JPH0618302A - Flowmeter - Google Patents

Abstract

PURPOSE:To prevent influences of a turbulent flow at the downstream of a supporting member supporting a branch passage in a main passage. CONSTITUTION:An air flowmeter 1 for measuring the amount of suction air to an automobile engine has an opening 3 on the upstream side and an opening 5 on the downstream side, constituting part of a passage for the suction air. A cocoon-shaped central member is supported by four ribs 140, 150 (only two of four are indicated in the drawing) approximately at the center of the air passage in the air flowmeter 1. A part of the suction air is introduced from an incoming opening 410 into a branch pipe 420. After the air flows in a measuring pipe 430, it runs outside the branch pipe 420 and exits through outgoing openings 440, 450. At this time, the flow rate is measured by sensors 570, 580. Since the outgoing openings 440, 450 are located on the upper stream side than the ribs 140, 150, the turbulent flow at the surface and downstream of the ribs 140, 150 do not act to the outgoing openings 440, 450. Accordingly, the disturbance of the flow inside the branch passage, and the change of the ratio of the flow rate between the branch passage and the whole air passage can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluid flow meter for detecting the flow rate of a fluid, and more particularly to a fluid flow meter for forming a branch passage in a main passage through which the fluid flows and measuring the flow rate of the fluid flowing in the branch passage. Regarding

[0002]

2. Description of the Related Art Conventionally, as this type of fluid flow meter, an air flow meter for detecting the amount of intake air drawn into an automobile engine has been known.

For example, an "air flow meter" disclosed in Japanese Patent Laid-Open No. 60-185118 is known. This air flow meter supports a cylindrical member in a substantially central portion of an intake passage through which intake air to the engine flows, and forms a branch passage in the member to measure the amount of air flowing in the branch passage by a thermal method. It is measured by a flow meter.

[0004]

In the case where the branch passage is formed substantially in the center of the main passage like the above air flow meter,
Since air is introduced into the branch passage from approximately the center of the main passage, it is possible to introduce a flow rate that corresponds well to the flow rate of the main passage into the branch passage. You can know exactly. Also, since the temperature of the branch passage changes in response to the temperature of the air flowing through the main passage with good responsiveness, when installing a thermal type flow meter in the branch passage, outside the main passage, for example, from the engine room, It is possible to measure the flow rate accurately without being easily affected by the temperature disturbance.

However, in the air flow meter as disclosed in the above publication, the outlet of the branch passage opens downstream from the stay for supporting the branch passage in the main passage, so that the turbulence caused by this stay is generated. The flow may act on the outlet of the branch passage. And when turbulence acts on the outlet opening,
Not only may the flow in the branch passage be disturbed or the flow rate introduced into the branch passage may be changed, but also the ratio between the flow rate in the main passage and the flow rate in the branch passage may change.

In view of the above-mentioned problems of the prior art, the present invention provides a flowmeter for forming and supporting a branch passage in the main passage, particularly by improving the position of the branch passage outlet,
It is an object of the present invention to reduce the effect of turbulence on the outlet of the branch passage and enable accurate flow rate measurement.

[0007]

In order to solve the above problems, the present invention provides a main passage through which a fluid flows, a central member provided at a substantially central portion of the main passage, a wall surface of the main passage, and A support member that connects the central member and supports the central member at substantially the center of the main passage, and an inlet opening into the central member to introduce a part of the fluid flowing through the main passage,
A branch passage formed in the central member and through which a fluid introduced from the introduction port flows, a sensor provided in the branch passage for measuring a flow rate in the branch passage, and upstream of a downstream end of the support member. The technical means called a flow meter is provided, which has an outlet opening at a predetermined portion of the central member located on the side and returning the fluid flowing through the branch passage to the main passage again.

