JPH07113671A - Heating resistor - Google Patents

Abstract

PURPOSE:To obtain a heating resistor having a balanced temperature distribution and an improved operability. CONSTITUTION:Lead wires 2 are bonded to the opposite ends of an insulator pipe having a recessed section and a winding of a resistor 4 is formed thereon spirally with recession grooves used for positioning. Moreover, the whole is overcoated. By using a heating resistor constructed in this way and having a balanced temperature distribution, an effect of improving the measuring accuracy of a thermal type air flowmeter is produced. Moreover, the recession grooves in the opposite end parts are helpful in positioning the resistor at the time of an operation of winding it and this produces an effect of improving operability.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a heating resistor of an air flow meter, and more particularly to a thermal air flow meter using the heating resistor.

[0002]

2. Description of the Related Art As a structure of a heating resistor, a support made of an insulator is formed by a cylindrical pipe, lead wires are adhered to both ends of the support, and the resistor is spirally wound around the pipe. As an example of coating the surface with glass, there is JP-A-60-60521. However, in the heating resistor having this structure, when the resistor is spirally wound around the pipe-shaped support, there is a problem in that workability is poor and the winding cannot be performed evenly because there is no positioning at the end of the winding start. . Further, the heating resistor in which the resistor is wound in a non-uniform manner has a variation in temperature distribution when heated, which causes an error in measuring the air flow rate.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides a heating resistor for a thermal air flow meter, which produces a heating resistor having an even temperature distribution, has good workability, and has improved measurement accuracy. Has a purpose.

[0004]

This is achieved by making the cross section of the support formed by the lead wire of the heating resistor and the insulator holding the resistor resistive. The shape of the groove can also be achieved by forming a rectangular, triangular, or semicircular cross-sectional shape.

Alternatively, it can be achieved by providing notches at both ends of the pipe-shaped support and positioning the notches as a reference when winding the resistor around the pipe-shaped support.

[0006]

In the heating resistor in which the resistor is spirally wound around the cylindrical pipe, the temperature in the vicinity of the central portion is high and the temperature at both ends is low. The amount of heat generated by the resistor near the center easily reaches the prescribed heating temperature because it can directly heat the pipe, but at both ends, part of the heat is released to the adhesive and lead wires by heat conduction, so the temperature near the center Equilibrium occurs at lower temperatures. That is, the temperature distribution has a peak point at the center of the heating resistor.

Originally, if a spiral winding can be formed evenly from one end of the pipe to the other end of the pipe, the entire pipe will be heated uniformly and a stable temperature distribution can be obtained. It is difficult to make a spiral winding evenly from one end to the other. This is because when winding the resistor spirally, it is difficult to climb the resistor from the lead wire to the end of the pipe when starting to wind, and to climb the resistor from the pipe to the lead wire at the end of winding. This is because the pitch of the first and the last one turn becomes extremely large, and there is no winding at both ends of the pipe, and a heating resistor wound around the center is wound. In the temperature distribution of such a heating resistor, the peak temperature near the center becomes extremely high, and the temperature tends to decrease at both ends of the pipe. Moreover, since the peak temperature of the temperature distribution of the heating resistor rises extremely, only the peak temperature portion becomes abnormally sensitive to the air flow. On the contrary, since the temperature distribution at both ends decreases, the sensitivity to the air flow becomes insensitive, and it is unstable because it has two different characteristics in one heating resistor, which causes noise and increases the accuracy of air flow measurement. Adversely affect.

In the present invention, in order to uniformly wind the spiral winding of the resistor from one end to the other end of the pipe, concave grooves are provided at both ends for positioning. When the resistor rides on the pipe from the lead, the spiral groove can be started by positioning the groove. Also, after the winding end portion is positioned along the groove, the winding can be ended, and the winding can be performed at a uniform pitch from end to end of the pipe. Since the temperature distribution of this heating resistor is evenly wound from the end to the end of the pipe, the heating resistor has a well-balanced temperature distribution with a small temperature difference between the center and both ends. It is a heating resistor of excellent quality.

[0009]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is an external projection view of a heating resistor of the present invention,
FIG. 2 is a sectional structural view of the heating resistor of the present invention, FIG. 3, FIG.
5, FIG. 6 and FIG. 7 are embodiments of the present invention, FIG. 8 is a temperature distribution diagram of a known heating resistor and a heating resistor of the present invention, and FIG. 9 is a thermal air flow meter using the present invention. FIG.

The structure of the heating resistor of the present invention will be described with reference to FIGS. Reference numeral 1 is a pipe-shaped support body that holds a lead wire and a resistor formed of an insulator such as alumina or zirconia. Reference numeral 2 is a lead wire fixed to both ends of the pipe 1 with an adhesive 3. The resistor 4 is spirally wound around the pipe 1 to form a resistor. Furthermore, an overcoat glass 5 is applied to cover the entire surface of the resistor.

