JPS6162819A - Karman vortex flowmeter - Google Patents

Abstract

PURPOSE:To make it possible to detect the generation frequency of a Karman vortex from a low flow amount region to a high flow amount region, by altering the amplifying ratio of an AC amplifier for amplifying a vortex signal corresponding to the sucking amount of air. CONSTITUTION:A hot wire type vortex detector 2 is arranged in the downstream side of the vortex body placed in a flowline and a current is supplied to said hot wire type vortex detector 2 by a current amplifier 7. A bridge circuit 1 generates an output signal corresponding to the generation frequency of a Karman vortex from the change in the resistance of the hot wire type vortex detector 2 and outputs the same to BPF8 through a differential amplifier 6. BPF8 permits only the passage of vortex generation frequency and supplies said frequency to an AC amplifier 11. The AC amplifier 11 amplifies said vortex signal to output the same to a terminal C through a comparator 17. A change- over switch 13 is provided to the feedback route of the amplifier 11 and changed over corresponding to the output of a flow amount discrimination circuit 14, that is, the sucking amount of air to alter the amplifying degree of the amplifier 11 to the value corresponding to the sucking amount of air.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a Karman vortex flow rate needle for measuring the flow rate of intake air mainly drawn into an automobile engine.

[Conventional technology]

Electronically controlled engines that measure the intake air flow rate of the engine and increase or decrease the fuel injection amount based on this intake air flow rate require accurate measurement of the intake air flow rate.

Conventionally, as a means of measuring the intake air flow rate of an engine, there is a Karman vortex flowmeter using a Karman vortex.

This Karman vortex flowmeter has a flow path 21 as shown in FIG.
A vortex generator 1 is installed approximately perpendicularly to the intake air flow in the center of the
A Karman vortex 19 is generated downstream of this vortex generator 18 in response to the intake air flow rate, and this Karman vortex 19 is detected by a hot wire type vortex detector located downstream of the vortex generator 18. 2 is used to detect the generation frequency of the Karman vortex 19, and from this the intake air flow rate is detected.

A current is supplied to the hot wire 2 in advance so that it reaches a certain temperature, and the hot wire 2 is cooled every time the Karman vortex 19 passes through the hot wire 2. Therefore, at the same frequency as the generation frequency of the Karman vortex 19, The resistance value of the hot wire 2 fluctuates. In addition, the hot wire 2 constitutes a bridge circuit with other resistors,
The balance of the bridge circuit collapses according to the change in the resistance value of the hot wire 2, and this unbalanced voltage is input to the differential amplifier and amplified.
The output of this differential amplifier is input to a current amplifier, and current is supplied from this current amplifier so that the hot wire 2 has a constant temperature.

In addition, the output signal of the differential amplifier includes an AC change that occurs each time the Karman vortex passes, and a DC change that occurs due to changes in the steady cooling state of the hot wire 2 due to increases and decreases in the intake air flow rate. It changes as shown in FIG. 3 depending on the intake air flow rate.

The output signal of the differential amplifier is passed through a bandpass filter circuit to D
C changes are cut, only the Karman vortex generation frequency band is passed, this signal is amplified with an AC amplifier, this amplified signal is converted into a rectangular wave by a comparator, and this rectangular wave is counted and inhaled. I am looking for the air flow rate.

[Problem that the invention seeks to solve]

Here, as shown in FIG. 3, in a high flow rate region, the energy of the Karman vortex is large, so the amplitude of the alternating current component of the output signal of the differential amplifier is large. Conversely, in a low flow rate region, the energy of the Karman vortex is small, so the change in resistance of the hot wire is small, and the amplitude of the alternating current component of the output signal of the differential amplifier becomes small, resulting in a deterioration of the S/N ratio. Therefore, if the amplification factor of the AC amplifier is set constant, and the amplification factor is determined so that the output signal of the AC amplifier is not distorted in the high flow rate range, the output signal of the AC amplifier will be distorted in the low flow rate range. The amplitude becomes small, and the comparator cannot obtain sufficient amplitude for rectangular wave conversion, and as shown in FIG. 4, the rectangular wave is missing, making it impossible to count the positive r* Karman vortex generation frequency.

As a method to improve the detection accuracy of Karman vortices in the low flow rate region, a low-pass filter is operated only in the low flow rate region as shown in Japanese Patent Application Laid-Open No. 59-7215.
Although this signal is amplified and made into a rectangular wave in order to prevent the /N from deteriorating, the above points have not been sufficiently improved.

Therefore, it is an object of the present invention to provide a Karman vortex flowmeter that can detect accurate intake air flow rates by increasing the detection accuracy of the Karman vortex generation frequency from the low flow rate region of the intake air flow to the DC N region. It is in.

