A FUEL INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES, IN PARTICULAR BIG, SLOW MARINE DIESEL ENGINES

Abstract: A fuel injection pump for internal combustion engines, in particular big, slow marine diesel engines, for supply of a variable amount of fuel to an injection nozzle positioned in the working cylinder of the engine, said injection nozzle having a spring-loaded needle in the nozzle aperture, and which pump comprises a barrel (2), in which a plunger (3) with an upper edge (4) formed between the end surface and the side surface of the plunger and at least one helically extending oblique cut-off edge (6), is movable, which oblique cut-off edge (6) defines a recess (5) in the side surface of the plunger, which recess is connected through an axial duct (9) with the end surface of the plunger, and in which the wall of the barrel (2) has at least one cut-off hole (11), which opens into a surrounding supply chamber containing the fuel under moderate pressure, said at least one hole at the travel of the plunger from the bottom to the top position being covered by the side surface of the plunger below the upper edge and being later uncovered by the oblique cut-off edge for diversion of excess fuel at the end of the effective pump stroke. To overcome problems due to erosion and pressure oscillation in pumps of big dimensions, the pumps are designed such that at least one of the cut-off holes (11) contains a flow limiting means (13) placed at a distance from the wall of the barrel, said means defining a chamber (20) positioned between the cylindrical wall of the barrel (2) and the flow-limiting means.

Description: A FUEL INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES, IN PARTICULAR BIG, SLOW MARINE DIESEL ENGINES The present invention relates to a fuel injection pump for internal combustion engines, in particular big, slow marine diesel engines, for supply of a variable amount of fuel to an injection nozzle posi- tioned in the working cylinder of the engine, said injection nozzle having a spring-loaded needle in the nozzle aperture, said pump comprising a barrel, in which a plunger with an upper edge formed between the end surface and the side surface of the plunger and at least one helically extending oblique cut-off edge, is movable, which oblique cut-off edge defines a recess in the side surface of the plunger, which recess is connected through an axial duct with the end surface of the plunger, and in which the wall of the barrel has at least one cut-off hole, which opens into a surrounding supply chamber containing the fuel under moderate pressure, said at least one hole at the travel of the plunger from the bottom to the top position being covered by the side surface of the plunger below the upper edge and being later uncovered by the oblique cut-off edge for diversion of excess fuel at the end of the effective pump stroke. In conventional fuel injection pumps each oblique cut-off edge is matched by a hole through the wall of the barrel, and the plunger is designed such that this hole at the beginning of the travel of the plunger is covered by the upper edge of the plunger, and the same hole is later exposed by the oblique cut-off edge, when the set amount of fuel has been supplied to the injec- tion nozzles. Such an arrangement has worked satisfac- torily in small and mediumsized engines, but in big, slow diesel engines problems arise which can be traced back to the big dimensions of the pumps and to measures, which have to be taken in order to dampen pressure variations in the injection system at the start and at the end of the effective pump stroke. The problems may be erosion on the side surfaces of the plunger stemming from cavitation in the holes on account of high flow velocity. An increase of the cross section of the holes can, however, not be made straight away, as the holes, when uncovered by the oblique cutoff edge, are to delay the pressure relief by exerting a certain flow resistance. This delay is necessary in order to prevent cavitation in the nozzles and to prevent combustion gas from entering the injection nozzles. It is also desirable, if possible, to obtain a comparatively big bearing surface between plunger and barrel in the area at the upper edge of the plunger to reduce the risk of seizures in this area, when fuel with inferior lubricating properties is used. In German Offenlegungsschrift No. 2532 205 a fuel injection pump is disclosed, in which a plunger at the travelling from the bottom to the top position covers and later uncovers a relief hole in the barrel for diversion of excess fuel to an annular space surrounding the pump barrel, and in which, in the return pipe from the annular space, several orifice members have been provided with a view to reducing the risk of cavitation. The above-mentioned prior art has been described as less effective in US-A-5015 160, which discloses an arrangement, which during the covering of the relief hole takes care of establishing a pressure of 50 bar in a circular space around the barrel. The pressure is maintained by means of a non-return valve in a suction duct and a spring-loaded pressure valve in a return duct. The arrangement is complicated and the maintenance thereof is difficult on account of the numerous components. The object of the invention is to provide a fuel injection pump, by means of which and through simple and reliable means an effective prevention of erosion in the area adjacent to the upper edge of the plunger is obtained. This object is according to the invention met by the characteristics of the fuel injection pump disclosed in the characterizing clause of claim 1. In the fuel injection pump according to the inven- tion, the flow-limiting means are positioned in the cut-off holes in the wall of the barrel. In this way, a considerably increased pressure is created in the interspace between the plunger and the flow-limiting means, which is merely an orifice member, said pressure effectively preventing cavitation in the area adjacent to the upper edge of the plunger, irrespective of the momentarily high flow velocities which occur. Even though the increased pressure is relieved via the orifice member, in which also considerable flow veloc- ities occur, the measures taken, which relative to the prior art are extremely simple, have turned out to be efficient, either by diminishing cavitation itself or by transferring it to other areas, in which no erosion occurs. The invention is in particular applicable in fuel pumps, in which the beginning and the end of the effective pump stroke are controlled by means of separate sets of holes. According to the invention the orifice member is placed in the set of holes initiating the pump stroke. According to the invention the orifice member has such an aperture that the static pressure in the cutoff hole in front of the top amounts to 10-20% of the delivery pressure of the pump. It has surprisingly turned out that a strong throttling of the fuel relieved does not unfavourably influence the building up of pressure prior to the injection. The invention will now be described in detail with reference to the drawing, in which Fig. 1 is an axial view through a fuel injection pump according to the invention. Fig. 2 is a sectional view of a cross section through the wall of the barrel along the line II-II according to Fig. 1, Fig. 3 is a diagram showing the pressure in the pump according to the invention during a fuel injection, and Figs 4a, 4b, and 4c schematically show cut-off holes in a longitudinal, sectional view. The fuel injection pump 1, shown in axial view in Fig. 1, comprises a barrel 2, in which a plunger 3 is movable. The barrel 2 is adapted to be built into a pump housing of conventional design, which comprises a supply chamber surrounding the middle portion of the barrel and to which excess fuel may be diverted, and from where, during the course of the return stroke of the plunger, fuel may be supplied to the barrel. The plunger 3 comprises an upper edge 4 formed between the end and side surfaces of the plunger. The plunger, moreover, comprises a recess 5, which in the direction of the end surface of the plunger is defined by an oblique cut-off edge 6 extending helically along the side surface of the plunger. The oblique cut-off edge 6 covers an angle of for instance 120°, and normally a plunger is provided with two oppositely positioned cutoff edges 6. The plunger 2 is provided with coupling means 7 for a rotating mechanism, by means of which the plunger may be rotated for adjustment of the delivery amount, and coupling means 8 for a roller guide adapted to move the plunger axially. These mechanisms are not part of the invention and may be conventionally designed. The plunger 3 also comprises an axial duct 9 connecting the recess 5 with the space 10 above the end surface of the plunger 4. The pump is adapted to deliver a variable amount of fuel to the injection nozzles in the working cylinders of a diesel engine. The delivery amount is adjusted by rotating of the plunger 3. The effective pump stroke is initiated by the fact that the edge at the end surface 4 of the plunger during its upwards movement covers a set of timing and cut-off holes 11 in the barrel 2 of the pump, and the effective pump stroke ends, when the oblique cut-off edge 6 uncovers a set of relief holes 12 , whereby the pressure in the pump chamber above the end surface 4 of the plunger is relieved through the axial duct 9, the recess 5 and the cut-off holes 12 to the supply chamber surrounding the barrel 2. In fuel injection pumps for big, slow diesel engines, for instance for marine use, special problems arise on account of the big dimensions of the pump and the high pressures, at which the fuel is injected, said problems being met by the pump described by use of separate, specifically designed timing holes and relief holes in the beginning and at the end of the effective pump stroke. By using separate sets of holes, the timing holes can be designed such that cavitation stemming from disruption of the flow of fuel, which is expelled at big velocity, is effectively prevented, the relief holes are designed such that a suitable dampening of the diverted fuel is obtained, until the risk of pressure oscillations, which may lead to penetration of cylinder gasoline into the injection nozzles, has been overcome, or such that cavitation in the injection nozzles is prevented. Moreover, the bearing surface between the upper portion of the plunger and the wall of the barrel may be given a proper size by an appropriate dimensioning of the axial spacing between the holes 11 and 12. The timing holes are conventionally designed with bigger cross section than the relief holes 12. The cavitation may, however, according to the invention be most effectively prevented by placing an orifice member 13 at the outlet of the timing hole to the supply chamber, as shown in Fig. 2. The orifice member provides such a flow passage that the pressure in the timing hole in front of the orifice member substantially exceeds the pressure in the supply chamber immediately before the cut-off hole is covered, when the edge of the end surface 4 of the plunger passes. The flow resistance in the orifice member leads to such a retarded breaking down of the pressure at the side surface of the plunger that no cavitation occurs. The relief holes 12 , which are uncovered by the oblique cut-off edge 6, are normally designed with a longitudinal profile in the shape of a diffusor and are provided with the smallest cross section at the wall of the barrel. The small cross section at the wall of the barrel is desirable in order to obtain a quick exposure of the hole 12 and thus a well-defined pressure relief sequence in the injection system. The diagram in Fig. 3 shows the pressure sequence in a fuel injection pump according to the invention drawn as a function of the crank angle. The fully drawn curve indicates the pressure in the pump chamber 10. The curve shows that the pressure in the pump chamber starts to increase as soon as the plunger 3 is moved upwards, but the steep increase starts at 14, where the timing holes 11 are covered by the plunger below its upper edge 4. At 15 the injection nozzles are opened, and at the continued pump stroke the set amount of fuel is injected in the working cylinder of the engine. At 16, the cut-off holes are uncovered, following which the pressure in the pump chamber falls in a dampened course, which counteracts pressure oscillations in the injection system and thus ensures a correct closing function of the needles in the injection nozzles. A dotted line 17 shows the pressure sequence in the chamber between the orifice member and the side of the plunger, the chamber being provided with an appropri- ately dimensioned orifice member 13. It will be seen that a gradual pressure fall can be obtained, said pressure fall effectively preventing cavitation in the side hole adjacent to the plunger side. The invention is not limited to fuel injection pumps with separate timing and cut-off holes in the pump barrel, but may with also successfully be used in fuel injection pumps, in which the number of cut-off holes is identical with the number of oblique cut-off edges on the plunger, i.e. where the beginning and the ending of an injection event are made by means of the same holes in the wall of the barrel. In this design of the pump, the flow-limiting means constitutes both the means for preventing cavitation and the associated erosion of the plunger and the means, which substan- δ tially governs the breakdown of pressure during relief at the end of the effective pump stroke. Figs 4a, 4b and 4c show schematic embodiments of cut-off holes, viewed in longitudinal section. Fig. 4a thus shows an embodiment, in which the flow-limiting means in the shape of an orifice member 21 is placed in a cut-off hole 20 close to its outlet 22 into the supply chamber. In this embodiment maximum size of the chamber, which is pressurized by cut-off and relief, and consequently the biggest possible volume in the chamber between orifice member and inlet and thus the best possible pressure maintenance is obtained. The orifice member may be designed with several ducts or with a flow direction of the ducts under an angle relative to the axis of the cut-off hole. An advantage of the ducts forming an angle with the axis of the cutoff hole is that the fluid relieved does not get perpendicularly in touch with an opposite supply chamber wall, and that the risk of erosion of said wall is reduced. The chamber between the wall of the barrel and the orifice member may, moreover, have a non-cylindrical shape. The shape may for instance be conical such that the cut-off aperture in the wall of the barrel is somewhat smaller than the diameter of the chamber, in which the orifice member has been inserted. In this way the flow-controlling effect is distributed to the hole in the wall of the barrel and to the orifice member, which may be advantageous, if there are no separate timing and cut-off holes. In Fig. 4b the orifice member 23 is positioned approximately in the middle of the hole 20, which results in a smaller chamber, but also in a bigger distance from the orifice member 23 to the opposite wall of the supply chamber, where the liquid flowing from the orifice member may cause erosion. Fig. 4c shows a preferred embodiment of a cut-off hole 20 provided with an orifice member. The orifice member 24 is positioned substantially in the middle of the cut-of hole which in the direction towards the outlet 22 to the supply chamber is designed as a diffusor 25. The object of the diffusor 25 is to reduce the velocity of the jet leaving the orifice member. Through a suitable dimensioning of the orifice member 21, 23 or 24, such a building up of pressure in front of the orifice member at the cut-off may be obtained when the cut-off hole is covered that the cavitation risk is eliminated, and such a dampening of the relief is obtained that the break down of pressure may take place without substantial pressure oscillations. An additional dampening may, if desired, be established by a suitable design of the axial duct in the plunger.

Claims: P A T E N T C L A I M S 1. A fuel injection pump for internal combustion engines, in particular big, slow marine diesel engines, for supply of a variable amount of fuel to an injection nozzle positioned in the working cylinder of the engine, said injection nozzle having a spring-loaded needle in the nozzle aperture, and which pump comprises a barrel, in which a plunger with an upper edge formed between the end surface and the side surface of the plunger and at least one helically extending oblique cut-off edge, is movable, which oblique cut-off edge defines a recess in the side surface of the plunger, which recess is connected through an axial duct with the end surface of the plunger, and in which the wall of the barrel has at least one cut-off hole, which opens into a surrounding supply chamber containing the fuel under moderate pressure, said at least one hole at the travel of the plunger from the bottom to the top position being covered by the side surface of the plunger below the upper edge and being later uncovered by the oblique cut-off edge for diversion of excess fuel at the end of the effective pump stroke, and in which means are provided with a view to providing, during a part of the travel of the plunger, an increased static pressure in at least one of the cutoff holes, c h a r a c t e r i z e d in that the means for increasing the static pressure are an orifice member accommodated in the cut-off hole and with an aperture reduced to such an extent relative to the cross section of the cut-off hole that prior to and during the cut-off, a building up of pressure occurs in the cut-off hole in front of the orifice member. 2. A fuel injection pump according to claim 1, and in which the beginning and the end of the effective pump stroke are controlled by separate sets of holes, c h a r a c t e r i z e d in that the orifice member is placed in the set of holes initiating the pump stroke. 3. A fuel injection pump according to claim 2, ch a r a c t e r i z e d in that the orifice member has such an aperture that the static pressure at the cut-off amounts to 10 - 20% of the supply pressure of the pump.

Inventors: FLARUP JOHANNES, PEDERSEN ERIK DUE, FLARUP, JOHANNES, PEDERSEN, ERIK, DUE
Applicants: FLARUP JOHANNES, MAN B & W DIESEL GMBH, PEDERSEN ERIK DUE, FLARUP, JOHANNES, MAN B & W DIESEL A/S, PEDERSEN, ERIK, DUE
Application year: 1998
Main classification: F02M59
IPC codes: F02M59