Abstrict A highly accurate, low-cost and easy-to-handle heating resistor
type flow meter has a main air flow passage body forming a main
air flow passage for allowing air flowing therethrough. A measuring
module has a heating resistor for measuring a flow rate of the air
inserted inside the main air flow passage body: The measuring module
comprises the heating resistor inside an auxiliary air flow passage
body forming an L-shaped auxiliary air flow passage having an inlet
opening portion opening in a direction perpendicular to a main flow
line of the air and an outlet opening portion opening in a direction
parallel to the main flow line. The main air flow passage body comprises
an orifice on a periphery of the inner side wall positioned in an
upstream side of the air flow passage body. Both of the inlet opening
portion and the outlet opening portion are arranged within a flow
flux zone formed by extending the air flow from a top edge of the
orifice in a direction parallel to the main flow line.
Claims What is claimed is:
1. A heating resistor type flow meter, comprising a main air flow
passage body forming a main air flow passage for allowing a measurable
fluid to flow therethrough; and a measuring module having a heating
resistor for measuring a flow rate of said fluid to be measured,
said measuring module arranged inside said main air flow passage
body, wherein
said measuring module comprises said heating resistor inside an
auxiliary air flow passage body forming an auxiliary air flow passage
having at least one bent portion and an inlet opening portion opening
in a direction substantially perpendicular to a main flow line of
said fluid to be measured and an outlet opening portion opening
in a direction substantially parallel to said main flow line;
said main air flow passage body comprising an orifice on a periphery
of the inner side wall positioned upstream of said air flow passage
body;
both said inlet opening portion and said outlet opening portion
being arranged within a flow flux zone formed by an imaginary extension
of said measured fluid from a top edge of said orifice in a direction
parallel to said main flow line.
2. The heating resistor type air flow meter according to claim
1 wherein a dimension of said orifice is set so that an effective
cross-sectional area ratio of said orifice to an effective cross-sectional
area of said main air flow passage at a position of said orifice
is within a range of about 70.about.90%.
3. The heating resistor type air flow meter according to claim
1 wherein said orifice is formed such that an upstream side half
of said orifice is approximately arc-shaped and a direction of a
wall surface in the downstream side half is nearly normal to the
direction of said main flow line.
4. An intake pipe structural member comprising a main air flow
passage body having a main air flow passage and a hole adapted to
have a measuring module inserted therethrough composing a heating
resistor type air flow meter said measuring module comprising said
heating resistor inside an auxiliary air flow passage body to form
an L-shaped auxiliary air flow passage having an inlet opening portion
opening direction perpendicular to a main flow line of a fluid to
be measured and an outlet opening portion opening in a direction
parallel to said main flow line, said intake pipe structural member
constituting as said main air flow passage, and an orifice being
provided on a periphery of an inner side wall of said main air flow
passage body upstream of said auxiliary air flow passage body.
5. An intake pipe structural member comprising an orifice of a
main air flow passage body at an intake air outlet position of said
intake pipe structural member, said main air flow passage body containing
a heating resistor type air flow meter comprising a main air flow
passage body forming a main air flow passage for allowing a measurable
fluid to flow therethrough; and a measuring module having a heating
resistor for measuring a flow rate of said fluid to be measured,
said measuring module arranged inside said main air flow passage
body, wherein
said measuring module comprises said heating resistor inside an
auxiliary air flow passage body forming an L-shaped auxiliary air
flow passage having an inlet opening portion opening in a direction
perpendicular to a main flow line of said fluid to be measured and
an outlet opening portion opening in a direction parallel to said
main flow line;
said main air flow passage body comprising an orifice on a periphery
of an inner side wall thereof positioned upstream of said auxiliary
air flow passage body;
both said inlet opening portion and said outlet opening portion
being arranged within a flow flux zone formed by an imaginary extension
of said measured fluid from a top edge of said orifice in a direction
parallel to said main flow line, said orifice being separated from
said auxiliary air flow passage body.
6. A fuel control system of an internal combustion engine for controlling
a fuel supply rate using an air flow rate signal obtained from the
heating resistor type air flow meter comprising a main air flow
passage body forming a main air flow passage for allowing a measurable
fluid to flow therethrough; and a measuring module having a heating
resistor for measuring a flow rate of said fluid to be measured,
said measuring module arranged inside said main air flow passage
body, wherein
said measuring module comprises said heating resistor inside an
auxiliary air flow passage body forming an L-shaped auxiliary air
flow passage having an inlet opening portion opening in a direction
perpendicular to a main flow line of said fluid to be measured and
an outlet opening portion opening in a direction parallel to said
main flow line;
said main air flow passage body comprising an orifice on a periphery
of an inner side wall thereof positioned upstream of said auxiliary
air flow passage body;
both said inlet opening portion and said outlet opening portion
being arranged within a flow flux zone formed by an imaginary extension
of said measured fluid from a top edge of said orifice in a direction
parallel to said main flow line.
Description BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of 8-231620 the disclosure
of which is expressly incorporated by reference herein.
The present invention relates to an air flow meter for measuring
an air flow rate, and more particularly to a heating resistor type
air flow meter suitable for measuring an intake air flow rate of
an internal combustion engine of a vehicle.
The conventional way of improving the measuring accuracy of a heating
resistor type air flow meter used in an internal combustion engine
under a pulsating flow condition, as disclosed in Japanese Patent
Application Laid-Open No. 2-1518 provides a flow passage having
an L-shaped detecting tube. That is, the flow passage comprises
a wall against backward flow so that the back flow does not directly
impinge on the heating resistor. Although such a flow passage construction
cannot suppress back flow, it is possible to moderate a so-called
binary-value phenomenon, that is, decrease of a detected value in
the heating resistor type air flow meter which is caused when a
pulsation amplitude of air flow increases.
Further, a flow passage construction having an orifice is disclosed
in Japanese Patent Application Laid-Open No. 1-110220. In this construction,
a heating resistor is arranged just downstream of an orifice inside
a detecting tube which is a nearly straight and short tube parallel
to the main flow direction.
In the prior art described above, it is impossible to measure flow
speed by identifying direction of the flow. Therefore, when averaged
output signals of the heating resistor type air flow meter are plotted
as the boost pressure is being varied by gradually opening the throttle
valve while rotating speed of the engine is kept constant, the averaged
output signal gradually increases, but shows a jump-up phenomenon
at boost pressures above a certain point indicating a plus side
measuring error to an actual flow speed (flow rate), as shown in
FIG. 12(b). The phenomenon is caused by the amplitude of pulsation
of the heating resistor type air flow meter gradually increasing
as opening degree of the throttle valve is increased and finally
back flow occurs at opening degrees of the throttle valve above
a point B, as shown in FIG. 12(b). The heating resistor type air
flow meter cannot identify flow direction. Therefore, when back
flow occurs, the averaged output increases because flow speed is
equally detected independently of forward flow and back flow. It
is known that this phenomenon often occurs particularly in an engine
having four or less cylinders at a comparatively low rotating speed
range of 1000 to 2000 rpm, and hardly occurs in an engine having
more than four cylinders.
It is possible to reduce the error caused by back flow by employing
one of the prior art teachings described above in which a wall against
backward flow is provided in the flow passage so that the back flow
does not directly impinge on the heating resistor. However, the
error can be reduced by only a half. This is because when back flow
occurs, forward flow increases by an amount of the back flow at
the same time.
Further, it is difficult to prevent the back flow in an intake
flow passage from occurring because of structures of the engine
and the intake flow passage. Accordingly, in order to reduce the
error caused by back flow, it is necessary to employ a complex method
such as a structure in which an amount of back flow rate is subtracted
from an amount of forward flow rate or a structure in which both
of a forward flow rate and a back flow rate are separately measured.
An object of the present invention is to provide a low-cost and
easy-to-handle heating resistor type flow meter by improving the
measuring accuracy, including deviation accuracy, under pulsating
flow accompanying back flow when the heating resistor type flow
meter is mounted on a vehicle.
A heating resistor type flow meter to attain the above object comprises
a main air flow passage body forming a main air flow passage for
allowing a fluid to be measured flowing therethrough; and a measuring
module having a heating resistor for measuring a flow rate of the
fluid to be measured, inserted inside the main air flow passage
body, wherein
the measuring module comprises the heating resistor inside an auxiliary
shaped auxiliary air flow passage body forming an L-shaped auxiliary
air flow passage having an inlet opening portion opening in a direction
perpendicular to a main flow line of the fluid to be measured and
an outlet opening an portion opening in a direction parallel to
the main flow line;
the main air flow passage body comprises an orifice on a periphery
of the inner side wall positioned in an upstream side of the air
flow passage body; and both of the inlet opening portion and the
outlet opening portion are arranged within a flow flux zone formed
by extending the fluid to be measured from a top edge of orifice
in a direction parallel to the main flow line.
