JP2021156599A - Pressure detection device and internal combustion engine with pressure detection device - Google Patents

Abstract

To improve the practicality of a pressure detection device by defining a range of insulating properties of a pressure receiving portion and a covering portion formed on a body portion of the pressure detection device.SOLUTION: A pressure detecting device 5 includes: a metal tubular housing 30; a diaphragm head 40 attached to the tip end side of the housing 30 and receiving pressure from a combustion chamber; a piezoelectric element 10 that is provided inside the housing 30 and generates a charge signal according to the pressure received by the diaphragm head 40; and an insulating layer 80 that continuously covers the outer peripheral surface of the diaphragm head 40 and the outer peripheral surface of the housing 30 on the side of the diaphragm head 40. The insulating layer 80 is a film configured to obtain an insulating resistance of 510 Ω or more.SELECTED DRAWING: Figure 4

Description

The present invention relates to a pressure detector and an internal combustion engine with a pressure detector.

As a pressure detecting device for detecting the pressure in a combustion chamber of an internal combustion engine or the like, a device using a signal generating unit such as a piezoelectric element has been proposed. This type of pressure detector includes, for example, a tubular housing (body part) made of a conductor, and a diaphragm made of a conductor and attached to one end side of the body part to receive pressure from the outside. It is provided with a head (pressure receiving part) and a piezoelectric element (signal generating part) provided inside the body part, which is electrically connected to the pressure receiving part and generates a signal according to the pressure received by the pressure receiving part. There is a device in which the ground of the signal generating unit and the housing are electrically connected via the unit. Further, in this type of pressure detecting device, for example, by inserting it into a communication hole provided in the cylinder head of an internal combustion engine, the housing and the cylinder head are electrically connected, and the pressure receiving portion faces the combustion chamber. Will be placed. At this time, the cylinder head functions as a grounding body, and the ground of the signal generating portion may be grounded via the pressure receiving portion, the housing, and the cylinder head.

Here, by attaching a housing (conductor) electrically connected to the ground of the signal generation unit to a mounted body (for example, a cylinder block) made of a conductor, the housing and the mounted body are made conductive. Further, when the configuration in which the mounted body is grounded is adopted, noise may enter the pressure detection device from the mounted body through the housing. Then, such noise can be a factor that causes an error in the pressure obtained based on the output from the signal generating unit.

Patent Document 1 has a configuration in which, as a means for suppressing the influence of this kind of noise, a covering portion made of an insulator continuously covers the outer peripheral surface of the pressure receiving portion and the outer peripheral surface of the body portion on the pressure receiving portion side. It is disclosed.

Japanese Patent No. 6606483

The pressure detection device is attached by inserting it into the communication hole provided in the cylinder head of the internal combustion engine, etc., but since the pressure receiving part receives a large pressure, the outer shape of the pressure detection device and the inner wall shape of the communication hole High accuracy is required. Therefore, the thinner the covering portion that covers the pressure receiving portion and the body portion, the better. On the other hand, when the same material is used as the insulator, the insulating property of the covering portion becomes lower as the thickness becomes thinner. Therefore, at a minimum, the covering portion needs to have an insulating property capable of removing noise that needs to be removed.

An object of the present invention is to determine the range of insulating properties of the pressure receiving portion and the covering portion formed on the body portion of the pressure detecting device, and to enhance the practicality of the pressure detecting device.

The pressure detection device of the present invention that achieves the above object is formed of a tubular body portion made of a conductor, and is attached to one end side of the body part while being composed of a conductor, and receives pressure from the outside. It is composed of a pressure receiving portion, a signal generating portion provided inside the body portion, which is electrically connected to the pressure receiving portion and generates a signal according to the pressure received by the pressure receiving portion, and an insulator. The outer peripheral surface of the pressure receiving portion and the covering portion that continuously covers the outer peripheral surface of the body portion on the pressure receiving portion side are provided. The covering portion is a film made of the insulator configured to obtain an insulation resistance of 510 Ω or more.
Here, regarding the insulating resistance, the covering portion has a minimum value of 510 Ω and a maximum value of the resistance value obtained when the thickness of the insulator is 0.1 mm. It may be composed of the insulator having a thickness of 510 Ω as a minimum value and a thickness of 0.1 mm as a maximum value.
Further, a male screw is provided on the outer peripheral surface of the body portion, the covering portion has a minimum value of 510 Ω with respect to the insulation resistance, and the thickness of the insulator is set to the size of the gap between the male screw and the female screw corresponding to the male screw. The size of the gap between the male screw and the female screw corresponding to the male screw, with the thickness of the insulator having the maximum resistance value obtained at the time of It may be composed of the insulator having the maximum value.
Further, the pressure detecting device is further provided with a processing unit that is electrically connected to the signal generating unit and that processes and outputs the signal generated by the signal generating unit. When electrically disconnected, the insulation resistance of the coating is 1 MΩ or more.
From another point of view, the internal combustion engine with a pressure detection device of the present invention has a cylinder head having a communication hole for communicating between the combustion chamber on the one end side and the outside of the combustion chamber on the other end side. It is attached to the cylinder head by being inserted into the communication hole, and also includes a pressure detecting device for detecting the pressure in the combustion chamber. Then, the pressure detecting device is arranged so as to straddle the inside and the outside of the communication hole, and has a tubular body portion composed of a conductor and a one end side of the body portion composed of a conductor. A signal generation that is attached and is provided inside the fuselage portion and receives pressure from the combustion chamber, is electrically connected to the pressure receiving portion, and generates a signal corresponding to the pressure received by the pressure receiving portion. It is provided with a portion and a covering portion which is composed of an insulator and continuously covers a portion of the outer peripheral surface of the pressure receiving portion and the outer peripheral surface of the body portion, which is located inside the communication hole. The covering portion is a film made of the insulator configured to obtain an insulation resistance of 510 Ω or more.

According to the present invention, the range of insulating properties of the pressure receiving portion and the covering portion formed on the body portion of the pressure detecting device can be defined, and the practicality of the pressure detecting device can be enhanced.

It is a schematic block diagram of the pressure detection system which concerns on embodiment. It is an enlarged view of the part II of FIG. It is a schematic block diagram of a pressure detection device. It is sectional drawing of the IV-IV part of FIG. It is an enlarged view of the V part of FIG. It is an enlarged view of the VI part of FIG. It is a flowchart for demonstrating the manufacturing method of the pressure detection apparatus. It is a schematic block diagram of the film forming apparatus used for forming an insulating layer. It is a figure which shows schematic the electric structure of the pressure detection device and the control device by this embodiment. It is a figure which shows the outline of the induction noise resistance test. It is a chart which shows the result of the induction noise resistance test. It is a graph which plotted the test result of FIG. It is a figure which shows typically the electric structure of a pressure detection device and a control device when an insulating layer is not formed in the housing of a pressure detection device. It is a graph which shows the relationship between the output voltage of a pressure detection apparatus and the insulation property of an insulating layer at the time of disconnection of a ground wire. It is a figure which shows schematic the electric structure of the pressure detection device and the control device when a capacitor is arranged on the path connecting a circuit board and a housing. It is a chart which shows the result of the test of the potential difference between grounds. It is a graph which plotted the test result of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[Pressure detection system configuration]
FIG. 1 is a schematic configuration diagram of a pressure detection system according to the present embodiment.
FIG. 2 is an enlarged view of part II of FIG.
This pressure detection system supplies power to the pressure detection device 5 for detecting the pressure (combustion pressure) in the combustion chamber C in the internal combustion engine 1 and the pressure detection device 5, and internal combustion is based on the pressure detected by the pressure detection device 5. It includes a control device 6 that controls the operation of the engine 1, and a transmission cable 8 that electrically connects the pressure detection device 5 and the control device 6 to transmit an electric signal.

Here, the internal combustion engine 1 whose pressure is to be detected includes a cylinder block 2 in which a cylinder 2a is formed, a piston 3 that reciprocates in the cylinder 2a, and a piston 3 that is fastened to the cylinder block 2 and burns together with the piston 3 and the like. It has a cylinder head 4 that constitutes a chamber C. Further, the cylinder head 4 is provided with a communication hole 4a for communicating the combustion chamber C and the outside. The communication hole 4a is formed from the first hole 4b, the inclined portion 4c whose diameter gradually increases from the hole diameter of the first hole 4b, and the hole diameter of the first hole 4b from the combustion chamber C side. Also has a second hole 4d with a large hole diameter. In the present embodiment, the cylinder block 2 and the cylinder head 4 are made of a conductive metal material (cast iron or aluminum). Therefore, metal is exposed on the inner peripheral surface of the communication hole 4a provided in the cylinder head 4. Further, on the surrounding wall forming the second hole 4d, a female screw 4e into which the male screw 332a of the housing 30 described later described in the pressure detecting device 5 is screwed is formed.

[Pressure detector]
The pressure detection device 5 will be described in detail below.
FIG. 3 is a schematic configuration diagram of the pressure detection device 5. FIG. 4 is a cross-sectional view of the IV-IV portion of FIG. FIG. 5 is an enlarged view of the V portion of FIG. FIG. 6 is an enlarged view of the VI portion of FIG.

The pressure detection device 5 holds a sensor unit 100 having a piezoelectric element 10 that converts the pressure in the combustion chamber C into an electric signal, a signal processing unit 200 that processes an electric signal from the sensor unit 100, and a signal processing unit 200. The holding member 300 and the holding member 300 are provided. When the pressure detecting device 5 is attached to the cylinder head 4, the diaphragm head 40, which will be described later, of the sensor unit 100 is inserted into the communication hole 4a formed in the cylinder head 4 first. In the following description, the left side of FIG. 4 is the front end side (one end side) of the pressure detection device 5, and the right side is the rear end side (the other end side) of the pressure detection device 5.

(Sensor part)
First, the sensor unit 100 will be described.
The sensor unit 100 includes a piezoelectric element 10 that converts the received pressure into an electric signal, and a housing 30 that is tubular and has a cylindrical hole for accommodating the piezoelectric element 10 and the like. .. Hereinafter, the direction of the center line of the columnar hole formed in the housing 30 is simply referred to as the direction of the center line.

Further, the sensor unit 100 is provided so as to close the opening on the tip side of the housing 30, and is provided between the diaphragm head 40 on which the pressure in the combustion chamber C acts, and between the diaphragm head 40 and the piezoelectric element 10. A first electrode portion 50 and a second electrode portion 55 arranged on the opposite side of the piezoelectric element 10 from the first electrode portion 50 are provided.

Further, the sensor unit 100 is provided with an insulating ring 60 that electrically insulates the second electrode unit 55 and an end portion of a covering member 23 described later of the signal processing unit 200, which is provided on the rear end side of the insulating ring 60. The outer peripheral surface of the diaphragm head 40 and the housing 30 are composed of a coil spring 70 interposed between the support member 65 supporting the support member 65, the second electrode portion 55, and the conduction member 22 described later, and a film made of an insulator. An insulating layer 80 provided so as to continuously cover the outer peripheral surface on the tip side is provided.

The piezoelectric element 10 as an example of the signal generation unit has a piezoelectric body that exhibits a piezoelectric action of the piezoelectric vertical effect. The piezoelectric longitudinal effect refers to an action in which a charge is generated on the surface of the piezoelectric body in the direction of the charge generation axis when an external force is applied to the stress application axis in the same direction as the charge generation axis of the piezoelectric body. The piezoelectric element 10 according to the present embodiment is housed in the housing 30 so that the center line direction is the direction of the stress application axis. Here, the piezoelectric element 10 and the housing 30 are arranged with a gap between the side surface of the piezoelectric element 10 and the inner wall surface of the housing 30 so as not to come into direct contact with each other.

Next, a case where the piezoelectric lateral effect is used for the piezoelectric element 10 will be illustrated. The piezoelectric lateral effect refers to an action in which a charge is generated on the surface of the piezoelectric body in the direction of the charge generation axis when an external force is applied to the stress application axis located at a position orthogonal to the charge generation axis of the piezoelectric body. A plurality of piezoelectric bodies formed thinly in a thin plate shape may be laminated, and by laminating in this way, the electric charge generated in the piezoelectric body can be efficiently collected to increase the sensitivity of the sensor. Examples of the piezoelectric single crystal include the use of langasite-based crystals (langasite, langateite, langanite, LGTA) having a piezoelectric longitudinal effect and a piezoelectric lateral effect, quartz, gallium phosphate, and the like. The piezoelectric element 10 of the present embodiment uses a Langatate single crystal as the piezoelectric body.

The housing 30 as an example of the body portion has a first housing 31 provided on the front end side and a second housing 32 provided on the rear end side.
The first housing 31 is a thin-walled cylindrical member in which cylindrical holes 310 formed so as to have different diameters stepwise from the front end side to the rear end side are formed inside. On the outer peripheral surface of the first housing 31, a protruding portion 315 protruding from the outer peripheral surface is provided at the center in the center line direction over the entire area in the circumferential direction.
The hole 310 is composed of a first hole 311 formed in order from the front end side to the rear end side, and a second hole 312 having a hole diameter larger than the hole diameter of the first hole 311. The protruding portion 315 has an inclined surface 315a whose diameter gradually increases from the front end side to the rear end side at the front end portion, and a vertical surface 315b perpendicular to the center line direction at the rear end portion.

The second housing 32 is a tubular member in which cylindrical holes 320 formed so as to have different diameters stepwise from the front end side to the rear end side. An outer peripheral surface 330 formed so that the diameter is gradually different toward the rear end side is provided.
The holes 320 are formed from the first hole 321 and the second hole 322 having a hole diameter smaller than the hole diameter of the first hole 321 and the hole diameter of the second hole 322, which are formed in order from the front end side to the rear end side. From the third hole 323 with a large hole diameter, the fourth hole 324 with a hole diameter larger than the hole diameter of the third hole 323, and the fifth hole 325 with a hole diameter larger than the hole diameter of the fourth hole 324. It is composed.
The hole diameter of the first hole 321 is the outer peripheral surface of the first housing 31 so that the tip end portion of the second housing 32 is fitted (press-fitted) to the rear end portion of the first housing 31. It is set to be less than or equal to the diameter of.

The outer peripheral surface 330 has a first outer peripheral surface 331, a second outer peripheral surface 332 having an outer diameter larger than the outer diameter of the first outer peripheral surface 331, and a second outer peripheral surface 332 from the front end side to the rear end side. From the outer diameter of the third outer peripheral surface 333 having an outer diameter larger than the outer diameter of, the fourth outer peripheral surface 334 having an outer diameter larger than the outer diameter of the third outer diameter surface 333, and the outer diameter of the fourth outer peripheral surface 334. Is also composed of a fifth outer peripheral surface 335 having a small outer diameter. At the tip of the second outer peripheral surface 332, a male screw 332a screwed into the female screw 4e of the cylinder head 4 is formed. A first sealing member 71, which will be described later, is fitted into the third outer peripheral surface 333 by a clearance fit, and the dimensional tolerance between the outer diameter of the third outer peripheral surface 333 and the inner diameter of the first sealing member 71 is, for example, zero. It is set to be 0.2 mm from. The rear end portion of the fourth outer peripheral surface 334 is formed as a regular hexagonal prism having six chamfers at equal intervals in the circumferential direction. At the central portion of the fifth outer peripheral surface 335 in the center line direction, a recess 335a recessed from the outer peripheral surface is formed over the entire circumference.

Further, in the second housing 32, the transition portion from the fourth hole 324 to the fifth hole 325, that is, the tip end portion of the fifth hole 325 is covered with the substrate of the covering member 23 described later of the signal processing unit 200. An abutting surface 340 is provided to which the end surface of the portion 232 on the distal end side abuts. The abutting surface 340 is formed with a pin recess 340a into which a second connection pin 21b of the printed wiring board 210 of the signal processing unit 200, which will be described later, is inserted.

Since the first housing 31 and the second housing 32 are located close to the combustion chamber C, it is desirable to manufacture the first housing 31 and the second housing 32 using a material that can withstand an operating temperature environment of at least -40 to 350 [° C.]. Specifically, it is desirable to use a stainless steel material having high heat resistance, for example, JIS standard SUS630, SUS316, SUS430 and the like.

The diaphragm head 40 as an example of the pressure receiving portion has a cylindrical tubular portion 41 and a plate-shaped closing portion 42 provided on the distal end side of the cylindrical portion 41 and closing the distal end side of the tubular portion 41. doing. Further, the diaphragm head 40 further has a chamfered portion 43 provided by chamfering the outer peripheral surface at the boundary portion between the tubular portion 41 and the closed portion 42 at 45 °. Since the diaphragm head 40 exists in the combustion chamber C having a high temperature and a high pressure, it is desirable that the diaphragm head 40 is made of an alloy having high elasticity and excellent durability, heat resistance, touch resistance, and the like. For example, it can be exemplified as SUH660.

The closing portion 42 is provided on the front end side, that is, the central portion of the surface thereof, and is provided on the front end side, that is, the central portion on the back surface thereof, which is recessed on the piezoelectric element 10 side, and the back surface protruding toward the piezoelectric element 10. It has a convex portion 422 and. In the closed portion 42, the back surface convex portion 422 is located on the back surface of the front surface concave portion 421.

The first electrode portion 50 is a columnar member formed so as to have a stepwise different diameter from the front end side to the rear end side, and the outer diameters of the first columnar portion 51 and the first columnar portion 51. It is composed of a second cylindrical portion 52 having a larger outer diameter. The outer diameter of the first cylindrical portion 51 is smaller than the inner diameter of the tubular portion 41 of the diaphragm head 40, and the outer diameter of the second cylindrical portion 52 is substantially the same as the hole diameter of the first hole 311 of the first housing 31. Is. Then, the end surface on the front end side of the first cylindrical portion 51 is the back surface convex portion 422 of the closing portion 42 of the diaphragm head 40, and the end surface on the rear end side of the second cylindrical portion 52 is the front end side surface of the piezoelectric element 10. Arranged to touch. At least one of the contact between the outer peripheral surface of the second cylindrical portion 52 and the inner peripheral surface of the first housing 31 and the contact between the end surface on the distal end side of the first cylindrical portion 51 and the diaphragm head 40 occurs. As a result, the tip of the piezoelectric element 10 is electrically connected to the housing 30.
The first electrode portion 50 causes the pressure in the combustion chamber C to act on the piezoelectric element 10, and the end face on the rear end side of the second cylindrical portion 52, which is the end face on the piezoelectric element 10 side, is the piezoelectric element 10. It is formed to a size that can push the entire surface of the end face. Further, in the first electrode portion 50, both end faces in the center line direction are parallel (orthogonal in the center line direction) and smooth so that the pressure received from the diaphragm head 40 can be evenly applied to the piezoelectric element 10. It is formed.
It can be exemplified that the material of the first electrode portion 50 is stainless steel.

