JPH08166271A - Thermal type air flow rate detecting apparatus - Google Patents

Abstract

PURPOSE: To detect the flowing direction and the flow rate of sucked air and improve the reliability of a thermal-way air flow rate detecting apparatus. CONSTITUTION: An insulated substrate 29 is a metal core substrate composed by forming surface layers 29B, 29C of a ceramic on both side faces of a metal material with high thermal conductivity used as a base material 29A, and a heat radiating resistor body 30, a first temperature sensing resistor 31, and a second temperature sensing resistor 32 are formed as thin films on a center part, an upper stream side, and a down stream side, respectively. Since the temperature of the insulated substrate 29 changes so quickly, the change corresponding to the air flow can be quick and intense, so that detection operation can be carried out quickly and the detection sensitivity can be heightened.

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. 8 and 9 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 an air flow rate detecting device main body which constitutes the main body of the thermal type air flow rate detecting device 1. The air flow rate detecting device main body 3 is molded by means such as insert molding as shown in FIG. A winding portion 4 formed in a stepped column shape for winding a reference resistance 14 which will be described later in the form of a wire, and a substantially disc-shaped portion located at the base end side of the winding portion 4 will be described later. A terminal portion 5 integrally provided with terminal pins 8A to 8D,
A detection holder 6 that extends in the radial direction of the intake pipe 2 from the tip end side of the winding portion 4 and positions a heating resistor 9 and a temperature compensating resistor 11, which will be described later, at the center of the intake pipe 2 and an outside of the intake pipe 2. A circuit casing 7 to be described later, which is located and connected to the terminal portion 5.
It is composed of and.

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 projecting from the terminal portion 5 of the air flow rate detecting device main body 3. For example, four terminal plates (not shown) embedded in the winding portion 4 and the detection holder 6 of the air flow rate detection device main body 3 are integrally provided, and are provided in a connector portion (not shown) of the circuit casing 7. It is detachably connected.

Reference numeral 9 denotes a hot film type heat generating resistor provided in the detection holder 6 of the air flow rate detecting device main body 3 via terminals 10A and 10B. The heat generating resistor 9 is sensitive to temperature changes and has a resistance value. Formed by winding a platinum wire or depositing a platinum film on an insulative cylinder made of a ceramic material such as aluminum oxide (hereinafter referred to as "alumina") that is made of a temperature-sensitive material such as platinum It is composed of a small-diameter heating resistor element. Then, the heating resistor 9 is supplied with electricity from a battery (not shown),
For example, when heat is generated at temperatures of 240 ° C. before and after 240 ° C. and 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 the flow rate detection signal is detected. Is to be 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 main body 3 of the air flow rate detecting device. The temperature compensating resistor 11 is an insulating material 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 connected between terminals 12A and 12B provided upright on the detection holder 6.

Reference numeral 13 denotes a protective cover mounted on the detection holder 6 of the main body 3 of the air flow rate detecting device.
3 is a detection holder 6 on which a heating resistor 9 and a temperature compensating resistor 1 are mounted.
After mounting No. 1, it is attached to the detection holder 6 as shown by the arrow in FIG. 9 so as to protect the heat generating resistor 9 and the temperature compensating resistor 11 and allow the intake air to flow. In FIG. 9, the heat generating resistor 9 and the temperature compensating resistor 1
In order to clearly show No. 1, the protective cover 13 is shown in a state of being removed from the detection holder 6.

Further, 14 is a reference resistance consisting of a winding resistance wound around the winding part 4 of the air flow rate detecting device main body 3, and both ends of the reference resistance 14 are erected on the winding part 4. The terminals 15A and 15B are connected to the heating resistor 9 in series. 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 terminals 15B and 10A via another terminal plate. Further, the terminal pin 8C is connected to the terminals 10B and 12 via another terminal plate.
B is connected, and the terminal pin 8D is connected to the terminal 12A via another terminal plate.

The conventional thermal air flow rate detecting device 1 thus constructed has a terminal portion 5 of the air flow rate detecting device body 3 when detecting the intake air flow rate of an automobile engine or the like.
Is connected to the connector portion of the circuit casing 7 via each terminal pin 8, the detection holder 6 of the air flow rate detection device main body 3 and the like is inserted into the intake pipe 2 through the mounting hole 2A, and the mounting hole 2A By attaching the circuit casing 7 from the outer peripheral side of the intake pipe 2 to the heat generating resistor 9 provided in the detection holder 6,
And the temperature compensating resistor 11 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. A bridge circuit is composed of the compensating resistor 11 and the flow rate adjusting resistor, and the heat generating resistor 9 is supplied 240 ° C. before by energizing these to the outside.
Heat at a later temperature.

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. 8 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. Since it is sucked in the direction of arrow A (forward direction) toward, the flow velocity of the air flowing in the intake pipe 2 is repeatedly pulsated as shown in FIG. 6 in accordance with the opening and closing of each intake valve. become.

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 (minus) like between 2 and an air flow that flows in the direction of arrow B (reverse direction) is generated, which causes a problem that the intake air flow rate is erroneously detected.

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, a thermal type air flow rate detecting device according to claim 1 uses a metal material having good heat conductivity as a base material and insulates at least one side surface of the base material. A metal core substrate formed by depositing a surface layer made of a material, a heating resistor provided at the center of the surface layer side of the metal core substrate, and a front and a rear of the heating resistor separated from the air flow direction. And a first temperature sensitive resistor provided on the surface layer of the metal core substrate.

According to a second aspect of the present invention, the first temperature sensitive resistor and the second temperature sensitive resistor are connected in parallel, and the resistance of the first temperature sensitive resistor and the second temperature sensitive resistor. A flow direction detection means that compares the values and outputs a flow direction detection signal corresponding to the flow direction of air, and a bridge circuit that includes the heating resistor, and detects a change in the resistance value of the heating resistor as a flow rate detection signal. Based on the flow direction detection signal detected by the flow direction detection means and the flow direction detection signal detected by the flow direction detection means, when the air flow direction is the forward direction, the flow rate detection signal from the flow rate detection means is output as it is, Sometimes, a flow rate signal output means for inverting and outputting the flow rate detection signal from the flow rate detection means is provided.

According to the third aspect of the present invention, the temperature control means for holding the metal core substrate at a constant temperature by controlling the current applied to the heating resistor to heat the heating resistor, and the first sensor. First flow rate detecting means for detecting a first flow rate signal by a change in resistance value of the temperature resistance, and second flow rate detection for detecting a second flow rate signal by a change in resistance value of the second temperature sensitive resistor. Means and the first flow rate detection signal output from the first flow rate detection means and the second flow rate detection signal output from the second flow rate detection means are calculated to output the flow rate detection signal. And a flow rate detection signal calculation means.

[0022]

Since the heating resistor and the first and second temperature sensitive resistors are formed on the metal core substrate as in claim 1, the metal core substrate has a greater reaction to temperature than the ceramic substrate. In addition, the temperature of the substrate differs between the heating resistor and the positions of the first and second temperature sensitive resistors, and when the air flow is in the forward direction, the first temperature sensitive resistor on the upstream side is cooled. The second temperature-sensitive resistor on the downstream side is heated by the heat of the heat-generating resistor, and a difference occurs in the resistance value of each temperature-sensitive resistor.

According to a second aspect of the present invention, the first temperature-sensitive resistor and the second temperature-sensitive resistor are connected in parallel to form the flow direction detecting means. The resistance value is compared with that of the second temperature-sensitive resistor, and when the second temperature-sensitive resistor is larger, it is determined that, for example, the air flow is in the forward direction.
If the temperature sensitive resistor is larger, it can be determined that the air flow is in the opposite direction.

Further, a flow rate detecting means comprising a bridge circuit including the heat generating resistor is provided, and a change in the resistance value of the heat generating resistor in the flow rate detecting means is taken out as a flow rate detecting signal. Based on the air flow direction detected by the direction detecting means, the flow rate detection signal is directly output as a positive voltage signal when the air flow direction is a forward direction, and is reversed when the air flow direction is a reverse direction and a negative voltage signal is output. Can be output as

According to a third aspect of the present invention, when the temperature control means controls the current value applied to the heating resistor to keep the heating resistor at a constant temperature, for example, when a forward air flow occurs, First located upstream of the heating resistor
The cooling amount of the temperature-sensitive resistor is large, and the
Since the temperature-sensitive resistor is cooled by the air that has received heat from the heat-generating resistor, the cooling amount of the second temperature-sensitive resistor becomes small.

As a result, of the respective signals of the first flow rate signal output from the first flow rate detection means and the second flow rate detection signal output from the second flow rate detection means, for example, the first flow rate signal Is larger than the second flow rate signal, the flow rate detection signal calculation means can subtract the second flow rate signal from the first flow rate signal to output the positive flow rate detection signal. it can. On the other hand, when the flow of air is in the opposite direction, when the first flow rate signal becomes smaller than the second flow rate signal among the flow rate signals output from the flow rate detection means, the flow rate detection signal calculation means operates. By subtracting the second flow rate signal from the first flow rate signal, it is possible to output the negative flow rate detection signal.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

First, the first embodiment of the present invention will be described with reference to FIGS.
An example of is shown.

In the figure, 21 is a thermal type air flow rate detecting device according to the present embodiment, 22 is a flow meter main body which constitutes the main body of the thermal type air flow rate detecting device 21, and the flow meter main body 22 is a conventional technique. Almost the same as the air flow rate detection device main body 3 described above, a winding portion 24 around which a reference resistance 23 having a resistance value R1 is wound.
A terminal portion 25 located at the base end side of the winding portion 24 and integrally provided with a plurality of terminal pins (not shown); and a radial direction of the intake pipe 2 from the tip end side of the winding portion 24. The detection holder 26 is extended and the circuit casing 27, which will be described later, is provided.

However, a slot (not shown) for detachably mounting an insulating substrate 29, 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, temperature sensing resistors 31 and 32, which will be described later, are positioned in the center of the intake pipe 2 via an insulating substrate 29. A protective cover (not shown) similar to the protective cover 13 described in the related art is attached to the detection holder 26.

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 it has a fitting portion 27A that fits into A, the circuit casing 27 has a flow rate adjusting resistor 36, a differential amplifier circuit 37, etc. described later on an insulating substrate (not shown) made of, for example, a ceramic material. It is designed to be built with these installed. 28A and 28B are terminals to which the winding of the reference resistor 23 is connected.

Reference numeral 29 denotes an insulating substrate attached to the detection holder 26. The insulating substrate 29 is formed of a metal core substrate and has a length dimension of 1 as shown in FIGS.
A base material 29A, which is formed in a rectangular flat plate shape having a width of about 5 to 20 mm and a width of about 3 to 7 mm, and is made of a metal having good thermal conductivity such as SUS material, and the base material 29.
The surface layers 29B and 29C are formed (coated) on both side surfaces of A and are formed of an insulating material such as alumina, glass, or aluminum nitride. Further, the insulating substrate 29 has a fixed end removably attached to the slot of the detection holder 26 on the base end side and a free end on the tip end side.

By thus forming the insulating substrate 29 as a metal core substrate, it can be made a substrate that can be easily warmed and cooled easily, and a large temperature change is caused by overheating by the heating resistor 30 and cooling by the intake air, which will be described later. Can react quickly.

Reference numeral 30 denotes a heating resistor forming a heating resistor formed on the surface layer 29B of the insulating substrate 29. The heating resistor 30 is formed on the insulating substrate 29 by means of printing or sputtering. By depositing the film, it is formed so as to have a resistance value RH, and is formed on the upstream side with respect to the air flow direction (direction of arrow A), and the surface area (mounting area) of the heating resistor 30 is formed. ) Is increased as much as possible so that, for example, the contact area with the intake air flowing through the intake pipe 2 can be increased.

The heating resistor 30 has a current value controlled by a current controlling transistor 42, which will be described later, and generates heat so as to keep the temperature at a constant temperature (for example, about 240 ° C.).

Reference numerals 31 and 32 denote the first and second temperature sensitive resistors formed on the surface layer 29B of the insulating substrate 29 together with the heat generating resistor 30, and the first temperature sensitive resistor 31 is the heat generating resistor. Three
0 is formed on the upstream side of 0 so as to have a resistance value RT1, and the second temperature sensitive resistor 32 is formed on the downstream side of the heating resistor 30 so as to have a resistance value RT2. Has been done.

The temperature distribution on the insulating substrate 29 will be described with reference to FIG.

First, the heating resistor 30 is kept at 240 ° C. before and after the control described later, and when there is no air flow, the heat from the heating resistor 30 is similarly transmitted in the width direction of the insulating substrate 29. , As shown by the solid line, it decreases with an equal slope. The first and second temperature sensitive resistors 3 at this time
The detected temperatures at 1 and 32 are the same T0.

When an air flow in the direction of arrow A (forward direction) occurs, heat moves to the left as shown by the alternate long and short dash line, and the first temperature-sensitive resistor 31 is directly cooled by air, The second temperature-sensitive resistor 32 receives heat from the heat-generating resistor 30, and the temperature T detected by the first temperature-sensitive resistor 31 is detected.
The relationship between A1 and the temperature TA2 detected by the second temperature sensitive resistor 32 is TA1.
<TA2, and the resistance values R1 and R2 of the temperature sensitive resistors 31 and 32 at this time are R1 <R2.

Further, when an air flow in the direction of arrow B (reverse direction) occurs, heat moves to the right as shown by the chain double-dashed line, and the second temperature-sensitive resistor 32 is directly cooled by air. The first temperature-sensitive resistor 31 receives heat from the heat-generating resistor 30 so that TB1> TB2, and each resistance value R1,
R2 is R1> R2.

Reference numerals 33, 33, ... Depict, for example, six electrodes formed on the base end side of the insulating substrate 29. The electrodes 33 are arranged in a row in the width direction of the insulating substrate 29 at predetermined intervals. By inserting the base end side of the insulating substrate 29 into the slot of the detection holder 26, it is connected to each terminal (not shown) on the detection holder 26 side. Then, the heating resistor 30 and the temperature sensitive resistor 31 formed on the insulating substrate 29 are connected to the electronic components provided in the circuit casing 27 via the electrodes 33, respectively. The processing circuit for flow rate detection shown is configured.

Next, FIG. 5 shows a processing circuit for flow rate detection according to this embodiment.

In FIG. 5, reference numeral 34 denotes a flow rate detecting circuit composed of a bridge circuit for outputting a flow rate detecting signal. The flow rate detecting circuit 34 includes a heating resistor 30, a temperature compensation resistor 35, a reference resistor 23 and a resistance value. And a flow rate adjusting resistor 36 having R2, and configured as a bridge in which products of resistance values of opposite sides are equal to each other. A connection point a between the heating resistor 30 and the temperature compensating resistor 35 is a current control transistor 42 described later. The connection point b between the reference resistor 23 and the flow rate adjusting resistor 36 is connected to the ground.

In the flow rate detecting circuit 34, the heating resistor 30, the reference resistor 23, the temperature compensating resistor 35, and the flow rate adjusting resistor 36 are connected in series, and the respective connection points c,
d is connected to the input terminal of the differential amplifier circuit 37, and
The connection point c is connected to an inversion circuit 44 and a selection circuit 45 described later.

The signal output from the differential amplifier circuit 37 becomes the current control voltage VA of the current control transistor 42 that controls the applied current to the flow rate detection circuit 34. On the other hand, the output from the connection point c of the flow rate detection circuit 34 becomes the voltage across the reference resistor 23, and the output voltage is the heating resistor 3
0 becomes a flow rate detection voltage V1 (flow rate detection signal) indicating the degree of cooling by the flow rate.

Here, the temperature compensation resistor 35 is provided in the detection holder 26 in the vicinity of the heating resistor 30.
Moreover, the temperature compensating resistor 35 is not affected by the flow of the intake air, and the resistance value RK changes only depending on the temperature of the air.

In the flow rate detection circuit 34 thus constructed, when the flow rate detection circuit 34 is in a balanced state, the current control voltage VA from the differential amplifier circuit 37 becomes zero and the flow rate detection circuit 34 is balanced from the connection point c. Reference resistance 23 when in the state
The voltage across both ends of is output to the inversion circuit 44 and the selection circuit 45. On the other hand, when the balance of the flow rate detection circuit 34 is lost, that is, when the heat generating resistor 30 is cooled by the intake air, the resistance value RH of the heat generating resistor 30 becomes small. The current control voltage VA is output to the base of the current control transistor 42. As a result, the current control transistor 42 is connected to the flow rate detection circuit 34.
The flow rate detection circuit 34 is returned to the equilibrium state by controlling the current applied to the cooling resistor 30 to keep the cooled heating resistor 30 at a constant temperature.
At this time, the increased current value output from the connection point c of the flow rate detection circuit 34 is detected as the voltage across the reference resistor 23, and this voltage is supplied to the inverting circuit 44 and the selection circuit 45 as the first flow rate detection voltage V1. Output.

Next, 38 shows a flow direction detecting circuit which constitutes a flow direction detecting means together with a comparison circuit 41 which will be described later.
The flow direction detection circuit 38 includes the first and second temperature sensitive resistors 3
1 and 32 and reference resistors 39 and 40, each of which is configured as a bridge circuit in which resistance values on opposite sides are equal, and the connection point e of the first and second temperature sensitive resistors 31 and 32 is a sub power supply VS ( 3V), for example, and the reference resistance 3
The connection point f of 9, 40 is connected to the ground.

The flow direction detection circuit 38 has a first
Temperature sensitive resistor 31, reference resistor 39, second temperature sensitive resistor 3
2 and the reference resistor 40 are respectively connected in series, the respective connection points g and h are connected to the input terminal of the comparison circuit 41, and the comparison circuit 41 is connected to the selection circuit 45. Thus, when the flow direction detection circuit 38 is in the equilibrium state, that is, when the intake air is not flowing, the temperature sensitive resistor 3
Since there is no difference between the resistance values RT1 and RT2 of 1 and 32, the output from the comparison circuit 41 becomes zero. Further, when the balance of the flow direction detection circuit 38 is lost, that is, when the resistance values RT1 and RT2 of one of the temperature sensitive resistors 31 and 32 are changed by the air flow, the connection point of the flow direction detection circuit 38 is detected. From gh, the difference in resistance value (RT1−RT2) is used as a voltage for comparison circuit 4
A signal indicating the flow direction of the intake air (hereinafter, flow direction detection voltage V2 ") is output to the selection circuit 45 based on the difference between the resistance values.

FIG. 6 shows the relationship between the flow velocity of the intake air and the flow direction detection voltage V2. When the flow direction of the intake air is the A direction (forward direction), the comparison circuit 41 outputs a predetermined voltage value. Output the flow direction detection voltage V2 which becomes V0,
When the air flow direction changes from the A direction to the B direction (reverse direction), the comparison circuit 41 outputs the flow direction detection voltage V2 having a voltage value of zero.

Reference numeral 42 denotes a current control transistor. The current control transistor 42 has a collector side connected to the battery voltage VB and a base side connected to the differential amplifier circuit 37.
Of the flow rate detection circuit 3 connected to the output side of the
4 is connected to the connection point a. The current control transistor 42 controls the emitter current by changing the base current with the current control voltage VA from the differential amplifier circuit 37. As a result, the current control transistor 42 controls the current value applied to the flow rate detection circuit 34, and performs feedback control for keeping the temperature of the heating resistor 30 constant.

Reference numeral 43 denotes a flow rate signal output circuit as a flow rate signal output means, and the flow rate signal output circuit 43 is composed of an inversion circuit 44 and a selection circuit 45 which will be described later.

Reference numeral 44 represents an inverting circuit connected between the connection point c of the flow rate detecting circuit 34 and the selecting circuit 45. The inverting circuit 44 inverts the flow rate detecting voltage V1 from the flow rate detecting circuit 34 to select the circuit. It outputs to 45.

Reference numeral 45 denotes a selection circuit which constitutes the flow rate signal output means together with the inverting circuit 44, and the selection circuit 45 outputs the flow direction detection voltage V2 from the flow direction detection circuit 38 output through the comparison circuit 41 (FIG. 6). , For example, in the case of the forward direction, the flow rate detection voltage V1 from the flow rate detection circuit 34 is output from the output terminal 46 to the control unit (not shown) as the output signal Vout, and in the case of the reverse direction, the inverting circuit 44. The negative signal from the output signal V
The output is output from the output terminal 46 to the control unit.

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

Here, when the flow of the intake air is in the direction of arrow A (forward direction), the first temperature-sensitive resistor 31 located on the upstream side of the insulating substrate 29 is cooled by this flow of air. The second temperature-sensitive resistor 32 located on the downstream side receives heat from the heat-generating resistor 30. As a result, the balance of the flow direction detection circuit 38 is lost, and the voltage value V0 is output from the comparison circuit 41.
Then, the forward flow direction detection voltage V2 is output.

Further, the heating resistor 30 is cooled by the flow of the intake air, and the resistance value RH of the heating resistor 30 is reduced by this cooling. However, the differential amplifier circuit 37 and the current control transistor 42 cause the heating resistor 30 to decrease. In order to keep 30 at a constant temperature, the current value applied to the flow rate detection circuit 34 is increased, and the increased current value is detected by the reference resistor 23 as the voltage across it. As a result, the flow rate detection circuit 3
A positive flow rate detection voltage V1 is output from the inverter 4 to the inversion circuit 44 and the selection circuit 45. The positive flow rate detection voltage V1 input to the inversion circuit 44 is output to the selective circuit 45 as an inverted negative flow rate detection voltage V1 '.

Then, in the selection circuit 45, the comparison circuit 41
Based on the flow direction detection voltage V2 from the flow rate detection circuit 3
Positive flow rate detection voltage V1 inputted from 4 and inverting circuit 44
Is selected from the negative flow rate detection voltage V1 'input from the above. In this case, since the flow direction detection voltage V2 is the forward direction, the positive flow rate detection voltage V1 is selected and the output terminal 46 is selected.
Positive flow rate detection voltage V toward the control unit
1 is output as the output signal Vout.

Since the base current of the current control transistor 42 is controlled based on the signal output from the differential amplifier circuit 37, feedback control is performed to keep the heating resistor 30 at a constant temperature. .

On the other hand, when the air flow is in the direction of arrow B (reverse direction), the second temperature sensitive resistor 32 located on the downstream side of the heat generating resistor 30 on the insulating substrate 29 receives this air. The first temperature-sensitive resistor 31, which is cooled by the flow and is located on the upstream side, receives heat from the heating resistor 30. As a result, the balance of the flow direction detection circuit 38 is lost and the comparison circuit 41 outputs the flow direction signal voltage V2 in the reverse direction in which the voltage value is zero.

As described above, since the heating resistor 30 is cooled by the flow of the intake air, the resistance value RH of the heating resistor 30 becomes small and the balance of the flow rate detecting circuit 34 is lost. As a result, a positive flow rate detection voltage V1 is output from the flow rate detection circuit 34 to the selection circuit 45, and
The negative flow rate detection voltage V1 'is also output to the selection circuit 45 via the inversion circuit 44, and in the selection circuit 45, the comparison circuit 41
The negative flow rate detection voltage V1 'is selected based on the reverse flow direction detection voltage V2 from
′ Is output from the output terminal 46 to the control unit as the output signal Vout.

Thus, the control unit can accurately detect the flow rate of the intake air based on the output signal Vout, perform accurate air-fuel ratio control, and improve engine performance.

Here, in the thermal type air flow rate detecting device 21 according to the present embodiment, the heating resistor 3 is provided on the insulating substrate 29.
0 is formed on the upstream side of the heating resistor 30.
Since the second temperature-sensitive resistor 32 is formed on the downstream side of the temperature-sensitive resistor 31, the temperature-sensitive resistors 31 and 32 can detect the air flow direction, and the heat-generating resistance The flow rate of the intake air can be detected from the change in the resistance value of the body 30. As a result, the flow rate of the intake air can be detected and the direction thereof can be accurately detected.

Further, since the heat generating resistor 30 and the temperature sensitive resistors 31, 32 are formed on the insulating substrate 29 so as to extend from the base end side toward the tip end side, a limited surface space can be effectively used. The heating resistor 30 and the temperature-sensitive resistor 31 can be formed compactly by using the heating resistor 30, and the surface area (mounting area) of the heating resistor 30 can be increased as much as possible. And
The contact area of the heat generating resistor 30 and the temperature sensitive resistor 31 with respect to the air flow in the intake pipe 2 can be increased, and the resistance values RH and RT can be sensitively changed in response to the air flow. Since the plurality of resistors 30, 31, 32 are formed on the single insulating substrate 29, the number of parts can be reduced.

Further, in this embodiment, the heating resistor 3
Due to the positional relationship between 0 and the first and second temperature sensitive resistors 31 and 32, the flow direction of air can be detected depending on whether or not the heat generated by the heating resistor 30 is affected, and an accurate flow rate can be detected. be able to.

Furthermore, the insulating substrate 29 of the present embodiment is provided with a base material 29A made of a metal having good thermal conductivity,
Since the base material 29A is formed by coating (coating) the surface layers 29B and 29C made of an insulating material on both side surfaces of the base material 29A, it quickly reacts to heat conduction from the heating resistor 30 and cooling by an air flow. As shown in FIG. 4, the heating resistor 30 and the first and second
The temperature difference between the temperature sensitive resistors 31 and 32 can be increased.

As a result, the first and second temperature sensitive resistors 31,
The flow direction can be accurately detected by the difference between the resistance values RT1 and RT2 of 32, and the flow direction of the intake air can be accurately detected. Further, the resistance values of the resistors 30, 31, 32 can be quickly changed with respect to the temperature, the reaction of the output signal Vout with the change of the flow rate is enhanced, and the accurate flow rate detection at the start of the automobile engine is started. The heat-up time can be shortened.

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, 3 can be detected.
It is possible to reliably detect the flow direction of the air based on the changes in the resistance values RT1 and RT2 of 2 and 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 reverse flow. The flow rate can be detected with high accuracy.

Next, FIG. 7 shows a second embodiment according to the present invention. The feature of this embodiment is that a metal core substrate is used as a single insulating substrate, and a heating resistor, This is because the second temperature-sensitive resistor was formed into a film and the flow rate detection signal calculation means was used in the detection circuit for detecting the flow rate and flow direction of the intake air. The same components as those in the first embodiment described above are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 7, reference numeral 51 denotes a current control circuit as a temperature control means for controlling the current value applied to the heating resistor 30 to keep the temperature of the heating resistor 30 constant.
The current control circuit 51 calculates the difference between the flow rate detection circuit 34 including the heating resistor 30, the temperature compensation resistance 35, the reference resistance 23, and the flow rate adjustment resistance 36, and the connection points c and d of the flow rate detection circuit 34. A connection point a between the differential amplifier circuit 37 for outputting the current control voltage VA and the flow rate detection circuit 34,
and a current control transistor 42 for controlling the value of the current applied to b.

In the current control circuit 51 thus constructed, when the flow rate detection circuit 34 is in a balanced state, the output voltage from the differential amplifier circuit 37 (current control voltage V
A) becomes zero. On the other hand, when the balance of the flow rate detection circuit 34 is lost, that is, when the heat generating resistor 30 is cooled by the intake air, the resistance value RH of the heat generating resistor 30 becomes small. A voltage difference is generated between the two and the current control voltage VA is output from the differential amplifier circuit 37 toward the base of the current control transistor 42. As a result, the current control transistor 42 is connected to the flow rate detection circuit 34.
The flow rate detection circuit 34 is returned to the equilibrium state by controlling the current applied to the cooling resistor 30 to keep the cooled heating resistor 30 at a constant temperature.

Here, the current control transistor 42
Has a collector side connected to the battery voltage VB, a base side connected to the output side of the differential amplifier circuit 37, and an emitter side connected to one end of the connection point a of the flow rate detection circuit 34. The current controlling transistor 42 is
Output from the differential amplifier circuit 37 (current control voltage VA)
Controls the emitter current according to the change of the base current. The current control transistor 42 controls the current value applied to the flow rate detection circuit 34 to control the heating resistor 30.
Feedback control is performed to maintain the temperature of the constant temperature.

Reference numeral 52 denotes a first flow rate detecting circuit as a first flow rate detecting means. The first flow rate detecting means 52 has a first temperature sensitive resistor 31 having a resistance value RT1 and a reference resistor 39.
Is connected in series, the first flow rate detection circuit 52 is connected between the battery voltage VB and the ground, and the connection point i between the first temperature sensitive resistor 31 and the reference resistor 39 is connected. Is connected to a flow rate detection signal calculation circuit 54 described later. Further, the first flow rate detection circuit 52 outputs the change in the resistance value RT1 of the first temperature sensitive resistor 31 as the first flow rate voltage V3.

Reference numeral 53 indicates a second flow rate detecting circuit as a second flow rate detecting means. The second flow rate detecting circuit 53 is constructed in substantially the same manner as the first flow rate detecting circuit 51 and has a resistance value R.
A second temperature sensitive resistor 32 having T2 and a reference resistor 40 are connected in series, and the second flow rate detection circuit 53 is connected between the battery voltage VB and the ground. Connection point j between the temperature-sensitive resistor 32 and the reference resistor 40
Are connected to the differential amplifier circuit 54. In addition, the second flow rate detection circuit 53 determines the resistance value RT2 of the second temperature sensitive resistor 32.
Is output as the second flow rate voltage V4.

Reference numeral 54 denotes a flow rate detection signal calculation circuit as a flow rate detection signal calculation means.
The connection points i and j of the first and second flow rate detection circuits 52 and 53 are connected to the input side of, and the control unit (not shown) is connected to the output side. Then, the flow rate detection signal arithmetic circuit 54 is configured as a differential amplifier circuit which performs the following arithmetic operation and outputs the output signal Vout.

[0076]

## EQU1 ## Vout = (V3-V4) * k, where k: constant

As described above, the flow rate detection signal arithmetic circuit 5
In 4, the output signal Vout can be output as a signal including the flow rate and the flow direction of the intake air by calculating the difference between the first and second flow rate voltages V3 and V4.

Also in the thermal type flow rate detecting device of the present embodiment constructed as described above, the flow rate including the flow direction of the intake air can be detected and the insulating substrate can be detected as in the case of the first embodiment. Since the structure of 29 is a metal core substrate, it is possible to rapidly and largely react to a temperature change due to overheating of the heating resistor 30 and a temperature change due to cooling of the intake air, and it is possible to enhance the detection sensitivity to the flow rate.

In each of the above embodiments, the first and second temperature sensitive resistors 31 and 32 are described as generating heat.
The present invention is not limited to this, and the first and second temperature sensitive resistors 31,
The first and second temperature sensitive resistors 31 and 32 may detect heat using the heat generated by the heat generating resistor 30 without applying a voltage to 32.

In each of the above embodiments, the flowmeter main body 22
Although the reference resistance 23 wound around the winding portion 24 of the above is provided so as to project into the intake pipe 2, the present invention is not limited to this, and the circuit casing 2 provided outside the intake pipe 2, for example.
The reference resistor 23 may be arranged in the unit 7 together with the flow rate adjusting resistor 36 and the like.

Further, in each of the above embodiments, the insulating substrate 29 is used.
Formed the surface layers 29B and 29C on both side surfaces of the base material 29A, but the present invention is not limited to this, and the resistors 30, 31 and
The film 32 may be formed only on one side surface on which the film is formed, and the temperature compensation resistor 35 may be formed on the insulating substrate 29.

[0082]

According to the invention of claim 1, a metal core substrate is used as an insulating substrate, and a heating resistor and first and second temperature sensitive resistors are formed on the substrate, whereby the metal core substrate is Since the reaction with respect to temperature is larger and quicker than that of the ceramic substrate, the temperature of the substrate differs at the positions of the heating resistor and the first and second temperature sensitive resistors. For example, when air is flowing in the forward direction, the first temperature-sensitive resistor on the upstream side is cooled, and the second temperature-sensitive resistor on the downstream side is heated by the heat of the heating resistor, A large difference occurs in the resistance value of each temperature sensitive resistor, and the flow rate detection sensitivity can be increased. Furthermore, since the metal core substrate is easy to warm and cool, the heat-up time can be shortened, and erroneous detection of the flow rate at the start can be reduced.

According to the second aspect of the present invention, the first temperature-sensitive resistor and the second temperature-sensitive resistor are connected in parallel to form the flow direction detecting means. The resistance values of the resistor, the second temperature sensitive resistor and the resistance value of the second temperature sensitive resistor are compared, and when the second temperature sensitive resistor is larger, it is determined that the air flow is in the forward direction, and the first sense is detected. When the temperature resistance is larger, it can be determined that the air flow is in the opposite direction.

Further, a flow rate detecting means comprising a bridge circuit including the heat generating resistor is provided, and a change in the resistance value of the heat generating resistor in the flow rate detecting means is taken out as a flow rate detecting signal. Based on the air flow direction detected by the direction detecting means, the flow rate detection signal is directly output as a positive voltage signal when the air flow direction is a forward direction, and is reversed when the air flow direction is a reverse direction and a negative voltage signal is output. Can be output as Then, the flow rate including the flow direction can be accurately detected.

According to the third aspect of the present invention, the temperature control means keeps the heating resistor at a constant temperature, and the flow direction and the flow rate are detected from the difference between the first and second flow rate detection means. For example, when a forward air flow is generated, the cooling amount of the first temperature-sensitive resistor located upstream of the heating resistor is large, and the second temperature-sensitive resistor located downstream of the heating resistor is the heating resistor. The amount of cooling of the second temperature-sensitive resistor becomes small because it is cooled by the air that receives heat from the second temperature-sensitive resistor.

As a result, for example, of the first flow rate signal output from the first flow rate detection means and the second flow rate detection signal output from the second flow rate detection means, for example, the first flow rate signal. Is larger than the second flow rate signal, the flow rate detection signal calculation means can subtract the second flow rate signal from the first flow rate signal to output the positive flow rate detection signal. it can.

On the other hand, when the air flow is in the opposite direction, for example, when the first flow rate signal becomes smaller than the second flow rate signal among the flow rate signals output from the flow rate detecting means, the flow rate detection signal is detected. The calculating means can output the negative flow rate detection signal by subtracting the second flow rate signal from the first flow rate signal. Then, the flow rate including the flow direction 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 shows a heating resistor formed on an insulating substrate and a first
FIG. 6 is a plan view showing the temperature-sensitive resistor and the second temperature-sensitive resistor.

FIG. 3 is a cross-sectional view as seen from a direction indicated by arrows III-III in FIG. 2;

FIG. 4 is an explanatory diagram showing a radiation state of heat on an insulating substrate.

FIG. 5 is a circuit diagram showing a circuit configuration of a thermal type air flow rate detecting device according to a first embodiment.

FIG. 6 is a characteristic diagram showing a relationship between a flow velocity of intake air and a flow direction detection voltage V2.

FIG. 7 is a circuit diagram showing a circuit configuration of a thermal type air flow rate detecting device according to a second embodiment.

FIG. 8 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. 9 is a perspective view showing a flowmeter main body, a heat generation resistance and the like according to a conventional technique.

[Explanation of symbols]

 21 Thermal Air Flow Rate Detector 22 Flow Meter Main Body 23 Reference Resistance 29 Insulating Substrate 29A Base Material 29B, 29C Surface Layer 30 Heating Resistor 31 First Temperature Sensitive Resistor 32 Second Temperature Sensitive Resistor 34 Flow Rate Detection Circuit ( Flow rate detection means 38 Flow direction detection circuit (flow direction detection means) 41 Comparison circuit 43 Flow rate signal output circuit (flow rate signal output means) 44 Inversion circuit 45 Selection circuit 51 Current control circuit (temperature control means) 52 First flow rate detection Circuit (first flow rate detection means) 53 Second flow rate detection circuit (second flow rate detection means) 54 Flow rate detection signal calculation circuit (flow rate detection signal calculation means)

Claims (3)

[Claims] 1. A metal core substrate having a base material made of a metal material having good thermal conductivity and a surface layer made of an insulating material formed on at least one side surface of the base material, and a metal core substrate positioned at the center of the surface layer side of the metal core substrate. And a first and second temperature-sensitive resistors provided on the surface layer of the metal core substrate, spaced apart before and after the air flow direction of the heating resistor. Thermal type air flow rate detection device. 2. The first temperature-sensitive resistor and the second temperature-sensitive resistor are connected in parallel, and the resistance values of the first temperature-sensitive resistor and the second temperature-sensitive resistor are compared. Flow direction detecting means for outputting a flow direction detecting signal corresponding to the flow direction of air, and a flow rate detecting means for extracting a change in resistance value of the heat generating resistor as a flow rate detecting signal, the flow rate detecting means including a bridge circuit including the heat generating resistor. And based on the flow direction detection signal detected by the flow direction detection means, when the air flow direction is the forward direction, the flow rate detection signal from the flow rate detection means is output as it is, and when the air flow direction is the reverse direction, the flow rate detection means is output. 2. The thermal air flow rate detection device according to claim 1, further comprising a flow rate signal output means for inverting and outputting the flow rate detection signal from. 3. A temperature control means for holding the metal core substrate at a constant temperature by controlling an electric current applied to the heating resistor to heat the heating resistor, and a resistance of the first temperature sensitive resistor. A first flow rate detecting means for detecting a first flow rate signal by a change in a value; a second flow rate detecting means for detecting a second flow rate signal by a change in a resistance value of the second temperature-sensitive resistor; Flow rate detection signal calculation means for calculating the difference between the first flow rate detection signal output from the first flow rate detection means and the second flow rate detection signal output from the second flow rate detection means and outputting the flow rate detection signal. The thermal air flow rate detection device according to claim 1, comprising: