JP5893920B2 - Detection system and detection device - Google Patents

Description

  The present invention relates to a detection system that detects a physical quantity and a detection device that detects a physical quantity.

  For example, in an apparatus such as an automobile having an internal combustion engine, a plurality of detection devices that detect pressure, temperature, and the like are mounted in the device, and a control called an ECU (Engine Control Unit) is based on the detection results of these detection devices. The device controls the operation of the internal combustion engine. Here, the control device and the detection device are usually an electric wire for supplying power from the control device to the detection device, an electric wire for sending a signal from the detection device to the control device, and a ground between the control device and the detection device. It connects using the electric wire for making it common.

  For example, Patent Document 1 discloses an in-vehicle power steering apparatus system that includes an ECU unit and a current sensor unit that detects a current flowing in a current path. The ECU unit and the current sensor unit are connected to a power supply line, a signal output, and the like. A technique is described in which a connection is made using three wires, that is, a wire and a ground wire, and a disconnection of the ground wire is detected using a circuit having an N-channel FET and a resistor.

JP 2008-51722 A

Here, the detection device and the control device are normally connected to the grounding body. For this reason, when the detection device and the control device are further connected via a grounding wire, they are electrically connected via a path other than the grounding wire. There was a risk that the broken wire could not be detected.
On the other hand, even if a configuration in which the detection device and the control device are simply not connected via a ground line is employed, a signal processing circuit is used when there is a difference between the ground potential of the detection device and the ground potential of the control device. As a result, there is a concern that an error included in the detection amount obtained based on the output signal becomes large.
An object of the present invention is to eliminate the need for an electric wire used for grounding a signal processing circuit and to reduce noise in an output signal from the signal processing circuit.

The detection system of the present invention includes a detection element that detects a change in physical quantity, a signal processing circuit that processes a detection signal output from the detection element, the detection element and the signal processing circuit, and the signal A housing that is electrically connected to a grounding body, and a constant voltage for supplying a constant voltage to the signal processing circuit in the detector A supply / voltage connected to the detection unit via a constant voltage supply line and an output signal transmission line for transmitting an output signal output from the signal processing circuit , and further electrically connected to the grounding body A processing unit, wherein the detection unit uses the voltage value of the constant voltage supplied via the constant voltage supply line as a reference and does not use the ground potential in the signal processing circuit as a reference. It is characterized by further comprising a working voltage generating circuit to create a working voltage to be used in the signal processing circuit.

In this detection system, the detection element includes a piezoelectric element that detects pressure using a piezoelectric body, and the signal processing circuit integrates a charge signal input from the piezoelectric element using an operational amplifier. Then, an integration circuit for converting the charge signal into a voltage signal, and the voltage signal input from the integration circuit is amplified using another operational amplifier, and the obtained amplified signal is sent to the output signal transmission line. An amplifier circuit that outputs to the supply / processing unit via the operational voltage generator circuit provided in the integrating circuit and the other operational amplifier provided in the amplifier circuit, It is preferable to supply the working voltage respectively. Thereby, even when an amplified signal is obtained based on a weak charge signal, noise contained in the amplified signal can be reduced.

The operational amplifier provided in the integrating circuit and the other operational amplifier provided in the amplifier circuit are each a single power source that uses the constant voltage supplied through the constant voltage supply line as a power source. work, the working voltage generating circuit is an inverting input terminal of the other operational amplifier which is provided to the non-inverting input terminals and said amplifier circuit of the operational amplifier provided in the integrating circuit, supplied with each of the working voltage It is preferable to do. Thereby, the voltage created by the use voltage creation circuit can be set to only one polarity.

  From another viewpoint, the detection apparatus of the present invention includes a detection element that detects a change in physical quantity, a signal processing circuit that processes a detection signal output from the detection element, the detection element, and the signal A housing to which a processing circuit is attached, a constant voltage supply means for supplying a constant voltage to the signal processing circuit, an output signal transmission means for transmitting an output signal output from the signal processing circuit, and the signal A connection means for connecting a ground in the processing circuit to the casing, and a voltage value of the constant voltage supplied via the constant voltage supply means as a reference, and a potential of the ground in the signal processing circuit as a reference And a use voltage generation circuit that generates a use voltage used in the signal processing circuit.

In this detection apparatus, the detection element includes a piezoelectric element that detects pressure using a piezoelectric body, and the signal processing circuit integrates a charge signal input from the piezoelectric element using an operational amplifier. Then, the integration circuit for converting the charge signal into a voltage signal, the voltage signal input from the integration circuit is amplified using another operational amplifier, and the obtained amplified signal is supplied to the output signal transmission means . further comprising an amplifier circuit for outputting to the outside through the working voltage generating circuit is in the other operational amplifier provided in the operational amplifier and the amplifier circuit provided in the integrated circuit, each of the working voltage Is preferably supplied . Thereby, even when an amplified signal is obtained based on a weak charge signal, noise contained in the amplified signal can be reduced.

  ADVANTAGE OF THE INVENTION According to this invention, while reducing the electric wire used for grounding of a signal processing circuit, the noise in the output signal from a signal processing circuit can be reduced.

1 is a schematic configuration diagram of an internal combustion engine according to an embodiment. It is an enlarged view of the II section of the pressure detection apparatus shown in FIG. It is a schematic block diagram of a pressure detection apparatus. It is sectional drawing of the IV-IV part of the pressure detection apparatus shown in FIG. It is an enlarged view of the V section of the pressure detection apparatus shown in FIG. It is an enlarged view of VI part of the pressure detection apparatus shown in FIG. It is a circuit block diagram in a mounting substrate. It is an example of the circuit block diagram of the power supply circuit provided in the mounting board | substrate. It is a figure for demonstrating the structure of a control apparatus. It is a figure for demonstrating the electrical connection relationship of an internal combustion engine, a pressure detection apparatus, a control apparatus, and a transmission cable. It is a flowchart for demonstrating the procedure of the disconnection detection operation | movement at the time of start-up of an internal combustion engine.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an internal combustion engine 1 according to the present embodiment. 2 is an enlarged view of the II part of the pressure detection device 5 shown in FIG.
The internal combustion engine 1 includes a cylinder block 2 having a cylinder 2a, a piston 3 that reciprocates in the cylinder 2a, a cylinder head 4 that is fastened to the cylinder block 2 and forms a combustion chamber C together with the cylinder 2a, the piston 3, and the like, It has. Here, both the cylinder block 2 and the cylinder head 4 are made of conductive aluminum, cast iron, or the like. The internal combustion engine 1 is mounted on the cylinder head 4 to detect the pressure in the combustion chamber C, and a control device that controls the operation of the internal combustion engine 1 based on the pressure detected by the pressure detection device 5. 6, an electric signal is transmitted between the pressure detection device 5 and the control device 6, and between the pressure detection device 5 and the control device 6, which is interposed between the pressure detection device 5 and the cylinder head 4 and maintains the airtightness in the combustion chamber C. A transmission cable 8.

