GB2119030A - Fuel pumping apparatus - Google Patents

Abstract

A fuel pumping apparatus of the rotary distributor type has a distributor 12 which has passages 23 connected to a bore 18 containing pumping plungers 17. The plungers 17 are actuated by varying rate cam lobes on a cam ring 36. One of the passages 23 can register with a spill port 29 formed in a sleeve surrounding the distributor member. A spill valve 31 is provided to control flow through the spill port so that the amount of fuel supplied by the apparatus can be varied and also the rate of fuel delivery can be varied by cam actuating means 37 enabling the utilisation of different parts of the cam lobes. <IMAGE>

Description

SPECIFICATION Fuel pumping apparatus This invention relates to a rotary distributor fuel pumping apparatus ofthe kind comprising a pumping plunger contained within a bore, cam means operable to impart inward movement to the pumping plunger, the distributor member acting to place said bore in communication with outlet ports in turn whereby fuel will be delivered to the outlet ports in turn during successive inward movements of the plunger.

Such apparatus is well known in the art and there are many variations. For example apparatus is known in which a throttle or other means is used to control the amountoffuel supplied to the bore during the filling period thereof. With this arrangement the timing ofthe start of fuel delivery varies as the quantityoffuel isvaried sincethe end ofthefuel delivery always occurs atthe sametime. Such apparatus is usually provided with an adjustable cam meanswherebythevariation ofthe start of fuel delivery which takes place with varying fuel quantity, can be compensated for, the cam means also providing for desired timing adjustmentto suitthe operating requirements ofthe engine to which fuel is supplied.

Another form of apparatus is known in which the bore is completely filled with fuel during the filling period thereof and in orderto control fuel quantity some fuel is spilled from the bore during the inward movement ofthe plunger. The fuel can be spilled utilising a spill muff on the distributor member and it can be arranged that the timing of fuel delivery is independent on the quantity of fuel supplied but that timing variation can be achieved using the muff. The muff adds to the length ofthe distributor member and introduces additional leakage paths.

In a furtherform of the apparatus fuel can be spilled using a distributor member which is also reciprocable and forms the pumping plunger. A spill port is provided which hasto be covered bythedistributor member during its initial axial movement by the cam means. This form of apparatus gives constant start of injection irrespective offuel quantity and timing variation is effected by altering the setting of the cam means.

The profile of the active or leading flank of the cam means determines the rate atwhich fuel is supplied by the apparatus since it determines the rate of inward movement ofthe plunger. In mostforms of apparatus the actual profile of the leading flank has to be chosen to achieve the best overall performance. For some modern engines however it is required that both the timing and the rate of fuel delivery should be variable during operation of the engine and the object of the present invention is to provide an apparatus ofthe kind specified in a form in which this can be achieved.

According to the invention an apparatus ofthe kind specified comprises means for adjusting the setting of the cam means whereby the instant of inward movement ofthe plunger can be altered in relation to a drive shaft of the apparatus, a spill port positioned to communicate with said bore, and valve means for controlling the flow of fuel through said spill port, said cam means including active or leading flanks having a varying rate whereby the timing of delivery of fuel and the rate of fuel delivery can be altered during use of the apparatus and the fuel quantity is determined by the period during the inward stroke of the plunger during which the spill port is closed.

One example of a fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure lisa sectional side elevation of the apparatus; and Figure 2 is a diagram showing the profile of a cam lobe forming part of the apparatus.

Referring to the drawings the pumping apparatus comprises a housing generally indicated at 10 and which accommodates a fixed sleeve 11 which defines a bore in which is housed a rotary cylindrical distributor member 12. The distributor member is coupled to a drive shaft 13 which extends to the exterior ofthe housing for connection in use to a rotary part of the associated engine to which fuel isto be supplied by the apparatus. The drive shaft mounts an annular member 14, this being coupled to the drive shaft by splines and the member extends about an enlarged portion of the distributor member. The annular member defines a pair of slots which accommodate shoes 15 mounting rollers 16 respectively.The shoes engage the outer ends respectively of pumping plungers 17 which are housed in a transverse bore 1 8formed in the distributor member and which communicates with a longitudinal passage 19.

The passage 19 at one point, communicates with a delivery passage 20 which can register in turn with outlet passages 21 only one of which is shown, formed in the sleeve 11 and which communicate with outlets 22 formed in the housing. The outlets 22 in use, are connected to the injection nozzles respectively ofthe associated engine. The passage 19 also communicates with a plurality of inlet'spill passages 23 which extend to the periphery ofthe distributor member.

The apparatus also includes a low pressure supply pump 24 which has an outlet connected to a supply passage 25 formed in the sleeve 11. The pump 24 has an inlet which is connected to a fuel inlet 26 ofthe apparatus and a relief valve generally indicated at 27 is provided to control the outlet pressure ofthe supply pump. The supply passage 25 communicates with an inlet port 28 which opens onto-the periphery of the distributor member at a position such that the passages 23 can register therewith. Also formed in the sleeve is a spill port 29 and this is also positioned so thatthe passages 23 can registertherewith.Flow of fuel through the spill port is controiled by a spill valve generally indicated at 30 and which includes a valve member31 biasedto an open position by means of a spring 32, the valve can be moved to the closed position by supplying electric currentto an electro magnetic device generally indicated at 33 and which includes an armature 34 coupled to the valve member 31. Fuel which flows pastthe valve member 31 flows to an outlet 35 on the housing.

In order to effect inward movement ofthe plungers 17, the rollers 16 engage with the internal peripheral surface of an annular cam ring 36 iocated within the housing and which can be moved angularly aboutthe axis of rotation of the distributor member, by means of an actuating device 37. The device 37 may be operated byfuel under pressure from the outlet ofthe supply underthecohtrol for example of an electromagnetically operated valve.

The cam lobes on the cam ring 36 are disposed in pairs and there are as many lobes as there are outlet ports 22 and passages 23. The profiles ofthe leading flanks ofthe cam lobes are shown in Figure 2 and it will be seen thatthey are of the so-called variable rate type. In Figure 2 plungermovementis plotted vertically while the relative angular movement of the roller and cam lobe is plotted horizontally. As will be seen from Figure 2 depending upon which part ofthe cam profile is used, the amount of movement ofthe plungerandhencethequantityoffuel delivered bythe apparatus, will varyfora given relative angular movement ofthe distributor member and cam means.

Thus itwill be seen from the diagram that differing quantities 01, Q2 can be obtained forthe same relative angularmovementT. Itwill be appreciated thatthe quantity Q2 being largerthan Q1 there is an increased rate of fuel delivery. Conversely if the quantities are maintained the same then the periods will differ.

Considering now the operation of the apparatus. As shown, a passage 23 is in communication with the inlet port 28 and this represents thefilling phase of the apparatus. Fuel is supplied to the bore 18 atan unrestricted rateandthe plungers 17are moved outwardlytheirmaximum extent as determined by contact ofthe rollers 16 with the internal peripheral surface ofthe cam ring or alternatively by suitable stops. As the distributor member rotates the passage 23 will move out ofregisterwith the inlet port 28 and the delivery passage 20 will move into register with an outlet 21. In addition, a passage 23 will move into registerwith the spill port 29.Moreover, the rollers 16 startto move up the leading flanks ofthe respective cam lobes so that fuel is displaced from the bore 18 and flows into the longitudinai passage 19. If the spill valve 30 is closed then fuel will flow through the delivery passage 20to an outlet 21 and hence to the associated engine. If during the inward movement of the plunger 17, the valve 30 is opened the flow-of fuel through an outlet 22 will cease and the fuel will then flowthrough the spill port 29 and to the outlet 35 for re-introduction into the fuel system. A passage 23 will be in register with the spill port 29 during the whole timethe plungers can partake of inward movement.

The period of closure ofthe spill valve 30 deter mines the amount of fuel which is supplied to the associated engine. Moreover, the instant of closure of the valve determinesthetiming ofthe start of delivery fuel. If the valve is closed later during the inward movement of the plungers then as will be seen from Figure 2, the rate of fuel delivery is high whereas if the valve is closed earlier, at least the initial rate offlow of fuel will be reduced. If spill valve 30 is operated at the same time during each cycle, angularadjustment ofthecam ring 36wi11 determine whetherthe fuel is supplied at a low or high rate. It is clearly necessary in this case, to adjustthetime during which the spill valve is closed in accordance with the rate of fuel deliveryto ensure that the fuel quantity remains the same.

The operation ofthe spill valveand alsothecam actuating mechanism 37 are best effected b means of an electronic control circuit. In orderforthísto function with the required accuracy, it is necessaryfor the control circuitto be supplied with signals indica tive ofthe angular position of the distributor member and this is achieved in the particular example, by means ofatransducer38which providessignalsto the control system as teeth formed on a toothed wheel 39 mountedonthe member 14, movepastthe transducer.

Claims (6)

1. A rotary distributorfuel pumping apparatus comprising a pumping plunger contained within a bore, cam means operable to impart inward movementto the pumping plunger, said distributor member acting to place said bore in communication with outlet ports in turn so thatfuel will be delivered to the outlet ports in turn during successive inward movements ofthe pumping plunger, means for adjusting the setting of the cam means wherebythe instant of inward movementofthe plunger can be altered in relation to a drive shaft of the apparatus, a spill port position to communicate with said bore, and valve means for controlling theflow offuel through said spill port, said cam means including active or leading flanks having a varying ratewherebythetiming of deliveryoffuel and the rateoffuel delivery can be altered during use ofthe apparatus and the fuel quantity is determined bythe period during the inward stroke of the plunger, during which the spill port is closed.

2. An apparatus according to Claim 1 in which said spill port is formed in a sleeve surrounding the distributor member, the distributor member having passages communicating with said bore and positioned to register in turn with said spill port.

3. An apparatus according to Claim 2 in which saidvalve means is located in part mounted on a housing carrying said sleeve.

4. An apparatus according to Claim 1 or Claim 2 in which said valve means is electrically operated.

5. An apparatusaccordingto Claim 1 including means for adjusting the angular position of the cam means about the axis of rotation ofthe distributor member.

6. A rotary distributorfuel pumping apparatus comprising the combination and arrangement of parts substantially as herein before described with reference to the accompanying drawings.