U.S. patent number RE34,403 [Application Number 07/810,111] was granted by the patent office on 1993-10-12 for hot-wire type air flow meter and an internal combustion engine with the same.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Nobukatsu Arai, Tadao Osawa, Yoshihito Sekine, Hiroatsu Tokuda, Mitsukuni Tsutsui, Toshifumi Usui.
United States Patent |
RE34,403 |
Arai , et al. |
October 12, 1993 |
Hot-wire type air flow meter and an internal combustion engine with
the same
Abstract
A compact hot-wire type air flow meter for an internal
combustion engine with a high measuring accuracy is provided with a
primary flow path forming an intake air passage and an auxiliary
flow path incorporating therein a hot-wire element for measuring
the intake air. The auxiliary flow path is defined by a flow path
in an axial direction of the primary flow path and a flow path in a
radial direction of the primary flow path.
Inventors: |
Arai; Nobukatsu (Ushiku,
JP), Sekine; Yoshihito (Niihari, JP),
Osawa; Tadao (Katsuta, JP), Tokuda; Hiroatsu
(Katsuta, JP), Usui; Toshifumi (Katsuta,
JP), Tsutsui; Mitsukuni (Naka, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
27319662 |
Appl.
No.: |
07/810,111 |
Filed: |
December 19, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
207525 |
Jun 16, 1988 |
04887577 |
Dec 19, 1989 |
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Foreign Application Priority Data
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Jun 17, 1987 [JP] |
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62-148993 |
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Current U.S.
Class: |
123/494; 123/478;
73/114.34 |
Current CPC
Class: |
F02D
41/187 (20130101); F02M 51/02 (20130101); G01F
5/00 (20130101); G01F 1/6842 (20130101); F02M
69/465 (20130101) |
Current International
Class: |
F02D
41/18 (20060101); F02M 69/46 (20060101); F02M
51/02 (20060101); G01F 1/684 (20060101); G01F
5/00 (20060101); F02D 005/00 () |
Field of
Search: |
;123/494,472,478,480,488
;73/178,204,861 ;338/315 ;364/431,510,588 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0173946 |
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Mar 1986 |
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EP |
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023818 |
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0000 |
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JP |
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0135127 |
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0000 |
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JP |
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0185118 |
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0000 |
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JP |
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Primary Examiner: Nelli; Raymond A.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus
Claims
We claim:
1. A hot-wire type air flow meter comprising a primary flow path
constituting an intake air passage of an internal combustion
engine, a hot-wire element for measuring intake air, and an
auxiliary flow path provided substantially entirely within said
primary flow path and having mounted therein said hot-wire element,
said auxiliary flow path having an L-shaped configuration including
a flow path portion formed in an axial direction of said primary
flow path and a flow path portion formed in a radially inward
direction of said primary flow path and extending at least half way
across said primary flow path, and wherein said auxiliary flow path
portion in the axial direction of said primary flow path is
provided eccentrically with respect to said primary flow path.
2. A flow meter according to claim 1, wherein said hot-wire element
is provided in the flow path portion formed in the axial direction
of said primary flow path.
3. The flow meter according to claim 1, wherein a throttle for
throttling air flow is provided at an inlet portion of said
auxiliary flow path.
4. The flow meter according to claim 1, wherein a member for
forming said primary flow path is integral with a member for
forming said auxiliary flow path.
5. The flow meter according to claim 1, wherein the auxiliary flow
path portion formed in the radial direction of said primary flow
path comprises a plurality of outlet openings at the end thereof
opposite said auxiliary flow path portion formed in the axial
direction.
6. A hot-wire type air flow meter according to claim 1, said
auxiliary flow path portion defined in an axial direction of said
primary flow path having a check valve for preventing a counter
flow back to said auxiliary flow path, said check valve being
located in an outlet portion of said auxiliary flow path.
7. An internal combustion engine comprising the hot-wire air flow
meter; an rpm sensor for sensing an rpm of the internal combustion
engine; a fuel injection means for injecting fuel into the sucked
air; and a controlling means for determining the corresponding fuel
injection amount on the basis of the sucked air-flow rate detected
by said hot wire type air flow sensor and the rpm detected by said
rpm sensor, and for outputting a command signal for the determined
fuel injection amount to said fuel injection means, wherein said
hot-wire type air flow meter comprises a primary flow path
constituting an intake air passage of an internal combustion
engine, a hot-wire element for measuring intake air, and an
auxiliary flow path provided substantially entirely within said
primary flow path and having mounted therein said hot-wire element,
said auxiliary flow path having an L-shaped configuration including
a flow path portion formed in an axial direction of said primary
flow path and a flow path portion formed in a radially inward
direction of said primary flow path and extending at least half way
across said primary flow path, and wherein said auxiliary flow path
portion in the axial direction of said primary flow path is
provided eccentrically with respect to said primary flow path.
8. A hot-wire type air flow meter comprising a hollow body forming
a primary flow path constituting an intake air passage of an
internal combustion engine; a hot wire element for measuring intake
air; and an auxiliary flow path formed in a radial arm disposed in
said primary flow path within said hollow body and having said
hot-wire element mounted therein; said radial arm having a bore
extending therethrough in the direction of said primary flow path,
a groove in the downstream surface thereof and communicating with
said bore, and a cover plate secured over said groove to form said
groove into a channel having an opening into said primary flow path
serving as an outlet for said auxiliary flow path.
9. A hot-wire type air flow meter as claimed in claim 8, wherein
said bore communicates with said groove intermediate the ends of
said groove and said cover plate covers said groove so as to
provide a pair of outlets for said auxiliary flow path at opposite
ends of said groove.
10. A hot-wire type air flow meter as claimed in claim 8, wherein
said radial arm extends completely across said primary flow path
within said hollow body.
11. A hot-wire type air flow meter comprising a hollow body forming
a primary flow path constituting an intake air passage of an
internal combustion engine; a hot wire element for measuring intake
air; and an auxiliary flow path formed in a circumferential
projection extending into said primary flow path within said hollow
body and having said hot wire element mounted therein; said
circumferential projection having a bore extending therethrough in
the direction of the primary flow path, a circumferential groove in
the downstream surface thereof and communicating with said bore,
and a cover plate secured over said downstream surface to form said
groove into a channel having an opening into said primary flow path
and serving as an outlet for said auxiliary flow path. .Iadd.
12. A thermal type air-flow meter, comprising a body member forming
a primary flow path constituting an intake air passage of an
internal combustion engine, a thermal resistor for measuring an
intake air, an auxiliary flow path provided in said primary flow
path and having said thermal resistor mounted thereon, a projecting
portion integrated with said body member forming said primary flow
path and having the auxiliary flow path formed thereon, said
primary flow path having in the neighborhood of an outlet of the
auxiliary flow path, a cross-sectional area which is less than the
cross-sectional area at the inlet of the auxiliary flow path, with
the formation of said projecting portion changing between said
outlet said inlet. .Iaddend. .Iadd.13. A thermal type air flow
meter as claimed in claim 12, further comprising a circuit unit
mounted on a outer portion of said body forming said primary air
flow path for taking out as an electrical signal a measure of heat
released from said thermal resistor to the air flowing in said
auxiliary path, a molding member containing a wiring element for
electrically connecting said circuit unit to said thermal resistor,
and said projecting portion integrated with said body forming with
said body a reducing cross-sectional area portion of said primary
flow path. .Iaddend. .Iadd.14. A thermal type air flow meter as
claimed in claim 12, wherein said projecting portion formed in said
primary flow path connects an inner wall of the primary flow path
at the location of the circuit unit mounted on the outer portion of
the body forming the primary flow path to the inner wall opposite
thereto through a center portion of the primary flow path, thereby
dividing the primary flow path into two sections. .Iaddend.
.Iadd.15. A thermal type air flow meter as claimed in claim 13,
wherein said molding member containing the wiring element passes
through said projecting portion and is integrated with said circuit
unit, thereby allowing the thermal resistor to be disposed in said
auxiliary flow path coincident with a central axis of the primary
flow path. .Iaddend. .Iadd.16. A thermal type air flow meter as
claimed in claim 12, wherein said projecting portion in which said
auxiliary flow path is formed is provided in a central portion of
the primary flow path through a rib integrated with the body
forming said primary flow path, and a portion of said auxiliary
flow path downstream of said thermal resistor is formed by part of
a wall surface of said projecting portion and a cover member
serving as a counter flow member. .Iaddend. .Iadd.17. A thermal
type air flow meter, comprising a body forming a primary flow path
constituting an intake air passage of an internal combustion
engine, a projecting member formed integral with said body and
disposed in said primary flow path so as to restrict the
cross-sectional area of said primary flow path by amount which vary
along the length of said projecting member according to a
predetermined curvature of said projecting member. .Iaddend.
.Iadd.18. An air flow meter comprising a primary flow path
constituting an intake air passage of an internal combustion
engine, a thermal-type element for measuring intake air, and an
auxiliary flow path provided substantially entirely within said
primary flow path and having mounted therein said element, said
auxiliary flow path having an L-shaped configuration including a
flow path portion formed in an axial direction of said primary flow
path and a flow path portion formed in a radially inward direction
of said primary flow path and extending at least half way across
said primary flow path, and wherein said auxiliary flow path
portion in the axial direction of said primary flow path is
provided eccentrically with respect to said primary flow path.
.Iaddend. .Iadd.19. A flow meter according to claim 18, wherein
said element is provided in the flow path portion formed in the
axial direction of said primary flow path. .Iaddend. .Iadd.20. The
flow meter according to claim 18, wherein the throttle for
throttling air flow is provided at an inlet portion of said
auxiliary flow path. .Iaddend. .Iadd.21. The flow meter according
to claim 18, wherein a member for forming said primary flow path is
integrated with a member for forming said auxiliary flow path.
.Iaddend. .Iadd.22. The flow meter according to claim 18, wherein
auxiliary flow path portion formed in the radial direction of said
primary flow path comprises a plurality of outlet openings at the
end thereof opposite said auxiliary flow path portion formed in the
axial direction. .Iaddend. .Iadd.23. A flow meter according to
claim 18, said auxiliary flow path portion defined in an axial
direction of said primary flow path having a check valve for
preventing a counter flow back to said auxiliary flow path, said
check valve being located in an outlet portion of said auxiliary
flow path. .Iaddend. .Iadd.24. An internal combustion engine
comprising an air flow meter; an rpm sensor for sensing an rpm of
the internal combustion engine; a fuel injection means for
injecting fuel into the sucked air; and a controlling means for
determining the corresponding fuel injection amount on the basis of
the sucked air flow rate detected by said air flow meter and the
rpm detected by said rpm sensor, and for outputting a command
signal for the determined fuel injection amount to said fuel
injection means, wherein said air flow meter comprises a primary
flow path constituting an intake air passage of an internal
combustion engine, a thermal-type element for measuring intake air,
and an auxiliary flow path provided substantially entirely within
said primary flow path and having mounted therein said element,
said auxiliary flow path having an L-shaped configuration including
a flow path portion formed in an axial direction of said primary
flow path and a flow path portion formed in a radially inward
direction of said primary flow path and extending at least half way
across said primary flow path, and wherein said auxiliary flow path
portion in the axial direction of said primary flow path is
provided eccentrically with respect to said primary flow path.
.Iaddend. .Iadd.25. A air flow meter comprising a hollow body
forming a primary flow path constituting an intake air passage of
an internal combustion engine; a thermal-type element for measuring
intake air; and an auxiliary flow path formed in a radial arm
disposed in said primary flow path within said hollow body and
having said element mounted therein; said radial arm having a bore
extending therethrough in the direction of said primary flow path,
a groove in the downstream surface thereof and communicating with
said bore, and a cover plate secured over said groove to form said
groove into a channel having an opening into said primary flow path
serving as an outlet for said auxiliary flow path. .Iaddend.
