GB2329850A - Liquid filter with slot shaped air vent - Google Patents

Abstract

A filter unit includes an air collection chamber 32 arranged to collect air from a flow of liquid flowing through a filter 26, the air collection chamber having an outlet in the shape of a slot 30 that allows air to escape with the filtered liquid. A tubular baffle 28, defines the air collection chamber, and has a narrow slot extending along its length. The slot may be of uniform width, or alternatively may taper or have another profile. Liquid flows through the filter medium and upwardly through the interior of the baffle. Air collected within the air collection chamber escapes through the slot so that the cross-sectional area of the slot available for air to escape through depends on the quantity of air collected within the air collection chamber. The arrangement is suitable for removing contaminants from a flow of fuel.

Description

FILTER This invention relates to a filter for use in separating contaminants from a supply of fuel to an internal combustion engine. In particular, the invention relates to a filter which also separates air from the fuel supply, the collected air being released into the fuel on the clean side of the filter in a controlled manner.

EP 0547951 describes a filter in which fuel flows in a generally radial direction through an annular filter medium from an outer position to an inner position. A baffle is located within a central passage of the filter medium and defines with the filter medium an annular air collection chamber. The upper end of the baffle is provided with one or two small openings through which air can escape from the air collection chamber in a controlled manner and continue with the flow of fuel in the form of a series of small air bubbles.

It has been found that such an arrangement is highly sensitive to the fuel flow velocity which affects the pressure drop across the small openings.

At low fuel velocities, the pressure drop may be insufficient to cause air to escape at a sufficiently high rate to avoid air building up in the air collection chamber. Such a build-up of air may result in air being released from beneath the baffle in an uncontrolled manner. At high fuel levels, the pressure drop across the small opening may cause air to escape from the air collection chamber too quickly which can have an adverse effect upon the operation of a fuel pump located downstream of the filter.

It is an object of the invention to provide a filter in which the disadvantageous effects described hereinbefore are reduced.

According to the present invention there is provided a filter comprising an air collection chamber arranged to collect air from a flow of fuel flowing through the filter, and outlet means whereby air can escape from the air collection chamber and continue with the flow of fuel out of the filter, wherein the outlet means comprises a slot.

The slot conveniently extends generally vertically. The provision of such a slot is advantageous as the area through which air can escape from the air collection chamber is dependent upon the quantity of air collected within the air collection chamber.

The slot may be of uniform width, or alternatively may taper or have another profile.

The invention is applicable to filters of the type in which fuel flow through the filter medium is in either a generally radial direction or a generally vertical direction, and is applicable to both the filter and agglomerator flow directions.

The invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 illustrates a filter in accordance with an embodiment of the invention; Figures 2 and 3 are enlarged views of part of Figure 1 illustrating operation of this embodiment; and Figure 4 is a view of an alternative embodiment.

The filter illustrated in Figure 1 is intended for use in removing contaminants from a flow of diesel fuel to a compression ignition internal combustion engine. The filter is located, in use, between a fuel reservoir and a low pressure feed pump, the feed pump being arranged to draw fuel from the reservoir through the filter, and to supply fuel at relatively low pressure to a high pressure fuel pump.

The filter comprises a generally cylindrical housing 10 having a filter cartridge 12 located therein. The filter housing 10 includes an inlet opening 14 and an outlet opening 16. The filter cartridge 12 is sealed by means of an O-ring 18 to the lower end of the housing 10, and an annular seal 20 is located between the upper surface of the filter cartridge 12 and the upper end wall of the housing 10.

The filter cartridge 12 comprises upper and lower support plates 22, 24, and an annular filter medium 26 located between the upper and lower support plates 22, 24. The filter medium 26 conveniently comprises a pleated paper filter member which is of star-like configuration when viewed from above or below. The upper support plate 22 includes a central opening, and a tubular baffle 28 depends from the upper support plate 22, the baffle 28 surrounding the opening in the upper support plate 22. A narrow slot 30 extends along the length of the baffle 28.

The slot 30 is of uniform width along its entire length.

In use, fuel is supplied through the inlet opening 14 to an annular chamber defined between the exterior of the filter medium 26 and the housing 10. Fuel from this chamber flows in a generally radial inward direction, passing through the filter medium 26, to an inner chamber defined by the filter cartridge 12. It will be appreciated that as the fuel passes through the filter medium 26, contaminants carried by the flow of fuel are removed by the filter medium 26.

As air carried with the flow of fuel is of relatively low density, the air tends to separate from the fuel as indicated by the dashed arrows in Figure 1, and flows upwardly collecting in an air collection chamber 32 defined between the baffle 28 and the inner periphery of the filter medium 26.

The fuel flows upwardly through the interior of the baffle 28, the fuel leaving the housing 10 through the outlet opening 16. The fuel subsequently flows to the feed pump, and from there to the high pressure fuel pump.

The air collected within the air collection chamber 32 is able to escape therefrom through the slot 30, and it will be appreciated that the crosssectional area of the slot 30 available for air to escape through depends upon the quantity of air collected within the air collection chamber 32.

Where the quantity of air collected within the air collection chamber 32 is relatively low, for example as illustrated in Figure 2, the area available for fuel to escape from the air collection chamber 32 is relatively small.

Such small quantities of air tends to collect in the air collection chamber 32 when fuel is flowing through the filter at a relatively high velocity. In such circumstances, a relatively high pressure drop occurs across the slot 30 thus a relatively high force is exerted on the air urging the air through the slot 30. As only a relatively small area is available for air to escape from the air collection chamber 32, the flow rate of air from the air collection chamber 32 is restricted, even though the pressure drop across the slot is relatively high, thus avoiding an excessive quantity of air continuing with the flow of fuel out of the filter.

Figure 3 illustrates the case where the fuel velocity is relatively low, and in these circumstances a relatively large quantity of air tends to collect in the air collection chamber 32 as the pressure drop across the slot 30 is relatively low, thus the force urging the air through the slot 30 is low. In such circumstances, although the force urging air through the slot 30 is low, as a relatively high cross-sectional area of the slot 30 is available for air to escape through, the flow rate of air is maintained at a sufficiently high rate to ensure that an excessive quantity of air does not build up, hence avoiding the release of large slugs of fuel in an uncontrolled manner through the baffle 28 and outlet 16.

Although the description hereinbefore is of a filter of the type in which fuel flows from a radially outer position to a radially inner position, the invention is also applicable to filters of the type in which the direction of fuel flow is in the reverse radial direction. The invention is also applicable to filters of the type in which fuel flows in a direction generally parallel to the axis of the filter, and such an arrangement is illustrated in Figure 4.

In the arrangement illustrated in Figure 4, the filter comprises a generally cylindrical housing 10 within which a filter cartridge 12 is located. The upper end surface of the filter housing 10 includes an inlet opening 14 and an outlet opening 16 which communicate with a fuel reservoir and a low pressure fuel pump, respectively.

The filter cartridge 12 comprises upper and lower annular support plates 22, 24 which are secured to one another by a tubular member 25 which extends along the axis of the filter, in use. The upper and lower support plates 22, 24 are perforated to enable fuel flow therethrough. The upper and lower support plates 22, 24 support a pleated paper filter medium 26 which is of coiled form. Appropriate O-rings 18 are located to seal the filter cartridge 12 to the housing 10 to ensure that fuel flow between the inlet and outlet openings 14, 16 requires the fuel to flow through the filter medium 26.

Located within the central tubular member 25 is an axially extending baffle 28, the upper end of which is provided with a slot 30 which, in use, extends in a generally vertical direction. The upper end of the baffle 28 is carried by and sealed to an annular member 32 which is sealed to the interior of the tubular member 25.

In use, fuel enters the filter through the inlet opening 14 and passes through the filter medium 26. The fuel exits the filter medium 26 at the lower end thereof and flows towards the lower end of the baffle 28. The fuel then flows upwardly through the baffle, through the central opening of the member 34 and through the tubular member 25 to exit the filter through the outlet opening 16. As air carried with the flow of fuel is less dense than the fuel, the air tends not to enter the baffle 28, and instead flows in the direction indicated by the dashed arrows in Figure 4 to enter an air collection chamber 32 defined between the baffle 28 and tubular member 25. As in the embodiment illustrated in Figure 1, air from the air collection chamber 32 is permitted to escape from the air collection chamber 32 through the slot 30 in a controlled manner to continue with the flow of fuel towards the low pressure feed pump and high pressure pump.

Although the arrangement illustrated in Figure 4 is of the type in which the fuel flows through the filter medium is in the generally downward, agglomerator flow, direction, the invention is also applicable to arrangements in which fuel flows upwardly through the filter medium.

In the embodiments described hereinbefore, the slot 30 is of uniform width. It will be appreciated, however, that the profile of the slot may be modified depending upon the intended use of the filter and the quantities of air which the fuel pumps located downstream of the filter are able to accommodate without detrimentally effecting the operation of the pumps. For example, the slot 30 may be modified to be of tapering form to either increase or decrease the rate at which air is permitted to escape from the air collection chamber 32 for any given velocity of fuel.

Further, rather than tapering in a uniform manner, the profile of the slot 30 may be of any appropriate shape.

Claims (4)

1. CLAIMS 1. A filter comprising an air collection chamber arranged to collect air from a flow of fuel flowing through the filter, and outlet means whereby air can escape from the air collection chamber and continue with the flow of fuel out of the filter, wherein the outlet means comprises a slot.
2. 2. A filter as claimed in Claim 1, wherein the slot extends generally vertically, in use.
3. 3. A filter as claimed in Claim 1 or Claim 2, wherein the slot is of uniform width.
4. 4. A filter substantially as hereinbefore described with reference to any one of the accompanying drawings.