Abstrict An air flow meter for an internal combustion engine comprises an
intake air passage of an internal combustion engine, which is composed
of a primary flow passage and an auxiliary flow passage having a
specified length and a portion adapted to project within the primary
flow passage and made substantially parallel to the direction of
the air flow passing through the primary flow passage. A sensor
for measurement of an intake air flowrate is disposed within the
auxiliary flow passage. The primary flow passage is provided with
a portion where the cross-sectional area of the primary flow passage
is gradually reduced. In the vicinity of this cross-sectional area
reducing portion, there is disposed an outlet of the auxiliary flow
passage.
Claims What is claimed is:
1. An air flow meter for an internal combustion engine comprising
an intake air passage of an internal combustion engine, said intake
air passage being composed of a primary flow passage and an auxiliary
flow passage having a specified length and having a portion which
projects within said primary flow passage and is disposed substantially
in parallel to the direction of an air flow passing through said
primary flow passage, and a sensor for measurement of an intake
air flow rate, said sensor being disposed within said auxiliary
flow passage, said intake air passage further having a cross-sectional
area change portion provided at a wall surface of said primary flow
passage, said primary flow passage being changed in cross-sectional
area at said cross-sectional area change portion, an outlet of said
auxiliary flow passage being located in an area where the lines
of an air flow in the primary flow passage are compressed by said
portion of change in cross-sectional area, and wherein the auxiliary
flow passage is disposed away from the center axis of said primary
flow passage and in close proximity to a wall surface of said primary
flow passage, and said outlet of the auxiliary flow passage is directed
away from said wall surface of said primary flow passage.
2. An air flow meter for an internal combustion engine according
to claim 1 wherein the center axis of said outlet of said auxiliary
flow passage is located within a zone which extends from a first
position corresponding to an end of reduction in cross-sectional
area of said cross-sectional area change portion of said primary
flow passage to a second position upstream of said first position
and spaced from said first position by a distance corresponding
to the radius of said primary flow passage upstream of said cross-sectional
area change portion.
3. An air flow meter for an internal combustion engine according
to claim 1 wherein the axis of said outlet of said auxiliary flow
passage is located within a zone which extends from a first position
corresponding to an end of reduction in cross-sectional area of
said cross-sectional area change portion of said primary flow passage
to a second position upstream of said first position and spaced
from the beginning of reduction in cross-sectional area of said
cross-sectional area change portion by no more than approximately
the radius of said outlet.
4. An air flow meter for an internal combustion engine according
to claim 1 wherein said cross-sectional area change portion of
said primary flow passage is conical and the angle of said cross-sectional
area change portion to the wall of said primary flow passage is
not less than 10.degree..
5. An air flow meter for an internal combustion engine according
to claim 1 wherein said cross-sectional area change portion of
said primary flow passage is in the form of an internal step-walled
hollow-cylinder having different diameters with a diameter transition
therebetween.
6. An air flow meter for an internal combustion engine according
to claim 4 or 5 wherein the diameter of a section of said primary
flow passage upstream of said cross-sectional area change portion
is 1.1. times or more as large as that of a section downstream therefrom.
7. An air flow meter for an internal combustion engine, comprising:
a main passage forming part of an air intake flow passage of the
internal combustion engine;
a measuring element for measuring a quantity of air drawn in the
main passage; and
a member forming a bypass passage disposed in said main passage
and containing said measuring element;
wherein said main passage includes a throttled portion formed between
the bypass passage and a position in said main passage where a throttle
valve is to be located downstream of the bypass passage; and
wherein said member forming said bypass passage has an L-shaped
configuration including a first flow path portion formed in an axial
direction of said main passage at a position offset from the center
axis of said main passage, and a second flow path portion formed
in a radially inward direction of said main passage and having an
outlet opening into said main passage; and
wherein the center axis of said outlet of said second flow path
portion is located within a zone from the downstream end of said
throttled portion to a position which is upstream therefrom by a
distance corresponding to the radius of said main passage upstream
of said throttled portion.
8. An air flow meter according to claim 7 wherein said throttled
portion of said main passage is in the form of an internally step-walled
hollow cylinder having different diameters with a diameter transition
part therebetween.
9. An air flow meter according to claim 7 wherein the diameter
of said main passage upstream of said throttled portion is 1.1 times
the diameter of said main passage downstream of said throttled portion.
10. An air flow meter for an internal combustion engine, comprising:
a main passage forming part of an air intake flow passage of the
internal combustion engine;
a measuring element for measuring a quantity of air drawn in the
main passage; and
a bypass passage disposed in said main passage and containing said
measuring element;
wherein said main passage includes a throttled portion formed between
the bypass passage and a position in said main passage where a throttle
valve is to be located downstream of the bypass passage;
wherein said bypass passage has an L-shaped configuration including
a first flow path portion formed in an axial direction of said main
passage, and a second flow path portion formed in a radially inward
direction of said main passage and having an outlet opening into
said main passage; and
wherein the downstream end of said throttled portion is located
in said main passage in a region which extends from the center axis
of said outlet of said bypass passage to a point spaced from the
center axis of the outlet of said bypass passage downstream therefrom
by a distance approximately equal to the radius of said main passage
upstream of said throttled portion.
11. An air flow meter according to claim 10 wherein said throttled
portion of said main passage is in the form of an internally step-walled
hollow cylinder having different diameters with a diameter transition
part therebetween.
12. An air flow meter according to claim 10 wherein the diameter
of said main passage upstream of said throttled portion is 1.1 times
the diameter of said main passage downstream of said throttled portion.
13. An air flow meter for an internal combustion engine, comprising:
a main passage forming part of an air intake flow passage of the
internal combustion engine;
a measuring element for measuring a quantity of air drawn in the
main passage; and
a member forming a bypass passage disposed in said main passage
and containing said measuring element;
wherein said main passage includes a throttled portion formed between
the bypass passage and a position in said main passage where a throttle
valve is to be located downstream of the bypass passage; and
wherein said member forming said bypass passage has an L-shaped
configuration including a first flow path portion formed in an axial
direction of said main passage, and a second flow path portion formed
in a radially inward direction of said main passage and being disposed
at least partly within the area of said throttled portion.
14. An air flow meter according to claim 13 wherein said second
flow path portion extends diametrically with respect to said main
passage in a direction transverse to an axis of the throttle valve.
15. An air flow meter for an internal combustion engine, comprising:
a main passage forming part of an air intake flow passage of the
internal combustion engine;
a measuring element for measuring a quantity of air drawn in the
main passage; and
a bypass passage disposed in said main passage and containing said
measuring element;
wherein said main passage includes a throttled portion formed between
the bypass passage and a position in said main passage where a throttle
valve is to be located downstream of the bypass passage;
wherein said bypass passage has an L-shaped configuration including
a first flow path portion formed in an axial direction of said main
passage at a position offset from the center axis of said main passage,
and a second flow path portion formed in a radially inward direction
of said main passage and having an outlet opening into said main
passage; and
wherein said throttled portion is located in said main passage
in a region which is contiguous to the second flow path portion
of said bypass passage.
Description BACKGROUND OF THE INVENTION
The present invention relates to a hot-wire type air flow meter
based on the use of an auxiliary flow passage and, more particularly,
to an engine control device which is suitable for use as an intake
air flow-rate sensor for a gasoline engine of an automobile.
In various internal combustion engines, particularly in a gasoline
engine of an automobile, the range of control thereof is very wide
in respect of the number of revolutions and output and the engine
is subjected to strict regulation of exhaust gas. Therefore, an
accurate air fuel ratio control is always required to be performed
irrespective of the operational conditions of the engine.
Under the above-mentioned existing circumstances, a microcomputer-control
type engine control device has in recent years been widely adopted
in which the air fuel ratio or the ignition timing is controlled
using a microcomputer operating on the basis of a synthetic decision
on various operational conditions of the engine including an intake
air flow thereof.
Meanwhile, what is called "hot-wire type air flow meter"
has recently been employed as an air flow sensor for such engine
control. Examples thereof are disclosed in Japanese Patent Unexamined
Publications Nos. 58-109815 and 58-109816. In these prior art examples,
an intake air passage of an internal combustion engine is constituted
by a primary flow passage and auxiliary flow passage allowed to
project within the primary flow passage and having a specified length,
the auxiliary flow passage having a portion extending substantially
in parallel with the flow of the air passing through the primary
flow passage. Namely, said prior art examples show the hot-wire
type air flow meter of auxiliary flow passage system, in which a
sensor element for an intake air flowrate is disposed in said auxiliary
flow passage.
An outlet of the auxiliary flow passage is opened in the vicinity
of an enlarged section of the primary flow passage, or is opened
at a straight pipe section.
However, in the above-described prior art, no consideration is
given to the stability of air flow at the outlet of the auxiliary
flow passage where the sensor element is disposed. Namely, the turbulence
of air flow, which has nothing to do with the pulsation of air flow
due to the revolutions of the engine involved, vigorously occurs
at said outlet, thus raising a problem that such turbulence of air
flow is likely to have undesirable effects upon the metering of
the intake air flow rate.
To cope with this problem, a means for solving the same has been
proposed in which a rectifying member such as a mesh member or honeycomb
member is provided over the intake air flow passage so as to stabilize
the flow of intake air. In this proposal, however, a considerable
increase in manufacturing cost, inherently results.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an air flow meter
for use in an internal combustion engine which enables sufficient
stabilization of air flow without employing any member likely to
become a cause of rise in the manufacturing cost, thereby enabling
measurement of air flow always with high accuracy.
The above object can be achieved by forming the configuration of
a primary flow passage in such a manner that the flow of air in
the primary flow passage is restricted in the vicinity of an outlet
of the auxiliary flow passage.
The air flowing out of the auxiliary flow passage merges into the
flow of air in the primary flow passage in the vicinity of the outlet
of the auxiliary flow passage. In a region where the primary flow
passage is restricted in the vicinity of the outlet of the auxiliary
flow passage, the flow of air is compressed. That is, a straightening
of the lines of flow takes place. In consequence, the flow of air
around the sensor element within the auxiliary flow passage also
is stabilized. In consequence, it is possible to obtain the result
of detection in the flow of air having no turbulence.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of an air flow meter for an internal combustion
engine according to a first embodiment of the present invention;
FIG. 2 is a side sectional view of the first embodiment;
FIG. 3 is a side sectional view taken along line 3--3 in FIG. 4
of an air flow meter for an internal combustion engine according
to a second embodiment of the present invention;
FIG. 4 is a plan view of the second embodiment of the present invention;
FIG. 5 is an enlarged bottom view illustrating a state of the internal
passages of the air flow meter according to the second embodiment
of the present invention;
FIGS. 6 and 7 are side views of the second embodiment as taken
from different directions, respectively;
FIG. 8 is a view illustrating a throttle valve; and
FIGS. 9 and 10 are side views showing the manner in which a hot-wire
module is mounted.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An air flow meter for an internal combustion engine in accordance
with the present invention will now be described in detail with
reference to the illustrated embodiments.
FIGS. 1 and 2 show an air flow meter for an internal combustion
engine in accordance with a first embodiment of the present invention.
The air which has been taken in from an air cleaner (not shown)
by a negative intake pressure of the engine is restricted in the
form of a bell mouth at an inlet 2a of a throttle body 1. Thereafter,
the flow of the air is divided into two parts, one of which passes
through a primary flow passage 2 and the other of which passes through
an auxiliary flow passage 3.
An inlet of the auxiliary flow passage 3 is shaped like a hollow
cylinder and the axis thereof is in parallel with the axis of the
primary flow passage 3. The auxiliary flow passage 3 is eccentrically
disposed within the primary flow passage 2.
The air which flows into the auxiliary flow passage 3 passes through
a cylindrical portion 4 having a length of 10 mm or more to reach
a hot-wire element section 5. In this section 5 heat is taken away
therefrom in accordance with the flow velocity of the air passing
therethrough. Therefore, an electric current is supplied from a
hot-wire module 6 to the section 5 in order to supplement the amount
of heat thus lost.
By causing generation of the output proportional to the level of
said electric current from the hot-wire element section 5 it is
possible to obtain an output therefrom which corresponds to the
flow velocity of the air. A specified quantity of fuel is supplied
to the engine involved correspondingly to a level of that output,
thus providing an optimum air fuel ratio with respect to the engine.
