JPH0814977A - Thermal type flowmeter - Google Patents

Abstract

PURPOSE:To provide a thermal type flowmeter which is improved in responsiveness by providing the winding starting point and winding terminating point of a resistance winding as closer to the outermost ends of a supporting body as possible. CONSTITUTION:A thermal fowmeter is provided with a flow rate measuring resistor 30 composed of a platinum wire 105, temperature compensating resistor, and control circuit which adjusts the energizing amount of the resistor 30 in accordance with the detecting value of the temperature compensating resistor. The platinum wire 105 which is wound around an aluminum bobbin 100 as a resistor is wound around the bobbin 100 from one end to the other end of the bobbin 100. The length L1 of the no-winding part between the winding starting point 105a of the wire 105 to the second turn of the wire 105 on one end of the bobbin 100 and the length L2 of the no-winding part between the wiring terminating point 105b to the second turn of the wire 105 from the wiring terminating end are set so that the ratio of the length L1 or L2 to the total length L0 of the bobbin 100 can satisfy a relation L1/L0<=0.125 or L2/L1<=0.125. Therefore, the wire 105 uniformly generates heat and the variation of the temperature distribution due to the flow rate of a fluid becomes small.

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 for forming a branch passage in a main passage through which a fluid flows and measuring the flow rate of the fluid flowing in the branch passage. Regarding

[0002]

2. Description of the Related Art There are various known methods for measuring the intake air amount of an internal combustion engine, such as a movable vane type and a Karman vortex type. Further, the thermal type flow meter is widely used because of its generally good response and ability to measure the mass flow rate of air. Further, it is known that a part of the air flowing through the intake pipe is guided to a bypass pipe, and a platinum wire as a flow rate detecting unit is attached to the bypass pipe.

As a conventional example of the winding structure of the temperature sensitive resistor as the platinum wire, there is one disclosed in JP-A-59-162413. This is intended to improve the responsiveness by providing a dense and dense winding method of the resistor (winding) on the support body around which the platinum wire is wound. That is, the winding pitch is changed when the resistor is wound. The winding wound in the axial direction of the support is densely wound on both ends of the winding and sparsely wound on the central side. This one focuses on the temperature distribution that the center part of the support becomes relatively hot according to the normal winding method, prevents concentrated heat generation of the flow rate detection part, and makes the temperature distribution uniform. The resistance value per unit of the temperature sensitive resistor formed on the insulating support is made larger at both end portions than at the central portion.

[0004]

However, as a method of improving the response when the flow rate changes in the conventional thermal type flow meter, a method of winding a platinum wire which is a resistor by providing sparseness and denseness on the outer periphery of the support body. Since it is necessary to change the winding pitch at the time of winding, it cannot be said that the manufacturing technique is easy to make. Further, in the dense portion of the platinum wire, the gap between the adjacent platinum wires on the support is forced to have a value smaller than the thickness of the platinum wire. This requires high-precision production technology for the winding process, resulting in poor productivity during winding work.

The inventor conducted experiments by paying attention to the temperature distribution ratio between the temperature at both ends of the resistance wire wound on the support and the temperature at the center of the resistance wire wound on the support. . As a result, the inventor
As shown in, the winding wound around the outer periphery of the alumina bobbin 100, which is the support, has the winding start point 52 and the winding end point 54, both of which are the support.
A fixed distance L ₁ and L ₂ from the outermost end of the same diameter part of
I paid attention to the fact that it is only in the position.

According to an experiment conducted by the inventor, the temperature distribution of the resistance wire wound around the outer periphery of the alumina bobbin 100 during operation of such a thermal type flow meter is, as shown in FIG. 10, a winding start point 52 and a winding end point. It was found that the rising slope portion of the temperature near the position of the point 54, that is, near both ends, was remarkably generated. Due to this, the temperature change near the winding start point 52 and the winding end point 54 at a low flow rate and the temperature change near the winding start point 52 and the winding end point 54 at a high flow rate are shown in FIG. It is quite large, as shown by the dotted and solid lines. That is, especially at the positions of the winding start point 52 and the winding end point 54, the temperature difference between the low flow rate temperature and the high flow rate temperature is large. It was thought that this deteriorated the responsiveness.

