JPS63210718A - Air flowmeter - Google Patents

Abstract

PURPOSE:To securely place the air flow in a sensing passage in a laminar state and to accurately measure intake air capacity by forming the lead-out part of as sensor device on the internal wall of the sensing passage by using a heating insulating material. CONSTITUTION:A terminal collar 4 which is the lead-out part of the sensor device arranged in the sensing passage 21, a support member for the sensor device, and a terminal holder 5 are made of heat insulating materials. Heat generated by an internal combustion engine is therefore not conducted to the lead wires 70 of an air flow rate sensor 7 and a temperature compensating sensor 8. Consequently, the heat generated by the internal combustion engine is not conducted to the flow rate sensor 7 and temperature compensating sensor 8 because of heat radiation from the internal wall of the sensing passage 21. Consequently, the air flow in the sensing passage is put in the laminar state without being affected by the heat generated by the internal combustion engine and the intake air capacity is accurately detected.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to an air flow meter, and in particular to an air flow meter that is disposed in the intake pipe of an internal combustion engine and uses a hot wire sensor device such as platinum as its sensor. It is related to flowmeters.

(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.

Furthermore, in such an air flow meter, the cylindrical body or the member constituting the bypass passage may be
A technique has also been proposed in which it is formed from a material having heat insulating properties.

The technique is disclosed in, for example, Japanese Utility Model Publication No. 57-50530,
It is described in Japanese Patent Application Laid-Open No. 56-30616.
.

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

(1) In order to accurately determine the amount of intake air n1, 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 provided in a cylindrical body disposed in an intake pipe, the airflow within the cylindrical body is highly turbulent, making it difficult to bring the airflow into a laminar state.

Therefore, even if the air flow meter is configured such that the cylindrical body is made of a heat insulating material so that the heat generated by the internal combustion engine is not transmitted to the hot wire sensor, the amount of intake air cannot be measured very accurately. Can not.

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, there is a risk that the blast wave will be detected as 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, making the air flow meter complicated and large.

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

(Means and effects for solving the problems) In order to solve the above-mentioned problems, the present invention provides a sensing passage provided with a hot wire type sensor device therein, and an intake passage around the sensing passage. At the same time, a communication passage is provided so as to communicate the sensing passage with a side surface of each of the intake passages, and an inner wall portion of the sensing passage of the air flow meter main body or a support member of the sensor device is provided.
It is characterized by the fact that it is made of a material that has heat insulating properties or a material that has high heat insulating properties.

This prevents the heat generated by the internal combustion engine from being transmitted to the sensor device, and the air flowing into the sensing passage is spread radially by the airflow passing through the intake passage via the communication passage. As a result, the airflow within the sensing passage can be reliably brought into a laminar flow state.

As a result, it is possible to produce the effect that the intake air amount can be measured extremely accurately without making the air flow meter too large in the air flow passage direction.

Furthermore, since the blast wave caused by the backfire does not flow into the sensing passage where the sensor device is arranged, the blast wave can be measured as an intake air amount, and the life of the sensor device is not shortened. can be caused.

(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 and the circuit board 11 (FIG. 1) disposed inside the cover 13 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 in the direction of the arrow.

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, as shown in FIG. 1, a cylindrical hole IH is bored in the center of the upstream body 1, and a cylindrical collar 3 and a terminal collar are provided in the cylindrical hole IH. 4 is placed. The inner walls of the collar 3 and the terminal collar 4 constitute a sensing passage 21 for detecting the amount of intake air.

The terminal collar 4 is made of a material with heat insulating properties such as resin or ceramic, or a material with high heat insulating properties (hereinafter referred to as a heat insulating material).

The airflow upstream end of the collar 3 (hereinafter referred to as the tip), that is, the tip of the sensing passage 21, in this example, protrudes further upstream of the airflow than the tip of the intake passage 29, which will be described later. However, it may be on the same plane as the tip of the intake passage 29, or it may be set back to the downstream side of the air flow from the tip.

Furthermore, although the collar 3 is depicted as being separate from the upstream body 1 (FIG. 1), it may be formed integrally.

A plurality of intake passages IA are bored outside the collar 3 and the terminal collar 4 of 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. The lead wire 70 of the sensor 7.8 is led out of the upstream body 1 through the terminal holder 5 attached to the upstream body 1 by a male thread 19D.

The terminal holder 5 is a support member of the sensor device consisting of the sensors 7 and 8 and the lead wire 70 drawn out from them, and like the terminal collar 4, it is made of a heat insulating material such as resin or ceramic. There is.

In this embodiment, the terminal collar 4 and the terminal holder 5 are depicted as separate bodies (FIG. 1), but they may be formed integrally.

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 70 is connected to this circuit board 11.

In addition to the intake air amount detection circuit, the circuit board 11 is provided with 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 connection with 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 such that its central portion protrudes toward the upstream side of the airflow, but the present invention is not limited to this.
It may be formed in a flat plate shape or with a concave portion on the downstream side of the air flow (1°. Also, the intake passage formed in the upstream body 1 is formed around the rectifier 6 in the downstream body 2. A plurality of two intake passages are formed to correspond to the IA.

