JP3184401B2 - Thermal air flow detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

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

[0004] In the drawing, reference numeral 1 denotes a thermal air flow detecting device provided in the middle of an intake pipe 2. The thermal air flow detecting device 1 is directed toward a combustion chamber (not shown) of an engine body. In order to detect the flow rate of the intake air flowing in the direction A shown in the drawing, it is provided in the middle of the intake pipe 2 via a mounting hole 2A.

Reference numeral 3 denotes a flow meter main body which constitutes a main body of the thermal type air flow detecting device 1. The flow meter main body 3 is formed as shown in FIG. 9 by means such as insert molding and has a winding shape. A winding portion 4 formed in a stepped cylindrical shape for winding a later-described reference resistor 14, and a substantially disk-shaped portion located on the base end side of the winding portion 4 and having terminal pins 8 A to 8 8D is provided integrally with the terminal portion 5 and extends in the radial direction of the intake pipe 2 from the distal end side of the winding section 4. It comprises a detection holder 6 to be positioned and a circuit casing 7 described below to which the terminal 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 protection cover mounted on the detection holder 6 of the flowmeter main body 3. The protection cover 13 is shown in FIG. 9 after mounting the heating resistor 9 and the temperature compensation 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 FIG. 8, the protective cover 13 is removed from the detection holder 6 in order to clearly show the heating resistor 9 and the temperature compensation resistor 11.

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

In the thermal air flow detecting device 1 of the prior art constructed as described above, when detecting the intake air flow rate of an automobile engine or the like, the terminal portion 5 of the flow meter main body 3 is connected via each terminal pin 8. Te while connected to the connector portion of the circuit casing 7, the flowmeter body 3 of the detection holder 6 or the like inserted through the mounting hole 2A into the intake pipe 2, from the outer periphery of the intake pipe 2 to the said mounting Tsukeana 2A By mounting the circuit casing 7,
Heating resistor 9 and temperature compensation resistor 1 provided on detection holder 6
1 is disposed at the center of the intake pipe 2.

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

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

[0015]

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

That is, in an engine body having a multi-cylinder cylinder, the intake air is forced into each cylinder every time each intake valve (not shown) is opened as the piston reciprocates in each cylinder. As shown in FIG. 5, the flow velocity of the air flowing through the intake pipe 2 is repeatedly increased and decreased in accordance with the opening and closing of each intake valve as shown in FIG. become.

In particular, when the engine speed reaches from a low speed range to a middle speed range and the intake and exhaust volumes increase, the intake valve and the exhaust valve (not shown) overlap, and one of the exhaust The part may blow back into the intake pipe 2 with the opening of the intake valve, and at this time, the times t1, t shown in FIG.
The flow velocity becomes negative (minus) as shown in FIG. 2, and an airflow flowing in the direction of arrow B (reverse direction) is generated, which causes a problem that the intake air flow rate is erroneously detected.

The present invention has been made in view of the above-described problems of the prior art, and the present invention can prevent erroneous detection of an intake air flow rate due to a reverse air flow, and can greatly improve flow rate detection accuracy. It is an object of the present invention to provide a thermal air flow detecting device according to the present invention.

[0019]

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. When cooled by air flowing in the intake pipe
For flow rate detection that detects the change in resistance value of air as the flow rate of air
This is applied to a thermal air flow rate detecting device having a heat generating resistance.

A feature of the structure adopted in the first aspect of the present invention is that the heat generating resistor for detecting the flow rate is formed on an insulating substrate attached to the main body of the flow meter, and at least a length direction of the insulating substrate is measured. The heating resistor is formed on the insulating substrate so as to be separated from the heating resistor on the downstream side in the flow direction of the air, and has a resistance value when cooled by the air. A single temperature-sensitive resistor that changes according to the flow direction of air is provided, and the temperature-sensitive resistor is connected in parallel with a fixed resistor provided in the flowmeter main body, so that the airflow with the fixed resistor is established. A flow direction detecting means for detecting a direction , and the temperature-sensitive resistor detects a voltage;
By applying it at a lower temperature than the heating resistor
That is, the heat is generated .

[0021]

In the invention according to claim 2, the heating resistor is formed so as to extend from a base end side to a front end side of the insulating substrate,
The temperature sensing resistor is formed by a single resistive film extending distally from the proximal side of the insulating substrate located downstream of the heating resistor to the flow direction of the air.

