Pressure detection device and pressure detection system having first and second housings electrically insulated from each other

A pressure detection device includes: a piezoelectric element that detects a pressure change via a diaphragm head or the like; a circuit board that is provided with a processing circuit that performs electrical processing with respect to a charge signal outputted from the piezoelectric element; a conductive housing member, which has conductivity and is disposed to cover (house) the circuit board, and which is connected to the ground of the circuit board; and a housing (a leading end side housing, the diaphragm head and a rear end side housing), which houses the piezoelectric element, the circuit board and the housing member, and which is electrically insulated from the piezoelectric element, the circuit board and the housing member.

TECHNICAL FIELD

The present invention relates to a pressure detection device and a pressure detection system.

BACKGROUND ART

As a device for detecting a pressure in a combustion chamber of an internal combustion engine or the like, a device using a detection element, such as a piezoelectric element, is suggested.

For example, in Patent Document 1, there is described a pressure detection device including: a cylindrical housing; a diaphragm attached to a tip end side of the housing; a piezoelectric element disposed on a rear end side of the diaphragm in the housing to detect a pressure acting via the diaphragm; a first electrode section which is provided between the diaphragm and the piezoelectric element to abut both of them in the housing; a second electrode section which is provided on a rear end side of the piezoelectric element in the housing to abut the piezoelectric element; an insulating ring which is provided on a rear end side of the second electrode section in the housing to abut the second electrode section; a support member which is provided on a rear end side of the insulating ring in the housing to abut the insulating ring; a pressure member which houses, in the housing, the first electrode section, the piezoelectric element, the second electrode section, the insulating ring and the support member inside thereof, and which is fixed to the housing to pressurize the first electrode section in the axial direction of the housing to thereby cause a load to act on the piezoelectric element.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

Here, if a noise enters inside the pressure detection device from the outside, the noise is superposed to the output from the detection element. Due to superposition of the noise in this manner, an error in the pressure to be detected is increased.

An object of the present invention is to suppress superposition of the noise from the outside to the output from the detection element.

Solution to Problem

A pressure detection device of the present invention includes: a detection element that detects a change in pressure; a first housing that has conductivity and houses the detection element inside thereof; and a second housing that has conductivity and houses the first housing inside thereof, wherein the first housing and the second housing are electrically insulated.

Moreover, the pressure detection device further includes an insulating member that has an insulating property and is disposed between the first housing and the second housing to electrically insulate the first housing and the second housing.

Moreover, the pressure detection device further includes a processing circuit that applies electrical processing to a detection signal detected by the detection element, wherein the processing circuit is housed in the first housing, and a ground of the processing circuit and a ground of the detection element are connected to the first housing.

Moreover, the pressure detection device further includes a DC suppressing part that connects the ground of the processing circuit and the first housing while suppressing passage of DC current.

Moreover, the second housing has the conductivity higher than that of the first housing, and the first housing has resistance to acids higher than that of the second housing.

Moreover, the first housing holds the detection element from a leading end side and a rear end side of the first housing to impart a load to the detection element, and wherein the pressure detection device further includes: a deformation member that is attached to a leading end side of the second housing and is deformed upon receiving pressure from outside; an insulating transmission member that has an insulating property and is provided between the deformation member and the detection element inside the second housing, and transmits the pressure acting on the deformation member to the detection element; and a fixing member that fixes the first housing to the second housing in a state where the first housing is electrically insulated from the deformation member and the second housing.

Moreover, the first housing shows a cylindrical shape and includes a projection part that projects outward on an outer circumferential surface thereof, and the fixing member holds the projection part with an inner circumferential surface of the second housing via the insulating member to fix the first housing to the second housing.

Moreover, the first housing includes: a first imparting member that is disposed outside the detection element, electrically connected to a leading end side of the detection element and electrically insulated from a rear end side of the detection element, to thereby impart the load from the leading end side of the detection element; and a second imparting member that is provided on a rear end side of the first imparting member, electrically connected to the first imparting member, and electrically insulated from the detection element, to thereby impart the load from the rear end side of the detection element by being fixed to the first imparting member.

Moreover, the pressure detection device further includes: a conduction member that is housed inside the first housing and is electrically connected to a rear end side of the detection element, to thereby conduct a detection signal outputted from the detection element, wherein the first housing is electrically connected to a leading end side of the detection element and is electrically insulated from the conduction member, to thereby serve as a ground of the detection element.

Moreover, from another standpoint, a pressure detection system of the present invention includes: a detection device including: a detection element that detects a change in pressure; a processing circuit that applies electrical processing to a detection signal outputted by the detection element; an electrical conduction member that has conductivity and is disposed to cover at least a part of the processing circuit, and is connected to a ground of the processing circuit; and a housing that houses the detection element, the processing circuit and the electrical conduction member, the housing being electrically insulated from the detection element, the processing circuit and the electrical conduction member, and mounted to a grounded conductor in a state of being in contact with the conductor; and a supplying and processing device that is connected to the detection device via a supply line for supplying power-supply voltage to the processing circuit, a transmission line for transmitting an output signal outputted from the processing circuit and a ground line to be connected to the electrical conduction member or the ground of the processing circuit, and is connected to the conductor by a system different from a system via the ground line, to supply the power-supply voltage to the detection device and to apply processing to the output signal inputted from the detection device.

Moreover, from another standpoint, a pressure detection system of the present invention includes: a detection device including: a detection element that detects a change in pressure; a processing circuit that applies electrical processing to a detection signal outputted by the detection element; a first housing that has conductivity and is disposed to cover at least a part of the processing circuit, and is connected to a ground of the processing circuit; a second housing that has conductivity and houses the first housing, and is mounted in a state of being in contact with a grounded conductor; and an insulating member that has an insulating property and is disposed between the first housing and the second housing to electrically insulate the first housing and the second housing; and a supplying and processing device that is connected to the detection device via a supply line for supplying power-supply voltage to the processing circuit, a transmission line for transmitting an output signal outputted from the processing circuit and a ground line to be connected to the first housing or the ground of the processing circuit, and is connected to the conductor by a system different from a system via the ground line, to supply the power-supply voltage to the detection device and to apply processing to the output signal inputted from the detection device.

Advantageous Effects of Invention

According to the present invention, it is possible to suppress superposition of the noise from the outside to the output from the detection element.

DESCRIPTION OF EMBODIMENTS

Hereinafter, exemplary embodiments according to the present invention will be described in detail with reference to attached drawings.

[Configuration of Pressure Detection System]

FIG. 1is a schematic configuration view of a pressure detection system1related to the exemplary embodiments.

The pressure detection system1includes: a pressure detection device20that detects a pressure (combustion pressure) in a combustion chamber C in an internal combustion engine10; a controller80that performs power feeding to the pressure detection device20and controls operation of the internal combustion engine10based on the pressure detected by the pressure detection device20; and a connection cable90that electrically connects the pressure detection device20and the controller80.

Here, the internal combustion engine10, from which the pressure is to be detected, includes: a cylinder block11inside of which a cylinder is formed; a piston12that reciprocates inside the cylinder; and a cylinder head13that is fastened to the cylinder block11to constitute a combustion chamber C together with the piston12and so forth. Moreover, the cylinder head13is provided with a communication hole13athat causes the combustion chamber C to be communicated with the outside. Inside the communication hole13a, female screws (not shown) are formed to attach the pressure detection device20to the internal combustion engine10by screwing male screws (not shown) formed on an outer circumferential surface of the pressure detection device20. Then, the cylinder block11that constitutes the internal combustion engine10, the piston12and the cylinder head13are composed of a metallic material having conductivity, such as cast iron or aluminum. Note that, both end portion side of the communication hole13a, there is provided a sealing member (not shown) interposed between the cylinder head13and the pressure detection device20to keep airtightness in the combustion chamber C.

[Configuration of Pressure Detection Device]

FIG. 2is a perspective view of the pressure detection device20in Exemplary embodiment 1. Moreover,FIG. 3is a cross-sectional view (a III-III cross-sectional view inFIG. 2) of the pressure detection device20. Further,FIG. 4is an enlarged cross-sectional view of a leading end side of the pressure detection device20.

The pressure detection device20as an example of a detection device includes a detection part30that detects a pressure and a processing part50that performs various kinds of processing to electric signals obtained with detection of the pressure by the detection part30. Then, the pressure detection device20is attached to the internal combustion engine10shown inFIG. 1so that the detection part30faces the combustion chamber C (downward inFIG. 1) and the processing part50faces the outside (upward inFIG. 1). Note that, in the following description, inFIG. 2, a side heading for lower left in the figure (detection part30side) is referred to as “leading end side” of the pressure detection device20and a side heading for upper right in the figure (processing part50side) is referred to as “rear end side” of the pressure detection device20. Moreover, in the following description, a centerline direction of the pressure detection device20indicated by a dot-and-dash line inFIG. 2is simply referred to as a centerline direction.

The detection part30includes a leading end side housing31mated with a leading end side of a rear end side housing51(which will be described in detail later) provided to the processing part50and a diaphragm head32attached to a leading end side of the leading end side housing31.

Of these, the leading end side housing31is a member having a hollow structure and showing a cylindrical shape as a whole. The leading end side housing31is composed of a metallic material having conductivity and high resistance to acids, such as stainless steel. The leading end side housing31includes a first leading end side housing311that is positioned relatively close to the leading end side thereof and a second leading end side housing312that is positioned relatively close to the rear end side thereof. Here, by applying laser welding to an outer circumferential surface on the rear end side of the first leading end side housing311and an inner circumferential surface on the leading end side of the second leading end side housing312, the leading end side housing31has a configuration integrating both. Then, to the leading end side of the first leading end side housing311, the diaphragm head32is attached by laser welding, and, to the rear end side of the second leading end side housing312, the rear end side housing51is attached by fitting. Note that, on the outer circumferential surface of the center portion in the centerline direction of the second leading end side housing312, the male screws (not shown), which are engaged with the female screws (not shown) provided on the inner circumferential surface of the communication hole13a(refer toFIG. 1) of the cylinder head13, are formed.

On the other hand, the diaphragm head32as an example of a deformation member shows a disk shape as a whole. The diaphragm head32is composed of a metallic material having conductivity and high resistance to heat and acids, such as stainless steel. Particularly, in this example, the diaphragm head32and the above-described leading end side housing31are composed of the same material. The diaphragm head32includes: a pressure receiving surface (front surface)32athat is exposed to the outside (combustion chamber C side) to receive a pressure; a concave part32bthat is provided by cutting a rear surface, which is the back side of the pressure receiving surface32ain a ring shape; and a convex part32cthat projects, as a result of presence of the concave part32b, from the center portion of the rear surface of the pressure receiving surface32atoward the rear end side. The diaphragm head32is provided to close an opening part of the leading end side of the first leading end side housing311. Then, at a boundary portion between the diaphragm head32and the first leading end side housing311, laser welding is applied around the outer circumferential surface.

Moreover, the detection part30further includes: a piezoelectric element33; an insulating plate34; a leading end electrode member35; a rear end electrode member36; a first pressure member37; a second pressure member38; a support member39; an insulating pipe40; a first insulating ring41; a second insulating ring42; a third insulating ring43; a fourth insulating ring44; and a fifth insulating ring45, which are disposed (housed) inside the leading end side housing31.

The piezoelectric element33as an example of a detection element shows a columnar shape as a whole. The piezoelectric element33is provided with a piezoelectric body showing a piezoelectric action of piezoelectric longitudinal effect. The piezoelectric longitudinal effect refers to generation of charge on a surface of the piezoelectric body in the direction of a charge generating axis when an external force is applied to a stress application axis in the same direction as the charge generating axis of the piezoelectric body. The piezoelectric element33is disposed inside the leading end side housing31and on the rear end side of the diaphragm head32. The piezoelectric element33is housed in the leading end side housing31so that the centerline direction thereof is in the same direction as the stress application axis. Here, the piezoelectric element33is disposed inside the insulating pipe40provided inside the first pressure member37which is provided inside the leading end side housing31. Moreover, the outer diameter of the piezoelectric element33is slightly smaller than the inner diameter of the insulating pipe40that houses the piezoelectric element33inside thereof. Then, the surface on the leading end side of the piezoelectric element33is in contact with the surface on the rear end side of the leading end electrode member35. On the other hand, the surface on the rear end side of the piezoelectric element33is in contact with the surface on the leading end side of the rear end electrode member36. Moreover, the outer circumferential surface of the piezoelectric element33faces the inner circumferential surface of the insulating pipe40.

In this manner, by providing the insulating pipe40between the inner circumferential surface of the first pressure member37and the outer circumferential surface of the piezoelectric element33, the first pressure member37and the piezoelectric element33are not directly in contact with each other.

Next, a case in which piezoelectric transversal effect is used for the piezoelectric element33will be exemplified. The piezoelectric transversal effect refers to generation of charge on a surface of the piezoelectric body in the direction of a charge generating axis when an external force is applied to a stress application axis in a position orthogonal to the charge generating axis of the piezoelectric body. Plural piezoelectric bodies formed into thin plate shape may be laminated for configuration, and, by laminating in this manner, it is possible to efficiently collect charges generated in the piezoelectric body, to thereby increase sensitivity of a sensor. As the piezoelectric body that can be used for the piezoelectric element33, use of langasite crystal (langasite, langatate, langanite, LTGA), quartz or gallium phosphate having the piezoelectric longitudinal effect and the piezoelectric transversal effect can be shown as examples. Note that, in the piezoelectric element33of the exemplary embodiment, langasite single crystal is used as the piezoelectric body.

The insulating plate34as an example of an insulating transmission member shows a disk shape as a whole. The insulating plate34is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina. The insulating plate34is disposed at a position to close an opening part on the leading end side of the first pressure member37provided inside the leading end side housing31. Then, the insulating plate34is disposed on the rear end side of the diaphragm head32and on the leading end side of the leading end electrode member35. Moreover, the outer diameter of the insulating plate34is slightly smaller than the inner diameter of the opening part provided to the leading end side of the first pressure member37, and is slightly larger than the outer diameter of the convex part32cof the diaphragm head32. Then, the surface on the leading end side of the insulating plate34is in contact with the convex part32cof the diaphragm head32. On the other hand, the surface on the rear end side of the insulating plate34is in contact with the surface on the leading end side of the leading end electrode member35. Moreover, the outer circumferential surface of the insulating plate34faces the inner circumferential surface of the opening part provided to the leading end side of the first pressure member37.

The leading end electrode member35shows a columnar shape as a whole. The leading end electrode member35is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel. The leading end electrode member35is disposed inside the first pressure member37provided inside the leading end side housing31. However, different from the above-described piezoelectric element33, the leading end electrode member35is not housed inside the insulating pipe40. Then, the leading end electrode member35is disposed on the rear end side of the insulating plate34and on the leading end side of the piezoelectric element33. Moreover, the outer diameter of the leading end electrode member35is slightly smaller than the inner diameter of the first pressure member37that houses the leading end electrode member35inside thereof. Then, the surface on the leading end side of the leading end electrode member35is in contact with the surface on the rear end side of the insulating plate34and the surface on the back side of the opening part provided to the leading end side of the first pressure member37. On the other hand, the surface on the rear end side of the leading end electrode member35is in contact with the surface on the leading end side of the piezoelectric element33. Moreover, the outer circumferential surface of the leading end electrode member35faces the inner circumferential surface of the first pressure member37.

The rear end electrode member36shows a columnar shape as a whole. The rear end electrode member36is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel. The rear end electrode member36is disposed inside the first pressure member37provided inside the leading end side housing31. Here, the leading end side of the rear end electrode member36is disposed inside the insulating pipe40provided inside the first pressure member37. In contrast thereto, the rear end side of the rear end electrode member36is disposed outside the insulating pipe40. At the center portion on the surface of the rear end side in the rear end electrode member36, a countersunk hole36afor inserting the leading end side of the second pressure member38is formed. Moreover, the outer diameter of the rear end electrode member36is substantially the same as the outer diameter of the piezoelectric element33and is slightly smaller than the inner diameter of the insulating pipe40. Then, the surface on the leading end side of the rear end electrode member36is in contact with the surface on the rear end side of the piezoelectric element33. On the other hand, the surface of the rear end side of the rear end electrode member36is in contact with the surface on the leading end side of the first insulating ring41, and the bottom surface of the countersunk hole36aprovided to the rear end side of the rear end electrode member36is in contact with the leading end side of the second pressure member38. Moreover, the leading end side of the outer circumferential surface of the rear end electrode member36faces the inner circumferential surface of the insulating pipe40. In contrast thereto, the rear end side of the outer circumferential surface of the rear end electrode member36faces the inner circumferential surface of the first pressure member37via an air gap. In this manner, by providing the insulating pipe40and the air gap between the inner circumferential surface of the first pressure member37and the outer circumferential surface of the rear end electrode member36, the first pressure member37and the rear end electrode member36are not directly in contact with each other.

The first pressure member37shows a cylindrical shape as a whole. The first pressure member37is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel. The first pressure member37is provided inside the leading end side housing31and the insulating plate34is disposed to close the opening part provided to the leading end side thereof, and the first pressure member37houses the piezoelectric element33, the leading end electrode member35, the rear end electrode member36, the second pressure member38, the leading end side of the support member39, the insulating pipe40and the first insulating ring41inside thereof. Then, the first pressure member37is disposed on the rear end side of the diaphragm head32and on the leading end side of a buffer member55(which will be described in detail later) constituting the processing part50. Moreover, the outer diameter of the first pressure member37differs depending on the position in the centerline direction; however, at all the positions, the outer diameter of the first pressure member37is smaller than the inner diameter of the leading end side housing31(more specifically, the first leading end side housing311). Further, the inner diameter of the first pressure member37is, at the positions facing the insulating plate34, the leading end electrode member35, the insulating pipe40(the piezoelectric element33and the rear end electrode member36) and the first insulating ring41, larger than the outer diameters of these components, and at the position facing the support member39, slightly smaller than the outer diameter of the support member39. Here, between the outer circumferential surface on the rear end side of the first pressure member37and the inner circumferential surface on the rear end side of the first leading end side housing311, the second insulating ring42is disposed at a position relatively on the leading end side, and the third insulating ring43is disposed at a position relatively on the rear end side. Then, the surface of the leading end side (surface on the front side of the opening part) of the first pressure member37faces the convex part32bprovided to the rear end side of the diaphragm head32. On the other hand, the rear end side of the first pressure member37is in contact with the leading end side of the buffer member55. Moreover, the rear end side of the outer circumferential surface of the first pressure member37is in contact with the inner circumferential surface of the second insulating ring42, and the rearmost end side thereof faces the third insulating ring43via the air gap. Further, the leading end side of the outer circumferential surface of the first pressure member37faces the inner circumferential surface of the first leading end side housing311via the air gap. In this manner, by providing the air gap formed by the concave part32bbetween the surface on the leading end side of the first pressure member37and the rear surface of the diaphragm head32, and by providing the second insulating ring42between the outer circumferential surface of the first pressure member37and the inner circumferential surface of the first leading end side housing311of the leading end side housing31, the leading end side housing31, the diaphragm head32and the first pressure member37are not directly in contact with one another. In contrast thereto, the inner circumferential surface of the first pressure member37is directly in contact with the outer circumferential surface of each of the leading end electrode member35, the insulating pipe40, the first insulating ring41and the support member39. Moreover, the inner circumferential surface of the first pressure member37is not directly in contact with the outer circumferential surface of each of the piezoelectric element33and the rear end electrode member36.

The second pressure member38shows a spiral shape as a whole, and is a coil spring expanding and contracting in the centerline direction. The second pressure member38is composed of a metallic material having conductivity, which is higher than the conductivity of the leading end side housing31, such as brass. The second pressure member38is disposed inside the first pressure member37provided inside the leading end side housing31to pass through the support member39and the first insulating ring41positioned inside the first pressure member37to reach the countersunk hole36aof the rear end electrode member36. Then, the second pressure member38is disposed on the rear end side of the rear end electrode member36and on a leading end side of a conduction member53(which will be described in detail later) provided to the processing part50. Moreover, the outer diameter of the second pressure member38is smaller than the inner diameter of the opening part provided on the leading end side of the support member39, the inner diameter of a through hole provided to the first insulating ring41and the inner diameter of the countersunk hole36aof the rear end electrode member36. Further, the inner diameter of the second pressure member38is larger than an outer diameter of a leading end side convex part53a(which will be described in detail later) provided on the leading end side of the conduction member53. Then, the leading end side of the second pressure member38is in contact with the rear end electrode member36by being inserted into the countersunk hole36aof the rear end electrode member36. On the other hand, the rear end side of the second pressure member38is in contact with the conduction member53due to insertion of the leading end side convex part53aof the conduction member53. Moreover, the leading end side on the outer circumferential surface of the second pressure member38faces the inner circumferential surface of the countersunk hole36aof the rear end electrode member36and the inner circumferential surface of the through hole of the first insulating ring41. Further, the rear end side on the outer circumferential surface of the second pressure member38faces the inner circumferential surface of the support member39via the air gap. In this manner, by providing the air gap between the inner circumferential surface of the support member39and the second pressure member38, the support member39and the second pressure member38are not directly in contact with each other.

The support member39shows a cylindrical shape as a whole. The support member39is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel. The support member39is disposed inside the leading end side housing31, and the leading end side thereof is positioned inside the first pressure member37and the rear end side thereof is positioned outside the first pressure member37. Moreover, the support member39houses the rear end side of the second pressure member38inside thereof, and also houses the leading end side of conduction member53and covering member54(which will be described in detail later) positioned on the leading end side of the processing part50. Then, the support member39is disposed on the rear end side of the first insulating ring41and on the leading end side of a housing member56(which will be described in detail later) constituting the processing part50. Moreover, the outer diameter of the support member39is slightly larger than the inner diameter of the first pressure member37. Further, the inner diameter of the support member39differs depending on the position in the centerline direction; however, at all the positions, the inner diameter of the support member39is larger than the outer diameters of the conduction member53and the covering member54provided to the processing part50. Then, the surface of the leading end side (surface on the front side of the opening part) of the support member39is in contact with the surface on the rear end side of the first insulating ring41. On the other hand, the surface on the rear end side of the support member39faces the covering member54via the air gap. Moreover, the outer circumferential surface of the support member39is in contact with the inner circumferential surface of the first pressure member37. Further, the inner circumferential surface of the support member39faces the second pressure member38, the conduction member53and the covering member54via the air gap. In this manner, by providing the air gap between the inner circumferential surface of the support member39and the second pressure member38, the conduction member53and the covering member54, the support member39is not directly in contact with the second pressure member38, the conduction member53and the covering member54.

The insulating pipe40shows a cylindrical shape as a whole. The insulating pipe40is composed of a synthetic resin material having an insulating property, such as LCP (Liquid Crystal Polymer). The insulating pipe40is disposed inside the first pressure member37provided inside the leading end side housing31. The insulating pipe40houses the leading end side of the piezoelectric element33and the rear end electrode member36inside thereof. Then, the insulating pipe40is disposed on the rear end side of the rear end electrode member35and on the leading end side of the first insulating ring41. Moreover, the outer diameter of the insulating pipe40is slightly smaller than the inner diameter of the first pressure member37. Further, the inner diameter of the insulating pipe40is slightly larger than the outer diameter of each of the piezoelectric element33and the rear end electrode member36. Then, the leading end side of the insulating pipe40faces the surface on the rear end side of the leading end electrode member35. On the other hand, the rear end side of the insulating pipe40faces the surface on the leading end side of the first insulating ring41. Moreover, the outer circumferential surface of the insulating pipe40faces the inner circumferential surface of the first pressure member37. Moreover, the inner circumferential surface of the insulating pipe40faces the outer circumferential surface of each of the piezoelectric element33and the outer circumferential surface of the rear end electrode member36. In this manner, by providing the insulating pipe40and the air gap formed by the insulating pipe40between the first pressure member37and the piezoelectric element33and the rear end electrode member36, the first pressure member37is not directly in contact with the piezoelectric element33and the rear end electrode member36.

The first insulating ring41shows an annular shape as a whole. The first insulating ring41is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina. The first insulating ring41is disposed inside the first pressure member37provided inside the leading end side housing31. At the center portion of the first insulating ring41, a through hole that penetrates through the first insulating ring41is formed along the centerline direction. Moreover, the outer diameter of the first insulating ring41is slightly smaller than the inner diameter of the first pressure member37. Further, the inner diameter of the through hole in the first insulating ring41is slightly larger than the outer diameter of the second pressure member38. Then, the surface on the leading end side of the first insulating ring41is in contact with the surface on the rear end side of the rear end electrode member36. On the other hand, the surface on the rear end side of the first insulating ring41is in contact with the surface on the leading end side of the support member39. Moreover, the outer circumferential surface of the first insulating ring41faces the inner circumferential surface of the first pressure member37. Further, the inner circumferential surface of the first insulating ring41faces the outer circumference of the second pressure member38.

The second insulating ring42shows an annular shape as a whole. The second insulating ring42is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina. The second insulating ring42is disposed inside the leading end side housing31and on the rear end side and outside the first pressure member37. At the center portion of the second insulating ring42, a through hole that penetrates through the second insulating ring42is formed along the centerline direction. Moreover, the outer diameter of the second insulating ring42is slightly larger than the inner diameter of the leading end side housing31(more specifically, the first leading end side housing311). Further, the inner diameter of the second insulating ring42is slightly smaller than the outer diameter of the first pressure member37. Then, the surface on the leading end side of the second insulating ring42is in contact with a surface on a rear end side of a projection part that projects from the outer circumferential surface of the first pressure member37toward the outside. On the other hand, the surface on the rear end side of the second insulating ring42is in contact with the surface on the leading end side of the third insulating ring43. Moreover, the outer circumferential surface of the second insulating ring42is in contact with the inner circumferential surface of the leading end side housing31. Further, the inner circumferential surface of the second insulating ring42is in contact with the outer circumferential surface of the first pressure member37.

The third insulating ring43shows an annular shape as a whole. The third insulating ring43is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina. The third insulating ring43is disposed inside the leading end side housing31and outside the first pressure member37. At the center portion of the third insulating ring43, a through hole that penetrates through the third insulating ring43is formed along the centerline direction. Moreover, the outer diameter of the third insulating ring43is slightly larger than the inner diameter of the leading end side housing31(more specifically, the first leading end side housing311). Further, the inner diameter of the third insulating ring43is larger than the outer diameter of the first pressure member37, and larger than the inner diameter of the second insulating ring42. Then, the surface on the leading end side of the third insulating ring43is in contact with the surface on the rear end side of the second insulating ring42. On the other hand, the surface on the rear end side of the third insulating ring43faces the air gap provided to the rear end side of the third insulating ring43. Moreover, the outer circumferential surface of the third insulating ring43is in contact with the inner circumferential surface of the leading end side housing31. Further, the inner circumferential surface of the third insulating ring43faces the outer circumferential surface of the first pressure member37via the air gap.

The fourth insulating ring44as an example of an insulating member shows an annular shape as a whole. The fourth insulating ring44is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina. The fourth insulating ring44is disposed inside the leading end side housing31(more specifically, the second leading end side housing312) and on the rear end side and outside of the housing member56(which will be described in detail later) provided to the processing part50. At the center portion of the fourth insulating ring44, a through hole that penetrates through the fourth insulating ring44is formed along the centerline direction. Moreover, the outer diameter of the fourth insulating ring44is slightly larger than the inner diameter of the leading end side housing31. Further, the inner diameter of the fourth insulating ring44is slightly smaller than the outer diameter of the housing member56. Then, the surface on the leading end side of the fourth insulating ring44is in contact with the inner circumferential surface of the leading end side housing31. On the other hand, the surface on the rear end side of the fourth insulating ring44is in contact with the outer circumferential surface of the housing member56. Moreover, the outer circumferential surface of the fourth insulating ring44is in contact with the inner circumferential surface of the leading end side housing31. Further, the inner circumferential surface of the fourth insulating ring44is in contact with the outer circumferential surface of the housing member56.

The fifth insulating ring45as an example of the insulating member shows an annular shape as a whole. The fifth insulating ring45is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina. The fifth insulating ring45is disposed inside the leading end side housing31(more specifically, the second leading end side housing312) and outside the housing member56(which will be described in detail later) provided to the processing part50. At the center portion of the fifth insulating ring45, a through hole that penetrates through the fifth insulating ring45is formed along the centerline direction. Moreover, the outer diameter of the fifth insulating ring45is slightly larger than the inner diameter of the leading end side housing31. Further, the inner diameter of the fifth insulating ring45is slightly smaller than the outer diameter of the housing member56. Then, the surface on the leading end side of the fifth insulating ring45is in contact with the inner circumferential surface of the leading end side housing31. On the other hand, the surface on the rear end side of the fifth insulating ring45is in contact with the outer circumferential surface of the housing member56. Moreover, the outer circumferential surface of the fifth insulating ring45is in contact with the inner circumferential surface of the leading end side housing31. Further, the inner circumferential surface of the fifth insulating ring45is in contact with the outer circumferential surface of the housing member56.

In this manner, by providing the fourth insulating ring44and the fifth insulating ring45between the leading end side housing31and the housing member56constituting the processing part50, the leading end side housing31and the housing member56are not directly in contact with each other.

[Configuration of Processing Part]

The processing part50includes: the rear end side housing51mated with the above-described leading end side housing31(more specifically, the second leading end side housing312); and a connection member52provided so that the leading end side thereof is housed inside the rear end side of the rear end side housing51and the rear end side thereof is exposed to the outside of the rear end side of the rear end side housing51to be connected to the connection cable90(refer toFIG. 1).

Of these, the rear end side housing51is a member having a hollow structure and showing a cylindrical shape as a whole. The rear end side housing51is composed of a metallic material having conductivity and high resistance to acids, such as stainless steel. Then, to the leading end side of the rear end side housing51, the rear end side of the leading end side housing31(specifically, the second leading end side housing312) is attached by fitting, and, to the rear end side of the rear end side housing51, the connection member52is attached by setting in.

On the other hand, the connection member52shows a columnar shape as a whole. The connection member52includes a base material composed of a synthetic resin material having an insulating property, such as PPT (Polypropylene Terephthalate), wiring composed of a metallic material having conductivity, such as copper, terminals, and so forth. However, of the connection member52, the portion (the outer circumferential surface) to be brought into contact with the above-described rear end side housing51is composed of the synthetic resin material, to thereby prevent a metallic material from being exposed in the portion (from being brought into contact with the connection member52). Moreover, on the leading end side of the connection member52, a first substrate side terminal521, a second substrate side terminal522and a third substrate side terminal523, each of which serves as an electrical connection terminal, are provided to project toward the leading end side. In contrast thereto, on the rear end side of the connection member52, an opening part520having a concave shape and opening toward the rear end side is formed. Then, inside the opening part520, a first connection terminal52a, a second connection terminal52band a third connection terminal52cto be connected to the connection cable90(refer toFIG. 1) are provided to project toward the rear end side. Here, the first substrate side terminal521, the second substrate side terminal522and the third substrate side terminal523are electrically connected to the first connection terminal52a, the second connection terminal52band the third connection terminal52c, respectively.

Moreover, the processing part50further includes: the conduction member53; the covering member54; the buffer member55; the housing member56; the circuit board57and a holding member58, which are disposed (housed) inside the leading end side housing31and/or the rear end side housing51.

The conduction member53shows a rod shape as a whole. The conduction member53is composed of a metallic material having conductivity, such as brass. The conduction member53is provided with, at the leading end thereof, the leading end side convex part53ahaving a diameter smaller than that of the center portion in the centerline direction, and at the rear end thereof, the rear end side convex part53bhaving a diameter smaller than that of the center portion in the centerline direction. The support member53is disposed inside the leading end side housing31, and the leading end side thereof is positioned inside the first pressure member37, the rear end side thereof is positioned inside the housing member56, and a middle portion thereof between the leading end side and the rear end side is positioned inside the buffer member55. Then, the conduction member53is disposed on the rear end side of the second pressure member38and on the leading end side of the circuit board57. Moreover, the outer diameter of the leading end side convex part53aof the conduction member53is slightly larger than the inner diameter of the second pressure member38. Further, the outer diameter of the rear end side convex part53bof the conduction member53is substantially the same as an inner width of a rear end holding part54a(which will be described in detail later) provided to the covering member54. Still further, the outer diameter of the center portion of the conduction member53in the centerline direction is substantially the same as the inner diameter of the covering member54. The conduction member53is disposed to penetrate through the through hole provided to the covering member54along the centerline direction; the leading end side convex part53aprojects toward the leading end side of the leading end of the covering member54and the rear end side convex part53bprojects toward the rear end side than the concave part provided to the rear end side of the covering member54. Then, the leading end side convex part53aof the conduction member53is in contact with the second pressure member38by being inserted into the inside of the second pressure member38. On the other hand, the rear end side convex part53bof the conduction member53is set into the rear end holding part54aprovided to the covering member54. Moreover, the outer circumferential surface of the center portion of the conduction member53in the centerline direction is in contact with the inner circumferential surface of the covering member54.

The covering member54shows a cylindrical shape as a whole. The covering member54includes a base material composed of a synthetic resin material having an insulating property, such as PPT, wiring composed of a metallic material having conductivity, such as copper, terminals, and so forth. However, of the covering member54, the portion (the outer circumferential surface) facing the support member39, the buffer member55and the housing member56is composed of the synthetic resin material, to thereby prevent a metallic material from being exposed in the portion. Moreover, on the rear end side of the covering member54, the rear end holding part54a, which is composed of a metallic material and sets the rear end side convex part53bof the conduction member53in to hold thereof, is provided. The covering member54is disposed inside the leading end side housing31, and the leading end side thereof is positioned inside the first pressure member37, the rear end side thereof is positioned inside the housing member56, and a middle portion thereof between the leading end side and the rear end side is positioned inside the buffer member55. Then, the covering member54is disposed on the rear end side of the second pressure member38and on the leading end side of the circuit board57. The outer circumferential surface of the covering member54has a shape in which the outer diameter increases in a stepwise manner from the leading end side toward the rear end side. At the center portion of the covering member54, a through hole that penetrates through the covering member54is formed along the centerline direction. Moreover, the outer diameter on the leading end side of the covering member54is smaller than the inner diameter of the support member39and the outer diameter on the rear end side of the covering member54is smaller than the inner diameter of the housing member56. Further, the inner diameter of the covering member54is substantially the same as the outer diameter of the center portion of the conduction member53in the centerline direction. Then, the leading end of the covering member54is in contact with a rear end of a bulging part provided to the leading end side of the conduction member53and having the outer diameter slightly larger than that of the center portion of the conduction member53in the centerline direction. On the other hand, the rear end of the covering member54is in contact with the leading end of the circuit board57. Moreover, the outer circumferential surface of the covering member54faces the inner circumferential surface of the support member39via the air gap. Further, the inner circumferential surface of the covering member54is in contact with the conduction member53.

The buffer member55shows a spiral shape as a whole, and is a coil spring expanding and contracting in the centerline direction. The buffer member55is composed of a metallic material having conductivity, such as brass. The buffer member55is disposed inside the leading end side housing31, and the leading end side thereof is positioned outside the first pressure member37and the rear end side thereof is positioned outside the housing member56. In other words, the buffer member55is disposed over the first pressure member37and the housing member56. Moreover, the outer diameter of the buffer member55is smaller than the inner diameter of the leading end side housing31(specifically, the first leading end side housing312). Further, the inner diameter of the buffer member55is slightly smaller than the outer diameter of the rear end of the first pressure member37and the outer diameter of the leading end side of the housing member56. Then, the outer circumference of the buffer member55faces the leading end side housing31via the air gap. On the other hand, the inner circumference of the leading end side of the buffer member55is in contact with the outer circumferential surface on the rear end side of the first pressure member37, and the inner circumference of the rear end side of the buffer member55is in contact with the outer circumferential surface on the leading end side of the housing member56. In this manner, by providing the air gap between the outer circumference of the buffer member55and the inner circumferential surface of the leading end side housing31, the buffer member55and the leading end side housing31are not directly in contact with each other.

The housing member56as an example of a first housing shows a cylindrical shape as a whole. The housing member56is composed of a metallic material having conductivity, such as brass. The housing member56is provided over the inner portion of the leading end side housing31and the inner portion of the rear end side housing51. Then, the housing member56is disposed on the rear end side of the first pressure member37and on the leading end side of the connection member52. The outer circumferential surface and the inner circumferential surface of the housing member56have a shape in which the outer diameter and the inner diameter increase in a stepwise manner from the leading end side toward the rear end side. At the center portion of the housing member56, a through hole that penetrates through the housing member56is formed along the centerline direction. Moreover, the outer diameter on the leading end side of the housing member56is smaller than the inner diameter of the leading end side housing31and the outer diameter on the rear end side of the housing member56is smaller than the inner diameter of the rear end side housing51. Here, between the outer circumferential surface of the housing member56and the inner circumferential surface of the leading end side housing31, the fourth insulating ring44is disposed at a position relatively on the leading end side, and the fifth insulating ring45is disposed at a position relatively on the rear end side. Further, the inner diameter on the leading end side of the housing member56is larger than the outer diameter of the covering member54, the inner diameter on the rear end side of the housing member56is slightly smaller than the outer diameter of the holding member58, and the inner diameter of the middle portion positioned between the leading end side and the rear end side of the housing member56is slightly larger than the outer diameter of the circuit board57. Then, the leading end side of the housing member56is in contact with the rear end side of the buffer member55. On the other hand, the rear end side of the housing member56faces the connection member52via the air gap. Moreover, the outer circumferential surface on the leading end side of the housing member56faces the leading end side housing31via the fourth insulating ring44, the fifth insulating ring45and the air gap formed by these rings, and the outer circumferential surface on the rear end side of the housing member56faces the rear end side housing51via the air gap.

The circuit board57shows a rectangular plate shape as a whole. The circuit board57performs various kinds of processing using electric circuits to an electric signal caused by a weak charge outputted by the piezoelectric element33in response to the received pressure (a charge signal: an example of a detection signal), and is configured with a so-called printed wiring board. The circuit board57is provided over the inner portion of the leading end side housing31and the inner portion of the rear end side housing51. Moreover, the circuit board57is disposed on the rear end side of the conduction member53and the covering member54and on the leading end side of the connection member52. Further, the entirety of the circuit board57is disposed inside the housing member56, and, between the outer circumferential surface on the rear end side of the circuit board57and the inner circumferential surface on the rear end side of the housing member56, the holding member58is provided. Then, on the rear end side of the circuit board57, a voltage receiving terminal57c, an output signal terminal57dand an output ground terminal57eto be connected to the above-described first substrate side terminal521, second substrate side terminal522and third substrate side terminal523are provided. Here, the voltage receiving terminal57c, the output signal terminal57dand the output ground terminal57eare electrically connected to the first substrate side terminal521, the second substrate side terminal522and the third substrate side terminal523, respectively. Note that, though details will be described later, the voltage receiving terminal57cis used for feeding power supply to the circuit board57, the output signal terminal57dis used for outputting the signals from the circuit board57, and the output ground terminal57eis used for grounding of the circuit board57. The details of the circuit board57will be described later.

The holding member58shows a cylindrical shape as a whole. The holding member58includes a base material composed of a synthetic resin material having an insulating property, such as PPT, wiring composed of a metallic material having conductivity, such as copper, and so forth. The holding member58is provided over the inner portion of the leading end side housing31and the inner portion of the rear end side housing51, and at a position inside the housing member56and outside the circuit board57. Then, the holding member58is disposed on the rear end side of the fifth insulating ring45and on the leading end side of the connection member52. At the center portion of the holding member58, a through hole that penetrates through the holding member58is formed along the centerline direction. Moreover, the outer diameter of the holding member58is slightly larger than the inner diameter on the rear end side of the housing member56. Further, the inner diameter on the leading end side of the holding member58is slightly smaller than the outer diameter of the circuit board57. Then, the outer circumferential surface of the holding member58is in contact with the inner circumferential surface on the rear end side of the housing member56. On the other hand, the inner circumferential surface on the leading end side of the holding member58is in contact with the outer circumferential surface on the rear end side of the circuit board57. Here, the outer circumferential surface of the wiring provided to the holding member58is in contact with the inner circumferential surface of the housing member56, and the inner circumferential surface of the wiring is connected to an input ground terminal57b(which will be described in detail later) of the circuit board57.

[Electrical Connection Structure in Pressure Detection Device]

Here, an electrical connection structure in the pressure detection device20will be described.

In the pressure detection device20, an end surface on the rear end side of the piezoelectric element33(positive pole) is electrically connected to the rear end electrode member36made of metal, and the rear end electrode member36is connected to the conduction member53made of metal via the second pressure member (coil spring)38made of metal. Then, the conduction member53made of metal is electrically connected to, of the covering member54basically composed of an insulating body, the rear end holding part54amade of metal, and the rear end holding part54ais electrically connected to an input signal terminal57a(refer toFIG. 5to be described later) provided to the circuit board57. Hereinafter, an electrical route from the surface on the rear end side of the piezoelectric element33to the input signal terminal57aof the circuit board57via the rear end electrode member36, the second pressure member38, the conduction member53and the rear end holding part54ais referred to as “positive route”.

On the other hand, in the pressure detection device20, an end surface on the leading end side of the piezoelectric element33(negative pole) is electrically connected to the leading end electrode member35made of metal, and the leading end electrode member35is connected to the buffer member55made of metal via the first pressure member37made of metal (and the support member39made of metal). Then, the buffer member55made of metal is electrically connected to the housing member56made of metal, and the housing member56is electrically connected to the input ground terminal57b(refer toFIG. 5to be described later) provided to the circuit board57via the wiring made of metal provided to the holding member58basically composed of the insulating body. Hereinafter, an electrical route from the surface on the leading end side of the piezoelectric element33to the input ground terminal57bof the circuit board57via the leading end electrode member35, the first pressure member37(the support member39), the buffer member55, the housing member56and the wiring of the holding member58is referred to as “negative route”.

On the other hand, in the pressure detection device20, the leading end side housing31(the first leading end side housing311and the second leading end side housing312) made of metal is electrically connected to the diaphragm head32made of metal and the rear end side housing51made of metal. Hereinafter, an electrical route from the diaphragm head32to the rear end side housing51via the leading end side housing31is referred to as “housing route”.

In this manner, in the pressure detection device20in the exemplary embodiment, the negative route exists outside the positive route. Then, the positive route and the negative route are electrically insulated by the insulating pipe40, the first insulating ring41, the covering member54and the air gap formed by these components.

Moreover, in the pressure detection device20, the housing route exists outside the negative route. Then, the negative route and the housing route are electrically insulated by the insulating plate34, the second insulating ring42, the third insulating ring43, the fourth insulating ring44, the fifth insulating ring45and the air gap formed by these components.

Then, in the pressure detection device20, since the positive route and the negative route are electrically insulated, and the negative route and the housing route are electrically insulated, the positive route and the housing route result in being electrically insulated.

Note that, in the following description, the leading end side housing31, the diaphragm head32and the rear end side housing51are collectively referred to as “housing60” (an example of a second housing) in some cases (refer toFIG. 2, andFIGS. 8 to 11to be described later). Moreover, in the following description, the leading end electrode member35, the first pressure member37, the support member39, the buffer member55and the housing member56are collectively referred to as “shielding body70” in some cases (refer toFIGS. 8 to 11).

Here, in the pressure detection device20, the housing60is a portion exposed to the outside, and in particular, the diaphragm head32is a portion facing the combustion chamber C that increases acidity with combustion. In contrast thereto, the shielding body70is a portion housed inside the housing60in the pressure detection device20, and, in this example, also a portion forming the negative route. Therefore, it is preferable that the shielding body70is composed of a material having conductivity higher than that of the housing60, and it is preferable that the housing60is composed of a material having resistance to acids higher than that of the shielding body70.

[Configuration of Circuit Board]

FIG. 5is a schematic configuration view of the circuit board57provided to the pressure detection device20.

The circuit board57includes: a printed wiring board571on which wiring (a circuit pattern) for implementing one or more electronic components (circuit elements) is formed; and a processing circuit572implemented on the printed wiring board571.

In the exemplary embodiment, as the printed wiring board571, a so-called glass-epoxy substrate, which is based on glass fabric base material epoxy resin, is used. Then, on the circuit board57, as input/output terminals, the input signal terminal57a, the input ground terminal57b, the voltage receiving terminal57c, the output signal terminal57dand the output ground terminal57eare provided.

Here, to the input signal terminal57a, the positive route in the pressure detection device20is connected, whereas, to the input ground terminal57b, the negative route in the pressure detection device20is connected. On the other hand, to the voltage receiving terminal57c, the output signal terminal57dand the output ground terminal57e, the first substrate side terminal521, the second substrate side terminal522and the third substrate side terminal523are connected, respectively (refer toFIG. 3). Note that, on the circuit board57, the input ground terminal57band the output ground terminal57eare connected.

Moreover, the processing circuit572includes: an integrating circuit572athat integrates the charge signal inputted from the piezoelectric element33via the input signal terminal57ato convert thereof into a voltage signal; and an amplifier circuit572bthat amplifies the converted voltage signal to output thereof to the output signal terminal57d. Here, to the integrating circuit572aand the amplifier circuit572b, a power-supply voltage for operating thereof is supplied via the voltage receiving terminal57c. Moreover, the grounds of the integrating circuit572aand the amplifier circuit572bare connected to the input ground terminal57band the output ground terminal57e. Note that, in this example, the processing circuit572is configured with a so-called integrated circuit (IC).

[Pressure Detection Operation by Pressure Detection Device]

Now, pressure detection operation by the pressure detection device20will be described.

When the internal combustion engine10is operating, a pressure generated inside the combustion chamber C (combustion pressure) is imparted to the pressure receiving surface32aof the diaphragm head32. In the diaphragm head32, the pressure received by the pressure receiving surface32ais transferred to the convex part32con the back side, and is further transferred from the convex part32cto the insulating plate34. Then, the pressure transferred to the insulating plate34is transferred to the leading end electrode member35; thereby the pressure acts on the piezoelectric element33held between the leading end electrode member35and the rear end electrode member36, to thereby, in the piezoelectric element33, generate charges corresponding to the received pressure. The charges generated in the piezoelectric element33are supplied to the input signal terminal57aof the circuit board57as the charge signal via the positive route, namely, the rear end electrode member36, the second pressure member38, the conduction member53and the rear end holding part54a. The charge signal supplied to the circuit board57is subjected to integral processing in the integrating circuit572ato be converted into the voltage signal, and further subjected to amplification processing in the amplifier circuit572bto be made into an output signal. Then, the output signal outputted from the amplifier circuit572bis transmitted from the output signal terminal57dof the circuit board57to the outside (here, a transmission line92of the connection cable90and the controller80) via the second substrate side terminal522and the second connection terminal52bprovided to the connection member52.

FIG. 6is a block diagram of the controller80.

The controller80as an example of a supplying and processing device includes: a power supply part81that generates the power-supply voltage for the pressure detection device20by reducing a voltage (for example, +12V) supplied from a battery (not shown) to about 5V; an ECU (Engine Control Unit)82that controls operation of the internal combustion engine10based on the output signal inputted from the pressure detection device20; and a device housing83that houses the power supply part81and the ECU82inside thereof. The ECU82is configured with a so-called one-chip microcomputer and incorporates an MPU (Micro-processing unit) that performs various kinds of arithmetic processing, a ROM (Read Only Memory) that stores programs executed by the MPU, a RAM (Random Access Memory) that stores data temporarily generated in executing the programs by the MPU, and so forth.

