Abstrict The present invention whose object is to provide a hot wire type
of flow meter capable of accurately detecting a flow rate under
various conditions required for satisfying a desire for low fuel
consumption of an engine system and space saving in an engine room,
the present invention being characterized in a hot wire type of
air flow meter including a main flow passage forming an air intake
flow passage of an internal combustion engine, a hot wire element
measuring intake air, and a bypass having the hot wire element therein
and disposed in the main flow passage, the hot wire type of air
flow meter comprising: a flow passage forming the bypass, and formed
in the axial direction of the main flow passage; and a flow passage
forming the bypass and formed in the radial direction of the main
flow passage, the flow passage having a structure designed in such
a manner that the upper stream portion of an outlet portion thereof
projects over the lower stream portion of the same.
Claims What is claimed is:
1. A hot wire type of air flow meter, comprising: a main flow passage
forming part of an air intake flow passage of an internal combustion
engine, a hot wire element for measuring intake air, and a bypass
passage having said hot wire element therein and disposed in said
main flow passage, said bypass passage including:
(a) a first flow passage forming one part of said bypass passage
and extending in the axial direction of said main flow passage;
and
(b) a second flow passage forming another part of said bypass passage
and extending in the radial direction of said main flow passage,
said second flow passage having an outlet opening formed in an end
portion thereof, said end portion having a windscreen projection
extending, with respect to the air flow in said main passage, radially
beyond the outlet opening on the upper stream side of said end portion
so as to shield said outlet opening from air flow in said main flow
passage and prevent the air flow in said main flow passage from
directly impacting on air flowing out of said bypass passage at
said outlet opening.
2. A hot wire type of air flow meter according to claim 1 wherein
said hot wire element is disposed in said first flow passage of
said bypass passage.
3. A hot wire type of air flow meter according to claim 1 wherein
said first flow passage is provided eccentrically with respect to
the axis of said main flow passage.
4. A hot wire type of air flow meter according to claim 1 wherein
a throttle for contracting the width of the flow entering said bypass
passage is provided at the inlet portion of said bypass passage.
5. A hot wire type of air flow meter according to claim 1 wherein
a member forming said main flow passage and a member forming said
first and second bypass passages are formed integral with each other.
6. A hot wire type of air flow meter, comprising: a main flow passage
forming part of an air intake flow passage of an internal combustion
engine, a hot wire element for measuring intake air, and a bypass
passage having said hot wire element therein and disposed in said
main flow passage, said bypass passage including:
(a) a first flow passage acting as an air flow line in the same
direction as the air flow line of air passing through said main
flow passage; and
(b) a second flow passage acting as an air flow line extending
across said air flow line of said main flow passage, said second
flow passage having an outlet opening formed in an end portion thereof,
said end portion having a windscreen projection extending, with
respect to the air flow in said main passage, beyond the outlet
opening on the upper stream side of said end portion so as to shield
said outlet opening from air flow in said main flow passage and
prevent the air flow in said main flow passage from directly impacting
on air flowing out of said bypass passage at said outlet opening.
7. A hot wire type of air flow meter according to claim 6 wherein
said hot wire element is disposed in said flow line of said first
flow passage.
8. A hot wire type of air flow meter according to claim 6 wherein
said first flow passage is disposed eccentrically with respect to
the axis of said main flow passage.
9. A how wire type of air flow meter, comprising: a main flow passage
forming part of an air intake flow passage of an internal combustion
engine, a hot wire element for measuring intake air, and a bypass
passage having said hot wire element therein and disposed in said
main flow passage, said bypass passage including:
(a) a first flow line forming one part of said bypass passage and
extending in the axial direction of said main flow passage; and
(b) a second flow line forming another part of said bypass passage
and extending rat an angle to the direction of said main flow passage,
this second flow line having a windscreen projecting member extending
in the direction of said second flow line beyond an outlet opening
of said bypass passage for preventing direct impingement of the
main stream of air in said main flow passage against air exiting
said outlet opening, thereby shielding said outlet opening from
air flow in said main flow passage.
10. A hot wire type of air flow meter for an internal combustion
engine, comprising:
a main flow passage forming an air intake flow passage;
a bypass passage disposed at least partly within said main flow
passage for diverting a portion of the air flowing in said main
flow passage; and
a hot wire element disposed in said bypass passage for measuring
intake air;
wherein said bypass is formed by a first flow passage extending
in the axial direction o said main flow passage, and a second flow
passage extending at an angle to the axis of said main flow passage
from the downstream end of said first flow passage and having an
outlet portion with an outlet opening from which air passes from
said bypass passage into said main flow passage; and
wherein said second flow passage of said bypass passage is formed
with a windscreen projecting portion extending in the direction
of said second flow passage beyond said outlet opening on the side
of said second flow passage which is upstream with respect to the
air flow in said main flow passage, so that said projecting portion
shields air exiting said outlet opening from direct impingement
by the air flow in said main flow passage.
11. A hot wire type air flow meter according to claim 10 wherein
said first flow passage extends perpendicular to said second flow
passage so that said bypass passage is L-shaped.
12. A hot wire type air flow meter according to claim 10 wherein
said main flow passage and said bypass passage are formed in an
integral structure.
13. A hot wire type air flow meter according to claim 10 wherein
said bypass passage is disposed entirely within said main flow passage.
14. A hot wire type air flow meter according to claim 13 wherein
said second flow passage extends in the circumferential direction
of said main flow passage.
15. A hot wire type air flow meter according to claim 10 wherein
said hot wire element is disposed in said first flow passage.
16. A hot wire type air flow meter according to claim 10 wherein
said first flow passage is disposed eccentrically with respect to
the axis of said main flow passage.
17. A hot wire type air flow meter according to claim 10 wherein
said first flow passage is concentric with the axis of said main
flow passage.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hot wire type of air flow meter, and
more particularly to a hot wire type of air flow meter as used in
an air intake system of an automobile for detecting and controlling
the quantity of intake air.
