Abstrict The measurement of volume flows or mass flows in the intake system
of motor vehicle internal combustion engines plays a significant
role in reducing pollutant emissions. Therefore, an ultrasonic flow
meter for measuring a flow rate of a fluid flowing in a primary
flow direction is described. The ultrasonic flow meter has at least
two ultrasonic transducers, the ultrasonic transducers being capable
of emitting and/or receiving ultrasonic waves at an angle .alpha.
to the primary flow direction which is different from 90.degree..
Furthermore, the ultrasonic flow meter has at least one guide element
which is entirely or partially situated in the fluid. This guide
element diverts at least one part of the flowing fluid in such a
way that in the diversion, a velocity component is transferred to
at least one part of the flowing fluid perpendicular to the primary
flow direction. Guide vanes or displacers in particular are described
as guide elements. In addition, turbulators may be provided on the
guide elements, the turbulators generating a longitudinal fluid
bed along the guide elements and thus causing the flow of the fluid
to have a better contact with the guide elements when flowing around
them. This reduces turbulences within the ultrasonic flow meter.
Compared to the devices known from the related art, the ultrasonic
flow meters described are distinguished by an improved signal-to-noise
ratio and accordingly by a higher measuring precision.
Claims 1. An ultrasonic flow meter for measuring a flow velocity of a
fluid flowing in a primary flow direction, comprising: at least
two ultrasonic transducers capable of at least one of emitting and
receiving an ultrasonic wave at an angle .alpha. to the primary
flow direction that is different from 90.degree.; and at least one
guide element one of entirely and partially situated in the flowing
fluid, wherein: the at least one guide element diverts at least
one part of the flowing fluid in such a way that in the diversion,
a velocity component perpendicular to the primary flow direction
is imparted to the at least one part of the flowing fluid.
2. The ultrasonic flow meter as recited in claim 1 wherein: the
ultrasonic wave from a first one of the at least two ultrasonic
transducers can reach a second one of the at least two ultrasonic
transducers in linear and reflection-free propagation.
3. The ultrasonic flow meter as recited in claim 1 further comprising:
at least one reflection surface, wherein: the ultrasonic wave from
a first one of the at least two ultrasonic transducers can reach
a second one of the at least two ultrasonic transducers in linear
propagation after at least one reflection on the at least one reflection
surface.
4. The ultrasonic flow meter as recited in claim 1 wherein: the
at least one guide element includes at least one guide vane tilted
in relation to the primary flow direction.
5. The ultrasonic flow meter as recited in claim 1 wherein: at
least a first guide element and a second guide element of the at
least one guide element are situated in the flowing fluid in a lamellar
pattern.
6. The ultrasonic flow meter as recited in claim 1 wherein the
at least one guide element includes at least one displacer.
7. The ultrasonic flow meter as recited in claim 6 further comprising:
a flow pipe through which the flowing fluid flows, wherein: the
at least one displacer locally narrows a flow cross section of the
flow pipe.
8. The ultrasonic flow meter as recited in claim 1 wherein: the
at least one guide element includes at least one turbulator that
generates a spatially limited eddy area in the flowing fluid in
a vicinity of the at least one guide element.
9. The ultrasonic flow meter as recited in claim 1 wherein: at
least one of the at least two ultrasonic transducers and the at
least one guide element are integrated into an insertion sensor
that can be inserted into a flow pipe.
10. The ultrasonic flow meter as recited in claim 9 further comprising:
at least one electronic control unit integrated into the insertion
sensor for at least one of activating and reading out at least one
of the at least two ultrasonic transducers.
11. The ultrasonic flow meter as recited in claim 9 further comprising:
at least one reflection element including at least one reflection
surface and being integrated into the insertion sensor, wherein:
the flow pipe includes at least one pipe wall, and the at least
one reflection element in the insertion sensor inserted into the
flow pipe is at a distance from the pipe wall in such a way that
the flowing fluid can flow along the at least one reflection element
on both sides of the at least one reflection surface.
12. The ultrasonic flow meter as recited in claim 9 wherein: for
the purpose of reducing signal echoes, at least one of a component
and a surface of the insertion sensor includes one of: a material
that suppresses a reflection of the ultrasonic wave, and a layer
that suppresses a reflection of the ultrasonic wave.
Description FIELD OF THE INVENTION
[0001] Ultrasonic flow meters are used in the automotive industry,
in particular in the intake system of internal combustion engines,
for measuring volume flow or mass flow. Typically ultrasonic transducers
are used which are capable of both emitting ultrasonic waves into
a fluid and receiving ultrasonic waves. The propagation time of
ultrasonic signals which are transmitted from an emitter to a receiver
is influenced by the flow of the fluid. It is possible to infer
the flow velocity of the fluid from the degree of influence of the
propagation time.
BACKGROUND INFORMATION
[0002] British Published Patent Application No. 2 101 318 describes
an ultrasonic flow meter in which two ultrasonic transducers are
mounted on opposite sides of a pipe through which a fluid (112)
flows. The transducers are situated slightly offset with respect
to one another, so that ultrasonic waves emitted by one transducer
and received by the second transducer propagate at an angle to the
flow direction of the fluid which is different from 90.degree..
[0003] In addition to the system described in British Published
Patent Application No. 2 101 318 ultrasonic flow meters are also
known in which ultrasonic waves emitted by an ultrasonic transducer
are initially reflected one time or multiple times before they are
received by a second ultrasonic transducer situated on the same
side of the pipe through which the fluid flows as the first ultrasonic
transducer. Such systems are described, for example, in European
Published Patent Application No. 0 477 418 in British Published
Patent Application No. 1 541 419 and in Japanese Published Patent
Application No. 59100820. In European Published Patent Application
No. 0 477 418 A1 a unit made up of two ultrasonic transducers and
one reflector system is integrated into a coherent unit which may
be installed in a measuring tube.
[0004] FIG. 1 shows the operating principle of these measuring
systems corresponding to the related art. A fluid 112 for example,
air, flows through a flow pipe 110 in an essentially laminar flow
at a flow velocity v.sub.FL 114. Two ultrasonic transducers 116
and 118 are mounted on opposite sides of flow pipe 110 in such a
way that first ultrasonic transducer 116 is able to emit ultrasonic
waves, which may be received by second ultrasonic transducer 118
these ultrasonic waves propagating at a velocity v.sub.UL 120 at
an angle .alpha. to flow velocity 114 which is different from 90.degree..
In the system depicted here, the ultrasonic waves of ultrasonic
transducer 116 propagate toward ultrasonic transducer 118 at a velocity
v.sub.UL,1 which is higher than in an unmoving fluid 112 due to
the motion of fluid 112 at velocity 114. v.sub.UL,1=v.sub.UL+v.sub.FLcos
.alpha. (1)
[0005] v.sub.UL stands for the propagation velocity of the ultrasonic
waves in an unmoving fluid. In contrast, if ultrasonic waves are
emitted by ultrasonic transducer 118 and received by ultrasonic
transducer 116 these waves propagate at a velocity v.sub.UL,2 which
is lower than propagation velocity v.sub.UL in unmoving fluid 112.
v.sub.UL,2=v.sub.UL-v.sub.FLcos .alpha. (2)
[0006] Comparing a propagation time t.sub.1 which a signal needs
from ultrasonic transducer 116 to ultrasonic transducer 118 with
a propagation time t.sub.2 which an ultrasonic signal needs from
ultrasonic transducer 118 to ultrasonic transducer 116 allows flow
velocity v.sub.FL 114 of the fluid to be determined: v FL = L 2
cos .times. .times. .alpha. ( 1 t 1 - 1 t 2 ) ( 3 )
[0007] A similar calculation of flow velocity v.sub.FL may also
be performed for reflection systems such as described in EP 0 477
418 A1 for example.
[0008] The systems described in the related art, however, all have
the problem that angle .alpha. in FIG. 1 must be sufficiently small
for a successful flow measurement, but at least substantially smaller
than 90.degree.. This results in the problem that it is not possible
to fit the surfaces of ultrasonic transducers 116 118 flush to
the inside surface of flow pipe 110. Protrusions 122 are thus formed
in flow pipe 110 in the area of ultrasonic transducers 116 118
which result in turbulences and flow separations. These turbulences
cause pressure fluctuations and may result in interfering signal
contributions which are superimposed on the actual ultrasonic signals
as noise.
[0009] Another disadvantage of these turbulences and flow separations
is that contaminants or particles such as dust, oil, or water droplets
contained in the flowing medium tend to be deposited in the turbulence
zones. One possible remedy is to insert wedge-shaped adaptor elements
which fill up protrusions 122 of flow pipe 110 but are permeable
to ultrasonic waves. However, the disadvantage here is that the
layer thickness of the wedge-shaped adaptor elements varies over
the cross section of an emitted ultrasound beam. This makes resonance
adjustment for efficient ultrasound injection into the flowing medium
difficult. Furthermore, such a construction responds sensitively
to structure-borne noise injected into flow pipe 110.
SUMMARY OF THE INVENTION
[0010] The present invention therefore provides an ultrasonic flow
meter for measuring the volume flow and/or the mass flow of a fluid
which may be used in particular in the intake system of a motor
vehicle internal combustion engine.
[0011] The present invention is based on an ultrasonic flow meter
corresponding to the related art for measuring a flow velocity of
a fluid flowing in a main flow direction. At least two ultrasonic
transducers are used, it being possible for the ultrasonic transducers
to emit ultrasonic waves into the flowing fluid at an angle to the
primary flow direction which is different from 90.degree. or receive
ultrasonic waves. The core of the present invention is that at least
one guide element is situated in the fluid, diverting at least one
part of the flowing fluid, and that in the diversion, a velocity
component perpendicular to the primary flow direction is transferred
to at least one part of the flowing fluid.
[0012] The present invention may be applied to both linear systems
such as described, for example, in GB 2 101 318 A and reflection
systems such as presented in EP 0 477 418 A1. EP 0 477 418 A1 describes
how, for example, a reflection plate may be used as a guide vane
for flow harmonization. Nonetheless, the present invention goes
beyond this and uses at least one guide element, which is in particular
able to divert the flow in such a way that the flow is optimally
adapted to the protrusions described above which are caused by an
ultrasonic transducer let into the wall of a flow pipe.
[0013] The guide elements may be implemented in different ways.
Guide elements tilted in relation to the primary flow direction
of the fluid have proven to be advantageous in particular. The guide
elements, the tilted guide vanes in particular, may be situated
in the fluid in a lamellar pattern, for example.
[0014] Furthermore, instead of guide vanes, it is advantageously
possible to use displacers which, for example, locally narrow the
flow cross section of the flow pipe.
[0015] Furthermore, the described system may also be entirely or
partly integrated into an insertion sensor which may be used in
the flow pipe. In this connection, in particular, one or multiple
ultrasonic transducers as well as an electronic control unit may
be integrated into the insertion sensor for activating and/or reading
out at least one ultrasonic transducer. The electronic control unit
for reading out at least one ultrasonic transducer may, for example,
contain electronics for preprocessing received signals. Appropriate
electronic plug-and-socket connections may also be integrated for
contacting the insertion sensor. Furthermore, at least one reflection
element having a reflection surface may be integrated into the insertion
sensor, making it possible to implement, for example, one of the
reflection systems described above. Advantageously, the at least
one reflection element is inserted into the flow pipe in such a
way that fluid is able to flow on both sides of the reflection surface
along the reflection body. This has the advantage in particular
that if the reflection element is not in contact with the wall of
the flow pipe, water droplets that may be contained in the flow
are precipitated on the flow pipe as a wall film before flowing
through the insertion sensor, the wall film then being able to flow
through the flow pipe without wetting or contaminating the reflection
surface and thus interfering with the reflection.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 shows a schematic diagram of a system for ultrasonic
flow measuring.
[0017] FIG. 2A shows a system for ultrasonic flow measuring according
to the related art having two diametrically opposed ultrasonic transducers
without guide elements.
[0018] FIG. 2B shows a system for ultrasonic flow measuring having
two diametrically opposed ultrasonic transducers having two guide
vanes tilted against a primary flow direction of the fluid including
a depiction of the separation areas.
[0019] FIG. 3 shows a system for ultrasonic flow measuring having
two ultrasonic transducers, a reflection surface and a guide vane
tilted against the primary flow direction of the fluid.
[0020] FIG. 4 shows an embodiment alternative to FIG. 3 of a system
integrated into an insertion sensor having two guide vanes tilted
against the primary flow direction of the fluid.
[0021] FIG. 5 shows an embodiment alternative to FIG. 4 having
a plurality of guide vanes situated in a lamellar pattern and tilted
against the primary flow direction of the fluid.
[0022] FIG. 6A shows a side view of an embodiment alternative to
FIGS. 3 through 5 having complex guide elements.
[0023] FIG. 6B shows a sectional depiction of the system according
to FIG. 6A having a section plane perpendicular to the primary flow
direction of the fluid.
[0024] FIG. 6C shows a top view of a first embodiment of the complex
guide elements according to FIGS. 6A and 6B.
[0025] FIG. 6D shows a front view of the embodiment according to
FIG. 6C.
[0026] FIG. 6E shows a second embodiment of the complex guide elements
according to FIGS. 6A and 6B.
[0027] FIG. 6F shows a front view of the embodiment according to
FIG. 6E.
[0028] FIG. 6G shows a third embodiment of the complex guide elements
according to FIGS. 6A and 6B.
[0029] FIG. 6H shows a front view of the embodiment according to
FIG. 6G.
[0030] FIG. 7 shows a system for ultrasonic flow measuring having
two diametrically opposed ultrasonic transducers including a displacer.
