JPH0854270A - Thermal type air flow rate detector - Google Patents

Abstract

PURPOSE:To improve the detection accuracy of flow rate by comparing flow rate signals outputted from first and second flow rate detection means to output flow direction signal. CONSTITUTION:When the flow of sucked air is in the normal direction in a detection circuit 44, a selection circuit 50 selects a flow rate addition voltage V3 outputted from an addition circuit 47 or an inversion flow rate addition voltage V3' outputted from an inversion circuit 49 based on a direction detecting voltage Vb from a comparison circuit 48. In this case, as the voltage Vb is a signal indicating the flow in the normal direction, the voltage V3 is selected and the voltage V3 as the flow in the normal direction is outputted as output signal VOUT to a control unit at an output terminal. On the other hand, when the flow of air is in the opposite direction, as the voltage Vb is a signal indicating the flow in the opposite direction, the voltage V3' is selected and the voltage V3' as the flow in the opposite direction is outputted as output signal VOUT to the control unit at the output terminal.

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

A conventional thermal air flow rate detecting device will be described with reference to FIGS. 8 and 9.

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 formed by means such as insert molding as shown in FIG. A winding portion 4 formed in a stepped columnar shape for winding a reference resistor 14 described below, and a substantially disk-shaped portion located on the base end side of the winding portion 4 and having terminal pins 8A to 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 to be described later are provided at the center of the intake pipe 2. A detection holder 6 for positioning and a circuit casing 7 to be described later, which is located outside the intake pipe 2 and to which a terminal portion 5 is connected, are roughly configured.

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. 8, 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 main body 3 is inserted into the intake pipe 2 through the mounting hole 2A in a state where it is connected to the connector portion of the circuit casing 7 and the circuit is inserted into the mounting hole 2A from the outer peripheral side of the intake pipe 2. By installing the casing 7,
Heating resistor 9 and temperature compensation resistor 1 provided on the detection holder 6
1 is arranged at 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.

[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. 8 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 in the intake pipe 2 repeatedly pulsates as shown in FIG. 4 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 when the intake valve is opened, the time t1, t shown in FIG.
The flow velocity becomes negative (minus) like between 2 and an air flow that flows 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-mentioned problems of the prior art, and 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. It is an object of the present invention to provide a thermal type air flow rate detecting device.

[0019]

According to a first aspect of the present invention, there is provided a thermal type air flow rate detecting device, wherein a flow meter main body having a base end side attached to an intake pipe, an insulating substrate provided in the flow meter main body, A heating resistor provided on the insulating substrate and cooled by intake air flowing in the intake pipe, and a heating resistor located on the insulating substrate and separated from the heating resistor in front of and behind the heating air flow direction. And the first and second temperature-sensitive resistors that are formed by changing the respective resistance values according to the flow direction of the intake air, and control the current value applied to the heating resistor to control the heating resistor. Temperature control means for generating heat to maintain the insulating substrate at a constant temperature, first flow rate detection means for detecting a first flow rate signal by a change in resistance value of the first temperature sensitive resistor, and second flow rate detection means. The second flow rate signal is generated by changing the resistance value of the temperature sensitive resistor. The second flow rate detection means to be output, the first flow rate signal output from the first flow rate detection means, and the second flow rate signal output from the second flow rate detection means are added to add the flow rate addition signal. And a first flow rate signal output from the first flow rate detection means and a second flow rate signal output from the second flow rate detection means are compared to output a flow direction signal. When the flow direction detection means and the flow direction signal output from the flow direction detection means are detected to be forward flow signals, the flow rate addition signal output from the addition means is output as a flow rate detection signal, and the reverse flow rate signal is output. When it is detected that the flow signal is a directional flow signal, the flow rate signal output means outputs a signal obtained by inverting the flow rate addition signal output from the addition means as a flow rate detection signal.

In the thermal type air flow rate detecting device adopted by the invention of claim 2, the flowmeter main body whose base end side is attached to the intake pipe, the insulating substrate provided on the flowmeter main body, and the insulating substrate are provided on the insulating substrate. And a heating resistor that is cooled by intake air flowing in the intake pipe, and is formed on the insulating substrate and is formed in front of and behind the heating resistor in the flow direction of the inflowing air. The first and second temperature-sensitive resistors whose resistance values change in accordance with the flow direction of air, and the current value applied to the heating resistors are controlled to cause the heating resistors to generate heat and the insulating substrate. Of the first temperature sensitive resistor, a first flow rate detecting means for detecting a first flow rate signal by a change in the resistance value of the first temperature sensitive resistor, and a resistance of the second temperature sensitive resistor. Second flow for detecting the second flow signal by the change in value Subtraction for calculating a difference between the detection means and the first flow rate signal output from the first flow rate detection means and the second flow rate signal output from the second flow rate detection means to output the flow rate detection signal. It is composed of means.

According to a third aspect of the present invention, the insulating substrate includes a main substrate portion on which a free end is formed on the front end side and the heating resistor and the first and second temperature sensitive resistors are formed into a film, A sub-board portion located on the base end side of the main board portion and attached to the flowmeter main body, for separating the heating resistor from the flowmeter main body, and a position between the sub-board portion and the main board portion. A slit that extends from one side in the width direction of the insulating substrate to the other side and suppresses the heat from the heating resistor from being transferred to the sub-board portion. The purpose is to provide an auxiliary heater for heating.

[0022]

According to the first aspect of the present invention, the first and second temperature-sensitive resistors are provided on the insulating substrate so as to be spaced apart before and after the heating resistor with respect to the flow direction of the intake air. It forms the body. Then, the temperature control means controls the current value applied to the heating resistor to maintain the insulating substrate at a constant temperature.

In this state, for example, when a forward flow of intake air occurs in the intake pipe, the cooling amount of the first temperature-sensitive resistor located on the front side of the heating resistor is large and that of the first temperature-sensitive resistor located on the rear side is large. Since the temperature-sensitive resistor 2 is cooled by the air that has received heat from the heat-generating resistor, the cooling amount is small. Accordingly, for example, of the first flow rate signal output from the first flow rate detection means and the second flow rate signal output from the second flow rate detection means, for example, the first flow rate signal is the second flow rate signal. When the flow rate signal becomes larger than the flow rate signal, the flow rate signal is output as a flow rate addition signal by the adding means, and the flow direction detecting means compares the signals to output a flow direction signal indicating a forward flow. The signal output means outputs the flow rate addition signal as a flow rate detection signal.

On the other hand, when the flow of the intake air is in the opposite direction, for example, the second flow rate signal of each flow rate detecting means output from each flow rate detecting means becomes larger than the first flow rate signal. In this case, the flow rate signals are output as flow rate addition signals by the addition means, the flow direction detection means compares the signals, and a flow direction signal indicating a reverse flow is output, and the flow rate signal output means outputs the flow rate addition signals. The signal is inverted and output as a flow rate detection signal.

According to a second aspect of the present invention, the first and second temperature-sensitive resistors are provided on the insulating substrate, spaced apart before and after the heating resistor with respect to the flow direction of the intake air. It forms the body. Then, the temperature control means controls the current value applied to the heating resistor to maintain the insulating substrate at a constant temperature.

In this state, for example, when a forward flow of intake air is generated in the intake pipe, the cooling amount of the first temperature-sensitive resistor located on the front side of the heating resistor is large and that of the first temperature-sensitive resistor located on the rear side is large. Since the temperature-sensitive resistor 2 is cooled by the air that has received heat from the heat-generating resistor, the cooling amount is small. Accordingly, for example, of the first flow rate signal output from the first flow rate detection means and the second flow rate signal output from the second flow rate detection means, for example, the first flow rate signal is the second flow rate signal. When it becomes larger than the flow rate signal, the subtraction means subtracts the second flow rate signal from the first flow rate signal to output a positive flow rate detection signal.

On the other hand, when the flow of the intake air is in the opposite direction, for example, the second flow rate signal of each flow rate detecting means output from each flow rate detecting means becomes larger than the first flow rate signal. In this case, the subtracting means subtracts the second flow rate signal from the first flow rate signal to output a negative flow rate detection signal.

According to the third aspect of the invention, the auxiliary heater can be formed on the single insulating substrate together with the heating resistor, the first and second temperature sensitive resistors, and the number of parts can be reduced. Then, by forming a slit between the sub-substrate part on which the auxiliary heater is formed into a film and the main substrate part on which the heating resistor and the first and second temperature-sensitive resistors are formed into a film, for example, the heat-generating resistor is formed. It is possible to prevent heat from escaping from the main board part heated by the body to the sub board part, and to raise the temperature of the main board part early, and at the same time, the sub board part can be heated early by the auxiliary heater. The heat can be suppressed from escaping from the flowmeter to the main body.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 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 technique are designated by the same reference numerals, and the description thereof will be omitted.

First, the first embodiment of the present invention will be described with reference to FIGS.
An example of is shown.

In the figure, 21 is a thermal air flow rate detecting device according to the present embodiment, 22 is a flow meter main body which constitutes the main body of the thermal air flow rate detecting device 21, and the flow meter main body 22 is a conventional technique. Almost the same as the flowmeter body 3 described above, the winding portion 24 around which the reference resistors 23A and 23B having the resistance value R1 are wound.
A terminal portion 25 located at the base end side of the winding portion 24 and integrally provided with a plurality of terminal pins (not shown); and a radial direction of the intake pipe 2 from the tip end side of the winding portion 24. The detection holder 26 is extended and the circuit casing 27, which will be described later, is provided.

However, a slot (not shown) for detachably mounting an insulating substrate 29, which will be described later, is formed in the flowmeter main body 22 on the base end side of the detection holder 26, and the detection holder 26 is shown in FIG. As shown in the center of the intake pipe 2,
A heating resistor 31, 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 38, a differential amplifier, etc., which will be described later, mounted on an insulating substrate (not shown) made of, for example, a ceramic material. In this state, these are built in. 28A and 28B are the reference resistors 2
This is a terminal to which three windings are 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.

Here, as shown in FIG. 2, the insulating substrate 29 is located on the front end side and has a heating resistor 31 and first and first heating resistors 31 which will be described later.
The main substrate portion 29A on which the second temperature-sensitive resistors 32 and 33 are formed, and the base substrate portion 29A, which is located on the base end side and is attached to the detection holder 26, detects the heating resistor 31. While being separated from the holder 26, the auxiliary heater 34 includes a sub-substrate portion 29B having a film formed thereon.
The slit 30 is provided between 9B and the main board portion 29A from one side in the width direction toward the other side (the direction of the arrow A where the intake air flows).
Are formed.

Reference numeral 31 denotes a heat generating resistor forming a heat generating resistor formed on the main substrate portion 29A of the insulating substrate 29. The heat generating resistor 31 is provided on the main substrate portion 29A by means such as print printing or sputtering. By depositing a platinum film on the intermediate resistance portion 31A, which is formed to have a resistance value RH and extends in the width direction at the middle portion of the main substrate portion 29A in the length direction, and the middle resistance portion 31A. Extending in opposite directions in the longitudinal direction of the main board portion 29A from both ends of the first
It is composed of second extension resistance portions 31B and 31C.

Here, the intermediate resistance portion 31A and the extension resistance portions 31B and 31C of the heating resistor 31 are formed into a crank shape as a whole, so that the heating resistor 31 and a temperature-sensitive resistor described later are provided on the main board portion 29A. 32 and 33 are formed compactly, and the surface area (mounting area) of the heat generating resistor 31 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.

The current value of the heating resistor 31 is controlled by a current control transistor 42 described later,
The insulating substrate 29 is also kept at a constant temperature by heating so as to keep the temperature at a constant temperature (for example, about 240 ° C.).

