GB2253445A

GB2253445A - Fuel pumping apparatus

Info

Publication number: GB2253445A
Application number: GB9104792A
Authority: GB
Inventors: Christopher Stringfellow; Arthur James York
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1991-03-07
Filing date: 1991-03-07
Publication date: 1992-09-09
Also published as: GB9104792D0

Abstract

Fuel injection pumping apparatus includes a spill passage 21 in communication with the pumping chamber and controlled by a valve member 22 defined on a piston 23 which is slidable in a cylinder 19. The valve member is biased into engagement with a seating about the spill passage 21, by means of a spring 24. The valve member 22 is movable away from the seating by fluid under pressure supplied through a passage 34 to the cylinder, and the spilled fuel flows into the cylinder to further displace the piston. A restricted orifice 30A is provided to damp the movement of the piston 23 and the valve member. <IMAGE>

Description

FUEL PUMPING APPARATUS This invention relates to a liquid fuel injection pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a plunger reciprocable within a bore, a cam for imparting inward movement to the plunger, an outlet from the bore and through which fuel can flow to an outlet port of the apparatus, a valve seating defined about a spill passage connected to the bore, a piston slidable within a cylinder, a valve member defined on the piston, the valve member being shaped for cooperation with the seating and being urged into engagement therewith by resilient means, a drilling formed in the piston, the inner end of said drilling communicating with said spill passage, a plug slidable in said drilling, the area of said drilling being comparable to the area of the valve seat so that the valve member is substantially pressure balanced and means for applying fluid pressure to said piston to lift the valve member from the seating thereby to spill fuel from the bore, the spilled fuel flowing into said cylinder to assist the movement of the valve member away from the seating.

An apparatus of the aforesaid kind is known from EP 0413453. The provision of the plug and the attendant pressure balancing of the valve member allows the resilient means or spring which biases the piston to be only slightly stronger than is necessary to return the valve member into contact with the seating after the completion of the inward movement of the plunger. As a result when the valve member is lifted from the seating during inward movement of the plunger, the piston and valve member move very quickly to reduce the pressure in the bore and in the passages of the apparatus and the pipeline connecting the outlet port to the associated fuel injection nozzle of the engine.Whilst rapid reduction of the pressure in the bore is desirable in order that there should be a sharp cut off in the flow of fuel through the nozzle to obtain optimum exhaust emissions, it is found that too rapid a reduction of the pressure can lead to so called nozzle "blow by" in which combustion gases flow through the spray orifice or orifices of the nozzle into the various chambers and passages in the nozzle and it is also possible for cavities to be formed within the apparatus leading to cavitation erosion. Both these effects are undesirable and the object of the invention is to provide an apparatus of the kind specified in an improved form.

According to the invention an apparatus of the kind specified comprises a restricted orifice through which fluid displaced by the piston during the movement of the piston and valve member away frcm the seating flows, the restricted orifice acting to damp the movement of the piston.

An example of a fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawing which is a part sectional side elevation of a portion of the apparatus.

Referring to the drawing the apparatus comprises a rotary distributor member 10 which is journaled in a fixed sleeve 11 forming part of a body 12. The distributor member in use, is driven in timed relationship with the associated engine. A portion of the distributor member extends from the sleeve and there is formed therein a transverse bore 13 in which is mounted a pair of pumping plungers 14. In the particular example, which shows a pump for supplying fuel to a four cylinder engine, a further transverse bore is provided and a further pair of plungers are located therein in order to increase the pumping capacity of the apparatus.

The bores are disposed at right angles to each other and the inner portions of the bores communicate with a longitudinal passage 15 extending within the distributor member and communicating with an outwardly extending delivery passage 16.

The plungers 14 are arranged to be moved inwardly by the action of cam lobes formed on the internal peripheral surface of a cam ring 17 which surrounds the distributor member and during the inward movement of the plungers 14, the delivery passage 16 registers with one of a plurality of outlet ports 17 which communicate with outlets 18 in the body, the outlets 18 in use being connected to the injection nozzles of the associated engine.

Alternately arranged with the outlet ports 17 are inlet ports 17A which communicate with a source of fuel under pressure, conveniently the outlet of a vane pump 17B the rotary part of which is coupled to the distributor member. In use, during the whole time the plungers are moved inwardly, the delivery passage 16 is in register with an outlet port 17 and fuel can be supplied to the associated engine. As the distributor member rotates, the delivery passage 16 moves out of register with an outlet port 17 and into register with an inlet port so that fuel can now flow to the bores 13 to urge the plungers outwardly by an amount which is determined by the base circle of the cam ring or by stop plates not shown, it being appreciated that normally cam followers including rollers, will be interposed between the plungers 14 and the cam lobes.Instead of using the delivery passage to fill the bores with fuel, separate inlet passages may be provided in the distributor member in which case the inlet ports will not be in the same radial plane as the outlet ports.

piston against the action of the spring. The flow of fuel into the annular space is conveniently controlled by a control valve generally indicated at 32 and which itself is controlled by an electro-magnetic actuator 33.

Supply of electric current to the actuator is under the control of an electronic control system not shown.

Extending from the aforesaid annular space are in the particular example, four axially disposed passages 34 which have radially disposed portions 35 opening onto the periphery of the distributor member at a position so that they can register with a first connecting port 36 formed in the body and sleeve. Also formed in the body and sleeve is a second connecting port 37 which extends from the periphery of the distributor member and the two connecting ports can be placed in communication with each other by the valve 32. The connecting port 37 is positioned to register with passages 38 formed in the distributor member and communicating with the longitudinal passage 15.Within the valve 32, the connecting port 37 is closed by a valve member 39 when the actuator is energised and the pressure of fuel within the connecting port 37 lifts the valve member 39 from its seating to permit flow of fuel into the connecting port 36 and through one of the passages 34 into the annular space when the actuator is de-energised. As previously stated the flow of electric current to the actuator 33 is controlled by an electronic control system and the actuator is arranged to be de-energised when a predetermined inward movement of the pumping plungers has taken place. When the actuator is de-energised fuel at high pressure is supplied to the annular space and this acts upon the end face of the piston to move the piston against the action of the spring 24. The initial movement lifts the valve member 22 from the seating and substantially unrestricted flow of fuel can then take place into the annular space by way of the port 21. This flow of fuel results in a reduction in the pressure of fuel and termination of the flow of fuel to the associated engine.

The valve 32 can have other forms for example, it may comprise a shuttle movable by fuel displaced by a further pair of plungers, the shuttle after a predetermined movement, effecting a connection between the ports 36, 37. The predetermined movement of the shuttle is adjustable to enable control of the quantity of fuel supplied by the apparatus to be effected.

The purpose of the orifice 30A is to provide a restriction to the flow of fuel from the interior of the cap and as a result a dashpot action is created to restrict the rate of movement of the piston. The practical effect of this is to reduce the rate of reduction of pressure in the bore, the various passages within the apparatus, the pipelines connecting the outlets 18 to the associated fuel injection nozzles and the various passages and chambers within the nozzles.

This helps to reduce nozzle "blow by" and cavitation within the apparatus but at the same time by careful choice of the size of the orifice a sufficiently rapid closure of the valve member of the nozzle can be obtained to achieve optimum exhaust emissions.

When the crests of the cam lobes are reached the plungers are allowed to move outwardly and the spring 24 urges the piston towards the position in which it is shown. This movement results in displacement of the fuel spilled into the aforesaid space back into the bores 13 to effect outward movement of the plungers. Such fuel as is lost by leakage together with the fuel delivered to the associated engine, is made up by a flow of fuel from the fuel supply pump by way of an inlet port and the passage 16. In order to ensure that the movement of the piston 23 under the action of the spring 24 is not hindered as the projection approaches the seating, a leakage path may be provided from the annular space.The leakage path is provided by a restricted drilling or it can be formed by ensuring that leakage of fuel can take place along the working clearance defined between the piston and the cylinder in which it is located. In the example the ports 36 and 37 are isolated from the passages 35 and 38 except during the inward movement of the plungers. However, if desired the connections need not be ported so that by maintaining the valve 32 in the open position whilst the piston 23 is returning to the position shown, there will be no need for the aforesaid restricted passage or clearance. In order to prevent the orifice 30A restricting the return motion of the piston and valve member a non-return valve may be provided which opens to by pass the orifice.

As shown in the plug 27 and the extension are formed in one piece. They can however be divided with the plug being biased into contact with the extension.

Moreover, the plug can be biased away from the extension in the direction towards the valve member and in this case the plug moves to absorb the fuel delivered from the bore during the initial inward movement of the-plungers.