JP2920530B2 - Control device for occupant restraint system with piezoelectric acceleration sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an occupant restraint device for controlling the operation of an occupant restraint device such as an airbag device. The present invention relates to a control device for an occupant restraint device using a piezoelectric acceleration sensor including a piezoelectric element that generates a corresponding voltage. 2. Description of the Related Art An automobile is often equipped with an occupant restraint device such as an airbag device for protecting an occupant in the event of a collision. Such occupant restraint systems are typically only activated in the event of a vehicle collision. Therefore, it is necessary to use a sensor for detecting a vehicle collision in a control device for controlling the operation of the occupant restraint device. An acceleration sensor is generally used as the collision detection sensor. When the acceleration sensor detects a deceleration of the vehicle larger than a predetermined value, that is, a negative acceleration, it is determined that a collision has occurred in the vehicle, and the occupant restraint device is driven. [0003] Conventionally known as a control device for an occupant restraint device using such an acceleration sensor is an operation control device for an airbag device as disclosed in Japanese Patent Publication No. 58-22377. is there. In the control device, a piezoelectric acceleration sensor is used to operate the airbag device at the time of a collision of an automobile. In a piezoelectric acceleration sensor, a plate-shaped piezoelectric element is attached so as to be distorted in accordance with the magnitude of acceleration at that time, and a change in the amount of electricity generated due to the distortion is taken out. Therefore, the piezoelectric element is provided with electrodes for detecting a change in the amount of electricity on one or both surfaces. Since such a piezoelectric acceleration sensor has a simple structure, is small and lightweight, and has a wide measurement level range, it is most often used for a control device such as an occupant restraint device mounted on an automobile. The control device described in the above publication is
The acceleration generated in the vehicle is constantly detected by such a piezoelectric acceleration sensor, a voltage corresponding to the magnitude of the acceleration at that time is generated, and when the detected voltage is equal to or higher than a predetermined value, the inflator is activated to operate the airbag. Is expanded and deployed. Conventionally, a piezoelectric acceleration sensor used for a control device of such an occupant restraint system is considered to be sufficient for the purpose of detecting only acceleration, and the electrode provided on one surface of the piezoelectric element is a single electrode. It was supposed to be. [0005] By the way, an occupant restraint device such as an airbag device must be reliably operated at the time of a vehicle collision. On the other hand, if it operates even during normal traveling, it may hinder driving. Therefore, the acceleration sensor for detecting the collision needs to be always kept normally in order to accurately detect the acceleration generated in the vehicle at that time. Therefore, it is essential that the acceleration sensor used in the control device of such an occupant restraint device be periodically diagnosed. However, the conventional piezoelectric acceleration sensor has only a sensor function for detecting acceleration as described above. Therefore, in order to perform the diagnosis, it is necessary to provide special auxiliary equipment such as a vibration device and mechanically apply vibration, impact, and the like to the sensor. Such ancillary equipment is generally large and cannot be always mounted on a general automobile such as a passenger car.
In addition, for example, in the case of an airbag device, once activated, it cannot be reused. Therefore, when diagnosing the sensor in this manner, it is necessary to prevent the inflator from erroneously operating. for that reason,
When diagnosing a piezoelectric acceleration sensor, it is necessary to remove only the sensor part from the vehicle. As a result, in the case of a vehicle equipped with a conventional occupant restraint system using a piezoelectric acceleration sensor, the vehicle itself must be regularly brought to a maintenance shop or the like in order to diagnose the acceleration sensor. Have been. SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to provide a piezoelectric acceleration sensor used in a control device of an occupant restraint apparatus while the occupant restraint apparatus is installed in a vehicle. It is an object of the present invention to obtain a control device for an occupant restraint device, which can easily make a diagnosis at any time. According to the present invention, a voltage corresponding to the acceleration of a vehicle is generated by a piezoelectric acceleration sensor. In the control device of the occupant restraint device that operates the restraint device, the electrode attached to the piezoelectric element of the acceleration sensor is divided into a plurality of parts, and a part of the electrodes is used as a signal corresponding to the distortion of the piezoelectric element. The electrodes are used as output terminals, and the rest of the electrodes are used as input terminals to which a diagnostic voltage signal is input. A drive circuit for operating the occupant restraint device and a diagnostic circuit for performing self-diagnosis of the piezoelectric acceleration sensor are connected to the output terminal. The diagnostic voltage signal is a signal in which the drive circuit of the occupant restraint device does not operate depending on the signal output from the output terminal when the diagnostic voltage signal is input, for example, a sufficiently low voltage signal. With this configuration, when acceleration occurs in the vehicle, the piezoelectric element of the piezoelectric acceleration sensor is distorted, and a voltage signal corresponding to the acceleration at that time is output from its output terminal. That is, the acceleration is detected by the sensor. When the acceleration at that time is extremely large and a voltage equal to or higher than a predetermined value is output from the acceleration sensor, it is determined that the vehicle has collided, and the drive circuit for operating the occupant restraint device is driven.
