JPH04366728A - Bypass unit for flow rate sensor - Google Patents

Abstract

PURPOSE:To provide the bypass unit of a flow rate sensor, which properly realizes a laminar flow condition. CONSTITUTION:The bypass unit of a flow rate sensor includes two flow passages 6 and 7 through which fluid comes in and out, and a chamber 10 communicated with the flow passages 6 and 7. And fluid is introduced to a sensor pipe 15 out of the chamber 10 through branched flow passage 12 and 13. The inside of the chamber 10 is provided with fluid introduction holes 24 and 25 which are housed in a gap interspaced with the inner wall of the chamber 10 while being formed coaxially with both the flow passages 6 and 7, a bypass axial body 20 including through holes which are bored out of the fluid introduction holes 24 and 25 to the circumferential direction, and is also provided with a cut-off case 18 which has a communicating through hole 31 bored on its circumferential surface and cuts off a space between the bypass axial body 20 and the inner wall of the chamber 10 with the exception of the communicating through hole.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bypass unit that can be used, for example, in a thermal mass flow sensor.

0002

2. Description of the Related Art Conventionally, it has been known that it is necessary to obtain a laminar flow state in order to detect the flow rate in a fluid bypass section. For this reason, various laminar flow elements are installed in the bypass section, and as a laminar flow element, Japanese Patent Laid-Open No. 60-1
A device as shown in Japanese Patent No. 0120 is known.

However, the laminar flow element is easily installed by being press-fitted with the inserted wire bent, and if the wire is bent, the pressure difference between the inlet and outlet of the laminar flow element will affect the flow rate. Since it is no longer proportional, the flow rate cannot be detected with high accuracy. In particular, if the wire becomes extremely bent, vortices will occur in the fluid and the differential pressure will not be constant, making it unsuitable for practical use.

[0004] Furthermore, when the flow path leading to the bypass section where the laminar flow element is provided continues for a long time in a straight line in the bypass section, or when the flow rate of the fluid is small, the turbulence of the fluid flowing into the bypass section is small. . However, in many cases, the flow path is bent just before reaching the flow meter and reaches a bypass section. It is known that a difference occurs in the sensor output depending on the state of bending, and in order to eliminate this problem, a mesh-shaped rectifier filter is placed near the inlet of the bypass section. In this case, a problem arises in that pressure loss increases in this part.

Furthermore, there is a limit to the measurement resolution of the sensor, and there are also the following limitations to the flow rate that can flow through the sensor pipe or bypass. In other words, the pressure difference △P1 between the inlet and outlet of the sensor tube and the flow rate Q1 of the fluid flowing through the sensor tube
When the differential pressure ΔP1 and the flow rate Q1 become larger than a predetermined value, the proportional relationship between them collapses and the flow rate cannot be detected with high accuracy. In addition, the proportional relationship between the differential pressure △P2 between the inlet and outlet of the bypass section and the flow rate Q2 of the fluid flowing through the bypass section collapses when the differential pressure △P2 and the flow rate Q2 become larger than a predetermined value. It is not possible to perform accurate detection. In other words, in the range where the differential pressure is proportional to the flow rate, it can be treated as laminar flow, but as the differential pressure and flow rate increase, the differential pressure becomes 2 times the flow rate.
This results in turbulent flow that increases in proportion to the multiplication factor, making it unsuitable for flow rate detection.

[0006] Now, considering laminar flow, generally a Reynolds number RD of 2320 or less is called laminar flow, and the Reynolds number RD is as follows: RD = (4Qρ)/(πDη)...
It is expressed as (1). Here, Q: volumetric flow rate ρ of the fluid flowing through the tube; density η of the fluid flowing through the tube; viscosity D of the fluid flowing through the tube; equivalent diameter of the tube. From equation (1), it is understood that in order to increase Q while keeping RD constant, D should be increased. However, in order to increase the diameter of the sensor tube and the diameter of the bypass section, there is a limit to the size of the sensor itself. There are also methods to do the same.

However, in order to widen the range of flow rates to be measured and to make measurements compatible with various fluids, a large number of various laminar flow elements are required. .

