Claims:We Claim:
1. A fuel injection pump (300), comprising at least

a housing (302) comprising at least an inlet (312) adapted to receive fuel from a metering unit (320) and a bore to accommodate a plunger (306); characterized in that
said housing (302) comprises a flow path (400) in a manner such that first end is in flow communication with a leak oil groove (317) and the second end is in flow communication with inlet path (312) of said pump at connection point (410).

2. The fuel injection pump (300) of claim 1, wherein said second end of said flow path 400 is upstream to said inlet (312) and downstream to said metering unit 320.

3. The fuel injection pump (300) of claim 1, wherein said pump is an oil lubricated fuel injection pump 300.

4. A fuel injection system, comprising at least:
a fuel tank, a filter , a metering unit 320; and a fuel injection pump 300, said fuel injection pump 300 comprising at least a housing (302), said housing 302 comprising at least an inlet (312) adapted to receive fuel from a metering unit (320) and a bore to accommodate a plunger (306); characterized in that

said housing (302) comprises a flow path (400) in a manner such that first end of it is connected to leak oil groove (317) and the second end is connected to the inlet path of the pump (312) at connection point (410)

5. The fuel injection system of claim 4, wherein a throttle is located down stream of Metering Unit (320), upstream of connection point (410).
, Description:Field of the invention
[0001] This invention relates to the field of fuel injection pump with oil lubrication.

Background of the invention
[0002] In oil lubricated fuel injection pumps, engine oil from an oil sump is used lubricate parts of the pump like roller tappet and roller. The oil and fuel mix over the plunger clearances. Measures need to be taken to minimize mixing of oil and fuel. The oil which mixes with fuel and gets pressurized along with the fuel and is transported to the rail and injector and eventually into the engine cylinder where it burns. The residual ash in the oil will then cause loading of after treatment device like Diesel particulate filter. The fuel that mixes in the plunger clearance with oil and reaches the lubrication oil sump will lead to engine oil dilution.

[0003] FIG. 1 illustrates a fuel injection pump in a fuel injection system. A plunger 106 reciprocates in the barrel 102 of the fuel injection pump, when the cam 103 rotates. The roller tappet 104 and roller 105 are lubricated by the oil in the oil sump 110 either by sump lubrication or a special lubrication path in the engine. During the suction stroke, the plunger moves downwards creating a suction in the plunger room 111, which allows the fuel to be drawn from the inlet line 112, through the inlet valve 113. The fuel at inlet line 112 received from the metering unit 120, meters required quantity fuel to be pressurized. During the pressurization stroke, the plunger moves up by the cam rotation, and fuel is pressurized and delivered to the rail 114, through the outlet valve 115. During these movements of the plunger part of the fuel pressurized in the plunger room 111 will leak past the plunger through plunger clearance 116 and reach the leak oil groove 117. Some portion of the fuel will further move from the leak oil groove and reach the oil sump 110, leading to oil dilution. During the same plunger movement some oil which is lubricating the roller tappet 104 and roller 105, will pass through the plunger clearance 116 and reach the leak oil groove 117. Further some portion of the oil will pass further and reach the plunger room 111 and eventually reach the rail and injector, and will get injected into the combustion chamber where it is burnt. The residual ash from the oil then gets deposited in after treatment device like the diesel particle filter. The oil and fuel mixed in the leak oil groove 117, can be routed in different ways in the low pressure circuit of the fuel injection system. In this case, the leak oil groove is connected back to the tank 122 through the pump backflow 123, which is connected to the bypass path 124 from pump inlet path 112. In this case the oil mixed in the plunger leak groove 117, upon reaching the fuel tank 122, can cause fuel colour to change, for example darker shade of diesel, which is not desirable.

Brief description of the accompanying drawing
[0004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:

[0005] FIG. 1 illustrates a fuel injection pump in a fuel injection system illustrating the scenario of oil mixing with fuel;

[0006] FIG. 2 illustrates a fuel injection pump in a fuel injection system illustrating the scenario of fuel mixing with oil; and

[0007] FIG. 3 illustrates a fuel injection system.

Detailed description of the embodiments
[0008] FIG. 2 illustrates a fuel injection pump 201 in a fuel injection system. The fuel injection pump comprises a housing (202) comprising at least an inlet (212) adapted to receive fuel from a metering unit (220) and a bore to accommodate a plunger (206). The housing (202) comprises a flow path (400) in a manner such that first end is in flow communication with a leak oil groove (217) and the second end is in flow communication with inlet path (212) of said pump at connection point. The leak oil groove 217 is connected to the inlet line 212 of the pump. The connection point 210 being in between the metering unit 220 and the inlet valve 212. The connecting point 210 can be within the pump 200, or in the low pressure line pipes in case the metering unit 120 is mounted separately from the pump. The connecting point 210 is kept as close as possible to the inlet vale 212. The oil which is from the leak oil groove 217, will now be drawn by the plunger during suction stroke and then pressurized, and sent to rail and injector, eventually combusted in the engine cylinder, thus avoid oil mixing into the fuel tank and causing darkening of the fuel.

