JPH0695028B2 - Karman vortex sensor output signal processor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an output signal processing device of a Karman vortex sensor used as an air flow meter for measuring an intake air amount of an engine, for example.

[Conventional technology]

Generally, as an air flow meter for measuring an intake air amount of an engine, a Karman vortex sensor having advantages such as small size is being developed recently. In the Karman vortex sensor, for example, Japanese Patent Laid-Open Nos. 58-80524 and 5
As shown in No. 8-80525, a Karman vortex generator is inserted in a pipe in which a fluid flows, and pressure fluctuations alternately generated near both sides of the Karman vortex generator are piped through a pair of pressure transmission passages. The velocity of the fluid is detected by transmitting it to the vibration plate outside the road and photoelectrically detecting the rotational displacement of the vibration plate.
In this case, a sinusoidal electric signal corresponding to the rotational displacement of the diaphragm is obtained, converted into a pulse signal, and the pulse signal is processed to obtain the fluid velocity. In addition,
The velocity of the fluid is proportional to the frequency of the pulse signal of the Karman vortex sensor under a predetermined condition.

As a method of processing the pulse signal of the Karman vortex sensor, there is a method of counting the number of pulses within a fixed time and directly determining the frequency, that is, the fluid flow rate. In this case, in order to obtain an accurate fluid flow rate, The number of pulses to be counted must be made sufficiently large, and therefore the above-mentioned fixed time must be set large, resulting in poor responsiveness. For this reason, it is usual to obtain the frequency by detecting each period of the pulse signal and calculating the reciprocal thereof (for example, Japanese Patent Laid-Open Nos. 60-53811 and 53812).

[Problems to be solved by the invention]

The method of obtaining the frequency, that is, the flow rate of the fluid by detecting the period of the pulse signal and calculating the reciprocal thereof is
Although the responsiveness is improved, the influence of the fluctuation of the cycle due to the pulsation of the flow rate is large. For this reason, in order to reduce such an effect (smoothing), it is necessary to perform a smoothing process or obtain an average period within a fixed time. However, as the smoothing process, it is general to weight and average the smoothed value up to the previous value and the latest value for each cycle update, and therefore, when the flow rate increases, the cycle update becomes faster,
There is a problem that the smoothing effect cannot be obtained. On the other hand, in order to obtain a stable value in the low flow rate range when obtaining the average period within a fixed time, the above fixed time must be lengthened. Therefore, there is a problem that the responsiveness becomes low.

[Means for solving problems]

An object of the present invention is to obtain a flow rate in which fluctuations due to pulsation of the flow rate are smoothed by a smoothing effect without sacrificing responsiveness, and the means is shown in FIG. There is.

In FIG. 1, the Karman vortex sensor generates an output signal having a frequency corresponding to the flow rate of the fluid, and the waveform shaping means waveform-shapes the output of the Karman vortex sensor to generate a pulse signal.
The pulse number counting means counts the pulse number CKRMN of the pulse signal within a predetermined time, and the pulse cycle total calculation means calculates the total sum STQF of the pulse signal cycles within the predetermined time. As a result, only when the number of pulses within a predetermined time is not 0,
The average period calculating means calculates the average period T within the predetermined time by dividing the sum STQF of the pulse signal periods by the number of pulses CKRMN, and the smoothed value calculating means has already calculated the average period T calculated. An averaging process including weighting is performed between the smoothed value (TQF) and the smoothed value TQ of the average period T.
Calculate F. Then, the flow rate calculating means calculates the flow rate Q = K / TQF (K: constant) of the fluid using the smoothed value TQF.

[Action]

According to the above-mentioned means, the average period for each predetermined time is obtained and the smoothing process is performed at the same time. Therefore, even when the flow rate is increased, the average period process within the predetermined period is performed to some extent. The effect is maintained, and in the low flow rate region, when the number of pulses is 0, the averaging process and the averaging value update are not performed, so that the averaging process interval is substantially increased, and therefore, it is necessary to increase the predetermined time. Since it does not exist, responsiveness does not decrease.

〔Example〕

 Embodiments of the present invention will be described below 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 FIG. 2, 1
Karman vortex sensor 1 consisting of a pair of columnar vortex generators 11 and 12
Is vertically inserted into the intake passage 2 of the engine. Double rectifying grids 3 and 4 are provided upstream of the vortex generators 11 and 12,
This improves the proportional characteristic of the flow rate Q and the Karman vortex frequency f in a wide flow rate range.