[0008]

[Problems to be Solved by the Invention] In order to solve the above problem, Japanese Utility Model Application Publication No. 59-72514 discloses a system in which a cylindrical core is provided in the center of the bypass section to obtain laminar flow. According to the configuration of such a bypass section, Japanese Patent Application Laid-open No. 60-1
Although the laminar flow element shown in Publication No. 0120 can eliminate turbulent flow caused by bending of the wire, the fluid flowing into the bypass section is directly at the fluid inlet of the sensor, which causes noise. There was a problem with detecting vortices. Furthermore, the need to provide bypass sections of various sizes in order to widen the range of flow rates to be measured cannot be solved. Furthermore, the flow rate was increased to 10
When reducing the amount to 0 cc or less, the processing accuracy of the outer circumferential surface of the core and the inner wall of the bypass round hole must be extremely high, which poses the problem of requiring many man-hours and increasing the cost.

The present invention was made to solve the problems of the bypass structure of conventional flow rate sensors, and its purpose is to realize an appropriate laminar flow state and to easily change the measured flow rate range. It is an object of the present invention to provide a bypass unit for a flow rate sensor that can be used.

0010

[Means for Solving the Problems] A bypass unit for a flow rate sensor according to the present invention has two flow channels through which fluid enters and exits, and a chamber communicating with the flow channels, and from which fluid flows through a branch channel. In a bypass unit of a flow rate sensor having a structure for guiding a flow rate sensor to a sensor pipe, a fluid introduction hole is accommodated in the chamber with a gap between it and the inner wall of the chamber and is formed coaxially with the second flow path. and a through hole bored in the outer circumferential direction from the fluid introduction hole.

[0011] The above-mentioned bypass unit is provided with a blocking case having a communicating hole bored in the peripheral surface and blocking the connection between the bypass shaft body and the inner wall of the chamber except for the communicating hole. It is characterized by

Furthermore, in the above bypass unit, a plurality of the communicating holes are formed at different distances in the longitudinal direction of the blocking case, and the lid is closed except for any one of the communicating holes. It is characterized by being made and closed.

[0013] The bypass unit according to the present invention has two channels through which fluid enters and exits, and a chamber communicating with the channels,
A bypass unit for a flow rate sensor having a structure in which fluid is guided from this chamber to a sensor pipe via a branch flow path, the chamber having a gap between the chamber and the inner wall of the chamber, and having a gap between the second flow path and the inner wall of the chamber. A bypass shaft that is coaxially provided and allows fluid to flow into the gap, and a plurality of communication holes are formed at different distances in the longitudinal direction of the circumferential surface, and any one of the communication holes is formed. The chamber is characterized by being provided with a blocking case which is closed with a lid and which blocks the connection between the bypass shaft body and the inner wall of the chamber except for the first communication through hole.

[0014]

[Operation] Since the bypass unit of the flow rate sensor according to the present invention is constructed as described above, the fluid arriving from the flow path reaches the fluid introduction hole and flows toward the outer circumference through the through hole without reaching the front of the fluid introduction hole. Since it is transparent, it provides conditions for starting laminar flow without the large pressure loss that occurs with mesh filters.

Furthermore, by providing the cutoff case, laminar flow is realized between the inner wall of the cutoff case and the outer circumferential surface of the bypass shaft, and even when the flow rate is small, machining of this generally flat part is possible. It is only necessary to improve accuracy, and processing becomes easier.

Furthermore, the range of differential pressure in the sensor tube can be changed by selecting the communication through-hole in the blocking case, making it possible to easily measure a wide range of flow rates.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A bypass unit for a flow rate sensor according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 7 of the accompanying drawings. In these figures, the same components are designated by the same reference numerals and redundant explanations will be omitted.