Reference numerals 32 and 33 denote first and second temperature sensitive resistors formed on the main substrate portion 29A together with the heat generating resistor 31, and the first and second temperature sensitive resistors 32 and 33 are resistors. Value RT
1 and RT2, respectively, are formed by depositing a temperature sensitive material such as platinum on the insulating substrate by means such as print printing or sputtering, and flow in the intake pipe 2 in the direction of arrow A, for example. The heating resistor 31 is arranged on the main substrate portion 29A in front of and behind the heating resistor 31 in the flow direction of the intake air (width direction of the main substrate portion 29A).

Here, the first temperature-sensitive resistor 32 is located between the intermediate resistance portion 31A of the heating resistor 31 and the first extension resistance portion 31B, and is parallel to the extension resistance portion 31B. It is formed in a rectangular shape so as to extend. The second temperature sensitive resistor 33 is located between the intermediate resistance portion 31A and the second extension resistance portion 31C, and is formed in a rectangular shape so as to extend parallel to the extension resistance portion 31C. The temperature sensitive resistors 32 and 33 are formed on the main substrate portion 29A with a substantially uniform area, and are normally heated by applying a current from the battery voltage VB as shown in FIG. The temperature resistors 32 and 33 are cooled by the flowing air, so that the resistance value decreases and the flow rate of the air is detected with high sensitivity.

Further, the arrangement relationship among the heating resistor 31, the first temperature sensitive resistor 32, and the second temperature sensitive resistor 33 is as follows.
Since the first temperature-sensitive resistor 32, the heat-generating resistor 31, and the second temperature-sensitive resistor 33 are arranged in this order from the upstream side with respect to the forward flow of the intake air (direction indicated by the arrow A), the intake is performed. When the air flows in the forward direction indicated by the arrow A, the first temperature-sensitive resistor 3
2 is directly cooled by the intake air, and the second temperature sensitive resistor 33 receives heat from the heat generating resistor 31. As a result, the resistance value RT1 of the first temperature-sensitive resistor 32 becomes smaller according to the flow rate, and the resistance value R1 of the second temperature-sensitive resistor 33 becomes smaller.
T2 remains virtually unchanged.

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 33 is directly cooled by the intake air, and the first sensation is obtained. The temperature resistor 32 receives the heat from the heating resistor 31. As a result, the resistance value RT2 of the second temperature sensitive resistor 33 becomes smaller in accordance with the flow rate, and the resistance value RT1 of the first temperature sensitive resistor 32 does not substantially change.

As a result, by comparing the resistance value RT1 of the first temperature sensitive resistor 32 and the resistance value RT2 of the second temperature sensitive resistor 33, whether the flow direction of the intake air is the forward direction, It is possible to determine whether it is in the opposite direction.

Reference numeral 34 denotes an auxiliary heater, and the auxiliary heater 3
Reference numeral 4 is located on the sub-board portion 29B of the insulating substrate 29, and like the above-mentioned heating resistor 31, temperature-sensitive resistors 32 and 33, the temperature-sensitivity of platinum or the like is obtained by means such as print printing or sputtering. The material is formed into a film having a resistance value RHS. Further, the auxiliary heater 34 heats the sub-substrate portion 29B of the insulating substrate 29, so that the main substrate portion 29A
The heat from the (heating resistor 31) is prevented from escaping to the detection holder 26 via the sub-board portion 29B. Further, since the slit 30 is formed between the main substrate portion 29A and the sub substrate portion 29B, the auxiliary heater 34
It prevents the first temperature sensitive resistor 32 from being heated by the heat from the first and second temperature sensitive resistors 3 at the time of detection.
The heat from the auxiliary heater 34 is prevented from being applied to 2, 33. On the other hand, since the auxiliary heater 34 is connected between the emitter of the current control transistor 42 and the ground via the resistor 43, the applied current is controlled by the current control of the current control transistor 42.

Reference numerals 35, 35, ... Depict, for example, six electrodes formed on the base end side of the insulating substrate 29. The electrodes 35 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 electrodes 35.
The first, the first and the second temperature sensitive resistors 32 and 33, the auxiliary heater 34 and the like are connected to respective electronic components provided in the circuit casing 27 to form a processing circuit for flow rate detection shown in FIG. There is.

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

In FIG. 3, reference numeral 36 is a temperature control means for maintaining the temperature of the insulating substrate 29 at a constant temperature by controlling the current value applied to the heating resistor 31 to keep the temperature of the heating resistor 31 constant. The current control circuit 36 includes a heating resistor 31, a temperature compensation resistor 3
Bridge circuit 40 including 7 and adjusting resistors 38 and 39
A differential amplifier circuit 41 that outputs a difference from the connection points c and d of the bridge circuit 40, and a current control transistor 42 that controls a current value applied to the connection points a and b of the bridge circuit 40. The bridge circuit 40 is configured so that the products of the resistance values of the opposite sides are equal, and the connection point a between the heating resistor 31 and the temperature compensating resistor 37 is connected to the emitter side of the current control transistor 42 and the auxiliary side. It is connected to one end of the heater 34, and the connection point b with the adjusting resistors 38 and 39 is connected to the other end of the auxiliary heater 34 via the ground and the resistor 43.

On the other hand, in the bridge circuit 40,
The heating resistor 31 and the adjusting resistor 38 are connected in series, and the temperature compensating resistor 37 and the adjusting resistor 39 are connected in series, and their connection points c and d are connected to the input terminal of the differential amplifier circuit 41.

Here, the temperature compensation resistor 37 is provided in the detection holder 26 in the vicinity of the heating resistor 31.
Moreover, the temperature compensating resistor 37 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 40 thus constructed, the output from the differential amplifier circuit 41 becomes zero when the bridge circuit 40 is in a balanced state. On the other hand, when the balance of the bridge circuit 40 is lost, that is, when the insulating substrate 29 is cooled by the intake air and the temperature of the heating resistor 31 is lowered accordingly, the resistance value R of the heating resistor 31 is reduced.
Since H is small, a voltage difference is generated between the connection points c and d, and the current control voltage Va is output from the differential amplifier circuit 41 toward the base of the current control transistor 42. As a result, the current control transistor 42 controls the current applied to the bridge circuit 40 to bring the cooled heating resistor 31 to a constant temperature and returns the bridge circuit 40 to the equilibrium state. At this time, the insulating substrate 29 can also return to a constant temperature.