The second electrode portion 55 is a columnar member, and is arranged so that the end face on the front end side comes into contact with the end face on the rear end side of the piezoelectric element 10 and the end face on one end side comes into contact with the insulating ring 60. Will be done. A columnar projecting portion 55a projecting from the end surface to the rear end side is provided on the end surface of the second electrode portion 55 on the rear end side. The protruding portion 55a has a base end portion on the end face side and a tip portion having an outer diameter smaller than the outer diameter of the base end portion. The outer diameter of the protruding portion 55a is set smaller than the inner diameter of the insulating ring 60, and the length of the protruding portion 55a is set longer than the width (length in the center line direction) of the insulating ring 60. The tip is exposed from the insulating ring 60. The second electrode portion 55 is a member that acts to apply a constant load to the piezoelectric element 10 with the first electrode portion 50, and the end face on the piezoelectric element 10 side is the piezoelectric element 10. It is formed in a size that can push the entire surface of the end face, and is formed in a parallel and smooth surface. The outer diameter of the second electrode portion 55 is set to be smaller than the hole diameter of the second hole 312 of the first housing 31, and the outer peripheral surface of the second electrode portion 55 and the first housing 31 There is a gap between it and the inner peripheral surface.
It can be exemplified that the material of the second electrode portion 55 is stainless steel.

The insulating ring 60 is a cylindrical member made of alumina ceramics or the like, and its inner diameter (hole diameter at the center) is slightly larger than the outer diameter of the base end of the protruding portion 55a of the second electrode portion 55. The outer diameter is set to be substantially the same as the hole diameter of the second hole 312 of the first housing 31. The second electrode portion 55 is arranged so that the protruding portion 55a is inserted into the hole at the center of the insulating ring 60 so that the center position and the center of the second hole 312 of the first housing 31 are the same. It is arranged so as to be.

The support member 65 is a tubular member having a plurality of columnar holes 650 having different diameters formed inside from the front end side to the rear end side and having the same outer peripheral surface.
The holes 650 are formed from the first hole 651, the second hole 652 having a hole diameter larger than the hole diameter of the first hole 651, and the hole diameter of the second hole 652, which are formed in order from the front end side to the rear end side. Also consists of a third hole 653 with a large hole diameter. The hole diameter of the first hole 651 is larger than the outer diameter of the base end portion of the protruding portion 55a of the second electrode portion 55, and the protruding portion 55a is exposed to the inside of the support member 65. The hole diameter of the second hole 652 is larger than the outer diameter of the tip portion of the conduction member 22 of the signal processing unit 200, which will be described later. The hole diameter of the third hole 653 is smaller than the outer diameter of the end portion of the covering member 23 of the signal processing unit 200, which will be described later, and the covering member 23 is fitted into the surrounding wall forming the third hole 653 by fitting. Will be combined. As a result, the support member 65 functions as a member that supports the end portion of the cover member 23.

The inner diameter of the coil spring 70 is equal to or greater than the outer diameter of the tip of the protruding portion 55a of the second electrode portion 55 and smaller than the outer diameter of the base end portion, and the outer diameter is the diameter of the insertion hole 22a of the conduction member 22 described later. Smaller than The tip of the protruding portion 55a of the second electrode portion 55 is inserted inside the coil spring 70, and the coil spring 70 is inserted into the insertion hole 22a of the conduction member 22, which will be described later. The length of the coil spring 70 is set to a length that can be interposed between the second electrode portion 55 and the conductive member 22 in a compressed state. As the material of the coil spring 70, it is preferable to use an alloy having high elasticity and excellent durability, heat resistance, touch resistance and the like. Further, it is preferable to enhance the electric conduction by plating the surface of the coil spring 70 with gold.

The insulating layer 80 as an example of the covering portion is formed of an insulating material having a low thermal conductivity, and is exposed to the outside in the diaphragm head 40 and to the outside in the first housing 31. The first, excluding all of the surfaces and a part of the front end side of the surface exposed to the outside in the second housing 32 (excluding the fourth outer peripheral surface 334 and the fifth outer peripheral surface 335 which are relatively rear end sides). The outer peripheral surface 331, the second outer peripheral surface 332, and the third outer peripheral surface 333) are continuously covered.

The material of the insulating layer 80 may be an inorganic material or an organic material as long as it is an insulating material. Here, as an example, it is assumed that the insulating layer 80 made of an inorganic material is used. As the inorganic material constituting the insulating layer 80, ceramics (including amorphous) having excellent durability, heat resistance, corrosion resistance and the like are preferably used, and examples thereof include zirconia, alumina, silica and DLC (diamond-like carbon). Can be done. Further, oxide ceramics, nitride ceramics, carbide ceramics and the like other than those listed here may be used. On the other hand, examples of the organic material constituting the insulating layer 80 include PI (polyimide), PTFE (polytetrafluoroethylene), PEEK (polyetheretherketone) and the like.

The insulating layer 80 may have a single-layer structure or a structure in which a plurality of layers are laminated, but here, as an example, the insulating layer 80 composed of a plurality of layers is used. More specifically, the insulating layer 80 of the present embodiment includes a first insulating layer 81 (an example of a first coating layer) formed on the outer peripheral surface of an object to be formed (housing 30, diaphragm head 40). The second insulating layer 82 (an example of the second coating layer) formed on the first insulating layer 81 and having different characteristics from the first insulating layer 81 has different characteristics from the second insulating layer 82. Moreover, it is provided with a third insulating layer 83 (an example of a third coating layer) formed on the second insulating layer 82. However, the first insulating layer 81 and the third insulating layer 83 may have the same characteristics.

Here, "different characteristics" includes both those having different characteristics due to different constituent materials themselves and those having different characteristics due to different structures even if the constituent materials are the same. Regarding the latter, for example, crystalline / amorphous, particle size, porosity and the like can be mentioned.

In the present embodiment, stabilized zirconia in which yttria oxide is added as a stabilizer to zirconia is used as the first insulating layer 81 to the third insulating layer 83 constituting the insulating layer 80, respectively. Then, in the present embodiment, the first insulating layer 81 and the third insulating layer 83 are made denser than the second insulating layer 82 (the second insulating layer 82 is the first insulating layer 81 and the third insulating layer 81). The film is sparser than the insulating layer 83).

In the present embodiment, the insulating layer 80 has a three-layer structure, but it may have a single-layer structure, a two-layer structure, or a four-layer structure or more.

Here, the relationship between the housing 30 (first housing 31, the second housing 32) and the diaphragm head 40 based on the pressure detecting device 5 and the insulating layer 80 will be described. In the following, the housing 30 and the diaphragm head 40 are collectively referred to as a “housing unit”.

The housing unit of this embodiment is made of a metal material (stainless steel in this example) as described above. On the other hand, the insulating layer 80 is made of an inorganic material (stabilized zirconia in this example) as described above. Therefore, in the present embodiment, the conductivity of the insulating layer 80 is lower than the conductivity of the housing unit.

Then, in the present embodiment, each material is selected so that the thermal conductivity of the insulating layer 80 is lower than the thermal conductivity of the housing unit. In this example, the thermal conductivity of stabilized zirconia is 2-3 (W / m · K) and the thermal conductivity of stainless steel is 16-27 (W / m · K).

Further, in the present embodiment, each material is selected so that the melting point of the insulating layer 80 is higher than the melting point of the housing unit. In this example, the melting point of stabilized zirconia is 2715 (° C.) and the melting point of stainless steel is 1400 to 1500 (° C.).

Further, in the present embodiment, each material is selected so that the coefficient of linear expansion of the insulating layer 80 is close to the coefficient of linear expansion of the housing unit. In this example, the coefficient of linear expansion of stabilized zirconia is 10-11 ( ^10-6 / K) and the coefficient of linear expansion of stainless steel is 9-18 ( ^10-6 / K).

(Signal processing unit)
Next, the signal processing unit 200 will be described.
The signal processing unit 200 as an example of the processing unit has a circuit board unit 21 that at least amplifies an electric signal that is a weak charge obtained from the piezoelectric element 10 of the sensor unit 100, and a circuit board that charges the electric charge generated in the piezoelectric element 10. It includes a rod-shaped conductive member 22 that leads to the portion 21, a covering member 23 that covers the circuit board portion 21, the conductive member 22, and the like, and an O-ring 24 that seals the circuit board portion 21 and the like.

The circuit board unit 21 has a printed wiring board 210 on which electronic components and the like constituting a circuit for amplifying a weak electric charge obtained from the piezoelectric element 10 of the sensor unit 100 are mounted. A first connection pin 21a for electrically connecting the rear end portion of the conductive member 22 and a second connection pin 21b for grounding and positioning are soldered to the front end portion of the printed wiring board 210. It is connected by such as. Further, at the rear end of the printed wiring board 210, three third connection pins 21c that are electrically connected to the control device 6 via the connector 8a at the tip of the transmission cable 8 are connected by soldering or the like. ing. The three third connection pins 21c are used for supplying the power supply voltage and the GND voltage from the control device 6 to the printed wiring board 210 and the output voltage from the printed wiring board 210 to the control device 6, respectively.

The conducting member 22 is a rod-shaped (cylindrical) member, and an insertion hole 22a into which the tip of the protruding portion 55a of the second electrode portion 55 is inserted is formed at the tip portion. The rear end portion of the conducting member 22 is electrically connected to the printed wiring board 210 of the circuit board portion 21 via a conducting wire. Examples of the material of the conductive member 22 include brass and beryllium copper. In this case, brass is desirable from the viewpoint of workability and cost. On the other hand, beryllium copper is desirable from the viewpoint of electrical conductivity, high temperature strength, and reliability.

The covering member 23 is connected to a conductive member covering portion 231 that covers the outer periphery of the conductive member 22, a substrate covering portion 232 that covers the side surfaces and the lower surface of the printed wiring board 210 of the circuit board portion 21, and a third printed wiring board 210. It has a connector portion 233 that covers the periphery of the connection pin 21c and into which the connector 8a at the tip of the transmission cable 8 is fitted.

The conductive member covering portion 231 covers the distal end portion of the conductive member 22 so as to be exposed in the center line direction, and the outer peripheral surface 240 formed so as to have a gradually different diameter from the distal end side to the rear end side is formed. It is provided. The outer peripheral surface 240 has a first outer peripheral surface 241 and a second outer peripheral surface 242 having an outer diameter larger than the outer diameter of the first outer peripheral surface 241 and a second outer peripheral surface 242 from the front end side to the rear end side. It is composed of a third outer peripheral surface 243 having an outer diameter larger than the outer diameter of the third outer peripheral surface 243 and a fourth outer peripheral surface 244 having an outer diameter larger than the outer diameter of the third outer diameter surface 243. The diameter of the first outer peripheral surface 241 is larger than the diameter of the third hole 653 of the support member 65, and the tip portion of the conduction member covering portion 231 forms the third hole 653 of the support member 65. It is fitted (press-fitted) with a tight fit. The diameter of the second outer peripheral surface 242 is formed to be smaller than the diameter of the hole 322 of the second hole 322 of the second housing 32, and the diameter of the third outer peripheral surface 243 is the diameter of the third hole 323 of the second housing 32. It is formed smaller than the hole diameter of. Further, the diameter of the fourth outer peripheral surface 244 is larger than the diameter of the fourth hole 324 of the second housing 32, and the rear end portion of the conductive member covering portion 231 is the fourth hole of the second housing 32. It is fitted (press-fitted) into the surrounding wall forming the 324 by a tight fit. As a result, the conductive member covering portion 231 is supported by contacting at least both ends in the center line direction with the support member 65 and the second housing 32, respectively, so that the conductive member covering portion 231 conducts even in a poor vibration environment. The adverse effect on the member 22 can be suppressed, and it is possible to avoid disconnection of the connecting portion of the conductive member 22 and poor contact due to vibration.

The substrate covering portion 232 is basically a cylindrical portion, and a rectangular opening 232a for installing the printed wiring board 210 inside is provided on the side surface thereof. Further, a ring groove 232b for an O-ring 24 for sealing the inside of the housing 30 and the installation portion of the printed wiring board 210 is formed on the rear end side of the substrate covering portion 232.

The connector portion 233 is a thin portion formed so as to project from the rear end side end surface 232c of the substrate covering portion 232 and cover the periphery of the three third connection pins 21c connected to the printed wiring board 210. The rear end portion of the connector portion 233 is open so that the connector 8a provided at the tip end portion of the transmission cable 8 can be received inside. Further, a hole 233a for communicating the inside and the outside is formed on the rear end side of the connector portion 233, and the hook provided in the connector 8a of the transmission cable 8 is hooked on the hole 233a to catch the transmission cable. The connector 8a of 8 is prevented from falling off from the connector portion 233.

The covering member 23 configured as described above is molded of an insulating material such as resin. Further, the covering member 23 is integrally molded together with the conductive member 22, the first connecting pin 21a, the second connecting pin 21b, and the three third connecting pins 21c. More specifically, in the covering member 23, the heated resin is pushed into a mold in which the conductive member 22, the first connecting pin 21a, the second connecting pin 21b, and the three third connecting pins 21c are set. It is molded by.

When the signal processing unit 200 is unitized, the printed wiring board 210 of the circuit board unit 21 is inserted from the opening 232a of the molded covering member 23 and installed in the central portion of the substrate covering portion 232. When the printed wiring board 210 is installed, the tips of the first connection pin 21a, the second connection pin 21b, and the three third connection pins 21c are passed through the through holes penetrated in the plate thickness direction and soldered. .. After that, the first connecting pin 21a and the conducting member 22 are connected by using a conducting wire. Further, the O-ring 24 is mounted in the ring groove 232b of the substrate covering portion 232 of the covering member 23. The O-ring 24 is a well-known O-ring made of fluorine-based rubber.

(Holding member)
Next, the holding member 300 will be described.
The holding member 300 is a thin-walled cylindrical member, and a protruding portion 300a protruding inward from the inner peripheral surface is provided at the rear end portion. After the holding member 300 is mounted on the second housing 32, the holding member 300 is crimped from the outside by applying pressure to a portion corresponding to the recess 335a provided on the fifth outer peripheral surface 335. As a result, the holding member 300 becomes difficult to move with respect to the housing 30, and the signal processing unit 200 is prevented from moving with respect to the housing 30.

[Electrical connection structure in pressure detector]
Next, the electrical connection structure of the pressure detection device 5 will be described.

(Positive route)
In the pressure detection device 5, the end face (positive electrode) on the rear end side of the piezoelectric element 10 is electrically connected to the second metal electrode portion 55, and the second electrode portion 55 is connected via the protruding portion 55a. It is electrically connected to the metal coil spring 70. Further, the coil spring 70 is electrically connected to the metal conduction member 22, and the conduction member 22 is electrically connected to the positive signal electrode of the printed wiring board 210 via the first connection pin 21a. NS. Hereinafter, the electrical path from the end face on the rear end side of the piezoelectric element 10 to the positive signal electrode of the printed wiring board 210 via the conductive member 22 or the like is referred to as a “positive path”.

(Negative route)
On the other hand, in the pressure detection device 5, the end face (negative electrode) on the tip end side of the piezoelectric element 10 is made of a first metal housing 31 and a second metal through a first metal electrode portion 50 and a diaphragm head 40. It is electrically connected to the housing 32 (housing 30). Further, the second housing 32 is electrically connected to the negative signal electrode of the printed wiring board 210 via the second connection pin 21b. Hereinafter, the electrical path from the end surface of the piezoelectric element 10 on the distal end side to the negative signal electrode of the printed wiring board 210 via the diaphragm head 40, the housing 30, and the like is referred to as a “negative path”.

(Relationship between positive and negative paths)
In the pressure detection device 5 of the present embodiment, a negative path exists outside the positive path. In other words, the positive path is contained inside the negative path. An insulating ring 60 and a covering member 23, each of which is composed of an insulator, are arranged between the positive path and the negative path. Therefore, the positive path and the negative path are electrically insulated by these insulating ring 60 and the covering member 23, and an air gap existing in a part between the two paths.

[Installation of pressure detector]
When the pressure detecting device 5 configured as described above is mounted on the cylinder head 4 of the internal combustion engine 1, the diaphragm head 40 of the sensor unit 100 is first formed in the cylinder head 4 in the communication hole 4a. It is inserted and the male screw 332a formed in the second housing 32 of the housing 30 is screwed into the female screw 4e formed in the communication hole 4a of the cylinder head 4. The pressure detecting device 5 is attached to the cylinder head 4 in a state where the first sealing member 71 and the second sealing member 72 are arranged between the cylinder head 4 and the pressure detecting device 5. At this time, the outer peripheral surfaces of the cylindrical portion 41 and the chamfered portion 43 of the diaphragm head 40, the outer peripheral surface of the first housing 31, the first outer peripheral surface 331 of the second housing 32, and the second outer peripheral surface. The 332 faces the inner peripheral surface of the communication hole 4a of the cylinder head 4. Here, in the present embodiment, the insulating layer 80 is provided on all of the outer peripheral surfaces of the housing units (housing 30 and diaphragm head 40) constituting the pressure detection device 5 and which are housed in the communication hole 4a. In reality, the insulating layer 80 provided in the pressure detection device 5 faces the inner peripheral surface of the communication hole 4a of the cylinder head 4. On the other hand, the fourth outer peripheral surface 334 of the second housing 32, which is not provided with the insulating layer 80, is exposed to the outside of the cylinder head 4.

Then, with the pressure detecting device 5 inserted into the cylinder head 4 of the internal combustion engine 1, a clamp (not shown) is attached to the portion of the regular hexagonal column formed at the rear end of the fourth outer peripheral surface 334 of the pressure detecting device 5. do. The surface of this clamp is covered with an insulator, and the clamp is fixed to the cylinder head 4 with a bolt (not shown), and the pressure detection device 5 is pressed and fixed to the cylinder head 4 by the clamp.

By doing so, when the pressure detection device 5 is attached to the cylinder head 4, the housing unit including the housing 30 and the diaphragm head 40 is not electrically connected to the metal cylinder head 4, and is printed wiring. It is connected to the GND voltage of the control device 6 via the board 210. As described above, the pressure detecting device 5 of the present embodiment is provided with the insulating layer 80, so that the pressure detecting device 5 is electrically insulated from the cylinder head 4 to be mounted.

[Seal member]
Next, the seal member 7 will be described.
The seal member 7 has a first seal member 71 and a second seal member 72. The first seal member 71 is provided with an end surface in the tightening direction of the pressure detection device 5 on the surrounding wall forming the communication hole 4a in the cylinder head 4 and a fourth outer peripheral surface 334 of the housing 30 of the pressure detection device 5. It is arranged between the end face on the tip side of the cylindrical part. As a result, the first sealing member 71 seals between the cylinder head 4 and the pressure detecting device 5. The second seal member 72 is arranged between the inclined portion 4c of the communication hole 4a of the cylinder head 4 and the inclined surface 315a of the first housing 31 of the housing 30 of the pressure detecting device 5. As a result, the second sealing member 72 seals between the cylinder head 4 and the pressure detecting device 5.