The present invention has been made paying attention to such a point, and improves the responsiveness by setting the winding start point and the winding end point of the resistance winding as close to the outermost end of the support as possible. It is an object of the present invention to provide a thermal type flow meter which has high accuracy and improved accuracy.

[0008]

According to a first aspect of the present invention, there is provided a thermal type flow meter, wherein a flow rate measuring resistor provided in a channel and a temperature compensating resistor provided in the channel. In the thermal type flow meter, which comprises a control circuit that adjusts the amount of electricity to the flow rate measuring resistor according to the detected value of the temperature compensating resistor, the flow rate measuring resistor is a rod-shaped insulation. The resistance wire is wound around the outer circumference of the support, and the resistance wire is wound from one end to the other end of the outer circumference of the support, and the resistance wire is wound near the end of the outer circumference of the support. Ratio of the length L ₁ on one side of the non-existing portion to the total length L ₀ of the support L ₁ /
It is characterized in that L ₀ is a predetermined value or less.

According to a second aspect of the thermal type flowmeter, a flow rate measuring resistor provided in the flow channel, a temperature compensating resistor provided in the flow channel, and the temperature compensating resistor are provided. In a thermal type flow meter having a control circuit that adjusts the amount of electricity to the flow rate measuring resistor according to the detected value, the flow rate measuring resistor is one end to the other end of a rod-shaped insulating support. A resistance wire wound up to one end of the support, the length L ₁ of one end of the resistance wire-free portion from the beginning of winding of the resistance wire to the second winding, and the other end of the support. When defined as the length L ₂ on the other end side of the portion without resistance winding from the winding end of the resistance wire to the second winding in the opposite direction, the length L ₁ or L on one side of the portion without resistance winding of the support. The ratio of ₂ to the total length L ₀ of the support is L ₁ / L ₀ ≦ 0.125, or L ₂ /
It is characterized in that L ₀ ≦ 0.125.

According to a third aspect of the present invention, in the thermal type flow meter, the support is rod-shaped, and both ends thereof are provided with engaging portions to which the resistance wire is hooked. According to a fourth aspect of the present invention, in the thermal type flow meter, the engaging portion is one or more grooves formed in an outer peripheral end portion of the support body. The thermal flowmeter according to a fifth aspect of the present invention is characterized in that the locking portion is one or more grooves formed along an axial direction formed on an outer peripheral portion of the support body.

According to a sixth aspect of the thermal type flowmeter, the resistance wire is a platinum wire. A thermal type flow meter according to a seventh aspect is characterized in that a protective film is formed on the resistance wire wound around the outer periphery of the support.

[0012]

According to the thermal type flowmeter of claim 1 or 2, the winding start point and the winding end point of the resistance wire of the flow rate measuring resistor are located near both ends of the support.
Responsiveness can be improved by minimizing the temperature change between the temperature of the resistance wire at the end of the support when the flow rate is low and the temperature when the flow rate is high.

According to the thermal type flowmeter of claim 3, 4 or 5, when winding the resistance wire, the winding of the resistance wire is easily caught and fixed at the engaging portion of the support, so that the end portion of the support is easily fixed. The resistance wire can be easily wound up to a position close to. According to the thermal type flow meter of claim 5, since the cross-sectional shape of the support is uniform from one end to the other, the support can be manufactured by extrusion molding with good productivity, and at this time, Since the support can be easily manufactured only by modifying the conventional extrusion mold, the cost increase can be reduced.

According to the thermal type flowmeter of claim 6, since the platinum wire is used, it is excellent as a heating element and has good sensitivity.
According to the thermal type flow meter of the seventh aspect, the function of the temperature sensing portion is not impaired, damage is less likely to occur, and the durability is good.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) An embodiment in which the present invention is applied to a thermal type flow meter for measuring the amount of intake air taken into an automobile engine will be described. First, the overall configuration of the thermal type flow meter will be described.