Moreover, the controller80further includes: a voltage transmission terminal80athat transmits the power-supply voltage from the power supply part81toward the pressure detection device20; a receiving terminal80bthat receives the output signal from the pressure detection device20; and a ground terminal80cfor sharing a ground potential with the pressure detection device20. Note that, in this example, the ground of each of the power supply part81and the ECU82is connected to the ground terminal80c, and the ground terminal80cis also connected to the device housing83.

[Configuration of Connection Cable]

FIG. 7is a cross-sectional view of the connection cable90.

The connection cable90includes: a supply line91; the transmission line92; a ground line93; a drain wire94; a shielding part95; and a braided part96. Then, each of the supply line91, the transmission line92and the ground line93includes a conductor part configured with a tinned annealed copper strand wire and an insulating part that is composed of silicon rubber or the like and covers an outer circumference of the conductor part to insulate thereof.

Moreover, the transmission line92and the ground line93are pair-stranded. Then, the drain wire94is configured with the tinned annealed copper strand wire or the like and vertically attached to (or twisted around) the pair-strand transmission line92and ground line93. The shielding part95is configured by twisting an aluminum Mylar tape, in which aluminum is evaporated on one surface of PET tape, or copper foil around the transmission line92, ground line93and drain wire94. The braided part96is configured by braiding cotton threads, silk threads or the like, and covers the supply line91and the transmission line92, the ground line93and the drain wire94unified by the shielding part95, to thereby unify these components. Here, it may be possible to configure the braided part96to cover the shielding part95(the transmission line92and the ground line93) only, and the supply line91may exist as a solid wire (separate body).

Then, one end of the supply line91is connected to the voltage receiving terminal57cprovided to the circuit board57and the other end of the supply line91is connected to the voltage transmission terminal80aprovided to the controller80. Moreover, one end of the transmission line92is connected to the output signal terminal57dprovided to the circuit board57and the other end of the transmission line92is connected to the receiving terminal80bprovided to the controller80. Further, one end of the ground line93is connected to the output ground terminal57eprovided to the circuit board57and the other end of the ground line93is connected to the ground terminal80cprovided to the controller80.

[Electric Connection Structure of Pressure Detection System]

FIG. 8is a diagram for illustrating an electrical connection structure of the pressure detection system1of the exemplary embodiment. Note that, inFIG. 8, a battery100carried aboard a vehicle or the like is shown together with the internal combustion engine10(the same is true forFIGS. 9 to 11to be described later).

First, a connection relationship inside the pressure detection device20will be described.

In the pressure detection device20, the rear end side, namely, the positive pole side of the piezoelectric element33is connected to the input signal terminal57aof the circuit board57via the positive route, and the leading end side, namely, the negative pole side of the piezoelectric element33is connected to the input ground terminal57bof the circuit board57via the negative route. Moreover, on the circuit board57, each of the input signal terminal57a, the input ground terminal57b, the voltage receiving terminal57c, the output signal terminal57dand the output ground terminal57eis connected to the processing circuit572.

Further, in the pressure detection device20, the output ground terminal57eprovided to the circuit board57(the input ground terminal57bmay also be used) is connected to the shielding body70including the housing member56that houses the circuit board57inside thereof. Then, in the pressure detection device20, the shielding body70and the housing60that houses the shielding body70inside thereof are insulated.

Next, a connection relationship inside the controller80will be described.

In the controller80, the output side of the power supply part81is connected to the voltage transmission terminal80a, and the input side of the ECU82is connected to the receiving terminal80b. Moreover, in the controller80, a grant side of the power supply part81and the ECU82are connected to the ground terminal80cand the device housing83.

Subsequently, a connection relationship between the pressure detection device20and the internal combustion engine10will be described.

In the exemplary embodiment, as described by use ofFIG. 1, the pressure detection device20is attached to the internal combustion engine10by screwing the pressure detection device20into the cylinder head13(more specifically, the communication hole13a) provided to the internal combustion engine10. Therefore, the housing60(the first leading end side housing311) constituting the pressure detection device20is connected to the internal combustion engine10(the cylinder head13).

Further, a connection relationship between the internal combustion engine10and the controller80and the battery100will be described.

A positive electrode101of the battery100is connected to the power supply part81provided to the controller80. On the other hand, a negative electrode102(an example of a conductor) of the battery100is connected to the internal combustion engine10and the device housing83of the controller80. Moreover, the negative electrode102of the battery100is connected (grounded) to a body of a vehicle.

Still further, a connection relationship between the pressure detection device20, the internal combustion engine10, the connection cable90and the controller80will be described.

First, regarding the supply line91constituting the connection cable90, one end thereof is connected to the voltage receiving terminal57cprovided to the circuit board57of the pressure detection device20and the other end thereof is connected to the voltage transmission terminal80aprovided to the controller80. Moreover, regarding the transmission line92constituting the connection cable90, one end thereof is connected to the output signal terminal57dprovided to the circuit board57of the pressure detection device20and the other end thereof is connected to the receiving terminal80bprovided to the controller80. Further, regarding the ground line93constituting the connection cable90, one end thereof is connected to the output ground terminal57eprovided to the circuit board57of the pressure detection device20and the other end thereof is connected to the ground terminal80cprovided to the controller80. Still further, regarding the drain wire94constituting the connection cable90and being in contact with the shielding part95, one end thereof is connected to the internal combustion engine10, and the other end thereof is connected to the device housing83of the controller80. In this manner, both ends of the drain wire94provided to the connection cable90are grounded.

Note that, though the description was omitted here, in actuality, the connection cable90is connected to the circuit board57via the connection member52provided to the pressure detection device20(refer toFIG. 3).

Therefore, in actuality, one end of the supply line91is connected to the first connection terminal52aof the connection member52and, via the first substrate side terminal521of the connection member52, connected to the voltage receiving terminal57cof the circuit board57. Moreover, in actuality, one end of the transmission line92is connected to the second connection terminal52bof the connection member52and, via the second substrate side terminal522of the connection member52, connected to the output signal terminal57dof the circuit board57. Further, in actuality, one end of the ground line93is connected to the third connection terminal52cof the connection member52and, via the third substrate side terminal523of the connection member52, connected to the output ground terminal57eof the circuit board57.

In the pressure detection device20of the pressure detection system1in the exemplary embodiment, the housing60that houses the piezoelectric element33, the circuit board57, the shielding body70and so forth inside thereof is connected (grounded) to the negative electrode102of the battery100via the internal combustion engine10. In contrast thereto, inside the housing60, the shielding body70that electrically shields the piezoelectric element33and the circuit board57from the outside by housing these components inside thereof and functions as a grounded system for these piezoelectric element33and circuit board57is connected (grounded) to the negative electrode102of the battery100via the connection cable90(the ground line93) and the controller80. Then, in the pressure detection device20, the housing60and the shielding body70are insulated.

The pressure detection device20of the exemplary embodiment is attached to the internal combustion engine10, and, when the internal combustion engine10is carried aboard a vehicle, noise of frequency of the order of kHz (hereinafter, referred to as low-frequency noise) generated in a horn, headlights, wipers comes into the cylinder head13of the internal combustion engine10. Then, in the exemplary embodiment, since, of the pressure detection device20, the housing60composed of metal is attached to the cylinder head13composed of metal, the low-frequency noise coming into the cylinder head13also propagates to the housing60of the pressure detection device20.

Here, in the pressure detection device20of the exemplary embodiment, the housing60is electrically insulated from the positive route and the negative route from the piezoelectric element33to the circuit board57. Therefore, the low-frequency noise propagated from the cylinder head13to the housing60of the pressure detection device20becomes unlikely to be transferred to the circuit board57. As a result, fluctuations (variations) in the ground potential in the circuit board57due to the low-frequency noise is suppressed, and therefore, it becomes possible to reduce fluctuations (variations) in the output signal outputted from the circuit board57.

Moreover, when the internal combustion engine10of the exemplary embodiment is carried aboard a vehicle, radio waves of the order of MHz used by mobile phones, radio, television and so forth usually fly around the vehicle. When the radio waves are emitted to the circuit board57provided to the pressure detection device20, noise of frequency of the order of MHz (hereinafter, referred to as high-frequency noise) is generated in the circuit board57.

Here, in the exemplary embodiment, the circuit board57is covered with (housed in) the housing member56made of metal and constituting the shielding body70. Therefore, the radio waves emitted to the pressure detection device20from the outside are shielded by the shielding body70including the housing member56, to be less likely to reach the circuit board57. As a result, fluctuations (variations) in the ground potential in the circuit board57due to the high-frequency noise is suppressed, and therefore, it becomes possible to reduce fluctuations (variations) in the output signal outputted from the circuit board57.

Then, in the exemplary embodiment, since the shielding body70also serves as the negative route, the configuration of the pressure detection device20is easily formed as compared to a case in which the shielding body70and the negative route are separately provided.

[First Modified Example of Electrical Connection Structure of Pressure Detection System]

FIG. 9is a diagram for illustrating a first modified example of the electrical connection structure of the pressure detection system1.

In the example shown inFIG. 9, the connection relationship inside the pressure detection device20, the connection relationship inside the controller80, the connection relationship between the pressure detection device20and the internal combustion engine10, and the connection relationship between the internal combustion engine10and the controller80and the battery100are same as those described inFIG. 8.

However, in the example shown inFIG. 9, the points that the connection cable90does not include the ground line93, one end of the drain wire94provided to the connection cable90is not connected to the internal combustion engine10, but is connected to the output ground terminal57eof the circuit board57in the pressure detection device20, and the other end of the drain wire94is not connected to the device housing83of the controller80, but is connected to the ground terminal80cof the controller80are different from the example shown inFIG. 8.

Then, also in the pressure detection system1shown inFIG. 9, similar to the system shown inFIG. 8, it becomes possible to reduce fluctuations (variations) in the output signal due to the low-frequency noise and the high-frequency noise coming into the circuit board57from the outside. In particular, in the example shown inFIG. 9, the potential of the shielding part95connected to (brought into contact with) the drain wire94in the connection cable90can be made in common with the potential of the shielding body70provided to the pressure detection device20(the ground potential of the pressure detection device20). Therefore, as shown inFIG. 8, by connecting one end of the drain wire94to the internal combustion engine10, the low-frequency noise is less likely to be superimposed on the output signal in the transmission line92as compared to a case in which the potential of the shielding part95is made in common with the potential of the internal combustion engine10where the low-frequency noise possibly exists.

Moreover, in the pressure detection system1shown inFIG. 9, as compared to the configuration shown inFIG. 8, there is also an advantage of being capable of reducing the number of core wires constituting the connection cable90(three wires to two wires).

[Second Modified Example of Electrical Connection Structure of Pressure Detection System]

FIG. 10is a diagram for illustrating a second modified example of the electrical connection structure of the pressure detection system1.

In the example shown inFIG. 10, the connection relationship inside the pressure detection device20, the connection relationship inside the controller80, the connection relationship between the pressure detection device20and the internal combustion engine10, and the connection relationship between the internal combustion engine10and the controller80and the battery100are same as those described inFIG. 8.

However, in the example shown inFIG. 10, the point that one end of the drain wire94provided to the connection cable90is not connected to the internal combustion engine10, but is connected to the shielding body70in the pressure detection device20is different from the example shown inFIG. 8.

Then, also in the pressure detection system1shown inFIG. 10, similar to the system shown inFIG. 8, it becomes possible to reduce fluctuations (variations) in the output signal due to the low-frequency noise and the high-frequency noise coming into the circuit board57from the outside. In particular, in the example shown inFIG. 10, the potential of the shielding part95connected to (brought into contact with) the drain wire94in the connection cable90can be made in common with the potential of the shielding body70provided to the pressure detection device20(the ground potential of the pressure detection device20). Therefore, as shown inFIG. 8, by connecting one end of the drain wire94to the internal combustion engine10, the low-frequency noise is less likely to be superimposed on the output signal in the transmission line92as compared to a case in which the potential of the shielding part95is made in common with the potential of the internal combustion engine10where the low-frequency noise possibly exists.

Moreover, in the pressure detection system1shown inFIG. 10, as compared to the configuration shown inFIG. 8, there are two grounded systems that connect the pressure detection device20and the controller80(the ground line93and the drain wire94). Therefore, even when disconnection or the like occurs in one of the ground line93and the drain wire94, it becomes possible to keep the ground common to the pressure detection device20and the controller80by the other remaining line, and thereby system redundancy can be increased.

[Third Modified Example of Electrical Connection Structure of Pressure Detection System]

FIG. 11is a diagram for illustrating a third modified example of the electrical connection structure of the pressure detection system1.

In the example shown inFIG. 11, the connection relationships inside each device and between devices are basically the same as those described inFIG. 10.

However, in the example shown inFIG. 11, the point that the pressure detection device20further includes a capacitor573(an example of a DC suppressing part) connected to the output ground terminal57eand the shielding body70is different from the example shown inFIG. 10. Note that, in this example, the capacitor573is attached to the circuit board57; however, the capacitor573may be attached to a portion different from the circuit board57.

Then, also in the pressure detection system1shown inFIG. 11, similar to the system shown inFIG. 8, it becomes possible to reduce fluctuations (variations) in the output signal due to the low-frequency noise and the high-frequency noise coming into the circuit board57from the outside. Moreover, in the pressure detection system1shown inFIG. 11, as same as the system shown inFIG. 10, the potential of the shielding part95connected to (brought into contact with) the drain wire94in the connection cable90can be made in common with the potential of the shielding body70provided to the pressure detection device20(the ground potential of the pressure detection device20). Therefore, as shown inFIG. 8, by connecting one end of the drain wire94to the internal combustion engine10, the low-frequency noise is less likely to be superimposed on the output signal in the transmission line92as compared to a case in which the potential of the shielding part95is made in common with the potential of the internal combustion engine10where the low-frequency noise possibly exists.

Moreover, as described above, in the pressure detection system1shown inFIG. 10, since there are two grounded systems that connect the pressure detection device20and the controller80(the ground line93and the drain wire94), even in the state in which one of them is disconnected, it is possible to keep the ground in common by using the other line. However, for example, even in the case in which disconnection occurs in the ground line93, since the current flows through the supply line91and the drain wire94, it becomes impossible to detect disconnection in the ground line93. In contrast thereto, in the example shown inFIG. 11, in the pressure detection device20, the shielding body70and the output ground terminal57e, to which one end of the ground line93is connected, are connected via the capacitor573. This allows, under the condition that disconnection does not occur in the ground line93, when DC voltage is applied between the voltage transmission terminal80aand the ground terminal80cin the controller80, DC current to flow in the supply line91and the ground line93. In contrast thereto, under the condition that disconnection occurs in the ground line93, when the DC voltage is applied between the voltage transmission terminal80aand the ground terminal80cin the controller80, the DC current does not flow in the disconnected ground line93, and in addition, due to existence of the capacitor573, the DC current does not flow to the drain wire94that is not disconnected. Therefore, when the capacitor573is provided to the pressure detection device20, based on whether or not the DC current is passed, it becomes possible to detect disconnection in the ground line93.

Further, in the example shown inFIG. 11, as same as the system shown inFIG. 10, there are two grounded systems that connect the pressure detection device20and the controller80(the ground line93and the drain wire94). Therefore, even when disconnection or the like occurs in the ground line93and the drain wire94, it becomes possible to keep the common ground by any other remaining line, and thereby system redundancy can be increased.

Here, in the example shown inFIG. 11, the capacitor573is used as the DC suppressing part; however, the DC suppressing part is not limited thereto and, for example, a diode in which a side close to the output ground terminal57eserves as a cathode may be used.

Note that, in the exemplary embodiment, the housing60of the pressure detection device20is composed of a metallic material having conductivity; however, the material is not limited thereto, and the housing60may be composed of a material having the insulating property, such as alumina ceramics or zirconia ceramics. In this case, it becomes unnecessary to insulate the housing60and the shielding body70via the various kinds of insulating members (the insulating plate34, the fourth insulating ring44and the fifth insulating ring45) and the air gap.

Moreover, in the exemplary embodiment, the piezoelectric element33, the positive route and the circuit board57are covered with (housed in) the shielding body70; however, at least part of the circuit board57is covered (housed), an effect of reducing the noise is generated as compared to a case in which the circuit board57is not at all covered (housed).

