Abstrict An air flow meter has a body forming a main passage defining an
intake air passage of an internal combustion engine. An auxiliary
passage within the main passage has a longitudinal passage in the
axial direction and at least one transverse passage in the radial
direction of the main passage. The auxiliary passage is defined
by a member having a radially directed portion connected to an internal
wall of the main passage. A hollow space is provided in the radially
directed portion to render the wall thickness of the radially directed
portion substantially uniform. Additionally, the hollow space is
separated from the longitudinal passage by an auxiliary member which,
in a preferred embodiment, surrounds a heat sensitive resistor.
Claims We claim:
1. An air flow meter comprising: a body forming a main passage
defining an intake air passage of an internal combustion engine;
auxiliary passage defining means unitarily molded with said body
and arranged in said main passage to form an auxiliary passage having
a longitudinal passage in the axial direction of said main passage
and at least two transverse passages in the radial direction of
said main passage; said auxiliary passage defining means having
radially directed portions thereof defining said transverse passages
respectively connected to an internal wall of said main passage;
a heat-sensitive resistor arranged in said longitudinal passage
of said auxiliary passage for metering the flow rate of intake air;
said heat sensitive resistor being connected to a holder in only
one of said transverse passages; and another of said transverse
passages having a hollow space therein, the wall thickness of the
auxiliary passage defining means being rendered substantially uniform,
said hollow space being separated from said longitudinal passage
by an auxiliary member forming part of said auxiliary passage defining
means.
2. An air flow meter according to claim 1 wherein said auxiliary
passage defining means is made of a synthetic resin.
3. An air flow meter according to claim 1 wherein said body and
said auxiliary passage defining means are integrally molded of a
synthetic resin.
4. An air flow meter according to claim 1 wherein said auxiliary
member substantially surrounds said heat-sensitive resistor and
has an aperture therein forming part of said longitudinal passage.
5. An air flow meter according to claim 1 wherein seal means are
disposed between said auxiliary member and said portion of the auxiliary
passage defining means in which said hollow space is located to
provide a gas-tight seal between said hollow space and said longitudinal
passage.
6. An air flow meter according to claim 1 wherein a hole having
a small cross-sectional area is disposed in said auxiliary member
to connect said hollow space with said longitudinal passage.
7. An air flow meter according to claim 1 wherein an annular passage
is provided between said auxiliary member and said radially directed
portion defining said other transverse passage having said hollow
space therein.
8. An air flow meter according to claim 1 wherein the auxiliary
member is integrally molded with the auxiliary passage defining
means to form a portion of said longitudinal passage.
9. An air flow meter according to claim 1 wherein said auxiliary
member is formed with a flow regulating grid transversely of the
auxiliary air passage upstream of said heat sensitive resistor for
stabilizing the air flow through said longitudinal passage.
10. An air flow meter according to claim 1 wherein flow regulating
grids are integrally formed with said auxiliary member upstream
and downstream of said heat sensitive resistor.
11. An air flow meter according to claim 1 wherein said auxiliary
member is made of an electrically conductive material.
12. An air flow meter according to claim 1 wherein said body is
integrally formed with a throttle body which houses a throttle valve
for controlling the intake air flow rate of the internal combustion
engine.
Description BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an air flow meter for metering the flow
rate of intake air of an internal combustion engine and, more particularly,
to an air flow meter having a flow metering heat-sensitive resistor
located in an auxiliary passage which is in turn arranged in a main
passage forming an intake air passage.
2. Description of the related art
A known hot-wire air flow meter for an internal combustion engine,
as disclosed in U.S. Pat. No. 4887577 has a body forming a main
passage defining an intake air passage of an internal combustion
engine; an auxiliary passage forming member arranged in the main
passage and forming an auxiliary passage having a longitudinal passage
in the axial direction of the main passage leading to transverse
passages formed in the radial direction of the main passage; and
a heat-sensitive resistor arranged in the longitudinal passage of
the auxiliary passage for metering the flow rate of intake air.
The resistor is located in a radial holder across the main passage
which must necessarily be transversely thickened to accommodate
the resistor across the air flow passage. So as to provide a symmetrical
construction across the main passage the auxiliary passage forming
member is thickened transversely across the longitudinal passage
at the opposite side of the holder of the heat-sensitive resistor,
as shown in FIG. 4 of the said U.S. patent, so as to provide support
for the portion defining tile auxiliary passage.
JP-A-61-53518 (1986) and JP-A-64-10127 (1989) disclose the holder
of the heat-sensitive resistor constructed such that a protecting
member for the heat-sensitive resistor is disposed around the heat-sensitive
resistor.
The member forming the auxiliary passage necessarily has its internal
shape and size determined according to the air flow specification
requirement of the auxiliary passage and since the outer wall forms
part of the main passage, its external shape and size exert serious
influences upon the air flow of the main passage. If this external
shape is not correct, an increase in pressure loss occurs, and vortexes
are established in the air flow. As a result, the hot-wire air flow
meter output fluctuates (herein termed "output noise")
which results in a decrease in accuracy of a fuel injection unit
controlled thereby.
The prior art thus far described has failed to take into consideration
the need for a uniform thickness and reduction in thickness of the
auxiliary passage forming member but has determined tile internal
and external shapes and sizes from the above-specified necessary
specifications of the auxiliary passage and the main passage. As
a result, the auxiliary passage forming member has tended to have
a thick portion extending transversely to the main passage which
causes a problem in that the product weight is increased. Even more
importantly, because the body and the auxiliary passage forming
member are integrally molded, if the auxiliary passage forming member
is solid and relatively thick both axially and transversely of the
main passage, and if it is made of a synthetic resin, a large shinkage
normally occurs due to molding shrinkage, which then causes another
problem in that the desired shape and size cannot be obtained resulting
in decreased accuracy (see FIG. 5 described later herein). If the
auxiliary passage forming member is made of a metal, such as aluminum,
a similar but less serious problem arises than when synthetic resin
is used.
If the thickness of the auxiliary passage forming member is to
be made uniform, on the other hand (as shown in FIG. 6 described
later herein), the external shape is incorrect to raise a further
problem in that the aforementioned pressure loss and output noise
occur due to the member having a flat leading surface. Also, such
a construction is not symmetrical across the main passage since
the axial length of the resistor holder is greater than that of
the auxiliary passage forming member.
Moreover, the prior art technologies, as disclosed in JP-A-61-53518
(1986) and JP-A-64-10127 (1989), are directed to the protecting
member for the heat-sensitive resistor, and neither has the object
of improving the shape and size accuracies of the auxiliary passage
forming member.
The present invention seeks to overcome the foregoing disadvantages.
A first specific object of the present invention is to provide
an air flow meter in which the auxiliary passage forming member
has reduced wall thickness without increasing the pressure loss
and the output noise.
A second specific object of the present invention is to provide
an air flow meter which can not only eliminate the aforementioned
thick portion but also protect the heat-sensitive resistor arranged
in the auxiliary passage.
A third specific object of the present invention is to provide
an air flow meter which can not only eliminate the aforementioned
thick portion but also reduce the output error caused by the intake
pulsations of an internal combustion engine.
A fourth specific object of the present invention is to provide
an air flow meter which can not only eliminate the aforementioned
thick portion but also reduce the fluctuations of the air flow in
the auxiliary passage and the meter output noise.
SUMMARY OF THE INVENTION
According to this invention there is provided an air flow meter
comprising: a body forming a main passage defining an intake air
passage of an internal combustion engine; auxiliary passage defining
means arranged in said main passage to form an auxiliary passage
having a longitudinal passage in the axial direction of said main
passage and at least one transverse passage in the radial direction
of said main passage; said auxiliary passage defining means having
a radially directed portion thereof connected to an internal wall
of said main passage; and a heat-sensitive resistor arranged in
said longitudinal passage of said auxiliary passage for metering
the flow rate of intake air, wherein a hollow space is provided
in said radially directed portion to render the wall thickness of
the auxiliary passage defining means substantially uniform and said
hollow space is separated from said longitudinal passage by an auxiliary
member.
Advantageously, said auxiliary passage defining means is made of
a synthetic resin, and conveniently, said body and said auxiliary
passage defining means are integrally molded of a synthetic resin.
In a preferred embodiment said auxiliary member surrounds said
heat-sensitive resistor and has an aperture therein forming part
of said longitudinal passage.
Advantageously, seal means are disposed between said auxiliary
member and said portion of the auxiliary passage defining means
in which said hollow space is located to provide a gas-tight seal
between said hollow space and said longitudinal passage.
In an embodiment of the invention there is provided a passage having
a small cross-sectional area disposed in said auxiliary member to
connect said hollow space with said longitudinal passage.
