JPH0690060B2 - Karman vortex sensor output signal processor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an output 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, a vane type flow meter was the mainstream as an air flow meter for measuring the intake air amount of the engine,
Recently, a Karman vortex sensor having advantages such as small size is being developed. In the Karman vortex sensor, for example,
As shown in JP-A-58-80524 and JP-A-58-80525, a Karman vortex generator is inserted in a pipe through which a fluid flows,
By transmitting the pressure fluctuations alternately generated in the vicinity of both sides of the Karman vortex generator to the diaphragm outside the conduit via a pair of pressure transmission passages, the rotational displacement of this diaphragm is photoelectrically detected. The velocity of the fluid is detected. In this case, a sinusoidal electric signal corresponding to the rotational displacement of the diaphragm is obtained to obtain the fluid velocity.

When the flow rate of the fluid is obtained from the frequency of the output signal of the Karman vortex sensor described above, the frequency and the air amount are not completely proportional, and therefore the flow rate is generally corrected according to the frequency.
(Reference: JP-A-56-616).

[Problems to be solved by the invention]

However, an engine air flow meter is required to have high response and particularly high accuracy in a low flow rate region. Therefore, in the conventional method of correcting the flow rate with the frequency, the lower the flow rate, the lower the frequency, so it takes time to obtain an accurate value.
In addition, since the correction is performed with uniform weight in any frequency range, there is a problem that the response is poor, and further, the correction accuracy is insufficient in the low flow rate range, and the unbalance becomes excessive accuracy in the high flow rate range.

[Means for solving problems]

It is an object of the present invention to correct the lower flow rate region with higher accuracy while ensuring responsiveness, and to obtain high air-fuel ratio control accuracy over the entire range when applied to an engine. The means is shown in FIG. Shown.

In FIG. 1, the Karman vortex sensor generates an output signal having a period Ti corresponding to the flow rate of the fluid, and the period detecting means detects the period Ti of the output signal of the Karman vortex sensor. The correction coefficient calculation means calculates the correction coefficient K according to the cycle Ti. As a result, the flow rate calculating means calculates the flow rate Q = K / Ti of the fluid according to the correction coefficient K for correcting the deviation of the flow rate characteristic of the intake air amount of the engine and the cycle Ti.

[Work]

According to the above-described means, the flow rate Q is inversely proportional to the cycle Ti, and therefore, if the error of the flow rate is corrected according to the cycle Ti, the correction is performed with higher accuracy in the lower flow range.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings starting from FIG.

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

As shown in FIG. 2 (B), the diaphragm 5 is supported by a pair of span bands 6a and 6b on the rotating shaft including the center of gravity thereof, and the span bands 6a and 6b are held by the frame portion 7. Has been done. Therefore, the vibrating plate 5 has a frame portion 7 due to external vibration
Almost no vibration occurs in the up-and-down vibration, and therefore, rotational vibration occurs only in accordance with the pressure fluctuation in the pressure transmission passage 4 due to the Karman vortex.

In FIG. 2A, 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 vibrating plate 5 acts as a light reflecting plate. Therefore, when the vibrating plate 5 rotationally vibrates due to the Karman vortex pressure, the output signal of the photodiode 9 causes the vortex frequency f
Becomes a sine wave. The present invention relates to processing a sinusoidal output signal of the photodiode 9.

FIG. 3 is a circuit diagram showing an embodiment of the output signal processing device of the Karman vortex sensor according to the present invention, which is constituted by, for example, a microcomputer. In FIG. 3, the portion surrounded by the one-dot chain line is configured as a microcomputer, but the waveform shaping circuit 34
May be provided in the Karman vortex sensor 31.

The sinusoidal output signal of the Karman vortex sensor 31 is supplied to the waveform shaping circuit 34, where the sinusoidal signal is converted into a rectangular wave signal. This rectangular wave signal is supplied to one interrupt input of the CPU 35. As a result, the CPU 35 executes the interrupt routine shown in FIG. 4 described later in response to the rising edge of the rectangular wave signal. 36 is a free-run counter that counts the clock signal CLK and always generates the current time CNT, 37 is a ROM that stores programs and constants in advance, and 38 is a RA that temporarily stores data
M and 39 are input / output interfaces. A crank angle sensor 32, a fuel injection valve 33, and the like are connected to the input / output interface 39.

The circuit operation of FIG. 3 will be described with reference to FIG.

FIG. 4 shows an intake air amount calculation routine, which is started by the rising edge of the rectangular wave signal of the waveform shaping circuit 34 as shown in FIG. In step 401, free-run counter 36
Then, the current time CNT is read out, and in step 402, the vortex generation period Ti is calculated by Ti ← CNT−CNTO, where CNTO is calculated according to the time of the last interrupt. In step 403, the current time CNT is set to CNTO in preparation for the next interrupt.

In step 404, the correction coefficient K for correcting the deviation of the flow rate characteristic of the intake air amount of the engine is interpolated by the one-dimensional map shown in FIG. 6 stored in the ROM 37, and in step 405, the intake air amount Q is ← Calculate with K / Ti.

Then, in step 406, this routine ends.

The above-described intake air amount Q is used for calculating the fuel injection amount TAU together with the engine rotation speed Ne calculated based on the output signal of the crank angle sensor 32, and the fuel injection valve 33 is set at a predetermined timing. It will be operated.

As shown in FIG. 6, when the map of the correction coefficient K is created at regular intervals by the period Ti, the correction coefficient K is calculated in the low flow rate region as compared with the case where the map of the correction coefficient K is created at regular intervals by the vortex frequency f. It can be seen that the accuracy of is improved. That is, in the low flow rate region, when the vortex frequency f is created at equal intervals, an error occurs by an amount indicated by a chain line.

〔The invention's effect〕

As described above, according to the present invention, since the flow rate of the fluid is corrected based on the vortex generation cycle Ti, the flow rate detection accuracy can be improved even in the low flow rate measurement region where the cycle is long, and the Karman vortex sensor can be used as an internal combustion engine. When used as an air flow meter of an engine, the air-fuel ratio control is improved, which is useful for idling stability and the like.

[Brief description of drawings]

1 is a block diagram showing the configuration of the present invention, FIG. 2 (A) is a sectional view showing an example of a Karman vortex sensor, and FIG. 2 (B) is a plan view of the diaphragm 5 of FIG. 2 (A). 3 is a circuit diagram showing an embodiment of an output signal processing device for a Karman vortex sensor according to the present invention, FIG. 4 is a flow chart for explaining the circuit operation of FIG. 3, and FIG. 5 is FIG. 6 is a timing chart of the output signal of the waveform shaping circuit, and FIG. 6 is a graph for explaining the correction coefficient K in step 405 of FIG. 1 ... Pipe line, 2 ... Vortex generator, 3 ... Eddy pressure intake hole, 4 ... Pressure transmission passage, 5 ... Vibration plate, 8 ... Light emitting means, 9 ... Light receiving means, 31 ... Karman vortex sensor.

Claims (1)

[Claims] 1. A Karman vortex sensor for generating an output signal of a cycle corresponding to a flow rate of a fluid, a cycle detecting means for detecting a cycle of an output signal of the Karman vortex sensor, and an intake air amount of an engine according to the cycle. Output signal processing of a Karman vortex sensor, which comprises: a correction coefficient calculating means for calculating a correction coefficient for correcting the deviation of the flow rate characteristic of the above; and a flow rate calculating means for calculating the flow rate of the fluid according to the correction coefficient and the cycle. apparatus.