Abstrict A Karman vortex flow meter has a detection passages located along
a fluid flow in a duct 1. Flow outlets of the detection passage
are disposed on an end face of a vortex generation element and flow
inlets 3 are disposed upstream from the flow outlets. Heating coils
for detecting flow velocity change of a fluid caused by a negative
pressure of a Karman vortex are mounted in the detection passage,
and swell portions are formed upstream from the heating coils in
the detection passage. The flow meter that can prevent water drops,
bubbles, etc., from adhering to heating coils, etc., and detect
Karman vortexes stably.
Claims What is claimed is:
1. A Karman vortex flow meter for detecting a period of Karman
vortexes to measure a flow velocity or flow rate, said flow meter
comprising:
a duct into which a fluid flows;
a vortex generation element disposed in said duct to produce the
Karman vortexes;
a detection passage arranged along a fluid flow in said duct and
having a flow outlet disposed on an end face of said vortex generation
element and a flow inlet disposed on a wall face of said duct upstream
from said flow outlet;
detection means placed in said detection passage for detecting
variation of a flow velocity of a fluid in said detection passage
caused by a negative pressure of the Karman vortex; and
a swell portion formed upstream from said detection means in said
detection passage.
2. The Karman vortex flow meter as claimed in claim 1 wherein
said flow inlet of said detection passage is disposed on a wall
face on a top of said duct, wherein said swell portion is formed
just above said flow inlet, and wherein a lower face of said swell
portion communicated with said flow inlet is formed as a taper.
3. The Karman vortex flow meter as claimed in claim 1 wherein
a water repelling filter is installed in said swell portion.
4. The Karman vortex flow meter as claimed in claim 1 wherein
an exit of said swell portion communicated with said detection passage
does not face an entrance of said swell portion communicated with
said flow inlet and is projected from a wall face of said swell
portion.
5. The Karman vortex flow meter as claimed in claim 1 wherein
said flow inlet of said detection passage is made up of a plurality
of holes each having a passage diameter smaller than a passage diameter
of said detection passage.
6. The Karman vortex flow meter as claimed in claim 5 wherein a
total passage area of said plurality of holes is larger than a passage
area of said detection passage.
7. The Karman vortex flow meter as claimed in claim 1 wherein
a heating coil is mounted as means for detecting a flow velocity
in said detection passage and a flow velocity is measured in response
to a current change of said heating coil.
8. A Karman vortex flow meter for detecting a period of Karman
vortexes to measure a flow velocity or flow rate, said flow meter
comprising:
a duct into which a fluid flows;
a vortex generation element disposed in said duct to produce the
Karman vortexes;
a detection passage arranged along a fluid flow in said duct and
having a flow outlet disposed on an end face of said vortex generation
element and a flow inlet disposed on a wall face of said duct upstream
from said flow outlet; and
detection means placed in said detection passage for detecting
variation of a flow velocity of a fluid in said detection passage
caused by a negative pressure of the Karman vortex,
wherein said flow inlet is made up of a plurality of holes each
having a passage diameter smaller than a passage diameter of said
detection passage.
9. The Karman vortex flow meter as claimed in claim 8 wherein
a heating coil is mounted as means for detecting a flow velocity
in said detection passage and a flow velocity is measured in response
to a current change of said heating coil.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a Karman vortex flow meter used with
internal combustion engines of vehicles, etc., for measuring the
flow velocity and quantity of a fluid and in particular to a method
using heating coils, etc., for detecting Karman vortexes.
2. Description of Related Art
The methods using heating coils for detecting Karman vortexes are
those for detecting Karman vortexes occurring on a fluid directly
by means of heating coils and for detecting a subflow produced by
alternately occurring Karman vortexes.
The former method is described, for example, in Unexamined Japanese
Patent Publication 57-86013 (1982) as shown in FIG. 7 and the latter
is described, for example, in Unexamined Japanese Patent Publication
57-17864 (1982) as shown in FIG. 8.
In FIG. 7 a vortex generation element 102 is installed in a duct
101 where a fluid flows and heating coils 109a and 109b are placed
symmetrically in a vortex pass area downstream from the vortex generation
element 102. In the structure, Karman vortexes 107 produced by a
fluid flow indicated by an arrow 110 are detected as an increase
or decrease in a heating current fed into the heating coils 109a
and 109b for measuring the flow velocity or quantity according to
the Karman vortex period.
In FIG. 8 a heating coil is put in a through hole 250 piercing
both sides of a vortex generation element 202 installed in a duct
101 where a fluid flows, and a flow produced in the through hole
250 as Karman vortexes 207 occur is converted into an AC signal
synchronized with the vortex occurrence using a radiation amount
change of the heating coil 209. The flow velocity or quantity is
measured from the frequency or period of the AC signal.
The conventional Karman vortex flow meters introduce the following
problems:
If heating coils are installed directly in the duct through which
a fluid passes as shown in FIG. 7 when the fluid contains dust,
the dust will accumulate in the heating coils as the flow meter
is used for a long term. Since the accumulated dust hinders the
heating coils in heat radiation, electric output of the heating
coils decreases and in the end, Karman vortexes cannot be detected.
If two holes are made on the side faces of the vortex generation
element and the through passage is disposed so as to connect the
holes as shown in FIG. 8 Karman vortexes alternately occurring
via the through passage interfere with each other, causing Karman
vortexes to sometimes occur unstably.
To solve the problems, a Karman vortex flow meter as shown in FIGS.
9A and 9B has been proposed.
In FIGS. 9A and 9B, a vortex generation element 2 for generating
Karman vortexes is installed in a duct 1 into which a fluid flows
and detection passages 5 are disposed along the fluid flow in the
duct 1. Each detection passage 5 has a flow outlet 4 formed in the
end face of the vortex generation element 2 and a flow inlet 3 formed
in the top wall face of the duct 1 upstream from the flow outlet
4. Further, heating coils 9 for detecting a flow velocity change
in the detection passages 5 caused by a negative pressure of a Karman
vortex and supports 8 for supporting the heating coils 9 are located
in the detection passages 5.
The above mentioned Karman vortex flow meter is described in detail
in a copending U.S. patent application No. 08/553901 filed on
Nov. 6 1996.
The Karman vortex flow meter of the structure in FIG. 9 can prevent
dust having a heavy specific gravity from flowing into the detection
passages 5; however, if the fluid contains water drops or bubbles
having a comparatively light specific gravity, the water drops or
bubbles enter the detection passages. Residence of the water drops
or bubbles can hinder the heating coils from detecting Karman vortexes
or fuse the heating coils.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an improvement
in the Karman vortex flow meter shown in FIG. 9 and more particularly
to a Karman vortex flow meter which, even if the fluid to be measured
contains water drops or bubbles, can prevent the water drops or
bubbles from flowing into a detection passage and always detect
Karman vortexes stably.
According to the invention, there is provided a Karman vortex flow
meter comprising a detection passage being arranged along a duct
in which a vortex generation element is installed and having a flow
outlet disposed on an end face of the vortex generation element
and a flow inlet disposed on a wall face of the duct upstream from
the flow outlet, detection means being placed in the detection passage
for detecting a flow velocity change of a fluid in the detection
passage caused by a negative pressure of the Karman vortex, and
a swell portion being formed upstream from the detection means.
The flow inlet of the detection passage is disposed on a wall face
on a top of the duct, the swell portion is formed just above the
flow inlet, and a lower face of the swell portion communicated with
the flow inlet is formed like a taper.
Further, a water repelling filter is installed in the swell portion.
Further, the exit of the-swell portion from which a fluid flows
out does not face the entrance of the swell portion into which a
fluid flows and is projected from a wall face of the swell portion.
Further the flow inlet of the detection passage is made up of a
plurality of holes each having a passage diameter smaller than a
passage diameter of the detection passage.
Further, the total passage area of the holes is made larger than
the passage area of the detection passage.
According to the invention, there is provided a Karman vortex flow
meter comprising a detection passage being arranged along a duct
in which a vortex generation element is installed and having a flow
outlet disposed on an end face of the vortex generation element
and a flow inlet disposed on a wall face of the duct upstream from
the flow outlet, and detection means being placed in the detection
passage for detecting a flow velocity change of a fluid in the detection
passage caused by a negative pressure of the Karman vortex, the
flow inlet of the detection passage being made up of a plurality
of holes each having a passage diameter smaller than a passage diameter
of the detection passage.
A heating coil is mounted as means for detecting a flow velocity
in the detection passage and a flow velocity is measured in response
to a current change of the heating coil.
According to the above described invention, when a fluid containing
water drops or bubbles is caused to flow into the Karman vortex
flow meter having the structure, the fluid also passes through the
detection passage as it passes through the duct. At this time, the
water drops or bubbles in the fluid also pass through the flow inlet.
When the water drops or bubbles passing through the flow inlet arrive
at the swell portion, the flow velocity once slows down. Thus, the
water drops or bubbles are trapped in the swell portion and most
of them stop here.
The water drops or bubbles trapped on the taper-like bottom of
the swell portion are discharged by gravity from the flow inlet
when inflow of the fluid stops.
Further, if the swell portion is provided with a water repelling
filter, it becomes harder for water drops or bubbles to enter the
detection passage.
A guiding inlet projecting from the swell portion wall face is
formed, whereby the water drops or bubbles trapped on the top wall
face of the swell portion do not flow into the depth of the detection
passage.
If the passage area of the flow inlet is small, water drops or
bubbles become hard to pass through the flow inlet. Therefore, a
plurality of flow inlets are formed as smaller holes than the detection
passage, whereby water drops or bubbles are hard to enter the detection
passage.
If the sum of the passage areas of the flow inlets (holes) is made
larger than the detection passage area, detection of Karman vortexes
is not hindered.
Further, water drops or bubbles do not flow into the detection
passage simply by making up the flow inlet of the detection passage
of a plurality of holes each having a passage diameter smaller than
the passage diameter of the detection passage.
A larger electric signal can be provided by using a heating coil.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIGS. 1A and 1B are a plan view and a sectional side view showing
a Karman vortex flow meter according to a first embodiment of the
invention;
FIG. 2 is a fragmentary sectional view showing a swell portion
of a detection passage according to a second embodiment of the invention;
FIG. 3 is a fragmentary sectional view showing a swell portion
of a detection passage according to a third embodiment of the invention;
FIG. 4 is a fragmentary sectional view showing a swell portion
of a detection passage according to a fourth embodiment of the invention;
FIG. 5 is a fragmentary sectional view showing a swell portion
of a detection passage according to a fifth embodiment of the invention;
FIG. 6 is a fragmentary sectional view showing a detection passage
according to a sixth embodiment of the invention;
FIG. 7 is a view showing a conventional Karman vortex flow meter;
FIG. 8 is a view showing a conventional Karman vortex flow meter;
and
FIGS. 9A and 9B are a plan view and a sectional side view showing
a Karman vortex flow meter related to the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
First embodiment:
FIGS. 1A and 1B are a plan view and a sectional side view showing
a Karman vortex flow meter according to a first embodiment of the
invention.
In FIG. 1 a vortex generation element 2 is vertically installed
in a duct into which a fluid indicated by an arrow 10 flows and
detection passages 5 having flow outlets 4 on side faces of the
vortex generation element 2 and flow inlets 3 on top wall faces
of the duct 1 upstream from the flow outlets 4 are disposed substantially
in parallel with a flow in the duct 1.
The detection passages 5 contain supports 8 on which heating coils
9 are put. Swell portions 11a and 11b are formed upstream from the
heating coils 9 in the detection passages 5.
In the Karman vortex flow meter having the structure, when a fluid
flows into the duct 1 in the direction of the arrow 10 Karman vortexes
7 occur on the rear of the vortex generation element 2. Assuming
that a Karman vortex 7 occurs at the flow outlet 4 a negative pressure
is applied around the flow outlet 4 whereby the fluid flows into
the detection passage 5 through the flow inlet 3 higher in pressure
than the flow outlet 4. The heating coil 9 detects the fluid flow
in the detection passage 5. At this time, water drops or bubbles
12 contained in the gas also flow into the detection passage 5 with
the inflow of the fluid through the flow inlet 3. When the water
drops or bubbles passed through the flow inlet 3 arrive at the first
swell portion 11a, the flow velocity lowers, thus the water drops
or bubbles 12 are trapped in the first swell portion 11a. Water
drops or bubbles 12 not trapped by the first swell portion 11a are
trapped in the second swell portion 11b.
When the fluid thus reaches the heating coil 9 the water drops
or bubbles 12 in the fluid disappear or little exist. Therefore,
the water drops or bubbles do not adhere to the heating coil 9 or
the support 8 or little adhere thereto if they adhere; detection
of a fluid (gas) flow is not hindered.
If the fluid contains a small amount of water drops or bubbles
12 only one swell portion 11 may be formed; if it contains a large
amount of water drops or bubbles 12 three or more swell portions
11 may be formed.
Second embodiment:
FIG. 2 shows a swell portion of a detection passage according to
a second embodiment of the invention.
In the figure, numeral 111 is a taper-like lower face of a swell
portion 11 formed upstream from a detection passage 5. Parts identical
with or similar to those previously described with reference to
FIG. 1 are denoted by the same reference numerals in FIG. 2 and
will not be discussed again.
In the structure, since the flow velocity of a fluid flowing in
through a flow inlet 3 lowers at the swell portion 11 a flow line
indicated by an arrow 6 is drawn. Thus, water drops or bubbles 12
in the fluid having a heavy specific gravity stay in the swell portion
11 and soon adhere to the lower face 111 as shown in FIG. 2. When
the amount of the water drops or bubbles 12 adhering to the lower
face 111 increases and no fluid flows in, the water drops or bubbles
12 on the lower face 111 are discharged by gravity from the flow
inlet 3 along the taper face of the lower face 111.
Third embodiment:
FIG. 3 shows a swell portion of a detection passage according to
a third embodiment of the invention.
In the figure, a water repelling filter 13 is installed in a swell
portion 11. Parts identical with or similar to those previously
described with reference to FIG. 2 are denoted by the same reference
numerals in FIG. 3.
In the structure, water drops or bubbles 12 flowing into the swell
portion 11 are trapped not only on the wall face of the swell portion
11 as the flow velocity lowers as in FIG. 2 but also by the water
repelling filter. Therefore, water drops or bubbles 12 do not flow
into the detection passage 5.
Fourth embodiment:
FIG. 4 shows a swell portion of a detection passage according to
a fourth embodiment of the invention.
In the figure, a detection passage 5 has a guiding inlet 5a projecting
toward the inside from the wall face not opposed to a flow inlet
3 of the swell portion 11.
In the fourth embodiment, water drops or bubbles 12 flowing into
the swell portion 11 are trapped on the wall face of the swell portion
11 as in FIG. 2 but the water drops or bubbles 12 trapped on the
upper side than the guiding inlet 5a of the detection passage 5
do not flow into the detection passage 5 because the guiding inlet
5a projects from the wall face of the swell portion.
Fifth embodiment:
FIG. 5 shows a swell portion of a detection passage according to
a fifth embodiment of the invention.
In the figure, flow inlets 3 consist of inlets 3a, 3b, . . . each
having a passage diameter d2 smaller than a passage diameter d1
of a detection passage 5. Water drops or bubbles 12 contained in
a fluid have various particle sizes. Thus, the smaller the passage
diameter d2 of the flow inlet 3a, 3b, . . , the fewer the amount
of water drops or bubbles 12 passing through the flow inlet. If
the total area of the flow inlets 3a, 3b, . . . is larger than the
area of the detection passage 5 a fluid flow occurring in the detection
passage 5 caused by Karman vortexes is not hindered.
Sixth embodiment:
FIG. 6 shows a flow inlet of a detection passage according to a
sixth embodiment of the invention.
In the figure, a plurality of flow inlets 3 are communicated directly
with a detection passage 5 and no swell portion is formed. If the
flow inlets 3 are sufficiently small as in FIG. 6 water drops or
bubbles 12 do not flow into the detection passage 5 as in FIG. 5.
However, since the total area of the flow inlets 3 is not larger
than the area of the detection passage 5 a fluid flow occurring
in the detection passage 5 caused by Karman vortexes is a little
hindered.
According to the invention, since water drops or bubbles passing
through the flow inlet are trapped in the swell portion, water drops
or bubbles flowing into the detection passage decrease, not adversely
affecting detection of a fluid flow in the detection passage; stable
flow quantity detection is enabled.
According to the invention, the flow inlet of the detection passage
is disposed on the top of the dust, the wall face of the swell portion
on the flow inlet side is formed like a taper, and the swell portion
is formed just above the flow inlet, whereby the water drops or
bubbles passing through the flow inlet can be trapped in the swell
portion for preventing them from flowing into the detection passage,
and the trapped water drops or bubbles can also be discharged by
gravity from the flow inlet when inflow of the fluid stops.
According to the invention, the swell portion is provided with
the water repelling filter, whereby the trap effect is furthermore
improved, making water drops or bubbles hard to enter the detection
passage.
According to the invention, a guiding inlet projecting from the
swell portion wall face is formed, whereby the water drops or bubbles
trapped on the top wall face of the swell portion do not flow into
the depth of the detection passage.
According to the invention, a plurality of flow inlets are formed
as smaller holes than the diameter of the detection passage, whereby
water drops or bubbles becomes extremely hard to enter the detection
passage.
According to the invention, since the sum total of the passage
areas of the flow inlets (holes) is made larger than the detection
passage area, a fluid flow in the detection passage is not hindered
and detection of Karman vortexes is not affected.
According to the invention, water drops or bubbles become hard
to flow into the detection passage simply by making up the flow
inlet of the detection passage of a plurality of holes each having
a passage diameter smaller than the passage diameter of the detection
passage.
According to the invention, a larger electric signal can be provided
by using a heating coil. |