Here, in the exemplary embodiment, the circuit board57is covered (housed) by use of the housing member56showing the cylindrical shape; however, the housing member56is not limited thereto and, for example, a metal braid, in which a metal is braided, or the like may be used.

Further, in the exemplary embodiment, both ends of the drain wire94provided to the connection cable90are grounded; however, grounding is not limited thereto, and one end grounding may be possible. However, when both ends of the drain wire94are grounded, as compared to the case in which one end of the drain wire94is grounded, incoming of noise into the circuit board57is suppressed with ease.

[Configuration of Pressure Detection Device]

FIG. 12is a side view of the pressure detection device20in Exemplary embodiment 2.FIG. 13is a cross-sectional view (a XIII-XIII cross-sectional view inFIG. 12) of the pressure detection device20.FIG. 14is an enlarged cross-sectional view of a leading end side of the pressure detection device20.

The pressure detection device20in the exemplary embodiment includes: a housing part130exposed to the outside; a detection mechanism part140which includes various kinds of mechanisms for detecting pressure and provided so that almost entirety of which is housed in the housing part130and part (a connection member154to be described later) of which is exposed to the outside; and a sealing part170attached to an outer circumferential surface of the housing part130. Then, the pressure detection device20is attached to the internal combustion engine10shown inFIG. 1so that the left side inFIG. 12(the portion where the housing part130is exposed) faces toward the combustion chamber C (the lower side inFIG. 1) and right side inFIG. 12(the portion where the detection mechanism part140is exposed) faces toward the outside (upward inFIG. 1). Moreover, in this state, the sealing part170is positioned inside the communication hole13aprovided to the cylinder head13. Note that, in the following description, inFIG. 12, a side heading for left in the figure is referred to as “leading end side” of the pressure detection device20and a side heading for right in the figure is referred to as “rear end side” of the pressure detection device20. Moreover, in the following description, a centerline direction of the pressure detection device20indicated by a dot-and-dash line inFIG. 12is simply referred to as a centerline direction.

[Configuration of Housing Part]

The housing part130includes: a leading end side housing131; a diaphragm head132attached to a leading end side of the leading end side housing131; and a rear end side housing133attached to a rear end side of the leading end side housing131. Here, in the exemplary embodiment, the leading end side housing131and the rear end side housing133function as an example of the second housing, and the diaphragm head132functions as an example of the deformation member.

The leading end side housing131is a member having a hollow structure and showing a cylindrical shape as a whole. The leading end side housing131is composed of a metallic material having conductivity and high resistance to heat and acids, such as stainless steel.

The leading end side housing131includes a first leading end side housing1311that is positioned relatively close to the leading end side thereof and a second leading end side housing1312that is positioned relatively close to the rear end side thereof. Here, by applying laser welding to an outer circumferential surface on the rear end side of the first leading end side housing1311and an inner circumferential surface on the leading end side of the second leading end side housing1312, the leading end side housing131has a configuration integrating both. Then, to the leading end side of the first leading end side housing1311, the diaphragm head132is attached by laser welding, and, to the rear end side of the second leading end side housing1312, the rear end side housing133is attached by fitting.

Here, the outer circumferential surface of the first leading end side housing1311is provided with a concave part1311afor putting a first sealing member171(which will be described in detail later) constituting the sealing part170. Moreover, inside the first leading end side housing1311, there are a portion on the leading end side set as a first diameter and a portion on the rear end side set as a second diameter, which is larger than the first diameter, and at a boundary of these two portions, an inside stepped part1311bthat connects both portions is provided.

On the other hand, the outer circumferential surface of the second leading end side housing1312is provided with a concave part1312afor putting a second sealing member172(which will be described in detail later) constituting the sealing part170together with the first sealing member171. Moreover, of the outer circumferential surface of the second leading end side housing1312, on the rear end side than the above-described concave part1312a, a ring-shaped rib part1312bprojecting outward is provided. The rib part1312bis, as described above, used for fixing the pressure detection device20to the internal combustion engine10(more specifically, the cylinder head13).

The diaphragm head132shows a disk shape as a whole. The diaphragm head132is composed of a metallic material having conductivity and high resistance to heat and acids, such as stainless steel. Particularly, in this example, the diaphragm head132and the above-described leading end side housing131are composed of the same material.

The diaphragm head132includes: a pressure receiving surface (front surface)132athat has a concave part132bformed at the center portion on the leading end side thereof and is exposed to the outside (combustion chamber C side) to receive a pressure; a concave part132cthat is provided by cutting a rear surface, which is the back side of the pressure receiving surface132ain a ring shape; and a convex part132dthat projects, as a result of presence of the concave part132c, from the center portion of the pressure receiving surface132a(the portion where the concave part132bis formed) toward the rear end side. The diaphragm head132is provided to close an opening part of the leading end side in the first leading end side housing1311. Then, at a boundary portion between the diaphragm head132and the first leading end side housing1311, laser welding is applied around the outer circumferential surface.

The rear end side housing133is a member having a hollow structure and showing a cylindrical shape as a whole. The rear end side housing133is composed of a metallic material having conductivity and high resistance to heat and acids, such as stainless steel. However, since the rear end side housing133is positioned outside the internal combustion engine10in the state where the pressure detection device20is mounted to the internal combustion engine10, materials having resistance to heat and resistance to acids lower than those of the above-described leading end side housing131can be used.

The rear end side housing133includes a first rear end side housing1331that is positioned relatively close to the leading end side thereof and a second rear end side housing1332that is positioned relatively close to the rear end side thereof. Here, by fitting an outer circumferential surface on the leading end side of the second rear end side housing1332into an inner circumferential surface on the rear end side of the first rear end side housing1331, the rear end side housing133has a configuration integrating both. Then, to the leading end side of the first rear end side housing1331, the leading end side housing131(more specifically, the second leading end side housing1312) is attached by fitting, and, to the rear end side of the second rear end side housing1332, a connection member154(which will be described in detail later) is attached by setting in.

[Configuration of Detection Mechanism Part]

The detection mechanism part140includes: a piezoelectric element141; a leading end electrode member142; a first rear end electrode member143and a second rear end electrode member144. Moreover, the detection mechanism part140includes: an insulating ring145; a first coil spring146; a conduction member147; and a holding member148. Further, the detection mechanism part140includes: a pressure member149; a support member150; a second coil spring151; and a housing member152. Still further, the detection mechanism part140includes: a circuit board153; the connection member154; a ground plate155; and an O-ring156. Moreover, the detection mechanism part140includes a butting pipe157. Then, the detection mechanism part140includes: an insulating pipe160; a first insulating member161; a second insulating member162; and a third insulating member163.

The piezoelectric element141as an example of the detection element shows a columnar shape as a whole. The piezoelectric element141is provided with a piezoelectric body showing a piezoelectric action of piezoelectric longitudinal effect. The piezoelectric longitudinal effect refers to generation of charge on a surface of the piezoelectric body in the direction of a charge generating axis when an external force is applied to a stress application axis in the same direction as the charge generating axis of the piezoelectric body. The piezoelectric element141is disposed inside the leading end side housing131and on the rear end side of the diaphragm head132. The piezoelectric element141is housed in the leading end side housing131so that the centerline direction thereof is in the same direction as the stress application axis. Here, the piezoelectric element141is disposed inside the insulating pipe160provided inside the pressure member149which is provided inside the leading end side housing131. Moreover, the outer diameter of the piezoelectric element141is slightly smaller than the inner diameter of the insulating pipe160that houses the piezoelectric element141inside thereof. Then, the surface on the leading end side of the piezoelectric element141is in contact with the surface on the rear end side of the leading end electrode member142. On the other hand, the surface on the rear end side of the piezoelectric element141is in contact with the surface on the leading end side of the rear end electrode member143. Moreover, the outer circumferential surface of the piezoelectric element141faces the inner circumferential surface of the insulating pipe160. In this manner, by providing the insulating pipe160between the inner circumferential surface of the pressure member149and the outer circumferential surface of the piezoelectric element141, the pressure member149and the piezoelectric element141are not directly in contact with each other.

Next, a case in which piezoelectric transversal effect is used for the piezoelectric element141will be exemplified. The piezoelectric transversal effect refers to generation of charge on a surface of the piezoelectric body in the direction of a charge generating axis when an external force is applied to a stress application axis in a position orthogonal to the charge generating axis of the piezoelectric body. Plural piezoelectric bodies formed into thin plate shape may be laminated for configuration, and, by laminating in this manner, it is possible to efficiently collect charges generated in the piezoelectric body, to thereby increase sensitivity of a sensor. As the piezoelectric body that can be used for the piezoelectric element141, use of langasite crystal (langasite, langatate, langanite, LTGA), quartz or gallium phosphate having the piezoelectric longitudinal effect and the piezoelectric transversal effect can be shown as examples. Note that, in the piezoelectric element141of the exemplary embodiment, LTGA single crystal is used as the piezoelectric body.

The leading end electrode member142shows a columnar shape as a whole. The leading end electrode member142is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel. Moreover, at the center portion of the surface on the leading end side of the leading end electrode member142, an insulating film142aformed by coating a ceramic material, which includes alumina, zirconia or the like, showing the insulating property is provided. Here, the insulating film142aas an example of the insulating transmission member shows, for example, a circular shape; the diameter thereof is larger than the diameter of the convex part132dprovided to the rear surface of the diaphragm head132and smaller than the diameter of the opening part provided to the leading end side of the pressure member149.

The leading end electrode member142is disposed inside the pressure member149provided inside the leading end side housing131. Then, the leading end electrode member142is disposed on the rear end side of the diaphragm head132and on the leading end side of the piezoelectric element141. However, different from the above-described piezoelectric element141, the leading end electrode member142is not housed inside the insulating pipe160. Moreover, the outer diameter of the leading end electrode member142is slightly smaller than the inner diameter of the pressure member149that houses the leading end electrode member142inside thereof. Then, of the surface on the leading end side of the leading end electrode member142, the region at the center portion where the insulating film142ais provided is in contact with the surface on the rear end side of the convex part132dprovided to the rear surface of the diaphragm head132. Moreover, of the surface on the leading end side of the leading end electrode member142, the region at a periphery portion where the insulating film142ais not provided is in contact with the surface on the back side of the opening part provided to the leading end side of the pressure member149. On the other hand, the surface on the rear end side of the leading end electrode member142is in contact with the surface on the leading end side of the piezoelectric element141. Moreover, the outer circumferential surface of the leading end electrode member142faces the inner circumferential surface of the pressure member149.

The first rear end electrode member143shows a disk shape as a whole. The first rear end electrode member143is composed of a metallic material having conductivity, high resistance to heat, and small difference in thermal expansion with the piezoelectric element141, such as stainless steel.

The first rear end electrode member143is disposed inside the pressure member149provided inside the leading end side housing131. Then, the first rear end electrode member143is disposed on the rear end side of the piezoelectric element141and on the leading end side of the second rear end electrode member144. Here, the first rear end electrode member143is disposed inside the insulating pipe160provided inside the pressure member149. Moreover, the outer diameter of the first rear end electrode member143is substantially the same as the outer diameter of the piezoelectric element141and is slightly smaller than the inner diameter of the insulating pipe160. Then, the surface on the leading end side of the first rear end electrode member143is in contact with the surface on the rear end side of the piezoelectric element141. On the other hand, the surface on the rear end side of the first rear end electrode member143is in contact with the surface on the leading end side of the second rear end electrode member144. Moreover, the outer circumferential surface of the first rear end electrode member143faces the inner circumferential surface of the insulating pipe160.

In this manner, by providing the insulating pipe160between the inner circumferential surface of the pressure member149and the outer circumferential surface of the first rear end electrode member143, the pressure member149and the first rear end electrode member143are not directly in contact with each other.

The second rear end electrode member144shows a spinning-top shape as a whole and a cross section thereof shows a T shape. The second rear end electrode member144is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel. The second rear end electrode member144includes: a main body part144athat shows a disk shape and is positioned at the leading end side; a first convex part144bthat shows a columnar shape and projects from the center portion on the surface on the rear end side of the main body part144atoward the rear end side; and a second convex part144cthat shows a disk shape and projects from the rear end of the first convex part144btoward the rear end side further. Here, the diameter of the first convex part144bis smaller than the diameter of the main body part144a, and the diameter of the second convex part144cis smaller than the first convex part144b.

The second rear end electrode member144is disposed inside the pressure member149provided inside the leading end side housing131. Here, the leading end side of the main body part144ain the second rear end electrode member144is disposed inside the insulating pipe160provided inside the pressure member149. In contrast thereto, a portion on the rear end side thereof in the second rear end electrode member144is disposed outside the insulating pipe160. Moreover, the outer diameter of the main body part144ain the second rear end electrode member144is substantially the same as the outer diameter of the piezoelectric element141and is slightly smaller than the inner diameter of the insulating pipe160. Then, the surface on the leading end side of the main body part144ain the second rear end electrode member144is in contact with the surface on the rear end side of the first rear end electrode member143. On the other hand, the surface on the rear end side of the main body part144ais in contact with the surface on the leading end side of the insulating ring145. Moreover, the leading end side of the outer circumferential surface of the first convex part144bin the second rear end electrode member144is in contact with the inner circumferential surface of the insulating ring145, and the rear end side thereof faces the inner circumferential surface of the support member150via the air gap. Further, the outer circumferential surface of the second convex part144cin the second rear end electrode member144faces the inner circumferential surface of the support member150via the air gap, and in addition, is in contact with the conduction member147via the first coil spring146mounted on the outer circumferential surface. In this manner, by providing the insulating pipe160, the air gap and the insulating ring145between the inner circumferential surface of the pressure member149and the outer circumferential surface of the second rear end electrode member144, the pressure member149and the second rear end electrode member144are not directly in contact with each other. Moreover, by providing the air gap between the inner circumferential surface of the support member150and the outer circumferential surface of the second rear end electrode member144, the support member150and the second rear end electrode member144are not directly in contact with each other.

The insulating ring145shows an annular shape as a whole. The insulating ring145is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina.

The insulating ring145is disposed inside the pressure member149provided inside the leading end side housing131. Then, the insulating ring145is positioned on the rear end side of the main body part144ain the second rear end electrode member144and on the leading end side of the support member150. Here, inside the through hole provided to the insulating ring145, the first convex part144bin the second rear end electrode member144is disposed. Moreover, the outer diameter of the insulating ring145is slightly smaller than the inner diameter of the pressure member149. Further, the inner diameter of the through hole in the insulating ring145is slightly larger than the outer diameter of the first convex part144bin the second rear end electrode member144. Then, the surface on the leading end side of the insulating ring145is in contact with the surface on the rear end side of the main body part144ain the second rear end electrode member144. On the other hand, the surface on the rear end side of the insulating ring145is in contact with the surface on the leading end side of the support member150. Moreover, the outer circumferential surface of the insulating ring145faces the inner circumferential surface of the pressure member149. Further, the inner circumferential surface of the insulating ring145faces the outer circumferential surface of the first convex part144bin the second rear end electrode member144.

The first coil spring146shows a spiral shape as a whole, and expands and contracts in the centerline direction. The first coil spring146is composed of a metallic material having conductivity, which is higher than the conductivity of the leading end side housing131, such as brass, and the surface thereof is gold-plated.

The first coil spring146is provided inside the leading end side housing131, and is disposed inside the pressure member149and inside the support member150. Then, the first coil spring146is disposed on the rear end side of the second rear end electrode member144and on the leading end side of the conduction member147. In other words, the first coil spring146is disposed over the second rear end electrode member144and the conduction member147. Here, the leading end side of the first coil spring146is wound around the second convex part144cof the second rear end electrode member144, and the rear end side of the first coil spring146is inserted into the leading end side concave part147aprovided to the leading end side of the conduction member147. Then, the inner diameter of the first coil spring146is larger than the outer diameter of the second convex part144cand is smaller than the outer inner diameter of the first convex part144bin the second rear end electrode member144. On the other hand, the outer diameter of the first coil spring146is smaller than the inner diameter of the leading end side concave part147ain the conduction member147. As a result, the leading end of the first coil spring146is butting against the boundary portion (the stepped part) between the first convex part144band the second convex part144cin the second rear end electrode member144, and the leading end side of the first coil spring146is in contact with the outer circumferential surface of the second convex part144cin the second rear end electrode member146. In contrast thereto, the rear end of the first coil spring146is butting against the bottom part of the leading end side concave part147ain the conduction member147, and the rear end side of the first coil spring146is in contact with the inner circumferential surface of the leading end side concave part147ain the conduction member147. Moreover, the outer circumference of the first coil spring146faces the inner circumferential surface of the support member150via the air gap. In this manner, by providing the air gap between the inner circumferential surface of the support member150and the first coil spring146, the support member150and the first coil spring146are not directly in contact with each other.

