Fluid sprinkling – spraying – and diffusing – Fluid pressure responsive discharge modifier* or flow... – Fuel injector or burner
Reexamination Certificate
2003-06-18
2004-09-21
Hwu, Davis (Department: 3752)
Fluid sprinkling, spraying, and diffusing
Fluid pressure responsive discharge modifier* or flow...
Fuel injector or burner
C239S533300, C239S533900, C239S585100, C239S585500, C239S088000
Reexamination Certificate
active
06793159
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The invention relates to a fuel injector.
BACKGROUND OF THE INVENTION
When using a fuel injector, precisely metered quantities of fuel are injected into in a combustion chamber of an internal combustion engine. With regard to future common rail injection systems, the fuel is intended to be injected at a pressure of up to 2000 bar, for which reason efforts are being made to design fuel injectors capable of handling particularly high pressure.
A conventional fuel injector will be described in detail in the following with reference to
FIG. 1
which shows a cross-section through the fuel injector.
The fuel injector comprises an actuator housing GA′ and an actuator unit A′ arranged therein which has an operative connection by way of a lever H′ and a valve piston V′ with a control valve S′. The control valve S′, which is arranged in a valve chamber VK′, separates a control chamber SK′ from a return line R′. The control chamber SK′ is arranged beneath the valve chamber VK′ and connected by way of an outlet restrictor AD′ to the valve chamber VK′. The valve chamber VK′ is arranged in a control module ST′.
The control chamber SK′ lies adjacent to an upper end of a control piston K′. The control piston K′ is arranged so as to be movable inside a drilled hole in a piston module KM′ and lies adjacent to side surfaces of the piston module KM′ which are formed by the drilled hole. The drilled hole thus serves as a guide for the control piston K′.
The control piston K′ is connected to a coupling rod KS′ which is arranged in a spring pocket F′. The spring pocket F′ is arranged in the piston module KM′ and is connected to the return line R′ such that a low pressure exists in the spring pocket F′. The coupling rod KS′ has a spring plate T′. A spring FE′ is tensioned between the spring plate T′ and the control piston K′.
The coupling rod KS′ is in contact with a nozzle needle D′ which is arranged in a drilled hole in a nozzle body DK′ arranged beneath the piston module KM′. The drilled hole in the nozzle body DK′ has a high pressure chamber HK′ into which a high pressure inlet Z′ opens out which extends from the control module ST′ as far as the high pressure chamber HK′. An inlet restrictor ZD′ is arranged between the high pressure inlet Z′ and the control chamber SK′.
When the actuator unit A′ is actuated, then the control valve S′ is opened so that fuel drains from the valve chamber VK′ by way of the return line R′. As a result, fuel flows from the control chamber SK′ by way of the outlet restrictor AD′ into the valve chamber VK′ and it actually flows more quickly than fuel flows from the high pressure inlet Z′ by way of the inlet restrictor ZD′ into the control chamber SK′. As a consequence of this, the pressure in the control chamber SK′ falls such that the force acting from above on the nozzle needle D′ is reduced and the nozzle needle D′ lifts from its valve seat. As a result, fuel issues from the fuel injector.
When the actuator unit A′ is deactivated, then the control valve S′ closes so that a pressure is built up once again in the control chamber SK′ by way of the inlet restrictor ZD′. As a result of the spring FE′, as a result of the low pressure in the spring pocket F′ and as a result of the hydraulic force resulting on the basis of the greater cross-sectional area of the control piston K′ when compared with the cross-sectional area of the nozzle needle D′ in the area of the guide in the nozzle body DK′ just a small rise in pressure in the control chamber SK′ is sufficient in order to press the nozzle needle D′ downwards against its valve seat such that the fuel injector closes quickly.
A disadvantage associated with the conventional fuel injector is the tapering and thin wall of the nozzle body in the area where the high pressure inlet opens out into the high pressure chamber. The resistance to high pressure of the fuel injector is consequently not very high.
A further disadvantage consists in the fact that a continuous leakage occurs between the high pressure chamber and the spring pocket in which a low pressure prevails, and between the spring pocket and the control chamber, which leads to a loss in the efficiency of the fuel injector. The greater the pressure difference between the high pressure chamber or the control chamber and the spring pocket, the more pronounced is the continuous leakage.
SUMMARY OF THE INVENTION
The object of the invention is to set down a fuel injector which is suitable for higher pressures when compared with the prior art.
This object can be achieved by a fuel injector having the following features: The fuel injector comprises a control module with a piston guide extending downwards, in which a control piston is arranged. The fuel injector further comprises a nozzle body with a top surface on which the control module is mounted and which has a drilled hole in whose lower section is arranged a nozzle needle which has an operative connection with the control piston and in whose upper section is arranged the piston guide of the control module. A high pressure inlet which opens out into the drilled hole at the top surface is arranged in the control module. The drilled hole is designed such that fuel which escapes from the fuel injector when the nozzle needle lifts from its valve seat is replaced, whereby fuel from the high pressure inlet flows through the drilled hole in the direction of the valve seat. High pressure is thus applied to the entire drilled hole.
Since the high pressure inlet opens out into the drilled hole of the nozzle body at the top surface of the nozzle body and thus does not open out sideways into a drilled hole, no tapering thin wall which would be at risk of failure under high pressure conditions is present between the drilled hole and the high pressure inlet. The fuel injector therefore exhibits a high resistance to pressure and is thus suitable for high pressures.
Since the high pressure inlet is arranged only in the control module and not in the nozzle body where the construction space particularly in the lower section is greatly restricted, the problem of walls which are too thin for high pressures around the high pressure inlet does not generally arise.
A valve chamber is provided, for example, which is separated from a return line by means of a control valve. In addition, the fuel injector can comprise a control chamber which lies adjacent to the upper end of the control piston. High pressure is applied to the control chamber by way of an inlet restrictor, whereby the inlet restrictor is connected hydraulically to the high pressure inlet. The inlet restrictor is thus connected at least indirectly to the high pressure inlet. The valve chamber and the control chamber are connected to one another by way of an outlet restrictor.
In order to guarantee rapid closure of the fuel injector, as a result of the absence of a difference in cross-sectional area between control piston and nozzle needle in the area of the guide in the control module and thus of the absence of the hydraulic force component in the direction of closure of the nozzle needle it is advantageous to provide a bypass restrictor, by way of which high pressure is applied to the valve chamber, whereby the bypass restrictor is connected hydraulically to the high pressure inlet. The bypass restrictor is thus connected at least indirectly to the high pressure inlet in hydraulic terms. When the control valve lifts from its valve seat, then fuel drains off from the valve chamber into the return line. Fuel drains off from the control chamber through the outlet restrictor more quickly than can flow into the control chamber through the inlet r
Bloching Wolfgang
Schürz Willibald
Baker & Botts L.L.P.
Hwu Davis
Seimens Aktiengesellschaft
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