Alternatively, an annular passage is provided between said auxiliary
member and said hollow space.
In another preferred embodiment of the invention the auxiliary
member is integrally molded with the auxiliary passage defining
means to form a portion of said longitudinal passage.
Preferably, said auxiliary member is formed with a flow regulating
grid transversely of the auxiliary air passage upstream of said
heat sensitive resistor for stabilizing the air flow through said
longitudinal passage.
Advantageously, flow regulating grids are integrally formed with
said auxiliary member upstream and downstream of said heat sensitive
resistor.
So as to reduce capacitance problems said auxiliary member is made
of an electrically conductive material.
So as to provide an integrated unit said body is integrally formed
with a throttle body which houses a throttle valve for controlling
the intake air flow rate of the internal combustion engine.
In order to achieve the first specific object, the present invention
provides a hollow space in the auxiliary passage defining means
which is substantially separated from the longitudinal auxiliary
passage.
In order to achieve the second specific object, of the present
invention, the hollow space is separated from the longitudinal auxiliary
passage by an auxiliary member which surrounds the heat-sensitive
resistor and forms part of the longitudinal passage.
In order to achieve the third specific object, the present invention
provides a passage having a small cross-sectional area between the
hollow space and the longitudinal passage.
In order to achieve the fourth specific object, the present invention
provides the auxiliary member with an integral flow regulating grid
for stabilizing the air flow through the longitudinal passage.
In this invention the auxiliary passage forming member is formed
to produce a hollow space therein, and the hollow space is substantially
separated from the auxiliary passage, so that the solid and thick
portion of the auxiliary passage forming member required in U.S.
Pat. No. 4887577 FIG. 4 is eliminated without influencing the
shapes and sizes of the main passage and the auxiliary passage.
As a result, the auxiliary passage forming member can have its weight
reduced and is not so susceptible to shrinkage if made of a synthetic
resin or the like.
The hollow space is separated from the longitudinal passage by
the auxiliary member which surrounds the heat-sensitive resistor
and forms part of tile longitudinal passage. In addition, since
the heat-sensitive resistor attached to a circuit module is located
in the auxiliary member, it can be prevented from being damaged
at a time before the circuit module is .fitted in the body forming
the air passage.
In the running condition of an engine with the throttle valve opened
nearly to its full stroke, the intake air is synchronized with the
opening or closing operation of the engine intake valve to establish
a pulsating flow. These intake pulsations are also established in
the main passage of tile hot-wire air flow meter. In the auxiliary
passage, tile pulsations are likewise established, although their
amplitude is smaller than that of the main passage because they
are damped by the auxiliary passage. These pulsations give errors
to the output of the hot-wire air flow meter, as is well known in
the art. By forming a passage having a small cross-sectional area
to connect between the aforementioned hollow space and the auxiliary
longitudinal passage, the hollow space is able to act as an air
reservoir or damper to reduce the intake pulsations on the heat-sensitive
resistor and, accordingly, to reduce the output errors of the hot-wire
air flow meter due to the intake pulsations of the internal combustion
engine. Because of tile small cross-sectional area of the passage,
moreover, the accuracy is little influenced by the hollow space
in the presence of a steady intake air flow.
The fluctuations of the air flow hitting the heat-sensitive resistor
can be reduced to decrease the output noise by the action of a flow
regulating grid which may be made integral with the auxiliary member.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described, by way of example, with reference
to the accompanying drawings in which:
FIG. 1 shows a top plan view, partially in section, of a hot-wire
air flow meter in accordance with one embodiment of the present
invention;
FIG. 2 shows a longitudinal cross-section taken along double arrow-headed
line II--II of FIG. 1;
FIG. 3 shows a bottom view of the air flow meter shown in FIG.
1;
FIG. 4 shows a cross-section taken along double arrow-headed line
IV--IV of FIG. 3;
FIGS. 5 and 6 are views corresponding to FIG. 4 but showing the
prior art cross-sections;
FIG. 7 shows a longitudinal section similar to FIG. 2 but of a
hot-wire air flow meter in accordance with another embodiment of
the present invention;
FIGS. 8 to 11 show longitudinal cross-sections of an auxiliary
passage portion of the hot-wire air flow meter in accordance with
other embodiments of the present invention;
FIG. 12 shows a cross-section taken along double arrow-headed line
XII--XII of FIG. 11;
FIG. 13 shows a longitudinal cross-section corresponding to FIG.
