GB2422177A

GB2422177A - Rotary distributor fuel pump having pilot pumping plungers

Info

Publication number: GB2422177A
Application number: GB0600240A
Authority: GB
Inventors: Malcolm Higgins
Original assignee: Stanadyne LLC
Current assignee: Stanadyne LLC
Priority date: 2005-01-18
Filing date: 2006-01-06
Publication date: 2006-07-19
Also published as: BRPI0600161A; CN1824943A; GB0600240D0; FR2881478A1; US20060159572A1

Abstract

A rotary distributor fuel pump 10 has a rotor with a plurality of main pumping plungers 42 for delivering high pressure fuel to a plurality of fuel ports 20 each associated with a respective fuel injector. The pump also has a plurality of pilot pumping plungers 36 and associated pilot pumping passages 48 fluidly connectable to the discharge ports and a means of timing the actuation of the pilot plungers for advance overlap phasing relative to the actuation of the main plunger to deliver fuel from the pilot plungers to the discharge ports in advance of fuel delivered by the main pumping plungers. The pump may have a cam profile 52 surrounding the main and pilot plungers with the axes A2, A1 of the main and pilot plungers having an angular offset.

Description

PILOT INJECTION PUMP

FieJd of the Invention The present invention relates generally to high pressure pumps for fuel injection systems and, more particularly, to a rotary distributor fuel pump for such systems.

Background of the Invention

Motor vehicles are required to comply with increasingly stringent limits on noise and exhaust emissions. Published research has demonstrated that noise and emissions from internal combustion engines are influenced by the time history of the fuel flow through the injector spray holes, otherwise known as the "rate-shape" of injection.

Considerable effort has been expended to control the rate-shape and timing of injection in response to the specific requirements of a particular engine application. Previous efforts at controlling the rate- shape of injection include modifications to the injector assembly and fuel pump.

One type of fuel pump of particular relevance to the present invention is a rotary distributor fuel pump. In this type of well-known fuel pump, a distributor rotor rotates within a substantially tubular hydraulic head. The distributor rotor includes a pair of opposed reciprocating plungers, movement of which is controlled by angularly spaced inwardly directed cam lobes of a cam ring. The cam ring for a rotary distributor fuel pump typically includes a cam lobe for each cylinder of the engine. Diametrically opposed cam lobes operate on cam followers to simultaneously actuate the pumping plungers. Passages in the distributor rotor sequentially register with fuel feed passages in the hydraulic head to supply fuel to a pumping chamber defined between the opposed reciprocating plungers. Rotation of the distributor rotor interrupts communication between the fuel feed passage of the hydraulic

I

head and the pumping chamber. Continued rotation of the distributor rotor brings the cam follower rollers into engagement with one pair of diametrically opposed cam lobes. The cam lobes act through the cam rollers and shoes to force the plungers inwardly to pressurize fuel contained in the pumping chamber to a high injection pressure.

Pressurized fuel from the pumping chamber is delivered by a fuel delivery passage to one of a series of discharge passages extending from the Pumping chamber to the surface of the distributor rotor. The discharge passages sequentially register with distributor ports associated with the fuel injector for each cylinder of the internal combustion engine.

Fuel is fed to the rotary distributor fuel pump by a transfer pump, typically located in the pump assembly. Fuel pressurized by the transfer pump flows into the pump chamber when the inlet ports are aligned with each inlet passage. it is possible by prolonging the compression stroke of each pumping cycle to provide the timing authority for a pilot and primary injection. However, extending the compression stroke of each cam lobe necessarily reduces the rotational angle available for returning the pumping plungers and filling the pumping chamber with fuel. liming authority is limited because the time period provided by the available rotational angle ultimately leaves insufficient time to re-fill the pumping chamber for the next injection event.

There is a need in the art for a rotary distributor fuel pump that expands the available timing authority for providing pilot and primary injection events.

According to a first aspect of the invention there is provided a rotary distributor fuel pump having a rotor including a plurality of simultaneously actuated main pumping plungers for delivering high pressure fuel sequentially through a main discharge passage to a plurality of discharge ports each associated with a respective fuel injector, the improvement comprising a distinct plurality of simultaneously actuated pilot pumping plungers and associated pilot pumping passage fluidly connectable to said discharge ports, and means for timing the actuation of the pilot plungers for advance overlap phasing relative to the actuation of the main plungers whereby fuel discharged by the pilot plungers through the associated pilot passage is delivered to a discharge port in advance of fuel delivered to the same discharge port from the main discharge plungers.

