JPS5921485B2 - flow rate or flow rate detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a detector for detecting the flow velocity or flow rate of fluid, and in particular, pulsations may occur in the air flow depending on the driving conditions, such as the intake air of an engine of an automobile. The present invention relates to a detector that can accurately detect a flow rate or flow rate without being affected by the flow state of a fluid, even when the flow state is unknown.

Generally, a flow rate or flow rate detector called a Karman vortex flow meter utilizes the fact that the frequency of Karman vortex generated by a rod-shaped vortex generator placed in a fluid is proportional to the flow rate or flow rate. The relationship between the two is uniquely determined by the dimensions of the flow pipe and the vortex generator, and there is no change over time, and the flow velocity or flow rate is detected by the number of vortices released. It has advantages such as easy digital processing of the detection signal.

However, on the other hand, there is a fundamental drawback in that under pulsating flow, the generation of stable Karman vortices is hindered, and the ability to measure flow velocity or flow rate is impaired.

For example, when measuring the intake air amount of an automobile engine, etc., when the engine is operating in a partial load region, the intake pulsation is small, so it is possible to measure the intake air amount with extremely high accuracy using a Karman vortex flow meter. , When the throttle valve is almost fully opened during sudden acceleration of a car, pulsations occur in the intake airflow in the air duct hose and throttle chamber, so the generation of the Karman vortex itself is affected.D. The generation of the Karman vortex is synchronized with the pulsation. This makes accurate flow rate or flow measurements impossible. In addition to the above-mentioned Karman vortex flowmeter, the flow rate or flow rate is also measured by detecting the degree of cooling of a hot wire stretched in the fluid (cooling degree x flow rate) as the amount of decrease in resistance value or voltage, etc. There is a hot wire flow rate (flow rate) meter.

This type of current meter has the advantage of having a wide measurement range, good responsiveness, no loss of measurement function due to pulsations, and the ability to measure mass flow rate.
There is a drawback that measurement errors occur over time because the heat dissipation characteristics change due to dirt on the surface of the heating wire. Therefore, it has been necessary to calibrate measurement errors by installing a reference flow rate generator or other flowmeter in the flow pipe, or by removing the hot-wire type current meter from the flow pipe. Furthermore, when other devices are provided in the flow pipe as described above, there are also problems such as the need to change the flow pipe. This invention has been made in view of the above points, and includes a rod-shaped vortex generator disposed in a pipe through which fluid flows so as to be substantially perpendicular to the flow, and a vortex generator that periodically generates a vortex. Two thermal detectors are installed at positions perpendicular to the fluid flow within a region where the generated Karman vortices can be detected and are symmetrical with respect to the central axis of the rod-shaped vortex generator, and these thermal detectors a heating current control circuit for heating the thermal detector and maintaining its temperature constant; and a varying voltage appearing across the terminals of each thermal detector due to alternating temperature changes in each thermal detector. A first detection circuit extracts a signal corresponding to the difference between the signals and forms and outputs a pulse signal synchronized with the generation period of the Karman vortex from the signal, and a first detection circuit that adds or averages the two fluctuating voltage signals. a second detection circuit that outputs an analog signal according to the average flow velocity of the fluid; a pulse signal that detects the state of the fluid flow and outputs a pulse signal from the first detection circuit when the flow is in a steady state; By providing a switching circuit that outputs the analog signal that the second detection circuit outputs when in a pulsating state, the thermal detector can have a detection function as a hot wire current velocity (flow rate) meter and a function as a Karman vortex detection element. To provide a flow velocity or flow rate detector that has both sides and can automatically use its functions depending on the state of fluid flow, making use of only the advantages of two types of detectors that are fundamentally different in principle. It is something.

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a perspective view showing the structure of a vortex generator and a thermal detector of a detector according to the present invention.

In the figure, reference numeral 1 denotes a rod-shaped vortex generator, and one end thereof is provided with a mounting plate 3 having a through hole 3a for attaching the vortex generator 1 in the flow pipe 2, as shown in FIG. . The shape of the vortex generating body 1 is not limited to the quadrangular prism shown in the figure, but may be any shape such as a cylinder, a triangular prism, or a polygonal prism as long as it is symmetrical with respect to the fluid flow shown by arrow A in FIG. Reference numerals 4 and 5 denote an L-shaped support body and a T-shaped support body made of a conductive material, respectively, and are implanted on the surface 1a of the vortex generator 1 located on the downstream side of the fluid.

The L-shaped supports 4, 4 and the T-shaped support 5 are electrically connected to electrodes 4a, 4b} and 5a provided on the mounting plate 3 of the vortex generator 1, respectively. Note that if the vortex generator 1 is made of an insulator such as plastic material, the connecting wires between each of the supports 4 and 5 and each of the electrodes 4a, 4b, and 5b can be embedded independently. However, if the vortex generator 1 is made of a conductive material such as a metal material, it is necessary to insulate them from each other. Further, two L-shaped supports may be used instead of the T-shaped support 5, and two electrodes may be provided instead of the electrode 5a, so that the number of electrodes is four in total. Reference numerals 6 and 7 indicate hot wires as thermal detectors using metal wires such as tungsten wires or platinum wires, which are parallel to the vortex generator 1 in the longitudinal direction of the vortex generator 1 and parallel to each other. Further, as shown in FIG. 3, the L-shaped support 4, 4 and each tip of the T-shaped support 5 by spot welding, brazing, or the like.

It is said that the region in which the Karman vortex generated by the vortex generator 1 can stably pass through the flow channel 2 is about 10 to 20 times the width of the vortex generator 1 in the flow direction. }, and the hot wires 6 and 7 may be stretched within this area.

゛In addition, the diameter of the hot wires 6 and 7 needs to be 100μψ or less in consideration of responsiveness, but it is not necessarily smaller than this in consideration of requirements such as detection flow velocity range, hot wire size, hot wire intensity, and output signal level. It doesn't have to be.

Furthermore, the lengths of the hot wires 6 and 7 may be shorter than the length of the vortex generator 1 in the longitudinal direction as shown in FIGS. If the length of the body 1 is short, it may be approximately the same length. In short, it is sufficient that the hot wires 6 and 7 are stretched symmetrically with respect to the central axis of the flow pipe 2 in the longitudinal direction. In order to satisfy the above-mentioned conditions, the vortex generator 1 with the hot wires 6 and 7 stretched thereon is inserted in the middle of the flow pipe 2 so as to be substantially perpendicular to the flow of the fluid, A bolt 8 is screwed into the through hole 3a and fixed.

Next, before explaining the contents of the processing circuit for the signals obtained by the hot wires 6 and 7, the detection principle of the flow velocity or flow rate detector according to the present invention will be described.

As shown in FIG. 3, when the fluid flowing from the direction of arrow A hits the front surface of the vortex generator 1, Karman vortices are generated and released alternately from both sides of the vortex generator 1, and the heat rays 6 and 7 are generated. Since the hot wires 6 and 7 pass alternately, they are cooled alternately.

Now, when the Karman vortex passes through the hot wire 6, the passing flow velocity U6 of the fluid is expressed as U, where the average flow velocity of the fluid is u, and the flow velocity variation accompanying the passage of the Karman vortex is expressed as ΔUSln(i)t.
6-U+ΔUSlnCL)t・・・・・・・・・
・It can be expressed as (1).

On the other hand, since the hot wire 7 is stretched at a symmetrical position with respect to the central axis of the hot wire 6 and the vortex generating body 1, the flow velocity fluctuations are opposite in phase to the hot wire 6 side.

Therefore, the passing flow velocity U7 is U7-U-ΔUsin
ct) t ...... (to).

Therefore, if we take the difference between these passing flow velocities U6 and U7, we get U
6-U7=2ΔUslnωt '3゜0゜゜1゜゜(
3), since the average flow velocity component is removed, only the flow velocity fluctuation component synchronized with the generation period of the Karman vortex is left.

Also, if we take the sum of the passing flow velocities U6 and U7, then U6+U7=
2U (4) Since the flow velocity fluctuation is removed, only the average flow velocity is obtained.

Here, the heat dissipation characteristics of the hot wire are generally 12Rcxs7/ton...
・(5) (1: heating current value, R: resistance value of hot wire, u: flow velocity of fluid) In the above equation, the resistance value R of the hot wire is constant (
If the heating temperature is kept constant), the relationship between the voltage appearing at both ends of the hot wire and the flow velocity u is Vu4...
...(6), and when this is shown as a line diagram, it becomes as shown in Fig. 4.

Therefore, the maximum positive and negative fluctuation amount Δu with respect to the average flow velocity u of the passing flow velocity U6, U7 of each hot wire 6, 7 shown in equations (1) and (2) is the voltage fluctuation at the terminal of the hot wires 6, 7 ( V6 and V7), ΔV1<ΔV2 (4th
(see figure), and its amplitude fluctuates periodically.

Therefore, ideally, the terminal voltage V of the hot wire should be raised to the fourth power and corrected so as to have a linear relationship, and then this voltage needs to be added or subtracted. However, in general, the flow velocity fluctuation due to the Karman vortex is smaller than the average flow velocity u, so there is no problem even if the above-mentioned correction is not performed. This is not a problem, especially when subtracting and taking only the flow velocity fluctuation that is synchronized with the generation period of the Karman vortex, since only that period is important.
Further, even when averaging and taking only the average flow velocity, correct average flow measurement can be performed by holding the upper limit peak value of the fluctuation (indicated by the two-dot chain line) of the average voltage v due to the fourth power error.

Next, a circuit embodying the detection principle described above will be described with reference to FIG.

In FIG. 5, parts corresponding to those in FIG. 1 are designated by the same reference numerals. Further, the electrode 5a shown in FIG. 1 is grounded. In the figure, 9 is a heating current control circuit, and the heating wire 6
The heating temperature of the heating wire 6, which decreases due to the heat removal action of the Karman vortices periodically generated by the vortex generator 1, is kept constant by increasing it in accordance with the degree of decrease. be.

This heating current control circuit 9 consists of a heating wire 6 and a resistor R as shown in the figure.
1 to R3, a differential amplifier including an operational amplifier 0P1 and resistors R4 to R7, and a feedback circuit including a transistor Tr and resistors R8 and R. This heating current control circuit 9 is configured so that the unbalanced voltage of the Wheatstone bridge circuit, that is, the difference between the voltage at point a, which is the terminal voltage of the hot wire 6, and the voltage at point b, which is the connection point between resistors R2 and R3, is zero. It has come to work in such a way that it becomes That is, when the heating temperature of the hot wire 6 decreases due to an increase in flow velocity due to the generation of Karman vortices, the resistance value also decreases accordingly.

As a result, the balance of the Wheatstone bridge circuit collapses, and the differential amplifier amplifies the unbalanced voltage, so that the heating current increases until the base potential of the transistor Tr, which constitutes the feedback circuit, rises above V and the unbalanced voltage becomes zero. is increasing. However, although this heating current control circuit 9 can sufficiently follow small changes such as fluctuations in flow velocity caused by Karman vortices, it is difficult to keep the heating temperature of the hot wire 6 constant when the flow velocity itself changes rapidly due to pulsations or the like. Therefore, a variable voltage signal V6 corresponding to the voltage between the terminals of the hot wire 6 as shown in FIG. 6, for example, is outputted to the output point c. As mentioned above, the relationship of V,
8 and a transistor Tr2.
Ill do it.

Therefore, when the output point dl<v, as shown in FIG. 6, a variable voltage signal V7 corresponding to the voltage across the terminals of the hot wire 7 having an opposite phase to the variable voltage signal V6 is output. Of course, this signal V
The relationship V7C (U4) also holds true between 6 and the flow velocity u.
11 is the difference (V, -V
6) is extracted from the signal Q (see Figure 6), and a pulse signal Q synchronized with the generation period of the Karman vortex is extracted from the signal Q.
It is the first detection circuit that forms and outputs the signal V
6, operational amplifier 0P3 and resistor Rl that differentially amplifies V7,
.about.R22, a Φ capacitor C for shaping the waveform of the output signal Q thereof, a waveform shaping circuit consisting of resistors R23 to R2, and an operational amplifier 0P3.

12 is an analog signal P' obtained by removing the fourth root error from an analog signal P (see FIG. 6) corresponding to the average flow velocity of the fluid obtained by averaging both the above-mentioned fluctuating voltage signals V6 and V7. A second detection circuit that forms and outputs
Resistors R26 and R27 with equal resistance values are used to lower the levels of the fluctuating voltage signals V6 and V7 to 1/2 and add them to obtain P=(V6+V7)/2, and these resistors R26 and R27
An upper limit consisting of a diode D, a resistor R28, and a capacitor C2 for outputting an analog signal V obtained by removing the fourth root error (see Figure 4) from the averaged analog signal P output from the connection point e of It consists of a peak hold circuit.

13 is a switching circuit which detects the state of the fluid flowing in the duct 2 with a pulsation detector 14, and when the flow is in a substantially steady state, a pulse signal Q' outputted by the first detection circuit 11; When in a pulsating state, the analog signal B output from the second detection circuit 12 is switched to be output to a flow rate indicator or a control circuit (not shown).

Furthermore, when the detector according to the present invention is used to measure the amount of intake air in an engine such as an automobile, pulsations occur in the intake air flow mainly when the throttle valve installed in the throttle chamber is fully opened. This is caused by pressure fluctuations due to engine piston movement that are transmitted to air passages (for example, air duct hoses, etc.).

Therefore, a throttle valve switch that is turned on when the throttle valve is almost fully opened is used as the pulsation detector 14, or the engine suction negative pressure in the intake manifold decreases when the throttle valve opens. The presence or absence of pulsation is detected using a negative pressure sensor or the like that outputs a signal when the pressure becomes less than a predetermined value, and when the throttle valve is almost fully open or the engine suction negative pressure is less than a predetermined value, the switching circuit 13 outputs an analog signal P'. , and at other times, the pulse signal Q'' may be output. In this way, for example, as shown in FIG. Since a pulse signal q synchronized with the period is output, the period T during which the fluid flow is in a pulsating state depends on its frequency or period.
2, an analog signal V corresponding to the average flow velocity of the fluid is output, so depending on the level, it is possible to always accurately measure the flow rate or flow velocity regardless of the state of the fluid.

FIG. 7 shows another embodiment of the detection circuit for a detector according to the present invention, in which parts corresponding to those in FIG. 5 are given the same reference numerals. In this circuit, resistors R2, , R3O,
One piece of the Wheatstone pritz, which is configured with R, , is formed by a circuit in which the hot wires 6 and 7 are connected in series, and the average temperature (total resistance value) of the hot wires 6 and 7 is controlled by the heating current control circuit 15.
The heating current is controlled so that the current is constant.

Unfortunately, this heating current control circuit 15 includes resistors R32 to R37.
, an operational amplifier 0P4, and a transistor Tr3, the heating current control circuits 9 and 10 shown in FIG. 5 are constructed in the same manner. Then, a variable voltage signal V7 corresponding to the change in the resistance value of the hot wire 7 is taken out from the connection point g of the hot wires 6 and 7, and a variable voltage signal V6+ corresponding to the total resistance value of the hot wires 6 and 7 is taken out from the point f.
V7 can be taken out.

The voltage signal extracted from this point f is applied to resistors R38 and R39.
The voltage signal at point h (V6+V7
)/2 and the fluctuating voltage signal V7 taken out from point g are manually input to a first detection circuit 16 constituted by a differential amplifier consisting of resistors R4O-R43 and an operational amplifier 0P5 for differential amplification. If the degree of amplification is set to 2, the output signal Q will be as follows, and as in the previous embodiment, a signal Q corresponding to the difference between the fluctuating voltage signals V6 and V7 is obtained, and if this is waveform-shaped, it can be synchronized with the generation period of the Karman vortex. The second detection circuit 17 is simply a buffer circuit using an operational amplifier 0P6, and the voltage signal V6+V7 at point f is manually inputted via a resistor R3 forming a part of a Wheatstone bridge. The impedance is converted and output as an analog signal P corresponding to the average flow velocity of the fluid.

In this case, the upper limit peak hold circuit for correcting the fourth root error is omitted. The output switching between the pulse signal Q' and the analog signal P thus obtained is the same as in the previous embodiment.

This method simplifies the circuit and is preferable in practice.

As described above, according to the present invention, the thermal detector has both the detection function as a hot wire flow rate meter and the function as a Karman vortex detection element, and also Since the functions can be used separately, it is possible to use a hot wire flow rate (flow rate) meter and a Karman vortex flow rate (flow rate) meter.
It combines the advantages of both types of meters and enables highly accurate flow rate or flow rate measurement at all times depending on the flow condition.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing the structure of the vortex generator and the hot wire of the detector according to the present invention, and Fig. 2 shows the vortex generator with the hot wire shown in Fig. 1 attached to the flow pipe. FIG. 3 is a sectional view taken along the line V-V in FIG. 2, FIG. 4 is a line diagram for explaining the detection principle of the detector according to the present invention, and FIG. 6 is a circuit diagram showing an embodiment of the detection circuit of the device, and FIG. 6 is a diagram for explaining the operation of the embodiment shown in FIG. The figure is a circuit diagram showing another embodiment of the detection circuit of the detector according to the present invention.・L-shaped support, 5...T-shaped support, 6, T...
...Hot wire, 9, 10, 15...Heating current control circuit, 11, 1 6...First detection circuit, 12, IT...Second Detection circuit, 1 3
・・・・・・Switching circuit, 1 4 ・・・・Pulsation detector.

Claims (1)

[Claims] 1. A rod-shaped vortex generator disposed in a pipe through which fluid flows so as to be substantially orthogonal to the flow, and an area where vortices periodically generated by the vortex generator can be detected. two thermal detectors disposed perpendicularly to the flow of the fluid and symmetrically with respect to the central axis of the rod-shaped vortex generator; a heating current control circuit for maintaining a constant temperature, and a signal responsive to the difference in fluctuating voltage signals appearing across the terminals of each thermal detector due to alternating temperature changes of each of the thermal detectors. a first detection circuit that extracts the signal, forms a pulse signal synchronized with the generation period of the vortex from the signal, and outputs the pulse signal; a second detection circuit that outputs an analog signal; a pulse signal that detects the flow state of the fluid and outputs a pulse signal from the first detection circuit when the flow is in a substantially steady state;
A flow rate or flow rate detector comprising a switching circuit that outputs an analog signal outputted by the second detection circuit when in a pulsating state. 2. Two thermal detectors are installed along the longitudinal direction of the vortex generator within a passage area of vortex rows generated alternately from both side surfaces of the vortex generator parallel to the fluid flow. The flow rate or flow rate detector according to claim 1, which is a hot wire. 3. A patent characterized in that the two thermal detectors are hot wires each stretched by a support provided integrally with the vortex generator and inserted and attached together with the vortex generator into a measurement flow pipe. Flow velocity or flow rate detector according to claim 1 or 2.