JPS63271120A - Heat ray type air flow meter - Google Patents

Abstract

PURPOSE:To decrease the quantity of the heat which heats a bobbin or escapes along the bobbin by constituting a titled flow meter into bobbinless structure. CONSTITUTION:A partially crushed flat part is previously provided to a metallic core wire 2 which has resilience and can be etched. A platinum wire 3 is continuous wound on this metallic core wire 2 and after the core wire is cut to a prescribed length, lead wires 6 are welded thereto and alumina 4 is deposited by an electrophoresis method and burned. Furthermore, the internal core wire 2 is dissolved away by etching and after the surface is coated with glass 5, the load wires 6 are welded to supporting members 7, by which a heating resistor 1 is completed.

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]

The conventional bobbin type hot wire air flow meter
As described in No. 6326, a lead wire is inserted into a bobbin made of ceramic or the like and a platinum wire is wound around it, resulting in poor workability and difficulty in automating production. In addition, the amount of heat escaping through the bobbin itself cannot be ignored, which has the disadvantage of slow response. On the other hand, in the case of a bobbin-less structure that compensated for this drawback, there were problems with durability such as vibration, heat resistance, and thermal shock because there was no bobbin.

[Problem that the invention seeks to solve]

In the heat generating resistor described in the above-mentioned prior art, it is difficult to automate the work of inserting and bonding the wire into a bobbin made of ceramics or the like because the bobbin is small and eccentric. In addition, in winding work, there is a large diameter difference between the lead wire and the bobbin, and it is difficult to automate winding from the lead wire to the bobbin and from the bobbin to the lead wire.

There were also problems with the platinum wire being easily damaged and the pitch becoming irregular when unwinding. Furthermore, the amount of heat that heats the bobbin and escapes through the bobbin itself cannot be ignored, resulting in a drawback that the response is delayed.

On the other hand, in the case of a bobbinless structure that compensates for the above drawbacks, there are problems in mechanical strength, heat resistance, heat shock resistance, and other durability because there is no high-strength and thermally stable ceramic bobbin. Furthermore, when a perfectly circular metal core wire is used, the pitch of the winding wire can easily shift due to external force during handling after continuous winding, so it was necessary to consider countermeasures.

The purpose of the present invention is to provide a hot-wire air type winding system that can improve responsiveness without sacrificing mechanical strength, eliminates the need to insert lead wires, enables continuous high-speed automation of winding, and prevents pitch drift. Our purpose is to provide flowmeters.

[Means for solving problems]

The above purpose is to create a heat generating resistor by partially crushing a flexible and etched metal core wire in advance to create a flat part, winding a platinum wire around the surface of the flat part, and cutting it to a predetermined length. , connect the lead wire to the flat part. Furthermore, alumina is deposited on the winding part using electrophoresis and fired.
This is achieved by removing the metal core wire by etching and then creating a bobbin-less structure coated with glass.

[Effect]

Since it has a bobbin-less structure, unlike the ceramic bobbin type, the amount of heat that heats the bobbin and escapes through the bobbin can be greatly reduced, improving responsiveness.

In addition, unlike the conventional ceramic bobbin type, there is no step between the lead wire and the bobbin, and since continuous high-speed automatic winding on a flexible metal core wire is an existing technology, productivity is greatly improved. can. Also, the metal core wire is partially flattened.

The platinum wire wound around this part will be subject to large distortions and will not move even if an external force is applied to it. Therefore, since this portion acts as a stopper for pitch deviation of the winding, pitch deviation can be prevented even if an external force is applied in a process after winding.

The lead wires are attached by welding or brazing, unlike the conventional ceramic bobbin type, which requires no lead wire insertion work, so workability is good and automation is possible. By depositing the alumina film on the winding portion by electrophoresis, the film is homogeneous and has a high porosity, and the film thickness can be controlled with high precision. Therefore, when removing the metal core wire by etching, the etching solution can penetrate through these pores, and the metal core wire can be easily etched away, thereby making it possible to obtain a hollow bobbin-less structure. Alumina is heat resistant.

It has thermal shock resistance and mechanical strength of 9, and since the coating material glass penetrates into the pores of alumina and acts to close them, even higher strength can be expected.

〔Example〕

The present invention will be explained in detail below.

FIG. 1 is a structural diagram of a heating resistor according to the present invention.

The heating resistor 1 for detecting the amount of intake air is made by continuously winding a platinum wire 3 around a partially flattened metal core wire 2 to a predetermined length, as shown in the manufacturing process diagram of FIG. After cutting, lead wires 6 are welded, and alumina 4 is deposited by electrophoresis and fired. Further, the internal metal core wire 2 is dissolved and removed by etching, and after being covered with glass 5, the supporting member 7
Weld the lead wire 6 to.

Heat generating resistor 1 and air temperature sensing resistor 8 having such structure
As shown in FIG. 3, there is a main passage 10 through which most of the intake air passes, and a bypass passage 1 through which a part of the intake air is divided.
1 in the bypass passage 11 of the body 12. FIG. 4 shows a drive circuit 20 for a hot wire air flowmeter, in which the heating resistor 1. Air temperature detection resistor7.
Operational amplifier 21, 22. Power transistor 23. Capacitor 24. Consisting of resistors 25 to 29, the (+) pole of the battery is connected to the collector terminal voltage 30 of the power transistor 23, the (-) pole of the battery is connected to the earth terminal 31 of the resistor 25, and the resistor 25 and the heating resistor 1 Connected to the connection point 32 is an input terminal of a microcomputer that controls the engine using the output signal of the hot wire air flow meter.

In such a configuration, the power transistor 23 supplies current to the heat generating resistor 1 to heat it, and controls the heat generating resistor 1 so that the temperature is always higher than the air temperature detecting resistor 7 by a certain amount. At this time, the air temperature detection resistor 7 allows only a very small current to flow so that heat generation is negligible, and is used for temperature correction of the intake air by detecting the intake air temperature. When the air flow hits the heating resistor 1, the drive circuit operates to control the temperature difference between the heating resistor 1 and the air temperature sensing resistor 8 to be constant as described above.
This operation reduces the voltage difference across the heating resistor 1 to the resistor 26.
Feedback is applied so that the voltage divided by 27 and the voltage amplified by the operational amplifier 22, which is the voltage drop across the resistor 25 caused by the current flowing through the heating resistor 1, are always equal. Therefore, when the air flow rate changes, the current flowing through the heating resistor 1 changes, and the air flow rate can be measured by the voltage drop across the resistor 25 corresponding to the current.

With the above configuration, the heat generated in the platinum wire 3 of the heating resistor 1 can be used to heat the bobbin as in the conventional bobbin type, and the amount of heat transmitted through the bobbin and escaping can be greatly reduced. The transient response when the air flow rate suddenly changes is greatly improved.

In addition, according to this configuration, there is no problem of wire breakage during winding or variations in the winding pitch, and continuous high-speed automatic winding can be performed, and even if external force is applied during the work after winding, the winding pitch remains unchanged. No deviation occurs. Furthermore, it is possible to solve the problem of insufficient mechanical strength, which is a general drawback of the bobbinless type, and to improve durability such as heat resistance and thermal shock resistance. Furthermore, according to this embodiment, there is no hole on the end face of the bobbin unlike in the conventional bobbin type.
Therefore, there is no fear that water, oil, dirt, etc. that enter the device during actual use will enter the interior through this hole and deteriorate performance.

〔Effect of the invention〕

According to the present invention, it is possible to provide a hot-wire air flowmeter with improved responsiveness, improved durability such as mechanical strength, heat resistance, and thermal shock resistance, and excellent workability.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of a heating resistor, FIG. 2 is a manufacturing process diagram of the heating resistor, FIG. 3 is a sectional view of a hot wire air flow meter, and FIG. 4 is a drive circuit diagram. DESCRIPTION OF SYMBOLS 1... Heating resistor, 2... Metal core wire, 3... Platinum wire. 4...Alumina membrane, 5...Glass coating, 6...Lead wire, tail 10 b---11-F Yaei 7---Entoku 1 Japanese cutting

Claims (1)

[Claims] 1. As a means for measuring the intake air flow rate of an electronically controlled fuel injection device of an internal combustion engine, a heating resistor installed in an air passage and a current of the heating resistor are controlled, and the heating In a hot wire air flowmeter comprising a drive circuit that extracts the output voltage of the resistor as a signal corresponding to the air flow rate, the heat generating resistor is formed of a metal core wire having flexibility and etching property,
For example, using molybdenum wire, iron wire, etc., press this core wire partially in advance to provide a flat part, then wind a platinum wire around the surface, cut it to a predetermined length, and attach the lead wire to the flat part. are connected by welding or brazing, then alumina is deposited on the surface of the platinum wire by electrophoresis, fired, the metal core wire is removed by etching, and the surface of the alumina is further coated with glass. Hot wire air flow meter. 2. A hot wire air flowmeter according to claim 1, characterized in that the alumina film is deposited by electrophoresis after etching the metal core wire.