It can be exemplified that the first sealing member 71 is a gasket made of an insulator such as PTFE. The cross-sectional shape is preferably S-shaped or substantially rectangular. When the pressure detection device 5 is tightened to the cylinder head 4, the first seal member 71 is deformed so as to shorten the length in the tightening direction by receiving a force in the tightening direction, and the airtightness in the combustion chamber C is reduced. To increase. That is, the contact pressure generated between the first seal member 71 and the cylinder head 4 when the pressure detection device 5 is screwed into the cylinder head 4, and the housing 30 between the first seal member 71 and the pressure detection device 5 The contact pressure generated between the two increases. As a result, it is possible to prevent combustion gas from leaking between the first seal member 71 and the cylinder head 4, and between the first seal member 71 and the housing 30 of the pressure detection device 5. Further, since the first sealing member 71 is made of an insulator, the end surface on the tip end side of the columnar portion provided with the fourth outer peripheral surface 334 of the pressure detecting device 5 and the cylinder head 4 are separated from each other. I try not to connect electrically.

It can be exemplified that the second sealing member 72 is a ring-shaped O-ring made of stainless steel or aluminum and having a circular cross section. When the pressure detection device 5 is tightened to the cylinder head 4, the second seal member 72 is formed by the inclined portion 4c of the communication hole 4a of the cylinder head 4 and the inclined surface 315a of the first housing 31 of the housing 30. It deforms by receiving a force in the direction intersecting the tightening direction, and enhances the airtightness in the combustion chamber C. That is, when the pressure detection device 5 is screwed into the cylinder head 4, the contact pressure generated between the second seal member 72 and the inclined portion 4c of the communication hole 4a of the cylinder head 4 and the second seal member 72 The contact pressure generated between the first housing 31 of the housing 30 and the inclined surface 315a of the first housing 31 increases. As a result, it is possible to prevent combustion gas from leaking between the second seal member 72 and the cylinder head 4, and between the second seal member 72 and the housing 30 of the pressure detection device 5.

[Manufacturing method of pressure detector]
FIG. 7 is a flowchart for explaining a method of manufacturing the pressure detection device 5.

First, a welding step of welding the first housing 31 and the diaphragm head 40 and welding the first housing 31 and the second housing 32 is performed (step 10). More specifically, first, the tip end side of the first housing 31 is inserted (press-fitted) from the rear end side of the diaphragm head 40, and the rear end side of the diaphragm head 40 and the tip end side of the first housing 31 are formed. The diaphragm head 40 and the first housing 31 are welded (joined) by irradiating the contacting portion (outer peripheral surface) with a laser beam from a direction intersecting the center line direction (for example, a direction orthogonal to the center line direction). )do. Subsequently, the tip end side of the second housing 32 is inserted (press-fitted) from the rear end side of the first housing 31, and the rear end side of the first housing 31 and the tip end side of the second housing 32 come into contact with each other. The first housing 31 and the second housing 32 are welded (joined) by irradiating the portion (outer peripheral surface) with a laser beam from a direction intersecting the center line direction (for example, a direction orthogonal to the center line direction). )do. As a result, a housing unit in which the diaphragm head 40 and the first housing 31 and the second housing 32 are integrated is obtained. In step 10, the order of laser welding may be changed before and after. Further, in step 10, a welding method other than laser welding may be used.

Next, an insulating layer forming step of forming the insulating layer 80 on the outer peripheral surface of the housing unit obtained in step 10 is executed (step 20). Here, as an example, a step of forming the insulating layer 80 of the above-mentioned three-layer structure (first insulating layer 81, second insulating layer 82, and third insulating layer 83) will be described. In this insulating layer forming step, in order to obtain the insulating layer 80 having a three-layer structure, first, the first insulating layer forming step of forming the first insulating layer 81 is executed (step 21), and then the second insulating layer is formed. The second insulating layer forming step of forming the 82 is executed (step 22), and finally, the third insulating layer forming step of forming the third insulating layer 83 is executed (step 23). Further, in the insulating layer forming step of the present embodiment, the insulating layer 80 is not formed on the fourth outer peripheral surface 334 and the fifth outer peripheral surface 335 of the second housing 32 among the outer peripheral surfaces of the housing unit. To. Then, in the present embodiment, as a method for forming the insulating layer 80, fine powder (raw material particles) of the dried raw material (ceramics in this case) is conveyed in a gas (carrier gas) in a solid phase state from a nozzle. The AD (aerosol deposition) method was used, which realized a low-temperature and high-speed thick film coating by injecting and colliding with a formation target (here, a housing unit). The details of the film formation by the AD method will be described later.

Subsequently, an assembly step of assembling various members constituting the pressure detection device 5 such as the piezoelectric element 10 is executed from the rear end side of the housing unit in which the insulating layer 80 is formed on the outer peripheral surface in step 20 (step 30). .. From the above, the pressure detection device 5 is obtained.

[Membrane film]
FIG. 8 is a schematic configuration diagram of a film forming apparatus 500 used for forming the insulating layer 80.
The film forming apparatus 500 is connected to a chamber 510 that internally accommodates a housing unit to be film-deposited, a pedestal 510 that is provided in the chamber 510 and to which the housing unit is attached, and a chamber 510, and depressurizes the inside of the chamber 510. It is equipped with a rotary pump 530. Further, the film forming apparatus 500 accommodates a gas cylinder 540 for supplying a carrier gas and a raw material particle (for example, DLC particle) 550 inside, and an aerosol in which the raw material particle 550 is aerosolized by the carrier gas supplied from the gas cylinder 540. It includes a generator 560 and a nozzle 570 that is provided in the chamber 510 and ejects aerosolized raw material particles 550 supplied from the aerosol generator 560 toward a housing unit attached to a pedestal 520.

In the film forming apparatus 500 of the present embodiment, the pedestal 520 is provided so as to be movable in all directions in the chamber 510, and the nozzle 570 not only faces the housing unit attached to the pedestal 520 but also faces the nozzle 570. For example, it can be slanted and opposed to each other.

Then, in the present embodiment, the first insulating layer having different characteristics is adjusted by adjusting the particle size of the raw material particles 550 used in the film forming apparatus 500, the injection speed of the carrier gas and the raw material particles 550 from the nozzle 570, and the like. 81, the second insulating layer 82 and the third insulating layer 83 are formed.

In the present embodiment, the insulating layer 80 constituting the pressure detection device 5 is formed by the AD method described above, but the method for forming the insulating layer 80 is not limited to this. Examples of other methods for forming the insulating layer 80 include various PVD (physical vapor deposition) methods, various CVD (chemical vapor deposition) methods, and various coating (spin coating, dip coating, spray coating, etc.) methods. Be done.

[Pressure detection operation by pressure detection device]
Then, the pressure detection operation of the internal combustion engine 1 by the pressure detection device 5 will be described.
When the internal combustion engine 1 is operating, the pressure (combustion pressure) due to the combustion gas generated in the combustion chamber C is applied to the tip end side (surface) of the closed portion 42 in the diaphragm head 40. In the diaphragm head 40, the pressure received on the front surface concave portion 421 side is transmitted to the back surface convex portion 422 on the back surface side, and acts on the piezoelectric element 10 sandwiched between the first electrode portion 50 and the second electrode portion 55. As a result, the piezoelectric element 10 is charged according to the combustion pressure. Then, the electric charge generated in the piezoelectric element 10 is supplied to the circuit board portion 21 via the second electrode portion 55, the coil spring 70, and the conduction member 22. The electric charge supplied to the circuit board unit 21 is amplified by the circuit board unit 21, and then a voltage corresponding to the electric charge is applied to the third connection pin 21c and the transmission cable 8 connected to the circuit board unit 21. It is supplied to the control device 6 via.

[Effect of insulating layer]
The pressure detection device 5 of the present embodiment is attached to the internal combustion engine 1 (more specifically, the cylinder head 4), and when the internal combustion engine 1 is mounted on an automobile, it is generated outside the internal combustion engine 1. Noise enters the cylinder head 4 of the internal combustion engine 1.

Here, in the present embodiment, of the outer peripheral surfaces of the housing unit (housing 30 and diaphragm head 40) constituting the pressure detection device 5, a portion facing the inner peripheral surface of the communication hole 4a provided in the cylinder head 4. The insulating layer 80 was provided in the. Therefore, in the present embodiment, the negative path in the pressure detection device 5 and the cylinder head 4 of the internal combustion engine 1 are electrically insulated from each other. Therefore, the noise that has entered the cylinder head 4 is less likely to be propagated to the printed wiring board 210 via the housing unit of the pressure detection device 5 due to the presence of the insulating layer 80. As a result, the fluctuation (fluctuation) of the potential in the printed wiring board 210 due to noise is suppressed, and the fluctuation (fluctuation) of the output signal output from the printed wiring board 210 to the outside (control device 6 or the like) is suppressed. Can be reduced.

[Insulation of insulating layer]
The pressure detection device 5 is attached by being inserted into the communication hole 4a provided in the cylinder head 4, and the diaphragm head 40 of the sensor unit 100 receives a very large pressure. Therefore, the outer shape of the pressure detection device 5 and the communication hole High precision is required for the inner wall shape of 4a. Further, a male screw 332a is formed in the housing 30 of the sensor unit 100, and a female screw 4e is formed in the communication hole 4a. When the pressure detection device 5 is attached to the cylinder head 4, the male screw 332a of the sensor unit 100 communicates with the housing 30. It is screwed into the female screw 4e of the hole 4a. Therefore, if the insulating layer 80 is formed thick, it becomes difficult to attach the pressure detecting device 5 to the cylinder head 4. Further, if the pressure detecting device 5 is forcibly inserted into the communication hole 4a, the insulating layer 80 may be damaged. Therefore, from the viewpoint of mounting the pressure detecting device 5 on the cylinder head 4, the thinner the insulating layer 80 is, the better.

