Abstrict A Karman's vortex street flow meter has two conduits through which
a fluid to be measured flows, a vortex generating portion disposed
at a junction where those portions of the fluid flowing through
the respective conduits join each other, a plurality of vortex stabilizers
disposed at predetermined equal intervals downstream of the vortex
generating portion, and a detector for detecting the frequency at
which vortices of a Karman's vortex street are generated downstream
of the vortex generating portion to sense the flow speed or the
flow rate of the fluid.
Claims What is claimed is:
1. A Karman's vortex street flow meter comprising:
a conduit means, the upstream end of said conduit means being a
pair of upstream conduits having the upstream ends spaced from each
other laterally of the conduit means for receiving a fluid to be
measured thereinto, the downstream end of said conduit means being
a single downstream conduit into which said upstream conduits merge,
the walls of said upstream conduits forming a vortex generating
portion between said upstream conduits at the junction where said
upstream conduits merge into said single downstream conduit, and
a detector in said single downstream conduit and spaced downstream
of said vortex generating portion for detecting the frequency at
which vortices of a Karmen' s vortex street are generated downstream
of said vortex generating portion for use in determining the flow
speed or flow rate of the fluid.
2. A Karmen' s vortex street flow meter as claimed in claim 1 wherein
said vortex generating portion is a transversely extending wall
extending between the downstream end of the walls of said pair of
upstream conduits.
3. A Karmen' s vortex street flow meter as claimed in claim 2 further
comprising at least one vortex stabilizer in said single downstream
conduit spaced downstream of said vortex generating portion and
upstream of said detector for stabilizing the generation of vortices
of said Karmen' s vortex street.
4. A Karmen' s vortex street flow meter as claimed in claim 3 wherein
said vortex stabilizer is a strip of material with the width thereof
perpendicular to the direction of flow in said single downstream
conduit.
5. A Karmen' s vortex street flow meter as claimed in claim 3 wherein
said vortex stabilizer is a rod having a trapezoidal cross-section
with the parallel sides perpendicular to the direction of flow of
fluid in said single downstream conduit.
6. A Karmen' s vortex street flow meter as claimed in claim 3 wherein
there is a plurality of vortex stabilizers in the form of strips
of material with the width thereof perpendicular to the direction
of flow of fluid and spaced at equal intervals from said vortex
generating portion, and further comprising a further vortex stabilizer
in the form of a strip connected to said transversely extending
wall and having a width the ratio of which to the width of said
conduit wall is not less than unity.
7. A Karmen' s vortex street flow meter as claimed in claim 2 wherein
said pair of upstream conduits have cross-sections substantially
equal in area to each other.
8. A Karmen' s vortex street meter as claimed in claim 1 in which
said upstream conduits diverge in the upstream direction.
9. A Karmen' s vortex street flow meter as claimed in claim 1 in
which said upstream conduits are in spaced parallel relationship
in the upstream direction.
10. A Karmen' s vortex street flow meter as claimed in claim 1
further comprising a receiver having an air cleaner extending across
the cross-section thereof, an air introduction port on one side
of said air cleaner, and the upstream ends of said upstream conduits
extending into said receiver on the other side of said air cleaner.
Description BACKGROUND OF THE INVENTION
This invention relates to a Karman's vortex street flow meter comprising
a pair of conduits having a fluid to be measured introduced thereinto,
and a detector for detecting the flow rate or flow speed of the
measured fluid by detecting a frequency at which vortices of a Karman's
vortex street are generated downstream of a junction where the measured
fluid flowing through one of the conduits joins that flowing through
the other conduit.
There have been already proposed a variety of types of the so-called
Karman's vortex street flow meters comprising a conduit having a
fluid to be measured flowing therethrough, a vortex generating rod
immersed in the fluid flowing through the conduit perpendicularly
to the direction of flow of the fluid to generate a Karman's vortex
street downstream of the rod and a detector for detecting the frequency
at which vortices of the Karman's vortex street are generated thereby
to measure the flow rate or flow speed of the fluid.
