JPS5892957A - Thermal flow meter - Google Patents

Abstract

PURPOSE:To prevent a change with the passage of time due to adhesion of dust on a resistor surface, by a method wherein a part, where no metal film of which the resistor consists is adhered, is formed in a belt at an upstream side of a temperature-sensitive resistor. CONSTITUTION:A part, where no metal film 3 is formed, is formed in a belt at an upstream side of a temperature-sensitive resistor 1 or a side positioned facing opposite to a flaw direction A and along a surface, in an axial direction, of a supporter 2. A part, where no metal film 3 is formed on a surface in the axial direction, is formed in a belt at a downstream side also. A peripheral angle theta1 of the beltlike part with no metal film is selected within a range of 60-170 degree, and a peripheral angle theta2 of a beltlike part at a downstream side within a range of 40-90 degree. The peripheral angle of the parts with the metal film 3 across the temperature-sensitive resistor 1 are respectively set to 90 degree or more. Even if dusts accumulate at the upstream side of the temperature- sensitive resistor 1, no change in radiation characteristic of the resistor is produced, and this permits the reliable detection of flow rates.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal flowmeter, and in particular, a temperature-sensitive resistor is disposed in a flow path, and a control circuit that supplies heat-generating current to the temperature-sensitive resistor is used to control the temperature of the flow. The present invention relates to a thermal flowmeter that outputs a flow rate detection signal while maintaining the temperature of the temperature-sensitive resistor substantially constant by balancing the amount of heat dissipated and the amount of heat generated to the temperature-sensitive resistor.

This type of thermal flow meter is suitable for detecting the intake air flow rate of an automobile engine, for example. In other words, in the engine control of automobiles, etc., 1 ignition timing, air fuel ratio, EG ratio (
Various types of control methods are implemented, such as exhaust gas recirculation system (exhaust gas recirculation system) or l5C (idle speed control), but these engine controls usually detect intake flow rate along with engine speed, intake negative pressure, etc., and use these detection signals. This is done while constantly detecting the engine condition. The thermal flowmeter according to the present invention is suitable for detecting the intake flow rate of such an automobile engine, but is not limited thereto, and can also be used for detecting the flow rate of other gases or liquids. can.

As this type of thermal flowmeter, one has been proposed that uses a temperature-sensitive resistor in which a thin film of metal such as platinum is formed as a resistor on the surface of a cylindrical support made of an insulating material such as ceramic. . This temperature-sensitive resistor is placed in the flow, and an electrical output corresponding to the amount of heat removed from the temperature-sensitive resistor is extracted depending on the flow rate. in this case.

It is controlled by an electronic circuit so that the difference between the temperature of the temperature-sensitive resistor and the intake air temperature is almost constant1. At this time, the temperature of the temperature sensitive resistor is controlled to be 220C, and the difference therebetween is controlled to be a constant 170C.

Figure 1 is a diagram illustrating a temperature-sensitive resistor of a conventional thermal flowmeter.The temperature-sensitive resistor 1 is a resistor mounted on the surface of a cylindrical support made of an insulator such as ceramic (alumina, etc.). A metal film 3 made of platinum or the like is formed as a metal film 3. Electrode portions are formed at both ends of the temperature-sensitive resistor 1, and supports 4 made of conductive metal are bonded to the electrode portions. A resistance is formed in the middle part of the temperature-sensitive resistor 1 excluding the electrodes at both ends, and the resistor generates heat due to the current supplied through the support 4, and the amount of heat is generated by the fluid to be measured flowing in the direction shown by arrow A. be taken away. Therefore, by controlling this current so as to supply a current commensurate with the amount of heat dissipated (by heat transfer) from the temperature-sensitive resistor to the fluid, and maintaining the temperature of the temperature-sensitive resistor almost constant, the current can be reduced. The flow rate is detected from the voltage value required for supply.

However, in the conventional temperature-sensitive resistor, as shown in Figure 1,
A resistor made of a metal film 3 was formed on the entire surface of the cylindrical support. For this reason, when the temperature-sensitive resistor 1 is installed in a flow as shown in FIG. There is a problem in that dust accumulates over time, resulting in measurement errors or changes in measured values over time due to changes in the heat transfer coefficient.