According to the third aspect of the present invention, the insulating substrate comprises a main substrate portion having a fixed end attached to the flowmeter main body at a base end side and a free end at a distal end side, and a sub-substrate portion.
A slit extending from the distal end toward the proximal end is formed between the sub-board portion and the main board portion, and a temperature compensation resistor for compensating a temperature change of air is formed in the sub-board portion. The main substrate portion, the heating resistor extending from the base end to the distal end, and the temperature-sensitive member extending from the base end to the distal end while being separated downstream from the heating resistor in the direction of air flow. it is a formed comprising constituting a resistor.

According to a fourth aspect of the present invention, the flow direction detecting means outputs a flow direction detection signal corresponding to the flow direction of air based on whether or not the resistance value of the temperature-sensitive resistor is smaller than a fixed resistance. Configuration.

Further, in the invention of claim 5 , the heating resistor forms a bridge circuit for outputting a flow rate detection signal,
Further, based on the flow rate detection signal output from the bridge circuit and the flow direction detection signal detected by the flow direction detection means, when the flow direction of the air is forward, the flow rate detection signal is output as it is, In the case of the direction, a flow signal output means for inverting and outputting the flow detection signal is provided.

[0026]

According to the above construction, according to the first aspect of the present invention, the heating resistor and a single temperature-sensitive resistor can be formed compactly on the insulating substrate by utilizing the limited surface space of the insulating substrate. Can be as large as possible. Since a single temperature-sensitive resistor is formed on the insulating substrate so as to be separated from the heat-generating resistor on the downstream side in the air flow direction, the temperature-sensitive resistor located downstream from the heat-generating resistor is , influenced by heat from the heating resistor when the air flow direction is forward, no longer be cooled directly I by the forward air flow, thereby, the temperature sensing resistor of resistance
Change is that a small. On the other hand, the air flow direction is reversed.
That when, the temperature sensitive resistors is ing the upper Nagaregawa than the heating resistor
In, the temperature sensitive resistors Rukoto affected by heat from the heating resistor
Without would be cooled directly by the air flow, the resistance value change significantly. As described above, the direction of air flow can be detected based on whether or not the resistance value of the temperature-sensitive resistor changes significantly.

In addition, a voltage is applied to the temperature- sensitive resistor.
Configuration to generate heat at a lower temperature than the heating resistor
Therefore , the difference between the direct cooling by the air flow and the cooling by the air flow through the heating resistor can be more reliably determined.

According to the second aspect of the present invention, since the heating resistor and the temperature-sensitive resistor are formed on the single insulating substrate so as to extend from the base end to the tip end, the contact area with the air flow is increased. As a result, the change in resistance value can be increased, and the number of components can be reduced.

According to the third aspect of the present invention, a heating resistor, a temperature-sensitive resistor, and a temperature compensation resistor can be formed on a single insulating substrate, and the number of components can be reduced. By forming a slit between the sub-substrate portion on which the temperature compensation resistor is formed and the main substrate portion on which the heating resistor and the temperature-sensitive resistor are formed, the heating resistor and the temperature-sensitive resistor can be formed. Thus, it is possible to prevent heat from escaping from the heated main substrate portion to the sub-substrate portion, and to raise the temperature of the main substrate portion at an early stage.

According to a fourth aspect of the present invention, the flow direction detecting means is constituted by connecting the temperature-sensitive resistor and the fixed resistor in parallel.
Means that the resistance value of the temperature-sensitive resistor is smaller than the fixed resistance
Whether or not the flow direction detection signal corresponds to the air flow direction
Since it configured to output a if the fixed large resistance value of the temperature sensing resistor than resistor can, for example, determined to be the forward direction of the air flow, reverse if the resistance value is smaller It can be determined that it is an air flow.

Further, according to the fifth aspect of the present invention, a bridge circuit including the heating resistor is formed, a change in the resistance value of the heating resistor in the bridge circuit is extracted as a flow rate detection signal, and the resistance of the temperature-sensitive resistor is detected. The flow direction of the air is detected by a flow direction detecting means for comparing the value with the resistance value of the fixed resistor, and when the air flow direction is the forward direction, the flow rate detection signal can be output as it is as a positive voltage signal, and when the air flow direction is the reverse direction, It can be inverted and output as a negative voltage signal.

[0032]

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

First, FIGS. 1 to 5 show a first embodiment according to the present invention.
The following shows an example.

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 a reference resistor 23 having a resistance value R1 is wound, and a plurality of terminal pins (shown in FIG. Z)
And a detection holder 26 extending in the radial direction of the intake pipe 2 from the distal end side of the winding portion 24.
And a circuit casing 27 described later.

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

Reference numeral 27 denotes a circuit casing provided on the outer peripheral side of the intake pipe 2 so as to close the mounting hole 2A of the intake pipe 2. The circuit casing 27 is substantially the same as the circuit casing 7 described in the prior art. The mounting hole 2 of the intake pipe 2 is formed.
Although the circuit casing 27 has a fitting portion 27A that fits into the A, the circuit casing 27 is formed on an insulating substrate (not shown) made of, for example, a ceramic material or the like. 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 is formed by depositing a platinum film on the insulating substrate 29 by means such as printing or sputtering. The resistance R
H, and is formed on the upstream side with respect to the air flow direction (the direction of arrow A) to increase the surface area (mounting area) of the heating resistor 30 as much as possible. The contact area with the intake air flowing through the intake pipe 2 can be increased.

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

Numeral 31 denotes an insulating substrate 29 together with the heating resistor 30.
The temperature-sensitive resistor 31 is formed on the insulating substrate 29 by printing or sputtering or the like so that the temperature-sensitive resistor 31 has a resistance value RT. It is formed on the insulating substrate 29 by being separated downstream of the heating resistor 30 with respect to the flow direction of the intake air flowing in the intake pipe 2 in the direction indicated by the arrow A (the width direction of the insulating substrate 29). It is arranged. The temperature-sensitive resistor 31 is normally supplied with a current from the sub power supply VS as shown in FIG. 3 and generates heat at a lower temperature than the heat-generating resistor 30 as shown in FIG. Substrate 2
By cooling with air flowing along the surface of 9,
The resistance value RT changes greatly, and the direction of air flow can be detected with high sensitivity by the bridge circuit 37 and the comparison circuit 41 described later.

Here, the resistance value RT of the temperature-sensitive resistor 31 is shown.
Corresponds to the air flow direction and air velocity as shown in FIG.
And change . When the flow of air in the intake pipe 2 is a forward flow (the direction of arrow A), the temperature-sensitive resistor 3
Since 1 is located downstream of the heating resistor 30, temperature sensitive resistors 31 ing to contact the warmed by the heating resistor 30 air. For this reason, the temperature-sensitive resistor 31 is
Under the influence of heat from the body 30, the resistance value RT of the temperature-sensitive resistor 31 gradually decreases, and even when the flow velocity becomes high (the flow rate increases), the resistance value RB of a fixed resistor 38 described later.
It will never be smaller . Hand, if the air flow in the intake pipe 2 becomes reverse direction (arrow B direction), since the temperature sensitive resistor 31 is positioned upstream of the heating resistor 30, sensitive resistance temperature 31 without being affected by heat from the heating resistor 30, the reverse direction of the cold <br/> or directly by the air flow, the resistance value of the temperature sensitive resistor 31 RT is decreased rapidly
It becomes smaller than the resistance value RB of the fixed resistor 38 .

.. Denote, for example, four electrodes formed at the base end side of the insulating substrate 29. The electrodes 32 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, by connecting the heating resistor 30 and the temperature-sensitive resistor 31 formed on the insulating substrate 29 via the respective electrodes 32 to the respective electronic components provided in the circuit casing 27, FIG. The processing circuit for flow rate detection shown is configured.

FIG. 3 shows a processing circuit for detecting a flow rate according to this embodiment.

In FIG. 3, reference numeral 33 denotes one bridge circuit for outputting a flow rate detection signal.
Are the heating resistor 30, the temperature compensation resistor 34, and the reference resistor 23.
And a flow regulating resistor 35 having a resistance value R2.
Each of the bridges is configured as a bridge in which the products of the resistance values of the opposite sides are equal, and a connection point a between the heating resistor 30 and the temperature compensation resistor 34 is connected to the emitter side of a current control transistor 42 described later. Flow adjustment resistor 35
Is connected to the ground.

