JPH0580076A - Method for self-diagnosis of sensor signal processing circuit - Google Patents

Abstract

PURPOSE:To enable removal of a cause of erroneous decision by a method wherein an output value of a processing circuit at the time of self-diagnosis is monitored at two different time points and it is detected whether a difference between output values monitored at the different time points is within prescribed limits or not. CONSTITUTION:The sensitivity of a sensor output VOUT is determined on the basis of a G input at a point A. Based on the G input at the point A and the G input at a point B which are monitored, subsequently, a difference between them, that is, whether the value of A-B=DELTAV is within prescribed limits or not, is checked. When the result is YES, checking of the sensor output is ended. When it is NO, a filter fault flag is set ON and it is detected that a filter circuit 3 is not normal. In conclusion, whether the inclination of the sensor output VOUT (the time constant of the circuit 3) is normal or not is determined on the basis of the value of the potential difference DELTAV between the point A and the point B, and thereby it can be detected whether the function of the circuit 3 deteriorates or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a self-diagnosis method for a sensor signal processing circuit, and more particularly to a self-diagnosis method for an acceleration sensor signal processing circuit used in an airbag control device.

[0002]

2. Description of the Related Art FIG. 2 shows an acceleration sensor signal processing circuit of this type.
1 shows the overall configuration of the device for self-diagnosis of the road.
It is an acceleration sensor, and depending on the detected acceleration,
Resistor forming a wedge (for example, a piezo element) R1
Acceleration / deceleration is configured so that the resistance value of 1 to R14 changes
The output voltage corresponding to the frequency is supplied to the differential amplifier 2. Next
The output signal from the differential amplifier 2 is a bandpass filter.
Input to the filter unit 3 and in the bandpass filter unit 3
The output signal from the differential amplifier 2 includes a DC component
Low frequency components below a certain frequency (no acceleration / deceleration has occurred)
Sometimes output from the acceleration sensor 1 and the differential amplifier 2
Slow based on direct current component or power supply fluctuation
Fluctuation components) and high-frequency components above a certain frequency
(High frequency noise components) are cut off,
Only the output signal component within the constant frequency band is
Output voltage V of signal processing circuit 6_OUTIs output as
Voltage V _OUTIs A / D converted by the A / D converter 4,
The output of the A / D converter 4 is used as a so-called G input for collision determination.
It is input to the CPU 5. In this way when a vehicle crashes
When the deceleration of the vehicle exceeds a predetermined value, the G
The CPU 5 judges the collision of the vehicle by the input,
It is supposed to activate the dog.

Conventionally, for example, every time the ignition switch is turned on, an output check of the acceleration sensor signal processing circuit (checking whether the sensor can operate normally) is performed. That is, for example, as described above, every time the ignition switch is turned on, a check signal as shown in FIG. 3 (A) is output from the CPU 5 to the signal processing circuit 6 side, which turns on the transistor Q for a moment. R2 to R4 are resistors), which causes the acceleration sensor 1 forming the bridge to lose its balance and generate a sensor output V _OUT having a waveform as shown in FIG. 3B from the acceleration sensor 1. .. Normally, the sensor output V _OUT is not 0 V in a steady state in which the acceleration / deceleration is not applied to the sensor 1 (for example, 0.5 V).
V)) (therefore, an offset adder is usually connected to the output side of the filter section 3), which causes a disconnection of the output side of the signal processing circuit 6 and the sensor. It is designed so that it can be distinguished from a steady state in which no acceleration / deceleration is applied. In this way, when the check signal is output, the sensor output voltage V _OUT , which is always 0.5 V, for example, temporarily fluctuates as shown in FIG. 3 (B).

In the prior art, the sensor output voltage V _OUT, which fluctuates during the check signal output (see (A) in (2) of FIG. 3), is shown in (B) of (2) of FIG. To be 1
That is, only the value at point A at time t ₀
By monitoring in U5, the CPU 5 determines whether or not the sensitivity of the sensor signal processing circuit 6 is normal.

That is, if the sensor output value at the point A is smaller than a predetermined value (that is, if the sensitivity is too small),
When the vehicle collides, the airbag does not operate. On the other hand, if it is larger than the predetermined value (that is, if the sensitivity is too high), the airbag will operate when it is not needed. Must be within a predetermined range. Thus, by checking whether the sensor output value at the point A is within a predetermined range, the sensor signal processing circuit 6 including the sensor 1 It was determined whether the sensitivity was normal.

However, in such a conventional technique,
Is simply the sensor output V as described above. _OUTSensitivity check
For example, the filter unit 3
The capacitor for cutting DC components installed in the
(For example, a leak failure) The filter part due to
Due to the abnormality of 3, the acceleration sensor 1 and the differential amplification
The DC component output from the unit 2 and the power supply voltage fluctuation component
The sensor output V without being cut_OUTSuperimposed on
In case such as_OUTShould be removed from
The error component as described above causes an abnormality in the filter unit 3.
Therefore, it is superimposed on the collision determination signal and causes an erroneous determination.
In such cases), it is possible to accurately check for such abnormalities.
Cannot be performed, which may cause an erroneous determination in the collision determination.
There was a problem with that.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and when the sensor output is checked, the output processing filter section is abnormal (particularly the DC component used in the filter section). It is also possible to check whether or not there is a deterioration in the filter function due to deterioration of the cutting capacitor, etc.), and thereby check whether or not the error component that causes the above-mentioned erroneous determination is superimposed on the sensor output. It is the one.