2. Background of the Invention
Hitherto, as disclosed in Japanese Patent Unexamined Publication
No. 50-50520 Japanese Patent Unexamined Publication No. 50-146369
and Japanese Patent Unexamined Publication No. 55-69021 there is
a hot wire type of air flow meter for an internal combustion engine
so constituted that a straight-shaped bypass (branch pipe) is disposed
in the central portion of a main pipe and hot wire elements are
disposed therein. However, in the structure disclosed in Japanese
Patent Unexamined Publication No. 50-50520 such hot-wire element
is not protected from reverse heat due to backfire caused from incorrect
engine ignition timing. To this end, a structure for protecting
the hot wire element against backfire has been disclosed, for example,
in Japanese Patent Unexamined Publication No. 55-69021. However,
a hot wire element generally has characteristics such that the output
therefrom is reduced although the average flow velocity increases
in a case where the same is disposed in a flow having a large pulsation
due to the nonlinear heat transfer coefficient thereof. Therefore,
any of the above-described structure cannot correctly detect the
flow rate of a pulsation flow.
As disclosed in Japanese Utility Model Unexamined Publication No.
56-135127 in a bypass in which a hot wire element is disposed in
the main pipe, in order to perform protection against the above-described
backfire or correctly detect the flow rate of the pulsation flow,
the fluid resistance at the bypass in the lower stream to the hot
wire element is enlarged, additionally, the outlet and inlet ports
of the bypass are formed in parallel or substantially in parallel
to the main stream. That is, the dynamic pressure acting at the
outlet and inlet ports of the bypass is reduced even if a reverse
flow is generated and the flow reaching the hot wire element also
is damped so that backfire resistance is improved. Since the outlet
port of the bypass opens directly and substantially in parallel
to the main stream, the flow in the bypass is slightly changed due
to the static pressure change caused from mixture of flows at this
portion. It leads to generation of noise in the output from the
hot wire element. Although high frequency noise can be reduced by
a filter disposed in the circuit, the abovedescribed type of noise
causes a system control problem when, for example, the engine is
operated at a low speed. Furthermore, from the viewpoint of hardware,
the structure produces production (cost and weight) and reliability
(the number of parts) problems since the axial length is too long
and the component parts for the bypass are difficult to mount.
On the other hand, structures have been disclosed, for example,
in Japanese Patent Unexamined Publication No. 56-76012 in which
a bypass in which a hot wire element is disposed is formed outside
the main stream in order to prevent the above-described type of
backfire and stabilize the outputs.
However, problems arise in these structures, as pointed out in
Japanese Patent Unexamined Publication No. 56-76012 that flow rate
detection error in large due to the thermal conditions, such as
thermal conduction from the engine, heating of the hot wire element,
and in the case of an automobile, engine heat and rise in temperature
in the engine compartment due to solar radiation. That is, since
the bypass portion provided with the hot wire element has a large
thermal capacity and is formed with a relatively tight width in
the inner portion of a body wall, there is not a large area for
conducting the heat of the intake air. Furthermore, the bypass is
formed to perform a good thermal conduction of the air flow passing
therein. Therefore, the temperature of the air flow in the bypass
is affected by the temperature of the passage wall of the bypass,
causing a large temperature difference from that of the main flow.
It leads to enlargement of the error in measurement of the intake
air flow rate.
Some of the disclosures relate to a structure which cannot withstand
strong engine backfire and are incapable of correctly detecting
the average flow rate of the pulsation flow, so that such devices
cannot be put to practical use. Some of them are incapable of correctly
measuring the flow rate under certain thermal conditions and are
also incapable of being sufficiently controlled to have the engine
operated at the most suitable air-fuel ratio due to increase in
the noise in the output. Therefore, it interrupts cleaning of the
exhaust gas from the engine, improvement in fuel consumption and
operability. On the other hand, some of them are insufficient in
reduction of the axial length of the main flow meter body, that
is, they are insufficient in reduction of the length of the intake
pipe, weight of the body and manufacturing cost. Therefore, problems
arise that the pressure loss in the intake pipe increases, and the
weight of the system including the engine becomes heavier, preventing
improvement in engine fuel consumption and reduction of the engine
room space.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a hot wire type
of flow meter capable of correctly detecting flow rate under a variety
of conditions needed for achieving low fuel consumption of the engine
system and small space in the engine compartment.
Another object of the present invention is to provide an internal
combustion engine capable of controlling the most suitable air-fuel
ratio by using the above-described type of hot wire type of air
flow meter.
In order to achieve the above-described objects, a hot wire type
of flow meter according to the present invention includes a main
flow passage forming an air intake flow passage of an internal combustion
engine, a hot wire element measuring intake air, and a bypass having
the hot wire element therein and disposed in the main flow passage.
Such a flow meter comprises: a flow passage forming the bypass and
formed in the axial direction of the main flow passage; and a flow
passage forming the bypass and formed in the radial direction of
the main flow passage, the flow passage having the structure designed
in such a manner that the upper stream portion of an outlet portion
thereof projects over the lower stream portion of the same.
An internal combustion engine according to the present invention
comprises: the above-described hot wire type of air flow meter;
a speed sensor for detecting the engine speed; a fuel injection
device for injecting fuel into the intake air; and a control device,
responsive to a quantity of intake air detected by the hot wire
type of air flow meter and the engine speed detected by the speed
sensor, for obtaining a corresponding amount of fuel to be injected,
and outputting an instruction to inject fuel by the thus-obtained
quantity to the fuel injection device.
As a result of the features as described above, since the area
serving for heat exchange between the bypass wall and the main stream
can be widened, the temperature of the bypass wall can be always
maintained to the level approximate to the intake air temperature
so that temperature characteristics can be improved.
