Fuel filter

Abstract: A fuel filter element includes an annular filter medium (12) which is supported on a lower support plate (14). Fuel flows downwardly through the medium and then through apertures (15) at the outer periphery of the support plate. The support plate is provided with depending annular baffles (17, 18), the outer one (17) being adjacent the apertures (15) but inwardly thereof. The baffles and support plate form an air collection chamber from which air escapes at a controlled rate through an orifice (20) into a central outlet tube (11).

Description: This invention relates to fuel filter elements of the kind having an outer casing, an inner tube which extends within the casing, a filter medium which is located between the outer wall of the tube and the inner wall of the casing and upper and lower annular support plates which extend between the casing and the tube to support the filter medium, the plates being apertured to allow fuel flow through the filter medium, the fuel flowing downwardly through the filter medium, in use. FR-A-2548920 describes such an arrangement which shows in cross-section two apertures in the lower support plate adjacent its outer periphery. Such filter elements are well known in the art and have two forms one being where in use, the element is clamped between upper and lower housing parts with the upper housing part defining a fuel inlet connection and a fuel outlet connection and the lower housing part defining a bowl which affords communication between the lower end of the tube and the apertures in the lower support plate. The two housing parts and the filter element may be clamped by a central bolt which extends with clearance through the tube. The upper housing part defines an annular chamber open to the apertures in the upper support plate and communicating with the fuel inlet connection. In addition the upper housing part defines a central spigot which locates in sealing relationship in the upper portion of the tube, the spigot being hollow and communicating with the outlet connection. Such an arrangement is described in GB 886623. The other form of element is for use where the element is in screw thread engagement or is otherwise secured to a housing part similar to the aforesaid upper housing part. The role of the lower housing part is effected by a bowl portion which is an integral part of the casing of the element. Such an arrangement is described in EP-A-0400223. The filter element forms part of the fuel supply system of an engine and downstream of the filter element are components of the fuel system such as a high pressure fuel injection pump. The fuel as supplied for use contains solid contaminant, water in the form of small droplets and air. The solid contaminant is retained to a substantial extent by the filter medium and the water and air pass through the filter medium. Since the injection pump contains steel parts which are machined to a high degree of accuracy and have small working clearances, it is necessary to ensure that as much of the water as possible is removed from the fuel in order to minimise the risk of rust formation. So far as the air is concerned, the high pressure pump is designed to cope with small quantities of air supplied to the pump but large quantities of air may upset its operation. The object of the invention is achieved by the subject-matter of Claim 1; advantageous embodiments thereof are defined in the dependent claims. An example of a filter element in accordance with the invention will now be described with reference to the accompanying drawing which shows the element in diagrammatic side elevation. The element comprises an outer casing 10 of hollow cylindrical form within which is positioned a central tube 11. Intermediate the outer surface of the tube 11 and the inner surface of the casing 10 is an annular filter medium 12 which conveniently is formed by winding at least two strips of filter paper about the central tube, the longitudinal edges of the paper being coated with adhesive in such a manner so that as winding takes place, "V" shaped pockets are formed. At the upper end of the filter medium there is provided an upper support plate which has a central opening to receive the upper end of the tube. The outer peripheral edge of the support plate is conveniently secured to the casing by a rolling operation. The upper support plate is also provided with a plurality of apertures through which fuel can flow into the open ends of the pockets of the filter medium. In the use of the element it is secured to a support housing (not shown) which defines a fuel inlet chamber above the support plate and has a depending spigot which locates in sealing relationship within the upper end of the central tube 11. The spigot is hollow and is connected to a fuel outlet and the inlet chamber is connected to a fuel inlet. At its lower end the filter medium 12 rests on a lower support plate 14 which is provided with angularly spaced and radially disposed supporting ribs on which the filter medium rests. Conveniently the support plate rests upon a step defined at the junction of the casing and a bowl portion 16 integrally formed with the casing. Adjacent its outer periphery the lower support plate is provided with a plurality of apertures 15 and it is also provided with first and second annular baffles which extend downwardly from the main body of the support plate. The outer baffle 17 is located adjacent to but inwardly of the apertures 15 and the inner baffle 18 has a slightly smaller diameter than the tube 11 and it forms an entrance 19 to the lower end of the tube. The lower end of the tube forms a seal with the support plate. In operation, when fuel is supplied to the inlet the fuel flows downwardly through the filter medium 12 and substantially all the solid contaminant is retained in the medium. Air and water contained in the fuel pass through the medium and flow into the space defined by the bowl portion, through the apertures 15. The fuel flows to the entrance 19 and during such flow the water by sedimentation action, falls to the bottom of the bowl portion 16 together with at least some of the fine particles of solid contaminant which have passed through the filter medium. The air which flows through the apertures 15 collects in the annular air collection chamber which is defined by the baffles 17, 18 and the support plate.This air is allowed to escape from the air collection chamber at a controlled rate through a restricted orifice 20 which conveniently is formed in the portion of the lower support plate which extends inwardly of the tube. Alternatively the orifice may be located in the inner baffle 18 adjacent the support plate as shown in dotted in the drawing. The air collection chamber is of substantial volume as compared with known elements in which the air collection chamber is formed using a further tube, within the inner tube. The action of the baffles 17, 18 and the positioning of the apertures 15 is to lengthen the path along which the fuel must flow between the apertures 15 and the lower end of the tube thereby to allow more time for the sedimentation action to take place. Although as described the bowl portion is formed integrally with the casing 10, the bowl portion may be formed by a separate housing part which is secured against the lower edge of the casing 10. In this case the two housing parts and the filter element are clamped together using a bolt which extends through the central tube. Moreover, instead of providing the apertures 15 in the form of circular holes, the apertures may have the form of arcuate slots.

Claims: A fuel filter element comprising an outer casing (10), an inner tube (11) which extends within the casing, a filter medium (12) which is located between an outer wall of the tube and an inner wall of the casing, and upper and lower annular support plates (13, 14) which extend between the casing and the tube to support the filter medium, the plates being apertured to allow fuel flow through the filter medium, the fuel in use flowing downwardly through the filter medium (12), the apertures (15) in the lower support plate (14) being located adjacent the outer periphery thereof and depending from the lower support plate are first and second annular baffles the outer one (17) of which is located adjacent to but inwardly of said apertures (15) and the inner one (18) of which defines an entrance (19) to the lower end of the tube (11), said baffles (17, 18) and the lower support plate (14) defining an air collection chamber, and an orifice (20) through which air collecting in said chamber can escape at a controlled rate to the interior of said inner tube (11). A fuel filter element according to Claim 1, characterised in that said lower support plate (14) extends inwardly beyond the inner peripheral surface of the tube (11), the orifice (20) being formed in the portion of the support plate overhanging the tube. A fuel filter element according to Claim 1, characterised in that said orifice (20) is formed in the inner baffle (18).

Inventors: BRADFORD PETER FRANCIS, BRADFORD, PETER FRANCIS
Applicants: LUCAS IND PLC, LUCAS INDUSTRIES PUBLIC LIMITED COMPANY
Application year: 1995
Main classification: F02M37
IPC codes: F02M37, B01D35