Abstrict A hot-wire air-flow meter for internal combustion engines is integrated
with a throttle valve so that the throttle valve is disposed immediately
downstream of the outlet port of a bypass air passage of the air-flow
meter. The shaft of the throttle valve inclines at most 45.degree.
against a line connecting between the axis of the inlet port of
the bypass air passage and the axis of the main air passage of the
air-flow meter, whereby disturbance caused by the throttle valve
in minimized. Further, a bent duct is disposed upstream of the air-flow
meter so that a plane on which a bent axis of the bent duct is disposed
crosses the above-mentioned line at an angle of at most 45.degree.,
whereby influence of the bent duct on the flow rate measuring accuracy
is minimized.
Claims What is claimed is:
1. A hot-wire air-flow meter for measuring the flow rate of air
flowing from an air cleaner into an internal combustion engine,
comprising:
means for defining main air passage having a venturi portion, said
main air passage means including a flow meter body made of one piece
and a ring rigidly inserted in said flow meter body for forming
said venturi portion;
a bypass air passage defined by said main air passage defining
means so as to bypass said main air passage, said bypass air passage
having an inlet port upstream of said venturi portion and an outlet
port downstream of said venturi portion, said inlet port being a
bore made in said flow meter body so as to open to said main air
passage and said outlet port being opened to said main air passage
and positioned so that the center of said outlet port is disposed
at a position angularly distant 230.degree.-310.degree. from said
inlet port;
thermosensitive means disposed in said bypass air passage for electrically
detecting the flow rate of air flowing therein; and
a throttle valve turnably mounted on said main air passage defining
means immediately downstream of said outlet port of said bypass
passage by a valve shaft of said throttle valve so that a relative
angular position of said valve shaft to a line connecting the central
axis of said inlet port of said bypass air passage and the central
axis of said main air passage is at most 45.
2. The hot-wire air-flow meter as defined in claim 1 wherein said
outlet port of said bypass air passage is disposed in a perpendicular
direction to said throttle valve shaft.
3. The hot-wire air-flow meter for measuring the flow rate of air
flowing from an air cleaner into an internal combustion engine,
comprising:
a flow meter body made of one piece defining therein a main air
passage;
a ring rigidly inserted in said flow meter body and forming a venturi
position;
a bypass air passage defined by said flow meter body so as to bypass
said main air passage, said bypass air passage having an inlet port
upstream of said venturi portion and an outlet port downstream of
said venturi portion, said inlet port being a bore made in said
flow meter body so that the central axis of said bore is in parallel
to the central axis of said ring;
thermosensitive means disposed in said bypass air passage for electrically
detecting the flow rate of air flowing therein;
a throttle valve turnably mounted on said flow meter body immediately
downstream of said outlet port of said bypass passage by a valve
shaft of said throttle valve so that a relative angular position
of said valve shaft to a line connecting between the central axis
of said inlet port of said bypass air passage and the central axis
of said main air passage is at most 45.degree.; and
a bent duct for fluidly connecting said flow meter body to said
air cleaner, said bent duct being mounted on said flow meter body
so that the central axis of said throttle valve shaft crosses, at
an angle of at most 45.degree., a plane on which the axis of said
bent duct is disposed.
4. The hot-wire air-flow meter as defined in claim 3 wherein said
outlet port of said bypass air passage is opened to said main air
passage and positioned so that the center of said outlet port is
disposed at a position angularly distant 230.degree.-310.degree.
from the said inlet port.
5. The hot-wire air-flow meter as defined in claim 4 wherein said
outlet port of said bypass air passage is disposed in a perpendicular
direction to said throttle valve shaft.
6. The hot-wire air-flow meter as defined in claim 3 wherein said
bypass passage inlet port is round and subjected to total pressure
in the air passage, upstream of said venturi portion, said bypass
air passage outlet port being rectangular and subjected to a static
pressure in the air passage.
7. The hot-wire air-flow meter as defined in claim 6 wherein the
axis of said throttle valve shaft crosses, at right angle, a plane
which includes therein central the axis of said ring and passes
the centers of said ring and said bypass passage outlet port.
8. The hot-wire air-flow meter as defined in claim 3 wherein said
bent duct is bent about a right angle.
Description BACKGROUND OF THE INVENTION
The present invention relates to a hot-wire air-flow meter, and
particularly to a hot-wire air-flow meter for automobile engines
in which a throttle valve for controlling the flow rate of air sucked
into the engine is integrated.
An internal combustion engine for automobiles has a fuel supply
system comprising a fuel supply line and an air induction line.
In the fuel supply system, air purified by an air cleaner is introduced
into the engine through a passage. The passage is provided with
a fuel supply port, a throttle valve for controlling the flow rate
of air flowing into the engine and a hot-wire air-flow meter for
measuring the airflow rate. In a conventional internal combustion
engine for automobiles, there is a relatively large distance between
the throttle valve and the air-flow meter. Namely, the former is
arranged near a collector inlet of an intake manifold, and the latter
immediately downstream of the air cleaner. When installing them
in an automobile which has a cramped engine compartment, it is necessary
to integrate the hot-wire air-flow meter and the throttle valve
in order to improve mounting easiness and space and reduce the cost
of the fuel supply system. FIG. 1 of Japanese Laid-open Patent Application
No. 55-104718 shows an integrated flow meter and throttle valve
which is mounted on the collector of the intake manifold.
Further, when the space within the engine compartment is limited,
an upstream side of the air-flow meter and a downstream side of
the air cleaner are communicated by means of a bent duct, as disclosed
in Japanese Laid-open Patent Application No. 57-103016. The bent
duct, which is bent immediately upstream of the air-flow meter,
causes turbulence; therefore in the prior art there is provided
a rectifier between the air-flow meter and an air cleaner in order
to rectify the turbulence of the air flow.
Turbulence raises the problem that the output voltage of the air-flow
meter with respect to the volume of air becomes high with the integrated
type of meter, compared with the output voltage of a separate meter
in which the air-flow meter is separated from the throttle valve
with a relatively large distance, as above-mentioned. Further, the
waveform of the output voltage of the integrated meter shows large
pulsations compared with the separate meter. Therefore, it is difficult
for the hot-wire air-flow meter accompanied by the turbulence to
detect the real value of the air flow rate.
SUMMARY OF THE INVENTION
Accordingly an object of the present invention is to provide a
hot-wire air-flow meter with a throttle valve integrated therewith,
which has an excellent mounting efficiency and provides a high measuring
accuracy.
Another object of the present invention is to provide a hot-wire
air-flow meter which has a throttle valve integrated therewith,
which has good installation and provides a high measuring accuracy,
and which solves the above problem caused by the integration of
the throttle valve into the hot-wire air-flow meter and the arrangement
of a bent duct without providing any rectifiers between the air-flow
meter and an air cleaner.
During the development of this invention, it was confirmed experimentally
that the real air-flow rate cannot be detected if the hot-wire air-flow
meter and the throttle valve are integrated, and, furthermore, it
was confirmed that turbulence occurs in the air-flow if, for reasons
of space, a bent duct is provided immediately upstream of the air-flow
meter resulting in large pulsations in the output voltage of the
air-flow meter.
According to the present invention, a means of solving these problems
is such that the throttle valve is integrated with the hot-wire
air-flow meter so that the central axis of the shaft of the throttle
valve will be disposed at an angle of 0.degree.-45.degree. against
a line connecting between the central axis of a main air passage
of the flow meter and the central axis of a bypass passage provided
with a thermosensitive resistor used for measuring the air flow
rate.
Preferably, there is provided a means for obviating the adverse
effects resulting from the bent duct disposed immediately upstream
of the air-flow meter, in addition to the above-mentioned problem
solving means. The adverse-effect obviating means is such that the
bent duct is mounted so that a plane on which the axis of the bent
duct is disposed inclines to the central line of the throttle valve
shaft at an angle of at most 45.degree..
By the integrated hot-wire air-flow meter and throttle valve it
is meant that preferably a meter body for defining air passages
and mounting various parts is made of one piece on which the throttle
valve is mounted, otherwise the hot-wire air-flow meter and the
throttle valve are made into one unit in which the flow meter and
the throttle valve are disposed so that the distance between the
outlet of the bypass passage and the throttle valve shaft is less
than 100 mm.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a fuel supply system in which
a hot-wire air-flow meter of an embodiment of the present invention
is used;
FIG. 2 is a sectional front view of the hot-wire air-flow meter
in FIG. 1;
FIG. 3 is a sectional view taken along a line III--III of FIG.
2;
FIG. 4 is a graph showing a relation between inclination angles
.theta.1 and air-flow meter output voltage;
FIG. 5 and 6 are waveform diagrams of the output voltage of the
air-flow meter; and
FIG. 7 to 9 are waveform diagrams of air-flow meter output voltage.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A preferred embodiment of the invention will be described hereinunder,
referring to the drawings. A fuel injection system into which an
embodiment of the invention is incorporated will now be described
with reference to FIG. 1. Air enters from the intake portion of
an air cleaner 1 passes through a duct 3 and past a hot-wire air-flow
meter 5 and enters a collector 7. From this section, the air is
distributed to each branch of an intake manifold 11 communicating
with an internal-combustion engine 9 and is sucked into cylinders.
Meanwhile, fuel is sucked from a fuel tank 13 by a fuel pump 15
and the fuel, after being pressurized, is supplied to a fuel line
provided with a fuel damper 17 a fuel filter 19 an injector 21
and a fuel-pressure regulator 23. The pressure of the fuel is regulated
to a fixed level by the regulator 23 and is injected into the manifold
11 by the injector 21 mounted on the intake manifold 11. A signal
detecting the air-flow rate is output from the air-flow meter 5
to a control unit 25. A throttle valve opening sensor 27 is mounted
on a throttle valve 6 and a signal for detecting the degree of
opening of the throttle valve 6 is output from the sensor 27 to
the control unit 25. A temperature sensor 29 is mounted on the internal-combustion
engine 9 and a signal for detecting the temperature of the internal-combustion
engine 9 is output from the sensor 29 to the control unit 25. A
crank angle sensor is built into a distributor 31. Reference signals
for injection timing and ignition timing and a signal for detecting
the rotational speed are output from this sensor to the unit 25.
This completes the description of the fuel injection system.
Next, the hot-wire air-flow meter 5 will be described hereinunder
in detail, referring to FIGS. 2 and 3.
In FIG. 2 a flow meter body 50 or member is made of one piece
for defining main and bypass air passages 52 and 53 and for mounting
various parts. A ring 51 is rigidly inserted in a bore of the flow
meter body 50 to form a venturi portion of the main air passage
52. The bypass air passage 53 is made by vertical and horizontal
bores 531 and 532 formed in the flow meter body 50 and a channel
which is described later. The central axis of the vertical bore
531 is parallel to the central axis of the main air passage 52 at
the venturi portion, that is, to the central axis of the ring 51.
Thermosensitive resistors 54 or hot wires held by a plastic mold
55 are disposed in the vertical bore 531 of the bypass air passage
53 in order to measure air flow rate in the bypass air passage 53.
The vertical bore 531 communicates with the horizontal bore 532
with one end of the bore 532 being blocked by an insert 533. The
ring 51 has a recess on the outer surface at one end thereby forming
the above-mentioned channel 534 in cooperation with the inner wall
of the bore of the flow meter body 50. The channel 534 communicates
with the horizontal bore 532 and an outlet port 535 which is formed
rectangular at a position of 270.degree. from the vertical bore
531 as shown in FIG. 3. The angular central position of the outlet
port 535 is preferably about 230.degree.-310.degree. from the inlet
port 531 whereby the bypass passage becomes long and the pulsation
of air flow in the bypass passage 53 is partially absorbed. The
vertical bore 531 or inlet port of the bypass air passage 53 is
opened to the upstream side of the venturi portion so as to be subjected
to total pressure of the air-flow from the duct 3 and the outlet
port 535 is subjected to only static pressure.
The throttle valve 6 which is disposed immediately downstream
of the outlet port 535 comprises a valve body 61 and a throttle
valve shaft 62 securing thereon the valve body 61 and being turnably
supported by the flow meter body 50. The throttle valve 6 is positioned
so that the central axis of the throttle valve shaft 62 is disposed
on a line connecting the central axis of the vertical bore 531 and
the central axis of the venturi portion of the main air passage,
that is, the ring 51.
By the construction, influence on the air flow rate in the bypass
air passage 53 by the integration of the throttle valve 6 into the
air-flow meter 5 is minimized.
A description will be made of experiments with respect to a relative
angular position between the inlet port 531 and the throttle valve
shaft 62. The experiments were carried out using the same hot-wire
air-flow meter as the above-mentioned except that the angular position
of the throttle valve shaft 62 relative to the inlet port 531 of
the bypass air passage 53 can be set freely, under the condition
that air flows into the main air passage 52 uniformly. Measurements
were made of output voltage, and observed, when the air-flow rate
was set to 200 Kg/h and the relative angular position or angle .theta.1
as shown in FIG. 3 of the throttle valve shaft 62 with respect
to the inlet port 53 of the by-pass air passage 52 was varied. The
results are shown in FIG. 4 to 6. FIG. 4 shows the relationship
between output voltage with respect to the relative angular position
.theta.1. The real air-flow rate was detected when the air inlet
port 531 of the bypass passage 53 was located on the axial center
line of the throttle valve 6. However, if the relative angular position
.theta.1 was varied, an error began to emerge in the vicinity of
45.degree. and became a maximum at 90.degree.. If the relative angular
position .theta.1 was varied further, the error became gradually
smaller, and the real air-flow rate was measured again from around
135.degree.. FIGS. 5 and 6 show the results of observations of the
waveform of the output voltage when the relative angular position
.theta.1 is 0.degree. (180.degree.) and 90.degree., respectively.
These FIGS. 5 and 6 show that pulsations were large at 90.degree.
where the output voltage was high and the error was large. Accordingly,
the permissible range of .theta.1 is 0.degree.-45.degree. and 135.degree.-180.degree.,
that is to say, the inclination angle of the throttle valve shaft
62 to the line connecting the central axis of the inlet port 531
and the central axis of the ring 51 is at most 45.degree..
The outlet port 535 of the bypass air passage 53 is disposed in
a perpendicular direction to the throttle valve shaft 62. The throttle
valve opening at the position is larger than the other position
and influence of the pressure in the air flow by the throttle valve
6 is small compared with the other position.
Next, on the basis of the results of these experiments, a study
was made of the relationship between air-flow direction and the
output voltage in which the air inlet port 531 of the bypass passage
53 was positioned on the axial center line of the throttle valve
shaft 62. The experiments were conducted at an air-flow rate of
200 Kg/h, using such apparatus that the bent duct 3 is mounted on
the hot-wire air-flow meter 5 so that its position can be freely
varied with respect to the hot-wire air-flow meter 5. In the experiments
the axial centers of the inlet port 531 of the bypass passage 53
and the throttle valve shaft 62 were aligned and only the angular
position of the bent duct 3 was varied. The relative angular position
.theta.2 of the duct 3 is measured using, as a reference (.theta.2=0),
a line 8 perpendicular to the line connecting the central axis of
the inlet port 531 and the central axis of the ring 51. The output
voltage was measured, and the waveform of the output voltage was
observed. The results of the experiments are shown in FIGS. 7 to
9. The output voltage was high and the error largest when a plane
on which the axis of the bent duct 3 is disposed was aligned to
the reference line 8 namely, the throttle valve shaft 62 was perpendicular
to the air flow. When the relative angular position of the duct
3 was gradually varied, the output voltage dropped gradually, and
measurement of the real air-flow rate was obtained at 90.degree.
and 270.degree.. If experimental error is taken into consideration,
the permissible range of .theta.2 is 45.degree.-135.degree. or 230.degree.-315.degree..
The waveforms of the output voltage during this time are shown in
FIGS. 7 to 9. The pulsations were minimal when .theta.2 was 90.degree.
(FIGS. 7), detecting the real air-flow rate, while large pulsations
occurred when .theta.2 was 0.degree. and 180.degree. (FIGS. 8 and
9).
As described above, the present invention has the effect that an
inexpensive and compact hot-wire air-flow meter, integrated with
a throttle valve, and having an excellent mounting efficiency can
be mounted on an internal-combustion engine to provide an accuracy
equivalent to that of a conventional separate meter, even if a bent
duct is provided upstream of the air-flow meter. |