JP3073096B2 - Thermal air flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal air flow meter,
In particular, the present invention relates to a thermal air flow meter for detecting an intake air amount of an internal combustion engine.

[0002]

2. Description of the Related Art A conventional bobbin-type thermal air flow meter has a structure in which lead wires are inserted into both ends of a bobbin made of ceramic or the like, and the bobbin and the lead wire are sintered, as described in Japanese Utility Model Publication No. 56-96326. is there. Next, a platinum wire is wound around a bobbin, the lead wire and the platinum wire are welded, and the surface of the bobbin is coated with glass.

One of the features of this heating resistor is that glass is used for bonding the bobbin and the lead wire, thereby preventing the heat generated by the bobbin from escaping to the lead wire and improving the responsiveness. Is to improve.

[0004]

In the heating resistor described in the above prior art, no consideration is given to the shape stability of the molten glass at the time of bonding the glass to the bobbin and the lead wire. There is a drawback that the glass flows into the lead portions where the melted glass is unnecessary for bonding. For example, when glass flows into a lead wire, poor welding occurs when a platinum wire is welded to the lead wire in the next step. Also, when the melted glass flows on the inner wall of the bobbin or the lead wire, the shape of the completed bobbin-type heating resistor varies because the amount thereof is not constant, thereby causing variations in characteristics such as responsiveness and heat radiation characteristics. Was.

[0005] Further, when the glass flows on the inner wall of the bobbin or the lead wire, a gap is formed between the bobbin and the lead wire, and there is a possibility that foreign matter may enter the inside of the bobbin, and thus there is a problem in reliability.

Another drawback of the prior art is that if microscopic cracks are present in the glass, the cracks will develop due to the repetitive cold and heat stresses and external forces in a practical state, and the characteristics will change.

On the other hand, for example, it is conceivable to use a crystalline material as a glass material or a metal paste as an adhesive. However, when using crystalline glass, the progress of cracks is not suppressed even if the shape stability during firing of the glass is maintained, and when using a metal paste,
Although there is no concern about cracks, the heat generated in the bobbin escapes easily to the lead wire and the response is reduced, so that this does not solve the problem.

SUMMARY OF THE INVENTION It is an object of the present invention to prevent molten glass from flowing out into a lead wire and preventing glass from flowing into an unnecessary portion of an inner wall of a bobbin during glass bonding between a bobbin and a lead wire. It is to prevent poor welding at the time and to reduce variation in characteristics.

It is another object of the present invention to suppress the development of cracks in the glass bonded portion in a practical state and improve reliability.

[0010]

The above object can be attained by mixing powder such as alumina or zirconia in advance into glass material powder used for bonding the bobbin and the lead wire, and bonding using the powder. You.

[0011] It is also achieved by using porous alumina as the bobbin material.

[0012]

When an adhesive containing a ceramic powder such as alumina or zirconia in a glass powder is used, a part of the ceramic is melted into the glass in a process of melting the glass to form a glass-ceramic composite. At this time, the ceramic that has not been melted becomes a core, and the glass crystallizes. This can prevent the glass from flowing to the lead wires and the inner wall of the bobbin.

Further, since part of the ceramic remains in the glass even after bonding, it plays a role in suppressing the development of cracks in a practical state. That is, even if a minute crack occurs in the glass, the ceramic fine particles serve as a resistance and play a role of suppressing the progress of the crack.

On the other hand, by using porous alumina as the bobbin, even if the bobbin has a structure in which both ends of the bobbin are completely closed by the glass at the time of bonding and firing the lead wire and the bobbin with the glass, the inside of the bobbin can be prevented. The expanded air exits through the porous alumina, so that the molten glass is not pushed by the internal pressure. This can prevent the glass from flowing into the lead wire.

[0015]

An embodiment of the present invention will be described below.

FIG. 1 is a structural view of a heating resistor 1 according to the present invention. The heating resistor 1 has lead wires 3 at both ends of the bobbin 2.
Is inserted together with a paste obtained by mixing a glass 4 powder and a ceramics 5 powder with an appropriate solvent, and after bonding by firing, a metal wire 6 is wound around the surface and further coated with glass 7. As shown in the process diagram of FIG. 2, the connection between the bobbin 2 and the lead wire 3 of the heat generating resistor 1 is such that the glass 4 powder and the ceramics 5 powder are dispersed before firing, but when this is fired, the glass 4 melts. In this process, the ceramics 5 powder is dispersed in the glass and changes to a glass having a composition different from that of the initial glass 4. Further, in this process, the non-dispersed ceramic 5 powder becomes a nucleus, and a part of the glass is crystallized. This partial crystallization mechanism increases the viscosity of the glass and prevents the glass from flowing to the lead wires and the inner wall of the bobbin during firing.

As a combination of glass 4 powder and ceramics 5 powder necessary for partially crystallizing glass 4, lead borosilicate glass, lead glass, or zinc glass is used for glass 4.
The study was advanced by using alumina for the ceramics 5.

As a result, the average particle diameter of the alumina is in the range of 1 μm to 15 μm, although the ratio slightly varies depending on the firing conditions and the particle diameter of the alumina to be mixed in the partial crystallization. 30wt%
It turned out to be. FIG. 1 is a schematic view of a heating resistor manufactured by partial crystallization. In the case of this structure, the viscosity of the glass 4 melted during the firing process increases, so that the glass 4 hardly flows into the lead wire 3. Therefore, the stability of the shape of the heating resistor 1 can be improved, so that variations in responsiveness and heat radiation characteristics can be reduced.

Further, in the conventional product, if a minute crack is present in the glass 4, there is a phenomenon that the crack is developed by repeated stress of cold and heat or an external force in a practical state, and the characteristics are changed. However, according to the present example, it was found that even when a repeated stress or external force of cold and heat was applied, the growth rate of the crack was slow, and the progress of the crack was suppressed in the partially crystallized portion. That is, according to the present embodiment, it is possible to improve the reliability in a practical state.

As another example, as a result of studying partial crystallization by changing the type of ceramics 5 powder, similar results were obtained with zirconia powder. In this case also glass 4
The study was conducted using lead borosilicate glass, lead glass, and zinc glass.

As a result, for the partial crystallization, the firing conditions and the average particle size of zirconia to be mixed are in the range of 1 μm to 15 μm, and the ratio of alumina mixed with glass 4 is 5 watts.
It was found that the content was from 30% by weight to 30% by weight.

On the other hand, when a large number of heating resistors were manufactured in the above-described embodiment based on the partial crystallization, some of the lead wires 3 were found to cause the glass 4 to start flowing. According to the investigation, the lead wire 3 is inserted into both ends of the bobbin 2. Therefore, if both ends are closed with glass, the inside of the bobbin 2 becomes a sealed structure, and the air inside expands as the temperature rises during firing. Then, it was found that the glass 4 was pushed out.

Another embodiment invented to prevent this will be described below.

FIG. 3 is a schematic diagram in which the lead wire 3 is connected to the bobbin 2 according to the present embodiment. That is, the air permeability is improved by lowering the sintering density of the ceramic which is the material of the bobbin 2, and the internal air expansion accompanying the rise in temperature during firing is released from the bobbin. As a result of studying by changing the sintering density, it was found that when alumina was used as the material of the bobbin 2, the sintering density was effective at 85% or less. However, if the sintered density is 50% or less, the strength of the bobbin 2 cannot be obtained and is insufficient. Therefore, the optimum sintering density range of the bobbin 2 is set in the range of 50% to 85%.

According to this embodiment, the adhesive is ceramic 5
Even with ordinary glass 4 containing no powder, it is possible to reduce the flow of glass 4 into lead wire 3.

Further, by producing the heating resistor 1 in combination with the above-described embodiment based on partial crystallization, a greater effect can be expected.

FIG. 4 shows an example in which the heating resistor 1 is manufactured in this combination and the variation of the flow characteristics as a thermal air flow meter is measured. Fluctuation in flow characteristics is reduced by 2 /
It was confirmed that it could be reduced to 3 or less. It was also found that the effect was particularly large on the low flow rate side.

[0028]

According to the above-mentioned structure, the variation in the measurement accuracy of the flow rate can be reduced, and a great effect can be expected particularly on the low flow rate side. FIG. 4 shows a comparison with the conventional product.

[Brief description of the drawings]

FIG. 1 is a sectional view of a heating resistor according to the present invention.

FIG. 2 is a sectional view of the manufacturing process of FIG. 1;

FIG. 3 is a sectional view of a bobbin according to the present invention.

FIG. 4 is a view showing a characteristic variation measurement result of the thermal air flow meter according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating resistor, 2 ... Bobbin, 3 ... Lead wire, 4 ... Glass, 5 ... Ceramics, 6 ... Metal wire, 7 ... Glass coat.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/68

Claims (8)

(57) [Claims] 1. A heating resistor provided in an air passage and a current of the heating resistor are controlled as means for measuring an intake air flow rate of an electronic control fuel injection device of an internal combustion engine.
And a driving circuit for taking out the output voltage of the heating resistor as a signal corresponding to the air flow rate. In the thermal air flow meter, glass powder and ceramics are used as materials for bonding the bobbin and the lead wire of the heating resistor. A thermal air flow meter using a material mixed with powder. 2. The thermal air flow meter according to claim 1, wherein the ceramic powder is alumina, and the average particle size is in a range of 1 μm to 15 μm. 3. The thermal air flow meter according to claim 1, wherein the proportion of alumina mixed with the glass is 5 wt% to 30 wt%. 4. The thermal air flow meter according to claim 1, wherein the ceramic powder is zirconia, and the average particle size is in a range of 1 μm to 15 μm. 5. A thermal air flow meter according to claim 1, wherein the proportion of zirconia mixed with the glass is 5 wt% to 30 wt%. 6. A thermal air flow meter according to claim 6, wherein said heat generating resistor has a structure in which a lead wire is inserted into a bobbin, wherein porous alumina is used as a bobbin material. 7. The bobbin according to claim 6, wherein the bobbin has a sintered density of 5
A thermal air flow meter having a range of 0% to 85%. 8. The bobbin according to claim 1, wherein a material obtained by mixing glass powder and ceramic powder is used as a material for bonding the bobbin of the heat generating resistor and the lead wire, and the bobbin material is made of porous alumina. A thermal air flow meter characterized by using: