JPH0687022B2 - Hot wire air flow sensor and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hot-wire air flow sensor used for detecting the intake air amount of an automobile internal combustion engine and a method for manufacturing the same.

[Conventional technology]

A heating wire type air flow meter uses a heating resistor as a sensor, and by placing this heating resistor in an air flow, the air flow rate is measured. That is, by utilizing the fact that the radiant heat quantity of the heating resistor changes depending on the air flow rate, the current is changed so as to keep the temperature of the heating resistor constant according to the change of the air flow rate, and this current is detected. The air flow rate is indirectly measured. Since such an air flow meter has no moving parts and can directly measure the air flow rate, it is widely used for controlling the air-fuel ratio of an internal combustion engine of a vehicle.

As a heat generating resistor in the hot wire air flow sensor, for example, as described in Japanese Utility Model Publication No. 56-96326, an extremely thin metal wire such as platinum having a diameter of several tens of microns is wound around a bobbin such as ceramics. There is a rotating bobbin type.

Further, as described in JP-A-62-83622, there is also known a bobbin-less type in which a metal wire to be a heating resistor is wound around a metal core wire, glass-coated, and then the metal core wire is etched away with an acid. Has been.

[Problems to be Solved by the Invention]

In the bobbin type, the heat that heats the bobbin itself and the amount of heat that is transferred to the bobbin and transferred to the support cannot be ignored, and since the transient response is particularly delayed with respect to changes in the air flow rate, surging during sudden acceleration and deceleration of the vehicle There was a problem that it occurred.

On the other hand, in the bobbin-less type, there is no bobbin, so the responsiveness is excellent. However, the work of etching away the metal core wire around which the metal wire is wound with acid after firing the coated glass is complicated. In addition, since the glass surface is roughened by etching with an acid when removing the metal core wire, dust and ionic substances in the air adhere to the glass in the use environment to change the characteristics, which causes a problem of lowering reliability. It was

An object of the present invention is to solve these conventional problems and to improve the responsiveness, but also to simplify the manufacturing by eliminating the need for etching, and to improve the reliability. There is a way to provide.

[Means for Solving the Problems]

To achieve the above object, the present invention has an outer layer of glass having a softening point of 800 ° C. or higher, an inner layer covering a cavity with ceramics or a composite of glass and ceramics, and both ends of the coil electrically drawn to the outside. The metal wire is shaped like a wire and is embedded in the inner wall surface of the cavity.

Among the above constituent members, the ceramics are Al ₂ O ₃ , SiO ₂ , SiC, MgO.
Al ₂ O ₃ is mentioned as a typical example of the above, but it is possible to use any ceramics other than Al ₂ O ₃ . Further, a composite member of glass and alumina formed by permeating the outer layer glass member into the inner layer alumina or alumina-glass mixed member retains sufficient strength, and obtains a pre-heat wire type air flow sensor with high dimensional accuracy. Therefore, the alumina contained in the composite member has a volume ratio of 30 to 70%.

Furthermore, the present invention is a sublimable core wire, for example, molybdenum (Mo) core wire winding a metal wire of a heating resistor, and removing the lead-out portion of both ends of the wound wire, the surface of the wire Alumina or a mixture of alumina and glass is made porous in the inner layer, and a glass member having a softening point higher than the sublimation temperature of molybdenum of 800 ° C or more is attached to the outer layer in a porous state. The step of covering and heating these, first sublimate and remove the molybdenum core wire in a state where the glass member of the outer layer does not lose the porosity, and then heat it to a temperature at which the glass member of the outer layer flows or higher, and then the glass of the outer layer part The number of steps in which the member permeates into the porous alumina or the mixed member of alumina and glass having porosity in the inner layer part to perform two-step firing in which glass and alumina are composited in one heat treatment is reduced. It is obtained as also comprises. In the present specification, glass means a crystalline substance, and ceramics means a crystalline substance.

