U.S. patent application number 09/908271 was filed with the patent office on 2002-01-31 for plastic fuel tank having an arrangement for welding a component part in a fuel impermeable manner.
This patent application is currently assigned to Yachiyo Kogyo Kabushiki Kaisha. Invention is credited to Matsuzaki, Toru, Nakamura, Kazuhiro, Sato, Shoji, Seko, Mitsuhiro.
Application Number | 20020011490 09/908271 |
Document ID | / |
Family ID | 26596392 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020011490 |
Kind Code |
A1 |
Nakamura, Kazuhiro ; et
al. |
January 31, 2002 |
Plastic fuel tank having an arrangement for welding a component
part in a fuel impermeable manner
Abstract
In a plastic fuel tank comprising a main body having a laminated
structure including a layer made of gasoline barrier material and
an outer layer made of common plastic material, and a component
part adapted to be secured in a hole formed in the tank main body,
the component part includes at least a part made of weldable
plastic material and welded to a part of the tank main body made of
common plastic material, and a part made of gasoline barrier
material and extending across said component part so as to separate
the interior and exterior of the tank main body from each other.
The two parts of the component part may be permanently integral to
each other or may be detachably attached to each other. Thus, the
welding strength can be ensured while the permeation of HC through
the part made of the common plastic material can be avoided.
Inventors: |
Nakamura, Kazuhiro;
(Tochigi-ken, JP) ; Sato, Shoji; (Tochigi-ken,
JP) ; Matsuzaki, Toru; (Tochigi-ken, JP) ;
Seko, Mitsuhiro; (Tochigi-ken, JP) |
Correspondence
Address: |
Alan H. MacPherson
SKJERVEN, MORRILL, MACPHERSON, LLP
Suite 700
25 Metro Drive
San Jose
CA
95110
US
|
Assignee: |
Yachiyo Kogyo Kabushiki
Kaisha
|
Family ID: |
26596392 |
Appl. No.: |
09/908271 |
Filed: |
July 17, 2001 |
Current U.S.
Class: |
220/4.12 ;
220/4.13; 220/500; 264/109 |
Current CPC
Class: |
B29C 66/322 20130101;
Y10T 428/1352 20150115; B29C 66/8322 20130101; B60K 15/035
20130101; B29C 65/02 20130101; B29C 66/1226 20130101; B29C 66/12841
20130101; B29C 66/71 20130101; B60K 2015/03453 20130101; B29C
66/53247 20130101; B29C 66/1224 20130101; B60K 15/03177 20130101;
B29C 66/71 20130101; B29C 66/72343 20130101; B29L 2031/7172
20130101; B29C 66/1228 20130101; B60K 15/04 20130101; B29C 66/1286
20130101; B29K 2023/065 20130101 |
Class at
Publication: |
220/4.12 ;
220/4.13; 220/500; 264/109 |
International
Class: |
B65D 006/00; B65D
001/24; B65D 085/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 21, 2000 |
JP |
2000-220300 |
Dec 26, 2000 |
JP |
2000-394659 |
Claims
1. A plastic fuel tank, comprising a main body having a laminated
structure including a layer made of gasoline barrier material, an
outer layer made of weldable plastic material and a hole formed in
said main body so as to communicate an interior and exterior of
said tank main body with each other; and a component part fitted in
said hole, said component part including a first part made of
gasoline barrier material extending across said component part so
as to substantially separate the interior and exterior of said tank
main body from each other and a second part made of weldable
plastic material provided in a peripheral part of said component
part at which said component part is welded to a part of said outer
layer of said tank main body surrounding said hole.
2. A plastic fuel tank according to claim 1, further comprising a
seal member interposed between a peripheral part of said hole and
an outer circumferential surface of said component part to seal off
said welded part from the interior of said tank main body.
3. A plastic fuel tank according to claim 1, wherein said first
part of said component part made of the gasoline barrier material
includes an outer layer of said component part which is formed over
said second part and extends at least to a vicinity of said welded
part.
4. A plastic fuel tank according to claim 1, wherein said first
part of said component part includes a wall member of said
component part which extends to at least to a vicinity of said
welded part, and said second part includes an annular member
attached to said wall member so as to be interposed between said
first part and said welded part.
5. A plastic fuel tank according to claim 4, wherein said annular
member is interposed between opposing parts of said first part and
the outer layer of the tank main body.
6. A plastic fuel tank according to claim 4, wherein said second
part extends along an inner circumferential surface of said annular
member to at least a vicinity of said outer layer of said tank main
body.
7. A plastic fuel tank according to claim 4, wherein said second
part extends along an outer circumferential surface of said annular
member to at least a vicinity of said outer layer of said tank main
body.
8. A plastic fuel tank according to claim 1, wherein said gasoline
barrier material of said component part has a HC permeability
coefficient of 15 g-mm/m.sup.2 per day or less at 40.degree. C.
9. A method for making a plastic fuel tank comprising a main body
having a laminated structure including a layer made of gasoline
barrier material, an outer layer made of weldable plastic material
and a hole formed in said main body so as to communicate an
interior and exterior of said tank main body with each other; and a
component part fitted in said hole, said component part including a
first part made of gasoline barrier material extending across said
component part so as to substantially separate the interior and
exterior of said tank main body from each other and a second part
made of weldable plastic material provided in a peripheral part of
said component part at which said component part is welded to a
part of said outer layer of said tank main body surrounding said
hole, said method comprising the steps of: preparing a component
part having a peripheral part adapted to abut on said part
surrounding said hole, said peripheral part defining an annular
abutting surface defined by said first and second parts disposed
concentrically one next to the other, said second part at said
abutting surface projecting slightly beyond said first part at said
abutting surface; and thermally welding said abutting surface of
said component part to said part surrounding said hole to such an
extent that said first part at said abutting surface reaches at
least to an immediate vicinity of said part surrounding said hole
as a result of softening or melting of said second part at said
abutting surface.
10. A method for making a plastic fuel tank comprising a main body
having a laminated structure including a layer made of gasoline
barrier material, an outer layer made of weldable plastic material
and a hole formed in said main body so as to communicate an
interior and exterior of said tank main body with each other; and a
component part fitted in said hole, said component part including a
first part made of gasoline barrier material extending across said
component part so as to substantially separate the interior and
exterior of said tank main body from each other and a second part
made of weldable plastic material provided in a peripheral part of
said component part at which said component part is welded to a
part of said outer layer of said tank main body surrounding said
hole, said method comprising the steps of: preparing a component
part having a peripheral part adapted to abut said part surrounding
said hole, said peripheral part defining an annular abutting
surface defined by said first and second parts disposed
concentrically one next to the other, said second part at said
abutting surface defining a concentric annular recess; and
thermally welding said abutting surface of said component part to
said part surrounding said hole to such an extent that said first
part at said abutting surface bends and lies over said part
surrounding said hole without interfering with the welding of said
abutting surface of said component part to said part surrounding
said hole as a result of softening or melting of said second part
at said abutting surface.
11. A component part adapted to be fitted in a hole provided in a
plastic fuel tank main body, said fuel tank main body having a
laminated structure including a layer made of gasoline barrier
material and an outer layer made of weldable plastic material, and
said hole communicating an interior and exterior of said tank main
body with each other, said component part comprising: a first part
made of gasoline barrier material extending across said component
part so as to substantially separate the interior and exterior of
said tank main body from each other; and a second part made of
weldable plastic material provided in a peripheral part of said
component part at which said component part is welded to a part of
said outer layer of said tank main body surrounding said hole, said
peripheral part defining an annular abutting surface defined by
said first and second parts disposed concentrically one next to the
other, said second part at said abutting surface projecting
slightly beyond said first part at said abutting surface.