Flow meters of the types referred to are disclosed and claimed,
for example, in Japanese patent publication Nos. 1905/1969 and 9069/1981
and put to practical use as industrial measurement devices. There
are also known a variety of types of a sucked air detector comprising
the Karman's vortex street flow meter as described above utilized
to detect the amount of air sucked into an associated internal combustion
engine. Those sucked air detectors are disclosed and claimed, for
example, in Japanese laid-open utility model application No. 5008/1975
Japanese laid-open patent application No. 130718/1976 and put to
practical use. One of the conventional sucked air detectors has
comprised a Karman's vortex street flow meter such as disclosed
above, and an air cleaner disposed upstream of the Karman's vortex
street flow meter to clean sucked air passed through an air introduction
port. The sucked air introduced into the Karman's vortex steet flow
meter has been arranged to flow along a minimum length flow path
between the air introduction port and the inlet port of the Karman's
vortex street flow meter. In other words, the sucked air has flowed
through the central portion of the air cleaner in a concentrated
manner. As a result, only that central portion of the air cleaner
has been used to filter the air and has become greatly contaminated
and also may oftentimes be deformed by the stream of the sucked
air.
Furthermore it has been known to use the Karman's vortex street
flow meter as described above to detect the flow rate of a fluid
flowing in a pair of different directions through respective conduits.
In the latter case the flow rate of the fluid has been detected
either by disposing the Karman's vortex street flow meter in each
of the conduits or by disposing the Karman's vortex street flow
meter in a conduit following a junction where the fluid portions
flowing through the respective conduits have joined each other.
It is well known that, in order to rectify the measured fluid introduced
thereinto, Karman's vortex street flow meters are required to include
a conduit on the upstream side thereof having a length equal to
at least five times the diameter of the conduit for the same and
a conduit on the downstream side thereof having a length equal to
about three times that diameter. Thus the use of the Karman's vortex
street flow meters as described above has been disadvantageous in
that the conduit therefor becomes long.
Accordingly it is an object of the present invention to provide
a new and improved Karman's vortex street flow meter including a
vortex generating portion having a structure which is inexpensive
and simple as compared with the prior art structure.
It is another object of the present invention to provide a new
and improved sucked air detector utilizing the Karman's vortex street
flow meter as described in the preceding paragraph to detect an
amount of air sucked into an internal combustion engine.
SUMMARY OF THE INVENTION
The present invention provides a Karman's vortex street flow meter
comprising a pair of conduits into which a fluid to be measured
is introduced, a vortex generating portion disposed at a junction
where portions of the measured fluid flowing through the conduits
respectively join each other, and the detector for detecting a frequency
at which vortices of a Karman's vortex street are generated downstream
of the vortex generating portion thereby to sense the flow speed
or the flow rate of the fluid to be measured.
In a preferred embodiment of the present invention, the vortex
generating portion is formed of one part of the walls of the pair
of conduits and a plurality of vortex stabilizers in the form of
strips or rods are disposed downstream of the vortex generating
portion to stabilize the generation of the vortices downstream of
the vortex generating portion.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more readily apparent from the
following detailed description taken in conjunction with the accompanying
drawings in which:
FIG. 1 is a longitudinal sectional view of a sucked air detector
including a conventional Karman's vortex street flow meter to detect
an amount of air sucked into an associated internal combustion engine.
FIG. 2 is a longitudinal sectional view of one embodiment of a
sucked air detector including the Karman's vortex street flow meter
according to the present invention to detect an amount of air sucked
into an associated internal combustion engine;
FIG. 3 is a cross sectional view of the arrangement shown in FIG.
2 with the section taken on the line III--III of FIG. 2;
FIG. 4 is a longitudinal sectional view of the arrangement shown
in FIG. 2 with section taken on line IV--IV of FIG. 2;
FIG. 5 is a longitudinal sectional view of a modification of the
present invention;
FIG. 6 is a view similar to FIG. 5 but illustrating another modification
of the present invention; and
FIG. 7 is a view similar to FIG. 5 but illustrating still another
modification of the present invention.
Throughout the Figures like reference numerals designate identical
or corresponding components.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to FIG. 1 of the drawings, there is illustrated a
sucked air detector including a conventional Karman's vortex street
flow meter to detect the amount of air sucked into an associated
internal combustion engine. The arrangement illustrated comprises
a conventional Karman's vortex street flow meter including the main
body 10 in the form of a conduit composed of a plastic material,
an aluminum rectifier 12 disposed in an inlet port of the main body
10 a vortex generating rod 14 extending across the main body so
as to be immersed in the fluid flowing therethrough, in this case,
sucked air flowing through the conduit 10 to generate a Karman's
vortex street 16 downstream thereof and a vortex detector consisting,
for example, of an ultrasonic transmitter 18 and an ultrasonic receiver
18' disposed in opposed relationship on the opposite wells of the
conduit 10 downstream of the vortex generating rod 14 with the Karman's
vortex street therebetween.
The main body or conduit 10 includes an inlet portion with the
rectifier 12 extending into a sucked air receiver 20 of sheet iron
so that the rectifier 12 is opposed to an air introduction port
22 with an air cleaner 24 therebetween which, in turn, divides the
receiver into a pair of compartments. The air cleaner 24 is formed
of unwoven cloth.
In operation, sucked air is introduced into the receiver 20 through
the air introduction port 22 and then cleaned by the air cleaner
24 after which the air enters into Karman's vortex street flow meter
and the flow rate thereof is measured by the vortex detector 18-18'
in the manner well known in the art.
In the arrangement of FIG. 1 the sucked air flows along a minimum
length path between the air introduction port 22 and the rectifier
12 in the inlet port of the conduit 10. Thus the sucked air flowing
through the air cleaner is concentrated at the central portion thereof.
As a result, the central portion of the air cleaner 24 becomes very
contaminated and also may be deformed by the concentrated flow of
the sucked air.
The present invention seeks to eliminate the abovementioned disadvantages
of the arrangement shown in FIG. 1.
FIGS. 2 3 and 4 show one embodiment of a sucked air detector including
the Karman's vortex street flow meter according to the present invention
which detects the amount of air sucked into an associated internal
combustion engine. The arrangement illustrated comprises the Karman's
vortex street flow meter including the main body 10 in the form
of a rectangular cross-section conduit having that portion thereof
extending into the sucked air receiver 20 having a rectangular cross
section forked into a pair of somewhat diverged conduit portions
26 and 28 which are, in turn, provided at the upper ends as viewed
in FIG. 2 with respective rectifiers 12. As in the arrangement of
FIG. 1 the rectangular conduit is formed of a plastic material.
As shown in FIG. 3 the conduit portions 26 and 28 each have a rectangular
cross section substantially equal in area to each other and have
the lower ends as viewed in FIG. 2 merged into the main body or
conduit 10 so that the adjacent walls thereof have lower ends connected
to each other through a connecting wall 30 substantially perpendicular
to the longitudinal axis of the conduit 10 to form a vortex generating
portion. In other words, the vortex generating portion is formed
of one part of the walls of the conduit portions.
Then a plurality of vortex stabilizers 32 formed of a metallic
material, in this case three stabilizers, are disposed at predetermined
equal intervals below the connecting wall 30 within the conduit
10 with the uppermost stabilizer spaced from the connecting wall
30 by a predetermined interval which may be equal to the predetermined
equal intervals. Each of the vortex stabilizers 32 is in the form
of a strip substantially equal in width to the connecting wall 30
and centered on the longitudinal axis of the conduit 10 (see FIG.
2) while being suitably fixed at both ends to a pair of opposite
longer walls of the conduit 10 (see FIG. 4).
In other respects the arrangement shown in FIGS. 2 3 and 4 is
identical to that illustrated in FIG. 1.
When the associated internal combustion engine (not shown) is started,
air sucked into the engine passes through the air introduction port
22 and then the air cleaner 24 where it is cleaned. Then the air
is rectified by the rectifiers 12 and the rectified air is introduced
into the pair of conduit portions 26 and 28. When those portions
of the rectified air introduced into the conduit portions 26 and
28 respectively join each other, vortices are generated by the vortex
generating portion 30. At that time the vortex stabilizers 32 function
to maintain the generation of the vortices continuous and stable.
Thus there are generated downstream of the lowermost vortex stabilizer
32 periodic vortices corresponding to a flow speed or flow rate
of the sucked air resulting in the formation of a stable Karman's
vortex street 16. Then the vortex detector 18-18' detects the frequency
at which the vortices of the Karman's vortex street 16 are generated
resulting in the detection of the flow speed or flow rate of the
sucked air. Thereafter the sucked air is introduced into the engine.
From the foregoing it is seen that, since the sucked air flowing
through the air introduction port 22 is divided into a pair of streams
thereof flowing through the conduit portions 26 and 28 respectively,
the same is prevented from being concentrated at a single point
upon its passage through the air cleaner 24. Therefore the air cleaner
24 is prevented from being locally overly contaminated and also
from being deformed due to a concentrated stream of the sucked air.
Also the vortex generating portion 30 is disposed at the junction
where those portions of the sucked air flowing through the conduit
portions 26 and 28 respectively join each other and vortices are
apt to be generated, so that one part of the walls of the conduit
portions 26 and 28 can be utilized as the vortex generating portion
30 resulting in a simplified structure. Furthermore the rectangular
cross section of the conduit portions 26 and 28 is effective for
forming the vortex generating portion 30 and the vortex stabilizers
32 are effective particularly with a large change in flow rate of
air sucked into an associated internal combustion engine. That is,
the flow rate can be detected over a wide range.
FIG. 5 shows a modification of the present invention. The arrangement
illustrated is different from that shown in FIGS. 2 3 and 4 only
in that in FIG. 5 the pair of conduit portions 26 and 28 extend
parallel to the longitudinal axis of the conduit 10.
In another modification of the present invention illustrated in
FIG. 6 the pair of conduit portions 26 and 28 are curved so as to
be gradually diverged away from each other toward the inlet portions
thereof and the vortex stabilizer 32 is in the form of a rod having
a cross section of an inverted trapezoid. While a single vortex
stabilizer 32 is shown in FIG. 6 only for purposes of illustration,
it is to be understood that a plurality of vortex stabilizers 32
in the form of rods may be disposed as shown in FIG. 2 or 5.
FIG. 7 shows still another modification of the present invention.
The arrangement illustrated is different from that shown in FIG.
5 only in that in FIG. 7 the pair of conduit portions 26 and 28
have their inlet portions curved to be diverged away from each other
and the connecting wall 30 has connected thereto the uppermost one,
as viewed in FIG. 7 of a plurality of vortex stabilizers 32 in
this case four stabilizers, disposed in the manner as described
above in conjunction with FIG. 2. That vortex stabilizer 32 connected
to the connecting wall 30 has a width l the ratio of which to the
width h of the connecting wall 30 is not less than unity (1). This
measure is effective for further stabilizing the generation of the
Karman's vortex street 16. It has been found that if the width h
of the connecting wall 30 is greater than the width l of the vortex
stabilizers 30 this results in an unstable generation of continuous
vortices and therefore is not desirable. All the vortex stabilizers
may be substantially equal in width to one another.
From the foregoing it is seen that the present invention provides
a Karman's vortex street flow meter comprising a pair of conduit
portions for introducing a measured fluid thereinto, a vortex generating
portion disposed at a junction where those portions of the measured
fluid flowing through the pair of conduit portions respectively
join each other and detection means disposed downstream of the vortex
generating portion to detect the frequency at which vortices of
a Karman's vortex street are generated downstream of the vortex
generating portion thereby to detect the flow speed or flow rate
of the fluid to be measured. For detecting the flow speed or flow
rate of the fluid inflowing in a pair of different directions through
respective portions, the present invention can shorten the particular
measuring conduit as compared with a conventional Karman's vortex
street flow meter or meters. Also since the vortex generating portion
is disposed at the abovementioned junction where vortices are easily
generated, the resulting structure is simplified because the vortex
generating portion is formed of one part of walls of the the respective
conduits as described above. Also the rectangular cross section
of the conduit portions 26 and 28 is effective for forming the vortex
generating portion 30 as described above. In addition a plurality
of vortex stabilizers 30 in the form of strips or rods are effective
to permit detecting of the flow speed or a flow rate of the fluid
over a wide range of flow speeds or flow rates.
While the present invention has been illustrated and described
in conjunction with a few preferred embodiments thereof it is to
be understood that numerous changes and modifications may be resorted
to without departing from the spirit and scope of the present invention.
For example, the vortex stabilizer in the form of a rod may have
any suitable cross section other than that illustrated. Also the
vortex stabilizers may be omitted where there is only a small change
in flow speed or flow rate of the fluid. |