JPH06156184A - Method and device for measuring accelration - Google Patents

Abstract

PURPOSE:To execute the acceleration measurement with the optimum average value by making the averaged acceleration data over a certain period to be a reference acceleration, and when the difference between the maximum and minimum acceleration in the presumed period exceeding this set period is smaller than the difference in the preset period, averaging the acceleration data in the certain period successively, and thereby making the final reference acceleration. CONSTITUTION:The acceleration signal by an acceleration sensor 12 is transmitted to a microprocessor 14 through a high frequency filter,circuit 13, and the necessary processing for the collision judgement including the setting and presumption of the reference acceleration is executed. An acceleration measuring device defines the average value as the reference acceleration in the preset period where no external force is exerted on the acceleration sensor 12, while presuming the average value of the acceleration data Vg' as the reference acceleration in the presumed period where the subsequent exertion of the external force is considered only when the maximum value Vg'max-Vg'min. of the output fluctuation width in the preset period of the reference acceleration is maller than the maximum value Vg'max-Vg'min. of the fluctuation width of the acceleration sensor 12 in the preset period of the reference acceleration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration measuring method and an acceleration measuring device for correcting a zero point by using an average output value during a period when an external force is not acting on an acceleration sensor.

[0002]

2. Description of the Related Art In order to reduce fatal accidents of occupants due to vehicle collisions, it is urgent to introduce an air bag device for protecting a driver or a driving assistant sitting in a front seat from a collision impact.
For example, in the airbag device on the driver's side, the airbag is embedded in the central portion of the steering wheel of the vehicle,
When the vehicle receives an impact exceeding a certain limit due to a collision, the microprocessor issues a deployment trigger signal, ignites and detonates a detonator element called a squib, and explodes the airbag. The bag acts as a cushion between the steering wheel and the driver.

A vehicle collision determination device 1 shown in FIG. 7 determines a collision by performing offset integration on the output of the acceleration sensor 2 to determine a threshold value.
Is sent to the AD converter 4 via the high-pass filtering circuit 3, and the acceleration signal G (t) converted into a digital signal by the AD converter 4 is converted into an offset integrator 5
Supply to. The offset integrator 5 uses the acceleration signal G
For the value obtained by subtracting the maximum value of the acceleration signal generated during normal traveling from (t) as the offset Gs, the interval integration of [G (t) -Gs] dt is performed until the acceleration signal G (t) reaches the current value. Over a predetermined section of. The integrated output of the offset integrator 5 is supplied to the comparator 6 and compared with the threshold value Vr. When the integrated output exceeds the threshold value, it is determined that a collision occurs.
At the time of determination, a deployment trigger signal for the airbag is output.

As the acceleration sensor 2, for example, a semiconductor acceleration sensor in which a stress strain gauge is formed on a semiconductor substrate is used, and a stress strain gauge that utilizes the fact that the piezo resistance of the semiconductor changes when stressed and strained. The pressure-receiving surface is installed in the direction of travel of the vehicle. The output voltage of the acceleration sensor 2 is 0 to 5 V as shown in FIG.
However, in order to eliminate the influence of the DC component,
As shown in FIG. 9, the high-pass filtering circuit 3 having an extremely low cut-off frequency fc of about 0.3 Hz filters the high-pass filtering circuit 3 at the center of the output change width of 2.5 V, where the acceleration is zero. It is set to a zero point that gives 0 (G). That is,
Output voltage Vg of acceleration sensor 2 and acceleration data G (t)
Between them, the relationship of G (t) = H (Vg-2.5) is established via the conversion coefficient H, and when the output voltage Vg exceeds 2.5V, the deceleration and the output voltage Vg are If the voltage is less than 2.5V, it is determined that acceleration is acting. However, it is assumed that the deceleration occurs when an external force acts on the occupant of the vehicle in the traveling direction, and the acceleration occurs when the external force acts in a direction opposite to the traveling direction.

[0005]

A conventional collision determination device 1
Is an assembly error of the acceleration sensor 2 itself, or an influence of ambient temperature or secular change, inevitably causes a zero-point fluctuation of the sensor output, that is, drift, and if the position of the zero point is biased to the acceleration side or the deceleration side, the vehicle is in a stopped state However, there is a problem that the output voltage Vg of the acceleration sensor 2 does not match 2.5V even when the vehicle is running at a constant speed, and the output voltage characteristic deviates from that shown by the solid line in FIG. . Further, once such a drift occurs, it has a considerable influence on the collision determination in which the acceleration data is offset-integrated and the threshold determination is performed. For example, the collision determination is delayed and the airbag cannot be deployed in time, or the vehicle is curbed. However, there is a problem in that the airbag may be inadvertently inflated because it is erroneously determined to be a collision when the driver gets on the vehicle.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an acceleration sensor for detecting acceleration, and a certain amount of force which is apparent from the acceleration sensor immediately after the power is turned on. Reference acceleration setting means for averaging the acceleration data collected in a substantially constant cycle over the setting period by successive averaging, and setting the final average acceleration obtained at the time when the setting period is completed as the reference acceleration, Subsequent to the setting of the reference acceleration, it is executed in units of an estimation period having a length exceeding the setting period, and the difference between the maximum acceleration and the minimum acceleration during the estimation period is the maximum acceleration and the minimum acceleration obtained during the setting period. Acceleration data sampled from the acceleration sensor in a substantially constant cycle is averaged by successive averaging, provided that it is smaller than the difference from the acceleration, and obtained when the estimation period is completed. It is characterized in that it comprises a reference acceleration estimating means the final average acceleration estimated based acceleration.

According to the present invention, the reference acceleration estimating means estimates the difference between the maximum acceleration and the minimum acceleration within the estimation period for the next and subsequent times when the condition for estimating the reference acceleration is satisfied within the estimation period. It is characterized in that it is used for the condition judgment of.

[0008]

According to the present invention, the zero point of the acceleration sensor is set as the average value of the acceleration data during a certain set period during which it is clear that no external force is acting immediately after the power is turned on.
In the estimation period that follows the set period, the acceleration is calculated on the condition that the difference between the maximum acceleration and the minimum acceleration during the period longer than the set period is smaller than the difference between the maximum acceleration and the minimum acceleration obtained during the set period. By estimating the average value of the data as the reference acceleration, the zero point of the sensor output is set by the best method for each of the set period in which it is clear that no external force is acting and the estimated period in which random external force is considered. Determine the reference acceleration to apply.

Further, when the reference acceleration estimation condition is satisfied within the estimation period, the reference acceleration estimating means determines the difference between the maximum acceleration and the minimum acceleration within the estimation period as a condition determination for the next and subsequent estimations. By using it, the determination condition of the external force action during the reference acceleration setting period is set to be stricter each time the estimation is performed than the reference acceleration setting period, and the accuracy of the estimated reference acceleration is equal to or higher than the accuracy of the set reference acceleration.

[0010]

Embodiments of the present invention will be described below with reference to FIGS. 1 is a circuit configuration diagram showing an embodiment of a collision determination device to which the acceleration measuring device of the present invention is applied. FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG.
3 is a flow chart for explaining the main routine of the microprocessor shown in FIG. 1, FIG. 4 is a flow chart for explaining the timer interrupt operation after the reset release of the microprocessor shown in FIG. 1, and FIG. ,
6 is a flowchart for explaining a reference acceleration setting interrupt routine of the microprocessor shown in FIG.
3 is a flow chart for explaining a reference acceleration estimation interrupt routine of the microprocessor shown in FIG. 1.

A collision determination device 11 shown in FIG. 1 uses an acceleration signal obtained by an acceleration sensor 12 as a high-pass filter circuit 13 having an extremely low cutoff frequency fc of about 0.3 Hz.
To the microprocessor 14 via. The microprocessor 14 has a built-in AD converter, converts the acceleration signal of 0 to 5 V sent from the high-pass filtering circuit 13 into a digital signal with a predetermined quantization bit,
Performs all necessary processing for collision determination, including setting and estimation of reference acceleration. Therefore, the reference acceleration setting means and the reference acceleration estimating means are functionally included in the microprocessor 14. Further, the microprocessor 14 is connected to the drive circuit 17 for driving the detonation element 16 which is a deployment trigger of the airbag 15 to configure the collision determination device 11, but in the embodiment, the acceleration sensor 12 and the high range are provided. The filtering circuit 13 and the microprocessor 14 constitute the acceleration measuring device 10. As the acceleration sensor 12, a sensor in which a stress strain gauge whose piezoresistance changes due to stress is incorporated with the pressure receiving surface facing the traveling direction of the vehicle is used. The acceleration data G (k) obtained by AD conversion is used. It is almost the same as before that the collision determination is performed when the interval integral value exceeds the threshold value.

The microprocessor 14, which also serves as the reference acceleration setting means and the reference acceleration estimating means, is supported by various operation programs such as a reference acceleration setting interrupt routine and a reference acceleration estimating interrupt routine in addition to the main routine for collision determination. Has been. The main routine is performed according to the flow shown in FIG. 3. First, in order to start the vehicle engine, when the ignition key is operated to turn on the power, the reset signal is reset until the time T1 shown in FIG. 2 elapses. , Time T1
The reset is released when is passed. When the reset is released, the timer starts to operate in step (101) and the microprocessor 14 is activated to execute the program from the zero address. First, step (1
In step 02), initialization is performed. In step (103), the internal register of the microprocessor 14 is set. In step (104), the input / output mode and port output of each port are set. Further, in step (105), an initial diagnosis inside the collision determination device 11 is performed. In this initial diagnosis, step (1
In (06) and (107), it is diagnosed whether the power supply voltage or the auxiliary power supply voltage is normal, and further step (10)
In step 8), it is diagnosed whether or not each device in the drive circuit 17 operates normally, and in step (109) whether the detonator 16 is short-circuited or open. Then, after the judgment to permit the collision judgment is made in the judgment step (110), the collision judgment is made in the step (111) when both the section integral value and the impact force exceed a predetermined threshold value, Step (112) to step (110) for subsequent failure diagnosis
The operation of returning to is cyclically performed.

Further, since the timer starts operating at the same time as the program starts, the time T has passed since the reset was released.
When 2 has elapsed, the timer interrupt shown in FIG. 4 is performed, and in step (201), the interrupt is permitted together with the timer setting for executing the reference acceleration setting routine. As a result, in the subsequent step (202), the reference acceleration setting interrupt routine is activated and the interrupt timer starts operating. Here, the transition period of about 500 ms is provided for the time T1 + T2 (= Ti) before the reference acceleration setting program is started because the output of the acceleration sensor 12 immediately after the battery power is turned on is shown in FIG. 2 (A). As described above, after the output voltage 2.5V is once overshot to the target value, the transient period Ti elapses and then settles, and the transient occurs until the differential capacitor in the high-pass filtering circuit 13 is charged after the power is turned on. This is because the output fluctuation is inevitable.

When the reference acceleration setting program is started after the lapse of the transition period Ti, an external force is apparently not acting on the acceleration sensor 12 during the reference acceleration setting period. Acceleration is set continuously. In the embodiment, first, in step (301) of FIG. 5, the output voltage Vg of the acceleration signal is AD-converted, and in the following step (302) it is determined whether or not it is the first interrupt. If it is the first interrupt, the interrupt counter, that is, the counter for measuring the reference acceleration setting time is cleared in step (303), and immediately the interrupt count (INTC
1) is given to (NT). Next, in step (304), the maximum value Vgmax and the minimum value Vg of the acceleration data Vg.
An initial value Vg is set as gmin. In addition,
Even at this stage, immediately after the engine is started and the vehicle has not started yet, the acceleration sensor 12 is not receiving an external force, and the output of the acceleration sensor 12 can be considered to be stable during the set period T3. Therefore, the average acceleration Vgm of the acceleration data Vg during the period can be set as the reference acceleration.

