JPH0323544Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a piezoelectric sensor that is installed on the surface of a vibrating body such as an engine cylinder block that generates vibrations due to engine knocking or fuel injection to detect the vibrations.

Conventionally, this type of pinch-type piezoelectric sensor uses a vibrating body a such as a cylinder block, as shown in FIG.
There are electrodes 2, 2 on the front and back sides of the screw rod b protruding from the surface of the
The annular piezoelectric element 1 provided with is fitted by applying pressure washers 3, 3 to the upper and lower surfaces respectively, and then screwed onto the threaded rod b from above and tightening the nut c, so that the surface of the vibrating body a is and the tightening nut c, the piezoelectric element 1 is sandwiched between the piezoelectric element 1 and the tightening nut c, and compressive strain is generated in the piezoelectric element 1 by the detected vibrations of the vibrating body a that occur due to knocking, fuel injection, etc. As a result, an output signal synchronized with the vibration is extracted from the piezoelectric element 1.

By the way, in the conventional device having such a configuration,
The clamping washers 3, 3 that come into contact with the piezoelectric element 1 are usually made of nickel, iron, etc., and have a larger coefficient of thermal expansion than the piezoelectric element 1 made of a ceramic material such as PZT. Therefore, due to the difference in thermal expansion in the radial direction,
Shear stress acts between the piezoelectric element 1 and the washers 3, 3, damaging the electrode 1 of the piezoelectric element 1 and causing peeling, which is a cause of shortening the life of the piezoelectric element 1.

The present invention is aimed at eliminating the above-mentioned drawbacks of the conventional technology, and includes a buffer plate made of a low-expansion alloy containing nickel, manganese, and iron containing trace amounts of carbon and other elements as electrodes on the front and back sides of the piezoelectric element. The piezoelectric element is in contact with the surface, and the thermal expansion coefficient is close to that of the contact metal.
The shear stress caused by the difference in thermal expansion is alleviated as much as possible.

Embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 2 shows an example in which the present invention is applied to the conventional device shown in FIG. It is constructed by applying pressure washers 3, 3. In this case, since the abutting metal is the buffer plate 5 with a low coefficient of expansion, the sensor is attached to a vibrating body a that becomes hot, such as an engine cylinder block.
Even if the piezoelectric element 1 is attached to the piezoelectric element 1, the difference in thermal expansion between the piezoelectric element 1 and the abutting metal becomes small, and shear stress is prevented from being applied to the electrodes 2, 2 of the piezoelectric element 1.

In this embodiment, the washers 3, 3 may be omitted and the buffer plates 5, 5 may be used as washers.

Figures 3 and 4 show a second embodiment of the present invention, with 10
is a metal casing with an open top surface, a female screw 12 formed on the inner peripheral surface of the opening, and a through hole 15 formed in the center of the bottom wall 13 with an inclined surface 14 whose diameter expands downward. A plate packing 16 made of duralumin or the like having an outer diameter approximately equal to the inner diameter of the housing 10 and an annular buffer plate 1 made of a low expansion alloy or the like are disposed on the bottom wall 13.
7, a piezoelectric laminate 19 made up of piezoelectric elements 1 and 1 having electrodes on the upper and lower sides via a terminal plate 18, a buffer plate 17, and a plate packing 16 are sequentially laminated. The height of these laminates should not be higher than the depth of the casing 10. An insulating material 20 is inscribed in the inner surface of the piezoelectric laminate 19 to insulate the terminal plate 18 and a connecting pipe 26 to be described later.

Furthermore, a pressure receiving body 21 that is screwed onto the female screw 12 of the housing 10 is mounted on the laminate. The pressure-receiving body 21 has a male screw 22 on its outer periphery that is screwed into the female screw 12, and a through hole 23 having the same shape as the through hole 15 having an upwardly expanding sloping surface 24 on the inner surface at the center thereof. Furthermore, it has an operation hole 25 on its upper surface to enable rotation of the pressure receiving body 21. By this screwing operation of the pressure receiving body 21, a pressing force is applied to the piezoelectric elements 1, 1 through the plate packing 16, and the piezoelectric elements 1, 1 are held and fixed within the housing 10, and the amount of screwing of the pressure receiving body 21 is adjusted. This makes it possible to apply appropriate bias stress to the piezoelectric elements 1,1. The thickness of each component is determined in advance so that the upper surface of the pressure receiving body 21 and the upper surface of the casing 10 are flush with each other in the solidified state shown in FIG. Furthermore, the connecting pipe 2 is inserted into the insertion hole 30 formed by the unit.
6 and curve its upper end outward to form an inclined surface 2.
4, and also hang the lower end on the inclined surface 14.

A circular hole 27 is bored in the peripheral wall 11 of the casing 10, and the terminal plate 18 faces the circular hole 27 at the centrally-recessed portion. The conductive wire is inserted through the terminal board 18 and connected to the terminal board 18. Thus, an annular clamping type piezoelectric sensor having the insertion hole 30 is constructed.

The pinch type piezoelectric sensor has a screw rod b installed on the surface of a vibrating body a such as a cylinder block of an engine that generates vibrations to be detected such as knocking vibration or vibration accompanying fuel injection, which is an example of the vibrating body 1. The end of the screw rod b protrudes from the upper surface by fitting into the insertion hole 30 of the piezoelectric sensor, and a tightening nut c is tightened onto the end of the screw rod b to the upper surface of the pressure receiving body 21 of the pinch type piezoelectric sensor to secure the surface of the cylinder block 25. and a tightening nut 27.

The operation of the pinch type piezoelectric sensor having the above configuration will be explained.

When detected vibrations such as knocking occur in the cylinder block 25, the screw rod 2
6, the tightening nut 27 vibrates in a direction perpendicular to the mounting surface of the cylinder block 25, causing compressive strain in the piezoelectric element 1, 1 of the piezoelectric sensor in the axial direction. Therefore, a potential difference is generated between the upper and lower surface electrodes (not shown) of the piezoelectric elements 1, 1. The upper surface electrode of the upper piezoelectric element 7 and the lower surface electrode of the lower piezoelectric element 7 are connected to the pressure receiving body 21 and the casing 10 through the through hole 15 and grounded to the body. is taken out. Such a signal is subjected to processing such as amplification and wave rectification by an external device such as an amplifier, thereby making it possible to detect knocking, injection timing, etc.

A sensor that produces such an effect includes a piezoelectric element 1,
Buffer plates 1 are provided on the upper and lower surfaces of the piezoelectric laminate 19 consisting of
7 and 17 are in contact with each other, the coefficient of thermal expansion of the buffer plates 17 and 17 can be maintained even if the buffer plates 17 and 17 are installed in a place that is always under high temperature and subject to thermal shock, such as the engine cylinder block mentioned above. Since it is low, the difference in thermal expansion between the piezoelectric elements 1, 1 and the buffer plates 17, 17 becomes small, and generation of shear stress on the front and back sides of the piezoelectric elements 1, 1 is prevented.

In addition, as a threaded body, a spark plug or the like may be used instead of the threaded rod b. In addition, by increasing the thickness of the piezoelectric laminate 19, the upper and lower plate packings 1
6 and 16 can also be omitted.

As clarified by the above explanation, the present invention includes a buffer plate 17 made of a low expansion alloy containing nickel, manganese, and iron containing trace amounts of carbon and other elements on the electrode surface of the piezoelectric element 1. The piezoelectric element 1 and the abutting metal are brought into contact with each other, and the thermal expansion coefficients of the piezoelectric element 1 and the abutting metal are made close to each other, and the shear stress caused by the difference in thermal expansion is alleviated as much as possible, thereby preventing damage to the piezoelectric element 1. It has excellent effects such as

[Brief explanation of the drawing]

FIG. 1 is a vertical side view showing a conventional piezoelectric sensor, and FIG. 2 is a vertical side view of the first embodiment of the present invention.
3 and 4 show a second embodiment of the present invention, with FIG. 3 being a longitudinal sectional side view and FIG. 4 being a plan view showing half of the device taken along the line A--A in FIG. 1; piezoelectric element, 5; buffer plate, 10; housing, 1
7; Buffer plate, 19; Piezoelectric laminate, 21; Pressure receiving body.

Claims (1)

[Scope of utility model registration request] A piezoelectric element that has an annular shape and is fitted onto the shaft of a threaded body such as a bolt or spark plug that is threaded onto the surface of a vibrating body such as a cylinder wall of an internal combustion engine, and is crimped onto a clamping part of the threaded body. A pinch type piezoelectric sensor comprising: a buffer plate made of a low expansion alloy is brought into contact with the front and back electrode surfaces of the piezoelectric element.