GB2385385A

GB2385385A - Pump assembly

Info

Publication number: GB2385385A
Application number: GB0203613A
Authority: GB
Inventors: George Nicholas Felton; Robert A Trickett
Original assignee: Delphi Technologies Inc
Current assignee: Delphi Technologies Inc
Priority date: 2002-02-15
Filing date: 2002-02-15
Publication date: 2003-08-20
Also published as: GB0203613D0

Abstract

A pump assembly for use in an accumulator fuel system for an internal combustion engine comprises a single pumping plunger (30) which is reciprocable within a plunger bore (32) under the influence of a drive arrangement (40, 42, 46) to cause fuel pressurisation within a pumping chamber (30). The plunger bore (32) is provided with a port (31) through which fuel flows into and/or out of the pumping chamber (30), in use. The pumping plunger (30) is provided with a feature (51) to define a control edge (53) which is cooperable with the port (31) to control the quantity of fuel pumped within the pumping chamber (36) during a pumping cycle. The pump assembly further comprises control means (55, 57) for varying the angular position of control edge (53) relative to the port (31), thereby to vary the quantity of fuel which is pumped within the pumping chamber (36) during a pumping cycle.

Description

- 1 PUMP ASSEMBLY

The invention relates to a pump assembly for use in supplying high pressure fuel to a fuel injection system of a compression ignition internal combustion engine. In particular, the invention relates to a unit pump assembly having a pumping plunger which is driven by means of a cam shaft to cause pressurization of fuel within a pumping chamber for supply to an accumulator volume, such as a common rail.

One known common rail fuel pump assembly includes a plurality of plungers which are driven by means of a cam drive arrangement so as to pressurise fuel within respective pumping chambers for delivery to the fuel injection system associated with the engine. The cam drive arrangement includes a common eccentric cam surface, rotatable by means of a drive shaft, and it is common for such pumps to include three (or more) plungers which are equi-angularly spaced around the drive shaft. The cam surface is cooperable with all three of the plungers to cause phased, cyclical movement of the plungers and, hence, pressurization of fuel within the pumping chambers. High pressure fuel is delivered to a common rail for supply to the downstream fuel injectors.

Pump assemblies are also known in which a plurality of unit pumps are provided, each of which delivers fuel at high pressure to a separate high pressure fuel line. Each unit pump typically includes a tappet which is driven by means of a cam to drive pumping plunger movement, and is arranged to supply fuel to an injector for delivering fuel to an associated cylinder of the engine. In such pump assemblies it is therefore necessary to provide each engine cylinder with a set of separate pump components, consisting of a cam, a tappet, a unit pump, a high pressure line and an injector, with the cams for each set of pump components being carried on a common drive shaft.

- 2 Unit injectors are also known in which a pumping element and an injection nozzle are incorporated within a unitary housing, with one unit injector being provided for each engine cylinder.

So called "in line" pumps include a camshaft, a set of tappets and a set of pumping elements arranged within a unitary housing. Each pumping element has an associated pumping chamber which is connected to an associated injector through a separate high pressure fuel line.

Known fuel pumps of the aforementioned type each have their own advantages and disadvantages, and which type of pump is most suitable for use in any given engine will depend on many factors. It is desirable, however, for engine systems to be adaptable and interchangeable, and this, in particular, is one of the considerations addressed by the present invention.

According to a first aspect of the present invention, there is provided a pump assembly for use in an accumulator fuel system for an internal combustion engine, the pump assembly comprising: a single pumping plunger which is reciprocable within a plunger bore under the influence of a drive arrangement to cause fuel pressurization within a pumping chamber, the plunger bore being provided with a port through which fuel flows into and/or out of the pumping chamber, in use, wherein the pumping plunger is provided with a feature to define a control edge which is cooperable with the port to control the quantity of fuel pumped within the pumping chamber during a pumping cycle,

the pump assembly further comprising control means for varying the angular position of control edge relative to the port, thereby to vary the quantity of fuel which is pumped within the pumping chamber during a pumping cycle.

