Abstrict A U-shaped bypass passage is provided in an intake pipe. A part
of air flowing in the intake pipe is introduced into the bypass
passage. The bypass passage is arranged substantially perpendicularly
to a primary air flow direction in the intake pipe. A flow meter
element is disposed in the bypass passage for measuring air flow
amount. Turbulence reduction plates are integrally formed with the
bypass passage at an upper side and a lower side of an air inlet
thereof. The turbulence reduction plates are arranged substantially
in parallel with the primary air flow direction in the intake pipe,
and substantially perpendicularly to an air flow direction in the
bypass passage. Even when a secondary air flow arises around the
air inlet of the bypass passage, the turbulence reduction plates
shut the secondary air flow, thereby reducing an influence of the
secondary air flow.
Claims What is claimed is:
1. An air flow meter for measuring flow amount of air flowing in
an air passage, comprising: a U-shaped bypass passage, into which
a part of the air is introduced, provided in said air passage, said
bypass passage arranged substantially perpendicularly to a primary
air flow direction in said air passage and defining an air inlet;
a flow meter element disposed in said bypass passage; and a turbulence
reduction plate provided adjacent the air inlet of said bypass passage,
wherein said turbulence reduction plate extends substantially in
parallel with the primary air flow direction in the air passage,
and substantially perpendicularly to an air flow direction in said
bypass passage, said turbulence reduction plate is disposed at a
position of said air inlet, which is opposite to said flow meter
element, said bypass passage includes two fluid passages next to
and in parallel with each other, and a bent portion connecting the
two fluid passages, the two fluid passages are partitioned by a
partition wall, a venturi is formed within said partition wall at
the air inlet side thereof, and said turbulence reduction plate
is disposed at a position facing around a center of said venturi.
2. An air flow meter according to claim 1 wherein said turbulence
reduction plate is integrally formed with said bypass passage.
3. The air flow meter according to claim 1 wherein said turbulence
reduction plate is provided in the air passage and extends in the
air passage substantially in parallel with the primary air flow
direction and substantially perpendicularly to the air flow direction
in said bypass passage.
4. The air flow meter according to claim 1 wherein said turbulence
reduction plate reduces a secondary, turbulent flow of the primary
air flow having an air flow direction component parallel to the
air flow direction in said bypass passage.
5. The air flow meter according to claim 1 wherein the turbulence
reduction plate is disposed on an upstream side of the air inlet
of said bypass passage and extends in an upstream direction of the
primary flow in the air passage.
6. The air flow meter according to claim 1 wherein the turbulence
reduction plate is generally planar and is defined in a plane perpendicular
to the air flow direction in said bypass passage.
7. The air flow meter according to claim 1 wherein a plurality
of turbulence reduction plates are provided adjacent the air inlet,
one of said turbulence reduction plates extending in an upstream
direction of the primary flow from a vicinity of an upstream edge
of the air inlet of the bypass passage and a second of said turbulence
reduction plates disposed adjacent and upstream of said venturi.
8. The air flow meter according to claim 1 wherein said turbulence
reduction plate comprises a curved plate.
9. An air flow meter for measuring flow amount of air flowing in
an air passage, comprising: a U-shaped bypass passage, into which
a part of the air is introduced, provided in said air passage, said
bypass passage arranged substantially perpendicularly to a primary
air flow direction in said air passage and defining an air inlet;
a flow meter element disposed in said bypass passage; and a turbulence
reduction plate provided adjacent the air inlet of said bypass passage,
wherein said turbulence reduction plate extends substantially in
parallel with the primary air flow direction in the air passage,
and substantially perpendicularly to an air flow direction in said
bypass passage, and said turbulence reduction plate is mechanically
fastened to said bypass passage structure.
10. An air flow meter for measuring flow amount of air flowing
in an air passage, comprising: a U-shaped bypass passage, into which
a part of the air is introduced, provided in said air passage, said
bypass passage arranged substantially perpendicularly to a primary
air flow direction in said air passage and defining an air inlet;
a flow meter element disposed in said bypass passage; and a turbulence
reduction member provided in the air passage adjacent the air inlet
of said bypass passage, wherein said turbulence reduction member
includes a component extending in the air passage in a direction
perpendicularly crossing with an air flow direction in said bypass
passage, and said turbulence reduction member protrudes around said
air inlet and toward an air upstream side of said air passage.
