JPH0750009B2 - Piezoelectric pressure sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. 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 utilizing stress in a shearing direction.

2. Description of the Related Art Piezoelectric pressure sensors that utilize the inverse piezoelectric effect of generating electricity by applying force have been used more frequently than before. But,
The pressure sensor for an internal combustion engine, which is installed so that the pressure receiving surface is directly in the cylinder chamber, must withstand high temperature and high pressure in order to measure the combustion pressure. Therefore, the vertical effect type piezoelectric pressure sensor having the polarization axis direction and the applied pressure in the same direction has a problem that a pressure receiving area for receiving heat is large and a change in characteristics due to temperature is large. Therefore, a shear effect type pressure sensor that can reduce the size of the sensor and the pressure receiving area and that applies a pressure in the shear direction with respect to the polarization axis direction can be considered.

FIG. 2 shows a structure representing the basic principle of a conventional shear effect type pressure sensor. The figure (a) is a longitudinal cross-sectional view and the figure (b) is an exploded perspective view. A cylindrical piezoelectric element 11 having a polarization axis in the length direction and using the inner and outer peripheral surfaces of the cylinder as electrodes.
A cylindrical metal body 12 is fixed to the outer peripheral surface of the same with an adhesive or the like, and a metal body 13 having an axis for fixing the cylindrical piezoelectric element 11 is attached to support and fix the cylindrical piezoelectric element 11. If the cylindrical metal body 12 is fixed by a cylinder body or the like and the metal body 13 is used as a pressure receiving surface, an electric output according to the pressure can be obtained.

Problems to be Solved by the Invention The structure of the above-mentioned shear effect type pressure sensor has the piezoelectric element 11
Since the contact area between the cylindrical metal body 12 and the cylindrical metal body 12 is large, and the cylindrical shape is cylindrical, uniform adhesion is difficult. Therefore, there is a drawback that the variation between the sensors becomes large and the mass productivity is not suitable.

Means for Solving the Problems A casing having a mounting structure so that a pressure receiving surface is located in a measured region, and a polarization axis extending in the length direction provided inside the casing and electrodes on inner and outer peripheral surfaces. And a cylindrical piezoelectric element, wherein the cylindrical piezoelectric element has an inner peripheral portion of one end surface thereof,
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 surface is fixed to the contact portion with the outer peripheral electrode of the cylindrical piezoelectric element by a fixing member such as a metal having spring property. The fixing member is held by a printed circuit board made of ceramic or the like and the cushioning member is sandwiched between the fixing member and a member such as screwing, and the signal extraction of the inner peripheral electrode of the cylindrical piezoelectric element is also constituted by a spring member such as a coil spring. .

Action Since the outer peripheral part of the end surface of the cylindrical piezoelectric element is fixed and pressure is applied to the inner peripheral part of the other end surface by the pressure transmission member, stress acts on the cylindrical piezoelectric element in the shearing direction with respect to the polarization axis direction. become. The contact area with the fixing member that fixes both ends of the cylindrical piezoelectric element can be reduced, and the influence on heat can be reduced. In addition, since the signal extraction of the inner and outer electrodes of the cylindrical piezoelectric element is made of a member having a spring property, it is not necessary to secure a wire with good heat resistance and a space for wiring, and the signal is stable even when the shape changes due to thermal expansion. You can take it out. Further, since the portions that fix both ends are both ends of the cylindrical piezoelectric element, the processing accuracy can be easily increased and uniform force can be applied. Further, since the force per unit area is increased, the variation between the sensors can be reduced, which is suitable for mass production.

Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. FIG. 1 (a) is a vertical sectional view and FIG. 1 (b) is an exploded perspective view. The cylindrical piezoelectric element 3 having a polarization axis in the length direction and having electrodes on the inner and outer peripheral surfaces has a pressure transmission having a heat insulating effect by coating a heat resistant resin or a heat resistant resin on a metal or the like on the inner peripheral portion of the bottom surface. The member 2 is fixed and fixed to the central portion of the pressure receiving surface 1 ′ inside the housing 1 attached to the cylinder of the internal combustion engine by adhesion or the like. An element fixing member 4 made of metal or the like having a spring property so as to sandwich the outer peripheral surface electrode of the piezoelectric element 3 holds the outer peripheral portion of the upper end surface of the piezoelectric element 3, and further wiring as an intermediate terminal or an impedance conversion circuit. The metal plate 7 is sandwiched between the printed circuit board 5 made of ceramic or the like that constitutes the electric circuit 6 such as an amplifier, and the metal plate 7 is clamped and fixed by the fixing screw member 8 to be attached to the housing 1. A signal from the electrode on the inner peripheral surface of the piezoelectric element 3 is also taken out by using a spring member 10 such as a coil spring, which is connected to the printed circuit board 5 on which the electrodes are displaced together with the element fixing member 4. The printed circuit board 5 is intended to avoid direct heat from the housing 1 and to insulate the cylindrical piezoelectric element 3 from the inner and outer peripheral surface electrodes and the housing. Metal plate 7
Is a kind of cushioning member for producing a uniform load on the portion tightened by the fixing screw member 8.

Since the outer peripheral portion of the cylindrical piezoelectric element 3 is fixed and pressure is applied to the inner peripheral portion of the other end surface by the pressure transmitting member 2, stress acts on the cylindrical piezoelectric element 3 in the shearing direction with respect to the polarization axis direction. An output signal proportional to can be obtained. As a material for the cylindrical piezoelectric element 3, a piezoelectric ceramic material containing lead titanate as a main component exhibits high heat resistance, which is optimal, but the piezoelectric constant d ₃₁ is small and the piezoelectric constants d ₃₃ and d ₁₅ are high. A vertical effect type structure and a shear effect type structure are conceivable. However, in the case of the vertical effect type structure, since the pressure receiving area is large and is easily affected by heat, the shear effect type structure according to the present invention is optimal. Furthermore, since the contact area with the fixing member that fixes both ends of the cylindrical piezoelectric element 3 is small, the influence on heat can be reduced, and since the fixing portions are both ends of the cylindrical piezoelectric element 3, the processing accuracy can be easily increased. , Even force can be applied. Further, since the force per unit area is increased, the variation between the sensors can be reduced, which is suitable for mass production. Further, since the signal extraction of the inner and outer peripheral surface electrodes of the cylindrical piezoelectric element 3 is made of a member having a spring property, it is not necessary to secure a wire having good heat resistance and a space for wiring, and a shape change due to thermal expansion occurs. Also, due to the spring property, the contact with the electrode is maintained and the signal can be stably extracted.

Further, the fixing member 4 has a structure that does not come into contact with the housing 1 so as to be electrically insulated from the housing 1, or has a structure in which the outer peripheral portion of the fixing member 4 is coated with a heat-resistant resin, whereby the cylindrical piezoelectric The electrodes on the inner and outer peripheral surfaces of the element 3 are insulated from the housing 1. Therefore, the electric signal due to the pressure is shielded by the casing, that is, the vehicle body, so that the structure is resistant to noise.

EFFECTS OF THE INVENTION Since the pressure sensor of the present invention has a structure in which pressure is applied by the pressure transmitting member so that shear stress acts on both end faces of the cylindrical piezoelectric element, a fixing member that fixes both ends of the cylindrical piezoelectric element is used. The contact area can be reduced, and since the spring material is used for signal extraction, the influence on heat can be reduced. Further, since the fixing portions are both ends of the cylindrical piezoelectric element, the processing accuracy can be easily increased and a uniform force can be applied. Further, since the force per unit area is increased, the variation between the sensors can be reduced, which is suitable for mass production.

[Brief description of drawings]

FIG. 1 shows a piezoelectric pressure sensor according to an embodiment of the present invention,
2A is a longitudinal sectional view, FIG. 1B is an exploded perspective view, and FIG.
FIG. 1 is a shear effect type pressure sensor showing a conventional example. FIG. 1A is a vertical sectional view and FIG. 1B is an exploded perspective view. 1 ... Housing, 2 ... Pressure transmission member, 3, 11 ... Cylindrical piezoelectric element, 4 ... Fixing member, 5 ... Printed circuit board, 6 ... Electric circuit, 9 ... Cable, 10 ... Spring Element.

Claims (2)

[Claims] 1. A housing having a mounting structure such that a pressure receiving surface is located in a measured region, and a cylinder provided inside the housing and having a polarization axis in a longitudinal direction and having inner and outer peripheral surfaces as electrodes. And a cylindrical piezoelectric element, the cylindrical piezoelectric element has an inner peripheral 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 peripheral portion of the other end surface. The cylindrical piezoelectric element is held by a fixing member such as a metal having a spring property at the contact portion with the outer peripheral surface electrode, and the fixing member is fixed by a member such as screwing with a printed circuit board made of ceramic or the like sandwiching a buffer member. The piezoelectric pressure sensor is characterized in that the signal output from the inner peripheral surface electrode of the cylindrical piezoelectric element is also constituted by a spring member such as a coil spring. 2. The piezoelectric pressure sensor according to claim 1, wherein the electrodes on the inner and outer peripheral surfaces of the cylindrical piezoelectric element are electrically insulated from the housing.