JPH06230026A - Acceleration sensor - Google Patents

Abstract

PURPOSE:To provide an acceleration sensor which is not influenced by environment temperature and can accurately self-diagnose troubles such as minute breakage of a ptezoelectric element. CONSTITUTION:Capacitance detecting electrodes 14, 16 are provided on a first plane and capacitance detecting electrodes 15, 17 are provided on a second plane of a piezoelectric body 11 made of piezoelectric ceramics, and a first and a second capacitance detecting electrode pairs in which the piezoelectric body 11 is set as dielectric substance are constituted in the opposed directions of the first and second planes, so as to enable the respective capacitance of the first and second capacitance electrode pairs to be compared with each other.

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, a suspension control device used for improving riding comfort on a bad road, and the like.

[0002]

2. Description of the Related Art Conventionally, various types of acceleration detection methods have been put into practical use. Among them, the acceleration sensor using piezoelectric ceramics has a relatively simple structure and can be used at high temperatures. Therefore, in addition to the airbag system and suspension control device described above, an engine knocking detection device is also available. Furthermore, it is being widely used in vibration detection devices for various devices.

FIG. 5 is a perspective view showing a piezoelectric element used in a conventional acceleration sensor. In FIG. 5, a piezoelectric element 80 is a plate-shaped piezoelectric body 81 made of piezoelectric ceramics.
And an output electrode 82 and a capacitance detecting electrode 84 formed on one surface (the upper surface in the drawing), and a ground electrode 83 and a capacitance detecting electrode 85 formed on the other surface (the lower surface in the drawing). It is attached to 90. This piezoelectric element
The acceleration in the direction in which the output electrode 82 and the ground electrode 83 form a pair, that is, in the thickness (polarization) direction of the piezoelectric body 81 (indicated by the arrow a in the figure) is detected.

FIG. 6 is a block diagram showing a conventional acceleration sensor including the piezoelectric element 80. In FIG. 6, the conventional acceleration sensor includes a charge amplifier 71 connected to an output electrode 82 of a piezoelectric element 80, an output adjustment unit 72 connected to the same, which includes an acceleration signal output terminal 73, and a capacitance detection electrode 84. It has an oscillator 61 connected to and a self-diagnosis signal output terminal 64 connected to the capacitance detection electrode 85.
The acceleration sensor has two operation modes, which are a normal acceleration detection mode and a self-diagnosis mode described later. First, in the acceleration detection mode, the piezoelectric element 80 generates a detection voltage between the output electrode 82 and the ground electrode 83 according to the acceleration (vibration) applied in the thickness direction (direction of arrow a) of the piezoelectric body 81. , This detection voltage is applied to the charge amplifier
Then, the impedance conversion and output adjustment are performed by the output adjustment unit 72, and the acceleration detection signal is output from the acceleration signal output terminal 73.

By the way, the piezoelectric element 80 is used after the conventional acceleration sensor is used or during the process of assembling the sensor.
When an excessive acceleration is applied to the piezoelectric body 81, the piezoelectric body 81 may be broken or deteriorated, which may cause a failure. The conventional acceleration sensor has a self-diagnosis mode as a means for diagnosing this failure. In the self-diagnosis mode, an AC signal (or a pulse signal) may be input from the oscillator 61 to the capacitance detection electrode 84 to cause electrostatic discharge between the capacitance detection electrode 84 and the capacitance detection electrode 85 via the piezoelectric body 81. The diagnostic signal output terminal 64 uses the capacitive detection signal output from the capacitive detection electrode 85 by capacitive coupling as a self-diagnostic detection signal.
The failure is diagnosed by detecting the signal from the output and determining whether or not this signal is an output corresponding to the input signal.

[0006]

However, in the conventional acceleration sensor, since the self-diagnosis is performed based on the change in the electrostatic capacity of the piezoelectric body 81, for example, other than the failure of the piezoelectric body 81 such as the influence of the environmental temperature. If the electrostatic capacitance changes due to the above factor, there is a problem that an accurate self-diagnosis cannot be performed. In particular, when diagnosing a minute breakage of the piezoelectric body 81, it is necessary to detect a minute change in the capacitance,
The change in capacitance due to the influence of environmental temperature is a problem.

An object of the present invention is to provide an acceleration sensor capable of accurately diagnosing a failure such as minute breakage of a piezoelectric element without being affected by environmental temperature.

[0008]

According to the present invention, a piezoelectric body made of piezoelectric ceramic and having first and second surfaces facing each other, and an output electrode provided on the first surface, And a ground electrode provided on the second surface,
An acceleration sensor which outputs an acceleration signal from the output electrode according to an acceleration applied in a first direction, which is an opposite direction of the first and second surfaces, wherein the first and second
2 electrodes for capacitance detection are provided on each surface of the
An acceleration sensor characterized in that first and second capacitance detecting electrode pairs having the piezoelectric body as a dielectric are formed in the direction of and the respective capacitances of the first and second capacitance electrode pairs can be compared. Is obtained.

According to the invention, there is also provided said first and second
Surface of each of the electrodes is provided with a capacitance detecting electrode to form a first capacitance detecting electrode pair having the piezoelectric body as a dielectric in the first direction, and the second pair of piezoelectric ceramics are opposed to each other. A dielectric having a pair of capacitance electrodes is provided with a second direction in which the facing direction of the second capacitance electrode pair is different from the first direction.
It is possible to obtain an acceleration sensor characterized in that the capacitances of the first and second electrode pairs can be compared with each other.

According to the present invention, there is further provided an acceleration sensor having a comparing means for comparing the respective capacitances of the first and second electrode pairs, wherein the comparing means comprises the first and second electrodes.
An oscillator for applying alternating current signals having the same waveform and opposite phase to each one of the capacitive electrodes of the electrode pair, and detection for adding output signals from the other capacitive electrodes of the first and second electrode pairs. The acceleration sensor is obtained which has a rectifier circuit.

That is, according to the present invention, in an acceleration sensor including a piezoelectric element having an output electrode and a ground electrode, a capacitance detecting electrode having a capacitance by two electrodes is further provided on the same piezoelectric element as the piezoelectric element. Further, two electrodes are formed on the same or another piezoelectric element to form a capacitance detection electrode having a capacitance substantially equal to the capacitance.

Alternatively, in the aforementioned acceleration sensor,
A signal processing circuit for performing charge amplification or the like on an output signal from the output electrode of the piezoelectric element is provided, and a circuit for comparing and detecting the electrostatic capacitances of the two sets of capacitance detection electrodes is provided.

[0013]

In the present invention, two pairs of capacitance detecting electrodes are provided on the piezoelectric element, and an AC signal having the same waveform is input from the oscillator to one of the capacitance detecting electrodes. A capacitance detection signal is output from each of the other capacitance detection electrodes by capacitive coupling between the capacitance detection electrode pairs via the piezoelectric body.

Since the two sets of capacitance detection electrodes are placed in the same environment, the piezoelectric body is not damaged, the electrodes are not peeled off, or the wire is not broken even when the ambient temperature changes. If so, the magnitude (waveform) of each signal will be the same value. Conversely speaking, the output difference will not occur until an abnormal condition occurs, so that a failure of the acceleration sensor can be diagnosed. Further, by inputting AC signals having the same waveform and opposite phases to the two sets of capacitance detection electrodes and adding the respective capacitance detection signals, the self-diagnosis signal after the addition is
If the output is zero, it can be diagnosed as normal, and if it is output, it can be diagnosed as abnormal.

[0015]

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.

[Embodiment 1] FIG. 1 is a perspective view showing a piezoelectric element used in an acceleration sensor according to Embodiment 1, and FIG.
1 is a configuration diagram showing an acceleration sensor according to a first embodiment. still,
1 and 2, the same parts as or similar parts to those of the conventional example are designated by the same reference numerals as those in FIGS. 5 and 6. In FIG. 1, the piezoelectric element 10 attached to the base 20 is
A plate-shaped piezoelectric body 11 made of piezoelectric ceramics, an output electrode 12 formed on one surface (upper surface in the drawing), electrodes 14 and 16 for capacitance detection, and another surface (lower surface in the drawing) facing each electrode. The ground electrode 13 and the capacitance detection electrodes 15 and 17 formed on the. A polarization treatment is applied between the one surface and the other surface, and the output electrode 12 and the ground electrode 13, the capacitance detection electrodes 14 and 15, and the capacitance detection electrodes 16 and 17 form a pair, respectively. There is. The capacitance detection electrodes 14, 15, 16 and 17 all have the same area. This piezoelectric element detects acceleration in the direction in which the output electrode 12 and the ground electrode 13 form a pair, that is, in the thickness (polarization) direction of the piezoelectric body 11 (indicated by the arrow a in the figure).

Referring also to FIG. 2, this acceleration sensor has a charge amplifier 71 connected to the output electrode 12 of the piezoelectric element 10 and the acceleration signal output terminal 73 connected to the charge amplifier 71, as in the conventional example. It has the output adjustment part 72 provided. Further, this acceleration sensor has an oscillator 61 that outputs a predetermined AC signal (or pulse signal), and its output is branched into two, one of which is connected to the capacitance detection electrode 14 via an inverting circuit 62. The other side is directly connected to the capacitance detection electrode 16. Furthermore, the capacitive electrode 1
5 and 17 join and are connected to the input side of the detection rectification circuit 63, and the output of the detection rectification circuit 63 is connected to the self-diagnosis signal output terminal 64.

Next, the operation of the acceleration sensor according to this embodiment will be described. This acceleration sensor also has an acceleration detection mode and a self-diagnosis mode, like the conventional example. First,
In the acceleration detection mode, similarly to the conventional example, the piezoelectric element 10 detects between the output electrode 12 and the ground electrode 13 in accordance with the acceleration (vibration) applied in the thickness direction of the piezoelectric body 11 (direction of arrow a). Voltage is generated, and the detected voltage is supplied to the charge amplifier 71.
Then, the impedance conversion and output adjustment are performed by the output adjustment unit 72, and the acceleration detection signal is output from the acceleration signal output terminal 73.

On the other hand, in the self-diagnosis mode, when no acceleration is applied to the acceleration sensor, a predetermined AC signal (or pulse signal) is input from the oscillator 61 to the capacitance detecting electrode 16 of the piezoelectric body 10, and the inverting circuit is used. An AC signal having the same waveform and opposite phase is input to the capacitance detection electrode 14 through 62. Capacitance coupling between the capacitance detection electrode 16 and the capacitance detection electrode 17 via the piezoelectric body 11, and between the capacitance detection electrode 14 and the capacitance detection electrode 15 by capacitance coupling between the capacitance detection electrode 17 and the capacitance detection electrode 17 Capacitance detection signals having opposite phases are output from each of the 15 capacitors. Further, the both capacitance detection signals are input to the detection rectification circuit 63 in a form of addition and the oscillator 6
A self-diagnosis signal is obtained from the self-diagnosis signal output terminal 64 by detecting and rectifying the signal of 1.

Here, since both the electrode pairs, that is, the pair of the capacitance detecting electrodes 14 and 15 and the pair of the capacitance detecting electrodes 16 and 17 are formed on the same piezoelectric body 11, it is possible to reduce the ambient temperature. With respect to changes and the like, there is no difference in the capacitance detection signals output from each, and the output of the self-diagnosis signal after addition is substantially zero. On the other hand, when a failure such as breakage of the piezoelectric body 11 occurs, a difference occurs in the waveforms of both capacitance detection signals, and the self-diagnosis signal after addition is output. As described above, in this embodiment, the failure can be diagnosed by the self-diagnosis signal output from the self-diagnosis signal output terminal 64.

[Embodiment 2] FIG. 3 is a perspective view showing a piezoelectric element used in an acceleration sensor according to Embodiment 2, and FIG.
6 is a configuration diagram showing an acceleration sensor according to a second embodiment. FIG. still,
In FIGS. 3 and 4, the same or similar parts as those in the first embodiment are designated by the same reference numerals as those in FIGS. 1 and 2.