However, when the same material is used as the insulator, the insulating property of the insulating layer 80 becomes lower as it is made thinner. Therefore, with respect to the noise that needs to be removed, the insulating layer 80 needs to secure an insulating property that can remove the noise. Next, the range of insulation required in the insulating layer 80 is examined in consideration of the electrical influence on the pressure detection device 5 for some noise sources. Further, from the viewpoint of manufacturing the pressure detection device 5, attaching it to the cylinder head 4, and forming a film of the insulating layer 80, a realistic range of insulating properties of the insulating layer 80 will be examined.

(Examination of inductive noise resistance test)
First, an inductive noise resistance test is carried out to examine the insulating properties required for the insulating layer 80. In the inductive noise resistance test, noise based on a main noise source is generated, and the amount of output voltage fluctuation detected by the pressure detection device 5 is measured. Here, four main noise sources are assumed: "horn", "light", "wiper", and "igniter". In the "horn", the amount of output voltage fluctuation detected by the pressure detection device 5 when the horn (horn) of an automobile is sounded is measured. In the "light", the amount of output voltage fluctuation detected by the pressure detection device 5 is measured with the headlight of the automobile turned on. In the "wiper", the amount of output voltage fluctuation detected by the pressure detection device 5 is measured while the wiper of the automobile is operated. The "igniter" is an engine ignition device, which periodically generates a high voltage of several tens of kV to generate sparks, although the period differs depending on the engine speed. In the "igniter", each noise source of "horn", "light", and "wiper" and the igniter are driven at the same time, and the amount of output voltage fluctuation detected by the pressure detection device 5 is measured. Therefore, the output voltage fluctuation amount due to the "igniter" is measured by superimposing it on the output voltage fluctuation amount due to each noise source of the "horn", "light", and "wiper".

FIG. 9 is a diagram schematically showing the electrical structures of the pressure detection device 5 and the control device 6 according to the present embodiment. Referring to FIG. 9, in the pressure detection device 5, the piezoelectric element 10 and the IC (Integrated Circuit) 211 provided on the circuit board portion 21 of the signal processing unit 200 are electrically connected. The IC 211 is provided on the printed wiring board 210 of the circuit board unit 21, for example, and has a function of processing a signal from the sensor unit 100 of the signal processing unit 200. Further, the IC 211 is connected to the control device 6 by a harness (transmission cable 8) including a power supply line, a signal line, and a ground line. Specifically, the IC 211 is connected to the LPF (Low-pass filter) 602 of the control device 6 by a signal line (CPS Sig) via a resistor 212 of 470 Ω. Further, for the IC 211, the power supplied from the battery 9 is controlled by the voltage control unit (regulator: REG) 601 of the control device 6 to a voltage of 5 volts, and is controlled by the power supply line (+ 5V) as the power supply voltage. It is being supplied. Further, the power supply line is connected to the output of the IC 211 in the circuit board section 21 via a 5.1 kΩ resistor 213. Further, the ground of the IC 211 is branched at the circuit board section 21, and one is connected to the GND voltage of the control device 6 by a ground wire (GND). The GND voltage of the control device 6 is connected to the negative pole of the battery 9. The other is electrically connected to the housing 30 of the pressure detection device 5. Further, the signal line connecting the IC211 of the pressure detection device 5 and the LPF602 of the control device 6 is branched at the control device 6 and connected to the ground voltage of the control device 6 via a resistor 603 of 300 kΩ. Further, the cylinder head 4 to which the pressure detection device 5 is mounted is connected to the negative pole of the battery 9, but since the housing 30 of the pressure detection device 5 is formed with the insulating layer 80, the housing 30 and the cylinder It is not electrically connected to the head 4.

FIG. 10 is a diagram showing an outline of an induction noise resistance test. As shown in FIG. 10, in the induction noise resistance test, the pressure detection device 5 is attached to the control device 6 via the transmission cable 8, and the noise signal generator 401 is placed close to the transmission cable 8 at a predetermined distance for control. The output voltage of the device 6 is measured with an oscilloscope 402. The noise signal generator 401 is driven by a battery 9 connected to the noise signal generator 401, and generates pseudo noise from four noise sources, a "horn", a "light", a "wiper", and an "igniter". By arranging the cable connecting the noise signal generator 401 and the battery 9 and the transmission cable 8 connecting the pressure detection device 5 and the control device 6 in close proximity to each other, the cable of the noise signal generator 401 is changed to the transmission cable 8. It makes it easier to induce noise. Further, the cable of the noise signal generator 401 and the ground wire of the transmission cable 8 are electrically connected via the negative pole of the battery 9. With such a connection, not only the inductive noise between the cables but also the wraparound noise from the ground wire of the transmission cable 8 via the negative pole of the battery 9 can be evaluated at the same time as the inductive noise. ..

FIG. 11 is a chart showing the results of the induction noise resistance test. FIG. 12 is a graph plotting the test results of FIG. In the graph of FIG. 12, the vertical axis represents the output voltage fluctuation amount (unit: millivolt: mV), and the horizontal axis represents the resistance between the housing 30 of the pressure detection device 5 and the cylinder head 4 (insulation resistance due to the insulating layer 80). , Is a semi-logarithmic graph showing the horizontal axis on a logarithmic scale.

In the inductive noise resistance test, the output voltage fluctuation amount when the engine speed (igniter speed) was 666 rpm and 2000 rpm was measured for the above-mentioned three types of noise sources. In each figure, as test items, the noise caused by the noise source "horn" at the engine speed (igniter speed) of 666 rpm is "666 horn", the noise caused by the noise source "light" is "666 light", and the noise source "wiper". The noise caused by "666 wiper" is described as "666 wiper". Similarly, when the engine speed (igniter speed) is 2000 rpm, the noise caused by the noise source "horn" is "2000 horn", the noise caused by the noise source "light" is "2000 light", and the noise caused by the noise source "wiper" is "2000 light". 2000 wiper "is described.

With reference to FIG. 12, the graph of each test item converges at a resistance value of 300 Ω or 510 Ω or more. Referring to FIG. 11, the resistance value is 300Ω or more, and the output voltage fluctuation amount is smaller than 25 mV. In particular, when the resistance value is 510Ω or more, the measurement result is that the output voltage fluctuation amount exceeds 20 mV. There is one or less test item, and when the resistance value is 300, the measurement result is that the output voltage fluctuation amount exceeds 20 mV. There are three items ("666 horn", "666 wiper", "2000 wiper"). Therefore, from these test results, the minimum value of the insulation resistance of the insulating layer 80 that can eliminate the electrical influence of each noise source assumed in the inductive noise resistance test can be set to 510Ω.

(Examination of electrical effects due to disconnection detection structure)
Next, the insulation against electrical influences due to the disconnection detection structure will be examined. As described with reference to FIG. 9, the pressure detection device 5 and the control device 6 are connected by a signal line (CPS Sigma), a power supply line (+ 5V), and a ground line (GND). In the configuration shown in FIG. 9, when the ground wire is broken, the pressure detection device 5 does not operate. Then, the voltage of 5 volts supplied by the power supply line is acquired by the control device 6 as the output voltage of the pressure detection device 5, so that it is detected that the ground wire is broken. Here, for comparison, the electrical structure when the insulating layer 80 is not formed in the housing 30 of the pressure detection device 5 will be described.

FIG. 13 is a diagram schematically showing the electrical structure of the pressure detection device 5 and the control device 6 when the insulating layer 80 is not formed on the housing 30 of the pressure detection device 5. The configuration shown in FIG. 13 differs from the configuration shown in FIG. 9 only in that the housing 30 and the cylinder head 4 are electrically connected because the insulating layer 80 is not formed on the housing 30. Others are the same as the configuration shown in FIG.

As described in FIG. 9, the cylinder head 4 to which the pressure detection device 5 is mounted is connected to the negative pole of the battery 9. Therefore, in the configuration shown in FIG. 13, even if the ground wire connecting the pressure detection device 5 and the control device 6 is disconnected, the ground of the IC 211 is maintained in a grounded state via the housing 30 and the cylinder head 4. .. Therefore, the pressure detection device 5 operates normally, and the control device 6 cannot detect the disconnection of the ground wire.

In the pressure detection device 5 according to the present embodiment, as shown in FIG. 9, an insulating layer 80 is formed in the housing 30. Therefore, if the insulating property of the insulating layer 80 is sufficient, the path of grounding via the housing 30 and the cylinder head 4 can be blocked, and disconnection detection of the ground wire can be effectively performed.

FIG. 14 is a graph showing the relationship between the output voltage of the pressure detecting device 5 and the insulating property of the insulating layer 80 when the ground wire is broken. In the graph of FIG. 14, the vertical axis is the output voltage (unit: millivolt: mV), and the horizontal axis is the resistance between the housing 30 of the pressure detection device 5 and the cylinder head 4 (insulation resistance by the insulating layer 80). It is a semi-logarithmic graph which shows the axis on a logarithmic scale.