On the other hand, in the bridge circuit 33,
The heating resistor 30 and the reference resistor 23, the temperature compensating resistor 34 and the flow rate adjusting resistor 35 are respectively connected in series, and respective connection points c and d are connected to the input terminals of the differential amplifier circuit 36, and the connection point c is connected to the input terminal c. Inverting circuit 43 and selecting circuit 4 to be described later
4 is connected.

Here, the temperature compensation resistor 34 is provided on the detection holder 26 in the vicinity of the heating resistor 30.
The temperature compensating resistor 34 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 33 configured as described above, when the bridge circuit 33 is in a balanced state, the output from the differential amplifier circuit 36 becomes zero and the connection point c
Then, the voltage across the reference resistor 23 in the balanced state is output to the inverting circuit 43 and the selecting circuit 44. On the other hand, when the balance of the bridge circuit 33 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 current control transistor 42. As a result, the current control transistor 42 controls the current applied to the bridge circuit 33 to bring the cooled heating resistor 30 to a constant temperature and return the bridge circuit 33 to an equilibrium state. At this time, the amplified current value output from the connection point c of the bridge circuit 33 is
The voltage is detected as a voltage across the reference resistor 23, and this voltage is output to the inverting circuit 43 and the selecting circuit 44.

Reference numeral 37 denotes another bridge circuit which constitutes the means for detecting the flow direction of the intake air together with a comparison circuit 41 which will be described later. The bridge circuit 37 comprises the temperature-sensitive resistor 31, the fixed resistor 38 and the adjustment resistors 39 and 40. A connection point e between the temperature-sensitive resistor 31 and the fixed resistance 38 is connected to the sub power supply VS (for example, 3 V), and a connection point f between the adjustment resistances 39 and 40.
Is connected to earth.

Here, in the bridge circuit 37, the temperature-sensitive resistor 31 and the adjustment resistor 39, and the fixed resistor 38 and the adjustment resistor 40 are connected in series, respectively, and the connection points g and h are input terminals of the comparison circuit 41. , The temperature-sensitive resistor 31 and the fixed resistor 38 are connected in parallel. In the comparison circuit 41, the temperature-sensitive resistor 3
1 is compared with the resistance value RB of the fixed resistor 38, and when RT ≥ RB, a signal indicating a flow direction at which a predetermined voltage value V0 shown in FIG. 5 is obtained (hereinafter referred to as a "flow direction detection signal").
Is output to the selection circuit 44, and in the case of RT <RB, a flow direction detection signal whose voltage value becomes substantially zero is output to the selection circuit 44.

Here, the detection operation of the bridge circuit 37 will be described based on the relationship between the flow rate of the intake air and the flow direction detection signal shown in FIG. 5. When the flow direction of the intake air is the A direction (forward direction), Since the thermal resistor 31 is indirectly cooled by receiving the heat of the heating resistor 30, the resistance value becomes RT ≧ RB irrespective of the magnitude of the flow velocity as described above, and the flow direction detection output from the comparison circuit 41 is detected. The signal has a predetermined voltage value V0
Becomes On the other hand, when the flow direction of the air changes from the A direction to the B direction (reverse direction), the temperature-sensitive resistor 31 is directly cooled by the air without receiving the heat of the heat-generating resistor 30, so that the resistance value sharply increases. , And the flow direction detection signal has a voltage value of substantially zero.

Reference numeral 42 denotes a current control transistor. The current control transistor 42 has a collector connected to the battery voltage VB and a base connected to the differential amplifier 36.
, And the emitter side is connected to a connection point a of the bridge circuit 37. The current control transistor 42 controls the emitter current according to the output (current control voltage) from the differential amplifier circuit 36 and the base current changes. As a result, the current control transistor 42 controls the value of the current applied to the bridge circuit 37 to perform feedback control for maintaining the temperature of the heating resistor 30 at a constant temperature.

Reference numeral 43 denotes an inversion circuit connected between the connection point c of the bridge circuit 33 and the selection circuit 44. The inversion circuit 43 inverts the flow rate detection signal from the bridge circuit 33 and outputs it to the selection circuit 44. It is supposed to.

Reference numeral 44 denotes a selection circuit that constitutes a flow signal output means together with the inversion circuit 43. The selection circuit 44 outputs a flow direction detection signal from the bridge circuit 37 output via the comparison circuit 41 (see FIG. 5). For example, in the case of the forward direction, the flow rate detection signal from the bridge circuit 33 is output as an output signal Vout from the output terminal 45 to a control unit (not shown), and in the case of the reverse direction, the inversion circuit 43
Is output from the output terminal 45 to the control unit as an output signal Vout.

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 heating resistor 3 on the insulating substrate 29
The temperature-sensitive resistor 31 located on the downstream side of 0 is cooled via the heating resistor 30. As a result, a forward flow direction detection signal having the voltage value V0 is output from the comparison circuit 41.

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. However, the heating resistor 30 is reduced by the differential amplifier circuit 36 and the current controlling transistor 42. The current value applied to the bridge circuit 33 is increased in order to make the temperature of the bridge circuit 30 constant, and the increased current value is detected by the reference resistor 23 as a voltage between both ends. As a result, the bridge circuit 3
3 outputs a positive flow rate detection signal to the inversion circuit 43 and the selection circuit 44. The positive flow detection signal input to the inversion circuit 43 is output to the selection circuit 44 as an inverted negative flow detection signal.

Then, in the selection circuit 44, the comparison circuit 41
Is selected between the positive flow detection signal input from the bridge circuit 33 and the negative flow detection signal input from the inversion circuit 43 on the basis of the flow direction detection signal from Since the flow is in the forward direction, a positive flow detection signal is selected, and a positive flow detection signal is output from the output terminal 45 to the control unit as an output signal Vout.

Since the base current of the current control transistor 42 is controlled based on the signal output from the differential amplifier circuit 36, feedback control for keeping the heating resistor 30 at a constant temperature is performed. .

On the other hand, when the flow of air is in the direction of arrow B (reverse direction), the temperature-sensitive resistor 31 located on the insulating substrate 29 on the upstream side of the heating resistor 30 is caused by the flow of air. It is directly cooled, and the resistance value RT of the temperature-sensitive resistor 31 rapidly decreases. As a result, the comparison circuit 41 outputs a reverse flow direction detection signal having a voltage value of zero.

As described above, since the heating resistor 30 is cooled by the flow of the intake air, the resistance value RH of the heating resistor 30 decreases, and the bridge circuit 33
The equilibrium is broken. As a result, a positive flow rate detection signal is output from the bridge circuit 33 to the selection circuit 44, and
The negative flow rate detection signal is also supplied to the selection circuit 44 via the inversion circuit 43.
The selection circuit 44 selects a negative flow rate detection signal based on the reverse flow direction detection signal from the comparison circuit 41, and controls this negative flow rate detection signal as an output signal Vout from an output terminal 45. Output to the unit.

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

Here, in the thermal type flow detecting device 21 according to the present embodiment, the heating resistor 30 is formed on the insulating substrate 29 and the temperature-sensitive resistor 31 is formed downstream of the heating resistor 30. Therefore, the flow direction of the air can be detected by the temperature-sensitive resistor 31, and the flow rate of the intake air can be detected from the change in the resistance value of the heating resistor 30. Accordingly, the flow rate of the intake air can be detected, and the direction thereof can be accurately detected.

Further, since the heating resistor 30 and the temperature-sensitive resistor 31 are formed on the insulating substrate 29 so as to extend from the base end to the tip end, a limited surface space can be effectively used. The heating resistor 30 and the temperature-sensitive resistor 31 can be formed compactly, and the surface area (mounting area) of the heating resistor 30 can be reduced.
Can be as large as possible. The contact area between the heating resistor 30 and the temperature-sensitive resistor 31 with respect to the air flow in the intake pipe 2 can be increased, and the resistance values RH and RT can be changed in response to the air flow. And a plurality of resistors 3 on a single insulating substrate 29.
Since 0 and 31 are formed, the number of parts can be reduced.

Further, in this embodiment, it is possible to detect the direction of air flow by determining whether or not the heating resistor 30 is affected by the heat, based on the positional relationship between the heating resistor 30 and the temperature-sensitive resistor 31. It is possible to detect an accurate flow rate.

Further, since the flow direction detecting means is constituted by the bridge circuit 37 and the comparison circuit 41 for comparing the resistance value RT of the temperature-sensitive resistor 31 with the resistance value RB of the fixed resistor 38, the flow direction of the air is determined. More accurate detection is possible.

