JP3095322B2 - 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 above.

FIGS. 10 to 12 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 type 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. 11 after mounting the heating resistor 9 and the temperature compensating resistor 11 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,
In FIG. 10, the protection 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 through the mounting hole 2A, and the suction pipe 2 is inserted into the mounting hole 2A.
By mounting the circuit casing 7 from the outer peripheral side of the above, the heating resistor 9 and the temperature compensating resistor 11 provided on the detection holder 6 are arranged 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 in the direction indicated by the arrow A toward the combustion chamber of the engine body, the flow of the intake air cools the heat generating resistor 9 and causes the heat generating resistor 9 to cool. Is detected, a detection signal corresponding to the flow rate of the intake air is detected as a change in the output voltage based on the voltage between both ends of the reference resistor 14 connected in series with the heating resistor 9, and the change in the output voltage is detected. Output to control unit not shown. Further, the control unit calculates the fuel injection amount and the like based on the output voltage.

[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 rate 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. 10 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. 12, the flow rate of the air flowing through the intake pipe 2 repeatedly increases and decreases in accordance with the opening and closing of each intake valve. 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 12 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.

A feature adopted by the invention of claim 1 is that a bridge circuit is formed including the heating resistor, and a change in the resistance value of the heating resistor forming the bridge circuit is determined by a first circuit corresponding to a flow rate. A first flow rate detecting means for outputting as a flow rate detection signal, and first and second temperature-sensitive resistors which are provided before and after the heat-generating resistor and whose resistance value changes in the flow direction of the intake air. Forming a bridge circuit including the first and second temperature-sensitive resistors, and disturbing the balance of the bridge circuit due to a change in the resistance value of the first and second temperature-sensitive resistors. A second flow rate detecting means for outputting as a second flow rate detecting signal, and a second flow rate detecting means provided on an output side of the second flow rate detecting means and output from the second flow rate detecting means. Deform when the signal exceeds the specified flow range, and as a whole Flow rate detection signal deforming means for outputting as a flow rate signal; multiplying a second deformed flow rate signal output from the flow rate detection signal deforming means by a first flow rate detection signal output from the first flow rate detecting means; Thus, an intake air flow rate calculating means for calculating the intake air flow rate is provided.

According to the second aspect of the present invention, the heat generating resistor is formed on the insulating substrate attached to the flowmeter main body, and is formed in a film shape at least in a longitudinal direction of the insulating substrate. And the first and second temperature-sensitive resistors are respectively formed before and after the heat-generating resistor with respect to the flow direction of the intake air on the insulating substrate. 2 is constituted as a temperature-sensitive resistor.

[0022]

With the above construction, according to the first aspect of the present invention, the first flow rate detecting means forms a bridge circuit including a heating resistor, and responds to the flow rate based on a change in the resistance value of the heating resistor in the bridge circuit. The first flow rate detection signal is taken out, and the second flow rate detection means forms a bridge circuit including the first and second temperature sensing resistors, and the first and second temperature sensing means in the bridge circuit. A second flow rate detection signal having a flow direction corresponding to the flow rate of the intake air is output when the balance is lost due to the change in the resistance value of the resistance. Further, the cooling amount 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 power of the flow rate. Fluctuates greatly.

When the intake air flow rate exceeds a predetermined flow rate range based on the second flow rate detection signal from the second flow rate detection means, the flow rate detection signal transforming means converts the deformed flow rate signal into an intake air flow rate calculation. Output to the means. further,
The intake air flow rate calculating means multiplies the first flow rate detection signal by the modified flow rate signal to output a characteristic when the intake air flow rate is small as a linear detection signal.

On the other hand, when the intake air flow rate is equal to or higher than a predetermined flow rate based on the second flow rate detection signal in the deformed flow rate signal, the deformed flow rate signal is output as a constant signal. By multiplying the detection signal and the deformed flow rate signal, the output can be output as the intake air flow rate.

According to the second aspect of the present invention, the first and second temperature-sensitive resistors formed on the insulating substrate before and after the heating resistor with respect to the flow direction of the intake air are provided on the insulating substrate. Since the resistance value changes according to the flow direction of the air, when the first temperature-sensitive resistor has a smaller resistance value than the second temperature-sensitive resistor, for example, the air flow direction can be detected as the forward direction, When the second temperature-sensitive resistor has a smaller resistance value than the first temperature-sensitive resistor, the flow of air can be detected as the reverse direction. Further, the heating resistor on the single insulating substrate,
Since the second temperature-sensitive resistor is formed as a film, the number of components can be reduced.

[0026]

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 drawing, 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. 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 mounted. 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.

The heating resistor 30 has an intermediate resistance portion 30A and extension resistance portions 30B and 30C which have a crank shape as a whole, 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 39 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 of 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.

Here, 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 through 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.

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 a first flow rate detecting means together with a differential amplifier circuit 37 which will 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 the current control transistor 39,
The connection point b between the reference resistance 23 and the flow adjustment resistance 36 is connected to the ground.

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 multiplier circuit 45 via an amplifier circuit 38 described later. The signal output from the differential amplifier circuit 35 becomes the current control voltage of the current control transistor 39 for controlling the applied current of the bridge circuit 34, and the output from the connection point c of the bridge circuit 34 The voltage output from the amplifying circuit 38 as a voltage between both ends becomes a first flow detection voltage V1 as a first flow detection signal indicating the degree to which the heating resistor 30 is cooled 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 intake air.

In the bridge circuit 34 configured as described above, 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 at both ends of the reference resistor 23 in the balanced state is output to the multiplication circuit 45 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. The current control voltage is output to the base of the control transistor 39. As a result, the current control transistor 39 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. 45.

FIG. 4 shows the relationship between the flow rate Q of the intake air and the first flow rate detection voltage V1 as the flow rate detection signal. Is cooled to its original temperature (e.g., 240
(° C.) is detected as the voltage across the reference resistor 23. 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 a squared relationship.

In particular, when the suction flow rate is within the range of the predetermined flow rate Q0 in the idling state, the cooling amount of the heating resistor 30 fluctuates greatly, and is output from the connection point c of the bridge circuit 34 via the amplification circuit 38. The first flow detection voltage V1 varies greatly. Even when the air flow is in the reverse direction, if the flow rate is smaller than the predetermined flow rate -Q0, the first flow rate detection voltage V1 also fluctuates greatly.

Reference numeral 39 denotes a current control transistor. The current control transistor 39 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 39 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 39 controls the current value applied to the bridge circuit 34, and performs feedback control for keeping the temperature of the heating resistor 30 at a constant temperature.

Next, reference numeral 40 denotes another bridge circuit which constitutes a second flow rate detecting means together with a differential amplifier circuit 43 which will be described later. The bridge circuit 40 comprises the first and second temperature-sensitive resistors 31, 32 and other reference resistances 41 and 42, which are configured as bridges in which the resistance values of the corresponding sides are equal, and a connection point e between the first and second temperature-sensitive resistors 31 and 32.
Is connected to a sub power supply VS (for example, 3 V), and a connection point f of the reference resistors 41 and 42 is connected to the ground.

In the bridge circuit 40, the first temperature-sensitive resistor 31 and the reference resistor 41 are connected in series, and the second temperature-sensitive resistor 32 and the reference resistor 42 are connected in series. The differential amplifier 43 is connected to an input terminal of the differential amplifier 43, and the differential amplifier 43 is connected to a multiplier 45 via a limit circuit 44. Therefore, the bridge circuit 4
When 0 is in the equilibrium state, the flow rate Q of the intake air is zero, and there is no difference between the resistance values of the temperature-sensitive resistors 31 and 32. The second flow rate detection voltage V2 as the flow rate signal is zero. When the balance of the bridge circuit 40 is lost, that is, when the resistance value of one of the temperature-sensitive resistors 31 and 32 changes due to the airflow, the connection point gh of the bridge circuit 40 is changed.
The difference between the resistance values (RT1-RT2) is input to the differential amplifier circuit 43 as a voltage, and the difference between the resistance values is used as a second flow detection voltage V2 corresponding to the flow rate Q of the intake air. Is amplified and output.

The first temperature sensitive resistor 31 and the second temperature sensitive resistor 32 constituting the above-described bridge circuit 40 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 differential amplifier circuit 43 detects the difference between the resistance values, the differential amplifier circuit 43 outputs the second flow rate detection voltage V2 which is 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, and the second flow rate detection voltage V2 also detects the flow direction.

FIG. 5 shows the relationship between the flow rate Q of the intake air and the second flow rate detection voltage V2. When the direction of the flow of the intake air is in the direction A (forward), the differential amplifier circuit is used. 43, the positive second flow detection voltage V corresponding to the flow Q
2 is output, and when the air flow direction changes from the A direction to the B direction (reverse direction), the differential amplifier circuit 43 outputs a negative second flow detection voltage V2 corresponding to the flow Q.
The second flow rate detection voltage V2 is 1 /
It has a squared relationship.

In particular, when the suction flow rate is within the range of the predetermined flow rate Q0 at which the idling state is established, the cooling amount of the first temperature sensitive resistor 31 or the second temperature sensitive resistor 32 greatly varies, and therefore the bridge circuit The second flow detection voltage V2 output from the differential amplifier circuit 43 via the differential amplifier circuit 43 also fluctuates greatly. Even when the air flow is in the opposite direction, the predetermined flow rate-
If it is less than Q0, the second flow rate detection voltage V2 also fluctuates greatly.

Reference numeral 44 denotes a limit circuit connected to the output side of the differential amplifier circuit 43 as a flow rate detection signal deforming means. The limit circuit 44 is output from the bridge circuit 40 via the differential amplifier circuit 43. When the intake air flow rate Q is within the predetermined flow rate Q0 based on the second flow rate detection voltage V2, the second flow rate detection voltage V2 is used as it is as a modified flow rate voltage V3 serving as the flow rate signal section a, and a multiplier circuit 45 is provided. When the intake air flow rate Q exceeds the predetermined flow rate Q0, the transformed flow rate voltage V3 is transformed into a transformed signal section b (for example, a constant voltage Va) and outputted to the multiplying circuit 45 (FIG. 6).
reference).

Reference numeral 45 denotes a multiplication circuit which constitutes intake air flow rate calculation means. The multiplication circuit 45 outputs a first flow detection voltage V output from the bridge circuit 34 via the amplification circuit 38.
1 is multiplied by the modified flow rate voltage V3 output from the bridge circuit 40 via the differential amplifier circuit 43 and the limit circuit 44, thereby obtaining an output signal V that allows the flow direction and the flow rate Q to be determined.
0 is output from the output terminal 46 to a control unit (not shown). As a result, a positive output voltage V0 is output when the flow of the intake air is in the forward direction (direction of arrow A), and a negative output voltage is obtained when the flow of the intake air is in the reverse direction (direction of arrow B). V0 is output. Further, the output voltage V0 is output as a substantially linear characteristic with respect to the flow rate Q in the range of the predetermined flow rate Q0.

The thermal air flow detecting device 21 according to this 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, in the bridge circuit 40, the balance of the bridge circuit 40 is broken, and the positive second flow rate detection voltage V2 is output from the differential amplifier circuit 43.

Further, in the limit circuit 44, when the intake air flow rate Q is within the range of the predetermined flow rate Q0 based on the second flow rate detection voltage V2 from the differential amplifier circuit 43, the second flow rate detection voltage V2 is The output is output to the multiplication circuit 45 as the modified flow rate voltage V3 as it is, and when the flow rate Q exceeds the predetermined flow rate Q0, the modified flow rate voltage V3 is output to the multiplication circuit 45 as the constant voltage Va.

On the other hand, in the bridge circuit 34, 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 differential amplifier circuit 37 and the current control transistor 39 In order to keep the heating resistor 30 at a constant temperature, the value of the current applied to the bridge circuit 34 is increased, and this increased current value is detected by the reference resistor 23 as a voltage across the same. As a result, a positive first flow detection voltage V1 is output from the bridge circuit 34 to the multiplication circuit 45 via the amplification circuit 38.

The multiplying circuit 45 multiplies (multiplies) the deformed flow rate voltage V3 from the limit circuit 44 by the positive first flow rate detection voltage V1 output from the bridge circuit 34 via the amplifier circuit 38. Thus, the positive output voltage V0 is output from the output terminal 46 to the control unit.

As described above, in the present embodiment, when the intake air flow rate Q is within the range of the predetermined flow rate Q0, the deformed flow rate voltage V3 from the limit circuit 44 becomes the second flow rate detection voltage from the differential amplifier circuit 43. The signal is output to the multiplication circuit 45 as a flow signal portion a equal to V2. Then, the multiplying circuit 45 multiplies the first flow detection voltage V1 and the modified flow voltage V3, both of which have a relation of 1/2 to the flow Q, as shown in FIG.
As shown in FIG. 7, an output voltage V0 having a substantially linear characteristic with respect to the flow rate Q can be obtained. And the output voltage V0
Is linear with respect to the flow rate Q, the fluctuation of the flow rate Q near zero can be suppressed, and the intake air flow rate Q can be detected with high accuracy.

Further, when the intake air flow rate Q exceeds the predetermined flow rate Q0, the modified flow rate voltage V3 from the limit circuit 44 is used as a deformed signal section b (constant voltage Va) and the multiplication circuit 4
5 is output. In the multiplication circuit 45, the first flow rate detection voltage V1 having a relation of 1/2 to the flow rate Q is used.
Is multiplied by the constant deformed flow voltage V3 to obtain an output voltage V0 having characteristics as shown in FIG.

When the flow rate is within the range of the predetermined flow rate Q0, the output voltage V0 is substantially linear, and when the flow rate exceeds the predetermined flow rate Q0, the output voltage V0 is substantially the same as that of the thermal air flow rate detection device 1 in the prior art. Thus, fluctuations in the flow rate Q near zero can be suppressed, and the intake air flow rate Q can be detected with high accuracy.

Further, instead of the thermal air flow detecting device 1 used in the prior art, the thermal air flow detecting device 2 of the present embodiment is used.
By using 1, it is possible to prevent the erroneous detection of the flow rate near zero and correct the calculation of the fuel injection amount and the like without correcting the setting conditions and the like of the control unit.

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 40
And the differential amplifier circuit 43 outputs a negative second flow rate detection voltage V2, and the limit circuit 44 outputs the deformed flow rate voltage V3 depending on whether the flow rate is within a predetermined flow rate Q0 or not. Alternatively, a modified signal section b is provided, and the modified flow rate voltage V3 is output to the multiplying circuit 45.

Further, since the heating resistor 30 is cooled by the flow of the intake air as described above, the resistance value of the heating resistor 30 decreases, and a voltage corresponding to the flow rate is output from the bridge circuit 34. This voltage is supplied to the amplifier 38
And output to the multiplication circuit 45 as a positive first flow rate detection voltage V1. The multiplying circuit 45 multiplies (multiplies) the negative deformed flow rate voltage V3 from the limit circuit 44 by the first flow rate detection voltage V1 to set the intake air amount as a negative output voltage V0 to the output terminal 46. 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 heating resistor 30 of one bridge circuit 34 due to the flow rate Q is output to the multiplying circuit 45 as the first flow rate detection voltage V1 via the amplifier circuit 38, and the other bridge circuit 40 The change in resistance value due to the flow rate Q of the first and second temperature-sensitive resistors 31 and 32 is defined as a second flow rate detection voltage V2 which becomes positive and negative with respect to the flow direction via the differential amplifier circuit 43. When the flow rate is within the range of the predetermined flow rate Q0 based on the second flow rate detection voltage V2, the modified flow rate voltage V3 is output to the multiplying circuit 45 as the flow rate signal section a. V3 is output to the multiplication circuit 45 as a modified signal portion b. The multiplication circuit 45 multiplies the first flow rate detection voltage V1 by the modified flow rate voltage V3 to obtain the output terminal 4
6, the output voltage V0 can have a substantially linear characteristic with respect to the flow rate Q of the intake air even if the flow rate Q is within the range of the predetermined flow rate Q0. And the negative output voltage V0 in the flow of arrow B.

Further, by adjusting the amplification factor of the amplifier circuit 38, it is possible to obtain a more linear characteristic, to accurately detect the intake air flow rate Q, and to erroneously detect the backflow as in the prior art. 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. 8, 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. As a result, the heating resistor 30, the first and second temperature-sensitive resistors 31, 32, and the temperature compensating resistor 35 can be formed on the insulating substrate 29 ', and the number of components 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 temperature-sensitive resistors 55 and 56 via the insulating substrate 51. Furthermore, as shown by the two-dot chain line, the temperature compensation resistor 35
May be integrally formed.

Further, in the above embodiment, the flow meter main body 22
Although it has been described that one reference resistor 23 wound around the winding portion 24 is provided to protrude into the intake pipe 2, the present invention is not limited to this. The reference resistor 23 may be provided together with the flow rate adjusting resistor 36 and the like.

Further, in the above embodiment, the predetermined flow rate Q
Although 0 is set as the flow rate in the idling state, the present invention is not limited to this, and may be an arbitrary predetermined flow rate Q0.

On the other hand, in the above embodiment, when the intake air flow rate Q exceeds the predetermined flow rate Q0, the deformation flow rate voltage V3 becomes the constant voltage Va by using the limit circuit 44 as the flow rate detection signal deformation means. However, the present invention is not limited to this. When the intake air flow rate Q exceeds the predetermined flow rate Q0, the deformation signal portion b of the deformation flow rate voltage V3 is output to the flow rate Q. The voltage may be changed to a voltage that changes linearly.

In the above embodiment, the bridge circuit 34 constituting the first flow detecting means is formed by the heating resistor 30, the temperature compensating resistor 35, the reference resistor 23 and the flow regulating resistor 36. The present invention is not limited to this, and the bridge circuit 34 may be formed using fixed resistors instead of the temperature compensation resistors 35 and the flow rate adjustment resistors 36.

[0076]

As described above in detail, according to the first aspect of the present invention, the first flow rate detecting means is formed as a bridge circuit including a heating resistor, and the change in the resistance value of the heating resistor in the bridge circuit is determined. The first flow rate detection signal is taken out, and the second flow rate detection means is formed as a bridge circuit including the first and second temperature sensing resistors, and the balance of the bridge circuit is equal to the first and second temperature sensing resistors. A second flow rate detection signal corresponding to the flow rate of the intake air is output by the collapse due to the change in the resistance value. The flow rate detection signal deforming means deforms when the intake air flow rate exceeds a predetermined flow rate range based on the second flow rate detection signal from the second flow rate detection means, and outputs a deformed flow rate signal as a whole, By multiplying the first flow rate detection signal and the deformed flow rate signal by the intake air flow rate calculating means, it is possible to obtain a substantially linear flow rate of the intake air within a predetermined flow rate range.

As a result, the fluctuation of the intake air amount near zero can be suppressed, the intake air flow rate can be detected with high accuracy, and the air-fuel ratio control and the like can be effectively performed. In particular, erroneous detection of the intake air flow rate near zero can be prevented without correcting the setting conditions and the like of the control unit used so far, and the calculation of the fuel injection amount and the like can be accurately performed.

According to the second aspect of the present invention, the first and second temperature-sensitive resistors formed on the insulating substrate in front of and behind the heating resistor with respect to the flow direction of the intake air are provided on the insulating substrate. Since the resistance value changes according to the flow direction of the air, when the first temperature-sensitive resistor has a smaller resistance value than the second temperature-sensitive resistor, for example, the air flow direction can be detected as the forward direction, When the resistance value of the second temperature-sensitive resistor is smaller than that of the first temperature-sensitive resistor, the flow of air can be detected as the reverse direction, and the resistance values of the heating resistor and the first and second temperature-sensitive resistors can be detected. Can be sensitively changed by the air flow, 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 shows a first flow detection voltage V output from an amplifier circuit.
FIG. 4 is a characteristic diagram showing output characteristics with respect to a flow rate Q of FIG.

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 modified flow rate voltage V3 output from a limit circuit.
FIG. 6 is a characteristic diagram showing output characteristics with respect to a flow rate Q of the first embodiment.

FIG. 7 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. 8 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. 9 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. 10 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. 11 is a perspective view showing a flow meter main body, a heating resistor, and the like according to a conventional technique.

FIG. 12 is a characteristic diagram showing fluctuations in the flow velocity of intake air.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 21 Thermal air flow detector 22 Flowmeter main body 23 Reference resistance (one reference resistance) 29, 29 ', 51 Insulating substrate 30, 54 Heating resistor 31, 55 First temperature-sensitive 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, 43 Differential amplifier circuit 38 Amplifier circuit 40 Bridge circuit (second flow rate detecting means) 41, 42 Reference resistance ( Other reference resistances) 44 Limit circuit (flow detection signal deformation means) 45 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-57-93211 (JP, A) JP-A-62-812 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) G01F 1/68-1/699

Claims (2)

(57) [Claims] 1. A flowmeter main body having a base end attached to an intake pipe, and a heat generating resistor provided in the flowmeter main body and located in the intake pipe and cooled by intake air flowing through the intake pipe. In the thermal air flow detecting device, a bridge circuit including the heating resistor is formed, and a change in the resistance value of the heating resistor forming the bridge circuit is output as a first flow detection signal corresponding to a flow rate. A first flow rate detecting means, first and second temperature-sensitive resistors provided before and after the heat-generating resistor and having a resistance value that changes in a flow direction of the intake air; A bridge circuit including the second temperature-sensitive resistor is formed, and the collapse of the balance of the bridge circuit due to the change in the resistance value of the first and second temperature-sensitive resistors is changed to a second direction having a flow direction corresponding to the flow rate. Second flow rate detection output as flow rate detection signal Means, provided on the output side of the second flow rate detection means, and deformed when a second flow rate detection signal output from the second flow rate detection means exceeds a predetermined flow rate range, and as a whole a deformed flow rate signal By multiplying a flow rate detection signal deforming means, which is output as, and a second deformed flow rate signal output from the flow rate detection signal deforming means, with a first flow rate detection signal output from the first flow rate detecting means. A thermal air flow rate detecting device, comprising: an intake air flow rate calculating means for calculating an intake air flow rate. 2. The heat-generating resistor is formed as a heat-generating resistor formed on an insulating substrate attached to the flowmeter main body and extending in a film shape at least in a longitudinal direction of the insulating substrate. The first and second temperature-sensitive resistors are formed as film-formed first and second temperature-sensitive resistors separated from each other before and after the heating resistor with respect to the flow direction of the intake air on the insulating substrate. The thermal air flow detecting device according to claim 1, wherein the thermal air flow detecting device is constituted.