Tube joint for fuel tank

A tube joint for a fuel tank includes a joint body having a tubular shape, and a barrier layer covering the inner surface of the joint body. The joint body is formed of a material which is weldable to a tank body, and the barrier layer is formed of a material which has fuel impermeability and a predetermined hardness. The barrier layer has an extension portion extending from a distal end of the joint body along an axial direction of the joint body. The extension portion includes a projecting portion which protrudes radially and outwardly of the extension portion at or adjacent to a proximal end of the extension portion such that a seal groove is formed between the projecting portion and the joint body, and a nail portion which protrudes radially and outwardly of the extension portion at or adjacent to a distal end of the extension portion.

BACKGROUND OF THE INVENTION

The present invention generally relates to a tube joint for fuel tanks made of resin materials.

In recent years, plastic containers produced by blow molding have been used as a fuel tank of vehicles as they excel in rust preventative characteristics and weight reduction as well as their high productivity.

Various parts are attached to the tank body of the fuel tank through a tube joint. These parts include, for example, a vent valve, a check valve, and a fuel pump. The vent valve retains the internal pressure of the tank body at a certain level by discharging fuel evaporation gas that is held in a space above the oil level from the tank.

In the case where the tank body and the tube joint are both produced by the same kind of synthetic resin, such as high density polyethylene (hereinafter referred to as “HDPE”), they can be jointed by heat welding. This can simplify the manufacturing process of the fuel tank.

Since effusion of the fuel evaporation gas from the fuel tank causes air pollution, the tank body and its joint portion require low hydrocarbon permeability (hereinafter referred to as “fuel impermeability”). However, synthetic resin such as HDPE is relatively poor in fuel impermeability. For this reason, to restrict the permeation of hydrocarbon, it is considered to use so-called gasoline barrier materials having excellent fuel impermeability, such as ethylene-vinylalcohol copolymer (hereinafter referred to as “EVOH”). However, these gasoline barrier materials are poor in adhesion properties upon heat welding and difficult to satisfy the joint strength between the tank body and the tube joint.

To be more specific, the tube joint fixed to the tank body of the plastic fuel tank is preferably made of a material which has sufficient strength and rigidity, excellent gasoline swelling resistance and high fuel impermeability, and further which can be heat welded to the tank body. However, it is very difficult to produce this tube joint by a single material. Therefore, as disclosed in Japanese Laid-open Patent Application No. 2002-254938 (claim1, paragraphs [0006] to [0010], andFIG. 1), the tube joint (weld joint for the fuel tank) is integrally formed by coinjection molding two kinds of resins.

FIG. 3shows a sectional view partly and schematically showing a conventional tube joint of a fuel tank. As shown inFIG. 3, the tube joint110fixed to the tank body100of the fuel tank consists of a tubular joint body120and a barrier layer130for covering the inner surface of the joint body120. The joint body120is made of a first resin material weldable to the tank body100, and the barrier layer130is made of a second resin material that is adhesively and chemically reactive with the first resin material and that has better fuel impermeability than the first resin material. The barrier layer130is provided with an end portion131that protrudes from the distal portion121of the joint body120. Upon injection molding the barrier layer130on the inner surface of the joint body120, the end portion131is formed by the flow of the second resin material flowing from the proximal portion122of the joint body120that is fixed to the tank body100and through the distal portion121. The end face140where the end portion131and the distal portion121are joined together does not dispose in the end for the flow of the second resin material, and the second resin material is welded at a high temperature to the joint body120. This can provide a high degree of adhesive strength between the end portion131and the distal portion121. The tube joint110formed as above allows the joint body120to be heat welded to the tank body100as well as decreases the fuel permeability of the barrier layer130that covers the inner surface of the joint body120.

However, the above tube joint110has a drawback such that when a tube150is connected to the tube joint110, the fuel within the tank body100permeates outside from a gap between the tube joint110and the tube150or water droplets enter into the tank body100from the gap. Further, if a sufficient adhesion is not obtained between the different kinds of resin materials, the adhered surfaces may be peeled, leading to the entry of water droplets into the tank body100.

The tube150is inserted onto the end portion131of the tube joint110and thereafter engaged by a clamp by firmly clamping the outer periphery of the tube150, so that the tube150is not pulled out from the tube joint110. However, since the tube150is only supported between the two tubular surfaces, the tube150is pulled out relatively easily when it is pulled hard.

In view of the above, the present invention seeks to provide a tube joint of a fuel tank, which can firmly clamp the tube and which can provide a sufficient seal.

SUMMARY OF THE INVENTION

It is an aspect of the present invention to provide a tube joint for a fuel tank including: a joint body formed of a material which is weldable to a tank body, the joint body being tubular in shape; and a barrier layer covering an inner surface of the joint body, the barrier layer being formed of a material which has fuel impermeability and a predetermined hardness. In this tube joint, the barrier layer has an extension portion extending from a distal end of the joint body along an axial direction of the joint body, and the extension portion includes a projecting portion which protrudes radially and outwardly of the extension portion at or adjacent to a proximal end of the extension portion such that a seal groove is formed between the projecting portion and the joint body, and a nail portion which protrudes radially and outwardly of the extension portion at or adjacent to a distal end of the extension portion.

According to this tube joint, the seal groove is formed between the projecting portion of the extension portion and the joint body, so that a fluid-tight seal can be obtained between the joint body and the tube fitted onto the joint body. A fluid-tight seal can be obtained also at the contact surface between the extension portion and the joint body. Further, the nail portion provided at or adjacent to the distal end of the barrier layer that is formed of a material with a sufficient hardness can bite into the inner peripheral surface of the tube so as to prevent the tube from being pulled out from the tube joint. According to the present invention, since the joint body is weldable to the tank body, a firm welding can be obtained between the tube joint and the tank body. Further, since the barrier layer is formed of a material which excels in fuel impermeability, it is possible to prevent the fuel from permeating the tube joint.

Other features and advantages of the present invention will be apparent from the following description.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the accompanying drawings, one preferred embodiment of the present invention will be described below.

As shown inFIG. 1, a fuel tank T made of resin includes a resin tank body1for storing fuel, a lid member2for covering an opening of the tank body1, and a tube joint3for connecting a tube6(seeFIG. 2) that is further connected to an oil filler port of the vehicle body. In this embodiment, one end of the tube joint3which is attached to the tank body1is referred to as a proximal end, and the other end of the tube joint3is referred to as a distal end.

As shown inFIG. 1, a fuel supply passage4and a return passage5are integrally attached to the lid member2. The fuel supply passage4is for supplying fuel from a fuel pump (not shown) arranged within the tank body1to an engine of the vehicle, and a return passage5is for recycling excess fuel from the engine.

As seen inFIG. 2, the tank body1is formed by blow molding and has a three-layered structure including an outer layer1aas a surface layer, an inner layer1c, and an intermediate layer1binterposed between the outer layer1aand the inner layer1c. The outer layer1aand the inner layer1care made of a weldable material, such as high density polyethylene (HDPE). The intermediate layer1bis made of a material which excels in fuel impermeability, such as polyamide resin and polyacetal resin. Such a three-layered structure allows the outer layer1ato be heat welded with other component parts that are made of the same kind of resin material as the outer layer1a. Further, the intermediate layer1bhaving excellent fuel impermeability can prevent the fuel within the tank body1from permeating outside the tank body1.

As shown inFIG. 2, the tube joint3is fixed to the tank body1so as to protrude outwardly of the tank body1. The tube joint3is a joint for connecting one end of the tube6, the other end of which is connected to the oil filler port (not shown). The tube joint3consists of a joint body7which is heat welded to the tank body1, and a barrier layer8which covers the inner peripheral surface of the joint body7. The tube6connected to the tube joint3is made of an elastic material and has a diameter smaller than the outer periphery of the joint body7.

The joint body7is made of a weldable material, such as HDPE. The joint body7includes a tubular portion72for connecting the tube6, and a flange portion71formed at the proximal end of the tubular portion72. The flange portion71is provided with a weld portion71aaxially extending from the flange portion71, so that the joint body7can be heat welded to the outer layer1aof the tank body1through the weld portion71a. At a position slightly offset from the distal end of the tubular portion72is provided a projecting portion72awhich protrudes radially and outwardly of the tubular portion72.

The barrier layer8is made of polyamide that has excellent fuel impermeability and high hardness. The barrier layer8includes a tubular portion82covering the inner peripheral surface of the tubular portion72of the joint body7, a flange portion81continuously extending from the proximal end of the tubular portion82and covering the inner surface of the flange portion71, and an extension portion83axially extending from the distal end of the tubular portion72. As described above, the inner surface of the joint body7is entirely covered by the barrier layer8so as to prevent the fuel from permeating outside.