The primary flow passage 2 is constituted by an upstream portion
2b located at the inlet side of the throttle body 1 and having the
auxiliary flow passage 3 disposed therewithin, a downstream portion
2c located at the outlet side of the throttle body 1 and having
a throttle valve 7 disposed therewithin, and a tapered portion 8
located between the upstream portion 2b and the downstream portion
2c. The inner diameter of the downstream portion 2c is made smaller
than that of the upstream portion 2b. The cross-sectional area of
the upstream portion 2b is 1.1 times or more as large as that of
the downstream portion 2c.
Meanwhile, as described above, the air which has entered and passed
through the hot wire element 5 is caused to be bent at a bent portion
at right angles. Then, the air is discharged from the outlet portion
10 of the auxiliary flow passage into the primary flow passage 2
thus merging into the air within the primary flow passage 2.
On the other hand, the air which flows into the primary flow passage
2 is caused to flow through the upstream portion 2b and is then
restricted by a tapered portion 8 from which it advance toward the
downstream portion 2c. Consequently, the action of linearizing the
flow of air is performed, so that turbulence of the air flow is
suppressed by the tapered portion 8 to make the air flow sufficiently
stable.
The outlet 10 of the auxiliary flow passage 3 as shown, is located
in the vicinity of the tapered portion 8 of the primary flow passage
2. More specifically, in FIG. 2 the distance L between the axis
of the outlet portion 10 of the auxiliary flow passage 3 and the
downstream end of the tapered portion 8 is made smaller than at
least the radius of the primary flow passage 2. In an embodiment,
the distance L is made smaller than that which is 1.1 times as large
as the radius of the throttle valve 7.
Consequently, the air flowing through the auxiliary flow passage
3 is caused to flow out into the sufficiently stabilized air flow
within the primary flow passage 2 in the vicinity of the tapered
portion 8. Accordingly, the turbulence in the air flow in the vicinity
of the hot-wire element section 5 also is sufficiently suppressed,
whereby the air flow in the vicinity thereof is stabilized. As a
result, measurement of the flow rate of the air is obtained while
the air flow is sufficiently stabilized. Thus, it is possible to
easily obtain highly accurately measured results.
In the first embodiment, as clear from the Figure, the direction
of air which flows toward the outlet 10 of the auxiliary flow passage
from the bent portion 9 is perpendicular to the axis of the throttle
shaft.
Next, FIGS. 3 to 10 illustrate in detail an air flow meter for
an internal combustion engine in accordance with a second embodiment
of the present invention. The main construction thereof is the same
as that of the air flow meter in accordance with the first embodiment
of the present invention shown in FIGS. 1 and 2. Therefore, the
same parts or sections as those shown in FIGS. 1 and 2 are denoted
by like reference numerals, respectively.
The primary flow passage 2 of the throttle body 1 is constructed
as shown in FIG. 3. Namely, the inlet portion 2a is rounded or bell-mouthed
so that the flow of air may be smoothly restricted. At the inlet
portion 2a there is provided a stepped portion 2e at which a rectifying
mesh 12 is fixed, the mesh 12 being pressed from above by a snap
ring 13 so as to prevent the mesh 12 from being moved. The outer
periphery of the mesh 12 is fixed by caulking a metallic member
thereto so as to prevent the mesh 12 from being loosened. In the
vicinity of the outlet 10 of the auxiliary flow passage, the primary
flow passage 2 has its diameter sharply restricted at the tapered
portion 8. At a midway of the tapered position 8 a refluxing port
(not shown ) for blowby gas is opened. The upstream portion 2b of
the primary flow passage 2 between the inlet portion 2a and the
tapered portion 8 has no change in diameter. The downstream portion
2c of the primary flow passage 2 located after restriction thereof
made by the tapered portion 8 has no change in diameter up to a
position downstream of a measuring portion of the throttle valve
7. An inlet of an IAC (idle adjustment control) passage is open
in a zone between a position downstream of the tapered portion 8
in the vicinity of the outlet section 10 of the auxiliary flow passage
3 and a position upstream of the throttle valve 7. An outlet of
the IAC passage is open in a zone downstream of the throttle valve
7.
