Fuel tank cap

A fuel tank cap structure which enables a cover member to be readily attached to a casing body. The fuel tank cap includes the casing body and the cover member that is rotatable in one direction relative to the casing body via a ratchet mechanism when a torque of or above a predetermined level is applied to the cover member. The cover member has fitting projections that are held by an outer ring member of the casing body. The outer ring member has a plurality of slits, which cause the outer ring member to be elastically deformed when riding over the fitting projections, thereby facilitating the engagement of the fitting projections with the outer ring member.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cap of a fuel tank with a pressure 
control valve for controlling pressure in the fuel tank. 
2. Description of the Related Art 
One known example of fuel tank caps is disclosed in JAPANESE UTILITY PATENT 
PUBLICATION GAZETTE No. 6-88606. FIG. 38 is a sectional view illustrating 
a fuel tank cap 300. As shown in FIG. 38, the fuel tank cap 300 includes a 
plastic casing body 302 screwed to a filler neck FN of a fuel tank (not 
shown), a cover member 330 attached to the casing body 302, and a negative 
pressure valve 340 received in a valve chamber 304 of the casing body 302 
for controlling pressure in the fuel tank. The negative pressure valve 340 
includes a rubber valve body 342, a valve supporting member 346 with a 
fitting aperture 346a for supporting the valve body 342, and a spring 348 
for pressing the valve body 342. When the differential pressure between 
the tank pressure and the atmospheric pressure applied to the valve body 
342 increases to or above a predetermined level, the negative pressure 
valve 340 opens to make the tank pressure approach atmospheric pressure. 
There are four flange members 308 arranged along the circumference of the 
casing body 302. The respective flange members 308 manufactured by resin 
molding often have irregular dimensions, which causes torque fluctuations 
in a ratchet mechanism 320. One technique proposed for solving this 
problem joins the four flange members 308 to form a ring. This technique, 
however, increases the force required for pressing the cover member 330 
onto the casing body 302 and results in lengthy and labor intensive 
assembly. 
SUMMARY OF THE INVENTION 
The object of the present invention is thus to provide a fuel tank cap in 
which a cover member is readily attached to a casing body. 
At least part of the above and the other related objects is realized by a 
fuel tank cap for closing an inlet of a fuel tank filler neck. The fuel 
tank cap includes: a casing body attached to the filler neck; a cover 
member attached to an upper portion of the casing body, the cover member 
having a side wall and a top wall; and an attachment mechanism interposed 
between the casing body and the cover member to easily connect and join 
the cover member with the casing body. The attachment mechanism includes: 
an outer ring member formed on the upper portion of the casing body; and a 
fitting projection projected from the side wall of the cover member to 
prevent the cover member from slipping off the outer ring member. The 
outer ring member has a slit, which elastically deforms when the outer 
ring member rides over the fitting projection thereby attaching the cover 
member to the casing body. 
The fuel tank cap of the present invention has attachment means for joining 
the cover member with the casing body. The attachment means includes an 
outer ring member extending outward from an upper portion of a casing body 
in a radial direction, and a fitting projection formed on the cover 
member. The cover member is attached to the casing body by fitting the 
fitting projection into the outer ring member. The attachment procedure 
causes the fitting projection of the cover member to contact the outer 
ring member and apply a force which slightly deforms the outer ring member 
in an elastic manner. A slit formed in the outer ring member facilitates 
the elastic deformation of the outer ring member. The slit enables the 
outer ring member to readily ride over the fitting projection, thereby 
attaching the cover member to the casing body. The elastic deformation of 
the outer ring member enables the cover member to be readily attached to 
the casing body. 
The outer ring member may be divided by the slit and consist of a plurality 
of arc-shaped pieces. The outer ring member having the slit formed only in 
part of the outer ring member which does not break the outer ring member, 
however, has higher mechanical strength, which enhances the strength of 
the attachment of the cover member to the casing body. 
In accordance with one preferable application, the casing body has a 
plurality of joint members projected from the upper portion of the casing 
body in the radial direction to connect with the outer ring member, and a 
plurality of slits are arranged close to the plurality of joint members. 
It is preferable that the fitting projection rotatably supports the cover 
member while being fitted in the outer ring member. In this structure, the 
fuel tank cap has a ratchet mechanism located in the cover member and the 
upper portion of the casing body, which permits rotation of the cover 
member relative to the casing body when a torque of not less than a 
predetermined level is applied to the cover member. The ratchet mechanism 
includes a resilient claw element formed on an inner circumferential side 
of the joint members and a ratchet projection formed on the cover member 
to engage with the resilient claw element and generate a torque of not 
less than the predetermined level. 
In accordance with another preferable application, the fitting projection 
has a slant plane that presses and guides the outer ring member to reduce 
an outer diameter of the outer ring member toward the top wall of the 
cover member. In accordance with still another preferable application, the 
fuel tank cap further has a discharge projection formed on the side wall 
of the cover member and arranged close to the fitting projection, in order 
to discharge static electricity stored in the cover member to the filler 
neck. 
In one preferable structure, the fuel tank cap may have a pressure control 
valve disposed in the casing body. The pressure control valve may be a 
positive pressure valve that opens when the pressure in the fuel tank is 
higher than the atmospheric pressure by at least a predetermined value. 
The pressure control valve may alternatively be a negative pressure valve 
that opens when the pressure in the fuel tank is lower than the 
atmospheric pressure by at least a predetermined value.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 is a half sectional view illustrating a fuel tank cap 10 embodying 
the present invention. The fuel tank cap 10 is screwed to a filler neck FN 
having an inlet FNb through which a supply of fuel is fed to a fuel tank 
(not shown). The fuel tank cap 10 includes a casing body 20 composed of a 
synthetic resin material, such as, for example, polyacetal, a cover member 
40 attached to an upper portion of the casing body 20 and composed of a 
synthetic resin material, such as, for example, nylon, an inner cover 50 
for closing an upper opening of the casing body 20 to define a valve 
chamber 23, a positive pressure valve 60 and a negative pressure valve 70 
received in the valve chamber 23 to function as pressure control valves, 
and a gasket GS attached to the upper circumference of the casing body 20 
for sealing the casing body 20 from the filler neck FN. The positive 
pressure valve 60 includes a valve body 61, a valve support member 68 for 
supporting the valve body 61, and a means for pressing the valve body 61, 
such as, a coil spring 69, via the valve support member 68. The negative 
pressure valve 70 includes a valve body 71, and a means for pressing the 
valve body 61, such as, a coil spring 78. 
The positive pressure valve 60 and the negative pressure valve 70 control 
the pressure in the fuel tank according to the following process. In the 
state that the fuel tank cap 10 is screwed to the filler neck EN, when the 
tank pressure increases and the differential pressure between the tank 
pressure and the atmospheric pressure applied to the valve body 61 of the 
positive pressure valve 60 exceeds a predetermined level, the valve body 
61 moves upward against the pressing force of the coil spring 69 to open 
the positive pressure valve 60. When the tank pressure decreases and the 
differential pressure between the tank pressure and the atmospheric 
pressure applied to the valve body 71 of the negative pressure valve 70 
exceeds a predetermined level, on the other hand, the valve body 71 moves 
downward to open the negative pressure valve 70. When the positive 
pressure difference or the negative pressure difference between the tank 
pressure of the fuel tank and the atmospheric pressure becomes equal to or 
greater than the predetermined level, the positive pressure valve 60 or 
the negative pressure valve 70 opens to control the tank pressure to be 
within a predetermined range about the atmospheric pressure. 
The following describes the structure of the respective constituents of the 
fuel tank cap 10 of the present embodiment in detail. 
FIG. 2 is a half sectional view illustrating the casing body 20, FIG. 3 is 
a plan view of the casing body 20, and FIG. 4 is a bottom view of the 
casing body 20. The casing body 20 includes an outer tubular body 21 of a 
substantially cylindrical shape having threads 20a screwed to the inner 
wall of the filler neck FN and a valve chamber-forming member 22 disposed 
inside the outer tubular body 21. The valve chamber-forming member forms 
the valve chamber 23, in which the positive pressure valve 60 and the 
negative pressure valve 70 shown in FIG. 1 are received. 
FIG. 5 is an enlarged half sectional view illustrating the casing body 20 
when the inner cover 50 has not yet been set in the casing body 20. The 
outer tubular body 21 and the valve chamber-forming member 22 are 
integrally joined with each other via a horizontal joint member 28 and a 
plurality of vertical joint members 29. The horizontal joint member 28 is 
a ring element arranged slightly below the center of the valve 
chamber-forming member 22. The horizontal joint member 28 functions to 
separate the fuel tank from the atmosphere. Hollow portions 27 are formed 
in the space between the outer tubular body 21 and the valve 
chamber-forming member 22 and defined by the horizontal joint member 28 
and the vertical joint members 29. The vertical joint members 29 are 
upright walls extending radially to join the outer tubular body 21 with 
the valve chamber-forming member 22. 
The valve chamber-forming member 22 includes an upper wall element 24, a 
lower wall element 25 having a smaller diameter than the diameter of the 
upper wall element 24, and a bottom element 26 formed on the lower portion 
of the lower wall element 25. These elements are integrally formed to 
define the valve chamber 23. The valve chamber 23 has an upper chamber 23a 
in which the positive pressure valve 60 is received and a lower chamber 
23b in which the negative pressure valve 70 is received. The valve 
chamber-forming member 22 has an opening 24a on the upper end thereof, 
which is covered with the inner cover 50. A slant plane 30a is formed 
between the upper wall element 24 and the lower wall element 25. One end 
of the slant plane 30a forms a seat member 30, on which the valve body 61 
of the positive pressure valve 60 is seated. 
The hollow portions 27 formed in the casing body 20 reduce the total wall 
thickness of the casing body 20 and decrease the contraction of resin in 
the vicinity of the seat member 30. This improves the dimensional accuracy 
of the seat member 30 and ensures the high sealing property of the seat 
member 30. The lowered mechanical strength of the casing body 20 due to 
the existence of the hollow portions 27 is compensated by the vertical 
joint members 29 which join the outer tubular body 21 with the valve 
chamber-forming member 22. The hollow portions 27 make the casing body 20 
thin, shorten the time required for cooling and curing the resin, and 
shorten the molding cycle. 
