JPH08220129A - Acceleration sensor - Google Patents

Abstract

PURPOSE: To obtain a small-sized inexpensive acceleration sensor with self- diagnostic function by sustaining the opposite sides of a piezoelectric bimorph at a reference potential or the ground potential and obtaining the output from a bonded face. CONSTITUTION: In a piezoelectric bimorph, metal electrodes 1, 6 are arranged, while being connected to have a reference potential or the ground potential, on the outside of two piezoelectric elements 2, 7 bonded through metal plates 3a, 3b. Electrodes for excitation and detection are bonded oppositely each other as separated electrodes 4a, 4b, 5a, 5b on the inside of the piezoelectric elements 2, 7 in order to impart the self-diagnostic function. The metal plates 3a, 3b sandwiched by two piezoelectric elements 2, 7 are divided equally to the separated electrodes 4a, 4b, 5a, 5b. The metal plate 3a, 3b is provided with a lead-out terminal being used as a signal I/O terminal. Since a detection circuit is connected at four points, the piezoelectric bimorph is simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor,
More specifically, the present invention relates to the structure of an acceleration sensor that uses a bimorph piezoelectric material and has a self-diagnosis function.

[0002]

2. Description of the Related Art Acceleration sensors of this type are often used for vehicle control to detect an automobile collision and actuate an airbag system or the like, and therefore require a high degree of reliability and guarantee reliability. In order to do so, a self-diagnosis is performed including the sensor when the ignition is turned on.

A piezoelectric bimorph, which is an acceleration detecting portion of an acceleration sensor using a piezoelectric element, is usually formed in a rectangular plate shape. Then, one end thereof is fixed to a fixing member, and a voltage is generated by the deflection generated by the acceleration. The acceleration sensor detects the generated voltage with a detection circuit and transmits the information to the outside. An air bag system that operates by detecting a collision of a vehicle receives the information and operates the air bag system.

As shown in FIG. 4, the piezoelectric bimorph, which is an important acceleration detecting portion, has plate-like piezoelectric elements 24, 2 as shown in FIG.
8 is joined via a metal plate 26, and electrodes are formed on both surfaces thereof.

When the piezoelectric bimorph thus formed is incorporated into an acceleration sensor, it is necessary to fix the piezoelectric bimorph directly on the metal base in order to faithfully transmit the acceleration to the piezoelectric bimorph. Then, in order to reduce the size of the acceleration sensor itself, the lead pins for external device connection, which are arranged in advance on the metal base, and the piezoelectric bimorph, or the lead pins for external device connection, and the substrate on which the detection circuit is mounted are directly connected.

The external device connection terminals previously arranged on the metal base are hermetically sealed so that water droplets, gas, etc. do not enter the acceleration sensor. Then, a metal cap is put on and the base is welded to complete the acceleration sensor.

The self-diagnosis function for guaranteeing the reliability of the acceleration sensor is to excite the detecting portion by another piezoelectric element, detect the excitation by the detecting piezoelectric element, and inspect the detection output. A method for diagnosing whether the acceleration sensor is operating normally is known.

In FIG. 4, the two piezoelectric elements 24 and 28 bonded to each other via the metal plate 26 have electrodes formed on the both surfaces thereof by means of printing, sputtering, etc. The entire surface of the surface to be bonded is the electrode 2
5, 27 are formed, and polarization electrodes 23a, 23b and 29a, 29b which are divided into two are formed on the outer surfaces of the piezoelectric elements 24, 28.

As shown in FIG. 4, electrical input / output is performed by one of the pair of electrodes 23a, 29a or 2 of the metal plate 26 and the polarized electrode.
Since an excitation signal is input between 3b and 29b so that it can be detected by the other pair of electrodes, an acceleration sensor that uses a piezoelectric bimorph with a polarized electrode as a fixed end for fault diagnosis detects a piezoelectric bimorph. Five connections to the circuit are required.

