JPH04290937A - Piezo type pressure sensor - Google Patents

Abstract

PURPOSE:To enhance the high temp. reliability upon the signal transmitting line of a pressure sensor, and reduce the size in the radial direction. CONSTITUTION:A signal takeout metal piece 35 is pressed to an electrode furnished at the end face of a piezo element 33 through utilization of a previously given stress or the measuring pressure, and thereby poor contacting due to re-melting of solder, metal fatigue, etc., is precluded. Soldering process is eliminated by equipping the signal takeout metal piece 35 with a rod-shaped part 34 which transmits signal to the connector part 30 directly. A convex 36 is provided at the bottom surface of the metal piece 35 while a concave 37 provided at the top surface of a pressure transmitting member 38, and center alignment of an upper holddown screw 32, piezo element 33, and metal piece 35 is performed by fitting these convex and concave for locating relatively to each other, and thereby the contacting state of electrode is compensated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric pressure sensor suitable for detecting pressure such as combustion pressure in a cylinder of an internal combustion engine.

0002

2. Description of the Related Art Piezoelectric pressure sensors that utilize a piezoelectric effect that generates electric charges by applying stress have been widely used. Particularly recently, piezoelectric pressure sensors suitable for detecting combustion pressure in cylinders of internal combustion engines have been actively developed.

A conventional piezoelectric pressure sensor will be explained below with reference to the drawings. FIG. 6 shows, for example, JP-A-63-
1 shows the basic configuration of a piezoelectric pressure sensor that has been commonly used as described in Japanese Patent No. 109342. This figure shows a longitudinal cross-sectional view of the sensor, and here specifically shows a sensor configured to apply a shearing force to a piezoelectric element. The piezoelectric element 64 installed inside the sensor housing 61 is connected to the threaded part 65a of the upper fixing screw 65 and the threaded part 61 of the sensor housing 61.
It is pressed and fixed to the back surface of the pressure receiving surface 32 processed into a diaphragm shape via the pressure transmitting member 63 by the tightening force of the pressure transmitting member 63. Further, this piezoelectric element 64 is prestressed by the tightening force of the upper fixing screw 65. This prestress is also necessary for measuring negative pressure, especially when measuring the combustion pressure in the cylinder of an internal combustion engine. Further, as the pressure transmitting member 63, structural ceramic or the like having excellent insulation properties and mechanical strength is used.

Next, its operation will be explained. The force applied from the measurement area to the pressure receiving surface 62 is transmitted to the lower inner peripheral portion of the piezoelectric element 64 via the pressure transmitting member 63. Here, since the upper outer periphery of the piezoelectric element 64 is fixed by the upper fixing screw 65, shearing force is generated in the piezoelectric element 64. Charges corresponding to this shearing force are generated on the inner and outer peripheries of the piezoelectric element 64, and are detected as electrical signals by electrodes formed on the inner and outer circumferential surfaces. The generated charge in this case is taken out to the outside from the electrode on the outer peripheral surface by an upper fixing member 65, and from the electrode on the inner peripheral surface by a lead wire 66 attached by soldering.

[0005]

[Problems to be Solved by the Invention] However, in the piezoelectric pressure sensor having the above configuration, the electrodes on the inner circumferential surface are taken out using lead wires attached by soldering. As a result, the sensor housing 61 is heated to about 300° C., and at 300° C., the soldered portion between the signal extraction fitting and the lead wire is remelted, and pressure measurement may become impossible due to disconnection of the signal transmission system. In addition, in order to prevent the soldered part from remelting, it is possible to attach the lead wire using high melting point solder or an alternative metal, but in this case, if the lead wire is processed at a temperature exceeding the Curie point of the piezoelectric element 64, the piezoelectric This will cause deterioration of the element 64.

Further, as shown in the same figure, when the clip part 67 is used to make contact with the outer electrode and detect the electric charge,
A space is required between the outer surface of the piezoelectric element 64 and the sensor housing 61 to accommodate the clip portion 67, which prevents miniaturization of the sensor housing and makes it difficult to reduce the diameter of the mounting hole.

[0007]Furthermore, since the stress relaxation of metal is promoted at high temperatures, the springiness of the claws provided on the signal extraction fitting is likely to deteriorate, making it difficult to increase the durability of the contact with the electrode of the piezoelectric element 64. It was difficult.

