Claims:We Claim:

1. An overflow valve (10) for a high pressure fuel pump, said overflow valve (10) comprising:
a valve body (12);
a cap (14) adapted to be secured to the valve body (12); characterized in that
a memory spring (16) positioned within said valve body (12), a first end of said memory spring (16) in contact with said cap (14), and an opposite second end of said memory spring (16) in contact with a valve plate (18), said memory spring (16) adapted to increase its spring constant when it comes in contact with fuel at an elevated temperature to facilitate lifting said valve plate (18) thereby elevating a pressure of fuel in a fuel gallery of said high pressure fuel pump.
, Description:Field of the invention
[0001] This invention relates to an overflow valve for a high pressure fuel pump and more specifically to an overflow valve with a memory spring.

Background of the invention
[0002] DE 102009047113 A1 describes a fuel supply device. The fuel supply device has a supply pump, a high pressure pump and a flow limiting throttle in a supply line for the supply pump. The flow limiting throttle is mechanically coupled with an overflow valve by which the pressure of the fuel, is adjusted. The flow limiting throttle is controlled by a volume dependent pressure drop in a control line of the overflow valve.

Brief description of the accompanying drawing
[0003] Figure 1 illustrates a schematic diagram of an overflow valve of a high pressure fuel pump.

Detailed description of the invention
[0004] An overflow valve 10 for a high pressure fuel pump is described. The overflow valve 10 comprises a valve body 12 and a cap 14 adapted to be secured to the valve body 12. A memory spring 16 is positioned within the valve body 12, a first end of the memory spring 16 in contact with the cap 14, and an opposite second end of the memory spring 16 in contact with a valve plate 18, the memory spring 16 adapted to increase its spring constant when it comes in contact with fuel at an elevated temperature to facilitate lifting the valve plate 18 thereby elevating a pressure of fuel in a fuel gallery of the high pressure fuel pump.
[0005] Figure 1 illustrates a schematic diagram of an overflow valve 10 of the high pressure fuel pump. The overflow valve 10 comprises a valve body 12 and a fuel flow passage 13 positioned within the valve body 12. A memory spring 16 is inserted within the valve body 12 such that a first end of the memory spring 16 abuts against a valve plate 18 that is positioned against the fuel flow passage 13. A cap 14 is inserted within the overflow valve 10 such that the cap 14 abuts against the second end of the memory spring 16. The cap 14 is in sealing contact with the valve body 12 of the overflow valve 10 to prevent a flow of fuel out of the overflow valve 10.
[0006] The memory spring 16 that is inserted within the overflow valve 12 has a variable spring constant. More specifically, the memory spring 16 that is inserted within the overflow valve 12 has a spring constant of a particular value at its calibration temperature i.e. room temperature. As the temperature of the memory spring is increased by contacting it with higher temperature fuel, its stiffness correspondingly increases. If the temperature of the memory spring 16 is decreased by contacting it with lower temperature fuel, its stiffness correspondingly decreases. In an embodiment, the memory spring 16 may be manufactured from any material whose spring constant increases and decreases with increase and decrease in the fuel temperature respectively that comes in contact with it.
[0007] A working of the overflow valve 10 of the high pressure fuel pump is described as an example. When fuel at a low temperature flows though the gallery of the high pressure fuel pump, a portion of the fuel is channeled to the cylinders of the high pressure fuel pump. The remaining fuel is channeled to the overflow valve 10. The pressurized fuel enters through the fuel flow passage 13 and fills the valve body 12 that houses the memory spring 16. When the fuel is at a lower temperature, the memory spring 16 has a low spring constant and hence is compressed at a lower pressure of fuel thereby allowing the pressurized fuel to escape from the high pressure fuel pump via the overflow valve 10. Therefore, a desired quantity of pressurized fuel is delivered from the high pressure fuel pump for delivery to its fuel injector. During normal operation, the housing of the high pressure fuel pump increases in temperature which causes an increase in the temperature of fuel. The increased temperature fuel comes in contact with the memory spring 16 of the overflow valve 10. Due to the increase in the temperature of the memory spring 16 of the overflow valve 10, the spring constant of the memory spring 16 increases. The increase in the spring constant of the memory spring 16 causes the stiffness of the memory spring 16 to increase, thereby getting compressed at a higher pressure of fuel. As the memory spring compresses at a higher pressure, a higher quantity of fuel is retained within the high pressure fuel pump. Therefore, the higher fuel quantity is injected from the high pressure fuel pump via the delivery valve holder and the fuel injector. Due to the increased stiffness of the memory spring 16 of the overflow valve 10, the fuel that is pressurized and retained within the high pressure fuel pump as a consequence of the overflow valve 10 not opening at the earlier lower pressure now flows through the cylinders of the high pressure fuel pump from where it is delivered to each of the fuel injectors of the engine.
[0008] 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 components are envisaged and form a part of this invention. The scope of the invention is only limited by the scope of the claims.