JPH0789071B2 - 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 Japanese Patent Application Laid-Open No. 59-190623, it is provided in a straight portion 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 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 downstream of the sensor in the air flow direction.

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 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, since the straight portion of the bypass passage in which the sensor is arranged is bent and connected to the rear end portion of the bypass passage opened to the inner side surface portion of the intake pipe, the air flow is likely to be disturbed at the bent portion. Therefore, the sensor needs to be arranged avoiding the air flow downstream side of the straight portion of the bypass passage.

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

Furthermore, since the bypass passage is formed directly inside the intake side sidewall or on the outer surface of the sidewall, heat generated in the internal combustion engine is conducted to the wall surface forming the bypass passage,
The sensor or the air passing through the bypass passage may be heated. As a result, the measurement of the air flow rate becomes inaccurate.

Further, in an air flow meter in which a pipe-shaped bypass passage is arranged so as to cross the air passage of the air flow meter, precision is required for manufacturing the bypass passage, and manufacturing of the air flow meter is extremely troublesome. .

(2) 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, in this type of air flow meter, a technique for reducing the pulsation of the intake air flow has not been proposed yet, and the intake air amount cannot be measured very accurately.

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.

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 provides a sensing passage having a hot-wire sensor therein and a bottom portion on the downstream side of an air flow, and the sensing passage. In addition to providing an intake passage around the periphery of the sensing passage, a communication passage is provided so as to connect the sensing passage and the side surface of the intake passage, and further, a means for forming a concave bottom portion of the sensing passage is provided. There is.

As a result, the air flowing into the sensing passage is sucked through the communication passage so as to spread radially by the air flow passing through the intake passage, and the air flow is fed into the sensing passage. A laminar flow state can be reliably achieved without much movement in the air flow passage direction,
Further, the pulsation of the air flow passing through the sensing passage can be mitigated by the air damper effect of the air flowing into the recess.

Further, it is possible to bring about an effect that the blast from the backfire does not flow into the sensing passage in which the sensor is arranged.

(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
FIG. 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. In FIG. 5, the cover 13 shown in FIGS. 1 to 4 and the circuit board 11 arranged in the cover 13 are shown.
(FIG. 1) and the like 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 buffer member 9 is a columnar body shorter than the depth of the recess 30 and is arranged in the recess 30. The cushioning member 9 is fixed to the downstream body 2 with the male screw 19A. Thereby, the rear end of the sensing passage 21,
In other words, a concave buffer chamber 31 having a depth of X is formed at the bottom of the sensing passage 21.

Around the recess 30 of the downstream body 2, a plurality of intake passages 2A are formed 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 is formed along the surface of the downstream body 2 on the upstream body 1 side. The surface of the communication passage 22 on the upstream side of the air flow is formed smoothly so that the air flow passing through the sensing passage 21 can flow into the intake passage 29 without being disturbed.

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 passes through the sensing passage 21 without being formed too long. The generated air flow can be in a laminar flow state.

Further, since the recessed concave buffer chamber 31 is provided on the downstream side of the sensing passage 21 in the air flow, even if a pulsation occurs in the air flow passing through the air flow meter 100, the buffer is provided. The air flowing into the chamber 31 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 rate sensor 7 and the temperature compensation sensor 8 without causing the speed to change so much.

Therefore, it is possible to accurately detect the intake air amount without making the air flow meter so long in the air flow passage direction.

By the way, the optimum shape, size, or depth of the buffer chamber provided for smoothing or mitigating the air flow depends on the displacement of the internal combustion engine, the number of cylinders, the shape and length of the intake pipe, or It is determined by various factors such as the form of the vehicle in which the internal combustion engine is mounted, the shape and size of the intake passage and the sensing passage of the air flow meter.

The shape, size, or depth of this buffer chamber 31 depends on the recess 30.
This can be changed by exchanging the cushioning member 9 disposed inside for a different shape.

Below, the modification of a buffer member is demonstrated.

FIG. 6 is a sectional view of the second embodiment of the present invention, which is similar to FIG. 6, the same reference numerals as those in FIG. 1 denote the same or equivalent parts.

In FIG. 6, the cushioning member 209 arranged in the recess 30 at the rear end of the sensing passage 21 is formed so that the center portion thereof projects upstream of the air flow passing through the inside of the sensing passage 21.

In this example, the inner surface of the recess 30 and the cushioning member
The buffer chamber 231 formed by the surface of 209 has a depth Y.

Also in this air flow meter 200, the pulsation of the air flow passing through the sensing passage 21 is mitigated by the air damper action of the air flowing into the buffer chamber 231.

FIG. 7 is a cross-sectional view of the third embodiment of the present invention.
It is a figure similar to a figure. In FIG. 7, the same symbols as those in FIGS. 1 and 6 indicate the same or equivalent portions.

In FIG. 7, the cushioning member 309 arranged in the recess 30.
Is formed so that its central portion is dented on the downstream side of the air flow passing through the inside of the sensing passage 21.

In this example, the buffer chamber 331 formed by the surface of the buffer member 309 has a depth of Z.

Also in this air flow meter 300, the pulsation of the air flow passing through the sensing passage 21 is alleviated by the air damper action of the air flowing into the buffer chamber 331.

FIG. 8 is a cross-sectional view of the fourth embodiment of the present invention.
It is a figure similar to FIG. 8, the same reference numerals as those in FIGS. 1, 6, 7 indicate the same or equivalent portions. The fourth embodiment is a modification of the third embodiment.

In the first to third embodiments described above, the communication passage 22
Upstream body 1 of downstream body 2, which constitutes a part of
The surface on the side (the surface indicated by the symbol Q in FIG. 7), in other words, the surface of the communication passage 22 on the downstream side of the air flow is substantially perpendicular to the air flow flowing into the sensing passage 21. It is formed in a flat shape. 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 decrease.

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

In FIG. 8, the buffer member 409 is formed so as to project from the recess 30, and the surface on the upstream side of the air flow has a recess forming a buffer chamber 431 having a depth of Z1 at the center thereof, and A portion R that surrounds the surface of the communication passage 22 on the downstream side of the air flow
It has and. The portion R is formed so as to project toward the upstream side of the air flow.

In the air flow meter 400 having this configuration, the air flowing into the sensing passage 21 is smoothly sucked into the intake passage 29, so that the suction efficiency is improved. Further, the air damper action of the air flowing into the buffer chamber 431 reduces the pulsation of the air flow passing through the sensing passage 21.

By the way, the communication passage 22 is formed so as to introduce the airflow passing through the sensing passage 21 into the intake passage 29, and the optimum shape thereof is the displacement of the internal combustion engine and the number of cylinders. It is determined by various factors such as the shape and length of the intake pipe, the form of the vehicle in which the internal combustion engine is mounted, the shape and size of the intake passage and the sensing passage of the air flow meter.

Therefore, as in this embodiment, the buffer member has a communication passage.
If the portion R forming the surface on the downstream side of the air flow of 22 is integrally formed, the shape and size of the communication passage 22 can be changed when the cushioning member is replaced. The communication passage can be set to an optimum shape in accordance with the above-mentioned form.

FIG. 9 is a cross-sectional view of the fifth embodiment of the present invention.
It is the same figure as figure 7,8. In FIG. 9, the same symbols as those in FIGS. 1, 6, 7.8 indicate the same or equivalent portions. The fifth embodiment is a modification of the fourth embodiment.

In FIG. 9, the surface R of the communication passage 22 on the downstream side of the air flow is
Similar to the air flow meter 400 shown in FIG. 8, the intake passage 29
The surface R is integrally formed with the downstream body 502, though the surface R is formed so as to project to the upstream side of the air flow so that the air flow sucked therein is not disturbed.

A recess 30 is formed in a portion of the downstream body 502 corresponding to the bottom of the sensing passage 21, and a cushioning member 509 is arranged inside the recess 30. The buffer chamber 531 has a depth of Z2.

Also in the air flow meter 500 having this configuration, the air flowing into the sensing passage 21 is smoothly sucked into the intake passage 29, so that the suction efficiency is improved. Further, the pulsation of the air flow passing through the sensing passage 21 is alleviated by the air damper action of the air flowing into the buffer chamber 531.

In this way, the cushioning member arranged at the bottom of the sensing passage 21 is connected to the body of the air flow meter (in this example,
If the configuration is such that it can be detachably attached to the downstream body 2), even if the form of the internal combustion engine or the vehicle in which the internal combustion engine is mounted changes, the cushioning member can be changed to a different shape, The size and shape of the buffer chamber can be changed, whereby the pulsation of the air flow passing through the sensing passage 21 can be alleviated in an optimum state at all times regardless of the form of the internal combustion engine or the vehicle. .

In other words, regardless of the form of the internal combustion engine or the vehicle in which the internal combustion engine is mounted, a member other than the buffer member is used.
Can be shared.

Therefore, the air flow meter can be mass-produced and can be manufactured efficiently and inexpensively.

Note that the present invention is not limited to this, and the buffer member may be formed integrally with the body of the air flow meter.

In the above description, only one communication passage 22 is provided for each intake passage. However, the present invention is not limited to this, and two or more communication passages 22 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 sucking the air flow in the sensing passage 21 through the communication passage 22 to make the air flow in the sensing passage 21 a laminar flow.
The optimal shape, number and arrangement for that purpose are various shapes such as the sectional shape, size and length of the sensing passage 21 or the communication passage 22, or the displacement of the internal combustion engine, the number of cylinders, the intake pipe shape, the intake pipe length, etc. It changes depending on the factor.

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

Furthermore, although it has been described that the plurality of intake passages 29 are provided around the sensing passage 21 and one communicating passage 22 is formed in each of the sensing passages 21, the sensing passage 21 is surrounded by the intake passage 29.
That is, only one intake passage may be provided in the C-shape, and 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 portion 22 opens at the narrowest part of the venturi in FIG. The invention is not particularly limited to this, and the communication passage 22 may be formed so as to open at a position displaced from the narrowest part of the venturi to the upstream or downstream side of the air flow.

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 apparent from the above description, according to the present invention, a hot-wire sensor is provided inside, and an intake passage is provided around a sensing passage having a bottom portion on the downstream side of the air flow, and the sensing passage is provided. Since a communication passage that connects the passage and the side surface of the intake passage is provided, and the bottom portion of the sensing passage is formed to have a buffer chamber that is depressed toward the downstream side of the air flow passing through the sensing passage, Such an effect is achieved.

(1) Since the air flowing through the intake passage radially sucks the air flowing into the sensing passage from the bottom side thereof, the air does not move much in the air flow passage direction, and the laminar flow is ensured. It becomes a state.

Further, the pulsation of the air flow passing through the sensing passage is smoothed or mitigated by the air damper effect of the air flowing into the buffer chamber.

Therefore, it is possible to apply an air flow with a small velocity fluctuation to the hot wire type sensor without forming the air flow meter in the air flow passage direction so large, and to reliably and accurately measure the intake air amount by the sensor. be able to.

(2) Since the sensing passage communicates with the side surface of the intake passage, in other words, the sensing passage has a bottom portion, so that even if backfire occurs, the sensor arranged in the sensing passage will have a blast. Less likely to be exposed to

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. FIG. 9 is a sectional view of the fifth embodiment of the present invention. 1 …… Upstream body, 1A, 2A, 29 …… Intake passage, 2,502…
… Downstream body, 3 …… Press-fit collar, 4 …… Terminal collar, 5 …… Terminal holder, 7 …… Air flow sensor, 8 …… Temperature compensation sensor, 9,209,309,409,509 …… Cushioning member, 11 …… Circuit board, 21 ...... Sensing passage, 22 ...
… Communication passages, 30 …… recesses, 31,231,331,431,531 …… buffer chambers, 100,200,300,400,500 …… air flow meters

Claims (6)

[Claims] 1. An air flow meter provided in an intake pipe of an internal combustion engine for measuring an intake air amount, the sensing device being arranged substantially on a central axis of the intake pipe and having a bottom portion on the downstream side of the air flow. A flowmeter main body including a passage and at least one intake passage arranged in parallel with the sensing passage so as to surround the sensing passage; a heat ray sensor arranged in the sensing passage; A communication passage that communicates the sensing passage and the intake passage upstream of a bottom portion, and a buffer chamber formed in the bottom portion of the sensing passage to be recessed downstream of the communication passage. An air flow meter characterized by. 2. The air flow meter according to claim 1, wherein a buffer member for the fluctuation of the air flow in the sensing passage is arranged at the bottom of the buffer chamber. 3. The air flow meter according to claim 2, wherein a surface of the cushioning member on the air flow side is a substantially flat surface. 4. The air flow meter according to claim 2, wherein the surface of the buffer member on the air flow side is a concave surface. 5. The air flowmeter according to claim 2, wherein the surface of the buffer member on the air flow side is a convex surface. 6. The air flow meter according to any one of claims 2 to 5, wherein the cushioning member is removable and replaceable.