The shape of the polarized electrodes can be arbitrarily determined according to the structure of the piezoelectric bimorph itself, but in order to suppress pyroelectric noise, it is necessary that they have the same area in terms of the positional relationship of projection.

[0011]

As described above, the acceleration sensor using the piezoelectric bimorph having the polarized electrode as one end fixing for the fault diagnosis requires five connections between the piezoelectric bimorph and the detection circuit. Is becoming a factor that hinders mass production. Further, since five lands for connecting the board are required, it is impossible to downsize the board, which is a big obstacle to downsizing.

[0012]

In order to solve the above-mentioned problems, an acceleration sensor according to the present invention has two plate-shaped piezoelectric elements in a direction in which polarized electrodes are opposed to each other via two metal plates arranged in parallel. A piezoelectric bimorph formed by joining, a metal base having a lead pin, and a circuit board having a detection circuit for detecting the output of the piezoelectric bimorph, and a terminal for external connection is integrally formed on the metal plate, An acceleration sensor with a self-diagnosis function, wherein one end of a piezoelectric bimorph including the terminal is fixed on a metal base via a fixing member, and the piezoelectric bimorph has both surfaces held at a reference potential or a ground potential, The lead pins are connected so as to obtain an output, and are connected to the circuit board via terminals led out from the piezoelectric bimorph.

[0013]

The acceleration sensor, which uses the piezoelectric bimorph having the polarized electrode as one end for the purpose of failure diagnosis, has a problem in that the structure is complicated because the piezoelectric bimorph and the detection circuit require five connections.

Therefore, the two are joined together via a metal plate.
Electrodes that are connected so as to have a reference potential or a ground potential are arranged on the outer sides of the piezoelectric elements, and separation electrodes are arranged on the inner sides of the respective piezoelectric elements, and the separation electrodes are bonded so as to face each other. The metal plate sandwiched between the two piezoelectric elements is divided in the same manner as the separation electrode, and the terminals provided on the metal plate enable input / output. The upper and lower sides of the piezoelectric bimorph thus configured are sandwiched by electrode plates provided with terminals and fixed on a metal base.

The piezoelectric bimorph thus constructed is
The number of connections with the detection circuit is four, which makes it possible to provide an acceleration sensor having a simplified structure.

[0016]

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

FIG. 1 shows a conceptual diagram of the structure of a piezoelectric bimorph according to the present invention, FIG. 2 (a) is a substantially exploded view of the piezoelectric bimorph according to the present invention, and FIG. 2 (b) is a completed perspective view thereof.

As shown in FIG. 1, the piezoelectric bimorph according to the present invention is connected to the outside of two piezoelectric elements 2 and 7 which are joined via a metal plate so as to have a reference potential or a ground potential. The whole surface electrodes 1 and 6 are arranged. Further, inside the respective piezoelectric elements, excitation and detection electrodes for providing a self-diagnosis function are arranged as separation electrodes 4a, 4b and 5a, 5b so that the respective separation electrodes face each other. To join. The metal plates 3a and 3b sandwiched between the two piezoelectric elements are divided in the same manner as the separation electrodes.

As shown in FIG. 2, the metal plates 3a and 3b have lead-out terminals and are used as signal input / output terminals. The upper and lower sides of the piezoelectric bimorph thus configured are sandwiched by electrode plates 8 and 9 provided with terminals. The holes provided for connection to the terminals provided on the upper and lower electrode plates are located at positions corresponding to each other, as shown in FIG. 2 (b). In this way, the piezoelectric bimorph 10 is completed. For simplification, the piezoelectric elements 2 and 7 shown in FIG.
Was omitted.

FIG. 3 is a typical structural diagram of an acceleration sensor using the piezoelectric bimorph 10.