According to a second aspect of the invention there is provided a rotary distributor fuel pump having a plurality of simultaneously actuated main pumping plungers for delivering high pressure fuel sequentially to a plurality of discharge ports each associated with a respective fuel injector, a method of delivering a pilot discharge with the main discharge to each injector, comprising simultaneously actuating a plurality of pilot plungers in advance overlap phasing relative to the actuation of the main plungers and delivering the fuel discharged from the pilot plungers to the same discharge port in advance of the fuel delivered from the main discharge.

According to a third aspect of the invention there is provided a rotary distributor fuel injection pump comprising (a) a substantially tubular hydraulic head having a front end and a back end, a plurality of substantially coplanar fuel inlet ports spaced cirumferentially around the head, and a plurality of substantially coplanar fuel discharge ports spaced cirumferen-tially around the head; (b) a substantially cylindrical rotor closely coaxially situated within the head and supported for rotation therein, said rotor having a front portion extending axially from the front end of the hydraulic head and a back portion journalled in the head, said front portion including means for engaging a rotary drive; (c) a first plurality of substantially coplanar plunger bores situated in the front end and extending radially to a first common pumping chamber, each of said first plunger bores having a pumping plunger reciprocally situated therein; (d) a second plurality of substantially coplanar plunger bores situated in the front end and extending radially to a second common pumping chamber, each of said second plunger bores having a pumping plunger reciprocally situated therein; (e) a first inlet/discharge passage extending through the rotor from the first pumping chamber to the surface of the rotor, for sequential alignment with each of the inlet ports as the rotor is driven; (f) a second inlet/discharge passage extending through the rotor from the second pumping chamber to the surface of the rotor, for sequential alignment with each of the inlet ports as the rotor is driven; (g) a stationary cam profile including a plurality of angularly spaced lobes surrounding the first and second pumping plungers, respectively; (h) cam roller means situated between each pumping plunger and the cam profile; (I) whereby rotation of the rotor produces (I) simultaneous reciprocal movement of said first pumping plungers between a charging phase wherein fuel is drawn into the first pumping chamber through an inlet port and the first inlet/discharge passage and a first discharge phase wherein the drawn fuel is pressurized and discharged through the first inlet/discharge passage and a discharge port, (ii) simultaneous reciprocal movement of said second Pumping plungers between a charging phase wherein fuel is drawn into the second Pumping chamber through an inlet port and the second inlet passage and a second inlet/discharge phase wherein the drawn fuel is pressurized and discharged through the second inlet/discharge passage into a discharge port; and (j) wherein the first and second discharge phases are sequential said first and second inlet/discharge passages are configured to deliver said first and second fuel discharges to the same discharge port and said first and second fuel discharges partially overlap in time.

According to a fourth aspect of the invention there is provided a rotary distributor fuel pump comprising a hydraulic head with an outside surface and defining a cylindrical bore, said hydraulic head including a plurality of substantially coplanar fuel inlet ports and a plurality of substantially coplanar fuel discharge ports; a rotor received in said bore including: a plurality of main pumping plungers that are simultaneously actuated to deliver a main pulse of high pressure fuel sequentially through a main discharge passage sequentially to each of said fuel discharge ports; a plurality of pilot pumping plungers that are simultaneously actuated to deliver a pilot pulse of high pressure fuel through a pilot pumping passage sequentially to each of said fuel discharge ports; and an actuating assembly to actuate said pilot pumping plungers and said main pumping plungers, wherein said pilot pulse is delivered to each said fuel discharge port in advance of said main pulse and said pilot and main pulses partially overlap in time at each said fuel discharge port.

Thus using the invention there is provided a rotary distributor fuel pump according to aspects of the present invention which adds a separate pilot pumping chamber and associated pumping plungers and cam followers axially offset from the main pumping chamber and pumping plungers. The axis of the pilot plunger bores is angularly offset from the axis of the main plunger bores so that the pilot plungers are actuated by a different set of cam lobes of the cam profile. This arrangement allows one pumping chamber to be refilled while the other pumping chamber is being discharged. A pilot injection event well in advance of the main injection can take place without refilling problems because each pumping chamber fills once for an injection event that includes pilot and main injections.

Inlet/discharge passages from the pilot and main pumping chambers are ported to receive fuel from the same inlet port and deliver pressurized fuel to the same discharge port. A spill control valve is arranged to fluidly communicate with the discharge port during delivery of pressurized fuel. When actuated, the spill control valve conne the discharge port to a zone of low fuel pressure, allowing control of the output of the two pumping chambers by the conventional spill, pump, spill method. Alternatively, the output of the two pumping chambers can be controlled by modulating fuel inlet pressure or fuel inlet time to the pumping chambers.

The plunger size (diameter) associated with each pumping chamber can be optimized to produce a desired rate-shape of fuel delivery from the pump. The phase difference between the two pumping events is set by the angular offset between the pilot and main plunger bore axes.

Brief Description of the Figures

Figure 1 is a side sectional view of a rotary distributor fuel injection pump according to aspects of the present invention; Figure 2 is a left end sectional view of the rotary distributor fuel injection pump of Figure 1; and Figure 3 is a graphical representation of the fuel delivery rate, Pumping plunger displacement, pilot, main and control port alignment and spill valve operation for an exemplary operational embodiment of the rotary distributor fuel pump of Figure 1 according to aspects of the present invention.

Detailed Description of the Preferred Embodiment

An exemplary embodiment of a rotary distributor fuel injection pump according to the present invention is shown in Figures 1 and 2 and is generally designated by reference numeral io. A substantially tubular hydraulic head 12, having a front end 14 and a back end 16 defInes a plurality of substantially coplanar fuel inlet ports 18 spaced circumferentially around the head and a plurality of substantially coplanar fuel distributor ports 20 spaced circumferentially around the head. A Substantially cylindrical distributor rotor 22 is closely coaxially received in the tubular hydraulic head 12 and supported for rotation therein. The distributor rotor 22 has a front portion 24 extending axially from the front end of the hydraulic head and a back portion 26 journalle (at 28) to the hydraulic head 12. The front portion 24 of the distributor rotor includes a fixture 30 for engaging a rotary drive (not shown).

The front end 24 of the distributor rotor defines a first pair of substantially co-planar plunger bores 32a, 32b extending radially from a first pumping chamber 34. A pumping plunger 36a, 36b is situated for reciprocation in each of the plunger bores 32a, 32b, respectively. The front end 24 of the distributor rotor also defines a second pair of substantially co-planar plunger bores 38a, 38b extending from a second pumping chamber 40 axially offset from the first pumping chamber 34.

A Pumping plunger 42a, 42b is situated for reciprocation in each of the second plunger bores 38a, 38b, respectively. A first inlet/discharge passage 48 extends from the first pumping chamber 34 to the surface of the rotor 22, for sequential alignment with each of the inlet ports 18 and discharge ports 20. A second inlet/discharge passage 50 extends from the second pumping chamber 40 to the surface of the rotor, for sequential alignment with each of the inlet ports 18 and discharge ports 20. Figure 1 illustrates the first and second inlet/discharge passages 48, in solid lines in a rotational position aligned with a discharge port 20.

The first and second inlet/outlet passages 48, 50 are shown in broken lines in a rotational position aligned with an inlet port 18. Sequentiai alignment of the first and second inlet/discharge passages 48, 50 with the inlet ports 18 discharge ports 20 occurs as the rotor 22 is driven within the hydraulic head 12.

A stationary cam profile 52 surrounds the front end 24 of the distributor rotor 22. A first set of cam followers 54 are Situated between the first pair of pumping plungers 36a, 36b and the cam profile 52. A second set of cam followers 56 are situated between the second pair of pumping plungers 42a, 42b and the cam profile. As best shown in Figure 2, angularly spaced pairs of cam lobes actuate the two pairs of pumping plungers 36a, 36b and 42a, 42b to provide two pulses of pressurized fuel. The bores 32a, 32b and 38a, 38b in which the respective pairs of Plungers reciprocate are arranged at a relative angular orientation such that one pumping chamber is refilled while the other pumping chamber is being discharged. In the illustrated embodiment, the two pulses of pressurized fuel are applied to a common discharge port associated with a single injector to produce a pilot injection event well in advance of a main injection. The phase difference between the two pumping events is established by the radial position of the plunger bores relative to the cam lobes employed to actuate the respective pairs of Pumping plungers.

In the illustrated embodiment, a mechanical assembly accomplishes coordinated actuation of the pairs of pumping plungers.

Means for timing the actuation of the pairs of pumping chambers includes the cam profile 52, cam followers 54, 56 and the angular offset between the axis Al of the pilot plunger bores 32a, 32b and the axis A2 of the main plunger bores 38a, 38b. In the rotational position illustrated in Figure 2, the pilot pulse generated by pilot plungers 36a, 36b is almost complete and the main pulse generated by main pumping plungers 42a, 42b is about to begin. The illustrated cam profile 52 produces six coordinated, overlapping pilot/main high pressure fuel pulses for each full rotation of the rotor 22 relative to the hydraulic head 12. Each overlapping pilot/main fuel pulse is timed to coincide with fluid communication between the respective inlet/discharge passage 48, 50 and the discharge port 20 associated with the injector for an engine cylinder (not illustrated). While a particular mechanical assembly is illustrated for carrying out coordinated actuation of the pilot and main plungers, other means for timing the actuation of the plungers may occur to one of skill in the art. For example, the illustrated single cam surface 52 may be divided into two cam surfaces axially aligned with the cam followers of respective sets of plungers. Other hydraulic or electro- mechanical means for timing the actuation of the pilot plungers relative to the main plungers may Occur to one skilled in the art and are intended to be encompassed by the claim term "means for timing".

In the illustrated embodiment, each distributor port 20 on the hydraulic head 12 includes discharge passages 58, 60 that sequentially register with the first and second inlet/discharge passages 48, 50 from the pumping chambers 34, 40, respectively. Discharge passages 58, 60 communicate with a common discharge Opening 62 at the surface of the head 12. Each inlet port 18 on the hydraulic head 12 includes inlet passages 64, 66 that sequentially register with the first and second inlet/discharge passages 48, 50, respectively. Inlet passages 64, 66 communicate with a common inlet opening 68 at the surface of the head 12.

The back portion of the pump 10 includes an internal cavity 70. A discharge control valve 72 is situated in the cavity. A control passage 74 extends from the control valve 72 to a control port 76 at the surface of the rotor for sequential alignment with a control passage 78 communicating with the discharge opening 62 at the surface of the hydraulic head.

The illustrated configuration of the hydraulic head 12 permits fuel pressure at the distributor ports 20 to be controlled by a single control valve 72. The hydraulic head 12 is Configured to deliver the output of both pumping chambers 34, 40 to a common discharge port 20.

Alternatively, the hydraulic head 12 could be configured to deliver the output of each pumping chamber 34, 40 to separate discharge ports (not shown).

The plunger diameter can be optimized according to the application. In the illustrated embodiment, the diameter of Pumping plungers 36a, 36b is smaller than the diameter of pumping plungers 38a, 38b. This arrangement will produce different pump displacements 80, 84 and pumping rates 82, 86 for the two pumping chambers 34, 40 as shown in Figure 3. It will be noted that both sets of plungers are actuated by the same cam profile, so that if pump chamber sizes and pumping plunger diameters are identical, the pumping rate for the two Pumping chambers will be constant. By varying the pumping rate of the respective chambers, it is possible to tailor the rate shape of pump output as shown graphically in Figure 3. It can be seen that the maximum pumping rate 90 for the first chamber is less than the maximum pumping rate 92 for the second chamber. Since both sets of plungers are actuated by the same cam profile 52, the fuel delivery rate will increase linearly during the overlap 88 of fuel delivery from one pumping chamber to the next. The plunger bores 32a, 32b and 38a, 38b are arranged relative to each other and the cam profile 52 such that the second pumping chamber begins delivery 94 while fuel delivery from the first pumping chamber is declining 96.

Figure 3 illustrates relationships between components in the illustrated rotary distributor fuel pump 10. Curves 82 and 86 illustrate the pumping rate of the first and second pumping chambers 34, 40, respectively, in cubic millimeters (mm3/deg). Curve 98 illustrates the time-shape of registration of the first inlet/discharge passage 48 with the passage 58 leading to the discharge port 20. Curve 100 illustrates the time-shape of registration of the second inlet/discharge passage 50 with the passage 60 leading to the discharge port 20. Curves 98 and 100 illustrate the timeshape of fluid communication between the pumping chambers 34, 40 and the discharge port 20 corresponding to their respective discharge phases. Curve 102 illustrates the time-shape of registration between the first inlet/discharge passage 48 and passage 64 leading to the inlet port 18. Curve 104 illustrates the time-shape of registration between the second inlet/discharge passage 50 and the passage 66 leading to the inlet port 18. Curves 102 and 104 illustrate the time-shape of fluid communication between the pumping chambers 34, 40 and the inlet port 18 corresponding to the fill phases of the pumping chambers. Figure 3 clearly illustrates that the first pumping chamber is discharging 98 while the second pumping chamber is filling 104 and the second pumping chamber is discharging ioo while the first pumping chamber is filling 102.

Curve 106 illustrates the time-shape of registration between the control passage 74 and the control port 76 communicating with the discharge port 20. Curve 106 represents fluid communication between the control valve 72 and the discharge port 20. Curves 108 and 109 illustrate the time-shape of control valve actuation, representing a "spill" of pressurized fuel from the discharge port to a zone of low pressure.

This illustrates a "spill-pump-spill" method of controlling the output of the two pumping chambers 34, 40. Note that the control valve 72 is in fluid communication with the discharge port 20 for a time spanning a major portion of the discharge phases of both the first and second pumping chambers 34, 40.

While a preferred embodiment of the foregoing invention has been set forth for purposes of illustration, the foregoing description should not be deemed a limitation of the invention herein. Accordingly, various modifications, adaptations, and alternatives may occur to one skilled in the art without departing from the spirit and the scope of the present invention.

Claims

1. In a rotary distributor fuel pump having a rotor including a plurality of simultaneously actuated main pumping plungers for delivering high pressure fuel sequentially through a main discharge passage to a plurality of discharge ports each associated with a respective fuel injector, the improvement comprising: a distinct plurality of simultaneously actuated pilot pumping plungers and associated pilot pumping passage fluidly connectable to said discharge ports; and means for timing the actuation of the pilot plungers for advance overlap phasing relative to the actuation of the main plungers whereby fuel discharged by the pilot plungers through the associated pilot passage is delivered to a discharge port in advance of fuel delivered to the same discharge port from the main discharge plungers.

2. The improved rotary distributor fuel pump of claim 1, comprising a cam profile surrounding said main and pilot Pumping plungers and a cam follower between each of said main and pilot pumping plungers and said cam profile, wherein said main pumping plungers reciprocate in main plunger bores having a common first axis and said pilot pumping plungers reciprocate in pilot plunger bores having a common second axis, said means for timing including an angular offset between said first and second axes.

3. The improved rotary distributor fuel pump of claim 1 or claim 2, wherein said main pumping plungers reciprocate in substantially co-planar main plunger bores communicating with a main pumping chamber and said pilot pumping plungers reciprocate in substantially co-planar pilot plunger bores in communication with a pilot pumping chamber, said rotor having a rotational axis and said main plunger bores are axially offset along said rotational axis relative to said pilot plunger bores.

4. In a rotary distributor fuel pump having a plurality of simultaneously actuated main Pumping Plungers for delivering high pressure fuel sequentially to a plurality of discharge ports each associated with a respective fuel injector, a method of delivering a pilot discharge with the main discharge to each injector, comprising simultaneously actuating a plurality of pilot plungers in advance overlap phasing relative to the actuation of the main Plungers and delivering the fuel discharged from the pilot plungers to the same discharge port in advance of the fuel delivered from the main discharge.