As shown in FIG. 2, the thermal type flow meter 10 is shown in FIG.
Intake air is introduced from the left side and flows out to the right side in FIG. The upstream opening 11 of the thermal type flow meter 10 is inserted and attached to an air cleaner (not shown). On the other hand, the downstream opening 12 is inserted into an intake duct (not shown) having a diameter larger than that of the thermal flow meter 10, and is tightened from the outside by a belt (not shown).

The thermal type flow meter 10 comprises a central cylindrical portion 13, an upstream cylindrical portion 14 and a downstream cylindrical portion 15, and a circuit container 16 for accommodating a control circuit 16b outside the central cylindrical portion 13.
Are formed. Central cylindrical portion 13 and upstream cylindrical portion 14
A flow path is formed by connecting the and the downstream side cylindrical portion 15 respectively. A shell-shaped upstream housing 17 is attached to the upstream side of this flow path, and a downstream housing integrally formed as a part of a central housing 18 having a thermal sensor portion 20 therein and a downstream side cylindrical portion 15 on the downstream side. 19 is attached.

Inside the thermal sensor section 20, four support pins 22, 23, 24, 25 are insert-molded so as to project to the upstream side and the downstream side of the cylindrical resin section 21. The support pin protruding to the upstream side consists of two types, long and short,
The temperature compensating resistor 2 is provided between the shorter support pins 24, 25.
6 is attached, and the flow rate measuring resistor 30 is attached between the longer support pins 22 and 23. The temperature compensating resistor 26 and the flow rate measuring resistor 30 are electrically connected to the control circuit 16b by wiring (not shown). The temperature compensating resistor 26 and the flow rate measuring resistor 30 are temperature sensitive resistors. The flow rate measuring resistor 30 is a control circuit 16
Heat is generated by passing a current through b. On the other hand, the resistance value of the temperature compensating resistor 26 changes according to the temperature of the airflow flowing around the temperature compensating resistor 26. The temperature compensating resistor 26 and the flow rate measuring resistor 30 are controlled by the control circuit 16b so that the flow rate measuring resistor 30 is energized in such a manner that a predetermined temperature difference is always maintained in accordance with the ambient temperature of these resistors. .

Next, the structure of the control circuit 16b of the thermal type flow meter 10 will be described with reference to FIG. The terminal + B connected to the vehicle-mounted battery (not shown) is connected to the collector terminal of the power transistor 45 via a feedthrough capacitor (not shown). The power transistor 45 is connected to the temperature compensating resistor 26 and the flow rate measuring resistor 30.
The emitter terminal of is connected. The terminal GND, which is connected to the reference potential, is connected to the connection portion between the resistor 41 and the resistor 43.

The Wheatstone bridge circuit includes a resistor 4
1, 42, 43, the temperature compensating resistor 26, and the flow rate measuring resistor 30. Flow rate measuring resistor 30
And the resistance value of the resistor 43, and the product of the combined resistance value of the temperature compensating resistor 26 and the resistor 42 and the resistance value of the resistor 41 connected in series are equal. At this time, the resistors 41, 42 and 43 and the temperature compensating resistor 26 are arranged so that the Wheatstone bridge circuit is in a balanced state.
And the flow rate measuring resistor 30 are connected. The non-inverting input terminal of the operational amplifier 44 is connected to the connecting portion between the flow rate measuring resistor 30 and the resistor 41, and the inverting input terminal of the operational amplifier 44 is connected to the connecting portion between the resistor 42 and the resistor 43. ing. The output terminal of the operational amplifier 44 is connected to the base terminal of the power transistor 45, and this connection forms a feedback circuit. The output terminal VG is connected to the non-inverting input terminal of the operational amplifier 44, and the voltage V1 is output from this output terminal VG.

The specific structure of the flow rate measuring resistor 30 is shown in FIG. Hollow cylindrical alumina bobbin 10
Platinum leads 101 and 102 are inserted from both ends of 0, and the platinum leads 101 and 102 are made of glass 103, 1
Alumina bobbin 10 by 04 (104 is not shown)
It is adhesively fixed to the hollow portion of 0. Alumina bobbin 10
A platinum wire 105 serving as a resistor is wound around the outer periphery of 0, and is wound to the vicinity of both ends of the alumina bobbin 100, which is a supporter of the platinum wire 105, as compared with the related art. Further, the platinum wires 105 are wound around the outer periphery of the alumina bobbin 100 at equal intervals as in the conventional case, but since the resistance value is the same as that of the conventional product, the platinum wires 105 are slightly spaced from the conventional product. It is rolled. Both ends 106 and 107 of the platinum wire 105 are spot-welded to the platinum leads 101 and 102. Platinum wire 1
05, the alumina bobbin 100, and the leads 101 and 102, a protective film 108 having a characteristic that does not impair the function of the platinum wire 105 as the temperature sensitive resistor is formed. The protective film 108 is formed by applying glass and baking it.

The platinum wire 105 serving as a resistor may be a metal wire other than the platinum wire as long as it has a large temperature resistance coefficient, and the alumina bobbin 100 serving as a support.
However, other materials may be used as long as they have electrical insulation, and the leads 101 and 10 that are adhesively fixed to the alumina bobbin 100.
Other metals and substances may be used as long as they are electrically conductive. As shown in FIG. 2, the flow rate measuring resistor 30 and the temperature compensating resistor 26 described above are provided with support pins 22, 23, and 2.
4, 25 are arranged in the bypass branch passage.

The platinum wires 105 are wound around the alumina bobbin 100 from one end to the other end at equal intervals. Here, as shown in FIG. 1, the length L ₁ of one end portion of the portion without resistance winding from the winding start point 105a of the platinum wire to the second winding at one end portion of the alumina bobbin 100, the alumina bobbin 1
00 is defined as the length L ₂ on the other end side of the part without resistance winding from the winding end point 105b of the platinum wire at the other end of 00 to the second winding in the opposite direction, the length on one side of the part without resistance winding. L ₁
Alternatively, the ratio of L ₂ to the entire length L ₀ of the alumina bobbin 100 is set to be equal to or less than a predetermined value, for example, L ₁ / L ₀ ≦
0.125, or L ₂ / L ₀ ≦ 0.125 is set.

The reason for this is as follows. Generally, in this type of flow rate measuring resistor, a temperature distribution is generated in both the conventional example and the embodiment of the present invention for the following reason. Although the amount of heat generated by the platinum wire 105 wound around the alumina bobbin 100 is uniform per unit length, the central portion of the alumina bobbin 100 is hollow, and the leads 101, 102 are provided at both ends.
Also, there are glasses 103 and 104 as an adhesive for fixing the leads 101 and 102 to the alumina bobbin 100, and the heat capacities differ between the respective parts. Further, there is heat loss from the leads 101 and 102 from both ends.
Further, when the flow rate becomes high, the heat conduction from the temperature sensitive resistor 30 to the air becomes large, and the protective film 1 in contact with the platinum wire 105.
08, the alumina bobbin 100, and the leads 102 and 103 have a larger temperature difference.

Here, when the temperature distribution of the conventional flow rate measuring resistor is measured, it becomes as shown in FIG. The solid line of the graph shown in FIG. 10 shows the temperature distribution when the flow rate is low, and the dotted line shows the temperature distribution when the flow rate is high. When the flow rate is low and when the flow rate is high, there is a temperature difference near both ends and in the center where the platinum wire is not wound. Such a phenomenon that the difference in the temperature distribution caused by the difference in the flow rate between the low flow rate and the high flow rate becomes large causes the poor responsiveness. In the conventional example, since no heat is generated in the vicinity of the end portion where the platinum wire 105 is not wound, the difference in temperature distribution remarkably occurs due to the difference in air flow rate. For example, when the air flow rate changes from a low flow rate to a high flow rate, the temperature distribution on the resistor 30 also changes accordingly, from the temperature distribution at the low flow rate to the temperature distribution at the high flow rate. The time required for this temperature distribution to change is relatively long. That is, since the difference in temperature distribution is large, the response is relatively poor.

