GB2348007A

GB2348007A - Mass flow sensor with two upstream air temperature sensors for providing a corrected air temperature mesurement

Info

Publication number: GB2348007A
Application number: GB0003131A
Authority: GB
Inventors: Guy Hoffmann
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 1999-02-26
Filing date: 2000-02-14
Publication date: 2000-09-20
Anticipated expiration: 2020-02-14
Also published as: GB2348007B; GB0003131D0; GB9904429D0

Abstract

A mass flow sensor (10) comprising a silicon substrate (12) which is substantially annular and defines a recess (14) having an upstream edge (20) and a downstream edge (20); a membrane layer (16) secured to the silicon substrate and extending across the recess; a heating element (18) mounted on or in the membrane layer and positioned substantially centrally relative to the upstream and downstream edges of the recess; a first element (26) of an air temperature sensor (24) mounted on the substrate adjacent an outer edge (30,32) thereof; and a second element (28) of the air temperature sensor mounted on the substrate between the first element and the heating element. Provides a more accurate reading of air intake temperature.

Description

MASS FLOW SENSOR WITH AIR TEMPERATURE SENSOR Technical Field The present invention relates to a mass flow sensor having an air temperature sensor.

Background of the Invention A known mass flow sensor is described in US-A-5705745.

This known mass flow sensor comprises a silicon substrate having a recess therein, a membrane layer extending across the recess, and a heating element mounted on or in the membrane layer substantially centrally relative to the recess. Temperature measuring elements are position upstream and downstream of the heating element, between the heating element and the edges of the recess. It has been proposed to mount an air temperature sensor on the substrate to provide a measure of the intake air temperature. This temperature measurement signal is sent to the engine control module which controls the operation of the engine receiving the air. The problem with such an arrangement is that the proximity of the heating element of the mass flow sensor to the air temperature sensor element can result in a temperature rise in the air temperature sensor element, and hence can result in an inaccurate signal from the air temperature sensor.

Summary of the Invention The present invention seeks to overcome the above problem.

A mass flow sensor in accordance with the present invention comprises a silicon substrate which is substantially annular and defines a recess having an upstream edge and a downstream edge; a membrane layer secured to the silicon substrate and extending across the recess; a heating element mounted on or in the membrane layer and positioned substantially centrally relative to the upstream and downstream edges of the recess; a first element of an air temperature sensor mounted on the substrate adjacent an outer edge thereof; and a second element of the air temperature sensor mounted on the substrate between the first element and the heating element.

The present invention provides a more accurate reading of the temperature of the air passing across the mass flow sensor.

Brief Description of the Drawings The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a mass flow sensor in accordance with the present invention; Figure 2 is a plan view of the mass flow sensor of Figure 1; and Figure 3 is a plan view of an alternative mass flow sensor in accordance with the present invention.

Description of the Preferred Embodiment Referring to Figures 1 and 2, the present invention is a mass flow sensor 10 for monitoring the mass flow in a direction A across the sensor. The mass flow sensor 10 comprises a silicon substrate 12 which is substantially annular and defines a recess 14. A membrane layer 16 is secured to the substrate and extends across the recess 14. A heating element 18 is mounted on or in the membrane layer 16 substantially centrally relative to upstream and downstream edges 20 of the recess 14. Upstream and downstream temperature measuring elements 22 may also be positioned on or in the membrane layer 16 between the heating element 18 and the upstream and downstream edges 20 of the recess 14.

In accordance with the present invention, an air temperature sensor 24 is, in part, mounted on the substrate 12. The air temperature sensor 24 comprises first and second elements 26,28 which are mounted on the substrate 12. Relative to the outer edge 30 of the substrate 12, the second element 28 is positioned closer to the heating element 18 of the mass flow sensor 10 than the first element 26. The first element 26 is, therefore, subjected to less influence by the heating element 18 of the mass flow sensor 10 than the second element 28.

In the embodiment of Figures 1 and 2, the first element 26 is positioned adjacent to, and substantially parallel with, the upstream edge 32 of the substrate 12, and the second element 28 is positioned between the first element and the heating element 18 and substantially parallel with the first element. In the alternative embodiment of Figure 3, the first element 26 is substantially U-shaped and extends around the substrate 12 adjacent the outer edge 30 thereof. The second element 28 is also substantially U-shaped and is positioned between the first element and the heating element 18.

In use, the temperature difference between the first and second elements 26,28 is determined, and multiplied by a correction factor (which may be dependent on air flow velocity and/or on the relative geometry of the positions of the first and second elements with respect to the heating element).

The corrected difference is then deducted from the temperature reading from the first element to provide a more accurate signal of intake air temperature from the air temperature sensor. High air flow velocities tend to produce a smaller correction factor than low air flow velocities.

Claims

Claims 1. A mass flow sensor comprising a silicon substrate which is substantially annular and defines a recess having an upstream edge and a downstream edge; a membrane layer secured to the silicon substrate and extending across the recess; a heating element mounted on or in the membrane layer and positioned substantially centrally relative to the upstream and downstream edges of the recess; a first element of an air temperature sensor mounted on the substrate adjacent an outer edge thereof; and a second element of the air temperature sensor mounted on the substrate between the first element and the heating element.
2. A mass flow sensor as claimed in Claim 1, wherein the first element of the air temperature sensor is positioned adjacent to, and extends substantially parallel to, the upstream edge of the substrate; and wherein the second element extends substantially parallel to the first element.
3. A mass flow sensor as claimed in Claim 1, wherein the first element of the air temperature sensor is substantially U-shaped; and wherein the second element is substantially U-shaped.
4. A mass flow sensor as claimed in any one of Claims 1 to 3, wherein a temperature measuring element is positioned on or in the membrane layer between the heating element and the upstream edge of the recess and the downstream edge of the recess.
5. A mass flow sensor substantially as herein described with reference to, and as shown in, the accompanying drawings.