Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2000-10-06
2003-03-04
Williams, Hezron (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06526822
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for measuring various quantities concerning a flow, among others, relates to a flow rate and flow velocity measurement device using a detection element integrally formed on a detection element and/or a semiconductor chip depending on temperature, and relates to a measurement device suitably applied, for example, as a combustion controlling mass flow rate sensor of an engine for a vehicle or industry, or a mass flow rate sensor for an industrial air conditioning system and compressor pressurized air supply system and, furthermore, an air/fuel ratio controlling flow rate sensor of a domestic gas hotplate.
2. Description of the Related Art
In an engine combustion controlling mass flow rate sensor for a vehicle, an output change due to a pollution substance accumulation onto a detection element is a great problem. In order to solve this problem, in Japanese Patent Laid-Open No. 193863/1996 Gazette and the like there is proposed “to prevent an accumulation of pollution substance onto and an action of reverse flow on the detection element by providing a housing structure with an auxiliary passage for deflecting a part of air from a main air flow and a suitable opening portion”.
However, the housing structure of a sensor disclosed in the Japanese Patent Laid-Open No. 193863/1996 Gazette is effective for accumulation prevention of a pollution substance whose density is much higher than that of a measurement fluid but, as to the pollution substance whose density is relatively low, there is a fear that it enters into a divided flow passage and is accumulated onto the detection element. Further, in this sensor, since it is excessively intended to exclude an influence of the reverse flow, it becomes difficult to measure the reverse flow.
By the way, recently, in order to cope with an emission regulation and the like, there is desired a further high performance combustion controlling mass flow rate sensor, for example, a sensor capable of detecting both of normal flow and reverse flow. Incidentally, hitherto, also a flow passage structure of the sensor capable of detecting the reverse flow has been proposed but, in the case where the reverse flow is measured, a detection output of the same level as the normal flow has not been obtained, so that it is considered that a detection output correction by a control circuit is necessary.
SUMMARY OF THE INVENTION
An object of the invention is to provide a measurement device concerning a flow, in which an accumulation of the pollution substance onto the detection element is prevented. A further object of the invention is to provide a measurement device concerning a flow, which is capable of measuring the reverse flow similarly to the normal flow.
A measurement device of a first aspect of the invention has: a divided flow pipe which has a divided flow pipe passage basically curved in &OHgr;-shape form, and into which a flow in a main flow pipe, that is a detection object, is introduced; an inlet port of the divided flow pipe, which is formed in an outer peripheral side of the divided flow pipe, and opens in a face approximately orthogonal to a flow direction in the main flow pipe; a partition formed in the divided flow pipe; plural branch flow passages divided/formed by the partition so as to mutually branch and join in the divided flow pipe; and a detection element which is disposed so as to be exposed to a flow in, among the plural branch flow passages, the branch flow passage formed in the outer peripheral side of the divided flow pipe, and detects a quantity concerning the flow.
In this measurement device, in the divided flow pipe, a measurement fluid introduced into the divided flow pipe is sharply changed in its direction before it arrives an inlet of the branch flow passage in which the detection element exists. Therefore, the pollution substance whose inertia is high is prevented from entering into the branch flow passage in which the detection element exists. In addition, in the divided flow pipe, by means of further dividing the flow by the partition, it is possible to reduce a Reynolds number of the flow toward the detection element (because a flow sectional area becomes small), so that the flow in the vicinity of the detection element is adjusted and it is possible to perform a high accuracy detection. That is, according to this measurement device, by effectively branching the measurement fluid and changing it in its direction, in regard to both of the pollution substance mixed in the measurement fluid whose density is higher than that of the measurement fluid and the pollution substance whose density is relatively low, these pollution substances are all prevented from accumulating on a detection face of the detection element, so that there is provided a measurement device which is excellent in pollution resistance and whose detection output change is low over a long period.
In a measurement device of a second aspect of the invention, the divided flow pipe has a flow passage structure basically symmetrical with the detection element being made a center. According to the flow passage structure of such a symmetrical structure, since the flow in a divided flow pipe passage for the normal flow and the flow in the divided flow pipe passage for the reverse flow become symmetrical, it becomes unnecessary to particularly compensate a detection output in case of the reverse flow.
Preferably, by constituting the measurement device on the basis of the first and second aspects, as well as being excellent in pollution resistance, a similar detection output level can be obtained in regard to both of the normal flow and the reverse flow.
A measurement device of a third aspect of the invention has: a detection element which is disposed so as to be exposed to a flow in, among the plural branch flow passages, the branch flow passage formed in an inner peripheral side or an intermediate portion of the divided flow pipe, and detects a quantity concerning the flow; and a throttle formed in a flow passage between an inlet port of the divided flow pipe and an inlet of the branch flow passage in which a detection face of the detection element is exposed to the flow therein. In this manner, in case where the detection element is exposed to the branch flow passage of the inner peripheral side or the intermediate portion in which a direction change of the flow introduced into the divided flow pipe inlet port is relatively small in comparison with the branch flow passage of the outer peripheral side, the accumulation of the pollution substance onto the detection element is suitably prevented by providing the throttle.
A measurement device of a fourth aspect of the invention has: a divided flow pipe which has a divided flow pipe passage basically curved in &OHgr;-shape form, and into which a flow in a main flow pipe, that is a detection object, is introduced; an inlet port of the divided flow pipe, which is formed in an one end outer peripheral side of the divided flow pipe passage, and opens in a face approximately orthogonal to a flow direction in the main flow pipe; an outlet port of the divided flow pipe, which is formed in the other end top of the divided flow pipe passage, and opens in a face approximately parallel to a flow direction in the main flow pipe; a partition which is formed in the divided flow pipe, one end of which extends till a vicinity of the inlet port, and the other end of which extends while being spaced from the outlet port; plural branch flow passages divided/formed by the partition so as to mutually branch and join in the divided flow pipe; and a detection element which is disposed so as to be exposed to a flow in, among the plural branch flow passages, the branch flow passage formed in an outer peripheral side of the divided flow pipe, and detects a quantity concerning the flow. Since this measurement device has an asymmetrical flow passage structure, it is suitable especially in case of measuring the normal flow.
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