JP2530988B2 - Thermal 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 type flow meter, and more particularly to a thermal type flow meter using a temperature sensitive resistor.

[0002]

2. Description of the Related Art An air flow meter (hereinafter referred to as AFM) using a temperature sensitive resistor is used for controlling an internal combustion engine having a fuel injection device capable of quickly and accurately responding to control of high horsepower, low fuel consumption, exhaust gas and the like. Has been. In such a thermal type flow meter, for example, as shown in JP-A-55-43448, a φ0.5 mm alumina bobbin is wound with a φ20 μm fine platinum wire, and glass is over - coated on the wound wire. Temperature-sensitive resistor (hereinafter referred to as HW) that uses a linear resistor as a heating resistor
Was used.

[0003]

4 and 5 show the structure of a conventional HW, FIG. 4 is a perspective view, and FIG. 5 is an X of FIG.
The sectional view of the part is shown. In these figures, 1 is an alumina pipe, 2 is a lead, 3 is a platinum thin wire, and 4 is glass. However, since the HW is a thin wire, the HW often breaks due to fluctuations in tension during winding and frictional forces at the time of winding up and down the end of the alumina bobbin, which significantly impairs mass productivity and is expensive.

Further, as the demand for turbocharged vehicles has increased in recent years, the range of intake air flow rate of vehicles has also increased,
It has become necessary to improve the accuracy of AFM flow rate measurement.

The present invention makes it possible to provide an inexpensive thermal type flow meter using a highly sensitive temperature sensitive resistor against such a situation.

[0006]

In order to solve the above-mentioned problems, the structure of the present invention is as follows: (1) Leads are inserted into both ends of a cylindrical body, and both ends are connected to each of the leads. In a thermal type flow meter in which a heating resistor is disposed on the cylindrical body, and the heating resistor is covered with glass, and the temperature sensing resistor is a component of a bridge, the temperature sensing resistor is outside the cylindrical body. made of a platinum thin film deposited in a spiral shape, and platinum thin film is deposited on the entire surface except the inner peripheral center portion of the cylindrical body to the surface
It is characterized by having a structure . (2) In (1), the cylindrical body is made of alumina.
It is characterized by

(3) Leads are provided on both ends of the cylindrical body, respectively.
Inserted and connected to each of the leads at both ends
A heat resistor is arranged on the cylindrical body, and the heat resistor is
Temperature-sensitive resistor made coated with La Graphics and components of Buritsuji
In the thermal type flow meter, the temperature-sensitive resistor is the cylindrical body.
Consisting of a platinum thin film spirally deposited on the outer surface,
Platinum thin film in both end faces of the cylinder and both ends of the cylinder
The platinum paste present between the circumference and the lead and
Both ends of the cylinder overlap to form a unitary structure
It is characterized by (4) In (3), the cylindrical body is made of alumina.
The thermal type flow meter according to claim 3, wherein:

[0008]

[Action] thermal flow meter of the present invention, the temperature sensitive resistor constituting the Buritsuji is becomes more spirally consists platinum film was deposited heating resistor to the cylindrical outside surface of the platinum thin film cylinder For the structure that is attached to the entire surface except the center of the inner circumference
Therefore, the platinum thin film and the lead are connected on both sides of the cylindrical body.
It was electrically connected to both the inner circumference and both end faces of the cylinder.
Therefore, the risk of poor contact and disconnection can be greatly reduced. What
On the outer surface of the cylindrical body,
It consists of a platinum thin film deposited in a spiral shape and is a heating resistor.
This platinum thin film is used on both end faces of the cylinder and on the cylinder.
Integrated with the platinum paste formed on the inner circumference of the end
Even in the case of the structure, the lead and the heating resistor can be reliably electrically connected, so that a product excellent in terms of manufacturing and performance can be provided.

[0009]

EXAMPLES Examples will be described below.

