JP3133609B2 - 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.

FIG. 9 to FIG. 11 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 a flow meter main body constituting a main body of the thermal air flow detecting device 1, and the flow meter main body 3 is formed as shown in FIG.
A winding part 4 formed in a stepped column shape for winding a reference resistance 14 which will be described later in the form of a winding, and a substantially disk-shaped part located at the base end side of the winding part 4, Terminal pins 8A to 8D
Is extended in the radial direction of the intake pipe 2 from the distal end side of the winding part 4, and a heating resistor 9 and a temperature compensation resistor 11 described later are positioned at the center of the intake pipe 2. And a circuit casing 7 to be described later to which the terminal portion 5 is connected outside the intake pipe 2.

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 flowmeter main body 3, and each of the terminal pins 8 is a flowmeter. It is provided integrally with, for example, four terminal plates (not shown) embedded in the winding part 4 of the main body 3 and the detection holder 6 and is detachably connected to a connector part (not shown) of the circuit casing 7. Is what is done.

Reference numeral 9 denotes a hot film type heating resistor provided on the detection holder 6 of the flow meter main body 3 via the terminals 10A and 10B. The heating resistor 9 changes its resistance value in response to a temperature change. A platinum wire is wound around an insulating cylinder made of a ceramic material such as aluminum oxide (hereinafter, referred to as "alumina") or a platinum film is formed by depositing a platinum film. And a heating resistor element having a small diameter. The heat generating resistor 9 is heated by, for example, a temperature before and after 240 ° C. by energization from a battery (not shown), and is cooled by intake air flowing in the intake pipe 2 in the direction of arrow A. The resistance value changes in accordance with the flow rate of the intake air, and a flow rate detection signal is output.

Reference numeral 11 denotes a temperature compensation resistor provided on the detection holder 6 of the flowmeter main body 3 located on the upstream side of the heating resistor 9, and the temperature compensation resistor 11 is formed on an insulating substrate made of a ceramic material such as alumina. Is formed by depositing a platinum film using a means such as sputtering, and both ends of the platinum film are connected to the terminal 1 provided upright on the detection holder 6.
It is connected between 2A and 12B.

Reference numeral 13 denotes a protective cover mounted on the detection holder 6 of the flowmeter main body 3. The protective cover 13 is shown in FIG. 10 after the heating resistor 9 and the temperature compensating resistor 11 are mounted on the detection holder 6. As shown by the arrow, it is attached to the detection holder 6 to protect the heat generating resistor 9 and the temperature compensating resistor 11 and allow the flow of intake air. In addition,
FIG. 9 shows a state in which the protective cover 13 is removed from the detection holder 6 in order to clearly show the heating resistor 9 and the temperature compensation resistor 11.

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

In the thermal air flow detecting device 1 of the prior art constructed as described above, when detecting the intake air flow rate of an automobile engine or the like, the terminal portion 5 of the flow meter main body 3 is connected via each terminal pin 8. In a state of being connected to the connector portion of the circuit casing 7, the detection holder 6 and the like of the flowmeter main body 3 are inserted into the intake pipe 2 via the mounting hole 2A, and the circuit is inserted into the mounting hole 2A from the outer peripheral side of the intake pipe 2. By attaching the casing 7,
Heating resistor 9 and temperature compensation resistor 1 provided on detection holder 6
1 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 direction indicated by the arrow A (forward direction) in FIG. 9 and flows in the direction indicated by the arrow B (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. 11, 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 In some cases, the portion may blow back into the intake pipe 2 with the opening of the intake valve, and at this time, the time t1 shown in FIG.
The flow velocity becomes negative (minus) as during t2, and arrow B
An airflow flowing in the direction (reverse direction) is generated, and a problem arises 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 reverse air flow, and can greatly improve the flow rate detection accuracy. It is another object of the present invention to provide a thermal air flow rate detection device in which a detection signal is made linear with respect to a flow rate.

[0019]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a flowmeter main body having a base end attached to an intake pipe, and provided on the flowmeter main body located in the intake pipe. The present invention is applied to a thermal air flow detecting device having a heat generating resistor cooled by intake air flowing through the intake pipe.

[0020] Then, <br/> feature configuration invention of claim 1 is employed, formed by a bridge circuit including the heating resistor
Is a first flow rate detecting means for outputting a change in the resistance value of the heating resistors forming the bridge circuit as a first flow rate detection signal, prior to said heat generating resistor, after the provided apart from the intake air first respective resistance value changes according to the flow direction, and the second temperature sensitive resistor, the first, is formed by the second temperature sensitive resistor laden other bridge circuit, said first, second the thus the resistance value change of the second temperature sensitive resistor intake air
Of the output of the second flow rate detecting means for outputting a second flow rate detection signal corresponding to the flow direction, from the second flow rate detecting means
From the second flow rate detection signal and the first flow rate detection means.
And a intake air flow rate calculation means for calculating an intake air flow rate by multiplying the first flow rate detection signal output
Configuration .

[0021] In the invention of claim 2, wherein the heat generating resistor, the is-deposit formed on mounted on an insulating substrate to flowmeter body, a heating resistor extending in a film form on at least the longitudinal direction of the insulating substrate configured as the first, second temperature sensing resistor, before the heat generating resistor to the flow direction before Ki吸 incoming air,
After first being-deposit formed on each apart from the insulating substrate, Ru configured Tei as a second thermo-sensitive resistor.

[0022]

[Action] With the above configuration, in the first aspect of the present invention, a first flow rate test which is formed as a bridge circuit including a heat generation resistance
Output means outputs a resistance value change of the heat generating resistor in a bridge circuit as a first flow rate detection signal. The second flow rate detecting means, the first, including a second temperature-sensitive resistor is formed as another bridge <br/> di circuit, first the balance of the other bridge circuit, the second temperature-sensitive and against the intake air flow rate by collapse in the resistance value variation of the resistance and outputs a second flow rate detection signal with the flow direction. The amount of cooling of the heating resistor and the first or second temperature sensing resistor is determined by the flow rate of the intake air, and this cooling amount is proportional to the half of the flow rate. Further, since each signal output from the first flow rate detecting means and the second flow rate detecting means is also proportional to the half power of the flow rate, the respective signals are multiplied by the intake air flow rate calculating means to obtain the intake air. It is possible to output a detection signal that is linear with respect to the flow rate.

[0023] According to the invention of claim 2, the first, second temperature sensitive resistor with previous Shi pairs in the flow direction of the intake air fever resistor, after spaced to form on the insulating substrate, Since the resistance value changes according to the flow direction of the intake air,
When the first temperature-sensitive resistor has a smaller resistance value than the second temperature-sensitive resistor, for example, the flow direction of air can be detected as a forward direction, and the second temperature-sensitive resistor is detected as the first temperature-sensitive resistor. When the resistance value is smaller than the above, the air flow can be detected as the reverse direction. Furthermore, since the heating resistor and the first and second temperature-sensitive resistors are formed on a single insulating substrate, the number of components can be reduced.

[0024]

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.

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 which constitutes a main body of the thermal air flow detecting device 21, and the flow meter main body 22 is a conventional one. In substantially the same manner as the flowmeter body 3 described above, a winding portion 24 around which one reference resistor 23 having a resistance value R1 is wound, and a plurality of terminal pins (located on the base end side of the winding portion 24). (Not shown), and a detection holder 2 extending in the radial direction of the intake pipe 2 from the distal end of the winding part 24.
6 and a circuit casing 27 described later.

However, a slot (not shown) is formed in the flow meter main body 22 at the base end side of the detection holder 26 so that an insulating substrate 29 described later can be detachably attached thereto. As shown in the center of the intake pipe 2,
The heating resistor 30 and the like, which will be described later, are positioned via the 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. As shown in FIG. 2, the insulating substrate 29 is made of an insulating material such as glass, alumina, or aluminum nitride and has a length of about 15 to 20 mm. It is formed in a rectangular flat plate having a width of about 3 to 7 mm. 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.

Reference numeral 30 denotes a heating resistor which forms a heating resistor formed on the insulating substrate 29. The heating resistor 30 has a resistance value obtained by depositing a platinum film by means such as printing or sputtering. RH. As shown in FIG. 2, the heating resistor 30 is located at an intermediate portion in the length direction of the insulating substrate 29 and extends in the width direction. And first and second extension resistance portions 30B and 30C extending in opposite directions to each other.

Here, the heating resistor 30 has the intermediate resistor portion 30A and the extension resistor portions 30B and 30C as a whole having a crank shape, so that the heating resistor 30 and the first and second sense elements are formed on the insulating substrate 29. In addition to forming the heating resistors 31 and 32 compactly, the 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. I have.

The current value of the heating resistor 30 is controlled by a current control transistor 43 described later.
It is heated so as to keep the temperature at a constant temperature (for example, about 240 ° C.).

Reference numerals 31 and 32 denote first and second temperature-sensitive resistors formed by depositing a temperature-sensitive material such as platinum on the insulating substrate 29 by means such as printing or sputtering. The first temperature-sensitive resistor 31 is formed so as to have a resistance value RT1 on the upstream side, and the second temperature-sensitive resistor 32 is formed so as to have a resistance value RT2 on the downstream side. A film is formed.

The first temperature-sensitive resistor 31 is located between the intermediate resistor 30A and the first extension resistor 30B of the heating resistor 30, and is parallel to the extension resistor 30B. It is formed in a rectangular shape so as to extend. The second temperature-sensitive resistor 32 is located between the intermediate resistor 30A and the second extension resistor 30C, and is formed in a rectangular shape so as to extend in parallel with the extension resistor 30C. The temperature sensitive resistors 31 and 32 are formed with a substantially uniform area on the insulating substrate 29. Normally, a current is applied from the sub power supply VS as shown in FIG. , The temperature-sensitive resistors 31, 32
Is effectively cooled by the flowing air, and the flow direction of the air can be detected with high sensitivity as a decrease in the resistance value.

Further, the first temperature-sensitive resistor 31 is located on the upstream side with respect to the forward flow of the intake air (the direction of arrow A), and the second temperature-sensitive resistor 32 is located on the downstream side. The heating resistor 30 is located between the temperature-sensitive resistors 31 and 32. Thereby, when the intake air flows in the forward direction indicated by arrow A, the first temperature-sensitive resistor 31 is cooled and the second temperature-sensitive resistor 31 is cooled.
When the temperature-sensitive resistor 32 receives heat from the heating resistor 30, the resistance value RT1 of the first temperature-sensitive resistor 31 decreases, and the resistance value RT2 of the second temperature-sensitive resistor 32 substantially decreases. Does not change.

On the other hand, when the flow of the intake air flowing in the intake pipe 2 is in the direction indicated by the arrow B in the opposite direction, the second temperature-sensitive resistor 32 is cooled, and the first temperature-sensitive resistor 31 is cooled. Receives the heat from the heating resistor 30, the resistance value RT2 of the second temperature sensing resistor 32 decreases, and the first temperature sensing resistor 3
The resistance value RT1 of 1 does not substantially change. As a result, the first
The resistance value RT1 of the temperature-sensitive resistor 31 and the second temperature-sensitive resistor 32
By comparing the resistance value RT2 with the resistance value RT2, it is determined whether the flow direction of the intake air is the forward direction or the reverse direction.

Reference numerals 33, 33,... Denote, for example, five electrodes formed at the base end side of the insulating substrate 29. The electrodes 33 are arranged in rows 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. Then, the heating resistor 3 formed on the insulating substrate 29 via each of the electrodes 33.
The zero, first, second temperature-sensitive resistors 31, 32, and the like are connected to each electronic component provided in the circuit casing 27, and constitute a processing circuit for flow rate detection shown in FIG.

Next, FIG. 3 shows a processing circuit for detecting a flow rate according to the present embodiment.

In FIG. 3, reference numeral 34 denotes one bridge circuit which constitutes first flow rate detecting means together with a differential amplifier circuit 37 to be described later.
0, a temperature compensating resistor 35, a reference resistor 23, and a flow rate adjusting resistor 36 having a resistance value R2. 35 is connected to the emitter side of a current control transistor 43 to be described later, and a connection point b between the reference resistor 23 and the flow control resistor 36 is connected.
Is connected to earth.

In the bridge 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, and the connection point “c” is connected to the multiplication circuit 44 via the amplifier circuit 38 described later. The signal output from the differential amplifier circuit 37 becomes the current control voltage of the current control transistor 43 that controls the current applied to the bridge circuit 34. on the other hand,
The output from the connection point c of the bridge circuit 34 is the reference resistance 2
3, the voltage output through the amplifier circuit 38 is the first flow detection voltage V as a first flow detection signal indicating the degree to which the heating resistor 30 is cooled by the flow.
It becomes 1.

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 intake air.

In the bridge circuit 34 thus configured, when the bridge circuit 34 is in a balanced state, the current control voltage from the differential amplifier circuit 37 becomes zero,
From the connection point c, the voltage between both ends of the reference resistor 23 in the balanced state is output to the multiplication circuit 44 via the amplification circuit 38. On the other hand, when the balance of the bridge 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 current control voltage is output to the base of the control transistor 43. Thus, the current control transistor 43 controls the current applied to the bridge circuit 34 to bring the cooled heating resistor 30 to a constant temperature and return the bridge circuit 34 to an equilibrium state. At this time, the increased current value output from the connection point c of the bridge circuit 34 is detected as a voltage between both ends of the reference resistor 23, and this voltage is amplified by the amplifier circuit 38 and is multiplied as the first flow rate detection voltage V1. 44.

FIG. 4 shows the relationship between the flow rate Q of the intake air and the first flow rate detection voltage V1 as a flow rate detection signal. The change in the first flow rate detection voltage V1 depends on the flow rate Q. When 30 is cooled, the original temperature (eg, 24
0 ° C.) to the reference resistance 23
Is detected as a voltage between both ends. When the flow direction of the intake air is the direction A (forward direction), the amplifier circuit 38 outputs a positive first flow rate detection voltage V1 corresponding to the flow rate Q, and the flow direction of the air is changed from the direction A. Even in the case of the change in the direction B (reverse direction), the first flow rate detection voltage V1 only detects the change in the resistance value due to the cooling of the heating resistor 30.
And outputs a positive first flow rate detection voltage V1 corresponding to. The first flow detection voltage V1 is １ ／ of the flow Q.
It has the following function.

Next, reference numeral 39 denotes another bridge circuit which constitutes a second flow rate detecting means together with a differential amplifier circuit 42 which will be described later. The bridge circuit 39 comprises the first and second temperature-sensitive resistors 31, consists 32 and other reference resistor 40 and 41 is configured as a bridge resistance of the sides are equal pairs toward each connection point of the first, second temperature sensitive resistors 31 and 32 e
Is connected to a sub power supply VS (for example, 3 V), and a connection point f between the reference resistors 40 and 41 is connected to the ground.

In the bridge circuit 39, the first temperature-sensitive resistor 31 and the reference resistor 40 are connected in series, and the second temperature-sensitive resistor 32 and the reference resistor 41 are connected in series. The differential amplifier 42 is connected to an input terminal of the differential amplifier 42, and the differential amplifier 42 is connected to a multiplier 44. Therefore, when the bridge circuit 39 is in an equilibrium state, when the flow rate Q of the intake air is zero, the temperature-sensitive resistor 31,
Since there is no difference between the resistance values of the resistance value 32, the second flow detection voltage V2 as the second flow detection signal output via the differential amplifier circuit 42 becomes zero. When the balance of the bridge circuit 39 is lost, that is, when the resistance value of one of the temperature-sensitive resistors 31 and 32 changes due to the airflow, the resistance value from the connection point gh of the bridge circuit 39 is changed. Difference (RT1-
RT2) is input to the differential amplifier circuit 42 as a voltage, and the difference between the resistance values is multiplied by the differential amplifier circuit 42 as a second flow detection voltage V2 having a flow direction that changes with respect to the flow rate Q of the intake air. Output to the circuit 44.

The first temperature-sensitive resistor 31 and the second temperature-sensitive resistor 32 constituting the above-described bridge circuit 39 each have a flow rate Q which is similar to that of the heating resistor 30 with respect to the flow rate of the intake air. Changes in proportion to the half power of. However, since the difference between the resistance values is detected by the differential amplifier circuit 42, the differential amplifier circuit 42 outputs the second flow rate detection voltage V2 which becomes positive when the flow rate Q is in the A direction (positive direction). But,
In the direction B (reverse direction), a negative second flow rate detection voltage V2 is obtained.

FIG. 5 shows the relationship between the flow rate Q of the intake air and the second flow rate detection voltage V2 as the second flow rate detection signal. The direction of the flow of the intake air is the direction A (forward direction). In this case, a positive second flow rate detection voltage V2 corresponding to the flow rate Q is output from the differential amplifier circuit 42. When the air flow direction changes from the A direction to the B direction (reverse direction), The dynamic amplification circuit 42 outputs a negative second flow rate detection voltage V2 corresponding to the flow rate Q. The second flow rate detection voltage V2 has a relation of 1/2 to the flow rate Q.

Reference numeral 43 denotes a current control transistor. The current control transistor 43 has a collector connected to the battery voltage VB and a base connected to the differential amplifier 37.
And the emitter side is the bridge circuit 3
4 is connected to the connection point a. The current control transistor 43 controls the emitter current by changing the base current with the current control voltage from the differential amplifier circuit 37. As a result, the current control transistor 43 controls the value of the current applied to the bridge circuit 34, and performs feedback control to keep the temperature of the heating resistor 30 at a constant temperature.

Reference numeral 44 denotes a multiplication circuit constituting the intake air flow rate calculation means. The multiplication circuit 44 outputs a first flow detection voltage V output from the bridge circuit 34 via the amplification circuit 38.
1 and the second flow rate detection voltage V2 output from the bridge circuit 39 via the differential amplifier circuit 42, an output signal V0 indicating the flow direction and the intake air flow rate is output from the output terminal 45 to the control unit ( (Not shown). As a result, the flow of the intake air flows in the forward direction (arrow A).
Direction), a positive output voltage V0 is output, and if the flow of the intake air is in the reverse direction (direction B), a negative output voltage V0 is output. Further, the output voltage V0 is output with a linear characteristic with respect to the flow rate Q.

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 bridge circuit 39 is broken, and the positive second flow rate detection voltage V2 is output from the differential amplifier circuit 42.

Further, 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, but the heating resistor 30 is reduced by the differential amplifier circuit 37 and the current controlling transistor 43. In order to make 30 a constant temperature, the value of the current applied to the bridge 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, a positive first flow rate detection voltage V1 is output from the bridge circuit 34 to the multiplication circuit 44 via the amplification circuit 38.

In the multiplication circuit 44, the second flow detection voltage V2 from the differential amplifier circuit 42 and the bridge circuit 34
Is multiplied (multiplied) by the positive first flow rate detection voltage V1 output from the amplifier 38 through the amplifier circuit 38, thereby outputting a positive output voltage V0 from the output terminal 45 to the control unit.

As described above, the first flow rate detection voltage V1 and the second flow rate detection voltage V2 both have a voltage value corresponding to the flow rate Q of the intake air.
Because of the squared relationship, the multiplication result shows that the output voltage V0 has a substantially linear characteristic with respect to the flow rate Q as shown in FIG. Further, since the output voltage V0 is linear with respect to the flow rate Q, fluctuations in the flow rate Q near zero can be suppressed, and the intake air flow rate Q can be detected with high accuracy.

On the other hand, when the flow of air is in the direction of arrow B (reverse direction), the second temperature-sensitive resistor 32 located on the downstream side of the insulating substrate 29 is cooled by the flow of air. The first temperature-sensitive resistor 31 located on the upstream side receives heat from the heating resistor 30. As a result, the bridge circuit 39
And the differential amplifier circuit 42 outputs a negative second flow rate detection voltage V2.

As described above, since the heating resistor 30 is cooled by the flow of the intake air, the heating resistor 30 is cooled.
Of the bridge circuit 34, a voltage corresponding to the flow rate is output from the bridge circuit 34, and this voltage is amplified by the amplifier circuit 38 and becomes a first positive flow rate detection voltage V1.
4 is output. The multiplication circuit 44 multiplies (multiplies) the negative second flow detection voltage V2 from the differential amplifier circuit 42 by the first flow detection voltage V1.
The intake air amount is output as a negative output voltage V0 from the output terminal 45 to the control unit.

As a result, the control unit can accurately detect the flow rate of the intake air based on the output voltage V0, perform accurate air-fuel ratio control, and improve the engine performance.

Thus, in the thermal air flow detecting device 21 according to the present embodiment, the heating resistor 30 is formed on the insulating substrate 29, and the first and second heating resistors 30 are located before and after the heating resistor 30. Since the second temperature-sensitive resistors 31 and 32 are formed, the number of components can be reduced, and the direction of air flow can be detected by the first and second temperature-sensitive resistors 31 and 32. The flow rate of the intake air can be detected from the change in the resistance value of the heating resistor 30.

Further, a change in the resistance value of the heat generating resistor 30 of one bridge circuit 34 due to the flow rate Q is output to the multiplying circuit 44 as a first flow rate detection voltage V 1 via the amplifier circuit 38, and the other bridge circuit 39. The change in resistance value due to the flow rate Q of the first and second temperature-sensitive resistors 31 and 32 is supplied to the multiplication circuit 44 via the differential amplifier circuit 42 as a second flow rate detection voltage V2 which is positive or negative with respect to the flow direction. Output. Then, the multiplying circuit 44 outputs the first flow detection voltage V1 and the second flow detection voltage V1.
Is multiplied by the flow detection voltage V2, the output voltage V0 from the output terminal 45 can have a linear characteristic with respect to the flow rate Q of the intake air. The voltage V0 can be used, and the negative output voltage V0 can be used in the flow of arrow B.

Further, by adjusting the amplification factor of the amplifier circuit 38, a more linear characteristic can be obtained, an accurate detection of the intake air flow rate can be performed, and an erroneous detection of the backflow as in the prior art can be performed. Can be prevented.

Further, since the first and second temperature-sensitive resistors 31, 32 are heated by the sub power supply VS, the temperature-sensitive resistors 31, 32 are cooled by the flow of air.
Of the air flow direction can be detected with high sensitivity.

In the above embodiment, the temperature compensation resistor 35
Has been described as being provided near the detection holder 26,
The present invention is not limited to this. As shown in a first modified example of FIG. 7, a slit S is formed in the insulating substrate 29 'from the distal end side to the proximal end side so that the first substrate portion 29A' 2 substrate part 2
9B ', a heating resistor 30 and first and second temperature-sensitive resistors 31, 32 are formed on the first substrate portion 29A', and a temperature is formed on the second substrate portion 29B '. The compensation resistor 35 is formed in a film shape. Thereby, one insulating substrate 2
Heating resistor 30 and first and second temperature-sensitive resistors 3 on 9 '
1, 32 and the temperature compensating resistor 35 can be deposited, and the number of parts can be greatly reduced.

In the above embodiment, the heating resistor 30 formed on the insulating substrate 29 and the first and second temperature-sensitive resistors 3 are formed.
2 are formed as shown in FIG. 2, but the present invention is not limited to this, and as in a second modification shown in FIG.
52, 53 extending from the distal side to the proximal side of the
Is formed, and the insulating substrate 51 is formed by the slits 52 and 53.
Are divided into first, second, and third substrate portions 51A, 51B, and 51C, and the first, second, and third substrate portions 51A, 51B, and 5C are separated.
Heating resistor 54 and first temperature-sensitive resistor 5 are connected to 1C, respectively.
5. The second temperature-sensitive resistor 56 may be formed as a film. In this case, it is desirable that the first substrate portion 51A has a relatively large surface area than the other substrate portions 51B and 51C. Further, in the case of this modification, the slit 5
Since the resistors 54, 55, and 56 are separated by 2 and 53, it is possible to reduce the influence of the heat of the heating resistor 54 on the resistors 55 and 56 via the insulating substrate 51. Furthermore, the temperature compensation resistor 35 may be integrally formed as shown by a two-dot chain line.

Further, in the above-described embodiment, the first temperature-sensitive resistor 31 is provided on the upstream side in the flow direction of the intake air, and the second temperature-sensitive resistor 32 is provided on the downstream side. The present invention is not limited to this. The first temperature-sensitive resistor 31 may be located on the downstream side, and the second temperature-sensitive resistor 32 may be located on the upstream side. May be inverted and output to the multiplication circuit 44.

Further, in the above-described embodiment, the one reference resistor 23 wound around the winding portion 24 of the flowmeter main body 22 is described as being provided to protrude into the intake pipe 2, but the present invention is not limited to this. Instead, for example, the configuration may be such that the reference resistor 23 is disposed together with the flow rate adjusting resistor 36 and the like in the circuit casing 27 provided on the outer periphery of the intake pipe 2.

In the above embodiment, the bridge circuit 34 constituting the first flow rate detecting means is formed by the heating resistor 30, the reference resistor 23, the temperature compensating resistor 35 and the flow rate adjusting resistor 36. However, the bridge circuit 34 may be formed by using fixed resistors as the temperature compensation resistor 35 and the flow rate adjustment resistor 36.

[0066]

As has been described above in detail, according to the invention described in claim 1, formed as a bridge circuit including a heat generation resistance
The first flow rate detecting means is outputs a resistance value change of the heat generating resistor in a bridge circuit as a first flow rate detection signal,
The second flow rate detecting means formed as another bridge circuit including the first and second temperature-sensitive resistors is connected to another bridge circuit .
Outputting a second flow rate detection signal corresponding to a flow direction of the intake air in accordance with a change in the resistance value of the first and second temperature sensing resistors ;
Intake air flow rate multiplied by the first and second flow rate detection signals
Since it has a configuration with a calculation means, the flow of inflow air
Direction and flow rate can be accurately detected. That is,
The amount of cooling of the heating resistor and the first or second temperature sensing resistor is determined by the flow rate of the intake air, and the cooling amount is proportional to the square of the flow rate. each flow test which is output from the means and the second flow rate detecting means
Signal becomes proportional to the square root of the flow rate output, the inhalation air flow rate calculation means by multiplying these detected flow rate signal
Accordingly, the linear characteristic determined from the calculation results of the intake air flow rate
Can Mel, it is possible to obtain an output signal proportional to an intake air flow rate Rutotomoni, the flow direction and flow rate of the inlet air can be accurately detected.

According to the second aspect of the present invention , the absolute
A heating resistor is formed on the edge substrate, and
Form a first, second temperature sensitive resistor spaced after previous pair Shi fever resistor in the flowing direction of the intake air, to these first
1, since each of the resistance value is configured to change, the first thermo-sensitive resistor is the resistance value than the second temperature sensitive resistor smaller in accordance with the second temperature sensitive resistor flow direction of the intake air Sometimes, for example, the direction of air flow can be detected as forward,
When the second thermo-sensitive resistor is smaller resistance value than the first temperature-sensitive resistor, Ru can detect the flow of air as the reverse direction.
Therefore , the resistance values of the heating resistor and the first and second temperature-sensitive resistors can be sensitively changed by the airflow, and the flow direction can be accurately detected. Furthermore, since the heating resistor and the first and second temperature-sensitive resistors are formed on a single insulating substrate, the number of components can be reduced.

[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 an embodiment is attached to an intake pipe.

FIG. 2 is a plan view showing a heating resistor and first and second temperature-sensitive resistors formed on an insulating substrate.

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

FIG. 4 is a characteristic diagram showing an output characteristic with respect to a flow rate Q of a first flow rate detection voltage V1 output from a differential amplifier circuit.

FIG. 5 is a characteristic diagram showing an output characteristic of a second flow detection voltage V2 output from the differential amplifier circuit with respect to a flow rate Q.

FIG. 6 is a flow rate Q of the output voltage V0 output from the multiplication circuit.
FIG. 6 is a characteristic diagram showing output characteristics with respect to.

FIG. 7 is a plan view showing a heating resistor, first and second temperature-sensitive resistors, and a temperature compensation resistor formed on an insulating substrate according to a first modified example.

FIG. 8 is a plan view showing a heating resistor and first and second temperature-sensitive resistors formed on an insulating substrate according to a second modification.

FIG. 9 is a longitudinal sectional view showing a state in which a thermal air flow detecting device according to the prior art is attached to an intake pipe.

FIG. 10 is a perspective view showing a flow meter main body, a heating resistor, and the like according to the related art.

FIG. 11 is a characteristic diagram showing fluctuations in the flow velocity of intake air.

[Explanation of symbols]

 21 Thermal Air Flow Detector 22 Flow Meter Main Body 23 Reference Resistance (One Reference Resistance) 29, 29 ', 51 Insulating Substrate 30, 54 Heating Resistor 31, 55 First Temperature Sensing Resistor 32, 56 Second Temperature sensing resistor 34 Bridge circuit (first flow rate detecting means) 35 Temperature compensation resistor 36 Flow rate adjusting resistance 37, 42 Differential amplifier circuit 38 Amplifier circuit 39 Bridge circuit (second flow rate detecting means) 40, 41 Reference resistance ( Other reference resistances) 44 Multiplication circuit (intake air flow rate calculation means)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-105018 (JP, A) JP-A-62-812 (JP, A) JP-A-62-14328 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) G01F 1/68-1/699

Claims (2)

(57) [Claims] 1. A flowmeter main body having a base end side attached to an intake pipe, and a heat generating resistor provided in the flowmeter main body located in the intake pipe and cooled by intake air flowing through the intake pipe. the thermal type air flow detecting device comprising Te, formed by a bridge circuit including a pre-Symbol heating resistor, a first for outputting a change in the resistance value of the heating resistors forming the bridge circuit as a first flow rate detection signal a flow rate detecting means, before the pre-Symbol heating resistor, later provided separated, first, and second temperature sensitive resistors each resistance value changes according to the flow direction of the intake air, said first, in addition to the bridge circuit including a second temperature sensitive resistor
Ri is formed, sub first, the resistance value change of the second temperature sensitive resistor
Wherein the second flow rate detecting means for outputting a second flow rate detection signal corresponding to the flow direction of the intake air, said second output from the second flow rate detecting means detected flow rate signal and said first I A thermal air flow detecting device, comprising: an intake air flow rate calculating means for calculating an intake air flow rate by multiplying by a first flow rate detection signal output from the flow rate detecting means. Wherein said heat generating resistor is film deposited formed on an insulating substrate attached to the flowmeter body, configured as a heating resistor extending in a film form on at least the longitudinal direction of the insulating substrate, the first the second temperature-sensitive resistor, before the previous Ki吸 incoming air heat generating resistor to the flow direction of, after prior spaced respectively
2. The thermal air flow detecting device according to claim 1, wherein the thermal air flow detecting device is configured as first and second temperature-sensitive resistors formed on the insulating substrate .