Hot-wire air flow meter

Measuring and testing – Simulating operating condition – Marine

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G01M 1500

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active

049861158

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BRIEF SUMMARY
DESCRIPTION



Background of the Invention

This invention relates to a hot-wire air flow meter and, more particularly, to a hot-wire air flow meter for internal combustion engines which forms a part of and air intake system of an automobile engine and which detects and controls a quantity of air drawn in the air intake system.
Hot wire air flow meters of the aforementioned type are disclosed in commonly assigned co-pending U.S. application Ser. Nos. 07/207,255 and 07/260,781.
Conventional hot-wire air flow meters for internal combustion engines are described in, for example Japanese Utility Model Application Laid-Open No. 170682/1984, Japanese Patent Application Laid-Open No. 79162/1985, and Japanese Utility Model Application Laid-Open No. 25558/1986, wherein the hot-wire air flow meter is located close to the throttle valve with a part or all of the fuel injection valves installed in the main air passage at a point downstream of the air flow meter inlet and upstream of the throttle valve. This type of air flow meter has a throttled portion formed on the wall surface of the main passage, somewhere downstream of a bypass passage outlet and upstream of the throttle valve. In a range downstream of the bypass passage outlet and upstream of the throttled portion inlet, there is no section of the main passage that is constant in cross section. As a result, in this region of the main passage, the pressure acting on a plane perpendicular to the main air flow is not stable, nor is the air speed distribution. This in turn gives rise to a problem that these unstable conditions have adverse effects on the air flow speed in the bypass passage which is varied accordingly.
The conventional air flow meters also have no special measures to reduce variations in the main-bypass air flow ratio, which results in an inability to detect the amount of air taken in with precision.
The object of this invention is to provide a hot-wire air flow meter that can stabilize the speed distribution of air drawn in and thereby measure the quantity of air accurately.
Another object of the invention is to provide an internal combustion engine that can perform an optimum control on air-fuel ratio by using the above hot-wire air flow meter.
A further object of the invention is to provide a method of manufacturing the above hot-wire air flow meter with ease.
The hot-wire air flow meter according to this invention includes a main passage forming an air intake flow passage for the internal combustion engine, a hot-wire element for measuring the quantity of air drawn in and a bypass passage installed in the main passage and containing the hot-wire element. The bypass passage includes a first passage formed along the main passage axis and a second passage formed in the radial direction of the main passage, with a throttled portion formed between the bypass passage and a throttle valve located downstream of the bypass passage.
The internal combustion engine according to this invention includes the above-mentioned hot-wire air flow meter, a speed sensor to detect the revolution speed of the engine, fuel injectors to inject fuel into drawn in air, and a controller to determine the amount of fuel to be injected according to the quantity of air intake detected by the hot-wire air flow meter and the revolution speed detected by the revolution speed sensor and to output to the fuel injectors signals representing the calculated amount of fuel to be injected.
The method of manufacturing the above-mentioned hot-wire air flow meter according to this invention is characterized in that the hot-wire air flow meter is die-cast by using inner molds, with the inner molds including: an inner mold having an abutting surface and an overlapping surface and being adapted to form the throttled portion, with a two divisible inner molds forming the bypass passage.
Since the construction of this invention has a large area for heat-exchange between the bypass passage wall and the main flow, the temperature in the bypass passage wall is always maintained close to the temperat

REFERENCES:
patent: 4179925 (1979-12-01), Graham
patent: 4472965 (1984-09-01), Krapp et al.
patent: 4478075 (1984-10-01), Oyama et al.
patent: 4739651 (1988-04-01), Smith

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