JPH0321452Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention is a Karman vortex generator inserted into a fluid flowing in a pipe, for example, in order to measure the intake air amount of an engine such as an automobile. This invention relates to a Karman vortex flow meter that measures flow rate by detecting the Karman vortex street generated by.

[Prior art and its problems] A vortex flowmeter for measuring the intake air amount of this type of engine is known, for example, in Japanese Patent Publication No. 34046/1983. The vortex flowmeter disclosed in this publication employs a configuration in which one rectifying grid is attached to the upstream side of the throttle tube at the entrance of the conduit. When conducting experiments on a vortex flow meter with such a configuration, it was found that due to the rectifying effect of the rectifying grid, the linearity in the low speed range is lower than that in the high speed range. Therefore, it has been desired to improve measurement accuracy by improving linearity in the low speed range.

[Purpose of invention]

In view of the above-mentioned points, the purpose of the present invention is to provide a Karman vortex flowmeter that effectively solves the problems of the conventional technology, has a simple configuration, and improves the linearity of measurement accuracy in the low flow velocity region. shall be.

[Key points of the idea]

In order to achieve this purpose, the present invention
In a Karman vortex flowmeter that measures the flow rate by detecting the Karman vortex street generated by a vortex generator inserted into a pipe through which a fluid to be measured flows, a constrictor is installed upstream of the position where the excess generator is inserted in the pipe. an upstream rectifying grating and a downstream rectifying grating are provided immediately before and after the constricted part, respectively, and the mesh of the upstream rectifying grating is finer than that of the downstream rectifying grating. .

[Example of idea]

Next, one embodiment of the present invention will be described in detail based on the drawings.

FIG. 1 shows a schematic diagram of an embodiment of the present invention, in which A is a front sectional view and B is a side view. In the figure, the Karman vortex flowmeter 1 mainly includes a pipe line 2, a Karman vortex generator 3 inserted into the pipe line 2, a Karman vortex detector 4, and upstream and downstream rectifying gratings 5, 6. Conduit 2
is formed into a square shape in this embodiment. The Karman vortex generating body 3 includes an upstream columnar body 7 having an isosceles triangular cross section and a downstream columnar body 8 having a trapezoidal cross section. In addition, the Karman vortex detection unit 4
The flow rate is measured by detecting the Karman vortex street generated in the fluid flow by the Karman vortex generator 3.

Incidentally, the upstream rectifying grid 5 has a large outer diameter and is disposed immediately in front of the large diameter side of the throttle tube 9 installed upstream of the Karman vortex generator 3. Also,
The downstream rectifying grid 6 has a small outer diameter and is disposed immediately after the small diameter side of the throttle tube 9. The upstream and downstream rectifying gratings 5 and 6 each consist of a large number of honeycomb-like structures made of thin aluminum foil with a thickness of approximately 20 μm to 50 μm. In this embodiment, the upstream and downstream rectifying gratings 5 and 6 have a honeycomb structure in which the upstream rectifying grating 5 has a mesh size of approximately 1/8 inch, and the downstream rectifying grating 6 has a mesh size of approximately 1/8 inch. Formed to about /4 inch,
Therefore, the upstream rectifying grid 5 has a finer mesh than the downstream rectifying grid 6. In addition, 10
is a temperature detector that detects fluid temperature.

FIG. 2 is a characteristic diagram of flow velocity V (in the range of 1 m/sec to 100 msec) versus Strouhal number st. This second
In the figure, characteristic line A shows the experimental results of one embodiment of the present invention, and the linearity is about ±2%. On the other hand, characteristic line B shows the experimental results when the conventional rectifying grid has one stage. This characteristic line B has a lower linearity in the low region than the characteristic line A of this embodiment, so its linearity as a whole is about ±3.7.
It is about %. As is clear from the experimental results, according to the present invention, the upstream and downstream rectifying gratings 5 and 6 are arranged immediately before and after the throttle pipe 9, and the mesh of the upstream rectifying grating 5 is replaced by the mesh of the downstream rectifying grating. By making the mesh smaller than 6, the measurement accuracy is greatly improved.

Note that if the mesh of the downstream rectifying grating 6 is made finer than that of the upstream rectifying grating 5, there is a tendency that the generation of Karman vortex street decreases in the low speed region and the measurement range decreases, but as in the present invention, It is believed that by making the mesh of the downstream rectifying grid 6 rougher than that of the upstream rectifying grid 5, fine turbulence is generated throughout the pipe line 1, facilitating the generation of the Karman vortex street.

[Effect of idea]

As described above, according to the present invention, the upstream rectifying grid 5 and the downstream rectifying grid 6 are arranged on the upstream side and the downstream side of the throttle part 9 provided at the entrance of the pipe, respectively, and the upstream rectifying By forming the grid with finer mesh than the downstream rectifying grid, the problem of the prior art that the linearity in the low speed range is reduced can be effectively solved with a simple configuration, and therefore the straightness in the low speed range can be improved. Effects such as improved performance, improved measurement accuracy, and wider measurement range can be achieved.

[Brief explanation of the drawing]

Fig. 1 shows a schematic configuration diagram of an embodiment of the present invention, Fig. A is a front sectional view thereof, Fig. B is a side sectional view thereof, and Fig. 2 is a diagram for explaining linearity in the measured flow velocity range. It is a flow velocity-Strohal number characteristic diagram. 1: Karman vortex flow meter, 2: pipe line, 3: Karman vortex generator, 5: upstream rectification grid, 6: downstream rectification grid, 9: throttle tube.

Claims (1)

[Scope of utility model registration request] In a Karman vortex flowmeter that measures the flow rate by detecting the Karman vortex street generated by a vortex generator inserted into a pipe through which a fluid to be measured flows, a constrictor is installed upstream of the position where the excess generator is inserted in the pipe. A section 9 is provided, and immediately before and after this constriction section 9,
A Karman vortex flow rate characterized in that an upstream rectifying grating 5 and a downstream rectifying grating 6 are provided, and the meshes of the upstream rectifying grating 5 are finer than those of the downstream rectifying grating 6. Total.