That is, each time the reference acceleration setting interrupt routine is executed, the kth interrupt is made by the following successive average calculation Vgm (k) = {(k-1) Vgm (k-1) + Vg} / k. Average acceleration Vg obtained by
m (k) is required. Step (306) is a step of performing a sequential averaging operation, and immediately after the first interrupt,
Vg itself is set to the average value Vgm (1), but in the second and subsequent interrupts, the step (305) of setting the maximum value of Vg to Vgmax and the minimum value thereof to Vgmin is executed following the judgment step (302). After that, a successive averaging step (306) is performed. In step (307) following step (306), the number of interrupts is checked. If the number of interrupts is less than the specified number IT, the number of interrupts is incremented in step (308) and the process returns to the main routine. On the other hand, the judgment step (30
When it is determined in 7) that the number of interrupts has reached the specified number IT, the average value Vgm (n) finally obtained by the n-th interrupt is the reference acceleration 0 (G) that gives a zero point in step (309). Is set as. Further, in response to the setting of the reference acceleration, the collision determination is permitted for the first time in the following step (310). In the embodiment, the time until the collision determination permission is issued, that is, the reference acceleration setting period T3, is, for example, 5
A time of about 00 ms is given. Then, in step (311), the timer necessary for the next reference acceleration estimation is set, and at the same time, interrupt permission is also made. Then, in the final step (312), an interrupt routine for reference acceleration estimation is started.

As described above, in the reference acceleration setting routine, since it is clear that no external force is applied, the reference acceleration that gives the zero point of the sensor output is set using the average value obtained when the period is completed. However, since there is a concern that the reference acceleration once set may drift over time, the reference acceleration estimation routine is continuously executed by a timer interrupt after that. Since the reference acceleration estimation routine corrects the reference acceleration assuming that the vehicle is running and the acceleration sensor 12 is receiving an external force, the reference acceleration setting routine needs to be more accurate than the reference acceleration setting routine. While following along with the following conditions. That is, i) In order to determine whether or not the output voltage Vg 'of the acceleration sensor during the estimation period is stable, the difference between the maximum acceleration Vg'max and the minimum acceleration Vg'min during the period is obtained during the setting period. Is smaller than the difference ΔG between the maximum acceleration Vgmax and the minimum acceleration Vgmin, that is, Vg′max−Vg′min <ΔG (= Vgmax−Vgmin), and ii) estimation of the reference acceleration within one estimation period. When the condition is satisfied, the difference between the maximum acceleration Vg'max and the minimum acceleration Vg'min within this estimation period is used for the condition determination for the next and subsequent estimations instead of the above ΔG.
iii) The estimation period is longer than the set period T3,
The reference acceleration estimation routine is executed while observing the above three conditions.

In the actual reference acceleration estimation routine, as shown in FIG. 6, in step (401), the output voltage Vg of the acceleration signal is first AD-converted, and the subsequent step (40).
In 2), it is judged whether it is the first interrupt. If it is the first interruption, in step (403), a difference ΔG = Vgmax−Vgmin between the maximum acceleration Vgmax and the minimum acceleration Vgmin obtained during the set period is obtained. Next, in step (404), the estimation frequency counter, that is, the counter for measuring the reference acceleration estimation time is cleared, and 1 is given to the estimation frequency (SCNT). Next, in step (304), initial values Vg 'are set to the maximum value Vg'max and the minimum value Vg'min of the acceleration data Vg. At this stage,
Considering the case where the engine is started, the acceleration sensor 12 must be treated as if it is receiving an external force. Therefore, if it is found in the judgment step (402) that the interruption is the second transition, the maximum value of Vg 'is set to Vg'max and the minimum value of Vg' is set to Vg'min in step (406). , And shifts to the judgment step (407).

In the judgment step (407), in the case of the first estimation period, ΔG (= Vgmax-Vgmi during the set period already obtained in step (403).
The magnitude relationship of Vg'max-Vg'min with respect to n), that is, Vg'max-Vg'min <ΔG is determined. However, in the second and subsequent estimation periods, Vg'max-Vg'min in the estimation period already estimated is used instead of ΔG in the set period. And
If Vg'max-Vg'min during the estimation period is equal to or less than the maximum change width ΔG, it can be considered that the vehicle is stopped or is traveling at a constant speed, so in step (409) following step (408), Sequential average calculation Vg'm (k) = {(k-1) Vg'm (k-1) + Vg '} / k The average estimated acceleration V obtained in the k-th estimation
Find g'm (k).

After the step (408), the estimated number of times is checked. If the estimated number of times is less than the prescribed number ST, a step (41) following the judgment step (409).
In step 0), the estimated number of steps is incremented and the process returns to the main routine. On the other hand, when it is determined in the judgment step (409) that the estimated number of times has reached the specified number ST, the average value Vg′m (n) obtained last gives a zero point in step (411). (G). Further, in the subsequent step (412), the maximum change width ΔG set during the setting period is replaced with the maximum error Vg′max−Vg′min during the estimation period,
Tighten the estimation conditions. And finally, step (41
In 3), the estimated reference acceleration Vg 'is set for Vgmax and Vgmin during the set period. If it is found in the judgment step (407) that Vg'max-Vg'min ≧ ΔG, it is considered that the vehicle is accelerating or decelerating. Therefore, the estimation frequency counter is set in step (414). clear. Then, in the following step (415), Vg'max and Vg'm during the estimation period
The estimated reference acceleration Vg 'is set for in.

As described above, the acceleration measuring device 10 is
In the set period in which it is clear that no external force is acting on the acceleration sensor 12, the average value V obtained at the end of the period
In the estimation period in which gm (n) is set as the reference acceleration Vg that gives the zero point of the sensor output, and the random action of the external force following the setting period is considered, the output fluctuation range of the acceleration sensor 12 within the period longer than the setting period. Maximum value V
g'max-Vg'min is the maximum value of the output fluctuation width of the acceleration sensor 12 within the reference acceleration setting period Vgmax-Vgmin
Only when it is smaller than the above, it is determined that it is a period in which no external force is applied to the acceleration sensor 12, and the average value of the acceleration data Vg ′ is estimated as the reference acceleration that gives the zero point of the sensor output. The acceleration set as can be accurately corrected each time the estimation period is repeated, so that even if the zero point of the acceleration sensor 12 drifts due to individual differences of the acceleration sensor 12 itself, changes in environmental temperature, deterioration over time, and the like. It is possible to always measure the acceleration with the latest and optimum average value.

Further, when the estimation condition of the reference acceleration is satisfied within the estimation period, the difference Vg'max-Vg'min between the maximum acceleration and the minimum acceleration within this estimation period is used as the condition determination for the subsequent estimation. By using it, not only the criteria for external force action in the reference acceleration estimation period becomes stricter than in the reference acceleration setting period, but also in the reference acceleration estimation period that appears repeatedly thereafter, the second time rather than the first time,
Since the condition determination for estimation is gradually made stricter such as the third time than the second time, the estimation accuracy of the reference acceleration can be made equal to or higher than the accuracy of the set reference acceleration, and the acceleration sensor 12 The zero point of the sensor output can be corrected to the latest value as much as possible, and can be utilized for collision determination and the like.

[0022]

As described above, according to the present invention, the zero point of the acceleration sensor is set as the average value of the acceleration data during a certain set period during which it is clear that the external force is not acting immediately after the power is turned on. In the estimation period that follows the set period, the acceleration is calculated on the condition that the difference between the maximum acceleration and the minimum acceleration during the period longer than the set period is smaller than the difference between the maximum acceleration and the minimum acceleration obtained during the set period. By estimating the average value of the data as the reference acceleration, during the set period when it is clear that no external force is acting, the average value obtained immediately before the period is completed is set as the reference acceleration that gives the zero point of the sensor output. During the estimation period in which the random force of external force following the setting period is considered, the maximum value of the output fluctuation range of the acceleration sensor within the period is within the reference acceleration setting period. Only when the output fluctuation range of the acceleration sensor is smaller than the maximum value, it is judged that it is a period during which no external force is acting on the acceleration sensor, and the average value of the acceleration data is used as the reference acceleration that gives the zero point of the sensor output. As a result, the acceleration set as the reference acceleration can be accurately corrected at each estimation period that is repeated thereafter, and as a result, due to individual differences in the acceleration sensor itself, changes in environmental temperature, deterioration over time, etc. Even if the zero point of is drifting, the acceleration effect can be measured with the latest and optimum average value.

