JP3418525B2 - 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 detecting the flow rate of a fluid to be measured, which uses a heat-sensitive (heat-generating) resistor, and more particularly, to prevent foreign matter in the fluid from adhering to the resistance temperature detector. It relates to a structure to prevent.

[0002]

2. Description of the Related Art Conventionally, a thermosensitive flow rate sensor for detecting a flow rate from a thermal equilibrium state based on a bridge circuit including a thermosensitive resistor and a temperature measuring resistor arranged in a fluid is disclosed in, for example, Japanese Patent Laid-Open No. 4-291117. Has been done. In this thermosensitive flow sensor, a small ceramic substrate is used as the resistance temperature detector arranged in the fluid in order to enhance the detection response of the fluid temperature. This resistance temperature detector has a surface of the resistor covered with a coating agent having a good heat transfer property except for the terminal portion, and is electrically joined to the terminal of the insert-molded holder.

FIG. 8 shows the structure of this conventional heat-sensitive flow rate sensor. In FIG. 8, a detection tube 2 is provided at a predetermined position in a housing 1 which is a main passage for a fluid, and the detection tube 2 has a predetermined position. The heat-sensitive resistor 3 and the temperature-measuring resistor 4 are arranged at the positions, and a bridge circuit is configured with the resistors R1 and R2.
Further, both inputs of the differential amplifier 101 are connected to the connection points b and f of the bridge circuit, the output of the differential amplifier 101 is connected to the base of the transistor 102, and the transistor 102 is connected.
The emitter is connected to one end a of the bridge circuit, and the collector is connected to the positive electrode of the power supply 103. In the above configuration, when the voltages at the connection points b and f become equal, the bridge circuit reaches the equilibrium state, at which time the current IH corresponding to the flow rate flows through the thermosensitive resistor 3, and the voltage VO at the point b becomes IH × RI.
This voltage VO is used as a flow rate signal.

[0004]

In the heat-sensitive flow rate sensor constructed as described above, the resistance temperature detector 4 arranged in the fluid has a structure shown in FIGS. 9 (a), 9 (b) and 9 (c). As shown in FIG. 3, a ceramic substrate 4a having a small thickness is used, the surface of the resistor is covered with a coating agent 4c having a good heat transfer property except for the terminal portion 4b, and the holder 5 is inserted and molded. It is electrically connected to the ascending terminals 5a, 5a. Here, in order to further improve the detection response of the fluid temperature, as shown in FIGS. 10A, 10B, and 10C, two resistance temperature detectors 4 and 4 having a small heat capacity are connected via the lead 4c. Connected in series to terminal 5b,
The one attached to 5b is proposed. However, according to this, as shown in FIGS. 11A and 11B, dust and carbon dust 8 in the fluid are directly accumulated on the front surface 4m of the resistance temperature detector 4 in front of the resistance temperature detector 4 and Responsiveness decreases. Further, a leakage current flows through the carbon dust 8, and the leakage current component cannot be ignored on the bridge circuit, which causes a problem of causing a characteristic change.

The present invention has been made in order to solve the above-mentioned problems, and foreign matter such as dust and carbon dust in a fluid is less likely to adhere to the resistance temperature detector 4 and is excellent in heat sensitivity over time. The purpose is to obtain a flow sensor.

[0006]

According to the invention of claim 1, the fluid to be measured is prevented from directly contacting the resistance temperature detector.
A shield was placed in front of the resistance temperature detector.

According to the second aspect of the invention, the shielding portion is formed so that the front portion projects in the upstream direction.

According to the third aspect of the present invention, the shield portion is integrated with the holder for holding the resistance temperature detector.

According to the fourth aspect of the present invention, the shielding portion is raised from the front portion of the holder, the rear frame is raised from the rear portion of the holder, and a lateral portion bridging the upper portion of the shielding portion and the upper portion of the rear frame. A frame was provided, and the leads at both ends of the resistance temperature detector were connected to the horizontal frame and a part of the holder facing the horizontal frame.

According to the fifth aspect of the present invention, grooves are formed on the side surface of the horizontal frame and the side surface of the holder facing the horizontal frame so as to face each other. The upper and lower grooves have leads protruding from both ends of the resistance temperature detector. Engaged.

In the invention of claim 6, the upper and lower grooves are formed such that the inlet side is inclined in the downstream direction with respect to the lower side. .

According to a seventh aspect of the present invention, the temperature measuring resistor is integrally formed with a terminal plate and a holder to which leads at both ends are connected.

[0013]

1 to 7 are views showing an embodiment of a heat-sensitive flow sensor according to the present invention, and the same parts as those in FIGS. 8 to 11 are designated by the same reference numerals. In this case, the holder 5 is installed on the base 1a in the cylindrical housing 1 as shown in FIGS. 3 and 4, but its position is in front of the detection tube 2 and on the detection tube 2. It is slightly offset from the vertical line 2a passing through the center to one side.

The holder 5 has a constant width W as shown in FIG. 1, and an elongated shielding portion 51 rises from the front part of the upper part thereof with the same width W as the holder 5. And a slender rear frame 52 having the same height as the shielding portion 51 from the rear portion of the upper portion of the holder 5 away from the shielding portion 51.
Rises. The front surface 51t of the shielding portion 51 projects in a "V" shape in the upstream direction, and the front surface 5t of the holder 5 also projects in a "V" shape to reduce resistance to fluid. It should be noted that, instead of the “<” shape, the protrusion may be “C” -shaped so as to have a rounded shape. The upper end of the shield 51,
A horizontal frame 53 bridges the upper end of the rear frame 52. A window 55 is formed in the holder 5, leaving a part including a portion facing the horizontal frame 53. Window 5
The upper part of 5 is a horizontal frame 54 facing the horizontal frame 53.

On one side surface of the upper and lower horizontal frames 53, 54, two grooves 53a, 54a extending in the upward and downward directions and opposed to each other in the upward and downward directions are provided at a predetermined distance. ing.

The upper and lower grooves 53a and 54a facing each other have a depth of about W1 / 2, and the widths of the inlets 53c and 54c are set wider than the bottoms 53b and 54ab. Leads 41, 41 at the upper and lower ends of the temperature resistors 4, 4
Are easy to engage. The leads 41, 41 engaged with the grooves 53a, 54a are fixed by an adhesive filled in or fitted into the grooves 53a, 54a. In this case, groove 5
3a and 54a are inlets 53c and 53b and 54b, respectively.
54c is slightly inclined in the downstream direction, and has a structure in which dust or carbon dust contained in the fluid from the upstream side does not easily enter the groove. The grooves 53a, 53a and the groove 5
4a, 54a, the upper connection terminal plate 55 and the lower terminal terminal plate 56 so as to contact the side surfaces of the leads 41, 41 at the upper and lower ends of the resistance temperature detector 4 housed at the bottom thereof. , 56 are provided. Each terminal board 55, 56 is vertically oriented and extends in the front and rear directions.

Both ends of the upper connection terminal plate 55 are embedded and integrated with the inner surface side of the shielding portion 51 and the inner surface side of the rear frame 52, and the lower side divided into front and rear portions. The terminal terminal plates 56, 56 are also integrated by embedding one end on the outer side thereof on the inner surface side of the shielding portion 51 and the inner surface side of the rear frame 52.

In this case, the leads 41 on the upper side and the connection terminal plate 55 on the upper side, and the leads 41 on the lower side and the front and rear terminal terminal plates 56, 56 have solder connection portions or welded joint portions 57, 57. Are connected to each other via. That is, when viewed from the terminal terminal plates 56, 56, the resistance temperature detectors 4, 4
Are connected in series via the upper connection terminal plate 55.

According to the present embodiment, the holder 5 is electrically joined to each of the temperature measuring resistor 4 and the heat sensitive resistor 3 by the connecting plates 55 and 56 serving as insert terminals,
A temperature measuring resistor 4 is fixed upstream of the heat sensitive resistor 3 and arranged in the housing 1 so that a flow rate corresponding to an accurate temperature can be measured. Further, around the resistance temperature detectors 4 and 4, the shielding portion 1 of the holder 5, the rear frame 52, and the upper and lower horizontal frames 53 and 54 are shaped so as to surround the resistance temperature detectors 4 and 4. Since it is housed in the opening 9, it is located so as to cover most of the resistance temperature detectors 4 and 4 when viewed from the upstream side. If oil, dust contained in the air, and carbon dust 8 flow from the upstream, most of the dust accumulates on the front surface of the shielding portion 51 of the holder 5 and accumulates on the resistance temperature detector 4 as shown in FIG. Is reduced. Further, the cross-sectional shape of the shielding portion 51 is a forward projecting shape with low resistance to flow, and further, the positioning groove 5 of the resistance temperature detectors 4 and 4 is used.
3a and 54a are also opened while inclining toward the downstream so that dust does not accumulate.

As described above, according to this embodiment, by providing the shielding portion 51 of the holder 5 above and downstream of the resistance temperature detectors 4 and 4, dust and carbon dust contained in fluid such as air can be obtained. Has a structure in which it does not accumulate on the resistance temperature detectors 4 and 4, so that it is possible to suppress the characteristic change due to the leakage current to the accumulated dust portion without lowering the responsiveness.
Therefore, it is possible to obtain an excellent heat-sensitive flow rate sensor that is not affected by changes over time.

[0021]

According to the first aspect of the invention, the shielding portion is arranged in front of the resistance temperature detector so that the fluid to be measured does not directly contact the resistance temperature detector. Therefore, foreign matter such as dust and carbon dust is less likely to adhere to the resistance temperature detector, and the characteristic change due to the leak current can be suppressed.

