JPH07280613A - Air flow rate detector - Google Patents

Abstract

PURPOSE:To enhance accuracy in the detection of suction air flow by distinguishing the forward air flow from the reverse air flow in a casing. CONSTITUTION:A detection head 24 projecting into a casing 22 has first and second air channels 25, 26 formed symmetrically with respect to the axis O-O of the casing 22. The air channels 25, 26 are tapered in the opposite directions with respect to the directions of air flow (shown by arrows A and B). First and second heating resistors 28, 29 and temperature compensation resistors 33, 33 are disposed in the way of the air channels 25, 26. The air channel 25 is formed so that an upstream open end 25A has smaller diameter than a downstream open end 25B with respect to the forward air flow (shown by arrow A) whereas the air channel 26 is formed so that an upstream open end 26A has larger diameter than a downstream open end 26B with respect to the forward air flow (shown by arrow A).

Description

Detailed Description of the Invention

[0001]

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

[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. It is required to accurately detect the intake air flow rate in order to calculate the high accuracy.

Therefore, FIGS. 5 to 7 show a prior art air flow rate detecting device.

In FIG. 1, reference numeral 1 denotes an air flow rate detecting device provided in the middle of an intake passage of an automobile engine, for example, the air flow rate detecting device 1 includes a cylindrical casing 2 which constitutes a part of the intake passage, and Mounting hole 2 in the middle of casing 2
It is composed of a flowmeter main body 3 which will be described later and is arranged via A. The casing 2 of the air flow rate detection device 1 is located upstream of the throttle valve of the engine and connected in the middle of the intake pipe, and is directed in the direction of arrow A toward the combustion chamber (not shown) of the engine body. The flow rate of the intake air flowing through is detected by the flowmeter main body 3.

Reference numeral 3 denotes a flow meter main body which constitutes a main body of the 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 part 4 formed in a stepped column shape for winding the reference resistor 14, and a substantially disk-like shape which is located on the base end side of the winding part 4 and has terminal pins 8A to 8D described later. A detection holder that is integrally provided with the terminal portion 5 and that extends in the radial direction of the casing 2 from the tip side of the winding portion 4 and that positions a heating resistor 9 and a temperature compensating resistor 11, which will be described later, in the central portion of the casing 2. 6 and a circuit case 7, which will be described later, located outside the casing 2 and to which the terminal portion 5 is connected.

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

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 case 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. It is composed of a small-diameter heating resistor element 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 alumina. Has been done. Then, the heating resistor 9 is in a state of generating heat at a temperature of, for example, 240 ° C. before and after being energized by a battery (not shown), and when cooled by the intake air flowing in the direction of arrow A in the casing 2, 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 by means of sputtering or the like, and both ends of the platinum film are terminals 12 provided upright on the detection holder 6.
It is connected between A and 12B.

Reference numeral 13 denotes a protective cover mounted on the detection holder 6 of the flowmeter main body 3. The protective cover 13 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 air flow rate detecting device 1 of the prior art constructed as described above, the terminal portion 5 of the flowmeter body 3 is connected to each terminal pin 8 when detecting the intake air flow rate of an automobile engine or the like.
While connected to the connector part of the circuit case 7 via
The detection holder 6 of the flowmeter main body 3 is inserted into the casing 2 through the mounting hole 2A, and the circuit case 7 is mounted in the mounting hole 2A from the outer peripheral side of the casing 2 to provide the heat generation resistance provided in the detection holder 6. 9 and a temperature compensation resistor 11 are arranged in the central portion of the casing 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 case 7. The compensating resistor 11 and the flow rate adjusting resistor form a bridge circuit. Then, by continuously applying an electric current from the outside to the bridge circuit at the time of starting the engine, the heating resistor 9 is, for example, 240 ° C.
Heat is generated at the specified temperature before and after.

In this state, when the intake air flows in the direction of the arrow A toward the combustion chamber of the engine body in the casing 2, the heat generation resistance 9 is cooled by the flow of the intake air and the heat generation resistance 9 Since the resistance value changes, a detection signal corresponding to the flow rate of the intake air is detected as a change in the output voltage based on the voltage across the reference resistor 14 connected in series with the heating resistor 9.

