GB2114236A

GB2114236A - Fuel injection system

Info

Publication number: GB2114236A
Application number: GB08233410A
Authority: GB
Inventors: Don Charles Palmer
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1982-01-23
Filing date: 1982-11-23
Publication date: 1983-08-17
Also published as: GB2114236B

Abstract

A fuel injection system for a compression ignition engine includes a pump 10 for supplying fuel at high pressure to an injection nozzle 11. The outlet of the pump is connected to one end of a first cylinder 13 the other end of which extends into a second cylinder 14 of smaller diameter. The one end of the second cylinder remote from the first cylinder communicates with the nozzle 11. Respective pistons 16, 17 are located in the cylinders and the first cylinder has a spill port 19 which can be covered by the first piston following the opening of a bypass path defined by a groove 22 on the second piston. The delivery of fuel through the nozzle is initially at a slow rate as determined by the displacement of the second piston 17 followed by an interval during which the pistons move until the spill port is covered and in which fuel is supplied to the engine followed by delivery of fuel as determined by the pump. <IMAGE>

Description

SPECIFICATION Fuel injection system This invention relates to a fuel injection system for a compression ignition engine, the system including a high pressure pump which in use is operated in timed relationship with an associated engine and a fuel injection nozzle through which fuel is delivered to a combustion space ofthe engine.

It is known that with certain types of compression ignition engine the operation ofthe engine can be improved if a small quantity of fuel is introduced into a combustion chamber of the engine in advance of the main quantity of fuel and art a reduced rate of delivery.

The practical effect of the introduction ofthe small quantity of fuel is to reducethe noise generated by the engine.

It is an object ofthe present invention to provide a fuel injection system ofthe kind specified in a form in which an initial quantityoffuel is delivered through thenozzleata reduced ratefollowed bythemain quantity of fuel.

According to the invention a fuel injection system of the kind specified comprises a body defining first and second coaxial cylinders, the first cylinder having a larger diameterthan the second cylinder, first and second pistons slidable within the cylinders respectivelythe one end ofthe first cylinder remote from the second cylindercommunicating with an outlet of said pump and the one end of the second cylinder remote from thefirst cylinder communicating with said nozzle,aspill portformed inthewall ofthefirst cylinder, said port being positioned to be covered by the first piston during the movement ofthe pistons underthe action of liquid under pressure supplied by said pump, and a bypass path which can be opened between the one end ofthe second cylinder and the other end of the first cylinder during movement of the pistons by the action of liquid under pressure, said bypass path being opened before closure ofthe spill port by said first piston, the arrangement being such thatthe initial flow of fuel to the injection nozzle is effected by said second piston until the bypass path is opened, the flow of fuel to the nozzle then being halted until the spill port is covered by the first piston,the flow of fuel to the nozzlethen being efected by said first piston.

An example of a fuel injection system in accordance with the invention wili now be described with referenceto the accompanying diagrammatic drawing.

With reference to the drawing the fuel system includes a high pressure pump 10 which in use is driven in timed relationship with an associated engine. The pump may be of the conventional type of fuel pump either of the rotary distributortype or of the in-line type. Also shown in the drawing is a fuel injection nozzle 11 which is mounted in the cylinder head ofthe associated engine to direct fuel into a combustion space of the engine.

There is additionally provided a body 12 which defines a pair of coaxial cylinders, the first cylinder 13 being larger in diameterthan the second cylinder 14.

The second cylinder opens into a space 15 which communicates with the injection nozzle 11. Located in the cylinders 13, 14 respectively are a pair of pistons 16,17 the pistons being in end to end engagement.

The end ofthe first cylinder 13 remote from the second cylinder communicates with an outlet of the pump 10 and the pistons are biased towards this end of the cylinder 13 by means of a coiled compression spring 18which is located in the chamber 15.

Formed in the wall ofthe cylinder 13 is a spill port 19 which communicates with a source offuel 20 at low pressure. The source of fuel also communicates with the chamber 15 by way of a non-return valve 21 arranged to permitfuel flow into the chamber 1 Sfrom the source 20.

The port 19 is positioned to be covered by the piston 16 during its movement againstthe action of the spring 18 and in addition, a bypass path is provided which after a predetermined movement of the pistons against the action of the spring, connects the end of the cylinder 13 adjacent the cylinder 14, with the space 15. In the example this bypass path is defined by a groove or grooves 22 which are formed on the piston 17. The extent of movement of the pistons underthe action ofthe spring 18 is limited by means of a stop which is shown diagrammatically at 23.

