JPH0684899B2 - Air flow meter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an air flow meter, and particularly to an air flow rate sensor which is disposed in an intake pipe of an internal combustion engine and uses a hot-wire sensor such as platinum as its sensor. It is about the total.

(Prior Art) There are various types of air flow meters arranged in an intake pipe of an internal combustion engine. Among them, a so-called hot wire type air flow meter using a hot wire such as a platinum wire as a sensor is It is widely used because of its good response and the fact that the mass of air flowing per unit time can be measured.

In such an air flow meter, the sensor is provided in a cylindrical body arranged in the intake pipe, as described in, for example, JP-A-56-108911 and JP-A-59-158030. Alternatively, as described in JP-A-59-190623 or the like, it is provided in a straight path of a bypass passage arranged so as to branch from the intake passage in the intake pipe.

By the way, as is well known, since the air flow passing through the intake pipe is sucked by the reciprocating motion of the piston arranged in the cylinder of the internal combustion engine, the speed thereof varies according to the reciprocating motion. . That is, the air flow is a pulsating flow.

In the air flowmeters described in the above-mentioned respective publications, the pulsating flow may cause inaccurate measurement of the intake air amount.

Therefore, for example, as described in JP-A-57-64109 and JP-A-58-10612, in the air flow meter in which the hot wire type sensor is arranged in the bypass passage,
There has also been proposed an air flow meter configured to provide a surge tank or a diaphragm chamber formed so that atmospheric pressure acts on the bypass passage on the air flow downstream side of the sensor.

By configuring the air flow meter in this way, the pulsation of the air flow is alleviated, and the intake air amount can be measured relatively accurately.

(Problems to be Solved by the Invention) The above-described conventional technique has the following problems.

(1) When the sensor is provided in the tubular body disposed in the intake pipe, the air flow in the tubular body is often disturbed, and it is difficult to apply the air flow to the sensor in a laminar flow state. Is. Further, as a result, it becomes necessary to form the tubular body long in the air flow passage direction.

Therefore, the air flow meter becomes large at least in the air flow direction.

Further, when backfire occurs, the sensor is easily damaged by the blast and the life of the air flow meter is shortened.

Furthermore, even when backfire occurs, the blast air is detected as intake air, so the amount of intake air cannot be accurately measured.

(2) When the sensor is arranged in the bypass passage, the end portion of the bypass passage on the downstream side of the air flow is opened to the inner side surface portion of the intake pipe. Are sucked in, and as a result, the air flow in the bypass passage is likely to be relatively laminar.

However, when the rotational speed of the internal combustion engine increases and the velocity of the air flow passing through the intake pipe increases, the suction efficiency of the air flow flowing out of the bypass passage into the intake pipe decreases, and the air passing through the bypass passage decreases. There is a risk that the flow cannot be made laminar.

As a result, the measurement of the air flow rate becomes inaccurate.

(3) When the rotation speed of the internal combustion engine rises and the pulsation cycle of the air flow passing through the intake pipe becomes faster, the velocity fluctuation of the air flow becomes smaller and the velocity becomes substantially constant.

At this time, if a surge tank or a diaphragm chamber is provided on the downstream side of the bypass passage in the air flow, the air flow passing through the bypass passage can be efficiently sucked by the air damper effect of the surge tank or the diaphragm chamber. Or the airflow flowing into the surge tank or diaphragm chamber is excessively compressed and vibrates, and the airflow is disturbed on the downstream side of the airflow in the bypass passage. You may not be able to hit.

As a result, the measurement of the intake air amount becomes inaccurate when the rotation speed of the internal combustion engine is high.

The present invention has been made to solve the above problems.

(Means and Actions for Solving Problems) In order to solve the above problems, the present invention has a bottom portion on the downstream side of an air flow, and a sensing passage provided with a hot-wire type sensor therein, An intake passage arranged adjacent to the sensing passage is provided, and a communication passage is provided so as to connect the sensing passage and the intake passage, and
A feature is that a means for disposing a sliding body that moves in the air flow direction passing through the sensing passage in accordance with the rotation speed of the internal combustion engine is provided on the bottom portion.

