JPH0617810B2 - Thermal air flow meter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thermal air flow meter suitable for use in measuring the amount of intake air of, for example, an automobile engine.

[Conventional technology]

A conventional thermal air flow meter used for measuring the intake air amount of an engine, for example, is provided with a bypass air passage in the main air passage of an air intake meter, and a heating resistor for measuring the air amount is provided in the bypass air passage. There is a temperature-sensitive resistor for temperature compensation. The bypass passage in this type of flow meter is incorporated in the inner wall of the main air passage (downstream ring system), and is arranged in the main air passage as disclosed in JP-A-61-65053. (Axial flow method). Among them, in the so-called axial flow type, the bypass passage can be provided by utilizing the space of the main air passage without incorporating it into the inner wall of the main air passage, so that the body of the intake system can be downsized. Also,
Since the bypass passage itself is cooled by the flow of air in the main air passage, there are various advantages such that the flow rate can be measured without being affected by the thermal effect in the engine room.

[Problems to be Solved by the Invention]

By the way, the bypass passage of the axial flow type thermal air flow meter as described above has a location where the heating resistor is disposed and an upstream side of the location where the heating resistor is disposed along the passage in the air flow direction of the main air passage, Since the structure in which the downstream side of the heat generating resistor arrangement portion is bent in the direction orthogonal to the air flow direction of the main air passage is adopted, there are the following points to be improved.

That is, since a part of the bypass passage of the thermal air flow meter is orthogonal to the air flow direction of the main air passage, the presence of the bypass passage itself near the outlet of the bypass air passage in the main air passage causes a turbulent flow phenomenon such as vortex flow. Occurs, and this turbulent flow adversely affects the air flow in the bypass passage, and when engine pulsating flow such as engine blowback occurs in the main air passage, this pulsating flow passes through the bypass passage outlet. The flow of air in the bypass air passage is adversely affected, and as a result, the flow rate of air in the bypass passage corresponding to the throttle opening may fluctuate. Such an air flow rate fluctuation causes a fluctuation in the output of the thermal air flow meter, and two kinds of detection outputs are generated based on the fluctuation (binary phenomenon), or the flow meter output deviates from the normal value and bounces. This was the cause of the phenomenon of rising (jumping up phenomenon).

The present invention has been made in view of the above points, and an object thereof is to effectively prevent turbulence of an air flow generated near the bypass air passage outlet in the main air passage, and to prevent the influence of engine pulsation. The aim is to reduce the flow rate as much as possible, to normalize the flow of the bypass air passage, and to improve the measurement accuracy of the thermal air flow meter.

[Means for Solving the Problems]

The above object is to arrange a bypass air passage in the main air passage of the body that is a part of the intake system, and to generate a heating resistor for detecting the amount of intake air and a temperature sensing resistor for temperature compensation in the bypass air passage. In a so-called axial-flow type thermal air flow meter having a body, the outlet of the bypass air passage is opened in a direction substantially perpendicular to the intake air flow direction of the main air passage, and the bypass air passage outlet is provided. This is achieved by disposing an eaves portion for rectifying the intake air flow in the main air passage on the upstream side of.

[Action]

According to the present invention having such a configuration, when the intake air flowing in the main air passage passes through the bypass air passage installation location, the air flow in the main air passage passes through the eaves upstream of the bypass air passage outlet. Since it is rectified as a result, it is possible to effectively prevent the turbulence of the main air passage air flow near the outlet of the bypass air passage. Further, even if engine pulsation due to blowback on the engine side occurs in the main air passage, the outlet of the bypass air passage opens in a direction substantially at right angles to the intake air flow direction of the main air passage. The engine pulsation power is not directly applied, and its influence can be reduced. As a result, the flow of air in the bypass air passage can be kept normal, and the detection output of the heating resistor can be in a stable state.

〔Example〕

 An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a vertical sectional view showing an embodiment of the present invention, and FIG. 2 is a partial perspective view showing the vicinity of an outlet portion of a bypass air passage used in the above embodiment.

The hot-wire type air flow meter shown in FIG. 1 is of a so-called axial flow type. In the figure, reference numeral 1 is an aluminum die-cast body.
Has a main air passage 9 having an inner diameter φ70, and the bypass air passage 5 integrated with the body 1 is arranged in the main air passage 9. The bypass air passage 5 is located in the center of the main air passage 9 from the inlet to the location where the heat ray 2, the temperature sensitive resistor 3 and the like are arranged, and is bypassed downstream thereof. The air passage outlet 6 is bifurcated in a direction orthogonal to the air flow direction of the main air passage 9, and the outlet 6 reaches near the inner wall of the main air passage 9. That is, the bypass air passage 5 of this example has an inverted T shape as a whole. In addition, each outlet 6 of the bypass air passage 5
Are arranged on both side walls 5b (shown in FIG. 2) of the bypass air passage and are opened so as to be substantially perpendicular to the air flow direction of the main air passage 9. Further, in the portion of the bypass air passage 5 orthogonal to the air flow direction of the main air passage 9, the upper portion 5a has a semicircular cross section, and the outlet portion 6 is recessed from the bypass passage side wall 5b and the upper portion 5a. A part of the upper portion 5'a immediately above the outlet portion 6 projects from the outlet portion 6 in an eaves-like shape (a portion indicated by reference numeral 11). 5 c is the bottom of the bypass air passage 5. Bottom 5c
For the shape of, any one of the shapes shown in FIGS. 4 and 5 is adopted. In FIG. 4, the outer shape of the bottom portion 5c of the bypass air passage outlet 6 has a semicircular cross section. Further, in FIG. 5, the outer shape of the bottom portion 5c of the outlet of the bypass air passage has a chevron shape.

Reference numeral 7 denotes a fitting portion of the heat ray support body 12, and the fitting portion 7 extends from the inner wall of the main air passage 9 to a part of the bypass air passage 5 (main air passage 9
The heat wire support body 12 is fitted in the fitting portion 7. Reference numeral 8 is intake air passing through the bypass air passage 5.

One end of the heat wire support 12 facing the inside of the bypass air passage 5 is a step surface, and the heat wire 2 for measuring the air flow rate and the temperature sensitive resistor 3 for temperature compensation are arranged so as to project from each step surface. Reference numeral 4 is a control circuit connected to the heat ray support 12.

Therefore, in the present embodiment, the air 8a flowing into the bypass air passage 5 is divided into two directions after passing through the location where the heat wire 2 and the temperature sensitive resistor 3 are arranged, and the bypass air passage outlet 6 is provided.
Is blown out at right angles to the air flow direction of the main air passage 9. In this air flow process, the heating wire 2 detects the air flow rate.

Further, in the present embodiment, the influence is reduced by the turbulence of the air flow generated near the bypass air passage outlet 6 and engine pulsation such as sucking back from the engine side as follows.

That is, the flow of air in the main air passage 9 increases in flow especially in the fully open region of the throttle valve, and turbulent flow such as vortex is likely to occur near the installation portion of the bypass passage 5, but in the present embodiment,
Immediately upstream of the bypass air passage outlet 6, the eaves 11 has a rectifying function to prevent turbulent flow near the passage outlet 6. Further, even when there is engine backflow etc. in the main air passage 9, the bypass air passage outlet 6 is opened in a direction perpendicular to the air flow in the main air passage 9, so that the bypass air passage 5 will be backfired. It is possible to avoid the influence of engine pulsation power due to the above. Further, in this embodiment, in addition to these and the action, since the bottom portion 5c of the bypass air passage 5 has a semicircular cross section or a mountain-shaped outer shape, the air pulsating flow from the engine is shown in FIG. 4 and FIG. It is rectified at the bottom portion 5c as shown by the arrow 10. Arrow 8b in FIGS. 4 and 5
Shows the intake air flow of the main air passage 9, which is rectified by the semicircular upper portion 5 a of the bypass passage and the eaves 11. In this way, the flow of air in the bypass air passage 5 maintains a normal state without being affected by the flow state of the air in the main air passage 9, engine pulsation, etc.
It is possible to improve the accuracy of measuring the air flow rate by the hot wire.

FIG. 6 is experimental data showing a boost negative pressure-output voltage characteristic diagram of the hot-wire air flow meter of the present embodiment and a conventional axial-flow hot-wire air flow meter using the engine speed N as a parameter. The horizontal axis represents the boost negative pressure P, the vertical axis represents the output voltage (V) of the hot wire air flow meter, the solid line represents the characteristics of this embodiment, and the broken line represents the characteristics of the conventional example.

However, in the conventional example, as described in the section of [Problems to be Solved by the Invention], the bypass air passage is affected by engine pulsation and air turbulence in the main air passage, and as a result, in particular, When the throttle is fully open, a so-called binary phenomenon occurs, in which the output (detection value) of the air flow meter output voltage V drops or returns as shown by reference numeral 13, or the output voltage V changes as shown by reference numeral 14. There was also a phenomenon in which it jumped up and out of the proper value.

On the other hand, in the experimental data of the present embodiment, the binary phenomenon and the jumping phenomenon were not observed due to the fact that the rectifying action of the eaves 11 and the like and the influence of engine pulsation were almost eliminated.

FIG. 3 is a longitudinal sectional view showing a second embodiment of the present invention, in which the same reference numerals as those in the first embodiment show the same or common elements.

In this embodiment, the first point is that the bypass passage 5 has an elbow shape.
In addition to the above, the eaves 11 is added to the outlet 6 in the bypass passage 5 as in the first embodiment, and the outlet is directed in a direction orthogonal to the air flow direction of the main air passage 9 in the point different from the embodiment. Therefore, the same effect as the first embodiment can be obtained.

In addition, in the second embodiment, the length of the heat ray support 12 can be shortened, and the cost can be reduced.

〔The invention's effect〕

As described above, according to the present invention, the turbulence of the air flow generated near the bypass air passage outlet in the main air passage is effectively prevented, and the influence of engine pulsation is minimized,
It is possible to normalize the flow of the bypass air passage and improve the measurement accuracy of the hot wire air flow meter.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view showing a first embodiment of the present invention, FIG. 2 is a perspective view showing the vicinity of an outlet of a bypass air passage used in the first embodiment, and FIG. 3 is a second embodiment of the present invention. And FIG. 4 and FIG. 5 are sectional views showing a concrete mode of the bypass air passage outlet of the first and second embodiments, and FIG. 6 is a hot wire air flow rate of the first embodiment. It is the diagram which compared the output characteristic of the meter and the conventional hot wire type air flow meter. 1 ... Body, 2 ... Heat wire, 3 ... Temperature-sensitive resistor, 5 ...
Bypass air passage, 5c ... Bypass passage bottom, 6 ...
Bypass outlet, 10 ... Main air passage, 11 ... Eaves.

Claims (2)

[Claims] 1. A bypass air passage is arranged in a main air passage of a body which is a part of an intake system, a heating resistor for detecting an intake air amount in the bypass air passage, and a temperature sensing temperature compensation. In a hot-wire type air flow meter provided with a resistor, the outlet of the bypass air passage is opened in a direction substantially perpendicular to the intake air flow direction of the main air passage, and an eave is provided on the upstream side of the bypass air passage outlet. A thermal air flow meter, characterized in that it is provided with a section. 2. The thermal air flow meter according to claim 1, wherein the bypass air passage has a bottom outer shape of a passage outlet which is substantially semicircular or mountain-shaped in cross section.