Furthermore, since the bypass is formed perpendicular to the lower
stream of the hot wire element and having an outlet port surface
thereof formed in parallel to the main stream, the direct effect
of the dynamic pressure of the reversed flow on the outlet port,
and as well its flow velocity in the flow passage can be damped.
That is, introducing the force of the reversed flow due to backfire
or blowback into the bypass can be reduced, and the introduced flow
can be damped in the flow passage for the purpose of protecting
the hot wire element against damage. The rectifying elements of
the flow meter, such as a throttle portion of the inlet port of
the bypass, a mesh and a throttle portion of the inlet port of the
bypass (bell mouth shape) can reduce the disorder from the upper
stream of the flow meter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view illustrating an internal combustion
engine employing a hot wire type of air flow meter according to
the present invention;
FIG. 2 is a cross-sectional view illustrating a hot wire type of
air flow meter according to a first embodiment of the present invention;
FIG. 3 is a cross-sectional view taken along the line III--III
in FIG. 2.
FIG. 4 is a view taken along the line IV--IV in FIG. 2;
FIG. 5 is a cross-sectional view taken along the line V--V in FIG.
2;
FIG. 6 is a vertical cross-sectional view illustrating a second
embodiment of the present invention;
FIG. 7 is a cross-sectional view taken along the line VII--VII
in FIG. 6;
FIG. 8 is a vertical cross-sectional view illustrating a third
embodiment of the present invention;
FIG. 9 is a cross-sectional view taken along the line IX--IX in
FIG. 8;
FIG. 10 illustrates a fourth embodiment of the present invention;
FIG. 11 is a vertical cross-sectional view illustrating a fifth
embodiment of the present invention;
FIG. 12 is a cross-sectional view taken along the line XII--XII
in FIG. 11;
FIG. 13 is a vertical cross sectional view illustrating a sixth
embodiment of the present invention;
FIG. 14 is a cross-sectional view taken along the line XIV--XIV
in FIG. 13;
FIG. 15 is a vertical cross-sectional view illustrating a seventh
embodiment of the present invention;
FIG. 16 is a vertical cross-sectional view illustrating an eighth
embodiment of the present invention;
FIG. 17 is a vertical cross-sectional view illustrating a ninth
embodiment of the present invention;
FIG. 18 is a vertical cross-sectional view illustrating a tenth
embodiment of the present invention;
FIG. 19 is a vertical cross-sectional view taken along the line
XIX--XIX in FIG. 18;
FIGS. 20 21 and 22 illustrate an eleventh embodiment of the present
invention;
FIG. 23 is a vertical cross-sectional view illustrating a twelfth
embodiment of the present invention;
FIG. 24 is a cross-sectional view taken along the line XXIV--XXIV
in FIG. 23;
FIG. 25 is a vertical cross-sectional view illustrating a thirteenth
embodiment of the present invention;
FIG. 26 is a cross-sectional view taken along the line XXVI--XXVI
in FIG. 25;
FIG. 27 is a cross-sectional view taken along the line XXVII--XXVII
in FIG. 25;
FIG. 28 is a cross-sectional view illustrating a fourteenth embodiment
of the present invention;
FIG. 29 is a cross-sectional view taken along the line XXIX--XXIX
in FIG. 28;
FIG. 30 is a view taken along the line XXIX--XXIX in FIG. 29 in
which a state where an lattice body according to another embodiment
is employed in the state shown in FIG. 29;
FIGS. 31 and 32 illustrate the structure of a model with which
effect of the wind shield wall against noise is experimented; and
FIG. 33 illustrates the result of the experiment.
DESCRIPTION OF PREFERRED EMBODIMENTS
Embodiments of the present invention will now be described with
reference to the drawings.
FIG. 1 illustrates an embodiment of a system of an internal combustion
engine equipped with an electronic fuel injection device to which
an hot wire type of air flow meter for an internal combustion engine
according to the present invention is applied.
Air is taken in through an air filter 503 and is supplied to an
internal combustion engine (cylinder) 500 after it has passed through
a connecting pipe 504 a flow meter 1 and an air intake manifold
501. A bypass 12 projecting to a main passage 11 is formed in the
flow meter 1. A hot wire element 2a and a temperature compensation
element 2b formed integral with a detecting circuit 2 are provided
within the bypass 12 for the purpose of obtaining an output corresponding
to the total quantity of intake air by detecting air flow velocity
at this portion. A throttle valve 3 for controlling a quantity of
intake air is provided within the passage of the flow meter 1 this
throttle valve 3 being designed to act in synchronization with the
accelerator pedal of an automobile. The flow meter 1 is further
provided with an idle-speed control (ISC) valve 8 for controlling
a flow rate when the throttle valve 3 is completely closed (idling).
On the other hand, fuel introduced from a fuel chamber 505 by a
pump 506 is injected into an air intake manifold 501 by an injector
507 so that the fuel is supplied to the engine 500 together with
the air.
The control unit 510 receives an output signal from the hot wire
circuit 2 a signal representing the rotational angular degree of
the throttle valve 3 an output signal from an oxygen density sensor
508 disposed in an exhaust manifold 507 ah output signal from an
engine revolution speed sensor 509 and so forth, whereby a quantity
of fuel to be injected and the opening degree of an ISC valve 8
are calculated. In response to these calculations, the control unit
510 controls the injector 507 and the ISC valve 8.
FIGS. 2 to 5 illustrate a hot wire type of flow meter according
to a first embodiment of the present invention.
A body 20 is constituted by integrally diecast-forming a flow-meter
body 20a, a throttle valve body 20b and an ISC-valve body 20c. An
inlet port of the flow-meter body 20a is provided with a full-mesh
body 40 for rectifying the flow, while the inlet portion 21a of
the flow passage is designed in the form of a bell-mouth. A probe
holder block 30 in which a bypass 31 is formed is inserted into
the lower stream to the bell-mouth shaped portion from the outside
of the flow meter body 20a. The sensor circuit unit 2 is screw-fixed
to this probe holder block 30 by screws 41a and 41b in such a manner
that the hot wire element 2a and the temperature compensation element
2b are, as shown in the figure, disposed in the bypass 31b formed
in parallel to the main stream. As a result of the above-described
structure, the probe holder block 30 is detachable from the outer
surface of the body 20. In the throttle body 20b, the throttle valve
3 for controlling a quantity of air is formed in a flow passage
21c thereof and a valve shaft 4 for moving this throttle valve 3
is formed in such a manner that it penetrates the body 20b. A lever
mechanism 5 a spring 6 and a throttle position sensor are formed
outside the body 20b in such a manner that they are connected to
the shaft 4. The portion in the vicinity of the ISC valve body 20c
is provided with the ISC valve 8 for controlling the air flow rate
at the time of the engine idling, that is, when the throttle valve
3 is completely closed, and air flow passages 23 24 and 25 connected
to this ISC valve 8. Illustrated plugs 26 and 27 are provided for
plugging unnecessary passages which are not used as the flow passage
since each of the passages 23 and 25 are formed from the outer surface
of the body 20c. A pipe 9 serves to take out negative pressure in
the lower stream to the throttle valve 3.
An axial bypass 31b formed in parallel to the main flow passage
21 and having an inlet port 31a in the form of a bell-mouth disposed
in the upper stream portion of the flow meter body 20a is formed
in an upper portion 30a of the probe holder block 30. This bypass
31b has a circular cross-sectional shape of a relatively narrower
width than the main flow passage. In this upper portion 30a, a bypass
31c designed perpendicular to the above-described bypass 31b and
having an outlet port 31d whose opened face is arranged in parallel
to the main stream is formed in such a manner that the length thereof
is longer than the radius of the main flow passage. As a result
of this, a branch and mix flow passage system which consists of
the main flow passage 21 and the bypass 31 are constituted in the
flow meter. The bypass 31 is formed in such a manner that the flow
resistance thereof, that is, the pressure loss of the flow is larger
than that at the main stream due to the flow resistance factor caused
from the shape of a two-dimensional L-shaped right angle bent and
the frictional resistance factor of the passage wall. The hot wire
element 2a and the temperature compensation element 2b are disposed
in the bypass 31b in such a manner that a holder portion 2c formed
integral with the circuit unit 2 penetrates a hole disposed in the
probe holder block 30. As a result of the above-described structure,
since the major portion of the outer wall of the probe holder block
30 is positioned in contact with the main stream, the temperature
of the flow passage's wall of the bypass 31b can be maintained at
substantially the same temperature as that of the intake air so
that flow rate can be measured involving a relatively smaller error
even if outside heat is effected. Furthermore, introducing force
of reversed flow into the bypass 31 can be reduced so that the hot
wire element 2a and so forth can be protected. In addition, since
the flow passage resistance of the bypass 31 has a great effect
for damping pulsation, abnormal output caused from excessive intake
air pulsation can be prevented.
As described above, the axial bypass 31a has the throttle at the
inlet port portion 31a and is designed in such a manner that the
length thereof from the inlet port to the hot wire element 2a is
twice the inner diameter thereof. These structures assists, in association
with the full-mesh body 40 and the throttle, to reduce disorder
of the flow introduced from the upper stream of the flow meter and
thereby to achieve the low-noise system.
On the other hand, the bypass 31c is disposed so as to make the
length thereof longer than the radius of the main stream, that is,
the same is disposed at a portion 21b where the area of the main
flow passage 21 becomes minimum, this portion being below the throttle
valve shaft 4 disposed in the lower stream thereof. The outlet port
31d of the bypass 31c is a pent-roof member formed by extending
a wall 30b of the probe holder block, and direct contact of the
main stream thereto is prevented by an air shield wall 30d whose
lower stream wall surface is perpendicular to the main stream. Since
the outlet port is disposed in the main stream where the flow passes
smoothly with relatively reduced effect from the movement of the
throttle valve, and thanks to the provision of this pent-roof member,
occurrence of mixture of flows immediately behind the bypass outlet
port 31d is prevented, causing the velocity change in the bypass
to be prevented. As a result of this, a further low noise system
can be achieved. Furthermore, the circular cross-sectional shape
of the bypass 31c, each shape of the walls 30b and 30d in the upper
stream of the main stream and the circular shape of the wall 30c
in the lower stream thereto also contribute to reducing noises.
A throttle 22 disposed in the end portion of the throttle body
20b in the lower stream slightly positioned away from the bypass
outlet port 31d stabilizes the flow in the bypass 31 when the throttle
valve 3 is moved, that is, stabilizes the flow rate distribution
to the main flow passage 21 and bypass 31. As a result, the throttle
valve 3 can be disposed adjacent to the flow meter.
Therefore, in accordance with this embodiment, a hot wire type
of air flow meter capable of accurately measuring an amount of air
taken in an engine and exhibiting high reliability can be provided
only with a significantly short axial length thereof and at low
cost.
Since a throttle valve can be adjacently and integrally formed,
the weight can be reduced. Consequently, the purifying engine exhaust
gas, improvement of fuel consumption and reduction in its space
in the engine room can be achieved.
FIGS. 6 and 7 illustrate a hot wire type of air flow meter according
to a second embodiment of the present invention. The difference
from the first embodiment shown in FIGS. 2 to 5 will now be described.
A body 60 forming the air intake line and a probe holder block
63 disposed within the former are, unlike those in the first embodiment,
integrally diecast-formed. The probe holder 63 is provided, like
that in the first embodiment, with a bypass 62 which consists of
an axial circular-shaped bypass portion 62b having a circular cross-sectional
shape and a radial bypass portion 62c also having a circular cross-sectional
shape. The radial bypass 62c is formed by mechanically machining,
from outside, the wall of the body 60 at the opposite position to
the circuit unit 2. An outlet port face 62d of the bypass is counterbored
by an end mill or the like in the above-described direction. Therefore,
a windshield 64 of the outlet port face 62d includes, as shown in
FIG. 7 wall portions 65a and 65b covering the two sides of the
outlet port face 62d. The walls 65a and 65b covering the two sides
are further effective to reduce disorder of flow due to mixture
of flows. A hole bored for the purpose of performing boring and
counterboring is plugged by a plug 72. A rib body 66 is provided
for the purpose of smoothly passing molten metal at the time of
die-cast forming.
A flow meter inlet portion 61a is formed in a curved throttle shape
in such a manner that its curvature starts small and it becomes
then moderate. A full-mesh body 70 is fastened in the front-half
portion of the throttle by a snap ring 71. The length from the inlet
port of the axial bypass 62b to the hot wire element 2a is designed
to be longer than that described in the first embodiment According
to this embodiment, a further low noise hot wire type of flow meter
can be achieved only at a low cost.
FIGS. 8 and 9 illustrates a hot wire type of flow meter according
to a third embodiment of the present invention. In this embodiment,
a probe holder block portion (projecting portion to the main stream)
83 forming a bypass 82 is, like that in the second embodiment, integrally
diecast formed with a body 80. The difference from the second embodiment
lies in that a rib 86 connected to a portion 83 projecting to the
main stream for improving molten metal flow is designed in such
a manner that its upper stream front end portion extends from the
inlet port face 82a of the bypass to the upper stream of the flow.
As a result of such structure, the turned flow from the upper stream
of the flow meter is prevented so that the full-mesh body employed
in the first and second embodiments become needless. Another difference
from the second embodiment lies in that a radial bypass 82c disposed
perpendicular to a main stream 81 and a bypass 82b are machined
in the direction from the sensor circuit 2 from outside of the body
80. As a result of this, the wall in the lower stream of the wind
shield wall 84 is machined on the same level as the inner wall of
the radial bypass 82c. On the other hand, the outlet port face 82d
is machined in the direction of the throttle valve 3 by an end mill
or the like so that the wind shield wall 84 is, like that in the
second embodiment, formed such that it comprises side walls 85a
and 85b. An illustrated plug 86 is provided for the purpose of plugging
the hole bored for performing machining.
FIG. 10 illustrates a hot wire type of flow meter according to
a fourth embodiment of the present invention. A lower stream side
bypass 92c provided in a probe holder block 93 formed integral with
a body 90 is disposed to form a sharp angle relative to a upper
stream axial bypass 92b. The direction of machining is, like that
in the third embodiment, arranged from the detecting circuit 2.
The portion which does not serve as the flow passage is plugged
by a plug 95. As a result of such structure, a packing portion 2d
of the circuit unit can be arranged not to interrupt the boring
work, and as well the pipe line resistance of the bent portion can
be increased. Therefore, a further strong structure against backfire
can be achieved. An outlet port end 92d in the lower stream bypass
92c is machined in the direction from the throttle valve 3 so that
a part of a projecting portion 93 can be retained in the form of
a pent-roof member 94 and is formed in parallel to the main stream.
Although omitted from the illustration, another embodiment can
be employed in which the angle formed between the upper stream bypass
92b and the lower stream bypass 92c is made larger than a right
angle, that is, an obtuse angle. In this case, forming of the bypass
92c will be performed from outside of the body wall opposite to
the detecting circuit 2. By designing the angle formed by the bypass
92b and 92c to be an obtuse angle, the pipe line resistance in this
angled portion can be reduced. Therefore, the average flow velocity
in the bypass 92b can be increased. Since the flow velocity in the
bypass 92b is determined by the total pressure loss of the bypass
92 and the flow velocity and the pressure loss of the main flow
passage 91 the flow velocity in the bypass 92b can be adjusted
by determining this angle of the bent portion.
FIGS. 11 and 12 illustrates a hot wire type flow meter according
to a fifth embodiment of the present invention. In this embodiment,
a portion 113 which forms a bypass 112 projecting to the main
flow passage 111 is formed so as to be along the inner wall of a
body 110. Therefore, a lower stream bypass 112c perpendicular to
a upper stream bypass 112b is substantially faces radially, but
in the form of a circular arc of substantially 90.degree. facing
circumferentially. This shape can be machined by an end mill or
the like from the direction of the throttle valve 3. Therefore,
the wall of the lower stream bypass facing the throttle valve 3
is formed by an additional plate-like cover 115. The plate-like
cover 115 is fastened to a projecting wall 113 by bolts 116a and
116b. An outlet port 112d of the lower stream bypass is also formed
in parallel to the main stream, but the plate-like member 115 is
partially cut off. Therefore, it is arranged in such a manner that
a part of the projecting portion 113 becomes a wind shield wall
114 having a sufficient height to prevent main stream flow.
The pipe line flow resistance of the thus-formed bypass 112 is
substantially composed by the resistance of the right-angle bent
portion, the resistance due to the shape of the elbow having a square
cross-sectional shape and small curvature of substantially 90.degree.
and the frictional resistances of the flow passages. Therefore,
it can be, depending upon the way to select the cross-sectional
area, easily enlarged with respect to that in the first embodiment.
Therefore, the structure according to this embodiment exhibits excellent
backfire resistance and pulsation damping characteristic. Furthermore,
the above-described type of structure exhibits an advantage when
an injector :s disposed in front of the throttle valve as in a single
point injection system.
FIGS. 13 and 14 illustrate a hot wire of flow meter according to
a sixth embodiment of the present invention. This embodiment is
characterized in that a bypass having a relatively large fluid resistance
is arranged to be a projecting portion to a main flow passage having
a relatively small volume. That is, a bypass 132c disposed in the
lower stream to a bypass 132b in which the hot wire element is disposed
is shaped in the form of an annular shape. This bypass 132c is also
formed by an end mill or the like from the direction of the throttle
valve 3. A plate-like cover 135 is attached by a bolt 136. Furthermore,
a part of the projecting portion is, like that in the fifth embodiment,
arranged to be a wind shield wall.