1 and 2 show the structure of a temperature sensitive resistor used in a thermal type flow meter of one embodiment. FIG. 1 is a perspective view and FIG. 2 is a sectional view of a Y portion of FIG. FIG. 3 is an explanatory diagram of the structure of the AFM in which the temperature sensitive resistor of FIG. 1 and the temperature compensating resistor (hereinafter referred to as CF) are installed in the flow path. In these figures, the same parts as those in FIGS. 1 and 2 are designated by the same reference numerals. In these figures, 5 is a temperature sensitive resistor (hereinafter referred to as HF) having a thin film as a heating resistor, 6 , 6'is a platinum thin film constituting the heating resistor, 7 is a platinum paste, and 8 is a main passage. , 9 indicates a bypass passage, and 10 indicates a CF.

The main passage 8 is formed by connecting an upstream duct 11 and a downstream duct 12 formed by drawing a cold-rolled steel sheet into a sheet metal by brazing at the central portion. The downstream side of the upstream duct 11 annular co shaped projection 13 is formed, downstream duct 12
When combined with to form a-ring-shaped passage on the outer periphery of the main passage 8. An inflow port 14 is provided on the outer periphery of the ring-shaped passage, and an opening 16 is formed at the inner peripheral portion at a position 210 ° away from the inflow port 14 to join the narrowest portion 15 of the main passage 8. A mesh 17 is fixed upstream of the main passage 8.

A bypass module 19 in which the bypass passage 9 and a module portion 18 for accommodating a circuit for driving the HF 5 and CF 10 are integrated is formed by thin-walled aluminum die casting. The bypass inlet portion 20 projects and the length of the upstream portion of the HF 5 can be increased to obtain a rectifying effect. HF5
And CF10 are lead pins 22 embedded in the resin portion 21,
Spot-welded and fixed to the bypass side projections of 22, 23, and 23, respectively. The other ends of these lead pins enter the module case and are connected to the HF drive circuit 24 via a lead frame (not shown) or the like. Further, the outer periphery of the bypass module 19 on the downstream side of the bypass has a straight pipe portion 25 to which a pipe can be connected. Bypass module 19 is fixed at the main four screws in the flow path at the upstream portion through an O-ring plug the bypass upstream portion in a hole bored in a plane perpendicular from the upper passage 8 (not shown). An L-shaped rubber hose 2 is provided between the downstream side of the bypass passage 9 and the ring-shaped inlet 14 on the main passage side.
Connect at 6. The flange 27 is for directly connecting the AFM to the air cleaner.

Next, a method of manufacturing HF will be described.

Outer diameter φ0.35 as shown in FIGS. 1 and 2.
mm, an inner diameter of 0.2 mm in diameter, platinum thin film 6 on the alumina pipe 1 of length 2 mm, film thickness by barrel sputtering 6'2Myuemu～4
Apply μm film. The resistance value after sputtering is 1/50 to 1/100 of the target final resistance value, and the variation in resistance value is ± 15.
Within%. When barrel sputtering is performed on the alumina pipe 1, the conductor may enter the inner diameter portion of the alumina pipe and become conductive unless the length is 8 times or more the inner diameter of the alumina pipe 1. Next, the inner end and both end surfaces of the alumina pipe 1 are coated with the platinum paste 7 containing filler, the tip of the alumina paste is coated with platinum paste containing filler, and a lead is inserted and fixed by baking at 1000 ° C to 1200 ° C. The thin film is also heat-treated to crystallize into a durable and stable thin film. By taking such a structure, the platinum thin film 6,
6'and the lead 2 are connected to both inner circumferences of the alumina pipe 1 and
The alumina pipe 1 was electrically connected on both ends.
Therefore, the risk of poor contact and disconnection can be greatly reduced. Also
The alumina pipe 1 and the lead 2 are bonded to each other with a metal-containing fiber.
It is possible to connect using a paste containing la, but especially
By using platinum paste, which is the same substance as the platinum thin film,
The chemical bond with the platinum thin film is made more reliable, and the contact electric
It is possible to obtain a stable connection structure with little displacement. In addition , the resistance value became about 1/2 of the value after sputtering by the heat treatment, and the dispersion of the resistance value was ± 15%.

Next, resistance spiral trimming with a laser is carried out. When platinum resistance is subjected to ordinary resistance trimming, the temperature coefficient of platinum is large, so the resistance value of the platinum resistance is several hundred to several thousand Ω due to the heat of the laser during trimming. Prediction method trimming is used because it shows a large variation. For example, a method may be adopted in which the spiral trimming is stopped halfway and the remaining trimming length is calculated from the target resistance value based on the trimming length and the resistance value after trimming. Finally, the glass 4 is overcoated. The temperature-sensitive resistor thus obtained is subjected to aging by passing an overcurrent so as to suppress changes in the thin film over time.

The HF and CF thus manufactured are welded and fixed to the support terminals 22, 22, 23 and 23 and assembled into an AFM as shown in FIG. Electrically these H
F and CF are incorporated into the electric circuit shown in FIG. 6 and driven. That HF 5, CF10 constitute the bridge and the other resistors 28, 29. This bridges differential voltage between di and through the amplifier 30 differentially amplifies, constituting the fed back circuit for driving the transistor 31. The HF 5 is arranged in the bypass passage 9 together with the CF 10 and is controlled so as to always maintain a constant temperature difference T _R = 200 ° C. with respect to the ambient temperature. For the output voltage, V ₂ in FIG. 6 is adjusted to zero by a span adjustment circuit (not shown) and taken out as V ₀ .

The flow rate output Q is

[0018]

## EQU1 ## Q = aV ₀ ⁴ + bV ₀ ³ + cV ₀ ² + dV + e (1)

Is expressed as a fourth root function of V ₀ . Here, a, b, c, d, and e represent constants.

When the power supply voltage V _B = 14 V is supplied to the AFM for driving, V ₀ = 4.010 when Q = 100 Kg / h.
An output voltage of V is obtained, but V _{O PP} = 83 mV,
There was a fluctuation of N / S = ΔQ / Q = 8.28%. The main cause is not the electronic circuit itself,
This is due to the change in the amount of heat conduction of HF to the air flow. That is, the flow of air is large or small with the bypass diameter D ₁ ,
Although there is a slight change depending on the size of the distance from the bypass input to the HF mounting position l ₁ , the optimum value is D ₁ here.
= 10 mm and l ₁ = 30 mm.

FIG. 7 shows HF output fluctuation, so-called noise
In comparison with W, the horizontal axis and the vertical axis respectively show the flow rate (Kg / h) and the noise ΔQ / Q (%), that is, the maximum noise amount of the actual measurement as a ratio to the average value of the output. The ΔV / V value is converted into the ΔQ / Q value on the basis of the equation (1), and F and W represent HF and HW, respectively. There is a peak value in the vicinity of 40 to 80 kg / h on the graph, and the maximum noise of HW is about 9%, while the HF is reduced by 3% at the maximum and reaches 6% at the maximum. The sampling of the current emission control computer is performed every 20 ms to 800 μs, so that the sampling is completely random, and the error due to each time becomes a problem. Since the measurement accuracy of the required air flow rate cannot be improved unless the noise component is reduced, the effect on the accuracy of noise reduction due to HF is great.

Another factor for accuracy is responsiveness. Fig. 8 shows a comparative measurement of the responsiveness of HF and HW using the method of blowing high-pressure air.
ec), the vertical axis represents the air flow rate (Kg / h), that is, the voltage V
The _zero value (1) Yes with value converted into the flow rate Q values taken by the computer using the formula, F, W respectively HF (phi
0.36 mm, 2 l) and HW (φ0.55 mm, 2 l). As is clear from this figure, HF, H
The rising response in the case of W is about 100 ms and 1 sec, respectively.
Since the above is the case, the response time can be shortened to 1/10 or less by setting HF. By improving the response characteristics, the starting time is shortened as shown in FIG. 9, the followability when the air flow rate suddenly changes during acceleration of the vehicle is improved, and the drivability can be greatly improved. In FIG. 9, the horizontal axis represents time T (mse
c), the output voltage V ₀ (V) is plotted on the vertical axis, and V _B = 1
4.5V, Q = 13Kg / h, shows the case of a _{T h -T a = 200 ℃,} F, W respectively HF (0.35 mm, 2
1) and HW (φ0.50 mm, 2 l).

FIG. 10 is a case of T _h -T _a = 200 ℃ with those shown by comparing the power consumption of the HF and HW, √ the horizontal axis
^{Q (Kg / h) 1/} 2, the vertical axis Yes taken is ^{_{I h 2 (× 10~ 2 A}} 2), F, W respectively HF (0.35 mm, 2
1), HW (φ 0.5 mm, 2 l)
A and B are values of I _h ² when √Q = 0, respectively, and if the gradient of the curve is indicated, then I _h ² = A + B√Q. FIG As apparent from the case of HF, the power consumption by having fewer amount of heat conducted to the terminal through the lead all the heat capacity is small is reduced.

As described above, the HF of this embodiment is the conventional H
In addition to having such a merit in characteristics with respect to W, there is an advantage that the cost of the element can be reduced to about 1/2 of HW because mass production is possible by applying the semiconductor technology. The heat resistance is 450 ° C. or higher, which is equivalent to HW. −
T _R = 300 ° C 14V energization at 40 ° C ON 4sec, OFF 4
Even in the endurance test result of 100,000 sec, the output change is ΔQ / Q ≦ ± 2%, and the earthquake resistance is 50G, 10H.
_Z 〜 1KH _Z 2mm sweep, output change in 3 hours each for XYZ axis Δ
Q / Q ≦ ± 1% or less.

According to the above-mentioned embodiment, the noise can be reduced by up to 30 % in ΔQ / Q by adopting the small HF as the sensor element of the air flow meter. The response time was 3τ (95% because the heat capacity became smaller and the lead became thinner.
Response) can be shortened to 1/10 or less. Also, the manufacturing cost of the sensor element can be reduced to about 1/2 by applying the semiconductor manufacturing technology. According to the present invention, an inexpensive and highly accurate sensor element for AFM can be provided.

That is, for the temperature sensitive resistor used in the present invention, an alumina pipe is extruded and cut, and then platinum is deposited on the surface of the pipe by barrel sputtering. Then, the leads are baked on both ends of the pipe by using a platinum paste, and at the same time, the platinum thin film is heat-treated, and thereafter, trimmed in a spiral shape by a laser to overcoat the glass. Therefore, the laser spiral trimming work, which corresponds to the work for winding the HW wire for about 2 mm, is completed in about 2 seconds. Further, the resistor can be formed without applying any external force to the thin film resistor, and mass production is possible. Conductor width laser trimming spots are φ30μm a minimum can hold the function as H F if substantially the width or more. For trimming, if the outer diameter of the bobbin is not eccentric, resistance trimming is possible up to a fine bobbin of φ0.1 mm.

Therefore, if an alumina pipe or rod having such a small diameter can be produced, it is possible to easily produce an HF having a very small shape which could not be produced by HW. That is, in the case of HW, a bobbin having an outer diameter of 0.5 mm and a length of 2 mm was wound 37 times with a platinum wire of 20 .mu.m to obtain a resistance value of 20 .OMEGA .. However, if the outer diameter is φ0.35 mm and the length is 2 mm, it is necessary to set the wire thickness to φ16 μm in order to obtain the same resistance value. When the wire becomes thin in this way, the frequency of wire breakage during winding increases, and the price of the HW becomes even more expensive. On the other hand, when the outer diameter of HF is reduced, it can be easily dealt with by reducing the film thickness from 3 μm to 2 μm.

That is, the H-shape is smaller than that of the conventional HW.
By adopting F, as shown in FIG. 7, the influence of output voltage noise can be reduced by up to 30%. The reason for this is that the smaller element shape reduces the temperature distribution of the supporting parts such as the leads and terminals, and reduces the influence of turbulence caused by the wall surface flow. Further, as shown in FIG. 9, the response time is a rise 3τ response and the conventional HW is 1 sec, whereas the HF is 100 msec.
It is reduced to about 1/10 before and after. The cause is that the heat capacity of the element is 0.55 mm for HW outer diameter and φ for HF outer diameter.
It was reduced to about 1/2 at 0.37 mm and the lead wire diameter was H
The diameter of Wφ is 0.2 mm and HF is 0.15 mm, and the amount of heat conduction to the terminal is reduced. In addition, in HW, platinum winding is wrapped in overcoat glass with poor heat conductivity (λ _C = 0.64 kcal / mh ° C). While in line contact with the alumina pipe, the thermal conductivity (λ _A = 15.8) for HF.
This is due to the fact that the platinum thin film is in close contact with the alumina pipe with good kcal / mh ° C. Moreover, since the heat capacity is reduced, the power consumption is also reduced as shown in FIG.

The surface area of this HF is 2.25 mm ^2.
Hereinafter, the heat capacity is 0.13 × 10~ ³ cal / ℃ below, l / d
Good results are obtained when is 5.5 or more. The basis thereof will be described below with reference to FIGS. 11 to 13. The AFM used for the measurement has a bypass passage having an opening arranged side by side in the main passage, and HF5 and CF10 are welded and fixed to the straight pipe portion of the bypass by lead pins 22 and 23, respectively, and FIG. 11 is a perspective view of that portion. FIG. 12 is a Z-direction view of FIG. 11.
The measurement results are shown in FIG. 13, where the horizontal axis shows surface area (mm ² ), heat capacity (× 10 to ³ cal / ° C.), and 1 / d, and the vertical axis shows 3τ (ms). Is shown, and the case of l = 2 mm is shown.

For HF and CF, it is desirable to make the bypass passage diameter as small as possible in order to reduce the product price and weight.
Therefore, it is necessary to make the lengths of HF and CF as short as possible. On the other hand, the resistance value of the element is 10 to 20Ω due to the circuit configuration for obtaining the signal output, but in order to obtain this resistance value by trimming, the laser trimming spot minimum diameter is φ30 μm and the current density is 10, 0.
Since it must be used at less than 00 A / cm ² , the thickness of the thin film must be 1 μm to 4 μm, and an adhesive margin of 0.5 mm for fixing the leads to both ends of the alumina pipe is required. Overall, the bobbin must have a total length of 2 mm or more. The outer diameter is affected by molding techniques aluminum Napa type, the state of the art φ0.35mm following are difficult molding.

FIG. 13 shows a comparison of response characteristics of HF having a bobbin having a total length of 2 mm and a platinum thin film formed on bobbins having different outer diameters. The target values for evaluation of response characteristics are as follows. The data is based on. That is, the AFM is installed in the intake pipe of an automobile equipped with the multipoint fuel injection system.
In the feeling test of the acceleration response when the motor is installed and operated, those with a rise of 3τ 180 ms or less pass, and with more than that, delay may occur during acceleration and the driving feeling may be bad or bad. It has been evaluated. From these restrictions, the surface area of the HF element, the heat capacity, and the limit value of 1 / d are determined.
On the other hand, in the case of winding, the bobbin diameter is 0.4 mm and the lead diameter is φ.
If it is less than 0.2 mm, winding work becomes difficult and commercialization becomes impossible.

The thermal type flow meter using this temperature sensitive resistor is suitable for control of an internal combustion engine, particularly an internal combustion engine having a fuel injection device capable of quickly and accurately responding to control of high horsepower, low fuel consumption, exhaust gas and the like. .

In the above-mentioned embodiment, when manufacturing HF, as shown in FIG. 2, after depositing a platinum thin film on an alumina pipe, platinum paste containing a filler was applied to both ends and both end faces inside the alumina pipe. A lead having a platinum paste applied to its tip was inserted into the product, heat-treated and fixed by baking, and resistance spiral trimming was performed with a laser after crystallizing the platinum thin film. Sunawa <br/> Chi, as shown in FIG. 14, inserted first, those coated with filler containing a platinum paste on the inside at both ends and both the cross-section of the alumina pipe, the lead was coated cloth filler containing a platinum paste on the tip Fit and heat-treat to fix the lead to an alumina pipe by baking. A platinum thin film is deposited on the alumina pipe to which the lead is fixed by a barrel sputter. Next, the platinum thin film is heat-treated and crystallized to form a durable and stable thin film. Subsequent processing is performed in the same manner as the above-mentioned embodiment. This method requires more man-hours than the above-mentioned method , and in terms of electrical connection
Although slightly inferior, it is possible to produce HF having the same action and effect.

[0034]

INDUSTRIAL APPLICABILITY As described above, the present invention makes it possible to provide an inexpensive and highly accurate thermal type flow meter, which has a great industrial effect.

[Brief description of drawings]

FIG. 1 is a perspective view of a temperature-sensitive resistor of an essential part of an embodiment of a thermal type flow meter of the present invention.

FIG. 2 is a cross-sectional view of a Y portion of FIG.

FIG. 3 is an explanatory diagram of an air flow meter in which the temperature sensitive resistor of FIG. 1 is installed in a flow path together with a temperature compensating resistor.

FIG. 4 is a perspective view of a temperature sensitive resistor of a conventional thermal type flow meter.

5 is a cross-sectional view of the X part of FIG.

FIG. 6 is an explanatory diagram of an electronic circuit for driving the temperature sensitive resistor.

FIG. 7 is a diagram showing an output fluctuation of the temperature-sensitive resistor of the embodiment in comparison with that of the conventional temperature-sensitive resistor.

FIG. 8 is a diagram similarly showing comparison of response characteristics.

FIG. 9 is a diagram similarly showing a comparison of output start responses.

FIG. 10 is a diagram similarly showing power consumption in comparison.

FIG. 11 is a perspective view showing a mounted state of the temperature sensitive resistor and the temperature compensating resistor.

FIG. 12 is a cross-sectional view taken along arrow Z in FIG.

FIG. 13 is a characteristic diagram showing an effective use range of the temperature sensitive resistor of the thermal type flow meter of the present invention.

FIG. 14 Sense of essential parts of another embodiment of the thermal type flow meter of the present invention
It is a perspective view of a temperature resistance body.

[Explanation of symbols]

1 ... Alumina pipe, 2 ... Reed, 4 ... Glass, 5 ...
Temperature sensitive resistor (using thin film as heating resistor), 6 ... Platinum thin film, 7 ... Platinum paste, 8 ... Main passage, 9 ... Bypass passage, 10 ... Temperature compensation resistor.

Claims (4)

(57) [Claims] 1. A lead is inserted into both ends of a cylindrical body, and a heating resistor whose both ends are connected to each of the leads is disposed on the cylindrical body, and the heating resistor is covered with glass. In a thermal type flow meter having a temperature sensitive resistor as a constituent element of a bridge, the temperature sensitive resistor is formed of a platinum thin film spirally adhered to the outer surface of the cylindrical body, and the platinum thin film is formed inside the cylindrical body . It is attached to the entire surface except the center of the circumference.
A thermal type flow meter characterized by having a structure . 2. The cylindrical body is made of alumina.
The described thermal flow meter. 3. Leads are inserted into both ends of the cylindrical body, respectively.
And a heating resistor whose both ends are connected to each of the leads.
A body is disposed on the cylindrical body, and the heating resistor is made of glass.
Heat with a temperature-sensitive resistor coated on it as a component of the bridge
In the flow meter, the temperature-sensitive resistor is the outer surface of the cylindrical body.
Consisting of a platinum thin film spirally deposited on the
The membrane is formed on both end surfaces of the cylinder and the inner circumference of both ends of the cylinder.
Platinum paste interposed between the lead and the cylindrical body
That both ends of the
Characteristic thermal type flow meter. 4. The cylindrical body is made of alumina.
The described thermal flow meter.