JP6827866B2 - Detector and circuit board - Google Patents

Description

The present invention relates to a detection device and a circuit board for detecting a physical quantity.

For example, it is being considered to equip a device such as an automobile having an internal combustion engine with a detection device for detecting the combustion pressure of the internal combustion engine. In such a device, a control device called an ECU (Engine Control Unit) controls the operation of the internal combustion engine and the like based on the detection result of the combustion pressure by the detection device.

As a detection device of this type, one using an output element such as a piezoelectric element that outputs a signal according to the received pressure has been proposed.
For example, in Patent Document 1, a charge signal supplied from a piezoelectric element (output element) is integrated by an amplifier circuit including an operational amplifier and a capacitor, and the obtained voltage signal is amplified by an amplifier circuit and then output to a control device. It is stated that it should be done.

Japanese Unexamined Patent Publication No. 2013-156171

Here, when a configuration in which the control device and the detection device are connected via an electric wire is adopted, the electric wire may function as an antenna in response to an external radio wave or the like. Then, noise may invade the charge signal processing circuit provided in the detection device via the electric wire, and as a result, the noise may be superimposed on the signal output from the processing circuit.
An object of the present invention is to reduce noise in a voltage signal while suppressing a decrease in sensitivity to the charge signal when the charge signal from the output element is integrated into a voltage signal by an integrator circuit.

The detection device of the present invention outputs an output element that outputs a charge signal according to a change in physical quantity, an inverting input terminal to which the charge signal is input, a non-inverting input terminal to which a reference voltage is input, and an output signal. An operational amplifier having an operational amplifier, an inverting input terminal, and a feedback capacitor connected to the output terminal, and an integrating circuit that outputs a voltage signal obtained by integrating the charge signal as the output signal, and the inverting circuit. The input terminal includes an input side capacitor which is connected in parallel with the output element and has a smaller capacitance than the feedback capacitor.
In such a detection device, the integrating circuit further includes a feedback resistor connected in parallel with the feedback capacitor by being connected to the inverting input terminal and the output terminal, and the feedback capacitor and the feedback resistor are further provided. It can be characterized in that the time constant of is 1 sec or more.
Further, the integrating circuit further includes a feedback resistor connected in parallel with the feedback capacitor by being connected to the inverting input terminal and the output terminal, and the resistance value of the feedback resistor is 1 GΩ or more. Can be characterized.
Further, it can be characterized by further including an amplifier circuit that amplifies the voltage signal input from the integrating circuit.
From another point of view, the circuit board of the present invention has an inverting input terminal into which the charge signal is input from an output element that outputs a charge signal according to a change in physical quantity, and a non-inversion input terminal in which the reference voltage is input. A voltage signal including an arithmetic amplifier having an inverting input terminal and an output terminal for outputting an output signal, and a feedback capacitor connected to the inverting input terminal and the output terminal, and integrating the charge signal as the output signal. An input side capacitor which is provided so as to be connected to the inverting input terminal in parallel with the output element and has a smaller capacitance than the feedback capacitor, and the integrator circuit and the input side capacitor are mounted. Includes a substrate.

According to the present invention, when a charge signal from an output element is integrated by an integrator circuit into a voltage signal, it is possible to reduce noise in the voltage signal while suppressing a decrease in sensitivity to the charge signal.

It is a schematic block diagram of the pressure detection system which concerns on embodiment. It is a perspective view of the pressure detection device. It is sectional drawing (III-III sectional view of FIG. 2) of the pressure detection apparatus. It is an enlarged cross-sectional view of the tip side of a pressure detection device. It is a schematic block diagram of the circuit board provided in the pressure detection apparatus. (A) to (c) are diagrams showing the results of the BCI test in each circuit configuration as a graph. (A) and (b) are diagrams showing the shape of the output voltage waveform in each circuit configuration, respectively. It is a figure for demonstrating the relationship between the capacitance value of an input side capacitor and a feedback capacitor in each circuit configuration, and an output voltage waveform.

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 the pressure detection system 1 according to the embodiment.
The pressure detection system 1 supplies power to the pressure detection device 20 for detecting the pressure (combustion pressure) in the combustion chamber C in the internal combustion engine 10 and the pressure detection device 20, and is based on the pressure detected by the pressure detection device 20. It includes a control device 80 that controls the operation of the internal combustion engine 10, and a connection cable 90 that electrically connects the pressure detection device 20 and the control device 80.

Here, the internal combustion engine 10 whose pressure is to be detected includes a cylinder block 11 in which a cylinder is formed, a piston 12 that reciprocates in the cylinder, and a combustion chamber C that is fastened to the cylinder block 11 together with the piston 12 and the like. It has a cylinder head 13 constituting the above. Further, the cylinder head 13 is provided with a communication hole 13a that communicates the combustion chamber C with the outside. A female screw (not shown) is formed inside the communication hole 13a, and a male screw (not shown) formed on the outer peripheral surface of the pressure detection device 20 is screwed into the internal combustion engine 10 to detect pressure. The device 20 is attached. The cylinder block 11, the piston 12, and the cylinder head 13 that make up the internal combustion engine 10 are made of a conductive metal material such as cast iron or aluminum. A seal member (not shown) for maintaining airtightness in the combustion chamber C is provided between the cylinder head 13 and the pressure detection device 20 on both ends of the communication hole 13a. There is.

[Configuration of pressure detector]
FIG. 2 is a perspective view of the pressure detecting device 20. Further, FIG. 3 is a cross-sectional view of the pressure detecting device 20 (cross-sectional view of III-III in FIG. 2). Further, FIG. 4 is an enlarged cross-sectional view of the tip end side of the pressure detecting device 20.

The pressure detection device 20 as an example of the detection device includes a detection unit 30 that detects a pressure as an example of a physical quantity, and a processing unit 50 that performs various processes on an electric signal obtained by detecting the pressure by the detection unit 30. have. Then, in this pressure detection device 20, the detection unit 30 faces the combustion chamber C (downward in FIG. 1) and the processing unit 50 faces the outside (upward in FIG. 1) with respect to the internal combustion engine 10 shown in FIG. It is attached. In the following description, in FIG. 2, the side toward the lower left in the figure (detection unit 30 side) is referred to as the “tip side” of the pressure detection device 20, and the side toward the upper right in the figure (processing unit 50 side) is pressure. It is referred to as the "rear end side" of the detection device 20. Further, in the following description, the direction of the center line of the pressure detecting device 20 shown by the alternate long and short dash line in FIG. 2 is simply referred to as the center line direction.

[Configuration of detector]
The detection unit 30 includes a front end side housing 31 that fits with the front end side of the rear end side housing 51 (details will be described later) provided in the processing unit 50, and a diaphragm attached to the front end side of the front end side housing 31. It has a head 32.

Of these, the tip-side housing 31 is a member having a hollow structure and having a tubular shape as a whole. The tip-side housing 31 is made of a metal material such as stainless steel, which has both conductivity and high acid resistance. The front end side housing 31 includes a first front end side housing 311 relatively located on the front end side and a second front end side housing 312 relatively located on the rear end side. Here, in the front end side housing 31, both are formed by laser welding the outer peripheral surface on the rear end side of the first front end side housing 311 and the inner peripheral surface on the front end side of the second front end side housing 312. It is configured to integrate. Then, the diaphragm head 32 is attached to the tip side of the first front end side housing 311 by laser welding, and the rear end side housing 51 is fitted to the rear end side of the second front end side housing 312. It is attached. A male screw (not shown) that meshes with a female screw (not shown) provided on the inner peripheral surface of the communication hole 13a (see FIG. 1) of the cylinder head 13 on the outer peripheral surface of the central portion of the second tip-side housing 312 in the center line direction. (Not shown) is formed.

On the other hand, the diaphragm head 32 is a member having a disk shape as a whole. The diaphragm head 32 is made of a metal material such as stainless steel, which has conductivity and high heat resistance and acid resistance. In particular, in this example, the diaphragm head 32 and the tip-side housing 31 are made of the same material. The diaphragm head 32 has a recess provided by annularly cutting out a pressure receiving surface (front surface) 32a that receives pressure by being exposed to the outside (combustion chamber C side) and a back surface that is the back side of the pressure receiving surface 32a. Due to the presence of the recess 32b, the pressure receiving surface 32a has a convex portion 32c that protrudes from the central portion of the back surface toward the rear end side. The diaphragm head 32 is provided so as to close the opening on the distal end side of the first distal end side housing 311. The boundary between the diaphragm head 32 and the first distal end side housing 311 is laser welded over the entire outer peripheral surface.

Further, the detection unit 30 is a piezoelectric element 33, an insulating plate 34, a front electrode member 35, a rear end electrode member 36, a first pressurizing member 37, and a second, which are arranged (accommodated) inside the front end side housing 31. A pressurizing member 38, a support member 39, an insulating pipe 40, a first insulating ring 41, a second insulating ring 42, a third insulating ring 43, a fourth insulating ring 44, and a fifth insulating ring 45 are further provided.

The piezoelectric element 33 as an example of the output element is a member having a columnar shape as a whole. The piezoelectric element 33 includes a piezoelectric body that exhibits a piezoelectric action of a piezoelectric vertical effect. The piezoelectric longitudinal effect means that when an external force is applied to a stress application shaft in the same direction as the charge generation axis of the piezoelectric body, a charge is generated on the surface of the piezoelectric body in the charge generation axis direction. The piezoelectric element 33 is located inside the front end side housing 31 and is arranged on the rear end side of the diaphragm head 32. The piezoelectric element 33 is housed in the front end side housing 31 so that the center line direction is the direction of the stress application axis. Here, the piezoelectric element 33 is inside the first pressurizing member 37 provided inside the tip-side housing 31, and inside the insulating pipe 40 provided inside the first pressurizing member 37. Have been placed. Further, the outer diameter of the piezoelectric element 33 is slightly smaller than the inner diameter of the insulating pipe 40 accommodating the piezoelectric element 33 inside. The front end side surface of the piezoelectric element 33 is in contact with the rear end side surface of the front end electrode member 35. On the other hand, the surface on the rear end side of the piezoelectric element 33 is in contact with the surface on the front end side of the rear end electrode member 36. Further, the outer peripheral surface of the piezoelectric element 33 faces the inner peripheral surface of the insulating pipe 40. In this way, by providing the insulating pipe 40 between the inner peripheral surface of the first pressurizing member 37 and the outer peripheral surface of the piezoelectric element 33, the first pressurizing member 37 and the piezoelectric element 33 come into direct contact with each other. do not do.

