Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
1998-09-25
2001-05-01
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
C073S202000, C073S118040
Reexamination Certificate
active
06223594
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application relates to and incorporates herein by reference Japanese Patent Application No. 9-278886 filed on Oct. 13, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air flow amount measuring apparatus for measuring flow amount of air flowing in an air flow passage, which may be applied to an intake system of an internal combustion engine, for instance.
2. Related Art
Conventionally, thermal type air flow amount measuring apparatuses (air flow meters) are known as disclosed in Japanese Utility Model Publications No. 6-23942 and No. 5-24189.
In the air flow meter disclosed in Japanese Utility Model Publication No. 6-23942, a convex part is formed at the upstream side of a heater wire and a step is formed at the downstream-side terminal end of the convex part. This step at the downstream-side terminal end disturbs the flow of air and generates periodical vortexes. A thermal sensing unit responds to periodical variations in the flow speed caused by the vortexes, resulting in possible detection errors due to periodical variation.
In the airflow meter disclosed in Japanese Utility Model Publication No. 5-24189, a pair of dust-proofing members are provided for effectively restricting oil and dust from adhering on electrical leads of a hot film type sensing unit. Those dust-proofing members stabilize accuracy in measurement of the air flow amount by suppressing changes in the heat radiation characteristics of the sensing unit caused by an accumulation of dust.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thermal type air flow amount measuring apparatus that accurately measures a flow amount of air.
It is another object of the present invention to provide a thermal type air flow amount measuring apparatus which rectifies a flow of air flowing to a sensing unit in a compact size.
For achieving the above object, an air flow amount measuring apparatus, a flow rectifying throttle unit is provided together with a thermal sensing unit in a bypass passage. Support members for supporting the thermal sensing unit are positioned downstream of the throttle unit at a behind or downstream position relative to the flow of air. As the thermal sensing unit is exposed in the flow of air rectified by the throttle unit, a measurement of flow amount can be attained stably under a condition in which turbulence is less likely to occur. Further, as dust in the air is less likely to adhere to the support members, an output of the thermal sensing unit can be maintained at a highly accurate value.
Preferably, the bypass passage is formed in an inverted U-shape, and the throttle unit is formed in an inlet-side bypass passage in which turbulence is less likely to occur. Further, support members of the thermal sensing unit are positioned behind (downstream of) the throttle part so that dust in the air is less likely to adhere to the support members. The bypass passage area is in a rectangular shape and the throttle part is provided on two parallel sides located at the same position in the air flow direction.
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Kohno Yasushi
Kondo Minoru
Koyama Hideki
Nagasaka Ryo
Takiguchi Tomoyuki
Denso Corporation
Fuller Benjamin R.
Nixon & Vanderhye PC
Patel Jagdish
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