GB2236288A

GB2236288A - A plastics fuel tank, e.g. for a vehicle

Info

Publication number: GB2236288A
Application number: GB8920681A
Authority: GB
Inventors: Ronald Peter Pardy
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1989-09-13
Filing date: 1989-09-13
Publication date: 1991-04-03
Also published as: GB8920681D0

Abstract

A spacer body 16 is located in the tank internal space and welded to opposite walls 12, 14 of the tank in order to prevent the tank expanding under the influence of high internal pressures. The spacer (16) may have a region which is adapted to rupture when subjected to a tension load above a predetermined limit. The spacer can be incorporated in the tank when the tank is blow moulded by being supported on a support pin (30) which is pulled out of the spacer and out of the tank after moulding. <IMAGE>

Description

A FUEL TANK This invention relates to a fuel tank, in particular a plastics fuel tank for use in a motor vehicle.

Although fuel tanks always have vent passages for venting excess vapour pressure, under extreme conditions pressure can build up inside the tank and cause the tank to expand.

This is particularly a problem with plastics fuel tanks where the inherent rigidity of the wall material is less than that of a metal tank.

It has been proposed to provide resistance to tank expansion by forming a pair of opposing pillars in opposite tank walls, which pillars meet at the centre of the tank such that their meeting tips can be welded together to hold the opposite sides of the tank a correct distance apart.

This proposal has however the disadvantage that if an excess of pressure is produced in the tank, such that the central support has to yield to allow the tank to expand to cope with the pressure, then there is a risk that the tank wall would be ruptured. Additionally, this proposal also results in a substantial reduction in the internal volume of the tank.

According to the present invention, there is provided a plastics fuel tank having a pair of opposite walls and an internal spacer welded internally to each wall to maintain the walls at a predetermined distance apart.

The spacer is preferably arranged generally centrally within the tank between the major walls of-the tank.

In a preferred embodiment, the spacer has a region between its ends which is adapted to rupture when the spacer is subjected to a tension load above a predetermined limit.

In this way, the tank walls can be supported against one another by a spacer component housed wholly within the internal volume of the tank. The spacer can be of skeletonlike construction so that it occupies a minimum volume within the tank. Because the spacer in no way contributes to the continuity of the walls of the tank, it can be constructed so as to rupture if the pressure in the tank builds up, at a load which is less than that required to destroy the welds by which the spacer is attached at its ends to the walls.

The invention also provides a method of manufacturing a plastics fuel tank by blow-moulding wherein a spacer is located inside the parison and within the mould before the mould is closed and wherein when the mould is closed the spacer makes contact with opposite faces of the blowmoulding and becomes welded to those faces during the moulding operation.

The spacer is preferably supported in the mould by a support pin which extends through the wall of the asmoulded tank and which can be pulled out of the spacer and Out of the tank after moulding, leaving a small aperture in the tank wall which is thereafter sealed.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view through a fuel tank in accordance with the invention; Figure 2 is a side view of the tank of Figure 1; Figure 3 is a schematic illustration of a stage in the manufacturing process; Figure 4 is a schematic illustration of a subsequent stage in the process; and Figure 5 illustrates a spacer for use in accordance with the invention.

Figure 1 shows a tank 10 which is illustrated in the drawings as being of rectangular form. In practice the tank will be of an irregular form, but the actual overall shape of the tank makes no difference to the principles to be described in the following.

The tank has a top wall 12 and a bottom wall 14. When there is fuel in the tank, there is always a vapour space above the fuel. The vapour space is vented, but under high ambient temperatures the pressure in the vapour space above the fuel can rise to a level, in spite of the vent, which would cause some expansion of the tank. Expansion of the tank would become visible as an outward bowing of the walls 12 and 14. This can lead to a number of disadvantages. In particular, when the fuel level in the tank is low, outward bowing of the bottom of the tank can result in the fuel pick up tube being stranded above the fuel surface. For similar reasons, distortion of the tank in this way will cause the surface of the fuel to fall and the level sensing float will produce an abnormally low reading.

To prevent this a spacer 16 is located inside the tank and is welded to the inside surface of each of the walls 12 and 14. When the vapour pressure in the tank rises, then the spacer 16 will be put into tension and will resist outward movement of the walls 12 and 14.

As can be seen in Figure 5, the spacer 16 has end plates 18, 20 which are annular in form and are intended to be welded to the inner faces of the tank walls 12, 14. This provides a relatively large weld area.

The end plates 18 and 20 are connected to each other by two webs 22, 24 which are arranged at right angles to one another. The webs are arranged so that when the spacer is put under excessive tension, the webs will rupture before the welds between the end plates 18 and 20 and the walls 12 and 14 are destroyed. In the embodiment illustrated in Figure 5, weakening slots 26 are provided in the webs to form an area of weakness which will rupture first. The webs 22 and 24 occupy very little volume within the tank, so the inclusion of this spacer member does not compromise the internal volume of the tank to any noticeable extent. A wide variety of other constructions can however be used to form the spacer and to construct it in such a way that it will, if necessary, yield in the right place and at the right tension level.

The spacer 16 can be incorporated in the tank when the tank is manufactured. Plastic fuel tanks are generally manufactured by blow-moulding. In blow-moulding a tubular blank or parison is trapped between two mould halves and is then inflated. The plastics material is forced out against the mould walls and takes up the shape of the mould walls.

During the process the mould and the parison are heated so that the plastics material of the parison softens.

The spacer 16 is designed so that its overall height is slightly less than the distance between the internal surfaces of the walls 12 and 14, at the point in the tank where the spacer is to be located. As a result, when the mould is closed with the spacer inside the spacer will interfere with both walls and because of the temperature conditions inside the mould a welding process will take place by which the spacer will be welded to both walls. It may be desirable to heat the end plates 18,20 to assist in this welding process.

The spacer can be supported both within the parison 27 and within the mould 28 on a support rod 30 which is a push fit in a socket 34 on the spacer. As can be seen in Figure 4, when the mould is closed the rod 30 extends out of the mould through one wall and therefore will project through the wall of the finished moulded tank. When the moulding process is completed, and the tank is taken out of the mould the rod can be simply pulled axially out of the socket 34 and out through the side of the mould leaving the spacer in position and a small access hole in the wall of the tank. To finish the tank this access hole is blanked off with a closure patch 32 (Figure 2).

Claims

1. A plastics fuel tank having a pair of opposite walls and an internal spacer welded internally to each wall to maintain the walls at a predetermined distance apart.

2. A fuel tank as claimed in Claim 1, wherein the spacer is arranged generally centrally within the tank between the major walls of the tank.

3. A fuel tank as claimed in Claim 1 or Claim 2, wherein the spacer has a region between its ends which is adapted to rupture when the spacer is subjected to a tension load above a predetermined limit.

4. A fuel tank as claimed in any preceding claim, wherein the spacer is of skeleton-like construction so that it occupies a minimum volume within the tank.

5. A method of manufacturing a plastics fuel tank by blow moulding wherein a spacer is located inside the parison and within the mould before the mould is closed and wherein when the mould is closed the spacer makes contact with opposite faces of the blow moulding and becomes welded to those faces during the moulding operation.

6. A method as claimed in Claim 5, wherein the spacer is supported in the mould by a support pin which extends through the wall of the as-moulded tank and which can be pulled out of the spacer and out of the tank after moulding, leaving a small aperture in the tank wall which is thereafter sealed.

7. A plastics fuel tank substantially as herein described with reference to and as shown in the accompanying drawings.

8. A method of manufacturing a plastics fuel tank, substantially as herein described with reference to and as shown in the accompanying drawings.