Abstrict An fluid flow meter for measuring a flow amount of gas. The fluid
flow meter comprising a casing installed to a conduit in which a
measured gas flows. The casing includes a main body section defining
a board installation recess, and a peripheral wall section projecting
from the main body section and surrounding the board installation
recess. A part of the peripheral wall section is cut out to form
an installation plate insertion groove, the part abutting to an
inside of the conduit. An installation plate is provided including
a board installation section disposed in the board installation
recess, and an element installation section extending from the board
installation section through the installation plate insertion groove
to an outside of the board installation recess. A circuit board
is disposed on the board installation section of the installation
plate, electronic parts being provided to the circuit board. A gas
flow sensor element is disposed on the element installation section
of the installation plate, the gas flow sensor element detecting
a flow amount of the measured gas. A silicon-containing filler is
disposed in the board installation recess of the casing to cover
the circuit board. Additionally, a fluorine-containing sealant is
disposed in the board installation recess at a portion close to
the installation plate insertion groove, the fluorine-containing
sealant sealing the installation plate insertion groove so as to
maintain the silicon-containing sealant inside the board installation
recess.
Claims What is claimed is:
1. A fluid flow meter comprising: a casing installed to a conduit
in which a measured gas flows, said casing comprising a main body
section defining a board installation recess, and a peripheral wall
section projecting from the main body section and surrounding the
board installation recess, a part of the peripheral wall section
being cut out to form an installation plate insertion groove, the
part abutting to an inside of the conduit; an installation plate
comprising a board installation section disposed in the board installation
recess, and an element installation section extending from the board
installation section through the installation plate insertion groove
to an outside of the board installation recess; a circuit board
disposed on the board installation section of said installation
plate, electronic parts being provided to said circuit board; a
gas flow sensor element disposed on the element installation section
of said installation plate, said gas flow sensor element detecting
a flow amount of the measured gas; a silicon-containing filler disposed
in the board installation recess of said casing to cover the circuit
board, said silicon-containing filler being formed of a material
containing silicon; and a fluorine-containing sealant disposed in
the board installation recess at a portion close to the installation
plate insertion groove, said fluorine-containing sealant sealing
the installation plate insertion groove so as to maintain said silicon-containing
sealant inside the board installation recess, said fluorine-containing
sealant being formed of a material whose major component is a polymer
containing fluorine.
2. A fluid flow meter as claimed in claim 1 wherein the gas sensor
element extends through the installation plate insertion groove
into the board installation recess so that a part of the gas flow
sensor element is located within the board installation recess,
a surface of the part of the gas flow sensor element being covered
with said fluorine-containing sealant.
3. A fluid flow meter as claimed in claim 1 further comprising
a stopper member connected to said casing and located within the
installation plate insertion groove of said casing to close the
installation plate insertion groove so as to prevent the fluorine-containing
sealant from flowing out through the installation plate insertion
groove.
4. A fluid flow meter as claimed in claim 3 wherein said casing
comprising a passage forming member disposed at a position abutting
to the element installation section of said installation plate,
said passage forming member being formed with a groove, and a lid
member secured to the passage forming member to close the groove
so as to form a bypass passage through which a part of gas flowing
in the conduit flows, said gas flow sensor element projecting in
the bypass passage.
