JP3123798B2 - Pressure detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a pressure detecting device provided with a pressure sensor for detecting a change in a cylinder internal pressure of an internal combustion engine by a piezoelectric element.

[0002]

2. Description of the Related Art A detection element such as a piezoelectric element and a pressure transmission rod is housed in a metal shell mounted in a screw hole for mounting a sensor provided in a cylinder head of an internal combustion engine, and a lower end face located in a cylinder. A pressure sensor is known in which a diaphragm is sealed to the piezoelectric element, and the internal pressure of the cylinder is transmitted to the piezoelectric element via the diaphragm and the pressure transmission rod, and an electric signal proportional to the magnitude of the internal pressure is taken out from the element. is there. In general, a piezoelectric element made of a ceramic material such as lead zirconate titanate or lead titanate is used as the piezoelectric element.

[0003]

However, such a pressure sensor is exposed to a high combustion temperature (1000 ° C.) together with the internal pressure of the cylinder, like a spark plug. Its Curie point is about 250 ° C for lead zirconate titanate and about 350 ° C for lead titanate.
° C and lower than the combustion temperature.
The temperature of the element part becomes extremely high (around 400 ° C.), which degrades the piezoelectric characteristics due to depolarization and the like, and cannot be used. Therefore, usually, a cooling means for maintaining the piezoelectric element at an appropriate temperature is used after being added. For this reason, there were drawbacks in that the structure was complicated, large, and the price was high. There are also problems such as the temperature dependence of the piezoelectric element, in which the generated charge increases as the temperature increases, and the pressure in the cylinder cannot be accurately detected due to pyroelectric characteristics.

On the other hand, in order to solve such a drawback, it is necessary to use a SiO ₂ single crystal having no temperature dependency and pyroelectric properties or a single crystal piezoelectric material having the same effect as these single crystals, instead of the ceramic piezoelectric material. It is conceivable that these single-crystal materials have a smaller amount of generated electric charge than ceramic-based piezoelectric materials, and thus are susceptible to noise from the spark plug and noise such as radio waves, resulting in a poor S / N ratio. There is a problem.

Therefore, in Japanese Patent Application No. 3-125414,
A device using a circular or square plate-like piezoelectric element made of lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), or a single crystal piezoelectric material having the same effect as these single crystal materials has been proposed. The Curie point of this lithium niobate is as high as about 1200 ° C., and is characterized by excellent heat resistance and low temperature dependence. LiTaO ₃ , S
It has excellent characteristics that the generated charges are large and the S / N ratio is good compared to iO ₂ . However, although the element characteristics are excellent, when the pressure sensor is a structure, the component size changes due to the temperature difference during combustion (temperature difference between each member), and the output is similar to the pyroelectric characteristic. Sometimes occurred. An object of the present invention is to eliminate the problems of the conventional configuration.

[0006]

According to the present invention, a metal shell mounted on a cylinder of an internal combustion engine is provided with a shaft hole having a detection opening located in the cylinder, and a piezoelectric element is provided inside the shaft hole.
A pressure sensor that houses a detection element such as a pressure transmission rod, and further seals the opening end of the shaft hole with a metal diaphragm, and uses a single crystal piezoelectric material of lithium niobate as the piezoelectric element; and And a filter having a function of removing a low-frequency component of the output voltage; and a plate-like piezoelectric element of the pressure sensor.
Is a lithium niobate having a Z-axis component of 20 ° or less in the polarization direction.
Made of a Y-cut single crystal piezoelectric material.
The threshold value for removing the low frequency of the data is 0.01HZ to 1.0H.
A pressure detecting device which is in the range of Z.

[0007]

When a pressure sensor is mounted on an engine block and its internal pressure is detected, the temperature changes drastically, for example, the temperature changes between idling, high rotation, and high load. When the pressure sensor is attached to a portion where the temperature changes drastically, the output tends to fluctuate (drift) as shown in FIG. 8 due to pyroelectric characteristics. This output fluctuation results in a low-frequency output waveform.

