JPH102767A - Flow rate measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve higher measuring accuracy by reducing measuring error in a transient state and preventing the measurement of the flow rate of a reversed gas. SOLUTION: A housing 3 is mounted in a tube body 1, and a path 4 for measurement is formed between the upstream side end face 3A and the downstream side end face 3B is the housing 3. A thermosensitive resistor 5 is disposed in the path 4 for measurement and connected to a flow rate detection circuit in a circuit casing 7. Moreover, a bypass path 8 is formed in the housing 3, to be branched off in the course of path 4 for measurement and a branch inflow port 8C thereof, is opened in the path 4 for measurement on the downstream side from the thermosensitive resistor 5. A branch outflow part 8D of a bypass path 8 is opened on the downstream side end face 3B of the housing 3 near an internal wall 1A of a pipe body 1. When a reverse flow is generated in the pipe body 1, a reverse flow flowing into the path 4 for measurement from the outflow port 4B is made to flow out to the downstream side of the housing 3, through the bypass path 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device for measuring a flow rate or a flow rate (hereinafter referred to as a flow rate) of a gas flowing through a pipe, and is used, for example, for measuring an intake air amount in an engine of an automobile or the like. The present invention relates to a suitable flow measurement device.

[0002]

2. Description of the Related Art In general, in an engine of an automobile or the like, the flow rate of intake air taken into each cylinder of the engine is measured by a flow rate measuring device provided in the middle of an intake pipe. By mixing the fuel with the intake air, a mixture having a concentration (mixing ratio) suitable for combustion is supplied to each cylinder.

In this type of conventional flow rate measuring device, a housing of the flow rate measuring device is mounted in an intake pipe, and a measurement passage for measuring an intake air amount is formed in the housing as a main passage. The measurement passage is a through hole extending in the axial direction of the intake pipe. Most of the intake air flowing through the intake pipe flows downstream of the housing through a gap formed between the inner wall of the intake pipe and the housing, and a part of the intake air flows through the measurement passage. It flows downstream.

In the measurement passage, a flow rate detecting element formed of a heat-sensitive resistor such as a platinum wire and changing the calorific value in accordance with the flow rate of the gas to be measured is provided in an exposed state. The element is connected to a flow detection circuit or the like provided outside the intake pipe.

[0005] In the conventional flow rate measuring device configured as described above, a part of the intake air flowing through the intake pipe flows through the measurement passage, and cools the flow rate detecting element according to the flow rate. As a result, the resistance value of the flow detection element decreases,
The amount of decrease in the resistance is detected by a flow rate detection circuit, and the amount of intake air in the intake pipe is measured based on the detection result.

[0006]

In the above-mentioned prior art, the flow rate detecting element detects the flow rate based on a change in resistance value when the flow rate detecting element is cooled by the intake air. Is cooled by the airflow flowing in the forward direction from the intake port of the engine to each cylinder of the engine, and also cooled by the airflow flowing in the reverse direction. There is a problem of measurement.

That is, the intake air flowing through the intake pipe is sucked into the cylinder when the intake valve is opened in accordance with the reciprocation of the piston in each cylinder. Becomes pulsating. Then, in this state, if the exhaust gas blows back into the intake pipe due to the overlap between the intake valve and the exhaust valve, or if the intake valve presses the intake air by opening or closing the valve, the intake air temporarily flows backward. Sometimes.

For this reason, in the prior art, when the intake air flows backward, the detected value of the flow rate may become larger than the actual value, and the measurement accuracy of the intake air amount based on the detected value decreases. is there.

If the amount of intake air changes suddenly, the flow rate detecting element is cooled in an unstable state due to the turbulence of the air flow generated in the measurement passage, so that the amount of intake air changes gradually. In some cases, a detection value different from that in the case where the detection is performed is obtained, and there is a problem that the intake air amount cannot be accurately measured.

