JPH07239258A - Thermal air flow rate detector - Google Patents

Abstract

PURPOSE:To enhance accuracy in the detection of flow rate of suction air by making it possible to decide whether the air is flowing forward or reversely. CONSTITUTION:An insulating board 28 is fixed detachably, on the base end side thereof, to the detection holder of a flowmeter body projecting into a suction pipe. The insulating board 28 is separated, by means of a slit 29, into a main board part 28A and a subboard part 28B in the direction of air flow. A crank-shaped heating resistor 30 extending in the longitudinal direction of the insulating board 28 and temperature-sensitive resistors 31, 32 extending in parallel with the extended resistor parts 30B, 30C of the heating resistor 30 while spaced apart therefrom in front and rear thereof are formed on the main substrate part 28A whereas a temperature compensation resistor 33 is formed on the subsubstrate part 28B. The contact area with the air flow is increased for the heating resistor 30 and the temperature-sensitive resistors 31, 32 so that the resistances thereof can be varied sensitively with high response to the air flow.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal type air flow rate detecting device which is preferably used for detecting an intake air flow rate of an automobile engine or the like.

[0002]

2. Description of the Related Art Generally, in an engine for an automobile or the like, a mixture of fuel and intake air is burned in a combustion chamber of an engine body, and a rotational output of the engine is taken out from the combustion pressure. Detecting the intake air flow rate is an important factor in calculating

Therefore, FIGS. 7 and 8 show a conventional thermal air flow rate detecting device.

In the figure, reference numeral 1 denotes a thermal type air flow rate detecting device provided in the middle of an intake pipe 2. The thermal type air flow rate detecting device 1 is directed toward a combustion chamber (not shown) of an engine body. In order to detect the flow rate of the intake air flowing in the direction A shown, the intake pipe 2 is provided with a mounting hole 2A in the middle thereof.

Reference numeral 3 denotes a flow meter main body which constitutes the main body of the thermal type air flow rate detecting device 1. The flow meter main body 3 is formed by means such as insert molding as shown in FIG. A winding portion 4 formed in a stepped columnar shape for winding a reference resistor 14 described below, and a substantially disk-shaped portion located on the base end side of the winding portion 4 and having terminal pins 8A to 8D is integrally provided, and is extended in the radial direction of the intake pipe 2 from the tip end side of the winding part 4, and a heating resistor 9 and a temperature compensating resistor 11 to be described later are provided at the center of the intake pipe 2. A detection holder 6 for positioning and a circuit casing 7 to be described later, which is located outside the intake pipe 2 and to which a terminal portion 5 is connected, are roughly configured.

Reference numeral 7 denotes a circuit casing provided on the outer peripheral side of the intake pipe 2 so as to close the mounting hole 2A of the intake pipe 2, and the circuit casing 7 is made of an insulating resin material or the like and has a bottom portion. A fitting portion 7A that fits into the mounting hole 2A of the intake pipe 2 is integrally provided on the side. The circuit casing 7 incorporates a flow rate adjusting resistor, a differential amplifier (both not shown), and the like mounted on an insulating substrate made of, for example, a ceramic material.

Reference numerals 8A, 8B, 8C, and 8D denote four terminal pins (collectively referred to as terminal pins 8) axially protruding from the terminal portion 5 of the flowmeter body 3, and each of the terminal pins 8 is a flowmeter. It is provided integrally with, for example, four terminal plates (not shown) embedded in the winding portion 4 of the main body 3 and the detection holder 6, and is detachably connected to the connector portion (not shown) of the circuit casing 7. It is what is done.

Reference numeral 9 denotes a hot film type heating resistor provided on the detection holder 6 of the flowmeter main body 3 via terminals 10A and 10B. The heating resistor 9 is sensitive to temperature changes and its resistance value changes. It is composed of a small-diameter heating resistor element formed by winding a platinum wire or depositing a platinum film on an insulating cylinder made of a temperature-sensitive material such as platinum and made of a ceramic material such as alumina. Has been done. When the heating resistor 9 is energized by a battery (not shown), the heating resistor 9 is heated at a temperature of, for example, 240 ° C. before and after it is cooled by the intake air flowing in the intake pipe 2 in the direction of arrow A. The resistance value changes according to the flow rate of the intake air, and a detection signal of the flow rate is output.

Reference numeral 11 denotes a temperature compensating resistor provided on the upstream side of the heat generating resistor 9 and provided in the detection holder 6 of the flowmeter main body 3. The temperature compensating resistor 11 is on an insulating substrate made of a ceramic material such as alumina. It is formed by depositing a platinum film on the substrate by means of sputtering or the like, and both ends of the platinum film are terminals 12 provided upright on the detection holder 6.
It is connected between A and 12B.

Reference numeral 13 denotes a protective cover which is mounted on the detection holder 6 of the flowmeter main body 3. The protective cover 13 has a heating resistor 9 and a temperature compensating resistor 11 mounted on the detection holder 6, and is shown in FIG. As shown by the arrow, it is attached to the detection holder 6 to protect the heat generating resistance 9 and the temperature compensating resistance 11 and allow the intake air to flow. Note that in FIG. 7, in order to clearly show the heating resistor 9 and the temperature compensating resistor 11, the protective cover 13 is shown in a state of being removed from the detection holder 6.

Reference numeral 14 denotes a reference resistance consisting of a winding resistance wound around the winding portion 4 of the flowmeter main body 3, and the reference resistance 14 has terminals at both ends thereof standing on the winding portion 4. 15A and 15B, which are connected in series with the heating resistor 9. Here, among the terminal pins 8, the terminal pin 8A is connected to the terminal 15A via the terminal plate, and the terminal pin 8B is connected to the terminal 15A via another terminal plate.
B, 10A. The terminal pin 8C is connected to the terminals 10B and 12B via another terminal plate, and the terminal pin 8D is connected to the terminal 12A via another terminal plate.

In the conventional thermal air flow rate detecting device 1 thus constructed, when detecting the intake air flow rate of an automobile engine or the like, the terminal portion 5 of the flow meter main body 3 is inserted through the terminal pins 8. The detection holder 6 of the flowmeter main body 3 is inserted into the intake pipe 2 through the mounting hole 2A in a state where it is connected to the connector portion of the circuit casing 7 and the circuit is inserted into the mounting hole 2A from the outer peripheral side of the intake pipe 2. By installing the casing 7,
Heating resistor 9 and temperature compensation resistor 1 provided on the detection holder 6
1 is arranged at the center of the intake pipe 2.

In this case, the heating resistor 9 and the reference resistor 14 are connected in series, and the temperature compensating resistor 11 is connected in series to the flow rate adjusting resistor in the circuit casing 7. The compensating resistor 11 and the flow rate adjusting resistor form a bridge circuit. And
By continuously applying an electric current from the outside to the bridge circuit when the engine is started, the heating resistor 9 is connected to, for example, 240
Make sure to generate heat at the specified temperature before and after ℃.

In this state, when intake air flows through the intake pipe 2 toward the combustion chamber of the engine body in the direction of arrow A, the flow of the intake air cools the heat generating resistor 9 and the heat generating resistor 9 is cooled. Of the reference resistor 14 connected in series with the heating resistor 9, a detection signal corresponding to the flow rate of the intake air is detected as a change in the output voltage.

[0015]

By the way, in the above-mentioned prior art, the fact that the heating resistor 9 is cooled by the flow of the intake air flowing through the intake pipe 2 is utilized to change the resistance value of the heating resistor 9. Since the intake air flow rate is detected based on this, the heat generating resistor 9 is cooled by the intake air flow flowing in the direction A (forward direction) shown in FIG. 7 and flows in the direction B (reverse direction) shown in FIG. There is a problem in that the air flow is also cooled and the intake air flow rate is erroneously detected by the air flow in the opposite direction.

That is, in an engine body having a multi-cylinder cylinder, intake air is introduced into each cylinder each time an intake valve (not shown) is opened as the piston reciprocates in each cylinder. As it is sucked in the direction A (forward direction) indicated by arrow, the flow velocity of the air flowing in the intake pipe 2 repeatedly increases and decreases as illustrated in FIG. 4 according to the opening and closing of each intake valve. Come to do.

In particular, when the engine speed reaches from a low speed region to a medium speed region and the like, and the intake and exhaust amounts increase, the intake valve and the exhaust valve (not shown) overlap each other and the exhaust gas Since the part may blow back into the intake pipe 2 when the intake valve is opened, the time t1, t shown in FIG.
The flow velocity becomes negative (negative) like between 2 and an air flow that flows in the direction of the arrow B (reverse direction) is generated, and the intake air flow rate is detected to be excessive than the actual flow rate by this air flow, and A / There is a problem that the F control cannot be performed accurately.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention can prevent erroneous detection of the intake air flow rate due to the air flow in the opposite direction, and can greatly improve the flow rate detection accuracy. It is an object of the present invention to provide a thermal type air flow rate detecting device.

[0019]

In order to solve the above-mentioned problems, the present invention provides a flowmeter main body provided in the middle of an intake pipe and provided with a flow rate adjusting resistance and a reference resistance, and a flowmeter main body which is located in the intake pipe. The present invention is applied to a thermal air flow rate detection device that is provided in the flowmeter main body and includes a heat generation resistance cooled by intake air flowing in the intake pipe and a temperature compensation resistance for compensating for a temperature change of the intake air. It

The feature of the configuration adopted by the invention of claim 1 is that the heat generating resistance is formed on an insulating substrate attached to the flowmeter body, and a film is formed at least in the length direction of the insulating substrate. It consists of a heating resistor that extends in a
Further, the first and the second are formed on the insulating substrate so as to be spaced apart in front of and behind the heating resistor with respect to the flow direction of the intake air, and have resistance values that change depending on the flow direction of the intake air. There is a temperature sensitive resistor.

According to a second aspect of the present invention, the heating resistor is provided with an intermediate resistance portion which is located at an intermediate portion in the length direction of the insulating substrate and extends in the width direction, and both end sides of the intermediate resistance portion. Extending in opposite directions from each other in the length direction of the insulating substrate,
A second extension resistance portion, and the first temperature-sensitive resistor is located between the first extension resistance portion and the intermediate resistance portion and formed in parallel with the first extension resistance portion. The second temperature-sensitive resistor is located between the second extension resistance portion and the intermediate resistance portion and is formed in parallel with the second extension resistance portion.

Further, in the invention as set forth in claim 3, the insulating substrate is composed of a main substrate portion and a sub-substrate portion whose base end side is a fixed end attached to the flowmeter body and whose tip end side is a free end. A slit extending from the front end side toward the base end side is formed between the sub board part and the main board part, and the sub board part is integrally connected to the main board part at the base end side, and The heat generating resistor and the first and second temperature sensitive resistors are formed on the main substrate portion, and the temperature compensating resistor is formed on the sub substrate portion. .

Furthermore, in the invention described in claim 4,
The first and second temperature sensitive resistors are formed of a resistor material having a resistance value larger than that of the heat generating resistor, and heat from the heat generating resistor causes the first and second temperature sensitive resistors to pass through the insulating substrate. The temperature sensitive resistor is heated.

On the other hand, in the invention of claim 5, the first and second temperature sensitive resistors are formed of a resistor material having a resistivity corresponding to that of the heating resistor, and the first and second temperature sensing resistors are formed together with the heating resistor. The first and second temperature sensitive resistors are configured to generate heat by applying a voltage from the outside.

Further, in the invention according to claim 6, the heating resistor is connected to the ground through a reference resistor, the voltage across the reference resistor is taken out as a flow rate detection signal, and the first and second electrodes are connected. Flow rate signal output that detects the flow direction of the intake air based on the resistance value of the temperature sensitive resistor, and outputs the flow rate detection signal as it is when the flow direction of the intake air is the forward direction, and inverts when the flow direction of the intake air is the reverse direction. A structure including means is adopted.

[0026]

With the above structure, in the invention of claim 1, the first and second temperature sensitive resistors formed on the insulating substrate are separated from each other before and after the heat generating resistor in the flow direction of the intake air. Since the resistance value changes in accordance with the flow direction of the intake air, when the resistance value of the first temperature-sensitive resistor becomes smaller than that of the second temperature-sensitive resistor, for example, the air flow direction is set to the forward direction. When the resistance value of the second temperature-sensitive resistor becomes smaller than that of the first temperature-sensitive resistor, the air flow direction can be detected as the reverse direction.

According to the second aspect of the invention, the heating resistor and the first and second temperature sensitive resistors can be compactly formed by effectively utilizing the limited surface space of the insulating substrate. The surface area (mounting area) can be increased as much as possible.

Further, according to the third aspect of the invention, the temperature compensating resistor can be formed on the single insulating substrate together with the heating resistor and the first and second temperature sensitive resistors, and the number of parts can be reduced. it can. Then, by forming a slit between the sub-board portion on which the temperature compensation resistor is formed and the main substrate portion on which the heating resistor and the first and second temperature-sensitive resistors are formed, for example, the heating resistor It is possible to prevent heat from escaping from the main substrate portion heated to the sub-substrate portion to raise the temperature of the main substrate portion early.

Furthermore, in the invention of claim 4,
The second temperature-sensitive resistor can be heated by the heat from the heat-generating resistor via the insulating substrate, and by cooling either one of the first and second temperature-sensitive resistors according to the flow direction of air, The direction of air flow can be detected more reliably.

On the other hand, in the invention of claim 5, the first and second temperature-sensitive resistors can be made to generate heat together with the heat-generating resistor by applying a voltage from the outside. It is possible to raise the temperature early and surely improve the responsiveness when detecting the flow direction.

Further, in the invention of claim 6, the flow rate detection signal is taken out from the voltage across the reference resistor connected between the heating resistor and the ground, and the resistances of the first and second temperature sensitive resistors are obtained. Since the flow direction of the intake air can be detected based on the value, the flow rate detection signal can be directly output as a positive voltage signal when the flow direction of the intake air is a forward direction, and can be inverted as a negative voltage signal when the flow direction is the reverse direction. Can be output.

[0032]

Embodiments of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those of the conventional technique shown in FIG. 7 described above are designated by the same reference numerals, and the description thereof will be omitted.

1 to 4 show the first embodiment of the present invention.

In the figure, reference numeral 21 is a thermal air flow rate detecting device according to this embodiment, 22 is a flow meter main body constituting the main body of the thermal air flow rate detecting device 21, and the flow meter main body 22 is a conventional technique. Almost the same as the flowmeter body 3 described above, the reference resistance 23
Of the winding part 24, a terminal part 25 located on the base end side of the winding part 24 and integrally provided with a plurality of terminal pins (not shown), The detection holder 26, which extends from the tip side in the radial direction of the intake pipe 2, and a circuit casing 27, which will be described later, are roughly configured.

However, a slot (not shown) for detachably mounting an insulating substrate 28, which will be described later, is formed in the flowmeter main body 22 on the base end side of the detection holder 26, and the detection holder 26 is shown in FIG. As shown in FIG. 3, a heating resistor 30 and the like, which will be described later, are positioned in the center of the intake pipe 2 via an insulating substrate 28. A protective cover (not shown) similar to the protective cover 13 described in the prior art is attached to the detection holder 26 of the flowmeter main body 22.

Reference numeral 27 denotes a circuit casing provided on the outer peripheral side of the intake pipe 2 so as to close the mounting hole 2A of the intake pipe 2, and the circuit casing 27 is substantially the same as the circuit casing 7 described in the prior art. Formed, mounting hole 2 for intake pipe 2
Although having a fitting portion 27A that fits into A, the circuit casing 27 has a flow rate adjusting resistor 34, a differential amplifier 41, etc., which will be described later, on an insulating substrate (not shown) made of, for example, a ceramic material. These are built in when mounted.

Reference numeral 28 denotes an insulating substrate attached to the detection holder 26. The insulating substrate 28 is made of an insulating material such as glass, aluminum oxide (alumina) or aluminum nitride and has a length of 15 to 20 mm before and after. The width dimension is 4 to 7 mm before and after, and is formed in a rectangular flat plate shape. Further, the insulating substrate 28 has the detection holder 2 on the base end side.
It becomes a fixed end that is detachably attached to the slot of 6,
The tip side is the free end.

Here, as shown in FIG. 2, the insulating substrate 28 extends in a strip shape from the base end side to the tip end side and has a relatively large surface area, and the main substrate part 28A.
A sub-board portion 28B having a surface area smaller than that of the main board portion 28A and extending in a strip shape from the base end side toward the tip end side in parallel with
The sub-board portion 28B is located upstream of the main board portion 28A with respect to the intake air flow in the direction of arrow A.

An elongated slit 29 extending from the front end side to the base end side of the insulating substrate 28 is formed between the sub substrate portion 28B and the main substrate portion 28A. The slit 29 is formed in the main substrate portion 28A in the width direction of the insulating substrate 28.
The sub-board portion 28B and the sub-board portion 28B are separated from each other with a minute gap therebetween so as to be thermally insulated from each other, and the sub-board portion 28B is integrally connected to the main board portion 28A at the base end side.

Reference numeral 30 denotes a heating resistor formed on the main substrate portion 28A of the insulating substrate 28, which constitutes a heating resistor. The heating resistor 30 is provided on the main substrate portion 28A by means such as print printing or sputtering. An intermediate resistance portion 30A formed by depositing a platinum film on the main substrate portion 28A and extending in the width direction at the middle portion of the main substrate portion 28A, and the main substrate portion 28A from both end sides of the intermediate resistance portion 30A. First and second extension resistance portions 30B, 3 extending in opposite directions in the length direction of the
It is composed of 0C.

Here, the intermediate resistance portion 3 of the heating resistor 30.
0A and the extension resistors 30B and 30C have a crank shape as a whole, so that the heating resistor 30 and the temperature-sensitive resistors 31 and 32 described later are compactly formed on the main board portion 28A, and the heating resistor 30 Increase the surface area (mounting area) as much as possible.
The contact area with the intake air flowing in the direction can be increased.

Further, the heating resistor 30 is connected to the ground via the reference resistor 23 having a resistance value R1 as shown in FIG. 3, and the heating resistor 30 is almost the same as the heating resistor 9 described in the prior art. By external energization, for example, 240 ° C before,
The subsequent temperature causes heat. When the heating resistor 30 is cooled by the air flow in the intake pipe 2, the resistance value RH of the heating resistor 30 changes in accordance with the flow rate of air, so that the reference resistor 23 and the heat generation shown in FIG. The voltage across the reference resistor 23 can be taken out as a flow rate detection signal from the connection point a with the resistor 30.

Reference numerals 31 and 32 denote first and second temperature-sensitive resistors formed on the main substrate portion 28A together with the heating resistor 30, and the temperature-sensitive resistors 31 and 32 have a temperature coefficient of resistance (ppm / ppm).
Formed by depositing a metal film such as nickel or tungsten having a high temperature (.degree. C.) by means such as print printing or sputtering, and for example, the flow direction of the intake air flowing in the intake pipe 2 in the direction of arrow A (main substrate). Part 28A
Are arranged on the main board portion 28A in front of and behind the heating resistor 30 with respect to the width direction).

Here, the first temperature-sensitive resistor 31 is located between the intermediate resistance portion 30A and the extension resistance portion 30B of the heating resistor 30, and has a rectangular shape so as to extend in parallel with the extension resistance portion 30B. Has been formed. Further, the second temperature sensitive resistor 32 is located between the intermediate resistance portion 30A and the extension resistance portion 30C,
It is formed in a rectangular shape so as to extend parallel to the extension resistance portion 30C. The temperature sensitive resistors 31 and 32 are formed on the main board portion 28A with a substantially equal area, and the heat from the heating resistor 30 normally causes the main board portion 28A to heat.
Are heated to the same temperature as each other.

Further, when the temperature-sensitive resistors 31 and 32 are heated by the heat from the heat-generating resistor 30, when they come into contact with the air flowing in the intake pipe 2 in the directions of arrows A and B, the air Each resistance value RT by being cooled by the flow
1, RT2 changes. When the intake air flows in the intake pipe 2 in the direction of arrow A (forward direction), the heating resistor 3
Since the temperature sensitive resistor 31 located on the upstream side of 0 is largely cooled by this air flow, the resistance value RT1 of the temperature sensitive resistor 31 is greatly reduced. On the other hand, since the temperature-sensitive resistor 32 on the downstream side comes into contact with the airflow after being heated by the heat from the heat-generating resistor 30, the temperature-sensitive resistor 32 is not cooled so much and the temperature-sensitive resistor 32 is not cooled. The resistance value RT2 of the temperature resistor 32 hardly changes.

On the other hand, the inside of the intake pipe 2 is in the direction of arrow B (reverse direction).
When the air flows to the temperature sensing resistor 32, the temperature sensing resistor 32 located upstream of the heat generating resistor 30 is greatly cooled by the air flow in the opposite direction, and the resistance value RT2 of the temperature sensing resistor 32 is greatly reduced. On the other hand, the resistance value RT1 of the temperature-sensitive resistor 31 on the downstream side hardly changes. Therefore, it is possible to determine whether the air flow is in the forward direction or the reverse direction based on the difference between the resistance values RT1 and RT2 between the temperature sensitive resistors 31 and 32.

Reference numeral 33 denotes a temperature compensating resistor formed on the sub-substrate portion 28B of the insulating substrate 28. The temperature compensating resistor 33 has substantially the same structure as the temperature compensating resistor 11 described in the prior art, and is printed or sputtered. It is formed by depositing a platinum film on the sub-substrate portion 28B by using such means. The temperature compensating resistor 33 has a resistance value RK larger than that of the heating resistor 30, and is connected to the ground via a flow rate adjusting resistor 34 having a resistance value R2 as shown in FIG. Further, the temperature compensating resistor 33 and the flow rate adjusting resistor 34
A connection point b between and is connected to an inverting input terminal of a differential amplifier 41 described later.

Reference numerals 35, 35, ... Depict, for example, six electrodes formed on the base end side of the insulating substrate 28. The electrodes 35 are arranged in a row in the width direction of the insulating substrate 28 at a predetermined interval. By inserting the base end side of the above into the slot of the detection holder 26, it is connected to each terminal (not shown) on the side of the detection holder 26. At this time, the electrodes 35 have the heating resistor 30, the first and second temperature sensitive resistors 3 respectively.
1, 32 and the temperature compensating resistor 33, etc. are connected between the emitter side of the current control transistor 37 described later and the ground, and the heat generating resistor 30, the temperature sensitive resistors 31, 32, the temperature compensating resistor 33, etc. The processing circuit for flow rate detection shown in FIG. 3 is configured together with each electronic component provided in the circuit casing 27.

Next, the processing circuit for flow rate detection will be described with reference to FIG.

In the figure, 36 is a DC power source having a battery voltage VB, 37 is a current control transistor whose collector side is connected to the DC power source 36, and the current control transistor 37 has an emitter side with a heating resistor 30, It is connected to the temperature sensitive resistors 31 and 32 and the temperature compensation resistor 33, and the base side is connected to the output terminal of the differential amplifier 41. The current control transistor 37 controls the current applied (powered) from the DC power supply 36 to the heating resistor 30, the temperature sensitive resistors 31, 32 and the temperature compensation resistor 33 based on the output signal from the differential amplifier 41. is doing.

Reference numerals 38 and 39 denote adjusting resistors connected between the temperature sensitive resistors 31 and 32 and the ground via connection points c and d, and the adjusting resistors 38 and 39 have the same resistance value R3. However, the connection points c and d with the temperature sensitive resistors 31 and 32 are connected to the respective input terminals of the comparator 40 described later. Then, of the series connection parts of the temperature sensitive resistors 31 and 32 and the adjustment resistances 38 and 39, one of the series connection parts is the temperature compensation resistor 3.
A bridge circuit is configured together with the serial connection portion of 3 and the flow rate adjusting resistor 34.

Reference numeral 40 denotes a comparator which compares the voltage levels at the connection points c and d and outputs the larger voltage. The output terminal of the comparator 40 is the non-inverting input terminal of the differential amplifier 41 described later. It is connected. Here, the temperature sensitive resistors 31, 3
As described above, the resistance values RT1 and RT2 of 2 greatly decrease the resistance value RT1 of the temperature sensitive resistor 31 when the air flow flowing in the intake pipe 2 is in the forward direction (direction indicated by the arrow A), and (Arrow B
Direction), the resistance value RT2 of the temperature sensitive resistor 32 is greatly reduced.

As a result, when the air flow is in the forward direction, the voltage level at the connection point c becomes higher than that at the connection point d, and the output voltage corresponding to the voltage level at the connection point c is output from the comparator 40 to the differential amplifier 41. It is output to the inverting input terminal. When the air flow is in the opposite direction, the voltage level at the connection point d becomes higher than that at the connection point c, and the output voltage corresponding to the voltage level at the connection point d is output from the comparator 40 to the differential amplifier 41. When the connection points c and d have the same voltage level, the output voltage corresponding to the voltage level at this time is output from the comparator 40 to the differential amplifier 41.

Reference numeral 41 denotes a differential amplifier built in the circuit casing 27 together with the current controlling transistor 37, the comparator 40, etc., and the inverting input terminal of the differential amplifier 41 is composed of the temperature compensating resistor 33 and the flow rate adjusting resistor 34. The non-inverting input terminal is connected to the output terminal of the comparator 40. The output terminal of the differential amplifier 41 is connected to the base of the current controlling transistor 37, and based on the potential difference between the output terminal of the comparator 40 and the connection point b, the DC power supply 36 causes the heating resistor 30, the temperature sensing element. Resistors 31, 32
The current applied to the temperature compensation resistor 33 (power supply) is controlled by the current control transistor 37.

Reference numeral 42 indicates another comparator whose input side is connected to the connection points c and d. The output side of the comparator 42 is connected to a selection circuit 44 which will be described later, and the comparator 42 has a voltage level between the connection points c and d. Based on the output signal as shown in FIG. 4, it is output to the selection circuit 44. As a result, the output voltage Vout output from the selection circuit 44 is selected (inverted) into a positive or negative voltage depending on the actual direction of the air flow.

That is, as shown in FIG. 4, the flow velocity of the air flowing through the intake pipe 2 repeatedly pulsates by increasing and decreasing in response to opening and closing of the intake valve (not shown). Then, for example, in the middle speed range of the engine, the intake valve and the exhaust valve (not shown) overlap each other, and a part of the exhaust gas may blow back into the intake pipe 2 as the intake valve opens. At this time, as shown in FIG.
The flow velocity becomes negative (minus) such as between the times t1 and t2 in the middle, and an air flow flowing in the opposite direction (the direction of arrow B) is generated.

In this case, when the air flow in the intake pipe 2 is in the forward direction (direction indicated by the arrow A), the voltage level at the connection point c becomes higher than the connection point d, so that the output signal of the comparator 42 is as shown in FIG. The voltage V0 (ON state) is output to the selection circuit 44 as shown in FIG. On the other hand, the air flow is in the opposite direction (arrow B
Direction), the voltage level at the connection point d becomes higher than that at the connection point c, so that the output signal of the comparator 42 is output to the selection circuit 44 when the voltage becomes substantially zero level (OFF state).

Reference numeral 43 represents an inverting circuit provided between the selection circuit 44 and the connection point a between the heating resistor 30 and the reference resistor 23. The inverting circuit 43 is provided in the inverting circuit 43.
Flow rate detection signal (reference resistance 2
3) is inverted from a positive voltage signal to a negative voltage signal and output to the selection circuit 44.

Further, reference numeral 44 denotes a selection circuit which constitutes flow rate signal output means together with the inverting circuit 43 and the like.
The input side of 4 is connected to the connection point a, the inverting circuit 43 and the comparator 42, and its output terminal 45 is connected to an external control unit (not shown) or the like. And
When the output signal from the comparator 42 is in the ON state, since the air flow in the intake pipe 2 is in the forward direction, the selection circuit 44 causes the selection circuit 44 to detect the flow rate from the connection point a (voltage across the reference resistor 23).
Is output to the output terminal 45 as it is as a positive voltage signal. On the other hand, when the output signal from the comparator 42 is in the OFF state, the air flow in the intake pipe 2 is in the opposite direction, and therefore the selection circuit 44 inverts the flow rate detection signal from the connection point a.
Then, the signal is output to the output terminal 45 in the state of being inverted to the negative voltage signal.

Thermal air flow rate detection device 21 according to the present embodiment
Has a configuration as described above. Next, a flow rate detecting operation of the intake air flowing through the intake pipe 2 will be described.

First, at the same time when the engine body is started, the heat generating resistor 30, the temperature sensitive resistors 31, 32 and the temperature compensating resistor 3 are supplied from the DC power source 36 via the current controlling transistor 37.
3 is applied to heat the heat generating resistor 30 at temperatures before and after 240 ° C., and the heat from the heat generating resistor 30 is applied to the temperature sensitive resistor 3 via the main substrate portion 28A of the insulating substrate 28.
1, 32 are heated (heated).

In this state, when the intake air flows in the intake pipe 2 in the direction of arrow A (forward direction) shown in FIG.
Since the heating resistor 30 attached to the detection holder 26 of the flowmeter main body 22 via the insulating substrate 28 and the temperature-sensitive resistor 31 on the upstream side are cooled by the airflow at this time, the resistance value of the heating resistor 30 is reduced. RH and the resistance value RT1 of the temperature sensitive resistor 31 decrease corresponding to the flow velocity of the intake air, and the connection point a shown in FIG.
As the voltage level of the connection point c increases, the voltage level of the connection point c becomes larger than the connection point d, and the output voltage corresponding to the voltage level of the connection point c is output from the comparator 40 to the differential amplifier 41.

As a result, the output voltage of the comparator 40 becomes higher than the voltage level of the connection point b, and the differential amplifier 41 determines, based on the potential difference between the output terminal of the comparator 40 and the connection point b.
From the DC power supply 36 to the heating resistor 30, the temperature sensitive resistors 31 and 3
2 and the current applied to the temperature compensation resistor 33 (power supply) are controlled via the current control transistor 37. As a result, a larger current is supplied to the heating resistor 30 and the temperature sensitive resistor 31 as compared with the temperature sensitive resistor 32 and the temperature compensation resistor 33, so that the temperature of the heating resistor 30 again approaches 240 ° C. The heat-sensitive resistor 31 is heated by the heat from the heat-generating resistor 30 via the insulating substrate 28. In this case, since the temperature sensitive resistor 32 is in a higher temperature state than the temperature sensitive resistor 31, the heating resistor 3
The heat from 0 is substantially transmitted to the temperature sensitive resistor 31 side.

At this time, the voltage level at the connection point a rises according to the current supplied to the heating resistor 30 and the reference resistor 23, which increases or decreases in accordance with the flow rate of the intake air flowing through the intake pipe 2. Therefore, the flow rate detection signal (voltage across the reference resistor 23) from the connection point a is output as it is to the output terminal 45 as a positive voltage signal by the selection circuit 44, and the flow rate of the intake air is detected by the output voltage Vout at this time. To do.

On the other hand, when a backflow in the direction of the arrow B occurs in the intake pipe 2, the temperature sensitive resistor 32, which is on the upstream side of the heat generating resistor 30 with respect to the airflow in the opposite direction, is in the opposite direction. It is cooled together with the heating resistor 30 by the air flow. The resistance value RT2 of the temperature-sensitive resistor 32 is greatly reduced, whereas the resistance value RT1 of the temperature-sensitive resistor 31 on the downstream side hardly changes. Therefore, the voltage level at the connection point d is The output voltage corresponding to the voltage level at the connection point d becomes larger than that at the connection point c, and the output voltage corresponding to the voltage level at the connection point d changes from the comparator 40 to the differential amplifier 41.
Is output to.

As a result, the differential amplifier 41 determines that the DC power supply 3 is based on the potential difference between the output terminal of the comparator 40 and the connection point b.
6 controls the current applied to (power-supplied to) the heating resistor 30, the temperature sensitive resistors 31 and 32, and the temperature compensation resistor 33 via the current control transistor 37.
As a result, 0 again generates heat up to a temperature of 240 ° C. before and after 240 ° C., and heat from the heat generating resistor 30 heats the temperature sensitive resistor 32 via the insulating substrate 28.

Then, in this case, the voltage level at the connection point d is changed to the connection point c by the air flow in the opposite direction (the direction of arrow B).
The output signal of the comparator 42 has a voltage of substantially zero level (OF) between the times t1 and t2 shown in FIG.
Since the F state) is output to the selection circuit 44, the selection circuit 44 outputs the flow rate detection signal from the connection point a to the inversion circuit 4.
The reverse air flow rate can be detected by causing the output voltage to be output to the output terminal 45 in the state of being inverted to a negative voltage signal at 3 and setting the output voltage Vout at this time to a negative value.

Thus, according to the present embodiment, the base end side of the insulating substrate 28 is detachably attached to the detection holder 26 of the flowmeter body 22 which is provided so as to project into the intake pipe 2, and the insulating substrate 2 is attached.
8 is divided into a main board portion 28A and a sub-board portion 28B in the air flow direction by a slit 29 extending from the front end side to the base end side, and a crank shape is formed on the insulating board 28 to form the insulating board 28. Of the heating resistor 30 extending in the length direction of the heating resistor, and first and second temperature-sensitive resistors spaced apart in front of and behind the heating resistor 30 and extending in parallel with the extension resistance portions 30B and 30C of the heating resistor 30. Since 31 and 32 are configured to form a film, the following operational effects can be obtained.

That is, when a current is applied to the heat generating resistor 30 from the external DC power source 36 through the current controlling transistor 37 to heat the heat generating resistor 30 at a temperature of 240 ° C. before and after, The heat from the heating resistor 30 is transmitted to the first and second temperature sensitive resistors 31 and 32 through the insulating substrate 28, and the temperature sensitive resistors 31 and 32 can be heated to a required temperature.

When an air flow such as intake air is generated in the intake pipe 2 in this state, one of the temperature sensitive resistors 31 and 32 located upstream of the air flow at this time. 31 (32) is the temperature-sensitive resistor 32 (31) on the downstream side.
Since it is cooled by the air flow more than that, a difference occurs in the resistance values RT1 and RT2 of the temperature sensitive resistors 31 and 32, and based on the difference in the resistance values RT1 and RT2 between the temperature sensitive resistors 31 and 32. It is possible to reliably detect whether the air flow at this time is the forward direction or the reverse direction.

Further, since the heating resistor 30 is cooled by the air flow at this time and the resistance value RH of the heating resistor 30 changes in accordance with the flow rate of air, the reference resistor 23 and the heating resistor shown in FIG. The voltage across the reference resistor 23 can be taken out as a flow rate detection signal from the connection point a with the body 30 and is output from the output terminal 45 as a positive or negative voltage signal by the selection circuit 44, whereby the output at this time is output. Voltage V
The flow rate of air can be accurately detected based on out.

On the other hand, the heating resistor 30 formed on the main substrate portion 28A of the insulating substrate 28 is provided with an intermediate resistance portion 30A which is located at an intermediate portion in the length direction of the main substrate portion 28A and extends in the width direction.
First and second extension resistance portions 30B and 3 extending from the intermediate resistance portion 30A in opposite directions in the length direction of the main substrate portion 28A.
0C, and the first and second temperature sensitive resistors 31 and 32 are formed on the main substrate portion 28A so as to extend in parallel along the extension resistance portions 30B and 30C.
By effectively utilizing the limited surface space of the main board portion 28A, the heating resistor 30 and the first and second temperature sensitive resistors 31,
32 can be formed compactly, and the surface area (mounting area) of the heating resistor 30 can be increased as much as possible.

As a result, the contact area of the heat generating resistor 30 and the temperature sensitive resistors 31, 32 can be made large with respect to the air flow flowing in the intake pipe 2, and the resistance values RH, R of these can be obtained.
T1 and RT2 can be changed sensitively and highly responsive to the air flow.

Further, by forming a slit 29 extending from the front end side toward the base end side between the main board portion 28A and the sub-board portion 28B of the insulating board 28, the main board portion 2 is formed.
8A and the sub-board portion 28B are separated from each other in the air flow direction, and the temperature compensating resistor 33 is formed on the sub-board portion 28B. Therefore, the heating resistor 30 is formed on the single insulating substrate 28.
Further, the temperature compensating resistor 33 can be formed as a film together with the temperature sensitive resistors 31 and 32, and the number of parts can be reduced. The slit 29 can prevent heat from escaping from the main board portion 28A heated by the heating resistor 30 to the sub-board portion 28B, and the temperature of the main board portion 28A can be raised early.

Therefore, according to this embodiment, the flow rate of the intake air flowing through the intake pipe 2 can be reliably detected based on the resistance value RH of the heating resistor 30, and the temperature sensitive resistors 31, 32 can be detected.
The flow direction of the air can be reliably detected based on the difference between the resistance values RT1 and RT2 between the intake air and the intake air even when the exhaust gas is blown back into the intake pipe 2 in the middle speed range of the engine or the like to cause backflow. The flow rate can be detected with high accuracy.

Next, FIGS. 5 and 6 show a second embodiment of the present invention. The feature of this embodiment is that the first and second temperature sensitive resistors formed on the insulating substrate are connected to the heating resistors. The structure is made of a resistor material having a resistivity corresponding to the body, and the first and second temperature sensitive resistors together with the heat generating resistor are made to generate heat by applying a voltage from the outside. In this embodiment, the same components as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the figure, reference numeral 51 denotes an insulating substrate according to the present embodiment, and the insulating substrate 51 can be attached / detached to / from the slot of the detection holder 26 on the base end side thereof in substantially the same manner as the insulating substrate 28 described in the first embodiment. It is a fixed end that is attached to, and the free end is on the tip side. However, the insulating substrate 51 is formed of an insulating material such as glass, aluminum oxide (alumina), or aluminum nitride into a rectangular flat plate shape, and has a length dimension of 15 to 20 mm before and after and a width dimension of 3 mm.
~ 5mm before and after.

Reference numeral 52 denotes a heating resistor forming a heating resistor formed on the insulating substrate 51. The heating resistor 52 is substantially the same as the heating resistor 30 described in the first embodiment.
An intermediate resistance portion 52A which is formed by depositing a platinum film on the insulating substrate 51 using a means such as print printing or sputtering, and which is located at an intermediate portion in the length direction of the insulating substrate 51 and extends in the width direction; The intermediate resistance portion 52A is composed of first and second extension resistance portions 52B and 52C extending in opposite directions in the length direction of the insulating substrate 51 from both ends thereof.

Here, the intermediate resistance portion 5 of the heating resistor 52.
2A and the extension resistance portions 52B and 52C are formed into a crank shape as a whole to compactly form the heat generating resistor 52 and the temperature sensitive resistors 53 and 54, which will be described later, on the insulating substrate 51, and the surface area of the heat generating resistor 52. (Mounting area) can be increased as much as possible, and for example, the contact area with the intake air flowing in the intake pipe 2 in the direction of arrow A can be increased.

The heating resistor 52 is connected to the ground via the reference resistor 23 having a resistance value R1 as shown in FIG.
The heating resistor 52 generates heat at a temperature of, for example, 240 ° C. before and after being energized from the outside, in substantially the same manner as the heating resistor 9 described in the prior art. When the heating resistor 52 is cooled by the airflow in the intake pipe 2, the resistance value RH of the heating resistor 52 changes in accordance with the flow rate of air, so that the reference resistor 23 and the heat generation shown in FIG. The voltage across the reference resistor 23 can be taken out as a flow rate detection signal from the connection point a with the resistor 52.

Reference numerals 53 and 54 denote first and second temperature sensitive resistors formed on the insulating substrate 51 together with the heating resistor 52.
The temperature-sensitive resistors 53 and 54 are formed by depositing a platinum film by means such as print printing or sputtering like the heat-generating resistor 52. For example, the intake air flowing in the intake pipe 2 in the direction of arrow A They are arranged on the insulating substrate 51 in front of and behind the heating resistor 52 with respect to the flow direction (width direction of the insulating substrate 51).

