JPH04198719A - Thermal air flow meter - Google Patents

Abstract

PURPOSE:To dispense with a lead wire and the wire bonding work by connecting a film type resistor formed on a substrate made of a heating element to a control circuit with terminal pins buried in a substrate supporter, and fixing the pins to the substrate. CONSTITUTION:A terminal pin 3 is formed into an L-shape at one end, and the end face of a shorter side is stuck to the electrode extraction section 5 of a film type resistor 2 with solder. The longer side of the L-shape passes through a substrate supporter 4 at a fixed interval from a substrate 1 and connected to an external control circuit. A lead wire which is weak in mechanical strength is not required to be used, and no bonding work is required. The pin 3 serves to reinforce a heating element, the mechanical strength of the heating element is improved, and the heat conduction loss to the pin 3 can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thermal air flow meter for measuring the flow rate of air taken into, for example, an automobile engine, and particularly relates to a heating element thereof.

[Prior Art] FIG. 5 is a schematic configuration diagram showing the configuration of a heating element of a conventional thermal air flowmeter disclosed in, for example, Japanese Patent Laid-Open No. 189416/1983. Further, FIG. 6 is a cross-sectional configuration diagram showing a state in which the element shown in FIG. 5 is installed in a duct. In the figure, (1)
is a substrate, (2) is a temperature-dependent film resistor formed on the substrate (1), (4) is a substrate support, (8) is a substrate holder, (9) is a lead wire, ( lO) is the support (4
〉It is a wire that is glued to the surface.

The operation of the device configured in this way will be explained. When a current is passed through the temperature-dependent film resistor (2), heat is generated due to Joule heat, and the film resistor (2) functions as a heating element. The current flowing through the membrane resistor (2) is feedback-controlled so that the difference between the temperature of the membrane resistor (2) and the intake air temperature is constant. In other words, constant temperature difference feedback control is performed. If the heat transfer coefficient between the fluid and the membrane resistor (2) is h, the surface area of the membrane resistor (2) is S, and the temperature difference between the membrane resistor (2) and the fluid is ΔT, then the membrane resistor ( 2
) and air is expressed as H=h-5・ΔT...(A). Further, assuming that the resistance of the schematic resistor (2) is RHL and the heating current flowing therein is (■), the Joule heat W generated by the schematic resistor (2) is expressed as W=RH·■2 . . . (B). In a state of thermal equilibrium, W=H holds true, so RH-I2=h-8·ΔT . . . (C). Generally, the heat transfer coefficient is expressed by the experimental formula h=A+B-Q' ---(D) where A and B are constants, so the heating current I should be measured while keeping the temperature difference △T constant. The flow rate Q is obtained by

[Problems to be solved by the invention] - However, when a heating element having the structure as shown in Fig. 5 is installed as shown in Fig. 6, the extremely thin lead wire is directly exposed to the fluid, so its mechanical Strength becomes weaker. Further, it is necessary to form lead wires on the substrate support and then perform wire bonding, which increases the number of steps.

This invention was made to solve the above-mentioned problems, and aims to provide a thermal air flow meter that can increase the mechanical strength of a heating element and contribute to expanding the usage environment.

[Means for Solving the Problems] A thermal air flow meter according to the present invention connects a schematic resistor formed on a substrate of a heat generating element and a control circuit to two embedded in a substrate support holding one end of the substrate. It is electrically connected using a terminal pin.

[Function] In the thermal air flowmeter of the present invention, since direct electrical connection is made through the terminal pin, there is no need to use lead wires with weak mechanical strength, and no bonding work is required. Furthermore, the terminal pins also play a role of reinforcing the heating element, improving the mechanical strength of the heating element.

[Example Figures 1 (a), (b), 2 (a), (b), 3 (a), (b), and 4 (a), (b) are shown in this figure, respectively. An example of a heating element related to a thermal air flow meter of the invention is shown,
Each figure (a) is a front view thereof, and each figure (b) is a side view thereof. In the figure, (1) is an insulating substrate, (2) is a substrate (1
), (3) is the terminal pin, (4) is the substrate support, (5) is the electrode extraction part of the schematic resistor (2), and (6) is the solder etc. The conductive material (7) is a heat insulating material such as polyimide. The substrate (1) is fixed in a cantilever structure, with one end serving as a fixed end inserted into a substrate-thick groove provided in the substrate support (4), and the other end serving as a free end.

In the embodiment shown in Figure 1, the terminal pin (3)
has an L-shaped bend at one end, and is bonded with a conductive material such as solder so that the end surface of the short side contacts the electrode extraction part (5) of the schematic resistor (2). . The terminal pin (3) is bonded to the board (1) only at the electrode extraction part (5), and the long side of the L shape supports the board while maintaining a constant distance from the board (1). It passes through the body and is connected to external control circuits.

By adopting such a configuration, it is not necessary to use lead wires having low mechanical strength, and bonding work is also not necessary. Furthermore, since the terminal pins also play a role of reinforcing the heating element, the mechanical strength of the heating element is improved. Further, since the terminal pin is not in contact with the substrate except for the electrical contact portion, heat conduction loss to the bottle is also reduced. Therefore, the usage environment of the thermal air flow meter can be expanded.

In the embodiment shown in FIG. 2, the terminal pin (3) has one end bent into an L-shape, and the short side of the terminal pin (3) is connected to the electrode extraction portion (5) by soldering. It is bonded with a conductive material such as. Furthermore, the space between the long side of the L-shaped terminal pin (3) and the board (1) is filled with a heat insulating material that has an adhesive effect, such as polyimide, and the terminal pin (3) and the board (1) are This increases the adhesive strength of the bottle and reduces heat conduction loss to the bottle.

In the embodiment shown in Figure 3, the terminal pin (3)
has a shape such as a semi-cylindrical shape with at least one flat surface on the side surface, and one end of the flat surface is a schematic resistor (2
) is electrically connected via solder or the like at the electrode lead-out portion (5), and the other end passes through the substrate support (4) and is connected to an external control circuit. In addition, the electrode extraction part (
For parts other than 5), connect the board (1) and terminal pin (3).
) is bonded to, for example, a polyimide film through a heat insulating material that has an adhesive effect.

This embodiment also eliminates the need for lead wires.
Bonding work is also no longer necessary. Furthermore, the terminal pins also play a role of reinforcing the heating element, improving the mechanical strength of the heating element. Furthermore, since the terminal pins are fixed to the board using a heat insulating resin or the like, heat conduction loss to the pins is also reduced. Therefore, the usage environment of the thermal air flow meter can be expanded.

In the embodiment shown in FIG. 4, the terminal pin (3) has a shape with at least one flat surface on the side surface, as in the embodiment shown in FIG.
It is electrically connected via solder or the like at the electrode extraction part (5), and the other end passes through the substrate support (4) and is connected to an external control circuit. In addition, part or all of the electrode extraction part and the exposed parts of the substrate (1) up to the substrate support (4) below and the terminal pins (3) are covered with a heat insulating material that has an adhesive effect, such as polyimide. The board (1) and the terminal pin (3) are bonded together. This embodiment has the same effect as the above embodiment.

[Effects of the Invention] As described above, according to the present invention, the wiring connection between the film resistor formed on the substrate of the heating element and the control circuit is made by the terminal pin embedded in the substrate support, and the terminal pin is soldered. Or, since it is directly fixed to the board using heat insulating material, etc., lead wires and wire bonding work are not required. Also, the terminal pins play a role of reinforcing the heating element, improving the mechanical strength of the heating element, and improving the usage environment. This has the effect of providing a thermal air flow meter that can contribute to the expansion of .

[Brief explanation of the drawing]

Figure 1 (a), (b), Figure 2 (a), (b), Figure 3 (a), (b), Figure 4 (a), (b) respectively show the heat related to this invention. The formula is a front view, each figure (b) is a side view, Figure 5 is a schematic configuration diagram showing the structure of the heating element of a conventional thermal air flowmeter, and Figure 6 is the installation of a conventional heating element in a duct. FIG. In the figure, (1) is a substrate, (2) is a membrane resistor, (3) is a terminal pin, (4) is a substrate support, and (5) is an electrode extraction part of the membrane resistor (2). In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] It has a film resistor with temperature-dependent resistance formed on the substrate,
One end of the substrate is held by a substrate support, a heating element is disposed in the fluid flow path, and a heating element is disposed outside the fluid flow path and connected to the membrane resistor to control the current flowing therein. In a thermal air flow meter equipped with a control circuit, an electrode take-out portion of the membrane resistor and one end of a terminal pin embedded in the substrate support are electrically connected to connect the membrane resistor and the control circuit. Thermal air flow meter.