JPH05322921A - Acceleration sensor and air bag system using the same - Google Patents

Abstract

PURPOSE:To enhance the fail-safe functions of a sensor and a system by performing the self-diagnosis for the fault, the deterioration of performances and the time change of an acceleration sensor. CONSTITUTION:When a diagnosis mode is set, a diagnostic signal VG is generated in a diagnostic power supply 22 provided in a signal applying part 19. The signal is added to a detecting voltage VS1 in an adder 23. The result is applied to a fixed electrode 7 of a sensor. Thus, electrostatic force corresponding to acceleration is generated between the fixed electrode 7 and a movable electrode 6. In the sound case, the mass part 6 is adequately displaced. The change in capacitance between the movable electrode and the fixed electrode when the diagnostic signal is generated is detected, and the acceleration sensor undergoes self-diagnosis. The force corresponding to the acceleration can be the mechanical vibration generated with electromagnetic force or an electrostrictive element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor and an air bag system using the acceleration sensor.

[0002]

2. Description of the Related Art For example, as a sensor for detecting the acceleration of an automobile or the like, a capacitance type, a strain gauge type and the like are known. These capture the state of the mass portion which is displaced according to the acceleration, from the change in capacitance or the amount of strain.

As an example, an electrostatic capacitance type acceleration sensor using a fine processing technique of silicon or the like is known, and as disclosed in Japanese Patent Application Laid-Open No. 1-253657, a pulse width modulation servo is disclosed. Some have applied technology.

This has a movable electrode (corresponding to a mass portion) which is displaced in response to acceleration, and at least a pair of fixed electrodes arranged so as to face the movable electrode, and a pulse train voltage is applied to one of the fixed electrodes. , And the reverse voltage is applied to the other. With these applied voltages, an electrostatic force that can control the position of the movable electrode (electrostatic servo control) is exerted between the fixed electrode and the movable electrode, and when the movable electrode is displaced from the reference position,
The displacement is captured by the change in the electrostatic capacitance between the movable electrode and the fixed electrode.

Then, based on the change signal of the electrostatic quantity, the electrostatic force is applied to the movable electrode so that the movable electrode can return to the reference position (the electrostatic capacitance becomes the reference value). It is variably controlled by changing the application time ratio per hit, and the acceleration is detected based on the average value of the fixed electrode applied voltage or the change signal of the electrostatic capacity.

In addition, there is a capacitance type acceleration sensor which does not apply electrostatic servo.

[0007]

Accelerometers used for automobiles are used for vehicle control such as suspension control and anti-skid brake control, and for airbag systems, but the environment in which they are used is severe but high. Reliability is required. Therefore, fail-safe measures are required for sensor failures and performance degradation.

In particular, an airbag may cause a serious accident because failure of a sensor, deterioration of performance, and changes in characteristics with time lead to non-operation during a vehicle collision or malfunctions other than during a collision. Higher reliability is required than other sensors.

The present invention has been made in view of the above points, and an object of the present invention is to enhance the fail-safe function by detecting an abnormality such as a failure of an acceleration sensor, a performance deterioration, or a change in characteristics over time.

[0010]

In order to achieve the above object, the present invention basically proposes the following problem solving means.

That is, in an acceleration sensor having a mass portion that is displaced according to acceleration, and converting the displacement of the mass portion into an electric signal to detect acceleration, a force corresponding to the acceleration is applied to the mass portion by a diagnostic signal. And means for self-diagnosing the acceleration sensor from the sensor output when the diagnostic signal is generated.

[0012]

According to the present invention having the above-described structure, when the normal acceleration detection mode is changed to the diagnostic mode and a diagnostic signal is generated, the mass section is forced to generate a force (e.g., electrostatic force) corresponding to the acceleration based on the diagnostic signal. , Electromagnetic force, mechanical vibration, etc.) is given.

In this case, if the mass section is normally displaced and a detection signal corresponding thereto is output, there is no abnormality, but if an abnormality such as a failure or performance deterioration occurs in the detection system, the detection signal is output. Or the output characteristics do not appear properly. By applying the sensor output mode caused by these diagnostic signals to the determination level for diagnosis, the state of the sensor such as the mass part can be self-diagnosed, and the fail-safe function of the system can be operated based on the diagnostic result. ..

[0014]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1A is a diagram showing the operating principle of the capacitance type acceleration sensor according to the first embodiment of the present invention, and FIG. 1B is a circuit diagram thereof.

This sensor comprises a signal applying section 19, an acceleration detecting element 18, a capacitance detecting section 13, an amplifying section 14, and a circuit 15 serving as a self-diagnosis means.

The acceleration detecting element 18 is a silicon beam 5.
And a pair of fixed electrodes 7 and 8 arranged to face the movable electrode 6.

The silicon beam 5 and the movable electrode 6 are integrally formed by etching the silicon 9 from both sides (microfabrication technology). The beam 5 may be composed of either a single beam or a plurality of beams. Movable electrode 6 which is the mass part
Are formed, and the remaining portions become spacers 9a and 12 that surround the movable electrode 6.

The fixed electrodes 7 and 8 are made of a metal material such as aluminum, and are formed on the glass plates 10 and 11 by vapor deposition or any other suitable method. The glass plates 10 and 11 are arranged in parallel via the spacers 9a and 12 while aligning the fixed electrodes 7 and 8 with the movable electrode 6, respectively, and are anodically bonded to the spacers 9a and 12. Movable electrode 6
And an initial gap do is secured between the fixed electrodes 7 and 8.

The signal application unit 19 applies a signal VS1 or VS2 (the VS1 and VS2 will be described later) necessary for acceleration detection to each of the fixed electrodes 7 and 8 in the normal acceleration detection mode, and a diagnostic mode. Sometimes diagnostic signal V
G is added to VS1 and applied to one fixed electrode 7 to serve as a means for applying a force equivalent to acceleration to the movable electrode 6.

The movable electrode 6 is displaced by receiving an inertial force due to the acceleration to be detected. When the movable electrode 6 is displaced, the electrostatic capacitance C1 between the movable electrode 6 and the fixed electrode 7 and the movable electrode 6
-The capacitance C2 between the fixed electrodes 8 changes.

The capacitance detector 13 has a rectangular wave AC voltage VS2 generated by the signal applying unit 19 and its inverted voltage VS.
The difference ΔC between C1 and C2 is detected by 1 (the detection mechanism of ΔC is described later), converted into a voltage and output. The output voltage Vo from the capacitance detection unit 13 is the amplification unit 14
By being amplified and adjusted by, the linear output voltage Vout proportional to the acceleration is obtained.

With such a structure, it is possible to detect a high acceleration (about ± 100 G) up to a relatively high frequency (about 1 kHz) with an inexpensive and simple structure.

An example of a specific circuit of the acceleration sensor will be described with reference to FIG.

In this sensor circuit, the oscillator 20 and the inverter 21 are elements of the signal applying section 19, and the output voltage VS1 inverted by the inverter 21 does not generate the voltage VG from the self-diagnosis power supply 22. In the diagnostic mode (normal acceleration detection mode), the voltage is directly applied to the fixed electrode 7 through the adder 23, and the output voltage VS2 of the oscillator 20 is applied to the fixed electrode 8.

In the acceleration detecting element 18, the capacitors C1 and C2 are equivalently connected in series, and the middle thereof is the capacitance detecting section 1.
3 is connected to the inverting terminal side of the operational amplifier 25, and the non-inverting terminal side of the operational amplifier 25 is connected to the constant voltage source 37 of the reference voltage Vα.