Therefore, a filter is used as a threshold at a predetermined low frequency, and only a pressure waveform having a frequency equal to or higher than the threshold is transmitted, and a low frequency lower than the frequency is removed, thereby removing a waveform corresponding to a drift of the output. can do. This threshold is in the range of 0.01 Hz to 1.0 Hz .
You. If it is less than 0.01 HZ, drift cannot be satisfactorily removed, and if it exceeds 1.0 HZ, the original pressure waveform is deformed and it becomes impossible to detect an appropriate pressure, resulting in a decrease in accuracy. This is because there is a risk of doing so. Sa
In order to reduce the pressure sensitivity to 10 atmospheres or less, the Z axis
Component angle θ of 20 ° or less is good,
Waves are also easier. Also noteworthy are X-cut products and Y
After preparing and examining each product,
The piezoelectric material has better piezoelectric characteristics than the X-cut material.
As well as good mechanical strength.
It has been certified. Therefore, the plate-like piezoelectric element of the pressure sensor
Of lithium niobate whose Z-axis component is less than 20 °
A Y-cut crystal piezoelectric material was used.

[0009]

FIG. 1 shows an embodiment of a pressure sensor S applied to the present invention. Reference numeral 1 denotes a male screw 2 screwed to a cylinder block on the outer periphery of a lower end 1a, and a tightening tool such as a spanner on the outer periphery of an upper end 1b. A metal shell 1 having a bolt structure formed with a hexagonal portion 3 which conforms to the above, and a shaft hole 4 is formed therein. This shaft hole 4 has different diameter holes 4a, 4b, 4c penetrating the lower end portion 1a side and a large diameter hole 4 penetrating the upper end portion 1b side.
and d are continuously formed. The different diameter holes 4a, 4b, 4
c, the metal plate 5, the first terminal member 6, the piezoelectric element 7 having electrodes 7 a and 7 b provided on the front and back surfaces, respectively, of the hole 4 b on the middle diameter side from the hole 4 a on the small diameter side. A second terminal member 8 and an electric insulating ring 9 are sequentially arranged in layers, and are insulated from the metal shell 1 by an insulating material 10 covering the periphery of the laminate. In addition, a connecting hand 8 a for connecting to a signal carrying cable 16 described later protrudes from the upper surface of the second terminal member 8 through the insulating ring 9.

Further, the pressure transmitting rod 1 is provided in the hole 4a on the small diameter side.
1 is pressed into contact with the metal plate 5 at one end, and the other end is bonded to a metal diaphragm 12 joined so as to hermetically seal the end surface of the lower end 1a of the metal shell 1. The metal diaphragm 12 needs to have heat resistance, and is preferably made of, for example, a heat-resistant metal material such as Inconel or SUS630. Further, a spring ring 13 is provided between the stepped portions of the holes 4a and 4b of the metal shell 1 and the pressure transmitting rod 11, and the spring ring 13 causes a distortion caused by a difference in thermal expansion and a difference in heat transfer between the components and a male screw portion. Absorbs the stress caused by elongation or the like due to the tightening torque. A holding screw 18 is screwed into the female screw formed in the large-diameter hole 4c to apply a predetermined preload to the piezoelectric element 7 with the screw 18 so as to correspond to a negative pressure state at the time of introducing the intake air during combustion. I have.

On the inner surface of the large-diameter hole 4d on the hexagonal portion 3 side,
A step 4d 'is formed, a metal sleeve 14 having a flange 14a seated thereon is fitted therein, and a sealing member 15
The annular thin piece 3a protruding from the upper end of the hexagonal portion 3 is bent together with the b and the electric contact member 15a to be crimped inward.

One end of a signal carrying cable 16 is inserted and fixed inside the metal sleeve 14.
A relay conductor 17 in which a more bare core wire 16a is insulated and coated.
Is connected to the second terminal member 8 via the. However, one electrode of the piezoelectric element 7 is connected to the core 16a of the cable 16 through the second terminal member 8 and the relay conductor 17, and the other electrode is connected to the first terminal member 6, the metal plate 5, and the transmission rod pressure transmission. It is grounded to the metal shell 1 through the rod 11.

Although the configuration up to this point is conventionally known, a feature of the pressure sensor S constituting the present invention is that a piezoelectric element 7 disposed between the first terminal member 6 and the second terminal member 8 is provided. To
A circular shape made of lithium niobate (LiNbO ₃ ) (FIG. 2)
(See FIG. 3) or a rectangular (see FIG. 3) plate-like piezoelectric element.

