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Pilot injection pumpRelated Patent Categories: Pumps, Expansible Chamber Type, Moving Cylinder, Unidirectionally Rotating CylinderPilot injection pump description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060159572, Pilot injection pump. Brief Patent Description - Full Patent Description - Patent Application Claims
FIELD OF THE INVENTION [0001] 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 [0002] 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. [0003] 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 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. [0004] 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. Timing 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. [0005] 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. SUMMARY OF THE INVENTION [0006] A rotary distributor fuel pump according to aspects of the present invention 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. [0007] 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 connects 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. [0008] 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 [0009] FIG. 1 is a side sectional view of a rotary distributor fuel injection pump according to aspects of the present invention; [0010] FIG. 2 is a left end sectional view of the rotary distributor fuel injection pump of FIG. 1; and [0011] FIG. 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 FIG. 1 according to aspects of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [0012] An exemplary embodiment of a rotary distributor fuel injection pump according to the present invention is shown in FIGS. 1 and 2 and is generally designated by reference numeral 10. 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 journalled (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). [0013] 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. FIG. 1 illustrates the first and second inlet/discharge passages 48, 50 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. Sequential 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. [0014] 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 FIG. 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. [0015] 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 A1 of the pilot plunger bores 32a, 32b and the axis A2 of the main plunger bores 38a, 38b. In the rotational position illustrated in FIG. 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". [0016] 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. [0017] 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. [0018] 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). [0019] 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 FIG. 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 FIG. 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. Continue reading about Pilot injection pump... Full patent description for Pilot injection pump Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Pilot injection pump patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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