Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2002-04-15
2004-01-20
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06679114
ABSTRACT:
This application is based on Application No. 2001-155299, filed in Japan on May 24, 2001, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermosensitive flow rate sensor including a heating element, the thermosensitive flow rate sensor measuring the flow velocity or flow rate of a fluid based on a heat transfer phenomenon where a heat is transferred to the fluid from the heating element or a portion heated by the heating element, the thermosensitive flow rate sensor being used to measure an intake air flow rate in an internal combustion engine, for example.
2. Description of the Related Art
FIG. 9
is a plan showing a detecting element used in a conventional thermosensitive flow rate sensor, and
FIG. 10
is a cross section taken along line X—X in
FIG. 9
viewed from the direction of the arrows.
In
FIGS. 9 and 10
, a flat substrate
1
is constituted by a silicon substrate having a thickness of approximately 0.4 mm. An electrically-insulating support film
2
made of silicon nitride, etc., having a thickness of 1 &mgr;m is formed on a surface of the substrate
1
by performing a method such as sputtering, chemical vapor deposition (CVD), etc. A heating element
4
constituted by a thermosensitive resistor film of platinum, etc., is formed on the support film
2
. The heating element
4
is constructed so as to be formed with electric current paths by depositing a thermosensitive resistor film of platinum, etc., having a thickness of 0.2 &mgr;m on the support film
2
by performing a method such as vapor deposition or sputtering, etc., and patterning the thermosensitive resistor film by using a method such as photolithography, or wet or dry etching, etc. A fluid temperature detector
5
similarly composed of a thermosensitive resistor film of platinum, etc., is formed on the support film
2
away from the heating element
4
. The fluid temperature detector
5
is constructed so as to be formed with electric current paths by depositing a thermosensitive resistor film of platinum, etc., having a thickness of 0.2 &mgr;m on the support film
2
by performing a method such as vapor deposition or sputtering, etc., and patterning the thermosensitive resistor film by using a method such as photoengraving, or wet or dry etching, etc. In addition, an electrically-insulating protective film
3
made of silicon nitride, etc., having a thickness of 1 &mgr;m is formed by performing a method such as sputtering, CVD, etc., on the heating element
4
and the fluid temperature detector
5
.
The heating element
4
is connected through first and second connection patterns
9
a
and
9
b
and first and fourth lead patterns
7
a
and
7
d
to first and fourth electrodes
8
a
and
8
d
for electrically connecting a detecting element to an external circuit. The fluid temperature detector
5
is connected through second and third lead patterns
7
b
and
7
c
to second and third electrodes
8
b
and
8
c
for electrically connecting the detecting element to an external circuit. The protective film
3
is removed from portions of the first to fourth electrodes
8
a
to
8
d
so as to be connected to an external circuit by a method such as wire bonding.
In addition, a flow rate detection diaphragm
12
is constructed by forming a cavity
13
under a region where the heating element
4
is formed. More specifically, a rear-surface protective film
10
is formed on a rear surface of the flat substrate
1
(a surface on the opposite side from the surface on which the support film
2
is formed), and then an etched hole
11
is formed by partially removing the rear-surface protective film
10
by a method such as photolithography at a position on the rear side of the region where the heating element
4
is formed. Thereafter, the flow rate detection diaphragm
12
is constructed by applying alkali etching, for example, to the flat substrate
1
exposed through the etched hole
11
to remove part of the flat substrate
1
and form the cavity
13
.
The detecting element
14
constructed in this manner is disposed such that the flow rate detection diaphragm
12
is exposed to the flow of the fluid being measured. Moreover, in each of the figures, an arrow
6
indicates the direction of flow of the fluid being measured.
The detecting element
14
has a flat shape, as described above, and when the diaphragm
12
is disposed so as to be perpendicular to the direction of flow of the fluid being measured, fluid pressure acts on the diaphragm
12
, giving rise to damage to the diaphragm
12
when the fluid being measured is flowing at high velocity, and dust in the fluid being measured may also accumulate on the diaphragm portion, changing the rate of heat transfer from the heating element
4
to the fluid being measured, thereby giving rise to drifts in the detected flow rate. In such cases, the flat detecting element
14
is disposed generally parallel to the direction of flow of the fluid being measured or so as to be inclined at a predetermined angle relative to the direction of flow of the fluid being measured.
When the flat detecting element
14
is disposed generally parallel to the direction of flow of the fluid being measured or so as to be inclined at a predetermined angle relative to the direction of flow of the fluid being measured, disturbances may arise in the flow of the fluid being measured in the vicinity of the cavity
13
, or irregularities may arise in the flow of the fluid being measured in the vicinity of the heating element
4
due to irregularities in the shape of a leading edge portion of the detecting element
14
resulting from chipping, etc. These irregularities in the flow of the fluid being measured in the vicinity of the heating element
4
lead to decreased precision in flow rate detection.
Thus, in order to solve the problems described above in cases where the flat detecting element
14
is disposed generally parallel to the direction of flow of the fluid being measured or so as to be inclined at a predetermined angle relative to the direction of flow of the fluid being measured, it has been proposed in Japanese Patent Non-Examined Laid-Open No. 11-326000, for example, that the detecting element be disposed inside a recess portion formed on a flat support.
FIG. 11
is a partial perspective showing a support construction of the conventional detecting element described in Japanese Patent Non-Examined Laid-Open No. 11-326000.
In
FIG. 11
, a support
16
is formed into a flat shape, and is mounted to a base member
20
. A recess portion
18
having a slightly larger external shape than the detecting element
14
is formed on a surface of the support
16
. The detecting element
14
is disposed inside the recess portion
18
such that a surface of the detecting element
14
is positioned generally in a common plane with a surface of the support
16
. The first to fourth electrodes
8
a
to
8
d
of the detecting element
14
are electrically connected by wires
19
to lead wires
17
disposed in the base member
20
. A cover
21
is mounted to the base member
20
, and the first to fourth electrodes
8
a
to
8
d
and the wires
19
are protected by the cover
21
.
Hence, disturbances in the flow of the fluid being measured arising in the vicinity of the cavity
13
are suppressed, and the flow of the fluid being measured is smoothed by the arc shape of an upstream end portion of the support
16
, reducing irregularities in the flow of the fluid being measured in the vicinity of the heating element
4
that are generated by irregularities in the shape of the leading edge portion of the detecting element
14
.
Next, a method for detecting the flow rate of a fluid being measured using the detecting element
14
will be explained.
Because the fluid temperature detector
5
is separated from the diaphragm portion
12
, heat generated by the heating element
4
is not transferred to the fluid temperature detector
5
. Because the fluid temperature detector
5
is not positioned downstream
Mack Corey D.
Mitsubishi Denki & Kabushiki Kaisha
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