The pipe line flow resistance of the thus-formed bypass 132 is
composed by the resistance of the substantially right-angle bent
portion, the resistance due to the shape of the elbow having a square
cross-sectional shape and a relatively large curvature of substantially
270.degree. and the frictional resistances of the relatively long
flow passage. Therefore, it can be longer than the fifth embodiment.
Therefore, it is advantageous when it is applied to an engine involving
a relatively large air intake pulsation.
FIG. 15 illustrates a hot wire type of flow meter according to
a seventh embodiment of the present invention. This embodiment is
characterized in that a bypass having a rather great flow resistance
than that of the sixth embodiment is formed with its widthwise dimensions
limited. A body 150 is individually formed. A bypass 152 is formed
in a probe holder block 153 coupled to the circuit unit 2 this
bypass comprising a bypass 152b formed in parallel to a main flow
passage 151 a bypass 152c formed perpendicular to the same, a bypass
152d formed perpendicular to this bypass 152c and extending to upper
stream direction of the main stream and a bypass 152e formed perpendicular
to this bypass 152d and facing radially. Each of the bypasses is
designed to have a circular cross-sectional shape, and the portion
which does not serve as the flow passage is plugged by plugs 155
156. A portion 154 formed by further extending the wall of the block
153 disposed in the upper stream of the main stream is formed so
as to serves as a wind shield wall to protect the outlet port of
the bypass 152e.
The flow resistance of the thus-formed bypass 152 is composed by
the resistance due to the shape of the line formed by three right
angle bent portions and the resistance in porportional to the relatively
long distance of the flow passage. Therefore, the resistance is
further increased with respect to the sixth embodiment. As a result,
it is advantageous when used in an engine involving a great air
intake pulsation. Furthermore, the flow rate distribution to the
bypass with respect to that to the main stream can be reduced in
the great flow rate region, that is, the maximum flow velocity attacking
the hot wire element 2a can be reduced so that an effective measurement
against dust adhesion contamination driving a long time period can
be taken.
FIG. 16 illustrates a hot wire type of flow meter according to
an eighth embodiment of the present invention. A probe holder block
163 is individually formed from a body 160 but is coupled with
the detecting circuit 2 and is detachable to the body 160. An outer
port face 162d of a bypass 162c formed perpendicular to the main
stream is, as shown in the figure, inclined with respect to the
main stream. Therefore, introduction of the reversed flow into the
bypass easily caused by such structure is prevented by a stopper
valve 165 formed by a thin steel plate or the like. The stopper
valve 165 is, with the aid of a retainer 166 secured to a probe
holder block 163 by a bolt 167. The stopper valve is, in a normal
state, and as shown in the figure, arranged to be opened for the
purpose of excessively interrupting the flow through the bypass
outlet and making the flow downward. It is arranged to stop the
outlet port 162d by a dynamic pressure effected at the time of occurring
the reversed flow so that introduction of the reversed flow into
the bypass is prevented. When the dynamic pressure is released,
it returns to the state shown in the figure. Since the bypass outlet
port face is made inclined, the roll of the wind shield is performed
by the upper stream side wall with respect to the main stream of
the entire wall forming the bypass 162c.
FIG. 17 illustrates a hot wire type of flow meter according to
a ninth embodiment of the present invention. A block holder block
173 is formed integral with a body 170. The difference from the
above-described embodiments lies in that a bypass outlet port 172a
is opened at the central portion of a main stream 171. Therefore,
a radial bypass 172c formed perpendicular to an axial bypass 172b
formed in parallel to the main stream is arranged from the central
portion of the main stream toward the inner wall of the flow passage.
A radial bypass 172c is formed by a wall in the lower stream of
the main stream and a molded cover 174. The molded cover 174 is
fastened by a bolt 175. As a result of the thus-formed structure,
a bypass outlet port 172d is protected by the probe holder block
173 serving as a wind shield so that the bypass flow passing through
the outlet is not affected by the main stream. The difference of
the structure according to this embodiment from the above detecting
circuit 2 lies in that a circuit unit 176 having a relatively long
holder portion 177 is employed. An advantage involved in this embodiment
is that, since the inlet port 172a of the bypass is disposed at
the central portion of the main stream 171 a relatively stabilized
flow rate distribution characteristics and noise characteristics
can be obtained. On the other hand, since the length of the bypass
172 needs to be insufficient, causing the pulsation stabilization
to be slightly insufficient.
FIGS. 18 and 19 illustrate a hot wire type of flow meter according
to a tenth embodiment of the present invention. In this embodiment,
the whole body of a bypass 182 is disposed outside a main flow passage
181 but is disposed within a flow meter body 180. That is, the
inlet port of the bypass 182b is arranged to be on the same level
as the inlet port of the main stream 181. A bypass 182c in the lower
stream to a hot wire element 185 is designed to be an annular shape
surrounding the main flow passage 181. The outlet port 182d opens
in the circumferential wall of the main flow passage which is expanded
to be a stepped shape immediately in front of the outlet port 182d.
That is, the radius of the main flow passage in which the outlet
port 182d is provided is enlarged than the radius of the main stream
immediately in front of the same by substantially the width of the
outlet port 182d. Therefore, since the main flow passage wall 183
immediately in front of the outlet port 182 d has a roll as a wind
shield wall, any unnecessary pressure loss can be prevented and
low noise system can be achieved.
FIGS. 20 and 21 illustrate a hot wire type of flow meter according
to an eleventh embodiment of the present invention. A probe holder
block 203 is individually formed from a body 200 with the inside
thereof being provided with a bypass 202b formed in parallel to
the main stream and a radial bypass 202c having a relatively longer
length with respect to that described in the first embodiment. This
bypass 202c is formed in the lower stream of the main stream by
a groove having a square cross sectional shape and a cover 205.