On the other hand, when the temperature distribution of the resistor 30 according to the embodiment of the present invention is measured, it becomes as shown in FIG. The solid line of the graph shown in FIG. 4 shows the temperature distribution when the flow rate is low, and the dotted line shows the temperature distribution when the flow rate is high. In FIG. 4, it is understood that the difference in temperature distribution between the low flow rate and the high flow rate is smaller than that in the conventional example shown in FIG. This is because the platinum wire 105 is uniformly wound from one end to the other end of the alumina bobbin 100 and the unwound portion is small, so that the heat generation is made uniform and sufficient heat is generated even at the end, so that there is a change in the flow rate. It is based on the fact that the temperature change is small and the temperature is stable. That is, in the embodiment of the present invention, the platinum wire 105 is evenly wound up to the end portion to make the heat generation uniform and suppress the difference in temperature distribution due to the difference in air flow rate. Therefore, according to the resistor 30 of the present embodiment, even when the air flow rate changes from a low flow rate to a high flow rate, the change in temperature distribution is small, the time required for changing the temperature distribution is short, and the responsiveness is improved. .

The shape of the alumina bobbin 100 will be described. This alumina bobbin 100 is the alumina bobbin 1
00 has a shape such that the platinum wire 105 can be wound from one end to the other end without winding slip. The platinum wire 105 is pressed and fixed to the shoulder of the alumina bobbin 100 by the tension during winding. This pressing force is determined by the tension during winding and the angle formed by the platinum wire 105 at the shoulder of the alumina bobbin 100. The stronger the tension or the narrower the angle, the stronger the pressing force. Winding the platinum wire 105 near both ends of the alumina bobbin 100 now widens the angle formed by the shoulder of the alumina bobbin 100, so the pressing force is weakened, and as a result, the platinum wire 10
Rolling slip of 5 is likely to occur. Moreover, although the winding of the platinum wire 105 can be prevented by increasing the tension during winding, the platinum wire 105 is broken during the winding or the platinum wire 105 is partially extended, which causes a problem in durability. Therefore, the following alumina bobbin 10 is used to prevent the platinum wire 105 from winding and slipping.
A shape of 0 is possible.

In order to realize the formation of resistors (windings) in the vicinity of both ends of the alumina bobbin 100, which is a support, as shown in FIG. 5, a platinum wire 105 is formed on the circumference of the alumina bobbin 100.
An engaging portion 120 for hooking is provided. The locking portion 120 is
The groove is an axially extending groove on the outer circumference of the alumina bobbin 100, and the cross-sectional shape of the groove is triangular. In this case, six locking portions 120 are formed at equal intervals in the outer circumference direction.

Platinum wires 105 are fixed by locking portions 120 at both ends of the outer circumference of the alumina bobbin 100, so that the platinum wires 105 can be prevented from winding slippage. Therefore, during winding, the alumina bobbin 100 can be wound without fear of winding slippage.
Resistor formation (winding) near both ends of can be easily performed. Since the alumina bobbin 100 is manufactured by extrusion molding and can be easily manufactured only by modifying the mold at the time of extrusion, the flow rate measuring resistor 30 having good responsiveness without manufacturing cost is manufactured. it can.

According to the present embodiment, the platinum wire 105 is wound up to the vicinity of both ends of the alumina bobbin 100 as a support of the flow rate measuring resistor to obtain a uniform temperature distribution on the flow rate measuring resistor 30 and change the flow rate. Time responsiveness can be improved. Further, since the platinum wire 105 is wound at even winding intervals, it can be easily manufactured in manufacturing. Furthermore,
The gap between the adjacent platinum wires 105 can be formed to be equal to or larger than that of the conventional example, and there is an advantage that high precision production technology is not required.

The circuit operation of the control circuit 16b of the thermal type flow meter 10 will be described below with reference to FIG. Here, V1, V2, V3, and V4 represent the voltages of the parts with the symbols. The resistor 41 converts the current flowing through the flow rate measuring resistor 30 into a voltage V1.
And a resistor 42 and a resistor 43 connected in series.
Means to convert the current flowing through the temperature compensating resistor 26 into a voltage and detect the voltage V2. By inputting the detected voltages V1 and V2 to the non-inverting input terminal and the inverting input terminal of the operational amplifier 44, the potential difference generated by the voltage V1 and the voltage V2 is differentially amplified and connected to the output terminal of the operational amplifier 44. The voltage of the base terminal of the power transistor 45 is controlled. By controlling the voltage of the base terminal, the temperature difference between the temperature compensating resistor 26 and the flow rate measuring resistor 30 is kept to be, for example, about 200 ° C.

When a voltage is applied to the Wheatstone bridge circuit composed of the resistors 41, 42 and 43, the temperature compensating resistor 26 and the flow rate measuring resistor 30, the voltage is applied to the non-inverting input terminal of the operational amplifier 44. A voltage V2 is generated at V1 and the inverting input terminal. The magnitude relationship between the voltages V1 and V2 is V
When 1> V2, the output voltage V4 of the operational amplifier 44 rises. Along with this, the emitter voltage V3 of the power transistor 45 also rises. As the voltage V3 rises, the current flowing through the flow rate measuring resistor 30 rises, and the heat generation temperature of the flow rate measuring resistor 30 rises. As a result, the resistance value of the flow rate measuring resistor 30 increases and the voltage V1 decreases. On the other hand, the voltage V1 decreases and the magnitude relationship between the voltages V1 and V2 is V1.
When <V2, the output voltage V4 of the operational amplifier 44 decreases. Therefore, the emitter voltage V3 of the power transistor 45 also drops. Due to this decrease in the voltage V3, the current flowing through the flow rate measuring resistor 30 decreases, and the heat generation temperature of the flow rate measuring resistor 30 decreases. As a result, the resistance value of the flow rate measuring resistor 30 decreases, the voltage V1 increases, and the voltage V1 increases.
Since the magnitude relationship of V2 is V1> V2, the above control is repeated again. Thus, the operational amplifier 44 outputs the output voltage V4
Thus, the power transistor 45 is controlled so that the magnitude relationship between the voltages V1 and V2 is V1 = V2, and the amount of electricity supplied to the flow rate measuring resistor 30 is adjusted.

On the other hand, when the heating current flowing through the flow rate measuring resistor 30 is I and the resistance value of the flow rate measuring resistor 30 is RH, the flow rate measuring resistor 30 consumes (I ² · RH) power. Fever. Since this heat generation power (I ² · RH) is radiated to the air flowing through the flow path, the amount of heat taken by the air changes depending on the increase or decrease in the flow rate of the air flowing through the flow path. Therefore, the temperature of the flow rate measuring resistor 30 changes according to the air flow rate, and the resistance value RH also tends to change. However, by the Wheatstone bridge circuit described above, the operational amplifier 44 controls the power transistor 45 so that the resistance value RH of the flow rate measuring resistor 30 does not change, and the flow rate measuring resistor 30 is controlled.
The energization amount of is changed. That is, by changing the heating current I according to the air flow rate, (I ² · RH) is changed so that RH is always controlled to a predetermined resistance value. Therefore, the heating current I has a value having a correlation with the air flow rate, is converted into a voltage V1 by the resistor 41, and is output via an amplifier circuit (not shown).

Next, the platinum wire 10 of the flow measurement resistor 30 is used.
As a means for preventing winding slippage when winding 5, a locking means as shown in FIGS. 6, 7 and 8 is used as a modification instead of the locking portion 120 formed on the outer circumference of the alumina bobbin 100 shown in FIG. Can be considered. (Second Embodiment) For example, the engaging portion 130 shown in FIG. 6 is a groove extending along the axial direction on the outer peripheral portion of the alumina bobbin 100 and formed at equal intervals in the peripheral direction. belongs to. As a method of forming the locking portion shown in FIG. 6, it can be easily manufactured by only modifying the die at the time of extrusion by extrusion molding as in the formation of the locking portion 120 shown in FIG.

(Third Embodiment) Locking portion 140 shown in FIG.
Is a groove that also extends along the axial direction on the outer peripheral portion of the alumina bobbin 100, and the groove shape has a right angle in the groove depth portion, and four grooves are formed at equal intervals in the peripheral direction. The method of forming the locking portion shown in FIG. 7 can also be easily manufactured by just adjusting the die at the time of extrusion by extrusion molding as in the case of forming the locking portion 120 shown in FIG.

(Fourth Embodiment) Locking portion 150 shown in FIG.
Is a groove having a triangular cross section formed only at both ends of the alumina bobbin 100, and the groove becomes deeper toward both ends. As a method of manufacturing the locking portion 150, for example, after forming the alumina bobbin 100 by extrusion, firing, and then machining, the groove can be formed.

(Experimental data) Next, FIG. 9 shows an experimental result obtained by using the structure of the flow rate measuring resistor by the thermal type flow meter of the present invention. The experimental conditions are as follows. When a platinum wire is wound around the outer periphery of an alumina bobbin, unwound parts of the platinum wire are generated at both ends of the alumina bobbin. The unwound part of the platinum wire has a length L ₁ on one side and a length L ₂ on the other side. Was changed. Here, in the test product used in the experiment, the length L ₁ on one side and the length L ₂ on the other side are equal in manufacturing (L ₁
= L ₂ ) was used. The air flow rate was changed by a thermal flow meter using a flow rate measuring resistor having various winding-free portions at both ends of the alumina bobbin, and the flow rate output was measured. Air flow rate is, for example, 3 g / sec to 20 g / s
When the flow rate was increased stepwise to ec, the delay time (responsiveness) until reaching the flow rate output of 95% was measured with respect to the final flow rate output after the flow rate change.

The experimental results are shown in FIG. FIG. 9 shows the responsivity measurement results, and shows the dimensional ratio L ₁ / L ₀ between the length L ₁ on one side of the unwound portion of the platinum wire at both ends of the alumina bobbin and the total length L _{0 of the} alumina bobbin. The horizontal axis represents the flow rate, and the vertical axis represents the delay time (response time) until the flow rate output reaches 95% of the final flow rate output from the flow rate output before change to the final flow rate output after change. Here, for convenience, the length L ₁ on one side of the unwound portion of the platinum wire is the length from the hooked position of the platinum bobbin shoulder portion to the second turn.

As can be seen from the experimental results shown in FIG. 9, the response is improved by making the portions L ₁ and L ₂ where the platinum wire is not wound relatively smaller. In order to satisfy the responsiveness of 200 ms or less, which is ideal for engine control, the length of one side of the part of the alumina bobbin where the platinum wire is not wound is L ₁ (= L
₂ ) and the dimensional ratio L ₁ / L of the total length of alumina bobbin L _0
0 may be set to 0.125 or less. In addition, L ₁ / L ₀ ≦
If it is 0.125, even if there are variations in manufacturing, the change in responsiveness is small and there is no problem in engine control. As for the shape of the alumina bobbin having the hooked portion of the platinum wire, similarly, the shapes of FIG. 6, FIG. 7, and FIG. 8 also allow winding up to near both ends of the alumina bobbin (L ₁ / L ₀ ≦ 0.125). .

As described above, the method of winding the platinum wire of the flow rate measuring resistor 30 has been described in the present embodiment, but the present invention is applied to the method of winding the platinum wire of the temperature compensating resistor 26. Of course, you can. Although alumina was used as the support in the examples, in the present invention,
The material is not limited to alumina as long as it is an electrically insulating material, and other materials such as zirconia may be used.

Further, in this embodiment, the flow rate measuring resistor 3 is used.
Although a platinum wire was used as the heat generating material of No. 0, in the present invention, it is not limited to platinum as long as it can be used as the heat generating material, and other materials such as nickel alloy may be used.
Furthermore, in the present embodiment, the glass containing lead oxide was used as the protective film 108 covering the flow rate measuring resistor 30, but in the present invention, the glass containing lead oxide is used as the electrically insulating substance. The material is not limited, and other materials such as alumina may be used.

