CLIAMS:We Claim:
1. A fuel injector (10), said fuel injector (10) comprising:
a nozzle needle (12);
a distance piece (14) positioned proximate said nozzle needle (12);
a coil spring (16) positioned proximate to said nozzle needle (12); characterized in that
a disc spring (18) positioned between a bottom surface (20) of said distance piece (14) and a shoulder (22) of said nozzle needle (12) and in contact with said shoulder (22), said coil spring (16) adapted to compress until said disc spring (18) contacts said bottom surface (20) of said distance piece (14), and said disc spring (18) adapted to compress when said disc spring (18) contacts said bottom surface (20) of said distance piece (14).
2. The fuel injector (10) in accordance with Claim 1 wherein said nozzle needle (12) translates at a first rate until said disc spring (18) contacts said bottom surface (20) of said distance piece (14), and wherein said nozzle needle (12) translates at a second rate when said disc spring (18) contacts said bottom surface (20) of said distance piece (14), said first rate greater being than said second rate. ,TagSPECI:The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention:
[001] This invention relates to a disc spring, and more specifically to a disc spring for a fuel injector.

Background of the invention:
[002] Fuel is channelled to a fuel injector, where it is delivered to an engine cylinder. When the fuel is channelled to the fuel injector, the pressure exerted by the fuel against a nozzle needle causes the nozzle needle to translate against a force of a coil spring. The nozzle needle stops moving against the coil spring when a bottom surface of a distance piece of the fuel injector comes in contact with a shoulder of the nozzle needle. During this period, fuel is injected from the fuel injector into the engine cylinder. During this process, the rate at which the nozzle needle translates to open and close the outlet of the fuel injector remains constant. In order to open and close the outlet of the fuel injector at variable rates, a disc spring is used in combination with the coil spring in the fuel injector.

[003] U.S. Patent Number 4,768,719: During the injection process, the valve needle executes an initial lift or stroke where only the closing spring is effective as a counter force. A defined preliminary injection quantity is injected into the combustion chamber of the engine. The initial lift or stroke is included when the upper front side of the valve needle comes to rest on the lower front side of the intermediate bush. The valve needle remains in this position until the fuel pressure, which continues to increase, overcomes the counter forces of the two closing springs. The valve needle, together with the intermediate bush, is then moved further in the opening direction by the distance hg until it has travelled its total stroke. The latter is limited and determined by means of the ring shoulder at the intermediate bush and the intermediate disk.

Brief description of the accompanying drawings
[004] An exemplifying embodiment of the invention is explained in principle below with reference to the drawing. The drawing is:
[005] Figure 1 shows a schematic view of a disc spring for a fuel injector.

Detailed Description of the invention:
[006] As shown in Figure 1, a fuel injector 10 is described. The fuel injector 10 comprises a nozzle needle 12 and a distance piece 14 positioned proximate to the nozzle needle 12. A coil spring 16 is positioned proximate to the nozzle needle 12. A disc spring 18 is positioned between a bottom surface 20 of the distance piece 14 and a shoulder 22 of the nozzle needle 12. The disc spring 18 is in contact with the shoulder 22 of the nozzle needle. The coil spring 16 is adapted to compress until the disc spring 18 contacts the bottom surface 20 of the distance piece 14, and the disc spring 18 is adapted to compress when the disc spring 18 contacts the bottom surface 20 of the distance piece 14.

[007] The fuel injector 10 includes a nozzle needle 12. The nozzle needle 12 is positioned proximate to an outlet of the fuel injector 10. The nozzle needle 12 is lifted upwardly when fuel is channeled into the fuel injector 10 to facilitate injecting fuel from the outlet of the fuel injector 10. A coil spring 16 is positioned proximate to an upper portion of the nozzle needle 12 and is displaced along the direction of translation of the nozzle needle 12 when the nozzle needle 12 is lifted upwardly.

[008] The nozzle needle 12 comprises a shoulder 22 defined proximate to the upper portion of the nozzle needle 12. A distance piece 14 is positioned proximate to the nozzle needle 12 such that a gap 24 is defined between a bottom surface 20 of the distance piece 14 and the shoulder 22 of the nozzle needle 12. A disc spring 18 is placed within the gap 24 defined between the bottom surface 20 of the distance piece 14 and the shoulder 22 of the nozzle needle 12. Specifically, the disc spring 18 is located on the shoulder 22 of the nozzle needle 12 and circumscribes the nozzle needle 12. A gap 24 is maintained between the bottom surface 20 of the distance piece 14 and the disc spring 18 while the fuel injector 10 is not operational. The disc spring 18 undergoes compression after the gap 24 between the disc spring 18 and the bottom surface 20 of the distance piece 14 is closed by the upward movement of the nozzle needle 12.

[009] An operation of the disc spring 18 for the fuel injector 10 is described as an example. When fuel is channeled within the fuel injector 10, the pressurized fuel causes the nozzle needle 12 to lift upwardly, thereby channeling fuel from an outlet of the fuel injector 10. Untill the disc spring 18 contacts with the bottom surface 20 of the distance piece 14, the nozzle needle 12 moves upwardly against a force of the coil spring 16. Therefore, this movement of the nozzle needle 12 is translated to the movement of the coil spring 16. When the disc spring 18 contacts with the bottom surface 20 of the distance piece 14, the disc spring 18 gets compressed. After the disc spring 18 contacts with the bottom surface 20 of the distance piece 14, the upward movement of the nozzle needle 12 causes the compression of the coil spring 16 as well as compression of the disc spring 18. Therefore, the nozzle needle 12 needs to overcome the resistance offered by the coil spring 16 as well as that of the disc spring 18 to translate upwardly. The nozzle needle 12 continues to translate upwardly untill the disc spring 18 has been fully compressed. The nozzle needle 12 continues to translate upwardly untill the disc spring 18 has been partially compressed to an extent as specified by a user. This compression of the disc spring 18 and the coil spring 16 causes the rate at which the nozzle needle 12 is translated upwardly to decrease.

[0010] The nozzle needle 12 translates upwardly at a first rate until the disc spring 18 contacts the bottom surface 20 of the distance piece 14. The nozzle needle 12 translates upwardly at a second rate when the disc spring 18 contacts the bottom surface 20 of the distance piece 14. The first rate is greater than the second rate.

[0011] When the pressure caused by the fuel decreases in the fuel injector 10, the nozzle needle 12 translates in the downward direction. When the nozzle needle 12 translates in the downward direction, the coil spring 16 and the distance piece 14 translate in the downward direction with the translation of the nozzle needle 12. Therefore, the translation of the nozzle needle 12 is due to the force offered by the coil spring 16 as well as the disc spring 18. After the disc spring 18 looses contact with the bottom surface 20 of the distance piece 14, the coil spring 16 gets decompressed with the further translation of the nozzle needle 12 in the downward direction. The nozzle needle 12 continues to translate downwardly untill the disc spring 18 has been fully decompressed.

[0012] The above described disc spring 18 for a fuel injector 10 is cost effective and highly reliable. The disc spring 18 is compressed by the upward translation of the nozzle needle 12 after it has contacted with the bottom surface 20 of the distance piece 14. Due to the coil spring 16 and the disc spring 18 being compressed due to the upward translation of the nozzle needle 12, the rate at which the nozzle needle 12 is translated upwardly decreases. Therefore, the insertion of the disc spring 18 within the gap 24 defined between the distance piece 14 and the nozzle needle 12 changes the rate of translation of the nozzle needle 12 in the upward direction. In addition, the insertion of the disc spring 18 within the gap 24 defined between the distance piece 14 and the nozzle needle 12 changes the rate of translation of the nozzle needle 12 in the downward direction. Moreover, the modular nature of each sub-system of the disc spring 18 for a fuel injector 10 facilitates easy disassembly and replacement of individual system components as required.

[0013] It must be understood that the embodiments explained in the above detailed description is only illustrative and does not limit the scope of this invention. The scope of this invention is limited only by the scope of the claims. Many modification and changes in the embodiments aforementioned are envisaged and are within the scope of this invention.