Therefore, according to the present embodiment, the flow rate of the intake air flowing through the intake pipe 2 can be reliably detected based on the resistance value RH of the heating resistor 30, and the resistance value RT of the temperature-sensitive resistor 31 can be determined. It is possible to reliably detect the flow direction of the air based on the change, and to detect the flow rate of the intake air with high accuracy even when the exhaust gas flows back into the intake pipe 2 in the middle speed range of the engine and a backflow occurs. Can be.

Next, FIGS. 6 and 7 show the second embodiment according to the present invention.
This embodiment is characterized in that a heating resistor, a temperature-sensitive resistor, and a temperature compensation resistor are formed on a single insulating substrate. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

In the figure, reference numeral 51 denotes an insulating substrate according to the present embodiment. The insulating substrate 51 is formed in a rectangular flat plate shape using an insulating material such as glass, alumina, or aluminum nitride. The main substrate portion 51A and the sub-substrate portion 51B have a free end on the distal end side, and a slit 52 extending from the distal end side to the proximal end side is formed between the substrate portions 51A and 51B. ing. The sub-substrate portion 51B is located upstream of the main substrate portion 51A with respect to the flow of the intake air in the forward direction (the direction indicated by the arrow A). Are formed.

Reference numeral 53 denotes a heating resistor, and the heating resistor 5
Reference numeral 3 denotes a main substrate portion 51 formed by printing or sputtering a temperature-sensitive material such as platinum on the main substrate portion 51A of the insulating substrate 51 so as to have a resistance value RH.
A film is formed in the length direction of A, and the heating resistor 30 described above is formed.
Similarly to the above, the current value is controlled by the current control transistor 42 described in the first embodiment, so that heat is generated at a constant temperature (for example, about 240 ° C.).

Reference numeral 54 denotes a temperature-sensitive resistor positioned upstream of the heating resistor 53. The temperature-sensitive resistor 54 has a resistance value RT on the main substrate portion 51A. The material is formed into a film by means of print printing or sputtering.

Reference numeral 55 denotes a temperature compensating resistor as a temperature compensating resistor.
It is formed by depositing a platinum film using means such as print printing or sputtering. The temperature compensating resistor 55 is connected to the heating resistor 53.
It has a larger resistance value RK than that of the first embodiment, and is not affected by the flow of intake air, and detects only a temperature change.

.. Denote, for example, five electrodes formed on the base end side of the insulating substrate 51. The electrodes 56 are arranged in a row at a predetermined interval in the width direction of the insulating substrate 51. By inserting the base end side of the insulating substrate 51 into the slot of the detection holder 26, it is connected to each terminal (not shown) on the detection holder 26 side.

As described above, by attaching the insulating substrate 51 of the second embodiment to the flowmeter main body 22 of the above-described first embodiment, a flow detection processing circuit (about the same as that of the above-described first embodiment) is provided. FIG. 7), and constitutes a processing circuit for flow rate detection having a bridge circuit 33 'for detecting the flow rate and a bridge circuit 37' for detecting the flow direction of the air.

In the thermal type flow rate detecting device of this embodiment having the above-described configuration, the flow rate and the flow direction of the intake air can be detected as in the first embodiment.

That is, the heating resistor 53 on the insulating substrate 51 is cooled by the intake air, and the resistance value of the heating resistor 53 decreases, so that a flow rate detection signal is output from the bridge circuit 33 'and the inverting circuit 43 is output. Outputs a negative flow rate detection signal to the selection circuit 44.

On the other hand, the bridge circuit 37 'compares the resistance values of the temperature-sensitive resistor 54 and the fixed resistor 38 to determine whether the direction of the flow of the intake air is the forward direction or the reverse direction. This signal is supplied to the selection circuit 4
4 is output. As a result, the selection circuit 44 selects a positive or negative flow rate detection signal based on the flow direction detection signal from the bridge circuit 37 '(comparing circuit 41) and outputs it as an output signal Vout to the control unit. As a result, the control unit performs accurate air-fuel ratio control based on the amount of intake air in which the flow direction is also detected.

In this embodiment, the heating resistor 53, the temperature-sensitive resistor 54, and the temperature compensation resistor 55 are formed on a single insulating substrate 51. Also, the number of parts can be reduced.