The piezoelectric bimorph 10 has one end fixed on the fixing member 14 placed on the metal base 15, and the terminals provided on the piezoelectric bimorph 10 are connected to the lead pins 18, 19, 20 previously installed on the metal base 15. To electrically connect. After that, the substrate 12 on which the detection circuit is mounted is fixed to the upper portion thereof, together with the lead pins 17 and 21 which are preliminarily installed on the metal base and do not use the piezoelectric bimorph,
The lead pins 18, 19, 2 via the piezoelectric bimorph
0 is the land 13a, 13b, 13c, 13d, 1 of the substrate
3e and 13f are electrically connected and assembled so as to operate as an acceleration sensor.

As shown in FIG. 1, the terminals of the metal plates 8 and 9 which must be connected so as to maintain the reference potential or the ground potential of the piezoelectric bimorph must be electrically connected outside the piezoelectric bimorph. However, since the holes provided for connecting to the terminals of the metal plates 8 and 9 are located at the positions corresponding to each other, the lead pins 20 can be connected at once.

After that, the metal cap 11 is covered, and welding is performed at the metal base peripheral portion 22 to complete the airtightness of the acceleration sensor.

According to the above-mentioned structure, the excitation signal is input between the lead pins 18 and 20, the detection signal is output between the lead pins 18 and 19, and the other lead pins supply the power supply for the detection circuit. It is possible to easily and efficiently assemble an acceleration sensor capable of performing the above.

Further, since the number of lead pins for connecting also the detection circuit substrate is small, the number of lands is small and the substrate can be downsized, so that the acceleration sensor can be downsized.

Furthermore, since both surfaces of the piezoelectric bimorph are held at the reference potential or the ground potential, it is possible to provide an acceleration sensor having excellent noise resistance and high reliability.

[0027]

As described above, according to the present invention, the number of connecting points between the piezoelectric bimorph and the detection circuit is reduced, and since it is possible to easily manufacture the construction method, a compact and inexpensive acceleration sensor with a self-detection function can be provided. Can be provided. Moreover, since both surfaces of the piezoelectric bimorph are held at the reference potential or the ground potential, it is possible to provide an acceleration sensor having excellent noise resistance and high reliability.

[Brief description of drawings]

FIG. 1 is a structural conceptual diagram of a piezoelectric bimorph according to the present invention.

FIG. 2 is a configuration diagram of a piezoelectric bimorph according to the present invention.

FIG. 3 is a structural diagram of an acceleration sensor according to the present invention.

FIG. 4 is a conceptual diagram of the structure of a conventional piezoelectric bimorph.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Full surface electrode 2 Piezoelectric element 3a, 3b Metal plate 4a, 4b Separation electrode 5a, 5b Separation electrode 6 Full surface electrode 7 Piezoelectric element 8 Electrode plate 9 Electrode plate 10 Piezoelectric bimorph 11 Metal cap 12 Substrate 13a, 13b, 13c, 13d, 13e , 13f Land 14 Fixing member 15 Metal base 16 Lead pin 17 Lead pin 18 Lead pin 19 Lead pin 20 Lead pin 21 Lead pin 22 Metal base peripheral part 23a, 23b Polarized electrode 24 Plate piezoelectric element 25 Full surface electrode 26 Metal plate 27 Full surface electrode 28 Plate piezoelectric element 29a, 29b polarized electrodes

Claims (1)

[Claims] 1. A piezoelectric bimorph in which two plate-shaped piezoelectric elements are joined in a direction in which polarized electrodes are opposed to each other through two metal plates arranged in parallel, a metal base provided with a lead pin, and a piezoelectric bimorph. And a circuit board on which a detection circuit for detecting the output of is connected, a terminal for external connection is integrally formed on a metal plate, and one end of the piezoelectric bimorph including the terminal is fixed on a metal base via a fixing member. The piezoelectric bimorph is an acceleration sensor with a self-diagnosis function. Both sides of the piezoelectric bimorph are held at a reference potential or a ground potential and connected so as to obtain an output from the joint surface, and lead pins are derived from the piezoelectric bimorph. An acceleration sensor, which is connected to a circuit board via a terminal.