.Iadd.26. A air flow meter as claimed in claim 25, wherein said
bore communicates with said groove intermediate the ends of said
groove and said cover plate covers said groove so as to provide a
pair of outlets for said auxiliary flow path at opposite ends of
said groove. .Iaddend. .Iadd.27. A air flow meter as claimed in
claim 25, wherein said radial arm extends completely across said
primary flow path within said hollow body. .Iaddend. .Iadd.28. A
air flow meter comprising a hollow body forming a primary flow path
constituting an intake air passage of an internal combustion
engine; a thermal type element for measuring intake air; and an
auxiliary flow path formed in a circumferential projection
extending into said primary flow path within said hollow body and
having said element mounted therein; said circumferential
projection having a bore extending therethrough in the direction of
the primary flow path, a circumferential groove in the downstream
surface thereof and communicating with said bore, and a cover plate
secured over said downstream surface to form said groove into a
channel having an opening into said primary flow path and serving
as an outlet for said auxiliary flow path. .Iaddend.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a hot-wire type air flow meter,
and more particularly to a hot-wire type air flow meter for an
automotive internal combustion engine, which constitutes an intake
system of the internal combustion engine, and is adapted to detect
and control the flow rate of intake air.
As shown in, for example, Japanese Utility Model Unexamined
Publication No. 56-135127 and Japanese Patent Unexamined
Publication No. 60-185118, there has been provided a conventional
passage structure for a hot-wire type air flow meter for an
automotive engine, in which an auxiliary flow path is formed in an
intake pipe; a hot-wire element is arranged in the auxiliary flow
path; an obstacle or a complicated bent flow path that is long in
the axial direction is provided downstream of the hot-wire element
for the purpose of protecting the hot-wire element against a
backfire or a backblow of the engine and for the purpose of
preventing an abnormal output of the hot-wire element caused by the
pulsation of the engine. In such a flow meter, since the auxiliary
path portion including the hot-wire element is formed in such
manner as to exposed to the primary flow, an output error caused by
the temperature increase of the flow meter body is small. However,
this arrangement requires a long physical length in the axial
direction and a large number of mechanical parts which are
difficult to mount. Therefore, this arrangement suffers from
defects in compactness and cost.
Also, as disclosed in, for example, Japanese Patent Unexamined
Publication Nos. 57-23818 and 57-113926, there has been proposed an
arrangement in which a hot-wire type air flow meter and a throttle
valve means are disposed close to each other in an integral body.
In Japanese Patent Unexamined Publication No. 57-23818, the same
techniques as those in the foregoing two publications are adopted
in the arrangement in which the auxiliary passage within which the
hot-wire element is disposed is defined by a straight pipe and is
formed in the central portion of the primary passage. However, in
the publication '818, there is no protection for the hot-wire
element against backfire and backblow of the engine. The throttle
valve downstream of the primary flow might serve as a protection
means under the condition where it is almost closed, but the
throttle valve will have no use as protection means under the full
or almost full open condition thereof. Also, in addition to this
problem, this arrangement suffers from another problem in which the
flow within the auxiliary flow path tends to become unstable in
response to the movement of the throttle valve. Japanese Patent
Unexamined Publication No. 57-113926 discloses an auxiliary flow
path in which a hot-wire element is disposed within a body wall
having a large thermal capacity and having no wide relative
transfer area, said auxiliary flow path having an L-shape formed by
a first flow path parallel to a primary flow and a second flow path
perpendicular to the first flow path. With such an arrangement, it
is possible to protect the hot-wire element against blowback or
backfire of the engine. However, due to the structure of the
auxiliary flow path, since air of the primary flow cannot flow
around the auxiliary flow path wall, the temperature of the
auxiliary flow path wall is highly increased due to the heat
generated by the hot-wire element as well as the heat transferred
from the engine. As a result, the air within the auxiliary flow
path is heated so that the difference in temperature between the
air in the auxiliary flow path and the air in the primary flow path
is large. Thus, it is impossible to exactly measure the flow rate
of the intake air.
The foregoing prior art is silent with respect to the need for
reduction of the pipe length between the hot-wire type air flow
meter and the throttle valve means. Therefore, the prior art
suffers from the problems of increase of pressure loss in the
intake passage and of increase of weight and cost of the equipment.
Moreover, the prior art encounters the following difficulties: (1)
a heat generation of the hot-wire element; (2) a temperature
increase of the auxiliary flow path wall around the hot-wire
element due to thermal invasion from the outside, that is, an error
due to a difference between a temperature of the actual intake air
and the temperature of the air flowing through the auxiliary flow
path while impinging against the hot-wire element and a temperature
compensation element; (3) a countermeasure against a change of the
flow rate distribution ratio between the primary flow path and the
auxiliary flow path due to the swirl or change of the intake air or
the change of flow downstream of the flow meter, even if the
constant distribution is intended; a reduction of flow turbulence
within the auxiliary flow path, that is, the reduction of the
output noises; (4) a protection for the elements against the
counterflow due to the backblow or backfire and the pulsation, and
(5) a countermeasure against abnormal output.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a
hot-wire type air flow meter which is compact with a high measuring
precision.
Another object of the present invention is to provide an internal
combustion engine which is capable of controlling an air/fuel ratio
in a suitable manner with use of the above-described hot-wire type
air flow meter.
In order to attain these and other objects, according to the
present invention, there is provided a hot-wire type air flow meter
comprising a primary flow path constituting an intake air passage
of an internal combustion engine, a hot-wire element for measuring
an intake air, and an auxiliary flow path provided in the primary
flow path, having therein said hot-wire element, the auxiliary flow
path being defined by a flow path formed in an axial direction of
the primary flow path and flow paths formed in a radial direction
of the primary flow path.
According to the present invention, there is provided an internal
combustion engine comprising the above-described hot-wire type air
flow meter, a speed sensor for detecting an rpm of the engine, a
fuel injection means for injecting fuel into an intake air, and a
control means for determining a fuel injection amount based upon
the rpm detected by the speed sensor and a flow rate of the intake
air detected by the hot-wire type air flow meter, and for
outputting a command signal for injecting the determined fuel
injection amount to said fuel injection means
According to the present invention, a hot-wire element is disposed
in an auxiliary flow path independent of a primary flow path,
thereby reducing an adverse effect of turbulence in the primary
flow path. Also, in the auxiliary flow path having a small diameter
relative to that of the primary flow path, a distance between the
auxiliary flow path inlet and the hot-wire element is twice longer
than the diameter of the auxiliary flow path or more, thereby
performing a rather rectification of the flow to reduce the noises.
Also, the auxiliary flow path downstream of the element is bent, so
that the flow at the bent portion and the pressure damping effect
prevent a damage of the hot-wire element due to the counter flow
and reduce the adverse effect of the pulsation. According to the
present invention, the distance from the inlet of the auxiliary
flow path to the element is twice longer than the diameter of the
auxiliary flow path or more, and the inlet of the auxiliary flow
path is constructed so that it projects into the primary flow path
at a constant distance from a body inner wall or a portion
connecting the body inner wall and the auxiliary flow path.
Furthermore, a bent auxiliary flow path having a flow path wall of
the projecting portion wall has a short axial length downstream of
the element and may be coupled substantially directly to a throttle
valve means, to thereby solve various problems due to noises,
pulsation and counter flows.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a cross-sectional view showing one embodiment of the
invention;
FIG. 2 is a cross-sectional view taken along the line II--II of
FIG. 1;
FIG. 3 is a cross-sectional view taken along the line III--III;
FIG. 4 is a cross-sectional view showing another embodiment of the
invention;
FIG. 5 is a cross-sectional view taken along the line V--V of FIG.
4;
FIG. 6 is a cross-sectional view taken along the line VI--VI of
FIG. 4;
FIG. 7 is a cross-sectional view showing another embodiment of the
invention;
FIG. 8 is a cross-sectional view taken along the line VIII--VIII of
FIG. 7;
FIG. 9 is a cross-sectional view showing another embodiment of the
invention;
FIG. 10 is a cross-sectional view taken along the line X--X of FIG.
9;
FIG. 11 is a cross-sectional view showing another embodiment of the
invention;
FIG. 12 is a cross-sectional view taken along the line XII--XII of
FIG. 11;
FIG. 13 is a cross-sectional view showing another embodiment of the
invention;
FIG. 14 is a cross-sectional view taken along the line XIV--XIV of
FIG. 13;
FIG. 15 is a cross-sectional view taken along the line XV--XV of
FIG. 13;
FIG. 16 is a cross-sectional view showing a part of an auxiliary
flow path according to an embodiment of the invention;
FIG. 17 is a cross-sectional view taken along the line XVII--XVII
of FIG. 16;
FIG. 18 is a cross-sectional view showing a part of an auxiliary
flow path according to another embodiment of the invention;
FIG. 19 is a cross-sectional view taken along the line XIX--XIX of
FIG. 18;
FIG. 20 is a cross-sectional view showing another embodiment of the
invention;
FIG. 21 is a cross-sectional view taken along the line XXI--XXI of
FIG. 20;
FIG. 22 is a cross-sectional view showing another embodiment of the
invention;
FIG. 23 is a cross-sectional view taken along the line XXIII--XXIII
of FIG. 22;
FIGS. 24, 25, 26 and 27 are cross-sectional views showing other
embodiments of the invention;
FIG. 28 is a cross-sectional view taken along the line
XXVIII--XXVIII of FIG. 27;
FIG. 29 shows a modification of a part shown in FIG. 27; and
FIG. 20 is a view showing a system of an electronic fuel injection
means according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
One embodiment of the present invention will now be described with
reference to FIGS. 1, 2 and 3. A body 1 constitutes an intake
passage of an internal combustion engine. Intake air is introduced
from the left side in FIG. 1. The internal combustion engine is
connected on the downstream side of the flow.
The body 1 forms a substantially cylindrical primary flow path 3. A
projecting portion 2 that is formed integrally with the body 1 is
disposed in the primary flow path 3. At a tip end of the projecting
portion 2, there is provided an auxiliary flow path 4 that is
parallel to the primary flow path 3 and has inlet opening at the
central portion of the primary flow path 3. Also, a hole in
communication with the outside of the body 1 is formed in the
projecting portion 2. In that hole, there is received a mold unit
13 of a support member 11 for a hot-wire element 10 connected to a
circuit unit 14. As a result, the hot-wire element 10 and a
temperature compensation element 12 are disposed in the auxiliary
flow path 4. Downstream of the auxiliary flow path 4, a bent
auxiliary flow path 5 having a short axial length is formed by
walls 2a, 2b and 2c of the projecting portion 2 and a cover 6. A
throttle valve 20 for controlling a whole air flow rate is disposed
at the downstream side of the bent auxiliary flow path 5. The
throttle valve 20 is opened/closed by a valve drive shaft 21. A
link mechanism (not shown) connected to the shaft 21 is provided
outside the body 1. The link mechanism is normally driven by a
cable connected to an accelerator pedal of the vehicle.
Incidentally, the cover 6 is mounted at a rear end of the
projecting portion 2 by bolts 7 and 8 prior to the mounting of the
throttle valve 20 and the valve drive shaft 21.
An opening portion 4a of the auxiliary flow path 4 is mounted so
that it is separated by a distance that is twice as long as the
inner diameter of the auxiliary flow path 4 or more, from an inner
wall 1a of the body 1 and from a wall 2d of a connecting portion
between the projecting portion 2 and the body 1. Also, the opening
portion 4a is in the form of a bellmouth.
An inner wall 1a of the body 1 and an outer wall 2e or the like,
forming the auxiliary flow path 4 of the projecting portion 2 are
configured so that the flow path is .[.expended.]. .Iadd.expanded
.Iaddend.toward the upstream side. On the other hand, an inner wall
1b of the body 1 at which the throttle valve 20 is provided is
finished by machining in such manner is to have the same diameter
as other's. Before the machining work, the wall 1b is in the form
of a cone converging toward the leftside of FIG. 1. With such
technique, the flow path may be cast-molded by using removable core
molds having a division plane in the vicinity of the projecting
portion wall 2a. The core molds may be removed in the right and
left directions.
The blank arrows indicate the flow of air. Although almost of the
air entering from the left hand in FIG. 1 will flow through the
primary flow path 3, a part of the air will be introduced into the
auxiliary flow path 4. Since the inlet 4a of the auxiliary flow
path is sufficiently separated from the walls 1a and 2d, the flow
having a relatively low turbulence is introduced into the auxiliary
flow path 4.
Also, the bellmouth of the inlet 4a of the auxiliary flow path
.[.4a.]. .Iadd.4 .Iaddend.may entrain a large amount of air to
thereby increase the air flow speed in the vicinity of the inner
wall 2f of the auxiliary flow path 4. However, the friction effect
of the inner wall 2f of the auxiliary flow path 4 up to the
hot-wire element causes the flow within the auxiliary flow path 4
to be sufficiently rectified so that the flow immediately before
the hot-wire element 10 has a uniform flow speed distribution.
A ratio of a inlet diameter of the bellmouth to the diameter of the
auxiliary flow path 4 is in the range of 1.6 to 1.2.
Correspondingly, a ratio of the distance from the inlet to the
hot-wire element 10 to the diameter of the auxiliary flow path 4 is
in the range from about 4 to 2. However, this relation is changed
in accordance with actual dimensions of the diameter of the
auxiliary flow path 4 but is not a so-called one-to-one
relation.
In the downstream of the hot-wire element 10, the flow is curved
upwardly to be introduced into the bent auxiliary flow path 5, and
subsequently is impinged against the inner wall of the body to flow
out to the right and left through the outlets 5a and 5b to be
immerged into the main flow. Such a flow path arrangement has an
effect to damp the counter flow from the engine and to prevent the
propagation of the pulsation to the vicinity of the hot-wire
element 10.
According to the foregoing embodiment, with a short axial
dimensions, it is possible to provide a hot-wire type air flow
meter for an internal combustion engine, which is free from various
problems such that noises are made due to the turbulence of flow,
unstable outputs are generated due to the affect of the pulsation,
and the hot-wire element is damaged due to the backblow of the
engine. Namely, the advantages of the compactness, the lightweight
and the low cost may be enjoyed. The flow meter body and the
throttle valve unit body that cannot be formed integrally in the
prior art may be formed in a single integral body unit. Since the
length of the intake passage is reduced, the arrangement is
available in reduction in unduly pressure loss, lightweight and low
cost.
FIGS. 4 to 6 show a second embodiment of the invention. The
difference over the first embodiment shown in FIGS. 1 to 3 will be
explained. A projecting portion 42 is formed integrally with the
upper and lower walls of a body 41 (or is integral with the right
and left walls of the body, i.e., in the axial direction of the
throttle valve drive shaft 21, if desired). With such an
arrangement, it is possible to form bent auxiliary flow paths 45
downstream of the auxiliary flow path 44 in the up and down
directions. Also, the outlet surface of the auxiliary flow path 44,
i.e., a rear end face 42a of the projecting portion 42 is made in a
flat surface. This makes it easy to perform a machining work
because of the reduction of the surface roughness. Also, an
auxiliary flow path cover 46 is formed in U-shape in cross section
unlike the simple planar plate as in the first embodiment. The
cover 46 is also mounted on the rear end face of the projecting
portion 42 by means of bolts 7 and 8. Since the auxiliary flow path
46 is made of a member separated from the body, it is possible to
finish the rear end face 42a of the projecting portion 42.
Therefore, it is possible to reduce the surface roughness of the
inner surface of the bent auxiliary flow paths 45 as a whole. Also,
it is possible to obtain a good sealing effect on the connecting
portions. This is effective to avoid the case where the performance
of the hot wire element 10 is unstable due to the unstability of
the flow within the bent auxiliary flow paths and the insufficiency
of the pressure seal against the primary flow path.
It is apparent that, in the first embodiment, the same effect as in
the second embodiment may be ensured by making the rear end face of
the projecting portion 2 flat and using the U-shaped cover instead
of the planar cover 6.
The effect of the second embodiment in which the bent auxiliary
flow paths 45 are provided in the up and down direction is the
interference effect in front of the auxiliary flow path 44 in the
case where the pulsation is produced. Namely, the second embodiment
is more available against the pulsation. However, in the second
embodiment, since the flow path resistance is decreased, it is
desired that some modification such as reduction of the area of the
outlets 45a to 45d be made in conformity with the engine.
There is no difference in structural effect between the first and
second embodiments.
FIGS. 7 and 8 show a third embodiment of the invention. An
auxiliary flow path 74 in parallel to a primary flow path 73 is
provided at a portion near to the inner wall of the body 71 rather
than the tip end of the projecting portion 72 from the body 71. The
bent auxiliary flow path 75 downstream of the auxiliary flow path
74 is defined by a rear end wall 72a of the projecting portion 72
and an auxiliary flow path cover 76 mounted on the wall 72a by a
bolt 7. The rear end portion of the projecting portion 72 extends
close to the central portion of the primary flow path 73.
Therefore, the flow within the bent auxiliary flow path 75 is first
directed from the inner circumferential wall of the body 71 along
the wall 72a toward the central portion of the primary flow path
73. Then, the air is made to flow from the bent auxiliary flow path
outlet 75a toward the right and left and downwardly. Downstream of
the bent path 75, the throttle valve 20 and the drive shaft 21 are
disposed within the integral body in the same manner as in the
first and second embodiments.
According to the features of the third embodiment, it is possible
to reduce a length of a molded portion 83 integral with the circuit
unit 84, which is available in cost. Also, since the projecting
portion 72 may be relatively short, it is possible to reduce the
flow resistance of the primary flow path 73. Also, since the mass
corresponding to the overhang portion is small, the structure is
advantageous against the vibration in comparison with the first
embodiment. However, the turbulence in the flow entering into the
auxiliary flow path 74 is somewhat larger. Therefore, it is desired
that, for that reason, the diameter of the bellmouth be enlarged
and the distance to the hot-wire element 10 of the auxiliary flow
path 74 be elongated.
The basic effect of the third embodiment is substantially the same
as that of the first embodiment.
FIGS. 9 and 10 shows a fourth embodiment of the invention.
Unlike the first through third embodiments, a body 91 is made of a
single unit of a hot-wire type flow meter. A projecting portion 92
is formed substantially in the same manner as the first embodiment.
An auxiliary flow path 94 is formed at an end of the projecting
portion 92. A part of the bent auxiliary flow path 95 is formed
along a rear end face 92a of the projecting portion 92. The rest of
the bent auxiliary flow path 95 is formed so as to project outside
the primary flow path 93 and to enter the body 91 to be branched
into the right and left sides from the upper side in the range of
about 90 degrees as shown in FIG. 10. Therefore, the outlets of the
bent auxiliary flow path 95 are located on both sides as shown in
FIG. 10. The flow path surface of the portion downstream of the
bent auxiliary flow path 95 is formed by a gasket 96. Namely, a
body of the throttle valve unit independent of the flow meter body
91 is coupled through the gasket to the flow meter body with bolt
holes 98a to 98d.
Since the bent auxiliary flow path 95 may be elongated, the fourth
embodiment may be applied to an engine which suffers from a large
pulsation.
FIGS. 11 and 12 show a fifth embodiment of the invention, which a
reinforcement rib 8 is added to the structure shown in the first
embodiment. More specifically, there are provided a part for
forming the auxiliary flow path 4 at the tip end of the projecting
portion 2 of the first embodiment and a rib 8 connected to an
opposite inner wall of the body 1. With such an arrangement, it is
possible to increase a strength for an earthquake-proof and reduce
a deformation of the projecting portion 2 during the cast molding.
The other effects are the same as those of the first
embodiment.
FIGS. 13 to 15 show a sixth embodiment of the invention. A
projecting portion 132 from the body 131 is formed by ribs 137 and
138 formed in a direction perpendicular to the mold portion 13
connected to the circuit unit 14 and a cylindrical portion 132
defining the auxiliary flow path 134. Therefore, the molded portion
13 of the circuit unit 14 is passed through a wall of the body 131
and once crosses the primary flow path 133 to penetrate a hole of
the projecting portion 132, so that the hot element 10 is disposed
within the auxiliary flow path 134. An O-ring 139 is disposed at a
portion of the molded portion 13 inserted into the hole of the
projecting portion 132. The O-ring 139 serves to impart the seal
effect between the primary flow path 133 and the auxiliary flow
path 134. A bent auxiliary flow path 135 is defined by a rear end
face of the projecting portion 132 and a cover 136. Two outlets
135a and 135b are formed in the up and down direction of the cover
136. The outlets 135a and 136b are formed so that the flow
therethrough is rather returned back to the upstream side. This is
because the length of the bent auxiliary flow path is short and the
orientation of the outlets may compensate for this shortage.
The advantage of this embodiment is that, since the projecting
portions 137, 138 and 132 are located in the direction of the
throttle valve drive shaft 21 that is inherently an obstacle or
block against the primary flow path 133, it is possible to reduce
the substantial flow resistance within the primary flow path 133.
Also, in this embodiment, the inlet portion 133a of the primary
flow path 133 is in the form of a bellmouth to thereby impart the
rectifying effect.
The various embodiments of the invention have been described but it
is apparent that in any of the embodiments, the cover member of the
bent auxiliary flow path is not necessarily mounted by bolts. Any
other mounting means such as bonding or adhesive may be used and it
is possible to seal the contact portion of the projecting portion
rear face and the cover with seal material.
FIGS. 16 and 17 show a seventh embodiment of the invention which is
substantially the same structure as that of the sixth embodiment.
However, in the seventh embodiment, flow paths 140a, 140b or the
like perpendicular to the primary flow are formed in the cover 139.
According to this embodiment, since a flow path cross section of
each of the flow path 140a, 140b may be reduced, it is possible to
further reduce the axial length.
FIGS. 18 and 19 show an eighth embodiment of the invention which is
substantially the same structure as that of the sixth embodiment.
However, in the eighth embodiment, the flow path 142 perpendicular
to the primary flow is in the form of a disc, that is, if the
bypass flow path 134 is included, the flow path 142 is in the form
of a mushroom. According to the present embodiment, it is possible
to reduce the axial length in comparison with the seventh
embodiment.
