Claims:We Claim:
1.A common rail fuel injector (100), said common rail fuel injector (100) comprising at least:
- a control chamber (110);
- a first orifice (105) situated on one lateral side of said control chamber (110);
- a control piston (115) located below said control chamber (110);
- at least two radially disposed annular grooves (125) disposed on said control piston (115);
characterized in said control piston (115):
- a second orifice (120) situated on said control piston (115);
- at least two cross holes (130a,130b) disposed at the same axial location as said radially disposed annular grooves (125).
2. The common rail fuel injector (100) as claimed in claim 1, where said second orifice (120) is situated on the other lateral side as that of the first orifice (105) and is located below said first orifice (105) when said fuel injector (100) is held in assembly position
, 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
[0001] The present disclosure relates generally to common rail fuel injectors, and more particularly to common rail fuel injectors for injector rate shaping control.

Background of the invention
[0002] In current common rail fuel injector design, rate shaping of injection characteristics is not possible because the common rail fuel injector closing is relatively slower.
[0003] The common rail fuel injector is a product built as an assembly of accurate components with precise actuations and functioning. When the solenoid valve is actuated the ball lifts off from valve seat and the fuel in pressure chamber is released to low pressure area.
[0004] As the solenoid is closed, the ball returns to its seat, the high-pressure fuel from inlet connector enters the valve chamber actuating the valve piston, nozzle needle back thereby closing the fuel injection. In order to ensure this electro-hydraulic actuation is the valve piece has two cross holes the “inlet and outlet” holes.
[0005] Because of this there is a lot of combustion noise and also the boot shape injection characteristics can be controlled & varied
Brief description of the accompanying drawings
[0006] An embodiment of the disclosure is described with reference to the following accompanying drawings,
[0007] Figure 1 illustrates a fuel injection pump in accordance with an embodiment of our invention.
Detailed description of the drawings
[0008] Figure 1 illustrates a common rail fuel injector (100). The common rail fuel injector (100) comprises among other things at least a control chamber (110), a first orifice (105) situated on one lateral side of said control chamber (110), a control piston (115) located below said control chamber (110) and at least two radially disposed annular grooves (125) disposed on said control piston (115).

[0009] In one embodiment of the common rail fuel injector (100), an additional inlet hole (120) is provided in the valve piece and in the control piston (115) annular groove (125) two cross holes (130a,130b) are provided. Inlet hole 2 (120) is provided on valve piece shaft opposite & just below to inlet hole 1(105) where the area of inlet hole 1 & 2 (105,120) together is equal to the area of inlet hole in the current embodiment. Control piston (115) is having annular groove (125) & two cross holes (130a,130b) are provided. These cross holes (130a,130b) are open in central hole from the top.
[0010] When current given to injector, the valve ball starts lifting, and the control piston (115) will get partially lifted therefore there will be faster opening of control piston (115). In this scenario, inlet hole 2 (120) is in blocked condition. Fuel enters combustion chamber only through inlet hole 1(105) and hence pressure drop in control chamber (110) is relatively faster compared to existing design, hence needle lifts fast in initial phase.
[0011] Then the control piston (115) lifts further then inlet hole 2 (120) opens into the cross holes (130a,130b) and hence pressure drop in control chamber (110) slows down and also the movement of control piston (115) resulting in boot shape injection characteristics. The characteristics of boot shape injection can further be varied / controlled by varying the cross-hole diameter. Fuel discharges to low pressure zone from outlet hole.
[0012] Valve piston lifts further and inlet hole 2 (120) closes, resulting in increased pressure drop in control chamber (110) , hence faster movement of control piston (115) and fuel discharges to low pressure zone. Valve ball is in full lift condition & piston (115) position is at extreme top. When the valve ball closes, that is, it experiences fuel throttling, the control piston (115) starts moving down, resulting in pressure started rising in control chamber, hence faster downward movement of control piston (115).
[0013] Finally, when the valve ball is completely resting on seat, the control piston (115) drops further, then inlet hole 2 (120) opens into the cross holes (130a,130b) and hence pressure starts building in control chamber (110) & needle starts closing.
[0014] There will be faster closing of control piston (115), inlet hole 2 (120) is in blocked condition. Pressure will build-up in the control chamber (110) through inlet hole 1 (105), due to this needle will get closed faster compared to existing design.
[0015] The proposed embodiment has significant advantages. Firstly, it leads to combustion noise reduction and performance improvement. And secondly, the cross-hole (130a,130b) diameter and overlap dimensions with inlet hole 2 (120) are additional application parameters with which boot shape injection characteristics can be controlled & varied.
[0016] It must be understood that the embodiments explained in the above detailed description are only illustrative and do not limit the scope of this invention. Any modification to the common rail fuel injector (100) are envisaged and form a part of this invention. The scope of this invention is limited only by the claims.