Field of the invention

This invention relates to the field of fuel injection system.

Background of the invention

Fuel injection pumps inject a desired quantity of fuel into the combustion chamber at a specified pressure. The piston used in fuel injection pumps, reciprocates within the chamber of the fuel injection pump, through roller tappet and cam. As the piston reciprocates, it brings along with it lubrication oil that is used for lubrication of cam and tappet. The heat and pressure developed near the top side of roller tappet, results in lubrication oil forming a mist within that chamber. This mist dragged by the reciprocating piston, mixes with fuel that is received from the inlet of fuel injection pump. The fuel that contains lubrication oil is then delivered to the injector. The lubrication oil present in fuel act as impurities thereby decreasing the quality of fuel injected.

Hence there is a need for a device that prevents mixing of lubricating oil and fuel and also for a means to prevent build up of pressure and lubrication oil mist within the pump chamber.

US patent publication US 20100102518 discusses about a temperature adaptive dynamic shaft seal assembly. The seal assembly includes a coil spring and a shape memory alloy element. The coil spring is disposed in contact with the elastic seal member and configured for applying a compressive force to the elastic seal member. The shape memory alloy element is configured for applying pressure to the coil spring to increase the compressive force.

State of Art.

FIGS. 1-2 illustrate a sealing member 106 provided on a pump housing 101 of a fuel injection pump 100. In the existing arrangement there exists a sealing member 106 and elastic energizer 109 in-between the piston 102 and the pump housing 102. The sealing member 106 and the elastic energizer 109 are fixed on the pump housing 101 and the seal lip is in contact with the reciprocating piston 102. The sealing member 106 restricts the flow due to pressure and drag. A gap is created between the piston 102 and the sealing member 106 due to fluid forces acting at high pressure and velocity. This leads to reduction in effectiveness of the sealing member 106.

Object of the invention.

It is an object of the invention to prevent mixing of lubricant with fuel in a fuel injection pump.

Brief description of the accompanying drawing

The invention is disclosed in detail in the description and illustrated in the accompanying drawing:

FIGS. 1-2 illustrate a sealing member provided on a barrel housing of a fuel injection pump.

FIG. 3 illustrates a fuel injection pump incorporating the embodiments of the present invention.

FIG. 4 illustrates a sealing member provided on the piston.

Detailed description of the embodiments

FIG. 3 illustrates a fuel injection pump 100 incorporating the embodiments of the present invention. The fuel injection pump 100 comprises pump housing 101 and a piston 102. The piston 102 is adapted to reciprocate within the pump housing 101 by means of a roller tappet 104 and a cam 105. The rotary motion of the cam 105 is transmitted into a linear motion of the piston 102 through the roller tappet 104. The reciprocating motion of the piston between the bottom dead center (BDC) and the top dead center (TDC) results in the fuel that is received in the fuel gallery to be pressurized.

Owing working movement of the piston 102, the lubricating oil from the engine is used to lubricate the cam 105 and moving parts of the roller tappet 104. Due to reciprocating action of the piston 102 and a roller tappet 104 a lubricating oil mist is formed on top of the roller tappet 104 which in turn deposits on the piston 102 surface and the outer surface exposed inside the spring chamber of the fuel injection pump 100. The piston 102 moves inside the pump housing 101 of the fuel injection pump 100 through the working clearance.

When piston 102 moves from the bottom dead center (BDC) to top dead center (TDC), the lubricating oil is dragged and mixes with fuel also called as the working fluid. This kind of mixing is called Oil in Fuel (OiF) mix, and leads to problems with regards to complying with clinical emission norms.

Similarly, when piston 102 moves from TDC to BDC, the piston creates suction pressure in pump pressure chamber which is lower than the atmospheric pressure, in turn the piston 102 sucks the fuel as well as lubricating oil from the working clearance. This sucked lubrication oil mixes with fuel and is pumped out from the pump pressure chamber while piston 102 moves from BDC to TDC.

To overcome the above mentioned problem of mixing of lubricating oil with the working fluid, the piston 102 is provided with a sealing member 106 on its circumference for separating the working fluid from lubricating oil and for venting out the working fluid from the vent 107 and the lubricating oil from the vent 108 provided on the body of the fuel injection pump 100. The sealing member is housed within a cylindrical member 103 located below the pump housing 101. The inner surface of the cylindrical member 103 is coated with a slippery material 110 to have less friction and good fluid separation. The sealing member 106 is provided on the piston 102 through interference fit.

As illustrated in FIG. 3, the sealing member that is present on the piston will not deform due to high velocity of the fluid that is the lubricating oil or the fuel as the respective fluid is not dragged by the piston 102 during respective a stroke, that is during the forward stroke and the backward stroke of the piston 102.

The sealing member 106 interfaces with the cylindrical member 103 and the sealing member 106 continuously presses against the cylindrical member 103.The sealing member 106 further comprises an elastic energizer 109. The function of the elastic energizer 109 is to maintain sufficient contact pressure between the sealing member 106 and the inner surface of the cylindrical member 103. The elastic energizer 109 expands, for exerting contact pressure between the sealing member 106 and the cylindrical member 103 depending upon the increase in pressure of the working fluid and the lubricating oil. The elastic energizer 109 is selected from a group comprising a spring and an O-ring.

It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. 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.

WE CLAIM:

1. A fuel injection pump 100, comprising:

a pump housing 101;

a piston 102 adapted to reciprocate within said pump housing 101 and a cylindrical member 103 located below said pump housing 101, by means of a roller tappet 104 and a cam 105, characterized in that

said piston 102 provided with a sealing member 106 on its circumference for separating the working fluid from lubricating oil and for venting out said working fluid from the vent 107 and said lubricating oil from the vent 108 provided on the roller tappet 104.

2. The fuel injection pump 100 of claim 1, wherein said sealing member 106 is provided on said piston 102 through interference fit.

3. The fuel injection pump 100 of claim 1, wherein said sealing member 106 interfaces with said cylindrical member 103.

4. The fuel injection pump 100 of claim 1, wherein said sealing member 106 further comprises an elastic energizer 109.

5. The fuel injection pump 100 of claim 1, wherein inner surface of said cylindrical member 103 is coated with a slippery material 110.

6. The fuel injection pump 100 of claim 1 and 4, wherein said elastic energizer 109 expands, for exerting contact pressure between said sealing member 106 and said cylindrical member 103 depending upon the increase-in pressure of said working fluid and said lubricating oil.

7. The fuel injection pump 100 of claim 1 and 4, wherein said elastic energizer 109 is selected from a group comprising a spring and an O-ring.