JPH02661Y2 - - 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 piezoelectric sensor, as shown in Fig. 1, has a screw rod b protruding from the surface of a vibrating body a such as a cylinder block, and an annular piezoelectric element c having electrodes d and d on the front and back sides. A tightening nut f (pinching part) which is fitted by applying clamping washers e and e to the upper and lower surfaces respectively, and which is further screwed onto the screw rod b from above to form a screw body with the screw rod b. is tightened, and the piezoelectric element c is held between the surface of the vibrating body a and the tightening nut f, and the vibrating body a
By causing compressive strain in the piezoelectric element c due to detected vibrations occurring with knocking, fuel injection, etc., an output signal synchronized with the vibrations is extracted from the piezoelectric element c.

By the way, in the conventional device having such a configuration,
Since the tightening by the tightening nut f (pinching part) is received only by the piezoelectric element c, the nut f at the time of installation is
Fatigue accumulates due to over-tightening or continuous squeezing pressure, which tends to cause cracks and breakage of the piezoelectric element c, and has disadvantages such as a short service life.

The present invention aims to eliminate the above-mentioned drawbacks of the conventional art, and includes mounting an annular piezoelectric element inside a metal casing with an open top surface and a through hole formed in the center of the bottom wall. A pressure-receiving body is screwed onto a female screw formed on the inner peripheral surface of the upper part, and the piezoelectric element is pressed and held by the pressure-receiving body to constitute a piezoelectric sensor, and the pressure accompanying the tightening of the screw body is transferred to the pressure-receiving body. By screwing the piezoelectric element into the housing, the piezoelectric element is released from the peripheral wall of the housing to relieve pressure on the piezoelectric element, thereby preventing damage to the piezoelectric element due to the pinching pressure of the pressure receiving body.

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

1 is a metal casing with an open top surface, a female screw 2 formed on the inner peripheral surface of the opening, and a through hole 5 formed in the center of the bottom wall 3 with an inclined surface 4 whose diameter expands downward. A piezoelectric laminate 9 is provided on the bottom wall 3 of the piezoelectric laminate 9, which includes piezoelectric elements 7, 7 having upper and lower electrodes via a plate packing 6 made of duralumin or the like having an outer diameter approximately equal to the inner diameter of the housing 1, and a terminal plate 8. and plate packing 6 are sequentially laminated. The height of these laminates should not be higher than the depth of the casing 1. An insulating material 10 is inscribed in the inner surface of the piezoelectric laminate 9 to insulate the terminal plate 8 and a connecting pipe 16 to be described later.

Furthermore, a pressure receiving body 11 screwed onto the female screw 2 of the housing 1 is disposed on the laminate. The pressure receiving body 11 has a male screw 1 on its outer periphery that is screwed into the female screw 2.
2, and a through hole 13 having the same diameter as the through hole 5 and having an inclined surface 14 whose diameter expands upward at the center thereof,
Further, it has an operation hole 15 on its upper surface to enable rotation of the pressure receiving body 11. By this screwing operation of the pressure receiving body 11, a pressing force is applied to the piezoelectric elements 7, 7 from above through the plate packing 6, and the piezoelectric elements 7, 7 are held and fixed within the housing 1. By adjusting the amount of spiral movement of the pressure receiving body 11, an appropriate bias stress can be applied to the piezoelectric elements 7, 7. The thickness of each component is determined in advance so that the upper surface of the pressure receiving body 11 and the upper surface of the housing 1 are substantially flush with each other in the solidified state shown in FIG. Further, the connecting pipe 16 is placed in the insertion hole 20 formed by the unit, and its upper end is curved outward to hang on the inclined surface 14, and the lower end is similarly hung on the inclined surface 4.

A circular hole 17 through which the terminal plate 8 faces is bored in the middle of the peripheral wall 1a of the housing 1.
A conductive pipe 18 is fitted into the terminal plate 18, a conductive cord 19 is inserted through the pipe 18, and the conductive wire is connected to the terminal plate 8. Thus, an annular piezoelectric sensor A having an insertion hole 20 is constructed.

The installation of the piezoelectric sensor A will be explained.

The insertion hole 20 of the piezoelectric sensor A is inserted into a threaded rod 26 installed on the surface of a cylinder block 25 of an engine that generates detected vibrations such as knocking vibrations or vibrations associated with fuel injection, which is an example of the vibrating body a. A tightening nut 27 (squeezing part) is fitted into the piezoelectric sensor A so that the end of the screw rod 26 protrudes from the upper surface of the piezoelectric sensor A, and the end portion of the screw rod 26 forms a screw body together with the screw rod.
is screwed onto the top surface of the pressure receiving body 11 of the piezoelectric sensor A, and the piezoelectric sensor A is attached to the cylinder block 2.
5 and the tightening nut 27. This clamping force is transmitted to the peripheral wall 1a of the housing 1 due to the screw engagement between the female screw 2 of the housing 1 and the male screw 12 of the pressure receiving body 11, and is also transmitted to the piezoelectric laminate 9 via the upper plate packing 6. The voltage is transmitted as a divided voltage and acts on the piezoelectric elements 7, 7 as an appropriate bias stress.

Therefore, the piezoelectric sensor A is fixed to the vibrating body a without loosening, and at the same time, the tightening pressure is applied to the piezoelectric element 7,
7, so its damage is prevented.

The operation of the 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 elements 7, 7 of the piezoelectric sensor A in the axial direction. For this reason, the piezoelectric element 7,
A potential difference is generated between the upper and lower surface electrodes of 7. 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 11 and the casing 1 through plate packings 6, 6, and are grounded to the body. A signal is extracted. 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.

Instead of the tightening nut 27, a bolt may be screwed into the cylinder block 25 from the insertion hole 20 of the piezoelectric sensor A, and the head (pinching part) of the bolt may be brought into contact with the upper surface of the piezoelectric sensor A. . In addition, a spark plug or the like can also be used as the threaded body. Furthermore, by increasing the thickness of the piezoelectric laminate 9, the upper and lower plate packings 6, 6 can be omitted.

As clarified from the above description, the present invention has an open top surface and a through hole 5 in the center of the bottom wall 3.
An annular piezoelectric element 7 is mounted in a metal casing 1 formed with Since the element 7 is held under pressure, the pressure associated with tightening the screw body escapes from the screw connection between the housing 1 and the pressure receiving body 11 to the peripheral wall 1a side, and the tightening pressure applied to the piezoelectric element 7 is relieved, resulting in an appropriate bias. This causes stress and alleviates damage to the piezoelectric element 7 when tightening the screw body and fatigue of the piezoelectric element 7 due to continuous application of clamping force, thereby extending the life of the piezoelectric element 7 as much as possible. It has excellent effects such as:

[Brief explanation of the drawing]

FIG. 1 is a vertical side view showing a conventional piezoelectric sensor, and FIGS. 2 and 3 show an embodiment of the present invention.
The figure is a longitudinal side view, and FIG. 3 is a plan view showing a half section taken along the line AA in FIG. 2. 1... Housing, 2... Female screw, 6... Plate packing, 7, 7... Piezoelectric element, 9... Piezoelectric laminate, 1
1...Pressure receiving body, 12...male screw, 20...insertion hole, A...piezoelectric sensor.

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. In the piezoelectric sensor, an annular piezoelectric element is mounted in a metal housing whose top surface is open and a through hole is formed in the center of the bottom wall, and a female screw is formed on the inner peripheral surface of the upper part of the housing. A piezoelectric sensor characterized in that a pressure receiving body is screwed onto the top of the piezoelectric sensor, and the piezoelectric element is pressed and held by the pressure receiving body.