Claims:We Claim
1. A fuel pump (10), said fuel pump (10) comprising:
a housing (12);
a plunger (14) positioned within said housing (12);
a bottom spring plate (16) in contact with at least a part of said plunger (14);
a first spring (18) located between said housing (12) and said bottom spring plate (16), said first spring (18) adapted to be compressed when said plunger (14) compresses fuel within said fuel pump (10); characterized in that
a second spring (20) coupled between said housing (12) and said bottom spring plate (16), said second spring (20) is positioned within said first spring (18).

2. The fuel pump (10) in accordance with Claim 1 wherein said second spring (20) is concentrically positioned with respect to said first spring (18).

3. The fuel pump (10) in accordance with Claim 1 wherein said second spring (20) is adapted to be compressed when said plunger (14) compresses fuel through said fuel pump (10).

4. The fuel pump (10) in accordance with Claim 1 wherein said second spring (20) is adapted to apply a resistive force against said bottom spring plate (16) after said first spring (18) is compressed substantially.

5. The fuel pump (10) in accordance with Claim 1 wherein said second spring (20) is adapted to apply a tensile force on said bottom spring plate (16), thereby causing displacement of said bottom spring plate (16) after said plunger (14) of said fuel pump (10) has reached its top dead center position.

6. The fuel pump (10) in accordance with Claim 1 wherein a stiffness of said second spring (20) is lower than a stiffness of said first spring (18). , Description:Field of the invention
[0001] This invention relates to a fuel pump that is driven by a cam.

Background of the invention
[0002] Russian Patent Application Number 2079695 C describes a compact fuel injection pump for a small-sized engine. The fuel injection pump for light fuel comprises a housing with a sleeve, and a plunger cavity disposed therein. The fuel injection pump comprises an injection metering valve, a spring, a pusher, and a return spring. According to the invention, the return spring is located inside the pumping chamber and supported on the plunger. An additional spring is arranged in the inner cavity of the pusher that rests on the pusher. A plunger is placed within a sleeve that forms a part of the housing of the fuel injection pump. A spring dosing valve is located in the discharge chamber. The return spring is placed in the discharge chamber of the plunger. The pusher is provided with a roller, which is associated with a cam of the pusher. An additional spring resting on the pusher is installed in the inner cavity.

Brief description of the accompanying drawing
[0003] Figure 1 illustrates a fuel pump in accordance with one embodiment of this disclosure.

Detailed description of the invention
[0004] Figure 1 illustrates a fuel pump 10 in accordance with one embodiment of this disclosure. The fuel pump 10 comprises a housing 12 and a plunger 14 positioned within the housing 12. A bottom spring plate 16 is in contact with at least a part of the plunger 14. A first spring 18 is located between the housing 12 and the bottom spring plate 16, the first spring 18 adapted to be compressed when the plunger 14 compresses fuel within the fuel pump 10. A second spring 20 is coupled between the housing 12 and the bottom spring plate 16, the second spring 20 is positioned within the first spring 18.

[0005] The fuel pump 10 comprises a housing 12. A plunger 14 is positioned within the housing 12 of the fuel pump 10 and facilitates delivering fuel from the fuel pump 10. A bottom spring plate 16 is coupled to the plunger 14 and reciprocates the plunger 14 to deliver fuel from the fuel pump 10. A first end of the bottom spring plate 16 is connected to the plunger 14 while an opposite second end of the bottom spring plate 16 is coupled to a roller tappet (not shown) of the fuel pump 10. The rotation of the cam of the fuel pump 10 facilitates lifting the roller tappet and hence the bottom spring plate 16 in order to facilitate delivering fuel from the fuel pump 10.
[0006] A first spring 18 is connected between the bottom spring plate 16 and the housing 12 of the fuel pump 10. The first spring 18 is compressed by the upward translation of the bottom spring plate 16 until the plunger 14 of the fuel pump 10 reaches the top dead center. Therein, the first spring 18 applies a tensile force on the bottom spring plate 16, thereby causing the bottom spring plate 16 to undergo displacement of the plunger 14 from the top dead center position to the bottom dead center position.
[0007] A second spring 20 is positioned within the first spring 18. The second spring 20 is positioned within the first spring 18 such that the second spring 20 is concentrically positioned within the first spring 18. The second spring 20 is connected between the housing 12 and the bottom spring plate 16 of the fuel pump 10. A first end of the second spring 20 is connected to the housing 12 while the opposite second end of the second spring 20 is left free. The second spring 20 is compressible when the bottom spring plate 16 moves upwardly from the bottom dead center position to the top dead center position of the fuel pump 10. Moreover, the second spring 20 offers a tensile force to the bottom spring plate 16 to make the bottom spring plate 16 move downwardly from the top dead center position of the fuel pump 10. In an exemplary embodiment, the stiffness of the second spring 20 is lower than the stiffness of the first spring 18. In an alternate exemplary embodiment, the stiffness of the second spring 20 is higher than the stiffness of the first spring 18.
[0008] A working of the fuel pump 10 is described as an example. When the cam rotates, the bottom spring plate 16 is lifted upwardly by the roller tappet to facilitate delivering fuel from the fuel pump 10. During the upward translation of the bottom spring plate 16, the first spring 18 starts getting compressed. After the first spring 18 is compressed to a small extent, the second spring 20 that is positioned within the first spring 18 also gets compressed. However, during the initial compression of the first spring 18, while the first spring 18 exerts a force on the bottom spring plate 16, there is minimum force exerted by the second spring 20 on the bottom spring plate 16. Therefore, the energy expended by the bottom spring plate 16 to raise the second spring 20 is also minimal. When the second spring 20 has been raised until it has almost reached the top dead center position, the bottom spring plate 16 experiences an additional resistive force that is exerted by the second spring 20. When the bottom spring plate 16 reaches a displacement pertaining to the top dead center position of the plunger 14 of the fuel pump 10, the second spring 20 applies a tensile force on the bottom spring plate 16. The tensile force applied by the second spring 20 on the bottom spring plate 16 causes the bottom spring plate 16 to move downwardly. At the same time, the first spring 18 applies a tensile force on the bottom spring plate 16 to move downwardly while at the same time allowing the roller tappet to maintain surface contact with the cam throughout the downward movement of the bottom spring plate 16. The tensile force applied by the first spring 18 and the second spring 20 on the bottom spring plate 16 causes the bottom spring plate 16 to move downwardly while maintaining surface contact between the cam and the roller tappet throughout the downward movement of the bottom spring plate 16. Therefore, the combined forces exerted by the first spring 18 and the second spring 20 on the bottom spring plate 16 causes the roller tappet to always maintain surface contact with the cam, regardless of the speed of rotation of the cam. Therefore, at high rotational speeds of the cam, the roller tappet always maintains surface contact with the cam without disengaging from the cam. The second spring 20 therefore helps in maintaining surface contact between the roller tappet and the cam throughout the downward movement of the bottom spring plate 16 at different operational speeds of the cam by offering an additional resistive force in addition to the resistive force offered by the first spring 18.
[0009] It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to leverage and dimensions of various levers are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.