JPS6212256Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a Karman vortex flowmeter for measuring the intake air amount, etc. of an internal combustion engine.

In recent years, so-called electronically controlled fuel injection engines have been developed that detect the intake air amount of an engine and control the fuel injection amount accordingly.

In such an engine, it is necessary to accurately measure the amount of intake air, and for this purpose, various measuring devices have been considered.

One example is a Karman vortex flow meter as shown in FIGS. 1 and 2, for example. As shown in the figure, a vortex generator 2 is placed approximately in the center of the duct 1. This vortex generator 2 is provided with a through hole 3 that penetrates the duct 1 so as to be perpendicular to the flow inside the duct 1. At both openings of the through hole 3, pressure fluctuations occur due to the generation of Karman vortices that occur alternately. Due to the pressure difference, an alternating flow is generated inside the through hole 3.

A hot wire probe 4 that generates heat when a constant current is supplied is placed in the middle of the through hole 3. When the hot wire probe 4 is cooled by an alternating current and its resistance value changes, the hot wire temperature control circuit 5 The current value that increases or decreases based on resistance changes is captured as a Karman vortex periodic signal.

This eddy detection signal is processed by a waveform shaping circuit 6 into a rectangular pulse wave with a predetermined slice level as a reference, and then sent to an edge controller 8 inside a control circuit 7.

The edge controller 8 outputs a trigger signal to the counter 9 in synchronization with the rise (or fall) of the square pulse wave, and the counter 9 receives the time signal (( clock pulses). This allows us to measure the generation period of Karman vortices.
That is, the flow velocity within the duct 1 is detected.

Then, the flow rate signal from the counter 9 is input to the arithmetic circuit 11 to calculate the flow rate (eg, volumetric flow rate). In this way, the flow rate is measured.

By the way, if the representative dimension of the vortex generator 2 placed in the duct 1 is D, and the velocity of the flow is v, then the generation period (frequency) [Hz] of the Karman vortex has the relationship shown by the following equation, and in the normal case are proportional as shown in Figure 3.

f=st.v/D...(1) (where st is Strohaus's constant) However, in this conventional device, the above
st becomes a variable in relation to the Reynolds number, and outside a predetermined Reynolds number range, for example in a low flow velocity region where the Reynolds number is small, the generation period of the Karman vortex by the vortex generator 2 is no longer proportional to the flow velocity v.

Therefore, there is a problem in that it becomes virtually impossible to measure the flow rate in such a case.

In particular, in this case, in the period measurement method of counting clock pulses, as in the conventional device, the generation period of the Karman vortex becomes very long, so the counter 9 may overflow and read that the period is short, resulting in an incorrect flow rate. In order to calculate or prevent this, the number of bits in the counter 9 must be increased, resulting in an increase in cost.

This idea was made by focusing on such conventional problems, and in the speed region where the Reynolds number is small and Karman vortices do not occur according to the proportional relationship of equation (1) above, the predetermined maximum period or minimum frequency The purpose of the present invention is to provide a Karman vortex type flow rate measuring device that avoids variations in measured values and increases the reliability of the instrument by calculating the flow velocity based on the flow rate and approximately measuring the flow rate.

Hereinafter, embodiments of the present invention will be described based on the drawings. In FIGS. 4 and 5, 1 is a duct, 2 is a vortex generator, and the details thereof are the same as in FIG. It is connected to circuit 5.

Therefore, when a Karman vortex is generated by the flow in the duct 1 and the resistance value of the hot wire probe 4 changes due to the alternating flow in the through hole 3 due to the pressure fluctuation, the current increases or decreases accordingly. The value is captured as the Karman vortex detection signal.

Then, this vortex detection signal is sent from the hot wire temperature control circuit 5 to the waveform shaping circuit 6, and the rectangular pulse wave 1
After being processed in step 2, it is input to the edge controller 8 inside the control circuit 13.

In the edge controller 8, the pulse wave 12
Trigger signals 14 are output one after another in synchronization with the rising (or falling) of , and are sent to the counter 9.

The counter 9 counts the time signal 15 from the first trigger signal until receiving the next trigger signal, that is, from the inter-trigger signal clock pulse generation circuit 10, and inputs this to 16 comparators.

The comparator 16 compares the counted value Kn with a predetermined value M (time in this embodiment) inputted from the limiter setting circuit 17, and calculates Kn.
If ≦M, Kn is sent as is to the arithmetic circuit 11 as the flow velocity signal 18, and if Kn>M, M is input to the arithmetic circuit 11 instead of Kn.

In this case, M is set to a value corresponding to the lowest frequency fmin (highest period) of the Karman vortex which is proportional to the velocity v in the above equation (1).

Then, the calculation circuit 11 calculates the flow rate based on Kn or M. As a result, the flow rate can be measured in a region where the flow velocity v of the flow in the duct 1 and the generation period of the Karman vortex are in a proportional relationship, as well as in a low flow velocity region where the Reynolds number is small and the two are not in a proportional relationship.

That is, when a Karman vortex is generated at a period proportional to the flow in the duct 1, the actual measured value of the period is directly input to the arithmetic circuit 11 and measured.
Therefore, the flow rate can be accurately determined,
Optimal data can be obtained.

On the other hand, when the generation period of the Karman vortex is not proportional to the velocity v in a low flow velocity region, the comparator 16 as a means for determining this determines that the preset value M is given priority over the actually measured value of the period. The signal is supplied to the arithmetic circuit 11 from a limiter setting circuit 17, which serves as a means for outputting a signal with the highest period (or lowest frequency) within the proportional speed region. Then, the flow rate is approximately measured based on this M.

This M is quite large, so the flow is quite slow and the measurements are well approximated.

For this reason, it is prevented that flow rate measurement becomes impossible or that the measured values become unstable due to large variations as in the conventional example, and the reliability of the measuring device is further improved.

6 and 7 show other embodiments of the present invention, in which the vortex detection signals input within a certain predetermined time are used instead of the period measurement method of counting clock pulses as in the previous embodiment. Specifically, the square pulse wave 12 processed by the waveform shaping circuit 6 is sent to the control circuit 19.
The generation frequency of the Karman vortex is detected by counting the edge pulses 21 which are input to the internal edge pulse generation circuit 20 and output in synchronization with the rising edge of the pulse wave 12, etc., and the flow rate is measured.

In this frequency counting method, 24 edge pulse counters are opened for a predetermined period of time based on signals 23 from 22 gate controllers, and the frequency of the Karman vortex is measured during this period.

This frequency count value Ln is then input to the comparator 26 together with a predetermined value N (in this case, the lowest frequency within the proportional speed region) from the limiter setting circuit 25.

The comparator 26 sends Ln to the flow velocity signal 18 if Ln≧N, and sends N to the arithmetic circuit 11 if Ln<N. Then, the arithmetic circuit 11 calculates and measures the flow rate based on these. Even in this case, the accuracy of measuring the flow rate can be improved, and a sufficient approximate value can be obtained in a low flow rate region.

FIG. 8 shows another embodiment of the present invention,
Signal from waveform shaping circuit 6 (square pulse 12)
is calculated by a so-called microcomputer 27 to measure the flow rate.

The square pulse 12 is input to an edge controller 29 and a free lining counter 30 via a waveform processing circuit 28, and an output signal of the edge controller 29 is sent to a PIA (Peripheral Interface Adapter) 31.

The free lining counter 30 measures time in parallel with the signal from the waveform processing circuit 28, and the free lining counter 30 measures time in parallel with the signal from the waveform processing circuit 28, and measures the time in parallel with the signal from the edge controller 29.
When a command is received from the CPU 32, the time measurement value (added time) at that time is sent to the CPU 32 via the PIA 31.

At the same time, the PIA 31 transmits the interrupt request IRQ to the CPU 32.

When an IRQ is applied, the CPU 32 calculates the difference between the time measurement value and its previous value (set in the ROM 33), and this difference value P, that is, the period of the vortex, is determined in advance.
If it is smaller than the set value M stored in the ROM 33, that P is stored in the RAM 34 as data. If it is larger than the set value M, M is stored in the RAM 34.

The data in this RAM 34 is calculated by another program (not shown) via the I/O section 35.
Obtained as a flow rate value.

The flowchart in this case is as shown in FIG.

In each example, the flow rate is calculated and measured using a predetermined value in the low flow velocity region where the generation period of Karman vortices is unstable, but the flow rate is also calculated and measured using a predetermined value. , it is possible to measure the flow rate in the same manner, and in this way, a measuring device more suitable for practical use can be obtained.

As explained above, according to the present invention, in the low flow velocity region where the flow velocity and the generation cycle of Karman vortices are not proportional, the vortices in the proportional region are Since we have provided a means to output the highest cycle or lowest frequency signal of In addition to increasing reliability, if this measuring device is used, for example, when controlling the air-fuel ratio by detecting the intake air amount of an internal combustion engine, it has the effect of significantly increasing the stability of the engine.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional device, Figure 2 is a structural diagram of a Karman vortex generator, Figure 3 is a graph showing velocity, vortex period, and frequency in a proportional relationship region, and Figure 4
The figure is a block diagram showing an embodiment of the present invention, Fig. 5 is a time chart thereof, Fig. 6 is a partial block diagram showing another embodiment of the present invention, Fig. 7 is a time chart thereof, and Fig. 8 9 is a partial configuration diagram showing another embodiment of the present invention, and FIG. 9 is a flowchart thereof. DESCRIPTION OF SYMBOLS 1... Duct, 2... Vortex generator, 5... Hot wire temperature control circuit, 6... Waveform shaping circuit, 8... Edge controller, 9... Counter, 10... Clock pulse generation circuit, 11... Calculation Circuit, 16...
Comparator, 17... Limiter setting circuit, 20... Edge pulse generation circuit, 22... Gate controller, 24... Edge pulse counter, 25... Limiter setting circuit, 26... Comparator, 27... Microcomputer, 29 ...Etsuji controller, 30...Free lining counter, 31...PIA, 32...
...CPU, 33...ROM, 34...RAM.

Claims (1)

[Scope of utility model registration request] In a Karman vortex type flow measurement device that places a vortex generator in the flow in a duct and calculates the flow rate by converting the period or frequency of the generated vortex into an electrical signal, the flow velocity and the generation period of the vortex are calculated. and a means for outputting a signal of the highest period or lowest frequency within the proportional region, and a means for outputting a signal of the highest period or lowest frequency in the proportional region, and a means for determining a low flow rate region in which the ratio is not proportional, and a means for outputting a signal of the highest period or lowest frequency in the proportional region, A Karman vortex flow meter characterized by calculating flow rate with priority.