JPH077011B2 - Piezoelectric acceleration sensor - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor mounted on a moving object to detect the acceleration of the moving body, and more particularly to a case fixed to the moving body. The present invention relates to a piezoelectric acceleration sensor including a displaceably mounted oscillator and a piezoelectric element that detects a relative displacement of a moving body of the oscillator and generates a voltage proportional to the relative displacement.

(Prior Art) In general, acceleration sensors that detect the acceleration of a moving object are roughly classified into four types: piezoelectric type, electrokinetic type, servo type, and strain gauge type sensors. Among these sensors, the piezoelectric type sensor is most often used in the general acceleration measurement field, and the other sensors are mainly used in the special measurement field.

In such a general piezoelectric acceleration sensor, a vibrator is attached to a case fixed to a moving object so as to be capable of relative displacement, and a piezoelectric element is surface-bonded to the vibrator. It is configured to generate a voltage proportional to the acceleration of the moving body by being distorted by the relative displacement of the oscillator.

By the way, in automobiles, it is required to make driving operation as simple as possible and to obtain a more comfortable driving feeling. Therefore, it is necessary to perform finer control regarding various controls of the automobile. Therefore, along with the recent development of electronic control technology, electronic control is rapidly becoming popular in the technical field of automobiles. In that case, it is necessary to grasp the running state of the vehicle or the operating state of various parts such as the engine, and for that purpose, various sensors are provided in the automobile. For example, the piezoelectric acceleration sensor as described above is also used to know the acceleration of the vehicle.

An example of the use of such a piezoelectric acceleration sensor in an automobile is an operation control circuit of an airbag device as disclosed in Japanese Patent Publication No. 58-22377. An acceleration sensor that detects an acceleration of a predetermined magnitude is used in the operation control circuit to operate the airbag device. The acceleration sensor is of a piezoelectric type, and when the deceleration of the vehicle reaches a predetermined magnitude, it is detected and a voltage signal is output. Then, the output signal causes the explosive in the combustion chamber of the airbag device to explode, and the airbag is inflated to hold the occupant at the seat position.

Such an acceleration sensor needs to be normally operating in order to accurately detect the acceleration of the vehicle. Therefore, it is essential to regularly diagnose the acceleration sensor.

(Problems to be Solved by the Invention) By the way, the conventional piezoelectric acceleration sensor as described above is
It has only a sensor function to detect acceleration. Therefore, in order to diagnose the sensor, it is necessary to mechanically apply vibration or shock to the sensor. For that purpose, special auxiliary equipment such as a vibration device is required. Since such ancillary equipment is generally formed in a large size in many cases, it cannot always be installed in a general automobile such as a passenger car. As a result, in order to diagnose the sensor, it is unavoidable to remove the sensor from the vehicle and bring it to a place where a vibration device or the like is installed to perform the diagnosis. Therefore, it takes time and effort to easily diagnose the acceleration sensor anytime and anywhere.

The present invention has been made in view of such a problem, and an object thereof is to obtain a piezoelectric acceleration sensor that can be easily and always diagnosed in a state of being installed in a vehicle.

(Means for Solving the Problems) In order to achieve this object, in the present invention, the electrode attached to the piezoelectric element of the piezoelectric acceleration sensor is divided into a plurality of electrodes. Then, some of these electrodes are used as output terminals for outputting a voltage signal proportional to acceleration, and the rest of these electrodes are used as input terminals for inputting a diagnostic voltage signal.

(Operation) With this configuration, when acceleration is generated in the moving body, the oscillator of the sensor is relatively displaced with respect to the moving body, and the relative displacement distorts the piezoelectric element to generate a voltage proportional to the acceleration. Is generated and the voltage signal is output from the output terminal. That is, the acceleration is detected by the sensor.

