Abstrict A cylindrical vortex generator of a Karman shedding flow meter
is set in an inlet tube of an air cleaner of a combustion engine.
An air flow uniforming device such as a wire netting is disposed
in the inlet tube at a position upstream of the vortex generator
for producing in the inlet tube a turbulent but considerably uniformed
air flow directed toward the vortex generator. A bypass means is
arranged in the inlet tube to make a bypass flow of air directed
toward the vortex generator when the combustion engine is under
high speed operation.
Claims What is claimed is:
1. An air induction apparatus for feeding a combustion engine with
air which is metered by using a Karman vortex shedding flow meter
to control as a result of this meterage the amount of fuel fed to
the engine, comprising:
an inlet tube of an air cleaner which is arranged upstream of the
engine proper;
a cylindrical vortex generator of said flow meter, said generator
being disposed in said inlet tube in a manner to be perpendicular
to the longitudinal axis of said inlet tube;
a first wire netting disposed in said inlet tube at a position
upstream of said vortex generator in a manner to be perpendicular
to the longitudinal axis of said inlet tube;
a second wire netting disposed in said inlet tube at a position
upstream of said first wire netting in a manner to be perpendicular
to the longitudinal axis of said inlet tube, said second wire netting
producing a turbulent but uniformed air flow directed toward said
vortex generator upon flowing of the air in said inlet tube;
means for defining an opening in said inlet tube at a position
upstream of said first wire netting;
a damper door swingably connected to said inlet tube to selectively
open and close said opening; and
damper door operator for operating said damper door in such a manner
that under low speed operation of the engine, the damper door closes
said opening, and under high speed operation of the engine, the
damper door opens said opening.
2. An air induction apparatus as claimed in claim 1 in which said
auxiliary opening is located downstream of said flow uniforming
device but upstream of said generator.
3. An air induction apparatus as claimed in Claim 1 in which said
damper door operator comprises:
an arm secured to said damper door to move therewith;
a lost motion linkage connecting said arm to an actuator of an
actuator in such a manner that when an operation of said actuator
exceeds a predetermined value, the arm is moved allowing said damper
door to open and
a spring arranged to bias said arm in a direction to allow said
damper door to close said auxiliary opening.
4. An air induction apparatus as claimed in claim 1 in which said
damper door operator comprises:
an arm secured to said damper door to move therewith;
an electromagnet mounted to said tube for attracting said arm in
a direction to allow said damper door to open when electrically
energized; and
a spring disposed between said electromagnet and said arm to bias
said arm in another direction to allow said damper door to close
said auxiliary opening.
5. An air induction apparatus as claimed in claim 4 in which said
electromagnet is energized when said Karman vortex shedding flow
meter senses a condition wherein the flow rate of air passing through
said tube exceeds a predetermined level.
6. An air induction apparatus as claimed in claim 1 in which said
second wire netting has a mesh size finer than that of said first
wire netting.
7. An air induction apparatus as claimed in claim 1 in which said
auxiliary opening is located just below said air flow uniforming
device leaving an enlarged section of said tube at a position upstream
of said vortex generator.
8. An air induction apparatus as claimed in claim 7 in which an
inner wall surface of said enlarged section which faces said auxiliary
opening is smoothly curved so as to smoothly guide the air passing
therethrough.
9. An air induction apparatus as claimed in Claim 7 further comprising
a partition wall which is disposed in said enlarged section to divide
the same into first and second sections, said first section being
a section through which the air passing through said air uniforming
device passes, said second section being a section through which
the air passing through said auxiliary opening passes.
10. An air induction apparatus having a tube through which air
to be metered by a Karman vortex shedding flow meter passes, said
air induction apparatus comprising:
a vortex generator of said flowmeter, said generator being disposed
in said tube for generating vortexes in the air flow;
an air flow uniforming device disposed in said tube upstream of
said vortex generator for producing in the tube a turbulent but
uniformed flow of air directed toward said vortex generator; and
bypass means for making a bypass flow of air directed toward said
vortex generator when increase in air flow rate in the tube is required,
said bypass means comprising means defining an opening in said tube
at a position upstream of said vortex generator, a damper door hingedly
mounted to said tube so as to selectively open and close said opening,
and damper door operator for operating said damper door in a manner
that when an increased flow rate of air in the tube is required,
said damper door opens, and when a decreased flow rate of air in
tube is required, said damper door closes, said opening being located
just below said air flow uniforming device leaving an enlarged section
of said tube at a position upstream of said vortex generator.
11. An air induction apparatus as claimed in claim 10 in which
an inner wall surface of said enlarged section which faces said
opening of said means is smoothly curved so as to smoothly guide
the air passing therethrough.
12. An air induction apparatus as claimed in claim 10 further
comprising a partition wall which is disposed in said enlarged section
to divide the same into first and second sections, said first section
being a section through which the air coming from said air uniforming
device passes, said second section being a section through which
the air coming from said opening passes.
Description FIELD OF THE INVENTION
The present invention relates in general to an air induction apparatus
for a combustion engine, and more particularly to such an air induction
apparatus cooperating with a Karman vortex shedding flow meter.
BACKGROUND OF THE INVENTION
It is known to those skilled in the art that, under certain condition,
a "Karman vortex street" is shed in the wake of bluff
cylindrical bodies when a flow of air is perpendicular to the generators
of the cylinder. The shedding of vortices occurs periodically first
from one side of the body and then from the other in accordance
with the velocity of the air flow. Thus, by counting the number
of the vortices created by the body in a unit time, the flow rate
of the fluid can be measured. One of the vortex shedding flow meters
to which the above mentioned theory is practically applied is schematically
shown in FIG. 1 which is attached herewith. The flow meter shown
generally comprises a vortex shedding body 10 in the form of cylinder
with a diametrically extending through hole 12 a sensing means
14 such as electrically heated platinum plate or wire disposed in
the moddile of the through hole 12 and a control circuit 16. In
operation, the sensing means 14 produces signal representing the
numbers of vortices produced in the wake of the body 10 under flowing
of the air in the direction of the arrow A. The control circuit
16 evaluates practically the amount of air by computing the signals
issued from the sensing means 14 for controlling as a result of
this evaluation utilization circuit.
In some of the modern combustion engine driven vehicles, the vortex
shedding flow meter of the type mentioned above is used for measuring
the amount of air entering the engine to control as a result of
this measurement the amount of fuel metered to the engine. The vortex
shedding body 10 of the meter is usually set in an inlet tube of
an air cleaner of the engine. However, if the inlet tube is not
sufficiently long, air flow rate distribution is irregularly changed
inevitably as will be understood from FIG. 2 so that the flow rate
of the air which flows in the vicinity of the vortex shedding body
10 is frequently changed. Furthermore, when the air flow rate is
small and/or the flowing air forms laminar flow in the inlet tube,
there appears a considerable difference in air flow rate between
a portion near the inner surface of the inlet tube and near the
center of the tube. These will cause that accurate air flow measurement
is not made by the Karman vortex shedding flow meter.
One of measures for solving the above mentioned problem is to provide
the inlet tube with an air flow uniforming device such as a wire
netting at a position upstream of the vortex shedding body 10. With
this device, a turbulent but considerably uniformed air flow is
produced upon flowing of the air in the inlet tube. Experiments
have revealed that the presence of the air flow uniforming device
permits accurate measurement of the flow meter especially when the
flow rate is low.
Thus, such induction apparatus as just mentioned can perform accurate
control of air-fuel ratio of the air-fuel mixture when the engine
is under low speed operation, such as, under idling condition. However,
when a high speed operation of the engine where a big volume of
air is necessary is required, the presence of the flow uniforming
member causes a trouble in that a considerable resistance of air
flow is produced causing drop of output power of the engine.
SUMMARY OF THE INVENTION
Accordingly, an essential object of the present invention is to
provide an air induction apparatus of a combustion engine which
is free from the above mentioned problem.
It is an object of the present invention to provide an air induction
apparatus by which accurate measurement of air flow rate is achieved
when the flow rate is relatively low and by which smooth feeding
of air into the engine is achieved when big volume of air is required
by the engine.
