Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
2002-01-17
2003-09-09
Lefkowitz, Edward (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06615655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flow rate detecting element used in a thermosensitive flow rate sensor which measures the flow rate of a fluid. The present invention also relates to an element holder which accommodates the flow rate detecting element when the flow rate detecting element is put into practical use.
The flow rate detecting element of the present invention can be used for measuring the flow rate of various fluids such as gases and/or liquids, preferably gases, and particularly air and/or a mixture of gases. The flow rate detecting element of the present invention can be preferably used for measuring the flow rate of, in particular, the air intake into an internal combustion engine.
2. Description of the Related Art
The applicant of this patent application has filed an application for patent (Japanese Patent Kokai Publication No. 11-23338) related to a thermosensitive flow rate detecting element based on an operating principle similar to that of the present invention. FIG.
9
(
a
) shows a schematic plan view of a key portion in a basic embodiment of the invention of the above Japanese Patent Kokai Publication, and FIG.
9
(
b
) shows a schematic sectional view taken along lines IXB—IXB in FIG.
9
(
a
).
In
FIG. 9
, reference numeral
31
denotes a flat substrate made of a silicon semiconductor,
32
denotes an insulating support film made of silicon nitride,
34
,
35
,
36
and
37
denote thermosensitive resistors made of, for example, platinum, where
34
is a heating resistance section,
35
and
36
are temperature detecting resistance sections and
37
is a comparative resistance section, and
33
denotes an insulating protective film made of silicon nitride.
As shown in FIG.
9
(
b
), the flat substrate
31
has a recess
38
in the right-hand portion thereof, formed by removing a part of the substrate in a predetermined size and shape by etching or other method. The flat substrate
31
also has a notch
39
in the left-hand portion thereof, formed by removing a part of the substrate in a predetermined size and shape by etching or other method, so that the notch
39
having a cross section of substantially triangular shape with the base thereof lying at the lower surface of the substrate
31
does not reach the upper surface of the substrate
31
. The terms “lower surface” and “upper surface” are used herein in correspondence to the lower and upper positions in the drawings which show the longitudinal sectional view of the flow rate detecting element of the present invention, for the convenience of description.
On the upper surface of the flat substrate
31
, the support film
32
and the protective film
33
are sequentially laminated. Provided between the support film
32
and the protective film
33
are the heating resistance section
34
, the temperature detecting resistance sections
35
,
36
, and the comparative resistance section
37
being formed in predetermined patterns as shown in FIG.
9
(
a
). A portion enclosed by two-dot and a dash line in FIG.
9
(
a
), which includes the heating resistance section
34
and the temperature detecting resistance sections
35
,
36
that are provided on both sides of the heating resistance section
34
, constitutes a heating resistance region section
40
. The heating resistance region
40
consists of a thin film comprising the support film
32
and the protective film
33
placed one on another, and constitutes a so-called diaphragm structure with the recess
38
formed on the bottom side so as not to contact the flat substrate
31
.
Formed in the flat substrate
31
on the lower surface side of the comparative resistance section
37
is the notch
39
which opens only on the lower surface of the flat substrate
31
. A portion of the flat substrate
31
remains on the side which is in contact with the support film
32
.
In use condition of the flow rate detecting element having the constitution described above, the resistance sections
34
,
35
,
36
and
37
are connected to circuits not shown. When a fluid, for example air, flows in the direction indicated by arrow
50
, the comparative resistance section
37
contacts with the flowing air via the protective film
33
to sense the temperature of the air. The temperature of the heating resistance section
34
is set to remain higher than the temperature being measured at the comparative resistance section
37
by a predetermined margin. For the application to an internal combustion engine of automobile, for example, temperature of the heating resistance section
34
is controlled to maintain a level 200 degree centigrade higher than the temperature being measured at the comparative resistance section
37
.
Heat generated by the heating resistance section
34
is transmitted to the temperature detecting resistance sections
35
,
36
via the support film
32
and the protective film
33
. Since the temperature detecting resistance section
35
and the temperature detecting resistance section
36
are disposed at positions symmetrical with respect to the heating resistance section
34
which is located at the center as shown in
FIG. 9
, there is no difference in the resistance between the temperature detecting resistance section
35
and the temperature detecting resistance section
36
when there is no fluid flow. Also since the comparative resistance section
37
is located at a predetermined distance from the heating resistance section
34
, heat generated by the heating resistance section
34
is substantially not transmitted to the comparative resistance section
37
, so that the temperature of the comparative resistance section
37
is nearly equal to the temperature of the surrounding fluid, for example air.
When a fluid, for example air, flows in the direction indicated by the arrow
50
over the flow rate detecting element having such a constitution as described above, since the temperature of the heating resistance section
34
is set to a level generally higher than the fluid temperature to be measured, the temperature detecting resistance section
35
located in the upstream is cooled by the fluid to a lower its temperature. The temperature detecting resistance section
36
located in the downstream, on the other hand, receives the heat generated by the heating resistance section
34
and conveyed by the fluid, and therefore shows either a less drop in the temperature or a rise in the temperature. As a result, when the fluid flows in the direction indicated by the arrow
50
, temperature of the temperature detecting resistance section
35
located in the upstream becomes lower than that of the temperature detecting resistance section
36
located in the downstream, while the difference in the resistance between the two temperature detecting resistance sections
35
and
36
becomes larger as the flow rate or the velocity of the fluid increases. Thus the flow rate or the velocity of the fluid can be measured by sensing the difference in the resistance between the temperature detecting resistance section
35
and the temperature detecting resistance section
36
.
When the fluid flows in a direction opposite to the arrow
50
, since the temperature of the temperature detecting resistance section
36
located in the upstream becomes lower than that of the temperature detecting resistance section
35
located in the downstream, contrary to the case described above, direction of the fluid flow can also be determined.
The thermosensitive flow rate detecting element as described above is accommodated in an element holder when it is practically used, in order to avoid the turbulence of the fluid flow and to achieve an effective contact of the fluid with the heating resistance section or the comparative resistance section. The applicant of this patent application has also filed an application for patent (Japanese Patent Kokai Publication No. 10-293052) on the element holder.
The flow rate detecting element described above measures flow rate by means of the heat transmission phenomenon of the flui
Kawai Masahiro
Sakai Yuichi
Taguchi Motohisa
Tsutsumi Kazuhiko
Yamakawa Tomoya
Lefkowitz Edward
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Thompson Jewel V.
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