The vortex generator 12 is provided with a pair of vortex pressure intake holes and a pressure transmission passage (not shown) for transmitting pressure fluctuations in the intake holes to the outside of the intake passage 2. As a result, a rotational moment is generated in the diaphragm therein due to the pressure fluctuation in the pressure transmission passage. Therefore, the diaphragm vibrates rotationally according to the pressure fluctuation in the pressure transmission passage due to the Karman vortex. Thus, when the diaphragm vibrates rotationally, a sinusoidal electric signal having the vortex frequency f is photoelectrically (or ultrasonically) generated 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 1 is supplied to the waveform shaping circuit 51, where the sinusoidal signal is converted into a pulse signal. This pulse signal is CPU52
Is supplied to one interrupt input of the. As a result, the CPU 52 executes the interrupt routine shown in FIG. 3, which will be described later, in response to the rise of the pulse signal, for example. Reference numeral 53 is a clock generation circuit for generating various clock signals. One clock signal is supplied to one interrupt input of the CPU 52, and as a result, the CPU 52 causes the interrupt routine shown in FIG. To execute. Further, another clock signal of the clock generation circuit 53 is supplied to the counter 54 for detecting one cycle of the pulse signal described above. The counter 54 is for detecting the rising cycle of the pulse signal. 55
Is an input / output interface, 56 is a ROM for storing programs and constants in advance, and 57 is a RAM for temporarily storing data.

The operation of the control circuit of FIG. 2 will be described with reference to the flowcharts of FIGS.

FIG. 3 is a calculation routine for updating the pulse number counter CKRMN and the pulse period total counter STQF, which is executed at every pulse rise of the waveform shaping circuit 51. That is, the pulse number counter CKRMN is incremented by one in step 301, the pulse period D is fetched from the counter 54 in step 302, and the counter 54 is cleared for the next operation cycle. Next, at step 303, the pulse period D fetched at step 302 is added to the pulse period total counter STQF, and at step 304, this routine ends.

As described above, the counter 54 is cleared each time the pulse signal of the waveform shaping circuit 51 rises, and counts a predetermined clock signal, for example, a 0.25 ms signal, and advances.

FIG. 4 shows a flow rate Q calculation routine, which is executed for each output signal (4 ms) of the clock generation circuit 53. Step 401
Then, other interrupts are prohibited so that the Karman vortex interrupt shown in FIG. 3 is generated during the execution of this interrupt process and a calculation error does not occur. Next, in step 402, it is judged whether or not the pulse number counter CKRMN is 0, and if it is 0, that is, if there is no Karman vortex interrupt at all, after jumping to step 409 after interrupting other interrupts in step 408 The process ends. If not 0, go to step 403
Pulse period total counter which is the cumulative value of the period until then
A value T obtained by dividing the value of STQF by the Kalman signal interrupt count CKRMN, that is, an average period every 4 ms is calculated. Then, at step 404, each counter CKRMN, STQF is cleared, and at step 405 other interrupts are permitted, and then the average period T obtained at step 403 and the smoothed value TQF obtained so far are not weighted. The value averaged in is set as a new TQF, that is, TQF ← (TQF + T) / 2. Next, at step 407, the flow rate Q is calculated by Q ← K / TQF and stored in the RAM 57. Then, the process proceeds to step 408, and this routine ends.

In step 406, if the smoothed value TQF is not sufficiently stable, it is possible to weight TQF ← (3TQF + T) / 4.

According to the routines of FIGS. 3 and 4, as shown in FIG. 5, the average period T is calculated only when the rising edge of the Karman vortex signal occurs within a fixed time (4 ms), and the averaged value TQF is calculated.
Will be updated. That is, even if the flow rate increases, the number of times of smoothing does not increase, but the smoothing effect can be maintained to some extent by the average period processing. Further, in the low flow rate region, the number of averaging treatments and the number of annealing treatments decrease, so that the averaging treatment interval substantially increases.

〔The invention's effect〕

As described above, according to the present invention, a smoothing effect can be provided even if the flow rate increases, and a stable value can be obtained even in the low flow rate range without increasing the measurement time. be able to.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention, FIG. 2 is a diagram showing an embodiment of a Karman vortex output signal processing device according to the present invention, and FIGS. 3 and 4 are control circuits of FIG. A flow chart for explaining the operation, and FIG. 5 is a timing chart for supplementary explanation of the flow charts of FIGS. 3 and 4. 1: Karman vortex sensor, 11, 12: Vortex generator, 2: Intake passage, 3, 4: Rectifying grid, 5: Control circuit.

Claims (1)

[Claims] 1. A Karman vortex sensor for generating an output signal having a frequency according to the flow rate of a fluid, a waveform shaping means for shaping a waveform of the output of the Karman vortex sensor to generate a pulse signal, said within a fixed time. A pulse number counting means for counting the number of pulses of the pulse signal, a pulse period total operation means for computing the sum of the cycles of the pulse signals within the fixed time, and the number of pulses of the pulse signal within the fixed time is Only when it is not 0, an average period calculating means for calculating the average period within the certain time by dividing the total sum of the period of the pulse signal by the number of pulses, and the calculated average period has not already been calculated. A smoothing value calculating means for calculating an averaged value of the average period by performing an averaging process including weighting between the smoothing value and a flow rate calculating means for calculating the flow rate of the fluid using the smoothing value. Output signal processing unit of Karman vortex sensor having a.