Here, the current control transistor 42
Has a collector side connected to the battery voltage VB, a base side connected to the output side of the differential amplifier circuit 41, and an emitter side connected to the connection point a of the bridge circuit 40 and one end of the auxiliary heater 34. The current control transistor 42 controls the emitter current in response to the base current changing by the output (current control voltage Va) from the differential amplifier circuit 41. As a result, the current control transistor 42 controls the current value applied to the bridge circuit 40 to perform feedback control for keeping the temperature of the heating resistor 31 (insulating substrate 29) at a constant temperature.

Next, reference numeral 44 denotes a detection processing circuit located on the lower side in FIG. 3, and the detection processing circuit 44 is a first processing described later.
Flow rate detection circuit 45, second flow rate detection circuit 46, addition circuit 47, comparison circuit 48, inversion circuit 49 and selection circuit 5
0, and the detection processing circuit 44 includes a first and a second
The flow and direction of intake air are detected based on changes in resistance values RT1 and RT2 of the temperature sensitive resistors 32 and 33.

Reference numeral 45 denotes a first flow rate detecting circuit as a first flow rate detecting means. The first flow rate detecting circuit 45 detects the resistance value R1 from the first temperature-sensitive resistor 32 having a resistance value RT1. The flow rate detection circuit 45 is connected between the battery voltage VB and the ground, and the heating resistor 31 and the reference resistor 2 are connected in series.
The connection point e with 3A is the addition circuit 47 and the comparison circuit 4 which will be described later.
8 is connected. In addition, the first flow rate detection circuit 45
Outputs the change in the resistance value RT1 of the first temperature sensitive resistor 32 as the first flow rate voltage V1.

Reference numeral 46 denotes a second flow rate detecting circuit as a second flow rate detecting means. The second flow rate detecting circuit 46 is constructed in substantially the same manner as the first flow rate detecting circuit 45 and has a resistance value RT2. And a reference resistor 23B having a resistance value R1 are connected in series. The flow rate detecting circuit 46 is connected between the battery voltage VB and the ground. Temperature resistor 33 and reference resistor 23
The connection point e with A is connected to the adder circuit 47 and the comparison circuit 48. In addition, the second flow rate detection circuit 46 changes the resistance value RT2 of the second temperature sensitive resistor 33 to the second flow rate voltage V.
Output as 2.

Reference numeral 47 denotes an adding circuit as an adding means,
The input side of the adding circuit 47 is connected to the connection point e of the first flow rate detecting circuit 45 and the connection point f of the second flow rate detecting circuit 46, and the inverting circuit 49 and the selecting circuit 50 are connected to the output side. ing. The flow rate addition voltage V3 as the flow rate addition signal output from the adder circuit 47 is given by the following expression 1.

[0056]

[Equation 1] V3 = V1 + V2

Reference numeral 48 denotes a comparison circuit as a flow direction detecting means, and a connection point e of the first flow rate detection circuit 45 and a connection point f of the second flow rate detection circuit 46 are provided on the input side of the comparison circuit 48.
And are connected, and the selection circuit 50 is connected to the output side. Then, the comparison circuit 48 compares the first flow rate voltage V1 and the second flow rate voltage V2. When V1> V2, the flow of the intake air is in the forward direction. Therefore, the voltage value V shown in FIG.
The direction detection voltage Vb of 0 is output, and when V1 <V2, the flow of the intake air is in the opposite direction, so the direction detection voltage Vb of zero voltage value is output to the selection circuit 50.

Reference numeral 49 denotes an inverting circuit connected between the adding circuit 47 and the selecting circuit 50. The inverting circuit 49 inverts the flow rate adding voltage V3 output from the adding circuit 47 and inverts the flow rate adding voltage V3 '. To the selection circuit 50.

Reference numeral 50 indicates a selection circuit which constitutes the flow rate signal output means together with the inverting circuit 49. The selection circuit 50 is, for example, forward based on the direction detection voltage Vb (see FIG. 4) output through the comparison circuit 48. In case of direction, adder circuit 47
From the output terminal to the control unit (not shown) as the output signal Vout, and in the case of the reverse direction, the inverted flow rate addition voltage V3 from the inversion circuit 49.
′ Is output from the output terminal to the control unit as the output signal Vout.

Thermal air flow rate detection device 21 according to the present embodiment
Has a configuration as described above. Next, the detection processing circuit 4
The operation of detecting the flow rate of the intake air in No. 4 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 32 located on the upstream side of the insulating substrate 29 is caused by the flow of the intake air. The second temperature-sensitive resistor 33, which is cooled and positioned on the downstream side, receives heat from the heating resistor 31. As a result, the first flow rate voltage V1 output from the first flow rate detection circuit 45 is
It becomes larger than the second flow rate voltage V2 output from the second flow rate detection circuit 46, and the voltage value V0 from the comparison circuit 48.
The direction detection voltage Vb in the forward direction is output to the selection circuit 50.

The adder circuit 47 adds the input flow rate voltages V1 and V2 and outputs the result as a flow rate addition voltage V3 to the selection circuit 50 and the inverting circuit 49 in the subsequent stage, and the inverting circuit 49 inverts the inverted flow rate addition. The voltage V3 'is output to the selection circuit 50.

Here, in the selection circuit 50, the comparison circuit 48
The flow rate addition voltage V3 output from the adder circuit 47 and the inverted flow rate addition voltage V3 'output from the inversion circuit 49 are selected based on the direction detection voltage Vb from the direction detection voltage Vb. Since the signal has a voltage value V0 and indicates a forward flow, the flow rate addition voltage V3 is selected and the flow rate addition voltage V3, which becomes the forward flow, is output from the output terminal to the control unit as the output signal Vout.