  As shown in FIG. 2, the transmission cable 8 includes two cables, that is, a first cable 81 and a second cable 82, and for connecting the first cable 81 and the second cable 82 to the pressure detection device 5. And a connector 80. Here, each of the first cable 81 and the second cable 82 is constituted by an insulated wire in which an outer peripheral surface of a conductor portion made of a tinned annealed copper stranded wire is covered with a resin insulator. In the present embodiment, the first cable 81 functions as a constant voltage supply line, and the second cable 82 functions as an output signal transmission line. Thus, the transmission cable 8 of the present embodiment does not have a ground line.

  As shown in FIG. 2, the cylinder head 4 is formed with a communication hole 4 a that communicates the combustion chamber C with the outside. From the combustion chamber C side, the communication hole 4a has a hole diameter larger than the first hole part 4b, the inclined part 4c whose diameter gradually increases from the hole diameter of the first hole part 4b, and the hole diameter of the first hole part 4b. A large second hole 4d. A female screw 4e into which a male screw 332a of the housing 30 (described later) formed in the pressure detection device 5 is screwed is formed on the surrounding wall forming the second hole 4d.

Below, the pressure detection apparatus 5 is explained in full detail.
FIG. 3 is a schematic configuration diagram of a pressure detection device 5 as an example of a detection unit or a detection device. 4 is a cross-sectional view of the IV-IV portion of the pressure detection device 5 shown in FIG. FIG. 5 is an enlarged view of a V portion of the pressure detection device 5 shown in FIG. FIG. 6 is an enlarged view of a VI part of the pressure detection device 5 shown in FIG.

  The pressure detection device 5 includes a sensor unit 100 having a piezoelectric element 10 that converts the pressure in the combustion chamber C into an electric signal, a signal processing unit 200 that processes an electric signal from the sensor unit 100, and a signal processing unit 200. Holding member 300. When the pressure detection device 5 is mounted on the cylinder head 4, the diaphragm head 40 (described later) of the sensor unit 100 is inserted into the communication hole 4 a formed in the cylinder head 4 first. In the following description, the left side of FIG. 4 is the front end side of the pressure detection device 5, and the right side is the rear end side of the pressure detection device 5.

First, the sensor unit 100 will be described.
The sensor unit 100 includes a piezoelectric element 10 that converts received pressure into an electrical signal, and a housing 30 that is cylindrical and in which a cylindrical hole that accommodates the piezoelectric element 10 and the like is formed. . Hereinafter, the center line direction of the cylindrical hole formed in the housing 30 is simply referred to as a center line direction.

The sensor unit 100 is provided so as to close the opening on the distal end side of the housing 30, and is provided between the diaphragm head 40 on which the pressure in the combustion chamber C acts, and between the diaphragm head 40 and the piezoelectric element 10. The first electrode unit 50 and the second electrode unit 55 disposed on the opposite side of the piezoelectric element 10 from the first electrode unit 50 are provided.
The sensor unit 100 is provided with an insulating ring 60 made of alumina ceramic that electrically insulates the second electrode unit 55 and a rear end side of the insulating ring 60, and a covering member 23 described later of the signal processing unit 200. And a coil spring 70 interposed between the second electrode portion 55 and a conductive member 22 described later.

  The piezoelectric element 10 has a piezoelectric body that exhibits the piezoelectric action of the piezoelectric longitudinal effect. The piezoelectric longitudinal effect refers to the action of generating charges on the surface of the piezoelectric body in the direction of the charge generation axis when an external force is applied to the stress application axis in the same direction as the charge generation axis of the piezoelectric body. The piezoelectric element 10 according to the present embodiment is housed in the housing 30 so that the center line direction is the direction of the stress application axis.

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

As shown in FIG. 5, the housing 30 as an example of the housing includes a first housing 31 provided on the front end side and a second housing 32 provided on the rear end side.
The first housing 31 is a thin-walled cylindrical member having a cylindrical hole 310 formed therein so as to have a diameter that gradually changes from the front end side to the rear end side. On the outer peripheral surface, a projecting portion 315 that protrudes from the outer peripheral surface is provided in the central portion in the center line direction over the entire region in the circumferential direction.
The hole 310 includes a first hole 311 and a second hole 312 having a diameter larger than the diameter of the first hole 311 formed in order from the front end side to the rear end side. The protrusion 315 has an inclined surface 315a whose diameter gradually increases from the front end side to the rear end side at the front end portion, and a vertical surface 315b perpendicular to the center line direction at the rear end portion.

As shown in FIG. 4, the second housing 32 is a cylindrical member in which a cylindrical hole 320 is formed so that the diameter gradually changes from the front end side to the rear end side. An outer peripheral surface 330 is formed on the outside so that the diameter is gradually changed from the front end side to the rear end side.
The hole 320 includes a first cylindrical hole 321 having a first hole diameter, a second cylindrical hole 322 having a second hole diameter smaller than the first hole diameter, and a second hole diameter. A third cylindrical hole 323 having a larger third hole diameter, a fourth cylindrical hole 324 having a fourth hole diameter larger than the third hole diameter, a fifth cylindrical hole 325 having a fifth hole diameter larger than the fourth hole diameter, Consists of
The first hole diameter in the first cylindrical hole 321 is such that the front end of the second housing 32 is fitted (press-fit) to the rear end of the first housing 31 with an interference fit. It is set to be less than the diameter.

The outer peripheral surface 330 has a first outer peripheral surface 331, a second outer peripheral surface 332 having an outer diameter larger than the outer diameter of the first outer peripheral surface 331, and an outer diameter of the second outer peripheral surface 332 from the front end side to the rear end side. A third outer peripheral surface 333 having a larger outer diameter, a fourth outer peripheral surface 334 having an outer diameter larger than the outer diameter of the third outer peripheral surface 333, and a fifth outer periphery having an outer diameter smaller than the outer diameter of the fourth outer peripheral surface 334 A surface 335.
A male screw 332 a that is screwed into the female screw 4 e of the cylinder head 4 is formed at the tip of the second outer peripheral surface 332. A first seal member 71, which will be described later, is fitted into the third outer peripheral surface 333 with a clearance fit, and the dimensional tolerance between the outer diameter of the third outer peripheral surface 333 and the inner diameter of the first seal member 71 is, for example, from zero to 0.2 mm. Is set to be The rear end portion of the fourth outer peripheral surface 334 is formed as a regular hexagonal column having six chamfers at equal intervals in the circumferential direction. When the pressure detecting device 5 is fastened to the cylinder head 4, the portion formed in the regular hexagonal column is a portion into which a tightening tool is fitted and a rotational force applied to the tool is transmitted. A concave portion 335a that is recessed from the outer peripheral surface is formed over the entire circumference in the center portion of the fifth outer peripheral surface 335 in the center line direction.

  As shown in FIG. 6, the second housing 32 is a transition portion from the fourth cylindrical hole 324 to the fifth cylindrical hole 325, and the signal processing unit 200 will be described later at the tip of the fifth cylindrical hole 325. An abutting surface 340 against which an end surface on the front end side of the substrate covering portion 232 of the covering member 23 to be abutted is provided. The abutting surface 340 is formed with a pin recess 340a into which the second connection pin 21b of the circuit board unit 21 in the signal processing unit 200 described later is inserted.

  Since the first housing 31 and the second housing 32 exist at a position close to the combustion chamber C, it is desirable to manufacture the first housing 31 and the second housing 32 using a material that can withstand an operating temperature environment of at least −40 to 350 [° C.]. Moreover, since the 1st housing 31 and the 2nd housing 32 are used for the earthing | grounding of each part accommodated in the housing 30 so that it may mention later, it is desirable to manufacture using the material which has electroconductivity. Specifically, it is desirable to use a stainless steel material having conductivity and high heat resistance, for example, JIS standard SUS630, SUS316, SUS430, or the like.

As shown in FIG. 5, the diaphragm head 40 has a cylindrical cylindrical portion 41 and an inner portion 42 formed inside the cylindrical portion 41.
The rear end portion of the cylindrical portion 41 is fitted (press-fitted) with the front end portion of the first housing 31 of the housing 30 with an interference fit, and enters the inside of the front end portion, and the end surface 31a at the front end portion. And an abutting surface 41b against which the end surface 31a abuts when fitted.
The inner part 42 is a disk-shaped member provided so as to close the opening on the front end side in the cylindrical part 41, and a protruding part that protrudes from this surface to the piezoelectric element 10 side at the center part on the rear end side surface. 42a is provided. Further, a concave portion 42b that is recessed from this surface to the piezoelectric element 10 side is provided at the center of the inner portion 42 on the front end side surface.
The material of the diaphragm head 40 is preferably made of an alloy having high elasticity and excellent durability, heat resistance, touch resistance, and the like because it exists in the combustion chamber C at a high temperature and a high pressure. For example, SUH660 can be illustrated.

The first electrode portion 50 is a columnar member formed so as to have a stepwise difference in diameter from the front end side to the rear end side, and has a radius larger than the radius of the first columnar portion 51 and the first columnar portion 51. The second cylindrical portion 52. The outer diameter of the first cylindrical portion 51 is smaller than the inner diameter of the entry portion 41 a of the diaphragm head 40, and the outer diameter of the second cylindrical portion 52 is substantially the same as the hole diameter of the first hole 311 of the first housing 31. The end surface on the front end side of the first cylindrical portion 51 is in contact with the protruding portion 42 a of the inner side portion 42 of the diaphragm head 40, and the end surface on the rear end side of the second cylindrical portion 52 is in contact with the front surface side of the piezoelectric element 10. Are arranged as follows. When the outer peripheral surface of the second cylindrical portion 52 is in contact with the inner peripheral surface of the first housing 31 and / or the end surface on the distal end side of the first cylindrical portion 51 is in contact with the diaphragm head 40, the distal end of the piezoelectric element 10 is obtained. The part is electrically connected to the housing 30.
The first electrode portion 50 applies pressure in the combustion chamber C to the piezoelectric element 10, and the end surface on the rear end side of the second cylindrical portion 52, which is the end surface on the piezoelectric element 10 side, is the end surface of the piezoelectric element 10. It is formed in a size that can push the entire surface. In addition, the first electrode portion 50 has both end surfaces in the center line direction formed as smooth surfaces so that the pressure received from the diaphragm head 40 can be applied to the piezoelectric element 10 evenly, and the first electrode portion 50 has a center line direction. Are provided substantially in parallel with each other along a plane orthogonal to each other.
An example of the material of the first electrode unit 50 is stainless steel.

The second electrode portion 55 is a columnar member, and is disposed such that the end surface on the front end side is in contact with the end surface on the rear end side in the piezoelectric element 10 and the end surface on the rear end side is in contact with the insulating ring 60. A columnar projecting portion 55 a that projects from the end surface to the rear end side is provided on the end surface on the rear end side of the second electrode portion 55. The protrusion 55a has a base end portion on the end face side and a tip end portion having an outer diameter smaller than the outer diameter of the base end portion. The outer diameter of the protruding portion 55a is set smaller than the inner diameter of the insulating ring 60, and the length of the protruding portion 55a is set longer than the width of the insulating ring 60 (the length in the center line direction). The tip is exposed from the insulating ring 60. The second electrode portion 55 is a member that acts to apply a constant load to the piezoelectric element 10 between the second electrode portion 50 and the end face on the piezoelectric element 10 side (tip side) is a piezoelectric element. 10 is formed to have a size capable of pressing the entire end face on the rear end side of the surface 10 and a flat surface parallel to the end face on the rear end side of the piezoelectric element 10. The outer diameter of the second electrode portion 55 is set to be smaller than the hole diameter of the second hole 312 of the first housing 31, and the outer peripheral surface of the second electrode portion 55 and the inner peripheral surface of the first housing 31 are set. There is a gap between them.
An example of the material of the second electrode portion 55 is stainless steel.

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

The support member 65 is a cylindrical member in which a plurality of cylindrical holes 650 having different diameters are formed inside from the front end side to the rear end side, and the diameter of the outer peripheral surface is the same.
The holes 650 are formed in order from the front end side to the rear end side, and have a first hole 651, a second hole 652 having a diameter larger than the diameter of the first hole 651, and a diameter larger than the diameter of the second hole 652. A third hole 653. The diameter of the first hole 651 is larger than the outer diameter of the base end portion of the protruding portion 55 a of the second electrode portion 55, and the protruding portion 55 a is exposed to the inside of the support member 65. The hole diameter of the second hole 652 is larger than the outer diameter of the distal end portion of the conductive member 22 of the signal processing unit 200 described later. The hole diameter of the third hole 653 is smaller than the outer diameter of the end portion on the front end side of the covering member 23 of the signal processing unit 200 described later, and the covering member 23 is fitted to the surrounding wall forming the third hole 653. Mated. Thereby, the support member 65 functions as a member that supports the end portion of the covering member 23.

  The coil spring 70 has an inner diameter that is equal to or larger than the outer diameter of the distal end portion of the protruding portion 55a of the second electrode portion 55 and smaller than the outer diameter of the proximal end portion, and the outer diameter is smaller than the diameter of the insertion hole 22a of the conductive member 22 described later. Is also small. The distal end portion of the protruding portion 55a of the second electrode portion 55 is inserted inside the coil spring 70, and the coil spring 70 is inserted into an insertion hole 22a of the conductive member 22 described later. The length of the coil spring 70 is set to a length that can be interposed in a compressed state between the second electrode portion 55 and the conductive member 22. As a material of the coil spring 70, an alloy having high elasticity and excellent durability, heat resistance, touch resistance and the like may be used. Further, it is preferable to increase electrical conduction by applying gold plating to the surface of the coil spring 70.

Next, the signal processing unit 200 will be described.
As shown in FIGS. 3 and 4, the signal processing unit 200 is generated in the piezoelectric element 10 and the circuit board unit 21 that at least amplifies an electric signal that is a weak charge obtained from the piezoelectric element 10 of the sensor unit 100. A rod-shaped conductive member 22 that guides electric charges to the circuit board portion 21, a cover member 23 that covers the circuit board portion 21, the conductive member 22, and the like, and an O-ring 26 that seals the circuit board portion 21 and the like are provided.

  The circuit board unit 21 includes a mounting board 210 on which electronic components and the like constituting a circuit for amplifying a weak charge obtained from the piezoelectric element 10 of the sensor unit 100 are mounted. An input side first connection pin 21a for electrically connecting a rear end portion of the conductive member 22 and an input side second connection pin 21b for grounding and positioning are soldered to the front end portion of the mounting substrate 210. Connected by attaching. In addition, at the rear end portion of the mounting substrate 210, an output side first connection pin 21c and an output side second pin for electrical connection with the control device 6 via a connector 80 provided at the front end portion of the transmission cable 8. The connection pin 21d is connected by soldering or the like. The output-side first connection pin 21c is used to supply a power supply voltage (external power supply voltage Vc described later) from the control device 6 to the mounting board 210, and the output-side second connection pin 21d is controlled from the mounting board 210. It is used to supply an output voltage (external output voltage Vo described later) to the device 6.

  The conductive member 22 is a rod-shaped (columnar) member, and an insertion hole 22a into which the distal end portion of the protruding portion 55a of the second electrode portion 55 is inserted is formed at the distal end portion. The rear end portion of the conductive member 22 is electrically connected to the mounting substrate 210 of the circuit board portion 21 via a conductive wire (not shown) and the input-side first connection pin 21a. Examples of the material of the conductive member 22 include brass and beryllium copper. In this case, brass is desirable from the viewpoint of workability and cost. On the other hand, beryllium copper is desirable from the viewpoints of electrical conductivity, high temperature strength, and reliability.

  The covering member 23 includes a conductive member covering portion 231 that covers the outer periphery of the conductive member 22, a substrate covering portion 232 that covers the side surface and the bottom surface of the mounting substrate 210 of the circuit board portion 21, and a first output side connected to the mounting substrate 210. A connector portion 233 that covers the periphery of the connection pin 21c and the output-side second connection pin 21d, and into which a connector 80 provided at the distal end portion of the transmission cable 8 is fitted.

As shown in FIG. 3, the conductive member covering portion 231 extends along the center line direction and covers the conductive member 22 so that the distal end portion is exposed.
Further, the conductive member covering portion 231 is composed of a plurality of cylindrical portions so that the outer diameters are gradually changed from the front end side to the rear end side. Specifically, a first cylindrical portion 241 having a first outer diameter, a second cylindrical portion 242 having a second outer diameter smaller than the first outer diameter, and a second outer diameter from the front end side to the rear end side. A third cylindrical portion 243 having a larger third outer diameter and a fourth cylindrical portion 244 having a fourth outer diameter larger than the third outer diameter are formed side by side.
The first outer diameter of the first cylindrical portion 241 is formed larger than the hole diameter of the third hole 653 of the support member 65. As a result, the leading end of the conductive member covering portion 231 is fitted (press-fitted) into the surrounding wall forming the third hole 653 of the support member 65 with an interference fit.

As shown in FIG. 3, the conductive member covering portion 231 is provided with a plurality of convex portions 250 that protrude from the outer peripheral surface of the conductive member covering portion 231 and each extend in the center line direction. In the present embodiment, the convex portion 250 is provided on the first convex portion 251 provided at the distal end portion of the second cylindrical portion 242 of the conductive member covering portion 231 and the fourth cylindrical portion 244 provided on the conductive member covering portion 231. Two convex portions 252 are provided.
In this example, four first convex portions 251 are provided on the outer peripheral surface of the second cylindrical portion 242 at intervals of 90 degrees along the circumferential direction. Further, four second convex portions 252 are provided at intervals of 90 degrees along the circumferential direction on the outer peripheral surface of the fourth cylindrical portion 244.
In this example, the four first convex portions 251 are formed integrally with the second cylindrical portion 242 in the conductive member covering portion 231, and the four second convex portions 252 are formed in the conductive member covering portion 231. It is integrally formed with the fourth cylindrical portion 244.

  In the signal processing unit 200, as shown in FIG. 5, the four first convex portions 251 provided in the second cylindrical portion 242 come into contact with the walls forming the second holes 322 in the second housing 32, respectively. . Further, as shown in FIG. 6, the plurality of second convex portions 252 provided in the fourth cylindrical portion 244 abuts against the wall forming the fourth hole 324 in the second housing 32. As a result, the conductive member covering portion 231 is supported by the second housing 32.

  The substrate covering portion 232 is basically a cylindrical portion, and a rectangular opening 232a for installing the mounting substrate 210 therein is provided on the side surface thereof. A ring groove 232b for the O-ring 26 for sealing the inside of the housing 30 and the mounting board 210 installation portion is formed on the rear end side of the substrate covering portion 232.

  The connector part 233 protrudes from the end face 232c on the rear end side in the board covering part 232, and is formed so as to cover the periphery of the output side first connection pin 21c and the output side second connection pin 21d connected to the mounting board 210. It is a thin part. The rear end portion of the connector portion 233 is open so that the connector 80 provided at the front end portion of the transmission cable 8 can be received therein. Further, a hole 233a that connects the inside and the outside is formed on the rear end side of the connector portion 233, and a hook provided on the connector 80 of the transmission cable 8 is hooked on the hole 233a, so that the transmission cable The eight connectors 80 are prevented from dropping from the connector portion 233.

  The covering member 23 configured as described above is formed of an insulating material such as resin. The covering member 23 is integrally formed with the conductive member 22, the input side first connection pin 21a, the input side second connection pin 21b, the output side first connection pin 21c, and the output side second connection pin 21d. More specifically, the cover member 23 is set with the conductive member 22, the input side first connection pin 21a, the input side second connection pin 21b, the output side first connection pin 21c, and the output side second connection pin 21d. Molded by pressing the heated resin into the mold.

  When unitizing the signal processing unit 200, the mounting substrate 210 of the circuit board unit 21 is inserted from the opening 232 a of the formed covering member 23 and installed in the center of the substrate covering unit 232. When the mounting substrate 210 is installed, the input side first connection pin 21a, the input side second connection pin 21b, the output side first connection pin 21c, and the output side second connection pin 21d are inserted into the through holes penetrating in the plate thickness direction. Pass through each tip of and solder. Then, the input side 1st connection pin 21a and the conduction member 22 are connected using a conducting wire. Further, the O-ring 26 is attached to the ring groove 232 b of the substrate covering portion 232 of the covering member 23. The O-ring 26 is a well-known O-shaped ring made of fluorine-based rubber.