[0009] The plunger 206 reciprocates in the barrel or housing 202, when the cam rotates. The roller tappet 204 and roller 205 are lubricated by the oil in the oil sump 211 either by sump lubrication or a special lubrication path in the engine. During the suction stroke, the plunger moves downwards creating a suction in the plunger room 211, which allows the fuel to be drawn from the inlet line 212, through the inlet valve 212. The fuel at inlet line is received from the metering unit 220, which meters required fuel to be pressurized. During the pressurization stroke, the plunger moves up by the cam rotation, and fuel is pressurized and delivered to the rail 214, through the outlet valve 215. During these movements of the plunger part of the fuel pressurized in the plunger room 211 will leak past the plunger through plunger clearance 316 and reach the leak oil groove 217. Some portion of the fuel will further move from the leak oil groove and reach the oil sump 210, leading to oil dilution. During the same plunger movement some oil which is lubricating the roller tappet 204 and roller 205, will pass through the plunger clearance 316 and reach the leak oil groove 217. Further some portion of the oil will pass further and reach the plunger room 311 and eventually reach the rail and injector, and will get injected into the combustion chamber where it is burnt. The residual ash from the burnt oil then gets deposited in after treatment device like the Diesel particle filter. The oil and fuel mixed in the leak oil groove 217, is routed and is connected to the inlet line of the pump by the bore 200. The connection point 410 being in between the metering unit 220 and the inlet valve 212. The connecting point 210 is kept as close as possible to the inlet vale 212. The oil which is from the leak oil groove 217, will now be drawn by the plunger through the connection point 210, inlet line and inlet valve 212 during suction stroke and then pressurized, and sent to rail and injector, eventually combusted in the engine cylinder, thus avoid oil mixing into the fuel tank and causing darkening of the fuel.

[0010] FIG. 3 illustrates a fuel injection system. The fuel injection system comprises at least a fuel tank (300), a filter (302) , a metering unit 304 and a fuel injection pump 300, the fuel injection pump 300 comprises at least a housing 306, the housing 306 comprises an inlet 303 adapted to receive fuel from a metering unit 304 and a bore to accommodate a plunger 308. The housing 306 of the fuel injection pump 300 comprises a flow path 310 in a manner such that a first end 312 of said flow path 310 is in flow communication with the bore of the fuel injection pump 300 and a second end 314 of the flow path 310 is in flow communication with the inlet 303. The connecting point 410 can be within the pump 300, or in the low pressure line pipes in case the metering unit 320 is mounted separately from the pump. Fig.3 shows connection point 410 outside the pump in the low pressure pipes. A throttle valve 305 located upstream from the inlet 302 of the fuel injection pump 300. The throttle valve is a zero delivery throttle valve. The throttle valve is a banjo fitting.

[0011] The working of the fuel injection system will be as described further. Fuel from the fuel tank flows through the filter and reaches the metering unit 304. The metering unit 304, based upon the requirement, decides the quantity of fuel that needs to be delivered to the fuel injection pump 300. The fuel that enters the fuel injection pump 300 is pressurized and delivered to the rail 316 for injection into the engine cylinders. The fuel injection pump 300, being oil lubricated, sucks oil from the oil sump, during working of the fuel injection pump 300. The oil lubricates the components of the fuel injection pump 300 and is vented out of the fuel injection pump 300 through the flow path 310. The force of the plunger 308 that is reciprocating within the housing 306, causes the oil to enter the flow path 310 and reach inlet 303 of the fuel injection pump 300 through the second end 314 of the flow path 310. Before reaching the inlet 303, the oil also mixes with the fuel that is flowing out of the metering unit 304. Hence the fuel mixed with oil flows into the inlet 302 of the fuel injection pump 300 (during the next cycle of working of the fuel injection pump). The pressurized oil from the fuel injection pump 300 is then sent to the rail 316 for injection into the engine cylinder (s). The oil that is present in the fuel is burnt in the engine cylinder over the entire range of working of the pump/ engine. The fuel injection system, as explained above, having a path for flow of oil, that is located after the metering unit 304, presents a good compromise between diesel blackening and oil dilution.

[0012] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention in terms of the type of oil lubricated pump and the type of flow path used. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.