According to the present invention, because increase of flow speed
within the flow flux zone formed by the orifice reduces an effect
of back flow flowing in the auxiliary air flow passage body having
the both opening portions arranged within the flow flux zone, the
measuring accuracy can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, advantages and novel features of the present invention
will become apparent from the following detailed description of
the invention when considered in conjunction with the accompanying
drawings wherein:
FIG. 1 is a cross-sectional front view showing an embodiment of
a heating resistor type air flow meter in accordance with the present
invention.
FIG. 2 is a side view showing the heating resistor type air flow
meter of FIG. 1 seen from the upstream side.
FIG. 3 is a circuit diagram showing the construction of the heating
resistor type air flow meter of FIG. 1.
FIGS. 4(a) and 4(B) are diagrams showing the mechanism for reducing
a jump-up error by an orifice in accordance with the present invention.
FIGS. 5A and 5D are views of air flow distribution in ducts without
and with orifices, respectively, and showing the mechanism for reducing
a binary-value phenomenon by an orifice in accordance with the present
invention.
FIG. 6 is a graph showing the relationship between orifice dimension
and jump-up error.
FIG. 7 is a graph showing the relationship between position of
an orifice relative to inlet and outlet ports of an auxiliary air
passage and output noise.
FIG. 8 is a cross-sectional view showing another embodiment of
a heating resistor type air flow meter in accordance with the present
invention.
FIG. 9 is a cross-sectional view showing a further embodiment of
a heating resistor type air flow meter in accordance with the present
invention.
FIG. 10 is an enlarged view showing a joint portion of FIG. 9.
FIG. 11 is a view showing an embodiment of an internal combustion
engine of an electronic fuel injection control type mounting a flow
meter in accordance with the present invention.
FIGS. 12A and 12B are diagrams explaining a jump-up error of a
flow meter under pulsating flow.
FIG. 13 is a diagram explaining a binary-value phenomenon of a
flow meter under pulsating flow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The heating resistor type air flow meter (hereinafter referred
to as "flow meter") comprises a measuring module 52 for
measuring flow rate, a body 53 that is, a main air flow passage
body 20 and parts for attaching the body 53 to the measuring module
52 such as screws 54a, a seal 54b and so on which form a main air
flow passage 22.
A hole 25 is bored on a wall of the main air flow passage body
20 of the body 53 forming the main air flow passage 22 and the
measuring module 52 of an auxiliary air flow passage body 10 is
inserted through the hole 25 and fixed to the main air flow passage
body 20 using the screws 54a so as to maintain mechanical strength
between a mounting surface of the main air flow passage 20 and a
mounting surface of a housing 1. The seal 54b is attached between
the measuring module 52 and the body 53 of the main air flow passage
body 20 to keep air-tightness.
The measuring module 52 is mainly composed of the housing 1 containing
a circuit board 2 for mounting a drive circuit to be described later
and the auxiliary air flow passage body 10 made of a non-conductive
material. In the auxiliary air flow passage body 10 a heating resistor
3 for detecting an air flow rate and a temperature-sensing resistor
4 for compensating intake air temperature are arranged so as to
be electrically connected to the circuit board 2 through a support
body 5 made of a conductive material. That is, the housing 1 the
circuit board 2 the heating resistor 3 the temperature-sensing
resistor 4 the auxiliary air flow passage 10 and so on are integrated
in a unit as the measuring module 52.
In regard to the operational principle of flow measurement in the
above-mentioned flow meter, the construction of circuit will be
described first. FIG. 3 is a circuit diagram showing the construction
of the heating resistor type air flow meter of FIG. 1. The drive
circuit formed on the circuit board 2 of the flow meter is composed
of roughly a bridge circuit and a feedback circuit. The bridge circuit
is constructed by the heating resistor 3 (RH) for measuring an intake
air flow rate, the temperature-sensing resistor 4 (RC) for compensating
intake air temperature and resistors R10 and R11 and heating current
Ih is conducted to the heating resistor RH being controlled by feedback
using an operation amplifier OP1 so as to keep a constant temperature
difference between the heating resistor RH and the temperature-sensing
resistor RC to output an output signal V2 corresponding to an air
flow rate. When the air flow speed is fast, the heating current
Ih is increased since an amount of heat dissipated from the heating
resistor RH is large. On the other hand, when the air flow speed
is slow, the heating current may be small since an amount of heat
dissipated from the heating resistor RH is small. Therein, since
the amount of heat dissipated from the heating resistor RH is independent
of the direction of air flow, that is, forward flow or back flow,
the heating current Ih flows even when air flows backward and as
a result the jump-up phenomenon of the flow meter occurs.
