Abstrict An axial flow thermo-type air flow meter for internal combustion
engines has a spider disposed in a main air passage formed in a
body and having formed therein an auxiliary air flow passage including
an axial auxiliary air flow passage portion accommodating a heat-generating
resistor element for detecting a rate of engine intake air flow.
The auxiliary air flow passage also includes more than one radial
air flow passage portions which are connected to the axial air flow
passage portion and curved and turned at their radially outer ends
and then extend radially inwardly to outlet ends open to the main
air passage, whereby the total length of the auxiliary air flow
passage is increased to decrease the influence of pulsation of engine
intake air flow on the air flow meter. Positioning of the outlet
openings of the auxiliary air flow passage within a range of a radius
from the axis of the main air flow passage, which radius is 1/2
of the radius of the main air flow passage, is effective to reduce
fluctuation of the electric output of the air flow meter due to
an unbalanced air flow velocity distribution occurring upstream
of the air flow meter.
Claims What is claimed is:
1. An axial flow thermo-type air flow meter comprising: a body
having formed therein a main air flow passage through which an intake
air flows in a radial wall portion disposed in said main air flow
passage and having formed therein an auxiliary air flow passage
through which a part of the intake air flows, said auxiliary air
flow passage accommodating a heat-generating resistor element for
detecting a rate of engine intake air flow, said auxiliary air flow
passage including an axial auxiliary air flow passage portion having
an inlet open to said main air flow passage and extending parallel
to said main air flow passage and at least one radial auxiliary
air flow passage portion extending in a direction substantially
perpendicular to said main air flow passage and having an outlet
open to said main air flow passage, said heat-generating resistor
element being disposed in said axial auxiliary air flow passage
portion, and wherein said radial auxiliary air flow passage portion
is formed in one plane perpendicular to the axis of the main air
flow passage and includes a first part which extends substantially
linearly in a radial direction from said axial auxiliary air flow
passage portion to a point adjacent an inner peripheral wall of
said main air flow passage, a second part connected to said first
part and which changes the direction of the air flow through said
radial auxiliary air flow passage portion at said point by substantially
180.degree. and a third part which extends substantially linearly
in a radial direction from said second part to said outlet.
2. An axial flow thermo-type air flow meter according to claim
1 wherein second part of said radial auxiliary air flow passage
portion comprises at least one curved portion disposed between said
first and third parts.
3. An axial flow thermo-type air flow meter according to claim
1 wherein said auxiliary air flow passage includes a single radial
auxiliary air flow passage portion connected to said axial auxiliary
air flow passage portion and a plurality of air flow passage portions
which branch from said single radial air flow passage portion and
extend to respective outlet openings.
4. An axial flow thermo-type air flow meter according to claim
1 wherein the inlet opening of said axial auxiliary air flow passage
portion is located substantially at a center of said main air flow
passage, wherein said auxiliary air flow passage includes a plurality
of radial auxiliary air flow passage portion formed in a plurality
of different directions, and wherein said radial wall portion has
a shape which corresponds to said radial auxiliary air flow passage
portions formed in the plurality of different directions and divides
said main air flow passage into a plurality of main air flow passage
portions, the outlet openings of said radial auxiliary air flow
passage portions respectively opening to said plurality of main
air flow passage portions.
5. An axial flow thermo-type air flow meter according to claim
1 wherein the inlet opening of said axial auxiliary air flow passage
portion is located substantially at a center of said main air flow
passage, wherein said radial auxiliary air flow passage portion
has at least one curved portion for changing a direction of the
air flow by 180.degree. in a plane substantially perpendicular to
the axis of said main air flow passage, and wherein the outlet opening
of said auxiliary air flow passage is located at a given position
of said main air flow passage.
6. An axial flow thermo-type air flow meter according to claim
1 wherein the inlet opening of said axial auxiliary air flow passage
portion is located within said main air flow passage at a given
position offset from a center of said main air flow passage, wherein
said radial auxiliary air flow passage portion has at least one
curved portion for changing the direction of the air flow by 180.degree.
in a plane substantially perpendicular to said main air flow passage,
and wherein the outlet opening of the auxiliary air flow passage
portion is located at a given position of said main air flow passage.
