JPH07333027A - Thermal air flowmeter - Google Patents

Abstract

PURPOSE:To improve the sensitivity by measuring the direction of flowing and the flow rate of sucked air accurately to prevent erroneous detection caused by changes in flow in the normal and opposite directions. CONSTITUTION:A bridge circuit 34 is constituted of a heating resistor 30, a temperature compensating resistor 35 and resistor 36 and 23 and a change in resistance value of the heating resistor 30 when cooled is outputted to an inverting circuit 44 as flow rate detection voltage Va based on the flow rate of sucked air. On the other hand, second thermosensitive resistors 31 and 32 are provided before and after the heating resistor 30 to form a bridge circuit 39 being combined with resistors 40 and 41 and changes in resistance values of the resistors 31 and 32 are outputted to the inverting circuit 44 through a sample holding circuit 43 as the direction of flow detection voltage Vb based on the flow rate of the sucked air from a comparator circuit 42. Then, the flow rate detection voltage Va is inverted by the inverting circuit 44 when the flow is opposite in direction to obtain an output voltage V0 indicating the direction of flow and the flow rate.

Description

Detailed Description of the Invention

[0001]

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

[0002]

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

Therefore, FIGS. 7 to 9 show a conventional thermal air flow rate detecting device.

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

Reference numeral 3 denotes a flow meter main body which constitutes the main body of the thermal type 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. Note that in FIG. 7, in order to clearly show the heating resistor 9 and the temperature compensating resistor 11, the protective cover 13 is shown in a state of being removed from the detection holder 6.

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

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

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

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

[0015]

By the way, in the above-mentioned prior art, the fact that the heating resistor 9 is cooled by the flow of the intake air flowing through the intake pipe 2 is utilized to change the resistance value of the heating resistor 9. Since the intake air flow rate is detected based on this, the heat generating resistor 9 is cooled by the intake air flow flowing in the direction A (forward direction) shown in FIG. 7 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 the arrow, the flow velocity of the air flowing in the intake pipe 2 repeatedly pulsates as shown in FIG. 9 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. The present invention can prevent erroneous detection of the intake air flow rate due to the air flow in the opposite direction, and can greatly improve the flow rate detection accuracy. An object of the present invention is to provide a thermal type air flow rate detection device in which a detection signal is linear with respect to a flow rate.

[0019]

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

A feature of the invention of claim 1 is that a bridge circuit is formed by including the heating resistor, and a change in the resistance value of the heating resistor forming the bridge circuit corresponds to a flow rate detection signal. And the flow rate detecting means for outputting as the heat generating resistor, and the first and second resistors which are provided before and after the heat generating resistor and whose resistance value changes in the flow direction of the intake air.
And a flow direction detection means for detecting as a flow direction detection signal corresponding to the flow direction of the intake air based on the resistance values of the first and second temperature resistances, and the flow from the flow direction detection means. When the flow rate of the intake air is in the opposite direction based on the sample hold signal from the sample hold means, the sample hold means uses the flow rate detection signal output from the flow rate detection means as the sample hold signal based on the direction detection signal. Only, the signal inverting means for inverting the flow rate detection signal output from the flow rate detecting means is provided.

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

[0022]

With the above structure, in the first aspect of the invention, the flow rate detecting means forms the bridge circuit including the heat generating resistance, and the flow rate detecting means corresponds to the flow rate based on the change in the resistance value of the heat generating resistance in the bridge circuit. The signal is taken out, and the flow direction detecting means outputs the flow direction of the intake air as a flow direction detection signal from the change in the resistance value of the first and second temperature-sensitive resistors. The sample hold means outputs the flow rate detection signal output from the flow rate detection means as a sample hold signal based on the flow direction detection signal from the flow direction detection means, and the signal inversion means outputs the flow rate detection signal from the sample hold means. By inverting the flow rate detection signal output from the flow rate detecting means based on the sample hold signal, the signal from the signal inverting means can be a signal indicating the flow rate and the flow direction of the intake air flow rate.

