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DE-112017001254-B4 - Thermal flow meter

DE112017001254B4DE 112017001254 B4DE112017001254 B4DE 112017001254B4DE-112017001254-B4

Abstract

Thermal flow meter, which includes the following: a secondary passage (307) configured to receive a portion of the fluid flowing in a main passage (124); and a flow rate measuring unit (451) arranged in the side passage (307), the side passage (307) comprising: a first passage (351) provided on a measuring surface side of the flow rate measuring unit (451); a second passage (352) provided on a rear surface side of the flow rate measuring unit (451); and a slope passage (361) which is provided on a downstream side in a forward direction of the fluid in the second passage (352) with respect to an outlet of the second passage (352), and the inclined passage (361) has a first inclined surface (371) on one side of the first passage (351) with respect to the flow rate measuring unit (451), wherein the first inclined surface (371) slopes from one side of the second passage (352) to the side of the first passage (351) with respect to the forward direction, wherein the inclined passage (361) has a second inclined surface (372) opposite the first inclined surface (371) in a direction perpendicular to a measuring surface (451a) of the flow rate measuring unit (451), and the second inclined surface (372) is inclined from the side of the second passage (352) to the side of the first passage (351) with respect to the forward direction, and wherein an inclination angle Θ2 of the second inclined surface (372) with respect to the forward direction is greater than an inclination angle Θ1 of the first inclined surface (371) with respect to the forward direction.

Inventors

  • Masashi Fukaya
  • Shinobu Tashiro
  • Akira Uenodan
  • Naoki Saito
  • Tomoaki Saito

Assignees

  • HITACHI ASTEMO, LTD.

Dates

Publication Date
20260513
Application Date
20170413
Priority Date
20160531

Claims (7)

  1. A thermal flow meter comprising: a secondary passage (307) configured to receive a portion of the fluid flowing in a main passage (124); and a flow rate measuring unit (451) arranged in the secondary passage (307), the secondary passage (307) comprising: a first passage (351) provided on a measuring surface side of the flow rate measuring unit (451); a second passage (352) provided on a rear surface side of the flow rate measuring unit (451); and a sloping passage (361) provided on a downstream side in a forward direction of the fluid in the second passage (352) with respect to an outlet of the second passage (352), and the sloping passage (361) has a first sloping surface (371) on one side of the first passage (351) with respect to the flow rate measuring unit (451), the first sloping surface (371) sloping from one side of the second passage (352) to the side of the first passage (351) with respect to the forward direction, the sloping passage (361) having a second sloping surface (372) relative to the first sloping surface (371) in a direction perpendicular to a measuring surface (451a) of the flow rate measuring unit (451), and the second sloping surface (372) sloping from the side of the second passage (352) to the side of the first passage (351) inclines with respect to the forward direction, and wherein an inclination angle Θ2 of the second inclined surface (372) with respect to the forward direction is greater than an inclination angle Θ1 of the first inclined surface (371) with respect to the forward direction.
  2. Thermal flow meter according to Claim 1 , wherein the secondary passage (307) has a section on the downstream side in the forward direction with respect to the inclined passage (361), wherein the section on the side of the first passage (351) with respect to the second passage (352) is provided in a direction perpendicular to the measuring surface (451a) of the flow rate measuring unit (451).
  3. Thermal flow meter according to Claim 1 , wherein the secondary passage (307) in a section perpendicular to the measuring surface (451a) of the flow rate measuring unit (451) parallel to the forward direction has an extended line of the first inclined surface (371) and an extended line of the measuring surface (451a) which intersect on the downstream side in the forward direction with respect to the measuring surface (451a).
  4. Thermal flow meter according to Claim 1 , wherein the secondary passage (307) comprises: a straight passage configured to receive the portion of the fluid flowing in the main passage (124); a discharge outlet configured to discharge the portion of the fluid flowing in the straight passage; and a branching passage branching off from the straight passage on an upstream side in the forward direction of the fluid flowing in the straight passage with respect to the discharge outlet, and the first passage (351), the second passage passage (352) and the incline passage (361) are provided in the branch passage.
  5. Thermal flow meter according to Claim 1 , comprising the following: a flat casing (310) arranged in the main passage (124), wherein the casing limits the secondary passage (307), wherein the measuring surface (451a) of the flow rate measuring unit (451) is perpendicular to a thickness direction of the casing (310).
  6. Thermal flow meter according to Claim 1 , wherein the secondary passage (307) has a second inclined passage (362) on an upstream side in the forward direction with respect to an inlet of the first passage (351), and the second inclined passage (362) has a third inclined surface (373) on the side of the second passage (352) with respect to the flow rate measuring unit (451), wherein the third inclined surface (373) inclines from the side of the second passage (352) to the side of the first passage (351) with respect to the forward direction.
  7. Thermal flow meter according to Claim 6 , wherein the second inclined passage (362) has a fourth inclined surface (374) relative to the third inclined surface (373) in a direction perpendicular to the measuring surface (451a) of the flow rate measuring unit (451), and the fourth inclined surface (374) is inclined from the side of the second passage (352) to the side of the first passage (351) with respect to the forward direction.

Description

Technical field The present invention relates to a thermal flow meter. State of the art A conventional thermal flow meter is known to be a flow meter comprising: a bypass arranged in a main passage through which fluid flows, wherein the bypass receives a portion of the fluid; a flow meter element arranged in the bypass, wherein the flow meter element is configured with a heating resistance pattern; and a support to which the flow meter element is attached (see, for example, claim 1 in patent literature 1). The conventional flow meter comprises a first fluid passage section and a second fluid passage section. The first fluid passage section has a surface on which the flow meter is mounted and a passage forming a secondary passage area. The second fluid passage section has a surface on the side opposite the surface on which the flow meter is mounted and a passage forming a secondary passage area. In the conventional flow meter, the passage forming a surface of the first fluid passage section, positioned on the upstream side of the fluid flow and opposite the flow meter, has an inclined surface that directs the fluid flow to the flow meter. The inclined surface has at least two sides facing in opposite directions. The configuration allows dust to rebound on the inclined surface provided on the opposite surface on the upstream side with respect to the heating resistance pattern in the fluid passage section on the side of the heating resistance pattern, thus preventing the dust from flowing with the fluid flow to the heating resistance pattern. This allows the flow meter to be provided in a way that prevents damage or contamination of the flow meter element comprising the heating resistance pattern, and the flow meter itself exhibits excellent dust resistance in an unsteady flow field, such as a pulsating flow, and displays high reliability and virtually no characteristic error (see, for example, paragraph 0009 in patent reference 1). Patent literature 2 discloses a sensor arrangement for determining at least one parameter of a fluid medium flowing through a channel. The sensor arrangement comprises at least one sensor chip arranged in the channel for determining the parameter of the fluid medium. The sensor chip is mounted in a sensor carrier projecting into the channel. The sensor carrier has a leading edge arranged transversely to the flow of the fluid medium, which in turn has at least one turbulator configured to generate vortices in the flowing fluid medium in the region of the sensor carrier. Patent literature 3 discloses a device for measuring a gas flow rate, comprising a tube body whose interior serves as a passage for a flowing gas to be measured. A housing, having a generally U-shaped bypass passage, is formed integrally with the tube body. A plate-shaped flow rate sensing element is arranged in a first passage of the bypass passage, wherein a passage restriction section is arranged in a second passage of the bypass passage downstream of the first passage in the flow direction. Patent literature 4 discloses a protective device for a measuring element in a measuring device. Patent literature 5 discloses an air mass meter for internal combustion engines with one measuring channel. Patent literature 6 discloses a sensor device for detecting at least one flow property of a fluid medium, in particular for detecting the air flow in the intake tract or charge air tract of an internal combustion engine. List of known writings Patent literature Patent literature 1: JP 2012-93203 APatent literature 2: DE 10 2008 042 155 A1Patent literature 3: DE 197 24 659 A1Patent literature 4: DE 199 53 776 A1Patent literature 5: DE 10 2011 051 196 A1Patent literature 6: DE 10 2012 224 049 A1 Brief description of the invention Technical problem The conventional thermal flow meter has the disadvantage that the increase in the counterflow direction in the first fluid passage section due to the counterflow of the fluid during the pulsation of the fluid causes the flow rate to be measured by the flow meter element to fall below the actual flow rate, leading to an increase in the measurement error. The present invention was made in consideration of the problem and an object of the present invention is to provide a thermal flow meter which makes it possible for the measurement error when fluid pulsates to fall below that of a conventional thermal flow meter. Solution to the problem To solve this problem, the thermal flow meter of the present invention comprises: a secondary passage configured to receive a portion of the fluid flowing in a primary passage; and a flow rate measuring unit arranged in the secondary passage. The secondary passage has: a first passage provided on a measuring surface side of the flow rate measuring unit; a second passage provided on a rear surface side of the flow rate measuring unit; and an inclined passage provided on a downstream side in a forward direction of the fluid in the second passage with resp