Referring to FIG. 14, when the insulation resistance by the insulating layer 80 is 1 kΩ (1.E + 03) or more, the output voltage of the pressure detection device 5 is approximately 5 volts (5000 mV), and the housing 30 and the cylinder head 4 It can be seen that the route connecting the above is completely blocked. Therefore, from this result, the minimum value of the insulation resistance of the insulating layer 80 required for performing the disconnection detection can be set to 1 kΩ. Further, looking at the graph of FIG. 14 in more detail, the output voltage of the pressure detection device 5 is about 5 volts even at 1 kΩ, but the output voltage of the pressure detection device 5 converges at 10 kΩ (1.E + 04) or more. It has almost stopped fluctuating. Therefore, the minimum value of the insulation resistance of the insulating layer 80 required to detect the disconnection may be set to 10 kΩ.

If the disconnection detection function based on the above configuration is not provided, or if disconnection detection is performed by a method different from the above configuration, it is necessary to secure the above-mentioned 1 kΩ (or 10 kΩ) insulation resistance in the insulating layer 80. No. Therefore, in this case, as described with reference to FIGS. 9 to 12, it is sufficient to secure an insulation resistance of 510 Ω or more in the insulating layer 80 that can eliminate the influence of noise caused by the main noise sources.

(Study on electrical effect due to potential difference between grounds)
Next, the insulation property against the electrical influence due to the potential difference between grounds will be examined. As described above, when the disconnection detection structure is incorporated into the electrical structure including the pressure detection device 5 and the control device 6, the ground of the IC 211 provided on the circuit board portion 21 of the signal processing unit 200 is transferred to the housing 30 and the cylinder head 4. It is necessary to block the path that electrically connects with. In the above example, this path is blocked by providing the insulating layer 80 formed in the housing 30 with sufficient insulating properties. However, the configuration for blocking this route is not limited to the above. For example, this path can also be blocked by providing a capacitor in the path from the ground of the IC 211 to the housing 30.

FIG. 15 is a diagram schematically showing the electrical structures of the pressure detection device 5 and the control device 6 when the capacitor is arranged on the path connecting the circuit board portion 21 and the housing 30. The configuration shown in FIG. 15 differs from the configuration shown in FIG. 9 only in that the capacitor 90 is electrically cut off by arranging the capacitor 90 on the path connecting the circuit board portion 21 and the housing 30. Others are the same as the configuration shown in FIG. In the configuration shown in FIG. 15, the insulating layer 80 is formed on the housing 30, and the housing 30 and the cylinder head 4 are not electrically connected to each other. However, since the path from the ground of the IC 211 to the housing 30 and the cylinder head 4 is blocked by the capacitor 90, the disconnection detection structure is maintained even if the insulation resistance of the insulating layer 80 is smaller than 1 kΩ as described above. ..

Here, consider the potential difference between grounds. In considering the potential difference between grounds, it is assumed that the housing 30 and the cylinder head 4 are electrically connected as shown in FIG. 13 without considering the insulating layer 80.

In the configuration shown in FIG. 15, the ground of the cylinder head 4 and the control device 6 are both connected to the negative pole of the battery 9. Therefore, theoretically, there is no potential difference between the cylinder head 4 and the ground of the control device 6. However, in reality, both the cylinder head 4 and the control device 6 are physically separated from the negative pole of the battery 9, and the wiring between them acts as a resistor. A potential difference may occur between 4 and the ground of the control device 6. This also applies to the configurations shown in FIGS. 9 and 13.

If the path from the ground of the IC 211 to the cylinder head 4 via the housing 30 is connected as in the configuration shown in FIG. 13, the path connected to the negative pole of the battery 9 constitutes a closed circuit. Therefore, even if a potential difference occurs between the cylinder head 4 and the ground of the control device 6, a current flows through this closed circuit and the potential difference is immediately eliminated. On the other hand, in the configuration shown in FIG. 15, since the capacitor 90 is arranged on the path (between the circuit board portion 21 and the housing 30) and the path is cut off, the cylinder head 4 and the ground of the control device 6 are grounded. The potential difference between them is not eliminated.

If there is a potential difference between grounds as described above, noise due to this may occur. Specifically, when an AC signal due to disturbance is applied to the housing 30 in the presence of a potential difference between grounds, the electric charge accumulated in the housing 30 acts on the piezoelectric element 10 from the housing 30, and the piezoelectric element 10 applies pressure. It is possible that a signal (noise) is output even though it has not been received.

In the pressure detection device 5 according to the present embodiment, as shown in FIG. 15, an insulating layer 80 is formed in the housing 30. Therefore, if the insulating property of the insulating layer 80 is sufficient, it is possible to prevent the AC signal due to the disturbance from being applied to the housing 30 and suppress the generation of noise due to the potential difference between the grounds. Hereinafter, a test in which an AC voltage is applied between the cylinder head 4 and the ground of the control device 6 and the output voltage (noise) of the piezoelectric element 10 is measured while changing the insulation resistance of the insulating layer 80 will be described.

FIG. 16 is a chart showing the results of the above-mentioned inter-ground potential difference test. FIG. 17 is a graph plotting the test results of FIG. In the graph of FIG. 17, the vertical axis is the output voltage (AC voltage Vpp, the unit is millivolt: mV), and the horizontal axis is the resistance between the housing 30 of the pressure detection device 5 and the cylinder head 4 (due to the insulating layer 80). Insulation resistance) is a semi-logarithmic graph showing the horizontal axis on a logarithmic scale.

In this test of the potential difference between grounds, a 2 μF capacitor was used as the capacitor 90, and the housing 30 was compared with the housing 30.

1Vp-p sine wave / frequency 0.01kHz, 0.1kHz, 1kHz, 10kHz

The output voltage of the sensor unit 100 was measured by applying the above four types of AC voltage and gradually changing the insulation resistance of the insulating layer 80 from 0Ω (short) to 5GΩ. In FIG. 16, “open” is the acquired data when the sensor unit 100 is covered with a rubber cap or the like to achieve a completely insulated state.

Referring to FIG. 16, the insulation resistance of the insulating layer 80 is 1 MΩ or more, and the output voltage with respect to the applied voltage of all frequencies is 1 mV or less. Further, referring to the graph of FIG. 17, the graph of each frequency converges at 1 MΩ (1.E + 06) or more. Therefore, from this result, the minimum value of the insulation resistance of the insulating layer 80 required to be unaffected by the potential difference between grounds is set to 1 MΩ.

It should be noted that the potential difference between the cylinder head 4 and the ground of the control device 6 is such that the potential difference does not occur due to, for example, devising the layout, or the potential difference is small enough not to cause the above-mentioned electrical influence. Can be. As an example, it is conceivable to arrange the internal combustion engine 1 and the control device 6 at close positions. In such a case, it is not necessary to secure the above-mentioned 1 MΩ insulation resistance in the insulating layer 80. Therefore, in this case, as described with reference to FIGS. 9 to 12, it is sufficient to secure an insulation resistance of 510 Ω or more in the insulating layer 80 that can eliminate the influence of noise caused by the main noise sources.

(Examination of the maximum value of insulation resistance of the insulating layer)
In the above study, assuming a noise source, the minimum value of the required insulation resistance of the insulating layer 80 is derived based on the electrical influence of the noise source on the pressure detection device 5. By the way, the insulation resistance of the insulating layer 80 increases as the thickness of the insulating layer 80 increases. Therefore, from the viewpoint of insulating property, in order to improve the insulating property of the insulating layer 80, it is more effective to form the insulating layer 80 thicker. However, as described above, high accuracy is required for the outer shape of the housing 30 and the inner wall shape of the communication hole 4a for mounting the pressure detection device 5 on the cylinder head 4. Therefore, the insulating layer 80 cannot be made infinitely thick, and the upper limit of the thickness of the insulating layer 80 is such that the male screw 332a of the sensor unit 100 is not damaged when screwed into the female screw 4e of the communication hole 4a. There is a need. The insulation resistance of the insulating layer 80 formed to this thickness can be said to be the practical maximum value of the insulation resistance.

The thickness of the insulating layer 80 that is not damaged when the male screw 332a of the sensor unit 100 is screwed into the female screw 4e of the communication hole 4a can be specified based on the gap between the male screw 332a and the female screw 4e that is allowed by design. As an example, the male screw 332a of the sensor unit 100 is used as an M8 male screw, and the gap between the male screw 332a and the female screw 4e, the thickness of the insulating layer 80, and the insulation resistance are examined.

The male screw 332a of the sensor unit 100 and the female screw 4e of the communication hole 4a have the following dimensions and tolerances based on JIS B 0205-4 and JIS B 0209-3.

Reference dimension Nominal: M8, Pitch: 1.25 mm, Crest height: 0.677 mm, Male screw outer diameter: 8 mm, Effective diameter: 7.188 mm, Female screw inner diameter: 6.647 mm

Tolerance (screw with nominal diameter 8 mm, pitch 1.25 mm)
Female thread tolerance range class: 6G, effective diameter ES (upper tolerance): +188 μm, effective diameter EI (lower tolerance): + 28 μm, inner diameter ES: +293 μm, inner diameter EI: +28 μm,

Male thread tolerance class: 6 g, effective diameter es (upper tolerance): -28 μm, effective diameter ei (lower tolerance): -146 μm, inner diameter es: -28 μm, outer diameter ei: -240 μm,

Regarding the root diameter of the screw, JIS B 0209-3 only states that "the valley bottom shape of the body of the dimensional tolerance female screw and the male screw must not exceed the boundary of the reference chevron at any point." No specific diameter value is specified.

The gap between the male screw 332a and the female screw 4e is obtained as the difference between the outer diameter of the male screw 332a and the valley diameter of the female screw 4e, or the difference between the inner diameter of the female screw 4e and the valley diameter of the male screw 332a. As described above, a specific numerical value is not specified for the valley diameter, but for the male screw 332a, for example, a value of design information or an actually measured value can be obtained. Therefore, using the inner diameter of the female screw 4e and the valley diameter of the male screw 332a, the gap between the male screw 332a and the female screw 4e is obtained as follows. The value of the valley diameter of the male screw 332a below is an example.

Range of inner diameter of female screw 4e:
6.647mm + 0.293mm ~ 6.647mm + 0.028mm
Maximum inner diameter of female screw 4e: 6.940 mm (= 6.647 mm + 0.293 mm)

Range of valley diameter of male screw 332a: 6.269 mm to 6.592 mm
Minimum value of valley diameter of male screw 332a: 6.269 mm

Difference between the maximum inner diameter of the female screw 4e and the minimum valley diameter of the male screw 332a:
0.671 mm (= 6.940 mm to 6.269 mm)

The above difference is the total of the gaps generated on both sides of the male screw 332a and the female screw 4e in the radial direction. Therefore, the gap between the male screw 332a and the female screw 4e is

0.3355 mm (= 0.671 mm / 2)

Will be.

From here, the maximum value of the thickness of the insulating layer 80 can be set within a range within the gap between the male screw 332a and the female screw 4e. As an example, the maximum value of the thickness of the insulating layer 80 is assumed to be 0.1 mm, and the insulating resistance of the insulating layer 80 is obtained. The value of the insulation resistance according to the thickness of the insulating layer 80 differs depending on the type of the material of the insulating layer 80. For example, a DLC film, which is one of the materials of a typical insulating layer 80, exhibits an insulation resistance of 1 MΩ at a thickness of about 0.001 mm. Therefore, when the insulating layer 80 having a thickness of 0.1 mm is formed by the DLC film, an insulating resistance having a resistance value of 100 MΩ can be obtained. This is the minimum value (510Ω) of the insulation resistance of the insulation layer 80 that can eliminate the electrical influence of each noise source assumed in the above-mentioned induction noise resistance test, and the insulation layer 80 required to detect disconnection. It is a value larger than either the minimum value of the insulation resistance (1 kΩ) or the minimum value of the insulation resistance of the insulation layer 80 (1 MΩ) required to be unaffected by the potential difference between grounds.

Further, as another example of the material of the typical insulating layer 80, consider the case where the passive film of _{Cr 2} O _{3 is used for the insulating layer 80.} In this case, the thickness of the passivation that can be formed is at most several nm, and fits in the gap between the male screw 332a and the female screw 4e described above. The value of the insulation resistance of the insulating layer 80 having a thickness of several nm is several hundred MΩ. This is also the minimum value (510Ω) of the insulation resistance of the insulation layer 80 that can eliminate the electrical influence of each noise source assumed in the above-mentioned induction noise resistance test, and the insulation layer 80 required to detect disconnection. It is a value larger than either the minimum value of the insulation resistance (1 kΩ) or the minimum value of the insulation resistance of the insulation layer 80 (1 MΩ) required to be unaffected by the potential difference between grounds.

As described above, if the thickness of the insulating layer 80 is 0.1 mm, the insulation resistance required to eliminate the generation of noise due to the various noise sources described above even if the insulating layer 80 is formed of various materials. A resistance value exceeding the above can be obtained. Therefore, as an example, the maximum thickness of the insulating layer 80 may be 0.1 mm, and the insulating resistance value at this time may be the maximum resistance value of the insulating layer 80. Further, as an example, the maximum thickness of the insulating layer 80 may be 0.3355 mm, which is the gap between the male screw 332a and the female screw 4e, and the insulating resistance value at this time may be the maximum value of the resistance value of the insulating layer 80. .. Then, in the insulating layer forming step (see FIG. 7), the insulating layer is set from the minimum value (510Ω, 1kΩ, 1MΩ) of the insulating resistance of the insulating layer 80 capable of eliminating the target noise to the maximum value determined as described above. The insulating layer 80 may be formed as a range in which the insulation resistance value of 80 can be taken.

In other words, the thickness of the insulating layer 80 required to obtain the minimum value of the insulating resistance (510Ω, 1kΩ, 1MΩ, etc.) of the insulating layer 80 that can eliminate the target noise varies depending on the material of the insulating layer 80, It is thinner than 0.1 mm, which is the maximum value of the above thickness. Therefore, in the insulating layer forming step (see FIG. 7), the thickness required to obtain the minimum value of the insulating resistance is set as the minimum value of the thickness of the insulating layer 80, and the value from this minimum value to 0.1 mm is set as the minimum value of the insulating layer 80. The insulating layer 80 may be formed as a range in which the thickness of the above can be taken. For example, when a DLC film is formed as the insulating layer 80, it is 0.000000015 mm to obtain an insulation resistance value of 510 Ω or more, 0.000001 mm to obtain an insulation resistance value of 1 kΩ or more, and 1 MΩ to obtain an insulation resistance value. 0.001 mm can be used as the minimum value of the thickness of the insulating layer 80.

Although the present embodiment has been described above, the technical scope of the present invention is not limited to the above embodiment. For example, in the above embodiment, the maximum value of the insulation resistance was examined in the case where the DLC film was formed as the insulating layer 80 and the case where _{the passivation film of Cr 2} O ₃ was formed, but it is used as the insulating layer 80. The maximum value of the insulation resistance can be individually obtained from the maximum value of the thickness of the insulating layer 80 for the material of. In addition, various changes and alternative configurations that do not deviate from the scope of the technical idea of the present invention are included in the present invention.

1 ... Internal combustion engine, 2 ... Cylinder block, 3 ... Piston, 4 ... Cylinder head, 5 ... Pressure detector, 6 ... Control device, 7 ... Seal member, 8 ... Transmission cable, 9 ... Battery, 10 ... Piezoelectric element, 21 ... Circuit board part, 22 ... Conduction member, 23 ... Covering member, 24 ... O ring, 30 ... Housing, 40 ... Diaphragm head, 50 ... First electrode part, 55 ... Second electrode part, 60 ... Insulation ring, 65 ... Support member, 70 ... Coil spring, 80 ... Insulation layer, 81 ... First insulation layer, 82 ... Second insulation layer, 83 ... Third insulation layer, 90 ... Capacitor, 100 ... Sensor unit, 200 ... Signal processing unit , 210 ... Printed wiring board, 211 ... IC, 300 ... Holding member

Claims (6)

A tubular body made of conductors and
A pressure receiving part that is composed of a conductor and is attached to one end side of the body part and receives pressure from the outside.
A signal generating unit provided inside the body portion, which is electrically connected to the pressure receiving unit and generates a signal according to the pressure received by the pressure receiving unit.
It is composed of an insulator and includes a covering portion that continuously covers the outer peripheral surface of the pressure receiving portion and the outer peripheral surface of the body portion on the pressure receiving portion side.
The coating portion is a pressure detection device which is a film made of the insulator configured to obtain an insulation resistance of 510 Ω or more. The covering portion is
Regarding the insulation resistance, the insulator having the minimum value of 510Ω and the maximum value of the resistance value obtained when the thickness of the insulator is 0.1 mm, or
The pressure detection device according to claim 1, further comprising the insulator having a thickness of 510 Ω as a minimum value and a thickness of 0.1 mm as a maximum value. A male screw is provided on the outer peripheral surface of the body portion.
The covering portion is
Regarding the insulation resistance, the insulator having a minimum value of 510 Ω and a maximum value of the resistance value obtained when the thickness of the insulator is the size of the gap between the male screw and the female screw corresponding to the male screw, or
2. The pressure detector of the description. A processing unit that is electrically connected to the signal generating unit and processes and outputs the generated signal by the signal generating unit.
Electrically connected to the processing unit via a cable including a power supply line for supplying power to the processing unit, a ground line for supplying a ground voltage to the processing unit, and a signal line for transmitting a signal output from the processing unit. Further equipped with a control unit
The processing unit and the body unit are electrically connected to each other.
It has a disconnection detection structure that detects that the ground wire of the cable is disconnected.
The pressure detection device according to claim 1, wherein the insulation resistance of the covering portion is 1 kΩ or more. A processing unit that is electrically connected to the signal generating unit and that processes and outputs the generated signal by the signal generating unit is further provided.
The processing unit and the body unit are electrically disconnected and are not connected to each other.
The pressure detection device according to claim 1, wherein the insulation resistance of the covering portion is 1 MΩ or more. A cylinder head having a communication hole that communicates the combustion chamber on one end side and the outside of the combustion chamber on the other end side.
It is attached to the cylinder head by being inserted into the communication hole, and is provided with a pressure detecting device for detecting the pressure in the combustion chamber.
The pressure detector is
A cylindrical body portion that is arranged so as to straddle the inside and the outside of the communication hole and is composed of a conductor.
A pressure receiving portion composed of a conductor and attached to one end side of the body portion to receive pressure from the combustion chamber, and a pressure receiving portion.
A signal generating unit provided inside the body portion, which is electrically connected to the pressure receiving unit and generates a signal according to the pressure received by the pressure receiving unit.
It is composed of an insulator, and includes a covering portion that continuously covers a portion of the outer peripheral surface of the pressure receiving portion and the outer peripheral surface of the body portion that is located inside the communication hole.
The covering portion is an internal combustion engine with a pressure detection device, which is a film made of the insulator configured to obtain an insulation resistance of 510 Ω or more.

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