FIG. 1 shows a heating resistor of a thermal type air flow meter according to the present invention. By providing the groove 6 in the pipe 1, when the resistor 4 rides on the pipe 1 from the lead wire 2 during winding work, the spiral winding can be started with the groove of the pipe 1 as a positioning. Also, after the winding end portion is positioned along the concave groove, the winding end can be finished, and the pipe 1 can be wound with a uniform pitch from end to end with high precision. The groove shape of the cross section of the pipe 1 may be a quadrangle shown in FIG. 3, a semicircle shown in FIG. 4, or a triangle shown in FIG. Further, the embodiment shown in FIG. 6 is an example in which notches 7 are provided at both ends of the pipe and the notches 7 are used to position the winding start and winding end of the resistor 4. In the embodiment shown in FIG. 7, a large number of notches 7 are formed in the pipe 1 for positioning the winding start and winding end of the resistor 4.

FIG. 8 is a temperature distribution diagram when a heating current is applied to the heating resistor. When current is applied to the heating resistor,
The temperature distribution of the known heating resistor has a peak point near the center of the support and a low temperature at both ends. This is because the amount of heat of heating in the winding part near the central part directly heats the pipe 1, resulting in a peak-shaped temperature distribution, but since both ends are not wound at the beginning and end, the ends are heated. Not done. In addition, since the amount of heating heat is conducted to the lead wire 2 and the adhesive 3, the temperature distribution at both ends is extremely lower than that in the central part, resulting in an unstable temperature distribution having a peak near the central part of the heating resistor. Become. Further, since the windings are concentrated in the central part, the central part is concentrated and heated, so that the peak temperature of the temperature distribution extremely rises, and only the peak temperature part becomes abnormally sensitive to the air flow. On the contrary, since the temperature distribution at both ends is low, the sensitivity to the air flow becomes insensitive, and two heating elements having different characteristics are obtained in one heating resistor, resulting in an unstable heating resistor. Therefore, if the air flow to be measured is uneven or irregular, the heat transfer from the heating resistor to the air flow becomes unstable, which deteriorates the measurement accuracy and increases noise.

On the other hand, according to the present invention, since the spiral winding of the resistor is performed for positioning the groove of the pipe, the resistor is wound evenly from one end to the other so that the entire pipe is heated uniformly. The temperature distribution of is trapezoidal and has a balanced temperature distribution without extreme peak points. If the temperature distribution of the heating resistor is balanced, even if uneven air flow or non-uniform air flow is supplied to the heating resistor, the heat transfer from the heating resistor to the air is stable and the heating resistor has high measurement accuracy. Can be obtained.

FIG. 5 shows an embodiment of a thermal air flow meter using the heating resistor of the present invention. 8 is the heating resistor of the present invention,
Reference numeral 9 is a temperature sensitive resistor for measuring the temperature of intake air, 10 is a body accommodating an air passage and a drive circuit, and 11 is a drive circuit for converting the air flow rate from the heating resistor 8 and the temperature sensitive resistor 9 into an electric signal. is there. Thus, by installing the heating resistor 8 of the present invention in the air passage, it is possible to provide a thermal air flow meter with high measurement accuracy.

[0016]

According to the present invention, it is possible to supply a heating resistor having good workability and a stable temperature distribution, and
There is an effect that it is possible to provide a heating resistor of a thermal type air flow meter with improved measurement accuracy of the intake air flow rate.

[Brief description of drawings]

FIG. 1 is an external projection view of a heating resistor of the present invention.

FIG. 2 is a sectional view of a heating resistor of the present invention.

FIG. 3 is a sectional view of an example.

FIG. 4 is a sectional view of an example.

FIG. 5 is a sectional view of an example.

FIG. 6 is an external projection view of the example.

FIG. 7 is an external projection view of the example.

FIG. 8 is a temperature distribution diagram of a heating resistor.

FIG. 9 is a cross-sectional view of the thermal air flow meter of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Support body, 2 ... Lead wire, 3 ... Glass adhesive, 4 ... Resistor, 5 ... Overcoat glass, 6 ... Recessed groove, 7 ... Notch groove, 8 ... Heating resistor, 9 ... Temperature sensitive resistor 10 ... Body, 11 ... Drive circuit.

Claims (3)

[Claims] 1. An air flow meter which heats a heating resistor to a predetermined temperature and detects an air flow rate from a heating current value required at this time, in a lead wire of the heating resistor and alumina, zirconia or the like holding the resistor. A heating resistor, characterized in that a groove is provided in a cross section of a pipe-shaped support body made of an insulator, and positioning is performed when the resistor body is wound around the support body. 2. The heating resistor according to claim 1, wherein the cross section of the pipe-shaped support has a triangular, semicircular, or quadrangular concave shape. 3. The heating resistor according to claim 1, wherein notches are provided at both ends of the pipe-shaped support for positioning when the resistor is wound around the support.