JPS6326846B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a thermal flow meter in which a fluid passage is provided with a self-heating hot wire, and the flow rate of the fluid is measured based on the amount of heat released by the hot wire.

Conventionally, in order to measure the flow rate of fluid flowing through a flow tube, it has been common to use a thermal flowmeter in which a self-heating hot wire is stretched in a plane perpendicular to the flow. 1 and 2 illustrate a conventional device having the above-mentioned configuration, in which the hot wire 3 is arranged in a shape of a letter or an inverted V in a plane perpendicular to the flow of the fluid passage 2 in the flow tube 1. The ends are connected to output terminals 5a and 5b.
It is connected to the.

Therefore, when the hot wire 3 is energized and maintained in a self-heating state, the temperature of the hot wire 3 decreases due to the passage of fluid, and its resistance value decreases. This temperature change indicates the amount of heat dissipated by the hot wire 3, and by utilizing the fact that this is proportional to the flow rate of fluid passing through it, the flow rate of the fluid can be determined from the change in resistance value or the change in terminal voltage.

However, although such a device is effectively used to measure the flow rate in a steady state, it cannot be used to measure the amount of air intake in the intake manifold of an automobile engine equipped with an electronically controlled fuel injection device. When the flow velocity has different flow velocity distribution in the direction perpendicular to the flow (see Figure 3) or has a temporal distribution such as pulsating flow (see Figure 4), the plane perpendicular to the flow The amount of heat dissipated from a hot wire stretched inside the interior only indicates a value corresponding to the flow velocity of one cross section, and does not necessarily indicate a value corresponding to the average flow velocity of the fluid, so the measured value is the true value of the average of each cross section. It has the disadvantage that the flow rate is different from that of the current flow rate.

The present invention has been made in view of the above points, and even when the fluid flow in a pipe has a flow velocity distribution that differs spatially and temporally as described above, the true flow rate corresponding to the average flow velocity can be calculated. The purpose of the present invention is to provide a thermal flowmeter that can measure .

Therefore, in the thermal flowmeter according to the present invention, the hot wire is bent multiple times in a direction having both a component perpendicular to the fluid flow direction and a component parallel to the fluid flow direction. When viewed in the direction of the central axis, the belt is stretched so as to be approximately symmetrical with respect to the central axis.

Hereinafter, the present invention will be explained with reference to the embodiments shown in FIGS. 5 to 10, but the same parts as the conventional example shown in FIGS. .

Referring to FIGS. 5 to 7, 4a and 4b are pins for fixing the hot wire 3. In this embodiment, the hot wire 3 is connected downwardly and rearward from the upper output terminal 5a of the flow tube 1 to the pin 4a. The first part 3a reaches
, a second portion 3b extending from the pin 4a almost horizontally and slightly rearward to reach the pin 4b, and a third portion 3c extending upward and rearward from the pin 4b to reach the output terminal 5b.

Further, FIGS. 8 to 10 show another embodiment of the present invention, in which 6 is a hot wire support extending in the longitudinal direction through the center of the flow tube 1, and the hot wire 3 is connected to the upper output terminal 5a. a first portion 3a extending downward and rearward from the pin 4a to the lower pin 4a; a second portion 3b extending upward and rearward from the pin 4a to a point 6a on the support 6; and a second portion 3b extending horizontally and slightly rearward from the point 6a. It reaches the pin 4b on the side of the flow tube 1, and further horizontally and slightly backwardly passes through the point 6b of the support 6 and reaches the pin 4.
c, and in the same way, the horizontal and slightly backward tensioning of the flow tube 1 in the almost diametrical direction is repeated until points 6c and 6 are reached.
d and 6e to reach point 6f, and a fourth portion 3d extending upward and slightly rearward from point 6f to reach upper output terminal 5b.

With this configuration, the flow rate of the fluid can be determined by energizing the hot wire 3 to keep it in a self-heating state and detecting the temperature drop of the hot wire 3 due to passage of the fluid from the change in resistance value or the change in terminal voltage.

Here, in any of the above embodiments, the hot wire 3
is bent multiple times in the flow tube 1 forming the fluid passage 2 in a direction having both a component perpendicular to the fluid flow direction (direction of connection mark A) and a component parallel to the flow direction of the fluid as shown in the figure. When viewed in the direction of the central axis (FIGS. 6 and 9), it is tensioned so that it is approximately symmetrical with respect to the central axis. The hot wire 3 is tensioned substantially uniformly over the area, and the total resistance value of the hot wire 3 represents the flow rate corresponding to the average flow velocity in that area.

As described above, according to the present invention, the hot wire is stretched not only in the area perpendicular to the flow path but also in a predetermined area parallel to the flow direction, so that the hot wire is stretched only in the plane perpendicular to the flow. It is possible to directly measure the average value of the flow rate passing through the cross-section of the flow tube, without indicating the flow rate of only one cross-section, unlike a conventional thermal flowmeter in which one or more of these flowmeters are strung together. In addition, since the hot wire was stretched so as to be approximately symmetrical with respect to the central axis when viewed in the direction of the central axis of the flow tube, the resistance change of the hot wire was The result shows the average flow rate, and even if the flow has spatial and temporal distribution, it is possible to measure the true flow rate corresponding to the average flow velocity.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of a flow tube with a conventional thermal flow meter, FIGS. 2 a and b are cross-sectional views along the line FIG. A flow velocity distribution diagram of each cross section when the flow velocity distribution is different in the flow direction, FIGS. 5 to 7 are diagrams showing one embodiment of the present invention, in which FIG. 5 is a perspective view of a flow tube, and FIG. 6 is a perspective view of a flow tube.
The figure is a cross-sectional view, Figure 7 is a longitudinal cross-section, and Figure 8 is a vertical cross-sectional view.
10 to 10 are views showing other embodiments of the present invention, in which FIG. 8 is a perspective view of the flow tube, FIG. 9 is a cross-sectional view thereof, and FIG. 10 is a longitudinal cross-sectional view thereof. 1...flow tube, 2...fluid passage, 3...heat wire, 4
a, 4b, 4c...Pin for fixing hot wire, 5a, 5b
...Hot wire output terminal, 6...Hot wire support.

Claims (1)

[Claims] 1. In a thermal flow meter in which a hot wire that generates heat by itself is installed in a fluid passage and the flow rate of the fluid is measured based on the amount of heat released by the hot wire, the hot wire is inserted into a flow tube forming the fluid passage in the direction of the flow of the fluid. A thermal flow rate characterized in that the flow tube is bent multiple times in a direction having both orthogonal components and parallel components, and is stretched so as to be substantially symmetrical with respect to the central axis when viewed in the direction of the central axis of the flow tube. Total.