JP2001021459A - Apparatus for setting flow rate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase further the number of selection of set flow rates without making large an apparatus for setting the flow rate by a critical flow Venturi tube. SOLUTION: A plurality of Venturi tubes 18a-18d are set in parallel to each other between a branching part 15 and a joining part 16. A switching valve 19 is set for opening/closing a branching channel 17a-17d through the Venturi tube 18a-18d. The branching channels 17a-17d are switched to be opened/closed by the selector valves 19, so that the number of selectable set-flow rates can be increased to the number of Venturi tubes and further to a total of the number of Venturi tubes and a plurality of combinations of the Venturi tubes. The apparatus can switch a larger number of set flow rates while an increase of a total shape is suppressed as far as possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate setting device provided with a critical flow venturi interposed in a gas flow path in, for example, a constant volume dilution type gas sampling device.

[0002]

2. Description of the Related Art When measuring the amount of harmful components contained in exhaust gas from automobiles, a gas sampling device of a constant volume dilution system is used. FIG. 8 shows a configuration example of such a gas sampling device. As shown, the sampling device 2 connected to the exhaust muffler of the vehicle 1 comprises a mixing section 4 having an air introduction pipe 3 and a critical flow venturi 5.
And a suction blower 6 are sequentially provided.

[0003] Exhaust gas from the automobile 1 is supplied to the air introduction pipe 3.
Is diluted by the air introduced through the filter 7, and when the flow rate of the exhaust gas increases or decreases, the flow rate of the dilution air also increases or decreases. The sum of the dilution air flow rate and the exhaust gas flow rate indicates the critical flow of the critical flow venturi 5. It is configured to be maintained at a flow rate. As described above, a part of the mixed gas of the exhaust gas and the air at a constant flow rate obtained by the critical flow venturi 5 is sampled through the sampling pipe 8, and the amount of the harmful component is measured by a gas analyzer (not shown).

By the way, the flow rate set by the critical flow venturi 5 depends on the size of an automobile engine,
That is, it is necessary to change according to the displacement, and for this purpose, it is necessary to replace the critical flow venturi 5. Therefore, a patent publication 2689242 discloses a venturi exchanging apparatus which facilitates such an operation of exchanging the critical flow venturi 5. In the device, as shown in FIG. 9, the critical flow venturi 51
The introduction part 51a is divided into an introduction part 51a, a throat part 51b, and a pressure recovery part 51c.
2, the pressure recovery unit 51c is fixed to a gas outlet pipe 55 to which a suction blower 54 is connected.

[0005] A carriage 56 is provided which can move left and right in an upper end area of the pressure recovery section 51c.
On the upper side, a plurality of throat portions 51b having different critical flow rates are arranged in parallel. These throat portions 51b are fixed to a holding base 58 to which air cylinders 57 are attached at both ends.

According to this configuration, the carriage 56 is moved right and left to position the throat portion 51b having a desired critical flow rate on the pressure recovery portion 51c.
By lowering the holding base 58 by 7 ・ 57, the lower end of the throat portion 51b is fitted to the upper end of the pressure recovery portion 51c. Next, an operation of operating the air cylinder 59 provided around the bellows 52 to extend the bellows 52, that is, an operation of lowering the introduction portion 51a is performed, and the lower end of the introduction portion 51a is moved to the throat portion 51b. Is fitted to the upper end.

As a result, a gas flow path in which the critical venturi 51 having a desired critical flow rate is interposed is formed. In order to change the set flow rate, the throat part 51b that has been connected up to that time is removed in the reverse procedure, and then the bogie 5 is connected.
6 is moved to position the throat portion 51b having a desired critical flow rate on the pressure recovery portion 51c, and the same operation as described above is performed.

[0008]

However, in the apparatus having the above configuration, if the number of throat portions 51b is four, for example, the number of switching of the set flow rate is also four. Accompanying throat part 5
It is necessary to increase the number of 1b, and the apparatus becomes large.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to increase the number of switching of the set flow rate without increasing the size of the apparatus. A setting device is provided.

[0010]

Accordingly, a flow rate setting device according to claim 1 is a flow rate setting device having a plurality of critical flow venturis for setting a gas flow rate, wherein the flow rate setting device is provided on each of an upstream side and a downstream side of each venturi. A branch section and a junction section surrounded by a box body are provided, and each venturi is connected in parallel between the branch section and the junction section, and a branch flow path from the branch section to the junction section through each venturi is respectively provided. An opening and closing means for opening and closing is provided.

[0011] According to this configuration, by performing the switching of the opening and closing of the branch flow path by each opening and closing means, the branch portion and the merging portion can be brought into a state in which they are communicated with each other by one venturi first. Alternatively, a plurality of venturis can communicate with each other. In the former case, the set flow rate is given by the individual critical flow rate of each Venturi, and in the latter case, it is a flow rate obtained by adding the critical flow rates of the respective Venturi to each other. Therefore, the number of set flow rates that can be switched can be made larger than the number of venturis, so that the device can be switched with a larger set flow rate while minimizing the size.

According to a second aspect of the present invention, in the flow rate setting device, each opening / closing means is formed by a cylinder provided with a valve body reciprocating in a direction of a flow path through a venturi on a tip end side of a cylinder rod. And

According to this configuration, the exclusive space in the direction perpendicular to the flow direction of each branch flow path can be made smaller than, for example, a configuration using a butterfly valve as the opening / closing means. In other words, in the configuration in which the butterfly valve is interposed in each branch flow path, the driving unit protrudes to the side of each branch flow path, but in the configuration in which the cylinder is provided as the opening and closing means as described above, the cylinder rod is used. In addition, a cylinder tube serving as a driving unit for the branch tube is provided along the flow direction of each branch flow path. Therefore, even in a configuration in which a plurality of venturis are juxtaposed, it is possible to reduce the size by bringing them closer to each other.

Further, the cylinder is mounted so that the valve element reciprocates, for example, in the junction, and the opening of each branch flow path to the junction is opened and closed by the valve element. Can be used also as the space in the merging section, so that the overall size can be reduced.

According to a third aspect of the present invention, the opening / closing means is provided at a downstream communication point where each venturi communicates with the junction.

By providing the opening / closing means on the downstream side of the venturi in this manner, so that the valve element in the open state is located on the downstream side of the venturi, the sound speed of the gas flowing into the venturi reaches the flow velocity. The influence of the above-mentioned valve body on the gas flow is minimized, thereby improving the flow rate accuracy.

According to a fourth aspect of the present invention, there is provided a flow rate setting device including a box in which a gas introduction pipe and a gas outlet pipe are connected, and in which the internal space is divided into a gas inlet pipe side and a gas outlet pipe side. A partition plate is provided, and each venturi is penetrated and fixed to the partition plate.

According to this configuration, for example, as compared with a case where a box body surrounding the branch portion on the upstream side of the venturi and a junction portion on the downstream side are formed separately from each other, these branch portions and the junction portion are different from each other. Since it is formed in one box, the overall configuration is simple and the overall shape can be further reduced in size. Also, in mounting each of the venturis, it is only necessary to fix the venturi to the partition plate at one point penetrating the partition plate, so that the mounting structure is simpler.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 Next, a specific embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, the flow rate setting device according to the present embodiment includes an upstream box 12 having a gas introduction pipe 11 and a downstream box having a gas outlet pipe 13 connected to a suction blower (not shown). A space surrounded by the upstream box 12 is formed as a branch portion 15, and a space surrounded by the downstream box 14 is formed as a junction 16.

The upstream box 12 and the downstream box 14
And, in the case of the figure, four branch flow paths 17a
17b are provided, and the branch part 15 and the merging part 16 are configured to communicate with each other through these branch flow paths 17a to 17b, and the venturis 18a to 18d and the on-off valves are respectively connected to the branch flow paths 17a to 17b. (Opening / closing means) 19 ...
And are sequentially interposed.

Each of the venturis 18a to 18d is formed to have a different critical flow rate CFa, CFb, CFc, CFd. Each of the on-off valves 19 is constituted by an air-driven butterfly valve. Each of the venturis 18a to 18d is connected to a first connection pipe 2 having a straight pipe shape.
1 are connected to the upstream box body 12, and each of the venturis 18 a to 18 d and the on-off valves 19 are connected to the second connection pipe 2.
2 are connected to each other. Furthermore, each on-off valve 1
9 are connected to the downstream box 14 via the third connection pipes 23, respectively.

FIG. 2 shows an example of the actual configuration of the flow rate setting device having the above configuration. That is, the upstream box 12 and the downstream box 14
Are fixed, and between these, the venturis 18a-18
4 and four branch flow paths 17a to 17d in which the open / close valve 19 is interposed, respectively. In this case, the center lines of the branch flow paths 17a to 17d are formed so as to be located at the respective vertex positions of the square.

The apparatus having the above-described structure is interposed at the position of the critical flow venturi 5 in the gas sampling apparatus 2 shown in FIG. 8, and has the gas inlet pipe 11 at the downstream end of the mixing section 4 and the gas outlet pipe 13 sucked. Each of them is connected to the blower 6 and used.

For example, the first branch flow path 17a from the left in FIG. 1 (hereinafter, the first branch flow path 17a, the second branch flow path 17b, and the third branch flow path
c, referred to as a fourth branch channel 17d. Each Venturi 18a
18d and the on-off valve (opening / closing means) 19... When individually described, the first to fourth vocabulary are added from the left side in the same manner as described above. When only the on-off valve 19 is opened, the exhaust gas from the automobile 1 is diluted by air introduced from the air introduction pipe 3 through the filter 7, and a mixed gas of the diluted air and the exhaust gas is shown in FIG. Gas introduction piping 1
1 flows into the branch portion 15.

The first branch flow path 17 from the branch portion 15
The gas that has flowed into a is passed through the first venturi 18a,
The flow velocity gradually increases according to the shape of the throttle, and reaches the speed of sound at the narrowest portion of the venturi 18a. by this,
The flow rate flowing through the first venturi 18a, that is, the flow rate downstream of the mixing unit 4 in the sampling device 2 is maintained at the critical flow rate CFa of the first venturi 18a determined by the sound velocity and the diameter of the narrowest part. Is done.

Accordingly, even when the flow rate of the exhaust gas from the automobile 1 fluctuates, the amount of air obtained by subtracting the flow rate of the exhaust gas from the critical flow rate CFa is introduced into the mixing section 4 through the air introduction pipe 3 and mixed with the air. The gas volume is above the critical flow rate CFa
Is maintained. Then, a part of the mixed gas having a constant flow rate is sampled through the sampling pipe 8, and the amount of the harmful component is measured by a gas analyzer (not shown).

By the way, the flow rate of the gas flowing downstream of the mixing section 4 needs to be an amount corresponding to the displacement of the automobile 1 for measuring the exhaust gas, as described above.
In this case, according to the flow rate setting device described above, the set flow rate according to the displacement of the vehicle 1 is set to each of the branch flow paths 17a to 17a.
7d can be easily changed simply by switching the on / off valves 19... Provided between the four venturis 18a whose critical flow rates are different from each other.
It can be changed beyond the number of ~ 18d.

That is, the first branch flow path 17 shown in FIG.
a, the critical flow rate CFa of the first venturi 18a becomes the set flow rate as described above, while the critical flow rate of the second venturi 18b is opened when only the second open / close valve 19 is opened. In the state where CFb only opens the third on-off valve 19, the critical flow rate CFc of the third venturi 18c
However, when only the fourth on-off valve 19 is opened, the critical flow rate CFd of the fourth venturi 18d becomes the set flow rate.

Further, for example, the first and second on-off valves 19.1
9 is opened, the sum of the critical flow rates (CFa + CFb) of the first venturi 18a and the second venturi 18b becomes the set flow rate. When all of the on-off valves 19 are opened, the critical flow rate of The sum (CFa + CFb + CFc + CFd) is the set flow rate. That is, there are 15 combinations in which any one of these four on-off valves 19 is selected to open the valve. Therefore, if there are no overlapping critical flow rates obtained in accordance with these combinations, the combination can be changed. This means that 15 set flow rates are prepared.

As described above, in the apparatus having the above configuration,
Since the set flow rate can be easily switched by switching the opening and closing of each of the on-off valves 19, the switching work is facilitated. In addition, since the number of switching of the set flow rate can be increased, it is possible to use a more compact apparatus shape and widely support exhaust gas measurement of automobiles having various displacements.

In the above embodiment, each of the branch passages 17a
Opening / closing valves 19 for opening / closing through to 17d are connected to each venturi 18a.
18d, the flow rate accuracy is improved. That is, the gas flowing into the first venturi 18a from the branch portion 15, for example, is accelerated according to the shape of the throttle as described above, and reaches a sonic speed inside. By being provided on the downstream side, the influence of the on-off valve 19 on the flow state up to the sonic velocity as described above is suppressed as much as possible, and therefore, the above-mentioned flow state is obtained without occurrence of disturbance. As a result, the flow rate accuracy is improved.

[Embodiment 2] Next, another embodiment of the present invention will be described with reference to FIGS. In addition,
For convenience of explanation, members having the same functions as the members shown in FIGS. 1 and 2 are denoted by the same reference numerals, and detailed description thereof will be omitted. The same applies to still other embodiments described later.