On the other hand, when the air flow is in the direction of arrow B (reverse direction), the second temperature-sensitive resistor 33 located on the insulating substrate 29 on the upstream side with respect to this flow of the air. The first temperature-sensitive resistor 32, which is cooled by the flow and is located on the downstream side, receives heat from the heating resistor 31. As a result, the second flow rate voltage V output from the second flow rate detection circuit 46.
2 becomes larger than the first flow rate voltage V1 output from the first flow rate detection circuit 45, and the comparison circuit 48 outputs the reverse direction detection voltage Vb having a voltage value of zero to the selection circuit 50.

Further, in the adding circuit 47, the flow rate adding voltage V3
To the selecting circuit 50 and the inverting circuit 49, and the inverting circuit 49 outputs the inverted inverting flow rate addition voltage V3 'to the selecting circuit 50.

Further, in the selection circuit 50, the comparison circuit 48
The flow rate addition voltage V3 output from the adder circuit 47 and the inverted flow rate addition voltage V3 'output from the inversion circuit 49 are selected based on the direction detection voltage Vb from the direction detection voltage Vb. Since it is a signal indicating a reverse flow having a voltage value of zero, the reverse flow summing voltage V3 'is selected and the flow summing voltage V3, which becomes a reverse flow from the output terminal to the control unit, is output as the output signal Vout. To do.

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

Next, the current control circuit 36 for keeping the temperature of the insulating substrate 29 at a constant temperature will be described.

When the heating resistor 31 (insulating substrate 29) is cooled by the intake air, a difference occurs between the connection points c and d, and this difference is generated in the differential amplifier circuit 41 by the current control voltage V.
Detected as a. Then, the emitter current of the current control transistor 42 is controlled by the current control voltage Va output from the differential amplifier circuit 41 to generate the heating resistor 3
The heating resistor 31 (insulating substrate 29) can be maintained at a constant temperature by increasing the current applied to the heating resistor 31.

As a result, since the temperature of the insulating substrate 29 is constantly set to a constant temperature, the flow rate detection in the temperature sensitive resistors 32 and 33 can be accurately performed, and the intake air flow rate can be detected with higher accuracy. Can be done.

Further, since the current control circuit 36 is provided independently of the detection processing circuit 44 for detecting the flow rate and the flow direction, the heating resistor 31 has a constant temperature up to a certain temperature such as when the engine of the automobile is started. Even when the temperature has not risen, the first and second temperature-sensitive resistors 32 and 33 are the same as the heating resistor 3.
Since it is heated simultaneously by 1, it is possible to prevent a large error from occurring even before the insulating substrate 29 reaches a constant temperature. Further, the heat type air flow rate detection device 21 according to the present invention can significantly shorten the heat-up time as compared with the case of the thermal type air flow rate detection device that detects the flow rate by utilizing the resistance value change of the heating resistor 31. Therefore, it is possible to reliably prevent erroneous control of the A / F control when the engine is started.

Thus, in the thermal type air flow rate detecting device 21 according to the present embodiment, the heating resistor 31 is formed on the insulating substrate 29, and the first and second sensations are provided before and after the heating resistor 31. Since the temperature resistors 32 and 33 are formed, the number of parts can be reduced, and the first and second temperature sensitive resistors 32 and 33 can detect the air flow direction and flow rate.

In the detection processing circuit 44, the first
The flow rate detection circuit 45 detects the change in the resistance value RT1 according to the flow rate of the first temperature sensitive resistor 32 as the first flow rate voltage V1, and the second flow rate detection circuit 46 detects the second temperature sensitive resistor. Three
The change of the resistance value RT2 according to the flow rate of 3 is changed to the second flow rate voltage V
Detect as 2. Further, the adder circuit 47 adds the flow rate voltages V1 and V2 and outputs the result as a flow rate added voltage V3 to the selection circuit 50 and the inversion circuit 49, and the inversion circuit 49.
Then, input the flow rate addition voltage V3 to the inverted flow rate addition voltage V
It is output to the selection circuit 50 as 3 '. On the other hand, the comparison circuit 4
In step 8, the magnitudes of the first and second flow rate voltages V1 and V2 are compared, and the forward or reverse direction detection voltage Vb is output to the selection circuit 50. Then, in the selection circuit 50, when the flow of the intake air is in the positive direction based on the direction detection voltage Vb, the flow rate addition voltage 3 from the addition circuit 47 is selected and output from the output terminal as the output signal Vout to the control unit. On the other hand, when the flow of the intake air is in the reverse direction, the reverse flow rate addition voltage V3 'from the reverse circuit 49 can be output to the control unit as the output signal Vout.

As described above, it is possible to prevent the flow rate in the reverse direction from being detected as a positive flow rate as in the prior art, and it is possible to accurately detect the flow rate and the flow direction of the intake air.

Further, in the current control circuit 36 for keeping the temperature of the insulating substrate 29 constant, the current control circuit 36 is constituted by the bridge circuit 40 including the heating resistor 31, the differential amplifier circuit 41 and the current control transistor 42. Therefore, when the temperature of the insulating substrate 29 decreases, the heating resistor 3
1 also decreases, and this decrease is output as a current control voltage Va from the differential amplifier circuit 41 as a difference with the temperature compensation resistor 37, and is applied to the bridge circuit 40 by the current control transistor 42 according to the current control voltage Va. The current value to be applied can be adjusted, and the insulating substrate (heating resistor 31) can always be maintained at a constant temperature. And the above-mentioned first,
The flow rate detected by the second flow rate detection circuits 45 and 46 can be detected more accurately.

Further, the current control circuit 36 includes the first and second temperature sensitive resistors 32 even when the heat generating resistor 31 has not reached a certain temperature such as when the engine of the automobile is started. , 33, the detection is performed, but the insulating substrate 29
Since the upper heating resistor 31 and the temperature-sensitive resistors 32 and 33 are heated almost at the same time, they are detected by the first and second temperature-sensitive resistors 32 and 33 even before the insulating substrate 29 reaches a constant temperature. It is possible to prevent a large error from occurring in the flow rate voltages V1 and V2. As a result, the thermal air flow rate detection device 21 according to the present embodiment can shorten the heat-up time until the start of accurate flow rate detection.