In view of the above-mentioned points, the present invention provides a highly reliable piezoelectric pressure sensor that can reliably extract a charge even at a temperature that melts solder. It is an object of the present invention to provide a piezoelectric pressure sensor having a structure whose diameter can be easily reduced. Another purpose is to provide a piezoelectric pressure sensor with excellent durability and reliability at high temperatures.

[0009]

[Means for Solving the Problems] In order to achieve the above objects, the present invention provides a casing having a pressure receiving surface, and a pressure transmitting device provided inside the casing and having one end in contact with a surface on the back side of the pressure receiving surface. a piezoelectric element provided inside the housing and provided at the other end of the pressure transmission member, a pair of charge collection electrodes provided facing each other with the piezoelectric element in between, and the pair of charges. This piezoelectric pressure sensor is characterized by being provided with a charge extraction member processed so as to come into contact with either one of the collecting electrodes.

Further, a charge extraction electrode is provided, and the charge extraction electrode is drawn out from charge collection electrodes on the upper surface or the lower surface of the piezoelectric element, or both of the upper and lower surfaces, and a charge extraction member is placed in contact with the charge extraction electrode. This is a piezoelectric pressure sensor characterized by being provided with.

[0011] Also, a charge extraction member is provided between the pressure transmission member and the piezoelectric element, and a convex portion provided at the center of the charge extraction member is fitted into a recess provided at the center of the pressure transmission member. It is a piezoelectric pressure sensor.

Further, the piezoelectric pressure sensor is characterized in that the charge extraction member includes a rod-shaped portion extending toward the outside of the casing.

[0013] Also, a piezoelectric pressure sensor characterized in that the rod-shaped part is used as a part of a connector with a signal transmission cable, and further characterized in that these charge extraction members are made of phosphor bronze. It is.

[0014]

[Function] According to the above-described structure, the present invention uses a charge extraction member which is processed into a plate spring shape and inserted to take out the charge from the inner peripheral electrode of the piezoelectric element, and further fixes the lead wire by crimping or wrapping. Furthermore, the structure is such that the charge extraction member is stretched toward the outside of the sensor housing, and a lead wire is soldered to its tip, or the stretched tip itself is used as part of the connector. This makes it possible to reliably extract the generated charge even when the sensor is exposed to high temperatures, such as in an internal combustion engine, and provides a highly reliable piezoelectric pressure sensor that is extremely useful in practice. Effects can be obtained.

Furthermore, by extracting the signal from the signal extraction electrode provided on the piezoelectric element, the structure can be easily miniaturized and the diameter of the mounting hole reduced.

Furthermore, by using phosphor bronze as the material for the charge extraction member, contact failures due to metal fatigue and the like are eliminated, and charge can be extracted reliably even at high temperatures.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the piezoelectric pressure sensor of the present invention will be described with reference to the drawings.

FIG. 1 shows a cross section of a piezoelectric pressure sensor according to a first embodiment of the present invention. In the figure, 11 is the sensor housing;
12 is a pressure receiving surface, 13 is a pressure transmitting member, 14 is a piezoelectric element,
15 is an upper fixing screw, 16 is a lead wire, and 17 is a charge extraction member.

A pressure receiving surface 1 is provided at the lower end opening of the sensor housing 11.
2 are joined by welding, brazing, integral formation, or other methods, and this pressure receiving surface 12 is located toward the area to be measured. The back surface of the pressure receiving surface 12 is in surface contact with the pressure transmitting member 13. This pressure transmission member 13 uses an insulator such as a structural ceramic material, and has a cylindrical piezoelectric material at its tip that has a polarization axis in the length direction and electrodes (not shown) on the inner and outer peripheral surfaces. An element 14 is installed, and its lower inner peripheral portion is held by a pressure transmitting member 13. This piezoelectric element uses as a piezoelectric material lead titanate, which exhibits heat resistance and stable properties at high temperatures, as a main component, to which Mn, La, etc. are added. Further, an upper fixing screw 15 is located above the piezoelectric element 14, and the piezoelectric element 14
It holds the upper outer periphery of. This upper fixing screw 15
The pressure transmitting member 13 is pressed against the pressure receiving surface 12 via the piezoelectric element 14 by the tightening force, thereby fixing each member and applying prestress to the piezoelectric element 14. Incidentally, this upper fixing screw 15 is electrically connected to an electrode formed on the outer periphery of the piezoelectric element 14, and also plays the role of extracting electric charge. Seventeen charge extraction members are provided to extract the electric charge generated on the inner periphery of the piezoelectric element 14, and a lead wire 16 is fixed to the tip thereof by crimping, wrapping, or the like.