12. A component part according to claim 11, wherein said second
part projecting beyond said first part at said abutting surface
defines a convex surface.
13. A component part according to claim 11, wherein said second
part projecting beyond said first part at said abutting surface
defines a slanted flat surface which is withdrawn on a side
adjacent to said first part.
14. A component part adapted to be fitted in a hole provided in a
plastic fuel tank main body, said fuel tank main body having a
laminated structure including a layer made of gasoline barrier
material and an outer layer made of weldable plastic material, and
said hole communicating an interior and exterior of said tank main
body with each other, said component part comprising: a first part
made of gasoline barrier material extending across said component
part so as to substantially separate the interior and exterior of
said tank main body from each other; and a second part made of
weldable plastic material provided in a peripheral part of said
component part at which said component part is welded to a part of
said outer layer of said tank main body surrounding said hole, said
peripheral part defining an annular abutting surface defined by
said first and second parts disposed concentrically one next to the
other, said second part at said abutting surface defining a
concentric annular recess.
Description
TECHNICAL FIELD
[0001] The present invention relates to a plastic fuel tank, and in
particular to a plastic fuel tank including a component part which
is secured in a hole of a tank main body by thermal welding.
BACKGROUND OF THE INVENTION
[0002] There is a growing trend to use plastic fuel tanks made of
blow molded plastic material owing to their simplicity in avoiding
rusting and reducing weight, and achieving a high productivity.
High density polyethylene (HDPE) typically used for blow molding
has a high HC (hydrocarbon) permeability or has a low barrier
capability so that the material is not suitable for use in fuel
tanks as it is because of the possibility of polluting the
atmosphere.
[0003] It is desirable to use a high barrier capability material
such as ethylene vinyl alcohol copolymer (EVOH) when permeation of
HC needs to be controlled. Such a so-called gasoline barrier
material is not only expensive but also has a relatively low
resistance to impacts. Therefore, it is not practical to make the
entire gasoline tank with a gasoline barrier material in view of
the cost and mechanical strength.
[0004] A component part which is molded separately, such as a
filler neck and a breather pipe, is typically required to be
attached to a blow molded fuel tank by thermal welding. However, a
gasoline barrier material is unsuitable for thermal welding. If the
component part is made of gasoline barrier material, it is
difficult to attach the component part to the tank main body with
an adequate strength.
[0005] To eliminate such a problem, it has been proposed to form
the tank main body with a laminated material having a film of
gasoline barrier material sandwiched between common plastic
material such as high density polyethylene, and the component part
mostly by gasoline barrier material but also by common plastic
material in the part to be welded by using coinjection.
[0006] This proposal can eliminate the problem associated wit the
bonding strength, but because the bonded part which is made of
common plastic material having a low barrier capability is directly
exposed to the environment inside and outside the tank, the
permeation of HC through such bonded part may create a problem.
[0007] It is conceivable to make the component part by using
weldable material and cover it with gasoline barrier material.
However, because the end surfaces of the weldable material and
gasoline barrier material are located one next to each other on the
welding surface for the fuel tank, the gasoline barrier which would
not merge with the fuel tank may interfere with the thermal welding
and an adequate mechanical strength of the welding connection for
the component part may not be achieved.
BRIEF SUMMARY OF THE INVENTION
[0008] In view of such problems of the prior art, a primary object
of the present invention is to provide a plastic fuel tank which
provides both an adequate bonding strength and a barrier capability
even when a component part is secured in a hole provided in the
tank main body.
[0009] A second object of the present invention is to provide a
plastic fuel tank including a component part secured in a hole
provided in the tank main body which provides both a high
mechanical strength and a low HC permeability.
[0010] A third object of the present invention is to provide a
plastic fuel tank including a component part secured in a hole
provided in the tank main body which can be manufactured
economically.
[0011] A fourth object of the present invention is to provide a
plastic fuel tank including a component part secured in a hole
provided in the tank main body which is easy to manufacture.
[0012] According to the present invention, such objects can be
accomplished by providing a plastic fuel tank, comprising a main
body having a laminated structure including a layer made of
gasoline barrier material, an outer layer made of weldable plastic
material and a hole formed in the main body so as to communicate an
interior and exterior of the tank main body with each other; and a
component part fitted in the hole, the component part including a
first part made of gasoline barrier material extending across the
component part so as to substantially separate the interior and
exterior of the tank main body from each other and a second part
made of weldable plastic material provided in a peripheral part of
the component part at which the component part is welded to a part
of the outer layer of the tank main body surrounding the hole.
[0013] Thus, because the parts at which the fuel tank main body and
component part are welded to each other are made of common plastic
material while the parts which are directly exposed to HC gas or
the atmosphere are covered by gasoline barrier material, the
bonding strength and HC impermeability can be achieved at the same
time without any compromise. It was discovered that the California
evaporated emission standards (LEV-II) can be met if the gasoline
barrier material of the component part has a HC permeability
coefficient of 15 g-mm/m.sup.2 per day or less at 40.degree. C.
[0014] A seal member may be interposed between a peripheral part of
the hole and an outer circumferential surface of the component part
to seal off the welded part from the interior of the tank main
body. This allows the section of the common plastic material on the
inner circumferential surface of the hole to be shielded so that
the permeation of HC through the part made of the common plastic
material can be even more favorably controlled.
[0015] According to a preferred embodiment of the present
invention, the first part of the component part made of the
gasoline barrier material includes an outer layer of the component
part which is formed over the second part and extends at least to a
vicinity of the welded part. According to another preferred
embodiment of the present invention, the first part of the
component part includes a wall member of the component part which
extends to at least to a vicinity of the welded part, and the
second part includes an annular member attached to the wall member
so as to be interposed between the first part and the welded part.
The second part may extend either along an inner or outer
circumferential surface of the annular member to at least a
vicinity of the outer layer of the tank main body.
[0016] If the component part consists of two pieces, a mount base
welded to the fuel tank main body and a component main body
detachably attached to the mount base, the functional part of the
component part which is mounted to the fuel tank can be repeatedly
detached, and the maintenance work for the component part can be
simplified.
[0017] To allow the two parts both made of weldable material to be
welded together in such a manner as to achieve an adequate bonding
strength without being interfered by the gasoline barrier layer,
the method for making the plastic fuel tank may comprise the steps
of preparing a component part having a peripheral part adapted to
abut on the part surrounding the hole, the peripheral part defining
an annular abutting surface defined by the first and second parts
disposed concentrically one next to the other, the second part at
the abutting surface projecting slightly beyond the first part at
the abutting surface, and thermally welding the abutting surface of
the component part to the part surrounding the hole to such an
extent that the first part at the abutting surface reaches at least
to an immediate vicinity of the part surrounding the hole as a
result of softening or melting of the second part at the abutting
surface.
[0018] Thus, the end surface of the outer layer made of gasoline
material can substantially abut the outer surface of the fuel tank
for an optimum sealing result whenthe dimension of the weldable
material is reduced as a result of softening or melting during the
process of welding the weldable material to the fuel tank. The
second part projecting beyond the first part at the abutting
surface may define a convex surface or a slanted flat surface which
is withdrawn on a side adjacent to the first part. In particular,
if the dimension of the step is determined so as to match the
reduction in the dimension of the welded part of the weldable
material so that the end surface of the outer layer made of
gasoline barrier material abuts the outer surface of the fuel tank
when the weldable material is welded to the fuel tank, a
particularly favorable result can be obtained in achieving the
welding strength and gasoline barrier capability both in a
satisfactory manner.
[0019] Alternatively, instead of having the second part at the
abutting surface project slightly beyond the first part at the
abutting surface, the second part at the abutting surface may
define a concentric annular recess to achieve a same goal. The
annular recess prevents the thermally softened gasoline barrier
material from flowing toward the weldable material so that the
gasoline material layer would not flow into the welding interface
between the two parts both made of weldable material, and an
adequate bonding strength can be achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Now the present invention is described in the following with
reference to the appended drawings, in which:
[0021] FIG. 1 is a fragmentary longitudinal sectional view of an
essential part of a first embodiment of the present invention;
[0022] FIG. 2 is a view similar to FIG. 1 showing a second
embodiment of the present invention;
[0023] FIG. 3 is a view similar to FIG. 1 showing a third
embodiment of the present invention;
[0024] FIG. 4 is a longitudinal sectional view showing a fourth
embodiment of the present invention;
[0025] FIGS. 5 to 8 are enlarged sectional views showing various
modifications of end surfaces of the component parts prepared for
thermal welding; and
[0026] FIG. 9 is a longitudinal sectional view showing a fifth
embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] FIG. 1 is a longitudinal sectional view of an essential part
of a fuel tank embodying the present invention. Referring to FIG.
1, the tank main body 1 is formed by a laminated structure having a
barrier layer 1c made of gasoline barrier material such as EVOH
sandwiched and bonded between a pair of main material layers 1a and
1b made of common plastic material such as HDPE which is suitable
for welding. A hole 3 is formed in an appropriate part of the tank
main body 1 for mounting a separate component part 2 such as a
filler neck or a breather pipe.
[0028] The component part 2 comprises a main part 2a made of common
plastic material which is weldable or suitable for welding, an
outer layer 2b directly exposed to the environment of the exterior
of the tank and made of gasoline barrier material, and a flange 5
formed in an axially intermediate part of the component part 2 and
adapted to closely engage a part of the outer surface of the tank
main body 1 which is made of common plastic material and surrounds
the hole 3. The main part 2a and outer layer 2b of the component
part 2 may be integrally formed by coinjection or otherwise
permanently joined to each other.
[0029] The flange 5 is provided with an annular end surface
directed in an axially downward direction as seen in FIG. 1. The
outer surface of the tank main body 1 and the lower end surface of
the flange 5 are integrally joined to each other by per se known
thermal welding (see Japanese patent application No.
11-126639).
[0030] By thus covering the outer surface of the component part 2
which is directly exposed to the environment outside the tank main
body 1 with the outer layer 2b made of gasoline barrier material,
the barrier capability (capability to control the permeation of HC)
that is required of the component part can be achieved. Because the
main part 2a is made of common plastic material, the surface which
is required to be thermally welded is made of the common plastic
material, and the required bonding strength can be ensured.
Furthermore, the part of the component part 2 made of the gasoline
barrier material extends to the bonding surface for the tank main
body 1 so that the barrier capability of the component part 2 can
be achieved.
[0031] Only the outer layer 2b of the component part 2 which is
exposed to the atmosphere was made of gasoline barrier material in
the foregoing embodiment, but the barrier layer may also be formed
on the internal surface of the component part 2 exposed to the
interior of the tank main body or may be formed as an intermediate
layer.
[0032] FIG. 2 shows a second embodiment of the present invention.
Because the tank main body 1 is not different from that of the
first embodiment, the parts corresponding to those of the first
embodiment are denoted with like numerals without repeating
description of such parts. The component part 12 of this embodiment
comprises a first part 12b which directly separates the interior
and exterior of the tank main body 1 from each other, a second part
12a which directly contacts the part of the tank main body 1 at the
lower surface of the outer peripheral part of the first part 12b,
and a third part 12c which is located substantially inside the tank
main body 1, the first to third parts 12b, 12a and 12c being
integrally formed by coinjection.
