GB2123892A

GB2123892A - A diesel engine fuel injection system

Info

Publication number: GB2123892A
Application number: GB08318796A
Authority: GB
Inventors: Harold Edgar Bottomley
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-07-14
Filing date: 1983-07-12
Publication date: 1984-02-08
Also published as: GB8318796D0; GB2123892B

Abstract

Excess fuel from the injection pump (13) is returned to the filter (12). An exhaust-heated exchanger with a thermostatically controlled bypass valve may be provided between the fuel lift pump (11) and the filter. The vessel (24) may contain a float valve which only opens the inlet to the pipe (21) to the tank (10) when air is present in the vessel. The vessel (24) may form part of the injection pump or filter. <IMAGE>

Description

SPECIFICATION Afuel injection system This invention concerns a system for injecting fuel into an internal combustion engine such as a diesel engine.

One ofthe most common problems experienced with fuel supply systemsfor diesel engines is the inadvertent leakage of air into the fuel supply line caused either by a perforated diaphragm in the main fuel lift pump, by an unsealed pipe connection or by drawing airfrom the fuel tank when the tank is almost empty, and the air passes to the injection pump and then to the injectors themselves causing fuel starvation in the engine. Air locks produced in this way can cause a diesel engine to stall and make it difficult to restart. Another problem is that under extremely cold conditions the diesel fuel thickens to theextentthat it can block the usual fuel filter in the supply pipe to the injection pump.This causes a vacuum lock in the pump and again prevents the continuous supply of fuel to the engine.

An object ofthe present invention is to provide a device which can be incorporated into the fuel supply line to the injection pump, which substantially overcomes the problems of air locking and vacuum locking as described above.

According to the present invention, a fuel injection system for an internal combustion engine comprises a fuel supply tank, a lift pump to draw fuel from the tank and pass it continuously to a filter, an injection pump connected to the filter for receiving filtered fuel therefrom, and a series of lines supplying fuel from the injection pump to a like number of injectors on the engine, characterised by means disposed in the fuel supply line to the injection pump and providing a separate passage directto said supplytankto permit fuel surplus to that required at the injection pump to return through said passage to the supply tank and to permit any air entrained within the fuel entering said means, to escape to said tank with said returned fuel.

An embodiment of the invention will now be described, byway of example only, with reference to the accompanying drawings, in which: Fig. lisa schematic layout of a fuel injection system incorporating means in accordance with the invention; and Fig. 2 is a schematic illustration of said means.

The system includes a fuel supply tank 10, a fuel lift pump 11, a filter bowl 12, an injection pump 13, and a series of pipes 14 to supply fuel from the injection pump 13 to the injectors 15 on the engine 16. Pipework generally indicated at 20 provides a flow circuitforfuel through the system in the direction indicated by arrows 17. A device 18, in accordance with the invention, is disposed in the pipeline 20 between filter bowl 12 and injection pump 13. Excess fuel return pipes 21 and 22 complete the fuel flow circuit to return surplus fuel to the tank 10 from device 18 and the injectors 15 respectively. A pipe 23 serves to return surplus fuel from the injection pump 13 to the filter 12.

Referring now to Fig. 2, the device 18 comprises a vessel 24 which is connected to filter bowl 12 via a pipe 25 and connector 26, to pipe 21 as indicated, and to injection pump 13 via a pipe 27. In Fig. 2, the pipe 21 is shown as connected to the side ofthe vessel 24 in the upper region thereof but it can be connected to the top as shown simply in Fig. 1.

In a conventional fuel supply line to a diesel engine the outlet pipe from filter bowl 12 is connected directly to the input of injection pump 13 so that any air trapped in the system and passing through the filter bowl is passed with the fuel directly into the injection pump and via pipes 14tothe injectors 15on the engine. As discussed above, air locks in the pump 13 frequently occur causing the engine to stall.

Now, bythe provision of pipe 21 leading back to the supply tank 10, any air entering the vessel 24will rise naturally within the vessel and pass into the pipe 21 and thus directly back to the tank 10. Fuel, free of entrained air, passes bygravitytothe injection pump.

This simple expedient effectively prevents air bubbles from entering pipe 27 so that air locks cannot be created in the engine. Any airtrapped in the injection pump casing can escape via pipe 27 and vessel 24, to pipe 21.

Since the lift pump 11 always supplies fuel considerably in excess ofthat required bythe engine it is perfectly satisfactory to direct all of the surplus fuel and any air entrapped therein back to the tank 10. The injection pump 13 requires a continuous supply of fuel and thus surplus fuel from the pump is directed via pipe 23 back to the filter bowl 12. Again, surplusfuel fed in the normal way to injectors 15 is permitted to return via pipe 22 and pipe 21 tothetank. By circulating the fuel constantly through the pump and backto tank the whole contents of the tank and of the supply system are maintained at an elevated temperature since much ofthe pipework 21 passes through the engine compartment and is continuously reheated whilst the engine is running.

The vessel 24 is designed to be large enough to contain sufficientfuel to run the engine up to normal operating temperature. In this way, in very cold conditionswhen the fuel filter bowl often becomes blocked bythickenedfuel,there isalwaysan adequate supply of fuel in the vessel 24to startthe engine and to run itfora period long enough to raisethetemperature of the fuel in the filter bowl 12 which thus becomes less viscous and the phenomenon known as "waxing" of the fuel is overcome. Similarly, when it is necessaryto replace the filter element within the bowl 12 there is sufficient fuel in the vessel 24forthe engine to be restarted and to run continuously without the need to bleed air out of the system.The air introduced into the filter bowl during the changing operation escapes along pipe 21 tothetank10.Conventionallyit has always been necessary to bleed the whole fuel system when the filter element is changed, and this operation has had to be carried out by skilled or semi-skilled personnel. With the device 18fitted, it is quite possible for unskilled personnel to replace the filterelementwithout having to undergo the previous ly inevitable bleeding operation.

Experimentaily, the applicant has deliberately intro duced air into the fuel line upstream of the filter bowl 12 and has confirmed that all ofthe air has escaped via pipe 21 to the supplytank 10, none of the air entering the injection pump 13. On a diesel engine having a 2.5 litre cylinder capacity, it has been found that something oftheorderof5 litresoffuel is returned to the supply tank 10 in a period of about 6 minutes when the engine is "idling", so that there is a constant and considerable recirculation offuel through the whole system.Whilstthis provides sufficient preheating of thefuel in most conditions, to prevent "waxing" and generally to enhance the performance of the engine, there may be provided, if necessary, a heat exchanger which is interposed in the pipework between lift pump 11 and filter bowl 12, and is physically in contact with the vehicle exhaust system thus to provide extra preheating forthe fuel. In average climatic conditions, however, this further expedient is unnecessary. If a heat exchanger is included in the system, then a thermostatically responsive divertervalve could be used to direct the fuel selectively through the heat exchanger orto bypass it, according to the conditions.

In an engine of the size mentioned above and used typically in a taxi cab, the vessel 24, is ideally about 5 cms in diameterand about7.5cms in height, For largerengines, a largervessel would be provided to ensure that sufficient fuel can be contained therein to enable the engine to run upto working temperature.

The device indicated generally at 18 in Fig. 1 can be made available with its ancilliary pipes and connections, in kitformforeasyadaption by unskilled personnel. This operation would simply involve cutting the pipe between the filter bowl 12 and the injection pump 13and insertingthedevicewith its return pipe 21 connected to the tank. If the device isto be included in manufacture then conveniently it can be attached to or housed within the injection pump casing or the filter bowl casing.

In a modified form of the invention where the lift pump does not provide substantial excess fuel it may be necessary to introduce within vessel 24 a float valve which closes off pipe 21 when the vessel becomes filled with fuel. In the operation of this embodiment any air entering the vessel 24 would causethefuel level therein to drop thus opening the valve and allowing the air to escape along line 21 to the tank.

Provided no further air entersthe vessel then the fuel level therein rises and thefloatvalve closes pipe 21.

For practical purposes such afloatvalve arrange- ment is unnecessary since in nearly all fuel injection systems the lift pump 11 is designed to deliver substantial excess fuel at a rate which is determined bythe speed of operation of the engine, so that the excess fuel is sufficient to permit continuous and substantial recirculation offuel to the supply tank 10.

As a further precaution againsttrapped air in the system, the injection pump 13 conventionally has a venting portwhich is normally closed, this port can be connected permanently to the vessel 24thusto provide a furtherdirect routeforthe escape of any air becoming trapped in the injection pump casing.

Claims

1. Afuel injection system for an internal combus tion engine comprising a fuel supply tank, a lift pump to draw fuel from the tank and pass it continuouslyto a filter, an injection pump connected to the filterfor receiving filtered fuel therefrom and a series of lines supplying fuel from the injection pump to a like number of injectors on the engine, characterised by means disposed in the fuel supply line to the injection pump and providing a separate passage direct to said supplytankto permitfuel surplus to that required at the injection pump to return th rough said passage to the supply tank and to permit any air entrained within the fuel entering said means, to escape to said tank with said return fuel.

2. Afuel injection system according to Claim 1, in which said means comprises a vessel having an inlet for receiving the fuel from said filter, a first outlet disposed near the bottom of said vessel for discharging fuel to said injection pump, and a second outlet disposed nearthetopofsaidvessel and connected via said separate passage directto said fuel supply tank.

3. Afuel injection system according to Claim 2, wherein said inlet and said upper and lower outlets are continuously open and wherein said vessel provides the only passage forfuel from the filtertothe injector pump.

4. Afuel injection system according to Claim 2, including a surplus fuel return pipe connected between said injection pump and saidfilterto permit excessfuel'to return from said injection pump to said filter to permit excess fuel to return from said unjection pump to said filter.

5. Afuel injection system according to Claim 2, including a surplus fuel return pipe providing a passage for excess fuel from said injectors on the engine, to said separate passage, forthe return of excess fuel to said fuel supplytank.

6. Afuel injection system according to Claim 2, in which said vessel is attached directlyto or integral with a casing for said injection pump.

7. Afuel injection system according to Claim 2, wherein said vessel is attached directly to or integral with a casing forsaid filter.

8. Afuel injection system according to Claim 1, including an air venting port on said injection pump with permanent connection to said separate passage such that air entering the injection pump from the engine can escape to said fuel supplytank with said return fuel.

9. Afuel injection system according to Claim 1, including a heat exchangerthrough which fuel passes in its passage to said filter.

10. Afuel injection system according to Claim 1, including afloatvalve in said vessel adaptedto close said second outletwhen said vessel isfilled with fuel, and to open said second outlet automatically when some ofthe fuel content of said vessel is displaced by air in the upper region thereof.

11. Means for preventing air locks and vacuum locks in fuel injection systems comprising a vessel adapted to be disposed in the fuel supply line to an injection pump and providing separate passage direct to a fuel supply tank to permit fuel surplus to that required at the injection pump to return through said passage to said supply tank and to permit any air entrained within the fuel entering said means, to escape to said tank with said return fuel.

12. Afuel injection system for an internal combustion engine, substantially as hereinbefore described, with reference to and as illustrated in the accompanying drawings.

13. Means for preventing air locks and vacuum locks in an internal combustion engine, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.