The present invention relates to a hydraulic machine provided with a particle trap.

BACKGROUND OF THE INVENTION

In fuel injectors, fuel cleanliness is paramount to the successful operation of all fuel injection equipment. Failure to ensure an adequate level of filtration results in deterioration of sensitive parts of the system, including valve seats, guides in the high pressure parts of the pump, drivetrain components and injectors.

The sources or abrasive debris are built-in or generated by wear and are in suspension from the fuel in the tank. Respectively, these are traditionally minimised by adequate washing and clean room assembly or designing to minimise wear, and providing paper-type filters as part of the system which are changed according to a maintenance schedule.

Whilst every effort is made to minimise wear of components downstream of the inlet filter, inevitably, some debris is generated over the lifetime of a pump. This is a particular problem to pumps which include the cambox in the filling circuit. In the prior art 'twin filters' having a second paper filter element are currently used in some heavy duty FIE systems. Said twin- filters re-filter fuel after it has passed through the transfer pump, but this is not applied to pumps which fill from the cambox. The debris generated in the pump downstream of the inlet filter causes further wear.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a hydraulic machine comprising a shaft, rotating about a rotational axis and a fluid circuit for circulation of a fluid around said shaft, the fluid being, in use when the shaft is rotating, radially outwardly centrifuged. The hydraulic machine is further provided with a particle trap fixed to the shaft, said particle trap being arranged in the fluid circuit and being adapted to capture and retain particles flowing in the fluid.

Particularly, the particle trap comprises a trap housing fixed to the shaft, said trap housing defining a blind hole open in the fluid circuit and outwardly extending from the opening in the fluid circuit toward a blind end.

Also, the particle trap further comprises a retaining member arranged inside the blind hole and defining a lower chamber, between the through opening in the fluid circuit and the retaining member and, an upper chamber between the retaining member and the blind end. The retaining member is provided with an orifice so that, in use particles flowing in the fluid are outwardly centrifuged and enter the lower chamber then pass through the orifice to enter the upper chamber where they are trapped and retained.

The retaining member is shaped having a concave side arranged toward the lower chamber and, the concave shape has a pointy tip, the through opening being arranged at said tip.

Also, the retaining member protrudes inside the upper chamber therein creating a trap for particles.

In an embodiment, the shaft is a composite camshaft comprising a cylindrical shaft over which is fixedly engaged a cam member. The particle trap is arranged in said cam member, the blind hole extending in the cam member and opening in the inner cylindrical face of the cam member.

Particularly, the retaining member is fixed inside said blind hole.

In an alternative, the retaining member is snapped in the hole.

More precisely, in a specific application, the machine is a fuel pump provided with a cam box having a housing defining an internal volume in which rotates, in use, the composite camshaft actuating a pumping unit.

In this pump application, the particle trap is a hole drilled in the cam member.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 is an axial section of a high pressure fuel pump provided with a particle trap.

Figure 2 is a magnified section of the particle trap of figure 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is now described in reference to a high pressure fuel pump 10 represented on figure 1 adapted to be arranged on an internal combustion engine in order to deliver high pressure fuel to fuel injectors not represented.

The fuel pump 10 is of a cambox type and it comprises a housing 12 defining an internal volume V wherein is arranged a camshaft 14 rotating about a rotational axis Al between bearings 16 and, a pumping unit 18 operating about a pumping axis A2 perpendicular to the rotational axis Al . The camshaft 14 is of the type known by the skilled person as a composite camshaft comprising a cylindrical shaft 15 over which is fixedly engaged a cam member 20 having an outer profiled face 22 and an inner cylindrical face 24 engaged over the shaft 15 and fixed onto it.

The pumping unit 18 comprises a pumping head 26 having a housing 28 provided with an axial A2 bore 30 wherein is slidably arranged a plunger 32 protruding outside the pumping head housing 28 and extending toward an end provided with a cam follower 34 permanently in contact with the outer profiled face 22 of the cam. A spring 36 arranged around the plunger 32 is compressed between the head housing 28 and a spring seat 38 fixed to the plunger 32, the spring 36 generating a force permanently biasing the cam follower 34 onto the cam member 20. As it is well known, the bore 30 further defines between a blind end of the bore and an extremity of the plunger a compression chamber 40 having an inlet 42 for low pressure fuel to enter and an outlet 44 for high pressure fuel to exit.

In use, fuel F at low pressure circulating in the internal volume V ensures lubrication of the camshaft 14 rotating between the bearings 16 and of the cam follower 34 cooperating with the cam member 20. In a lower portion LV of the internal volume V, the circulation circuit 46 within which flows said low pressure fuel F comprises a space S comprised between the end of the camshaft 14 and the housing 12, said space S being represented on the left of figure 1, the circuit 46 further comprises a first conduit 48 axially Al drilled inside the camshaft 14, opening in said space S and extending toward an end defining a T-junction 50 wherefrom depart radial channels 52, two being represented on the figure but more could be arranged, opening in grooves 54 provided on the peripheral cylindrical face of the cylindrical shaft 15. As visible on the figure, the grooves 54 extend in the axial direction Al below the cam member 20, the right end of the groove 54, as per the arbitrary orientation of the figure, is closed while the left extremity extends beyond the cam member 20 and enables fluid communication with an upper portion UV of the internal volume V, said fluid communication being ensured through a clearance laterally comprised between the cam member 20 and the housing 12.

The fuel circulation circuit 46 further comprises particle traps 56, two being represented on the figure, although only one or more than two could be arranged. Said particle trap 56, visible on figure 1 and detailed on figure 2, comprises a blind hole 58 drilled in the cam member 20 and opening in the inner cylindrical face 24. As visible on figure 1, although not being mandatory for operation, the blind hole 58 is drilled at an angle of approximately 45° relative to the axes Al or A2 in order to enable the manufacturing operation and passage of the drill. The cam member 20 is arranged on the shaft 15 so the bling hole 58 opens in a groove 54 of the circulation circuit 46. Inside the blind hole 58 is arranged a retaining member 60 so that the internal space of the blind hole is divided in a lower chamber LC, extending between the opening of the blind hole 58 in the groove 54 and the retaining member 60 and, an upper chamber UC between the retaining member 60 and the blind end of the hole 58.

In an alternative embodiment, the particle trap 56 can be independent from the cam member 20. The trap 56 can comprise its own trap housing provided with the blind hole 58 Anyway, it is important for the trap to operate to be arranged so the dense debris particles are subject to centrifuge effect so that they pass into the trap 56.

The retaining member 60 has an ogive shape, a dome shape or a conical shape are also possible alternatives, and it is arranged in the blind hole 58 so that the lower chamber LC is concave and the upper chamber UC is convex. The wall of the retaining member is provided with a through orifice 62 arranged at the top of the ogive shape, said orifice 62 creating a permanent fluid communication between the lower LC and the upper UC chambers. In order to maintain the retaining member 60 in position in the blind hole 58, the retaining member 60 is provided on its external face with an annular crown 64 that is complementary engaged in a peripheral annular groove 66 provided on the peripheral face of the blind hole 58. Said engagement ensures the fixation of the retaining member 60 inside the hole 58. Modes of fixation alternative to the snap-in shown on the figures are possible, for instance gluing, brazing, should materials allow such process, are possible. The snap-in shown enables the retaining member 60 to be a plastic moulded part easily deformable to engage it inside the hole 58 until the crown 64 snaps, or clips, in the groove 66. It is desired that the retaining member 60 seals in the blind hole 58 reasonably well to prevent particles from 'leaking' back into the flow path when the pump is stationary.

In operation, the camshaft 14 rotates and the fuel flows in the circulation circuit 46 from the space S and inside the first conduit 48 then, the fuel is naturally centrifuged through the radial channels 52 toward the grooves 54. The fuel F may carry undesirable particles P of higher density than the fuel. Said particles P are therefore naturally directed by centrifugal force in the blind hole 58 where the concave face of the retaining member 60 drives said particle toward the orifice 62 enabling the entry of said particle P in the upper chamber UC. Once in there, the particles are trapped and remain permanently inside said convex upper chamber UC.

The invention has been disclosed in the context of a high pressure fuel pump but, the particle trap 56 can be successfully implemented in any hydraulic machine wherein a fluid is centrifuged in a flow circuit flows. Furthermore, although the method of filtering debris will require centrifugal motion acting on both the fluid and any particles within that fluid, it is not necessary to have a centrifugal motion to move fluid to the location of the filter. The flow of fluid to the centrifugal filter can be achieved by other methods that create a pressure difference between regions of fluid. For instance the trap 60 could be placed in a drilling between two regions of different pressure, but still relying on centrifugal force to trap particles. LIST OF REFERENCES

V internal volume to the housing

Al rotational axis

A2 pumping axis

S space

LV lower portion of the internal volume

UV upperportion of the internal volume

LC lower chamber

UC upper chamber

F fuel

10 fuel pump - hydraulic machine

12 housing

14 camshaft

15 cylindrical shaft

16 bearings

18 pumping unit

20 cam member

22 outer face

24 inner face

26 pumping head

28 housing of the pumping head

30 bore

32 plunger

34 cam follower

36 spring

38 spring seat

40 compression chamber

42 inlet

44 outlet

46 circulation circuit

48 first conduit

50 T-junction

52 radial channels

54 groove

56 particle trap

58 blind hole

60 retaining member

62 orifice

64 crown

66 annular groove.