JPS6254125A - Signal processor for output of karman vortex sensor - Google Patents

Abstract

PURPOSE:To obtain a flow rate whose variance due to pulsation or the like is smoothed, by generating an output signal having a frequency corresponding to the flow rate of a fluid by a Karman vortex sensor. CONSTITUTION:A Karman vortex sensor 1 generates the output signal having the frequency corresponding to the flow rate of the fluid, and a waveform shaping means shapes the waveform of the output of the sensor 1 to generate a pulse signal. A pulse number counting means counts a number CKRMN of pulses of the pulse signal in a certain time, and a pulse period total sum operating means operates a total sum STQF of periods of the pulse signal in a certain time. As the result, an average period operating means divides the total sum STQF of periods of the pulse signal by the pulse number CKRMN to operate an average period T in the certain time only when the pulse number in the certain time is not 0, and a dull value operating means operates a dull value TQF of the average period T. A flow rate operating means uses this value TQF to operate a flow rate Q of the fluid in accordance with Q=K/(TQF) (K is a constant).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an output signal processing device for a Karman vortex sensor used as an air flow meter for measuring the intake air amount of an engine, for example.

[Conventional technology]

In general, Karman vortex sensors, which have advantages such as small size, have recently been developed as air flow meters for measuring the intake air amount of an engine.

In the Karman vortex sensor, for example,
As shown in No. 80524 and Japanese Patent Application Laid-Open No. 58-80525, a Karman vortex generator is inserted into a pipe through which fluid flows, and the pressure fluctuations that occur alternately near both sides of the Karman vortex generator are expressed as a pair of pressures. The velocity of the fluid is detected by transmitting the fluid to a diaphragm outside the pipe through the transmission path and photoelectrically detecting the rotational displacement of the diaphragm. In this case, a sinusoidal electric signal corresponding to the rotational displacement of the diaphragm is obtained, this is converted into a pulse signal, and the velocity of the fluid is obtained by processing this pulse signal. Note that the velocity of the fluid is in a proportional relationship with the frequency of the pulse signal of the Karman vortex sensor under predetermined conditions.

One method of processing the pulse signal of the Karman vortex sensor is to directly determine the frequency, that is, the fluid flow rate, by counting the number of pulses within a certain period of time.In this case, in order to obtain an accurate fluid flow rate, The number of pulses counted must be made sufficiently large, and therefore the above-mentioned fixed time must be set large, resulting in poor responsiveness. For this reason, the frequency is usually determined by detecting each period of the pulse signal and calculating its reciprocal (for example, Japanese Patent Laid-Open No. 60-53811, 5
Publication No. 3812).

[Problem that the invention seeks to solve]

The method of determining the frequency, that is, the fluid flow rate, by detecting the period of the pulse signal mentioned above and calculating its reciprocal is as follows:
Although the responsiveness is improved, the influence of cycle fluctuations due to ttfft pulsations is large. Therefore, in order to reduce (smooth) such effects, it is necessary to perform smoothing processing or obtain an average period within a certain period of time. However, in general, the smoothing process weights and averages the previous rounded value and the latest value every time the cycle is updated, so as the flow rate increases, the cycle updates become faster, and so on. There is a problem that no improvement effect can be obtained, and on the other hand, if you want to obtain a stable value in a low flow rate region when obtaining the average period within a certain period of time, the above-mentioned -' constant time must be lengthened. Therefore, there is a problem that the responsiveness becomes low.

[Means for solving problems]

The purpose of the present invention is to obtain a flow rate in which fluctuations due to pulsation of 2 it are smoothed by a smoothing effect without sacrificing responsiveness, and the means for achieving this is shown in FIG. ing.

In FIG. 1, the Karman vortex sensor generates an output signal with a frequency corresponding to the flow rate of fluid, and the waveform shaping means shapes the output of the Karman vortex sensor to generate a pulse signal.

The pulse number counting means counts the number of pulses CKRMN of the pulse signal within a certain period of time, and the pulse period sum calculation means calculates the sum of the periods of the pulse signal within the certain period of time, 5TQF.

As a result, only when the number of pulses within a certain period of time is not O, the average period calculation means calculates the sum of the periods of the pulse signal 5TQ.
By dividing F by the number of pulses CKRMN, the average period T within the fixed time is calculated, and the rounded value calculating means calculates the rounded value TQF of this average period TO. Then, the flow rate calculation means uses the smoothed value TQF to calculate the flow rate ff1 of the fluid.
It calculates /TQF (K: constant) for Q=.

[For production]

According to the above-mentioned means, the averaging period for each fixed period of time is obtained and the smoothing process is performed at the same time. Therefore, even when the flow rate increases, the averaging period within a certain period of time can be used to obtain the average period for a certain period of time. The smoothing effect is maintained and in the low flow region, when the number of pulses is O, averaging processing and smoothing value update are not performed, so the averaging processing interval is substantially increased, and the above-mentioned fixed time is therefore increased. Since it is not necessary, responsiveness does not deteriorate.

〔Example〕

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a diagram showing an embodiment of the output signal processing device of the Karman vortex sensor according to the present invention. In Figure 2, 1
A Karman vortex sensor 1 consisting of a pair of columnar vortex generators 11 and 12 is vertically inserted into an intake passage 2 of an engine. A double rectifying grid 3 is provided upstream of the vortex generators 11 and 12.
, 4 are provided, thereby improving the proportionality between the flow IQ and the Karman vortex frequency over a wide flow rate range.