2 but of a hot-wire air flow meter according to a further embodiment
of the present invention;
FIG. 14 shows a longitudinal cross-section showing an embodiment
in which the hot-wire air flow meter of FIG. 2 is integrated with
a throttle body, and
FIG. 15 shows a longitudinal cross-section of yet another embodiment
of the invention.
In the Figures like reference numerals denote like parts.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The hot-wire air flow meter shown in FIGS. 1 to 3 has a body 1
with an internal main passage 2 defining an intake air passage of
an internal combustion engine. Inside the main passage 2 is an auxiliary
passage forming member 20. The auxiliary passage forming member
20 has an auxiliary passage 3 which is composed of a longitudinal
passage 4 formed in the axial direction of the main passage 2 and
transverse passages 5 and 6 formed in the radial direction of the
main passage 2. The transverse passages 5 and 6 have their downstream
wall formed by a cover 8 which is attached to the body 1 by screws
7.
In the longitudinal passage 4 there are arranged a heat-sensitive
resistor 9 for metering the flow rate of air and a heat-sensitive
resistor 10 for measuring the air temperature, although it is to
be understood only one heat sensitive resistor :is required but
two are preferred for improved accuracy. The resistors may be of
a so-called hot-wire type or may be of thin film.
Screwed onto the outside of the body 1 there is a circuit module
11 for controlling the air flow meter.
The hot-wire air flow meter of the present embodiment meters the
flow rate of intake air of the internal combustion engine by supplying
a heating current to the heat-sensitive resistor 9 the value of
which current is varied to control the temperature of the heat-sensitive
resistor 9 to be a substantially higher constant level than that
of the heat-sensitive resistor 10. The velocity of the air flow
hitting the heat-sensitive resistor 9 in the auxiliary passage 3
is determined from the value of the heating current which is thus
indicative of the flow rate of the intake air of the main passage
2 since the air flow rate in the auxiliary passage 3 has a constant
relation to the flow rate in the main passage 2.
The circuit module 11 has a base 12 made of a metal, support pins
13 and 14 made of electric conductors for the heat-sensitive resistors
9 and 10; a synthetic resin holder 17 molded integrally with terminals
15 and 16 welded to the support pins 13 and 14; a housing 27 and
a cover 28 defining a casing; and a control circuit unit 30 connected
with the terminals 15 and 16 through an aluminum wire 29.
The heat-sensitive resistors 9 and 10 are welded to the support
pins 13 and 14 respectively.
Externally of that portion of the synthetic resin holder 17 which
is ill the body 1 there is attached a protector 19 with a radially
inner end thereof surrounding the heat-sensitive resistors 9 and
10 to form an auxiliary member which defines part of the longitudinal
passage 4 of the auxiliary passage forming member 20. The protector
19 is adhered to the holder 17.
The auxiliary passage forming member 20 of the body 1 is provided
with a tubular portion of substantially uniform wall thickness radially
extending from the inner wall of the body 1 to define a circularly
cross-sectioned hole 21 which is closed at its radially inner end
by insertion of the radially inner, leading end, portion of the
protector 19 acting as the aforementioned auxiliary member. Thus,
the leading end (radial inner end) portion of the protector 19 has
an aperture substantially the same shape and size as that of the
internal diameter of the longitudinal passage 4 to form part of
the longitudinal passage 4.
The body 1 is integrally molded with the auxiliary passage, using
a thermoplastic resin such as a polyester resin mixed with a reinforcing
material such as glass fibers or the like. The hole 21 is integrally
formed at the time of molding the body 1 by extracting a molding
pin in the direction of the mounting face of the circuit module
11.
On the outer circumference of the holder 17 there is fitted an
O-ring 22 for ensuring a gas tight fit between the body 1 and the
circuit module 11.
An air flow honeycomb regulating grid 23 is fitted in the entrance
of the main passage 2 of the body 1 to smooth out the air flow,
i.e. remove disturbances in the main passage 2.
The intake air introduced into the entrance of the main passage
2 is partially shunted into the longitudinal passage 4 as indicated
by arrows 24 and thence into the transverse passages 5 and 6 as
indicated by arrows 25 until it is returned to the main passage
through apertures in the walls defining tile transverse passages
5 and 6 as indicated by arrows 26.
Next, the operation of the present embodiment will be described
in detail.