On the other hand, when a diagnostic voltage signal is input to the input terminal of the piezoelectric acceleration sensor, when the sensor is normal, distortion occurs in the piezoelectric element in proportion to the input voltage. That is,
This is equivalent to a state where the piezoelectric element is distorted by the acceleration of the vehicle. Then, a voltage signal of a predetermined magnitude is output from the output terminal of the piezoelectric acceleration sensor. Therefore, the voltage signal confirms that the sensor is normal. Further, if the sensor is abnormal, even if a diagnostic voltage signal is input, a voltage signal of a 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. In this case, since the diagnostic voltage signal is a signal that does not activate the drive circuit of the occupant restraint device, the occupant restraint device does not operate even if the diagnostic voltage signal is input to the piezoelectric acceleration sensor. Thus, the piezoelectric acceleration sensor has a sensor function of detecting acceleration and a self-diagnosis function of detecting abnormality of the sensor itself. Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 show an example of a piezoelectric acceleration sensor used in a control device of an occupant restraint system according to the present invention. FIG. 1 is a longitudinal sectional view of the sensor, and FIG. It is the top view of the principal part of the sensor seen from the arrow A direction. As is apparent from FIG. 1, the piezoelectric acceleration sensor includes a cylindrical case 1. The case 1 is formed of a metal or a conductive resin, and has a protruding portion 1a at the center of the bottom surface. The center of the circular vibrator 2 made of a thin metal plate is fixed to the protruding portion 1a by an appropriate fixing means. The outer peripheral edge of the vibrator 2 is free, and the outer peripheral edge can be displaced relative to the case 1 by bending and deforming the vibrator 2.
One surface of a piezoelectric element 3 formed of piezoelectric ceramics is surface-bonded to the vibrator 2. A thin plate-shaped electrode 4 made of silver is attached to the other surface of the piezoelectric element 3. As is apparent from FIG. 2, the electrode 4 is divided into four parts. Then, the divided first to fourth electrodes 4a to 4d
Are insulated from each other. In this way,
A piezoelectric acceleration sensor 5 is formed. When the piezoelectric acceleration sensor 5 is used as a vehicle collision detection sensor, the case 1 is fixed to the vehicle body such that the vibrator 2 is bent by the collision. For example, the axis of the case 1 is made to coincide with the traveling direction of the vehicle. The vibrator 2 is grounded via the case 1 and the vehicle body. FIG. 3 is a circuit diagram showing an operation control device of an automobile airbag device as an example of a control device of an occupant restraint device according to the present invention, in which the piezoelectric acceleration sensor 5 is incorporated. As is apparent from this figure, the first and third electrodes 4a and 4a of the piezoelectric acceleration sensor 5 facing each other.
The first and second output lines 6 and 7 are connected to c, respectively. The output lines 6 and 7 are connected to one and connected to the non-inverting input terminal of the amplifier 8. The amplifier 8
Are connected to the first calculation circuit 9. Also,
The output side of the calculation circuit 9 is connected to the first drive circuit 10. The drive circuit 10 is connected to the base of a first transistor 12 that forms a first switch of an inflator 11 that inflates and deploys an airbag. The energizing circuit of the inflator 11 includes the inflator 11
As a second switch, another second transistor 1
3 is provided in parallel with the first transistor 12. The output terminal of the amplifier 8 is also connected to the base of the second transistor 13 via the second calculation circuit 14 and the second drive circuit 15. Further, the inflator 11 has a third
It is connected to a power supply 17 via a 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, 14 are only activated when the output of the amplifier 8, which has a magnitude corresponding to a very large deceleration, such as occurs in a vehicle during a collision, is input.
Output signals are sent to the first and second drive circuits 10 and 15, respectively. Therefore, when the output of the amplifier 8 is relatively small, no signal is output from any of the calculation circuits 9 and 14. 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 piezoelectric acceleration sensor 5, respectively.
Are connected respectively. Those input lines 18, 19
Are connected to a single line and connected to the pulse generation circuit 20. A diagnosis circuit 21 is also connected to the pulse generation circuit 20. The output terminal of the amplifier 8 is connected to the diagnostic circuit 21, and the output side of the diagnostic circuit 21 is connected to the display lamp 22. The pulse signal generated from the pulse generation circuit 20 has a relatively low voltage. Next, the operation of the operation control device for an airbag device configured as described above will be described. As described above, the piezoelectric acceleration sensor 5 is fixed to the vehicle body, for example, such that the axis of the case 1 coincides with the traveling direction of the automobile. Therefore, when the vehicle starts running and acceleration occurs in the vehicle, the vibrator 2 of the sensor 5 bends in accordance with the acceleration, and the outer peripheral edge is displaced relative to the case 1. The relative displacement of the vibrator 2 causes distortion in the piezoelectric element 3 in proportion to the relative displacement, and the piezoelectric element 3 generates a voltage having a magnitude proportional to the amount of the distortion. The voltage is output from the first and third electrodes 4a and 4c. That is, the first and third electrodes 4a, 4c
Constitutes an output terminal of the sensor 5. In that case, the first
Since the third electrode 4a and the third electrode 4c are arranged to face each other, their outputs are averaged. Therefore, the voltage signals output from the electrodes 4a and 4c have higher accuracy. Thus, the acceleration generated in the vehicle is detected by the piezoelectric acceleration sensor 5. 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 are amplified. The amplified output signal is input to the first and second calculation circuits 9 and 14. When the acceleration of the vehicle is smaller than the predetermined value, the output of the amplifier 8 is also small, so that each of the calculation circuits 9 and 14 does not emit any output signal. Therefore, the airbag device does not operate. When the vehicle receives a large deceleration exceeding a predetermined value due to a collision or the like, the output signal of the sensor 5 becomes extremely large. Therefore, each of the calculation circuits 9 and 14 determines the result by an operation and generates an output signal. Then, the respective drive circuits 10 and 15 are operated by the output signal, and the first and second transistors 12 and 13 are turned on. 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 energization circuit of the inflator 11 is closed. As a result, the inflator 11 operates to explode the explosive and inflate an airbag (not shown). Thereby, the occupant is held in the seat. In that case, the first calculation circuit 9, the first
Since the circuit including the drive circuit 10 and the first transistor 12 and the circuit including the second calculation circuit 14, the second drive circuit 15, and the second transistor 13 are provided in parallel, one of the circuits is provided. Even if it fails, the airbag device operates. That is, the piezoelectric acceleration sensor 5
, Constitute a redundant system. Further, even if one of the first and second switches and the third switch 16 is closed for some reason even if the deceleration of the vehicle is not large, 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. In this way, the operation control device of the airbag device constantly monitors the acceleration generated in the vehicle, and reliably operates the airbag device in the event of a collision of the vehicle. Can be prevented. On the other hand, in diagnosing whether the piezoelectric acceleration sensor 5 operates normally, the pulse generation circuit 20 outputs a diagnostic voltage pulse signal. The pulse signal is input to the second and fourth electrodes 4b and 4d of the sensor 5. That is, the second and fourth electrodes 4b, 4d