An outlet port 202d of the bypass comprises a wind shield wall 204
formed by extending the probe holder block 203 in the upper stream
of the main stream and as well a wind shield wall 206 formed by
extending a cover 204 in the lower stream. In this embodiment, the
width of the wind shield wall 206 is made smaller than that of the
bypass 202c.
The reason for this is to prevent the bypass flow at the outlet
port thereof from being excessively disordered by the cover 206.
This measurement is a critical factor to enhance the effect of the
upper stream wind shield. The wind shield wall 204 for the outlet
port 202d in the upper stream of the main stream is, as described
above, effective to reduce noise at the time of normal state, that
is, when the flow is normal. On the other hand, the wall 206 in
the lower stream can significantly reduce the introduction force
of the reversed flow due to backfire or blowback into the bypass.
That is, the flow can be separated into two currents by this wind
shield 206 and the two currents interfere with each other in front
of the bypass outlet 202d so that the introducing force can be weakened.
This type of structure exhibits an excellent intake air pulsation
damping characteristics when used in an engine involving occurrence
of frequently blowback.
FIG. 22 illustrates a hot wire type of flow meter according to
a minor change of the eleventh embodiment of the present invention.
A cover 225 is designed in such a manner that the width thereof
is maintained to outlet ports 222d and 222e at which side walls
223a and 223b forming a radial bypass 222c are cut off. Therefore,
the width of the portion corresponding to the wind shield wall 204
shown in FIG. 20 is made large for the purpose of forming wind shield
walls 224a and 224b to serve for the bypass outlets 222d and 222e.
FIGS. 23 and 24 illustrate a hot wire type of flow meter according
to a twelfth embodiment of the present invention. This embodiment
is characterized in that the structure shaped like the eleventh
embodiment is formed in a probe holder block formed integral with
a body 230. A radial bypass 232c is bored from outside of the body,
and its outlet port 232d is also machined by an end mill or the
like in the same direction. At this time, in order to form a wind
shield wall 234 in the upper stream of the main stream and a wind
shield wall 236 in the lower stream of the same, a probe holder
block 233 is formed. A plug 235 plugs an unnecessary hole after
the machining has been completed. An effect obtained in this embodiment
is, in principle, the same as that obtained in the eleventh embodiment,
but the structure can be performed easier, causing cost to be reduced.
FIGS. 25 26 and 27 illustrate a hot wire type of flow meter according
to a thirteenth embodiment of the present invention.
The body 1 constitutes the air intake line of an internal combustion
engine. Air is introduced from left in the figures. The internal
combustion engine is disposed in the lower stream (right in FIG.
1) of the flow.
The body 1 in principle forms a cylindrical main flow passage 303.
An inlet port 303a of the main flow passage 303 is designed in the
form of a bell-mouth. The projecting portion 2 is formed on the
inner wall of the body 1 to the main flow passage 303. At the front
end portion of this projecting portion 302 is formed the bypass
304 in parallel to the main flow passage 303 in such a manner that
a bell-mouth shaped inlet port 304a thereof is disposed at the central
portion of the main flow passage 303. The inlet port 304a is formed
projecting over a wall 302a of the projecting portion, and the distance
from the inlet port 304a to a hot wire element 310 is twice the
inner diameter of the bypass. The hot wire element 310 secured to
a support column 311 is, together with a temperature compensation
element 312 disposed within the bypass 304 as illustrated. As a
result of this, a hole through which a molded portion 313 of the
support column 311 coupled to the circuit unit can be inserted from
outside of the body 1 is formed in the projecting portion 302. In
the lower stream of the hot wire element 310 a lattice body 307
in the shape of a honeycomb made of an aluminum foil is formed by
inserting and coupling from the rear end portion of the projecting
portion 302. In the lower stream of the lattice body 307 a bent
bypass 305 is formed by a rear end wall 302b of the projecting portion
302 and a cover 306. The cover 306 is secured to the projecting
portion 302 by, in this case, bolts 308 and 309. In the main stream
303 in the lower stream of the cover 306 with the throttle valve
3 being driven by the shaft 4 coupled to the body 1 is disposed.
An inner wall 303b of the main flow passage 303 is shaped in such
a manner that it allows the flow passage to be enlarged toward the
upper stream. On the other hand, an inner wall 303c of the main
flow passage 303 adjacent to the position at which the throttle
valve 3 is disposed is formed to maintain the constant diameter
by machining, but it is molded in such a manner that the diameter
of the portion in the vicinity of the rear end surface 302b of the
projecting portion 302 is made relatively small. That is, the body
1 is molded and made of a casted material manufactured with an intermediate
mold (casting) capable of being removed to both right and left directions,
the mold being arranged to be split at the surface adjacent to the
rear end wall 302b of the projecting portion 302.
A void arrow illustrates the air flow. Thanks to the throttle effect
of the bell-mouth shape of the inlet port 303a of the main flow
passage and the structure in which the inlet portion 304a of the
bypass, a relatively rectified flow is introduced into the bypass
304. Furthermore, by virtue of the friction of the inner wall of
the bypass 304 the flow in the bypass 304 can be rectified so that
an effect can be obtained that a flow in which disorder is prevented
and having a uniform flow velocity distribution can be obtained
immediately before a hot wire element 310. In the immediately lower
stream portion of the lattice body 307 the flow is bent by 90.degree.
and is caused to flow upward within the bent bypass 305 along the
rear end wall 302b of the projecting portion. At the position bent
by 90.degree., the flow is disordered and becomes unsteady due to
the pulsation of the engine. However, the lattice body 307 exhibits
an effect to damp the changes in the flow and the pressure so that
they are prevented from transmission to the upper stream. The flow
in the bent bypass 305 is, as shown in FIG. 27 attacks the inner
wall of the main pass, and is overflowed through bent bypass outlets
305a and 305b so as to be joined in the main stream. A cover 306
forming the bent bypass 305 prevents the direct introduction of
the reversed flow due to backfire of the engine into the bypasses
305 and 304 and the bent bypass 305 itself has an effect to damp
the reversed flow and the pulsation.