Also, if you input the diagnostic voltage signal to the input terminal of the sensor,
When the sensor is normal, the piezoelectric element is distorted in proportion to the voltage. That is, it is equivalent to a state in which the piezoelectric element is distorted by the vibration acceleration of the sensor vibrator. Since the piezoelectric element generates a voltage in proportion to the strain, a voltage signal of a predetermined magnitude with respect to the diagnostic voltage signal is output from the output terminal. Therefore, the voltage signal confirms that the sensor is normal.

If the sensor is abnormal, even if a diagnostic voltage signal is input, a voltage signal of a predetermined magnitude corresponding to the input signal is not output from the output terminal. Alternatively, no voltage signal is output. Thereby, it is recognized that the sensor is abnormal.

As described above, the sensor has a sensor function of detecting acceleration and a self-diagnosis function of detecting abnormality of the sensor itself.

(Examples) Examples of the present invention will be described below with reference to the drawings.

In the drawings, FIGS. 1 and 2 show an embodiment of a piezoelectric acceleration sensor according to the present invention, and FIG. 1 is a longitudinal sectional view of the sensor.
The drawing is a plan view seen from the direction of arrow A in FIG.

As is apparent from FIG. 1, the central portion of the circular vibrator 2 is fixed to the central protruding portion 1a of the cylindrical case 1 made of metal or conductive resin by an appropriate fixing means. The outer peripheral end of the vibrator 2 is free, and can be displaced relative to the case 1 by the flexural deformation of the vibrator 2. One surface of a piezoelectric element 3 made of piezoelectric ceramics is surface-bonded to the vibrator 2. The thin plate electrode 4 made of silver is attached to the other surface of the piezoelectric element 3.

As is clear from FIG. 2, the electrode 4 is formed by being divided into four pieces, and the divided first to fourth electrodes 4a.
~ 4d are each insulated from each other.

In this way, the piezoelectric type acceleration sensor 5 is formed.

FIG. 3 is a circuit diagram showing an operation control circuit of an automobile airbag apparatus in which such a piezoelectric acceleration sensor 5 and its self-diagnosis circuit are incorporated.

As is clear from this figure, the first and second output lines 6 and 7 are connected to the first and third electrodes 4a and 4c facing each other, and these output lines 6 and 7 are connected to one. Now, it is connected to the non-inverting input terminal of the amplifier 8. The output terminal of the amplifier 8 is the first calculation circuit 9 in the operation control circuit of the airbag device.
It is connected to the. The output side of the calculation circuit 9 is the first drive circuit
Further, the drive circuit 10 is connected to the base of a first transistor 12 which constitutes a first switch of an inflator 11 of the airbag device. In the energizing circuit of the inflator 11, another second transistor 13 is provided as a second switch of the inflator 11 in parallel with the first transistor 12. The output terminal of the amplifier 8 is also
In parallel with the connection circuit with the first transistor 12, it is connected to the base of the second transistor 13 via the second calculation circuit 14 and the second drive circuit 15. The inflator 11 is connected to the power supply 17 via the third switch 16. The third switch 16 is operated by, for example, a mechanical acceleration sensor that detects acceleration by an inertial body.

The first and second calculation circuits 9 and 14 respectively drive the first and second drive circuits when the output of the amplifier 8 having a magnitude corresponding to an extremely large deceleration that occurs in the vehicle due to a vehicle collision or the like is input. An output signal is issued to the circuits 10 and 15. Therefore, when the output of the amplifier 8 is relatively small, both calculation circuits 9 and 14 are designed not to output any output signal.

On the other hand, the first and second input lines 18 and 19 are connected to the second and fourth electrodes 4b and 4d of the sensor 5, respectively, and these input lines 18 and 19 are connected to one pulse generating circuit. Connected to 20. A diagnostic circuit 21 is also connected to the pulse generation circuit 20. Further, the output terminal of the amplifier 8 is connected to the diagnostic circuit 21, and the output side of the diagnostic circuit 21 is a display lamp.
Connected to 22.

The case 1 of the piezoelectric acceleration sensor 5 is fixed to the vehicle body, and the vibrator 2 of the sensor 5 is grounded via the case 1 and the vehicle body.

Next, the operation of the operation control circuit of the airbag device in which the piezoelectric acceleration sensor 5 according to the present embodiment is incorporated will be described.

When a car starts running, acceleration occurs in the car. When acceleration occurs in the vehicle, the sensor 5 is proportional to the acceleration.
The oscillator 2 is relatively displaced with respect to the case 1. Due to such relative displacement of the vibrator 2, a strain proportional to the relative displacement is generated in the piezoelectric element 3, and the piezoelectric element 3 generates a voltage having a magnitude proportional to the strain amount. The voltage is first,
It is output from the third electrodes 4a and 4c. That is, the first and the third
The electrodes 4a and 4c form the output terminal of the sensor 5. In that case, since the first and third electrodes 4a and 4c are arranged so as to face each other, their outputs are averaged.
Therefore, the voltage signals output from the electrodes 4a and 4c have higher accuracy.

In this way, the piezoelectric acceleration sensor 5 detects the acceleration generated in the vehicle.

Output signals from the first and third electrodes 4a and 4c are input to the non-inverting input terminal of the amplifier 8 through the first and second output lines 6 and 7 and amplified. The amplified output signal is the first and second calculation circuits.
Input to 9,14.

When the acceleration of the vehicle is smaller than the predetermined value, the output of the amplifier 8 is also small, so that both calculation circuits 9 and 14 generate no output signal. Therefore, the airbag device does not operate.

When the vehicle has a large deceleration exceeding a predetermined value due to a collision or the like, the output signal of the sensor 5 also becomes extremely large.
Therefore, both calculation circuits 9 and 14 carry out a calculation and generate an output signal. The output signals activate the drive circuits 10 and 15 to make the first and second transistors 12 and 13 conductive. That is, the first and second switches are closed.

On the other hand, when such a large deceleration occurs in the vehicle, the mechanical acceleration sensor also operates, so that the third switch 16 is also closed. Therefore, the energizing circuit of the inflator 11 is closed. As a result, the inflator 11 is activated to explode the explosive and inflate the airbag (not shown). Thereby, the occupant is held in the seat. In that case, a circuit including the first calculation circuit 9, the first drive circuit 10, and the first transistor 12, the second calculation circuit 14, the second drive circuit 15, and the second
Since the circuit including the transistor 13 is provided in parallel, the airbag device operates even if one of the circuits fails. That is, the piezoelectric acceleration sensor 5
The signal transmission circuit from 1) forms a redundant system.

Further, even if the deceleration of the vehicle is not large, even if one of the first and second switches and the third switch 16 is closed for some reason, the energizing circuit of the inflator 11 is not closed. Therefore, the inflator 11 does not operate, and malfunction of the airbag device is prevented.

On the other hand, in diagnosing whether the piezoelectric acceleration sensor 5 operates normally, the pulse generation circuit 20 outputs a diagnostic pulse signal. The pulse signal is input to the second and fourth electrodes 4b and 4d of the sensor. That is, the second,
The fourth electrodes 4b and 4d are input terminals for the diagnostic pulse signal. When the sensor 5 operates normally, the piezoelectric element 3 is distorted when receiving a voltage due to such a pulse signal. That is, the piezoelectric element 3 is in the same state as when mechanical force is applied. Therefore, the piezoelectric element 3 generates piezoelectricity proportional to the strain. The generated voltage is output from the first and third electrodes 4a and 4c, and the output signal is amplified by the amplifier 8 and input to the diagnostic circuit 21. Further, since the diagnostic pulse signal from the pulse generating circuit 20 is also input to the diagnostic circuit 21, the diagnostic circuit 21 determines whether the output signal from the sensor 5 is set for the diagnostic signal. To judge. If it is determined that the output signal is the set signal, it is determined that the sensor 5 is normal,
The diagnostic circuit 21 turns on the display lamp 22. Therefore,
It is confirmed that the piezoelectric acceleration sensor 5 operates normally.

When the sensor 5 is in an abnormal state such as a failure,
When the voltage generated by the diagnostic signal from the pulse generating circuit 20 is received, the voltage element 3 is not distorted at all, or even if it is generated, the distortion is not proportional to the magnitude of the voltage of the diagnostic signal.
The magnitude of the voltage generated by the distortion is also not proportional to the magnitude of the voltage of the diagnostic signal. Therefore,
The sensor 5 outputs no signal at all, or outputs a defective signal which is not a setting signal corresponding to the diagnostic signal even if it is output. If no signal is input or if such a defect signal is input, the diagnostic circuit 21 determines that the sensor 5 is abnormal and does not turn on the display lamp 22. Thereby, it is recognized that the piezoelectric acceleration sensor 5 is abnormal. In this way, the second and fourth electrodes 4b and 4d, the pulse generating circuit 20, the diagnostic circuit 21, and the display lamp 22 constitute a self-diagnostic circuit of the sensor 5.

By the way, it is conceivable that the output signal of the sensor 5 at the time of diagnosis of the sensor 5 is also input to the airbag operation control circuit, and the signal causes the inflator 11 to malfunction. Therefore, in order to avoid such malfunction, even if the output signal of the sensor 5 at the time of diagnosis is input to the calculation circuits 9 and 14, the calculation circuits 9 and 14 drive the output signal by the signal.
You need to make sure you don't call out at 10,15. In that case, the calculation circuits 9 and 14 are designed to output to the drive circuits 10 and 15 only when a signal of a predetermined magnitude, that is, an extremely large signal due to a vehicle collision or the like is input. If the output signal of the sensor 5 is relatively small, the drive circuits 10 and 15 will not operate. Therefore, the pulse generation circuit 20 may be designed so as to emit a diagnostic pulse having a relatively small voltage.

FIG. 4 is a plan view similar to FIG. 2, showing another embodiment of the piezoelectric acceleration sensor according to the present invention.

The same reference numerals are given to the portions corresponding to those in the above-mentioned embodiment, and the description thereof will be omitted.

As is apparent from FIG. 4, the first electrode 4a and the third electrode 4c are electrically connected to each other by the pair of first connecting portions 23,23. Similarly, the second electrode 4b and the fourth electrode 4d are electrically connected to each other by the pair of second connecting portions 24, 24.

With such a configuration, considering the case where the sensor 5 is incorporated into the operation control circuit of the airbag device shown in FIG. 3, for example, the outputs connected to the first and third electrodes 4a and 4c Even if one of the lines 6 and 7 is broken, the output can be reliably obtained from the other output line 7 and 6. In that case, since the voltages generated at the first and third electrodes 4a and 4c are both output, the function of the sensor 5 does not deteriorate. That is, in the piezoelectric sensor 5 of this embodiment, a redundant system is formed by connecting the first and third electrodes 4a and 4c and connecting the output lines 6 and 7 to the electrodes 4a and 4c, respectively. To be done. Similarly, the second and fourth electrodes 4b, 4
Even if one of the input lines 18 and 19 connected to d is disconnected, the other input line 19 and 18 is connected to the second and fourth electrodes 4b and 4d.
Since the diagnostic pulse signal can be reliably input to
The function of the sensor 5 does not deteriorate. That is, also in this case, a redundant system is formed.

As described above, the piezoelectric acceleration sensor 5 has a self-diagnosis function of diagnosing whether the sensor itself is normal or abnormal, in addition to the sensor function of detecting acceleration.

Therefore, when diagnosing the sensor, the state of the sensor 5 can be surely grasped by giving the diagnostic pulse signal to the sensor 5 with the sensor 5 installed in the vehicle. In that case, it is necessary to incorporate the pulse generation circuit 20, the diagnostic circuit 21, and the indicator lamp 22 into the operation control circuit of the airbag device, but it is extremely easy to incorporate them, and moreover, a space for incorporation is especially required. do not need. Therefore, a vibrating device for vibrating the sensor 5 is not necessary and it is not necessary to remove the sensor 5 from the vehicle, so that the sensor 5 can be easily diagnosed at all times. Thereby, the sensor 5
Can always be maintained in a normal state.

Although the electrode 4 is divided into four in the above-described embodiment, the present invention is not limited to this, and the number of divisions can be set appropriately. Electrode 4
Can be divided into two. In that case, one of the electrodes 4 may be used for outputting an acceleration signal and the other one may be used for inputting a diagnostic pulse signal, but since there is only one input / output line, no redundant system is formed. Therefore, it is desirable to divide the electrode 4 into four or more parts in order to form a redundant system.

Further, in the above-described embodiment, the piezoelectric acceleration sensor 5 is used in the operation control circuit of the airbag device.
The sensor 5 can be used for general acceleration measurement as well as other control circuits of an automobile requiring an acceleration signal.

(Effects of the Invention) As is clear from the above description, according to the present invention, the electrodes provided in the piezoelectric element of the piezoelectric acceleration sensor are divided into a plurality of parts, and a part of the divided electrodes outputs an acceleration detection signal. The sensor has both a sensor function for detecting the acceleration of the moving body and a diagnostic function for diagnosing the state of the sensor itself, since the rest are the input terminals to which the diagnostic voltage signal is input. Becomes That is, by outputting a voltage proportional to the acceleration of the moving body generated by the piezoelectric element from the output terminal, the acceleration of the moving body can be reliably detected. Further, by supplying an electrical diagnostic signal to the input terminal of the sensor, a strain is generated in the piezoelectric element, the voltage generated by the piezoelectric element due to the strain is output from the output terminal, and the output corresponds to the diagnostic signal. An abnormal state of the sensor can be reliably detected by simply examining whether or not it is a thing. Therefore, since the sensor does not have to be removed from the vehicle, it is possible to diagnose the sensor easily and at any time in a short time without any trouble. Moreover, since special auxiliary equipment such as a vibration device for vibrating the sensor is not required, the equipment cost is not required, which is extremely economical.

Further, there is an effect that the piezoelectric acceleration sensor and its self-diagnosis circuit can be easily incorporated into an operation control circuit of a device controlled by vehicle acceleration such as an airbag device without requiring any space.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing an embodiment of a piezoelectric acceleration sensor according to the present invention, and FIG. 2 is a view of the piezoelectric acceleration sensor seen from the direction of arrow A in FIG. A plan view and FIG. 3 are circuit diagrams showing a state in which the piezoelectric acceleration sensor and its self-diagnosis circuit are incorporated in an operation control circuit of an airbag device in an automobile, and FIG. 4 is a piezoelectric acceleration sensor according to the present invention. It is a top view similar to FIG. 2 which shows another Example. 1 ... Case, 2 ... Transducer 3 ... Piezoelectric element, 4 ... Electrode 4a ... 1st electrode (output terminal) 4b ... 2nd electrode (input terminal) 4c ... 3rd electrode (output terminal) 4d ... 4th electrode (input) Terminal) 5 ... Piezoelectric acceleration sensor

Claims (1)

[Claims] 1. A flat plate-shaped vibrator mounted on a case fixed to a moving body so as to be relatively displaceable, a piezoelectric element having one surface bonded to the vibrator, and a piezoelectric element on the other surface of the piezoelectric element. A piezoelectric type that is provided with an attached electrode, and when the moving body is accelerated, the vibrator displaces relative to the case and the piezoelectric element is distorted to generate a voltage proportional to the acceleration. In the acceleration sensor, the electrode is divided into a plurality of parts, a part of the divided electrode is an output terminal for outputting a voltage signal proportional to the acceleration, and the other part of the electrode is a diagnostic voltage signal. A piezoelectric acceleration sensor that is used as an input terminal for inputting.