JPS58109814A - Air flow meter - Google Patents

Abstract

PURPOSE:To prevent the accumulation of water at a by-pass line, by opening the slit at the outlet opening part to the lowest part of the Venturi inner wall for the by-pass line to which a hot wire for measurement of air flow is provided. CONSTITUTION:The slit at an outlet 7 of a circular line 4b of a by-pass 4 is opened to the lowest part of the inner wall of a Venturi 3. The by-pass 4 contains a hot wire 5 for detection of air current velocity for the purpose of measurement of intake quantity of an internal combustion engine. Therefore the accumulation of water is prevented for the line 4b via the Venturi 3 which generates the negative pressure, and the water is easily discharged. This can prevent the working incapability of an air flow meter which is caused by the accumulation of water or freezing in the winter season.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an intake air flow rate detection device for an internal combustion engine, and particularly to an air flow meter using a hot wire.

When an air flow meter with a hot wire installed in the bypass passage that bypasses the main air passage is used horizontally, the inlet and outlet of the bypass passage are connected by a tubular passage, but eventually water collects in the annular passage. There is a problem that the bypass passage is blocked. It is a problem if this water gets stuck in the straw in winter.

SUMMARY OF THE INVENTION An object of the present invention is to provide an air 70-meter that can prevent water from accumulating in the bypass passage in a bypass air flow meter that branches into a main air passage.

An embodiment of the present invention will be described with reference to FIG. 1.2. The air flow meter 1 is located in the main air passage 2a.

2b, a bench area 3, a bypass passage 4, a horizontal passage 4a% reward passage 4b, a hot wire element 5, and a hot wire drive circuit 6. The bypass passage 4 opens and branches into the venturi 3 portion, and the other end opens into the main air passage 2b upstream of the venturi 3. The hot wire element 5 is located in the side passage 4 of the bypass passage.
m, and is connected to the hot wire drive circuit 6.

The air to be metered flows into the main air passage 2b, the venturi 3, and the main air passage 2m. At this time, since the bench area 3 is constricted, negative pressure is generated, and an air flow is generated in the bypass passage 4 due to the pressure difference with the main air passage 2b. This air flow rate is measured by the hot wire element 5. This is already well known, and by detecting the flow velocity in the bypass passage 4, the entire O! ! Air flow rate can be measured.

The lower outlet of the bypass passage 4 is opened at least at the lowest part of the inner wall of the venturi 3, allowing water to drain out.

Also, the negative pressure of the venturi is several tens of mHg.
Once this happens, the water will drain easily.

According to the present invention, even if water accumulates in the annular passage, the water can easily drain out, so that the air flow meter does not become inoperable due to water accumulation.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an air flow meter according to an embodiment of the present invention, and FIG. 2 is a view taken along arrow P. 1... Air flow meter, 2a, 2b... Main air passage, 3... Venturi, 4... Bypass passage, 4a
...Horizontal passage, 4b...Circular passage, 7...Exit. Agent Patent Attorney Akio Takahashi

Claims (1)

[Claims] 1. Install a hot wire in the bypass passage, and place it above the horizontal gap where the bypass inlet passes through the center of the air flow meter.
An air flow meter in which an outlet opens downward from a horizontal plane passing through the center, and the opening is in the form of a slit, and the air flow meter has at least a slit opened at the lowest S of the inner wall of the bench area.