The piezoelectric element 7 made of a single crystal may be a circular plate, but is preferably a rectangular plate as shown in FIG. 3 from the viewpoint of economy and mass productivity. In this case, as shown in FIG. By applying a grid-shaped cutting line t to one large single crystal substrate s, a large number of piezoelectric elements 7, 7... Can be manufactured at once without waste. Further, it is desirable that the thickness has an outer dimension of 0.3 mm to 1.5 mm. That is, these single crystal materials have poor mechanical strength and may be broken by a normal cutting method such as a diamond cutter, an ultrasonic cutter, a laser beam, or the like, but have a thickness of 0.3 mm to 1.
Limiting it to 5 mm solves this problem. If it exceeds 1.5 mm, cracks may occur due to thermal shock during cutting. Therefore, it is preferable that the thickness be 1.0 mm or less. However, if it is less than 0.3 mm, there is a problem in mechanical impact at the time of cutting. Further, in such a pressure sensor, accuracy and parallelism of the pressure receiving surface are required, and the surface is usually polished in many cases.

Further, the electrodes 7a and 7b to be attached to the front and back surfaces of the piezoelectric element 7 can be formed by plating, vapor deposition, or the like. However, in order to enhance the adhesion to the piezoelectric element, a metal such as nickel or silver is used. It is preferable to use an organic metal ink dispersed in an organic solvent and form and print this by printing. In this case, after printing the organic metal ink, first,
By laminating the second terminal members 6 and 8 and firing them integrally, the adhesion between the piezoelectric element and the electrode and between the electrode and the terminal member is increased, and the poor contact during use is reliably prevented. There are advantages to

Next, the pyroelectric characteristics of a piezoelectric element using a lithium niobate single crystal as the piezoelectric element 7 were confirmed by the following means. Test the pyroelectric properties of lithium niobate single crystal cut products at various angles as samples, alternately immersing them in a tank containing 0 ° C silicone oil and a tank containing 150 ° C silicone oil. did. The result was as shown in FIG. Where x is the element size φ
With an outer diameter of 6 × 0.5 t, y is φ4 × 0.
The outer diameter of 7t is shown. The vertical axis indicates the charge generated by the temperature change, and the horizontal axis indicates the angle θ of the Z-axis component. Here, the angle θ of the Z-axis component is defined as shown in FIG. 6, and refers to the deviation angle of the polarization axis from the plane direction (X, Y directions) in the thickness direction (Z direction). That is, θ = 90 ° refers to a polarization in the same direction as the thickness direction,
θ = 0 ° means that the surface is polarized in the plane direction.

From these results, it was found that the smaller the Z-axis component, the better. In order to make the pressure sensitivity equal to or less than 10 atm, the angle θ of the Z-axis component is preferably equal to or less than 20 °, more preferably equal to or less than 5 atm and equal to or less than 10 °, and the filtering on the circuit is facilitated. . In these cuts, the piezoelectric properties were also sufficient. In particular, there is no Z direction (θ
= 0) The sample was very good with almost no pyroelectricity. Then, in a sample having no Z direction (θ = 0), X-cut and Y-cut products were prepared and examined. The Y-cut product had better piezoelectric characteristics than the X-cut product. It is almost equivalent to other cuts,
Further, good results were also obtained in mechanical strength.

From these results, as the pressure sensor S, a Y-cut product of lithium niobate was used, and the above-described assembly was performed by ultrasonic cutting with an outer diameter of φ5 × 0.5 t. The inner and outer diameters of the diaphragm were also φ7 / φ9, and the thickness of the diaphragm was 0.15 mm. Also,
The pressure with the holding screw 14 was set to 10 MPa.

FIG. 9 shows the pressure sensor S having such a configuration.
And a high-pass filter F having a function of removing a low-frequency component of the output voltage of the charge amplifier A is sequentially connected to the charge amplifier A for converting the charge generated by the pressure sensor S into a voltage. Comprising such a pressure sensing device,
The pressure sensor S was mounted on an engine having a total displacement of 2000 cc, and the relationship between the low-frequency threshold value of the high-pass filter F and the combustion pressure waveform passing through the high-pass filter F was examined.

FIG. 7 shows various changes of the threshold value for cutting the low frequency of the high-pass filter F. The engine rotation is set to idling (1200 rpm) and 5000 rpm.
Shows the combustion pressure waveform when constant. Here, the dashed line at the center is a reference line indicating the atmospheric pressure. From this waveform diagram, at 0.01 Hz to 0.5 Hz, a raw waveform without a filter (indicated by a broken line) at any rotation speed.
This means that the waveforms do not greatly differ, and proper accuracy can be maintained. Also, in the case of 1HZ, it can be seen that, although a slight deviation from the raw waveform occurs at the time of idling, the predetermined accuracy can be maintained. However, it has been found that when the high-pass filters having the thresholds of 2HZ and 3HZ are provided, drift occurs at a low level, which is significantly different from the raw waveform, and causes an error of 1 atm or more.

