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DE-112017001165-B4 - Thermal flow meter

DE112017001165B4DE 112017001165 B4DE112017001165 B4DE 112017001165B4DE-112017001165-B4

Abstract

Thermal flow meter, including: a secondary channel (307) that receives part of a fluid (30) flowing through a main channel (124); and a flow metering unit (451) located in the secondary channel, wherein the secondary channel comprises: a first passage (351) provided on a measuring surface side (451a) of the flow measuring unit; a second passage (352) provided on a rear side (451b) of the flow measuring unit; and an inclined passage (361) provided upstream of an inlet (351a) of the first passage in a forward flow direction (F) of the fluid in the first passage, wherein the secondary channel is further provided on a wall surface on the side of the second passage with a convex section (381) which projects in a thickness direction towards an opposite wall surface on the side of the first passage, and wherein the convex section in the region of the inclined passage has an inclined surface (371) which is inclined with respect to the forward flow direction from one side of the second passage to one side of the first passage in order to be closer to the side of the second passage than the flow measuring unit.

Inventors

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

Assignees

  • HITACHI ASTEMO, LTD.

Dates

Publication Date
20260513
Application Date
20170420
Priority Date
20160607

Claims (5)

  1. Thermal flow meter comprising: a secondary channel (307) that receives a portion of a fluid (30) flowing through a main channel (124); and a flow meter (451) arranged in the secondary channel, the secondary channel comprising: a first passage (351) provided on a measuring surface side (451a) of the flow meter; a second passage (352) provided on a rear side (451b) of the flow meter; and an inclined passage (361) provided upstream of an inlet (351a) of the first passage in a forward flow direction (F) of the fluid in the first passage, whereby the secondary channel is further provided on a wall surface on the side of the second passage with a convex section (381) which projects in a thickness direction towards an opposite wall surface on the side of the first passage, and whereby the convex section in the region of the inclined passage has an inclined surface (371) which is inclined with respect to the forward flow direction from one side of the second passage to one side of the first passage in order to be closer to the side of the second passage than the flow measuring unit.
  2. A thermal flow meter comprising: a secondary channel (307) that receives a portion of a fluid (30) flowing through a main channel (124); and a flow meter (451) arranged in the secondary channel, the secondary channel comprising: a first passage (351) provided on a measuring surface side (451a) of the flow meter; a second passage (352) provided on a rear side (451b) of the flow meter; and an inclined passage (361) provided upstream of an inlet (351a) of the first passage in a forward flow direction (F) of the fluid in the first passage, wherein a wall surface (304a) of the secondary channel on the side of the second passage slopes in a thickness direction to an opposite wall surface protrudes from the sides of the first passage, and wherein an inclined surface (371) is provided at an end section of the wall surface on an upstream side of the fluid in the forward flow direction in the region of the inclined passage, which is inclined with respect to the forward flow direction from one side of the second passage to one side of the first passage in order to be closer to the side of the second passage than the flow measuring unit.
  3. Thermal flow meter according to Claim 1 or 2 , wherein in a cross-section of the secondary channel (307) parallel to the forward flow direction (F) and perpendicular to the measuring surface (451a) of the flow measuring unit (451) an extension line (L1) of the inclined surface (371) and an extension line (L2) of the measuring surface intersect in the forward flow direction in front of a flow measuring surface.
  4. Thermal flow meter according to Claim 1 or 2 , wherein the secondary channel (307) comprises: a straight passage (307A) which receives a portion of the fluid (30) flowing through the main channel (124); an outlet opening (312) which discharges a portion of the fluid flowing through the straight passage; and a branched passage (307B) upstream of the outlet opening in the forward flow direction (F) of the fluid flowing through the straight passage, and the first passage (351), the second passage (352) and the inclined passage (361) are provided in the branched passage.
  5. Thermal flow meter according to Claim 1 or 2 , furthermore comprising a flat housing (310) arranged inside the main channel (124) and defining the secondary channel (307), wherein the measuring surface (451a) of the flow measuring unit (451) is perpendicular to a thickness direction of the housing.

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 secondary channel arranged in a main channel through which a fluid flows and which receives a portion of the fluid; a flow measuring element arranged inside the secondary channel and having a heating resistance structure formed therein; and a support on which the flow measuring element is mounted (see claim 1 etc. of PTL 1 described below). The conventional flow meter comprises a first fluid channel section and a second fluid channel section. The first fluid channel section consists of a surface on which a flow measuring element is mounted and a passage-forming surface of the secondary channel. The second fluid channel section consists of a surface on the opposite side of the surface on which a flow measuring element is mounted and the passage-forming surface of the secondary channel. In a conventional flow meter, the passage-forming surface of the first fluid channel section, which is opposite the flow-sensing element on the upstream side of the fluid flow, has an inclined surface that causes the fluid flow to be aligned with the flow-sensing element. This inclined surface consists of two or more surfaces with different orientations. With the above configuration, it is possible to suppress dust from rebounding off an inclined surface located on the opposite side of the upstream heating element of the fluid channel section, back towards the heating element, and then flowing with the fluid flow to the heat-generating element. This makes it possible to suppress breakage or contamination of the flow-measuring element configured with the heating element and to provide a highly reliable flow meter that exhibits excellent dust resistance even in a highly variable flow field, such as a pulsating flow, and in which characteristic errors are minimal (see paragraph 0009, etc., of the same literature). List of reference literature Patent literature PTL 1: JP 2012-93203 A A thermal flow meter with a configuration similar to the invention, but with a differently designed chamfer of the flow passages in front of the flow measuring surface, is in DE 10 2012 224 049 A1 described. Another flow meter with similarities to the present invention is disclosed in DE 199 53 776 A1. Summary of the invention Technical problem With conventional thermal flow meters, there is a risk that the flow velocity measured by the flow measuring element may be lower than the actual flow velocity, so the measurement error can increase if the flow velocity of the fluid flowing through the first fluid channel section becomes lower than the flow velocity of the fluid flowing through the second fluid channel section during the pulsation of the fluid. The present invention was conceived in view of the above problem, and one object of the present invention is to provide a thermal flow meter that is able to reduce measurement error when a fluid is pulsating compared to the prior art. Solution to the problem To solve the above problem, the present invention proposes the thermal flow meters defined in the independent claims. Further advantageous embodiments are described in the dependent claims. Advantageous effects of the invention According to the thermal flow meter of the present invention, it is possible, by means of the first inclined surface of the inclined passage, which is provided in the forward flow direction upstream of the inlet of the first passage, to deflect the fluid flowing through the secondary channel from the side of the second passage to the side of the first passage when the fluid pulsates. This increases the flow rate of the fluid flowing through the first passage in the forward flow direction, and prevents a measured flow velocity from being under the actual flow velocity decreases, and it is possible to reduce the measurement error compared to the state of the art. Brief description of the drawings [ 1 ] 1 Figure 1 is a schematic view representing an example of a system with a thermal flow meter according to a first embodiment, which is not an embodiment of the present invention.[ 2A ] 2A is a front view of the thermal flow meter according to the first embodiment.[ 2B ] 2B is a left side view of the in 2A thermal flow meter shown.[ 2C ] 2C is a rear view of the in 2A thermal flow meter shown.[ 2D ] 2D is a right side view of the in 2A thermal flow meter shown.[ 3A ] 3A is a front view of the in 2A The thermal flow meter shown is in a state in which its front cover has been removed.[ 3B ] 3B is a rear view of the in 2C The thermal flow meter shown is in a state in which a rear cover has been removed.[ 4A ] 4A is a cross-sectional view along a line IVA-IVA of the in 2C thermal flow meter shown.[ 4B ] 4B is a cross-sectional view along a line IVB-IVB of the in 2C thermal flow meter shown.[ 5 ] 5 is a schematic diagram of a secondary channel of the in 4A and 4B thermal flow