[0033] In this case also, because the first part 12b separating the
interior and exterior of the tank main body 1 from each other is
made of gasoline barrier material, it provides the gasoline barrier
capability. Because the second part 12a directly engaging the outer
surface of the tank main body 1 and thermally welded thereto is
made of the common weldable plastic material, the required bonding
strength can be ensured. In this case also, because the first part
12b made of gasoline barrier material extends to the bonding
surface for the tank main body 1 along the outer circumference of
the second part 12a, the barrier capability of the component part
12 can be achieved. The third part may be made of any material
which is preferably resistant to fuel, and may not be made of
gasoline barrier material.
[0034] FIG. 3 shows a third embodiment of the present invention. In
this case, the component part 22 is substantially entirely made of
gasoline barrier material, and only an annular portion 22a on the
lower surface of an outer peripheral part of the flange portion 25
is made of common plastic material. The two parts are integrally
formed by coinjection.
[0035] The tank main body 21 has a two layered structure including
a barrier layer 21a formed on an inner surface thereof. A seal
member 6 made of gasoline barrier material is interposed between
the inner circumferential surface of the hole 23 of the tank main
body 21 and the outer circumferential surface of the component part
22 fitted in the hole 23.
[0036] In this case, because the component part 22 which separates
the interior and exterior of the tank main body 21 from each other
is entirely made of gasoline barrier material, the barrier
capability can be achieved. Because common plastic material is used
for the annular portion 22a which engages the outer surface of the
tank main body 21 made of the common material and is thermally
welded thereto, the required bonding strength can be achieved.
Furthermore, because the seal member 6 made of gasoline barrier
material is interposed between the tank main body 21 and the
corresponding part of the component part 22, the permeation of HC
through the part of the tank main body 21 made of the common
plastic material and exposed at the wall surface of the hole 23 can
be substantially entirely avoided. The seal member 6 is preferably
interposed between the inner circumferential surface of the hole 23
and the opposing part of the component part 22, but may also be
interposed between a flange of the component part and the opposing
surface of the tank main body which may be either the inner or
outer surface thereof. In the case of the illustrated embodiment,
the seal member 6 is interposed between the flange 25 and the outer
surface of the tank main body 21 as well as between the inner
circumferential surface of the hole 23 and the opposing part of the
component part 22.
[0037] The evaporative emission standards of the state of
California (LEV-II) require that the total fuel permeation of a
component part mounted to a gasoline tank to be no more than 37.5
mg/day (measurement based on the MIN SHED--Sealed Housing for
Evaporative Determination). The fuel permeation of a component part
having its outer surface covered by a barrier layer was measured as
illustrated in FIG. 1. In the case of a component part using EVOH
having a fuel permeation coefficient of 0.014 g-mm/m.sup.2 per day
at 40.degree. C., the fuel permeation of the component part was
0.04 mg/day. In the case of a component part using PA12 having a
fuel permeation coefficient of 5.6 g-mm/m.sup.2 per day at
40.degree. C., the fuel permeation of the component part was 14
mg/day. This test was repeated a number times changing the external
material each time. According to these tests, it was found that the
LEV-II regulations can be met if the barrier layer is made of
material having a fuel permeation coefficient of 15 g-mm/m.sup.2
per day or less. The HC permeation coefficient was measured by the
cup method which is described in the following.
[0038] A prescribed amount of gasoline fuel is filled into a
flanged cylindrical cup made of impermeable metallic material, and
a sheet made of the material to be tested is placed over the mouth
of the cup. A disk formed with an opening having a prescribed area
is placed over the sheet, and attached to the cup. The cup is
subjected to a soak test at room temperature to 80.degree. C. (to
promote the permeation of the test fuel). The weight of the sample
in this enclosed state is measured at the accuracy of 1 mmg, and
thereafter measured at a regular interval again at the accuracy of
1 mmg at room temperature to 80.degree. C. The permeation of the
sample fuel is given as a weight reduction rate (permeation
coefficient) at the time when a saturation point is reached or the
weight reduction rate has become constant. The barrier capability
is evaluated according to the permeation coefficient.