7. An axial flow thermo-type air flow meter according to claim
5 wherein the outlet of said radial auxiliary air flow passage
portion is located within a distance from the axis of said main
air flow passage which is 1/2 of the radius of the main air flow
passage.
8. An axial flow thermo-type air flow meter according to claim
6 wherein the outlet of said radial auxiliary air flow passage
portion is located within a distance from the axis of said main
air flow passage which is 1/2 of the radius of the main air flow
passage.
9. An axial flow thermo-type air flow meter including a body having
formed therein a main air flow passage through which an intake air
flows and a radial wall portion disposed in said main air flow passage
and having formed therein an auxiliary air flow passage through
which a part of the intake air flows, said auxiliary air flow passage
accommodating a heat-generating resistor element for detecting a
rate of engine intake air flow, said auxiliary air flow passage
including an axial auxiliary air flow passage portion having an
inlet open to said main air flow passage and extending parallel
to said main air flow passage and at least one radial auxiliary
air flow passage portion extending in a direction substantially
perpendicular to said main air flow passage and having an outlet
open to said main air flow passage, said heat-generating resistor
element being disposed in said axial auxiliary air flow passage
portion, wherein said radial auxiliary air flow passage portion
is formed in said radial wall portion such that the outlet opening
thereof is located substantially at a central portion of said main
air flow passage, and wherein said radial auxiliary air flow passage
portion includes a first part which extends radially from said axial
auxiliary air flow passage portion to a point adjacent an inner
peripheral wall of said main air flow passage, a second part extending
from said first part and which changes the direction of the air
flow through said radial auxiliary air flow passage portion by substantially
180.degree., and a third part extending from said second part radially
inwardly to said outlet.
10. An axial flow thermo-type air flow meter including a body having
formed therein a main air flow passage through which an intake air
flows and a radial wall portion disposed in said main air flow passage
and having formed therein an auxiliary air flow passage through
which a part of the intake air flows, said auxiliary air flow passage
accommodating a heat-generating resistor element for detecting a
rate of engine intake air flow, said auxiliary air flow passage
including an axial auxiliary air flow passage portion having an
inlet open to said main air flow passage and extending parallel
to said main air flow passage and at least one radial auxiliary
air flow passage portion extending in a direction substantially
perpendicular to said main air flow passage and having an outlet
open to said main air flow passage, said heat-generating resistor
element being disposed in said axial auxiliary air flow passage
portion, wherein said radial auxiliary air flow passage portion
is formed in one plane perpendicular to the axis of the main air
flow passage and includes first and second linear portions connected
by a portion which is bent in order to change the direction of the
air flow within said radial auxiliary air flow passage portion by
substantially 180.degree., with the outlet of said radial auxiliary
air flow passage portion being located within a distance from the
axis of said main air flow passage which is one-half of the radius
of the main air flow passage.
11. An axial flow thermo-type air flow meter including a body having
formed therein a main air flow passage through which an intake air
flows and a radial wall portion disposed in said main air flow passage
and having formed therein an auxiliary air flow passage through
which a part of the intake air flows, said auxiliary air flow passage
accommodating a heat-generating resistor element for detecting a
rate of engine intake air flow, said auxiliary air flow passage
including an axial auxiliary air flow passage portion having an
inlet open to said main air flow passage and extending parallel
to said main air flow passage and at least one radial auxiliary
air flow passage portion extending in a direction substantially
perpendicular to said main air flow passage and having an outlet
open to said main air flow passage, said heat-generating resistor
element being disposed in said axial auxiliary air flow passage
portion, wherein said radial auxiliary air flow passage portion
is formed in said radial wall portion such that the outlet opening
thereof is located substantially at a central portion of said main
air flow passage, and wherein said radial auxiliary air flow passage
portion is formed in one plane perpendicular to the axis of the
main air flow passage and has first and second linear portions coupled
by at least one curved portion for changing the direction of air
flow in said radial auxiliary air flow passage portion by substantially
180.degree.
Description BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a thermo-type air flow meter,
and more particularly, to an axial flow thermo-type air flow meter
suitably used to measure the rate of intake air flow in internal
combustion engines for automobiles, the axial flow thermo-type air
flow meter being of the type in which an auxiliary air flow passage
with a heat-generating resistor element for detecting the rate of
engine intake air flow accommodated therein is disposed within a
main air flow passage.