Next, a case where the piezoelectric lateral effect is used for the piezoelectric element 33 will be illustrated. The piezoelectric lateral effect means that when an external force is applied to a stress application axis located at a position orthogonal to the charge generation axis of the piezoelectric body, a charge is generated on the surface of the piezoelectric body in the direction of the charge generation axis. A plurality of piezoelectric bodies formed thinly in the shape of a thin plate 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 material that can be used in the piezoelectric element 33 include langasite crystals (langasite, langateite, langanite, LTGA) having a piezoelectric longitudinal effect and a piezoelectric lateral effect, quartz, gallium phosphate, and the like. can do. In the piezoelectric element 33 of the present embodiment, a Langasite single crystal is used as the piezoelectric body.

The insulating plate 34 is a member having a disk shape as a whole. The insulating plate 34 is made of a ceramic material such as alumina, which has insulating properties and high heat resistance. The insulating plate 34 is arranged at a position that closes an opening existing on the tip side of the first pressurizing member 37 provided inside the tip side housing 31. The insulating plate 34 is arranged on the rear end side of the diaphragm head 32 and on the front end side of the tip electrode member 35. Further, the outer diameter of the insulating plate 34 is slightly smaller than the inner diameter of the opening provided on the tip end side of the first pressurizing member 37, and slightly larger than the outer diameter of the convex portion 32c of the diaphragm head 32. The surface on the tip end side of the insulating plate 34 is in contact with the convex portion 32c of the diaphragm head 32. On the other hand, the surface on the rear end side of the insulating plate 34 is in contact with the surface on the front end side of the tip electrode member 35. Further, the outer peripheral surface of the insulating plate 34 faces the inner peripheral surface of the opening provided on the tip end side of the first pressurizing member 37.

The tip electrode member 35 is a member that exhibits a columnar shape as a whole. The tip electrode member 35 is made of a metal material such as stainless steel, which has both conductivity and high heat resistance. The tip electrode member 35 is arranged inside the first pressurizing member 37 provided inside the tip side housing 31. However, unlike the piezoelectric element 33 described above, the tip electrode member 35 is not housed in the insulating pipe 40. The tip electrode member 35 is arranged on the rear end side of the insulating plate 34 and on the front end side of the piezoelectric element 33. Further, the outer diameter of the tip electrode member 35 is slightly smaller than the inner diameter of the first pressurizing member 37 that houses the tip electrode member 35 inside. The front end side surface of the tip electrode member 35 is in contact with the rear end side surface of the insulating plate 34 and the back side surface of the opening provided on the front end side of the first pressurizing member 37. On the other hand, the rear end side surface of the tip electrode member 35 is in contact with the front end side surface of the piezoelectric element 33. Further, the outer peripheral surface of the tip electrode member 35 faces the inner peripheral surface of the first pressurizing member 37.

The rear end electrode member 36 is a member that exhibits a columnar shape as a whole. The rear end electrode member 36 is made of a metal material such as stainless steel, which has conductivity and high heat resistance. The rear end electrode member 36 is arranged inside the first pressurizing member 37 provided inside the front end side housing 31. Here, the tip end side of the rear end electrode member 36 is arranged inside the insulating pipe 40 provided inside the first pressurizing member 37. On the other hand, the rear end side of the rear end electrode member 36 is arranged outside the insulating pipe 40. A counterbore 36a for inserting the tip end side of the second pressurizing member 38 is formed in the central portion of the rear end side surface of the rear end electrode member 36. Further, the outer diameter of the rear end electrode member 36 is substantially the same as the outer diameter of the piezoelectric element 33, and is slightly smaller than the inner diameter of the insulating pipe 40. The surface on the front end side of the rear end electrode member 36 is in contact with the surface on the rear end side of the piezoelectric element 33. On the other hand, the surface on the rear end side of the rear end electrode member 36 is in contact with the surface on the front end side of the first insulating ring 41, and the bottom surface of the counterbore hole 36a provided on the rear end side of the rear end electrode member 36 is formed. It is in contact with the tip end side of the second pressurizing member 38. Further, the tip end side of the outer peripheral surface of the rear end electrode member 36 faces the inner peripheral surface of the insulating pipe 40. On the other hand, the rear end side of the outer peripheral surface of the rear end electrode member 36 faces the inner peripheral surface of the first pressurizing member 37 via an air gap. In this way, by providing the insulating pipe 40 and the air gap between the inner peripheral surface of the first pressure member 37 and the outer peripheral surface of the rear end electrode member 36, the first pressure member 37 and the rear end electrode member 37 are provided. It does not come into direct contact with 36.

The first pressurizing member 37 is a member having a tubular shape as a whole. The first pressurizing member 37 is made of a metal material such as stainless steel, which has both conductivity and high heat resistance. The first pressurizing member 37 is provided inside the distal end side housing 31, and an insulating plate 34 is arranged so as to close the opening provided on the distal end side, and the piezoelectric element 33, It houses the front end electrode member 35, the rear end electrode member 36, the second pressurizing member 38, the tip end side of the support member 39, the insulating pipe 40, and the first insulating ring 41. The first pressurizing member 37 is arranged on the rear end side of the diaphragm head 32 and on the tip end side of the cushioning member 55 (details will be described later) constituting the processing unit 50. Further, the outer diameter of the first pressurizing member 37 differs depending on the position in the center line direction, but is smaller than the inner diameter of the tip side housing 31 (more specifically, the first tip side housing 311) at all positions. .. Further, the inner diameter of the first pressurizing member 37 is outside of the insulating plate 34, the tip electrode member 35, the insulating pipe 40 (piezoelectric element 33, the rear end electrode member 36), and the portion facing the first insulating ring 41. It is larger than the diameter and slightly smaller than the outer diameter of the support member 39 at the portion facing the support member 39. Here, between the outer peripheral surface on the rear end side of the first pressurizing member 37 and the inner peripheral surface on the rear end side of the first front end side housing 311, the second insulation is provided at a position relatively on the front end side. A third insulating ring 43 is arranged at a position where the ring 42 is relatively on the rear end side. The front end side surface (front surface side surface of the opening) of the first pressurizing member 37 faces the recess 32b provided on the rear end side of the diaphragm head 32. On the other hand, the rear end side of the first pressurizing member 37 is in contact with the tip end side of the cushioning member 55. Further, the rear end side of the outer peripheral surface of the first pressurizing member 37 is in contact with the inner peripheral surface of the second insulating ring 42, and the rearmost end side thereof faces the third insulating ring 43 via an air gap. There is. Further, the tip end side of the outer peripheral surface of the first pressurizing member 37 faces the inner peripheral surface of the first tip end side housing 311 via an air gap. In this way, an air gap is provided by the recess 32b between the front end side surface of the first pressurizing member 37 and the back surface of the diaphragm head 32, and the outer peripheral surface of the first pressurizing member 37 and the tip end side housing. By providing the second insulating ring 42 between the inner peripheral surface of the first front end side housing 311 of 31, the tip side housing 31, the diaphragm head 32, and the first pressurizing member 37 can be directly connected to each other. Do not touch. On the other hand, the inner peripheral surface of the first pressurizing member 37 is in direct contact with the outer peripheral surfaces of the tip electrode member 35, the insulating pipe 40, the first insulating ring 41 and the support member 39. Further, the inner peripheral surface of the first pressurizing member 37 does not come into direct contact with the outer peripheral surfaces of the piezoelectric element 33 and the rear end electrode member 36.

The second pressurizing member 38 is a member that exhibits a spiral shape as a whole, and is a coil spring that expands and contracts in the center line direction. The second pressurizing member 38 is made of a metal material such as brass, which has conductivity and is more conductive than the front end side housing 31. The second pressurizing member 38 is inside the first pressurizing member 37 provided inside the tip-side housing 31, and is a support member 39 and a first insulation located inside the first pressurizing member 37. It is arranged so as to pass through the ring 41 and reach the counterbore hole 36a of the rear end electrode member 36. The second pressurizing member 38 is arranged on the rear end side of the rear end electrode member 36 and on the tip end side of the conduction member 53 (details will be described later) provided in the processing unit 50. The outer diameter of the second pressurizing member 38 is the inner diameter of the opening provided on the tip end side of the support member 39, the inner diameter of the through hole provided in the first insulating ring 41, and the rear end electrode member 36. It is smaller than the inner diameter of the counterbore 36a. Further, the inner diameter of the second pressurizing member 38 is larger than the outer diameter of the tip side convex portion 53a (details will be described later) provided on the tip end side of the conduction member 53. The tip end side of the second pressurizing member 38 is in contact with the rear end electrode member 36 by being inserted into the counterbore hole 36a of the rear end electrode member 36. On the other hand, the rear end side of the second pressurizing member 38 is in contact with the conduction member 53 by inserting the tip-side convex portion 53a of the conduction member 53. The tip end side of the outer peripheral surface of the second pressurizing member 38 faces the inner peripheral surface of the counterbore 36a of the rear end electrode member 36 and the inner peripheral surface of the through hole of the first insulating ring 41. Further, the rear end side of the outer peripheral surface of the second pressurizing member 38 faces the inner peripheral surface of the support member 39 via an air gap. By providing an air gap between the inner peripheral surface of the support member 39 and the second pressurizing member 38 in this way, the support member 39 and the second pressurizing member 38 do not come into direct contact with each other.

