Abstrict 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.
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.
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. 30 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 an 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 mechnism 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 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 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 an 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 dimension,
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 98 a 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, in 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 area 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 doughnat-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 inpinging 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
from 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 outlet 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 available against the backblow
or backfire. The embodiment is advantageous against the contamination
due to a long service 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 a 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 output 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 510 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. |