GB2569135A

GB2569135A - Camshaft of a high pressure fuel pump

Info

Publication number: GB2569135A
Application number: GB1720328.2A
Authority: GB
Inventors: Jones David
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2017-12-06
Filing date: 2017-12-06
Publication date: 2019-06-12
Also published as: GB201720328D0

Abstract

A camshaft 22, for a high pressure fuel pump 10 of an i.c. engine, comprises a cam 26 having a peripheral face 28 extending between a front face 32 and a parallel rear face 30. A cam follower cooperates with the peripheral face 28. A cut-out 40 is provided in the front face 32, the cut-out 40 extending, eg with decreasing depth, from a front end 48 in the front edge 34 of the front face 32, to a rear end 50 that is inside the front face 32. Fuel is pressurized in the cut-out 40 generating rearward axial forces while fuel leaking from the cut-out rear end 50 lubricates the front face 32. The cut-out 40 may have a rectangular cross-section and may extend in a direction (D40, fig.3) perpendicular to a camshaft radius (R, fig.3). A plurality of cut-outs 40 may be arranged side-by-side. The cam 26 may be integral with its driveshaft; alternatively, the cam and driveshaft may be independent members, eg of different steels.

Description

CAMSHAFT OF A HIGH PRESSURE FUEL PUMP

TECHNICAL FIELD

The present invention relates to a camshaft of a high pressure fuel pump.

BACKGROUND OF THE INVENTION

In a high pressure fuel pump a camshaft driven in rotation by a belt and pulley or by gears rotates in a cambox and urges a piston to reciprocal displacements pressurising fuel in a compression chamber. In use, a transverse front face of a cam is pressed against a thrust face of the pump housing, the relative sliding wearing said faces. The axial forces frontwardly pushing the camshaft are generated hydraulically by net pressure forces in the cambox and mechanically by slight belt-misalignment with belt-driven pumps, or most commonly by the axial component of force for helically gear-driven pumps.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a camshaft of a high pressure fuel pump of an internal combustion engine injection equipment, said camshaft extending along a longitudinal axis and comprising a driveshaft and a cam. Said cam defines a peripheral face, a front side face transverse to said axis and a parallel rear side face, wherein a cut-out is dug in said front face. The cut-out extends from a front end that is in the front edge of said front face to a rear end that is inside said front face, said cut-out being provided in an area that is, in use, in surface contact against a pump housing thrust face.

Said cut-out may have a bevelled profile having a decreasing depth from said front end to said rear end and, the cut-out rear end depth may be null.

the cut-out may have a rectangular cross-section with two opposed side walls, said a bottom face to the front face.

From the front end to the rear end, the cut-out may follow a general direction that is substantially aligned with the rotational direction of the camshaft, following said general direction, the front end is ahead to the rear end.

The cam may be provided with a plurality if cut-outs regularly arranged on the cam front face.

In an embodiment, said camshaft may be a monobloc part, the cam being integral to the driveshaft.

In another embodiment, said camshaft may be a composite component, the cam being an independent member fixed onto the driveshaft.

In said another embodiment, the driveshaft and the cam member may be made out of different steel.

The invention further extends to a high pressure fuel pump having a housing defining a camshaft bore and a piston bore, a camshaft, as described in the preceding lines, being arranged in the camshaft bore.

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 comprising a camshaft as per the invention.

Figure 2 is a 3D view of a cam of said camshaft.

Figure 3 is a view from a front end of said camshaft.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows in axial section along a longitudinal axis L, a high pressure fuel pump 10 adapted to be in a diesel fuel injection equipment of an internal combustion engine. Said pump 10 has a body 12 internally defining a camshaft bore 14 extending along said longitudinal axis L and, a perpendicular piston bore 16 that is in another plan than the section plan of figure 1. Said camshaft bore 14 is blind on a rear side 10R of the pump, there defining a rear bearing 18R and, in an opposite front side 10F of the pump said bore 14 opens defining a large aperture 20 for a camshaft 22 to be inserted and arranged in said bore 14 during the assembly of the pump. Once said camshaft 22 is in place said aperture 20 is closed by fixing a front plate 24 on said body 12, the front plate 24 being provided with an aperture defining a front bearing 18F coaxial to the rear bearing 18R. The camshaft 22, arranged between said rear 18R and front 18F bearings, has a front end 22F extending outside the pump through said front bearing 18F for enabling complementary engagement of rotational driving means such as gears or a belt and pulley.

The camshaft 22 is provided with a cam 26 that, in the embodiment of figure 1 is integral to a driveshaft and that, in another embodiment (not shown) is a separate member press-fitted, or fixed by any other means, over said driveshaft. Whichever embodiment, integral or composite, the driveshaft defines a cylindrical rear journal and a cylindrical front journal slidably rotatable in said rear 18R and front 18F bearings, the cam 26 being arranged between said journal faces and facing the opening intersection between the piston bore 16 and the camshaft bore 14, thus enabling a cam follower cooperating with a piston to engage the cam 26 and to follow the profile of the cam peripheral face 28. Said peripheral face 28 axially L extends between a rear side face 30 and a front side face 32 and, in the example shown on figures 2 and 3, said front face 32 is directly the side face of the cam which intersects the cam peripheral face 28 along a front edge 34 that follows the profile of said peripheral face. In the alternative of figure 1, a circular flange 36 is arranged on the front side of the cam and, said front face 32 is integral to said flange 36, the front edge 34 being in this case a circle. The front face 32 is in sliding contact against a thrust face 38 integral to the front plate 24, said thrust face 38 defining a transverse annular flat area surrounding the aperture of the front bearing 18F.

In use the camshaft 22 rotates and is pushed by combined hydraulic and mechanical frontward forces and, to prevent or at least to mitigate wear between the front face 32 and the thrust face 38, said front face 32 is provided with a cutout 40, as shown on figures 2 and 3, that opens on the front edge 34 of the front face 32.

Said cut-out 40 defines an area of the front face 32 where material has been removed forming a groove in said front face 32. In the embodiment presented on the figures, the cut-out 40 is dug in said front face 32 defining a bevelled bottom face 42 bordered by an inner wall 44, closer to the axis L, and an outer wall 46 more distant from the axis L. The bottom face 42 extends along a cut-out direction D40, substantially perpendicular to a camshaft radius R, from a front end 48 arranged in said front edge 34, where the cut-out depth is maximum, to a rear end 50 where the depth is null, the bottom face 42 intersecting directly the front face 32. As it is visible, the inner 44 and outer 46 walls of the cut-out have are narrow triangles with long sides extending between the front end 48, where they are distant from one another by the depth of the cut-out and, the rear end 50 where they join a common rear end 50. Also, considering the rotational direction of the camshaft, the front end 48 of the cut-out is ahead to the rear end 50, so that in use, the camshaft rotation forces fuel to enter the front end 48 of the cut-out said fuel being pushed toward the rear end 50 where it gets squeezed between the bevelled bottom face 42 and the thrust face 38 of the front plate. The fuel pressurised in the cut-out 40 generates axial rearward forces acting against the frontward forces previously mentioned. Moreover, some fuel leaking by the cut-out read end 50 lubricate the front face and the thrust face helping to reduce wear. When the front face 32 is against the thrust face 38, the cut-out 40 shown in the example, has a rectangular cross section which long sides remain unchanged and short sides reduce as approaching the rear end of the cut-out.

The camshafts shown on figures 2 and 3 are designed for a clockwise rotational direction, arrow A22, and therefore the front end 48 of the cut-out is ahead, or more advanced in said direction, than the rear end 50.

In alternative, not shown, the cut-out 40 can take other shapes, for instance the cut-out may be a groove with a continuous circular profile or any other smooth profile. The depth can either be constantly decreasing as shown in the example or more abruptly closer to the rear end. Also, the embodiment shows one cut-out while several smaller cut-out may be arranged side by side.

Moreover, the cam 26 of the camshaft of figure 3 is a symmetrical two lobes cam 26 and, for balancing the camshaft, it is provided with two cut-outs 40 diametrically opposed and substantially parallel to one another. Balance of shaft is a major concern and the multitude of cut-outs 40 increases the effect of the pressure-building mechanism.

LIST OF REFERENCES

L longitudinal axis

R radius

D40 direction of the cut-out

A22 direction of rotation of the camshaft pump

10R rear side of the pump

10F front side of the pump body camshaft bore piston bore

18R rear bearing

18F front bearing aperture camshaft

22F front end of the camshaft front plate cam peripheral face of the cam rear face of the cam front face of the cam front edge of the front face flange thrust face of the front plate cut-out bottom face inner wall outer wall front end of the cut out rear end of the cut out

Claims

1. Camshaft (22) of a high pressure fuel pump (10) of an internal combustion engine injection equipment, said camshaft extending along a longitudinal axis (L) and comprising a driveshaft and a cam (26), said cam defining a peripheral face (28), a front side face (32) transverse to said axis (L) and a parallel rear side face (30), wherein a cut-out (40) is dug in said front face (32) the cut-out extending from a front end (48) that is in the front edge (34) of said front face, to a rear end (50) that is inside said front face, said cut-out being provided in an area that is, in use, in surface contact against a pump housing thrust face (38).

2. Camshaft (22) as claimed in the preceding claim wherein said cut-out has a bevelled profile having a decreasing depth from said front end (48) to said rear end (50).

3. Camshaft (22) as claimed in claim 2 wherein the cut-out rear end (50) depth is null.

4. Camshaft (22) as claimed in any one of the preceding claims wherein the cut-out has a rectangular cross-section with two opposed side walls (44, 46), said a bottom face (42) to the front face (32).

5. Camshaft (22) as claimed in any of the preceding claims wherein, from the front end (48) to the rear end (50), the cut-out follows a general direction (D40) that is substantially aligned with the, in use, rotational direction (A22) of the camshaft.

6. Camshaft (22) as claimed in claim 5 wherein following said general direction (D40), the front end (48) is ahead to the rear end (50).

7. Camshaft (22) as claimed in any one of the preceding claims wherein the cam is provided with a plurality if cut-out (40) regularly arranged on the cam front face.

8. Camshaft (22) as claimed in any one of the preceding claims, said camshaft being a monobloc part, the cam being integral to the driveshaft.

9. Camshaft (22) as claimed in any one of the claims 1 to 7 said camshaft

5 being a composite component, the cam being an independent member fixed onto the driveshaft.

10. Camshaft (22) as claimed in claim 9 wherein the driveshaft and the cam member are made out of different steel.

11. High pressure fuel pump (10) having a housing (12) defining a camshaft bore (14) and a piston bore (16), a camshaft (22) as claimed as in any one of the preceding claims being arranged in the camshaft bore.