In other words, there is a stagnation in the gap portion 5 where there is almost no flow velocity, and the heat dissipation effect from the resistor 3 is different from that in other portions where the flow velocity is present, which causes the problem of measurement error. there were. In addition to this.

Since dust accumulates on the upstream side of the gap 5, the heat dissipation effect from the resistor differs from other normal parts depending on the amount of accumulated dust, and the flow rate measurement value becomes curved over time. There was a problem in that accurate measurements were difficult due to

Furthermore, in conventional thermal flowmeters, a metal film is formed on the entire surface including the downstream side of the temperature-sensitive resistor, so there is no current leakage caused by repeated intake and exhaust air flow, as in the case of the intake passage of an automobile engine. When pulsation occurs and the pulsation becomes intense, a reverse flow occurs from the engine side.9 This reverse flow is also detected in the same way as a forward flow, which is a drawback. In other words, when detecting the amount of intake air in the engine, although it is desired to detect only the intake amount, the flow rate in the opposite direction to the intake air is also detected at the same time. There was a problem that detection errors occurred.

SUMMARY OF THE INVENTION An object of the present invention is to provide a one-heat type flowmeter that eliminates the above-mentioned drawbacks of the prior art and prevents deterioration over time due to dust accumulation on the surface of a resistor.

The present invention attempts to achieve the above object by providing a band-shaped portion on the upstream side of the temperature-sensitive resistor to which the metal film forming the resistor is not attached.

That is, according to the present invention, the temperature-sensitive resistor is provided with a metal film formed on the surface of a cylindrical support, the temperature-sensitive resistor is installed in a flow, and the temperature-sensitive resistor is disposed in accordance with the flow rate. In a thermal flowmeter that generates an electrical output corresponding to the amount of heat being carried away,
There is provided a thermal flow meter characterized in that a band-shaped portion where the metal film is not formed is provided on the axial surface of the support body upstream of the temperature-sensitive resistor.

In this case, if a belt-shaped portion is provided on the axial surface of the support body on the downstream side of the temperature-sensitive resistor, pulsation will occur due to backflow, as in the case of intake air of an automobile engine. Even if

Accurate intake flow rate measurement can be performed by detecting only the forward flow excluding this reverse flow.

The present invention will be described in detail below with reference to FIGS. 3 to 5.

3 and 4 are views for explaining the first embodiment of the present invention, in which a support 2 is provided on the upstream side of the temperature-sensitive resistor 1, that is, on the side facing the flow direction A of the fluid to be measured. Along the axial surface,
A band-shaped portion is provided where the metal film 3 is not formed. Also, on the downstream side of the temperature-sensitive resistor 1, a band-like portion is provided on the axial surface of the support 2 where the metal film 3 is not formed. The rest of the structure is substantially the same as that of the temperature-sensitive resistor explained with reference to FIG. 4 and 4 are connected to each other.

The circumferential angle of the band-shaped portion without a metal film formed on the upstream side of the temperature-sensitive resistor 1, that is, the angle θ1 shown in FIG. 4, is, for example, 60.
It is preferable to select the angle between 40 degrees and 170 degrees, while the circumferential angle of the band-shaped portion on the downstream side of the temperature-sensitive resistor where no metal film is formed, that is, the angle θ2 in FIG. 4, is within the range of about 40 degrees to 90 degrees. It is preferable to select the temperature sensitive resistor 1.
The circumferential angles of the parts having the metal film 3 on both sides of are each 90
It is preferable to provide at least one degree or more. For example, in Figure 4, if θ is selected to be 120 degrees, θ on the downstream side should be approximately 60 degrees at most, and the portions with metal films on both sides should be left at least 90 degrees each. is preferred.

FIG. 5 is a sectional view of a second embodiment of the thermal flowmeter of the present invention, and is a view showing a portion corresponding to the cross section of FIG. 4.

In the case of FIG. 5, only on the upstream side of the temperature-sensitive resistor 1, that is, on the side facing the flow direction A of the fluid to be measured.

A portion where the metal film 3 is not formed is formed in a band shape on the axial surface of the support 2. There is no portion on the downstream side where no metal film is formed. The embodiment shown in FIG. 5 is suitable for use when there is no large pulsation in the flow and there is no risk of large errors in measurement values caused by backflow. The angle θ1 in FIG. 5, that is, the circumferential angle of the part where no metal film is formed.