According to the second aspect of the present invention, since the shielding portion is formed so that the front portion projects in the upstream direction, foreign matter is less likely to adhere to the shielding portion itself, and turbulent flow to the fluid is suppressed. You can

According to the third aspect of the present invention, the number of parts can be reduced as compared with the case where the shield part is separately provided because the shield part is integrated with the holder for holding the resistance temperature detector.

According to the fourth aspect of the present invention, the shielding portion is raised from the front portion of the holder, the rear frame is raised from the rear portion of the holder, and the upper portion of the shielding portion and the upper portion of the rear frame are bridged. Since a horizontal frame is provided, and the leads at both ends of the resistance thermometer are connected to this horizontal frame and a part of the holder to which the horizontal frame faces, it is possible to surround the entire circumference of the resistance temperature detector, It is possible to further suppress the adhesion of foreign matter.

According to the fifth aspect of the present invention, grooves that face each other are provided on the side surface of the horizontal frame and the side surface of the holder that the horizontal frame faces, and the leads projecting from both ends of the resistance temperature detector in the upper and lower grooves. Since the temperature sensor is engaged, it is easy to mount the resistance temperature detector and the reliability of the mounting portion can be improved.

In the invention of claim 6, since the upper and lower grooves are formed such that the inlet side is inclined in the downstream direction with respect to the lower side, foreign matter can be suppressed from adhering to the grooves.

According to the seventh aspect of the present invention, since the terminal plate to which the leads at both ends of the resistance temperature detector are connected is integrated with the holder, it is possible to save the trouble of mounting the terminal plate by complicated mounting means such as screwing.

[Brief description of drawings]

FIG. 1 is a perspective view of a main part showing an embodiment of the present invention.

FIG. 2 is a sectional view showing an embodiment of the present invention.

FIG. 3 is a front view showing an embodiment of the present invention.

FIG. 4 is a sectional view showing an embodiment of the present invention.

FIG. 5 is a sectional view showing an embodiment of the present invention.

FIG. 6 is a configuration diagram showing an embodiment of the present invention.

FIG. 7 is a block diagram showing the operation of the present invention.

FIG. 8 is a circuit configuration diagram showing an example of a conventional example.

FIG. 9 is a configuration diagram showing an example of a conventional example.

FIG. 10 is a configuration diagram showing an example of a conventional example.

FIG. 11 is a block diagram showing the operation of a conventional example.

[Explanation of reference numerals] 1 housing, 2 detection tube, 3 thermosensitive resistor, 4 resistance thermometer, 4a ceramic substrate, 4b terminal of resistance thermometer, 4c coating agent, 5 holder, 6
Circuit configuration part, 7 Fluid flow direction, 8 Carbon dust, dust, 9 Opening part, 51 Shielding part, 52 Rear frame, 53 Upper horizontal frame, 53a groove, 54 Lower horizontal frame, 54a groove, 55 Connection terminal board, 56 Terminal terminal board, 57 solder connection part, 101 differential amplifier, 102 transistor, 103 power supply.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01F 1/00-9/02

Claims (7)

(57) [Claims] 1. A flow rate detecting device including a temperature-sensitive thermosensitive resistor and a temperature measuring resistor arranged in a fluid passage to be measured .
Equipped with a bridge circuit, this bridge circuit is in a balanced state
When the current reaches the measured current based on the current flowing through the thermal resistor
A thermosensitive flow sensor for measuring the flow rate of a body, characterized in that a shielding portion is arranged in front of the resistance thermometer so that the fluid to be measured does not directly contact the resistance thermometer. . 2. The heat-sensitive flow sensor according to claim 1, wherein the shielding portion is formed so that the front portion thereof projects in the upstream direction. 3. The heat-sensitive flow sensor according to claim 1, wherein the shield portion is integrated with a holder that holds a resistance temperature detector. 4. The shield part is raised from the front part of the holder, and the rear frame is raised from the rear part of the holder,
A horizontal frame bridging the upper part of the shielding part and the upper part of the rear frame was provided, and the leads at both ends of the resistance temperature detector were connected to the horizontal frame and a part of the holder facing the horizontal frame. The heat-sensitive flow rate sensor according to claim 1, wherein 5. A groove facing the upper and lower sides is provided on the side surface of the horizontal frame and a side surface of the holder where the horizontal frame faces each other. The thermal flow sensor according to claim 4, wherein the thermal flow sensor is combined. 6. The heat-sensitive flow sensor according to claim 5, wherein the upper and lower grooves are formed such that the inlet side is inclined downstream with respect to the lower side. 7. The heat-sensitive flow sensor according to claim 3, wherein the holder is integrated with a terminal plate to which leads at both ends of the resistance temperature detector are connected.