In the prior art, as shown in FIG. 5 the auxiliary passage forming
member 20 is a solid member across the longitudinal passage 4 symmetrical
with and at the side opposed to the holder 17. As a result, the
required shape and size cannot be sustained due to uneven wall thickness
causing uneven shrinkage at the time of molding, as indicated by
solid line 32 even if the mold shape and size is made to conform
to the required shape and size, as indicated by tile chain broken
line 31. The thickened portion also raises a problem of increased
weight. If, as is also known in the prior art, and as shown in FIG.
6 the walls of the auxiliary passage forming member 20 are uniform,
the shape and size of the leading side (that is, at the side of
the main passage 2) of the auxiliary passage forming member 20 is
flat, not rounded as in FIG. 5 and it has a greater width across
tile main passage than depth longitudinally along the main passage
so is not symmetrical with the holder 17 many vortexes 33 and 34
are established on the upstream and side faces of the auxiliary
passage forming member 20 by the air flow 35 which flows in the
main passage 2 hitting the upstream face of the auxiliary passage
forming member 20. These vortexes 33 and 34 reduce the effective
area of the main passage 2 to cause the problem of increasing the
pressure loss. Still worse, the vortexes establish pressure fluctuations
in the exit of the transverse passage 5 so that fluctuations in
the flow velocity of the auxiliary passage 3 are induced to augment
the output noise.
In the present invent i on, on tile contrary, the auxiliary passage
forming member 20 is not solid due to the hole 21 formed therein,
so the walls are more uniform in thickness and the shape and size
of the auxiliary passage forming member 20 at the side of the main
passage 2 is optimized for performance. Thus, there arises the effect
that the desired shape and size can be achieved. Another effect
is that the weight can be reduced to an extent corresponding to
the volume of tile hole 21.
A further effect is that the protector 19 in combination with holder
17 can form a sub-assembly which prevents the heat-sensitive resistor
9 from being damaged prior to insertion into the orifice formed
by the forementioned molding pin.
FIG. 7 shows another embodiment of the present invention, in which
tile same members as those of the embodiment shown in FIGS. 1 to
3 are designated with the reference numerals whereas the corresponding
members which have their shapes and sizes changed are designated
by the same reference numeral but with a suffix A.
The difference in the FIG. 7 embodiment from that shown in FIGS.
1 to 3 is in that the longitudinal passage 4 of the latter has its
entrance located generally at the center of tile main passage 2
and in that the transverse passage is branched into two transverse
passages 4 and 5. In the embodiment of FIG. 7 on the contrary,
a longitudinal passage 4A has its entrance offset from the center
of the main passage 2 and only one transverse passage 5A is formed.
The remaining structure is identical so that the same operations
and effects as those of the embodiment of FIG. 1 are likewise obtained.
FIG. 8 shows still another embodiment of the present invention.
In this embodiment, the end portion of a protector 19B, which locates
in tile hole 21 is formed with an external circumferential groove,
in which an O-ring 36 is fitted to improve the gas tightness between
the hole 21 and the longitudinal passage 4. In this embodiment,
the influences of the hole 21 upon the air flow in the auxiliary
passage 3 can be eliminated to improve the metering accuracy, especially
in a low flow rate range.
FIG. 9 shows a further embodiment of the present invention. The
fitting portion of the protector 19C in the hole 21 is formed with
a hole 37 having a small cross-sectional area through which the
hole 21 is connected to the longitudinal passage 4 in the vicinity
of the heat-sensitive resistor 9.
In the embodiment of FIG. 9 the hole 21 connected through the
small hole 37 acts as an air reservoir or a damper upon the air
flow pulsations of the longitudinal passage 4 due to tile intake
pulsations of the internal combustion engine so that it can reduce
the pulsations of the air flow that contact the heat-sensitive resistor
9. As a result, output error of the hot-wire air flow meter due
to the intake pulsations of the internal combustion engine is reduced.
Since, moreover, the hole 37 has a small effective cross-sectioned
area, the hole 21 and the hole 37 exert few influences upon the
meter output accuracy when there is a steady air flow.
FIG. 10 shows a further embodiment of the present invention, in
which tile fitting portion of the protector 19D in the hole 21 is
given a smaller external diameter than the internal diameter of
the hole 21 to leave an annular clearance 38 so that the same effects
as those of the embodiment of FIG. 9 may be obtained.