11. An air flow meter according to claim 10 wherein said turbulence
reduction member is integrally formed with said bypass passage.
12. An air flow meter according to claim 10 wherein said turbulence
reduction member is disposed at a position of said air inlet, which
is opposite to said flow meter element.
13. An air flow meter according to claim 12 wherein said bypass
passage includes two fluid passages next to and in parallel with
each other, and a bent portion connecting the two fluid passages,
the two fluid passages are partitioned by a partition wall, a venturi
is formed within said partition wall at the air inlet side thereof,
and said turbulence reduction member is disposed at a position facing
around a center of said venturi.
14. An air flow meter according to claim 10 wherein said turbulence
reduction plate reduces a secondary, turbulent flow of the primary
air flow having an air flow direction component parallel to the
air flow direction in said bypass passage.
15. The air flow meter according to claim 10 wherein the turbulence
reduction plate is disposed on an upstream side of the air inlet
of said bypass passage and extends in an upstream direction of the
primary flow in the air passage.
16. An air flow meter for measuring flow amount of air flowing
in an air passage, comprising: a U-shaped bypass passage, into which
a part of the air is introduced, provided in said air passage, said
bypass passage arranged substantially perpendicularly to a primary
air flow direction in said air passage and defining an air inlet;
a flow meter element disposed in said bypass passage; and a turbulence
reduction member provided in the air passage adjacent the air inlet
of said bypass passage, wherein said turbulence reduction member
includes a component extending in the air passage in a direction
perpendicularly crossing with an air flow direction in said bypass
passage, and wherein said turbulence reduction member is entirely
formed over said air inlet.
17. An air flow meter according to claim 16 wherein said turbulence
reduction member is integrally formed with said bypass passage.
18. An air flow meter according to claim 16 wherein said turbulence
reduction member is disposed at a position of said air inlet, which
is opposite to said flow meter element.
19. An air flow meter according to claim 18 wherein said bypass
passage includes two fluid passages next to and in parallel with
each other, and a bent portion connecting the two fluid passages,
the two fluid passages are partitioned by a partition wall, a venturi
is formed within said partition wall at the air inlet side thereof,
and said turbulence reduction member is disposed at a position facing
around a center of said venturi.
20. An air flow meter according to claim 16 wherein said turbulence
reduction plate reduces a secondary, turbulent flow of the primary
air flow having an air flow direction component parallel to the
air flow direction in said bypass passage.
21. The air flow meter according to claim 16 wherein the turbulence
reduction plate is disposed on an upstream side of the air inlet
of said bypass passage and extends in an upstream direction of the
primary flow in the air passage.
22. An air flow meter for measuring flow amount of air flowing
in an air passage, the air passage defining a primary flow direction
of air flow therethrough, air flow in the air passage including
a secondary flow which is substantially perpendicular to the primary
flow direction, said air flow meter comprising: a bypass passage
disposed in the air passage, the bypass passage having an upstream
passage extending substantially perpendicular to the primary flow
direction, the upstream passage having an air inlet which is opened
toward an upstream of the primary flow; a flow meter element disposed
in the upstream passage; and a turbulence reduction plate disposed
adjacent the air inlet, the turbulence reduction plate being disposed
on an outside of the bypass passage and extending in an upstream
direction of the primary flow, the turbulence reduction plate extending
substantially in parallel with the primary flow direction and substantially
perpendicularly to a flow direction of the secondary flow, thereby
reducing the secondary flow before entering the air inlet, wherein
the turbulence reduction plate is a first plate disposed on one
side of the air inlet, and further comprising a second turbulence
reduction plate disposed on another side of the air inlet, the second
plate being disposed outside the bypass passage and extending in
an upstream direction of the primary flow, the second plate extending
substantially in parallel with the primary flow direction and substantially
perpendicularly to the flow direction of the secondary flow, thereby
reducing the secondary flow before entering the air inlet.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an air flow meter having a flow
meter element, suitable for use in an intake pipe of vehicle internal
combustion engine.