5. An air flow meter for intake air of an automotive internal combustion
engine, comprising: a casing installed to an intake air pipe in
which intake air flows, said casing comprising a main body section
defining a board installation recess, and a peripheral wall section
projecting from the main body section and surrounding the board
installation recess, a part of the peripheral wall section being
cut out to form first and second end portions which are separate
from each other to define therebetween an installation plate insertion
groove, the part abutting to an inside of the conduit, the first
and second end portions having respectively first and second edges
which face each other and parallel with each other; an installation
plate comprising a board installation section disposed in the board
installation recess, and an element installation section extending
from the board installation section through the installation plate
insertion groove to an outside of the board installation recess;
a circuit board disposed on the board installation section of said
installation plate, electronic parts being provided to said circuit
board; an air flow sensor element disposed on the element installation
section of said installation plate, said air flow sensor detecting
a flow amount of intake air, said air flow sensor element comprising
a temperature sensing resistor; a silicon-containing filler disposed
in the board installation recess of said casing to cover the circuit
board, said silicon-containing filler being formed of a material
containing silicon; a fluorine-containing sealant disposed in the
board installation recess at a portion close to the installation
plate insertion groove, said fluorine-containing sealant sealing
the installation plate insertion groove so as to maintain said silicon-containing
sealant inside the board installation recess, said fluorine-containing
sealant being formed of a material whose major component is a polymer
containing fluorine; and a plate-shaped stopper member connected
to said casing and inserted in the installation plate insertion
groove of said casing and fitted between the first and second edges
of the respective first and second end portions of the peripheral
wall section of said casing, said stopper member having a tip end
in contact with said air flow sensor element, the temperature sensing
resistor of said air flow sensor element and said silicon-containing
filler being located respectively on opposite sides of said stopper
member.
Description BACKGROUND OF THE INVENTION
[0001] This invention relates to improvements in a fluid flow meter
for detecting a flow amount of gas, and more particularly to the
fluid (air) flow meter suitable for detecting a flow amount of intake
air of an automotive engine and the like.
[0002] In general, automotive engines or the like are arranged
such that the flow amount of intake air of the engine is detected
by an air flow meter or sensor, and then the injection amount or
the like of fuel is determined in accordance with a detected value
of the intake air flow amount, thereby forming air-fuel mixture
having an appropriate air-fuel ratio upon mixing intake air and
fuel
[0003] A typical one of air flow meters used for the above purpose
is disclosed in Japanese Patent Provisional Publication No. 2000-2572
and arranged as follows: An air flow meter includes a casing installed
to an intake air pipe in which intake air flows. The casing includes
a main body section defining a board installation recess, and a
peripheral wall section projecting from the main body section and
surrounding the board installation recess. A part (abutting to the
inside of the intake air pipe) of the peripheral wall section is
cut out to form an installation plate insertion groove. An installation
plate is provided including a board installation section disposed
in the board installation recess, and an element installation section
extending from the board installation section through the installation
plate insertion groove to outside of the board installation recess.
A circuit board is disposed on the board installation section of
the installation plate. Electronic parts are provided to the circuit
board. Additionally, an air flow sensor element is disposed on the
element installation section of the installation plate so as to
detect a flow amount of intake air.
[0004] In such an air flow sensor element, a temperature sensing
resistor and a heater are formed on a silicon substrate by using
metal thin film made of platinum or the like. The air flow sensor
element is formed extending through the installation plate insertion
groove into the board installation groove so that a part of the
air flow sensor is located within the board installation groove.
The part of the air flow sensor is connected to the circuit board
to constitute a bridge circuit and the like. The temperature sensing
resistor of the air flow sensor element is to be in contact with
flow of intake air and cooled by intake air, under a condition where
the temperature sensing resistor is heated by the heater. At this
time, change in temperature (electrical resistance value) of the
temperature sensing resistor is detected as a flow amount of intake
air.
[0005] During operation of the engine, a part of intake air flowing
the intake air pipe tends to penetrate into the board installation
recess through the installation plate insertion groove. Accordingly,
for example, a silicon-containing material gel is previously filled
in the board installation recess and then solidified thereby covering
the circuit board with this silicon-containing material, thus protecting
the circuit board from dust, water and the like contained in intake
air, in the above conventional technique disclosed in Japanese Patent
Provisional Publication No. 2000-2572.
[0006] However, most automotive vehicles are equipped with an evaporative
emission control system and/or an exhaust gas recirculating system.
In the evaporative emission control system, evaporative gas or fuel
gas generated within a fuel tank is flown into the intake air passageway
to be mixed with intake air in order to prevent the evaporative
gas from being released to the atmospheric air. The evaporative
gas mixed with intake air is supplied to the engine to be combusted.