The conduction member147shows a rod shape as a whole. The conduction member147is composed of a metallic material having conductivity, such as brass, and the surface thereof is gold-plated. The conduction member147is provided with, at the leading end thereof, the above-described leading end side convex part147a, and at the rear end thereof, the rear end side convex part147bhaving a diameter smaller than that of the center portion in the centerline direction and projecting toward the rear end side.

The conduction member147is disposed inside the leading end side housing131, and almost all the portions thereof except for the leading end portion and the rear end portion (the rear end side convex part147b) are disposed inside the holding member148. Moreover, the leading end side of the conduction member147is positioned inside the pressure member149, the rear end side of the conduction member147is positioned inside the housing member152, and a middle portion thereof between the leading end side and the rear end side is positioned inside the second coil spring151. Then, the conduction member147is disposed on the rear end side of the first coil spring146and on the leading end side of the circuit board153. The conduction member147is disposed to penetrate through the through hole provided to the holding member148along the centerline direction. Then, the outer diameter of the leading end portion of the conduction member147(the portion not covered with the holding member148) is larger than the inner diameter of the holding member148and is smaller than the inner diameter of the support member150. Further, the outer diameter of the rear end portion of the conduction member147(the rear end side convex part147b) is substantially the same as an inner width of a holding part provided to the holding member148. Still further, the outer diameter of the center portion of the conduction member147in the centerline direction is substantially the same as the inner diameter of the holding member148. Then, the leading end side concave part147aof the conduction member147is in contact with the first coil spring146by inserting the rear end side of the first coil spring146into the leading end side concave part147a. On the other hand, the rear end side convex part147bof the conduction member147is set into the holding part provided to the holding member148. Moreover, the outer circumferential surface of the leading end portion of the conduction member147faces the inner circumferential surface of the support member150via the air gap. Further, the outer circumferential surface of the center portion of the conduction member147in the centerline direction faces the second coil spring151via the holding member148and the air gap. Still further, the outer circumferential surface of the rear end portion of the conduction member147faces the inner circumferential surface of the housing member152via the air gap and the holding member148. In this manner, by providing the air gap and the holding member148between the inner circumferential surface of the support member150and the outer circumferential surface of the conduction member147, the support member150and the conduction member147are not directly in contact with each other. Moreover, by providing the air gap and the holding member148between the inner circumferential surface of the second coil spring151and the outer circumferential surface of the conduction member147, the second coil spring151and the conduction member147are not directly in contact with each other. Further, by providing the air gap between the inner circumferential surface of the housing member152and the outer circumferential surface of the conduction member147, the housing member152and the conduction member147are not directly in contact with each other.

The holding member148is formed by integrating a portion positioned on the leading end side and showing a cylindrical shape and a portion positioned on the rear end side and showing a plate-like shape. The holding member148includes a base material composed of a synthetic resin material having an insulating property, such as PPT (Polypropylene Terephthalate), wiring composed of a metallic material having conductivity, such as copper, terminals, and so forth. In the portion positioned on the leading end side of the holding member148, the conduction member147is housed, and, to the portion positioned on the rear end side of the holding member148, the circuit board153is mounted. In this manner, the holding member148has a function of holding the conduction member147and the circuit board153.

Of the holding member148, a portion (the outer circumferential surface) facing the support member150, the second coil spring151and the housing member152is composed of the synthetic resin material, to thereby prevent a metallic material from being exposed in the portion. Moreover, of the holding member148, a portion (the inner circumferential surface) facing the middle portion positioned between the leading end portion and the rear end portion of the conduction member147is also composed of the synthetic resin material, to thereby prevent a metallic material from being exposed in the portion. Moreover, on the rear end side of the cylindrical portion in the holding member148, the holding part, which is composed of a metallic material and sets the rear end side convex part147bof the conduction member147in to hold thereof, is provided. To the holding part, wiring for electrically connecting to a signal input terminal (not shown) of the circuit board153is attached.

The holding member148is provided over the inner portion of the leading end side housing131and the inner portion of the rear end side housing133. Moreover, the leading end side of the holding member148is positioned inside the pressure member149, the rear end side of the conduction member147is positioned inside the housing member152, and a middle portion thereof between the leading end side and the rear end side is positioned inside the second coil spring151. Then, the holding member148is disposed on the rear end side of the insulating ring145and on the leading end side of the connection member154.

The outer diameter of the cylindrical portion positioned on the leading end side of the holding member148is smaller than the inner diameter of the support member150and the outer diameter of the plate-like portion positioned on the rear end side of the covering member is smaller than the inner diameter of the housing member152at the portion. Moreover, the outer circumferential surface on the leading end side of the cylindrical portion of the holding member148faces the inner circumferential surface of the support member150and the inner circumferential surface of the second coil spring151via the air gap. Further, the outer circumferential surface on the rear end side of the cylindrical portion and the outer circumferential surface of the plate-like portion in the holding member148are in contact with the inner circumferential surface of the housing member152or face the inner circumferential surface of the holding member152via the air gap.

The pressure member149as an example of the first housing or a first imparting member shows a cylindrical shape as a whole. The pressure member149is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel.

FIG. 15is a perspective view of the pressure member149. Hereinafter, also with reference toFIG. 15, a configuration of the pressure member149will be described. Note that, inFIG. 15, the lower left side in the figure indicates the leading end side and the upper right side in the figure indicates the rear end side.

The pressure member149of the exemplary embodiment includes: a leading end cylindrical part1491that is positioned at the most leading end side and is provided with an opening part at the leading end thereof; a middle cylindrical part1492that is disposed at the rear end side of the leading end cylindrical part1491; and a rear end cylindrical part1493that is positioned on the rear end side of the middle cylindrical part1492and at the most rear end side. In the pressure member149, the outer diameter of the middle cylindrical part1492is larger than those of the leading end cylindrical part1491and the rear end cylindrical part1493, and the outer diameter of the rear end cylindrical part1493is larger than that of the leading end cylindrical part1491. Then, the pressure member149further includes: a leading end stepped part149bthat connects the leading end cylindrical part1491and the middle cylindrical part1492at a boundary portion therebetween; and a rear end stepped part149cthat connects the middle end cylindrical part1492and the rear end cylindrical part1493at a boundary portion therebetween. Note that the inner diameter of the pressure member149is the same size except for the opening part provided to the leading end. Therefore, in the pressure member149, the thickness of the middle cylindrical part1492is larger than the thickness of the rear end cylindrical part1493, and the thickness of the rear end cylindrical part1493is larger than the thickness of the leading end cylindrical part1491. Consequently, in the pressure member149, the middle cylindrical part1492is least likely to be deformed, whereas, the leading end cylindrical part1491is most likely to be deformed (likely to function as a spring). Here, in the exemplary embodiment, the leading end stepped part149b, the middle cylindrical part1492and the rear end stepped part149cfunction as an example of the projection part.

Moreover, of the pressure member149, on the outer circumferential surface of each of the leading end stepped part149b, the middle cylindrical part1492and the rear end stepped part149c, an insulating film149asuccessively formed by coating a ceramic material, which includes alumina, zirconia or the like, showing the insulating property is provided (refer toFIG. 14). Here, in the exemplary embodiment, the insulating film149afunctions as an example of the insulating part.

The pressure member149is provided inside the leading end side housing131so that the leading end cylindrical part1491is on the leading end side. Inside the pressure member149, the piezoelectric element141, the leading end electrode member142, the first rear end electrode member143, the second rear end electrode member144, the insulating ring145, the leading end side of the support member150, the insulating pipe160, the first coil spring146, the leading end side of the conduction member147and the leading end side of the holding member148are housed. Then, the pressure member149is disposed on the rear end side of the diaphragm head132and on the leading end side of the housing member152. Moreover, the outer diameter of the pressure member149differs among the leading end cylindrical part1491, the middle cylindrical part1492and the rear end cylindrical part1493; however, at all the positions, the outer diameter of the pressure member149is smaller than the inner diameter of the leading end side housing131. Further, the inner diameter of the pressure member149is, at the positions facing the leading end electrode member142and the insulating pipe160(the piezoelectric element141, the first rear end electrode member143, the second rear end electrode member144and the insulating ring145), slightly larger than the outer diameters of these components, and at the position facing the support member150, substantially the same as the outer diameter of the support member150.

Here, between the outer circumferential surface of the rear end cylindrical part1493provided to the rear end side of the pressure member149and the inner circumferential surface on the rear end side of the first leading end side housing1311, the butting pipe157is disposed.

Then, the surface on the leading end side (surface on the front side of the opening part) of the leading end cylindrical part1491in the pressure member149faces the convex part132cof the diaphragm head132via the air gap. On the other hand, the rear end side of the rear end cylindrical part1493faces the first insulating member161via the air gap. Moreover, the outer circumferential surface of the leading end cylindrical part1491faces the inner circumferential surface of the first leading end side housing1311via the air gap. Further, the outer circumferential surfaces of the leading end stepped part149b, the middle cylindrical part1492and the rear end stepped part149care in contact with the insulating film149a, and face the inner circumferential surface of the first leading end side housing1311via the insulating film149a. Still further, the outer circumferential surface of the rear end cylindrical part1493faces the inner circumferential surface of the butting pipe157via the air gap. In this manner, by providing the air gap and the insulating film149abetween the outer circumference of the pressure member149and the inner circumferential surfaces of the first leading end side housing1311and the inner circumferential surfaces of the butting pipe157, the pressure member149is not directly in contact with the first leading end side housing1311and the butting pipe157.

The support member150as an example of a second imparting member shows a cylindrical shape as a whole. The support member150is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel.

The support member150is disposed inside the leading end side housing131, and the leading end side thereof is positioned inside the pressure member149and the rear end side thereof is positioned outside the pressure member149. Moreover, the support member150houses, inside thereof, the rear end side of the second rear end electrode member144(the first convex part144band the second convex part144c), the first coil spring146, the leading end side of the conduction member147and the leading end side of the holding member148. Then, the support member150is disposed on the rear end side of the insulating ring145and on the leading end side of the housing member152. Moreover, the outer diameter of the support member150is substantially the same as the inner diameter of the pressure member149. Further, the inner diameter of the support member150is different depending on the positions in the centerline direction; the inner diameter of the support member150is larger than the outer diameter of the second rear end electrode member144at the position facing the second rear end electrode member144, larger than the outer diameter of the first coil spring146at the position facing the first coil spring146, larger than the outer diameter of the conduction member147at the position facing the conduction member147, and larger than the outer diameter of the holding member148at the position facing the holding member148. Then, the surface of the leading end side (surface on the front side of the opening part) of the support member150is in contact with the surface on the rear end side of the insulating ring145. On the other hand, the surface on the rear end side of the support member150faces the housing member152via the air gap. Moreover, the leading end side of the outer circumferential surface of the support member150is in contact with the inner circumferential surface of the pressure member149, and the rear end side of the outer circumferential surface of the support member150is in contact with the leading end side of the second coil spring151. By a second welding part159obtained by laser welding applied around the inner circumferential surface of the rear end side in the pressure member149and the outer circumferential surface of the support member150facing the portion, the pressure member149and the support member150are joined and fixed. In contrast thereto, the inner circumferential surface of the support member150faces the second rear end electrode member144, the first coil spring146, the conduction member147and the holding member148via the air gap. In this manner, by providing the air gap between the inner circumferential surface of the support member150and the second rear end electrode member144, the first coil spring146, the conduction member147and the holding member148, the support member150is not directly in contact with the second rear end electrode member144, the first coil spring146, the conduction member147and the holding member148.

The second coil spring151shows a spiral shape as a whole, and expands and contracts in the centerline direction. The second coil spring151is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel, and the surface thereof is gold-plated. In this manner, in the exemplary embodiment, the material is different between the first coil spring146and the second coil spring151.

The second coil spring151is disposed inside the leading end side housing131, and the leading end side thereof is positioned on the rear end side and outside of the support member150and the rear end side thereof is positioned on the leading end side and outside of the housing member152. In other words, the second coil spring151is disposed over the support member150and the housing member152. Moreover, the outer diameter of the second coil spring151is smaller than the inner diameter of the leading end side housing131(more specifically, the second leading end side housing1312). Further, the inner diameter of the second coil spring151is slightly smaller than the outer diameter on the rear end side of the support member150and the outer diameter on the leading end side of the housing member152. Then, the outer circumference of the second coil spring151faces the inner circumferential surface of the leading end side housing131via the air gap. In this manner, by providing the air gap between the outer circumference of the second coil spring151and the inner circumferential surface of the leading end side housing131, the second coil spring151and the leading end side housing131are not directly in contact with each other.

The housing member152shows a cylindrical shape as a whole. The housing member152is composed of a metallic material having conductivity, which is higher than the conductivity of the leading end side housing131, such as brass or stainless steel, and the surface thereof is gold-plated.

FIG. 16is a perspective view of the housing member152. Hereinafter, also with reference toFIG. 16, a configuration of the housing member152will be described. Note that, also inFIG. 16, the lower left side in the figure indicates the leading end side and the upper right side in the figure indicates the rear end side.

The housing member152of the exemplary embodiment includes: a first cylindrical part1521that is positioned at the most leading end side and is provided with an opening part at the leading end thereof; a second cylindrical part1522that is disposed at the rear end side of the first cylindrical part1521; a third cylindrical part1523that is positioned on the rear end side of the second cylindrical part1522; and a fourth cylindrical part1524that is positioned on the rear end side of the third cylindrical part1523. In the housing member152, the outer diameter becomes larger in the order of the first cylindrical part1521, the second cylindrical part1522, the third cylindrical part1523and the fourth cylindrical part1524. In other words, in the housing member152, the diameter increases in a stepwise manner (four steps) from the leading end side toward the rear end side. Then, the housing member152further includes: a first stepped part152athat connects the first cylindrical part1521and the second cylindrical part1522at a boundary portion therebetween; a second stepped part152bthat connects the second cylindrical part1522and the third cylindrical part1523at a boundary portion therebetween; and a third stepped part152cthat connects the third cylindrical part1523and the fourth cylindrical part1524at a boundary portion therebetween. Note that, in the housing member152, different from the above-described pressure member149, the thickness thereof is set at a certain size regardless of the position in the centerline direction. Therefore, in the housing member149, the inner diameter becomes larger in the order of the first cylindrical part1521, the second cylindrical part1522, the third cylindrical part1523and the fourth cylindrical part1524.

The housing member152is provided over the inner portion of the leading end side housing131and the inner portion of the rear end side housing133so that the first cylindrical part1521is on the leading end side. Inside the housing member152, the rear end side of the conduction member147, the rear end side of the holding member148, the circuit board153and the ground plate155are housed. Then, the housing member152is disposed on the rear end side of the support member150and on the leading end side of the connection member154. Moreover, the outer diameter of the housing member152differs among the first cylindrical part1521, the second cylindrical part1522, the third cylindrical part1523and the fourth cylindrical part1524; however, at all the positions, the outer diameter of the housing member152is smaller than the inner diameters of the leading end side housing131and the rear end side housing133. Further, the inner diameter of the housing member152also differs among the first cylindrical part1521, the second cylindrical part1522, the third cylindrical part1523and the fourth cylindrical part1524; however, the inner diameter of the housing member152is larger than the outer diameter of each member housed inside thereof.