[Means for solving problems]

In order to solve the above problems, the present invention provides vortex detection that detects the generation frequency of the Karman vortex that is generated in response to the intake air flow rate on the downstream side of the vortex generator that is substantially orthogonal to the intake air flow. The Karman vortex flow meter is equipped with an AC amplifier that amplifies the vortex signal output from the vortex detector, and a changing device that changes the amplification factor of the AC amplifier in accordance with the intake air flow rate.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 2, the Karman vortex 19 generated on the downstream side of the vortex generator 18 in the flow path 21 is detected by the hot wire type vortex detector 2. The configuration of the signal processing circuit of the Karman vortex flow meter, which determines the flow rate from the Karman vortex generation frequency, is as shown in Figure 1.
4.5, a differential amplifier 6 that detects unbalance of the bridge circuit 1, and a current amplifier 7 that applies a current to the bridge circuit 1 based on the output signal of the differential amplifier 6. , an AC amplifier 11 having a bandpass filter circuit 8, a resistor 9 connected in series, and a resistor 10 connected in parallel; , a resistor 12 for changing the amplification factor of the AC amplifier 11 determined by the ratio of the series resistor 9 and the feedback resistor, a switch circuit 13 serving as a changing device for switching conduction or non-conduction to the resistor 12, and a switch circuit. 13 to 0N-
A flow rate determination circuit 14 that provides an OFF signal and an AC amplifier 1
1 and a comparator 17 that converts the amplified output signal into a rectangular wave.

The flow rate determination circuit 14 also includes a smoothing circuit 15 that extracts a DC level proportional to the flow rate from the output signal of the differential amplifier 6.
and a comparator 16 that determines the flow rate based on its DC level.

In FIG. 1, the output signal of the differential amplifier 6 is indicated by a, the output signal of the AC amplifier 11 is indicated by b, and the output signal of the comparator 17 is indicated by C.

The operation of the above configuration will be described below.

The hot wire 2 installed downstream of the vortex forming body 18 placed in the flow path 21 is supplied with current from a current amplifier 7 so as to have a certain temperature in advance.

At this time, each time the Karman vortex 19 passes through the hot wire 2, the hot wire 2 is cooled, so the resistance value of the hot wire 2 changes at the same frequency as the generation frequency of the Karman vortex 19, and accordingly the bridge circuit 1 is balanced. My body collapses. However, the unbalanced voltage of the bridge circuit 1 is immediately amplified by the differential amplifier 6, and the current amplifier 7 adjusts the current supplied to the bridge circuit 1 based on the output signal a, so the temperature of the hot wire 2 remains constant. is maintained.

The output signal a of the differential amplifier 6 includes an AC change that occurs each time the Karman vortex 19 passes, and a DC change that occurs because the steady cooling state of the hot wire 2 changes due to an increase or decrease in the flow rate. It changes as shown in Figure 3 depending on the flow rate.

The bandpass filter circuit 8 uses the output signal a of the differential amplifier 6.
On the other hand, it is set to pass only the vortex generation frequency band after canting the DC variation. The signal whose noise component has been reduced by this bandpass filter circuit 8 is amplified by an AC amplifier 11 to become an output signal, which is converted into a rectangular wave by a comparator 17 in the next stage, and becomes an output signal C.

Note that the comparator 17 is provided with hysteresis to prevent it from malfunctioning due to noise components contained in the output signal of the AC amplifier 11.

The circuit shown in FIG. 1 is configured to increase the amplification factor of the AC amplifier 11 in the low flow rate region, and to reduce the amplification factor of the AC amplifier 11 in the high flow rate region to the extent that the output signal is not distorted. has been done. This switching of the amplification factor is performed by switching the resistance value of the feedback resistor of the AC amplifier 11. In other words, switching the resistance value of the feed bank resistor is performed by turning the switch circuit 13 ON-OF-F in the resistor 12 and the switch circuit 13, which are connected in parallel with the resistor 10. If it is OFF, the resistance value of the feedback resistor is the resistance value of the resistor 10, and if the switch circuit 13 is 0N, the resistance value of the feedback resistor is the parallel resistance value of the resistor 10 and the resistor 12, that is, the resistance value of the resistor 1°. The resistance value of RIO1 and the resistance value of resistor 12 are R
If I2, the resistance value of the feedback resistor is (RI.

XRI2)/(RIO+RI2), which is a smaller value than when the switch circuit 13 is OFF. Therefore, when the switch circuit 13 is OFF, the amplification factor of the AC amplifier is set to a large amplification factor, and when it is ON, a small amplification factor is set.

In order to control this switch circuit 13, the intake air flow rate is determined from the output signal a of the differential amplifier 6. Since the DC level of the signal a changes depending on the flow rate as shown in FIG. 3, the DC level is extracted from the signal a by the smoothing circuit 15. Next, the comparator 16 in the next stage
The flow rate is determined by comparing the C level with a reference voltage, and if the flow rate is above a certain level, an ON signal is sent to the switch circuit 13. That is, the comparator 15 determines whether the flow rate is above or below a certain level, and if it is below, sends an OFF signal to the switch circuit li'813 to turn off the AC amplifier 1.
If the flow rate exceeds a certain level, an ON signal is sent to the switch circuit 13 to reduce the amplification factor of the AC amplifier 11.

