Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
1999-08-23
2002-05-28
Fuller, Benjamin R. (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06393907
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a flow rate sensor employing a flow rate detecting device which has a heating element and which is used for measuring the flow velocity or flow rate of a fluid according to a heat transfer phenomenon where a heat is transferred from the heating element or from a part heated by the heating element to the fluid. The present invention is applied to, for example, a flow rate sensor for use in measuring an intake air amount of an internal combustion engine.
2. Description of the Related Art
Japanese Unexamined Patent Publication Nos. 62-43522 and 4-2967 disclose known flow rate detecting devices each of which has a diaphragm structure and which is used in a flow rate sensor of such a type.
FIG. 24
is a plan view of a flow rate detecting device for use in a conventional flow rate sensor.
FIG. 25
is a sectional view taken in the direction of arrows on line XXV—XXV of FIG.
24
.
In the device shown in
FIGS. 24 and 25
, a plate-like substrate
1
is constituted by a silicon substrate about 0.4 mm thick. A 1-&mgr;m-thick insulative supporting film
2
made of silicon nitride is formed on a surface of the plate-like substrate
1
by performing a method, such as sputtering or CVD. Moreover, a heating element
4
constituted by a thermo-sensitive platinum resistor film is formed on the supporting film
2
. This heating element
4
is configured in the following process in such a manner as to form a current path. Namely, a 0.2-&mgr;m-thick thermo-sensitive platinum film is first formed on the surface of the plate-like substrate
1
by using a vapor deposition or sputtering method. Then, patterning is performed on this thermo-sensitive resistor film by employing a photolithographic method and a wet (or dry) etching method. Furthermore, a fluid temperature detecting element
5
similarly constituted by a thermo-sensitive platinum resistor film is formed on the supporting film
2
apart from the heating element
4
. This fluid temperature detecting element
5
is constructed in a process similar to the process of forming the heating element
4
. First, a 0.2-&mgr;m-thick thermosensitive platinum film is formed on the surface of the plate-like substrate
1
by using a vapor deposition or sputtering method. Subsequently, patterning is performed on this thermo-sensitive resistor film by performing a photolithographic method and a wet (or dry) etching method. Thus, this fluid temperature detecting element
5
is formed in such a way as to form a current path. Moreover, an insulative protective coat
3
is formed on the heating element
4
and the fluid temperature detecting element
5
by producing a 1-&mgr;m-thick film made of silicon nitride through the sputtering or CVD method.
This heating element
4
is connected through connection patterns
9
a and
9
b
and lead patterns
7
a
and
7
d
to electrodes
8
a
and
8
d
for connecting the flow rate detecting device to an external circuit. Further, the fluid temperature detecting element
5
is connected through lead patterns
7
b and
7
c
to electrodes
8
a
and
8
d
for connecting the flow rate detecting device to an external circuit. Electrodes
8
a
to
8
d
are electrically connected to an external circuit by a method, such as a wire bonding. Thus, the protective coat
3
is removed from the electrodes
8
a
to
8
d.
Moreover, a cavity
13
is formed under a portion in which the heating element
4
is formed. Thus, a diaphragm
12
for detecting a flow rate is configured. Namely, a back-surface protecting coat
10
is first formed on the back surface (that is, a surface opposite to the surface on which the supporting film
2
is formed) of the plate-like substrate
1
. Subsequently, the back-surface protecting coat
10
is partly removed at a place on the back surface side of the region, on which a heating element
4
is formed, by performing a photolithographic method. Thus, an etching hole
11
is formed. Thereafter, a part of the plate-like substrate
1
is removed by performing, for example, alkali etching on the plate-like substrate
1
exposed from the etching hole
11
, so that the cavity
13
is formed. Consequently, the diaphragm portion
12
for detecting a flow rate is formed.
A flow rate detecting device
14
configured in this manner is arranged so that the diaphragm
12
for detecting a flow rate is exposed to a flow of a fluid to be measured. Incidentally, in these figures, arrows
6
indicate the direction of flow of the fluid to be measured.
Meanwhile, the flow rate detecting device
14
is shaped like a plate, as described above. In the case where the diaphragm
12
is placed in such a manner as to face the direction of flow of the fluid to be measured, a wind pressure is applied to the diaphragm
12
, so that a failure of the diaphragm
12
is caused at a high flow rate. Further, dust contained in the fluid to be measured deposits on a diaphragm portion, with the result that drift in the flow rate detecting characteristics occurs. In such cases, the plate-like flow rate detecting device
14
is placed almost parallel to or at a predetermined angle with respect to the direction of flow of the fluid to be measured.
Furthermore, in the case that the plate-like flow rate detecting device
14
is placed almost parallel to or at a predetermined angle with respect to the direction of flow of the fluid to be measured, disturbance in flow of the fluid to be measured occurs in the vicinity of the cavity
13
. Moreover, unevenness in the shape of the front edge portion of the flow rate detecting device
14
, which is caused due to the chipping thereof, results in variation in flow of the fluid to be measured. This variation in the flow of the fluid to be measured, which is caused in the vicinity of the heating element
4
, leads to reduction in accuracy of the flow rate detecting characteristics.
Thus, there has been previously proposed a flow rate sensor in which the flow-rate detecting device
14
is placed in a recess portion
18
provided in a plate-like supporting element
16
, as illustrated in
FIG. 26
, to thereby prevent disturbance in flow of the to-be-measured fluid from occurring in the vicinity of the cavity
13
, and in which the upstream-side end portion of the supporting element
16
is formed in an arcuated shape, thereby straightening the flow of the to-be-measured fluid and reducing variation in flow of the to-be-measured fluid, which would occur owing to unevenness in the shape of the front edge portion of the flow rate detecting device
14
.
FIG. 26
is a perspective view of a primary part of the conventional flow rate detecting device.
In the device of
FIG. 26
, the supporting element
16
is shaped like a plate and attached to a base member
20
. Further, the recess portion
18
, whose perimeter is a little longer than that of the flow rate detecting element
14
, is provided in a surface portion of the supporting element
16
. The flow rate detecting device
14
is disposed in the recess portion
18
so that the top surface of the flow rate detecting device
14
is almost flush with the top surface of the supporting element
16
. Moreover, the electrodes
8
a
to
8
d
of the flow rate detecting device
14
are electrically connected to leads
17
, which are disposed in the base member
20
, through wires
19
. Furthermore, a cover
21
is attached to the base member
20
, so that the electrodes
8
a
to
8
d
and the wires
19
are protected by the cover
21
.
In the case that the fluid to be measured flows only on the surface of the flow rate detecting device
14
in a low flow rate range. However, in a high flow rate range, movement of the fluid to be measured occurs between the recess portion
18
provided in the supporting element
16
and the flow rate detecting device
14
. Namely, as illustrated in
FIGS. 27 and 28
, a flow
22
of the to-be-measured fluid flowing on the surface of the flow rate detecting device
14
and a flow
23
thereof flowing between the recess portion
18
and the flow rate detecting
Uramachi Hiroyuki
Yamakawa Tomoya
Yonezawa Fumiyoshi
Fuller Benjamin R.
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
Thompson Jewel V.
LandOfFree
Thermo-sensitive flow rate sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thermo-sensitive flow rate sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermo-sensitive flow rate sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2878124