EP0611117A1

EP0611117A1 - Fuel pumping apparatus

Info

Publication number: EP0611117A1
Application number: EP94300867A
Authority: EP
Inventors: George Nicholas Felton
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1993-02-12
Filing date: 1994-02-04
Publication date: 1994-08-17
Also published as: GB9302840D0; JPH06294360A

Abstract

A fuel pumping apparatus of the rotary distributor type includes a distributor member (12) having a delivery passage (21) which can communicate with outlet ports in turn to distribute fuel to the injection nozzles of an engine in turn. The distributor member also includes a balance passage (50) which can also register with the outlet ports in turn. The balance passage communicates with a source of fuel so that intermediate deliveries of fuel to each outlet, the pressure in that outlet is reduced to that of the source.

Description

This invention relates to fuel pumping apparatus for supplying fuel to a multi-cylinder compression ignition engine and of the kind comprising a housing, a rotary distributor member journalled in the housing, a plurality of outlet ports formed in the housing and opening onto the periphery of the distributor member at angularly spaced positions about the axis of rotation thereof, a plurality of outlets in the housing, said outlets being connected by outlet passages to the outlet ports respectively and in use being connected to respective injection nozzles of an associated engine, a high pressure fuel pump in the housing, said high pressure fuel pump including a pumping chamber and a cam actuated pumping plunger which is driven inwardly in timed relationship with the associated engine, to pressurise the fuel in said pumping chamber, a delivery passage in the distributor member, the delivery passage communicating with the pumping chamber and being arranged to register in turn with the outlet ports so that fuel is supplied to the injection nozzles in turn during successive inward movements of the pumping plunger, means for controlling the quantity of fuel delivered to the engine, and a low pressure pump for supplying fuel to the pumping chamber during the outward movement of the pumping plunger, the low pressure pump including a rotor.
An example of such an apparatus is seen in EP-A-0383546 in which the pump member is in the form of a pair of plungers which are driven inwardly by the action of cam lobes formed on the internal peripheral surface of a cam ring. The bore which accommodates the plungers is formed in the rotary distributor member and the apparatus includes a spill valve operable during inward movement of the plungers to spill fuel from the pumping chamber thereby to terminate the delivery of fuel to the associated engine.
The pressure at which fuel is being supplied to modern engines tends to be increasing in order to satisfy exhaust emission requirements. Furthermore, in order to ensure rapid closure of the pressure actuated valves in the fuel injection nozzles again to minimise pollutants in the engine exhaust, the flow area of the spill valve is such as to ensure a rapid reduction in the pressure in the pumping chamber and therefore in the connected outlet port, outlet, the pipeline which is connected between the outlet and the fuel injection nozzle, and the fuel injection nozzle itself. The rapid reverse flow of fuel can lead to over or under pressurisation of the fuel in the fuel column between the outlet port and the nozzle when the delivery means has moved out of register with the outlet port. The over or the under pressurisation can result in irregularity in the volume of fuel delivered to the engine. Such an irregularity can occur even when unloading delivery valves or other valves are mounted in or adjacent the outlets.
The object of the present invention is to provide an apparatus of the kind specified in an improved form.
According to the invention in an apparatus of the kind specified there is provided in the distributor member, a balance passage which opens onto the periphery of the distributor member to register in turn with said outlet ports, said balance passage communicating with a source of fuel whereby intermediate successive deliveries of fuel through each outlet port, the outlet port will be brought into register with the balance passage so that the pressure at the outlet port will be stabilized at the pressure of said source of fuel.
In the accompanying drawings:-

Figure 1 is a diagrammatic part sectional view of the apparatus, and
Figure 2 is a view to an enlarged scale of a practical embodiment of part of the apparatus seen in Figure 1.

Referring to the drawings, the apparatus comprises a body 10 in which is mounted a fixed sleeve 11 defining a bore to receive a rotary cylindrical distributor member 12. The distributor member has an enlarged diameter portion projecting from the bore and in use is driven in timed relationship with an associated engine.
Formed in the enlarged portion of the distributor member is a transverse bore 13 in which is mounted a pair of pump members in the form of plungers 14 the outer ends of which engage cam followers 15 each cam follower comprising a shoe 16 and a roller 17. The rollers engage the internal peripheral surface of an annular cam ring 18 which is mounted within the body 10. The angular position of the cam ring is adjustable by means of a fluid pressure operable spring biased piston 19, in known manner.
On the internal peripheral surface of the cam ring there is formed a plurality of pairs of cam lobes which extend from the base circle of the cam ring. As the distributor member rotates, the rollers engage with the leading flanks of the cam lobes to impart inward movement to the pumping plungers 14. The portion of the bore 13 intermediate the plungers forms the pumping chamber of a high pressure pump and is in communication with a longitudinal passage 20 which at one point communicates with a delivery passage 21 positioned to register in turn with a plurality of outlet ports 22 formed in the sleeve and connected by outlet passages 22A to outlets 23 respectively which are connected in use to the injection nozzles of the associated engine. The delivery passage is positioned close to the end of the distributor member remote from the enlarged portion. There may be provided in the outlet passages 22A, so called unloading delivery valves which act to allow the return of a predetermined quantity of fuel from the pipelines connecting the outlets to the injection nozzles when delivery of fuel closes. As an alternative the outlet passages 22A may incorporate so called snubber valves which act to damp the return flow of fuel towards the pump in order to reduce the risk of cavities forming in the pipelines and the nozzles.
At another position the passage 20 is in communication with a plurality of radially disposed inlet passages 24 which are positioned to register in turn with inlet ports 25 formed in the sleeve 11 and communicating by way of an on/off valve 26, with the outlet of a low pressure fuel supply pump 27 having a fuel inlet 28. Although not shown, the inlet and outlet of the supply pump 27 are interconnected by way of a relief valve and the rotary part of the pump is coupled to the distributor member. By reason of the relief valve, the output pressure of the low pressure pump 27 varies in accordance with the speed at which the distributor member is driven and the aforesaid piston 19 is subjected to the outlet pressure of the low pressure pump so that the angular setting of the cam ring 18 depends upon the speed of the associated engine.
The passage 21 is arranged to register with an outlet port 22 during the whole time the plungers 14 are moved inwardly so that fuel displaced from the bore 13 can flow to the associated engine. As the distributor member rotates and after the rollers have moved over the crests of the cam lobes, the passage 21 moves out of register with an outlet port 22 and an inlet passage 24 moves into register with an inlet port 25. Fuel is therefore supplied to the bore 13 from the outlet of the low pressure pump and the plungers 14 are moved outwardly to their maximum extent so that the rollers engage the base circle of the cam ring.
As described there is no method of controlling the quantity of fuel supplied through an outlet 23. In order to achieve the desired control, there is provided a further transverse bore 29 in the enlarged portion of the distributor member and located in the bore is a pair of further or auxiliary plungers 30 the outer ends of which engage the shoes 16 so that the auxiliary plungers are moved inwardly at the same time as the pumping plungers. The bore 29 is in constant communication with a circumferential groove 31 formed in the periphery of the distributor member and this groove is in constant communication with one end of a shuttle cylinder 32 which for convenience is defined by the bore of a sleeve 33 which is angularly adjustable within the housing 10 but is restrained from axial movement. Slidable within the shuttle cylinder 32 is a shuttle 34 which is biased by a spring 34A towards the one end of the cylinder.
Formed in the sleeve 33 is a pair of axially spaced ports 36 and 37. The port 36 is in constant communication with a circumferential groove 38 formed on the distributor member whilst the port 37 is in constant communication with a port 39 which is formed in the sleeve 11 and which opens onto the periphery of the distributor member at a position to register with the inlet passages 24. The registration of the port 39 with an inlet passage 24 is arranged to occur during the time the pumping plungers 14 are moved inwardly. The shuttle 34 is provided with a groove 40 which is in constant communication with the port 36 and extending from the groove 40 is an inclined groove 41 which as will be explained, is positioned to register with the port 37 after a predetermined movement of the shuttle. The shuttle is angularly adjustable and for this purpose is provided with an arm 42 which is coupled to an actuating mechanism in the form of a governor 42A. By moving the shuttle 34 angularly the extent of movement of the shuttle away from said one end of the cylinder before the port 37 is brought into register with the groove 41, can be adjusted.
Also provided is a normally closed spill valve generally indicated at 43 and including a piston 44 which is housed within a cylinder 45 defined in an extension of the distributor member 12. The piston 44 is integral with a valve member 46 which co-operates with a seating defined in the end wall of the cylinder 45, the seating being located at one end of a passage 47 which communicates with the pumping chamber. The piston 44 is biased by a spring 48 so that the valve member 46 engages with the seating and the spring is sufficiently strong to ensure that the valve member 46 is held in sealing engagement with the seating.
Operation starts with the items in the positions shown in Figure 1 which corresponds to the commencement of inward movement of the pumping plungers 14 and the auxiliary plungers 30. As the distributor member rotates the plungers 14 will displace fuel from the bore 13 and delivery of fuel to the associated engine will take place through an outlet 23 and if provided, the delivery valve opens to allow fuel flow. At the same time the auxiliary plungers 30 are moved inwardly and fuel is displaced into the inner end of the cylinder 32 containing the shuttle 34. The shuttle therefore starts to move against the action of the spring 34A and this movement will continue so long as the auxiliary plungers are moved inwardly. At some point during the movement of the shuttle the port 37 is brought into register with the groove 41 and fuel at the high pressure developed in the pumping chamber by the plungers 14 is supplied to the inner end of the cylinder 45 and this fuel acts upon the piston 44 to urge the piston against the action of the spring 48. As soon as the piston 44 starts to move, the valve member 46 is lifted from its seating and the remaining fuel which is displaced by the plungers 14 can flow into the cylinder 45 through the passage 47 thereby displacing the piston 44 against the action of the spring 48. As soon as the valve member 46 moves away from the seating the pressure in the pumping chamber falls rapidly as also does the pressure in the passages 20, 21 and the outlet port 22 and the pipeline connecting the outlet 23 to the nozzle. The rapid reduction in pressure allows rapid closure of the valve member in the nozzle. If a delivery valve is fitted, this valve allows a predetermined volume of fuel to flow back to the outlet port before it closes. By varying the angular position of the shuttle 34 the extent of movement of the shuttle before the port 37 registers with the groove 41 can be controlled and therefore the position during the inward movement of the plungers 14 at which the valve 43 is opened. Thus by moving the shuttle angularly the quantity of fuel which can be supplied to the associated engine can be varied. As stated, the arm 42 is connected to the governor 42A which will be either of the so-called all-speed type or the so-called two-speed type. The sleeve 33 can also be moved angularly and two ways of achieving this are illustrated. In the first case a fluid pressure operable piston 59 is provided, the piston being spring biased against the action of the outlet pressure of the low pressure pump. By connecting the piston to the sleeve 33, so called torque control can be obtained. Another way of moving the sleeve is by means of an air pressure responsive diaphragm 60 which is responsive to the pressure of air delivered to the associated engine, the piston 59 and the diaphragm 60 can if desired, both be provided to control the position of the sleeve.
When the plungers have completed their inward movement the plungers can then move outwardly and fuel is returned from the one end of the cylinder 45 to the bore 13 by movement of the piston 44 by the spring 48. In addition the passage 21 moves out of register with the outlet port. However, since fuel may have been supplied to the associated engine, fuel is supplied through one of the inlet passages 24 to the bore 13 to ensure that the plungers move outwardly their maximum extent. The shuttle 34 will also be urged towards the inner end of the cylinder 32 displacing fuel back to the bore 29. Any additional fuel which is required to make up for leakage, is supplied by means of auxiliary filling ports 61 connected to the outlet of the fuel supply pump and communicating at the appropriate time, with a passage 62 in the distributor member and which is in communication with the bore 29. The plungers 30 are moved outwardly to their maximum extent.
As stated the rapid reduction in pressure which takes place when the spill valve 43 is opened can lead to over or under pressurisation of the fuel in the fuel column which extends between the outlet port 22 and the fuel injection nozzle, when the delivery passage 21 has moved out of register with the outlet port. In the case where an unloading delivery valve is provided the over or under pressurisation exists in the portions of the fuel column on opposite sides of the delivery valve. If the degree of over or under pressurisation were the same for the fuel columns associated with each of the outlet ports the quantity of fuel supplied to the engine at each delivery would be the same. Unfortunately in practice the conditions in each column of fuel tend to be different and furthermore vary. It is proposed therefore to connect each outlet port 22 in turn to a source of fuel at a substantially constant pressure between deliveries of fuel through the port. Conveniently this source of fuel is near to the distributor member.
As stated and as shown in Figure 2, the delivery passage 21 is located adjacent the end of the distributor member remote from the enlarged portion thereof and mounted on the end of the distributor member so as to rotate therewith is the rotor 51 of the low pressure pump 27. The rotor is provided with a plurality of radial slots in which are slidable vanes 52 respectively and these are outwardly biased into engagement with the internal surface of a cam ring 53 secured in the body 10. Within the rotor and communicating with the inner ends of the slots is a space which is connected to the outlet of the low pressure pump. The fuel pressure in the space acts on the inner edges of the vanes to provide the main outward biasing force the remaining biasing force being provided by light springs.
There is also provided in the distributor member a balance passage 50 and this is drilled from the end of the distributor member at an angle to the axis of rotation thereof. The passage breaks out onto the cylindrical surface of the distributor member at a position so that it can register in turn with the outlet ports 22. The other end of the balance passage 50 is in communication with said space. The balance passage is positioned so that when the delivery passage 21 is in register with an outlet port 21, the balance passage will be in register with one of the other outlet ports. The communication of the balance passage with an outlet port provides the desired equalisation and stabilization of the pressures in the fuel columns between the outlet ports and the delivery valves and if no such valves are provided or if snubber valves are provided, the associated pipelines.
It is desirable that the communication of the balance passage with an outlet port should only take place when there is no other demand for fuel from the low pressure pump. This is not so as to avoid the fluctuations in the outlet pressure of the low pressure pump which will occur when for example fuel is being supplied to the pumping chamber of the high pressure pump, but to avoid having to increase the size of the low pressure pump.
The invention is also applicable to distributor type pumps in which quantity of fuel supplied to the engine is effected by control of the amount of fuel which is drawn into the pumping chamber during the filling stroke of the pump.

Claims

A fuel pumping apparatus for supplying fuel to a multi-cylinder compression ignition engine comprising a housing (10, 11), a rotary distributor member (12) journalled in the housing, a plurality of outlet ports (22) formed in the housing and opening onto the periphery of the distributor member at angularly spaced positions about the axis of rotation thereof, a plurality of outlets (23) in the housing, said outlets being connected by outlet passages (22A) to the outlet ports (22) respectively and in use being connected to respective injection nozzles of an associated engine, a high pressure fuel pump in the housing, said high pressure fuel pump including a pumping chamber and a cam actuated pumping plunger (14) which is driven inwardly in timed relationship with the associated engine, to pressurise the fuel in the pumping chamber, a delivery passage (21) in the distributor member, the delivery passage communicating with the pumping chamber and being arranged to register in turn with the outlet ports (22) so that fuel is supplied to the injection nozzles in turn during successive inward movements of the pump member (14), means (34) for controlling the quantity of fuel delivered to the engine and a low pressure pump (27) for supplying fuel to the pumping chamber during the outward movement of the pump member (14) the low pressure pump including a rotor (51), characterised by a balance passage (50) formed in the distributor member (12) and opening onto the periphery of the distributor member to register in turn with said outlet ports (22), said balance passage communicating with a source of fuel whereby intermediate successive deliveries of fuel through each outlet port, the outlet port will be brought into register with said balance passage so that the pressure at the outlet port will be stabilized at the pressure of said source of fuel.
An apparatus according to Claim 1, characterised in that said source of fuel is near the distributor member.
An apparatus according to Claim 1, in which said rotor (51) is secured to one end of the distributor member to rotate therewith, characterised in that said balance passage (50) communicates with a space defined in the rotor, said space containing fuel under pressure and forming said source of fuel.
An apparatus according to Claim 3, in which said delivery passage (21) is located adjacent said one end of the distributor member characterised in that the balance passage (50) opens onto the periphery of the distributor member in the same axial plane as the delivery passage and extends within the distributor member at an angle to the axis of rotation thereof to said end of the distributor member.
An apparatus according to Claim 3, characterised in that said space is in communication with the outlet of the low pressure pump (27) and that the communication of the balance passage (50) with an outlet port (22) takes place only during the period of communication of the delivery passage (21) with another outlet port.