Field of the invention

This invention relates to the field of fuel injection system.

Background of the invention

Conventional fuel injection pumps deliver a specified quantity of fuel under high pressure to the injector fitted on a cylinder of an IC engine. The fuel injection pump has a plunger and housing assembly. The plunger reciprocates within the housing assembly guided by a spring guide enclosed in the spring chamber. The reciprocation of the plunger is by means of roller tappet that follows a cam shaft. The reciprocation of the plunger opens and closes the inlet port that receives fuel and delivers pressurized fuel to the outlet port. High pressure develops in the spring chamber in a fuel injection pump as a result of lubricating oil entering the spring chamber through the clearances that are present in the housing of the fuel injection pump. During the forward stroke of the of the plunger in the fuel injection pump, high pressure in the spring chamber causes the lubricating oil to enter the fuel gallery, thereby resulting in mixing of the lubricating oil and fuel that in turn reduces the engine performance.

Hence, there is a need for preventing contamination of the fuel by relieving the high pressure in the spring chamber of the fuel injection pump and improving the engine performance.

Object of the invention.

It is an object of the invention to prevent mixing of lubricant with fuel in a fuel injection pump by reducing the spring chamber pressure.

Advantages of the invention

The advantage of this invention as claimed in the independent claim is to prevent build up of pressure in the spring chamber due to accumulation of lubrication oil, which leads to overflowing of lubrication oil in the spring chamber of the fuel injection pump. Another advantage of the invention is improvement in the engine efficiency as a result of preventing contamination of the fuel by lubricating oil for the pump.

Brief description of the accompanying drawings

Different modes of the invention are disclosed in detail in the description and illustrated in the accompanying drawings:

Figure 1 illustrates a fuel injection pump in accordance with the present invention; and Figure 2 illustrates a graph of spring chamber pressure versus cam angle.

Detailed description of the embodiments

Figure 1 illustrates a fuel injection pump 101. The fuel injection pump 101 comprises a pump housing 102 and a plunger 105. The pump housing 102 has at least one inlet 103 and one outlet 104. A plunger 105 is adapted to reciprocate in the pump housing 102 by means of a roller tappet 106 and a cam 107. The plunger 105 is guided by a spring guide 108 enclosed in a spring chamber 109.

In the fuel injection pump 101 the cam 107 is rotated by a drive shaft. As the cam 107 rotates, a roller tappet 106 follows the cam 107 and converts rotary motion of the cam 107 into linear motion of the plunger 105. The pressure is built up in the fuel injection pump 101 as plunger 105 moves upwards within the pump housing 102. The traverse of the plunger 105 within the pump housing 102 is guided by means of a plunger 105 spring that is accommodated in a spring chamber 109. The traverse of the plunger 105 within the pump housing 102 for a single upward and downward movement is stroke of the plunger 105. The fuel that is received from the inlet 103 is pressurized by the plunger 105. The fuel at
high pressure is then delivered to the cylinders through an injector.

Lubricating oil enters the fuel injection pump 101 through the gaps between the pump housing 102 and the roller tappet 106, the opening between the pump housing 102 and the guide pin, and finally through the opening between the pump housing 102 and the control rod. During the upward movement of the plunger 105, due to excessive splashing of lubricating oil onto the fuel injection pump 101, lubricating oil enters the spring chamber 109 which can lead to building up of high pressure in the spring chamber 109. The increase in pressure in the spring chamber 109 may cause the lubricating oil to enter the fuel chamber and mix with the fuel that is received from the inlet 103. As a result, the pressurized fuel supplied by the pump may have traces of lubricating oil leading to deterioration in engine performance.

To prevent the building up of pressure in the spring chamber 109, the spring guide 108 is provided with a vent hole 110 to vent the lubricating oil collected in the spring chamber 109 regulate pressure in the spring chamber 109. The vent fluidly connects the spring chamber 109 to a drive train provided in the crank case. In one embodiment of the invention the length of the vent hole 110 is equal to the length of the spring guide 108. As the lubricating oil is vented out of the fuel injection pump 101, the distance travelled by the plunger 105 between the opening and closing of the inlet 103 increases as the plunger 105 has improved freedom to reciprocate in the spring chamber 109, thereby increasing the quantity of injected fuel and hence increasing the engine performance.

Figure 2 illustrates a graph of spring chamber 109 pressure versus cam angle. Curves CI and C2 illustrate the variations in the spring chamber 109 pressure in the fuel injection pump 101 with and without vent hole 110 in the spring guide 108 of the fuel injection pump 101 respectively. During the forward stroke as the plunger 105 traverses upwards, pressure is built up in the spring chamber 109 in presence of the lubricating oil that has entered through the three entry points. Hence during the upward stroke of the plunger 105, the plunger 105 has to perform more work in presence of lubricating oil thereby increasing the pressure in the spring chamber 109 as illustrated in curve C2. When a vent hole 110 is

introduced in the spring guide 108 it is observed from the graph that there is reduction in pressure in the spring chamber 109 with a vent hole 110 as illustrated in curve CI, compared to a fuel injection pump 101 without a vent hole 110 in the spring guide 108. The lubricating oil thus passes out of the vent hole 110 and relieves the excess pressure. As the pressure is relieved the plunger 105 has freedom to traverse more distance thereby increasing the quantity of fuel injected into the cylinder. In one embodiment it is observed that there is a reduction of spring chamber 109 pressure by about 69% when compared to a fuel injection pump 101 without vent hole 110 as illustrated in curves CI and C2.

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 (101), comprising:

a pump housing (102) having at least one inlet (103) and at least one outlet (104);

a plunger (105) adapted to reciprocate in said pump housing (102) by means of a roller
tappet (106) and cam (107), said plunger (105) guided by a spring guide (108) enclosed in a
spring chamber (109);

characterized in that,

said spring guide (108) is provided with a vent hole (110) to regulate pressure in said spring
chamber (109).

2. The fuel injection pump (101) of claim 1, wherein said vent hole (110) relieves pressure build up in said spring chamber (109) during operation of said fuel injection pump (101).

3. The fuel injection pump (101) of claim 1, wherein the length of said vent hole (110) is equal to the length of said spring guide (108).

4. The fuel injection pump (101) of claim 1, wherein said vent hole (110) fluidly connects said spring chamber (109) to a drive train.