The present invention has been made in view of the above-described problems of the prior art, and can prevent the flow rate of a gas flowing backward from being measured, stabilize the gas flow, and reduce the measurement error in a transient state. It is an object of the present invention to provide a flow measurement device capable of improving measurement accuracy.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that a pipe having an air passage through which a gas to be measured flows is provided, and the pipe is diametrically arranged in the pipe. A transversely extending housing, and a diametrically central portion of the housing, axially penetrating the housing, an inlet opening at an upstream end surface of the housing, and an outlet opening at a downstream end surface of the housing. A main passage opening in the main passage, a flow detection element provided in the middle of the main passage for detecting a flow rate of gas flowing through the main passage, and an upstream side located in the downstream of the flow detection element in the middle of the main passage. And a bypass passage whose downstream side is located near the inner wall of the pipe body and is opened at the downstream end face or side face of the housing.

[0012] With this configuration, the gas that flows backward in the pipe is utilized in the main passage at the center of the pipe, utilizing the fact that the pressure of the gas becomes smaller near the inner wall than the center of the pipe and becomes stable. When the gas flows into the pipe, the backflow can be quickly discharged to the vicinity of the inner wall of the pipe via the bypass passage, and the backflow can be prevented from reaching the flow rate detecting element. In addition, since the main passage is communicated with the vicinity of the inner wall of the tube via the bypass passage on the way, even when the gas flow rate in the tube rapidly changes, the pressure fluctuation in the main passage can be stabilized near the inner wall. Can be buffered by the applied pressure.

Further, in the invention according to claim 2, the inflow port of the main passage is formed with a full-circle expanding portion at an opening end thereof.

Accordingly, at the upstream open end of the main passage,
Since the gas in the pipe flows into the main passage while being throttled by the entire circumference expanding portion, the velocity of the gas flowing into the main passage from the inflow port can be increased, and pressure fluctuations generated on the downstream side of the housing from the outflow port. Even when transmitted to the main passage, the pressure fluctuation can be prevented from propagating to the flow rate detecting element by the gas flowing from the inlet.

Further, in the invention according to the third aspect, a chamfered portion is formed in the bypass passage at a branch inlet which branches off from the main passage.

Thus, the backflow that has entered the main passage can be smoothly guided from the branch inlet into the bypass passage by the chamfered portion, and can be discharged to the vicinity of the inner wall of the pipe via the bypass passage. .

Further, in the invention described in claim 4, the bypass passage is formed in an L shape with respect to the housing.

[0018] Accordingly, when a backflow enters the bypass passage from the outflow side, the backflow can be prevented from flowing into the main passage, and the length of the bypass passage can be made longer. The buffer effect of the passage can be increased.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the accompanying drawings, taking as an example the case where the present invention is used to measure the intake air amount of an engine such as an automobile.

FIGS. 1 to 5 show a first embodiment according to the present invention.

In FIG. 1, reference numeral 1 denotes a pipe having a connection portion such as a flange at both ends to constitute the flow rate measuring apparatus according to the present embodiment. The pipe 1 is made of, for example, a metal material or a resin material. It is formed as a long cylindrical body having an inner diameter D by the above method. The pipe 1 has an upstream end connected to an air cooler or the like that sucks outside air, and a downstream end connected to an intake manifold extending toward each cylinder of the engine. The inside of the tube 1 is a ventilation passage 2 through which intake air flows from the upstream side to the downstream side, and the inner wall 1
A is provided with a housing 3 described later.

Reference numeral 3 denotes a housing provided in the tube 1, and the housing 3 is formed in a substantially rectangular parallelepiped shape by, for example, a metal material or a resin material. The housing 3 has its upper end and lower end fixed to the inner wall 1 </ b> A of the tube 1, and extends in the tube 1 in the axial direction with the housing 3 disposed so as to cross the ventilation path 2 in the diametrical direction. Also, housing 3
A measurement passage 4 to be described later is formed between the upstream end face 3A and the downstream end face 3B.