[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 casing 2 is utilized, and based on the change in the resistance value of the heating resistor 9. Since the configuration is such that the intake air flow rate is detected, the heating resistor 9 is cooled by the intake air flow flowing in the direction A (forward direction) shown in FIG. There is a problem that the flow rate 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. Is sucked in the direction of arrow A (forward direction), the flow velocity of the air flowing through the casing 2 repeatedly pulsates as shown in FIG. 7 in accordance with the opening and closing of each intake valve. Like

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 casing 2 due to the opening of the intake valve, the time t shown in FIG.
The flow velocity becomes negative (minus) such as between 1 and t2, and an air flow that flows in the direction of the arrow B (reverse direction) is generated, and this air flow detects the intake air flow rate excessively than the actual flow rate. Therefore, there is a problem that the A / F control cannot be performed accurately.

The present invention has been made in view of the above-mentioned problems of the prior art, and the present invention can reliably discriminate a forward air flow and a reverse air flow flowing in the casing, and can detect the intake air flow rate with high accuracy. It is an object of the present invention to provide an air flow rate detection device capable of significantly improving the air flow rate and accurately performing A / F control.

[0019]

In order to solve the above-mentioned problems, the invention according to claim 1 has a cylindrical casing which constitutes a part of an intake passage, and extends radially inside the casing. As described above, the detection head is attached to the casing, and the detection head is provided so that the air flows in the forward and reverse directions flowing in the casing flow, and the flow velocity is increased with respect to the forward air flow. A first air passage for slowing the flow velocity with respect to the reverse air flow, and the first air passage is provided independently of the first air passage so that the forward and backward air flows through the detection head; A second air passage for slowing the flow velocity for a forward air flow and a fast flow velocity for the reverse air flow, and the first air passage are provided in the first air passage. First detecting means for detecting a flow rate of air flowing through the inside, and the second detecting means. Provided care passage adopts a configuration comprising a second detecting means for detecting the flow rate of air flowing in the air passage of the second.

In this case, as in the second aspect of the invention, the flow rate of the air flowing in the casing is determined based on the first and second flow rate detection signals output from the first and second detecting means, respectively. A flow rate signal output means for outputting a corresponding flow rate signal is provided, and the flow rate signal output means compares the first and second flow rate detection signals to obtain a positive value when the airflow flowing in the casing is in the forward direction. It is preferable to output the flow rate signal and output a negative flow rate signal when the air flow is in the opposite direction.

Further, as in the invention described in claim 3, the first and second air passages are formed in the detection head so as to be spaced apart from each other in the radial direction of the casing and to expand in opposite directions to each other. The first air passage has a structure in which the passage area is larger on the downstream side than on the upstream side with respect to the forward airflow flowing in the casing, and the second air passage is formed in the positive airflow flowing in the casing. It is preferable that the passage area be larger on the upstream side than on the downstream side with respect to the directional air flow.

Further, as in the invention described in claim 4,
The first and second detecting means are respectively provided at least in the middle of the first and second air passages, and the first and second detecting means are provided.
By being cooled by the air flow flowing in the air passage of
First and second resistance values that change according to the flow rate of the air flow
It suffices if the heat resistance is used.

[0023]

With the above construction, in the invention described in claim 1,
When the intake air flows in the forward direction in the casing, the air flow has a high flow velocity in the first air passage and has a low flow velocity in the second air passage. As a result, the first detection means provided in the first air passage can detect the flow rate of the intake air at a flow rate (flow velocity) larger than that of the second detection means. Further, when the air flows in the opposite direction in the casing, this air flow flows in the second air passage at a high flow velocity and in the first air passage has a low flow velocity, and thus is provided in the second air passage. The second detection means can detect the air flow rate at this time with a flow rate (flow velocity) larger than that of the first detection means.

According to the second aspect of the invention, the air flowing in the casing based on the first and second flow rate detection signals output from the first and second detection means by the flow rate signal output means, respectively. A flow rate signal corresponding to the flow rate can be output, and by comparing the first and second flow rate detection signals, when the air flow flowing in the casing is in the positive direction, this flow rate signal is regarded as a positive flow rate signal. It can be output, and when the air flow is in the opposite direction, it can be output as a negative flow rate signal.

According to the third aspect of the present invention, when the intake air flows in the forward direction in the casing, the first air passage has a passage area on the downstream side with respect to the upstream side with respect to the air flow. Is larger, the resistance to the air flow can be surely reduced, and the flow velocity of the air flowing in the forward direction can be increased. On the other hand, in the second air passage in which the passage area is larger on the upstream side than on the downstream side with respect to the forward direction air flow in the casing, a large resistance is given to the air flow at this time. , The flow velocity of the air flowing in the forward direction can be made slower than that in the first air passage.