Description of the Related Art
Hot-wire type air flow meters have been proposed in, for example,
Japanese Patent Unexamined Publication Nos. 57-64109 and 61-65053.
These hot-wire type air flow meters each have an auxiliary air flow
passage which extends in a direction substantially perpendicular
to a main air flow passage and which has a portion for changing
the direction of air flow by 180.degree..
In the air flow meter disclosed in Japanese Patent Unexamined Publication
No. 57-64109 a radial auxiliary air flow passage is separated into
two portions by a partitioning wall extending in the radial direction,
and the connecting portion of these two separate portions is formed
by an axial air flow passage. As the air flow passage is separated
into two parts by the partitioning plate, the structure of the air
flow meter mounted on an engine is complicated. Furthermore, since
the corner portion of the air flow passage which changes the direction
of air flow by 180.degree. is made of a thin plate, pressure loss
in the air flow passage is increased, thus decreasing the air flow
velocity and increasing changes generation of air flow velocity,
with a resultant in the noises in the output of the hot-wire type
air flow meter. In the air flow meter disclosed in Japanese Patent
Unexamined Publication No. 61-65053 the direction of the air flow
in the auxiliary air flow passage is changed by 180.degree. in total
by using two right-angled elbow tubes each of which changes the
direction of the air flow passage by 90.degree.. In this example,
the air flow passage is not formed in the same plane, as in the
former type of air flow meter. Consequently, the structure of the
air flow meter mounted on the engine is complicated. Furthermore,
pressure loss at the right-angled elbow tube portions is large,
and the same problems as those of the former type thus occur. Japanese
Patent Unexamined Publication No. 1-206223 discloses an axial hot-wire
type air flow meter in which an auxiliary flow passage is formed
within a main air flow passage. In this air flow meter, the auxiliary
air flow passage includes an axial auxiliary air flow passage portion
having an inlet open to the main air flow passage and extending
parallel to the main air flow passage, and two radial auxiliary
air flow passage portions formed in a straight line in directions
perpendicular to the direction of the main air flow passage and
in the radial directions and respectively having outlets open to
the main air flow passage in the vicinity of the peripheral wall
of the main air flow passage. A hot-wire element is disposed within
the axial auxiliary air flow passage portion.
In four cylinder engines, the two-value phenomena of the average
output voltage (inversion of the output) of the air flow meter caused
by pulsations in the engine intake air flow are a serious problem.
Occurrence of the two-value phenomena may be reduced by attenuating
the magnitude of the pulsations which is achieved by increasing
the total length of the auxiliary air flow passage. However, in
the conventional axial hot-wire type air flow meters, it is not
always possible to provide a sufficiently long radial auxiliary
air flow passage portion because the provision of such a passage
may be hindered due to the specification of an engine or the configuration
of a tube of an air intake system. This results in the generation
of the two-value phenomena.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide a hot-wire
type air flow meter which is less affected by pulsations of the
engine intake air flow which occur downstream of the meter.
Upstream of the air flow meter are disposed an air cleaner and
a duct which may be the cause of the occurrence of separation and
swirled air flow. Consequently, air flow velocity distribution in
which air flow velocities are varied at the radial and circumferential
positions of a main air flow passage, that is, an unbalanced air
flow velocity distribution, occurs on the upstream side of the air
flow meter due to the separation or swirled air flow. This unbalanced
air flow velocity distribution pattern is varied according to the
position and shape of the air cleaner and the duct. Conventional
hot-wire type air flow meters in which the outlets of two radial
auxiliary air flow passage portions are open in the vicinity of
the peripheral wall of the main air flow passage are readily affected
by changes in such unbalanced air flow velocity distribution, and
their measured values thus change as the unbalanced air flow distribution
changes. In the design of the passages of the intake air system,
the position and shape of the air cleaner and duct vary depending
on the type of vehicles. Therefore, provision of an air flow meter
which is readily affected by changes in the air flow velocity distribution
requires adjustment for accurate measurement of air flow rate. Such
an air flow meter cannot be generalized.
A second object of the present invention is to provide a hot-wire
type air flow meter which is less affected by changes in an unbalanced
air flow velocity distribution which occurs upstream of the air
flow meter.
To achieve the above-described objects, the present invention provides
an axial flow thermo-type air flow meter which includes a body having
formed therein a main air flow passage through which an intake air
flows and a radial wall portion disposed in the main air flow passage
and having formed therein an axuiliary air flow passage through
which a part of the intake air flows. The auxiliary air flow passage
accommodates a heat-generating resistor element for detecting a
rate of engine intake air flow. The auxiliary air flow passage includes
an axial auxiliary air flow passage portion having an inlet open
to the main air flow passage and extending parallel to the main
air flow passage and at least one radial auxiliary air flow passage
portion extending in a direction substantially perpendicular to
the main air flow passage and having an outlet open to the main
air flow passage. The heat-generating resistor element is disposed
in the axial auxiliary air flow passage portion. The radial auxiliary
air flow passage portion is formed in one plane perpendicular to
the axis of the main air flow passage and is bent at least at one
portion thereof to change the direction of the air flow by substantially
180.degree..
In a preferred form, the inlet opening of the axial auxiliary air
flow passage portion is located at the center of the main air flow
passage, and the radial auxiliary air flow passage portion is formed
by a single air flow passage portion connected to the axial auxiliary
air flow passage portion and either a plurality of air flow passage
portions which branch from the single air flow passage portion and
extend to the respective outlet openings or a single air flow passage
portion which extends to the outlet opening thereof.
In another preferred form, the outlet opening of the radial auxiliary
air flow passage portion is located within a range of a radius from
the axis of the main air flow passage, which radius is 1/2 of the
radius of the main air flow passage.
In a further preferred form, the radial auxiliary air flow passage
portion is formed in the radial wall portion such that the outlet
opening thereof is located at the central portion of the main air
flow passage.
In the present invention, the radial auxiliary air flow passage
portion is curved at least at one portion thereof in a single plane
substantially perpendicular to the main air flow passage so, that
it changes a direction of the air flow by substantially 180.degree..
Consequently, the length of the radial auxiliary air flow passage
portion can be increased, thereby reducing pulsations sufficiently.
Furthermore, since the air flow passage is formed in a single plane,
the structure of the air flow meter can be simplified. Furthermore,
if the portion for changing the direction of the air flow by 180.degree.
is smoothly curved in order to achieve reduction in the pressure
loss, reduction in the air flow velocity will be prevented, and
generation of noises in the output due to changes in time caused
by separated air flow which is generated at a corner portion of
the curved portion will also be reduced. In consequence, the output
of the air flow meter can be made stable and the two-value phenomena
due to pulsations in the engine intake air flow will not be readily
generated.
Changes in the unbalanced air flow velocity distribution which
occur upstream of the air flow meter due to changes in the position
and the shape of an air cleaner and a duct are larger in the peripheral
portion of the main air flow passage than at the central portion
thereof. Thus, positioning of the inlet and outlet openings of the
auxiliary air flow passage within a range of a radius from the axis
of the main air flow passage, which radius is 1/2 of the radius
of the main air flow passage, will be effective to reduce the influence
of changes in the unbalanced air flow velocity distribution.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an end view, taken in the direction indicated by an arrow
I in FIG. 2 of a first embodiment of a hot-wire type air flow meter
according to the present invention, showing the state thereof in
which a passage cover is removed;
FIG. 2 is a sectional view of the hot-wire type air flow meter
taken along the line II--II of FIG. 1;
FIG. 3 shows the positional relation of outlet openings of an auxiliary
air flow passage with to a main air flow passage;,
FIGS. 4A to 4D respectively show different unbalanced air flow
velocity distribution patterns to illustrate changes of such air
flow velocity distributions and influence thereof on the air flow
meter;
FIG. 5 shows the two-value phenomena;
FIG. 6 is an end view similar to FIG. 1 but shows a second embodiment
of the hot-wire type air flow meter according to the present invention;
and
FIGS. 7 to 13 are end views similar to FIG. 1 but show third to
ninth embodiments of the hot-wire type air flow meter according
to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A first embodiment of the present invention will be described below
with reference to FIGS. 1 to 5.
Referring first to FIGS. 1 and 2 a body 1 made by aluminum die
casting has a main air flow passage 2 in it. In the main air flow
passage 2 a spider 3 formed integrally with the body 1 is disposed
across the main air flow passage 2 in the radial direction thereof.