Further, the sub-substrate portion 51B on which the temperature compensation resistor 55 is formed, a heating resistor 53, and a temperature-sensitive resistor 54 are formed.
By forming the slit 52 between the main substrate 51A and the main substrate 51A, it is possible to prevent, for example, the heat of the heating resistor 53 from affecting the temperature compensating resistor 55. Can be activated.

[0079]

[0080]

[0081] Incidentally, in each of the foregoing embodiments, flowmeter body 22
Although the reference resistor 23 wound around the winding portion 24 is provided so as to protrude into the intake pipe 2, the present invention is not limited to this. For example, the circuit casing 2 provided outside the intake pipe 2
A configuration may be adopted in which the reference resistor 23 is provided in the unit 7 together with the flow rate adjusting resistor 35 and the like.

[0082] Further, in each of the foregoing embodiments, the bridge circuit 33 that outputs a flow rate detection signal (33 '), the heating resistor 3
0 (53), temperature compensation resistor 34 (temperature compensation resistor 5
5) Although it is formed from the reference resistor 23 and the flow adjustment resistor 35, the present invention is not limited to this, and the bridge circuit 33 (using a fixed resistor as the temperature compensation resistor 34 (temperature compensation resistor 55) and the flow adjustment resistor 35) is used. 33 ').

[0083]

As described in detail above, according to the first aspect of the present invention, a single temperature-sensitive resistor is formed on an insulating substrate so as to be separated from the heat-generating resistor on the downstream side in the air flow direction. The resistor is connected in parallel with a fixed resistor provided in the flowmeter main body, constitutes a flow direction detecting means for detecting a flow direction of air , and the temperature-sensitive resistor is configured to apply a voltage.
The heating resistor is configured to generate heat at a lower temperature than the heating resistor, so that the flow rate of air can be detected by a change in resistance value when the heating resistor is cooled by air flowing through the intake pipe, and It is possible to detect whether the flow direction of the air is the forward direction or the reverse direction by the change in the resistance value of the temperature sensitive resistor. Therefore, the heating resistor on the insulating substrate
By forming a single temperature-sensitive resistor on the downstream side, it is possible to detect the flow direction and flow rate of the air, prevent erroneous detection of the intake air flow rate due to the air flow in the opposite direction, and reduce the flow rate. Detection accuracy can be greatly improved. Further, the heating resistor on an insulating substrate and a single temperature sensitive resistor on the downstream side
It is only necessary to form a surface limited space insulation substrate can be effectively used, it is possible with the insulating substrate can be formed compactly, as large as possible a surface area of the heating resistor.

In this case, the voltage is applied to the temperature- sensitive resistor .
Configuration to generate heat at a lower temperature than the heating resistor
Therefore , in the temperature-sensitive resistor, it is possible to distinguish between the direct cooling by the airflow and the cooling by the airflow through the heating resistor, and to detect the flow direction of the air more accurately.

According to the second aspect of the present invention, since the heating resistor and the temperature-sensitive resistor formed on the insulating substrate extend from the base end to the tip end, the contact area with the air flow can be increased. The change in the resistance value can be increased, and the detection sensitivity can be improved. Further, the heating resistor and the temperature-sensitive resistor can be formed compactly by effectively utilizing the surface space of the insulating substrate.

According to the third aspect of the present invention, a heating resistor, a temperature-sensitive resistor, and a temperature compensation resistor can be formed on a single insulating substrate, and the number of components can be reduced. Further, by forming a slit between the sub-substrate portion forming the temperature compensation resistor and the main substrate portion forming the heating resistor and the temperature-sensitive resistor, for example, the heat of the heating resistor becomes the temperature compensation resistor. The influence can be prevented, and the detection sensitivity can be improved.

[0087] In the present invention of claim 4, the fixed resistor flow direction detecting means the temperature sensitive resistor constructed by connecting in parallel, Re flow
The direction detecting means determines that the resistance value of the temperature-sensitive resistor is a fixed resistance.
Flow depending on the direction of air flow
Since the direction detection signal is output , the flow direction is determined by comparing the resistance values of the temperature-sensitive resistor and the fixed resistor.
When the temperature-sensitive resistor is larger than the resistance value of the fixed resistance, it can be determined that the airflow is in the forward direction, for example, and when it becomes smaller, it can be determined that the airflow is in the reverse direction.

Further, according to the fifth aspect of the present invention, a bridge circuit including a heating resistor is formed, and a change in the resistance of the heating resistor in the bridge circuit is extracted as a flow rate detection signal. The flow direction of the air is detected by comparing the resistance values of the fixed resistors, and when the flow direction of the intake air is the forward direction, the flow rate detection signal can be directly output as a positive voltage signal, and when the flow direction of the intake air is the reverse direction, the flow direction detection signal is inverted. It can be output as a negative voltage signal. Then, the direction and the flow rate of the intake air can be detected to accurately control the air-fuel ratio and the like.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a state in which a thermal air flow detecting device according to a first embodiment is attached to an intake pipe.

FIG. 2 is a plan view showing a heating resistor and a temperature-sensitive resistor 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 first embodiment.

FIG. 4 is a characteristic diagram showing a change in resistance value of a temperature-sensitive resistor with respect to a flow velocity.

FIG. 5 is a characteristic diagram showing a relationship between a flow rate of intake air and a flow direction detection signal.

FIG. 6 is a plan view showing a heating resistor, a temperature-sensitive resistor, an auxiliary heater, and a temperature compensation resistor formed on an insulating substrate according to a second embodiment.

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

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

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

[Description of Signs] 21 Thermal air flow detector 22 Flow meter main body 23 Reference resistor 29, 51 Insulating substrate 30, 53 Heating resistor 31, 54 Temperature sensing resistor 33, 33 'Bridge circuit 34 Temperature compensation resistor 35 Flow rate adjustment Resistance 36 Differential amplification circuit 37, 37 'Bridge circuit (flow direction detecting means) 41 Comparison circuit 43 Inverting circuit 44 Selection circuit (flow rate signal output means) 51A Main board 51B Sub-board 55 Temperature compensation resistor (temperature compensation resistor) )

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G01F 1/68-1/699

Claims (5)

(57) [Claims] 1. A flowmeter main body having a base end attached to an intake pipe, and a change in a resistance value provided in the flowmeter main body located in the intake pipe and cooled by air flowing through the intake pipe. And a heat generating resistor for detecting the flow rate of the air as a flow rate of air.The heat generating resistor for detecting the flow rate is formed on an insulating substrate attached to the main body of the flow meter, It is constituted by a heating resistor extending in a film shape at least in a length direction of the insulating substrate, and is formed on the insulating substrate so as to be separated from the heating resistor on the downstream side in the flow direction of the air. A single temperature-sensitive resistor whose resistance value when cooled changes according to the flow direction of air is provided, and the temperature-sensitive resistor is connected in parallel with a fixed resistor provided on the flowmeter main body. Together with the fixed resistance A flow direction detecting means for detecting a flow direction of air is constituted , and the temperature-sensitive resistor is operated by applying a voltage.
A thermal air flow detecting device, wherein heat is generated at a lower temperature than the heating resistor . 2. The heating resistor is formed so as to extend from a base end side to a tip end side of the insulating substrate.
Downstream of the heating resistor to the flow direction of the air
Position to the composed formed by a single resistive film extending distally from the proximal side of the insulating substrate according to claim 1 Symbol placement of the thermal air flow rate detecting device. 3. The insulating substrate comprises a main substrate portion having a fixed end attached to the flowmeter main body on a base end side and a free end on a distal end side, and the sub-substrate portion and the main substrate portion. And a slit extending from the distal end toward the proximal end, and a temperature compensation resistor for compensating for a temperature change of air is formed on the sub-substrate, and the main substrate is The heating resistor extending from the base end to the tip end; and the temperature-sensitive resistor extending from the base end to the tip end while being spaced downstream from the heating resistor in the direction of air flow. thermal air flow detecting device according to claim 1 Symbol placement. 4. The flow direction detection means outputs a flow direction detection signal corresponding to the flow direction of air based on whether or not the resistance value of the temperature-sensitive resistor is smaller than a fixed resistance. Item 4. A thermal air flow detecting device according to item 1, 2 or 3 . 5. The heating resistor constitutes a bridge circuit for outputting a flow rate detection signal, and further based on a flow rate detection signal output from the bridge circuit and a flow direction detection signal detected by the flow direction detection means. 5. The heat generating apparatus according to claim 4, further comprising a flow rate signal output unit that outputs the flow rate detection signal as it is when the flow direction of the air is forward, and inverts and outputs the flow rate detection signal when the flow direction is reverse. Type air flow detector.