JPS6224154A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To reduce the number of power sources to one while facilitating the use thereof, by fixing a piezo-electric ceramics on a diaphragm to form a center fixed type piezo-electric disc while it is supported at the center thereof. CONSTITUTION:The acceleration generated in an automobile is transmitted to a diaphragm 4 through a substrate 4 to deflect it. A piezo-electric ceramics 7 deflects together with the diaphragm 4 to generate double distortions due to tension and compression. An electric charge proportional to the distortion is generated in the ceramics 7 and the electric charge gathered to an electrode on the top surface thereof is introduced to a circuit section of a printed circuit board 9 with a lead 8. Moreover, the impedance of the ceramics 7 is converted with a impedance conversion circuit from the high to low level. Then, after the removal of unnecessary frequency components with a filter circuit, the charge is outputted to a receiving circuit at an output leader line 11. On the other hand, the electric charge gathered on an electrode on the undersurface of the ceramics is led in the order of the electrode, the diaphragm 4, the substrate 3, an housing 14 and an earth pattern of a substrate 9 to reach a shielding wire 13. The circuit section of the substrate 9 is driven by a power fed from a power source supply line 12.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an acceleration sensor that detects or measures the acceleration of a vehicle or the like that runs on an internal combustion engine.

(Prior art) Conventionally, piezoelectric acceleration sensors are generally used as this type of acceleration sensor, and the frequency required for acceleration detection is 0.
．． Since it has a low frequency of 2 to 200 Hz, it is equipped with an impedance conversion circuit.

Such a conventional acceleration sensor will be explained with reference to FIGS. 3 and 4. FIG. 3 shows an RT ceramic 1 used in a conventional acceleration sensor, which has a U-shaped slit 1a in the center to form a cantilever beam. Figure 4 is a circuit diagram of a conventional acceleration sensor.The conventional acceleration sensor consists of the cantilever-shaped piezoelectric ceramic 1 shown in Figure 3 and an impedance conversion circuit that converts the impedance of the piezoelectric ceramic 1 into a small resistance value. It is composed of 2.

The operation of the acceleration sensor having such a configuration as well as the configuration of the impedance conversion circuit 2 will be explained.

When acceleration is applied to a housing (not shown) that fixes the cantilevered piezoelectric ceramic 1, the piezoelectric ceramic 1 deflects and generates a voltage proportional to the acceleration.

If this generated power is output as it is, piezoelectric ceramics 1
Since the impedance of the receiver is large, it is subject to inductive noise, or if the input impedance of the circuit is small, the loss becomes large, and as a result, the output voltage becomes small, making it impossible to function as an acceleration sensor.

The impedance conversion circuit 2 is intended to improve this phenomenon.

It is placed near the piezoelectric ceramic 1, built into the acceleration sensor, and outputs with low output impedance.

The input resistance of the impedance conversion circuit 2 is at least IO
Since it is necessary to set the resistance to MΩ or more, a field effect transistor (hereinafter referred to as FET) 2a is used, and furthermore, FET is used.
In order to eliminate the latch-up phenomenon of the ET, it is necessary to provide a pure resistance R at the input of the FET. Furthermore, this pure resistance R
The cutoff frequency on the low frequency side is determined by

(Problems to be Solved by the Invention) However, in the acceleration sensor having such a configuration, since the capacitance of the piezoelectric ceramic 1 cannot be increased, there is a problem that the pure resistance R becomes a large resistance value. For example, the capacity of one cantilever-shaped piezoelectric ceramic 1 is 50
If 0 pF and the cutoff frequency on the low frequency side is 0.51 (z, then the resistance value of pure resistor R is R = 1/2π0.5
500 x 10-” = 700MΩ.

This resistance value is about the same as the insulation resistance of the printed circuit board,
The problem is that the resistance value decreases due to moisture.

Further, when a dynamic amplifier (not shown) is used for FET input, two power supplies are required in addition to the power supply for the dynamic amplifier, which makes it difficult to use as an acceleration sensor.

The present invention solves the above-mentioned problems and aims to provide an acceleration sensor that requires only one power source and is easy to use.

(Means for Solving the Problems) In order to solve the above problems, one aspect of the present invention is to increase the capacity by one order of magnitude or more by making a piezoelectric disk, in which piezoelectric ceramics are fixed to a diaphragm, fixed at the center. However, by reducing the impedance of the piezoelectric ceramic described above by one order of magnitude or more, and by incorporating both amplification and p-wave circuits into the acceleration sensor, the receiver can be used as a circuit as is.

In addition, it has a flat shape that is easy to install inside a car, and the wiring harness can be removed from the side and assembled easily, making it easy to use and highly reliable.

(Function) By fixing piezoelectric ceramics to a diaphragm with a fixed center to form a center-fixed piezoelectric disk, it is possible to improve the efficiency of detecting acceleration and to significantly reduce the impedance of the piezoelectric ceramics. In addition, it becomes easier to design a single circuit, requires only one power supply, has a wide frequency range, lowers the cutoff frequency especially on the low frequency side, and eliminates the effects of moisture.

In addition, the flat structure in which the wire harness is taken out from the side makes it easy to install inside the vehicle and to assemble it, thereby improving reliability.

(Example) Embodiments of the present invention will be described with reference to FIGS. 1 and 2.

FIGS. 1(a), (b), and (c) are a plan view, a front sectional view, and a side view of an acceleration sensor according to the present invention, respectively, and FIG. 2 is an enlarged sectional view of a main part thereof.

In FIG. 2, the piezoelectric disk is located at the central portion 3a of the substrate
By using the welding annular projection 3b formed at the upper end of
A diaphragm 4 welded to a substrate 3 at the center.

Piezoelectric ceramics 7 coated on both upper and lower surfaces to form positive and negative electrodes 5 and 6.
The upper surface of the diaphragm 4 and the electrode 6 on the lower surface of the piezoelectric ceramic 7 are fixed by adhesive.

In FIG. 1, a conductive wire 8 connected to an electrode 5 on the top surface of a piezoelectric ceramic 7 by soldering or the like is connected to a circuit section of a printed circuit board 9. As shown in FIG. The circuit section is composed of a circuit for the purpose of impedance conversion, output amplification, and p-wave, to which an output line 11 of a lead cord 10, a power supply 4% 12, and a shield line 13 are connected.

A housing 14 is welded and fixed on the entire circumference of the substrate 3 using an annular welding projection 14a formed on the inner peripheral edge of the lower end surface of the housing 14. The printed circuit board 9 placed on the shoulder of a stepped portion provided on the inner periphery of the housing 14 is fixed by a cap 16 press-fitted onto the outer periphery of the housing 14 via a retaining ring 15.

The stepped portion formed on the outer periphery of the upper end surface of the housing 14 includes
The O-ring 17 is attached, and the insertion hole for the lead cord 10 provided in the side wall of the housing 14 is filled with a sealant 18, and in addition to the entire circumference welding of the housing 14 and the board 3, Spaces A and B, which house the piezoelectric disk and circuit section, respectively, have a completely sealed structure.

The lead cord 10 is fixed to the acceleration sensor by caulking the stopper 19 inside the housing 14 so that it does not fall out from the housing 14, and by caulking the wire harness portion 3C formed on the extension of the board 3. be done.

In addition, as shown in FIG. 1(a), the main body of the board 3 is diamond-shaped, and mounting through holes 20 are provided at both ends of the rhombus, which are shown by dashed lines in FIG. 1(C). It can be attached to an automobile or the like using a mounting screw 21 and a spring washer 22 as shown in FIG.

The operation of the acceleration sensor having such a configuration will be explained. When an acceleration sensor is attached to a car, the acceleration generated in the car is transmitted from the car body to the diaphragm 4 via the substrate 3, causing the diaphragm 4 to bend. The piezoelectric ceramics 7 adhesively fixed to the diaphragm 4 bends together with the diaphragm 4, generating image distortion due to tension and compression. An electric charge proportional to this amount of strain is generated in the piezoelectric ceramic 7, and the electric charge collected on the upper electrode 5 is transferred to the printed circuit board 9 by the conductor 8.
The high impedance of the piezoelectric ceramic 7 is converted to low impedance by the impedance conversion circuit, and further amplified by the amplifier circuit, and then unnecessary frequency components are removed by the F-wave circuit and the output is output from the output line 11. It is output to a receiving circuit (not shown). On the other hand, the charges collected on the electrode 6 on the lower surface are led to the shield wire 13 in the order of the electrode 6 → diaphragm 4 → substrate 3 → housing 14 → the ground pattern of the printed circuit board 9. In addition, the printed circuit board 9
The circuit section is driven by the power supplied by the power supply line 12.

(Effects of the Invention) As explained above, according to the present invention, piezoelectric ceramics constitute a piezoelectric disk adhesively fixed to a diaphragm,
Furthermore, since it is supported at the center of the piezoelectric disk, the capacitance of the piezoelectric ceramic can be increased to 7000 pF, so it is driven by a power supply and has a wide frequency band in the low frequency range. It is possible to obtain an acceleration sensor that has excellent characteristics, is highly stable against temperature, and does not suffer from a decrease in the insulation resistance of the printed circuit board due to moisture.

In addition, the piezoelectric ceramics and circuit section are built in a completely sealed structure, making it highly reliable.Furthermore, the built-in circuit section amplifies and removes unnecessary frequency components, resulting in a large output.

In addition, since the structure is simple, assembly workability is good and work integrity is extremely high. Furthermore, since it has a flat and compact structure with a wire harness section on the side, it is possible to realize an acceleration sensor that is easy to install in automobiles and the like.

[Brief explanation of the drawing]

FIGS. 1(a), (b), and (c) are respectively a plan view, a cross-sectional view, and a side view of an acceleration sensor according to the present invention;
FIG. 2 is an enlarged sectional view of a main part thereof, and FIGS. 3 and 4 are a perspective view and a circuit diagram of a piezoelectric ceramic of a conventional acceleration sensor, respectively. 1.7... Piezoelectric ceramics, 2... Invinidance conversion circuit section, 2a... Field effect transistor, 3... Substrate, 3a... Central protrusion, 3b, 14
a... Annular projection for welding, 3c... Wire harness part, 4... Vibration plate, 5, 6... Electrode, 8... Conductor wire, 9... Printed circuit board, lO... Lead code,
11... Output take-out line, 12... Power supply line, 13
...Shield wire, 14...Housing, 15...
Holding ring, 16...Cap, 17...0 ring, 18...Sealant, 19...Stopper, 20...
・For installation, use through hole, 21... mounting screw, 22...
Spring washer. lU...-11JJII conversion for rebuttal T Figure 1 (c) Figure 2

Claims (1)

[Claims] A diaphragm whose center part is fixed to a protrusion formed in the center of the substrate, a piezoelectric disc made of piezoelectric ceramics to which one electrode is adhesively fixed, and an impedance connected to the other electrode of the piezoelectric ceramics with a conductive wire. It has a built-in circuit section for the purpose of conversion, amplification, and filtering, and is equipped with a lead cord for output extraction and power supply that connects to this circuit section, and has a completely sealed structure in which the space containing the piezoelectric disk and the circuit section is built in. An acceleration sensor characterized by: