JPH08105778A - Thermal type flowmeter - Google Patents

Abstract

PURPOSE: To provide a thermal type flowmeter, which can prevent the attachment of dust to lead members. CONSTITUTION: This is a thermal type flowmeter 1, which has terminal plates 12, which are provided uprightly on a flow path, a heat sensitive resistor 11 and a pair of lead members 21 for connecting the terminal plates 12 and the heat sensitive resistor 11. On the upstream of the lead members 21, dust removing members 31, which are in parallel with the lead members 21 and arranged so as not to disturb a flow 80 of fluid to be measured to the heat sensitive resistor 11, are provided. When the fluid to be measure is the intake air of an engine, the diameters of the dust removing member 31 and the lead member 21 are made approximately equal. A breadth L of the dust removing member 31 is made to be 0.4-1.1 times of a breadth Lo of the lead member 21. An interval H between the dust removing member 31 and the lead member 21 is made to be 2-6.7 times of a longitudinal width of the lead member 21. These magnifications are preferable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type flow meter for measuring the intake air flow rate of an engine.

[0002]

2. Description of the Related Art A thermal type flow meter is used to measure the intake air flow rate of an automobile engine. When a temperature-sensitive resistor in which a metal resistor with a large temperature coefficient of resistance is wrapped around a cylindrical frame is placed in the flow of the fluid to be measured, the amount of heat dissipated from the temperature-sensitive resistor is It is almost proportional to the temperature difference between the fluid to be measured and the square root of the flow velocity. Since the resistance value of the temperature sensitive resistor changes when heat is taken away, the flow velocity (flow rate) of the fluid to be measured can be measured using a resistance bridge having the temperature sensitive resistor inserted in one side. The thermal type flow meter is a flow meter using this principle.

A change in the equilibrium condition of the bridge caused by a change in the temperature of the fluid to be measured is compensated by a temperature compensating resistor inserted on the other side of the bridge. However,
Dust is contained in the intake air of the engine, and this dust is suppressed to a substantially constant level on the surface of the temperature sensitive resistor due to combustion, etc., but it may accumulate if it adheres to the lead member of the temperature sensitive resistor. This causes the thermal characteristics of the temperature sensitive resistor to change, which is one of the causes of characteristic changes and deterioration of response characteristics.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and suppresses adhesion of dust and the like contained in a fluid to be measured, and is inexpensive and excellent in measurement accuracy and response characteristics. The present invention aims to provide a thermal flow meter.

[0005]

According to the present invention, a thermal flow rate is obtained by arranging a temperature sensitive resistor having a large temperature coefficient of resistance in a flow path of a fluid to be measured and connecting the temperature sensitive resistor to one side of a bridge circuit. The thermal flowmeter comprises a pair of terminal plates standing in the flow path of the fluid to be measured, and a temperature-sensitive resistor formed in a cylindrical frame having a central axis perpendicular to the flow. , A pair of lead members connecting between both ends of the temperature-sensitive resistor and the terminal plate, the lead members having a cylindrical shape parallel to a central axis of the cylindrical frame. Is provided on both end surfaces of the frame of the above-mentioned frame, and at the upstream position of the streamline of the fluid to be measured surrounding the lead member, the flow of the fluid to be measured to the temperature sensitive resistor is parallel to the lead member. The thermal type flow meter is characterized in that a dust removing member arranged so as not to disturb is provided.

What is most noticeable in the present invention is that the lead member is provided on both end surfaces of the cylindrical frame in a direction parallel to the central axis of the cylindrical frame, and the lead member is provided at the upstream position of the lead member. That is, the dust removing member is provided in parallel with the member so as not to disturb the flow of the fluid to be measured with respect to the temperature sensitive resistor. Further, in the above, the terminal plate and the lead member form a part of the conductive member that constitutes the bridge circuit. Some of the temperature-sensitive resistors are made of thin metal wires, and some are made of thin-film or thick-film resistors.

In the thermal type flow meter in which the fluid to be measured is the intake air of the engine, the vertical width D of the dust removing member is set to 0.9 to 1.1 times the vertical width d of the lead member, and The lateral width L is set to _0.4 to 1.1 times the lateral width L ₀ of the lead member, starting from the end portion of the lead member on the terminal plate side, and the distance H between the dust removing member and the lead member is the vertical width of the lead member. It is preferably between 2.0 and 6.7 times d.