In the exhaust gas recirculating system, a part of exhaust gas is
recirculated through the intake air pipe into the engine in order
to purify exhaust gas.
[0007] As a result of operation of the evaporative emission control
system and/or the exhaust gas recirculating system, intake air flowing
through the intake air pipe possibly contains the volatile (fuel)
components of gasoline or light oil (diesel fuel). Consequently,
when intake air penetrates into the board installation recess of
the air flow meter and comes into contact with the silicon-containing
material, there is the possibility that the silicon-containing material
deteriorates owing to its swelling and melts to be flown out, because
the silicon-containing material is low in durability against the
volatile (fuel) components.
[0008] Thus, in the conventional technique, the silicon-containing
material within the board installation recess may melt and flow
out though the installation plate insertion groove so as to adhere
onto the temperature sensing resistor and the like. This may make
unstable the detection accuracy of the measured air flow amount
while lowering the reliability of the air flow meter.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide an improved
fluid (air) flow meter which can effectively overcome drawbacks
encountered in similar conventional fluid flow meters.
[0010] Another object of the present invention is to provide an
improved fluid (air) flow meter using a fluid flow sensor element,
which can stably detect the flow amount of a measured fluid at a
high accuracy throughout a long time, while improving the reliability
of the fluid flow meter.
[0011] A further object of the present invention is to provide
an improved fluid (air) flow meter using a fluid flow sensor element,
in which a silicon-containing material or filler filled in a board
installation recess of a casing can be effectively prevented from
being deteriorated by a component contained in a measured fluid.
[0012] An aspect of the present invention resides in a fluid flow
meter comprising a casing installed to a conduit in which a measured
gas flows. The casing includes a main body section defining a board
installation recess, and a peripheral wall section projecting from
the main body section and surrounding the board installation recess,
a part of the peripheral wall section being cut out to form an installation
plate insertion groove, the part abutting to an inside of the conduit.
An installation plate is provided including a board installation
section disposed in the board installation recess, and an element
installation section extending from the board installation section
through the installation plate insertion groove to an outside of
the board installation recess. A circuit board is disposed on the
board installation section of the installation plate, electronic
parts being provided to the circuit board. A gas flow sensor element
is disposed on the element installation section of the installation
plate, the gas flow sensor element detecting a flow amount of the
measured gas. A silicon-containing filler is disposed in the board
installation recess of the casing to cover the circuit board, the
silicon-containing filler being formed of a material containing
silicon. Additionally, a fluorine-containing sealant is disposed
in the board installation recess at a portion close to the installation
plate insertion groove, the fluorine-containing sealant sealing
the installation plate insertion groove so as to maintain the silicon-containing
sealant inside the board installation recess, the fluorine-containing
sealant being formed of a material whose major component is a polymer
containing fluorine.
[0013] Another aspect of the present invention resides in an air
flow meter for intake air of an automotive internal combustion engine.
The air flow meter comprising a casing installed to an intake air
pipe in which intake air flows. The casing includes a main body
section defining a board installation recess, and a peripheral wall
section projecting from the main body section and surrounding the
board installation recess, a part of the peripheral wall section
being cut out to form first and second end portions which are separate
from each other to define therebetween an installation plate insertion
groove, the part abutting to an inside of the conduit, the first
and second end portions having respectively first and second edges
which face each other and parallel with each other. An installation
plate includes a board installation section disposed in the board
installation recess, and an element installation section extending
from the board installation section through the installation plate
insertion groove to an outside of the board installation recess.
A circuit board is disposed on the board installation section of
the installation plate, electronic parts being provided to the circuit
board. An air flow sensor element is disposed on the element installation
section of the installation plate, the air flow sensor detecting
a flow amount of intake air, the air flow sensor element including
a temperature sensing resistor. A silicon-containing filler is disposed
in the board installation recess of the casing to cover the circuit
board, the silicon-containing filler being formed of a material
containing silicon. A fluorine-containing sealant is disposed in
the board installation recess at a portion close to the installation
plate insertion groove, the fluorine-containing sealant sealing
the installation plate insertion groove so as to maintain the silicon-containing
sealant inside the board installation recess, the fluorine-containing
sealant being formed of a material whose major component is a polymer
containing fluorine. Additionally, a plate-shaped stopper member
is connected to the casing and inserted in the installation plate
insertion groove of the casing and fitted between the first and
second edges of the respective first and second end portions of
the peripheral wall section of the casing. The stopper member has
a tip end in contact with the air flow sensor element. The temperature
sensing resistor of the air flow sensor element and the silicon-containing
filler are located respectively on opposite sides of the stopper
member.
[0014] The other objects and features of this invention will become
understood from the following description with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the drawings, like reference numerals designate like
parts and elements throughout all figures, in which:
[0016] FIG. 1 is a vertical sectional view of an embodiment of
a fluid flow meter according to the present invention, in a condition
to be installed to a conduit;
[0017] FIG. 2 is a front elevation, partly in section, of the fluid
flow meter of FIG. 1;
[0018] FIG. 3 is a vertical sectional view taken in the direction
of arrows substantially along the line III-III of FIG. 2;
[0019] FIG. 4 is an enlarged fragmentary front view of a casing
of the fluid flow meter of FIG. 1 illustrating a silicon-containing
filler, a fluorine-containing sealant and the like;
[0020] FIG. 5 is an enlarged fragmentary sectional view taken in
the direction of arrows substantially along the line V-V of FIG.
4;
[0021] FIG. 6 is an enlarged fragmentary perspective view showing
a passage forming member in a condition made before installation
of a lid member to the passage forming member, in the fluid flow
meter of FIG. 1;
[0022] FIG. 7 is a vertical sectional view similar to FIG. 1 but
showing a modified embodiment of the fluid flow meter according
to the present invention, in a condition to be installed to a conduit;
and
[0023] FIG. 8 is an enlarged fragmentary sectional view similar
to FIG. 5 but showing an essential part of the modified embodiment
of FIG. 7 and illustrating a silicon-containing filler, a fluorine-containing
sealant and the like in a casing.
DETAILED DESCRIPTION OF THE INVENTION
[0024] Referring now to FIG. 1 of the drawings, an embodiment of
a fluid or gas flow meter according to the present invention is
illustrated. In this embodiment, the fluid flow meter is an air
flow meter for measuring an amount of air flowing though an intake
air passageway or pipe of an internal combustion engine of an automotive
vehicle. A cylindrical conduit 1 formed of plastic (synthetic resin),
metal or the like is coaxially connected or inserted in the intake
air pipe. Conduit 1 is formed thereinside an air flow passage 2
through which intake air (or measured fluid or gas) flows from the
side of an air cleaner (not shown) to the side of combustion chambers
(not shown) of the engine. A peripheral cylindrical wall 3 of conduit
1 is formed with a cylindrical boss section 4 which extends radially
outwardly. The inside of boss section 4 is in communication with
air flow passage 2.
[0025] The air flow meter includes a casing 11 which forms the
main body of the air flow meter and is formed of plastic, metal
or the like. As shown in FIGS. 2 and 3 casing 11 includes an installation
section 12 a circuit accommodating section 14 and a passage forming
member 18 and the like which are formed integral with each other
to constitute casing 11. A major part of casing 11 is inserted in
and fitted inside boss section 4 of conduit 1. An installation section
12 of casing 11 is fitted to the tip end portion of boss section
4 and provided with a connector section 13 having pin terminals
13A located outside conduit 1.
[0026] Circuit accommodating section 14 is formed generally box-shaped
and rectangular in section, and extends from installation section
12 to the inside of conduit 1 so that the tip end portion of circuit
accommodating section projects inside the conduit 1. Circuit accommodating
section 14 includes an accommodating casing 14A which is opened
to the left side in FIG. 3. A lid plate 14B closes the opened side
of accommodating casing 14A upon being put on the accommodating
casing 14A. Lid plate 14B is formed generally rectangular in section.
Accommodating casing 14A of circuit accommodating section 14 has
a main body section (not identified) which is formed thereinside
with a board installation recess 15 in which a circuit board 23
discussed after is installed.
[0027] As shown in FIG. 6 accommodating casing 14A has a peripheral
wall section 14A1 which projects from the main body section of the
accommodating casing 14A and is located generally surrounding board
installation recess 15. Peripheral wall section 14A1 has a generally
straight portion which faces a bypass passage 21 which will be discussed
after. A central part of the straight portion of peripheral wall
section 14A1 is cutout to form a generally rectangular cutout (in
section). As a result, two end portions (no numerals) which face
each other and separate from each other are formed. An installation
plate insertion groove 16 is formed between the two end portions
of peripheral wall section 14A1. Two end portions of peripheral
wall section 14A1 has respectively two edges which extend parallel
with each other, and are respectively formed with fitting holes
17 17.
[0028] Passage forming member 18 is formed integral with a projected
end of circuit accommodating section 14 which projects inside the
conduit 1. Passage forming member 18 is formed of plastic, metal
or the like and integral with accommodating casing 14A of circuit
accommodating section 14. Passage forming member 18 is formed with
a generally U-shaped groove 18A which opens to the side of passage
forming member 18.
[0029] A lid member 19 is provided to be installed to the side
of passage forming member 18 so as to close U-shaped groove 18A
at the side of passage forming member 18. Lid member 19 is formed
of plastic plate, metal plate or the like, and integrally formed
at its outer peripheral portion with two claw portions 19A, 19A
which project toward circuit accommodating section 14 as shown in
FIGS. 4 and 6. Lid member 19 is integrally formed with a stopper
member 20 which is located between two claw portions 19A, 19A and
will be discussed after. Lid member 19 is fixed to the side surface
of the passage forming member 18 for example, by means of adhesion
or the like upon fitting of respective claw portions 19A, 19A to
fitting holes 17 17 thereby closing the side of U-shaped groove
18A. As a result, U-shaped bypass passage 21 is formed.
[0030] Stopper member 20 formed in passage forming member 18 is
a plate-shaped small piece which projects from lid member 19 toward
installation plate insertion groove 16 and has a width corresponding
to that of installation plate insertion groove 16. Additionally,
in a condition where lid member 19 is installed to passage forming
member 18 stopper member 20 closes installation plate insertion
groove 16 and has its tip end portion which is generally in contact
with the surface of a base plate 24A at a position between a temperature
sensing resistor 24B and a connecting section 24C of an air flow
sensor element 24 which will be discussed after, as shown in FIGS.
4 and 5. It will be understood that stopper member 20 is fitted
between the opposed edges of the end portions of the peripheral
wall section 14A1.
[0031] With the above arrangement, stopper member 20 is disposed
in a manner to isolate the inside of board installation recess 15
from bypass passage 21 thereby preventing a gel material of a sealant
27 from flowing out through installation plate insertion groove
16 during assembly operation of the air flow meter and preventing
the sealant 27 from being dispersed out owing to deterioration with
age during use of the air flow meter, as will be discussed in detail
after. The sealant 27 is formed of a material whose major component
is a polymer (fluororesin) containing fluorine.
[0032] Bypass passage 21 is formed between passage forming member
18 (having groove 18A) and lid member 19 and bent to be generally
U-shaped as shown in FIGS. 2 and 6. Bypass passage 21 has a one
end portion serving as an air inflow opening 21A which opens to
the inside of the conduit 1 at a position upstream of the installation
plate insertion groove 16. The other end portion of bypass passage
21 serves as an air outflow opening 21B which is opened to the bottom
surface side of passage forming member 18.
