GB2292697A - Filter - Google Patents

Abstract

A fuel filter element includes an outer casing with an inner tube 14 therein. The casing and tube are spaced by a fuel filtering medium through which fuel flows in the downward direction when the element is in use, the fuel then flowing upwardly through the inner tube to an outlet. Located within the inner tube is a further tube 21 which has a flange 23 at its upper end which is in sealing engagement with the inner surface of the inner tube. The lower end of the further tube is located below the lower end of the inner tube and the two tubes and the flange form an air collection chamber. Formed in the flange is an orifice 26 through which air can escape at a controlled rate from the chamber into the inner tube. <IMAGE>

Description

FILTER This invention relates to fuel filter units of the kind comprising a filter element having an outer casing and an inner tube with filter medium interposed between the casing and the tube, the filter unit further including an upper housing part and a lower housing part between which the filter element is located, means for securing the housing parts and filter element in assembled relationship, the upper housing part defining a fuel inlet and a fuel outlet, the fuel outlet communicating with the interior of said inner tube and the fuel inlet communicating with a space defined within the upper housing part, the arrangement being such that fuel flows into the space from the inlet and then from the space downwardly through the filter medium and then upwardly through said inner tube to the outlet, the filter medium acting to retain solid contaminate.

Such filter units are well known in the art and in use water and air entrained in the fuel pass through the filter medium. The water tends to accumulate in the lower housing part and may be drained therefrom and the air passes to the outlet.

The apparatus downstream of the filter unit for example a high pressure fuel injection pump, is designed to cope with air entrained with the fuel but if large quantities of air are suddenly supplied to the pump the operation of the pump can be disturbed.

EP-A-0579484 shows a filter element which is modified so as to form a collection chamber for the air when it has passed through the filter medium, a wall of the collection chamber defining a small orifice through which the air can escape to the outlet in a steady stream.

In the example shown in Figure 1 of EP-A-0579484 the collection chamber is defined by part of the inner surface of the aforesaid inner tube, the outer surface of a further tube which is located within the inner tube in spaced relationship therewith and an annular partition wall which extends between the tubes and forms the upper wall of the collection chamber. At its lower end the collection chamber is open to receive air flowing from the lower end of the filter medium.

The further tube, the partition wall and the inner tube may be formed as a moulding from synthetic resin material in which case the further tube and the inner tube are concentric. Such an arrangement however results in a difficult moulding operation because of the need to keep the wall thickness of the tubes to a minimum in order to allow an adequate fuel flow, and because of the need to provide a collection chamber of adequate volume. In order to achieve these objects it may be necessary to increase the diameter of the inner tube thereby reducing the radial thickness of the filter medium of the diameter of the casing is not increased. Moreover, following the moulding operation it is not easy to check the size of the orifice.

As an alternative and as illustrated in the attached drawings, the further tube and the partition wall may be formed as a separate item which is located in the inner tube after the filter element has been constructed.

In the accompanying drawings: Figure 1 shows in diagrammatic form an engine fuel system, and Figure 2 is a perspective view of part of the filter element seen in Figure 1.

Referring to Figure 1 of the drawings there is illustrated an engine fuel system which includes a conventional distributor type fuel injection pump 1 having a fuel inlet 2 and a plurality of fuel outlets 3 which in use are connected to the injection nozzles of the associated engine. The apparatus includes a high pressure pump and also a low pressure pump which supplies fuel to the high pressure pump. The inlet 2 is connected to the outlet 5 of a fuel filter unit 4. The inlet 6 of the fuel filter unit is shown in the drawing as being connected to the outlet of a diaphragm type lift pump 7 although in many instances the inlet 6 is directly connected to the fuel tank.The fuel filter unit comprises upper and lower housing parts 8, 9 between which is located a filter element 10, the housing parts and the filter element being retained in assembled relationship by means of a through bolt 11.

