WO2016165857A1

WO2016165857A1 - Fuel pump

Info

Publication number: WO2016165857A1
Application number: PCT/EP2016/053478
Authority: WO
Inventors: Levent AKIN
Original assignee: Delphi International Operations Luxembourg S.À R.L.
Priority date: 2015-04-13
Filing date: 2016-02-18
Publication date: 2016-10-20
Also published as: GB201506173D0; EP3283756A1; EP3283756B1

Abstract

A fuel pump (10) having a head member (12) provided with a blind bore (14) in which a piston (26) is adapted to perform a pumping cycle by reciprocating along the main axis (X1) of the bore (14) between a top dead center (TDC) position and a bottom dead center (BDC) position. The piston (26) reciprocates under the influence of a rotating cam (36) cooperating with a follower assembly (34), a spring (46) compressed between the head member (12) and the follower assembly (34biasing the follower assembly (34) toward the cam (36). The pump (10) further comprises a stopper member (48) having resilient properties and being arranged to generate additional biasing force onto the follower assembly (34) when around TDC.

Description

Fuel pump TECHNICAL FIELD

The present invention relates generally to a fuel pump having a piston reciprocating in a bore under the influence of a cam follower fixed to the piston and rolling on a rotating cam. The invention particularly focuses on the cam follower assembly.

BACKGROUND OF THE INVENTION

Fuel injection equipment's comprise high pressure pump aiming at pressurizing fuel at several thousands of bars prior to flow said fuel to injectors that spray the fuel in combustion chambers of and internal combustion engine. Well known pumps comprise a pump head member provided with an inlet and an outlet both opening in a compression chamber that is near the blind end of a bore in which a piston slidably reciprocates along the pumping axis of the bore. The piston performs a pumping cycle between a Top Dead Centre (TDC) position around which fuel in the compression chamber is compressed and released toward the injectors and, a Bottom Dead Centre (BDC) position around which fuel is aspired in the chamber. The piston reciprocates under the influence of a cam rotating about a cam axis perpendicular to the pumping axis. The cam is followed by a follower assembly combined to an external extremity of the piston, said follower assembly typically having a cup-like body member in which a roller is free to rotate about a rolling axis perpendicular on the piston axis and parallel to the cam axis. Furthermore, a spring is compressed between the pump head member and the follower assembly in order to permanently bias the follower assembly against the cam.

Known problem is due to loss of roller/cam contact around TDC, said loss of contact damages the cam track surface and/or the roller surface. Regular increase in pressure, increase in rotational speed, or increase in pumping volume simply enhances that risk of lift-off.

SUMMARY OF THE INVENTION

It is an object of the invention to resolve or at least mitigate the above mentioned problem in proposing a fuel pump having a head member provided with a blind bore in which a piston is adapted to perform a pumping cycle by reciprocating along the main axis of the bore between a top dead center (TDC) position and a bottom dead center (BDC) position. The fuel is pressurized during the cycle in a compression chamber defined between the top extremity of the piston and the blind end of the bore. The piston reciprocates under the influence of a rotating cam cooperating with a follower assembly combined to the piston. The pump further comprises a spring compressed between the head member and the follower assembly in order to bias the follower assembly toward the cam. The pump further comprises a stopper member having resilient properties and being arranged to generate additional biasing force onto the follower assembly when around TDC.

In a particular embodiment, the stopper member is tubular and is engaged around the piston between the pump head member and the follower assembly so that it is axially compressed when the follower assembly approaches TDC.

Also, the stopper member is passive around BDC which means it does not generate any compression force on the follower assembly when around BDC.

Particularly, the stopper member comprises composite plastic material.

In another embodiment, the stopper member comprises a deformable cartridge filled with pressurized gas.

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 of a fuel pump as per the invention, the pump being in TDC position.

Figure 2 is similar to figure 1 the pump being in BDC position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In reference to the figures is represented a high pressure fuel unit pump 10 of fuel injection equipment. The unit pump 10 comprises a head member 12 provided with a blind bore 14 axially extending along a main axis XI and opening centrally in an under face 16 of a turret projection 18 that downwardly protrudes from the underside 20 of the head member 12. An inlet poppet valve 22, arranged at the top of the bore 14 controls a fuel inlet orifice 24 opening into the bore 14.

For clarity purposes this description utilizes the arbitrary orientation of the figures and words and expressions such as "top, bottom, under, over ..." may be utilized without any intention to limit the scope of the invention. Also, the bore 14 is identified as a "blind" bore even if it is open on its very top where is arranged the inlet orifice 24 controlled by the poppet valve 22. Indeed, in operation the inlet valve 22 sealingly closes the inlet orifice 24, the bore 14 actually being blind. In alternative embodiments of the pump said inlet valve may be radially arranged relative to the bore while an outlet check valve is arranged on the very top of the bore. A truly permanently blind bore can also be considered.

A shaft-like piston 26 slidably arranged in the bore 14 is partially inside the head member 12, where its top extremity 28 defines with the blind end of the bore a compression chamber 30 and also, partially extending outside the pump head member 12, downwardly protruding from the turret projection 18 toward a lower end 32. A cam follower assembly 34 is combined to the lower end 32, the follower assembly 34 cooperating with a rotating cam 36 which rotations about a cam axis X2 actuate the piston 26 in reciprocal axial XI displacements inside the bore 14.

The follower assembly 34 comprises a cup-like body 38 provided with aligned bearing means 40 for a roller 42 to freely rotate about a roller axis X3 perpendicular to the main axis XI and parallel to the cam axis X2. Inside the cuplike body 38 is arranged a spring seat member 44 for receiving a coil spring 46 axially XI arranged around the piston 26 and compressed between said spring seat member 44 and the underside 20 of the head member. The final upper spirals of the spring 46 are engaged around the turret 18 for the compression spring to be guided and to generate an upward force on the pump head member 12 and an opposite downward force on the follower assembly 34.

In operation the piston 26 reciprocally translates between a top dead center (TDC) position, represented figure 1 and, after a 90° rotation of the cam a bottom dead center (BDC) position represented figure 2, the stroke of the piston 26 depending on the profile of the cam 36. The angle of rotation, here 90°, depends on the cam profile which here has two lobes. Alternative cam design having just one lobe, or three, or four or more lobes enable to reach BDC after an angle rotation of 180° or 60° or 45°.

As visible on the figures, the pump assembly 10 further comprises a stopper member 48 engaged around the piston 26 and inside the spring 46 spirals between the turret 18 and the spring seat member 44. The tubular- like stopper member 48 is made of deformable resilient material such as plastic material or composite materials. In alternative embodiments the stopper member 48 can comprise a deformable cartridge filled with pressurized gas. Also, in still another alternative, the stopper member 48 could comprise the stack up of a plurality of disk springs cooperating with each other. As an example of a stopper member made with composite materials, the stopper member 44 could comprise an upper face and a lower face made of material of high toughness that is resistant to impact, steel is a possibility and, between these extreme faces, the stopper 44 could comprise an elastic core made, for instance, of unidirectional fiber plastic, said direction being the axial direction perpendicular to the upper and lower faces, so that when the stopper is compressed around TDC, the upper and lower faces receive the impact respectively with the turret and with the spring member, while the core axially compresses, the fibers distorting. During this deformation, the core damps the movement of the piston and the elasticity stored in the core during compression generates an additional force when the piston has passed TDC and is moving back toward BDC.

As visible on figure 2, the stopper member 48 is shorter in length than the axial length portion of the piston 26 protruding outward the turret 18 when in BDC so that, the stopper member 48 is not in contact with the spring seat member 44. In fact the stopper member 48 may be axially XI free, contacting neither the spring seat 44 nor the turret 18. In a preferred embodiment, the stopper member 48 is fixed to the turret 18, and just its lower extremity is not in contact in BDC.

As visible on figure 1, the stopper member 48 is axially lengthier than the axial length portion of the piston 26 protruding outward the turret 18 when around TDC so that, the stopper member 48 is compressed between the spring seat member 44 and the turret projection 18.

In use, during a revolution of the cam 36, the stopper member 48 is axially XI compressed when around TDC and, it generates on the follower assembly 34 a downward force adding to the spring force in order to bias the follower assembly 34 on the cam 36 and, when around BDC the stopper member 48 is not compressed, it takes its free length and does not generate any axial force.

In an alternative embodiment, the stopper member 48 could have a free axial length substantially equal to the axial length portion of the piston protruding outward the turret 18 when at BDC so that, in BDC the stopper member 48 is in contact without being compressed both with the turret 18 and the spring seat 44 and, as the cam 36 rotates, the stopper member 44 progressively compresses until reaching a maximum compression rate when at TDC.

LIST OF REFERENCES

mam axis

cam axis

roller axis

TDC Top Dead Center

BDC Bottom Dead Center

10 high pressure fuel unit pump

12 head member

14 blind bore

16 under face of a turret assembly

18 turret projection

20 underside of the pump head

22 inlet poppet valve

24 inlet orifice

26 shaft- like piston

28 top extremity of the piston

30 compression chamber

32 lower end of the piston

34 cam follower assembly

36 cam

38 cup-like body

40 bearing means

42 roller

44 spring seat member

46 coil spring

48 stopper member

Claims

1. Fuel pump (10) having a head member (12) provided with a blind bore (14) in which a piston (26) is adapted to perform a pumping cycle by reciprocating along the main axis (XI) of the bore (14) between a top dead center (TDC) position and a bottom dead center (BDC) position, fuel being pressurized during the cycle in a compression chamber (30) defined between the top extremity (28) of the piston and the blind end of the bore (14), the piston (26) reciprocating under the influence of a rotating cam (36) cooperating with a follower assembly (34) combined to the piston (32), the pump (10) further comprising a spring (46) compressed between the head member (12) and the follower assembly (34) in order to bias the follower assembly (34) toward the cam (36),

characterized in that

the pump (10) further comprises a stopper member (48) having resilient properties and being arranged to generate additional biasing force onto the follower assembly (34) when around TDC.

2. Fuel pump (10) as claimed in the preceding claim wherein the stopper member (48) is tubular and is engaged around the piston (26) between the pump head member (12) and the follower assembly (34) so that it is axially (XI) compressed when the follower assembly (34) approaches TDC.

3. Fuel pump (10) as claimed in claim 2 wherein the stopper member (48) is passive around BDC not generating any compression force on the follower assembly (34).

4. Fuel pump (10) as claimed in any one of the preceding claims wherein the stopper member (48) comprises the stack up of a plurality of disk springs cooperating with each other.

5. Fuel pump (10) as claimed in any one of the preceding claims wherein the stopper member (48) comprises plastic material.

6. Fuel pump (10) as claimed in any one of the preceding claims wherein the stopper member (48) comprises composite material.

7. Fuel pump (10) as claimed in claim 6 wherein the stopper member (48) comprises an upper face and a lower face made of material of high toughness that is resistant to impact such as steel and, between these extreme faces, the stopper member (48) comprises an elastic core.

8. Fuel pump (10) as claimed in claim 7 wherein said elastic core comprises unidirectional fiber plastic, said uni-direction being the axial direction perpendicular to the upper and lower faces,

9. Fuel pump (10) as claimed in any one of the claims 1 to 3 wherein the stopper member (48) comprises a deformable cartridge filled with pressurized gas.