Furthermore, the auxiliary heater 34 is attached to the insulating substrate 2
It is formed on the sub-board portion 29B of No. 9 and the sub-heater portion 29B of the insulating substrate 29 is heated by the auxiliary heater 34. Therefore, it is possible to assist the heating resistor 31 to heat the insulating substrate 29. As a result, the heat of the main substrate 29A can be prevented from escaping to the flowmeter main body 22 via the sub-substrate 29B, the temperature change of the insulating substrate 29 can be reduced, and the detection sensitivity of the flow rate and the flow direction can be reduced. Can be improved.

Further, a slit 30 is formed between the main substrate portion 29A and the sub-substrate portion 29B of the insulating substrate 29, and the slit 30 affects the heat of the auxiliary heater 34 on the first temperature sensitive resistor 32. Since it is formed so as not to affect the thermal influence of the auxiliary heater 34 on the first temperature-sensitive resistor 32, it is possible to effectively prevent the flow rate of the intake air from changing to the first and second flow rate detecting circuits 45. , 46 can be accurately detected.

Next, FIG. 5 and FIG. 6 show a second embodiment of the present invention.
This embodiment is characterized in that the heating resistor, the first and second temperature sensitive resistors, the auxiliary heater and the temperature compensating resistor are formed on the single insulating substrate as a film, and suction is performed. This is because a subtraction circuit was used as a detection circuit for detecting the flow rate and the flow direction of air. The same components as those in the first embodiment described above are designated by the same reference numerals, and the 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 made of an insulating material such as glass, alumina, aluminum nitride or the like into a rectangular flat plate shape, and the base end side is attached to the detection holder 26. The first and second substrate parts 51 having fixed ends and free ends on the tip side.
A and 51B, the first and second substrate portions 51A,
A first slit 52 extending from the front end side toward the base end side is formed between 51B. The second substrate portion 51B is located upstream of the first substrate portion 51A with respect to the flow of intake air in the forward direction (arrow A direction), and will be described later on the second substrate portion 51B. The temperature compensation resistor 58 is formed.

The first board portion 51A has a rectangular main board portion 51A1 with the free end side at the tip side.
And a sub-board portion 51A2 which is located on the base end side of the main board portion 51A1 and is attached to the detection holder 26,
A second slit 53 is formed between the sub-substrate portion 51A2 and the main substrate portion 51A1 so as to communicate with the first slit 52 from one side in the width direction toward the other side (direction of arrow A). . In addition, the first slit 52 and the second slit 5
It is not always necessary to communicate with 3 as shown in FIG.

Reference numeral 54 denotes a heating resistor, which is a heating resistor 5.
4 has a temperature sensitive material such as platinum deposited on the main substrate portion 51A1 of the insulating substrate 51 by means such as print printing or sputtering so as to have a resistance value RH;
Similar to the heating resistor 31 according to the first embodiment, the intermediate resistor portion 54A and the first and second portions extending in opposite directions in the length direction of the insulating substrate 51 from both end sides of the intermediate resistor portion 54A.
In the same manner as the heating resistor 31 described above, by controlling the current value by the current control transistor 42 described in the first embodiment, a constant temperature (for example, about 240 ° C.) is formed. ) With heat.

Reference numerals 55 and 56 denote first and second temperature sensitive resistors, and the first and second temperature sensitive resistors 55 and 56 have resistance values RT.
A temperature sensitive material such as platinum is deposited on the main substrate portion 51A1 of the insulating substrate 51 by means such as print printing or sputtering so as to have 1 and RT2 respectively. The first temperature-sensitive resistor 55 includes a first extension resistor portion 54B and an intermediate resistor portion 54A of the heating resistor 54.
Is formed so as to be parallel to the extension resistance portion 54B, and the second temperature-sensitive resistor 56 includes the second extension resistance portion 54C of the heating resistor 54 and an intermediate resistance portion. 54
It is located between A and A, and is formed so as to be parallel to the second extension resistance portion 54C. Further, with respect to the heating resistor 54, the first temperature-sensitive resistor 55 is located on the upstream side with respect to the forward flow of the intake air (the direction of arrow A), and the second temperature-sensitive resistor 56 is It is located on the downstream side.

Reference numeral 57 denotes an auxiliary heater, which is the auxiliary heater 5.
7 is located on the sub-board portion 51A2 of the insulating substrate 51 and is printed with a temperature-sensitive material such as platinum like the heating resistor 54 and the first and second temperature-sensitive resistors 55 and 56 described above. It is formed into a film having a resistance value RHS by means such as printing or sputtering. Further, the auxiliary heater 57 is the insulating substrate 5
By heating the first sub-board portion 51A2, the heat from the main board portion 51A1 (heating resistor 54) is transferred to the sub-board portion 51A.
2 is prevented from escaping to the detection holder 26.
Further, since the slit 53 is formed between the main board portion 51A1 and the sub-board portion 51A2, the first temperature-sensitive resistor 55 is prevented from being heated by the heat from the auxiliary heater 57. .

Reference numeral 58 represents a temperature compensating resistor as a temperature compensating resistor, and the temperature compensating resistor 58 is the second substrate portion 5.
1B, and is formed by depositing a platinum film using a means such as print printing or sputtering. The temperature compensating resistor 58 has a resistance value RK larger than that of the heat generating resistor 54, and is not affected by the flow of intake air, and detects only the temperature change.

Denote 59, 59, ..., For example, seven electrodes formed at the base end side of the insulating substrate 51. The electrodes 59 are arranged in a row in the width direction of the insulating substrate 51 at a predetermined interval. 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 mounting the insulating substrate 51 in the second embodiment on the flowmeter main body 22 according to the above-described first embodiment, the processing circuit for detecting the flow rate according to the above-described first embodiment can be substantially constructed. Similarly, a current control circuit 36 and a detection processing circuit 60 according to the present embodiment are configured as shown in FIG.

