Claims:CLAIMS
We Claim:

1. A spring retainer plate (112) for a pump, said spring retainer plate (112) characterized by a counter bore (115) to accommodate a removable shim (114).

2. A spring retainer plate (112) according to claim 1 wherein said counter bore (115) has a hole (117).

3. A spring retainer plate (112) according to claim 1 forms part of a fuel pump (100).

4. A spring retainer plate (112) according to claim 1 wherein said spring retainer plate (112) forms part of an oil pump.

5. A pump (100) comprising :

- a housing (102);
- a cylinder bore disposed in said housing (102);
- a plunger (104) moving reciprocally in said cylinder bore;
- a spring (110) to bring said plunger (104) to a known position;
- a spring retainer plate (112) holding said spring in position;
said spring retainer plate (112) characterized by a counter bore (115) to accommodate a removable shim (114)

6. A pump (100) according to claim 5 wherein duration of stroke of said plunger (104) is adjusted by thickness of said shim (114).
, Description:Complete Specification:

The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed.
Field of the invention
[001] This invention relates to the field of fuel pumps to supply fuel to an internal combustion engine.

Background of the invention

[002] Fuel pumps to supply fuel to an internal combustion engine are known in prior arts. The fuel pumps comprise a housing, a bore in the housing, a plunger moving reciprocally in the bore. The plunger is driven by a roller tappet which in turn is moved by a cam. A spring with pre-loaded tension brings the plunger to an original position. The spring is coupled to a retainer plate. In the prior arts, when the effective stroke of the plunger had to be adjusted to a particular engine, the spring retainer plates with different thicknesses were used. This leads to the necessity of manufacturing of the spring retainer plates with different thicknesses. This leads to expensive manufacturing processes. Also manufacturing and keeping stock of the spring retainer plates with different thickness is a cumbersome process.

[003] Some prior arts disclose using shims to vary the pre-tension of the spring to adjust the timing of the fuel injection. US patent 6719224 discloses a fuel injector where shim is used to pre-tension of the spring to adjust the timing of the fuel injection.

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:

FIG. 1 illustrates a pump having a spring retainer plate with a removable shim

Fig. 2 and Fig. 3 illustrate exploded view of the spring retainer plate.

Detailed description of the embodiments

[005] FIG. 1 illustrates a fuel pump 100. The fuel pump is just referred as pump. The pump comprises a housing 102, a plunger 104 in a barrel. A roller tappet 106 is integrated into the pump 100 and is driven by a cam of an engine which is not shown. The pump also comprises a pump chamber 108, a spring 110, a spring retainer plate 112 and a shim 114.

[006] The invention proposes a spring retainer plate 112 for a pump 100, the spring retainer plate 112 characterized by a counter bore 115 to accommodate a removable shim 114.

[007] The roller tappet 106 forces the plunger 104 towards the delivery valve 116. When the roller tappet 106 pushes the plunger 104 to the farthest point towards delivery valve, the position of the plunger 104 is referred as top dead centre (TDC). The plunger 104 is returned to non-delivery position by the spring 110. When the plunger 104 is at the farthest point in a direction opposite to delivery valve, the position of the plunger 104 is referred as bottom dead centre (BDC). The plunger 104 and the bore form the pump chamber 108 where the fuel is received and pressurized. The fuel enters into the pump chamber 108 through an inlet 118 in the bore when the plunger 104 is moving towards BDC. This is called suction stroke of the pump 100. When the plunger 104 starts moving towards the TDC, it closes the inlet 118. Once the inlet 118 is completely closed and the plunger 104 is still moving towards TDC, the pressure of the fuel increases in the pumping chamber 108. Once the pressure of the fuel in the pumping chamber 108 exceeds the pre-loaded pressure of the delivery valve 116, the delivery valve 116 opens and the fuel under high pressure is delivered to a common rail or a fuel injector which are not shown. The distance travelled by the plunger 104 from the closure of the inlet 118 to the TDC is referred as effective stroke of the pump 100. During the effective stroke the fuel gets pressurized.

[008] To effectively inject the fuel into the engine, the effective stroke of the pump 100 needs to be controlled accurately. If the effective stroke is not controlled accurately, the fuel may be injected at wrong timing leading to unburnt gases in the exhaust, low efficiency of the engine etc.

[009] As the pump components like plunger, retainer spring plate, roller tappet etc. will have manufacturing tolerances, the effective stroke needs to be adjusted for each engine during assembly and calibration of the engine. Also the effective stroke itself is of shorter length, typically in the order of few millimetres, the above tolerances are to be compensated accurately while adjusting the effective stroke.

[010] In the prior arts, the effective stroke was adjusted by using retainer spring plate of different thicknesses. In the prior arts, as the end of the plunger sits on to the retainer spring plate, if a thicker retainer spring plate is used, it will occupy more space and the plunger will have less length to travel to reach TDC. This way the effective stroke was reduced. If a thinner retainer spring plate is used, it will occupy less space and the plunger will have more length to travel to reach TDC. This way the effective stroke was increased. This leads to manufacture of retainer spring plates of different thicknesses. During the calibration of the engine, retainer spring plate of appropriate thickness was assembled in the pump.

[011] Manufacturing and maintaining stocks of retainer spring plates of varying thicknesses is expensive and cumbersome process.

[012] The invention proposes a simple modification in the retainer spring plate 112 thereby eliminating need of manufacturing and storing of retainer spring plates of varying thicknesses.

[013] Fig. 2 and fig. 3 disclose an enlarged view of part of the pump 100. The retainer spring plate 100 has a counter bore 115 where the shim 114 is removably placed. The end of the plunger is placed on the shim 114. So a new element 114 has been brought in between the retainer spring plate 112 and the plunger 104. The shim is slidably inserted in the counter bore.

[014] According to the invention, only one type of retainer spring plate is manufactured with a fixed thickness. Shims with different thicknesses are manufactured. While calibrating the engine, the shim with appropriate thickness is selected and inserted into the counter bore 115 of the retainer spring plate 112. As the plunger 104 sits on to the shim 114, the thickness of the shim 114 decides the effective stroke. If the shim 114 is thicker, the effective length is shorter. If the shim 114 is thinner, effective stroke is longer.

[015] The shim 114 is in the form of a disc, simple in construction. Shims of different thicknesses can be manufactured easily.

[016] The shim 114 can be easily inserted into the counter bore 115 just by sliding. For removing the shim, there is a hole 117 provided in the retainer spring plate bottom. A pin through the hole 117 is used to push the shim 114 out of counter bore 115 while removing.

[017] Thus by eliminating the complex and expensive process of manufacturing of spring retainer plates of different thicknesses, the invention achieves the same result of varying effective stroke of the plunger by using shims of different thicknesses. The manufacturing process of shims is simple and inexpensive compared to manufacturing the spring retainer plates of different thisknesses.

[018] In one embodiment the spring retainer plate 112 may be part of a pump 100 for pumping fuel. In another embodiment the spring retainer plate 112 may be part of a pump 100 for pumping oil. The pump 100 could be used to pump fuel, oil or any other fluid.