Fuel injector

Details Fuel injector Fuel injector

1999-10-12

2001-05-22

Scherbel, David A. (Department: 3752)

Fluid sprinkling, spraying, and diffusing

Unitary injection nozzle and pump or accumulator plunger

C239S533900, C423S446000

Reexamination Certificate

active

06234404

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a fuel injector for use in the delivery of fuel to a combustion space of an internal combustion engine. In particular, the invention relates to a fuel injector of the type intended for use in a fuel system of the accumulator or common rail type, the injector being of the type controlled using a piezoelectric actuator.
BACKGROUND OF THE INVENTION
In a known piezoelectrically actuated fuel injector, a piezoelectric actuator is operable to control the position occupied by a control piston, the piston being moveable to control the fuel pressure within a control chamber defined, in part, by a surface associated with the valve needle of the injector to control movement of the injector. Such an arrangement suffers from the disadvantage that fuel tends to leak from the control chamber past the piston, such a parasitic escape of fuel resulting in the injector being relatively inefficient. Further, during injection, the restriction to fuel flow formed by the passages and fuel lines whereby the injector is connected to a common rail may result in the fuel injection pressure falling to an unacceptable level.
Another problem with known injectors is that pressure waves transmitted along the fuel passages and lines may give rise to undesirable needle movement during injection and may be of sufficient magnitude to cause secondary injections.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a fuel injector in which the disadvantageous effects described hereinbefore are of reduced effect.
According to the present invention there is provided a piezoelectrically actuable fuel injector comprising a fuel inlet arranged, in use, to receive fuel under high pressure from a source of pressurized fuel, an outlet, and an accumulator volume located between the inlet and the outlet, a piezoelectric actuator being located within the accumulator volume and being operable to move a control piston to modify the fuel pressure within a control chamber.
Such an arrangement is advantageous in that the end of the control piston remote from the control chamber may be exposed to fuel at high pressure. The fuel pressure drop along the length of the piston may therefore be reduced, and as a result leakage of fuel from the control chamber can be reduced. Further, it will be appreciated that by providing the injector with such an accumulator volume, depending upon the capacity of the accumulator volume, the effect of the fall in fuel pressure due to the fuel passages and lines upstream of the fuel inlet can be reduced.
An articulated connection is conveniently provided between the actuator and the control piston. Such an arrangement permits compensation for slight manufacturing inaccuracies. The articulated connection is conveniently arranged to permit the application of a retracting force to the piston upon energizing the actuator in such a manner as to reduce the length thereof. This is conveniently achieved by arranging for a seal to be formed between the actuator and the piston such that, upon the length of the actuator being reduced, a partial vacuum is drawn in a volume between the actuator and the piston serving to draw the piston to follow the movement of the end of the actuator.
The volume between the piston and the actuator may communicate with the control chamber, if desired.
The actuator is conveniently provided with a flexible sealant coating, preferably an electronics conformal sealant coating. The provision of such a coating reduces the risk of damage to the actuator due to the application of fuel under high pressure thereto. The fuel pressure acting upon the actuator further keeps the stack under compression which reduces the risk of propagation of cracks in the actuator.


REFERENCES:
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patent: 5651345 (1997-07-01), Miller et al.
patent: 5697554 (1997-12-01), Anwaerter et al.
patent: 5875764 (1999-03-01), Kappel et al.
patent: 1 751 543 (1970-08-01), None
patent: 0 324 905 (1989-07-01), None

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