2. Description of Related Art
An air flow meter is used for measuring intake air flow amount
of an internal combustion engine. The air flow meter is disposed
in a bypass passage within an engine intake pipe. The air flow meter
has a flow meter element and a heat sensing element, and measures
the intake air flow mount base on a value of electric current supplied
into the flow meter element.
When the engine operates, the intake air flow amount fluctuate
relatively remarkably, so that pulsating flow arises in the intake
air flow. The pulsating flow disorders an air flow introduced into
the bypass passage, thereby causing a measurement error of the intake
air flow amount.
JP-A-8-285659 discloses an air flow meter in which two turbulence
reduction grills are provided. The turbulence reduction grills are
disposed at an inlet of main air passage and arranged in parallel
with each other. Grill directions of these turbulence reduction
grills are off-set by 45 degrees to reduce turbulence in the intake
air flowing into the main air passage, thereby stabilizing air which
flows into the bypass passage.
However, since two turbulence reduction grills are provided at
the inlet of the main air flow passage, pressure loss is increased
in the main air passage, thereby worsening an engine performance.
Further, costs for forming two turbulence reduction grills and for
press-inserting or insert-forming the turbulence reduction grills
to the inlet of the main air flow passage are increased.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce an influence of
pulsating flow without increasing a pressure loss by a simple structure,
thereby improving measurement accuracy with reducing manufacturing
cost and the pressure loss.
According to a first aspect of the present invention, a U-shaped
bypass passage is provided in an air passage. The bypass passage
is arranged substantially perpendicularly to a primary air flow
direction in the air passage and defines an air inlet. A turbulence
reduction plate is provided around an air inlet of the bypass passage,
and the turbulence reduction plate is arranged substantially in
parallel with the primary air flow direction in the air passage,
and substantially perpendicularly to an air flow direction in the
bypass passage.
Even when a secondary air flow, of which direction is in parallel
with an air flow direction in the bypass passage, arises around
the air inlet of the bypass passage, the turbulence reduction plate
shuts the secondary air flow, thereby reducing an influence of the
secondary air flow. Thus, air flow introduced into the bypass passage
is stabilized, thereby improving the air flow amount measurement
accuracy. Here, the turbulence reduction plate is disposed substantially
in parallel with a primary air flow direction in the air passage,
so that pressure loss caused by the turbulence reduction plate is
enough small, thereby introducing no influence on an engine efficiency.
Further, the turbulence reduction plate is simply structured and
provided, thereby reducing the manufacturing cost.
According to a second aspect of the present invention, the bypass
passage includes two fluid passage next to and in parallel with
each other, and a bent portion connecting the two fluid passages.
A partition wall partitions the two fluid passages, and a venturi
is formed at the air inlet side of the partition wall. The turbulence
reduction plate is disposed at a position facing around a center
of the venturi.
Thus, the primary air flowing into the venturi is prevented from
being disordered while the turbulence reduction plate effectively
reduces the influence of the secondary flow, so that stable venturi
effect can be attained. The air having passed through the venturi
introduces negative pressure acting on an air outlet of the bypass
passage, so that the air flow speed in the bypass passage is increased,
thereby improving the air flow amount measurement accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
Additional objects and advantages of the present invention will
be more readily apparent from the following detailed description
of preferred embodiments thereof when taken together with the accompanying
drawings in which:
FIG. 1 is a cross-sectional side view showing an attachment position
of the air flow meter;
FIG. 2 is a front view showing the attachment state of the air
flow meter;
FIG. 3 is a cross-sectional side view showing a bent intake pipe
and an attachment position of the air flow meter;
FIG. 4A is a schematic view showing a stationary secondary air
flow in the intake pipe;
FIG. 4B is a schematic view showing a pulsating secondary air flow
in the intake pipe;
FIG. 5 is a graph showing experimental data of measurement errors
in the present air flow meter and in a conventional air flow meter;
FIG. 6 is a front view showing a turbulence reduction member (first
modification);
FIG. 7 is a front view showing a turbulence reduction member (second
modification), and
FIG. 8 is a front view showing a turbulence reduction member (third
modification).
