This invention relates to liquid pumps, particularly liquid pumps usable for pumping fuel, such as in petrol injection systems of internal combustion engines.

In one aspect, this invention comprises a liquid pump comprising first and second pump means, the first pump means- being operable tα pump liquid,admitted to the liquid pump-, under- pressure, to the second pump means, the second pump means- being operable- to deliver pressurised liquid therefrom to Liquid delivery means of the liquid pump. Preferably, the first pump means comprises a gear pump or other positive displacement pump operable to pressurise a gallery from which gallery fuel is in use admitted to the second pump means. Preferably too, said gallery is provided with overflow means permitting restricted outflow of liquid from said gallery. The second pump means preferably comprises a plurality of pistons and cylinders together with means for admitting liquid to the cylinders for pumping therefrom under action of reciprocation of the pistons. The pistons are preferably arrayed around a central axis and provided

with eccentric means for moving the pistons to effect said reciprocation. Preferably, said eccentric means includes a body having a plurality of faces, a separate one of which is arranged to impart said reciprocation to a respective one of said pistons. Preferably, the said body is mounted so as in use to execute an orbiting motion to effect said reciprocation. It is preferred that means is provided whereby the eccentricity of said body may be varied in use of the pump. In this case, it is preferred that the body is biased to a position of maximum eccentricity by resilient bias means arranged to be compressed under movement of the body to reduce the eccentricity _t the body occupying a position of maximum: eccentricity during low speed conditions such as cranking and a suitable minimum eccentricity during" higher speed conditions-

The invention also provides a liquid metering device, couplable to the output of a liquid pump such as a liquid pump of this invention, said liquid metering device comprising a first member having a space therein and a second cylindrical member in said space, said members being mounted for relative rotation one relative to the other, said first member having first port means for admission of liquid to said space and second port means for outflow of liquid therefrom, said second member having a first transfer cavity therein which, at a condition of alignment of said first port means occurring during relative rotation of the members, can receive liquid from said first port means, and transfer means being provided for then delivering at least a part of the so received liquid

from said transfer cavity to said second port means when, thereafter during said relative rotation, a condition of alignment occurs between said transfer cavity and said second port means. Preferably, said members are relatively rotatable about a common axis, and said transfer means comprises an element carried by said second member and movable axially of said first and second members and being arranged to extend into said transfer cavity to displace liquid therefrom to said second port means. Preferably, the liquid metering device includes third port means in said first member arranged for delivery of liquid into a second transfer cavity in said second member, said element being- arranged to extend, into said second transfer cavity whereby to be acted on by liquid flow from said third port means into said second cavity for moving the said element to effect said displacement of liquid in the first transfer cavity. Preferably too, the liquid metering device includes fourth port means in said first member and arranged whereby to receive- liquid from the said second transfer cavity when the second transfer cavity is aligned with said fourth port means, said first, second, third and fourth port means being arranged whereby, during said relative rotation of said members, admission of said liquid from said first port means to said first transfer cavity causes a portion of said element then within said first transfer cavity to be acted on by liquid pressure to move said element to displace liquid from said second transfer cavity to said fourth port means, whereby displacement of liquid from said first and second transfer cavities to said third, second and fourth ports respectively is effected by oppositely

directed reciprocating movements of said element under admission of liquid to the respective second and first cavities. Preferably, means is provided for varying the stroke of said element during said reciprocatory movements whereby to vary the amount of liquid displaced from the said cavities to the second and fourth ports in use. Preferably too, for the purpose of varying the angular positions at which said displacement occurs, during each complete relative revolutionary movement between the first and second members, variable displacement means is provided for variably displacing the first member about the axis of the second member whereby to vary the relative positions of the said ports. Preferably the variable displacement means comprises means sensitive to pressure derived from said liquid pump, whereby to effect such variable displacement, in accordance with that pressure, in a direction tending to relatively advance the times during each revolution of said second member at which displacement of liquid from the said transfer cavities is effected. The said pressure may be the delivery pressure of said first pump means or of said second pump means but is preferably the pressure of liquid at the outlet of said first pump means and said advance is preferably arranged to occur when said pressure of liquid at the outlet of said first pump means rises.

The above described arrangement for advancing the relative angular positions at which liquid displacement occurs has an advantage where the liquid pump is a fuel pump operated from an engine in that

the pressure of liquid fuel delivery from the aforementioned first pump means, where this is a positive displacement pump, whilst being primarily dependent on speed of rotation of the drive thereto and thus on the speed of rotation of the internal combustion engine which in use drives the gear pump, may also be made to be in part influenced by load on the engine. More particularly, under heavy load the liquid pump can be arranged to deliver, from the second pump means, a greater quantity of liquid fuel than is the case where the engine runs under low load conditions. As a result, for constant speed running, the output pressure from the first pump means will be dependent on engine load, decreasing with, increase in load. Thus, under heavy load, there will be a secondary effect on the aforementioned varying of the times of delivery from the liquid pump so that under high load conditions there will be a relative angular retardation of the position during each relative revolution of the first and second members at which fuel delivery occurs.

Where the pump with which said liquid metering device is used as a fuel pump for an internal combustion engine, the said means for varying the volume of delivered fuel is preferably arranged so as to be coupled, in use, to an output regulating device such as the accelerator where the engine is intended for coupling for driving a vehicle.

Thus, in accordance with a still further aspect of the invention there is provided a liquid pump as first above described wherein said first pump means is

adapted to provide an output liquid delivery rate therefrom which is dependent on the speed at which the first pump means is driven, said second pump means being adapted to cause said delivery pressure from the first pump means to be lowered under conditions of high flow from the liquid pump; said liquid pump having delivery means for periodically delivering liquid from the second pump means at predetermined times during operating cycles of period inversely proportional to said speed, and means responsive to delivery pressure from the first pump means to vary the ratio of a time interval to the said period of a said cycle, said time interval being the interval measured from, initiation of that said cycle to the time at which said delivery occurs in that said cycle. In another preferred aspect of the invention, a pressure sensitive valve is provided sensitive to the output pressure from said second pump means and operable to return liquid delivered from said second ^" pump means to a liquid supply to the first pump means under the condition that the pressure exceeds a predetermined value.

The invention is further described with reference to the accompanying drawings in which:

Figure 1 is a schematic view of a fuel supply system including a pump constructed in accordance with the inventio ;

Figure 2 is formed in two parts 2a and 2b which join on the line "X-X" shown to form an axial cross-section of the pump of figure 1;

Figures 3a and 3b are diagrammatic scrap cross sections substantially on the line 3-3 in figure 2, but showing two different conditions of two cooperating parts of the pump of figure 2;

Figure 4 is a cross section on the line 4-4 in figure 2;

Figures 5 to 14 inclusive are diagrammatic cross sections illustrating the manner of operation of fuel metering means incorporated into the pump of figure 2 and in which figures 5, 8, 11 and 14 are cross sections on the line 5-5 in figure 2, figures 6, 8, 12 and 15 are cross sections on the lines 6-6 in figure 2 and figures 7, 10, 13 and 16 are cross sections on the line 7-7 of figure 2, and which figures 5 to 7 inclusive show conditions prevailing at a condition of zero rotational displacement between two members of the metering means, figures 8 to 10 inclusive show condition of 90° phase displacement between those members, figures 11 to 13 show condition of lβ0 ^σ phase displacement between the members, and figures 14 to 16 show a condition of 270° phase displacement between the members;

Figure 17 is a scrap cross section showing a valve associated with one cylinder of a high pressure pump stage incorporated into the pump of figure 2, being a view taken approximately on the line 17-17 in figure 4.

Referring firstly to figure 1, the fuel supply system shown therein generally comprises a fuel tank 10, a

subsidiary fuel pump 12 and a main fuel pump 14. The fuel pump 12 is connected via a line 15 to the tank 10 and operates to supply fuel at low pressure to the pump 14 via a filter 16. The fuel line 18 from filter 16 is connected to an inlet gallery 20 forming part of pump 14. Fuel so-delivered to the gallery 20 is fed via an inlet 22 to a gear pump 24 also forming part of fuel pump 14. Gear pump 24 in turn supplies fuel to a low pressure gallery 26 formed in the body of pump 14. From gallery 26, fuel is fed to a high pressure pump 28 via a drilled gallery 30. Output from pump 28 is fed to two fuel distributors 32, 34 via a branched fuel gallery 36.

The pump 14 is intended to pump liquid fuel such as petroleum which, in its lighter spirits, has a tendency to vaporise easily. A bleed choke line 38 is provided from gallery 26, via which a small amount of fuel in the gallery 26 can be returned back to the• tank 10 continuously. This return is arranged at the highest point in the gallery 26 and serves to assist in removal of any gasified fuel or trapped air from the gallery 26.