Reference numeral 4 denotes a measurement passage as a main passage for measuring the amount of suction air in the ventilation passage 2. The measurement passage 4 has a cross-sectional area S extending in the axial direction of the tubular body 1 as shown in FIG. One end is formed in the housing 3 as a hole, and one end is located at the center in the diameter direction of the housing 3 and is an inflow opening 4A opening to the upstream end face 3A, and the other end is an outflow opening 4B opening to the downstream end face 3B. I have.

Reference numeral 5 denotes a heat-sensitive resistor 5 as a flow rate detecting element for detecting a flow rate or a flow rate flowing in the measurement passage 4. The heat-sensitive resistor 5 is formed of a heat-sensitive material such as a platinum wire, and measures the intake air temperature. The measurement passage 4 is attached to the distal end side of the support 6 together with a resistor (not shown) for use in measurement.
Is exposed within. Further, the heat-sensitive resistor 5 and the resistor are connected to a flow rate detection circuit in a circuit casing 7 to be described later via wiring or the like (neither is shown) in the support portion 6.

The heat-sensitive resistor 5 is cooled by the airflow flowing through the measurement passage 4 while being heated so as to have a predetermined resistance value by being supplied with electricity from the flow rate detection circuit. The resistance value is changed according to the flow velocity (flow rate) of the flow.

Reference numeral 7 denotes a circuit casing mounted on the outer wall of the tubular body 1. The circuit casing 7 accommodates the flow rate detection circuit. The flow rate detection circuit includes a heat sensitive resistor 5 and a bridge circuit together with the resistor. Are configured to detect a change in the resistance value of the thermal resistor 5 or the like as a voltage signal.

Reference numerals 8 denote bypass passages according to the present embodiment. Each of the bypass passages 8 has an L-shape as a whole as shown in FIGS. It is formed in the housing 3 so as to sandwich it. The bypass passage 8 is connected to the pipe 1 from the middle of the measurement passage 4.
Radial passages 8A, 8 extending radially toward inner wall 1A
A, and axial passages 8B, 8B extending in the axial direction from the distal end side of each radial passage 8A toward the downstream side of the tubular body 1.

The base end of each of the radial passages 8A is located downstream of the thermal resistor 5 and opens into the measuring passage 4, and each of the bypass passages 8 branches off from the measuring passage 4. The entrances 8C, 8C are provided. Each branch inlet 8C is opened in the measurement passage 4 at the same axial position.

On the other hand, the distal end of each axial passage 8B
The downstream end face 3 of the housing 3 is located near the inner wall 1A of the housing 3.
B are formed as branch outlets 8D, 8D for allowing a part of the gas flowing into each bypass passage 8 from the branch inlet 8C to flow out to the downstream side of the housing 3.

Here, each branch outlet 8D has an opening area S 1 corresponding to the sectional area S of the measurement passage 4.

[0031]

(Equation 1) The distance d at the position farthest radially inward from the inner wall 1A of the tube 1 is smaller than the inner diameter D of the tube 1.

[0032]

(Equation 2) It is formed so that it becomes.

The flow rate measuring apparatus according to the present embodiment has the above-described configuration, and its operation will be described with reference to FIGS.

First, when the intake air flows through the pipe 1 in the forward direction as shown on the left side in FIG. 3, a part of the intake air flows into the measurement passage 4 from the inflow port 4A as shown by the arrow A. And
It passes around the thermal resistor 5. As a result, the resistance value of the heat-sensitive resistor 5 decreases in accordance with the flow velocity (flow rate) of the passed air. Therefore, a change in the resistance value is detected by the above-described flow rate detection circuit, and the inside of the tube 1 is detected based on the detection result. Measure the amount of intake air.

The air flow passing through the heat-sensitive resistor 5 is divided into three directions, a part of which flows out of the outlet 4B of the measurement passage 4, and the remaining part flows into each bypass passage 8 from the branch inlet 8C. And flows out of each branch outlet 8D to the downstream side of the housing 3.