Further, in the second aspect of the invention, the first and second temperature sensitive resistors formed on the insulating substrate are separated from each other before and after the heat generating resistor with respect to the flow direction of the intake air. Since the resistance value changes depending on the flow direction of air, when the resistance value of the first temperature-sensitive resistor is smaller than that of the second temperature-sensitive resistor, for example, the air flow direction can be detected as the forward direction, When the resistance value of the second temperature-sensitive resistor is smaller than that of the first temperature-sensitive resistor, the air flow can be detected in the opposite direction. In addition, a heating resistor,
Since the second temperature-sensitive resistor is film-formed, the number of parts can be reduced.

[0024]

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.

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

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

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

Reference numeral 29 denotes an insulating substrate attached to the detection holder 26. As shown in FIG. 2, the insulating substrate 29 is made of an insulating material such as glass, alumina or aluminum nitride and has a length dimension of about 15 to 20 mm. It is formed in the shape of a rectangular flat plate having a width of about 3 to 7 mm. Further, the insulating substrate 29 has a fixed end removably attached to the slot of the detection holder 26 on the base end side and a free end on the tip end side.

Reference numeral 30 denotes a heating resistor forming a heating resistor formed on the insulating substrate 29. The heating resistor 30 has a resistance value obtained by depositing a platinum film by means of printing or sputtering. Formed to have RH. Further, as shown in FIG. 2, the heating resistor 30 is located at an intermediate portion in the lengthwise direction of the insulating substrate 29 and has an intermediate resistance portion 30A extending in the width direction, and from both ends of the intermediate portion 30A in the lengthwise direction. It is composed of first and second extension resistance portions 30B and 30C extending in opposite directions.

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

The current value of the heating resistor 30 is controlled by a current control transistor 38 described later,
It is heated so that the temperature is kept constant (for example, about 240 ° C.).

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

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

Further, the first temperature-sensitive resistor 31 is located upstream with respect to the forward flow of the intake air (the direction of arrow A), and the second temperature-sensitive resistor 32 is located downstream. In addition, the heating resistor 30 is located between the temperature sensitive resistors 31 and 32. As a result, when the intake air flows in the forward direction indicated by the arrow A, the first temperature-sensitive resistor 31 is cooled and the second temperature-sensitive resistor 31 is cooled.
The resistance value RT1 of the first temperature-sensitive resistor 31 is reduced and the resistance value RT2 of the second temperature-sensitive resistor 32 is substantially reduced by receiving the heat from the heat-generating resistor 30. Does not change to

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

Reference numerals 33, 33, ... Denote, for example, five electrodes formed on the base end side of the insulating substrate 29. The electrodes 33 are arranged in a row in the width direction of the insulating substrate 29 at a predetermined interval. By inserting the base end side of the insulating substrate 29 into the slot of the detection holder 26, it is connected to each terminal (not shown) on the detection holder 26 side. Then, the heating resistor 3 formed on the insulating substrate 29 via the respective electrodes 33.
0, the first and second temperature sensitive resistors 31, 32, etc. are connected to respective electronic parts provided in the circuit casing 27 to form a processing circuit for flow rate detection shown in FIG.

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

In FIG. 3, reference numeral 34 designates one bridge circuit which constitutes a flow rate detecting means together with a differential amplifier circuit 37 which will be described later. The bridge circuit 34 includes a heating resistor 30, a temperature compensating resistor 35 and one reference resistor. 23 and a flow rate adjusting resistor 36 having a resistance value R2, which are configured as a bridge in which the products of the resistance values of the opposite sides are equal, and the connection point a between the heating resistor 30 and the temperature compensation resistor 35 is a current control transistor. 38 is connected to the emitter side, and a connection point b between the reference resistor 23 and the flow rate adjusting resistor 36 is connected to the ground.

In the bridge circuit 34, the heating resistor 30, the reference resistor 23, the temperature compensating resistor 35, and the flow rate adjusting resistor 36 are connected in series, respectively.
d is connected to the input terminal of the differential amplifier circuit 37, and the connection point c is a sample hold circuit 43 and an inverting circuit 4 which will be described later.
4 is connected. The signal output from the differential amplifier circuit 35 becomes the current control voltage of the current control transistor 38 that controls the applied current to the bridge circuit 34,
The output from the connection point c of the bridge circuit 34 is the reference resistance 2
3 becomes the voltage across both ends of the voltage, and this voltage becomes the flow rate detection voltage Va as a flow rate detection signal indicating the degree to which the heating resistor 30 is cooled by the flow rate.

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

In the bridge circuit 34 thus constructed, when the bridge circuit 34 is in a balanced state, the current control voltage from the differential amplifier circuit 37 becomes zero and
From the connection point c, the voltage across the reference resistor 23 (flow detection voltage Va) in the equilibrium state is the sample hold circuit 4
3 and the inverting circuit 44. On the other hand, bridge circuit 3
4 is out of balance, that is, when the heating resistor 30 is cooled by the intake air, the resistance value RH of the heating resistor 30 becomes small. The current control voltage is output to the base of. As a result, the current control transistor 3
Reference numeral 8 controls the current applied to the bridge circuit 34 to keep the cooled heating resistor 30 at a constant temperature.
Return 4 to equilibrium. At this time, the increased current value output from the connection point c of the bridge circuit 34 is
Is detected as a voltage across both ends of the signal and is output to the sample hold circuit 43 and the inverting circuit 44 as a flow rate detection voltage Va.

Here, as shown in the first stage of FIG. 4, when the flow rate Q of the intake air fluctuates in the positive and reverse directions, the flow rate detection voltage Va as the flow rate detection signal shown in the second stage has the reverse flow rate Q. When the flow becomes the directional flow, the flow again becomes the positive direction, and the flow rate detection voltage Va can detect the flow rate Q, but cannot detect the flow direction. The point at which the flow rate detection voltage Va turns back when the flow of the intake air changes from the forward direction to the reverse direction and from the reverse direction to the forward direction is referred to as a folding voltage value Va0.

Reference numeral 38 denotes a current controlling transistor. The current controlling transistor 38 has a collector side connected to the battery voltage VB and a base side connected to the differential amplifier circuit 37.
Connected to the output side of the bridge circuit 3 on the emitter side.
4 is connected to the connection point a. The current control transistor 38 controls the emitter current by changing the base current with the current control voltage from the differential amplifier circuit 37. As a result, the current control transistor 38 controls the value of the current applied to the bridge circuit 34, and performs feedback control to keep the temperature of the heating resistor 30 at a constant temperature.

Next, 39 shows the other bridge circuit which constitutes the flow direction detecting means together with the comparison circuit 42 which will be described later. The bridge circuit 39 is the first and second temperature sensitive resistors 3.
1 and 32 and other reference resistors 40 and 41, each of which is configured as a bridge whose corresponding sides have the same resistance value, and the connection point e of the first and second temperature sensitive resistors 31 and 32 is a sub power supply VS. (For example, 3V), the reference resistance 4
The connection point f of 0 and 41 is connected to the ground.

In the bridge circuit 39, the first temperature sensitive resistor 31 and the reference resistor 40 are connected in series, and the second temperature sensitive resistor 32 and the reference resistor 41 are connected in series.
h is connected to the input terminal of the comparison circuit 42, and the comparison circuit 4
The output terminal of 2 is connected to the inverting circuit 44 through the sample hold circuit 43. Therefore, when the bridge circuit 39 is in the equilibrium state, since the flow rate Q of the intake air is zero, there is no difference in the resistance values of the temperature sensitive resistors 31 and 32, and the temperature sensitive resistors 31 and 32 are output via the comparison circuit 42. The flow direction detection voltage Vb as the flow direction detection signal has a voltage value of zero. On the other hand, when the balance of the bridge circuit 39 is lost, that is, due to the flow of the intake air, either one of the temperature sensitive resistors 31, 32 is
When the resistance value of No. 2 changes, the difference in resistance value (RT1−RT2) is input as a voltage from the connection point gh to the comparison circuit 42, and the flow direction of the intake air is changed based on the difference in resistance value. The signal shown below (hereinafter referred to as “flow direction detection voltage Vb”) is output to the sample hold circuit 43.

Here, in the third stage of FIG. 4, the intake air flow rate Q
The relationship of the flow direction detection voltage Vb with respect to is shown. When the flow direction of the intake air is the A direction (forward direction), the comparison circuit 42 outputs the flow direction detection voltage V having a predetermined voltage value Vb0.
b is output, and when the air flow direction changes from the A direction to the B direction (reverse direction), the comparison circuit 42 outputs the flow direction detection voltage Vb having a voltage value of zero.

Reference numeral 43 denotes a sample and hold circuit as sample and hold means connected to the output side of the comparison circuit 42. The sample and hold circuit 43 is a bridge circuit 3
4 for waveform-modifying the flow rate detection voltage Va output from the comparator circuit 42 based on the flow direction detection voltage Vb output from the comparison circuit 42. The sample hold voltage V shown in the fourth stage of FIG.
When the flow direction detection voltage Vb has a predetermined voltage value Vb0 as in c, the flow rate detection voltage Va is output as it is, and when the flow direction detection voltage Vb has a voltage value zero, the flow rate detection voltage Va.
Is held at the return voltage value Va0, and this value is output.

Reference numeral 44 denotes an inverting circuit as a signal inverting means. The inverting circuit 44 has an operational amplifier 45 and an input resistor 46 connected between the inverting terminal of the operational amplifier 45 and the connection point c of the bridge circuit 34. It is composed of a feedback resistor 47 connected between the inverting terminal and the output terminal of the operational amplifier 45. The output side of the sample hold circuit 43 is connected to the non-inverting terminal of the operational amplifier 45, and each of the resistors 4 is connected.
6, 47 have the same resistance value. The inversion circuit 44 transforms the flow rate detection voltage Va output from the bridge circuit 34 based on the sample hold voltage Vc output from the sample hold circuit 43.

That is, as shown in the fifth stage of FIG. 4, when the flow of intake air is in the positive direction, the flow rate detection voltage Va and the sample hold voltage Vc have the same waveform, so the flow rate detection voltage Va is directly output voltage. Output as V0. On the other hand, since the amplification factor is -1 when the flow of the intake air is in the opposite direction, the output voltage V0 changes the flow rate detection voltage Va to the return voltage value while the sample hold voltage Vc is held at the return voltage value Va0. Output as a waveform inverted with respect to Va0. As a result, the output voltage V0 corresponding to the flow rate Q and the flow direction of the intake air is output to the control unit (not shown).

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

Here, when the flow of the intake air is in the direction of arrow A (forward direction), the first temperature-sensitive resistor 31 located on the upstream side of the insulating substrate 29 is cooled by this flow of air. The second temperature-sensitive resistor 32 located on the downstream side receives heat from the heat-generating resistor 30. As a result, the bridge circuit 39 loses balance, and the comparator circuit 42 outputs the positive flow direction detection voltage Vb (predetermined voltage value Vb0).

In the bridge circuit 34, the heating resistor 30 is cooled by the flow of the intake air, and the resistance value RH of the heating resistor 30 is reduced by this cooling, but the differential amplifier circuit 37 and the current control transistor 38 are used. In order to keep the heating resistor 30 at a constant temperature, the current value applied to the bridge circuit 34 is increased, and the increased current value is detected by the reference resistor 23 as the voltage across it. As a result, the positive flow rate detection voltage Va is output from the bridge circuit 34 to the inverting circuit 44.

Further, in the sample hold circuit 43,
The flow rate detection voltage Va output from the comparison circuit 42 is waveform-shaped based on the flow direction detection voltage Vb, and the flow direction detection voltage Vb has a predetermined voltage value Vb0. Therefore, the flow rate detection voltage Va is set as the sample hold voltage Vc. Output.

In the inverting circuit 44, the flow rate detection voltage Va is waveform-transformed based on the sample hold voltage Vc, and there is no difference between the flow rate detection voltage Va and the sample hold voltage Vc. The output voltage V0 corresponding to the flow rate and the positive flow direction is output to a control unit (not shown).

On the other hand, the air flow is in the direction of arrow B (reverse direction).
In the case of, the second located on the downstream side of the insulating substrate 29
The temperature-sensitive resistor 32 of is cooled by this air flow,
The first temperature-sensitive resistor 31 located on the upstream side is the heating resistor 3
Receive heat from 0. As a result, the balance of the bridge circuit 39 is lost, and the comparison circuit 42 outputs the reverse flow detection voltage Vb having a voltage value of zero.

In the bridge circuit 34, the heating resistor 30 is cooled by the flow of the intake air in the reverse direction, and the positive flow rate detection voltage Va is output to the inverting circuit 44 by this cooling.

Further, in the sample hold circuit 43,
The flow rate detection voltage Va output from the comparison circuit 42 is waveform-transformed based on the flow direction detection voltage Vb, and since the flow direction detection voltage Vb has a voltage value of zero, the return voltage value Va0 of the flow rate detection voltage Va is a sample hold voltage. Output as Vc.

In the inverting circuit 44, the flow rate detection voltage Va is waveform-transformed based on the sample hold voltage Vc, and the sample hold voltage Vc has a folding voltage value Va0. Therefore, the flow rate detection voltage Va is folded voltage value Va0. And output as the output voltage V0.

As a result, the output voltage V0 output from the inverting circuit 44 changes the flow rate and the flow direction as shown in the fifth stage of FIG. 4 even when the flow direction of the flow rate Q fluctuates in the forward and reverse directions. It can be detected accurately and continuously.

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

Further, the resistance value change due to the flow rate Q of the heating resistor 30 of one bridge circuit 34 is output to the inverting circuit 44 as the flow rate detection voltage Va, and the first and second temperature sensing of the other bridge circuit 39 is performed. A change in resistance value due to the flow rate Q of the resistors 31 and 32 is output as a flow direction detection voltage Vb that is positive or negative with respect to the flow direction via the comparison circuit 42.
Further, in the sample hold circuit 43, the flow rate detection voltage Va is waveform-transformed based on the flow direction detection voltage Vb, the flow rate detection voltage Va is output as it is in the case of the forward direction flow, and the flow rate detection voltage Va in the case of the reverse direction flow. The return voltage value Va0 is output to the inverting circuit 44 as the sample hold voltage Vc. Then, in the inverting circuit 44, the flow rate detection voltage Va is waveform-transformed based on the sample hold voltage Vc, the flow rate detection voltage Va is output as it is as the output voltage V0 when the flow is in the forward direction, and the flow rate is flowed when it is in the reverse direction. It is possible to output the detected voltage Va as a voltage inverted at the folding voltage value Va0. As a result, the output voltage V0 output from the inverting circuit 44 can be set to a voltage indicating the flow direction and flow rate of the flow rate Q, and the flow rate Q of the intake air can be continuously and accurately detected. .

Further, the first and second temperature sensitive resistors 3
Since the sub power supplies VS generate heat for 1, 32,
The resistance values RT1 and RT2 of the temperature sensitive resistors 31 and 32 can be sensitively changed by the cooling action of the air flow, and the air flow direction can be detected with high sensitivity.

As a result, the control unit enables accurate engine control by performing air-fuel ratio control, ignition timing control, injection amount control, etc. based on the averaged flow rate Q.

In the above embodiment, the temperature compensation resistor 35
Although it has been described that it is provided near the detection holder 26,
The present invention is not limited to this, and as shown in the first modified example of FIG. 5, a slit S is formed in the insulating substrate 29 ′ from the front end side toward the base end side to form the first substrate portion 29A ′ and the first substrate portion 29A ′. Board part 2
9B ', a heating resistor 30, first and second temperature sensitive resistors 31 and 32 are formed on the first substrate portion 29A', and a temperature is formed on the second substrate portion 29B '. The compensation resistor 35 is formed in a film shape. As a result, the heat generating resistor 30, the first and second temperature sensitive resistors 31 and 32, and the temperature compensating resistor 35 can be formed as a film on the insulating substrate 29 ', and the number of parts can be significantly reduced.

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

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

Furthermore, in the above embodiment, the bridge circuit 34 constituting the flow rate detecting means is formed of the heating resistor 30, the temperature compensating resistor 35, the one reference resistor 23 and the flow rate adjusting resistor 36. However, the bridge circuit 34 may be formed by using a fixed resistance instead of the temperature compensation resistance 35 and the flow rate adjustment resistance 36.

[0068]

As described above in detail, in the invention of claim 1, the flow rate detecting means forms a bridge circuit including a heating resistor, and a change in resistance value of the heating resistor in the bridge circuit is used as a flow rate detection signal. The take-out and flow direction detecting means are
A flow direction detection signal corresponding to the flow rate of the intake air when the bridge circuit is composed of the second temperature-sensitive resistor and the reference resistor, and the balance of the bridge circuit is disrupted by the change in the resistance value of the first and second temperature-sensitive resistors. Is output. Further, the sample-hold means waveform-modifies the flow rate detection signal based on the flow direction detection signal into a sample hold signal, and the signal inversion means detects the flow rate only when the flow of the intake air is in the reverse direction based on the sample hold signal. By inverting the signal, the flow direction and flow rate of the intake air can be detected by the signal from the signal inverting means.

As a result, erroneous detection due to fluctuations in the output voltage in the forward and reverse directions can be prevented, the intake air flow rate can be detected with high accuracy, and air-fuel ratio control and the like can be effectively performed.

Further, in the invention of claim 2, the first and second temperature-sensitive resistors formed on the insulating substrate are separated from each other in front of and behind the heating resistor with respect to the flow direction of the intake air. Since the resistance value changes depending on the flow direction of air, when the resistance value of the first temperature-sensitive resistor is smaller than that of the second temperature-sensitive resistor, for example, the air flow direction can be detected as the forward direction, When the resistance value of the second temperature-sensitive resistor is smaller than that of the first temperature-sensitive resistor, the air flow can be detected in the opposite direction, and the resistance values of the heating resistor and the first and second temperature-sensitive resistors can be detected. Can be sensitively changed by the air flow, and the flow direction can be accurately detected. Furthermore, since the heating resistor and the first and second temperature sensitive resistors are formed on the single insulating substrate, the number of parts can be reduced.

[Brief description of drawings]

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

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

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

FIG. 4 is a characteristic diagram showing the voltage from each circuit with respect to the flow rate Q according to the embodiment.

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

FIG. 6 is a plan view showing a heating resistor and first and second temperature-sensitive resistors formed on an insulating substrate according to a second modification.

FIG. 7 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. 8 is a perspective view showing a flowmeter main body, a heat generation resistance and the like according to a conventional technique.

FIG. 9 is a characteristic diagram showing fluctuations in the flow velocity of intake air.

[Explanation of symbols]

 21 Thermal Air Flow Rate Detection Device 22 Flowmeter Main Body 23 Reference Resistance 29, 29 ', 51 Insulating Substrate 30, 54 Heating Resistor 31, 55 First Temperature Sensitive Resistor 32, 56 Second Temperature Sensitive Resistor 34 Bridge Circuit (flow rate detection means) 35 Temperature compensation resistance 36 Flow rate adjustment resistance 37 Differential amplification circuit 39 Bridge circuit (flow direction detection means) 42 Comparison circuit 43 Sample hold circuit (sample hold means) 44 Inversion circuit (signal inversion means)

Claims (2)

[Claims] 1. A flowmeter main body having a proximal end attached to an intake pipe, and a flowmeter main body located inside the intake pipe,
In a thermal type air flow rate detecting device comprising a heating resistor cooled by intake air flowing in the intake pipe, a bridge circuit is formed including the heating resistor, and a resistance value of the heating resistor forming the bridge circuit. Flow rate detecting means for outputting the change in the above as a flow rate detection signal corresponding to the flow rate, and the first and second resistance values which are provided in front of and behind the heat generating resistance and whose resistance value changes in the flow direction of the intake air. And a flow direction detection means for detecting as a flow direction detection signal corresponding to the flow direction of the intake air based on the resistance values of the first and second temperature resistances, and the flow from the flow direction detection means. Sample hold means for waveform-modifying the flow rate detection signal output from the flow rate detection means into a sample hold signal based on the direction detection signal; and a sample holder from the sample hold means. Only when the flow of intake air based on a field signal of the reverse, the flow signal to invert the flow rate detection signal outputted from the detection means reversing means and the thermal air flow detecting device, characterized in that the provided. 2. The heating resistor is formed as a film on an insulating substrate attached to the flowmeter body, and is formed as a heating resistor extending in a film shape at least in a length direction of the insulating substrate. The first and second temperature-sensitive resistors are formed as film-formed first and second temperature-sensitive resistors separated from each other in front of and behind the heating resistor in the flow direction of the intake air on the insulating substrate. The thermal air flow rate detection device according to claim 1, which is configured.