FIGS. 20 and 21 show a ninth embodiment of the invention. The
projection portion 210d, provided with the auxiliary flow path 212,
which is integral with the body 210 and projected into the primary
flow path 211 is formed through about 90 degrees along the inner
wall of the body. Therefore, the auxiliary flow path 212c
perpendicular to the auxiliary flow path 212b in parallel with the
primary flow path 211 is oriented in the radial direction and in
the circumferential direction to form a semicircular shape. The
fluid resistance of the auxiliary flow path 212c is composed of a
passage configuration resistance and a frictional resistance of an
elbow passage having a square cross section of small curvature of
about 90 degrees and a substantially right angled bend. By
selecting the passage cross sectional are of the auxiliary flow
path 212c, it is possible to increase the fluid resistance of this
part in comparison with the foregoing embodiment. The downstream
wall of the auxiliary flow path 212c against the primary flow is
formed by the planar cover 213 which is fixed to the projecting
wall 210d by means of bolts 214a and 214b. In this embodiment, in
the case where an injector is to be disposed before the throttle
valve 3 due to some causes, for example, the application of a
single point injection system, the above-described arrangement is
necessary. In this case, for instance, it may be the case that the
throttle valve shaft is arranged at an angle of 45 degrees with
respect to the direction in which the molded portion 2c for holding
the hot-wire element is oriented. This is available to reduce the
pressure loss as a whole at a high flow rate. The other effects of
the ninth embodiment are the same as those of the first through
third embodiments.
FIGS. 22 and 23 show a tenth embodiment of the present invention.
In this embodiment, it is intended that the auxiliary flow path
having a relatively large fluid resistance is formed in the
projecting portion having a relatively small volume. More
specifically, a flow path 222c perpendicular to the auxiliary flow
path 222b in which the hot-wire element is disposed is formed in a
doughnut-shape. With such an arrangement, the projecting portion
220d of the body 220 projecting into the primary flow path 221 is
small in comparison with the flow passage length of the auxiliary
flow path 222c. The wall of the auxiliary flow path 222c on the
downstream side against the primary flow is formed by a planar
cover 223 fixed to the projecting portion 220 by a bolt 224 or the
like. The flow resistance of the auxiliary flow path 222c is
composed of a passage configuration resistance of an elbow having a
square cross section with a relatively high curvature of about 270
degrees and a substantially right-angled bend, and a frictional
resistance of the somewhat longer passage length. Except for the
case that the cross section of the auxiliary flow path 222c is
extremely increased, it is possible to increase the fluid
resistance, i.e., the equivalent length of the passage in
comparison with the foregoing embodiments. Thus, the arrangement of
the tenth embodiment is available for an internal combustion engine
in which a backblow is large, a backfire is likely to be generated
or an intake pulsation is large. The other effects of the tenth
embodiment are the same as those of the first through third
embodiments.
FIG. 24 shows an eleventh embodiment of the invention which
realizes the auxiliary flow path having a relatively large fluid
resistance with a structure in which the axial dimension is not
increased. In a probe holder block 230 which is a separate member
from a body 240 and is coupled to a circuit unit 2, the entire
auxiliary flow path 242 is formed of an auxiliary flow path 242b in
parallel with the primary flow path 241, an auxiliary flow path
242c having a square cross section and directed perpendicular to
the flow path 242b, an auxiliary flow path 242d directed to the
upstream side against the primary flow, perpendicular to the
auxiliary flow path 242c, and an auxiliary flow path 242e directed
in the radial direction, perpendicular to the auxiliary flow path
242d. The downstream wall of the auxiliary flow path 242c relative
to the primary flow is formed by a planar cover 243 which is fixed
to the holder block 230 by means of a bolt 244. In this embodiment,
since the length of the auxiliary flow path 242b upstream of the
hot-wire element 2a is short due to its structure, a mesh member
245 is provided at an inlet opening of the body 240. Also, the
upstream wall of the holder block 230 relative to the primary flow
is extended further into the primary flow relative to the outlet of
the auxiliary flow path 242e so that the primary flow is prevented
from impinging directly to the outlet of the auxiliary flow path
242e, thus stabilizing the static pressure thereat and the flow
within the auxiliary flow path to reduce the noises.
In this embodiment, the fluid resistance of the auxiliary flow path
242 is composed of a frictional resistance in proportion to the
long passage length and a passage configuration resistance element
composed of three right-angled bends. The equivalent length of the
passage the eleventh embodiment is longer than that of the tenth
embodiment. In other words, the effect of this embodiment is strong
against the backblow, backfire and intake pulsation as in the tenth
embodiment. Also, if the fluid resistance of the auxiliary flow
path, and in particular, the configuration resistance are
increased, it is possible to decrease the flow rate distribution
ratio of the auxiliary flow path to the primary flow path at a high
flow rate (high speed region). This makes it possible to reduce the
flow rate in the vicinity of the hot-wire element and is available
against the contamination due to adhesion of dust or foreign
matters.
In this embodiment, in view of the working formation of the
auxiliary flow path 242, the auxiliary flow path 242 is separately
formed form the body 240 and detachably mounted to the body 240.
However, it is apparent that, if the formation of the auxiliary
flow paths 242c and 242e is carried out by boring from the outside
of the body, it is possible to form the auxiliary flow path
integrally with the body.
FIG. 25 shows a twelfth embodiment of the invention, in which an
auxiliary flow path 252b in parallel to the primary flow path 251
an an auxiliary flow path 252c perpendicular to the auxiliary flow
path 252b are formed in a projecting portion 250d of the body 250,
and further an outlet opening 252d of the auxiliary flow path is
formed so as to be directed in the downstream direction of the
primary flow with a check valve 254. Since the output opening 252d
is perpendicular to the primary flow, if the counter flow due to
the backblow or backfire is produced, without any modification, the
counter flow within the auxiliary flow path is remarkable in
comparison with the foregoing embodiments in which the oullet
surface of the auxiliary flow path is in parallel with the primary
flow. This is avoided by the check valve 254. The check valve 254
made of thin plate material is supported by a retainer 255 that is
short in length than the check valve 254 and fixed thereto by a
bolt 256. Also, in order to largely hinder the flow from the
auxiliary flow path outlet 252, the check valve 254 is constructed
so that it is normally opened toward the retainer 255 as shown in
FIG. 25. When the counter flow is generated, the dynamic pressure
is applied to the check valve 255 to thereby clog the auxiliary
flow path 252d to prevent the counter flow from entering into the
auxiliary flow path 252.
