JPS6217619A - Apparatus for processing output signal of karman vortex sensor - Google Patents

Abstract

PURPOSE:To enable the control of an air/fuel ratio with high accuracy over an entire region by correcting a flow amount with higher accuracy in a low flow amount region while response is secured, by correcting the flow amount of a fluid on the basis of a vortex generation cycle. CONSTITUTION:A cycle detection means detects the cycle Ti corresponding to the flow amount of a fluid generated by a Karman vortex sensor and the correction coefficient K corresponding to the detected cycle Ti is operated by a correction coefficient operation means. Therefore, a flow amount operation means operates the flow amount Q=K/Ti of the fluid corresponding to the coefficient K and the cycle Ti. Because the flow amount is inversely proportional to the cycle Ti, if the error of the flow amount Q is corrected corresponding to the cycle Ti, a low flow amount region is corrected with higher accuracy and, at the time of the adaptation to an engine, high air/fuel ratio control accuracy can be obtained over an entire region.

Description

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

[Conventional technology]

In general, the vane flow meter was the mainstream air flow meter for measuring the amount of intake air in 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 pressure fluctuations that occur alternately near both sides of the Karman vortex generator are transferred to the pipe through 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 to obtain the velocity of the fluid.

When obtaining the fluid flow rate from the frequency of the output signal of the above-mentioned Karman vortex sensor, the frequency and air volume are not completely proportional, so it is common to correct the flow rate according to the frequency (
Reference: Japanese Unexamined Patent Publication No. 56-616).

[Problem that the invention seeks to solve]

However, engine air flow meters are required to have high response and high accuracy, especially in the low flow rate range.

Therefore, in the conventional method of correcting flow rate using frequency, it takes time to obtain an accurate value because the frequency is low in the low flow rate range, and it also requires correction with uniform weighting in all frequency ranges. There were problems in that the response was poor, and there was also an imbalance in which correction accuracy was insufficient in the low flow rate region and excessive accuracy in the high flow rate region.

[Means for solving problems]

The purpose of the present invention is to highly accurately correct the low flow rate range while ensuring responsiveness, and to obtain high air-fuel ratio control accuracy over the entire range when applied to an engine. is shown.

In FIG. 1, the Karman vortex sensor generates an output signal with a period T corresponding to the flow rate of fluid, and the period detecting means generates an output signal with a period T of the output signal of the Karman vortex sensor.

Detect. The correction coefficient calculating means calculates the correction coefficient K according to the period T. As a result, the flow rate calculation means calculates the correction coefficient and the cycle! tlIT, depending on the fluid flow rate Q=/
This is for calculating Ti.

[Operation] According to the above-mentioned means, since the flow IQ is inversely proportional to the period 3tlIT, if the error in the flow rate is corrected according to the period T, the low flow rate region can be corrected with high accuracy.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings from FIG. 2 onwards.

! 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 line 1, and this vortex generator 2 has a pair of overpressure intake holes 3 and a pressure A pressure transmission passage 4 is provided for transmitting fluctuations to the outside of the pipe 1. As a result,
A rotational moment is generated in the vibration Fi5 due to pressure fluctuations in the pressure transmission passage 4.

Note that, as shown in FIG. 2(B), the diaphragm 5 is supported by a pair of span bands 6a and 6b on a rotation axis that includes its center of gravity, and the span bands 6a and 6b are further held by a frame 7. has been done. Therefore, the diaphragm 5 hardly vibrates due to the vertical vibration of the frame portion 7 caused by external vibration, and therefore rotates and vibrates only in response to pressure fluctuations in the pressure transmission passage 4 due to 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. This 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 addition, in FIG. 3, the part surrounded by the one-dot chain line is configured as a microcomputer, but the waveform shaping circuit 3
4 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 34, where the sinusoidal signal is converted into a rectangular wave signal. This square wave signal is supplied to one interrupt input of CPU 35. As a result, the CPIJ 35 executes an interrupt routine shown in FIG. 4, which will be described later, in response to the rise of the rectangular wave signal. 36 is a free running counter that counts the black/white signal CLK and always generates the current time CNT;
37 is a ROM that stores programs, constants, etc. in advance; 38
A RAM 39 (also an input/output interface) temporarily stores data. For example, a crank angle sensor 32, a fuel injection valve 33, etc. are connected to the input/output interface 39.

The operation of the circuit shown in FIG. 3 will be explained with reference to FIG.

FIG. 4 shows an intake air amount calculation routine, which starts at the rise of the rectangular wave signal from the waveform shaping circuit 34 as shown in FIG. In step 401, the current time CNT is read from the free run counter 36, and in step 402, the vortex generation period T is calculated as TI←CNT-CNTO, where CNTO is calculated based on the time of the previous interrupt. In step 403, the current time CNT is set as CNTO in preparation for the next interruption.

In step 404, a correction coefficient K is calculated by interpolation using the one-dimensional matrix shown in FIG. 6 stored in the ROM 37, and in step 405, the intake air amount Q is set to /T at Q4-.

Calculate by

The routine then ends at step 406.

Note that the above-mentioned intake air iQ is used, for example, together with the engine rotational speed N0 calculated based on the output signal of the crank angle sensor 32, to calculate the fuel injection amount TAU, and operates the fuel injection valve 33 at a predetermined timing. I will let you do it.

As shown in Fig. 6, if the map to the correction coefficient is created at equal intervals with the period T, the correction coefficient will be lower in the low flow region than if the map to the correction coefficient is created at equal intervals with the vortex frequency It can be seen that the accuracy is improved. In other words,
In a low flow rate region, if the vortex frequency f is created at equal intervals, an error will occur by the amount shown by the chain line.

〔Effect of the invention〕

As explained above, according to the present invention, the fluid flow rate is set to the vortex generation period T! Since it is corrected based on
When the Karman vortex sensor is used as an air flow meter for an internal combustion engine, air-fuel ratio control is improved, which is useful for idling stability and the like.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of the present invention, Figure 2 (A)
is a cross-sectional view showing an example of a Karman vortex sensor, FIG. 2(B) is a plan view of the diaphragm 5 of FIG. 2(A), and FIG. 4 is a flowchart for explaining the operation of the circuit shown in FIG. 3, FIG. 5 is a timing chart of the output signal of the waveform shaping circuit shown in FIG. 3, and FIG. 7 is a graph illustrating the correction coefficient K in step 405. 1... Pipeline, 2... Vortex generator, 3...
Vortex pressure control hole, 4... Pressure transmission passage, 5... Vibration plate, 8... Light emitting means, 9... Light receiving means,
31... Karman vortex sensor. Figure 3 Figure 4 Figure 6

Claims (1)

[Claims] 1. A Karman vortex sensor that generates an output signal with a period corresponding to the flow rate of fluid; a period detection means that detects the period of the output signal of the Karman vortex sensor; and a correction coefficient according to the period. An output signal processing device for a Karman vortex sensor, comprising: a correction coefficient calculation means for calculating the correction coefficient; and a flow rate calculation means for calculating the flow rate of the fluid according to the correction coefficient and the period.