If the amount of intake air in the tube 1 changes suddenly and turbulence or pressure fluctuation occurs in the measurement passage 4, the air flow near the inner wall 1A of the tube 1 Suppresses these turbulences and pressure fluctuations through each bypass passage 8,
The air flow in the measurement passage 4 is promptly returned to a steady state.

That is, as shown on the right side in FIG. 3, the pressure in the tube 1 is within a range of 1/5 of the inner diameter D from the inner wall 1A of the tube 1 (in the vicinity of the inner wall 1A) as shown by a characteristic line P. It becomes smaller than the central part and becomes stable. For this reason, by connecting the measurement passage 4 to this position via each bypass passage 8, airflow and pressure fluctuation in the measurement passage 4 are buffered.

Next, as shown in FIG. 4, when the intake air flows backward from the downstream side in the tubular body 1 due to pulsation or the like, a part of this backward flow flows into the measurement passage 4 from the outlet 4B. Show B
And before reaching the thermal resistor 5, the branch inlet 8
C flows into each of the bypass passages 8 and the branch outlet 8D
From the housing 3 to the downstream side.

In this case, in each bypass passage 8, as described above, the pressure at the branch outlet 8D side is smaller than that at the branch inlet 8C side, which is stable. The backflow is pressed by the above-described airflow in the direction of arrow A, and the backflow flows together with the flow in the direction of arrow A toward the branch outlet 8D on the low pressure side.
And does not reach the thermal resistor 5.

Thus, in the present embodiment, each of the bypass passages 8 is located downstream of the thermal resistor 5 so that
And the branch outlet 8D of each of the bypass passages 8 is opened near the inner wall 1A of the tubular body 1. Therefore, when a backward flow occurs in the tubular body 1, this backward flow is generated in FIG. As shown by arrow B, the housing 3 is connected via the bypass passage 8.
Can smoothly flow out to the downstream side, and the backflow can reliably be prevented from reaching the thermal resistor 5.

Even if the amount of intake air in the tube 1 changes suddenly, the turbulence and pressure fluctuation in the air flow in the measurement passage 4 due to the sudden change in the amount of air in the tube 1 can be reduced via the bypass passages 8. The pressure can be reliably buffered by the pressure near the inner wall 1A.
The flow of air inside can be quickly returned to a stable state.

Therefore, according to the present embodiment, the thermal resistor 5
Thus, it is possible to reliably prevent the flow rate of the air flowing backward in the pipe 1 from being detected, to reliably reduce the error in the detection of the air flow rate in the transient state, and to reduce the case where the intake air is pulsating or in the transient state. Measurement accuracy in certain cases can be greatly improved.

Since the backflow in the tubular body 1 does not reach the thermal resistor 5, the same thermal resistor 5 as in the prior art is used without using, for example, a thermal resistor capable of correcting the reverse flow. Thus, the flow measurement device capable of coping with the backflow can be configured, and the performance of the flow measurement device can be improved without increasing the cost.

Further, the inner wall 1A of the tube 1 in which a part of the air flow in the measurement passage 4 is reduced in pressure by each bypass passage 8
Since the air flows out to the vicinity, the pressure loss of the air flow in the measurement passage 4 can be reduced.

Further, since each bypass passage 8 is formed in an L-shape, when a backflow enters from the branch outlet 8D of each bypass passage 8, the backflow can be suppressed from flowing into the measurement passage 4. At the same time, the length of each of the bypass passages 8 can be made longer, and each of the bypass passages 8 against pressure fluctuations and the like can be formed.
Can reliably increase the buffering action.

Further, since the branch inlets 8C are opposed to each other at the same axial position of the measurement passage 4, for example, when pulsation of pressure or the like propagates from the branch outlet 8D side of each bypass passage 8, each bypass inlet 8C These pulsations can interfere with each other and be attenuated between the passages 8.

As shown as a modification of the present embodiment in FIG. 5, for example, four bypass passages 9, 9,... Are formed between the measurement passage 4 and the vicinity of the inner wall 1A of the tube 1. It may be.