The fluid resistance of the auxiliary flow path 252 of this
embodiment is composed of a passage configuration resistance of the
two right-angled bends and a passage frictional resistance and is
smaller than that of the eleventh embodiment. However, because of
the provision of the check valve, this embodiment is a available
against the backblow or backfire. The embodiment is advantageous
against the contamination due to a long surface life as described
in conjunction with the eleventh embodiment. Incidentally, the
auxiliary flow path 252c of this embodiment is formed in a circular
cross section from the outside of the body 250. Blind plugs 253 and
257 are provided for the respective flow path formations.
FIG. 26 shows thirteenth embodiment of the invention. According to
this embodiment, it is possible to attain a simple structure which
increase the fluid resistance of the auxiliary flow path as in the
tenth to twelfth embodiments, that is, which is suitable for an
internal combustion engine in which suffers from a large backblow
or backfire or for an internal combustion engine which generates a
large intake pulsation, and which is advantageous against the
foreign matter adhesion for a long time. A throttle 262e is
provided downstream of a hot-wire element 2a of an auxiliary flow
path 262b in parallel to a primary flow, formed in a projecting
portion 260d of a body 260, thereby reducing a cross sectional area
(diameter) of the auxiliary flow path 262c perpendicular to the
primary flow relative to the auxiliary flow path 262b parallel to
the primary flow. Also, an enlarged portion 262f is provided before
an outlet 262d of the auxiliary flow path 262c, so that an area of
the outlet 262d is equal to that of the inlet 262a of the auxiliary
flow path 262b.
By providing the throttle 262e and reducing the diameter of the
flow path 262c to thereby add the passage configuration resistance
of reduction and enlargement, it is possible to increase the fluid
resistance of the auxiliary flow path downstream of the hot-wire
element 2a, in particular, the fluid resistance against the counter
flow. Accordingly, it is possible to attain the foregoing effects.
Also, the area of the outlet 262d is increased and the cross
sectional area of the flow path 260d is set to the relatively large
level, so that it is possible to reduce the static pressure loss
due to the dynamic pressure change from the inlet to the outlet and
it is possible to reduce the passage friction resistance of the
flow path 260d. Thus, the flow rate distribution ratio in the low
flow rate region may be relatively increased.
FIGS. 27 to 29 show still another embodiment of the present
invention to attain the objects of the invention.
As auxiliary flow path 272 opened to a central portion of a primary
flow path 271 of a projecting portion 270d of a body 270 is defined
only by an auxiliary flow path 272b parallel to the primary flow.
The surface of the projecting portion 270d on the downstream side
relative to the primary flow is made flat. On this surface, there
is provided a check valve 273 for closing the outlet 272d of the
auxiliary flow path when the dynamic pressure of the counter flow
is applied to that surface. The check valve 273 is backed up by a
retainer 274 that has a shorter length than that of the check valve
273. The retainer 274 is fixed to the outlet portion 270d by means
of bolts 275 and 276. A circuit unit 282 has a long molded portion
272c. A hot-wire element 282a and a temperature compensation
element 282b are disposed in the auxiliary flow path 272b.
Owing to the above-described effect of the check valve, according
to this embodiment, it is possible to realize a hot-wire type flow
meter for an internal combustion engine, with a short axial
dimension, in which the temperature characteristics are excellent.
The flow meter is resistive against the backblow or backfire of the
engine. However, in this arrangement, since the auxiliary flow path
272 has a short passage length, there are problems such that the
reduction effect of the pulsation is small and the flow rate
reduction effect in the high flow rate region is not attained.
FIG. 29 shows a partial modification of the embodiment shown in
FIG. 27. In this modification, in the auxiliary flow path 292b, a
throttle 292e is provided downstream of the hot-wire element 282a
whereby it is possible to reduce the flow rate within the auxiliary
flow path 292b in the high flow rate region and to somewhat damp
the pulsation.
The internal combustion engine to which the invention pertains will
be described with reference to FIG. 30. FIG. 30 shows a system of
the internal combustion engine provided with an electronic control
type fuel injection unit to which the automotive hot-wire type air
flow meter according to the invention is applied.
Air for cylinders 500 is sucked through an air filter 503 and is
made to flow through a connector pipe 504, a flow meter 1 and an
intake manifold 501. The flow meter 1 is provided with an auxiliary
flow path 22 projected into a primary flow path 21. A hot-wire
element 2a and a temperature compensation element 2b that is in
unison with a circuit unit 2 are provided within the auxiliary flow
path 22, thereby detecting the flow rate of air through this
portion to obtain an outlet relative to the overall intake air flow
rate. A throttle valve 3 for controlling the intake air flow rate,
that is associated with an acceleration pedal of an vehicle is
provided in the passage of the flow meter 1. Furthermore, an idle
speed control (ISC) valve 8 for controlling a flow rate at the
throttle valve fully closed condition (idle speed) is disposed in
the flow meter 1.
On the other hand, fuel is injected into the intake manifold 501
from an injector 507 by an injection pump 506 coupled to a fuel
reservoir 505 and is supplied to the engine 500 together with the
air.
Into a control unit 501, there are inputted an output signal of the
hot-wire element circuit unit 2, a rotational angle signal of the
throttle valve 3, an output signal of an oxygen concentration
sensor 508 provided in an exhaust manifold 511, an output signal of
an engine rpm sensor 509 and the like. Thus, a fuel injection
amount and the ISC valve opening degree are calculated. In response
to the calculation results, the injector 507, the ISC valve 8 and
the like are controlled. Also, a data table of the fuel injection
amounts corresponding to the intake air flow rate and the rpm is
stored in the control unit 510, so as to immediately determine the
intake air flow rate on the basis of the hot-wire element and the
fuel injection amount on the basis of the rpm from the rpm sensor,
thus controlling the fuel injection amount to be injected from the
injection unit.
* * * * *