The gear pump 24 is a positive displacement pump of conventional kind and operates to deliver a quantity of fuel to gallery 26 which is proportional to the speed of rotation thereof. Both the gear pump 24 and the pump 28 are, as described in more detail later, driven by an internal combustion engine (not shown) with which the pump 14 is in use associated so that as engine speed increases so will the speed of the pump 24 and so will the pressure of fuel delivered to

gallery 26. A certain amount of fuel so-delivered is taken off by pump 28, but a relief line 34 is provided connected to line 32 and including a restricting choke 40 which serves to deliver, back to the inlet gallery 20, fuel from the gallery 26 where insufficient fuel has been taken via gallery 20 to pump 28 to maintain the fuel pressure in the gallery 26 at below a predetermined maximum value established by the orifice size of the choke 40. A pressure release valve 46 is also connected to the gallery 36 from the pump 28 to distributors 32, 34 and this is set to open under predetermined pressure conditions in gallery 36 whereby to deliver, via a gallery 48, fuel from the gallery 36 back to the gallery 20. Thus, if insufficient fuel is being delivered from the distributors 32, 34 so that pressure in gallery 36- is beyond the preset pressure of operation for the relief valve 46, that pressure is relieved by fuel flow via the valve 46 and gallery 48 back to the inlet gallery 20. Excess fuel from the distributors 32, 34 and which may, by leakage of components therein, not be presented to outlets therefrom, is returned via interior housings and shafts of the pump 14 (not shown in figure 1) which communicate with a branched line 50 to the gallery 20.

Generally, the pump 28 serves to raise the operating pressure of fuel admitted thereto to sufficient pressure for operation of fuel injectors 52,54 and the distributors 32 and 34 operate to distribute the so-pressurised fuel to the injectors. The particular pump described here is adapted for use in a engine of the kind described in my copending patent application

No. 35853/78, particularly being an engine in which there are two fuel injectors for each cylinder of the engine. Distributor 34 serves to supply fuel to the injectors 52 each of which supplies fuel at one location for each engine cylinder, whilst distributor 32 operates to distribute fuel to the injectors 54, each of which is arranged to supply fuel at another location for each cylinder. The arrangement of the engine described in my copending patent application is such that the distributor 34 need only supply fixed volumes of fuel to the injectors 52 regardless of engine speed or load, the injectors 52 being arranged to inject fuel into small subsidiary combustion chambers in which ignition of. fuel is first effected in each cylinder of the engine. On the other hand, the injectors 54 are required to be provided with quantities of fuel which are dependent on engine load, since these injections are associated with main combustion chambers of each cylinder of the engine, which main combustion chambers are arranged so that ignition of fuel therein is caused by contact with igniting fuel charges from the aforementioned auxiliary combustion chambers.

Turning now to figure 2, the pump 14 is shown in more detail as including an inlet shaft 56 which drives both of the component pumps 24 and 28 of the pump 14. Pump 24 includes two meshing gears 82, 84 of which gear 84 is drivingly coupled to shaft 56 and gear 82 is drivingly coupled to a shaft 90 parallel to shaft 56. Both shafts 90 and 56 are journalled for free rotation in a housing 80 of the pump. The gears 82, 84 run in a generally "8"-shaped cavity 92 in the

housing 80, opposed faces of which sealingly engage side faces of the gears 82,84. The gallery 20 is indicated in figure 2 , this communicating with the cavity 92 at a location adjacent the nip between the two gears 82, 84 but to one side of the nip when viewed parallel to the axes of the gears. Fuel supplied to the gallery 20 is passed to this nip and passes through the cavity 92 around the peripheries of the gears 82, 84 in the cavities between adjacent teeth of the gears, as the gears rotate pursuant to driving of shaft 56. Fuel so passing around the gears is delivered to gallery 26, which gallery communicates with the cavity 92 at a location adjacent the nip between gears 82, 84, but at the opposite side, of that nip to the location where the gallery 20 communicates with cavity 92.

As shown in figure 4, the pump 28 includes four pistons 98 arrayed in an equiangular array about the axis of shaft 56. These are lengthwise reciprocable in radial cylinders 106 retained in housing 80. At innermost ends, the pistons have convex bases 115 with outwardly extending flanges 114, and these bases 115 rest on the interior surfaces of bases 116a of cup-shaped elements 116. The cup-shaped elements 116 have side wall portions 116b of hollow cylindrical form which are slidably mounted in bores 118 (figure 2) coaxial with the respective pistons 98. Resilient compression springs 120 are arranged around the outer surfaces of the cylinders 106 and exert resilient pressure between outwardly stepped surface portions 122 on the exteriors of the cylinders 106 and the flanges 114 on the pistons 98, whereby the pistons are

resiliently biased radially inwardly towards the axis of the shaft 56. The springs 120 are accommodated within annular spaces defined between the interior surfaces of the side wall portions 116b of the cup-shaped elements 116 and the exterior surfaces of the cylinders 106.

Flat surfaces of the bases 116a of the elements 116, closest the axis of the shaft 56, rest upon respective flat surfaces 124 of a square element 126. Element 126 has a circular bore 128 therethrough and a cylindrical cam member 130 having a circular periphery is neatly accommodated within bore 128 so that the element 124 is freely rotatable about the member 13Q» The member 130 has an opening 132 therethrough which is of elongate rectangular transverse cross-section.. This is neatly accommodated over a square cross-sectioned portion 56a of shaft 56 so that member 130 is non-rotatable relative to the shaft 56 but slidable radially of the shaft 56 in the direction of the longer dimension of the rectangular cross-section of opening 132. To either axial side of the element 126 and member 130, there are provided on the shaft 56 two outwardly extending flange members 136, 138. These flange members have square central apertures therethrough and these are neatly accommodated over the portion 56a of shaft 56 whereby the flange members 136, 138 are irrotatable relative to the shaft 56. Pins 140, of which only one is shown in the drawings, extend parallel to the axial direction shaft 56 and through openings in the member 130. Portions of these pins extend from opposed transverse side faces of the member 130 to be accommodated in slots 136a, 138a on

inner faces of the flange members 136, 138 which slots are directly opposed to the transverse side faces of the element 126. The slots 136a, 138a extend in directions which are parallel to the longer dimension of the cross section of the opening 132 through member 130.

The flange members 136,138 are positioned between, on the one hand, an outward step 133 in the periphery of the shaft 56 and, on the other hand, a retaining element 135 splined onto the shaft 56, and are precluded from axial movement away from the step 133 by a circlip 137 engaged in a grove in the shaft. The flange members 136, 138 serve to retain the member. 130 and element 126 whilst permitting these to move in the radial direction of the longer cross sectional dimension of the opening 132 in member 130, the latter movement being accompanied by movement of the ends of pins 140 in slots 136a, 138a.

The radial sliding movement of the member 130 which is permitted relative to the axis of shaft 56 permits the member 130 to be positioned over a range of variable eccentricities relative to the axis of the shaft 56. In figures 2 and 4, the member 130 is shown positioned at a maximum eccentricity at which one shorter side surface 132a of the rectangular cross-section of the opening 132 is adjacent one face of the square cross-sectioned portion 56a of shaft 56. From this position, the member 130 is movable in the direction shown by arrow "B" in figure 4 so that the eccentricity is reduced. The minimum eccentricity permissible is established at a condition at which the

other shorter side surface 132b of the opening 132 is brought into engagement with outer ends of radially extending pins 148, 150 (figure 2) received in radial bores 152, 154 in portion 56a of shaft 56. These pins rest on basal portions of the bores 152, 154 and extend therefrom to outer ends thereof which project somewhat from the portion 56a of shaft 56.

In the inoperative position of the pump 14, the member 130 is biased to a condition of maximum eccentricity by means of resilient compression springs 160, 162 positioned in the bores 152, 154. Springs 160, 162 rest on outwardly extending lower flanges formed on the pins 148,. 150, and extend around the respective pins 148, 150 so as to bear, at outer ends thereof, against the surface 132b of the opening 132..

Under the condition of rotation of the shaft 56, the eccentric positioning of the member 130 causes the axis of that member, and the aligned axis of the element 126, to execute a circular orbiting motion around the axis of the shaft 56, the member 130 being driven positively by virtue of the coupling between the member and the shaft 56, as provided by the pins 140 and flange members 136, 138, and by the interengagement of the non-circular opening 132 on the non-circular cross-sectioned portion 56a of the shaft 56. Thus, the point of maximum eccentricity on the outer surface of the member 130 likewise executes a circular motion about the axis of shaft 56. Element 126 is carried around with member 130, but is generally constrained against bodily rotation about the axis of shaft 56 by virtue of the four radially