FIGS. 11 and 12 show a further embodiment of the present invention,
in which a protector 19E is preferably integral with honeycomb flow
regulating grids 39 and 40. By such an expedient, the disturbances
of the air flow in the auxiliary passage 3 can be stabilized by
the air regulating grids 39 and 40 to feed the heat-sensitive resistor
9 with an air flow having few disturbances. As a result, the outpost
noise can be reduced. In such an embodiment, the flow regulating
grids are disposed upstream and downstream of the heat-sensitive
resistor 9. However, it is possible for only one, upstream, flow
regulating grid to be used, although the effect of reducing the
output noise may be reduced. A grid or grids located in the auxiliary
passage are much smaller than a grid in the main passage and have
a similar desired effect but at lower cost due to their small size
relative to a grid in the main passage.
FIG. 13 shows another embodiment of the present invention, in which
a protector 19F is made of an electric conductor such as a metal
or a conductive synthetic resin and has its radially outer end portion
41 connected electrically with the base 12 which is also made of
an electric conductor. Here, the conductive synthetic resin of the
protector 19F is molded by mixing metal powder or metal fibers into
a synthetic resin. By such an expedient, the base 12 is electrically
connected in respect of high frequencies with the ground potential
portion of the control circuit unit 30 (as shown in FIG. 2) which
is accommodated in the circuit module 11. Also, because the protector
19F is made of an electric conductor which covers the heat-sensitive
resistor 9 so the heat-sensitive resistor 9 is shielded from external
electric noise such as electric waves. As a result, the hot-wire
air flow meter can be prevented from being erroneously operated
by electric noise external of the meter.
FIG. 14 shows yet another embodiment of the present invention,
in which the hot-wire air flow meter of FIGS. 1 to 3 is integrated
with a throttle body 42 equipped with a throttle valve 43 for controlling
the flow rate of the intake air of the internal combustion engine.
The remaining structure is identical to that of the embodiment of
FIGS. 1 to 3. Such an embodiment attains the additional effect that
the intake system can be made light and compact. The body 1 of the
hot-wire air flow meter and the throttle body 42 are made of one
part in the embodiment shown in FIG. 14 but may be made of different
parts and integrated by means of, for example, screws.
In the yet further embodiment of FIG. 15 the holder 17 is as in
the prior art and does not have a protector 19 shrouding the resistors
9 10 so does not protect the resistors when sub-assembled. The
hole 21 instead of being formed from the circuit module side of
the body, is formed from the opposite side thereof and a radially
inner closure is formed by integral wall, auxiliary member 191.
The hole may have an outer cover (not shown) to prevent ingress
of water. Such a construction, although not providing protection
for the resistors 9 10 has the advantage of avoiding the use of
protector 19 whilst enabling the auxiliary passage defining means
to have approximately uniform wall thickness.
In the embodiments thus far described, the auxiliary passage is
molded integrally with the body 1 but it may, alternatively, be
made separate from the body and fitted in the body 1.
Furthermore, although two heat sensitive resistors are preferred,
which may be of wire or thin film, only one heat sensitive resistor
is necessary for operation of the meter.
Since the present invention is constructed as described hereinbefore,
it can achieve the following effects.
Since a space is formed in the auxiliary passage forming member
which is separated from the auxiliary passage, the auxiliary passage
forming member can be made having a substantially uniform wall thickness
without influencing the shapes of the main passage and the auxiliary
passage. As a result, the auxiliary passage forming member can have
its weight reduced and can be made in the desired shape and size,
even if made of a synthetic resin.
Since, moreover, the auxiliary member 19 arranged around the outer
circumference of the heat-sensitive resistor separates the space
formed in the auxiliary passage forming member from the auxiliary
passage and forms part of the auxiliary passage, the heat-sensitive
resistor is shrouded and is prevented from being hit and damaged
prior to insertion into the meter.
If the aforementioned separating portion formed by the auxiliary
member is provided with a passage having a small cross-sectional
area, the aforementioned space can act as a damper to reduce the
pulsations of the intake air in the region of the heat-sensitive
resistor and, accordingly, the output errors of the hot-wire air
flow meter due to the pulsations of the intake air of the internal
combustion engine are reduced.
Also, if the flow regulating grid is integrated with the auxiliary
member, it acts to reduce the fluctuations of the air flow contacting
the heat-sensitive resistor, thereby reducing the output noise.
It is to be understood that the invention has been described with
reference to exemplary embodiments, and moficiations may be made
without departing from the spirit and scope of the invention as
defined ill the appended claims.
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