JPS63307316A - Hot wire type air flowmeter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hot wire air flow meter, and more particularly to a hot wire air flow meter for detecting the intake air flow rate of an internal combustion engine.

[Conventional technology]

In a conventional hot wire type air flow meter, as described in Japanese Patent Application Laid-Open No. 59-31412, a support body for holding a heating resistor was constructed of a plastic base integrated with a housing.

[Problem that the invention seeks to solve]

For this reason, the temperature rises due to self-heating of the power transistor, which is a part of the drive circuit, resulting in a disadvantage that the operating environment becomes harsh and the life of the connection part of the power transistor is shortened.

This will become a hindrance to further increase in engine room temperature in the future.

An object of the present invention is to provide a hot wire flowmeter with improved reliability by lowering the temperature of the components of the drive circuit.

[Means for solving problems]

The above object is achieved by insert molding the base of an AM and creating a structure separate from the housing when plastic molding the support that holds the heating resistor, instead of integrally molding it with the housing as in the conventional case. achieved.

[Effect]

When the base material is changed from plastic to aluminum, its thermal conductivity increases from 0.19KcaQ/mh'c to 1
It will increase significantly to 80KcaN/mh'c. Therefore, self-heating of the power transistor forming a part of the drive circuit can be released to the outside, and temperature rise of the power transistor etc. can be prevented.

〔Example〕

Hereinafter, the invention will be described in detail according to the drawings. FIG. 1 is a structural diagram of the heating resistor, and FIG. 2 is a circuit diagram showing the principle of operation.

The heating resistor 1 for detecting the intake air flow rate and the intake air temperature measuring resistor 2 use the same element, and a platinum wire 10 is mounted on an alumina bobbin 101 with a diameter of φ0.5 and a length of 21W+.
After winding 2 and welding both ends to the lead wire 103,
It has a thin glass coating 104 on its surface.
As shown in the top view of the hot-wire air flow meter in Figure 3 and the cross-sectional structural diagram in Figure 4, these have a main passage 105 through which most of the intake air passes, and a bypass passage 106 through which a portion of the intake air flows. It is installed in the bypass passage of the body 107.

The drive circuit 100 includes the heat generating resistor 1 described above, the intake air temperature measuring resistor 2, an operational amplifier 3, a 4° power transistor 5. Consisting of resistors 6 to 10, the collector terminal 11 of the power transistor 5 is connected to a battery, the earth terminal 12 of the resistor 6 is connected to one pole of the battery, and the connection point 13 between the resistor 6 and the heating resistor 1 is connected. is connected to the input terminal of a microcomputer that controls the engine using the output signal of the hot wire air flow meter.

Heating the heating resistor 1 by the power transistor 5,
The temperature is kept a certain amount higher than the intake air temperature. At this time, only a minute current is allowed to flow through the intake air temperature measuring resistor 2 so that heat generation is negligible, and the intake air temperature measuring resistor 2 has the same value as the intake air temperature. Detected as resistance value. Here, when the air flow hits the heat generating resistor 1, the drive circuit is operated so that the temperature difference between the heat generating resistor 1 and the intake air temperature measuring resistor 2 is always constant. This operation is performed by adding the voltage drop across resistor 6 caused by the current flowing through heat generating resistor 1 to the voltage obtained by dividing the potential difference between both ends of heat generating resistor 1 by resistors 7 and 8, and the voltage drop across resistor 6 described above. Feedback is applied so that the voltage amplified by operational amplifier 3 is always equal. Therefore, when the air flow rate changes, the current flowing through the heating resistor 1 changes, and the air flow rate is read by the voltage drop across the resistor 6 in accordance with the current.

In one aspect of the present invention, the holder 17 is formed by insert molding the support 14, 15 that holds the heating resistor 1 and the aluminum base 16. Furthermore, the metal case 19 is bonded to the drive circuit board 18 having the drive circuit section, and then fixed to the base 16 by bonding, and the plastic housing 20 is also bonded and fixed at the same time. In such a configuration, the amount of heat generated in the operational amplifier 3 of the drive circuit section can be released to the body 107 via the base 16 of the AQ, and a rise in temperature of the drive circuit section can be prevented. If, for example, an ode bottle 21 is press-fitted into a part of the ha base 16 and connected to the case 19 by spot welding to provide grounding, the resistance to radio wave interference can be improved.
The structure can be greatly simplified compared to the conventional example, and the principle of parts and productivity can be improved. In addition, the amount of warpage can be reduced compared to a resin base, and the stress that sometimes occurs when tightening screws, for example, can be reduced, thereby preventing cracks in the drive circuit section.

〔Effect of the invention〕

According to the present invention, it is possible to reduce the temperature of the components of the drive circuit, and it is possible to provide a hot wire air flow meter with improved reliability.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of the heating resistor, Figure 2 is a circuit diagram showing the operating principle, Figure 3 is a top view of the hot wire air flow meter of the present invention,
FIG. 1 shows its cross-sectional structure. 1... Heat generating resistor, 2... Air temperature measuring resistor, 1
4゜15...Support, 16...Base, 19...
Case. 3rd stitch 10'/

Claims (1)

[Claims] 1. A heating resistor installed in an air passage to measure the air flow rate, controlling the current of the heating resistor, and extracting the output voltage of the heating resistor as a signal corresponding to the air flow rate. In a hot-wire air flowmeter having a drive circuit, a first component made of plastic in which a support for holding the heating resistor and a metal base are insert-molded, and a bottom of a bottomed box-shaped metal case are provided with the drive circuit. 1. A hot wire air flowmeter characterized in that a second component has a circuit section adhesively fixed thereto, a plastic housing is further bonded to the first component, and then the second component is adhesively fixed. 2. The hot wire air flow meter according to claim 1, wherein the metal base material is made of Al, and furthermore, an ord pin is press-fitted into a part of the metal base material.