JPH06109761A - Error judgement method for acceleration sensor - Google Patents

Abstract

PURPOSE:To enable an error to be detected, regarding acceleration detection signals outputted within a normal signal output range, by differentiating an acceleration detection signal, and making a comparison between the differentiated signal and the predetermined threshold value. CONSTITUTION:A pair of diagonal nodes of piezoresistance elements 8a to 8d having a bridge connection are connected to a power supply and driven on direct current. The elements 8a to 8d, when exposed to acceleration, generate strain, and thus a potential difference appears between other diagonal nodes. A microcomputer 40 performs the execution of various types of control, using the potential difference, and makes judgement about the occurrence of an error in an acceleration sensor 10. That is, a detected signal is differentiated and a low-frequency component is eliminated from the signal. Also, the sensor 10 is judged in terms of whether a signal showing such a sharp change as exceeding a threshold value is thereby detected, via comparison between the differentiated signal and the predetermined threshold value. When a sharp change in acceleration is repeatedly detected, the sensor 10 is judged to be generating a certain error.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor abnormality determination method, and more particularly to an acceleration sensor abnormality determination method for detecting abnormal vibration of an acceleration detection signal.

[0002]

2. Description of the Related Art In recent years, with the advancement of vehicle control,
There is a demand for detection of acceleration generated in a vehicle, and an acceleration sensor is used to satisfy this demand. The acceleration sensor is used, for example, in an antilock brake system (ABS) that prevents wheel lock during sudden braking.

As such an acceleration sensor, a semiconductor type sensor is widely used because of its small size, excellent mass productivity, and stable accuracy. A semiconductor type acceleration sensor is provided with a weight on a beam made of semiconductor such as silicon, and this is fixed to the base material with both ends or cantilever,
This is a configuration in which the strain generated in the beam due to acceleration is converted into an electric signal.

By the way, since the acceleration sensor is a sensor used for vehicle control as described above, when the acceleration sensor itself fails, it is necessary to detect the abnormality and perform some fail-safe processing. For this reason,
Conventionally, a semiconductor type acceleration sensor having an abnormality detecting function is known (Japanese Patent Laid-Open No. 63-132171).

The acceleration sensor described in the above publication is provided with a monitoring circuit for monitoring whether or not the electric signal output according to the acceleration is output within a normal range, and the signal is output outside the normal range. It is a configuration that detects an abnormality when there is.

Therefore, when the acceleration sensor is destroyed and an electric signal in a range that is not output in a normal state is output, the abnormality can be detected promptly, and the vehicle control using the acceleration sensor can be performed. Reliability can be reliably ensured.

[0007]

By the way, such an acceleration sensor is used for measuring the acceleration and the like in the front-rear direction generated during acceleration and deceleration. Therefore, it is necessary to suppress the influence of vibration and the like when the vehicle is running. In other words, the acceleration sensor is used to measure the acceleration that fluctuates at a relatively low frequency among various kinds of acceleration that occur in the vehicle, and is required to have a configuration that is not affected by the acceleration that fluctuates at a high frequency.

Therefore, conventionally, the vehicle-mounted acceleration sensor is generally used while being immersed in the liquid.
In this case, the portion of the beam that detects the acceleration is immersed in the liquid, and the time when the beam is distorted is delayed relative to the time when the acceleration is generated. Therefore, when the acceleration fluctuates appropriately at a high frequency, the strain generated in the beam is canceled out. In other words, this acceleration sensor detects only the acceleration that fluctuates at a relatively low frequency among the accelerations that occur in the vehicle.

However, when the acceleration sensor is used by immersing it in the liquid as described above, if the liquid leaks or a bubble adheres to the beam portion for some reason, the acceleration sensor is influenced by the acceleration which fluctuates at a high frequency. Will be received. Therefore, the acceleration detection signal output from the acceleration sensor becomes a signal that is extremely unreliable in which a disturbance component due to vibration of the vehicle or the like is superimposed.