In FIG. 3, a part of the piezoelectric element 30 and a whole of the capacitive element 40 are attached to the base 50. The piezoelectric element 30 includes a plate-shaped piezoelectric body 31 made of piezoelectric ceramics, an output electrode 32 and a capacitance detection electrode 34 formed on one surface (upper surface in the figure) of the piezoelectric element 30, and the other surface (FIG. It has a ground electrode 33 and a capacitance detection electrode 35 formed on the inner and lower surfaces). A polarization treatment is applied between one surface and the other surface, and the output electrode 32
And the ground electrode 33, and the capacitance detection electrodes 34 and 3
Each of the 5 is paired. This piezoelectric element detects acceleration in the direction in which the output electrode 32 and the ground electrode 3 form a pair, that is, in the thickness (polarization) direction of the piezoelectric body 31 (indicated by arrow a in the figure).

On the other hand, the capacitance element 40 includes a piezoelectric body 41 having the same material and thickness as the piezoelectric body 31, a capacitance detection electrode 42 formed on one surface (the left back surface in the drawing) and the other surface (the drawing). It has a capacitance detection electrode 43 formed on the front surface in the middle right side). Both electrodes are paired and have the same area as the capacitance electrodes 34 and 35, and their capacitance is
And the capacitance between the capacitance electrode 35 and the capacitance electrode 35 are substantially equal to each other. Further, the piezoelectric body 40 includes the capacitance electrode 42 and the capacitance electrode 4
3 is the direction opposite to the piezoelectric element 30 (indicated by arrow b in the figure).
Direction of the output electrode 32 and the ground electrode 33 of, that is,
It is attached to the base 50 so as to be orthogonal to the acceleration detection direction.

Referring also to FIG. 4, this acceleration sensor is similar to the first embodiment in that the charge amplifier 71, the output adjusting section 72, the acceleration signal output terminal 73, the oscillator 61, the inverting circuit 62, and the detection circuit. It has a rectifier circuit 63 and a self-diagnosis signal output terminal 64.

Next, the operation of the acceleration sensor according to the second embodiment will be described. This acceleration sensor also has an acceleration detection mode and a self-diagnosis mode as in the first embodiment. In the acceleration detection mode, similarly to the first embodiment, the detected voltage from the piezoelectric element 30 according to the acceleration in the direction of the arrow a is subjected to impedance conversion and output adjustment, and the acceleration detection signal is output from the acceleration signal output terminal 73.

On the other hand, in the self-diagnosis mode, when no acceleration is applied to the acceleration sensor, a predetermined AC signal (or pulse signal) is input from the oscillator 61 to the capacitance detecting electrode 42 of the capacitance element 40, and the inverting circuit is used. An AC signal having the same waveform and opposite phase is input to the capacitance detection electrode 34 of the piezoelectric element 30 through 62. Between the capacitance detection electrode 42 and the capacitance detection electrode 43 via the piezoelectric body 41, and between the capacitance detection electrode 34 and the capacitance detection electrode 45 via the piezoelectric body 31.
Due to the capacitive coupling between and, capacitance detection signals of opposite phases are output from the capacitance detection electrodes 43 and 35, respectively. Further, both capacitance detection signals are added to the detection rectification circuit 63 to be detected and rectified with the signal of the oscillator 61, thereby obtaining a self-diagnosis signal from the self-diagnosis signal output terminal 64.

Here, the piezoelectric body 31 and the piezoelectric body 41 have substantially the same electrostatic characteristics, and the capacitance detection electrode 34 is used.
Since the pair of capacitance detection electrodes 35 and 35 and the pair of capacitance detection electrodes 42 and 43 have the same electrostatic capacitance value, the capacitance detection electrodes 35 and 43 output the changes with respect to the environmental temperature and the like. There is no difference in the detected capacitance detection signal, and the output of the self-diagnosis signal after addition is substantially zero. On the other hand, the piezoelectric body 3
When a failure such as breakage of 1 occurs, a difference occurs in the waveforms of both capacitance detection signals, and an output is generated in the self-diagnosis signal after addition. As described above, in this embodiment, the failure can be diagnosed by the self-diagnosis signal output from the self-diagnosis signal output terminal 64.

