Abstrict A flow meter includes a tubular member having a main passage in
which fluid flows. A branch passage member disposed in the main
passage has a branch passage in which the fluid flows. A support
member connects the branch passage member and a wall of the tubular
member, and supports the branch passage member within the main passage.
A partition arrangement disposed in the branch passage divides the
branch passage into a plurality of sub passages extending along
a flow of the fluid. A flow-rate measuring resistor is disposed
in a region of the branch passage downstream of the partition arrangement
for sensing a rate of a flow of the fluid in the branch passage.
A control circuit electrically connected to the flow-rate measuring
resistor is operative for calculating a measurement value from an
output signal of the flow-rate measuring resistor. An outlet formed
in the branch passage member is operative for connecting the branch
passage with the main passage to enable the fluid to move from the
branch passage into the main passage after the fluid meets the flow-rate
measuring resistor. The partition arrangement includes a partition
plate. A length of a part of the partition plate, measured along
a direction of the fluid flow, depends on a position of the part.
Claims What is claimed is:
1. A flow meter comprising:
a tubular member having a main passage in which fluid flows;
a branch passage member disposed in said main passage and having
a branch passage in which the fluid flows;
a support member connecting said branch passage member and a wall
of said tubular member, and supporting said branch passage member
within said main passage;
a partition arrangement disposed in said branch passage and dividing
said branch passage into a plurality of sub passages extending along
a flow of the fluid, said sub passages converging at a meeting position
downstream of said partition arrangement;
a flow-rate measuring resistor disposed in a region of said branch
passage downstream of said partition arrangement and also downstream
of said meeting position for sensing a rate of a flow of the fluid
in said branch passage;
a control circuit electrically connected to said flow-rate measuring
resistor for calculating a measurement value from an output signal
of said flow-rate measuring resistor; and
an outlet formed in said branch passage member for connecting said
branch passage with said main passage to enable the fluid to move
from said branch passage into said main passage after the fluid
meets said flow-rate measuring resistor;
wherein said partition arrangement comprises a partition plate,
and a length of a part of said partition plate, measured along a
direction of the fluid flow, depends on a position of said part.
2. The flow meter of claim 1 wherein said partition plate has
a downstream end formed with a step, a projecting portion, and a
recessed portion.
3. The flow meter of claim 2 wherein said projecting portion and
said recessed portion are of a rectangular wave shape.
4. The flow meter of claim 1 wherein a cross-section of said partition
plate, taken along a fiat plane parallel to the direction of the
fluid flow, has a streamline shape.
5. A hot-wire air flow meter for measuring a rate of an air flow
in an air passage, comprising:
means for dividing the air passage into a main passage and a sub
passage;
a partition arrangement disposed in said sub passage and dividing
said sub passage into a plurality of passages which converge at
a meeting position downstream of said partition arrangement; and
a hot-wire sensor disposed in a region of said sub passage downstream
of said partition arrangement and also downstream of said meeting
position;
wherein said partition arrangement comprises a partition plate,
and a length of a part of said partition plate, measured along a
direction of the fluid flow, varies as said part moves from an outer
portion of said sub passage toward a center of said sub passage.
6. The hot-wire air flow meter of claim 5 wherein said partition
plate has a downstream end formed with a step.
7. A flow meter comprising:
a tubular member having a main passage in which fluid flows at
a given flow rate;
a branch passage member disposed in said main passage and having
a branch passage in which the fluid flows at a branch flow rate
corresponding to a part of said given flow rate;
a support member connecting said branch passage member and a wall
of said tubular member, and supporting said branch passage member
within said main passage;
a partition arrangement disposed in said branch passage and dividing
said branch passage into a plurality of sub passages extending along
a flow of the fluid, said sub passages converging at a meeting position
downstream of said partition arrangement;
a flow-rate measuring resistor disposed in a region of said branch
passage downstream of said partition arrangement and also downstream
of said meeting position for sensing said branch flow rate;
a control circuit electrically connected to said flow-rate measuring
resistor for calculating said given flow rate based on said branch
flow rate sensed by the flow-rate measuring resistor; and
an outlet formed in said branch passage member for connecting the
branch passage with said main passage to enable the fluid to move
from said branch passage into said main passage after the fluid
meets said flow-rate measuring resistor;
wherein said partition arrangement comprises a partition plate,
and a length of a part of said partition plate, measured along a
direction of the fluid flow, depends on a position of said part.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a flow meter such as a device for detecting
the rate of a flow of fluid. This invention relates to, for example,
an air flow meter provided in an air induction passage of and internal
combustion engine.