In this case, however, the acceleration sensor itself is apparently functioning normally, and the acceleration detection signal remains within the normal output range. Therefore, unlike the above-described conventional abnormality detection function, such an abnormality cannot be detected by the method of determining that the sensor is abnormal because the acceleration detection signal of the acceleration sensor is output to the abnormal region.

The present invention has been made in view of the above points, and by monitoring the behavior of the acceleration detection signal of the acceleration sensor, the abnormality of the acceleration detection signal output in the normal output range is detected. It is an object of the present invention to provide an acceleration sensor abnormality determination method that enables detection of.

[0012]

The above-mentioned problems are based on the acceleration detection signal of an acceleration sensor formed by immersing a beam for acceleration detection, which outputs an electric signal corresponding to the amount of strain caused by acceleration, in a liquid. A method for determining an abnormality of an acceleration sensor, comprising: a first process M1 for differentiating an acceleration detection signal of the acceleration sensor; and a differentiation of the acceleration detection signal, as shown in the principle diagram of FIG. A second process M2 that compares the signal with a predetermined threshold value, and the acceleration sensor based on the differential signal that is determined to have exceeded the predetermined threshold value in the second process M2. This is solved by the acceleration sensor abnormality determination method including the third process M3 of determining whether or not an abnormality has occurred.

[0013]

In the acceleration sensor abnormality determining method having the above structure, in the first process M1, the acceleration detection signal of the acceleration sensor is differentiated and the low frequency component is removed from the signal. Therefore, when the acceleration sensor is not affected by the vibration of the vehicle and detects only the acceleration that fluctuates at a low frequency that occurs when the vehicle is accelerated or decelerated, the differential signal obtained by differentiating the acceleration detection signal is almost It constantly becomes “0”.

Also, with the acceleration fluctuating at low frequencies,
When the acceleration that fluctuates at a high frequency is detected, the differential signal becomes a high frequency signal that oscillates around "0". Further, the amplitude at this time increases as the rate of change in acceleration detected by the acceleration sensor increases.

The second processing M2 is the first processing M.
By comparing the differential signal obtained in 1 with a predetermined threshold value, it is determined whether or not the acceleration sensor detects an acceleration that shows a rapid change to the extent that the threshold value is exceeded.

Further, the third processing M3 determines whether or not the acceleration sensor frequently detects a rapid acceleration change, based on the comparison result in the second processing M2. Then, when rapid changes in acceleration are frequently detected, it is determined that some abnormality has occurred in the acceleration sensor.

[0017]

2 is a block diagram showing an example of a system having a function of detecting abnormality of an acceleration sensor according to an embodiment of the method of the present invention. Further, FIG. 3 is a block diagram of an example of an acceleration sensor used in this system. The system configuration for executing the method of this embodiment will be described below with reference to these figures.

In FIG. 3, reference numeral 10 is an acceleration sensor, and reference numeral 2 is a main body of the acceleration sensor 10, which is a cantilever corresponding to an acceleration detecting beam. Cantilever 2
It is cut out from a semiconductor substrate such as silicon and is cantilevered and fixed to the base 20, as shown in FIG.

A weight 4 is provided at the free vibration end of the cantilever 2, and a thin portion 6 is provided between the fixed end of the cantilever 2 and the fixed end. Therefore, when the acceleration G acts in the direction perpendicular to the cantilever 2 (the direction of the arrow in FIG. 3), the cantilever 2 bends according to the law of inertia, and the thin portion 6 bends.

The thin portion 6 has reference numerals 8a to 8d in FIG.
Piezoresistive films 8 formed by bridge-connecting the piezoresistors shown in FIG. 2 are attached, and when the thin portion 6 is bent, the piezoresistors 8a to 8d are distorted according to the bending. become.

