GB2540548A

GB2540548A - Novel pump design

Info

Publication number: GB2540548A
Application number: GB1512683.2A
Authority: GB
Inventors: Cheron Antonin; Emery Charlie
Original assignee: Delphi International Operations Luxembourg SARL
Current assignee: Delphi International Operations Luxembourg SARL
Priority date: 2015-07-20
Filing date: 2015-07-20
Publication date: 2017-01-25
Also published as: GB201512683D0

Abstract

An arrangement adapted to provide a reciprocating drive to a plunger 2 of a fuel pump comprising: a drive shaft (3, fig 1) having an eccentric 4 located thereon, and a rider 5 located on the eccentric. The rider has a surface 6, which may be flat. The plunger is connected to the surface via a mechanical joint and arranged such that rotation of the drive shaft causes movement of said surface including a component comprising reciprocating movement in a first axis, causing corresponding reciprocation of the plunger; the joint allows relative movement between the surface and plunger in a direction perpendicular to said first axis. The mechanical joint can be a dovetail arrangement. The plunger may be fitted to a tappet, which forms the joint with the surface. The mechanical connection removes the need for a spring.

Description

Novel Pump Design

Field of the Invention

This disclosure relates to fuel pumps and has particular application in piston driven fuel pumps, such as those driven by a plunger arrangement, adapted to reciprocate to pressurize fuel in a chamber.

Background to the Invention

Some Diesel pumps currently utilise a technology called “Slipper Tappet”. This technology relies on an eccentric orbiting surface which allows translation of circular motion (e.g. from a rotating shaft) to linear motion in order to provide translation movement of a plunger to provide linear pumping motion.

In such arrangements, generally speaking, a drive shaft is driven with an eccentrically located circular lobe, often referred to as an “eccentric”, over which a rider is fitted. Rotation of the drive shaft (and eccentric lobe) causes a circular type motion of the rider causing the rider (vertical) surface to also move up and down in a reciprocating motion. This drives a tappet/plunger (rod) arrangement so as to provide movement of a plunger to pressurize fuel in a chamber.

In pumps based on a rider-tappet arrangement driven by an eccentric on the driveshaft, the plunger or plungers (and the tappet if present between the rider and each plunger) are usually held in contact with the rider by a return spring. This spring compresses and extends to follow the compression and suction strokes.

There are two issues with this arrangement. The contact force the spring applies to the plunger and/or tappet increases as the plunger approaches Top Dead Centre (TDC). Therefore the spring is subject to fatigue failure, and the forces applied are far superior to what is needed in most working conditions. The force required from this spring depends on the moving masses of the spring and tappet, the drive shaft rotational speed and the stroke. Every time either of these parameters is increased, the spring has to be redimensioned and sometimes it becomes impossible to pack a spring stiff enough and with sufficiently low stresses in the available space. If the spring force is not high enough, not only may the plungers may lose contact (having the effect of a reduced stroke hence a loss of volumetric efficiency), but also the rider may rotate (its normal motion is a circular translation) with the potential to destroy the pump and cause severe damage to the engine.

It is known to maintain contact between plunger and rider by using a clip that holds the plunger on the rider surface. This design requires the running face of the rider and tappet to remain parallel and for the spring to return the plunger and tappet with such velocity to maintain contact with the running surface (else catastrophic failure can occur). Should the rider rotate, the tappet and rider will collide at a relative position that geometry does not allow and a seizure or breakage will occur. Should the spring not return the tappet and plunger at sufficient rate, then contact will be lost and seizure and damage will occur. In one design this clip concept comprises a thin spring steel clip that holds a plunger down to a rider. The principle is similar but has the limitations of requiring a footed plunger concept which has speed and pressure limitations.

An alternative exists, in the form of a C-shaped component that clamps the plunger assemblies of a multi-plunger pump against the rider, but this solution uses a lot of space inside the cam box, around the rider.

The need for higher pump speeds require the tappet return springs to be capable of returning the plunger faster from the TDC position thereby increasing the dynamic stress. To do this the spring forces are required to be greater which means that the static stresses are also higher. These conditions bring the springs operating range closer to the fatigue life limits

Modem applications are requiring ever increasing pump running speed but still with tight packaging requirements. This means that is becoming very difficult to design a spring that will be capable of high durability at these speeds leading to spring failures that would be catastrophic to pump operation (pump seizure).

It is an object of the invention to overcome the problems of rider rotation, insufficient spring performance and spring fatigue.

Statement of the Invention

In one aspect of the invention is provided an arrangement adapted to provide a reciprocating drive to a plunger of a fuel pump comprising: a drive shaft having an eccentric located thereon, and a rider located on said eccentric, said rider including a surface, and wherein said plunger is mechanically connected to said surface via a mechanical joint and arranged such that rotation of the drive shaft causes movement of said surface including a component comprising reciprocating movement in a first axis, causing corresponding reciprocation of said plunger, characterized where said joint allowing relative movement between said surface and plunger in a direction perpendicular to said first axis.

The said surface may be a flat surface.

Said joint preferably allows relative movement between said surface and plunger in a direction perpendicular to the drive shaft axis and does not allow relative movement between said surface and said plunger in said first axis.

Preferably said mechanical joint comprises a dovetail arrangement.

The plunger is preferably fixedly connected to a tappet, and said tappet forms said mechanical joint with said rider surface.

The surface of said rider preferably includes a dove-tailed groove or ridge forming part of said mechanical joint with a corresponding dovetail ridge or groove on said tappet or plunger.

So in one aspect is provided that mechanically engages the tappet and plunger to the rider in the vertical dimension whilst still allowing lateral translation.

Brief Description of Drawings

The invention will now be described by way of example and with reference to the following figures of which:

Figure 1 shows a schematic cross section though a prior art drive arrangement for a reciprocating fuel pump; and.

Figures 2a, b, c, d show schematic representations of one example of the invention.

Detailed Description of the Invention

Figure 1 shows a schematic cross section though a prior art drive arrangement 1 for a reciprocating fuel pump. The pump is driven by a plunger 2 which moves up and down (arrow A) in a reciprocating fashion to pressurize fuel in a pump chamber (not shown). The reciprocating movement of the plunger is provided by an eccentric and rider arrangement. A drive shaft 3 is rotated on which is located a circular lobe or eccentric 4. Over this eccentric is located and positioned a rider 5 which has a flat surface 6 at the top and may additionally have a flat surface at the bottom. Rotation of the drive shaft causes the rider to have a particular rotational type movement whilst being generally maintained in the same alignment. The movement is such that the surface 6 is caused to move with vertical (up and down) component as shown by the arrow B (this is the motion that it imparts to the tappet and thus plunger - arrow A) but also has a small translational component left to right in the drawing shown as arrow C. Typically a tappet 7 may be optionally is provided rides on the rider and which is connected to the plunger. The tappet is used to retain a spring 8, supported by a portion of the pump housing 9. The spring acts to maintain contact of the tappet against the surface of the cam rider. For stability, a similar tappet spring arrangement may be positioned against the lower surface of the cam rider.

The problems of the above arrangement are described above.

Figure 2 shows a schematic representation of one example of the invention.

Figure 2a shows a schematic view of an example of the invention and shows a view of an arrangement from the same elevation perspective as figure 1. Figure 2b shows a sectional schematic view in the direction of arrow X of figure 2a. Figure 2c shows the circled region D of figure 2b in more detail. Figure 2d shows an isometric view of the arrangement.

In the example of figure 2a b and c, a plunger 2 is fitted to a tappet 7 by means of e.g., an interference fit. The bottom surface of the tappet includes a dovetailed groove which is adapted to conform to similar dovetail profiled ridge formed in the rider top surface. It is to be understood that the plunger and tappet may be formed as a single component, and hence the tappet effectively dispensed with, and that the groove may alternatively be located on the rider surface and the ridge on the rider or tappet bottom surface.

Thus the tappet/rider surface is provided with a dovetailed joint, which allows the tappet to slide relative to the rider surface in the direction of arrow C. This is also the equivalent direction to arrow C in figure 1 also. Of course the sliding joint may be provided by other configuration.

Figure 2d shows an isometric perspective.

Such a sliding joint (dovetail joint or similar) will not only maintain a minimal relative articulation between tappet and rider components (based only on interface clearance), reducing chance of drivetrain instability, but also eliminating (or at least reducing) the need of a return spring. In examples, a clipping mechanism or similar may be required to maintain contact between the plunger and tappet. The skilled person would understand how to select suitable joint conditions from material hardness, surface finish, lubrication etc..

The dovetail/sliding joint maintains a parallel running surface and is more pertinent to a multi plunger pump as most if not all single plunger pumps utilise the differing “Roller Shoe” technology.

The mechanical connection removes the need for a spring and so eliminates the risk and also reduces pump component count.. The issues linked with the fact that a conventional spring has to compress and extend by the amount of stroke are solved by the fact that the device filling the same function is attached to the rider rather than the pump’s housing or other fixed part (usually the bottom face of the hydraulic heads), therefore the distance between its contact with the plunger assembly and the opposite contact (with the rider) stays constant regardless of the working conditions. In reality there are strains, but these are only due to stresses in components when subjected to forces and are negligible compared to the compression seen by a conventional spring.

The issue of “rider rotation” is solved by the fact that by adequate dimensioning, the examples of the invention maintain the sliding face of the rider sufficiently parallel to the plunger assembly’s mating face. Minimal separation is permitted by working clearances between parts or the unavoidable material elasticity of the components, but no significant rotation is possible. In addition, whereas a conventional spring applies a contact force between rider and plunger assembly even when not needed (during the compression stroke for example), causing friction forces (hence energy consumption and wear), a rigid component assembled with only working clearances does not add to the contact force already generated by pumping pressure. Minimal clearance even appears at the down stroke, helping with lubrication as this clearance is filled with fuel acting as the lubricant.

Aspects of the invention can be applied to all slipper-tappet pump arrangements, regardless of the number of pumping plungers. In a family of pumps, every plunger (or plunger assembly) and clamp can be identical, only the number of flats and corresponding sliding slots on the rider must change The distance between rider and hydraulic head can be reduced, because the constraints associated with coil spring minimum length are avoided.

One feature permitting these advantages are due to the fact that the device maintaining the plunger against the drive train is not an elastic component placed between the plunger and fixed parts of the pump (the conventional spring), but a relatively rigid one placed between the plunger and the drivetrain, eliminating the variation of distance between die contact surfaces of said device.

Claims

1. An arrangement adapted to provide a reciprocating drive to a plunger of a fuel pump comprising: a drive shaft having an eccentric located thereon, and a rider located on said eccentric, said rider including a surface, and wherein said plunger is mechanically connected to said surface via a mechanical joint and arranged such that rotation of the drive shaft causes movement of said surface including a component comprising reciprocating movement in a first axis, causing corresponding reciprocation of said plunger, characterized where said joint allowing relative movement between said surface and plunger in a direction perpendicular to said first axis.

2. An arrangement as claimed in claim 1 wherein said surface is a flat surface.

3. An arrangement as claimed in claims 1 or 2 wherein said joint allows relative movement between said surface and plunger in a direction perpendicular to the drive shaft axis.

4. An arrangement as claimed in claims 1 to 3 wherein said joint does not allow relative movement between said surface and said plunger in said first axis..

5. An arrangement as claimed in claims 1 to 4 wherein said mechanical joint comprises a dovetail arrangement.

6. An arrangement as claimed in claims 1 to 5 wherein said plunger is fixedly connected to a tappet, and said tappet forms said mechanical joint with said rider surface.

7. An arrangement as claimed in claims 1 to 6 wherein said surface of said rider includes a dovetailed groove or ridge forming part of said mechanical joint with a corresponding dovetail ridge or groove on said tappet or plunger.