[Brief description of drawings]

FIG. 1 is an enlarged partial sectional view showing a resistor portion of a thermal type flow meter according to a first embodiment of the present invention.

FIG. 2 is a sectional view of the thermal type flow meter according to the first embodiment of the present invention.

FIG. 3 is a control circuit diagram of the thermal type flow meter according to the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a relationship between a winding position and a temperature of a platinum wire according to the first embodiment of the present invention.

FIG. 5A is a side view of an alumina bobbin according to the first embodiment of the present invention. (B) is a cross-sectional view thereof.

FIG. 6A is a side view of an alumina bobbin according to a second embodiment of the present invention. (B) is a cross-sectional view thereof.

FIG. 7A is a side view of an alumina bobbin according to a third embodiment of the present invention. (B) is a cross-sectional view thereof.

FIG. 8A is a side view of an alumina bobbin according to a fourth embodiment of the present invention. (B) is a cross-sectional view thereof.

FIG. 9 is a characteristic diagram showing a relationship between a ratio of a portion without a winding and responsiveness according to the first embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a relationship between a winding position of a platinum wire and a temperature in a conventional example.

[Explanation of symbols]

 26 Temperature Compensating Resistor 30 Flow Rate Measuring Resistor 100 Alumina Bobbin (Support) 101 Platinum Wire Lead 102 Platinum Wire Lead 103 Glass 105 Platinum Wire (Resistance Wire) 105a Winding Start Point 105b Winding End Point 120 Locking Part 130 Locking Part 140 Locking part 150 Locking part

Claims (7)

[Claims] 1. A flow rate measuring resistor provided in a flow channel, a temperature compensating resistor provided in the flow channel, and the flow rate measuring resistor according to a detection value of the temperature compensating resistor. In a thermal type flow meter provided with a control circuit for adjusting the amount of electricity to the resistor, the flow rate measuring resistor comprises a resistance wire wound around the outer periphery of a rod-shaped insulating support, and the resistance wire is the support wire. A length L ₁ on one side of a portion of the body which is wound from one end to the other end on the outer periphery and the resistance wire is not wound in the vicinity of an end of the outer periphery of the support, and an overall length L _{0 of the} support. The ratio L ₁ / L ₀ is less than or equal to a predetermined value. 2. A flow rate measuring resistor provided in the flow channel, a temperature compensating resistor provided in the flow channel, and the flow rate measuring resistor according to a detected value of the temperature compensating resistor. In a thermal type flow meter having a control circuit that adjusts the amount of electricity to the resistor, the flow rate measuring resistor is a resistance wire wound from one end to the other end of a rod-shaped insulating support, The length L ₁ on one end side of the portion without resistance winding from the winding start to the second winding of the resistance wire on one end of the support, and from the winding end of the resistance wire on the other end of the support in the opposite direction. When defined as the length L ₂ on the other end side of the portion without resistance winding up to the second winding, the length L ₁ or L ₂ on one side of the portion without resistance winding of the support and the overall length of the support. The ratio of L ₀ is L ₁ / L
₀ ≦ 0.125, or L ₂ / L ₀ thermal flow meter, characterized in that ≦ 0.125. 3. The support body is rod-shaped, and is provided with locking portions at both ends to which the resistance wire is hooked.
The described thermal flow meter. 4. The thermal type flow meter according to claim 1, wherein the engaging portion is one or more grooves formed in an outer peripheral end portion of the support body. 5. The thermal type flow meter according to claim 3, wherein the engaging portion is one or more grooves formed along an outer peripheral portion of the support member and extending along an axial direction. 6. The thermal type flow meter according to claim 1, wherein the resistance wire is a platinum wire. 7. The protective film is formed on the resistance wire wound around the outer periphery of the support.
6. The thermal type flow meter according to any one of 6 above.