Here, the current control circuit 36 is connected to the first
Since it is as described in the embodiment, the description of the operation is omitted.

Reference numeral 60 represents a detection processing circuit according to the present embodiment. The detection processing circuit 60 includes the first flow rate detection circuit 45,
The second flow rate detection circuit 46 and the differential amplifier circuit 6 described later.
1 and 1.

Here, reference numeral 61 denotes a differential amplifier circuit as a subtracting means, and the input side of the differential amplifier circuit 61 has the first and first terminals.
The connection points e and f of the second flow rate detection circuits 45 and 46 are connected, and a control unit (not shown) is connected to the output side. Then, the differential amplifier circuit 61 is configured to perform an operation such as the following Expression 2 and output an output signal Vout.

[0091]

[Formula 2] Vout = (V1−V2) × k where k is a constant

In this way, by calculating the difference between the first and second flow rate voltages V1 and V2 in the differential amplifier circuit 61, the output signal Vout is output as a signal including the flow rate and the flow direction of the intake air. can do.

Also in the thermal type flow rate detecting device of the present embodiment constructed as described above, the flow rate and the flow direction of the intake air can be detected and the insulating substrate 29 of the insulating substrate 29 can be detected similarly to the first embodiment. By separately providing the current control circuit 36 for holding the temperature at a constant temperature and the detection processing circuit 60, it is possible to shorten the heat-up time until the accurate flow rate detection is started when the engine of the automobile is started. .

In each of the above embodiments, the heating resistor 31 and the first and second temperature sensitive resistors 32 and 33 formed on the insulating substrate 29 are formed as shown in FIG. Not limited to this, as in the modified example shown in FIG. 7, slits 72 and 73 extending from the tip side to the base end side of the insulating substrate 71 are formed, and the insulating substrate 71 is moved to the first side by the slits 72 and 73. , The second and third board portions 71A, 71B, 71C, and the first, second and third board portions 71A, 71B, 71
The heating resistor 74, the first temperature-sensitive resistor 75, and
The second temperature sensitive resistor 76 may be formed as a film. In this case, it is desirable that the first board portion 71A has a relatively large surface area as compared with the other board portions 71B and 71C. Further, in the case of this modification, the slit 7
Since the resistors 74, 75, and 76 are divided by 2, 73, it is possible to reduce the influence of the heat of the heating resistor 74 on the temperature-sensitive resistors 75 and 76 via the insulating substrate 71. Furthermore, the temperature compensating resistor 37 as indicated by the chain double-dashed line may be integrally formed.

Further, in the above embodiment, the first temperature sensitive resistor 32 (55) is provided on the upstream side with respect to the flow direction of the intake air.
Although the second temperature sensitive resistor 33 (56) is provided on the downstream side, the present invention is not limited to this, and the first temperature sensitive resistor 32 is provided.
(55) may be positioned on the downstream side and the second temperature sensitive resistor 33 (56) may be positioned on the upstream side. In this case, the direction detection voltage Vb from the comparison circuit 48 is inverted and output to the selection circuit 50. do it.

Further, in each of the above embodiments, the flowmeter main body 2
Although it has been described that the reference resistance 23 wound around the second winding portion 24 is provided so as to project into the intake pipe 2, the present invention is not limited to this. For example, the reference resistance 23 is provided 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 38 and the like.

Further, in each of the above embodiments, the auxiliary heater 3
Although it has been described that the auxiliary heaters 34 and 57 are provided, the present invention can be used without the auxiliary heaters 34 and 57.

[0098]

According to the invention of claim 1, on the insulating substrate, the first and second sensing elements are spaced apart in front of and behind the heating resistor with respect to the flow direction of the intake air. A temperature resistor is formed, and the current value applied to the heating resistor is controlled by the temperature control means to keep the insulating substrate at a constant temperature. When it occurs, the cooling amount of the first temperature-sensitive resistor located on the front side of the heating resistor is large, and the second temperature-sensitive resistor located on the rear side is cooled by the air receiving heat from the heating resistor. Therefore, the cooling amount becomes small. Accordingly, for example, of the first flow rate signal output from the first flow rate detection means and the second flow rate signal output from the second flow rate detection means, for example, the first flow rate signal is the second flow rate signal. When the flow rate signal becomes larger than the flow rate signal, the flow rate signal is output as a flow rate addition signal by the adding means, and the flow direction detecting means compares the signals to output a flow direction signal indicating a forward flow. The signal output means can output the flow direction and the flow rate by using the flow rate addition signal as the flow rate detection signal.

On the other hand, when the flow of the intake air is in the opposite direction, for example, the second flow rate signal among the flow rate detecting means output from each flow rate detecting means becomes larger than the first flow rate signal. In this case, the flow rate signals are output as flow rate addition signals by the addition means, the flow direction detection means compares the signals, and a flow direction signal indicating a reverse flow is output, and the flow rate signal output means outputs the flow rate addition signals. It is possible to invert the signal and output the flow direction and the flow rate as a flow rate detection signal. Therefore, the control unit can accurately perform the air-fuel ratio control based on the flow rate addition signal and improve the engine performance.

According to the second aspect of the present invention, the first and second temperature-sensitive resistors are provided on the insulating substrate, spaced apart before and after the heating resistor with respect to the flow direction of the intake air. By forming a body and controlling the current value applied to the heating resistor by the temperature control means to keep the insulating substrate at a constant temperature, for example, a forward flow of intake air occurs in the intake pipe. In this case, the cooling amount of the first temperature-sensitive resistor located on the front side of the heating resistor is large, and the second temperature-sensitive resistor located on the rear side is cooled by the air receiving heat from the heating resistor. Therefore, the cooling amount becomes small. This allows
Of the respective signals of the first flow rate signal output from the first flow rate detection means and the second flow rate signal output from the second flow rate detection means, for example, the first flow rate signal is greater than the second flow rate signal. When becomes larger, the subtraction means subtracts the second flow rate signal from the first flow rate signal to output the flow direction and the flow rate as a positive flow rate detection signal.

On the other hand, when the flow of the intake air is in the opposite direction, for example, the second flow rate signal of each flow rate detecting means output from each flow rate detecting means becomes larger than the first flow rate signal. In this case, by subtracting the second flow rate signal from the first flow rate signal by the subtracting means, the flow direction and the flow rate can be output as the negative flow rate detection signal.

According to the third aspect of the invention, the auxiliary heater can be formed on the single insulating substrate together with the heating resistor, the first and second temperature sensitive resistors, and the number of parts can be reduced. Then, by forming a slit between the sub-substrate part on which the auxiliary heater is formed into a film and the main substrate part on which the heating resistor and the first and second temperature-sensitive resistors are formed into a film, for example, the heat-generating resistor is formed. It is possible to prevent heat from escaping from the main board part heated by the body to the sub board part, and to raise the temperature of the main board part early, and at the same time, the sub board part can be heated early by the auxiliary heater. The heat can be suppressed from escaping from the flowmeter to the main body. Then, the heat-up performance at the engine start can be improved, and the flow rate detection accuracy and responsiveness at the engine start can be improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a state in which a thermal air flow rate detection device according to a first embodiment is attached to an intake pipe.

FIG. 2 is a plan view showing a heating resistor, first and second temperature-sensitive resistors and an auxiliary heater 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 a first embodiment.

FIG. 4 is a characteristic diagram showing a relationship between a flow velocity of intake air and a direction detection voltage Vb.

FIG. 5 is a plan view showing a heating resistor, first and second temperature sensitive resistors, an auxiliary heater and a temperature compensation resistor formed on an insulating substrate according to a second embodiment.

FIG. 6 is a circuit diagram showing a circuit configuration of a thermal type air flow rate detecting device according to a second embodiment.

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

FIG. 8 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. 9 is a perspective view showing a flowmeter main body, a heat generation resistance and the like according to a conventional technique.

[Explanation of symbols]

 21 Thermal Air Flow Rate Detection Device 22 Flowmeter Main Body 23A, 23B Reference Resistance 29, 51, 71 Insulating Substrate 29A, 51A1 Main Substrate 29B, 51A2 Sub Substrate 30, 52, 53 Slit 31, 54, 74 Heating Resistor 32 , 55, 75 First temperature sensitive resistor 33, 56, 76 Second temperature sensitive resistor 34, 57 Auxiliary heater 36 Current control circuit (temperature control means) 40 Bridge circuit 41 Differential amplifier circuit 42 Current control transistor 44, 60 Detection processing circuit 45 First flow rate detection circuit (first flow rate detection means) 46 Second flow rate detection circuit (second flow rate detection means) 47 Addition circuit (addition means) 48 Comparison circuit 49 Inversion circuit 50 Selection circuit (flow rate signal output means) 61 Differential amplifier circuit (subtraction means)

Claims (3)

[Claims] 1. A flowmeter main body having a base end side attached to an intake pipe, an insulating substrate provided on the flowmeter main body, and heat generated by being cooled by intake air flowing through the intake pipe provided on the insulating substrate. A resistor and a resistor located on the insulating substrate and spaced apart from the heating resistor in the flow direction of the inflowing air. The resistance values of the resistors change according to the flow direction of the intake air. First and second temperature sensitive resistors,
A temperature control means for controlling a current value applied to the heat generating resistor to heat the heat generating resistor to keep the insulating substrate at a constant temperature; and a first temperature varying means for changing the resistance value of the first temperature sensitive resistor. Flow rate signal detecting means for detecting the flow rate signal of the second temperature sensing element, second flow rate detecting means for detecting the second flow rate signal based on a change in the resistance value of the second temperature sensitive resistor, and the first flow rate detecting means. Output from the first flow rate detection means, and addition means for adding a first flow rate signal output from the second flow rate detection means and a second flow rate signal output from the second flow rate detection means to output a flow rate addition signal. Flow direction detecting means for comparing the first flow rate signal and the second flow rate signal output from the second flow rate detecting means to output a flow direction signal, and a flow direction output from the flow direction detecting means When we detect that the signal is a forward flow signal The flow rate addition signal output from the adding means is output as a flow rate detection signal, and when it is detected as a flow signal in the opposite direction, a signal obtained by inverting the flow rate addition signal output from the adding means is output as a flow rate detection signal. And a thermal air flow rate detection device comprising: 2. A flowmeter main body whose base side is attached to an intake pipe, an insulating substrate provided on the flowmeter main body, and heat generated by being cooled by intake air flowing through the intake pipe provided on the insulating substrate. A resistor and a resistor located on the insulating substrate and spaced apart from the heating resistor in the flow direction of the inflowing air. The resistance values of the resistors change according to the flow direction of the intake air. First and second temperature sensitive resistors,
A temperature control means for controlling a current value applied to the heat generating resistor to heat the heat generating resistor to keep the insulating substrate at a constant temperature; and a first temperature varying means for changing the resistance value of the first temperature sensitive resistor. Flow rate signal detecting means for detecting the flow rate signal of the second temperature sensing element, second flow rate detecting means for detecting the second flow rate signal based on a change in the resistance value of the second temperature sensitive resistor, and the first flow rate detecting means. From the first flow rate signal output from the second flow rate detecting means and the second flow rate signal output from the second flow rate detecting means, and the subtracting means outputting the flow rate detecting signal. Detection device. 3. The insulating substrate has a main substrate portion on which a front end side is a free end and the heating resistor and the first and second temperature-sensitive resistors are formed into a film, and a base of the main substrate portion. A sub-board portion located at an end side and attached to the flowmeter main body, for separating the heating resistor from the flowmeter main body, and located between the sub-board portion and the main board portion. An auxiliary heater that extends from one side in the width direction to the other side and that suppresses the heat from the heating resistor from being transferred to the sub-board section, and the sub-board section heats the sub-board section. The thermal air flow rate detecting device according to claim 1 or 2, further comprising: