GB2577677A

GB2577677A - High pressure pump shoe

Info

Publication number: GB2577677A
Application number: GB1815387.4A
Authority: GB
Inventors: Guerrato Diego; Mccrindle Christopher
Original assignee: Delphi Technologies IP Ltd
Current assignee: Delphi Technologies IP Ltd
Priority date: 2018-09-21
Filing date: 2018-09-21
Publication date: 2020-04-08
Anticipated expiration: 2038-09-21
Also published as: GB201815387D0; GB2577677B

Abstract

A high pressure pump arrangement including a cam and a pump plunger, the cam being adapted to provide reciprocating motion to a pump plunger via a shoe arrangement, the shoe arrangement includes a shoe that includes at least one internal recess 11. Preferably the shoe arrangement includes a longitudinal roller 4 in contact with the cam surface, where the shoe is located between the distal end of the plunger and the roller. The internal recess is preferably perpendicular to the axis of the roller. The recess may comprise a slot, hole or bore with a circular or elliptical cross section. The shoe may be formed from an upper section and a lower section that when brought together provide the recess, where the upper portion comprises a top surface adapted to contact the distal end of the plunger and includes a protrusion on the opposite surface and where the bottom surface includes a corresponding recess adapted to receive the protrusion with the recess being provided between the distal end of the protrusion and the bottom dace of the recess.

Description

HIGH PRESSURE PUMP SHOE

TECHNICAL FIELD

This invention relates to high pressure fuel pumps and particular application of high pressure fuel pumps which comprise a cam driven plunger adapted to pressurize fuel in a pressurization chamber.

BACKGROUND OF THE INVENTION

The maximum fuel pressure delivered by e.g. common rail fuel pumps is increasing with more stringent emissions controls. As the pumping pressure increases, the drivetrain, that connects the engine to the pumping element, is working under more and more severe conditions. Single plunger pumps are usually equipped with a multi lobe cam and rolling follower that moves in and out as it rolls on the cam. To complete the mechanism another element usually named shoe is required. The shoe's task is to ensure that the roller moves along a designed path as the cam rotates. The shoe pivots and slides on a guide which is fixed in the pump housing.

A roller follows the cam surface and slides with a hydrodynamic bearing within the shoe. The film within the hydrodynamic bearing is critical to the function of the pump preventing high friction loads, component wear and cam scuffing.

It is an object of the invention to provide improved shoe designs to enhance lubrication between shoe and roller at the mating surfaces.

SUMMARY OF THE INVENTION

In one aspect is provided a high pressure pump arrangement including a cam and a pump plunger, said cam adapted to provide reciprocating motion to a pump plunger, via a shoe arrangement, said shoe arrangement including a shoe; where said shoe includes at least one internal recess.

Said recess may comprises a slot, hole or bore.

Said shoe arrangement includes a longitudinal roller in contact with said cam surface, and wherein said shoe is located between the distal end of said pump plunger and said roller.

Said internal recess is arranged preferably generally perpendicular to the axis of said roller.

The cross section of said bore or hole is preferably circular or elliptical.

Said shoe may be formed from an upper portion and a lower portion, such that that when located together provided said at least one internal recess.

Said upper portion may comprise a top surface adapted to contact the distal end of the plunger and includes a protrusion on the opposite surface thereof, and said bottom portion includes an appropriately formed recess adapted to receive said protrusion, said internal recess being provided between the distal end of said protrusion and the bottom face of the recess.

Either the top surface of said bottom portion or the top surface of said bottom portion include raised portions on either side end when viewed perpendicular to said roller longitudinal axis, providing a centrally located gap or recess between said the top surface of said bottom portion and the top surface of said bottom portion.

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 shows a schematic representation of a portion of a prior art design of high pressure pump system; Figure 2a and b shows an example according to one embodiment;.

-Figures 3a 3b and 3c show a further embodiment -Figures 4a 4b and 4c show a further refined embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 shows a schematic representation of a portion of a prior art design of high pressure pump system which details arrangement between a cam, of which is partially shown by reference numeral 2 and plunger (piston) 8. A barreled roller 1 is located between the cam 2 and a shoe 3. In normal operating conditions, the shoe, held by a guide 5, acts as a bearing while a roller 1 acts as a journal and a lubricating film 6 is generated between the parts. The figure shows a cut away portion of the shoe 3 to show the lubrication film 6 and how its thickness varies. Rotation of the cam moves the barelled roller up and down consequently,moving the shoe up and down which in turn moves the plunger up and down.

The profile of the roller 4 i.e. in its axial direction as shown by the thick double headed arrow is designed in such a way that contact pressure between the roller and the cam is kept within safe boundaries, but the out coming fluid film shapes generated between the running surfaces of the shoe and the roller, makes the lubrication difficult. In fact as the rotating motion of the roller is entraining the lubricating liquid 6 which is effectively formed in the gap thereof, a large amount of it is flowing towards the roller ends where the gap is larger. Only a small part of the fluid near the median plane of the roller is actually providing the hydrodynamic. This has the unwanted consequence of reducing the film gap and concentrating the hydrodynamic pressure on a small portion of the running surfaces 7. To make things worse the shoe and the pumping element (plunger piston) 8 meet on a small region 9 above the roller that causes local deformation of the shoe, further encouraging pressure concentration.

Description of the Invention.

According to one aspect, examples provide designs which effectively change the effective running surface profile of the shoe 7 and hence the gap profile/fluid film, 6, thus spreading the hydrodynamic pressure over a larger region especially at high load. The resulting minimum film thickness increase dropping asperity contact, friction, wear and debris generation. The overall pump mechanical efficiency is also be improved. In aspects of the invention provided an internal gap or recess is provided in the shoe which spreads the plunger load towards the ends of the shoe; this allows e.g. deformation of the lower surface of the shoe to provide this effect.

The effective running surface profile of the shoe 7 and hence the gap profile/fluid film, 6, is changed by reducing the stiffness in the central region of the shoe; so i.e. in examples according to the invention, geometric features are provided which reduces the stiffness in the central region of the shoe. As the plunger load increases, designs according to such examples elastically deform in a such a way that the shoe running surface 7/10 and the roller profile 4 generate a more uniform film.

In a general aspect, the shoe is provided with an internal gap or recess which provides the requisite deformation to generate a more uniform film.

Example 1

In one aspect the shoe is provided with a hole or recess. The hole is preferably round (circular) or elliptical. The hole or recess is preferably arranged generally perpendicular to the longitudinal axis of the roller. The hole may be formed such that it goes all the way through to the other side of the shoe or may be partial such that it does not i.e the hole/recess can be any depth.

Figure 2a and b shows an example according to this aspect. Figure 2 is similar to figure 1 and has the same reference numerals. However here one or more holes (not necessarily circular) 11 are located e.g. on the median plane of a thus modified shoe 10, perpendicular to the roller. Figure 2b shows an isometric view of the complete modified show 10 with round hole 11. A generally rounded shape will avoid any stress concentration, while variations in the exact size, shape and location would be readily envisaged by the skilled person and according to, e.g. optimization for the specific design and application. Other components are the same with the same reference numerals as figure 2.

Example 2

Now will be described examples where the shoe internal gap is provided by the shoe being formed in two or more sub-components (parts) such that when assembled together, an internal gap is formed between them.

One of these embodiments is shown in figure 3 a, b, c -this includes a two component shoe assembly of the shoe 12 having a shoe upper portion 12a which has a protrusion 13 that locates into an appropriately formed recess 14 in a lower shoe portion 12b part of the shoe. The upper and lower portions of the shoe are so dimensioned that a gap 17 is formed between the face 15 (distal end) of the protrusion in the upper shoe portion and the (bottom face 16) recess in the lower shoe portion. This gap 17 is shown more clearly in figure 3c which is similar to figures 1 and 2 where similar components have similar reference numerals. So the figure shows the shoe comprising upper and lower shoe portions together arranged in the cam driven plunger arrangement.

The protrusion and complementary recess acts to both guide the components into the correct position and provide for the gap dimension which thus act to select the correct shoe stiffness in the key region 18. There is thus preferably a sufficient gap between the protrusion 13 and the bottom of the recess 16 to avoid any contact even in the most severe ruining conditions.

Further Example

In a further revised and refined embodiment shown in figure 4 a, b, and c. The design is similar to that of figure 3 with like reference numerals referring to the same components. Here the top surface of the lower portion of the shoe has in one or more places, some material removed to provide slight recess region(s) 20 to provide additional gaps. This recess is arranged perpendicular to the axis of the roller so as to form at least two side walls or protrusion or raised portions 22,23 at either edge/side of the lower shoe portion when viewed or with respect to the perpendicular to the roller axis. In the example given, a recess in the top surface of the bottom shoe portion is in the form of a cut away portion 20 such that an additional gap 21 is provided and the contact between the upper and lower shoe portions is only at the two end surfaces 22 and 23 of the top portion of the lower shoe, said ends being at spaced locations with respect to the central longitudinal axis of the roller. This arrangement directs the load towards the shoe ends. This arrangement distributes the load and allows the shoe stiffness to be varied in the key region.

Claims

CLAIMS1. A high pressure pump arrangement including a cam and a pump plunger, said cam adapted to provide reciprocating motion to a pump plunger, via a shoe arrangement, said shoe arrangement including a shoe; where said shoe includes at least one internal recess.
2. An arrangement as claimed in claim 1 wherein said recess comprises a slot, hole or bore.
3. An arrangement as claimed in claim 1 where said shoe arrangement includes a longitudinal roller in contact with said cam surface, and wherein said shoe is located between the distal end of said pump plunger and said roller.
4. An arrangement as claimed in claims 3 wherein said internal recess is arranged generally perpendicular to the axis of said roller.
5. An arrangement as claimed in claim 1 to 4 wherein the cross section of said bore or hole is circular or elliptical.
6. An arrangement as claimed in claims 1 to 5 where said shoe is formed from an upper portion and a lower portion, such that that when located together provided said at least one internal recess.
7. An arrangement as claimed in claim 6 wherein said upper portion comprises a top surface adapted to contact the distal end of the plunger and includes a protrusion on the opposite surface thereof, and said bottom portion includes an appropriately formed recess adapted to receive said protrusion, said internal recess being provided between the distal end of said protrusion and the bottom face of the recess.
8. An arrangement as claimed in claim 6 wherein either the top surface of said bottom portion or the top surface of said bottom portion include raised portions on either side end when viewed perpendicular to said roller longitudinal axis, providing a centrally located gap or recess between said the top surface of said bottom portion and the top surface of said bottom portion.