Further, according to the present invention, the reference acceleration estimating means estimates the difference between the maximum acceleration and the minimum acceleration within the estimation period from the next time onward when the reference acceleration estimation condition is satisfied within the estimation period. By using the condition judgment of
In addition to making the external force action determination conditions stricter in the reference acceleration estimation period than in the reference acceleration setting period, even in the reference acceleration estimation period that appears repeatedly thereafter,
The second estimation period is longer than the second estimation period, and the third estimation period is longer than the second estimation period.
This makes the estimation accuracy of the reference acceleration equal to or higher than the accuracy of the set reference acceleration, corrects the zero point of the sensor output of the acceleration sensor to the latest value as much as possible, and can be used for collision judgment etc. Play.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an embodiment of a collision determination device to which an acceleration measuring device of the present invention is applied.

FIG. 2 is a signal waveform diagram of each part of the circuit shown in FIG.

3 is a flowchart for explaining a main routine of the microprocessor shown in FIG.

FIG. 4 is a flowchart for explaining a timer interrupt operation after reset release of the microprocessor shown in FIG.

5 is a flowchart for explaining a reference acceleration setting interrupt routine of the microprocessor shown in FIG.

6 is a flow chart for explaining a reference acceleration estimation interrupt routine of the microprocessor shown in FIG.

FIG. 7 is a circuit block diagram showing an example of a collision determination device to which a conventional acceleration measuring device is applied.

8 is an output voltage characteristic diagram of the acceleration sensor shown in FIG.

9 is a diagram showing a filtering characteristic of the high-pass filtering circuit shown in FIG. 7.

[Explanation of symbols]

 10 Acceleration Measurement Device 11 Collision Judgment Device 12 Acceleration Sensor 13 High-pass Filtering Circuit 14 Microprocessor

Claims (3)

[Claims] 1. Acceleration data collected from an acceleration sensor for detecting acceleration in a substantially constant cycle over a constant set period in which it is clear that no external force is acting immediately after power-on, and averaged by successive averaging. Then, the final average acceleration obtained at the time when the setting period is completed is set as the reference acceleration, and, following the setting of the reference acceleration, it is executed in units of an estimation period having a length exceeding the setting period. Acceleration data collected from the acceleration sensor at a substantially constant cycle is provided on condition that the difference between the maximum acceleration and the minimum acceleration during the estimation period is smaller than the difference between the maximum acceleration and the minimum acceleration obtained during the setting period. An acceleration measuring method comprising averaging by a sequential averaging operation, and estimating a final average acceleration obtained at the time when the estimation period is completed as a reference acceleration. 2. An acceleration sensor that detects acceleration and acceleration data that is sampled at a substantially constant cycle over a constant set period in which it is clear that no external force is applied from the acceleration sensor immediately after the power is turned on. Reference acceleration setting means for averaging by the average calculation and setting the final average acceleration obtained at the time when the setting period is completed to the reference acceleration, and estimating the length beyond the setting period following the setting of the reference acceleration It is executed in units of a period, and if the difference between the maximum acceleration and the minimum acceleration during the estimation period is smaller than the difference between the maximum acceleration and the minimum acceleration obtained during the setting period, the acceleration sensor is almost Reference acceleration that estimates the final average acceleration obtained at the time when the estimation period is completed as the reference acceleration by averaging the acceleration data collected in a fixed cycle by successive averaging An acceleration measuring device, comprising: a degree estimating means. 3. The reference acceleration estimating means, when the estimation condition of the reference acceleration is satisfied within the estimation period, determines the difference between the maximum acceleration and the minimum acceleration within the estimation period for condition estimation for the next and subsequent times. The acceleration measuring device according to claim 2, wherein the acceleration measuring device is used for.