FIGS. 28 to 29 illustrate a hot wire type of flow meter according
to a fourteenth embodiment of the present invention. An inlet port
343a of a main flow passage 343 is tapered such that the inner wall
thereof is relatively rapidly contracted toward the lower stream
side. A straight bypass 344b formed in parallel with a main flow
passage 343 and a bypass pipe 344 forming a bent bypass 344c are
inserted and coupled in a projecting portion 342 formed by machining
the inner wall of the body 1. An inlet port 344a of the bypass pipe
344 is disposed away from a main flow passage wall 343b or a projecting
portion wall 342a, but adjacent to the rear end portion of the tapered
portion of the main flow passage inlet port 343a. An inlet port
344a of the bypass pipe 344 is also tapered reducing the diameter
thereof toward the lower stream. The distance from the inlet port
344a to the hot wire element is, in this case, arranged to be twice
the diameter of the bypass. A molded portion 353 formed integral
with a circuit 354 penetrates the body 1 and the upper wall of the
bypass pipe 344 so that a hot wire element 350 is disposed within
the bypass 344b. A lattice body 347 is disposed at the outlet portion
of the bypass pipe 344 in the lower stream of the bent bypass 344c.
The taper shape of the inlet portion 343a of the main flow passage
exhibits an effect to increase the air flow introduced into the
bypass (pipe) 344 since it throttles the air introduced and further
to reduce the disorder of the flow passing through the opening 344a
of the bypass. The taper shape of the opening portion 344a of the
bypass and the length of the bypass 344b to the hot wire element
350 contributes to rectifying the flow attacking the hot wire and
to making the flow velocity uniform so that the system noise can
be reduced.
The bent bypass 344c and the lattice body 347 are effective to
damp the reversed flow and the pulsation transmitted from the engine
so that the hot wire element can be protected from the reversed
flow and effective to stabilize the output. Furthermore, the lattice
body 347 at the outlet port of the bypass pipe 344 prevents transmission
of the disorder of the main flow due to the discharged air from
the bypass outlet 344d to the upper stream. In this embodiment,
since the bent bypass 344c can be formed by using a pipe, it is
advantageous to provide the lattice body at the outlet portion of
the pipe.
FIG. 30 shows a structure that honeycomb shaped (hexagon) lattice
body 307 or the 347 is designed to be a square shape in the cross
section thereof.
In the thirteenth embodiment shown in FIGS. 25 to 27 the projecting
portion 302 and the bypass cover 306 formed integral with the body
and the wall to which the circuit unit 2 of the body 1 is secured
may be integrally formed so as to be inserted into and coupled to
the body.
FIGS. 31 to 32 illustrates the structure of a model to which an
experiment on the effect of the dimension of the wind shield walls
against noise was subjected. Therefore, this structure is included
within embodiments of the present invention. FIG. 33 shows a result
of this experiment.
Referring to the structural drawing, experiment conditions and
so forth will now be described. A prove holder block 253 coupled
to the circuit unit 2 is individually formed from a body 250. A
bypass 252 is formed in the block 253 this bypass comprising an
axial bypass 252b formed in parallel to a main flow passage 251
and a radial bypass 252c. The radial bypass 252c is, when the same
is not assembled, machined by an end mill from the direction of
the throttle valve 3 to be a flow passage having a cross-sectional
shape of a square having a width d and depth w. A cover 256 secured
by a bolt 257 is attached to the radial bypass 252c. On the other
hand, the axial bypass is designed to be a flow passage having the
cross sectional shape of a circular of an inner diameter of l. In
order to reduce the upper stream disorder, a relatively long axial
direction is achieved by attaching a pipe 255.
FIG. 33 shows a result of the experiment performed in such a manner
that a standard round air filter (annular shape) is used in the
upper stream of the body 250 under a relatively reduced drift state,
and a full-mesh body is not provided at the inlet of the flow meter.
The flow rate illustrated as 10 g/sec, 40 g/sec and 140 g/s is changed
by a sonic stand. In order to examine the relationship between the
height h of a wind shield 254 and the axial width w of the outlet
port of the bypass, a plurality of wind shield walls 254 each having
different height h are used in such a manner that they are changed.
The illustrated experiment result is obtained in a case where the
ratio b/d of the width b of the wind shield wall and the width d
of the bypass outlet port (radial direction) is 1.5. The axis of
abscissa shown in FIG. 33 is h/w. As can be clearly seen from the
experiment result shown in FIG. 33 noise can be, depending upon
the flow rate, that is, the degree of the flow velocity, reduced
if an air shield wall having at least h/w of substantially 0.5 or
more is used with respect to a case of no air wind shield wall.
Within a region from h/w=0.5 to 1.0 the noise is rapidly reduced
in accordance with increase in the height of a wind shield wall,
but the noise is not significantly reduced even if the height is
further increased. Therefore, an effective noise reduction effect
can be obtained when h/w.gtoreq.0.6 and a sufficient noise reduction
effect can be obtained when h/w.gtoreq.1.0.
Furthermore, the ratio b/d of the width d of an outlet port of
the bypass and the width b of a wind shield wall also affect the
noise reduction effect. When the ratio is substantially 1.3.ltoreq.b/d.ltoreq.2.0
the effect can be enhanced qualitatively. That is, if b/d is too
small, turning of the main stream occurs at the side surface, causing
the effect to be deteriorated even if h/w is excellent. On the other
hand, if it is too large, the wind shield wall acts as a resistance
against the main stream. It is unfavorable on the view point of
reduction in the entire pressure loss.
As described above, according to the present invention, an accurate
measurement of a flow rate can be performed even under various conditions
since the above-described structure prevents the reversed flow to
a bypass due to backfire or blowback to the bypass and thereby disorder
of the flow at the upper stream portion of the flow meter. |