In the acceleration sensor according to the second embodiment, the capacitance element 40 is fixed to the base 50 as a whole separately from the piezoelectric element 30, and the capacitance detection electrode 42 and the capacitance detection electrode 43 are opposed to each other. Is formed in a direction (arrow b direction) orthogonal to the acceleration detection direction (arrow a direction), the capacitor 40 is used as the piezoelectric body 30 when the sensor is actually used (acceleration is applied in the arrow a direction). It is hard to break down compared to. Therefore, the possibility that both of the two capacitive electrode pairs will fail is lower than that of the first embodiment, and the reliability is high.

In the present invention, the electrode pair (output electrode and ground electrode) for detecting acceleration and the two pairs of capacitance detecting electrodes are separately provided. It is also possible to use the pair as one set of capacitance detection electrode pairs.

[0030]

As described above, the acceleration sensor according to the present invention is capable of accurately diagnosing a failure such as a minute breakage of a piezoelectric element without being affected by the ambient temperature.

[Brief description of drawings]

FIG. 1 is a perspective view showing a piezoelectric element used in an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing an acceleration sensor according to a first embodiment of the present invention.

FIG. 3 is a perspective view showing a piezoelectric element used in an acceleration sensor according to a second embodiment of the present invention.

FIG. 4 is a configuration diagram showing an acceleration sensor according to a second embodiment of the present invention.

FIG. 5 is a perspective view showing a piezoelectric element used in an acceleration sensor according to a conventional example.

FIG. 6 is a configuration diagram showing an acceleration sensor according to a conventional example.

[Explanation of symbols]

10, 30, 80 Piezoelectric element 11, 31, 41, 81 Piezoelectric body 12, 32, 82 Output electrode 13, 33, 83 Ground electrode 14 to 17, 34, 35, 42, 43, 84, 85
Capacitance detection electrodes 20, 50, 90 Base 40 Capacitor 61 Oscillator 62 Inversion circuit 63 Detection rectification circuit 64 Self-diagnosis signal output terminal 71 Charge amplifier 72 Output adjustment unit 73 Acceleration signal output terminal

Claims (3)

[Claims] 1. A piezoelectric body comprising piezoelectric ceramics, having first and second surfaces facing each other, an output electrode provided on the first surface, and a ground provided on the second surface. An acceleration sensor that has an electrode and outputs an acceleration signal from the output electrode according to an acceleration applied in a first direction that is a facing direction of the first and second surfaces. Two capacitance detection electrodes are provided on each of the surfaces, and first and second capacitance detection electrode pairs having the piezoelectric body as a dielectric are formed in the first direction.
An acceleration sensor characterized in that the respective capacitances of the second capacitance electrode pair can be compared with each other. 2. A piezoelectric body made of piezoelectric ceramics, having a first and a second surface facing each other, an output electrode provided on the first surface, and a ground provided on the second surface. An acceleration sensor that has an electrode and outputs an acceleration signal from the output electrode according to an acceleration applied in a first direction that is a facing direction of the first and second surfaces. Surface of each of the electrodes is provided with a capacitance detecting electrode to form a first capacitance detecting electrode pair having the piezoelectric body as a dielectric in the first direction, and the second pair of piezoelectric ceramics are opposed to each other. A dielectric provided with a capacitive electrode pair is provided such that the facing direction of the second capacitive electrode pair is a second direction different from the first direction, and the respective capacitances of the first and second electrode pairs are provided. The acceleration sensor is characterized in that Nsa. 3. An acceleration sensor having a comparing means for comparing the respective capacitances of the first and second electrode pairs, wherein the comparing means is one capacitance electrode of each of the first and second electrode pairs. And an oscillator for applying alternating current signals having the same waveform and opposite phases to each other, and a detection rectifier circuit for adding output signals from the other capacitive electrodes of the first and second electrode pairs, respectively. The acceleration sensor according to claim 1 or 2.