Are input terminals for a diagnostic voltage signal. When the sensor 5 operates normally, the piezoelectric element 3 is distorted when receiving a voltage based on such a pulse signal. That is, the piezoelectric element 3 is in the same state as when a force is applied mechanically. Therefore, the piezoelectric element 3 generates a voltage proportional to the distortion. Then, the generated voltage is output from the first and third electrodes 4a and 4c, which are output terminals, and the output signal is amplified by the amplifier 8 and input to the diagnostic circuit 21. The diagnostic circuit 21 includes a pulse generation circuit 2
A diagnostic pulse signal from 0 is also input. Diagnostic circuit 2
1 judges whether the signal output from the sensor 5 is a set signal with respect to the diagnostic pulse signal. If the output signal is as set, the sensor 5 determines that the sensor 5 is normal, and 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, the piezoelectric element 3 does not generate any distortion or receives the distortion even when receiving the voltage based on the diagnostic pulse signal from the pulse generating circuit 20. Even if it occurs, the distortion is not proportional to the magnitude of the voltage of the diagnostic pulse signal. And
The magnitude of the voltage generated by the distortion is not proportional to the magnitude of the voltage of the diagnostic pulse signal. Therefore, no signal is output from the sensor 5, or even if it is output, it becomes a failure signal that is not a setting signal corresponding to the diagnostic pulse signal. The diagnostic circuit 21 determines that the sensor 5 is abnormal when the signal from the pulse generation circuit 20 is input, when the signal from the sensor 5 is not input, or when such a defective signal is input. Then, the display lamp 22 is not turned on. Thereby, it is recognized that the piezoelectric acceleration sensor 5 is abnormal. Thus, the second and fourth electrodes 4b, 4b,
The self-diagnosis of the piezoelectric acceleration sensor 5 can be performed by inputting the diagnostic voltage signal to 4d. By the way, the output signal of the sensor 5 at the time of self-diagnosis of the piezoelectric acceleration sensor 5 is also input to the drive circuit of the airbag device. Therefore, the signal may cause the inflator 11 to malfunction. Therefore, in order to avoid such a malfunction,
Output signals of the sensor 5 at the time of diagnosis are calculated by the calculation circuits 9 and 14.
, The drive circuits 10 and 15 do not operate. That is, as described above, the calculation circuit 9,
Reference numeral 14 is designed to output a signal 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. on the other hand,
The pulse generation circuit 20 is designed to transmit a diagnostic pulse signal having a relatively low voltage, so that the output signal of the sensor 5 at the time of diagnosis is relatively small. Therefore, when the piezoelectric acceleration sensor 5 performs self-diagnosis, the driving circuit 1
0,15 does not work. FIG. 4 shows another example of the piezoelectric acceleration sensor used in the control device of the occupant restraint device according to the present invention.
FIG. 3 is a plan view similar to FIG. 2. This piezoelectric acceleration sensor 5
In the case of (1), 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 a pair of second connection portions 24, 24. With this configuration, considering that the sensor 5 is incorporated in, for example, the operation control device of the airbag device shown in FIG. 3, the output line connected to the first and third electrodes 4a and 4c. Even if one of the lines 6 and 7 is broken, an output can be reliably obtained from the other output lines 7 and 6. In that case, the first and third electrodes 4
Since the voltages generated at a and 4c are both output, the sensor function of the sensor 5 does not deteriorate. That is, in the piezoelectric acceleration sensor 5, 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. You. Similarly, the second and fourth electrodes 4
Even if one of the input lines 18 and 19 connected to b and 4d is disconnected, the diagnostic pulse signal is reliably input to the second and fourth electrodes 4b and 4d from the other input line 19 and 18. Therefore, the self-diagnosis function of the sensor 5 does not decrease. That is, also in this case, a redundant system is formed. As described above, the piezoelectric acceleration sensor 5 used in the present invention has a self-diagnosis function for diagnosing whether the sensor itself is normal or abnormal, in addition to a sensor function for detecting acceleration. I have. At the time of the diagnosis, an occupant restraint device such as an airbag device does not malfunction. Therefore, the diagnosis of the control device of the occupant restraint device including the piezoelectric acceleration sensor 5 can be performed while the occupant restraint device is mounted on the vehicle. As a result, the diagnosis is performed very accurately, and the sensor 5 can be always maintained in a normal state. In the above description, the electrode 4 of the piezoelectric acceleration sensor 5 is divided into four parts. However, the present invention is not limited to this, and the number of divisions can be set as appropriate. For example, the electrode 4 may be divided into two parts. In that case, one of the electrodes 4 may be used for signal output, and the other may be used for diagnostic pulse signal input. However, in such a case, since each of the input and output lines becomes one,
No redundant system is formed. In order to form a redundant system, it is desirable that the electrode 4 be divided into four or more. Also, as an occupant restraint device using the piezoelectric acceleration sensor 5, an airbag device has been described as an example,
The control device using the acceleration sensor 5 can be applied to other occupant restraint devices such as a safety belt device that operates at the time of an automobile collision. As is apparent from the above description, according to the present invention, the electrode provided on the piezoelectric element of the piezoelectric acceleration sensor is divided into a plurality of parts, and a part of the divided electrodes is used as a signal. Since the output terminal is used as an output terminal and the remaining input terminal is used as an input terminal for inputting a diagnostic voltage signal, the sensor performs self-diagnosis of the state of the sensor itself in addition to the sensor function for detecting vehicle acceleration. It also has a diagnostic function to perform. When the voltage output from the output terminal is greater than a predetermined value, the occupant restraint device is operated, so that it can function in the same manner as a conventional control device for an occupant restraint device. Further, since the diagnostic voltage signal input to the input terminal is a signal in which the drive circuit of the occupant restraint device does not operate depending on the signal output from the output terminal at that time, malfunction of the occupant restraint device during diagnosis is also prevented. be able to. Therefore, the diagnosis can be performed at any time while the occupant restraint device is mounted on the vehicle, and the control device can always be kept in a normal state.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectional view showing an example of a piezoelectric acceleration sensor used for a control device of an occupant restraint device according to the present invention. FIG. 2 is a plan view of a main part of the piezoelectric acceleration sensor as viewed from the direction of arrow A in FIG. FIG. 3 is a circuit diagram showing an operation control device of an airbag device of an automobile as an example of a control device of an occupant restraint device according to the present invention. FIG. 4 is a plan view similar to FIG. 2, showing another example of a piezoelectric acceleration sensor used in the present invention. [Description of Signs] 3 Piezoelectric element 4 Electrode 4a First electrode (output terminal) 4b Second electrode (input terminal) 4c Third electrode (output terminal) 4d Fourth electrode (input terminal) 5 Piezoelectric acceleration sensor 9 First Calculation circuit 10 First drive circuit 11 Inflator 14 Second calculation circuit 15 Second drive circuit 20 Pulse generation circuit 21 Diagnostic circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01P 21/00 G01P 15/00 G01P 15/09 B60R 21/32

Claims (1)

(57) [Claims] An electrode is provided on at least one surface, and comprises a piezoelectric element attached to the vehicle so as to be distorted according to the magnitude of the acceleration when acceleration is generated in the vehicle. A piezoelectric acceleration sensor that generates a voltage corresponding to the acceleration at that time by taking out from the electrodes, and is configured to operate the occupant restraint device when a detection voltage output from the piezoelectric acceleration sensor is equal to or more than a predetermined value. The electrode is divided into a plurality of parts, and some of the divided electrodes are output terminals for outputting a signal corresponding to the distortion of the piezoelectric element. In addition, the other part of the electrode is an input terminal to which a diagnostic voltage signal is input, and a drive circuit for operating the occupant restraint device is provided to the output terminal. And a diagnostic circuit for performing self-diagnosis of the piezoelectric acceleration sensor, wherein the diagnostic voltage signal input to the input terminal is a signal at which the drive circuit does not operate depending on a signal output from the output terminal at that time. A control device for an occupant restraint device provided with a piezoelectric acceleration sensor.