Next, its operation will be explained. The pressure applied to the pressure-receiving surface 12 due to pressure fluctuations occurring within the measurement area is transmitted to the lower inner peripheral portion of the piezoelectric element 14 by the pressure transmission member 13, and the piezoelectric element 14 tends to be pushed up. Here, since the upper outer periphery of the piezoelectric element 14 is held down by the upper fixing screw 15, a downward force is applied to the outer periphery of the piezoelectric element 14 and an upward force is applied to the inner periphery of the piezoelectric element 14. A shearing force is generated. Charges corresponding to this shearing force are generated on the inner and outer peripheral electrode portions of the piezoelectric element 14, and are extracted as electrical signals from the lead wire 16 via the upper fixing screw 15 and the charge extraction member. This charge extraction member 1
7 is made of phosphor bronze and processed into a plate spring shape so as to be pressed against the inner periphery of the piezoelectric element 14, and is fixed by its frictional force and is electrically conductive.

As described above, according to this embodiment, by using the charge extraction member 17 to extract the electric charge generated in the electrode on the inner circumferential surface, soldering is not required and the temperature reaches a high temperature like that of an internal combustion engine. Charges can be reliably extracted even when there is a possibility.

Next, a second embodiment of the present invention will be explained. FIG. 2 shows a second embodiment of the present invention, in which a charge extraction member 27 is extended toward the outside of the sensor housing 21, and the method of contacting with the piezoelectric element 24 and the method of processing that part This is the same as the first invention. In this case, since the portion to which the lead wire 26 is connected is at a lower temperature than the piezoelectric element 24, it can be easily fixed using soldering. Of course, even in this case, it is also possible to connect the lead wires 26 by crimping or wrapping.

As described above, in this embodiment, it is possible to prevent poor contact due to solder melting of the lead wire, which is a problem in cases where there is a possibility of high temperatures such as in an internal combustion engine, and a highly reliable piezoelectric type pressure sensor can be supplied.

Next, a third embodiment of the present invention will be explained. FIG. 3 shows a cross section of a piezoelectric pressure sensor according to an embodiment of the present invention. In the figure, reference numeral 31 denotes a sensor housing made of metal, and one surface of the sensor housing 31 is provided with a pressure receiving surface 39 processed into a diaphragm shape. This pressure receiving surface 39 is installed in a region to be measured, for example, inside a cylinder of an internal combustion engine. Inside the sensor housing 31, one end of a pressure transmitting member 38 made of an insulating material (for example, ceramic) is provided so as to be in contact with the back surface of the pressure receiving surface 39, and a cylindrical piezoelectric element 33 is provided at the other end. ing. The lower inner peripheral portion of this cylindrical piezoelectric element 33 is held by a pressure transmitting member 38 via a signal extraction fitting 35. Furthermore, the outer peripheral portion of the upper end of the piezoelectric element 33 is held down by an upper fixing screw 32. The tightening force of the upper fixing screw 32 presses the piezoelectric element 33, the signal extraction fitting 35, and the pressure transmission member 38 against the pressure receiving surface 39, fixing each member and fixing the piezoelectric element 33.
A prestress is applied to the At this time, the protrusion 36 of the signal extraction fitting 35 fits into the recess 37 of the pressure transmission member 38, and the signal extraction fitting 35 and the pressure transmission member 38 are positioned with high precision. In addition, the piezoelectric element 33 and the pressure transmission member 3
8 is positioned with high precision on the inner wall of the sensor housing 31, so the piezoelectric element 33 and the signal extraction fitting 35 are positioned with high precision. In addition, the rod-shaped portion 3 of the signal extraction fitting 35
4 is directly connected to the connector section 30.