When the rectangular wave AC voltage VS1 rises (VS2 falls), C1 is charged and C2 is discharged. At this time, the charge Q1 that moves from C1 to the capacitor Cf on the operational amplifier 25 side (the charge seems to move due to the current that flows during charging / discharging), and C2 to Cf
The charge Q2 that moves to

[0028]

## EQU1 ## Q1 = C1.VS Q2 = -C2.VS.

Here, VS is the voltage value (peak value) of the AC voltages VS1 and VS2. Further, VS is smaller than a self-diagnosis voltage VG described later, and when only VS is applied, the electrostatic force applied to the movable electrode is so small that it can be ignored.

The charge Qf stored in the capacitor Cf is the sum of Q1 and Q2, and is represented by the following equation.

[0031]

## EQU00002 ## Qf = Q1 + Q2 = (C1-C2) VS Further, the voltage V across the capacitance Cf is expressed by the following equation.

[0032]

## EQU3 ## V = Qf / Cf = (C1-C2) VS / Cf The output Vo of the operational amplifier 24 is the voltage V across the capacitance Cf.
Vo is expressed by the following equation.

[0033]

## EQU4 ## Vo =-(C1-C2) VS / Cf + Vα In this way, the capacitance difference ΔC between C1 and C2 when the movable electrode 6 is displaced according to the acceleration is converted into the voltage Vo. Then, the switch 34 is closed in synchronization with the rising of the voltage VS1, the voltage Vo is sampled and held by the capacitor 35, and amplified by the amplifier 26 to become the output voltage Vout. In this way, the acceleration is converted into an electric signal and detected.

The operation of the acceleration sensor in the self-diagnosis mode will be described.

In the present embodiment, means for applying an electrostatic force equivalent to acceleration to the movable electrode (mass part) 6 by the diagnostic signal VG includes one fixed electrode 7 for acceleration detection, a diagnostic voltage source 22, and an adder. 23.

The voltage VG from the diagnostic voltage source 22 is input to the adder 23 only in the diagnostic mode, added to the voltage VS1 from the inverter 21, and the voltage waveform applied to the detection element 18 at this time is shown. 2 shows. As shown in FIG.
G + VS1 is applied to the fixed electrode 7 to generate an electrostatic force having a magnitude corresponding to acceleration between the fixed electrode 7 and the movable electrode 6, whereby the movable electrode 6 is forcibly displaced to the fixed electrode 7 side. To do.

Assuming that the distance between the fixed electrode 7 and the movable electrode 6 is d, the area of the movable electrode 6 is S, and the dielectric constant between the fixed electrode 7 and the movable electrode 6 is ε, the fixed electrode 7 and the movable electrode 6 are The electrostatic force Fs acting between 6 is expressed by the following equation.

[0038]

## EQU00005 ## Fs = .epsilon.SVG ² / 2d ^2, that is, the movable electrode 6 causes the fixed electrode 7 to move due to this electrostatic force.
By displacing to the side, the capacitance C1 formed between the fixed electrode 7 and the movable electrode 6 increases, and conversely, the fixed electrode 8
The capacitance C2 formed between the movable electrodes 6 decreases.

In this state, AC voltages VS1 and VS2 for capacitance detection are applied to the fixed electrodes 7 and 8, respectively, so that the capacitance detection unit 13 including the capacitor 24 and the operational amplifier 25 causes the capacitance C1 Capacitance C
The difference ΔC from 2 is detected by the same principle as the above acceleration detection. Fig. 3 shows the measured acceleration G and the DC voltage V for self-diagnosis.
The relationship with G is shown.

Assuming that the spring constant of the cantilever 5 is kt, the inertial force Fa and the reaction force Ft from the cantilever balance during acceleration measurement, so the displacement x of the movable electrode 6 from the reference position is expressed by the following equation.

[0041]

Equation 6 x = mG / kt From Equation 5 and Equation 6, Equation 7 is derived.

[0042]

(D−x) ² x = εSVG ² / 2kt Equation 8 and Equation 7 are derived from Equations 6 and 7.

[0043]

[Equation 8]

FIG. 3 is a graph showing the relationship between the acceleration G and the voltage VG for self-diagnosis expressed by the equation (8).

From FIG. 3, it is understood that when a certain voltage VG1 for self-diagnosis is applied, the displacement amount of the movable electrode 6 due to the electrostatic force Fs is equal to that when the acceleration G1 is applied.

Therefore, the output voltage of the sensor when the self-diagnosis voltage VG1 is applied becomes equal to the output when the acceleration G1 is applied. By using this characteristic, it is possible to diagnose whether or not the static characteristic of the sensor output (the characteristic of the sensor output value that should be originally obtained with respect to the acceleration) is changing with time. Further, by measuring the time required for the output voltage of the sensor to reach a certain level, it is possible to diagnose the sensor dynamic characteristics (here, the dynamic characteristics are the sensor output response characteristics with respect to acceleration). The diagnosis means (diagnosis unit) will be described later as an example in the airbag system of FIG.

FIG. 4 shows the relationship between the self-diagnosis signal (rectangular wave VG) used for the diagnosis and the output voltage Vout of the sensor.

For example, the time Tr (time constant) at which the voltage Vr becomes 63% of the maximum output voltage Voh is read by an electronic circuit, a microcomputer, or the like, and it is determined whether it is within a certain comparison reference time or more. Therefore, the sensor failure can be self-diagnosed. That is, when it is normal to output a response waveform such as the curve 40, the curve 4
In the case of response waveforms such as 1 and 42, the time Tr to reach Vr becomes long, and self-diagnosis of dynamic characteristics can be performed.

Further, as described above, by comparing the maximum voltage of the sensor output obtained in the diagnostic mode with the normal value, it is possible to self-diagnose a sensor failure or a change in static characteristics over time (for example, a curve). 42).

In this embodiment, self-diagnosis of sensor failure, deterioration of characteristics, and change over time is carried out based on the above-mentioned sensor dynamic characteristics and static characteristics.

By having such a self-diagnosis function, the fact that the acceleration sensor detection system has failed is displayed, or the static characteristics and dynamic characteristics of the sensor do not change over time. In this case, by providing a means (for example, a microcomputer) for correcting the change in the characteristic over time, it is possible to always ensure proper management of the sensor and to operate a fail-safe function such as preventing malfunction. .. In addition, if the latter correction function is given, it is possible to reduce cost and work time because it is not necessary to replace parts in addition to system malfunction prevention.

FIG. 5 shows the circuit configuration of the second embodiment of the present invention. In the figure, the same reference numerals as those in the first embodiment indicate the same or common elements.

The present embodiment differs from the first embodiment in that the signal applying section 19 is provided with a first oscillator 20 and a second oscillator 28, and the first oscillator 20 generates a signal VS for detecting acceleration. The second oscillator 28 generates a diagnostic signal VG, and these oscillators are switched by the switch 27.

FIG. 6 shows the waveform of the voltage applied to the acceleration detecting element 18.

In the diagnostic mode, the switch 27 is connected to the second oscillator 28. Here, the amplitude VG of the rectangular wave of the second oscillator 28 is larger than the amplitude Vs of the rectangular wave of the first oscillator 20, and the duty ratio is large (for example, 95 to 99%).

As described above, when the rectangular wave VG is applied to the detection element 1, the electrostatic force acts and the movable electrode 6 is displaced from the reference position. By detecting the displacement amount and the temporal change of the movable electrode 6 at this time from the sensor output, it is possible to self-diagnose the sensor failure, the characteristic change, and the like.

The output voltage of the operational amplifier 25 at this time is
It can be expressed by the following equation.

[0058]

## EQU00009 ## Vo =-(C1-C2) VG / Cf + V.alpha. This is the same as the expression 5 in the embodiment shown in FIG. 2 except that the voltage VS is replaced with the voltage VG (VS <VG). ..

Therefore, the use of this embodiment has the effect that the sensitivity of the sensor can be increased and the diagnosis can be performed accurately.

Further, since an adder circuit is not required, there is an effect that it can be realized with a simpler circuit configuration.

FIG. 7 shows an example of the self boosting circuit applied to the above embodiment.