The auxiliary air flow passage body 10 of a "passage structure
forming an L-shaped detecting tube" forms a nearly L-shaped
auxiliary air flow passage 13. That is, the passage 13 comprises
a longitudinal passage 13a and a lateral passage 13b which is composed
of an auxiliary air passage inlet port 11 opening in a direction
perpendicular to a main flow line of the forward direction 23 of
air flow; the longitudinal passage 13a extending parallel to the
main flow line from the auxiliary air passage inlet port 11; the
lateral passage 13b communicating with the longitudinal passage
13a and bending nearly at right angle, and extending perpendicular
to the main flow line; and an auxiliary air passage outlet port
12 positioned at the rear end of the longitudinal passage 13a and
opening parallel to the main flow line. In general, the heating
resistors such as the heating resistor 3 and the temperature-sensing
resistor 4 are arranged on inner portion of the longitudinal passage
13a.
On the other hand, the main air flow passage body 20 of the body
53 comprises an orifice 21 formed on a periphery of the inner side
wall the main air flow passage body 20 positioned in an upstream
side of the inserted air flow passage body 10; and the both opening
portions (surfaces), the auxiliary air passage inlet port 11 of
the inlet opening portion (surface) of the auxiliary air flow passage
body 10 and the auxiliary air passage outlet port 12 of the outlet
opening portion (surface), are arranged within a flow flux zone
D formed by extending air flow 23 in the forward direction of the
fluid to be measured from a top edge of the orifice 21 in a direction
parallel to the main flow line. As shown in FIG. 1 the inside of
the zone surrounded by the flow lines G1 G2 extends in the direction
parallel to the main flow line from the top edge of the orifice
21. For instance, the flow flux zone corresponding to a cylinder
having an inner diameter D, when the main air flow passage body
20 is cylindrical as shown in FIG. 2.
That is, as shown in FIG. 2 the shape of the main air flow passage
body 20 to be inserted with the auxiliary air flow passage body
10 is nearly cylindrical (circular-tube-shaped), and an effective
cross-sectional area defined by the flow flux of the air flow of
the fluid to be measured flowing through the main air flow passage
22 formed by the main air flow passage body 10 includes configurational
positions of the inlet and outlet opening portions (the auxiliary
air flow passage inlet port 11 and the auxiliary air flow passage
outlet port 12) of the auxiliary air flow passage body 10.
In other words, the orifice 21 is provided in the periphery of
the inner side wall of the main air flow passage body 20 positioned
in an upstream side of the inserted air flow passage body 10. The
cross-sectional shape of the orifice 21 is a venturi-shape having
its center axis nearly equal to that of the main air flow passage
22 an upstream side of the orifice 21 is nearly arc-shaped and
a direction of a wall surface of the orifice 21 in the downstream
side is nearly normal to the direction of the forward air flow 23.
Further, in regard to the configuration of the orifice and the inlet
and outlet ports of the auxiliary air flow passage inlet port 11
and the auxiliary air flow passage outlet port 12 of the auxiliary
air flow passage body 10 both of the auxiliary air flow passage
inlet port 11 and the auxiliary air flow passage outlet port 12
are arranged in the inner side of the orifice diameter D (the flow
flux zone D in the figure) when seen from the upstream side, as
shown in FIG. 2. It is preferable that the auxiliary air flow passage
inlet port 11 is arranged at a position in the wall side of the
passage and near the inner side of the flow line G1 shown in FIG.
1 and the auxiliary air flow passage outlet port 12 is arranged
at a position in the wall side of the passage and near the inner
side of the flow line G2 shown in FIG. 1.
The reason why the upstream side half of the orifice 21 is formed
arc-shaped (bell-mouth shaped) is that the air flow near the center
of the flow passage downstream of the orifice 21 is prevented from
being disturbed, and the reason why the direction of the wall surface
in the downstream side half is formed nearly normal to the direction
of the main flow line is that the forward air flow 23 downstream
of the orifice 21 is easily flow separated. By doing so, it is possible
to increase flow speed of forward flow under pulsating flow condition
downstream and inside the diameter of the orifice 21 without disturbing
the flow.