As a result, the volume of the buffer chamber changes or disappears in accordance with the rotation speed of the internal combustion engine, and the cross-sectional area of the communication passage on the sensing passage side changes, so that the rotation speed of the internal combustion engine is high or low. First, the airflow passing through the sensing passage is always efficiently sucked into the intake passage, and as a result, the airflow is not disturbed and the airflow passing through the sensing passage can be surely made into a laminar flow state. it can.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of FIG. 3 taken along line BB, FIG. 2 is a side view of the first embodiment of the present invention, and FIG. 3 is a book of FIG. 2 seen from the upstream side of the air flow. Front view of the first embodiment of the invention, Fourth
2 is a rear view of the first embodiment of the present invention as viewed from the downstream side of the air flow in FIG. 2, and FIG. 5 is a cross-sectional view taken along the line C-C of FIG. In FIG. 4, the pipe shown in FIG.
45, the dynamic pressure detector 46, and the drive device 47, and also in FIG. 5, the cover 13 shown in FIGS. 1 to 4 and the circuit board 11 (FIG. 1) arranged in the cover 13. ) Etc. are omitted.

First, in FIG. 2, the air flow meter 100 is arranged in an intake pipe of an internal combustion engine mounted on a vehicle. Air flow meter 100
Are connected to joints 101 and 102 at both ends thereof, the joint 101 being on the air cleaner (not shown) side of the intake pipe, and the joint 102 being the fuel injection valve and the throttle valve of the intake pipe (both (Not shown) side, respectively.

Therefore, the air sucked from the air cleaner passes in the direction of arrow A.

Next, in FIGS. 1, 3, and 5, a large-diameter portion 1B having an inner diameter substantially the same as the inner diameter of the joint 101 is formed on the upstream body 1 at the connection portion side with the joint 101. An annular groove 1Z for arranging an O-ring and a plurality of bolt holes 1Y for connecting with the joint 101 are formed around the large diameter portion 1B.

An annular groove 1W for arranging an O-ring 15 and a plurality of internal threads 18B (Fig. 5) are formed on the side of the upstream body 1 facing the downstream body 2.

In the central portion of the upstream body 1, in this example,
As shown in FIG. 1, a cylindrical press-fit collar 3 and a terminal collar 4 are arranged. The press-fit collar 3
The inner wall of the terminal collar 4 constitutes a sensing passage 21 for detecting the intake air amount.

The press-fit collar 3 and the terminal collar 4 are made of resin,
It is made of a material such as ceramic or metal.

Further, the press-fit collar 3 and the terminal collar 4 are
It may be integrally formed with the upstream body 1 and / or the terminal holder 5 and the like described later.

Although the end of the press-fitting collar 3 on the upstream side of the air flow (hereinafter referred to as the front end), that is, the front end of the sensing passage 21, is drawn so as to project to the upstream side of the air flow with respect to an intake passage 29 described later. It may be configured so as to be flush with the tip end portion of the intake passage 29, or to be retracted downstream of the tip end portion in the air flow direction.

A plurality of intake passages 1A are formed outside the press-fit collar 3 and the terminal collar 4 of the upstream body 1.

Inside the terminal collar 4, a hot-wire type air flow rate sensor 7 and a temperature compensation sensor 8 are arranged. The lead wires of the sensors 7 and 8 are drawn out of the upstream body 1 via a terminal holder 5 attached to the upstream body 1 by a male screw 19D.

The terminal holder 5 is made of a material such as resin, ceramic, metal or the like.

An intake air amount detection circuit for detecting the intake air amount using the air flow rate sensor 7 and the temperature compensation sensor 8 is formed on the circuit board 11 fixed to the outer wall of the upstream body 1. The lead wire is connected to the circuit board 11.

In addition to the intake air amount detection circuit, the circuit board 11 receives a signal output from the detection circuit in order to inject fuel from the fuel injection valve according to the intake air amount detected by the detection circuit. A control circuit that amplifies and sets the valve opening time (duty ratio) of the fuel injection valve based on the amplified signal is formed. Since the intake air amount detection circuit and the control circuit are publicly known, description thereof will be omitted.

The circuit board 11 is covered with a resinous cover 13 having a characteristic of blocking electrical disturbance. The cover 13 is attached to the upstream body 1 with a male screw 19C in a state where the gasket 14 is arranged between the cover 13 and the upstream body 1.

Reference numeral 12 is a power control resistance element.

Next, referring to FIGS. 1 and 4 and 5,
The joint 102 is connected to the joint 102 side.
A large diameter portion 2B having an inner diameter substantially the same as the inner diameter of
Further, an annular groove for arranging an O-ring is provided around the large diameter portion 2B.
2Z and a plurality of bolt holes 2Y for connecting with the joint 102 are formed.

A cylindrical recess 30 is formed in the downstream body 2 so as to correspond to an end portion of the sensing passage 21 on the downstream side of the air flow (hereinafter, referred to as a rear end portion). The recess 30 is bored so that its central axis coincides with the direction of the air flow passing through the sensing passage 21.

An actuator 40 is attached to the downstream side body 2 on the downstream side of the recess 30 in the air flow direction.
In the actuator 40, the tip end of a rod 41 that operates in the central axis direction is arranged in the recess 30, and the sliding direction of the rod 41 is the central axis of the recess 30, that is, the sensing passage 21. It is mounted so that it is aligned with the direction of air flow through it.

The actuator 40 can be composed of an electromagnetic sonia solenoid, a pneumatic cylinder, a hydraulic cylinder, or the like, and in this example, the magnitude of the forward / backward movement of the rod 41 changes according to its input signal. Is configured.

The sliding body 42 is arranged in the recess 30 and fixed to the tip of the rod 41. In this embodiment, the sliding body 42 is formed so that it is shorter than the depth of the recess 30 and the central portion thereof projects toward the upstream side of the air flow passing through the sensing passage 21.

As a result, a concave buffer chamber 31 is formed at the rear end of the sensing passage 21, in other words, at the bottom of the sensing passage 21.

An air hole 43 is formed in the sliding body 42 so that the front end portion and the rear end portion thereof communicate with each other, that is, the total pressure of the air flow passing through the sensing passage 21 can be detected. Has been done.

An air hole 44 is formed in the downstream body 2 so that the rear end of the recess 30 and the rear end of the downstream body 2 communicate with each other.

In addition, the sensing passage 21 has an air hole so that the static pressure of the air flow passing through the passage 21 can be detected.
97 is drilled. Although part of the air hole 97 is omitted in FIG. 1, the air hole 97 is formed so as to connect the inner wall of the sensing passage 21 and the rear end of the downstream body 2.

The dynamic pressure detector 46 is connected to the air hole 44 via a pipe 45 and to the air hole 97 via a pipe 99.

The dynamic pressure detector 46 detects the dynamic pressure of the air flow based on the total pressure and static pressure of the air flow passing through the sensing passage 21. Since the structure of the dynamic pressure detector 46 is well known, its description is omitted.

The drive device 47 detects the dynamic pressure detector 46, so that the rod 41 of the actuator 40 protrudes toward the upstream side of the air flow as the dynamic pressure of the air flow at the rear end of the sensing passage 21 increases. The actuator 40 is energized.

A plurality of intake passages 2A are formed around the rectifier 6 in the downstream body 2 so as to correspond to the intake passages 1A formed in the upstream body 1.

The downstream body 2 is placed in the annular groove 1W of the upstream body 1 at O.
It is fixed to the upstream body 1 with the ring 15 arranged. Since the fixation is formed on the upstream body 1, the screw 18
It is performed by screwing a male screw 19B (Fig. 4) into B (Fig. 5).

The intake passage 29 formed by the intake passages 1A and 2A is formed to be parallel to the sensing passage 21.

Further, in this embodiment, the intake passage 29 is formed in a venturi shape, but the present invention is not limited to this, and may be formed in a simple tubular shape. .

The upstream body 1, the terminal collar 4, and the downstream body 2 are, as shown in FIGS.
When they are joined, the sensing passage 21
The communication passage 22 is formed so as to communicate with the side wall of each intake passage 29.

In this embodiment, the surface of the communication passage 22 on the downstream side of the air flow passing through the sensing passage 21 is formed along the surface of the downstream body 2 on the upstream body 1 side. Further, the surface of the communication passage 22 on the upstream side of the air flow passing through the sensing passage 21 is formed smoothly so that the air flow passing through the sensing passage 21 flows out into the intake passage 29 without being disturbed. Has been done.

In the first embodiment of the present invention having the above configuration, when the operation of the internal combustion engine equipped with the air flow meter 100 is started, air is sucked from the air cleaner arranged at the tip of the intake pipe of the internal combustion engine. , Passes through the air flow meter 100 in the direction of arrow A (Figs. 1 and 2). As described above, since the sensing passage 21 is open to the side wall of each intake passage 29,
The air flowing into the sensing passage 21 is sucked into the intake passages 29 from the communication passage 22.

Here, as described above, each of the intake passages 29 has the same shape, and as shown in FIGS. 3 to 5, the adjacent ones thereof have the same distance from each other, and It is formed so that the distance from the center of the sensing passage 21 is equal.

Further, each of the communication passages 22 is also formed to have the same shape.

As a result, the air that has flowed into the sensing passage 21 uniformly flows out so as to spread radially at the rear end of the sensing passage 21, so that the sensing passage 21 and, by extension, the air flow meter 100 in the air flow passage direction will not be much. The air flow passing through the sensing passage 21 without being formed for a long time,
It can be in a laminar flow state.

Further, when the dynamic pressure of the air flow at the rear end of the sensing passage 21 is low, that is, when the rotational speed of the internal combustion engine is low, the sliding body 42 is retracted to the downstream side of the air flow, so that the rear end of the sensing passage 21. In the portion, a concave buffer chamber 31 that is recessed toward the downstream side is formed. Therefore, the air flow meter 10
Even if there is pulsation in the air flow passing through the inside of the
The air flowing into 1 functions as a so-called air damper, whereby the pulsation of the air flow passing through the sensing passage 21 is smoothed or alleviated. As a result,
It is possible to apply a stable air flow to the air flow sensor 7 and the temperature compensation sensor 8 with the speed not fluctuating so much.

When the dynamic pressure of the air flow at the rear end of the sensing passage 21 increases, that is, when the rotation speed of the internal combustion engine increases, the sliding body 42 gradually advances to the air flow upstream side, and the depth of the buffer chamber 31, that is, the volume. Becomes smaller gradually. Then, when the rotation speed of the internal combustion engine reaches the maximum rotation speed, a concave buffer chamber is provided at the rear end of the sensing passage 21 as indicated by reference numeral 42A.
Since 31 is not formed, the air flow passing through the sensing passage 21 is efficiently sucked into the intake passage 29 via the communication passage 22.

As a result, even if the number of revolutions of the internal combustion engine increases, the air flow is not disturbed on the air flow downstream side of the sensing passage, and the air flow in the laminar flow state can be reliably applied to the sensors 7 and 8. .

Therefore, it is possible to always accurately detect the intake air amount without making the air flow meter so long in the air flow passage direction and regardless of the speed of the internal combustion engine.

By the way, in this embodiment, the sliding body 42 constitutes the bottom surface of the buffer chamber 31 when the sliding body 42 is retracted to the downstream side of the air flow, and when it is projected to the upstream side of the air flow. , The surface of the communication passage 22 on the downstream side of the air flow passing through the sensing passage 21.

When the rotational speed of the internal combustion engine is low, the optimum shape, size, or depth of the buffer chamber 31 formed for smoothing or mitigating the pulsation of the air flow passing through the sensing passage 21 is Various factors such as the displacement of the internal combustion engine, the number of cylinders, the shape and length of the intake pipe, the form of the vehicle in which the internal combustion engine is mounted, or the shape and size of the intake passage and the sensing passage of the air flow meter. Determined by

On the contrary, when the engine speed is high, the sensing passage 21
The optimum shape or size of the communication passage 22 and the bottom of the sensing passage 21 for efficiently sucking the air flow passing through the inside into the intake passage 29 is also the displacement of the internal combustion engine, the number of cylinders, and the shape of the intake pipe. And the length, the form of the vehicle in which the internal combustion engine is mounted, or the shape and size of the intake passage and the sensing passage of the air flow meter.

Therefore, in the description relating to FIG. 1, the buffer chamber 31
The sliding body 42 that constitutes the bottom of the above is described as being formed so that the central portion thereof projects toward the upstream side of the air flow passing through the inside of the sensing passage 21, but the present invention is not limited to this in particular. It is desirable that the shape is set according to the various factors described above. Specifically, in the sliding body 42, the portion forming the bottom of the buffer chamber 31 is
It may be formed so as to have a concave portion or to have a planar shape which is perpendicular to the air flow passing through the sensing passage 21.