Here, the first temperature sensitive resistor 53 is located between the intermediate resistance portion 52A and the extension resistance portion 52B of the heating resistor 52, and has a rectangular shape so as to extend in parallel with the extension resistance portion 52B. Has been formed. The second temperature sensitive resistor 54 is located between the intermediate resistance portion 52A and the extension resistance portion 52C,
It is formed in a rectangular shape so as to extend parallel to the extension resistance portion 52C. The temperature sensitive resistors 53 and 54 are formed on the insulating substrate 51 with substantially equal areas, and are energized from the outside together with the heat generating resistor 52 so that they have a predetermined temperature (lower than the heat generating resistor 52). ) And generate substantially the same resistance values RT1 and RT2.

When the temperature-sensitive resistors 53 and 54 come into contact with the air flowing in the intake pipe 2 in the directions A and B in this state, the temperature-sensitive resistors 53 and 54 are cooled by the air flow to generate their respective resistances. The values RT1 and RT2 change. That is, when the intake air flows in the intake pipe 2 in the direction of arrow A (forward direction),
Temperature-sensitive resistor 53 located upstream of the heating resistor 52
Are greatly cooled by this air flow, and the temperature sensitive resistor 5
The resistance value RT1 of 3 is greatly reduced. On the other hand, since the temperature-sensitive resistor 54 on the downstream side comes into contact with the air flow after being heated by the heat from the heat-generating resistor 52, the temperature-sensitive resistor 54 is not cooled so much and the temperature-sensitive resistor 54 is not cooled. Resistance value R of the temperature resistor 54
T2 hardly changes.

On the other hand, the inside of the intake pipe 2 is in the direction of arrow B (reverse direction).
When the air flows into the temperature sensitive resistor 54, the temperature sensitive resistor 54 located upstream of the heat generating resistor 52 is greatly cooled by the air flow in the opposite direction, and the resistance value RT2 of the temperature sensitive resistor 54 is significantly reduced. On the other hand, the resistance value RT1 of the temperature-sensitive resistor 53 on the downstream side hardly changes. Therefore, it is possible to determine whether the air flow is in the forward direction or the reverse direction based on the difference between the resistance values RT1 and RT2 between the temperature sensitive resistors 53 and 54.

Reference numerals 55, 55, ... Depict, for example, five electrodes formed on the base end side of the insulating substrate 51. The electrodes 55 are arranged in a row in the width direction of the insulating substrate 51 at predetermined intervals. By inserting the base end side of the above into the slot of the detection holder 26, it is connected to each terminal (not shown) on the side of the detection holder 26. At this time, each electrode 55 has the heating resistor 52 and the first and second temperature sensitive resistors 53 and 54 shown in FIG.
Of the heat generating resistor 52 and the temperature sensitive resistors 53, 54, etc. are connected with the electronic parts provided in the circuit casing 27 together with the processing circuit for flow rate detection shown in FIG. Constitute.

Reference numeral 56 denotes a temperature compensating resistor. The temperature compensating resistor 56 has substantially the same structure as the temperature compensating resistor 11 described in the prior art, and is printed on an insulating substrate (not shown) different from the insulating substrate 51. It is formed by depositing a platinum film using a means such as printing or sputtering.
The temperature compensating resistor 56 has a resistance value RK larger than that of the heat generating resistor 52, and is grounded via the flow rate adjusting resistor 34 having a resistance value R2 like the temperature compensating resistor 33 described in the first embodiment. (See FIG. 6). The connection point b between the temperature compensation resistor 56 and the flow rate adjustment resistor 34 is connected to the inverting input terminal of the differential amplifier 41.

Thus, in this embodiment having such a structure, it is possible to obtain substantially the same operational effects as in the first embodiment, but particularly in this embodiment, the first and second temperature-sensitive resistors are provided. The bodies 53 and 54 are made of a resistor material having a resistivity corresponding to that of the heating resistor 52, and the temperature sensitive resistors 53 and 54 are formed.
Since the heat generating resistor 52 and the heat generating resistor 52 are configured to generate heat by applying a voltage from the outside, the temperature sensitive resistors 53 and 54 can be caused to generate heat at the start of the engine and can be quickly heated to a predetermined temperature. The temperature rise can be promoted, and the responsiveness when detecting the flow rate and flow direction of air can be effectively improved.

In the second embodiment, the insulating substrate 5
Although the heating resistor 52 and the temperature sensitive resistors 53 and 54 are formed on the first substrate, and the temperature compensating resistor 56 is formed on another insulating substrate, the second embodiment is replaced with, for example, the first embodiment. Like the insulating substrate 28 described in 1., the insulating substrate 51 is composed of a main substrate portion and a sub substrate portion, and a heating resistor 52 and temperature sensitive resistors 53 and 54 are formed on the main substrate portion. You may make it form the temperature compensation resistance 56 on it.

Also, with respect to the insulating substrate 28 described in the first embodiment, the main substrate portion 28A and the sub substrate portion 28 are not always required.
B does not need to be configured, and the heating resistor 3 is formed on a single insulating substrate like the insulating substrate 51 described in the second embodiment.
0 and the temperature sensitive resistors 31 and 32 are formed, and the temperature compensation resistor 3
3 may be formed on another insulating substrate.

Further, in each of the above embodiments, the flowmeter main body 2
Although it has been described that the reference resistance 23 wound around the second winding portion 24 is provided so as to project into the intake pipe 2, the present invention is not limited to this. For example, the reference resistance 23 is provided inside the circuit casing 27 provided outside the intake pipe 2. The reference resistor 23 may be arranged together with the flow rate adjusting resistor 34 and the like.

[0091]

As described in detail above, according to the present invention, as described in claim 1, heat is generated by the heating resistor extending in the form of a film at least in the length direction on the insulating substrate attached to the flowmeter main body. A resistor is formed, and on this insulating substrate,
Since the first and second temperature sensitive resistors which are separated from each other in front of and behind the heat generating resistor with respect to the flow direction of the intake air and whose resistance values change according to the flow direction of the intake air are provided,
When the resistance value of the first temperature-sensitive resistor becomes smaller than that of the second temperature-sensitive resistor, the flow direction of air can be detected as the forward direction, and the second temperature-sensitive resistor can detect the first temperature-sensitive resistor. When the resistance value is smaller than that of the resistor, the air flow direction can be detected as the reverse direction. Therefore, it is possible to prevent erroneous detection of the intake air flow rate due to the air flow in the opposite direction, improve the flow rate detection accuracy, and reliably improve the reliability of the A / F control.

