THERMAL TYPE FLOW SENSOR

• US 20080016959A1
• Filed: 07/17/2007
• Published: 01/24/2008
• Est. Priority Date: 07/21/2006
• Status: Active Grant

• Current Assignee: Hitachi Astemo Ltd. (Hitachi, Ltd.)
• Original Assignee: Hitachi Automotive Systems Limited (Hitachi, Ltd.)
• Inventors: Watanabe, Izumi, Yamada, Masamichi, Matsumoto, Masahiro, NAKANO, Hiroshi
• Granted Patent: US 7,685,874 B2
• Time in Patent Office: Days
• US Class Current: 73/204.26
• CPC Class Codes: G01F 1/6842 with means for influencing the fluid flow
• CPC Class Codes: G01F 1/6845 Micromachined devices

Abstract

A thermal type flow sensor includes a base portion provided along the direction of a fluid flowing through a main passage, and a sensor element mounted on the base portion and having an exothermic resistor formed on a substrate for detecting the fluid flow rate. The base portion has a rectangular recessed portion in which the sensor element fixed so that the surface of the detecting portion of the sensor element is positioned lower than an upper edge of the recessed portion. A wall portion of the measuring passage facing the sensor element is constricted. The exothermic resistor is disposed along the fluid passage and spaced away from the upstream side upper edge of the recessed portion and cannot be substantially affected by a fluid flow disturbance due to a step portion formed between the upper edge of the recessed portion and the detecting portion surface.

Claims

1. A thermal type flow sensor comprising:

a base portion provided along the flowing direction of a fluid passing through a main passage; and

a sensor element mounted on the base portion and equipped with an exothermic resistor formed on a substrate for detecting the flow rate of the fluid passing through main passage;

the thermal type flow sensor being featured in that a rectangular recessed portion is formed in the base portion, that the sensor element is fixedly fitted in the recessed portion in a manner that the surface of detecting portion of the sensor element is positioned lower than an upper edge of the recessed portion, that a wall portion of measuring passage which is located to face the sensor element is constricted, and that the exothermic resistor is disposed along a passage of the fluid and spaced away from the upstream side upper edge of the recessed portion so that the exothermic resistor cannot be substantially affected by a disturbance of flow of the fluid that may be caused to generate due to a step portion formed between the upper edge of the recessed portion and the surface of detecting portion of the sensor element.

3. The thermal type flow sensor according to claim 1, wherein the constricted portion is configured such that the cross-sectional area of the passage is gradually reduced from the upstream side upper edge of the recessed portion to the downstream side thereof and the exothermic resistor of sensor element is mounted on the downstream side of the narrowest portion in the constricted passage and away from the upstream side thereof.

4. The thermal type flow sensor according to claim 3, wherein the surface of detecting portion of the sensor element is set in relation to a distance between the upstream side upper edge of the recessed portion and a center of the exothermic resistor in such a way as to satisfy an expression of:

L>

D·

α

, wherein L is a distance between the upstream side upper edge of the recessed portion and a center of the exothermic resistor;

D is a depth of the step portion between the upper edge of the recessed portion and the surface of detecting portion of the sensor element; and

α

is an average gradient of the constricted portion.

5. The thermal type flow sensor according to claim 1, wherein the center of the exothermic resistor is spaced away, along the flowing direction of fluid, from the upstream side upper edge of the recessed portion by a distance of 1.5 mm or more.

6. The thermal type flow sensor according to claim 1, wherein the sensor element is mounted at a length of 3 mm or more as measured from the upstream side edge thereof to the downstream side edge thereof.

7. The thermal type flow sensor according to claim 1, wherein the center of the exothermic resistor is off-set from the center of the sensor element toward the downstream side.

8. The thermal type flow sensor according to claim 1, wherein eaves projecting over the sensor element and extending along the flowing direction of fluid is formed on the upstream side upper edge and/or the downstream side upper edge of the recessed portion.

9. The thermal type flow sensor according to claim 8, wherein the eaves is formed to have a tapered surface extending downward from the proximal end thereof.

2. A thermal type flow sensor comprising:

a main passage having therein a sub-passage formed along a flowing direction of a fluid for enabling part of the fluid to pass therethrough;

a base portion provided in the sub-passage and along the flowing direction of the fluid passing through a sub-passage; and

a sensor element mounted on the base portion and equipped with an exothermic resistor formed on a substrate for detecting the flow rate of the fluid passing through main passage;

the thermal type flow sensor being featured in that a rectangular recessed portion is formed in the base portion, that the sensor element is fixedly fitted in the recessed portion in a manner that the surface of detecting portion of the sensor element is positioned lower than an upper edge of the recessed portion, that a wall portion of measuring passage which is located to face the sensor element is constricted, and that the exothermic resistor is disposed along a passage of the fluid and spaced away from the upstream side upper edge of the recessed portion so that the exothermic resistor cannot be substantially affected by a disturbance of flow of the fluid that may be caused to generate due to a step portion formed between the upper edge of the recessed portion and the surface of detecting portion of the sensor element.

10. The thermal type flow sensor according to claim 2, wherein the sub-passage is provided with at least one constricted portion in a midway between the upstream end of the sub-passage and the recessed portion.