JPH0420820A - Vibration detector - Google Patents

Abstract

PURPOSE:To maintain airtightness at the time of application of a thermal shock to prevent a drop in reliability by making a volume of an opposite space extremely smaller than a volume of a terminal side space of a vibrating board which is formed with cuts on an outer periphery. CONSTITUTION:A space 22 which is enclosed by a case 1 and a vibrating board 2 formed with cuts 2c on a periphery is a volume of a fraction of a volume of a space 21 which is enclosed by a cover 5 and the vibrating board 2, while a depth of the space 22 is made approximately equal to a thickness of the vibrating board 2, that is approximately 1mm. With this constitution, expansion of internal air due to application of a terminal shock is limited approximately within only the space 21 so that the space 22 is close to a negligible level. As a result, airtightness of a steel terminal 6 or other parts is at a level not influenced by the space 22 and even if the vibrating board 2 formed with cuts on the outer periphery is used, reliability in detecting vibration will not drop.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a vibration detector for detecting knocking by detecting vibrations of an internal combustion engine using a piezoelectric element.

[Prior Art] Fig. 2 shows a conventional vibration detector of this type, and in the figure, a case (1) made of steel has screws M (1 m) for attaching to an internal combustion engine m (not shown); It has a seating surface (lc). A diaphragm (2) made of a metal material has a vibrating surface (2a) to which a disc-shaped piezoelectric element (3) that converts vibration into an electric signal is adhered concentrically, and a peripheral part (2b) for fixation.
has. The resin cover (5) is thermoformed to include the steel terminal (6), has a peripheral portion (5a) for fixation, and insulates the terminal (6) from the reference electrode. Terminal (
6) The top electrode of the piezoelectric element (3) is the lead wire (4)
connected by. In addition, the diaphragm (2), disc spring (7), and cover (5) are sequentially inserted into the case (1) and fixed by the fastening part (1b), and the diaphragm (2) is fixed by this fixing part. is fixed.

A conventional vibration detector is configured as described above, and has a case (1
) is used to fix the seat surface (1c) of the vibration detector in contact with the internal combustion engine. The vibration plate (2) is moved from the case (1) to
) and the piezoelectric element (3), the vibration is transmitted to the piezoelectric element (3).
) generates a detection signal proportional to the vibration, and the detection signal is output to the terminal (6) with reference to the electrode on the diaphragm bonding side.

The conventional vibration detector as described above has two spaces: a space (20) surrounded by the diaphragm (2) and the case (1), and a space (21) surrounded by the diaphragm (2) and the cover (5). is the peripheral part (2b
) , (5a) The basic structure is divided by fixed parts. When a thermal shock is applied to such a detector, the airtightness of the steel terminal (6) portion of the resin cover (5) is a key point for reliability. The structural element of this is the space (21), and the breathing action through the terminal (6) due to thermal expansion of air in this space (21) has a large influence.

Now, the shape of the diaphragm (2) is not a simple disk, but a gear-shaped plate with multiple notches (2c) formed on the outer periphery as shown in Figure 3 to improve temperature characteristics. , notch (2
The outer periphery of c) is located at the periphery (5a) of the cover (5). Then, when the thermal shock is applied, not only the space (21) but also the space (20) act together as an airtight element.

[Problems to be Solved by the Invention] In the conventional vibration detector as described above, when a diaphragm is used with a notch formed on the outer periphery, the spaces on both sides of the diaphragm (2
0) and (21) communicate with each other, and their thermal expansion deteriorates the airtightness of parts such as the steel terminal (6), reducing the reliability of vibration detection.

This invention was made in order to solve the above-mentioned problem, and its purpose is to obtain a vibration detector in which the reliability of vibration detection does not deteriorate even when a diaphragm with a notch formed on the outer periphery is used. do.

[Means for Solving the Problems] The vibration detector according to the present invention has a diaphragm having a notch formed in its outer periphery so that the volume of the space on the terminal side is reduced to a fraction of the volume of the space on the opposite side. That is.

[Function] In this invention, the expansion of air that occurs when a thermal shock is applied occurs only in the space on the terminal side, and is at a negligible level in the space on the opposite side.

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which a notch (2c) as shown in FIG. 3 is formed in the diaphragm (2). A space (2) surrounded by a case (1) and a diaphragm (2)
2) is a small volume that is a fraction of the space (21) surrounded by the cover (5) and the diaphragm (2); for example, the depth of the space (22) is smaller than that of the diaphragm (2). The thickness is approximately 11 mm.

In addition, the same reference numerals as in FIG. 2 indicate the same or corresponding parts.

With the above configuration, the expansion of the internal air due to the application of thermal shock occurs almost only in the space [21], and the space (22) is close to a negligible level.As a result, the steel terminal (6) part,
and other airtightness are at a level that is not affected by the space (22).

Furthermore, in a knock sensor that detects the vibration of an automobile engine, the amplitude of the diaphragm (2) is on the order of microns, and the depth of the cut in the part that forms the space <22> of the metal case (1) is extremely large. It can be made smaller.

“[Effects of the invention] As described above, according to the present invention, for a diaphragm with a notch, the volume of the space on the opposite side of the space on the terminal side is reduced to a fraction of that of the space on the terminal side. Airtightness is maintained when heat shock is applied, and reliability does not deteriorate.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional side view of an embodiment of the present invention, FIG. 2 is a partially sectional side view of a conventional vibration detector, and FIG. 3 is a partially sectional plan view of the same. (1)・Case, (2・)・Diaphragm, (2c
)...notch, (3) pressure element, (5) cover, (6) terminal, (21), (22) -space. In each figure, the same reference numerals indicate the same or corresponding parts. Representative Person Zeng I Teru Booth υjt Force Pressure Red + 7Jl Nail- Hatute Space W) Figure 2 W-, Figure 3

Claims (1)

[Claims] A diaphragm with multiple notches formed on the outer periphery and a disk-shaped piezoelectric element bonded to the center, a steel case and a resin cover that clamp and fix the outer periphery of the diaphragm. and a steel terminal provided through the cover, and the volume of the space surrounded by the diaphragm and the case is a fraction of the volume of the space surrounded by the diaphragm and the cover. Vibration detector.