The present invention relates to a fuel pump having a cambox in which a camshaft cooperates with a piston, said camshaft having a cam arrangement minimising the mechanical stresses in the cam or/and in the housing of the cambox.

BACKGROUND OF THE FNVENTION

A fuel injection equipment of an internal combustion engine comprises a pump receiving low pressure fuel and delivering high pressure fuel to fuel injectors. Constant efforts are made to increase the outlet fuel pressure toward 3000 bar and above in order to improve combustion and fuel efficiency of the engine and also to decrease the overall size of the pump for enabling easier packaging in the engine compartment of a vehicle. Both trends are detrimental to the pump durability as tending to increase the mechanical stresses internal to the pump.

SUMMARY OF THE FNVENTION

Accordingly, it is an object of the present invention to resolve at least partially the above mentioned problems in providing a fuel pump of a fuel injection equipment of an internal combustion engine, said pump comprising a camshaft rotating about a main axis in a cambox and cooperating with a piston to reciprocally slide in a bore and alternatively vary the volume of a compression chamber defined in a pumping head.

Furthermore, the camshaft comprises a shaft member and a cam member arranged between a rear bearing, registered in a recess of the housing of the cambox and, a front bearing registered in a through bore of a front plate fixed on said housing; the cam being in an inner space defined between said housing and said front plate, said cam having a peripheral outer face, a transverse front side next to the front bearing and a transverse rear side next to the rear bearing.

The cam member comprises a core fixed on the shaft and an outer sleeve arranged over the core, the piston cooperating with the outer face of said sleeve, the core being narrower than the sleeve so that an annular recess, is defined on at least one side of the cam.

In another aspect of the invention, the outer sleeve may be integral to the core.

In another aspect of the invention, the cam may be integral to the shaft.

In another aspect of the invention, the core may be integral to the shaft. In another aspect of the invention, the outer sleeve may be inserted over the core.

In another aspect of the invention, the core and the outer sleeve define a front annular recess on the front side of the cam and, a rear annular recess on the rear side of the cam.

In another aspect of the invention, the cambox may be further provided with a rear annular member surrounding the recess wherein is arranged the rear bearing, said rear annular member being integral to the housing and protruding in the inner space.

In another aspect of the invention, said rear annular member may be engaged in the rear recess of the cam.

In another aspect of the invention, the cambox may be further provided with a front annular member surrounding the bore wherein is arranged the front bearing, said front annular member being integral to the front plate and protruding in the inner space S.

In another aspect of the invention, the front annular member may be engaged in the front recess of the cam. 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 a section view of a cam actuated pump as per the invention, a camshaft being in a BDC position.

Figure 2 is similar to figure 1, the camshaft being in TDC position.

Figure 3 is a 3D exploded view of an embodiment of the camshaft. Figure 4 is a 3D view of the camshaft of figure 3 when assembled. DESCRIPTION OF THE PREFERRED EMBODIMENTS

A diesel internal combustion engine fueled with direct injection has an injection equipment 10 wherein fuel pressurised by a pump 12 is delivered to injectors. The pump 12 comprises a pumping head fixed onto a cambox 14, a cam 16 of a camshaft 18 rotating about a cam axis X between a front bearing 20 and a rear bearing 22 urges a piston to reciprocally slide in a bore and for varying the volume of a compression chamber defined in the pumping head. The cambox 14 has a housing 24 closed by a front plate 26 which defines an inner space S wherein the cam 16 and a cam follower, provided at an end of the piston, cooperate. The rear bearing 22 is a sleeve registered in a recess 28 arranged in the housing 24 and, the front bearing 20 is another sleeve registered in a through bore 30 arranged in the front plate 26 and, between said bearings, the cam 16 defines a peripheral outer face 32 that is in contact with the cam follower, a transverse front side 34 next to the front bearing 20 and, an opposed transverse rear side 36 next to the rear bearing 22.

The embodiment presented on the figures shows a composite camshaft 18 wherein the cam 16 is an independent member inserted with press-fit over a shaft 38 between a cylindrical front bearing face 40 and a cylindrical rear bearing face 42. The cam 16 comprises a central core 44 having an axial X hole 46 complementary engaged over the shaft 38 and, an integral outer sleeve 48 defining said peripheral outer face 32 that is in contact with the cam follower.

In alternative constructional combinations not shown, the cam 16 can be entirely integral to the shaft 38 or, the core 44 only could be integral to the shaft 32, the outer sleeve 48 being an independent member inserted over the core 44 or also, the shaft 38, the core 44 and the outer sleeve 48 can be three distinct members assembled afterward. The design choice depends upon compromised made between, for instance, manufacturing process and material selections.

Whatever the embodiment, the outer sleeve 48 is larger than the core member 44 and is centred over it thus defining a front recess 50, or front undercut, arranged on the front side 34 of the cam and, an opposed rear recess 52, or rear undercut, arranged on the rear side 36 of the cam, said recesses 50, 52 surrounding the opposed openings of the axial hole 46, the front edge area 54 and the rear edge area 56 of the outer sleeve defining the peripheral wall of the recesses 50, 52. Moreover, an annular rear member 58 integral to the housing 24 surrounds the rear bearing recess 52 and protrudes in the inner space S, said annular member 58 engaging the rear recess 52 of the cam without touching any of the faces of the cam maintaining a gap between the faces of the annular member 58 and the faces of the rear recess 52. Symmetrically, an annular front member 60 integral to the front plate 26 surrounds the bore 30 and protrudes in the inner space S, said annular member 60 engaging the front recess 50 of the cam without touching the cam maintaining a gap between the faces of the annular member 60 and the faces of the front recess 50.

Said arrangement enables several pump embodiment each providing solution to at least one of the known issues. For instance, the size of the pump 12 can be decreased by bringing the front plate 26 closer the housing. Also the front 54 and rear 56 edges of the cam outer sleeve are provided with enhanced resilient properties, said areas being able to slightly deflect under the forces applied on the outer face 32 of the sleeve member by the cam follower. Moreover, thanks to the front 60 and rear 58 annular members the axial length of the bearings 20, 22 may be increased.

In yet another embodiment, the cam 16 can be non-symmetrical, outer sleeve 48 not being centred over the central core 44, this enabling for instance to increase the length of a bearing.

LIST OF REFERENCES

X main axis

s inner space

10 injection equipment

12 pump

14 cambox

16 cam

18 camshaft

20 front bearing

22 rear bearing

24 cambox housing

26 front plate

28 recess

30 bore 32 peripheral outer face of the cam

34 front side of the cam

36 rear side of the cam

38 shaft

40 front bearing face

42 rear bearing face

44 central core

46 axial hole

48 outer sleeve

50 front recess

52 rear recess

54 front edge area of the outer sleeve

56 rear edge area of the outer sleeve

58 annular rear member

60 annular front member