[Work]

In the present invention, the metal wire of the heating resistor is wound in a coil shape on a molybdenum core wire having sublimability, and a metal lead wire serving as an electrical outlet is welded to the tip end portion of alumina or alumina and glass in the inner layer. The mixed member is integrated by firing after adhering a glass member having a softening point of 800 ° C or more to the outer layer, but since the molybdenum core wire is conductive and short-circuits between the lead wires, first the temperature is 800 ° C. After heating to remove the molybdenum core wire by sublimation, the temperature is raised to a temperature at which the glass member of the outer layer flows, and the glass member of the outer layer is permeated into alumina or the alumina-glass mixed member of the inner layer, and the inner layer is made of glass. And a two-step firing to form a composite member of alumina. Therefore, the glass member attached to the outer layer does not hinder the sublimation removal of the molybdenum core wire,
It is necessary to maintain sufficient porosity during the sublimation and evaporation of molybdenum, and the softening point is 800 ° C, which is higher than the sublimation temperature of molybdenum.
It is necessary to have the above characteristics.

For example, a platinum wire having high heat resistance and high corrosion resistance is used as the metal wire, and a platinum iridium alloy is used for the lead wire. In addition, molybdenum oxidizes at high temperature and sublimes at about 795 ° C, but when subliming the molybdenum core wire, sufficient oxygen is replenished to prevent sublimation volatilization and volatilization. It is necessary that the member and the glass member of the outer layer have sufficient voids. When sublimating and removing this molybdenum core wire, if the outer layer glass member flows at a temperature lower than the sublimation temperature of molybdenum, it will cover the surface before sublimation of molybdenum, and the core wire will remain inside. . Further, even if the glass of the outer layer does not flow at a temperature lower than the sublimation temperature of molybdenum, those having a characteristic that the softening point is lower than the sublimation temperature of molybdenum have a low fluidity due to the influence of sublimed molybdenum oxide, Alternatively, the permeation into the mixed member of alumina and glass becomes insufficient, and the dense composite layer of glass and alumina cannot be provided. Therefore, if the glass having a softening point of 800 ° C. or more is attached as an outer layer, the effect of molybdenum oxide that sublimes is small, and the glass penetrates into the voids of the alumina or the alumina-glass mixed member after the sublimation removal of the molybdenum core wire. A dense composite layer of glass and alumina can be obtained by a single heat treatment. Therefore, the etching step for removing the core wire is not required, and the work can be simplified. Further, it is possible to solve the problem of reliability deterioration due to etching roughness.

Here, when metal lead wires are welded to both ends of a metal wire wound around a sublimable molybdenum core wire and only a glass member is adhered to the surface, the molybdenum core wire melts the hollow portion after being removed by sublimation. Not only is the glass member buried, but the surface of the glass is strong, and the metal wire wound into a coil contracts and deforms. However, if an alumina member or a mixture member of alumina and glass is adhered to the inner layer and a glass member is adhered to the outer layer, the alumina serves as a skeleton and the glass is immersed, so that a dense composite member of glass and alumina can be obtained. it can.

In addition, when only one layer of glass and alumina mixed member is adhered and fired to obtain a composite member, since the voids are filled with softened and fluidized glass to densify, a composite of the premixed glass member is used for compounding. This is not preferable because it causes contraction of the member, which makes it difficult to control the dimensions and causes variations in the sensor characteristics due to changes in the coiled metal shape and dimensions. Therefore, alumina or a mixture of alumina and glass is adhered to the inner layer, and a glass member is adhered to the outer layer and fired. However, if the volume ratio of the adhered alumina member is high, the permeability of the glass member into the alumina member is poor, and the obtained composite is obtained. The member has low strength. Further, when the volume ratio of the alumina member is low, the permeability of the glass member into the alumina member is good, but the ratio of the glass member in the obtained composite member is high, and as described above, the shape of the coiled metal wire due to contraction and It causes dimensional changes. As a result of experimental examination, if the volume ratio of the alumina to be composited with the glass is 70 to 30%, the permeability to the alumina or alumina / glass mixed member adhered to the inner layer of the glass member adhered to the outer layer is good. It was confirmed that a heat wire type air flow rate sensor having a glass / alumina composite member having a necessary and sufficient strength as an inner layer and an outer layer covered with glass was obtained with high accuracy.

Here, one of the methods for adhering glass, alumina, or a mixture of alumina and glass is electrophoretic deposition (electrodeposition). Aluminum nitrate and magnesium nitrate are used as electrolytes, and ethyl alcohol is used as an organic solvent. There is a suspension used. Of course other electrolytes,
Electrodeposition is possible even if an organic solvent is used, and therefore the present invention is not limited thereto. However, the above-mentioned suspension of aluminum nitrate, magnesium nitrate, and ethyl alcohol is easy to handle in the production of the hot-wire air flow sensor according to the present invention. In this way, when glass powder is suspended in a solution of aluminum nitrate and magnesium nitrate, the glass components are eluted and the electrodeposition solution becomes unstable,
The electrodeposition layer becomes non-uniform. Therefore, from the viewpoint of controlling the electrodeposition liquid, it is necessary to select a glass having high stability as the glass to be mixed with alumina.

For example, in the case of trying to obtain a hot wire type air flow rate sensor composed of a glass member having a softening point lower than the sublimation temperature of molybdenum in the outer layer and a softening point in the inner layer composed of glass and alumina lower than the sublimation temperature of molybdenum, As described above, a glass member having a softening point lower than the sublimation temperature of molybdenum reacts with sublimed molybdenum, loses its original properties, and its fluidity is significantly reduced, resulting in insufficient penetration into the inner-layer alumina voids. . Therefore, the inner layer of alumina or a mixed member of alumina and glass is electrodeposited and fired, after removing the molybdenum core wire, glass is attached to the outer layer and fired again,
Two heat treatments are required to fully permeate the glass of the outer layer into the voids of the alumina of the inner layer to form a composite of alumina and the glass member. According to this method, handling strength is required so that glass adheres to the inner layer portion of the first heat treatment. When the inner layer portion is a single layer of alumina, the firing temperature is lower than the sintering temperature of alumina, so the strength after removal of the molybdenum core wire by sublimation is low. Therefore, the glass / alumina mixed member is electrodeposited on the inner layer to increase the strength after firing once, but as described above, the glass / alumina mixed electrodeposition liquid is unstable.

According to the present invention, the molybdenum core wire is removed by sublimation and the glass member of the outer layer permeates into the voids of the alumina member of the inner layer to form a composite of alumina and the glass member in a single heat treatment. But it doesn't matter at all. Therefore, a highly stable electrodeposition liquid in which powder of only alumina is suspended can be used, and the workability is high because the electrodeposition liquid can be easily managed. Of course, even if the inner layer to be electrodeposited is a mixed member of glass and alumina, it is possible to obtain a hot wire type air flow sensor with high strength and high accuracy.

In the hot wire type air flow rate sensor thus obtained, most of the heat generated by energizing the metal wire is not transferred to the bobbin and escaped to the support unlike the conventional bobbin type, but is transferred to the air. Therefore, the high responsiveness peculiar to the bobbinless method can be obtained. In addition, since it has a softening point of 800 ° C or higher and is coated with glass that has excellent corrosion resistance and thermal shock resistance, it does not deteriorate the sensor performance depending on the operating environment. An air flow meter is obtained.

Therefore, an embodiment of the present invention will be described with reference to the drawings.

[Embodiment 1] FIG. 1 is a partially cutaway sectional view showing an embodiment of a hot wire type air flow sensor of the present invention.

In FIG. 1, the hot wire air flow sensor 1 is a heating resistor by passing an electric current through a platinum wire 2 having a coil shape. The platinum wire 2 is wound in a coil shape with the axial center line of the hollow portion 6 substantially as the center, and the lead wires 3 of a platinum iridium alloy are connected to the both ends of the platinum wire 2 at connection portions 21. The cavity 6 has a structure in which it is sealed by a glass member 5 as an outer layer and a composite member 4 of glass and alumina as an inner layer, and the lead wire 3 is supported by the glass member 5 and the composite member 4. Also, platinum wire 2
Are arranged so as to be embedded in the inner wall surface of the composite member 4 of the inner layer of glass and alumina, so that the platinum wire 2 is firmly supported by the composite member 4.

Next, a method of manufacturing the hot wire air flow sensor 1 will be described with reference to FIG.

First, as shown in FIG. 2 (a), the platinum wire 2 is spirally wound around the molybdenum core wire 7 by an automatic winding machine. In this embodiment, a platinum wire 2 having a diameter of 30 μm is used.
It was wound around a 0.5 mm molybdenum core wire 7. Next, as shown in FIG. 2B, the molybdenum core wire 7 is cut into a predetermined length (4 mm in this embodiment), and the lead wires 3 of platinum iridium alloy are connected to both ends of the platinum wire 2. Part 21
Weld with. In this case, the lead wire 3 has a diameter of 0.13
The thing of mm was used.

After this, the alumina member is filled around the molybdenum core wire 7 around which the platinum wire 2 is wound by an electrophoresis method so that the filling rate is about 50%.
And the glass member was further adhered to the upper surface by the dipping method. Then, by baking the thus obtained material in an oxidizing atmosphere furnace, the molybdenum core wire 7 was sublimated and removed to form the cavity 6, as shown in FIG. 2 (c). Also, two layers of the composite member 4 of alumina and glass and the glass member 5 could be formed around the cavity 6.

The glass member 5 used here is an Al ₂ O ₃ —SiO ₂ -based glass, and has characteristics of a viscosity of 10 ²⁶ poise at a temperature of 860 ° C. and a viscosity of 10 ⁴ poise at 1180 ° C. Then, in the firing of FIG. 2 (c), as the temperature rises, the molybdenum core wire 7
Oxidation progresses to MoO ₃ , and when the temperature reaches 795 ℃, it becomes MoO ₃ .
₃ sublimates, but the glass member 5 having a viscosity of 10 ^7.6 poise at a temperature of 860 ° C., that is, a softening point of 860 ° C. retains voids. Therefore, the sublimate of MoO ₃ is a void of the alumina member and the glass member 5. Volatilize from. When the temperature reaches 1200 ° C after the molybdenum core wire is maintained at 850 ° C for 5 hours to complete the sublimation removal, the viscosity of the glass member 5 becomes 10 ₄ poise or less and begins to permeate into the voids of the alumina member. Although the firing was completed after holding for 2 hours, the glass member 5 completely penetrated into the voids of the alumina member to form the dense glass / alumina composite member 4 and the hot wire air flow sensor covered with the glass member 5. Got 1. This hot wire type air flow sensor 1
As shown in the enlarged view of FIG. 2D, since the glass member 5 covers the inside of the platinum wire 2 wound in a coil, the platinum wire 2 can be more firmly supported. .

According to this method, as compared with the conventional bobbinless method, a complicated work for removing the core wire by etching is eliminated, and the sublimation of the metal core wire 7 having sublimability and the combination of the glass member 5 and the alumina member are combined. Since it can be fired once, workability is greatly improved.

A specific example of a hot-wire air flow meter using this hot-wire air flow sensor 1 is shown in FIG. In this specific example, the same one as the hot-wire air flow sensor 1 is used as the resistance temperature detector 8 for air temperature measurement. Hot wire type air flow sensor 1
The resistance temperature detector 8 is fixed to a support 9 in a bypass passage 82 of a body 83 having a main passage 81 for intake air and a bypass passage 82 as shown in FIG.

FIG. 4 shows a specific example of the detection circuit of the hot-wire air flow meter, which includes a hot-wire air flow sensor 1, a resistance temperature detector 8, and operational amplifiers 10,1.
1, power transistor 12, capacitor 13, resistors 14 ~ 1
It is composed of 8. The (+) pole of the battery (not shown) is connected to the collector terminal 19 of the power transistor 12.
The negative terminal of the battery is connected to the ground terminal 20 of the resistor 14, and the connection point between the resistor 14 and the hot wire air flow sensor 1
The input terminals of a microcomputer (not shown) for controlling the engine using the output signal of the present hot wire air flow meter are connected to 31.

In such a configuration, the power transistor 12 supplies an electric current to the hot-wire air flow sensor 1 to heat it, and controls so that the temperature is always higher than the resistance temperature detector 8 by a constant temperature. Only a small amount of current that allows heat generation to be ignored is passed through the resistance temperature detector 8, and the temperature of the intake air is detected by this, which is used for correcting the temperature of the intake air. When the air flow hits the hot-wire air flow sensor 1, the temperature difference between the hot-wire air flow sensor 1 and the resistance temperature detector 8 is controlled to be always constant by the operation of the detection circuit. Therefore, when the air flow rate changes, the current flowing through the hot wire type air flow rate sensor 1 changes, and the air flow rate is measured by the voltage drop appearing in the resistor 14 according to the current.

FIG. 5 shows the response characteristics of the hot-wire air flow meter of this embodiment. The voltage of the hot-wire type air flow meter was measured when the air flow rate was switched from a low flow rate of about 20 kg / h to a high flow rate of about 200 kg / h, and the voltage was converted to a flow rate and shown on the vertical axis. As is clear from the figure, the final value arrival time is significantly improved as compared with the conventional bobbin type, and it is understood that it is equivalent to the conventional bobbinless type.

Therefore, even when the vehicle is suddenly accelerated or decelerated, the hot-wire air flow meter outputs a signal in accordance with the true change in the air amount, so that the appropriate injection amount of the injector can be determined and the surging problem can be solved. .

The improved responsiveness is that the heat generated in the platinum wire 2 of the hot-wire air flow sensor 1 does not heat the bobbin or travel through the bobbin and escape to the support unlike the conventional bobbin type. , Because it reacts accurately to changes in the amount of air.

Further, the hot wire air flow meter of this embodiment has higher reliability than the conventional bobbinless type. This is because the hot-wire air flow sensor of this embodiment is coated with glass having excellent characteristics of corrosion resistance and thermal shock resistance, so that it has good environmental resistance against air during use and This is because the glass surface was roughened by the acid etching in the bobbinless method, but the surface is smooth in this embodiment.

[Example 2] In the same manner as in Example 1, a platinum wire 2 having a diameter of 30 µm was wound around a molybdenum core wire 7 having a diameter of 0.5 mm by an automatic winding machine, and both ends were cut into a length of 4 mm for one sensor. The lead wire 3 of platinum iridium alloy with a diameter of 0.13 mm is welded at 21, and the filling rate of the mixed member of alumina and glass is about 50 by the electrophoresis method.
% So that the glass member 5 was further attached by the dipping method. Here, the mixing member is 20% glass and 80% alumina.
However, this glass member is made of Al ₂ O ₃ -SiO ₂ glass having a viscosity of 10 ^7.6 poise at a temperature of 860 ° C and a viscosity of 10 ⁴ poise at 1180 ° C. The same member as the member 5 was used. When these are fired in an oxidizing atmosphere furnace, the molybdenum core wire 7 is oxidized to become MoO ₃ , and when the temperature exceeds 795 ° C., MoO ₃ is sublimated and removed. After holding at 850 ℃ for 5 hours to complete the sublimation removal of molybdenum core wire, 12
The firing was completed by holding at 00 ° C. for 2 hours. However, since the glass member in the mixed member of alumina and glass facilitates the permeation of the glass member 5 of the same member, it is as dense as or more fine than that obtained in Example 1. A hot wire air flow sensor 1 was obtained in which the composite member 4 of alumina and glass was formed and the surface was covered with a smooth glass member.

When the characteristics of the hot wire air flow meter using this hot wire air flow sensor were measured, the same results as those described in Example 1 were obtained.

Example 3 Hereinafter, the glass member and the ceramic member shown in FIG. 1 were carried out by using glass members having various compositions and various kinds of ceramic members, and those glass members had a softening point of 800 ° C. or higher. And has a volume ratio of ceramics of a composite member obtained by infiltrating glass into a ceramic member or a mixed member of ceramics and glass.
If it is up to 70%, the hot wire air flow sensor 1 shown in FIG.
I was able to get

In the present embodiment, the ceramic member or the mixed member of ceramics and glass is attached by the electrophoresis method or the glass member 5 by the permeation method. However, other than the electrophoresis method or the permeation method, for example, they are attached in a paste form. Even by the way
The hot wire air flow sensor 1 shown in FIG. 1 can be obtained.

Therefore, the present invention can be applied to all glass members having the characteristics described in the present invention, and ceramic members or ceramic-glass composite members having the characteristics described in the present invention, other than those described in the examples. The method can be applied to any method of obtaining a heating resistor by coating with a method other than the electrophoresis method.

〔The invention's effect〕

As is clear from the above description, according to the hot-wire air flow sensor of the present invention, since the surface is coated with glass excellent in corrosion resistance and impact resistance, dust in the air, ionic substances, etc. High reliability can be maintained without deterioration of characteristics. Further, since the inside is hollow, it is possible to obtain high responsiveness equivalent to that of the conventional bobbinless system.

Further, according to the manufacturing method of the present invention, not only the complicated etching work with acid is not required, but the sublimation of the metal core wire having sublimability and the compounding of glass and ceramics are performed in one firing. Therefore, the workability can be greatly improved.

[Brief description of drawings]

FIG. 1 is a partially cutaway sectional view showing an embodiment of a hot wire type air flow sensor of the present invention, and FIGS. 2 (a), (b), (c),
(D) is a process drawing showing an embodiment of a method for manufacturing a hot-wire air flow sensor according to the present invention, and FIG. 3 is a configuration diagram showing a specific example of a hot-wire air flow meter using the hot-wire air flow sensor,
FIG. 4 is a circuit diagram showing a specific example of the detection circuit of the air flow meter, and FIG. 5 is a characteristic diagram showing response characteristics in comparison between the conventional and the present invention. 1 ... Hot wire type air flow sensor, 2 ... Platinum wire, 3 ...
... Lead wire, 4 ... Composite member, 5 ... Glass member, 6 ...
… Cavity, 7 …… Molybdenum core wire.

Claims (3)

[Claims] 1. A coil-shaped metal wire in which an outer layer covers glass with a softening point of 800 ° C. or higher, an inner layer covers ceramics or a composite of glass and ceramics, and both ends are electrically drawn to the outside. A hot-wire air flow sensor, wherein the hot-wire air flow sensor is arranged so as to be embedded in the inner wall surface of the cavity. 2. The ceramic contained in the inner layer is 30 to
The hot wire air flow sensor according to claim 1, having a volume ratio of 70%. 3. A process of winding a metal wire around a sublimable metal core wire, wherein ceramics or a mixed member of ceramics and glass is adhered to the metal core wire wound around the metal wire, and further a glass member is formed on the surface thereof. A step of adhering and covering, by firing the thus obtained, the metal core wire is removed by sublimation, and at the same time, the glass member is permeated into a gap between the ceramics or the ceramic-glass mixing member to form a composite. A method of manufacturing a hot-wire air flow sensor, comprising the step of: