JPH0298634A - Heat ray type air flow meter - Google Patents

Abstract

PURPOSE:To decrease the fluctuation in the resistance value of an exothermic resistor and to inprove the reliability in the juncture by providing a hollow part to the inner side of a winding which forms the insulating layer of the exothermic resistor and connecting both ends of the winding and lead wires respectively at one point. CONSTITUTION:The exothermic resistor as a means of measuring the intake air flow rate of an internal combustion engine is constituted of the winding 3 wound with a platinum wire 3, an alumina layer 2 formed on the winding 3, a glass layer 1 formed on the alumina layer 2, the lead wires 4 for external drawing out provided to both ends of the winding 3 and supporting pins 6 which support the winding 3 and the lead wires 4. The hollow part 5 is provided to the inner side of the winding 3 wound with the exothermic resistor. The winding 3 and the lead wires 4 are connected at one point by the platinum wire 7 for connection at both ends of the winding 3 of the exothermic resistor. The fluctuation in the resistance value of the exothermic resistor is suppressed to a low level in this way and the reliability in the juncture of the platinum winding and the lead wire is improved.

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 having a heating resistor suitable 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. 632, in the manufacturing process of a heating resistor, a platinum wire is inserted into a bobbin made of ceramic or the like and wound therein. On the other hand, a hot wire air flow meter with a bobbin-less structure involves winding a platinum wire continuously around a metal core wire with etching properties in the manufacturing process of one heating resistor. The lead wires were welded and connected.

[Problem to be solved by the invention]

In the above conventional technology, in the bobbin type hot wire air flowmeter, a lead wire is inserted into the bobbin and platinum wire is wound in the manufacturing process of one heating resistor, which makes workability poor and production automation difficult. Moreover, the amount of heat escaping through the bobbin itself could not be ignored, causing a problem of delayed response. A hot wire air flowmeter with a bobbinless structure compensates for the problems of the bobbin type.
In the manufacturing process of the heat generating resistor, a metal core wire is pressed at a constant pitch, and then a platinum wire is continuously wound on the surface of the metal core wire and cut at the pressed parts.

Since the lead wire is welded to this i@ end, if the pitch of each winding is 60 to 70 μm, it is very difficult to weld the lead wire onto the winding at a predetermined position at one point. There was a problem in that the number of windings between the coils varied, and the resistance value of the heating resistor also varied widely, resulting in the resistance value not falling within the specified value. Further, if the resistance values of the heat generating resistors vary greatly, there is a problem in that it takes time to adjust the resistance in the drive circuit when one heat generating resistor is incorporated into a hot wire type air flowmeter and initial characteristic adjustment is performed. Furthermore, since the number of turns of the platinum wire connected to the lead wire is not constant, there is also a problem in the reliability of this connection (junction).

SUMMARY OF THE INVENTION An object of the present invention is to provide a hot wire type air flow meter that can suppress variation in resistance value of a heating resistor to a small value and improve reliability of a connecting portion between a platinum winding and a lead wire.

[Means to solve the problem]

The above purpose is to insert a lead wire into both ends of an etching metal pipe in the manufacturing process of a heating resistor, caulk the ends, and then wind a certain number of turns of platinum wire on the surface of the metal pipe. At the same time, one heating resistor is formed by a process such as welding both ends of the platinum winding and the lead wire at one point, forming an insulating layer on the surfaces of the metal pipe and the platinum winding, and then removing the metal pipe by etching. This is achieved by a hot wire type air flowmeter which has a hollow part inside the winding formed with the insulating layer of the body, and in which both ends of the winding are connected to a lead wire at one point.

[Effect]

The above-mentioned hot-wire air flowmeter is manufactured by inserting lead wires into both ends of a metal pipe having etching property during the manufacturing process of a heating resistor having a bobbin-less structure, and then caulking both ends of the metal pipe. When a wire is fixed and supported on a metal pipe, a certain number of turns of platinum wire is wound on the surface of the metal pipe, and both ends of the platinum wire are connected at one point on the surface of the lead wire near both ends of the metal pipe.
Metal The accuracy of the number of turns of platinum wire wound on the pipe surface is ±
Since the precision of the winding after removing the metal pipe can be set to 0 turns, the accuracy of the winding can be ±0 turns, so the diameter of the platinum wire, the outer diameter of the above metal pipe, and the platinum winding, which is considered to be the cause of the variation in the resistance value of the remaining heating resistor. Even including the effects of variations in pitch, etc., variations in the resistance value of the heating resistor can be suppressed to less than 2.5%, and both ends of the platinum wire and the lead wire are always connected reliably at only one point. Since the connection is made, the reliability of the connection is ensured.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 6.

FIG. 1 is a structural diagram of a heating resistor showing an embodiment of a hot wire air flow meter according to the present invention. In FIG. 1, 1 is a glass layer, 2 is an alumina layer, 3 is a platinum wire (winding wire), 4 is a lead wire, 5 is a hollow part, 6 is a support pin, and 7 is a platinum wire for connection. This heating resistor consists of a winding 3 in which a platinum wire 3 is wound, an alumina layer 2 formed on the first winding 3, and an alumina layer 2.
It consists of a glass layer 1 formed on the outside, and lead wires 4 and 5 for external extraction provided at both ends of the winding 3, and support pins (supporting bodies) 6 that support the winding 3 and the lead wire 4. A hollow part 5 is formed inside the winding 3 wound around the body, and the winding 3 and the lead wire 4 are connected at one point by a connecting platinum wire 7 at both ends of the winding of the heating resistor. ), and the tip of the lead wire 4 enters the hollow portion 5.

FIG. 2 is a manufacturing process diagram of the heating resistor shown in FIG. 1. Second
In the figure, 8 is a metal pipe with etching properties, 9
is the platinum wire for connection. First, the lead wire 4 is inserted into both ends of the etched metal pipe 8 shown in FIG. 2, and then both ends of the metal pipe 8 are caulked to fix and support the lead wire 4 to the metal pipe 8. Next, the platinum wire 3 is wound a certain number of turns on the surface of the metal pipe 8, and the platinum wire 3 is wound on the surface of the glue 84 near both ends of the metal pipe 8.
The two ends of the connecting platinum wires 7 and 9 are welded together at one point. For this purpose, first, for example, the connecting platinum wire 9 is welded at one point on the surface of one of the lead wires 4, and then the connecting platinum wire 9 is welded at one point on the surface of the metal pipe 8. After a certain number of turns of platinum wire 3 is wound on the lead wire 3, a connecting platinum wire 7 is welded at one point onto the surface of the other lead wire 4 on the opposite side. Further, the metal pipe 8, the surface of the metal pipe 8, the platinum 13 wound twice, and the connecting platinum wire 7°9.
After forming an alumina layer 2 thereon and firing, the metal pipe 8 is removed by etching. Then alumina layer 2
A glass layer 1 is coated on the surface of the glass layer 1, and finally a lead wire 4 is welded to the support pin 6.

FIG. 3 is a sectional view of the arrangement of the hot wire flowmeter having the heating resistor shown in FIG. 1. FIG. In Figure 3, 2° is intake air, 2°
1 is the air flow sensor body, 22 is the main passage, 23
24 is a bypass passage, 24 is a basic drive circuit, 25 is a heating resistor, and 26 is an air humidity sensing resistor. Heat generating resistor 25 and air temperature sensing resistor 2 having the structure shown in FIG. 1 (FIG. 2)
6 is an electronically controlled fuel injection device for the internal combustion engine (not shown)
As a means for measuring the intake air flow rate, the air flow sensor body 21 has a main passage 22 through which most of the intake air 20 passes and a bypass passage 23 through which a portion of the intake air 20 is divided. A basic drive circuit 24 is installed.

FIG. 4 is a circuit diagram of the basic drive circuit 24 of FIG. In FIG. 4, 31 is a resistor, 32 is a power transistor, 33, 34, 36, 39 are resistors, 37, 38 is an amplifier, and 40 is an output connection point.

41 is a collector terminal, and 42 is an emitter terminal.

This basic drive circuit 24 includes the heating resistor 25, air temperature sensing resistor 26, amplifiers 37, 38, power transistor 32, and resistors 31, 33, 34, 36, 39.
The positive electrode of a battery (not shown) is connected to the collector terminal 41 of the power transistor 32, and the negative electrode of the battery is connected to the ground terminal of the resistor 3. 25 connection points 4
o is output as a voltage proportional to the air flow rate, and is configured to be connected from the output connection point 40 of the hot wire type airflow meter to the input terminal of a microcomputer (not shown) that controls the engine.

In this configuration, the power transistor 32 supplies a driving current to the heat generating resistor 25 to heat it, and controls the heat generating resistor 25 so that the temperature is always higher than that of the air temperature detecting resistor 26 by a certain amount. At this time, the air temperature detection resistor 26 allows only a very small current, which generates negligible heat, to flow, detects the intake air temperature, and uses it for temperature correction of the intake air. When the intake air flow hits the heat generating resistor 25, the basic drive circuit 24 operates so that the temperature difference between the temperature detected by the heat generating resistor 25 and the air temperature detection resistor 26 always remains constant as described above. controlled. This operation is performed by the heating resistor 25.
Resistor 3 generated by the voltage value obtained by dividing the voltage difference between both ends of by resistors 33° and 34 and the current flowing through heating resistor 25.
Feedback control is performed so that the voltage values obtained by amplifying the voltage drop of 1 by the amplifier 38 are always equal. Therefore, when the air flow rate of the intake air 20 changes, the heating resistor 25
The air flow rate can be measured by detecting the voltage drop across the resistor 31 according to the change in the current flowing through the resistor 31 .

According to the hot wire air flowmeter having the heat generating resistor 25 of this embodiment, the number of turns of the platinum wire 3 wound around the heat generating resistor 25 can be adjusted to an accuracy of ±O turns, so that the resistance value of the heat generating resistor 25 can be adjusted to ±O turns. The reason for the accuracy variation is that the remaining platinum wire 3
variation in the diameter of the metal pipe 8, variation in the outer diameter of the metal pipe 8,
Although variations in the pitch between the platinum wires 3 can be cited, the overall accuracy of the resistance value due to variations in these three points is ±2.5.
% or less. Therefore, the heating resistor 25
It also becomes easy to adjust the resistance in the basic drive circuit 24 when the basic drive circuit 24 is incorporated.

FIG. 5 is a structural diagram of a heating resistor showing another embodiment of the hot wire air flow meter according to the present invention. In Figure 5, the first
The same reference numerals as in the figure indicate corresponding parts, and 50 is another hollow part. As a method of connecting the lead wire 4, this heat generating resistor is designed to generate arc sparks between the lead wire 4 and both end surfaces of a metal core wire (not shown) having etching properties that initially existed in the hollow portion 50 during the manufacturing process. Figure 2 shows the heating resistor of this embodiment, which employs percussion welding in which both ends of the metal core wire are temporarily melted, and the lead wire 4 is press-fitted thereto for connection (joining). There is no deformation of both ends of the hollow portion 5 due to caulking of the metal pipe 8. According to this embodiment, the accuracy of the resistance value of the heating resistor can be suppressed to about ±2.5% or less, similar to the embodiment shown in FIG.

FIG. 6 is a tlI diagram of a heating resistor showing still another embodiment of the hot wire air flow meter according to the present invention.

In FIG. 6, 51 is yet another hollow portion.

This heating resistor has the same structure as the conventional example.

The difference from the conventional example is that the hollow part 5 is first formed in the manufacturing process.
After first welding the lead wire 4 to the flat portions at both ends of the metal core wire (not shown) having etching properties that existed in 1, the platinum wire 3 was wound a certain number of turns on the surface of the metal core wire,
Platinum # for connecting both ends of platinum wire 3! 7 as lead wire 4
It is connected (joined) by welding a single point on the top. According to this embodiment, like the embodiments shown in FIGS. 1 and 5, the accuracy of the resistance value of the heating resistor can be suppressed to about ±2.5% or less.

Further, according to each of the above embodiments, the metal pipe 8 that was initially present in the hollow part of the heating resistor during the manufacturing process
Or, in the process of winding the platinum wire 3 around the metal core wire, the lead wire 4 is first connected to the metal pipe 8 or both ends of the metal core wire.
Since both ends of the platinum wire 3 are welded at one point on the surface of the connecting platinum wire 7.9 at the beginning and end of winding, the resistance accuracy of the heating resistor is ±2.5%. In addition to being able to keep the lead wire to a level smaller than the conventional example, there is also the problem that when the lead wire is later welded to both ends of the platinum wire wound around the metal core wire, parts of the platinum wire near both ends become tangled. solved, and the platinum wire 3, that is, the platinum wire 7 for connection,
Since the wire 9 is reliably connected to the lead wire 4 at one point, the reliability of the connection can also be improved.

〔Effect of the invention〕

According to the present invention, the platinum wire of the heating resistor of the hot wire air flowmeter and the lead wire are connected at one point.

Variations in the resistance value of the heating resistor can be kept small, reducing the time required to adjust the resistance in the initial circuit module when it is incorporated into an air flow sensor, and also ensuring that the platinum wire and lead wire are always connected at one point. The reliability of the connection can be improved because the platinum wires are connected to A low-cost heating wire with a heating resistor that has a small resistance variation and improves the reliability of the connection between the lead wire and the platinum winding due to the elimination of the process of removing frayed wires. There are advantages that a type air flow meter can provide.

[Brief explanation of drawings]

Fig. 1 is a structural diagram of a heating resistor showing an embodiment of the hot wire air flow meter according to the present invention, Fig. 2 is a manufacturing process diagram of the heating resistor shown in Fig. 1, and Fig. 3 is a diagram of the heating resistor shown in Fig. 1. Fig. 4 is a circuit diagram of the basic drive circuit of Fig. 3.
FIG. 6 is a structural diagram of a heat generating resistor showing another embodiment of the present invention, and FIG. 6 is a structural diagram of a heat generating resistor showing still another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1...Glass layer, 2...Alumina layer, 3...Platinum wire, 4...Lead wire, 5,50.51...Hollow part,
6... Support pin, 7, 9... Platinum wire for connection, 8...
- Metal pipe, 24... Basic drive circuit, 25... Heat generating resistor, 26 Air temperature sensing resistor.

Claims (1)

[Scope of Claims] 1. As a means for measuring the intake air flow rate of an internal combustion engine, there is provided a heating resistor comprising a winding installed in an air passage and formed with an insulating layer, a lead wire for external extraction, and its support. , a hot wire air flowmeter comprising a drive circuit that controls the current of the heating resistor and takes out the output voltage of the heating resistor as a signal corresponding to the intake air flow rate, wherein the insulating layer of the heating resistor is 1. A hot wire air flowmeter characterized in that the formed winding has a hollow portion inside, and both ends of the winding are connected to a lead wire at one point. 2. The hot wire air flowmeter according to claim 1, wherein the tip of the lead wire is inserted into the hollow portion.