The support member 39 is a member having a tubular shape as a whole. The support member 39 is made of a metal material such as stainless steel, which has conductivity and high heat resistance. The support member 39 is provided inside the front end side housing 31, and the front end side thereof is located inside the first pressurizing member 37 and the rear end side is located outside the first pressurizing member 37. ing. Further, the support member 39 accommodates the rear end side of the second pressurizing member 38, and the tip of the conduction member 53 and the covering member 54 (details will be described later) located on the tip side of the processing unit 50. Containing the side. The support member 39 is arranged on the rear end side of the first insulating ring 41 and on the front end side of the accommodating member 56 (details will be described later) constituting the processing unit 50. Further, the outer diameter of the support member 39 is slightly larger than the inner diameter of the first pressurizing member 37. Further, the inner diameter of the support member 39 varies depending on the position in the center line direction, but is larger than the outer diameter of the conduction member 53 and the covering member 54 provided in the processing unit 50 at all positions. The front end side surface (front side surface of the opening) of the support member 39 is in contact with the rear end side surface of the first insulating ring 41. On the other hand, the surface on the rear end side of the support member 39 faces the covering member 54 via an air gap. Further, the outer peripheral surface of the support member 39 is in contact with the inner peripheral surface of the first pressurizing member 37. Further, the inner peripheral surface of the support member 39 faces the second pressurizing member 38, the conduction member 53, and the covering member 54 via an air gap. In this way, by providing an air gap between the inner peripheral surface of the support member 39 and the second pressurizing member 38, the conduction member 53, and the covering member 54, the support member 39 and the second pressurizing member 38, The conductive member 53 and the covering member 54 do not come into direct contact with each other.

The insulating pipe 40 is a member having a cylindrical shape as a whole. The insulating pipe 40 is made of a synthetic resin material such as LCP (Liquid Crystal Polymer) having insulating properties. The insulating pipe 40 is arranged inside the first pressurizing member 37 provided inside the tip-side housing 31. The insulating pipe 40 houses the piezoelectric element 33 and the tip end side of the rear end electrode member 36 inside. The insulating pipe 40 is arranged on the rear end side of the tip electrode member 35 and on the tip end side of the first insulating ring 41. Further, the outer diameter of the insulating pipe 40 is slightly smaller than the inner diameter of the first pressurizing member 37. Further, the inner diameter of the insulating pipe 40 is slightly larger than the outer diameter of each of the piezoelectric element 33 and the rear end electrode member 36. The tip end side of the insulating pipe 40 faces the rear end side surface of the tip electrode member 35. On the other hand, the rear end side of the insulating pipe 40 faces the front end side surface of the first insulating ring 41. The outer peripheral surface of the insulating pipe 40 faces the inner peripheral surface of the first pressurizing member 37. Further, the inner peripheral surface of the insulating pipe 40 faces the outer peripheral surface of the piezoelectric element 33 and the outer peripheral surface of the rear end electrode member 36. In this way, by providing an air gap between the first pressurizing member 37 and the piezoelectric element 33 and the rear end electrode member 36 by the insulating pipe 40 and the insulating pipe 40, the first pressurizing member 37 and the piezoelectric element 33 are provided. And does not come into direct contact with the rear end electrode member 36.

The first insulating ring 41 is a member that exhibits an annular shape as a whole. The first insulating ring 41 is made of a ceramic material such as alumina, which has insulating properties and high heat resistance. The first insulating ring 41 is arranged inside the first pressurizing member 37 provided inside the tip-side housing 31. A through hole is formed in the central portion of the first insulating ring 41 so as to penetrate the first insulating ring 41 along the center line direction. Further, the outer diameter of the first insulating ring 41 is slightly smaller than the inner diameter of the first pressurizing member 37. Further, the inner diameter of the through hole of the first insulating ring 41 is slightly larger than the outer diameter of the second pressurizing member 38. The surface on the front end side of the first insulating ring 41 is in contact with the surface on the rear end side of the rear end electrode member 36. On the other hand, the surface on the rear end side of the first insulating ring 41 is in contact with the surface on the front end side of the support member 39. The outer peripheral surface of the first insulating ring 41 faces the inner peripheral surface of the first pressurizing member 37. Further, the inner peripheral surface of the first insulating ring 41 faces the outer peripheral surface of the second pressurizing member 38.

The second insulating ring 42 is a member that exhibits an annular shape as a whole. The second insulating ring 42 is made of a ceramic material such as alumina, which has insulating properties and high heat resistance. The second insulating ring 42 is inside the front end side housing 31, and is arranged on the rear end side and outside of the first pressurizing member 37. A through hole is formed in the central portion of the second insulating ring 42 so as to penetrate the second insulating ring 42 along the center line direction. Further, the outer diameter of the second insulating ring 42 is slightly larger than the inner diameter of the tip side housing 31 (more specifically, the first tip side housing 311). Further, the inner diameter of the second insulating ring 42 is slightly smaller than the outer diameter of the first pressurizing member 37. The surface on the tip end side of the second insulating ring 42 is in contact with the surface on the rear end side of the protruding portion protruding outward from the outer peripheral surface of the first pressurizing member 37. On the other hand, the surface on the rear end side of the second insulating ring 42 is in contact with the surface on the tip end side of the third insulating ring 43. Further, the outer peripheral surface of the second insulating ring 42 is in contact with the inner peripheral surface of the front end side housing 31. Further, the inner peripheral surface of the second insulating ring 42 is in contact with the outer peripheral surface of the first pressurizing member 37.

The third insulating ring 43 is a member that exhibits an annular shape as a whole. The third insulating ring 43 is made of a ceramic material such as alumina, which has insulating properties and high heat resistance. The third insulating ring 43 is arranged inside the tip-side housing 31 and outside the first pressurizing member 37. A through hole is formed in the central portion of the third insulating ring 43 so as to penetrate the third insulating ring 43 along the center line direction. Further, the outer diameter of the third insulating ring 43 is slightly larger than the inner diameter of the tip side housing 31 (more specifically, the first tip side housing 311). Further, the inner diameter of the third insulating ring 43 is larger than the outer diameter of the first pressure member 37 and larger than the inner diameter of the second insulating ring 42. The surface on the front end side of the third insulating ring 43 is in contact with the surface on the rear end side of the second insulating ring 42. On the other hand, the surface of the third insulating ring 43 on the rear end side faces the air gap provided on the rear end side. Further, the outer peripheral surface of the third insulating ring 43 is in contact with the inner peripheral surface of the front end side housing 31. Further, the inner peripheral surface of the third insulating ring 43 faces the outer peripheral surface of the first pressurizing member 37 via an air gap.

The fourth insulating ring 44 is a member that exhibits an annular shape as a whole. The fourth insulating ring 44 is made of a ceramic material such as alumina, which has insulating properties and high heat resistance. The fourth insulating ring 44 is inside the tip side housing 31 (more specifically, the second tip side housing 312), and is a housing member 56 (details will be described later) provided in the processing unit 50. It is arranged on the rear end side and on the outside. A through hole is formed in the central portion of the fourth insulating ring 44 so as to penetrate the fourth insulating ring 44 along the center line direction. Further, the outer diameter of the fourth insulating ring 44 is slightly larger than the inner diameter of the front end side housing 31. Further, the inner diameter of the fourth insulating ring 44 is slightly smaller than the outer diameter of the accommodating member 56. The surface of the fourth insulating ring 44 on the tip end side is in contact with the inner peripheral surface of the tip end side housing 31. On the other hand, the surface on the rear end side of the fourth insulating ring 44 is in contact with the outer peripheral surface of the accommodating member 56. Further, the outer peripheral surface of the fourth insulating ring 44 is in contact with the inner peripheral surface of the front end side housing 31. Further, the inner peripheral surface of the fourth insulating ring 44 is in contact with the outer peripheral surface of the accommodating member 56.

The fifth insulating ring 45 is a member that exhibits an annular shape as a whole. The fifth insulating ring 45 is made of a ceramic material such as alumina, which has insulating properties and high heat resistance. The fifth insulating ring 45 is inside the tip side housing 31 (more specifically, the second tip side housing 312), and is a housing member 56 (details will be described later) provided in the processing unit 50. It is located on the outside. A through hole is formed in the central portion of the fifth insulating ring 45 so as to pass through the fifth insulating ring 45 along the center line direction. Further, the outer diameter of the fifth insulating ring 45 is slightly larger than the inner diameter of the tip-side housing 31. Further, the inner diameter of the fifth insulating ring 45 is slightly smaller than the outer diameter of the accommodating member 56. The surface of the fifth insulating ring 45 on the tip end side is in contact with the inner peripheral surface of the tip end side housing 31. On the other hand, the surface on the rear end side of the fifth insulating ring 45 is in contact with the outer peripheral surface of the accommodating member 56. Further, the outer peripheral surface of the fifth insulating ring 45 is in contact with the inner peripheral surface of the front end side housing 31. Further, the inner peripheral surface of the fifth insulating ring 45 is in contact with the outer peripheral surface of the accommodating member 56.

In this way, by providing the fourth insulating ring 44 and the fifth insulating ring 45 between the tip-side housing 31 and the housing member 56 constituting the processing unit 50, the tip-side housing 31 and the housing member 56 can be provided. Does not come into direct contact.

[Configuration of processing unit]
The processing unit 50 is a rear end side housing 51 that fits with the rear end side of the above-mentioned front end side housing 31 (specifically, the second front end side housing 312), and the front end side is the rear end side housing 51. A connecting member that is housed inside the rear end side and is provided so that the rear end side is exposed to the outside of the rear end side of the rear end side housing 51 and is a connection target of the connection cable 90 (see FIG. 1). It has 52 and.

