator part, 17 ... Metal fitting, 19 ... Outer electrode, 31 ... Hexagon part, 33 ... Gasket, 35 ... Mounting seat part, 37 ... Screw part, 41 ... Pressure sensor, 43 ... Sensor output cable, 51: piezoelectric element, 53: insulator, 55:
Plate packing, 57 ... case, 59 ... connection terminal.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Takahiro Suzuki 14-18 Takatsuji-cho, Mizuho-ku, Nagoya-shi, Aichi F-term (reference) 2F055 AA23 BB14 CC11 DD19 EE23 FF11 FF38 GG49 3G019 KA28 KD17 5G059 AA04 AA10 KK03

Claims (1)

[Claims] A piezo-electric element is provided in a mounting seat of a metal shell of an ignition plug which generates spark discharge between electrodes, and a pressure in a cylinder of an internal combustion engine is detected by detecting a change in a plug tightening load by the piezo-electric element. An ignition plug with a built-in pressure sensor that outputs an electric signal according to a detected pressure from a sensor output cable, wherein polycrystalline PbNb ₂ O ₆ is used as the piezoelectric element. .