The fuel filter element comprises a cup shaped casing having a side wall 12 and a base wall 13 which defines a central aperture. Within the casing there is provided an inner tube 14 the lower end of which rests on the base wall about the central aperture and may be located by a plurality of integral upstanding lugs extending inwardly from the base wall. The upper end of the inner tube 14 is located by means of an upper perforated closure plate 15 and intermediate the closure plate, the inner wall of the inner tube, the inner wall of the casing 12 and the upper surface of the base wall, is a paper filter medium 16 which conveniently is formed by a plurality of turns of filter paper which are secured together to form generally V shaped inlet pockets and generally V shaped outlet pockets.

The upper housing part defines a space 1 7 which is in communication with the inlet 6 and it also defines a depending spigot 18 which locates in sealed relationship within the inner tube 14. The outlet 5 of the filter unit communicates with an annular space defined within the spigot about the securing bolt 11.

The lower housing part 9 defines a space 19 in the lower portion of which water contained within the fuel may collect. Conveniently the base wall of the lower housing part is provided with a removable plug 20 whereby the collected water may be drained.

Within the inner tube 14 there is mounted a further tube 21 which at its upper end is provided with an outwardly extending partition wall in the form of a flange which forms an air tight seal with the inner surface of the inner tube 14. The further tube 21 projects downwardly below the level of the base wall 13 and it defines with the inner surface of the inner tube a collection chamber 22. The flange is provided with an orifice and in use, fuel enters the space 1 7 in the upper housing part and then flows downwardly through the filter medium 16. Solid contaminant is retained in the filter element and fuel then flows downwardly through openings in the base wall 13 of the casing and then as indicated by the arrow 23, flows upwardly within the further tube to the outlet 5.Water which passes through the filter medium collects as described and air which flows through the filter medium passes into the collection space 22 and then by way of the orifice, at a controlled rate to the outlet 5.

Figure 2 shows to an enlarged scale the further tube 21, the securing bolt 11 and the inner tube 14. The flange 23 is shown and is provided with a circumferential groove 24 to receive a seal ring so as to establish an air tight seal with the inner surface of the inner tube 14. It will also be noted that the further tube 21 is not concentric with the securing bolt 11 or the inner tube 14. This allows the orifice 26 which is formed in the flange 23 to be positioned in the widest portion of the flange so as to facilitate the formation of the orifice. Conveniently the flange and the further tube 21 are formed by moulding from synthetic resin material.

Near its lower end the inner tube 21 is provided with a part circumferential rib 27 which provides for location of the further tube and Figure 2 illustrates the engagement of the rib 27 with the lugs which are utilised to locate the inner tube 14 relative to the casing. It will be understood that the unit comprising the flange 23 and the further tube 21 can be fitted within the inner tube 14 during manufacture of the filter element or it can be supplied as a separate item for assembly into the filter element by the user.

Claims (2)

1. A fuel filter element for incorporation into a fuel filter unit, the element comprising an outer casing, an inner tube located with clearance within the casing, a filter medium located between the inner surface of the casing and the outer surface of the inner tube, the filter element in use being arranged so that fuel flows downwardly through the filter medium and then separately through the inner tube to an outlet, the filter element further including a further tube which extends into the lower end of the inner tube so that the lower end of the further tube lies below the lower end of the inner tube, the further tube being smaller in diameter than the inner tube, a flange formed integrally with and at or adjacent the upper end of the further tube, means for establishing a fuel tight seal between the rim of said flange and the inner surface of the inner tube, the interior of the further tube conveying fuel which has passed through the filter medium into the inner tube and the flange together with the inner surface of the inner tube and the adjacent outer surface of the further tube forming an air collection chamber, and an orifice formed in said flange to permit air to escape at a controlled rate from said chamber into the inner tube, said further tube and the flange being formed separately from said inner tube for assembly therein.

2. An element according to claim 1, in which the longitudinal axis of the further tube is offset relative to the longitudinal axis of the inner tube, said orifice being formed in the widest portion of the flange.