Of these, the rear end side housing 51 is a member having a hollow structure and exhibiting a tubular shape as a whole. The rear end side housing 51 is made of a metal material such as stainless steel, which has conductivity and high acid resistance. Then, the rear end side of the front end side housing 31 (specifically, the second front end side housing 312) is attached to the front end side of the rear end side housing 51 by fitting, and the rear end side is attached to the rear end side. The connecting member 52 is attached by fitting.

On the other hand, the connecting member 52 is a member having a columnar shape as a whole. The connecting member 52 comprises a base material made of a synthetic resin material such as PPT (Polypropylene Terephthalate) having insulating properties, and wiring and terminals made of a metal material such as copper having conductivity. Includes. However, of the connecting member 52, the portion (outer peripheral surface) that comes into contact with the rear end side housing 51 described above is made of a synthetic resin material, and the metal material is not exposed to this portion (not in contact with the connecting member 52). It has become like. Further, on the tip end side of the connecting member 52, a first substrate side terminal 521, a second substrate side terminal 522, and a third substrate side terminal 523, each of which is an electrical connection terminal, are provided so as to project toward the tip end side. Has been done. On the other hand, on the rear end side of the connecting member 52, an opening 520 having a concave shape and opening toward the rear end side is formed. Then, inside the opening 520, the first connection terminal 52a, the second connection terminal 52b, and the third connection terminal 52c to be connected to the connection cable 90 (see FIG. 1) project toward the rear end side. It is provided. Here, the first board side terminal 521 is electrically connected to the first connection terminal 52a, the second board side terminal 522 is electrically connected to the second connection terminal 52b, and the third board side terminal 523 is electrically connected to the third connection terminal 52c. Has been done.

Further, the processing unit 50 is arranged (accommodated) inside the front end side housing 31 and / or the rear end side housing 51, and is a conduction member 53, a covering member 54, a cushioning member 55, a housing member 56, and a circuit board 57. And a holding member 58 is further provided.

The conducting member 53 is a member having a rod shape as a whole. The conductive member 53 is made of a conductive metal material such as brass. The conductive member 53 is provided with a tip-side convex portion 53a having a diameter smaller than that of the central portion in the center line direction at the tip thereof, and a rear end having a diameter smaller than that of the central portion in the center line direction at the rear end. A side convex portion 53b is provided. The conduction member 53 is provided inside the front end side housing 31, the front end side thereof is inside the first pressurizing member 37, the rear end side is inside the accommodating member 56, and the front end side and the rear end side are provided. The intermediate portions located between and are located inside the cushioning member 55, respectively. The conduction member 53 is arranged on the rear end side of the second pressurizing member 38 and on the front end side of the circuit board 57. Further, the outer diameter of the tip-side convex portion 53a of the conduction member 53 is slightly larger than the inner diameter of the second pressurizing member 38. Further, the outer diameter of the rear end side convex portion 53b of the conduction member 53 is substantially the same as the inner width of the rear end holding portion 54a (details will be described later) provided on the covering member 54. Furthermore, the outer diameter of the central portion of the conductive member 53 in the center line direction is substantially the same as the inner diameter of the covering member 54. The conducting member 53 is arranged so as to penetrate a through hole provided in the covering member 54 along the center line direction, and the tip-side convex portion 53a protrudes toward the tip side from the tip end of the covering member 54 and is a rear end. The side convex portion 53b projects toward the rear end side of the concave portion provided on the rear end side of the covering member 54. The tip-side convex portion 53a of the conduction member 53 is in contact with the second pressurizing member 38 by being inserted inside the second pressurizing member 38. On the other hand, the rear end side convex portion 53b of the conduction member 53 is fitted into the rear end holding portion 54a provided on the covering member 54. Further, the outer peripheral surface of the central portion of the conductive member 53 in the center line direction is in contact with the inner peripheral surface of the covering member 54.

The covering member 54 is a member having a tubular shape as a whole. The covering member 54 includes a base material made of a synthetic resin material such as PPT having insulating properties, and wiring and terminals made of a metal material such as copper having conductivity. However, of the covering member 54, the portion (outer peripheral surface) facing the support member 39, the cushioning member 55, and the accommodating member 56 is made of a synthetic resin material so that the metal material is not exposed to this portion. There is. Further, on the rear end side of the covering member 54, a rear end holding portion 54a made of a metal material and which fits and holds the rear end side convex portion 53b of the conduction member 53 is provided. The covering member 54 is provided inside the front end side housing 31, the front end side thereof is inside the first pressurizing member 37, the section end side thereof is inside the accommodating member 56, and the front end side and the rear end side thereof. The intermediate portions located between the sides are located inside the cushioning member 55, respectively. The covering member 54 is arranged on the rear end side of the second pressurizing member 38 and on the front end side of the circuit board 57. The outer peripheral surface of the covering member 54 has a shape in which the outer diameter increases stepwise from the front end side to the rear end side. A through hole is formed in the central portion of the covering member 54 so as to penetrate the covering member 54 along the center line direction. The outer diameter of the covering member 54 on the tip end side is smaller than the inner diameter of the support member 39, and the outer diameter of the covering member 54 on the rear end side is smaller than the inner diameter of the accommodating member 56. Further, the inner diameter of the covering member 54 is substantially the same as the outer diameter of the central portion in the center line direction of the conductive member 53. The tip of the covering member 54 is provided on the tip side of the conduction member 53 and is in contact with the rear end of the bulging portion having a slightly larger outer diameter than the central portion in the center line direction of the covering member 54. On the other hand, the rear end of the covering member 54 is in contact with the tip of the circuit board 57. Further, the outer peripheral surface of the covering member 54 faces the inner peripheral surface of the support member 39 via an air gap. Further, the inner peripheral surface of the covering member 54 is in contact with the conductive member 53.

The cushioning member 55 is a member that has a spiral shape as a whole, and is a coil spring that expands and contracts in the center line direction. The cushioning member 55 is made of a conductive metal material such as brass. The cushioning member 55 is provided inside the front end side housing 31, and the front end side thereof is located outside the first pressurizing member 37, and the rear end side is located outside the accommodating member 56. That is, the cushioning member 55 is arranged so as to straddle the first pressurizing member 37 and the accommodating member 56. Further, the outer diameter of the cushioning member 55 is smaller than the inner diameter of the tip side housing 31 (specifically, the second tip side housing 312). Further, the inner diameter of the cushioning member 55 is slightly smaller than the outer diameter of the rear end of the first pressurizing member 37 and the outer diameter of the tip side of the accommodating member 56. The outer circumference of the cushioning member 55 faces the front end side housing 31 via an air gap. On the other hand, the inner circumference on the tip end side of the cushioning member 55 contacts the outer peripheral surface on the rear end side of the first pressurizing member 37, and the inner circumference on the rear end side of the cushioning member 55 is the outer circumference on the tip end side of the accommodating member 56. It is in contact with the surface. In this way, by providing an air gap between the outer circumference of the cushioning member 55 and the inner peripheral surface of the tip-side housing 31, the cushioning member 55 and the tip-side housing 31 do not come into direct contact with each other.

The accommodating member 56 is a member having a tubular shape as a whole. The accommodating member 56 is made of a conductive metal material such as brass. The accommodating member 56 is provided so as to straddle the inside of the front end side housing 31 and the inside of the rear end side housing 51. The accommodating member 56 is arranged on the rear end side of the first pressurizing member 37 and on the tip end side of the connecting member 52. The outer peripheral surface and the inner peripheral surface of the accommodating member 56 have a shape in which the outer diameter and the inner diameter increase stepwise from the front end side to the rear end side. A through hole is formed in the central portion of the accommodating member 56 so as to penetrate the accommodating member 56 along the center line direction. Further, the outer diameter of the accommodation member 56 on the front end side is smaller than the inner diameter of the front end side housing 31, and the outer diameter of the rear end side of the accommodation member 56 is smaller than the inner diameter of the rear end side housing 51. Here, between the outer peripheral surface of the accommodating member 56 and the inner peripheral surface of the distal end side housing 31, the fourth insulating ring 44 is located relatively on the distal end side, and is relatively on the rear end side. A fifth insulating ring 45 is arranged on the floor. Further, the inner diameter on the tip end side of the accommodating member 56 is larger than the outer diameter of the covering member 54, the inner diameter on the rear end side of the accommodating member 56 is slightly smaller than the outer diameter of the holding member 58, and the tip end side of the accommodating member 56. The inner diameter of the intermediate portion located between the rear end side and the rear end side is slightly larger than the outer diameter of the circuit board 57. The tip end side of the accommodating member 56 is in contact with the rear end side of the cushioning member 55. On the other hand, the rear end side of the accommodating member 56 faces the connecting member 52 via an air gap. Further, the outer peripheral surface of the accommodating member 56 on the distal end side faces the distal end side housing 31 via the fourth insulating ring 44, the fifth insulating ring 45, and the air gap formed by these, and the rear end of the accommodating member 56. The outer peripheral surface on the side faces the rear end side housing 51 via an air gap.

