GB2194001A

GB2194001A - Fuel injection pump

Info

Publication number: GB2194001A
Application number: GB08717321A
Authority: GB
Inventors: Christopher Howard Best
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1986-08-16
Filing date: 1987-07-22
Publication date: 1988-02-24
Also published as: GB8619992D0; GB8717321D0

Abstract

A fuel injection pump includes a sleeve 12 loosely mounted within an aperture 11 in a housing 10. A plunger 14 is slidable in the sleeve and during inward movement fuel is displaced from the sleeve to an outlet 15. the flow of fuel through the outlet can be terminated by opening a spill passage 16 or by the opening of a further spill path including a port 22 in the sleeve and a groove 26 on the plunger. The port 22 connects with a passage 23 in the housing which incorporates a valve 24 which can be closed for engine starting purposes. In order to prevent damage to a seal member 28 positioned between the sleeve and the aperture due to high pressure pulsations, the clearance between the sleeve and aperture is reduced so as to damp the pulsations before they reach the seal member. <IMAGE>

Description

SPECIFICATION Fuel injection pump This invention relates to a fuel injection pump for supplying fuel to an internal combustion engine, the pump being of the kind comprising a plunger reciprocable within a bore, an outlet from one end of the bore, a valve for controlling the spillage of fuel from said one end of the bore during inward movement of the plunger in the bore, a port formed in the wall of the bore, passage means in the plunger which at a predetermined position during the inward movement of the plunger is brought into register with said port to place said end of the bore in communication with said port and a further valve operable to prevent flow of fuel through said port.

The provision of the port and passage means enables the pump to continue to supply fuel at a limited rate, in the event that the valve operator or its control systems becomes defective. When starting the associated engine it is necessary to prevent flow of fuel through said port in order to supply an extra amount of fuel to the engine and for this purpose the further valve is closed. It is the usual practice to form the bore in a sleeve which is mounted in the pump housing and in this manner the material of the sleeve can be selected for its hardwearing properties with the housing being formed from a cheaper and usually a lighter material. With this arrangement the port must extend through the sleeve and into the housing and as a result the interface between the sleeve and the housing is subject to the pressure in the port.

It is possible and indeed it is known in fuel injection pumps to mount a sleeve in a housing and to have ports which are subject to high pressure extending therethrough. Such a sleeve is an interference fit in the housing and in the fitting of the sleeve special assembly techniques are employed to minimise stress in and distortion of the sleeve. It is very difficult if not impossible to replace the sleeve in the event of wear.

In another form of pump the sleeve is a slack fit within the housing and a seal arrangement is provided to prevent escape of fuel along the clearance between the sleeve and the wall of the aperture in the housing into for example the lubricating oil of the plunger actuating mechanism.- In such an arrangement it is the normal practice to provide an "0" ring elastomeric seal member which is adequate when low fuel pressures are involved. However such a seal member is unable to withstand high pressure pulsations to which it will be subjected when a pump of the kind specified is in use and is supplying extra fuel for starting purposes.

According to the invention a fuel injection pump of the kind specified comprises a housing, a sleeve member secured within an elongated aperture in the housing, said sleeve member defining said bore, the port being formed in said sleeve and having a continuation in the housing, an annular seal member positioned between the exterior surface of the sleeve member and the wall of said aperture, the seal member being located at a position which is spaced axially from said port on the side thereof remote from said one end of the bore and the clearance between said surface and said wall being such as to attenuate the pressure waves travelling along said clearance from said port towards the seal member.

Examples of fuel injection pump will now be described with reference to the accompanying drawings which are all sectional side elevations of part of the pump.

Referring to Figure 1 of the drawings the pump comprises a housing 10 in which is formed an elongated cylindrical aperture 11 in which is located a sleeve member 12. The sleeve member can be retained within the aperture by means of a screw threaded retaining ring. The sleeve member defines a bore 13 in which is slidably mounted a pumping plunger 14. The inner or one end of the bore communicates with an outlet 15 which in use is connected to an injection nozzle of an associated engine and communicating with the one end of the bore is a passage 16 flow of fuel through which is controlled by a valve 17 the setting of which is determined by an electromagnetic operator 18. Conveniently the valve is biased to the open position by means of a spring 19.

The plunger extends from the opposite end of the bore and as shown is biased away from said one end of the bore by a plunger return spring 20. It is moved inwardly towards the one end of the bore by a cam 21 which is driven in timed relationship with the associated engine. Instead of the return spring 20 a desmodromic mechanism may be employed to positively actuate the plunger.

Formed in the wall of the sleeve member is a port 22 which is continued in the housing 10 by means of a passage 23. The passage 23 contains a further valve 24 the setting of which is controlled by an operator 25. For registration with the port 22 there is provided on the periphery of the plunger a circumferential groove 26 which communicates by way of passage means 27 in the plunger, with said one end of the bore. The groove 26 is arranged to communicate with the port 22 near to the end of the inward movement of the plunger by the cam. Moreover, a further port 29 is formed in the sleeve at a position so that it is uncovered by the plunger as the latter nears the limit of its outward movement.

In the normal operation of the pump, fuel can flow into the one end of the bore during outward movement of the plunger, through the passage 16 with the valve 17 in the open position. In addition, fuel can also flow into the one end of the bore during the final outward movement of the plunger, through the port 29. During inward movement of the plunger fuel is displaced from the one end of the bore back through the passage 16 until such time as the valve 17 is closed and when closure of the valve occurs the fuel is displaced through the outlet 15 to the associated fuel injection nozzle. The flow of fuel to the nozzle will continue until the valve 17 is opened and the period of closure and the instant of closure considered in terms of degrees of cam rotation, determines the timing of fuel delivery and also the extent of fuel delivery.The operator 18 will in most instances, be controlled by an electronic control system. During the final inward movement of the plunger the groove 26 will move into register with the port 22 and thereafter even if the valve 17 is in the closed position, fuel flow through the outlet 15 will cease and the remaining quantity of fuel in the one end of the bore will be displaced through the port 22.

In the event of failure of the valve 17 it is possible to run the associated engine at low power, by physically closing the valve 17 and using a valve 30 as a throttle to control the amount of fuel which is drawn into the bore during the final outward movement of the plunger. It is thus possible to operate the engine at limited power to enable for example a vehicle powered by the engine to be driven at low speed.

For starting the associated engine it is necessary to supply an amount of fuel in excess of the normal maximum amount of fuel which is determined by the opening of the groove to the port 22. For the supply of extra fuel therefore it is necessary to prevent fuel flow through the port 22 and for this purpose the valve 24 is closed. The flow of fuel through the outlet can therefore continue until the plunger has moved its maximum extent towards the one end of the bore. When the pump is operated in this condition however the port and the passage 23 are subjected to the high pressure of fuel which exists in the one end of the bore during injection of fuel and as a result it is possible for fuel to leak between the exterior surface of the sleeve member 1 2 and the wall of the aperture 11 in which it is mounted.Such flow of fuel away from said one end of the bore can result in fuel flowing into the lubricating oil for the plunger actuating mechanism. In order to prevent this an "0" ring seal member 28 is provided and is located'within a circumferential groove formed in the exterior surface of the sleeve member. The seal member engages the wall of the aperture 11 to provide a seal and in the normal operation of the pump the seal is subjected only to the comparatively low pressures which exist in the port 22. When supplying an excess of fuel for starting purposes however the seal will be subject to the high pressure pulsations generated during the delivery of fuel to the associated engine and the pressure pulsations will destroy the seal.

In order to attenuate the pressure pulsations to which the seal is subjected, the clearance between the exterior surface of the sleeve member 12 and the wall of the aperture 11 in which it is mounted, is reduced at least over that portion lying between the port 22 and the seal member 28. The pressure pulsations therefore are reduced to an amplitude which the seal member can withstand. Conveniently the diametral clearance between the sleeve and the aperture of that portion lying between the port 22 and the seal is 3-6 microns and the length of said portion is substantially 12 mm.

In the example shown in Figure 2 a groove 32 is formed in the bore 13 and this communicates with a further groove 33 formed in the outer peripheral surface of the sleeve at a position between the seal 28 and port 22. In use any leakage of fuel along the working clearance between the plunger and the sleeve collects in the groove 32 and is returned to the passage 23. The risk of fuel contamination of the lubricating oil for the cam is therefore minimised.

A modified arrangement of the pump is seen in Figure 3. This is the same as the pump shown in Figure 2 with the addition of a passage 34 formed in the housing 10 amd in communication with the groove 33. The passage 34 extends to a drain or to the fuel supply source. With the passage 34 the seal 28 is completely protected against the high pressure pulsations which can occur when the valve 24 is closed for the purpose of obtaining excess fuel for starting purposes. In this case the reduced clearance besides attenuating the high pressure pulsations minimises the ioss of fuel to the groove 33 and passage 34 when the groove 26 is uncovered to the port 22 with the valve 24 closed.

Claims

1. A fuel injection pump for supplying fuel to an internal combustion engine, the pump being of the kind comprising a plunger reciprocable within a bore, an outlet from one end of the bore, a valve for controlling the spillage of fuel from said one end of the bore during inward movement of the plunger in the bore, a port formed in the wall of the bore, passage means in the plunger which at a predetermined position during the inward movement of the plunger is brought into register with said port to place said end of the bore in communication with said port, a further valve operable to prevent flow of fuel through said port, a housing, a sleeve member secured within an elongated aperture in the housing, said sleeve member defining said bore, the port being formed in said sleeve and having a continuation in the housing, an annular seal member positioned between the exterior surface of the sleeve member and the wall of said aperture, the seal member being located at a position which is spaced axially from said port on the side thereof remote from said one end of the bore and the clearance between said surface and said wall being such as to attenuate the pressure waves travelling along said clearance from said port towards the seal member.

2. A pump according to Claim 1 including a groove defined between the plunger and the sleeve at a position to collect fuel leaking along the working clearance between the plunger and the sleeve said groove communicating with said port.

3. A pump according to Claim 2 including a further groove defined between the sleeve and the aperture at a position adjacent the seal member and on the side thereof presented to the port, said grooves communicating with each other.

4. A pump according to Claim 3 including a passage in the housing connected with said further groove, said passage connecting with a drain.

5. A pump according to any one of the preceding claims in which the diametral clearance between the sleeve and the aperture is between 3 and 6 microns, the distance between said port and said seal member being substantially 12.0 mm.

6. A fuel injection pumping apparatus for supplying fuel to an internal combustion engine comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.