JPS6056220A - Output signal processor for karman's vortex sensor - Google Patents

Abstract

PURPOSE:To prevent erroneous detection of flow rate by calculating flow rate in terms of average cycle and using the average cycle of the previous computation when a large cycle associated with missings of a pulse. CONSTITUTION:A sinusoidal output signal of a Karman's vortex sensor 31 is fed to a waveform shaping circuit 32, where said sinusoidal signal is converted into a square wave signal. The square wave signal is fed to an interrupt input of a CPU33, which executes an interrupt routine according to the rising of the square wave signal. The step 402 of the interrupt routine, a value TQFX is taken in from a cunter 35, which is reset. Then, at the step 403, TQFX<=K1.TQF (K; constant) is set and when TQFX>K1.TQF is met, missings are determined to occur in the output pulse of the waveform shaping circuit 32. Then, a shift is made directly to the step 405. At the step 405, the average cycle TQF is used to compute the air intake Q in terms of QK2/TQF. Then, the return is made.

Description

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

Conventional technology In general, the Hoehn type flow meter was the mainstream air flow meter for measuring the intake air amount of an engine.
Recently, Karman vortex sensors have been developed which have advantages such as small size. In the Karman vortex sensor, for example,
JP-A-58-80524 and JP-A-58-8052
As shown in No. 5, a Karman vortex generator is inserted into a pipe through which fluid flows, and the pressure fluctuations generated alternately near both sides of the Karman vortex generator are transferred to the pipe via a pair of pressure transmission passages. The velocity of the fluid is detected by transmitting the signal to an external diaphragm and photoelectrically detecting the rotational displacement of this diaphragm. In this case, a sinusoidal electrical signal corresponding to the rotational displacement of the diaphragm is obtained, this is converted into a rectangular wave signal, and the velocity of the fluid is obtained by counting each pulse period of this rectangular wave signal.

However, in the conventional type described above, no measures have been taken to prevent pulse loss due to instantaneous interruption of the sensor signal line or decrease in sensor output in low-speed areas, and as a result, when pulse loss occurs, The measured flow rate will be less than the actual flow rate. Therefore, when used as an air flow meter for an engine, there is a problem in that the air-fuel ratio is controlled to the lean side, resulting in a decrease in engine output torque, deterioration of exhaust gas, etc.

Purpose of the Invention The purpose of the present invention is to solve the problems of the conventional type described above.
Based on the concept of calculating flow rate using the average cycle,
When the detected cycle becomes unusually large from the above average cycle, it is assumed that there is a missing pulse, and the flow rate is calculated based on the average cycle from the previous calculation.Therefore, it is used as an engine air flow makeup. in case of,
The purpose is to prevent lean side control of the air-fuel ratio to prevent a decrease in engine output torque, deterioration of exhaust gas, etc.

Structure of the Invention The structure of the present invention for achieving the above object is shown in FIG. 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 signal of the Karman vortex sensor to generate a rectangular wave signal. The period detection means is one period T of the rectangular wave signal.
is detected and sent to the comparison means, while the multiplication means multiplies the average period TQF calculated in advance by a predetermined value by 1 and sends it to the comparison means. The comparison means is the detected period TQFX.
The average period multiplied by the predetermined value Kl is compared with 1·TQF. As a result, when TQFX≦1・TQF,
The average period updating means updates the average period TQF using the detected period TQFX. Then, the flow rate calculating means calculates the flow rate of the fluid using the average period.

EXAMPLES Hereinafter, the present invention will be described in detail with reference to FIG. 2 and subsequent drawings.

FIG. 2(A) is a sectional view showing an example of a Karman vortex sensor. In FIG. 2(A), a vortex generator 2 is provided at the center of the pipe 1, and this vortex generator 2 has a pair of vortex pressure intake holes 3 and an intake hole 3. A pressure transmission passage 4 for transmitting pressure fluctuations to the outside of the pipe line 1 is provided. As a result,
A rotational moment is generated in the diaphragm 5 due to pressure fluctuations in the pressure transmission passage 4 .

As shown in FIG. 2(B), the diaphragm 5 is supported on a rotation axis including its center of gravity by a pair of span hands 6a and 6b, and is further supported by a span band 6a.

6b is held by the frame portion 7. Therefore, the diaphragm 5 hardly vibrates due to the vertical vibration of the frame 7 caused by external vibration.
Therefore, rotational vibration occurs only in response to pressure fluctuations within the pressure transmission passage 4 due to the Karman vortices.

In FIG. 2(A), 8 is a light emitting diode as a light emitting means, and 9 is a photodiode as a light receiving means. That is, in this case, the diaphragm 5 acts as a light reflecting plate, and therefore, when the diaphragm 5 rotates and vibrates due to Karman vortex pressure, the output signal of the photodiode 9 becomes a sine wave with a vortex frequency f. The present invention relates to processing of the sinusoidal output signal of the photodiode 9.

FIG. 3 is a circuit diagram showing an embodiment of an output signal processing device for a Karman vortex sensor according to the present invention, which is configured by, for example, a microcomputer. In FIG. 3, the portion surrounded by the dashed line is configured as a microcomputer, but the waveform shaping circuit 32 may be provided within the Karman vortex sensor 31.

The sinusoidal output signal of the Karman vortex sensor 31 is supplied to a waveform shaping circuit 32, where the sinusoidal signal is converted into a rectangular wave signal. This square wave signal is supplied to the interrupt input of the CPII 33, and as a result, the CPU 33 executes an interrupt routine shown in FIG. 4, which will be described later, in response to the rise of the square wave signal. 34 is a clock generation circuit that generates various clock signals, 35 is a counter for detecting one cycle of the rectangular wave signal of the waveform shaping circuit 32, 36 is an input/output interface, and 37 is a program, constants, etc. ROM for storing data in advance, 3B is R for temporarily storing data.
It is AM.

FIG. 4 is a flowchart for explaining the circuit operation of FIG. 3, and is an intake air amount calculation routine. The interrupt step 401 starts with the rise of the rectangular wave signal of the waveform shaping circuit 32 as shown in FIG.
Counter 35 is reset for the next calculation cycle. In this case, the value T of the counter 35 is the period TQFXo, TQI'XI, and the period of the rectangular wave signal shown in FIG.
Corresponds to one of...

Next, in step 403, TQFX≦K 1- TQF, where K1 is a constant, for example, 1,1 to 1.9.
set between.

The TQF determines the average period of a predetermined number m of T leaves. That is, when T[IFX becomes abnormally larger than the average period T[IF and TFX>Kl·TQF, it is assumed that the output pulse of the waveform shaping circuit 32 is missing, and the process directly proceeds to step 405. On the other hand, if TQFX≦1・
If it is TQF, the average period TQF is updated in step 404. In other words, (m-1) T Kano + T [1FX TQF ←□. Note that m is set in a range of 2 to 16.

In step 405, the average period TQF is used to increase the intake air amount Q to Q4- by 2/TQF, where K2 is calculated using a constant, and in step 406 this routine ends.

In this way, as shown in FIGS. 5(A) and 5(B), when the captured period, for example, TOFX2, deviates significantly from the average period TQF, it is assumed that a pulse is missing, and the average period TQF is not updated. , that is, the previous average period TQF
is maintained. Note that the average period TQF' indicates the case where the average period is updated using the above-mentioned period TQFX2,
Thereafter, the average period TQF' becomes larger than the average period TQF as a whole, and therefore the measured intake air amount Q becomes smaller than the actual intake air amount.

Note that when the above-described device is applied to an automobile air flow meter, the determination in step 403 of the above-described flowchart is performed when the idle switch is on.
On the other hand, when the idle switch is off, step 40
It is also possible to directly proceed to step 404 without performing the determination in step 3.

As explained in the detailed description of the invention, according to the invention, the flow rate (intake air amount) is calculated using the average period, and when a large period due to missing pulses is detected, the average period from the previous calculation is used. This prevents erroneous detection of flow rate due to missing pulses, and therefore, when used as an engine air flow meter, it prevents the air-fuel ratio from becoming leaner, reducing engine output torque, deteriorating exhaust gas, etc. can be prevented.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of the present invention, Figure 2 (A)
Figure 2 (B) is a cross-sectional view showing an example of a Karman vortex sensor.
4 is a plan view of the diaphragm 5 in FIG. A flowchart for explaining circuit operation, and FIGS. 5(A) and 5(B) are timing diagrams showing supplementary explanation of the flowchart in FIG. 4. 1: Pipeline, 2: Vortex generator, 3: Temperature pressure Intake hole, 4: Pressure transmission passage, 5: Vibration plate, 8: Light emitting means, 9: Light receiving means, 3
1: Karman vortex sensor, 32: waveform shaping circuit. Patent Applicant Toyota Motor Corporation Patent Application Agent Patent Attorney Akira Aoki Patent Attorney Hakodate Japanese Patent Attorney Akira Yamaguchi Patent Attorney Masaya Nishiyama

Claims (1)

[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 signal of the Karman vortex sensor to generate a rectangular wave signal, and detects one cycle of the rectangular wave signal. a multiplying means for multiplying a predetermined average period by a predetermined value; a comparing means for comparing the detected period with an average period multiplied by the predetermined value; an average period updating means for updating the average period using the detected period when the average period is equal to or less than the multiplied average period; and a flow rate calculation means for calculating the flow rate of the fluid using the average period. Karman vortex sensor output signal processing device.