The circuit board 57 is a member having a rectangular plate shape as a whole. The circuit board 57 performs various processing using an electric circuit on an electric signal (charge signal) due to a weak charge output by the piezoelectric element 33 according to the received pressure, and is composed of a so-called printed wiring board. Has been done. The circuit board 57 is provided so as to straddle the inside of the front end side housing 31 and the inside of the rear end side housing 51. Further, the circuit board 57 is arranged on the rear end side of the conduction member 53 and the covering member 54 and on the front end side of the connection member 52. Further, the entire circuit board 57 is arranged inside the accommodating member 56, and the circuit board 57 is located between the outer peripheral surface on the rear end side of the circuit board 57 and the inner peripheral surface on the rear end side of the accommodating member 56. A holding member 58 is provided. Then, on the rear end side of the circuit board 57, the power receiving terminal 570c, the output signal terminal 570d, and the output ground to be connected to the first board side terminal 521, the second board side terminal 522, and the third board side terminal 523 described above are connected. A terminal 570e is provided. Here, the power receiving terminal 570c is electrically connected to the first board side terminal 521, the output signal terminal 570d is electrically connected to the second board side terminal 522, and the output ground terminal 570e is electrically connected to the third board side terminal 523. Although details will be described later, the power receiving terminal 570c is used to supply power to the circuit board 57, the output signal terminal 570d is used to output a signal from the circuit board 57, and the output grounding terminal 570e is grounded to the circuit board 57. Used for. The details of the circuit board 57 will be described later.

The holding member 58 is a member having a tubular shape as a whole. The holding member 58 includes a base material made of a synthetic resin material such as PPT having insulating properties, and wiring made of a metal material such as copper having conductivity. The holding member 58 straddles the inside of the front end side housing 31 and the inside of the rear end side housing 51, and is provided at a position inside the accommodating member 56 and outside the circuit board 57. The holding member 58 is arranged on the rear end side of the fifth insulating ring 45 and on the tip end side of the connecting member 52. A through hole is formed in the central portion of the holding member 58 so as to pass through the holding member 58 along the center line direction. Further, the outer diameter of the holding member 58 is slightly larger than the inner diameter of the rear end side of the accommodating member 56. Further, the inner diameter of the holding member 58 on the tip end side is slightly smaller than the outer diameter of the circuit board 57. The outer peripheral surface of the holding member 58 is in contact with the inner peripheral surface on the rear end side of the accommodating member 56. On the other hand, the inner peripheral surface on the tip end side of the holding member 58 is in contact with the outer peripheral surface on the rear end side of the circuit board 57. Here, the wiring provided on the holding member 58 comes into contact with the inner peripheral surface of the accommodating member 56 on its outer peripheral surface, and is connected to the input ground terminal 570b (see FIG. 5 described later) of the circuit board 57 on the inner peripheral surface thereof. Will be done.

[Electrical connection structure in pressure detector]
Here, the electrical connection structure of the pressure detection device 20 will be described.
In the pressure detection device 20, the end face (positive electrode) on the rear end side of the piezoelectric element 33 is electrically connected to the metal rear end electrode member 36, and the rear end electrode member 36 is a metal second pressurizing member. It is connected to the metal conducting member 53 via the (coil spring) 38. The metal conductive member 53 is electrically connected to the metal rear end holding portion 54a of the covering member 54 basically composed of an insulator, and the rear end holding portion 54a is connected to the circuit board 57. It is electrically connected to the input signal terminal 570a (see FIG. 5 described later) provided in. In the following, the input signal terminal 570a of the circuit board 57 is reached from the rear end side surface of the piezoelectric element 33 via the rear end electrode member 36, the second pressurizing member 38, the conduction member 53, and the rear end holding portion 54a. The electrical path is referred to as the "positive path".

On the other hand, in the pressure detection device 20, the end face (negative electrode) on the tip end side of the piezoelectric element 33 is electrically connected to the metal tip electrode member 35, and the tip electrode member 35 is the metal first pressurizing member 37. It is electrically connected to the metal cushioning member 55 via (and the metal support member 39). Then, the metal cushioning member 55 is electrically connected to the metal accommodating member 56, and the accommodating member 56 is provided via a metal wiring provided in the holding member 58 which is basically composed of an insulator. Therefore, it is electrically connected to the input ground terminal 570b (see FIG. 5 described later) provided on the circuit board 57. In the following, the circuit board 57 is routed from the front end side surface of the piezoelectric element 33 via the wiring of the tip electrode member 35, the first pressurizing member 37 (support member 39), the cushioning member 55, the accommodating member 56, and the holding member 58. The electrical path leading to the input ground terminal 570b of the above is referred to as a "negative path".

On the other hand, in the pressure detection device 20, the metal front end side housing 31 (first front end side housing 311 and second front end side housing 312) is the metal diaphragm head 32 and the metal rear end side housing. It is electrically connected to 51. Hereinafter, the electrical path from the diaphragm head 32 to the rear end side housing 51 via the front end side housing 31 is referred to as a “housing path”.

As described above, in the pressure detection device 20 of the present embodiment, a negative path exists outside the positive path. The positive path and the negative path are electrically insulated by the insulating pipe 40, the first insulating ring 41, the covering member 54, and the air gap formed by these.

Further, in the pressure detecting device 20, the housing path exists outside the negative path. The negative path and the housing path are electrically connected by the insulating plate 34, the second insulating ring 42, the third insulating ring 43, the fourth insulating ring 44, the fifth insulating ring 45, and the air gap formed by these. Is insulated.

Then, in the pressure detecting device 20, the positive path and the negative path are electrically insulated, and the negative path and the housing path are electrically insulated, so that the positive path and the housing are electrically insulated. The path is electrically isolated.

In the following description, the front end side housing 31, the diaphragm head 32, and the rear end side housing 51 may be collectively referred to as "housing 60" (see FIGS. 2 and 3). Further, in the following description, the tip electrode member 35, the first pressurizing member 37, the support member 39, the cushioning member 55, and the accommodating member 56 may be collectively referred to as a “shielding body 70” (see FIG. 3). ..

Here, the housing 60 is a portion exposed to the outside in the pressure detecting device 20, and in particular, the diaphragm head 32 is a portion facing the combustion chamber C whose acidity increases with combustion. On the other hand, the shield 70 is a portion housed inside the housing 60 in the pressure detecting device 20, and in this example, it is also a portion forming a negative path. Therefore, the shield 70 is preferably made of a material having a higher conductivity than the housing 60, and the housing 60 is preferably made of a material having a higher acid resistance than the shield 70.

When the pressure detection device 20 of the present embodiment is attached to the cylinder head 13 of the internal combustion engine 10 shown in FIG. 1, the cylinder head 13 and the housing 60 come into contact with each other to bring the cylinder head 13, the cylinder block 11 and the like into contact with each other. The metal member of the internal combustion engine 10 including the housing 60 and the housing 60 are electrically connected. However, as described above, in the pressure detection device 20 of the present embodiment, since the positive path, the negative path, and the housing path are electrically insulated, the metal member and the pressure of the internal combustion engine 10 The positive and negative paths of the detector 20 will be electrically isolated.

[Circuit board configuration]
FIG. 5 is a schematic configuration diagram of a circuit board 57 provided in the pressure detection device 20.
The circuit board 57 of the present embodiment includes a printed wiring board 570 on which wiring (circuit pattern) for mounting a plurality of electronic components (circuit elements) is formed. Further, the circuit board 57 further includes an integrator circuit 571, an amplifier circuit 572, a noise suppression circuit 573, and a power supply circuit (Vreg) 574 mounted on the printed wiring board 570.

In this circuit board 57, the charge signal (input charge Qi described later) input from the piezoelectric element 33 is converted into a voltage signal (internal output voltage Vi described later) by integrating with the amplifier circuit 571, and the amplifier circuit 571 The output signal (external output voltage Vo, which will be described later) obtained by amplifying the voltage signal input from the amplifier circuit 572 is output to the outside (for example, the control device 80 shown in FIG. 1). Further, the noise suppression circuit 573 suppresses the superposition of noise on the charge signal input from the piezoelectric element 33 to the circuit board 57. Then, the power supply circuit 574 creates and outputs a voltage (internal power supply voltage Vr, which will be described later) used in the integrator circuit 571 and the amplifier circuit 572.

In this embodiment, a so-called glass epoxy board based on a glass cloth base epoxy resin is used as the printed wiring board 570. The printed wiring board 570 is provided with an input signal terminal 570a, an input grounding terminal 570b, a power receiving terminal 570c, an output signal terminal 570d, and an output grounding terminal 570e as input / output terminals.

Here, the positive path in the pressure detection device 20 is connected to the input signal terminal 570a, and the negative path in the pressure detection device 20 is connected to the input ground terminal 570b. That is, the positive electrode (back side) of the piezoelectric element 33 is connected to the input signal terminal 570a, and the negative electrode (front side) of the piezoelectric element 33 is connected to the input ground terminal 570b. On the other hand, the power receiving terminal 570c is connected to the first board side terminal 521, the output signal terminal 570d is connected to the second board side terminal 522, and the output ground terminal 570e is connected to the third board side terminal 523 ( (See FIG. 3). In the circuit board 57, the input ground terminal 570b and the output ground terminal 570e are connected.

The integrator circuit 571 includes a first operational amplifier OP1, a feedback capacitor C1, and a feedback resistor R1. In the integrating circuit 571, the inverting input terminal of the first operational amplifier OP1 is connected to the input signal terminal 570a. Further, the non-inverting input terminal of the first operational amplifier OP1 is connected to the output end (out) of the power supply circuit 574. Further, the output terminal of the first operational amplifier OP1 is connected to the non-inverting input terminal of the second operational amplifier OP2 (details will be described later) provided in the amplifier circuit 572. Furthermore, one end of the feedback capacitor C1 is connected to the inverting input terminal of the first operational amplifier OP1, and the other end of the feedback capacitor C1 is connected to the output terminal of the first operational amplifier OP1. One end of the feedback resistor R1 is connected to the inverting input terminal of the first operational amplifier OP1, and the other end of the feedback resistor R1 is connected to the output terminal of the first operational amplifier OP1. Therefore, the feedback capacitor C1 and the feedback resistor R1 are connected in parallel to the inverting input terminal and the output terminal of the first operational amplifier OP1.