According to the present invention, there is provided an air induction
apparatus having a tube through which air to be metered by a Karman
vortex shedding flow meter passes, the air induction apparatus comprising:
a vortex generator of the flow meter disposed in the tube for generating
vortices in the air flow; an air flow uniforming member disposed
in the tube upstream of the vortex generator for producing in the
tube a turbulent but uniformed flow of air directed toward the vortex
generator; and bypass means for making a bypass flow of air directed
toward the vortex generator when air the amount of which exceeds
a predetermined level is required to pass through the tube.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of the present invention will become
clear from the following description when taken in conjunction with
the accompanying drawings, in which:
FIG. 1 is a diagrammatical view for explaining the principle of
operation of the "Karman vortex shedding flow meter" used
for measurement of flow rate of air;
FIG. 2 is a schematical view for explaining the frequent change
of air flow rate distribution which appears in an inlet tube of
an air cleaner when no air flow uniforming device is arranged in
the inlet tube;
FIG. 3 is a schematical perspective view of an air induction apparatus
for explaining the principle of the invention;
FIGS. 4 5 and 6 are sectional views of first, second and third
embodiments of the air induction apparatus of the present invention;
FIG. 7 is a schematical perspective view of fourth embodiment of
the air induction apparatus of the invention;
FIG. 8 is a sectional view taken on the line VIII--VIII of FIG.
7;
FIG. 9 is a sectional view of a fifth embodiment of the air induction
apparatus of the invention;
FIG. 10 is a graph showing reduction of air flow resistance upon
high power requirement of the combustion engine, which is achieved
by the air induction apparatus of the invention; and
FIGS. 11A and 11B are sketches of waveforms explaining the results
of vortex shedding flow meters which cooperate with the air induction
apparatus of the invention and with a conventional air induction
apparatus, respectively.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIG. 3 there is schematically illustrated an air
induction apparatus of the present invention, as being generally
designated by numeral 10. The apparatus 10 shown comprises an air
cleaner casing 13 in which a filter element (not shown) is disposed.
Although not shown in the drawings, the air cleaner casing 13 is
directly or indirectly connected to fuel supply means mounted on
a combustion engine proper. An inlet tube or snorkel tube 14 is
fixed to the air cleaner casing 13 in a conventional manner so that
the ambient air is introduced into the tube 14 in the direction
of arrows A, upon operation of the engine. Although the inlet tube
14 now shown has a form of rectangular prism, there is no limitation
in form of the inlet tube of the invention. Denoted by numeral 16
is a vortex shedding body which has substantially the same form
as the body 10 of FIG. 1 mentioned before. As shown, the body 16
is disposed in the inlet tube 14 in a manner to be perpendicular
to the flow of air passing through the tube 14. A first net member
or wire netting 18 having a mesh size less than 40 mesh (ASTM) is
disposed in the inlet tube 14 at a position upstream of the vortex
shedding body 16. Preferably, the net member 18 is arranged to be
perpendicular to the air flow in the tube 14. A second net member
or wire netting 20 is disposed in the most upstream portion of the
inlet tube 14 preferably, in a manner to be perpendicular to the
air flow in the tube 14. The second net member 20 has a mesh size
finer than that of the first net member 18 for example greater
than 40 mesh (ASTM).
The inlet tube 14 is formed with an opening 22 between the first
and second net members 18 and 20 preferably near the second net
member 20 as shown. A damper door 24 is hingedly mounted to the
tube 14 so as to be swingable toward the interior of the inlet 14.
The damper door 24 has size to seal the opening 22. As will be understood
from the description which follows, a damper door operator cooperates
with the damper door 24 in such a manner that when the amount of
air flow is relatively small, the damper door 24 closes the opening
22 and when the amount of air exceeds a predetermined level, the
damper door 24 opens the opening 22. Thus, when the combustion engine
is under low speed operation, such as under idling condition, to
necessitate a small amount of air, all the air to be fed into the
engine passes the second net member 20. Under this, uniformed air
flow is produced in the inlet tube 14 so that accurate measurement
by the vortex shedding flow meter is achieved. While, when the engine
is under high speed operation necessitating a big volume of air,
a bypass passage for the air fed into the engine is provided by
the damper door 24 with a result that the air feeding to the engine
is smoothly made without affecting the output power of the engine.
Furthermore, under such big volume flow, it is recognized that "Karman
vortex sheet" is intensely shed minimizing the error of measurement
made by the flow meter. The first net member 18 is used for trapping
dust particles suspended in the air passing through the bypass opening
22.
A first example of the damper door operator is shown in FIG. 4
as denoted by numeral 26a. The operator 26a comprises a spring 28
which is arranged to urge the damper door 24 in a direction to close
the opening 22. Thus, when a magnitude of vacuum force in the inlet
tube due to air flowing in the same exceeds the biasing force of
the spring 28 the damper door 24 opens the opening 22 for the bypass
feeding of the air.