The spider 3 has in it an auxiliary air flow passage 4 through which
a part of intake air passes. The auxiliary air flow passage 4 includes
an inlet opening 4a open to the central portion of the main air
flow passage 2 an axial auxiliary passage portion 4b connected
to the opening 4a and formed parallel to the main air flow passage
2 and two radial auxiliary passage portions 4e and 4f formed in
directions perpendicular to the main air flow passage 2 and in radial
directions, which are separated from each other by 180.degree.,
and respectively having outlet openings 4c and 4d open to the main
air flow passage 2. The radial auxiliary passage portions 4e and
4f each are in the form of a groove which opens to the end face
of the spider 3. The grooves which form the radial auxiliary passage
portions 4e and 4f are closed by a passage cover 5 which is fixed
to the end face of the spider 3 by means of attaching screws 6.
FIG. 1 shows the state in which the passage cover 5 is removed.
Reference numerals 6a denote screw holes into which the attaching
screws 6 are screwed. The two radial auxiliary passage portions
4e and 4f respectively have substantially semi-circular smoothly
curved portions 4g and 4h which change the directions of air flows
by substantially 180.degree.. The outlet openings 4c and 4d of these
radial auxiliary passage portions 4e and 4f are each located within
the range of a radius from the axis of the main air flow passage
which radius is 1/2 of the radius of the main air flow passage,
as shown in FIG. 3.
The spider 3 having the two radial auxiliary air flow passage portions
4e and 4f divides the main air flow passage 2 having the circular
cross-section into two main air flow passage portions 2a and 2b.
The outlet openings 4c and 4d of the radial auxiliary air flow passage
portions 4e and 4f are respectively open to the main air flow passage
portions 2a and 2b.
Within the axial auxiliary air flow passage portion 4b are disposed
a heat-generating resistor element 7 for detecting the rate of engine
intake air flow and a temperature resistor element 8 for detecting
the temperature of intake air. An electronic control module 9 for
converting the rate of engine intake air flow detected by the heat-generating
resistor element 7 into an electric signal is mounted on the outer
surface of the body 1.
After air enters the body 1 it flows into both the main air flow
passage 2 and the auxiliary air flow passage 4 as indicated by
arrows in FIG. 2. The air which flows into the auxiliary air flow
passage 4 flows first through the axial auxiliary air flow passage
portion 4b where it makes contact with the heat-generating resistor
body 7 and the temperature resistor element 8 and then flows into
both the radial auxiliary air flow passage portions 4e and 4f. In
these radial auxiliary air flow passage portions 4e and 4f, air
flows first outwardly, then passes through the curved portions 4g
and 4h which are curved by about 180.degree. near the peripheral
wall of the main air flow passage 2 then flows inwardly in the
radial direction and finally flows out of the auxiliary air flow
passage from the outlet openings 4c and 4d into the main air flow
passage portions 2a and 2b at the central portion of the main air
flow passage 2. It is to be noted that the body 1 may also be made
of materials other than aluminum, such as plastics.
In the thermo-type air flow meter designed in the manner described
above, if it is assumed that the pressure loss of the auxiliary
air flow passage 4 is equal to the pressure loss of the main air
flow passage 2 between the inlet and outlet openings of the auxiliary
air flow passage 4 the relation between the main air flow passage
2 and the auxiliary air flow passage 4 is expressed as follows:
##EQU1## Lm: The equivalent length of the main air flow passage
U: The air flow velocity in the main air flow passage
Cm: The resistance coefficient of the main air flow passage
lb: The equivalent length of the auxiliary air flow passage
u: The air flow velocity in the auxiliary air flow passage
Cb: The resistance coefficient of the auxiliary air flow passage
Therefore, using ##EQU2## the dynamic relation between the velocity
of the main air flow and the velocity of the auxiliary air flow
is expressed as follows: ##EQU3##
Thus, it is possible to decrease the pulsating changes in the velocity
of the auxiliary air flow relative to dynamic pulsating changes
in the velocity of the main air flow by increasing the overall length
lb of the auxiliary air flow passage relative to the length Lm of
the main air flow passage between the inlet and outlet openings
of the auxiliary air flow passage.
In the four-cylinder engines, the two-value phenomena of the output
voltage of the air flow meter caused due to pulsations in the engine
intake air is a serious problem. More specifically, as the boost
pressure (vacuum) is increased by increasing the opening of a throttle
valve, the air flow rate detected by the air flow meter increases.