FIG. 4 shows a cross-sectional view of the piezoelectric element 33 and an electrode arrangement diagram. Charge collection electrodes 42 and 44 are provided on the inner and outer surfaces of the piezoelectric element 33 and are connected to signal extraction electrodes 41 and 43, respectively.

Next, the operation of the piezoelectric pressure sensor of this embodiment will be explained. When the pressure of the region to be measured is applied to the pressure receiving surface 39, the force is transmitted to the lower inner peripheral portion of the piezoelectric element 33 through the pressure transmitting member 38 and the signal extraction fitting 35. On the other hand, the upper outer peripheral portion of the piezoelectric element 33 is connected to the upper fixing screw 3.
2, a shearing force is applied to the piezoelectric element 33, and charges corresponding to the applied force are generated in the piezoelectric element 33 and collected on the charge collection electrodes 42 and 44. The charges on the charge collection electrode 42 are guided to the signal extraction electrode 41, and the charges on the charge collection electrode 44 are guided to the signal extraction electrode 43. Since the upper fixing screw 32 is in contact with the signal extraction electrode 41 on the top surface of the piezoelectric element 33, the electric charge of the signal extraction electrode 41 is transferred to the sensor housing 3.
1 to the connector section 30. On the other hand, since the signal extraction metal fitting 35 is in contact with the signal extraction electrode 43, the electric charge of the signal extraction electrode 43 is guided to the connector part 30 through the rod-shaped part 34, and is extracted as a pressure signal by the cable. Therefore, there is no need for a space between the charge collecting electrode 42 and the inner wall of the sensor housing 31, and it is possible to easily reduce the diameter of the sensor and the diameter of the mounting hole.

Upper fixing screw 32 and signal extraction fitting 35
The piezoelectric element 33 is in contact with the signal extraction electrodes 41 and 43.
The contact force does not deteriorate even at high temperatures because the pre-stress applied to the contact area and the measured pressure of the area to be measured are used. To align the centers of the upper fixing screw 32 and piezoelectric element 33, fit the piezoelectric element 33 inside the highly precisely machined sensor housing 31, and attach the upper fixing screw 32 to a threaded part provided on the inner wall of the sensor housing. The centers of the piezoelectric element 33 and the signal extraction fitting 35 are aligned by fitting the piezoelectric element 33 into the step at the base of the rod-shaped portion 34. Further, the signal extraction fitting 35 and the pressure transmission member 38 are aligned by fitting the protrusion 36 of the signal extraction fitting 35 and the recess 37 of the pressure transmission member 38. Since the pressure transmitting member 38 is fitted to the inner wall of the sensor housing which is machined with high precision, the pressure transmitting member 38 and the piezoelectric element 33 are positioned with high precision. Therefore, since the signal extraction fitting 35 is aligned both above and below with respect to the piezoelectric element 33, reliable and highly accurate alignment can be achieved. In this way, the upper fixing screw 32 and the signal extraction metal fitting 35
and charge collection electrodes 41 and 43 provided on the piezoelectric element 33
It is possible to achieve highly accurate positioning with the contact lens, ensuring good contact at all times.

Although brass is used as the material for the signal extraction fitting 35 in this embodiment, phosphor bronze may also be used as in the previous embodiment, which is a metal with good electrical conductivity and strong resistance to metal fatigue. It can be anything.

As described above, according to this embodiment, a signal of measured pressure can be reliably extracted, and a highly reliable sensor at high temperatures can be realized.

[0030] The rod-shaped portion 14 also has a signal extraction fitting 15.
The tip fits into the connector part and there is no soldering part, so even if the sensor is exposed to high temperatures, the problem of wire breakage due to re-melting of the soldered part can be avoided, making it even more reliable at high temperatures. Sensors can be realized.

Although shear stress was used in this embodiment, it can also be applied to pressure detection using compressive stress, and although signal extraction electrodes were provided on both the top and bottom surfaces of the piezoelectric element, two electrodes were provided only on the top or bottom surface. Two electrodes may be configured.

[0032]

As described above, in the piezoelectric pressure sensor of the present invention, the shape and material of the charge extraction member for extracting the electric charge generated in the piezoelectric element are improved, eliminating the need for soldering, and reducing metal fatigue. By providing a charge extraction member that does not have contact failure due to contact failure, it is possible to reliably extract the generated charge even when the sensor such as in an internal combustion engine may reach high temperatures. Sensors can be supplied, and extremely useful effects can be obtained in practice.

Furthermore, by providing two signal extraction electrodes on the end face of the piezoelectric element and extracting the pressure signal therefrom, it is possible to realize a piezoelectric pressure sensor with a structure that allows easy reduction in the diameter of the sensor and the diameter of the mounting hole. .

[0034]Also, a convex portion is provided on the signal extraction fitting and a recessed portion is provided on the pressure transmission member to align the piezoelectric element, the signal extraction fitting, and the upper fixing screw. By making contact with the signal extraction electrode and extracting the signal using the contact force, the contact force does not decrease even at high temperatures, and reliable signal extraction is possible.
A piezoelectric pressure sensor with excellent durability can be realized.

[0035] In addition, by directly guiding the electric charge to the connector and transmitting the signal using the rod-shaped part provided on the signal extraction fitting, reliable signal transmission is possible without disconnection due to re-melting of the soldered part even at high temperatures, resulting in further high-temperature durability. A piezoelectric pressure sensor with excellent performance can be realized.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a piezoelectric pressure sensor according to a first embodiment of the present invention.

[Fig. 2] A cross-sectional view of a piezoelectric pressure sensor according to a second embodiment of the present invention.

[Fig. 3] Cross-sectional view of a piezoelectric pressure sensor according to a third embodiment of the present invention

FIG. 4: Cross-sectional view of a piezoelectric element in a third embodiment of the present invention.

[Fig. 5] Assembly layout diagram of each member in the third embodiment of the present invention

[Figure 6] Cross-sectional view of a conventional piezoelectric pressure sensor

[Explanation of symbols]

11 Sensor housing 12 Pressure receiving surface 13 Pressure transmission member 14 Piezoelectric element 15 Upper fixing screw 16 Lead wire 17 Charge extraction member 21 Sensor housing 22 Pressure receiving surface 23 Pressure transmission member 24 Piezoelectric element 25 Upper fixing screw 26 Lead wire 27 Charge extraction member 30 Connector part 31 Sensor housing 32 Upper fixing screw 33 Piezoelectric element 34 Rod-shaped part 35 Signal extraction fitting 36 Convex part 37 Recess 38 Pressure transmission member 39 Pressure receiving surface 41 Signal extraction electrode (outside) 42 Charge collection electrode (outside) 43 Signal extraction electrode (inside) 44 Charge collection electrode (inside)

Claims (6)

[Claims] 1. A housing having a pressure receiving surface, a pressure transmitting member provided inside the housing and having one end in contact with a surface on the back side of the pressure receiving surface, and a pressure transmitting member provided inside the housing and said pressure transmitting member. A piezoelectric element provided at the other end of the member, a pair of charge collection electrodes provided facing each other with the piezoelectric element in between, and a charge extraction member that is in pressure contact with at least one of the pair of charge collection electrodes. A piezoelectric pressure sensor characterized by: 2. A housing having a pressure receiving surface, a pressure transmitting member provided inside the housing and having one end in contact with a back surface of the pressure receiving surface, and a pressure transmitting member provided inside the housing and other parts of the pressure transmitting member. A piezoelectric element provided at an end, a pair of charge collection electrodes provided opposite to each other with the piezoelectric element in between, and charge extraction drawn from the charge collection electrode to the top or bottom surface of the piezoelectric element, or to both the top and bottom surfaces of the piezoelectric element. A piezoelectric pressure sensor comprising an electrode and a charge extraction member that contacts the charge extraction electrode. 3. A charge extraction member is provided between the pressure transmission member and the piezoelectric element, and a convex portion provided at the center of the charge extraction member is fitted into a recess provided at the center of the pressure transmission member. The piezoelectric pressure sensor according to claim 2. 4. The charge extraction member according to claim 1, wherein the charge extraction member includes a rod-shaped portion extending toward the outside of the casing.
3. The piezoelectric pressure sensor according to 2 or 3. 5. The piezoelectric pressure sensor according to claim 4, wherein the rod-shaped portion is used as a part of a connector with a signal transmission cable. 6. The piezoelectric pressure sensor according to claim 1, wherein the charge extraction member is made of phosphor bronze.