Field of the invention
[001] This invention relates to the field of fuel injection systems for an internal
combustion engine. The invention relates in specific to a high pressure fuel pump.
Background of the invention
[002] High pressure fuel pumps are used in fuel injection pumps. The pups receive fuel through inlet, pressurize them using a plunger and deliver the pressurized fuel to the engine. As the plunger moves reciprocally, it needs to be lubricated using the engine oil. Part of fuel leaks around the plunger through the sealing and there are chances that the fuel so leaked gets mixed with the engine oil. In some cases the leaked fuel is collected and returned to the inlet.
[003] The prior art WO 2016/012142 A1discloses a high-pressure fuel pump, in particular a plug-in pump, for a fuel injection system of an internal combustion engine, comprising a housing part having a cylinder bore in which a pump piston is reciprocally movably accommodated, and a sealing arrangement for separation of the media oil and fuel within the cylinder bore, a leakage duct for the removal of a leakage quantity being formed in the housing part.
Brief description of the accompanying drawing
[004] Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawing:
[005] Fig. 1 illustrates a high pressure fuel pump according to one embodiment of the invention

Detailed description of the embodiments
[006] FIG. 1 illustrates a typical high pressure fuel pump100. The high pressure fuel pump is just referred as pump in this document. The pump 100 comprises a housing 102, a plunger 104 which moves reciprocally in a bore in the housing102, an inlet connector 106 and an inlet valve 108 to receive fuel, an outlet bore 109 through which the pressurized fuel is delivered to the engine and a return path 110 which returns excess fuel to the fuel reservoir which is not shown. The outlet bore 109 is in perpendicular plane to the view of the fig. 1.
[007] The plunger is driven by a roller tappet which is driven in turn by a cam shaft of the engine which is not shown. The roller tappet pushes the plunger 104 in the direction of the compression chamber 111 and the spring 113 pulls the plunger in the direction of the roller tappet thereby causing the compression stroke and the suction stroke respectively.
[008] During the suction stroke, the inlet valve 108 opens and the plunger 104 moves in the direction of roller tappet because of the spring tension. The fuel is sucked into the compression chamber 111. When the plunger 104 starts moving in the direction of the compression chamber 111, the inlet valve 108 closes, the fuel is pressurized in the compression chamber 111. Once the pressure increases in the compression chamber 111, the pressurized fuel is delivered through the outlet bore 109 to the engine. This cycle repeats as long as the engine is running.
[009] As the plunger 104 moves reciprocally in the bore, the movement needs lubrication for the roller tappet and roller which connect the plunger to the camshaft, which are not shown in fig. The lubrication is provided by engine oil which is circulated by an oil pump which is not shown. The lubrication oil is circulated from

the bottom of the plunger. There is a sealing ring 112 at one end of the plunger 102. The sealing ring 112 prevents leakage of fuel into the lubrication oil.
[010] As the plunger 104 moves reciprocally to pressurize the fuel, part of the fuel sticks to the plunger 104 and is collected near the sealing ring 112. In some of the prior arts, the fuel collected near the sealing ring is passed through a passage which is connected to the inlet of the pump. In prior arts, during normal operation of the pump, the fuel so collected near the sealing ring is directed to the inlet. But in prior arts, if the sealing ring breaks down, then there is possibility that the fuel from the inlet flows towards the sealing ring and then mixes with the lubrication oil as the sealing ring is broken.
[011] To isolate this problem, the invention proposes a passage 114 from the sealing ring 112 to the return path 110 of the pump 100. According to the invention, during the normal operation of the pump 100, the fuel collected near the sealing ring 112 is directed towards the return path 110 of the pump 100. When the sealing ring 112 breaks down, there is no chance of fuel flowing from the inlet valve 108 towards the sealing ring 112 as the inlet valve 108 is isolated from the passage 114.
[012] The passage 114 connects the portion at the top of the sealing ring 112 to the return path 110. This passage 114 is drilled in the housing during the manufacturing and assembly of the pump components. The passage 114 is a straight bore. The passage 114 can be drilled from sealing ring side to the return path. Alternatively the passage 114 can be drilled from return path side to the sealing ring side.
[013] The invention has advantage that the passage 114 proposed is simple to drill because the passage 114 is in a straight line. The passage 114 may be of uniform diameter or may be tapering in shape.

[014] As the components of the pump 100 may be manufactured separately and then assembled, drilling a straight passage 114 is easier during the manufacturing of the components. The housing may be manufactured, the passage 114 may be drilled and then the plunger and the return path parts may be assembled further. As the passage 114 is a straight bore, the drilling of the passage 114 becomes easier.

CLAIMS
We Claim:
1. A pump (100) comprising :
- a housing (102);
- a plunger (104) moving in a bore in said housing (102);
- an inlet connector (106) and an inlet valve (108) in said housing (102), to receive fuel for pressurizing;
- an outlet bore (109) to deliver pressurized fuel;
- a return path (110) in said housing (102) to return excess fuel;
- a sealing ring (112) to prevent mixing of fuel with lubricating oil;
said pump (100) characterized by a fuel passage (114) from top of sealing ring (112) to return path (110).
2. A pump (100) according to claim 1 wherein said fuel passage (114) is drilled from return passage (110) till sealing ring (112)
3. A pump (100) according to claim 1 wherein said fuel passage (114) is drilled from sealing ring (112) till return passage (110)
4. A pump (100) according to claim 1 wherein said fuel passage (114) is in a straight line
5. A pump according to claim 1 wherein said fuel passage (114) is of uniform diameter
6. A pump according to claim 1 wherein said fuel passage (114) is tapering in shape