Next, the holding member 300 will be described.
The holding member 300 is a thin cylindrical member, and as shown in FIG. 4, a protruding portion 300 a that protrudes inward from the inner peripheral surface is provided at the rear end portion. After the holding member 300 is mounted on the second housing 32, the holding member 300 is caulked by pressurizing a portion corresponding to the concave portion 335 a provided in the fifth outer peripheral surface 335 from the outside. Thereby, the holding member 300 becomes difficult to move with respect to the housing 30, and the signal processing unit 200 is prevented from moving with respect to the housing 30.

Next, the configuration of the mounting substrate 210 in the circuit board unit 21 of the signal processing unit 200 will be described. FIG. 7 shows a circuit configuration diagram of the mounting substrate 210.
The mounting board 210 of this embodiment includes a printed wiring board 211 on which wiring (circuit pattern) for mounting one or a plurality of electronic components (circuit elements) is formed. The mounting board 210 further includes a protection circuit 212, an integration circuit 213, an amplification circuit 214, and a power supply circuit (Vreg) 216 mounted on the printed wiring board 211. In the present embodiment, among these, the integration circuit 213 and the amplification circuit 214 have a function as a signal processing circuit, and the power supply circuit 216 has a function as a use voltage generation circuit.

  In the mounting substrate 210 of the present embodiment, a charge signal as an example of a detection signal input from the piezoelectric element 10 via the protection circuit 212 is converted into a voltage signal by integration by the integration circuit 213, and after the conversion Are amplified by the amplification circuit 214 and output to the outside (for example, the control device 6 shown in FIG. 1). During this time, the power supply circuit 216 creates and outputs a power supply voltage (an internal power supply voltage Vi described later) used in the integration circuit 213 and the amplifier circuit 214.

  In this embodiment, a so-called glass epoxy substrate based on a glass cloth base epoxy resin is used as the printed wiring board 211. The printed wiring board 211 is provided with an input signal terminal 211a, an input ground terminal 211b, a power supply terminal 211c, and an output signal terminal 211d as input / output terminals. Among these, the input signal terminal 211 a is connected to the end face on the rear end side of the piezoelectric element 10 through the input side first connection pin 21 a, the conductive member 22, the coil spring 70, and the second electrode portion 55. The input ground terminal 211b is connected to the second housing 32 via the input-side second connection pin 21b. Further, the power terminal 211c is connected to the first cable 81 (see FIG. 2) via the output-side first connection pin 21c and the connector 80. Furthermore, the output signal terminal 211d is connected to the second cable 82 (see FIG. 2) via the output-side second connection pin 21c and the connector 80.

  The protection circuit 212 includes a diode, and an anode is connected to the input ground terminal 211b side, and a cathode is connected to the input signal terminal 211a side.

  The integrating circuit 213 includes a first operational amplifier OP1, an integrating capacitor C1, and a feedback resistor R1. In the integrating circuit 213, the inverting input terminal of the first operational amplifier OP1 is connected to the input signal terminal 211a. Further, the non-inverting input terminal of the first operational amplifier OP1 is connected to the output terminal (out) of the power supply circuit 216. Further, the output terminal of the first operational amplifier OP1 is connected to a non-inverting input terminal of a second operational amplifier OP2 (details will be described later) provided in the amplifier circuit 214. Furthermore, one end of the integrating capacitor C1 is connected to the inverting input terminal of the first operational amplifier OP1, and the other end of the integrating capacitor C1 is connected to the output terminal of the first operational amplifier OP1. One end of the feedback resistor R1 is connected to the inverting input terminal of the first operational amplifier OP1, and the other end of the feedback resistor R1 is connected to the output terminal of the first operational amplifier OP1. Therefore, the integrating capacitor C1 and the feedback resistor R1 are connected in parallel to the inverting input terminal and the output terminal of the first operational amplifier OP1.

  The amplifier circuit 214 includes a second operational amplifier OP2, a first setting resistor R2a, and a second setting resistor R2b. In the amplifier circuit 214, the inverting input terminal of the second operational amplifier OP2 is connected to the output terminal (out) of the power supply circuit 216 via the first setting resistor R2a. The non-inverting input terminal of the second operational amplifier OP2 is connected to the output terminal of the first operational amplifier OP1 provided in the integrating circuit 213. Further, the output terminal of the second operational amplifier OP2 is connected to the output signal terminal 211d. Furthermore, one end of the second setting resistor R2b is connected to the inverting input terminal of the second operational amplifier OP2, and the other end of the second setting resistor R2b is connected to the output terminal of the second operational amplifier OP2.

  The power supply circuit 216 has an input terminal (in) connected to the power supply terminal 211c and an output terminal (out) connected to the integration circuit 213 (more specifically, the first operational amplifier OP1 provided in the integration circuit 213). A non-inverting input terminal) and an amplifier circuit 214 (more specifically, a first setting resistor R2a provided in the amplifier circuit 214), and a ground terminal (GND) thereof is connected to the output ground terminal 211e, and Connected to the input ground terminal 211b.

  In the mounting substrate 211 of the present embodiment, an input charge Qi is input as an input signal (charge signal) from the piezoelectric element 10 to the input signal terminal 211a. An external power supply voltage Vc (an example of DC + 5.0 V in this example) is applied from the control device 6 to the power supply terminal 211c. Further, an external output voltage Vo as an example of an output signal is output from the output signal terminal 211 d to the control device 6. The input ground terminal 211b is set to a ground potential (GND potential) by being connected to a grounding body provided outside the mounting substrate 211.

  The integration circuit 213 integrates the input charge Qi input from the piezoelectric element 10 and outputs the obtained internal output voltage Vi to the amplification circuit 214. At this time, the input charge Qi is supplied from the input signal terminal 211a to the inverting input terminal of the first operational amplifier OP1. On the other hand, an internal power supply voltage Vr serving as a reference voltage is applied from the power supply circuit 215 to the non-inverting input terminal of the first operational amplifier OP1. As described above, the integration circuit 213 of the present embodiment is configured as an integration circuit using the first operational amplifier OP1. However, the non-inverting input terminal of the first operational amplifier OP1 is not set to the GND potential (grounded) but is set to the internal power supply voltage Vr. This is because the first operational amplifier OP1 operates with a single power supply (details will be described later) and that the input charge Qi can take both positive and negative values.

  The amplification circuit 214 amplifies the internal output voltage Vi input from the integration circuit 213, and outputs the obtained external output voltage Vo toward the outside (for example, the control device 6 shown in FIG. 1). At this time, the internal power supply voltage Vr output from the power supply circuit 216 is applied to the inverting input terminal of the second operational amplifier OP2 via the first setting resistor R2a. The external output voltage Vo output from the output terminal of the second operational amplifier OP2 is applied to the inverting input terminal of the second operational amplifier OP2 via the second setting resistor R2b. On the other hand, the internal output voltage Vi output from the output terminal of the first operational amplifier OP1 in the integrating circuit 213 is applied to the non-inverting input terminal of the second operational amplifier OP2. As described above, the amplifier circuit 214 of the present embodiment is configured as an inverting amplifier circuit using the second operational amplifier OP2.