[0008]

According to the structure of the present invention described above, the central member is supported by the supporting member at the substantially central portion of the main passage.
An inlet, a branch passage, and an outlet are formed in the central member, and a sensor is provided in the branch passage to measure the flow rate of the fluid. Moreover, since the outlet of the branch passage formed in the central member is provided on the upstream side of the downstream end portion of the support member that supports the central member at substantially the center of the main passage, the fluid generated downstream of the support member is formed. Turbulent flow is prevented from acting on the outlet of the branch passage. Therefore, the turbulence of the flow in the branch passage is reduced, and the flow rate that exactly corresponds to the flow rate in the main passage is introduced and flown into the branch passage. Therefore, the flow rate can be accurately measured by the sensor provided in the branch passage.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a thermal air flow meter for measuring the amount of intake air drawn into an automobile engine will be described below with reference to FIGS. 1, 2 and 3.

FIG. 1 is a sectional view of a thermal type air flow meter, and FIG.
2 is a view as seen from the direction of arrow A in FIG. Note that FIG. 1 shows the I-I cross section of FIG. Intake air is introduced into the air flow meter 1 from the left side in the figure and flows out to the right side in the figure. The upstream opening 3 of the air flow meter 1 is inserted and attached to an air cleaner (not shown). On the other hand, the downstream opening 5 is inserted into an intake duct (not shown) having a diameter larger than that of the air flow meter 1, and is tightened from the outer periphery by a belt (not shown).

The air flow meter 1 includes a central cylindrical portion 100, an upstream cylindrical portion 200 and a downstream cylindrical portion 300 which form an intake passage.
It has and. A circuit container 110 accommodating a control circuit is integrally formed on the outside of the central cylindrical portion 100 made of resin, and a lid is put on the circuit container 110. A control circuit for a thermal sensor, which will be described later, is housed in the circuit container 110. Further, on the outside of the central cylindrical portion 100, fixing nuts 111 and 11 are provided.
Support portions 115 and 117, in which 3 is insert-molded, are molded. The inner side of the central cylindrical portion 100 is formed into a cylindrical shape, and four ribs 120, 130, 140, and
150 is integrally molded. Furthermore, the rib 120,
A cylindrical central housing 160 is integrally formed at the tips of 130, 140 and 150. Central housing 1
60 has a partition wall 163 in the center thereof.
A hole 165 is opened in the center of 3.

The upstream cylindrical portion 200 made of resin is formed in such a shape that the inner cross-sectional area thereof gradually widens toward the downstream side, the bell mouth portion 210 is formed at the upstream end portion, and the bell mouth portion 210 is attached to the outer periphery. There is a step for use. And
The upstream side cylindrical portion 200 is inserted inside the central cylindrical portion 100 and fixed to the central cylindrical portion 100.

The resin-made downstream cylindrical portion 300 is formed with a straight pipe portion 310 which is inserted into an intake duct (not shown), and is fixed to the downstream end portion of the central cylindrical portion 100. The inner side of the downstream side cylindrical portion 300 is formed into a cylindrical shape, and four ribs 320, 330, 340 and 350 are integrally formed toward the inside. Further, ribs 320, 330, 340, 350
A bowl-shaped downstream housing 360 is integrally formed at the tip of the.

The four ribs 320, 330, 34
0 and 350 are ribs 12 extending from the central cylindrical portion 100.
It is located on the downstream side of 0, 130, 140, 150 and assembled in a sectional shape as shown in FIG. Further, the bowl-shaped downstream housing 360 closes the downstream side of the central housing 160 supported by the central cylindrical portion 100, and is assembled into a smooth shell shape.

A shell-shaped resin-made upstream housing 400 is inserted and fixed on the upstream side of the central housing 160 supported by the central cylindrical portion 100. Upstream housing 40
An inlet opening 410 is opened at the center of the upstream side of 0, and a branch pipe 420 linearly extending from the inlet opening 410 toward the downstream is integrally formed inside the upstream housing 400. A measuring pipe 430 is inserted at the downstream end of the branch pipe 420. The measuring pipe 430 includes an inner pipe 433 made of stainless steel and an outer pipe 435 made of resin.
A bell mouth is formed on the upstream side of 3, and its inner diameter is smaller than that of the branch pipe 420. Further, outlet openings 440 and 450 are provided outside the shell-shaped upstream housing 400 along the circumferential direction. A plurality of outlet openings 440 and 450 are formed as slit-shaped openings extending in the circumferential direction over substantially the entire circumference. Further, the outlet openings 440 and 450 are opened so as to be inclined toward the downstream side from the inside to the outside of the upstream housing 400. Moreover, the wall surface on the downstream side from the upstream side is more inclined toward the downstream side, so that air can be smoothly discharged.