The vortex generator 12 is provided with a pair of overpressure intake holes and a pressure transmission passage that transmits pressure fluctuations in the intake holes to the outside of the intake passage 2 (not shown). As a result, pressure fluctuations in the pressure transmission passage create rotational moments in the diaphragm therein. Therefore, the diaphragm rotates and vibrates in response to pressure fluctuations in the pressure transmission passage due to the Karman vortices. When the diaphragm rotates and vibrates in this way, a sinusoidal electrical signal with a vortex frequency r is generated photoelectrically (or using ultrasonic waves) and supplied to the control circuit (for example, a microcomputer) 5.

In the control circuit 5, the sinusoidal output signal of the Karman vortex sensor I is supplied to a waveform shaping circuit 51, where the sinusoidal signal is converted into a pulse signal.

This pulse signal is provided to one interrupt input of CPU 52. As a result, the CPLI 52 executes an interrupt routine shown in FIG. 3, which will be described later, in response to, for example, the rising edge of the pulse signal. 53 is a clock generation circuit that generates various clock signals, one of which is C.
is fed to one interrupt input of PU52, resulting in C
The PU 52 executes the interrupt routine shown in FIG. 4 at predetermined intervals, for example, every 4 ms.

Further, another clock signal from the clock generation circuit 53 is supplied to a counter 54 for detecting one cycle of the above-mentioned pulse signal. This counter 54 is for detecting the rising cycle of the pulse signal. 55 is a human output interface, 56 is R for storing programs, constants, etc. in advance.
OM, 57 is a RAM that temporarily stores data.

The operation of the control circuit shown in FIG. 2 will be explained with reference to flowchart 1 in FIGS. 3 and 4.

FIG. 3 shows an arithmetic routine for updating the pulse number counter CKRMN and the pulse period summation counter 5TQF, which is executed every time the pulse of the waveform shaping circuit 51 rises. That is, in step 301, the pulse number counter CKR
MN is incremented by one step, and in step 302, the pulse period is taken in from the counter 54, and the counter 54 is cleared for the next calculation cycle. Next, in step 303, the pulse period! Step 3 to III summation counter 5TQF
Pulse frequency captured in 02! The tIID is calculated and the routine ends at step 304.

Note that, as described above, the counter 54 is connected to the waveform shaping circuit 51.
It is cleared every time the pulse signal rises, and is incremented by counting a predetermined clock signal, for example, a 0.25m5 signal.

FIG. 4 shows a calculation routine for the flow rate Q, which is executed every output signal (4 ms) from the clock generation circuit 53. In step 401, other interrupts are prohibited so that the Karman vortex interrupt shown in FIG. 3 does not occur during execution of this interrupt process and cause a calculation error. Next, in step 402, it is determined whether the pulse number counter CKRMN is O or not, and if it is 0, that is, there is no Karman vortex interrupt even once, step 402 is performed.
After allowing other interrupts in step 8, the process jumps to step 409 and ends the interrupt processing. If not, the process proceeds to step 403, where the value T obtained by dividing the value of the pulse period total counter 5TQF, which is the cumulative value of the periods up to that point, by the number of Kalman signal interrupts CKRMN, that is, the average period every 4 ms is calculated. Then, in step 404, each counter CKRMN and 5TQF are cleared, and in step 405, other interrupts are enabled, and then the average period T obtained in step 403 and the previous average value TQF are calculated without weighting. The average value is set as a new TQF, and TQF←(TQF×T)/2. Next, in step 407, flow [Q to Q--/
It is calculated by TQF and stored in RAM 57. The routine then proceeds to step 408 and ends this routine.

Note that in step 406, if the smoothed value TQF is not sufficiently stable, it is also possible to weight it as follows: '[' Q F←(3TQF+T)/4.

According to the routines shown in FIGS. 3 and 4, the average period 'I' is calculated only when the rising edge of the Karman vortex signal occurs within a certain period of time (4 ms), as shown in FIG. TQF is updated. In other words, even if the flow rate increases, the number of times of smoothing processing does not increase, but the smoothing effect can be maintained to some extent by averaging period processing. Further, in the low flow rate region, the number of average periodic processing and smoothing processing decreases, and therefore, the average periodic processing interval substantially increases.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to have a smoothing effect even when the flow rate increases, and moreover, stable values can be obtained even in the low flow rate range without increasing the measurement time. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a diagram showing an embodiment of the Karman vortex output signal processing device according to the present invention, and FIGS. 3 and 4 are diagrams showing the control circuit of FIG. Flowchart for explaining the operation. FIG. 5 is a timing diagram for supplementary explanation of the flowcharts in FIGS. 3 and 4. 1: Karman vortex sensor, 11.12: vortex generator, 2: intake passage, 3.4: rectifier grid, 5: control circuit. Figure 3

Claims (1)

[Scope of Claims] 1. A Karman vortex sensor that generates an output signal with a frequency corresponding to the flow rate of fluid; a waveform shaping means that shapes the output of the Karman vortex sensor to generate a pulse signal; and within a certain period of time. pulse number counting means for counting the number of pulses of the pulse signal within the certain time; pulse period sum calculation means for calculating the sum of the periods of the pulse signal within the certain time; an average period calculating means for calculating an average period within the certain time period by dividing the sum of the periods of the pulse signal by the number of pulses only when the number of pulses is not 0; and calculating a smoothed value of the average period. An output signal processing device for a Karman vortex sensor, comprising: a smoothed value calculating means; and a flow rate calculating means for calculating the flow rate of the fluid using the rounded value.