JP3148940B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor suitable for an airbag system used for ensuring safety in the event of an automobile collision and a suspension control device used for improving riding comfort on a rough road.

[0002]

2. Description of the Related Art Conventionally, various types of acceleration detection have been put to practical use. Among them, an acceleration sensor using piezoelectric ceramics has a simple structure and can be used at a high temperature, and thus is widely used for detecting vibration of various machines and detecting knocking of an automobile engine.

FIG. 2 is a perspective view showing a piezoelectric element of a conventional piezoelectric acceleration sensor. 2, the piezoelectric element 20 has a substantially cylindrical shape, and has an output electrode 21 formed on one end face and an earth electrode 23 formed on the other end face. When the piezoelectric element 20 vibrates in the axial direction of a substantially column, a force F = k1 × α (k1 is a proportional constant, α is an acceleration) acts on the piezoelectric element, and between the output electrode 21 and the ground electrode 23, A voltage V = k2 × F (k2 is a proportional constant) is generated.
That is, the voltage generated at the output electrode of the piezoelectric element is proportional to the acceleration.

When an acceleration sensor using the above-described piezoelectric element 20 is mounted on a safety device such as an airbag, it is necessary to diagnose the failure of the acceleration sensor and the disconnection of the signal processing circuit. Two main conventional diagnostic means are shown below.

[0005] A mechanical vibration is applied to the piezoelectric element 20, an output signal of the acceleration sensor is obtained, and a diagnostic circuit (not shown) determines whether or not the output signal outputs a signal corresponding to the mechanical vibration amount. Judge by such as.

A driving electrode (not shown) is previously provided on the piezoelectric element.
A pulse signal is input to the driving electrode (separate excitation oscillation), the acceleration sensor is separately excited to obtain an output signal of the acceleration sensor, and the output signal is a signal corresponding to the pulse signal value. Is determined by a diagnostic circuit (not shown) or the like.

[0007]

However, the above-mentioned diagnostic means requires a drive system (oscillator, amplifier, shaking table) for applying mechanical vibration, that is, a relatively complicated structure, There is a problem that the space is increased and the cost is increased. On the other hand, in the diagnosing means, except for the vicinity of the resonance frequency of the piezoelectric element, the piezoelectric element hardly oscillates separately, and the output signal value of the acceleration sensor becomes small. There is a problem that there is fear.
Further, with respect to the separately excited oscillation at the resonance frequency, the drive frequency of the pulse signal must be adjusted for each acceleration sensor due to individual variations and characteristic changes (environmental changes due to temperature, etc.) of the resonance frequency of the piezoelectric element. There is a problem.

An object of the present invention is to provide an acceleration sensor capable of performing a self-diagnosis with a relatively simple configuration capable of determining whether or not the acceleration sensor can be detected.

[0009]

According to the present invention, there is provided a piezoelectric element and an output electrode provided on one end surface of the piezoelectric element, wherein the piezoelectric element responds to an acceleration applied in an axial direction thereof. Based on the output electrode, in an acceleration sensor that outputs an acceleration signal, an input electrode provided on the one end surface of the piezoelectric element, and a self-excited signal for self-exciting the piezoelectric element to the input electrode. An acceleration sensor characterized by having a self-excited oscillator for outputting is obtained.

That is, in order to achieve the above object, the present invention provides an acceleration sensor comprising a piezoelectric element having an output electrode and a ground electrode, or a signal processing circuit for amplifying an output signal from the output electrode, such as charge amplification. In the acceleration sensor, an input electrode is formed on the same piezoelectric element as the piezoelectric element, and a self-excited oscillator utilizing piezoelectric characteristics between the input electrode and the ground electrode is provided.

[0011]

In general, between a pair of electrodes of a piezoelectric element (for example, between the output electrode 11 and the ground electrode 13 in FIG. 1), as shown in FIG. ₀ , equivalent mass L, equivalent compliance C, and equivalent resistance R (various constants).
In the present invention, the input electrode is formed on the piezoelectric element, and a self-excited oscillator utilizing various piezoelectric characteristics between the input electrode and the ground electrode is provided, whereby the self-excited oscillation between the input electrode and the ground electrode is performed in a predetermined state. The piezoelectric element self-oscillates, and an output voltage corresponding to the self-oscillation amount is generated from the output electrode. That is, since a considerable amount of output signal is obtained by self-excited oscillation, it is possible to diagnose the failure of the piezoelectric element such as the damage of the element, the peeling of the electrode and the disconnection, and the presence or absence of the disconnection of the signal processing circuit.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An acceleration sensor according to an embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an acceleration sensor according to this embodiment, that is, a perspective view of a piezoelectric element and a signal processing circuit diagram. In FIG. 1, the acceleration sensor according to the present embodiment
The piezoelectric element 10 has a substantially cylindrical shape, and a signal processing circuit 30 connected to the piezoelectric element 10. The piezoelectric element 10
It has an output electrode 11 formed in a circular shape on its upper surface, an input electrode 12 formed in an annular shape on the same surface as the output electrode 11, and an earth electrode 13 formed on its lower surface.

The signal processing circuit 30 includes a charge amplifier 31 connected to the output electrode 11 of the piezoelectric element 10 and a charge amplifier 3
1 and an output adjusting unit 32 having an output terminal 35
And the input terminal 34 connected to the input electrode 12 of the piezoelectric element.
And a self-excited oscillator 33 having The input electrode 12
Is connected to the base of the transistor 40 in the self-excited oscillator 33. The constants such as the resistance in the self-excited oscillator 33 are set so that self-oscillation can be performed in consideration of various piezoelectric characteristics (various constants) between the input electrode 12 and the ground electrode 13.

Next, the operation of the acceleration sensor according to this embodiment will be described. Now, the output electrode 11 and the ground electrode 1
When acceleration is applied in the direction of 3 (circular direction of the piezoelectric element 10), a compressive force or a tensile force acts inside the piezoelectric element 10, and a voltage (charge) is generated on the output electrode 11. Performs the conversion, and the output adjustment unit 3
2, the output is adjusted to obtain a predetermined output. That is, an output proportional to the acceleration is obtained as described above.

Further, a diagnostic operation of the present acceleration sensor will be described. Now, when no acceleration is applied to the acceleration sensor, for example, before the start of driving of the automobile, a constant voltage is applied to the input terminal 34 of the self-excited oscillator 33, and the self-excited oscillator is connected between the input electrode 12 and the ground electrode 13. The self-oscillation of the piezoelectric element 10 by 33 causes the output terminal 11 to output a considerable amount of output signal (voltage) to the output electrode 11. Here, when a failure of the piezoelectric element 10 (breakage of the element, peeling of the electrode, disconnection, etc.) occurs, the output signal (voltage) changes, and failure of the signal processing circuit 30 (disconnection of the connection, functional deterioration). ) Occurs, the output value from the output terminal 35 changes. That is, if there is a failure or abnormality in the piezoelectric element 10 and the signal processing circuit 30, the output voltage of the acceleration sensor indicates an abnormal value, so that the abnormality can be detected and self-diagnosis is possible.

[0017]

According to the acceleration sensor of the present invention, an input electrode provided on one end face provided with an output electrode of a piezoelectric element and a self-excitation signal for self-exciting the piezoelectric element are output to the input electrode. Since a self-excited oscillator is provided, a drive system for applying mechanical vibration is not required, and the self-diagnosis of the acceleration sensor can be performed at a small space and at low cost.

Further, irrespective of the influence of the resonance frequency of the piezoelectric element, environmental noise, etc., a reliable self-diagnosis without malfunction can be performed. Further, at the time of the self-diagnosis, it is not necessary to adjust the drive frequency of the pulse signal for each acceleration sensor due to individual variations and characteristic changes (environmental changes due to temperature or the like) of the resonance frequency of the piezoelectric element.

[Brief description of the drawings]

FIG. 1 is a perspective view and a signal processing circuit diagram of a piezoelectric element used in an acceleration sensor according to an embodiment of the present invention.

FIG. 2 is a perspective view of a piezoelectric element used for a conventional acceleration sensor.

FIG. 3 is an electrical equivalent circuit diagram near the resonance point of the piezoelectric element shown in FIG.

[Explanation of symbols]

 10, 20 Piezoelectric element 11, 21 Output electrode 12 Input electrode 13, 23 Ground electrode 30 Signal processing circuit 31 Charge amplifier 32 Output adjustment unit 33 Self-excited oscillator 34 Input terminal 35 Output terminal 40 Transistor

Claims (1)

(57) [Claims] 1. A piezoelectric element comprising: a piezoelectric element; and an output electrode provided on one end surface of the piezoelectric element. The piezoelectric element transmits an acceleration signal to the output electrode based on an acceleration applied in an axial direction of the piezoelectric element. In an acceleration sensor that outputs, the input electrode provided on the one end surface of the piezoelectric element, to the input electrode,
An acceleration sensor, comprising: a self-excited oscillator that outputs a self-excited signal for self-exciting the piezoelectric element.