Thermal Flow Meter

• US 20150122011A1
• Filed: 05/15/2013
• Published: 05/07/2015
• Est. Priority Date: 06/15/2012
• Status: Active Grant

• Current Assignee: Hitachi Astemo Ltd. (Hitachi, Ltd.)
• Original Assignee: Hitachi Automotive Systems Limited (Hitachi, Ltd.)
• Inventors: Morino, Takeshi, Tashiro, Shinobu, Tokuyasu, Noboru, Hanzawa, Keiji, Inoue, Atsushi
• Granted Patent: US 10,018,492 B2
• Time in Patent Office: Days
• US Class Current: 73/204.22
• CPC Class Codes: F02D 2200/101 Engine speed
• CPC Class Codes: F02D 31/005 by controlling a throttle by-pass
• CPC Class Codes: F02D 37/02 one of the functions being ignition
• CPC Class Codes: F02D 41/182 for the control of a fuel injection device
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/6845 Micromachined devices
• CPC Class Codes: G01F 1/692 Thin-film arrangements
• CPC Class Codes: G01F 1/6965 comprising means to store calibration data for flow signal calculation or correction
• CPC Class Codes: G01F 5/00 Measuring a proportion of the volume flow

Abstract

Provided is a thermal flow meter through which a measurement with high accuracy and has a discharge function. In a thermal flow meter 300 of the invention, a part of a measurement target gas 30 flowing through the main passage 124 flows into a bypass passage. A drainage passage 3528 is provided in the bypass passage to communicate a bypass passage 4232 on the inlet port (between the inlet port 350 and the measurement surface 430 serving as the air flow sensing portion) and a bypass passage 4234 on the outlet port (between the measurement surface 430 serving as the air flow sensing portion and the outlet port 352). The drainage passage 3528 includes a through hole 3512. The through hole 3512 includes an inlet port 3542 which penetrates a wall surface 4212 forming the bypass passage 4232 on the inlet port and is opened in the bypass passage 4232 on the inlet port, and an outlet port 3544 which is opened in a rear surface 4213 of the wall surface. Water 3552 flowing into the bypass passage is guided to the through hole 3512, and guided to the bypass passage 4234 on the outlet port through the drainage passage 3528, and discharged to the main passage 124. Therefore, an influence of the water flowing into a measuring portion can be reduced, and the measurement accuracy can be improved.

Claims

1. A thermal flow meter comprising:

a bypass passage for flowing a part of a measurement target gas flowing through a main passage; and

a flow rate detection circuit for measuring a flow rate of the measurement target gas flowing through the main passage by performing heat transfer with the measurement target gas flowing through the bypass passage, wherein

the bypass passage includes an inlet port for flowing the measurement target gas, an outlet port for returning the measurement target gas to the main passage, and an air flow sensing portion which is arranged between the inlet port and the outlet port and measures the flow rate by performing heat transfer between the flow rate detection circuit and the measurement target gas,

a second passage is further provided to communicate a bypass passage on the inlet port between the inlet port of the bypass passage and the air flow sensing portion and a bypass passage on the outlet port between the air flow sensing portion in the bypass passage and the outlet port, and

the second passage includes an inlet port which passes through a wall surface forming the bypass passage on the inlet port of the bypass passage and is opened in the bypass passage on the inlet port, and an outlet port which is opened in a rear side of the wall surface forming the bypass passage on the inlet port.

2. The thermal flow meter according to claim 1, wherein

a flange for supporting the thermal flow meter is provided,

the inlet port of the bypass passage and the outlet port of the bypass passage are arranged in an end portion of the thermal flow meter in a direction opposite to the flange,

the air flow sensing portion is arranged in the direction of the flange from the inlet port of the bypass passage and the outlet port of the bypass passage,

the bypass passage on the inlet port is formed to approach the air flow sensing portion from the inlet portion of the bypass passage while being curved,

the bypass passage on the inlet port is formed to include a bypass passage trench on the inlet port and a cover for covering the bypass passage trench on the inlet port, and

the through hole of the second passage is provided in a wall surface positioned in a direction opposite to the flange of the bypass passage trench on the inlet port.

3. The thermal flow meter according to claim 1, wherein a protrusion for suppressing the flow of a gas is provided on a downstream side of the through hole in the second passage, and

the second passage is formed by taking a detour round a leading end of the protrusion.

4. The thermal flow meter according to claim 1, wherein the bypass passage on the inlet port is formed such that a cross-sectional area of the bypass passage on the inlet port is gradually narrowed as it goes from the opening of the through hole of the second passage toward the air flow sensing portion.

5. The thermal flow meter according to claim 1, wherein a bypass passage trench on the inlet port for forming the bypass passage on the inlet port and a first cover for forming the bypass passage on the inlet port by covering the bypass passage trench on the inlet port are provided in one surface of the thermal flow meter,

a bypass passage on an outlet port trench for forming the bypass passage on the outlet port and a second cover for forming the bypass passage on the outlet port by covering the bypass passage on the outlet port trench are provided in the other surface of the thermal flow meter, and

the through hole of the second passage is opened in the bypass passage trench on the inlet port which is provided on the one surface of the thermal flow meter.

6. A thermal flow meter comprising:

a bypass passage for flowing a part of a measurement target gas flowing through a main passage;

an air flow sensing portion for measuring a flow rate of the measurement target gas flowing through the main passage by performing heat transfer with the measurement target gas flowing through the bypass passage; and

a housing which includes a resin bypass passage for forming the bypass passage and protects the air flow sensing portion, wherein

the bypass passage includes an inlet port for flowing the measurement target gas, and an outlet port for returning the measurement target gas to the main passage,

the air flow sensing portion is arranged between the inlet port of the bypass passage and the outlet port of the bypass passage and performs heat transfer with the measurement target gas to measure the flow rate,

a bypass passage on the inlet port for connecting the inlet port of the bypass passage and the air flow sensing portion is provided in one surface of the bypass passage of the housing,

a bypass passage on the outlet port for connecting the air flow sensing portion and the outlet port of the bypass passage is provided in the other surface of the bypass passage of the housing, and

a second passage is provided in a wall between the bypass passage on the inlet port and the bypass passage on the outlet port to penetrate the wall.