JPS63210727A - Air flowmeter - Google Patents

Abstract

PURPOSE:To reduce the influence of an air blast due to a backfire and to accurately measure an intake air capacity by forming a step part on the internal wall of a sensing passage on the upstream side of an air flow. CONSTITUTION:The step part 3A which is smaller than the internal diameter of the sensing passage 21 is formed at the tip part of the sensing passage 21 (tip part of pressed-in collar 3). Therefore, even if the air blast due to the backfire enters the sensing passage 21 through a communicating passage 21, the air blast strikes on the step part 3A and hardly flows out of the sensing passage 21 to the upstream side of the air flow. Consequently, the hot blast hardly passes in the sensing passage 21 and the dynamic pressure based upon the air blast is applied to neither a flow rate sensor 7 nor a temperature compensating sensor 8. Therefore, even if the backfire is generated, neither the flow rate sensor 7 nor the temperature compensating sensor 8 becomes short in life and the air blast is never detected as the intake air. Consequently, the influence of the air blast is reduced and the intake air capacity is accurately measured.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an air flow meter, and in particular to an air flow meter that is placed in the intake pipe of an internal combustion engine and uses a hot wire sensor such as platinum as the sensor. It is related to the meter.

(Prior Art) There are various types of air flow meters placed in the intake pipe of an internal combustion engine. Among them, the so-called hot wire type air flow meter that uses a hot wire such as a platinum wire as a sensor is one of the most popular types. It is widely used because of its good response and ability to measure the mass of air flowing per unit time.

In such an air flow meter, the sensor is disclosed in, for example, Japanese Unexamined Patent Publication No. 56-108911, Japanese Utility Model Application No. 59-1580.
As described in Japanese Patent Publication No. 30, etc., it is provided in a cylindrical body disposed in the intake pipe, or
As described in Japanese Patent No. 190623, etc., the bypass passage is provided in a straight portion of a bypass passage arranged to branch from an intake passage in an intake pipe.

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

(1) To accurately measure the amount of intake air, it is necessary to make the air passing through the intake pipe into a laminar flow state and apply it to the sensor.

However, when the sensor is installed in a cylindrical body disposed in the intake pipe, the airflow within the cylindrical body is often turbulent, and it is often difficult to make the airflow into a laminar state. Moreover, as a result, the cylindrical body must necessarily be formed to be long in the airflow passing direction.

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

Another drawback is that when a backfire occurs, the sensor is easily damaged by the blast, which shortens the life of the air flow meter.

Furthermore, even when a backfire occurs, the blast wave is detected as intake air, making it impossible to accurately measure the amount of intake air.

(2) When the sensor is disposed in the bypass passage, the end of the bypass passage on the downstream side of the air flow is open to the inner side surface of the intake pipe, so the air in the bypass passage is is drawn in, and as a result, the air flow within the bypass passage tends to be relatively laminar.

However, since the straight portion of the bypass passage in which the sensor is disposed is bent and connected to the rear end portion of the bypass passage that opens to the inner side surface of the intake pipe, airflow is likely to be disturbed at the bent portion. Therefore, the sensor needs to be placed away from the downstream side of the air flow in the straight portion of the bypass passage.

As a result, the bypass passage must be formed relatively long, and the air flow meter becomes larger in the air flow direction.

Furthermore, since the bypass passage is formed directly inside the side wall of the intake pipe or on the outer surface of the side wall, heat generated in the internal combustion engine is conducted to the wall surface constituting the bypass passage.
There is a risk that the sensor or the air passing through the bypass passage may be heated. This results in inaccurate airflow measurements.

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

(Means and operations for solving the problems) In order to solve the above-mentioned problems, the present invention includes a sensing passage provided with a hot wire sensor inside the sensing passage, and a sensing passage arranged so as to surround the sensing passage. In addition to providing a communicating passage so as to communicate the sensing passage with a side surface of the intake passage, and further forming a stepped portion at the tip of the sensing passage. It has characteristics.

As a result, the air flowing into the sensing passage is sucked through the communication passage so as to spread radially by the airflow passing through the intake passage, so that the airflow inside the sensing passage It is possible to produce the effect of reliably achieving a laminar flow state without moving much in the flow direction.

In addition, the blast wave from the backfire is transmitted through the communication path.
It is difficult for the blast wave to flow into the sensing passage where the sensor is disposed, and even if it does, the blast wave is blocked at the stepped portion and does not flow out from the sensing passage to the upstream side of the air flow. Therefore, the dynamic pressure of the blast is not applied to the hot wire type sensor, and the effect of not affecting the sensor and the measurement of the amount of intake air can also be produced.

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

Figure 1 is a cross-sectional view of Figure 3 taken along line B-B, Figure 2 is a side view of the first embodiment of the present invention, and Figure 3 is a book view of Figure 2 from the upstream side of the air flow. Front view of the first embodiment of the invention, fourth
The figure is a rear view of the first embodiment of the present invention when FIG. 2 is viewed from the downstream side of the air flow, and FIG. 5 is a cross-sectional view taken along the line CC in FIG. 1.

In FIG. 5, the cover 13 shown in FIGS. 1 to 4,
Also, the circuit board 11 (FIG. 1) disposed inside the cover 13 and the like are omitted.

First, in FIG. 2, an air flow meter 100 is placed in an intake pipe of an internal combustion engine mounted on a vehicle.

The air flow meter 100 has joints 101 at both ends.
and 102 are connected, the joint 101 is connected to the air cleaner (not shown) side of the intake pipe, and the joint 102 is connected to the fuel injection valve and throttle valve (both not shown) sides of the intake pipe. be done.

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

Next, the first. 3. In Figure 5, upstream body 1
A large diameter portion IB having an inner diameter that is almost the same as the inner diameter of the joint 101 is formed on the connecting portion side with the joint 101, and an annular groove for arranging an O-ring is formed around the large diameter portion IB. IZ and a plurality of bolt holes IY for connection with the joint 101 are formed.

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

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

The press-fit collar 3 is formed so that the inner wall of the air flow upstream end (hereinafter referred to as the tip) has a so-called bell mouth shape so that air flows smoothly into the press-fit collar 3. . Further, the bell mouth portion is formed such that the inner diameter at its narrowest portion is smaller than the inner diameter of the sensing passage 21 described above.

That is, a stepped portion 3A having an inner diameter smaller than the inner diameter of the sensing passage 21 is formed at the tip of the sensing passage 21.

The press-fit collar 3 and the terminal collar 4 are made of resin,
It is made of materials such as ceramics and metals.

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

The tip of the press-fit collar 3, that is, the sensing passage 2
1 is drawn to protrude upstream of the air flow than an intake passage 29, which will be described later.
It may be configured so as to be flush with the tip of the tip 9 or to be retreated from the tip on the downstream side of the air flow.

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

Inside the terminal collar 4, a hot wire type air flow sensor 7 and a temperature compensation sensor 8 are arranged. Each of the sensors 7.8 is arranged at a position such that the turbulence (vortex) of the air flow generated on the downstream side of the stepped portion 3A does not hit the sensor 7.8.

The lead wires of the air flow rate sensor 7 and the temperature compensation sensor 8 are led out of the upstream body 1 through a terminal holder 5 attached to the upstream body 1 with a male screw 19D.

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

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

In addition to the intake air amount detection circuit, the circuit board 11 includes 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 is formed which amplifies the signal and sets the valve opening time (duty ratio) of the fuel injection valve based on the amplified signal. Since the intake air amount detection circuit and the control circuit are well known, a description thereof will be omitted.

The circuit board 11 has a characteristic of blocking electrical disturbances.
It is covered with a resin cover 13. The cover 13 is attached to the upstream body 1 with a male screw 19C, with a gasket 14 disposed between the cover 13 and the upstream body 1.

Reference numeral 12 is a resistance element for power control.

At the end of the sensing passage 21 on the downstream side of the air flow (hereinafter referred to as the rear end), there is a downstream body 2 which will be described later.
A rectifier 6 attached to the central part of the rectifier 6 is disposed.

The rectifier 6 may be formed integrally with the downstream body 2.

Next, in FIG. 1.4.5, the downstream body 2
On the side of the connecting part with the joint 102, there is a large diameter part 2B having an inner diameter that is almost the same as the inner diameter of the joint 102.
Further, an annular groove 22° for arranging an O-ring and a plurality of bolt holes 2Y for connecting to the joint 102 are formed around the large diameter portion 2B.

As described above, the downstream body 2 has a male thread 19A corresponding to the rear end of the sensing passage 21.
The rectifier 6 is fixed by.

The rectifier 6 constitutes the bottom of the sensing passage 21 .

In this example, the rectifier 6 is formed so that its center portion protrudes toward the upstream side of the air flow.
The present invention is not particularly limited to this, and may be formed in a flat plate shape or with a recessed portion on the downstream side of the air flow.

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

The downstream body 2 is fixed to the upstream body 1 with the O-ring 15 disposed in the annular groove IW of the upstream body 1. The above-mentioned fixing is done by a female thread 18B (FIG. 5) formed on the upstream body 1.