A second example of the damper door operator is shown in FIG. 5
as denoted by numeral 26b. The operator 26b comprises an electromagnet
30 supported on the inlet tube through a bracket 32 a spring 34
disposed about the electromagnet 30 and an arm 36 secured to the
hinged portion of the damper door 24. Lead wires of the magnet 30
are connected to the vortex shedding flow meter. When the flow meter
senses a condition in which big volume flow of air in the inlet
tube 14 is required, it issues a signal to energize the electromagnetic
30 to attract the arm 36 against the biasing force of the spring
34 to open the opening 22.
A third example of the damper door operator is shown in FIG. 6
as designated by numeral 26c. The operator 26c comprises a lost-motion
linkage 38 connecting an arm secured to the shaft 42 of the throttle
valve 44 to the arm 36 and a spring 46 arranged to urge the damper
door 24 in a direction to close the opening 22. When the throttle
valve 44 rotates in a direction of the arrow F and exceeds a predetermined
open position for high output power of the engine, the lost-motion
linkage 38 pulls the arm 36 rightwardly in this drawing moving the
damper door 24 in the opening direction of arrow B.
Referring to FIGS. 7 and 8 there is schematically illustrated
another type air induction apparatus according to the invention,
as generally designated by numeral 10'. For facilitation of drawing
and description, substantially same parts will be designated by
the same numerals as in the case of FIG. 3 the detailed explanation
of which will be omitted from the following. In this embodiment,
a slight change is made at the upstream portion of the inlet tube
14 of FIG. 3. As best seen from FIG. 8 the upstream portion of
the inlet tube 14 is formed enlarged, leaving a smoothly curved
inner wall surface 48 therein. A partition plate 50 is set in the
upstream portion to divide the same into first and second sections
52 and 54. The plate 50 lies parallel with the longitudinal axis
of the inlet tube 14. The second net member 20 is set in the upstream
portion of the first section 52 and the damper door 24 is swingably
set in the upstream portion of the second section 54. Any of the
damper door operators (first, second and third examples shown in
FIGS. 4 5 and 6) can be used for operation of the damper door 24.
With this arrangement, smooth feeding of big volume of air to the
engine is achieved even when the engine is under high speed operation.
A modification of the air induction apparatus of FIGS. 7 and 8
is shown in FIG. 9 as designated by numeral 10". In this modification,
a flat but inclined surface 56 is formed instead of the smoothly
curved inner wall surface 48 of FIGS. 7 and 8 and the damper door
24 is set at the downstream end of the partition plate 50. Furthermore,
the partition plate 59 has a wedge-shaped cross section, as shown,
to assure a reliable mixing of air in the first and second sections
52 and 54.
FIG. 10 is a graph showing the relationship between the amount
of air passing through the inlet tube 14 and the air flow resistance
appearing in the inlet tube 14 which is achieved by the air induction
apparatus of the invention. For comparison, a conventional case
without the above-mentioned air bypass means is carried on the graph
with being represented by a broken line. As will be understood from
this graph, the air induction apparatus of the invention shows a
considerable reduction of air flow resistance at a higher range
of the air flow amount.
FIGS. 11A and 11B show respective waveforms explaining the results
of vortex shedding flow meters which are cooperated with the air
induction apparatus of the invention and the conventional induction
apparatus which has no air flow uniforming device, under a condition
where a relatively small amount of air passes through the inlet
tube. As will be well understood from these graphs, the vortex shedding
flow meter cooperating with the air induction apparatus of the invention
produces quite stable waveforms.
Although in the previous description, it is explained that the
vortex shedding body 16 is located in the inlet tube 14 of the air
cleaner casing 13 it is also possible to locate such body in a
connecting tube (not shown) located between the air cleaner casing
and the fuel supply means of the combustion engine. In this case,
the air flow uniforming device such as the first wire netting 18
should be also located in the connecting tube upstream of the vortex
shedding body 16 but the second wire netting 20 is no more necessary.
From the foregoing description, it will be appreciated that according
to the air induction apparatus of the invention, accurate measurement
of air flow rate is achieved when the flow is relatively low and
smooth feeding of air into the combustion engine is made when the
engine is under high speed operation. |