Purging air from a fuel line

Abstract: In order to purge air from the fuel system of an engine, when the engine (18) is first installed in a vehicle, a svacuum pump (28) is connected to the fuel line (16) at a position close to the engine and all the air in the fuel line is sucked out. Before the vacuum is released, a plug (40) is placed in the air outlet (38) to prevent any air re-entering the fuel system.

Description: FIELD OF THE INVENTION This invention relates to the purging of air from a fuel line, and in particular to a method of purging and to an air purging device for use in a fuel line. The invention is particularly applicable to an air purging operation carried out on a vehicle at the time of construction of the vehicle, before the engine is first started in the vehicle. BACKGROUND TO THE INVENTION In order to draw the first charge of fuel from the fuel tank to the engine through the initially air-filled fuel lines, it is conventional to crank the engine so that the fuel pump draws the air out of the fuel lines. Once all the air has been pumped out, the fuel follows. However purging the air in this way takes time, in particular because the fuel pump is not designed to pump air and is not very efficient at pumping air. It is desirable to find a way in which the air can be purged from the fuel circuit more quickly than before. SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a method of purging a fuel line which extends from a fuel tank to a fuel consuming unit (eg an engine), the method comprising the steps of connecting a vacuum pump to an air outlet from the line, evacuating air from the line, plugging the air outlet whilst the vacuum in the line is maintained, and subsequently removing the vacuum pump from the line. Preferably the vacuum pump continues to run until the air outlet has been plugged. Since the method set out above is intended for use only at the time when the vehicle is first assembled, on a production line, the plugging of the air outlet is preferably permanent. Evacuation of the air from the line is preferably continued until liquid fuel is sensed at the air outlet. The air outlet is preferably positioned in the fuel line as close as possible to the fuel consumer unit and upstream of any filter in the line. Where the method is carried out on a vehicle production line, the vacuum pump can be positioned alongside the line with a vacuum head for sealing connection to the air outlet. According to a second aspect of the invention there is provided an air purge device to be fitted in a fuel line for carrying out the method set forth above the device including a fuel flow passage to allow passage of fuel along the line and through the device, an air outlet adapted to be connected to a vacuum pump and communicating with the fuel flow passage and a moveable plug adapted to be moved to close the air outlet. Preferably the device includes a spigot at each end of the fuel flow passage, the spigots being designed to have fuel pipes connected to them. The air outlet preferably leads into a space between the spigots and is formed by a hollow tubular body onto which a vacuum head can be connected. The moveable plug can be pre-mounted in the air outlet in a position in which it does not obstruct the air outlet but can be moved axially once evacuation is complete to a position where it does close the air outlet. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of the fuel system of a motor vehicle: Figure 2 is a perspective view of an air purge device in accordance with the invention; and Figures 3, 4 and 5 illustrate three different stages in the method of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS Figure 1 shows a fuel tank 10 with a filler pipe 12 and a cap 14. A fuel feed line 16 leads from the tank towards an engine 18. The engine (which in this case is a diesel engine) has a fuel pump 20 which draws fuel from the tank 10 through a filter 22 to the engine. The invention can however also be applied to a petrol engine. When the vehicle is first assembled, the engine is installed, the tank is installed and the fuel line which connects the two is installed. At this stage the fuel line is completely filled with air and before fun from the tank 10 can reach the engine, this air has to be purged from the system. As has already been pointed out, it is possible to purge this air by operation of the pump 20 which can be achieved by cranking the engine using an external power source. However it takes an appreciable period of time for the pump to purge the volume of air which is present. To overcome this difficulty, the invention provides for the use of an air purge device 24 which is positioned in the fuel pipe 16 close to the fuel pump 20. The device 24 has an air outlet which mates with a vacuum head 26 connected to a vacuum pump 28 by a flexible pipe 30. When the head 26 is engaged with the device 24, the vacuum pump 28 draws the air out of the line 16and out of the filter 22, and draws fuel from the tank 10 through the pipe and through the filter practically up to the engine. Thereafter the engine will fire without delay when it is initally cranked over. The detail of the device 24 is shown in Figure 2 by way of example. There is a fuel passage 32 through the device which ends in fuel line connection spigots 34 at each end. These have conventional annularly ridged exteriors to retain the ends of the fuel lines. The air outlet is via a cylindrical portion 36 which communicates with the passage 32 and via a circular aperture 38. A plug 40 on the end of a stem 42 is fitted, initially at the top of the cylinder 36 in a position where it closes the top end of the cylinder but allows communication between the air outlet and the fuel passage. The plug can however be pushed down the cylinder 36 as will be described now with reference to Figures 3, 4 and 5. Figure 3 shows the vacuum head 26 fitted off the air outlet of the device 24, and the arrow 44 indicates air being evacuated from the fuel passage 32 and from the remainder of the fuel line 16. As the air is evacuated, fuel will be sucked from the tank 10 and will flow through the device and into the pipe 30. As soon as fuel is present in the pipe 30, sufficient evacuation of the line 16 has taken place and the plug 40 is then forced downwards in the direction of the arrow 46 (Figure 4) so that it blocks the air outlet. Fuel now flows only along the passage 32. It is important that the downward movement of the plug 40 is carried out at a time when the head 26 is still connected to the device, and whilst the vacuum is maintained. The fuel line will then be full of fuel up to the mid point of the passage 32, and when the engine is turned over there is only a minimal volume of air which has to be drawn through the engine before fuel reaches the cylinders. The final stage in the process is the removal of the vacuum head 26 leaving the closed air purge device which remains as a permanent part of the vehicle and will not thereafter be disturbed. The vacuum pump 28 with its vacuum head 26 is mounted alongside the assembly line so that as each vehicle moves along the assembly line, the fuel line can be purged and then sealed so that at any time thereafter the engine can be started without delay. The invention thus provides a simple device and operating method by which air can be purged, leaving two significant reductions in assembly line time. The head 26 can be constructed in such a way that it senses the arrival of liquid fuel in the pipe 30 and then automatically forces home the plug 40 without any separate operator input.