The extension portion83positions on the side where the tube6is inserted, and includes a projecting portion83awhich protrudes radially and outwardly of the extension portion83at or adjacent to the proximal end, and a nail portion83bwhich also protrudes radially and outwardly of the extension portion83at or adjacent to the distal end. To be more specific, the projecting portion83aand the nail portion83bare formed such that they face to the inner peripheral surface of the tube6. The projecting portion83aand the nail portion83bare tapered such that the diameter thereof increases gradually from the distal end toward the proximal end to ease the insertion of the tube6from the distal end side of the tube joint3.

The projecting portion83ais adjacent to the distal end of the tubular portion72of the joint body7, and together with the projecting portion72ait defines the seal groove11on the outer periphery of the tube joint3. An O-ring is fitted onto the seal groove11, so that a fluid-tight seal can be obtained between the tube6and the tubular portion72. A fluid-tight seal can be obtained also at the contact surface between the projecting portion83aand the distal end of the tubular portion72, so that even if the adhered surfaces may be peeled, entry of water droplets into the tank body can be prevented. Various seal materials other than the O-ring10may be arranged on the seal groove11.

The nail portion83bbites into the inner peripheral surface of the tube6and prevents the tube6from being pulled out from the tube joint3. To be more specific, since the nail portion83bis made of polyamide that is a material having high hardness, when the nail portion83bis press fitted into the tube6made of an elastic material and the tube6is reduced its diameter, the nail portion83bfirmly contacts with and bites into the inner surface of the tube6so as to prevent the tube6from being pulled out.

To prevent the pulling-out of the tube6, it is preferable to set the distance L between the projecting portion83aand the nail portion83bto a certain amount. Being the distance L too short, the tube6does not wedge into the recess portion83cformed between the projecting portion83aand the nail portion83b. Therefore, the nail portion83bdoes not bite into the inner peripheral surface of the tube6.

In order to reliably prevent the pulling-out of the tube6, the outer periphery of the tube6may be firmly clamped by a clamp.

The tube joint3as previously described is formed by coinjection molding so that the joint body7and the barrier layer8are formed integral to each other. The joint body7and the barrier layer8, which are made of different kinds of materials, can be firmly adhered by coinjection molding. Since both the joint body7and the outer layer1aof the tank body1are made of HDPE, the tube joint3can be fixed to the tank body1by heat welding the joint body7to the outer layer1a. Further, since the barrier layer8which entirely covers the inner peripheral surface of the joint body7is made of polyamide, fuel permeation from the tank body1can be prevented.

According to the tube joint3as described previously, various advantages can be obtained.

For example, when the tube6is connected to the tube joint3, the end of the tube6is press fitted from the nail portion83bside of the barrier layer8. Since the nail portion83bis formed as a taper gradually increasing its diameter from the distal end toward the proximal end of the extension portion83, the nail portion83bguides the tube6toward the proximal end of the extension portion83while enlarging the diameter of the tube6. This can ease the connection of the tube6to the tube joint3.

Further, the O-ring10to be fitted onto the seal groove11ensures a seal between the tube6and the tube joint3. Since the seal groove11is formed by the projecting portion83aand the projecting portion72a, the O-ring10to be fitted onto the seal groove11also seals the adhered surfaces between the projecting portion83aand the distal end of the tubular portion72. Therefore, even if the projecting portion83a(extension portion83) is peeled from the distal end side of the tubular portion72to form a gap, it is possible to prevent water droplets and the like from entering into the tube joint3from the gap.

Furthermore, when the tube6is connected to the tube joint3and is reduced its diameter, the nail portion83bmade of a material having high hardness bites into the inner surface of the tube6. Therefore, even if the tube6is pulled toward the distal end side of the tube joint3, the nail portion83brestricts the displacement of the tube6and thus prevents the pulling-out of the tube6.

The tube joint3according to the above embodiment can be modified such that instead of providing only one nail portion83bas described above, two or more nail portions83bare provided along the axial direction of the extension portion83. The plurality of nail portions83bbite into the inner surface of the tube6to firmly restrict the displacement of the tube6, which can prevent the pulling-out of the tube6in a more reliable manner.

Although the present invention has been described above with reference to a specific embodiment thereof, it is to be understood that various changes and modifications may be made without departing from the scope of the invention.

In the preferred embodiment, the tube joint3has been described for a tube connected to the oil filler port (so-called filler tube). However, the present invention can be adapted to a tube joint for connecting various kinds of tubes. The present invention may be used as a joint for connecting the fuel supply passage4or the fuel return passage5.