By doing so, as shown in experimental data (FIGS. 2 and 3) described later, in the thermal type flow meter for measuring the flow rate of the intake air of the engine, the vertical width D of the dust removing member is set.
Is approximately the same as the vertical width d of the lead member (0.9 to 1.1 times), and the lateral width L of the dust removing member and the distance H between the lead member are set within the above range, so that the response characteristics (including starting This is because it is possible to maintain good measurement accuracy without substantially deteriorating the characteristics (the same applies hereinafter).

In the above description, the vertical width D of the dust removing member
Is the dimension of the dust removing member perpendicular to both the central axis of the cylindrical frame of the temperature sensitive resistor and the flow direction of the fluid to be measured (Fig. 1). The lateral width L of the dust removing member is the length in the direction parallel to the lead member starting from the connecting portion of the lead member with the terminal plate and heading toward the temperature sensitive resistor (FIG. 1).

[0010]

In the thermal type flow meter according to the present invention, the dust removing member is arranged in the upstream position of the lead member in parallel with the lead member. By setting the vertical width D and horizontal width L of the dust removing member and the distance H between the lead member to appropriate values, dust does not adhere to the lead member and the flow of the fluid to be measured does not have the dust removing member. It can be made to be almost the same as the case.

That is, since the specific gravity of dust is usually larger than that of the fluid to be measured, by setting the above D, L, and H to proper values, most of the dust that travels straight toward the lead member 2 as shown in FIG. Is captured by colliding with the dust removing member 3 as indicated by broken lines 813 and 814, and dust that does not collide with the dust removing member 3 and rides on the flow of the fluid to be measured and reaches the position of the lead member 2 is indicated by broken lines. As indicated by 811 and 812, the lead member 2 passes without colliding.

On the other hand, the flow of the fluid to be measured, which has a low specific gravity, passes through the dust removing member 3 which is an obstacle, and then the solid line 80
As indicated by reference numerals 1 and 802, the lead member 2 is reached as in the case where the dust removing member 3 is not provided. Further, by preventing the dust removing member from projecting largely toward the temperature sensitive resistor side, the change in the flow of the fluid to be measured with respect to the temperature sensitive resistor can be made slight (see FIG. 1).

That is, the dust is captured by the dust removing member without changing the thermal characteristics of the lead portion and the temperature sensitive resistor so that the dust that cannot be captured by the dust removing member hardly adheres to the lead member. be able to. Further, since the accumulation of dust on the lead member is suppressed, it is possible to extremely reduce the deterioration of the detection accuracy and the change of the response characteristic of the thermal type flow meter over time.

Providing the dust removing member as described above upstream of the lead member is extremely easy to manufacture, and the cost hardly increases. As described above, according to the present invention, it is possible to provide an inexpensive thermal flowmeter that suppresses adhesion of dust and the like contained in the fluid to be measured and is excellent in measurement accuracy and response characteristics.

[0015]

【Example】

Example 1 A thermal type flow meter according to an example of the present invention will be described with reference to FIGS. In this example, as shown in FIG. 1, a temperature sensitive resistor 11 having a large temperature coefficient of resistance is arranged in the flow path of the fluid to be measured, and the temperature sensitive resistor 11 is connected to one side of a bridge circuit (not shown). It is the thermal type flow meter 1. The thermal type flow meter 1 is composed of a pair of terminal plates 1 standing in a flow path of a fluid to be measured.
2, a temperature-sensitive resistor 11 in which a heating wire is wound around a cylindrical frame 111 having a central axis perpendicular to the flow 80 of the fluid to be measured, which is indicated by an arrow, and between both ends of the heating wire and the terminal board 12. It has a pair of lead members 21 to be connected.

The lead member 21 is projectingly provided on both end surfaces of the frame 111 in a direction parallel to the central axis of the frame 111, and at the upstream position of the streamline (see FIG. 8) surrounding the lead member 21,
A dust removing member 31 is provided which is parallel to the lead member 21 and is arranged so as not to disturb the flow of the fluid to be measured with respect to the temperature sensitive resistor 11.

The fluid to be measured is the intake air of an automobile engine. The vertical width D of the dust removing member 31 in the direction perpendicular to the central axis of the frame 111 and the flow 80 is equal to the lead member 21.
0.9 to 1.1 of the vertical width d defined in
It's in between. In addition, the lead member 2 of the dust removing member 31
The horizontal width L in the direction parallel to the lead member 21 starting from the connection portion 211 of the first terminal plate 12 is between 0.4 and 1.1 times the similarly defined horizontal width L ₀ of the lead member 21. is there. The parallel distance H between the dust removing member 31 and the lead member 21 is 2.0 to 6.7 which is the vertical width d of the lead member 21.
It's in between.

The above description will be supplemented. Terminal board 12
Is a conductive member installed in the intake pipe line parallel to the flow of intake air, and is connected to one side of the bridge circuit. The temperature sensitive resistor 11 and the lead member 21 are joined to the terminal plate 12 in a direction orthogonal to the flow 80 of the intake air. A dust removing member 31 is arranged parallel to the lead member 21 on the tip end side of the terminal plate 12 (upstream side of the intake air flow) on the streamline of the intake air reaching the lead member 21. Although both the lead member 21 and the dust removing member 31 are wires having a circular cross section, they may have a rectangular cross section (square column). The dust removing member 31 and the lead member 21 have substantially the same diameter (D = 0.9).
~ 1.1d).

Next, the function and effect of the thermal type flow meter of this example will be described. The dust removing member 31 is arranged upstream of the lead member 21, but both have substantially the same diameter, and the distance H between them is 2.0 times or more the vertical width d of the lead member 21.
Therefore, even in the portion where the dust removing member 31 and the lead member 21 are parallel (the portion where the lead member 21 is behind the dust removing member 31), the flow of the intake air reaching the lead member 21 does not change significantly.

On the other hand, the dust and the like in the intake air are not gases, and therefore have a significantly larger specific gravity than the intake air. Therefore, in the portion where the dust removing member 31 and the lead member 21 are parallel to each other, the dust or the like that collides with the dust removing member 31 is captured by the dust removing member 31, and the dust or the like that has passed above and below the dust removing member 31 has an inertial force. As a result, it goes straight and almost does not collide with the lead member 21.

Then, the dust removing member 31 and the lead member 2
Since the length L of the parallel portion of 1 is at least 0.4 times the lateral width L ₀ of the lead member 21, dust or the like that collides with the lead member 21 is significantly reduced. Therefore, the amount of dust and the like adhering to the lead member 21 is significantly reduced.

Further, the horizontal width L of the dust removing member 31 is 1.1 times or less at maximum of the horizontal width L ₀ of the lead member 21, and the flow of intake air reaching the temperature sensitive resistor 11 hardly changes. That is,
The amount of dust and the like adhering to the lead member 21 is greatly reduced over the years, while the flow of intake air to the temperature sensitive resistor 11 and the like hardly changes. Therefore, the measured value, the response time, and the start-up time of the thermal flow meter 1 do not change much, while the amount of dust adhering to the lead member 21 is significantly reduced, and the measured value of the thermal flow meter 1 over time The change of is greatly reduced.

In the above, the startup time is the time constant of the time change until the measured value (output) stabilizes after the thermal type flow meter is powered on, and the response time is the input (intake flow rate). Is the time constant of the change curve of the measured value when the value is changed stepwise. Next, the above operation will be described more specifically based on the measured data.

That is, as shown in FIG. 2, the dust removing member 3
0.4 to 1 1 of width L of the width L ₀ of the lead member 21.
In the range of 1, the change in measurement accuracy with respect to the initial value (solid line) is significantly reduced (about 30% or less) compared to the conventional product (broken line), as shown in FIG. b),
As shown in (c), the changes in the activation time and the response time are suppressed to a low level. Then, if it deviates from the above region, the characteristics deteriorate rapidly. In the figure, chain lines 831 and 832 are allowable limit values.

Further, as shown in FIG. 3, the dust removing member 3
When the distance H between the lead member 21 and the lead member 21 is in the range of 2.0 to 6.7 of the vertical width d of the lead member 21, as shown in (a), the measurement accuracy (solid line) of this example is that of the conventional product (broken line) (B) and (c), the response characteristics hardly change. In the figure, the thin line 83
3,834 is an allowable limit value.

Further, the linear dust removing member 31 is attached to the terminal board 1.
It is extremely easy to manufacture and inexpensive to provide in No. 2. As described above, according to this example, it is possible to provide an inexpensive thermal flow meter that suppresses the adhesion of dust and the like contained in the intake air and is excellent in measurement accuracy and response characteristics.

Example 2 In this example, as shown in FIG.
0 vertically, and the dust removing member 32 is connected to the lead member 22.
It is another embodiment formed in the extension part of. That is, in the first embodiment, the terminal plate 12 is arranged parallel to the flow 80, whereas the terminal plate 13 of this example is arranged perpendicular to the flow 80.

Further, the dust removing member 32 is the lead member 2
The extension part of 2 is bent parallel to the lead member 22 and is arranged upstream of the lead member 22. In this example, since the dust removing member 32 and the lead member 22 are not separate members, the configuration is simple, and the number of steps for joining the dust removing member 32 to the terminal plate 13 is unnecessary. For others,
This is the same as in the first embodiment.

Embodiment 3 As shown in FIG. 5, this embodiment is another embodiment in which the dust removing member 33 is formed by bending the tip portion of the terminal plate 14 in Embodiment 1. Dust removing member 33 and terminal plate 1
Since it is integrated with 4, the number of steps such as joining the dust removing member 33 to the terminal plate 14 is not necessary because it is not a separate member, and the configuration is simple.

The diameter of the dust removing member 33 is the same as that of the terminal board 14.
It is not necessary to be the same as the other parts, and it is possible to make the diameter substantially the same as that of the lead member 21 as in the case of the first embodiment and to dispose it in the same manner as the first embodiment. Further, as shown in FIG. 5, when the dust removing member 33 has a larger diameter than the lead member 21, the distance H from the lead member 21 is made larger than that in the first embodiment, and the intake air is appropriate for the lead member 21. To hit.
Others are the same as in the first embodiment.

Embodiment 4 As shown in FIG. 6, this embodiment is another embodiment in which the dust removing member 34 in Embodiment 3 is attached as a separate member to the end portion of the terminal plate 12. The dust removing member 34 is a separate member made of synthetic resin and is attached to the tip of the terminal plate 12. Others are the same as in the third embodiment.

Embodiment 5 As shown in FIG. 7, this embodiment is another embodiment in which the dust removing member 35 in Embodiment 3 is a plate-like member. That is, the dust removing member 35 is formed by pressing the inside of the tip of the cylindrical terminal plate 15 into a plate shape. Others are the same as in the third embodiment.

In the first to fifth embodiments, the temperature sensitive resistor 11 has a frame 111 wound with a thin wire, but the present invention is not limited to this. For example, a thin film type sensor is used. A temperature sensitive resistor having another configuration such as a temperature sensitive resistor or a thick film type temperature sensitive resistor may be used.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part of a thermal type flow meter according to a first embodiment.

FIG. 2 is a characteristic diagram when the lateral width L of the dust removing member is changed in the thermal type flow meter of the first embodiment.

FIG. 3 is a characteristic diagram when the distance H between the dust removing member and the lead member is changed in the thermal type flow meter of the first embodiment.

FIG. 4 is a perspective view of a main part of a thermal type flow meter according to a second embodiment.

FIG. 5 is a perspective view of a main part of a thermal type flow meter according to a third embodiment.

FIG. 6 is a perspective view of a main part of a thermal type flow meter according to a fourth embodiment.

FIG. 7 is a perspective view of essential parts of a thermal type flow meter according to a fifth embodiment.

FIG. 8 is a schematic diagram of a flow of a fluid to be measured, dust and the like between a dust removing member and a lead member in the thermal type flow meter of the present invention.

[Explanation of Codes] . . Thermal flow meter, 11. . . Temperature-sensitive resistor, 12-15. . . Terminal plate, 21, 22. . . Lead member, 31-35. . . Dust removing member, 80. . . flow,

Claims (4)

[Claims] 1. A thermal type flow meter comprising a temperature-sensitive resistor having a large temperature coefficient of resistance arranged in a flow path of a fluid to be measured, and the temperature-sensitive resistor being connected to one side of a bridge circuit, The thermal type flow meter comprises a pair of terminal plates erected in the flow path of the fluid to be measured, a temperature sensitive resistor formed in a cylindrical frame having a central axis perpendicular to the flow, and the temperature sensitive resistance. It has a pair of lead members connecting between both ends of the body and the terminal plate, and the lead members are both end faces of the cylindrical frame in a direction parallel to the central axis of the cylindrical frame. Is arranged at a position upstream of the streamline of the fluid to be measured surrounding the lead member so as not to disturb the flow of the fluid to be measured with respect to the temperature sensitive resistor. A thermal type flow meter characterized by being provided with a dust removing member. 2. The temperature sensitive resistor according to claim 1,
A thermal flow meter, characterized in that a thin wire is wound around the cylindrical frame. 3. The temperature sensitive resistor according to claim 1, wherein:
A thermal type flow meter characterized in that a thin film or thick film resistor is formed on the cylindrical frame. 4. The vertical width in a direction perpendicular to the central axis and the flow of the cylindrical frame of the dust removing member according to claim 1, claim 2 or claim 3,
The horizontal width L of the dust removing member in the direction parallel to the lead member starting from the connecting portion of the dust removing member with the terminal plate is equal to the horizontal width L of the lead member. ₀ to 0.4 to 1.1 times, and the parallel distance H between the dust removing member and the lead member is 2.0 to 6.7 times the vertical width d of the lead member. And the fluid to be measured is the intake air of an automobile engine, a thermal type flow meter.