This is done by screwing together the screw 19B (Fig. 4).

The intake passage 29 constituted by each intake passage IA and the intake passage 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 simply be formed in a cylindrical shape. .

The upstream body 1 and the terminal collar 4, as well as the downstream body 2, have a first. 3. As shown in FIG. 5, a communication passage 22 is formed such that the sensing passage 21 communicates with the side wall of each intake passage 29 when they are joined.

In this embodiment, the communication path 22 is formed along the bottom of the sensing path 21, that is, along the side surface of the rectifier 6.

In the first embodiment of the present invention having the above configuration, when the internal combustion engine equipped with the air flow meter 100 starts operating, air is sucked from the air cleaner disposed 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 mentioned above, the sensing passage 21 connects each intake passage 2 via the communication passage 22.
9, the air flowing into the sensing passage 21 flows from the communication passage 22 to each intake passage 29.
sucked inside.

Here, as described above, each intake passage 29 has the same shape, and as shown in FIGS. 3 to 5, the distances between adjacent ones are equal, and each The sensing passages 21 are formed so that the distances from the center thereof are equal. Furthermore, the shape of each of the communicating passages 22 is also the same.

As a result, the air flowing into the sensing passage 21 uniformly flows out from the center of the rear end of the sensing passage 21 in a radial manner, so that the air flow passing through the sensing passage 21 is A laminar flow state can be achieved without much movement in the passing direction.

Here, as described above, since the sensor 7.8 is arranged at a position where it is not affected by the turbulence of the air flow generated in the stepped portion 3A, the sensor 7.8 is Airflow can be applied.

Therefore, the intake air amount can be accurately detected without making the sensing passage 21 and, by extension, the air flow meter 100 too long in the air flow passage direction.

Furthermore, since the sensing passage 21 has a bottom portion, in other words, the sensing passage 21 opens to the side surface of the intake passage 29 through the communication passage 22, so that even if a backfire occurs, the blast wave will be removed. It is difficult to flow into the sensing passage 21 through the communication passage 22.

Even if the blast wave of the backfire were to flow into the sensing passage 21 through the communication passage 22, the tip of the sensing passage 21 (the tip of the press-fit collar 3) would have a larger diameter than the inner diameter of the sensing passage 21. Also small step part 3A
, the blast wave hits the stepped portion 3A and is difficult to flow out from the sensing passage 21 to the second air flow side.

As a result, the blast wave becomes difficult to pass through the sensing passage 21, and the air flow sensor 7 and temperature compensation sensor 8
Dynamic pressure from the blast wave is not applied to the area.

Therefore, even if the backfire occurs, the life of the air flow rate sensor 7 and the temperature compensation sensor 8 will not be shortened, or the blast wave will not be detected as intake air.

FIG. 6 is a cross-sectional view of a second embodiment of the invention, and is similar to FIG. 1. In FIG. 6, the same reference numerals as in FIG. 1 refer to the same or equivalent parts, so a description thereof will be omitted.

The bell mouth portion of the press-fit collar 3 shown in FIG. It is formed so that it is located at the top.

On the other hand, the press-fit collar 203 disposed in the air flow meter 200 shown in FIG. In addition, the portion extending from the narrowest portion to the inner wall of the sensing passage 21 is formed smoothly.

Furthermore, the air flow rate sensor 7 and the temperature compensation sensor 8 are arranged at positions where they are not affected by the airflow that is disturbed at the narrowest part of the stepped portion 203A.

In this example as well, the air passing through the sensing passage 21 via the communication passage 222 is uniformly sucked so as to spread radially by the air flow passing through each intake passage 29.
The air flow within the sensing passage 21 becomes laminar.

Also, even if a backfire occurs, the blast wave will be transferred to the communication path 2.
22 into the sensing passage 21, and even if it were to flow into the sensing passage 21, the blast wave would be blocked at the stepped portion 203A, and the blast wave would flow from the sensing passage 21 to the upstream side of the air flow. It becomes difficult to leak out. Therefore, the air flow rate sensor 7 and the temperature compensation sensor 8 are not damaged by backfire, and backfire is not detected as the amount of intake air.

Now, in the above description, the communication path 22 was explained as being formed along the bottom of the sensing path 21, but the present invention is not particularly limited to this.

In other words, the communication passage 22 sucks the air passing through the sensing passage 21 with the flow of air passing through the intake passage 29, and brings the air passing through the sensing passage 21 into a laminar flow state. The optimal shape for this depends on various factors such as the shape, size, and length of the sensing passage 21 or the intake passage 29, the displacement of the internal combustion engine, the number of cylinders, the shape of the intake pipe, and the length of the intake pipe. Change. Therefore, it is desirable that the communication path 22 be formed in a shape that corresponds to each of the above factors.

Further, although only one communication passage 22 is provided for each intake passage 29, the present invention is not particularly limited to this, and two or more communication passages 22 may be provided.

Further, surrounding the sensing passage 21, intake passages 29 having a circular shape and the same size when viewed from the airflow passing direction are arranged so that the distance between adjacent passages is equal to each other, and Although four are formed so that the distances from the center are equal, the present invention is not limited to this.

In other words, the intake passage 29 is for making the air flow in the sensing passage 21 a laminar flow by suctioning the air flow in the sensing passage 21 through the communication passage 22, and the intake passage 29 is designed to make the air flow in the sensing passage 21 laminar. The shape, number and arrangement of the sensing passages 21 or the communication passages 22 depend on the cross-sectional shape,
Size, length, or displacement of the internal combustion engine, number of cylinders,
It changes depending on various factors such as intake pipe shape and intake pipe length.

Therefore, it is desirable that the shape, number, and arrangement of the intake passages 29 be modified depending on the various factors described above.

Furthermore, although the intake passage 29 has been described as being arranged in multiple stages around the sensing passage 21, and one communicating passage 22 is formed in each of the stages, the intake passage 29 is arranged in a C-shape so as to surround the sensing passage 21. Provide only one intake passage,
A plurality of communication passages may be formed in the intake passage, or one C-shaped communication passage may be formed along the intake passage.

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. 1 and 6. The present invention is not particularly limited to this, and the communication passage 22 may be formed to open at a position shifted upstream or downstream of the air flow from the narrowest part of the venturi.

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

(Effects of the Invention) As is clear from the explanation below, according to the present invention, the ζ intake passage is provided around the sensing passage which is provided with a hot-wire sensor therein, and the intake passage is connected to the sensing passage and the intake passage. Since a communication path communicating with the side surface is provided, and a stepped portion is formed at the tip of the sensing path, the following effects can be achieved.

(1) Since the sensing passage communicates with the side surface of the intake passage through a communication passage, even if backfire occurs,
The blast wave becomes difficult to flow into the sensing passage through the communication passage.

Even if the blast wave flows into the sensing passage, the blast wave is blocked by the stepped portion and becomes difficult to flow out from the sensing passage to the upstream side of the air flow.

Therefore, the dynamic pressure of the blast is not applied to the sensor, and the life of the sensor will not be shortened or deteriorated due to backfire.

Furthermore, since the blast wave caused by the backfire is not measured as the amount of intake air, it is possible to always accurately measure the amount of intake air.

(2) The air flowing into the sensing passage is suctioned radially from the bottom side by the airflow passing through the intake passage, so the air does not move much in the airflow passage direction, ensuring a laminar flow. become a state.

Therefore, the laminar air flow can be applied to the hot wire sensor without making the air flow meter too large in the air flow passing direction, and the intake air amount can be reliably and accurately measured by the sensor. be able to.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of FIG. 3 taken along line B-B. FIG. 2 is a side view of the first embodiment of the invention. FIG. 3 is a front view of the first embodiment of the present invention when 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 when FIG. 2 is viewed from the downstream side of the air flow. FIG. 5 is a sectional view of FIG. 1 taken along line CC. FIG. 6 is a sectional view of a second embodiment of the invention. 1..." Second-stream side body, IA, 2A, 29... Intake passage, 2... Downstream side body, 3,203... Press-fit collar, 3A, 203A... Stepped portion, 4...・Terminal collar, 5... Terminal holder, 6... Rectifier, 7... Air flow sensor, 8... Temperature compensation sensor,
11... Circuit board, 21... Sensing passage, 22
...Communication path, 100.200...Air flow meter agent Michito Hiraki and 1 other person Figure 2 Figure 3 18 H Doji

Claims (3)

[Claims] (1) An air flow meter installed in an intake pipe of an internal combustion engine to measure intake air flow rate, comprising a sensing passage arranged approximately on the central axis of the intake pipe, and surrounding the sensing passage. a flow meter body including at least one intake passage arranged parallel to the sensing passage; and a hot wire sensor arranged in the sensing passage; An air flow meter characterized by having a stepped section. (2) The air flow meter according to claim 1, further comprising a communication passage communicating the sensing passage and the side surface of the intake passage. (3) The air flow meter according to claim 1 or 2, wherein the sensing passage has a bottom on the downstream side of the air flow.