Further, in the invention of claim 2, the heating resistor and the first and second temperature sensitive resistors can be compactly formed by effectively utilizing the limited surface space of the insulating substrate. Since the surface area (mounting area) can be made as large as possible, the contact area between the heating resistor and each temperature sensitive resistor can be set large for the air flow flowing in the intake pipe, and these resistance values can It can be sensitively and highly responsive to flow.

Further, according to the third aspect of the present invention, the temperature compensating resistor can be formed on the single insulating substrate together with the heating resistor and each temperature sensitive resistor, and the number of parts can be reduced. Then, by forming a slit between the sub-board portion on which the temperature compensation resistor is formed and the main substrate portion on which the heating resistor and each of the temperature-sensitive resistors are formed, for example, the main heating element is heated. It is possible to prevent heat from escaping from the substrate portion to the sub-substrate portion, raise the temperature of the main substrate portion early, and improve the responsiveness at the time of engine start.

Furthermore, in the invention of claim 4,
By heating the second temperature-sensitive resistor with the heat from the heat-generating resistor via the insulating substrate, one of the first and second temperature-sensitive resistors can be surely set according to the flow direction of air. Therefore, the air flow direction can be effectively detected, and the cost can be reduced.

On the other hand, in the fifth aspect of the invention, since the first and second temperature sensitive resistors are made to generate heat together with the heat generating resistors by voltage application from the outside, each of the temperature sensitive resistors is started when the engine is started. It is possible to generate heat and quickly heat to a predetermined temperature, accelerate the temperature rise of the heating resistor, and effectively improve the responsiveness when detecting the flow rate and flow direction of air.

Further, in the invention of claim 6, the flow rate detection signal is taken out from the voltage across the reference resistor connected between the heating resistor and the ground, and the resistance of the first and second temperature sensitive resistors is obtained. Since the air flow direction can be detected based on the value, the flow rate detection signal can be directly output as a positive voltage signal when the air flow direction is a forward direction, and can be inverted and output as a negative voltage signal when the air flow direction is the reverse direction. It is possible,
The flow rate of the intake air can be detected with high accuracy even when the exhaust gas is blown back into the intake pipe and a reverse flow occurs in the middle speed range of the engine.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a thermal air flow rate detecting device according to a first embodiment of the present invention in a state where it is attached to an intake pipe.

FIG. 2 is a plan view showing a heating resistor, each temperature-sensitive resistor, a temperature compensation resistor, etc. formed on an insulating substrate.

FIG. 3 is a circuit diagram showing a circuit configuration of a thermal type air flow rate detecting device according to a first embodiment.

FIG. 4 is a characteristic diagram showing a relationship between a flow velocity of intake air and an output signal of a comparator.

FIG. 5 is a plan view showing a heating resistor and each temperature sensitive resistor formed on an insulating substrate according to a second embodiment.

FIG. 6 is a circuit diagram showing a circuit configuration of a thermal type air flow rate detecting device according to a second embodiment.

FIG. 7 is a vertical cross-sectional view showing a conventional thermal air flow rate detection device attached to an intake pipe.

FIG. 8 is a perspective view showing a flowmeter main body, a heat generation resistance and the like according to a conventional technique.

[Explanation of symbols]

 2 Intake pipe 21 Thermal air flow detector 22 Flowmeter body 23 Reference resistance 24 Winding part 26 Detection holder 27 Circuit casing 28,51 Insulation board 28A Main board part 28B Sub-board part 29 Slit 30,52 Heating resistor 30A, 52A Intermediate resistance part 30B, 30C, 52B, 52C Extension resistance part 31, 53 First temperature-sensitive resistor 32, 54 Second temperature-sensitive resistor 33, 56 Temperature compensation resistance 34 Flow rate adjustment resistance 35, 55 Electrode 36 DC Power supply 37 Current control transistors 40, 42 Comparator 41 Differential amplifier 43 Inversion circuit 44 Selection circuit (flow rate signal output means)

Claims (6)

[Claims] 1. A flowmeter main body provided in the middle of an intake pipe, provided with a flow rate adjusting resistance and a reference resistance, and intake air which is provided in the flowmeter main body inside the intake pipe and flows in the intake pipe. In a thermal type air flow rate detecting device comprising a heat generating resistance cooled by a heat absorbing resistor and a temperature compensating resistor for compensating the temperature change of the intake air, the heat generating resistor is provided on an insulating substrate attached to the flow meter main body. The heating resistor is formed and extends in a film shape at least in the length direction of the insulating substrate, and is separated from the heating resistor on the insulating substrate with respect to the flow direction of the intake air. A thermal air flow rate detection device, comprising: first and second temperature-sensitive resistors that are formed according to the flow direction of the intake air. 2. The heating resistor has an intermediate resistance portion extending in the width direction at an intermediate portion in the length direction of the insulating substrate, and both ends of the intermediate resistance portion in the length direction of the insulating substrate. The first temperature sensitive resistor is formed between first and second extension resistance portions extending in directions opposite to each other, and the first temperature-sensitive resistor is located between the first extension resistance portion and the intermediate resistance portion. Is formed in parallel with the second extension resistance part, and the second temperature-sensitive resistor is formed between the second extension resistance part and the intermediate resistance part and is formed in parallel with the second extension resistance part. The thermal type air flow rate detection device according to claim 1. 3. The insulating substrate is composed of a main substrate portion and a sub-substrate portion whose base end side is a fixed end attached to the flowmeter body and whose front end side is a free end. A slit extending from the front end side toward the base end side, and the sub-board portion is integrally connected to the main board portion at the base end side, and the main substrate portion has the heating resistor. 3. The thermal air flow rate detection device according to claim 1, wherein the body and the first and second temperature-sensitive resistors are formed into a film, and the temperature compensation resistance is formed into a film on the sub-board portion. 4. The first and second temperature sensitive resistors are made of a resistor material having a resistance value larger than that of the heating resistor, and the heat from the heating resistor causes the heat to pass through the insulating substrate. The thermal air flow rate detecting device according to claim 1, wherein the first and second temperature sensitive resistors are heated. 5. The first and second temperature sensitive resistors are formed of a resistor material having a resistivity corresponding to that of the heat generating resistor,
4. The thermal air flow rate detection device according to claim 1, wherein the first and second temperature sensitive resistors together with the heating resistor are configured to generate heat by applying a voltage from the outside. 6. The heating resistor is connected to ground via a reference resistor, the voltage across the reference resistor is taken out as a flow rate detection signal, and based on the resistance values of the first and second temperature sensitive resistors. A flow rate signal output means for detecting a flow direction of intake air, outputting the flow rate detection signal as it is when the flow direction of the intake air is forward, and inverting and outputting the flow rate detection signal when the flow direction is reverse. The thermal air flow rate detection device according to 2, 3, 4 or 5.