The upstream housing 400 is the central housing 1.
It is inserted and fixed on the upstream side of 60. At this time, the downstream end of the branch pipe 420 contacts the upstream end faces of the plate-shaped ribs 167 and 169 radially formed inside the central housing 160. It should be noted that FIG. 1 illustrates two of the four plate-shaped ribs radially provided, 167 and 169. As a result, a predetermined gap is formed between the downstream end of the measuring pipe 430 and the partition wall 163 of the central housing 160, and an air passage from the downstream end of the measuring pipe 430 to the outer peripheral side of the measuring pipe 430 and the branch pipe 420. Is secured. The central member formed by the upstream housing 400, the central housing 160, and the downstream housing 360 is assembled in a cocoon shape with a smooth outer shape.

Here, between the upstream side of the outlet openings 440 and 450 of the upstream housing 400 and the upstream cylindrical portion 200, a throttle portion having the narrowest cross-sectional area of the intake passage is formed. The flow path cross-sectional area at the position indicated by the medium-dot chain line B is the smallest. As a result, the airflow that has flowed in from the upstream side opening 3 is throttled by the throttle portion and is rectified so as to have a uniform flow along the outer circumference of the upstream housing 400.

Further, in the hole 165 of the partition wall 163,
The sensor unit 500 is inserted from the downstream side,
Is fixed to the partition wall 163. The sensor unit 500 includes a cylindrical resin unit 510, four support pins 520, 530,
It is formed by insert-molding 540 and 550 and fixing a fixing flange 560 to one end side. The support pins projecting upstream consist of two types, long and short, and two long 520, 53
One sensor 570 is supported between 0 and two short 5
One sensor 580 is supported between 40 and 550. The sensors 570 and 580 are made by winding a platinum wire around the outer circumference of a ceramic bobbin and connecting the lead wires at both ends of the bobbin, and those having the same characteristics are used.

Further, the space formed between the central housing 160 and the downstream housing 360, and the circuit container 11
0, a conductive member is disposed through the inside of the rib 140, and this conductive member is connected to a support pin projecting to the downstream side of the sensor unit 500 via a flexible wiring board (not shown). Therefore, the control circuit housed in the circuit container 110 is connected to the sensor via the conductive member, the flexible wiring board, and the support pin.

In the embodiment described above, the intake passage is formed inside the upstream cylinder portion 200, the central cylinder portion 100 and the downstream cylinder portion 300. And the upstream housing 4
00, the central housing 160, and the downstream housing 360 form a cocoon-shaped central member, which is supported at the center of the intake passage by four ribs. Then, the intake air mainly flows outside the central member.

Further, a branch pipe 420, a measuring pipe 430, a measuring pipe 430 and a partition wall 163 are provided between the upstream housing 400 and the central housing 160 from the inlet opening 410.
A branch passage is formed through the gap between and to reach the outlet openings 440 and 450. Therefore, a part of the air flowing in the intake passage passes through the branch pipe 420 from the inlet opening 410 and is introduced into the measurement pipe 430. And the partition wall 16
3 to change the direction of the flow in the radial direction, and further flow through the outside of the branch pipe 420 toward the outlet openings 440, 450. Then, it again flows into the intake passage from the outlet openings 440 and 450. At this time, the outlet openings 440 and 450
Since the cross-sectional area of the intake passage in the vicinity is narrowed, the flow velocity of the intake passage increases, and the pressure in the vicinity of the outlet openings 440 and 450 becomes negative pressure, so that the air in the upstream housing 400 is sucked out.