However, when the boost pressure is increased to a value higher
than a certain level, which is achieved by opening the throttle
valve almost fully, the air flow rate detected by the air flow meter
decreases, as shown in FIG. 5. This means that there are two boost
pressures (openings) corresponding to the air flow rate detected
when the boost pressure is higher than the certain level. Hence,
the control unit cannot determine the corresponding operation condition
when it receives electric signals representing those two values.
This is the two-value phenomena. Since an increase in lb with respect
to Lm is effective to decrease pulsations in the auxiliary air flow
passage, as described above, the increase in lb is very effective
for preventing the two-value phenomena.
In the present embodiment, it order to realize the structure in
which the outlet openings 4c and 4d of the radial auxiliary air
flow passage portions 4e and 4f are each located substantially at
the central portion of the main air flow passage, the curved portions
4g and 4h for changing the directions of air flows by substantially
180.degree. are respectively provided in the radial auxiliary air
flow passage portions 4e and 4f. In this way, the length of each
of the radial auxiliary air flow passage portions 4e and 4f can
be made greater than the radius of the main air flow passage 2.
Particularly, since the outlet openings 4c and 4d of the radial
auxiliary air flow passage portions 4e and 4f are located within
an area having a diameter of 1/2 of the diameter `d` of the main
air flow passage in this embodiment, the length of each of the radial
auxiliary air flow passage portions 4e and 4f can be made about
two times that of the radius of the main air flow passage 2. As
a result, pulsations in the intake air flow in the auxiliary air
flow passage can be reduced, to thereby decrease the occurrence
of the two-value phenomena caused by the pulsations in the engine
intake air flow.
Next, the static relation between the velocity of the main air
flow and the velocity of the auxiliary air flow at a steady time
is expressed as follows: ##EQU4##
So, it is apparent that the velocity of the auxiliary air flow
is dependent upon the velocity of the main air flow.
As stated above, the distribution of the air flow velocity on the
upstream side of the air flow meter changes in accordance with the
structure of an air cleaner and the shape of a duct. FIGS. 4A to
4D show examples of the air flow velocity distribution pattern.
In the pattern shown in FIG. 4A, the velocity of air flow is substantially
uniform in all the radial and circumferential positions. In the
patterns shown in FIGS. 4B to 4D, the velocity of air flow is distributed
non-uniformly in the radial and circumferential directions. Similar
air flow velocity distributions occur in the vicinity of the outlet
openings of the auxiliary air flow passage. As is clear from FIGS.
4A to 4D, changes in the air flow velocity caused by changes in
an unbalanced air flow distribution pattern are greater in the vicinity
of the peripheral wall which defines the body 1 than in the central
portion of the main air flow passage.
When the conventional air flow meter shown in FIG. 4A in which
outlet openings 10a and 10b of the auxiliary air flow passage are
provided in the vicinity of the peripheral wall of the main flow
passage is subjected to the above-described changes in the air flow
velocity distribution, the air flow velocity `u` in the auxiliary
air flow passage easily changes because of relatively large changes
in the air flow velocity `U` in the main air flow passage in the
vicinity of the wall. Particularly, this tendency increases in the
case in which the auxiliary air flow passage has a single outlet
opening. Even when the auxiliary air flow passage has two outlet
openings, as shown in FIG. 5 if the air flows in a distribution
pattern unbalanced to one side of the center of the main air flow
passage, as in the cases shown in FIGS. 4B and 4C, changes in the
passage resistance are greater than the cases shown in FIGS. 4A
and 4D in which the air flows at both sides of the center, thus
readily generating changes in the air flow velocity.
In the air flow meter, changes in the air flow velocity in the
vicinity of the center of the main air flow passage are less than
those in the vicinity of the peripheral wall except for special
cases. Therefore, positioning of the outlet openings 4c and 4d of
the radial auxiliary air flow passage portions 4e and 4f in the
central portion of the main air flow passage 2 as in the described
embodiment, is effective to decrease fluctuation of the electric
output of the air flow meter which occurs when distribution of the
air flow velocity (the unbalanced air flow) changes in the vicinity
of the inlet opening.
In this embodiment, since not only the inlet opening 4a of the
auxiliary air flow passage 4 but also the outlet openings 4c and
4d thereof are disposed at the central portion of the main air flow
passage 2 the air flow meter is less affected by changes in the
air flow velocity distribution, and can thus be used in the air
intake systems designed in various manners.