Since the power supply voltage of the sensor is a relatively low voltage of about 5 V, it is more effective to boost the voltage for self-diagnosis.

The booster circuit is a charge pump circuit composed of an oscillator 50 (may be shared with the oscillator 20), FET transistors 51 and 52, capacitors 53 and 56, and diodes 54 and 55.

The charges accumulated in the capacitor 53 due to the switching of the transistors 51 and 52 are
Charged to 6. By repeating this at the oscillation frequency, a voltage close to about −VCC is boosted.

With such a circuit configuration,
The boosted voltage for self-diagnosis can be realized with a simple circuit configuration, and the circuit can be integrated.

FIG. 8 shows another embodiment of the booster circuit.

This embodiment comprises an oscillator 50 (may be shared with the oscillator 20), a switch 60, a power supply voltage 61, a transformer 62, and a resistor 63.

By adopting such a circuit configuration, there is an effect that a higher boosted rectangular wave can be easily generated.

FIG. 9 shows an embodiment of the system configuration.

In this embodiment, an acceleration sensor 70, a microcomputer 75, and an airbag 76 are provided, and the microcomputer 75 is further provided with an airbag starting unit 71, a diagnosis unit 72, and a fail-safe function unit 73.

As the acceleration sensor 70, for example, a capacitance type sensor as described above is used.

FIG. 1 is a control flowchart of the above system.
This will be described with reference to 1.

In a normal case where the diagnosis start signal is not output from the diagnosis unit 72 (when self-diagnosis is not performed), the acceleration signal output from the acceleration sensor 70 indicates whether the airbag activation unit 71 operates the airbag. Then, the airbag 76 is controlled.

At the time of self-diagnosis, a diagnosis start signal is output from the diagnosis unit 72, and the acceleration sensor 70 enters the diagnosis mode. Then, the signal output from the acceleration sensor 70 passes through the diagnostic section 72 again to determine whether or not there is a failure. In the case of failure, the fail-safe function section 73 is activated to prevent the airbag 76 from malfunctioning. Starting unit 71
The operation of is locked and the driver is notified of the failure by an indicator or the like.

Further, when the diagnostic signal from the acceleration sensor indicates a characteristic change, the diagnostic unit is set to output a correction signal to the airbag activating unit.

With the system configuration as described above, the reliability of the system can be improved as compared with the conventional one.

FIG. 11 shows another embodiment of the self-diagnosis of the present invention.

In this embodiment, by winding a fine wire 80 such as a metal wire around the detecting element 18 around the coil, an electromagnetic force acts upward, and the movable electrode 6 is displaced upward. Self-diagnosis of the sensor can be performed based on the magnitude of the electromagnetic force and the amount of displacement of the movable electrode 6 (eventually, the change in ΔC) at this time.

Even with such a configuration, there is an effect that the self-diagnosis can be easily performed.

In addition, self-diagnosis can be performed by using a piezoelectric element and applying a pseudo acceleration. Further, it is possible to apply the method described above to an inspection device before shipment of a sensor or a system.

Further, also in a strain gauge type acceleration sensor having a weight serving as a mass part and an elastic support with a strain gauge supporting the weight, the same diagnostic system means as those in the above-mentioned respective embodiments is used. It is possible to configure.

For example, with the same configuration, a weight is formed by fine processing of a semiconductor, a fixed electrode dedicated to diagnosis is arranged facing the weight, and electrostatic force due to the diagnostic signal is applied. Given between the weight and the fixed electrode,
Self-diagnosis of the acceleration sensor by detecting the change in resistance value of the strain gauge, or self-diagnosis of the acceleration sensor by detecting the change in capacitance between the weight and the fixed electrode when the diagnostic signal is generated. Just set it.

[0083]

As described above, according to the present invention, the self-diagnosis of the acceleration sensor can notify an abnormality such as a sensor failure or performance deterioration, thereby improving the reliability of the system.

Further, it is possible to diagnose changes in the output characteristics of the sensor over time, and if the characteristics are corrected based on the result of this diagnosis, the soundness of the sensor and the system can be maintained without replacing the detection element. ..

[Brief description of drawings]

FIG. 1 is a block diagram and a circuit diagram of an acceleration sensor according to a first embodiment of the present invention.

FIG. 2 is a voltage waveform diagram in a diagnostic mode applied to the detection element used in the first embodiment.

FIG. 3 DC voltage VG for self-diagnosis with respect to measured acceleration G
Diagram showing the relationship between

FIG. 4 is an explanatory diagram showing a time change of a rectangular wave VG for self-diagnosis and an output voltage Vout.

FIG. 5 is a circuit diagram of an acceleration sensor according to a second embodiment of the present invention.

FIG. 6 is a voltage waveform diagram applied to the detection element of the second embodiment.

FIG. 7 is a circuit diagram showing an example of a booster circuit used in each of the above embodiments.

FIG. 8 is a circuit diagram showing another example of the booster circuit used in each of the above embodiments.

FIG. 9 is a block diagram of an airbag system according to a third embodiment of the present invention.

FIG. 10 is a control flowchart of the airbag system.

FIG. 11 is a perspective view showing an acceleration sensor according to a fourth embodiment of the invention.

[Explanation of Codes] 6 ... Movable electrodes (mass parts), 7, 8 ... Fixed electrodes, 13 ... Capacitance detection part, 18 ... Acceleration sensor detection element part, 19 ... Signal application part (acceleration detection signal and diagnostic signal Applicator,), 22 ... Diagnostic voltage source, 80 ... Coil

Front page continuation (72) Inventor Tetsuo Matsukura 2520 Takaba, Takata, Ibaraki Prefecture, Hitachi Automotive Systems Division (72) Inventor Hirokazu Fujita 2520, Takaba, Katsuta, Ibaraki Hitachi, Ltd. Automotive Equipment Co., Ltd. (72) Inventor Masayoshi Suzuki, 2520 Takaba, Katsuta-shi, Ibaraki, Takaba, Hitachi, Ltd.Automotive Equipment Division (72) Inventor, Masahiro Matsumoto 4026, Kuji-machi, Hitachi, Ibaraki Hitachi, Ltd., Hitachi Research Laboratory

Claims (15)

[Claims] 1. A mass part that displaces in response to acceleration,
In an acceleration sensor that detects the acceleration by converting the displacement of the mass part into an electric signal, a means for applying a force equivalent to the acceleration to the mass part by a diagnostic signal, and an acceleration sensor based on the sensor output when the diagnostic signal is generated. And a means for performing self-diagnosis of the acceleration sensor. 2. A mass unit that displaces in response to acceleration,
In an acceleration sensor that detects the acceleration by converting the displacement of the mass part into an electric signal, a means for applying a force equivalent to the acceleration to the mass part by a diagnostic signal, and an acceleration sensor based on the sensor output when the diagnostic signal is generated. Means for self-diagnosis, means for notifying that the self-diagnosis result is a failure, and diagnosis that the result of the self-diagnosis is a change over time in the sensor output characteristics that does not lead to a failure. And a means for correcting the characteristic of the acceleration sensor, the acceleration sensor. 3. The means for applying a force equivalent to acceleration to the mass part according to claim 1 or 2, wherein the mass part is electrostatically or electromagnetically or externally mechanically vibrated on the basis of the diagnostic signal. An acceleration sensor characterized by comprising any mechanism that provides 4. The capacitance according to claim 1, wherein the acceleration sensor has a capacitance between a movable electrode that serves as the mass portion and a fixed electrode that faces the movable electrode. Is a capacitance-type acceleration sensor that detects acceleration by detecting the change in the force, and the means for applying a force equivalent to the acceleration to the mass part is configured to apply the diagnostic signal to the fixed electrode (the fixed electrode faces both surfaces of the movable electrode). If it is arranged, it is configured by a signal application unit that applies an electric force to one fixed electrode) to generate an electrostatic force for displacing the movable electrode, and the means for performing the self-diagnosis is configured to perform the self-diagnosis when the diagnostic signal is generated. 2. An acceleration sensor, wherein the acceleration sensor is set to self-diagnose by detecting a change in capacitance between the movable electrode and the fixed electrode. 5. The acceleration sensor according to claim 1, wherein the acceleration sensor includes a weight serving as a mass portion,
A strain gauge type acceleration sensor comprising: an elastic support body with a strain gauge supporting the weight, wherein the weight is formed by fine processing of a semiconductor, and the means for applying a force equivalent to acceleration to the mass portion is A fixed electrode dedicated to diagnosis arranged opposite to the weight, and a signal application unit for applying the diagnostic signal to the fixed electrode to generate an electrostatic force for displacing the weight, The means for self-diagnosis detects a change in resistance value of the strain gauge, or detects a change in capacitance between the weight and the fixed electrode when the diagnostic signal is generated to self-diagnose the acceleration sensor. An acceleration sensor characterized by being set as follows. 6. The means for applying a force equivalent to acceleration to the mass part according to claim 1, wherein the mass part is a coil for generating an electromagnetic force by the diagnostic signal, and the coil is a sensor. An acceleration sensor characterized by being wound around the circumference of. 7. The self-diagnosis means according to claim 1, wherein the self-diagnosis means determines the diagnostic signal and the sensor output value or the diagnostic signal and the sensor output value. An acceleration sensor having a function of diagnosing the presence or absence of a failure of the acceleration sensor based on a time change until reaching a level. 8. The self-diagnosis means according to claim 1, wherein the self-diagnosis means determines a sensor static characteristic from the diagnostic signal and a sensor output value. On the other hand, an acceleration sensor having a function of self-diagnosis of (a characteristic of a sensor output value that should be originally obtained). 9. The self-diagnosis means according to claim 1, wherein the self-diagnosis means detects a sensor movement based on a signal for the diagnosis and a temporal change in the sensor output value until reaching a predetermined level. An acceleration sensor having a function of diagnosing characteristics (here, dynamic characteristics are sensor output response characteristics with respect to acceleration). 10. The method according to any one of claims 1 to 9.
2. The acceleration sensor according to the item 1, wherein the diagnostic signal is amplified by using a charge pump circuit that is integrated into an IC, and the amplified signal voltage is applied to a unit that applies a force equivalent to the acceleration. 11. The method according to any one of claims 1 to 9.
2. The acceleration sensor according to the item 1, wherein the diagnostic signal is amplified by using a transformer, and the amplified signal voltage is applied to a unit that applies a force equivalent to the acceleration. 12. The method according to any one of claims 4 to 6.
In the above item 1, when the diagnostic signal is generated, the battery power supply voltage is set to be directly applied to the fixed electrode or the coil through a terminal different from the circuit of the acceleration detection system. .. 13. An airbag system for activating an airbag when a vehicle collision is detected, wherein the vehicle collision detection system includes an acceleration sensor having a mass portion that responds to acceleration generated during the vehicle collision, and a displacement of the mass portion. To an electric signal to determine a collision, and as a fail-safe system, a means for applying a force equivalent to acceleration to the mass portion by a diagnostic signal, and a sensor for generating the diagnostic signal. An airbag system comprising: means for self-diagnosing the acceleration sensor based on the output; and means for notifying that the self-diagnosis result is abnormal if the self-diagnosis result is abnormal. 14. The device according to claim 13, further comprising means for correcting the characteristic when the result of the self-diagnosis is a diagnosis that the characteristic relating to a correctable sensor output is a change over time. Airbag system. 15. The self-diagnosis means according to claim 14, wherein the time-dependent change of the sensor static characteristic is diagnosed from the diagnostic signal and the sensor output value, and the diagnostic signal and the sensor output value have a predetermined level. An airbag system having a function of diagnosing a change with time in sensor dynamic characteristics based on a change with time before reaching the air conditioner.