In a preferred embodiment, the pump assembly includes an outlet valve arrangement which is arranged to control the delivery of pressurised fuel from the pumping chamber directly to the accumulator volume through a high pressure fuel line.

Preferably, the accumulator volume takes the form of what is commonly referred to as a "common rail" containing fuel at high pressure for delivery to a plurality of injectors. The common rail may be of tubular configuration (i.e. axially extending), or may be of generally spherical configuration (i.e. of the type having a central hub from which radially extending delivery flow paths extend to the injectors).

The pump assembly may, but need not, be manufactured to include the drive arrangement. In one embodiment the drive arrangement may include a tappet assembly including a tappet member which is cooperable with a roller member to cause reciprocating motion of the pumping plunger upon rotation of a driven cam, m use.

The pump assembly of the present invention provides the advantage that it can be readily incorporated into existing engine installations originally intended for use with separate unit fuel injection pumps whilst preserving the existing engine layout, as there is no requirement to modify the existing pump mounting, cam drive shaft location or pump drive arrangement. Production costs associated with re-tooling an engine production line can also therefore be avoided.

- 4 The pump assembly also provides the advantage that only that quantity of fuel required for an injection event is pumped during a pumping cycle by virtue of the control means and the control feature on the pumping plunger. In existing pump designs, it is known to pump an excess quantity of fuel on each pumping stroke, with the excess being spilled to a drain port prior to delivery to the injectors. The pump assembly of the present invention provides improved mechanical efficiency over such known pump designs.

In a preferred embodiment, the pumping plunger is preferably provided with a groove, recess or flat on its outer surface to define the control edge, an open end of the groove, recess or flat being in communication with the pumping chamber. Preferably, the control feature takes the form of a helical or angled groove. The plunger bore may be provided in a main pump housing, the main pump housing being provided with a spill/fill passage, one end of which defines the port in the plunger bore and the other end of which is in communication with an inlet chamber to which fuel is delivered, in use, from a low pressure source, for example a low pressure pump.

Preferably, the main pump housing is provided with a filling passage containing a non-return valve, one end of the filling passage communicating with the pumping chamber and the other end of the filling passage being in communication with an inlet chamber to which fuel is delivered, in use, frown a low pressure pump.

In use, the pumping plunger is driven inwardly within the plunger bore during a pumping stroke by means of the drive arrangement. Upon commencement of the pun1ping stroke, the groove communicates with the port such that, as the

- s - pumping plunger starts to move, fuel within the pumping chamber spills back through the spill/fill passage to the inlet chamber. After the plunger has moved part way through its range of travel, a point will be reached at which the control edge becomes misaligned with the port and the outer surface of the pumping plunger closes the port to prevent the further spill of fuel back through the spill/fill passage. Further plunger movement results in fuel pressurization within the pumping chamber to a high level. The quantity of fuel pumped during the pumping stroke is therefore determined by the point during travel of the pumping plunger at which the conko1 edge on its outer surface becomes misaligned with the port and the outer surface of the pumping plunger closes the port. The point at which the outer surface of the pumping plunger closes the port is determined by the angular position of the pumping plunger within the plunger bore relative to the port.

During a return shroke of the pumping cycle, the spill/fill passage defines a supplementary filling passage for fuel in circumstances in which the groove on the surface of the pumping plunger communicates with the port. In one mode of operation, the spill/fill passage defines a spill passage for fuel flow from the pumping chamber during at least a part of a pumping stroke and in circumstances in which the groove communicates with the port.

Preferably, the control means take the form of a conko1 sleeve which is cooperable with the pumping plunger to vary the angular position of the pumping plunger relative to the port.

The pumping plunger is preferably provided with an annular member, preferably a flatted annular member, through which the pumping plunger is coupled to the control sleeve. The control sleeve may be connectable with a control rack of the associated engine.

- 6 The pump assembly preferably includes a high pressure fuel line which communicates with the pumping chamber through the outlet valve arrangement, wherein the high pressure fuel line is substantially coaxially aligned with the pumping plunger.

According to a second aspect of the present invention, there is provided an accumulator fuel system comprising: a pump assembly having a pumping plunger which is reciprocable within the plunger bore under the influence of a drive arrangement to cause fuel pressurization within a pumping chamber, the plunger bore being provided with a port through which fuel flows into and/or out of the pumping chamber, in use, an accumulator volume to which pressurised fuel is delivered directly through a high pressure fuel line, and from which pressurised Mel is delivered to an injector of the fuel system, wherein the pumping plunger is provided with a feature to define a control edge which is cooperable with the port to control the quantity of fuel pumped within the pumping chamber during a pumping cycle, the pumping plunger further being provided with control means for varying the angular position of the control edge relative to the port, thereby to vary the quantity of fuel pumped within the pumping chamber during a pumping cycle.

Preferably, the accumulator volume takes the form of a common rail for fuel at high pressure for delivery to a plurality of injectors.

- 7 An inlet of the common rail is in communication with an outlet of the pump assembly by means of the high pressure fuel line, the pump outlet thereby being remotely spaced from the common rail inlet. Thus, the pump assembly delivers fuel to a separate, intermediate fuel volume, in the form of a common rail, through the high pressure fuel line, the fuel system including a high pressure delivery line through which fuel is delivered from the common rail to the injector(s). The injector(s) of the fuel system is therefore spaced apart from the pump assembly.

According to a further aspect of the invention, there is provided a multi pump assembly including at least two pump assemblies in accordance with the first aspect of the invention, wherein the control sleeve of each pump assembly is connectable to a common engine control rack.

The multi pump assembly provides the advantage that an increased and controllable quantity of fuel can be delivered to the common rail during a pumping cycle in an efficient manner.

It will be appreciated that optional and/or preferable features of the pump assembly of the first aspect of the invention may also be incorporated within the other aspects of the invention.

The invention will now be described, by way of example only, with reference to the accompanying figures in which: Figure 1 is a schematic diagram of a fuel system in accordance with one aspect of the present invention'

- 8 Figure 2 is a view, shown part in section, of a part of a common rail pump assembly in accordance with a second aspect of the present invention, Figures 3 and 4 illustrate two different cam surface profiles which may be used in a drive arrangement for the pump assembly in Figure 2.

Referring to Figure 1, a common rail fuel system for an internal combustion engine includes a low pressure pump 10 which receives fuel from a low pressure reservoir 12 through a filter arrangement 14. The low pressure pump 10 supplies fuel through a first supply line 16 to an inlet 54 of a high pressure pump, referred to generally as 18. The high pressure pump 18 is arranged to cause pressurization of a controllable quantity of fuel to a relatively high level, and delivers high pressure fuel through a second supply line 20 to an accumulator volume in the form of a common rail 22. The common rail 22 is of generally spherical configuration and includes a plurality (four in the illustration shown) of high pressure fuel lines 24 which extend from a central hub of the rail 22. Each one of the high pressure fuel lines 24 is arranged to supply fuel to an injector 26 of the fuel system (only one of which is shown), from where fuel is delivered to an associated engine cylinder or other combustion space. The injector may be of conventional type, the design and operation of which would be well known to a person familiar with this field of

technology. For example, the injector may be of the electromagnetically or piezoelectrically actuable type, may be of the direct actuation type or may be of the type including a hydraulic amplifier arrangement for controlling injector valve needle movement.