[0033] An installation plate 22 is disposed in circuit accommodating
section 14 and formed, for example, of a rectangular metal plate
or the like. Installation plate 22 includes a board installation
section 22A which is disposed in board installation recess 15 of
accommodating casing 14A. Circuit board 23 is mounted on board installation
section 22A. Installation plate 22 further includes an element installation
section 22B which extends from board installation section 22A and
projects through installation plate insertion groove 16 into bypass
passage 21. Element installation section 22B is formed with a rectangular
recess 22C in which air flow sensor element 24 discussed after is
installed.
[0034] Circuit board 23 is generally rectangular in plan and mounted
on board installation section 22A. Circuit board 23 is accommodated
in board installation recess 15 in circuit accommodating section
14. Additionally, a plurality of electronic parts are mounted on
circuit board 23 and adapted to make input and output of electrical
signals between it and air flow sensor element 24. These electronic
parts are connected to pin terminals 13A of connector section 13
through bonding wires and the like.
[0035] Air flow sensor element 24 is installed to element installation
section 22B and includes a base plate or substrate 24A which is
formed generally into the shape of an elongate rectangle and formed
of a silicon plate or the like, as shown in FIG. 5. Base plate 24A
is fixed in recess 22C of element installation section 22B of installation
plate 22. Temperature sensing resistor 24B is mounted on base plate
24A and formed of a metal thin film formed of platinum or the like.
A heater (not shown) is provided to heat temperature sensing resistor
24B.
[0036] Temperature sensing resistor 24B is located at a one side
of base plate 24A in the direction of length of the base plate and
exposed in bypass passage 21. The other side of base plate 24A in
the length direction of the base plate serves as a connecting section
24C including a plurality of electrode pads (not shown) extending
respectively from temperature sensing resistor 24B and heater, and
the like. Connecting section 24C extends to the inside of circuit
accommodating section 14 through installation plate insertion groove
16 of circuit accommodating section 14 and over stopper member 2.
Electrode pads and the like are connected to circuit board 23 through
bonding wires 25 25 . . . .
[0037] Temperature sensing resistor 24B of air flow sensor element
24 is to be in contact with flow of intake air and cooled by intake
air, under a condition where the temperature sensing resistor is
heated by heater. At this time, change in temperature (electrical
resistance value) of temperature sensing resistor 24B is detected
as a flow amount of intake air and output as a detection signal
out of the air flow meter through circuit board 23 connector section
13 and the like.
[0038] An insulating silicon-containing filler 26 is disposed or
filled in board installation recess 15 of circuit accommodating
section 14. For example, silicon-containing filler 26 is formed
by filling a gel of a silicon-containing material into the board
installation recess 15 and then by solidifying the filled gel. The
silicon-containing filler is, for example, made of a material whose
major component is silicone resin. As shown in FIGS. 3 and 5 the
almost whole of circuit board 23 is covered with silicon-containing
filler 26 and fluorine-containing sealant 27.
[0039] Insulating fluorine-containing sealant 27 is filled and
disposed around installation plate insertion groove 16 and in board
installation recess 15 of circuit accommodating section 14. Fluorine-containing
sealant 27 is formed of a material whose major component is a polymer
containing fluorine, such as fluororesin. The fluorine-containing
sealant is, for example, of a rubber-like elastomeric material which
is called a fluorine-containing elastomer. Fluorine-containing sealant
27 is formed by previously applying a gel polymer material containing
fluorine as shown in FIGS. 4 and 5 and then by solidifying the gel
polymer material. Fluorine-containing sealant 27 is highly durable
and resistant to volatile (fuel) components of gasoline, light oil
(diesel fuel) and the like.
[0040] Fluorine-containing sealant 27 is applied and adhered around
the opening of installation plate insertion groove 16 and the inner
or upper surface of stopper member 20. Accordingly, fluorine-containing
sealant 27 seals a small clearance formed among members or sections
defining installation plate insertion groove 16 installation plate
22 the surface of air flow sensor element 24 and stopper member
20 and closes installation plate insertion groove 16 to maintain
an air-tight seal in cooperation with stopper member 20. Fluorine-containing
sealant 27 can prevent intake air flowing in conduit 1 from penetrating
into circuit accommodating section 14 thereby protecting circuit
board 23 bonding wires 25 and the like from dust, water and the
like in intake air. Additionally, fluorine-containing sealant 27
can interrupt the contact of silicon-containing filler 26 with intake
air. This prevents silicon-containing filler 26 from melting and
leaking outside upon deterioration of silicon-containing filler
caused by contact of the silicon-containing filler with the volatile
components, even in case that the volatile components are contained
in intake air.
[0041] Manner of operation of the above air flow meter will be
discussed hereinafter.
[0042] First, during operation of the engine, intake air flows
in a direction indicated by an arrow A in conduit 1 as shown in
FIG. 1. At this time, a part of intake air flows through air inflow
opening 21A of passage forming member 18 into bypass passage 21
and flows through outflow opening 21B into conduit 1 after passing
through the position of air flow sensor element 24 in its flow-straightened
state. Here, air flow sensor element 24 detects the flow amount
of intake air flowing in conduit 1 and produces and outputs a detection
signal out of the air flow meter through circuit board 23 connector
section 13 and the like.
[0043] At this time, circuit board 23 and the like in casing 11
can be protected from foreign matters such as dust, water and the
like because the circuit board and the like are interrupted in contact
with intake air under the action of silicon-containing filler 26
and fluorine-containing sealant 27.
[0044] Additionally, even in case that intake air contains fuel
gas (evaporated gas) and/or volatile components of gasoline, light
oil or the like contained in exhaust gas, silicon-containing filler
26 can be securely prevented from melting and leaking out owing
to contact with the volatile components in intake air because installation
plate insertion groove 16 in circuit accommodating section 14 is
closed or blocked with fluorine-containing sealant 27 having a high
durability to the volatile components.
[0045] During assembly of casing 11 as shown in FIG. 6 after
installation plate 22 circuit board 23 air flow sensor element
24 and the like are assembled in the side of accommodating casing
14A of circuit accommodating section 14 lid member 19 is installed
to the side surface of the passage forming member 18 thereby closing
the opened side of the U-shaped groove 18A so as to form bypass
passage 21. By this, installation plate insertion groove 16 in the
accommodating casing 14A is generally isolated by stopper member
20 of lid member. Then, the air flow sensor element 24 comes into
a condition where the connecting section 24C is disposed inside
board installation recess 15 while the temperature sensing resistor
24B is disposed in bypass passage 21.
[0046] The gel (polymer) material which will become fluorine-containing
sealant 27 is applied around installation plate insertion groove
16 and stopper member 20 from the opened side of accommodating casing
14A and solidified thereby forming fluorine-containing sealant 27.
Further, the gel (material) which will become silicon-containing
filler 26 is filled in the board installation recess 15 and solidified
thereby forming silicon-containing filler 26.
[0047] Thus, circuit board 23 comes into a condition in which the
whole of it is generally covered with silicon-containing filler
26 and fluorine-containing sealant 27. Then, lid plate 14B is installed
to the opened side of accommodating casing 14A to close board installation
recess 15 thereby assembling casing 11.
[0048] As apparent from the above, according to the embodiment
of the present invention, fluorine-containing sealant 27 is disposed
in board installation recess 15 of circuit accommodating section
14 at a position around installation plate insertion groove 16.
Consequently, for example, even in case that intake air flowing
through bypass passage 21 contains the volatile (fuel) components,
a slight clearance formed among the members or sections defining
installation plate insertion groove 16 installation plate 22 the
surface of air flow sensor element 24 and stopper member 20 can
be securely sealed with fluorine-containing sealant 27 having a
high durability and good elastomeric characteristics thereby maintaining
a stable isolation of silicon-containing filler 26 inside circuit
accommodating section 14 from intake air.
[0049] Thus, fluorine-containing sealant 27 can securely prevents
silicon-containing filler 26 from melting and leaking out through
installation plate insertion groove 16 of circuit accommodating
section 14 so as to adhere to temperature sensing resistor 24B and
the like of the air flow sensor element 24 owing to contact of silicon-containing
filler 26 with the volatile (fuel) components contained in intake
causing deterioration of the silicon-containing filler. This can
maintain a detection operation of air flow sensor element 24 in
a good condition for a long time, while improving the durability
and reliability of the air flow meter.
[0050] In the embodiment, fluorine-containing sealant 27 is disposed
within circuit accommodating section 14 at the position around installation
plate insertion groove 16 and therefore a major part (other than
a part covered with the fluorine-containing sealant) of circuit
board 23 can be covered with silicon-containing filler 26 which
is formed as a generalized product from the gel of the silicon-containing
material or the like, within the circuit accommodating section 14.
This saves the amount of use of fluorine-containing sealant 27 thus
achieving a cost reduction of the air flow meter.
[0051] Further, lid member 19 for passage forming member 18 has
stopper member 20 which closes installation plate insertion groove
16 of circuit accommodating section 14 and therefore fluorine-containing
sealant 27 is merely required to seal the slight clearance formed
around stopper member 20 within installation plate insertion groove
16 thereby stably exhibiting a good sealing performance with a small
amount of fluorine-containing sealant.
[0052] Furthermore, during assembly of the air flow meter, stopper
member 20 can be readily disposed in installation plate insertion
groove 16 by installing lid member 19 onto passage forming member
18. Merely by applying the gel polymer material (becoming as fluorine-containing
sealant 27) around installation plate insertion groove 16 and solidifying
the gel polymer material after installation of the lid member, fluorine-containing
sealant 27 can be readily filled among respective bonding wires
25 and the like without forming clearance.
[0053] Moreover, during the above operation of filling fluorine-containing
sealant 27 stopper member 20 can prevent the gel polymer material
from flowing out to the side of temperature sensing resistor 24B
of air flow sensor element 24 through installation plate insertion
groove 16 thereby smoothly carrying out the filling operation of
the fluorine-containing sealant. During use of the air flow meter,
stopper member 20 can prevent fluorine-containing sealant 27 from
dispersing out of the position owing to deterioration with age or
the like, thus improving a durability of the air flow meter.
[0054] While circuit accommodating section 14 and passage forming
member 18 have been shown and described as being formed integral
with each other in casing 11 in the embodiment, it will be understood
that the principle of the present invention may be applied to the
air flow meter arranged such that passage forming member 18' is
formed integral with conduit 1' (not with casing 11') while element
installation section 22B' of installation plate 22' is inserted
into bypass passage 21' from the upper side of passage forming member
18', as shown in a modified embodiment illustrated in FIGS. 7 and
8. In this case, a lid member 31 is installed to the tip end side
of circuit accommodating section 14' so as to tightly close a space
between accommodating casing 14A' and lid plate 14B' as shown in
FIG. 8. lid member 31 has a stopper member 32 for closing installation
plate insertion groove 16'.
[0055] As appreciated from the above, according to the present
invention, the fluorine-containing sealant is disposed in the board
installation recess of the casing at the position around installation
plate insertion groove. Consequently, for example, even in case
that a measured fluid or gas contains the volatile (fuel) components,
the installation plate insertion groove can be securely sealed with
fluorine-containing sealant 27 having a high durability against
the volatile components thereby maintaining a stable isolation of
the silicon-containing filler filled inside the board installation
recess of the casing from the measured fluid. This can securely
prevent the silicon-containing filler from melting and leaking out
through the installation plate insertion groove of the circuit accommodating
section so as to adhere to the sensor part and the like of the air
flow sensor element owing to contact of the silicon-containing filler
with the volatile (fuel) components contained in the measured fluid
causing deterioration of the silicon-containing filler. Thus, a
detection operation of the air flow sensor element can be maintained
in a good condition for a long time, while improving the durability
and reliability of the air flow meter.
[0056] The contents of Japanese Patent Application No. 2000-376454
filed Dec. 11 2000 is incorporated by reference. |