Then, the flow rate of the air flowing through the branch passage is measured by the sensors 570 and 580 located inside the measuring pipe 430. Here, one sensor is used for temperature measurement, the other sensor is heated to a predetermined temperature, and its heat radiation amount changes according to the air flow rate. Then, the control circuit housed in the circuit container 110 detects the electric power required to heat the sensor to a predetermined temperature, and outputs this electric power as an output signal indicating the measured flow rate. The output signal output from the control circuit is supplied to the fuel injection amount control device or the like and used for calculating the fuel injection amount.

In the above embodiment, the outlet openings 440, 45.
Since the throttle portion B is formed on the upstream side of 0, the negative pressure that acts on the outlet openings 440 and 450 acts evenly over the entire circumference in the circumferential direction. Therefore, even if there is a deviation in the air flow that flows in from the upstream opening 3, the deviation can be rectified and acted on the outlet openings 440 and 450.

Further, although the separation of the air flow generated on the surface of the central member also influences the outlet openings 440 and 450, since the outlet openings 440 and 450 are opened at a position near the upstream of the central member where the separation is relatively small. It is possible to obtain stable operation in a wide range from low flow rate to high flow rate.

Further, the outlet openings 440 and 450 are provided with ribs 12.
0, 130, 140, 150 open upstream from the branch passages without being affected by the turbulence generated by the separation of the airflow generated on the rib surface and the turbulence generated at the downstream end of the rib. Can be drained.

Further, since the outlet openings 440 and 450 are opened to the outer circumference of the upstream housing 400 over substantially the entire circumference, they are affected by the flow of the entire intake passage. Therefore, it is possible to prevent the flow rate in the branch passage from fluctuating due to a part of the turbulent flow.

As described above, in this embodiment, the flow of air at the outlet openings 440 and 450 can be maintained in a state where there is little turbulence, and the ratio between the total flow rate of the intake passage and the flow rate of the branch passage can be accurately determined. It is possible to maintain the above ratio, and it is possible to accurately detect the flow in the entire intake passage by measuring the flow rate in the branch passage.

Further, the outlet openings 440 and 450 are opened so as to be inclined from the inside to the outside of the shell-shaped upstream housing 400 toward the downstream side, and the wall surface from the upstream side to the downstream side is larger toward the downstream side. It is inclined. And
The openings 440 and 450 are formed on the upstream side of the upstream housing 400, that is, in the enlarged portion where the outer diameter of the central member gradually increases toward the downstream side. The upstream cylindrical portion 200 located near the outer circumference of the enlarged portion is formed with a gradually increasing portion whose inner diameter gradually increases toward the downstream side. Here, the enlarged portion of the central member is formed such that the gradual increase rate of the outer peripheral diameter thereof is smaller than the gradual increase rate of the inner peripheral diameter of the gradual increase portion.

With this structure, the flow in the intake passage first flows along the enlarged portion of the central member, so that it is inclined toward the outer radial direction with respect to the axial direction. Further, due to the gradually increasing portion of the upstream side cylindrical portion 200, the flow of the main passage inclined along the central member is inclined further outward.

On the other hand, the flow flowing out of the outlet openings 440 and 450 is inclined toward the downstream side because the openings are inclined toward the downstream side.
It is possible to join the flow of the intake passage inclined toward the outer diameter direction at a small angle. Therefore, the two flows can be smoothly merged, and the collision between the two flows is significantly reduced. Therefore, it is possible to prevent the flow in the intake passage from being throttled due to the collision of the flows and to increase the pressure loss, and it is possible to reduce the intake resistance in the air flow meter 1. Therefore, the intake air can be smoothly drawn into the internal combustion engine, and the engine output can be improved.

Further, the gradually increasing portion of the upstream side cylindrical portion 200 is formed so that the gradually increasing rate thereof is larger than that of the enlarged portion of the central member, so that the area of the intake passage on the downstream side of the outlet openings 440, 450 is increased. The rate of increase of
It is larger than that on the upstream side. Therefore, the outlet opening 44
Even when the air flowing out from 0, 450 merges with the air flowing in the intake passage, the increase in the air flow rate prevents the flow in the intake passage from being throttled. For this reason,
It is possible to prevent the flow from being narrowed due to the increase in the flow rate and the pressure loss from increasing. Therefore, air can be smoothly drawn into the internal combustion engine, and the engine output can be improved.