In operation, when liquid under pressure is deli vered bythepump l0thepistonsl6and l7startto move against the action of the spring 18. The piston 17 displaces fuel from the chamber 15 to the injection nozzle 11 and the flow of fuel is at a reduced rate as compared with the delivery of the pump 10 by virtue of thefactthatthe piston 17 is smaller in diameterthan the piston 16. Fuel displaced by the piston 16 flows through the spill port 19 backto the source of fuel 20 and during delivery offuel to the nozzle, the valve 21 is closed. The delivery of fuel in this manner continues until the grooves are exposed to the chamber 15.

When this occurs the fuel pressure in the chamber 15 is reduced to that of the source and a spring loaded valve in the injection nozzle closes to preventfurther flow offuel to the engine. As the pistons continue to move a pointwill be reached atwhich the spill port 19 is closed by the piston 16 and further movement againstthe action ofthe spring 18 causes fuel to be displaced once again to the injection nozzle and hence to the associated engine. The flow of fuel once the spill port 19 has been covered is at a increased rate and is equal to the rate of displacement of liquid by the pump 10.

When delivery of fuel by the pump ceases an unloading valve inthe pump 10 ailowsfuelto be displaced backtowardsthe pump, this displacement being effected by means of the spring 18. During displacement of the pistons the valve 21 opensto permit fuel to flow into the chamber 15. As soon as the port 19 is uncovered fuel can flow into the cylinder 13 and the pressure of fuel acting on the piston 16 assists the action ofthe spring.

It will be appreciated thatthe maximum displacement of the pistons must be at least equal to and preferably greater than the maximum displacement of the pump 10. Furthermore, itwill be appreciated that if the pump 10 is set to deliver a small volume of liquid, the movement of the pistons may not be sufficientto cover the spill port 19. lnthissituation all the fuel delivered to the engine would be at a reduced rate.

The quantity offuel delivered in this case may not be sufficientto cause operation ofthe engine and in most cases there will be a need to supply some fuel at the increased rate. With the arrangement described there is an interval between the termination ofdelivery of fuel atthe low rate and the commencement of fuel deliveryatthe high rate and this interval can be controlled by adjusting the lengths ofthe grooves 22 and/orthe position of the spiil port 19.

The non-return valve 21 may be replaced by a port controlled bythe piston 17, the port being covered during the initial movement of the pistons.

Claims

1. Afuel injection system for a compression ignition engine, the system including a high pressure pump which in use is operated in timed relationship with an associated engine and a fuel injection nozzle through which fuel is delivered to a combustion space of the engine, the system further including a body defining first and second coaxial cylinders, the first cylinder having a larger diameterthanthe second cylinder,firstandsecond pistons slidablewithin the cylinders respectively the one end ofthe first cylinder remotefrom the second cylinder communicating with an outletofsaid pump and the one end ofthe second cylinder remote from the first cylinder communicating with said nozzle, a spill portformed in the wall of the first cylinder, said port being positioned to be covered by the first piston during the movement of the pistons underthe action of liquid under pressure supplied by said pump, and a bypass path which can be opened between the one end ofthe second cylinder and the other end ofthe first cylinder during movement of the pistons by the action of liquid under pressure, said bypass path being opened before closure ofthe spill port by said first piston, the arrangement being such thatthe initial flow of fuel to the injection nozzle is effected by said second piston until the bypass path is opened,theflowoffueltothe nozzle then being halted until the spill port is covered by the first piston, the flow of fuel to the nozzle then being effected by said first piston.

2. A system according to Claim 1 including resilient means biasing the pistons towards the one end of thefirst cylinder, and valve means through which fuel can be admitted to the one end of the second cylinder during movement of the pistons underthe action of said resilient means.

3. Asystem according to Claim 2 including a source of fuel at low pressure, said source being connected to the one end of the second cylinder through said valve means.

4. Asystem according to Claim 3 in which said valve means comprises a non return valve.

5. Asystemaccordingto Claim3inwhichsaid valve means comprises a port formed in said second cylinder said port communicating with said source, said port being covered by said second piston during the initial movement of the pistons under the action of fuel under pressure supplied by the pump.

6. A system according to any one of the preceding claims in which said bypass path comprises a groove formed on the second piston, said groove being uncovered to the opposite ends of said second cylinder after a predetermined movement of the pistons under the action offuel under pressure supplied by the pump.

7. Asystem according to any one of the preceding claims including a stop to limitthe movement of the pistons towards the one end ofthe first cylinder.

8. Afuel injectionsystemfora compression ignition engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawing.