JP2925420B2 - Resistor element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistance element having a lead with improved durability, and a heat-sensitive flowmeter using the resistance element for detecting a flow rate or a flow velocity of a fluid in an internal combustion engine. The resistor element according to the present invention can be suitably used for a resistance thermometer.

[0002]

2. Description of the Related Art Conventionally, a resistor element has a thin film type in which a metal thin film is used for a metal resistor and a thin film is formed on the outer surface of a cylindrical body, and a thin metal wire is used for a metal resistor. A winding type is known.

[0003] The wound resistor element has a disadvantage that it is difficult to obtain a resistor element having a high resistance value.
In order to increase the resistance value, it is necessary to enlarge the cylindrical body or to make the platinum wire thin. However, when the cylindrical body is enlarged, the heat capacity increases, so that the response of the resistor element deteriorates. When the platinum wire is made thin, the platinum wire is easily broken, and it becomes difficult to wind the platinum wire around the tubular body. .

Therefore, in recent years, a thin film resistor element using a metal thin film instead of a platinum wire as a metal resistor has been used. In the case of the thin film type, the resistance value of the thin film resistor is adjusted from several ohms to 1000
Can be adjusted to ohms.

[0005] Any type of resistor element is suitably used as a detecting element for detecting the flow rate or flow velocity of a fluid. In such a case, the resistor element is made of stainless steel provided in the fluid. The leads at both ends are fixed to a conductive support such as by spot electric welding or the like. This conductive support is fixed to a resin or the like.

[0006]

However, when manufacturing such a resistor element, various stresses are applied to the lead during the step of inserting the lead into the cylindrical ceramic or other steps, and the lead may be damaged. May bend.
Then, the mechanical strength of the lead decreases. For such reasons, if the lead does not have sufficient mechanical strength, the resistor element is spot-welded to the conductive support, or the resistor element is used as a component of a thermal flow meter. For example, when a tensile stress is applied to the lead, the lead may be broken. Therefore, it is required to prevent such a decrease in mechanical strength of the lead and to improve the durability.

[0007]

Means for Solving the Problems As a result of intensive studies on this problem, the degree of decrease in mechanical strength of the lead caused by bending of the lead is determined by the grain size of the crystal grains on the lead surface, in particular, FIG. It has been found that it depends on the particle size in the axial direction and the vertical direction of the lead as shown in FIG.

That is, according to the present invention, a metal resistor is formed around the outer surface of the cylindrical electrical insulator, and the surface of the metal resistor is covered with a protective layer. The lead is inserted and fixed, and the metal resistor is a resistor element electrically connected to each of the leads. In the resistor element, the average value of the crystal grains on the surface of the lead in the axial direction and the perpendicular direction of the lead is obtained. Is 10 μm or less. In the present invention, it is preferable that the maximum value of the particle size is 10 μm or less. Further, in the present invention, it is preferable that the surface of the lead is made of platinum or an alloy containing platinum.

According to the present invention, the metal resistance of the resistor element detects a flow rate of the fluid, and measures the flow rate of the fluid based on a temperature-dependent resistance change of the metal resistance. Is provided.

[0010]

The degree of decrease in mechanical strength of a lead due to bending of a lead depends on the grain size of crystal grains on the surface of the lead, particularly, the grain size in the direction perpendicular to the axial direction of the lead, that is, the transverse grain size. I found to do. Therefore, when the average value of the lateral grain size of the crystal grains on the lead surface is set to 10 μm or less, the degree of such decrease in mechanical strength can be reduced.
Further, it is more preferable to set the maximum value of the transverse particle size to 10 μm.

As will be described later, the crystal grains on the lead surface often refer to crystal grains of platinum or an alloy containing platinum.

FIG. 2 shows a resistor element to which the present invention is applied.
And a wound-type resistor element as shown in FIG. Hereinafter, a method for manufacturing a resistor element to which the present invention is applied will be described. As a material of the tubular body 12, an electrically insulating ceramic such as alumina or quartz is preferably used. Those having an outer diameter of about 0.3 to 1 mm are practically preferable. The length is preferably about 2 mm.

A method of manufacturing a thin-film resistor element as shown in FIG. 2 is performed by forming a cylindrical body 12 of ceramics or the like by a known method such as sputtering, physical vapor deposition (PVD), chemical vapor deposition (CVD), or plating. A metal thin film is formed. The metal thin film does not necessarily have to adhere to the surface of the cylindrical body, and an intermediate layer made of glass or the like may be interposed between the cylindrical body 12 and the metal thin film 18.

Next, this metal thin film is formed into an appropriate shape such as a spiral shape or a meandering shape by laser trimming or the like to obtain a thin film resistor having a specific resistance value. The metal is preferably platinum or an alloy containing platinum. The thickness of the thin film is preferably from 0.2 to 1.5 μm. By adjusting the thickness of the thin film and, for example, the spiral pitch, the resistance value of the thin film resistor can be adjusted from several ohms to 1000 ohms.

The step of inserting the lead into the cylindrical body 12 may be performed before the final glass coating step, and before the thin film forming step.
It may be performed at any time between the thin film forming step and the trimming step and between the trimming step and the glass coating step.

The lead 14 is a metal wire having a diameter of about 0.15 mm, and specifically, a platinum wire, a platinum alloy wire, a stainless steel or FeNi alloy wire coated with a platinum film, or the like is used. The leads 14 inserted at both ends of the tubular body 12 are adhered and fixed using a conductive adhesive such as a mixed paste of platinum and glass. Thus,
The conductive adhesive forms an adhesive portion 16 that electrically connects the lead 14 and the platinum thin film 18.

The use of a conductive adhesive is not essential, and the tubular body 12 and the lead 14 are fixed with an adhesive having no conductivity, and the lead 14 and the platinum thin film 18 are fixed.
May be electrically connected by applying a conductive paste.

Finally, a protective layer 19 made of glass or the like is formed so as to cover the metal thin film 18 formed around the cylindrical body 12 and the electrical connection portion 16. For example, a powder of lead borosilicate glass is used as a slurry, and the slurry is adhered to the surface of the cylindrical body 12 by dipping, blade coating, spray coating or the like. After the slurry attached to the surface is dried and fired, the protective layer 19 is formed.

The method of manufacturing the wound resistor element as shown in FIG. 3 is basically the same as the method of manufacturing the thin film resistor element. However, the difference is that instead of forming a metal thin film, a highly conductive wire 18 ′ such as a platinum wire is wound around the cylindrical body 12, and the wire 18 ′ is connected to the lead 14 by welding. In the wound resistor element, the bonding portion 16 does not need to be conductive. For example, a diameter of 0.5 mm and a length of 2 m
3 mm platinum wire with a diameter of 20 μm on a cylindrical alumina bobbin
Winding at a pitch of 5 μm results in a resistance of about 20 ohms.

Such a resistor element can be used as a detection element of a thermal flow meter. The thermal type flowmeter controls the temperature of the heating resistor, the temperature compensation resistor that senses the fluid temperature, and the output of this heating resistor corresponding to the fluid flow rate. And a drive circuit for extracting the signal as a converted signal. FIG. 4 shows a circuit diagram of a drive circuit of the thermal flow meter. In general, a thermal flow meter is provided with a pair of two resistor elements, one of which is a fluid temperature compensating element 21 and the other is a heating element 22, which is disposed in a fluid flow passage 24 through which a fluid to be measured passes. Have been. The temperature compensation element 21 and the heating element 22 form a bridge together with the other resistors 30 and 32. The temperature compensating element 21 is set to have the same temperature as the fluid to be measured, while the temperature of the heating element 22 is higher than the temperature compensating element 21 by a predetermined temperature of about 100 to 200 ° C. Feedback control is performed by the differential amplifier 26. At this time, a minute current with negligible heat generation is allowed to flow through the temperature compensating element 21 so as to compensate the amount of heat generated by the heat generating element 22 with the temperature of the fluid to be measured.

Under such an energization control,
When the air flow rate changes, the current amount of the heating element 22 and the resistor 30 connected in series to the heating element 22 changes. Therefore, the power required to heat the heating element 22 depends on the amount of current flowing through the heating element 22 or the amount of current flowing through the resistor 30 as shown in the drawing, that is, the amount of current output between the output terminals 28. Understandably, and thus, the amount and velocity of the fluid passed through the fluid passage 24 can be calculated and measured. In such a thermal flow meter, the pair of leads 14 of the resistor element 10 are supported by a pair of conductive supports protruding from the wall of the insulating member forming the fluid flow path.
Such a resistor element 10 is stretched over a pair of conductive supports, and the resistor element 10 is disposed in the fluid flow path. That is,
The resistor element is fixed to a conductive support made of stainless steel or the like by a welded portion in which leads at both ends are spot-welded. The conductive support is fixed to an insulating member such as a resin. It is preferable that the fluid passage 24 be provided separately from the main fluid passage.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. However, the present invention is not limited by the following examples.

(Examples 1 to 4, Comparative Example 1) [Method of Manufacturing Resistor Element] First, as a method of manufacturing a lead,
A 50 mm Ni-Fe alloy round bar having a diameter of 2 mm was inserted into a platinum pipe having a predetermined size, and then passed through a die to prepare a 5 mm thick platinum-coated wire having a diameter of 0.15 mm. This wire was heat-treated at the annealing temperature and time shown in Table 1. As a result, the average value of the grain size of the crystal grains on the surface of the wire in the direction perpendicular to the direction of the wire was as shown in Table 1. In addition, as such an average value, on a scanning electron microscope photograph, in the center part of the lead wire, the grain size of each of five crystal grains arranged in the axial direction of the lead wire in the direction perpendicular to the lead wire axial direction was obtained. The maximum diameter was measured, and the average value of the five was adopted. This wire was cut so as to have a length of 20 mm, and platinum-clad NiFe alloy leads having different lateral grain sizes of platinum crystal grains on the surface were prepared.

An alumina pipe having an outer diameter of 0.5 mm, an inner diameter of 0.22 mm, and a length of 2 mm was used as the cylindrical body 12, and a platinum thin film having a thickness of 0.4 μm was formed on the outer surface thereof by a known sputtering method. Next, the platinum thin film is spirally trimmed with a laser to obtain a resistance value of 20.
The platinum thin film 18 was formed so as to become ohmic. Then, a lead having a diameter of 0.15 mm manufactured as described above was inserted into both ends of the bobbin on which the platinum thin film 18 was formed, and bonded with a platinum-based adhesive composed of 60% by volume of platinum and 40% by volume of glass. This was fired in air at 600 ° C. for 10 minutes to fix the lead and the bobbin. A glass having a melting point of about 580 ° C. is applied to the bobbin portion of this element precursor,
The protective layer was formed by baking in air at 580 ° C. for 5 minutes to obtain a resistor element 10.

[Test Method for Resistor Element] The lead 14 of the resistor element 10 thus obtained is parallel to the axial direction of the cylindrical body 12.
Was first bent 90 degrees and then returned to the original parallel direction.
Then, a 700 g weight is applied to the resistor
A g-weight tensile load was applied to determine whether the lead 14 would break. For each of the annealing conditions, this test was performed with 10 resistor elements, and the number of broken elements is summarized in Table 1.

[0026]

[Table 1]

(Examples 5 to 8, Comparative Example 2) Examples 1 to 4
From Comparative Example 1, the thickness of the platinum film of the lead 14 was 5 μm.
m was changed to 10 μm, and other than that, the same lead as the above example was prepared including the annealing conditions. That is, a lead of a platinum-clad NiFe alloy having a diameter of 0.15 μm and a thickness of a platinum coating of 10 μm was prepared. Using this lead, a resistor element was prepared in the same manner as described above, and the same breaking test was performed. Table 2 summarizes the annealing conditions, the lateral grain size of the surface crystal grains, and the number of elements whose leads were broken in the breaking test.

[0028]

[Table 2]

(Examples 9 to 12, Comparative Example 3)
4 and Comparative Example 1, the lead diameter was changed from 0.15 mm to 0.2 mm, and other than that, the same lead as that of the above example was prepared including the annealing conditions. That is, a lead of a platinum-clad NiFe alloy having a diameter of 0.2 μm and a thickness of a platinum coating of 5 μm was prepared. Using this lead, a resistor element was prepared in the same manner as described above, and the same breaking test was performed. Table 3 summarizes the annealing conditions, the lateral grain size of the surface crystal grains, and the number of elements whose leads were broken in the breaking test.

[0030]

[Table 3]

[0031]

As described above, in the resistor element according to the present invention, since the average value of the crystal grains on the surface of the lead in the direction perpendicular to the axial direction of the lead is 10 μm or less, the lead is bent. Thus, a decrease in mechanical strength due to this can be reduced, and the durability of the resistor element can be improved. Further, by using such a resistor element as a detection element of a thermal flowmeter, the durability of the detection element can be improved.

[Brief description of the drawings]

FIG. 1 is a conceptual explanatory diagram of crystal grains on a lead surface.

FIG. 2 is a longitudinal sectional view showing a specific example of a thin film resistor element to which the present invention is applied.

FIG. 3 is a longitudinal sectional view showing a specific example of a wound thin resistor element to which the present invention is applied.

FIG. 4 is a circuit diagram of a drive circuit of a thermal flow meter to which the present invention is applied.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lead surface 2 Crystal grain 3 Grain size (lateral grain size) in the direction perpendicular to the axial direction of the lead 4 Axial direction of the lead 5 Lead center 10 Resistor element 12 Cylindrical body 14 Lead 16 Adhesive part 18 Metal thin film 18 'metal Thin wire 19 Protective layer 20 Drive circuit 21 Temperature compensation element 22 Heating element 26 Differential amplifier 28 Output terminal 30 Resistance 32 Resistance

──────────────────────────────────────────────────続 き Continuation of front page (51) Int.Cl. ⁶ identification code FI H01C 17/00 H01C 17/00 L (58) Fields investigated (Int.Cl. ⁶ , DB name) H01C 7/00 G01F 1 / 68 G01K 7/18 G01P 5/12 H01C 1/14 H01C 17/00

Claims (4)

(57) [Claims] 1. A metal resistor is formed around an outer surface of a tubular electrical insulator, and a surface of the metal resistor is covered with a protective layer.
Leads are inserted and fixed to both ends of the cylindrical electrical insulator, respectively, and the metal resistor is a resistor element electrically connected to each of the leads. A resistor element, wherein an average value of particle diameters in a direction perpendicular to the direction is 10 μm or less. 2. The resistor element according to claim 1, wherein the maximum value of the particle size is 10 μm or less. 3. The resistor element according to claim 1, wherein the surface of the lead is made of platinum or an alloy containing platinum. 4. The method according to claim 1, wherein the metal resistor of the resistor element detects a flow rate of the fluid, and measures the flow rate of the fluid based on a temperature-dependent resistance change of the metal resistor. A heat-sensitive flow meter.