GB2054060A - Fuel injection system - Google Patents

Abstract

A fuel injection system for an engine includes a plurality of pump/injectors 9 each incorporating a pumping plunger actuated by movement of a respective armature 41 forming part of an electromagnetic device. The extent of movement of the armature under the return motion of a spring determines the amount of fuel which will be supplied to the engine at the next stroke. This movement is determined by an adjustable lever 54 and the levers of the individual injectors are interconnected by a linkage 55, 56 to a single actuating device 58 having associated with it a transducer 69 to provide a signal indicative of the setting of the levers 54. <IMAGE>

Description

SPECIFICATION Fuel injection systems This invention relates to a fuel injection system for supplying fuel to an internal combustion engine and of the kind comprising a plurality of individual injection pumps each including a reciprocable pumping plunger and means within the pulp for actuating the associated plunger, each pump having associated therewith a fuel injection nozzle through which the fuel displaced by the associated plunger flows in use, to a combustion space of the engine.

It is known to operate the plungers by hydraulic actuating means which in turn is controlled by an electrically operated valve means. It has been suggested that the plungers can be operated directly by an electrically powered device. The supply of electrical power to the valve means or the device is controlled by a control system which is supplied with signals representative of various desired and actual engine operating parameters and with signals indicative of the position of the rotating parts of the engine, so that the delivery of fuel occurs at the correct time.The control of the fuel quantity presents a further problem and it has been proposed that the control can be achieved using transducers associated with the pumps respectively to sense the position of the plungers and supply a signal to the control system which by partly energising the valves or the devices, is able to halt the movement of the plungers during their filling strokes. The provision of the transducers and their connection to the control system adds to the complexity of the fuel system and in addition the control system is made complex because it needs to be able to respond to the signals from each transducer and supply the necessary holding current to maintain the position of the associated plunger whilst at the same time being capable of supplying current to other of the fuel pumps.In addition the fuel quantity supplied to each injector can vary depending upon the relative accuracy of the transducers.

The object of the present invention is to provide a system of the kind specified in a simple and convenient form.

According to the invention in a fuel system of the kind specified each fuel pump includes an adjustable stop member operable to determine the position attained by the pump plunger during its filling stroke, linkage means interconnecting the stop members, an actuating mechanism for setting the position of said linkage means and a transducer for providing a signal indicative of the setting of said stop members, said signal in use being supplied to a control system which controls the operation of said actuating mechanism.

In the accompanying drawings.

Figure 1 is a diagrammatic drawing of one example of a fuel system in accordance with the invention, and Figure 2 is a sectional side elevation showing part of the system seen in Figure 1.

Referring to the drawings, the fuel system comprises a plurality of pump/injectors 9 equal in number to the number of cylinders of the associated engine. The pump injectors are illustrated in detail in Figure 2 and with reference to Figure 2, each pump injector comprises a housing 10 which is of generally cylindrical form.

The housing 10 is provided with a first boss portion 11 extending axially from the housing and a second boss portion 12 which extends laterally from the housing. Both boss portions are provided with screw threads.

The first boss portion is of hollow form and defines an internal step 1 3 against which is located the flange of a pump barrel 14. The pump barrel 14 extends with clearance within a cylindrical chamber 1 5 defined within the housing.

The flange of the pump barrel 14 is held in engagement with the step 1 3 by means of a sleeve 1 6 one end of which engages the flange.

The other end of the sleeve is of reduced diameter and engages with a flange 17 formed on an injection nozzle assembly generally indicated at 18. The flange 1 7 of the nozzle assembly is engaged by a retaining nut 19 which is in screw thread engagement with the boss portion 1 The retaining nut defines a cylindrical aperture through which part of the nozzle assembly extends and in use, the end face of this part of the nozzle assembly together with the end face of the retaining nut 1 9 are exposed within the combustion chamber of an engine. As shown, a step on the retaining nut is located against a copper or like washer shown in dotted outline at 20 and which is located against a step defined in a bore formed in the cylinder head of the engine.