FIG. 8 shows the state when the engine speed is changed. Even though the pressure sensor S using the piezoelectric element 7 having no pyroelectric characteristics and temperature characteristics is applied, without the high-pass filter F, the entire waveform fluctuates up and down, and engine drift may occur. I understand. Even when a high-pass filter F having a threshold value of 0.01 Hz is connected, the drift appears on the waveform. However, in the case where the high-pass filter F having the threshold values of 0.05 HZ, 0.1 HZ and 0.3 HZ was connected, the drift could be removed on the waveform. This drift can be sufficiently dealt with by the high-pass filter F having a threshold value of 1 HZ or less.

Thus, the threshold value is 0.01 HZ to 1.0 HZ.
It can be said that the high-pass filter F in the range of the above can eliminate the drift, does not greatly differ from the raw waveform, and has an acceptable accuracy. Preferably, a better result can be obtained by using a high-pass filter F having a threshold value of 0.05 to 0.5 Hz.

[0023]

The pressure sensing device of the present invention is as described above, and the piezoelectric element mounted inside the metallic shell has LiNb having a Curie point higher than the combustion temperature in the cylinder.
Since a pressure sensor using a single-crystal piezoelectric material of O ₃ is used, there is no need to cool the piezoelectric element by a cooling means as in the related art. The Yuse not be a pyroelectric property by the polarization direction of the Z-axis component of the piezoelectric element is a 20 ° or less, Y-cut
Good piezoelectric properties and excellent
The strength is also good. Further, since a device (charge amplifier A) for converting charges generated by the pressure sensor into a voltage and a filter F having a function of removing a low-frequency component of the output voltage are connected to the pressure sensor S,
Drift of the combustion waveform caused by low frequency output caused by temperature change or the like is removed, and a stable combustion waveform can be obtained. Thus, the present invention has an excellent effect of providing a high-precision pressure detecting device which is small in size, inexpensive, has a good output waveform, and has no pyroelectricity.

[Brief description of the drawings]

FIG. 1 is a vertical sectional side view of a pressure sensor showing one embodiment of the present invention.

FIG. 2 is a perspective view of a piezoelectric element 7 formed in a circular shape.

FIG. 3 is a perspective view of a piezoelectric element 7 formed in a rectangular shape.

FIG. 4 is a perspective view showing a cutting means of the piezoelectric element 7;

FIG. 5 is a graph showing the influence of a pyroelectric effect on cut products of various angles of a lithium niobate single crystal.

FIG. 6 is a coordinate diagram showing the concept of the angle θ of the Z-axis component.

FIG. 7 is a waveform chart showing the relationship between a high-pass filter F having a different threshold value and its output waveform at 1200 rpm and 5000 rpm.

FIG. 8 is a waveform chart showing drift when the number of revolutions is changed.

FIG. 9 is a conceptual diagram showing a basic configuration of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal shell 7 Piezoelectric element 11 Pressure transmission rod S Pressure sensor A Charge amplifier F High-pass filter

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hirofumi Hayashiko 14-18 Takatsuji-cho, Mizuho-ku, Nagoya Japan Special Ceramic Industry Co., Ltd. (56) References JP-A-62-81572 (JP, A) JP-A-62-81572 Sho-62-219808 (JP, A) Sho-sho 63-84539 (JP, U) Sho-sho 64-15139 (JP, U) Sho-sho 61-126620 (JP, U) Sho-sho 62-35243 (JP) , U) (58) Fields investigated (Int.Cl. ⁷ , DB name) G01L 23/10 G01L 9/08 G01L 1/16

Claims (1)

(57) [Claims] 1. A metal shell mounted on a cylinder of an internal combustion engine includes a shaft hole having a detection opening located in the cylinder, and a detection element such as a piezoelectric element or a pressure transmission rod is housed in the shaft hole. Further, a pressure sensor in which the opening end of the shaft hole is sealed with a metal diaphragm, a pressure sensor using a single-crystal piezoelectric material of lithium niobate as the piezoelectric element, and a device for converting electric charges generated by the pressure sensor into a voltage, and a filter having a function of removing a low-frequency component of the output voltage, the pressure
The plate-like piezoelectric element of the sensor has a Z-axis component in the polarization direction of 20 °
The following Y-cut products of single crystal piezoelectric material of lithium niobate
A threshold for removing low frequency of the filter,
A pressure sensing device, wherein the pressure sensing device is in a range of 0.01 Hz to 1.0 Hz .