JP2775011B2 - Flow detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate detection device for detecting a flow rate by determining a flow rate of a fluid moving in a pipe.

[Conventional technology]

For example, fuel moves in the direction of the engine at an arbitrary speed to a fuel pipe for supplying fuel from a fuel tank to a vehicle engine. The instantaneous fuel flow data at this time is important data for engine control, and it is also possible to calculate the fuel consumption and fuel consumption based on the fuel flow data.

An ultrasonic Doppler system has been proposed as one of the flow rate detecting devices for detecting the flow rate based on the flow velocity of the fluid flowing in the pipe.

FIG. 7 shows the configuration of the proposed flow rate detection device. In FIG. 7, reference numeral 1 denotes a fuel pipe through which fuel A flows, and reference numerals 15 and 16 are provided side by side on the pipe wall of the fuel pipe 1 to transmit ultrasonic waves. A transmitter and a receiver for transmitting and receiving, respectively. The fuel A moves at a predetermined flow rate from the fuel tank toward the engine as described above. The ultrasonic wave from the transmitter 15 is transmitted from the direction in which the fuel A moves at a predetermined angle θ with respect to the moving direction of the fuel A.
Sent to.

In the configuration described above, the fuel A flowing through the fuel pipe 1 contains countless and random fine bubbles B. Then, when an ultrasonic wave is transmitted from the transmitter 15 into the fuel A at an angle θ, the ultrasonic wave is reflected by each bubble B in the fuel A, and the reflected wave is received and detected by the receiver 16. At this time, if the transmission frequency of the ultrasonic wave from the transmitter 15 is f _s , the frequency f f of the reflected wave received by the receiver 16
_r is v: Flow velocity of fuel A c: Sound velocity in fuel A Therefore, the Doppler frequency f _d is And by measuring the Doppler frequency f _d ,
The flow velocity v of the fuel A can be obtained. Also, the fuel pipe 1
Is known, the flow rate of the fuel A can be detected.

[Problems to be solved by the invention]

In the above-described conventional apparatus, when the flow velocity v is low, the Doppler frequency f _d becomes small, and it becomes difficult to accurately measure the frequency f _d , and an error occurs in the flow velocity v obtained from Expression (2). .

Further, if the ultrasound angle theta sent as theta = 90 °, the intensity of the reflected wave is maximized, the Doppler frequency f _d is not generated becomes cos [theta] = 0 in Equation (2). Thus, the setting is made such that θ <90 ° to generate the Doppler frequency f _d , but the intensity of the reflected wave is reduced and the S / N is deteriorated.

Therefore, an object of the present invention is to provide a flow rate detection device that can accurately detect the flow rate due to the flow rate of a fluid even when the flow rate is low and has a good S / N.

[Means for solving the problem]

In order to solve the above-mentioned problems, a flow rate detecting device according to the present invention is a flow rate detecting device that detects a flow rate of a fluid based on a flow rate of a fluid flowing in a pipe, wherein a sound absorbing rubber provided on an inner wall of the pipe, Transmitting means for transmitting ultrasonic waves to the liquid, which is provided through the tube wall and the sound absorbing rubber, and which is provided in the liquid of the ultrasonic wave which is provided through the tube wall of the tube and the sound absorbing rubber. Receiving means for receiving a reflected wave reflected by a point scatterer due to bubbles, and detecting means for detecting the number of fluctuations in sound pressure amplitude according to the moving speed of the liquid based on the reflected wave received by the receiving means, Computing means for computing the flow rate of the liquid from the number of fluctuations detected by the detecting means.

[Action]

In the above configuration, the ultrasonic wave transmitted from the transmitting means is reflected on the point scatterer by the myriad of bubbles in the liquid,
Spatial fluctuation of the sound pressure amplitude is formed in the reflection space. At this time, when the point scatterer moves with the movement of the liquid, the spatial fluctuation of the sound pressure amplitude also moves at the same speed. Therefore, the reflected wave is received from the receiving means, the number of fluctuations in the sound pressure amplitude corresponding to the moving speed of the liquid is detected by the detecting means based on the received reflected wave, and the moving speed is calculated from the number of fluctuations by the calculating means. The flow rate of the liquid is detected by the calculation. Moreover, the sound wave absorbing rubber is provided on the inner wall, and the transmitting means and the receiving means are provided through the tube wall and the sound absorbing rubber, so that the ultrasonic wave incident on the tube wall is absorbed and only the reflected wave from the point scatterer can be detected. Thus, reliable flow velocity detection can be realized.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a view showing one embodiment of a flow detecting device according to the present invention, in which 1 is a fuel pipe, 2 is a transmitter for transmitting ultrasonic waves, and 3 is a receiver for receiving reflected waves of ultrasonic waves. It is. Reference numeral 14 denotes a sound absorbing rubber attached to the entire inner wall of the fuel tube 1 for detecting the flow velocity, and the transmitter 2 and the receiver 3 are attached through the tube wall and the sound absorbing rubber 14 so that their sound waves can be detected. The transmitting surface and the sound receiving surface are in contact with the fuel A inside the tube. The transmitter 2 is set so that the ultrasonic wave from the transmitter 2 is transmitted in a direction perpendicular to the moving direction of the fuel A. Further, the sound absorbing rubber 14 is set so that the product ρc value of the density ρ and the sound speed c has a value equal to the product of the density of the fuel A and the sound speed.

In the above configuration, the operation principle of the present invention will be described.

As described above, countless bubbles B are distributed in the fuel A, but it is considered that a large number of minute point scatterers are irregularly and sufficiently finely distributed when viewed from the reflection of sound waves.

When an ultrasonic wave is incident on such a point scatterer, the reflected wave forms a spatial fluctuation of the sound pressure amplitude in the reflection space, that is, a sound pressure amplitude distribution. The flow velocity can be detected by detecting the sound pressure amplitude distribution.

That is, as shown in FIG. 1, when the wavelength λ of the ultrasonic wave from the transmitter 2 is uniform and the linearity is good, when the ultrasonic wave enters the detection target where the point scatterers are distributed, Reflection occurs at each point scatterer. At this time, the phases of the reflected waves from each point scatterer randomly interfere with each other, and the sound pressure formed by reflected waves in the space due to the interference is such that a large portion and a small portion of the sound pressure amplitude are randomly distributed. . Here, when the average pitch between the point scatterers becomes smaller than the wavelength λ of the ultrasonic wave, the average pitch of the distribution of the magnitude of the sound pressure amplitude on a surface equidistant from the point scatterer which is a reflecting surface in space. (For example, from the point of large sound pressure amplitude,
The average distance to the next larger point) takes on a saturated value.
A state where the magnitude of the amplitude of the reflected sound pressure is randomly distributed in the space is called a speckle state.

In FIG. 1, the beam width of the ultrasonic wave transmitted to the fuel A is denoted by w, the distance between the center of the fuel tube 1 and the receiver 3 is denoted by R, and the point scatterer to be detected has a velocity V ( (The capital letter V is a vector representation of speed), the sound pressure amplitude formed in the space by the reflected wave also moves at speed V. Therefore, the receiver 3 provided in the fuel pipe 1 shown in FIG. 1 detects the movement of the sound pressure amplitude distribution as shown in FIGS. 2A and 2B as a temporal output amplitude fluctuation. That is, spatial speckle is detected by the output amplitude fluctuation. 2 (a) and 2 (b), when the moving speed V of the detection target is high, the number of sound pressure amplitudes per unit time increases, and when the moving speed V decreases, the number of sound pressure amplitudes decreases.

FIG. 3 shows an embodiment of a device for obtaining the moving speed V (flow velocity) of the fuel A from the sound pressure amplitude characteristic of the reflected wave obtained by the receiver 3, wherein 4 is an envelope detector, and 5 is an envelope detector. A DC blocking circuit, 6 is a zero-cross counter, and 7 is an arithmetic circuit.

In this configuration, the envelope component shown in FIG. 4B is detected by the envelope detector 4 of the sound pressure amplitude signal of FIG. 4A output from the receiver 3, and the intensity I of the received sound pressure amplitude is detected. (= | P | ² ) (the capital letter P is a vector representation of sound pressure). Next, by passing this envelope component through the DC blocking circuit 5, the DC component is blocked, and only the AC component shown in FIG. 4 (c) is output. That is, the variation ΔI of the intensity I (= I− <I
>;<I> is the average value of I). The variation ΔI is input to the zero-cross counter 6 to calculate the number N ₀ of zero-crosses n ₁ , n ₂ ... Per unit time. The zero cross number N ₀ is a value corresponding to the moving speed V of the point scatterer.
Then, the detected number of zero crosses N ₀ is input to the arithmetic circuit 7, which calculates the moving speed V. Here, the relationship between the number of zero crosses N ₀ and the moving speed V is Therefore, the arithmetic circuit 7 calculates the moving speed V from the input N _{0 according} to the equation (3).

Here, as shown in FIG. 5, assuming that an ultrasonic wave is perpendicularly incident on a boundary surface between the medium X and another medium Y, as shown in FIG.
The reflectance H and the transmittance T are Z ₁ = ρ ₁ c ₁ , Z ₂ = ρ ₂ c ₂ ρ ₁ : density of the medium I, c ₁ : sound velocity of the medium I ρ ₂ : density of the medium II, and c ₂ : sound velocity of the medium I. Therefore, from the equation (6), if Z ₁ = Z ₂ , H =
It becomes 0, and all the ultrasonic waves incident on the medium Y pass through the medium Y and are not reflected by the medium X.

Therefore, in FIG. 1, if the ρc value of the sound absorbing rubber 14 is set to be equal to the ρc value of the fuel A, the ultrasonic wave from the transmitter 2 passes through the ultrasonic wave without being reflected by the bubble B in the fuel A. The sound reaches the sound absorbing rubber 14 on the side opposite to the sound absorbing rubber 14 on the transmitter 2 side. At this time, since the ρc value of the sound absorbing rubber 14 is equal to the ρc value of the fuel A, H = 0 from the equation (6), and all the ultrasonic waves are transmitted by the sound absorbing rubber 14.
Through. Ultrasonic waves are sufficiently attenuated in the rubber 14,
It does not reflect again on the wall surface of the fuel pipe 1 and enter the fuel A. As described above, since the receiver 3 detects only the reflected wave due to the bubble B in the fuel A, the speckle can be accurately detected.

6 (a) and 6 (b) show another embodiment of the present invention using a sound absorbing rubber. In FIG. 6 (a), the ultrasonic wave from the transmitter 2 is applied to the moving direction of the fuel A. In this case, the receiver 3 is attached to the sound absorbing rubber 14 on the side opposite to the transmitter 2 in FIG. The other configuration is the same as that of FIG.

1 and FIGS. 6 (a) and 6 (b), the ρc value of the sound absorbing rubber 14 may be a value that is close to the ρc value of the fuel A, and the same effect is obtained.
In FIGS. 1 and 6 (a) and (b),
The device for detecting the flow velocity from the reflected wave from the receiver 3 is the third device.
What is necessary is just to use the apparatus of a figure.

Furthermore, in the above-described embodiment, the pipe through which the fluid flows is used as the fuel pipe because the example in which the flow rate of the fuel as the fluid is detected is shown.

〔effect〕

As described above, according to the present invention, even if the moving speed of the liquid is low, the speed and the flow rate can be accurately detected, and the receiver detects only the reflected wave due to bubbles in the liquid. S / S
N is also good.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a flow rate detecting device according to the present invention, FIG. 2 is a diagram showing characteristics of reflected waves detected by the receiver of FIG. 1, and FIG. FIG. 4 is a diagram showing an example of an apparatus for calculating a flow rate based on the above, FIG. 4 is a waveform diagram of each part of the apparatus of FIG. 3, FIG. 5 is a diagram for explaining the operation of the embodiment of FIG. 1, and FIG. FIG. 7 is a view showing another embodiment of the flow detecting device according to the present invention. FIG. 7 is a view showing an example of a conventional flow detecting device. 1 ... fuel tube, 2 ... transmitter, 3 ... receiver, 4,8 ...
Envelope detector, 5,11 …… DC blocking circuit, 6,12 ……
Zero cross counter, 7 arithmetic circuit, 14 acoustic rubber, A fuel, B air bubble.

Claims (1)

(57) [Claims] 1. A flow detecting device for detecting a flow rate of a fluid based on a flow rate of a fluid flowing in a pipe, wherein a sound absorbing rubber provided on an inner wall of the pipe, and a sound absorbing rubber penetrating through the pipe wall and the sound absorbing rubber of the pipe. Transmitting means for transmitting an ultrasonic wave to the liquid, a reflected wave provided through the wall of the tube and a sound absorbing rubber, and reflected by a point scatterer by bubbles contained in the liquid of the ultrasonic wave Receiving means for receiving the signal; detecting means for detecting the number of fluctuations in the sound pressure amplitude corresponding to the moving speed of the liquid based on the reflected waves received by the receiving means; and detecting the flow rate of the liquid from the number of fluctuations detected by the detecting means. And a calculating means for calculating the flow rate.