GB2282190A

GB2282190A - Fuel pump

Info

Publication number: GB2282190A
Application number: GB9319282A
Authority: GB
Inventors: Christopher Wood
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1993-09-17
Filing date: 1993-09-17
Publication date: 1995-03-29
Also published as: GB9319282D0

Abstract

A rotary distributor fuel injection pump has a rotary distributor member 12 on one end of which is mounted the rotor 30 of a low pressure vane type pump 25. The vane pump has an arcuate inlet port 36 and an arcuate outlet port 37. The action of the vane pump cause an out of balance force to be applied to the distributor member and thus is balanced by providing a recess 40 connected to the outlet port 37 of the vane pump, the recess being formed in the wall of the bore which houses the distributor member. The recess is positioned so that the fuel pressure therein develops a force which opposes the out of balance force applied to the distributor member by the rotor. <IMAGE>

Description

FUEL PUMP This invention relates to a rotary distributor type fuel pumping apparatus for supplying fuel to a compression ignition engine and of the kind comprising a rotary distributor member mounted in a bore in a body and driven in synchronism with the associated engine, the distributor member defining a delivery passage which registers in turn with a plurality of outlet ports formed in the body, the apparatus including a bore which is connected to the delivery passage and the bore carrying a pumping plunger which is driven inwardly in the bore by the action of cam means so that fuel is delivered to the outlet ports in turn during successive inward movements of the pumping plunger, a low pressure vane type fuel pump having a rotor which is secured to the distributor member and a stator ring mounted in the body, and passage means through which fuel from an outlet of the low pressure pump can be supplied to the bore to effect outward movement of the pumping plunger.

In a known form of apparatus the low pressure vane type pump is provided with a single arcuate inlet port which is connected to a source of fuel and a single arcuate outlet port. As a result the fuel pressure which is developed by the pump generates an out of balance force on the rotor and this force is transmitted to the distributor member. The working clearance between the distributor member and the wall of the bore in the body is very small and the fuel which is supplied to the engine acts as the lubricant. If the low pressure fuel pump is constructed to provide an increased fuel pressure or is made larger to increase the output flow rate, the out of balance force is increased and the lubricant film between the distributor member and the surface of the bore in which it is located, may break down.Breakdown of the lubricant film will lead to damage to the surfaces of the distributor member and the bore and possible seizure.

It would be possible to achieve balance of the forces acting on the rotor by providing a further arcuate inlet port and a further arcuate outlet port however, this would require a more complex shape for the internal surface of the stator ring and also additional passages to connect the arcuate inlet and outlet ports. As an alternative to achieving balance of the forces acting on the rotor, the size of the distributor member could be increased to provide an increased bearing area but this would require modification of more or less all the remaining components of the apparatus.

The object of the present invention is to provide an apparatus of the kind specified in a simple and convenient form.

According to the invention in an apparatus of the kind specified there is formed in the surface of the bore in which the distributor member is mounted, a recess which is connected to the outlet of the low pressure pump, the recess being positioned so that the force developed on the distributor member by the fuel pressure in the recess opposes the out of balance force developed on the rotor.

An example of an apparatus in accordance with the invention will now be described with reference to the accompanying drawings in which: Figure 1 is a sectional side elevation of part of the apparatus, and Figure 2 is a diagrammatic end view illustrating the invention.

Referring to Figure 1 of the drawings the apparatus comprises a body 10 in which is mounted a sleeve 11 in which is mounted a rotary cylindrical distributor member 12. The body and sleeve define a plurality of equiangularly spaced outlet ports 13 which open onto the periphery of the distributor member and which at their outer ends, are connected to the injection nozzles respectively of the associated engine. The distributor member is provided with a delivery passage 14 which by way of a longitudinal passage 15, is connected to a bore 16 which mounts a pair of pumping plungers 17. At their outer ends the plungers are engaged by cam followers 18 respectively and these include rollers which can engaged with the internal peripheral surface of an annular cam ring 19 located within the body.The internal surface of the cam ring is provided with a plurality of pairs of inwardly extending cam lobes and these as the distributor member is rotated by a drive shaft 20, in synchronism with the associated engine, impart inward movements to the plungers 17 each time the delivery passage 14 is in register with an outlet port. Fuel is therefore supplied to the outlet ports in turn during successive inward movements of the pumping plungers 17. As is well known, the cam ring 19 is angularly adjustable about the axis of rotation of the distributor member to achieve variation of the timing of delivery of fuel to the engine, the angular movement being achieved by a piston 22 which is coupled to the cam ring by means of a peg 23, the piston being located within a cylinder 24.

In order to supply fuel to the bore 16 a low pressure vane type pump generally indicated at 25 is provided. The low pressure pump delivers fuel to an inlet port 26 which opens onto the periphery of the distributor member and which is positioned to register in turn with a plurality of inlet passages 27 which communication with the passage 15. The communication of the inlet port 26 with an inlet passage 27 takes place during the time when the delivery passage 14 is out of register with an outlet port 13 and whilst the plungers 17 are allowed to move outwardly by the cam lobes. In the particular example the low pressure pump 25 delivers fuel to a supply passage 28 formed in the sleeve 11 and this communicates by way of an angularly adjustable throttle member 29 with the passage 26.The throttle member 29 is one example only of achieving control of the amount of fuel which is delivered by the apparatus to the associated engine and it functions by restricting the amount of fuel which is supplied to the bore 16. As an alternative the bore may be completely filled with fuel in which case the throttle member is not provided and a quantity of fuel which is expelled from the bore during inward movement of the plungers may be spilled by a suitable valve.

The low pressure pump 25 includes a rotor 30 which is secured to the distributor member and surrounding the rotor is a stator ring 31 which is secured in the body 10. The internal surface of the stator ring is eccentric relative to the axis of rotation of the distributor member and is engaged by the tips of vanes 32 carried by the rotor. The end plates of the vane type pump are constituted on one side by the adjacent end surface of the distributor member and the sleeve 11 and on the other side by a housing 33 which is secured to the body 10 and which houses a relief valve 34. The housing 33 defines a fuel inlet 35 which is connected to a source of fuel. The housing 33 is also formed in its face presented to the rotor with an arcuate inlet port 36 which is connected to the interior of the housing 33 and therefore to the inlet 35.

The end of the passage 28 opens on the end face of the sleeve in an arcuate outlet port 37 and the end face of the housing 33 is provided with a similar port so that a spring loaded valve element 38 forming part of the relief valve 34, is exposed to the outlet pressure of the low pressure pump. The valve element 38 with increasing outlet pressure moves to expose a port 39 so that fuel can flow from the outlet port 37 to the inlet port 36 for the purpose of controlling the outlet pressure of the low pressure pump.

The vane pump operates in the usual manner and as will be appreciated from Figure 2, the outlet pressure of the pump acts on the rotor 30 to produce a force which is indicated by the arrow F in Figure 2. Since the rotor is mounted on the distributor member, this force is also transmitted to the distributor member. In order to oppose this force there is provided in the surface of the sleeve 11, a recess or pattern of recesses 40 which is connected by suitable drillings, to the passage 28 so that in the use of the apparatus the recess contains fuel at the outlet pressure of the low pressure pump. The position of the recess 40 is chosen so that a force is produced on the distributor member which is generally opposed to the force F which is developed on the rotor of the low pressure pump.

As the outlet pressure of the low pressure pump increases so also does the balancing force so that there is less risk of breakdown of the fuel film between the distributor member and the internal surface of the sleeve.

Claims

1. A rotary distributor type fuel pumping apparatus for supplying fuel to a compression ignition engine comprising a rotary distributor member mounted in a bore in a body and driven in synchronism with the associated engine, the distributor member defining a delivery passage which registers in turn with a plurality of outlet ports formed in the body, the apparatus including a bore which is connected to the delivery passage and the bore carrying a pumping plunger which is driven inwardly in the bore by the action of cam means so that fuel is delivered to the outlet ports in turn during successive inward movements of the pumping plunger, a low pressure vane type fuel pump having a rotor which is secured to the distributor member and a stator ring mounted in the body, passage means through which fuel from an outlet of the low pressure pump can be supplied to the bore to effect outward movement of the pumping plunger, a recess formed in the surface of the bore in which the rotary distributor member is mounted, a passage connecting the recess with the outlet of the low pressure pump and said recess being positioned so that the force developed on the distributor member by the fuel pressure in the recess oppose the out of balance force developed on the rotor.