JPH07333026A - Thermal air flowmeter - Google Patents

Abstract

PURPOSE:To improve the sensitivity of a thermal air flowmeter by measuring the direction of flow and the flow rate of sucked air to prevent changes, especially near the zero of the flow rate. CONSTITUTION:A bridge circuit 34 is constituted of a heating resistor 30, a temperature compensation resistor 35 and resistors 36 and 23 and a change in resistance value RH of the heating resistor 30 when cooled is outputted to a multiplying circuit 45 as first flow detection voltage V1 based on the flow rate of sucked air. On the other hand, a bridge circuit 40 is constituted of first thermosensitive resistors 31 and 32 arranged before and after the heating resistor 30 and reference resistors 41 and 42 and changes in the resistance values of the thermosensitive resistors 31 and 32 are outputted as a second flow rate detection voltage V2 based on the flow rate of the suction air. Then, the voltage V2 is outputted to the multiplying circuit 45 as a deformed flow rate voltage V3 through a limit circuit 44 and the voltages V1 and V3 are multiplied with the multiplying circuit 45 thereby obtaining an output voltage V0 almost linear with respect to the flow rate within a specified range of the flow rate.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Generally, in an engine for an automobile or the like, a mixture of fuel and intake air is burned in a combustion chamber of an engine body, and a rotational output of the engine is taken out from the combustion pressure. Detecting the intake air flow rate is an important factor in calculating the above.

Therefore, FIGS. 10 to 12 show a conventional thermal air flow rate detecting device.

In the figure, reference numeral 1 denotes a thermal type air flow rate detecting device provided in the middle of an intake pipe 2. The thermal type air flow rate detecting device 1 is directed toward a combustion chamber (not shown) of an engine body. In order to detect the flow rate of the intake air flowing in the direction A shown, the intake pipe 2 is provided with a mounting hole 2A in the middle thereof.

Reference numeral 3 denotes a flow meter main body which constitutes the main body of the thermal air flow rate detecting device 1. The flow meter main body 3 is molded by means such as insert molding as shown in FIG.
A winding portion 4 formed in a stepped cylindrical shape for winding a winding-shaped reference resistor 14 to be described later, and a substantially disk-shaped portion located at the base end side of the winding portion 4 and described later. Terminal pins 8A-8D
Is integrally provided, and is extended in the radial direction of the intake pipe 2 from the tip end side of the winding part 4, and a heating resistor 9 and a temperature compensating resistor 11, which will be described later, are positioned in the central portion of the intake pipe 2. And a circuit casing 7 to be described later, which is located outside the intake pipe 2 and to which the terminal portion 5 is connected.

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

Reference numerals 8A, 8B, 8C, and 8D denote four terminal pins (collectively referred to as terminal pins 8) axially protruding from the terminal portion 5 of the flowmeter body 3, and each of the terminal pins 8 is a flowmeter. It is provided integrally with, for example, four terminal plates (not shown) embedded in the winding portion 4 of the main body 3 and the detection holder 6, and is detachably connected to the connector portion (not shown) of the circuit casing 7. It is what is done.

Reference numeral 9 denotes a hot film type heating resistor provided on the detection holder 6 of the flowmeter main body 3 via terminals 10A and 10B. The heating resistor 9 is sensitive to temperature changes and its resistance value changes. Formed by winding a platinum wire or depositing a platinum film on an insulating cylinder made of a temperature-sensitive material such as platinum and made of a ceramic material such as aluminum oxide (hereinafter referred to as "alumina"). It is composed of a small-diameter heating resistor element. When the heating resistor 9 is energized by a battery (not shown), the heating resistor 9 is heated at a temperature of, for example, 240 ° C. before and after it is cooled by the intake air flowing in the intake pipe 2 in the direction of arrow A. The resistance value changes according to the flow rate of the intake air, and a detection signal of the flow rate is output.

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

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

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

In the conventional thermal air flow rate detecting device 1 thus constructed, when detecting the intake air flow rate of an automobile engine or the like, the terminal portion 5 of the flow meter main body 3 is inserted through the terminal pins 8. The detection holder 6 of the flowmeter body 3 is inserted into the intake pipe 2 via the mounting hole 2A in a state where the intake pipe 2 is connected to the connector portion of the circuit casing 7.
By mounting the circuit casing 7 from the outer peripheral side, the heat generating resistor 9 and the temperature compensating resistor 11 provided in the detection holder 6 are arranged in the center of the intake pipe 2.

