Internal-combustion engines – Charge forming device – Fuel injection system
Reexamination Certificate
1999-12-17
2001-08-21
Moulis, Thomas N. (Department: 3747)
Internal-combustion engines
Charge forming device
Fuel injection system
C239S124000
Reexamination Certificate
active
06276335
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention is based on a fuel injection valve of the type known from European Patent Disclosure EP 0 690 223 A2.
In so-called common rail systems, the injection nozzles for the various cylinders of the engine are supplied with fuel from a central high-pressure line. To assure the lowest possible emissions, low fuel consumption and quiet engine operation, all the injection valves must inject the fuel exactly identically into the engine. This can be assured only if all the injection valves have the same opening behavior at exactly the same time at an operating point.
For accurate control of the injection event with common rail systems, electromagnetic or piezoelectrically controlled valves, which are located in front of the actual injection valve, are therefore known from the prior art. In a fuel injection valve of this kind, the nozzle needle is moved via a control piston. The control piston is moved via the pressure in the control chamber. The precision of the injection event is determined by the motion of the control piston, which depends on the pressure in the control chamber and thus on the flow through throttles and a switching valve.
OBJECT AND SUMMARY OF THE INVENTION
It is therefore an object of the present invention to create a fuel injection valve for high-pressure injection of fuel from a central high-pressure line into combustion chambers, in which the opening and closing operation of the switching valve and the flow of fuel through the switching valve are controllable as precisely as possible.
The fuel injection valve according to the invention has an advantage that the hydraulic flow through the switching valve can be specified precisely, even at low rail pressure and a short valve stroke. To that end, the flow upstream of the switching valve is constricted and expanded in a purposeful way, using an especially designed throttle geometry. After the contraction through the throttle inlet, the fuel flow expands again in such a way, given the throttle geometry according to the invention, in the direction of the throttle wall that because of an optimal pressure difference at the valve, the hydraulic flow is increased, and the opening motion of the valve ball away from the valve seat is reinforced.
Because of the advantageous design of the throttle, the flow resistance is reduced, so that even at a short switching valve stroke and a low rail pressure, a high flow is brought about. The high flow leads to a high-flow velocity at the entrance into the throttle.
The static pressure therefore drops down to the vapor pressure of the fuel, and vapor formation, or in other words cavitation, occurs. As a result of this effect, which ensues, given the throttle geometry of the invention, at the lowest possible rail pressures and shortest possible switching valve strokes, the hydraulic flow is now determined only by the pressure upstream of the throttle and by the inlet geometry (given a constant fuel temperature and a constant fuel type) and is independent of the valve stroke. Because of the defined hydraulic flow, the injection onset, which is electronically controlled via the corresponding switching valves, of a plurality of injection nozzles that are supplied from a common high-pressure line is reliably synchronized.
In a preferred embodiment, the diameter of a diffuser at the transition to the cone seat is only slightly less than the seat diameter. As a result, the largest possible hydraulic cross section of the valve as the valve ball lifts from the seat is attained.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of preferred embodiments taken in conjunction with the drawings.
REFERENCES:
patent: 5464156 (1995-11-01), Ricco et al.
patent: 5694903 (1997-12-01), Ganser
patent: 5890653 (1999-04-01), Kelly
patent: 5975428 (1999-11-01), Rotschin
patent: 6102302 (2000-08-01), Nishimura
patent: 6145492 (2000-11-01), Lixl
Betz Lorenz
Boehland Peter
Egler Walter
Hentschel Ralf
Greigg Edwin E.
Greigg Ronald E.
Moulis Thomas N.
Robert & Bosch GmbH
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