JP3174234B2 - Thermal air flow detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In general, in an automobile engine or the like, a mixture of fuel and intake air is burned in a combustion chamber of an engine body, and the rotational output of the engine is obtained from the combustion pressure. Detecting the intake air flow rate is an important factor in calculating the following equation.

FIGS. 8 and 9 show a conventional thermal air flow detecting device.

[0004] In the drawing, reference numeral 1 denotes a thermal air flow detecting device provided in the middle of an intake pipe 2. The thermal air flow 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 in the drawing, it is provided in the middle of the intake pipe 2 via a mounting hole 2A.

[0005] Reference numeral 3 denotes an air flow detecting device main body constituting a main body of the thermal type air flow detecting device 1, and the air flow detecting device main body 3 is formed by means such as insert molding as shown in FIG. A winding portion 4 formed in a stepped column shape for winding a linear reference resistor 14 to be described later, and a substantially disk-shaped portion located at a base end side of the winding portion 4 and described later. A terminal portion 5 integrally provided with terminal pins 8A to 8D,
A detection holder 6 extending in the radial direction of the intake pipe 2 from the distal end side of the winding part 4 and positioning a heating resistor 9 and a temperature compensating resistor 11, which will be described later, at the center of the intake pipe 2; A circuit casing 7 described below to which the terminal portion 5 is connected
It is roughly composed of

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

Reference numerals 8A, 8B, 8C, and 8D denote four terminal pins (generally referred to as terminal pins 8) projecting in the axial direction from the terminal portion 5 of the main body 3 of the air flow detecting device. It is provided integrally with, for example, four terminal plates (not shown) embedded in the winding part 4 of the air flow detecting device main body 3 and the detection holder 6, and is provided on a connector part (not shown) of the circuit casing 7. It is connected detachably.

Reference numeral 9 denotes a hot film type heating resistor provided on the detection holder 6 of the main body 3 of the air flow detecting device via the terminals 10A and 10B. The heating resistor 9 reacts sensitively to a temperature change and has a resistance value. Is formed by winding a platinum wire or depositing a platinum film on an insulating cylinder made of a ceramic material such as aluminum oxide (hereinafter, referred to as "alumina"). And a heating resistor element having a small diameter. The heating resistor 9 is energized by a battery (not shown),
For example, when heat is generated at temperatures before and after 240 ° C. and the air is cooled by the intake air flowing in the direction of the arrow A in the intake pipe 2, the resistance value changes according to the flow rate of the intake air, and the flow rate detection signal Is output.

Reference numeral 11 denotes a temperature compensation resistor provided on the detection holder 6 of the air flow detection device main body 3 located on the upstream side of the heating resistor 9, and the temperature compensation resistor 11 is an insulating material made of a ceramic material such as alumina. A platinum film is formed 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 detecting device.
Reference numeral 3 denotes a heating resistor 9 and a temperature compensation resistor 1 on the detection holder 6.
1 is mounted on the detection holder 6 as shown by an arrow in FIG. 9 to protect the heating resistor 9 and the temperature compensating resistor 11 and allow the flow of intake air. In FIG. 9, the heating resistor 9 and the temperature compensating resistor 1 are shown.
In order to clearly indicate 1, the protection cover 13 is shown removed from the detection holder 6.

Further, reference numeral 14 denotes a reference resistance comprising a winding resistance wound around the winding part 4 of the air flow 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, of 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 the other terminal plates. The terminal pins 8C are connected to the terminals 10B and 12B via another terminal plate.
B, and the terminal pin 8D is connected to the terminal 12A via another terminal plate.

The conventional thermal air flow detecting device 1 constructed as described above detects the terminal portion 5 of the air flow detecting device main body 3 when detecting the intake air flow of an automobile engine or the like.
Is connected to the connector portion of the circuit casing 7 via each terminal pin 8, and the detection holder 6 and the like of the air flow detecting device main body 3 are inserted into the intake pipe 2 through the mounting hole 2A, and the mounting hole 2A By mounting the circuit casing 7 from the outer peripheral side of the intake pipe 2 to the
And a temperature compensation resistor 11 is disposed at the center of the intake pipe 2.

In this case, by connecting the heating resistor 9 in series with the reference resistor 14 and connecting the temperature compensating resistor 11 in series with the flow rate adjusting resistor in the circuit casing 7, the heating resistor 9, the reference resistor 14, and the temperature A bridge circuit is composed of the compensation resistor 11 and the flow rate adjustment resistor, and the bridge circuit is energized from the outside so that the heating resistor 9 is 240 ° C.
Heat is generated at a later temperature.

In this state, when the intake air flows in the intake pipe 2 toward the combustion chamber of the engine body in the direction indicated by the arrow A, the flow of the intake air cools the heating resistor 9 so that the heating resistor 9 is cooled. , The detection signal corresponding to the flow rate of the intake air is detected as a change in the output voltage based on the voltage across the reference resistor 14 connected in series with the heating resistor 9.

[0015]

By the way, in the above-mentioned prior art, the resistance value of the heating resistor 9 is changed by utilizing the cooling of the heating resistor 9 by the flow of the intake air flowing through the intake pipe 2. Since the configuration is such that the intake air flow is detected based on the intake air flow, the heating resistor 9 is cooled by the intake air flow flowing in the arrow A direction (forward direction) in FIG. 8 and flows in the arrow B direction (reverse direction). It is also cooled by the air flow, and there is a problem that the air flow in the opposite direction erroneously detects the intake air flow rate.

That is, in an engine body having a multi-cylinder cylinder, the intake air is forced into each cylinder every time each intake valve (not shown) is opened as the piston reciprocates in each cylinder. As shown in FIG. 6, the flow velocity of the air flowing through the intake pipe 2 repeatedly increases and decreases according to the opening and closing of each intake valve, as shown in FIG. become.

In particular, when the engine speed reaches from a low speed range to a middle speed range and the intake and exhaust volumes increase, the intake valve and the exhaust valve (not shown) overlap, and one of the exhaust The part may blow back into the intake pipe 2 with the opening of the intake valve, and at this time, the times t1, t shown in FIG.
The flow velocity becomes negative (minus) as shown in FIG. 2, and an airflow flowing 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-described problems of the prior art, and the present invention can prevent erroneous detection of an intake air flow rate due to a reverse air flow, and can greatly improve flow rate detection accuracy. It is an object of the present invention to provide a thermal air flow detecting device according to the present invention.

[0019]

According to a first aspect of the present invention, there is provided a thermal type air flow rate detecting device comprising a base material made of a metal material having good heat conductivity and at least one side of the base material. It includes a metal core substrate formed by forming a surface layer made of an insulating material, and a heating resistor provided on the surface layer side of the metal core substrate. The first aspect of the invention is characterized in that the heating resistor is provided.
On the surface layer of the metal core substrate, the first and the second heating cores are spaced apart from each other before and after the heating resistor in the air flow direction.
A second temperature-sensitive resistor is provided, and the first and second temperature-sensitive resistors are connected in parallel to each other with respect to a power supply, and are connected in the air flow direction
The configuration is such that a corresponding detection signal is output .

[0020] The inventions of claim 2, good thermal conductivity metal material
Base material is insulated on at least one side of the base material
A metal core substrate formed by forming a surface layer made of a material,
Heating resistor provided on the surface layer side of the metal core substrate
Air flow provided on a surface layer of the metal core substrate.
In the direction away from each other before and after the heating resistor
1, a second thermo-sensitive resistor, said first temperature sensing resistor and the second temperature sensing resistor is connected in parallel, the first temperature-sensitive resistor and the second temperature sensitive resistor A flow direction detecting means for comparing a resistance value and outputting a flow direction detection signal corresponding to a flow direction of air, and a bridge circuit including the heating resistor, wherein a change in the resistance value of the heating resistor is detected as a flow rate. Based on the flow direction detection signal detected by the flow direction detection unit and the flow direction detection signal detected by the flow direction detection unit. is you are configured to Ru and a flow rate signal output means for inverting the flow rate detection signal from the flow amount detecting means when the.

[0021] The inventions of claim 3, good thermal conductivity metal material
Base material is insulated on at least one side of the base material
A metal core substrate formed by forming a surface layer made of a material,
Heating resistor provided on the surface layer side of the metal core substrate
Air flow provided on a surface layer of the metal core substrate.
In the direction away from each other before and after the heating resistor
1, a second temperature-sensitive resistor, and temperature control means for controlling the current applied to the heat-generating resistor to cause the heat-generating resistor to generate heat, thereby maintaining the metal core substrate at a constant temperature;
First flow rate detecting means for detecting a first flow rate signal based on a change in the resistance value of the first temperature sensitive resistor, and detecting a second flow rate signal based on a change in the resistance value of the second temperature sensitive resistor. Calculating a difference between a first flow rate detection signal output from the first flow rate detection means and a second flow rate detection signal output from the second flow rate detection means; configuration Ru and a flow rate detection signal operation means for outputting a detection signal
It is with.

[0022]

According to the present invention, the heating resistor and the first and second temperature-sensitive resistors are formed on the metal core substrate. Therefore, the metal core substrate has a greater response to temperature than the ceramic substrate. The temperature of the substrate is different between the position of the heating resistor and the position of the first and second temperature-sensitive resistors. When the flow of air is in the forward direction, the first temperature-sensitive resistor on the upstream side is cooled. Then, the second temperature-sensitive resistor on the downstream side is heated by receiving the heat of the heat-generating resistor, and a difference occurs between the resistance values of the respective temperature-sensitive resistors.

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 of the second temperature-sensitive resistor is compared with the resistance value of the second temperature-sensitive resistor.
If the temperature-sensitive resistor is larger, it can be determined that the airflow is in the opposite direction.

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

In a state where the current value applied to the heating resistor is controlled by the temperature control means and the heating resistor is maintained at a constant temperature, for example, when a forward air flow is generated, The first located upstream of the heating resistor
The amount of cooling of the temperature-sensitive resistor of the second
Is cooled by the air that has received heat from the heat generating resistor, so that the amount of cooling of the second temperature sensitive resistor is small.

Thus, 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 calculating means can output a positive flow rate detection signal by subtracting the second flow rate signal from the first flow rate signal. it can. On the other hand, when the flow of air is in the reverse direction, when the first flow signal is smaller than the second flow signal among the flow signals output from the flow detection means, the flow detection signal calculation means By subtracting the second flow rate signal from the first flow rate signal, a negative flow rate detection signal can be output.

[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 technology are denoted by the same reference numerals, and description thereof will be omitted.

First, FIGS. 1 to 6 show a first embodiment according to the present invention.
The following shows an example.

In the figure, reference numeral 21 denotes a thermal air flow detecting device according to the present embodiment, 22 denotes a flow meter main body constituting a main body of the thermal air flow detecting device 21, and the flow meter main body 22 is a conventional one. The winding part 24 around which the reference resistor 23 having the resistance value R1 is wound, substantially in the same manner as the air flow detecting device body 3 described above.
And 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). And a circuit casing 27 to be described later.

However, a slot (not shown) for detachably mounting an insulating substrate 29 to be described later is formed at the base end side of the detection holder 26 in the flowmeter main body 22, and the detection holder 26 is shown in FIG. As shown in FIG. 2, temperature-sensitive resistors 31, 32 and the like, which will be described later, are positioned at the center of the intake pipe 2 via an insulating substrate 29. The detection holder 26 is provided with a protective cover (not shown) similar to the protective cover 13 described in the related art.

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. The circuit casing 27 is substantially the same as the circuit casing 7 described in the prior art. The mounting hole 2 of the intake pipe 2 is formed.
Although the circuit casing 27 has a fitting portion 27A that fits into the A, the circuit casing 27 is formed on an insulating substrate (not shown) made of, for example, a ceramic material, etc. These are built-in while mounted. 28A and 28B are terminals to which the windings of the reference resistor 23 are connected.

Reference numeral 29 denotes an insulating substrate mounted on the detection holder 26. The insulating substrate 29 is formed of a metal core substrate and has a length of 1 as shown in FIGS.
A base material 29A formed of a rectangular flat plate having a width of about 5 to 20 mm and a width of about 3 to 7 mm and made of a metal having good heat conductivity such as a SUS material;
A comprises surface layers 29B and 29C formed on both sides of A by an insulating material such as alumina, glass, or aluminum nitride. The base end of the insulating substrate 29 is a fixed end detachably attached to a slot of the detection holder 26, and the front end is a free end.

As described above, by forming the insulating substrate 29 as a metal core substrate, the substrate can be easily heated and cooled, and a large temperature change can be 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 which constitutes a heating resistor formed on the surface layer 29B of the insulating substrate 29. The heating resistor 30 is formed of platinum on the insulating substrate 29 by means such as printing or sputtering. By forming a film, the film is formed to have a resistance value RH, is formed on the upstream side with respect to the direction of air flow (direction of arrow A), and has a surface area (mounting area) of the heating resistor 30. ) Is increased as much as possible, for example, so that the contact area with the intake air flowing through the intake pipe 2 can be increased.

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

Reference numerals 31 and 32 denote the heaters with the heating resistor 30 interposed therebetween.
FIG . 3 shows first and second temperature-sensitive resistors formed on a surface layer 29B of an insulating substrate 29 together with a thermal resistor 30; the first temperature-sensitive resistor 31 is located upstream of the heat-generating resistor 30; The second temperature-sensitive resistor 3 is formed so as to have a resistance value RT1.
A film 2 is formed on the downstream side of the heating resistor 30 so as to have a resistance value RT2. And the first and second
The temperature-sensitive resistors 55 and 56, as shown in FIG.
It is connected in parallel to the source VS.

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

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

When the air flow in the direction of arrow A (forward direction) occurs, the heat moves to the left as indicated by the dashed line, and the first temperature-sensitive resistor 31 is directly cooled by the air, The second temperature-sensitive resistor 32 receives heat from the heat-generating resistor 30, and the detected temperature T of the first temperature-sensitive resistor 31.
The relationship between A1 and the detected temperature TA2 of the second temperature-sensitive resistor 32 is TA1
<TA2, and the relationship between the resistance values RT1 and RT2 of the temperature-sensitive resistors 31 and 32 at this time is RT1 < RT2 .

Further, when the air flow in the direction of arrow B (reverse direction) occurs, the heat moves to the right as shown by the two-dot chain line, and the second temperature-sensitive resistor 32 is directly cooled by the air. The first temperature-sensitive resistor 31 receives heat from the heat-generating resistor 30, and the relationship between the two detected temperatures is: TB1> T
B2, and the relationship between the resistance values RT1 and RT2 is RT1 > RT2 .

Reference numerals 33, 33,... Denote, for example, six electrodes formed on the base end side of the insulating substrate 29. The electrodes 33 are arranged in a row at a predetermined interval in the width direction of the insulating substrate 29. 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. By connecting the heating resistor 30 and the temperature-sensitive resistor 31 formed on the insulating substrate 29 via the respective electrodes 33 to the respective electronic components provided in the circuit casing 27, FIG. The processing circuit for flow rate detection shown is configured.

Next, FIG. 5 shows a processing circuit for detecting a flow rate according to the present embodiment.

In FIG. 5, reference numeral 34 denotes a flow detection circuit constituted by a bridge circuit for outputting a flow detection signal. The flow detection circuit 34 includes a heating resistor 30, a temperature compensation resistor 35, a reference resistor 23, and a resistance value. A flow control resistor 36 having a resistance value R2 is formed as a bridge in which the products of the resistance values of the opposing sides are equal. A connection point a between the heating resistor 30 and the temperature compensation resistor 35 is connected to a current control transistor 42 described later. And the connection point b between the reference resistor 23 and the flow adjustment resistor 36 is connected to the ground.

In the flow rate detection circuit 34, the heating resistor 30 and the reference resistor 23, and the temperature compensating resistor 35 and the flow rate adjusting resistor 36 are connected in series, respectively.
d is connected to the input terminal of the differential amplifier circuit 37,
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 for controlling the current applied 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 between both ends of the reference resistor 23 and the output voltage is the heating resistor 3
0 is a flow detection voltage V1 (flow detection signal) indicating the degree of cooling by the flow.

Here, the temperature compensation resistor 35 is provided on the detection holder 26 in the vicinity of the heating resistor 30.
The temperature compensation 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 configured, when the flow rate detection circuit 34 is in an equilibrium state, the current control voltage VA from the differential amplifier circuit 37 becomes zero and the current control voltage VA from the connection point c is balanced. Reference resistance 23 when in state
Are output to the inverting circuit 44 and the selecting circuit 45. On the other hand, when the balance of the flow detection circuit 34 is lost, that is, when the heating resistor 30 is cooled by the intake air, the resistance value RH of the heating resistor 30 is 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.
Is controlled to keep the cooled heating resistor 30 at a constant temperature and return the flow rate detection circuit 34 to an equilibrium state.
At this time, the increased current value output from the connection point c of the flow detection circuit 34 is detected as a voltage across the reference resistor 23, and this voltage is used as a first flow detection voltage V1 by the inversion circuit 44 and the selection circuit 45. Output.

Next, reference numeral 38 denotes a flow direction detection circuit which constitutes a flow direction detection means together with a comparison circuit 41 described later.
The flow direction detection circuit 38 includes the first and second temperature-sensitive resistors 3.
1 and 32 and reference resistances 39 and 40, which are configured as a bridge circuit in which the resistance values of the opposing sides are equal to each other. A connection point e between the first and second temperature sensitive resistors 31 and 32 is connected to the sub power supply VS ( 3V) and the reference resistance 3
The connection points f at 9, 40 are connected to ground.

The flow direction detecting circuit 38 is provided with a first
When the temperature-sensitive resistor 31 and the reference resistor 39 are connected in series,
In both cases , the second temperature-sensitive resistor 32 and the reference resistor 40 are connected in series, and respective connection points g and h are connected to the input terminals of the comparison circuit 41, and the comparison circuit 41 is connected to the selection circuit 45. I have. As described above, when the flow direction detection circuit 38 is in an equilibrium state, that is, when the intake air is not flowing, there is no difference between the resistance values RT1 and RT2 of the temperature-sensitive resistors 31 and 32. The output is zero. Also,
When the balance of the flow direction detecting circuit 38 is lost, that is, when the resistance values RT1 and RT2 of one of the temperature-sensitive resistors 31 and 32 change due to the airflow, the flow direction detecting circuit 38
Of the connection point g-h is input to the comparison circuit 41 as the difference in resistance value (RT1-RT2) voltage, a signal indicating the flow direction of the intake air based on the difference in resistance (hereinafter, "the flow direction detection that the voltage V2 ") is outputted to the selection circuit 45.

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. Outputs the flow direction detection voltage V2 that is V0,
When the air flow direction changes from the direction A to the direction B (reverse direction), the comparison circuit 41 outputs a 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 connected to the battery voltage VB and a base connected to the differential amplifier 37.
And the emitter side is connected to the flow rate detection circuit 3
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 signal output circuit as flow signal output means. The flow signal output circuit 43 includes an inverting circuit 44 and a selecting circuit 45 described later.

Reference numeral 44 denotes an inversion circuit connected between the connection point c of the flow detection circuit 34 and the selection circuit 45. The inversion circuit 44 inverts the flow detection voltage V1 from the flow detection circuit 34 and selects the selection circuit. 45.

Reference numeral 45 denotes a selection circuit which constitutes a flow signal output means together with the inversion circuit 44. The selection circuit 45 outputs a flow direction detection voltage V2 from the flow direction detection circuit 38 output via 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 as the output signal Vout from the output terminal 46 to a control unit (not shown), and in the case of the reverse direction, the inversion circuit 44. Signal from the output signal V
Out is output from the output terminal 46 to the control unit.

The thermal air flow detecting device 21 according to the present embodiment
Has the configuration as described above. Next, the operation of 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 the flow of the air. The second temperature-sensitive resistor 32 located on the downstream side receives the heat from the heating resistor 30. As a result, the balance of the flow direction detection circuit 38 is broken, and the voltage value V0 is output from the comparison circuit 41.
And outputs a forward flow direction detection voltage V2.

The heating resistor 30 is cooled by the flow of the intake air, and the cooling reduces the resistance value RH of the heating resistor 30. The heating resistor 30 is reduced by the differential amplifier circuit 37 and the current control transistor 42. In order to keep the temperature at 30 constant, the value of the current applied to the flow rate detection circuit 34 is increased, and the increased current value is detected by the reference resistor 23 as a voltage between both ends. As a result, the flow rate detection circuit 3
4 outputs a positive flow rate detection voltage V1 to the inversion circuit 44 and the selection circuit 45. The flow rate detection voltage V1 of positive input to the inverting circuit 44 is output to the selection 択回 path 45 as a negative flow rate detection voltage V1 'obtained by inverting.

Then, in the selection circuit 45, the comparison circuit 41
Flow detection circuit 3 based on the flow direction detection voltage V2 from
4 and the inversion circuit 44
Is selected from the negative flow rate detection voltage V1 'input from the controller. In this case, since the flow direction detection voltage V2 is in the forward direction, the positive flow rate detection voltage V1 is selected and the output terminal 46 is selected.
To the control unit from the positive flow detection voltage V
1 is output as an 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 for keeping the heating resistor 30 at a constant temperature is performed. .

On the other hand, when the flow of the air is in the direction of arrow B (reverse direction), the second temperature-sensitive resistor 32 located on the insulating substrate 29 on the downstream side of the heat-generating resistor 30 generates the air. The first temperature-sensitive resistor 31 located on the upstream side is cooled by the flow and 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 reverse flow direction signal voltage V2 having a voltage value of 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 decreases, and the balance of the flow detection circuit 34 is lost. As a result, a positive flow detection voltage V1 is output from the flow 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.
The negative flow detection voltage V1 'is selected based on the reverse flow direction detection voltage V2 from
'As an output signal Vout from the output terminal 46 to the control unit.

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 the engine performance.

Here, in the thermal air flow detecting device 21 according to the present embodiment, the heating resistor 3 is placed on the insulating substrate 29.
0 and a first 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 direction of air flow can be detected by the respective temperature-sensitive resistors 31, 32, and the heat-generating resistor 31 can be detected. From the change in the resistance value of the body 30, the flow rate of the intake air can be detected. Accordingly, the flow rate of the intake air can be detected, and the direction thereof can be accurately detected.

Further, since the heating resistor 30 and the temperature-sensitive resistors 31 and 32 are formed on the insulating substrate 29 so as to extend from the base end to the tip end, a limited surface space can be effectively used. The heating resistor 30 and the temperature-sensitive resistor 31 can be formed compact by utilizing 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 between the heating resistor 30 and the temperature-sensitive resistor 31 with respect to the air flow in the intake pipe 2 can be increased, and these resistance values RH and RT can be changed in response to the air flow in a sensitive manner. Since a plurality of resistors 30, 31, and 32 are formed on a single insulating substrate 29, the number of components can be reduced.

In this embodiment, the heating resistor 3
The direction of air flow can be detected based on the positional relationship between the zero and the first and second temperature sensing resistors 31 and 32 depending on whether or not the heating resistor 30 is affected by heat, and an accurate flow rate can be detected. be able to.

Further, the insulating substrate 29 of the present embodiment is provided with a base material 29A made of a metal having good heat conductivity,
Since the surface layers 29B and 29C made of an insulating material are formed (coated) on both side surfaces of the base material 29A, it reacts quickly to heat conduction from the heating resistor 30 and cooling by 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,
It is possible to accurately detect the flow direction based on the difference between the 32 resistance values RT1 and RT2, and to accurately detect the flow direction of the intake air. Further, the resistance values of the resistors 30, 31, 32 with respect to the temperature can be quickly changed, the response of the output signal Vout accompanying the change in the flow rate can be increased, and the accurate flow rate detection at the start of the vehicle engine can be started. Heat-up time can be shortened.

Therefore, according to the present 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.
2 can be reliably detected based on the change in the resistance values RT1 and RT2 of the intake air 2. Even when exhaust gas blows back into the intake pipe 2 in the middle speed range of the engine and a reverse flow occurs, the intake air 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 for a single insulating substrate, and a heating resistor, The second temperature-sensitive resistor is formed as a film, and the flow rate detection signal calculating means is used in a circuit for detecting the flow rate and the flow direction of the intake air. The same components as those in the first embodiment described above are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 7, reference numeral 51 denotes a current control circuit as temperature control means for controlling a current value applied to the heating resistor 30 to keep the temperature of the heating resistor 30 constant.
The current control circuit 51 determines the difference between the flow rate detection circuit 34 including the heating resistor 30, the temperature compensation resistor 35, the reference resistor 23, and the flow rate adjustment resistor 36, and the connection points c and d of the flow rate detection circuit 34. A connection point a between a differential amplifier circuit 37 that outputs a 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 configured, when the flow rate detection circuit 34 is in an equilibrium 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 heating resistor 30 is cooled by the intake air, the resistance value RH of the heating resistor 30 is small. , A voltage difference is generated, 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.
Is controlled to keep the cooled heating resistor 30 at a constant temperature and return the flow rate detection circuit 34 to an equilibrium state.

Here, the current control transistor 42
The collector side is connected to the battery voltage VB, the base side is connected to the output side of the differential amplifier circuit 37, and the emitter side is connected to one end of the connection point a of the flow rate detection circuit. The current control transistor 42 is
Output from the differential amplifier circuit 37 (current control voltage VA)
Controls the emitter current as the base current changes. The current control transistor 42 controls the current value applied to the flow rate detection circuit 34 to
The feedback control is performed to keep the temperature at a constant temperature.

Reference numeral 52 denotes a first flow rate detection circuit as first flow rate detection means. The first flow rate detection circuit 52 includes a first temperature-sensitive resistor 31 having a resistance value RT1 and a reference resistor 39.
Are connected in series, and the first flow rate detection circuit 52 is connected between the battery voltage VB and the ground, and a 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 detection circuit 52 outputs a change in the resistance value RT1 of the first temperature-sensitive resistor 31 as a first flow voltage V3.

Reference numeral 53 denotes a second flow rate detection circuit as second flow rate detection means. The second flow rate detection circuit 53 has substantially the same configuration as the first flow rate detection circuit 52, and has a resistance value R
The second flow rate detection circuit 53 is connected between the battery voltage VB and the ground by connecting a second temperature sensing resistor 32 having T2 and a reference resistor 40 in series. Point j between the temperature-sensitive resistor 32 and the reference resistor 40
Is connected to the flow signal operation circuit 54. Also, the second
The flow rate detection circuit 53 outputs the change in the resistance value RT2 of the second temperature-sensitive resistor 32 as the second flow rate voltage V4.

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

[0076]

Vout = (V3−V4) × k where k is a constant

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

In the thermal type flow rate detecting device of this embodiment thus constructed, the flow rate including the flow direction of the intake air can be detected as well as the insulating substrate, as in the first embodiment. Since the structure of 29 is a metal core substrate, the temperature change due to the overheating of the heating resistor 30 and the temperature change due to the cooling of the intake air can be quickly and largely reacted, and the detection sensitivity to the flow rate can be increased.

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,
Heat may be detected by the first and second temperature-sensitive resistors 31 and 32 using the heat generated by the heat-generating resistor 30 without applying a voltage to the resistor 32.

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

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

[0082]

According to the first aspect of the present invention, a metal core substrate is used as an insulating substrate, and a heating resistor and first and second temperature-sensitive resistors are provided on the metal core substrate in the direction of air flow. On the other hand, before and after the heating resistor, the first and second
The first and second temperature sensitive resistors are formed so as to be located .
The temperature-sensitive resistors are connected in parallel to the power supply and
The configuration is such that it outputs a detection signal corresponding to the flow direction of the metal core substrate, which takes advantage of the characteristic of the metal core substrate that the response to the temperature is larger and quicker than the ceramic substrate. The temperature of the substrate can be varied at the position of the resistor, and the direction of air flow can be detected.
Ru can be out. When the air is flowing in the forward direction, for example, 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. Therefore, a large difference occurs between the resistance values of the respective temperature sensitive resistors, and the flow rate detection sensitivity can be increased.
In addition, metal core substrates are easy to warm and cool ,
The heat-up time at the start of the gin can be shortened, and the erroneous detection of the flow rate at the start of the engine 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 a flow direction detecting means. The resistance value of the resistor and the resistance value of the second resistor are compared with each other. If the resistance value of the second resistor is larger, it is determined, for example, that the airflow is in the forward direction. If the temperature resistor is larger, it can be determined that the airflow is in the opposite direction.

Further, there is provided a flow rate detecting means comprising a bridge circuit including the heat generating resistor, a resistance value change of the heat generating resistor in the flow rate detecting means is taken out as a flow rate detection signal, and the flow rate signal output means is provided with the flow rate detecting means. Based on the flow direction of the air detected by the direction detecting means, when the flow direction of the air is the forward direction, the flow rate detection signal is output as it is as a positive voltage signal, and when the flow direction is the reverse direction, the flow rate detection signal is inverted and the negative voltage signal is inverted. 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 heating resistor is maintained at a constant temperature by the temperature control means, 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 airflow occurs, the cooling amount of the first temperature sensitive resistor located on the upstream side of the heating resistor is large, and the second temperature sensitive resistor located on the downstream side is the heating resistor. Since the second temperature-sensitive resistor is cooled by the air receiving the heat from the second temperature-sensitive resistor, the amount of cooling of the second temperature-sensitive resistor is reduced.

Thus, 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 calculating means can output a positive flow rate detection signal by subtracting the second flow rate signal from the first flow rate signal. it can.

On the other hand, when the flow of air is in the opposite direction, when the first flow signal is smaller than the second flow signal among the flow signals output from the respective flow detection means, the flow detection signal is output. The arithmetic means can output a 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 the drawings]

FIG. 1 is a longitudinal sectional view showing a state in which a thermal air flow detecting 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 heating resistor.
FIG. 3 is a plan view showing a second temperature-sensitive resistor and a 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 heat radiation state on an insulating substrate.

FIG. 5 is a circuit diagram showing a circuit configuration of the thermal air flow detecting device according to the 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 air flow detecting device according to a second embodiment.

FIG. 8 is a longitudinal sectional view showing a state in which a thermal air flow detecting device according to a conventional technique is attached to an intake pipe.

FIG. 9 is a perspective view showing a flow meter main body, a heating resistor, and the like according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Thermal air flow 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 detection means) 53 Second flow detection circuit (second flow detection means) 54 Flow detection signal calculation circuit (flow detection signal calculation means)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-58-162823 (JP, A) JP-A-4-105018 (JP, A) JP-A-62-14328 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) G01F 1/68-1/699

Claims (3)

(57) [Claims] 1. A metal core substrate formed by forming a surface layer made of an insulating material on at least one side surface of a metal material having good heat conductivity as a base material, and provided on the surface layer side of the metal core substrate. In the thermal type air flow detecting device comprising the heating resistor, the surface layer of the metal core substrate on which the heating resistor is provided is separated before and after the heating resistor with respect to the direction of air flow. first, a second thermo-sensitive resistor provided, first, second temperature sensitive resistor is connected in parallel to the power source was
A thermal air flow detecting device configured to output a detection signal corresponding to a flow direction of air. 2. A metal core substrate comprising 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 provided on the surface layer side of the metal core substrate. A first and a second heating resistor provided on a surface layer of the metal core substrate and separated before and after the heating resistor with respect to a flow direction of air.
A second temperature-sensitive resistor, the first temperature-sensitive resistor and the second temperature-sensitive resistor are connected in parallel, and the resistance value of the first temperature-sensitive resistor and the second temperature-sensitive resistor A flow direction detection means for comparing the flow direction of the air to output a flow direction detection signal, and a bridge circuit including the heating resistor, wherein a change in the resistance value of the heating resistor is used as a flow rate detection signal. Based on the flow direction detection signal detected by the flow direction detection unit, the flow detection unit takes out the flow detection signal from the flow detection unit when the flow direction of the air is in the forward direction, and outputs the flow detection signal from the flow direction detection unit in the reverse direction. And a flow signal output means for inverting and outputting a flow detection signal from said flow detection means. 3. A metal core substrate comprising 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 provided on the surface layer side of the metal core substrate. A first and a second heating resistor provided on a surface layer of the metal core substrate and separated before and after the heating resistor with respect to a flow direction of air.
A second temperature-sensitive resistor; temperature control means for controlling the current applied to the heat-generating resistor to cause the heat-generating resistor to generate heat so as to maintain the metal core substrate at a constant temperature; First flow rate detecting means for detecting a first flow rate signal based on a change in resistance value of a resistor; and second flow rate detecting means for detecting a second flow rate signal based on a change in resistance value of the second temperature sensitive resistor. And a flow rate for calculating a difference between a first flow rate detection signal output from the first flow rate detection means and a second flow rate detection signal output from the second flow rate detection means to output a flow rate detection signal. A thermal air flow detection device having a configuration including a detection signal calculation means.