directed resilient forces applied thereto from the springs 120 via the elements 116 and by virtue of the surfaces 124 being flat and engaged with the flat radially innermost surfaces of the bases 116a of elements 116. Thus, the eccentric rotational movement of the element 130 causes the member 126 to execute an orbiting motion around the axis of the shaft 56 while, at the same time, maintaining the side faces 124 thereof in constant orientations relative to the axes of the pistons and cylinders of the pump 28. Thus, the orbiting motion of the element 126, when resolved along the mutually perpendicular axes of the cylinders 106, produces component motions thereof which drive the pistons 98 so as to cause these to execute reσiprocatory motions. Radially outward motions of the pistons are caused by direct outward components of the movement of the element 126 while radially inward movements are caused by the springs 120 which, as mentioned, resiliently bias the pistons inwardly. The motions of the pistons are arranged so that the reciprocatory motions thereof as executed in use of the pump are phase displaced by 90°, one with respect to the preceding one reckoned around the axis of the shaft 56. In figures 2, one piston 98, that to the upper side of the shaft 56 as shown, is shown at a position of maximum outward reciprocatory motion whilst the opposite piston 98 is shown at a position of maximum inward movement. At this condition the remaining two pistons 98 occupy intermediate positions in the reciprocatory motion, as shown in figure 4.

Fuel from the gallery 26 is supplied to the spaces between the outer ends of the pistons 98 and the outer ends of the interiors of cylinders 106 via ports of which one port only, designated by reference numeral 180 is visible in figure 2, being that port associated with the uppermost cylinder 106. The ports 180 for the remaining cylinders are, however, similar, as shown in figure 4. Likewise, the interconnections provided by the gallery 30 from the gallery 26 to the pump 28 are not fully shown in figure 2 save that a portion of the gallery 30 is shown in housing 80, by broken lines, being- that portion which leads from the lowermost depicted cylinder to the gallery 26. The gallery 30 is, however, branched so as to deliver fuel respectively to the four ports 180 associated with the four cylinders. The ports 180 also act as outlet ports for the four cylinders and inlet and outlet via the ports is controlled by respective valves 190. The valves 190 are similar and the following description of the valve 190 as shown in figure 17 is to be taken as being equally applicable to each of the valves 190. The valve 190 shown comprises an elongate cylindrical body 189 formed in two parts 192, 194 which are arranged end to end and sealingly retained within a bore 196 in the housing 80. The body 189 defines an elongate central cavity 198 which communicates with the port 180. The inlet gallery 30 communicates with one axial end portion 198a of the cavity 198 via an inlet port 200. A ball 202 in end portion 198a of cavity 198 is resiliently biased by a spring 206 to normally close port 200. However, under influence of pressure from the fuel in gallery 30 on a radially inwardly directed stroke of the piston 98 of the

cylinder 106 with which the valve 190 is associated, the fuel can act upon the ball 202 so as to press it, against resilient bias of the spring 206, inwardly away from port 200 to permit fuel to flow from gallery 30 through the inlet port 200 into the portion 198a of the cavity 198. From this portion 198a, the fuel can flow into the cylinder 106 via the port 180 which port communicates directly with cavity portion 198a.

The end of the body 189 opposite port 200 has an outlet port 210. During the aforedescribed admission of fuel to the port 180 via the cavity portion 198a, liquid flow from the cavity portion 198a via the port 210 is prevented by a second ball 212 which is retained in a second portion 198b of cavity 198 and which is resiliently biased, by a- spring 214, against a valve seat 220 formed in an apertured partition wall 198c between the cavity portions 198a, 198b whereby to block flow through the partition wall. The spring 214 is made sufficiently strong so as to prevent the ball 212 being moved away from the seat 220 under influence of pressure of fuel then in the chamber 198, it being borne in mind that such pressure is relatively reduced under the described condition of radially inward movement of the piston during which fuel is being admitted to the cylinder. On subsequent radial outstroke of the piston 98, the fuel in the cylinder space above the piston is forced back into the cavity portion 198a through the port 180. Under this condition, the ball 202 is acted upon by the fuel pressure to firmly press it back against the port 200 to prevent fuel return back through gallery 30. On the other hand, the fuel pressure in the cavity 198a

then rises to a high level sufficient to overcome the resilient bias of spring 214 thus forcing the ball 212 from the seat 220 to permit outflow of fuel from the chamber 198 through the aperture in the partition wall 198c thence through the cavity portion 198b to the outlet port 210.

The outlet ports 210 ^° of the valves 190 are connected together at a branched end of the gallery 36 which leads to the two fuel distributors 32 and 34.

The fuel distributor 34 includes a generally cylindrical body 230 accommodated within housing 80 and having a central bore 232 therewithiπ- A cylindrical spindle 234 is neatly accommodated within bore 232 so as to be free running therewithin. The- outer surface of spindle 234 sealingly engages the surface of bore 232. Spindle 234 is attached to shaft 56 so as to be driven by the shaft during operation of the pump 14.

Spindle 234 has an axial bore 234a therethrough and three central shaft members 235, 236, and 237 are retained therein at axially spaced positions. These present therebetween two cavities 300, 302 within the spindle. Cavity 300 is bounded at opposite ends by an end surface 235a of member 235 and an end surface 236a of member 236. Cavity 302 is bounded by an axial end surface 236b of member 236 and by an axial end surface 237a of member 237. Member 237 has however, extending from surface 232a, an axial spigot 237b. The peripheries of members 235, 236, 237 sealingly engage the inner periphery of bore 234a. Members 235, 236

may be axially immovable relative to spindle 234 but element 237 is axially slidable for a purpose described later. Cavities 300, 302 open to the exterior of the spindle 234 via ports 238, 248 formed in the side wall of the spindle 234. Ports 238, 248 are displaced relative to each other by 180° around the periphery of the spindle 234.

The body 230 is non-rotatably received in the main housing 80 of the pump and has a number of ports in the side wall thereof. Most of these ports are not visible in figure 2 but are shown in figures .5 to 17. More particularly at the cross sectional location of the cavity 300, body 230 has four equiangularly disposed ports, 280, 282, 284 and 286 which extend through the side wall thereof to provide communication to the exterior surface of the spindle 234. Similarly, at the cross-sectional location of the cavity 302, there are four further ports through the side wall of the housing 230, these being ports 288, 290, 292 and 294, again arrayed at equiangular locations around the periphery of the body 230.

Member 236 has a central axial bore therethrough and this has a pin 304 retained therein for neat sliding and sealing movement in the axial direction of the spindle 234. The bore within which pin 304 extends opens at opposite ends to the cavities 300, 302, and free ends 304a, 304b of the pin 304 project into the cavities from surfaces 236a and 236b respectively. The pin 304 is movable between two extreme positions axially within the spindle 234. At one extreme, the pin end 304a thereof engages the end surface 235a on

member 235, being the defining surface of cavity 300 opposite that from which pin end 304a extends into the cavity. At the other extreme, the pin end 304b engages the end of the spigot 237b on the surface 237a of the member 237 opposite the surface 236b from which the pin end 304b extends into cavity 302.

The ports 280, 284, 290 and 294 are each connected to the gallery 36 from the high pressure pump 28. The ports 282, 286, 288 and 292 are connected to respective outlets from the pump 14, of which only one outlet 336, being that associated with one of the outlet ports 282, 286, is shown in Figure 2. These outlets are in use connected to the individual injectors 52.

Figures 5 to 7 illustrate a condition of distributor 34- where cavity 300 is brought, at port 238 into fluid flow alignment with inlet port 280 and at which the cavity 302 is via port 248 in alignment with the outlet port 292. It will first be assumed that, immediately before reaching the condition illustrated in figures 5 and 6, the pin 304 is first positioned so that it extends fully into cavity 300 whereby the pin end 304a engages the surface 235a. In this condition, because of the communication provided from the ports 280 and 238 to the cavity 300, high pressure fuel from the high pressure pump 28 can pass along the gallery 36 to the port 280 and thence into the cavity 300. As a result of this, there is a high fuel pressure in the cavity 300. It is supposed, that, at this time, too, there is a quantity of fuel within the cavity 302. A consequence of the admission of high pressure fuel

into the cavity 300 is to cause that fuel to bear against the transverse end face of the pin 304 at the end 304a thereof whereby to move the pin from left to right as viewed in figure 2 to the position shown in figure 7, under influence of that pressure. This movement is terminated when the pin end 304a engages the end surface 237a at spigot 237b. The movement of the pin causes corresponding displacement of a volume of fuel from the cavity 302 out through the port 292 which is at this time aligned with the port 248 from cavity 302 and thence to the outlet associated with port 292. On 90° of rotational movement of the spindle 234, the ports 238, 248 of cavities 300, 302 are aligned, relative to the various ports in the member 230 as shown in figures 8 to 10. In this case, fuel admitted through port 290 can pass into cavity 302 whereby the high pressure thereof causes the pin 304 to be moved lengthwise from the position shown in figure 7 so as to cause the pin end 304a to enter cavity 300 whereby to displace fuel therein, being fuel that had been retained in the cavity 300 following the inlet of fuel thereinto via the port 280 as mentioned. The displaced fuel passes out through port 284. Figures 11 to 13 illustrate the condition at a further 90° of rotation of the spindle, fuel here being taken into cavity 300 from port 284 and being displaced from cavity 302 by movement of the pin 304 into cavity 302, the fuel in cavity 302 leaving via port 288. At the condition of figures 14 to 16, at which 270° of rotation has occurred, the port 294 is positioned for admission of fuel to cavity 302 whereby to move pin 304 to eject fuel from cavity 300 via port 282.

The distributor 34 is provided with means for permitting variation of the quantity of fuel delivered from the outlet ports thereof. Thus, as mentioned, member 237 is slidable within the interior bore of shaft portion 236, and this movement varies the axial - width of the cavity 302 whereby to also vary the maximum permissible stroke of the pin 304 by varying the axial position of spigot 237a. A set screw 340 is threadedly received in a threaded bore 342 in housing 80 coaxial with spindle 234 and this carries a ball 246 at its inner end which ball engages an outer end of the member 237. Thus, by screwing- set screw 340 inwardly, the member 237 can be moved axially to the left as shown in figure 2 to reduce the permissible allowed stroke of the pin 304, whilst withdrawal of the set screw by unscrewing it causes the permissible stroke to be increased. Although no specific mechanism is provided to cause member 237 to move with the set screw 340 when it is unscrewed, pressure in the cavity 302 present in use serves to bias the member 237 against the ball 246 ^" .

The distributor 32 is generally of like form to the distributor 34 and, in figure 2, like components in the distributor 32 are designated by like reference numerals to those described in relation to the distributor 34. The following description of the distributor 32, then, relates only to differences in construction between the two distributors.

Firstly, in the distributor 32, the pin 304 is made of rather larger diameter than the pin 304 in the distributor 34 whereby to displace greater volumes of

fuel into the outlet ports, bearing in mind the need for the distributor 32 to supply the aforementioned injectors which supply the main combustion chamber fuel requirements. Secondly, the set screw 340 is, in the distributor 32, replaced by a slidable cylindrical element 350 received in a bore 352 in housing 80. Element 350 is axially aligned with the axis of spindle 234 of distributor 32 and has retained at its inner end a ball 354 which bears against the outer end of member 237 of distributor 32.

A control member 358 is positioned at the outer end of element 350 and is rotatable about an axis offset from the axis of spindle 304 of distributor 32. This has an outstanding radial arm 360 movable to turn member 358 about its axis. Member 358 is prevented from axial movement in a direction away the outer end of the element 350 by a thrust bearing 364 which engages an end closure 366 threadedly received in threaded bore 368 in housing 80. Member 358 has a ramped cam surface 370 extending around the axis of member 358 and this is positioned to be adjacent the outermost end of element 350. A ball 372 is interposed and retained between the ramp surface 370 and the outer end of the element 350. On turning of arm 360 to rotate the member 358 about its axis, the point at which the ball 372 engages the ramp surface 370 is varied along the circumferential length of the cam surface. Bearing in mind that, in use, the element 350 is axially biased by fluid pressure in the distributor 32 so as to cause the ball 372 to be engaged with the surface 370, the described turning motion of the member 358 causes variation in the axial

positioning of the element 350 to effect variation in the positioning of the member 237 of distributor 32 whereby to effect variation of the stroke of the pin 304 and thus to vary the quantity of fuel delivered by the distributor 32.

The spindle 234 of the distributor 32 is driven from the shaft 90 via an advancing mechanism 382. Mechanism 382 includes an annular piston 384 coaxially mounted relative to shaft 90 and having inner and outer peripheral side surfaces which slidingly and sealingly engage inner and outer surfaces 388a, 388b of an annular cavity 388 in housing 80, also coaxially arranged relative to shaft 90. Cavity 388 is closed at one end by an inner transverse surface of piston 384 and at the other end by an opposed transverse end surface 388c of housing 80. Cavity 388 is connected to gallery 26 by a drilling 390.

Mechanism 382 further includes two cooperating annular cam-members 392, 394. Member 392 is splined on shaft 90 so as to be driven by the shaft but axially movable relative thereto. Member 394 is freely rotatably carried on a bearing 396 on shaft 90. The spindle 234 of distributor 32 is coupled to member 394 so as to be rotatable therewith, the coupling being by interengaging splines on these parts. Thrust bearings 398, 400 are interposed, on the one hand, between piston 384' and member 392 and, on the other hand, between member 394 and an opposed transverse wall of housing 80. A helical compression spring 404 is interposed between members 392, 394 so as to normally resiliently bias these away from each other to a limit

position shown in figure 2 at which the piston 384 engages surface 388c of cavity 388, whilst the element 394 is biased against the bearing 400.

The members 392, 394 each have an equiangularly spaced array of ramp projections 406, 408 respectively. These have ramped cam surfaces 406a, 408a which surfaces 406a, 408a engage with each other. Figure 3a illustrates the members 392, 394 at the condition of figure 2. By application of fluid pressure into cavity 388, piston 384 can be moved away from the end surface 388c of cavity 388 thereby to move member 392 correspondingly against the resilient bias of spring 404. During this movement,, the cam surfaces 406a of the projections 406 on member 392 slide over the corresponding cam surfaces 408a of the projections 408 on member 394, as the distance between the two members 392, 394 is correspondingly reduced. Figure 3b shows a condition at which the spacing has been so reduced, and it will be noted therefrom that the effect of the sliding over each other of the surfaces 406a, 408a is to impart a component of relative rotational movement to the member 394 as compared with the member 392. The relative rotational positions assumed by the members 392, 394 is thereby variable by varying the fluid pressure within cavity 388 to vary the positioning of the piston 384. Thus, during driving of spindle 234 of distributor 32 from shaft 90 via coupling 382, the relative rotational positions in each rotational cycle at which outlet of liquid from the distributor 32 occurs can be varied.

It is the case that the pressure in the gallery 26 is primarily dependent on the speed of operation of the pump 24 since, being a gear pump, the delivery rate into the gallery 26 is proportional to driving speed. Since shaft 56 is in use driven by the internal combustion engine to which the pump is fitted for supply of fuel, the pressure in the gallery 26 will thus be dependent on the speed of rotation of the engine. Likewise, then, the relative phase displacement between the members 392, 394 and thus between the shaft 90 and the spindle 234 of distributor 32 is proportional to the engine speed. The direction of relative phase displacement between the shaft 90 and spindle 234 which occurs on increase in speed is arranged such as to cause the angular positions in each rotational cycle of the spindle 234 at which outlet of fuel occurs to be relatively advanced in each cycle as compared with that prevailing at lower speeds. By this means it is ensured that as engine speed increases fuel injection into the injectors 54 is, as is required for normal operation of fuel injected engines, made earlier in each operating cycle of the engine.

While, as described, the primary influence on fuel pressure in the gallery 26 is the speed of rotation of the engine to which the pump 14 is attached, a secondary influence on that pressure arises because the pressure is also dependent upon the volume of fuel taken per unit time from the gallery by the pump 28. The rate of removal of fuel from the gallery by the pump 28 is in turn a function of engine load, because greater volumes will be displaced from the distributor

32 as engine load increases. Thus, although the pump 14 will in general operate to advance the angular positions in each cycle of operation thereof at which fuel is delivered, in accordance with engine speed, there will also be some retarding effect where the engine runs under heavy load. The angular fuel delivery positions of the spindle 234 of distributor 32 will be advanced in accordance with engine speed of the engine runs at constant load, but if the engine runs at constant speed, the angular fuel delivery positions will be retarded with increasing load. This has been found to be particularly desirable, since a slight retarding effect in fuel admission is desirable under heavy load conditions.

While, as described, the set screw 340 is normally pre-set to provide fixed predetermined quantities of fuel to be- delivered from the distributor 34, it is possible to interconnect the set screw with housing 80 by a bimetallic spiral element operable to rotate the set screw in accordance with temperature in a way providing for increased fuel delivery quantities to the auxiliary combustion chambers of the engine under the condition of low temperature operation to give a richer air-fuel mixture under those conditions.

The described distributors are arranged each to supply four fuel injectors. Thus, the shaft 56 should be arranged to be driven at one half of the engine crank-shaft speed in order to derive the necessary supply to each injector once in every full four-stroke cycle, or at crank-shaft speed if applied to a two-stroke engine.

The described manner of varying the eccentricity of the member 130 ensures that under initial starting conditions, where there is little liquid pressure in the cylinders 106, there is maximum eccentricity and thus maximum stroke of the pistons. By this means, during initial cranking at start up, a relatively greater volume of fuel is initially delivered from the cylinders. On buildup of fluid pressure as a condition of normal operation is approached, however, fluid pressure in the cylinders is such as to cause the eccentricity of the member 103 to be reduced to its minimal condition by virtue of greater forces being applied by the pistons through the cup shaped elements 116 to the member 130 whereby to overcome the spring bias provided by the springs 160, 162.

The described pump has been advanced in the context of a pump suitable for operating a particular form of internal combustion engine of the kind described in my copending patent application No. 35853/78. However, it will be appreciated that the pump is readily adaptable to supply fuel to fuel injectors of other kinds of internal combustion engine. In particular, engines not having the described subsidiary combustion chambers may be supplied only from the distributor 32 in which case the distributor 34 may be omitted.

The described arrangement has been advanced merely by way of explanation and many modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.