The unit housing 1 has a rectangular external shape,
As shown in FIG. 1, piping fittings 2 and 3 are connected to both sides with bolts. The piping fittings 2 and 3 have threaded portions 4 and 5 that protrude from their outer ends so that they can be connected to piping. The threaded parts 4 and 5 of the piping fittings 2 and 3 are located at the center of the side surface of the unit housing 1, and the flow passages 6 and 7 are located on the outer periphery of the threaded parts 4 and 5.
is formed. A seal ring guide 8 and a seal ring 9 are interposed at the joint between the piping fittings 2 and 3 and the unit housing 1 to prevent fluid leakage. In the unit housing 1, a cylindrical large-diameter chamber 10 is formed from the center on the left side of the figure, and a small-diameter guide path 11 is formed in a cylindrical shape from the center on the right side of the figure. A branch path 12 is formed penetratingly from the center of the chamber 10 to the upper surface thereof, and similarly, a branch path 13 is formed penetratingly from the center portion of the guide path 11 to its upper surface. A sensor housing base 16 provided with a sensor tube 15 is screwed onto the upper part of the branch passages 12 and 13 via a seal 14 having a hole communicating with the sensor tube. The sensor tube 15 is provided with heating resistors 171 and 172, and a bridge circuit is constructed with resistors (not shown) to detect the flow rate using a known method. A hollow cylindrical blocking case 18 is inserted into the chamber 10, and has an outer diameter smaller than the inner wall thereof, and a flange 19 having a diameter that contacts the inner wall of the chamber 10 at one end. Inside the cutoff case 18, a substantially cylindrical bypass shaft body 2 is provided.
0 is inserted.

The bypass shaft 20 has flanges 21 and 22 on both sides, and a cylindrical core 23 in the center, as shown in a side view in FIG. 2(a) and in a sectional view in FIG. 2(b). have From the lateral center portions of the flanges 21 and 22, bottomed fluid introduction holes 24 and 25 are coaxially connected to the channels 6 and 7 (conducting channel 11).
is formed up to the end of the cylindrical core portion 23. Flange 2
1, 22 and the cylindrical core 23 is a neck 26 having a narrow diameter.
, 27 are formed, and the neck portions 26, 27 and the fluid introduction hole 24,
25, there are through holes 28, 29 extending from the center of the circle to the outer periphery.
Eight holes are formed radially. In addition, flange 2
The outer circumferential diameters of the cylinders 2 and 23 are larger than the outer circumferential diameter of the cylindrical core part 23, so that a gap is created between the cylinders and the blocking case 18 through which fluid flows.

As the plan view of the blocking case 18 is shown in FIG. 3, for example, three communication holes 31 (31A to 31C) are bored at different distances from the flange 19 in the longitudinal direction. Only one of these is used,
The other communicating holes 31 are closed by the lid 32 as shown in FIG. 4 and are not used.

In the bypass unit constructed as described above, the gap 40 between the cutoff case 18 and the inner wall of the chamber 10 is configured to be sufficiently wider than the gap 50 between the cutoff case 18 and the bypass shaft 20. Here, when the fluid is assumed to flow from left to right in the figure, the fluid that has arrived at the fluid introduction hole 24 collides with the front wall of the fluid introduction hole 24, and the flow is slightly slowed down to the through hole 24.
8 to the neck 26. This neck 26 serves as a "pressure reservoir", and together with the fact that the neck 27 serves as a "pressure reservoir", the neck 27 and the gap 50 between the neck 27 become a channel, realizing laminar flow. . On the other hand, the pressure at the upstream end of the sensor tube 15 is equal to the pressure at the neck 26 without displacement because the branch passage 12, the gap 40, and the communication hole 31 are sufficiently wider than the gap 40. Further, the pressure at the lower end of the sensor tube 15 is equal to the pressure at the neck 27 . Therefore, the differential pressure detected by the sensor tube 15 is from the neck 26 to the neck 27.
The differential pressure will be up to.