Next, FIG. 6 shows a second embodiment according to the present invention. In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. And However, a feature of the present embodiment is that a full-circle expanding portion 11 described later is formed at an inlet 4A of the measurement passage 4 and a chamfered portion 12 is formed at a branch inlet 8C of each bypass passage 8.

Here, the flow rate measuring device according to the present embodiment is substantially the same as the first embodiment, and the housing 3 disposed in the pipe 1, the measuring passage 4, the thermal resistor 5, and each bypass A passage 8 and the like are provided.

Reference numeral 11 denotes a full-circle widening portion formed at the inflow port 4A of the measurement passage 4. The full-circle widening portion 11 is formed such that the inflow port 4A side of the measurement passage 4 is convexly curved toward the open end thereof. The diameter of the air flow is reduced by the diameter of the air inlet 4A, and serves as a throttle for the airflow flowing into the measurement passage 4 from the inflow port 4A.

Reference numerals 12 and 12 denote chamfers formed at the branch inlet 8C of each bypass passage 8, respectively.
Is formed by chamfering the downstream side of the opening end of the branch inlet 8C into a convexly curved shape.

In this embodiment constructed as described above, substantially the same operation and effect as those of the first embodiment can be obtained. However, in this embodiment, in particular, the air flow flowing from the inflow port 4A is expanded all around. Since the flow is restricted by the portion 11, the inflow velocity can be increased, and the backflow can be more reliably prevented from reaching the thermal resistor 5 from the outflow port 4B by this air flow. Further, this backflow is removed from the inside of the measurement passage 4 by the respective chamfers 12 to the branch inlets 8C of the respective bypass passages 8.
It can be guided smoothly inside.

Next, FIG. 7 shows a third embodiment according to the present invention. In this embodiment, the same reference numerals are given to the same components as those in the first embodiment, and the description thereof will be omitted. And However, a feature of this embodiment is that the branch outlet 21D of each bypass passage 21 is opened to the side surface 3C of the housing 3.

Here, the bypass passages 21 and 21 (only one is shown) are formed in the housing 3 at positions sandwiching the measurement passage 4 in the upward and downward directions, as in the first embodiment. It has a branch inlet 21A that branches off from the measurement passage 4 on the downstream side of 5, and a radial passage 21B extending radially from the branch inlet 21A toward the vicinity of the inner wall 1A.

However, in this embodiment, each bypass passage 2
1, a side passage 21C extending from the distal end of the radial passage 21B toward the oblique downstream side to the side surface 3C of the housing 3 is formed, and the distal end side of the side passage 21C is formed on the side surface 3C of the housing 3. A branch outlet 21D that opens is formed.

The branch outlet 21D is located downstream of the branch inlet 21A, opens near the inner wall 1A of the tube 1, and is furthest away from the inner wall 1A of the tube 1 radially inward. The distance d at the position is formed so as to satisfy the equation (2).

In this embodiment constructed as described above, substantially the same operation and effect as those of the first embodiment can be obtained. In this embodiment, in particular, the branch outlet 21D of each bypass passage 21 is connected to the housing. Because it was opened on the side 3C of 3,
It is possible to reliably prevent the backflow from entering each bypass passage 21.

In the first and second embodiments,
The branch outlet 8D of each bypass passage 8 is connected to the inner wall 1A of the tubular body 1.
However, the present invention is not limited to this, and the branch outlet 8D may be separated from the inner wall 1A as long as it is within 1/5 of the inner diameter D from the inner wall 1A of the tube 1. .

In each of the above embodiments, the upper and lower ends of the housing 3 are fixed to the inner wall 1A of the tube 1. However, the present invention is not limited to this, and only the upper end or the lower end is fixed. And may be formed integrally with the tube 1.

