US20080006633A1

US20080006633A1 - Fuel cap

Info

Publication number: US20080006633A1
Application number: US11/386,288
Authority: US
Inventors: Hiromitsu Yoshida
Original assignee: Asteer Co Ltd
Current assignee: Asteer Co Ltd
Priority date: 2005-04-22
Filing date: 2006-03-22
Publication date: 2008-01-10
Also published as: JP2006298242A

Abstract

A fuel cap comprising a seal ring 1 mounted on a cap trunk portion 223 to realize liquid tightness and gas tightness, wherein the seal ring 1 includes a ring body 11 and an elastic support portion; the ring body 11 has a sizing relation between an external diameter Dc of the cap trunk portion 223 and an internal diameter Din of the ring body 11 which is Dc<Din, and has a C-shaped section formed by a wedged circumferential groove opening outward in radial direction of the ring; and the elastic support portion is a plurality of the elastic members 12,13,14,15,16 or one of the elastic flanges 17,18, or combination thereof, and disposed on the inner circumference side of the ring body 11 and protrudes with an amount of a radially inward protrusion d set at (Din−Dc)/2 or greater.

Description

TECHNICAL FIELD

The present invention relates to a fuel cap for closing the filler neck of a feed oil pipe extending from the fuel tank of an automobile or the like.

BACKGROUND OF THE INVENTION

The general fuel cap is constituted to have a seal ring mounted on a cap trunk portion to be inserted into a filler neck, for example, as disclosed in JP-A-2005-009661. This fuel cap realizes, when fastened on the filler neck, a liquid tightness and a gas tightness by pressing the seal ring onto a cap sealing face, such as the lower face of the upper flange and the filler neck sealing face of the cap trunk portion, such as the upper edge or the inner face of the filler neck. These liquid tightness and gas tightness are effectively exhibited when the central axis of the cap trunk portion is correctly aligned with the center of the seal ring. For this exhibition, the external diameter Dc of the cap trunk portion and the internal diameter Din of the ring body are held in a sizing relation of Dc≧Din, and the seal ring is tightly mounted on the cap trunk portion. Thus, the seal ring is prevented from being positionally offset in the radial direction of the cap trunk portion.

SUMMARY OF THE INVENTION

The seal ring is made of synthetic rubber such as nitrile rubber or fluorine-containing rubber so that it absorbs the liquid fuel or its vapor and to thereby swell. In other words, the internal diameter Din of the ring body becomes larger after the swelling than before the swelling. Therefore, the seal ring is designed such that the external diameter Dc of the cap trunk portion and the internal diameter Din of the ring body may take the sizing relation of Dc≧Din after the swelling. This implies that the internal diameter Din of the ring body is far smaller than the external diameter Dc of the cap trunk portion when the seal ring is mounted. In order to prevent the positional displacement of the seal ring in the direction of the central axis of the cap trunk portion, however, the cap trunk portion is provided with the lower flange paired to the upper flange as being the cap sealing face. Therefore, to mount the seal ring over the lower flange takes needless time and labor.
Even in the sizing relation of Dc≧Din appropriate for preventing the positional displacement of the swelled seal ring in its radial direction, moreover, this positional displacement is prevented by fastening the seal ring with respect to the cap trunk portion. This fastening of the seal ring on the cap trunk portion is one of disincentives for keeping the liquid tightness and the gas tightness, in case the internal pressure P in the feed oil pipe changes or in case the position of the fuel cap comes out of balance.
Diameter of the seal ring is going to expand in a radially outward direction by increasing the internal pressure P in the filler neck while being associated with the generation of the fuel vapor. In this case, it is desirable to enhance the liquid tightness and the gas tightness by the seal ring so that especially the sealing face of the filler neck is designed to contact with the seal ring in a radial direction in which the seal ring is radially expanded. Thus, the seal ring having a diameter expanded radially outward is pressed more forcibly onto the sealing face of the filler neck thereby to exhibit the liquid tightness and the gas tightness in proportion to the internal pressure P. At this stage, however, the radial expansion of the seal ring led by the internal pressure P is obstructed because of aforementioned fastening of the seal ring. Accordingly, there is still a problem that it is getting harder to enhance the liquid tightness and the gas tightness in response to an increase of the internal pressure P.
When the fuel cap is subjected to pried loads by an external force applied, on the other hand, a part of the cap is obliquely raised with respect to the filler neck thereby to pull the cap sealing face away from the filler neck sealing face. As a result, the raised side (hereinafter be referred to as a pried side) of the cap is pulled away from the cap sealing face or the filler neck sealing face in response to inclination of the cap trunk portion, and thereby that loosening of the liquid tightness and the gas tightness may arise. Thus, the fuel cap in the prior arts, in which the positional displacement of the seal ring is prevented to occur by fastening the seal ring on the cap trunk portion, has a problem that the liquid tightness and the gas tightness cannot be kept in necessary and sufficient condition when the pried loads applied.
The seal ring disclosed in JP-A-2005-009661 is that, in the procedure to fasten the fuel cap, the sealing portions formed on the upper face and the inner circumference side and on the lower face of the seal ring are sequentially pressed onto the filler neck sealing face or the cap sealing face thereby to realize the liquid tightness and the gas tightness. However, even this seal ring of JP-A-2005-009661 has failed to solve the aforementioned problem of the mounting work or the problem that the liquid tightness and the gas tightness become lower as the fuel cap is pried. In order to solve the aforementioned individual problems, therefore, it has been contemplated by investigating the seal ring to develop the fuel cap which can exhibit the liquid tightness and the gas tightness necessary and sufficient even when the pried loads applied.
As a result of the investigations, there is developed a fuel cap comprising a seal ring mounted on a cap trunk portion to realize liquid tightness and gas tightness, wherein the seal ring includes a ring body and an elastic support portion; the ring body has a sizing relation between an external diameter Dc of the cap trunk portion and an internal diameter Din of the ring body which is Dc<Din, and has a C-shaped section formed by a wedged circumferential groove opening outward in radial direction of the ring; and the elastic support portion is disposed on the inner circumference side of the ring body and protrudes with an amount of a radially inward protrusion d set at (Din−Dc)/2 or greater. In this regard, the sizing relation between the external diameter Dc of the cap trunk portion and the internal diameter Din of the ring body, and the amount of the radially inward protrusion d of the elastic support portion belong to the design values in the seal ring post-swelled.
In the fuel cap of the invention, the alignment between the central axis of the cap trunk portion and the center of the seal ring, that is, the positioning role of the seal ring with respect to the cap trunk portion is taken by the elastic support portion to be brought into abutment against the outer face of the cap trunk portion. Thus, the ring body of the seal ring is loosely fitted on the cap trunk portion so that the ring body can be radially expanded by the internal pressure P to be applied to a clearance ΔD formed by the elastic support portion (i.e. the clearance ΔD between the outer face of the cap trunk portion and the inner circumference side of the ring body). In this structure, moreover, when the pried loads applied, the internal pressure is applied from the clearance ΔD to the inner circumference side of the ring body thereby to elastically deform the elastic support portion positioned on the fulcrum side while being pried so that the ring body can move in the radial direction of the cap trunk portion. Thus, the seal ring is released from the influences of the inclination of the cap trunk portion caused by being pried. In addition, the elastic support portion acts to suppress the torsion of the ring body at the time when the seal ring is mounted on the cap trunk portion.
The specific elastic support portion can be exemplified by a plurality of circumferentially arranged elastic ridges. In this case, the ring body is supported through the elastic ridges abutting at their leading end portions against the cap trunk portion, so that the seal ring is mounted on the cap trunk F portion. Thus, the ring body is so loosely fitted on the cap trunk portion that the individual elastic ridges arranged interruptedly in the circumferential direction are brought at their individual leading end portions against the outer face of the cap trunk portion. In this regard, the ring body is so mounted on the cap trunk portion as is deformed into a generally polygonal shape in a top plan view to have the elastic ridges at their corners, if the clearance ΔD set by the elastic ridges is set greater than (Din−Dc)/2. When the pried loads applied, moreover, the elastic flange positioned on the fulcrum side can be elastically deformed to move the ring body in the radial direction of the cap trunk portion.
The size, shape and number of the elastic ridges are basically arbitrary. Especially the shape may be such a cantilever shape as is easy to be elastically deformed, because the shape affects to the difficulty or ease of the elastic deformation. The specific elastic ridges can be exemplified by vertical members extending in the circumferentially perpendicular direction, or horizontal members extending in the circumferential direction. The vertical members or the horizontal members may be molded integrally with the ring body, or the separate vertical members or horizontal members may be fixed to the ring body.
In order to stabilize the support of the ring body, the elasticity of the elastic ridges may be suppressed. For example, the elastic ridges may be exemplified by cross members extending in the mutually-perpendicular directions. These cross members are shaped by combining the vertical members and the horizontal members. In order to facilitate the elastic deformation, on the contrary, it is arbitrary to use cantilever support members or center-impeller support members bridged in the circumferential direction as the elastic ridges. These cross members, cantilever support members or center-impeller support members may be molded integrally with the ring body or separate cross members, cantilever support members or center-impeller support members may be so molded as are fixed on the ring body. These elastic ridges may also be a combination of elastic ridges of different shapes. In order to locate the seal ring stably and precisely with respect to the cap trunk portion, it is desirable to dispose the elastic ridges in kind equiangularly on the inner circumference side of the ring body.
As a mode in which the horizontal members being the elastic ridges are continuously integrated, furthermore, the elastic support portion can also be exemplified by an elastic flange extending on the inner side in the circumferential direction of the ring body. This elastic flange supports the ring body by having its inner circumference edge in abutment against the cap trunk portion thereby to mount the seal ring on the cap trunk portion. Moreover, the seal ring can be moved in the radial direction of the cap trunk portion by elastically deforming the portion of the elastic flange on the fulcrum side when the pried loads applied. The elastic flange may be molded integrally with the ring body, or the individual elastic flange may be fixed on the ring body.
In order to prevent the torsion of the elastic flange itself, moreover, an auxiliary ring having a larger thickness than a thickness t of the elastic flange may be disposed at the inner circumference edge of the elastic flange. The seal ring using the elastic flange having the auxiliary ring as the elastic support portion is constituted such that the ring body and the auxiliary ring are aligned with each other, and such that the ring body and the auxiliary ring are jointed by the elastic flange. In this case, the elastic flange itself can be made to have a smaller thickness t than that of the case, in which the auxiliary ring is not provided. The elastic flange and the auxiliary ring may also be molded integrally with the ring body. Moreover, an individual auxiliary ring may be fixed to the elastic flange, and this elastic flange may be fixed to the ring body.
The fuel cap of the invention mounts the seal ring which can be correctly positioned while being loosely fitted on the cap trunk portion and which can be radially expanded by the internal pressure P in the feed oil pipe. As a result, the fuel cap has effects to facilitate the mounting work of the seal ring and not to deteriorate the liquid tightness and the gas tightness when the pried loads applied. Moreover, the present invention can be applied to the existing fuel caps only by exchanging the seal ring since the structure of the fuel cap in the invention is similar but the particular of the seal ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a seal ring having vertical members disposed as elastic ridges on the inner circumference side of a ring body;
FIG. 2 is a sectional view of the seal ring, taken along line a-a of FIG. 1;
FIG. 3 is an expanded sectional view of a portion encircled in FIG. 2 indicated by an arrow A;
FIG. 4 is a sectional view showing the state, in which a fuel cap having the seal ring of FIG. 1 mounted therein is fastened in a filler neck;
FIG. 5 is a sectional view showing the state, in which a fuel cap having the seal ring of FIG. 1 mounted therein is pried in a filler neck;
FIG. 6 is a fragmentary top plan view of the seal ring having horizontal members disposed as the elastic ridges on the inner circumference side of the ring body;
FIG. 7 is an expanded sectional view corresponding to FIG. 3 showing the seal ring of FIG. 6;
FIG. 8 is a fragmentary top plan view of the seal ring having cross members disposed as the elastic ridges on the inner circumference side of the ring body;
FIG. 9 is an expanded sectional view corresponding to FIG. 3 showing the seal ring of FIG. 8;
FIG. 10 is a fragmentary top plan view of the seal ring having cantilever support members disposed as the elastic ridges on the inner circumference side of the ring body;
FIG. 11 is an expanded sectional view corresponding to FIG. 3 showing the seal ring of FIG. 10;
FIG. 12 is a fragmentary top plan view of the seal ring having center-impeller support members disposed as the elastic ridges on the inner circumference side of the ring body;
FIG. 13 is an expanded sectional view corresponding to FIG. 3 showing the seal ring of FIG. 12;
FIG. 14 is a fragmentary top plan view of the seal ring having an elastic flange disposed as an elastic support portion on the inner circumference side of the ring body;
FIG. 15 is an expanded sectional view corresponding to FIG. 3 showing the seal ring of FIG. 14;
FIG. 16 is a fragmentary top plan view of the seal ring having an auxiliary ring disposed as the elastic support portion on the inner circumference side of the ring body; and
FIG. 17 is an expanded sectional view corresponding to FIG. 3 showing the seal ring of FIG. 16.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention are described in the following with reference to the accompanying drawings.
A fuel cap 2 of an embodiment has a general structure including an outer cap 21 and an inner cap 22, as shown in FIG. 4. A seal ring 1 is mounted on a cap trunk portion 223 locating between an upper flange 221 for mounting the outer cap 21 thereon and a lower flange 222 pairing up with the upper flange 221. The fuel cap 2 clamps and crushes the seal ring 1 between the lower face of the upper flange 221, a cap sealing face 23 and a filler neck sealing face 31 so that the liquid tightness and the gas tightness are worked effectively.
As shown in FIGS. 1 to 3, the seal ring 1 is molded of synthetic rubber integrally with: a ring body 11 of a C-shaped section having an upper and a lower lip portions 112,113 across a wedged circumference groove 111 on the outer circumference side thereof; and a plurality of vertical members 12 as the elastic ridge disposed on the inner circumference side of the ring body 11. The ring body 11, as shown in FIG. 4, exhibits the liquid tightness and the gas tightness by pressing the upper lip portion 112 onto the cap sealing face 23 and pressing the lower lip portion 113 onto the filler neck sealing face 31 while the fuel cap 2 is fastened in a filler neck 3. The vertical member 12 includes a base portion 121 as being of the outer edge of the member having an arc shape corresponding to that of the inner circumference face of the ring body 11, and a leading end portion 122 as being of the inner edge of the member having a straight shape corresponding to that of the outer face of the cap trunk portion 223.
The ring body 11 has a sizing relation between the external diameter Dc of the cap trunk portion 223 and the internal diameter Din of the ring body 11 which is Dc<Din, in the design values after having swelled. Moreover, the vertical members 12 protrude from the ring body 11 with an amount of a radially inward protrusion d set at (Din−Dc)/2, in the design values after having swelled. The proper protrusion d of the vertical members 12 is about 0.5 to 1.5 mm, preferably about 1.0 mm. As a result, the seal ring 1 is mounted in the fuel cap 2, as apparent from FIG. 1, such that the leading end portions 122 of the vertical members 12 abut against the outer face of the cap trunk portion 223 thereby to support the ring body 11 through the vertical members 12. In other words, the ring body 11 is loosely fitted on the cap trunk portion 223 thereby to form a clearance ΔD between the outer face of the cap trunk portion 223 and the inner circumference side of the ring body 11.
In this embodiment, eight vertical members 12 are disposed at an equal interval in the circumferential direction. The individual vertical members 12 have the same shape and size so that the seal ring 1 can have its center aligned with the central axis of the cap trunk portion 223 when the leading end portions 122 of all the vertical members 12 are brought into abutment against the outer face of the cap trunk portion 223. Meanwhile, no restriction is made on the number of the vertical members 12. In order to position the seal ring 1 precisely and stably with respect to the cap trunk portion 223, however, it is preferable that the number of the vertical members 12 goes to three through twelve. This description on the setting of the number and interval of the vertical members 12 can likewise apply to the other elastic ridges, as will be described hereinafter. Since the ring body 11 is loosely fitted on the cap trunk portion 223, moreover, the seal ring 1 can be mounted on the cap trunk portion 223 more easily than the seal ring of the prior arts, in which the ring body 11 is fastened on the cap trunk portion 223.
The clearance ΔD to be formed between the individual vertical members 12 acts, when the fuel cap 2 is secured, to prevent the ring body 11 from being tightened to the cap trunk portion 223 caused by the swelling. Simultaneously, the clearance ΔD also acts to apply a rising internal pressure P in the feed oil pipe to the inner circumference side of the ring body 11 thereby to expand the ring body 11 radially outward depending on the internal pressure P. This will enable to press the upper and lower lip portions 112,113 more forcibly to the cap sealing face 23 and the filler neck sealing face 31 respectively so that the liquid tightness and the gas tightness can be enhanced depending on the internal pressure P.
The function of the clearance ΔD, in which the internal pressure P applied through the clearance ΔD to the inner circumference side of the ring expands diameter of the ring body 11, leads to an advantage that the liquid tightness and the gas tightness can be retained necessarily and sufficiently even while the fuel cap 2 is being pried. When the fuel cap 2 is pried, as shown in FIG. 5, the cap sealing face 23 and the filler neck sealing face 31 leave each other on the pried side. In the seal ring 1 of the invention, however, it is possible to keep the state, in which the internal pressure P is applied from the clearance ΔD to the inner circumference side of the ring to radially enlarge the pried side portion of the ring body 11 thereby to press the upper and lower lip portions 112,113 further onto the cap sealing face 23 and the filler neck sealing face 31, respectively. Thus, the liquid tightness and the gas tightness of the fuel cap 2 are ensured necessarily and sufficiently.
On the fulcrum side when the pried loads applied, on the other hand, the cap sealing face 23 and the filler neck sealing face 31 come close to each other thereby further to crush the ring body 11, so that the upper and lower lip portions 112,113 are pressed onto the cap sealing face 23 and the filler neck sealing face 31, respectively, and thereby to enhance the liquid tightness and the gas tightness. Even if, however, the internal pressure P is applied through the clearance ΔD to the inner circumference side, the ring body 11 on the fulcrum side is hardly radially enlarged. When the internal pressure P increases, the vertical members 12 positioned on the fulcrum side are rather elastically deformed to move the seal ring 1 toward the pried side in the radial direction. Thus, the upper and lower lip portions 112,113 on the pried side are pressed more forcibly by the cap sealing face 23 and the filler neck sealing face 31 thereby to ensure the liquid tightness and the gas tightness depending on the internal pressure P. As a result, the thickness t of the vertical members 12 may be set within a range of 0.5 mm to 1.5 mm in the case of using the seal ring 1 made of nitrile rubber having a spring hardness of 50, for example, so that the vertical members 12 can be elastically deformed.
The seal ring 1 to be mounted on the fuel cap 2 in the present invention is required functions of which the seal ring 1 can be positioned with respect to the cap trunk portion 223 by providing the elastic support portion on the inner circumference side of the ring body 11, and of which the ring body 11 can be radially enlarged easily by applying the internal pressure P to the clearance ΔD formed by the elastic support portion. In this regard, elastic ridges or an elastic flange having shapes in place of that of the exemplified vertical members 12 can also be used as the elastic support portion, as will be described in the following.
The seal ring 1 shown in FIGS. 6 to 7 has a plurality of horizontal members 13, of which the aforementioned vertical members 12 are turned by 90 degrees, mounted as the elastic ridges at an equal interval on the inner circumference side of the ring body 11. The horizontal members 13 are exemplified to have a shape of an isosceles triangle in a top plan view, and the apex of this isosceles triangle as a leading end portion 131 is to abut against the outer face of the cap trunk portion 223. As shown in FIGS. 6 and 7, moreover, the horizontal members 13 can also be formed into a trapezoidal shape in a top plan view having a wide leading end portion 131 formed into an arc-shape along the outer face of the cap trunk portion 223. Both types of the horizontal members 13 are required to have a high shaping precision at the leading end portion for positioning the seal ring 1 with respect to the cap trunk portion 223. What to adopt any of the horizontal members 13 having those individual shapes may be selectively chosen in accordance with the conditions demanded for the individual products, such as the molding cost, the elastic performance required, and so on. An amount of the protrusion d of the horizontal members 13 may be set at (Din−Dc)/2 or greater, as in the case of the aforementioned vertical members 12. Moreover, the thickness t of the horizontal members 13 may also be set within the range of 1.0 mm to 1.5 mm, in case the seal ring 1 is made of nitrile rubber of a spring hardness of 50, for example.