Further, as in the invention described in claim 4,
By configuring the first and second detecting means by the first and second heat generating resistances, the first and second heat generating resistances depend on the flow velocity of the air flowing in the first and second air passages. As a result, the resistance value changes, and at this time, the flow rate of the air flowing in each air passage can be taken out as a value proportional to the flow velocity from the change in the resistance value.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIGS. In the embodiment, the same components as those in the conventional technique shown in FIG. 5 described above are designated by the same reference numerals, and the description thereof will be omitted.

In the figure, reference numeral 21 denotes an air flow rate detecting device according to this embodiment. The air flow rate detecting device 21 is substantially the same as the air flow rate detecting device 1 described in the prior art, and has a cylindrical casing 22 and the casing. 22 and a flowmeter main body 23 mounted via a mounting hole 22A.

However, in the air flow rate detecting device 21 according to the present embodiment, the flowmeter main body 23 is formed into a substantially columnar shape by means such as insert molding as shown in FIGS. Extended detection head 24
And a circuit case 27 described later. The detection head 24 of the flowmeter main body 23 has its base end side connected to the circuit case 27, and its front end side at a position facing the mounting hole 22A of the casing 22 in the radial direction.
It is in contact with the inner peripheral surface of 2.

Reference numerals 25 and 26 denote first and second air passages that penetrate the detection head 24 in the radial direction and are bored in the detection head 24. The air passages 25 and 26 are the central axis O of the casing 22. -O is formed in the detection head 24 so as to be separated from each other in the opposite direction by a certain dimension in the radial direction.
It has a taper shape that expands in directions opposite to each other with respect to the direction of the air flow flowing inside (directions indicated by arrows A and B).

Here, the first air passage 25 is formed such that the opening end 25A on the upstream side has a smaller diameter than the opening end 25B on the downstream side with respect to the air flow flowing in the casing 22 in the forward direction (direction indicated by the arrow A). The passage area on the side of the opening end 25B is
It is about twice as large as the passage area on the 5A side.
The first air passage 25 has a flow velocity of an air flow flowing in the casing 22 in the forward direction (direction indicated by an arrow A).
The speed is increased within 5 and the flow velocity is decreased with respect to the air flow in the opposite direction (direction indicated by arrow B).

That is, when the intake air flows in the forward direction (direction indicated by the arrow A) in the casing 22 at a flow rate of, for example, about 100 kg / h, as indicated by the solid line q1 shown in FIG. The air flows in the air passage 25 in the positive direction at a flow velocity of about 10 m / s. On the other hand, a backflow in the direction of arrow B occurs in the casing 22, and the flow rate at this time is 100
Even when it becomes about kg / h, the air flow at this time in the air passage 25 flows in the opposite direction at a flow rate of about 5 m / s, as shown by the characteristic line q2 shown by the one-dot chain line in FIG. The flow velocity is reduced to about 1/2.

The second air passage 26 is provided in the casing 2
The opening end 26A on the upstream side is formed to have a larger diameter than the opening end 26B on the downstream side with respect to the air flow flowing in the positive direction (the direction indicated by the arrow A) in 2, and the passage area on the opening end 26A side is the opening end 26B.
It is about twice as large as the passage area on the side. Then, the second air passage 26 changes the flow velocity of the air flow flowing in the casing 22 in the forward direction (the direction indicated by the arrow A).
In FIG. 4, the characteristic line q2 is slowed down, and for the air flow in the opposite direction (the direction of arrow B), the flow velocity is increased as the characteristic line q1 shown in FIG. There is.

Reference numeral 27 denotes a circuit case provided on the outer peripheral side of the casing 22 so as to close the mounting hole 22A of the casing 22, and the circuit case 27 is formed in substantially the same manner as the circuit case 7 described in the prior art. Although it has a fitting portion 27A that fits into the mounting hole 22A of the casing 22, the circuit case 27 has a fitting head 27A at the fitting portion 27A.
The base end side of is detachably connected. Then, the circuit case 27 is mounted on a insulating substrate (not shown) made of, for example, a ceramic material or the like, on which reference resistors 32, flow rate adjusting resistors 36, differential amplifiers 42, 43, 44, etc., are mounted. , It is configured to incorporate these.

28 and 29 are terminals 30A, 30B, 31A and 31 in the middle of the air passages 25 and 26, respectively.
3A and 3B show first and second heat generating resistors provided via B. The heat generating resistors 28 and 29 are composed of a heat generating resistor element or the like having a small diameter substantially like the heat generating resistor 9 described in the prior art.
As shown in, the connection point a is connected to the reference resistors 32 and 32 having the resistance value R1.
1 and a2 are connected in series. The connection points a1 and a2 between the heating resistors 28 and 29 and the reference resistors 32 are connected.
Is connected to the non-inverting input terminals of differential amplifiers 42 and 43 described later.

The heat generating resistors 28 and 29 constitute first and second detecting means together with temperature compensating resistors 33 and 33 which will be described later, and a voltage is applied from a direct current power source 37 which will be described later when the engine is operating. As a result, heat is generated at a temperature of 240 ° C. before and after, for example. When the intake air flows through the casing 22 as the engine operates, the heating resistors 28, 29 are cooled by the respective air flows flowing in the air passages 25, 26, so that the flow velocity (flow rate) of this air flow is increased. ), The resistance values of the heating resistors 28 and 29 are RH1 and R
H2 changes. As a result, the reference resistors 32 and 3 shown in FIG.
The voltage across the reference resistors 32 and 32 can be taken out as the first and second flow rate detection signals V1 and V2 from the connection points a1 and a2 between the 2 and the heating resistors 28 and 29.

Numerals 33 and 33 denote temperature compensating resistors which are provided apart from the heat generating resistors 28 and 29 at intermediate positions of the air passages 25 and 26 via terminals 34A, 34B, 35A and 35B, respectively. The resistor 33 is formed by depositing a platinum film on an insulating substrate made of, for example, a ceramic material such as alumina by using a method such as sputtering, almost like the temperature compensating resistor 11 described in the prior art. Both ends are between terminals 34A and 34B, which are erected in the air passages 25 and 26, respectively, and 35
It is connected between A and 35B.

Here, each of the temperature compensating resistors 33 has a constant resistance value RK larger than that of the heat generating resistors 28 and 29.
As shown in FIG. 5, the flow rate adjusting resistors 36 and 36 having the resistance value R2 are connected in series via the connection points b1 and b2. Further, a connection point b between each temperature compensation resistor 33 and each flow rate adjustment resistor 36
1 and b2 are connected to the inverting input terminals of the differential amplifiers 42 and 43. The temperature compensating resistor 33, the heat generating resistors 28, 29, etc., together with the electronic components provided in the circuit case 27, form a processing circuit for flow rate detection shown in FIG.

Next, the processing circuit for flow rate detection will be described with reference to FIG.

In the figure, 37 is a DC power supply having a battery voltage VB, 38 and 39 are current control transistors whose collectors are connected to the DC power supply 37, and the current control transistors 38 and 39 have their emitters heated. Resistance 28,
29 and each temperature compensation resistor 33 via connection points c1 and c2, and the base side is connected to the output terminals of the differential amplifiers 42 and 43. The current control transistors 38 and 39 are connected to the heating resistors 28 and 29 from the DC power supply 37.
Also, the current applied (powered) to each temperature compensation resistor 33 and the like is controlled based on the output signals from the differential amplifiers 42 and 43.

Reference numerals 40 and 41 denote bridge circuits as first and second detecting means composed of heat generating resistors 28 and 29. The bridge circuit 40 has the heat generating resistor 28 and the reference resistor 3.
2, a temperature compensating resistor 33 and a flow rate adjusting resistor 36, which are configured as a bridge in which the products of the resistance values of the opposing sides are equal. A connection point c1 between the heating resistor 28 and the temperature compensation resistor 33 is connected to the emitter side of the current control transistor 38, and a connection point d1 between the flow rate adjusting resistor 36 and the reference resistor 32 is connected to the ground. The bridge circuit 40 changes the resistance value RH1 of the heating resistor 28 when the heating resistor 28 is cooled by the airflow flowing in the air passage 25, thereby changing the reference resistance 32.
The first flow rate detection signal V1 based on the voltage across the reference resistor 32 is output from the connection point a1 between the heating resistor 28 and the heating resistor 28.

The bridge circuit 41 has a heating resistor 29,
Reference resistance 32, temperature compensation resistance 33 and flow rate adjustment resistance 3
The bridge is composed of 6 and has the same product of resistance values on opposite sides. The connection point c2 between the heating resistor 29 and the temperature compensation resistor 33 is connected to the emitter side of the current control transistor 39, and the connection point d2 between the flow rate adjusting resistor 36 and the reference resistor 32 is connected to the ground. The bridge circuit 41 is connected to the air passage 26
When the heating resistor 29 is cooled by the air flow flowing inside,
By changing the resistance value RH2 of the heating resistor 29,
The second flow rate detection signal V2 based on the voltage across the reference resistor 32 is output from the connection point a2 between the reference resistor 32 and the heating resistor 29.

42 and 43 are current control transistors 3
8 and 39 show the first and second differential amplifiers incorporated in the circuit case 27 together with the inverting input terminals of the differential amplifiers 42 and 43 between the temperature compensating resistors 33 and the flow rate adjusting resistors 36. Connected to the connection points b1 and b2, and the non-inverting input terminals are connection points a1 between the heating resistors 28 and 29 and the reference resistors 32,
It is connected to a2. Then, the differential amplifier 42 (4
In 3), the output terminal is a current control transistor 38 (39).
Connected to the bases of the connection points a1, b1 (connection points a2,
Based on the potential difference between b2), the currents applied from the DC power supply 37 to the heating resistor 28 (29) and the temperature compensation resistor 33 (power supply) are controlled by the current control transistors 38 and 39.

Reference numeral 44 denotes another differential amplifier which constitutes the flow rate signal output means. The differential amplifier 44 has a non-inverting input terminal connected to the connection point a1 of the first bridge circuit 40 and an inverting input terminal. Is connected to the connection point a2 of the bridge circuit 41. The differential amplifier 44 has a connection point a1
, A2 comparing the flow rate detection signals V1 and V2,

[0045]

## EQU1 ## Vout = K.times. (V1-V2) where K is the amplification factor, and the output voltage Vou corresponding to the flow rate of the intake air flowing in the casing 22 in the direction of arrow A is calculated.
t is output from the output terminal 45.

The air flow rate detecting device 21 according to the present embodiment has the above-mentioned structure. Next, the flow rate detecting operation of the intake air flowing through the casing 22 will be described.

First, at the same time when the engine body is started, a voltage is applied from the DC power source 37 to the heat generating resistors 28 and 29 and the temperature compensating resistors 33 through the current controlling transistors 38 and 39. Heat resistance 2 at temperature
8 and 29 are heated.

In this state, when the intake air flows in the casing 22 in the direction of arrow A (forward direction) shown in FIG. 1, the first and second air passages 2 formed in the detection head 24 are formed.
5, 26, the velocity of the air flow becomes faster on the air passage 25 side as shown by the solid line in FIG. 4, and on the air passage 26 side as shown by the dashed line on FIG. In addition, the flow velocity of the air flow becomes slower than that of the characteristic line q1.

As a result, among the first and second heat generating resistors 28 and 29 provided in the air passages 25 and 26, the heat generating resistor 28 is larger than the heat generating resistor 29 and is cooled by the air flow at this time. Therefore, the resistance value RH1 of the heating resistor 28 is much smaller than the resistance value RH2 of the heating resistor 29, and in the first bridge circuit 40 shown in FIG.
The voltage level at the connection point a1 with the second bridge circuit 41 becomes higher than the voltage level at the connection point a2 of the second bridge circuit 41, and the first and the first voltages output from the connection points a1 and a2 as the voltage across each reference resistor 32. 2, the flow rate detection signal V1,
A voltage difference corresponding to the air flow rate at this time occurs in V2.

The differential amplifier 44 outputs the output voltage Vout from the output terminal 45 based on the flow rate detection signals V1 and V2 at this time from the equation (1), and outputs the output voltage Vou.
Since the flow rate signal corresponding to the actual intake air flow rate can be obtained by t, and the flow rate detection signal V1 in this case has a voltage value larger than that of the flow rate detection signal V2, the output voltage Vout is regarded as a positive flow rate signal. Can be output.

In the bridge circuits 40 and 41, the heating resistors 28 and 29 are cooled by the air flow at this time, and the connection point a
Since the voltage levels of 1 and a2 are higher than the voltage levels of the connection points b1 and b2, the differential amplifiers 42 and 43 are based on the potential difference between the connection points a1 and a2 and the connection points b1 and b2. The current applied (powered) from 37 to the heat generating resistors 28 and 29 and the temperature compensating resistors 33 is controlled via the current controlling transistors 38 and 39. A larger current is supplied to the heating resistors 28 and 29 than the temperature compensating resistors 33, so that the heating resistors 28 and 29 again generate heat at a temperature close to 240 ° C.

At this time, the heating resistors 28, 29
And the voltage level at the connection points a1 and a2 increases in accordance with the current supplied to each reference resistor 32, which is
Since it increases or decreases according to the flow rate of the intake air flowing in 2,
The differential amplifier 44 outputs the output voltage Vout to the output terminal 45 as a positive flow rate signal based on the flow rate detection signals V1 and V2 from the connection points a1 and a2, and the output voltage Vout at this time.
The flow rate of intake air is detected by.

On the other hand, when the engine speed reaches from the low speed region to the medium speed region, the intake and exhaust amounts increase, and the intake valve and the exhaust valve (not shown) overlap each other. When the intake valve is opened, the blow-back flow velocity in the casing 22 becomes negative (minus), and a backflow in the direction of the arrow B in the casing 22 occurs as illustrated as times t1 and t2 in FIG. When it occurs, the velocity of the air flow becomes faster on the side of the air passage 26 of the detection head 24 as shown by the characteristic line q1 in FIG. 4, and on the side of the air passage 25 as shown by the characteristic line q2 in FIG. Therefore, the heat generating resistance 29 provided in the middle of the air passage 26 is larger than the heat generating resistance 28 provided in the middle of the air passage 25, and is cooled by the air flow at this time.

As a result, the resistance value RH2 of the heating resistor 29 is much smaller than the resistance value RH1 of the heating resistor 28, and in the second bridge circuit 41 shown in FIG. 3, the connection point a2 between the heating resistor 29 and the reference resistor 32 is connected. Voltage level at the connection point a1 of the first bridge circuit 40 becomes higher, and the first and second flow rate detection signals V1 output from the connection points a1 and a2 as the voltages across the reference resistors 32.
, V2 has a voltage difference corresponding to the air flow rate at this time.

The differential amplifier 44 outputs the output voltage Vout from the output terminal 45 based on the flow rate detection signals V1 and V2 at this time from the equation (1), and outputs the output voltage Vou.
The flow rate signal corresponding to the actual intake air flow rate can be obtained by t. In this case, the flow rate detection signal V1 has a smaller voltage value than the flow rate detection signal V2.
The output voltage Vout comes to be output as a negative flow rate signal.

Thus, according to this embodiment, the casing 2
In the detection head 24 which is provided so as to project into the inside of the casing 2, first and second air passages 25 and 26 are formed at positions symmetrical with respect to the central axis OO of the casing 22, and the air passages 25 and 2 are formed.
6 has a taper shape that expands in directions opposite to each other with respect to the direction of the air flow (directions of arrows A and B), and the first and second heating resistors 28 are provided in the middle of the air passages 25 and 26. , 29
And the temperature compensation resistors 33, 33 are provided,
The following operational effects can be obtained.

That is, the first air passage 25 is formed such that the opening end 25A on the upstream side has a smaller diameter than the opening end 25B on the downstream side with respect to the air flow in the forward direction (direction indicated by arrow A). By making the passage area on the opening end 25B side larger than the passage area on the opening end 25A side, the flow velocity of the air flow flowing in the forward direction (direction indicated by the arrow A) in the casing 22 can be increased in the air passage 25 and the reverse direction. The flow velocity can be slowed for the air flow in the direction (arrow B direction).

On the other hand, the second air passage 26 is formed so that the opening end 26A on the upstream side has a larger diameter than the opening end 26B on the downstream side with respect to the air flow in the forward direction (the direction of the arrow A). By making the passage area on the side of the opening end 26A larger than the passage area on the side of the opening end 26B, the flow velocity of the air flow flowing in the casing 22 in the forward direction (arrow A direction) can be slowed in the air passage 26, and The flow velocity can be increased for the air flow in the direction (arrow B direction).

As a result, when the intake air flows in the casing 22 in the forward direction, the heat generating resistor 28 is the heat generating resistor 29 of the first and second heat generating resistors 28, 29 provided in the air passages 25, 26. The resistance value RH1 of the heat generating resistor 28 decreases more greatly than the resistance value RH2 of the heat generating resistor 29 by being cooled by the airflow at this time. The first and second flow rate detection signals V1 and V2 output from the connection point a1 of the bridge circuit 40 and the connection point a2 of the bridge circuit 41 shown in FIG. The voltage difference corresponding to the air flow rate can be generated.

As a result, the differential amplifier 44 outputs the output voltage V according to the equation (1) based on the flow rate detection signals V1 and V2.
Out can be output from the output terminal 45, and a flow rate signal corresponding to the actual intake air flow rate can be taken out by the output voltage Vout. In this case, the flow rate detection signal V1 has a voltage value larger than that of the flow rate detection signal V2. Therefore, the output voltage Vout can be output as a positive flow rate signal.

When a backflow in the direction of arrow B occurs in the casing 22, the air passage 26 of the detection head 24 is detected.
The flow velocity of the air flow becomes faster on the side of the air passage 25 and the flow velocity of the air flow becomes slower on the side of the air passage 25. Therefore, the heat generating resistance 29 provided in the middle of the air passage 26 is larger than the heat generating resistor 28 provided in the middle of the air passage 25. Can greatly cool, and the resistance value RH2 of the heating resistor 29
Is greatly reduced below the resistance value RH1 of the heating resistor 28,
A voltage difference corresponding to the air flow rate at this time can be generated in the first and second flow rate detection signals V1 and V2 output from the connection points a1 and a2.

The differential amplifier 44 outputs the output voltage Vout from the output terminal 45 based on the flow rate detection signals V1 and V2 at this time from the equation (1), and outputs the output voltage Vou.
A flow rate signal corresponding to the actual intake air flow rate can be obtained by t, and in this case, the flow rate detection signal V1 has a smaller voltage value than the flow rate detection signal V2, so the output voltage Vout is regarded as a negative flow rate signal. Can be output.

Thus, according to the present embodiment, the flow rate of the intake air flowing through the casing 22 is controlled by the heating resistors 28, 29.
The output voltage Vout can be taken out by the voltage difference between the flow rate detection signals V1 and V2 output from the connection points a1 and a2 based on the resistance values RH1 and RH2 of the output voltage Vout. It is possible to reliably detect whether it is a positive flow rate signal or a negative flow rate signal. Therefore, the flow rate of the intake air can be detected with high accuracy even when the exhaust gas is blown back into the casing 22 in the middle speed range of the engine or the like, and the reliability of the A / F control is ensured. There are various effects such as improvement.

In the above embodiment, the temperature compensating resistor 3 is provided along with the first and second heat generating resistors 28 and 29 in the middle of the first and second air passages 25 and 26 formed in the detecting head 24.
However, the present invention is not limited to this, and for example, the temperature compensation resistor may be provided outside the air passages 25 and 26 and provided at any position in the casing 22 that comes into contact with the air flow. You may

Further, in the above-mentioned embodiment, the first and second heat generating resistors 2 provided in the middle of the first and second air passages 25 and 26.
First and second bridge circuits 40, 4 composed of 8, 29, etc.
However, the present invention is not limited to this, and various flow rate detecting means such as an ultrasonic flow rate detecting means may be used. The detection means may be configured.

[0066]

As described in detail above, according to the present invention, as described in claim 1, the first and second air passages are formed in the detection head extending in the casing in the radial direction, and the intake air is prevented. Since the air flow is configured to flow at a high flow velocity in the first air passage and to be slow in the second air passage when flowing in the forward direction in the casing, the air flow is provided in the first air passage. With the first detecting means, the air flow rate in the forward direction can be detected with a flow rate (flow velocity) larger than that of the second detecting means, and when the air flows in the reverse direction in the casing,
By the second detection means provided in the second air passage, the air flow rate at this time can be detected with a flow rate (flow velocity) larger than that of the first detection means. Therefore, it is possible to prevent erroneous detection of the intake air flow rate due to the reverse air flow,
The flow rate detection accuracy can be improved, and the reliability of A / F control can be reliably improved.

According to the second aspect of the invention, the flow rate signal output means flows in the casing based on the first and second flow rate detection signals respectively output from the first and second detection means. A flow rate signal corresponding to the air flow rate can be output, and by comparing the first and second flow rate detection signals, when the air flow flowing in the casing is in the positive direction, the flow rate signal can be changed to a positive flow rate. It can be output as a signal, and can be output as a negative flow rate signal when the air flow is in the opposite direction.

Further, when the intake air flows in the forward direction in the casing as in the invention described in claim 3, in the first air passage, the passage area is more downstream than the upstream side with respect to this air flow. And the second air passage has a structure in which the passage area is larger on the upstream side than on the downstream side with respect to the air flow in the forward direction, so that the resistance to the air flow in the forward direction is increased in the first air passage. The flow velocity in the positive direction can be made surely small and the flow velocity in the positive direction can be increased, a large resistance to the air flow in the forward direction can be provided in the second air passage, and the flow velocity in the positive direction can be made slower than that in the first air passage. You can

Further, as in the invention described in claim 4,
By configuring the first and second detecting means by the first and second heat generating resistances, the first and second heat generating resistances can be adjusted according to the flow velocity of the air flowing in the first and second air passages. Each resistance value is changed with the change of the resistance value at this time, and the flow rate of the air flowing in each air passage can be taken out as a value proportional to the flow velocity, and the detection accuracy of the flow rate can be improved.
The reliability of A / F control can be reliably improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an air flow rate detecting device according to an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view taken along line II-II in FIG.

FIG. 3 is a circuit diagram showing a circuit configuration of an air flow rate detection device.

FIG. 4 is a characteristic diagram showing a relationship between a flow rate of air flowing in a casing and a flow velocity in an air passage.

FIG. 5 is a vertical cross-sectional view showing an air flow rate detecting device according to a conventional technique.

FIG. 6 is a perspective view showing a flowmeter main body, a heat generation resistance and the like according to a conventional technique.

FIG. 7 is a characteristic diagram showing changes in the flow velocity of air flowing in the casing.

[Explanation of symbols]

 21 Air Flow Rate Detection Device 22 Casing 23 Flow Meter Main Body 24 Detection Head 25 First Air Passage 26 Second Air Passage 27 Circuit Case 28 First Heat Generation Resistance 29 Second Heat Generation Resistance 32 Reference Resistance 33 Temperature Compensation Resistance 36 Flow Rate Adjustment resistor 37 DC power supply 38, 39 Current control transistor 40 First bridge circuit (first detection means) 41 Second bridge circuit (second detection means) 44 Differential amplifier (flow rate signal output means) V1, V2 flow rate detection signal

Claims (4)

[Claims] 1. A cylindrical casing forming a part of an intake passage, a detection head attached to the casing so as to extend in the casing in a radial direction, and a forward and reverse direction flowing in the casing. A first air passage, which is provided in the detection head so that an air flow is circulated, and which has a high flow velocity for a forward air flow and a low flow velocity for a reverse air flow; Independently of the first air passage, the detection head is provided so that air flows in forward and reverse directions,
A second air passage for reducing the flow velocity for the forward air flow and a high flow velocity for the reverse air flow, and the first air passage are provided in the first air passage. A first detecting means for detecting a flow rate of air flowing therein, and a second detecting means provided in the second air passage for detecting a flow rate of air flowing in the second air passage. Air flow rate detection device. 2. Flow rate signal output means for outputting a flow rate signal corresponding to the flow rate of air flowing in the casing based on the first and second flow rate detection signals respectively output from the first and second detection means. The flow rate signal output means compares the first and second flow rate detection signals to output a positive flow rate signal when the air flow flowing in the casing is in the positive direction, and to output the positive flow rate signal in the reverse direction. The air flow rate detection device according to claim 1, wherein the air flow rate detection device is configured to output a negative flow rate signal at a certain time. 3. The first and second air passages are formed in the detection head so as to be spaced apart from each other in a radial direction of the casing and to expand in opposite directions, and the first air passage is formed in the casing. Is configured such that the passage area is larger on the downstream side than on the upstream side with respect to the positive-direction air flow flowing in the casing, and the second air passage is formed on the downstream side with respect to the positive-direction air flow flowing in the casing. The air flow rate detection device according to claim 1 or 2, wherein the passage area is increased on the upstream side. 4. The first and second detection means are respectively provided at least in the middle of the first and second air passages, and are cooled by an air flow flowing in the first and second air passages. The air flow rate detection device according to claim 1, wherein the air flow rate detection device is configured by the first and second heating resistors whose resistance value changes according to the flow rate of the air flow.