JP2927114B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor incorporated in an airbag device for an automobile and the like, and more particularly, to a structure of a self-diagnosis circuit for the acceleration sensor.

[0002]

2. Description of the Related Art Conventionally, as an acceleration sensor of this type, as shown in FIG. 3, a piezoelectric element 10 for detecting the direction and magnitude of an applied acceleration, and a signal processing circuit for processing an output signal from the piezoelectric element 10 11 and a self-diagnosis circuit 12 for diagnosing the occurrence of a failure in these components. The signal processing circuit 11 includes an impedance conversion unit 13 connected to the piezoelectric element 10, a filter unit 14, and an amplifier unit. 15. The output voltage from the signal processing circuit 11, that is, the sensor output v _101, is taken into the airbag control means 17 through the measurement / calculation means 16, and is output from the airbag control means 17.
It is adapted to direct the necessary operations for the entire air bag system for a motor vehicle (not shown) on the basis of the sensor output v _101. The measurement / calculation means 16 and the airbag control means 17 are configured by using a computer.

On the other hand, a self-diagnosis circuit 12 is provided to prevent a serious situation from occurring due to a failure of the acceleration sensor.
An AC signal output means 19 connected to, and a pulse generating means 20 for outputting a timing signal v ₁₀₂ having a predetermined number of pulses for the AC signal outputting means 19, the AC signal outputting means 19 Timing signal v ₁₀₂
AC signal v ₁₀₃ in synchronization with the cycle of is output to the piezoelectric element 10. Also, the self-fault diagnostic circuit 12 includes a measurement means 21 for measuring the sensor output v ₁₀₁ output from the signal processing circuit 11 when input AC signal v ₁₀₃ to the piezoelectric element 10, a failure based on the measurement result A judgment unit 22 for judging the occurrence of the occurrence is provided, and the operation of the whole circuit is controlled by a diagnosis control unit 23. The measuring means 21, the determining means 22, and the diagnostic controlling means 23
Are also configured using a computer.

Meanwhile, the frequency of the acceleration applied as an external force to the piezoelectric element 10 constituting the acceleration sensor, the sensor output v ₁₀₁ is the output voltage from the signal processing circuit 11, characteristic curve A shown by solid lines in FIG. 4 It is common to have the relationship represented by Note that FIG.
That is, while the horizontal axis in the characteristic diagram showing the relationship between the acceleration frequency and the sensor output indicates the acceleration frequency (Hz),
The vertical axis indicates the sensor output (mV). However, when a failure occurs in the piezoelectric element 10 or the signal processing circuit 11 that constitutes the acceleration sensor, the low-frequency cutoff frequency in the characteristic curve A is reduced as shown by the virtual line segments in FIG. In addition to shifting to a high frequency side (indicated by an arrow B) and a high-frequency cutoff frequency shifting to a low frequency side (indicated by an arrow C),
The sensor output in the G sensitivity flat region increases or decreases (indicated by arrows D and E).

[0005] Therefore, in the acceleration sensor having the above configuration, failure diagnosis is performed according to the following procedure. That is, this failure diagnosis is performed immediately before the operation of the vehicle equipped with the vehicle airbag device. For example, when the engine is started, the airbag control unit 17 performs the diagnosis control forming the self-failure diagnosis circuit 12. The means 23 is instructed to execute the failure diagnosis.

[0006] That is, in the fault diagnosis execution results in the output of the timing signal v ₁₀₂ is instructed to the pulse generating means 20 from the diagnosis control unit 23, first, first, the characteristic curve shown in FIG. 4 A timing signal v having a frequency f ₁ near the lower cutoff frequency at A
₁₀₂ is output from the pulse generation means 20 to the AC signal output means 19. Then, this AC signal output means 19
It will be applied to the piezoelectric element 10 AC signal v ₁₀₃ in synchronization with the cycle of the timing signal v ₁₀₂ is outputted from the sensor output as an output voltage corresponding to the AC signal v ₁₀₃ which applied from signal processing circuit 11 v ₁₀₁ is output. Then, the sensor output v ₁₀₁ will be captured by the measuring means 21, the presence or absence of failure, based on the measurement result in the determination means 22, i.e., the low band cut-off frequency close to the frequency f ₁ is high in the characteristic curve A It is determined whether or not the frequency has shifted to the frequency side.

Subsequently, timing signals v ₁₀₂ having frequencies f ₂ and f ₃ near the G sensitivity flat region and the high frequency cut-off frequency in the characteristic curve A shown in FIG. After the same operation is repeatedly performed, the determination means 22 determines whether or not a failure has occurred according to the same procedure. And
The timing signal v having any of the above frequencies f _{1 to} f _{3
According to 102} , the piezoelectric element 1 constituting the acceleration sensor
If 0 or a failure in the signal processing circuit 11 is not detected, the operation of the vehicle is started as it is, and
If the occurrence of a failure is detected, necessary measures will be taken.

[0008]

The conventional acceleration sensor is configured to perform a failure diagnosis based on an AC signal, but it takes a long time to stabilize the AC signal. This is usually required, so that it takes a long operation time to execute the failure diagnosis, which is not practical. Furthermore, the pulse generating means 20 in the self-diagnosis circuit 12 must output three types of timing signals having different frequencies, and unless the measuring means 21 can minutely sample the repetitive waveform of the AC signal. Therefore, these physical circuits have a very complicated configuration, and there is a disadvantage that the configuration requires a great deal of trouble.

The present invention has been made in view of these inconveniences, and can simplify the actual circuit configuration of the self-diagnosis circuit, and can reduce the operating time during execution of the failure diagnosis. It is an object of the present invention to provide an acceleration sensor capable of achieving a significant reduction.

[0010]

In order to achieve the above object, an acceleration sensor according to the present invention comprises: a piezoelectric element to which acceleration is applied; a signal processing circuit for processing an output signal from the piezoelectric element; A self-diagnosis circuit for diagnosing whether or not a failure has occurred in these components. The self-diagnosis circuit is connected to the piezoelectric element via a capacitor, and has a value corresponding to the output voltage from the signal processing circuit. Diagnostic voltage generating means for applying a diagnostic voltage preliminarily trimmed so as to be applied to the piezoelectric element in response to the input of the diagnostic start voltage, and outputting a diagnostic start voltage to the diagnostic voltage generating means, and Diagnostic control means for controlling the operation of the entire circuit;
Measuring means for measuring a sensor output voltage from the signal processing circuit every time a predetermined time has elapsed after the output of the diagnosis start voltage;
Determining means for determining whether or not a failure has occurred based on a measurement result of the sensor output voltage obtained every time a predetermined time has elapsed.

[0011]

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

FIG. 1 is a circuit block diagram showing a schematic configuration of an acceleration sensor according to this embodiment. FIG. 2 is an explanatory diagram showing waveforms of output voltages. Reference numeral 1 in FIG. 1 denotes a self-failure diagnosis circuit. I have. Since the entire configuration of the acceleration sensor except for the self-diagnosis circuit 1 is not fundamentally different from that of the conventional example, the same reference numerals in FIG. 1 denote the same parts as in FIG. Detailed description here is omitted.

This acceleration sensor, as shown in FIG.
A piezoelectric element 10 to which acceleration is applied;
And a self-diagnosis circuit 1 for diagnosing the presence or absence of a failure in these components. The signal processing circuit 11 outputs a sensor as an output voltage corresponding to acceleration. output v ₁ is adapted to be output.

The self-failure diagnosis circuit 1 is constructed by utilizing a diagnosis voltage generating means 3 connected to the piezoelectric element 10 via a capacitor 2 having a predetermined capacitance value and a computer, thereby operating the entire circuit. And diagnostic control means 4 for controlling the cooperatively. Then, while the diagnosis start voltage v ₂ e.g. 5v shown in Dejiitaru signal "1" is output for the diagnosis voltage generating means 3 from the diagnosis control unit 4, the inverting amplifier configuration diagnostic voltage generated using a The step voltage v ₄ corresponding to the input diagnosis start voltage v ₂ is output from the means 3. The diagnosis voltage v ₃ is applied to the piezoelectric element 10 by the step voltage v ₄ . become. Here, the results in the diagnosis when a voltage v ₃ to the piezoelectric element 10 is applied,
To the piezoelectric element 10, than by transients when the step voltage v ₄ output from the diagnostic voltage generating means 3 is connected via a capacitor 2 is switched instantaneously. At this time, the diagnostic voltage generating means 3 is not limited to an inverting amplifier.

The diagnosis voltage v ₃ is trimmed in advance so as to have a value corresponding to the sensor output v ₁ from the signal processing circuit 11. The diagnostic stop voltage of, for example, 0 V indicated by the digital signal “0” is output to the diagnostic voltage generator 3. Although not shown in FIG. 1, a DC voltage output means is provided between the diagnostic voltage generating means 3 and the diagnostic control means 4, and the diagnostic control means 4 is provided.
Diagnostic start voltage v ₂ or diagnosis stop voltage based on the instruction may output a diagnostic voltage generating means 3 from the DC voltage output means from the course.

Further, the self-failure diagnosis circuit 1 comprises a measuring means 5 for measuring the output voltage v ₁ from the signal processing circuit 11 every time a predetermined time has elapsed after outputting the diagnosis start voltage v ₂ , And a judgment unit 6 for judging the presence or absence of a failure based on the data. The measurement unit 5 and the judgment unit 6 are also configured by using a computer.

Next, a description will be given of the operation of executing the fault diagnosis in the acceleration sensor having the above-mentioned configuration with reference to FIG. 2 showing the waveforms of the output voltages. The horizontal axis in FIG. 2 indicates the elapsed time (ms), while the vertical axis indicates the sensor output (V).

The failure diagnosis of the acceleration sensor is performed by starting the engine of the vehicle equipped with the vehicle airbag device. Execution of failure diagnosis is instructed from the airbag control means 17.

When the execution of the failure diagnosis is instructed, first, the diagnosis control means 4 sends a signal to the diagnosis voltage generation means 3 as shown in FIG.
Will be diagnosed starting voltage v ₂ of 5v as shown in (a) is outputted, the step voltage as shown in FIG. 2 from the diagnosis voltage generating means 3 for the diagnosis start voltage v ₂ is inputted (b) v _{results 4} is output, so that the step voltage v at diagnosis voltage v ₃ corresponds to the output of ₄ is applied through the capacitor 2 to the piezoelectric element 10. It should be noted that a diagnosis stop voltage of 0 V is output from the diagnosis control means 4 to the diagnosis voltage generation means 3 at times other than when the failure diagnosis is executed, so that the failure diagnosis in the acceleration sensor is not executed.

Then, the diagnostic voltage v ₃ applied to the piezoelectric element 10 is processed by passing through the signal processing circuit 2, as shown in FIG. 2 (c). so that the sensor output v ₁ is outputted with a step response waveform. Incidentally, the sensor output v ₁ having this step response waveform and the characteristic curve A in the characteristic diagram showing the relationship between the acceleration frequency and the sensor output shown in FIG. 4 have a specific relationship corresponding to each other. The sensor output v ₁ indicating the initial voltage value α in the step response waveform is obtained by adding the timing signal v ₁₀₂ of the frequency f ₃ , and the sensor output v ₁ indicating the next voltage value β is the timing signal of the frequency f ₂ v _{If 102} was added, further, the sensor output v ₁ showing a later stage of the voltage value γ is the sensor output v in the case of adding the timing signal v ₁₀₂ frequency f _1
It corresponds to each of ₁₀₁ . Therefore, each time elapses diagnosis start voltage v a predetermined time after the _second output, i.e., after measured by the measuring means 5 a sensor output v ₁ at every t _1, t _2, t ₃ after a lapse of FIG. 2 (c), the resulting By judging the measurement result obtained by the judging means 6, it becomes clear whether or not a failure has occurred based on the shift state of the characteristic curve A shown in FIG. Here, t ₁ ,
t ₂ and t ₃ are set to 0.2 ms, _2.5 ms and 50 ms, respectively.
ms.

That is, a failure in the piezoelectric element 10 and the signal processing circuit 11 constituting the acceleration sensor occurs at the frequency f ₁ near the low-frequency cutoff frequency in the characteristic curve A shown in FIG. and high frequency cut-off frequency close to the frequency f ₃ is shifted, and is than the sensor output at the G sensitivity flat zone is detected by increasing or decreasing, if f ₁ is shifted to the high frequency side 2C shows that the voltage value γ in FIG. 2C is lower than a certain required value, and that the voltage value α is higher than the required value when f ₃ is shifted to a lower frequency side. As a result, the determination means 6 determines that a failure has occurred. At this time, f ₁ is 0
(Zero), the voltage value γ becomes a predetermined constant value. If f ₁ shifts to a lower frequency side, the voltage value γ approaches the fixed value, while f ₃ is ∞ (infinity). In this case, the voltage value α becomes a predetermined constant value, and if the frequency f ₃ shifts to the higher frequency side, the voltage value α approaches the constant value.

Further, when the sensor output in the G sensitivity flat region increases and shifts along the arrow D, the voltage value β in FIG. 2C rises above a certain required value. On the other hand, when the sensor output decreases and shifts along the arrow E, the voltage value β decreases. Then, these measurement results are also taken into the judging means 6 and judged, and it becomes clear whether or not there is a failure. At any of the voltage values α, β, and γ, if no failure is detected in the piezoelectric element 10 or the signal processing circuit 11 that constitutes the acceleration sensor, the operation of the vehicle is started as it is. If the occurrence of the event is detected, necessary measures will be taken.

[0023]

As described above, the acceleration sensor according to the present invention is configured to perform a failure diagnosis based on the step voltage, and does not use an AC signal that requires a long time for stabilization. The operation time during the execution of the diagnosis can be significantly reduced. Further, the diagnostic control means constituting the self-diagnosis diagnostic circuit need only output a single diagnostic start signal, and its measuring means need only sample and measure only three points on the step response waveform. Also, there is an effect that the configuration of the actual circuit can be simplified and the labor required for the configuration can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram illustrating a schematic configuration of an acceleration sensor according to an embodiment.

FIG. 2 is an explanatory diagram showing waveforms of respective output voltages in the present embodiment.

FIG. 3 is a circuit block diagram showing a schematic configuration of an acceleration sensor according to a conventional example.

FIG. 4 is a characteristic diagram showing a relationship between an acceleration frequency and a sensor output in a conventional example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Self-failure diagnosis circuit 2 Capacitor 3 Diagnosis voltage generation means 4 Diagnosis control means 5 Measurement means 6 Judgment means 10 Piezoelectric element 11 Signal processing circuit v ₁ Sensor output (output voltage) v ₂ Diagnosis start voltage v ₃ Diagnosis voltage

Claims (1)

(57) [Claims] 1. A piezoelectric element (10) to which acceleration is applied, a signal processing circuit (11) for processing an output signal from the piezoelectric element (10), and a self-failure diagnosis for diagnosing the occurrence of a failure in these elements. A self-failure diagnosis circuit (1) comprising: a capacitor (2);
The diagnostic voltage (v ₃ ) is connected to the piezoelectric element (10) through the oscillating circuit and is trimmed in advance to a value corresponding to the output voltage (v ₁ ) from the signal processing circuit (11).
The diagnosis start voltage (v ₂₎ diagnosis voltage generating means in response to the input applied to the piezoelectric element (10) with (3), the diagnostic start voltage with respect to the diagnostic voltage generating means (3) (v ₂₎ And a diagnostic control means (4) for controlling the operation of the entire circuit, and a sensor output voltage (v) from the signal processing circuit (11) every time a predetermined time elapses after the output of the diagnosis start voltage (v ₂ ). ₁ ) measuring means (5) for measuring a predetermined time
An acceleration sensor comprising: judgment means (6) for judging whether or not a failure has occurred based on a measurement result of the sensor output voltage (v ₁ ) obtained every time .