Further, the ribs 120, 130, 140, 1
Ribs 320, 330, 340, 350 downstream of 50
Are formed between the downstream housing 360 and the downstream cylindrical portion 300. The rib acts to prevent the straight pipe portion 310 from being deformed. That is, the rib prevents the straight pipe portion 310 from being deformed when the belt is fastened to the straight pipe portion 310 of the downstream side cylindrical portion 300 via the intake duct. Further, when the temperature is high, the straight pipe portion 310 is deformed by the tightening force of the belt, and a gap is formed between the intake duct and the downstream side cylinder portion 300, and air flows in through this gap, which causes excess air into the engine. It is possible to prevent the reduction of the output of the engine due to the intake of air and the reduction of the air-fuel ratio.

Next, another embodiment to which the present invention is applied will be described with reference to FIG. Here, differences from the embodiment shown in FIG. 1 will be described. Also in this embodiment, four ribs are formed toward the inside of the intake passage, as in the above-described embodiments, and the central member is supported at the center of the intake passage. Then, the outlet openings of the branch passages are ribs 121, 131, 14
1, 151 (121 and 131 are not shown). Furthermore, the ribs 121, 131, 141,
Ribs 321, 331, 34 are provided at the downstream end of 151.
1, 351 (321 and 331 are not shown) are formed. In this embodiment, the central housing 161 comprises a cylindrical portion 162 and a wall portion 164 having a diameter smaller than that of the cylindrical portion 162, and the wall portion 164 has ribs 121, 131, 141 and 15 respectively.
Supported by 1. Therefore, four thin arc-shaped passages are formed between the cylindrical portion 162 and the wall portion 164. In FIG. 4, two of the four passages 166 and 16 are shown.
8 are shown. Then, these passages are directly connected to the outlet openings 441 and 451.

Further, an upstream housing 401 having an inlet opening 411 is fixed on the upstream side of the cylindrical portion 162,
Inside the cylindrical portion 162, a metal measuring pipe member 431 having a pipe formed in the center of the disc is fixed. The branch pipe member 4 is provided between the inlet opening 411 and the measurement pipe member 431.
21 is provided to connect the inlet opening 411 and the conduit of the measuring pipe member 431.

Therefore, in this embodiment, a part of the air in the intake passage is introduced into the branch passage from the inlet opening 411, passes through the branch pipe member 421 and the measuring pipe member 431, and passes through the wall portion 164.
Colliding with and changing the flow direction in the radial direction, the passages 166, 1
Through 68 to outlet openings 441, 451. Moreover, at the position indicated by the one-dot chain line C in the figure, the air flow meter 2
Of the intake passage, the narrowed portion C having the smallest passage cross-sectional area is formed, and the narrowed portion C is formed at the position indicated by the alternate long and short dash line D in the figure.
Next to this, a narrowed portion D having a narrow passage cross-sectional area is formed. Therefore, the airflow flowing from the upstream opening 3 is rectified by the narrowest narrowed portion C in the circumferential direction into a substantially uniform flow, and then flows to the narrowed narrowed portion D. Then, a negative pressure is generated in the throttle portion D due to the increase of the flow velocity, and the outlet openings 441 and 45 are formed.
The air in the branch passage is sucked out from 1.

Therefore, according to this embodiment, since the outlet openings 441 and 451 are provided downstream of the throttle portion C,
The flow deviation in the vicinity of the outlet openings 441 and 451 can be reduced, and the flow rate in the branch passage can stably correspond to the flow rate in the entire intake passage. Also, the outlet opening 441,
Since 451 is opened over almost the entire circumference except for the ribs, an average negative pressure according to the flow rate of the entire intake passage can be made to act on the outlet opening, and the flow rate flowing out of the branch passage can be the flow rate of the entire intake passage. Can be maintained at a desired ratio. Further, in this embodiment, the outlet opening 441,
Since 451 is provided between the ribs, the air can flow out from the branch passage without being affected by the turbulent flow generated downstream of the ribs. Therefore, problems such as turbulent flow occurring in the branch passage and the flow rate in the branch passage not corresponding to the flow rate in the entire intake passage are prevented, and accurate flow rate measurement is possible.

