Measuring and testing – Volume or rate of flow – Proportional
Reexamination Certificate
2001-08-10
2003-06-17
Williams, Hezron (Department: 2855)
Measuring and testing
Volume or rate of flow
Proportional
C073S118040
Reexamination Certificate
active
06578414
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a split-flow-type flowmeter for measuring parameters related to flow, particularly flow rate and flow velocity. More particularly, the invention relates to a split-flow-type flowmeter using a temperature-dependent detection element and/or a detection element integrally formed on a semiconductor chip; for example, a split-flow-type flowmeter favorably applicable to a mass flow sensor for use in combustion control of a vehicle 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
Japanese Patent Application Laid-Open (kokai) No. 8-5427 discloses a split-flow-type flowmeter to be attached to an intake system of an internal combustion engine. In order to accurately measure flow rate in a main-flow pipe along the regular flow direction (directed from an air intake toward the internal combustion engine), the disclosed split-flow-type flowmeter is designed such that the structure of a split-flow passage, the position of a flow inlet of the passage, and the position of a flow outlet of the passage are determined so as to avoid influence of a pulsating flow; i.e., so as not to detect a pulsation component.
Specifically, the split-flow-type flowmeter disclosed in Japanese Patent Application Laid-Open (kokai) No. 8-5427 is characterized in the following:
(1) The center of an opening of the flow inlet of a flow splitter tube is located at a position on a flow cross section of the main-flow pipe where flow is theoretically of an average flow velocity, for the following reason. When the flow inlet is located at a position where the flow velocity is higher than the average flow velocity (at a position biased toward the center of the main-flow pipe), a measurement error on the plus side arises. By contrast, when the flow inlet is located at a position where a flow velocity is lower (at a position biased toward the wall surface of the main-flow pipe), a measurement error on the minus side arises.
(2) The split-flow passage assumes the shape of the letter L such that a downstream flow path extending on a flow cross section of the main-flow pipe is longer than an upstream flow path extending in parallel with the flow direction in the main-flow pipe, thereby yielding an inertial effect. The inertial effect cancels a measurement error on the minus side which arises from delay in detection response upon occurrence of a pulsating flow in the main-flow pipe.
(3) The flow inlet of the split-flow passage opens on a surface (flow cross section) facing toward a direction opposite the flow direction in the main-flow pipe. The flow outlet of the split-flow passage opens on a surface parallel to the flow direction in the main-flow pipe. Thus, pressure at the flow inlet is always higher than that at the flow outlet, thereby preventing backflow from the flow outlet.
(4) A heating resistor and a temperature-sensing resistor, which constitute a hot-wire flowmeter, are disposed apart from each other in the split-flow passage.
(5) The heating resistor and the temperature-sensing resistor are located within the main-flow pipe.
The split-flow-type flowmeter disclosed in Japanese Patent Application Laid-Open (kokai) No. 8-5427 can measure a flow rate accurately when a flow direction or flow rate remains unchanged for a relatively long period of time; i.e., the flowmeter can measure an average flow rate over a long period of time. However, the split-flow-type flowmeter cannot measure the flow rate of a varying flow with good response. This is because the split-flow-type flowmeter is designed such that the structure of the split-flow passage, the position of the flow inlet of the passage, and the position of the flow outlet of the passage are determined so as not to detect pulsation.
SUMMARY OF THE INVENTION
In view of the foregoing, a primary object of the present invention is to provide a split-flow-type flowmeter capable of measuring the flow rate of a pulsating flow. Another object of the present invention is to provide a construction of a split-flow-type flowmeter facilitating achievement of the primary object of the invention. A further object of the present invention is to provide a split-flow-type flowmeter allowing easy optimization of the position of a flow inlet/flow outlet of a flow splitter tube according to the diameter of a main-flow pipe and capable of measuring a flow rate accurately.
To achieve the primary object mentioned above, the present invention provides a split-flow-type flowmeter characterized in that a split-flow passage assumes a flow path structure that is symmetrical with respect to a plane passing through a detection element or with respect to the detection element; a flow inlet and a flow outlet of the split-flow passage open in opposition to each other along a flow direction in a main-flow pipe and are symmetrically positioned with respect to a flow cross section of the main-flow pipe; in order to divert into the split-flow passage a portion of flow having a relatively high flow velocity from the main-flow pipe, the center of opening of the flow inlet/flow outlet of the split-flow passage is positioned between the center of the flow cross section of the main-flow pipe and an average-flow-velocity position at which flow in the main-flow pipe is of an average flow velocity, as observed on the flow cross section of the main-flow pipe.
The split-flow-type flowmeter of the present invention provides the following advantages.
(1) Since the flow inlet and the flow outlet are structured and arranged symmetrically and the split-flow passage assumes the form of a flow path that is symmetrical with respect to the detection element, a regular flow component and a backflow component can be detected with equivalent response.
(2) Since the flow inlet and the flow outlet of the split flow passage open into the main-flow pipe at a position of high flow velocity, the flowmeter can capture a pulsating flow, an abrupt change in flow direction in the main-flow pipe, and abrupt variations in flow rate. Thus, the flow rate can be measured with good response.
(3) Thus, the split-flow-type flowmeter of the present invention can be favorably applied to measurement of a flow rate in the main-flow pipe in which flow may pulsate.
(4) Furthermore, the split-flow-type flowmeter of the present invention can measure, with equivalent response, a regular flow component and a backflow component of a pulsating flow in the main-flow pipe.
The present invention further provides the following constructions of the split-flow-type flowmeter mentioned above. Specifically, the present invention provides a construction of a split-flow-type flowmeter comprising an introduction unit for diverting therein a portion of flow from the main-flow pipe, and a detection unit having a detection element and a flow path peripheral to the detection element and in which, with the introduction unit and the detection unit attached to the main-flow pipe, flow paths belonging to the respective units communicate with each other directly or indirectly to thereby establish the split-flow passage. The present invention further provides a construction of a split-flow-type flowmeter comprising an introduction unit inserted into the main-flow pipe and having a flow inlet for diverting therein a portion of flow from the main-flow pipe, a flow outlet for discharging the portion of flow, and a first flow path communicating with the flow inlet and the flow outlet that is symmetrical with respect to a predetermined plane; and a detection unit having a second flow path that is symmetrical with respect to a predetermined plane and a detection element exposed to flow within the second flow path. Herein, the term “a predetermined plane” means a plane parallel to a flow cross section of the main-flow pipe as observed in an assembled condition. That is, the first flow path and the second fl
Kohmura Yoshihiko
Kojima Takio
Maeda Shunsuke
Oshima Takafumi
Miller Takisha S
NGK Spark Plug Co. Ltd.
Sughrue & Mion, PLLC
Williams Hezron
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