In this case, the heating resistor 9 and the reference resistor 14 are connected in series, and the temperature compensating resistor 11 is connected in series to the flow rate adjusting resistor in the circuit casing 7. A bridge circuit is composed of the compensating resistor 11 and the flow rate adjusting resistor, and the heat generating resistor 9 is supplied 240 ° C. before by energizing these to the outside.
Heat at a later temperature.

In this state, when intake air flows through the intake pipe 2 toward the combustion chamber of the engine body in the direction of arrow A, the flow of the intake air cools the heat generating resistor 9 and the heat generating resistor 9 is cooled. Of the reference resistor 14 connected in series with the heating resistor 9, a detection signal corresponding to the flow rate of the intake air is detected as a change in the output voltage, and the change in the output voltage is detected. Output to a control unit (not shown). Further, the control unit calculates the fuel injection amount and the like based on this output voltage.

[0015]

By the way, in the above-mentioned prior art, the fact that the heating resistor 9 is cooled by the flow of the intake air flowing through the intake pipe 2 is utilized to change the resistance value of the heating resistor 9. Since the intake air flow rate is detected based on this, the heat generating resistor 9 is cooled by the intake air flow flowing in the direction A (forward direction) shown in FIG. 10 and flows in the direction B (reverse direction) shown in FIG. There is a problem in that the air flow is also cooled and the intake air flow rate is erroneously detected by the air flow in the opposite direction.

That is, in an engine body having a multi-cylinder cylinder, intake air is introduced into each cylinder each time an intake valve (not shown) is opened as the piston reciprocates in each cylinder. Since it is sucked in the direction A (forward direction) indicated by arrow, the flow velocity of the air flowing through the intake pipe 2 is repeatedly pulsated as shown in FIG. 12 according to the opening and closing of each intake valve. become.

In particular, when the engine speed reaches from a low speed region to a medium speed region and the like, and the intake and exhaust amounts increase, the intake valve and the exhaust valve (not shown) overlap each other and the exhaust gas Since the part may blow back into the intake pipe 2 with the opening of the intake valve, the time t1 shown in FIG.
The flow velocity becomes negative (t2), as indicated by t2.
There is a problem that an air flow flowing in the direction (reverse direction) is generated, and 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. The present invention can prevent erroneous detection of the intake air flow rate due to the air flow in the opposite direction, and can greatly improve the flow rate detection accuracy. An object of the present invention is to provide a thermal type air flow rate detection device in which a detection signal is linear with respect to a flow rate.

[0019]

In order to solve the above problems, the present invention provides a flowmeter main body having a base end side attached to an intake pipe, and a flowmeter main body located inside the intake pipe, The present invention is applied to a thermal air flow rate detecting device including a heat generation resistance cooled by intake air flowing in the intake pipe.

A feature of the invention of claim 1 is that a bridge circuit is formed by including the heating resistor, and a change in the resistance value of the heating resistor forming the bridge circuit corresponds to a flow rate. First and second temperature-sensitive resistors that are provided before and after the heat-generating resistor and are separated from the first flow-rate detecting means that outputs as a flow-rate detection signal, and have a resistance value that changes in the flow direction of the intake air. And a bridge circuit is formed including the first and second temperature-sensitive resistors, and the unbalance of the bridge circuit due to a change in the resistance value of the first and second temperature-sensitive resistors causes a flow direction corresponding to the flow rate. Second flow rate detecting means for outputting as a second flow rate detecting signal, and a second flow rate detecting means provided on the output side of the second flow rate detecting means and outputted from the second flow rate detecting means. When the signal exceeds the specified flow rate range, it is deformed, and as a whole Shaped flow rate signal output means for deforming the flow rate detection signal, a second modified flow rate signal output from the flow rate detection signal deforming means, and a first flow rate detection signal output from the first flow rate detection means. The intake air flow rate calculating means for calculating the intake air flow rate is provided.

Further, in the invention of claim 2, the heating resistor is formed on the insulating substrate attached to the flowmeter main body, and the heating resistor extends in a film shape at least in the length direction of the insulating substrate. The first and second temperature-sensitive resistors are formed as a film and are separated from each other in front of and behind the heat-generating resistor in the flow direction of the intake air on the insulating substrate. It is configured as a temperature sensitive resistor of No.2.

[0022]

With the above structure, in the first aspect of the 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 sensitive resistors, and the first and second temperature sensitive circuits in the bridge circuit are formed. A second flow rate detection signal having a flow direction corresponding to the flow rate of the intake air is output due to the imbalance caused by a change in the resistance value of the resistance. Further, the cooling amount of the heat generating resistance and the first temperature sensitive resistance or the second temperature sensitive resistance is determined by the flow rate of the intake air, and this cooling rate is proportional to the 1/2 power of the flow rate. The fluctuation of is large.

When the intake air flow rate exceeds the predetermined flow rate range on the basis of the second flow rate detection signal from the second flow rate detection means, the flow rate detection signal transformation means calculates the modified flow rate signal from the intake air flow rate. Output to the means. further,
The intake air flow rate calculating means multiplies the first flow rate detection signal and 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 the predetermined flow rate based on the second flow rate detection signal in the modified flow rate signal, the modified flow rate signal is output as a constant signal, and the intake air flow rate calculation means outputs the first flow rate. It is possible to output the intake air flow rate by multiplying the detection signal and the modified flow rate signal.

Further, in the invention of claim 2, the first and second temperature sensitive resistors formed on the insulating substrate are separated from each other in front of and behind the heating resistor with respect to the flow direction of the intake air. Since the resistance value changes depending on the flow direction of air, when the resistance value of the first temperature-sensitive resistor is smaller than that of 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 air flow can be detected in the opposite direction. In addition, a heating resistor,
Since the second temperature-sensitive resistor is film-formed, the number of parts can be reduced.

[0026]

Embodiments of the present invention will be described below with reference to FIGS. In the embodiments, the same components as those of the above-described conventional technique are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, 21 is a thermal type air flow rate detecting device according to the present embodiment, 22 is a flow rate meter main body which constitutes the main body of the thermal type air flow rate detecting device 21, and the flow rate meter main body 22 is a conventional technique. Similar to the flowmeter body 3 described above, a winding portion 24 around which one reference resistance 23 having a resistance value R1 is wound, and a plurality of terminal pins (located at the base end side of the winding portion 24) (Not shown) integrally provided, and the detection holder 2 extending in the radial direction of the intake pipe 2 from the tip side of the winding portion 24.
6 and a circuit casing 27 which will be described later.

However, a slot (not shown) for detachably mounting an insulating substrate 29 described later is formed on the base end side of the detection holder 26 in the flowmeter main body 22, and the detection holder 26 is shown in FIG. As shown in the center of the intake pipe 2,
A heating resistor 30, which will be described later, and the like are positioned via the insulating substrate 29. A protective cover (not shown) similar to the protective cover 13 described in the related art is attached to the detection holder 26.

Reference numeral 27 denotes a circuit casing provided on the outer peripheral side of the intake pipe 2 so as to close the mounting hole 2A of the intake pipe 2, and the circuit casing 27 is substantially the same as the circuit casing 7 described in the prior art. Formed, mounting hole 2 for intake pipe 2
Although it has a fitting portion 27A that fits into A, the circuit casing 27 has a flow rate adjusting resistor 36, a differential amplifier circuit 37, etc. described later on an insulating substrate (not shown) made of, for example, a ceramic material. It is designed to be built with these installed. 28A and 28B are terminals to which the winding of the reference resistor 23 is connected.

Reference numeral 29 denotes an insulating substrate attached to the detection holder 26. 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 dimension of about 15 to 20 mm. It is formed in the shape of a rectangular flat plate having a width of about 3 to 7 mm. Further, the insulating substrate 29 has a fixed end removably attached to the slot of the detection holder 26 on the base end side and a free end on the tip end side.

Reference numeral 30 denotes a heating resistor forming 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 of printing or sputtering. Formed to have RH. Further, as shown in FIG. 2, the heating resistor 30 is located at an intermediate portion of the insulating substrate 29 in the lengthwise direction and extends in the width direction, and an intermediate resistance portion 30A extending in the lengthwise direction from both end sides of the intermediate resistance portion 30A. The first and second extension resistance portions 30B and 30C extend in opposite directions.

Here, since the heating resistor 30 has the intermediate resistance portion 30A and the extension resistance portions 30B and 30C as a whole in the shape of a crank, the heating resistor 30 and the first and second senses are formed on the insulating substrate 29. The temperature resistors 31 and 32 are made compact, and the surface area (mounting area) of the heating resistor 30 is increased as much as possible so that, for example, the contact area with the intake air flowing through the intake pipe 2 can be increased. There is.

The heating resistor 30 has a current value controlled by a current control transistor 39 described later,
It is heated so that the temperature is kept constant (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 print printing or sputtering. The first temperature-sensitive resistor 31 is formed on the upstream side so as to have a resistance value RT1, and the second temperature-sensitive resistor 32 is positioned on the downstream side so as to have a resistance value RT2. A film is formed.

Here, the first temperature-sensitive resistor 31 is located between the intermediate resistance portion 30A of the heating resistor 30 and the first extension resistance portion 30B, and is parallel to the extension resistance portion 30B. It is formed in a rectangular shape so as to extend. Further, the second temperature-sensitive resistor 32 is located between the intermediate resistance portion 30A and the second extension resistance portion 30C, and is formed in a rectangular shape so as to extend parallel to the extension resistance portion 30C. The temperature sensitive resistors 31 and 32 are formed with a substantially uniform area on the insulating substrate 29, and a current is normally applied from the sub power source VS as shown in FIG. Since the heat is generated in the temperature sensitive resistor 31, 32
Are 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 upstream with respect to the forward flow of the intake air (the direction of arrow A), and the second temperature-sensitive resistor 32 is located downstream. In addition, the heating resistor 30 is located between the temperature sensitive resistors 31 and 32. As a result, when the intake air flows in the forward direction indicated by the arrow A, the first temperature-sensitive resistor 31 is cooled and the second temperature-sensitive resistor 31 is cooled.
The resistance value RT1 of the first temperature-sensitive resistor 31 is reduced and the resistance value RT2 of the second temperature-sensitive resistor 32 is substantially reduced by receiving the heat from the heat-generating resistor 30. Does not change to

On the other hand, when the flow of the intake air flowing through the intake pipe 2 is in the opposite direction of the arrow B, the second temperature sensitive resistor 32 is cooled and the first temperature sensitive resistor 31. By receiving heat from the heat-generating resistor 30, the resistance value RT2 of the second temperature-sensitive resistor 32 becomes small and the first temperature-sensitive resistor 3
The resistance value RT1 of 1 does not substantially change. As a result, the first
Resistance value RT1 of the temperature sensitive resistor 31 and the second temperature sensitive resistor 32 of
By comparing with the resistance value RT2 of the above, 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 on the base end side of the insulating substrate 29. The electrodes 33 are arranged in a row in the width direction of the insulating substrate 29 at a predetermined interval. 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 the respective electrodes 33.
0, the first and second temperature sensitive resistors 31, 32, etc. are connected to respective electronic parts provided in the circuit casing 27 to form a processing circuit for flow rate detection shown in FIG.

Next, FIG. 3 shows a processing circuit for flow rate detection according to this embodiment.

In FIG. 3, reference numeral 34 designates one bridge circuit which constitutes a first flow rate detecting means together with a differential amplifier circuit 37 which will be described later. The bridge circuit 34 is the heating resistor 3
0, a temperature compensating resistor 35, one reference resistor 23, and a flow rate adjusting resistor 36 having a resistance value R2, which are configured as a bridge in which the resistance values of opposite sides are equal to each other. The connection point a with 35 is connected to the emitter side of the current control transistor 39,
A connection point b between the reference resistor 23 and the flow rate adjusting resistor 36 is connected to the ground.

In the bridge circuit 34, the heating resistor 30, the reference resistor 23, the temperature compensating resistor 35, and the flow rate adjusting resistor 36 are connected in series, 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 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 that controls the applied current to the bridge circuit 34, and the output from the connection point c of the bridge circuit 34 is the reference resistor 23. The voltage which becomes the both-ends voltage and is output through the amplifier circuit 38 becomes the first flow rate detection voltage V1 as the first flow rate detection signal indicating the degree to which the heating resistor 30 is cooled by the flow rate.

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

In the bridge circuit 34 thus constructed, when the bridge circuit 34 is in a balanced state, the current control voltage from the differential amplifier circuit 37 becomes zero and
From the connection point c, the voltage across 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 becomes small, so that the current from the differential amplifier circuit 37 is reduced. 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 returns the bridge circuit 34 to the equilibrium state. At this time, the increased current value output from the connection point c of the bridge circuit 34 is detected as the voltage across the reference resistor 23, this voltage is amplified by the amplifier circuit 38, and is multiplied as the first flow rate detection voltage V1. It is output to 45.

Here, 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 and the heating resistance 30 When it is cooled, the original temperature (eg 240
The increased current value required for returning to (° C.) is detected as the voltage across the reference resistor 23. When the flow direction of the intake air is the A direction (forward direction), the amplification circuit 38 outputs a positive first flow rate detection voltage V1 corresponding to the flow rate Q, and the air flow direction is from the A direction. Even when changing to the B direction (reverse direction), the first flow rate detection voltage V1 only detects a change in resistance value due to cooling of the heating resistor 30, so that the flow rate Q from the amplifier circuit 38 is detected.
To output a positive first flow rate detection voltage V1. The first flow rate detection voltage V1 is 1/2 of the flow rate Q.
It has a relationship of square.

In particular, when the intake flow rate is within the range of the predetermined flow rate Q0 in the idling state, the cooling amount of the heating resistor 30 varies greatly, so that it is output from the connection point c of the bridge circuit 34 through the amplifier circuit 38. The first flow rate detection voltage V1 varies greatly. Further, even when the air flow is in the opposite direction, when the flow rate is smaller than the predetermined flow rate -Q0, the first flow rate detection voltage V1 also greatly changes.

Reference numeral 39 denotes a current control transistor. The current control transistor 39 has a collector side connected to the battery voltage VB and a base side connected to the differential amplifier circuit 37.
Connected to the output side of the bridge circuit 3 on the emitter side.
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 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.

Next, 40 indicates the other bridge circuit which constitutes the second flow rate detecting means together with the differential amplifier circuit 43 which will be described later. The bridge circuit 40 includes the first and second temperature sensitive resistors 31, 32 and the other reference resistors 41 and 42, which are configured as a bridge in which the resistance values of the corresponding sides are equal, and the connection point e of the first and second temperature sensitive resistors 31 and 32.
Is connected to a sub power source VS (for example, 3V), and the 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. It is connected to the input terminal of the differential amplifier circuit 43, and the differential amplifier circuit 43 is connected to the multiplication circuit 45 via the 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 in the resistance values of the temperature sensitive resistors 31 and 32. Therefore, the second output is performed via the differential amplifier circuit 43. The second flow rate detection voltage V2 as the flow rate signal becomes zero. Further, when the balance of the bridge circuit 40 is lost, that is, when the resistance value of either one of the temperature sensitive resistors 31 and 32 changes due to the air flow, the connection point gh of the bridge circuit 40.
The difference in resistance value (RT1−RT2) is input to the differential amplifier circuit 43 as a voltage, and this difference in resistance value is used as the second flow rate detection voltage V2 corresponding to the flow rate Q of the intake air. It is amplified by and output.

The first temperature-sensitive resistor 31 and the second temperature-sensitive resistor 32, which constitute the bridge circuit 40 described above, respectively have a flow rate Q with respect to the flow rate of the intake air, similar to the heating resistor 30. It changes in proportion to the 1/2 power of. However, since the differential amplifier circuit 43 detects the difference in resistance, the differential amplifier circuit 43 outputs a second flow rate detection voltage V2 that is positive when the flow rate Q is in the A direction (positive direction). But,
In the B direction (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 intake air flow rate Q and the second flow rate detection voltage V2. When the intake air flow direction is the A direction (forward direction), the differential amplifier circuit From 43, a positive second flow rate detection voltage V corresponding to the flow rate 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 the negative second flow rate detection voltage V2 corresponding to the flow rate Q.
The second flow rate detection voltage V2 is 1 / the flow rate Q.
It has a squared relationship.

In particular, when the intake flow rate is within the range of the predetermined flow rate Q0 in which the idling state is reached, the cooling amount of the first temperature sensitive resistor 31 or the second temperature sensitive resistor 32 fluctuates greatly, so the bridge circuit The second flow rate detection voltage V2 output from 40 via the differential amplifier circuit 43 also fluctuates greatly. Even if the air flow is in the opposite direction, the specified flow rate-
When it is smaller than Q0, the second flow rate detection voltage V2 similarly 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 modifying means, and 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 range of the predetermined flow rate Q0 based on the second flow rate detection voltage V2, the second flow rate detection voltage V2 is used as the modified flow rate voltage V3 which becomes the flow rate signal section a as it is, and the multiplication circuit 45 is used. When the intake air flow rate Q exceeds the predetermined flow rate Q0, the modified flow rate voltage V3 is modified into a modified signal portion b (for example, a constant voltage Va) and output to the multiplication circuit 45 (FIG. 6).
reference).

Reference numeral 45 denotes a multiplication circuit which constitutes the intake air flow rate calculation means, and the multiplication circuit 45 outputs the first flow rate detection voltage V output from the bridge circuit 34 through 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 to obtain the output signal V which shows the flow direction and the flow rate Q.
0 is output from the output terminal 46 to the control unit (not shown). As a result, a positive output voltage V0 is output when the intake air flow is in the forward direction (arrow A direction), and a negative output voltage is when the intake air flow is in the reverse direction (arrow B direction). V0 is output. Further, the output voltage V0 is output as a characteristic that is substantially linear with respect to the flow rate Q in the range of the predetermined flow rate Q0.

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

Here, when the flow of the intake air is in the direction of arrow A (forward direction), the first temperature-sensitive resistor 31 located on the upstream side of the insulating substrate 29 is cooled by this flow of air. The second temperature-sensitive resistor 32 located on the downstream side receives heat from the heat-generating resistor 30. As a result, in the bridge circuit 40, the balance of the bridge circuit 40 is lost, 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 set. The modified flow rate voltage V3 is output as it is to the multiplication circuit 45, and when the flow rate Q exceeds a predetermined flow rate Q0, the modified flow rate voltage V3 is output to the multiplication circuit 45 as a 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 resistance value RH of the heating resistor 30 is reduced by this cooling, but the differential amplifier circuit 37 and the current control transistor 39 are used. In order to keep the heating resistor 30 at a constant temperature, the current value applied to the bridge circuit 34 is increased, and the increased current value is detected by the reference resistor 23 as the voltage across it. As a result, the positive first flow rate detection voltage V1 is output from the bridge circuit 34 to the multiplication circuit 45 via the amplification circuit 38.

Then, the multiplication circuit 45 multiplies (multiplies) the modified flow rate voltage V3 from the limit circuit 44 and the positive first flow rate detection voltage V1 output from the bridge circuit 34 through the amplifier circuit 38. As a result, the positive output voltage V0 is output from the output terminal 46 to the control unit.

As described above, in this embodiment, when the intake air flow rate Q is within the predetermined flow rate Q0, the modified flow rate voltage V3 from the limit circuit 44 is the second flow rate detection voltage from the differential amplifier circuit 43. It is output to the multiplication circuit 45 as a flow rate signal portion a equal to V2. Then, the multiplication circuit 45 multiplies the first flow rate detection voltage V1 and the modified flow rate voltage V3, which both have a relationship of 1/2 power with respect to the flow rate Q, as shown in FIG.
As shown in, it is possible to obtain the output voltage V0 having a substantially linear characteristic with respect to the flow rate Q. 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.

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 the modified signal section b (constant voltage Va) in the multiplication circuit 4.
Output to 5. Then, in the multiplication circuit 45, the first flow rate detection voltage V1 which has a relation of 1/2 to the flow rate Q
Can be multiplied by a constant deformed flow rate voltage V3 to obtain an output voltage V0 having the characteristics shown in FIG.

When the flow rate is within the range of the predetermined flow rate Q0, the characteristic is made to be substantially linear, and when the flow rate exceeds the predetermined flow rate Q0, the output voltage V0 which is substantially the same as that of the thermal air flow rate detecting device 1 in the prior art is set. Therefore, the variation 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 type air flow rate detecting device 1 used in the prior art, the thermal type air flow rate detecting device 2 of this embodiment is used.
By using 1, the erroneous detection of the flow rate near zero can be prevented and the calculation of the fuel injection amount and the like can be accurately performed without correcting the setting conditions of the control unit and the like.

On the other hand, when the air flow is in the direction of arrow B (reverse direction), the second temperature-sensitive resistor 32 located on the downstream side of the insulating substrate 29 is cooled by this air flow, 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
Is out of balance, the negative second flow rate detection voltage V2 is output from the differential amplifier circuit 43, and the modified flow rate voltage V3 is set to the flow rate signal part a depending on whether or not the limit circuit 44 is within the predetermined flow rate Q0. Alternatively, the modified flow rate voltage V3 is output to the multiplication circuit 45 as the modified signal section b.

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 becomes small, and the bridge circuit 34 outputs a voltage corresponding to the flow rate. This voltage is the amplification circuit 38
And is output to the multiplication circuit 45 as a positive first flow rate detection voltage V1. Then, the multiplication circuit 45 multiplies (multiplies) the negative deformed flow rate voltage V3 from the limit circuit 44 and the first flow rate detection voltage V1 to set the intake air amount as a negative output voltage V0 and output terminal 46. To output 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 the accurate air-fuel ratio control, and improve the engine performance.

Thus, in the thermal type air flow rate detecting device 21 according to the present embodiment, the heating resistor 30 is formed on the insulating substrate 29, and the first and first heaters 30 are located in front of and behind the heating resistor 30, respectively. Since the two temperature sensitive resistors 31 and 32 are formed, the number of parts can be reduced, and the air flow direction 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, the resistance value change due to the flow rate Q of the heating resistor 30 of one bridge circuit 34 is output to the multiplication circuit 45 as the first flow rate detection voltage V1 via the amplifier circuit 38, and the other bridge circuit 40 is also provided. The resistance value change of the first and second temperature sensitive resistors 31 and 32 due to the flow rate Q is set to the 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 multiplication circuit 45 as the flow rate signal section a, while when the predetermined flow rate Q0 is exceeded, the modified flow rate voltage V3 is output. V3 is output to the multiplication circuit 45 as the modified signal section b. The multiplication circuit 45 multiplies the first flow rate detection voltage V1 and the modified flow rate voltage V3 to output the output terminal 4
Even if the flow rate Q is within the range of the predetermined flow rate Q0, the output voltage V0 from 6 can have a substantially linear characteristic with respect to the flow rate Q of the intake air. Output voltage V0, and in the flow indicated by arrow B, a negative output voltage V0.

Furthermore, 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.

Furthermore, since the first and second temperature sensitive resistors 31 and 32 are heated by the sub power source VS, the temperature sensitive resistors 31 and 32 are cooled by the air flow.
The resistance values RT1 and RT2 can be sensitively changed, and the air flow direction can be detected with high sensitivity.

In the above embodiment, the temperature compensation resistor 35
Although it has been described that it is provided near the detection holder 26,
The present invention is not limited to this, and as shown in a first modification of FIG. 8, a slit S is formed in the insulating substrate 29 ′ from the front end side toward the base end side to form the first substrate portion 29A ′ and the first substrate portion 29A ′. Board part 2
9B ', a heating resistor 30, first and second temperature sensitive resistors 31 and 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 heat generating resistor 30, the first and second temperature sensitive resistors 31 and 32, and the temperature compensating resistor 35 can be formed as a film on the insulating substrate 29 ', and the number of parts can be significantly reduced.

Further, in the above-mentioned embodiment, the heating resistor 30 and the first and second temperature sensitive resistors 3 formed on the insulating substrate 29 are formed.
1 and 32 are formed as shown in FIG. 2, the present invention is not limited to this, and as in the second modification shown in FIG.
52, 53 extending from the distal end side to the proximal end side of the
And the insulating substrate 51 is formed by the slits 52 and 53.
Is divided into first, second and third substrate parts 51A, 51B and 51C, and the first, second and third substrate parts 51A, 51B and 5C are separated.
1C has a heating resistor 54 and a first temperature-sensitive resistor 5 respectively.
5, the second temperature sensitive resistor 56 may be formed as a film. Further, in this case, it is desirable that the first substrate portion 51A has a relatively large surface area as compared with the other substrate portions 51B and 51C. Further, in the case of this modification, the slit 5
Since the resistors 54, 55, 56 are separated by 2, 53, it is possible to reduce the influence of the heat of the heating resistor 54 on the temperature sensitive resistors 55, 56 via the insulating substrate 51. Furthermore, as shown by the chain double-dashed line, the temperature compensation resistor 35
May be integrally formed.

Further, in the above embodiment, the flowmeter main body 22
Although the one reference resistor 23 wound around the winding part 24 of the above is provided so as to project into the intake pipe 2, the present invention is not limited to this, and for example, inside the circuit casing 27 provided on the outer periphery of the intake pipe 2. The reference resistor 23 may be arranged together with the flow rate adjusting resistor 36 and the like.

Furthermore, in the above embodiment, the predetermined flow rate Q
Although 0 is taken as the flow rate in the idling state, the present invention is not limited to this and may be any given flow rate Q0.

On the other hand, in the above embodiment, by using the limit circuit 44 as the flow rate detection signal deforming means, when the intake air flow rate Q exceeds the predetermined flow rate Q0, the modified flow rate voltage V3 becomes the constant voltage Va. However, the present invention is not limited to this, and when the intake air flow rate Q exceeds the predetermined flow rate Q0, the deformation signal portion b of the modified flow rate voltage V3 with respect to the flow rate Q is output. It may be transformed into a linearly changing voltage.

Further, in the above embodiment, the bridge circuit 34 constituting the first flow rate detecting means is formed of the heating resistor 30, the temperature compensating resistor 35, the one reference resistor 23 and the flow rate adjusting resistor 36. The present invention is not limited to this, and instead of the temperature compensation resistor 35 and the flow rate adjustment resistor 36, a fixed resistor may be used to form the bridge circuit 34.

[0076]

As described above in detail, in the invention of claim 1, the first flow rate detecting means is formed as a bridge circuit including a heating resistor, and the resistance value change of the heating resistor in the bridge circuit is The second flow rate detecting means is formed as a bridge circuit including the first and second temperature sensitive resistors, and the balance of the bridge circuit is equal to that of the first and second temperature sensitive resistors. The second flow rate detection signal corresponding to the flow rate of the intake air is output because the second flow rate detection signal is output due to the change in the resistance value. Further, 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 detecting signal from the second flow rate detecting means, and outputs a deformed flow rate signal as a whole, By multiplying the first flow rate detection signal and the modified flow rate signal by the intake air flow rate calculation 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 and the calculation of the fuel injection amount and the like can be accurately performed without correcting the setting conditions of the control unit that have been used up to now.

According to the second aspect of the invention, the first and second temperature-sensitive resistors formed on the insulating substrate are separated from each other before and after the heating resistor with respect to the flow direction of the intake air. Since the resistance value changes depending on the flow direction of air, when the resistance value of the first temperature-sensitive resistor is smaller than that of 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 air flow can be detected in the opposite 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 the single insulating substrate, the number of parts can be reduced.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a state in which a thermal air flow rate 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 a thermal type air flow rate detecting device according to an embodiment.

FIG. 4 is a first flow rate detection voltage V output from an amplifier circuit.
It is a characteristic diagram which shows the output characteristic with respect to the flow rate Q of 1.

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

[FIG. 6] Modified flow rate voltage V3 output from the limit circuit
It is a characteristic diagram which shows the output characteristic with respect to the flow rate Q of.

FIG. 7 is a flow rate Q of the output voltage V0 output from the multiplication circuit.
It is a characteristic diagram which shows the output characteristic with respect to.

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

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

FIG. 11 is a perspective view showing a flowmeter main body, a heat generation resistance 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]

 21 Thermal Air Flow Rate Detection Device 22 Flow Meter 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-sensitive resistor 34 Bridge circuit (first flow rate detection means) 35 Temperature compensation resistance 36 Flow rate adjustment resistance 37,43 Differential amplification circuit 38 Amplification circuit 40 Bridge circuit (second flow rate detection means) 41,42 Reference resistance ( Other reference resistance) 44 Limit circuit (flow rate detection signal transforming means) 45 Multiplier circuit (intake air flow rate computing means)

Claims (2)

[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 inside the intake pipe and cooled by intake air flowing in the intake pipe. In the thermal type air flow rate detecting device, the bridge circuit is formed by including the heat generating resistance, and the change in the resistance value of the heat generating resistance forming the bridge circuit is output as a first flow rate detecting signal corresponding to the flow rate. A first flow rate detecting means, first and second temperature-sensitive resistors that are provided in front of and behind the heat generating resistor and have a resistance value that changes with respect to the flow direction of the intake air; A bridge circuit is formed by including a second temperature-sensitive resistor, and the second circuit having a flow direction corresponding to the flow rate causes an imbalance in the bridge circuit due to a change in the resistance value of the first and second temperature-sensitive resistors. Second flow rate detection output as flow rate detection signal And a second flow rate detection signal provided on the output side of the second flow rate detection means and deformed when the second flow rate detection signal output from the second flow rate detection means exceeds a predetermined flow rate range. By multiplying the flow rate detection signal deforming means for outputting as A thermal air flow rate detection device comprising: an intake air flow rate calculation means for calculating an intake air flow rate. 2. The heating resistor is formed as a film on an insulating substrate attached to the flowmeter body, and is formed as a heating resistor extending in a film shape at least in a length 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 in front of and behind the heating resistor in the flow direction of the intake air on the insulating substrate. The thermal air flow rate detection device according to claim 1, which is configured.