Here, between the rear end side of the second cylindrical part1522and the second stepped part152bin the housing member152and the inner circumferential surface of the second leading end side housing1312, the first insulating member161is disposed. Moreover, between the rear end side of the third cylindrical part1523and the third stepped part152cin the housing member152and the inner circumferential surface of the second leading end side housing1312, the second insulating member162is disposed. Further, between the fourth cylindrical part1524in the housing member152and the first rear end side housing1331, the third insulating member163is disposed.

Then, the surface on the leading end side (surface on the front side of the opening part) of the first cylindrical part1521in the housing member152faces the surface on the rear end side of the support member150via the air gap. Moreover, the first cylindrical part1521is in contact with the second coil spring151. On the other hand, the rear end side of the fourth cylindrical part1524faces the holding member148. Moreover, the outer circumferential surface of the first cylindrical part1521and the first stepped part152afaces the inner circumferential surface of the second leading end side housing1312via the air gap. Further, the outer circumferential surface of the second cylindrical part1522faces the inner circumferential surface of the second leading end side housing1312via the air gap and the first insulating member161. Still further, the second stepped part152bfaces the inner circumferential surface of the second leading end side housing1312via the first insulating member161. Moreover, the outer circumferential surface of the third cylindrical part1523faces the inner circumferential surface of the second leading end side housing1312via the air gap and the second insulating member162. Further, the outer circumferential surface of the third stepped part152cfaces the inner circumferential surface of the second leading end side housing1312via the second insulating member162. Further, the outer circumferential surface of the fourth cylindrical part1524faces the inner circumferential surface of the second leading end side housing1312via the air gap, and faces the inner circumferential surface of the first rear end side housing1331via the air gap and the third insulating member163. In this manner, by providing the air gap, the first insulating member161, the second insulating member162and the third insulating member163between the outer circumference of the housing member152and the second leading end side housing1312and the first rear end side housing1331, the housing member152is not directly in contact with the second leading end side housing1312and the first rear end side housing1331.

The circuit board153shows a rectangular plate shape as a whole. The circuit board153performs various kinds of processing using electric circuits to an electric signal caused by a weak charge outputted by the piezoelectric element141in response to the received pressure, and is configured with a so-called printed wiring board. The circuit board153is provided over the inner portion of the leading end side housing131and the inner portion of the rear end side housing133. Moreover, the circuit board153is disposed on the rear end side of the conduction member147and on the leading end side of the connection member154. Further, the circuit board153is installed to the holding member148and the entirety thereof is disposed inside the housing member152.

On the circuit board153, there are installed: an integrating circuit that integrates an input signal (charge signal) inputted from the piezoelectric element141to convert thereof into a voltage signal; an amplifier circuit that amplifies the voltage signal inputted from the integrating circuit to generate an output signal; and a power supply circuit that serves as a power supply for elements, such as operational amplifiers, constituting these integrating circuit and amplifier circuit (all of them are not shown in the figure).

The connection member154shows a columnar shape as a whole. The connection member154includes a base material composed of a synthetic resin material having an insulating property, such as PPT, wiring composed of a metallic material having conductivity, such as copper, terminals, and so forth. However, of the connection member154, the portion (the outer circumferential surface) to be brought into contact with or to face the second rear end side housing1332is composed of the synthetic resin material, to thereby prevent a metallic material from being exposed in the portion. Moreover, on the rear end side of the connection member154, an opening part having a concave shape and opening toward the rear end side is provided. Then, on the leading end side of the connection member154, there is provided a board-side connector154athat projects toward the leading end side and is electrically connected to the circuit board153. On the other hand, on the rear end side of the connection member154and inside the above-described opening part, there is provided a cable-side connector154bthat projects toward the rear end side and is to be connected to the connection cable90shown inFIG. 1. Moreover, a concave part is provided around the outer circumferential surface of the leading end side in the connection member154, and the O-ring156is attached to the concave part.

The leading end side of the connection member154is positioned inside the second rear end side housing1332, and the rear end side thereof is positioned outside the second rear end side housing1332. Then, inside the second rear end side housing1332, the O-ring156attached to the outer circumferential surface of the connection member154is in contact with the inner circumferential surface of the second rear end side housing1332.

The outer diameter of the cylindrical portion positioned on the leading end side of the connection member154is smaller than the inner diameter of the second rear end side housing1332. In contrast thereto, the outer diameter of the cylindrical portion positioned on the rear end side of the connection member154is substantially the same as the outer diameter of the second rear end side housing1332. Moreover, the leading end side of the connection member154faces the inner circumferential surface of the second rear end side housing1332via the air gap or the O-ring156.

The ground plate155shows a strip shape as a whole. The ground plate155is composed of a metallic material having conductivity, such as phosphor bronze, and the surface thereof is gold-plated.

The ground plate155is provided over the inner portion of the leading end side housing131and the inner portion of the rear end side housing133; the leading end thereof is positioned inside the housing member152and above the circuit board153, and the rear end thereof projects toward the rear end side than the rear end of the housing member152. Then, the leading end side of the ground plate155is electrically connected to the ground terminal (not shown) of the circuit board153, and the rear end side of the ground plate155is electrically connected to the inner circumferential surface of the fourth cylindrical part1524in the housing member152.

The O-ring156shows an annular shape as a whole. The O-ring156is composed of a synthetic resin material having the insulating property and high resistance to heat, permeability and acids, such as PTFE (Polytetrafluoroethylen).

The O-ring156is attached to the outer circumferential surface of the connection member154, and is to be sandwiched between the outer circumferential surface of the connection member154and the inner circumferential surface of the second rear end side housing1332when the connection member154is attached to the second rear end side housing1332.

The butting pipe157as an example of a fixing member shows a cylindrical shape as a whole. The butting pipe157is composed of a metallic material having conductivity and high resistance to heat, such as stainless steel.

The butting pipe157is disposed inside a region in the leading end side housing131where the first leading end side housing1311and the second leading end side housing1312overlap each other and inside the first leading end side housing1311. Then, the butting pipe157is positioned on the rear end side of the middle cylindrical part1492in the pressure member149and on the leading end side of the first insulating member161. Moreover, the outer diameter of the butting pipe157is substantially the same as the inner diameter of the rear end side in the first leading end side housing1311that houses the butting pipe157. On the other hand, the inner diameter of the butting pipe157is larger than the outer diameter of the rear end cylindrical part1493in the pressure member149. Then, the surface on the leading end side of the butting pipe157is in contact with the rear end stepped part149c(the formation surface of the insulating film149a) in the pressure member149. On the other hand, the surface on the rear end side of the butting pipe157faces the surface on the leading end side of the first insulating member161via the air gap. Moreover, the outer circumferential surface of the butting pipe157is in contact with the inner circumferential surface on the rear end side of the first leading end side housing1311. By a first welding part158obtained by laser welding applied around the inner circumferential surface of the rear end side in the first leading end side housing1311and the outer circumferential surface of the butting pipe157facing the portion, the first leading end side housing1311and the butting pipe157are joined and fixed. In contrast thereto, the inner circumferential surface of the butting pipe157faces the outer circumferential surface of the rear end cylindrical part1493in the pressure member149via the air gap. In this manner, by providing the insulating film149aand the air gap between the rear end stepped part149cand the rear end cylindrical part1493in the pressure member149and the butting pipe157, the butting pipe157and the pressure member149are not directly in contact with each other.

The first welding part158is formed by laser welding applied around the inner circumferential surface of the rear end side in the first leading end side housing1311and the outer circumferential surface of the butting pipe157.

The second welding part159is formed by laser welding applied around the inner circumferential surface of the rear end side in the pressure member149and the outer circumferential surface of the support member150.

The insulating pipe160shows a cylindrical shape as a whole. The insulating pipe160is composed of a synthetic resin material having an insulating property, such as LCP (Liquid Crystal Polymer). The insulating pipe160is disposed inside the pressure member149provided inside the leading end side housing131. Inside the insulating pipe160, the piezoelectric element141, the first rear end electrode member143and the leading end side of the main body part144ain the second rear end electrode member144are housed. Then, the insulating pipe160is disposed on the rear end side of the leading end electrode member142and on the leading end side of the insulating ring145. Moreover, the outer diameter of the insulating pipe160is slightly smaller than the inner diameter of the pressure member149. Further, the inner diameter of the insulating pipe160is slightly larger than the outer diameter of each of the piezoelectric element141, the first rear end electrode member143and the main body part144ain the second rear end electrode member144. Then, the leading end side of the insulating pipe160faces the surface on the rear end side of the leading end electrode member142. On the other hand, the rear end side of the insulating pipe160faces the surface on the leading end side of the insulating ring145. Moreover, the outer circumferential surface of the insulating pipe160faces the inner circumferential surface of the pressure member149. Further, the inner circumferential surface of the insulating pipe160faces the outer circumferential surfaces of the piezoelectric element141, the first rear end electrode member143and the main body part144ain the second rear end electrode member144. In this manner, by providing the insulating pipe160and the air gap formed by the insulating pipe160between the pressure member149and the piezoelectric element141, the first rear end electrode member143and the main body part144ain the second rear end electrode member144, the first pressure member149is not directly in contact with the first rear end electrode member143and the second rear end electrode member144.

The first insulating member161shows a cylindrical shape in the leading end side thereof and an annular shape in the rear end side thereof. The first insulating member161is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina.

The first insulating member161is disposed inside the leading end side housing131. Then, the first insulating member161is disposed outside the second cylindrical part1522and the second stepped part152bin the housing member152(refer toFIG. 16). Moreover, the outer diameter of the first insulating member161is slightly smaller than the inner diameter of the second leading end side housing1312of the corresponding portion, and the inner diameter of the first insulating member161is slightly larger than the outer diameter of the housing member152of the corresponding portion. Then, the outer circumferential surface of the first insulating member161is in contact with the second leading end side housing1312, and the inner circumferential surface of the first insulating member161is in contact with the housing member152.

The second insulating member162shows an annular shape as a whole. The second insulating member162is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina.

The second insulating member162is disposed at a position on the rear end side than the first insulating member161inside the leading end side housing131. Then, the second insulating member162is disposed outside the third cylindrical part1523and the third stepped part152cin the housing member152(refer toFIG. 16). Moreover, the outer diameter of the second insulating member162is slightly smaller than the inner diameter of the second leading end side housing1312of the corresponding portion, and the inner diameter of the second insulating member162is slightly larger than the outer diameter of the housing member152of the corresponding portion. Then, the outer circumferential surface of the second insulating member162is in contact with the second leading end side housing1312, and the inner circumferential surface of the second insulating member162is in contact with the housing member152.

In this manner, by providing the air gap, the first insulating member161and the second insulating member162between the leading end side housing131(the second leading end side housing1312) and the housing member152, the leading end side housing131and the housing member152are not directly in contact with each other.

The third insulating member163shows a cylindrical shape as a whole. The third insulating member163is composed of a ceramic material having an insulating property and high resistance to heat, such as alumina.

The third insulating member163is disposed at a position on the rear end side than the second insulating member162inside the rear end side housing133. Then, the third insulating member163is positioned outside the fourth cylindrical part1524in the housing member152. Moreover, the outer diameter of the third insulating member163is substantially the same as the inner diameter of the first rear end side housing1331, and the inner diameter of the third insulating member163is larger than the outer diameter of the fourth cylindrical part1524in the housing member152. Then, the outer circumferential surface of the third insulating member163is in contact with the inner circumferential surface of the first leading end side housing1331, and part on the leading end side of the inner circumferential surface of the third insulating member163is in contact with the housing member152and the other part thereof faces the housing member152via the air gap.

The sealing part170includes a first sealing member171that is positioned relatively close to the leading end side thereof and a second sealing member172that is positioned relatively close to the rear end side thereof. Note that, in the state where the pressure detection device20is attached to the internal combustion engine10, the first sealing member171and the second sealing member172butt the inner circumferential surface of the communication hole13aprovided to the cylinder head13(refer toFIG. 1).

The first sealing member171has a hollow structure and shows a cylindrical shape as a whole. The first sealing member171is composed of a synthetic resin material having an insulating property and high resistance to heat and acids, such as PTFE.

The first sealing member171is set in the concave part1311aprovided to the outer circumferential surface of the first leading end side housing1311. Then, the inner diameter thereof is slightly smaller than the outer diameter of the concave part1311aand the outer diameter thereof is slightly larger than the inner diameter of the communication hole13a.

The second sealing member172shows an annular shape as a whole, and an O-ring is used here. The second sealing member172is also composed of a synthetic resin material having an insulating property and high resistance to heat and acids, such as PTFE.

The second sealing member172is set in the concave part1312aprovided to the outer circumferential surface of the second leading end side housing1312. Then, the inner diameter thereof is slightly smaller than the outer diameter of the concave part1312aand the outer diameter thereof is slightly larger than the inner diameter of the communication hole13a.

[Electrical Connection Structure in Pressure Detection Device]

Here, the electrical connection structure in the pressure detection device20will be described.

In the pressure detection device20, an end surface on the rear end side of the piezoelectric element141(positive pole) is electrically connected to the conduction member147made of metal via the first rear end electrode member143made of metal, the second rear end electrode member144made of metal and the first coil spring146made of metal. Then, the conduction member147made of metal is electrically connected to an input terminal (not shown) provided to the circuit board153via the holding part, wiring and terminal made of metal provided to the holding member148. Hereinafter, an electrical route from the surface on the rear end side of the piezoelectric element141to the circuit board153via the first rear end electrode member143, the second rear end electrode member144, the first coil spring146, the conduction member147and the holding member148is referred to as “positive route”.

On the other hand, in the pressure detection device20, an end surface on the leading end side of the piezoelectric element141(negative pole) is electrically connected to the ground terminal (not shown) provided to the circuit board153via the leading end electrode member142made of metal, the pressure member149made of metal, the support member150made of metal (the second welding part159), the second coil spring151made of metal, the housing member152made of metal and the ground plate155made of metal. Hereinafter, an electrical route from the surface on the leading end side of the piezoelectric element141to the circuit board153via the leading end electrode member142, the pressure member149, the support member150, the second coil spring151, the housing member152and the ground plate155is referred to as “negative route”.

On the other hand, in the pressure detection device20, the diaphragm head132made of metal is electrically connected to the rear end side housing133(the first rear end side housing1331and the second rear end side housing1332) made of metal via the leading end side housing131(the first leading end side housing1311and the second leading end side housing1312) made of metal. Moreover, in the pressure detection device20, the first leading end side housing1311made of metal is electrically connected to the butting pipe157(the first welding part158) made of metal. Hereinafter, an electrical route from the diaphragm head132to the rear end side housing133and the butting pipe157via the leading end side housing131is referred to as “housing route”.

(Relationship Between Positive Route and Negative Route)

Here, in the pressure detection device20in the exemplary embodiment, the negative route exists outside the positive route. To put it another way, the positive route is housed inside the negative route. Then, the positive route and the negative route are electrically insulated by the insulating pipe160, the insulating ring145, the holding member148and the air gap formed between both routes. Here, in the exemplary embodiment, the negative route serves as an example of a first electrical route, and the positive route serves as an example of a second electrical route.

(Relationship Between Negative Route and Housing Route)

Moreover, in the pressure detection device20, the housing route exists outside the negative route. To put it another way, the negative route is housed inside the housing route. Then, the negative route and the housing route are electrically insulated by the insulating film142aprovided to the leading end electrode member142, the insulating film149aprovided to the pressure member149, the first insulating member161, the second insulating member162, the third insulating member163and the air gap formed between both routes.

(Relationship Between Housing Route and Positive Route)

Moreover, in the pressure detection device20, as a result, the housing route exists outside the positive route. To put it another way, the positive route is housed inside the housing route. Then, as described above, since the positive route and the negative route are electrically insulated, and the negative route and the housing route are electrically insulated, the housing route and the positive route result in being electrically insulated.

Here, the housing part130constituting the housing route is a portion exposed to the outside in the pressure detection device20, and in particular, the diaphragm head132is a portion facing the combustion chamber C that increases acidity with combustion. In contrast thereto, each portion constituting the positive route and the negative route is a portion housed inside the housing part130in the pressure detection device20. Therefore, it is preferable that each member constituting the positive route and the negative route is composed of a material having conductivity higher than that of each member constituting the housing route (the housing part130), and it is preferable that each member constituting the housing route (the housing part130) is composed of a material having resistance to acids higher than that of each member constituting the positive route and the negative route.

[Assembling Procedures of Pressure Detection Device]

Next, assembling procedures of the pressure detection device20used in the exemplary embodiment will be described.

First, the leading end side of the first leading end side housing1311and the rear surface side (the convex part132dside) of the diaphragm head132are caused to face and butt against each other. Then, in this state, laser welding is applied round the boundary portion between the first leading end side housing1311and the diaphragm head132.

Next, into the first leading end side housing1311in a structure including the first leading end side housing1311and the diaphragm head132, the pressure member149is inserted from the rear end side with the leading end cylindrical part1491serving as the leading end side. At this time, insertion of the pressure member149is performed until the leading end stepped part149bprovided to the outer circumferential surface of the pressure member149butts against the inside stepped part1311bprovided to the inner circumferential surface of the first leading end side housing1311. With this, the leading end stepped part149bof the pressure member149and the insulating film149aprovided to the outer circumferential surface of the middle cylindrical part1492are brought into contact with the inner circumferential surface of the first leading end side housing1311. Moreover, into the opening part provided to the leading end side of the leading end cylindrical part1491in the pressure member149, the convex part132dof the diaphragm head132is inserted.

Substantially, between the inner circumferential surface of the first leading end side housing1311and the outer circumferential surface of the rear end cylindrical part1493in the pressure member149, the butting pipe157is inserted from the rear end side. At this time, until the leading end side of the butting pipe157butts against the rear end stepped part149cprovided to the pressure member149, the butting pipe157is inserted. With this, the insulating film149aprovided to the rear end stepped part149cof the pressure member149is brought into contact with the leading end side of the butting pipe157.

In this state, the rear end side of the first leading end side housing1311and the butting pipe157are subjected to laser welding around thereof, to thereby form the first welding part158. At this time, by sandwiching the middle cylindrical part1492of the pressure member149between the inside stepped part1311bof the first leading end side housing1311and the leading end side of the butting pipe157, the pressure member149is fixed to the first leading end side housing1311. Consequently, the positioning of the pressure member149with respect to the first leading end side housing1311and the diaphragm head132is performed.

Next, into the pressure member149in a structure including the first leading end side housing1311, the diaphragm head132, the pressure member149and the butting pipe157, the leading end electrode member142, the insulating pipe160, the piezoelectric element141, the first rear end electrode member143, the second rear end electrode member144, the insulating ring145and the support member150are inserted in this order from the rear end side. Note that, when the leading end electrode member142is inserted into the pressure member149, the surface on which the insulating film142ais formed is set to the leading end side. Moreover, when the second rear end electrode member144is inserted into the pressure member149, the main body part144ais set to the leading end side and the second convex part144cis set to the rear end side. At this time, the insulating film142aprovided to the leading end side of the leading end electrode member142to be housed in the pressure member149is brought into contact with the convex part132dprovided to the rear end side of the diaphragm head132. Moreover, inside the insulating pipe160, the piezoelectric element141, the first rear end electrode member143and the leading end side of the main body part144ain the second rear end electrode member144are disposed. Further, the first convex part144band the second convex part144cof the second rear end electrode member144are exposed to the inside of the leading end side of the support member150via a hole provided to the insulating ring145.

In this state, adjustment of position of the support member150in the centerline direction with respect to the pressure member149is performed, and thereby the load (preload) applied to the piezoelectric element141via the pressure member149and the support member150is adjusted.

Then, after the adjustment of position of the support member150in the centerline direction with respect to the pressure member149is finished, the rear end side of the pressure member149and the support member150are subjected to laser welding around thereof, to thereby form the second welding part159. At this time, the leading end side of the piezoelectric element141is fixed to the pressure member149via the leading end electrode member142, and the rear end side thereof is fixed to the pressure member149via the first rear end electrode member143, the second rear end electrode member144, the insulating ring145and the support member150. Moreover, in this state, the pressure member149has already been fixed to the first leading end side housing1311and the diaphragm head132. Therefore, the piezoelectric element141to be housed in the pressure member149is fixed to the diaphragm head132in a state in which a predetermined preload is imparted. Consequently, the positioning of the pressure member149, the support member150and the piezoelectric element141with respect to the first leading end side housing1311and the diaphragm head132is performed.

Subsequently, into the support member150in a structure, to which components up until the support member150are attached, the first coil spring146is inserted from the rear end side, to be mounted onto the second convex part144cof the second rear end electrode member144exposed inside the leading end side of the support member150. Moreover, to the rear end side of the support member150in the above-described structure, the second coil spring151is inserted from the rear end side to be mounted. Further, into the first leading end side housing1311in the above-described structure, the second leading end side housing1312is screwed from the rear end side to be attached. Still further, into the second leading end side housing1312, the first insulating member161and the second insulating member162are inserted in this order from the rear end side. With this, the first insulating member161is butted against the stepped part provided to the leading end side in the second leading end side housing1312and is positioned, and the second insulating member162is butted against the stepped part provided to the rear end side in the second insulating member1312and is positioned.

On the other hand, in a process different from the assembly of the above-described structure, into the leading end side of the holding member148, the conduction member147is inserted from the leading end side. Moreover, to the rear end side of the holding member148, the circuit board153including the ground plate155is attached. At this time, the rear end side convex part147bof the conduction member147attached to the holding member148and the circuit board153are electrically connected. Then, into the housing member152, the holding member148, to which the conduction member147and the circuit board153(the ground plate155) are mounted, is inserted from the rear end side with the conduction member147as the leading end side. At this time, the holding member148is inserted until the boundary portion between the cylindrical portion and the plate-like portion (the leading end side of the plate-like portion) in the holding member148butts against the inner circumferential surface of the second stepped part152bprovided to the housing member152. With this, the leading end side of the cylindrical portion in the holding member148and the leading end side of the conduction member147exposed from the cylindrical portion in the holding member148(the leading end side concave part147a) project toward the leading end side than the first cylindrical part1521. Moreover, the inner circumferential surface of the housing member152and the rear end side of the ground plate155are brought into contact with each other.

Then, into the second leading end side housing1312in a structure, to which components up until the second insulating member162are attached, the housing member152including the conduction member147, the circuit board153(the ground plate155) and the holding member148is inserted from the rear end side with the first cylindrical part1521as the leading end side. At this time, the housing member152is inserted until the second stepped part152bprovided to the housing member152butts against the first insulating member161attached to the inside of the second leading end side housing1312(until the third stepped part152cprovided to the housing member152butts against the second insulating member162attached to the inside of the second leading end side housing1312). With this, the rear end side of the second cylindrical part1522and the outer circumferential surface of the second stepped part152bin the housing member152are brought into contact with the inner circumferential surface and the surface on the rear end side of the first insulating member161. Moreover, the rear end side of the third cylindrical part1523and the outer circumferential surface of the third stepped part152cin the housing member152are brought into contact with the inner circumferential surface and the surface on the rear end side of the second insulating member162. On the other hand, the rear end side of the first coil spring146is inserted into the leading end side concave part147aof the conduction member147and the rear end of the first coil spring146butts against the bottom portion of the leading end side concave part147a. Moreover, the first cylindrical part1521of the housing member152is inserted into the rear end side of the second coil spring151and the rear end of the second coil spring151butts against the first stepped part152aof the housing member152. As a result, the first coil spring146and the second coil spring151are brought into a state of being contracted in the centerline direction as compared to a state before inserting the housing member152into the above-described structure.

Subsequently, into the second leading end side housing1312in a structure, to which components up until the housing member152are attached, the first rear end side housing1331and the third insulating member163are inserted from the rear end side and are attached. With this, the outer circumferential surface of the fourth cylindrical part1524in the housing member152is brought into contact with the inner circumferential surface of the third insulating member163. Moreover, into the first rear end side housing1331, the second rear end side housing1332is inserted from the rear end side.

Then, into the second rear end side housing1332in a structure, to which components up until the second rear end side housing1332are attached, the connection member154, on the outer circumferential surface of which the O-ring156is mounted, is inserted from the rear end side with the board-side connector154aas the leading end side. At this time, the O-ring156mounted on the connection member154enters inside the second rear end side housing1332to be brought into contact with the second rear end side housing1332. Moreover, the circuit board153and the board-side connector154aprovided to the connection member154are electrically connected.

Finally, into the concave part1311aof the first leading end side housing1311in a structure, to which components up until the connection member154are attached, the first sealing member171is attached and the second sealing member172is attached to the concave part1312aof the second leading end side housing1312.

Thus, assembly of the pressure detection device20is completed.

[Pressure Detection Operation by Pressure Detection Device]

Now, pressure detection operation by the pressure detection device20will be described.

When the internal combustion engine10is operating, a pressure generated inside the combustion chamber C (combustion pressure) is imparted to the pressure receiving surface132aof the diaphragm head132. In the diaphragm head132, the pressure received by the pressure receiving surface132ais transferred to the convex part132don the back side, and is further transferred from the convex part132dto the leading end electrode member142via the insulating film142a. Then, the pressure transferred to the leading end electrode member142acts on the piezoelectric element141held between the leading end electrode member142and the first rear end electrode member143, to thereby, in the piezoelectric element141, generate charges corresponding to the received pressure. The charges generated in the piezoelectric element141are supplied to the input signal terminal (not shown) of the circuit board153as the charge signal via the positive route. The charge signal supplied to the circuit board153is subjected to various kinds of processing in the circuits implemented onto the circuit board153to be converted into the output signal. Then, the output signal outputted from the circuit board153is transmitted to the outside (here, the connection cable90and the controller80) via the connection member154.

[Effect of the Exemplary Embodiment]

In the pressure detection device20of the exemplary embodiment, by fixing the positional relationship of the pressure member149and the support member150in the centerline direction, the piezoelectric element141is held between the pressure member149and the support member150to impart the predetermined load to the piezoelectric element141. Then, the pressure member149to house the piezoelectric element141inside thereof, which was in the state of being in contact with the inner circumferential surface of the leading end side housing131via the insulating film149a, is fixed to the leading end side housing131by use of the butting pipe157. This makes it possible to electrically insulate the pressure member149and the leading end side housing131and to fix the piezoelectric element141to the housing part130(the leading end side housing131) via the pressure member149and the support member150in the state of suppressing variations in load.

Moreover, in the pressure detection device20of the exemplary embodiment, the insulating film142ais provided to the leading end side of the leading end electrode member142existing between the piezoelectric element141and the diaphragm head132. This makes it possible to electrically insulate the leading end electrode member142and the diaphragm head132.

Here, in the exemplary embodiment, there is provided the configuration in which the above-described leading end electrode member142and pressure member149also serve as the negative route of the piezoelectric element141; by adopting the above-described configuration, it is possible to electrically insulate the negative route from the housing route including the leading end side housing131and the diaphragm head132.

The pressure detection device20of the exemplary embodiment is attached to the internal combustion engine10, and, when the internal combustion engine10is carried aboard a vehicle, noise of frequency of the order of kHz (hereinafter, referred to as low-frequency noise) generated in a horn, headlights, wipers comes into the cylinder head13of the internal combustion engine10. Then, in the exemplary embodiment, since, of the pressure detection device20, the housing part130composed of metal is attached to the cylinder head13composed of metal, the low-frequency noise coming into the cylinder head13also propagates to the housing part130of the pressure detection device20.

Here, in the pressure detection device20of the exemplary embodiment, the housing route including the housing part130is electrically insulated from the positive route and the negative route from the piezoelectric element141to the circuit board153. Therefore, the low-frequency noise propagated from the cylinder head13to the housing part130of the pressure detection device20becomes unlikely to be transferred to the circuit board153via the pressure member149, the support member150, the conduction member147and so forth. As a result, fluctuations (variations) in the potential in the circuit board153due to the low-frequency noise is suppressed, and therefore, it becomes possible to reduce fluctuations (variations) in the output signal outputted from the circuit board153to the outside (the controller80or the like).

Moreover, when the internal combustion engine10is carried aboard a vehicle, radio waves of the order of MHz used by mobile phones, radio, television and so forth usually fly around the vehicle. When the radio waves are emitted to the conduction member147provided to the pressure detection device20, noise of frequency of the order of MHz (hereinafter, referred to as high-frequency noise) results in being transferred to the circuit board153.

Here, in the pressure detection device20in the exemplary embodiment, by use of the pressure member149and the support member150, the conduction member147is covered. Therefore, the radio waves emitted to the pressure detection device20from the outside are shielded by the pressure member149and the support member150, to be less likely to be transferred to the conduction member147. As a result, fluctuations (variations) in the potential in the circuit board153due to the high-frequency noise is suppressed, and therefore, it becomes possible to reduce fluctuations (variations) in the output signal outputted from the circuit board153to the outside.

Moreover, in the exemplary embodiment, by use of the housing member152made of metal, the circuit board153is covered. Therefore, the radio waves emitted to the pressure detection device20from the outside are shielded by the housing member152, to be less likely to reach the circuit board153. As a result, fluctuations (variations) in the potential in the circuit board153due to the high-frequency noise is suppressed, and therefore, it becomes possible to further reduce fluctuations (variations) in the output signal outputted from the circuit board153to the outside.

Note that, in the exemplary embodiment, by providing the insulating film142ato the leading end side of the leading end electrode member142, the leading end electrode member142constituting the negative route and the diaphragm head132constituting the housing route are electrically insulated; however, the insulation method is not limited thereto. For example, between the leading end electrode member142and the diaphragm head132, an insulating plate composed of a ceramic material having the insulating property and high resistance to heat, such as alumina, may be disposed.

Moreover, in the exemplary embodiment, by providing the insulating film149ato part of the outer circumferential surface of the pressure member149(the middle cylindrical part1492, the leading end stepped part149band the rear end stepped part149c), the pressure member149is electrically insulated from the first leading end side housing1311and the butting pipe157constituting the housing route; however, the insulation method is not limited thereto. For example, between the pressure member149and the first leading end side housing1311and the butting pipe157, it may be possible to dispose an insulating ring composed of a ceramic material having the insulating property and high resistance to heat, such as alumina, or to form an air gap.

Moreover, by disposing the first insulating member161between rear end side of the second cylindrical part1522and the second stepped part152bin the housing member152and the inner circumferential surface of the second leading end side housing1312, the second insulating member162between rear end side of the third cylindrical part1523and the third stepped part152cin the housing member152and the inner circumferential surface of the second leading end side housing1312, and the third insulating member163between the fourth cylindrical part1524in the housing member152and the first rear end side housing1331, the housing member152constituting the negative route is electrically insulated from the leading end side housing131and the rear end side housing133constituting the housing route; however, the insulation method is not limited thereto. For example, it may be possible to form an insulating film on part of the outer circumferential surface of the housing member152by coating a ceramic material containing alumina, zirconia or the like and showing the insulating property, or to form an air gap between the housing member152and the leading end side housing131and the rear end side housing133.

Further, in the exemplary embodiment, the first leading end side housing1311and the butting pipe157are fixed by use of the first welding part158; however, the fixing method is not limited thereto, and, for example, both of them may be fixed by screwing or the like. Still further, in the exemplary embodiment, the pressure member149and the support member150are fixed by use of the second welding part159; however, the fixing method is not limited thereto, and, for example, both of them may be fixed by screwing or the like.

Moreover, in the exemplary embodiment, the first rear end electrode member143and the second rear end electrode member144are disposed as separate members; however, disposition is not limited thereto, and, for example, it may be possible to replace the first rear end electrode member143and the second rear end electrode member144with a single member to be disposed.

Further, in the exemplary embodiment, the leading end electrode member142is not housed inside the insulating pipe160; however, disposition is not limited thereto, and the leading end electrode member142may be housed inside the insulating pipe160.

Still further, in the exemplary embodiment, the description is given by taking the case in which the piezoelectric element141is used as the detection element for pressure in the pressure detection device20as an example; however, the detection element is not limited thereto, and, for example, a strain gage, a spaced electrode or the like may be used.

REFERENCE SIGNS LIST