[0039] FIG. 4 shows an arrangement for mounting a vent valve 31 to
a fuel tank main body 1 given as a fourth embodiment of the present
invention. The fuel tank main body 1 is made by blow molding, and
comprises at least a surface layer made of weldable material such
as HDPE and a gasoline barrier material layer, and its upper wall
is formed with a mounting hole 3 for the vent valve 31. The fuel
tank main body 1 may not be different from those of the previous
embodiments.
[0040] The vent vale 31 is normally open so as to release vapor in
the space above the fuel surface to an external canister not shown
in the drawings, but closes when the fuel level has reached a
prescribed level by sloshing to prevent the fuel from flowing into
the passage leading to the canister. The vent valve 31 is attached
to the upper wall of the fuel tank main body 1 with a part of the
vent valve located inside the fuel tank. Because this vent valve is
not different from a per se known vent valve, its detailed
description is omitted in this disclosure.
[0041] The vent valve 31 comprises a valve function part 33 made of
fuel resistant material such as polyacetal and a support base 32
made of weldable material such as HDPE that can be welded to the
surface layer of the fuel tank main body 1. An upper part of the
valve function part 33 is provided with a flange 38 which abuts the
outer surface of the upper wall of the fuel tank main body 1.
[0042] The support base 32 is disk-shaped and abuts the outer
surface of the upper wall of the fuel tank main body 1. A hose
joint 37 is provided in the upper part thereof for allowing
communication with a canister. The support base 32 is integrally
formed with an outer layer 35 made of gasoline barrier material
such as EVOH over the entire surface thereof that is directly
exposed to the environment outside the fuel tank, for instance, by
coinjection. The surface of the support base 32 opposing the fuel
tank main body 1 is formed with a recess 36 for closely receiving
the part of the valve function part located above the flange 38,
and it is contemplated to thermally weld the outer peripheral part
34 of the recess 36 to the outer surface of the fuel tank main body
1.
[0043] The support base 32 is welded to the fuel tank main body 1
so that the valve function part 33 is fixed to the fuel tank main
body 1 via the support base 32. This welding can be executed by
making use of a known thermal welding process which may consist of
thermally softening the projecting lower surface of the outer
peripheral part 34 of the recess 36 and pressing it against the
fuel tank main body 1 with the flange 38 of the valve function part
33 interposed between the opposing surfaces of the support base 32
and the upper wall of the fuel tank main body 1.
[0044] A step as indicated by dimension A in FIG. 5 is defined
between the lower end surface of the outer peripheral part 34 of
the support base 32 and the lower end surface of the outer layer 35
prior to welding the support base 32 to the fuel tank main body 1.
The step dimension A is so determined as to match the reduction in
the dimension of the lower surface of the outer peripheral part 34
when it is heated by applying a heater H and pushed against the
fuel tank main body 1.
[0045] If the step dimension A is excessive, although the bonding
strength of the welded part can be ensured, the gasoline barrier
capability is compromised because of the resulting gap between the
lower end surface of the outer layer 35 and the outer surface of
the fuel tank main body 1. If no such step is provided in the end
surface of the peripheral part 34, the outer layer 35 made of
gasoline barrier material and softened by the heater H may flow
into the weld interface between the peripheral part 34 and the
opposing surface of the fuel tank main body 1, and this may
significantly impair the quality of welding between them.
[0046] It is therefore most preferable to determine the dimension A
so as to allow the lower end surface of the outer layer 35 to just
engage the outer surface of the fuel tank main body 1 when the
outer peripheral part 9 made of the weldable plastic material is
finally welded to the outer surface of the fuel tank main body 1.
In view of the inevitable manufacturing errors and variations in
the dimensional reduction of the peripheral part 34 as a result of
welding, it is difficult to achieve both the welding of the outer
peripheral part 9 and the engagement of the end surface of the
outer layer 35 in a precise manner. However, it has been
experimentally established that the interference of the outer layer
35 with the weld interface can be avoided to an extent necessary to
ensure a reasonable mechanical strength of the welded part simply
by providing the step in such a manner as to allow the outer
peripheral part to engage the heater H slightly before the lower
surface of the outer layer 35 does.
