JP2827796B2 - Thermal flow sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-sensitive flow sensor for measuring a flow rate of a fluid.

[0002]

2. Description of the Related Art FIGS.
FIG. 1 is a view showing a conventional heat-sensitive flow rate sensor disclosed in Japanese Patent Publication No. 25 and Japanese Utility Model Publication No. 3-109126. A body 4 is arranged, and the measuring pipe 2 is supported by a support 5 at substantially the center of the main conduit 1. The heating element 3 and the temperature measuring element 4 are temperature-dependent resistors, and a bridge is formed together with the resistors R1 and R2. 7 is connected to one end a of the bridge. These control circuits are contained in the control circuit case 8.

Next, the operation will be described. When a constant flow rate of fluid is flowing in the main conduit 1, the supply voltage to the bridge circuit is controlled by the operation amplifier 6 so that the temperature of the heating element 3 becomes higher than the fluid by a constant temperature, and the equilibrium state is established. ing. When the flow rate of the fluid increases in this state, the heating element 3 is cooled, the resistance value changes, the bridge circuit becomes unbalanced, and the supply voltage to the bridge circuit is increased by the operational amplifier 6. As a result, the heating element 3 is heated and the resistance value returns to the original value, thereby restoring the equilibrium state of the bridge circuit. The resistors R1 and R2 are fixed resistors, and are determined so that the bridge circuit is balanced by the resistance value of the heating element at a temperature higher than the temperature of the fluid measured by the temperature measuring element 4. Next, when the temperature of the fluid changes, the resistance value of the temperature measuring element 4 changes, and the heating element 3 is controlled to a temperature having a different resistance value in order to maintain the balance of the bridge.

The heating element 3 is disposed in the measuring pipe 2 in the main conduit 1 and treats the flow velocity detected by the heating element 3 as a representative flow velocity in the main conduit 1 to control a predetermined passage cross-sectional area. It is used as information on the total flow rate of the fluid passing through the pipe 1. This is because the heating element 3 is provided at a predetermined position of the main conduit 1 without using the measurement pipe 2.
The same applies to the case where is provided.

[0005]

As described above, in the conventional heat-sensitive flow sensor, the heating element 3 for detecting the flow rate is disposed at a predetermined position in the cross section of the main conduit 1, so that the main conduit 1 is not connected to the main conduit 1. It is not possible to detect the total flow velocity that passes. Therefore, to detect the total flow through the main conduit 1,
The ratio of the flow velocity of the portion where the heating element 3 is provided to the average flow velocity of the fluid passing through the main conduit 1 needs to be kept constant according to the average flow velocity of the fluid passing through the main conduit 1. However, when a drift occurs in the fluid flowing into the main conduit 1, the ratio of the flow velocity at the portion where the heating element 3 is disposed to the average flow velocity of the fluid passing through the main conduit 1 becomes different.

For example, when used for measuring the intake air amount of an automobile engine, an air cleaner is present upstream of the main conduit 1. The air cleaner removes foreign matter such as dust in the intake air by an air cleaner element made of a nonwoven fabric or filter paper. If the air cleaner element becomes dirty, the flow velocity distribution of the fluid flowing into the main conduit 1 changes from the initial state. . Further, a throttle valve is provided downstream of the main conduit 1, and the ratio of the average flow velocity of the main conduit 1 to the flow velocity of the portion where the heating element 3 is disposed is determined by the opening degree of the throttle valve which changes according to the operating condition. Fluctuates.

Under such conditions, the conventional thermal flow sensor can accurately measure the total flow rate of the fluid passing through the main conduit 1 even if the flow rate at the position where the heating element 3 is provided can be detected. I couldn't do that. In addition, since dust mixed in the fluid flowing into the main conduit 1 collides with the inertial force according to the flow velocity, the dust accumulates on the heating element 3 and the heat transfer coefficient from the heating element 3 to the fluid is reduced. There is a problem that the measurement accuracy cannot be maintained for a long time.
Although there is a flow meter of a type in which dust attached to the heating element 3 is incinerated by so-called burn-off, dust that cannot be completely incinerated by the burn-off remains attached to the heating element 3.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a heat-sensitive flow sensor which can accurately detect a flow rate even when a drift occurs, and is hardly contaminated. .

[0009]

A thermal type flow sensor according to the present invention comprises a main conduit which is a fluid passage, and a measuring conduit in which the heating element is disposed inside. Wherein the inflow port of the measurement pipeline is located downstream of the outflow port of the measurement pipeline, and the cross-sectional area of the main conduit at the portion where the outflow port of the measurement pipeline is located is determined by the measurement pipeline. Is smaller than the cross-sectional area of the passage of the main conduit where the inflow port is located, so that the pressure is reduced. In this configuration, the inflow port of the measurement pipeline does not face the inflow direction of the fluid flowing into the main conduit.

[0010]

According to the present invention, the flow rate distribution of the fluid flowing into the main conduit is reduced because the pressure drop portion where the outlet of the measuring pipe is located is once narrowed upstream of the inlet of the measuring pipe. And stabilize the flow near the entrance of the measurement pipeline. On the other hand, the flow rate of the fluid flowing into the measuring pipe depends on the pressure at the outlet of the measuring pipe, but the outlet of the measuring pipe extends in the circumferential direction of the main conduit or the measuring pipe. If it is provided at a plurality of locations or is wide open around the circumference, the pressure distribution of the fluid flowing into the main conduit can be averaged, and the flow rate less affected by the flow velocity distribution of the fluid flowing into the main conduit can flow into the measurement pipe. . Therefore, even if a drift occurs in the fluid flowing into the main conduit, accurate measurement can be performed.

According to the second aspect of the present invention, since the direction of the fluid flowing into the measuring conduit is different from the direction of the fluid flowing into the main conduit, dust having an inertial force mixed into the fluid is prevented from flowing. For the most part, the flow proceeds in the direction of the flow of the main conduit, making it difficult to enter the measurement pipeline, making it difficult for dust to adhere to the heating element, and making it resistant to contamination.

Furthermore, in the third aspect of the present invention, since a plurality of outlets of the measuring pipe are provided in the circumferential direction of the measuring pipe, when the flow flowing into the main conduit is not uniform, the flow is prevented. The pressure distribution generated near the outlet can be averaged. Further, in the invention according to claim 4, since a plurality of supports for supporting the measurement pipeline are provided around the main conduit, it is possible to form a pressure drop portion having an outlet of the measurement pipeline, The support strength can be improved, the flow velocity distribution of the fluid flowing into the main conduit can be made uniform, and the sensitivity as a flow sensor can be improved by increasing the flow velocity of the fluid flowing through the measurement pipe.

[0013]

【Example】

Embodiment 1 FIG. An embodiment of the present invention will be described below with reference to FIGS. 1 is a vertical sectional side view, FIG. 2 is a view of FIG. 1 from the right side, and FIG. 3 is a cross-sectional view taken along line III-III of FIG. 1. The description is omitted. In the figure, reference numeral 9 denotes an outlet of the measuring pipe 2 where the fluid passing through the measuring pipe 2 joins the main conduit 1, 10 denotes an inlet of the measuring pipe 2, and 11 denotes a fluid flowing into the main conduit 1. , 12 is a flow of the fluid flowing into the inlet 10 of the measuring pipe 2, 13 is a flow flowing out of the outlet 9 of the measuring pipe 2, and 14 is a flow of the main pipe 1 through the measuring pipe 2. A support 15 for supporting in the center is a cone portion for smoothly narrowing the flow path of the main conduit 1.

The basic operation is the same as that of the prior art,
In the present invention, the flow rate of the fluid flowing into the main conduit 1 is reduced at the portion 16 near the outlet 9 of the measuring conduit 2 of the main conduit 1 because the passage cross-sectional area is reduced. Faster and lower pressure. On the other hand, the measurement pipeline 2 located downstream of the outlet 9 of the measurement pipeline 2 in the main conduit 1
In the portion 17 near the inflow port 10, the passage cross-sectional area is expanded again and the pressure is recovered, so that the fluid flows in the measurement pipeline 2 according to the flow rate flowing into the main conduit 1, The heating element 3 measures the flow rate. That is, while the pressure in the portion 16 where the pressure is reduced is low, the pressure in the measurement pipe 2 is recovered and increased similarly to the portion 17, so that the fluid in the measurement pipe 2 is in a state the pressure is higher than the flow of the portion 16, in principle that fluid is fluid at the outlet 9 from flowing from high to low-pressure is sucked, fluid from the inlet 10 into the measurement conduit 2 Flows.

Even when the flow velocity vector of the fluid flowing into the main conduit 1 is not uniform (the flow velocity and the direction are not uniform due to the fluid going straight or swirling due to the state of the air cleaner or the movement of the throttle valve), the leading direction is not changed. The flow velocity distribution is made uniform by the pressure loss in the portion 16 of the pipe 1 where the passage cross-sectional area is reduced. The flow rate flowing into the measuring pipe 2 depends on the pressure at the outlet 9 of the measuring pipe 2 near the pressure drop section (16), but in this embodiment, a plurality of flow rates near the pressure drop section. Since the outlet 9 is provided, the pressure distribution caused by the influence of the flow velocity distribution of the fluid flowing into the main conduit 1 is made uniform, and the flow rate flowing into the measurement pipe 2 is reduced.
It is hardly affected by the flow velocity distribution of the fluid flowing into the pipe.

Further, in this embodiment, the inlet 10 of the measuring pipe 2 is provided so as not to oppose the direction of the fluid flowing into the main conduit 1, so that it is mixed in the fluid flowing into the main conduit 1. Since most of the dust has an inertial force in the direction 11, the dust advances in the flow direction of the main conduit 1 and does not easily enter the measurement pipeline 2, so that the dust hardly adheres to the heating element 3.

Embodiment 2 FIG. Another embodiment of the present invention is shown in FIGS.
Referring to FIG. Basic operations and reference numerals are the same as those in the first embodiment, and a description thereof will be omitted. In this embodiment, the outlet 9 of the measuring pipe 2 is provided widely in the circumferential direction, so that when the flow flowing into the main conduit 1 is uneven,
The effect of averaging the pressure distribution generated in the vicinity of the outlet 9 can be enhanced.

In this embodiment, a plurality of supports 14 for supporting the measuring pipe 2 are provided on the circumference of the main conduit 1 in substantially equal divisions, whereby the outlet 9 of the measuring pipe 2 is provided. Since the pressure drop portion can be formed, the support strength is improved, the flow velocity distribution of the fluid flowing into the main conduit 1 is made uniform, and the sensitivity as a flow sensor is improved by increasing the flow velocity of the fluid flowing through the measurement pipe 2. And so on. In this embodiment, three supports 14 are provided, but by increasing the number, the effect of making the flow velocity distribution uniform can be obtained. On the other hand, the pressure loss of the flow sensor is increased by providing a plurality of supports 14, but in this embodiment, the cross-sectional shape of the support 14 is streamlined as shown in FIG. 6, and the increase in pressure loss is minimized.

[0019]

As described above, according to the present invention, the inlet of the measuring pipe is located downstream of the outlet of the measuring pipe, and the outlet of the measuring pipe is used for measuring. Since the pressure is lower than the pressure at the inlet of the conduit, the effect of reducing the measurement flow error caused by the drift is obtained.

Further, according to the second aspect of the present invention, there is an effect that a heat-sensitive type flow sensor which is less contaminated by dust in the measurement fluid can be obtained. Further, according to the third aspect of the invention, even if the flow flowing into the main conduit is not uniform, an effect is obtained that the pressure distribution generated near the outlet is averaged. Further, according to the fourth aspect of the invention, there is obtained an effect that the support strength can be improved and the sensitivity of the flow sensor can be improved by increasing the flow velocity of the fluid flowing through the measurement pipe.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional side view showing a first embodiment of the present invention.

FIG. 2 is a view of FIG. 1 as viewed from the right.

FIG. 3 is a sectional view taken along line III-III in FIG. 1;

FIG. 4 is a longitudinal sectional side view showing Embodiment 3 of the present invention.

FIG. 5 is a view of FIG. 4 as viewed from the right.

FIG. 6 is a sectional view taken along line VI-VI in FIG. 4;

FIG. 7 is a vertical sectional side view showing a conventional device.

8 is a view of FIG. 7 as viewed from the right.

FIG. 9 is a diagram showing a configuration of a bridge resistor arrangement of a conventional device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main conduit 2 Measurement pipeline 3 Heating element 4 Temperature measuring body 9 Measurement pipeline outflow port 10 Measurement pipeline inflow port 14 Support

Continuation of front page (72) Inventor Masahiro Kawai 840 Chiyoda-cho, Himeji-shi Mitsubishi Electric Corporation Himeji Works (56) References JP-A-4-184222 (JP, A) JP-A-60-185116 (JP, A (58) Fields surveyed (Int.Cl. ⁶ , DB name) G01F 1/68

Claims (4)

(57) [Claims] 1. A thermal flow sensor that measures the flow rate of a fluid based on the amount of heat deprived from a heating element due to the passage of a fluid, wherein a main conduit serving as a fluid passage and a heating element inside the main conduit are provided. And a measurement pipeline disposed, wherein an inlet of the measurement pipeline is located downstream of an outlet of the measurement pipeline, and a portion where the outlet of the measurement pipeline is located. A heat-sensitive flow rate sensor, wherein the cross-sectional area of the passage of the main conduit is smaller than the cross-sectional area of the passage of the main conduit in a portion where the inflow port of the measurement conduit is located, so that the pressure is reduced. 2. The heat-sensitive flow sensor according to claim 1, wherein an inlet of the measurement pipe is not opposed to an inflow direction of the fluid flowing into the main conduit. 3. The heat-sensitive flow rate sensor according to claim 1, wherein a plurality of outlets of the measurement pipeline are provided in a circumferential direction of the measurement pipeline. 4. A measurement conduit is provided in the main conduit by providing a plurality of supports having a streamlined cross section, at least a portion of which is present between the inner diameter of the main conduit and the outer diameter of the measurement conduit. The thermal flow sensor according to claim 1, wherein the sensor is held.