The acceleration sensor 10 is entirely immersed in the liquid 30. Therefore, the free vibration end of the cantilever 2 vibrates due to the resistance of the liquid 30. Therefore, the responsivity of the vibration of the cantilever 2 to the fluctuation of the acceleration G is worse than that in the case where the liquid 30 is not present, and the fluctuation frequency of the acceleration capable of following the vibration becomes a lower value. This means that the frequency characteristic of the acceleration sensor 10 can be appropriately set by appropriately setting the viscosity of the liquid 30.

Taking the case where it is desired to measure the acceleration generated during acceleration / deceleration of the vehicle, in general, the fluctuation frequency of the acceleration generated during acceleration or deceleration is at a level considerably lower than the frequency of vibration generated during traveling of the vehicle. . For this reason,
If the viscosity of the liquid 30 is set appropriately, the cantilever 2
It is possible to follow the fluctuation of the acceleration that occurs during acceleration and deceleration, and not to track the fluctuation of the acceleration that occurs due to running vibration.

The acceleration sensor 10 utilizes the above-mentioned characteristics and, in a normal state, is capable of accurately detecting the longitudinal acceleration of the vehicle without being affected by the traveling vibration when the vehicle is traveling. It is configured to be able to.

As shown in FIG. 2, the bridge-connected piezoresistors 8a to 8d are driven by direct current with a pair of diagonal nodes connected to a constant current power supply. Therefore, when the cantilever 2 detects the acceleration and the thin portion 6 bends according to the acceleration, the piezoresistors 8a to 8d are formed.
Then, a distortion corresponding to the bending occurs, and a potential difference occurs between the other diagonal nodes that are not connected to the DC power supply.

The other diagonal node is connected to the input port 41 of the microcomputer 40 and supplies a potential difference signal corresponding to the acceleration detected by the acceleration sensor 10.

The microcomputer 40 uses this potential difference signal to execute processing for performing various known controls, and the acceleration sensor 10 is operated by the method according to the present invention according to a flow chart shown in FIG. This is a part for determining abnormality of. Incidentally, this microcomputer 4
0 is an input port 41, a central processing unit (CPU) 42,
It is composed of an output port 43, a memory 44, and a bus 45 that connects these to each other.

Input port 4 of the microcomputer 40
1 includes a converter that digitizes an analog signal supplied from the acceleration sensor 10. Output port 43
Is connected to the fail safe mechanism 50, and when the microcomputer 40 determines that the acceleration sensor 10 is abnormal, supplies a signal to that effect to the fail safe mechanism 50. The memory 44 is a random access memory (RAM) and a read only memory (ROM).
And a microcomputer 4 in its ROM.
The program to be executed by 0 is stored.

The operation of the system of this embodiment will be described below. Prior to that, the abnormal mode of the acceleration sensor 10 and the state of the acceleration detection signal in that mode will be described.

FIG. 4 is a diagram showing the relationship between the longitudinal acceleration a of the vehicle and the acceleration detection signal of the acceleration sensor 10.

When the acceleration sensor 10 is normal, FIG.
As indicated by the solid line in (A) and (B), the acceleration sensor 1
0 outputs a signal that is symmetrical with respect to the positive acceleration and the negative acceleration with the acceleration "0" as the center and that is substantially proportional to the absolute value of the acceleration a.

The relationship indicated by the broken line in FIG. 4A represents the first pattern of the abnormal signal output from the acceleration sensor 10, and shows the relationship in which the signal in the normal state is shifted. The abnormal signal having this pattern may occur, for example, when an abnormality occurs in the power supply system. Further, the relationship indicated by the alternate long and short dash line in FIG. 4A represents the relationship between the abnormal signal of the second pattern and the acceleration a. This signal is output, for example, when a disconnection occurs in the circuit of the acceleration sensor 10 or the acceleration sensor 10 itself is damaged.

By the way, such an abnormal signal is output to a region where it is not output if the output value of the acceleration sensor 10 is normal. Therefore, for abnormalities in these patterns, an appropriate threshold value V _ER is set as shown in FIG. 4A, and when a signal lower than V _ER is output, the acceleration sensor 1
It can be determined that 0 is abnormal, and this method has been conventionally used.

The relationship shown by the broken line in FIG. 4B shows the relationship between the acceleration signal a and the abnormal signal of the third pattern output from the acceleration sensor 10. This signal is a signal that appears when the acceleration sensor 10 detects the acceleration a originally to be detected by the acceleration sensor 10 as well as the acceleration generated by the vibration of the vehicle, and the free vibration end of the cantilever 2 is sufficiently immersed in the liquid 30. If not, it will occur.

As shown in FIG. 4 (B), the abnormal signal of this pattern is output in a normal region as the acceleration detection signal of the acceleration sensor 10 and is different from the abnormal signals of the first and second patterns. Abnormalities cannot be detected even when compared with V _ER . However, the acceleration detection signal oscillates around a normal value that should be originally output for the acceleration a, and the accuracy of the control performed based on this signal is significantly deteriorated.

Therefore, in order to improve the reliability of the vehicle control performed using the acceleration detection signal, it is necessary to detect this pattern abnormality. The system of the present embodiment attempts to detect the abnormality by paying attention to the fact that the abnormal signal of this pattern is affected by the vibration of the vehicle and fluctuates in a relatively early cycle.

FIG. 5 shows a time chart for explaining the processing executed by the microcomputer 40, and FIG.
Indicates the flow chart of this process. Hereinafter, the process of detecting the abnormality of the third pattern based on the acceleration detection signal of the acceleration sensor 10 will be described in detail with reference to the drawings.

FIG. 5A shows the acceleration detection of the acceleration sensor 10.
Indicates the outgoing signal. In the figure, time t ₁The previous waveform is
The speed sensor 10 normally detected the acceleration a of the vehicle.
It means that. Where time t₁At some
Due to this, for example, bubbles in the liquid 30 attach to the cantilever 2.
If you wear it, the acceleration sensor 10 will measure
Acceleration detection signal for acceleration a that should be generated, traveling vibration, etc.
Acceleration due to the acceleration that should not be detected due to
The detection signal is superimposed and output.

Therefore, as shown in FIG. 5A, the acceleration detection signal at this time fluctuates in a relatively slow cycle, but vibrates greatly in a relatively fast cycle. Therefore, if it is possible to determine whether or not the acceleration detection signal of the acceleration sensor includes the vibration having a relatively short cycle and a large amplitude, it is possible to determine whether or not the acceleration detection signal is normal.

For this purpose, for example, a method of counting the number of signals having an amplitude exceeding a predetermined level within a predetermined time and judging by the number is considered. However, as described above, the acceleration detection signal is accompanied by fluctuations of a relatively slow cycle, and when trying to count the number of amplitudes of the acceleration detection signal in this state, the predetermined level for determining that it is abnormal is changed. The need arises.

Therefore, in the present embodiment, in order to remove the low frequency component from the acceleration detection signal, the acceleration detection signal is differentiated to generate a differential signal da / dt as shown in FIG. 5 (B). Since this da / dt signal is a signal focused only on the rate of change of the output waveform, the fluctuation component is almost removed, and only the high-frequency / high-amplitude component of the output waveform is extracted.

That is, the differential signal da / dt always shows a value near "0" unless the acceleration sensor 10 is affected by the acceleration generated by the vibration of the vehicle, and when it is affected by the acceleration. , Shows a large amplitude centered on "0" in a relatively early cycle.

Therefore, as shown in FIG. 5B, an appropriate threshold value A _ER is set to exceed this threshold value A _ER .
By counting the da / dt signal as an abnormal signal, it is possible to count the wave number of the high frequency / high amplitude signal included in the acceleration detection signal of the acceleration sensor 10.

FIG. 5C shows a time chart of the counter C for counting the number of times the da / dt signal shown in FIG. 5B exceeds the threshold value A _ER . As shown in FIG. 5C, the counter C is divided at every predetermined time Ti, and counts the wave number of the da / dt signal which exceeds the threshold value A _ER during that period.