The downstream body 2 is fixed to the upstream body 1 with an O-ring 15 disposed in the annular groove IW of the upstream body 1. The fixation is performed by screwing the male thread 19B (FIG. 4) into the female thread 18B (FIG. 5) formed on the upstream body 1.

The intake passages IA and the intake passages 29 formed by the two intake passages are formed to be parallel to the sensing passage 21.

1. In this embodiment, the intake passage 29 is formed to have a venturi shape, but the present invention is not limited to this, and for example, it may be formed simply to have a cylindrical shape. It's okay to be.

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 so 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, 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
The air is sucked from the communication passage 22 into each of the intake passages 29 .

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. Moreover, the shape of each of the communication 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 directed in the direction of passage. Laminar flow can be achieved reliably without much movement. therefore,
The intake air amount can be accurately detected by the air flow sensor 7 and the temperature compensation sensor 8 without making the air flow meter 100 too large in the air flow passage direction.

Further, a terminal collar 4 which is a drawer part for the sensor device disposed in the sensing passage 21, and a terminal holder 5 which functions as a support member for the sensor device.
is formed of a heat insulating material as described above, so that the heat generated by the internal combustion engine is not transferred to the lead wires 70 of the air flow rate sensor 7 and the temperature compensation sensor 8 by thermal conduction, and as a result, the The heat generated by the internal combustion engine is not transferred to the sensor 7.8 via the lead wire 70 by thermal conduction.

Moreover, the heat generated by the internal combustion engine is no longer transmitted to the air flow rate sensor 7 and the temperature compensation sensor 8 by heat radiation from the inner wall of the sensing passage 21.

Therefore, the intake air amount can be detected more accurately by each of the sensors 7.8 without being affected by the heat generated by the internal combustion engine.

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.

In FIG. 6, the terminal collar 204 is made of a material that does not have heat insulation properties, but its inner wall has
A heat insulating coating 210 is applied with a heat insulating material.

In this air flow meter 200 as well, as in the first embodiment, the heat generated by the internal combustion engine is difficult to be transmitted from the inner wall of the sensing passage 21 to the sensors 7.8 by heat radiation.

Therefore, the intake air amount can be accurately detected by the air flow rate sensor 7 and the temperature compensation sensor 8 without being affected by the heat generated by the internal combustion engine.

Although the terminal collar 204 is depicted as being separate from the collar 3 and the upstream body 1 in FIG. 6, it may be depicted as being integrated with the collar 3 and/or the upstream body 1. may be formed.

FIG. 7 is a sectional view of the third embodiment of the present invention, and the first,
It is a figure similar to FIG. 6. In FIG. 7, the same reference numerals as in FIGS. 1 and 6 refer to the same or equivalent parts, so a description thereof will be omitted.

In FIG. 7, the terminal collar 4 and the terminal holder 5 arranged in the cylindrical hole IH are made of a heat insulating material as in the first embodiment, but in this air flow meter 300, , color 303 is also resin,
It is made of a heat insulating material such as ceramic.

In this way, not only the portion of the inner wall of the sensing passage 21 from which the lead wire 70 of the sensor 7.8 is drawn out (that is, the inner wall of the terminal collar in this example), but also the almost entire surface of the inner wall of the sensing passage 21 is covered. If the air flow meter 300 is made of a heat insulating material, the heat generated by the internal combustion engine will not be transmitted from the inner wall of the sensing passage 21 to the sensors 7 and 8 by thermal radiation, so that the air flow meter 300 can measure the amount of intake air. can be done more precisely.

FIG. 8 is a sectional view of the fourth embodiment of the present invention.
This is a diagram similar to Figure 6.7. In Figure 8, 1.6
．． Since the same reference numerals as in FIG. 7 refer to the same or equivalent parts, the explanation thereof will be omitted.

In FIG. 8, the collar 3 and the terminal collar 204 disposed in the cylindrical hole IH are made of a material that does not have heat insulation properties, but form their inner walls, that is, the inner walls of the sensing passage 21. The sections are each provided with a thermally insulating coating 210,410 of a thermally insulating material.

Also in the air flow meter 400 having the above configuration, as in the third embodiment, the heat generated by the internal combustion engine is completely prevented from being transmitted from the inner wall of the sensing passage 21 to the sensors 7 and 8 by thermal radiation. Since the air flow meter 2
The amount of intake air can be accurately measured using 00.

Now, in each of the above embodiments, the terminal holder 5 has been described as being formed of a heat insulating material, but the present invention is not limited to this, and for example, the terminal holder 5 is made of a heat insulating material. When the distance to the sensor is relatively long and the heat generated by the internal combustion engine is difficult to transfer to the lead wire 70 of each sensor 7.8 due to thermal conduction, or even if it is transferred, the output signal of each sensor 7.8 If it does not affect the terminal holder 5,
may be made of a material that does not have heat insulating properties.

In this case, if the terminal collar is made of a material that does not have heat insulating properties as shown in FIGS. 6 and 8, the terminal collar may be formed integrally with the terminal holder 5. .

Conversely, the heat generated by the internal combustion engine
In cases where heat radiation from the inner wall of the sensor 7.1 is difficult to be transmitted to each sensor 7.8, or even if it is transmitted, the heat radiation from the sensor 7.
In the case where the output signal of 8 is not affected, only the terminal holder 5 may be formed of a heat insulating material.

Furthermore, in the above description, at least the portion of the inner wall of the sensing passage 21 that constitutes the sensor device drawer
Although the terminal holder constituting the support member of the sensor device has been described as being formed of a heat insulating material, the present invention is not limited to this, and the air flow meter The entire body of may be formed from a thermally insulating material.

Further, although the communication path 22 has been described as being formed along the surface of the rectifier 6 whose central portion is formed to protrude toward the upstream side of the air flow, in the present invention, the communication path 22 is particularly limited to this. It is not limited.

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 communicating path 22 be formed in a shape that corresponds to each of the above factors.

Furthermore, two or more communicating passages 22 may be provided for one intake passage 29.

Further, around the sensing passage 21, an intake passage 29 having a circular shape and the same size as seen from the air flow passage direction is provided.
, so that the distances between adjacent objects are equal,
Although four are formed so that the distances from the center of the sensing passage 21 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, and the optimum The shape and number vary depending on various factors such as the cross-sectional shape, size, and length of the sensing passage 21 or the communication passage 22, the displacement of the internal combustion engine, the number of cylinders, the shape of the intake pipe, and the length of the intake pipe. Therefore, it is desirable that the shape and number of the intake passages 29 be modified depending on the various factors described above.

Furthermore, although it has been described that the intake passage is arranged in multiple stages around the sensing passage 21 and one communication passage is formed in each of the stages, the intake passage surrounds the sensing passage 21.
That is, only one C-shaped intake passage may be provided, 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 has a venturi shape, the intake passage is formed so that the communication passage opens at the narrowest part of the venturi in FIG. However, the communication path may be formed to open at a position shifted upstream or downstream from the narrowest part of the venturi.

Furthermore, it goes without saying that the shape of the inner wall of the sensing passage 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 above description, according to the present invention, the following effects are achieved.

(1) The heat generated by the internal combustion engine is not transferred to the sensor arranged in the sensing passage through thermal conduction and/or thermal radiation, and the air flows into the sensing passage due to the airflow passing through the intake passage. Since the air is sucked radially from the bottom side, the air flow passing through the sensing passage can be reliably brought into a laminar flow state without making the sensing passage too long in the airflow passing direction.

Therefore, the intake air amount can be accurately measured without making the air flow meter too large in the airflow passing direction.

Moreover, the air flow meter can be manufactured lightweight and inexpensively.

(2) Since the sensing passage communicates with the side surface of the intake passage, in other words, since the sensing passage has a bottom, even if a backfire occurs, the sensor disposed within the sensing passage Less exposed to blast waves.

As a result, the sensor life is less likely to be shortened or deteriorated due to backfire.

Furthermore, since the blast wave caused by the backfire is less likely to be measured as the amount of intake air, the amount of intake air can always be accurately measured.

[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. FIG. 7 is a sectional view of a third embodiment of the present invention. FIG. 8 is a sectional view of a fourth embodiment of the present invention. 1... Upstream body, IA, 2A, 29... Intake passage, IH... Cylindrical hole, 2... Downstream body, 3゜3
03... Collar, 4,204... Terminal collar, 5... Terminal holder, 6... Rectifier, 7...
・Air flow rate sensor, 8...Temperature compensation sensor, 11...
- Circuit board, 21... Sensing path, 22... Communication path, 7o... Lead wire, 100°200.300.
400--Air flow meter, 21o. 410...Thermal insulation coating agent Patent attorney Michito Hiraki and 1 other person Figure 3 IS IY 2nd Figure 6 Figure 7 Figure 8

Claims (7)

[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 flowmeter body having at least one intake passage arranged parallel to the sensing passage; and a hot wire sensor device arranged in the sensing passage; An air flow meter characterized in that the drawer part is made of a heat insulating material. (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. (4) The air flow rate according to any one of claims 1 to 3, characterized in that at least a drawer portion of the sensor device on the inner wall of the sensing passage is formed separately from the flowmeter main body. Total. (5) An air flow meter installed in an intake pipe of an internal combustion engine to measure the 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 having at least one intake passage arranged in parallel with the sensing passage, and a hot wire sensor device arranged in the sensing passage; An air flow meter characterized in that the support member is formed of a heat insulating material. (6) The air flow meter according to claim 5, further comprising a communication passage communicating the sensing passage and a side surface of the intake passage. (7) The air flow meter according to claim 5 or 6, wherein the sensing passage has a bottom on the downstream side of the air flow.