The inner cover 50 has a central recess 52 on the center of an inner cover 
body 51 and a cylindrical support member 53 formed along the circumference 
of the central recess 52. The cylindrical support member 53 is formed in a 
tubular shape to be inserted through the opening 24a of the valve 
chamber-forming member 22. The circumference of the inner cover body 51 
forms an outer ring element 54 having four positioning ribs 57 arranged at 
equal intervals along the circumference. The positioning ribs 57 are 
projected downward to be inserted into the hollow portions 27 between the 
outer tubular body 21 and the valve chamber-forming member 22. The inner 
cover body 51 of the inner cover 50 also has a flow aperture 58 for 
connecting the valve chamber 23 with the atmosphere. 
The opening 24a of the valve chamber-forming member 22 is covered with the 
inner cover 50, which is welded to an upper peripheral portion 24b by 
ultrasonic welding. FIG. 6 is an enlarged sectional view showing the state 
in which the inner cover 50 is welded to the upper peripheral portion 24b, 
and FIG. 7 illustrates the state in which the inner cover 50 has not yet 
been welded to the upper peripheral portion 24b. 
Referring to FIGS. 6 and 7, the inner cover 50 is mounted on the upper 
peripheral portion 24b of the valve chamber-forming member 22. The 
positioning ribs 57 of the inner cover 50 are positioned and inserted into 
the hollow portions 27, so that the cylindrical support member 53 of the 
inner cover 50 is inserted into the upper chamber 23a. Thus, the inner 
cover 50 on the valve chamber-forming member 22 is positioned across a 
predetermined gap Sb from the inner wall surface of the valve 
chamber-forming member 22. This assembly can then be exposed to an energy 
source, such as, ultrasound, to fuse together the inner cover 50 and the 
valve chamber-forming member 22 together. For example, an ultrasonic horn 
is set on the inner cover 50 to provide ultrasonic vibrations. The 
ultrasonic vibration causes part of the resin to be fused and welded at 
the joint between the upper peripheral portion 24b and the inner cover 50. 
Part of the fused resin may flow out of the joint. Since the narrow gap Sb 
is formed between the valve chamber-forming member 22 and the cylindrical 
support member 53 of the inner cover 50, the fused resin flows through the 
gap Sb to be cooled and cured. Primarily the gap Sb between the inner wall 
surface of the valve chamber-forming member 22 and the cylindrical support 
member 53 functions as a flash trap. This construction effectively 
prevents the resin fused caused by, for example, ultrasonic welding from 
entering the valve chamber 23 or the positive pressure valve 60 and the 
negative pressure valve 70 and deteriorating the sealing property. 
FIG. 8 is a perspective view illustrating the casing body 20. A flange 
member 33 for supporting the cover member 40 (see FIG. 1) is formed on the 
upper circumference of the outer tubular body 21. The flange member 33 
includes an inner ring member 34 formed on the outer tubular body 21, an 
outer ring member 35 disposed outside and slightly above the inner ring 
member 34, and four joint members 36 arranged along the circumference for 
connecting the inner ring member 34 with the outer ring member 35. 
The inner ring member 34 has resilient claw elements 37a formed thereon. 
The resilient claw elements 37a and ratchet projections 49 (see FIG. 9) of 
the cover member 40 constitute a ratchet mechanism 37. The ratchet 
mechanism 37 allows a rotation of the cover member 40 only in one 
direction and, when the rotation causes a torque equal to or greater than 
a predetermined level, races the cover member 40, so as to prevent the 
fuel tank cap 10 from being excessively rotated in the closing direction. 
FIG. 9 shows engagement of the ratchet mechanism 37. Each resilient claw 
element 37a includes resilient piece 37c extending from a step element 37b 
on the inner ring member 34 and a click 37d formed on one end of the 
resilient piece 37c. The resilient piece 37c is held by the step element 
37b to overhang the inner ring member 34 across a gap 37e. The ratchet 
projections 49 are slantly formed over the whole circumference of a top 
wall 41 of the cover member 40. The ratchet projections 49 are arranged 
circularly on the center portion of the top wall 41 to engage with the 
clicks 37d. 
In the ratchet mechanism 37 thus constructed, the ratchet projection 49 
going toward the click 37d in a clockwise direction d1 comes into contact 
with the click 37d at an obtuse angle. When the force is equal to or 
greater than a predetermined level at this moment, the ratchet projection 
49 presses down and rides over the click 37d. This causes the cover member 
40 to be rotated relative to the casing body 20. The ratchet projection 49 
going toward the click 37d in a counterclockwise direction d2, on the 
other hand, comes into contact with the click 37d at an acute angle and 
can not ride over the click 37d. This causes the cover member 40 to be 
rotated integrally with the casing body 20. 
The operation of the ratchet mechanism 37 is explained in the example of 
opening and closing the inlet FNb with the fuel tank cap 10. When a 
rotational force is applied in the clockwise direction d1 to the cover 
member 40 positioned at the inlet FNb, the cover member 40 is rotated 
integrally with the casing body 20 via the ratchet mechanism 37. The 
clicks 37d of the ratchet mechanism 37 engage with the ratchet projections 
49, so that the torque of the cover member 40 is transmitted to the casing 
body 20 and the cover member 40 is rotated integrally with the casing body 
20. The fuel tank cap 10 is accordingly screwed into the inlet FNb via the 
threads 20a and a one start screw (not shown). When the torque exceeding a 
predetermined level is applied to the cover member 40, that is, when the 
torque applied is greater than the torque required for screwing the fuel 
tank cap 10 into the filler neck FN, the clicks 37d slide against the 
ratchet projections 49. This causes the cover member 40 to be raced with 
respect to the casing body 20 and prevents the fuel tank cap 10 from being 
excessively rotated in the closing direction. When the user rotates the 
cover member 40 in the counterclockwise direction d2, the cover member 40 
is rotated integrally with the casing body 20 via the ratchet mechanism 
37, so that the fuel tank cap 10 is removed from the inlet FNb. 
As shown in FIG. 8, the inner circumference of the flange member 33 forms 
the inner ring member 34, and the resilient claw elements 37a of the 
ratchet mechanism 37 are formed on the inner ring member 34. This means 
that the resilient claw elements 37a are disposed on the inner side of the 
flange member 33. This arrangement reduces contraction of the resin and 
realizes injection molding with the high dimensional accuracy. Namely this 
arrangement reduces the dimensional errors of the resilient claw elements 
37a, makes the sliding torque of the cover member 40 substantially 
constant, and enables the ratchet mechanism 37 to work stably. 
Referring to FIG. 10, the joint members 36 of the flange member 33 extend 
outward and slightly upward from the outer circumference of the inner ring 
member 34. There is a space Sp between the joint members 36. The space Sp 
decreases the amount of the resin used for the flange member 33 to reduce 
the weight, and facilitates the manufacture of the ratchet mechanism 37. 
The position of the space Sp corresponds to the gap 37e of the resilient 
claw element 37a. In the process of injection molding the casing body 20, 
a slide mold SF1 is inserted through the space Sp, so that the gap 37e of 
the ratchet mechanism 37 can be provided readily. 
FIG. 11 is an enlarged sectional view illustrating the joint member 36 of 
the flange member 33. As shown in FIG. 11, the joint member 36 has an 
L-shaped cross section including a horizontal element 36h and a vertical 
element 36v integrally formed with the horizontal element 36h. The joint 
member 36 has a fragile portion that is broken to separate the cover 
member 40 from the casing body 20 when an excessive external force is 
applied to the cover member 40, for example, due to deformation of an 
outer plate of the automobile (not shown). As shown in FIG. 12, V grooves 
are formed as notches 36a1 through 36a4 on the outer face of the joint 
member 36, whereas V grooves are formed as notches 36b1 through 36b3 on 
the inner face of the joint member 36. An angle (1 of the plane connecting 
the notch 36a1 with the notch 36a1 is set equal to 60 degrees, an angle (2 
of the plane connecting the notch 36a2 with the notch 36b2 is equal to 45 
degrees, and an angle (3 of the plane connecting the notch 36a3 with the 
notch 36b3 is equal to 0 degree, that is, in the diametral direction. 
These notches form the fragile portion, on which the joint member 36 is 
broken and separated. When the cover member 40 receives an external force 
in a direction d3 (axial direction), a break starts from the notches 36a1 
and 36b1 to separate the joint member 36 on the plane connecting the 
notches 36a1 and 36b1 with each other. When the cover member 40 receives 
an external force in a direction d4, a break starts from the notches 36a2 
and 36b2 to separate the joint member 36 on the plane connecting the 
notches 36a2 and 36b2. When the cover member 40 receives an external force 
in a direction d5 (diametral direction), a break starts from the notches 
36a3 and 36b3 to separate the joint member 36 on the plane connecting the 
notches 36a3 and 36b3 with each other. 
The fragile portion is readily broken when an external force is applied to 
the joint member 36 of the flange member 33 in any one of the vertical 
direction d3, the slant direction d4, and the horizontal direction d5. 
This structure eliminates a scatter of the breaking load on the joint 
member 36, irrespective of the direction of the external force applied. 
FIGS. 13 and 14 show modifications of the structure of FIG. 12 having joint 
members of different shapes with notches at different positions. Referring 
to FIG. 13, a joint member 136 has an L-shaped cross section including a 
horizontal element 136h and a vertical element 136v integrally formed with 
each other. The horizontal element 136h has notches 136a1 and 136b1 
constituting a first fragile portion, and the vertical element 136v has 
notches 136a2 and 136b2 constituting a second fragile portion. The first 
fragile portion and the second fragile portion are broken respectively on 
the planes connecting the corresponding notches to separate the joint 
member 136. 
Referring to FIG. 14, a joint member 236 is arranged in an inclined 
orientation and has notches 236a1 and 236b1 constituting a first fragile 
portion and notches 236a2 and 236b2 constituting a second fragile portion. 
Another notch 236a3 is further formed between the notches 236a1 and 236a2, 
in order to facilitate the break of the second fragile portion. The joint 
member 236 may have any shape and arrangement as long as it has the first 
fragile portion and the second fragile portion. 
FIG. 15 is an enlarged sectional view illustrating an end of the flange 
member 33 of the outer tubular body 21. Referring to FIG. 15, the gasket 
GS is disposed below the flange member 33, and is interposed between the 
inlet FNb of the filler neck FN and the flange member 33. A seal support 
element 21a is formed on the lower periphery of the flange member 33. The 
seal support element 21a has a radius RS that is smaller than a radius RG 
of the outer circumferential surface of the gasket GS. Setting the radius 
RS of the seal support element 21a smaller than the radius RG of the 
gasket GS has the following effects on the sealing property. 
When the fuel tank cap 10 is screwed into the inlet FNb, the gasket GS is 
pressed against the seal support element 21a and sealed at two sealing 
lines SL1 and SL2. In the conventional structure, the seal support element 
has the same radius as that of the gasket and is sealed along 
substantially the whole surface. Compared with this conventional 
structure, the structure of the embodiment has the greater sealing force 
at both the sealing lines SL1 and SL2 and ensures the high sealing 
property between the fuel tank and the atmosphere. 
FIG. 16 is a half sectional view illustrating the cover member 40, FIG. 17 
is a bottom view of the cover member 40, and FIG. 18 is a perspective view 
of the cover member 40. The cover member 40 is detachably attached to the 
flange member 33. The cover member 40 includes a top wall 41, a handle 
member 42 projected from the top wall 41, and a side wall 43 extending 
from the outer circumference of the top wall 41. The cover member 40 is 
composed of a conductive resin and integrally formed by injection molding. 
Eight fitting projections 45 are projected inside the side wall 43. The 
fitting projections 45 are fitted in the outer ring member 35 of the 
flange member 33, so that the cover member 40 is attached to the casing 
body 20 via the flange member 33. 
The cover member 40 is assembled to the casing body 20 in the following 
manner. As shown in FIG. 19, the opening of the cover member 40 is 
positioned on the outer ring member 35 of the casing body 20, and the 
cover member 40 is pressed into the casing body 20. The fitting 
projections 45 of the cover member 40 then come into contact with the 
outer ring member 35 having slits 35a. The slits 35a slightly deform the 
outer ring member 35 in an elastic manner when the outer ring member 35 
rides over the fitting projections 45. The elastic deformation of the 
outer ring member 35 enables the outer ring member 35 to readily ride over 
the fitting projections 45, so as to attach the cover member 40 to the 
casing body 20. The deformation of the outer ring member 35 facilitates 
the attachment of the cover member 40 to the casing body 20. 
As shown in FIG. 19, a discharge projection 46 for discharging the static 
electricity to the filler neck FN is formed on each fitting projection 45. 
When the user who is electrostatically charged manually touches the cover 
member 40 in a dried atmosphere, the static electricity is discharged 
between the discharge projections 46 of the cover member 40 and the filler 
neck FN. This causes the static electricity to be grounded to the filler 
neck FN and prevents the user from receiving a shock from the static 
electricity when removing the fuel tank cap 10. The discharge projection 
46 is formed integrally with the fitting projection 45. The long and 
narrow discharge projection 46 is accordingly molded easily and reinforced 
by the fitting projection 45 to have a sufficiently large mechanical 
strength. The discharge projections 46 have the following function when 
the cover member 40 is attached to the casing body 20. The discharge 
projections 46 are positioned in the slits 35a of the outer ring member 35 
when the cover member 40 is pressed into the casing body 20. This enables 
the discharge projections 46 to be guided by the slits 35a and further 
facilitates the attachment of the cover member 40 to the casing body 20. 
As shown in FIGS. 19 and 20, anti-shaving projections 47 are further formed 
on the top wall 41 of the cover member 40. The anti-shaving projections 47 
are formed at the positions corresponding to the fitting projections 45 on 
the side wall 43. The anti-shaving projection 47 is arranged on the 
approximate center of a parting line PLa and has substantially the same 
height as that of the parting line PLa. The anti-shaving projections 47 
prevent the parting line PLa from being slid against the outer ring member 
35 of the cover member 40 and shaved. FIG. 21 shows the state of injection 
molding the fitting projection 45 and the peripheral elements of the cover 
member 40. A slide mold SF2 is used for injection molding since the 
fitting projection 45 is protruded from the side wall 43 and undercut in 
injection molding. The slide mold SF2 is arranged to be slidable in the 
direction of the arrow in FIG. 21 and forms its trace as the parting line 
PLa of the top wall 41. The anti-shaving projections 47 having 
substantially the same height as that of the parting line PLa cause the 
outer ring member 35 to slide thereon and effectively prevent the parting 
line PLa from being slid against the outer ring member 35 and shaved to 
resin powder, when the cover member 40 is rotated relative to the casing 
body 20 via the ratchet mechanism 37. 
The following describes the positive pressure valve 60 and the negative 
pressure valve 70 received in the valve chamber 23. FIG. 22 is an enlarged 
sectional view illustrating the positive pressure valve 60 and the 
negative pressure valve 70. The positive pressure valve 60 is disposed in 
the upper chamber 23a of the valve chamber 23, and the negative pressure 
valve 70 in the lower chamber 23b. FIG. 23 is an enlarged sectional view 
illustrating the positive pressure valve 60. 
The positive pressure valve 60 includes the valve body 61 composed of, for 
example, fluororubber, the valve support member 68, and the coil spring 
69. The valve body 61 is a disc having a lower seat surface 62 and a 
fitting member 65 with a valve flow hole 63 on the center thereof. The 
fitting member 65 has a side supporting recess 66 formed in the side wall 
thereof. The valve body 61 is attached to the valve support member 68 by 
fitting the fitting member 65 into a fitting aperture 68a of the valve 
support member 68. A spring support element 68b is formed on the upper 
surface of the valve support member 68. The spring support element 68b 
supports one end of the coil spring 69, whereas the other end of the coil 
spring 69 is supported by the cylindrical support member 53 of the inner 
cover 50 (FIG. 22). Namely the coil spring 69 is held between the inner 
cover 50 and the valve support member 68. 
The positive pressure valve 60 thus constructed controls the pressure in 
the fuel tank in the following manner. In the state that the fuel tank cap 
10 is attached to the filler neck FN, when the tank pressure increases to 
exceed a predetermined level, the valve body 61 and the valve support 
member 68 lift up against the pressing force of the coil spring 69, and 
the fuel tank is connected to the atmosphere via the valve chamber 23. 
When the connection returns the pressure in the fuel tank to or below the 
predetermined level, the valve body 61 is pressed down by the pressing 
force of the coil spring 69 and closed. The valve body 61 opens and closes 
in this manner, to make the differential pressure applied thereto not 
greater than the predetermined level. 
A rear face 62a of the valve body 61 is supported by the lower face of the 
valve support member 68. A ring recess 64 is formed in the outer 
circumferential portion of the valve body 61. A ring groove 61b is formed 
in the seat surface 62 of the valve body 61 and located inside the ring 
recess 64. 
The ring recess 64 and the ring groove 61b have the following functions and 
effects. When the valve body 61 of the positive pressure valve 60 is moved 
from the open position in the closing direction by the pressing force of 
the coil spring 69 as shown in FIG. 24, the seat surface 62 of the valve 
body 61 comes into contact with the seat member 30. The seat member 30 is 
thus in contact with the center of the seat surface 62 having the ring 
recess 64. Since the valve body 61 has a thin wall at the ring recess 64, 
the seat surface 62 is deformed by the seat member 30. 
When the seat surface 62 is pressed against the seat member 30, the valve 
body 61 is seated onto the seat member 30 while keeping the horizontal 
attitude and being supported by the valve support member 68 on both the 
inner circumferential side and the outer circumferential side of the ring 
recess 64. The seat surface 62 is in line contact with the ridge of the 
seat member 30 and is seated not in the inclined attitude but in the 
horizontal attitude, thereby ensuring high sealing property. The small 
contact area between the seat surface 62 and the seat member 30 realizes 
the ideal valve-opening characteristic, that is, an abrupt rise in the 
open position. The ring groove 61b is formed in the seat surface 62 of the 
valve body 61 to equalize the deflection in the vicinity of the ring 
recess 64 of the seat surface 62, thereby further improving the sealing 
property. 
The seat member 30 of the casing body 20 has the shape discussed below. As 
shown in FIG. 25, the seat member 30 is formed on the apex of an acute 
angle with respect to the seat surface 62 of the valve body 61. This 
structure enables a line contact in the sealed position and improves the 
sealing property. An angle (1 of the slant plane 30a of the seat member 30 
is set equal to 25 degrees, in order to exert the following effects. 
A radius r1 of the seat member 30 is a critical design feature required to 
achieve the high sealing property of the present invention. When the seat 
member 30 has the radius r1, the comparison of the case where the angle 
.theta.1=25 degrees with the case where the angle .theta.1=45 degrees as 
shown in FIG. 26. Because of the limit of resin molding, there is 
substantially no difference in a radius r2 between these two cases. The 
seat member 30 accordingly has a wall thickness VT1 in the case of the 
angle .theta.1=25 degrees and a wall thickness VT2 in the case of the 
angle .theta.1=45 degrees, where VT1 is less than VT2. The smaller angle 
.theta.1 of the seat member 30 reduces its wall thickness VT1 and 
decreases the sink mark due to the resin contraction. This increases the 
plane accuracy of the seat member 30 and improves the sealing property. 
FIG. 27 is a sectional view illustrating a modified structure of the seat 
member 30 shown in FIG. 25. In the structure of FIG. 27, a seat member 130 
has a first slant plane 130a and a second slant plane 130b formed on 
either side thereof. The first slant plane 130a has an angle .theta.1=25 
degrees and the second slant plane 130b has an angle .theta.3=45 degrees; 
that is, the angle between the two slant planes is 110 degrees. When the 
radii r1 and r2 of the seat member 130 are fixed to given values, the 
greater angle of the second slant plane 130b reduces a wall thickness VT3 
and further improves the plane accuracy of the seat member 130. 
FIG. 28 is a sectional view illustrating the negative pressure valve 70, 
and FIG. 29 is an enlarged sectional view illustrating an essential part 
of the negative pressure valve 70. The negative pressure valve 70 includes 
the valve body 71 composed of a resin, and the coil spring 78 spanned 
between a spring support step 72 of the valve body 71 and the bottom 
element 26 for pressing the valve body 71. A seat member 76 extends upward 
from the valve body 71 to be seated on and separated from the valve body 
61 of the positive pressure valve 60. 
The negative pressure valve 70 works in the following manner. When the fuel 
tank has the negative pressure relative to the atmospheric pressure and 
the differential pressure applied to the valve body 71 becomes equal to or 
greater than a predetermined level, the valve body 71 moves downward 
against the pressing force of the coil spring 78 as shown in FIG. 29. The 
valve body 71 is accordingly separated from the seat surface 62 of the 
valve body 61. At this moment, the valve body 61 is seated on the seat 
member 30. In that state, a passage is made between the valve body 71 and 
the valve body 61. The fuel tank is thus connected to the atmosphere via 
the passage between the valve body 71 and the lower wall element 25 and a 
connection aperture 26a of the bottom element 26. This cancels the state 
of negative pressure in the fuel tank. When the differential pressure 
applied to the valve body 71 is less than the pressing force of the coil 
spring 78, the valve body 71 is closed. 
As shown in FIG. 29, the valve body 71 of the negative pressure valve 70 
has a tapered element 75 on an outer circumferential member 74. The 
tapered element 75 is tapered to make the distance from the lower wall 
element 25 of the valve chamber-forming member 22 gradually narrower. The 
tapered arrangement enables the negative pressure valve 70 to have the 
flow property shown in FIG. 30. FIG. 30 shows the relationship between the 
differential pressure and the flow Q, where the solid line shows data of 
the negative pressure valve 70 of the embodiment and the broken line shows 
data of a comparative example corresponding to a known pressure valve. 
It is preferable that the negative pressure valve 70 has the property of 
abruptly increasing the flow Q as shown by the one-dot chain line, in 
order to keep the pressure in the fuel tank within a predetermined range. 
Whereas the flow Q gradually increases with an increase in differential 
pressure in the comparative example, the flow Q abruptly increases in the 
negative pressure valve 70 of the embodiment, which is close to the ideal 
flow property. The tapered arrangement of the tapered element 75 of the 
negative pressure valve 70 increases the differential pressure applied to 
the valve body 71 and thereby abruptly increases the valve-opening force. 
Referring back to FIG. 28, the connection aperture 26a is formed in the 
bottom element 26 of the casing body 20. The connection aperture 26a is 
arranged apart from the sealed portion of the valve body 71, that is, 
close to the center of the bottom element 26. Even when the fuel 
contaminated with foreign matters flows through the connection aperture 
26a into the lower chamber 23b, the position of the connection aperture 
26a enables the fuel to hit against the valve body 71 and be returned to 
the fuel tank through the connection aperture 26a. This prevents foreign 
matter present in the fuel from entering the sealed portion of the valve 
body 71. The foreign matters accordingly do not interfere with the opening 
and closing operations of the valve body 71 nor damage the sealing 
property. 
FIG. 31 is a plan view illustrating the cover member 40, and FIG. 32 is an 
enlarged sectional view showing the lower end portion of the cover member 
40. As shown in FIGS. 31, 32, 16, and 17, the four discharge projections 
46 for discharging the static electricity to the filler neck FN are formed 
on the inner surface of the side wall 43 of the cover member 40 to be 
arranged at the interval of 90 degrees along the circumference. When the 
user who is electrostatically charged manually touches the cover member 40 
in a dried atmosphere, the static electricity is discharged between the 
discharge projections and the filler neck FN and grounded to the filler 
neck FN. 
The conditions of electric discharge whereby the user is not shocked when 
removing the fuel tank cap 10 are: (1) that discharge of electricity is 
securely performed irrespective of the closing state of the fuel tank cap 
10; and (2) that discharge of electricity proceeds gently and does not 
cause a large shock. The discharge projections 46 have the following 
structure in order to satisfy these conditions. 
(1) As shown in FIG. 32, the discharge projections 46 are projected in the 
axial direction, and a discharge distance L1 from the filler neck FN is 
set to be not greater than about 1 mm or preferably not greater than about 
0.85 mm. When the discharge distance L1 is greater than about 1 mm the 
break voltage increases and the gentle discharge characteristics are not 
obtained. 
(2) The discharge projections 46 are formed as long and narrow projections 
in an opening-closing direction d3 of the fuel tank cap 10, that is, in 
the axial direction. In response to the opening or closing operation of 
the fuel tank cap 10, the cover member 40 moves integrally with the casing 
body 20 relative to the filler neck EN in the opening-closing direction 
d3. The discharge projections 46 also move in the same direction, and the 
discharge distance L1 from the end of the inlet FNb of the filler neck FN 
is constant in the range of a length L2 in the axial direction. Namely the 
discharge distance L1 is allowed to be constant in the range of the length 
L2 irrespective of the closing state of the fuel tank cap 10. This ensures 
the stable discharge characteristics. 
(3) As shown in FIG. 31, the discharge projections 46 are arranged at the 
angle of 45 degrees with respect to the handle member 42 of the cover 
member 40. This arrangement is ascribed to the following reason. As shown 
in FIGS. 31 and 33, the handle member 42 of the cover member 40 is 
projected from the top wall 41 and injection molded to have the maximum 
resin contraction in a radial direction D1 and the minimum resin 
contraction in another radial direction D2, which is perpendicular to the 
radial direction D1. If the discharge projections 46 are arranged in the 
radial directions D1 and D2, the discharge distance from the filler neck 
FN is varied to change the discharge characteristics. The discharge 
projections 46 are accordingly arranged in radial directions D3 and D4 of 
45 degrees, which give the intermediate resin contraction between those in 
the radial directions D1 and D2. Namely the four discharge projections 46 
are arranged concentrically with the center of the cover member 40. 
Irrespective of the closing state of the fuel tank cap 10, the four 
discharge projections 46 are arranged on the same circle about the center 
of the cover member 40. This makes the discharge distance from the end of 
the filler neck EN constant and ensures stable discharge characteristics. 
(4) As shown in FIGS. 16, 31, and 33, discharge slits 46a having 
substantially the same length as that of the discharge projection 46 are 
formed on both sides of each discharge projection 46. The discharge slits 
46a separate the forces in the directions of arrows b1 and b2 accompanied 
by the resin contraction in the first and the second radial directions D1 
and D2, thereby reducing the effect of resin contraction on the discharge 
projection 46 and decreasing the variation in discharge distance L1. 
(5) The volume resistivity of the cover member 40 is about 10.sup.4 to 
about 10.sup.9 .OMEGA..multidot.cm. The volume resistivity at the site of 
the discharge projections 46 is lower than the other portions of the cover 
member 40. The upper limit of the volume resistivity is set to be not 
greater than about 10.sup.9 .OMEGA..multidot.cm to ensure the electrical 
conductivity, whereas the lower limit is set to be not less than about 
10.sup.4 .OMEGA..multidot.cm to prevent the voltage between the discharge 
projection 46 and the filler neck FN from increasing abruptly. The lower 
volume resistivity at the site of the discharge projections 46 enables the 
static electricity in the cover member 40 to be quickly led to the 
discharge projections 46. The discharge projections 46 enable the static 
electricity in the cover member 40 to be gently discharged and grounded 
via the filler neck FN, without causing an abrupt increase in voltage 
between the discharge projections 46 and the filler neck EN. 
The volume resistivity of the cover member 40 discussed above is obtained 
by mixing conductive whiskers, conductive fillers, or conductive carbon 
with the resin material for injection molding. FIG. 34 is a graph showing 
the volume resistivity at various measurement points on the cover member 
40. FIG. 35 shows measurement points P1 through P4 on the cover member 40. 
In the graph of FIG. 34, a measurement curve A denotes the volume 
resistivity when 5 parts by weight of conductive whiskers and 10 parts by 
weight of conductive carbon are mixed with 100 parts by weight of 
polyamide (PA). A measurement curve B denotes the volume resistivity when 
20 parts by weight of conductive carbon are mixed with 100 parts by weight 
of polyamide (PA). One example of the conductive whiskers is Dentol (trade 
name, manufactured by Otsuka Chemical Co., Ltd.), and one example of the 
conductive carbon is Balkan XC-72 (trade name, manufactured by Cabot Co., 
Ltd.) 
The conductive material, such as conductive whiskers, conductive fillers, 
or conductive carbon, is mixed with an insulating resin material, such as 
polyamide. Using only a conductive resin to obtain the above volume 
resistance lowers the resulting mechanical strength of the cover member 40 
and does not fulfill the anti-shock condition of the cover member 40. 
The measurement points P1 through P4 of the cover member 40 shown in FIG. 
35 are set to have the volume resistivity shown in FIG. 34. The volume 
resistivity at the measurement point P4 on the discharge projection 46 is 
set to be lower than those at the measurement points P1 through P3 on the 
cover member 40. This is attained by the following process. A gate Gt of 
an injection molding machine is set on the center of the cover member 40 
as shown in FIG. 35. The molten resin is charged from the gate Gt through 
the top wall 41 and the side wall 43 to the discharge projections 46. The 
conductive material is collected at a higher density at positions further 
from the gate Gt. The discharge projections 46 are set at the final 
charging position of the molten resin that is injected from the gate Gt. 
This causes the conductive material to be collected at a higher 
concentration in the discharge projections 46 than in any other part of 
the cover member 40, thereby enhancing the electrical conductivity of the 
discharge projections 46. 
As discussed previously, the discharge slits 46a are formed on both sides 
of each discharge projection 46 along the circumference. The discharge 
slits 46a surround the discharge projection 46 and lead the flow of molten 
resin to the final charging position, thereby further increasing the 
density of the conductive material and improving the electrical 
conductivity. 
(6) FIG. 36 is a sectional view of the discharge projection 46 in the 
horizontal direction. As shown in FIG. 36, the discharge projection 46 has 
a semi-circular-shaped top portion 46b. A planar top portion 46Ab of a 
discharge projection 46A shown in FIG. 37(A) often causes an abrupt 
discharge of electricity, whereas a sharp top portion 46Bb of a discharge 
projection 46B shown in FIG. 37(B) causes a gentle discharge of 
electricity. For better discharge characteristics, it is thus preferable 
that the discharge projection has the sharp top portion like the discharge 
projection 46B. The sharp top portion 46Bb of the discharge projection 
46B, however, causes a recess of a mold for molding the discharge 
projection 46B to be clogged and makes it difficult to remove the resin 
residue. In this embodiment, the discharge projection 46 accordingly has a 
semi-circular-shaped top portion 46b, which effectively allows the resin 
residue to be removed from the mold and forms the discharge projection 46 
to the fixed shape. 
The present invention is not restricted to the above embodiment, but there 
may be many other modifications, changes, and alterations without 
departing from the scope or spirit of the main characteristics of the 
present invention. 
(1) In the above embodiment, the discharge projections 46 are formed 
integrally with the cover member 40. As long as the discharge projections 
46 have the function of sufficiently discharging electricity, they may be 
formed separately from the cover member. 
(2) In the embodiment, the discharge projections 46 are formed by the 
injection molding to have the smaller volume resistivity than any other 
part of the cover member 40. Another possible process applies a conductive 
material on the surface of the discharge projections 46. 
(3) In the above embodiment, the electricity is discharged between the 
discharge projections 46 and the filler neck FN. The discharge of 
electricity may, however, be carried out between the discharge projections 
46 and a member of the automobile body as long as it faces the discharge 
projections 46 and can ground the static electricity in the cover member 
40. 
It should be clearly understood that the above embodiment is only 
illustrative and not restrictive in any sense. The scope and spirit of the 
present invention are limited only by the terms of the appended claims.