The heating resistor type flow meter in accordance with the present
invention comprises a main air flow passage body forming a main
air flow passage for allowing a fluid to be measured flowing therethrough;
and a measuring module having a heating resistor for measuring a
flow rate of the fluid to be measured, inserted inside the main
air flow passage body, wherein the measuring module comprises the
heating resistor inside an auxiliary air flow passage body forming
an L-shaped auxiliary air flow passage having an inlet opening portion
opening in a direction perpendicular to a main flow line of the
fluid to be measured and an outlet opening portion opening in a
direction parallel to the main flow line; the main air flow passage
body comprises an orifice on a periphery of the inner side wall
positioned in an upstream side of the air flow passage body; and
both the inlet opening portion and the outlet opening portion are
arranged within a flow flux zone formed by extending the fluid to
be measured from a top edge of the orifice in a direction parallel
to the main flow line.
Description will be made below the mechanism for reducing the jump-up
error and the binary-value phenomenon caused by the effect of back
flow by providing the orifice in the upstream side of the L-shaped
auxiliary air flow passage body which is a characteristic of the
present invention. Initially, comparison of effects of presence
and absence of the orifice will be described, referring to FIGS.
4A, 4B, 5A, 5B.
FIG. 4A and 4B show waveforms for cases without orifice and with
orifice, respectively. In a case of a conventional flow meter without
orifice, when back flow occurs in the main air flow passage as shown
by the waveform of FIG. 4A, the waveform of an actually detected
signal becomes a waveform folded at a line nearly zero flow speed
as shown by the hatched lines since the flow direction cannot be
detected solely by the heating resistor. Further, by employing the
L-shaped auxiliary air flow passage described above, it is possible
to prevent back flow from entering into the auxiliary air flow passage
as shown by the waveform of effect of auxiliary air flow passage
of FIG. 4A.
Furthermore, when an amplitude of flow speed is large enough to
cause back flow at an average flow speed of U1 in the case without
orifice, it is possible to prevent back flow from entering into
the auxiliary air flow passage by the effect of auxiliary air flow
passage. However, an average value of a waveform, taking response
time lag of the heating resistor into consideration, is increased
by .DELTA.U1 since an amount corresponding to back flow is not subtracted
from the average value and accordingly the forward flow is increased
by the corresponding amount. The value .DELTA.U1 is a detected error
due to back flow.
On the other hand, in a case of arranging an orifice in the upstream
side of the L-shaped auxiliary air flow passage, since flow separation
eddies are generated in the downstream side of the orifice, the
effective crosssectional area of the main air flow passage is narrowed,
the average flow speed U2 becomes faster than U1 and the pulsating
amplitude is also increased in the portion in which the auxiliary
air flow passage is arranged. However, since as to the back flow
there is no means for reducing effective cross-sectional area in
the portion of the auxiliary air flow passage, that is, the orifice
in the upstream side of the auxiliary air flow passage is not related
to the back flow, the values .DELTA.U1 and .DELTA.U2 as the effect
of back flow (flow rate of back flow) become nearly equal. That
is, it is possible to increase the average flow speed solely without
changing back flow rate by arranging the orifice in the upstream
side of the auxiliary air flow passage.
Therefore, from the above relations, that is, U1<U2 .DELTA.U1=.DELTA.U2
the relation (.DELTA.U1/U1)>(.DELTA.U2/U2) is satisfied, and
accordingly the measuring error (jump-up error) of the flow meter
due to back flow in the case of providing the orifice in the upstream
side of the auxiliary air flow passage can be reduced compared to
the measuring error in the case without the orifice.
On the other hand, provision of the orifice in the upstream side
of the auxiliary air flow passage has another effect that it is
possible to moderate a so-called binary-value phenomenon, that is,
decrease of a detected value in the flow meter which is caused when
a pulsation amplitude of air flow increases and even without occurrence
of back flow. As shown in FIG. 13 the binary-value phenomenon is
a decrease in output signal which is caused when intake back pressure
is varied by gradually opening a throttle valve while the rotating
speed of an engine is kept constant. The reason why this phenomenon
is caused is that the output characteristic of the heating resistor
in regard to air flow rate (flow speed) has a non-linear relation.
When such a phenomenon occurs, a control system of an engine cannot
perform an accurate fuel control because there are two different
operating conditions to an equal indication value of flow rate.
As having been described above in connection with the prior art,
this phenomenon can be avoided to a certain degree by arranging
a heating resistor inside an L-shaped auxiliary air flow passage
having a bent portion without orifice. However, in order to moderate
the binary-value phenomenon for all kinds of engines, it is necessary
to optimize the shape of the auxiliary air flow passage for each
kind of engine. On the other hand, the orifice in the upstream side
of the auxiliary air flow passage provided in the heating resistor
type air flow meter in accordance with the present invention is
effective for moderating the binary-value phenomenon for all kinds
of engines. The binary-value phenomenon will be described below,
referring to FIGS. 5A and 5B showing flow velocity distributions
for cases without orifice and with orifice, respectively.
As shown in FIGS. 5A and 5B, a flow distribution of air flow in
a duct generally shows a parabolic distribution in a steady state
condition. However, under a pulsating flow condition, the distribution
profile changes from the parabolic flow velocity distribution to
a flat velocity distribution as the amplitude of flow speed is gradually
increased. With comparing the flow velocity distribution by presence
and absence of the orifice, the distribution in the case without
orifice is seen in FIG. 5A and the distribution in the case with
orifice is seen in FIG. 5B.
Referring to FIG. 5B, when the orifice 21 exists, air is difficult
to flow in the vicinity of the wall surface of the main air flow
passage 22 since the vicinity of the wall is shadowed by the orifice
21. Thereby, speed of the air flow in the other portion, that is,
in the downstream portion of the zone D (for example, cylindrical
portion having an inner diameter of D) of the orifice 21 is extremely
increased. Further, an increased amount of flow speed is larger
in a position in the wall side of the passage apart from the center
the passage of the inner diameter downstream portion of the orifice
21 shown in the figure than in the center of the passage. This is
the reason why the auxiliary air flow passage inlet port 11 is arranged
at a position in the wall side of the passage and near the inner
side of the flow line G1 and the auxiliary air flow passage outlet
port 12 is arranged at a position in the wall side of the passage
and near the inner side of the flow line G2.
As described above, between the increased amount of flow speed
.DELTA.U1' at a position in the wall side of the passage shown in
FIG. 5A and the increased amount of flow speed .DELTA.U2' at a position
in the wall side of the passage shown in FIG. 5B there is a relation
.DELTA.U1'<.DELTA.U2'. Therefore, by appropriately arranging
the inlet port and the outlet port of the auxiliary air flow passage
in the downstream portion of the zone D, flow speed of air flowing
in the auxiliary air flow passage is also increased as an amplitude
of pulsation increases. Therefore, even if an output of the heating
resistor is decreased due to the non-linearity, the increased amount
of flow speed increasing the flow speed flowing in the auxiliary
air flow passage compensates for the corresponding decreasing amount.
However, when the dimension (inner diameter D) of the orifice is
reduced too much, the increased amount of flow speed becomes excessively
large and consequently there occurs a phenomenon that the output
of the heating resistor increases regardless of absence of occurrence
of back flow. Therefore, in taking it into consideration a decrease
in the effect of back flow and a reduction of the binary-value phenomenon,
a ratio of the effective cross-sectional area A1 of the main air
flow passage 20 to the effective cross-sectional area A2 of the
orifice 21 (the effective crosssectional area of the zone D) should
be set to an optimum value to be described below.
Since the effect of increasing flow speed described above is large
at a position where flow speed is large, it is important that the
inlet port and the outlet port of the auxiliary air flow passage
are arranged in a downstream portion inside the zone D (for example,
cylindrical portion having a diameter D) of the orifice 21. That
is, it is necessary that the inlet port 11 of the auxiliary air
flow passage opening nearly normal to the direction of the main
flow line of the air flow should be arranged in such a configuration
that kinetic pressure directly acts on the inlet port 11 and the
outlet port 12 of the auxiliary air flow passage opening nearly
parallel to the direction of the main flow line of the air flow
should be arranged in such a configuration that sucking effect in
the outlet port is increased by giving kinetic pressure in the upstream
side of the outlet port and generating flow separation eddies.
Further, since the outlet port 12 of the auxiliary air flow passage
opens nearly parallel to the direction of the main flow line of
the air flow, it is required to suppress loss by collision of air
flow with the wall surface of the main air flow passage body 20.
Therefore, the outlet port 12 of the auxiliary air flow passage
should be arranged appropriately apart from the wall surface.
Results of an experimental study on the above-mentioned orifice
dimension using a actual vehicle will be described below, referring
to FIG. 6 and FIG. 7.
A test was conducted using an engine on a bench in the same procedure
as in FIGS. 12A and 12B by gradually opening the throttle valve
while keeping constant rotating speed of the engine, and an detected
error indicating the heating resistor at full open state of the
throttle valve was plotted with varying dimension (inner diameter
D) of the orifice. From the test, in regard to dimension of the
orifice as shown in FIG. 5B and FIG. 6 an effect of reducing the
jump-up error due to back flow could be obtained in a range of the
contraction ratio R=(A2/A1).gtoreq.7%, where A1 is the effective
cross-sectional area of the main air flow passage in which the auxiliary
air flow passage was placed, and A2 is the effective cross-sectional
area of the orifice having an inner diameter of D.
On the other hand, when the contraction ratio R was smaller than
70%, it was found that the output was caused to increase. The reason
is that the detected flow speed itself increases downstream of the
orifice when the amplitude of the pulsating flow increases, as described
above. A test result at a rotating speed with back flow not occurring
is also shown in the figure for purpose of reference. It was confirmed
that the output rapidly increases with a contraction ratio R<70%.
Therefore, it may be preferable that the ratio of the cross-sectional
area A2 of the orifice to the cross-sectional area A1 of the main
air flow passage in which the auxiliary air flow passage was placed
satisfies the relation R=(A2/A1).gtoreq.70%. However, in taking
the case of the contraction ratio R of 100% (corresponding to the
conventional technology) into consideration, it can be said that
the range 90%.gtoreq.R.gtoreq.70% is preferable. Particularly, in
order to reduce the error to one-half, the range 80%.gtoreq.R.gtoreq.70%
is preferable. Further, it has been confirmed from the test result
that the effect of reducing the jump-up error is good when 90%.gtoreq.R.gtoreq.70%
and a distance L from the orifice 21 to the inlet opening portion
11 shown in FIG. 1 is near a value satisfying the relation L=0.7D.
Description will be made below on the relationship between positional
relationship of the orifice and the inlet and outlet ports of the
auxiliary air flow passage and output noise of the flow meter under
a steady state condition, referring to FIG. 7 in which the ordinate
indicates value of output noise and the abscissa indicates contraction
ratio R as in FIG. 6.
Dimension of a sample orifice used in this test had a contraction
ratio R of nearly 60%. Therefore, a contraction ratio R smaller
than 60% means that the both positions of the inlet port and outlet
port of the auxiliary air flow passage are within a zone shadowed
by the orifice 21 (a wall side zone outside a zone surrounded by
the main flow lines G1 and G2 shown in FIG. 1).
As shown in FIG. 7 within the range of the contraction ratio R
of 100.about.60%. the output noise decreases as the contraction
ratio R is decreased. However, in the range of the contraction ratio
smaller than 60%, the output noise is clearly increased. That is,
when the both positions of the inlet port and outlet port of the
auxiliary air flow passage are within the zone D (the zone within
the zone surrounded by the main flow lines G1 and G2 shown in FIG.
1), the output noise is small. It has been found that the output
noise can be reduced basically by increasing the contraction ratio
R, that is, by decreasing the dimension of the orifice to increase
flow speed of the air. Further, it has been found that flow in the
main air flow passage is disturbed and accordingly output noise
is increased when then orifice exists upstream and flow separation
occurs downstream, that is, the both positions of the inlet port
and the outlet port of the auxiliary air flow passage are within
the zone shadowed by the orifice 21.
From the above result, both the inlet port and the outlet port
require that upstream flow is not disturbed since a value of flow
speed in the auxiliary air flow passage is determined by a pressure
difference between the inlet port and the outlet port. Therefore,
in a case of an orifice or the like arranged in the upstream side
of the auxiliary air flow passage, it is necessary to take the relative
positions of the inlet port and the outlet port of the auxiliary
air flow passage and the dimension of the orifice into consideration
from viewpoint of output noise.
From the results of FIG. 6 and FIG. 7 in order to reduce the jump-up
error and the output noise, it can be said that the range 90%.gtoreq.R.gtoreq.70%
is preferable.
FIG. 8 is a cross-sectional view showing another embodiment of
a heating resistor type air flow meter in accordance with the present
invention. The figure shows a cross-sectional side view of the flow
meter in which a straight pipe 41a having an orifice forming a main
air flow passage is integrated as a part of an air cleaner clean
side 41 of an air cleaner 68. The air cleaner 68 of one of intake
pipe structural members composing the intake system is composed
of the air cleaner clean side 41 integrating the straight pipe 41a
having the orifice of the main air flow passage body 20 as a unit
and an air cleaner dirty side 42 and an air filter element 43.
In this embodiment, the orifice 21 is provided in an intake air
outlet portion of the air cleaner clean side 41 (a duct placed in
the downstream side of the air filter 43), and the straight pipe
41a as the flow meter is integrally connected downstream of the
orifice, and the measuring module 52 of the auxiliary air flow passage
10 shown in FIG. 1 is inserted into a hole 25 provided on a wall
surface of the straight pipe 41a having the orifice. In this embodiment,
since the air cleaner 68 of an existing intake pipe structural member
serves as the main air flow passage body 20 having the orifice 21
and the hole 25 a dedicated air flow passage is not required and
accordingly the system cost can be reduced.
FIG. 9 is a cross-sectional view showing a further embodiment of
a heating resistor type air flow meter in accordance with the present
invention. The figure shows the flow meter in which an orifice 21
is provided in a part of an air cleaner clean side 41 and further
a main air flow passage body 20 is connected to the air cleaner
clean side 41. FIG. 10 is an enlarged view showing the joint portion
of FIG. 9. The figure shows the details of the joint portion of
a soldering portion 47 and the joint portion 48.
This embodiment is basically the same as the embodiment of FIG.
8 but the outlet opening portion of the intake air outlet portion
of the air cleaner 68 is formed in a bell-mouth shaped orifice 21
and a body 53 of the main air flow passage body 20 of the flow meter
is mechanically connected to the downstream side by bonding or screw
fastening in the soldering portion 47 and the joint portion 48.
That is, the orifice of the main air flow passage body composing
the heating resistor type air flow meter is separated from the main
air flow passage body, and the orifice is provided in the intake
air outlet portion of the intake pipe structural member to be connected
with the main air flow passage. In this embodiment, since the existing
intake pipe structural member serves as the orifice 21 a dedicated
air flow passage is not required. Further, an exiting heating resistor
type air flow meter without orifice can be used. Accordingly, the
system cost can be reduced.
FIG. 11 is a view showing an embodiment of an internal combustion
engine of an electronic fuel injection control type mounting a flow
meter in accordance with the present invention. The figure shows
an embodiment of a fuel control engine for controlling a fuel supplying
rate using an air flow rate signal obtained from a heating resistor
type air flow meter of the present embodiment.
Referring to the figure, intake air 67 to be sucked is taken in
an engine cylinder 62 through an intake system composed of an air
cleaner 67 a body 53 of the flow meter, a duct 55 a throttle body
58 an intake manifold 59 having an injector 60 to which fuel is
supplied and so on. On the other hand, exhaust gas generated in
the engine cylinder 62 is exhausted through an exhaust manifold
64.
A control unit 66 receives an airflow rate signal output from a
measuring module 52 of the flow meter, a throttle valve angle signal
output from a throttle valve angle sensor 57 an oxygen concentration
signal output from an oxygen concentration meter 65 provided in
the exhaust manifold 64 an engine rotating speed signal output
from an engine rotating speed meter 61 and so on. The control unit
66 sequentially calculates these signals to obtain an optimum fuel
injecting rate and an optimum idling air control valve opening degree,
and controls the injector 60 and the idle air control valve 56 using
the obtained values so as to supply a flow rate of fuel matching
with an intake air flow rate.
Since an intake air flow rate can be appropriately measured in
the internal combustion engine of an electronic fuel injection control
type mounting the flow meter in accordance with the present invention,
the electronic fuel injection control can be properly performed
and consequently an amount of unburned fuel gas in the exhaust gas
can be reduced.
According to the present invention, increase of flow speed in the
flow flux zone formed by the orifice of a simple structure reduces
the jump-up error under pulsating flow accompanying back flow when
a heating resistor type flow meter is mounted on a vehicle and the
bad effect of the binary-value phenomena, and thereby a low-cost
and highly accurate heating resistor type flow meter can be provided.
Further, appropriate fuel control can be performed when a driver
steps on the accelerator, and therefore there is an effect in cleaning
of exhaust gas of an internal combustion engine of an electronic
fuel injection type.
Although the invention has been described and illustrated in detail,
it is to be clearly understood that the same is by way of illustration
and example, and is not to be taken by way of limitation. The spirit
and scope of the present invention are to be limited only by the
terms of the appended claims.
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