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
(First Embodiment)
As shown in FIGS. 1 and 2 an air flow meter 13 is attached to
a mounting hole 12 of an intake pipe 11 of internal combustion engine.
The air flow meter 13 includes a circuit module 14 and a flow meter
unit 15. The flow meter unit 15 is rectangular cylindrically formed,
and extends from the mounting hole 12 toward the center axis of
the intake pipe 11. The flow meter unit 15 includes an upstream
side fluid passage 18a and a downstream side fluid passage 18c.
The upstream side fluid passage 18a and the downstream side fluid
passage 18c extend in the radial direction of the intake pipe 11
and provide a partition wall 17 therebetween. The upstream side
fluid passage 18a extends in parallel with the downstream side fluid
passage 18c, and communicates with the downstream side fluid passage
18c through a bent portion 18b. In this way, a U-shaped bypass passage
18 is formed in the flow meter unit 15. The cross sectional area
A1 of the upstream side fluid passage 18a is smaller than the cross
sectional area A2 of the downstream side fluid passage 18c.
The flow meter unit 15 includes an air inlet 19 at the upstream
side thereof. A part of primary air flowing in the intake pipe 11
is introduced into the upstream side fluid passage 18a through the
air inlet 19. A venturi 16 is integrally formed at the lower end
of the partition wall 17. The venturi 16 is in parallel with a primary
air-flow direction. An air outlet 22 of the bypass passage 18 is
formed above the venturi 16. Air having passed through the bypass
passage 18 merges with the air having passed through the venturi
16 at the downstream side of the venturi 16.
Turbulence reduction plates 23 24 are integrally resin formed
at the upper side and lower side of the air inlet 19 respectively.
The turbulence reduction plates 23 24 are arranged in parallel
with the primary air-flow direction, and perpendicularly to an air-flow
direction in the bypass passage 18. The lower turbulence reduction
plate 24 is located to face a center portion of the venturi 16.
As shown in FIG. 2 latitudinal width of each turbulence reduction
plate 23 24 is approximately the same as or slightly larger than
the latitudinal width of the bypass passage 18. As shown in FIG.
1 axial protrusion length of each turbulence reduction plate 23
24 is set as large as possible within a range not to prevent the
flow meter unit 15 from being inserted into the mounting hole 12
of the intake pope 11. The turbulence reduction plates 23 24 are
formed such that they protrude toward the upstream side of the intake
pipe 11.
The circuit module 14 covers the top opening of the flow meter
unit 15. A flow meter element (heat generating element) 29 and a
heat sensing element 30 are respectively attached below the circuit
module 14 by support members 31 32 while providing a predetermined
interval therebetween. The flow meter element 29 and the heat sensing
element 30 are disposed at an upper area of the upstream side fluid
passage 18a. Here, since the cross sectional area A1 of the upstream
side fluid passage 18a is smaller than the cross sectional area
A2 of the downstream side fluid passage 18c, air-flow speed in the
upstream side fluid passage 18a is larger than that in the downstream
side fluid passage 18c. As the air-flow speed is higher, flow measurement
accuracy is more improved. Thus, the flow meter element 29 is disposed
in the upstream side fluid passage 18a. Since the heat sensing element
30 detects a temperature of the air touching the flow meter element
29 the heat sensing element 30 is required to be disposed close
to the flow meter element 29 within a range that radiation of the
flow meter element 29 does not influence the heat sensing element
30.
A circuit board (not illustrated) controlling a current supply
into the flow meter element 29 and the heat sensing element 30 is
installed in the circuit module 14. A connector 34 for connecting
a wire harness (not illustrated) is insert-formed at the side wall
of the circuit module 14. An intake air temperature sensor 35 (see
FIG. 2) is disposed below the circuit module 14 and protrudes downwardly.
The intake air temperature sensor 35 is located next to the flow
meter unit 15 to detect a temperature of the air flowing through
the intake pipe 11.
The circuit module 14 includes a fitting projection 36 at the bottom
surface thereof, and a flange 20 of the flow meter unit 15 is fused
or adhered to the fitting projection 36. An O-ring 37 is provided
at the outer periphery surface of the fitting projection 36 and
seals the inner surface of the mounting hole 12. The air flow meter
13 is screwed to the mounting hole 12 by plug-in method while the
bottom surface of the circuit module 14 contacts the upper edge
of the mounting hole 12.
In the air flow meter 13 a part of primary air flowing through
the intake pipe 11 is distributed into the upstream side fluid passage
18a and the venturi 16. The air introduced into the upstream side
fluid passage 18a changes the flow direction thereof substantially
perpendicularly to the primary air flow direction, and flows through
the bypass passage 18 i.e., upstream side fluid passage 18a, bent
portion 18b, and downstream side fluid passage 18c. The air having
passed through the bypass passage 18 merges with the air having
passed through the venturi 16 at the downstream side of the venturi
16. At the merging portion, the air having passed through the venturi
16 introduces negative pressure acting on the air outlet 22 of the
bypass passage 18 so that the air flow speed in the bypass passage
18 is increased. The circuit module 14 controls an electric current
supplied into the flow meter element 29 such that a temperature
difference between temperature of heat generated by the flow meter
element 29 and temperature detected by the heat sensing element
30 is constant. Bypass air flow amount is measured based on the
electric current value at the air flow meter element 29 and the
intake air flow amount is attained.
Next, functions of the turbulence reduction plates 23 24 will
be explained. In the intake pipe 11 as shown in FIGS. 4A and 4B,
there arises a secondary air flow in addition to the primary air
flow, and direction of which is parallel with the center axis C
of the intake pipe 11. The secondary air flow swirls in the intake
pipe 11. When the intake pipe is bent as shown in FIG. 3 the secondary
air flow remarkably arises as shown in FIGS. 4A and 4B. The secondary
air flow arises due to transmission of engine intake air fluctuation.
As shown in FIG. 4A, even when the air flow is stationary flow,
two secondary flows arises symmetrically in the intake pipe 11.
When the intake air fluctuation increases and the air flow in the
intake pipe 11 becomes pulsating flow, the stationary secondary
flow is pushed outwardly as shown in FIG. 4B. Thereby, there arises
a pulsating secondary flow at the center area of the intake pipe
11 swirling in the opposite swirling direction of the stationary
secondary flow.
Here, as shown in FIG. 4A, direction of the stationary secondary
flow around the air inlet 19 is approximately the same as of the
stationary secondary flow in the upstream side fluid passage 18a.
However, as shown in FIG. 4B, direction of the pulsating secondary
flow around the air inlet 19 is approximately opposite to the direction
of the pulsating secondary flow in the upstream side fluid passage
18a.
In the conventional air flow meter, the turbulence reduction plates
23 24 are not provided around the air inlet 19 of the bypass passage
18. Thus, when the direction of the secondary flow around the air
inlet 19 is approximately the same as the secondary flow in the
upstream side fluid passage 18a, amount of the air introduced into
the bypass passage 18 increases due to the secondary flow. When
the direction of the secondary flow around the air inlet 19 is approximately
opposite to the direction of the stationary flow in the upstream
side fluid passage 18a, the air is prevented from flowing into the
bypass passage 18 thereby reducing the air flow amount into the
bypass passage 18. Thus, fluctuation of the secondary flow direction
causes fluctuation of the air flow amount into the bypass passage
18 thereby introducing a measurement error.
However, in the present embodiment, the turbulence reduction plates
23 24 are formed at the upper side and the lower side of the air
inlet 19 respectively. The turbulence reduction plates 23 24 are
substantially formed in parallel with the primary air-flow direction,
and perpendicularly to the air flow in the bypass passage 18. Thus,
the turbulence reduction plates 23 24 shut both stationary secondary
flow and pulsating secondary flow at the front of the air inlet
19 thereby reducing the influence of the secondary flows. Accordingly,
flow of the air introduced into the bypass passage 18 is stabilized,
so that the intake air flow amount is accurately measured.
Further, since the lower turbulence reduction plate 24 is located
at the position facing the center of the venturi 16 the turbulence
reduction plate 24 prevents the primary air flow into the venturi
16 from being disordered. Thus, stable venturi effect can be attained.
The venturi 16 introduces negative pressure around the air outlet
22 of the bypass passage 18 and the negative pressure sucks the
air inside the bypass passage 18 to increase the air flow speed
in the bypass passage 18.
For example, as shown in FIG. 5 in the conventional air flow meter,
measurement error of the intake air flow amount is relatively large
at an engine normal rotation speed range 1200-2500 rpm. In the present
embodiment, the turbulence reduction plates 23 24 stabilize the
air flowing into the bypass passage 18 so that the measurement
error of the intake air flow amount is reduced.
Here, when the engine rotation speed is lower than about 1100 rpm,
the measurement error of the intake air flow amount is abruptly
increased, because back air flow arises when the engine rotation
speed is low. In a hot-wire type air flow meter 13 since back flow
is not distinguished from fair flow, the back flow is measured as
the fair flow, so that the measured intake air flow amount becomes
larger than the actual flow amount by back flow amount.
In the present embodiment, since the turbulence reduction plates
23 24 are arranged in parallel with the primary air flow direction
in the intake pipe 11 pressure loss due to the turbulence reduction
plates 23 24 is enough small, thereby introducing no influence
on an engine efficiency. The turbulence reduction plates 23 24
are simply provided, so that manufacturing cost is reduced.
(Modifications)
According to the above-described embodiment, the turbulence reduction
plates 23 24 are formed at the upper side and the lower side of
the air inlet 19 respectively. Alternatively, only one turbulence
reduction plate 23 or 24 may be provided. The measurement error
of the intake air flow amount is caused by two secondary flows of
which direction is the same as the air flow direction in the upstream
side fluid passage 18a, and of which direction is opposite to the
air flow direction in the upstream side fluid passage 18a. The influence
of the former is larger than that by the latter. Thus, when only
one turbulence reduction plate is provided, the turbulence reduction
plate had better be disposed at the lower side of the air inlet
19 that is, the turbulence reduction plate had better be disposed
at an opposite side of the flow meter element 29. By this, the turbulence
reduction plate shut the secondary flow whose direction is the same
as the air flow direction in the upstream side fluid passage 18a,
which worst influence air flow amount measurement, at the front
of the air inlet 19 thereby reducing the influence of the secondary
flow effectively.
In the above-described embodiment, the turbulence reduction plate
23 24 are integrally formed around the air inlet 19 of the bypass
passage 18 without increasing the manufacturing cost. Alternatively,
a separate turbulence reduction plate may be adhered, screwed, or
mechanically fixed to the bypass passage.
In the above-described embodiment, the turbulence reduction plate
23 24 are arranged perpendicularly to the air flow in the bypass
passage 18 for reducing the influence of the secondary flow. Alternatively,
as long as the influence of the secondary flow is reduced, other
turbulence reduction member may be used.
For example, as shown in FIG. 6 arc-like bent turbulence reduction
members 41 42 may be provided. As shown in FIG. 7 cross-sectional
triangle turbulence reduction members 43 44 may be provided. As
shown in FIG. 8 a grille-like turbulence reduction member 45 may
be provided. That is, the turbulence reduction members 41-45 having
a surface approximately perpendicular to the air flow direction
in the bypass passage 18 may be provided around the air inlet 19.
By this, the turbulence reduction members 41-45 shut the secondary
flow around the air inlet 19 thereby reducing the influence of
the secondary flow. Thus, flow of the air introduced into the bypass
passage 18 is stabilized, so that the intake air flow amount is
accurately measured.
In this case, the turbulence reduction members 41-45 had better
protrude around the air inlet 19 and toward the upstream side of
the intake pipe 11.
Further, as shown in FIGS. 6-8 the turbulence reduction members
41-45 had better be entirely formed over the air inlet 19. By this,
the turbulence reduction members 41-45 further effectively shut
the secondary flow.
Here, the turbulence reduction members 41-45 may be screwed, adhered,
or mechanically fixed to the bypass passage 18. However, the turbulence
reduction members 41-45 are desired to be integrally resin-formed
with the bypass passage 18 for reducing the manufacturing cost.
The present invention is not restricted to be used for the air
flow meter for measuring intake air flow amount in an internal combustion
engine, and may be used for measuring air flow amount in miscellaneous
air passages. |