JPH0843162A - Thermal air flow rate detector - Google Patents

Abstract

PURPOSE:To enhance accuracy in the detection of flow rate of sucked air by deciding whether air is flowing forward or reversely. CONSTITUTION:A first heating resistor 29 and a second heating resistor 30 are formed, respectively, in the upstream and downstream on an insulating board. Variation of each resistance RH1, RH2 is inputted, in the form of flow rate voltage V1, V2, to a differential amplifier 41. In case of forward air flow, V1>V2 and the differential amplifier 41 delivers an output voltage Vout higher than a bias voltage V0. In case of reverse air flow, V1<V2 and the differential amplifier 41 delivers an output voltage Vout lower than the bias voltage V0. Consequently, the output voltage Vout can be detected accurately.

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. 6 and 7 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 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 is mounted on the detection holder 6 with a heat generating resistor 9 and a temperature compensating resistor 11, and then, 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. In FIG. 6, the protective cover 13 is removed from the detection holder 6 in order to clearly show the heat generating resistor 9 and the temperature compensating resistor 11.

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) indicated by the arrow in FIG. 6 and flows in the direction B indicated by the arrow (reverse direction). 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, intake air is supplied to each cylinder each time an intake valve (not shown) is opened in response to reciprocating motion of the piston in each cylinder. Since it is sucked inward in the direction of arrow A (forward direction), the flow velocity of the air flowing in the intake pipe 2 is repeatedly increased and decreased as illustrated in FIG. 8 in accordance with the opening and closing of each intake valve. Becomes pulsating.

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 type air flow rate detecting device which is provided in the flowmeter main body and is composed of a heat generating resistance cooled by intake air flowing in the intake pipe.

The feature of the configuration adopted by the invention of claim 1 is that the heat generating resistor is formed in a film shape on an insulating substrate attached to the flowmeter body, and is located on the upstream side with respect to the flow direction of the intake air. A first flow rate that outputs a first flow rate signal from a change in the resistance value of the first heat generation resistor, which is composed of a first heat generation resistor located at Detecting means; second flow rate detecting means for outputting a second flow rate signal based on a change in resistance value of the second heating resistor; first flow rate signal for outputting the second flow rate signal; and second flow rate signal for outputting from the first flow rate detecting means.
The difference calculation means for outputting the difference from the second flow rate signal output from the flow rate detection means as the flow rate detection signal.

According to the second aspect of the invention, the reference signal is added to the flow rate detection signal output from the difference calculation means.

According to a third aspect of the present invention, the first flow rate detecting means and the second flow rate detecting means are respectively provided with temperature compensating resistors for compensating the temperature of the intake air.

[0023]

With the above construction, in the first aspect of the invention, the first heating resistor located on the upstream side and the second heating resistor located on the downstream side in the flow direction of the intake air are provided on the insulating substrate. Are formed in a film shape, and the first heating resistor and the second heating resistor have different resistance values depending on the flow direction of the intake air, and the difference in the resistance value is the first flow rate. Signal and second
Is output as a flow rate signal. Then, the difference calculation means can calculate the difference between the first flow rate signal and the second flow rate signal and output it as a flow rate detection signal that detects the flow direction and flow rate of the intake air.

In the invention of claim 2, the reference signal is added to the output signal from the difference calculation means,
The flow rate detection signal can be detected electrically in a positive range.

In the third aspect of the present invention, the intake air is provided by providing the first flow rate detecting means and the second flow rate detecting means in the flowmeter main body with temperature compensation resistors for compensating the temperature of the intake air. The temperature of the first and second heating resistors can be maintained at a constant temperature regardless of the temperature.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those of the prior art shown in FIGS. 6 and 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 which constitutes 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
A winding portion 24 around which the windings A and 23B are wound, a terminal portion 25 located on the base end side of the winding portion 24 and integrally provided with a plurality of terminal pins (not shown), A detection holder 26 extending from the tip end side of the portion 24 in the radial direction of the intake pipe 2 and a circuit casing 27 described later are roughly configured.

However, a slot (not shown) for detachably mounting an insulating substrate 28, which will be described later, is formed on the flowmeter main body 22 at 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 adjustment resistor 37A, 3A to be described later on an insulating substrate (not shown) made of, for example, a ceramic material.
7B, the differential amplifier 39, etc. are mounted, and these are built in.

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 ceramic, aluminum oxide (alumina) or aluminum nitride, and is formed in a rectangular flat plate shape. .

The insulating substrate 28 has a base end side which is a fixed end detachably attached to the slot of the detection holder 26, and a front end side which is a free end, and a second substrate portion 28A and a second end.
A slit 28C is formed between the base plate portion 28B and the base plate portion 28B and extends between the front end side and the base end side between the base plate portions 28A and 28B. In addition, the first substrate portion 28A is configured so that the second substrate portion 28B acts against the flow of the intake air in the forward direction (direction indicated by an arrow A).
It is formed on the upstream side of.

Reference numerals 29 and 30 denote a first heat generating resistor and a second heat generating resistor, respectively, which constitute a heat generating resistor. The heat generating resistors 29 and 30 are made of an insulating substrate 28 by means such as print printing or sputtering. By depositing a platinum film on the substrate parts 28A, 28B of
H2 is formed, the first heating resistor 29 is located upstream of the intake air (arrow A side), and the second heating resistor 30 is located downstream of the intake air (arrow B side). Are arranged.
Further, the slit 28C allows the heating resistors 29, 30 to be formed.
The spaces are insulated.

When the heating resistors 29 and 30 come into contact with the air flowing in the intake pipe 2 in the directions of arrows A and B at a predetermined temperature (for example, 240 ° C.), they are cooled by this air flow. By doing so, the respective resistance values RH1 and RH2 change. Then, when the intake air flows in the intake pipe 2 in the direction of arrow A (forward direction), the first heating resistor 29 located on the upstream side is greatly cooled by this air flow. The resistance value RH1 of is greatly reduced.
On the other hand, the second heating resistor 30 located on the downstream side
Comes into contact with the air flow after being heated by the heat from the first heating resistor 29, the heating resistor 30 is not cooled so much, and the resistance value RT2 of the heating resistor 30 is substantially Does not change to

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 second heating resistor 30, the second heating resistor 30 located on the upstream side with respect to the flow in the arrow B direction is greatly cooled by the air flow in the opposite direction, and the resistance value RH2 of the heating resistor 30 is greatly increased. On the other hand, the resistance value RH1 of the first heat generating resistor 29 on the downstream side hardly changes. Therefore, the resistance value RH1 between the heating resistors 29 and 30,
It is possible to determine whether the airflow is in the forward direction or the reverse direction based on the difference in RH2.

Reference numerals 31, 31, ... Show, for example, four electrodes formed on the base end side of the insulating substrate 28. The electrodes 31 are arranged in a row in the width direction of the insulating substrate 28 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 31 connects the heating resistors 29 and 30 to the emitter side of the current control transistors 33 and 34, which will be described later, and the reference resistor 23.
It is connected between A and 23B, and these heating resistors 29,
Reference numeral 30 constitutes a processing circuit for flow rate detection shown in FIG. 3 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, 32 is a DC power supply having a battery voltage VB, 33 and 34 are current control transistors whose collectors are connected to the DC power supply 32, and the current control transistors 33 and 34 have their emitters heated. Resistor 2
Connection point c to 9, 30 and temperature compensation resistors 36A, 36B
1 and c2 are connected, and the base side is a differential amplifier 3
It is connected to the output terminals of 9, 40. Then, the current control transistors 33 and 34 apply the currents applied (supplied) from the DC power source 32 to the heating resistors 29 and 30 and the temperature compensation resistors 36A and 36B, etc. from the differential amplifiers 39 and 40. , Vb2.

Reference numeral 35 denotes one bridge circuit which constitutes the first flow rate detecting means. The bridge circuit 35 includes a heating resistor 29, a temperature compensating resistor 36A, a reference resistor 23A and a flow rate adjusting resistor 37A having a resistance value R2. And is configured as a bridge in which the products of the resistance values of the respective resistance sides are equal. Further, the heating resistor 29 and the reference resistor 23A, the temperature compensation resistor 36A and the flow rate adjusting resistor 37A are
They are connected in series, and their connection points are a1 and b1.
Is connected to the input terminal of a differential amplifier 39 described later, and the connection point a1 is connected to the input terminal of another differential amplifier 41 described later. Further, the heating resistor 29 and the temperature compensation resistor 3
The connection point c1 with 6A is connected to the emitter side of the current controlling transistor 33, and the reference resistor 23A and the flow rate adjusting resistor 3 are connected.
The connection point d1 with 7A is connected to the ground.

Then, the bridge circuit 35 has an arrow A
When the heating resistor 29 is cooled by the directional air flow, the resistance value RH1 of the heating resistor 29 changes, so that the reference resistor 23A and the heating resistor 29 are connected at both ends of the reference resistor 23A. The first flow rate voltage V1 as the first flow rate signal is output based on the voltage. A change in the temperature of the intake air is detected as a change in the resistance value RT of the temperature compensation resistor 36A, and this change in the resistance value RT is output from the connection point b1 to the differential amplifier 39 as the temperature compensation voltage VT1.

Reference numeral 38 denotes the other bridge circuit as the second flow rate detecting means having substantially the same structure as that of the bridge circuit 35. The bridge circuit 38 is the heating resistor 30,
Temperature compensation resistor 36B, reference resistor 23B and resistance value R2
Flow rate adjusting resistor 37B having a heat generating resistor 3
0 and the reference resistor 23B, and the temperature compensation resistor 36B and the flow rate adjusting resistor 37B are connected in series, and their connection points a2 and b2 are connected to the input terminal of the differential amplifier 40 described later, and the connection point a2 is the other. It is connected to the input terminal of the differential amplifier 41. Further, the connection point c2 between the heating resistor 30 and the temperature compensating resistor 36B is connected to the current controlling transistor 34.
The connection point d2 between the reference resistor 23B and the flow rate adjusting resistor 37B is connected to the ground.

The bridge circuit 38 is connected to the arrow B.
When the heating resistor 30 is cooled by the air flow in the directional direction, the resistance value RH2 of the heating resistor 30 changes, so that both ends of the reference resistor 23B from the connection point a2 between the reference resistor 23B and the heating resistor 30 are changed. A second flow rate voltage V2 is output as a second flow rate signal based on the voltage. Further, a change in the temperature of the intake air is detected as a change in the resistance value RT of the temperature compensation resistor 36B, and this change in the resistance value RT is output from the connection point b2 to the differential amplifier 40 as a temperature compensation voltage VT2.

Reference numerals 39 and 40 denote first and second differential amplifiers built in the circuit casing 27, respectively.
The inverting input terminals of 9, 40 are temperature compensation resistors 36A, 36B.
Connection points b1 and b between the flow rate adjusting resistors 37A and 37B
2 and the non-inverting input terminals are heating resistors 29, 30
Is connected to the connection points a1 and a2 between the reference resistances 23A and 23B, and the output terminal of the differential amplifier 39 (40) is connected to the base of the current control transistor 33 (34). From the differential amplifiers 39 and 40, the connection point a
The current control voltages Vb1 and Vb2 based on the potential difference between 1 and b1 (connection points a2 and b2) are supplied to the current control transistor 33.
Input to the base of (34), and in the current control transistor 33 (34), the heating resistor 29 (3
0) and the current applied to the temperature compensation resistor 36A (36B) are controlled.

Reference numeral 41 denotes another differential amplifier which constitutes the difference calculation means, and the non-inverting terminal of the differential amplifier 41 is connected to the connection point a1 of the first bridge circuit 35 via the input resistor 42. The inverting input terminal is connected to the connection point a2 of the second bridge circuit 38 via the input resistor 43. In addition,
The input resistors 42 and 43 have the same resistance value.

Reference numeral 44 denotes a reference power supply, and the reference power supply 44 outputs a reference voltage VS as a reference signal.
The first flow rate voltage V1 is added and applied.

The differential amplifier 41 has a connection point a1,
Calculate the difference between the flow rate signals V1 and V2 from a2,

[0047]

## EQU1 ## Vout = K.times. (V1 + VS-V2) = K.times. (V1-V2) + K.times.VS = K.times. (V1-V2) + V0 where K is the amplification factor V0 is the bias voltage. The output voltage Vout corresponding to the flow rate of the intake air flowing through the intake pipe 2 is output from the output terminal 45.

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 is started, the DC power source 3
2 applies a voltage to the heating resistors 29, 30 and the temperature compensating resistors 36A, 36B via the current controlling transistors 33, 34, and heats the heating resistors 29, 30 at a temperature of 240 ° C. before and after, for example. Let

In this state, when the intake air flows in the direction A (the positive direction) shown by the arrow in FIG. 1, the first heating resistor 29 located on the upstream side of the air flow is affected by this air flow. The second heating resistor 30 that is cooled and positioned downstream is hardly cooled by receiving heat from the first heating resistor 29, so that the first heating resistor 29 is cooled significantly and the resistance value RH1 is The resistance value RH2 does not change because the second heating resistor 30 is not cooled so much.
As a result, the first flow rate voltage V1 output from the connection point a1 of the bridge circuit 35 increases and the bridge circuit 38
The second flow rate voltage V2 output from the connection point a2 of the above does not change much. As a result, the differential amplifier 41 outputs the output voltage Vout as shown in FIG.
(Characteristic line 46A) is obtained. When the flow rate Q is zero, the output voltage Vout becomes the bias voltage V0.

On the other hand, when the intake air flows in the direction B (reverse direction) shown by the arrow in FIG. 1, the second heat generating resistor 30 located upstream of the air flow is cooled by the flow of the air and the resistance is reduced. The value RH2 becomes smaller and the first
The heat generating resistor 29 receives the heat from the second heat generating resistor 30 and is hardly cooled, and the resistance value RH1 does not change. As a result, the second flow rate voltage V2 output from the connection point a2 of the other bridge circuit 38 increases, and the first flow rate voltage V1 output from the connection point a1 of the one bridge circuit 35.
Does not change much. As a result, the output voltage Vout (characteristic line 46B) as shown in FIG. 4 is obtained from the differential amplifier 41 with respect to the flow rate Q in the reverse direction.

In the bridge circuits 35 and 38, the heating resistors 29 and 30 are cooled by the airflow at this time, and the voltage level at the connection points a1 and a2 is higher than the voltage level at the connection points b1 and b2. From the differential amplifier 39, 40
Is based on the potential difference (temperature compensation voltage Vb1, Vb2) between the connection points a1 and a2 and the connection points b1 and b2 from the DC power supply 32 to the heating resistors 29 and 30 and the temperature compensation resistors 36A and 36A.
A power supply applied (powered) to B or the like is controlled via the current control transistors 33 and 34. The heating resistor 29,
A larger current is supplied to the temperature compensating resistors 36A and 36B, so that the heat generating resistors 29 and 30 generate heat again at a temperature close to 240 ° C.

At this time, the heating resistors 29, 3
0 and the current levels supplied to the reference resistors 23A and 23B, the voltage levels at the connection points a1 and a2 increase, which increases or decreases in accordance with the flow rate of the intake air flowing through the intake pipe 2. Therefore, the differential amplifier 41 Is based on the flow rate voltages V1 and V2 from the connection points a1 and a2, the output voltage Vout is output to the output terminal 45 as a voltage larger than the bias voltage V0 in the forward flow, and is output in the reverse flow. The voltage Vout is output to the output terminal 45 as a voltage smaller than the bias voltage V0, and the flow rate of the intake air at this time can be detected by the output voltage Vout.

On the other hand, when the engine speed reaches from a low speed region to a medium speed region and the like, intake is performed, the exhaust amount is increased, and the intake valve and the exhaust valve (neither is shown) overlap, so that the exhaust gas is exhausted. Part of the air flow rate becomes negative (minus) in the exhaust pipe 2 due to the opening of the intake valve, and as shown as time t1 and t2 in FIG. When the reverse flow occurs, the cooling amount of the second heating resistor 30 becomes larger than the cooling amount of the first heating resistor 29. As a result,
The resistance value RH2 of the second heating resistor 30 is much smaller than the resistance value RH1 of the first heating resistor 29, and the connection point of the bridge circuit 35 whose voltage level at the connection point a2 of the other bridge circuit 38 is one. The voltage level becomes larger than the voltage level at a1, and the reference resistors 23A, 2 are connected from the connection points a1, a2.
A voltage difference corresponding to the air flow rate at this time occurs in the first and second flow rate voltages V1 and V2 output as the voltage across 3B.

The differential amplifier 41 outputs the output voltage Vou according to the equation (1) based on the flow rate voltages V1 and V2 at this time.
t is output from the output terminal 45, and the output voltage Vout is used to extract a flow rate signal corresponding to the actual intake air flow rate.
In this case, the flow rate voltage V1 has a smaller voltage value than the flow rate voltage V2, and the output voltage Vout is a voltage smaller than the bias voltage V0 (see the characteristic line 46B in FIG. 4).

Thus, in the thermal air flow rate detecting device according to the present embodiment, the flowmeter main body 22 is provided in the middle of the intake pipe 2, and the flowmeter main body 22 is provided with the upstream side in the flow direction of the intake air. The first heat generating resistor 29 located on the side and the second heat generating resistor 30 located on the downstream side are provided in the insulating substrate 28 in the form of a film, and the processing circuit of the air flow rate detecting device is provided with the first heat generating resistor. Bridge circuit 35 which outputs the first flow rate voltage V1 from the change of the resistance value RH1 of the heating resistor 29 and the change of the resistance value RH2 of the second heat generating resistor 30 located on the downstream side to the second flow rate voltage V1. The bridge circuit 38 that outputs V2 and the differential amplifier 41 that outputs the output voltage Vout from the difference between the first flow rate voltage V1 and the second flow rate voltage V2 are provided. The effect can be obtained.

That is, on the insulating substrate 28, the first heating resistor 29 is formed in the form of a film on the upstream side with respect to the forward direction of the air flow (the direction of arrow A), and the second heating resistor 29 is formed on the downstream side. Heating resistor 3
Since 0 is formed in a film shape, the first heat generating resistor 29 is cooled significantly and the second heat generating resistor 30 is positioned on the upstream side in the forward air flow (direction indicated by the arrow A). Since the heat generating resistor 29 receives the heat and is not cooled so much, its resistance value becomes RH1 <RH2, and the flow direction and the flow rate can be detected by the difference in the resistance value. On the other hand, in the air flow in the opposite direction (arrow B direction), the second heating resistor 30 is cooled significantly, and the first heating resistor 29 heats the second heating resistor 30 located on the upstream side. Since it is not cooled down so much, the resistance value becomes RH1> RH2, and the flow direction and the intake air flow rate can be detected by the difference in the resistance value.

As a result, when the intake air flows in the forward direction (direction indicated by the arrow A), the first and second heating resistors 29,
Among the heat generating resistors 30, the heat generating resistor 29 is larger than the heat generating resistor 30 and is cooled by the air flow at this time, and the resistance value RH1 of the heat generating resistor 29 is greatly reduced than the resistance value RH2 of the heat generating resistor 30. The connection point a of the bridge circuit 35 shown in FIG.
1 and each reference resistor 2 from the connection point a2 of the bridge circuit 38
A voltage difference corresponding to the air flow rate at this time can be generated in the first and second flow rate voltages V1 and V2 output as the voltages across 3A and 23B.

As a result, the flow rate voltage V is increased by the differential amplifier 41.
Based on 1 and V2, the output voltage Vout according to the equation 1 is output from the output terminal 45 and the output voltage Vout is output.
Therefore, the flow rate detection signal corresponding to the actual intake air flow rate can be taken out. In this case, the first flow rate voltage V1 has a larger voltage value than the second flow rate voltage V2. Therefore, the output voltage Vout is changed to the bias voltage V0. Output can be greater than.

When the intake air flowing through the intake pipe 2 is in the opposite direction (the direction of arrow B), the heating resistor 30 of the first and second heating resistors 29, 30 is the heating resistor. The resistance value RH2 of the heat generating resistor 30 decreases more than the resistance value RH1 of the heat generating resistor 29. Then, from the connection point a1 of the bridge circuit 35 and the connection point a2 of the bridge circuit 38 shown in FIG. 3, to the first and second flow rate voltages V1 and V2 output as the voltages across the reference resistors 23A and 23B, A voltage difference corresponding to the air flow rate can be generated.

As a result, the flow rate voltage V is increased by the differential amplifier 41.
Based on 1 and V2, the output voltage Vout according to the equation 1 can be output from the output terminal 45, and the output voltage Vou can be output.
A flow rate detection signal corresponding to the actual intake air flow rate can be obtained by t, and the second flow rate voltage V2 in this case has a voltage value larger than the first flow rate voltage V1. Therefore, the output voltage Vout is set to the bias voltage. The output can be smaller than V0.

Thus, according to this embodiment, the flow rate of the intake air flowing through the intake pipe 2 is determined by the flow rate voltage output from the connection points a1 and a2 based on the resistance values RH1 and RH2 of the heating resistors 29 and 30. Due to the voltage difference between V1 and V2, the output voltage Vou
It can be taken out as t, and the direction of the air flow at this time can also be reliably detected depending on whether the output voltage Vout is larger than the bias voltage V0. Therefore, 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 2 in the middle speed range of the engine or the like to cause a backflow, and the reliability of the A / F control is ensured. It has various effects such as being improved.

Next, FIG. 5 shows a second embodiment according to the present invention. The feature of this embodiment is that temperature compensation resistors are provided in the first heating resistor and the second heating resistor, respectively. Especially. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the figure, reference numeral 51 denotes an insulating substrate attached to the detection holder 26. The insulating substrate 51 is made of an insulating material such as glass ceramic, aluminum oxide (alumina), or aluminum nitride in the shape of a rectangular flat plate. Has been done.

The insulating substrate 51 has a base end side which is a fixed end detachably attached to the slot of the detection holder 26 and a front end side which is a free end and a second substrate portion 51A.
A slit 51C is formed between the base plate portion 51B and the base plate portion 51B and extends from the front end side toward the base end side between the base plate portions 51A and 51B. In addition, the first substrate portion 51A has a second substrate portion 51B with respect to the flow of the intake air in the forward direction (arrow A direction).
It is formed on the upstream side of.

Reference numerals 52 and 53 denote a first heat generating resistor and a second heat generating resistor, respectively, which constitute a heat generating resistor. The heat generating resistors 52 and 53 are made of an insulating substrate 51 by means such as print printing or sputtering. By forming a platinum film on the substrate portion 51B of the above, the resistance values RH1 and RH2 are formed to be equal, and the first heating resistor 52 is located on the upstream side of the intake air (arrow A side) and The heating resistor 53 is arranged at the downstream side of the intake air (the arrow B side).

Reference numerals 54 and 55 denote first temperature compensating resistors.
Of the temperature compensating resistor and the second temperature compensating resistor, respectively. The temperature compensating resistors 54 and 55 are formed by depositing a platinum film on the substrate portion 51A of the insulating substrate 51 by means of printing or sputtering. By doing so, they are formed to have equal resistance values RK and RK. Also, the insulating substrate 5
The slit 51C of 1 heat-insulates between the heat generating resistors 52 and 53 and the temperature compensating resistors 54 and 55.

Reference numerals 56, 56, ... Depict, for example, eight electrodes formed on the base end side of the insulating substrate 51. The electrodes 56 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 56 connects the heating resistors 52 and 53 to the emitter side of the current controlling transistors 33 and 34, which will be described later, and the reference resistor 23.
A and 23B are connected between these heating resistors 52,
Reference numeral 53 constitutes a processing circuit for flow rate detection shown in FIG. 3 together with each electronic component provided in the circuit casing 27.

Also in this embodiment having such a configuration, the flow rate and flow direction of the intake air can be detected almost in the same manner as in the first embodiment.

Further, in this embodiment, since the heat generating resistors 52 and 53 and the temperature compensating resistors 54 and 55 are formed in a film shape on the insulating substrate 51, it can be made compact.

In each of the above-mentioned embodiments, the first flow rate voltage V1 from the bridge circuit 35 which serves as the first flow rate detecting means.
Although the reference voltage VS from the reference power source 44 is applied to and added to, the present invention is not limited to this, and even if the reference power source 44 is connected to the output terminal 45, the second flow rate voltage V2 is negative. A reference voltage may be applied.

In each of the above embodiments, the flowmeter main body 22
Of the reference resistor 23 (23A, 23
B) has been described as being provided so as to project into the intake pipe 2, but the present invention is not limited to this, and for example, the reference resistor 23 is provided in the circuit casing 27 provided outside the intake pipe 2, and the flow rate adjustment resistors 37A, 37B, etc. It may be arranged together with the above.

[0073]

As described in detail above, in the invention of claim 1, the heat generating resistance is provided on the insulating substrate mounted on the flowmeter main body on the upstream side with respect to the flow direction of the intake air. A second heat generating resistor formed in a film shape on the downstream side of the body, and a first flow rate detecting means for outputting a first flow rate signal based on a change in resistance value of the first heat generating resistor; Second flow rate detection means for outputting a second flow rate signal based on a change in resistance value of the heating resistor, and difference calculation means for outputting a difference between the first flow rate signal and the second flow rate signal as a flow rate detection signal. And a configuration including. For example, when the flow direction of the intake air is the forward direction, the first heating resistor is cooled more than the second heating resistor, the resistance value becomes lower, and each flow rate output from each flow rate detecting unit is decreased. Differences occur in the signals. Then, the difference between the respective flow rate signals is calculated by the difference calculating means, whereby the flow rate detection signal including the flow direction and flow rate of the intake air can be output. As a result, the intake air flow rate can be accurately detected, and the A / F control of the engine can be performed with high accuracy.

According to the second aspect of the invention, the reference signal is added to the flow rate detection signal output from the difference calculation means, so the reference signal is added to the flow rate detection signal output from the difference calculation means. Therefore, the intake air flow rate can be electrically output within a positive range.

In the third aspect of the present invention, the temperature of the intake air is adjusted by providing the first flow rate detecting means and the second flow rate detecting means with temperature compensation resistors for compensating the temperature of the intake air. Regardless, the temperatures of the first and second heating resistors can be maintained at a constant temperature, and the flow direction and flow rate of the intake air can be accurately detected.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a state in which a thermal air flow rate detection device according to a first embodiment is attached to an intake pipe.

FIG. 2 is a plan view showing first and second heating resistors 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 an output voltage Vout with respect to a flow rate Q of one intake air.

FIG. 5 is a plan view showing first and second heat generating resistors and a pair of temperature compensating resistors formed on an insulating substrate according to the second embodiment.

FIG. 6 is a vertical cross-sectional view showing a state in which a thermal air flow rate detecting device according to a conventional technique is attached to an intake pipe.

FIG. 7 is a perspective view showing a flowmeter main body, heat generation resistance and the like according to a conventional technique.

FIG. 8 is a characteristic diagram showing a change in flow velocity due to intake air.

[Explanation of symbols]

 21 Thermal Air Flow Detector 22 Flowmeter Main Body 23A, 23B Reference Resistance 24 Winding Part 28,51 Insulation Substrate 29,52 First Heating Resistor 30,53 Second Heating Resistor 35 Bridge Circuit (First Flow rate detection means) 36A, 36B Temperature compensation resistance 38 Bridge circuit (second flow rate detection means) 39, 40 Differential amplifier 41 Differential amplifier (difference calculation means) 44 Reference power supply 54, 55 Temperature compensation resistor (temperature compensation) Resistance) V1 first flow rate voltage (first flow rate signal) V2 second flow rate voltage (second flow rate signal) Vout output voltage (flow rate detection signal) VS reference voltage

Claims (3)

[Claims] 1. A thermal type air flow rate detecting device comprising: a flowmeter main body mounted in the middle of an intake pipe; and a heat generating resistance provided in the flowmeter main body and cooled by intake air flowing in the intake pipe. A first heating resistor located upstream in the flow direction of the intake air and a second heating resistor located downstream in the flow direction of the intake air. And a second flow rate detecting means for outputting a first flow rate signal from a change in the resistance value of the first heat generating resistor, and a second flow rate detecting means for changing the resistance value of the second heat generating resistor. Of the second flow rate signal output from the first flow rate detection means and the second flow rate signal output from the second flow rate detection means. And a difference calculation means for outputting as a flow rate detection signal. And a thermal type air flow rate detecting device. 2. The thermal air flow rate detection device according to claim 1, wherein a reference signal is added to the flow rate detection signal output from the difference calculation means. 3. The thermal air flow rate detection device according to claim 1, wherein each of the first flow rate detection means and the second flow rate detection means is provided with a temperature compensation resistor for compensating the temperature of the intake air. means.