Figure 2 shows the high pressure fuel pump 18 in more detail, and from which it can be seen that the pump 18 includes a single cylindrical pumping plunger 30 which is slidable within a plunger bore 32 provided in a pump housing 34 to

- 9 - cause pressurization of fuel within a pumping chamber 36. The pumping plunger 30 forms a sliding fit within the plunger bore 32 such that fuel within the pumping chamber 36 is unable to leak between the pumping plunger 30 and the plunger bore 32, in use. The pumping plunger 30 is driven by means of a drive arrangement, referred to generally as 38, including a generally tubular tappet member 40, a roller member 42 and a cam 80 which is driven by a drive shaft (not shown). The roller 42 is arranged to cooperate with a surface 46 of the cam 80 such that, as the drive shaft is rotated the cam is driven and the roller 42 is caused to ride over the cam surface 46. The roller 42 and the tappet 40 are reciprocable within a guide bore 44 provided in an engine housing 39 which is secured to the pump housing 34. An internal surface of the tappet 40 is provided with an annular groove, within which an abutment plate 47 for a return spring 48 is mounted. The abutment plate 47 is provided with a central opening through which a lower portion 30_ of the plunger 30 extends to couple the plunger 30 to the abutment plate 47 and, thus, to the tappet 40. The return spring 48 is arranged to urge the tappet and roller arrangement 40,42 outwardly from the guide bore 44 (downward in the orientation shown in Figure 2) into engagement with the cam surface 46 and therefore serves to allow the pumping plunger 30 to be urged outwardly from the plunger bore 32 to perform a return stroke of a pumping cycle, as described in further detail below. The outer surface of the pumping plunger 30 is provided with a recess, groove or slot 51 of helical or angled form which defines a control edge 53. The control edge 53 is cooperable with a port 31 within the plunger bore 32 to control a supplement flow of fuel into the pumping chamber 36 and a spill flow of fuel out of the pumping chamber 36 during filling and pumping phases of the pumping cycle respectively. The port 31 is defined by an open end of a drilling provided in the pump housing 34 which defines a spill/fill passage 61.

- 10 Tle other end of the spill/fill passage 61 is in communication with an inlet chamber 59 defined within the pump housing 34 to which fuel is delivered, in use, from the pump inlet 54.

An intermediate portion 30b of the pumping plunger 30 is received within a tubular member in the form of a control sleeve 55 arranged between a lower face of the pump housing 34 and the abutment plate 47 for the return spring 48.

An upper end ofthe control sleeve 55 is coupled to a drive member 57 which, in turn, is coupled to an engine control rack to permit the angular position of the control sleeve 55 to be varied. The intermediate portion 30b of the pumping plunger 30 carries a flatted annular collar 50 which is coupled to the sleeve 55 such that, as the angular position of the control sleeve 55 is adjusted by means of the control rack, the angular position of the pumping plunger 30 within the plunger bore 32 is altered. In this way the relative angular positions of the control edge 53 and the port 31 can be adjusted so as to vary the quantity of fuel which is pumped during a pumping cycle, as described in further detail below. In use, Intel from the first supply line 16 in Figure 1 is delivered to the pump inlet 54 frown where it flows through a flow passage (not visible in Figure 2) to the inlet chamber 59. The pump housing 34 is also provided with a further drilling which dehmes a primary filling passage 37 through which fuel is delivered from the inlet chamber 59 to the pumping chamber 36.

Communication between the inlet chamber 59 and the pumping chamber 36 through the primary filling passage 37 is controlled by means of an inlet check valve arrangement or non-return valve arrangement, referred to generally as 56, including a valve abutment member 60 which defines a valve seat 62 with which a check valve member 58 is engageable. The valve abutment member 60

- 11 is provided with axially and radially extending passages which communicate with one another such that, when the check valve member Sg is caused to lift front the valve seat 62, fuel delivered to the inlet chamber 59 is able to flow into the radially extending passage in the valve abutment member 60, into the axially extending passage and past the valve seat 62 into the primary filling passage 37. Although not shown in Figure 2, in practice it may be desirable to provide the inlet check valve 56 with a relatively low spring pre-load to urge the check valve member 58 into a position in which it engages the valve seat 62. The pump assembly 18 also includes an outlet delivery valve arrangement, referred to generally as 64. The outlet valve arrangement 64 takes the form of a ball valve having a ball 66 which is engageable with a further valve seat 68 to control fuel flow between the pumping chamber 36 and a high pressure supply line 70. The outlet valve arrangement 64 may be provided with an outlet valve spring (not shown) having a relatively low pre-load? which serves to urge the ball 66 into engagement with the further valve seat 68.

The high pressure supply line 70 is defined by a passage provided in an insert member 72 located, in part, within a further bore 73 provided within the pump housing 34 and partially extending from the pump housing 34. The high pressure supply line 70 is substantially coaxially aligned with the pumping plunger 30 and is arranged to communicate, at its end remote from the pump housing 34, with an end of the second supply line 20 to the common rail 22.

Thus, in use, high pressure fuel delivered Mom the pumping chamber 36 to the hilly pressure supply line 70 is able to flow into the second supply line 20, and into the common rail 22, for delivery to the injectors 26.

- 12 In use, as the drive shaft is rotated and the roller 42 rides over the cam surface 46. the tappet 40 is caused to reciprocate within the guide bore 44. As the tappet 40 is coupled to the pumping plunger 30, axial movement is therefore imparted to the pumping plunger 30 as the tappet 40 moves. A pumping cycle consists of two phases. During a filling phase, the inlet check valve 56 is open to permit fuel delivered to the inlet chamber 59 to flow into the pumping chamber 36 through the primary filling passage 37, and the outlet valve arrangement G4 is held closed by means of high pressure fuel within the high pressure supply line 70 to the common rail. During that part of the filling phase tor which the groove 51 aligns with the port 31, fuel is also able to flow into the pumping chamber 36 through the spill/fill passage 61 such that, in such circumstances, the passage 61 defines a supplementary filling passage for the pumping chamber 36. The pumping plunger 30 is urged outwardly from the plunger bore 32 to perform a return stroke due to the force exerted on the lower portion 30_ ofthe pumping plunger 30 by the return spring 48 acting through the central opening in the abutment plate 47.

During the first part of the subsequent pumping phase of the pumping cycle, the pumping plunger moves inwardly into the pumping chamber 36 as fuel is caused to flow from the pumping chamber 36 towards the inlet 54 through the spill/fill passage 61. Flow towards the inlet 54 may also occur through the inlet check value 56 if the pressure generated in the pumping chamber 36 is insufficient to cause the inlet check value 56 to close. During a subsequent part of the pumping phase, the control edge 53 on the surface of the plunger 30 becomes misaligned with the port 31 and the flow of fuel from the pumping chamber 36 through the spill/fll passage 61 is terminated. The inlet check value 56 is then caused to close due to increasing fuel pressure within the pumping chamber 36 as the plunger 30 moves further inwardly under the drive of the tappet 40, thereby preventing further flow of fuel into the pumping

- 13 chamber 36 from the inlet chamber S9 and a return flow of fuel from the pumping chamber 36 to the inlet chamber 59. Additionally, as fuel pressure within the pumping chamber 36 increases further, the outlet valve arrangement 64 is caused to open to permit pressurised fuel within the pumping chamber 36 to flow into the high pressure flow line 70. During the pumping phase the pumping plunger 30 is urged inwardly within the plunger bore 32, under the influence of the tappet 40 cooperating with the roller 42 and the driven cam surf ce 46, to cause fuel pressurization within the pumping chamber 36.

The sequence of events during a pumping cycle will now be described in further detail. At the start of the pumping cycle, the pumping plunger 30 adopts its innermost position within the plunger bore 32 (i.e. uppermost position in the orientation in Figure 2) and fuel pressure within the pumping chamber 36 is high due to the pressurization caused by the previous pumping stroke. The outlet valve arrangement 64 is closed due to the equalization of fuel pressures in the pumping chamber 36 and the high pressure supply line 70. Due to the coupling between the pumping plunger 30 and the tappet 40' the tappet 40 is also at its innermost position in the guide bore 44 at the start of the pumping cycle. Upon commencement of its return stroke, the plunger member 30 is initially allowed to retract from the plunger bore 32 due to decompression within the pumping chamber 36 and retraction of the tappet 40 under the force of the return spring 48 as the roller 42 rides over the cam surface 46. As the pumping chamber 36 is decompressed, a point will be reached at which the pressure in the pumping chamber 36 falls below the pressure required to lift the check valve member 58 from the valve seat 62 due to the flow of fuel into inlet chamber 59, and the next filling phase commences.

- 14 During the return stroke, the pumping plunger 30 is either in a position in which the groove 51 communicates with the port 31, or the outer surface of the pumping plunger 30 closes the port 31. For positions in which the port 31 is closed (as shown in Figure 2), there is no supplemental filling of the pumping chamber 36 through the spill/fill passage 61 and fuel is only able to flow into the pumping chamber 36 through the primary filling passage 37 (if the inlet check valve 56 is open). When the pumping plunger 30 is retracted further from the plunger bore 32, the control edge 53 aligns with the port 31 such that, during a subsequent part of the return stroke, filling of the pumping chamber 36 is supplemented by a flow of fuel through the spill/fill passage 61 into the groove 51 and, hence, into the pumping chamber 36.

Such further movement of the pumping plunger 30 outwardly from the plunger bore 32 is effected by a force exerted on the lower portion of the pumping plunger 30 by the return spring 48 acting through the central opening in the abutment plate 47. Retraction of the tappet 40 from the guide bore 44 (i.e. outward movement of the tappet 40 from the bore 44) occurs under the force of the return spring 48, causing the roller 42 to ride over the cam surface 46.

During the filling phase, the ball 66 of the outlet valve arrangement 64 remains seated against the further valve seating 68 due to high pressure fuel within the high pressure supply line 70 and due to the force of the outlet valve spring.

After the tappet 40 reaches its outermost position within the guide bore 44, the roller 42 is urged in an upward direction (in the illustration shown in Figure 2) as it follows the cam surface 46, thereby causing the tappet 40 to be urged inwardly within the guide bore 44 and, hence, the pumping plunger 30 to be driven inwardly within the plunger bore 32. Initially, when the pumping plunger 30 adopts its outermost position within the plunger bore 32, the groove 51 is aligned with the port 31 such that, as the pumping plunger 30 starts to

- 15 move inwardly within the bore 32, fuel within the pumping chamber 36 is able to spill back through the spill/fill passage 61 to the inlet chamber S9. In such circumstances the passage 61 therefore defines a spill passage for fuel flow from the pumping chamber 36 to the inlet chamber 59. Further movement of the pumping plunger 30 under the drive of the tappet 40 causes the control edge 53 to become misaligned with the port 31 and the outer surface ofthe pumping plunger 30 closes the port 31. Fuel within the pumping chamber 36 is therefore no longer able to escape through the spill/fill passage 61 and fuel pressure within the pumping chamber 36 starts to increase. Moreover, a point will be reached part way through the pumping stroke at which the check valve member 58 of the inlet check valve 56 is urged against its seating due to increasing fuel pressure within the pumping chamber 36, thereby preventing the further flow of fuel into or out of the pumping chamber 36 through the primary filling passage 37.

As the plunger pumping stroke continues, fuel within the pumping chamber 36 is pressurised to a sufficiently high level to cause the ball 66 to lift from the further valve seating 68, thereby permitting pressurised fuel to flow from the pumping chamber 36 into the high pressure supply line 70 and, hence, to the supply line 20 to the common rail 22.

At the end of the pumping stroke, when the pumping plunger 30 reaches the end of its range of travel, the ball 66 will be urged against the t;rther valve seating 68 due to high pressure Mel within the high pressure supply line 70 and the force of the outlet valve spring, thereby holding high fuel pressure within the high pressure flow line 70, the second supply line 20 and, hence, within the common rail 22.

- 16 As the pumping plunger 30 is coupled to the tappet 40, the extent of plunger movement during the return and pumping strokes is substantially constant for all quantities of pumped fuel.

The quantity of fuel delivered to the pumping chamber 36 during the filling phase is determined by the time for which the inlet check valve 56 is held open to permit fuel flow into the pumping chamber 36 and the time for which the groove 51 on the surface of the pumping plunger 30 is aligned with the port 31 to permit supplemental fuel flow through the spill/fill passage 61 into the pumping chamber 36. The time for which the inlet check valve 56 is held open is determined by the spring rate of the inlet valve spring (if provided), the hydraulic force acting on the check valve member 58 as fuel is pressurised within the pumping chamber 36 and the speed of the associated engine which determines the rate of movement of the tappet 40.

The quantity of fuel pumped within the pumping chamber 36 during one pumping cycle is determined by the point during the plunger pumping stroke at which the control edge 53 becomes misaligned with the port 31 and the surface of the pumping plunger 32 closes the port 31 to terminate thespill of fuel back to the inlet chamber 59 through the spill/fill passage 61. The point during the plunger stroke at which the control edge 53 becomes misaligned with the port 3 l can he controlled by varying the angular position of the control sleeve 55 and, hence, the angular position of the pumping plunger 30 relative to the port 31. In order to achieve a maximum pumped volume of fuel, the pumping plunger 30 is rotated to a position in which the groove 51 on the plunger does not communicate with the port 31 during any part of the pumping plunger stroke so that no fuel within the pumping chamber 36 can spill back through the spill/fill passage 6l to the inlet chamber 59. Conversely. to achieve zero pumping, the control sleeve 55 is rotated to a position in which the groove 51

- 17 on the surface ofthe pumping plunger 30 is always in communication with the port 31 such that, throughout the full pumping stroke, fuel within the pumping chamber 36 is spilled back through the spill/fill passage 61 to the inlet chamber 59. The provision of the groove 51 on the pumping plunger 30 and the means for altering the angular position of the pumping plunger 30 within the plunger bore 32 provide the advantage that only that quantity of fuel required for an injection event is pumped during a pumping cycle. In existing pump designs, it is known to pump an excess quantity of fuel on each pumping stroke, with the excess being spilled to a drain port prior to delivery to the injectors. The pump assembly of the present invention therefore provides improved mechanical efficiency over such known pump designs.

The cam drive arrangement for the pump assembly is typically arranged to have a cam surface with one cans lobe per injection event. Figure 3 shows the cam drive arrangement which may be used in a two cylinder engine, and in which the cam 80, driven by means of an engine drive shaft 82, has a cam surface provided with two cam lobes. Figure 4 shows the cam drive arrangement for a three cylinder engine, in which the cam 80 has a three lobed cam surface.

If the quantity of fuel required for an in jection event is greater than that which can be provided by a single pump assembly, two or more pump assemblies may be used, both of which take the form described previously with reference to Figure 9. Conveniently, in a multi pump assembly the control sleeve 55 of each pulp assembly is controlled by means of a common engine rack.

- 18 It will be appreciated that, although the pump assembly of the present invention is shown to include a tappet drive arrangement which cooperates with the cam other drive arrangements are also envisaged, for example shoe and roller arrangements.

Claims

- 19 CLAIMS

1. A pump assembly for use in an accumulator Mel system for an internal combustion engine, the pump assembly comprising: a single pumping plunger which is reciprocable within a plunger bore under the influence of a drive arrangement to cause Mel pressurization within a pumping chamber, the plunger bore being provided with a port through which fuel flows into and/or out of the pumping chamber, in use, wherein the pumping plunger is provided with a feature to define a control edge which is cooperable with the port to control the quantity of fuel pumped within the pumping chamber during a pumping cycle, the pump assembly further comprising control means for varying the angular position of control edge relative to the port, thereby to vary the quantity of fuel which is pumped within the pumping chamber during a pumping cycle.