[0060]

As described in detail above, according to the first aspect of the present invention, the bypass passage is located downstream of the flow rate detecting element and branched from the main passage, and the downstream side of the bypass passage is connected to the pipe. Since the structure is designed to open near the inner wall of the body, when the gas flows backward in the pipe, utilizing the fact that the pressure of the gas becomes smaller near the inner wall than in the center of the pipe, this backflow is passed through the bypass passage. This allows the fluid to smoothly flow out to the downstream side of the housing, thereby reliably preventing the backflow from reaching the flow rate detecting element. Further, even when the flow rate in the pipe suddenly changes, the pressure fluctuation in the main passage due to the change can be reliably buffered through the bypass passage by the stable pressure near the inner wall of the pipe. Therefore, it is possible to reliably prevent the flow rate of the backflow from being detected, to reliably reduce the flow rate detection error in the transient state, and to greatly improve the measurement accuracy when the gas is pulsating or in the transient state. Can be improved.

According to the second aspect of the present invention, since the full-circle expanding portion is formed at the inflow opening end of the main passage, the gas in the pipe flows into the main passage while being throttled by the full-circular expanding portion. Thus, the velocity of the gas flowing into the main passage from the inflow port can be reliably increased. Therefore, even when a pressure fluctuation or the like generated on the downstream side of the housing is transmitted from the outlet to the main passage, it is possible to reliably prevent the pressure fluctuation from propagating to the flow rate detecting element by the gas flowing from the inlet. .

Further, according to the third aspect of the present invention,
Since a chamfer was formed at the branch inlet of the bypass passage,
The backflow that has entered the main passage can be smoothly guided from the branch inlet into the bypass passage by the chamfered portion, and can be reliably discharged to the vicinity of the inner wall of the pipe via the bypass passage.

According to the fourth aspect of the present invention, since the bypass passage is formed in an L shape, when a backflow enters the bypass passage from the outflow side, the backflow flows into the main passage. And the size of the bypass passage can be made long, and the buffering effect of the bypass passage against pressure fluctuations and the like can be reliably increased.

[Brief description of the drawings]

FIG. 1 is a cutaway perspective view of a main part showing a flow measuring device according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view as seen from the direction of arrows II-II in FIG.

FIG. 3 is an explanatory diagram showing a state in which intake air flows in a forward direction in a pipe;

FIG. 4 is an explanatory diagram showing a state in which intake air flows backward in a pipe.

FIG. 5 is a cross-sectional view showing a flow measurement device according to a modification of the first embodiment of the present invention.

FIG. 6 is a longitudinal sectional view showing a flow rate measuring device according to a second embodiment of the present invention.

FIG. 7 is a cutaway perspective view of a main part showing a flow measuring device according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pipe 1A Inner wall 2 Ventilation path 3 Housing 3A Upstream end face 3B Downstream end face 3C Side face 4 Measurement passage (main passage) 5 Heat-sensitive resistor (flow detection element) 8, 9, 21 Bypass passage 8C, 21A Branch inlet 8D, 21D Branch outlet 11 All-round widened part 12 Chamfered part

Claims (4)

[Claims] 1. A tubular body having a ventilation passage through which a gas to be measured flows, a housing provided so as to cross the tubular body in a diametric direction, and a shaft located at a central portion in a diametrical direction of the housing. A main passage having an inlet opening at the upstream end face of the housing and an outlet opening at the downstream end face of the housing, and a gas provided in the middle of the main passage and flowing through the main passage. A flow rate detecting element for detecting the flow rate of
An upstream side is located downstream of the flow rate detecting element, and a branch path is branched from the middle of the main passage, and a downstream side is located near an inner wall of the pipe body and is opened at a downstream end face or side face of the housing. Flow measurement device. 2. The flow rate measuring device according to claim 1, wherein the inflow port of the main passage is formed with a full-width expansion portion at an open end thereof. 3. A chamfered portion is formed in the bypass passage at a branch inlet that branches off from the main passage.
Or the flow measuring device according to 2. 4. The flow measuring device according to claim 1, wherein the bypass passage is formed in an L shape with respect to the housing.