FIG. 3 is an exploded perspective view showing a main part of the flow rate setting device according to the second embodiment. This device also has, for example, four venturis 18a to 18d as described above.
Are arranged in parallel with each other. The venturis 18a to 18d form a ring-shaped packing 31 and a cylinder holding ring 32 so as to cover the four through holes 14b formed in the upper wall surface 14a of the downstream box 14 from above, respectively. Through this, it is fixed on the upper wall surface 14 a of the downstream box 14.

Each of the cylinder holding rings 32 is provided with four holding rods 33... Hanging downward from the lower surface thereof. Mounting plate 3
4 are fixed, and on each lower surface of these cylinder mounting plates 34,
Air cylinders 35 constituting opening / closing means are respectively mounted.

As shown in FIG. 4, a disc-shaped valve body 35b is provided at the tip of a cylinder rod 35a extending upward through the cylinder mounting plate 34 in each of the air cylinders 35. By operating the air cylinder 35 so that the valve body 35b closes the center through hole 32a of the cylinder holding ring 32 from below as shown on the left side in FIG. The branch flow path is closed. On the other hand, as shown on the right side of FIG.
By holding the valve body 35b at a position separated downward from the cylinder holding ring 32, the branch flow path is opened.

As described above, in the present embodiment, the opening / closing means is constituted by the air cylinder 35 provided at the tip of the cylinder rod 35a with the valve 35b reciprocating along the flow path direction through each of the venturis 18a to 18d. Have been. Then, each of the branch flow paths 1 is
By selecting and opening and closing 7a to 17d, the set flow rate can be easily switched in the same manner as described above, and the number of set flow rate switching can be increased with a more compact device shape. Also in the present embodiment, since the cylinders 35 for opening and closing the branch flow paths 17a to 17d are provided on the downstream side of the venturis 18a to 18d, the flow rate accuracy is improved as described above.

Further, by configuring the opening / closing means by the cylinder 35 as in the present embodiment, the size can be further reduced and the accuracy can be improved as compared with the case where the opening / closing means is configured by the butterfly valve as in the first embodiment. Can be achieved. In other words, as shown in FIG. 1, when the on-off valve 19 composed of a butterfly valve is interposed in each of the branch passages 17a to 17d, the venturi 18 is attached for its attachment.
It is necessary to provide connecting pipes 22 and 23 composed of straight pipes having substantially the same diameter as the downstream ends of the downstream ends a to 18d on both the upstream side and the downstream side of the on-off valve 19. May be required, and miniaturization may be difficult.

In the open state, the venturis 18a to 18a
Since the disc-shaped valve element 19a is present in a flow path having substantially the same diameter as the diameter of the downstream end at 18d, a turbulent flow or the like occurs at this location depending on the condition of the set flow rate. In some cases, this may affect the flow in the turbulence and cause the flow rate accuracy to be lost. The opening / closing valve 19 composed of a butterfly valve has a relatively large air drive section 19b for driving the valve element 19a as shown in FIG. Since it is configured to protrude to the side, a predetermined exclusive floor area is required, and miniaturization may be difficult.

On the other hand, when the opening / closing means is constituted by a cylinder 35 as in the present embodiment, as shown in FIG. 17d can be configured to open and close an opening communicating with the junction 16. That is, in this case,
Instead of a configuration in which the opening / closing means is interposed in each of the branch flow paths 17a to 17d, it can be provided on the merging portion 16 side, so that the length dimension of each of the branch flow paths 17a to 17d can be made as small as possible. In this case, the valve body 35b in the valve-open state is located in the junction 16 so that each of the branch flow paths 17
The effect on the flow state within a to 17d is also reduced,
This also improves the flow accuracy.

In addition to the cylinder rod 35a, its driving section (cylinder tube) is also connected to each of the branch passages 17a to 17a.
Since the structure extends along the direction of the flow path d and does not protrude to the side, the overall occupied floor area can be minimized. Particularly, in the present embodiment, the air cylinder 35 is configured to be suspended from the upper wall surface 14a of the downstream box body 14 and the entire air cylinder 35 is incorporated in the junction 16 so that Can be further downsized.

[Embodiment 3] FIG. 5 shows a flow rate setting device according to still another embodiment of the present invention. This device also has air cylinders 35.
Opening / closing means is constituted by these air cylinders 35.
4 is fixed to the bottom wall surface 14c. A valve body 35b is provided at the tip of each cylinder rod 35a extending upward through the lower wall surface 14c in the same manner as described above, and the valve body 35b allows the venturis 18a to 18d to communicate with the junction 16 with the upper wall surface. It is configured to open and close the through opening 14a.

According to this configuration, only the cylinder rods 35a and the valve bodies 35b are located in the junction 16 so that the gas flowing into the junction 16 through the branch passages 17a to 17d is formed. However, with respect to the flow when flowing out to the gas outlet pipe 13 through the junction 16,
The effect of each cylinder 35 is reduced as much as possible. Particularly, by configuring the valve body 35b in the valve open state to be held at a position lower than the opening position of the gas outlet pipe 13, the gas reaching the gas outlet pipe 13 from each of the branch passages 17a to 17d. Disturbance in the flow due to the valve body 35b is suppressed as much as possible. This allows each Venturi 18
The influence of the turbulence on the downstream side on the flow in a to 18d is further reduced, and the flow rate accuracy is improved.

Embodiment 4 Next, still another embodiment of the present invention will be described with reference to FIG. As shown in the figure, in the flow rate setting device in the present embodiment, a box body 41 is provided in which the gas introduction pipe 11 is connected to the upper wall surface and the gas outlet pipe 13 is connected to the bottom side wall surface, respectively.
A partition plate 42 for partitioning the internal space up and down is attached to the inside of the box 41, and the upper side of the partition plate 42
5. The lower part is formed as a junction 16.

The four venturis 18a to 18 similar to the above-described four venturis 18a to 18 have a structure penetrating through the partition plate 42, respectively.
d is fixed to the partition plate 42. In addition, box 4
The air cylinder 35 is attached to the bottom wall surface 41a of the first ventilator in the same manner as in the third embodiment, and the valve body 35b at the tip of each cylinder rod 35a is brought into contact with and separated from the downstream end of each of the venturis 18a to 18d. To 18d.

According to this configuration, the branching section 15 and the joining section 1
6 is simpler than the case where the box bodies respectively surrounding 6 and 6 are formed separately from each other. Further, in mounting the venturis 18a to 18d, compared with a case where mounting flanges are provided at the upstream end and the downstream end, for example, and the upper and lower portions are fixed to each other, in the above case, the Since it is sufficient to fix to the partition plate 42 at the location, the configuration of the mounting portion is also simplified, and the overall shape can be further reduced.

In mounting the venturis 18a to 18d, for example, as shown in the figure, a flange projecting radially is provided integrally at an intermediate position in the vertical direction on the outer peripheral surface of each of the venturis 18a to 18d and fixed. In addition to the structure, an arbitrary mounting structure such as a structure fixed by a split flange separate from each of the venturis 18a to 18d, a structure in which the partition plate 42 is divided into two and the respective venturis 18a to 18d are sandwiched and fixed, and the like. Can be adopted. In addition, the part fixed to the partition plate 42 is the Venturi 18
The position is not limited to the middle position in the vertical direction in a to 18d, but may be fixed at the upper end position or the lower end position, for example.

Although the specific embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made within the scope of the present invention. For example, in Embodiments 2 and 3 described with reference to FIGS. 3 to 5, flanges that extend radially outward are provided at the upper and lower ends of each of the venturis 18a to 18d so that these venturis 18a to 18d are located on the upstream side. Although the structure which is fixed to each wall surface of the box body 12 and the downstream box body 14 is illustrated, for example, as shown in FIG. 7, straight pipe connection pipes 43 and 44 are provided at upper and lower ends of each of the venturis 18 a to 18 d. It is also possible to adopt a structure for mounting. In this case, these connection pipes 4
A connection structure in which the upper and lower ends of the venturis 18a to 18d are inserted and fitted into the respective ends of the connection pipes 3 and 44, and the connection pipes 43.4
By forming at least one of the flexible pipes 4 as a flexible pipe that can expand and contract in the axial direction, the work of attaching and detaching the venturis 18a to 18d at the time of maintenance or the like becomes easy.

Further, in each of the above-described embodiments, an example is described in which four venturis 18a to 18d are provided. However, as long as two or more venturis 18a to 18d are provided, an arbitrary number of venturis can be provided. In the above description, the example in which the venturis 18a to 18d whose critical flow rates are different from each other is provided,
It is also possible to incorporate a venturi having the same critical flow rate.

In the second to fourth embodiments described with reference to FIGS. 3 to 7, the air cylinder 35 is connected to the venturi 18a.
A configuration in which the flow rate accuracy is maintained by being provided at the junction 16 downstream of 〜18d is described as an example.
In the flow rate setting device described in 2.4, each branch flow path may be opened and closed on the upstream side of the venturis 18a to 18d.

Further, in the above description, a flow rate setting device which is incorporated and used in a constant volume dilution type gas sampling device for measuring the amount of harmful components in the exhaust gas of an automobile has been described as an example. The present invention can be applied to other devices to be set.

[0051]

As described above, in the flow rate setting device according to the first aspect of the present invention, a plurality of venturis are connected in parallel between the branch part and the junction part, and the branch flow path through each venturi is opened and closed. The number of set flow rates that can be switched can be increased to the number obtained by adding the number of combinations of these venturis to the number of venturis. Therefore, it is possible to provide a device capable of switching a larger set flow rate while minimizing the size of the overall shape as much as possible.

In the flow rate setting device according to the second aspect, since each opening / closing means is formed by a cylinder having a valve element which reciprocates along the flow path through the venturi, for example, a butterfly valve is used as the opening / closing means. Compared to the configuration,
In particular, the exclusive space in the direction orthogonal to the flow direction of each branch flow path can be made smaller, and the stroke space required for the reciprocation of the valve body can also be used as, for example, the space in the junction. This also makes it possible to reduce the overall size.

In the flow rate setting device according to the third aspect, since the opening and closing means is provided at the downstream communication point where each of the venturis communicates with the merging section, it is necessary to wait until the sound velocity of the gas flowing into the venturi from the branch reaches the flow velocity. The influence of the valve element on the gas flow is minimized, thereby improving the flow rate accuracy.

In the flow rate setting device according to the fourth aspect, the partition plate is provided in the box in which the gas introduction pipe and the gas discharge pipe are connected, and each venturi is penetrated and fixed to the partition plate. A branch portion on the upstream side of
Compared to the case where the box surrounding the downstream merging section is formed separately from each other, the overall configuration is simpler, and each venturi is attached to the partition plate at one point penetrating the partition plate. Since it is sufficient to fix, the mounting structure is simpler.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of a flow rate setting device according to an embodiment of the present invention.

FIG. 2 is a perspective view showing an example of an actual device configured by adopting the basic configuration of FIG. 1;

FIG. 3 is a perspective view showing main components of a flow rate setting device according to another embodiment of the present invention.

FIG. 4 is a partially cutaway sectional view showing an assembled state of the flow rate setting device of FIG. 3;

FIG. 5 is a longitudinal sectional view showing a flow rate setting device according to still another embodiment of the present invention.

FIG. 6 is a longitudinal sectional view showing a flow rate setting device according to still another embodiment of the present invention.

FIG. 7 is a longitudinal sectional view showing a flow rate setting device according to still another embodiment of the present invention.

FIG. 8 is a schematic diagram showing a configuration of a gas sampling device used for measuring an amount of harmful components in exhaust gas of an automobile.

FIG. 9 is a cross-sectional view of a conventional apparatus for switching a set gas flow rate by replacing a venturi.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Gas introduction pipe 12 Upstream box 13 Gas lead-out pipe 14 Downstream box 15 Branch part 16 Junction part 17a-17d Branch flow path 18a-18d Venturi 19 Opening / closing valve (opening / closing means) 35 Air cylinder (opening / closing means) 35a cylinder Rod 35b Valve body 41 Box body 42 Partition plate

Claims (4)

[Claims] 1. A flow rate setting device comprising a plurality of critical flow venturis for setting a gas flow rate, wherein a branch portion and a junction portion each surrounded by a box are provided on an upstream side and a downstream side of each venturi. The flow rate is characterized in that each of the venturis is connected in parallel with each other between the branch portion and the junction portion, and opening / closing means for opening and closing a branch flow path from the branch portion to the junction portion through each venturi is provided. Setting device. 2. A flow rate according to claim 1, wherein each opening / closing means is formed by a cylinder provided with a valve body reciprocating in a direction of a flow path through a venturi on a tip end side of a cylinder rod. Setting device. 3. The flow rate setting device according to claim 1, wherein the opening / closing means is provided at a downstream communication point where each venturi communicates with the junction. 4. A box in which a gas inlet pipe and a gas outlet pipe are connected is provided, and a partition plate for dividing an internal space into a gas inlet pipe side and a gas outlet pipe side is provided in the box body. 4. The flow rate setting device according to claim 1, wherein each of the venturis is penetrated and fixed to the plate.