That is, in FIG. 5 (C), an abnormality occurs in the acceleration sensor 10 at time t ₁ , and the da
Assuming that the amplitude of the / dt signal exceeds the threshold value A _ER , the counter C starts counting from time t ₁ and continues counting until the divided time Ti ends. Then, the count value is reset once and the counting is started again.

In this embodiment, when the value of the counter C exceeds a predetermined threshold value C _ER , it is determined that the acceleration sensor 10 has an abnormality, and the count value does not reach C _ER within a predetermined time Ti. Determines that the acceleration sensor 10 is functioning normally. Therefore, when the acceleration detection signal of the acceleration sensor 10 behaves as shown in FIG. 5A, the count value of the counter C is C at time t ₂ as shown in FIGS. 5C and 5D. _{When ER} is exceeded, the abnormality flag indicating abnormality of the acceleration sensor 10 is turned on.

In the system of this embodiment, the above-described abnormality determination processing is executed by the microcomputer 40. The routine executed by the microcomputer 40 will be described below along the flow chart shown in FIG.

When this process is started, first, the above-mentioned predetermined time Ti is measured. That is, the elapsed time “t _(n) − from the abnormality determination start time t ₀ to the current time t _(n) is displayed on the timer T.
Substitute "t ₀ " (step 101) and compare the timer T with the predetermined time Ti (step 102).

If this processing is the first time, it is determined that the predetermined time Ti has not yet elapsed (T <Ti), so the routine proceeds to step 103, where the acceleration detection signal a supplied from the acceleration sensor 10 is read. . Then, the acceleration detection signal a is differentiated to generate a differential signal da / dt (step 104), and the da / dt signal is compared with a predetermined threshold value A _ER (step 105).

As described above, if it is in a normal state, da / d
The acceleration detection signal a does not suddenly change to such an extent that t> A _ER, and if it is determined that da / dt> A _{ER in} step 105, it is possible that an abnormality has occurred in the acceleration sensor 10. Conceivable.

Therefore, in step 105, da / dt>
If it is determined that A _ER, to count how it is determined that the number of times da / dt> A _ER, "the counter C of the count value C
_The counter C is rewritten with _(n) "=" previous count value C _(n-1) +1 "(step 10).
6). Then, this count value C _(n) is compared with a predetermined threshold value C _ER (step 107), and C _(n) > C _ER
If da / dt> A _ER frequently occurs to such an extent that the acceleration sensor 10 has an abnormality, the abnormality flag is turned on (step 108).

In step 105, da / dt> A
_When it is determined that the acceleration sensor 10 is not the _ER, it is determined that no sign of abnormality appears in the acceleration sensor 10, and the processing of this time is ended as it is. On the other hand, if it is determined in step 107 that C _(n) > C _ER is not satisfied, it cannot be determined that the acceleration sensor 10 is abnormal yet, and the process is terminated without turning on the abnormality flag.

When this process is started every predetermined time from the next time onward, the above step 1 is repeated until it is determined in step 102 that the timer T has reached the predetermined time Ti.
01 to 108 are repeatedly executed.

On the other hand, if it is judged at step 102 that T ≧ Ti, the timer is reset to step 109.
Then, the current time t _(n) is replaced with the starting time t ₀ of the timer T. Then, in step 110, the count value C _(n) of the counter C is cleared, and this processing is ended.

Therefore, as described with reference to FIG. 5C, in the acceleration detection signal a output from the acceleration sensor 10 during the predetermined time Ti, the component satisfying da / dt> A _ER is C _ER.
If more than one is included, the error flag is turned on,
In other cases, the acceleration sensor 10 is determined to be normal.

