GB2569172A

GB2569172A - High pressure fuel pump

Info

Publication number: GB2569172A
Application number: GB1720502.2A
Authority: GB
Inventors: T D Mchattie James
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2017-12-08
Filing date: 2017-12-08
Publication date: 2019-06-12
Anticipated expiration: 2037-12-08
Also published as: GB2569172B; GB201720502D0

Abstract

A high pressure fuel pump of an internal combustion engine is disclosed. The pump comprises a body 12 housing a camshaft 22 adapted to rotate about a camshaft axis X. The cam 26 cooperates via a cam follower 28 with a piston translating along a pumping bore 14 axis Z. The cam follower comprises a shoe member 34 and knuckle 32 which allow three rotational degrees of freedom between the pumping axis and the camshaft axis. The knuckle may have a spherical face 50 which is in sliding contact against a complementary spherical face of the shoe. The shoe face may be either convex or concave. The under face of the knuckle may define a cylindrical hollow in which one or more rollers may be arranged. Contact overstresses due to misalignment of the roller are avoid and so is the potentially for breakages.

Description

TECHNICAL FIELD

The present invention relates to a high pressure pump and, more particularly to a cam follower of said pump.

BACKGROUND OF THE INVENTION

In a high pressure fuel pump, a cam follower arranged between a camshaft and a piston cooperate to pressurise fuel in a compression chamber. Said cam follower comprises a tappet reciprocally guided in a pumping bore, said tappet having a piston side in contact with the piston, said side being pushed by a spring and, a cam side which holds a roller urged against the peripheral face of a cam. The roller rolls about an axis parallel to the camshaft axis and it contacts the cam along a thin line area. Contact overstress that may lead to breakage is due to misalignment of the roller. A very small rotation about the axis of said pumping bore rapidly reduces the roller-to-cam contact area consequently rising the contact load to a breaking point.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to resolve the above mentioned problems in providing a high pressure fuel pump of an internal combustion engine fuel injection equipment, the pump having a body housing a camshaft adapted to rotate about a camshaft axis and cooperating via a cam follower with a piston. The piston translates in a bore along a pumping axis. The cam follower comprises a shoe member and a knuckle allowing the three rotational degrees of freedom between the pumping axis and the camshaft axis.

The knuckle may be a semi-spherical member having a spherical face in sliding contact against a complementary spherical face of the shoe thus ensuring said three rotational degrees of freedom.

Opposed to said spherical face the knuckle has an under face defining a cylindrical hollow wherein the roller is arranged.

In an embodiment, the shoe spherical face is convex.

In another embodiment, the shoe spherical face is concave.

The cam follower may comprise two rollers arranged parallel to one another, both rollers being in contact against the peripheral face of said cam.

Said two rollers are arranged in two parallel cylindrical hollows provided in the knuckle under face.

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 pump provided with a cam follower as per the invention.

Figures 2 and 3 and 3D exploded sketches of said cam follower.

Figures 4 to 9 are 3D sketches of said cam follower illustrating a translation degree of freedom about a pumping axis.

Figures 10, 11 and 12 are sketches of said cam follower illustrating the rotational degree of freedom about a camshaft axis (Fig. 10), about a transverse axis (Fig. 11) and about said pumping axis (Fig. 12).

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 is a section of a high pressure diesel fuel pump 10 adapted to be arranged in an injection equipment of an internal combustion engine. Said pump 10 has a body 12 internally defining a pumping bore 14 extending, along a pumping axis Z, between an inner end where said pumping bore 14 perpendicularly opens in a camshaft bore 16 extending along a longitudinal axis X and, an outer end closed by a pumping head 18 fixed to an outer face of the body 12. A turret member 20 integral to the pumping head extends in the pumping bore 14 between an under face of the pumping head and a turret end face. The head 18 is internally provided with a piston bore coaxial to the turret and to the pumping bore, said bore extending between a blind end defining a compression chamber and an open end opening in said turret end face.

In said camshaft bore 16, a camshaft 22 having a cam 24 is rotatable about said camshaft axis X between two bearings, said cam 24 having a peripheral face 26 followed by a cam follower 28 cooperating with a piston 30 slidably guided in said piston bore.

The cam follower 28 comprises a knuckle 32 arranged between a shoe member 34, cooperating with the piston 30, and two rollers 36, 38 rolling on said cam peripheral face 26.

The shoe member 34 is reciprocally guided along the pumping axis Z in the inner end of the pumping bore, either having its peripheral face 40 directly against the faces of the bore or, sliding in a shoe guide 42 press-fitted in said bore. Said peripheral face 40 can have a rectangular or polygonal cross section as commonly known, or a circular cross section as shown in figures 2 and 3. The shoe 34 has a piston side 44 receiving the bottom end 31 of the piston. A pump spring 46 engaged around the turret is compressed between the pumping head under face and said shoe piston side 44 permanently pushing the cam follower toward the camshaft. Opposite to the piston side 44, the shoe has a cam side 46 defining a spherical concave face 48.

Below the shoe 34 (following the arbitrary top-down orientation of the figures) the cam follower 28 comprises said knuckle 32 that is a semi-spherical member having a convex spherical top face 50 complementary to the concave face 48 of the shoe member, said two complementary spherical faces being engaged in a sliding surface contact. Opposite said top face 50, the knuckle has a flat under face 52 wherein the two rollers 36, 38 are rotatably arranged in two parallel hemicylindrical hollows 54, 56 having their hollow axis substantially parallel to said flat under face 52.

When assembled as shown on figure 1, the spring 46 downwardly pushes the shoe member 34, then the knuckle 32 and finally the rollers 36, 38 that are urged in permanent contact against the cam peripheral face 26.

The generatrixes of the cam peripheral face 26 are parallel to the camshaft axis X and, the cam follower 28 enables each of the rollers 36, 38 to maintain a permanent contact with one of said generatrix regardless minor misalignments, thus, this minimises stresses generated by the surface contact pressure between the roller and the cam. Indeed the sliding of the shoe 34 enables a translation degree of freedom TZ along said pumping axis Z (figures 4-9) and, the knuckle 32 to shoe 34 spherical link enables the three rotational degree of freedom RX about the camshaft axis X (figure 10), about the pumping axis RZ (figure 12) and, about a transverse axis RY (figure 11) perpendicular to both axes

X, Z. Having two parallel rollers stabilises the general orientation of the rollers and also of the knuckle.

Moreover, as it is sketched, the rotational degree of freedom RZ bout the pumping axis Z due to the spherical knuckle 32 cooperating with the spherical shoe 34 can be enhanced by shaping the shoe as a cylindrical member and enabling the shoe to rotate in the shoe guide, or in the pump body.

In the figures 11 and 12 misalignments are strongly exaggerated. In use, the rotational moves are very small and, to last and perform in time the knuckle/shoe contact requires lubrication of the spherical contact spherical. Such lubrication can be provided by arranging grooves (not shown) in at least one of the two surfaces, lubricant flowing in said grooves or, by drilling one or several channels opening in a middle area of said surfaces and their bringing lubricant fluid.

LIST OF REFERENCES

X longitudinal axis

Y transverse axis

Z pumping axis

TZ, RX, RY, RZ degrees of freedom fuel pump body of the pump pumping bore camshaft bore pumping head turret camshaft cam peripheral face of the cam cam follower piston bottom end of the piston knuckle shoe roller roller peripheral face of the shoe shoe guide shoe piston side spring concave spherical face - shoe under face convex spherical face - knuckle top face knuckle under face cylindrical hollow cylindrical hollow

Claims

CLAIMS:

1. High pressure fuel pump (10) of an internal combustion engine fuel injection equipment, the pump (10) having a body (12) housing a camshaft (22) adapted to rotate about a camshaft axis (X) and cooperating via a cam follower (28) with a piston (30) translating along a pumping axis (Z), said cam follower (28) comprising a shoe member (34) and a knuckle (32) allowing the three rotational degrees of freedom (RX, RY, RZ) between the pumping axis (Z) and the camshaft axis (X).

2. Pump (10) as claimed in the preceding claim wherein a spherical face (50) of the knuckle is in sliding contact against a complementary spherical face (48) of the shoe ensuring said three rotational degrees of freedom.

3. Pump (10) as claimed in claim 2 wherein opposed to said spherical face (50), the knuckle (32) has an under face (52) defining a cylindrical hollow (54, 56) wherein the roller (36, 38) is arranged.

4. Pump (10) as claimed in claim 3 wherein the shoe spherical face (48) is convex.

5. Pump (10) as claimed in claim 3 wherein the shoe spherical face (48) is concave.

6. Pump (10) as claimed in any of the preceding claims wherein the cam follower (28) comprises two rollers (36, 38) arranged parallel to one another, both rollers being in contact against the peripheral face (26) of said cam.

7. Pump (10) as claimed in claim 6 taken in combination with any one of the claims 3 to 5 wherein said two rollers (36, 38) are arranged in two parallel cylindrical hollows (54, 56) provided in the knuckle under face (52).