Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2001-05-03
2002-10-29
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06470743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a heat-sensitive flow rate sensor for measuring flow rate such as amount of intake air of an internal combustion engine. More particularly, the invention relates to an improved heat-sensitive flow rate sensor for measuring velocity or flow rate of a fluid to be measured on the basis of heat transfer phenomenon caused by a heating element or a part heated by the heating element.
2. BACKGROUND ART
FIG. 16
is a plan view showing a flow rate-detecting element in the form of a diaphragm construction used in one of conventional heat-sensitive flow rate sensors.
FIG. 17
is a sectional view taken along the line A—A in FIG.
16
. In
FIGS. 16 and 17
, numeral
14
is a flow rate-detecting element. In this flow-rate detecting sensor
14
, on the surface of a flat plate-like substrate
1
composed of silicon 0.4 mm thick, an insulating support film
2
composed of silicon nitride of 1 &mgr;m in thickness is deposited by spattering, CVD, or any other similar method. Further, on the support film
2
, a heating element
3
composed of a heat-sensitive resistance film of platinum, etc. of 0.2 &mgr;m in thickness is deposited by evaporation, spattering, or any other similar method. On the heating element
3
, patterns serving as current passage are formed by photomechanical process, wet or dry etching, or any other similar method. Further, a fluid-temperature detector
4
composed of a heat-sensitive resistance film of platinum, etc. of 0.2 &mgr;min thickness is formed in the same method as mentioned. Furthermore, on both of the heating element
3
and fluid-temperature detector
4
, an insulating protection film
5
composed of silicon nitride, etc. of 1 &mgr;m in thickness is deposited by spattering, CVD, or any other similar method. The heating element
3
is connected, through connecting sections
9
a
,
9
b
and lead sections
7
a
,
7
d
, to electrodes
8
a
,
8
d
for electric connection to outside. The fluid temperature-detector
4
is connected through lead sections
7
b
,
7
c
to electrodes
8
b
,
8
c
. The protection film
5
is removed from the portions of electrodes
8
a
to
8
d
to allow electric connection to outside by wire bonding or any other similar method. Further, after forming an etching hole
11
in a backside protection film
10
formed on the opposite face of the support film
2
of the flat plate-like base
1
, a cavity
13
being a hollow part is formed by applying alkali etching or the like. Thus, a diaphragm
12
for detecting a flow rate is constructed. An arrow
6
indicates a flowing direction of a fluid to be measured.
Furthermore, as described in the Japanese Patent Publication (unexamined) No. 142020/1998, in case that the flat plate-like flow rate-detecting element
14
of is placed into a fluid to be measured in almost parallel to or at a predetermined angle therefrom, the flow rate-detecting element
14
is placed on the accommodating portion of a supporting member
16
, in order to prevent turbulence occurring in the vicinity of the cavity
13
, peeling or the like occurring in the front edge portion of the flow rate-detecting element
14
. As shown in
FIG. 18
, the supporting member
16
has a concave accommodating portion
18
to accommodate the flow rate-detecting element
14
, and is electrically connected to a detection circuit board through terminals
17
arranged on a base member
20
. In
FIG. 18
, numeral
19
is wires and numeral
21
is a cover. This type of flow rate-detecting element with a diaphragm construction is publicly known, as is also disclosed in the Japanese Patent Publication (unexamined) No. 2967/1992 and others.
FIG. 19
is a front view showing a structure of the heat-sensitive flow rate sensor according to the foregoing prior art, and
FIG. 20
is a transverse sectional view taken along the B—B in FIG.
19
. In this conventional heat-sensitive flow rate sensor, a detection pipe passage
100
is placed inside a main passage
101
for a fluid to be measured, and the flow rate-detecting element
14
mounted on the supporting member
16
is placed in the detection pipe passage
100
. In
FIGS. 19 and 20
, numeral
102
is a case for accommodating a detection circuit board
104
, numeral
103
is a connector, and numeral
105
is a shield member.
FIG. 21
shows a detection circuit of such conventional heat-sensitive flow rate sensor. The detection circuit board
104
is arranged into a generally used fixed-temperature difference control, and the detection circuit has a bridge circuit including the heating element
3
and the fluid-temperature detector
4
. In
FIG. 21
, R
1
to R
5
are fixed resistance, OP
1
and OP
2
are operational amplifiers, TR
1
and TR
2
are transistors, and BATT is a power supply. The detection circuit, except the heating element
3
and the fluid-temperature detector
4
, is arranged on the detection circuit board
4
. The detection circuit is driven so as to keep point (a) and point (b) in
FIG. 21
at almost the same potential, and controls a heating current IH of the heating element
3
. When increasing the velocity of a fluid to be measured, amount of heat transferred from the heating element
3
to the fluid to be measured increases thereby the heating current IH supplied to the heating element
3
being increased. Velocity and flow rate of the fluid to be measured can be obtained by detecting the heating current IH as a voltage Vout at both ends of R
3
, and such information can be transferred through the connector
103
in
FIG. 19
to ECU (electronic control unit).
In the conventional heat-sensitive flow rate sensor of above construction, when mounting the flow rate-detecting element
14
on the accommodating portion
18
in the supporting member
16
, the fluid to be measured flows passing through only the surface of the flow rate-detecting element
14
in a small flow rate region. On the other hand, however, in a large flow rate region, a certain amount of the fluid to be measured flows into a gap between the flow rate-detecting element
14
and the accommodating portion
18
in the supporting member
16
. Such a flow into the gap is hereinafter referred to as underflow.) Hence, a disadvantage exists in that accuracy in flow rate detection is lowered.
FIGS. 22 and 23
show the underflow. In
FIGS. 22 and 23
, numeral
22
indicates a flow of a fluid to be measured, and numeral
23
indicates a flow of an underflow. To cope with the mentioned disadvantage, for example, the Japanese Patent Publication (unexamined) No. 26343/1997 discloses a structure in which groove-like slots are provided in the accommodating portion of an supporting member along the peripheral edge of a flow rate-detecting element, in order to prevent the underflow produced in the large flow rate region from contacting directly the flow rate-detecting element. Such a structure, however, can not sufficiently prevent the underflow, because the underflow guided by the slots sometimes flows round into the gap formed by the cavity. Furthermore, the Japanese Patent Publication (unexamined) No. 2573/2000 discloses a structure in which one side, either upstream or downstream side, of a flow rate-detecting element is brought into close contact with one side of the accommodating portion in a supporting member in order to prevent the underflow. It is, however, very difficult to bring the side of a flow rate-detecting element into close contact with the side of the accommodating portion. This is because at the time of fixing the flow rate-detecting element to the bottom face of the accommodating portion using some adhesive, the heating element moves slightly as the adhesive is dried. A further problem exists in that it is essential to of connecting the side of the flow rate-detecting element to strictly control dimensional accuracy, surface roughness, etc. of the sides of the accommodating portion and the flow rate-detecting element, which eventually results in low productivity.
SUMMARY OF THE INVENTION
The present invention was made to solve the above-
Hamada Shingo
Uramachi Hiroyuki
Yonezawa Fumiyoshi
Fuller Benjamin R.
Mitsubishi Denki & Kabushiki Kaisha
Thompson Jewel V.
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