As in the case of Fig. 4, it is preferable to select the angle within the range of about 60 degrees to 170 degrees.

□ As a method of manufacturing a band portion without forming a metal film as explained above with reference to Figs. A method of attaching particles by sputtering: After depositing a metal film such as platinum on the entire surface of support 2 by sputtering, masking the areas where the metal film is needed and removing the metal film from the areas where the metal film is not needed by reverse sputtering. Alternatively, after a metal film is formed on the entire surface of the support 2 by sputtering, this metal film is heat-treated to partially melt it into a state similar to metal, and then the necessary parts are masked and the metal film is removed from unnecessary parts. There are methods to remove the resistor by melting it with a laser71 or scraping it off with sandbrush.The sputtering described here is as follows: 1. A metal target (metal to be attached) such as platinum or nickel and a support. The body 2 (the member on which the metal film is to be formed) is placed in argon gas, and a voltage is applied between them to cause the argon gas particles to collide with the metal target to knock out metal molecules, and the metal particles are used as a support. It is a method of electrically attaching the film, and the reverse sputtering is a method in which the metal film attached to the support 2 is struck with argon gas particles, contrary to the sputtering described above. is given.

According to the embodiment described above with reference to FIGS. 3 to 5, even if dust accumulates on the upstream side of the temperature-sensitive resistor 1, the resistor (
There is no change in the heat dissipation characteristics of the metal film 3), so there is no change in the heat transfer characteristics of the temperature-sensitive resistor even after long-term use, and the output characteristics remain constant even after long-term use (no change over time). A highly reliable thermal flowmeter that can always accurately detect the flow rate can be obtained.

Furthermore, according to the embodiments shown in FIGS. 3 and 4, a portion where the metal film 3 is not formed is also provided on the downstream side of the temperature-sensitive resistor 1, so that only the forward current component is detected without detecting the reverse flow component. By doing so, it is possible to obtain a thermal flow meter that maintains the output characteristics at an appropriate value even in a region of intense pulsation and can detect an accurate flow rate value close to the true average flow rate.

Furthermore, in the case of the embodiments shown in Figs. 3 and 4, no metal film is formed on the downstream side, so there is resistance to backfire that occurs when the backflow from the engine occurs, as in the case of measuring the intake air amount of the engine. (1) Therefore, there is no risk of the resistor being damaged by backfire flames, etc., and the output characteristics do not change even in the case of backfire, and the thermal type can always accurately detect the flow rate. A flow meter is obtained.

As is clear from the above description, according to the present invention, even if dust accumulates on the upstream side of the temperature-sensitive resistor installed in the flow, it is removed from the temperature-sensitive resistor according to the heat transfer characteristics, that is, the flow rate. No change occurs in the heat properties.

It is possible to maintain constant electrical output characteristics at all times,
As a result, a thermal flowmeter capable of accurately detecting flow rate even after long-term use is obtained.

[Brief explanation of the drawing]

Fig. 1 is a perspective view illustrating the main parts of a conventional thermal flowmeter, Fig. 2 is an explanatory diagram illustrating the state of flow around a temperature-sensitive resistor, and Fig. 3 is a thermal flowmeter according to the present invention. FIG. 4 is a sectional view of the temperature-sensitive resistor shown in FIG. 3;
FIG. 5 is a sectional view of a portion corresponding to FIG. 4 of another embodiment of the thermal flowmeter of the present invention. 1... Temperature-sensitive resistor, 2... Cylindrical support, 3...
Metal film (resistor), 4... Support, A... Flow direction of fluid to be measured, θ8. θ2...Circle H button L in the part where the metal film is not formed Plan 2 Mouth 3 Figure %4-Figure 5

Claims (1)

[Claims] 1. A temperature-sensitive resistor having a metal film formed on the surface of a cylindrical support, and the temperature-sensitive resistor is installed in a flow. In a thermal flowmeter that generates an electrical output corresponding to the amount of heat carried away from a temperature-sensitive resistor according to the flow rate, the metal film is formed on the axial surface of the support body upstream of the temperature-sensitive resistor. A thermal flow meter characterized by having a band-shaped section that does not cover the area. 2. The thermal flowmeter according to claim 1, wherein a band-shaped portion where the metal film is not formed is provided on the axial surface of the support body also on the downstream side of the temperature-sensitive resistor. .