Also in the case of this embodiment, the rib 12
The ribs 321, 331, 341, and 351 formed on the downstream side of 1, 131, 141, and 151 prevent deformation of the downstream side cylindrical portion 300, and prevent deformation when connected to the intake duct and tightened with a belt. it can.

In the embodiment of FIG. 1, the inside and outside of the branch pipe are used as branch passages, so that a longer branch passage can be made compact as compared with the embodiment of FIG. 4, and when the intake air amount changes. The sensor responsiveness, or the responsiveness to the engine intake pulsation and backflow can be adjusted by the passage shape.

Further, in the case where the outlet opening is formed between the ribs as shown in FIG. 4, the length of the rib on the upstream side of the outlet opening in the flow direction is shortened so that the upstream end face of the rib and the rib surface are separated from each other. It can be expected to suppress the influence of turbulent flow generated at. Therefore, in the embodiment of FIG. 4, the length of the rib along the flow direction is shorter than that of the embodiment of FIG. Further, in the embodiment of FIG. 1, the outlet openings 440 and 450 are opened on the upstream side of the outlet openings 441 and 451 of the embodiment of FIG. Therefore, in the embodiment of FIG. 1, the ribs can be formed up to the upstream side as compared with the embodiment of FIG. 4, and high strength can be obtained.

Further, in the above-mentioned embodiments, the housing of the air flow meter constituting a part of the intake passage is divided into a plurality of parts in the flow direction of the intake passage and assembled. Moreover, the sensor portion is inserted axially from the wall surface on the downstream side of the branch passage. Therefore, when assembling the air flow meter, it suffices to assemble the parts each having a substantially cylindrical outer shape in the axial direction, and the assembling work can be facilitated.

[0041]

According to the above-described structure and operation of the present invention, since the outlet of the branch passage is opened on the upstream side of the downstream end of the support member, it is affected by the turbulent flow generated by this support member. Instead, the fluid can flow out from the branch passage to the main passage. Therefore, it is possible to prevent turbulence in the flow of the fluid in the branch passage and fluctuation in the flow rate, and it is possible to accurately measure the flow rate.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment to which the present invention is applied.

FIG. 2 is a view on arrow A in FIG.

3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a sectional view of another embodiment to which the present invention is applied.

[Explanation of symbols]

 1 Air Flowmeter 3 Upstream Side Opening 5 Downstream Side Opening 100 Central Cylindrical Section 160 Central Housing 140 Rib 150 Rib 200 Upstream Cylindrical Section 300 Downstream Cylindrical Section 340 Rib 350 Rib 360 Downstream Housing 400 Upstream Housing 410 Inlet Opening 420 Branch Pipe 430 Measuring tube 440 Outlet opening 450 Outlet opening 500 Sensor section

Front page continuation (72) Inventor Tsunemitsu Kato 1-1, Showa-cho, Kariya, Aichi Prefecture, Nihon Denso Co., Ltd. (72) Inventor Takao Ban, 1-1, Showa-cho, Kariya, Aichi Prefecture, Nihondenso Co., Ltd. (72) Inventor Kunihiro Umezu 1-1-1, Showa-cho, Kariya city, Aichi prefecture, Nihon Denso Co., Ltd.

Claims (1)

[Claims] 1. A main passage through which a fluid flows, a central member provided at a substantially central portion of the main passage, a wall surface of the main passage and the central member are connected, and the central member is formed substantially in the main passage. A support member that is supported in the center, an inlet opening into the central member for introducing a part of the fluid flowing through the main passage, and a branch passage formed in the central member for flowing the fluid introduced from the inlet, A sensor provided in the branch passage for measuring the flow rate in the branch passage and an opening at a predetermined portion of the central member located upstream of the downstream end of the support member and flowing through the branch passage. An outlet for returning fluid to the main passage again.