In the present embodiment, the first operational amplifier OP1 as an example of the operational amplifier operates with a single power supply (+ 5.0V), and its open loop gain is 110 (dB). The first operational amplifier OP1 is connected to the power receiving terminal 570c via a wiring (not shown), and the power supply voltage (+ 5.0V) is supplied via the power receiving terminal 570c. Further, the feedback capacitor C1 is composed of a multilayer ceramic capacitor, and its capacitance value is 560 pF. Further, the resistance value of the feedback resistor R1 is 2.3 GΩ, that is, 1 GΩ or more. Therefore, the time constant of the integrating circuit 571 is C1 × R1 = 1.288 sec, that is, 1 sec or more.

Here, when the time constant is less than 1 sec, for example, when the rotation speed of the internal combustion engine 10 is low (for example, 200 rpm), the actual output voltage value drops from the voltage value that should be originally output. Occurs. The reason for this is that the amount of charge charged in the integrating circuit 571 leaks through the feedback resistor R1 immediately before being converted to voltage due to the short time constant (the resistance value of the feedback resistor R1 is small). It is caused by going away. Therefore, by setting the time constant to 1 sec or more, it is possible to suppress charge leakage (reduce the influence of leakage) in the feedback capacitor C1 even at a low rotation speed. In order to realize this, it is necessary to increase the resistance value of the feedback resistor R1, and as a result, a resistance value of GΩ or more is required. Even when the resistance value of the feedback resistor R1 is small, if the capacitance value of the feedback capacitor C1 is large, the time constant can be set to 1 sec or more, but this is not preferable for the following reasons.

The physical formula for converting the input charge Qi generated by the piezoelectric element 33 into the internal output voltage Vi by the integrating circuit 571 is Vi = Qi / C1. Here, assuming that the amount of charge of the input charge Qi is the same, the larger the capacitance value of the feedback capacitor C1, the smaller the voltage value of the obtained internal output voltage Vi. However, in the control device 80, the voltage value per MPa is defined as a predetermined magnitude (for example, + 5V). Therefore, the amplifier circuit 572 provided after the integrating circuit 571 amplifies the internal output voltage Vi to match the above specifications. Therefore, as the voltage value of the internal output voltage Vi becomes smaller, it becomes necessary to increase the amplification factor in the amplifier circuit 572, but the amplifier circuit 572 also amplifies the noise, so that the amplification factor is made too large. That is not desirable.
Therefore, in the present embodiment, the time constant of 1 sec or more is realized by increasing the resistance value of the feedback resistor R1 without increasing the capacitance value of the feedback capacitor C1.

The amplifier circuit 572 includes a second operational amplifier OP2, a first set resistor R2a, and a second set resistor R2b. In the amplifier circuit 572, the inverting input terminal of the second operational amplifier OP2 is connected to the output end (out) of the power supply circuit 574 via the first setting resistor R2a. Further, the non-inverting input terminal of the second operational amplifier OP2 is connected to the output terminal of the first operational amplifier OP1 provided in the integrating circuit 571. Further, the output terminal of the second operational amplifier OP2 is connected to the output signal terminal 570d. Furthermore, one end of the second setting resistor R2b is connected to the inverting input terminal of the second operational amplifier OP2, and the other end of the second setting resistor R2b is connected to the output terminal of the second operational amplifier OP2. ..

In the present embodiment, the second operational amplifier OP2 operates with a single power supply (+ 5.0V), and its open loop gain is 110 (dB). The second operational amplifier OP2 is connected to the power receiving terminal 570c via a wiring (not shown), and the power supply voltage (+ 5.0V) is supplied via the power receiving terminal 570c. The resistance value of the first set resistor R2a is 10 (kΩ). Further, the resistance value of the second set resistor R2b is 51 (kΩ).

In the present embodiment, the amplification factor of the amplifier circuit 572 is set to be 4 to 13 times, and here, the amplification factor is 6 times (= 1 + R2b / R2a). However, if the influence of noise is not particularly concerned, the amplification factor may be outside the above range, and the resistance value may not be on the order of kΩ if there is no problem in withstand voltage and current resistance. Good.

The noise suppression circuit 573 includes an input side capacitor C0. One end of the input side capacitor C0 is connected to the input signal terminal 570a. Further, the other end of the input side capacitor C0 is connected to the input ground terminal 570b. Therefore, the input side capacitor C0 constituting the noise suppression circuit 573 on the circuit board 57 is connected in parallel with the piezoelectric element 33 provided outside the circuit board 57.

In the present embodiment, the input side capacitor C0 is composed of a multilayer ceramic capacitor, and its capacitance value is 100 pF. As described above, in the present embodiment, the capacitance value (100 pF) of the input side capacitor C0 provided in the noise suppression circuit 573 is the capacitance value (560 pF) of the feedback capacitor C1 provided in the integrator circuit 571. Is smaller than

The input end (in) of the power supply circuit 574 is connected to the power supply terminal 570c, and the output end (out) of the power supply circuit 574 is the first operational amplifier OP1 provided in the integrator circuit 571 (more specifically, the integrator circuit 571). It is connected to the non-inverting input terminal) and the amplifier circuit 572 (more specifically, the first set resistor R2a provided in the amplifier circuit 572), and its grounding end (GND) is connected to the input grounding terminal 570b and the output grounding terminal 570e. It is connected.

[Pressure detection operation by pressure detection device]
Then, the pressure detection operation by the pressure detection device 20 will be described.
When the internal combustion engine 10 is operating, the pressure (combustion pressure) generated in the combustion chamber C is applied to the pressure receiving surface 32a of the diaphragm head 32. In the diaphragm head 32, the pressure received by the pressure receiving surface 32a is transmitted to the convex portion 32c on the back side, and further transmitted from the convex portion 32c to the insulating plate 34. Then, the pressure transmitted to the insulating plate 34 is transmitted to the front end electrode member 35 and acts on the piezoelectric element 33 sandwiched between the front end electrode member 35 and the rear end electrode member 36. An electric charge is generated according to the pressure received. The electric charge generated in the piezoelectric element 33 is a charge signal to the input signal terminal 570a of the circuit board 57 via a positive path, that is, the rear end electrode member 36, the second pressurizing member 38, the conduction member 53, and the rear end holding portion 54a. Supplied as. The charge signal supplied to the circuit board 57 is converted into a voltage signal by being integrated by the integrating circuit 571, and further amplified by the amplifier circuit 572 to be an output signal. Then, the output signal output from the amplifier circuit 572 is externally (here, here) from the output signal terminal 570d of the circuit board 57 via the second board side terminal 522 and the second connection terminal 52b provided on the connection member 52. It is transmitted to the connection cable 90 and the control device 80).

[Operation of circuit board]
At this time, the circuit board 57 performs the following operations.
First, the input charge Qi is input to the input signal terminal 570a from the piezoelectric element 33 as an input signal (charge signal). Further, an external power supply voltage Vc (DC + 5.0V in this example) is applied to the power receiving terminal 570c from the control device 80. Further, the external output voltage Vo is output from the output signal terminal 570d toward the control device 80. The input ground terminal 570b and the output ground terminal 570e are set to the ground potential (GND potential) by connecting the output ground terminal 570e to a ground body (not shown) provided outside the circuit board 57. Will be done. Here, the grounding body is not provided on the metal member such as the cylinder head 13 constituting the internal combustion engine 10, but on the control device 80 side connected via the connection cable 90.

The integrating circuit 571 integrates the input charge Qi input from the piezoelectric element 33, and outputs the internal output voltage Vi as an example of the obtained voltage signal to the amplifier circuit 572. At this time, the input charge Qi is supplied from the input signal terminal 570a to the inverting input terminal of the first operational amplifier OP1 via the noise suppression circuit 573. On the other hand, an internal power supply voltage Vr, which is a reference voltage, is applied from the power supply circuit 574 to the non-inverting input terminal of the first operational amplifier OP1. As described above, in the present embodiment, the integrating circuit 571 is configured as an integrating circuit using the first operational amplifier OP1. However, the non-inverting input terminal of the first operational amplifier OP1 is not set to the GND potential (grounded), but is set to the internal power supply voltage Vr. This is because the first operational amplifier OP1 operates with a single power supply and the input charge Qi can take both positive and negative values.

The amplifier circuit 572 amplifies the internal output voltage Vi input from the amplifier circuit 571, and outputs the obtained external output voltage Vo to the outside (for example, the control device 80 shown in FIG. 1). At this time, the internal power supply voltage Vr output from the power supply circuit 574 is applied to the inverting input terminal of the second operational amplifier OP2 via the first set resistor R2a. Further, an external output voltage Vo output from the output terminal of the second operational amplifier OP2 is applied to the inverting input terminal of the second operational amplifier OP2 via the second setting resistor R2b. On the other hand, the internal output voltage Vi output from the output terminal of the first operational amplifier OP1 in the integrating circuit 571 is applied to the non-inverting input terminal of the second operational amplifier OP2. As described above, the amplifier circuit 572 of the present embodiment is configured as an inverting amplifier circuit using the second operational amplifier OP2.

The noise suppression circuit 573 suppresses the superposition of noise due to the AC component on the input charge Qi input from the piezoelectric element 33. Here, in the present embodiment, the capacitance value of the input side capacitor C0 in the noise suppression circuit 573 is set to be smaller than the capacitance value of the feedback capacitor C1 in the integration circuit 571, so that the input charge Qi is increased. , The noise suppression circuit 573 (input side capacitor C0) side is supplied more to the integration circuit 571 (feedback capacitor C1) side than the noise suppression circuit 573 (input side capacitor C0) side, and the input charge Qi, that is, the decrease in sensitivity to the charge signal is suppressed. There is.

The power supply circuit 574 converts the external power supply voltage Vc (DC + 5.0V in this example) input via the power receiving terminal 570c into a lower internal power supply voltage Vr (DC + 1.0V in this example) and outputs it.

