GB2294509A - Rotary fluid pump - Google Patents

Abstract

A rotary fuel pump for supplying fuel to a diesel engine includes a pumping plunger 18a operable by a cam 20a to pressurise fuel for supply to an engine and a spill valve 38 operable to spill pressurised fuel to control the amount of fuel supplied to the engine. The spit fuel acts upon a recovery plunger 18b which in turn acts upon a recovery cam 20b to recover some of the energy contained in the spilled fuel. In an alternative arrangement a volume of controllable capacity is arranged to communicate with the delivery side of the pump, the capacity being increased to reduce the delivery pressure in a regenerative manner. The invention is also applicable to rotary distributor pumps of the kind having a combined distributor and pumping member which reciprocates and rotates. <IMAGE>

Description

ROTARY FLUID PUMP This invention relates to a rotary fuel pump, primarily for use as a diesel engine fuel injection pump, in which fuel is pressurised for distribution to working locations and spilled at appropriate times during the pumping cycle.

Spilling fuel can create a problem in such pumps in that the pressure and kinetic energies in the spilt fuel are dissipated as heat which can give rise to non-uniform heating of the pump, leading to possible distortion and even seizure of the mechanism, particularly when the pump is operating at or near its full load rated speed.

An object of the present invention is to provide a fuel pump in which this problem is overcome in a simple and convenient manner.

In the rotary fuel pump according to the present invention, spilt fuel is caused to work regeneratively on a working eiement.

Conveniently, the working element is a recovery plunger arranged to work against a cam surface under the influence of the spilt fuel.

In a typical pump of the invention, fuel is pressurised by the action of a cam on a pumping plunger, the cam surface for the recovery plunger being conveniently arranged to be effective during the spill phase of the pump, either on a distinct regenerative cam or on the cam driving the pumping plunger and between the lobes thereof.

Typically, the spilt fuel is supplied to a recovery volume between a pair of opposed recovery plungers engaging the cam surfaces.

Preferably, the passageway conveying the spilt fuel to the recovery volume and the passageway conveying pressurised fuel for distribution to the working locations are of substantially the same uniform diameter.

The invention will further be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a cross sectional view of a rotary distributor pump in accordance with an embodiment of the invention; and Figure 2 shows diagrammatic views of parts of the pump of Figure 1.

The pump illustrated in the drawings is a rotary distributor pump for use in distributing pressurized fuel to the cylinders of an associated four cylinder diesel engine. The pump comprises an elongate cylindrical disixibuior rnernrJer 10 which is rotatable within a sleeve 12, driven In timed relation with the associated engine by a drive shaft 11. An end portion 1ûA of the distributor member 10 is of enlarged diameter and is rotatable within a pair of cam rings 14, 16 each of which is provided with four equi-angularly spaced cam lobes 14a, 16a (Figure 2). Each of the cam lobes 14a, 16a includes a leading flank 14b, 16b and a trailing flank 14c, 16c. The cam ring 14 is angularly adjustable, in use, in order to adjust the timing of fuel delivery to the engine.The cam ring 16 in the example is fixed with respect to the pump housing, but may be angularly adjustable and possibly be arranged to move with the cam ring 14.

The enlarged end region of the distributor member 10 is provided with a pair of diametrically extending through bores 17a, 17b whIch are spaced apart from one another in the axial direction of the distributor member 10, each of the bores 17a, 17b being aligned with a respective one of the cam rings 14, 16.

A pair of opposed plungers 1 8a are reciprocable within the bore 1 7a, each plunger 18a having at its outer end a shoe 20a which in turn carries a roller 22a. In use, the rollers 22a are arranged to engage with the inner surface of the associated cam ring 14, and to reciprocate under the influence of the cam lobes 14a. In like manner the bore 1 7b has a pair of opposed recovery plungers 18b reciprocable therein these plungers having shoes 20b carrying rollers 22b for engagement with cam lobes 1 6a formed on the inner surface of the cam ring 16. The recovery plungers 1 7b define between them a so called recovery volume.

In practice for increased fuel delivery each bore 1 7a, 1 7b together with the associated plungers is duplicated with the additional bores for a four cylinder engine being disposed at right angles to the bores seen in Figure 1.

The distributor member 10 is provided with an axially extending passage 24 which communicates at one end with the through bore 1 7a between the inner ends of the plungers 18a associated with the cam ring 14. At its other end, the passage 24 communicates with a radially extending delivery passage 30 which is positioned so as to register in turn, upon rotation of the distributor member, with one of four delivery ports 32 (only one of which is shown in Figure 1) provided in the sleeve 12, from where the fuel passes through an associated delivery valve 34 and by a pipeline to a respective fuel injection nozzle of an associated engine.

The axially extending passage 24 also communicates with four radially extending inlet passages 26 (shown by dashed lines in Figure 1) which are arranged to register, in turn, with an inlet port 28 provided in the sleeve 12, as the distributor member rotates. The inlet port 28 is arranged to receive fuel at a relatively low pressure from a fuel pump, usually a rotary vane pump, which may be driven from the smaller end of the distributor member 10 or directly by the drive shaft 11.

The inlet passages 26 are also arranged to register intermittently with a spill port 36 as the distributor member 10 rotates, the spill port 36 communicating with a spill valve 38 which controls communication between the spill port 36 and four spill passages 40 (shown by dashed lines in Figure 1) which extend generally parallel to the axially extending passage 24 and communicate via converging end portions 40b thereof, with the through bore 17b associated with the cam ring 16. Each spill passage 4u cui-n*-llu*íidies Wii;l dfl dflfluldr passage 40a formed in the distributor member 10 and permitting communication between the spill passages 40 and the spill valve 38 for all angular positions of the distributor member 10.Conveniently the spill valve 38 is spring biased to the open position and is closed by energising an electromagnetic actuator the operation of which is controlled by an electronic control system.

In use, the distributor member 10 is driven by the drive shaft 11 so as to rotate in the direction indicated by arrows 'A' of Figure 2, rotation of the distributor member 10 resulting in one of the inlet passages 26 registering with the inlet port 28. Fuel supplied at low pressure by the fuel pump flows through the inlet port 28, inlet passage 26 and into the axially extending passage 24 along which it flows into the through bore 17a. The pressure of the fuel is sufficient to push the plungers 1 8a outwards into engagement with the internal surface of the cam ring 14, intermediate the lobes 14a.

Continued rotation of the distributor member 10 results in communication between the inlet passage 26 and inlet port 28 being broken and the delivery passage 30 then registers with one of the delivery ports 32 and one of the inlet passages 26 registers with the spill port 36. Shortly after such registration has occurred, the rollers 22a come into contact with the leading flanks 14b of respective ones of the cam lobes 14a provided on the cam ring 14, resulting in the pumping plungers 18a being pushed inwardly (as shown by arrow 'B' in Figure 2).

The spill valve 38 is closed prior to the plungers being moved inwardly and the fuel in the through bore 1 7a is pressurized and flows through the delivery passage 30 and delivery port 32 to be delivered through the delivery valve 34 to a high pressure pipeiine carrying the fuel to the injection nozzle for the appropriate cylinder of the engine.

When the desired quantity of fuel has been delivered to the associated engine, the actuator is de-energised to allow the spill valve 38 to open thereby connecting the spill port 36 with the spill passages 40 to terminate delivery of fuel to the engine cylinder. Such communication permits the high pressure fuel from the axially extending passage 24 to flow through the spill passages 40 to the recovery volume defined between the recovery plungers 18b. The lobes 1 6a of the second cam ring 16 are arranged with their trailing flanks 16c aligned with the plungers 18b at this time to permit outward movement of the plungers 18b as shown by arrow 'C' in Figure 2.It will be recognised that the high pressure fuel applied to the plungers 18b upon opening of the spill valve 38 pushes them outwards, causing the rollers 22b associated therewith to engage against the trailing flanks 1 6c of the associated cam lobes 16a.

The fuel pressure acting on the inner ends of the recovery plungers 1 8b results in a reaction force being applied to the distributor member as the rollers associated with the plungers are urged into engagement with the trailing flanks 16c. The reaction force acts on the drive shaft 11 in the direction of the arrow A and the torque required to drive the drive shaft is reduced due to the regenerative work carried out by the recovery plungers 18b.

In practice something more than the mere transfer of a volume of fuel under pressure between bores is allowed to take place. At the instant of opening of the spill valve 38 the fuel in the bore 1 7a, the axially extending passage 24, the inlet passage 26 and the delivery passage 30 is at high pressure and is moving towards the injector. The fuel in the spill port 36 is also at high pressure but can be considered as being static.

The fuel in the passages 40a, 40 and the recovery volume i.e.

downstream of the spill valve is at low pressure and conveniently there is a cavity in the recovery volume or what is easier to arrange, a clearance between the rollers 22b and the trailing flanks 16c of the cam lobes 16a.

This is to ensure that the recovery volume is always ready to receive fuel flowing past the spill valve. Fluid wave theory teaches that when in such circumstances the spill valve is opened a negative pressure wave travels in the fuel column upstream of the spill valve in the direction away from the spill valve and is reflected back towards the spill valve, the wave travelling at the speed of sound in the fuel. The practical effect is that the previously pressurised column of fuel is depressurised but attains velocity and moves to the downstream side of the spill valve to impose a pressure on the recovery plungers 18b urging the associated rollers into engagement with the trailing flanks 16c of the cam lobes thereby resulting in a reaction force acting to assist rotation of the distributor member.During this process a cavity will be formed on what was the upstream side of the spill valve. In theory heat generated by adiabatic compression of the fuel is all recovered but in practice it is to be expected that a certain amount of heat will be generated due to flow losses in the system and the difficulty of totally optimising the system but will be substantially less than in conventional spill type distributor pumps. It is thought that up to 50% of the energy in the spilled fuel can be reclaimed.

The pump can function as described without the cavity in the recovery volume or the clearance between the rollers and the trailing flanks 16c.

The pressurised column of fuel then acts directiy and immediately on the recovery plungers. A zero or negative wave will travel up the column of fuel from the recovery plungers dropping the pressure in the various drillings to the required value. This is only possible by careful positioning of the cams.

Further rotation of the distributor member 10 after the spillage of fuel has been completed results in the communication between the spill port 36 and the inlet passage and between the delivery passage 30 and the delivery port 32 being broken. The spill valve 38 is closed by energising the actuator and the fuel at low pressure in the bore 1 7b is allowed to flow to a drain through ports and passages not shown. As an alternative if the spill valve is left open, the fuel in the bore 1 7b can be returned to the bore 17a as the plungers 18b are moved inwardly by the leading flanks 16b of the cam 16. This will probably require a period of dwell at the crests of the cam lobes 1 6a and displacement to the left of the leading flanks 16b.Continued rotation of the distributor results in the next one of the inlet passages 26 moving into communication with the inlet port 28 to replenish the fuel supplied to the engine, and the pumping cycle is repeated.

In order to maximise the amount of regenerative work performed, it is desirable for all of the passages to be of substantially uniform diameter, since sudden changes in diameter result in the creation of a complex pattern of pressure waves in the fuel column from which the energy cannot conveniently be recovered, with a consequent generation of heat in that part of the pump resulting from the eventual viscous damping of said waves.

As an alternative to providing a second cam ring of the type described above together with associated plungers, a volume of controllable capacity may be arranged to communicate with the fuel delivery line or with the delivery valve 34 so that after delivery of the desired amount of fuel to an injector, the capacity of the volume is increased to reduce the pressure in the fuel line in a regenerative manner, and if desired, to result in a rapid reduction in fuel line pressure, suitable valves being used to control communication between the volume and the fuel line to permit the pressure in the volume to be reduced.

By careful selection of the cam forms and/or pump volumes, the regenerative action of the pump may be obtained for a given operative condition, such as the full load rated speed of the pump.

The volumetric rate of the recovery plungers and the trailing flanks 16c of the cam lobes 16a will need to be greater than the pumping rate of the pumping plungers and the leading flanks 14b of the cam lobes 14a at the point of spill in order to compensate for continued pumping. In most cases the factor will be less than 1.5 times.

Energy stored in volumes connected to but not strictly forming part of the fuel column is recovered by the fact that the fuel in said volumes will decompress into the fuel column forming pressure waves which can then act on the recovery plungers.

The invention may be applied to other forms of spill pump for example rotary distributor pumps of the kind in which the distributor member besides rotating to achieve the fuel distributing function is also axially nIuvdbi tu pruvide the pumping action.

Claims (3)

1. A rotary fuel pump, primarily for use as a diesel fuel injection pump, in which fuel is pressurised for distribution to working locations and is spilled at appropriate times during the pumping cycle, the spilt fuel being caused to work regeneratively on a working element.

2. A fuel pump according to claim 1 in which said working element is a recovery plunger which is openable against a cam surface under the influence of the spilt fuel.

3. A fuel pump according to claim 2 in which the fuel is pressurised by the action of a cam on a pumping plunger, the cam surface for the recovery plunger being either on said cam or on a separate regenerative cam.