Claims: A method of purging a fuel line (16) which extends from a fuel tank (10) to a fuel consuming unit (18), the method being characterised by the steps of connecting a vacuum pump (28) to an air outlet (38) from the line, evacuating air from the line, plugging the air outlet whilst the vacuum in the line is maintained, and subsequently disconnecting the vacuum pump from the line. A method as claimed in Claim 1, characterised in that the air outlet (38) is positioned in the fuel line (16) as close as possible to the fuel consuming unit (18) and upstream of any filter (22) in the line. An air purge device to be fitted in a fuel line for carrying out the method claimed in Claim 1 or Claim 2, the device (24) including a fuel flow passage (32) which allows passage of fuel along the line and through the device, an air outlet (38) adapted to be connected to a vacuum pump and communicating with the fuel flow passage and a moveable plug (40) adapted to be moved to close the air outlet. A device as claimed in Claim 3, which includes a spigot (34) at each end of the fuel flow passage (32), the spigots being designed to have fuel pipes connected to them. A device as claimed in Claim 3 or Claim 4, characterised in that the air outlet (38) leads into a space between the spigots (34) and is formed by a hollow tubular body (36) onto which a vacuum head (26) of a vacuum pump (28) can be connected. A device as claimed in Claim 5, characterised in that the moveable plug (40) is premounted in the tubular body (36) in a position in which it does not obstruct the air outlet (38) but can be moved axially once evacuation is complete to a position where it does close the air outlet (38). A motor vehicle having an engine (18), a fuel tank (10), a fuel line (16) connecting the engine and the tank and an air purge device as claimed in any one of Claims 4 to 6 included in the fuel line.

Inventors: STALKER GEORGE CARLTON, TURNER DAVID BRIAN, STALKER, GEORGE CARLTON, TURNER, DAVID BRIAN
Applicants: FORD FRANCE, FORD MOTOR CO, FORD WERKE AG, FORD FRANCE S. A., FORD MOTOR COMPANY, FORD MOTOR COMPANY LIMITED, FORD-WERKE AKTIENGESELLSCHAFT
Application year: 1990
Main classification: B60K15
IPC codes: F02M37, F02B1, B60K15