JPS63109342A - Piezoelectric type pressure sensor - Google Patents

Abstract

PURPOSE:To reduce the effect of heat, to enhance processing accuracy and to apply uniform force, by applying pressure by a pressure transmitting member so that shearing stress acts on both end surfaces of a cylindrical piezoelectric element. CONSTITUTION:A cylindrical piezoelectric element 3 has a pressure transmitting member 2 fixed to the inner peripheral part of the bottom surface thereof and is fixed to the central part of the pressure receiving surface 1' in a housing 1. A fixing member 4 is contacted with the outer peripheral part of the upper surface of the element 3 and a fixing screw member 7 is tightened to mount a heat insulating member 5 and a metal plate 6 to the housing 1 so as to fix both of them between the fixing member 4 and said screw member 17. Further, the member 5 avoids the direct conduction of heat from the housing 1 and attains the heat insulation of the element 3 not only from the electrodes on the inner and outer peripheral surfaces thereof but also from the housing 1 and the metal plate 6 generates the uniform load to the parts tightened by the member 7. Since the outer peripheral part of the end surface of the element 3 is fixed and pressure is applied to the inner peripheral part of the other end surface of the element 3 by the member, the stress in a shearing direction with respect to a polarizing axis direction acts on the element 3. Therefore, the effect of heat can be reduced by reducing the contact surface with the member 4 and processing accuracy can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pressure sensor suitable for detecting combustion pressure in a cylinder of an internal combustion engine, and more particularly to a shear effect type piezoelectric pressure sensor that utilizes stress in the shear direction.

Piezoelectric pressure sensors, which utilize the inverse piezoelectric effect to generate electricity by adding conventional technology, are better than conventional ones.However,
Pressure sensors for internal combustion engines, which are installed with their pressure-receiving surface directly into the cylinder chamber, must withstand high temperatures and pressures in order to measure combustion pressure. Therefore, a longitudinal effect type piezoelectric pressure sensor in which the polarization axis direction and the applied pressure are in the same direction has a problem in that the pressure receiving area that receives heat is large and the characteristics change greatly depending on temperature. Therefore, a shear effect type pressure sensor that applies pressure in the shear direction with respect to the polarization axis direction is considered, which can make the sensor smaller and reduce the pressure receiving area. FIG. 2 shows a structure representing the basic principle of a conventionally used shear effect type pressure sensor. Same figure (
Figure a) is a longitudinal cross-sectional view, and figure (b) is an exploded perspective view. A cylindrical metal body 9 is fixed with an adhesive or the like to the outer circumferential surface of a cylindrical piezoelectric element 8 having a polarization axis in the thickness direction and electrodes on the inner and outer circumferential surfaces of the cylinder, and a shaft to which the cylindrical piezoelectric element 8 is fixed. It has a structure in which a metal body 10 having a shape is attached to support and fix a cylindrical piezoelectric element 8. The cylindrical metal body 9 is fixed with a casing or the like, and the metal body 10 is
If this is the pressure-receiving surface, the electrical output can be changed according to the pressure.

Problems to be Solved by the Invention The structure of the shear effect type pressure sensor described above has a piezoelectric element 8.
The contact area between the metal body 9 and the cylindrical metal body 9 is large, and the cylindrical shape makes uniform adhesion difficult. Therefore, there was a drawback that the variation between the sensors was large (which made it unsuitable for mass production).

Means for Solving the Problems A housing having a mounting structure such that the pressure receiving surface is located within the measurement area, and a housing having a polarization axis in the thickness direction and electrodes on the inner and outer circumferential surfaces are provided inside the housing. a cylindrical piezoelectric element, and the cylindrical piezoelectric element has an inner peripheral portion of one end surface,
It is fixed to a pressure transmitting member that transmits the pressure of the pressure receiving surface and has a heat insulating effect, and the outer peripheral portion of the other end face is fixed with a fixing member such as metal.

The outer periphery of the end face of the cylindrical piezoelectric element is fixed, and pressure is applied to the inner periphery of the other end face by the pressure transmission member, so stress acts on the cylindrical piezoelectric element in the shear direction relative to the polarization axis direction. become. The contact area with the fixing member fixing both ends of the cylindrical piezoelectric element can be reduced, and the influence of heat can be reduced.

Furthermore, since the parts to be fixed are both ends of the cylindrical piezoelectric element, processing accuracy can be easily increased and uniform force can be applied. Furthermore, since the force per unit area is increased, variations between sensors can be reduced, making it suitable for mass production.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, with FIG. 1(a) being a longitudinal sectional view and FIG. 1(b) being an exploded perspective view. The cylindrical piezoelectric element 3 has a polarization axis in the thickness direction and electrodes on the inner and outer circumferential surfaces, and the inner circumferential portion of the bottom surface thereof is a pressure transmitting member that has a heat-insulating effect, such as heat-resistant resin or metal coated with heat-resistant resin. 2 is fixed, and is fixed by adhesive or the like to the center portion of the pressure receiving surface 1' inside the casing 1, which is attached to the cylinder of the internal combustion engine. A fixing member 4 made of metal or the like is in contact with the outer periphery of the upper surface of the piezoelectric element 3, and a fixing screw member 7 is tightened and fixed with a heat insulating member 5 such as ceramic and a metal plate 6 in between, thereby fixing the housing. It is attached to 1. The heat insulating member 5 prevents direct heat from the casing 1 and also provides insulation from the inner and outer circumferential electrodes of the cylindrical piezoelectric element 3 and from the casing. The metal plate 6 is a type of buffer member for creating a uniform load on the portion tightened by the fixing screw member 7.

Since the outer periphery of the cylindrical piezoelectric element is fixed and pressure is applied by the pressure transmission member to the inner periphery of the other end surface, stress acts on the cylindrical piezoelectric element in the shear direction with respect to the polarization axis direction. The contact area with the fixing member that fixes both ends of the cylindrical piezoelectric element is small, reducing the effect of heat.
Since the parts to be fixed are both ends of the cylindrical piezoelectric element, processing accuracy can be easily increased, and uniform force can be applied. Furthermore, since the force per unit area is increased, variations between sensors can be reduced, making it suitable for mass production. The fixing member 4 has a structure that does not come into contact with the casing 1 so as to provide electrical insulation from the casing 1, or a structure in which the outer periphery of the fixing member 4 is coated with heat-resistant resin, so that the cylindrical piezoelectric element 3 The inner and outer circumferential electrodes of the housing 1 are insulated from each other. Therefore, the electrical signal due to pressure is
Since it is shielded by the casing, that is, the vehicle body, it has a structure that is resistant to noise.

Effects of the Invention The present invention has a structure in which shear stress is applied to both end faces of a cylindrical piezoelectric element (as pressure is applied by a pressure transmitting member).
The contact area with the fixing member fixing both ends of the cylindrical piezoelectric element can be reduced, and the influence of heat can be reduced. Furthermore, since the parts to be fixed are both ends of the cylindrical piezoelectric element, processing accuracy can be easily increased and uniform force can be applied. Furthermore, since the force per unit area is increased, variations between sensors can be reduced, making it suitable for mass production.

[Brief explanation of the drawing]

FIG. 1 shows a piezoelectric pressure sensor according to an embodiment of the present invention,
Figure (a) is a longitudinal sectional view, figure (b) is an exploded perspective view, and
The figure shows a conventional shear effect type pressure sensor.
Figure a) is a longitudinal sectional view, and figure (b) is an exploded perspective view. DESCRIPTION OF SYMBOLS 1... Housing, 2... Pressure transmission member, 3.8... Cylindrical piezoelectric element, 4... Fixing member. Name of agent: Patent attorney Toshio Nakao and one other person (Figure 1) Figure 1 (Figure 1) Figure 2 αυ (I))

Claims (2)

[Claims] (1) A casing having a mounting structure so that the pressure receiving surface is located within the measurement area, and a cylindrical piezoelectric device installed inside the casing, having a polarization axis in the thickness direction and using the inner and outer circumferential surfaces as electrodes. The cylindrical piezoelectric element has an inner circumferential portion of one end surface fixed to a pressure transmitting member that transmits the pressure of the pressure receiving surface and has a heat insulating effect, and an outer circumferential portion of the other end surface of the cylindrical piezoelectric element is fixed to a pressure transmitting member that transmits the pressure of the pressure receiving surface and has a heat insulating effect. A piezoelectric pressure sensor characterized in that it is fixed with a fixing member. (2) The piezoelectric pressure sensor according to claim 1, wherein the electrodes on the inner and outer peripheral surfaces of the cylindrical piezoelectric element and the housing are electrically insulated.