The state of this abnormality flag is transmitted to the fail-safe mechanism 50 of FIG. 2 via the output port 41. When this flag is turned on, the fail-safe mechanism 50 determines that the acceleration detection signal of the acceleration sensor 10 is unreliable and performs a fail-safe process such as stopping the use of the acceleration detection signal a.

As described above, the acceleration sensor 10 is determined to be abnormal only when the da / dt signal exceeds the threshold value A _{ER a} predetermined number of times or more within the predetermined time Ti. When the acceleration change occurs, it is not detected as an abnormality of the acceleration sensor 10.

Therefore, in the system of this embodiment,
An abnormality of the acceleration sensor that cannot be detected by the conventional method, that is, an abnormality caused by the acceleration sensor being affected by vibration of the vehicle can be accurately detected, and vehicle control using the acceleration detection signal a is possible. The reliability of can be improved.

In this embodiment, the threshold is used for convenience.
Value A_ERDifferential signal da / dt exceeding
Constant C_ERIf there is more than one, it is regarded as abnormal
However, the threshold value A is not limited to this._ERTo
The number of differential signals that exceed exceeds a predetermined number C _EROf time to reach
The determination may be made based on the length.

Further, in these cases, the number of differential signals da / dt exceeding the threshold value A _ER is used as the basis for the abnormality determination, but the present invention is not limited to this and, for example, the differential signal da / dt. Of these, the cumulative value of the portion exceeding the threshold value A _ER may be used as the basis for the determination.

[0060]

As described above, according to the present invention, the acceleration detection signal output from the acceleration sensor is detected by monitoring the amplitude and the cycle of the differential signal obtained by differentiating the acceleration detection signal output from the acceleration sensor. It is possible to easily determine whether or not a high frequency / high amplitude signal is superimposed on the signal. For this reason, when the acceleration sensor detects an acceleration which is originally detected due to some reason and fluctuates at a relatively low frequency, and an acceleration which is caused by vibration of the vehicle and fluctuates at a relatively high frequency, Anomalies can be detected quickly.

That is, according to the conventional method, when the acceleration detection signal is output in the normal output range, the abnormality cannot be detected even if the signal is abnormal. On the other hand, according to the method of the present invention, such an abnormality can be detected, and the accuracy of abnormality determination can be improved as compared with the conventional method. Therefore, the reliability of the acceleration detection signal itself is improved, and the reliability of control using this signal as vehicle data can be improved.

[Brief description of drawings]

FIG. 1 is a principle diagram of an acceleration sensor abnormality determination method according to the present invention.

FIG. 2 is a configuration diagram of an example of a system that executes an embodiment of an acceleration sensor abnormality determination method according to the present invention.

FIG. 3 is a perspective view showing a configuration of an acceleration sensor used in the system of this embodiment.

FIG. 4 is a diagram for explaining an abnormal mode of the acceleration sensor.

FIG. 5 is a diagram for explaining an abnormality determination process in the system of this embodiment.

FIG. 6 is a flowchart of a process executed by the microcomputer of the system of this embodiment.

[Explanation of symbols]

 M1 first treatment M2 second treatment M3 third treatment 2 cantilever 4 weight 6 thin portion 8 piezoresistive film 8a-8d piezoresistive 10 acceleration sensor 30 liquid 40 microcomputer 41 input port 42 central processing unit (CPU) 43 Output port 44 Memory 45 Bus 50 Fail-safe mechanism

Claims (1)

[Claims] 1. An acceleration for determining abnormality of the acceleration sensor based on an acceleration detection signal of an acceleration sensor obtained by immersing a beam for acceleration detection, which outputs an electric signal corresponding to a strain amount caused by acceleration, in a liquid. A sensor abnormality determination method, comprising: first processing of differentiating an acceleration detection signal of the acceleration sensor; second processing of comparing a differential signal of the acceleration detection signal with a predetermined threshold; In the second process, a third process for determining whether or not an abnormality has occurred in the acceleration sensor based on the differential signal determined to have exceeded the predetermined threshold value. Sensor abnormality determination method.