Further, in the above description, as the dynamic pressure of the air flow passing through the sensing passage 21 increases, the sliding body 42 gradually protrudes toward the upstream side of the air flow, that is, the dynamic pressure and the sliding body 42. The relationship with the degree of protrusion (protrusion rate) is described as being linear, but the present invention is not limited to this and may be non-linear.

That is, the optimal protruding position of the sliding body 42 with respect to the dynamic pressure, that is, the rotation speed of the internal combustion engine, is the displacement of the internal combustion engine, the number of cylinders, the shape and length of the intake pipe, or the vehicle mounted with the internal combustion engine. Since it is determined by various factors such as the form, the intake passage of the air flow meter, the shape of the sensing passage, the size, etc., the dynamic pressure and the protrusion rate of the sliding body 42 are determined in consideration of these factors. It is desirable to determine the relationship.

FIG. 6 is a sectional view of the second embodiment of the present invention, which is similar to FIG. In FIG. 6, the same reference numerals as those in FIG. 1 indicate the same or equivalent portions, and thus the description thereof will be omitted.

In the above-described first embodiment, the surface of the downstream body 2 on the upstream body 1 side forming a part of the communication passage 22 passes through the sensing passage 21 of the communication passage 22, in other words. The surface on the downstream side of the air flow is formed in a plane shape that is substantially perpendicular to the air flow passing through the sensing passage 21.
In the air flow meter having such a communication passage, when the air flow is sucked into the intake passage 29, the air flow collides with the surface of the communication passage 22 on the downstream side of the air flow and is disturbed,
The suction efficiency may be reduced.

The second embodiment of the present invention was created to eliminate this drawback.

In FIG. 6, the sensing passage 2 of the downstream body 202
1 A recessed portion 30 forming a side wall of the buffer chamber 231 is formed in a portion corresponding to the rear end portion.

A portion R located outside the recess 30 and forming a surface of the communication passage 222 on the downstream side of the air flow passing through the sensing passage.
Are formed so as to protrude toward the upstream side of the air flow toward the recess 30.

In the air flow meter 200 having this configuration, the sliding body 42
The airflow can smoothly flow out into the intake passage 29 not only when it completely projects from the recess 30 as indicated by reference numeral 42B but also when the buffer chamber 231 is formed.

FIG. 7 is a sectional view of the third embodiment of the present invention. In FIG. 7, the same drawings as FIGS. 1 and 6 show the same or equivalent portions, and therefore the explanation thereof will be omitted.

The downstream body 302 of the air flow meter 300 shown in FIG. 7 is provided with the recess 30 as in the first and second embodiments. A slide body 342 fixed to the tip of the rod 41 of the actuator 40 is arranged in the recess 30.

The sliding body 342 is such that the buffer chamber is not formed when the rod 41 is most retracted to the downstream side of the air flow, that is,
The rod 41 is formed and arranged so that even when the rod 41 is most retracted to the downstream side of the air flow, the outer peripheral portion of the recess 30 that abuts the side wall of the recess 30 projects to the upstream side of the air flow with respect to the recess 30.

In the third embodiment of the present invention having the above-mentioned configuration, as described above, the buffer chamber is not formed when the rotation speed of the internal combustion engine is low, so the pulsation of the air flow cannot be alleviated so much.

However, the speed of the internal combustion engine increases and the sensing passage
21 As the dynamic pressure of the air flow at the rear end portion becomes higher, the sliding body 342, that is, the bottom portion of the sensing passage 21 projects as shown by reference numeral 42C, and the sensing passage 2 of the communication passage 322.
Since the part on the 1st side has a narrowed shape, the sensing passage 21
When the airflow passing through the inside is sucked into the intake passage 29, the airflow is diffused and the suction efficiency is not lowered.

In the above description, only one communication passage is provided for each intake passage, but the present invention is not limited to this, and two or more communication passages may be provided. Good.

Further, around the sensing passage 21, the intake passages 29, which have a circular shape when viewed from the air flow passage direction and have the same size, are arranged such that the distances between adjacent ones are equal to each other, and So that the distance from the center is equal,
Although four pieces are formed, the present invention is not particularly limited to this.

That is, the intake passage 29 is for making the air flow in the sensing passage 21 a laminar flow by sucking the air flow in the sensing passage 21 through the communication passage, and an optimum shape therefor. The number and arrangement of the sensing passages 21 or the communication passages vary depending on various factors such as the cross-sectional shape, size, and length of the sensing passage 21, the displacement of the internal combustion engine, the number of cylinders, the intake pipe shape, the intake pipe length, or the like.

Therefore, it is desirable that the shape, the number, and the arrangement of the intake passages 29 be modified according to the various factors.

Further, although it has been described that the plurality of the intake passages 29 are provided around the sensing passage 21 and one communicating passage is formed in each of the sensing passages 21, only one is provided in the C-shape so as to surround the sensing passage 21. An intake passage is provided, and a plurality of communication passages are provided in the intake passage, or C is provided along the intake passage.
You may make it form one V-shaped communicating path.

Furthermore, when the intake passage 29 has a venturi shape, the intake passage 29 is formed so that the communication passage opens at the narrowest part of the venturi in FIGS. However, the present invention is not particularly limited to this, and the communication passage may be formed so as to open at a position deviated from the narrowest part of the venturi to the upstream or downstream side of the air flow.

Furthermore, it goes without saying that the shapes of the sensing passage 21 and the communication passage may be set to any shape depending on various factors such as the number of cylinders of the internal combustion engine and the intake pipe length.

FIG. 8 is a sectional view of the fourth embodiment of the present invention. In FIG. 8, the same reference numerals as those in FIG. 1 represent the same or equivalent portions, and thus the description thereof will be omitted.

The air flow meter shown in FIG. 8 has a conventionally proposed bypass passage.

In FIG. 8, a body 491 of the air flow meter 400 is provided with an intake passage 429 and a sensing passage (adjacent to the intake passage 429) in which an air flow sensor 7 and a temperature compensation sensor 8 are arranged ( Bypass passage) 492 is formed. The sensing passage 492 communicates with the intake passage 429 through a communication passage 422 on the downstream side of the air flow.

The lead wires 70 of the sensors 7 and 8 are connected to a known air flow rate detection circuit (not shown).

A recess 430 is formed at the rear end of the sensing passage 492 in the direction of air flow passing through the sensing passage 492. A sliding body 42 is attached to the tip of the rod 41 arranged in the recess 430.

Also in the fourth embodiment of the present invention having the above configuration,
When the rotational speed of the internal combustion engine increases and the dynamic pressure of the air flow at the rear end of the sensing passage 492 increases, the sliding body 42 projects to the upstream side of the air flow and forms a buffer chamber 431, as indicated by reference numeral 42A. Therefore, the suction efficiency when the airflow is sucked into the intake passage 429 does not decrease, and the airflow passing through the sensing passage 492 can be reliably made into a laminar flow state. Therefore, the intake air amount can always be measured accurately regardless of the speed of the internal combustion engine.

Incidentally, in the air flow meter having the bypass passage as described above, unlike the air flow meter shown in FIGS. 1 to 7, since the air flow passing through the sensors 7 and 8 is not radially sucked, At the suction part, that is, at the rear end of the sensing passage 492, air may not flow uniformly.
Therefore, to apply a uniform air flow to the sensors 7,8,
The sensor must be arranged so as to avoid the rear end of the sensing passage 492, and as a result, it is necessary to form the sensing passage 492 relatively long in the air flow passage direction. Therefore, the air flow meter 400 is
Compared with the air flow meter shown in FIGS. 7 to 7, it is slightly larger in the air flow passage direction.

Now, in each of the embodiments described above, the sensing passage 21
Alternatively, a dynamic pressure detector 46 for detecting the dynamic pressure of the air flow at the rear end of 492 is provided, and the sliding body is moved in the direction of the air flow passing through the sensing passage according to the output signal of the dynamic pressure detector 46. However, in the present invention,
The invention is not particularly limited to this, and for example, the sliding body may be moved according to the air flow rate detected by the air flow rate sensor 7 and the temperature compensation sensor 8, and the rotation speed of the internal combustion engine may be changed. It is also possible to directly detect and move the sliding body according to the rotation speed.

Further, in the above embodiment, the sliding bodies 42, 342 were described as those in which the sliding amount changes depending on the rotation speed of the internal combustion engine, but the present invention is not particularly limited to this. It is also possible to judge only whether the rotation speed of the internal combustion engine is higher or lower than the reference rotation speed, and to control the sliding bodies 42, 342 only to two positions of projecting or retracting according to the result.

(Effects of the Invention) As is apparent from the above description, according to the present invention, the rotation speed of the internal combustion engine is provided at the bottom portion of the sensing passage provided with the hot-wire sensor inside, which is arranged on the downstream side of the air flow. According to the above, since a slide body that moves in the air flow passage direction is provided,
The following effects are achieved.

(1) When the buffer chamber is formed in the bottom portion, the volume of the buffer chamber changes or the buffer chamber disappears according to the rotation speed of the internal combustion engine. Further, when the buffer chamber is not formed in the bottom portion, the cross-sectional area of the end portion of the communication passage on the sensing passage side changes according to the rotation speed of the internal combustion engine.

Therefore, even if the rotation speed of the internal combustion engine changes, the air flow is not disturbed at the rear end of the sensing passage.

In addition, the suction efficiency of the airflow sucked from the sensing passage to the intake passage does not decrease, and the airflow passing through the sensing passage can always be made laminar.

As a result, the intake air amount can always be measured accurately.

(2) Since the sensing passage communicates with the side surface of the intake passage, in other words, the sensing passage has the bottom portion, so that even if backfire occurs, it is difficult for the blast to flow into the sensing passage. .

As a result, the life of the sensor is not shortened or deteriorated due to the backfire.

Further, since the blast caused by the backfire is less likely to be measured as the intake air amount, it is possible to always measure the accurate intake air amount.

[Brief description of drawings]

FIG. 1 is a sectional view of FIG. 3 taken along the line BB. FIG. 2 is a side view of the first embodiment of the present invention. FIG. 3 is a front view of the first embodiment of the present invention in which FIG. 2 is viewed from the upstream side of the air flow. FIG. 4 is a rear view of the first embodiment of the present invention in which FIG. 2 is viewed from the downstream side of the air flow. FIG. 5 is a sectional view of FIG. 1 taken along the line C-C. FIG. 6 is a sectional view of the second embodiment of the present invention. FIG. 7 is a sectional view of the third embodiment of the present invention. FIG. 8 is a sectional view of the fourth embodiment of the present invention. 1 …… Upstream body, 1A, 2A, 29,429 …… Intake passage, 2,20
2,302 ...... Downstream body, 3 ... Press-fit collar, 4 ... Terminal collar, 5 ... Terminal holder, 7 ... Air flow sensor, 8 ... Temperature compensation sensor, 11 ... Circuit board,
21,492 …… Sensing passage, 22,222,322,422 …… Communication passage, 30,430 …… Recessed portion, 31,231,431 …… Buffer chamber, 40 ……
Actuator, 41 …… Rod, 42,342 …… Sliding body, 46
...... Dynamic pressure detector, 47 …… Drive device, 100,200,300,400…
… Air flow meter, 491… Body

Claims (7)

[Claims] 1. An air flow meter installed in an intake pipe of an internal combustion engine for measuring an intake air flow rate, comprising: a sensing passage having a bottom portion on a downstream side of the air flow; and a sensing passage disposed adjacent to the sensing passage. At least 1
Two intake passages, a heat ray sensor arranged in the sensing passage, a recess formed in the bottom of the sensing passage in the air flow direction passing through the sensing passage, and arranged in the recess, A sliding body configured to be slidable in the air flow direction passing through the sensing passage, an actuator that moves the sliding body in the air flow direction passing through the sensing passage, and the actuator rotating the internal combustion engine. An air flow meter, comprising: a driving unit that urges according to the number. 2. The air flow meter according to claim 1, wherein the intake passage is formed so as to surround the sensing passage. 3. The air flow meter according to claim 1 or 2, further comprising a communication passage communicating with a side surface of the sensing passage and a side surface of the intake passage. 4. The driving mechanism according to claim 1, wherein the driving means biases the actuator according to a dynamic pressure of an air flow passing through the sensing passage. The air flow meter according to any of the above. 5. The driving means biases the actuator according to an air flow rate detected by the hot-wire sensor, according to any one of claims 1 to 3. Air flow meter described in. 6. The actuator according to claim 1, wherein the actuator is arranged such that a buffer chamber is formed by a side surface of the recess and the sliding body. Airflow meter described. 7. The sliding member is formed so that a central portion thereof projects toward an upstream side of an air flow passing through the inside of the sensing passage. An air flow meter according to any one of the items.