DETAILED DESCRIPTION
[0031] Similarly to FIG. 1 FIG. 2A shows an additional system
having two diametrically opposed ultrasonic transducers 116 118
which, in a direction transverse to primary flow direction 210 (i.e.,
parallel to flow velocity 114 in FIG. 1), are capable of exchanging
ultrasonic waves at an angle to primary flow direction 210 which
is different from 90.degree.. As an example, FIG. 2A shows two flow
lines 212 of the fluid. The flow of the fluid in the tube is predominantly
free from separation areas.
[0032] The two ultrasonic transducers 116 118 send signals to
one another, the propagation times of which, as described above,
allow a calculation of flow velocity v.sub.FL 114.
[0033] As shown in FIG. 2A, separation areas 214 are formed in
the areas of the protrusions 122 upstrean of ultrasonic transducers
116 and 118 within which laminar flow no longer prevails, but a
turbulent flow prevails instead. One result of these turbulences
is that the simple equation (1) (see above) for calculating the
superimpositions of the velocities of ultrasonic wave v.sub.UL and
of flow velocity v.sub.FL of the fluid no longer produce meaningful
results because flow velocity v.sub.FL of the fluid is no longer
unambiguously defined in these separation areas 214 in particular.
Furthermore, significant pressure fluctuations within the fluid
occur in these separation areas 214 as a result of which propagation
velocity v.sub.UL of the ultrasonic waves in fluid 112 is able to
fluctuate strongly. On the whole, these separation areas 214 which
are localized immediately upstream from ultrasonic transducers 116
and 118 including the eddies formed there cause a severe worsening
of the signal-to-noise ratio and accordingly a reduction of measuring
precision. In addition, the width of these separation areas 214
may fluctuate strongly with the temperature of the flowing fluid.
Using the system shown in FIG. 2A, it is only possible with great
difficulty to obtain a drift-free and precise flow detection in
an intake system of an internal combustion engine for the purpose
of complying with stringent exhaust gas standards.
[0034] In contrast, a modification according to the present invention
of the measuring system of FIG. 2A is shown in FIG. 2B. In this
embodiment according to the present invention, two guide vanes 216
and 218 are used, each of which is tilted in relation to primary
flow direction 210 of the fluid and which diverts parts 220 and
222 of the flow of the fluid in the direction of ultrasonic transducers
116 and 118 respectively. This has the result that flow lines 212
in the vicinity of the wall of flow pipe 110 are more strongly adapted
to the wall shape and protrusions 122 upstream from ultrasonic transducers
116 and 118. As a result, the flow velocity of the fluid receives
a component V.sup.S.sub.FL 226 perpendicular to primary flow direction
210 of the fluid, in the direction of ultrasonic transducers 116
and 118. As a result, separation areas 214 are strongly reduced
in the area of protrusions 122 as can be seen in FIG. 2B. In this
exemplary embodiment, separation areas 214 basically no longer project
into wave area 224 which is necessary for an exchange of ultrasonic
waves between ultrasonic transducers 116 and 118. This strongly
improves the measuring precision of flow velocity 114. Such an improvement
of measuring precision is not obtainable using the rectifier screens
known from the related art, which are primarily elements parallel
to primary flow direction 210 for example, a reflector body (see,
for example, EP 0 477 418 A1), which is used only for homogenizing
the flow.
[0035] Guide vanes 216 and 218 cause eddy areas 228 and 230 respectively,
to be formed downstream of these elements, which lie in wave area
224 of ultrasonic transducers 116 and 118 it being possible for
pressure fluctuations to occur within the eddy areas. However, these
pressure fluctuations may be compensated by an integrative measuring
characteristic of ultrasonic transducers 116 and 118 or a corresponding
electronic control unit for reading out ultrasonic transducers 116
and 118. For that reason, eddy areas 228 and 230 in wave area 224
which are generated by guide vanes 216 and 218 do not result in
a reduction of measuring precision.
[0036] The tilt angle of guide vanes 216 and 218 relative to primary
flow direction 210 of the fluid were selected in such a way that
the flow (i.e., flow lines 212) is in fact diverted slightly in
the direction of ultrasonic transducers 116 and 118; however, it
still has a sufficiently large component in the direction of propagation
velocity v.sub.UL. The result of this compromise is that it is still
possible to implement the measuring system described above (which
is no longer usable at an angle .alpha.=90.degree. between flow
velocity v.sub.FL 114 and propagation velocity v.sub.UL 120) of
the ultrasonic waves.
[0037] As shown in FIG. 2B, guide vanes 216 and 218 are designed
as flat bodies having straight, parallel edges, which is adequate
for most applications. As an alternative, guide vanes 216 and 218
may be designed rounded or pointed or aerodynamically favorable
for a uniform flow guidance on the particular upstream or downstream
edges. Furthermore, guide vanes 216 and 218 may be designed to be
curved or arched for a more specific guidance of the fluid, it also
being possible, for example, to vary a material thickness of guide
vanes 216 and 218 over one length of guide vanes 216 and 218 for
example, similar to an airfoil of an airplane.
[0038] As an alternative to the embodiment of the present invention
shown in FIG. 2B having two diametrically opposed ultrasonic transducers
116 and 118 embodiments having reflection systems (see above) may
also be used according to the present invention. An example of such
an embodiment is shown in FIG. 3. Two ultrasonic transducers 116
and 118 are again used in this case; however, in this exemplary
embodiment, they are integrated on the same side and tilted with
respect to one another in one wall of a flow pipe 110. The tilting
of ultrasonic transducers 116 and 118 again produces a protrusion
122 in which it is possible for separation areas 214 (not shown)
to form. In this exemplary embodiment, a space 310 is situated between
ultrasonic transducers 116 and 118 through which fluid 112 does
not flow and which, for example, may be used for accommodating an
electronic connecting device (for example, a plug-and-socket connection)
and/or for placing an electronic control device for activating and/or
reading out at least one of ultrasonic transducers 116 118. For
example, it is possible for the signals generated by ultrasonic
transducers 116 and 118 to be preprocessed in this electronic control
unit. Complete processing of the signals is also possible.
[0039] Furthermore, the system in FIG. 3 has a reflection surface
312 on the wall of flow pipe 110 which is capable of reflecting
ultrasonic signals of ultrasonic transducers 116 118. For example,
the wall material of flow pipe 110 may have adequate reflection
properties for ultrasonic waves. In addition, however, the inside
wall of the flow pipe may also be provided with an additional coating
in the area of reflection surface 312. Ultrasonic waves emitted
by one of ultrasonic transducers 116 118 are reflected on reflection
surface 312 so that they may be received by the other ultrasonic
transducer 116 118. More complex reflection systems are also possible
in which, for example, it is possible for ultrasonic waves to reflect
multiple times on different reflection surfaces 312 before they
reach the other ultrasonic transducer 116 118. It is possible in
this manner to increase, for example, the propagation time differences
and accordingly the measuring precision.
[0040] A guide vane 314 is again provided in this exemplary embodiment
which deflects one part of the flow of fluid 112 toward ultrasonic
transducers 116 118 or toward protrusion 122. Again, the formation
of a separation area 214 (not shown here) upstream from ultrasonic
transducers 116 118 is prevented or reduced in the area of protrusion
122 and thus the signal quality and the measuring precision of
the ultrasonic flow measuring is considerably improved.
[0041] FIG. 4 shows an alternative embodiment to the system in
FIG. 3 in which two guide vanes 410 and 412 tilted against primary
flow direction 210 of fluid 112 flowing through a flow pipe 110
are used. In this example, guide vanes 410 and 412 are again designed
as elongated flat bodies having two long parallel, straight side
walls. Curved guide vanes could also be used as an alternative,
which adapt better to the desired flow. In this exemplary embodiment,
guide vane 410 takes over the task of providing a velocity component
226 to fluid 112 perpendicular to protrusion 122 as a result of
which the flow is better adapted to the wall shape of the system.
Second guide vane 412 is used to adapt the flow again to primary
flow direction 210 after flowing through ultrasonic flow meter 414.
[0042] Flow pipe 110 may have, for example, a rectangular or round
or oval cross section and, for example, be designed as a cylinder.
A reflection system is again used in this exemplary embodiment similarly
to FIG. 3. In this case, however, the components of ultrasonic flow
meter 414 are integrated into an insertion sensor 416. Insertion
sensor 416 includes both ultrasonic transducers 116 and 118 space
310 lying between them, which, corresponding to the exemplary embodiment
described in FIG. 3 for example, may be used for the integration
of an electronic connecting device and/or an electronic control
unit (as a result of which the electronic connecting device and
the electronic control unit become components of insertion sensor
416) as well as a reflection element 418 which is provided with
a reflection surface 312. Furthermore, insertion sensor 416 has
a mount 420 which connects the individual components and aligns
them with one another. In this exemplary embodiment, guide vanes
410 and 412 are also affixed by mount 420 of insertion sensor 416
and make up an integral component of insertion sensor 416.
[0043] Ultrasonic transducers 116 and 118 send ultrasonic waves
to one another across wave area 224 the ultrasonic waves which
are emitted by one of ultrasonic transducers 116 118 being reflected
on reflection surface 312 before each reaches the other ultrasonic
transducer 116 118. Reflection element 418 is situated in flow
pipe 110 in such a way that it is at a distance from a wall of flow
pipe 110 and fluid 112 is able to flow around it on both sides.
This distance between flow pipe 110 and reflection element 418 makes
it possible for water droplets or other contaminants which may be
contained in the flow to precipitate onto the wall of flow pipe
110 as wall film 422 before flowing through ultrasonic flow meter
414. This wall film 422 or the liquid contained in it may flow through
flow pipe 110 without wetting reflection surface 312 and interfering
with the reflection of the ultrasonic waves. In contrast to similar
devices described in the related art (which, however have no guide
vanes 410 412), the device described including insertion sensor
416 has considerable advantages with respect to susceptibility to
interference by liquids and contaminants.
[0044] Guide vanes 410 412 integrated into insertion sensor 416
cause separation area 424 426 to be strongly reduced in the area
of protrusion 122. This is shown symbolically in FIG. 4 by reference
numerals 424 and 426 424 denoting the separation area without the
use of guide vanes 410 412 while reference numeral 426 denotes
the separation area when guide vanes 410 and 412 are used. Interfering
signals caused by separation area 424 and 426 respectively, are
thus considerably reduced by using guide vanes 410 412. It is not
possible to achieve such a reduction through suitable flow guidance
using the guide vanes for flow harmonization known from the related
art alone, which have no adjustment angle in relation to primary
flow direction 210 i.e., in particular through shaping of the mounts
of a reflection plate.
[0045] Mount 420 of insertion sensor 416 may be designed in particular
in such a way that it offers as little flow resistance as possible
to the flow of fluid 112. To that end, mount 420 may in particular
be made up of a plurality of webs which are shaped so as to have
as little flow resistance as possible. Similarly, mount 420 may
be designed in such a way that reflection element 418 together with
reflection surface 312 and mount 420 form a dish-shaped unit. This
dish-shaped unit may, for example, also have a plurality of openings
via which fluid 112 outside of insertion sensor 416 is in connection
with fluid 112 within insertion sensor 416. Reflection element 418
may be designed to be flat or curved, for example, for bundling
of the ultrasonic waves.
[0046] A preferred exemplary embodiment of an ultrasonic flow meter
414 designed as an insertion sensor 416 as an alternative to FIG.
4 is shown in FIG. 5. Instead of the two guide vanes 410 and 412
however, a plurality of guide vanes 510 and 512 are situated in
a laminar pattern in this exemplary embodiment. Guide vanes 510
and 512 respectively, are again tilted in relation to primary flow
direction 210 of the fluid, the tilt angle being larger the closer
guide vanes 510 512 are placed to ultrasonic transducers 116 118
or to the side of the wall of flow pipe 110 on which ultrasonic
transducers 116 118 are situated. Guide vanes 510 512 are thus
approximately adapted to an idealized shape of flow lines 212 (not
shown in FIG. 5).
[0047] In this exemplary embodiment each of guide vanes 510 512
situated in a lamellar pattern is situated in a guide vane area
514 and 516 respectively, guide vane area 514 being indicated by
shading in FIG. 5. These guide vane areas 514 and 516 are designed
in this example in such a way that none of guide vanes 510 512
projects into wave area 224 which would thus make it possible for
them to interfere with the propagation of ultrasonic waves between
ultrasonic transducers 116 and 118. For this purpose, guide vanes
510 512 have not only different tilt angles relative to primary
flow direction 210 of fluid 112 but also have a length which increases
as the distance from ultrasonic transducers 116 and 118 increases.
Compared to the related art and compared to the exemplary embodiment
shown in FIG. 4 guide vanes 510 512 designed in this way make
it possible to obtain a flow which is more uniform, turbulence-free
and low in separation, strongly increasing the measuring precision
of the device.
[0048] Furthermore, reflection surface 312 in this exemplary embodiment
is, as described above, provided with a coating. In particular,
it is possible to use metallic or ceramic coatings that are good
reflectors of ultrasonic waves. The reflection surface is advantageously
designed to be flat and provided with a slight roughness. As described
above, however, other embodiments are also possible. In selecting
the reflection coating of reflection surface 312 it should be noted
in particular that the propagation rate of ultrasonic waves in the
medium of the reflection coating as well as the density of the reflection
coating should be as different as possible from the corresponding
material parameters in the flowing medium in order to optimize the
reflective effect. Furthermore, reflection angle .alpha. (see FIG.
1) should be selected as a function of the material used for the
reflection coating in such a way that as little of the sound energy
as possible is converted into Rayleigh waves (surface waves).
[0049] To compensate for the usually non-optimally bundled transmission
or receive characteristics of ultrasonic transducers 116 118 it
may be advantageous to provide reflection surface 312 as described
above, with a slight curvature. Furthermore, parts of mount 420
reflection surface 312 and guide vanes 510 512 or layers additionally
applied to these components may be made from materials whose surfaces
suppress a reflection of ultrasonic waves in order to avoid or suppress
interfering signal echoes.
[0050] Additional embodiments of an ultrasonic flow meter 414 are
shown in FIGS. 6A through 6H as alternatives to FIGS. 3 through
5. Again, two guide elements 610 and 612 are introduced into a flow
pipe 110 and tilted in relation to primary flow direction 210 of
fluid 112 the two guide elements 610 and 612 in turn being positioned
symmetrically to one another similarly to, for example, guide vanes
410 and 412 in FIG. 4. FIG. 6A shows a sectional depiction of ultrasonic
flow meter 414 having a section plane parallel to primary flow direction
210; FIG. 6B shows a sectional depiction having a section plane
perpendicular to primary flow direction 210. FIGS. 6C through 6H
show various embodiments of guide elements 610 and 612 both as
a top view (FIGS. 6C, 6E, 6G) and as a front view (FIGS. 6D, 6F,
6H). Guide elements 610 612 are designed in such a way that backflows
also flow through the flow pipe with as little formation of turbulence
at the ultrasonic transducers as possible. For the mechanical attachment
and stabilization of guide elements 610 612 mounting plates 614
616 618 may be placed parallel to the flow direction. These mounting
plates 614 616 618 have the additional effect of calming the flow
of fluid 112 through flow pipe 110 thus reducing turbulences.
[0051] Guide elements 610 612 may be designed differently, for
example, they may be adapted to flowing fluid 112. FIGS. 6C and
6D show an embodiment in which guide element 610 612 has a guide
plate 620 having hills and valleys in profile (e.g., a "zigzag
line") instead of a flat guide vane. Hills 622 and valleys
624 extend parallel to the particular flow lines at the location
of guide elements 610 612 thus producing "flow channels"
which additionally stabilize the flow of fluid 112 through flow
pipe 110 and prevent turbulences.
[0052] As an alternative, as shown in FIGS. 6E, 6F, 6G and 6H,
"turbulators" 626 628 may also be provided on one side
or on both sides of guide elements 610 612 it also being possible,
for example, to situate the turbulators on a flat guide plate 620.
As shown in FIGS. 6D and 6E, these turbulators 626 628 may be,
for example, situated at intervals and may be situated across primary
flow direction 210 for example, at the top and/or at the bottom
of guide elements 610 612. These turbulators 626 628 cause longitudinal
eddy areas to form directly on the surface of guide elements 610
612. The result of this effect is that separation areas (see, for
example, reference numeral 228 230 in FIG. 2B) which form in primary
flow direction 210 are strongly reduced downstream from guide elements
610 612. Overall, the formation of this longitudinal fluid bed
around guide elements 610 612 favors an essentially laminar flow
guide elements 610 612. The pressure fluctuations or eddy areas
in wave area 224 of the ultrasonic metering is thus reduced, resulting
in an improvement of the signal-to-noise ratio of the ultrasonic
flow metering, thus strongly improving the measuring precision of
the measurement of the flow velocity. Turbulators 626 628 have
a rectangular (see FIGS. 6E and 6F) or triangular (see FIGS. 6G
and 6H) or also a polygonal, rounded or lamellar design, for example.
[0053] FIG. 7 shows another alternative embodiment of an ultrasonic
flow meter 414 which, similarly, for example, to the embodiment
shown in FIG. 2A and FIG. 2B, has two diametrically opposed ultrasonic
transducers 116 118 which are capable of exchanging ultrasonic
signals at an oblique (see FIG. 1) angle .alpha. which is different
from 90.degree. to primary direction of flow 210 of a fluid flowing
through a flow pipe 110. Based on the positioning of ultrasonic
transducers 116 118 oblique to primary direction of flow 210 protrusions
122 are again formed upstream from ultrasonic transducers 116 118.
Within these protrusions 112 separation areas 214 are formed, within
which eddies and accordingly pressure and velocity fluctuations
occur (see above).
[0054] In this exemplary embodiment, ultrasonic transducers 116
118 each have a piezoceramic disc, which has a metallic coating
on both sides and which is embedded in a vibration-damping plastic
material. In the direction of flowing fluid 112 the piezoceramic
disc is surrounded by a material whose characteristic acoustic impedance
is adjusted to a value between the corresponding values for the
piezoceramic material and the flowing medium. A suitable selection
of thickness and geometric shaping of this material layer produces
a resonance amplification and optimized transmission and receive
characteristics of ultrasonic transducers 116 118. Using an additional
plastic material in relation to flow pipe 110 (or if integrated
into an insertion sensor 416 in relation to a mount 420 of insertion
sensor 416), the vibration damping system configuration described
above is affixed in flow pipe 110. Electrical leads connected to
a control and evaluation circuit are connected to the electrodes
of the piezoceramic discs. The control and evaluation circuit and
the electrical leads are not shown in FIG. 7. The unit made up of
the piezoceramic discs and damping and impedance matching materials
is denoted in FIG. 7 as ultrasonic transducer 116 or 118.
[0055] The exemplary embodiment shown in FIG. 7 eliminates the
problem of the formation of separation areas 214 using, among other
things, a displacer 710. This displacer 710 may, for example, be
held in the interior of flow pipe 110 using one or multiple (not
shown in FIG. 7) mounting plates 614 (see FIG. 6A, for example).
Multiple displacers 710 may also be used instead of one single displacer
710. Displacer 710 locally reduces the cross section of flow pipe
110. This displaces the flow of fluid 112 more strongly into protrusions
122 upstream of ultrasonic transducers 116 and 118. This strongly
reduces the size of separation areas 214 in these protrusions. After
the fluid has flowed around the displacer, the cross section of
flow pipe 110 is re-widened. As shown in FIG. 7 displacer 710 may
be designed, for example, to be asymmetric in order to take into
account the asymmetric configuration of ultrasonic transducers 116
118. Because protrusion 122 upstream from ultrasonic transducer
116 in primary flow direction 210 appears earlier than protrusion
122 upstream from ultrasonic transducer 118 flow lines 212 in the
upper area of flow pipe 110 must be deflected upwards in the direction
of ultrasonic transducer 116 earlier than flow lines 212 in the
lower area of flow pipe 110 which are diverted in the direction
of ultrasonic transducer 118. Accordingly, displacer 710 in narrowing
area 712 is shaped asymmetrically. Similarly, the opposite end of
displacer 710 placed in primary flow direction 210 in widening area
714 of the flow is also shaped asymmetrically so as not to project
into wave area 224 oriented obliquely to primary flow direction
210.
[0056] It is possible for turbulences 716 to occur in widening
area 714 of the flow, in which part 220 of the flow displaced by
displacer 710 toward ultrasonic transducer 116 and part 22 of the
flow displaced toward ultrasonic transducer 118 flow together again.
By analogy to the exemplary embodiment shown in FIG. 2B, these turbulences
716 are not, however, as detrimental to measuring the flow velocity
to the same degree as turbulences in the area of separation areas
214. This is in particular due to the fact that relatively wide
ultrasound beams are used, causing wave area 224 to be relatively
wide. As a result, an average is calculated over the velocity differences
of fluid 112 within these turbulences 716 across the width of wave
area 224. In contrast, the amplitude of the pressure fluctuations
locally on the surfaces of ultrasonic transducers 116 118 is sharply
reduced. Therefore, as a whole, the amplitude of the occurring signal
interference diminishes strongly.
[0057] Furthermore, an additional guide element embodied as guide
vane 718 is used in the exemplary embodiment shown in FIG. 7. As
shown in FIG. 7 this guide vane 718 has a curved shape which is
adapted to the shape of flow lines 212 of fluid 112 in this area.
Guide vane 718 is situated in primary flow direction 210 "downstream"
from displacer 710 in order to take into account the fact that protrusion
122 upstream from ultrasonic transducer 118 in the primary flow
direction is situated after protrusion 122 upstream of ultrasonic
transducer 116. As a result, in addition to the asymmetry of displacer
710 already described, the occurrence of turbulences is further
reduced upstream from ultrasonic transducer 118.
[0058] Furthermore, in the embodiment shown in FIG. 7 additional
turbulators 720 are affixed to displacer 710 in the narrowing area
as are further turbulators 722 on the upstream side of guide vane
718 in relation to primary flow direction 210. Similarly to the
exemplary embodiments in FIG. 6D and FIG. 6E, these turbulators
720 722 may, for example, be designed as comb-like toothed structures.
Similarly to the embodiment described in FIG. 6D and FIG. 6E, longitudinal
eddy areas then primarily form along displacer 710 or guide vane
718. These result in an increased pulse exchange and accordingly
reduce the subsequent separation areas, in particular turbulences
716 in widening area 714 downstream from displacer 710. This may
generally result in an improved laminar flow around displacer 710
or guide vane 718 and the flow is stabilized. Turbulences 716 within
wave area 224 of the ultrasonic waves are also reduced and the measuring
precision is improved accordingly.
[0059] In FIG. 7 displacer 710 is used in combination with a measuring
system in which ultrasonic transducers 116 118 are located on diametrically
opposed sides of flow pipe 110.
[0060] Similarly, it is possible, however, to use displacers 710
in multiple ways in flow pipe 110 as well as for reflection systems
similarly to FIG. 3 for example. |