[0008]

In order to solve the above problems, according to the present invention, a sensor section and a filter circuit connected to the output side of the sensor section and outputting only a signal within a predetermined frequency band are provided. In self-diagnosing the provided sensor signal processing circuit, the output value of the processing circuit at the time of the self-diagnosis is monitored at two different times, and the difference between the output values monitored at each time is within a predetermined range. There is provided a self-diagnosis method for a sensor signal processing circuit, which is characterized by detecting whether or not there is.

[0009]

According to the above construction, it is detected whether or not the slope of the sensor output V _OUT (that is, the time constant of the filter circuit) is normal based on the value of the difference between the output values monitored at each time point. By detecting the characteristic (time constant) of the filter circuit in this manner, it is detected whether or not the function of the filter circuit is deteriorated, and the error component (described above) is added to the collision determination signal. It is possible to prevent such a direct current component, a power supply fluctuation component, a high frequency noise, etc.) from being superimposed, and to eliminate the cause of erroneous determination.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an operating method as one embodiment of the method of the present invention.
The flow chart shows the sequence, for example, the ignition
Every time the switch is turned on, start with step 1
As shown in (A) of (1) of FIG.
Output a check signal to turn on the transistor Q for a moment.
The balance of the sensor 1 forming the bridge
Then, the sensor output V as shown in (B) of (1) of FIG.
_OUTIs output. Then in step 3, at time t₀To
Output of the sensor (that is, output of the sensor at point A)
Power) V_OUTValue (that is, G input to the CPU)
I will Then, in step 4, after waiting for time t,
Time point t at step 5₁The sensor output at
As shown in (B) of (1) of 3
Output) V _OUTThe value of (ie G input to the CPU)
To monitor.

Then, in step 6, the sensor output V _OUT is based on the G input at the point A monitored in step 3.
To determine the sensitivity of. That is, as described above, it is checked whether or not the G input at the point A is within a predetermined range, and if YES (that is, within the predetermined range), the process immediately proceeds to step 8, and if NO, the step is performed. In step 7, the sensitivity defect flag is turned on, and the process proceeds to step 8.

Next, in step 8, based on the G input of the point A monitored in step 3 and the G input of the point B monitored in step 5, the difference, that is, AB = ΔV. It is checked whether the value of (see (B) of (1) in FIG. 3) is within a predetermined range. If yes (that is, within the predetermined range), the check of the sensor output at that time is completed, but if it is detected that the result is no, the filter is defective (that is, the capacitor A flag (due to deterioration or the like) is turned on to detect that the filter circuit 3 is not normal. That is, by detecting the value of ΔV, it is possible to monitor the slope of the sensor output V _OUT (shown in (B) of (1) of FIG. 3) when the check signal is output, and the slope is the filter circuit. Since it is determined by the time constant of 3, the points A and B above
It is determined whether or not the slope of the sensor output V _OUT (that is, the time constant of the filter circuit) is normal based on the value of the potential difference ΔV at the point, and whether or not the function of the filter circuit 3 is deteriorated by this. Can be detected.

When the value of ΔV detected in step 8 is not within the predetermined range, the signal component of the sensor output V _OUT output from the filter circuit 3 is out of the appropriate frequency band ( In other words, the sensor output V _OUT includes a component that causes an erroneous determination, such as a DC component to be cut by the filter circuit, a power supply voltage fluctuation component, or a low frequency component, or a high frequency noise component). Therefore, in such a case, as described above, the filter failure flag is turned on in step 9 to surely detect the abnormality of the filter circuit 3.

[0014]

According to the present invention, by checking not only the sensitivity of the sensor output but also the time constant of the filter circuit for processing the sensor output when checking the sensor output, It is possible to check whether or not the sensor output V _OUT outputs only a signal component in a predetermined frequency band, and an error signal component that causes an erroneous determination due to the functional deterioration of the filter circuit (due to deterioration of the capacitor or the like). However, it is possible to reliably detect whether or not it is included in the sensor output.

[Brief description of drawings]

FIG. 1 is a flowchart showing an operation procedure as one embodiment of a method of the present invention.

FIG. 2 is a diagram illustrating the overall configuration of an apparatus for checking the output of an acceleration sensor according to the method of the present invention.

FIG. 3 is a diagram for explaining the difference in the sensor output check method between the case of the method of the present invention and the case of the conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Acceleration sensor 2 ... Differential amplification part 3 ... Band pass filter part (filter circuit) 4 ... A / D converter 5 ... CPU 6 ... Acceleration sensor signal processing circuit

Claims (1)

[Claims] 1. Self-diagnosis of a sensor signal processing circuit comprising a sensor unit and a filter circuit connected to an output side of the sensor unit and outputting only a signal within a predetermined frequency band, at the time of self-diagnosis. Sensor signal processing, characterized in that the output value of the processing circuit is monitored at two different times, and whether or not the difference between the output values monitored at each time is within a predetermined range is detected. Circuit self-diagnosis method.