Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2002-05-07
2003-11-18
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
C073S202500
Reexamination Certificate
active
06647776
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a split-flow flowmeter for measuring parameters related to flow, particularly flow rate and flow velocity. More particularly, the invention relates to a split-flow flowmeter using an exothermic or endothermic detection element and/or a detection element integrally formed on a semiconductor chip; for example, a split-flow flowmeter favorably applicable to a mass flow sensor for use in combustion control of a vehicle engine or an industrial engine, a mass flow sensor for use in an industrial air-conditioning system or a compressed-air supply system, or a flow sensor for use in control of the air-fuel ratio of a household gas cooker.
2. Description of the Related Art
In recent years, the circumstances surrounding automobiles have shifted toward stronger consideration for the environment, as has been demanded by emission regulations and the like. In order to comply with such regulations, engine combustion must be controlled with higher accuracy, and in this connection a flowmeter must be able to accurately measure a flow rate within a suction pipe.
Conventionally, a split-flow flowmeter has been proposed as a flowmeter for measuring a flow rate within a suction pipe. The split-flow flowmeter detects a portion of flow diverted from a main-flow pipe (an object pipe of measurement) into a flow path thereof (hereinafter also referred to as a “split-flow passage” or a “flow splitter tube”) to thereby measure a flow rate in the main-flow pipe.
3. Problems to be Solved by the Invention
However, a conventionally proposed split-flow flowmeter involves the following problems: flow disturbance on a detection element is great; in particular, the measurement accuracy is low in measuring a low-flow-rate region.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a split-flow-type flowmeter capable of reducing flow disturbance in the vicinity of a detection element within a flow path thereof and capable of accurately measuring flow rate in a low-flow-rate region.
The above objects of the present invention have been achieved by providing a flowmeter for detecting a portion of flow diverted from a main-flow pipe, which is an object of measurement, into the same, using a detection element so as to measure parameters related to the flow within the main-flow pipe; i.e., a split-flow flowmeter, which comprises a detection element disposed to face a flow path through which a fluid to be measured flows, and a venturi structure adapted to throttle a flow directed toward the detection element to thereby reduce disturbance of the flow. The split-flow flowmeter is characterized in that the venturi structure is disposed opposite the detection element within the flow path and comprises a protrusion protruding toward the detection element within the flow path.
This split-flow flowmeter is mainly characterized in that a portion of the venturi structure assumes the form of a protrusion. However, the entire venturi structure (the venturi structure itself) may assume the form of a protrusion. In such a split-flow flowmeter, the venturi structure reduces flow disturbance in the vicinity of the detection element within the flow path of the split-flow flowmeter, whereby a flow rate can be accurately measured with small variations in output. Further, the protrusion reduces a region where resistance to flow arises, and can generate a large pressure difference, whereby the rate of flow passing through a clearance between the protrusion and the detection element can be easily increased even in measuring a low-flow-rate region, thereby greatly enhancing output. Further, in this split-flow-type flowmeter, since a region where resistance to flow arises is reduced, output is also enhanced in measuring in a medium-flow-rate region and a high-flow-rate region. Additionally, since throttling yields the effect of reducing disturbance, measurement can be carried out at high resolution, whereby a flow rate can also be accurately measured in medium- and high-flow-rate regions.
A preferred mode for carrying out the present invention will next be described.
According to a preferred mode for carrying out the present invention, a venturi structure partially protrudes (a protrusion is formed on the venturi structure); i.e., a portion of the venturi structure is formed into a protrusion. The protrusion is disposed opposite a detection element within a flow path of a split-flow-type flowmeter and protrudes toward the detection element within the flow path. An example of the detection element may be a diaphragm type in which a heater and two temperature sensors are formed for detecting a gas flow (as described in U.S. patent application Ser. No. 09/754,343, incorporated herein by reference, or European Patent Application No. 01300077.3 filed by the present applicant).
Preferably, the venturi structure is configured such that the outside wall of a bottom portion of a curved partition, which is disposed within a split-flow passage so as to impart substantially the shape of the letter &OHgr; to the passage, is disposed in the opposing proximity of the detection element. A protrusion is formed which protrudes toward the detection element from the outside wall of the curved partition. A height (B) of the protrusion is preferably in the range of 0.5-4.5 mm, a gap or clearance (A) between the protrusion and the detection element is preferably in the range of 0.3-3 mm and a thickness (Dt) of the protrusion is preferably in the range of 0.5-3 mm not exceeding the width or length of the detection element as measured in a gas flow direction, as may be understood by FIG.
9
. Preferably, the protrusion has a ridge-like shape as shown in
FIG. 11
, in which a ridge length (H) is preferably in the rage of 1-10 mm and the length of the detection element is within the ridge length (H). Importantly, the protrusion protrudes sharply. In other words, a convex radius (C) formed at a bottom skirt of the protrusion as shown in
FIG. 9
is about less than 2 mm. Each of these dimensional factors contributes to a sensitive detection of the pressure variation of a gas flowing over the detection element.
According to the preferred mode for carrying out the present invention, a portion or the entirety of a surface of the protrusion which faces the detection element is curved. This feature prevents the generation of vortexes or separation of flow in the vicinity of the protrusion, and thus disturbance of air flow is reduced, thereby enhancing output.
According to the preferred mode for carrying out the present invention, a section of the protrusion taken along a plane extending in a flow direction in a flow path (split-flow passage) of a split-flow flowmeter assumes, singly or in combination, any of a triangular shape, a rectangular shape, a polygonal shape, a spindle shape, a semicircular shape, and a semielliptic shape. This feature can greatly reduce a region where resistance to flow arises, thereby enhancing output in measurement not only in a low-flow-rate region but also in a high-flow-rate region.
According to the preferred mode for carrying out the present invention, the venturi structure comprises a plurality of protrusions. Employing a plurality of protrusions in combination can impart the desired flow rate characteristics to the flowmeter.
According to the preferred mode for carrying out the present invention, the flow path structure of the split-flow flowmeter is formed to have symmetry with respect to a plane including the centerline perpendicular to a detection portion of the detection element. Particularly, the plurality of protrusions are arranged symmetrically with respect to the plane. Such a split-flow-type flowmeter can equivalently measure a regular flow and a backflow.
According to the preferred mode for carrying out the present invention, the plurality of protrusions are formed or arranged opposite one another along the flow transversal direction of the flow path of the split-flow flowmeter. A groove or a space is formed bet
Kohmura Yoshihiko
Kojima Takio
Maeda Shunsuke
Oshima Takafumi
NGK Spark Plug Co. Ltd.
Patel Harshad
Sughrue & Mion, PLLC
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