  The power supply circuit 216 converts the external power supply voltage Vc (DC + 5.0V in this example) input via the power supply terminal 211c into a lower internal power supply voltage Vr (DC + 1.0V in this example) and outputs it. Details of the circuit configuration of the power supply circuit 216 will be described later.

  Here, the first operational amplifier OP1 provided in the integrating circuit 213 and the second operational amplifier OP2 provided in the amplifying circuit 214 are each operated by a single power source of DC + 5.0V. In each of the first operational amplifier OP1 and the second operational amplifier OP2, a positive power supply terminal (not shown) is connected to a power supply terminal 211c via a wiring not shown, and a negative power supply terminal (not shown) is connected. , And connected to the input ground terminal 211e via a wiring (not shown). Therefore, DC + 5.0V is supplied as an operating voltage to each of the first operational amplifier OP1 and the second operational amplifier OP2.

FIG. 8 shows an example of a circuit configuration diagram of the power supply circuit 216 provided on the mounting substrate 210.
The preceding stage of the power supply circuit 216 is a constant voltage circuit using a MOS transistor, and can be made a constant voltage source regardless of the applied voltage by appropriately selecting the size and resistance value of the transistor. The voltage Vb is always a constant voltage with respect to the GND level even if the external power supply voltage Vc changes. On the other hand, the voltage Va is always a constant voltage with respect to the external power supply voltage Vc level even if the GND level changes. The voltage Va is generally used as the constant voltage, but this time the voltage Vb is used. However, since the voltage between Vc and Va is normally a low voltage of about 1V, in this application, this is amplified and used by a non-inverting amplifier circuit provided at the subsequent stage of the constant voltage circuit. In the non-inverting amplifier circuit, the inverting terminal is normally connected to GND through a resistor. Here, however, voltage amplification based on Vc is performed by connecting to the external power supply voltage Vc.

Here, the electrical connection structure in the pressure detection apparatus 5 mentioned above is demonstrated.
First, the end face on the front end side of the piezoelectric element 10 is electrically connected to the metal housing 30 via the metal first electrode portion 50 and the diaphragm head 40.

  On the other hand, the end surface on the rear end side of the piezoelectric element 10 is electrically connected to the metal second electrode portion 55, and the second electrode portion 55 is connected to the metal coil spring 70 via the protruding portion 55 a. Electrically connected. The coil spring 70 is electrically connected to the metal conductive member 22, and the conductive member 22 is electrically connected to the input signal terminal 211 a of the mounting substrate 210 via the input-side first connection pin 21 a. . On the other hand, the outer diameter of the protrusion 55 a of the second electrode portion 55 is smaller than the hole diameter of the first hole 651 of the support member 65, and the outer diameter of the tip portion of the conductive member 22 is larger than the hole diameter of the second hole 652 of the support member 65. Is also small. That is, the second electrode portion 55, the coil spring 70, and the conductive member 22 are not electrically connected because they are not in direct contact with the support member 65. Therefore, the charge signal transmission path from the second electrode portion 55 to the mounting substrate 210 via the coil spring 70 and the conductive member 22 is formed by the insulating ring 60 and the covering member 23 each made of an insulator. It is electrically insulated from the metal housing 30.

  Further, the input ground terminal 211b of the mounting substrate 210 is electrically connected to the second housing 32 (housing 30) via the input-side second connection pin 21b. Furthermore, the power supply terminal 211c of the mounting substrate 210 is electrically connected to the first cable 81 via the output-side first connection pin 21c. Furthermore, the output signal terminal 211d of the mounting substrate 210 is electrically connected to the second cable 82 via the output-side second connection pin 21d.

When the pressure detecting device 5 configured as described above is attached to the cylinder head 4, the diaphragm head 40 of the sensor unit 100 is inserted into the communication hole 4a formed in the cylinder head 4 first, The male screw 332 a formed in the second housing 32 of the housing 30 is screwed into the female screw 4 e formed in the communication hole 4 a of the cylinder head 4.
By mounting the pressure detection device 5 on the cylinder head 4, the housing 30 is electrically connected to the metal cylinder head 4. Since the cylinder head 4 is in a state of being electrically grounded, in the pressure detection device 5, the tip portion of the piezoelectric element 10 is grounded via the housing 30. Here, in this example, the side surface of the piezoelectric element 10 and the inner wall surface of the housing 30 are in contact with each other, but the resistance value is extremely large because the piezoelectric element 10 is made of an insulator. The electric charge generated with the pressure change is generated at both ends of the piezoelectric element 10 in the center line direction.

Next, the seal member 7 will be described.
As shown in FIG. 2, the seal member 7 includes an end surface of the surrounding wall forming the communication hole 4 a in the cylinder head 4 in the tightening direction of the sensor unit 100, a third outer peripheral surface 333 of the housing 30 of the pressure detection device 5, It has the 1st seal member 71 arrange | positioned between the connection surfaces which connect 4 outer peripheral surface 334. FIG. In addition, the seal member 7 has a second seal member 72 disposed between the inclined portion 4c of the communication hole 4a of the cylinder head 4 and the inclined surface 315a of the first housing 31 of the housing 30 of the pressure detection device 5. doing.

  Next, the control device 6 constituting the pressure detection system of the internal combustion engine 1 together with the pressure detection device 5 will be described. FIG. 9 is a diagram for explaining the configuration of the control device 6. Here, FIG. 9A is a block diagram for explaining the hardware configuration of the control device 6, and FIG. 9B is a diagram for explaining a power feeding system in the control device 6. In addition, the control apparatus 6 may be called ECU (Engine Control Unit).

  The control device 6 as an example of the supply / processing unit includes signals output from various devices provided in a device (for example, an automobile) in which the internal combustion engine 1 is mounted, such as the pressure detection device 5 (in the case of the pressure detection device 5, an external device). Based on an input reception unit 61 that receives an input of the output voltage Vo), an MCU (Micro Control Unit) 62 that calculates a control amount based on various signals input via the input reception unit 61, and a calculation result by the MCU 62, An EEPROM (Electrically Erasable Programmable Read-Only Memory) 63 that stores data that should be stored even after the power is stopped, and a drive signal that outputs a drive signal for control to various devices based on the calculation result by the MCU 62 The output unit 64, a communication unit 65 that communicates with other control devices provided in the same device, and each unit (MCU 62, etc.) provided in the control device 6 And a power supply unit 66 for supplying power necessary for operating various devices (such as the pressure detecting device 5) provided outside the control device 6. .

  The input receiving unit 61 performs A / D conversion on an analog signal input from the outside to create a digital signal, or performs gain adjustment on the digital signal input from the outside, thereby allowing an input from the outside. The input signal is converted into a state usable by the MCU 62. In this example, the external output voltage Vo input from the pressure detection device 5 to the input receiving unit 61 is an analog signal.

  The MCU 62 is configured by a so-called one-chip microcomputer, and temporarily executes MPU (Micro-Processing Unit) that performs various arithmetic processing, ROM (Read Only Memory) that stores a program executed by the MPU, and program execution by the MPU. A RAM (Random Access Memory) or the like for storing generated data is incorporated.

  The EEPROM 63 is a non-volatile memory having a characteristic that stored data does not disappear even if power is not supplied. The EEPROM 63 provided in the control device 6 stores, for example, data on the result of failure diagnosis executed when the device equipped with the internal combustion engine 1 is started, and troubles occurring in the operation of the internal combustion engine 1.

  The drive signal output unit 64 performs D / A conversion on the digital signal as the calculation result input from the MCU 62 to create an analog signal, or adjusts the gain of the digital signal as the calculation result input from the MCU 62. By performing this, the output signal from the MCU 62 is converted into a state usable by various devices provided outside.

  The communication unit 65 converts a communication signal received from another control device to a level that can be processed by the MCU 62. Moreover, the digital signal input from MCU62 is converted into the communication signal suitable for the communication standard between other control apparatuses.

  The power supply unit 66 converts the battery voltage Vb (in this example, DC + 12V) input via an external power supply (for example, a battery in the case of an automobile) provided in a device on which the internal combustion engine 1 is mounted, to a lower operating voltage. It converts and supplies to MCU62 grade | etc., Which comprises the control apparatus 6. FIG. In addition, the power supply unit 66 converts the input battery voltage Vb into a lower external power supply voltage Vc and outputs it to the pressure detection device 5 provided outside the control device 6. Furthermore, the grounding end (GND) of the power supply unit 66 is connected to the outside (for example, the cylinder block 2 of the internal combustion engine 1 shown in FIG. 1). Thereby, each part (MCU62 etc.) which comprises the control apparatus 6 operate | moves using the electric potential of the ground terminal (GND) of the power supply part 66 as a reference | standard (ground). Note that the operating voltage output from the power supply unit 66 and the external power supply voltage Vc may have the same magnitude or different magnitudes.

  FIG. 10 is a diagram for explaining an electrical connection relationship among the internal combustion engine 1, the pressure detection device 5, the control device 6, and the transmission cable 8.

First, the connection relationship inside the pressure detection device 5 will be described.
In the pressure detection device 5, one end of the piezoelectric element 10 is connected to the input signal terminal 211a of the mounting substrate 210 via the input-side first connection pin 21a and the like. The other end of the piezoelectric element 10 is connected to the housing 30 (more specifically, the first housing 31) via a diaphragm head 40 (not shown in FIG. 10). The input ground terminal 211b provided on the mounting substrate 210 is connected to the housing 30 (more specifically, the second housing 32) via the input-side second connection pin 21b and the like. Furthermore, the power supply terminal 211c provided on the mounting board 210 is connected to the output side first connection pin 21c, and the output signal terminal 211d provided on the mounting board 210 is connected to the output side second connection pin 21d. Thus, in this Embodiment, the input side 2nd connection pin 21b has a function as a connection means.

Next, the connection relationship inside the internal combustion engine 1 will be described.
In the internal combustion engine 1, a cylinder block 2 and a cylinder head 4, both of which are made of metal, are arranged in contact with each other (see FIG. 1). Accordingly, the cylinder block 2 and the cylinder head 4 are connected to each other.

Subsequently, the connection relationship between the pressure detection device 5 and the control device 6 via the transmission cable 8 will be described.
The output side first connection pin 21 c provided in the pressure detection device 5 is connected to one end of the first cable 81 constituting the transmission cable 8, and the other end of the first cable 81 is provided in the control device 6. The power supply unit 66 (see FIG. 9) is connected to an output line (indicated by a solid arrow in the figure) of the external power supply voltage Vc. The output-side second connection pin 21 d provided in the pressure detection device 5 is connected to one end of the second cable 82 that constitutes the transmission cable 8, and the other end of the second cable 82 is provided in the control device 6. Connected to the input receiving unit 61 (see FIG. 9).

Further, the connection relationship between the pressure detection device 5 and the internal combustion engine 1 will be described.
The housing 30 provided in the pressure detection device 5 is attached to the cylinder head 4 as an example of the grounding body provided in the internal combustion engine 1 by screwing as described above. Therefore, the housing 30 and the cylinder head 4 both made of metal are connected.

Furthermore, the connection relationship between the control device 6 and the internal combustion engine 1 will be described.
A grounding end of a power supply unit 66 (see FIG. 9) provided in the control device 6 is connected to a cylinder block 2 provided in the internal combustion engine 1.

  In the present embodiment, the cylinder block 2 and the cylinder head 4 provided in the internal combustion engine 1 are connected as described above. Therefore, the ground of the piezoelectric element 10 in the pressure detection device 5, the ground of the mounting substrate 210 in the pressure detection device 5, and the ground of the power supply unit 66 (see FIG. 9) in the control device 6 are the cylinder block 2 and the cylinder head. 4 is set in common through the terminal 4.

  Here, the pressure detection device 5 of the present embodiment may be sold alone or sold with the transmission cable 8 attached to the pressure detection device 5. Among these, in the former, the output side first connection pin 21c functions as a constant voltage supply unit, and the output side second connection pin 21d functions as an output signal transmission unit. On the other hand, in the latter case, the first cable 81 connected to the output side first connection pin 21c is a constant voltage supply means, and the second cable 82 connected to the output side second connection pin 21d is an output signal transmission means. As each function.

  In the apparatus equipped with the internal combustion engine 1 of the present embodiment, when the internal combustion engine 1 is started, failure diagnosis of various devices mounted on the apparatus is executed. For example, in the pressure detection system, in addition to failure diagnosis of the pressure detection device 5, the transmission cable 8 (more specifically, the first cable 81 and the second cable 82) that connects the pressure detection device 5 and the control device 6. Failure diagnosis (disconnection detection) is performed.

FIG. 11 is a flowchart for explaining the procedure of the disconnection detection operation at the start of the internal combustion engine 1.
When an ignition switch (not shown) for starting the internal combustion engine is set to ON (step 101), the control device 6 sends the external power supply voltage Vo from the power supply unit 66 to the pressure detection device 5 via the transmission cable 8. Is started (step 12). Subsequently, the control device 6 performs a disconnection detection operation of the transmission cable 8 connecting the control device 6 and the pressure detection device 5 (step 13).

  When an affirmative determination (YES) is made in step 13, that is, when a disconnection is detected in the first cable 81 or the second cable 82 constituting the transmission cable 8, the control device 6 detects the disconnection in which cable. The data about whether or not it has been recorded is recorded in the EEPROM 63 built in the control device 6 (step 15). Subsequently, the control device 6 displays a message on the disconnection detected on the user interface (not shown) (step 16), and the series of processes is completed.

  On the other hand, if a negative determination (NO) is made in step 13, that is, if no disconnection is detected in the first cable 81 or the second cable 82 constituting the transmission cable 8, the control device completes the process as it is. To do.

  Here, in the present embodiment, the input ground terminal 211b provided on the mounting substrate 210 of the pressure detection device 5 is grounded via the housing 30 or the like. Therefore, for example, when the mounting substrate 210 of the pressure detection device 5 and the control device 6 are connected by a grounding cable (hereinafter referred to as a third cable), even if a disconnection occurs in the third cable, the input There is a concern that the disconnection of the third cable cannot be detected because continuity is obtained by grounding through the ground terminal 211b.

  On the other hand, in the present embodiment, the mounting substrate 210 of the pressure detection device 5 and the control device 6 are not connected by the third cable for grounding. This eliminates the need to detect disconnection of the grounding third cable.

Next, the pressure detection operation by the pressure detection device 5 of the present embodiment will be described.
During operation of the internal combustion engine 1, the combustion pressure generated in the combustion chamber C is applied to the inner portion 42 of the diaphragm head 40 of the sensor unit 100. The combustion pressure applied to the diaphragm head 40 acts on the piezoelectric element 10 sandwiched between the first electrode portion 50 and the second electrode portion 55, so that electric charges corresponding to the combustion pressure are applied to the piezoelectric element 10. Arise. The electric charge generated in the piezoelectric element 10 is supplied to the mounting board 210 of the circuit board part 21 as the input electric charge Qi through the second electrode part 55, the coil spring 70 and the conductive member 22. The input charge Qi supplied to the mounting board 210 is subjected to integration processing and amplification processing in various circuits provided on the mounting board 210, and then an external output voltage Vo corresponding to the charge is transmitted from the circuit board portion 21. It is supplied to the control device 6 via the cable 8.

  Many other electrical components are mounted on a device such as an automobile to which the pressure inspection device 5 is attached, and some of them, such as a start motor, a horn, and a light, have a very large current during operation. Flows. This large current flows into the body, which is a common ground for devices such as automobiles, and temporarily and locally varies the potential level. That is, in a device such as an automobile, a situation may occur in which the GND level varies depending on the location where the electrical component is grounded. When the difference in the GND level occurs between the pressure device 5 and the control device 6, the difference becomes an error in the measured pressure, and a correct measurement value cannot be obtained.

  On the other hand, in the present embodiment, the power supply circuit 216 provided on the mounting substrate 210 of the pressure detection device 5 uses the external power supply voltage Vc supplied from the control device 6 via the first cable 81 as a reference. The internal power supply voltage Vr was created without using the GND potential as a reference. In other words, the power supply circuit 216 creates the internal power supply voltage Vr based on the concept of DC-4.0 V from the external power supply voltage Vc, instead of the concept of DC + 1.0 V from the GND potential. For this reason, even when a difference occurs between the GND potential on the mounting substrate 210 and the GND potential on the control device 6, the difference in GND potential affects the external output voltage Vo output from the mounting substrate 210. It becomes difficult to give. Therefore, noise superimposed on the external output voltage Vo transmitted from the pressure detection device 5 to the control device 6 can be reduced.

  In the present embodiment, the disconnection detection of the transmission cable 8 that connects the pressure detection device 5 and the control device 6 using the piezoelectric element 10 has been described as an example. However, the present invention is not limited to this. The present invention can also be applied to detection of disconnection of the transmission cable 8 that connects the control device 6 and a detection device that detects various physical quantities such as temperature, humidity, or flow rate.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Cylinder block, 3 ... Piston, 4 ... Cylinder head, 5 ... Pressure detection apparatus, 6 ... Control apparatus, 8 ... Transmission cable, 10 ... Piezoelectric element, 21 ... Circuit board part, 22 ... Conductive member , 23 ... Cover member, 30 ... Housing, 61 ... Input receiving unit, 62 ... Micro control unit (MCU), 63 ... EEPROM, 64 ... Drive signal output unit, 65 ... Communication unit, 66 ... Power supply unit, 80 ... Connector, 81 ... 1st cable, 82 ... 2nd cable, 83 ... 3rd cable, 100 ... Sensor part, 200 ... Signal processing part, 210 ... Mounting board, 211 ... Printed wiring board, 212 ... Protection circuit, 213 ... Integration circuit, 214 ... Amplifying circuit, 215 ... DC cut-off circuit, 216 ... Power supply circuit, 300 ... Holding member

Claims (5)

A detection element for detecting a change in physical quantity, a signal processing circuit for processing a detection signal output from the detection element, the detection element and the signal processing circuit are attached, and a ground in the signal processing circuit is electrically A detection unit in which the case is electrically connected to a grounding body,
Connected to the detection unit through a constant voltage supply line for supplying a constant voltage to the signal processing circuit in the detection unit and an output signal transmission line for transmitting an output signal output from the signal processing circuit And a supply / processing unit electrically connected to the grounding body,
The detection unit is used in the signal processing circuit based on the voltage value of the constant voltage supplied via the constant voltage supply line and without using the ground potential in the signal processing circuit as a reference. A detection system further comprising a use voltage generation circuit for generating a voltage. The detection element includes a piezoelectric element that detects pressure using a piezoelectric body,
The signal processing circuit integrates the charge signal input from the piezoelectric element using an operational amplifier to convert the charge signal into a voltage signal, and the voltage signal input from the integration circuit And an amplification circuit that outputs the amplified signal obtained to the supply / processing unit via the output signal transmission line,
2. The detection according to claim 1, wherein the use voltage generation circuit supplies the use voltage to the operational amplifier provided in the integration circuit and the other operational amplifier provided in the amplification circuit. system. The operational amplifier provided in the integrating circuit and the other operational amplifier provided in the amplifier circuit each operate with a single power source using the constant voltage supplied via the constant voltage supply line as a power source. ,
The working voltage generating circuit is an inverting input terminal of the other operational amplifier which is provided to the non-inverting input terminal and the amplifier circuit of the operational amplifier provided in the integrating circuit, to supply each said working voltage The detection system according to claim 2, wherein: A detecting element for detecting a change in physical quantity;
A signal processing circuit for processing a detection signal output from the detection element;
A housing to which the detection element and the signal processing circuit are attached;
Constant voltage supply means for supplying a constant voltage to the signal processing circuit;
Output signal transmission means for transmitting an output signal output from the signal processing circuit;
Connection means for connecting a ground in the signal processing circuit to the housing;
Use to create a use voltage to be used in the signal processing circuit without using the voltage value of the constant voltage supplied through the constant voltage supply means as a reference and using the ground potential in the signal processing circuit as a reference A detection device including a voltage generation circuit. The detection element includes a piezoelectric element that detects pressure using a piezoelectric body,
The signal processing circuit integrates the charge signal input from the piezoelectric element using an operational amplifier to convert the charge signal into a voltage signal, and the voltage signal input from the integration circuit And an amplification circuit that outputs the amplified signal obtained to the outside via the output signal transmission means ,
5. The detection according to claim 4, wherein the use voltage generation circuit supplies the use voltage to the operational amplifier provided in the integration circuit and the other operational amplifier provided in the amplification circuit. apparatus.

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