GB2283539A - Fuel pumping apparatus - Google Patents

Abstract

A fuel pumping apparatus for supplying fuel to an internal combustion engine includes a pumping plunger (16) movable inwardly by a cam (19) to deliver fuel to an outlet. A spring biased hydraulically actuated spill valve (25) is provided and is movable by hydraulic pressure to its open position to allow fuel to spill from the bore. The hydraulic pressure is delivered from the bore (15) containing the pumping plunger and its application to the spill valve via passages (21), (38), (37) and (33) is controlled by a control valve (35). A fuel supply valve (44) is interposed between a source (48) of fuel under pressure and the control valve (35) and includes a valve member (45, Fig. 2) biased to the open position to allow fuel flow to and from the bore (15) when the control valve (35) is open. When the control valve is closed the valve member (45) of the supply valve (44) is moved to the closed position by the fuel pressure in the bore (15) acting via passages (21), (40) and (52, Fig. 2).

Description

FUEL PUMPING APPARATUS This i-nvention relates to a fuel pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a high pressure pump which is actuated in timed relationship with the associated engine, the high pressure pump including a pumping plunger slidable in a bore and a cam having a leading flank which is operable to move the plunger to displace fuel through an outlet to the associated engine, a hydraulically operable spill valve which can be triggered by a control pressure to an open position to terminate delivery of fuel to the engine, a control valve operable to apply the control pressure to the spill valve, said control pressure being derived from the outlet of the high pressure pump and means for supplying fuel to said bore from a source of fuel under pressure.

It is known in some forms of fuel pumping apparatus to allow some spillage of fuel from the bore before delivery of fuel takes place to the associated engine. This allows for variation of the relative position of the plunger and the leading flank of the cam lobe at which delivery of fuel takes place. By shaping the leading flank the initial rate of delivery of fuel can be varied by choosing the position on the leading flank at which delivery of fuel takes place.

With an apparatus of the kind specified in the opening paragraph of the specification the spill valve is used only to terminate delivery and it cannot be used to control the start of fuel delivery. The object of the present invention therefore is to provide an apparatus of the kind specified in which a controllable amount of fuel can be spilled from the bore before delivery of fuel to the associated engine takes place.

According to the invention an apparatus of the kind specified includes a fuel supply valve comprising a valve member which is biased to an open position to connect the source of fuel with the bore by way of said control valve whereby fuel can flow between said bore and the source of fuel when the control valve is in the open position and passage means through which fuel under pressure from the bore can act on the valve member to move it to the closed position when said control valve is closed.

An example of a fuel pumping apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a part sectional side elevation of the apparatus, and Figure 2 shows to an enlarged scale part of the apparatus seen in Figure 1.

Referring to the drawings the apparatus comprises a multi-part body 10 in which is secured a sleeve 11 within which is mounted a rotary cylindrical distributor member 12. The distributor member extends from the sleeve and is coupled to a rotary drive shaft 13 housed in the body, the drive shaft in use being coupled to a rotary part of the associated engine so that it is driven in timed relationship therewith.

The portion 14 of the distributor member which extends from the sleeve is of enlarged diameter and has formed therein a plurality of diametrically disposed bores 15 in each of which is mounted a pair of pumping plungers 16. At their outer ends the plungers engage cam followers 17 respectively which are guided in slots formed in an annular portion of the drive shaft 13 which extends about the enlarged portion 14 of the distributor member. Each cam follower includes a roller 18 which can engage the internal peripheral surface of an annular cam ring 19 which is mounted in the body and is movable angularly therein in known manner, by means of a fluid pressure operable piston 20.

Communicating with the bores 15 intermediate their ends is an axially disposed passage 21 which communicates with a radially disposed delivery passage 22. The delivery passage is positioned to register in turn with a plurality of outlet ports 23 only one of which is shown, the outlet ports being connected to outlets 24 mounted on the housing. The outlets 24 incorporate delivery valves respectively and in use, are connected to the injection nozzles respectively of the associated engine.

Formed on the internal surface of the cam ring 18 is a plurality of cam lobes each having a leading flank and a trailing flank. As the drive shaft rotates the leading flanks of the cam lobes impart inward movement to the pumping plungers 16 and during inward movement of the pumping plungers the delivery passage 22 is in register with an outlet port 23 so that the high pressure pump constituted by the plungers and the cam lobes, delivers fuel in turn to the outlet ports 23 during successive inward movements of the plungers.

The apparatus also includes a spill valve 25 which includes a valve member 26 mounted on a piston member 27 which is slidably accommodated within a cylinder 28 formed in the enlarged portion 14 of the distributor member. The piston member is biased by a coiled compression spring 29 in a direction towards the closed end of the cylinder 28 and opening into this end of the cylinder is a spill passage 30 which communicates with the bore 15 intermediate the inner ends of the plungers. At its point of entry into the cylinder 28 a seating is defined about the passage 30 and the valve member 26 is shaped for cooperation with this seating. The piston member also defines a central blind drilling the inner end of which communicates with the passage 30 by way of a narrow passage formed in the valve member.Located in the drilling is a balance plunger 31 which is engagable with a stop 32 and which has a diameter slightly larger than the seat diameter of the valve member 26. Opening into the aforesaid end of the cylinder 28 is a pair of passages 33 which communicate with a circumferential groove 34 formed in the periphery of the distributor member. The passages 33 have no direct communication with the bores 15 or the passage 21.

The apparatus includes an electromagnetically operable control valve 35 having a valve member 36 movable into engagement with a seating defined about a passage 37 which communicates with the circumferential groove 34. The valve member 36 when lifted from its seating connects the passage 37 with a further passage 38 which opens into a circumferential groove 39 formed in the periphery of the distributor member and connected to the passage 21 by branch passages 40. The valve member 36 is coupled to an armature 41 of an electromagnetic actuator 42 incorporating a solenoid winding 43.

The apparatus further includes a fuel supply valve which is generally indicated at 44 in Figure 1 and which is shown to enlarged scale in Figure 2. The fuel supply valve includes a valve member 45 slidable within a bore at one end of which there is formed an enlargement which is connected by means of a passage 46 to the circumferential groove 34.

At the one end of the bore there is formed a seating about a passage 47 which as shown in Figure 1, is connected to a low pressure fuel supply pump 48. Conveniently this pump includes a rotary part which may be mounted on the distributor member or the drive shaft. At the end of the bore opposite to the seating, there is formed an enlarged chamber 49 which is closed by a plug 50. The plug serves as an abutment for the valve member and the latter is biased towards the plug by means of a coiled compression spring 51. In addition, the chamber 49 is connected to the circumferential groove 39 by way of a passage 52.

Considering now the operation of the apparatus. The various parts of the apparatus are shown at the commencement of inward movement of the pumping plungers 16 with the passage 22 in communication with an outlet port 23 and with the control valve 35 in the open position and with the fuel supply valve 44 also in the open position. As the plungers move inwardly fuel displaced from the bore 15 can flow by way of the control valve 35 and the open fuel supply valve 44 back to the low pressure pump 48 so that no fuel is supplied to the associated engine.

When the control valve 35 is closed by energising the solenoid winding 43 the flow of fuel through the valve ceases and therefore the pressure of fuel within the passage 21 increases. The increase in pressure is communicated by way of the passage 52 to the chamber 49 of the fuel supply valve and causes displacement of the valve member 45 against the action of the spring 51 into engagement with the seating so that the connection between the circumferential groove 34 and the low pressure pump 48 is broken. The fuel which is displaced from the bores 15 flows through the passage 22 to the outlet port 23 and to the associated outlet 24 and is delivered to an injection nozzle of the associated engine. This flow of fuel will continue until the solenoid winding 43 is de-energised thereby allowing the control valve to open.As soon as the control valve opens fuel at the high pressure which is developed during inward movement of the plungers is transmitted to the inner end of the cylinder 28 of the spill valve 25, this flow of fuel taking place by way of the passages 33. The effect of this flow of fuel is to displace the piston 27 against the action of the spring 29 and to lift the valve member 26 from its seating thereby allowing fuel from the bores 25 to flow along the spill passage 30 into the cylinder 28. This flow of fuel takes place at a high rate and the piston 27 is displaced further against the action of its spring.

The flow of fuel into the cylinder causes a rapid drop in the pressure of fuel in the outlet 24 and the flow of fuel to the engine ceases. Fuel continues to be displaced into the cylinder as the plungers move inwardly. The strength of the spring 29 is such in relation to the end area of the piston, that the pressure of fuel applied to the valve member 45 of the fuel supply valve is sufficient to maintain the valve member in the closed position. When the plungers move over the crests of the cam lobes the fuel displaced into the cylinder 28 flows back into the inner ends of the bores 15 and only when the valve member 26 engages with the seating defined about the passage 30 does the fuel pressure in the bores 15 fall to a value such as to permit the spring 51 to move the valve member of the fuel supply valve to the open position.When this takes place fuel can flow into the bores 15 to effect full outward movement of the pumping plungers, from the low pressure pump 48 thereby replenishing the fuel supplied to the engine and any lost through leakage. The valve member of the fuel supply valve remains in the open position even when the plungers 16 start to move inwardly again, until the control valve 35 is closed. However, care must be taken to ensure so far as is possible, that the rise in pressure in the passages in the distributor due to the restriction offered by the valve 35, does not urge the valve member 45 into engagement with its seating and thereby trigger the spill valve 25.

The control valve 35 using the arrangement as described, by its closure, initiates delivery of fuel to the associated engine and by its opening applies a trigger pulse to the spill valve in order to terminate delivery of fuel to the engine. By this means it is possible to choose the instant as the plungers are being moved by the leading flanks of the cam lobes at which delivery of fuel to the engine takes place and by shaping the leading flanks of the cam lobes the initial rate of fuel delivery to the engine can be controlled. By moving the cam ring 19 angularly the timing of fuel delivery can be controlled. It is necessary however to correlate the position of the cam ring with the instant of closure of the control valve 35 so as to ensure that delivery of fuel takes place at the correct time.

The movement of the valve member 45 of the fuel supply valve can be damped either by incorporating a restrictor in the passage 52 or by providing a small clearance between the wall of the chamber 49 and a collar carried on the valve member and which forms an abutment for the spring 51.

Claims (1)

1. A fuel pumping apparatus for supplying fuel to an internal combustion engine and of the kind comprising a high pressure pump which is actuated in timed relationship with the associated engine, the high pressure pump including a pumping plunger slidable in a bore and a cam having a leading flank which is operable to move the plunger to displace fuel through an outlet to the associated engine, a hydraulically operable spill valve which can be triggered by a control pressure to an open position to terminate delivery of fuel to the engine, a control valve operable to apply the control pressure to the spill valve, said control pressure being derived from the outlet of the high pressure pump means for supplying fuel to said bore from a source of fuel under pressure, a first supply valve which includes a valve member biased to the open position and which connects the source of fuel which the bore by way of the control valve whereby fuel can flow between the bore and the source of fuel when the control valve is in the open position and passage means through which fuel under pressure from the bore can act on the valve member to move it to the closed position when said control valve is closed.