[0047] The outer peripheral part 34 can be made to project beyond
the end surface of the outer layer 35 in any manner as long as the
outer peripheral part 34 engages the heater H before the outer
layer 35 does when the support base 32 is applied to the heater H
immediately before welding. For instance, the end surface of the
outer peripheral part 34 may have a rounded convex shape as shown
in FIG. 6, or a slanted flat surface which is withdrawn on the side
adjoining the outer layer 35 as shown in FIG. 7.
[0048] By thus forming the outer layer 35 provided in the support
base 32 with gasoline barrier material, and withdrawing the outer
layer 35 to such an extent as not to interfere with the welding of
the outer peripheral part 34, the required bonding strength can be
ensured, and the gasoline barrier capability (the capability to
prevent permeation of HC) that is required of the component part
can be achieved at the same time because the part made of the
gasoline barrier material substantially reaches the outer surface
of the fuel tank main body 1, and the weldable part of the support
base 32 is prevented from contacting the environment outside the
fuel tank.
[0049] FIG. 8 shows yet another modification from the embodiment
illustrated in FIG. 5. In this embodiment, an annular recess 39 is
formed in a part of the surface of the outer peripheral part 34 of
the support base 32 made of weldable material and adapted to engage
the heater H adjacent to the outer layer 35 to allow the molten
weldable material to flow into the annular recess 39. The dimension
of the effective welding width B of the outer peripheral part 34 is
determined so that an adequate welding strength can be
achieved.
[0050] According to this arrangement, when the support base 32 is
pressed against the fuel tank main body 1 while the outer layer 35
is softened as a result of a contact with the heater H, the
tendency of the softened outer layer 35 to flow into the interface
between the weldable material and fuel tank main body 1 is opposed
by the pressure of the molten weldable material flowing into the
annular recess 39. As a result, the interference of the gasoline
barrier material layer with the welding of the weldable material
layer with the fuel tank main body 1 can be avoided.
[0051] FIG. 9 shows a fifth embodiment of the present invention. In
this embodiment, the component part comprises a function part 33
which is received in the mounting hole 3 of the fuel tank main body
and provided with a radial flange 38 located outside the fuel tank
main body 1, and an annular support base 42 which is interposed
between the flange 38 and the outer surface of the tank main body
1. The annular support base 42 is directly welded to the fuel tank
main body 1 around the hole 3, and nuts 40 are insert molded
therein along a common circle. The inner circumferential surface of
the support base 42 is formed with an outer layer 35 made of
gasoline barrier material.
[0052] In this case also, the welding surface of the support base
42 for the fuel tank main body 1 may be provided with a step as
illustrated in FIGS. 5 to 7 or an annular recess 39 as illustrated
in FIG. 8 so that the strength of the welded part of the support
base 42 is prevented from being impaired by the gasoline barrier
material.
[0053] The valve function part 33 is made of gasoline barrier
material, and is fixed to the support base 42 by passing threaded
bolts 41 through the flange 38 and threading with the inserted nuts
40 so that the valve function part 33 can be detachably mounted to
the fuel tank main body 1.
[0054] Because the outer layer 43 is only required to prevent
gasoline vapor from being released to the atmosphere, it may be
provided only on the side exposed to the atmosphere as illustrated
in FIG. 4 or on the side exposed to the environment inside the fuel
tank as illustrated in FIG. 9. In short, it may be provided on
either side which provides an optimum gasoline barrier property
depending on the configuration of the component part.
[0055] Although the present invention has been described in terms
of preferred embodiments thereof, it is obvious to a person skilled
in the art that various alterations and modifications are possible
without departing from the scope of the present invention which is
set forth in the appended claims.
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