2. A pump assembly as claimed in Claim l, further comprising an outlet

valve arrangement which is arranged to control the delivery of pressurised fuel from the pumping chamber directly to the accumulator volume through a high pressure fuel line.

3. A pump assembly as claimed in Claim l or Claim 2, including the drive arrangement.

4. A pump assembly as claimed in Claim 3, wherein the drive arrangement includes a tappet assembly including a tappet member which is cooperable with

- 20 a roller member to cause reciprocating motion of the pumping plunger upon rotation of a driven cam? in use.

5. A pump assembly as claimed in any of Claims I to 4, wherein the control feature provided on the surface of the pumping plunger takes the form of-a groove, recess or flat, wherein an open end of the groove, recess or flat being in communication with the pumping chamber.

6. A pump assembly as claimed in Claim 5, wherein the feature takes the form of a helical or angled groove.

7. A pump assembly as claimed in any of Claims 1 to 6, wherein the plunger bore is provided in a main pump housing, the main pump housing being provided with a spill/fill passage, one end of which defines the port in the plunger bore and the other end of which is in communication with an inlet chamber to which fuel is delivered, in use, from a low pressure pump.

8. A pump assembly as claimed in any of Claims I to 7, wherein the plunger bore is provided in a main pump housing, the main pump housing being provided with a filling passage containing a non-return valve, one end of the filling passage communicating with the pumping chamber and the other end of the filling passage being in communication with an inlet chamber to which fuel is delivered, in uses from a low pressure pump.

9. A pump assembly as claimed in any of Claims 1 to 8, including a control sleeve which is cooperable with the pumping plunger to vary the angular position of the pumping plunger relative to the port.

- 21

10. A pump assembly as claimed in Claim 9, wherein the pumping plunger carries an annular member through which the pumping plunger is coupled to the control sleeve.

11. A pump assembly as claimed in Claim 9 or Claim 10, wherein the control sleeve is connectable with a control rack of the associated engine.

12. A pump assembly as claimed in any of Claims 1 to 1 1, including a high pressure fuel supply line which communicates with the pumping chamber through the outlet valve arrangement, wherein the high pressure fuel supply line is substantially coaxially aligned with the pumping plunger.

13. An accumulator fuel system for an internal combustion engine, the fuel system comprising: a pump assembly having a pumping plunger which is reciprocable within the plunger bore under the influence of a drive arrangement to cause fuel pressurization within a pumping chamber, the plunger bore being provided with a port through which fuel flows into and/or out of the pumping chamber, in use, an accumulator volume to which pressurised fuel is delivered directly through a high pressure fuel line, and from which pressurised fuel is delivered to an injector of the fuel system, wherein the pumping plunger is provided with a feature to define a control edge which is cooperable with the port to control the quantity of fuel within the pumping chamber during a pumping cycle,

- 22 the pump assembly further comprising control means for varying the angular position of the control edge relative to the port, thereby to vary the quantity of fuel which is pumped within the pumping chamber during a pumping cycle.

14. A fuel system as claimed in Claim 13, wherein the accumulator volume takes the form of a common rail for containing fuel at high pressure for delivery to a plurality of injectors.

15. A fuel system as claimed in Claim 14, wherein an inlet of the common rail is in communication with an outlet of the pump assembly by means of the high pressure fuel line, the pump outlet thereby being remotely spaced from the common rail inlet.

16. A multi pump assembly comprising at least two pump assemblies as claimed in any of Claims 1 to 12, wherein the control sleeve of each pump assembly is connectable to a common engine control rack.

17. A pump assembly substantially as herein described with reference to the . accompanying drawings.

18. An accumulator fuel system substantially as herein described with reference to the accompanying drawings.