[Summary]
The pressure detection device 20 of the present embodiment is attached to the internal combustion engine 10, and when the internal combustion engine 10 is mounted on an automobile, noise having a frequency on the order of kHz generated by a crush, a headlight, a wiper, or the like (hereinafter referred to as Then, it is called low frequency noise) enters the cylinder head 13 of the internal combustion engine 10.

Further, when the internal combustion engine 10 of the present embodiment is mounted on an automobile, radio waves having a frequency on the order of MHz, which are usually used in mobile phones, radios, televisions, and the like, fly around the automobile. When this radio wave is applied to the circuit board 57 provided in the pressure detection device 20, noise having a frequency on the order of MHz (hereinafter referred to as high frequency noise) is generated on the circuit board 57.

Further, these noises enter the circuit board 57 via the connection cable 90 connected to the pressure detection device 20. This is because the connection cable 90 functions as an antenna.

Here, in the present embodiment, a noise suppression circuit 573 including an input side capacitor C0 is provided on the input side of the integration circuit 571 on the circuit board 57. As a result, it is possible to suppress the superposition of low-frequency to high-frequency noise on the charge signal (input charge Qi) supplied from the piezoelectric element 33 to the integration circuit 571 as compared with the case where the noise suppression circuit 573 is not provided. become. As a result, it is possible to reduce noise in the voltage signal (internal output voltage Vi) from the integrating circuit 571.

Further, in the present embodiment, the capacitance value of the input side capacitor C0 in the noise suppression circuit 573 is made smaller than the capacitance value of the feedback capacitor C1 in the integration circuit 571. As a result, the amount of input charge Qi supplied from the piezoelectric element 33 to the integrating circuit 571 side is larger than that in the case where the capacitance value of the input side capacitor C0 is equal to or higher than the capacitance value of the feedback capacitor C1. It becomes possible to do. As a result, it is possible to suppress a decrease in sensitivity to a charge signal (input charge Qi).

Further, in the pressure detection device 20 of the present embodiment, the housing 60 and the positive path and the negative path from the piezoelectric element 33 to the circuit board 57 are electrically insulated. Therefore, the low frequency noise propagated from the cylinder head 13 to the housing 60 of the pressure detection device 20 is less likely to be transmitted to the circuit board 57. As a result, the fluctuation (fluctuation) of the ground potential in the circuit board 57 due to the low frequency noise is suppressed, and the fluctuation (fluctuation) of the output signal (external output voltage Vo) output from the circuit board 57 is suppressed. It becomes possible to reduce.

Furthermore, in the present embodiment, the circuit board 57 is covered (accommodated) with the metal accommodating member 56 constituting the shield 70. Therefore, the radio waves radiated to the pressure detection device 20 from the outside are blocked by the shield 70 including the accommodating member 56, and it becomes difficult to reach the circuit board 57. As a result, the fluctuation (fluctuation) of the ground potential in the circuit board 57 due to the high frequency noise is suppressed, and the fluctuation (fluctuation) of the output signal (external output voltage Vo) output from the circuit board 57 is reduced. It becomes possible to make it.

Then, in the present embodiment, since the shield 70 also serves as a negative path, the configuration of the pressure detection device 20 can be simplified as compared with the case where the shield 70 and the negative path are separately provided. can do.

[Other]
In the present embodiment, the housing 60 of the pressure detection device 20 is made of a conductive metal material, but the present invention is not limited to this, and has insulating properties such as alumina ceramics and zirconia ceramics. It may be composed of materials. In this case, it is not necessary to insulate the housing 60 and the shield 70 via various insulating members (insulating plate 34, fourth insulating ring 44 and fifth insulating ring 45) and an air gap.

Further, in the present embodiment, the piezoelectric element 33, the positive path, and the circuit board 57 are covered (accommodated) by the shield 70, but at least a part of the circuit board 57 is covered (accommodated). If this is the case, the effect of reducing noise will be produced as compared with the case where the circuit board 57 is not covered (accommodated) at all.

Here, in the present embodiment, the accommodating member 56 having a tubular shape is used to cover (accommodate) the circuit board 57, but the present invention is not limited to this, and the accommodating member 56 is, for example, a metal. You may use a metal braid or the like woven with.

Furthermore, in the present embodiment, the pressure detecting device 20 for detecting the combustion pressure of the internal combustion engine 10 using the piezoelectric element 33 has been described as an example, but the present invention is not limited thereto. For example, it may be applied to a detection device that detects various physical quantities such as temperature, humidity, and flow rate.

Hereinafter, the present invention will be described in more detail based on Examples. However, the present invention is not limited to the following examples as long as the gist of the present invention is not exceeded.
The present inventor has produced a plurality of pressure detection devices 20 in which the presence / absence of the input side capacitor C0 on the circuit board 57 and the capacitance values of the input side capacitor C0 and the feedback capacitor C1 are different, and BCI (Bulk Current Injection). ) The evaluation by the test and the signal waveform of the output signal (external output voltage Vo) were evaluated.

[Sample used for evaluation]
Table 1 shows the relationship between the input side capacitor C0 and the feedback capacitor C1 in the 26 samples used in this evaluation.

Then, each sample shown in Table 1 will be described.
First, in the first sample S1 to the thirteenth sample S13, the capacitance value of the feedback capacitor C1 is fixed at 560 pF. On the other hand, in the 14th sample S14 to the 26th sample S26, the capacitance value of the feedback capacitor C1 is fixed at 2200pF. Hereinafter, the first sample S1 to the thirteenth sample S13 will be referred to as a "first group", and the 14th sample S14 to the 26th sample S26 will be referred to as a "second group".

First, in the first group, the first sample S1 does not have the input side capacitor C0 (described as “none”), and has a conventional configuration. Further, in the second sample S2 to the fourth sample S4, the capacitance values of the input side capacitor C0 are 100 pF, 220 pF, and 470 pF, respectively, which are smaller than the capacitance values of the feedback capacitor C1. Further, in the fifth sample S5, the capacitance value of the input side capacitor C0 is 560 pF, which is equal to the capacitance value of the feedback capacitor C1. Furthermore, in the sixth sample S6 to the thirteenth sample S13, the capacitance values of the input side capacitor C0 are 820pF, 1000pF, 2200pF, 3300pF, 5100pF, 6800pF, 8200pF, and 10000pF, respectively, and the feedback capacitor C1 is static. It is larger than the capacitance value.

On the other hand, in the second group, the 14th sample S14 does not have the input side capacitor C0 (described as “none”), and has a conventional configuration. Further, in the 15th sample S15 to the 20th sample S20, the capacitance values of the input side capacitor C0 are 100pF, 220pF, 470pF, 560pF, 820pF, and 1000pF, respectively, which are higher than the capacitance values of the feedback capacitor C1. It's getting smaller. Further, in the 21st sample S21, the capacitance value of the input side capacitor C0 is 2200 pF, which is equal to the capacitance value of the feedback capacitor C1. Furthermore, in the 22nd sample S22 to the 26th sample S26, the capacitance values of the input side capacitors C0 are 3300pF, 5100pF, 6800pF, 8200pF and 10000pF, respectively, which are larger than the capacitance values of the feedback capacitor C1. It has become.

Therefore, the first sample S1 and the 14th sample S14 are common in that they do not have the input side capacitor C0. Further, the second sample S2 to the fourth sample S4 and the fifteenth sample S15 to the twentieth sample S20 are common in that the capacitance value of the input side capacitor C0 is smaller than the capacitance value of the feedback capacitor C1. Further, the fifth sample S5 and the 21st sample S21 are common in that the capacitance value of the input side capacitor C0 is equal to the capacitance value of the feedback capacitor C1. Furthermore, the sixth sample S6 to the thirteenth sample S13 and the 22nd sample S22 to the 26th sample S26 are common in that the capacitance value of the input side capacitor C0 is larger than the capacitance value of the feedback capacitor C1. ..

[BCI test]
Next, the BCI test used for the evaluation of the pressure detection device 20 will be briefly described.
The BCI test is defined as an immunity standard corresponding to EMS (Electromagnetic Susceptibility) among EMC (Electromagnetic Compatibility) standards for automobiles, and is specified in, for example, ISO11452-4: 2011.

This time, while the connection cable 90 was attached to the pressure detection device 20, the BCI test was performed with the housing 60 of the pressure detection device 20 insulated from the outside via an air layer or the like. Here, the length of the connection cable 90 is set to 1 m. Further, in the BCI test, noise was applied to the connection cable 90 at a position 150 mm from the first connection terminal 52a to the third connection terminal 52c to which the connection cable 90 is attached. Further, the noise applied to the connection cable 90 is created by the AM modulation method, and the frequency range of the applied noise is set to exceed 0 and 1000 MHz (1 GHz) or less. Then, with noise applied to the connection cable 90, the amount of fluctuation in the voltage (external output voltage Vo) between the output signal terminal 570d and the output ground terminal 570e provided on the circuit board 57 (hereinafter, the output voltage). (Called the amount of fluctuation) was measured. In ISO11452-4: 2011, the frequency range of the noise to be applied is defined as 1 MHz to 400 MHz, and this time, the measurement is performed in a wider frequency range.

FIG. 6 is a graph showing the results of the BCI test in each circuit configuration. Here, FIG. 6A shows the result when the first sample S1 is used as the circuit board 57, and FIG. 6B shows the result when the first sample S1 is used as the circuit board 57, and the input signal terminal 570a and the input ground. The result when the terminal 570b is opened (not connected to the piezoelectric element 33) is shown, and FIG. 6C shows the result when the fifth sample S5 is used as the circuit board 57. In each of FIGS. 6A to 6C, the horizontal axis is the frequency (0 to 1000 MHz), and the vertical axis is the output voltage fluctuation amount (V), which is the fluctuation amount of the external output voltage Vo. There is.

First, in the example shown in FIG. 6A, it was found that there are regions in which the output voltage fluctuation amount becomes large in absolute value in the vicinity of 150 MHz, the vicinity of 260 MHz, the vicinity of 460 MHz, and the vicinity of 570 MHz, respectively. The maximum value of the output voltage fluctuation amount was +0.006V (+ 6mV), and the minimum value was −0.024V (-24mV).

Further, in the example shown in FIG. 6B, it was found that there is a region in which the output voltage fluctuation amount becomes large in absolute value in each of the vicinity of 160 MHz and the vicinity of 950 MHz. The maximum value of the output voltage fluctuation amount was +0.007V (+ 7mV), and the minimum value was −0.001V (-1mV).

Further, in the example shown in FIG. 6C, it was found that there are regions where the output voltage fluctuation amount becomes large in absolute value in each of the vicinity of 160 MHz, the vicinity of 250 MHz, the vicinity of 470 MHz, the vicinity of 570 MHz, and the vicinity of 940 MHz. The maximum value of the output voltage fluctuation amount was +0.006V (+ 6mV), and the minimum value was −0.011V (−11mV).

Here, since FIG. 6B shows the output voltage of the circuit board 57 in the state where the piezoelectric element 33 is not connected, the output voltage fluctuation amount is the smallest among these three. Further, when comparing FIG. 6 (a) and FIG. 6 (c), it can be seen that the output voltage fluctuation amount is smaller as shown in FIG. 6 (c).

Although detailed description is not given here, when the 14th sample S14 which does not have the input side capacitor C0 like the 1st sample S1 is used as the circuit board 57, the result is the same as that of the 1st sample S1 ( (See FIG. 6A) was obtained. Further, as the circuit board 57, the second sample S2 to the fourth sample S4, the sixth sample S6 to the thirteenth sample S13, and the fifteenth sample S15 to the 26th sample S26 having the same input side capacitor C0 as the fifth sample S5 are used. If so, the same result as that of the fifth sample S5 (see FIG. 6C) was obtained.

From the above results, it is understood that the output voltage fluctuation amount in the BCI test can be reduced by connecting the input side capacitor C0 in parallel with the piezoelectric element 33 on the input side of the integration circuit 571 in the circuit board 57.

[Output voltage waveform]
Subsequently, the output voltage waveform used for the evaluation of the pressure detection device 20 will be briefly described.
The internal combustion engine 10 whose pressure is detected by the pressure detection device 20 repeatedly repeats four strokes (in the case of a four-stroke engine) of a suction stroke, a compression stroke, a combustion stroke, and an exhaust stroke. Here, the pressure in the cylinder of the internal combustion engine 10 increases with time in the compression stroke and decreases with time in the subsequent combustion stroke. At this time, the peak (maximum value) of the pressure in the cylinder of the internal combustion engine 10 occurs near the top dead center. Then, the piezoelectric element 33 outputs a charge signal (input charge Qi) corresponding to the fluctuation of the pressure in the cylinder, and the amplifier circuit 571 outputs a voltage signal (internal output voltage Vi) in which the charge signal is integrated. The amplifier circuit 572 outputs an output signal (external output voltage Vo) obtained by amplifying the voltage signal.

FIG. 7 is a diagram showing the shape of the output voltage waveform in each circuit configuration. Here, FIG. 7A shows an output voltage waveform when the second sample S2 is used as the circuit board 57, and FIG. 7B shows an output voltage waveform when the eighth sample S8 is used as the circuit board 57. , Each is shown. In each of FIGS. 7A and 7B, the horizontal axis represents the elapsed time (sec) and the vertical axis represents the external output voltage Vo (V) of the circuit board 57. Further, each of FIGS. 7A and 7B shows the detection results when the internal combustion engine 10 is operated at the same and constant rotation speed.

First, in the example shown in FIG. 7A, the waveform of the external output voltage Vo accompanying the increase and decrease of the pressure has a triangular shape in which the peak value at the top is a point. On the other hand, in the example shown in FIG. 7B, the waveform of the external output voltage Vo accompanying the increase and decrease of the pressure has a rectangular shape in which the peak value at the top is a line. Here, as is clear from the operation of the internal combustion engine 10 described above, FIG. 7 (a) accurately represents the change in pressure in the internal combustion engine 10, whereas FIG. 7 (b) shows the internal combustion engine. This means that the change in pressure within 10 is inaccurately represented. Hereinafter, the output voltage waveform shown in FIG. 7A is referred to as a “normal waveform”, and the output voltage waveform shown in FIG. 7B is referred to as an “abnormal waveform”.

FIG. 8 is a diagram for explaining the relationship between the capacitance values of the input side capacitor and the feedback capacitor in each circuit configuration and the output voltage waveform. Here, in FIG. 8, the circuit configuration in which the normal waveform is obtained is described as “normal”, and the circuit configuration in which the abnormal waveform is obtained is described as “abnormal”.

First, when the first sample S1 and the 14th sample S14 having no input side capacitor C0 were used as the circuit board 57, a normal waveform was confirmed as in the second sample S2. Further, as the circuit board 57, the third sample S3, the fourth sample S4, and the fifteenth sample S15 to the twentieth sample S20 in which the capacitance value of the input side capacitor C0 is set to be less than the feedback capacitor C1 as in the second sample S2. A normal waveform was confirmed in the same manner as in the second sample S2.

On the other hand, when the fifth sample S5 and the 21st sample S21 in which the capacitance value of the feedback capacitor C1 is set to the same size as the input side capacitor C0 are used as the circuit board 57, the same as the eighth sample S8. An abnormal waveform was confirmed in. Further, as the circuit board 57, the sixth sample S6 to the thirteenth sample S13 and the 22nd sample S22 to the 26th sample S26 in which the capacitance value of the feedback capacitor C1 is set to be less than the input side capacitor C0 as in the eighth sample S8. An abnormal waveform was confirmed in the same manner as in the eighth sample S8.

In this way, when the input side capacitor C0 is connected in parallel with the piezoelectric element 33 on the input side of the integration circuit 571 on the circuit board 57, the capacitance value thereof is set higher than that of the feedback capacitor C1 provided in the integration circuit 571. It is understood that the output voltage waveform from the circuit board 57 can be made a normal waveform by making it smaller. This is because when the capacitance value of the input side capacitor C0 is set to the feedback capacitor C1 or more, the input charge Qi from the piezoelectric element 33 is more noise suppression circuit 573 (input side capacitor C0) than the integration circuit 571 (feedback capacitor C1). ) Is considered to be caused by a decrease in sensitivity.

The capacitance value of the input side capacitor C0 can be appropriately changed within a range smaller than the capacitance value of the feedback capacitor C1. Here, when it is desired to raise the frequency of the noise to be removed, the capacitance value of the input side capacitor C0 may be made smaller, and when it is desired to lower the frequency of the noise to be removed, the frequency may be lowered. , The capacitance value of the input side capacitor C0 may be made larger.

1 ... Pressure detection system, 10 ... Internal engine, 20 ... Pressure detection device, 30 ... Detection unit, 31 ... Tip side housing, 32 ... Diaphragm head, 33 ... Piezoelectric element, 34 ... Insulation plate, 35 ... Tip electrode member, 36 ... Rear end electrode member, 37 ... 1st pressurizing member, 38 ... 2nd pressurizing member, 39 ... Support member, 40 ... Insulated pipe, 41 ... 1st insulating ring, 42 ... 2nd insulating ring, 43 ... 3 Insulation ring, 44 ... 4th insulation ring, 45 ... 5th insulation ring, 50 ... Processing unit, 51 ... Rear end side housing, 52 ... Connection member, 53 ... Conduction member, 54 ... Coating member, 55 ... Buffer member , 56 ... accommodating member, 57 ... circuit board, 58 ... holding member, 60 ... housing, 70 ... shield, 80 ... control device, 90 ... connection cable, 570 ... printed wiring board, 571 ... integrator circuit, 572 ... amplification Circuit, 573 ... Noise suppression circuit, 574 ... Power supply circuit

Claims (5)

An output element that outputs a charge signal according to changes in physical quantities,
An operational amplifier having an inverting input terminal to which the charge signal is input, a non-inverting input terminal to which a reference voltage is input, and an output terminal for outputting an output signal, and the inverting input terminal and the output terminal are connected to each other. An integrator circuit that is equipped with a feedback capacitor and outputs a voltage signal obtained by integrating the charge signal as the output signal.
A detection device including an input side capacitor connected to the inverting input terminal in parallel with the output element and having a capacitance smaller than that of the feedback capacitor. The integrating circuit further includes a feedback resistor connected in parallel with the feedback capacitor by being connected to the inverting input terminal and the output terminal.
The detection device according to claim 1, wherein the time constants of the feedback capacitor and the feedback resistor are 1 sec or more. The integrating circuit further includes a feedback resistor connected in parallel with the feedback capacitor by being connected to the inverting input terminal and the output terminal.
The detection device according to claim 1, wherein the resistance value of the feedback resistor is 1 GΩ or more. The detection device according to any one of claims 1 to 3, further comprising an amplifier circuit for amplifying the voltage signal input from the integrating circuit. An operational amplifier having an inverting input terminal to which the charge signal is input from an output element that outputs a charge signal according to a change in physical quantity, a non-inverting input terminal to which a reference voltage is input, and an output terminal to output an output signal. An integrator circuit that includes an amplifier, a feedback capacitor connected to the inverting input terminal and the output terminal, and outputs a voltage signal obtained by integrating the charge signal as the output signal.
An input-side capacitor that is provided at the inverting input terminal so as to be connected in parallel with the output element and has a smaller capacitance than the feedback capacitor.
A circuit board including the integrating circuit and a substrate on which the input side capacitor is mounted.

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