The nozzle assembly includes a valve member 21 one end of which defines a head for cooperation with a seating. The valve member is biased to the closed position by means of a coiled compression spring 22. As will be appreciated by those skilled in the art the nozzle assembly is of the outwardly opening type which when fuel under pressure acts against the aforesaid valve head, the valve member is moved against the action of the spring to permit fuel to flow through an outlet.

Located within the bore defined in the pump barrel is a pumping plunger 23. The pumping plunger extends from the end of the barrel and defines a flange between which and the end of the pump barrel is located a coiled compression spring 24. The flanged end of the pumping plunger is provided with radially extending grooves and the movement of the pumping plunger under the action of the spring 24 is limited by abutment of the pumping plunger with a stop ring 25 which is located against a step defined in the housing.

Moreover, the pumping plunger is provided with a recess which as shown, receives the end of a push-rod 26.

Fuel is supplied to the space defined within the housing in a manner which will be explained. This fuel is under a small pressure and during outward movement of the pumping plunger under the action of the spring 24, fuel is drawn into the cylinder defined by the pump barrel. This fuel flows by way of a non-return valve so that when the plunger 23 is moved inwardly against the action of the spring 24 the non-return valve remains closed and the fuel displaced by the pumping plunger is supplied through the nozzle assembly.

The non-return valve comprises a valve member 27 having a shank portion 28 which is slidably supported within the bore in the pump barrel. The valve member also includes a valve head 29 which is of larger diameter than the shank portion and this in the closed position of the valve member, engages with an annular edge 30 defined at the end of an enlarged portion of the bore in the barrel. The valve member is urged to the closed position by a compression spring 31 and extending through the valve member is a bore 32. In addition, the barrel 14 is provided adjacent the flange, with a pair of radially extending ports 33. At their outer ends the ports 33 communicate with the space defined between the outer periphery of the pump barrel and the wall 1 5 of the chamber formed in the housing.At the inner ends, the ports communicate with a circumferential groove 34 formed in the periphery of the shank 28 of the valve member. Moreover, the shank 28 of the valve member is of a length such that towards the end of the stroke of the pumping plunger, the latter will engage with the shank and lift the valve member against the action of the spring 31. When this occurs towards the end of the delivery of fuel by the pumping plunger, the pressure of fuel supplied to the nozzle is lowered quickly to that obtaining in the chamber containing the pump barrel. The reason for this is that when the valve member is lifted the groove 34 places the ports 33 in communication with the enlarged portion of the bore beneath the head of the valve member.As a result of the rapid reduction in the fuel pressure, the head of the valve 21 can move quickly onto its seating and the risk of fuel being supplied through the nozzle assembly in an unatomised condition is minimised.

When the pumping plunger is returned under the action of the spring 24 the valve member 27 remains in a position such that the ports 33 are in communication with the bore and with the head 29 lifted from the edge 30. The reason for this is that fuel under pressure from the aforesaid chamber acts on the valve head and flow of fuel occurs into the bore occupied by the pumping plunger. The flow of fuel into the bore continues until the movement of the plunger is halted either by the stop ring 25 or earlier as will be explained.

As soon as movement of the plunger 23 is halted no further fuel can flow into the bore and the fluid pressures acting on the valve member 27 are equalised. As a result the valve member moves under the action of the spring 31 until the head engages the aforesaid edge. The communication of the ports 33 with the bore is therefore broken.

An electromagnetic device is provided for effecting movement of the piston 23. This movement is achieved through the push rod 26 which extends with clearance through a drilling 34a formed in a core member 35 conveniently formed integrally with the housing 10. The core member extends on the opposite side of the housing to the first boss portion 11. The core member is formed from magnetisable material and therefore in the present construction so is the housing 10. It will be appreciated however that the core member and the housing may be formed as separate parts.

The core member is of generally truncated conical configuration and it is provided with a plurality of circumferentially extending grooves 36. The grooves 36 define circumferentially extending ribs 37 and it will be noted that the further a particular rib is from the housing 10 the smaller is its diameter Moreover, this also applies to the depth of the grooves 36 and in general the width of the grooves increases as the distance from the housing 10 increases.

The outer surfaces of the ribs 37 are inclined to the axis of the core member and located within each groove is a winding 38. The windings conveniently are connected in series in such a fashion that when electric current is passed through the windings the direction of current flow in adjacent windings is in the opposite direction. In this manner adjacent ribs 37 when electric current is passed through the windings, will be magnetised to opposite magnetic polarity.

Conveniently one end of the series connected windings is connected to the core member whilst the other end of the series connected windings is led out to a terminal which is carried by an electrically insulating block 40 which is secured to the housing 10 as shown in Figure 3.

Surrounding the core member is an armature 41. This is also formed from magnetisable material and has a thin section. The armature 41 can be regarded as a number of hoops of reducing diameter connected together by inclined portions such as shown at 42, the internal faces of the inclined portions lying substantially parallel to the aforesaid faces of the ribs 37. The armature is of cup-shaped form and the base wall is provided with a pair of apertures 43 and a central aperture which receives a plug 44 in which is located the remote end of the push rod 26. In use, when the windings are supplied with electric current, the armature will move downwardly as shown in the drawing, to reduce the reluctance of the air gaps between the ribs and the inclined portions 42 of the armature. In so doing movement will be imparted to the pumping plunger 23.

Surrounding the armature is a hollow cup shaped cover 45 which is formed from nonmagnetic material conveniently as a die casting from a zinc based alloy. As will be seen from the drawing the cover has a stepped outer peripheral surface and the sides thereof taper to permit its withdrawal from the die cavity. The internal peripheral surface is also of stepped form and is shaped as will be described, to support the armature for axial movement. The end portion of the cover that is to say in general that portion extending between the aforesaid external step which is referenced 46 and the housing 10, is formed with four internal ribs 47 and defined between these ribs are recesses. As explained in order to permit the casting to be removed from the die, the internal surfaces are tapered.After removal from the die cavity, the ribs 47 are machined so as to define surfaces which extend parallel to the axis of the core member. As a result four bearing surfaces 48 are formed which are engaged by the armature at its wider end.

The cover is provided with four further ribs 49 and again when manufactured these are tapered to permit removal of the casting from the die.

Subsequently the internal surfaces of the ribs 49 are machined to provide bearing surfaces 50 engaging with complementary surfaces of the armature nearer the narrow end thereof. The space defined within the cover 35 is connected to a fuel inlet 52 formed in the boss 12 and in use, fuel can flow upwardly on the inside or the outside of the armature through the apertures 43 if it has flowed upwardly on the outside of the armature, and down the drilling 34a to the bore 15 in the housing. Thus cooling of the windings is achieved by the fuel. The pump/injector is retained in position with the bore in the cylinder head by means of a clamping ring 53 which is in engagement with the step 46 on the cover. The clamping ring is provided with a pair of ears in which are located apertures through which extend in use, threaded studs secured within apertures formed in the cylinder head of the engine.A pair of nuts 54 are engaged with the studs. One stud is shown in dotted outline in Figure 2.

The amount of fuel which is delivered through the nozzle depends upon the position of the plunger 23 at the end of the filling stroke. This as shown in Figure 1, is determined by means of an adjustable stop member in the form of a cam 54 which is carried upon a shaft supported for angular movement within the cover 45. The cam is engageable by the plug 44 of the armature 41, and connected to the shaft is a lever 55 which is coupled to a linkage 56 which is also connected to the respective levers 55 of the remaining pump/injectors.

The linkage 56 is coupled to one end of a further pivoted lever 57 the other end of which is provided with a spherical end located between a piston 58 and an abutment 59. The piston and abutment are slidable within a cylinder 60, the abutment being spring loaded by a coiled compression spring 61. The end of the cylinder containing the spring communicates with the outlet of a pump 61a which draws liquid conveniently fuel, from a tank 62. In the example the tank contains fuel and the outlet of the pump is connected to the fuel inlets 52 of the individual pump/injectors. The output pressure of the pump is controlled by a relief valve 63 and connected between the outlet of the pump and the cylinder 60 is a control valve 64. A point downstream of the valve 64 is connected by way of a restrictor 65 to drain.The valve 64 is electrically controlled and by reducing the degree of restriction offered by the valve so the pressure applied to the piston 58 is increased. As the pressure applied to the piston 58 increases the lever 57, and the linkage 56 and the levers 55 move the cam 54 to allow the armature and plunger 23 to move further outwardly. In other words the effective stroke of the plunger at the next stroke is increased and so an increased quantity of fuel will be supplied through the nozzle. Conversely, if the pressure applied to the piston 58 is reduced then the stroke of the plunger is reduced.

The valve 64 is controlled by a control system 66 which also acts as an engine governor. The system is supplied with a demand signal along a line 67 and with signals indicative of the position of the rotating parts of the engine along a line 68.

Signals are supplied by the control system to the windings of the pump/injectors to ensure that the latter are operated in timed relationship with the engine. The control system 66 is also provided with a signal indicative of the setting of the cams 54 by means of a transducer 69 which comprises a winding 70 wound upon a former surrounding the abutment 59. The latter varies the inductance of the winding 70, by its movement and the signal supplied to the control system is used in the control system to ensure that the setting of the valve 64 is adjusted so that the correct quantity of fuel is supplied to the engine appropriate for the particular desired and actual engine operating conditions.

Whilst a hydraulic actuating mechanism has been described for the purpose.of adjusting the linkage and the cams it will be appreciated that other forms of actuating mechanism could be used for example, an electrical motor or a pneumatic device.

Claims (9)

1. A fuel injection system for supplying fuel to an internal combustion engine and comprising a plurality of individual injection pumps each including a reciprocable pumping plunger, means within the pump for actuating the associated plunger, fuel injection nozzles associated with the pumps respectively and through which fuel displaced by the associated plungers flows, in use, to the combustion spaces of the engine, an adjustable stop member operable to determine the position attained by the pump plunger during its filling stroke, linkage means interconnecting the stop members, an actuating mechanism for setting the position of said linkage means and a transducer for providing a signal indicative of the setting of said stop members, said signal in use being supplied to a control system which controls the operation of said actuating mechanicm.

2. A system according to claim 1 in which said stop member comprises an adjustable cam.

3. A system according to claim 2 in which said means for actuating the pumping plunger comprises an electromagnetic device including an armature operatively connected to the pumping plunger.

4. A system according to claim 3 in which said adjustable cam is mounted upon a cover surrounding the electromagnetic device.

5. A system according to any one of the preceding claims in which said actuating mechanism comprises a fluid pressure operable piston located within a cylinder, resilient means biasing the piston to a position in which a minimum amount of fuel will be supplied to the engine and valve means operable to vary the fluid pressure applied to said piston.

6. A system according to claim 5 including a pivotal lever, one end of which is connected to a link connected in turn with the lever respectively of the pumps, the other end of the lever being interposed between said piston and an abutment for said resilient means.

7. A system according to claim 6 in which said abutment forms one part of said transducer, the other part of said transducer being constituted by a winding surrounding said abutment and carried on a fixed member defining a cylinder for said piston and said abutment.

8. A system according to claim 5 including a supply pump for supplying fuel under pressure to said fuel pumps, said valve means including a valve connected between the outlet of the supply pump and a cylinder containing said piston and a restricted passage from a point downstream of said valve whereby the pressure applied to said piston can be varied by adjustment of said valve.

9. A fuel injection system for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.