5. A rotary distributor fuel injection pump comprising: (a) a substantially tubular hydraulic head having a front end and a back end, a plurality of substantially coplanar fuel inlet ports spaced cirumferentially around the head, and a plurality of substantially coplanar fuel discharge ports spaced cirumferentiafly around the head; (b) a substantially cylindrical rotor closely coaxially situated within the head and supported for rotation therein, said rotor having a front portion extending axially from the front end of the hydraulic head and a back portion journalled in the head, said front Portion including means for engaging a rotary drive; (c) a first plurality of substantially coplanar Plunger bores situated in the front end and extending radially to a first common pumping chamber, each of said first Plunger bores having a Pumping plunger reciprocally situated therein; (d) a second plurality of substantially coplanar Plunger bores Situated in the front end and extending radially to a second common pumping chamber, each of said second Plunger bores having a pumping Plunger reciprocally Situated therein; (e) a first inlet/discharge passage extending through the rotor from the first Pumping chamber to the surface of the rotor, for sequential alignment with each of the inlet ports as the rotor is driven; (f) a second inlet/discharge passage extending through the rotor from the second pumping chamber to the surface of the rotor, for sequential alignment with each of the inlet ports as the rotor is driven; (g) a stationary cam profile including a plurality of angularly spaced lobes surrounding the first and second Pumping plungers, respectively; (h) cam roller mean Situated between each pumping Plunger and the cam profile; (i) whereby rotation of the rotor produces (I) simulaneous reciprocal movement of said first pumping plungers between a charging phase wherein fuel is drawn into the first Pumping chamber through an inlet port and the first inlet/discharge passage and a first discharge phase wherein the drawn fuel is pressurized and discharged through the first inlet/discharge passage and a discharge port, (ii) simultaneous reciprocal movement of said second pumping Plungers between a charging phase wherein fuel is drawn into the second Pumping chamber through an inlet port and the second inlet passage and a second inlet/discharge phase wherein the drawn fuel is pressurized and discharged through the second inlet/discharge passage into a discharge port; and (j) wherein the first and second discharge phases are sequentia', said first and second inlet/discharge passages are configured to deliver said first and second fuel discharges to the same discharge port and said first and second fuel discharges partially overlap in time.

6. The rotary distributor fuel injection pump of claim 5, wherein each discharge port comprises a first discharge passage in the head alignable with said first inlet/discharge passage in the rotor, a second discharge passage in the head alignable with said second inlet/discharge passage in the rotor, and a common discharge opening at the surface of the head.

7. The rotary distributor fuel injection pump of claim 5 or claim 6, wherein each inlet port comprises a first inlet passage in the head alignable with said first inlet/discharge passage in the rotor, a second inlet passage in the head alignable with said second inlet/discharge passage in the rotor, and a common inlet opening at the surface of the head.

8. The rotary distributor fuel injection pump of any of claims 5 to 7, wherein the back portion of the rotor includes an internal cavity, a discharge control valve situated in the cavity, a control passage extending from the control valve to a control port at the surface of the rotor for sequential alignment with each of the discharge ports in the head, whereby operation of the control valve diverts fuel into said control cavity and thereby limits the quantity of fuel discharged from the pump through the discharge port.

9. The rotary distributor fuel injection pump of claim 8, wherein each discharge port in the head includes a control passage extending from the discharge opening in the head to the control port.

10. The rotary distributor fuel injection pump of any of claims 5 to 9, wherein the first cam profile and a diameter of said first plungers define a first pumping chamber discharge quantity and rate and the cam profile and a diameter of said second plungers define a second pumping chamber discharge quantity and rate, and the first discharge quantity is smaller than the second discharge quantity and the first discharge rate is slower than the second discharge rate.

11. The rotary distributor fuel injection pump of any of claims 5 to 10, wherein said first plunger bores have a common first axis and said second plunger bores have a common second axis, an angular offset between said first and second axes timing the first and second discharge phases such that the total fuel discharge rate delivered to a discharge port during the overlap of the first and second discharge phases, increases linearly.

12. The rotary distributor fuel injection pump of any of claims 5 to 11, wherein the first and second discharge phases have respective maximum discharge rates, said first plunger bores have a common first axis and said second Plunger bores have a common second axis, an angular offset between said first and second axes timing the first and second discharge phases such that the second discharge phase begins while the first discharge rate is declining from maximum.

1 3. A rotary distributor fuel pump comprising: a hydraulic head with an outside surface and defining a cylindricaj bore, said hydraulic head including a plurality of substantially coplanar fuel inlet ports and a Plurality of substantially coplanar fuel discharge ports; a rotor received in said bore including: a plurality of main Pumping plungers that are simultaneously actuated to deliver a main pulse of high pressure fuel sequentially through a main discharge passage sequentially to each of said fuel discharge ports; a plurality of pilot Pumping plungers that are simultaneously actuated to deliver a pilot pulse of high pressure fuel through a pilot Pumping passage sequentially to each of said fuel discharge ports; and an actuating assembly to actuate said pilot Pumping Plungers and said main Pumping plungers, wherein said pilot pulse is delivered to each said fuel discharge port in advance of said main pulse and said pilot and main pulses Partially overlap in time at each said fuel discharge port.

14. A rotary distributor fuel pump, substantially as hereinbefore described with reference to the accompanying drawings.