GB2118059A

GB2118059A - Fuel filter units

Info

Publication number: GB2118059A
Application number: GB08305520A
Authority: GB
Inventors: Graham Rhys Levis; William Robert Burborough
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-04-13
Filing date: 1983-02-28
Publication date: 1983-10-26
Also published as: GB2118059B; GB8305520D0

Abstract

A fuel filter unit for incorporation into the fuel supply system of a compression ignition engine includes a mounting 18 defining a fuel inlet 26 and a fuel outlet 24. A base 19 can be secured to the mounting with a reservoir 20 adjacent the mounting and a filter element 22 between the reservoir and the base. The reservoir has a restricted outlet 29 positioned adjacent the inlet of the filter element and an inlet 27 to receive fuel from the fuel inlet 26 but normally most of the fuel flows down passage 25 bypassing the reservoir. In the event air enters through the fuel inlet 26 and passes through the outlet to a fuel pump 12 so as to stop the associated engine, fuel flows from the reservoir to the space below element 22 to provide a source of fuel to enable the engine to be restarted and run quickly to purge the system of air after fuel tank 11 has been refilled. The reservoir outlet 29 may have a valve which closes automatically when filter element 22 is removed. <IMAGE>

Description

SPECIFICATION Fuel filter units This invention relates to fuel filter units of the kind which are incorporated in the fuel supply system of a compression ignition engine fuel pump.

Known forms of fuel filter units for the purpose specified comprise a mounting member adapted in use to be mounted on the engine structure or some other convenient support structure, the mounting member having inlet and outlet flow connections for connection into the fuel supply system. Also forming part of the filter unit is a filter element which conveniently is a self-contained item including a casing which can be assembled in sealing relationship to the mounting. Usually the unit will include a base which can be secured to the mounting by means of a through bolt which extends through the element, the element being sandwiched between the mounting and the base.

The filter element includes a filter medium which is able to retain solid contaminant in the fuel which flows through the filter unit.

Periodically the element must be replaced and when this operation has been completed, a large volume of air is present in the fuel supply system.

A similar situation occurs when air has been drawn into the filter unit. This volume of air must be purged from the system and this can be achieved by special venting arrangements within the fuel pump. The process of purging the system is facilitated if the fuel system incorporates a large displacement priming pump such for example as a diaphragm type pump operated by the engine. In some fuel supply systems, however, such a pump is not provided for reasons of economy and the purging of the air has to be effected by a low pressure supply pump which forms part of the fuel pump. The displacement rate of the low pressure fuel supply pump will be greater than the rate at which fuel is delivered to the engine. However, it will not approach the displacement rate of a diaphragm pump. Moreover, the rate of displacement will depend upon the speed at which the engine is operating.

The purging of the air in the fuel supply system will therefore take some time and if the engine requires to be cranked for the whole of the purging process, there will be a considerable strain on the engine starting motor and also upon the storage accumulator.

The object of the present invention is to provide a fuel filter unit of the kind specified in a simple and convenient form.

According to the invention a fuel filter unit for the purpose specified comprises in combination, a mounting adapted to be secured in use to a support structure, a reservoir and a filter element secured to the mounting, said reservoir being disposed in use above the filter element, a fuel inlet and a fuel outlet in the mounting for connection respectively to a source of fuel and the fuel pump, a restricted outlet from the reservoir to the fuel inlet side of the filter element, an inlet to the reservoir and a flow passage extending between the fuel inlet and the inlet side of the filter element, the inlet to the reservoir being positioned so that it can receive fuel from said fuel inlet.

An example of a fuel filter unit in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a diagrammatic view of the system; and Figure 2 shows a modification to part of the system shown in Figure 1.

Referring to the drawings, the filter unit is indicated generally at 1 O, a source of fuel in the form of a fuel tank at 11, and a compression ignition engine fuel pump at 12, the fuel pump comprising a high pressure pump 13 having outlets 14 for connection to the injection nozzles respectively of an associated engine. The fuel pump also incorporates a low pressure pump 15 which supplies fuel to the pump 13, the fuel being drawn through an inlet conduit 16. Surplus fuel from the housing of the pump is returned to the fuel tank 11 by way of the conduit 17.

The filter unit is shown as a single unit but in practice it comprises a mounting 18 which will include support lugs whereby it can be secured to a suitable support structure. Also forming part of the filter unit is a base 19. Adjacent the mounting is a reservoir 20 and below the reservoir is a filter element 21. The filter element in practice includes an integral casing with a central tubular member.

The filter medium is of annular form and is indicated at 22.

The filter element has a central tubular component which at its lower end communicates with the interior of the base and which as will be observed from Figure 1, locates about a hollow spigot 23, there being disposed between the spigot and the tubular member, a sealing member.

The interior of the spigot is in communication with a fuel outlet 24 formed in the mounting and connected in use, to the conduit 16. The reservoir 20 is of annular form and a flow passage 25 is defined between the spigot 23 and the reservoir and through which fuel can flow to the fuel inlet side of the filter element from an inlet 26 formed in the mounting and connected in use, to the fuel tank. The inlet 26 opens to the space above the reservoir 20 and the latter is provided with reservoir inlets 27 in its upper wall. Preferably, the inner wall of the reservoir is extended upwardly to define a lip 28 which forms, in use, the equivalent of a weir to ensure that the inlets 27 will receive fuel which flows through the fuel inlet 26.

In the lower wall of the reservoir there is formed a restricted outlet 29 which is disposed adjacent the fuel inlet side of the filter element.

In use, the fuel drawn through the filter unit by the low pressure pump 1 5 flows from the tank 11 to the fuel inlet 26 and it can then take two paths.

One path is by way of the reservoir although a relatively small amount of fuel will flow along this path when the system has been in operation for some time. The reason for this is that the outlet 29 is restricted. Most of the fuel will flow over the weir created by the lip 28 and along the clearance 25 to the fuel inlet side of the filter element. The fuel passes through the filter element and any solid contaminant is removed, the clean fuel then flowing into the well defined by the base 19. From the aforesaid well the fuel flows upwardly through the fuel outlet 24 to the pump.

If the fuel tank is allowed to run dry, air will be drawn through the fuel inlet 26 but the pump 12 will continue to supply fuel until the air has passed through the filter medium and has collected in the base 19. When this occurs air will start to be drawn through the fuel outlet 24 and it can be expected that the engine will stop. The flow of fuel through the outlet 29 is at a restricted rate and will not be sufficient to maintain the engine in operation. After a period of time, however, and during which it is expected that the fuel tank will be replenished, the fuel in the reservoir 20 will flow through the outlet 29 and through the fuel element. If now an attempt is made to start the engine, the pump 1 5 will draw fuel from the well and will start to deliver fuel to the associated engine once the air has been drawn through the spigot 23, the outlet 24 and the conduit 16.

During this process fuel will also be drawn from the tank and in so doing air will flow through the fuel inlet 26. The moment fuel is supplied to the engine however the latter will start and it can then be run at a substantially unrestricted speed and providing the various volumes are carefully chosen, fresh fuel will flow through the inlet 26 before the fuel which was contained in the reservoir 20 is exhausted.

When fresh fuel flows through the inlet 26 the reservoir will start to fill but again this can only take place at a restricted rate because of the opening 29. Most of the fuel will flow to the well through the filter element. The air is vented from the reservoir through a vent 30 into the flow passage 25 and is gradually drawn through the fuel system and expelled by the venting arrangement in the pump.

When it is required to change the filter element 21 the base is removed to allow a fresh element to be assembled. The base is then replaced and the process of purging must take place. As soon as the new element has been placed in position, the fuel flowing from the reservoir will pass through the element and start to accumulate in the well. The starting procedure is as described above. If desired, the outlet 29 may be provided with a valve as shown at 31 in Figure 2. The valve drops to the closed position when the filter element is removed, thereby preventing flow of fuel through the outlet 29 until the element has been replaced.

Claims

1. A fuel filter unit for incorporation into the fuel supply system of a compression ignition engine fuel supply pump comprising in combination, a mounting adapted to be secured in use to a support structure, a reservoir and a filter element secured to the mounting, said reservoir being disposed in use above the filter element, a fuel inlet and a fuel outlet in the mounting for connection respectively to a source of fuel and the fuel pump, a restricted outlet from the reservoir to the fuel inlet side of the filter element, an inlet to the reservoir and a flow passage extending between the fuel inlet and the inlet side of the filter element, the inlet to the reservoir being positioned so that it can receive fuel from said fuel inlet.

2. A filter unit according to Claim 1 including a base secured in use below the filter element, said base defining a well into which flows the fuel which has passed through the filter element, said fuel outlet communicating with said well.

3. A filter unit according to Claim 2 in which said well communicates with said fuel inlet through a spigot which depends from said mounting, said reservoir being of annular form and defining with the exterior of the spigot part of said flow path.

4. A filter unit according to Claim 3 in which said inlet to the reservoir is formed in the upper wall thereof, the inner wall of the reservoir being extended upwardly to define a weir over which fuel flowing through the fuel inlet must flow to enter the annular space defined between the spigot and the inner wall of the reservoir.

5. A filter unit according to Claim 4 including a vent in said inner wall of the reservoir to allow air in said reservoir to flow into said flow passage.

6. A filter unit according to any one of the preceding claims including valve means located in said restricted outlet, said valve means acting to prevent flow of fuel through the restricted outlet when said filter element is separated from the reservoir.

7. A fuel filter unit for incorporation into the fuel system of a compression ignition engine substantially as hereinbefore described with reference to the accompanying drawings.