Therefore, in the case of measuring a small flow rate, the method shown in FIG.
As shown in FIG. 4, the communication hole 31A is used, and the other communication holes 31B and 31C are closed using the lid 32 shown in FIG. As a result, the maximum differential pressure generated over the entire length of the gap 40 can be effectively detected, and the differential pressure at the time of a small flow rate can also be accurately detected, making it possible to cope with a small flow rate. In addition, in the case of measuring a medium flow rate, the connecting hole 31B is used as shown in FIG. 6, and the other connecting holes 31A and 31C are closed, and in the case of measuring a large flow rate, the connecting hole 31B is used as shown in FIG. Using the communication hole 31C, close the other communication holes 31A and 31B in the same manner. In this way, in this embodiment, by selecting the communicating hole 31 that is closed by the lid 32 and changing the stroke of the gap 40, changes in the measured flow rate can be accommodated. Further, even when the gap 40 is narrowed to accommodate a small flow rate, the cutoff case 18 is cylindrical and has a substantially straight inner wall, making it easy to process it to a mirror finish or the like. Moreover, even when the bypass unit of the embodiment flows the fluid in the opposite manner to the above, the bypass shaft body is left-right symmetrical, and accurate measurement is possible. It should be noted that when the blocking case 18 is used as shown in FIGS. 5 to 7, the bypass shaft may have another shape as long as it forms the gap 40.

[0023]

[Effects of the Invention] As explained above, according to the present invention, the fluid arriving from the flow path reaches the fluid introduction hole, hits the wall in front of it, and reaches the "pressure release" through the through hole. , there is no large pressure loss as in the case of using a conventional mesh filter, and conditions are provided for the starting point of laminar flow to achieve proper laminar flow.

Furthermore, by providing the cutoff case, laminar flow is realized between the inner wall of the cutoff case and the outer circumferential surface of the bypass shaft, and even when the flow rate is small, it is generally possible to maintain a straight and flat part of the flow. This can be addressed by improving machining accuracy, making machining easier.

Furthermore, by selecting the communication through hole in the blocking case, the range of differential pressure in the sensor tube can be changed, and measurement of a wide range of flow rates can be easily handled by changing a small number of parts. Furthermore, when the bypass shaft body is made bilaterally symmetrical,
Even when fluid flows backwards, an accurate negative differential pressure can be obtained, making it possible to detect the flow rate of fluid from the opposite direction.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention.

FIG. 2 is a configuration diagram of main parts of an embodiment of the present invention.

FIG. 3 is a plan view of essential parts of an embodiment of the present invention.

FIG. 4 is a sectional view of a main part of an embodiment of the present invention.

FIG. 5 is a sectional view of a main part of an embodiment of the present invention.

FIG. 6 is a sectional view of a main part of an embodiment of the present invention.

FIG. 7 is a sectional view of a main part of an embodiment of the present invention.

[Explanation of symbols]

1 Unit housing
2.3 Piping fittings 4, 5 threaded part
6,7 Channel 10 Chamber
11 Guideway 1
2,13 Branch road
15 Sensor tube 18 Shutoff case
20 Bypass shaft body 24, 25 Fluid introduction hole
31A-31C communication hole

Claims (4)

[Claims] Claims: 1. A bypass unit for a flow rate sensor, which has a structure including two channels through which fluid enters and exits, and a chamber communicating with the channels, and guides the fluid from the chamber to a sensor pipe via a branch channel. , a fluid introduction hole accommodated in the chamber with a gap between it and the inner wall of the chamber and formed coaxially with the second flow path; and a transparent hole bored from the fluid introduction hole toward the outer circumference. A bypass unit for a flow rate sensor, comprising a bypass shaft having a hole. 2. A connecting hole is bored in the surrounding surface, and a blocking case is provided that blocks the connection between the bypass shaft body and the inner wall of the chamber except for the connecting hole. A bypass unit for a flow rate sensor according to claim 1. 3. A plurality of the communicating holes are formed at different distances in the longitudinal direction of the blocking case, and all but one of the communicating holes are covered and closed. The bypass unit for a flow rate sensor according to claim 1 or 2, characterized in that: 4. A bypass unit for a flow rate sensor having a structure including two channels through which fluid enters and exits, and a chamber communicating with the channels, and guiding the fluid from the chambers to the sensor pipe via a branch channel. , a bypass shaft body having a gap between the chamber and the inner wall of the chamber, provided coaxially with the second flow path, and allowing fluid to flow into the gap, and a bypass shaft body arranged at different distances in the longitudinal direction of the circumferential surface; A plurality of communication holes are formed in the chamber, and all but one of the communication holes are covered and closed, and a plurality of communication holes are formed between the bypass shaft body and the inner wall of the chamber. A bypass unit for a flow rate sensor, comprising a blocking case that blocks all but a communication hole.