GB1571137A

GB1571137A - Fuel injection pump

Info

Publication number: GB1571137A
Application number: GB41762/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-12-15
Filing date: 1977-10-07
Publication date: 1980-07-09
Also published as: NL7712294A; DK408477A; IN147084B; DE2749693B2; PL201795A1; NO773161L; DE2749693C3; DD131947A5; BR7708006A; BE861811A; SE7710292L; FR2374534A1; FR2374534B1; CH617751A5; AU2948777A; DE2749693A1; ES462683A1; JPS5375505A; IT1095661B; FI773385A

Description

(54) IMPROVEMENTS IN OR RELATING TO A FUEL INJECTION PUMP (71) We, SOCIETE D'ETUDE DE MACHINES THERMIQUES S.E.M.T., a French Body Corporate of 2, Quai de Seine, 93202 Saint-Denis, France, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to an improvement in a reciprocating plunger pump, more particularly a Diesel engine fuel-injection pump. The improvement allows rapid erosion and scaling of certain portions of the pump to be obviated.These phenomena are known to be caused by cavitation and impacts resulting from the very strong and quick pressure variations which take place at the end of each effective delivery cycle of the pump plunger at the moment the supply and discharge duct or ducts are abruptly reconnected to the pump delivery chamber.

The type of pump to which the improvement according to the invention applies is well known. Such a pump comprises a constant stroke plunger reciprocating longitudinally within the cylindrical bore of a barrel provided in the pump body. The fuel is led into the pump delivery chamber through one or several cross-ducts extending through the barrel and whose orifices are periodically closed by the lateral surface of the plunger for the whole duration of the effective delivery stroke thereof. Since the total plunger stroke is constant, the quantity of fuel delivered at each cycle is caused to vary by adjusting the said effective stroke, i.e. by adjusting the time during which the orifices of the said ducts are closed by the plunger lateral wall.To this end the lateral wall of the plunger is provided with a groove at least one edge of which is substantially helical and which leads to the upper portion of the piston to provide a discharge connection, at a given instant of each cycle, between the pump delivery chamber and the said ducts. Because the delivery pressure is much higher than the supply pressure the fuel abruptly returns to the said ducts as soon as the discharge connection is estblished, i.e.

as soon as a point of the helical edge reaches a location opposite the orifice of one of the said ducts. The delivery is then almost instantaneously stopped, thus allowing the quantity of fuel delivered by the pump at each cycle to be accurately determined. Moreover, the plunger can be of course rotated about its own longitudinal axis to retard or advance the instant of passage of the helical edge opposite the said orifice. This additional adjustment, allowing a kind of variation of the effective delivery stroke of the plunger, therefore allows the mean delivery rate of the pump to be adjusted although its plunger has a constant total stroke.This adjustment of the angular position is obtained quite conventionally by means of a slide key arrangement provided at the lower portion of the plunger and allowing the desired angular position of the plunger to be adjusted and maintained without hindering its constantstroke reciprocating motion.

The well-known problem that arises in such a pump type is that of cavitation. Indeed, there is quite a great pressure difference, during the effective stroke of the plunger, between the delivery chamber and the fuel supply and discharge system. By way of example, the delivery pressure often approximates 1000kg/cm2, whereas the fuel pressure in the pump supply system is only of the order of 2 kg/cm2. Under such conditions, the discharge i.e. the rapid back-flow of the fuel in excess in the delivery chamber at the end of an effective cycle of the plunger to the supply and discharge ducts takes place with great violence creating vortices or whirls and local negative-pressure regions in the said ducts, in proximity to their inner orifices.

Such phenomena are apt to cause rapid erosion and/or scaling both at the ends of supply and discharge passages and on the surface of the plunger itself.

It is known to eliminate such whirls and negative-pressure regions by dividing each common supply and discharge duct in the longitudinal direction to define a supply path and a discharge path while at the same time ensuring a connection between the two paths at the inner orifice of the duct to allow the fluid to easily pass from the supply path to the discharge path (at the instant of discharge) so as to prevent the formation of local lower or negative pressure regions and of vortices, thus obviating wear due to cavitation.This solution described by the Applicant and forming the subject matter of prior British patent Specification No. 1,505,269 consisted in inserting into the common duct an end-piece having the general shape of a flat plate or strip so dimensioned as to leave a passage-way in proximity to the orifice of the said common duct, allowing the fluid to circulate between the two longitudinal supply and discharge paths thus defined. This solution is satisfactory but the construction and positioning of the end-piece in the common duct are difficult to perform. In particular, the orien tation of the fiat plate or strip of the end-piece with respect to the direction of the back-jets of fuel propogated in the durts is of importance.It must be carefully adjusted at the time of mounting and care must be taken to avoid any subsequent disadjustment of the said orientation. Moreover, the end-piece itself is relatively easily damageable and difficult to make. Furthermore, the insertion of the end-piece into the common duct can cause additional stresses capable of subsequently leading to barrel cracking.

The present invention is of interest mainly for the reason that it allows the end-piece to be done away with.

According to the present invention there is provided a fuel injection pump comprising a cylindrical plunger reciprocable longitudin ally within the bore of a barrel, which barrel is provided with a plurality of mutually close transverse ducts for the supply and discharge of fuel at each cycle of operation of the pump, the plunger being provided on its external surface with a groove which communicates with a chamber defined in the bare of the barrel beyond one end of the plunger and with the transverse ducts, and at least one edge of the groove being of substantially helical configuration whereby the effective delivery stroke of the plunger can be adjusted by altering the angular position of the plunger in the bore about its own longitudinal axis with respect to the transverse ducts, and a means of providing at least momentary com muncation between at least two of the transverse ducts in proximity to the ori fices of the ducts opening into the bore.

In this manner the supply and discharge paths are materialized within the barrel con taining the plunger. Such a structure is advantageous and economical in the manufacturing stage. It is moreover more sturdy and more resistant in regard to the pressure waves that are propogated in the said ducts, because the relatively easily damageable element, namely the flat plate or strip used in the prior art is eliminated. In addition a connection is provided between at least some of the said closely extending ducts to obtain a compensating flow of fuel between the various discharge and supply paths to eliminate the regions of local negative pressure and the vortices resulting in cavitation.The said connection can be obtained by providing a small recess in the barrel wall, preferably between the orifices of the ducts, or a slot of a certain width made in the wall of the plunger above the substantially helical edge and in parallel relationship thereto. In the latter case the position and width of the slot are so selected as to allow the connection to be established for only a short instant from the moment said edge begins to uncover the orifice of one of the closely extending ducts.

The invention will now be described by way of example with reference to the appended drawing wherein: Figure 1 is a partial view of a pump according to the invention, with the barrel containing the plunger shown in section upon the line IIIIII of Figure 3 and with an extemal view of the piston placed in the barrel; Figure 2 is a view similar to that of Figure 1 and illustrates a possible modification of the pump according to the invention; Figure 3 is a partial view of the internal bore of the barrel, showing in particular the orifices of three closely extending ducts for the supply and the discharge of the fluid flowing in the pump; and Figure 4 diagrammatically illustrates a method of machining a connection hollow in the wall of the barrel bore.

Shown in the drawings is a pump comprising a barrel 11 provided with a central bore 12 with a plunger 13 reciprocating therein. The lower portion (not shown) of plunger 13 is provided with a slide key arrangement allowing the plunger to rotate about its longitudinal axis 14 without impeding its to-and-fro movement along the same axis, while at the same time allowing the plunger to be held in a given angular position determining the pump delivery rate. The plunger 13 is provided to this end with a lateral groove or recess 15 adapted to establish a communication between the delivery chamber 18 (shown partially and located beyond the transverse surface, 17 of the plunger) and the parallel ducts 20, 21 and 22 extending closely to one another and ensuring the supply and the discharge of the fuel admitted to the pump.One of the edges 16 of the recess 15 is helical, so that, by adjusting the angular position of the plunger 13 with respect to the respective orifices 20a, 21a and 22a of the said ducts leading into the bore 12, the plunger effective delivery stroke in each cycle, i.e. that portion of the plunger total stroke during which there is no connection between the chamber 18 and oue of these ducts can be adjusted.

According to a notable characteristic of the invention, several closely extending ducts for the supply and the discharge of the fluid are provided instead of the single common duct of larger section usually provided in most of the known devices. Thus, instead of drilling a single common duct and then dividing it longitudinally to form at least one supply path and one discharge path, it has been found preferable to provide three ducts close and parallel to one another, but smaller in diameter than the said single duct, so that the desired longitudinal separation is automatically ensured by the barrel metal itself remaining between the mutually close ducts.

There can be provided two or more ducts (three in the example illustrated), one or some of which are used more particularly for the supply (filling of the delivery chamber on the return stroke of the plunger) whereas the other or others serve more particularly to discharge the excess fuel (back-flow of the fuel expelled from the delivery chamber to these ducts at the beginning of the un covering of the corresponding orifices by the edge of the plunger groove) at the end of each effective delivery stroke of the plunger.

In the examples illustrated, where the orifices 20a, 21e, 22a are circular in shape and have their centres arranged on substantially one and the same circle 25, it is clear that the conduits 20 and 21 are used more particularly for the supply whereas the conduit 22 serves more particularly to discharge the fuel since its orifice 22a is the first to be opened by the edge 16 during upward movement (in Figure 1 and 2) of the plunger 13 at the end of its effective delivery stroke. However, the dis tinction between the supply ducts and the discharge ducts as defined hereabove is not the only peculiar feature of the invention. Pro visions must also be made for a connection between the ducts in proximity to their ori fices 20a, 21a and 22a, at least at the moment the edge 16 begins to uncover the orifice 22a under the above-defined conditions.

According to Figure 1, the said connection is obtained in a very simple manner by pro viding a recess 27 (also seen in Figure 3) in the wall of the barrel 11, within the bore 12 and more particularly in the region that separates the orifices of at least two (and preferably three) mutually close ducts 20, 21, 22. The said recess is so dimensioned as to overlap or encroach upon at least a portion of the edges of the orifices 20a, 21a and 22a to ensure a possibility of effective com munication between the ducts even when their orifices are covered by the lateral wall of the plunger 13. It is known from experience that the depth of the recess should pre ferably be comprised between 0.1 and 2 mm.

Figure 4 shows a method of making the recess 27. It is sufficient to introduce a milling cutter or tool 30 askew into the bore 12 before mounting the plunger, and then to drive the tool a small depth into the wall of the barrel 11, substantially be tween the said duct orifices or their future locations in case they have not yet been drilled. A positive guiding of the tool 30 is advantageously obtained by means of an adapted guiding cap 31 fitted at one end of the bore 12 and itself provided with a skew bore 32 serving as a guidway for the axle of the cutter 30. The latter may also be replaced by a grinding wheel or any other equivalent device.

Figure 2 illustrates another form of embodiment, in which it is not necessary to provide a recess such as 27. The communication which in this case is momentary, is obtained by means of a slot 33 parallel to the edge 16, provided in the lateral surface of the plunger in proximity to the groove 14, but not directly connected to the latter. The width and position of the slot 33 are selected to form a passageway 34 at the level of the orifices of the duct, during at least a short instant from the moment the edge 16 begins to uncover one of the orifices (22a).

This precisely is the situation illustrated in Figure 2. Otherwise stated, this communication is effectively established substantially during the time of rapid pressure variations in the pump resulting in cavitation phenomena. To obtain this result it is necessary, firstly, to ensure that the distance d defined between the slot edge nearest to the edge 16 and this edge itself substantially smaller than the diameter of the first orifice 22a uncovered, by the said edge during the effective delivery sroke of the plunger and, secondly, that the width Z of the slot 33 be substantially greater than the distance separating the portions closest to the orifices of at least two mutually close ducts.

Also in this case it has been found that the best results are obtained with a slot depth comprised between 0.1 and 2 mm.

The operation of the pump is quite simple and can obviously be inferred from the foregoing description. Whatever the selected from of embodiment, it is observed that at the instant of uncovering of the orifice 22a by the edge 16 a possibility of passage of the fuel between the ducts (through the passageway 34 or the recess 27) actually exists at least at that precise instant. There then occurs a rapid pressure drop from about 1000 kg/cm2 (which is the - pressure in the delivery chamber) to about 2 kg/cm2 (pressure in the supply system). This produces in the duct 22, approximately in the direction of arrow F, a jet of fuel of very high velocity which would tend to create vortices or whirls and regions of local negative pressure in the upper portion of this duct and which might result in rapid erosion due to cavitation and/or in scaling of the walls of the duct and the plunger.Owing however, to the structure provided by the invention, such negative pressure or lower-pressure regions are eliminated, the moment they are formed, by the fuel proceeding from the other ducts 20, 21 through the connecting passageways defined by either the hollow 27 or the slot 33.

WHAT WE CLAIM IS:- 1. A fuel injection pump comprising a cylindrical plunger reciprocable longitudinally within the bore of a barrel, which barrel is provided with a plurality of mutually close transverse ducts for the supply and discharge of fuel at each cycle of operation of the pump, the plunger being provided on its external surface with a groove which communicates with a chamber defined in the bore of the barrel beyond one end of the plunger and with the transverse ducts, and at least one edge of the groove being of substantially helical configuration whereby the effective delivery stroke of the plunger can be adjusted by altering the angular position of the plunger in the bore about its own longitudinal axis with respect to the transverse ducts, and a means of providing at least momentary communication between at least two of the transverse ducts in proximity to the orifices of the ducts opening into the bore.

2. A pump according to claim 1, in which the means of providing communication is at least partially constituted by a recess provided in the wall of the said barrel within the bore in at least the region of the wall that separates the orifices of at least two of the transverse ducts.

3. A pump according to claim 1 or 2, in which the means of providing communication is at least partially constituted by a helical slot provided in the external surface of the plunger, in proximity to the said groove and in parallel relationship to the said substantially helical groove edge.

4. A pump according to claim 3, in which the said orifices of the transverse ducts are of circular section, the distance defined between the slot edge nearest to the said groove edge and the latter being substantially smaller than the diameter of the first orifice uncovered by the said groove edge during the delivery stroke of the said plunger.

5. A pump according to claim 3 or 4, in which the width of the said slot is substantially greater than the distance separating the closest portions of the orifices of two of the said mutually close ducts.

6. A pump according to claim 2 or 3, in which the depth of the recesss and/or slot is comprised between 0.1 and 2 mm.

7. A method of providing the means of communication between the common supply and discharge ducts of a pump as claimed in any preceding claim, in proximity to the orifices of the said ducts which orifices open into the bore of the barrel containing the pump plunger, the method comprising introducing a milling cutter, grinding wheel, or other tool into the said bore, askew with respect to the axis of the said bore, before mounting the said plunger, and using the tool to make a hollow in the wall of the said bore, substantially between the said orifices or their future locations.

8. A method according to claim 7, in which a positive guiding of the spindle or axle of the said tool in the said skew position is effected, for example by means of a guiding cap fitted to one end of the said bore.

9. A fuel injection pump substantially as described herein with reference to and as illustrated in the appended drawing.

10. A method substantially as described herein with reference to and as illustrated in the appended drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

then occurs a rapid pressure drop from about

1000 kg/cm2 (which is the - pressure in the delivery chamber) to about 2 kg/cm2 (pressure in the supply system). This produces in the duct 22, approximately in the direction of arrow F, a jet of fuel of very high velocity which would tend to create vortices or whirls and regions of local negative pressure in the upper portion of this duct and which might result in rapid erosion due to cavitation and/or in scaling of the walls of the duct and the plunger. Owing however, to the structure provided by the invention, such negative pressure or lower-pressure regions are eliminated, the moment they are formed, by the fuel proceeding from the other ducts 20, 21 through the connecting passageways defined by either the hollow 27 or the slot 33.

WHAT WE CLAIM IS:- 1. A fuel injection pump comprising a cylindrical plunger reciprocable longitudinally within the bore of a barrel, which barrel is provided with a plurality of mutually close transverse ducts for the supply and discharge of fuel at each cycle of operation of the pump, the plunger being provided on its external surface with a groove which communicates with a chamber defined in the bore of the barrel beyond one end of the plunger and with the transverse ducts, and at least one edge of the groove being of substantially helical configuration whereby the effective delivery stroke of the plunger can be adjusted by altering the angular position of the plunger in the bore about its own longitudinal axis with respect to the transverse ducts, and a means of providing at least momentary communication between at least two of the transverse ducts in proximity to the orifices of the ducts opening into the bore.
2. A pump according to claim 1, in which the means of providing communication is at least partially constituted by a recess provided in the wall of the said barrel within the bore in at least the region of the wall that separates the orifices of at least two of the transverse ducts.
3. A pump according to claim 1 or 2, in which the means of providing communication is at least partially constituted by a helical slot provided in the external surface of the plunger, in proximity to the said groove and in parallel relationship to the said substantially helical groove edge.
4. A pump according to claim 3, in which the said orifices of the transverse ducts are of circular section, the distance defined between the slot edge nearest to the said groove edge and the latter being substantially smaller than the diameter of the first orifice uncovered by the said groove edge during the delivery stroke of the said plunger.
5. A pump according to claim 3 or 4, in which the width of the said slot is substantially greater than the distance separating the closest portions of the orifices of two of the said mutually close ducts.
6. A pump according to claim 2 or 3, in which the depth of the recesss and/or slot is comprised between 0.1 and 2 mm.
7. A method of providing the means of communication between the common supply and discharge ducts of a pump as claimed in any preceding claim, in proximity to the orifices of the said ducts which orifices open into the bore of the barrel containing the pump plunger, the method comprising introducing a milling cutter, grinding wheel, or other tool into the said bore, askew with respect to the axis of the said bore, before mounting the said plunger, and using the tool to make a hollow in the wall of the said bore, substantially between the said orifices or their future locations.
8. A method according to claim 7, in which a positive guiding of the spindle or axle of the said tool in the said skew position is effected, for example by means of a guiding cap fitted to one end of the said bore.
9. A fuel injection pump substantially as described herein with reference to and as illustrated in the appended drawing.
10. A method substantially as described herein with reference to and as illustrated in the appended drawing.