JPH0295213A - Vortex flowmeter - Google Patents

Abstract

PURPOSE:To measure a flow rate over a wide range by one vortex flowmeter by switching an ultrasonic wave phase detection system for a small flow rate range and a pressure detection system for a high flow rate range to detect vortexes. CONSTITUTION:A lattice type straightener 2 is arranged at the intake of the main body 1 of the air flowmeter to straighten a flow of air flowing in a vortex generation body 3. An ultrasonic wave transmitting element and an ultrasonic wave receiving element 5 are mounted opposite to each other on the wall surface of the main body 1 on the downstream side of the vortex generation body 3. An ultrasonic wave oscillator 20 drives the transmitting element 4 and generates the phase comparison signal of a phase detecting circuit 6 which compares the phase difference from the modulation wave of vortexes received by the element 5. Further, the received signal of the element 5 is inputted to a pressure detecting circuit 7. The outputs of the detecting circuit 6 and detecting circuit 7 are inputted to a decision circuit 10. The decision circuit 10 decides and selects the detecting circuit 6 or 7 according to the flow rate of the air. Namely, a vortex signal is outputted as the signal from the detecting circuit 6 in the small flow rate range or as the signal from the detecting circuit 7 in the high flow rate range.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex flowmeter that is capable of measuring normal pressure air supplied to an automobile engine over a wide flow rate range.

Conventional technology Automotive engines respond to technical issues such as large horsepower, high efficiency, and low NO2 by measuring air flow rate with high accuracy over a wide flow rate range and enabling complete combustion based on the air flow rate. There is a need for a flow meter that injects fuel. A vortex flowmeter is suitable as this flowmeter, and many proposals have been made regarding the flowmeter body, shape, vortex detection method, etc. The present applicant has proposed a "vortex flow meter" disclosed in Japanese Patent Publication No. 58-19970, which is equipped with a rectangular parallel conduit and an enlarged inlet with a square cross section equipped with a rectifier on the upstream side of the rectangular parallel conduit. A pair of ultrasonic wave transmitting/receiving devices consisting of a main body, a vortex generator disposed in the rectangular parallel conduit of the main body, and a piezoelectric element on the side of the conduit downstream of the vortex generator for detecting the vortex as a phase modulated signal by ultrasonic waves. We proposed a vortex flowmeter with a configuration in which elements are arranged. Furthermore, regarding the vortex detection method using the pair of ultrasonic wave transmitting/receiving elements, one proposed by the applicant was published in Japanese Utility Model Publication No. 57-25.
It is shown in the No. 140 publication. This method consists of a voltage-controlled oscillator that generates a high-frequency voltage that excites an ultrasonic transmitting element, and a phase of an output signal of an ultrasonic transducer that receives an ultrasonic signal modulated by one generated vortex φ2 = φ2' ± Δφ (φ2′
: average phase value of φ2, ±△φ: fluctuation component of φ2 caused by vortices) and the phase φ□ of the output signal of the oscillator. , a low-pass filter that extracts only −φ2′ and ±Δφ
It consists of a bandpass filter that extracts only the φ1−φ
The voltage controlled oscillator is controlled so that 2/ is always constant, and the vortex signal Δφ is output.

Problems with the Prior Art The above-mentioned vortex flowmeter detects the vortex signal in a non-contact manner as an ultrasonic modulation signal caused by the vortex, and does not extract energy from the generated vortex, so the detection sensitivity for small flow rates is extremely high. , and a vortex signal with excellent S/N ratio can be obtained, but when the flow velocity is large, there is a basic problem that detection exceeding the phase detection range of 0 to 2π is not possible. There are many ultrasonic components in the noise frequency and the frequency is close to the ultrasonic modulation signal due to the vortex, resulting in a deterioration of the S/N ratio, and when the propagation speed of the ultrasonic wave reaches a flow velocity that cannot be ignored, the received wave energy decreases. Decrease S/
This may worsen the S/N ratio, or the piezoelectric difference that occurs when the ultrasonic receiving element made of a bimorph piezoelectric element receives eddy fluctuation pressure that increases in proportion to the square of the flow velocity will further worsen the S/N ratio. The problem arises. In other words, since ultrasonic vortex detection directly detects the presence of vortices without contacting them, it is possible to detect small vortices in extremely low flow areas, but on the other hand, in high flow areas is the flow velocity 2
There were problems in that it could not be applied to the ultrasonic vortex detection method because of the excessively fluctuating differential pressure that increases in proportion to the power, and the flow rate measurement range was also limited and it could not be applied to measurements in the required high flow rate range.

The present invention for determination has been made in view of the above-mentioned problems, and detects vortices by switching between an ultrasonic phase detection method in a small flow region and a pressure detection method in a high flow region. It is possible to measure the flow rate over a wide range with one vortex flowmeter, and it is possible to switch between the ultrasonic phase detection method or the pressure detection method using a discrimination circuit that discriminates and selects according to the gas flow rate. The present invention provides a vortex flow meter that can continuously measure a wide range of gas flow rates with high accuracy.

Figure 1 is a block diagram for explaining an embodiment of the present invention. In the figure, 1 is the main body of an air flow meter for an automobile engine, which is housed in an air cleaner. A grid-shaped rectifier 2 is disposed at the inlet and rectifies the flow of air flowing into the vortex generator 3.

An ultrasonic wave transmitting element (hereinafter simply referred to as a wave transmitting element) 4 and an ultrasonic wave receiving element (hereinafter simply referred to as a wave receiving element) 5 are mounted on the wall surface of the main body 1 on the downstream side of the vortex generator 3. are mounted facing each other. In the figure, the propagation path of the ultrasonic wave is deviated in the flow direction by the air flow velocity, so when detecting a flow rate where the flow velocity cannot be ignored compared to the sound velocity, the wave receiving element 5 must be set in consideration of the maximum flow velocity. It is placed slightly downstream.

The wave transmitting and receiving elements 4 and 5 are made of the same piezoelectric element 1, for example, PZT.
A cone for ultrasonic impedance matching is attached to the orthogonal axis of a bimorph piezoelectric element plate. 20
is an ultrasonic oscillator which drives the wave transmitting element 4 and serves as a phase comparison signal for the phase detection circuit 6 which compares the phase difference with the vortex modulation signal received by the wave receiving element 5. Further, the wave reception signal of the wave reception element 5 is input to the pressure detection circuit 7. The received signal of the wave receiving element 5 includes a vortex signal whose phase is modulated by a vortex superimposed on an ultrasonic carrier signal. However, in the receiving element 5,
As the flow rate increases, an overfluctuation differential pressure that increases in proportion to the square of the flow rate is also applied, so a piezoelectric signal corresponding to the fluctuating pressure is generated as noise. This situation is shown in FIG. The piezoelectric signal is made dimensionless with a maximum flow rate Q of 1.0, and Q=0.
At a flow rate of 0.8, 0.9° 1.0, the vortex signal can be detected from the phase modulation signal at Q = 0.8 or less, and 2.3.4 in the figure is a conventional measurement method. Belongs to the impossible flow rate range. Since the piezoelectric signal includes an ultrasonic signal, in order to detect the vortex as a pressure signal, a symmetrical Tw tuned to the ultrasonic frequency is used as a circuit to remove the ultrasonic signal.
An in-T type filter 8 is used.

In FIG. 5, (b) is obtained from the signal of (a) by the symmetric T
It is obtained by passing through a win-T type filter 8.

The pressure detection circuit 7 includes the symmetrical Twin-T type filter 8 and a trigger circuit 9 that amplifies the signal (b) which is the output of the filter 8 to generate a pulse signal having a constant wave value and width.
The output of the phase detection circuit 6 and the pressure detection circuit 7 surrounded by the dotted line is input to the discrimination circuit 10, which outputs the vortex signal as a signal from the phase detection circuit 6 in the case of small flow foot loading, and outputs the vortex signal as a signal from the phase detection circuit 6, In the flow rate range, it is output as a signal from the pressure detection circuit 7.

FIG. 2 is a diagram showing details of the discrimination circuit 10, in which the output of the pressure detection circuit 7 is connected to the frequency-voltage conversion circuit (
F/V) 13, converted into voltage, and compared with a reference voltage corresponding to a flow rate, for example, Q=0.8, in a comparator 14. The vortex signal in the low flow rate region input from the phase detection circuit 6 to the input terminal 101 is input to the input terminal 101. AND gate 12.
This signal is output from the OR gate 16, but at a flow rate exceeding the reference voltage, the signal is ANDed by the inverter 15.
It is closed by the gate 12, and the signal in the high flow rate range at the terminal 102 is outputted from the OR circuit 16 to the terminal 11, allowing the needle side to be continuously measured over a wide range from the low flow rate range to the high flow rate range, which was previously impossible to measure. .

FIG. 3 is a diagram showing another embodiment of the present invention. In this embodiment, the wave receiving element 5 in the first @ is dedicated for transmitting the phase comparison signal of the phase detection circuit 6 in the low flow rate region, and A piezoelectric element 5a is disposed adjacent to the wave receiving element 5, and the piezoelectric element 5a
is specialized for pressure detection. Therefore, in the circuit elements shown in FIG. 1, the wave receiving element 5 is inputted only to the phase detection circuit 6, the piezoelectric element 5a is inputted only to the pressure detection circuit 7, and the other circuit elements act with the same symbols as in FIG. have. Note that the piezoelectric element 5a may have the same specifications as the wave receiving element 5.

FIG. 4 shows another embodiment, in which a piezoelectric element 5a is arranged on the wall surface of the main body 1 adjacent to the downstream side of the wave transmitting element 4 and facing the wave receiving element 5. The piezoelectric element 5a and the wave receiving element 5 are pressure detection elements that detect eddy fluctuation pressure, and each detection signal is introduced into a pressure detection circuit 71. The pressure detection circuit 71 includes a symmetrical Twin-T filter 8 on the receiving element 5 side, which is a filter that attenuates the excitation frequency of the transmitting element 4 oscillated by the ultrasonic oscillator 20, and a piezoelectric element 5.
A subtraction circuit 82 consisting of a differential amplifier circuit or the like that subtracts the output signals of the a-side symmetric Twin-T filter 81 and each of the symmetric Ttgin-'r filters 8.81; It consists of a trigger circuit 9 that converts the signal into pulses.

The phase detection circuit 6 and the discrimination circuit 10 are the same as those shown in FIG. 1, and their explanation will be omitted. The effect of the above-described configuration is to cancel the in-phase noise of the turbulence component contained in the air flow flowing through the main body 1, and double the vortex signal of the opposite phase component, thereby improving the S/N ratio. Therefore, in the figure, symmetrical Twin-T filters 8 and 81 are shown as filter circuits, but high-pass filtering is preferable because it also removes noise signals of high-frequency turbulence components. Although the explanation has been given with reference to FIG. 2 as an example of the discrimination circuit 10, since the air flow rate can be estimated in advance from the opening degree of the throttle valve and the rotation speed of the engine, these can be used as parameters to set the flow rate value. The present invention is not limited to the embodiment shown in FIG. 2, but also includes other flow rate determination means.

Effects Like a Savior 1 According to the vortex flowmeter of the present invention, the vortex flowmeter using the ultrasonic phase detection method, which conventionally had excellent small droplet sensitivity and enabled measurement with a small flow limit, acts on the wave transmitting and receiving element. What was impossible to measure in high flow areas due to the noise of the fluctuating pressure of the vortex, the fluctuating pressure is used as a pressure signal to detect the vortex, distinguish between the ultrasonic phase detection method and the pressure detection method, and output it continuously. This makes it possible to measure a wide range of flow rates using the same vortex flowmeter, and the same flowmeter can be applied to a wide horsepower range as an air flowmeter for automobile engines, which is highly economical.

[Brief explanation of drawings]

FIG. 1 is a block diagram for explaining one embodiment of the vortex flowmeter of the present invention, FIG. 2 is a detailed block diagram of the discrimination circuit in FIG. 1, and FIGS. FIG. 5, a block diagram for explaining another embodiment of the invention, is a diagram showing a received signal of an ultrasonic receiving element and a vortex signal according to the present invention. 1... Main body, 2... Rectifier, 3... Vortex generator, 4
, 5゜5a...piezoelectric element plate, 6...phase detection circuit,
7... Pressure detection circuit, 8... Symmetrical Twin-T circuit, 9... 1~Riga circuit, 10... Discrimination circuit, 11...
...Output, 20...Ultrasonic oscillator.

Claims (1)

[Scope of Claims] 1. A main body through which gas flows, a vortex generator disposed within the main body facing the flow, and a pair mounted opposite to the wall of the main body downstream of the vortex generator. In a vortex flowmeter consisting of a plate-shaped piezoelectric element, when the flow rate is low, one of the piezoelectric elements in the pair is used as an ultrasonic wave transmitting element and the other as a wave receiving element. The phase detection circuit includes a phase detection circuit that detects a modulated signal caused by the vortex of the ultrasonic wave produced by the piezoelectric element, and a pressure detection circuit that separates the piezoelectric signal generated by the fluctuating pressure of the vortex acting on the piezoelectric element at high flow rates, and the phase detection circuit. Alternatively, a vortex flowmeter characterized in that the pressure detection circuit is configured with a discrimination circuit that discriminates and selects according to the flow rate of gas. 2. When the flow rate is low, the vortex signal is a phase modulation signal generated by the ultrasonic vortex produced by the pair of piezoelectric elements, and when the flow rate is high, the vortex signal is a phase modulation signal generated by the ultrasonic vortex produced by the piezoelectric elements that form a pair, and when the flow rate is high, the vortex signal is generated by a piezoelectric element disposed adjacent to one of the piezoelectric elements. 2. A vortex flowmeter according to claim 1, characterized in that the piezoelectric signal is a piezoelectric signal of the applied vortex fluctuating pressure. 3. The vortex fluctuation pressure acting on the piezoelectric element is determined from the modulation signal of the vortex fluctuation pressure signal acting on the piezoelectric element and the ultrasonic signal,
A symmetric Twin having a frequency tuned to the ultrasound signal frequency.
3. The vortex flowmeter according to claim 1, wherein the ultrasonic signal is removed by a -T circuit. 4. At high flow rates, a piezoelectric element is placed adjacent to the downstream side of the ultrasonic transmitting element and facing the receiving element,
A filter element that removes high-frequency noise from the vortex fluctuation pressure signal of the piezoelectric element and wave receiving element, a subtraction circuit that obtains a differential output of the output of each filter, and the output of the subtraction circuit are used to convert the vortex signal at a high flow rate. 2. The vortex flowmeter according to claim 1, wherein the pressure is detected by a pressure detection circuit comprising a trigger circuit that outputs a pulse signal corresponding to the vortex signal.