As mentioned above, the amplification factor of the AC amplifier 11 is switched depending on the flow rate, and the output signal of this AC amplifier 11 is
As shown in the figure, the comparator 17 has a predetermined amplitude for rectangular wave conversion, and the comparator 1
The output signal C of No. 7 is the same from the low flow area to the high flow area.
As shown in the figure, a good rectangular wave is obtained.

Therefore, in this embodiment, by changing the feedback resistance of the AC amplifier 11 using the switch circuit 13 controlled by the flow rate discrimination circuit 14, the conduction/non-conduction of the resistor 12 provided in parallel with the resistor 10 is performed, so that the flow rate becomes lower than or equal to a predetermined flow rate. - Since the amplification factor of the AC amplifier 11 is configured to be changed as described below, the signal sent to the comparator 17 has sufficient amplitude from the low flow area to the high flow area, and the comparator 17 has a sufficient amplitude from the low flow area to the high flow area. A rectangular wave that can be reliably counted according to the flow rate up to a high flow rate region is outputted, the detection accuracy of the Karman vortex 19 is increased, and the detectable range of the Karman vortex 19 is expanded.

In the above-described embodiment, the amplification degree of the AC amplifier 11 with respect to the flow rate was switched only at one place, but as shown in FIG. If the configuration is such that the feedback resistance of the AC amplifier 11 is finely changed according to the flow rate and the amplification factor of the AC amplifier 11 is switched to one corresponding to each flow rate range, Karman vortex detection can be performed from the extremely low flow rate area to the extremely high flow rate area. Accuracy is further improved, and the range in which Karman vortices can be detected is further expanded.

Further, as shown in FIG. 7, a plurality of AC amplifiers 11 having different amplification factors are connected in parallel in advance, and the flow rate discrimination circuit 1
4, the same number of comparators 16 as the AC amplifiers 11 are provided in parallel, each having a reference voltage corresponding to the amplification factor of each AC amplifier 11, and the output signal of which AC amplifier 11 is selected from the signal of the comparator 16 of the flow rate determination circuit 14. A determination circuit 20, which serves as a change device for determining whether
It is also possible to use a configuration in which the waveform is converted into a rectangular wave.

Although the hot wire type vortex detector 2 is used in the above-described embodiment, any type of vortex detector may be used as long as the resistance value can be changed thermally, such as a hot film or a thermistor.

〔Effect of the invention〕

As described above, the present invention includes a vortex detector that detects the generation frequency of the Karman vortex that is generated in response to the intake air flow rate on the downstream side of the vortex generator that is substantially perpendicular to the flow of the intake air; Since the Karman vortex flowmeter is equipped with an AC amplifier that amplifies the vortex signal output from the vortex detector and a change device that changes the amplification factor of the AC amplifier according to the intake air flow rate, the vortex signal is Since the output signal is amplified with an amplification factor corresponding to the flow rate and output, the output signal has sufficient amplitude from the low flow rate region to the high flow rate region, which improves the detection accuracy of the Karman vortex generation frequency. This has the excellent effect of greatly improving the detection accuracy of the frequency at which Karman vortices occur, especially in the low flow rate range, and making it possible to accurately detect the intake air flow rate over the entire flow rate range.

[Brief explanation of the drawing]

Fig. 1 is a signal processing circuit diagram of a Karman vortex flow meter which is a main part of an embodiment of the present invention, and Fig. 2 shows the state of Karman vortices generated by a vortex generator provided in a flow path. 3 is a waveform diagram showing the output signal a, FIG. 4 is a waveform diagram when the signal shown in FIG. 3 is processed by a conventional signal processing circuit, and FIG. 5 is a waveform diagram showing the output signal a. Waveform diagrams when the illustrated signals are processed by the signal processing circuit of the Karman vortex flowmeter according to an embodiment of the present invention, and FIGS. 6 and 7 show essential parts of the embodiment of the present invention. It is a schematic circuit diagram. 2... Hot wire vortex detector, 11... AC amplifier, 13
... Switch circuit, 14... Flow rate discrimination circuit, 15.
... Hirayu circuit, 16... Comparator, 18... Vortex generator, 19... Karman vortex, 20... Judgment circuit.

Claims (1)

[Scope of Claims] A vortex detector that detects the generation frequency of a Karman vortex that is generated in response to the intake air flow rate on the downstream side of a vortex generator that is substantially perpendicular to the flow of the intake air; A Karman vortex flowmeter comprising: an AC amplifier that amplifies an output vortex signal; and a change device that changes an amplification factor of the AC amplifier according to an amount of intake air.