The present inventors have confirmed through experiments that the
aforementioned advantages can be similarly assured when the inlet
and outlet openings of the auxiliary air flow passage 4 are located
within a radius from the central axis of the main air flow passage
which is 1/2 of the radius of the main air flow passage.
A second embodiment of the present invention will be described
below with reference to FIG. 6 which is a view similar to FIG. 1
shows the state in which the passage cover is removed. In this embodiment,
three radial auxiliary air flow passage portions are formed in different
radial directions.
In the structure shown in FIG. 6 a spider 3A has a shape which
divides the main air flow passage 2 into three portions. The spider
3A has in it an axial auxiliary air flow passage portion 40 whose
inlet opening is located at the central portion of the main air
flow passage 2 and three radial auxiliary air flow passage portions
40a, 40b and 40c having the same form as that of the radial auxiliary
air flow passage portions 4e and 4f in the first embodiment. That
is, the radial auxiliary air flow passage portions 40a, 40b and
40c respectively have curved portions 40g, 40h and 40i for changing
the directions of air flows by about 180.degree., and outlet openings
40d, 40e and 40f thereof located at the central portion of the main
air flow passage 2. The aforementioned advantages of the first embodiment
can also be assured in the second embodiment. The radial auxiliary
air flow passage portions may be provided in the number of four
or more.
Other embodiments of the present invention will be described with
reference to FIGS. 7 to 9 which are views similar to FIG. 1 and
show the states of the air flow meters in which the passage covers
are removed.
In the third embodiment shown in FIG. 7 a cantilever type spider
3B has an axial auxiliary air flow passage portion 41 whose inlet
opening is located at the central portion of the main air flow passage
2 and one radial auxiliary air flow passage portion 41a having
the same form as that of the radial auxiliary air flow passage portions
4e and 4f in the first embodiment. That is, the radial auxiliary
air flow passage portion 41a has a curved portion 41c for changing
the direction of air flow by about 180.degree., and an outlet opening
41b thereof is located at the central portion of the main air flow
passage 2. The afore-mentioned advantages of the first embodiment
can also be assured in this third embodiment. Furthermore, in this
embodiment, since the spider 3B is of the cantilever type, resistance
to the air flow in the main air flow passage is reduced, thereby
decreasing pressure loss.
Furthermore, in this embodiment, a sensor unit consisting of the
spider 3B formed separately from the body 1 and an integral electronic
control module mounted on the spider 3B, may be detachably mounted
on the body 1. In this way, the structure of the body 1 which defines
the main air flow passage is simplified. Furthermore, since the
sensor unit can be handled as a single unit, initial adjustment
and maintenance of the electronic control module are facilitated.
In the fourth embodiment shown in FIG. 8 a spider 3C is disposed
across the main air flow passage 2 like the spider 3 shown in FIG.
1. The spider 3C has in it an axial auxiliary air flow passage portion
42 whose inlet opening is located at the central portion of the
main air flow passage 2 and a radial auxiliary air flow passage
portion 42a having a single outlet opening 42b at the central portion
of the main air flow passage 2 and two curved portions 42c and 42d
for respectively changing the direction of air flow by about 180.degree..
Consequently, the length of the auxiliary air flow passage is increased
to about four times that of the radius of the main air flow passage.
In this embodiment, since the length of the auxiliary air flow passage
is further increased, the two-value phenomena caused by pulsations
of the engine intake air flow downstream of the air flow meter can
be further reduced. This embodiment is particularly effective when
it is applied to the four-cylinder engines whose intake air flow
pulsates to a large degree.
