The invention relates to a fuel injection valve for internal combustion engines, such as is used for the injection of fuel into combustion chambers of fast-running auto-ignition internal combustion engines.
Fuel injection valves, such as are suitable for injecting fuel at high pressure into combustion chambers of internal combustion engines, are known for example from DE 10 2008 001 330 A1. Such fuel injection valves have a valve body in which there is arranged a longitudinally displaceable, piston-like valve needle. The compressed fuel, which is made available in a central high-pressure accumulator connected to the fuel injection valve, is introduced via multiple injection openings into a combustion chamber, wherein the nozzle needle opens and closes the injection openings. The longitudinal movement of the nozzle needle is controlled by way of the fuel pressure in a control chamber. The control chamber acts on that end of the nozzle needle which is averted from the valve seat, such that a closing force is exerted on the nozzle needle by the fuel pressure in the control chamber. By way of a control valve, the fuel pressure in the control chamber can be adjusted, such that the nozzle needle moves in a longitudinal direction in accordance with said pressure.
During the operation of the fuel injection valve, a high fuel pressure prevails at all times in the control chamber and also in the pressure chamber that surrounds the nozzle needle. When the internal combustion engine is shut down, however, said fuel pressure decreases to ambient pressure, such that the hydraulic closing force on the nozzle needle is eliminated, and the latter possibly opens in uncontrolled fashion. To prevent this, there is provided within the pressure chamber a closing spring which surrounds the nozzle needle and which, by way of its compressive preload, holds the nozzle needle in its closed position, even when the fuel pressure in the fuel injection valve has fallen to ambient pressure. In order that the closing spring can transmit the force optimally to the nozzle needle, there is formed on the outer side of the nozzle needle a shoulder against which a spring plate bears, with the closing spring resting in turn on said spring plate and thus exerting the closing force on the nozzle needle. The nozzle needle must therefore be equipped with a corresponding diameter step, which complicates the production process and thus increases production costs. Furthermore, the spring requires an adequate structural space in the pressure chamber, which limits a miniaturization of the fuel injection valve.
The fuel injection valve according to the invention has, in relation to this, the advantage that a compact and simple construction of the nozzle needle is made possible, without an impairment of functionality in relation to the known fuel injection valve. For this purpose, the fuel injection valve has a nozzle body with a pressure chamber formed therein, wherein the pressure chamber can be charged with fuel at high pressure. A piston-like nozzle needle is arranged in longitudinally displaceable fashion in the pressure chamber, which nozzle needle interacts, by way of a sealing surface formed on its combustion chamber-side end, with a nozzle seat formed in the nozzle body. In this way, the nozzle needle controls the flow of fuel from the pressure chamber to at least one injection opening. Furthermore, a sleeve is provided which receives that end of the nozzle needle which is averted from the nozzle seat, which sleeve delimits a control chamber, the pressure of which exerts a hydraulic force on the nozzle needle in the direction of the nozzle seat. In the control chamber there is arranged a closing spring which is arranged under compressive preload between the sleeve and the nozzle needle.
Since no shoulder is required on the outer side of the nozzle needle for the closing spring in order to transmit the closing force to the nozzle needle, the nozzle needle can be provided with a uniform diameter on the outer circumference over practically its entire length, which simplifies the production process, thus making it cheaper. Furthermore, the assembly composed of the sleeve, the closing spring and the nozzle needle can be assembled in a separate process, and then introduced as a whole into the nozzle body, wherein the closing spring remains protected within the sleeve, and thus cannot be damaged during the assembly process.
In a first advantageous refinement of the invention, the closing spring exerts a closing force on the nozzle needle in the direction of the nozzle seat, while said closing spring furthermore presses the sleeve against a throttle disk which delimits the control chamber. In this way, the force of the closing spring not only presses the nozzle needle against the nozzle seat but also presses the sleeve against the throttle disk, which is thus held positionally fixed within the fuel injection valve. Here, it is preferable for the sleeve to have, at its end side facing the throttle disk, a sealing edge by way of which said sleeve bears sealingly against the throttle disk.
In a further advantageous refinement, the closing spring is arranged under compressive preload between a shoulder, which is formed in the interior of the sleeve by a step of the internal diameter, and a shoulder of the nozzle needle, which shoulder is formed by a step in the external diameter. This simple design permits a compact arrangement of the components and separate assembly of sleeve, spring and nozzle needle outside the nozzle body. For adjustment of the force of the closing spring, it is furthermore advantageously provided that a compensating disk is arranged between the closing spring and the shoulder of the nozzle needle, by means of the thickness of which compensating disk the preload force of the closing spring can be adjusted.
Further advantages and advantageous refinements of the invention will emerge from the description and from the drawing.
The drawing illustrates an exemplary embodiment of the fuel injection valve according to the invention. In the drawing:
At the end averted from the combustion chamber, within the pressure chamber 3, there is arranged a sleeve 12 which, in a needle-guiding section 23, receives that end of the nozzle needle 5 which is averted from the nozzle seat. In this regard,
The shoulder 18 on the nozzle needle 5 is formed at the transition of the peg 14 to the rest of the nozzle needle 5, which has a greater diameter. Furthermore, a compensating disk 17 bears against the shoulder 18, which compensating disk is in the form of an annular disk and by means of the thickness of which compensating disk the preload of the closing spring 16 can be adjusted. To permit pressure equalization within the control chamber 20 without problems, there is formed between the peg 14 and the bore 22 a ring-shaped gap 27 which is of such a size that no pressure differences arise within the control chamber 20.
The mode of operation of the fuel injection valve is, as is already known from the prior art, such that the fuel pressure in the pressure chamber 3 and in the control chamber 20 at the start of the injection corresponds to the high fuel pressure made available by a fuel high-pressure accumulator. If it is the intention for an injection to be performed, the control chamber 20 is connected, via the outflow throttle 13 and the control valve (not illustrated), to a low-pressure chamber, such that the fuel pressure in the control chamber 20 falls. The nozzle needle 5 is thereupon pushed away from the nozzle seat 7 by the fuel pressure in the pressure chamber 3, such that the injection openings 8 are connected to the pressure chamber 3 and fuel is injected from the pressure chamber 3 via the injection openings 8 into a combustion chamber of the internal combustion engine. To end the injection, the control chamber 20 is flooded with fuel at high pressure again, such that the nozzle needle 5 slides back into its closed position again.
When the internal combustion engine is shut down, the pressure in the high-pressure accumulator falls, and thus after a certain time the pressure in the pressure chamber 3 of the fuel injection valve also falls, to a pressure which generally lies only slightly above ambient pressure. In this state, the nozzle needle 5 is substantially pressure-balanced in the longitudinal direction, that is to say it could be moved in the longitudinal direction without application of force. To prevent the possibility of the nozzle needle inadvertently opening up the injection openings in said state and fuel dripping into the combustion chamber, the closing spring 16 pushes the nozzle needle 5 into contact with the nozzle seat 7, and thereby closes the injection openings 8, even if the fuel injection valve and thus the pressure chamber 3 are unpressurized. For the actual operation of the fuel injection valve, that is to say for the longitudinal movement of the nozzle needle 5, the force of the closing spring 16 does not play a role or plays only a secondary role, because the hydraulic forces are greatly predominant in the presence of injection pressures of up to 2000 bar.
The sleeve 12, at its face side which is averted from the nozzle seat and by means of which it bears against the throttle disk 2, has a sealing edge 25 which is formed by two conical surfaces on the face side of the sleeve 12. The sleeve 12 bears by way of the sealing edge 25 against the throttle disk 2, such that effective and reliable sealing of the control chamber 20 with respect to the pressure chamber 3 is realized at that location. If the diameter of the sealing edge 25 substantially corresponds to the needle-guiding section 23 of the sleeve 12, the fuel pressure within the control chamber 20 does not give rise to any hydraulic forces on the sleeve 12, such that the latter remains in contact with the throttle disk 2 at all times, and reliably seals off the control chamber 20 at that location. The play between the nozzle needle 5 and the needle-guiding section 23 of the sleeve 12 is dimensioned such that, firstly, a longitudinal movement of the nozzle needle 5 is made possible without problems, but only very small amounts of fuel are exchanged between the pressure chamber 3 and the control chamber 20 through the remaining residual gap between the nozzle needle 5 and the needle-guiding section 23, which amounts are not of significance for the actual operation of the fuel injection valve.
Number | Date | Country | Kind |
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10 2013 212 269 | Jun 2013 | DE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/062893 | 6/18/2014 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2014/206851 | 12/31/2014 | WO | A |
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102004005451 | Aug 2005 | DE |
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Entry |
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International Search Report for Application No. PCT/EP2014/062893 dated Sep. 2, 2014 (English Translation, 3 pages). |
Number | Date | Country | |
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20160230721 A1 | Aug 2016 | US |