A blowby gas refluxing passage 20 is constructed as follows. Namely,
the blowby gas refluxing passage 20 which is open into an intake
manifold is allowed to pass through the contact surfaces of the
intake manifold with the throttle body 1 and extend in parallel
with the primary flow passage 2 of the throttle body. Thereafter,
the blowby gas refluxing passage 20 is orthogonally bent in an upstream
zone of the throttle valve 7 where the passage 20 confluxes into
the primary flow passage 2 (see FIGS. 5 and 6). The blowby gas passage
20 which is parallel to the primary flow passage 2 is formed by
die casting but undergoes no mechanical fabrication. For this reason,
the passage 20 is tapered (FIG. 6). The passage 21 which is orthogonal
to the blowby gas passage 20 is fabricated from outside the throttle
body 1 to the primary flow passage 2 and is closed by a plug 22
from outside (see FIG. 7). The outlet or refluxing port of the blowby
gas refluxing passage 20 is located at the inner wall surface of
the primary flow passage in a zone where no member obstructs that
outlet when the same is viewed from the upstream side of the primary
flow passage.
Between the contact surfaces of the intake manifold with the throttle
body 1 sealing is applied to render ineffective the communication
between the blowby gas passage 20 and the open air.
The IAC passage is constructed as follows. That is, as seen in
FIG. 5 IAC-passage opening at the side of the intake manifold is
formed by a groove 30 in the underside of the throttle body 1 while
the lower side portion of that opening is formed by an upper surface
of the intake manifold. The IAC passage opening is sealed from outside
by the gasket for sealing the interspacing between the throttle
body and the intake manifold.
The throttle valve 7 is constructed as follows. Namely, the throttle
valve 7 is a pressed article constituted by an Al plate member,
and an outer peripheral surface thereof is not subjected to machining.
The throttle valve 7 has a bore 7a so as to permit a specified amount
of air to leak when it is totally closed (see FIG. 8).
As a position spaced by 13 mm away from the mesh 12 toward the
downstream side, the mesh 12 being disposed at the inlet of the
primary flow passage, the inlet of the auxiliary flow passage is
disposed in parallel with the primary flow passage, and the auxiliary
flow passage is made eccentric by 20 mm from the axis of the primary
flow passage. The inlet portion of the auxiliary flow passage 3
is rounded by die casting. The auxiliary flow passage is formed
with a fabricated bore in such a manner that the bore is continuous
to the rounded shape and that the bore extend in parallel with the
primary flow passage. The auxiliary flow passage includes a hollow-cylinder
like member A having said fabricated bore and a hollow-cylinder
like member B intersecting the member A at right angles, the member
B crossing the primary flow passage in the form of a bridge. The
two hollow-cylinder like members A and B are made integral with
each other. At a corner defined between the members A and B is provided
a rib 3a extending in parallel with the primary flow passage, thereby
improving the fluidity of die casting and mechanical strength. The
hollow-cylinder like member B is orthogonal to that of the hollow-cylinder
like member A. The wall of the throttle body 1 which corresponds
to the hollow-cylinder like member A has a larger thickness at the
position of a hot-wire module so as to accommodate therein the break-preventing
type.
The outer configuration of the throttle valve 1 is constructed
as follows. The outer peripheral surface of the throttle body 1
is formed with a flat plate parallel to the primary flow passage
in such a manner as to be integral with the throttle body 1 whereby
the hot wire module 6 is mounted on that flat plate by means of
screws (see FIGS. 9 and 10).
According to the second embodiment explained above in connection
with FIGS. 3 to 10 the mesh 12 is provided at the inlet portion
of the primary flow passage 2. In addition, the tapered portion
8 is provided and the outlet portion 10 of the auxiliary flow passage
3 is located in the vicinity of the tapered portion 8. For these
reasons, the stabilization of air flow by the mesh 12 can be effected
simultaneously with that of air flow by location of that outlet
portion 10 in the vicinity of the tapered portion 8. Thus, even
in the case where turbulent flow is likely to occur due to a different
air cleaner or the like provided in front of the primary flow passage
2 it is possible to make a highly precise measurement of air flowrate.
According to the present invention, it is possible to reduce the
turbulence of air flow at the section of the primary flow passage
and auxiliary flow passage where air streams by restriction of the
air flow. Therefore, when the invention is applied to the hot-wire
type air flow sensor or the like, it is possible to lessen the variation
in level of the measuring output. This makes it possible to conduct
precise and stable measurement of air flow. Thus, it is possible
to control air fuel ratio of the engine with high accuracy. Thus,
it is possible to obtain with an inexpensive structure the effect
of reducing the fluctuation in number of the engine revolution of
an automobile.
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