In the fifth embodiment shown in FIG. 9 a spider 3D is of the
cantilever type, as in the case of the third embodiment shown in
FIG. 7. The spider 3D has in it an axial auxiliary air flow passage
portion 43 whose inlet opening is located at the central portion
of the main air flow passage 2 and a composite radial auxiliary
air flow passage portion 43e consisting of a single radial air flow
passage portion 43a connected to the axial auxiliary air flow passage
portion 43 and two divided air flow passage portions 43b and 43c
branching from the radial air flow passage portion 43a. The air
flow passage portions 43b and 43c of the radial auxiliary air flow
passage portion 43e respectively have outlet openings 43f and 43g
at the central portion of the main air flow passage. The portions
of the divided air flow passage portions 43b and 43c which are branched
from the single air flow passage portion 43a are curved to form
curved portions 43h and 43i for changing the direction of air flow
by about 180.degree.. In this embodiment, since the length of the
radial auxiliary air flow passage portion is further increased as
compared with the embodiment shown in FIG. 7 occurrence of the
two-value phenomena can be further reduced. Furthermore, it is possible
to form a sensor unit that can be detachably mounted on the body
1 by the spider 3D and the electronic control module 9 as in the
case of the embodiment shown in FIG. 7. Such a structure facilitates
initial adjustment and maintenance of the electronic control module.
Sixth to ninth embodiments of the present invention will be described
with reference to FIGS. 10 to 13. In the sixth embodiment shown
in FIG. 10 a spider 3E is disposed across the main air flow passage
2 like the spider 3 shown in FIG. 1. The spider 3E has in it an
axial auxiliary air flow passage portion 44 whose inlet is located
at the central portion of the main air flow passage 2 and a single
radial auxiliary air flow passage portion 44a having a curved portion
44c for changing the direction of air flow by about 180.degree..
An outlet opening 44b of the radial auxiliary air flow passage portion
44a is located at a position offset from the axis of the main air
flow passage 2.
In the seventh embodiment of the present invention, a spider 3F
is disposed across the main air flow passage 2. The spider 3F has
in it an axial auxiliary air flow passage portion 45 whose inlet
is located at a position offset from the axis of the main air flow
passage 2 and a single radial auxiliary air flow passage portion
45a having a curved portion 45c for changing the direction of air
flow by 180.degree.. An outlet opening 45b of the radial auxiliary
air flow passage portion 45a is also located at a position offset
from the axis of the main air flow passage.
In the eighth embodiment shown in FIG. 12 a spider 3G is disposed
across the main air flow passage 2 like the spider 3 shown in FIG.
1. The spider 3G has in it an axial auxiliary air flow passage portion
46 whose inlet opening is located at a position offset from the
axis of the main air flow passage 2 and a single radial auxiliary
air flow passage portion 46a having a curved portion 46c for changing
the direction of air flow by about 180.degree.. An outlet opening
46b of the radial auxiliary air flow passage 46a is located at the
central portion of the main air flow passage 2. Consequently, the
length of the auxiliary air flow passage can be increased to about
three times that of the radius of the main air flow passage.
In the ninth embodiment shown in FIG. 13 a spider 31 is disposed
across the main air flow passage, like the spider 3G shown in FIG.
12. The spider has in it an axial auxiliary air flow passage portion
47 whose inlet opening is located at a position offset from the
axis of the main air flow passage 2 and a single composite radial
auxiliary air flow passage portion 47e consisting of a single radial
air flow passage portion 47a connected to the axial auxiliary air
flow passage portion 47 and two air flow passage portions 47b and
47c branching from the air flow passage portion 47a, as in the case
of the embodiment shown in FIG. 9. The air flow passage portions
47b and 47c respectively have openings 47f and 47g at the central
portion of the main air flow passage. The portions of the air flow
passage portions 47b and 47c which branch from the air flow passage
portion 47a are curved to form portions 47h and 47i for changing
the direction of air flow by about 180.degree..
In each of the embodiments shown in FIGS. 10 to 13 the length
of the auxiliary air flow passage is increased, as in the preceding
embodiments. Consequently, the two-value phenomena caused by pulsations
in the intake air flow which occur downstream of the air flow meter
can be prevented very effectively.
In the embodiments shown in FIGS. 11 to 13 the inlet opening of
each of the axial auxiliary air flow passage portions 45 46 and
47 is offset from the center of the main air flow passage. Thus,
the inlet opening may have an elliptical form in order to enhance
stability thereof against the unbalanced air flow.
As will be understood from the foregoing description, it is possible
according to the present invention to provide a hot-wire type air
flow meter which is less affected by changes in the unbalanced air
flow distribution which occurs upstream of the spider and which
can be applied to the air intake systems designed in various manners.
It is also possible to provide a hot-wire type air flow meter which
decreases the occurrence of the two-value phenomena caused by pulsations
in the engine intake air flow and which is hence highly reliable.
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