2. Description of the Prior Art
Recently, some engines have been subjected to microcomputer-based
general control to improve their performances. In the case of automotive
engines, general engine control includes control of the A/F (air-to-fuel)
ratio of an air-fuel mixture supplied to the engines and control
of the rate of the fuel injection into the engines.
Usually, the A/F ratio control and the fuel injection rate control
require information of the rate of the flow of air drawn into the
engines. In typical cases, air flow meters disposed in air induction
passages of the engines detect the rate of the air flow into the
engines. Output signals of such air flow meters are used in the
A/F ratio control and the fuel injection rate control as an indication
of the rate of the air flow into the engines.
Some of air flow meters use a flow sensor of the hot-wire type.
Usually, hot-wire flow sensors are advantageous in cost as well
as dynamic range.
A prior-art air flow meter of the hot-wire type has a cylindrical
casing formed with a main air passage and a sub or branch air passage
which by-passes the main air passage. The cross sectional area of
the main passage and the cross sectional area of the branch passage
are in a predetermined relation so that the rate of the air flow
through the branch passage has a given relation with the rate of
the air flow through the main passage. Accordingly, only the rate
of the air flow through the branch passage is detected, and the
sum of the rates of the air flows through the main passage and the
branch passage is estimated from the detected air flow rate related
to the branch passage.
Regarding the prior-art air flow meter, a hot-wire resistor for
measuring an air flow rate is disposed in the branch passage. A
resistor for temperature compensation is also disposed in the branch
passage. The two resistors extend parallel to each other but occupy
different places as viewed in the direction of the air flow. The
two resistors are electrically connected to a control circuit via
leads.
In the prior-art air flow meter, the hot-wire resistor is exposed
to only the air flow in the branch passage. Therefore, the prior-art
air flow meter is advantageous in preventing the hot-wire resistor
from being contaminated by dust in air. In the case of automotive
use, the prior-art air flow meter follows an air cleaner element
in the direction of the air flow. The design including the branch
passage is effective in reducing a disturbance in the velocity distribution
of the air flow which is caused by the air cleaner element.
In the prior-art air flow meter, it is difficult to completely
remove such a disturbance from the velocity distribution of the
air flow. In addition, it is difficult to remove pulsations from
the air flow which are caused by operation of a related automotive
engine.
In automotive engines, a backfire tends to occur when an ignition
timing is excessively earlier than the normal timing. During the
occurrence of a backfire, shock wave caused by a high pressure and
a high temperature in engine cylinders travels back toward an upstream
side of a related engine. The hot-wire resistor in the prior-art
air flow meter tends to be damaged or deformed by backfire shock
wave. In addition, dust on the hot-wire resistor is burned by a
backfire and the resultant material is closely fixed to the hot-wire
resistor so that the hot-wire resistor is deteriorated.
Japanese published unexamined patent application 56-108910 discloses
an advanced air flow meter provided with an air flow buffer extending
upstream of a hot-wire resistor but downstream of an air cleaner
element. The air flow buffer reduces disturbances and pulsations
in an air flow which meets the hot-wire resistor. The air flow buffer
includes a stainless steel mesh or a ceramic honeycomb. Generally,
the air flow buffer effectively damps backfire shock wave which
travels between the engine and the air cleaner element. Accordingly,
the air flow buffer protects the hot-wire resistor from the backfire
shock wave.
In a range around a certain point of the air flow rate, the value
represented by the output signal of the air flow meter of Japanese
application 56-108910 tends to vary discontinuously as a function
of the air flow rate.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved flow meter.
A first aspect of this invention provides a flow meter comprising
a tubular member having a main passage in which fluid flows; a branch
passage member disposed in the main passage and having a branch
passage in which the fluid flows; a support member connecting the
branch passage member and a wall of the tubular member, and supporting
the branch passage member within the main passage; a partition arrangement
disposed in the branch passage and dividing the branch passage into
a plurality of sub passages extending along a flow of the fluid;
a flow-rate measuring resistor disposed in a region of the branch
passage downstream of the partition arrangement for sensing a rate
of a flow of the fluid in the branch passage; a control circuit
electrically connected to the flow-rate measuring resistor for calculating
a measurement value from an output signal of the flow-rate measuring
resistor; and an outlet formed in the branch passage member for
connecting the branch passage with the main passage to enable the
fluid to move from the branch passage into the main passage after
the fluid meets the flow-rate measuring resistor; wherein the partition
arrangement comprises a partition plate, and a length of a part
of the partition plate, measured along a direction of the fluid
flow, depends on a position of the part.
It is preferable that the partition plate has a downstream end
formed with a step, and the downstream end has a projecting portion
and a recessed portion.
It is preferable that the projecting portion and the recessed portion
are of a rectangular wave shape.
It is preferable that a cross-section of the partition plate, which
is taken along a flat plane parallel to the direction of the air
flow, has a streamline shape.
A second aspect of this invention provides a hot-wire air flow
meter for measuring a rate of an air flow in an air passage which
comprises means for dividing the air passage into a main passage
and a sub passage; a partition arrangement disposed in the sub passage
and dividing the sub passage into a plurality of passages; and a
hot-wire sensor disposed in a region of the sub passage downstream
of the partition arrangement; wherein the partition arrangement
comprises a partition plate, and a length of a part of the partition
plate, measured along a direction of the fluid flow, varies as the
part moves from an outer portion of the sub passage toward a center
of the sub passage.
It is preferable that the partition plate has a downstream end
formed with a step.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view of a flow meter according to a first
embodiment of this invention.
FIG. 2 is a sectional view of a partition arrangement taken along
the line II--II in FIG. 1.
FIG. 3 is a diagram of the relation between a measurement variation
and a flow rate regarding each of the flow meter of FIG. 1 and a
reference flow meter.
FIG. 4 is a sectional view of a portion of a flow meter according
to a second embodiment of this invention.
FIG. 5 is a sectional view of a partition arrangement taken along
the line V--V in FIG. 4.
FIG. 6 is a sectional view of a portion of a flow meter according
to a third embodiment of this invention.
FIG. 7 is a sectional view of a portion of a flow meter according
to a fourth embodiment of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
With reference to FIG. 1 an air flow meter 10 includes a body
having an upstream end and a downstream end. The upstream end of
the body of the air flow meter 10 is formed with an upstream opening
213. The upstream end of the body of the air flow meter 10 is inserted
into an air cleaner (not shown), and is connected thereto. The downstream
end of the body of the air flow meter 10 is formed with a downstream
opening 313 and is inserted into an air induction duct (not shown)
leading to an engine (not shown). A belt (not shown) extending around
the air induction duct fastens the air induction duct to the downstream
end of the body of the air flow meter 10.
The air flow meter 10 includes a barrel composed of an upstream
section 200 an intermediate section or a central section 100 and
a downstream section 300 sequentially and coaxially connected to
each other. The upstream barrel 100 the intermediate barrel 100
and the downstream barrel 300 define an air passage therein.
The air flow meter 10 includes an oval (egg-shaped) central member
14 disposed coaxially in the air passage. As will be made clear
later, the air flow meter 10 has an air passage therein which is
divided into a main air passage and a sub air passage (branch air
passage). The main air passage is defined between the central member
14 and the outer shell of the air flow meter 10. The sub air passage,
that is, the branch air passage, extends in the central member 14.
The central member 14 has a housing composed of an upstream section
400 an intermediate section 160 and a downstream section 360 sequentially
and coaxially connected to each other.
The central barrel 100 is made of, for example, resin. A container
110 is formed integrally with an outer portion of the central barrel
100. The container 110 accommodates a control circuit 114 for a
hot-wire sensor portion 500 which will be described later. The circuit
container 110 is provided with a lid (no reference numeral).
The central barrel 100 has cylindrical inner surfaces. The central
barrel 100 has a plurality of ribs including ribs 140 and 150. These
ribs are integrally formed with a major part of the central barrel
100. The ribs (including the ribs 140 and 150) extend radially inward
from the inner surfaces of the central barrel 100. It is preferable
that the ribs are angularly spaced. The intermediate housing 160
of the central member 14 is formed integrally with inner ends of
the ribs (including the ribs 140 and 150) so that the central member
14 is supported on the central barrel 100 by the ribs.
The upstream housing 400 of the central member 14 has a shape of
a bullet. The upstream housing 400 is made of, for example, resin.
The upstream housing 400 fits into the intermediate housing 160
of the central member 14 and is hence fixed thereto. A central
part of a front end of the upstream housing 400 has an inlet opening
410 which is immediately followed by a partition arrangement 15.
The inlet opening 410 forms an upstream end of the branch air passage.
The partition arrangement 15 is formed integrally with the upstream
housing 400. The partition arrangement 15 serves as both a heat
exchanger and a flow adjuster. The partition arrangement 15 is also
referred to as the heat exchanger member 15.
With reference to FIGS. 1 and 2 the partition arrangement 15 includes
a cylindrical portion 15a coaxial with the upstream housing 400.
The partition arrangement 15 also includes flat partition plates
15b extending parallel with the axis of the upstream housing 400.
The partition plates 15b radially and inwardly extend from the cylindrical
portion 15a, and meet at around the axis of the cylindrical portion
15a. The partition plates 15b are spaced by equal angular intervals
of, for example, 90 degrees. In other words, adjacent twos of the
partition plates 15b are perpendicular to each other. Accordingly,
the cylindrical portion 15a and the partition plates 15b define
axially-extending through-holes 15c which have, for example, a quadrant
cross section. The through-holes 15c lead from the inlet opening
410 and form a part of the branch air passage. The through-holes
15c are directed approximately toward a heater 570 and a thermometer
580. Specifically, the axially-extending surfaces of the partition
arrangement 15 which define the through-holes 15c are directed approximately
toward the heater 570 and the thermometer 580.
The upstream housing 400 includes a cylindrical tube 420 coaxially
following the partition arrangement 15 in the direction of an air
flow. The cylindrical tube 420 has a passage therein which communicates
with the through-holes 15c in the partition arrangement 15 and which
forms a part of the branch air passage. The cylindrical tube 420
is formed integrally with the partition arrangement 15.
A cylindrical measurement tube 430 coaxially fits into a downstream
end of the branch tube 420. The measurement tube 430 has a passage
therein which forms a part of the branch air passage. The inner
surfaces of the intermediate housing 160 are formed with radially-extending
plate ribs including ribs 167 and 169. These ribs are spaced at
equal angular intervals of, for example, 90 degrees. A downstream
end of the measurement tube 430 contact upstream portions of the
ribs (including the ribs 167 and 169) so that they are supported
on the intermediate housing 160 by the ribs. It is preferable that
the downstream edge of the branch tube 420 abuts against the upstream
edges of the ribs (including the ribs 167 and 169). The ribs (including
the ribs 167 and 169) provide given spacings between the downstream
end of the measurement tube 430 and a cylindrical wall member 163
of the intermediate housing 160. These spacings form a part of the
branch air passage, and extend between the downstream end of the
measurement tube 430 and an outlet opening (or outlet openings)
440 provided in the walls of the intermediate housing 160. The outlet
openings 440 form a downstream end of the branch air passage.
The outlet openings 440 communicate with a space between the intermediate
housing 160 and the intermediate barrel 100 which forms a part of
the main air passage. Thus, the downstream end of the branch air
passage is connected to the main air passage via the outlet openings
440.
The cylindrical wall member 163 of the intermediate housing 160
has an axial bore 165 in which a cylindrical resin base 510 of the
hot-wire sensor portion 500 is fixedly disposed. The hot-wire sensor
portion 500 includes support pins 520 530 540 and 550 mounted
on the resin base 510. The support pins 520 530 540 and 550 axially
extend through the resin base 510 and project from both upstream
and downstream ends of the resin base 510. The support pins 520
and 530 have longer portions projecting from the upstream end of
the resin base 510 while the support pins 540 and 550 have shorter
portions projecting from the upstream end of the resin base 510.
The heater 570 is electrically connected and mechanically supported
between ends of the longer pins 520 and 530. The heater 570 forms
a resistor (hot-wire resistor) for measuring an air flow rate. The
thermometer 580 is electrically connected and mechanically supported
between ends of the shorter pins 540 and 550.
The heater 570 includes a ceramic bobbin, a platinum wire wound
on the bobbin, and a pair of leads provided on the bobbin. Ends
of the platinum wire are electrically connected to the leads for
connection with the support pins 520 and 530. The platinum wire
in the heater 570 constitutes a temperature-responsive resistor
having predetermined characteristics (temperature response characteristics).
Similarly, the thermometer 580 includes a ceramic bobbin, a platinum
wire wound on the bobbin, and a pair of leads provided on the bobbin.
Ends of the platinum wire are electrically connected to the leads
for connection with the support pins 540 and 550. The platinum wire
in the thermometer 580 constitutes a temperature-responsive resistor
having predetermined characteristics (temperature response characteristics).
It is preferable that the characteristics of the temperature-responsive
resistor in the heater 570 are equal to the characteristics of the
temperature-responsive resistor in the thermometer 580.
Electrical conductors (not shown) extend between the circuit container
110 and a space defined between the intermediate housing 160 and
the downstream housing 360. The electrical conductors pass through
the walls of the rib 140. First ends of the electrical conductors
are connected to the control circuit 114 within the circuit container
110. Second ends of the electrical conductors are connected via
a flexible wiring member (not shown) to ends of the support pins
520 530 540 and 550 which project from the downstream end of
the resin base 510 of the hot-wire sensor portion 500. Therefore,
the control circuit 114 within the circuit container 110 is electrically
connected to the heater 570 and the thermometer 580.
The air flow meter 10 operates as follows. Air flows along the
direction "A" of FIG. 1 and enters the air flow meter
10. A portion of the air flows via the inlet opening 410 into the
branch air passage extending in the central member 14. A remaining
portion of the air flows into the main air passage extending between
the central member 14 and the outer shell of the air flow meter
10.
In the branch air passage, the air flows through the heat exchanger
member 15 after passing through the inlet opening 410. In cases
where the air has a disturbance in flow velocity, the disturbance
is reduced and suppressed as the air flows through the holes 15c
in the heat exchanger member 15. Thus, the air flow in the branch
air passage is adjusted by the heat exchanger member 15.
The air flowing into the branch air passage tends to be exposed
to an uneven temperature distribution caused by factors such as
an uneven temperature distribution of the air cleaner. Such an uneven
temperature distribution in the air might cause a temperature difference
between the heater 570 and the thermometer 580 which would result
in an error in the detection of an air flow rate by the air flow
meter 10. Such an uneven temperature distribution in the air is
reduced and suppressed by the heat exchanger member 15 as will be
described below.
In the heat exchanger member 15 the through-holes 15c are defined
between the cylindrical portion 15a and the partition plates 15b.
The cylindrical portion 15a and the partition plates 15b are integral
with the major part of the upstream housing 400 so that they are
in a substantially uniform temperature distribution. The air in
the through-holes 15c contacts the cylindrical portion 15a and the
partition plates 15b via large areas so that efficient heat exchange
can occur between the air in the through-holes 15c and the walls
of the heat exchanger member 15. Therefore, an uneven temperature
distribution in the air can be reduced and suppressed as the air
passes through the heat exchanger member 15.
The through-holes 15c in the heat exchanger member 15 are directed
approximately toward the heater 570 and the thermometer 580 so that
the air will exit from the heat exchanger member 15 in directions
toward the heater 570 and the thermometer 580. The air sequentially
passes through the branch tube 420 and the measurement tube 430
after exiting from the heat exchanger member 15. The air meets the
heater 570 and the thermometer 580 when flowing in the measurement
tube 430.
It is preferable that the effective cross-sectional area of the
branch air passage in the measurement tube 430 is smaller than the
effective cross-sectional area of the branch air passage in the
branch tube 420. In this case, the air flow in the branch air passage
is further adjusted by the measurement tube 430. Portions of the
air which meet the heater 570 and the thermometer 580 are substantially
equal in temperature as a result of operation of the heat exchanger
member 15. The effective cross-sectional area of the branch air
passage in the measurement tube 430 is preferably chosen so as to
provide an air flow velocity sufficient for measurement even when
the engine operates in conditions requiring only a small air supply
rate.
The heater 570 is heated by the control circuit 114 at a given
temperature relative to the temperature of the air in the measurement
tube 430. The heater 570 the thermometer 580 and the control circuit
114 cooperate to measure the rate (velocity) of the air flow in
the measurement tube 430. The control circuit 114 outputs an electric
signal representing the measured air flow rate. The output signal
of the control unit 114 is fed to a fuel injection control device
(not shown), and the measured air flow rate is used in determination
of a target fuel injection rate.
After the air exits from the measurement tube 430 the air encounters
the wall member 163 of the intermediate housing 160 and the resin
base 510 of the hot-wire sensor portion 500 so that the direction
of the air flow changes from the axial direction to the radial direction.
Then, the air flows toward the outlet opening 440 and moves thereinto.
The air passes through the outlet opening 440 and enters the main
air passage extending between the central member 14 and the outer
shell of the air flow meter 10.
The partition arrangement 15 will be further described. Downstream
edges of the partition plates 15b have stepped configurations (see
FIG. 1). An outer portion of each of the partition plates 15b is
greater in axial length (axial dimension) than an inner portion
thereof. In other words, the outer portion of each of the partition
plates 15b is greater than the inner portion thereof in dimension
along the direction of the air flow. Therefore, the air flow along
the inner portions of the partition plates 15b and the air flow
along the outer portions of the partition plates 15b are different
from each other in transitional flow rate point at which a laminar
flow is replaced by a turbulent flow. This design provides a wider
transitional flow rate rage. As a result, the value represented
by the output signal of the air flow meter 10 is hardly affected
by an abrupt change in a resistance to the air flow. In addition,
the value represented by the output signal of the air flow meter
10 is prevented from discontinuously varying as a function of the
air flow rate. In other words, the output signal of the air flow
meter 10 has a smooth relation with the air flow rate.
Experiments were performed on the air flow meter 10 and a reference
air flow meter. The reference air flow meter was similar to the
air flow meter 10 except that downstream edges of partition plates
15b of a partition arrangement 15 were devoid of steps. During the
experiments, a measurement variation of each of the air flow meter
10 and the reference air flow meter was monitored and plotted at
different points of an air flow rate. FIG. 3 shows the experimentally-obtained
relation between the measurement variation and the air flow rate
regarding each of the air flow meter 10 and the reference air flow
meter. As shown in FIG. 3 the air flow meter 10 was better than
the reference air flow meter in the relation between the measurement
variation and the air flow rate.
Second Embodiment
FIGS. 4 and 5 show a second embodiment of this invention which
is similar to the embodiment of FIGS. 1-3 except that the partition
arrangement 15 of FIGS. 1 and 2 is modified into a partition arrangement
15A.
A cross-section of each partition plate of the partition arrangement
15A, which is taken along a flat plane parallel to the direction
of an air flow, has a streamline shape. The streamline shape enables
even an air flow of a higher rate to move along the partition plate.
Therefore, heat exchange can be more efficiently executed between
air and the partition plate.
According to the embodiment of FIGS. 4 and 5 the partition arrangement
15A can execute sufficient heat exchange in a wide rage of the air
flow rate.
Third Embodiment
FIG. 6 shows a third embodiment of this invention which is similar
to the embodiment of FIGS. 1-3 except that the partition arrangement
15 of FIGS. 1 and 2 is modified into a partition arrangement 15B.
The downstream edge of each of partition plates in the partition
arrangement 15B has two steps. An outer portion of each partition
plate is greater in axial length (axial dimension) than an intermediate
portion thereof. The intermediate portion of each partition plate
is greater in axial length (axial dimension) than an inner portion
thereof.
Fourth Embodiment
FIG. 7 shows a fourth embodiment of this invention which is similar
to the embodiment of FIGS. 1-3 except that the partition arrangement
15 of FIGS. 1 and 2 is modified into a partition arrangement 15C.
Downstream edges of partition plates in the partition arrangement
15C have stepped configurations. An outer portion of each partition
plate is smaller in axial length (axial dimension) than an inner
portion thereof. |