These vertical members and horizontal members can be used in combination. In this modification, the vertical members and the horizontal members may be disposed alternately. In addition, a plurality of cross members 14 formed by combining the vertical member and the horizontal member, as shown in FIGS. 8 and 9, may be adopted as the elastic ridges. In case that these cross members 14 are used, an inner side edge of a vertical portion 141 including an apex formed by crossing the vertical portion 141 and a horizontal portion 142 as a leading end portion 143 abuts to the outer face of the cap trunk portion 223. These cross members 14 are constituted to suppress the elastic deformations as the elastic ridges. An amount of the protrusion d of the cross member 14 may be set at (Din−Dc)/2 or greater, as well as the aforementioned elastic ridges. Moreover, the thickness t of the vertical portions 141 and the horizontal portions 142 may be set to an equal thickness t or a different thickness t within the range of 0.5 mm to 1.5 mm, in the case of the seal ring made of nitrile rubber of a spring hardness of 50, for example.
The seal ring 1 shown in FIGS. 10 and 11 employs a plurality of cantilever support members 15 that can be relatively easier to elastically deform, as the elastic ridges. The cantilever support member 15 is constituted by cutting off the inner circumference side of the ring body 11 into a square shape in a top plan view, to form a concave part 114, and by fixing a base portion 152 formed at one end of a bent elastic member portion 151 to one end side of the concave part 114. The cantilever support member 15 supports the ring body 11 elastically against the cap trunk portion 223 by bringing the bent portion of the elastic member portion 151 as a leading end portion 153 into abutment against the outer face of the cap trunk portion 223. An amount of the protrusion d of the cantilever support member 15 is set at (Din−Dc)/2 or greater, and the length L and the thickness t of the cantilever support member 15 are adjusted depending on the elastic force required. The thickness t, for example, may be set within the range of 2.0 mm to 4.0 mm in the case of the seal ring 1 made of nitrile rubber of a spring hardness of 50.
The elastic ridge having stronger elastic force is exemplified by the elastic ridge formed by a center-impeller support member 16, as shown in the seal ring 1 of FIGS. 12 and 13. This center-impeller support member 16 is constituted by fitting a bent elastic member 161 in the concave part 114 which is formed by cutting off a portion of the ring body 11 on the inner circumference side into a square shape in a top plan view. The center-impeller support member 16 is constituted by fixing base portions 162,162 formed at the two ends of the elastic member portion 161, to the respective two ends of the concave part 114 and by bridging the elastic member portion 161 over the concave part 114. The center-impeller support member 16 supports the ring body 11 elastically to the cap trunk portion 223 by bringing the bent portion of the elastic member portion 161 as a leading end portion 163 into abutment against the outer face of the cap trunk portion 223. In this embodiment, a reinforcing rib 164 is formed on the inner side of the leading end portion 163 so as to reinforce the strength at the leading end portion 163. An amount of the protrusion d of the center-impeller support member 16 may be set at (Din−Dc)/2 or greater. Moreover, the length L and the thickness t of the center-impeller support member 16 are adjusted depending on the elastic force required. The thickness t, for example, may be set within the range of 1.0 mm to 4.0 mm in the case of the seal ring 1 made of nitrile rubber of a spring hardness of 50.
In place of the elastic ridges continued intermittently in circumferential direction, moreover, an elastic flange 17 integrated continuously in the circumferential direction can be used as the elastic support portion, as shown in FIGS. 14 and 15. This elastic flange 17 has not only elasticity but also resiliency. Unlike the elastic ridges, moreover, the elastic flange 17 has an inner circumference edge 171 continuing all over the circumference so that the seal ring 1 is precisely positioned especially with respect to the cap trunk portion 223. However, this elastic flange 17 has to be elastically deformed when the pried loads applied. For this necessity, the elastic flange 17, for example, may be set within the range from the combination of the protrusion d=0.8 mm and the thickness t=0.5 mm to the combination of the protrusion d=1.5 mm and the thickness t=1.0 mm in the case of the seal ring 1 made of nitrile rubber of a spring hardness of 50.
In order to prevent the torsion due to the flexibility of the elastic flange, an auxiliary ring 181 having a thickness larger than the thickness t of an elastic flange 18 may be disposed on the inner circumference edge 182 of the elastic flange 18, as shown in the seal ring 1 of FIGS. 16 and 17. Then, the auxiliary ring 181 suppresses the flexibility of the elastic flange 18 thereby to prevent the torsion of the elastic flange 18. As a result, it is possible to reduce the thickness t of the elastic flange 18. Specifically, the elastic flange 18 containing the auxiliary ring 181, for example, may be set within the range from the combination of the protrusion d=0.8 mm and the thickness t=0.3 mm to the combination of the protrusion d=1.5 mm and the thickness t=0.8 mm in the case of the seal ring 1 made of nitrile rubber of a spring hardness of 50.

Claims

1. A fuel cap comprising a seal ring mounted on a cap trunk portion to realize liquid tightness and gas tightness, wherein: the seal ring includes a ring body and an elastic support portion;

the ring body has a sizing relation between an external diameter Dc of the cap trunk portion and an internal diameter Din of the ring body which is Dc<Din, and has a C-shaped section formed by a wedged circumferential groove opening outward in radial direction of the ring; and

the elastic support portion is disposed on the inner circumference side of the ring body and protrudes with an amount of a radially inward protrusion d set at (Din−Dc)/2 or greater.

2. A fuel cap according to claim 1, wherein the elastic support portion includes a plurality of elastic ridges circumferentially arranged, and wherein the elastic ridges are vertical members extending in circumferentially perpendicular direction.

3. A fuel cap according to claim 1, wherein the elastic support portion includes a plurality of elastic ridges circumferentially arranged, and wherein the elastic ridges are horizontal members extending in circumferential direction.

4. A fuel cap according to claim 1, wherein the elastic support portion includes a plurality of elastic ridges circumferentially arranged, and wherein the elastic ridges are cross members extending in mutually-perpendicular direction.

5. A fuel cap according to claim 1, wherein the elastic support portion includes a plurality of elastic ridges circumferentially arranged, and wherein the elastic ridges are cantilever support members bridged in circumferential direction.

6. A fuel cap according to claim 1, wherein the elastic support portion includes a plurality of elastic ridges circumferentially arranged, and wherein the elastic ridges are center-impeller support members bridged in circumferential direction.

7. A fuel cap according to claim 1, wherein the elastic support portion is an elastic flange extending in circumferential direction of the ring body.

8. A fuel cap according to claim 1, wherein the elastic support portion includes an elastic flange extending in circumferential direction of the ring body, and an auxiliary ring disposed at the inner circumference edge of the elastic flange.